2011-05-18 FCST: CO/TX PH/OK/KS

[David Wolfson]

Wednesday is looking more and more interesting for quasi cold-core dynamics severe in the very general area of GCK. The 18Z models IMO are just now confirming what was showing earlier -- a very robust UL jet streak arriving late afternoon inducing a lee-side low in southeast CO. Upslope moisture return has been showing as quite good in the models, with mid-50s dews available at the dryline. Plenty of helicity and shear to my eye as well.

 

[David Wolfson]

Well... in line with much of the season so far, severe possibilities for the 18th (and the 19th as well) seem to be turning to crap, due to poorer than anticipated moisture return, phasing of the jet max, and general de-amplification of the short wave.

Part of the motive for starting this thread was needing to fly to DEN this week and scoping the chase possibilities. ATTM, I'm planning to leave most of the chase stuff -- and several hundred dollars of expenses -- safely at home.

 

[Ben_Jacobi]

Still new to forecasting so I'm just gonna throw in what I see

I just looked over the latest 00z NAM, and I have to say that I am excited to see the better moisture return. Dewpoints are reaching in the 60's range in sw OK and western north TX. CAPE isn't terribly impressive only 1000-1200 J/kg. There is also a decent mid level flow aprox 40kts and good curvature to the hodographs. Also, the NAM is showing a little precip breaking out along the Red River near Altus, OK. I wasn't overly impressed with NAM earlier this week, but if the trend contiues I think we could have a decent chance for a chase. Possibly even a localized one for me.

 

[David Wolfson]

I wasn't focusing that far south, but I'm not too happy with what I see down by the Red River ATTM. The problem with jet max phasing and the de-amplification of the wave I mentioned said another way means that you're in an environment of upper/mid level neutral or subsidence with little in the way of a disturbance to stir the pot. Rather high LCLs and a good dollop of CIN to the east, too. I'd guess you may be seeing some higher-based showers and a TX or two but nothing much rooted and rotating. FWIW, in the spirit of mutual education.

 

[Michael Riedl]

I too was worried about subsidence with the entire system but especially with the earlier days. Low over the East CONUS just throws a little kink into things. This day is looking less likely unless you want to try something in the Panhandles or Eastern CO, which is definitely possible.

 

[Ben Toms]

I'm surprised at how little instability the nam and gfs are putting out in eastern colorado on this day. Usually with dewpoints in the 50s, we see cape values poking around 1000 j/kg. The same issue applies to tomorrow, the 17th, as well. I think as the day gets closer we will start to see the instability rise a little bit which would mean the chance for a few LP-ish storms around the raton or somewhere east of that. Not a significant day by any means, but it could be a fun one to get out there and enjoy an upslope storm or two.

 

[Ben_Jacobi]

I wasn't focusing that far south, but I'm not too happy with what I see down by the Red River ATTM. The problem with jet max phasing and the de-amplification of the wave I mentioned said another way means that you're in an environment of upper/mid level neutral or subsidence with little in the way of a disturbance to stir the pot. Rather high LCLs and a good dollop of CIN to the east, too. I'd guess you may be seeing some higher-based showers and a TX or two but nothing much rooted and rotating. FWIW, in the spirit of mutual education.

Thank you David. I now see the error that I made. When I was referring to the mid level winds I was looking over the GFS which did show a disturbance moving through. Thank you for the clarification, my mistake.

 

[Jeff Snyder]

My primary concern for Wednesday is the location of the upper-level trough relative to the moisture. At 250 mb, it looks like the target area is in the right exit region of an upper-level jet streak, which, from the transverse circulation, is likely to result in subsidence across the area. The forecasts for 500 mb temps reflect this -- we're looking primarily at -8 to -9 C at 500 mb, which is a little warm for my liking considering the forecast dewpoints. Looking at forecast soundings, the tropospheric lapse rates above ~600 mb are moist adiabatic (or, between 500 and 600 mb, worse than moist adiabatic). In a typical day-before-the-day (or day-before-the-day-before-the-day ;P) fashion, the shear profiles below 700 mb look fantastic, with great curvature to the low-level hodograph across much of the area. Since the strong flow aloft is still relatively far upstream, deep-layer shear may not be particularly good. Actually, the trough is so far west that Oklahoma spends much of the day near the ridge axis.

The 12z GFS brings the warm front and moisture farther north/northwest than the 12z NAM, which has meaningful impacts on the collocation of decent CAPE / moisture, cooler 500 mb temps, and stronger flow aloft. Both the NAM and GFS show decent QPF along the dryline during the afternoon and evening, though the influence of relatively poor lapse rates on the intensity of any convection is uncertain.

 

[Jeff Snyder]

Let's start with observations before discussing model forecasts. 11 pm CDT observations indicate that the solid 60 F isodrosotherm is located from N of Del Rio towards San Antonio, then northeastward towards Centerville. There are a couple of stations showing 60-61 F N of there, but the "solid" 60 F tds are south of that arc. In northern Texas and southern Oklahoma, dewpoints are largely in the low-upper 50s. The warm front is analyzed across northern Texas and is primarily seen in wind, pressure, and moisture fields. Current (time sensitive!) GOES precipitable water seems to pick up the moisture S of the 60 F isodroso relatively well, although some cloud cover in the Texas is messing up the PW retrieval a bit. Current SPC/RUC Mesonalysis shows moisture advecting northward between I35 and I27 in northern Texas.

The 00z sounding from CRP sampled ~11 g/kg mixing ratio in the lowest 100 mb; the BRO sounding shows 11-14.5 g/kg in the lowest 200 mb. Current VWP from many of the eastern Texas 88Ds are currently showing 30-40 kts from the south or south-southwest 1-2 km AGL. The DYX VWP is showing a more intense LLJ, with 50-55 kts 1-2 km AGL from the south (or just a hair east of due south).

Both the NAM and the GFS indicate that further advection and mixing (when heating begins tomorrow morning and higher mixing ratios currently advecting northward on the strong LLJ begin to mix to the surface) will bump dewpoints >65 F tomorrow across much of Oklahoma east of the dryline. The vertical wind profiles on both models are forecast to be quite favorable for tornadic supercells, with beautiful low-level curvature, resulting in >100 m2/s2 0-1km SRH and >300 0-3 km SRH. Over the Oklahoma part of the target, mid- and upper-tropospheric flow is not forecast to be particularly strong, largely as a consequences of the trough being so far to the west. Regardless, 35-40 kts 0-6km wind difference ("shear") is forecast. Areas farther to the northwest, from southeastern CO, southwestern KS, and adjacent portions extreme northern TX PH and the OK PH, will be characterized by stronger flow aloft and stronger deep-layer shear values. I haven't looked at this target much, so I'll address primarily the more classic warm sector target E of the dryline.

One of my primary concerns for tomorrow is the mid-level thermo environment. It looks like the southern Plains will nearly be in the ridge axis aloft. This, combined with the the fact that Oklahoma may be affected by subsidence in the right exit region of the upper-level jet streak across the southwestern US (and nosing into Colorado), will yield some pretty unremarkable mid-level lapse rates and mid-level temps that are around -10 C. In addition, both the 00z NAM and GFS runs indicate >85% RH at 925 mb and 850 mb, indicative of low cloud cover, over a good part of the warm sector in Oklahoma tomorrow. There are indicates of slightly lower RH S of I40, however. The cloud cover may significantly hamper heating and create some CINH/capping issues. The models are currently showing a narrow sliver of territory along the dryline in western Oklahoma mixing sufficiently to reduce CINH to "breakable" levels, but this may be a significant problem tomorrow. The 00z NAM does not show QPF in western Oklahoma before 3z, though the 00z GFS does. Implied low-level convergence (from surface through 850 mb winds) looks pretty strong along the dryline and front from the eastern OK panhandle, southeastward towards Clinton/Weatherford, although forcing aloft is very weak (no noticeable DPVA, no help from the transverse circulation associated with jet streak, etc.).

In terms of a target (again, I'm limited to Oklahoma tomorrow), I'm not going to be specific since I think the visible satellite data will tell the story tomorrow. If clouds persist through the day, then I don't think it matters which target I choose, since they all may have a very high probability of busting. Otherwise, I'm inclined to find anywhere that sees more than a few hours of heating. Looking at the surface forecast from tonight's NAM and GFS, I'm inclined to hedge north if possible (NW OK through I40 area, where more strongly backed winds are forecast), where the low-level theta-e zone bends back to the northwest.

 

[Doug Drace]

Im with Jeff on this one. I think today is certainly worth a short trip from SC OK to WC OK near the general area of I-40 somewhere near the Weatherford-Yukon area. SPC has come out with a Slight Risk, 5% Tornado, which cooresponds pretty well with NAM/GFS placement of the small DL arch/bulge into the WF/Stationary Front through that area, NAM putting out 2000 j/kg of cape/with a breakable CIN in the -50 range. Just looked over the latest Vis Sat image as of 8:30am, and WC OK is already pretty well cleared of cloud cover, so that makes me a believer that the high cape numbers can be acheived. Biggest question in my mind is still whether of not we will see deep enough moisture to get a tornado or two, but even this time of year I wouldnt count it out as long as those low 60's Tds indeed make it back. The 50-55knt jet streak is looking pretty well timed late this evening between 22-0z, and WRF Hi-Res is developing a couple of supercell features in WC OK, along with one shorter lived in SW OK. We are definately gonna head out this afternoon, even with a higher end bust potential.

 

[Tim Marshall]

sees two chase targets today at 9AM: the upslope in southeast Colorado (Lamar target) and the dryline bulge in northwest Oklahoma (Buffalo target). I will be heading towards the southern target today since it is closest to me and will depart for Clinton shortly. The PROS are a strong, narrow jet associated with a closed low is moving toward both targets. At 500 mb, the exit region of the jet (12 hr RUC) has a difluent area across both targets. I like the backed winds this morning in northern OK and KS moving upslope into SE CO. The cap is breakable on the 12z DDC sounding with Tc of 85 but is stronger at OKC with Tc of 96. I like the clear skies in the Oklahoma target, where it will heat up today, and expect the low clouds in the Colorado target to dissipate later this morning. The CONS are the narrow axis of surface moisture (and thus CAPE)in both targets today, so I prefer the upslope target but can't get there from Dallas. There are weaker forecast winds at 500mb south of I-40 in Oklahoma, so I prefer getting as far north-northwest as I can in Oklahoma.

 

[Chip Redmond]

A feature that I am quite interested in is the progged 500mb vort max along the KS/OK border at 23z from the 13z RUC. RUC also has precipitation developing coinciding with the vort max around 23z as well. Forecast soundings along and just to the north of the bulge are quite impressive I agree with fairly large curves to the right. Should a storm go up, which I don't see the cap being to big of an issue in this area as the current stratiform layer will likely burn off by early afternoon, it will have several components to work with. The nose of 60+ dewpoints will be in the OK/KS border region along with increased surface winds associated with the LLJ. 0-1 Helicity values are anywhere from 200+ in this region and coinciding with the directional/speed shear in the lower levels as represented by the hodograph, I don't see any problem as to why they wouldn't rotate.

I would park myself on the east side of Enid if I were out today.

Chip

 

[Doug Drace]

We are targeting the Enid area. LCLs 1000-750m or less, crazy 0-1/0-3 EHIs, nice dryline bulge being progged by most models, really nice vort max should be a player by 5pm, 2000 cape, breakable cap, and clear skies just west of I-35. Tds already up to 60 in Hennessey from OK Mesonet....there may not be a lot of storms today, but at this point, I have little doubt there will be a few tornadoes, particularly I-40 to the NNW. Headed out from Ardmore to the Hennessey/Enid area in another hour, should put us there by 3pm, and can chill and adjust from there as the afternoon progresses. Really like the pokey storm motions being progged as well, should be an easy day to keep up with slow moving nasty tornadic supercells.

 

[Jeff Snyder]

I'm not finding very many "cons" for a significant tornado threat today in the central Oklahoma area (LAW to Hinton to Taloga to Guthrie to Purcell and back to LAW) if we get discrete thunderstorm development. The RUC and NAM continue to forecast ridiculous low-level hodographs, with extreme curvature (only too much in some cases). The thermo environment is not the best I've seen (with indications of a potential isothermal layer near 850 mb, and a CAPE-robber isothermal layer 500-600 mb on tue 18z NAM), but, where dewpoint depressions can stay <20 F, I think it won't matter too much anyway. Current vis sat is showing clumping Cu along much of the relatively diffuse dryline and arcing back into NW OK along the stationary front. Recent HRRR and RUC runs no longer are producing much int he way of convection, so we'll see. Considering the shear, though, I'm having a difficult time finding reasons why there's not a threat for significant tornadoes. Certainly not the best day, but with 10-20 kt storm motions W of I35 with beautiful low-level hodographs, I can't complain!

Note: winds behidn the dryline have backed a bit, with due S (and 30s-40s Tds) from Medicine Park northward. That isn't helping our convergence worries... There is very little in the way of forcing aloft today (and perhaps even large-scale subsidence / warming as shown by the CAPE robber signs).

 

[Chris Vagasky]

Convective initiation appearing to occur just north of Seiling, OK, and just north of Burkburnett, TX...north of the Red River.

Mesoanalysis shows 1500-2500 J/kg of CAPE in the area, and increasing helicity. LCLs a little high, but as the storms advance east, they may encounter more favorable environment for tornadoes.

Edit: That may be a smoke plume near the Red River.