Monday, June 8, 2009

June 7 Tornado/Wind Survey for Dallas/Polk Counties

The National Weather Service office out of Des Moines issued their public information statement regarding the tornado reports and damaging wind reports that were received as a severe and tornadic thunderstorm moved across Dallas and Polk counties on Sunday evening. The results of the survey indicated that a brief EF-0 tornado occurred south/southeast of Dallas Center. The tornado length was 1.5 miles long, with an average width of 100 yards; the tornado damage path was concentrated within a path of straight line winds which began near Adel and continued northeast. The reports of a tornado near the town of Grimes was investigated and the NWS determined that this was a results of straight line winds that occurred on the southern periphery of the supercell's mesocyclone. A nice image that the Des Moines NWS has posted to their website is below:




To read more details and the complete public information statement please view the survey link: Adel to Grimes Wind Damage Survey

Another Cool Week

Over the past couple of days I couldn't help but hear people whine about how 'cold' it was across northwest Iowa and adjacent areas that were north of the warm front that sparked off several rounds of thunderstorms. It is always ironic to me how people use the word 'cold' to describe the weather; if it was anytime between October and March then people would be very pleased and say that the past couple of days of weather has been 'warm'. Instead, just because we want to see temperatures in the 70s and 80s or even higher we start complaining that it is 'cold' outside. Thus, this posts title will be in regards to the continued cool weather that is expected for what looks to be the remainder of this week.

Today's temperatures range from the upper 50s to mid 60s across a majority of the state, while extreme southeast Iowa was able to stay in the warm sector for a while and saw highs in the 70s and lower 80s. We'll dry off tonight with low temperatures ranging from the mid 40s to mid 50s from north to south. The showers/thunderstorms will return to western Iowa during the evening hours on Tuesday; with highs in the mid 60s to mid 70s from northwest to southeast. The showers/thunderstorms will overspread much of the state overnight on Tuesday, with low temperatures in the 50s throughout the state. Scattered showers are likely to continue over the state on Wednesday, hindering high temperatures to the mid 60s to lower 70s from north to south.

Although there are a few rogue chances of a shower/thunderstorm, we should stay dry through the rest of the work week. High temperatures for Thursday and Friday should range from the lower to mid 70s. Low temperatures in the lower to upper 50s on Thursday night will increase a few degrees to the mid to upper 50s for Friday night.

Sunday, June 7, 2009

Severe Weather Update #2 - June 7

Three storms have formed in vicinity of the warm front across both Iowa and Nebraska, one of which has been tornado warned for over a half-hour now. The tornadic portion of the storm passed just 15 miles south of my previously mentioned virtual target area. This storm has yet to produce a tornado, although a few reports of a roughly organized wall cloud have came into the NWS. This storm continues to move east just north of the Kansas/Nebraska border, and a second storm that is severe warned near Falls City, NE capable of large hail. A third storm along the warm front that is severe warned is much further east in Iowa, near Adair, that is capable of large hail near quarters in size. This storm is moving in more of a northeast fashion.

It would appear that much of Iowa will see isolated thunderstorms this evening and overnight; the best areas for severe weather are likely to be over areas along/south of I-80. Thunderstorms appear to be forming rapidly near the Iowa/Missouri border and will likely be the start of an MCS that will move over southern and eastern Iowa capable of large hail and damaging winds.

No additional updates are likely this evening as the severe weather threat is playing out similar to forecasted.

Severe Weather Update #1- June 7

Just a quick update beings I have had a chance to look over the latest mesoscale analysis from the SPC. The warm front is very well defined across Nebraska and Iowa, with strong frontogenesis also occurring across southeast Nebraska and southwest Iowa. There is fairly high temperatures at 700hPa which is likely leading to some pretty good capping across much of eastern Kansas and into adjacent areas of NE/IA/MO. The vorticity maxima associated with the shortwave is now across central NE/KS and this may provide sufficient forcing to begin forming a cumulus field along the warm front. It would appear that all other factors are sufficient for strong supercellular storms this afternoon, wind shear greater than 40 kts, moderate to strong instability, and the good focus for thunderstorms.

We do have cloud cover and a few showers associated with the shortwave, and these may be a hindrance or a help to convective development. My current virtual chase target would be for Tecumseh, Nebraska...

Severe Weather - June 7

Once again a warm front will be draped across the plains states, from northern Kansas through southeast Nebraska and then across parts of southern/central Iowa. Areas along and south of this front are likely to see temperatures near/above 80 degrees this afternoon with surface dew points into the lower 60s. This will provide moderate to strong instability, and combined with ~40 knots of 0-3km wind shear across this sames area of eastern KS/NE and southern IA will provide an environment for supercells. The potential for supercells will be enhanced by an increasing low level jet across the plains states, and any outflow boundaries that may be situated in this warm sector. Thunderstorms should develop along these outflow boundaries in vicinity of the warm front, indicating likely areas of initiation to northeast Kansas, southeast Nebraska and potentially into southwest Iowa. Thunderstorms in the early stages are likely to contain very large hail and the potential for tornadoes; as storms continue into the overnight we could see one or more clusters of storms. These clusters are likely to continue the threat of large hail and especially damaging winds across the remainder of southern/eastern Iowa.

Additional updates are possible this afternoon as storms begin to develop...

Saturday, June 6, 2009

Severe Weather - June 6

Overnight convection associated with an MCS has continued to move through the state of Iowa this morning, and another cluster of precipitation is also moving across extreme northeast Nebraska and eastern South Dakota as well. This precipitation and its' evolution was a big question mark as to how it would affect the forecast for today's severe weather as it would influence the location of the warm front. It would appear that a cold pool has setup across parts of southeast South Dakota and adjacent areas of Minnesota and Iowa, however, areas behind this convection are already clearing indicating that there may only be a minimal effect from this mornings' precipitation across much of eastern Nebraska and western Iowa. In fact, elevated instability is already showing up across much of eastern Nebraska where clearing is already occurring.

Current SPC forecasts still indicate that they do not expect the front to have much of a northward surge at all today, leaving the primary focus for severe weather across southeast Nebraska and extreme northern Kansas. Once storms fire over that region this evening, they would then propagate northeastward along the warm front into western Iowa with the threats of damaging winds and large hail. This may be the more likely scenario, however, an eye will likely be kept on this front and its' northward progression throughout the day.

Severe weather will definitely be a possibility for areas south of a Kearney, NE to Sioux City, IA to Fort Dodge, IA line. All modes of severe weather would appear likely south of this line, including the threat of tornadoes in both discrete supercells and even in a more linear segments given strong shear values across the region. Once again however if the warm front is able to surge north across any portion of Nebraska/Iowa the threat of severe weather may move northward... Additional updates this afternoon may address this if it does indeed look to be occurring.

With prior plans in Vermillion, SD until ~7 PM I don't see any chasing occurring today unless the front can surge well north of its' current forecast. Tomorrow may be another chance with those details later tonight...

Friday, June 5, 2009

Severe Weekend Weather!

One of the more impressive setups for severe weather will take place beginning today and continue through the weekend for the northern/central Plains states. A broad western trough has finally moved into position to create southwesterly flow across the high plains today, and will make progress eastward over the next two days to continue this southwest flow into the central US. Today's severe weather threat will be held to the high plains due to meager moisture in place, and the more favorable upper level support is located across the high plains as well. Today's area of interest will include western Nebraska, northeast Colorado, and nearby adjacent areas including eastern Wyoming. The main threats with today's storms in the high plains will be very large hail and tornadoes given a strengthening low-level jet in the evening hours.

Tomorrow (Saturday) the lee cyclone begins to move off of the high plains and further east into Nebraska, with the aid of strong southerly jets just above the surface and an open Gulf of Mexico even at the surface we will see strong moisture return through the day and into the overnight. Moisture return will likely make it to near 60 or just above by Saturday evening, leading to only moderate instability across Nebraska and into western Iowa along/south of a warm front. The warm front location is somewhat in question, although this mornings' models locate this front from near Lincoln, NE to Clear Lake, IA and eastward towards Dubuque, IA. A dryline also situates itself southward from the low in central Nebraska, leading to other favorable areas for severe weather along this dryline through central Kansas. Shear values are favorable throughout this region, and initiation of storms appears likely nearest to the low pressure system in Nebraska and along/north of the warm front in NE/IA. Further south along the dryline could have explosive development if 700hPa temperatures well above 10C do not cap the convection. Storms that do develop and remain somewhat discrete will be supercellular in nature capable of large hail, damaging winds, and tornadoes. The more likely scenario will be for the storms to develop near the surface low and near the warm front, these storms will be capable of large hail/damaging winds. Given moderate moisture, storms may become surface based and definitely become capable of tornadoes as storms move along the warm front. An additional update on tomorrow may be posted later today if necessary...

Sunday is another day that holds very high potential for severe weather, given deeper and more sufficient moisture return south of the warm front that is once again expected to be draped from northern Nebraska through central/northern Iowa (Norfolk, NE to Sioux City, and near Clear Lake). While the warm front doesn't appear as defined on Sunday, likely due to convection debris/cloud cover from Saturday night, sufficient instability and lift would appear strong enough to erode the capping inversion that is once again present south of the warm front (10-12C 700 hPa temperatures). Once again storms should develop near the low pressure and near the warm front, capable of large hail/damaging winds/tornadoes given increasing shear values throughout the evening. As storms continue to develop near the low and further south along the dryline, it would appear that an MCS will once again develop and push east/northeast through Iowa capable of hail/winds. An update will be posted for Sunday either tonight/early tomorrow or potentially early Sunday.

I'm currently scheduled to photograph a wedding in Vermillion, SD on Saturday afternoon and early evening. Meaning I'm already in position for the potential on Saturday along the warm front and perhaps in position for Sunday in northeast Nebraska given an overnight stay. All of my chase gear will be with me needless to say...

Tuesday, June 2, 2009

Cooler Weather

Lows over the next few nights will be a ways below normal, while highs struggle and remain just below normal. Overnight lows tonight across the state will range from the lower 40s in the extreme northwest part of the state to the lower 50s across the southeast portions of the state. While partly to mostly cloudy skies remain across the state tomorrow we'll see highs ranging from from the upper 60s to lower 70s and northerly winds from 5-15 mph. Another chilly night is in store for Wednesday night, with skies clearing the lows will drop into the 40s for nearly the entire state.

Winds will begin to turn to the south once again on Thursday, and with partly cloudy skies highs will be back to near-normal from the lower 70s along the Mississippi to highs near 80 along the Missouri River. With meager moisture returning, lows overnight on Thursday will only drop into the lower to mid 50s from east to west across the state. We'll also see some slight chances of showers/thunderstorms move into the state for the overnight and continue through Friday night. Friday's highs will range from the lower 70s to the mid 70s, and overnight lows from near 50 in the north to the mid 50s in the south.

A blast of colder air will return for the weekend, and with that comes showers/thunderstorms across the state. More details on the weekend precipitation chances in the next update!

Monday, June 1, 2009

Weather Update - June 1

Despite a severe thunderstorm watch being issued for portions of southern Iowa, the severe weather threat has never really ramped up due to continue cloud cover and the lack of organized convection. The Storm Prediction Center has chosen to continue the watch over southern Iowa, but it would appear that storms will remain very unorganized through the evening hours.

Thunderstorms are likely to continue over much of southern Iowa, thus despite the lack of severe weather, the likelihood of flooding is fairly high due to the training of storms over the same areas. As the storms continue across the state tonight and into tomorrow, we'll finally clear off on Tuesday afternoon and stay that way until later this week. The next update will contain the forecast for the remainder of the week to see how warm or how cold we can manage to get!

Severe Weather Forecast - June 1

Welcome to June! Our first day will be welcomed with a warm front draped across the state, which will trigger afternoon/evening thunderstorms capable of large hail, damaging winds and even a tornado or two! After the cold front slid through parts of the state last night, the front will continue to slowly progress southward and may even stall out somewhat this afternoon with the warming air mass to its' south. Current forecasts indicate it to position itself near the I-80 corridor by 7 PM tonight.

For those that are along this front, just south/north of the boundary are going to be in a favorable position for thunderstorms this afternoon. Today is one of those warm front days where the instability is all south of the front, but the shear is mainly north. Which means any storms that are able to ride along the boundary to get the best of both sides will be the strongest and most organized of the day, and will be the most likely storms capable of a tornado or two. With flow otherwise parallel to the front, expect storms to eventually congeal into broken lines or clusters capable of large hail and a few wind gusts. Once again expect the thunderstorms to persist into the early nighttime hours with some severe potential.

As the low level jet increases tonight, this will push some elevated instability north of the boundary, likely over much of Iowa. This will also bring the chance for at least elevated storms capable of some large hail given this strong overrunning of moisture across the front in southern/central Iowa. These storms will likely be in clusters or broken lines given the better shear values that are north of the front.

I begin my part-time job this morning, thus am not expecting to chase today along the stalled boundary. Although if any significant changes in the tornado chances occur by early this afternoon I may have to take the quick dive south into the favorable chase area... Another update is possible early this afternoon...