11/05/05 FCST: MO/IL

[Jim Bishop]

Contrary to what John mentioned, I like the GFS solution. I indicates a stronger shortwave arriving a bit slower than the NAM indicates, and a deeper surface low. This provides a better likelyhood of more backed low level flow. As for precip - didn't think the GFS ever had a decent convective scheme, so I wouldn't expect it to produce precip under a strong cap. If the GFS verified the target region would be Northern Missouri, West Central Illinois, Southeast Iowa and I believe there would be a few tornadoes.

The moisture situation isn't the main issue here, but it's a concern since there is a lot of dry air over the plains scattered about. But even with modification from that airmass, moisture should be sufficient for severe storms given the forecast low level flow.

This setup is just too iffy at this point for me to make the drive from Houston, and I'm disapointed 'cause I really want to go chasing!

 

[Brett Adair]

The only thing that could possibly hinder this event is if the cap holds well into the evening and then as cells do fire diurnal decoupling takes effect. I would like to see this thing punch in more around the 18z timeframe. I am still with Nick, if you are good with late evening/night chasing, go for it. Plenty of parameters are there....and I don't think deep layer moisture will be a problem. LR's are also getting steeper on models in the best 0-1km region of SRH....approaching 8C/km.

SPC updated risk includes MI now. Looks as if the southern extent has been shaved somewhat.

 

[nickgrillo]

Very strongly agreed with Jim and Brett... I have no reason to call tomorrow a "bust". Even SPC mentions supercells and possible isolated tornadoes near the surface low across MO/IL -- and I have very good reasons to believe the same (strongly negatively-tilted trough, strong low-level wind fields/veering, strong instability, good moisture pooling). I have absolutely not a doubt in my mind, based on the latest model runs, there will be a few tornadic supercells tomorrow.

 

[Brett Adair]

Originally posted by nickgrillo
Very strongly agreed with Jim and Brett... I have no reason to call tomorrow a \"bust\". Even SPC mentions supercells and possible isolated tornadoes near the surface low across MO/IL -- and I have very good reasons to believe the same (strongly negatively-tilted trough, strong low-level wind fields/veering, strong instability, good moisture pooling). I have absolutely not a doubt in my mind, based on the latest model runs, there will be a few tornadic supercells tomorrow.

I believe that you will see some tornadic activity especially at the onset as the SFC low is deepening and picking up speed as NEward progression takes place near the vort max. This thing may break 995 mb with a powerful squall as it heads into IN by late evening/night. Good luck. Nick, send me a message on AIM if you have time. Screen name is MissStateWXDawg. Thanks.

 

[John Farley]

On looking again at the GFS, Jim may have a point - stronger surface low, and also a little better directional shear. OTOH, I'm not sure about instability - a little harder to tell - but only around -2 LI, which is less than ideal. Still, in my earlier post, I may have been a little over-focused on my local situation near STL - the GFS solution is farther north and would more likely require me to make an earlier decision, i.e. a hard choice between watching Michigan State (hopefully) beat Purdue and heading out earlier. Given that the action should be reasonably close, though, my final decision will likely be based on the morning RUC and/or just watching to see what fires within an hour or two's drive of the STL area.

 

[Jarrod Cook]

I will be in Peoria; so if something pops nearby, I will most likely go out and chase. ILX is talking about time frames later in the evening (i.e. 6 pm SE of the IL River), so if it is dark, then chasing won't be happening. Gotta remember that it gets dark around 5-5:30pm now :roll:

 

[John Farley]

Looking at this evening's NAM, directional shear over Illinois is looking better than on the last run. As a result, now the predicted EHI is up above 4 in southern IL - nice to see it go up instead of down as the event gets closer. There is also better agreement between the NAM and the GFS. The late afternoon HWO from LSX is talking about an increasing severe wx risk, including a possible "outbreak" of severe weather, including tornadoes. I think there is some real potential with this system in central or southern Illinois. It's looking more like a chase day. We'll see what the morning models and tomorrow's evolution of the setup bring.

 

[Kevin Askew]

Set up looks decent around this part. 60mile radius is a good bet. November can be good or bust around here. Wife & I have been out many times at night so nothing new there, just hard to get pics unless lots of lightning present. ATM, looks like we will set up shop from Sikeston MO. - Murfreesboro Il. Line. Almost certainly a dusk night event. Prolly head out based upon first MD of evening. Happy hunting & be careful to nightime chasers/spotters.
Kevin

 

[nickgrillo]

Currently in Bloomington, IL and getting ready for bed in a Super 8... 0z NAM continues a favorable environment for supercells and tornadoes by mid-afternoon tomorrow immediately e/se of the surface low. Strong instability (1500-2500 sbCAPE), strong low-level shear (200-300m2/s2) and favorable veering/sheared flow with height results in favorable deep-layer vertical shear profiles for long-lived updrafts. Low-level flow is very supportive of tornadoes... And given a low T-Td depression, storms should have no problem producing tornadoes across central/southern IL tomorrow.

 

[Brett Adair]

Originally posted by nickgrillo
Currently in Bloomington, IL and getting ready for bed in a Super 8... 0z NAM continues a favorable environment for supercells and tornadoes by mid-afternoon tomorrow immediately e/se of the surface low. Strong instability (1500-2500 sbCAPE), strong low-level shear (200-300m2/s2) and favorable veering/sheared flow with height results in favorable deep-layer vertical shear profiles for long-lived updrafts. Low-level flow is very supportive of tornadoes... And given a low T-Td depression, storms should have no problem producing tornadoes across central/southern IL tomorrow.

We shall see. Looking at regional data, I would certainly love to see that deeper moisture ploom that is down in MS currently advect into your region ASAP. Looks like some nice storms could go off south of there in an elevated fashion given the nicely mixed layer pronounced by soundings into TN/MS/LA/AL.

 

[Anthony Silver]

From the LSX NWS office

THERE IS POTENTIAL FOR AN OUTBREAK OF SEVERE
THUNDERSTORMS PRODUCING LARGE HAIL...DAMAGING WINDS...AND A FEWTORNADOES.

If I could chase today...I would definetly have my eyes on the St. Louis area as a target. The highest potential for tornadic activity looks to be aimed at this area. Best of luck to everyone who's heading out today.

 

[Robert Dewey]

NAM has this system really winding up over the Great Lakes tonight with incredibly deep height falls - but what makes it so amazing is just how compact this thing is predicted to be (and the associated height gradient). Speed shear will be beyond incredible, with nearly 70KNTS only a couple thousand feet AGL (according to BUFKIT). Meanwhile, SFC-based LI drops to 0 to -2C over MI between 00Z and 06Z - not all that unstable, but when you factor in the degree of shear and forcing available, even a line of showers becomes damaging.

If storms can remain singular, and manage to survive the very high shear - a threat for isolated tornadoes exists... It should be noted that most of the instability is piled up in the 0-1KM layer, and in situations like this it has been shown that the 0-1KM or 0-2KM layer is what really counts.

So, my bet would be on convection developing around 21Z or 00Z over eastern IA/western IL... Then forming into a squall line and rapidly spreading eastward towards IN by 06Z, then spreading eastward into lower MI / western OH by 09Z-12Z. By that time, I would be willing to bet that a line will be forced right along the cold front - possibly embedded within a rain shield... With the wind fields and degree of speed shear present in the 0-3KM layer, it would be very easy to bring these winds down (after the cold front passes, they will be mixing down anyway)...

 

[nickgrillo]

I'm still in Bloomington (or "Normal", IL) and still very much liking today. Per the latest NAM, we should see some pretty decent surface-based instability overlapping the best SRH in sw/wc IL this afternoon. The 60F Td Isodrosotherm is currently sliding into IL... With widespread upper 50 surface Tds currently across the area. Boundary layer should slowly destablize through the afternoon, with steep mid-level lapse rates and insolation to yield 1000-2000J/KG sbCAPE and weakening CINH. I would expect convection to initiate across sw/wc IL and se/ec MO shortly after 21z... Given forecast strong low-level shear (0-3km SRH currently >250m2/s2 across the area) and favorable deep-layer shear, the potential for a few violent tornadic supercells exists.

I will be heading s/sw of here within the hour...

 

[Mike Johnston]

Looking over this morning's NAM run and current obs, suggests that E Central MO may be the best target on today's setup. As Nick noted, surface observations this morning in good support of forecast instability (eg. 62 td at Cape Girardeau 8:00am) -- models showing CAPE will pool along SW/NE axis S Central MO to Central IN. Although overall windfields still look somewhat uni-directional with height, plenty of speed shear in the offing. W/ deepening surface low progged in central MO at 00z, best chance for backed surface winds just east of the low. Also, morning satellite shows clear slot over this area to support daytime heating.

Fairly strong cap in place over the target area, and - one thing to note, it is hard to get a handle on workable LFC heights, or whether there will even be a true LFC for all practical purposes. Quite an interesting setup today; good luck to all who are out in the field.

 

[Kiel Ortega]

Well, with the low level clouds I think might cause some big problems for today...the fact it's November makes it even worse. Further, from the soundings and satellite, I think that there will be trouble mixing out the clouds for good insolation as the BL is moist and cap is fairly strong. I like the RUC, being pretty conservative with the instability (and it's long skinny instability not the fat stuff). With as much forcing there will be I think a squall line with heavy rain as the threat. Can't rule out severe weather obviously, especially with the amount of shear and helicity progged for later. However, I think that the lapse rates (or lack there of) will keep instability low and the threat for tornadoes/large hail to a minimum.