Tornado outbreak - February 10-11, 8+ dead

[srainhoutx]

They issued an SVR on that cell. It had 60kts of rotation a few minutes ago, but thats weakening now. Looks like we are coming to an end of the appetizer. Main course starts Tuesday.

I agree RL3AO. A long day ahead for N TX/E OK come Tuesday.

[RL3AO]

Winds are starting to pick up with that line. Radar showing some 50+ kt winds 750 to 1000 ft above the ground.

[Bunkertor]

Hey, thanks a bunch for explaining. I´ll get through it tomorrow. It looks easier than the other pages. Bookmarked.

[Extremeweatherguy]

I'm watching Tuesday very closely. I might be going chasing with a group of people if things do in fact heat up.

[srainhoutx]

MESOSCALE DISCUSSION 0070
NWS STORM PREDICTION CENTER NORMAN OK
0703 PM CST SUN FEB 08 2009

AREAS AFFECTED...EXTREME ERN NM AND WRN TX

CONCERNING...SEVERE THUNDERSTORM WATCH 6...

VALID 090103Z - 090230Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 6 CONTINUES.

THE PRIMARY THREAT WILL TRANSITION TO ISOLATED STRONG WIND GUSTS FOR
THE REMAINDER OF WW VALID TIME...THOUGH SOME MARGINALLY SEVERE HAIL
REMAINS POSSIBLE WITHIN THE STRONGER CORES.

A SQUALL LINE EXTENDS N-S ACROSS EXTREME ERN NM THROUGH FAR W TX
NEAR FORT STOCKTON. THE LINE IS MOVING EAST AT 25 KT. 00Z RAOB DATA
FROM MIDLAND AND AMARILLO SHOW SCANT INSTABILITY AND LIMITED
BOUNDARY LAYER MOISTURE WITH UPPER 40S DEWPOINTS...CAPPED BY AN
ELEVATED MIXED LAYER BASED NEAR 700 MB. THE SLY LOW LEVEL JET WILL
STRENGTHEN TO 50+ KT WITHIN ZONE OF STRONG ASCENT AND HEIGHT FALLS
ASSOCIATED WITH AN EJECTING NEGATIVELY TILTED UPPER TROUGH. THE
RESULTING STRONG DEEP CONVERGENCE AND LIFT WILL LIKELY MODIFY THE
THERMODYNAMIC PROFILES AND REMOVE THE CAP...EFFECTIVELY MAINTAINING
A LINE OF FORCED LOW TOPPED CONVECTION THE REMAINDER OF THE EVENING
ACROSS WRN TX.

STRONG BULK SHEAR OF 50 KT WILL MAINTAIN POTENTIAL FOR ORGANIZED
STRUCTURES AND BOWING SEGMENTS WITHIN THE LINE. AN INCREASE IN THE
SWLY COMPONENT OF WINDS IN THE 700-500 MB LAYER IS LIKELY AS THE
UPPER TROUGH EJECTS NE. THIS MAY CONTRIBUTE TO AN EWD ACCELERATION
OF THE SQUALL LINE. GRADUAL DECREASE IN UPDRAFT STRENGTH AND HAIL
POTENTIAL WILL LIKELY OCCUR AS STORMS MOVE INTO AN INCREASINGLY
MARGINAL THERMODYNAMIC ENVIRONMENT. HOWEVER...STRONG FLOW JUST ABOVE
THE SURFACE AND POTENTIAL FOR EWD ACCELERATION OF THE LINE WILL HELP
SUSTAIN THE THREAT FOR ISOLATED STRONG WIND GUSTS NEXT COUPLE
HOURS...ESPECIALLY WITH ANY BOWING OR LEWP STRUCTURES.

..DIAL.. 02/09/2009


ATTN...WFO...LUB...AMA...MAF...ABQ...

[Dave]

MESOSCALE DISCUSSION 0071
NWS STORM PREDICTION CENTER NORMAN OK
0759 PM CST SUN FEB 08 2009

AREAS AFFECTED...WRN TX

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 090159Z - 090300Z

SQUALL LINE WILL APPROACH THE ERN EDGE OF WW 6 BY 03Z. THESE STORMS
ALONG WITH A THREAT OF ISOLATED DAMAGING WIND GUSTS IS EXPECTED TO
PERSIST BEYOND 03Z. WW 06 MIGHT NEED TO BE LOCALLY EXTENDED FOR AMA
AND LBB AREAS TO COVER THIS THREAT.

DESPITE THE VERY MARGINAL THERMODYNAMIC ENVIRONMENT WITH WEAK
INSTABILITY AND STRONG CAPPING IN WARM SECTOR...STRONG FORCING
ATTENDING THE EJECTING UPPER TROUGH AND ITS ASSOCIATED LOW LEVEL JET
AS WELL AS THE DEVELOPMENT OF A COLD POOL WILL HELP MAINTAIN A
FORWARD PROPAGATING LINEAR MCS THIS EVENING. THE THREAT OF ISOLATED
DAMAGING WIND GUSTS MAY PERSIST ACROSS WRN TX BEYOND THE CURRENT WW.

..DIAL.. 02/09/2009

[Ed Mahmoud]

From NCEP site, I can see simulated radar at 6 hour increments, it suggests Tuesday 6 pm isolated storms are a solid line by midnight. Utah U 3 hour precip shows rain has fallen between 6 pm and 9 pm Tuesday, and using CAPE and deep layer shear forecast, looking at FTW sounding from NIU site, maybe a tad less extreme than 12Z WRF sounding, but EHI still in excess of 3 with cloud base and free connection level below 1 km.

[Ed Mahmoud]

I think main show is Tuesday from near DFW to OKC and then Eastward into Arkansas and Louisiana Tuesday, but new WRF shows some most unstable CAPE Wednesday afternoon in the warm sector in the Ohio Valley with deep layer shear, more instability than 12Z run.





Edit to add for new visitors for post above this one. From StormTrack.org

So... how does one estimate and assess whether there is enough instability in an environment with a certain amount of helicity to potentially produce rotating storms and possible tornadoes? A useful tool is the energy helicity index (EHI), developed by John Hart and Josh Korotky, based on the data set of tornado cases that Bob Johns and I looked at.

The EHI is a simple equation that combines helicity and instability into one number for estimating and assessing these factors in a particular environment regarding potential for supercells. It is not a magic number or a "dynamite tool" for forecasting tornadoes. It is simply another piece of information that can be useful at times in forecasting supercells. It works well in some situations, and not so well in some others. This depends on many factors, such as the strength of winds higher up in the atmosphere and the location of sounding observation network sites.

The EHI equation is: EHI = (CAPE x H) / 160,000


In practical experience, I've found that EHI values approaching 2.5 or greater are significant and tend to be more indicative of supercells with potential for tornadoes.

[Ed Mahmoud]

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE AMARILLO TX
905 PM CST SUN FEB 08 2009

..TIME.. ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE.. ....MAG.... ..COUNTY LOCATION.. ST.. ...SOURCE....
..REMARKS..

0901 PM TSTM WND GST 4 NW AMARILLO 35.24N 101.87W
02/08/2009 M65 MPH POTTER TX BROADCAST MEDIA

LORENZO DE ZAVALA MIDDLE SCHOOL

&&

EVENT NUMBER AMA0901017

De Zavala was, of course, the first Vice President of the Republic of Texas.

[RL3AO]

Looks like Tuesday will be a late evening and post-dark event.

[RL3AO]

They added a slight (5T/15H/15W) over Iowa for today.



Tuesday was upped to 45%




DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1151 PM CST SUN FEB 08 2009

VALID 101200Z - 111200Z

...THERE IS A SLGT RISK OF SVR TSTMS LATE TUE AFTN/TUE NIGHT FROM
PARTS OF THE SRN PLAINS INTO THE LWR/MID MS VALLEY....

...SYNOPSIS...
A SUBSTANTIAL INCREASE IN CONVECTIVE POTENTIAL...INCLUDING THE RISK
FOR SEVERE STORMS...STILL APPEARS LIKELY ACROSS THE MIDDLE OF THE
COUNTRY DURING THIS FORECAST PERIOD...AS THE NEXT IN A SERIES OF
STRONG SHORT WAVE TROUGHS MIGRATES OUT OF THE FOUR CORNERS REGION.
THIS EAST NORTHEASTWARD ACCELERATION...OUT OF BROADER SCALE
TROUGHING WITHIN THE MAIN BELT OF POLAR WESTERLIES ACROSS THE
SOUTHWESTERN U.S...IS PROGGED...AS YET ANOTHER SIGNIFICANT IMPULSE
DIGS INTO THE NORTH CENTRAL PACIFIC COAST. IN THE WAKE OF A PRIOR
SYSTEM...WHICH INCLUDES A CYCLONE PROGGED TO BE SLOWLY WINDING DOWN
JUST WEST OF THE UPPER GREAT LAKES REGION...A MORE SOUTHERLY TRACK
APPEARS LIKELY TO SUPPORT LEE SURFACE CYCLOGENESIS IN CLOSE ENOUGH
PROXIMITY TO THE GULF OF MEXICO TO ALLOW FOR WEAK TO MODERATE
DESTABILIZATION IN THE WARM SECTOR.

LINGERING VARIABILITY/DISCREPANCIES AMONG MODEL DATA...WHICH COULD
AFFECT THE TIMING/LOCATION AND STRENGTH OF THUNDERSTORM
ACTIVITY...PRECLUDES A HIGHER CATEGORICAL OUTLOOK THAT COULD
POTENTIALLY ACCOMPANY A SYNOPTIC SYSTEM OF THIS STRENGTH.
HOWEVER...THE 09/00Z NAM RUN IS NOW SLOWER WITH THE PROGRESSION OF
THE UPPER SYSTEM THAN RECENT SREF HAVE INDICATED. THIS IS MORE IN
LINE WITH ECMWF AND GFS...CONTRIBUTING TO A SLIGHT WESTWARD SHIFT OF
HIGHER SEVERE PROBABILITIES...BACK TOWARD THE INTERSTATE 35 CORRIDOR
OF OKLAHOMA AND NORTH CENTRAL TEXAS...FOR LATE TUESDAY
AFTERNOON/TUESDAY NIGHT.

...SRN PLAINS THRU LWR HALF OF THE MISSISSIPPI VALLEY...
ALTHOUGH THE LOW-LEVEL RETURN FLOW OF MID 50S TO NEAR 60F SURFACE
DEW POINTS FROM THE WESTERN GULF OF MEXICO MAY INITIALLY BE ADVECTED
OFF TO THE EAST OF THE SOUTHERN PLAINS...A RAPID SURGE BACK TO THE
WEST IS ANTICIPATED DURING THE DAY TUESDAY. AND... MODELS INDICATE
MOISTURE VALUES WILL PROBABLY INCREASE AS THE BOUNDARY LAYER OVER
THE WESTERN GULF OF MEXICO CONTINUES TO SLOWLY MOISTEN. CONFIDENCE
IS INCREASING THAT A SIZABLE WARM SECTOR WILL EVOLVE ACROSS THE
SOUTHERN PLAINS INTO THE LOWER MISSISSIPPI VALLEY...WITH MIXED LAYER
CAPE ON THE ORDER OF 500-1000+ J/KG DEVELOPING AS LAPSE RATES
STEEPEN.

MID-LEVEL INHIBITION IS EXPECTED TO BE SUFFICIENTLY STRONG TO
PREVENT THE INITIATION OF STORMS PRIOR TO THE LATE AFTERNOON...
PERHAPS EARLY EVENING. BUT...GUIDANCE IS STILL SUGGESTIVE THAT
DISCRETE STORMS ARE A DISTINCT POSSIBILITY ACROSS PARTS OF NORTHEAST
TEXAS AND SOUTHEAST OKLAHOMA INTO WESTERN ARKANSAS BY THE EARLY
EVENING HOURS. A LOW-LEVEL CONFLUENCE ZONE/ZONE OF ENHANCED WARM
ADVECTION NEAR THE INTENSIFYING /50-70 KT/ 850 JET CORE...BENEATH
DIFLUENT UPPER FLOW...COULD PROVIDE THE FORCING FOR THIS ACTIVITY.
AND...IF THIS OCCURS...LARGE CLOCKWISE CURVED LOW LEVEL HODOGRAPHS
BENEATH STRONG WEST SOUTHWESTERLY MID/UPPER FLOW ...AHEAD OF AN
APPROACHING 90-100 KT 500 MB JET STREAK...WILL BE QUITE FAVORABLE
FOR SUPERCELLS CAPABLE OF PRODUCING TORNADOES.

ANY DISCRETE DEVELOPMENT IS EXPECTED TO SPREAD NORTHEASTWARD INTO/
THROUGH THE OZARK PLATEAU DURING THE EVENING HOURS...AS ADDITIONAL
STORMS FORM BACK TO THE WEST...NEAR OF JUST EAST OF THE INTERSTATE
35 CORRIDOR. THIS IS EXPECTED TO OCCUR ALONG OR JUST AHEAD OF AN
EASTWARD ADVANCING COLD FRONT...AS STRENGTHENING LINEAR FORCING
ENCOUNTERS THE BETTER MOISTURE ACROSS THE SOUTHEASTERN PLAINS. THE
EVOLUTION OF AN EXTENSIVE SQUALL LINE APPEARS POSSIBLE...ACCOMPANIED
BY THE POTENTIAL FOR STRONG CONVECTIVE GUSTS WITH THE RISK FOR
CONSIDERABLE WIND DAMAGE THROUGH THE NIGHT ...AS IT SURGES EASTWARD
INTO THE LOWER MISSISSIPPI VALLEY.

..KERR.. 02/09/2009

[srainhoutx]

I am becoming a bit more concerned for the Tuesday event. Sure would appear a Mod Risk is in the making. 06Z guidance is very impressive and I suspect later guidance will follow suit. Tuesday into Wednesday could be very interesting for a lot of real estate. Heads Up Folks.

[Ed Mahmoud]

WRF not looking good for Dallas Metro...



Strong wind fields, low cloud bases and LGC, fairly good instability...

[CrazyC83]

All that is needed for a moderate risk tomorrow is for the 45 to be hatched.

[srainhoutx]

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 7...CORRECTED
NWS STORM PREDICTION CENTER NORMAN OK
855 AM CST MON FEB 9 2009

CORRECTED FOR STORM TOPS

THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

EASTERN KANSAS
WESTERN MISSOURI

EFFECTIVE THIS MONDAY MORNING AND AFTERNOON FROM 855 AM UNTIL 100
PM CST.

HAIL TO 0.5 INCH IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70
MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 40
STATUTE MILES EAST AND WEST OF A LINE FROM 25 MILES NORTHEAST OF
SAINT JOSEPH MISSOURI TO 30 MILES EAST SOUTHEAST OF JOPLIN
MISSOURI. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU7).

REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
DO PRODUCE TORNADOES.

DISCUSSION...LINE OF LOW-TOPPED FORCED CONVECTION IS SURGING
NORTHEASTWARD INTO WESTERN MO. THIS ACTIVITY IS ASSOCIATED WITH A
VERY POWERFUL...NEGATIVELY-TILTED MID LEVEL SHORTWAVE TROUGH AND
VERY STRONG LOW LEVEL WIND FIELDS. DESPITE VERY WEAK INSTABILITY
AND NO DETECTABLE LIGHTNING ACTIVITY...LEADING EDGE OF CONVECTIVE
LINE WILL POSE A THREAT OF DAMAGING WINDS FOR ANOTHER FEW HOURS.

AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 0.5 INCH. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60
KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 300. MEAN STORM
MOTION VECTOR 24045.


...HART

[Bunkertor]

1728z and the winner is...

[Dave]

MESOSCALE DISCUSSION 0077
NWS STORM PREDICTION CENTER NORMAN OK
1028 AM CST MON FEB 09 2009

AREAS AFFECTED...PARTS OF WRN MO

CONCERNING...SEVERE THUNDERSTORM WATCH 7...

VALID 091628Z - 091730Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 7 CONTINUES.

LINE OF SHOWERS CONTINUES TO DIMINISH IN INTENSITY.

BROKEN CONVECTIVE LINE NOW MOVING ACROSS WRN MO CONTINUES TO
DIMINISH IN ORGANIZATION/INTENSITY PER RADAR IMAGERY OVER THE PAST
HALF HOUR. THE CELLS ARE EXPECTED TO MOVE OUT OF THE WW IN THE NEXT
HOUR OR SO...AND WHILE A FEW ISOLATED OCCURRENCES OF WIND GUSTS NEAR
SEVERE LEVELS WILL REMAIN POSSIBLE...OVERALL THREAT DOES NOT APPEAR
TO WARRANT NEW WW ISSUANCE.

..GOSS.. 02/09/2009

[Ed Mahmoud]

Moderate and hatched on 1730 SWODY2

[Bunkertor]

[srainhoutx]

Full Text...

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1130 AM CST MON FEB 09 2009

VALID 101200Z - 111200Z

...THERE IS A MDT RISK OF SVR TSTMS ACROSS PORTIONS OF NERN
TX...SERN OK AND SWRN AR...
...THERE IS A SLGT RISK OF SVR TSTMS FROM TX/OK EAST-NORTHEASTWARD
INTO PORTIONS OF THE LOWER/MID MS VALLEY...

ACTIVE AND WIDESPREAD SEVERE WEATHER IS EXPECTED LATE TUESDAY
AFTERNOON AND NIGHT FROM PORTIONS OF OK/TX EWD INTO PORTIONS OF THE
LOWER/MID VS VALLEY. EVOLUTION OF CONVECTION APPEARS
COMPLICATED...AND THIS PRECLUDES A LARGER MODERATE RISK AREA.
MONITOR TUESDAY/S DAY 1 OUTLOOKS FOR UPDATES ON THIS SITUATION.
...SYNOPSIS...
LONGWAVE TROUGH WILL REMAIN SITUATED ACROSS THE WRN/CENTRAL
CONUS...AS A FAST MOVING SHORTWAVE TROUGH SHIFTS EWD FROM THE SWRN
STATES INTO THE ARKLATEX AREA BY EARLY WED MORNING. A 90-100 KT MID
LEVEL IS FORECAST TO ACCOMPANY THE UPPER SYSTEM AND MOVE INTO SWRN
TX BY LATE AFTERNOON...AND AR OVERNIGHT. WHILE NAM/GFS SHOW A
DEEPENING SURFACE LOW LOCATED NEAR THE MO/AR BY 11/12Z... NAM MOVES
THE DEVELOPING SURFACE LOW EWD ACROSS NRN OK AND THE GFS THOUGH NRN
TX TUESDAY.

TX/OK NEWD INTO THE MID MS VALLEY...
CURRENTLY PREFER GFS SURFACE LOW SOLUTION AS THE MAIN UPPER FORCING
SPREADS FROM SWRN TX TOWARD THE ARKLATEX DURING THE
AFTERNOON/EVENING HOURS. HOWEVER...SURFACE LOW LIKELY WILL NOT
DEVELOP UNTIL LATE UNTIL MAIN UPPER SYSTEM SHIFTS EWD INTO FAR WRN
TX. SINCE THE COLD FRONT CURRENTLY MOVING THROUGH SRN TX IS EXPECTED
TO STALL LATER TODAY...THIS SHOULD ALLOWING CURRENT LOWER/MID 60S TO
RETURN NWWD INTO SJT/ABI/SPS AREAS OF WRN TX AND NWD INTO
OK...MAINLY ALONG AND S OF I-44...TUESDAY. THESE DEWPOINTS COMBINED
WITH DIURNAL HEATING AND STRONG COOLING ALOFT...500 MB TEMPERATURES
FROM -18C TO -20C...SHOULD YIELD MLCAPES FROM 1000-1500 J/KG BY LATE
TUESDAY.

STRONG 850 MB FRONTOGENESIS AND INCREASING FORCING IS SUGGESTIVE OF
THE INITIAL CONVECTION DEVELOPING AS A SQUALL IN THE SPS/ABI/SJT
AREA...IN ASSOCIATION WITH THE DEVELOPING SURFACE LOW/TRAILING
FRONT. VERY STRONG ENVIRONMENTAL WINDS AND THE EXPECTED FAST
TRANSLATIONAL MOTION OF THE LINE SHOULD FAVOR WIND DAMAGE.
HOWEVER...FURTHER EAST ACROSS NRN TEXAS...SRN/ERN OK AND WRN
ARKANSAS...DISCRETE STORMS ARE ALSO LIKELY TO DEVELOP
BY LATE AFTERNOON IN STRENGTHENING DIFFLUENCE ALOFT AND CONSEQUENT
LOW-LEVEL CONVERGENCE/WARM ADVECTION WITHIN INTENSIFYING /50-70 KT/
850 JET CORE. EFFECTIVE SHEAR AT 40-60 KT AND STRONG FORCING WILL BE
SUPPORTIVE OF SUPERCELLS. THERMODYNAMIC PROFILES AND ROTATING STORMS
INDICATE THE MAIN THREAT WILL BE LARGE HAIL. HOWEVER...20-30 KT LOW
LEVEL SHEAR AND LARGE CLOCKWISE CURVED LOW LEVEL HODOGRAPHS WILL
FAVOR TORNADOES...SOME STRONG. HOWEVER...WARM ADVECTION DURING THE
DAY MAY RESULT IN WEAKER CONVECTION THROUGHOUT THE DAY AND
COMPLICATE THE LOCATION AND EVOLUTION OF STRONG CONVECTION LATER IN
THE DAY.

STORMS AND SQUALL WILL SPREAD ENEWD INTO AR/LA/SRN MO OVERNIGHT
...AND POSSIBLY AS FAR EAST AS WRN TN/NWRN MS BY DAYBREAK WED.
DESPITE SOME WEAK NOCTURNAL COOLING VERY STRONG KINEMATICS AND UPPER
SYSTEM FAVOR A HIGH POTENTIAL FOR SEVERE WEATHER... INCLUDING
TORNADOES...TUESDAY NIGHT.

..IMY.. 02/09/2009