SWODY2
SPC AC 290554
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1254 AM CDT SAT AUG 29 2009
VALID 301200Z - 311200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
DANNY...OR THE REMNANTS OF DANNY...LIKELY WILL RAPIDLY ACCELERATE
THROUGH AND NORTHEAST OF THE CANADIAN MARITIMES DURING THIS
PERIOD...WITHIN STRONG SOUTHWESTERLY FLOW BETWEEN AN EASTERN
CANADIAN/U.S. UPPER TROUGH AND A STRONG WESTERN ATLANTIC RIDGE.
WHILE THE RIDGE WILL IMPEDE THE EASTWARD PROGRESSION OF THE UPPER
TROUGH...MODELS CONTINUE TO SUGGEST THAT AN EMBEDDED CLOSED LOW WILL
LIFT AWAY FROM THE GREAT LAKES REGION THROUGH THE EASTERN CANADIAN
PROVINCES. THIS IS EXPECTED TO LEAVE A WEAK AND WEAKENING CYCLONIC
MID/UPPER FLOW FROM THE PLAINS INTO THE ATLANTIC SEABOARD. AT THE
SAME TIME...A CLOSED LOW IS PROGGED TO GRADUALLY DRIFT EASTWARD
ACROSS THE NORTHERN INTERMOUNTAIN REGION...WITHIN BROADER SCALE
RIDGING ENCOMPASSING MUCH OF THE INTERMOUNTAIN WEST AND
ROCKIES...INTO THE HIGH PLAINS BY LATE SUNDAY NIGHT/EARLY MONDAY.
...ATLANTIC SEABOARD...
MODERATE TO STRONG SOUTHWESTERLY MID/UPPER FLOW...LIKELY TO
OVERSPREAD MID AND NORTHERN ATLANTIC COASTAL AREAS LATE SATURDAY
NIGHT INTO EARLY SUNDAY...COULD LINGER THROUGH MUCH OF SUNDAY BEFORE
WEAKENING/SHIFTING NORTHEASTWARD. THIS IS EXPECTED TO CONTRIBUTE TO
FAVORABLE DEEP LAYER SHEAR FOR SEVERE STORMS...IN A LINGERING VERY
MOIST PRE-FRONTAL ENVIRONMENT...PARTICULARLY FROM PARTS OF SOUTHEAST
VIRGINIA AND THE SOUTHERN DELMARVA PENINSULA INTO SOUTHEASTERN NEW
ENGLAND. HOWEVER...THE TIMING OF THE FRONTAL PASSAGE ACROSS THIS
REGION IS STILL UNCERTAIN...AND EARLY LOWER/MID TROPOSPHERIC
SUBSIDENCE WARMING AND DRYING COULD PRECLUDE THUNDERSTORM
DEVELOPMENT.
...SOUTH CENTRAL STATES...
MODELS ARE MORE CERTAIN ABOUT THE LIKELIHOOD OF A MID/UPPER
IMPULSE...PERHAPS A CONVECTIVELY ENHANCED OR GENERATED CYCLONIC
VORTICITY CENTER...PROGRESSING THROUGH THE LOWER MISSISSIPPI VALLEY
AND CENTRAL GULF STATES SUNDAY. WITHIN THE PRESENCE OF A LINGERING
MOIST AIR MASS CHARACTERIZED BY WEAK TO MODERATE POTENTIAL
INSTABILITY...VIGOROUS NEW STORM DEVELOPMENT APPEARS POSSIBLE ACROSS
PARTS OF SOUTHEAST LOUISIANA AND CENTRAL/SOUTHERN MISSISSIPPI AND
ALABAMA...BEFORE THE UPPER SYSTEM BECOMES INCREASINGLY SHEARED AS IT
LIFTS TOWARD THE SOUTHERN APPALACHIANS. HOWEVER...GUIDANCE IS
SUGGESTIVE THAT BOUNDARY LAYER HEATING ACROSS THE REGION WILL BE
SOMEWHAT MODEST...WHICH SEEMS LIKELY TO RESULT IN ONLY SPARSE
COVERAGE OF ANY POTENTIAL DAMAGING WIND/HAIL EVENTS...IN THE
PRESENCE OF GENERALLY WEAK SHEAR.
...LEE OF THE CENTRAL/SOUTHERN ROCKIES...
SUBSTANTIAL SURFACE HEATING SUNDAY MAY BE CONFINED TO THE IMMEDIATE
LEE OF THE HIGHER TERRAIN...ACROSS CENTRAL COLORADO INTO NORTHEAST
NEW MEXICO. AND MODELS SUGGEST THAT MIXED LAYER CAPE WILL MOST
LIKELY REMAIN BELOW 1000 J/KG...DESPITE THE CONTINUING PRESENCE OF
STEEP MID-LEVEL LAPSE RATES. HOWEVER... DEEP LAYER SHEAR MAY REMAIN
AT LEAST MARGINALLY FAVORABLE FOR SUPERCELLS BENEATH 20-30 KT
NORTHWESTERLY 500 MB FLOW...AND THIS PROBABLY WILL BE SUFFICIENT FOR
AT LEAST ONE OR TWO WIDELY SCATTERED STRONG/SEVERE STORMS DURING THE
LATE AFTERNOON AND EVENING HOURS.
...NORTHERN INTERMOUNTAIN REGION...
GUIDANCE IS STILL SUGGESTIVE THAT ANYTHING BEYOND WEAK
DESTABILIZATION WILL BE RATHER LOCALIZED BENEATH THE COLD CORE OF
THE UPPER LOW ON SUNDAY. BUT...COOL THERMODYNAMIC PROFILES WITH
STEEP LAPSE RATES MAY SUPPORT AT LEAST ONE OR TWO STRONG/SEVERE
STORMS WITH THE RISK FOR HAIL/DAMAGING WIND GUSTS ACROSS THE
MOUNTAINS OF EAST CENTRAL IDAHO/SOUTHWEST MONTANA INTO NORTHWEST
WYOMING.
..KERR.. 08/29/2009
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