2013-04-07 FCST: KS/OK/TX

[Jacob Ferden]

2013-04-07 FCST: KS/OK/TX

Preliminary Chase Target: Woodward, OK

Short Version: Am leaning towards chasing today, gambling that a supercell or two can develop along the dryline in Northwest Oklahoma. Tornado potential is not particularly high, but it is there and any storms that do develop before sundown should be fairly photogenic.

Long Version:

This is a highly conditional, “day before the day before the day” type of chase setup. As such, there are numerous issued surrounding convective initiation possibilities.

Tonight’s 00z GFS and NAM runs depict a small piece of energy transitioning through western Oklahoma by Sunday evening. 500 mb winds out of the WSW should combine with southerly low level winds to provide good directional shear for supercell development, although the GFS does show some slight veering to the SW at the 850 mb level. Winds at the low levels appear to be rather weak during the late afternoon, but these should increase into the evening.

Both the GFS and NAM depict surface dewpoints at or slightly above 60 F along the dryline in western Oklahoma. A concern is the speed and depth with which moisture would need to return from the Gulf to allow this to verify. As of this writing at about 4:10 AM, dewpoints along much of the Texas Gulf Coast remain in the high 50s. Temperatures near the dryline in OK should be well into the 70s to near 80 F by mid-afternoon. This amount of heating conceivably could cause dewpoints to mix out, resulting in an environment of widespread high 50s dewpoints which would be considerably less favorable.

The GFS, NAM, and 06z RAP all suggest CAPE values around 2,000 j/kg in NW OK by 00z. Again, realizing this instability would necessitate sufficient moisture return.

Capping will be a concern, particularly the farther south you get into Oklahoma. Both the NAM and RAP suggest a more favorable environment for initiation near and to the north of the Woodward, OK area, and indeed the RAP has for several hourly runs been breaking out convection in that area by 22z. The GFS suggests a more strongly capped environment, with CIN values appearing more prohibitive a farther distance north.

Progged LCL heights range over a tight gradient from over 2000 meters along the OK / TX border to less than 1000 meters just east of Woodward. This would suggest a scenario where storms will stand a better chance of a relatively increased tornado threat as they move ENEward.

Conclusion: With the main energy set to affect the region for Monday and Tuesday still to the west, my expectation is for one or two storms to develop in NW Oklahoma, and possibly a bit farther north into SW Kansas, in the early- to mid-evening. The primary threats would be very large hail and damaging winds, with an attendant tornado threat should storms manage to sustain themselves a bit farther east.

 

[Paul Schmit]

Hi everyone, pretty new to Stormtrack, but gearing up to cut my teeth on some chases this year after relocating closer to the S Plains after finishing grad school out on the east coast.

After Jacob's very thorough analysis, I'll just add a couple other observations. The cap today along and east of the dryline looks to be very robust, with most recent RAP indicating WAA regimes throughout western OK at both the 850 and 700mb levels during the 22Z-00Z periods, which seems to suggest the farther south one goes along a N-S corridor in the strip between Woodward and Enid, the less favorable cap breaking during daylight hours seems. Combine this with weak surface convergence along the dryline and a general lack of robust upper level energy and it's looking quite spotty. There is not really any distinguishing hike in vertical dtheta/dz along and east of the dryline throughout western OK to suggest that enhanced WAA and any attendant synoptic lift in the low levels would cause one area to capitalize before another area in terms of the very attractive falloff in moisture content above 850mb. Nevertheless, as one moves closer to the OK-KS border, in the vicinity of Alva, OK, there is significant cooling with height despite the 850-700mb WAA regime and the cap appears to break by 22Z on the lip of a southward encroaching area of 0 CINH before the end of daylight hours.

This area also exhibits pretty massive hodographs around the same time period, on the western fringe of a backed 25-30kt LLJ feature and pretty substantial veering of the wind profile with height, with the Alva-area on the southern end of a plume of ~200 0-1km helicities and 40-45kt 0-700mb shear. The attendant very slow southwesterly storm motion would lead me to believe that if anything can fire along or east of the dryline in the vicinity of Woodward, it could be carried slowly northeastward toward a very favorable atmospheric environment during the twilight hours. Given that the modest 500mb feature Jacob alludes to seems to be centered about the OK-KS border, with nontrivial CAPE, good SRH, and positioning on the northern cusp of the surface theta-e axis, I'd peg the NE-SW corridor between Woodward and Alva as a good focal point for severe weather and possibly late-day, early-evening increased tornadic potential.

 

[Mike Smith]

Both the 13 and 14Z HRRR show prime tornadic supercell conditions between 23Z and 03Z in an area bounded by Woodward (WWD) to Greensburg to north Wichita (KAAO) to Ponca City to WWD. Both runs show supercell initiation. Initiation also occurs, but farther north, on the 4km NAM. Vance (END) has a Td of 63° and moisture continues to move north.

Looks like very good chasing potential with storm motion around 25 mph. It also looks like an evening where people in the region should pay attention to the wx.

 

[David Biggar]

The 15Z run of the 4km RPM from WSI shows decent storm development relatively late in the day. Storms start to pop some time around 23Z, but peak activity holds off until 01-02Z. The timing also seems relatively regional with northern OK being favored during initial onset, then KS activity firing off during that 02Z time frame. It looks like there is sufficient energy available, but RAP and RUC extraction/RAP sounding for Wichita do show a robust cap as mentioned by Paul.

Should still be fun out there (RPM points at plenty of potential cells), best of luck to those chasing.

 

[Brian McKibben]

The 4km SPC WRF is encouraging. It breaks out discrete supercells from Wichita to Frederick between 00z and 01z

http://www.emc.ncep.noaa.gov/mmb/mpyle/spcprod/12/

 

[Jeff Snyder]

I am concerned about a band of thick cloud cover moving slowly northward across northwestern OK. Temps under this band drop from 67-70 to 60-62 F, temperatures that will preclude surface-based convection. This band of clouds appears to be very poorly timed, as I'm concerned it'll moved into the target area near peak heating (well, from now through the next few hours). For example, current temps are 60 in Alva (on N edge of thick clouds) and 68 in May Ranch (just N of N edge of same clouds). I can only see the 14z HRRR (didn't we see faster updates a couple of years ago?), but that run has 18z temps >= 70 F across the target area, indicating that it's not properly handling these clouds and associated lower-tropospheric stabilization. Insolation measured at the Alva mesonet site gas dropped from ~700 w/m2 to 160 w/m2 in the past 20 minutes as the clouds have moved in.

So, what are the options? Common sense would tell me that I'd have to target either N or S of this band of clouds, since clearly the cool temps are suboptimal. Since we're starting in the OKC area and haven't left yet, I'm not sure how far N we'll be able to target. I'm just fine with baroclinic boundaries associated with gradients in insolation (i.e., differential heating boundaries), but usually you want to be in the area where the warmer and higher CAPE air is to your south (typically the direction of storm inflow) as opposed to being on the N edge with cold, stable air to the S. My inclination would be to head up to ICT and head W, but our temporal constraints may prevent that.

 

[David Biggar]

My inclination would be to head up to ICT and head W, but our temporal constraints may prevent that.

That's a tough call, but models seemed to suggest good activity around ICT later on...question will be remaining sunlight to see stuff. Much better clearing over parts of Western KS. The svr warned cell near ICT popped even with some of that cloud cover. Good luck regardless of your decision.

 

[Tim Supinie]

That's a tough call, but models seemed to suggest good activity around ICT later on...

Well, the model output is useless at this point because it has no inkling of the clouds currently over northern OK, apparently.

FWIW, the mesoanalysis is hinting at a weakening in the cap in southwest OK. The sun is out, and dewpoints are near 60 F. No deep cumulus development in the area, though, and if a storm were to develop, it probably wouldn't have much time to do anything before it ran into the stable air to its east.

 

[Greg Blumberg]

To add into the mix, water vapor imagery shows a weak shortwave trough entering near AMA from the west. This should help in the lifting department, but I'm not certain the addition of that with the low level warm air advection + low level clouds will help very much, especially since the high level clouds over NW Oklahoma are associated with the trough. If nothing new forms as this trough approaches, I'd be hard pressed to say anything interesting will form today.

 

[Paul Schmit]

JWG is showing surface temp of 71 and T-Td depression of only 8F, with a small band of 75-80F temps advecting from the south. Could be a good point for storm initiation as short wave approaches, but the curving of the upper level cloud deck across northern OK into southeastern OK means it's probably pretty hopeless that a decent warm/moist reservoir could advect into central OK in time to sustain any storms that initiate along the dryline in the northern half of OK, especially given 20kt westerly storm motion in this region. KS definitely seems to be the "safest" play now, but per Jeff's observations, the massive pool of cooler air advecting into central KS could be poorly timed with the arrival of moisture along the developing cumulus field in west KS.

 

[Kelly Sugden]

Observed dewpoints were in the 50s, not 60s. KDDC raob shows mixing up to 700 hPa.