Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 190714
AFDLWX

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

.SYNOPSIS...
AN UPPER TROUGH AXIS WILL CLEAR THE AREA LATER TONIGHT...WITH
CANADIAN HIGH PRESSURE BUILDING TROUGH MONDAY. A SLOW MOVING
CUT OFF UPPER LEVEL LOW PRESSURE SYSTEM WILL HOVER AROUND THE EAST
COAST THROUGH MUCH OF NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
HIGH PRESSURE WILL BUILD INTO THE GREAT LAKES AND TENNESSEE VALLEY
OVERNIGHT WHILE A COLD FRONT CONTINUES TO MOVE OFF THE COAST. A
NORTHWEST FLOW IN BETWEEN THESE SYSTEMS WILL CONTINUE TO USHER IN
CHILLIER AIR DURING THIS TIME.

AN UPPER-LEVEL TROUGH WILL SWING THROUGH THE AREA...BRINGING SOME
CLOUDS WITH IT BUT ANY PRECIPITATION WILL BE LIGHT AND CONFINED TO
LOCATIONS ALONG AND WEST OF THE ALLEGHENY FRONT WHERE THERE IS AN
UPSLOPE COMPONENT TO THE LOW-LEVEL FLOW. THERE MAY BE ENOUGH COLD
AIR FOR A FEW FLURRIES OR SNOW SHOWERS ALONG THE RIDGE TOPS...BUT
LITTLE OR NO SNOW ACCUMULATION IS EXPECTED. MIN TEMPS WILL RANGE
FROM THE UPPER 20S AND LOWER 30S ALONG THE RIDGE TOPS OFF THE
ALLEGHENY HIGHLANDS...TO THE LOWER AND MIDDLE 40S ACROSS MOST
OTHER LOCATIONS.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/...
UPDATE...A FREEZE WATCH IS IN EFFECT FOR THE POTOMAC
HIGHLANDS...ALLEGHENY HIGHLANDS AND PORTIONS OF THE CENTRAL
SHENANDOAH VALLEY LATE SUNDAY NIGHT INTO MONDAY MORNING.

PREVIOUS DISCUSSION...

SFC HIGH PRESSURE CENTER ENTERS THE CWA FROM THE WEST
SUNDAY AFTERNOON...MOVING OFFSHORE MONDAY MORNING. GUSTY NWLY FLOW
THROUGH SUNDAY...EXPECT 30 MPH GUSTS THROUGH MUCH OF THE DAY.
DOWNSLOPING FLOW WILL WARM AS IT DESCENDS WITH MORNING CLOUDS OVER
THE MOUNTAIN QUICKLY DISSIPATING (ALONG WITH ANY LIGHT WINTRY MIX
PRECIP WEST OF THE ALLEGHENY FRONT). MAX TEMPS GENERALLY MID TO
UPR 50S AT LOWER ELEVATION. 60F POSSIBLE EAST OF THE BLUE RIDGE.

SUNDAY NIGHT...HIGH PRESSURE CROSSES THE MOUNTAINS IN THE
EVENING...TO THE CHESAPEAKE BAY BY SUNRISE. CLEAR...CALM...AND DRY
WILL MAKE FOR AN IDEAL RADIATIONAL COOL NIGHT. MIN TEMPS AROUND
FREEZING LIKELY PIEDMONT AND VALLEYS WEST OF THE BLUE RIDGE
(INVERSION FOR RIDGES). COULD NEED A FROST OR FREEZE HEADLINE FOR
NEARLY ALL OF THE CWA (GRIDDED GUIDANCE GENERALLY HAS A WARM BIAS
FOR INTERIOR SOUTHERN MARYLAND ON CLEAR/CALM NIGHTS). LOW TO MID 40S
FOR URBAN/NEAR SHORE.

RETURN FLOW MONDAY AS HIGH PRESSURE MOVES OFFSHORE AND LOW PRESSURE
APPROACHES FROM THE GREAT LAKES. MOISTURE RETURNS WITH RAIN CHANCES
INCREASING FROM THE WEST MONDAY AFTERNOON AHEAD OF AN AMPLIFYING
TROUGH. UPR TROUGH AXIS CROSSES THE CWA MONDAY NIGHT WITH LOW
CHANCES FOR LIGHT RAIN ACROSS THE CWA.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
ECMWF HAS 500MB CUT-OFF LOW OVER WESTERN PA TUESDAY NIGHT WITH VORT
MAX DROPPING DOWN WEST SIDE OF TROUGH. VORT MAX WILL ROUND THE
BOTTOM OF THE TROUGH WEDNESDAY MORNING AND MOVE OFFSHORE BY
WEDNESDAY EVENING. UPPER LEVEL LOW WILL CROSS CWA LATE TUESDAY INTO
WEDNESDAY AND MOVE OFFSHORE WEDNESDAY EVENING. BROAD UPPER LEVEL LOW
PRESSURE PATTERN WILL SET UP OVER CANADA AND NEW ENGLAND THROUGH THE
REST OF THE PERIOD. CWA WILL BE ON THE SOUTHERN EDGE OF THE TROUGH
WITH SHORTWAVE CROSSING AREA FRIDAY.

ALTHOUGH ANTICIPATED PATH OF THE SURFACE LOW WILL KEEP THE STRONGEST
OF ITS ASSOCIATED PRECIPITATION IN PA...OUR CWA LOOKS TO GET WET ALSO.
GREATEST OPPORTUNITY FOR PRECIPITATION APPEARS TO BE TUESDAY NIGHT
THROUGH THURSDAY.

&&

.AVIATION /07Z SUNDAY THROUGH THURSDAY/...
VFR CONDS THROUGH THE TAF PERIOD. NW WINDS LATE
TONIGHT...OCCASIONAL GUSTS TO 15KT POSSIBLE BUT NOT EXPECTED TO BE
FREQUENT ENOUGH TO INCLUDE IN TAFS. GUSTS BECOME MORE FREQUENT
SUNDAY MORNING THROUGH THE AFTERNOON. PREVAILING 20KT GUSTS IN
TAFS...BUT SOME GUSTS TO 25KT POSSIBLE. GUSTS EASE THROUGH THE
EVENING AS THE HIGH CENTER CROSSES INTO THE AREA.

VFR CONTINUES THROUGH MONDAY AS THE HIGH SHIFTS OFFSHORE. LOW
PRESSURE APPROACHES TUESDAY WITH RAIN CHANCES INCREASING. LOW
LINGERS INTO LATE IN THE WEEK.

&&

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

RETURN FLOW MONDAY AS HIGH PRESSURE MOVES OFFSHORE. LOW PRESSURE
DRIFTS OVER THE REGION THEN INTO THURSDAY.

&&

.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.

&&

$$
UPDATES TO SHORT TERM...AVIATION AND MARINE...KCS







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