February 10, 2009 Central Oklahoma Tornado Outbreak

We did not chase this day, since most of the severe weather came to OKC during the workday.
Here’s the SPC Day 1 Outlook

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1021 AM CST TUE FEB 10 2009

VALID 101630Z – 111200Z

…THERE IS A MDT RISK OF SVR TSTMS OVER PORTIONS OF CENTRAL/EASTERN
OK…NORTH CENTRAL AND NORTHEAST TX…NORTHWEST LA…AND MUCH OF
AR…

…THERE IS A SLGT RISK OF SVR TSTMS OVER MUCH OF THE SOUTHERN
PLAINS AND LOWER/MID MS VALLEY…

…A SIGNIFICANT SEVERE WEATHER OUTBREAK — INCLUDING SUPERCELLS
WITH STRONG TORNADOES — IS EXPECTED THIS AFTERNOON INTO TONIGHT FOR
ERN OK/NE TX…INTO WRN/CENTRAL AR AND NW LA…

MORNING WATER VAPOR SHOWS A VIGOROUS AND DIGGING SHORTWAVE TROUGH
OVER EASTERN AZ.  THIS FEATURE WILL ROTATE INTO TX THIS
EVENING…WHILE 110+ KT MID LEVEL JET NOSES INTO THE BIG BEND
REGION.  PARAMETERS REMAIN VERY FAVORABLE FOR NUMEROUS SEVERE
THUNDERSTORMS ACROSS PARTS OF THE SOUTHERN PLAINS THIS AFTERNOON AND
TONIGHT WITH A RISK OF WIDESPREAD DAMAGING WINDS…STRONG
TORNADOES…AND LARGE HAIL.

15Z SURFACE ANALYSIS SHOWS LOW LEVEL MOISTURE RETURNING RAPIDLY
NORTHWARD ACROSS EAST TX INTO OK/AR.  BY MID AFTERNOON…IT APPEARS
LIKELY THAT THE SURFACE DRYLINE WILL BECOME ESTABLISHED ROUGHLY
ALONG A LINE FROM W OF OKC…LAW…ABI.  HIGH CLOUDS ARE CLEARING
OUT OF THIS REGION…AND LOW CLOUDS WILL SLOWLY ERODE THIS MORNING.
THIS WILL ALLOW RELATIVELY STRONG HEATING ALONG THE DRYLINE AND LEAD
TO AFTERNOON MLCAPE VALUES AROUND 1000 J/KG.  FARTHER EAST…GREATER
LOW LEVEL MOISTURE WILL OFFSET MORE CLOUD COVER WITH MLCAPE OF OVER
1000 J/KG EXPECTED.

…DRYLINE INITIATION OK/TX…
GIVEN LATEST MODEL GUIDANCE AND OBSERVATIONAL TRENDS…
THUNDERSTORMS ARE EXPECTED TO DEVELOP 20-22Z ALONG DRYLINE OVER
WESTERN OK AND NORTHWEST TX.  THESE STORMS WILL LIKELY BE
SUPERCELLULAR WITH A RISK OF VERY LARGE HAIL AND TORNADOES.  THE
STORMS WILL BECOME MORE NUMEROUS BY EARLY EVENING /AFTER DARK/ AND
TRACK NORTHEASTWARD INTO NORTHEAST TX AND EASTERN OK.  MUCH STRONGER
VERTICAL SHEAR PROFILES IN THIS REGION /EFFECTIVE HELICITY OF 400+
M2/S2/ WILL ALSO INCREASE THE RISK OF STRONG TORNADOES.  HAVE CHOSEN
TO MAINTAIN CATEGORICAL MODERATE RISK FOR THIS AFTERNOON DUE TO
CONTINUED CONCERNS OVER THE QUALITY OF LOW LEVEL MOISTURE…BUT AN
UPGRADE TO HIGH RISK WILL REMAIN POSSIBLE AT 20Z.

…MAIN SQUALL LINE TX/EASTERN OK…
BY LATE AFTERNOON…THE PRIMARY UPPER FORCING WILL ARRIVE ALONG THE
DRYLINE/PACIFIC FRONT OVER NORTHWEST TX.  THIS WILL LIKELY RESULT IN
THE RAPID DEVELOPMENT OF AN INTENSE SQUALL LINE.  THIS ACTIVITY IS
EXPECTED TO TRACK EASTWARD ACROSS NORTH-CENTRAL AND CENTRAL TX
DURING THE EVENING WITH A RISK OF WIDESPREAD DAMAGING WINDS.  LOW
AND DEEP LAYER VERTICAL SHEAR PROFILES WILL BE VERY FAVORABLE FOR
EMBEDDED MESOCYCLONES AND THE RISK OF TORNADOES.  FORECAST SOUNDINGS
ALSO SUGGEST ONLY A WEAK CAP AHEAD OF THE SQUALL LINE…POSING THE
RISK OF MORE DISCRETE TORNADIC SUPERCELLS DURING THE EVENING.
STRONG TORNADOES WILL BE POSSIBLE OVER THIS REGION AS WELL.

…OVERNIGHT LA/AR/MO…
WIDESPREAD THUNDERSTORMS WILL ACCELERATE THROUGH THE EVENING AND
SWEEP EASTWARD INTO PARTS OF LA/AR/MO OVERNIGHT.  THE 500MB JET MAX
WILL INCREASE TO OVER 120 KT DURING THIS PERIOD…SUGGESTING A
CONTINUED RISK OF WIDESPREAD DAMAGING WINDS AND EMBEDDED TORNADOES
THROUGH MUCH OF THE NIGHT.  STORMS MAY REACH SOUTHERN IL/WEST
TN/NORTHWEST MS BY 11/12Z.

…NORTHERN OK/SOUTHERN KS…
MODEL GUIDANCE SUGGESTS THAT PRIMARY SURFACE LOW WILL BECOME
ESTABLISHED BY LATE AFTERNOON OVER SOUTHWEST KS…WITH BACKED LOW
LEVEL WINDS AND INCREASING MOISTURE INTO PARTS OF NORTHWEST
OK/SOUTHERN KS.  FULL SUNSHINE WILL LEAD TO STEEP LOW LEVEL LAPSE
RATES AND SUFFICIENT INSTABILITY FOR THE DEVELOPMENT OF ISOLATED
THUNDERSTORMS BY EARLY EVENING.  VERTICAL SHEAR PROFILES ARE WEAKER
IN THIS REGION THAN FARTHER SOUTHEAST.  HOWEVER… PARAMETERS
SUGGEST THE RISK OF A FEW SUPERCELLS CAPABLE OF LARGE HAIL AND
ISOLATED TORNADOES.

..HART.. 02/10/2009

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