11/05/05 FCST: MO/IL

[nickgrillo]

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...

 

[Robert Dewey]

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...

 

[Kurt Hulst]

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.

 

[John Farley]

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.

 

[Brett Adair]

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.

 

[HAltschule]

Nick...If you look at the NAT. Radar composite, you can already see the squall line taking shape in the form of heavy showers. Sure they may be supercells today...but given the cap and low level inversion this morning, it looks like it will be a late show. Clearly there will be a squall line moving through later in addition to some supercells. You have to remember, this is a totally different kind of setup than late spring. A strong linear temperature boundary is likely to produce a line of convection this time of year. Supercells will be a bonus when they develop...assuming they do. But I wouldn't blast anybody because they talk about a line with heavy rain. After all, it's ALREADY happening.

 

[Scott Weberpal]

A quick analysis of the 12z IL sounding shows a convective temp ~76F while the DVN sounding shows a convective temp. of ~78F. Given this, and the current lack of insolation across much of IL, just about all bets are off for surface based convection during daylight hours.

The only area that really catches my eye at this point is near where MO/IL/IA meet. This area should be just ahead of the SFC low along the WF. IF convection can go here, the potential for tornadic storms should be slightly enhanced. Keep an eye on the 0-3km CAPE...4/20/04 had little to nothing for instability except for a narrow band of enhanced (150-200 j/kg) of 0-3km CAPE along and hear the WF. However, even in that case, moisture is lacking much more than during the 4/20/04 event.

I don't think today will pan out enough to take me away from the Wisconsin/PSU game.

 

[brody_clifton]

16Z surface analysis, thing I really don't like is the cloud coverage south of the vis. sat indicated surface bounday. And the relatively small clear slot just borth of the boundary looks to be filling in with clouds as well.

 

[Brett Adair]

Hmmm....I still think some SFC based stuff is going to be possible pre-frontal if we can get something to break the mean layer cap. Looking like a hellacious inversion right now though with 700mb temps of 4-5C. Stuff north of the warm front is going to be isentrophic oriented, but the mid level "push" is coming in...

 

[nickgrillo]

Originally posted by HAltschule
Nick...If you look at the NAT. Radar composite, you can already see the squall line taking shape in the form of heavy showers. Sure they may be supercells today...but given the cap and low level inversion this morning, it looks like it will be a late show. Clearly there will be a squall line moving through later in addition to some supercells. You have to remember, this is a totally different kind of setup than late spring. A strong linear temperature boundary is likely to produce a line of convection this time of year. Supercells will be a bonus when they develop...assuming they do. But I wouldn't blast anybody because they talk about a line with heavy rain. After all, it's ALREADY happening.

Howie,
The activity currently ongoing in the form of "showers" has nothing to do with the main event itself (as you yourself stated)... I heard somebody making ridiculous accusations againest this setup, so I replied. When somebody likes or don't like a setup... They should indeed provide a list of meteorological facts on why they don't like it - not because they live 1,000 miles away and can't or won't chase. It gets on my nerves, especially the repeat offenders...

I'm currently in Springfield... And will probably end up heading w/sw from here within the next few hours.

 

[Robert Dewey]

Brody... I don't think cloud cover will affect todays setup much, if any. Instability is already building, and even if breaks do occur - the low November sun angle won't really add much but a degree or two (or three). I think the positive things going for this event are: 1) Degree of forcing, 2) Rapid cyclogenesis and height falls, and 3) The associated very intense low level wind field.

Given that, it is agreed that a squall line will most likely develop, and will persist even as instability diminishes (when the low level wind field really starts to scream). I can even imagine a rather widespread damaging wind event associated with a convective line of thunderstorms (or even heavy showers). BUT... Determining the potential for supercells is very difficult.

One could look at the shear and say "yep, that's strong shear"... But then you have to realized that the instability probably won't be strong enough to keep updrafts intact - it would really take 2500J/KG or higher to keep those things upright. Given the degree of shear, any "lone cells" will likely be blow apart, versus the linear stuff right along the front which will be dynamically driven via temperature gradients and mass/deep convergence. IF a cell is able to maintain itself in that supercell-unfriendly environment, then it would likely be tornadic...

Alot of "ifs" on the supercell thought...

 

[Andrew Khan]

RUC is distorting CAPE in all layers, for some reason...

The SPC has already just issued a valid MD for portions of the Great Lakes, including WI, IL, and other moderate areas. supercells look very potential with this system. CAPE is quite low, but I expect it to ascend later on in the primary heating hours, if cloud cover can subside. Tornado's look possible with any supercell that develops along the line, near Central IL....also there looks like there will be some very large hail in NW IL. There should be sufficient lift, for Hail threat, along the line.

 

[Kevin Askew]

Cloudcover clearing nicely Cent. MO SE to So. IL. Things will be getting interesting in several hours

 

[Kiel Ortega]

Originally posted by HAltschule
Nick...If you look at the NAT. Radar composite, you can already see the squall line taking shape in the form of heavy showers. Sure they may be supercells today...but given the cap and low level inversion this morning, it looks like it will be a late show. Clearly there will be a squall line moving through later in addition to some supercells. You have to remember, this is a totally different kind of setup than late spring. A strong linear temperature boundary is likely to produce a line of convection this time of year. Supercells will be a bonus when they develop...assuming they do. But I wouldn't blast anybody because they talk about a line with heavy rain. After all, it's ALREADY happening.

No, that's fine...I should have excluded the last sentence about the lapse rates (it was the result of looking at forecast soundings and not paying attention to which one I was looking at)...but a long night of drinking and typing while thinking got the best of me. However, there is a good point made in all of this: if lapse rates are already high, and looking up stream at TOP and SGF are about to peak (can't see lapse rates above dry adiabatic occuring), where is any more instability (especially SFC based) going to come from with all the clouds (MUCAPE hitting 1500 in spotty places, but LPL heights still over 1 km in those areas)? Further, SFC based parcels are going to be hard to lift once stuff gets going because I don't see BL lapse rates getting much better (and you need surface parcels, or at least some mixed parcels--and mixed CAPE currently is horrible as previously mentioned, for violent tornadic supercells, as a previous poster stated was possible). True there is a clear slot, but it ain't much of one. And it's November. Just a thought (should have waited for sobriety before typing).

 

[Brett Adair]

RUC shows 1000-500mb CAPE of 2000+ over portions of N AR/MO/Central IL/WRN IN from 21z through 00z with a deepening SFC low. The RUC is already initializing way to weak with the SFC low given charts indicate the low has already deepened to 1002mb about 50 miles SSE of MCI. I still think there is a descent shot at some tornadoes.