SEVERE WEATHER TONIGHT: New Tornado Watch: Memphis, Paducah KY & Little Rock until 3am CDT. Strong tornadoes possible. Update Pg 5.

Storm Prediction Center is calling for a risk of some strong to violent tornadoes today across the Missouri Valley, Arkansas, Mississippi Valley, Houston and Louisiana. Possibly into southern Illinois.

Also, threat for tornadoes in Nebraska & Kansas City area. SPC hints at a possible upgrade to HIGH RISK for areas around Shreveport and Little Rock.


DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0730 AM CDT FRI APR 23 2010

VALID 231300Z - 241200Z

...THERE IS A MDT RISK OF SVR TSTMS THIS AFTERNOON AND EVENING OVER
PORTIONS OF NORTHEAST TX...NORTHERN LA...MUCH OF AR...NORTHERN AND
WESTERN MS...AND WESTERN TN...

...THERE IS A SLGT RISK OF SVR TSTMS OVER MUCH OF THE ARKLATEX AND
LOWER MS VALLEY...ARCING NORTHWESTWARD INTO NEB....

...REGIONAL SEVERE WEATHER OUTBREAK INCLUDING THE POTENTIAL FOR
STRONG TORNADOES IS POSSIBLE TODAY OVER PORTIONS OF THE LOWER MS
VALLEY...

..TX/LA/AR/MS/TN THIS AFTERNOON AND EVENING

MORNING WATER VAPOR LOOPS SHOW A LARGE UPPER LOW IS IN PLACE OVER
THE SOUTHERN ROCKIES. SEVERAL SHORTWAVE TROUGHS ARE ROTATING THROUGH
THE BASE OF THE LOW INTO THE SOUTHERN PLAINS...AND EVENTUALLY INTO
THE MS VALLEY. ONE SUCH FEATURE APPEARS TO BE TRACKING ACROSS EAST
TX WHERE SCATTERED SHOWERS HAVE BEEN INCREASING. THIS ACTIVITY IS
FORECAST TO MOVE INTO PORTIONS OF AR/LA BY LATE MORNING/EARLY
AFTERNOON AND INTENSIFY. A COMBINATION OF DAYTIME HEATING AND RAPID
INFLUX OF NEAR 70F DEWPOINTS WILL YIELD AFTERNOON MLCAPE VALUES OF
2000-3000 J/KG...AND HELP TO PROMOTE VIGOROUS UPDRAFTS. THE
SUBSTANTIAL CAPPING INVERSION SHOWN ON THE 12Z LCH SOUNDING IS
EXPECTED TO WEAKEN BY EARLY AFTERNOON DUE TO LARGE SCALE FORCING AND
COOLING...FURTHER HELPING CONVECTIVE COVERAGE. FORECAST SOUNDINGS
FROM SEVERAL MODELS ALSO INDICATE THAT SUBSTANTIAL LOW LEVEL
VERTICAL SHEAR WILL DEVELOP BY AFTERNOON ACROSS THE MODERATE RISK
AREA /ESRH VALUES OF 300-500 M2/S2 SHOWN BY 00Z/. THE COMBINATION
OF DISCRETE INITIATION OF CONVECTION...AMPLE CAPE AND LAPSE
RATES...STRONG EFFECTIVE SHEAR...AND HIGH HELICITY VALUES GIVE
CONFIDENCE IN MAINTAINING THE FORECAST OF MULTIPLE TORNADOES /SOME
STRONG/ TODAY OVER THE MODERATE RISK AREA. THE CORRIDOR OF GREATEST
RISK APPEARS TO EXTEND ACROSS NORTHERN LA/SOUTHERN AR TO NEAR MEM.
NORTHEASTWARD EXTENT OF SEVERE/TORNADO THREAT IS UNCLEAR AND WILL BE
MODULATED BY RETURN SPEED OF SURFACE-BASED INSTABILITY INTO THAT
REGION.

..NEB/KS/MO THIS AFTERNOON

MODEL GUIDANCE IS IN AGREEMENT THAT A NARROW AXIS OF MODERATE
INSTABILITY WILL DEVELOP THIS AFTERNOON ALONG/AHEAD OF COLD FRONT
FROM CENTRAL/SOUTHEAST NEB INTO EASTERN KS AND WESTERN MO.
SUFFICIENT SURFACE HEATING AND DYNAMIC COOLING ALOFT WILL HELP TO
ERODE CAP AND LEAD TO THE DEVELOPMENT OF SCATTERED THUNDERSTORMS BY
MID/LATE AFTERNOON. ORIENTATION OF DEEP-SHEAR VECTOR NORMAL TO THE
BOUNDARY SUGGEST THE DISCRETE INITIATION IS LIKELY...WITH SUFFICIENT
LOW LEVEL SHEAR FOR A RISK OF A FEW TORNADOES TODAY.
OTHERWISE...SUPERCELLS CAPABLE OF VERY LARGE HAIL AND DAMAGING WINDS
ARE EXPECTED FOR SEVERAL HOURS THIS EVENING.

..EAST TX/LA/AR OVERNIGHT

THE MAIN SHORTWAVE TROUGH CURRENTLY OVER SOUTHERN AZ IS FORECAST TO
BECOME NEGATIVELY TILTED AND ROTATE INTO TX BY SATURDAY MORNING.
THIS IS LIKELY TO RESULT IN THE RAPID DEVELOPMENT OF INTENSE
THUNDERSTORMS ALONG THE COLD FRONT OVER EAST TX...WITH STORMS RACING
EASTWARD TOWARD THE LOWER MS VALLEY BY 12Z. LARGE HAIL...DAMAGING
WINDS...AND TORNADOES WILL ALL BE POSSIBLE WITH THESE STORMS. THIS
ACTIVITY WILL LIKELY BE THE START OF ANOTHER VERY ACTIVE SEVERE
WEATHER DAY OVER PARTS OF MS/LA/TN ON SATURDAY.

..HART/SMITH.. 04/23/2010

Last Edited by Plumas on 04/23/2010 08:04 PM