• A friendly and periodic reminder of the rules we use for fostering high SNR and quality conversation and interaction at Stormtrack: Forum rules

    P.S. - Nothing specific happened to prompt this message! No one is in trouble, there are no flame wars in effect, nor any inappropriate conversation ongoing. This is being posted sitewide as a casual refresher.

11/05/05 FCST: MO/IL

Status
Not open for further replies.
I would agree with what Nick is laying out here, if the NAM verifies. It is showing EHI of 3.4 southeast of St. Louis, which certainly is plenty for supercells. However, it often tends to overstate this a day ahead. Also - the GFS shows a rather different picture, with the system farther north, and quite a bit of the precip north of the front over the cold air, not in the warm sector. No convection around STL until after dark. Now, if the GFS moves toward what the NAM is predicting, it could be an interesting day. Latest Day 2 outlook from SPC has backed off a bit on the strong language. Since I am smack in the middle of the area of interest, it looks like a potentional local chase for me, if things go as the NAM is suggesting - I will have my gear ready go go, and will have one eye on football and one on the developing weather pattern!
 
Ever the pessimist, I'm going to say I'm still not convinced for tomorrow. Despite what the models say, I don't think there will be sufficient moisture to support convection worth driving any great distance for. Below is the observed and model initializations of 850mb mixing ratio for 12Z this morning. The upper-left panel is observed mrat, with NAM in the upper-right, GFS in the lower-left and NGM in the lower-right.
850_mrat_init_4p.gif
Note that each plot has the same contour base and interval. You'll see right off that the GFS is totally out to lunch on the moisture issue. Dynamically, it appears to over-develop the 300mb trough coming off the Rockies. Therefore, the GFS solution isn't likely to be too reliable. The NAM and NGM also seem to overmoisten the air, although the coarser resolution of the observed data makes this harder to determine. Still, it is cause to believe that the models are expecting more moisture in the next 24-36 hours than the actual conditions can provide.
Right now, KILX looks pretty shaky for convection (of course this may change in the next 24 hours).
skewt-kilx.gif

Even along the Gulf at KLCH, the moisture is pretty scant.
skewt-klch.gif
Since the low-level winds are still more southwesterly than southerly, I don't buy any great moisture advection in the next 24 hours.
Assuming the NAM solution is close enough to be reliable, there might be the chance of convective entertainment along and north of I-64 in the early afternoon, but I'll take my chances watching Purdue lose to Michigan State ( :cry: ) instead of making the drive to southern IL.


BC
 
I don't really see why you are talking moisture problems... There is already SFC Tds into the mid 50's into southern IL (with near 60F readings in the bootheel area)... This is compared to SFC Tds in the upper 30s and low 40s across this same area by this time yesterday (that is a 15-20F rise in Tds in less than 24hrs). I don't see why moisture would be "shallow" across this region by tomorrow... Forecast soundings indicate a fairly deep moist layer across the upper Mississipi valley (AR, MO into IL) tomorrow afternoon - and given the present conditions, I find this totally believable. If the models continue to indicate SFC Tds into the low 60s -- when they are currently in the mid 50s across the same area (and continuing favorable low-level wind trajectories) -- I have NO reason to doubt it (and neither does SPC or any WFOS across this area). It sure as heck looks pretty on the money to me...

NAM forecast for 18z (now):
<img src=http://www.rap.ucar.edu/weather/model/eta06hr_sfc_dewp.gif>

Current SFC obs:
<img src=http://www.rap.ucar.edu/weather/surface/2005110419_metars_lit.gif>
 
I love November, however this is not going to be anything to get excited about. IMO, there will be some decent thunderboomers over southern Ill. but thats about it. My prognostication is that there will be no tornadoes with this one. I'm more concerned with what is going to come over the Rocky's in the next few days. I'm gonna take some photo's of our mini-blizzard outside right now.

Cheers and good luck,

Jared
 
I think it's also important to remember that moisture also advects along an isentropic surface, so using the 850MB level might not be completely accurate.

Besides that, the system will be deepening rapidly - even if Td's don't reach the lower 60's, the strong forcing and speed shear should make up for it (especially tomorrow night across the Lakes). Although, most people don't chase lines, so it would probably be considered a "bust" anyway...
 
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!
 
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.
 
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.
 
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. :)
 
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.
 
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:
 
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.
 
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
 
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.
 
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.
 
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.
 
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)...
 
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...
 
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.
 
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.
 
Originally posted by 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.

LOL... Lapse rates are low?

<img src=http://www.spc.noaa.gov/exper/mesoanalysis/s2/laps.gif>

Hmm... 8c/km mid-level lapse rates is pretty steep... Squall line with heavy rains? There is already some SFC-based instability becoming available in southern IL/MO (500j/kg sbCAPE) and it's barely 10am in the morning... With NAM/RUC both calling for >1000J/KG by mid-afternoon. Low-level / vertical shear and instability alone should be supportive of tornadoes with ANY discrete storms that develop across this area... But then again, it's not the "fat" CAPE...

EDIT: In addition, it appears the RUC is underdoing sbCAPE -- latest analysis shows 500j/kg building across the area... While RUC only gives us 0.

--> http://www.rap.ucar.edu/weather/model/ruc0...hr_sfc_cape.gif (forecast CAPE)
--> http://www.spc.noaa.gov/exper/mesoanalysis/s2/sbcp.gif (current CAPE)

I believe the NAM is doing better for this situation...
 
Yeah, these strong forcing setups can be tricky. They usually produce low topped thunderless lines of convection - often accompanied by damaging winds. Some chasers probably wouldn't classify it as a "storm", but technically it's a convective process that brings damaging winds to the surface. The forcing along the front is usually strong enough to produce a band of showers along or just behind itself... And it's usually right within that band that the strongest "convective" winds occur (as the CAA blasts in and inversion heights rise dramatically tapping into the available 70KNT low level wind field). Damaging non-convective wind gusts can also persist 6-8 hours after the initial "convective" band.

Each time I observed such events, the SFC relative humidity is generally fairly high, with temperatures usually in the upper 40's to lower 60's MAX... It really throws standard "severe weather" forecasting out the window...
 
Latest look at SAT it looks like there maybe a clearing trend occuring in NE MO. And as Nick said the Lapse rates are pretty steep. Cape is increasing . Helicity is considerable and the trend of all the parameters to increase is occuring. Even with clouds there will bee enough forcing for ascent to get things going. The dewpoints are already in the upper 50's low 60's near and around STL.
 
I think there will be severe weather and probably at least a few tornadoes - the biggest issue looks to me like whether and to what extent the storms build south into the area with the best chance of surface-based storms in a highly-sheared environment, i.e. eastern MO and western IL - especially during the daylight hours. It is possible that most of this show will occur after dark (remember that's shortly after 5 p.m. now around here) - that really is my biggest concern. Nick is right that moisture does not look like an issue, TD already above or near 60 over much of IL. It actually feels sticky outside in Edwardsville - unusual for November! Since I am pretty much smack in the center of the area of interest, I will watch things from home and make a decision based on how the system evolves as the day goes on.
 
I agree with Nick in his post above, those lapse rates are rather steepe to be at 8C/km this early. Looking at the latest RUC I have here, profiles become very supportive as a 60-70kt exit jet region approaches late this evening. Well sustained elevated mixed layer is well established and will help keep initiation down as the inversion will hold strong throughout the afternoon. This will make for unseasonable SFC temperatures in advance of a SFC cyclone. With strong LL moisture advection taking place, and LCL heights lowering I give today a descent shot at going MDT later this afternoon on the 20z outlook. I think Nick is heading in the right direction with SRH 0-1km progged over 250m2/s2 across extreme ERN MO/SRN IL/SW IN.

RUC.jpg
 
Status
Not open for further replies.
Back
Top