
MESOSCALE DISCUSSION 0411
NWS STORM PREDICTION CENTER NORMAN OK
1247 PM CDT THU APR 09 2009
AREAS AFFECTED...ERN OK
CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY
VALID 091747Z - 092015Z
SEVERE STORMS ARE EXPECTED TO DEVELOP OVER E CNTRL OK BY 20-21Z.
THREAT WILL EXIST FOR SUPERCELLS CAPABLE OF PRODUCING LARGE HAIL AND
A FEW TORNADOES. TORNADO WATCH WILL LIKELY BE NEEDED BY 19-20Z.
THIS AFTERNOON A SHARPENING DRYLINE EXTENDS FROM DEEPENING SURFACE
LOW IN SW KS SEWD THROUGH CNTRL OK THEN SWWD THROUGH N CNTRL AND W
CNTRL TX. EAST OF THE DRYLINE...MULTILAYER CLOUD DECK WITH EMBEDDED
CONVECTION IS ADVANCING RAPIDLY EAST...ALLOWING FOR A CORRIDOR OF
PARTIAL CLEARING AND DIABATIC HEATING FROM N CNTRL TX THROUGH E
CNTRL OK. AXIS OF MID-UPPER 50S DEWPOINTS IS ADVECTING RAPIDLY NWD
THROUGH ERN OK BENEATH VERY STEEP 8+ C/KM MID LEVEL LAPSE RATES. AS
THE BOUNDARY LAYER CONTINUES TO WARM...MLCAPE FROM 1500-2000 J/KG
WILL LIKELY DEVELOP LATER THIS AFTERNOON. OBJECTIVE ANALYSIS
INDICATES THE ATMOSPHERE IS STILL CAPPED DUE TO PRESENCE OF THE WARM
EML. HOWEVER...AS AGEOSTROPHIC FORCING FOR ASCENT WITHIN EXIT REGION
OF APPROACHING UPPER JET BEGINS TO OVERTAKE THE CONVERGENCE AXIS
ALONG THE DRYLINE...THE CAPPING LAYER WILL LIKELY MOISTEN AND COOL
SUFFICIENTLY FOR CONVECTIVE INITIATION BY 20-21Z. COUPLED LOW-MID
LEVEL JET STRUCTURE WILL MAINTAIN LARGE LOW-LEVEL HODOGRAPHS AND
FAVORABLE BULK SHEAR FOR SUPERCELLS CAPABLE OF PRODUCING VERY LARGE
HAIL AND TORNADOES...INCLUDING POTENTIAL FOR ISOLATED STRONG
TORNADOES.
..DIAL.. 04/09/2009
ATTN...WFO...TSA...OUN...

MESOSCALE DISCUSSION 0412
NWS STORM PREDICTION CENTER NORMAN OK
1257 PM CDT THU APR 09 2009
AREAS AFFECTED...PARTS OF SRN KS / NRN OK
CONCERNING...SEVERE POTENTIAL...WATCH LIKELY
VALID 091757Z - 091900Z
SURFACE-BASED INITIATION IS POSSIBLE IN THE 1930-2100Z PERIOD ACROSS
PARTS OF SRN KS AND EXTREME NRN OK. LARGE HAIL AND ISOLD TORNADOES
WILL BE THE PRIMARY THREATS ONCE STORMS ORGANIZE AND MOVE INTO
MOISTURE AXIS.
LATEST SATELLITE IMAGERY SHOWS AREA OF IMPLIED ASCENT PUSHING EWD
OVER THE OK/TX PANHANDLES AS CU FIELD DEVELOPS OVER NWRN OK WITHIN
POST-DRYLINE THERMAL AXIS. SUBSTANTIAL LOW LEVEL MASS/MOISTURE
CONVERGENCE OVER THE OK/KS BORDER IS OCCURRING ALONG SLOWLY
RETREATING WARM FRONT/BULGING DRYLINE AHEAD OF DEEPENING SURFACE
CYCLONE SITUATED OVER SWRN KS. LATEST RUC FORECAST SOUNDINGS
INDICATE UNCAPPED SURFACE-BASED PARCELS AS EARLY AS 19-20Z. AS ZONE
OF STRONGER HEIGHT FALLS/DEEP ASCENT OVERSPREAD HIGHLIGHTED REGION
CONCURRENT WITH FURTHER DIABATIC HEATING--WILL RESULT IN STORMS
LIKELY INITIATING NEAR ABOVE DESCRIBED INTERSECTING BOUNDARIES.
ONCE STORMS DEVELOP...NNE-NELY STORM MOTIONS WILL ENABLE STORMS TO
CROSS INTO WELL DEFINED THETA-E AXIS ACROSS NRN OK EXTENDING NWWD
INTO SRN KS WITHIN BACKED LOW LEVEL FLOW. WITH RAPIDLY COOLING
MID-LEVEL PROFILES /-20 DEG C AT 500 MB PER LATEST DETERMINISTIC
OUTPUT/ WILL RESULT IN POTENTIAL MODERATE INSTABILITY /SBCAPE
1000-2500 J/KG/. LARGE LOW LEVEL VORTICITY INVOF DESCRIBED
BOUNDARIES AND ENHANCED CONVERGENCE WILL AUGMENT UPDRAFTS IN
VICINITY OF WARM FRONT/DRYLINE BULGE LEADING TO THE RISK OF ISOLD
TORNADOES...IN ADDITION TO LARGE HAIL.
..SMITH.. 04/09/2009
ATTN...WFO...SGF...TSA...TOP...ICT...OUN...DDC...