Big Severe Wx Outbreak around 10/18/07 in Plains

[dtrain44]

Agree with Speed. Will be interesting to see how the soundings look. This is great - finally some local weather to track at work!

With any luck, nothing too destructive will occur. I think a slow severe weather season around here might have people a little bit lulled to sleep.

[6SpeedTA95]

Agree with Speed. Will be interesting to see how the soundings look. This is great - finally some local weather to track at work!

With any luck, nothing too destructive will occur. I think a slow severe weather season around here might have people a little bit lulled to sleep.

Slow severe weather season? How about 4 slow seasons in a row. Its been pathetic really. In fact one of the guys out of Tulsa in June said that you could add the severe weather from 04/05/06 and through June of 07 together and it didn't equal an average spring. Things have been lifeless in Oklahoma for quite some time.

These storms fixing to move through my area (bville) are going to cause substantial mixing in the atmosphere. Perhaps we'll get a little sun out and have a little fun this afternoon

[6SpeedTA95]

dtrain, you work at NWS in norman?

[dtrain44]

Oh, no. I wish

I'm an accountant with idle time on his hands.

[6SpeedTA95]

Oh, no. I wish

I'm an accountant with idle time on his hands.

I hear ya

Depending on what happens at work here once I finish my MBA I may head back to OKC with the wife. But I hope things wokr out well here at work so I dont have to move.

[RL3AO]

So is there supposed to be new development behind this current line or in front of it? The dry line is still over the Western Panhandle.

[dtrain44]

There's a little bit of popcorn type stuff coming up ahead of the line - nothing too impressive just now. I think the expectation is that the line will move NE into KS/northern OK by late morning, with the dry line moving east and storm development occurring in late afternoon. Seems reasonable. Of course, that new tornado watch for central/SW OK includes areas well ahead of the current line of storms, which would indicate to me that the SPC is a bit worried about development out front of the line this morning.

IMO, this morning stuff bears watching, but any high end stuff will probably occur this afternoon if we can get some decent heating in that 11-3 window.

[RL3AO]

Personally I'm expecting a PDS watch for Central and Eastern Oklahoma later.

[dtrain44]

The pessimistic side of me would note that this spring, we had a day that looked exactly like this: wicked shear and some expectation of an outbreak, but a lack of heating made it tough to get enough instability. Of course, events in April hardly determine the outcome of a day in October, but it does remind me......

RL3AO, that could happen. I think we'll need a bit more certainty on initiation in the late afternoon before they go that route, but I'd expect that we've got 6-8 hours before the main event would start in the central and eastern part of the state. Good heating and we're virtually certain to get at least some convection, which should rapidly turn severe. PDS will depend less on the potential for long track tornadoes and very large hail (which seems to be there) and more on the ability of convection to get going.

[dtrain44]

Morning HWO from NWS Norman:

.DAY ONE...TODAY AND TONIGHT...

THUNDERSTORM OUTLOOK...
THERE IS A MODERATE RISK FOR SEVERE THUNDERSTORMS ACROSS CENTRAL AND
EASTERN OKLAHOMA THROUGH TONIGHT. A SLIGHT RISK EXISTS ELSEWHERE
OVER OKLAHOMA AND WESTERN NORTH TEXAS.

LOCATION...
THE MODERATE RISK IS LOCATED EAST OF A LINE EXTENDING FROM
CHEROKEE...TO WATONGA...TO DUNCAN AND WAURIKA. A SLIGHT RISK
EXTENDS EAST OF A ARNETT...TO ELK CITY...TO VERNON AND SEYMOUR
TEXAS LINE.

TIMING...
SEVERE STORMS WILL BE POSSIBLE THROUGH THIS EVENING. HOWEVER... THE
MOST LIKELY TIME FOR MORE WIDESPREAD SEVERE WEATHER WILL BE AFTER 2
PM.

IMPACTS...
IN THE MORNING... NICKEL SIZE HAIL AND WIND GUSTS TO 65 MPH.
DURING THE AFTERNOON AND EVENING HOURS... BASEBALL SIZE HAIL... WIND
GUSTS TO 70 MPH... AND TORNADOES.

RECOMMENDED ACTIONS...
STORM SPOTTER GROUPS AND EMERGENCY MANAGEMENT PERSONNEL ACROSS THE
RISK AREA SHOULD PLAN FOR SEVERE WEATHER OPERATIONS THROUGH THIS
EVENING.

DISCUSSION...
THUNDERSTORMS THAT DEVELOPED EARLY THIS MORNING WILL CONTINUE TO
MOVE ACROSS PORTIONS OF OKLAHOMA AND WESTERN NORTH TEXAS. THESE
STORMS HAD DEVELOPED DUE TO A STRONG LOW LEVEL JET. A FEW OF THESE
STORMS MAY BECOME SEVERE WITH STRONG WIND GUSTS AND LARGE HAIL.

A STRONG UPPER-LEVEL STORM WILL MOVE OVER OKLAHOMA AND NORTH TEXAS
THROUGHOUT THE DAY TODAY. THIS WILL BE COINCIDENT WITH THE
ADVANCEMENT OF A DRY LINE THROUGH WESTERN OKLAHOMA BY MID AFTERNOON.
MOISTURE WILL CONTINUE TO INCREASE AHEAD OF THE DRY LINE...ALLOWING
INSTABILITY TO BECOME SUFFICIENT FOR SEVERE THUNDERSTORMS AGAIN THIS
AFTERNOON. STRONG VERTICAL WIND SHEAR WILL ALSO DEVELOP...WHICH WILL
ALLOW THE ADVANCING DRY LINE TO TRIGGER SUPERCELL THUNDERSTORMS.
VERY LARGE HAIL... DAMAGING STRAIGHT-LINE WINDS... AND TORNADOES
WILL BE POSSIBLE THIS AFTERNOON AND EVENING...PRIMARILY IN THE
MODERATE RISK AREA. A LIMITING FACTOR WILL BE THE AMOUNT OF SHOWERS
AND THUNDERSTORMS AND CLOUD COVER THIS MORNING...WHICH WILL LIMIT
THE AVAILABLE INSTABILITY. THUNDERSTORMS WILL MOVE INTO EASTERN
OKLAHOMA THIS EVENING.

And Tulsa:

.DAY ONE...TODAY AND TONIGHT.
TORNADO.
RISK...ELEVATED.
AREA...EASTERN OKLAHOMA AND NORTHWEST ARKANSAS.
ONSET...AFTER 4 PM.

SEVERE THUNDERSTORM.
RISK...SIGNIFICANT.
AREA...EASTERN OKLAHOMA AND NORTHWEST ARKANSAS.
ONSET...AFTER 7 AM AND AGAIN AFTER 4 PM.

DISCUSSION...
A 40 TO 50 KNOT LOW-LEVEL JET COMBINED WITH STEEPENING LAPSE RATES HAS
RESULTED IN SCATTERED CONVECTION ACROSS THE AREA OVERNIGHT.
ADDITIONAL THUNDERSTORMS OVER WESTERN AND NORTHWESTERN OKLAHOMA
COULD AFFECT PARTS OF NORTHEAST OKLAHOMA EARLY THIS MORNING. A FEW
OF THE STRONGER STORMS MAY PRODUCE MARGINALLY SEVERE HAIL.

ATTENTION WILL TURN TO THE DRYLINE THAT WILL MIX INTO WESTERN TO
CENTRAL OKLAHOMA BY LATE AFTERNOON. HEATING WILL BE TEMPERED SOME BY
THE CLOUD COVER...ALTHOUGH LATE AFTERNOON SURFACE BASED CAPE VALUES
SHOULD STILL INCREASE TO AROUND 1000 J/KG. AS A 90 KNOT MID-LEVEL
JET AND HEIGHT FALLS PUNCH EAST INTO THE TEXAS PANHANDLE...SCATTERED
THUNDERSTORM DEVELOPMENT IS EXPECTED ALONG THE DRYLINE BY MID TO
LATE AFTERNOON. GIVEN THE VERY STRONG DEEP-LAYERED SHEAR...ANY
THUNDERSTORM THAT DEVELOPS WILL ROTATE AND QUICKLY BECOME SEVERE.

DISCRETE SUPERCELLS MAY BEGIN TO AFFECT PORTIONS OF EASTERN
OKLAHOMA BY LATE AFTERNOON...WITH THE POSSIBILITY OF A FEW
LONG-LIVED STRONG TORNADOES AND VERY LARGE HAIL. SEVERE THUNDERSTORMS
WILL QUICKLY SPREAD THROUGH THE REMAINDER OF EASTERN OKLAHOMA AND
NORTHWEST ARKANSAS...WITH THE THREAT ENDING ACROSS THE AREA AFTER
ABOUT 2 AM.

[Ed Mahmoud]

Drove through some tropical showers on the way to work, brief heavy rain, no thunder or lightning. Looks like area of greatest spin is about to Galveston, although it looks to be so embedded in the Southeast flow into the big stormit probably doesn't have a closed circulation.


Currently, out the office window of the Galleria, a stratus deck that is starting to break revealing blue skies, racing off to the Northwest.

Whatever remains of that remnant bit of vorticity should be in Arklatex this afternoon, wonder if that plays a role in evolution of severe weather there. May represent additional low level moisture/ added instability/lower cloud bases.

[Ed Mahmoud]

One differenc ebetween now and April working against severe, if clouds are slow to break, is that the sun angle and length of day are about the same as late February.


Stratus continues to thin/break out here in SE Texas, so the air heading for North Texas for late this afternoon is getting some daytime heating.

[CrazyC83]

Could be a long few days ahead.

HIGH risk upgrades perhaps?

[6SpeedTA95]

So is there supposed to be new development behind this current line or in front of it? The dry line is still over the Western Panhandle.

This current activity is the precourser for whats supposed to come this afternoon. Initation is expected right along I35 beginning between 3 and 5pm. This initiation is what should be monitored for long lived supercells. Although the rain now and cloud cover is limiting instability so the question is will instabality build enough to support supercells with all the early mixing? Given the low level jet and the negatively tilted closed core low and steepening lapse rates I think convection will be enough to overcome the lack of instability provided we hit at cape values of at least 750 joules/kg.

[6SpeedTA95]

Morning HWO from NWS Norman:

.DAY ONE...TODAY AND TONIGHT...

THUNDERSTORM OUTLOOK...
THERE IS A MODERATE RISK FOR SEVERE THUNDERSTORMS ACROSS CENTRAL AND
EASTERN OKLAHOMA THROUGH TONIGHT. A SLIGHT RISK EXISTS ELSEWHERE
OVER OKLAHOMA AND WESTERN NORTH TEXAS.

LOCATION...
THE MODERATE RISK IS LOCATED EAST OF A LINE EXTENDING FROM
CHEROKEE...TO WATONGA...TO DUNCAN AND WAURIKA. A SLIGHT RISK
EXTENDS EAST OF A ARNETT...TO ELK CITY...TO VERNON AND SEYMOUR
TEXAS LINE.

TIMING...
SEVERE STORMS WILL BE POSSIBLE THROUGH THIS EVENING. HOWEVER... THE
MOST LIKELY TIME FOR MORE WIDESPREAD SEVERE WEATHER WILL BE AFTER 2
PM.

IMPACTS...
IN THE MORNING... NICKEL SIZE HAIL AND WIND GUSTS TO 65 MPH.
DURING THE AFTERNOON AND EVENING HOURS... BASEBALL SIZE HAIL... WIND
GUSTS TO 70 MPH... AND TORNADOES.

RECOMMENDED ACTIONS...
STORM SPOTTER GROUPS AND EMERGENCY MANAGEMENT PERSONNEL ACROSS THE
RISK AREA SHOULD PLAN FOR SEVERE WEATHER OPERATIONS THROUGH THIS
EVENING.

DISCUSSION...
THUNDERSTORMS THAT DEVELOPED EARLY THIS MORNING WILL CONTINUE TO
MOVE ACROSS PORTIONS OF OKLAHOMA AND WESTERN NORTH TEXAS. THESE
STORMS HAD DEVELOPED DUE TO A STRONG LOW LEVEL JET. A FEW OF THESE
STORMS MAY BECOME SEVERE WITH STRONG WIND GUSTS AND LARGE HAIL.

A STRONG UPPER-LEVEL STORM WILL MOVE OVER OKLAHOMA AND NORTH TEXAS
THROUGHOUT THE DAY TODAY. THIS WILL BE COINCIDENT WITH THE
ADVANCEMENT OF A DRY LINE THROUGH WESTERN OKLAHOMA BY MID AFTERNOON.
MOISTURE WILL CONTINUE TO INCREASE AHEAD OF THE DRY LINE...ALLOWING
INSTABILITY TO BECOME SUFFICIENT FOR SEVERE THUNDERSTORMS AGAIN THIS
AFTERNOON. STRONG VERTICAL WIND SHEAR WILL ALSO DEVELOP...WHICH WILL
ALLOW THE ADVANCING DRY LINE TO TRIGGER SUPERCELL THUNDERSTORMS.
VERY LARGE HAIL... DAMAGING STRAIGHT-LINE WINDS... AND TORNADOES
WILL BE POSSIBLE THIS AFTERNOON AND EVENING...PRIMARILY IN THE
MODERATE RISK AREA. A LIMITING FACTOR WILL BE THE AMOUNT OF SHOWERS
AND THUNDERSTORMS AND CLOUD COVER THIS MORNING...WHICH WILL LIMIT
THE AVAILABLE INSTABILITY. THUNDERSTORMS WILL MOVE INTO EASTERN
OKLAHOMA THIS EVENING.

And Tulsa:

.DAY ONE...TODAY AND TONIGHT.
TORNADO.
RISK...ELEVATED.
AREA...EASTERN OKLAHOMA AND NORTHWEST ARKANSAS.
ONSET...AFTER 4 PM.

SEVERE THUNDERSTORM.
RISK...SIGNIFICANT.
AREA...EASTERN OKLAHOMA AND NORTHWEST ARKANSAS.
ONSET...AFTER 7 AM AND AGAIN AFTER 4 PM.

DISCUSSION...
A 40 TO 50 KNOT LOW-LEVEL JET COMBINED WITH STEEPENING LAPSE RATES HAS
RESULTED IN SCATTERED CONVECTION ACROSS THE AREA OVERNIGHT.
ADDITIONAL THUNDERSTORMS OVER WESTERN AND NORTHWESTERN OKLAHOMA
COULD AFFECT PARTS OF NORTHEAST OKLAHOMA EARLY THIS MORNING. A FEW
OF THE STRONGER STORMS MAY PRODUCE MARGINALLY SEVERE HAIL.

ATTENTION WILL TURN TO THE DRYLINE THAT WILL MIX INTO WESTERN TO
CENTRAL OKLAHOMA BY LATE AFTERNOON. HEATING WILL BE TEMPERED SOME BY
THE CLOUD COVER...ALTHOUGH LATE AFTERNOON SURFACE BASED CAPE VALUES
SHOULD STILL INCREASE TO AROUND 1000 J/KG. AS A 90 KNOT MID-LEVEL
JET AND HEIGHT FALLS PUNCH EAST INTO THE TEXAS PANHANDLE...SCATTERED
THUNDERSTORM DEVELOPMENT IS EXPECTED ALONG THE DRYLINE BY MID TO
LATE AFTERNOON. GIVEN THE VERY STRONG DEEP-LAYERED SHEAR...ANY
THUNDERSTORM THAT DEVELOPS WILL ROTATE AND QUICKLY BECOME SEVERE.

DISCRETE SUPERCELLS MAY BEGIN TO AFFECT PORTIONS OF EASTERN
OKLAHOMA BY LATE AFTERNOON...WITH THE POSSIBILITY OF A FEW
LONG-LIVED STRONG TORNADOES AND VERY LARGE HAIL. SEVERE THUNDERSTORMS
WILL QUICKLY SPREAD THROUGH THE REMAINDER OF EASTERN OKLAHOMA AND
NORTHWEST ARKANSAS...WITH THE THREAT ENDING ACROSS THE AREA AFTER
ABOUT 2 AM.

That pretty much sums it up.

[dtrain44]

Good points, Ed. Plus, there's just less daylight (which, of course, is just another way of making your point about the angle of the sun): it'll be pretty much dark by 6:30 here, which limits the potential for additional heating even more. These fall events can be very exciting, but they sometimes require a "perfect storm" kind of situation to get going. We'll know a lot more once these storms clear out of western/central OK and we see what the atmosphere does.

I think high risk is a bit premature now: I'm not sure what would happen before the 1730 Day 1 outlook, other than an extraordinary sounding, that would justify going high. I think they'll stay with a strongly worded moderate pending additional evidence.

Speed is right: any supercell type stuff will probably wait until late afternoon in central OK. I think we'll definitely get convection and that this convection will get very severe very quickly: question is how much there will be.

[dtrain44]

Sorry to take up all the space on this board.....

Short term forecast from NWS Norman: they seem to be thinking that significant severe this afternoon could be as far west as Lawton/Wichita Falls.

.NOW...
...REGIONAL WEATHER DISCUSSION...
AT 9 AM...CLUSTERS OF THUNDERSTORMS WERE DEVELOPING ALONG AND WEST
OF A LINE FROM KINGFISHER...TO HOBART...AND QUANAH...WITH MOVEMENT
TOWARD THE NORTHEAST AT 40 MPH. MOST OF THESE STORMS WERE BASED
ABOVE THE SURFACE...WITH EFFECTIVE CAPES BETWEEN 350 AND 700. STORM
DEVELOPMENT WAS IN RESPONSE TO A VIGOROUS UPPER LEVEL TROUGH NEAR
THE NEW MEXICO...WEST TEXAS BORDER...PROVIDING STRONG AND DEEP LIFT
OVER THE AREA. DESPITE THE LOW AMOUNT OF INSTABILITY...THE LARGE
AMOUNT OF VERTICAL WIND SHEAR SUPPORTS THE POSSIBILITY OF SEVERE
STORMS. HOWEVER...SEVERE STORMS ARE MOST LIKELY THIS AFTERNOON.

BY EARLY AFTERNOON....THE BASE OF A STRONG UPPER LEVEL TROUGH IS
FORECAST TO REACH CHILDRESS...WITH AN ASSOCIATED DRYLINE EXTENDING
FROM THE WESTERN OKLAHOMA BORDER...SOUTHWARD TO ABILENE. COOLER MID
LEVEL TEMPERATURES ASSOCIATED WITH APPROACH OF THE TROUGH...AND
GRADUAL HEATING AHEAD OF THE DRYLINE ARE EXPECTED TO CONTRIBUTE TO A
MODERATELY UNSTABLE AIRMASS AS THE DRYLINE MOVES INTO THE AREA.

AT THIS TIME...THE MOST LIKELY AREA FOR SEVERE THUNDERSTORMS BY THIS
AFTERNOON WILL BE ALONG AND NORTHEAST OF THE ADVANCING DRYLINE
EXTENDING FROM HOBART...TO LAWTON...AND WICHITA FALLS....WHERE
SUPERCELLS WILL BE POSSIBLE.
$$
JAMES

[Ed Mahmoud]

I imagine SPC will request a special 18Z sounding from offices in the vicinity.

Speaking of, I know how to find the normal 0Z/12Z soundings, does anyone know where to see special soundings?

[Ed Mahmoud]

The morning 12Z sounding from Norman already shows decent shear and instability

[6SpeedTA95]

The morning 12Z sounding from Norman already shows decent shear and instability

Thats actually kinda scary and there's been virtually no mixxing happening in the norman area