Schweizer Sturmforum

IN THIS ENVIRONMENT...STORMS SHOULD REMAIN
DISCRETE FOR THE LATE AFTERNOON AND EARLY EVENING HOURS. IN
ADDITION...LCL HEIGHTS ARE FORECAST TO REMAIN LOW WHICH COMBINED
WITH THE INSTABILITY AND STRONG LOW-LEVEL SHEAR WILL BE VERY
FAVORABLE FOR TORNADOES. LONG-TRACK STRONG OR EVEN VIOLENT TORNADOES
WILL BE POSSIBLE ESPECIALLY WITH SUPERCELLS THAT TRACK ALONG ANY
PRE-EXISTING BOUNDARIES OR CONVERGENCE ZONES.

MESOSCALE DISCUSSION 0454
NWS STORM PREDICTION CENTER NORMAN OK
1047 AM CDT FRI APR 07 2006

AREAS AFFECTED...ERN AR...NERN LA...CNTRL AND NRN MS...CNTRL AND NRN
AL

CONCERNING...SEVERE THUNDERSTORM POTENTIAL

VALID 071547Z - 071745Z

THUNDERSTORMS ARE EXPECTED TO DEVELOP OVER PORTIONS OF THE LOWER MS
VALLEY AND SPREAD EWD DURING THE DAY. SUPERCELLS WITH VERY LARGE
HAIL AND A FEW STRONG TORNADOES WILL BE THE PRIMARY THREATS. A WW
WILL LIKELY BE NEEDED FOR MUCH OF THIS AREA WITHIN THE HOUR.

THIS MORNING AN AXIS OF RICHER LOW LEVEL MOISTURE WITH DEWPOINTS IN
THE LOW TO MID 60S HAS SPREAD NEWD THROUGH THE LOWER MS VALLEY. THE
LATEST VISIBLE IMAGERY CONTINUES TO SHOW EXTENSIVE STRATUS.
HOWEVER...MIXING IS INCREASING AROUND THE EDGES OF THIS STRATUS DECK
WITH CLOUDS BECOMING MORE CONVECTIVE IN NATURE ACROSS ERN AR. THE
SPECIAL 14Z RAOB FROM JACKSON MS SHOWED SOME COOLING HAS OCCURRED IN
THE 850-700 MB LAYER WITH LITTLE CAP REMAINING. THIS SUGGEST ONLY A
MODEST AMOUNT OF SURFACE HEATING IS NEEDED WITHIN THE MOIST AXIS TO
PROMOTE SURFACE BASED THUNDERSTORM INITIATION. THE ATMOSPHERE WILL
CONTINUE TO DESTABILIZE AS STEEP MID LEVEL LAPSE RATES ADVECT EWD
ABOVE THE WARMING BOUNDARY LAYER. STORMS ARE EXPECTED TO DEVELOP
INITIALLY OVER SERN AR AND NRN MS THEN SPREAD EWD. A 30-40 KT SWLY
LOW LEVEL JET WILL PERSIST DOWNSTREAM FROM SEWD ADVANCING UPPER
TROUGH. THIS FEATURE AND A STRONG WSWLY MID LEVEL JET WILL
CONTRIBUTE TO FAVORABLE LOW LEVEL AND DEEP LAYER SHEAR FOR
SUPERCELLS. GIVEN THE NATURE OF THE THERMODYNAMIC AND KINEMATIC
PROFILES AND EXPECTED DISCRETE MODES...A FEW STRONG TORNADOES WILL
BE POSSIBLE.

..DIAL.. 04/07/2006

DISCUSSION...VERY POTENT TORNADIC SUPERCELL ENVIRONMENT IN PLACE
ACROSS TN VALLEY AHEAD OF DEEP SURFACE LOW OVER NERN KS. STRONG
DEEP LAYER SHEAR...VERY STEEP MID LEVEL LAPSE RATES...AND MDT TO
STRONG INSTABILITY WILL LEAD TO RAPID DEVELOPMENT OF SEVERE
THUNDERSTORMS OVER LOWER OH AND TN VALLEYS BY EARLY AFTERNOON.
TORNADIC SUPERCELLS ARE EXPECTED WITH POTENTIAL FOR VIOLENT/LONG
TRACK TORNADOES.