FXUS61 KLWX 251813
AFDLWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
113 PM EST FRI DEC 25 2009
.SYNOPSIS...
PRECIPITATION WILL DEVELOP AHEAD OF A WARM FRONT AND LOW PRESSURE
SYSTEM TODAY. LOW PRESSURE MOVES NORTH AND EAST OF THE AREA ON
SATURDAY. AFTER WEAK HIGH PRESSURE PASSES OVERHEAD SATURDAY NIGHT
AND SUNDAY...AN UPPER LEVEL LOW PRESSURE AND SURFACE COLD FRONT
WILL MOVE ACROSS SUNDAY NIGHT AND MONDAY...WITH HIGH PRESSURE
BUILDING IN FOR THE MIDDLE OF NEXT WEEK.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
WILL CONTINUE WITH THE WINTER WEATHER ADVISORY WEST OF THE BLUE
RIDGE. TEMPERATURES REMAIN IN THE UPPER 20S AND LOWER 30S ACROSS
MANY LOCATIONS. PRECIPITATION CONTINUES TO OVERSPREAD THE AREA
FROM THE SOUTHWEST. FURTHER EAST...TEMPERATURES HAVE RISEN ABOVE
FREEZING AND RAIN IS EXPECTED.
HAVE EXTENDED THE FLOOD WATCH TO INCLUDE THE SHENANDOAH VALLEY.
RAIN ACROSS THE SHENANDOAH VALLEY AS WELL AS FOR LOCATIONS EAST OF
THE BLUE RIDGE WILL BE MODERATE TO OCCASIONALLY HEAVY LATE THIS
AFTERNOON.
THE WIND ADVISORY REMAINS IN EFFECT THROUGH THIS AFTERNOON FOR THE
HIGHER ELEVATIONS ALONG THE POTOMAC HIGHLANDS. WINDS ALONG THE
RIDGE TOPS WILL GUST AROUND 45 MPH. ACROSS THE VALLEYS...WINDS
WILL BE MUCH LIGHTER DUE TO THE INVERSION.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/...
LARGE STORM SPINS A LITTLE NORTH INTO THE MIDWEST THIS EVENING.
MEANWHILE...WAVE OF LOW PRESSURE OVER NORTH CAROLINA LIFTS NORTHEAST
INTO THE MID ATLANTIC OVERNIGHT. RESULT WILL BE FOR RAIN ACROSS THE
CWA OVERNIGHT. HEAVIEST AXIS OF QPF MOVES THROUGH THE INTERSTATE 95
CORRIDOR DURING THE EVENING HOURS...WITH MINOR URBAN/SMALL STREAM
FLOOD PROBLEMS POSSIBLE.
TEMPERATURES WILL BE STEADY/SLOWLY RISING OVERNIGHT.
&&
.LONG TERM /SATURDAY THROUGH THURSDAY/...
COASTAL LOW WORKS NWD ACRS DELMARVA DRNG DAY SAT...WITH RAIN ENDING
FROM THE SW AS DRIER AIR PUNCHES IN FROM THE SW. WEAK HIGH PRESSURE
PASSES S OF THE AREA SAT NGT. UPR LOW WILL STILL BE SPINNING OVER
GREAT LAKES...WITH VORT MAXES PASSING ACRS THE AREA OVER THIS PD.
DOWNSLOPING FLOW SHUD KEEP MOST AREAS DRY...BUT LOW POPS ON SUN IN CASE
SOME SNOSHWR ACTIVITY CAN PASS THE APPALACHIANS...PSBLY BCMG RAIN SHOWERS
AS THEY WORK EAST.
UPR LOW FINALLY GETS CAUGHT IN POLAR JET AND MAKES A MOVE ACRS THE
NE CONUS ON SUN NGT/MON...WITH STRONG COLD FRONT MVG ACRS AND
SLIGHTLY BETTER CHANCE FOR PRECIP. BEHIND THE FRONT...UPSLOPE SNOW
LIKELY MON/TUE IN NW FLOW FOR THE WESTERN SLOPES OF ALLEGHENY FRONT.
HIGH PRESSURE PASSES THROUGH THE AREA FOR THE MIDDLE OF NEXT WEEK.
&&
.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
IFR CIGS WILL DEVELOP LATE THIS MORNING INTO EARLY THIS AFTERNOON.
RAIN WILL OVERSPREAD THE TERMINALS DURING THIS TIME. RAIN WILL
BEGIN AS A PERIOD OF FREEZING RAIN...ESPECIALLY ACROSS KCHO AND
KMRB. AFT 18Z...HEAVIER PRECIPITATION IS ALSO LIKELY TO PRODUCE
IFR VSBYS...WHICH WILL LAST AT LEAST TIL 12Z. ANY FREEZING RAIN
WILL CHANGE TO RAIN BY THE MIDDLE PORTION OF THIS AFTERNOON.
SUBVFR CONDS WITH RAIN CAUSING VSBY RESTRICTIONS AND LOW CIGS
THROUGH AT LEAST SAT MRNG. SKIES SHOULD CLEAR FIRST IN CHO THEN
WORKING NEWD WITH BWI/MTN BEING LATEST TO CLEAR...LIKELY LATE IN
AFTN. PATCHY VSBY RESTRICTIONS DUE TO FOG PSBL SAT NGT/SUN MRNG. VFR
CONDS ON SUN...WITH ANOTHER COLD FRONT AND CHANCE FOR PRECIP/SUBVFR
CONDS SUN NGT INTO MONDAY.
E WINDS 10 TO 15 MPH SAT BEFORE CDFNT PASSES ACRS MIDDAY...SHIFTING
WINDS TO NW AT SIMILAR SPEEDS THRU REMAINDER OF WEEKEND.
&&
.MARINE...
EASTERLY FLOW IS EXPECTED TO INTENSIFY THIS AFTERNOON...AND SMALL
CRAFT ADVISORY WILL CONTINUE TONIGHT. MODELS INDICATE STRONG
WINDS ALOFT FROM THE SOUTHEAST...BUT SHOULD HAVE PROBLEM MIXING
ANYTHING MORE THAN 30 KNOTS DOWN SO NO GALE WARNING WILL BE
ISSUED.
ELY FLOW IN ADVANCE OF CDFNT WILL BRING 15 TO 20 KT WINDS TO WATERS
THRU SAT MRNG...WITH GUSTS TO 25 KT PSBL. SCA CONT THRU THE MRNG.
CDFNT XPCD MIDDAY SAT...SWITCHING WINDS TO NW AT SPEEDS BELOW SCA
THRESHOLDS. CDFNT PASSES ACRS SUN NGT...WITH POTENTIAL FOR GUSTY
WINDS REACHING SCA CRITERIA ON MONDAY AND TUESDAY.
&&
.HYDROLOGY...
STRONG SLY FLOW AT MID LEVELS AND MOIST ELY FLOW AT LOW LEVELS WILL
RAISE PWATS TO OVER AN INCH ACRS THE SHENANDOAH VALLEY AS WELL AS
AREAS SOUTH AND EAST OF THE BLUE RIDGE. RAINFALL AMOUNTS OF 1 TO
1.5 INCHES MAY BE ENOUGH...TO CAUSE MINOR FLOODING...ESPECIALLY
WHEN COMBINED WITH WARMER TEMPERATURES MELTING THE
SNOWPACK...WHICH CONTAINS NEARLY 1 INCH LIQUID EQUIVALENT IN SOME
LOCATIONS. URBAN AREAS/SMALL STREAMS WILL BE PARTICULARLY AT
RISK...WHERE SNOW MAY HINDER DRAINAGE. FLOOD WATCH WILL BE KEPT UP
THIS AFTERNOON AND TONIGHT.
&&
.LWX WATCHES/WARNINGS/ADVISORIES...
DC...FLOOD WATCH THROUGH LATE TONIGHT FOR DCZ001.
MD...FLOOD WATCH THROUGH LATE TONIGHT FOR MDZ004>007-009>011-013-
014-016>018.
WINTER WEATHER ADVISORY UNTIL 3 PM EST THIS AFTERNOON FOR
MDZ003-501-502.
WIND ADVISORY UNTIL 6 PM EST THIS EVENING FOR MDZ501.
VA...FLOOD WATCH THROUGH LATE TONIGHT FOR VAZ025>027-029>031-
036>042-050>057.
WINTER WEATHER ADVISORY UNTIL 3 PM EST THIS AFTERNOON FOR
VAZ021-025>031.
WIND ADVISORY UNTIL 6 PM EST THIS EVENING FOR VAZ021.
WV...WINTER WEATHER ADVISORY UNTIL 3 PM EST THIS AFTERNOON FOR
WVZ050>055-501>504.
WIND ADVISORY UNTIL 6 PM EST THIS EVENING FOR WVZ054-501>503.
MARINE...SMALL CRAFT ADVISORY UNTIL NOON EST SATURDAY FOR ANZ530>534-
537>543.
SMALL CRAFT ADVISORY UNTIL 6 AM EST SATURDAY FOR ANZ535-536.
&&
$$
LASORSA/PELOQUIN/SBK
