3/31/08 FCST: OK/MO/IL/AR/TX

[Chad Cowan]

A significant and widespread severe threat is shaping up for Monday as strong vertical shear profiles will be co-located over a large warm sector from central IL into central TX. It's looking like we might get our first tornadoes of the year north of I-70 (except for January... in Wisconsin). The triple point (<1000mb deepening sfc low - 12z/29 WRF & GFS) and warm front in MO and IL looks to be the best target due to abundant LL moisture and the strong directional and moderate speed shear. The wild card will be the amount of insolation received after the elevated AM junk clears out. The best chance for tornadoes in the southern target area along the dryline and cold front appears to be in the afternoon before the strong LLJ moves off to the northeast. Widespread flooding will also be a major concern in the already saturated MS River valley as 2-3 inches of precip are forecast over the next few days.

 

[Donald Giuliano]

Looking at the 20080328 18z NAM, a few aspects of Sun/Mon remind of May 4/5 last year. I say this because initiation appears to be somewhat dicey Sun afternoon near/south of the triple point with weak shear in the afternoon...but then the wind shear picks up rapidly around sunset, the warm sector has plenty of cape with little/no capping through the nighttime hours, and things look really crazy Monday over much of the warm sector. I could, of course, also examine many differences between the two setups, but that's just no fun. My biggest concern right now is the progression of the cold front--that beast could easily surge south very rapidly and elevate/line everything out in a hurry on Monday.

Regardless, it'll be interesting to see how things pan out--and if the system is slower than progged hopefully there'll be the chance to catch the first monster tubes of the year where you actually *can* see them someplace other than straight ahead of or straight behind you on the road!

 

[Brett Roberts]

Looking at the 12z NAM that just rolled in, I'm interested in the somewhat significant slowing of the upper system for Monday, resulting in a stronger (999 mb) secondary surface low over SW KS by 00z and more backed low-level flow over the I-35 corridor. Before this morning, I was trying to make myself ignore Monday, since it vaguely reminded me of some high-hype setups that didn't quite live up to their potential in this area (10/17/07, 04/24/07, 03/30/06 come to mind)... but if this trend continues, it would seem Monday may hold great promise for good supercells in central and eastern OK/KS. I guess the only fly in the ointment could be the effects of leftover convection from Sunday evening or even Monday morning, but we'll know more about that as we approach the time of the event.

EDIT: I should note that the 12z GFS came in without this stronger secondary low, so low-level flow veers severely along the dryline by afternoon. I tend to agree with those who have posted in the Sunday thread that tomorrow should be the better of the two days chase-wise, especially given the uncertainties in storm mode and moisture depth on Monday.

 

[Scott Lincoln]

The triple point (<1000mb deepening sfc low - 12z/29 WRF & GFS) and warm front in MO and IL looks to be the best target due to abundant LL moisture and the strong directional and moderate speed shear. The wild card will be the amount of insolation received after the elevated AM junk clears out. The best chance for tornadoes in the southern target area along the dryline and cold front appears to be in the afternoon before the strong LLJ moves off to the northeast.

Looks like in some of the latest runs (midday Saturday) that the low is being pushed further north. This would put the triple point up into southern and eastern Iowa. Looks similar to some cold-core setups we've had in the Iowa area in past early springs. I'd say it will all depend on whether or not we can get enough clearing after the initial wave of stratiform rain. We'll also need to hope that the big influxes of moisture hold true. It seems a bit early for 60F+ dewpoints to make it past northern Missouri. I remember many times this would be forecasted, but the moisture just wouldn't quite make it.

 

[Eric Graham]

hey all. well looking into things this late at night and I'm liking what I see. And since the setup is so close (im here in Lafayette, IN) I can't resist plus I have the day off. Anywho I'm thinking my target area is just east of St Louis, MO. It's pretty much in the middle of the slight risk SPC has posted. Temps will be in the mid 60s plenty of moisture and descent shear. Hopefully this setup holds true for Mon.

 

[Derek Weston]

Looks like plenty of moisture. Looks like plenty of shear... but what type? Concerned unidirectional will equate to lines of storms. However, if we do have enough to get the spin needed, could be quite an impressive setup.

E. Oklahoma, Kansas through Central Missouri look to be in the thick of things. Perhaps up into SE Iowa if the moisture return is good enough. (current GFS) seems to think so. Illinois later on...

Ongoing storms/junk convection will also say something about how the day transpires. Looks like we'll possibly have an early day round from Kansas through parts of Mizzouri and possibly S.Iowa.

Potential here... but not overly confident for lots of rotating supercells.

 

[Adam Lucio]

GFS looks to bring at leaste mid 50s dewpoints at least up to the IL/WI border with isolated pockets in western IL and southwestern MO higher than that. SB CAPE looks best in eastern OK with decent ML cape across northern IL as well.

Shear looks to be unidirectional at this time which would favor a powerfull squall line given the quick advancement of the cold front. I dont think heating or moisture will be a problem but the amount of instability might with the threat of leftover convection, if we can get decent clearing I would expect some sups to develop before the line sweeps east across the entire risk area. There certainly is the potential for a widespread wind event.

Im not sure if Im chasing this one or not, I only reserved a half day off work. As much as I wouldnt like it I think I would make my target somewhere in central MO. I wouldnt be suprised to see SPC move that SLGT over northern IL as well.

 

[Jesse Risley]

I think the warm front has potential on this one as well, offering a favorably sheared environment with strong LLJ near 60KTS, lower LCLs and a respectable temperature gradient. The tornadic potential to the north will greatly depend on the amount of instability present via daytime heating.

I would expect to see a squall line sweep across the region in advance of the cold front as well, probably the most likely mode of convection across the NE 2/3 of the risk area.

 

[Tony Lyza]

We will be playing the I-80 corridor from Joliet to Kewanee tomorrow. I'm really thinking the warm front is going to have some fireworks on it. Intense low-level instability, good wind shear, and a subtle shortwave disturbance should help fuel low-topped supercells along the warm front. The low-level shear would support a strong tornado or two along the warm front.

 

[Scott Lincoln]

I think the warm front has potential on this one as well, offering a favorably sheared environment with strong LLJ near 60KTS, lower LCLs and a respectable temperature gradient. The tornadic potential to the north will greatly depend on the amount of instability present via daytime heating.

I would expect to see a squall line sweep across the region in advance of the cold front as well, probably the most likely mode of convection across the NE 2/3 of the risk area.

When I showed this setup to a few Des Moines NWS mets at the Central Iowa NWA conference, they gave me the impression that this looked like a cold-core low mini supercell setup, of course without the cold-core low. We tend to get these in Iowa in the early spring if we get a dynamic system with really good low level directional shear. Even just a few hours of heating can sometimes be enough to get things going.

The NMM 5km WRF really seems to want to form some strong convection in central to eastern Iowa, then with more storms forming further south in the reduced shear.

This threat seems really conditional though, the models need to be fairly close on the northward progression of the moisture tongue and we likely need to have the clouds to break up for a few hours.

 

[Mikey Gribble]

I am becoming a bit more confident that we might see a few weak tornadoes tomorrow in the Stillwater-OKC to Tulsa area. I hate veering low-level winds, but that isn't a show stopper tomorrow IMO (definitely a damper though). I think clearing over the warm sector will be problematic, but again I don't think this is going to stop the show. We should still get adequate instability without good insolation. Breaks in the clouds would help, but I'm not banking on it until shortly before initiation. There isn't a whole lot to say about the setup. Somewhat of a triple point should setup over N-central Oklahoma. I am hoping that we may get a more discrete or tail end storm just South of this where the initiating boundary becomes more N-S oriented instead of NE-SW (more parallel to shear vector). The NAM seems to be hinting at this too with it's precip. graphics. I am anxious to see the WRF radar reflectivity on this since storm mode and coverage could be an issue. Other than that things look halfway decent for a lower end tornado threat over the NE quadrant of Oklahoma. I posted a more complete forecast here...
http://loadedgunchasing.com/blog.html

 

[Dal Archer]

I am beginning to become more concerned about the mode of storms in my neck of the woods. The GFS is showing surface winds veering to a more southwesterly direction as early as 18Z which obviously spells more of a squall line setup.

That being said the NAM gives me a little more hope with more of a southerly flow at the surface and with the strong westerly component at 500mb maybe we can still get some early sup's before the linear storms take over completely.

A great deal may hinge on how quickly the low moves to the east and how much sun (if any) we can get before storms begin to fire.

Certainly worth chasing due to the close proximity, but I am not nearly as optimistic as I was earlier.

 

[Bill Hark]

Interesting scenario Monday afternoon with the potential for severe storms and possibly tornadoes. There is an approaching trough with 500 mb winds at 50-60 for most of E OK and KS, NE TX, and W MO and AR per the 12Z WRF. The GFS is similar. At the 250 level, the flow is more westerly with some divergence over eastern MO. CAPE will be marginal at 500 to 1000 but decent with forecast SRH around 300 m2s-2. I also like the forecast 60 degree dewpoints for eastern OK, 65 in Texas. I am expected severe storms ahead of the front. My biggest concern is veering surface winds as mentioned by others earlier in this thread. The main low is forecast to rapidly pass to the northeast (northcenteral MO by 18Z per GFS, northwest MO per WRF) causing the surface winds to veer. It is unclear if another low will form. There is a hint of more southerly to southeasterly winds in northeastern Texas. I am also worried about the effect of early morning convection. I have two areas of interest. The first is along the front by a “precip bullseye” on the WRF; Coffeyville, KS. My secondary area is in the Sherman, TX region mainly do to better dewpoints and possibly surface wind direction. I think the storms will transition to linear rapidly and the best tornadoes will be early.

Bill Hark

 

[Bill Schintler]

Chase Target for Monday, March 31

Chase target:
Pauls Valley, OK (40 miles south of OKC). While severe weather is likely over much of the warm sector, particularly favorable conditions may exist near the intersection of a dryline and cold front as winds locally back east of a developing mesoscale low.

Timing and storm mode:
Rain and storms will be ongoing in eastern OK during the morning hours. During the afternoon, partial clearing should take place and renewed convection will initiate in the target area at 2 PM CDT. Large hail will be the primary threat, but a small tornado probability also exists.

Synopsis:
This evening, the UA pattern is characterized by gradual amplification of broad WRN CONUS trough, as indicated by broad regions of large scale assent spreading over the Eastern Front Range of the Rockies in CO and south into ERN NM, the Four Corners area through WY, and also by 60m 12hr H5 height falls concentrated over SRN NV and AZ. H5 temperatures have also cooled by several degrees over the last 12 hours in SRN NV as the ULVL low continues to strengthen. A number of lead impulses have ejected ahead of this feature, the first of which now well N of Lake Superior. Another more subtle feature is lifting through NRN IL with attendant subsidence in its wake over IA which resulted in clearing there during the afternoon hours. Further S and W, a compact wave ahead of a 50kt H5 streak traveled E across the TX panhandle into NWRN OK which sparked ongoing convection along a CF/DL intersection in WRN OK. Elsewhere, strong capping had suppressed SFC-based convection due to persistent mid-level WAA with a 6C H7 thermal ridge over WRN OK. Moisture is plentiful in the warm sector as a strengthening LLJ is transporting an axis of 15C H85 moisture N into WRN and CNTRL OK while KFWD and KOUN soundings indicate mid-level lapse rates of 7-8C/km over deep and well-mixed moist layers.

Discussion:
Widespread convection will be ongoing during the morning hours from ERN OK NEWRD into IA within a zone of persistent WAA along and N of a SFC front. During the day, LLVL moisture will stream NWRD with SFC dewpoints AOA 60F reaching SERN IA by early afternoon. An axis of SFC dewpoints AOB 70F will surge N along the I-35 corridor in SRN OK. Daytime heating in combination with increasing moisture will result in increasing instability as the day progresses and ST pushes I of I-35. Warm sector convection should initiate along a CF/DL intersection. A combination of impressive shear parameters and instability will be favorable for a localized tornado threat. An axis of MLCAPE’s AOA 2000J/kg will surge N into SCNRTL OK. A 30kt SWRLY LLJ over backing SFC flow E of a developing SFC wave along the CF will result in impressive hodograph curvatures by 00Z. SFC-3km SRH’s in excess of 200m2/s2 will be juxtaposed with deep-layer shear of 60kts.
- bill
10:00 PM CDT, 03/30/08

 

[Bob Hartig]

I'm looking at tri-state border of IL/IA/MO, across the river from Burlington, or possibly just hang farther north near Davenport. Instability could be better, but Tds in this area will be around 60 and the helicities are compelling, as is 0-6k shear. Moreover, these factors have demonstrated consistency for several model runs. GFS is the wild card--in fact, it shows a ponderous cap--but NAM and RUC 13 seem to like the area. Embedded supercells aren't my first choice for a chase, but right now I'll take what I can get. Here's crossing my fingers and hoping.