DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 131236
SWODY1
SPC AC 131234

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0734 AM CDT MON MAY 13 2013

VALID 131300Z - 141200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM FAR NERN ORE INTO PARTS OF
ERN MT...

...SYNOPSIS...

THE LARGE-SCALE PATTERN WILL DEAMPLIFY THROUGH THE D1 PERIOD OWING
TO THE EWD PROGRESSION OF THE ERN CONUS TROUGH INTO THE WRN
ATLANTIC...AND THE UPSTREAM FLATTENING OF A RIDGE OVER THE CANADIAN
AND NRN ROCKIES. THE PRIMARY FEATURE OF INTEREST WITHIN THIS
BROAD-SCALE REGIME IS A POLAR BRANCH SHORT-WAVE TROUGH AND
ASSOCIATED 70-80 KT MIDLEVEL JET STREAK WHICH WILL TRANSLATE FROM
JUST OFF THE PACIFIC NW COAST TO SRN PARTS OF AB/SK AND THE NRN HIGH
PLAINS BY 14/12Z. IN THE LOW LEVELS...A CHINOOK-TYPE WARM FRONT
WILL CONTINUE EWD ACROSS THE GREAT PLAINS TODAY AHEAD OF A PACIFIC
COLD FRONT AND ATTENDANT SURFACE LOW WHICH WILL ADVANCE THROUGH THE
PACIFIC NW AND NRN INTERMOUNTAIN REGION INTO NRN HIGH PLAINS.

...NRN ROCKIES INTO NRN HIGH PLAINS THIS AFTERNOON INTO TONIGHT...

DAYTIME HEATING COUPLED WITH STEEP MIDLEVEL LAPSE RATES AND PW
VALUES OF 0.6-0.9 INCH WILL CONTRIBUTE TO AT LEAST A MARGINALLY
UNSTABLE AIR MASS TODAY AHEAD OF THE PACIFIC FRONT WITH SBCAPE
VALUES APPROACHING 500-800 J/KG. LATEST MODEL GUIDANCE SUGGESTS
THAT STORM INITIATION WILL OCCUR BY MID TO LATE AFTERNOON WITHIN TWO
SEPARATE REGIMES: 1) ALONG THE COLD FRONT WHERE LOW-LEVEL
CONVERGENCE/ASCENT WILL BE AUGMENTED BY DCVA ATTENDANT TO THE
MIGRATORY SHORT-WAVE TROUGH. THE OTHER INITIATION ZONE /2)/ APPEARS
TO BE FARTHER E OVER THE HIGH PLAINS OF CNTRL MT INVOF THE
DEVELOPING LEE CYCLONE AND WEAK WARM FRONT.

MODEL-DERIVED SOUNDINGS INDICATE THE ENVIRONMENT ALONG THE COLD
FRONT WILL BE CHARACTERIZED BY RELATIVELY COOL THERMODYNAMIC
PROFILES AND STRONG /50-70 KT/ DEEP-LAYER SHEAR WHICH WILL SUPPORT
BOWING LINE SEGMENTS AND PERHAPS SUPERCELLS CAPABLE OF DAMAGING
WINDS AND SEVERE HAIL. OVER CNTRL MT...A DEEPER PBL WITH LARGE T-TD
SPREADS IS ANTICIPATED WITH SLIGHTLY WEAKER --BUT STILL MORE THAN
SUFFICIENT /40-50 KT/-- VERTICAL SHEAR WHICH WILL PROMOTE HIGH-BASED
STORMS INCLUDING SUPERCELLS AND BOWING STRUCTURES WITH A RISK FOR
DAMAGING WINDS AND PERHAPS SOME HAIL. THIS THREAT MAY SPREAD INTO
ERN MT TONIGHT BEFORE THE STORMS GRADUALLY WEAKEN AS THE PBL COOLS
AND DECOUPLES.

...SRN FL THIS AFTERNOON...

A COLD FRONT...CURRENTLY JUST S OF A DAB-OCF LINE...WILL CONTINUE
SWD THROUGH THE REMAINDER OF THE FL PENINSULA BY TONIGHT. THIS
FRONT AND THE DEVELOPING SEA BREEZE BOUNDARIES ARE EXPECTED TO SERVE
AS FOCI FOR STORM DEVELOPMENT THIS AFTERNOON. THE 12Z OBSERVED
SOUNDINGS SHOWED WEAK MIDLEVEL LAPSE RATES WHICH WILL TEMPER THE
DEGREE OF AIR MASS DESTABILIZATION THROUGH THE PEAK OF THE DIURNAL
HEATING CYCLE. NONETHELESS...SUFFICIENT PARCEL BUOYANCY AND
VERTICAL SHEAR WILL EXIST TO SUPPORT MARGINAL STORM ORGANIZATION
WITH A LOW-PROBABILITY RISK OF DAMAGING WINDS.

..MEAD/MOSIER.. 05/13/2013

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