[LeArc] Severe Weather Forecast Discussion

[Andrew Revering]

Severe Weather Forecast Discussion
Sunday March 12, 2006 - Prepared by 
<http://www.aprweather.com/chase/>Andrew Revering

Summary
    * Significant tornado outbreak expected for 
Missouri, E Kansas, E Oklahoma, Arkansas, far NE 
TX, Central & Southern Illinois
    * More severe storms possible in parts of 
Indiana, Northern Mississippi and parts of Virginia.
    * Severe Weather Primary Targets:
        * Kansas City Metro & Vicinity
        * Kingston, MO
        * Chillicothe, MO
        * Kirksville, MO
        * Southern 2 Tier Counties of South-Central and Southeast Iowa
The Storm Prediction Center has issued a High 
Risk for severe storms with large hail, damaging 
winds and tornadoes. The risk is high for each of 
the 3 categories. Tornadoes are obviously the 
greatest concern due to their destructive nature.
Overnight severe storms are ongoing when I’m 
writing this. It appears that severe storms and 
tornadoes are possible Saturday night from 
Northern Arkansas, Southern Missouri, Southern 
Illinois, Southern Indiana and into Kentucky. As 
time goes on these storms should gradually 
weaken, but leave a broad area of heavy 
precipitation known as an MCS in its wake. Many 
in the Ohio River Valley may wake up to a lot of thunder Sunday morning.
Around 6-7 a.m. there should be a lull in 
nationwide activity as instability is at a 
minimum and capping is at a maximum. But it 
shouldn’t be long before the dynamics start to 
come back with the rise of the sun as severe 
storms could start developing as early as 8-9 
a.m. along the Missouri/Arkansas border region. 
By mid-day the storms I’m really worried about 
start developing in Kansas, Oklahoma and Western Missouri.
Low pressure in Northwest Kansas will *not* be 
the focus for severe storms, however it will 
bring up the energy and put it in place for 
severe storms to develop along the low’s 
boundaries. In particular the warm front 
extending from the low across northern Kansas 
into the Missouri/Iowa border region would be of 
greatest interest. A cold front or dryline setup 
sweeping ahead of the low into Eastern Kansas and 
down into Oklahoma may be a secondary area of development.
A sharp moisture gradient should exist in Kansas 
and Oklahoma in response to a dryline, with a 
cold front trailing behind that. Ahead of the 
dryline the warm front should be in an east-west 
orientation across Northern Kansas into Northern 
Missouri. Pooling of moisture into the triple 
point of these boundaries would be an obvious 
area of interest. Plenty of moisture depth 
throughout the area should mean ample moisture 
anywhere that a surface dew point can breach 55 
or so degrees F. This would mean eastern Kansas, 
Eastern Oklahoma and all of Missouri
 however 
northern Missouri and perhaps Southern Iowa would 
be a focal point being along the warm front later in the period.
The best instability would exist across Northern 
Missouri, just south of the warm front. Lifted 
Indices to -5c and SBCAPE values over 2000 joules 
should be plenty to sustain a strong storm. One 
interesting factor to note is the widespread 
availability of low level 3km MLCAPE which is a 
great indication of low level buoyancy. This can 
be associated to tornado development when focused 
along areas of strong surface vorticity such as a 
boundary. Initially an area that stands out is 
Eastern Kansas for this to occur with the greatest force.
A strong 850 jet should exist along the 
Kansas/Missouri border at about 40 knots. A 
general rule of thumb is that the most severe 
storms are just west of this jet axis, which 
again would hint at Kansas for strongest initial 
development. Deep Layer Shear of 60 to 70 and 
even 80 knots in this area not only suggest 
supercells, but would strongly emphasis the risk 
of tornadoes associated with ay supercell. One 
concern that is always had on a highly sheared 
day is the threat of having ‘too much shear’. 
It’s possible to have too much shear given a 
quantity of instability. However, this setup 
looks as if there should be more instability and 
just the right amount of shear given that amount 
of instability, without pushing the shear 
envelope too much. This gives us a strong amount 
of shear, but not too much that the storm cant 
handle it. The end result looks like the classic, 
perfect setup for cyclic tornadic supercells, 
especially along the warm front where storms can 
get rooted in the boundary and follow the warm 
front for some distance downstream (read: Missouri and Iowa).
Good vertical motion with limited capping in the 
area spell out an early initiation to me. This 
means tornadic supercells developing in Eastern 
or Northeastern Kansas around mid-day, and then 
traveling ENE along the warm front into 
Northwestern and North-Central Missouri and 
Southern or Southeastern Iowa later in the 
afternoon. Given the amount of shear proposed by 
the models, I can’t imagine the storms would have 
any reason to line out. Especially since the low 
is far separated from the action area, and the 
associated cold front/dryline will too remain farther to the west.
Again with good vertical motion and eroded 
capping, more tornadic storms may easily develop 
along old and new outflow boundaries in the warm 
sector. This could mean nothing less than 
widespread tornadic supercells throughout the central US on Sunday.
Low level directional shear is often a parameter 
that may or may not exist on a tornado day, 
however if it does exist it is a great enhancing 
tool for the situation. It appears that we will 
have excellent directional shear from the surface 
to about 850mb, especially in Southern Iowa and 
Northern Missouri. So not only are storms likely 
to be tornadic during initiation in Kansas, but 
they may not only hold their own but perhaps 
strengthen as they travel downstream into a more 
unstable and better sheared atmosphere in 
Missouri and Southern Iowa. 1km Helicity in these areas of 400 to over 500!
Other tornado parameters include LCL (cloud base) 
heights at an optimal level under 1000 meters, 
nice mid level dry intrusion and a high 0.4 1km 
VGP (vorticity generation potential).
What this all spells out is a big tornado 
outbreak. Storms will be chugging along at 40 MPH 
or better through tough terrain. I wouldn’t 
suggest chasers chase this one unless they are 
well trained. Spotters are going to be in big 
demand though as stationary citizens who can see 
all of what’s going to be out there are going to 
better cover area than a bunch of chasers that 
gang up on one storm. Also, I think this will be 
widespread. As I stated above, even big 
supercells and tornadoes quite possible off of 
the main boundaries with strong lift, instability 
and weak cap with outflow boundaries to work 
with. So this means supercells all over the 
place, and it’d be nice to have spotters on each 
of those storms, rather than all driving 
(chasing) towards one. Find a storm that develops 
and stick with it. They probably will all produce.
Now regarding area of greatest threat. I have a 
concern for the Kansas City area. Kansas City 
vicinity looks to be the area of initiation, and 
then traveling to points east-northeast. The KC 
metro has a real threat for tornadoes in and near 
the city starting near or just before noon local 
time. The greatest threat continues to the 
east-northeast through cities like Kingston, MO, 
Chillicothe, MO, Kirksville, MO and locations 
along the southern 2 Tier counties in Iowa, 
especially south-central and southeast Iowa.
Elsewhere on a broader scale I think severe 
storms and tornadoes are possible in all of 
Missouri, Northern Arkansas, Eastern Kansas, 
Eastern Oklahoma, Northern Mississippi, far 
Northeast Texas, Central and Southern Illinois 
(emphasis on central), parts of Indiana & 
Virginia. Severe storms could go well into the 
night with a general migration to the south like 
areas of far northeast Texas and Arkansas toward midnight.
To discuss this forecast, go here: 
<http://www.f5data.org>http://www.f5data.org and 
click on "Weather Discussion".


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