5/13/08 FCST: OK / TX / KS/ AR/ MO

[Ben McMillan]

With this evening’s model runs coming in any minute now, I thought it would be appropriate to start a thread for Tuesday’s severe potential in Oklahoma, Texas and parts of Arkansas and southeast Kansas.

As it stands right now, a strong cold front will move southward throughout the day Tuesday crossing the central plains and will extend somewhere from a Tulsa-OKC- Childress line by 00z.

Weaker upper-level flow than Saturday’s system and a strong cap will be two issues to overcome, but by 00z models are initiating storms in central Oklahoma and north Texas. A dryline will also set up from near Childress southward, and will provide a secondary focal point for storm development as the day goes on.

 

[Mike Hollingshead]

Tuesday looks pretty good to me down there in far sw OK, but mainly into portions of nw TX sw of Wichita Falls. That all hinges on how that secondary sfc low develops and backs the winds and sharpens the dryline. NAM has been pretty consistent in the whole thing though. Nice se sfc winds by 0z with 50 knots of wsw mid-level winds above the real juice for once. Toss in a 90 knot sw 300mb jet above it all, and there's not a whole lot not to like. 500mb temps prog'd to cool to -12 to -14c above the dl. Warm 700mb temps of 9c should help to keep things isolated. 850mb to 700mb winds pretty weak, but I don't know it will matter much with the rest going on with strong instability.

Wichita Falls FCST Sounding 0z

This year so far seems like a take what you can get year, and I will be very tempted to make the long costly trip, even if it's a 1 day'r(which it may not be).


The other area that has me moderately intrigued is far se KS(again). Shear vector up there comes a bit off the cold front, and there's also that main initial sfc low to think about.

The 0z FCST Sounding for Coffeyville is nothing to sneeze at. It's far from an ideal chase target for this day, but it's got some hope I think and is half the drive to the TX target from here($150 compared to $300 for gas, lol).

 

[Jeff Snyder]

It doesn't look too bad for supercells, but the tornado potential doesn't appear to be that great right now (IMO, obviously). >50kt 0-6km shear and strong instability resulting from 80-90/63-70 conditions sure sounds good for supercells in a relatively simple sense. However, I am very much concerned about the speed of the cold front plowing down the lee of the Rockies, and I have concerns that we may see an anafrontal situation wherein the convection has a rear-ward motion in a front-relative reference frame. We've seen this at least a couple of times so far this spring, so I'll be disappointed if we see it again. I also have concerns over relatively marginal low-level flow, particularly near 700mb (<25kts). As a result, the forecast hodographs valid at some locales (i.e. ABI) that I looked at earlier today showed the infamous S-shape (some height in the 850-700mb layer near the origin -- yuck!), and I've never chased a persistent supercell in an environment characterized by such a hodograph.

FDR forecast sounding -- relatively straight-line hodograph with strong instability and very strong deep-layer shear
ABI forecast sounding -- S-shaped or N-shaped hodograph... On this hodograph, it actually looks like there would be negative 1-3km SRH that would support left-splits or anticylonic supercells (the fcst storm motion vector looks to lie to the left of the 0.5-3km AGL section of the hodograph).

The 12z GFS run showed stronger 850mb and 700mb flow (IIRC), but the 850mb flow was very veered, advecting in 18-20+C 850mb temps. These positively-tilted troughs, in my experience, tend also to be associated with cold fronts that slide down the Plains relatively easily and quickly with veered pre-frontal 850mb flow. Not surprisingly, the 12z GFS shows no warm-sector precip before 00z.

Right now, per the last couple of NAM runs, it looks like a prudent target would be between the Red River and ABI. Normally, I'd target the triple point (which is near the Red River near Vernon by 00z per the 00z NAM), especially since the very hot temps (88-90+ F) behind the dryline "point" right to this area. However, given the speed of the cold front, I'd be concerned that a storm in this area would be undercut by the cold front. As such, I'm eyeing the areas a little farther down the dryline. Capping is a concern, but it appears that colder 500mb temps will move past the dryline around 00z, with steep lapse rates developing/advecting above the sfc dryline by late afternoon. I really hope this forecast changes a little, since I really have no motivation to chase between the Red River and Abilene again this year....

 

[Mikey Gribble]

I am concerned about weak flow at 700mb as well, but I am even more concerned about the veering 850mb winds the GFS has been showing. I am also not a fan of positively tilted troughs. If the NAM can come through with a deepening surface low over West Texas, backing 0-1km winds over the warm sector ahead of the triple point, then I think we may be in business.
As Jeff covered really well the hodographs are of some concern. I'm not a fan of the S shaped hodograph either. Hodographs right ahead of the dryline bulge that the NAM is forecasting are a little better (Mike linked one for Wichita Falls) and actually give us something to work with. If you took this hodograph and increased wind speeds in the 1-3km layer, that is a pretty damn good hodograph. That is hoping for a lot considering the 00 GFS shows a dead spot in 700mb flow also. The 12Z NAM had better 0-1 and 0-3km SRH, so I am going to wait for tomorrow mornings run before putting any more work into forecasting.
The main things that we need IMO is for 0-1km winds to back as forecast by the NAM (increase in speed at 850 would help a lot too) and for wind speeds in the 1-3km to increase. If that can happen I think we'll be in good shape.

 

[Chris Hovanic]

Given gas prices and other extenuating factors, a modest jaunt toward southeast Kansas appears probable for myself and a fellow co-worker on Tuesday.

Excellent moisture return is forecasted by the 5/12 0z NAM, with mid-upper 60s surface dewpoints reaching the target area by Tuesday evening resulting in favorably low LCL heights. This seems attainable with moisture return well underway by early Monday morning, combined with upper 60s dewpoints already present at KBRO, and a few low-mid 60s values noted along the SE TX coastline.

A southwesterly mid-level speed max is evident from northern OK into eastern Kansas on Tuesday, beneath generally S or SSW surface flow, contributing to nearly 60kts of 0-6km shear. This magnitude of this cloud-layer shear combined with surface-based and mixed-layer parcels both yielding CAPE values > 2000 J/KG should be more than sufficient for supercells. Convective initiation would likely happen shortly after 21z as several subtle shortwaves eject northeastward from the Desert Southwest upper low, encroaching upon the unstable airmass and associated boundaries at play. The left exit region of a 90kt upper-level jet streak also positions itself across SE KS on Tuesday evening, and would provide an additional impetus for convective development.

Low-level speed shear is reasonable across SE KS given the presence of a better organized and significantly stronger LLJ than in areas further southwest. Surface winds out of the S or SSW are somewhat of a concern, however given the aforementioned strong speed shear, 0-1km SRH values still climb to above 200 m2/s2 by Tuesday evening. Forecasted hodographs across the area demonstrate a near 90 degree 'critical angle' as defined by Giuliano/Esterheld between the low-level storm inflow vector and the 0-0.5km shear vector. This certainly piques my interest as far as tornado potential goes, given the other parameters already discussed. See this hodograph:

http://beta.wxcaster.com/cgi-bin/parse_skewt_trace.cgi?model=NAM&fcsthr=048&STATIONID=KCNU

Another factor to like across SE KS is greater low-level instability as compared to SW OK/NW TX, likely owing to weaker boundary-layer mixing. Roughly 8-10% of the total surface based or mixed-layer CAPE is contained within the inflow region of the storm, co-located within a moderately sheared region.

One obvious downfall to the SE KS target will be 0-6km shear vectors only somewhat normal to the boundaries at play, as the cold front overtakes the dryline much faster in this area. I would hope that 10km storm-relative winds of around 50kts, as well as a backing wind profile above 650mb would tend to keep anvil seeding to a minimum, and lead to the likelihood of more discrete storms, especially given the relatively modest upper-level forcing.

This is the one day per month where my co-worker and I actually have the same day off and can chase together. Here's to hoping for a big 'Super Tuesday'!

-Chris

 

[Mikey Gribble]

I totally agree with the potential over SE Kansas Chris and that will likely be my play unless the southern target starts looking a little better. The one thing that has been steering me away from the SE Kansas target was the shear vector being parallel to the boundary, but the 00Z NAM makes me feel a little better about that by showing broken convection along the cold front. If convection can avoid going linear quickly the storms over SE Kansas could definitely have some tornado potential. Even a tail end to a line/cluster could be a good play. It is also a heck of a lot closer to home for me.

 

[Derek Weston]

I'm going to throw the Northern half of Missouri out there as a possibly interesting northern target. NAM puts some nice shear in this area... better than most of the southern targets I'm seeing. Of course, question is instability. If we can get CAPE > 1500.... could get interesting.

 

[Ilya Neyman]

Several things that stick out to me with regards to computer model progs about this particular system are 1.) the very rich moisture Td's upper 60s-low 70s and PW's of 4-4.5 cm coming across the Red River Tuesday afternoon..(that's very quality moisture there) 2.) 50-60kt 500 flow (you're talking early-mid Spring values) 3.) 80-100kt WSW-SW jet 4.) very good directional shear 5.) high potential instability.

It's true that winds at the 850-700 mb levels are less than robust, however, they may be adequate as far as storm relative winds go, especially considering storm motions possibly on the order of 35-40 +? kts.

I say the 30% hatched zone is definitely warranted right now.

 

[mark plate]

Count me as unimpressed for now. The old but true saying of "upper low dig, nothing big" seems to apply well to Tuesday. The weak 700 mb winds, and shallow front sagging south through the high plains also do nothing to excite me. Expect storms to become much more numerous overnight as the front continues to sag south. To me, the tornadic threat seems fairly minimal overall.

 

[Jared Farrer]

The capping is a definit issue, if your not on the dryline when the winds start to back down it. If they do of course? But the middle level cooling thats supposed to take place around 500mb has made for some very fat cape! I am seeing lots of questionable shear issues as well, lots of veering in some places and weaker shear in the lower levels.

Some places do look good but those areas are not on the dryline and might not go up at all being I see no real upper level forcing?

 

[David Toner]

I'm surprised that there hasn't been more activity with this thread. Especially considering the SPC's day 2 convective outlook issued at 1149 states that they may need to upgrade to moderate risk and that the Kansas/Missouri area may be at a greater risk for tornados.

Looking at the forcast discussion from NWS Wichita they state "ANOTHER SEVERE WEATHER EVENT IS SHAPING UP ACROSS SOUTHEAST KANSAS
ON TUESDAY AS ANOTHER COLD FRONT PUSHES THROUGH THE FORECAST AREA.
THIS EVENT LOOKS QUITE SIMILAR IN LOCATION AND TIMING TO THIS PAST
SATURDAY..."

I agree that the models might be over estimating the moisture return and I certainly wouldn't go quite as far as Wichita did. But this could be a sleeper.

At this point I think my target is going to be SE Kansas, probably Parsons.

 

[Mikey Gribble]

In reality I will probably target Ardmore or Duncan tomorrow just because they have wifi, but if I was going to pick an area ahead of where I think the best storm will fire I would go with the area right ahead of the dryline along the Red River. I didn't spend much time on my forecasting tonight, so it is probably better to ignore it, but here it is. I just copied and pasted from my blog, hence the "post again" comments at the bottom.


A positively tilted trough will begin to affect the central and southern plains tomorrow. A very strong LLJ will rapidly advect moisture northward through tonight and tomorrow morning, with dewpoints in the upper 60's reaching SE Kansas by tomorrow afternoon. A cold front will extend from roughly Kansas City to where I35 intersects the KS-OK border and then meet up with a dryline near Oklahoma City. A dryline will extend SSW from the triple point along a Weatherford to Duncan to Stephenville line by tomorrow afternoon/evening.


There are a couple areas I like, but one stands out above the others if the cap can break. SE Kansas has been getting hyped by SPC, but it doesn't look so great in the latest run with lowlevel winds veering pretty badly by 00Z. 850mb winds are stronger over this area, so that is certainly a positive for it and should help to enlarge the lower portion of the hodograph, but the veering winds in the lowest 1km really worry me. The winds don't start veering until later in the afternoon though. They are still backed at 18Z, so if a storm can fire up here before low level winds start to veer then it may have a window to go tornadic.


The best area for tornadoes is likely to be near the Red River in southern Oklahoma. I would target the Duncan to Waurika area down here (and South of there 40 miles or so). I am a little worried about the cap down here, but steepening lapse rates, good moisture, and decent insolation should overcome the cap. The NAM is a little sluggish to break out convection down here though and that is what worries me a bit. A deepening surface low over West Texas should help to keep low level winds backed more in this area compared to points farther North. This area should also have good overlay of the moisture and thermal axis. 850mb winds will still be veering a little, but they are veering everywhere else to so there is no way around that one. In earlier runs weak flow at 700mb in this area concerned me, but now the NAM is showing >30kts, which should be fine. Deep layer shear and CAPE combinations will be quite favorable for supercells and with the shear vector being mostly normal to the boundary discrete supercells should be the favored mode of convection.


Overall I'm not really impressed with the tornado potential, but I could see us getting a couple tornadoes over southern Oklahoma and north Texas (40 miles or so either side of the Red River). I will make the call on if and where I'm chasing in the morning, but right now I would target the area I mentioned before near the Red River in southern Oklahoma.


I will probably post a quick update after I go over 00Z data a little closer. The next forecast will be posted early tomorrow morning.

 

[Bill Schintler]

Chase Target for Tuesday, May 13

Chase target:
Chico, TX (22 miles west of Denton).

Timing and storm mode:
Storms will fire along and just south of a cold front and dryline intersection at 6 PM CDT. Supercell storms will be likely early in convective evolution, with a transition to a linear complex later in the evening as the cold front surges into northern Texas.

Synopsis:
At 130 kt H3 streak was diving S down the back side of the positively-tilted WRN CONUS trough. At the SFC, moisture return has been slow over the previous 24 hours, however this is changing as an axis of mid-50 dewpoints is streaming NWRD into SCNTRL OK. A 40 kt LLJ was transporting +16C dewpoints currently in SRN and CNTRL TX NWRD and the FWD sounding indicated saturation in the H8-H9 layer. MDLs have a good handle on dewpoints, which should break 70F by the afternoon.

Discussion:
An axis of broken CI will overspread the region from the SW, blanketing roughly the SE half of OK by 00Z. Additionally, SC along and E of a line parallel to and 40 miles W of I-35 will signal the moisture return and may also impact insolation to some degree. MDLs agree on the evolution an area of 60kt H5 flow but differ on the details of a couple of mesoscale disturbances embedded within this flow over OK between 21Z-01Z. Capping will remain strong during the first part of the day with H7 temperatures AOA 10C, however mid-level cooling will commence by mid-afternoon as large scale assent overspreads the area and temperatures W of I-35 and S of the Red River rise into the low to mid 90s. Convection may fire first near the triple point SW of Ardmore, and storms should quickly become severe in an environment of strong instability and locally backing SFC flow. The SRN extent of convection along the DL should be limited by insolation by the aforementioned CI shield, and storms should not fire much S of I-20. Quality of shear is in question, with the strongest LLJ flow just E of the DL convection; however deep-layer shear to 60kts along with linear hodographs and strong instability will support storm organization.

- bill
11:45 PM CDT, 05/12/08

 

[Quintin Erdman]

Something to look at

Not that anyone should draw any conclusions from one model, but people in Oklahoma City should take notice of the newest run of the 4km WRF reflectivity model. It shows a supercell with almost looks like it shows a hook near the metro between 0-1z.


Something to keep an eye on.

Qman

 

[Brian Emfinger]

I am not too enthusiastic about the tornado potential either. All the hodographs I looked at from N Texas through SE KS look pretty crappy. I understand the SPC's reasoning behind the 10% hatched over the Eastern half of Oklahoma as the hodo's look better (still not great though) there than where the storms are likely to form but I am worried the storms could go linear quickly and already be a well formed line before it can get into the better better winds/shear. However, this could be one of those days where it will all come together for Central / Southern Oklahoma so I am in. The WRF runs I glanced are encouraging.

I will probably get to the Pauls Valley area first before refining my target further from there.