4/25/09 FCST: NE/KS/OK/TX

[Chris C Sanner]

Hi man, bad wrf today, the cold front its too fast for KS, maybe its better for Ok and TX penhandle, now we going to Greensburg and we will attempt the new emission.

What do you think chaser for western Kansas 25 April?

The NAM has sped the front up to the OK/KS border while the GFS has it back at the KS/NE still....I'm betting on the latter being more in line with reality. CAPEs are progged 2200-ish for Saturday though, and experience tells me they will be a touch higher than what the models are showing, so maybe 2500 with some localized areas of 3000. Generally speaking, I like the shear in place quite a bit and any isolate discrete cells which happen to go deviant to the right on their motions will probably have a great chance of producing given the better 0-1 KM shear they'll have to work with at that point. Way too early to target a spot, but I'm fully expecting everyone and their dog to be out chasing for sure

 

[Skip Talbot]

The models seem to agree on the general synopsis, but they disagree on the location of some of the features. The biggest difference I see is the triple point which is in the panhandles on the 12z WRF and in SC KS on the 12z GFS. Either way, it looks like strong instability is forecast to build in the warm sector with ample shear for supercells. I think we'll see an ehanced tornado threat as storms interact with that sagging front too. Depending on where the triple point settles, I will be anywhere from Amarillo to Salina. There is just too much discrepency right now to narrow down a target.

 

[Greg Blumberg]

I've been looking at the both the 12z NAM and GFS for the past few minutes. I personally am loving the GFS right now with the dynamics and pray that something of the sort will happen but then again, it's the GFS. The NAM brings some bad news though. With this new 12z run the 0z Sunday timeframe has come under it's jurisdiction and it's not looking good. It's forecasting that the upper level jet completely misses the target area (in terms of the good thermodynamics) around 0z Sunday. The ECMWF has the dynamics barely missing the target area, but not nearly as badly as the NAM. Both of those have me wondering if we'll have sufficient speed shear for this setup. I think so for now.

 

[Matthew Crowther]

I've been looking at the both the 12z NAM and GFS for the past few minutes. I personally am loving the GFS right now with the dynamics and pray that something of the sort will happen but then again, it's the GFS. The NAM brings some bad news though. With this new 12z run the 0z Sunday timeframe has come under it's jurisdiction and it's not looking good. It's forecasting that the upper level jet completely misses the target area (in terms of the good thermodynamics) around 0z Sunday. The ECMWF has the dynamics barely missing the target area, but not nearly as badly as the NAM. Both of those have me wondering if we'll have sufficient speed shear for this setup. I think so for now.

I have found that the NAM is usually inferior to the GFS at this time frame- and in this case the GFS speed is supported by other guidance such as the Canadian and SREF- so my confidence level for supercells and perhaps tornadoes on Saturday is still reasonably high. Still looks like SW Kansas or extreme NW Oklahoma as a very preliminary target. It will be a zoo if we have only a couple of supercells, but at least we will not yet have Vortex 2 to contend with. I will be chasing for sure, I was lucky enough to score a very cheap ticket from KATL to KICT, so include me as part of the horde..

 

[Greg Blumberg]

I have found that the NAM is usually inferior to the GFS at this time frame- and in this case the GFS speed is supported by other guidance such as the Canadian and SREF- so my confidence level for supercells and perhaps tornadoes on Saturday is still reasonably high. Still looks like SW Kansas or extreme NW Oklahoma as a very preliminary target. It will be a zoo if we have only a couple of supercells, but at least we will not yet have Vortex 2 to contend with. I will be chasing for sure, I was lucky enough to score a very cheap ticket from KATL to KICT, so include me as part of the horde..

I back you up on what you said about the NAM not doing well. Thought I had added that part to my post...lol. Oh well. Probably got way too excited over the GFS and forgot. Just looked at the SREF per your recommendation. I'm feeling better about the GFS.

 

[Jacob Ferden]

It's still quite early, but, as of right now, I think I would look on Saturday at the vicinity of Beaver, OK to Liberal, KS, or maybe slightly north of there, depending upon what I think about the cap as Saturday draws nearer. Sunday looks doubtful to me due to the presence of that cold front, but, who knows, a lot can change in the next couple of days.

 

[Alex Lamers]

I've been examining the NAM with respect to all other models, and I can't really come up with a good reason why it takes the cold front into northern Oklahoma by 00z Sunday. It appears that the NAM keeps the upper trough axis oriented from SW to NE from the southwestern deserts up into the high plains. All other available guidance seems to suggest that the upper trough will be broader than what the NAM is suggesting, and oriented more north-south from New Mexico up through the Rockies.

Not surprisingly, with the best upper level vorticity and divergence locked up over the Four Corners region on the NAM, that model fails to develop any discernible surface low, and instead has some sort of elongated surface trough from WI southwest into the panhandles of TX/OK. The other models have a more distinct surface low developing somewhere near the OK Panhandle because the main wave in the base of the trough is more progressive, allowing for low level cyclogenesis.

To be fair, it's still 3 days out and the NAM is supported by the 09Z SREF which certainly takes the cold front to near the KS-OK border by 00Z Sunday. I would suspect that's because the SREF is based around different perturbations of the NAM. In any event, even with little to no low-level cyclogenesis, it's not like there's a huge arctic air mass surging south, or a band of mdt-hvy precipitation behind the front to push the front south.

Therefore, I would expect some sort of mesoscale configuration with a surface low roughly over the center of the OK Panhandle, a cold front extending to the northeast towards Kansas City and Green Bay, and a dryline draped to the south over the Eastern Texas Panhandle and on into the rolling plains of West Texas. This whole setup is relatively similar to the GFS.

I think the best chasing could be somewhere about 25-50 miles east of whereever the surface low sets up. Flow in that region should be a little more backed at the surface. This should probably set up the best chasing territory somewhere near Woodward and Fairview in NW OK north to Protection and Medicine Lodge in SW KS. The GFS, which typically underforecasts instability, has MLCAPE on the order of 2000-2500 j/kg in this area. Moisture should be deep (extending above 850mb) and surface dewpoints should be well into the 60s. Overall it looks like a favorable setup for some supercells in that area.

AJL

 

[Mikey Gribble]

These are my favorite kind of setups. There are two primary places with good strong tornado potential on chases like this. A storm firing on the triple point or a storm firing along the dryline just south of the triple point that can get rooted in the boundary. If that can happen there is a good chance you'll get a cyclic tornado producer. That is very plausible with this situation because storm motions shouldn't be to perpendicular to the boundary (almost parallel for a right mover).

The second place with the highest probability of tornadoes (potentially strong) is with any storms developing down the dryline a ways that will remain discrete. If you target east-southeast of the triple about 40 miles ahead of the boundary, then you can keep both options open. You never know how the storms are going to come off the triple point or the dryline until it's starts to happen, and when storm mode means so much (like it does in this situation) the prudent thing to do is to hedge your bets by staying downstream IMO.
I posted a forecast on my blog early this morning. It needs to be updated, but I haven't gone over 12Z data. I will forecast and update it again when I get home. Here is the link http://loadedgunchasing.com/blog1/

 

[Andrew Stoller]

Crapper - the 18Z NAM pushes the front all the way into OK by 00z Sun., and the GFS is following suit, although not as far south. Not a big deal, but it might decrease surface cyclogenesis and lead to less backing of the surface winds.

At least moisture won't be a problem this go around!

 

[Andrew Ryan]

Crapper - the 18Z NAM pushes the front all the way into OK by 00z Sun., and the GFS is following suit, although not as far south. Not a big deal, but it might decrease surface cyclogenesis and lead to less backing of the surface winds.

At least moisture won't be a problem this go around!

I wouldn't sweat it. The 18z runs tend to do weird things. We'll have to wait and see what happens in the 00z runs.

 

[Adam Lucio]

I really want to throw out the 18Z NAM. It really plows that cold front trough and pushes everything down by the red river by 0Z SUN.

The 18Z GFS however has a nice 3000 j/kg CAPE bullseye in SC Kansas with backed winds along the KS/OK border. Not sure the 500mb trough lines up perfect with this as it is keeping the area of max vorticity over the OK panhandle but at least the GFS has been consistent with its runs on this system and right now Im hoping its the one that verifies.

Saturday still looking good per GFS. Its nice to not to have to worry about moisture for once, now if only we can get everything else to line up just a bit better.

EDIT: I guess I should have read Alexs post first...

 

[Mikey Gribble]

I'm on board with you too Alex. I always tend to trust the GFS a little more on the placement of surface features this far out and as you mentioned that is one wicked cold front screaming southward and I just don't understand it.

I also agree on the OK-KS border area target. I'd go DDC (initial target before heading south), but it all depends on where the dryline sets up. If it is looking like a triple point or barely south dryline storm could get rooted in the warm front then I'll hedge my bets and cheat east and north a bit, but otherwise I would get a little south of the OK border and watch satellite and surface obs.

I'm trying to remember which model was out to lunch last week and was placing the dryline back by I35 when the other one correctly had it farther east? Which one was right on that? Didn't the GFS have the eastern dryline placement correctly on that chase?

Besides history, the consistency I've seen in the GFS gives me confidence too. I don't know if we'll really get the 40kt 850mb winds it's showing, but it would be great if we did.
I'm wiped out and need to doze off for an hour or so, but I plan on getting back on the forecasting as soon as the 00Z NAM comes out.

 

[Greg Blumberg]

The 0z NAM run looks. So. Much. BETTER.

This run is giving a somewhat similar solution to the GFS's past couple of runs. I really don't have time to do a complete forecast and comparison of the models, so I'll do a quick summary. There's a beautiful curved hodograph with backed 850 mb winds across the Texas-Oklahoma border. Also, I see the cap is fully eroded by 0z on Sunday. I'm confused why the NAM has such low helicity values down there with the hodograph looking that impressive, but the EHI is around 2 or 3 for the 0-3 km layer. I'd still like to see LCLs a bit lower, and the upper level dynamics come together closer to the target area.

To put it shortly: I'm excited. It may be out a few more days, but I'm excited.

 

[Brandon McClung]

After scouring the 00z NAM this evening, the potential for some discrete supercells looks fairly promising. Starting off with the dynamics, the lower level dynamics look good. With sfc winds nearly out of the southeast and stout 850mb winds coming out of the south, this creates good speed and directional shear in the lower levels. This would contribute to good looking hodographs. In the upper levels you have good 500mb flow with decent forcing. I believe since the dynamics of this system aren't as strong that storms will have a better chance of staying discrete. The stronger jet dynamics seems to be behind the boundary, but the TX Panhandle and Western KS are still in the right entrance region of the jet, which still creates divergence aloft due to the ageostrophic flow. I think one of the main reasons that there would be weak helicity values, as Greg mentioned, would be due to the relatively weak storm relative winds, progged to 10-15kts at 5km.

However, great thermodynamics are in place. With instabilities approaching 2750-3000 J/kg, there is no moisture problem. Looking today at mesoanalysis and the OK Mesonet, dewpoints were approaching 55F and CAPE values were very stout near 2000 as well. Moisture and instability will not be a problem. Given good instabilities with lower helicities, this gives EHIs in the 2-3 range, which is enough to get me out. These EHIs partenered with steep mid-level lapse rates and LLRs close to the 8-9 range, makes me even more excited. Right now, I always try and position myself where the axes all aline, i.e. the thermal, moist axes, etc. Right now this looks to be in the far eastern TX Panhandle. I'd probably play a little south of the triple point where the shear vectors were more normal to the dryline boundary. Right now I would head west out of Norman, and watch from Shamrock, TX.

 

[Jason Boggs]

The latest NAM paints a pretty picture, and as everyone has said, moisture won't be a problem. I really think later trends will push the dryline a bit further west. Directional and speed shear looks really good, and the 850 winds (LLJ) increasing around dark will ramp up the helicity values. Right now, I'm going with a target in the eastern OK Panhandle north of Laverne near Rosston.