Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 280146
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
846 PM EST THU NOV 27 2014

.SYNOPSIS...
AN UPPER-LEVEL DISTURBANCE WILL PASS THROUGH THE AREA TONIGHT AND
HIGH PRESSURE WILL BUILD OVERHEAD FRIDAY. THE HIGH WILL MOVE OFF
THE COAST DURING THE WEEKEND. A COLD FRONT IS EXPECTED TO MOVE
THROUGH MONDAY.

&&

.NEAR TERM /THROUGH FRIDAY/...
SFC HIGH BUILDS IN TONIGHT BEHIND THE DEPARTING COLD FRONT WHILE
THE AREA REMAINS UNDERNEATH UPPR LVL TROUGH AS IT SLOWLY SWINGS TO
THE EAST. ALREADY SEEING SCT-NUM SNOW SHOWERS OVR AREAS ALONG AND
WEST OF THE ALLEGHENY FRONT AS INDICATED BY BOTH RADAR
REFLECTIVITY AND OBSERVER REPORTS WITH AROUND 1 INCH HAVING BEEN
REPORTED THUS FAR. NW FLOW WILL CONTINUE TO DEVELOP UPSLOPING SNOW
SHOWERS OVERNIGHT AND AS SUCH...WILL CONTINUE THE WINTER WX
ADVISORY CURRENTLY IN EFFECT FOR WESTERN HIGHLAND...GRANT AND
PENDLETON. IN ADDITION...AS SHORTWAVE ENERGY ROUNDS THE
TROUGH...COULD SEE ISO-SCT FLURRIES OCCUR OVER THE LOWER
ELEVATIONS AROUND THE BALTIMORE AND DC METRO AREAS THRU 05Z THOUGH
NO ACCUMS EXPECTED. FCST MIN TEMPS WILL RANGE FROM THE TEENS ALONG
THE ALLEGHENY FRONT TO THE LOW 30S NEAR WASHINGTON AND BALTIMORE.

THE UPPER-LEVEL DISTURBANCE WILL MOVE OFF TO THE EAST FRIDAY
WHILE HIGH PRESSURE BUILDS OVERHEAD. ANY LEFTOVER SNOW SHOWERS
ALONG THE ALLEGHENY FRONT WILL DIMINISH AND SUNSHINE IS EXPECTED.
HOWEVER...IT WILL BE COLD DUE TO THE NORTHWEST FLOW AHEAD OF THE
BUILDING HIGH. MAX TEMPS WILL BE BELOW CLIMO...RANGING FROM THE
20S IN THE MOUNTAINS TO THE LOWER 40S IN THE VIRGINIA PIEDMONT AND
SOUTHERN MARYLAND.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
PATTERN SHIFT AS WRN CONUS RIDGE BREAKS DOWN AS AN UPR TROUGH SHIFTS
SOUTH INTO THE PAC NW. AN ASSOCIATED WARM FRONT WILL MOVE EAST FROM
THE MIDWEST STATES AND INTO THE NRN MID-ATLANTIC. 00Z ECMWF/12Z GFS
SUGGEST LIFT FROM THIS FRONT WILL CAUSE PRECIP INTO THE CENTRAL
APPALACHIANS FRIDAY NIGHT. IN SPITE OF WARM AIR ADVECTION...THERMAL
PROFILES COOL ENOUGH FOR ALL SNOW. LIMITED POPS FOR NOW TO THE NWRN
THREE ZONES (WEST OF THE ALLEGHENY FRONT). MID-LEVEL CLOUDS
ELSEWHERE...THOUGH PLENTY OF COLD AIR AND LITTLE MIXING WILL ALLOW
FOR MIN TEMPS IN THE LOW TO MID 20S INLAND...UPR 20S NEAR SHORE.

WARM AIR ADVECTION CONTINUES THROUGH SATURDAY NIGHT IN SWLY FLOW
WITH PLENTY OF CLOUD COVER. TEMPERATURES MODERATE THROUGH THE
WEEKEND...REACHING NORMAL BY SUNDAY EVENING. TEMPS A BLEND OF
MAV/MET AND SREF OVERNIGHT/MOSGUIDE DURING THE DAY. BY THE TIME
PRECIP RETURNS TO WRN ZONES SATURDAY EVENING...IT SHOULD BE WARM
ENOUGH FOR RAIN. NOT EXPECTING FREEZING RAIN AT THIS TIME DUE TO THE
WARM NOSE DESCENDING...WILL HAVE TO LOOKOUT FOR THAT THOUGH. DRY
EAST OF THE ALLEGHENY FRONT WITH SWLY/SLY FLOW 10 MPH OR SO
MAINTAINED THROUGH SATURDAY NIGHT IN DECENT GRADIENT.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
HIGH PRESSURE SETS UP OFFSHORE FOR THE SECOND HALF OF THE WEEKEND
INTO EARLY NEXT WEEK. THIS WILL SET UP A SOUTHERLY FLOW AND BRING IN
WARMER TEMPERATURES...WITH HIGHS A FEW DEGREES ABOVE NORMAL EXPECTED
SUNDAY AND MONDAY.

A COLD FRONT WILL APPROACH FROM THE WEST LATE MONDAY...AND CROSS THE
AREA THROUGH TUESDAY. THIS WILL BRING THE REGION ITS NEXT CHANCE OF
PRECIPITATION...BUT TEMPERATURES SHOULD BE WARM ENOUGH FOR ALL RAIN.
SOME WET SNOWFLAKES MAY MIX IN ONCE THE COLD FRONT PASSES WITH ANY
LEFTOVER SHOWERS MONDAY EVENING ALONG THE MASON-DIXON LINE AND WEST
OF THE BLUE RIDGE MOUNTAINS MONDAY EVENING. NORTHWEST FLOW BEHIND
THE FRONT WILL LIKELY RESULT IN UPSLOPE SNOW SHOWERS OVERNIGHT
MONDAY NIGHT ALONG THE WESTERN RIDGES OF THE ALLEGHENY FRONT ONCE
TEMPERATURES DROP...BUT AIRMASS WILL BE MARGINAL SO ANY ACCUMULATION
POTENTIAL IS QUESTIONABLE.

A STRONG AREA OF HIGH PRESSURE /I.E. 1040 MB/ WILL BUILD TO THE
NORTH TUESDAY INTO TUESDAY NIGHT. MEANWHILE...THE AFOREMENTIONED
FRONT STALLS TO THE SOUTH...THEN SLOWLY RETURNS NORTH AS A WARM
FRONT TUESDAY NIGHT. THERE IS A STRONG SIGNAL FOR COLD AIR DAMMING
IN THE MODELS...WITH EVEN LOWER RESOLUTION GLOBAL MODELS SHOWING
TEMPERATURES BELOW FREEZING AS PRECIPITATION BEGINS OVER MUCH OF THE
SHENANDOAH VALLEY AND THE POTOMAC HIGHLANDS. ECMWF IS WARMER AT 850
MB AND DEEPER WITH LOW PRESSURE TO THE WEST RESULTING IN MORE
PRECIPITATION AND SUGGESTING A HIGHER ICE POTENTIAL ESPECIALLY WEST
OF THE METRO. GFS IS COLDER AT 850 MB AND WEAKER WITH LOW PRESSURE
TO THE WEST SUGGESTING LIGHTER QPF AND A MORE GENERIC WINTRY MIX OF
SNOW AND RAIN. FOR NOW...STICKING WITH A CHANCE OF RAIN/SNOW...BUT
WILL DEFINITELY NEED TO MONITOR AND FINE-TUNE OVER THE COMING DAYS
AS POTENTIAL IS THERE FOR OVERRUNNING PRECIP. OVER COLD AIR TO
RESULT IN WINTRY PRECIP OVER AT LEAST PART OF THE AREA TUESDAY NIGHT
INTO WEDNESDAY. LEFT OUT OF HWO FOR NOW BECAUSE 30 PERCENT
CONFIDENCE IS NOT THERE THAT WE WILL BE ISSUING HAZARDS GIVEN LARGE
SPREAD IN TIMING/TEMPERATURES.

MODELS/ENSEMBLES BEGIN TO DIVERGE AFTER THIS TIME IN RESPONSE TO A
PATTERN CHANGE ALOFT WITH MORE ZONAL FLOW OF PACIFIC ORIGIN TAKING
HOLD.

&&

.AVIATION /01Z FRIDAY THROUGH TUESDAY/...
VFR CONDITIONS THROUGH FRIDAY. NW FLOW WITH OCNL GUSTS
OVERNIGHT...BCMG MORE PERSISTENT AFTR 13Z FRIDAY.

VFR FRIDAY NIGHT THROUGH SATURDAY NIGHT. CALM FRIDAY NIGHT THEN
SWLY/SLY FLOW INCREASES TO 10-15 KT SATURDAY...10 KT THROUGH
SATURDAY NIGHT.

VFR EXPECTED SUNDAY W/ S FLOW 10-15 KTS. SUB-VFR POSSIBLE IN SCTD
SHWRS MON EVE W/ FROPA. WINDS BECOME W AND DIMINISH TO LESS THAN 10
KTS MON. FLOW BECOMES N THEN E BEHIND FROPA TUE W/ SUB-VFR PSBL IN
PCPN LATE TUE.

&&

.MARINE...
SCA REMAINS IN EFFECT FOR ALL WATERS THROUGH FRIDAY WITH GUSTS
20-25 KTS EXPECTED.

HIGH PRES OVERHEAD FRIDAY EVENING...WITH RETURN FLOW INCREASING
SATURDAY. SLY CHANNELING EXPECTED WITH SCA LIKELY BY LATE MORNING
SATURDAY CONTINUING WELL INTO SATURDAY NIGHT.

SOUTHERLY FLOW WITH GUSTS EXCEEDING SMALL CRAFT ADVISORY CRITERIA IS
LIKELY SUNDAY INTO SUNDAY EVENING AHEAD OF A COLD FRONT THAT WILL
SLOWLY CROSS THE WATERS LATE MONDAY. WINDS DIMINISH AS THE FRONT
PASSES...THEN STALLS NEAR THE WATERS THROUGH THE MIDDLE OF NEXT WEEK.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...WINTER WEATHER ADVISORY UNTIL 7 AM EST FRIDAY FOR VAZ503.
WV...WINTER WEATHER ADVISORY UNTIL 7 AM EST FRIDAY FOR WVZ501-505.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EST FRIDAY FOR ANZ530>543.

&&

$$






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