5/2/2006 FCST: NE/KS/OK/TX/SD/MN

[Jason Boggs]

As of right now, I'm not too excited about Tuesday's potential. Sure, there will be some high CAPE in some areas, but the speed shear in most of the risk are is rather pathetic. 25-30 kt winds at 500mb just won't cut it for long lived supercells. The updraft will get rained out fairly quickly in my opinion. I think the 30% risk area will have to be taken out of western OK. I'm just not seeing why the 30% risk is that far west. I'm not sure good moisture return will be in place in W Oklahoma at the time of storm initiation. Better moisture will be much further to the east. If I was to make a map of the highest risk area at this time, this is where I would place it:

 

[Kevin Scharfenberg]

Interesting setup for Tuesday in OK and surrounding areas...looks more like something you'd expect in mid to late June!! SSE winds at 10 kts at the surface and W to WNW winds at 30-35 kt at 6 km should yield sufficient bulk shear for supercells with sufficient instability. Boundaries for initiation are unclear at this hour, but the cap should be fairly weak. Doesn't look like a blockbuster day by any stretch, but something to keep an eye on. Will be interesting to see if we can recover to 65 dewpoints in a widespread area as depicted.

BTW, not worth its own thread, but there will be some good lower boundary layer vorticity along the stalled boundary in Oklahoma this afternoon. Don't be surprised if a landspout pops up under a towering cumulus somewhere along the boundary at peak heating.

 

[BrandonWhittington]

Well, I'm starting to favor the dryline a little more than I was wanting to. Seems to look like there is going to be a lot of convergence along it, with a very sharp moisture drop. Models are showing that temperatures should reach the the mid 80s by late afternoon. Models are also starting to hit at 60+ tds in the Eastern Texas and Oklahoma Panhandles. My only save and grace to chasing close to home is going to be how far the front pushes south. Front should stall in my opinion just south of the childress area, providing another boundary for storms to work with. Western Oklahoma is looking good for me. My target area is going to be woodward right now. I'm wanting to see just how sharp the dryline can get before any more plans.

 

[nickgrillo]

LOL... I wasn't aware that I was starting a thread for Tuesday with this topic (5/2/2006), I was referring to the Wednesday setup in the majority of my post up there... Well, since the topic has been started for Tuesday, I'll continue onward with the Tuesday conversation.

The latest NAM continues to show >4000 j/kg sbCAPE ahead of the surface boundary, with somewhat favorablely curved forecast hodographs across central KS by the mid-late afternoon, with sbCINH eroding to near non-existence (3-6 j/kg on most soundings) with sbCAPE increasing to 2500-4500 j/kg ahead of the boundary by 21-00z. The latest NAM shows slightly more veered surface flow across the warm sector, which has appeared to decrease 0-1km SRH -- yet the GFS puts the sfc low in the northern panhandles/southwest KS by 00z -- and keeps low-level flow relatively backed ahead of the dryline/sfc trof. The NAM soundings across the region show favorable deep-layer shear profiles for sustained supercells (e.g. 0-6km shear of 40-45 kts) with enough low-level veering and SRH to pose a potential tornado threat with the supercells. Assuming we do get the > 65 tds across the area to help yield the progged extreme CAPE, then I think we have a good supercell day on our hands (despite the relatively weak mid-upper flow, which of course is a good thing for a change, since the average storm motions shouldn't be more than 15 kts LOL) given there is plentiful deep-layer shear and SB instability to keep storms sustained. Yay, it's May!

I'm leaving for KS in a few hours (still need to get a few things done before I leave).

 

[Jeff Snyder]

Assuming we do get the > 65 tds across the area to help yield the progged extreme CAPE
[/b]

Well, I think that's one of the biggest question marks at this time... The morning-updated AFD from OUN indicated a likely MDT risk for parts of the area tomorrow, though the new Day 2 keeps that risk at a SLT. Current surface obs indicate that the >65F Tds are currently along the southeastern TX coast, making a little headway towards the OK/KS target area. The most rainfall from this past weekend fell east of I35, but recent rainfall as well as the fact that vegetation is now out of dormancy should yield some evapotranspiration efffects to the east of the dryline tomorrow. 12z RAOBs across southern TX and sw LA aren't entirely impressive in terms of moisture depth, that I would think that'd improve with time as return of the moisture continues. The current RUC is indicating 30-40kts flow at 925-850mb by 3z this evening across southern TX, so we may see a rapid return of moisture just off the surface overnight, with the higher mixing ratios mixing downward to the surface tomorrow morning (kind of like what we was last Friday in TX). However, we have seen plenty of days this year during which the NAM has been much too aggressive in moisture return (though some of that may have to do with aggressive surface moisture flux from evapotranspiration, which should be more in check given that we actually do have living vegetation now relative to March).

If we get the progged surface moisture, very strong CAPE should develop east of the dryline, primarily between I40 and I70), with the 12z NAM run indicating well over 4000 j/kg sbCAPE. Flow aloft isn't particularly strong (even 'marginal' in some areas), but strong directional shear is progged to yield deeplayer shear supportive of supercells. Nonlinear effects caused by convergence below cloud base may increase the low-level rather significantly in the proximity of any supercells, which would stretch the hodograph and provide favorable low-level shear given the low-level veering profile anticipated.

 

[samuel stone]

So I was looking through the Severe thunderstorm Event Index at some days that yielded supercells when 500 mb flow was 30kt at best, and what did I come across, June 12th, 2004 Mulvane day. Also Mulvane did not have as great of directional shear so I see no problem with deep layer shear being supportive supercells tommorow. I do think however moisture depth and resultant mixing of boundary layer along dryline could yield a problem with the LCL's.

 

[BrandonWhittington]

Winds here in Booker, TX have already turned to out of the southeast. Dew points in Gage is already 52. Also, I cant help but notice the dew points in South Texas. Dew points are already reaching 70 to 73 degrees along the coast. Models have a better handle on this senerio than past ones were they over estimate dewpoints. Dew points should increase throughout the night and most of the day on Tuesday. I'm going to favor the Northeast TX Panhandle, as the cool front/wind shift line moves into the area. Could get really interesting here in this area. With temperatures in the upper 80s to 90 degrees, and dew points near 60, CAPE should reach or exceed 2500 in some places. It does not take very much to get an isolated tornado in May here in the Panhandles. Just keep are fingers crossed.....

 

[Tim Marshall]

Looks like tomorrow is a marginal chase day in W and N OK. I expect higher dewpoints and thus, more thunderstorm activity than this evening. Upper winds are marginal at best for tornadic storms. However, 00z ETA shows a small disturbance coming through the area. Wednesday also looks like a marginal chase day in N OK. I'll check data in the morning. I have business in OKC and Blackwell so this could be a nice all expense paid BUSINESS TRIP. Looking for a little CAPE magic. Motto: If it is May, get out and chase. TM

 

[Bill Schintler]

Target:
10 miles south of Shattuck, OK (At the junction of US-283 and US-60, or about 30 miles SW of Woodward).

Timing:
High-based storm (or virga) initiation should take place at around 4 PM CDT in the Pampa, TX to Perryton, TX areas. Storms should become surface-based and reach severe limits as they cross the TX/OK border and enter an environment with deeper moisture and better low-level shear. The first severe warning, for Ellis CO. in OK, should be issued at around 5:30 PM CDT.

Comments:
Discrete, high-based supercell storms during the early evening hours, with an evolution into an MCS by mid-evening. Hail to 2.5â€￾ will be the primary severe SVR threat, while wind gusts to 80mph will also be likely.

Discussion:
Generally zonal ULVL pattern across the CONUS, and storms should fire in the vicinity of a dryline during the afternoon in OK as a compact wave approaches the area. MDL guidance suggests a compact H5 vort max at the exit region of a 45kt H5 streak, with an associated H7 short wave lifting into the target area by late afternoon.

The primary FCST concern is the amount and depth of SFC moisture and resulting instability. 00Z DDC and OUN soundings, both of which are N of a SFC WF, are fairly dry in the low levels; with the OUN indicating a 200mb deep moist layer with a mean Td of about 10C through this layer. FWD indicates a 140mb deep layer with a mean Td of 14C. Overnight, the veering LLJ will not assist in transporting any of this moisture into NWRN OK. The latest (00Z) NAM does seem to have a good handle on both the SFC and H85 dewpoints in OK. Still, it is my gut feeling to adjust the WWRD extent of the deep moisture during the afternoon hours as the MDLs may not resolve the shallow moist layer in the vicinity of the DL. Given a 20-25kt SWRLY flow of SFC and H85 temperatures in the mid-80s F by mid afternoon, expect that the DL should advance to the OK/TX border through 5 PM.

In any event, cloud bases will be high with SFC depressions of nearly 30F. This will result in LCL's in the 1600m to 2200m range from N to S across WRN OK with a deep and well mixed BL. Expect fairly steep mid-level lapse rates, with H7 temps of around 9C and H5 temps of around -14C. This will support MLCAPE's (100mb) in excess of 1500J/kG. Shear parameters will also be favorable, including LLVL hodographs with SRH's (0-3km) to 250m^2/s^2 and bulk shear to 45kts, under the aforementioned H5 streak. All of these parameters will support storm organization and supercells. Later in the evening, a developing 70kt LLJ will result in an evolution into a large MCS.

- bill

 

[Chad Ringley]

WRF 4.5 km NMM ran at 00 UTC tonight develops initial discrete cells in the E TX Panhandle between 23-01 UTC 2-3 May and then conslidates them into a forward-propogating MCS whcih moves across C OK, which is described very nicely in the new SPC SWODY1. Should note that the WRF did develop the ongoing convection in EC/E OK (whcih is currently ongoing E of OKC along I-40) at about the same time, but shifted a few counties S and E.

Here are some plots from the 2-3 May fcst cycle:

As Samuel pointed out, great tornadoes have been observed on really weak flow days (12 June 2004), evident that supercells can induce their own shear...but I believe these days are usually characterized by extreme CAPE and relatively low LCLs (on 12 June 04, Td were AOA 75F with Td Depressions 10-15F).

Hopefully we'll have lower than progged LCL heights tomorrow. GL to everyone going out!

An aside:
For some inexplicable reason, the WRF-ARW core isn't running over at NCEP. The Spring/Summer 4km WRF ARW forecasts, which were supposed to start on 18 April, haven't started yet. Anybody have any idea why?

 

[Mike Mezeul II]

Ken Fugate, Mike Bak, and myself will be leaving DFW within the hour for its look like Childress, TX. We'll be in my silver Frontier, so if ya see us out there feel free to say hi! Good luck to all who go out today and stay safe.

 

[Edward Ballou]

Though not quite in the CWA of this thread, I am intrigued by the northern setup closer to the low. Marginal CAPE values - 1500-2000 in SW MN. Hodograph for KOTG is really pretty. All the models are pretty much agreeing on Worthington with CAPE hovering at around 1700 (GFS) to 2300 (NAM). EHI at 2.8 with some good CIN combination over the area. Only problem with this setup is moisture. It is looking like that problem will be overcome though - here's hoping for it anyway.

Per FSD NWS text, the GFS has been pretty "on" with this system...so far. Chad's WRF images are also progging some moisture up this way. It looks as though things will fire right on top of Brookings or just east and roll on into MN.

Last note - I've noticed LCL values being very high or higher for the rest of this setup to the south. Though I know it's not everything, it seems like it could hamper some stuff. Wouldn't mind seeing a high based tube.

 

[Eric Whitehill]

I wouldn't discount an isolated tube in the Sioux Falls area.

Winds appear to be decent in that area, as well as a few other factors.

Cape, as of this mornings RUC run appears to be quite healthy,
approaching 1500j/kg.

Shear is not as healthy as I would like to see, however there appear
to be fairly decent southerly winds coming into the system, along with
dew points in the mid 50's. I am slightly concerned about the cap not
breaking, as at 21z there is still some CINH left around.

I would say precip breaking out around 5pmish, and then a possible
isolated weak tornado.

 

[Kevin Scharfenberg]

For the southern target at least, today is a great example of poor model performance. The 09Z RUC and 06Z NAM-eta show 12Z 500 mb winds of 20-25 kts over southern NM and far west TX, where the 12Z El Paso sounding and White Sands profiler are showing ~40 kts. So apparently there is something creeping up from northern old Mexico the models don't have a handle on that will make the shear profile better than progged.

On the other hand, the 09Z RUC had forecast 850 mb dewpoints at 12Z of 14-16C over north Texas...where the 12Z FWD sounding shows about 8C. So the model surface dewpoints approaching and exceeding 70F and SBCAPES of 4000+ by late in the day look very unlikely.

So, time to throw the NWP out the window and revert to actual meteorology... ;-) I'll go for good deep shear profiles for supercells but relatively weak low level shear. However that will be augmented by backed/channeled low-level flow in the wake of the morning thunderstorms. Good moisture will struggle to keep from mixing out with dewpoints holding in the lower half of the 60s over the risk area. Cloud bases will be relatively high.

A good day to chase if you can (I cannot - so get your cameras ready!)

Edited to add -- The 12Z models won't do any better, and this data flow problem at EMC will cascade to the next few model runs. Use NWP with extreme caution for awhile...

SPECIAL NCEP DISCUSSION
CENTRAL OPERATIONS/NCEP/NWS/WASHINGTON DC
1310 UTC TUE MAY 02 2006

021310Z...NCEP 12Z MODEL CYCLE. NCEP PLANS TO START THE
12Z NAM 40 MINUTES LATER THAN NORMAL WITHOUT ANY
CONVENTIONAL OBSERVATIONAL DATA. WE WILL RUN THE NAM IN A
FASTER THAN NORMAL MODE SO THE NAM MODEL SHOULD FINISH CLOSE
TO ITS NORMAL TIME. THE NGM WILL BE RUN ABOUT 40 MINUTES
LATE. WE WILL SOON MAKE A DECISION ON THE START OF THE
12Z GFS.
[/b]

 

[Kevin Scharfenberg]

Update: The 11Z and 13Z cycles of the RUC are producing totally garbage output that is affecting the SPC mesoanalysis page...and anything else that relies on RUC analysis and forecasts. Use ANY objective analyses today with EXTREME caution.