9/30/05 FCST: TX/OK/KS

[Mickey Ptak]

A strong shortwave forecast to move into the into TX Panhandle and Western OK by Friday afternoon. Forecasted hodograph taking some nice curvature and producing 6km overall shear at a forecasted value of 53 m/s – 3km at 39 m/s. Although the GFS is not doing very well with the thermodynamics, as expected, I think as soon time passes and this date come into the NAM’s forecast range we should see some better indices. Right now, via the GFS,the CAPE values only 500 j/kg. But the GFS never does well with that anyway.

Hodograph
www.mesomick.com/MiscImages/ForecastImages/12zGFS_093005hodo.jpg
Forecast Sounding
www.mesomick.com/MiscImages/ForecastImages/12Zgfs_093005ForecastScewT.jpg

EDIT: The images above are for Fredrick, OK.

Well that is my quick thought /wish-cast for Friday.

Mick

 

[nickgrillo]

I'd have to think GFS is underdoing SFC Td's just a bit... Yeah, there is some really nice wind fields across a small area of TX/OK panhandles in KS. The 108hr GFS shows precip breaking out across the TX/OK panhandles along and ahead the SFC trough. Strong directional and speed shear throughout the layer (backing SFC, 20knt southwesterly 850mb, 30-40knt westerly at 500mb and 60-80knt northwesterly at 250mb) indicates the potential for rotating updrafts... Yet, not sure if we can advect in at least 60F Td's to aid strong instability - To help with all that shear. All that shear will need at least a good 2000J/KG of SFC-based instability to get things really going. Obviously, the GFS has been underdoing boundary layer moisture... If it shows 500J/KG of CAPE with 50F Td's, I'd imagine we could get a good 2000-2500J/KG of CAPE with near 60F Td's.

If we can get some strong instability to go along with all that shear, then FRI will be a sweet day for the panhandles.

 

[Mickey Ptak]

Really much change in the GFS from yesterday but much to my surprise and dismay the NAM seems to point to a little less aggressive system.

GFS still forecasting great speed and directional shear at 850mb, 700mb, 500mb, and 250mb and is very aggressive with the 700mb and 500mb Vertical Velocities over the TX Panhandle.

The NAM on the other hand has painted a different picture to the upper are support. It slows things down just a bit and has the system over eastern NM by 00z Friday where as the GFS has it in the TX/OK panhandles by 00z. The NAM is also forecasting the upper air wind speeds slower than the GFS forecasts it to be.

The one thing, that I can see, that these two models do agree on is the lack of moisture. Both are forecasting Td’s barely making the 60deg in the concerned area. So in that case instability is shot also. This very well may hold true due the CF that is due to swing southward over OK and TX midweek, thus driving all the moisture down to the coast.

Now I am no expert on how models work so I have no idea which one
may have a better grip on this system. It’s still 84hr out so I have not given up all hope. As a good friend of mine once said "I am like monkey. I just point at the pretty colors".

Mick

 

[Mickey Ptak]

I suppose I am the only one interest in tomorrow’s opportunities.

NAM and GFS starting to agree on the placement of the shortwave over the cap rock by 00Z Friday. Both have been forecasting better moisture return for the area with the past two runs which is encouraging considering I had given up all hope due the lack of moisture. Now the Td are still only forecasted to be in the lower 60’s and that may still be pushing it. I think the key decision factor on me going is if there are pockets of higher Td temps over the Cap Rock. I think if we could a least get some low 60 Td over the Cap Rock we could see some very nice Supercells considering the elevation because the upper air dynamics are still favorable for Supercells.

This kind of reminds me of a Fall – May 12 2005 setup. Good dynamics but typical and questionable moisture. Would anyone else like to add / disagree with me?

EDIT: Just check my forecast with the SPC outlook and they seem to have the same thoughts about Friday so thats good at least.

Mick

 

[Tony Laubach]

I've got to agree that elevation is going to definately help a bit for this setup should things continue to prove interesting. I am seriously concerned with the TDs as I felt like I've been chasing in TDs that low all year and really didn't get a ton to show for it. I will admit my excitement with this system is a bit better that the previous few Sept systems in terms of overall chances for good storms, but I'm not really sold on this yet.

I still do like the shear over the area, and combined with ETA's forecasted CAPE values near 2000, I definately think there is a semi-decent chance for supercells to fire. While I'm not sure how much this resembles May 12, I would definately consider the trip if I can be sold enough on tomorrow's setup. Right now, I'm too climatological in terms of the passed 30 days of systems where they really didn't do a whole lot.

The closed low with this system which is kicking out tomorrow does keep my eyes open, though. Systems like this early in the year typically bring the monster snows to the Front Range and leave us Colorado chasers debating on whether to get east of it where better severe dynamics lie. This isn't a cold-core system like those, but it has that same look and feel to it.

Overall, its the moisture I am concerned about. If some more can creep in there, I would be happy.

 

[Mickey Ptak]

After looking at the archive data for May 12 2005 it really doesn’t look like it with the exception of the moisture. Here is a a link for that date for the surface data. Between 18Z and 00Z Td where only 61-63 deg yet we had some big time tornadoes. http://www.spc.noaa.gov/exper/archive/even...a/sfcloop.shtml

BUT, May 12 2005 did not have the closed low as Tony mentioned either. So as far as upper air dynamics are concerned it does not resemble the 12th at all with the exception of speed.

With only 700mb LCL forecasted, that extra high elevation may help some. I at least hope we can get some mid 60 Td but I would still go if they where at least low 60's

We will see though. Fingers crossed.

Mick

 

[nickgrillo]

SFC Td depressions of 20-30F across much of the Panhandle indicate activity will be mostly high-based in nature. Relatively weak low-level winds, combined with another zone of relatively weak flow in the 250mb layer indicate mostly multi-cellular updrafts -- trending towards outflow dominance. Further to the south... SFC moisture is progged to rise into the low 60s, and speed shear is a bit stronger. I'd have to think the severe threat with any convection north of CDS would diminish, as it moves into a relatively low thete-e boundary layer.

Further south (Jayton and points southward) where there is greater SFC-based instability (2000-2500) and boundary layer moisture, a couple supercells will be possible, given rather strong low-level veering - which yields favorable deep-layer shear profiles for rotating updrafts. Relatively weak low-level flow throughout the whole region pretty much limits any true tornado potential, yet... A tornado or two could occur south of Jayton (where there is a pocket of enhanced 0-1KM SRH), although the main threat should be large hail from any severe storm type.

 

[nickgrillo]

The latest 0z NAM run continues to indicate backed low-level flow, associated with a trough moving into the panhandle... Consident with SFC Td's into the low 60s. These factors combine with a destabilizing boundary layer and steep mid-level lapse rates, evident in the 0z CDS forecast sounding, to yield 2000J/KG MLCAPE and rapidly weakening CINH. Convergance ahead of the trough points to the Childress area for soonest initiation - with activity slowly developing/moving into southwest OK by late afternoon. 150-200 0-1KM SRH and strong deep-layer shear and favorably moist inflow supports a tornadic supercell or two.

If I was out chasing tomorrow, then I'd pick the Childress area for start.

 

[Andrew Khan]

There seems to be good supercell indices for the central TX panhandle, also to the SSE of that, there seem to be good supercell possibilities. I'm looking on the GOES SAT, and I think I am beginning to see some Towering Cumulus. I don't know about the tornado potential..it doesn't look very favorible. But Hail and wind threats likely exist. CAPE looks pretty weak, no extreme instability. There are also some strong veering winds, around the TX/OK panhandle. So I would say, that a supercell thunderstorm from this setup is quite possible...whether it will be tornadic or not...lets wait and see. So the main threats appear to be Large Hail, and strong SFC Winds.