DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 241929
SWODY1
SPC AC 241928

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0228 PM CDT TUE APR 24 2012

VALID 242000Z - 251200Z

...NO SVR TSTM AREAS FORECAST...

EARLIER THOUGHTS REGARDING THE EVOLUTION OF CONVECTION ACROSS THE
NRN ROCKIES INTO THE NRN HIGH PLAINS REMAIN. GREATEST POCKET OF
INSTABILITY...ON THE ORDER OF 1000 J/KG MLCAPE...CURRENTLY RESIDES
ACROSS ERN WA INTO NRN ID AND ISOLATED THUNDERSTORMS ARE BEGINNING
TO DEVELOP OVER THE HIGHER TERRAIN OF SHOSHONE/CLEARWATER/IDAHO
COUNTIES. SUBSTANTIAL SHEAR IS IN PLACE FOR THIS ACTIVITY TO SPREAD
DOWNSTREAM INTO MT WHERE VERY STEEP LAPSE RATES RESIDE.

FARTHER SOUTH...HAVE INCREASED THUNDERSTORM PROBABILITIES ACROSS
MUCH OF THE SRN ROCKIES TO ACCOUNT FOR VERY HIGH BASED CONVECTION
THAT IS DEVELOPING ACROSS THIS REGION. LATEST LIGHTING DATA SUGGEST
THESE UPDRAFTS ARE ATTAINING LEVELS SUFFICIENT FOR DISCHARGE AND
ISOLATED TSTMS WILL BE NOTED INTO THE EARLY EVENING HOURS.

..DARROW.. 04/24/2012

.PREV DISCUSSION... /ISSUED 1129 AM CDT TUE APR 24 2012/

...SYNOPSIS...
THE DEEP OCCLUDED LOW N OF LAKE ONTARIO WILL CONTINUE TO MOVE NWD
TOWARD JAMES BAY...WHILE A DEEP TROUGH WILL PERSIST OVER THE
ATLANTIC COAST. FARTHER W...THE PERSISTENT RIDGE OVER THE
INTERMOUNTAIN WEST IS BEGINNING TO BREAK DOWN AND SHIFT EWD TOWARD
THE HIGH PLAINS...AS ONE UPSTREAM SHORTWAVE APPROACHES SRN CA AND
ANOTHER TROUGH DIGS SEWD FROM THE GULF OF ALASKA TOWARD THE PAC NW
COAST. STEEP LAPSE RATES CONTINUE ACROSS THE INTERMOUNTAIN WEST AS
A RESULT OF STRONG SURFACE HEATING/MIXING THE PAST SEVERAL
DAYS...AND AN ELEVATED MIXED LAYER IS NOW OVERSPREADING THE PLAINS.

...NRN ROCKIES TO NRN HIGH PLAINS THIS AFTERNOON/EVENING...
12Z SOUNDINGS FROM BOI AND OTX SHOWED PW VALUES NEAR 0.80 INCH AND
THE POTENTIAL FOR MLCAPE NEAR 500 J/KG WITH DAYTIME HEATING OVER THE
HIGHER TERRAIN. ADDITIONALLY...A SERIES OF SUBTLE EMBEDDED SPEED
MAXIMA WILL EJECT NWD AND EWD AROUND THE NWRN PERIPHERY OF THE
RIDGE...CONTRIBUTING TO A FAVORABLE ENVIRONMENT FOR THUNDERSTORM
DEVELOPMENT THIS AFTERNOON ACROSS THE NRN ROCKIES. DEEP-LAYER
UNIDIRECTIONAL PROFILES WITH SOME SPEED SHEAR WILL SUPPORT MULTICELL
CLUSTERS...WHILE THE STEEP LAPSE RATES AND MODEST BUOYANCY WILL
SUPPORT A RISK FOR ISOLATED STRONG/DAMAGING WINDS AND SMALL HAIL
THIS AFTERNOON/EVENING.

SOME OF THE CONVECTION OVER THE MOUNTAINS COULD PROGRESS EWD/ENEWD
INTO THE STEEP LAPSE RATE ENVIRONMENT ACROSS MT WITH AN ATTENDANT
RISK FOR ISOLATED STRONG GUSTS WITH THE HIGH-BASED STORMS. FARTHER
E INTO WRN ND...SURFACE HEATING/MIXING COULD SUFFICIENTLY REDUCE
CONVECTIVE INHIBITION TO ALLOW ISOLATED STORM DEVELOPMENT NEAR THE
LEE TROUGH/CYCLONE LATE THIS AFTERNOON. INVERTED-V PROFILES WILL
SUPPORT SOME POTENTIAL FOR ISOLATED DAMAGING GUSTS...AND PERHAPS
SOME HAIL.

...CENTRAL PLAINS TO THE LOWER OH VALLEY THROUGH TONIGHT...
MORNING SOUNDINGS AND RECENT SURFACE OBSERVATIONS SHOW LIMITED
LOW-LEVEL MOISTURE FROM N TX TO KS/MO...AND THE SHORT-TERM MODEL
FORECASTS OF NEAR 60 F BOUNDARY LAYER DEWPOINTS BY MID AFTERNOON
APPEAR OVERDONE. THIS ALSO SUGGESTS THAT THE MOISTURE FEED JUST
ABOVE THE SURFACE INTO THE MID MS/LOWER OH VALLEY WAA ZONE WILL
REMAIN MARGINAL...SUCH THAT IT IS UNLIKELY THAT BUOYANCY WILL BECOME
SUFFICIENT FOR A SEVERE STORM RISK. MEANWHILE..STRONG SURFACE
HEATING WILL OCCUR ACROSS THE PLAINS...THOUGH WARMING TEMPERATURES
ABOVE THE SURFACE WILL TEND TO LIMIT THE DEPTH OF VERTICAL MIXING
AND MAINTAIN A CAP OVER THE ERN PLAINS. FARTHER W...TEMPERATURES IN
THE 90S WILL RESULT IN SURFACE MIXED LAYER EXTENDING AS HIGH AS 500
MB...AND A FEW DRY THUNDERSTORMS WILL BE POSSIBLE THIS AFTERNOON
ACROSS THE CENTRAL HIGH PLAINS.

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