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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