SWODY2
SPC AC 261727
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1227 PM CDT THU APR 26 2007
VALID 271200Z - 281200Z
..THERE IS A SLGT RISK OF SVR TSTMS FRI ACROSS PARTS OF THE MID
ATLANTIC COAST STATES....
..SYNOPSIS...
AT LEAST SLIGHT AMPLIFICATION OF THE LARGE-SCALE UPPER FLOW PATTERN
ACROSS THE U.S. IS UNDERWAY...AS AN UPPER RIDGE BUILDS INTO THE
PACIFIC COAST STATES...AHEAD OF AN EASTWARD PROGRESSING TROUGH
ACROSS THE EASTERN PACIFIC. A DOWNSTREAM TROUGH CONTINUES TO SPLIT
INTO SMALLER SCALE PERTURBATIONS OVER THE INTERMOUNTAIN WEST/ROCKIES
REGION...WITH A CLOSED LOW NOW DIGGING INTO THE SOUTHERN
PLATEAU/BAJA...AND ANOTHER SIGNIFICANT IMPULSE BEGINNING TO DIG TO
THE LEE OF THE NORTH CENTRAL ROCKIES.
MODELS INDICATE THAT THE LATTER IMPULSE WILL CONTINUE SOUTHEASTWARD
LATER TODAY THROUGH FRIDAY/FRIDAY NIGHT... MAINTAINING BROADER SCALE
UPPER TROUGHING EAST OF THE PLAINS...AS WEAKENING REMNANTS OF A
SOUTHERN BRANCH CLOSED LOW ACCELERATE INTO THE NORTHEASTERN STATES.
AS THE UPPER RIDGE SHIFTS EASTWARD INTO THE INTERMOUNTAIN
WEST/NORTHERN ROCKIES...THE CLOSED LOW IS FORECAST TO BECOME CUT OFF
OVER BAJA/THE NORTHWESTERN MEXICAN PLATEAU.
..MID ATLANTIC STATES...
THE SOUTHERN BRANCH CLOSED LOW DOES NOT APPEAR LIKELY TO ACCELERATE
INTO THE NORTHEASTERN STATES EN MASSE...WITH PERHAPS ONE IMPULSE
LIFTING THROUGH THE NORTHERN/CENTRAL APPALACHIANS EARLY IN THE
PERIOD...AND ANOTHER PROGRESSING EAST OF THE CENTRAL APPALACHIANS
LATER FRIDAY/FRIDAY EVENING. THIS WILL SLOW PROGRESSION OF A COLD
FRONT THROUGH THE MID ATLANTIC STATES...ALLOWING FOR DESTABILIZATION
OF A MOISTENING BOUNDARY. MODELS SUGGEST STRONGEST INSTABILITY WILL
EVOLVE ACROSS EASTERN VIRGINIA/NORTH CAROLINA...WHERE MIXED LAYER
CAPE MAY APPROACH 1000 J/KG...BENEATH 40-50 KT CYCLONIC 500 MB FLOW.
STRONGER SOUTHERLY LOW-LEVEL JET MAY ALREADY BE IN THE PROCESS OF
SHIFTING EAST OF THIS REGION...OFF NORTHERN/MID ATLANTIC COASTAL
AREAS BY PEAK AFTERNOON HEATING...BUT SHEAR PROFILES SHOULD REMAIN
SUFFICIENT FOR SUPERCELLS. AND...TIMING OF MID/UPPER FORCING WITH
THE SECOND IMPULSE SHOULD BE FAVORABLE TO ENHANCE CONVECTIVE
DEVELOPMENT DURING THE LATE AFTERNOON/EARLY EVENING HOURS. AN
ISOLATED TORNADO OR TWO IS POSSIBLE...BUT ANTICIPATED LOW-LEVEL
HODOGRAPHS AND THERMODYNAMIC STRUCTURE SEEM MOST SUPPORTIVE OF
DAMAGING DOWNBURSTS...IN ADDITION TO RISK OF HAIL.
..SRN PLATEAU/ROCKIES THROUGH CENTRAL STATES...
A RETURN FLOW MAY DEVELOP OFF THE WESTERN GULF OF MEXICO...BUT THIS
IS EXPECTED TO BE LIMITED IN THE WAKE OF PRIOR SYSTEM.
HOWEVER...FAVORABLE LARGE-SCALE FORCING ASSOCIATED WITH EVOLVING
UPPER FLOW PATTERN...AND STRONG DAYTIME HEATING ACROSS PARTS OF THE
SOUTHERN PLATEAU/ROCKIES AND SOUTHERN PLAINS...WILL CONTRIBUTE TO AT
LEAST A LOW RISK FOR THUNDERSTORMS ACROSS A BROAD AREA.
STORMS WILL BE MOST CONCENTRATED AHEAD OF DIGGING SHORT WAVE TROUGH.
VARIABILITY EXISTS AMONG THE MODELS CONCERNING THE TRACK OF THIS
FEATURE TO THE LEE OF THE ROCKIES...BUT THE GFS AND ECMWF SUGGEST
THAT THIS MAY BE MOST PROBABLE ACROSS THE CENTRAL PLAINS/ OZARK
PLATEAU REGION. ACTIVITY IS EXPECTED TO BE MOSTLY ROOTED IN AN
ELEVATED MOISTENING LAYER ASSOCIATED WITH LOW-LEVEL ISENTROPIC
ASCENT. BETTER MOISTURE RETURN/STEEPER LAPSE RATES AND LIFT COULD
BECOME BRIEFLY JUXTAPOSED ACROSS PARTS OF NORTHWEST TEXAS INTO
SOUTHWESTERN OKLAHOMA LATE FRIDAY AFTERNOON...WHEN/WHERE AN ISOLATED
STRONG/SEVERE STORM COULD DEVELOP IN A FAVORABLY SHEARED REGIME FOR
AT LEAST BRIEF UPDRAFT ROTATION.
..PACIFIC COAST STATES...
AS UPPER RIDGE AXIS SHIFTS TO THE EAST FRIDAY...A MOISTENING AIR
MASS/DAYTIME HEATING AND OROGRAPHY MAY CONTRIBUTE TO SCATTERED
THUNDERSTORMS ACROSS THE NORTHERN SIERRA NEVADA INTO THE SOUTHERN
CASCADES...POSSIBLY NORTHEASTWARD THROUGH PARTS OF CENTRAL/EASTERN
OREGON BY EARLY FRIDAY EVENING.
.KERR.. 04/26/2007
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