Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 131849 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 249 PM EDT SUN APR 13 2014 .SYNOPSIS...
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HIGH PRESSURE WILL REMAIN OFF THE EAST COAST THROUGH MONDAY. A COLD FRONT WILL MOVE THROUGH THE MID-ATLANTIC REGION LATE MONDAY NIGHT AND TUESDAY. HIGH PRESSURE WILL BUILD INTO THE AREA FOR THE SECOND HALF OF THE WEEK...WITH ANOTHER STORM SYSTEM APPROACHING BY NEXT WEEKEND.
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&& .NEAR TERM /THROUGH MONDAY/...
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FOR THE SECOND DAY IN A ROW...TEMPERATURES HAVE OVERACHIEVED EXPECTATIONS. YESTERDAY IT WAS DUE TO DRY AIR MIXING DOWN. TODAY WARM AIR ADVECTION IS HELPING YIELD THE WARMEST DAY SO FAR IN 2014 EVEN WITH MORE MOISTURE BEING ADVECTED IN ON SOUTHERLY FLOW. THIN HIGH CLOUDS COVER THE SKY BUT THE CONVECTIVE CU WE HAD YESTERDAY HAVE NOT BEEN ABLE TO DEVELOP YET TODAY. THE SOUTHERLY FLOW PERSISTS TONIGHT...WITH DEWPOINTS THAT WILL STAY STEADY OR PERHAPS EVEN RISE. WENT WITH LOWS AT OR SLIGHTLY ABOVE GUIDANCE DUE TO EXPECTED WINDS. WE DID DECOUPLE LAST NIGHT BUT THE INVERSION TONIGHT LOOKS LESS IMPRESSIVE AND DECOUPLING LESS LIKELY EXCEPT PERHAPS IN THE ERN WV PANHANDLE VALLEYS AND THE I-81 CORRIDOR. COULD AGAIN SEE LOW STRATUS DEVELOP MAINLY NEAR THE BAY. CLOUDS WILL INCREASE ON MONDAY AS THE UPPER RIDGE SHIFTS EAST AND AN UPPER TROUGH AND RELATED ENERGY APPROACHES. WENT ABOVE GUIDANCE FOR TEMPS YET AGAIN THOUGH CLOUD COVER WILL PLAY A HUGE ROLE. RAIN CHANCES DO ENTER THE PICTURE MAINLY WEST OF THE BLUE RIDGE IN THE AFTERNOON...WITH TERRAIN ENHANCING THE LIFT POTENTIAL AND THE CONVECTIVE TEMP EASILY BEING REACHED. TEMPS WILL BE HELD DOWN AGAIN ALONG THE BAY JUST AS THEY HAVE BEEN TODAY.
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&& .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
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SFC FRONT MOVES FROM THE OHIO VALLEY TO OUR DOORSTEP ON MONDAY NIGHT. DEEP MOISTURE WILL ADVECT IN AHEAD OF THE FRONT WITH SHOWERS AND PERHAPS TSTMS DEVELOPING. HEAVY RAIN IS POSSIBLE IN CONVECTION THAT DEVELOPS AFTER MIDNIGHT. TEMPERATURES WILL LIKELY NOT FALL BELOW 60 IN MOST AREAS...AND MAYBE NOT BELOW 65 IN THE METRO AREAS. THE COLD FRONT ADVANCES THROUGH THE AREA DURING THE DAY ON TUESDAY. THE POST-FRONTAL RAIN WILL LIKELY BE PUSHED NORTHWARD WITH TIME GIVEN THAT IS WHERE THE UPPER SUPPORT IS HEADED. BUT THERE WILL STILL BE PRECIP ALONG AND AHEAD OF THE FRONT LOCALLY...WITH AVERAGE RAINFALL STILL LOOKING TO BE AROUND AN INCH WITH SOME LOCALLY HIGHER AMOUNTS. THE BIG STORY TUESDAY WILL BE THE CHANGE IN TEMPERATURES. IN THE METRO AREAS...TEMPS WILL BE NEAR 70 IN THE MORNING...BUT ONLY IN THE 40S BY THE AFTERNOON RUSH. THERE WILL BE A BRIEF WINDOW FOR UPSLOPE SNOW /THE WINTER THAT REFUSES TO END/ ALONG THE ALLEGHENY FRONT TUESDAY AFTERNOON AND EARLY EVENING...AND I CANNOT EVEN RULE OUT A FEW SNOWFLAKES ON THE TRAILING END OF THE PRECIP FURTHER EAST. DRY CONDITIONS SHOULD PREVAIL BY MIDNIGHT TUESDAY NIGHT...WITH DEWPOINTS DROPPING INTO THE TEENS. DESPITE A DECENT BREEZE...LOWS NEAR FREEZING LOOK LIKELY NORTH AND WEST OF THE METRO AREAS WITH WIND CHILLS IN THE LOWER 20S. COULD BE NEAR RECORD COLD. HIGH PRESSURE QUICKLY BUILDS IN ON WEDNESDAY...LESSENING THE WINDS...BUT HIGHS WILL ONLY BE AROUND 50.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
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500 MB HEIGHT RISES ARE EXPECTED OVER THE MID-ATLANTIC REGION WEDNESDAY NIGHT INTO THURSDAY DOWNSTREAM OF AN AMPLIFYING TROUGH OVER THE GREAT PLAINS. AT THE SURFACE...STRONG SURFACE HIGH PRESSURE /I.E. ABOUT 1040 MB/ WILL DRIFT EAST ACROSS THE CANADIAN MARITIME PROVINCES. THIS SETUP WILL RESULT IN LOW-LEVEL EAST TO NORTHEAST FLOW AND COOL AIR DAMMING AS HIGHER PRESSURES WEDGE DOWN THE EASTERN SLOPES OF THE APPALACHIAN MOUNTAINS. GIVEN THIS PATTERN...ANOTHER UNSEASONABLY COOL NIGHT IS EXPECTED WEDNESDAY NIGHT WITH LOW TEMPERATURES DROPPING WELL INTO THE 30S...AND TO NEAR OR BELOW FREEZING FOR THE WESTERN HALF OF THE FORECAST AREA. WARM ADVECTION AT 850 MB ENSUES DURING THE DAY THURSDAY...BUT STRUGGLES TO REACH THE SURFACE WITH PERSISTENT EASTERLY FLOW AT THE SURFACE KEEPING HIGH TEMPERATURES IN CHECK /GENERALLY AROUND 60...SEVERAL DEGREES BELOW NORMAL/. CLOUDS WILL GRADUALLY INCREASE THROUGH THE DAY FROM SOUTH TO NORTH AS THE TROUGH OVER THE CENTRAL UNITED STATES SPAWNS SURFACE LOW DEVELOPMENT OVER THE LOWER MISSISSIPPI RIVER VALLEY. MODELS/ENSEMBLES DIVERGE ON THE HANDLING OF SHORTWAVE ENERGY PIVOTING AROUND THE GREAT PLAINS TROUGH THURSDAY NIGHT INTO FRIDAY...AND SUBSEQUENTLY DISAGREE WITH THE TRACK/STRENGTH OF THE RESULTANT SURFACE LOW. STUCK WITH WPC/ENSEMBLE MEAN APPROACH...WHICH DEPICTS A POTENTIAL FOR PRECIPITATION MOVING ACROSS THE AREA SOMETIME BETWEEN FRIDAY NIGHT AND SUNDAY MORNING. DAYTIME HIGHS LOOK TO STAY BELOW NORMAL LATE THIS WEEK INTO NEXT WEEKEND WITH INCREASING CLOUDS AND POTENTIAL PRECIPITATION.
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&& .AVIATION /19Z SUNDAY THROUGH FRIDAY/...
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VFR EXPECTED THROUGH MOST OF THE TAF PERIOD. CANNOT RULE OUT ANOTHER PERIOD OF MVFR STRATUS TONIGHT. THOUGH IT IS IN THE 18Z TAF FORECAST AT ALL TAF SITES EAST OF THE BLUE RIDGE...IT IS MOST LIKELY AT BWI/MTN. THIS WILL BE REASSESSED WITH THE 21Z/00Z UPDATE CYCLES. WILL CONTINUE TO BE WINDY OUT OF THE SOUTH...AROUND 15 KNOTS WITH GUSTS OVER 20 KNOTS TODAY AND MONDAY...AROUND 10 KNOTS AT NIGHT. LOW CIGS/VSBY EXPECTED BY LATE EVENING MONDAY AS SHRA/TSRA MOVE INTO THE AREA. THESE LOW CIGS/VSBY WILL CONTINUE THROUGH TUESDAY WITH A WIND SHIFT EXPECTED DURING THE DAY FROM SOUTHERLY TO NORTHERLY. BREEZY CONDITIONS PERSIST THROUGH TUESDAY NIGHT BUT WINDS LESSEN BY WEDNESDAY AS VFR CONDITIONS RETURN. VFR CONDITIONS ARE EXPECTED WEDNESDAY NIGHT THROUGH THURSDAY NIGHT ACCOMPANIED BY EASTERLY WINDS OF 5 TO 10 KNOTS.
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&& .MARINE...
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SMALL CRAFT ADVISORY NOW EXTENDED THROUGH MONDAY NIGHT. GUSTY WINDS OVER 20 KNOTS CURRENTLY OBSERVED OVER MOST OF THE WATERS...AND THIS WILL CONTINUE THROUGH MONDAY NIGHT. THERE WILL BE PERIODS BOTH TONIGHT AND TOMORROW NIGHT WITH LIGHTER WINDS...ESPECIALLY ON THE UPPER/MIDDLE TIDAL POTOMAC...BUT THE DURATION OF THE LIGHTER WINDS APPEARS TO BE SMALL ENOUGH TO JUST BLANKET THE SMALL CRAFT ADVISORY THROUGH THE PERIOD. THE ADVISORY WILL LIKELY HAVE TO BE EXTENDED THROUGH TUESDAY AND TUESDAY NIGHT...AND PROBABLY EVEN WEDNESDAY. THERE IS ALSO POTENTIAL FOR GALE FORCE GUSTS BEHIND THE FRONT TUESDAY AFTERNOON AND NIGHT. WINDS AND WAVES LIKELY DIMINISH TO BELOW SMALL CRAFT ADVISORY LEVELS WEDNESDAY NIGHT AS HIGH PRESSURE MOVES OVERHEAD. MARGINAL SMALL CRAFT ADVISORY GUSTS ARE POSSIBLE ON PARTS OF THE AREA WATERS THURSDAY AFTERNOON AND EVENING...WITH LIGHT EASTERLY FLOW AND SUB-SMALL CRAFT ADVISORY CONDITIONS FORECAST FOR THE END OF THE WEEK.
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&& .TIDES/COASTAL FLOODING...
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TIDAL ANOMALIES HAVE NOW TURNED POSITIVE AS SOUTHERLY FLOW PERSISTS. POSITIVE ANOMALIES WILL CONTINUE TO GRADUALLY INCREASE OVER THE NEXT 48 HOURS. ALTHOUGH CBOFS GUIDANCE KEEPS ALL WRN SHORE FCST POINTS BELOW MINOR COASTAL FLOOD THRESHOLD...WITH THE SOUTHERLY FLOW EXPECTED TO PERSIST THRU TUESDAY AND A FULL MOON UPCOMING...WE BELIEVE WATER LEVELS COULD APPROACH MINOR FLOOD CRITERIA AT THE MORE SENSITIVE LOCATIONS AROUND TIMES OF THE HIGHER HIGH TIDES EARLY MONDAY AND EARLY TUESDAY.
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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 6 AM EDT TUESDAY FOR ANZ530>543.
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&& $$ SYNOPSIS...JE NEAR TERM...JE SHORT TERM...JE LONG TERM...DFH AVIATION...JE/DFH MARINE...JE/DFH TIDES/COASTAL FLOODING...JE

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