4/30/04 FCST: Southern Plains


Looks as if, IF THE GFS VERIFIES, Friday could be a decent chase day across portions of the southern plains. The ETA and GFS have been butting heads for quite some time regarding the position of the upper low over the southern plains. With the ETA farther southwest than the GFS, it keeps the best mid-level wind speeds also southwest, pretty well removed from the warm sector. However, the GFS opens the low into a trough as the central US trough digs southward. Because of it's farther-northeast position, the jet streaks at various levels are much more favorably positioned for a decent severe weather day across se KS, eastern OK, and perhaps ne TX. By this time, some decent Gulf moisture should be in the area, east of the DL and south of the front. Forcing doesn't appear to be too strong with the front, as the cold front nearly halts with a low forming at the front/dl interface. Whatever the case, I'm hoping the GFS can verify and give us a decent chase day across the eastern portions of the southern plains. If the ETA verifies, however, things could be dissappointing. Whatever the case, I'm putting slightly more faith in the GFS, as it has been more consistent run-to-run, and it also gives me hope for a decent chase :)

At any rate, post away....
The ETA continues to come more in line with the GFS, especially in regards to the position and strength of the mid-upper low opening into a wave as it gets absorbed into the building central US trough....

Latest ETA and GFS both indicate some impressive instability (3500-4000 j/kg) building in ne OK and se KS by friday afternoon. In addition, 500mb near 45-50kts, 700mb near 40kts and 850mb winds near 30-40kts in ne OK. This on top of generally low-80 temps with near 70 tds should put the LCL in the moderately-low, but doable, category. ETA progged helicity is kind of weak, but I don't trust helicity graphics any more than about 12-18 hrs out, since it's so sensitive to minor changes in direction/speed anywhere in the lowest 3km.

This setup looks pretty similar to 4/22 (last Thursday), with a nearly stationary from from OKC to Coffeyville to STL, a cold front moving southward through sw OK, and a decent dryline. It's looking like ne OK and se KS could be game for some actual significant supercells on Friday...

I'm hoping the low comes out a little farther south, which should help push the better 500mb flow a little farther south into OK (including ne OK)... I needed a little reminder from the May 3rd, 1999 OUN evening sounding to remind myself that violent tornadoes are definately possible with 500mb winds <50kts (that sounding generally had all winds below 500mb <40-45kts), which is quite different from the 50-75kt 500mb flow most of the May outbreaks had last year...
The ETA still has a mid-level weakness over the warm sector, based on the 06 Z ETA. However, the GFS is still adamant that a good swath of 50+ kt winds at the mid-levels will be present on Friday. Both models still forecast a relatively weak LLJ, though. CAPE should be more than sufficient for tornadic supercells, so the degree of instablility may make up for a lack of shear(w/out consideration of low-level boundaries which may locally enhance shear). I would hope to see the cold front stall more on the next few runs before getting too excited. Certainly, though, this day has potential.

SPC has made mention for a tornado/high wind threat for tomorrow, but I'm afraid its a bit far east for me to make the trip for. That and I am getting into the home stretch with school, so unless a good weekend scenario sets up, I may be restricted til the middle of May.

As for tomorrow, glancing over things briefly this morning (ya know, just in case), the shear for tomorrow definitely looks better than today. The system will bump out of the rockies and head into the plains, creating a good wind profile as it moves eastward. CAPE values look really good and moisture will be more than good, I think. The drawback, you're chasing in the woods it appears. I would likely be heading for the TX/OK/AR border area.

As for me in Denver.. more snow!! :angryfire: Ugh, they're calling for up to 6 inches in the city, closer to 8, maybe 10 near my house. At this time last year, I was chasing hailstorms in Colorado, not snow! Ah well, such is weather in Denver, I suppose!
Friday chase

Seeing that both the ETA and GFS are beginning to agree with each other, I'm thinking the prospects for supercells is getting better. I like the northern edge of the CAPE max just east of the low/warm front where I think surface backing could help spur the tornadic threat. I'm not overly concerned about the upper air windfields, but rather the timing in which they arrive. Likewise, it also appears that the 850mb flow may be displaced further to the east as well. Regardless, I'm targeting an area from Ponca City to Bartlesville - subject to change.
Well... model inconsistency continues! The ETA has now reverted slightly back in regards to how its handling the opening low. The 12z run is slower with this process, and thus the low is farther southwest... With this, the best mid-upper level flow is removed from most of the warm sector. Grrrr.... The ETA has been particularly inconsistent and poor in handling what's going on. I'm awaiting the 12z GFS, as it has been quite a bit better than the ETA recently... If the low/trough hangs back as far west as the ETA is suggesting, I think the risk of persistent, non-HP supercells tomorrow is decreasing, as most of eastern OK would be experiencing weak mid-upper level flow.

Ugh, why do I bother looking at the ETA more than 24hrs ahead of time? Grrr...

On the brighter side, the latest run is considably weaker and farther north with the central US trough this weekend through early next week. This may result in less continental air intrusion into the Gulf, sparing us from having to worry about Gulf recovery as much for the system that appears to be taking shape for the end of next week... Oh wait, again I'm looking too far ahead...
No go for tommorow. I'll be in Dallas, BUT, my analysis. I'd target the more discrete threat along the dryline for any tornadic action. It looks to be a line along the front, so I'd hit somewhere around the middle south of the dryline for the best chance of discrete supercells. But its just a quick 15 min analysis so take it for what it's worth ;)
The models have moderately high values of CAPE by tomorrow morning in Southern OK/ Northern TX. Shear is not so great, but if that trough can just get here a little bit faster, everything could look pretty good. I wouldn't mind sitting in SW OK along the Red River sometime around 1PM-ish. We'll probably get a better idea with the new model runs tomorrow and what actually pans out at the 850mb level. The models seem to be underestimating the winds at 850mb per the SPC meso-analysis currently. Another good thig to watch is where the convection tonight will put down an outflow boundary for tomorrow.
Depending on how things look this afternoon, work will be slow for me today so I plan to provide play-by-play services in the nowcast thread once things break loose. If any of you are out and about feel free to check this afternoon and we'll provide a breakdown of the current happenings for you - - -
So far, the most optimistic numbers I can find (for my neck o' the woods) are from the 21Z RUC forecast for SPS. Nice LCLs, marginal LIs(-5.6), 1219/70 CAPE/CIN.
The negatives that stand out: narrow window of opportunity for discrete cells, poor visibility and overly optimistic surface temp forecast. Not completely in love with forecast Jet level winds.
Looking very similar to last Friday. That's both good and bad.

What a difference a day makes. There are many positive features I like
including that outflow boundary from last nights bow echo and narrow region of
backed winds over north-central Texas. With the approach of the upper system,
there will be sufficient vertical wind shear for supercells. While overabundant
moisture will eventually yield HP's and a squall line, I believe it is prudent
to get out there when convection initiates.
I also like the clearing on satellite south and west of Abilene. I believe
there will be tornadoes today and agree with the 5% area SPC outlined in their
13z outlook. The Dallas-Ft. Worth area is due for another hailstorm this
evening. Good luck. TIM M.
I and my partners Bill and Kanani are targeting Throckmorton (ofcourse) as a starting point and will adjust from there. we will have to adjust as we get information on the fly (childress wifi) since we have such a long drive from Amarillo and will be on the road by 10:30am so we can get south of the front before initiation. After yesterdays surprise wx we caught near childress today is just frosting, especially since we ridge out for a week. I am worried about any kind of heating taking place due to a ton of cloud clover but as the day wears on there should be more clearing in central Tx. Good luck to all those out there. If you see a white explorer with red/blue lights, stop and say hi (we are actually friendly :D )
I and my partners Bill and Kanani are targeting Throckmorton (ofcourse)

lol - Always the safest bet ... Throckmorton just doesn't seem to disappoint now does it ...

All the best to everyone down there today. Wish I was there - - - if there is any specific data needs that any of you have or would like to request, feel free to post what you would like and we'll be sure to watch the particulars for you. Not always in a position to do this, but should be fun today -

Enjoy your chase, Tim -
lol - Always the safest bet ... Throckmorton just doesn't seem to disappoint now does it ...

I blew a couple of tornadoes near Throckmorton in the past few years (original member of Throckmorton bust club) by either being a bit late or choosing the wrong storm. It got so bad my partner Kanani started calling me the "mayor of Throckmorton". she has a picture of me standing under the city limit sign flipping it off. We now joke about if there is a slight risk within 100 miles of there to go to that little town and sit there and wait for the tornado no matter what is happening elsewhere. So today its in the middle of my target area so here we go a driving to Throckmorton :lol:
I should be available all afternoon and evening for anyone who needs some nowcasting. Anyone needs my #, feel free to PM me.

Jay, be advised he wifi at Denny's in Childress yesterday evening was barely working VERY SLOW. We are targeting ABI with getting a further surface/sat update in Ranger and prob modify that target at that time.

You going for that boundary on satellite to eh? Hehe, I love how we think so much alike! :lol:
We're leaving OUN in about 20 mins... Initial target is Olney. We'll probably shift around as we head towards SPS. Whatever the case, I like the clearing in north TX... Already a few 70 degree Td observations over northcentral TX, on se sfc winds, which should then advect northwestward closer to SPS to Throckmorton line. Net shear / absolute wind speeds are kind of weak, but directional shear should make up for the lack of much speed shear.