4/2/10 FCST: TX/OK

[Skip Talbot]

The GFS has been showing a high amplitude trough over the southern Plains for several runs now. The ECMWF is in fairly good agreement with the position of this trough, and then NAM out to 84 hours (two days before the event) matches up fairly closely with the GFS at 84 hours with the trough coming on shore from the Pacific. There's also been good consistency on the moisture return. The GFS has been showing 60's dewpoints spreading across TX and maybe into OK and forecasted cape at 1000-2000 J/Kg. The 12z NAM is even more bullish with the moisture showing 60's dewpoints established into OK two days before the event. If these models do verify it looks like we are going to have a dryline setup from south central OK down through TX with more than enough shear, moisture, and instability for severe weather including supercells. A big concern I see with the setup is the southerly 500 mb winds a high amplitude trough would create. With a strong southerly LLJ also forecasted to be in place, we might be lacking in the directional shear and wind up with a big linear line training along the dryline. Today marks the three year anniversary of the March 28, '07 outbreak, which was also characterized by a high amplitude trough and dryline. Similar concerns were voiced about storm mode and movement but in the end it wound up being a huge tornado event. With bulk shear over 50 knots and a chance at 2000 J/Kg this is a setup you definitely don't want to turn your back on. If we do wind up getting a training line, there still might be some decent play at initiation before everything congeals. It might also be wise to setup further downstream to the north and move south, letting the storms come to you where you might be able to catch a break in the line or tail end charlie. So in conclusion, the models are all pointing at decent parameters for a severe weather event in the southern Plains this Friday. The biggest concern I have at this time is storm mode.

 

[Chris Wilburn]

The GFS has been showing a high amplitude trough over the southern Plains for several runs now. The ECMWF is in fairly good agreement with the position of this trough, and then NAM out to 84 hours (two days before the event) matches up fairly closely with the GFS at 84 hours with the trough coming on shore from the Pacific. There's also been good consistency on the moisture return. The GFS has been showing 60's dewpoints spreading across TX and maybe into OK and forecasted cape at 1000-2000 J/Kg. The 12z NAM is even more bullish with the moisture showing 60's dewpoints established into OK two days before the event. If these models do verify it looks like we are going to have a dryline setup from south central OK down through TX with more than enough shear, moisture, and instability for severe weather including supercells. A big concern I see with the setup is the southerly 500 mb winds a high amplitude trough would create. With a strong southerly LLJ also forecasted to be in place, we might be lacking in the directional shear and wind up with a big linear line training along the dryline. Today marks the three year anniversary of the March 28, '07 outbreak, which was also characterized by a high amplitude trough and dryline. Similar concerns were voiced about storm mode and movement but in the end it wound up being a huge tornado event. With bulk shear over 50 knots and a chance at 2000 J/Kg this is a setup you definitely don't want to turn your back on. If we do wind up getting a training line, there still might be some decent play at initiation before everything congeals. It might also be wise to setup further downstream to the north and move south, letting the storms come to you where you might be able to catch a break in the line or tail end charlie. So in conclusion, the models are all pointing at decent parameters for a severe weather event in the southern Plains this Friday. The biggest concern I have at this time is storm mode.

Excellent write up Skip. I agree with your thoughts and also have the same concerns about the high amplitude trough bringing in southerly 500mb flow and decreasing directional shear. What is really funny is I was just thinking the same thing about the 3 year anniversary of the 3-28-07 outbreak. I was also remembering how the 500mb winds were less than ideal and everybody had concerns. Of course the dryline lit up from the KS/NE border down to the TX panhandle south of I40. At least that gives us some hope. It sure looks like linear forcing as things stand now, but we still have 5 days and anything can change.

 

[Greg McLaughlin]

I still have concerns over moisture depth/quality as the NAM and GFS show meager dewpoints at 850mb 84hr out. The GFS develops a narrow tongue of higher 850mb dewpoints (8-12C) on 4/1 and a larger tongue on 4/2) although this still isn't great. Right now I am concerned about too much forcing and shear. I am not writing it off, however I have seen setups like this turn into a grunge-fest more times than not. April 6, 2001 is a prime example.

With that said I don't want to be the community Eeyore on here "just lookin for my tail", because the pattern change taking place definitely looks promising further down the road. Until the Gulf SSTs warm up, I have my concerns about moisture.

 

[Brett Roberts]

Until the ECMWF breaks consistency with its past several runs, I'll be more concerned with quality and depth of moisture than meridional upper winds. If we see a slower, closed-off solution at 500 mb, much of TX/OK and E NM could still be far enough ahead of the trough axis Friday afternoon for a zonal component to the upper winds. The 850-500 mb crossover shown on the 00z ECMWF looks fairly similar to the 2007-03-28 event Skip and Chris mentioned (maybe just a tad more backed at both levels).

What doesn't look similar to March 28 on the broad scale, unfortunately, is the deep trough over the western Atlantic. As Brian alluded to in the other thread, this blocking keeps a surface high parked over FL through the middle and end of the work week, and drier air may continue to be pumped into the Gulf from the NE. While the Td's shown on the 12z NAM for Wednesday evening look promising, I'm worried that even with two days of subsequent southerly low-level flow extending deep into the Gulf, we may not see that much of an increase in surface dew points or moisture depth. For comparison, we'd been in a broad eastern ridge/western trough pattern for nearly a week leading up to March 28, and the downstream trough was far less amplified.

That being said, I'll definitely be watching this closely with the rest of you, since we don't necessarily need 65 F Td's for a nice event this early in the season. Maybe one of the lucky few with full Euro access can chime in with the type of dew points it's showing for 00z Sat?

 

[Greg Blumberg]

I'll echo most of the above comments and save myself space. I will add that since the 12z GFS seems to be playing nicer with the 500 mb winds compared to past runs that depicted the meridional 500 mb winds, I'm thinking this will be a trend with the slowing down of the GFS as it comes into alignment with the ECMWF (granted that the ECMWF's solution sticks.)

Also, I have the moisture concerns, however comparing the buoy and ship observations down in the Gulf it doesn't completely seem like the Gulf took that hard of a hit today compared to what the models were forecasting. Not sure how much of a difference this makes, but it's something to keep in mind.

Brett, as for the dew points on 00z Saturday, I'd sit down try to estimate them using the HOOT ECMWF 850 RH and Temp products (http://hoot.metr.ou.edu/models/), but I've got an exam to study for. Perhaps someone else can do this and report back the calculated Tds to this thread.

 

[Eric Sipes]

I'll echo most of the above comments and save myself space. I will add that since the 12z GFS seems to be playing nicer with the 500 mb winds compared to past runs that depicted the meridional 500 mb winds, I'm thinking this will be a trend with the slowing down of the GFS as it comes into alignment with the ECMWF (granted that the ECMWF's solution sticks.)

Also, I have the moisture concerns, however comparing the buoy and ship observations down in the Gulf it doesn't completely seem like the Gulf took that hard of a hit today compared to what the models were forecasting. Not sure how much of a difference this makes, but it's something to keep in mind.

Brett, as for the dew points on 00z Saturday, I'd sit down try to estimate them using the HOOT ECMWF 850 RH and Temp products (http://hoot.metr.ou.edu/models/), but I've got an exam to study for. Perhaps someone else can do this and report back the calculated Tds to this thread.

I hope your right but, I don't necissarily agree that the 500mb winds look all that much better. I do agree that the GFS will slow it down a bit. Although, I am more biased toward the ECMWF solution.

It seems like a broken record this year but, my greatest concerns are moisture and less than ideal wind profiles. The upside is that the GFS is consistently pumping out 60Tds and CAPE values in excess of 2000J/kg. You really can't ignore those kind of numbers. I go deeper into the forecast HERE but, for now it's just a wait and see.

-Eric

 

[Chris C Sanner]

Past experience and climatology basically says to pay very close attention to what appears to be our biggest system yet of the Spring. Right now from observational data, it's very clear the Gulf took a hit again and whether we'll get the advertised moisture return indicated on the 12z NAM or not is dependent on a number of factors which will take some time to resolve. The 500 winds do worry me, but March 28, 2007 produced quite well due to the backed sfc winds despite the backed 500 flow. The two things which will need to be watched before we get to the 2nd will be the quality of the moisture return along with how the models handle the progression of the upper trough. Lots of details to sort out yet.

It's pretty apparent that this system bears watching for all involved and most likely there are at least two chase days and possibly more, marginal or not, waiting later this week. I posted some additional thoughts on my website, and will be updating my discussion on there through the week.

http://www.supercellhunting.com

 

[Matt Grantham]

For those interested, here's an image from the 12z Euro showing surface dewpoints. Not too shabby with a 60s spreading all the way into Kansas. The highest readings are around 62F along the dryline in NW Texas into western OK.

http://i204.photobucket.com/albums/bb32/wx4mat/ecmwfdew.png?t=1269827278

Another event worth noting, and perhaps a better analog to the upcoming event, was the March 23, 2007 in eastern New Mexico.

http://www.spc.noaa.gov/exper/archive/events/070323/index.html

 

[Patrick Marsh]

Not to rain on anyone's parade, but the trend in the operational GFS is to take the H500 trough from slightly positive tilt to neutral to slightly negative tilt and develop a closed low over central Texas. While the GEFS mean maintains an open wave, it does offer support to the possibility of a closed low in central Texas along with this positive-to-neutral-to-negative transition. This would result in increasing lift overspreading a rapidly cooling airmass north of the closed low. Not a good setup for isolated convective storms, but good for widespread rain and (most likely) non-severe thunderstorms. Using CAPE as a proxy for the combination of steep lapse rates, good moisture return, and warm surface temperatures (since the NCO GEFS plots don't include them), there is only a 50/50 chance of CAPE greater than 500 J/kg reaching the Red River. Not exactly something to get me excited this far in advance of the actual event...

The GEFS also suggests a potential for the closed low to stall / meander along the northern Gulf Coast in the wake of the departing shortwave trough. If this happens, moisture return will be hampered for the upstream trough forecast to move through early-to-mid next week. Just as we've seen all winter

Ultimately, I believe this lead wave is going to end up being sacrificial. Hopefully, however, it won't linger too long and scour out the Gulf of Mexico again.

 

[matt patterson]

Per the 12Z GFS, It seems as though sfc moisture wont be as big of an issue as the lack of moisture up through 850mb. The H500 winds dont appear to be as bad as previously thought (especially across SW/SC OK and NC Texas.. The thing that I am most concerned about is the lack of directional shear (which has been a concern for others) especially over the areas where the best instability resides... However, this is the GFS and albeit has not been the consistant model of choice... Merely my observations 4 days out.. I would be willing to be that one way or another that the 12z model looks nothing like what we will see friday afternoon... It has been a long winter and Im off on Friday so im chasing something... On another note... It might be noted that the QPF being spit out over NE/E OK are quite impressive in and of themselves....

 

[Mikey Gribble]

I am just going to copy and paste what I wrote on my blog instead of typing something out again. I have only glanced over this mornings runs so this is more random thoughts than a forecast...

I am going to post a forecast later after I get home. After glancing over the 12Z GFS I have a few comments to make. I still think the two major problems with this setup is the lack of directional shear due to backing mid level flow and too much forcing (too much convection/storms won't be discrete and storms firing too early may also be a problem).

Some smaller issues that concern me are morning convection and 850mb flow. The GFS has been very consistent in producing convection in the am. I'm not exactly sure what's initiating the convection, but I'll look into it later when I do my forecasting. Cloud cover and crapvection is always a concern though when you have morning convection like that. On the 850mb winds the models have been wanting to keep the stronger 850mb flow out over the warm sector quite a ways. If storms fire along the dryline they will have a pretty long treck to get into the strongest low level winds if the gfs ends up verifying. This has been a consistent trend so I'm becoming a little more concerned about it. I'm also not a fan of 850mb winds veering earlier in the day before backing. It seems like every time you are waiting on 850 winds to back it doesn't end up happening soon enough.

All that being said I do still think that this is a synoptically evident severe weather event. The CAPE and deep layer shear combination will be more than adequate for severe storms. I wouldn't be at all surprised to see the highest instability we've had so far this year in the plains if we get good insolation. Unlike a lot of people I'm not that worried about moisture return. The models have been very consistent in starting moisture advection on Wednesday. You don't get a very good fetch off the southern gulf until Thursday, but from then on the trajectories and wind speeds are pretty damn good, especially in the lowest portion of the BL. I will take three days of moisture advection ahead of a trough every time. Until I can start looking at forecast soundings and actual soundings I'm not going to worry about moisture depth or the potential for mixing down. I don't think that will be much of a problem, but until we can get forecast and actual soundings there's not a whole lot of reason to waster your time on this.

Like I mentioned before I do think this is a synoptically evident severe weather event, but the potential for cloud cover/crapvection over the warm sector and too much forcing/nondiscrete convection could very well mitigate the severe weather potential.

The tornado potential is obviously much harder to guess at this far out. The backing mid level winds and lack of directional shear can be an absolute killer for tornado potential. Typically when we have stacked or closing lows like this I will either cheat south far enough down the dryline to where mid level winds veer a bit more and storms tend to be more discrete or I play the warm front and hope that the backing surface winds will be enough to get it done. One way or another I will definitely try to offset the poor directional shear. With this setup the gfs has been keeping a nontypical surface pattern with a cold front rushing south. That doesn't scream tornadoes to me over the northern portion of the risk area so I doubt I'll consider that target if I chase.

Anyway, it is a complicated forecast and we still have a long ways to go so a lot can change. I will try to get a forecast posted tonight. If I don't I'll get one up tomorrow morning.

 

[Adam Lucio]

With such a stout cap in place the day before the event I am not as concerned with ongoing cloud cover and precip. The 12z GFS shunts away the CAP and associated CINH on Friday, as long as high clouds don't linger we should be able to get sufficent cape needed to spark the storms...if the EML gets pushed away in time. The instability axis looks to be very narrow as well.

The 12z GFS puts the I-35 corridor in play from about OKC southward. I suspect this will only get better as it falls in line with the NAM and EURO and hopefully the trend to slow down continues.

The highly amplified nature of the trough and lack of directional shear is my biggest concern at the moment. Surface flow backs best where there is less CAPE, but still might be enough to get the job done. Certainly a remnant boundary could greatly change SRH values, if any storms can develop Thursday under the progged cap.

This isn't an easy one, but then again when is it ever

 

[Greg McLaughlin]

I am not excited about what I am seeing today. The models are over-forecasting surface dew points across the southern Plains by as much as 5-15 degrees. Take a look at what the models were forecasting for 00z this evening and current obs (7:11pm as of this posting) and you will see the models aren't even close. I just don't see this system being a big player right now.

 

[Shane Adams]

I am not excited about what I am seeing today. The models are over-forecasting surface dew points across the southern Plains by as much as 5-15 degrees. Take a look at what the models were forecasting for 00z this evening and current obs (7:11pm as of this posting) and you will see the models aren't even close. I just don't see this system being a big player right now.

The models being wrong about current dewpoints is no more cause for alarm than when they show a great setup 4-5 days out; everything is whacked at this point. There's no way to tell what the recovery will be between now and Friday as of this post. For all we know the models could remain where they are between Tue-Thu while the next few days of southerly winds bring a deeper moisture fetch than what would be advertised.

Just like when we say "don't be too optimistic" this far out, the same applies for writing a system off. Now, if we're seeing this same variance Thursday night, I'll buy into it.

 

[JustinRudicel]

http://cimss.ssec.wisc.edu/tropic/real-time/tpw2/natl/main.html

The depth of moisture will be a concern but the wind setup has me more concerned.(Morning Crapvection) This is mostly a tease in my eyes as the setup to watch will be next Monday/Tuesday. This will be a preseason game with a couple starters but not the real team. The regular season starts next week but I'm hoping I am wrong. No worries as the long range indicators are all pointing to an active period coming up.