Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 010126 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 926 PM EDT THU APR 30 2015 .SYNOPSIS...
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LOW PRESSURE WILL IMPACT THE AREA THROUGH TONIGHT BEFORE MOVING OFFSHORE FRIDAY. HIGH PRESSURE WILL BUILD OVERHEAD DURING THE WEEKEND BEFORE SHIFTING TO THE SOUTH EARLY NEXT WEEK. A COLD FRONT MAY IMPACT THE AREA DURING THE MIDDLE PORTION OF NEXT WEEK.
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&& .NEAR TERM /THROUGH FRIDAY/...
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THUNDERSTORMS AND INTENSITY OF CONVECTION HAS BEEN ON THE WANE WITH SUNSET. ATMOSPHERE IS PROBABLY PRETTY WELL WORKED OVER AS THE PRECIP HAS BEEN FAIRLY WIDESPREAD EXCEPT CLOSER TO THE BAY. CLOSED UPPER LOW IS CURRENTLY OVER THE OHIO VALLEY AND WILL DIVE TOWARD THE CAROLINAS OVERNIGHT. THIS WILL HELP AN OFFSHORE LOW BEGIN TO STRENGTHEN. A SFC TROUGH EXTENDS FROM THE LOW TOWARD THE CENTRAL APPALACHIANS...WHICH IS REPRESENTED BY THE NW-SE ORIENTED BAND OF SHOWERS. WHILE COVERAGE/EVOLUTION IS A LITTLE IN QUESTION...EXPECT THE GENERAL TREND IS FOR THE SHOWERS TO PIVOT OVERNIGHT...EVENTUALLY BECOMING FOCUSED ACROSS THE SOUTHERN CWA BY DAYBREAK. WILL MONITOR THE TRENDS BUT IT IS POSSIBLE AREAS NE OF DC MAY NOT SEE MUCH ADDITIONAL SHOWER ACTIVITY ASSOCIATED WITH THIS SYSTEM. CLOUDS WILL LOWER OVERNIGHT AND THERE MAY BE SOME LIGHT FOG WHERE SHOWERS PERSIST...WITH RIDGETOPS POSSIBLY INTERSECTING THE CLOUD LAYER. TEMPERATURES FELL QUICKLY WITH THE SHOWERS AND EXPECT THEM TO SETTLE INTO THE MID 40S-LOWER 50S. THE COASTAL LOW WILL TAKE OVER OFF THE CAROLINAS ON FRIDAY...AS THE UPPER LOW BEGINS TO PUSH IT OUT TO SEA. THESE SYSTEMS COMBINED WILL INFLUENCE SENSIBLE WEATHER ELEMENTS INTO FRIDAY WITH OCCASIONAL SHOWERS...CLOUDY CONDITIONS. THE GREATEST COVERAGE OF SHOWERS IS EXPECTED IN CENTRAL VA/SOUTHERN MD...AS WELL AS THE POTOMAC HIGHLANDS DUE TO AN UPSLOPE COMPONENT. READINGS WILL NOT RISE ALL THAT MUCH ON FRIDAY GIVEN ONSHORE FLOW AND CLOUD COVER. AFTERNOON HIGHS ONLY IN THE UPPER 50S TO LOWER 60S ARE EXPECTED.
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&& .SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
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THE UPPER LOW AND SURFACE LOW WILL BE OFF THE NORFOLK COAST FRIDAY NIGHT. MOISTURE AND ISO SHOWERS WILL TAPER OFF WITH THE EXCEPTION OF THE POTOMAC HIGHLANDS. WEAK VORTICITY ADVECTION IS PROGGED ON THE BACK SIDE OF THE UPPER LOW AND A FEW SHOWERS WILL BE POSSIBLE OUT IN THE HIGHLANDS. FCST MIN TEMPS IN THE UPPER 40S LOW 50S EXPECTED FRIDAY NIGHT. HIGH PRESSURE WILL MOVE INTO THE MID-ATLANTIC SATURDAY. A SECONDARY TROUGH WILL SWING THROUGH THE REGION. COLD AIR ALOFT AND GOOD SFC HEATING WILL MAY PRODUCE A LITTLE INSTABILITY SATURDAY AFTERNOON. AS PVA MOVES INTO THE REGION ALONG THE TROUGH AXIS...SHOWERS MAY FORM ALONG AND EAST OF THE BLUE RIDGE MTNS AND SLOWLY TRACK EASTWARD. AT THIS TIME...COVERAGE SEEMS WEAK AND THEREFORE KEPT A CHANCE OF SHOWERS IN THE FORECAST. FCST MAX TEMPS IN THE UPPER 60S LOW 70S SATURDAY. LOSS OF DAYTIME HEATING WILL SUPPRESS ANY SHOWER ACTIVITY SAT NIGHT. HIGH PRESSURE WILL MOVE OVERHEAD. FCST MIN TEMPS IN THE 40S AND LOW 50S EXPECTED.
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&& .LONG TERM /SUNDAY THROUGH THURSDAY/... EXTENDED WARM-UP WITH SEVERAL DAYS OF HIGH TEMPS ABOVE CLIMO BEGINS SUN AND CONTINUES THROUGH MID WEEK...AS A RESULT OF HIGH PRESSURE AND CONTINUED RETURN FLOW INTO THE REGION. DEWPOINTS WILL ALSO BE INCREASING THROUGH THE PERIOD...WHICH WILL KEEP NIGHTTIME TEMPS U50S/L60S. PRECIP CHANCES VERY LOW THROUGH THE PERIOD...BUT COULD SEE UNSETTLED CONDITIONS RETURN WED ASSOCIATED WITH COLD FRONT THAT DROPS SOUTH AND STALLS NEAR OUR AREA. && .AVIATION /01Z FRIDAY THROUGH TUESDAY/...
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THE THREAT OF THUNDERSTORMS HAS ENDED AT THE TERMINALS. IN FACT...CONFIDENCE IS LOW ON HOW MUCH ADDITIONAL SHOWER ACTIVITY THE DC/BALTIMORE TERMINALS WILL SEE OVERNIGHT. OCCASIONAL SHOWERS A BETTER BET AT MRB/CHO. CIGS ARE EXPECTED TO DROP AT LEAST INTO THE MVFR RANGE...AND POSSIBLY IFR LATER TONIGHT...ALTHOUGH CONFIDENCE IN THESE CONDITIONS DECREASES WITH NE EXTENT. MVFR VSBYS MAY ALSO DEVELOP AT IAD...MRB AND CHO. DID NOT INCLUDE THESE ELSEWHERE FOR NOW. SHOWERS WILL PULL AWAY TO THE SE FRIDAY MORNING AND CIGS GRADUALLY IMPROVE FRIDAY AS LOW PRESSURE PULLS AWAY FROM THE REGION. WINDS WILL BE VARIABLE THIS EVENING DUE TO LINGERING OUTFLOW EFFECTS BUT WILL EVENTUALLY TAKE ON AN EASTERLY COMPONENT LATER TONIGHT UNTIL LATE FRIDAY. VFR CONDITIONS EXPECTED FRI NIGHT THROUGH SATURDAY. -SHRA POSSIBLE SATURDAY AFTERNOON BUT COVERAGE IS UNCERTAIN AT THIS TIME AND WILL LIKELY BE ALONG THE HIGHER TERRAIN. VFR CONDITIONS EXPECTED SUN AND MONDAY.
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&& .MARINE...
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LIGHT AND VARIABLE WINDS WILL INCREASE TONIGHT AS LOW PRESSURE DEEPENS OFF THE CAROLINAS. SCA CONDITIONS ARE LIKELY OVERNIGHT INTO FRIDAY WITH GUSTS OVER 20 KTS EXPECTED. SHOWERS WILL BE MOST LIKELY IN THE SOUTHERN MD BAY/LOWER POTOMAC THROUGH FRIDAY. SCA CONDITIONS ARE POSSIBLE GOING INTO FRIDAY NIGHT BUT UNCERTAINTY EXISTS WITH THE PLACEMENT OF THE SFC LOW AT THAT TIME. N-NE 10-15 KT WILL CONTINUE ON THE WATERS AND WEAKEN BY SATURDAY MORNING. POSSIBILITY OF SCA LATE MONDAY...ESPECIALLY OVER THE SOUTHERN WATERS.
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&& .TIDES/COASTAL FLOODING...
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A NORTHEAST WIND WILL INCREASE TONIGHT...THIS WILL KEEP WATER LEVELS ELEVATED BUT THE NORTHERLY COMPONENT WILL LIKELY KEEP ANOMALIES LOW ENOUGH SO WATER LEVELS REMAIN BELOW MINOR FLOODING THRESHOLDS WITH THE HIGH TIDE CYCLE LATE TONIGHT INTO FRIDAY MORNING. WILL HAVE TO MONITOR WHETHER ANOMALIES CAN RISE HIGH ENOUGH BY FRIDAY EVENING TO APPROACH MINOR FLOOD LEVELS BEFORE WINDS BECOME NORTHERLY.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL NOON EDT FRIDAY FOR ANZ530-531-535- 538-539. SMALL CRAFT ADVISORY UNTIL 6 PM EDT FRIDAY FOR ANZ532>534-536- 537-540>543.
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&& $$ SYNOPSIS...HAS NEAR TERM...ADS/KRW SHORT TERM...HAS LONG TERM...MSE AVIATION...ADS/HAS/MSE MARINE...ADS/HAS/MSE/KRW TIDES/COASTAL FLOODING...KRW/ADS

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