DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 271611
SWODY1
SPC AC 271609

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1109 AM CDT THU SEP 27 2012

VALID 271630Z - 281200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF THE CNTRL
AND SRN HIGH PLAINS...

...THERE IS A SLGT RISK OF SVR TSTMS OVER A SMALL PART OF THE MID
ATLANTIC STATES...

...SYNOPSIS...

A SPLIT FLOW PATTERN WILL CONTINUE THROUGH THE DAY-1
PERIOD...CHARACTERIZED BY THE POLAR BRANCH OF WESTERLIES ACROSS
CANADA AND THE NERN STATES...AND A LOWER-LATITUDE BRANCH OF HIGHER
MOMENTUM FLOW FROM THE SRN ROCKIES TO MID-ATLANTIC COAST. WITHIN
THIS BROADER-SCALE PATTERN...A COUPLE OF MORE SALIENT SHORTWAVE
TROUGHS/VORTICITY MAXIMA ARE PRESENT. THE FIRST WILL TRANSLATE FROM
THE MID/UPPER-OH VALLEY INTO THE MID-ATLANTIC STATES BY THIS EVENING
INTO TONIGHT. THE OTHER IS A WEAKENING UPPER LOW WHICH WILL SHEAR
SEWD INTO THE CNTRL HIGH PLAINS TODAY.

IN THE LOW-LEVELS...A SURFACE CYCLONE ASSOCIATED WITH THE FORMER
DISTURBANCE MENTIONED ABOVE WAS ANALYZED OVER SWRN OH AS OF 15Z.
THIS FEATURE IS FORECAST TO TRACK ENEWD ALONG ASSOCIATED SURFACE
FRONT...REACHING ERN PA/MD BY 28/12Z. MEANWHILE...A TRAILING COLD
FRONT WILL SETTLE SLOWLY SWD THROUGH THE OH VALLEY AND OZARKS WITH
WRN EXTENSION OF BOUNDARY OBSCURED BY CONSIDERABLE CONVECTIVE
OUTFLOW ACROSS THE SRN PLAINS.

...CNTRL/SRN HIGH PLAINS THIS AFTERNOON INTO TONIGHT...

OUTFLOW FROM NOCTURNAL TSTM DEVELOPMENT HAS RESULTED IN THE WWD/NWWD
ADVECTION OF A RELATIVELY MOIST BOUNDARY LAYER INTO ERN PARTS OF
CO/NM WHERE DEWPOINTS ARE COMMONLY IN THE LOW/MID 50S. THIS
MOISTURE COINCIDES WITH AN EML WHICH HAS BEEN MAINTAINED IN THE
IMMEDIATE LEE OF THE ROCKIES WHICH SHOULD ALLOW FOR MODEST AIR MASS
DESTABILIZATION /I.E. MLCAPE OF 500-1000 J PER KG/...ESPECIALLY
WHERE STRONGER DAYTIME HEATING CAN OCCUR.

THE COMBINATION OF LOW-LEVEL UPSLOPE FLOW AND DCVA ATTENDANT TO CO
DISTURBANCE ARE EXPECTED TO FOSTER AN INCREASE IN STORM COVERAGE AND
VIGOR BY MID TO LATE AFTERNOON. DEEP-LAYER SHEAR IS FORECAST TO BE
SLIGHTLY WEAKER THAN THAT ON WED...THOUGH VERTICALLY VEERING WIND
PROFILES AND A 30-40 KT BULK WIND DIFFERENCE IN THE 0-6 KM LAYER ARE
STILL EXPECTED. AS SUCH...THE SETUP WILL BE SUPPORTIVE OF
ORGANIZED/ROTATING STORMS CAPABLE OF HAIL AND DAMAGING WIND GUSTS.

...MID-ATLANTIC STATES THIS AFTERNOON INTO EVENING...

HIGHER WIND PROBABILITIES AND A SMALL CATEGORICAL SLIGHT RISK HAVE
BEEN INTRODUCED INTO THE REGION BASED ON THE ANTICIPATED ENHANCEMENT
IN CONVECTIVE DEVELOPMENT THIS AFTERNOON BY ABOVE-MENTIONED
SHORTWAVE TROUGH. CURRENT VISIBLE SATELLITE SUGGESTS THAT AREA
SHOULD EXPERIENCE RELATIVELY STRONG DAYTIME HEATING...WHICH WHEN
COUPLED WITH BOUNDARY LAYER DEWPOINTS IN THE LOW TO MID 60S WILL
YIELD AFTERNOON MLCAPE VALUES APPROACHING 1000-1500 J/KG.
MOREOVER...LOCALLY BACKED NEAR-SURFACE WINDS INVOF THE SURFACE FRONT
WILL ALIGN WITH 25-30 KT WLY WINDS IN THE MIDLEVELS...RESULTING IN A
VERTICALLY VEERING WIND PROFILE WITH 30-35 KT OF BULK WIND
DIFFERENCE IN THE 0-6 KM LAYER. THIS TYPE OF ENVIRONMENT WILL BE
SUPPORTIVE OF SOME STORM ORGANIZATION WITH THE PRIMARY HAZARD BEING
DAMAGING WIND GUSTS.

...LOWER ELEVATIONS OF THE SRN PLAINS INTO TN VALLEY THIS AFTERNOON
INTO EVENING...

ONE OR MORE STORM CLUSTERS MAY EVOLVE TODAY ALONG/S OF COMPOSITE
SYNOPTIC FRONT-OUTFLOW BOUNDARY. WHILE THE BOUNDARY LAYER REMAINS
MOIST...MIDLEVEL LAPSE RATES HAVE WEAKENED COMPARED TO PAST
DAYS...WHICH SHOULD LIMIT THE DEGREE OF AIR MASS DESTABILIZATION.
NONETHELESS...ISOLATED OCCURRENCES OF MAINLY DAMAGING WIND GUSTS
WILL BE POSSIBLE AS AGGREGATE COLD POOLS STRENGTHEN/DEEPEN LATER
TODAY INTO THIS EVENING.

..MEAD/MOSIER.. 09/27/2012

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