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

[Shane Adams]

I was much more excited from yesterday's run. Current version shows worse shear, no instability, and a very narrow corridor of "CAPE". IMO Monday looks more like 3-4-04 than 3-28-07, as it stands currently. The only positive I see are the h5 winds in NW Texas, which have a more westerly component than anywhere else. If I was going off of the current model for chasing tomorrow, I'd be sleeping in and not worried about charging batteries.

Fortunately, this is all still make-believe. I'll start paying attention this weekend, when it starts being for real.

 

[Jesse Risley]

I agree with Shane. The recent CAPE values should be taken into consideration, but as others have said the models are probably underdoing the CAPE values at 132 hours out. They'll probably rise between now and Monday.

Based on the current runs, it appears to be a mostly linear event to me, even given the respectable forcing for March. I would also expect the speed of the system will change between now and then.

 

[jamesmseitz]

The temps are looking in the 70’s yes but the timing and the cloud cover are not great. The cloud cover is forecasted for the entire area. And the last run shows everything closer to the 6 to 7 time frame. Pretty small heating window for a great day. With that said, its is still way to earlier to call it off. With later runs things might get together, the southerly winds look good, a dry line seems likely but pre frontal development seems like it will be hampered. Right now I say it will be a great light show.

 

[Derrick Herndon]

I would like to better understand this. Why should the CAPE be dependent on forecast time? Are not the same physics being used on the 24 hour forecast as the 132 hour? I know the resolution changes after the 180 hr but was not aware of any changes prior to that. Or is it just that the model is under-forecasting the low-level moisture/temperature (my guess)? If the GFS slows as forecast this would lead to less mid-level cold air advection into the Plains and less CAPE (though perhaps offset by warmer low levels).

I agree with Shane. The recent CAPE values should be taken into consideration, but as others have said the models are probably underdoing the CAPE values at 132 hours out. They'll probably rise between now and Monday.

Based on the current runs, it appears to be a mostly linear event to me, even given the respectable forcing for March. I would also expect the speed of the system will change between now and then.

 

[David Reimer]

I would like to better understand this. Why should the CAPE be dependent on forecast time? Are not the same physics being used on the 24 hour forecast as the 132 hour? I know the resolution changes after the 180 hr but was not aware of any changes prior to that. Or is it just that the model is under-forecasting the low-level moisture/temperature (my guess)? If the GFS slows as forecast this would lead to less mid-level cold air advection into the Plains and less CAPE (though perhaps offset by warmer low levels).

The GFS has constantly under done the CAPE levels on all of the events this year at that range. It has really picked increased the CAPE once we got within 72-84 Hours. So that is a trend that has been taken into account of their forecasts.

 

[Jesse Risley]

The models can often fail to accurately depict true instability values, even right before the event. I was referring to the fact that the GFS could be under-forecasting instability 132 hours out; things will probably change.

 

[Derrick Herndon]

Ok I can certainly agree with that. GFS has a tendency to under-forecast CAPE. It seems this would be related to what I see as a too cool bias in the lowest levels of the model in the warm sector. Need to see if that is quantified somewhere. I missed out on the 2007/03/28 event based on some personal bias about chasing early events and what I viewed at the time as insufficient deep layer shear. Will not make that mistake again.

 

[Brian Stertz]

When it comes to a dynamical system like this...1000-2000j/kg CAPEs could be all that is needed. The more important thing is to get the supercells to separate and move off the dryline. Hopefully the 500mb flow does not back too horrendously and make things uni-directional. I personally don't have much luck chasing all in all in the month of March, but then again there are firsts for everything. I am still favoring that SC Kansas and NW/NC Oklahoma area as my first guess target for Monday. Tornado climatology sure does support this area as a hot spot. Lots of data to pour over and surely some changes and twists are likely with this large system. Chase #1 for 2009 looks pretty likely at this point....

 

[Brandon Lawson]

Both models (GFS & ECMWF) have the system coming through pretty early. The models aren't going to forecast much CAPE when there is less time for moisture return and no daytime heating to work with. So the difference between getting really good and just so-so parameters on Monday is gonna come down to the timing of the system. I too think things will slow down a bit more, and the models should pick up on some better instability as Monday gets closer. And like Rich mentioned, the speed and forcing of this system is gonna make it harder to have backed mid-level flow without having things go linear pretty quickly. I'd prefer the 500mb low to be farther north to help veer the mid-level winds more.

As for the March 28, 2007 comparisons, it's really hard to do. You can compare winds, CAPE, and moisture, but you're only looking at a snapshot of the system as a whole.

For March 28th, you had a large cut-off low just sitting around for days pulling in moisture, accompanied by weak forcing. A lot of that moisture was already advancing northward, allowing March 23, 2007 (days before the 28th) to happen along the New Mexico/Texas border. This Monday, you have a much more dynamic system (negatively tilted trough) plowing through with no prior moisture return, which almost makes the two events uncomparable.

 

[John LaJoie]

Rocky,

After checking out the latest runs last night, this episode seems to be getting better and better with every hour. I agree that any cloud cover could deminish the severe threat a bit, but at this time, I'm ready to keep my eyes on this setup and plan to keep Monday open for chasing! And yes, twisterdata.com is a welcome site to find the information needed on a whim!

 

[David Wolfson]

A vigorous early season closed system stacked from the surface clear up to 200Mb over eastern CO with a stretched advection tongue wrapping around through NE screams cold-core for me. Though the timing is a bit uncertain the feature has been pretty consistent through recent runs.

If I were able, Sunday night would find me in one of Tucumcari's cheap motel rooms, rising early and planning on running ahead of the vort max through central-western KS to Kearney, NE.

 

[Rich Thompson]

Rich, do you have access to the Euro surface dewpoint forecast? I'm curious to find out if the Euro is more bullish with moisture return. I would suspect so, given that the faster 500 mb is further south (i.e., increasing downsloping/lee troughing which would lead to a deepening surface low closer to the moisture source).

The other thing is that the jet stream corridor in the GFS solution is fairly narrow, so storms on the south side would have deal with relatively warm 500 mb temps. In the Euro solution, the 500 mb flow is a bit more broad, suggestive of a weaker temperature gradient (c.f. the thermal wind relationship). Thus, cooler 500 mb temps and instability would be greater in the Euro solution than in the GFS solution.

Nevertheless, I think this "just in time" moisture return could be problematic (c.f. Rich's comment about a narrow warm sector). It really depends on whether or not we can manage a truly tropical fetch. At least, it will be better than 3/7!

EDIT: Yikes! I didn't realize how much convective feedback was likely impacting the instability progs for Monday in the GFS. The precip field goes gangbusters by 00z Tues leading to surface temperatures in the low 60s! Yeah, that won't get it done. Yet, the GFS still progs pockets of instability >1000 j/kg. Not too shabby, considering the whole dryline blows up! lol Anyhow, I imagine that the GFS forecast -- in fact -- represents a lower bound for instability on Monday.

Gabe,

Sorry for the slow response - I had to sleep sometime! Anyway, the 120 hr ECMWF (valid Monday evening) shows 56-60 F Tds from N TX into central KS ahead of the Pacific front/dryline. I compared the 00z 29 March 2007 soundings from OUN and DDC to the relatively greater CAPE forecasts near the Red River from the 120 hr GFS. The 2007 profiles were 3-6 C (~6-12 F) warmer through the entire lower troposphere compared to the GFS forecast soundings for Monday evening, and the mean mixing ratios were around 12 g/kg in 2007 versus 11 g/kg (lower 60s versus upper 50s at the same elevation) for the upcoming case. The net result is forecast soundings with MLCAPE on Monday evening that is about half of what was observed at 00z 3/29/07.

 

[Jim Bishop]

Both the narrow corridor of the forecast instability as well as the limited amount is of concern for Monday across Oklahoma/Texas and Kansas. But my main concern is the low level cloud cover from the rapid moisture return.

The GFS suggests 850mb relative humidity values of 90-100% throught the day east of the dryline. And with relatively warm 500mb temps, or rather poor lapse rates, I can't help but think the model is actually overdoing the CAPE forecast.

It is true, however, that 0-6km vertical shear will be very impressive, especially across Oklahoma into North Texas. And the 55 knot southerly 850mb jet will create insane 0-3km vertical shear, good for low level mesocyclones.

I think there will be too much forcing from Northwestern Oklahoma into Kansas with the intense vorticity maximum. The 500mb flow will also be too backed (southerly), promoting squall line development.

I'd be focused over the southern half of Oklahoma into Northwestern Texas along and east of the dryline for more discrete supercell development. Over that region you have 1)southwesterly 500mb flow which will help storms to move away from the dryline after forming, 2)less dynamic forcing, but enough to break the cap, and 3)really good 0-3km shear for tornadoes.

But I think the low level clouds will be a major limiting factor for Monday's event. Let's see how things progress in the models moving forward.

 

[Chris Lott]

With the 12z run, I'm still pointing towards the Red River for Monday. Extreme shear within the narrow band of CAPE ahead of the dryline is where I would look for the best development for cells to remain discrete. I'm still don't like the forecast instability. I believe that will lead to weaker updrafts. GFS wants to break out precip pretty early in the day which could also be a limiting factor. I agree with Jim that the 500mb winds are way too southerly farther north, forcing a squall line.

 

[Dustin Wilcox]

I agree with Jim that the 500mb winds are way too southerly farther north, forcing a squall line.

It's almost 6 one way half dozen the other, while midlevels veer more further South too do the LL's, further North midlevels are more Southerly, but you'll likely keep a little more Easterly component to the LL's. Regardless I'm not super pumped about this setup, and won't be until things look good on Saturday at the earliest. That being said if I were chasing based off of current model trends, I would likely end up in SC KS, this area seems to get the best combination of factors IMO. Seems to be on the noise of the good moisture and Theta advection, meanwhile it's near the base of the trough and midlevels try to stay a little more veered, and LL's in that region remain ever backed more so than further South along the DL. Again you can find better parameters elsewhere, though I think this is the region where the best combination can currently be found, as it is now, though I'm currently not real confident in it being enough to make for a friendly chase. Another area that is probably to much of a gamble to chase, but an area I wouldn't be surprised if a couple storms got to rotating would be the right front quadrant of the sfc low across extreme SW NE and NE panhandle area