2011-05-19 FCST: CO/TX/OK/KS

[Drew.Gardonia]

the 00Z GFS Run + 120 hours shows a system beginning in ERN CO, stretching down through SWRN KS, WRN OK, and N Cent TX down to Cent TX on Thursday. CAPE levels of 750-1750 j/kg, capping shouldn't be a problem, and soundings appear impressive with sfc temps in the 70's and 80's and dewpoints in the 60's, should create reasonable instability for supercell initiation in the afternoon. Burlington, CO appears to be an excellent starting point just in front of the dryline.

 

[Eddie Natenberg]

Dynamics for this trough look OK. Rather keep wind speeds low for better storm motions but it looks like the boundary layer moisture depth over the gulf will create a thin area of cape profiles next week for severe weather. Looks like the GEFS and EMCWF have been picking up on this, GEFS 2000 j/kg props are only 10% in s. OK, OUCH! Although I think we could see tornadoes, especially with such good directional shear and relatively focused area of pressure falls just east of the rockies, I am going to wait for a deeper moist boundary layer within the next few weeks (although I bet I will see some awesome LP structure pics from this event). I think surface temp climo anomalies in the southern NWS region say it all. On the upside it looks like we could get some strong forcing the week after (FINALLY!) indicated from the GEFS as baroclinic instabilities develops across the central pacific and propagates into the NAM region.

 

[Ben Toms]

Keep in mind, Eddie, that High Plains storms require less moisture/instability than the central plains storms do to drop a tornado. In Eastern Colorado, you can see tornadoes with dewpoints in the 50's. I have no doubt that next week will see a multi-day severe weather set-up (probably not outbreak) across Eastern Colorado, much of Kansas, the Texas/Oklahoma panhandles, parts of Central Oklahoma, and maybe further down into Texas assuming the GFS verifies. There are some issues I see with the NAM not pulling up as much moisture as the GFS for the early Colorado play, but with time this shouldn't be an issue. I'll start pinning down specifics in a few days once things start getting settled.

Edit: I think if this thread is for E CO, then the date should be changed to 5/17 or 5/18.

 

[Michael Riedl]

Well this day continues to look quite promising, with the cut off low ejecting pretty quickly. I especially love the very strong mid level jet that the GFS continues to prog for that night.

Key concerns will be morning convection again, and, believe it or not, moisture return.

The GFS and the NAM differ by quite a bit on moisture 84 hours out on todays 12z run. The GFS has 60 Td's all the way up into Central KS while the NAM barely has 60's into OK. The GFS gets much stronger Return flow getting going alot earlier than the NAM. This trend will need to be watched, not only for this dates but for all the dates this trough could affect. The cut off low over the Eastern part of the country could be quite problematic.

Flow appears to be pretty meridional but after examining soundings storm mode should be supercellular, heres a nice sounding from KEND.

Enid Sounding

 

[Logan Karsten]

I agree completely. The one thing I like about this week compared to last week is the trough isn't so slow to eject, but at the same time we don't have the moisture in place like we did last week. However, this could help limit the whole "morning convection" issue if moisture isn't already in place the day before. However, at this time it's too early to get into those details. If the moisture can come in at the right time, the dryline in KS/OK could see some good supercells. I also like how there is good flow at all levels, not just 500 mb. I guess winds could veer a little more with height, but I am not complaining. Definitely a day to keep an eye on.

 

[Doug Drace]

Just looked over the 12z GFS run on this day, I agree it looks somewhat promising to this point. As with with previous posts, it looks like moisture will be the biggest question with this, though SW OK looks to have no problem getting 60+ Tds back by 21z. Overall vertical profiles look better than last wednesday as well, good speed shear along with a more traditional veering profile from 500mb up, unlike the last one with those funky southerlies aloft and decent forecasted Hodos. 75+ temps, with at least a narrow tongue of 2000+ CAPE/low CIN, has me believing this just might be a doable chase day, especially for OK more than KS at this point, mostly cause of the better moisture potential. GFS also putting out pretty low LCLs along the DL in OK. If these parameters can hang in there till thursday, without the junkvection like last week, I like the odds at this point. Still 4-5 days out, and seen these things go completely downhill in recent history, but as I usually say, its MAY...somethings gotta give soon in the WEST. One other note, this looks like only the beginning of a **potentially active stretch in the southern plains.

**Saw this kind of multi-day potential flushed down the toilet last week...so its only cautious optomism for now

 

[Mikey Gribble]

I'm just going to copy and paste from my blog for now because I don't have much time. Below is a post I just made...

After looking at the 12Z NAM, which has picked up on Thursday my confidence is continuing to increase that we will see tornadoes on Thursday/Friday (one or the other or possibly both days).
There are differences between the NAM and GFS that affects where the best tornado potential sets up. The NAM is slightly slower and sets the triple point up over NW Kansas by Thursday afternoon. The GFS is much farther north with the surface low. The NAM also has more of a neutral tilt to the trough on Thursday, while the GFS takes on a negative tilt. The NAM solution would be much more preferable because it doesn't create as much of a meridional component to the mid level flow. IF the NAM were to verify the best area for tornadoes would be the triple point and northern portions of the dryline. With the GFS you have to get farther south to where mid level winds veer more and the southern portion of the dryline is the best for tornadoes. Even though there are substantial differences between the two models, the best tornado potential sets up across Kansas and possibly Oklahoma with both model solutions.
I am going with the NAM on the timing/location of the mid level jet streak and surface low on Thursday. It is pretty close in line with the ECMWF, while the GFS remains the outlier. This would put the greatest severe/tornado threat over the western half of Kansas on Thursday.
One concern is the NAM is showing the same low surface temps the GFS has been showing which keeps CAPE levels fairly weak for this time of year. It looks like 850RH are 95% through the day over the warm sector, which indicates low level stratus as the culprit.
The low level shear and hodographs are quite impressive with the NAM. Even with only weak CAPE in place with the NAM, tornadic supercells would be likely given 0-1km SRH >200 and 0-3km SRH >300 near the triple point and ahead of the dryline.
So as things stand now my biggest concern for Thursday is how much instability can we get. Shear profiles are good with both models, but slightly better with the NAM since it doesn’t back mid level winds as much (I favor the NAM since the GFS has botched shear profiles with similiar situations this year and GFS is outlier with evolution of trough).
I will get a map posted and go over the potential for Friday when I get home.

 

[Brett Roberts]

Mikey, I was surprised by the relatively modest SBCAPE being painted by the NAM along the dryline, too. Taking a closer look at things, it doesn't necessarily appear to me that surface temperatures are the culprit, as they are progged to be anywhere from ~75 F (NW KS) to ~85 F (W OK). Instead, poor mid-level lapse rates (especially between H7 and H5, where they're roughly moist adiabatic) may be to blame. This is a bit of a Catch-22, as these warmer mid-tropospheric temperatures result from the NAM's less progressive solution, which is desirable from a dynamic and kinematic standpoint.

Aside from the questionable instability, Thursday looks near-classic on this morning's NAM. The upper-level low still parked over the southern Appalachians is the one thing making me hesitant to call it a classic setup, and it certainly won't be doing us any favors in the moisture department. Even so, it's difficult not to get excited when you see low-level flow as strong and backed as it appears in the PTT-HLC corridor beneath strong southwesterlies aloft. Comparisons to May 22-23, 2008, are bound to be raised, and I'd argue this setup would appear on-par with those days if not for somewhat-inferior moisture return. Even so, W KS can typically get by on surface dew points in the 62-65 F range in May, so I'm fairly excited to see what subsequent runs hold.

 

[Mikey Gribble]

I agree lapse rates are not good Brett, with this mornings NAM run currently showing 850-500mb lapse rates in the 6-7 range. Still surface temperatures are in the low 70's over the warm sector ahead of the northern portion of the dryline. That isn't what you'd expect this time of year so I think both are problems.
Aside from the CAPE issue it is tough to nitpick anything at this point. Hodographs over the KS portion of the dryline are quite impressive. I am still at work though so I haven't really had a chance to take a close look at the NAM. Plan on doing that when I get home.

 

[Mikey Gribble]

Two major concerns with Thursday are thermodyamics and width of the instability axis. Those could both stand in the way of a good tornado setup because the shear is great. We really need at least the instability axis to be wider than currently forecast by the NAM over the northern portion of the dryline. With the current NAM solution I would drop south to where the instability axis is wider (low level shear is weaker too though). There is no reason to look at details that closely this far out though.
850mb winds backed at 50kts is a big attention getter with the NAM. That is impressive. Man if CAPE was better that would be a potent little setup over the northern part of the dryline/triple point. All we can do is hope it will start to look better. Even with the poor thermodynamics I would chase. A lot of times its surprising how storms manage to produce in low CAPE high shear environments, so I will probably be chasing Thursday regardless of how the CAPE issues shake out.

 

[Jeff Duda]

Two major concerns with Thursday are thermodyamics and width of the instability axis. Those could both stand in the way of a good tornado setup because the shear is great. We really need at least the instability axis to be wider than currently forecast by the NAM over the northern portion of the dryline. With the current NAM solution I would drop south to where the instability axis is wider (low level shear is weaker too though). There is no reason to look at details that closely this far out though.
850mb winds backed at 50kts is a big attention getter with the NAM. That is impressive. Man if CAPE was better that would be a potent little setup over the northern part of the dryline/triple point. All we can do is hope it will start to look better. Even with the poor thermodynamics I would chase. A lot of times its surprising how storms manage to produce in low CAPE high shear environments, so I will probably be chasing Thursday regardless of how the CAPE issues shake out.

As of the 00Z NAM, I agree with this very much, Mike. I also noticed that the deep layer shear axis (over the warm sector) is about as wide as the instability axis, if not narrower. Although there's a kickin-wide LLJ with a max of up to 60 kts in E KS with winds out of the S or SSE, 500 mb winds taper of pretty quickly as one goes east. In that light, this setup reminds me quite a bit of the system from last week, especially in the way it was closing up around 18Z in previous runs. It no longer is, which is making it more potent. Looks like the big issue is indeed instability. Looks like surface temps just aren't getting up to where they should. With that kind of moisture, if you could get surface temps 5-10 deg warmer, you'd be talking about 2500 - 3500 SBCAPE instead of 1500 - 2000. Given the structure of the low level height, temp, and wind fields the night before, it looks like there will be a fair amount of isentropic lift creating stratus and overnight/early morning storms, although the NAM indicates very little precip during the day south of the "warm front" (I put it in quotes since the warm front seems pretty diffuse with little wind shift or thermodynamic gradient along it.

ADD: On a personal note: given my locational bias and the epic, utter failure I experienced driving over 1000 miles for last Wednesday's set up only to white-sky cap bust in Pratt and miss all other daytime events including a handful of tornadoes that occurred less than 100 miles from my home, I will forego this event in favor of the wave continuing to progress eastward on Friday, and for the shortwave that will follow up a few days later. Both look better right now to me (I will post in threads for those days in the time to come). Granted, if the features for this event are progged farther east, my opinion will certainly change.

 

[Logan Karsten]

I tend to agree with most of the above posts. Looking at the 00Z NAM would has me very cautious heading that far out for such marginal looking instability. However, with the 00Z GFS coming in, I would say the verdict is still out. The 00Z GFS is hanging on to it's progressive solution, putting more moisture in place and better shear further east. Up until this point, the GFS continues to be the outlier, but it's holding out for some odd reason.

 

[Kelly Sugden]

I rarely use the NAM out past 24 hours as it is a short term mesoscale model and significant non-linear feedback mechanisms cause unreliable output past day one. As far as the GFS concerned, it has been way more progressive than compared to the ECMWF, GEM, and UKMET and looks to be an outlier. Think the position of the dryline 00Z Friday is too far east. The 16.12Z ECMWF shows it further west towards Dodge and the 17.00Z GEM is a compromise between the EC/GFS. Forecast soundings from the 12Z EC look good across C Kansas with 1500-2000 Jkg-1 of SBCAPE and 40-50 knots of 0-6km bulk shear. I have the day off Thursday and plan on chasing somewhere in Kansas. Will be interesting to see what the 17.00Z ECMWF shows. The model has been consistent so am not expecting much difference in the overall synoptic pattern.

 

[Mike Johnston]

The NAM looks to be trending in a favorable direction for severe on Thursday, albeit a bit further south - perhaps as much of a western/central Oklahoma threat as a western Kansas one. In particular, the surface temps are looking better from 85 to even above 90 in portions of western and central Oklahoma. Also, look at how nicely the forecast theta-e tongue seems to be developing right out ahead of the dryline. With better heat at the surface, and good moisture still in place, we're finally seeing some forecast CAPE values ~ 2,500 j/kg and broadening out in a wider area across south central Oklahoma. While the best 0-3km helicity isn't perfectly co-located with the best instability, both are in good proximity with some decent areas of overlap. Wind crossovers at all levels look very supportive of supercells.

 

[Tim Supinie]

Unfortunately, the 17/12Z GFS and NAM appear to be overdoing the moisture return. The GFS has the 50 F isodrosotherm well into Oklahoma by today at 18Z (still south of the Red River, as of 19Z) and the 60 F isodrosotherm into southern Oklahoma by tonight (I don't see that happening). The NAM, IMO, isn't quite as bad. It has 65 F+ dewpoints in deep south Texas by today at 18Z (still in the upper 50s and lower 60s down there), but is more realistic with the 50 F isodrosotherm (into southern Oklahoma by tonight).

This isn't a deal-breaker yet, as both models have do-able moisture in place 24 hours ahead of time, so pushing it back by 12 hours isn't going to kill anything. But it bears monitoring, since we knew moisture return was going to be an issue with this setup. I was surprised at the bullish moisture-return predictions on the GFS, especially since we're pulling up modified continental air from the Gulf today and tomorrow, and don't really start to tap tropical moisture until Thursday. But then, it's the GFS.