2/16/06 FCST: Lower/Mid-Mississippi Valley into Ohio Valley

[Andy Wehrle]

Could be an interesting day for those around the St. Louis area and other points in the warm sector. Although conditional given cap breakage and the lack of a near-surface stable layer over said warm sector, SPC included the infamous "strong tornadoes" phrase in the Day 2 discussion. :shock:

 

[Robert Dewey]

Very strong low level jet... If convection can make it as far north as DTX, damaging winds would be possible. If we don't get an ice storm, we darn well better get some severe convection (even if it's thunderless - I don't care).

 

[Skip Talbot]

NAM is showing strong vertical velocities and cap erosion around 0z near St. Louis and east. Prior to that the cap looks like its holding tight, waiting for that sweeping cold front to move through. Given the sharp boundary, amount of forcing, I'd expect a squall line to go up in southern IL, pushing through Carbondale and extending up to Effingham or Champaign. There are some rather extreme helicity values in the warm sector, but given the cap, I doubt they will be tapped by anything discrete.

 

[nickgrillo]

Re: 2/16/05 FCST: Central/Southern Mississippi Valley

Originally posted by Andy Wehrle
Could be an interesting day for those around the St. Louis area and other points in the warm sector. Although conditional given cap breakage and the lack of a near-surface stable layer over said warm sector, SPC included the infamous "strong tornadoes" phrase in the Day 2 discussion. :shock:

"The lack of a near-surface stable layer"? Well, that would be a good thing (maybe you just had a grammer error there)...

From my standpoint, I believe we have a decent chance at supercells tomorrow... NAM forecast soundings across southern Illinois (around the 21 z timeframe) show considerable surface-based CAPE. Some of the forecast soundings show the CIN layer eroding by 21 z, with a slender layer of positive buoyancy present. With the presence of at least moderate boundary layer instability and very strong low-level shear, I would have to say there is a pretty good shot at tornadoes. While I somewhat promised myself I wouldn't chase until March... I think tomorrow MIGHT talk me into an IL chase.

 

[Andy Wehrle]

Yeah...what I meant was that there is a good possiblity of a near-surface stable layer, and the tornado threat is conditional on there NOT being one.

With the strength of the LLJ I wonder if the SPC did not include the "strong tornado" wording with last November's Evansville event in mind. If I recall correctly the strong jet fueled a lone significant tornadic supercell despite the generally low instability.

 

[nickgrillo]

Originally posted by Andy Wehrle
Yeah...what I meant was that there is a good possiblity of a near-surface stable layer, and the tornado threat is conditional on there NOT being one.

With the strength of the LLJ I wonder if the SPC did not include the "strong tornado" wording with last November's Evansville event in mind. If I recall correctly the strong jet fueled a lone significant tornadic supercell despite the generally low instability.

Actually, I'm concluding a substantial case study about the "EVV" (and surrounding) tornadoes... There wasn't low instability at all. If you modified the Lincoln ob sounding to the 0700 UTC (about 40 mins prior to tornadogenesis) EVV sfc conditions... You got a solid ~2000 J/kg of CAPE. Additionally, if you go back to SPC mesoanalysis graphics to the timeframe of the tornadoes, you will see a jump in 3km CAPE (low-level CAPE) which implied the deep moisture and the lack of CIN. And in addition, you also had significantly low LFC and LCL heights.

There was an area of very strong 300mb divergence overhead during the tornado -- which helped lower surface pressure and created a mesolow analyzed at PAH at 0700 UTC. Sorry to hi-jack the thread, but I've been doing a lot of research on that day this past week... LOL...

However, with the presence of a 50-60 southwesterly LLJ, you will definitely get some substantial low-level moisture advected well into IL and IN tomorrow (and at least moderate boundary layer instability developing in central IL).

 

[Robert Dewey]

Originally posted by nickgrillo+--><div class='quotetop'>QUOTE(nickgrillo)</div>

<!--QuoteBegin-Andy Wehrle

Yeah...what I meant was that there is a good possiblity of a near-surface stable layer, and the tornado threat is conditional on there NOT being one.

With the strength of the LLJ I wonder if the SPC did not include the "strong tornado" wording with last November's Evansville event in mind. If I recall correctly the strong jet fueled a lone significant tornadic supercell despite the generally low instability.

Actually, I'm concluding a substantial case study about the "EVV" (and surrounding) tornadoes... There wasn't low instability at all. If you modified the Lincoln ob sounding to the 0700 UTC (about 40 mins prior to tornadogenesis) EVV sfc conditions... You got a solid ~2000 J/kg of CAPE. Additionally, if you go back to SPC mesoanalysis graphics to the timeframe of the tornadoes, you will see a jump in 3km CAPE (low-level CAPE) which implied the deep moisture and the lack of CIN. And in addition, you also had significantly low LFC and LCL heights.

There was an area of very strong 300mb divergence overhead during the tornado -- which helped lower surface pressure and created a mesolow analyzed at PAH at 0700 UTC. Sorry to hi-jack the thread, but I've been doing a lot of research on that day this past week... LOL...

However, with the presence of a 50-60 southwesterly LLJ, you will definitely get some substantial low-level moisture advected well into IL and IN tomorrow (and at least moderate boundary layer instability developing in central IL).[/b]

One of the best methods of future prediction is the analysis and study of past events and climatology. I would call it a method, not a threadjack.

This system is very dynamic, and ANY change in track will change things in a huge way for the DTX area. This might actually end up being quite a wind event for lower MI, in terms of convective potential and then several hours after frontal passage. Right now, frequent gusts of 60-70MPH appears quite likely along behind the front. With convective elements added in, I wouldn't be surprised to see a few reports of 70-80MPH.

This is one of those events that could either be classified as purely a synoptic scale windstorm, or a convective event. For the sake of this thread, I will keep things "convective"... But for the after-frontal passage stuff, I'll use the WeatherLab.

 

[Simon Brewer]

looks like it could be good tomorrow in southern or even central illinois, but I am concerned about the orientation of the cold front and the timing of convection. I'm pretty busy tomorrow, so I'll have decide whether I'm going to head up there by sometime in the very early morning hours.

 

[Aric Cylkowski]

I have been thinking about the low availability of CAPE tomorrow, and given the high helicity and very vigorous jet stream aloft (150 kts according to the 00z NAM), I am under the impression that the best area for potential tornadic activity is along and around a line from the MO Bootheel to the Cairo, IL area.

To better graphically identify the area in question, I have created the following thrown-together graphic in MSPaint (folks expecting GEMPAK quality should sit down before viewing this):

http://img48.imageshack.us/img48/9878/fore...st0216064ak.png

Of course, I'm only putting just a bit of confidence into this, seeing as its 24 hours away and that Mother Nature has a habit of changing her mind.

 

[Matthew Havin]

Additional HWO info from local offices:

STL
http://www.crh.noaa.gov/product.php?site=l...WO&issuedby=lsx

Lincoln IL
http://www.crh.noaa.gov/crnews/display_sto...d=1497&source=0

Paducah
http://www.crh.noaa.gov/product.php?site=P...WO&issuedby=PAH


This will be a race from the start with storms moving 50+, however I guess I am game tomorrow. I will be on standby in STL for a chase after 9 AM tomorrow morning, so if anyone in STL metro or travelling thru wants to meet up to chase give me a PM.