6/6/09 FCST: NE/CO/KS/OK

[Chad Cowan]

Well I am pretty set on my target area right now but it's more real estate than I would like for it to be. I'll be leaving KC around 11 with an initial target city of Marysville, KS but that is subject to what the 15z RUC has to say. What I'm expecting today is for supercells to fire along a surface boundary/ wind-shift line that extends northeast from a mesolow over Concordia, KS. I'm hoping the cap holds until around 7pm when the atmosphere will be primed for deep convection and the low-level wind fields in this area (along the sfc boundary) begin to back and strengthen significantly. This could trigger some back-building along this boundary and possibly training supercells. Given the increasing low-level shear and boundary layer moistening offsetting the loss of daylight, we could be looking at an appreciable tornado threat in northeast KS and northwest MO extending well after dark.

EDIT: 15z RUC is telling me that the best low-level turning around initiation should be in extreme northwest MO and extreme northeast KS. Given initiation away from the cold front, along this OFB/ wind-shift line, supercells and tornadoes are a real threat. I'm probably going to hold up around Hiawatha, KS. Like Mikey Gribble said, it's a day you'll want to cheat out in front of the easterly storm motions and give yourself the chance to jump on storms north or south.

 

[mikegeukes]

Strong cap on the 18Z Soundings for Topkea and Omaha
http://weather.cod.edu/data/raob/18Z/KTOP.skewt.18.GIF
http://weather.cod.edu/data/raob/18Z/KOAX.skewt.18.GIF

Mike

 

[Derek Weston]

SW quadrant of Iowa seems like the best play to me. (with a possible push towards the center of the state) Ought to be decent CAPE by 0z, and this location sets closer to the stronger LLJ further east into Iowa. Front should slice through center of the state, providing a focal point for thunderstorm development as the cap is projected (hopefully this is correct) to have eroded near 0z. Omaha to Des Moines corridor on 80, roughly, seems like it would be a nice place to set.

(not that it'll be important to watch how far east decent instability develops as we have a more favorably sheared environment further east into Iowa)

(edits: also interesting to note the weak area of low pressure that has developed on the NEB/IA border... perhaps aiding our shear situation across the area)

 

[Mike Johnston]

Notice the indication of an outflow boundary via Hastings, NE reflectivity - analyzed as a SW/NE-oriented arc roughly from Red Cloud to Nelson to just N of Hebron, drifting slowly southeast. Could turn out as a focus for convection later this afternoon, perhaps by then near area from Belleville, KS to Beatrice, NE.

Overall environment though, appears more favorable over SW through central IA, as a few others have commented - better backed low-level flow, a much nicer 500/850 crossover, along with helicities.

EDIT: Also, be aware of your Missouri River crossings. If you're forced to cross at Plattsmouth, you might have to pay a small toll to get on the rickety bridge.

 

[John Wetter]

I'd agree that IA is probably going to be the place... Also noted that boundary on Hastings 88D. It just looks crazy-capped right now.

I started a NOW on today: http://www.stormtrack.org/forum/showthread.php?t=20998

 

[Matthew E. Engelbrecht]

Based on current observational data and RUC model forecasts, the area in extreme southwest IA/southeast NE/northwest MO along or just west of I-29 would seem to be the location for initial development around 22z. Near and south of the warm front extending from the surface low between Omaha and Souix City - Fort Dodge, IA - near Waterloo, IA - Davenport, IA, backed surface winds will create curved hodographs necessary for rotating updrafts in cells which can move into this region, per area VWP and profilers. Wind profiles in ares closer to the MO border where storms could initiate may not be sufficient for supercells initially, but any storms that sustain themselves or develop further north and east into IA closer to the warm front and backed surface winds would have a better opportunity to evolve into supercells.

Further south in KS and OK, the severe threat seems more conditional with a strong cap in place. 700 mb temperatures in the 11-12C range with southwest winds blowing in from areas of TX and NM which have 13-14C temperatures may not allow but for very isolated storms to develop, if at all. The lack of a well defined upper level disturbance to enhance convergence along the dryline and triple point may inhibit convection in this region. Wind shear appears to be only be marginal for severe storms, if any develop.

Right now I would target an area near Nebraska City, NE to start out and be biased toward any convection developing to the northeast closer to I-80.