The SPC issued a Moderate Risk for today, Tuesday April 26th, in Plains

From the SPC:

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1248 AM CDT TUE APR 26 2016

VALID 261200Z – 271200Z

…THERE IS A MDT RISK OF SVR TSTMS FROM PORTIONS OF SRN NEB INTO KS
AND OK…

…THERE IS AN ENH RISK OF SVR TSTMS FROM THE CNTRL PLAINS SWD INTO
CNTRL TX…

…THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE CNTRL AND SRN PLAINS
INTO THE LOWER MO VALLEY…

…THERE IS A SLGT RISK OF SVR TSTMS FOR PARTS OF THE MID-ATLANTIC
STATES…

…THERE IS A MRGL RISK OF SVR TSTMS FROM THE CNTRL U.S. INTO THE OH
VALLEY AND MID-ATLANTIC STATES…

…SUMMARY…
SIGNIFICANT SEVERE THUNDERSTORMS WILL BE POSSIBLE ACROSS PARTS OF
THE SOUTHERN AND CENTRAL GREAT PLAINS THIS AFTERNOON INTO THE
NIGHTTIME HOURS. TORNADOES…SOME STRONG…WILL BE POSSIBLE…IN
ADDITION TO VERY LARGE HAIL AND DAMAGING WINDS. ADDITIONAL ISOLATED
STRONG TO SEVERE STORMS ARE POSSIBLE ACROSS PARTS OF THE OHIO VALLEY
TO THE MIDDLE ATLANTIC COAST REGION.

…SYNOPSIS…
CLOSED LOW/MID-LEVEL TROUGH OVER THE CNTRL-SRN ROCKIES WILL PIVOT
INTO THE PLAINS TODAY AND ACQUIRE A NEGATIVE TILT. A STRONG H5
70-KT JET WILL MOVE INTO THE CNTRL-SRN PLAINS STATES…WHILE A
MID-LEVEL SPEED MAX OVER THE LOWER GREAT LAKES MOVES EWD INTO
PORTIONS OF THE NORTHEAST TO THE S OF AN AMPLIFYING LARGER-SCALE
TROUGH OVER ERN CANADA. A LEE CYCLONE WILL REMAIN QUASI-STATIONARY
DURING THE DAY OVER THE CNTRL HIGH PLAINS BEFORE SLOWLY DEVELOPING
EWD ALONG THE NEB/KS BORDER. A TRIPLE POINT NEAR THE KS/NEB BORDER
WILL FEATURE A WARM FRONT EXTENDING ESEWD THROUGH THE MID MS VALLEY
/PERHAPS SPATIALLY AUGMENTED BY EARLY-DAY CONVECTIVE OUTFLOW/ WHILE
A DRYLINE SHARPENS DURING THE DAY SWD THROUGH KS/OK AND INTO TX.
FARTHER E…A COLD FRONT WILL PROGRESS ESEWD ACROSS PORTIONS OF THE
UPPER OH VALLEY INTO THE MID-ATLANTIC STATES AND THRU THE NJ/NY
COASTAL AREAS PRIOR TO EVENING.

…CNTRL PLAINS INTO THE LOWER MO VALLEY…
ISOLD-SCTD ELEVATED STORMS POSSIBLY ONGOING AT THE START OF THE
PERIOD WILL BE ASSOCIATED WITH A WAA REGIME NEAR A FRONT OVER NRN
KS/MO. THE THREAT FOR ISOLD LARGE HAIL WOULD ACCOMPANY THE STRONGER
UPDRAFTS. A LARGE CONSIDERABLE UNCERTAINTY EXISTS REGARDING THE
AMOUNT OF OUTFLOW AND THE MODIFICATION OF THE AIRMASS NEAR AND N OF
THE POTENTIAL EFFECTIVE BOUNDARY.

SLY LOW-LEVEL FLOW WILL ADVECT INCREASINGLY RICH MOISTURE WITH
SURFACE DEWPOINTS RISING INTO THE MID-UPPER 60S DEG F AND STRONG
HEATING WILL CONTRIBUTE TO STRONGLY TO VERY UNSTABLE CONDITIONS BY
THE AFTERNOON. THE CAP IS FORECAST TO ERODE AS STRONGER FORCING FOR
ASCENT OVERSPREADS THE DESTABILIZING AIRMASS DURING THE AFTERNOON.
MERIDIONAL COMPONENT TO THE MID-LEVEL FLOW IS EXPECTED FARTHER NW AS
FLOW STRENGTHENS. BACKED LOW-LEVEL FLOW NEAR/E OF THE TRIPLE POINT
AND ALONG THE COMPOSITE BOUNDARY WILL ACT TO ENLARGE HODOGRAPHS.
SUPERCELLS –SOME INTENSE– WILL BE CAPABLE OF ALL SEVERE HAZARDS
ACROSS SRN NEB INTO NRN KS NEAR THE BOUNDARY. UNTIL MESOSCALE
DETAILS BECOME LESS NEBULOUS…WILL REFRAIN FROM INTRODUCING HIGHER
TORNADO PROBABILITIES ACROSS SRN NEB/NRN AND NERN KS.

…CNTRL KS INTO OK/TX…
A COMPLICATED SCENARIO MAY UNFOLD THIS AFTERNOON SWD ALONG THE
DRYLINE AND WARM SECTOR. AS A RESULT…THE EXACT EVOLUTION OF STORM
DEVELOPMENT IS SOMEWHAT UNCERTAIN THIS AFTERNOON/EVENING.
NONETHELESS…RICH BOUNDARY-LAYER MOISTURE –SAMPLED BY MONDAY
EVENING SRN PLAINS RAOBS– WILL STREAM NWD BENEATH AN EML WITH VERY
STEEP H7-H5 LAPSE RATES /8-9 DEG C PER KM/. RAPID DESTABILIZATION
IS EXPECTED BY EARLY-MID AFTERNOON AS THE CAP WEAKENS WITH VERY
STRONG TO EXTREME BUOYANCY /3000-4500 J PER KG MLCAPE/ ALONG AND E
OF THE DRYLINE IN THE WARM SECTOR. STRENGTHENING/VEERING WIND
PROFILES WITH HEIGHT WILL YIELD 35-50 KT EFFECTIVE SHEAR. MODELS
CONTINUE TO SUGGEST A LOWER-LATITUDE PERTURBATION AND WEAK ASCENT
COUPLED WITH MOISTENING NEAR THE BASE OF THE CAP MAY ERODE
CONVECTIVE INHIBITION. ISOLD-SCTD STORM DEVELOPMENT MAY RESULT
WITHIN THE FREE WARM SECTOR. FURTHERMORE…STRONG HEATING AND
CONFLUENT LOW-LEVEL FLOW NEAR THE DRYLINE WILL AID IN STORM
DEVELOPMENT ALONG THE DRYLINE FROM KS SWD THRU WRN OK AND INTO WRN
N-CNTRL TX. EXPLOSIVE UPDRAFT DEVELOPMENT WILL STRONGLY FAVOR LARGE
HAIL –LIKELY GIANT HAIL EXCEEDING 3-4 INCHES IN DIAMETER– WITH THE
MORE DOMINANT/DISCRETE SUPERCELLS. WHILE LOW-LEVEL SHEAR APPEARS TO
BE TEMPERED DURING THE AFTERNOON /0-3 KM SRH GENERALLY BELOW 150 M2
PER S2/…SOME STRENGTHENING OF LOW-LEVEL SHEAR DURING THE LATE
AFTERNOON/EARLY EVENING WOULD BECOME MORE FAVORABLE FOR THE
POSSIBILITY FOR STRONG TORNADOES. AS STRONG H5 HEIGHT FALLS
OVERSPREAD THE REGION DURING THE EVENING…MORE WIDESPREAD STORM
DEVELOPMENT AND A CONTINUED RISK FOR ALL SEVERE HAZARDS WILL
PROBABLY CONTINUE INTO THE MID EVENING AND OVERNIGHT HOURS AS
ACTIVITY MOVES EWD AND ADDITIONAL STORMS FORM FARTHER S IN TX.

…OH VALLEY…
SHORTWAVE RIDGING WILL OCCUR DOWNSTREAM OF THE CNTRL U.S. TROUGH
WHILE A COLD FRONT PUSHES SWD INTO THE AREA. STRONG HEATING WILL
LEAD TO WEAK/MODERATE DESTABILIZATION. DIURNAL DEVELOPMENT OF
MULTICELLS MAY YIELD A MARGINAL WIND/HAIL RISK BUT THIS ACTIVITY
WILL LIKELY WEAKEN BY EARLY EVENING AS INSTABILITY WANES.

…PA/NJ AND MID-ATLANTIC STATES…
A COLD FRONT WILL PROGRESS ESEWD DURING THE DAY ACROSS THE REGION.
STRONG HEATING DEVELOPING AHEAD OF THE FRONT WILL STEEPEN 0-2 KM
LAPSE RATES. STRONG WLY MID-LEVEL FLOW /30-50 KT IN THE H7-H5
LAYER/ ATOP A DRY SUB-CLOUD/INVERTED-V PROFILE WILL SUPPORT THE
POTENTIAL FOR STRONG TO LOCALLY SEVERE DAMAGING WIND GUSTS WITH
ISOLD TO WIDELY SCTD STORMS THAT DEVELOP DURING THE AFTERNOON/EARLY
EVENING.

..SMITH/GLEASON.. 04/26/2016

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