SWODY1
SPC AC 091612
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1112 AM CDT MON MAY 09 2011
VALID 091630Z - 101200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF ERN WY...NWRN
NEB INTO PARTS OF THE DAKOTAS...
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE MID MS AND OH
VALLEYS...
...SYNOPSIS...
COLD UPPER LOW NWRN NV WILL CONTINUE DROPPING SSEWD TO NEAR LAS BY
12Z TUE AND IN THE PROCESS EJECT A SIGNIFICANT IMPULSE NEWD ACROSS
CENTRAL ROCKIES TO HIGH PLAINS. DOWNSTREAM UPPER RIDGE SHIFTS ONLY
SLOWLY EWD ACROSS MS VALLEY.
SURFACE LOW OVER CENTRAL NEB WILL MOVE ONLY SLOWLY NWD INTO SD AS
SECONDARY SURFACE LOW NOW NWRN CO WITH STRONG COLD FRONT EXTENDING
SWD ALONG CO/UT BORDER MOVES NEWD ACROSS CENTRAL ROCKIES THIS
AFTERNOON.
MUCH OF THE PLAINS STATES WILL BE CAPPED UNDER THE UPPER RIDGE BY A
PRONOUNCED EML WITH LAPSE RATES IN EXCESS OF 8C/KM EXTENDING EWD TO
THE LOWER OH/TN VALLEYS.
...NRN HIGH PLAINS...
AS THE MIDLEVEL VORTICITY MAXIMUM CURRENTLY SRN UT AND ASSOCIATED
JET STREAK TRANSLATES NNEWD INTO THE NRN HIGH PLAINS BY
TONIGHT...THE SURFACE LOW CURRENTLY OVER WRN NEB MAY DRIFT INTO
N-CNTRL NEB BY AFTERNOON WITH SECONDARY CYCLONE DEVELOPMENT FORECAST
OVER NERN CO. THIS SECONDARY LOW WILL THEN DEVELOP NEWD TO CNTRL OR
ERN SD BY 10/12Z WHILE ASSOCIATED WARM FRONT SLOWLY PIVOTS NWD/NEWD
THROUGH THE MID MO VALLEY.
WITH THE PRESENCE OF STEEP MIDLEVEL LAPSE RATES AND 850 MB DEWPOINTS
OF 10-12 C WRAPPING AROUND SURFACE LOW IT WILL SUPPORT MODERATE
ELEVATED INSTABILITY LATER THIS AFTERNOON WITH MUCAPE VALUES
APPROACHING 1000-2000 J/KG WWD INTO WRN SD/NERN WY.
LOW-LEVEL UPSLOPE FLOW COUPLED WITH INCREASING DCVA IN ADVANCE OF
MIDLEVEL IMPULSE ARE EXPECTED TO FOSTER SCATTERED TSTMS BY AFTERNOON
ACROSS ERN WY...THE NEB PNHDL AND WRN SD WITHIN A KINEMATIC
ENVIRONMENT FEATURING 40-50 KT OF DEEP SLY SHEAR. A FEW SEVERE
THUNDERSTORMS SHOULD DEVELOP BY MID/LATE AFTERNOON ERN BORDER AREA
OF WY AS FRONT AND LARGE SCALE ASCENT WITH UPPER VORT ENCOUNTER THE
MORE FAVORABLE THERMODYNAMIC ENVIRONMENT. PRIMARY THREAT WILL BE
LARGE HAIL...HOWEVER DAMAGING WINDS ALONG WITH AN ISOLATED
SUPERCELL/TORNADO THREAT WILL SPREAD NWD/NEWD INTO CNTRL SD AND SRN
PARTS OF ND OVERNIGHT WITHIN INTENSIFYING LOW-LEVEL WAA REGIME.
...MID MS/OH VALLEYS...
AS DISCUSSED IN PREVIOUS OUTLOOK THE CONVECTIVE EVOLUTION REMAINS
MORE UNCERTAIN DUE TO PROXIMITY OF REGION TO MIDLEVEL RIDGE AXIS.
THE PRESENCE OF BOUNDARY LAYER DEWPOINTS IN THE 60S AND DRY
ADIABATIC MIDLEVEL LAPSE RATES WILL LEAD TO AFTERNOON MLCAPE VALUES
APPROACHING 3000-4000+ J/KG ALONG AND W OF NW-SE ORIENTED WARM FRONT
WHICH EXTENDS FROM IA TO WRN TN VALLEY.
AREAS OF ONGOING ELEVATED STORMS FROM ERN MO NWD TO THE MORE
ORGANIZED MCS FROM NERN IA INTO WRN WI WILL BE CAPABLE OF
HAIL THROUGH THE EARLY AFTERNOON GIVEN THE VERY STEP
MIDLEVEL LAPSE RATES ALREADY IN PLACE. AS THE STRONG HEATING
DIMINISHES THE CINH ACROSS MID MS VALLEY STORMS MAY BECOME ROOTED IN
THE BOUNDARY LAYER THIS AFTERNOON OVER ERN MO/WRN IL WITH ACTIVITY
GROWING UPSCALE INTO A SEWD-MOVING MCS CAPABLE OF DAMAGING WINDS AND
HAIL. STILL MIXED SIGNALS ON MODEL OUTPUT REGARDING THE SEVERE
THREAT CONTINUING TOWARD THE TN VALLEY GIVEN THE EXPECTED GRADUAL
WEAKENING AND BACKING OF THE LOW LEVEL FLOW AND ASSOCIATED WARM
ADVECTION. BUT WITH THE DEVELOPMENT OF STRONG INSTABILITY...IF THE
CURRENT MCS NOW MOVING SEWD FROM IA/WI CAN TAP INTO THE BOUNDARY
LAYER A MORE ORGANIZED SEVERE THREAT INCLUDING WIND DAMAGE COULD
DEVELOP TOWARD THE TN VALLEY BY THIS EVENING.
...SWRN TX...
A HOT AND DEEPLY MIXED BOUNDARY LAYER IS EXPECTED TO ONCE AGAIN
DEVELOP TODAY INVOF DRYLINE. DEEP-LAYER VERTICAL SHEAR WILL REMAIN
ON THE MARGINS OF THAT SUPPORTIVE OF ORGANIZED UPDRAFTS /30 KT/.
HOWEVER...THE PRESENCE OF STEEP LOW TO MIDLEVEL LAPSE RATES AND
2000-3000 J/KG MLCAPE WILL FOSTER STRONG UPDRAFTS CAPABLE OF HAIL
AND LOCALLY DAMAGING WINDS. ANY STORMS THAT DEVELOP SHOULD REMAIN
RATHER ISOLATED AND DISSIPATE BY EVENING AS THE BOUNDARY LAYER COOLS
AND THE CONVECTIVE INHIBITION INCREASES.
..HALES/COHEN.. 05/09/2011
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