FXUS61 KLWX 050409
AFDLWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1109 PM EST FRI DEC 4 2009
.UPDATE...
QUICK UPDATE BASED ON 00Z MODELS. WINTER STORM WARNING COMING OUT
FOR SHEN VALLEY AND MTNS S OF GRANT CO AND WARREN CO. WINTER WX
ADVSRY EXPANDING INTO CHARLES AND KING GEORGE COUNTIES. ONSET
TIMING BEING ADJUSTED AS WELL...MIDDAY/EARLY AFTERNOON FOR METRO
AREAS.
&&
.SYNOPSIS...
LOW PRESSURE OVER THE NORTHERN GULF OF MEXICO WILL MOVE
NORTHEASTWARD UP THE EASTERN SEABOARD ON SATURDAY. RAIN WILL
CHANGE TO SNOW FROM WEST TO EAST AS COLDER AIR FILTERS INTO THE
MID ATLANTIC REGION. HIGH PRESSURE WILL MOVE INTO THE AREA SUNDAY
AND MONDAY. A COMPLEX LOW PRESSURE SYSTEM WILL TRACK NORTH OF THE
AREA WEDNESDAY.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
02Z SFC ANALYSIS REVEALS A COUPLE AREAS OF LOPRES OVER THE GULF OF
MEXICO...ONE OFF THE TX COAST AND THE OTHER NEAR FL. LOOP OF RADAR
IMAGERY THIS EVNG SHOWS AN EXPANDING AREA OF PRECIP STREAMING NWD
UP THE SOUTHEAST COAST. AHEAD OF AN APPROACHING MID-UPPER LVL
SHORTWAVE TROUGH...PRECIP WILL CONT TO EXPAND NWD TOWARDS SRN
PORTIONS OF THE CWFA LATE TNGT AS FAVORABLE ULVL JET DYNAMICS AND
ISENTROPIC LIFT INCREASES WHILE CYCLOGENESIS OCCURS OFF THE SOUTH
CAROLINA COAST. PRECIP WILL START OF AS RAIN...MIXING WITH SNOW
ACROSS HIGH ELEVATIONS ABOVE 2 KFT ALONG AND W OF THE BLUE RIDGE.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
AT THIS TIME WILL KEEP HEADLINES AS IS...WITH WINTER WX ADVISORIES
ACROSS THE WHOLE CWFA EXCLUDING LOWER SRN MD /WHERE PRECIP WILL
MSTLY BE RAIN/. HOWEVER...LATEST 21Z SREF AND 00Z NAM SUPPORTIVE OF
HIGHER SNOW AMTS OVER THE C SHEN VLY AND SRN POTOMAC HIGHLANDS
LATE SAT MRNG AND SAT AFTN THAT WOULD PUSH STORM TOTAL SNOW AMTS
TO LOWER WINTER STORM WRNG CRITERIA. WILL WAIT UNTIL REST OF
00Z MODEL GUIDANCE COMES IN TO MAKE FINAL DECISION IF WINTER
HEADLINES NEED TO BE UPGRADED FOR THE AFOREMENTIONED AREA.
PREVIOUS DISCUSSION...
COASTAL LOW INTENSIFIES OFF NC COAST THEN MOVES JUST EAST OF MD
EASTERN SHORE SAT AFTN. UPR SHRTWV PASSES W OF APPALACHIANS...WITH
850MB LOW CENTER PASSING ACRS SE VA. PLENTY OF LIFT ON NW SIDE OF
SYSTEM...THUS QPF RATHER IMPRESSIVE 0.25-0.50". TEMPS XPCD NEAR
40F IN THE MRNG...THEREFORE PRECIP SHUD BEING AS RAIN...AROUND 12Z
W OF BLUE RIDGE...SPREADING NEWD TO BALTIMORE METRO AND POINTS NE
BY 16Z. AFTER RAIN BEGINS...EVAPORATIVE COOLING WILL ALLOW TEMPS
TO FALL TO NEAR FREEZING...AND WITH VERTICAL THERMAL PROFILE IN
SUPPORT...PRECIP WILL CHANGE TO SNOW. WITH STRONG VERTICAL
MOTION...XPCT DECENT SNOWFALL RATES. HOWEVER...WITH RELATIVELY
WARM TEMPS...ACCUMULATIONS WILL BE HINDERED...PARTICULAR SE HALF
OF CWA...WHERE HIGHEST PRECIP AMOUNTS ARE FCST. SNOW ACCUMULATIONS
SHUD RANGE FROM 2 TO 4 INCHES ACRS MUCH OF THE CWA W OF INTERSTATE
95...WITH 1 TO 2 INCHES XPCD ALONG THE URBAN CORRIDOR. WITH WARMER
SFC TEMPS ACRS LOWER SOUTHERN MARYLAND...SNOWFALL ACCUMULATION
LOOK TO RMN MINIMAL.
&&
.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
SYSTEM WL EXIT TO THE NE OF THE CWA QUICKLY SAT NGT. XPCT SKIES TO
GO FM CLDY AT THE START OF SAT EVE TO CLR WHEN THE SUN RISES ON
SUNDAY. ALONG W/ 1ST SNOW COVER OF THE SEASON CLR SKIES WL AID IN
PRODUCING THE COLDEST NGT OF THE AUTUMN SO FAR - W/ TEMPS RANGING FM
THE L30S ALONG THE BAY TO THE MID TEENS IN THE HIGHLANDS. SAT NGT
SHOULD BE BRZY AS WELL...CREATING WINDS CHILLS RANGING FM M20S IN
THE E...TEENS W OF I-81...TO SINGLE DIGITS IN THE HIGHLANDS.
W/ HIGH PRES OVR THE RGN SUNDAY THERE SHOULD BE ABUNDANT SUNSHINE.
AFTN TEMPS SHOULD REACH THE LM40S W/ XCPTN OF HIGHER ELEVS. BLV AREA
WL BE DRY TO START THE NEW WK W/ HIGHS IN THE 40S...LOWS SUN NGT
PRIMARILY IN 20S THEN A FEW DEGS WARMER MON NGT. NEXT WX SYSTEM
(WED) LOOKS TO BE FAIRLY COMPLICATED - A DEEP LOW OVR MI W/ AN
OCCLUSION/PTNL TRIPLE PT XTNDG INTO THE MID ATLC. IT'S TOO ERLY
TO TRY TO NAIL DOWN P-TYPES...BUT I WOULDN'T BE SURPRISED IF THERE
WERE A PD OF FRZN PCPN (IP) DURG THE OVRNGT HRS TUE NGT AHD OF THE
WRM FNT. BUT FOR NOW WL WORD IT AS "CHC R-S" IN THE FCST.
ON WED WARM WRM FNT WL PUSH TO THE N AND PCPN WL BECOME MORE
INTERMITTENT. AFTR CD FNT MOVES THRU WINDS TURN TO THE
W...BRINGING THE PTNL FOR UPSLOPE SNSH IN THE HIGHLANDS WED NGT.
AFTR THE MIDWEEK STORM IT LOOKS LK AREA WL GET ANOTHER RESPITE AS
HIGH PRES RETURNS FOR THU AND FRI. END OF WK HIGHS IN MU40S MAJORITY
OF THE CWA. THU NGT THE COOLEST W/ LOWS IN THE 20S.
&&
.AVIATION /04Z SATURDAY THROUGH WEDNESDAY/...
CIGS LOWERING TO 4-5 KFT OVRNGT BEFORE LOWERING TO MVFR LVLS
AROUND DAYBREAK. PRECIP WILL START OUT AS RA AT FIRST...MIXING
WITH SNOW AROUND 10-14Z. AS COLD AIR PUSHES EWD...PRECIP WILL
CHANGE TO ALL SNOW FROM W TO E DURING THE LATE ACROSS WRN
TERMINALS AND AFTN ACROSS THE ERN TERMINALS. MVFR CIG/VSBY RAPIDLY
BCMG IFR AS PRECIP BECOMES ALL SNOW. SNOW SHUD CONT THRU ERY SAT
EVNG.
PCPN SHOULD END AT ALL TAF SITES DURG THE SAT EVE HRS...THEN VFR
CONDS W/ GUSTY NW WINDS...BCMG LGT SUN MRNG. VFR CONDS THRU THE 1ST
PART OF THE WORKWEEK...B4 NEXT SYSTEM CAUSES PROBS TUE NGT AND WED.
&&
.MARINE...
LGT WINDS WILL CONT THRU THE REST OF THE EVNG BEFORE INCREASING
LATE TNGT AS LOW PRESSURE DEVELOPS OFF THE CAROLINA COAST. BY SAT
MRNG...WINDS REACH SCA CRITERIA...AND SPEEDS WILL GRADUALLY INCR
TO 20 TO 25 KT.
ATTM GALE CONDS NOT XPCD THRU SAT NGT...THO DEPENDING ON TRACK OF
SFC LOW OFF THE MD EASTERN SHORE...HIGHER WINDS ARE PSBL LATE
SATURDAY.
WIDESPREAD PRECIPITATION BY SAT AFTN...WITH SIGNIFICANT VISIBILITY
RESTRICTIONS.
WINDS WL BE IN SMALL CRAFT CONDITIONS SAT NGT B4 DIMINISHING
LATE..AND THEN NO PROBS XPCTD ON WATERS SUN OR MON.
&&
.LWX WATCHES/WARNINGS/ADVISORIES...
DC...WINTER WEATHER ADVISORY FROM NOON TO 11 PM EST SATURDAY FOR
DCZ001.
MD...WINTER WEATHER ADVISORY FROM NOON TO 11 PM EST SATURDAY FOR
MDZ011-013-014-016.
WINTER WEATHER ADVISORY FROM 7 AM TO 9 PM EST SATURDAY FOR
MDZ003-501-502.
WINTER WEATHER ADVISORY FROM 10 AM TO 9 PM EST SATURDAY FOR
MDZ004>007-009-010.
VA...WINTER WEATHER ADVISORY FROM NOON TO 11 PM EST SATURDAY FOR
VAZ054>057.
WINTER STORM WARNING FROM 5 AM TO 7 PM EST SATURDAY FOR VAZ021-
025>027-029-030-036>040.
WINTER WEATHER ADVISORY FROM 7 AM TO 9 PM EST SATURDAY FOR
VAZ028-031.
WINTER WEATHER ADVISORY FROM 10 AM TO 9 PM EST SATURDAY FOR
VAZ041-042-050>053.
WV...WINTER STORM WARNING FROM 5 AM TO 7 PM EST SATURDAY FOR WVZ054-
055-501-502.
WINTER WEATHER ADVISORY FROM 7 AM TO 9 PM EST SATURDAY FOR
WVZ050>053-503-504.
MARINE...SMALL CRAFT ADVISORY FROM 4 AM SATURDAY TO 1 AM EST SUNDAY FOR
ANZ530>543.
&&
$$
