11/12/05 FCST: Upper Midwest through Southern Plains

[Bill Schintler]

Chase target for November 12

Chase target:
St. Joseph, MO.

Timing:
Storm initiation 4 PM CST.

Storm type:
Supercell storms early in evolution, transitioning into a squall line by early evening. A full spectrum of severe weather is expected, including isolated tornadoes. Storms will move rapidly to the northeast at 60 mph.

Discussion:
12Z UA analysis indicated 95kt H3 streak rounding base of opening trough in the ERN Rockies, along with attendant strong divergence in the right-rear quadrant of this feature lifting towards SRN KS.

At the surface a fairly deep moisture return was underway, as evidenced by a plume of surface dewpoints between 55F and 60F in CNTRL/ERN KS. KTOP 12z sounding indicated a 150mb deep moist layer, while KSGF was 300mb deep! Temperatures in the low-70’s by late afternoon will contribute to SBCAPE’s of only 1000J/kG. However, strong synoptic-scale forcing in association with the aforementioned streak and associated H5 vort max, in addition to 0-6km deep-layer shear to 70kts with long, slightly curving hodographs and resulting (0-3km) SRH’s to 400m^2/s^2 should result in a late-season severe WX event.

- bill

 

[nickgrillo]

16Z mesoanalysis indicates that boundary layer winds are backing in response to low-level frontogenesis occuring across eastern KS/NE with a strengthening cold front pushing east. Low-level instability is also increasing with mixed-layer CAPEs currently in the 500j/kg range ahead of the front (with them progged to increase to near 1000j/kg by early afternoon). Some intense convective development (including a few sustained supercells) is possible as lead shortwave trough plows into the region around 2PM. Strong deep-layer shear in excess of 45-60knts will be supportive of long-lived updrafts (with 200-350m2/s2 supportive of tornadoes) to the south of the deepening surface low early this afternoon. The best chance for tornadoes appears to be from Topeka e/ne into Des Mointes through late this afternoon. Further south, thunderstorms should build southwest from eastern KS into northeast TX along pre-dryline confluence -- which will probably become linear and possibley merge with convection further to the north shortly after 0z.

Overall, I would stick along/south of the I-80 corridor in western IA for this afternoon...

 

[Scott Lincoln]

The road networks in NW Missouri.... or almost anywhere in Missouri.... well, suck. I would say that if you are going to chase, stay out of Missouri. We couldn't catch up to a supercell moving only 35mph this summer.... because the roads just dont go one direction. A "east" highway could end up going any of the other cardinal directions. Very far SW iowa is somewhat bad as well, but has many more straight places and is in a grid-like pattern when possible. Once you start getting away from the Loess hills then the roads become straighter and more grid-patterned.... at least in Iowa.
Recommend a gazeteer strongly for anyone chasing in that area.

 

[Ronnie Bradley]

The road networks in NW Missouri.... or almost anywhere in Missouri.... well, suck. I would say that if you are going to chase, stay out of Missouri. We couldn't catch up to a supercell moving only 35mph this summer.... because the roads just dont go one direction. A "east" highway could end up going any of the other cardinal directions. Very far SW iowa is somewhat bad as well, but has many more straight places and is in a grid-like pattern when possible. Once you start getting away from the Loess hills then the roads become straighter and more grid-patterned.... at least in Iowa.
Recommend a gazeteer strongly for anyone chasing in that area.

Same here in Arkansas. You have the trees (lots of them) and hills over much of the state. Highways are very curvy and don't follow a grid. The exception is out east, toward Marion, West Memphis. The land is flat (vast areas of farmland) with few trees serving as windbreaks, except for Crowley's Ridge. The roads are more chaser friendly, mimiking the grid like pattern seen out west. US 64 mostly runs due east / west once you pass Agusta to Wynne. US Highway 49 runs SSW / NNE as does SR 1. If one were to chase in Arkansas, that small area east of the hills is the only option

 

[Bill Tabor]

Iowa is the place for me - within 200 mi. of the low, in the narrow intersection closest to the boundaries intersecting a triple point. With lower dewpoints and total CAPE than what we normally consider acceptable, this system has a few earmarks for the development of low-topped supercells to develop by afternoon closer to the pool of very cold air aloft. Just a thought, but I'd say extreme SW Iowa will be a great target today, so get close to the TP. It will be cool and grungy, with lots of elevated crud just to the east, so most chasers will wonder why they are there ... but the day still has the potential to end up like a dynamic, early spring system.

Excellent thought and observation Mike. With the strong dynamics in place, cold mid levels, and coincident nearby sfc low and triple point cold core mini sups could be a possibility I would think (though I am no expert in them). Not sure if we qualify for a 'closed' 500mb low, but perhaps what we have still works.

This from Davies' page:

Regardless of the detectable shear environment, many tornado settings from mini-supercells or low-topped storms near closed 500 mb lows have at least three ingredients in common:

A core of cold air aloft nearby, resulting in steep lapse rates and CAPE closer to the ground, suggesting potential for increased stretching in low levels
A surface "focus" area or boundary intersection located within 200 statute miles of the midlevel low, providing enhanced vorticity east of the associated surface low
An axis of late morning/afternoon surface heating with sunny skies that points northward into the surface "focus" area, increasing instability under the cold air aloft nearby.

http://members.cox.net/jondavies1/tornado_...orelow_tors.htm

Will be interesting to see what develops.

 

[Bill Tabor]

The road networks in NW Missouri.... or almost anywhere in Missouri.... well, suck. I would say that if you are going to chase, stay out of Missouri. We couldn't catch up to a supercell moving only 35mph this summer.... because the roads just dont go one direction. A "east" highway could end up going any of the other cardinal directions. Very far SW iowa is somewhat bad as well, but has many more straight places and is in a grid-like pattern when possible. Once you start getting away from the Loess hills then the roads become straighter and more grid-patterned.... at least in Iowa.
Recommend a gazeteer strongly for anyone chasing in that area.

Generally I agree with you though surprisingly I was able to chase somewhat slower moving storms back in Spring in MO at night and caught a tornado though somehow I found a fairly straight good road headed toward Springfield in the central/southwestern part of the state. See: http://www.tornadoxtreme.com/2005_Chases/A...il_21st_05.html

I've also had luck in AR but it was real tough keeping up while climbing mountains and going around constant turns in trees. If you chase these areas just expect that and you won't be disappointed.