Thursday, April 29, 2010

Wednesday, April 28, 2010

April 29, 2010 Chase Forecast

Chase #1 of 2010!

Time of Departure: ~12:30PM
Initial Target: Herington, KS

Discussion: Initial low pressure system over Nebraska will swiftly progress northeast into northern Minnesota by late evening. A trailing cold front will surge east/southeast over MN/IA/NE and into northern Kansas during the evening, intersecting with a dryline positioned over central Kansas/Oklahoma. Largely linear forcing expected along the cold front in the Northern Plains preludes any significant tornado risk despite very strong shear values given the howling winds throughout all levels. Thunderstorms should initiate along this cold front during the evening hours, likely unzipping the front the entire way from southern Minnesota into southern Nebraska and along the Kansas/Nebraska border. As this occurs a secondary low is forecast to form in central Kansas, enforcing the dryline and providing a source for some localized backing of the winds. As this occurs it would appear likely that convective initiation should ensue given enhanced convergence. Bulk shear values are undoubtedly sufficient for supercells during the evening with an increase in shear likely with the low level jet increasing and proving south-southeast winds at the surface during the early overnight. Moisture is a concern given only mid to upper 40s exist widely in the area of interest, however continued strong southerly flow should provide ~60 surface dew points by 00z tomorrow. Widespread 1000-1500 J/kg of mixed-layer CAPE should exist, however fairly substantial capping inversion should limit any development without the aid of at least moderate surface convergence. Given surface temperatures of mid 80s and dew points ~60, high LCL values are also of concern for tornado potential. Nonetheless, the risk is there for at least a storm or two to develop along the dryline or for the cold front to initialize a storm near the intersection of the two boundaries.

It is for this purpose that the initial target be just south of the expected cold front and dryline intersection, being close enough for a tail-end charlie situation along the front or close enough to close quickly on any development to the south along the dryline. Will update by early afternoon with additional thoughts after viewing the 00z runs tonight and the 12z runs tomorrow morning; along with a look at the current conditions as a fellow co-worker and I depart.

Tuesday, April 27, 2010

April 29 Severe Weather Forecast #1

A nice and cool day today with temperatures only into the low to mid 60s over the region. A few showers were able to develop thanks to the abundant sunshine and cool temperatures aloft, however nothing widespread or too significant. We'll see the winds turn to the south during the overnight tonight, beginning to bring back the warm and moist air that was shunted southeast with the cold front this past weekend. This will set the stage for a severe weather event Thursday evening and overnight as a large trough moves eastward onto the Plains.

Details are still sketchy despite being only 2 1/2 days out, with the GFS still playing catch-up with the NAM and especially the ECMWF/GEM models. Strong southerly flow at the surface and above the surface should yield sufficient moisture return with ~60 surface dew points to the Central Plains by Thursday evening. This southerly flow will continue into the evening hours, and combined with strong flow in the mid-levels from the west-southwest will yield strong shear values over the area of interest. The combination of instability and shear does yield 0-3km EHI values of 3-4 which given a surface based storm would likely be more than sufficient for rotation in the lowest portions of the storm. Other parameters to note would be mixed layer CAPE of 1000-1500 J/kg, deep layer (0-6km) shear of 45-55 knots with a vector more normal than not to the boundary over south-central Kansas and Oklahoma. Such strong wind fields throughout all of the levels will end up giving fairly quick storm motions of 30-40 mph to the northeast, which would be favorable for any storms moving off of the dryline and into an even higher dew point environment.

All of the above parameters would be more than sufficient for strong rotating supercells likely capable of tornadoes given the strong deep layer and storm-relative shear. However, there are definitely some negatives at this point with the setup on Thursday. Moisture return will be sufficient for thunderstorms, however given surface temperatures of 80+ degrees F will give way to ~20 degree F dew point depressions and LCL heights of 1500 meters or higher. This decreases the tornado potential initially, but with storm modification of the surrounding environment could definitely still yield tornadoes. A pronounced warm nose in the lower levels will also give way to some substantial inhibition for surface based parcels to initially develop. There are of course many other details which will hopefully become better defined by tomorrow night, but for now it does appear that the positives outweigh the negatives on this setup for severe weather.

An additional update is likely by tomorrow night, with the final details regarding my chasing opportunities with this setup. A quick glance beyond Thursday doesn't give much model consensus, but it would appear that a continued threat of showers and thunderstorms would appear likely.

Monday, April 26, 2010

A Few Nice Days Ahead

A few showers remained in the area today with the upper level low still hanging around over Iowa. These showers pivoted around the low this evening and will continue to do so overnight, giving areas a few hundredths to a tenth of an inch of rain in the heavier bands. A nice scene this evening in Kansas City with the showers moving through as the sun was lowering, created both some high contrast dark clouds and a nice sunset scene (including a brief rainbow). We'll dry out tomorrow and continue to remain dry with warming temperatures for Wednesday and Thursday.

The next chance for rain and severe weather for that matter will come on Thursday for the Central Plains. A deepening trough in the west will eject several waves of energy for late this week and through the weekend. Model forecasts have been very inconsistent in what the system will do in regards to a cold front Thursday night. This will have dramatic affects on both precipitation and especially severe weather chances for Friday and the weekend. A quick look at the potential on Thursday shows a great chance of thunderstorms given the strength of the forcing along the cold front that will likely be sweeping southeast across the Plains. A lot of questions still need to be answered regarding the specifics, but it would appear likely that at least a strong line of thunderstorms would sweep over parts of the Northern and Central Plains Thursday evening and overnight. Additional details regarding the severe weather potential on Thursday and the remainder of the week will be addressed in later updates. Finally have a few days off with what looks to be an active pattern, so may finally get a chase day in as well!

Friday, April 23, 2010

Severe Weather Potential - April 23

Another day with potentially significant severe weather across both the Central Plains and into the Gulf Coast. Yesterday was quite impressive, with multiple cyclic tornadic storms over eastern Colorado and western Kansas, and several tornadic storms in the Texas Panhandle. Another severe weather setup is available today with a surface low located along the western Kansas/Nebraska borders, a warm front extends eastward across southern Nebraska and into southeast Iowa; and a dryline ahead of the cold front should be positioned over far eastern Kansas by this evening. The dryline should extend well south into the Arklatex region, providing a trigger for development from southern Nebraska to as far as northeast Texas. There is very good agreement that thunderstorms initiating in the Arklatex region will move eastward off of the boundary, but continue to pose a significant threat of severe weather given parcel profiles and strong shear present throughout the overnight. However, in the interest of forecasting sake I am focusing on the northern potential given its' likelihood to affect the Kansas City Metro this evening.

Morning convection is currently on its' way out of eastern Kansas, with cloud cover extending back further west to encompass much of eastern Kansas. This should clear out over the next few hours, allowing for sufficient destabilization ahead of the dryline and south of the warm front. This should yield 2000-2500 J/kg of surface based CAPE, and mixed-layer CAPE nearing 2000 J/kg. Deep layer shear values of 40-50 kts with a vector out of the west-southwest should allow for fairly discrete storm development along the dryline in extreme southeast Nebraska and northeast Kansas. As these storms move off of the dryline they will continue to encounter a favorable air mass and likely even better low level shear given stronger backing of the winds. A mid-level jet (500 hPa) will enter the area during the evening hours, likely increasing the deep layer sheer values and providing support for additional storm development. Storm motion given the storm relative wind fields should be to the northeast at 20-35 mph, with any right-movement yielding motions of east-northeast around 25 mph. Storms will likely have enough directional shear to rotate, yielding sufficient tornado potential to mention tornadoes possible with any supercells that do develop in this area. In addition to the tornado potential, ample instability will be available for large hail growth.

Storm initiation should occur by 00z (7pm) in eastern Kansas along or just ahead of the dryline, with storms continuing well into the overnight as they move northeast. Based upon current forecasts, thunderstorms should enter the Kansas City metro ~10pm and exit by 2am. Severe weather is likely with any thunderstorm this evening and into the early overnight. I work the evening shift at work, thus will not be chasing or be able to provide updates. `

Thursday, April 22, 2010

Severe Weather Threat: April 22

Another day of severe weather potential across the Plains, with the threat now including portions of the Central Plains (southern Kansas). A warm front currently located just north of the Kansas/Oklahoma border will continue to progress slowly northward today, leading to widespread showers/thunderstorms north of the boundary and clearing skies and destabilization south of the boundary. By this evening the warm front should be located along a line extending from the southwest corner of Nebraska to ~Emporia, KS. Areas just along and south of this boundary will have the potential for severe weather this evening into the early overnight. At this point the best severe weather threat will be along the dryline in western portions of Kansas, Oklahoma and Texas. These areas will have better instability to go along with better convergence along the dryline boundary. Nonetheless, areas of southern Kansas, especially southwest Kansas, will have the potential for severe weather including large hail, isolated tornadoes, and a few damaging wind gusts. As mentioned, areas further west towards the dryline will see the higher risk for severe weather this afternoon/evening.

In addition to the severe weather threat, general showers/thunderstorms north of this boundary should persist through much of the day. These showers/thunderstorms are currently entering the Kansas City Metro and should continue well into the afternoon as the front only slowly progresses them northward. No severe weather threat is expected north of the boundary due to lack of instability.

An additional update is likely tonight to discuss any ongoing severe weather, and tomorrow threat for severe weather which will shift north and east and include the Kansas City Metro! Friday's severe weather threat will include the risks of very large hail, damaging winds and tornadoes...

Tuesday, April 20, 2010

First of Many Chances...

Scattered showers and even a thunderstorms every once in a while have continued over parts of Central Nebraska through much of the day in response to a shortwave that is slowly progressing southeast. These showers should continue to move southeast through the overnight, reaching the Kansas and Missouri borders during the early morning hours. Fairly dry conditions in the lower levels along with an increasingly unfavorable conditions for the shortwave should limit the potential for any widespread rain across much of Kansas/Missouri. However, recent models trends have stuck to a more localized area of 'energy' which may lead to an area of showers that could persist through much of the day tomorrow as it progresses across parts of Missouri. Even with this scenario, do not expect any significant rainfall and the day certainly does not look like a wash-out.

That wave is the first of many that will likely move through the Central Plains for this week, with an impressive trough and numerous shortwaves yielding plenty of rainfall and severe weather potential for Thursday through Saturday. Latest model trends continue to push back the timing of the event, leading to a more southerly positioning of the warm front and a more westerly positioning of the dryline. While this isn't that unexpected it was kind of a surprise as to the magnitude of the 'jump' south and west in a run-to-run basis.

Thursday in my mind continues to be the more favorable for photogenic tornadoes in my opinion. Surface based instability should be nearing 2000 J/kg over extreme southwest Kansas and the panhandles of Oklahoma/Texas; 75/60 surface parcels should yield low LCL's and sufficient moisture given higher elevations; and a favorable location along a jet maxima should yield sufficient upper level support. All of the aforementioned in conjunction with largely southeast flow at the surface should allow for supercells with 15-25kt storm motion capable of producing tornadoes.

Friday still holds the potential for tornadic supercells, and more than likely the more widespread severe weather event given a more pronounced warm front and dryline. Bulk shear values are more sufficient on Friday throughout the warm sector, however with slightly more unidirectional flow. Nonetheless, expect widespread severe weather along the dryline from central Kansas into north-central Texas with the potential for additional thunderstorms along the warm front given strong surface convergence.

More details regarding both Thursday and Friday, along with some potential on Saturday will be discussed in later updates...

Monday, April 19, 2010

A Week of Potential...

A fairly cool and calm weekend under northwest flow aloft, with highs in the 60s and overnight lows into the lower 40s. This 'chilly' weather is coming to an end already with a return of southerly winds at the surface by tomorrow. Temperatures rose into the upper 60s and a few 70s across much of the area today, with a few 50s still prevalent over the High Plains regions where down-slope hasn't aided their warm-up yet. A few small impulses of energy under northwest flow will bring the chance of showers and thunderstorms to the Central Plains on Tuesday into Wednesday. And beyond that we'll turn the attention to our next big trough that will come onto the Plains Thursday/Friday and likely become a vertically stacked low by the weekend. This trough and associated thermodynamic features will likely create the potential for a significant severe weather event, perhaps one of the first more prolific tornado producing events of the year.

Have to take at least a quick look at the northwest flow event for Tuesday into Wednesday as that will at least bring the chance of rain. A decent shortwave impulse currently along the Montana/Wyoming border will continue southeast, likely located in southern Nebraska by Tuesday afternoon. This should be enough to create the potential for showers and thunderstorms over south-central Nebraska into north-central Kansas by Tuesday evening. There is at least some elevated instability present, and while not likely being enough for anything severe it will at least bring in the chance of rumbles. Another location of interest will fall along the High Plains where at least modest moisture of upper 40s to near 50 surface dew points combined with ~70 degree temperatures should yield 500-1000 J/kg of surface based instability. This in conjunction with sufficient shear values and lifted indicies, and little inhibition, should warrant the potential for at least strong thunderstorms along western Kansas and the Kansas/Colorado borders tomorrow late afternoon and evening. While these thunderstorms may fade after dark, the low level jet should continue to support more organized showers/thunderstorms over central Kansas, and given upper level support at least showers over eastern Kansas as well. A few lingering showers can be expected Wednesday morning along the Kansas/Missouri borders, otherwise a dry day for the Plains on Wednesday.

This dry day on Wednesday with southerly flow will continue the moisture return to the Plains, aiding in the potential for at least a High Plains thunderstorm event on Thursday. A potent trough will be nearing the four-corners region by Thursday evening, promoting height falls across the High Plains and likely at least the initialization of a surface low along the Lee of the Rockies. Potential exists for both a dryline and warm front becoming pronounced by Thursday evening, promoting convective development along the Panhandles of Texas/Oklahoma and further north into southwest Kansas and adjacent areas of Colorado. Sufficient shear should be in place given southeast flow at the surface and increasing 500hPa flow from the southwest. At least elevated supercells would appear likely, with any surface based convection definitely yielding severe potential...

Friday is shaping up to be the day of interest as the trough ejects onto the Plains, centered along the eastern Colorado border. A surface low somewhere near/along the Kansas/Nebraska border should also set the stage for both a warm front and dryline intersection. A pronounced dryline should surge eastward during the day Friday, making it well into central Kansas/Oklahoma. Strong moisture return both at the surface and aloft, at least according to models, should yield surface-based instability of at least 1500 J/kg. While shear is expected to be strong given fairly significant wind speeds in both the mid and lower levels, there is some concern based on recent model runs of too much uni-directional flow leading to fast storm motions and the potential for broken lines of convection. Nonetheless, the potential for severe weather is definitely there and likely warrant at least a higher-end slight risk by the SPC. A lot of details will need to be worked out, such as the arrival of a shortwave disturbance and any morning convection and cloud cover. These such details will be discussed later as the event nears and the short-term models can have their opinions voiced on the matter.

Onto the weekend, it would appear that our vertically stacked low pressure system will meander across the Central Plains on both Saturday and Sunday. Given the cold air aloft, thunderstorms do appear possible on Saturday for areas of Kansas/Missouri and perhaps areas just north. Sunday appears to be a day of cloud cover and showers at this moment, which doesn't bode well for my Royals/Twins baseball game that I plan to attend. I'll continue to watch and hope for the push of the low to the east for Sunday and next week. Well into the future, expect the low to move out early next week and lead to at least some short-term ridging of the Plains, promoting a return of warm and moist air. Our next round of thunderstorms and perhaps severe weather will come with the next trough, currently slated by the GFS and ECMWF to come in for the first few days of May.

More details regarding any thunderstorms tomorrow evening will be posted tomorrow along with another look at the potential for the late week severe weather episode.

Friday, April 16, 2010

Rain & Return of Seasonable Weather

A cold front has pushed through a majority of the Central Plains over the past 24 hours, leaving us with more of a normal air mass for early April. Rainfall during the overnight was fairly heavy across parts of northeast Kansas and northwest Missouri, but decreased dramatically as it entered the Kansas City Metro. The 24-hour precipitation totals show this quite well:

St. Joseph - 0.59"
Kansas City Intl - 0.36"
Johnson Co. Exec - 0.06"
Olathe Airport - 0.04"
Lee's Summitt - 0.03"

We've cleared the skies out this evening, and with light northerly winds across the area will likely see some very crisp overnight lows tonight and for the next few nights as a high pressure system settles over the region. High temperatures over the weekend will be more typical for this time of the year, in the mid 60s for the Kansas City Metro. Into next week expect to see the high temperatures slowly moderate into the lower 70s, and lows should increase with the slow but sure increase in moisture and the exit of the high pressure center.

The next storm system for the Central Plains will likely come late next week as a cutoff low pressure system is forecast to finally push onto the Plains. There will likely be a limited severe weather threat as the system makes its' way across the Plains states given its' dynamic qualities. However, moisture return is a large question at this point and thus the quality of thermodynamics that this system has to work with will likely be its' limiting factor. Nonetheless it's the next thing in sight and will be watched as it comes onshore early next week and stalls along the West Coast.

Enjoy the sunny and more seasonable weekend!

Wednesday, April 14, 2010

A Round of Rain...

Several days of warm and sunny weather has most people spoiled into thinking summer is almost here already!  But, don't think winter has gone too far as there is plenty of winter weather still ongoing in some areas of the Rockies, including Montana and Wyoming where up to a foot of snow was falling yesterday on the backside of a strong dynamic upper level system that was also responsible for strong and even severe thunderstorms in the western Dakotas, western Nebraska and along the Colorado/Kansas border.  This upper level system was also the culprit to some severe thunderstorms on Monday across northern Iowa and southern Minnesota.  The upper level low will be pushed eastward over the next couple of days, allowing a cold front to push southward through the Plains states on Thursday and Friday.  With the meager moisture in place and the lack of dynamics aloft, any thunderstorms along the cold front should be general thunderstorms with perhaps a few marginal severe hail reports.

Today's showers and thunderstorm chances along the front extend from northern Minnesota/Wisconsin southwestward through Iowa, Nebraska and into western Kansas.  Showers and thunderstorms will move into southern Wisconsin and continue through Iowa/Nebraska and Kansas on Thursday as the cold front beings its' push south.  Finally we'll see the showers and thunderstorms make their way into the Midwest and areas of Missouri through the day on Friday.  Additional showers and thunderstorms are expected along western Oklahoma and Texas both today and tomorrow as a weak dryline will continue to focus for some additional development.  Some cooler continental air will follow the front, with high temperatures being knocked back down into the 60s here in Kansas City and more seasonable temperatures for most of the Plains.

For the long range we'll see a brief ridge build into the central US, that will continue into early next week.  Long range models have made a fairly drastic change in the past few runs compared to what was earlier depicted as a fairly quiet weather pattern now indicates that a strong storm system may move through the Plains states for mid-to-late week next week.  While this system may have the strong dynamics, there will likely be a question of how much moisture is in place even by then thanks to the ridge that will also affect the Gulf and its' attempt to return moisture to the Plains.  Of course this potential system is quite a ways out and there won't be much more thoughts on this until it nears a bit closer.

Friday, April 9, 2010

Warming Weekend...

Temperatures today got a few degrees above forecast thanks to absolutely clear skies and a bit more mixing than expected.  Similar trends should continue through the weekend and into much of early next week with highs ranging in the mid to upper 70s for the Kansas City area.  A weak front will stall along the KS/NE and MO/IA borders on Saturday night, and continue to hold for Sunday afternoon. This front may provide some precipitation for portions of the Plains on Sunday as it stalls out.  Steady southerly flow will allow for enough lift to provide some showers and thunderstorms Sunday afternoon over northern parts of Kansas/Missouri and perhaps adjacent areas of Nebraska and Iowa.  Given marginal dew points and sufficient heating there will be instability present, and enough shear to likely warrant at least the mention of strong thunderstorms.  I will be watching the potential on Sunday for parts of Kansas, given enough shear we could see a decent thunderstorm or two, especially after sunset.  This could provide a chance for some lightning photography if it is close enough and the storm motion isn't too fast, current forecast of east motion at 25 mph would be sufficient.

Besides these small chances of showers/thunderstorms during the evening/overnight on Sunday the weekend and early next week should be very nice.  Even with some clouds in the sky the temperatures will still rise into the 70s!  Wind speeds shouldn't be too gusty during the afternoon, leaving us with a very nice day to spend outside...  I may post a quick update on the chance of thunderstorms over the weekend, otherwise enjoy the sun!

Wednesday, April 7, 2010

Severe Weather Recap - April 4-6

The large trough and associated low pressure system and other surface features that had been in the eyes of chasers for nearly a week before even coming onshore has come and gone over the Plains. This past Sunday (April 4) through Tuesday (April 6) all had the potential to be some of the best days of chasing thus far for 2010. Now I realize given the way the early season (January-March) have turned out this isn't saying a whole lot, but comparatively many chasers were quite excited about the prospects. There were obviously some concerns with the setups on each day, as it is often hard to find a day that doesn't have some sort of concern. The lack of upper level support for Sunday and Monday were hard to miss, and with such a stout elevated mixed layer (EML) this allowed for a pretty good lack of significant storms until during/after sunset. The upper level support did arrive for Tuesday, but winds became largely unidirectional for most areas with only a narrow axis of good directional shear along the warm front in Iowa. The moisture concern which was largely discussed didn't show itself at the surface, but given the impressive EML that was in place the moisture just wasn't deep enough in my opinion. I could go on with a few more concerns and of course mention the positives that were in place for the events, but we'll continue on into what actually occurred each day.

In the end I can somewhat luckily say that I had to work throughout all three potential chase days, thus was not active in chasing any of the storms. I think it is fairly safe to say though that if I wasn't working that I would have likely favored going chasing for at least 1 or 2 of the days.

Sunday will actually be credited with the only tornado reports on the Plains, although not yet confirmed to my knowledge by the Kansas City or St. Louis NWS offices. (Note: There was a tornado report on Monday 4/5 in western Illinois) These tornado reports came from a rather impressive supercell that began its' life ~40 miles northeast of Kansas City and continued into western Illinois during the early overnight hours. A total of 4 tornado reports came from this storm as it passed through Howard, Randolph & Audrain counties between 7pm and 8:15pm. This storm also produced some of the largest hail reports (2.5" in diameter) and damaging winds. The storm was fairly photogenic, although any tornadoes were likely hidden within shrouds of rain. The worst part of this storm was likely its' speed (45 mph) and location within the hilly/winding roads of central Missouri. There were additional storms across parts of northern Oklahoma that came after dark and produced some large hail and damaging winds, but nothing of tornadic nature and largely photogenic.

Monday and another day featuring a warm front draped along the Iowa/Missouri borders and then a dryline play in Kansas/Oklahoma. No tornado reports and no significant severe weather to speak of out of the entire day/night with a majority of storms occurring across southern/central Iowa and only producing 1.0-1.75" diameter hail and some wind gusts of 60-70 mph. This will largely go down as a bust for most people as the only storms were well out of any target area by chasers.

Tuesday was turning out to be the day, with upper level support finally arriving and significant surface moisture still in place the hopes were high for most people. The SPC had targeted the warm front with a 10% tornado risk and kept the conditional hope of 5% tornado risk for the remainder of the dryline in Kansas/Oklahoma. Storms did initiate along the dryline/pre-frontal trough and the warm front in Iowa; however once again there were no tornadoes to speak of. Several tornado warnings were issued in Iowa, with there being some impressive damage that has been surveyed to be damaging straight-line winds of 95-105 mph! Other reports of damaging winds and large hail occurred across eastern Kansas and parts of Oklahoma, although storm motions of 45 mph were a disadvantage along with largely linear storm mode with embedded supercells over Kansas. The storms over Oklahoma came after dark once again given the strong inhibition (EML) that continued to be in place. Although not a lot of reports from chasers have came in regarding the storms on Tuesday, I think it'll be hard to get any highly photogenic storms out of what occurred.

With what is likely one of the worst starts in regards to tornadoes in several years, the largely linear and high precipitation storms thus far haven't produced anything amazing to my knowledge. The Kansas City metro has been off to a pretty good start in regards to just severe/strong thunderstorms with several days of morning and afternoon convection with some marginal hail and strong winds. Even today we managed to pull off a severe thunderstorm and 1.75" hail in Platte County with little instability and a surface observation of 58/44. Can't say I'm dissapointed in hearing the thunder multiple times thus far, and I'll look forward to warmer temperatures and an eventual return to slower moving and more discrete storms later in the Spring!

Now all eyes can turn to the next trough to enter the Plains, which should come sometime early next week! In the meantime, we'll focus on sunny skies and warming temperatures for Kansas City.

Tuesday, April 6, 2010

Severe Weather Potential - Apr. 6

A low pressure system is currently located over southeast Nebraska, and will slowly move into southern Iowa and eventually into northern Illinois during the overnight hours. A warm front is positioned to the east of the low, draped across southern Iowa, northern Illinois and further to the east. A cold front/dryline is to the south of the low, currently across eastern Kansas, central Oklahoma and into north-central Texas.  These frontal boundaries will be the focus for thunderstorm development this afternoon/evening given sufficient lifting and support from an upper level wave that should cross the Central Plains this afternoon.  Additional storms in the warm sector or away from the front are not expected due to the substantial mixed layer that should provided sufficient capping.  Given dew points into the upper 50s and lower 60s throughout the warm sector, with clearing skies allowing for moderate to strong destabilization along the fronts.  Deep layer shear is more than sufficient for supercells during initial development, however with time a largely unidirectional wind field will eventually support more of a linear storm mode.

Thunderstorm development should occur this afternoon both along the warm front in Iowa, and along the cold front in northwest Missouri and eastern Kansas.  Storms should continue to develop further south during the late afternoon and evening in eastern Kansas and into portions of Oklahoma along the dryline.  With initial surface based development, isolated nature of storms should support very large hail and perhaps a tornado.  The best tornado threat would appear to be along any portion of the warm front that can back winds to the southeast, otherwise given largely south/southwesterly flow at the surface the tornado threat should be minimal along the cold front.  As we progress into the evening, clusters or broken lines of thunderstorms are expected with more of a threat of large hail and perhaps gusty winds.  As we enter the overnight hours the instability should begin to wane, and given substantial capping otherwise it would appear more likely for storms to also wane after Midnight with a limited risk of any severe weather.

Kansas City should expect thunderstorms during the mid to late afternoon, with a risk of some large hail with any strong/severe thunderstorms. These thunderstorms should exit with the passing of the cold front later this evening...

Monday, April 5, 2010

Severe Weather Update - April 4

Just a brief update tonight on the severe weather threat for the remainder of the overnight. If you were unaware thus far, the threat in the Central Plains was limited by sufficient capping due to an elevated mixed layer and by the lack of upper level forcing to aid in storm development. As we neared sunset the combination of boundary layer decoupling and an increase in the low level jet likely contributed to thunderstorm development in extreme northeast Kansas. These thunderstorms have continued to develop spread both east/west along the warm/stationary front. These thunderstorms will likely continue and expand in coverage during the early overnight hours with the main severe weather threat being large hail. If a storm within the next hour or two can become surface based then a tornado threat would be enhanced (thus the basis on the tornado watch issuance), but the likelihood of this seems rather low. Storms will expand northeast as both the front and associated low pressure system slide northeast as well, with a continued threat for large hail and perhaps a few wind gusts across mainly southern Iowa and extreme northern Missouri, entering into areas of Illinois early tomorrow morning.

Additional development may be possible along the dryline as the low level jet increases even more during the early overnight. An attendant severe hail threat would include an elevated supercell in central Kansas/Oklahoma.

The next update will come with a look at the potential for severe weather on Tuesday for areas of Iowa, Missouri, Kansas and other areas of the Plains.

Severe Weather - Apr. 5

A recap of any severe weather will likely be posted once this system has exited the Plains entirely, as a round of severe/tornadic thunderstorms occurred yesterday afternoon/evening and additional rounds of thunderstorms are occurring this morning with more expected this afternoon.

Currently, elevated thunderstorms capable of producing large hail have been ongoing across parts of northeast Kansas and northwest Missouri, especially near the Kansas City Metro area.  A severe thunderstorm watch was issued for portions of the states through Noon today.  These storms are being fed by a strong southerly low level jet that continues to push moisture northward and will begin to push a warm front to the north today, likely situating near the Iowa/Missouri border this afternoon. In addition to the warm front, a dryline will be situated across central Kanas southward into Oklahoma which may be another focus for thunderstorm development.  Thunderstorm development along both frontal boundaries is somewhat in question due to a substantial capping inversion and elevated mixed-layer that will overspread the Plains states. 

Despite this, thunderstorm development should occur along the warm front this evening (7-9pm).  Given moderate instability and sufficient deep layer shear, supercells will be likely capable of producing very large hail, damaging winds, and tornadoes.  Storms should move along the warm front, continuing to be capable of all modes of severe weather through the evening and into the early overnight.  Additional storms will continue along the warm front into Illinois and other portions of the Midwest during the overnight hours continuing the severe weather threat of mainly damaging winds and large hail, although a tornado or two is still likely with any storms that continue along the warm front.

Development along the dryline across central Kansas into Oklahoma is very conditional given the substantial elevated mixed-layer and associated temperature inversion in the lower levels.  Strong instability should be present along/just ahead of the dryline this afternoon, however without continued convergence along the boundary there may not be sufficient lift for development of thunderstorms.  If an area of enhanced convergence can occur along the dryline and thunderstorm development can occur, there is no doubt that supercell(s) would be likely.  Once again all modes of severe weather will be likely with strong deep layer shear resulting in the potential for very large hail, damaging winds, and tornadoes.

Essentially a conditional, but very volatile severe weather setup today across parts of central Kansas, extreme southeast Nebraska, extreme southern Iowa and extreme northern Missouri.  The potential is there for a very strong supercell capable of significant hail, winds, and tornadoes.  I'm sure there will be plenty of storm chasers out to keep track of the situation live.  I once again am working the evening shift, thus will not be chasing this event (I keep telling myself it is only early April, plenty more opportunities).

Sunday, April 4, 2010

Severe Weather - Apr. 4

A true convergence of air masses will lead to severe weather potential stretching from extreme eastern Kansas to the northeast across northern Missouri, southeast Iowa and Illinois.  A cold front will slowly drift southeastward during the day today, at the same time a strong southerly flow will continue the return of warm air and moisture to the Central Plains.  By late this afternoon or early this evening a good bulk of warm air and moisture will begin to bisect the cold front, aiding in destabilization and convergence along the front.  A meager shortwave is shown in model forecasts, and should give at least a glancing blow to aid in storm initiation this evening, especially along the northeastward extent of the front in northeast Missouri and adjacent areas of IA/IL.  Further southwest, instability should be higher due to slightly higher moisture return by this evening, with SBCAPE values of 1000-1500 J/kg and MUCAPE values even higher (~2000 J/kg).  This may be enough when combined with the convergence along the front to initiate storms this evening which may be surface based for a short time as well.  If surface based storms can develop, they will be able to take advantage of some low level shear which will aid in the organization of supercells.  This may open up a small window of opportunity for a tornadic storm or two, however those risks at the moment seem quite low.  More likely scenario will be for elevated storms to develop along the front this evening over northern Missouri as the low level jet provides additional lift and support to parcels ~1km above the surface.  Elevated supercells are possible across northern Missouri, with the potential for large hail and a few damaging wind gusts.  Individual storms will move east/northeast oriented with the cold front, thus the potential will also be there for training storms capable of some localized flooding concerns.  The cold front will drift slowly southward overnight continuing the risk of thunderstorms into central Missouri and adjacent areas, before lifting back to the north Monday morning.

As I've mentioned before I work throughout the weekend and into next week, thus no chasing is planned.  For a local chase today I would suggest a target in northern Missouri, perhaps along a Macon to Moberly line dependent on where the front is when initiation occurs.  A brief update may be posted around Noon, otherwise any additional updates will be later tonight.

Saturday, April 3, 2010

Severe Weather Potential - Apr. 4/5/6

The first post in regards to severe weather potential for Sunday through Tuesday next week will encompass the entire event, subsequent posts will likely be broken into daily forecasts.  Unfortunately this will be another virtual chase target event as later today I begin my 7 day stretch of work. 

April 4 - Nonetheless another severe weather setup will take place as a trough enters the Plains states aiding in additional return moisture and co-located warm front moving northward.  This warm front will likely be positioned across parts of central/northern Kansas and into northern Missouri by tomorrow evening.  General upward trajectories of parcels would be sufficient for thunderstorm development, however increasing heights associated with the strengthening trough to the west will likely inhibit storm development during the afternoon hours.  An increase in low level flow associated with the nocturnal low level jet will likely provide additional lift and be enough to develop elevated thunderstorms during the early overnight Sunday. These thunderstorms will likely become widespread over northern Missouri during the overnight and move northeastward with time. Although the severe weather threat would appear low due to the elevated nature of convection, marginally severe hail and damaging winds may be a threat into the morning hours on Monday across parts of northern Missouri and perhaps adjacent areas of Iowa and Illinois.

April 5 - Ongoing morning convection over parts of eastern Missouri/Iowa and into Illinois will exit eastward, with a quickly recovering warm sector pushing the warm front further to the north.  Exact positioning of the warm front will be dependent upon any mesoscale cold pools and cloud cover, but a general positioning expected along northern Kansas/southern Nebraska and into southern Iowa by the late afternoon hours Monday.  Large scale trough will make progress onto the High Plains, with associated low pressure system developing over western Kansas/Nebraska.  A dryline will develop in association with the strengthening surface low, yielding largely southeast surface flow along the warm front and triple point areas.  This in conjunction with largely veering winds with height and an increase in speed should yield impressive hodographs throughout the warm sector.  Add sufficient daytime heating and moisture return with dew points of 60+, instability values should be moderate to strong leading to an impressive severe weather setup.  While limited inhibition is expected to the east along the warm front in parts of eastern Iowa/Missouri, sufficient capping should ensure over Nebraska/Kansas allowing for strong destabilization. Thus expect rapid development of thunderstorms during the evening hours both along the warm front and perhaps along the dryline, being isolated in nature will likely allow the potential for very large hail, damaging winds, and tornadoes.  Additional updates in regards to positioning of surface features will be likely, but an initial virtual target is expected along Highway 36 between Smith Center and Marysville in extreme northern Kansas.

April 6 - Large scale trough will continue its' movement across the Plains, with surface low pressure system moving across Iowa during the day Tuesday.  Associated warm front will likely have ongoing thunderstorms and see continuing development along the front throughout much of the day.  Cold front should sweep across eastern Nebraska/Kansas and into Iowa/Missouri during the early afternoon.  Additional thunderstorm development is expected along the cold front in the afternoon with limited inhibition.  Largely linear forcing will be in place with the cold front, thus expect line segments and/or broken line of thunderstorms to develop over mainly portions of Iowa/Missouri in the afternoon.  At this time it would appear that any severe weather threat would be limited to damaging winds and/or marginally severe hail associated with any convective line that does develop over parts of southern Iowa and northern Missouri.

Friday, April 2, 2010

April 2 Severe Weather

Just a quick post about the impressive line of thunderstorms that evolved through the overnight last night arriving in the Kansas City metro this morning.  As it was approaching the metro the storms organized into several line segments capable of producing damaging winds, and it did so throughout the Kansas City Metro and off to the northeast into south-central Iowa even.  Reports from the metro areas indicated widespread swaths of 60-70 mph winds with a few areas likely seeing close to 80 mph gusts given the damage.  Tree damage and damage to power poles were the main reports, other loose objects such as trampolines were also seen thrown into trees.  At least five tractor trailers were tipped over due to these heavy winds, and just north of the Metro on I-29 saw significant roof damage to a storage barn.  Additional details on the damage may be posted if any NWS office releases any special news statement.  To view each of the storm reports received in associated with this cold front from the overnight and into early this afternoon please see the link below:

Map of Storm Reports from 12AM - 2PM on April 2, 2010

Thursday, April 1, 2010

Severe Weather Potential - Apr. 1/2

Just a quick update for the potential of severe weather both today and tomorrow for the Plains states.  Today's threat is quite marginal given a stout temperature inversion in the lower levels ~800hPa, but given moderate surface based instability and marginal shear values any storms that could develop would likely be isolated and severe in nature. The initiation for any thunderstorms will come along a dryline situated from extreme south-central Nebraska through central Kansas/Oklahoma and into Texas.  This dryline intersects a cold front in south-central Nebraska and will also be retreating to the west by this evening. Marginal convergence along the dryline may initiate storms just above the temperature inversion, likely after sunset this evening. Although there is a small chance of surface based convection developing, mainly where instability is greater and convective temperatures can be met across south-central Kansas and central Oklahoma. Main threats with thunderstorms this evening/overnight would be large hail and gusty winds, on the small chance that a surface based thunderstorm can occur there would be an isolated tornado threat given moderate low level shear.

Tomorrows potential will be much greater for convection and the potential for severe thunderstorms given the decrease in low-level temperatures which will rid any inversions. A strong trough entering the Plains will lead to significant height falls and with both a cold front and dryline to aid in initiation.  Widespread precipitation is expected from the Northern Plains along the cold front, and further south into areas of Kansas/Missouri during the afternoon hours.  Other convection may linger during the morning hours even further south, but should be displaced from the dryline/cold front and allow for some heating to occur during the afternoon. Any heating that can occur during the afternoon will lead to increase probabilities of severe weather along the frontal boundaries with the best threat of redevelopment and severe weather coming along the dryline in eastern Oklahoma into northeast Texas.  These areas will have marginal shear, but given moderate instability will likely allow any thunderstorms to be severe in nature, with the threats of large hail and damaging winds, along with a tornado or two given strong vorticity (and stretching of the rotating column).  The potential for a few storms capable of damaging winds and large hail will extend northward into parts of eastern Kansas as well, but is highly dependent upon the amount of instability that can be managed with any clearing.  I may not have an additional update tonight/tomorrow, thus the inclusion of both days in this post. Chasing prospects do not warrant any chase given marginal parameters and distance for a good chase target.