Tuesday, May 6, 2008

May 6 Severe Weather Update

3 PM Update: Severe Thunderstorm Watch #266 has been issued to include portions of extreme western Iowa until 10 PM.

2:30 PM Update: Severe Thunderstorm Watch #265 remains in effect for portions of northwestern Iowa until 7 PM. Currently a small line of thunderstorms has continued to evolve as it enters a more favorable environment with the latest radar scans indicating continual expansion and strengthening. Currently severe thunderstorm warnings are issued for Yankton county South Dakota, and Cedar county in Nebraska. These two cells should continue to move eastward and cross into the state of Iowa before 4 PM.

More development is expected to the south of this current line and work into the state this afternoon. Both large hail and damaging winds are likely with the storms this afternoon for northwest Iowa.

More thunderstorms will continue to work into the state tonight, with the potential for damaging winds and large hail. Some parts of the state may see more than one round depending on how and where storms develop. More updates as we continue through the afternoon/evening and overnight will address these issues.

May 6 Severe Weather

Severe weather across the state is becoming increasingly likely, with the threats of very large hail and damaging winds now apparent. The SPC has issued a severe thunderstorm watch that covers portions of northwest Iowa until 7 PM this evening. Several cells of thunderstorms are likely this afternoon posting a threat of hail up to 2 inches in diameter and thunderstorm wind gusts upwards of 60 mph. Currently two severe thunderstorms are occurring in southern SD and southwestern MN, both posing a hail and wind threat.

As thunderstorms increase during the afternoon hours and into this evening, expect a complex of storms to begin to work its' way into Iowa. Several other clusters of severe thunderstorms are expected over central and eastern Nebraska, these may also pose a threat during the overnight hours for the state of Iowa. For those of you in Nebraska, large supercells capable of potentially dangerous hail is expected during the afternoon/evening hours. The threat should begin to change to more of a wind threat as storms congeal into an MCS for the overnight.

Heavy rains and potential flooding is another concern for the state of Iowa, to go along with the large hail and damaging winds. More information will be available as storms move into the state this afternoon.

Monday, May 5, 2008

May 6 Severe Weather Threat

It has been a long night of continuous work on school final projects, so not to much time to type things out. Not to mentioned I've typed of 10 pages of work already so the fingers are just kind of gliding across keys in hopes of hitting the right ones...

Severe weather threat for tomorrow looks to mainly be confined to tomorrow nights' MCS event that will roll through ahead of the cold front. A few thunderstorms may form tomorrow afternoon as convective temperatures are reached and the airmass becomes unstable on its' own. However, at this time the thunderstorms will likely be pulse-type in nature with little shear to keep them alive. Maybe a marginally severe hail or wind threat during the afternoon, but the action will likely be in the form of a squall line of some sort overnight on Tuesday into Wednesday.

I will post an update tomorrow morning on the threat for the day, along with what the SPC thinks on the day with their latest outlook. Look for that tomorrow, otherwise enjoy the sunny skies and temperatures in the upper 70s to upper 80s for Tuesday!

Sunday, May 4, 2008

Finals Week Weather

That's right, here at Iowa State we've reached the end of the semester. This week of May is finals week, which of course means that there will be exciting weather to take away from my concentration on what has to be done. This does look to be true, as warm weather and thunderstorms are all likely threats this week.

Today and tomorrow (Monday) look like amazing spring days, no chance of precip and mainly clear skies will help the temperatures warm nicely. Highs today expected to range from the mid 60s to lower 70s from east to west; tomorrow's highs warm even more to the lower 70s to a few 80s from east to west. Lows tonight in the low to mid 40s; Monday night lows in the upper 40s to mid 50s with increasing moisture.

Tuesday is the first day of interesting weather, as a cold front will begin to make its' way across the state during the late afternoon and overnight. Tuesday's highs before the front are expected to be in the mid to upper 70s with increasing moisture. The front should spark thunderstorms across WI/MN/SD/NE and northwestern Iowa during the evening. These thunderstorms are then expected to move east/southeastward throughout the overnight hours. Currently the Storm Prediction Center has labeled the state under a slight risk of severe weather due to this cold front, large hail and damaging winds look to be the threat throughout the overnight hours across the state. Lows will range from the mid 50s to mid 40s as the front moves through and bring cooler temperatures with northerly winds.

This front should stall out south of the state, leaving cool and wet weather for portions of the state on Wednesday as well. Highs on Wednesday should be in the 60s, with showers likely over the southern half of the state. Lows Wednesday night in the 40s with showers continuing over much of the state. By Thursday, only southeastern Iowa is under a chance of rain, however this should only last for the morning hours. Highs in the upper to lower 60s from west to east, with lows Thursday night in the mid to upper 40s throughout the state.

We'll warm up once again with increasing southerly winds and moisture for the end of the week. A chance of showers and thunderstorms also look to come into the forecast for the end of the week. Later updates will focus on the severe thunderstorm threat for Tuesday...

Friday, May 2, 2008

May 2 Severe Weather Update

Several showers and embedded thunderstorms have rolled through the state this morning and early afternoon. Currently these thunderstorms are occurring over Northern Iowa, with one thunderstorm warning issued earlier for Cerro Gordo and Worth counties for damaging winds up to 60 mph. Two reports have came out of that storm, one from Mason City and another from Thompson, IA; both with 60 mph and 59 mph measured wind gusts respectively.

With the lack of sunshine that occurred over the state this afternoon, the severe weather threat looks to have been limited. Extreme northeastern Iowa, mainly along the Mississippi are still in a favorable location for thunderstorms and showers to develop this afternoon/evening. Marginally severe hail and wind gusts are a threat with those storms, however tornadoes are also possible given the relation of the strong low pressure system that will be just to the west/northwest. A Mesoscale Discussion from the Storm Prediction Center indicates that they are watching portions of northeast Iowa, southeast Minnesota, southern Wisconsin and Illinois for the potential of severe weather including tornadoes. There is no watch posted at this time however...

May 2 Severe Weather

Thunderstorms will be widespread across the state today and are already ongoing this morning over eastern Iowa. Another line of thunderstorms/showers is in eastern Nebraska and should move into western Iowa before 10 AM. These thunderstorms should continue into the afternoon hours, where redevelopment is also possible in eastern Iowa along the cold front. The redevelopment of thunderstorms may lead to some isolated severe weather for the eastern third of the state. Main threat with these storms will be marginally severe hail and some strong wind gusts, however, an isolated tornado cannot be ruled out if sufficient heating can take place early this afternoon.

We cool down in the wake of this strong low pressure system, areas of western and central Iowa are already underway with their cool down as the cold front has pushed past and the low continues to pull down cooler air from the northwest and west.

More updates are possible later today if any severe weather is likely to occur

Thursday, May 1, 2008

Northwest Iowa Tornadoes (May 1)

Multiple tornado reports occurred on May 1 in northwest Iowa between 6:50 and 7:45 PM. The tornadoes occurred through Lyon and Sioux counties, near the towns of Rock Rapids, Sioux Center and other nearby towns such as Doon, Inwood, and George. The NWS in Sioux Falls has conducted a survey of the tornadoes, a total of 5 occurred in Sioux and Lyon counties. The longest and strongest tornado is one that began just north of highway B30 west of Carmel, IA and continued to the north/northwest passing just to the west of Rock Valley and finally lifted just south of highway A42, southeast of Inwood. This tornado which featured a path of nearly 13 miles and width of damage of up to 500 feet was rated an EF2 with winds 111 to 135 mph. More information and maps of the path and damage locations can be found on the Sioux Falls NWS Survey Page. In addition, the NWS in Sioux Falls has posted a summary of the events along with a few synoptic reviews as to what occurred in Sioux and Lyon counties.

NWS May 1 Tornadoes & Severe Weather Review

One storm chaser was on this storm and captured the entire life of at least two of the tornadoes, including the large tornado near Rock Valley, IA. Van DeWald, the storm chaser from Omaha, NE made the trip and was the one who captured the images that can be found on his Chase Account Page. He also had a video camera going, in which the video can be found on youtube: Video of the Rock Valley Tornado on May 1, 2008 (~7 PM)
Video copyright Van DeWald

Several pictures from local residents of the tornado and subsequent damage can be found on the KTIV weather blog. A few other pictures from locals can be found throughout the internet, some quick links to some via blogger uploads: Image 1, Image 2, and Image 3.

Other news sources have received some great video and pictures from locals as well. KELO out of Sioux Falls has three public videos that have been uploaded to their website, you can view them here.

The tornadoes from May 1 are unique in the way that they often appeared to be occurring underneath fairly weak showers and thunderstorms. In some cases appearing where there was little reflectivity present on the radar. Some initial statements are accounting these as landspouts, or essentially a tornado that is not associated with a thunderstorm's rotation. Early indications do show that there was strong rotation on KFSD radar, at least at the lowest level. I will be looking into the storms to see how extended this rotation was into the storm, but currently FSD NWS is calling these tornadoes instead of landspouts. I will post any future information on my findings in the coming days here...

8:00 AM May 2 Update: I've updated the post above with a few more screen grabs from Van DeWald's video camera and the video that he captured.
Also have a few images via KTIV that local residents sent in last night and this morning that were added.

May 2 Afternoon Update: Rearranged the post a bit, included new information and added in a link to the Sioux Falls NWS page they have about the event. Also more local images and video links were added.

5:30 PM May 2 Update: The Sioux Falls NWS has completed their survey of the tornadoes in northwest Iowa, this information was added to the page.

May 1 Severe Weather Update #2

I took a small trip outside of Ames late this afternoon/evening in hopes of some thunderstorms along a surging dryline in central Iowa. A nice CU field was present, and several towers tried to get going, but to no avail as they were all crushed by warm temperatures aloft. This wasn't the case in extreme northwest Iowa, as a strong dynamically driven system combined with the low pressure in the vicinity to create a favorable environment for rotating storms.

The first tornado report in Iowa came just before 7 PM near Sioux Center. As the storms continued to develop and grow, several more tornadoes were reported in Sioux and Lyon counties through 7:45 PM. The only damage report thus far was near Rock Valley where it hit a farmsted to the west of town. The second-hand report indicated that several buildings may have been hit, however the house looked okay. More detailed reports on those storms and subsequent tornadoes once Sioux Falls NWS conducts surveys and more images of the tornado(s) are available.

Currently the dryline is stalling out in central Iowa and may retrograde (move west) overnight tonight. Several isolated thunderstorms occurring central and eastern Iowa, with one severe thunderstorm warned storm in Black Hawk and Bremer counties. Quarter-sized hail is possible with that storm through 10 PM.

Other areas in the central US are still being pounded by severe and tornado warned storms, from central Oklahoma through eastern Kansas and into northern Missouri. These storms should continue to move north/northeast and into the state of Iowa during the overnight hours likely effecting mainly the eastern half of the state. These thunderstorms should move out during the morning hours, in time for another round potentially in the afternoon for eastern Iowa. Once again severe weather is a possibility for those storms in the eastern half of the state tomorrow afternoon, the best threat will likely be near the low pressure system center that may be somewhere in northeast Iowa. Once more information is known on the possible location of this low and the severe weather threat, later updates may relay that information.

May 1 Severe Weather Update

Currently going through a complicated forecast scenario for the central plains, with the potential for large hail, damaging winds and isolated tornadoes. Latest forecasts indicate that western Iowa is now becoming a more favorable target than previously thought, this will not only include southwestern Iowa, but northwest Iowa as well. Several ISU crew vehicles are hitting the road within the next hour heading towards western Iowa. Once again, stuck in class until ~5 PM, but will then make a decision with a 'local' chase not out of the question for this evening. Might not have another update on the blog until late this evening or after class depending on how the situation looks. The western third of the state of Iowa should be alert though this evening for the potential for severe weather...

May 1 Severe Weather Threat

Severe weather is likely over portions of the central plains, with all modes of severe weather (tornadoes, hail, and wind) possible. A strong low pressure system associated will begin to be cut-off during the late hours of the day. This low will be responsible for the setup of a triple point over some portion of either southeastern NE or eastern KS during the evening hours. The dryline and warm front intersection may be a key positioning for any severe weather initiation before midnight. As we head into th later nighttime hours, a cold front further to the west will begin to overtake the dryline and likely initiate convection in mainly linear form across the plains.

Several concerns still exist with the setup for severe weather, one being moisture return and the other being warm temperatures aloft creating a cap over the plains. The capping problem is a definite concern for the southern portion of the current outlook (southern KS and OK) where storms may not be able to initiate until the cold frontal passage ~Midnight. To the north, less moisture may exist, however cooling in the mid-levels may still weaken the cap enough to initiate convection during the late evening hours.

As far as chasing this setup, I am unable to be out of Ames until 5 PM. This limits me extensively on where I can be in time for a good storm. Depending on how things do look when my day on-campus ends, I will consider heading out locally. I may end up waiting for more of a linear mess to come to me during the early morning hours, as I could definitely use some lightning picture opportunities as I've missed the last few. More updates on my chase potential as well as the entire system in later updates during the day...

12:45 AM Update: SPC Day 1 will initially includes a large portion of the state under a slight risk of severe weather; areas west of a Mason City to Waterloo to Keokuk line. This slight risk is maximized for areas of southwestern Iowa, where the potential for tornadoes and large hail is greatest. Although current SPC wording doesn't indicate a lot of potential, not sure if I want to believe that currently. Later SPC updates may prove otherwise with an increased threat and potential moderate risk if moisture return can be realized...