Thursday, July 30, 2009

Cool & Calm July

Iowa has been both on the cool and calm side of the weather for the month of July despite a few events that have hit some parts of the state hard, including a few tornadoes and some very damaging hail across northeast Iowa last Friday. A rough and quick look at the mean temperatures over the month of July indicates that it is likely to be the coolest since 1992. For example, Estherville has a mean temperatures thus far of 66.8 degrees, which is second coolest since 1951!

The final day of the month looks to be just at, or just below normal for the state. We'll also get a good chance of some thunderstorms for the end of the month across at least the western half of the state. The severe weather threat appears minimal at the moment, but some small hail and gusty winds is not out of the question for the western third of the state. An update may be necessary if the potential for severe weather tomorrow night does increase...

We'll clear off and be near or just below normal for high temperatures once again through next week; low temperatures will be just below normal. A chance of thunderstorms and showers will work its' way back into the forecast for mid-week, otherwise it appears dry through the first week of August. The long range forecasts do indicate the possibility of a good ridge building into the central US through the first weeks of August which may finally lead to some above normal temperatures!

Friday, July 24, 2009

Severe Weather Update #1 - July 24

Both a Severe Thunderstorm Watch and Tornado Watch have been issued for portions of the state. Currently the bulk of thunderstorm action is confined to the northeast corner of the state where a supercell is beginning to take on tornadic characteristics and has prompted the tornado watch issuance. This storm has moved through areas of northeast Iowa with hail up to 1.50" in diameter and winds of at least 60 mph causing tree damage and at least one injury in Cresco.

While this storm is currently only severe warned, the latest scans have indicated rotation beginning to tighten and this storm may become tornadic within the next hour. With conditions continuing to become favorable for tornadoes, the SPC has issued a tornado watch for portions of eastern Iowa where this storms path appears to be at this time.

Additional development along the cold front across northern Iowa may occur through mid-afternoon, thus the severe thunderstorm watch continuing in effect until 5 PM for portions of the state.

Thursday, July 23, 2009

Severe Weather - July 24

A strong cold front and associated upper level features will aid in thunderstorm development this afternoon across a majority of the state. Given current forecasts for shear, instability, and the strong support with the cold front it would appear that all modes of severe weather are likely across the risk area including isolated tornadoes, very large hail, and damaging winds.

Strong warm air advection should occur through the morning hours and into the late afternoon, suppressing any convection from occurring. As the cold front continues to dive southeast in the evening it should be able to overcome any inhibition that is in place ahead of it in the warm sector. Initial storm development between 6-8 PM should be supercellular in nature given strong bulk wind shear, and given strong veering winds near the surface a tornado or two is possible. Given the strong forcing along the cold front, thunderstorms should quickly develop along the entire front near sunset. This will promote more of a broken line mode of severe weather, with large hail and damaging winds becoming the main threat for the nighttime hours.

Additional updates are likely this afternoon when mesoscale discussions and eventual watch(es) area issued.

Friday, July 17, 2009

A Quick Recap

Busy days ongoing for me has created a good lack of updates on my part. Just to review back to July 14, the severe weather threat did materialize, although much weaker than initially thought due to only convection along the front firing during the evening hours. Did manage to punch through a severe warned cell between Wallingford and Ringsted on the way back from a playoff baseball game. This cell didn't really back much punch in regards to wind, and no hail was found. A weakly photogenic shelf cloud was noted, but not captured...

After the cold front passed through the state we were left with some below average temperatures that have continued into tonight. Current temperatures early this morning range from the mid 50s to the upper 40s! High temperatures for Friday should range from the upper 60s to the mid 70s across the state from northeast to southwest; lows overnight will drop into the upper 40s to mid 50s across the state once again. The weekend will stay dry with highs in the upper 60s to mid 70s from east to west on Saturday, then from mid 70s to mid 80s by Sunday. Low to mid 50s for Saturday night temperatures, and mid 50s to lower 60s from east to west for lows on Sunday night.

We'll return to chances of thunderstorms and showers for the work week, with the best chances on Monday night in the west; Tuesday and Tuesday night for the central and eastern thirds, and the potential for a lingering shower or storm in the east on Wednesday. High temperatures in the upper 70s to mid 80s from east to west for the first half of the work week; with lows in the upper 50s to mid 60s. Look for an update on these chances of thunderstorms come early next week!

Monday, July 13, 2009

Severe Weather Potential - July 14

The potential for a significant severe weather event over portions of the central/northern plains is there for tomorrow, as potent surface features will be supported by strong upper air parameters. Two areas of interest are going to come into play, both of which have some very big question as to its' potential to produce significant severe weather. A lot of the questions may be answered tomorrow morning once the evolution of the MCS(s) from current severe/tornadic convection across SD/NE is known. An update during the overnight hours or during the early morning will hopefully give an idea as to which area of concern is greatest.

The most favorable target will likely be along a reinforced warm front or outflow boundary following tonights' convection that will setup across southeast Nebraska, southwest Iowa and across northern/western Missouri. Strong heating and moisture return will be in place for this area, providing extreme instability and likely strong lift. Upper air features better align with this area of instability and lift, aided by a shortwave that would likely aid in development. As with the case with most late season events with such extreme parameters in place is the capping concerns... Temperatures at 700hPa near the 12C mark will likely cap thing well into the afternoon, however, there is support with the models indicating that this capping inversion will be broken before 00z. A target in this area could come with some significant rewards, or you could end up with nice blue skies as the cap holds.

Another target area will be further north along the cold front which is forecasted to move into western Minnesota and near the SD/NE/IA/MN corners and into eastern Nebraska. Capping will be less of a concern here with a strong mechanism for storm development (cold front) and 700hPa temperatures less than 12C. Development is likely by the evening hours along the cold front throughout western Minnesota and into SD/IA/NE. The problem with the setup here arises with the displacement of instability and shear parameters, with strong instability present along/ahead of the cold front (especially at low levels), but the best shear further ahead of the front. Any development just ahead of the cold front may be able to tap into both instability and shear, thus able to put on a show... This would rely on any outflow boundaries from morning convection...

Additional updates likely within the next 8-12 hours... I will likely favor the secondary target area as it is quite local.

Friday, July 10, 2009

Chase Account - July 9

Several rounds of severe weather swept across portions of northwest Iowa yesterday, from mid-afternoon hail to evening and overnight storms that left hail, winds, and heavy rainfall across parts of the state. I made a trip out to view the storms on two occasions yesterday, once during the mid-afternoon hours between 3:30 and 4:30 PM. This was the initial round of storms that produced some large hail from the SD/IA borders eastward to near Highway 71. Upon arrival to the storms, they were weakening significantly and led to only heavy rains that would obscure your view pretty good. On this trip we would also arrive upon an accident that occurred just west of Ruthven, IA where it appeared a vehicle may have been pulling out of a private lane onto the highway and did not see the cross traffic. A bad scene there as both vehicles were badly damaged, however, have not heard any news about this accident and how either drivers/passengers fared.

The second chase came during the waning daytime hours, from ~8:30 PM to after 10 PM across portions along the Dickinson/Clay county lines and back towards Wallingford in Emmet county. Several occasions of strong lightning strikes, and torrential/blinding rains with the multiple storm cells that we crossed paths with. On the backside of the last cell to be severe warned across these counties we were able to capture several occasions of 3/4" hail and strong east-southeast winds of 40+ mph. Video was captured from the dash cam for the entire trip, however, nothing significant to really note and share... A nice local chase/spot to add on for the year; now we'll wait for some true summer isolated cells to actually have some photogenic quality to the storms!

Wednesday, July 8, 2009

Severe Weather Potential - July 9

A complicated forecast is in the works for the next 36 hours, and perhaps even longer, for Iowa and adjacent areas. A strong wave will initiate thunderstorms this afternoon across the western Dakotas and areas of Montana/Wyoming. These storms should develop into a large MCS, possible derecho, during the evening and overnight hours traversing the Dakotas and moving into western Minnesota by sunrise on Thursday. This MCS will likely be making a right turn throughout the night as the low level jet veers, making the projected path perhaps into northern Iowa between 6-10 AM tomorrow. While the severe weather threat would seem minimal, gusty winds nearing severe criteria is a definite possibility.

As this MCS clears, a stable layer will be left over and likely inhibit additional development until the later afternoon hours. With a cold front and strong disturbance coordinate to create sufficient lift to break and inhibition that will be present across northern Iowa and southern Minnesota. With wind fields increasing in strength throughout the lower and mid-levels, expect deep layer shear to be sufficient for supercells as the initial storm mode with damaging winds, large hail, and isoalted tornadoes all being possible. However, with time and more forcing along the cold front it would appear that the growth of another MCS is likely, yielding a damaging wind threat across the central portions of the state. More details into the forecast will be clear tomorrow morning when the extent of the morning MCS is known... Expect an additional update late tonight and early tomorrow as to the possibilities of severe weather across portions of Iowa.

Severe Weather Recap - July 7

A cluster of thunderstorms developed in eastern South Dakota during the afternoon hours yesterday, and entered into northwest Iowa during the evening hours. These clusters of storms were at times severe warned with the potential for both damaging winds and large hail, estimated 60 mph winds were reported and hail up to 1.5" in diameter also occurred. The severe weather was intermittent at best, with little in the way of damage reported.

I ventured outside of home for a short while as the leading edge of what was a bow echo entered the state in northern Emmet county. Upon arriving outside of Wallingford I did capture very brief video of a gustnado on this leading edge. I estimate the location of this gustnado near Dolliver, IA given its' distance away from me at that time. An otherwise uneventful night as gusty winds and heavy rains were all that occurred...

I will try to get a vidcap of the gustnado up at a later time... Along with a few panoramic images of the shelf as it entered Emmet county.

Tuesday, July 7, 2009

Severe Weather Update #1 - July 7

A Severe Thunderstorm Watch has been issued for portions of South Dakota, Nebraska, Minnesota, and Iowa until 10:00 PM this evening. This watch will cover the four corners of these states, thus including a majority of the counties within the Sioux Falls NWS CWA. Additional thunderstorms have formed outside of this watch area along a warm front/outflow boundary across portions of Iowa. These storms are expected to remain below severe limits, thus no watches or warnings have been issued for this area.

Forecasts and analysis of ongoing convection indicates that the severe weather threat for northwest Iowa will likely not come into play until the evening hours (after 5 PM).

Severe Weather Potential - July 7

A trough of low pressure and possible weak low pressure center should be located over central South Dakota this afternoon. A stationary boundary should extend eastward from this low over parts of eastern South Dakota, southern Minnesota and northern Iowa. This boundary and low pressure center should be the focus for thunderstorm development this afternoon and through the overnight hours, with the potential for severe weather.

While current forecasts indicate that thunderstorms will be more likely to develop in South Dakota, and move into MN/IA/NE during the evening/overnight hours there is potential for development along the frontal boundary during the afternoon and this is supported by a few high-resolution models this morning. Any thunderstorms that do develop this afternoon across the northern plains of SD/NE/IA/MN may be capable of damaging wind gusts and large hail, as well as an associated weak tornado or landspout threat. Storms are likely to congeal into clusters as the evening progresses and move southeastward with time with more of a damaging wind threat through the overnight hours into IA/MN and perhaps northeastern Nebraska.

Additional updates are possible this afternoon as storms develop or initiation becomes more defined...

Wednesday, July 1, 2009

A Few of Natures' Fireworks Possible

With the fourth of July weekend coming up, it looks like mother nature will try to give us some of her own fireworks as we head into the weekend. A storm system will bring the chances of thunderstorms across the state on Friday, and continue through the fourth over a majority of the state. While the chances are fairly small currently, any storms that do develop are likely to be strong and potentially severe with damaging winds and marginally severe hail. These storms would at least cause some problems with any outdoor plans for Friday evening and Saturday across the state. An additional update before this weekend begins may refine any details on the chances for strong/severe thunderstorm across the state...

The forecast otherwise couldn't be too much better for the state... Thursday's highs ranging from the mid 70s to mid 80s from northeast to southwest; overnight lows in the mid 50s to lower 60s. Fridays' highs in the lower to mid 80s across the state will give way to thunderstorms chances across the western half of the state; overnight lows in the lower to mid 60s across the state indicate the increase in moisture across the state. The fourth of July will bring in more cloudy weather across the state, but highs still within a few degrees of 80 across the state. Slight chances of thunderstorms would appear to exist across the entire state during the afternoon, subsiding in the overnight hours. Saturday night lows near 60 across the state will make for an enjoyable overnight. We'll finish off the holiday weekend with highs in the lower 80s and lows in the low to mid 60s leading us back into the workweek.