DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 031933
SWODY1
SPC AC 031931

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0231 PM CDT TUE SEP 03 2013

VALID 032000Z - 041200Z

...NO SVR TSTM AREAS FORECAST...

ASIDE FROM SLIGHT SPATIAL ADJUSTMENTS TO THE GENERAL TSTM AND SEVERE
PROBABILITY LINES...THE CURRENT FORECAST APPEARS ON TRACK WITH NO
SUBSTANTIVE CHANGES MADE.

..MEAD.. 09/03/2013

.PREV DISCUSSION... /ISSUED 1129 AM CDT TUE SEP 03 2013/

...SYNOPSIS...
AN UPPER LOW IS FORECAST TO REMAIN IN PLACE JUST OFF THE PAC NW
COAST THIS PERIOD...WHILE AN EXPANSIVE RIDGE PERSISTS FROM THE S
CENTRAL PORTION OF THE COUNTRY NWD ACROSS THE ROCKIES.
MEANWHILE...SLOW EWD PROGRESS OF THE ERN U.S. UPPER TROUGH IS
EXPECTED.

AT THE SURFACE...A ROUGHLY N-S BAROCLINIC ZONE WILL REMAIN OVER THE
PAC NW...WHILE IN THE EAST A COLD FRONT ADVANCES SLOWLY ACROSS THE
ATLANTIC COAST REGION THROUGH THE PERIOD.

...ERN NEW ENGLAND...
WHILE CLOUD COVER REMAINS FAIRLY EXPANSIVE ACROSS A GOOD PORTION OF
NEW ENGLAND...ADDITIONAL/MODEST PRE-FRONTAL DESTABILIZATION WILL
OCCUR INTO THIS AFTERNOON...SUPPORTING AN INCREASE IN CONVECTIVE
COVERAGE OVER SRN NEW ENGLAND...AND INITIATION OF ISOLATED STORMS
FARTHER N. A CLUSTER OF CELLS ONGOING ATTM INVOF LONG ISLAND MAY
PROVE TO BE THE MOST VIGOROUS CONVECTION OF THE EVENT AS THE
CONVECTION SPREADS/EXPANDS ENEWD ACROSS RI AND SERN MA.
HOWEVER...EXTENSIVE ANVIL DEBRIS WILL HINDER FURTHER DESTABILIZATION
AND THUS SHOULD LIMIT OVERALL SEVERE RISK. GIVEN MID-LEVEL FLOW IN
THE 35 TO 4O KT RANGE ACROSS THIS REGION...A FEW STRONGER CELLS WILL
LIKELY ORGANIZE LOCALLY THIS AFTERNOON. HOWEVER...OVERALL SEVERE
RISK STILL SEEMS LIKELY TO REMAIN BELOW SLIGHT RISK/15% COVERAGE
THRESHOLD.

...ERN NC VICINITY...
STORMS ARE ONGOING ATTM ACROSS PORTIONS OF ERN NC AND ADJACENT SERN
VA...AND ARE FORECAST TO INCREASE/EXPAND IN COVERAGE OVER THE NEXT
1-2 HOURS FROM SERN VA SWWD INTO ERN SC AS A VERY MOIST LOW-LEVEL
AIRMASS CONTINUES TO HEAT/DESTABILIZE. DESPITE LIKELIHOOD FOR
NUMEROUS STORMS BY THIS AFTERNOON...BACKGROUND WIND FIELD IS -- AND
IS EXPECTED TO REMAIN -- GENERALLY UNSUPPORTIVE OF SUBSTANTIAL
CONVECTIVE ORGANIZATION...AND THUS ISOLATED/PULSE-TYPE SEVERE RISK
IS EXPECTED TO BE MOST PREVALENT. STILL...THE DEGREE OF INSTABILITY
AND NUMBER OF STORMS EXPECTED SUGGESTS SOME POTENTIAL FOR UPSCALE
GROWTH DUE TO COLD POOL ORGANIZATION -- WHICH COULD LOCALLY ENHANCE
SEVERE RISK.

THAT SAID...EXPECTED SEVERE WEATHER COVERAGE OVERALL STILL APPEARS
LIKELY TO REMAIN BELOW 15%/SLIGHT RISK THRESHOLD -- AND THUS
PROBABILITY UPGRADE WILL BE LIMITED TO ONLY 5% COVERAGE ATTM. FOR
ADDITIONAL SHORT-TERM DETAILS...PLEASE REFER TO SWOMCD #1831.

...INTERIOR PAC NW...
SCATTERED STORM DEVELOPMENT IS FORECAST ACROSS THE PAC NW
VICINITY...IN CYCLONIC/SSWLY FLOW ALOFT AHEAD OF THE OFFSHORE UPPER
LOW. WITH A RELATIVELY MOIST/HIGH PW AIRMASS IN
PLACE...DIFFERENTIAL HEATING OVER THE HIGHER TERRAIN WILL RESULT IN
AT LEAST MODEST DESTABILIZATION AND SUBSEQUENT CONVECTIVE
INITIATION. THOUGH LOW-LEVEL FLOW IS PROGGED TO REMAIN FAIRLY
WEAK...THE BELT OF ENHANCED MID-LEVEL SSWLYS ATOP THE AREA MAY
SUPPORT LOCAL/MULTICELL ORGANIZATION...AND THUS POTENTIAL FOR A FEW
LOCALLY DAMAGING WIND GUSTS AND/OR HAIL EVENTS.

...NRN HIGH PLAINS/BLACK HILLS AREA...
DESPITE PRESENCE OF LARGE-SCALE UPPER RIDGING...A WEAK VORT MAX
MOVING SLOWLY ACROSS THE NRN HIGH PLAINS MAY NEUTRALIZE THE BROADER
TENDENCY FOR BACKGROUND SUBSIDENCE TO SOME DEGREE. AS
SUCH...DIFFERENTIAL HEATING OVER THE BLACK HILLS -- AND POSSIBLY
WEAK UPSLOPE FLOW INTO NWRN WY -- MAY ALLOW A COUPLE OF ISOLATED
CELLS TO DEVELOP THIS AFTERNOON.

SHEAR WILL REMAIN MODEST ACROSS THIS REGION. HOWEVER...A
DRY/WELL-MIXED BOUNDARY LAYER MAY FACILITATE POTENTIAL FOR A
STRONGER DOWNDRAFT OR TWO -- WARRANTING MAINTENANCE OF ONGOING 5%
WIND PROBABILITY IN THIS AREA. STORMS MAY LINGER INTO THE
EVENING...SHIFTING SEWD ACROSS SWRN SD AS A LOW-LEVEL JET
DEVELOPS...BUT EXPECT ANY SEVERE POTENTIAL TO WANE AFTER SUNSET AS
THE BOUNDARY LAYER STABILIZES.

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