Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 191420 AAA
AFDLWX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1020 AM EDT SUN OCT 19 2014

.SYNOPSIS...
AN UPPER TROUGH AXIS WILL CLEAR TODAT...WITH HIGH PRESSURE
BUILDING TROUGH MONDAY. A SLOW MOVING UPPER LEVEL LOW WILL CROSS
THE REGION TUESDAY AND PERSIST ALONG THE COAST THROUGH THURSDAY.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A SHARP UPPER TROUGH AXIS NOW PULLING AWAY FROM THE AREA AND THIS
LAST WAVE OF SUBSIDENCE WILL CONTINUE MAKING IT A BREEZY DAY.
SOLID 20-30KT GUSTS THAT BEGAN JUST AFTER DAWN WILL CONTINUE
THROUGHOUT THE AFTN AS GOOD BOUNDARY LAYER MIXING PUSHES THE
HIGHER GUSTS TOWARD THE SFC. THE EXIT OF THIS UPPER WAVE ALSO
TAKES THE CLOUD COVER AWAY OVER TIME. ONLY THE UPSLOPE STRATUS
WILL CONTINUE INTO THE AFTN HRS...CLEAR ELSEWHERE. A SECOND-
STRAIGHT DAY OF THE COOL/DRY CANADIAN AIRMASS BRINGING IN THE DRY
AIR. NOT ONLY WILL TEMPS BE PREVENTED FROM MAKING TOO MUCH OF AN
INCREASE TODAY BUT DEWPOINTS WILL DECREASE INTO THE L-M30S. THIS
BRINGS BACK THE CHILL TO THE AIR. THIS WILL SET THE AREA UP FOR
ONE OF THE COLDEST NIGHTS OF THE SEASON SO FAR.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
HIGH PRESSURE BUILDS OVERHEAD TONIGHT...AND THEN SHIFTS SEWD TO
THE NC COAST BY EARLY MONDAY MORNING. MOSTLY CLEAR SKIES AND LIGHT
WINDS WILL MAKE FOR AN IDEAL RADIATIONAL COOLING NIGHT. USED
COMBINATION OF MAV/MET GUIDANCE AND SREF FOR LOW TEMPS...WHICH ARE
FORECAST TO BE NEAR OR BELOW FREEZING ACROSS THE HIGHLANDS AND
PORTIONS OF THE CENTRAL SHENANDOAH VALLEY. A FREEZE WATCH HAS BEEN
ISSUED FOR THESE AREAS. FROST WILL ALSO BE POSSIBLE OVER A GOOD
PORTION OF THE FORECAST AREA. ONLY UNCERTAINTY REGARDING FROST AND
FREEZING TEMPS WILL BE THE ONSET OF WARM AIR ADVECTION AROUND THE
HIGH AS IT SHIFTS TO THE SE OF US...AND POTENTIAL ARRIVAL OF MID-
HIGH LEVEL CLOUDS. WILL LET LATER SHIFTS ASSESS THIS...SO WILL
REFRAIN FROM A FREEZE WARNING AND FROST ADVISORIES AT THIS TIME.

MONDAY...QUICK WARM UP AFTER A CHILLY NIGHT SINCE RETURN FLOW WILL
BE INCREASING AS HIGH PRESSURE SHIFTS OFFSHORE. A LOW PRESSURE
SYSTEM APPROACHES FROM THE GREAT LAKES MONDAY NIGHT. MOISTURE SLOWLY
RETURNS WITH SLIGHT POPS FOR RAIN BY LATE MONDAY AFTERNOON IN THE
POTOMAC HIGHLANDS. LOW CHANCE POPS THEN SPREAD EAST TO THE BLUE
RIDGE OVERNIGHT AS THE THE PARENT LOW CROSSES BUFFALO NY. THE SFC
TROUGH CROSSES THE CWA MONDAY NIGHT. THE LOW CROSSES THE CWA TUESDAY
NIGHT. LOW CHANCES FOR LIGHT RAIN ACROSS THE CWA AS DOWNSLOPING FLOW
WILL GREATLY LIMIT THE COVERAGE OF RAIN. TEMPERATURES NEAR NORMAL
WITH DOWNSLOPING FLOW COUNTERACTING CLOUD COVER FROM KEEPING
TEMPERATURES TOO LOW.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
CUT OFF LOW PRESSURE LINGERS ALONG THE MID-ATLANTIC COAST WEDNESDAY
AND THURSDAY. 00Z GFS/ECMWF OPERATIONAL RUNS DEPICTING UPR LOW
CROSSING THE CENTRAL MID-ATLANTIC TUESDAY NIGHT...THEN LINGERING
ALONG THE MID-ATLANTIC COAST THROUGH INTO THURSDAY NIGHT. NWLY FLOW
WITH PERIODIC RAIN...ALONG WITH NEAR NORMAL TEMPERATURES. COLD AIR
COMES IN THE WEST SIDE...AND MOISTURE NOW LOOKS GREATER...SO SOME
HIGHLAND SNOW IS POSSIBLE BOTH DAYS.

&&

.AVIATION /13Z SUNDAY THROUGH THURSDAY/...
VFR CONDS THROUGH THE TAF PERIOD...THROUGH GUSTY NW WINDS WILL BE
A CONCERN THROUGHOUT THE DAYTIME HRS. PEAK SFC GUSTS WILL BE THE
IN 25-30KT RANGE. HEADING INTO THE POST-SUNSET HRS
TONIGHT...WINDS WILL GRADUALLY DROP OFF W/ ONLY OCCASIONAL GUSTS
10-15KT THROUGH AROUND 3-4Z.

VFR CONTINUES THROUGH MONDAY AS THE HIGH SHIFTS OFFSHORE WITH RETURN
FLOW. LOW PRESSURE APPROACHES FROM THE NORTHWEST TUESDAY WITH
DOWNSLOPING FLOW LIMITING RAIN CHANCES. LOW LINGERS ALONG THE COAST
THROUGH THURSDAY WITH GUSTY NORTHWEST FLOW STARTING WEDNESDAY.

&&

.MARINE...
A SMALL CRAFT ADVISORY IS IN EFFECT FOR ALL OF THE WATERS INTO THE
EVE HRS. NWLY FLOW WITH GUSTS 25 TO 30 KT EXPECTED. WINDS DIMINISH
LATE TONIGHT AS HIGH PRESSURE CENTER CROSSES THE BAY LATE IN THE
NIGHT.

RETURN FLOW MONDAY AS HIGH PRESSURE MOVES OFF SHORE. LOW PRESSURE
DRIFTS OVER THE REGION MONDAY NIGHT AND TUESDAY...THEN LINGERS OFF
SHORE WEDNESDAY AND THURSDAY. EXTENDED SCA EXPECTED IN NWLY FLOW ON
BACK SIDE OF LOW WEDNESDAY INTO FRIDAY.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...FREEZE WATCH FROM LATE TONIGHT THROUGH MONDAY MORNING FOR
     MDZ501-502.
VA...FREEZE WATCH FROM LATE TONIGHT THROUGH MONDAY MORNING FOR
     VAZ025>027-029-503-504.
WV...FREEZE WATCH FROM LATE TONIGHT THROUGH MONDAY MORNING FOR
     WVZ050-055-501>506.
MARINE...SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR ANZ531>534-
     537-539>541-543.
     SMALL CRAFT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR ANZ530-
     535-536-538-542.

&&

$$
UPDATE...GMS
PREV DISCUSSION...KCS/BAJ









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