Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 011339
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
939 AM EDT WED OCT 1 2014

.SYNOPSIS...
HIGH PRESSURE WILL BUILD OVERHEAD THROUGH THURSDAY. A STRONG COLD
FRONT WILL APPROACH THE AREA FRIDAY BEFORE PASSING THROUGH FRIDAY
NIGHT INTO EARLY SATURDAY. HIGH PRESSURE WILL RETURN FOR THE
WEEKEND...BRINGING DRIER AND NOTICEABLY COOLER CONDITIONS. THE HIGH
WILL MOVE OFFSHORE EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AN UPPER LEVEL TROUGH WILL CONTINUE TO SPIN ACROSS THE NORTHEAST
THIS MORNING. A SHORTWAVE TROUGH EMBEDDED IN THE CYCLONIC FLOW
ALOFT AND THAT BROUGHT SHOWERS TO THE REGION THIS MORNING WILL
MOVE OFF THE EAST COAST THIS MORNING. AT THE SFC...A WEDGE OF HIGH
PRESSURE IS STRENGTHENING AS IT NOSES DOWN THE EASTERN SEABOARD.
LOW CLOUDS...PATCHES OF FOG AND DRIZZLE HAVE BEEN OBSERVED THIS
MORNING MAINLY ALONG AND EAST OF THE BLUE RIDGE MTNS FROM THE
PIEDMONT TO FREDERICK COUNTY MD.

CLOUDS FROM THE SHORTWAVE TROUGH WILL EXIT LATE THIS MORNING AND A
MIX OF SUN AND CLOUDS SHOULD BE OBSERVED ACROSS THE I-95 CORRIDOR
THIS AFTERNOON. FURTHER WEST AND AGAINST THE BLUE RIDGE AND
POTOMAC HIGHLANDS...LOW CLOUDS WILL BE HARDER TO MIX OUT AND THEREFORE
KEPT A MOSTLY CLOUDY FORECAST FOR THIS AREAS.

THE UPPER LEVEL TROUGH WILL MOVE EASTWARD TODAY BUT A FEW OTHER
VORT MAXES EXIST IN THE CYCLONIC FLOW ALOFT. ISO-SCT SHOWERS ARE
POSSIBLE WEST OF THE BLUE RIDGE. MOISTURE CONVERGENCE WILL ALSO
AID IN SHOWER DEVELOPMENT IN THIS AREA.

PREVIOUS DISCUSSION...
ANOTHER MODERATED OVERNIGHT PERIODS...ALTHOUGH LOWS WILL BE A COUPLE
DEG LOWER THAN THE CURRENT PERIOD - L-M50S. MORE PATCHY FOG AND
BATCHES OF LOW CLOUDS WILL COVER PARTS OF THE REGION. BLENDED THE
BIAS-CORRECTED MAV/MET/EURO FOR HIGHS AND LOWS FOR TODAY.

&&

.SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
AFTER THE LAST ARM OF THE EXITING UPPER LOW MOVES OFF THE COAST AND
AWAY FROM THE AREA EARLY THU...A BRIEF VISIT FROM A WEAK IN-SITU
HIGH PRES RIDGE WILL MOVE OVER THE AREA. THIS FEATURE WILL NOT ONLY
PREVENT PRECIP FOR THE DAY...IT WILL CLEAR OUT THE MORE DENSE
POCKETS OF LOW LEVEL MOISTURE BUILT-UP FROM PREVIOUS DAYS. STILL
SOME LOW-MID CLOUD DECKS DISPERSED ABOUT THE REGION FOR A GENERALLY
PARTLY SUNNY SKY BUT CERTAINLY MORE SUN POKING THRU THAN IN PAST
DAYS. HIGH TEMPS NOT EXPECTED TO BE ANY WARMER HOWEVER...AS A LIGHT
BUT STEADY ONSHORE FLOW WILL MODERATE CONDITIONS NEAR THE
SFC...DESPITE MORE SUN.

HIGH PRESSURE OVER NEW ENGLAND WILL CONTINUE TO WEDGE SOUTH AND
WEST INTO THE MID-ATLANTIC COAST THURSDAY NIGHT. LOW PRESSURE
WILL TRACK THROUGH THE GREAT LAKES WHILE A STRONG COLD FRONT
ASSOCIATED WITH THE LOW MOVES THROUGH THE MIDWEST. AN ONSHORE FLOW
IS EXPECTED TO INCREASE OVER OUR AREA IN BETWEEN THESE TWO SYSTEMS
AND THIS WILL CAUSE MOISTURE TO MOVE IN FROM THE ATLANTIC. ALSO
WARM AND MOIST AIR WILL OVERRUN THE RELATIVELY COOLER AIR AT THE
SURFACE. THIS WILL CAUSE PLENTY OF CLOUDS TO DEVELOP. A SHOWER OR
TWO CANNOT BE RULED OUT...BUT THAT HAS BEEN LEFT OUT OF THE
FORECAST SINCE LIFT WILL BE WEAK AND THE DEEP MOISTURE WILL REMAIN
TO OUR WEST. HOWEVER...THERE SHOULD BE ENOUGH LOW-LEVEL MOISTURE
TRAPPED UNDERNEATH THE SUBSIDENCE INVERSION FOR LOW
CLOUDS ALONG WITH PATCHY FOG AND DRIZZLE LATE THURSDAY NIGHT. MIN
TEMPS WILL RANGE FROM THE MIDDLE TO UPPER 50S ACROSS MOST
LOCATIONS TO THE LOWER 60S IN DOWNTOWN WASHINGTON AND BALTIMORE.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
LOW CLOUDS ALONG WITH PATCHY FOG AND DRIZZLE ARE EXPECTED FRIDAY
MORNING. CLOUDS SHOULD GIVE WAY TO SOME SUNSHINE ACROSS CENTRAL
VIRGINIA INTO THE SHENANDOAH VALLEY AND POTOMAC HIGHLANDS.
HOWEVER...LOW CLOUDS MAY HANG ON FOR A WHILE ACROSS THE
METROPOLITAN AREAS BEFORE GIVING WAY TO SOME SUNSHINE LATER IN THE
AFTERNOON.

THE STRONG COLD FRONT WILL MOVE INTO THE OHIO VALLEY FRIDAY BEFORE
PASSING THROUGH OUR AREA FRIDAY NIGHT INTO EARLY SATURDAY. A
SOUTHERLY FLOW AHEAD OF THE COLD FRONT WILL USHER IN PLENTY OF
MOISTURE ACROSS OUR REGION. LATEST GUIDANCE HAS SLOWED DOWN THE
TIMING OF THE FRONTAL PASSAGE...AND THIS MAKES SENSE GIVEN THE
FACT THAT THERE WILL BE PLENTY OF RIDGING AHEAD OF THIS SYSTEM
OVER THE WESTERN ATLANTIC. THEREFORE...THE POPS HAVE BEEN SLOWED
DOWN A BIT...WITH THE BEST CHANCE FOR SHOWERS OCCURRING LATE
FRIDAY THROUGH FRIDAY EVENING IN THE POTOMAC HIGHLANDS...FRIDAY
NIGHT IN THE SHENANDOAH VALLEY...AND OVERNIGHT FRIDAY INTO EARLY
SATURDAY FOR THE WASHINGTON AND BALTIMORE METROPOLITAN AREAS. THE
SYNOPTIC PATTERN SUGGESTS THAT A QLCS WOULD DEVELOP DUE TO THE
STRONG FORCING FROM THIS SYSTEM...BUT INSTABILITY LOOKS TO BE WEAK
AND IT WILL BE MOVING THROUGH AT AN UNFAVORABLE TIME FRIDAY NIGHT.
THERE WILL BE STRONG WINDS ALOFT FROM THE LOW-LEVEL JET THAT COULD
MIX DOWN...BUT WITH LITTLE TO NO INSTABILITY IT APPEARS THAT THE
THREAT FOR SEVERE WEATHER IS MINIMAL. WILL CONTINUE TO MONITOR
BECAUSE JUST A LITTLE MORE INSTABILITY WILL SIGNIFICANTLY ENHANCE
THE THREAT FOR GUSTY WINDS WITH A QLCS FRIDAY NIGHT.

THE COLD FRONT WILL MOVE AWAY FROM THE AREA SATURDAY AND HIGH
PRESSURE WILL RETURN FOR SATURDAY AFTERNOON THROUGH SUNDAY. A WEST
TO NORTHWEST FLOW BEHIND THE COLD FRONT WILL USHER IN DRIER AND
NOTICEABLY COOLER CONDITIONS DURING THIS TIME. AN UPSLOPE COMPONENT
TO THE LOW-LEVEL FLOW WILL CAUSE MORE CLOUDS ALONG AND WEST OF THE
ALLEGHENY FRONT WITH THE POSSIBILITY FOR A FEW SHOWERS. A COUPLE
SNOW SHOWERS ARE POSSIBLE SATURDAY NIGHT ALONG THE RIDGE TOPS.

THE HIGH WILL MOVE OFF THE COAST EARLY NEXT WEEK AND A SOUTHERLY
FLOW WILL BRING MILDER CONDITIONS DURING THIS TIME. ANOTHER COLD
FRONT MAY APPROACH DURING THE MIDDLE PORTION OF THE WEEK. SHOWERS
ARE POSSIBLE AHEAD OF THIS SYSTEM...ESPECIALLY TUESDAY.
HOWEVER...TIMING AND DETAILS REMAIN UNCERTAIN THIS FAR OUT.

&&

.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
TRAPPED LOW LEVEL MOISTURE CONTINUES TO CREATE PATCHY AREAS OF
LOW-MED RANGE VSBY FOG. ONLY ISOLATED DENSE FOG OBS
APPEARING...THROUGH A FEW MORE MAY POP-UP IN THE NEXT COUPLE OF HRS.
THE MAIN CONCERN IS FROM PATCHY LOW CIGS...ESP ACROSS THE PIEDMONT
AND SHEN VLY. LOTS OF RANDOM CIG HEIGHTS ACROSS THE AREA AS A
TURBULENT AND COMPLEX UPPER LOW ROTATES BY JUST TO OUR NORTH. THIS
FEATURE WILL REMAIN NORTH OF THE AREA TODAY...MOVING TOWARD THE ATLC
COAST BUT KEEPING A WAVE OF LOW-LEVEL MOISTURE CENTERED OVER THE
MID-ATLC THRU THE DAY. SHOWER ACTIVITY WILL BECOME MORE ISOLATED
HEADING INTO THE POST-DAWN HRS...AND GROUND FOG WILL DISSIPATE OFF -
AS WILL THE LOW DECKS BY MID MRNG. A LIGHT ENE SFC WIND WILL
CONTINUE THROUGHOUT THE DAY AND INTO TONIGHT. MORE PATCHY FOG AND
SOME LOW CLOUDS POSSIBLE AGAIN OVERNIGHT TONIGHT.

AN ONSHORE FLOW WILL CAUSE LOW CLOUDS OVERNIGHT THURSDAY ALONG
WITH PATCHY FOG AND DRIZZLE. IFR CONDITIONS ARE EXPECTED DURING
THIS TIME. THE LOW CLOUDS WILL HANG AROUND FRIDAY MORNING BEFORE
SLOWLY BREAKING FRIDAY AFTERNOON. A STRONG COLD FRONT WILL PASS
THROUGH THE TERMINALS FRIDAY NIGHT...BRINGING SHOWERS AND POSSIBLY
A THUNDERSTORM. WEST TO NORTHWEST WINDS ARE EXPECTED BEHIND THE
FRONT SATURDAY AND SUNDAY.

&&

.MARINE...
AN UPPER LOW OVER CNTRL PA WILL CONTINUE TO MOVE EAST TODAY. HIGH
PRES OFF THE ATLC COAST IS DIRECTING A STEADY ONSHORE SFC WIND OVER
THE WATERS. THIS FLOW WILL CONTINUE...BOTH DIRECTION AND RANGE OF
SPEEDS...THRU THE REST OF THE DAY - BELOW SCA CRITERIA. DRY WX AND
ONLY A LIGHT E-SE ONSHORE FLOW TONIGHT INTO THU...AS A HIGH PRES
RIDGE MOVES ACROSS THE AREA AND PREVENTS MUCH IN THE WAY OF PRECIP.

A STRONG COLD FRONT WILL APPROACH THE WATERS FRIDAY BEFORE PASSING
THROUGH LATE FRIDAY NIGHT INTO SATURDAY. SOUTHERLY WINDS WILL
INCREASE AHEAD OF THE FRONT. WINDS WILL SHIFT TO THE WEST-
NORTHWEST BEHIND THE FRONT LATER SATURDAY MORNING THROUGH SUNDAY.
A SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED FOR PORTIONS OF THE
WATERS AHEAD OF THE FRONT FRIDAY AFTERNOON INTO FRIDAY NIGHT...AND
ALSO BEHIND THE FRONT SATURDAY AND SUNDAY.

&&

.TIDES/COASTAL FLOODING...
AN ONSHORE FLOW HAS CAUSED TIDAL ANOMALIES TO INCREASE TO AROUND
ONE-HALF FOOT ABOVE NORMAL EARLY THIS MORNING. THE ANOMALIES
SHOULD NOT CHANGE MUCH SINCE THE ONSHORE FLOW WILL PERSIST
TODAY...BUT IT WILL BE LIGHT. THE HIGH TIDE THIS AFTERNOON AND
EARLY EVENING WILL BE THE LOWER OF THE TWO...SO MINOR TIDAL
FLOODING IS NOT EXPECTED. HOWEVER...THE HIGH TIDE CYCLE LATER THIS
EVENING INTO LATE WILL BE THE HIGHER OF THE TWO. MINOR TIDAL
FLOODING IS POSSIBLE FOR SENSITIVE AREAS ALONG THE WESTERN SHORE
OF THE MARYLAND CHESAPEAKE BAY AND THE SHORE OF THE UPPER TIDAL
POTOMAC RIVER.

THE ONSHORE FLOW WILL CONTINUE FOR THURSDAY THROUGH FRIDAY NIGHT.
THE FLOW WILL STRENGTHEN AND TURN MORE SOUTHERLY FRIDAY AFTERNOON
INTO FRIDAY NIGHT AHEAD OF A COLD FRONT. MINOR TIDAL FLOODING IS
POSSIBLE NEAR HIGH TIDE...ESPECIALLY DURING THE LATE NIGHT AND
EARLY MORNING TIDE CYCLE. WATER LEVELS SHOULD BE HIGHEST DURING
THE HIGH TIDE LATE FRIDAY NIGHT INTO EARLY SATURDAY MORNING.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...BJL
NEAR TERM...HAS/GMS
SHORT TERM...BJL/GMS
LONG TERM...BJL
AVIATION...BJL/HAS
MARINE...BJL/GMS
TIDES/COASTAL FLOODING...GMS






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