2/24/07 FCST: OH/KY/TN/IA/KS/MO/TX/LA/OK/IL/AR

[Skip Talbot]

Just a few observations about the 12z model runs:

With each run, the GFS has been gradually pushing the dewpoints further south to more believable levels for this time of year (remember the 60's Td's in central MO when the system first presented itself?). However, the depth of the low has remained consistent for the duration that the GFS has been tracking this system. In fact it has even deepened a few mb in the past couple runs.

The nam/wrf now extends out to Friday evening so we can start gauging it against the gfs. The nam/wrf has the low slightly deeper and further north (both good things I believe). The moisture extends further north with the low, but its a much thinner tongue.

 

[Bill Tabor]

The nam/wrf has the low slightly deeper and further north (both good things I believe). The moisture extends further north with the low, but its a much thinner tongue.

I agree deeper is better, but not sure why you think further north is. Seems to me the further south the low and warm front set up along with interaction from the short wave the more realistic it is to assume we have enough moisture return from the Gulf for chasing. I'd like to see the low start out west of CDS and remain easterly for awhile. The deeper srfc low further south would also aid in better / quicker moisture recovery.

 

[Michael O'Keeffe]

Question - what snow cover like in KS / OK?

Bill,
On the long drive back from the Storm Chaser Convention (Denver) to KC most of the snow had melted except for some shady spots and where very large drifts occured. Personally, I think the moisture may be slightly underdone because of the almost 6-8 inches of snow that has just melted in a matter of days across all of Kansas, that should keep the soil very moist and that could somewhat enhance the moisture content. Not terribly but maybe a few degress in the line of 1-2F. As for Oklahoma I'm not positive, but most likely it is the same story down there too.

 

[Craig Maire II]

I plan on going on my first chase of this year somewhere down in southern Kansas or North central Oklahoma (definitely still up in the air). It seems to me that the dewpoints and instability should be more than enough when combined with the triple point, strong shear etc. for supercells and tornados (plus there is excellent chase terrain and road networks in those areas.) I also believe that near the dryline/triple point I will have the best chance of encountering "isolated supercells" before they are swallowed up by a huge squalline. Keep in mind that I live in east central Iowa and haven't seen a "good" storm since October so I'll be happy with whatever I get (squalline, supercells, etc.) Now getting back to Iowa may end up being my biggest concern as a blizzard may be in progress in parts of Kansas, Nebraska and Iowa on Sunday

 

[Bill Schintler]

Saturday storm...?

Well, for grins:
Here's a summary of the GFS performance for the surface map valid 00Z, 02/25/07 (6 PM CST Saturday):

156 hr: 988 mb, near Kansas City
144 hr: 986 mb, between Peoria and Springfield, IL
132 hr: 986 mb, 30 mi SW of KS City
120 hr: 984 mb, 60 mi SSW of KS City
108 hr (latest run): 983 mb, 50 mi WSW of KS City

So, the last three runs have been quite stable, and this is also supported by the upper-level (H5) chart which also exhibited an anomaly in the 144 hr run (a much more open and more easterly H5 low as apposed to a compact closed low just left of the left-exit region of the H5 max shown by the last three runs).

The European and Canadian models and ensembles are also in reasonable agreement through Day-5. The latest ECMWF also develops a 983mb SFC low about 50 miles north of the GFS, while both the ECMWF and GEM have been consistent with strong high-pressure from the Hudson bay though the central Eastern Coastal areas during the period.

A few things are certain:
1) Low-level flow ahead of the system will send copious amounts of moisture northward.


2) A tight pressure gradient on the northwest side of the system will create blizzard conditions there.


3) In eastern Iowa, where I'm at, it looks like mainly a gray, rainy mess - although some convection appears likely, especially south of I-80.


4) Regarding severe/chasing potential - I wouldn't get overly excited. While this promises to be a severe outbreak in the warm sector, it's not going to be good "chasing" storms. Most of what we'll see are mini-supercells embedded in linear segments and larger convective areas, with extensive intervening low-cloudiness to get in the way of any storm structure that exists.


5) A possible exception to 4) will be in an area just east of the low during the early afternoon hours Saturday when the large area of AM precipitation works east and northeast and a clear slot with attendant heating takes place. 55F SFC/45F H85 dewpoints coupled with cold temperatures aloft (H5 low -22 to -24 C) will produce some decent CAPEs through about 15 kft. Shear is potentially quite impressive – a negating factor being the stacked nature of the low. Still, given the magnitude of and gradients of wind velocities in this area, it appears as though some very impressive speed shear should result in a small area east of the low. Also, a strong H85 jet over backed SFC flow along with low cloud base heights should enhance tornadic potential.

- bill

 

[Jim Bishop]

5) A possible exception to 4) will be in an area just east of the low during the early afternoon hours Saturday when the large area of AM precipitation works east and northeast and a clear slot with attendant heating takes place. 55F SFC/45F H85 dewpoints coupled with cold temperatures aloft (H5 low -22 to -24 C) will produce some decent CAPEs through about 15 kft. Shear is potentially quite impressive – a negating factor being the stacked nature of the low. Still, given the magnitude of and gradients of wind velocities in this area, it appears as though some very impressive speed shear should result in a small area east of the low. Also, a strong H85 jet over backed SFC flow along with low cloud base heights should enhance tornadic potential.

- bill

I was just looking at the latest GFS and totally agree with your assesment. This event is starting to look most favorable for low topped tornadic supercells immediately ahead of the low. The model shows a well defined clear slot moving through Oklahoma & Kansas around by 18z. The problem I have is the convective mess that forms at 12z ahead of the vort max over Western Oklahoma/Southwest Kansas. Hopefully that's not the main convection for the day or we are in serious trouble.

Assuming it's not and things clear out late in the morning, Central Kansas is starting to look like a good target for low topped tornadic suppercells late in the morning Saturday through midday. By Saturday afternoon everything looks like a mean squall line, probably with imbedded supercells and tornadoes. Not very chaseable!

 

[Mike Peregrine]

One thing I have noticed in years past, whenever a low-topped event does take shape (not saying that this is the case here - I'm not sure of the nature this low will finally take - who knows), but anyway, being that early spring, low-topped supercells do not require much in the way of instability (in fact, these setups can look downright uninteresting when it comes to CAPE), it really doesn't take much in the warm sector in the way of instability to encourage severity. So, so many times, these events are preceded by a murky, overcast, rainy, cold day that makes everyone say 'there's no way this can happen.' But the ingredients do come together and make it work quite nicely. All you need is a very narrow corridor of air that is just unstable enough to get the job done.

 

[Tom Dulong]

...But the ingredients do come together and make it work quite nicely. All you need is a very narrow corridor of air that is just unstable enough to get the job done.

Absolutely. That was the case for the 10 April 2005 Kansas cold core event.
We woke up to a relatively cool and cloudy morning in Hays, so we had doubts about any decent convection that day. However, several tornadoes occurred late that afternoon only one county west of Hays within a narrow corridor of
dewpoints in the mid to upper 50s.

 

[Danny Neal]

Absolutely. That was the case for the 10 April 2005 Kansas cold core event.
We woke up to a relatively cool and cloudy morning in Hays, so we had doubts about any decent convection that day. However, several tornadoes occurred late that afternoon only one county west of Hays within a narrow corridor of
dewpoints in the mid to upper 50s.

Same with 04/20/04. Remember the possibility for flooding too. Especially in Central Mo and IL. Already 15 inches of snow still on the ground. You get one of them HP sups or training effect going over all saturated and in some cases still frozen ground, it has no place to go but up! Not really a forecast but a reminder. Still way out but, so I wont post a forecast quite yet....

 

[Brian Stertz]

On that April 10, 2005 event, I was simply amazed how cool it felt (55-58 degrees), but the supercells were legit tornado producers. Not real strong tornadoes, but nice cones. Now back to the thread topic...looks like it is time to head to the usual spot for cold core tornadic supercells...down in the Pratt-Hutchinson KS corridor. That area is like a mecca for these type tornadic supercells through the years. If all things play out as currently forecasted, this will be the case again this Saturday. Still a bit leary of playing further east later on in that fast moving embedded supercell and probable squall line zone. So as it looks right now, there is one play I will be considering only early Saturday afternoon and thats in SC Kansas.

 

[Mike Peregrine]

Not real strong tornadoes, but nice cones.

Yes - there definitely seems to be a unique form of tornado produced by these unique storms. They don't seem particularly strong (although the one that Scott Currens, Darin Brunin and Dick McGowan caught a year ago last November in Jct City seemed strong enough to me). Seems like most of these mini supes like to produce slender tubes for the most part, screaming like heck up the landscape.

As for Saturday target - sooooo many things will finally shape that. It's hilarious that we're even talking about it right now. But you can bet that on Friday we are all going to be watching potential track of this low pretty dang close. If it indeed turns out to be a low-topped cold core chase, my personal thinking is to get tucked up as close to the low (or even NORTH of it) as I can. Seems like some really cool stuff goes on up there with these things. I don't like being too far south for a cold core setup. Seems like the storms riding that funky boundary that sets up are pretty sweet. Storm motions get pretty weird up there. Anyway, critical point will be positioning ... keeping track of storm track, along with where that tongue of instability winds up.

 

[Rodney Price]

I agree...Saturday is looking more and more interesting but definitely worried about the cells moving at warp speed. It's been interesting to watch the GFS slow this system down over the past few days. Hopefully that means a better chance of moisture return. Here's a great refresher on cold core low setups by Jon Davies. He posted this on his web page in the last week. http://members.cox.net/jdavies1/ Rodney Price

 

[Brian Stertz]

If it indeed turns out to be a low-topped cold core chase, my personal thinking is to get tucked up as close to the low (or even NORTH of it) as I can. Seems like some really cool stuff goes on up there with these things. I don't like being too far south for a cold core setup. Seems like the storms riding that funky boundary that sets up are pretty sweet. Storm motions get pretty weird up there. Anyway, critical point will be positioning ... keeping track of storm track, along with where that tongue of instability winds up.

Just have to remember to stay positioned near the occlusion point or even just a bit west or northwest. As deep as this surface low is forecasted to become, the occlusion pt. should stand out very clearly. I am hoping for a similar chase to the 4/10/05 event, but still unsure on a few of the more critical paramater overlaps. I guess it is time to bone up on Jon Davies "cold core" case studies, and then see how things mesh on the forecast models for Saturday's event.

 

[Mike Hollingshead]

This thing has, and continues to remind me of November 27, 2005. Just look at the upper low and sfc low positions on Davie's page for it.

http://members.cox.net/jondavies4/112705cks/112705cks.htm

It was even down to 987 west of ict by 17z. I remember the day clearly as I opted out of the severe side in KS to chase the blizzard in O'Neill. The main thing that got me to give up on the severe side was just how horrid the clouds were that morning. I think with such a vortmax one can toss the cloud cover factor out.

I guess I think it most resembles that day, that I can think of.

 

[Mike Peregrine]

Yeah ... seems like GFS has been pretty consistent with the movement of this storm. The difference between 96 hr and 120 hr makes it pretty apparent that this will be moving through quickly. Looks like an express train to convectionville. Hopefully things will trend a bit slower yet and keep things in chaseable terrain.

After looking at this, if I were using this as guidance for an early, early preliminary target, I might be inclined to go with Brian's earlier notion of somewhere west of ICT (Pratt might work). But a person would want to be there plenty early in the day (I'd want to arrive in the a.m. even). Convection should additionally show up by mid afternoon further to the northeast (I'm still thinking Emporia to Topeka somewhere). We'll see I guess. For convenience sake, I'll probably be forced to stick with a target that's closer to home on Saturday. Wherever we end up, it looks like a matter of hoping to see something as it blows by.