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

[Jared Farrer]

I think I may throw the GFS away because even the NAM even though it only goes out to 06z Sun it showing the trough still back near S California while the 18z GFS has the trough plowing into the High Plains at 06z Sun. So it appears that every model run the NAM, Euro, and GEM models are all in agreement with the GFS the outlier.

Add the JMA to that list! LOL. Basically all the models are coming into agreement, other than the GFS. I am not sure why it wants to throw that thing out there so fast. The most recent NAM runs are looking promising. It seems the big question (and forgive me for stating the obvious) is moisture. But with >24hr of return flow, not to mention the LLJ is going to be screaming and howling the night before. Im leaning towards it getting the job done!

I should add that there is however a cold front pretty much slamming the gulf as we speak unfortunatly?

 

[Greg McLaughlin]

Dewpoints in the central GOM are looking pretty good attm. Dewpoints are running 65-70. The big question has been will the forecast trajectories over the weekend stiffle moisture return as we get closer to the system ejecting out. Surface winds over the GOM are out of the northeast and east which may continue to advect drier modified Cp air into the eastern and northern GOM over the next couple of days. I think we will have a good idea on how the moisture situation will be shaping up by SUN am. I think we will be in good shape. Dewpoints are running 4-8 degrees higher than forecast at this time....at least per the GooFuS.

 

[Jeff Passner]

Dewpoints in the central GOM are looking pretty good attm. Dewpoints are running 65-70. The big question has been will the forecast trajectories over the weekend stiffle moisture return as we get closer to the system ejecting out. Surface winds over the GOM are out of the northeast and east which may continue to advect drier modified Cp air into the eastern and northern GOM over the next couple of days. I think we will have a good idea on how the moisture situation will be shaping up by SUN am. I think we will be in good shape. Dewpoints are running 4-8 degrees higher than forecast at this time....at least per the GooFuS.

I think this is well said as well as Rich Thompson's comments above. There will be some serious mixing over Texas on Sunday. Dew points across Oklahoma will be in the 40s the day before the "event." Not saying it can't work for Monday, but it becomes even more difficult if the dew points are in the low 50s on Monday morning in Oklahoma as I expect them to be. I think moisture is only part of the story on Monday; many more things will go right or wrong. If I were chasing this I would take a serious look at Southwest Nebraska/Northwest Kansas where the surface low will pull back mid-50s dew points, under tremendous 300-MB diffluence, a deepening surface low, and approaching jet max. It's out of my reach for Monday, but that might be my first target as long as there is some heating. As this system approaches, I think the typical model bias will be seen and this will shift west by Monday; with a dryline from Western Kansas to the Eastern Panhandle. With 700-MB winds of 50-60 knots forecasted, the stroms will be flying; however, these details are still beyond the time frame we can make any serious decisions yet. Many questions remain -- not just the surface dew points, but the depth of the moisture.

 

[Andrew Pritchard]

Yea I agree the GFS is not looking that good, but I remember May 22 and that was looking horrible on the GFS just before it showed up on the NAM and when it went on the NAM it looked like all hell could break loose. Could that be the case again, maybe or maybe not, but still we got time, I mean the setup this coming Sunday was showing 750 j/kg of CAPE on the GFS with maybe a small pocket of 1000 j/kg of CAPE, but when it hit the NAM there is 1500 j/kg and a widespread instability across from the Panhandles to Nebraska with at least 1000 j/kg of CAPE.

If you want to make that comparison, then I assume you've dually noted that the GFS currently forecasts a decent amount more moisture than the NAM does? If you want to buy the NAM, I'm guessing you're okay with leaving for your target area when the 12Z surface charts show td's in the upper 40's over your target area? A shallow, layer of upper 40's td's.

I agree that the GFS is an outlier in terms of handling of the jet streaks, but I don't care how you throw the jet stream, putting it however you'd like over a 30 mile wide band of 500-750 j/kg surface cape is only going to get you so far.

I'll be watching this one merely because I've got the potential to get time off and there is time to change, but me thinks it's been too long since a few people saw a deep trough in the plains. There is time for things to change a bit, but one thing is pretty clear. For at least a chunk of the time that we're watching the models for hope and change, the upper level winds will be pumping that moisture out across the Gulf and away from the plains.

I find it funny that some on here keep comparing this setup to every big trough / tornado outbreak that they can think of in this general area, but no one bothers to compare a day that busted or did not produce.

 

[Connor McCrorey]

The 0Z GFS is showing surface temperatures in the lower 60s across OK at 7 pm Monday, and upper 60s across NC TX. But NWS offices across the area are forecasting 70s. I personally think the GFS is underdoing instability, but we'll see.

 

[Andrew Pritchard]

The 0Z GFS is showing surface temperatures in the lower 60s across OK at 7 pm Monday, and upper 60s across NC TX. But NWS offices across the area are forecasting 70s. I personally think the GFS is underdoing instability, but we'll see.

Go ahead and raise the surface temperatures, and raise the t/td spreads even more while you're at it.

The problem is not how warm will it get, it's how moist will it get.

 

[David Reimer]

The 0Z GFS is showing surface temperatures in the lower 60s across OK at 7 pm Monday, and upper 60s across NC TX. But NWS offices across the area are forecasting 70s. I personally think the GFS is underdoing instability, but we'll see.

Also of interest is the fact the GFS has 500-750 CAPE at 0Z Tuesday (7 PM CDT Monday) but somehow that goes up to almost 2000 CAPE by 06Z Tuesday (1 AM CDT Tuesday). I believe the GFS is underdoing the CAPE as it has done with previous setup's this year. However, considering the fact its the outlier in this scenrio, I dont know why I am even discussing it. Also, the local meteorologists here in Dallas are taking a rather bold approach on the storm, mentioning a possible outbreak and introducing the chances of tornadoes, rather surprising for five days out.

As for me, I wont do an in-depth analysis until tomorrow morning when we can get the NAM/WRF's input on the day. However, Im confident the GFS is underdoing the CAPE, but overdoing moisture.

 

[Connor McCrorey]

Go ahead and raise the surface temperatures, and raise the t/td spreads even more while you're at it.

The problem is not how warm will it get, it's how moist will it get.

Well the NAM has 60s dews to DFW by 12Z Monday... Just sayin

 

[Gabe Garfield]

Go ahead and raise the surface temperatures, and raise the t/td spreads even more while you're at it.

The problem is not how warm will it get, it's how moist will it get.

Actually, that's not true: a warmer temperature profile below the LCL does help matters by increasing instability (c.f. a Skew-T). Intuitively, this makes sense. When you add solar energy to a "parcel," it converts the energy from kinetic to potential (through the addition of latent heat -- manifest by the breaking of water bonds from a liquid state to a gaseous state).

At the same time, though, you are right: more moisture would most certainly help out our instability issues. But, it's the combination of both moisture and heat that help to increase instability.

Regarding moisture vs. heat, I'll take a little bit more heat. I'm not as concerned about LCL height. Generally, unless it's a >20 F T/Td spread, tornadoes are still possible. So, if we can get, say, 75/55, I'll take it (given the extreme shear profiles).

 

[Mikey Gribble]

I'm with Gabe. I just got done looking over the 12Z run and I'm a little more worried about getting the temperature up a bit. The moisture bothers me too, but upper 50's can get the job done and like Gabe said the spread isn't an issue right now.
I only peeked at the 00Z gfs and it looked like it may be bringing surface temps up along and ahead of the dryline over Oklahoma and far southern Kansas. Let's hope that trend continues.

 

[Fred Gossage]

The GFS is way way too low with the surface temps in the warm sector. It's spitting out a massive amount of QPF around 0.01", and that is causing problems with the temperature fields. If there's any QPF, that automatically means that the model is forecasting cloud cover over the region. With the very paltry moisture above 925-mb and even drier air advecting in the mid-levels overtop the warm sector... in addition to the marginal sfc dewpoints...cloud cover will not be an issue once the sun comes up. Those surface temperatures on the GFS just are not reasonable. It's more likely that areas in Kansas and Oklahoma hit the low to mid 70s ahead of the dryline Monday afternoon. My biggest concern with the setup is the marginal boundary layer moisture, both in terms of surface dewpoints being advected northward, and the shallow nature of what moisture there is...making it easier for greater boundary layer mixing to occur Monday afternoon when the sun breaks out. I still think LCL/LFC heights are sufficiently low enough for tornadic potential, but given the trend toward a slower ejection of the system on the GFS (toward the Euro/MREF/every other model that's not the op GFS), and the subsequent veered mid/upper flow, the marginal boundary layer moisture may be the thing that keeps this from being a PDS Tornado Watch day along and ahead of the dryline. Put this thing in an alternate universe, where it would have rich moisture up to just above 850-mb, and surface dewpoints another 7+ deg F higher than progged... and you could be talking eventual High Risk potential.

 

[Ilya Neyman]

Seeing how we are still several days away from this *possible* event opinions can go back and forth before the system even makes it onshore, something progs indicate occurring roughly 48 hours from now. Since all we have to work with are models, models and more models, however, I think it's imperative to point out the nearly remarkable model consistency, both run-to-run and different suites. Despite the subtle and to be expected biases, most of our available guidance has been showing roughly the same thing, give or take degrees of amplification and timing.

The GFS has been the faster model, as is to be expected, and the last several runs have seen it slow down.

Moisture concerns, which I too seriously had several days ago, may not be as big of an issue in the end. I say this because even though the Gulf will be in the process of eroding from east to west, rapidly modifying air and enough of over-water trajectory, combined with decently-rich dewpoints should be located along the western Gulf as wind barbs go strongly onshore Sunday night.

While the GFS has been consistent in mid-upper 50 dewpoints overspreading the "mild" sector, it has continued to indicate a return to 60 in the vicinity of the Red River region.

With the temporal zone now entering the NAM's window of prognostics, I do think the finer resolution of this model will now be handling the overall evolution better than the GFS. The last couple of runs have already been trending toward a stronger and slower system, in line with European guidance. In addition, moisture progs are sizeably more impressive with the NAM vs. GFS attm. In particular the former indicates 60 dews pulling toward the Red River by 12Z a tongue of mid 60s coming into Texas. All this before lee cyclogenesis even begins to substantially commence due to a slower system overall.

As far as the temperatures are concerned, here too the NAM is warmer than the GFS, and this is noted by early morning temp progs of low to mid 60s evident as far north as Oklahoma.

Due to the above observations, and again all we have is pure model competition at this point, it would not be a far reach to have 60+ dewpoints overspread a warming and moistening sector Monday afternoon. This is especially backed up by 40+ knot southerly 925 flow and 50+ knot at 850. Rapid moisture transport, sometimes by downward mixing, is highly likely.

Latest GFS is also coming more in line with several other models in showing more veered 500 flow across a larger region. This seems to be at least partly in response to slower system timing.

Many questions remain, but at this point in time it is becoming more and more plausible that a severe weather episode, perhaps of substantial magnitude, may be in the making for early next week. The exact severity and region(s) of greatest impact are still to be determined.

 

[afischer]

I haven't been looking at this upcoming event closely by any means, but I am able to get a peek at the new 00Z ECMWF here at work so thought I would chime in. The 00Z ECMWF mass fields are in many ways a carbon copy of the 12Z run... some pretty remarkable run-to-run consistency. The ECMWF certainly continues to look more favorable from a convective mode standpoint especially for northern targets, with considerably more veered mid-level flow on the front side of the trough than the GFS... and thus 0-6 km bulk shear vectors crossing almost the entire length of the dryline at a respectable angle. (Whereas on the 00Z GFS, you need to get from about the KS-OK border southward to get a 45 deg angle crossover, with points north of that nearly parallel to the dryline and actually forecast to back a bit with time, i.e. suggestive of quick transition to squall line in those locations). I can't stray far from home Monday so I am glad to see the ECMWF keeping some hope for the northern targets. Whether that will pan out remains to be seen.

 

[Connor McCrorey]

The 06Z NAM is showing MUCH greater heating at the surface by 1 pm than the GFS could have dreamed of. Instability might not be as much of a problem as some were thinking

 

[Rich Thompson]

Seeing how we are still several days away from this *possible* event opinions can go back and forth before the system even makes it onshore, something progs indicate occurring roughly 48 hours from now. Since all we have to work with are models, models and more models, however, I think it's imperative to point out the nearly remarkable model consistency, both run-to-run and different suites. Despite the subtle and to be expected biases, most of our available guidance has been showing roughly the same thing, give or take degrees of amplification and timing.

The GFS has been the faster model, as is to be expected, and the last several runs have seen it slow down.

Moisture concerns, which I too seriously had several days ago, may not be as big of an issue in the end. I say this because even though the Gulf will be in the process of eroding from east to west, rapidly modifying air and enough of over-water trajectory, combined with decently-rich dewpoints should be located along the western Gulf as wind barbs go strongly onshore Sunday night.

While the GFS has been consistent in mid-upper 50 dewpoints overspreading the "mild" sector, it has continued to indicate a return to 60 in the vicinity of the Red River region.

With the temporal zone now entering the NAM's window of prognostics, I do think the finer resolution of this model will now be handling the overall evolution better than the GFS. The last couple of runs have already been trending toward a stronger and slower system, in line with European guidance. In addition, moisture progs are sizeably more impressive with the NAM vs. GFS attm. In particular the former indicates 60 dews pulling toward the Red River by 12Z a tongue of mid 60s coming into Texas. All this before lee cyclogenesis even begins to substantially commence due to a slower system overall.

As far as the temperatures are concerned, here too the NAM is warmer than the GFS, and this is noted by early morning temp progs of low to mid 60s evident as far north as Oklahoma.

Due to the above observations, and again all we have is pure model competition at this point, it would not be a far reach to have 60+ dewpoints overspread a warming and moistening sector Monday afternoon. This is especially backed up by 40+ knot southerly 925 flow and 50+ knot at 850. Rapid moisture transport, sometimes by downward mixing, is highly likely.

Latest GFS is also coming more in line with several other models in showing more veered 500 flow across a larger region. This seems to be at least partly in response to slower system timing.

Many questions remain, but at this point in time it is becoming more and more plausible that a severe weather episode, perhaps of substantial magnitude, may be in the making for early next week. The exact severity and region(s) of greatest impact are still to be determined.

It's been a boring winter and I'm cranky after finishing mids, but I just don't understand the optimism for Monday regarding the moisture/instability. Moisture quality and depth are both marginal (http://w1.spc.woc.noaa.gov/exper/soundings/09032000_OBS/). To make matter worse, the NAM shows exactly what I expect to see: Tds decreasing across TX each afternoon with mixing, such that there's little net moistening at the surface from day to day. Just because you have a fetch across the Gulf of Mexico does not guarantee anything useful about air mass modification. SSTs are very near the annual minimum, and the air mass flowing off the SE Atlantic coast and across FL is *not* cold, it's mainly dry. Trajectories from the E/NE across the Gulf that wind up in TX will traverse SSTs in the low-mid 70s for 1-2 days. Air temps are near the SSTs, so there's nothing to drive vertical mixing (sensible heat flux negligible). Net result? A shallow marine boundary layer with little hope of surviving vertical mixing over the continent.

The situation will be much like the last episode where we had sly winds across TX/OK for 5 days, yet almost no measurable increase in low-level moisture. You have to look for what will change to make the moisture profile "improve", and that's where I just don't see the odds in our favor, regardlless of the surface obs at a few Gulf buoys right now.

Does this mean we can't get severe storms Monday? Of course not! I'm just saying that a "tornado oubreak" seems unlikely given boundary layer dewpoints struggling to reach/maintain 60F in most of the warm sector, with the best "hope" lying with clouds to reduce surface heating/mixing! We need the majority of factors in our favor for these early season events to work - the presence of a strong trough and strong winds is not sufficient, unless you set the bar pretty low.

Rich T.