10/26/06 FCST: AR/MO/OK/TN/MS

Michael O'Keeffe

An interesting setup seems to be unfolding for Thursday in the S Plains and Mid Mississippi Valley. The best possibilty of supercells and tornadoes should be near the triple point somewhere in the N/C Arkansas, SE MO area. Favorable shear and CAPE values should be sufficent for at least a few tornadoes. We could see a small tornado event in these areas sometime Thursday afternoon and evening.
Latest models seem to think a good bit west of there for Thursday. Nam and gfs favoring maybe se KS, ne OK. That is quite the slow down so we'll see if it sticks on the next run or not. It seems like it has been a while since I've seen the two agree that much on location though! Both have the system pretty stacked, but perhaps there will be a good localized area to play in.
Latest models suggest E Oklahoma and NE Texas are the place to be tomorrow. A strong low is to be in place across C Oklahoma along with a strong dryline stretching from the surface low to NC Texas. Even though instability will be low I still think tornadoes are a threat especially along the dryline where cells can be more discrete in a better enviorment. It appears storms should fire in the late afternoon and move eastward into Arkansas by the evening and converge into a strong squall line.

Will be out, but still haven't found a target.
Looks good for Eastern Oklahoma and extreme Southeast Kansas shifting to Western Ark. and Southwest Missouri into the evening hours. The WRF show quite a sharp dryline on 00z Friday esp. in SE Oklahoma with around 60 to low 60's dews. Wind fields look really good......esp. speed shear and directional shear looks good as well. If we can achieve low 60's dews and around 1,000 SBCAPE something has a chance to be good. I will be out regardless as this will be one of those rare chases in the fall months. Will be interesting to see the next model runs.

Chris Wilburn
Well with each new run the forecast is to slow the system down even more. This will only help us out by pulling more moisture northward and shear will not be an issue. If things hold true we may have a north/central OK, and SC or SW KS chase tomorrow. All pending where the surface low ends up tommorrow.

Although I do not really have the time to chase it I will anyway.

Looking at the trend of the GFS and NAM slowing the shortwave; I think NW OK and SC KS look to be the best places; NE of the SFC LOW near the warmfront. There will be a relatively strong cap, but incredible vorticity advection with height and upper-divergence will fire sfc-based storms in the afternoon near the warm front.
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Surface-based convective initiation before sundown looks questionable to me from glancing at a few things. Deep southwesterly flow right off the surface suggests BL moisture could be quite shallow. I haven't looked at any model soundings, but the capping inversion mentioned by Alex would make sense. Large scale ascent doesn't seem to hit the deeper moisture until after sundown. Maybe I'm biased since I can't chase tomorrow.


Looking at things a little more closely, I agree with Simon... probably have to hug the surface low where the 850mb flow will be backed. The key will be whether low-level destabilization can occur within the warm frontal zone, and how long storms can persist in that zone before crossing into the cool/stable air.
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Things look pretty nice for tomorrow. Got my eye on the Stillwater/Tulsa area. Shear and dewpoints look good, nice little CAPE spike coming in around 0Z. Today's cool, drizzly, overcast yuk should be a thing of the past, so hopefully there will be some good destabilization and storms can get going before dark.

Unfortunately, I'll be stuck at work (what else is new:mad: !!), so I won't be heading out unless a miracle happens. Good luck and happy hunting to all!!!!!
Big Bust Potential... But,

..... A Big bust potential exists for tomorrow (10/26) but, being after my snow chase back in my hometwon in upper Mich. ... I guess now I can handle a little atmospheric mayhem ... if I can keep up with it.

Rapidly deepening cyclone over NW Okla. will materialize by midday... a warm front should lie across southern KS. by midafternoon and this may be the best place where storms if they stay discrete will have the best chance of tornadogenesis. But first the negatives:

With a nearly 100kt 500mb. jet max coming out by late afternoon.. this will create some honkin' major storm motions... my guess will be 50kts or better, especially any cells that form below a Stillwater/Hennessey line.. further north, maybe not quite as fast but still they'll be moving. Then, I noticed on the WRF, a sizeable dry bunch in the 700 to 850mb. this could throw a monkey wrench into things as well... so, could the 500mb. winds be almost too strong to get tornadoes to form?... and the strong dry punch as depicted by the WRF. That along with the forward speeds of the storms lead me to believe that anyone that see's anything more than a fast moving low topped supercell with some damaging gusts (70-80mph)but near 1.5" diameter hail will be fortunate...

Best chances will be once cells form, which could be from Pratt, KS. to Wichita on south and west to Woodward to Hennessey by 3pm.. they may stay discrete long enough to at least trigger a few TVS alarms... and who knows, a quick surface based spinup... then storms congeal into a raging squall line by early evening that will rake areas from Tulsa to Fayetteville Ark. on down to Longview TX. on east overnight.

Regardless of the negatives... I'll be on this tomorrow..I may have a couple of people chasing with me... hope all stay safe.


P.S I noticed on the DuPage site that some of the parameters including cape and helicity are outdated by a week.
While there is some disagreement in the timing and placement of the tripple point from the GFS and ETA (big suprise there). It looks as if north central OK and South Central KS between Enid, OK and Wichita, KS will be the best point to see any decent activity. CAPE of only about 1000 J/Kg are forecast which is a bit disappointing but strong vorticity max and low level shear could possibly "spin things up" IF descreet storms actually initiate before the cold front sweeps a squall line through. This looks to be one of those days where it will be a short time window and a small area for severe storm potential. Keep the engine running, and good luck ;)
I like so much 0-3km cape for tomorrow,that is to prefer in these situations rather than MLCAPE. I see a nice potential in the low layers and this could lead to the formation of some good (maybe mini)supercells in North/central-North/east-east Oklahoma, given the very nice shear profiles..

Not bad also for the 0-1km srh that could reach, on the late afternoon, very high values; so, I don't feel to rule out an eventual strong tornado (and November sometimes give us some nice surprises).

I saw some interesting forecast sounding (via Nam model):

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Tricky forecast... First of all, in regards to storm motion, the 0z NAM supports Bunkers storm motion of a reasonable 30-40kts north of I40, and closer to 25-30kts up along the OK/KS border. Looking at the forecast soundings, it appears as though ELs may be relatively low (~30kft), which means that the 500mb flow may not have as much of an influence on storm motion as usual since less of the storm is 'above' 500mb. I don't think Bunkers' motion takes the buoyancy depth into consideration, which may make it a little less reliable in "low-topped" supercell situations. Regardless, the very respectable 500mb flow is progged to result in strong deep-layer shear of 60-70kts near I40, increasing to 65-75kts across northern Oklahoma. The orientation of the shear vector (being nearly normal to the pacific cold front) would support discrete convective mode, but the intensity of low-level convergence along the front and intense forcing aloft from DPVA ahead of the impressive vort max may very well (and should very well) eventually yield a squall line.

The run-to-run and model-to-model consistency of the forecast valid tomorrow has been anything but desireable, particularly for those of us basing out of central OK, which is on the upstream edge of the threat area. I haven't been terribly impressed with the NAM-WRF this year, but my hopes are on it verifying relative to the GFS solution, which has persistently been forecasting a faster (and farther east) surface low and threat area for tomorrow (today now, I suppose). Of course, what I "want" has no bearing on what mother nature gives us, so... A survey of afternoon AFDs hints at the limited forecast confidence tomorrow, with a read of the HPC Model Diag. discussion lending support to the GFS (faster) solution and some NWSFOs disregarding the GFS solution while supporting other models (such as the UKMET and ECMWF). So far this year, I seem to remember the NAM-WRF forecasting amplifying troughs to dig too much, thus created over-amplified troughs that move too slowly. However, dprog/dt over the past day or two certainly supports a slower / more westward solution, which helps lend some credence to the NAM solution.

My initial interest for tomorrow was in northcentral Texas east of I35 (just south of the OK/TX border). However, I've been burned several times in the past couple of years in situations such as this (particularly last year, when I was in northcentral TX several times hoping for warm-sector activity in marginal moisture while others were scoring farther north and northwest). I'm now more firmly targeting northern Oklahoma, east of the surface low and near the warm front that the NAM progs to be near an Enid to Tulsa line by tomorrow afternoon. I'm a little nervous about widespread cloudcover and precip limiting destabilization along the warm front, creating a strong instability gradient which may result in storms developing east of the sfc low and moving ENE over the warm front into the stable airmass over extreme N OK and S KS. Convergence along the front in central OK and N TX looks to be pretty strong (per an examination of 850mb UVV forecasts), which may be enough for initiation by afternoon despite the strongest forcing aloft not 'catching up' to the front until after 0z. The NAM disgrees with this in that it does not have appreciable QPF in the warm sector before 0z; the GFS does indicate QPF in eastern OK by 0z, but a little far east for my chase taste. The 0z GFS is also a little more diffuse with the warm front across northern OK.

I'm concerned about the depth of the moisture tomorrow in Oklahoma owing to veered flow just off the surface. This flow profile is also yielding relatively straightline hodographs, though the 0z NAM is showing this less than previous NAM runs. The best curvature is, not surprisingly, farther to the north, nearer the front. For example, the PNC sounding valid at 0z tomorrow evening indicates >350m2/s2 0-1km SRH (indicative of the strong near-surface hodograph curvature). That said, the sounding is also very stable for a surface-based parcel. We've been battling poor moisture (depth and magnitude) for what seems like the entire year, and we've seen the consequences of relatively shallow moisture, which tends to mix out, particularly on days with strong mechanical and convective mixing. Speaking of instability, CAPE isn't impressive either, largely owing to weak lapse rates aloft (not much better than moist adiabatic).

Current target: Between Enid and Red Rock for initiation. I'd much rather chase 150mi to the west, where the terrain is more friendly to chasing, but that just doesn't happen it seems. Road options turn to garbage as one nears Tulsa, so I'm hoping I get lucky in this regard.
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Difficult forecasts... Forecast soundings from 12z model runs are pitiful north of I40, with very low CAPE (<400j/kg) and discouraging CINH. Meanwhile, moisture is progged to be deeper and richer farther south, helping to boost instability south of I40. For example, the AQR sounding valid 0z from the 12z RUC run shows ~1900 j/kg CAPE and a much more favorable-looking sounding. I'm slightly encouraged by the 850-700mb lapse rates on this morning's RAOBs. However, current OK mesonet shows westerly comp. to the sfc flow west of I35, which seems a bit early. In addition, pressure tendency maps from OK Mesonet indicate pressure rises across most of western OK, which certainly will not help back the flow (though this should reverse later this afternoon). I also don't like the veering-with-height-in-the-low-levels beneath backing-with-height-aloft wind profile. We've seen this semi S-shaped hodograph several times this year, and it's proved to be difficult to sustained cyclonic supercells (3-8-06 comes to mind).

There may be a risky cold-core play across far nw OK and eastern OK panhandle if the 12z RUC verifies.
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Currently sitting in Blackwell, OK with my friend Mark;can't decide whether to drive west to Buffalo, OK and hit cold core storms there along occluded front, or sit hear and play the nose of the warm sector east of Blackwell..... Very frustrating, because I want to go west, but I want to stay here.....I think I'm going to head west, no, stay here, no, head west!

I think I'll get some lunch first and decide on a full stomach.
Too... much... discussion... ... Can't... Keep... Up... ;-)

Still a difficult forecast. Surface pressures are finally dropping in response to diurnal heating and, more importantly, the approach of the intense upper low. I'd rather see the max pressure falls farther north and west (Mesonet indicates max pressure falls in se OK)., but oh well. Earlier this morning, a wind shift made it's way all the way to and east of I35, veering winds to the SW and dropping dewpoints into the low-mid 50s. Ugh.

CAPE was a limited factor north of I40 already, and Tds in the 58-60F range certainly don't help the cause. Farther south, moisture should be deeper and is of higher magnitude, but the 18z FWD sounding has a poor and "confused" hodograph, with negative 0-1km SRH indicating a propensity to support anticyclonic, left-moving supercells. I hate s-shaped hodographs (backing over veering or vice versa), since my experience tells me that it doesn't tend to favor either cyclonic or anticyclonic mesos, so you end up with transient, weak-moderate circulations.

All that said, my eyes are still to the north. CAPE will no doubt be more favorable for sustained supercells near the Red River, but (a) faster storm motions, (b) worse terrain, and (c) a bad road newtork discourage me from taking on that challenge -- I've chased SE of Ada enough in the past couple of years. If the winds in nc OK can be enough and for a long enough time, the higher moisture near and S of I40 may be able to advect to near the warm front. I don't really know what to expect, but I agree with dropping the 10% T prob.
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