Memorial Day Weekend Outbreak 2008

[Texas Snowman]

Saw on Joe B's blog today that he has severe weather concerns next week.

Have been on the road, no I-net coverage - so, I'll throw this question out there: any big threat coming up?

Tx Snowman

[Ed Mahmoud]

Maybe Joe is looking at the 0Z Euro (I'll mosy over in a minute to the PPV site and watch the video).

Deep trough by Thursday afternoon in the West, and a surface system with a well developed low level jet in the Plains.





The 12Z GFS is in general agreement on a big Western trough.

GFS model loop from PSU

[Ed Mahmoud]

Haven't watched video yet, but was based on something Dr. Cahir taught him as un undergrad at Penn State, combination of low forecasted pressure and high forecasted wet bulbs.

[Ed Mahmoud]

Haven't watched video yet, but was based on something Dr. Cahir taught him as un undergrad at Penn State, combination of low forecasted pressure and high forecasted wet bulbs.

Video based on same idea.

[Ed Mahmoud]

12Z GFS (and darn it, http://www.met.utah.edu/wx model site hasn't updated the models since April 30th, so I am using the AccuWx PPV site) shows storms moving into DFW next Friday afternoon with between 20 and 30 knot 850 mb winds and 4000 J/Kg of surface based CAPE.


Yowza.

[Texas Snowman]

Since I live north of D/FW, I don't like the word "yowza."

[RL3AO]

Lets see how consistent the models are in the next few days.

[CrazyC83]

It seems there is no end in sight...I don't think things will calm down until mid-June at least...

[Ed Mahmoud]

New 0Z GFS shows similar pattern. Forecast precip suggests some severe weather along the warm front as early as Wednesday in the Northern Plains, with Friday being the main severe day from about the Red River to as far North as South Dakota.

met.utah.edu/wx model site still hasn't updated in two weeks, so cheating a look at the GFS, best collocation on Friday of where precip and CAPE align is Oklahoma, generally East of I-35, and SE Kansas, into adjacent Arkansas and Missouri.

25 to 30 knot 850 mb winds from the SSW. In the precip with high CAPE area, winds lighter along frontal boundary, but while some 10 to 12 knot winds in SE Oklahoma, most of the area with precip has less than 10 knot surface winds.

Ack, AccuWx still has the 18Z GFS up. Ok, 18Z GFS at 174 hours isn't too different from 0Z at 168, although 18Z storms in Dallas Friday afternoon and the 0Z doesn't. Upper low is still well back in the Rockies.

Ok, the 18Z at 204 hours shows a 12 hour blob over Central Texas over 2 inches. So the 18Z anyway, carries the outbreak into Saturday.


Ok, 'rapid update' GFS from AccuWx is on to the 0Z run, and storms line up from SE Texas to Illinois, with Missouri and Illinois over 3000 J/Kg CAPE, and parts of Southern Illinois over 4000 J/Kg. 20 knot South 850 mb winds in the CAPE bullseye in Illinois. 35 knot SW 500 mb winds.



If this is all correct, Friday is bad, and Saturday even worse. Of course, the GFS drops in grid scale resolution after 180 hours, and this is all a week away.


But potentially an active spell Wednesday through Saturday, nearly border to border, from the Plains to the Western Ohio Valley.

[Ed Mahmoud]

Oh, and slow moving, so heavy rain may be an issue as well.

[Ed Mahmoud]

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0329 AM CDT SAT MAY 17 2008

VALID 201200Z - 251200Z

...DISCUSSION...
GFS AND ECMWF IN SLIGHTLY BETTER AGREEMENT THIS FORECAST...THOUGH
LARGE DIFFERENCES CONTINUE TO EXIST BETWEEN THE TWO MODELS. BOTH
MODELS FORECAST SIGNIFICANT AMPLIFICATION OF THE UPPER PATTERN
THROUGH THE FORECAST PERIOD...WITH A LARGE TROUGH EVOLVING OVER THE
WEST AND A SECOND TROUGH PERSISTING ACROSS THE EAST...SEPARATED BY A
SHARP RIDGE.

THE ECMWF REMAINS MUCH MORE PERSISTENT WITH THE ERN FEATURE...AND
THUS MAINTAINS A RIDGE OVER THE CENTRAL U.S. BETWEEN TWO
HIGHLY-AMPLIFIED TROUGHS -- A CLASSIC OMEGA BLOCK.

MEANWHILE...THE GFS IS MUCH WEAKER WITH THE ERN TROUGH/UPPER
LOW...ALLOWING THIS FEATURE TO PROGRESS SLOWLY EWD INTO THE WRN
ATLANTIC. AS THIS OCCURS...THE CENTRAL U.S. RIDGE SHIFTS SLOWLY EWD
INTO THE ERN U.S. THROUGH THE END OF THE PERIOD...THUS FACILITATING
THE EVENTUAL DEAMPLIFICATION OF THE LARGE WRN U.S. TROUGH BY DAY 8.

WHILE BOTH MODELS DEPICT DEEP SLY FLOW ACROSS THE CENTRAL U.S.
THROUGH THE FIRST HALF OF THE PERIOD -- AND THUS A RETURN OF GULF
MOISTURE WHICH SUGGESTS AN INCREASE IN CONVECTIVE POTENTIAL WITH
TIME...TIMING AND LOCATION OF ANY SEVERE EVENTS REMAINS DIFFICULT TO
DISCERN AT THIS TIME. THUS...WILL NOT ATTEMPT TO OUTLOOK ANY THREAT
AREAS ATTM.

..GOSS.. 05/17/2008

[CrazyC83]

SPC now picking it up - drew an area farther north with considerable uncertainty.

ZCZC SPCSWOD48 ALL
ACUS48 KWNS 180837
SPC AC 180837

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0337 AM CDT SUN MAY 18 2008

VALID 211200Z - 261200Z

...DISCUSSION...
EXTENDED MODELS -- THOUGH THEY CONTINUE TO DIFFER SOMEWHAT WITH
RESPECT TO THE UPPER PATTERN EVOLUTION...PARTICULARLY LATE IN THE
PERIOD -- PERSIST IN SUGGESTING A GENERAL INCREASE IN SEVERE
POTENTIAL OVER THE CENTRAL CONUS DURING THE LATTER HALF OF THE
UPCOMING WEEK. BOTH DEVELOP A LARGE TROUGH OVER THE WRN U.S. AND
SUBSTANTIAL NWD RETURN OF RICH GULF MOISTURE INTO THE PLAINS
STARTING DAY 4. WHILE SOMEWHAT MERIDIONAL...FLOW ALOFT SHOULD
REMAIN STRONG ACROSS THIS REGION -- AND THEREFORE EXPECT BOTH THE
KINEMATIC AND THERMODYNAMIC ENVIRONMENT TO BE SUPPORTIVE OF SEVERE
STORMS.

DIFFICULTY PERSISTS...HOWEVER...IN NARROWING DOWN THE REGION OF
GREATER THREAT -- BOTH SPATIALLY AND TEMPORALLY -- DUE TO MODEL
DIFFERENCES. ATTM...GREATEST POTENTIAL APPEARS TO EXIST DAYS 5-7
/I.E. THU. MAY 22 THROUGH SAT. MAY 24/ ACROSS PARTS OF THE CENTRAL
AND NRN PLAINS. THE GFS -- WHICH DEPICTS THE UPPER RIDGE FARTHER E
THAN THE ECMWF -- WOULD APPEAR TO FAVOR CENTRAL KS/CENTRAL NEB ALONG
ERN FRINGES OF A FAIRLY WELL-DEVELOPED SURFACE LOW. MEANWHILE...THE
ECMWF WOULD FAVOR A PRIMARY THREAT AREA FURTHER WWD -- ACROSS THE
CENTRAL AND NRN HIGH PLAINS -- WITHIN SELY UPSLOPE FLOW REGIME E OF
A SHARPER LEE TROUGH/LOW. ATTM...WILL INTRODUCE A THREAT AREA FOR
DAYS 5-7 ACROSS MUCH OF KS/NEB AND INTO PARTS OF ERN CO/ERN WY --
COVERING PORTIONS OF THE ENVELOPE ENCLOSING SOLUTIONS FROM BOTH
MODELS.

..GOSS.. 05/18/2008

CLICK TO GET WUUS48 PTSD48 PRODUCT

[Ed Mahmoud]

Looks like it might be dryline season over a good part of the Western High Plains...

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0359 AM CDT MON MAY 19 2008

VALID 221200Z - 271200Z

...DISCUSSION...
GFS/ECMWF CONTINUE TO DEPICT A VERY HIGH AMPLITUDE/OMEGA-BLOCK-TYPE
PATTERN ACROSS THE CONUS THIS PERIOD...WITH A DEEP TROUGH TO LINGER
OVER THE WEST UPSTREAM OF A VERY STRONG RIDGE OVER THE CENTRAL U.S.
THROUGH AT LEAST DAY 5-6. WHILE UNCERTAINTY INCREASES WITH RESPECT
TO THE EVENTUAL BREAKDOWN OF THIS BLOCKING PATTERN -- WHICH COULD
BEGIN AS EARLY AS DAY 7 -- SEVERE POTENTIAL REMAINS APPARENT OVER
THE HIGH PLAINS DAYS 4-6.

A VERY WARM/MOIST BOUNDARY LAYER SHOULD BE IN PLACE BY DAY 4 ACROSS
THE PLAINS...THOUGH STRONG RIDGE -- AND THUS SUBSIDENCE/CAPPING --
SHOULD KEEP THE CONVECTIVE THREAT SUPPRESSED WWD NEAR A HIGH PLAINS
DRYLINE. HOWEVER...WITH FAVORABLE INSTABILITY AND AMPLE SHEAR
ANTICIPATED INVOF THIS BOUNDARY...A MULTIPLE DAY THREAT FOR SEVERE
STORMS IS EVIDENT. WHILE THE GFS CONTINUES TO SUGGEST THAT THE
THREAT WILL BE SOMEWHAT FURTHER E THAN THE ECMWF...BOTH AGREE THAT
THE GREATEST POTENTIAL SHOULD BE FOCUSED SOMEWHERE WITHIN A ROUGHLY
200 MILE-WIDE AREA CENTERED OVER THE HIGH PLAINS. THUS...WILL
MAINTAIN A THREAT AREA OVER PARTS OF THE NRN AND CENTRAL HIGH
PLAINS...AND EXPAND THE AREA SWD THIS FORECAST TO INCLUDE PARTS OF
NM AND W TX.

..GOSS.. 05/19/2008

[CrazyC83]

Dryline outbreaks are very hard to predict, since they are dependant on capping and small differences can make the difference between a total bust and all heck breaking loose...

[CrazyC83]

Is it just me, or do the Thursday through Saturday dynamics look so similar to May 4-6, 2007?

[Ed Mahmoud]

30 to 40 knot 850 mb jet per Euro, and some directional shear between 850 mb and 850 mb.






12Z WRF shows precip Oklahoma to South Dakota. Looking at AccuWx PPV site for WRF specifics, because Utah U site still fubar, 1000 J/Kg all the way to Nebraska, 2000 to 3500 Joules/Kg Kansas into Oklahoma, deep layer shear generally 40 to 60 knots. EHI bullesye Northwest Kansas.

The NIU Storm Machine forecast skew-T generator seems cranky today, no forecast skew-Ts for Dodge City or McCook, NE

[CrazyC83]

30 to 40 knot 850 mb jet per Euro, and some directional shear between 850 mb and 850 mb.






12Z WRF shows precip Oklahoma to South Dakota. Looking at AccuWx PPV site for WRF specifics, because Utah U site still fubar, 1000 J/Kg all the way to Nebraska, 2000 to 3500 Joules/Kg Kansas into Oklahoma, deep layer shear generally 40 to 60 knots. EHI bullesye Northwest Kansas.

The NIU Storm Machine forecast skew-T generator seems cranky today, no forecast skew-Ts for Dodge City or McCook, NE

Shear of 40-60, is that significant enough for a tornado outbreak?

[Ed Mahmoud]

30 to 40 knot 850 mb jet per Euro, and some directional shear between 850 mb and 850 mb.






12Z WRF shows precip Oklahoma to South Dakota. Looking at AccuWx PPV site for WRF specifics, because Utah U site still fubar, 1000 J/Kg all the way to Nebraska, 2000 to 3500 Joules/Kg Kansas into Oklahoma, deep layer shear generally 40 to 60 knots. EHI bullesye Northwest Kansas.

The NIU Storm Machine forecast skew-T generator seems cranky today, no forecast skew-Ts for Dodge City or McCook, NE

Shear of 40-60, is that significant enough for a tornado outbreak?

40 knots is enough for organized severe weather and supercells with sufficient instability, IIRC in the ballpark of 1000 Joules/Kg, and weaker shear, 20 to 30 knots, is sufficent with higher instability.

40 to 60 knots and 2000+ J/Kg should be plenty sufficient.

[Ed Mahmoud]

And if you can get 5000 or 6000 Joules/Kg of CAPE, you don't need much deep layer shear at all.


25 knot deep shear and 6000+ J/Kg CAPE that produced an F-5 tornado nearby shortly after.



Link

[tornado92]

The jet stream set up for the next few days.

I'm keeping track of the Low to the Southwest. It could turn severe Thursday to Saturday