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

[Andrew Stoller]

I saw that Skip. Since the system looks to be speeding up and taking a more northerly track, the cold core option is looking better and better for any daytime tornadoes. Further south, it'll be well past 00z for full destabilization to realize as moisture return is maximized later in the day and into the evening.

 

[Andrew Stoller]

Ughhhhhh, the 12z GFS has the system off to the races now. Surface low is in eastern South Dakota by 00z for crying out loud!

 

[Jeff Snyder]

I'm not impressed. Even ignoring timing issues, this looks like a common early-season high shear, low CAPE setup. For the most part, such setups tend to disappoint in terms of warm-sector convection. I can come up with many early season chase opportunities that featured such high shear with very marginal instability, and it seems that the cold-core play tends to play out much better than the "typical" warm-sector play (ahead of the dryline, etc). I've had terrible luck with <1000 j/kg CAPE chases, particularly when the shear was as strong as it should be on Monday. Leaned-over towers, struggling to even sustain themselves, etc. I'd be much more optimistic if we had >60F Tds, but I'm not sure we'll even see solid 57-59F Tds. Again, environments with such low Tds HAVE produced 'warm-sector' tornadic supercells, but it seems much more uncommon compared to struggling, junky convection. >45 kts @ 850 mb, >55 kts at 700 mb, and >70 kts at 500 mb = jet-pack necessary to chase with 45-50+ kt storm motions.

I have a regional bias to the area S of I70, so I'm not as concerned about the speed of the trough ejection or the location of the sfc low (obviously heavily affected by the location and timing of the trough ejection) as long as the dryline / pacific cold front stays W of I35/I135 by 0z. The cold front surges rapidly southward and eastward after 0z, so a squall line seems likely regardless of what the DL/Pac front initiates during the afternoon. and early evening.

Despite the cons, I'll probably still chase since it's relatively close, and I'm eager to get back out chasing. My expectations are low, though, and I expect this chase to end like many of my past March-April chases.

 

[David Wolfson]

Not too much has changed in two days IMO, except the system is moving slightly quicker, with the best cold-core low top supercell opportunity up around Yankton, SD, by 00Z. Kearney, NE, is still on the route, but in the early afternoon time frame.

What I look for (thanks to experts like Jon Davies!) is a vigorous stacked system with marginal positive deep-layer instability and a tongue of dry, <0C at 700Mb, more-or-less, advecting rapidly around the core. Another ingredient is good surface heating in advance, which is rather so-so for this early-season setup, IMO. No outbreak, but a chance for a few weak tornadoes, FWIW.

 

[Robert Edmonds]

I'm probably heading out. So here's my brief thoughts. Most of this is based off the NAM, so keep this in mind. So like everyone has mentioned weak instability seems to be the biggest problem. However, it is march so this is to be expected. Between every model run the instability seems to change, but we do see ~1000J/kg (yes, usually less) cape pop up here and there from NE to OK. There is also the trend of higher instability to the north less to the south. However, the shear and helicity tends to weaken to the north. This is where my preferences in what I like to chase come in. Personally I get annoyed with fast moving storms. This means I'm sticking with a more southern target. NE, and most of KS area we're looking at storm motions of 45 mph or greater. This means I think I'll be sticking with a target in OK. Current plan is to be sitting on I-40 in the morning some where near Sayre, OK, and adjust from there (edit: not my target just where I think I'd like wake up and find my target from there). Perhaps I'll bust being this far south but oh well...

 

[michaelgray]

Clinton

Robert I would agree with you but maybe not quite this far west. My plan is to be sitting in Clinton on I-40 then Im in a good position if I want to head west or north..

 

[Brian Stertz]

Yeah this looks more and more like another March chase to sit out. Have seen this too many times where shear is just overpowering and the forcing just keeps everything right on the dryline...and even the favorable Nebraska target looks like it will struggle to get a mid 50 Td. Unless things radically change with forecast trends, I will be conserving the vacation day for down the road. Maybe Arkansas on Friday ??

 

[Brandon McClung]

as with all of you, i have been watching this system since wednesday. having already invested many hours in forecasting i am definitely going out. keep in mind there have been several studies done that show that with good shear and marginal instability, tornadoes can still be possible.

with that said, you have good lapse rates nosing in over NW Oklahoma, into southern KS. the dryline bulge seems to be pointing in that direction to. this inherently gives you good divergence aloft so i would expect storms to fire in that region. you also have 850mb winds straight out of the south progged at 50kts, which will increase low level hodographs and shear, making that area even sweeter.

i think it is to early to pick a target city, but NW OK looks good. good luck to those who chose to go out!

 

[Andrew Stoller]

FWIW, there's already 60 degree dewpoints in southeast Texas right now, and the RUC is forecasting 60+ degree dewpoints into central/north central Texas by this evening.

I'm hoping the NAM and especially the GFS is slightly under doing the amount of moisture that can return by Monday.

 

[David Reimer]

The 12Z WRF has continued the trend from the 0Z on placing the dryline from roughly Abilene to Oklahoma City at 0Z with CAPE from 1000-1500 with some isolated spots above 1500. It also has dews at ranging from 57-65 in most area's. I am still hoping the models are downplaying CAPE by having widespread light precipitation indicated, but with that, Im still half in half on Chasing Monday.

 

[jamesmseitz]

Don't worry everyone it probably will be a great day..... I decided to tell work that I will be there on Monday instead to chasing. Hence the day will be great and I will miss out ). really I am not liking that last runs as well. There will be a few good storms but it is early in the season and it is a longer drive for me..... I think I am ( sitting this one on the side lines..... watching my screen all day and seeing what will happen. Enjoy to all going. JMS

 

[Chris Vagasky]

I don't know if anybody here saw Harold Brooks' presentation at the NSWW this year...if not, it has been posted online:

http://www.norman.noaa.gov/nsww2009/talks/007_thu_brooks.pdf

The highlights:

Given "some" Wmax, mostly a function of shear:

* High shear - Tornadoes, hail
* Low shear - Wind
* Tornado intensity - function of shear

I have modified one chart from his presentation, placing a star where the Oklahoma environment figures to be based on the models and forecast soundings:

Adapted from Brooks (2009)
​

I've been following this system since the middle of last week. It is certainly very dynamic.

The UKMET, Euro, and WRF are in pretty good agreement with their placement of the low and show very good wind profiles.

UKMET and WRF have precip breaking out in similar locations across Western Oklahoma by 0z Tuesday.

I've got a little bit of confidence in the UKMET solution, it has been handling the location of systems pretty well recently.

It looks to be a good day for storms, and I'm planning for some sort of convective activity across western Oklahoma.

 

[Andrew Ryan]

Tds in the upper 40s to lower 50s here in Oklahoma. There may be a slim chance we may get to the Td we need, but I have low confidence in that. The winds right now in Norman are light at best. But it is overcast at the moment, so whatever moisture that does make it up here isn't gonna mix out too fast. Still something to watch over the next couple of days.

 

[Michael O'Keeffe]

We have a 50F dewpoint here on the SW side of KC and you can feel the humidity. Once again the 18z NAM is looking like the best model run out of the four. Below is the wxcaster SBCAPE values for 0z Mon. I think it gives a more detailed and accurate forecast of CAPE and you can get a good idea of where the CAPE is maximized. I think if the dews CAN reach 57-59F like mentioned we could see some tornadic sups in S KS/OK. The shear continues to look VERY VERY good for supercell formation, if we can get the instability then it should be a good day.

Edit: Another thing that is interesting over N Oklahoma is the split 500mb flow where the flow is SSW in Kansas and WSW in Oklahoma. That could prove significant as that divergence of the upper flow tends to be a hotspot.

 

[V. Gensini]

IMO:

Pros: Upper Level Divergence
Deep Layer Speed Shear
Narrow Window of Directional Shear

Cons:Mid Level Lapse Rates
Depth of Moisture
Amount of Moisture
Major Mixing
Timing of Shortwave (No time to build up instability)
Amount of Forcing! Everything to go linear quickly...
Warm Sector Cloud Cover
Storm Speeds


Definitely sitting this one out unless something major changes (which I don't see happening). Honestly, pending Monday morning's vis sat, if I was close enough, I would consider playing a Cold Core setup in N/NE NE.

FWIW...prob of a tor on 3-25: