FXUS61 KLWX 230215 AAA
AFDLWX
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
915 PM EST TUE DEC 22 2009
.SYNOPSIS...
HIGH PRESSURE WILL BUILD ACROSS THE REGION THROUGH WEDNESDAY NIGHT.
A SLOW MOVING FRONTAL SYSTEM...ASSOCIATED WITH A A STRONG STORM
OVER THE MIDWEST...WILL BRING WINTRY PRECIPITATION THEN RAIN TO
THE AREA LATE THURSDAY NIGHT INTO SATURDAY NIGHT. HIGH PRESSURE AND
COLD CONDITIONS ARE EXPECTED TO RETURN SUNDAY INTO EARLY NEXT WEEK.
&&
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
THE BIG QUESTION IS WHAT OVERNIGHT LOWS WILL BE W/ A STILL SOLID
SNOW PACK AND INCOMING BKN-SCT STRATUS DECK. DEWPOINTS LATE THIS
EVENING RANGE IN THE L-M20S. AS WITH LAST NIGHT LOWS NOT DROPPING
AS LOW AS MOST GUIDANCE SHOWED...SIGNS ARE POINTING TOWARD ANOTHER
NIGHT HIGHER THAN GUIDANCE. SEVERAL OBS HAVE EVEN RISEN A COUPLE
OF DEGREES IN THE PAST COUPLE OF HRS. SOME INSULATING A MODERATING
OF TEMPS TAKING PLACE...ESPECIALLY UNDER THE MORE STEADY CLOUD
COVER. LOCALES ACROSS NERN MD WHICH HAVE BEEN MOSTLY CLR SKIES
ONLY DOWN INTO THE L30S.
THE DEVELOPING STORM SYSTEM STREWN ACROSS THE CNTRL/SRN PLAINS AND
THE LOWER MISSISSIPPI VLY PUSHING A WEAK RIDGE AND PLENTY OF MID-
UPPER DECKS THRU THE OVERNIGHT HRS. WHATEVER WAVES OF THE LOW-
LEVEL STRATUS PUSH INTO THE CNTRL APLCNS...A SMALLER PORTION WILL
MAKE IT ACROSS THE RIDGELINES BUT SHOULD STILL BE ENOUGH TO KEEP
TEMPS FROM DROPPING INTO THE UPPER TEENS AS GUIDANCE PREDICTS.
EXPECTING THE NRN HALF TO ROUGHLY DROP INTO THE L-M20S AND M-U20S
ACROSS THE SRN ZONES WHERE DEWPOINTS REMAIN A TAD HIGHER ALONG W/
MORE CLOUD COVER.
DRY CONDITIONS FOR THE CWA...THOUGH A FEW FLURRIES ARE FALLING
BACK ACROSS CNTRL WV /NOT EXPECTED TO MOVE E OF THE ALLEGHENY MTN
RANGES.
&&
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
RDG AXIS MVS OHD TMRW. THIS SHUD MAKE FOR SUNNIER DAY. W/O MUCH WND
EITHER. WL KEEP SAME THEME GOING FOR MAXT. ONCE AGN TDA...OBS ABV
MOS...SO WL FCST ABV MOS. TAKING A CONSERVATIVE APPROACH-- DOESNT
LOOK LIKE MUCH CAA /H8 TEMPS ACTUALLY RISE/...BUT AM LEERY OF FCSTG
TOO FAR INTO THE 40S W/ A SNWPACK IN PLACE.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
THURSDAY INTO THURSDAY NIGHT...UPPER RIDGE CROSSES THE REGION WITH
CONTINUED MELTING OF THE SNOWPACK DURING THE DAY...INCREASING
TEMPERATURE TREND SEEN THE PAST FEW DAYS MAY BE LIMITED AS ONSHORE
FLOW BEGINS AS SFC HIGH CROSSES TO THE NORTH. LOW PRESSURE SYSTEM
MOVES UP WESTERN SIDE OF MS VALLEY TOWARDS NORTHERN PLAINS LOOKS TO
LINGER OUT THERE INTO THE WEEKEND.
LATE THURSDAY NIGHT THROUGH FRIDAY...
FRONTAL SYSTEM APPROACHES THE MID ATLANTIC THURSDAY NIGHT...PRECIP
CHANCES START LATE THURSDAY NIGHT. WITH DRY/WARM LAYER ALOFT AND
COLD SFC...ANY PRECIP WOULD START LIGHT...MOST LIKELY FREEZING
DRIZZLE. AS FRONTAL FORCING APPROACHES FRIDAY MORNING... MOISTURE
DEEPENS WITH ABOVE FREEZING TEMPERATURES ALOFT. COLD LAYER AT SFC
FRIDAY MORNING TO BE SHALLOW...EXPECT FREEZING RAIN...PERHAPS SOME
SLEET MIXED IN FOR DEEPER COLD AIR IN SHEN VLY.
WAA/PROGRESSION OF COASTAL FRONT TO RAPIDLY WARM/CHANGE PRECIP TO
ALL RAIN SOUTHERN MARYLAND/WESTERN SHORE OF THE BAY. EXPECT WESTWARD
EXPANSION OF THE WARMER AIR THOUGH PROGRESSION WEST OF THE BLUE
RIDGE UNCERTAIN ATTM. EXPECTING EXTENDED ACCRETING FREEZING RAIN
THREAT TO BE FOR VALLEYS WEST OF THE BLUE RIDGE...INCLUDING THE
SHENANDOAH VALLEY. UNCERTAINTY ABOUT SFC TEMPERATURES FRIDAY
AFTERNOON LED TO FREEZING RAIN/RAIN WX GRID OUT THERE. SHOULD DAMMED
TEMPERATURES REMAIN COLD ENOUGH...A QUARTER INCH OF ICE /ICE STORM
WARNING CRITERIA/ WOULD BE POSSIBLE IN PLACES. HOWEVER DUE TO
UNCERTAINTY...EXPECT SOME ACCRETING FREEZING RAIN ALONG AN WEST OF
THE BLUE RIDGE ON FRIDAY.
RAINFALL/FLOODING THREAT...50F DEWPOINT LINE CURRENTLY PROGGED TO
EXTEND THROUGH THE I-95 CORRIDOR FOR A FEW HOURS FRIDAY NIGHT BY
GFS/CANADIAN /ONLY SOUTHERN MD FROM EURO/. THIS WARM AIR...COMBINED
WITH RAINFALL WOULD MELT A MAJORITY OF REMAINING SNOW EAST OF THE
BLUE RIDGE...LEADING TO BOTH LOCAL/SMALL STREAM...AND POSSIBLY RIVER
FLOODING. A CHANGEOVER FROM FREEZING RAIN TO RAIN IS EXPECTED FRIDAY
AFTERNOON...SO MELT INDUCED FLOODING A POSSIBILITY OUT THERE TOO.
MORE DETAILS FROM SUBSEQUENT SHIFTS.
FRIDAY NIGHT INTO SATURDAY...SHOULD THE LOW PRESSURE SYSTEM LINGER
OVER THE MID WEST/NORTHERN PLAINS AS CURRENTLY PROGGED...THE FRONTAL
SYSTEM WOULD BE SLOW TO MOVE THROUGH THE CWA. FURTHER COMPLICATING
THE FROPA IS A MESO LOW DEVELOPING AND CROSSING THE AREA. CURRENTLY
EXPECTING PRECIP /MAINLY RAIN/ TO BEGIN TO TAPER OFF SW TO NE
THROUGH SATURDAY.
EXTENDED...UPPER TROUGH/COLD AIR LOOKS TO LINGER THROUGH THE REST OF
THE WEEKEND. UPSLOPE SNOW ALLEGHENY FRONT AND DRY/BELOW NORMAL
TEMPERATURES EAST.
&&
.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
VFR CONDS WL PREVAIL THRU CURRENT CYCLE. ANOTHER ROUND OF 3-4 KFT
LOW CLDS WILL SPILL OVER THE CNTRL APLCNS THRU MUCH OF THE LATE
NIGHT AND EARLY MRNG HRS. THIS ACTIVITY WILL BREAK-UP MORE INTO
THE PRE-DAWN HRS AND GENERAL CLEARING INTO WED AFTN. SFC WINDS
WILL REMAIN LIGHT AND MAINLY NWLY THRU THE PERIOD.
VFR CONTINUES INTO THURSDAY NIGHT WHEN ONSHORE FLOW
SATURATES...BRINGING LIGHT WINTRY PRECIP /MOST LIKELY FREEZING
DRIZZLE - THEN WARMER RAIN/ LATE THURSDAY NIGHT THROUGH FRIDAY.
ACCRETING BEST CHANCES FOR ACCRETING ICE IN THE SHEN VALLEY.
RAIN/IFR CONDITIONS THEN CONTINUE THROUGH SATURDAY.
&&
.MARINE...
LIGHT WLY WINDS WILL CONTINUE ACROSS THE WATERS OVERNIGHT. MAX
GUSTS NEAR 10KT IN ANY LOCATION...MORE OF THE SAME INTO WED. NO
FLAGS TMRW W/ HIPRES OHD.
ONSHORE FLOW BEGINS LATER THURSDAY...INCREASING TO SCA LEVELS ON
FRIDAY. SOME FREEZING DRIZZLE POSSIBLE EARLY FRIDAY...THEN RAIN
INTO THE WEEKEND.
&&
.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...NONE.
&&
$$
UPDATE...GMS
PREV DISCUSSION...HTS/BAJ
