3/30/06 FCST: IA/NE southward to central TX/LA

[John Thurston]

I know it is a long way out but it is already getting some media coverage and showing up under SPC experimental outlook.
Looking at GFS models temps in region in the 70's with dewpoints 60-70 with a strong surface flow from the south sucking Gulf moisture well north. Higher level winds are screaming and veering more to west in front of the approaching front. All this is anchored by a slow moving giant Low in the Dakotas.
At this point it is far enough out to plan to chase - will follow to see if consensus is if it will go linear and/or fast.

 

[Alex Lamers]

I am leaning towards the ECMWF and away from the GFS at the moment because the ECMWF more reasonably handles the shortwave ejecting into the Southern Plains later on Thursday, and actually develops a low, while the GFS just maintains the low to the north.

Looks like a possible round of severe weather in the Plains Thursday with a very active Friday attm to me. That being said...with the low developing late Thursday over the SP...could see the surface wind field back a little bit and give some decent evening chasing conditions.

Models far from consensus right now but expecting Friday to be the more active day attm.

 

[Alex Lamers]

OK looks like I will be wrong, but Thursday's risk area will need to be expanded to cover much of the midwest. SPC's 4-8 day outlook seems to be getting a relatively good handle on the situation. Tornado threat will follow real close to the low track I imagine, which is still somewhat in doubt given model uncertainty. At least they're converging on timing.

EDIT: Jeeez. Just wanted to point out that an analog of last night's GFS for Thursday that's coming up is May 8 1988 which was a record outbreak across the Upper Midwest and I believe it set the all time record for tornadoes in a day for Iowa. Still breaking down the analogs...will let you know if I find anything else interesting.

 

[Tony Lyza]

OK looks like I will be wrong, but Thursday's risk area will need to be expanded to cover much of the midwest. SPC's 4-8 day outlook seems to be getting a relatively good handle on the situation. Tornado threat will follow real close to the low track I imagine, which is still somewhat in doubt given model uncertainty. At least they're converging on timing.

EDIT: Jeeez. Just wanted to point out that an analog of last night's GFS for Thursday that's coming up is May 8 1988 which was a record outbreak across the Upper Midwest and I believe it set the all time record for tornadoes in a day for Iowa. Still breaking down the analogs...will let you know if I find anything else interesting.
[/b]

FWIW, I checked Severe Plot, it has 57 tornadoes recorded that day.

The 65-70°F air with the sfc Td of up to 60°F looks to punch all the way up to a line form Chicago to Sioux Falls Thursday-Friday. Right now, the LIs painted by the GFS are down to -6.40 around the Sioux Falls to Topeka line Thursday evening. Right now, it appears to me that most of the convection should go linear due to most unidirectional shear (GFS) As Alex pointed out, there may be a couple supercells near the sfc low, but currently, I doubt that there will be many of those.

 

[Alex Lamers]

AFTER OBSERVING MODEL RUNS FOR THE PAST FEW DAYS..THIS IS A
SYNOPTICALLY EVIDENT SEVERE WX EVENT...WHICH IS SEEN ABOUT 5 TIMES A
YEAR ACROSS THE COUNTRY.

-DVN-

I concur. This is looking like there will be an outbreak of svr wx somewhere in the Central US.

 

[Chris Lott]

After looking at the latest GFS, I'm liking Kansas more and more. I was looking at going out Thursday, possibly into OKC, which I may still do. As mentioned before, models are already showing good LI values across a wide swath of the middle of the U.S. Timing of this system I believe is still up in the air, but it does appear more evident that Thursday is the day.

 

[Simon Brewer]

I think there are two main possible target areas at play: first is northeast of the surface low across northcentral Kansas into southeastern Nebraska, and the second area appears to be from Central Oklahoma into Eastern/Northeastern Oklahoma. Eastern and Southeastern Kansas looks horrible at this time, but if the shortwave digs a little further south or north both of these possible targets will change significantly.

I personally like Northcentral KS/SE NE; being northeast of the surface low with incredible positive vorticity advection, steep lapse rates, great localized low-level shear and slower moving storms.

Sometimes I will go for the second area, which looks to be Central Oklahoma; great shear, faster moving storms, larger area of instability (most of the time)

Either target looks good right now; historically in setups like this I've caught tornadoes in both areas, so it will be a tough decision come early Thursday morning......I'm just glad there is a good looking setup.

 

[Justin Turcotte]

From my experience with this type of system I'd want to go where the upper level winds have a westerly component which is OK/TX. The wind field is advertised to be highly unidirectional north of there less the warm front boundary somwhere in NE where you at least get some backed surface flow. The NAM and GFS plant a solid dryline at 18z in OK/TX with robust upper flow and some turning with height. Main caviat I see is the potential for some morning convection which will need to clear out for some solar to destabilize the atmosphere.

 

[Jim Bishop]

I tend to agree with Simon on the idea of the two best areas based on the best dynamics. The shear will be incredible, no doubt, throughout East Oklahoma/Kansas/Nebraska. The key will be the best dynamics, and the main vort max and associated surface low is best area #1. There the low level shear will be maxamized east of the low and that's where the best tornado threat exists in my opinion. The other area will be wherever the upper jet streak is located (~250mb). The 27th 12z NAM has it moving through North Central/Northeast Oklahoma/SouthCentral Southeast Kansas, making that area best area #2. Either way there will be tornadic supercells all along the dryline, it's just the most long lived supercells will exist in those two areas. Unfortunately I'll be missing out on this event.

 

[Gabe Garfield]

Judging from this morning's Eta and GFS, I'd have to say that E. KS will be dealing with an MCS due to an unfavorable shear vector orientation for isolated storms. Limited moisture at the surface spells trouble for any storms trying to become tornadic (high LCLs). However, further north (NE/IA) could have a much better opportunity for discrete cells, and in the high shear/low LCL environment, a better potential for tornadoes.

In my opinion, I'm glad the models have some more time to make up their minds, because right now, it doesn't look great (save for extreme wind fields).

Gabe

 

[Jeff Snyder]

It certainly does appear as though moisture could very well be the limiting factor, which is relatively common for these early-season systems. Looking at the new 12z NAM output, the dryline appears to be nearly N-S along I35 and I135, which makes for a nearly 30-45degree angle between it and the deep-layer shear vector (Note: link will change when 12z data is replaced this evening). Now, this certainly isn't ideal, but it's much better than being parallel! With intense wind fields throughout the target area, keeping up with these thigns may be quite a challenge. Otherwise, if we assume some insolation to bump temps into the 70s, the dewpoint depressions will likely be in the 15-20F range owing to relatively dry upper-50 Tds. I'm also a little concerned about the fact that the all the models significantly overforecast moisture return with the last system we had (3-12), with the afternoon obs being 10 degrees lower than model forecast in many places. Current Surface Obs from the southern plains and the Gulf of Mex indicate that the true moisture is nowhere to be seen right now (or even much in the way of good modified cp air, with only 50-55F Tds in the northern Gulf), and the circulation pattern in the Gulf indicates that we won't see it.

Now, given the intensity and orientation of the vort max slamming through KS, I do think we may intense, linear upward motion that may try to force a squall line up there. I haven't looked too much farther north, since I'm not planning on chasing that way. However, as someone else has mentioned (Justin, IIRC), mid-upper level flow will be significantly backed in that area, which also tells me squall, or, maybe, supercells that cross the warm front quickly and become elevated.

My very, very prelim target? With more veered mid-upper level flow, slightly higher Tds, and a little more removed from intense forcing associated with DPVA from the vort max, I'm aiminig to stay in OK. I also hoping for something on Weds, as that looks pretty tasty if we can get initiation (but I'll save that for the other thread).

 

[Gabe Garfield]

Jeff, you gave in! lol

Yeah, I didn't actually look at the shear vector map when I made my previous comment...I inferred a bad orientation based on the backed flow at 500 mb and the southerly LLJ. While this unfavorable orientation will be problematic in E KS/NE/IA, it looks as though most of OK east of the dryline will have an excellent shot at discrete storms.

As far as moisture is concerned, the T-Td won't actually be too bad. Eta indicates low 70s Ts with low 60s Tds. Assuming a well-mixed boundary layer yields an LCL height of 500-600 m. Not too shabby...

Gabe

 

[nickgrillo]

I think there is enough low-level turning to make THUR a good cold-core day wherever the surface low finally settles (as of now, either southeast NE or northeast KS) with plenty of low-level moisture (helping to support a solid 500-750J/kg SBCAPE) and cold H5 flow (further steepening lapse rates) and very strong PVA. I do, indeed, hate to see that southerly 500mb flow -- but the low-level turning somewhat compensates for this (given the supercells will be shallow), and pretty much falls into a 'cold core' setting. I'll likely be leaving Detroit tomorrow, and play WED, and then head northeast for THUR (to the surface low).

 

[samuel stone]

I think mid-upper wind orientation is still somewhat favorable in southern Kansas for semi discrete activity and since I cant travel too far south into oklahoma and cold core setups (athough very tornado productive) arent somthing I feel like chasing right now, I think I will target Kan-Ok boarder region for now. If surface low ends up placing itself a little further south I may go Cold core though. Obviously we could use a little better moisture but low sixties have crept further north into central texas with latest surface obs and once that southerly wind kicks in as lee trough develops moisture will advect northward quickly so NAM moisture forecast may easily verify.

 

[Scott Lincoln]

Definitely looks fairly decent according to the GFS in BUFKIT for areas of SW Iowa and NW Missouri. I'm afraid that the low wont make it quite that far east on thursday though. The main limiting factors i see in the forecasted soundings right now is the over abundances of mid level moisture, keep the air from cooling fast enough to along for large amounts of instability. Definitely looks like there is potential along the dry line, but keep in mind that there are several instances of there being no tornadoes on the dryline and several near the surface low / boundary interactions when dealing with cold core systems. I think this one is going to be tough to forecast so far out, but definitely worth watching as it has potential for sure.