Storm Chase 2009 - Day 10 Discussion

[Nick F]

Well, SPC are keen to emphasis that supercells with large hail and perhaps a strong tornado may develop close to the warm front that is likely to parallel the N TX and Oklahoma or Red River Valley. Storm motions should move E or ESE and be fairly slow, so if you can latch onto one it should be fairly easy to keep up, despite terrain being awkward north of Dallas with river crossings being few and far between in the Red River Valley. Reminds me a little of Arkansas on 10th May last year, though storm motions should be slower. Given the 10% risk is for N Texas near the warm front where winds are turned favourably and CAPE will be high for tornadoes, you'd have to pick this area for storms rather than risk the dryline further SW in Texas, I would target somewhere like Denton to Sherman area. Going to be tough though, given the strong cap likely to be in place and no focused forcing - but at least this will keep any supercells that do develop discrete. I would advise the team not to core punch today given CAPE will be v. high ... lol.

DAY 1 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0100 AM CDT TUE MAY 05 2009

VALID 051200Z - 061200Z

...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF NORTH TX AND SRN

OK...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE SRN PLAINS

AND LOWER MS VALLEY...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE ERN

SEABOARD AND ERN GULF COAST STATES...

...SRN PLAINS...

A WEST NORTHWEST FLOW PATTERN WILL BE IN PLACE ACROSS THE PLAINS

STATES AS A LOW-LEVEL JET OVER WEST TX INCREASES MOISTURE FROM THE

SOUTH TODAY. ELEVATED THUNDERSTORMS SHOULD BE ONGOING ON THE NOSE OF

THE LOW-LEVEL JET IN WRN OK THIS MORNING WITH THIS ACTIVITY

SPREADING EWD ACROSS CNTRL AND ERN OK DURING THE AFTERNOON. SOUTH OF

THIS CLUSTER OF STORMS...MODEL FORECASTS SUGGEST THE WARM SECTOR

WILL BE UNDISTURBED ALLOWING FOR SUBSTANTIAL DESTABILIZATION. WITH

SFC DEWPOINTS IN THE MID TO UPPER 60S F ACROSS NORTH TX AND SRN

OK...MODERATE TO STRONG INSTABILITY SHOULD DEVELOP WITH SFC-BASED

CONVECTIVE INITIATION MOSTLY LIKELY IN SW OK OR NW TX DURING THE

LATE AFTERNOON WITH A CLUSTER OF SEVERE STORMS DEVELOPING EWD DURING

THE EARLY EVENING.

NAMKF FORECAST SOUNDINGS ALONG THE RED RIVER AT 00Z WEDNESDAY SHOW

AN IMPRESSIVE SHEAR AND THERMODYNAMIC ENVIRONMENT WITH 0-6 KM SHEAR

OF 55 TO 60 KT AND MLCAPE VALUES APPROACHING 3000 J/KG. THIS ALONG

WITH STEEP MID-LEVEL LAPSE RATES SHOULD BE SUPPORTIVE OF RAPID

SUPERCELL DEVELOPMENT WITH VERY EFFICIENT HAIL PRODUCTION. THE MORE

DOMINANT SUPERCELLS COULD CONTAIN VERY LARGE HAIL. IN

ADDITION...STRONG LOW-LEVEL SHEAR...LCL HEIGHTS BELOW 500 METERS AND

DEWPOINTS IN THE UPPER 60S F SHOULD BE FAVORABLE FOR TORNADOES WITH

THE POSSIBILITY OF A STRONG TORNADO AS THE LOW-LEVEL JET STRENGTHENS

IN THE EARLY EVENING. WIND DAMAGE WILL ALSO BE POSSIBLE ESPECIALLY

IF A TRANSITION TO A LINEAR MODE OCCURS DURING THE EVENING. AN

ENHANCED WIND DAMAGE THREAT COULD EXIST FURTHER EAST ALONG THE

INSTABILITY GRADIENT IF AN MCS ORGANIZES ACROSS NE TX INTO SW AR.

[Neilsouth]

Do these areas get storms like this every year ?.

Edited May 5, 2009 by neilsouth

[Paul]

Yep!

[Neilsouth]

Awesome

[nsrobins]

Reminds me a little of Arkansas on 10th May last year, though storm motions should be slower.

I think they'd be slower in most situations - those storms were moving at nearly 60mph and were a tad difficult to chase!

I think Paul S hit the nail on the head earlier: with a pretty stout cap in place an OFB from this mornings ongoing MCS is likely to play a significant role in forcing this evening. A bit too soon to pin a target but a quick sweep of available data would take me once again to the Vernon area for a lazy lunch.

[nsrobins]

Update 06 NAM:

It continues to be a tough call, so someone of my limited experience has only a slim chance of getting his one right. I think the SPC Moderate risk area is too far east. Moisture is not a problem, and although the composite radar breaks out ppn over the DFW area from 23Z, the best mean CAPE (3000+) and SRH (350+) are centred further west along the warm front in the Lubbock area. Throw in what looks like an ever tightening dryline bulge (impressive gradient there) on the I27 around Tulia and the money has to be on a shift west this afternoon, maybe Turkey, so long as something can pull the trigger and break the pretty hefty cap (not quite a death cap but close). For this you may need to rely on an OFB from the yet to develop and then fading MCS mess across OK.

This could be a case of sitting and hoping well into the afternoon, but if something does shoot it could be a beast.

[nsrobins]

The SPC update makes interesting reading, and they have indeed extended the Mod risk area westwards towards Lubbock to allow for the chance of the post MCS, dryline bulge late afternoon beasts should forcing be enough to break the cap. I'm thinking seriously of heading towards the Matador - Guthrie area assuming there's nothing of note to buzz around on this morning's developments closer to hand.

Luckily I'm not leading a group of chasers as it could be a win or bust later on. The cap holds - bust. The cap breaks and win. Like a pressure cooker lid popping off you get rapid convection and the chance of some beautiful supercells, and given the high SRH and shear with a veering LLJ, they'll readily spin.

[Roger J Smith]

Paul, I have the feeling that Big Spring will be the place to be later today, this convection over OK is elevated over a large stratus field and while it may remain active later, it may also be nothing worth driving to see either. There is already some clearing to the west and south of Big Spring, and the dry line looks like it is going to make slow progress out of far western TX towards perhaps Midland to Alpine later today. Anything north of Lubbock will probably stay under stable capped southeast flow.

There may also be some severe storms breaking out further south around Brady, but I foresee chase opportunities near the I-20 probably west rather than east of Big Spring at first. It will become very hot and humid south of a stalled front in this vicinity given the progged 582 dm thickness. Could be seeing dew points up into the mid-70s around Sonora and Brady by afternoon, and temps in the cleared zones near 93 F with 100 F dry air intruding from the west. Can't see much better than 78/65 in the east TX warned zone, which makes me suspicious that it won't amount to much especially given the distance factor.

[Paul Sherman]

Hi Roger

This is the hardest Forecast of the entire Chase and have spent the last 2 hours pouring over Models. I do like the I20 Corridoor for some Supercells to Fire but IS The Cap just too strong down there, the CINH Weakens considerably further East so At the Moment I am seriously thinking of Vernon to Graham to Abilene area for something at the moment, any thoughts on that.

Paul S

[nsrobins]

Hi Roger

This is the hardest Forecast of the entire Chase and have spent the last 2 hours pouring over Models. I do like the I20 Corridoor for some Supercells to Fire but IS The Cap just too strong down there, the CINH Weakens considerably further East so At the Moment I am seriously thinking of Vernon to Graham to Abilene area for something at the moment, any thoughts on that.

Paul S

I'm coming round to the DL bulge playing it's part on this one (main push just south of Lubbock) and I agree with Roger that the mess over and to your north is worth avoiding for the chance to catch a cap-busting beauty later on. I said Guthrie and will stick with that myself - certainly I'd stay well north of the I20.

[Roger J Smith]

Yep, it's a poser alright, when you say Vernon to Abilene, that gets almost to Big Spring so perhaps split the difference and head for some location just northeast of Abilene, if it does start looking like further west, you're not out of range, if Graham starts looking good, you're close to that as well. I don't think this will fire early in any case. Could well be multiple cells too, so there may not be one right answer to this puzzle. I will note this, actual severe weather in the past ten days has tended to occur somewhat to the southwest of consensus predictions, although not necessarily NW team locations. Upper level winds are WNW today which will suppress warm advection especially where air masses are overcast.

[Tony Gilbert]

I would certainly consider just east of Abilene on the I 20 corridor by mid afternoon, this should in fact be just east of the Triple Point though still along the warm front. RUC continues to suggest that the cap will erode from the underside as temps and humidity increase at surface.

RUC continues to break out convection near the Red River but this can only be elevated stuff derived from above the boundary layer. Hense tornadoes would in theory be much less likely for that region!

The I 20 will give an excellent means of keeping with these storms using any north exit to gain position from the SE quadrant of any storm cell. It is of great significance that low level directional shear could become synonymous with a full veer. Some real rapid rotation should be visible on any storms cloud base. IMO if they fire in this region we will most definitely get one or two strong tornadoes!

Time is of the essence with this one guys. I'd want to be there by 3pm at the latest !

Edited May 5, 2009 by Tony Gilbert

[Paul]

The team are about to set off on what could be a pretty intense day's chasing..

Paul has put together his daily briefing, which you can view here:

http://www.netweather.tv/index.cgi?action=...ase-video;sess=

Streaming is now live too:

http://www.netweather.tv/index.cgi?action=chaselive;sess=

[A.J]

blimey!, I've just come back from holiday, and thought I'd check up on the stormchase thread.....I didnt expect a zillion posts...lol.....guess I have a lot of catching up to do tonight.....Judging by the amount of posts, it looks a great success!

[Gorky]

Best combination of Shear and Cape seems be along I20 - Callahan and Eastland Counties right now but this will shift somewhat over time. Storms should fire north of there however on the warm front and given the slight WNW flow, storms may have some southerly component to their tracks, especially right movers if they hook onto a retreating warm front (I think this is progged to rereat and surge forward again tomorrow but I havn't the data to hand and it may just become a stationary front). I'd imagine storms firing on the warm front would be a couple of counties north of I20 (Knox, Baylor, Archer) and so these counties or counties just south would be a reasonable start. I certainly wouldn't say anything against Throckmorton and Young Counties to start from. (Throckmorton and Graham towns)

This is taken from a very brief look at the models by the way. I've been busy at work, have just got in and have to dash out again. It's not been researched as much as I normally would so I hope it is an accurate forecast, but pelase don't count on it

I'll pick this up again by 11pm and things may be getting going by then.

Anyways... gotta go.

[Nick F]

Alot of murk to contend with across much of central and Nern TX atm looking at vis. satellite, signs of it clearing from the west. Good idea to head towards Abilene where the skies will clear quicker than further east perhaps.

Strong cap in place may not break until 10-11pm at the earliest, NAM forecast soundings show cap gone by 00z Weds (UTC) for Abilene (KABI):

-18z

- 00z

Nice sickle shape on the hodograph indicating good turning of the winds and tornadic potential of any supercells that develop across west central Texas. Dryline should reach Abilene area by 00z tonight.

Possibilities further NE of OFB from elevated convection over Sern OK moving S and combining with warm front to develop some storms too as warm front moves north.

[Tony Gilbert]

Most recent RUC model update continues to suggest a chance of a weakened capping just west of Dallas Fort Worth. If conditions come together as suggested then steering winds could well put DFW on a high alert for tornadoes within the suburbs by evening! Obviously from this point onwards surface obs will tell much more.

My virtual chase position would by now take me just west of DFW on I 20 ready to exit north. Graham looks good.

Edited May 5, 2009 by Tony Gilbert

[Roger J Smith]

Would look for initiation between Snyder and Sweetwater with cells tracking towards Abilene, north side. Satellite looks active and cap should break rapidly around 2130z. Would suggest Anson just north of Abilene for 3:30 pm CDT staging.

[John Hanrahan]

Paul S

Currently Sat in Aspermont North of Abilene. Clear Skies now and Temps shooting up towards the High 70's

All about the Cap Now!

Only option would be to jog east towards Throckmorton if it fires along Highway 380

Paul S

[Nick F]

Atmosphere must feel juicy there Paul with local Td obs of 66-67F, just a waiting game now to see where the cap breaks first. Like Tony says, could be further east towards west of Fort Worth, winds are more backed to the SE to your east too:

[maidstone weather]

Some form of convection seems to be happening directly ahead of their car at the moment, beyond the buildings in front

Edited May 5, 2009 by maidstone weather

[Tony Gilbert]

Hi res vis sat is telling me much more than the one hr delay from obs; Dryline has shifted much further east in the last hr and instability feeds north under the edge of the residual cloud cover making contact within the next hr. Focus is on and around Jackboro

Edited May 5, 2009 by Tony Gilbert

[nsrobins]

http://www.spc.noaa.gov/products/md/md0710.html

Recent MD for the target area. I'm not moving from Guthrie yet as I can see the prominent dryline bulge is pushing east now. Paul's position in Aspermont is pretty good IMO. Initiation could only be an hour or so away now.

[chionomaniac]

Has the moderate risk been downgraded to slight?

[Nick F]

Has the moderate risk been downgraded to slight?

It has, but for the hail risk (from 45% to 30%) rather than tornado risk which remains at 10%.