3/23/09 FCST: NE, KS, OK

[Chris C Sanner]

While a few local offices and local media outlets are persistent at the chances of an 'outbreak' of severe weather Monday, I'm definitely not buying that hype. However, I think this is more than a good day to be chasing unless you only want to chase outbreak days and are scared of doing a little bit of forecasting

CAPE values are troublesome, but even moreso will be the depth of moisture. I'm afraid we could end up with some rather shallow moisture come Monday as we continue to mix down. The directional and speed shear is nice, so if there are any localized areas of higher CAPE with a discrete cell, you will be rewarded Monday for sure. The big problem with all the discussion so far is that we are still 3 days out, and I'm expecting the tone and topic of the discussion about the day to change quite a bit between now and then.

Right now, it looks like a day that can produce tornadoes with any discrete cell in the right area, but it is by no means a huge outbreak day if the 12z models verify. So if you do spend some time forecasting and nail the right target, I'd say you have a great chance to be rewarded Monday. But the Tornado threat should be rather localized to areas of higher instability and areas of locally deeper moisture which could develop.

EDIT: One thing that I forgot to add which I think is something people just aren't talking about are the storm motions. NNE at 40-50 kts will NOT be easy. So if it's a marginal day, you are going to have to really work hard for sure

 

[jamesmseitz]

The more I watch this system I am not seeing everything come together. Storm motion will be fast.... The lack of good moisture and shear tells me that everything at first might get torn apart until after dark as it gets the dew points further to the east. With all that said before, The light show will be good..... and still it warrants attention.

 

[Derek Weston]

Rather pessimistic now that we're seeing the NAM giving us nothing better to work with than roughly 500-1000CAPE.

Interesting with the GFS deepening the moisture (nose of 60-65 dew) and much better CAPE at 06z. That would be well after dark, however. (like Skip was noting)

If I could've been promised at least 1500 south along the dryline... would be feeling much more optimistic.

I do remember the NAM under-valuing CAPE at times last year.... in particular, May 22/23, if I'm not mistaken. (with the RUC having a habit of really overvaluing it that season) Not sure if that's a reasonable assumption for now, however.

 

[Daniel van Os]

The 55 Td isotherm

That would be an isodrosotherm

 

[Michael O'Keeffe]

Wow the 18z NAM is looking better for much of the region. It is showing a massive area of CAPE exceeding 1000 j/kg with incredible directional shear. The precip models are showing cells firing out ahead of the front as well over N OK/S KS. Helicities are INSANE after dark with 500 m2/s2 common over KS/OK. Hopefully this tread will continue as it is looking better to me.

Check it out at www.twisterdata.com

 

[Brandon Goforth]

FWIW, the 18Z NAM just jacked instability up enough to make it interesting again. 1000+ CAPE now ahead of the dryline with pockets of 1250 in W OK. That would certainly make a considerable difference IMO compared to 500-750 CAPE. No change in moisture and shear is still amazing. A line of precip now showing by 0Z south into NW TX.

Now we enjoy the roller coaster ride from run to run over the weekend.

 

[nickgrillo]

If the GFS is to be believed, then I'd have to say we're gonna have an extremely difficult time getting a supercell to sustain itself with those kinematic profiles, which are horrific; strong unidirectional flow (with 50-60kts of backed southeasterly 500mb flow across much of the warm sector) and very intense deep-layer forcing doesn't impress me at all. The NAM paints a different picture in terms of kinematic profiles; boundary layer directional shear is slightly better (increasing low-level SRH and the chance for a tornadic supercell) during the afternoon over a larger portion of the warm sector. It's still four days out, so it's worth watching.

 

[Brett Roberts]

It is interesting how significantly the 18z NAM wants to improve instability. Looking at the charts on TwisterData.com, surface theta-e is actually the same or slightly lower than last run. However, the 500 mb trough is a bit more negatively tilted and/or faster, leading to greater height falls and mid-level cooling along the dryline by 00z; I can only assume this is the source of the change in CAPE. Obviously these run-to-run nuances mean nothing at this timeframe, but if changes this minor in the timing of the trough's evolution are going to affect instability (and, as a result, the general magnitude of the event) so significantly, it's going to be a fun ride the next few days.

 

[Adam Lucio]

The only reason the NAM is bumping up CAPE is because Im home now and i DIDNT take Monday and Tuesday off to chase.

With that being said, from what Ive looked over so far, there have been some improvements. These next few days Im going to be glued to the latest runs. The speed and directional shear are there and if the NAMs bumping of the CAPE begins a trend we could be looking at a very active day. Lifted Index even goes to -7! Helicity values are impressive in OK with a nice little 550 bullseye.

With surface juice in the upper 50s possible and temps in the 70s I think we can get some good LCL heights.

Yesterday i set my target city as Woodward, OK and If I had to pick now I would shift that east a bit. I wont get ahead of myself though. Will have to keep watching but I wouldn't throw this setup in the garbage just yet

 

[Dustin Wilcox]

Call me crazy but I think per current model runs the NE CO and NE Panhandle border region looks golden for some N and maybe even NW moving tornadoes. I doubt I will be able to muster up the courage to ditch the more "typical" target areas, but that area looks nuts to me around the lunch hour...

 

[Eric Treece]

As of this moment I am going to agree with Dustin with the NE/KS/CO border. Some of the models seem to have the triple point near there, but the way the models have been fluctuating makes me wonder what the next run will have. Meanwhile all of the media outlets are casting this day as a "grab the kids and get in the cellar" kind of day. I am still not convinced.......but it is getting me in the spirit to chase!

 

[Gabe Garfield]

It is interesting how significantly the 18z NAM wants to improve instability. Looking at the charts on TwisterData.com, surface theta-e is actually the same or slightly lower than last run. However, the 500 mb trough is a bit more negatively tilted and/or faster, leading to greater height falls and mid-level cooling along the dryline by 00z; I can only assume this is the source of the change in CAPE. Obviously these run-to-run nuances mean nothing at this timeframe, but if changes this minor in the timing of the trough's evolution are going to affect instability (and, as a result, the general magnitude of the event) so significantly, it's going to be a fun ride the next few days.

I think you're right, Brett. I definitely like the trend -- a doozy of a trough, to be sure!

One thing I'd like to note is the progged storm motion on the 18Z NAM. Generally, the storm motion across the warm sector is 30-35 kts to the NNE. With this kind of storm motion, there is a considerably better opportunity for storms that develop along the dryline to remain in relatively unstable air for longer, even with the narrow corridor of instability that is forecast to develop. The 18Z NAM forecasts moderate instability to develop from western N TX all the way to the surface low. Should storms be able to avoid harmful interference, this would increase the likelihood -- in my opinion -- of a significant tornado event.

Now, of course, 60+ Tds would be ideal, but I know tornado outbreaks have happened in environments characterized by <60 Tds (especially on the High Plains). Also, I should like to note that the moisture depth is not a problem. If you look at the forecast soundings for 00Z Tues from the latest NAM, you can see that the moisture layer is at least 100 mb deep. So, in terms of Tds, what you see is what you get. And if mid-upper 50s is the rule, I'm not complaining.

 

[Andrew Stoller]

Stupid GFS. The 18z has sped the system up like it skipped time ahead by 6 hours. I sure hope that doesn't verify, because I'll have to leave at midnight to get to any kind of target area on time.

 

[Fred Gossage]

I don't think it's much of a concern. The operational GFS has been, and continues to be, an outlier with the timing of this system.

 

[Chris C Sanner]

Stupid GFS. The 18z has sped the system up like it skipped time ahead by 6 hours. I sure hope that doesn't verify, because I'll have to leave at midnight to get to any kind of target area on time.

I'd say don't get caught up on details like this too heavily just yet. Watch trends until we get closer to the date. The GFS is a major outlier in positioning the dryline/cold front in Central Oklahoma Tuesday...so unless other models come around I'd just note it and dismiss it for now.

Also, the 18z NAM inexplicably deepens moisture...so unless that becomes a trend, I'm not going to get too caught up in it. Right now if you get caught up with specific details...you are going to be on one heck of a roller coaster ride until Monday. I remember a few times on StormTrack guys were planning for chases in E. Oklahoma at this point (3-4 days out) and the chase ended up in the Eastern Texas Panhandle.

I guess my main point is to just watch trends and don't get caught up on too many specifics, just take note so you know if these small changes become trendy in the models, even though the ground truth on Monday will almost certainly be different in a lot of ways than what the models are even saying 12 hours out.