10/17/07 FCST: TX / OK / KS

[Rocky Rascovich]

Time to start a thread about Wednesday. Based on the latest models, surface cyclogenesis really cranks up early on this day over SW KS... Looking at the data initially, one with some forecasting experience would be druling over this set up, especially if it was during the main chase season. Good moisture return, strong speed shear and one heck of a 500mb. jet core punching into western Okla. However...The concerns I have though is too much cloud cover that may be present earlier on in the day, resulting in some instability issues. The newest GFS run seems it has sped up this system a tad, so timing will be critical to maximize the usage of day time heating.... Also, the GFS has a tendency to deepen these systems too much early on, only to have them considerably weaker when the event unfolds.. yesterday (10/14) is a good example.

I was strongly considering a trip up to the PACNW to watch the ferocious seas from the remnants of Ling Ling, after much pondering and anguish, I'm forgoing that for now and will focus on Wednesday here on the plains. If we can get enough destabilization ahead of the dryline, and with the projected shear forecasted.. this could be a big day, even a couple of significant tornadoes not out of the question. As of now, here in cntrl OK. appears to be the best spot.

Rocky&family

Chad and I were on the same wavelength as we posted about the same time. Mod's can use discretion on where to add this post.

 

[Chad Cowan]

A short-wave, negatively tilted trough will move into the central and southern plains on Wednesday. Ample return flow will provide mid-60's dewpoints into central KS, but lack of insolation and subsequent destabilization could be the 'fly-in-the-ointment' as extensive cloud cover and convection are expected to be ongoing Wednesday morning along and S of lifting warm front. According to 16/0z NAM, a 985mb surface low will be located in w KS, with a cold front trailing into ssw into eastern NM, and a dryline extending due S where potential surface based convection will be focused. Wind shear will not be lacking as 60+ kt midlevel winds out of the wsw will be juxtaposed over 40+ kt southerly LLJ in the warm sector.

I don't have a whole lot of confidence in the models right now after the two previous systems were progged as tornadic events but yielded four potential chase days and one tornado (maybe). The GFS and NAM are relatively in line with this system, with the GFS putting the low a little further south.

 

[Mikey Gribble]

We are dealing with the same problems as last time (a few days out). Moisture return, insolation, and the instability it contributes to appear to be potential problems. The shear once again looks quite good. Directional shear leaves something to be desired down along the dryline. The last two runs have been consistent in showing veering 850mb winds, which I absolutely hate to see. IMO the poor low level shear is what killed this Sunday's tornado potential and I am afraid that this system may have a similiar fate. It's definitely something to watch though.

 

[Brandon Lawson]

Right now, I'm hoping for the GFS to trend slightly more towards the NAM. The NAM is showing a more favorable position for the developing surface low on Wednesday and that should contribute to better moisture return, better directional shear, and better chasing terrain.

But at least both models are showing good dewpoints on Wednesday. If decent advection of moisture can begin sometime tomorrow afternoon, I think the biggest concern will be the insolation. And geez! The helicity values could go bonkers, come Wednesday assuming anything the NAM/GFS is showing, verifies.

 

[Brian Stertz]

Looks like we've got a dual supercell threat situation for Wed. just looking the models over. Looks like one option may be C/NC Kansas on the deep surface low...where some very steep lapse rates and decent LL shear will be by Wed. afternoon. The second area which features strong deep layer shear, very strong ascent, with a good combo of shear/instability in that sheared environment across much of C/S Oklahoma and N. Texas and along/ahead of the dryline. As mentioned in some circles, the threat for significant supercells and tornadoes is pretty good at least for the first few hrs. before things may tend to line out or segment. This certainly bears close monitoring of the models. I am hoping that there can be a pretty good dryslot that works up into C.Kansas to make things a bit more interesting in the areas around the deep surface low. This is where I've got my watchful eye.

 

[Ilya Neyman]

This setup has been catching my eye since last week when incidentally I was informed about Sunday's possibility (hadn't been keeping up with the models as vigorously till then).

It seems that we have a system that definitely bears watching as a "potential" but, as previously alluded to by the other posters, has some big ifs and flys in the ointment.

Going off a purely model-forecast run and then only based on the GFS and the NAM (haven't looked at ECMWF yet) there are some serious discrepencies with the timing. GFS cruises this thing over and through early in the day and blasts off to our east by evening, whereas the NAM is definitely showing a more severe-weather favorable scenario as far as western and central OK is concerned. The GFS does like to scoot systems some 6-18 hours faster than reality at times, but the NAM was actually a tad too slow it seems with last night's occurrence. If this thing deepens some coming out of the NM Rockies it should slow and only add to the negative tilt it is already forecast to exhibit on ejection.

The pros to this setup are 1) a vigorous system 2) good speed and directional shear (which Sunday lacked) 3) great forecast moisture-return (owing to the fact that this time around the Gulf is open for business as opposed to modified continental air that had a quick jog over the waters before making it up into the plains yesterday) and finally 4) low lcls and lfcs

Now the cons are obviously timing and the issues associated with that...both models show precip. and storminess breaking out by Wednesday morning across the warm sector and this would limit instability as the system is already in its approaching phase. Another thing is that the mid levels don't really seem that cool and that is what looks to be limiting the forecasted cape despite the great moisture return.

I was initially worried about the winds veering at 850 as well, however, a look at the forecast NAM sounding does show a nice and deep layer of moisture all the way up to past 800mb despite this. Now of course, thats going off the NAM which still has a good southerly compoent, the GFS has nothing at all by 00z.

A lot is gonna depend on what exactly happens leading up to this event and above all the system's speed and composure. Still though, if this does tap into its potential it's looking quite a bit more significant than Sunday.

 

[Justin E. Reed]

Dr. Greg Forbes on TWC is already forecasting a "big deal" on this day. He said "we expect tornadoes, just how many, we don't know, but this could the biggest event since May". Now this is a guy that is incredibly smart in this, so I'll take his word over anyone on here, but having so many people expecting a fair sized event, its very good. The worst seems to be focused around the 35 corridor from OKC to Wichita. And Friday, it marches toward my home, Nashville.

 

[Mikey Gribble]

I updated my blog with a forecast for anybody that is interested. http://loadedgunchasing.com/blog.html

Basically I am zeroing in on the Red River area. My biggest concern by far is the amount of precipitation and cloud cover over the warm sector. If we can get partial clearing and a little insolation along the river, I think we'll be in business. That is assuming the NAM holds steady on the low level shear this time (I'm not holding my breath). I don't like to see the 850mb winds veering, but I think this is some what offset by the strong wind fields (35kt at 850 over SW Oklahoma). Deep layer shear looks quite good again. Even with meager instability I think we'll see some severe reports along the Red River, but we are going to need the low level shear to at least stay where the NAM is forecasting it (or even improve) and it would be helpful to get a little more surface heating if we're going to get tornadoes. Otherwise, everything else looks OK IMO.

 

[Chris C Sanner]

As per the last two systems this one has looked pretty good for a few days but the key will be the last 24 hours. A few things jump out at me with this one though that makes it a bit better for more severe weather. The trough structure as a whole is much more conducive and the mid level temps are indicated to be a bit cooler across the board this time around. I noticed the NAM backed off on its precip forecast quite a bit and I've seen days where a ton of precip was forecasted that never happened (and vice versa to be fair). I'm not sold on this being a huge day just yet but if the parameters came together like they have the potential to do I'd bet on the I-44 Corridor and eastward seeing a pretty significant threat of Tornadic Supercells. Especially if we get 'lucky' and see the sun for a good bit of the day.

 

[Justin E. Reed]

The SPC is currently issuing a slight forecast, but they said that if trends continue, they will upgrade to MDT, I seriously doubt HIGH, but hey, weather can throw curveballs, highly unlikely though. I sense atleast half a dozen tornadoes at the low end of my thoughts. If less sun, damaging winds and large hail will be the main threat, but the more sun, the more likely for tornadoes. I'm then worried about an overnight squall line or derecho thru AR, and then we'll see what happens on Thursday, tornadoes possible then as well.

 

[Kevin Scharfenberg]

The forecast wind profiles and hodograph shapes on the 00Z NAM WRF-NMM are extremely favorable for tornadoes over NE OK into SE KS late Wednesday, progressing into SW MO and NW AR overnight Wednesday night. The big question will be surface-based instability, with the returning 65-70 dewpoints there may be a lot of convection and cloud cover around, somewhat limiting the thermodynamic potential. We may not know until noon Wednesday.

The model run-to-run consistency on the timing of the wave leaves a bit to be desired so will wait for another couple of runs before getting too excited.

 

[Justin E. Reed]

The Naval forecast offices are already hatching out OK, KS, AR, MO KS, and NE as areas to not fly into for WED for this, "severe thunderstorms with tornadoes are likely in the listed states, more localized and in-depth information will be available tomorrow around 00Z, but at this time, all flight planners shall condsider avoiding the mentioned areas. This will likely roll over into Thursday for the Ohio and Tennessee Valley regions, so take this into flight planning as well." Kinda of interesting language, which isn't used that often. This is all because of the SIGMETs and AIRMETs that are issued with severe weather. I expect a MDT risk thrown into the mix tomorrow morning when the SPC draws its first set of new maps for the day. If I had the control for the Green Light, I'd light it up, chasers get ready and have a good time in doing so!

 

[Donald Van Dyke]

I hope this post is okay, but I wanted to let folks know about some new model graphics quickly becoming available.

http://www.stormvista5.com/stormvista_model_page_free.htm
http://www.stormvista5.com/stormvista_model_page_gold.htm

Everything in the "free" link should remain free, while stuff in the "gold" link will be subscription, although right now all of it is open.

There's some decent looking graphics in there, and since it's new I wanted to let folks know about it. I especially like the county overlays in the regional images. Perhaps it will be useful to some chasers to zero in on specific areas. The hourly RUC is also there, and it actually goes out to 9 hours on the non-12 hour runs. I don't know why the NCEP page doesn't reflect that (only shows it out to 3 hours on the non-12 hour runs), but it's here anyway. Here's a few samples from the 00z NAM tonight.

http://stormvista5.com/models/nam/00z/nam-mslp-qpf_sp-48.png
http://stormvista5.com/models/nam/00z/nam2meter-dewpoint_sp-48.png
http://stormvista5.com/models/nam/00z/nam-sbcape_sp-48.png
http://stormvista5.com/models/nam/00z/nam-hlcy0_1000m_sp-48.png
http://stormvista5.com/models/nam/00z/nam-ehi_0-3km_sp-48.png
http://stormvista5.com/models/nam/00z/nam500mb-hgt_rvort_sp-48.png

The main website is http://www.stormvista.com/

Thanks.

 

[Justin E. Reed]

MDT RISK, possible HIGH

A moderate risk has been put up for all of Oklahoma east of I-35, SE KS, SW MO, and extreme NW AR for tomorrow. LONG-LIVED, DAMAGING TORNADOES POSSIBLE. It wouldn't shock me at all now to see a HIGH risk thrown into there later today or early Wednesday. Some of this isnt the best chase terrain, but you all can make it work. I wouldn't be surprised to see a MDT risk for Thrusday either for TN, AR, MS, KY, AL, MO, and IL . This has the chance to be a big 2 day event, with many tornadoes.

SPC Conv Outlook
http://www.spc.noaa.gov/products/outlook/day2otlk.html

 

[Rocky Rascovich]

Thanks Donald for that great link! Hopefully Storm Vista will work out and will give other pay sites a run for their money! SPC just released their day 2 and we're in a MOD risk for Wednesday now. I have a very ominous feeling about this. The only negatives is a worked over atmosphere from the morning convection that is expected. But there is such strong vertical velocities to this vortmax ejecting out that there still will be some intense storms. Currently, based on what data I've seen from the 0Z, I'd pick areas around TUL, PNC to OKC for the highest likelihood of tornadoes.