4/21/07 FCST: OK / KS / TX / NE

[afischer]

I wish to point out the 00z GFS run, which looks awesome (at least in a kinematic sense) for the TX panhandle. It's faster than the NAM,and it has nearly meridional 500mb flow north of I40 (or at least from the OK panhandle northward). However, the wind profiles near and just south of I40 are very impressive: SSE 850mb flow at 40kts, S-SSW 700mb flow at 55kts, SW 500mb at 60kts, WSW 250mb at 80-90kts.

I wonder if this isn't at least partly due to a convective "burp," in light of the strong QPF bullseye the GFS has immediately N/NW of that area at 00Z Sun. The NAM looks almost as impressive from a 0-1km agl flow perspective (especially by 03Z Sunday)... but what the GFS is showing screams 'convective feedback' to me. For example, it definitely looks like the forecast convective blob has "forced" the dryline unrealistically eastward thru the panhandles by 00Z Sun.

Just an observation from someone who hasn't been following this forecast event real closely.

 

[Jeff Snyder]

I wonder if this isn't at least partly due to a convective "burp," in light of the strong QPF bullseye the GFS has immediately N/NW of that area at 00Z Sun. The NAM looks almost as impressive from a 0-1km agl flow perspective (especially by 03Z Sunday)... but what the GFS is showing screams 'convective feedback' to me. For example, it definitely looks like the forecast convective blob has "forced" the dryline unrealistically eastward thru the panhandles by 00Z Sun.

Just an observation from someone who hasn't been following this forecast event real closely.

There is some modification due to convection, no doubt. For example, note that "warm pocket" at 500mb and cold pocket at 850mb, which may be an indication of the convective parameterization scheme modifying the temperature fields (and, by various relationships, the wind speeds and profiles). In addition, notice how the 850mb fields (T, winds, etc) change from 18z-00z, which doesn't appear to be entirely reasonable. However, even if you subjectively remove the effects, the "ambient" wind profiles are still quite impressive over the TX panhandle. Unfortunately, the GFS remains drier in terms of low-level moisture, compared to the NAM, and I consider the NAM moisture forecasts to be marginal (perhaps marginal at best).

 

[afischer]

Yeah, in reviewing some forecast soundings in the eastern TX panhandle, the GFS sr-hodographs aren't a whole heck of a lot larger in the low levels than the NAM at 00Z Sunday. The GFS' 850mb flow jumping locally to 50+ kts at that time frame was just a clue that the low-level response might be slightly overforecast due to the feedback. Doesn't look too bad though.

 

[Brian Stertz]

Tonight's 00z ETA forecast soundings at 00z Sat. look very favorable between Lubbock 91.5% supercell...0-6km shear 61 kts...0-3km SRH 294...CAPE 2284...EHI 3.3 and Plainview 85.6% supercell...0-6km shear 62 kts...0-3km SRH 301...CAPE 2123...EHI 3.1 ...lcl's a bit high but values forecasted factored realistically with storm/supercell interactions..I am betting on lower lcls in the real storm environment. From I-40 southward in the Texas Panhandle and S.Plains...0-6km shear vectors are perp. to the dryline leading credence to a window of discrete supercells moving off the dryline. (Thanks a million for the expl. on this Rich)

 

[Joey Ketcham]

New Day 2 came out with MDT risk from NEB/KS border down to the Texas panhandle. If we go out I'm thinking out in Western KS is probably were we will head. Just haven't pinpointed a target yet.

 

[Joey Ketcham]

IAll of this is leading me to flip-flop (optimistic, pessimistic, optimistic, etc). Oh well, that's part of the fun of chasing hype, I suppose.

I'm in the same boat as you Jeff, I keep flip-flopping as well - mainly because I'm up in SE Kansas and hate the thought of driving all that way and end up just watching these go up into a squall line. It looks like a descent setup, but not sure if it's going to be worth 800+ round trip drive. I'm beating my brains out trying to decide I want to make that drive or not..

 

[Todd Segraves]

I am currently planning on setting up shop in either Garden City, KS or Liberal, KS. This should give me good North/South road options ahead of the dryline. I plan on chasing the Northern edge of any dryline bulge that develops. If that doesn't happen I'll head South towards the TX panhandle, and try to get some good lp supercell photos.

 

[Ray Walker]

The models are starting to show better moisture and instability setting up friday afternoon. Also it looks to me as if the models are showing the dryline to be a bit further east than previous runs. At leat not in eastern NM. This settup is looking alot like the 3/28/07 setup in terms of what people think are going to happen. Everyone was saying that the storms would go linear once the formed ultimatly killing the tornadic potential. However that was not the case. Saturday is going to be a chasers dream in the Texas panhandle the way it looks to me right now. (However alot can change between now and then.).

 

[Joey Ketcham]

GFS and ETA still continue to show dew points in the 50's and cape of about 1500. Still looks about the same.

 

[Billy Griffin]

Still sticking with the TX panhandle rather than points north. Better CAPE values along the southern end of the dryline may help in getting better storm organization established. I almost envision this system having two distinct areas... low-topped cells in NW Kansas, with the more impressive cells down in the panhandles.

One thing that is always of concern, at least to me, when chasing the TX panhandle, is that darned ol' Canadian River valley. Road options are minimal in that area, and the canyons create their own topographical challenge for chasing (hills, river / creeks, trees, etc.) The canyons east of Amarillo make for some beautiful country, but can be a challenge when trying to navigate around a storm!

 

[Kenny Drake]

I just noticed the air mass at the surface that just pushed into the Gulf from the SE states has average temp of about 60F and Td's of about 45. Compare that with the mid 50s to low 60s Td's in TX/OK right now that mainly has to do with topography. Hopefully the air mass that is pushing into the Gulf right now seriously modifies before making it over Texas or dewpoints in TX/OK will actually fall as the LLJ kicks in...

My doubts will either be put down or diminished by the end of the day as the pressure falls on the lee of the Rockies start pulling the air mass over the SE US across the Gulf and north through Texas.

 

[Ray Walker]

No, the ETA is actually showing capes around 2500j/kg across a large section of the plains. The GFS shows dewpoints in the mid to upper 60s in the western gulf tomarrow afternoon. I really am starting to think that the dewpoints are going to be about the same as what they are right now or perhaps even just a little bit higher.
I am more than likely going to head towards Clinton for the night tonight that way I will be able to possition myself just a little bit easier than if I left Ada Ok tomarrow morning.

 

[Michael O'Keeffe]

I'm still chasing tomorrow. I will be heading to Dodge City later today and stay the night there. I think we could see storms initiating along I27 maybe a bit further west, but south of Amarillo should be the hotspot. I think as long as Tds can reach the 57-60F range we will see tornadoes and the cells will be taking on a easterly track which may enhance the tornado potential. (Watch out for the hail bombs though). I hoping for at least a photogenic lp supercell if nothing else.

Target: Plainview,TX

 

[Bob Schafer]

I'm leaning towards an initiation target of CVS and swrd. Can you say "tail-end charlie"? I also like that upper levels will be westerly there, and the road networks kick butt into that part of TX. Thermodynamics appear slightly
more favorable in NE PH region (at 00Z), though.

I'm hereby soliciting comments from the pros regarding what effects the polar jet interacting with the sub-tropical jet in that region may have on all this. I don't think I've seen anyone else comment on that. Would that enhance divergence?

 

[Glen Romine]

(3) The NAM has, for the past couple runs, put some sort of dryline bulge in the TX Panhandle with somewhat of a mesolow on the boundary that appears to be enhancing low-level thetae advection. It's evident on the 900 and 850 mb plots. Bottom line it will be in the Panhandle and exact placement or development of it will be impossible to find until tomorrow.

Just a note of caution that 900 mb is below ground level for much of the panhandle region and west. So, the information on these pressure levels is not really appropriate for use.

While I haven't followed the evolution of model forecasts for this event closely, it does appear the morning NAM has the core of the shortwave digging a bit deeper into southern NM during the evening, with a lead weaker shortwave triggering convection during the late afternoon. With the shift of the forcing further south, I'd want to be positioned further south as well where the deep layer veering profile looks more favorable. While the NAM forecast suggests the dryline formation just east of the TX/NM border now and advacing to around the I-27 corridor by 00Z, I'd expect this to be 100-150 miles too far to the east based on recent model bias.