2/24/11 FCST: OK, TX, LA, AR, MO

[Bill Tabor]

Hmm..latest 0z shows lead shortwave kicking off convection early from ABI to SPS then quickly translating east. By 15z it's already in eastern OK and extending just west of I35 in Tx. By 18z precip is already in AR/MO with just 'remnant' precip in Tx. Seems like this has sped it all back up 6 hours or at least 3.

Model keeps changing and no solutions look that great. Likely it will come down to the last model run before the event.

Things that have been constant so far:
Fairly poor instability
Strong upper level dynamics
Marginally good lower level directional sheer
Fast moving system
Pretty fast moving storms

During the day OK/TX I suspect this will mostly be a hail / wind event with widespread precip that blasts through quickly. Tornado threat limited with low probability of being caught

 

[Zack Hargrove]

Well, at first I was going to skip out on this system, but now me and a team are thinking about making our way out West from North Carolina on Thursday. We are thinking that we may leave Wed. night and drive into Western Tennessee, bunking the rest of the night. This way we can chase rested and we have a good early morning starting base to get as far West as we need to and as early as we need to. A lot has to come together for this system, but I've had chase fever for months now and worst case scenario is that I have an awesome road trip with 3 great friends. There are a few things I like about the system, though:

The Euro is trending further North than the GFS at this point and that could spread the energy a little further North. I like the Euro's surface low track. I am also hopeful that a dry slot will materialize over parts of Arkansas during the early afternoon which will help decrease stability. I love the the low level jet with this system, the moisture's there, and the upper level stuff is there.

We will have to see, but I think we're about 90% sure we're going to give this one a go.

 

[Skip Talbot]

SPC sounds like they've got a great handle on this event with the potential for a nocturnal tornado threat along the MS river valley. That screaming low level jet should continue to pump moisture right into the surface low after dark, where surface winds back nicely by 9pm in MS river valley. Little spikes in the tornado parameters are showing up across the MS river valley as well from 6pm onwards. That said, I still like eastern Oklahoma most for a chase target, not for a severe weather target.

The 12z NAM moved back up north with its placement of features, and is probably more in line with what the ECMWF is saying based on what I've read. There's a modest pool of instability forecast by the triple which will be moving across OK during the day, some colder mid level temps edging in from the west that will steepen midlevel lapse rates, and a hint of a dry punch that might help clear out some low clouds. The models are not firing precip over this area after the morning junkvection moves through, however, so storm initiation is in question. It would be a gamble to target this area (and heck maybe I'm completely wrong and there's a critical lack of lift or airmass recovery that far west later in the day), but I think the low chance of catching something here is better than what is almost surely going to be a very frustrating and futile attempt at a chase points east across AR and the MS river valley. A rather linear looking line is forecast to fire early across TX and OK and race east with northeast moving cells, due to the lack of capping and the early arrival of a very strong jet with mostly unidirectional wind profiles. Later on when the storm relative helicity really ramps up, any supercells will probably be embedded in a large cluster of cells. Tornadoes will probably be heavily rain wrapped, racing northeast, and wait until after dark when the directional shear and low level jet ramps up. Catching a glimpse of something down there will be extremely hard. So to summarize:

Eastern OK:

• Possibly a more discrete storm fueled by cold air aloft and modest instability near the triple point.
• Lower chance for supercells due to morning crapvection issues and trough/lift/shear being further east.
• Better chance at actually witnessing structure due to slightly better terrain, daytime intercept, and more discrete, possibly LP storm mode.

AR and MS River Valley:

• Fast moving line of cells with embedded supercells posing a nocturnal tornado threat due to strong moisture advection, very strong low level jet and dynamic lift.
• Almost guaranteed to get a storm.
• Low chance of witnessing supercell structure or tornado due to terrain, excessive storm speeds, embedded HP storm mode, and peak of event being after dark.

 

[Donovan Gruner]

I am definitely targeting East Oklahoma at this point... I agree with you Skip. 300 mb winds over E OK in the early to mid afternoon will be around 100 kts, more than sufficient to support a few lp storms. I would be more than happy to see that. Also, the polar jet seems to be joining the subtropical jet, which may enhance lift around that time. I think.

 

[Lanny Dean]

I am definitely targeting East Oklahoma at this point... I agree with you Skip. 300 mb winds over E OK in the early to mid afternoon will be around 100 kts, more than sufficient to support a few lp storms. I would be more than happy to see that. Also, the polar jet seems to be joining the subtropical jet, which may enhance lift around that time. I think.

300mb supporting LP storms? Not sure I understand this.

18z run painting the low further North with increased LI's and CAPE from just south of OKC. Interesting dry punch on the heels of the of the triple point...with cold temps aloft, should help to steepen lapse rates further than anticipated. Composite reflectivity showing some convection in my CWA by 18z, hopefully caused by the clearing from dry punch.

Hopefully the 00z run will paint a better and slower solution.

 

[Skip Talbot]

300mb supporting LP storms? Not sure I understand this.

I'm guessing he just meant supercells, and was inferring the storm mode would be LP from other parameters?

For what its worth, the 12z 4km WRF was plotting some discrete activity near OKC at 0z:
http://www.emc.ncep.noaa.gov/mmb/mpyle/cent4km/conus/12/refc_f36.gif

That's right in my target area, but I'm still worried how linear those cells might be if they do fire there given the veered surface winds. If they stick close to the tp/warm front there will probably be a better shot a supercell.

Also of interest is the updraft helicity:
http://www.emc.ncep.noaa.gov/mmb/mpyle/cent4km/conus/12/uphl_f36.gif

The blip in OK associated with the above reflectivities isn't that impressive, but what's more interesting is the complete lack of any activity with the AR storms.

 

[Jesse Risley]

Based on the 12z data, the ECMWF is still a tad further north and a little deeper (1000 mb) with the surface low, moving right on the MO/AR border at 00z FRI. The NAM continues to be more generous on CAPE values in the lowest 180 mb through 06z FRI, probably owed largely to the model wanting to depict some waning in the total cloud cover progs across far E OK and WC/C AR from 12z - 18z THUR.

While the NAM is a little more lax with progression and organization of the SFC low, I noticed that it wants to bring that tongue of warmer air into the OKC region by early THUR afternoon. However, the GFS, albeit more progressive and less generous (thermodynamically) to that area of OK, really shows some nicely backed SFC winds INVO the triple point across W TN/W KY/far NW MS between 00z and 06z FRI. There seems to be a marginally sufficient amount of CAPE so that, if storms can interact with the rather impressive low-level shear across the region, a few tornadoes would remain a distinct possibility across the region. I'd be keeping a close eye on the triple point/WF tomorrow to guage the best TOR potential; I have a feeling the slightly more northerly ECMWF progs might be the more salient solution at this time.

 

[Lanny Dean]

I'm guessing he just meant supercells, and was inferring the storm mode would be LP from other parameters?

For what its worth, the 12z 4km WRF was plotting some discrete activity near OKC at 0z:
http://www.emc.ncep.noaa.gov/mmb/mpyle/cent4km/conus/12/refc_f36.gif

That's right in my target area, but I'm still worried how linear those cells might be if they do fire there given the veered surface winds. If they stick close to the tp/warm front there will probably be a better shot a supercell.

Also of interest is the updraft helicity:
http://www.emc.ncep.noaa.gov/mmb/mpyle/cent4km/conus/12/uphl_f36.gif

The blip in OK associated with the above reflectivities isn't that impressive, but what's more interesting is the complete lack of any activity with the AR storms.

Skip,
as noted in my original FB post a week and a half ago, I really liked the Hobart OK area and points east/north and while this may be a little far west it coincides with the WRF. Although I think I was looking at the 25km and 12km together in conjuction with the NAM 18z. I usually do not post here in the Forecast forum for many reasons but this event has promted me simply becuase I find this event very interesting. LI's for this area were -4 to -6 and with the dry punch helping to steepen lapse rates I suspected that a storm or two may fire in this area. While simulated CAPE values were not above 500j/kg it certainly would not take much most particularly near the TP/warm front where winds may have an opportunity for an easterly component.

My thoughts right now are that if any storm do fire in this area they will likely go SUP. as long as they can stay close to the front/tp...the area that I find interesting *might be* from just south of Perkins to Cushing near 18z. I certainly could be way off base. Just like everybody else though, I am going to wait til the 00z run and go from there. At this point Chad and I and probably Jeff smith will be playing somewhere in my CWA or maybe even a little in OKC CWA to start.

 

[Donovan Gruner]

300mb supporting LP storms? Not sure I understand this.

I meant the 300 mb storm-relative winds may be 100+ kts. This could definitely be supportive of a more LP mode. As of now my initial target will be somewhere a bit east of OKC. The models tend to agree that the most instability will occur somewhere between OKC and McAlester around 18z. It also appears that the jet max will be located right over the same region around 18z as well, and with 60(ish) kts shear, should be enough to pop a few good sups. Like everyone else, also waiting for the 00z runs.

 

[cdcollura]

Good day all,

As per SPC, they got the area over AR and W MS as a moderate-risk with hatched plus enhanced wording of "strong tornadoes" possible. This area is AWEFUL for chasing (trees and poor road networks), not to mention fast storm motions. SE OK and NE TX (or even into the areas near DeQueen in SW AR) might have some promise for storms.

Best backed-winds and CAPE appear to be in the 3-6 PM CST time-frame from SW AR and points northeastward.

Good luck for anyone trying to tackle this first setup of 2011.

 

[Mike Johnston]

Looks like the system is slowing down a bit, surface low deepening, and the surface pressure gradients even taking on a bit of a negative tilt. Look at the latest RUC update: by 11z tomorrow, shows the surface low at 1004mb right over the TX panhandle whilst today's 12z NAM had it at 1007mb over SW OK at approx. the same time. RUC is also indicating greater instability developing earlier tomorrow and due easterly surface winds over northern OK. Not to overly emphasize the RUC, but sometimes when it sneaks up on the longer-term models it's a sign of things to come.

 

[Mike Smith]

Mike, agree with you 100%. In addition, the OUN and FTW soundings look better than I had expected in terms of amount of moisture and instability.

 

[Donovan Gruner]

00z NAM is showing a nice pocket of instability over C OK at 18z. CAPE values approaching 1250 to 1500 j/kg in a small area. Shear will easily be sufficient. The main question will be if the morning crap will clear out enough for this CAPE to be realized. A backyard chase would be very nice though.

 

[Bob Hartig]

There was a discussion of 0-3km CAPE here not long ago, and I think that's going to be a player in this scenario just as it was on New Years Eve. NAM maps on F5 Data show blobs of 75 J/kg in central AR moving into the MS River valley, and after looking at a few 18Z soundings, that appears to be conservative. Upwards of 90 J/kg 3km CAPE, and probably more, is forecast to set up in the heart and/or south of the H5 jet core, with good, stiff 850 winds underlying it. If that bears out, it'll be a nerve-wracking night down there in eastern AR/TN/northern MS. I wouldn't be too concerned about overall low CAPE when so much of what there is, is squeezed into the lower levels.

NOTE: When will I learn to look before I leap? Surface winds look nastily veered beneath all that deluxe 3km CAPE.

 

[Donovan Gruner]

00z GFS is also coming to agreement with the NAM. Decent area of CAPE around 1000 j/kg right over C OK. I like.