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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.

Ozark/Howell County Tornadoes, April 30, 2010

7:33 am in Storm Summaries by Ted Keller

The National Weather Service has completed its survey of the supercell thunderstorm which tracked over Ozark and Howell Counties Friday night and has determined that five separate touchdowns occurred with four of the twisters rated EF1 and one an EF0.  The complete report can be found here.

Rotation tightens over Bull Shoals Lake

The rotation was first detected in Boone county, Arkansas near Harrison.  The rotation really tightened up on radar while crossing Bull Shoals Lake while traveling northeast into Ozark county.  There are damage reports from near Pontiac and east of Gainesville.  The circulation passed north of Tecumseh.

Additional damage was produced in Dora and possibily near Siloam Springs.  The tornado then continued northeast and produced damage near Hillbilly Junction south of Willow Springs.

Tornado Approaching Willow Springs, MO. Photo by Jason Blum (still from video)

Storm chaser Jason Blum caught what is likely the tornado looking northwest from his position a few miles south of Willow Springs on Highway 63.

May Day Chase!

9:02 am in Storm Chase Discussion by Ted Keller

Saturday Severe Weather Outlook

It’s very possible I will be heading out east Saturday on a storm chase! If the computer models hold, the target area will be in the Missouri boot heel southward into eastern Arkansas.  Portions of Texas might be at risk as well.

The overall situation is a large upper level trough with two shorter waves (areas of stronger winds/every) rotating through this system.  The first of these waves will possible produce severe weather in the Ozarks Friday.

The second wave will come out into the threat area on Saturday.  It appears is if this feature can induce a weak low pressure system to form immediately to the west of the outlook area.  If this indeed happens, then the threat for significant severe weather will go up!

The 12 run of the NAM is interesting in that it shows an area of rather high EHI’s from northeast Texas to southern Tennesee.

I will update this chase forecast through the week as things can and do change from day to day.  Friday’s severe weather threat is covered in another blog!

Storm Chasing/Severe Potential Friday

10:32 am in Forecast Discussion, Severe Storms by Ted Keller

Severe Outlook for Friday

A deep pressure system will slowing lifting out of the southwestern U.S. Thursday through Saturday and spread some severe thunderstorms along with it. 

The Ozarks will be affected Friday by this system the way it looks now.  The main thrust of the severe weather will probably be over Oklahoma and Texas on this day but could occur anywhere in the green outline on the left.  There is a chance for discrete supercell to drift into our area Friday evening!

As the storm lifts into the  central U.S., it will set up additional severe weather and chasing opportunities today and Thursday.  Last night, there was a very photogenic tornado near Amarillo, TX.

Dew Point Forecast Thursday 7 pm

The maps for Thursday afternoon are fairly classic for a Texas/Oklahoma severe weather set-up.  The dew point map shown indicates a sharp change from orange (moist) to green (dry) over the area, a feature known as the dry line.  It represents an area of contrasting air masses and serves as a point where air collides (converges) and also may rotate (look for bulges).

The jet stream over this area is out of the southwest while winds at the surface are out of the southeast.  This provides the necessary structure for supercell thunderstorms to form and rotate.
This looks to me to be fairly good for tornado potential, given that this is a forecast and not reality!  Best of luck to chasers, stay safe!
On Friday, the set up shifts to eastern Kansas, Oklahoma and Texas.  The morning NAM computer run suggests that the Ozarks may have an interesting Friday evening as single or discrete supercells could slide into the area during the evening.
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