3/21/2007 FCST: TX / OK / KS / NE / IA

[BrandonWhittington]

Moisture Levels are spreading north at a pretty good clip. Canadian, TX TD is already sitting at 55 and this is expected to climb. The way things are looking, TDs should easily make it into the 60s before Wed. One thing I like to see, that is that the moisture be in place the day before the event. I have noticed that when the moisture is not present the day before, the Dryline seems to wash back and forth across the panhandles. With this being said, TDs are not going to be a problem at all. The one thing that does concern me with prospects of Wed is the amount of Rainfall we get here in the panhandles on Tuesday. This could limit and cool the surface and not allow a lot of heating to occur. But never the less, Wed looks to be a heck of a day for chasing. Also, I have pretty much thrown the GFS model out of my forcasting. There is just too much flopping between each run. I dont believe that the system will dig that far south...... Wed, as of right now, I feel that sticking around the warm front will be the key. Somewhere in the northern panhandles.....Also, does anyone really have an opinion on CAPE values on Wed??????? Everything I look at keeps flopping around...

 

[matt patterson]

Honestly CAPE values IMO will be next to impossible to nail down until the night before or morning of due to the models not interpreting where rain will be falling and how much convective crap gets left behind... I am exited about the prospects but it looks like it will be a day where we have to monitor data constantly to find the best spot....

 

[afischer]

Kind of stating the obvious here, but I think the "chaseability" of this set-up will hinge almost entirely on the character/timing of any lead impulses ejecting out of the mean trough position. The 12Z NAM and GFS are both forecasting a well-defined lead impulse (good), but they vary considerably on the timing and location of it (NAM appearing to be more favorable, which isn't saying much given the trough is still out in the Pacific). As a result, the forecast location/strength of the dryline and forecast shear profiles are all over the place, as well. Models also want to forecast a large batch of stratus ahead of the dryline, which I guess isn't surprising given the calendar month. With ~10 g/kg mean mixing ratios and -15C or -16C at 500mb, MLCAPE won't be outrageous by any means... maybe 1000-1500 j/kg given strong heating. This is plenty, of course, if everything lines up right.

 

[Ray Walker]

I really think wednesday has the potential for a pretty significant severe weather event across Oklahoma. The moisture will be deep, wind feilds will be strong, and the cap should be strong enough to keep things isolated. In my opinion Shamrock texas seems to be a good target as of right now. I will not be playing the warm front, mainly because I think there will be widespread precip develop along the warm front. Ya there might be some tornadic storms at first but then things should become widespread. The dryline should be a key player in this event and any outflow boundary that is present. The cap to the north will be broken to easily, allowing for widespread storms. The further to the south the more isolated the storms should be thanks to a stronger cap. Also windfeilds look stronger the further south you go, along with instability.

 

[Jim Bishop]

I find it very interesting that both the GFS & WRF back the surface & 850mb flow over the Texas Panhandle between 18Z & 00z. Both models still indicate the dryline will continue to mix east throughout the day, despite falling pressures west of the dryline. Assuming convection does indeed initiate along the dryline in the Texas Panhandle by the late afternoon/early evening, low level shear profiles would be supportive of tornadic supercells.

Considering good surface heating, increasing low level moisture throughout the day, an approaching upper trough, and many small ripples caught within the upper flow, it seems pretty clear that convection would indeed fire along the dryline.

 

[Brian Stertz]

Interesting scenario

It looks like there could be a two point severe wx focus for Wed. (3/21) based on the 18z MesoEta. It looks to me that target #1 will be across SW/SC/C Nebraska on the for sure triple point...and target# 2 will be on the dryline across SW/C Kansas southwest into the C/E OK & TX Panhandles. Timing of the strong 700/500mb neg. tilted wave looks pretty good for target# 1 to produce. It may be a slightly later show for target# 2, but still very interesting depending on what model you sink your teeth into. Lots of runs to go before deciding on a chase target to lock in.

 

[Michael O'Keeffe]

I like the Texas Panhandle around and east of Amarillo if the Eta varifies. I think this is where the best combo of shear, instability and helicity will be. Upper 50 dewpoints along the dryline will lead to strong convective development that is likely to become supercellular and tornadic. Storms may also be discrete enough for a long period of time. Target as of now is Claude, TX (SE of Amarillo on US287). Many more models to come out before a final target area is made.

 

[afischer]

It looks to me that target #1 will be across SW/SC/C Nebraska on the for sure triple point... Timing of the strong 700/500mb neg. tilted wave looks pretty good for target# 1 to produce. Lots of runs to go before deciding on a chase target to lock in.

00Z NAM remains consistent in this regard, with what seems to be a fairly well-timed shortwave trough into the central NE/KS border region. http://www.wxcaster.com/CONUS_ETA_500_GPHTMPVORT_72HR.gif It's also forecasting notably stronger CAPEs up there than previous runs, IIRC.

The 18Z GFS continued with the faster solution just like the 12Z GFS, which certainly wouldn't seem to bode as well for initiation around peak heating along the dryline... namely if the s/w is contributing to junky showers/elevated convection in the warm sector before the cap to surface parcels is able to erode. http://grib2.wxcaster.com/wxcaster4/CONUS_GFS_500_GPHTMPVORT_78HR.gif

 

[samuel stone]

oz nam shows a marked increase in temp and a solid increase in dew temp, nice 2000-2500 j/k cape because of it, really like that increase to
-6 LI too. Things are looking better thermodynamically at this point.

 

[Ray Walker]

I noticed this also samuel. The GFS has picked up on this also, although I think it is a day or so faster than the NAM. Moisture will not be a problem with this system, especially if we get heavy rains one day then the next it clears out allowing for surface heating and evaporation. One day this week or possibly more could easily turn out to be huge severe weather events across Oklahoma and Kansas, along with parts of Texas. All I can say is if surface heating takes place for very long along the dryline or outflow boundary anyday this week I think severe weather will be likely, especially Wednesday and Thursday.

 

[Adam Atkins]

Good thermodynamics present Wednesday, decent kinematics. Lack of potent embedded shortwave/jet streak is a concern and only modest surface pressure falls will occur during the afternoon so winds will be southerly and lack significant backing in the afternoon and evening. Discrete storms or outflow boundary interactions will be key for tornadic potential.

 

[Chris Wilburn]

New model runs will be out shortly, but going on last nights runs I am more excited about what we can expect on Wednesday. I like how last nights runs project more moisture with 60 dewpoints all the way into central Kansas and down the dryline to sw Oklahoma. This has raised forecasted CAPE values to 2,500 J/kg in western Oklahoma and southcentral Nebraska. Like the post above the surface winds really don't look to back too much, but upper level winds look good with 30-40kt 850mb winds/40-50 500mb winds. Storm speed shouldn't be of any real concern. I agree that it looks like there will be two areas of concern. The triple point in the Kansas/Nebraska area and the dryline to the south into sw Oklahoma. Still early yet as we still have some model runs left to work with to sort out the finer details. Have to like the moisture this system will have with it along with CAPE, esp. if we can actually get at least 2,000 J/kg as the models are forecasting at this point. SPC has a 15% risk on the Day 3 Outlook for the mentioned areas above.

 

[Doug Mitchell]

I just got Wednesday off of work so I will most likely be chasing in NC KS/SC NE. So far my target is Phillipsburg, KS although chase day is still 2 days off. Best instability is progged further north and best chance for storms to develop before dark should occur near the triple point.

 

[Chris C Sanner]

This looks to be a very active late-week part of the Spring Break (for us lucky College Students). The first day looks like it will be the 21st and I'm going to favor the NAM for my forecast here. First thing after looking at the models is that the EHI's are all forecasted to be above 2.5 North of I-40, I don't know why I've always favored higher EHIs, but it seems to always reward me,

Another thing I noticed is that the cap looks strong but breakable by isolated storms. The key will be getting clear skies to get instability and I think the second and more important key will be getting outflow from Tuesday's forecasted heavy precip across Oklahoma to setup W-E somewhere. Its way to early to set a target because of locations of outflow and such, but I'm certain I'll be in Western Oklahoma sometime Wednesday!

 

[Jim Bishop]

My oh my.. so the latest WRF has trended a little further north with the placement of the main fort max. It looks like it will pass through North Central Kansas/Soth Central Nebraska. That will be the triple point, and where initiation is very likely. I'm impressed with the low 60s dewpoints as far north as Central Nebraska, and the 2500 j/kg CAPE. With 500mb winds southwest around 50 knots, a 40-50 knot south-southwesterly 850mb jet underneath that, and southelry surface winds, things are looking pretty darn good for tornadic supercells to fire off the triple point/low over South-Central Nebraska, and further south along the dryline over Northern Kansas.

It seems like a more conditional threat for isolated (as apposed to widespread) supercells will exist across Southern Kansas, Western Oklahoma and Western North Texas along the dryline. There won't be much upper support and the cap will be quite strong. But you never know, a weak upper impulse aided with surface heating could break the cap.

I'm getting excited. But unfortunately for me the northern target is a bit far from Houston!