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Minnesota Tornado Throws a Pickup Truck One Half Mile!

2:16 pm in Extreme Weather, In the News, Severe Storms by Ted Keller

Storm Reports of Saturday, August 7, 2010

The National Weather Service has confirmed that the tornado which touched down in North Dakota and traveled east into Wilken County, Minnesota on Saturday was rated a low end EF4.  This means the storm had estimated peak winds of  170-175 mph.

The link to the National Weather Service assessment of the damage.

This was one of several tornadoes which touched down in Minnesota, North Dakota and Wisconsin on Saturday evening.

This area was slammed by a violent tornado outbreak on June 17th of this year.  A complete report on that outbreak can be found here.

One tornado on Saturday was caught on tape by a storm chaser crossing a road and then destroying a building.  According to the National Weather Service, about 14 buildings were destroyed by this twister.

A Wild Outbreak of Tornadoes

7:05 pm in Severe Storms, Storm Summaries by Ted Keller

No Place on Earth

can put the ingredients together for an outbreak of tornadoes quite like the central U.S. and the outbreak of May 10th, 2010 certainly reminds us of this fact.

Rope Tornado Near Yukon, OK. Photo by Chris Novy.

The outbreak came together as extremely unstable air was pulled northward ahead of a dry line.  At the same time, a very strong but compact area of intense air level winds (shortwave/jet max) moved over the area.

The alignment of the upper level winds and unstable air was going to last for only about six hours and in a relatively small area.  But in that time and space frame, numerous supercell thunderstorms quickly evolved, most into tornado-barring cells.

At this writing, the National Weather Service in Norman, Oklahoma has indentified ten areas where tornadoes likely tracked on this day.  More tornadoes occurred in Kansas and northeastern Oklahoma. This will be refined more as survey crews finish their painstaking task.  The death toll stands at five. 

NWS Reviews:

The Set Up

Low Wall Cloud, Multiple Vorticies. Photo by Allan Detrich.

It was a situation typical to the Great Plains but with the volume cranked way up.  It starts when a “trough” of low pressure develops over the western U.S.  This encourages steady southerly winds to blow over the central U.S. drawing humid air from the Gulf of Mexico northward.  On this day the dew points, a measure of moisture in the atmosphere, were quite high and this humidity helps to make the air unstable.  In fact, all else being equal, higher dew points will generally lead to more violent storms.

Unstable air is produced whenever you can warm the air at or near the surface of the earth while keeping things relatively cool aloft.  Moisture adds to the instability because when water vapor condenses back into visible cloud droplets, the energy in took to evaporate this water is released into the atmosphere.

Now on top of all of this, the jet stream winds, fueled mostly by differences in temperature from south to north, were howling!  These winds do several things.  The overall increase in wind speed with increasing height provides structure for developing thunderstorms and allows them to become “supercells”.  Also, the speed and directional changes in the wind close to the earth’s surface provide a spinning which the updrafts of a thunderstorm inherit.

Sometimes, the “wind shear” can be too strong and developing storms will get “sheared” off.  The winds on the outbreak day were strong enough to be a concern for this happening BUT the instability was so strong that the updrafts which make up a thunderstorm rose violently and were able to survive, even flourish, in this environment!

Chasing These Storms

The wind speeds were very high in the atmosphere leading to storms traveling over 60 mph!  This “storm motion” made these storms difficult to chase. Still, there were some shots.  The multiple-vortex tornado shot by Andy Gabrielson is stunning!

Some local chaser friends of mine Jason Blum, Dave Toner and Cody Hudson got themselves into a dangerous situation near Arkansas City, KS.  Their vehicle goes down a steep embankment.  Then the tornado passes nearly on top of them!

The Ozarks Missed This

Some may wonder since weather moves from west to east why the Ozarks didn’t see at least a weaker version of what happened out west, especially considering how fast the jet stream was.  The answer is that we were in much more stable air.  I watched as these storms literally fell apart while racing eastward.  The fast jet stream winds actually outpaced the ability to draw unstable air out ahead of the system.  Later on, we actually did have a tornado warning or two west and northwest of Springfield but this was mostly due to the incredible wind shear working on even the weakest updraft to see if can be coaxed into rotating.

Monday Severe Weather Threat

1:40 am in Forecast Discussion, Severe Storms by Ted Keller

High Risk on Our Doorstep Monday

The Storm Prediction Center upgraded their forecast overnight to a high risk in areas just to the west of the Ozarks with a moderate risk still forecast for the western portion of our viewing area.

A very potent upper level jet stream will interact with a rapid return of moisture near the ground to produce an explosive combination leading to the development of classic, discrete supercells which will likely bare tornadoes shortly after they fire through Oklahoma and Kansas late Monday afternoon.
There is a good chance that some of these cells will make it into the Ozarks Monday evening!  The chance for a tornado is fairly high in areas of extreme western Missouri and Arkansas beginning right around 7 pm.  It is possible for some of these storms to continue to move into the Ozarks later in the evening.
While the axis of unstable air is not forecast to shift east and be as strong as it will be in the initial storm formation area, severe weather is still a concern over all of the Ozarks Monday evening and overnight into early Tuesday!

Severe Weather Monday

10:27 am in Forecast Discussion, Severe Storms, Storm Chase Discussion, Storm Chasing by Ted Keller

Severe Outlook for Monday

This has been holding together for a few days now in the computer model forecasts so confidence is running higher that an outbreak of storms will occur over the central Great Plains Monday.

There has been some fluctuation in the position of the dry line which defines the western edge of the threat area,  If it ends up over central portions of Oklahoma and Kansas, the Ozarks would see whatever supercell thunderstorms do develop move into the area later that evening.

One computer model  (NAM) from 12z Friday has pushed the dryline back westward after trending more east the past few runs.  The GFS model is sticking with an “I-35″ (or thereabout) solution which is more east.

Since the event is still 78-84 hours away, there will likely be more adjusting of the position east or west.

The differences are arising because the speed and position of the shortwave trough are radically different between the NAM and GFS computer model!  I posted the images below.  This will make a HUGE difference in where the threat area ends up!  This position will shore up as soon as we get closer to Monday and the shortwave “comes ashore” to be sampled better by upper air measurements.

My friends Matt Gingery and Jill Gilardi will be out chasing on a special project starting Monday.  What a way to kick things off!  I wish them luck and safe travels!

I will be doing a special “Upstream” broadcast on Sunday evening, most likely after the 00z NAM comes out which will be after 9 pm sometime.  I’ll keep you posted!

NAM 500 mb 7pm MondayGFS 500mb at 7pm Monday

Storm Chase Results from May 1st

10:05 am in Storm Chasing, Storm Summaries by Ted Keller

A high risk for severe thunderstorms and long-tracked tornadoes existed for much of central and eastern Arkansas the afternoon of May 1st, 2010.  I went down there to chase this event.  When storms started firing, there were lots of them, most ended up tornado-warned.  Folks were anticipating the worst.  But in the end, very few tornadoes were produced.

Here’s my account of the chase and a bit about why so few tornadoes occurred on this day despite much anticipation.

We drove down via Willow Springs, MO to see the damage caused by an EF1 tornado Friday evening.  The Hillbilly Junction sustained roof damage as did an antique store just up a hill and to the east.  This was the last of five tornadoes produced by a supercell which started in Boone County, Arkansas.

We were a caravan of three with Dustin Elkins and Bo Hessee also driving.  We eventually wove our way down to White Hall which is just north of Pine Bluff.  Here, other chaser friends of ours had gathered including Dena Sanders and Brian DePriest.  The Tornado Intercept Vehicle (TIV) was there as were other chasers.

Boundary Moving Slowing North This Day

Of much interest early on was the very obvious boundary visible on radar stretching WSW/ENE south of Little Rock.  It was thought that this boundary would be able to supply more focused and localized storm relative helicity to storms forming along it.  Indeed several storms west of Little Rock did appear to have an increase in rotation while crossing this boundary.  But the storm motion was taking them across and not along this feature.  If a storm could have traveled along it, it might have produced the longer-track type of tornado which was feared on this day.

Storms became very numerous in southern Arkansas by the 6 o’clock hour.  In fact, too numerous really.  It became difficult to know which storm to chase!  We initially decided to get northeast of the Arkansas River toward the flat rice lands in and around Stutgartt.  But as supercells became tornado-warned in southern Arkansas, we decided to change the plan, back track a bit and try to get one of the southern storms.  While on the way, storms started firing north and south of Pine Bluff which eventually became tornado-warned.  The decision of the day was to not chase these storms and instead press on to the most southeast of all of the supercells which was going to cross highway 65 near Gould, AR.  The reasons we didn’t pursue the Pine Bluff storms were 1) we would have to travel back through the city of Pine Bluff, 2) the river crossing were limited and 3) there was too much rain, drizzle and just plain bad visibility east of these storms.

Radar Image w/Mesocyclone Indicator at 7:46 pm

So, on down highway 65 we traveled.  We were racing against dark really.  We got into position ahead of the well defined cell which had a great hook echo.  One more adjustment southeast to Gould was required due to the slight right turn the storm (and many supercells) started to take.

We saw some great formations and a likely wall cloud but as the storm passed just to our west, no tornado ever formed.  Reed Timmer and the Dominator crew was coming though Gould and we followed them briefly north chasing the same storm but eventually the chase was abandoned.

I’m waiting on the archived SPC data for this day to appear but I suspect that the reason more tornadoes were not generated on this day were due to low values of low level rotation and generally weaker than needed low level winds.

I am compiled a video log of the chase which should be finished by Thursday.

Major Outbreak Again!

8:19 am in Forecast Discussion, Severe Storms, Storm Chase Discussion by Ted Keller

High Risk Today!

The southeastern U.S. has taken a beating with the storms last Saturday and last night.  Now, another high risk has been posted for the area pictured. 

There is a tremendous amount of moisture as measured by the dew points (colored areas) on the inserted map.  This is poised and ready in the high risk area.  What will likely happen is an increase in south to southeasterly wind flow near the surface later this afternoon and evening.  Another jet stream “max” is coming up out of Texas which will help with the development of a low pressure area over the western portion of the threat area. The winds should respond to this feature.

The computer models have been showing this for a few days but with slightly different results.  The GFS has always been more aggressive with the low development.  The morning run of the NAM has come around on the winds a bit more.  This model is also forecasting 0-3km SRH of 150-300 at 21z (4pm), jumping to 300-350 by 7 pm with these values then expanding over all of eastern Arkansas by after dark.  CAPE is progged at over 2000.

The ongoing cells are likely to been producing severe weather by just after noon in some areas.  This is not the main show!  This is expected by early evening over the high risk area.

I will be out with the Mobile Weather Lab today.  I’ll cross my fingers on live streaming on Severe Studios.

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