Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 280222 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 922 PM EST FRI FEB 27 2015 .SYNOPSIS... HIGH PRESSURE WILL BUILD OVER PENNSYLVANIA TONIGHT THEN LINGER OVER THE CENTRAL MID-ATLANTIC THROUGH SATURDAY NIGHT BEFORE MOVING OFF THE COAST SUNDAY. A COLD FRONT WILL PASS THROUGH THE AREA SUNDAY NIGHT. HIGH PRESSURE BRIEFLY BUILDS MONDAY NIGHT...THEN A WARM FRONT THEN COLD FRONT WILL CROSS THE AREA TUESDAY AND WEDNESDAY. THE COLD FRONT LOOKS TO STALL ALONG THE CAROLINA COAST THROUGH THURSDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 02Z...1040MB SFC HIGH CENTERED FROM PITTSBURGH TO CNTRL OH. THIS WILL SHIFT OVER CNTRL PA AND INCREASE TO AROUND 1045MB THROUGH THE REST OF THE NIGHT. A COLD AIRMASS...SOURCED FROM CANADA. THE QUESTION FOR TONIGHT IS HOW COLD IT WILL GET. A SHORTWAVE OVER THE MID- SOUTH IS RISING THE ZONAL JET AND ASSOCIATED HIGH CLOUDS WILL COVER THE AREA LATE TONIGHT. THERE IS ALSO A DECENT PRESSURE GRADIENT THAT WILL KEEP 5-10MPH NLY/NWLY FLOW THROUGH THE NIGHT. WOULD GENERALLY GO ABOVE GUIDANCE BECAUSE OF THESE TWO LIMITING FACTORS...BUT GIVEN EXISTING SNOW OVER MOST OF THE AREA AND A FEW MORE HOURS OF CLEAR CONDITIONS...WENT A COUPLE DEGREES BELOW A MAV/MET/SREF BLEND...MIN TEMPS POSITIVE SINGLE DEGREES NW OF BALT-WASH AND ALL AREAS WEST OF THE BLUE RIDGE (SOME SUBZERO IN THE ALLEGHENIES)...AND TEENS BALT-WASH AND SRN MD TO CNTRL VA. WIND CHILLS DROP TO ZERO FOR MOST OF THE AREA...A LITTLE BELOW ZERO FOR NRN MD. BALTIMORE AND HARFORD COUNTIES HAVE A -5F WIND CHILL ADVISORY...BUT THINKING AROUND -3F AT THE LOWEST THERE LATE TONIGHT. WILL MENTION THESE COLD CONDITIONS IN THE HWO EVEN THOUGH IT IS NOT ADVISORY LEVEL AND IT HAS BEEN A COLD MONTH. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... HIGH PRESSURE WILL REMAIN OVERHEAD SATURDAY WHILE SHORTWAVE ENERGY PASSES THROUGH IN THE SOUTHWEST FLOW ALOFT. A BKN DECK OF HIGH AND MID- LEVEL CLOUDS ARE EXPECTED DUE TO THE SHORTWAVE ENERGY...BUT IT WILL REMAIN DRY. THE HIGH WILL CONTINUE TO BRING COLD CONDITIONS TO THE AREA. MAX TEMPS WILL RANGE FROM THE LOWER 20S IN THE MOUNTAINS TO THE MID AND UPPER 20S ACROSS MOST OTHER LOCATIONS. HIGH PRESSURE WILL SHIFT EAST OFF THE MIDDLE ATLANTIC COAST SATURDAY NIGHT. WINDS WILL SHIFT AROUND TO THE EAST AND SOUTHEAST OVERNIGHT WHICH WILL HELP DRAW LOW LEVEL MOISTURE INTO THE FORECAST AREA. MOST OF SATURDAY NIGHT WILL LIKELY REMAIN DRY...EXCEPT OVER THE WESTERN SLOPES OF THE ALLEGHENY FRONT WHERE SOME SNOW SHOWER ACTIVITY COULD DEVELOP. CLOUDS WILL BE ON THE INCREASE FROM WEST TO EAST BUT OVERNIGHT LOW TEMPERATURES WILL BE COLD WITH READINGS FALLING BACK TO THE TEENS TO LOWER 20S AREAWIDE. CHALLENGING FORECAST FOR SUNDAY INTO MONDAY. LOW PRESSURE WILL APPROACH FROM THE WEST AND WARMER AIR WILL OVERRUN A COLDER AIRMASS LEADING TO PRECIPITATION DEVELOPING FROM WEST TO EAST ACROSS THE MIDDLE ATLANTIC REGION. THE 12Z NAM IS MORE BULLISH WITH PRECIPITATION AND KEEPS THE COLD AIR IN PLACE WITH SUBFREEZING TEMPS ACROSS MUCH OF THE REGION INTO SUNDAY NIGHT. THE GFS AND ECMWF CONTINUE TO SHOW THE PRECIPITATION COMING IN LATER AND WITH WARMER TEMPERATURES. THIS MAKES FOR A PROBLEMATIC FORECAST WITH REGARD TO P- TYPE AND TIMING. COLD AIR TYPICALLY HOLDS IN LONGER THAN MODELS INDICATE AND HAVE THUS GONE WITH A CHANCE FOR SNOW TO START ON SUNDAY THEN GRADUALLY CHANGE THE PRECIPITATION OVER TO S/ZR/IP FROM SOUTH TO NORTH WITH PRECIP CHANGING TO RAIN OVER CENTRAL AND SOUTHERN PORTIONS OF THE FORECAST AREA INCLUDING DC/NOVA AND POINTS SOUTH. THIS REMAINS A HIGHLY UNCERTAIN FORECAST AND DETAILS WILL NEED TO BE REFINED OVER THE NEXT COUPLE OF DAYS. && .LONG TERM /MONDAY THROUGH FRIDAY/... UPPER LEVEL RIDGE BUILDING OVER REGION DURING FIRST HALF OF PERIOD WILL MOVE OFFSHORE WEDNESDAY NIGHT. WEAK PVA WILL CROSS REGION. UPPER LEVEL TROF WILL CROSS REGION THURSDAY. STRONGEST OF ENERGY WILL STAY NORTH OF AREA. FLOW BECOMING ZONAL FRIDAY. SURFACE HIGH WILL BUILD OVER THE AREA MONDAY BEFORE MOVING OFFSHORE TUESDAY. MOISTURE AND WARM AIR WILL ADVECT ACROSS THE AREA FROM SOUTHWEST TO NORTHEAST AS THE HIGH MOVES OFFSHORE. THERMAL PROFILES INDICATE THAT PRECIPITATION MAY START OFF AS A WINTRY MIX BEFORE WARMER AIR WORKS ITS WAY INTO THE AREA...CAUSING PRECIPITATION TO CHANGE TO RAIN TUESDAY NIGHT. ALL RAIN WILL FALL WEDNESDAY AND IT MAY TURN OUT QUITE WARM AS SOUTHERLY WINDS USHER IN WARMER AIR FROM THE SOUTH. THE COLD FRONT ASSOCIATED WITH THE LOW WILL PASS THROUGH WEDNESDAY NIGHT INTO THURSDAY. PRECIPITATION MAY END AS A PERIOD OF SNOW DURING THIS TIME...BUT DETAILS ARE UNCERTAIN. HIGH PRESSURE WILL BUILD TOWARD THE AREA LATE NEXT WEEK. && .AVIATION /02Z SATURDAY THROUGH WEDNESDAY/... VFR CONDITIONS ARE EXPECTED INTO SUNDAY. NORTHWEST WINDS WILL CONTINUE 5-10KT OVERNIGHT. LIGHT/VARIABLE FLOW SATURDAY/SATURDAY NIGHT UNDER HIGH PRESSURE. MVFR TO IFR CONDITIONS SUNDAY LATE MORNING INTO THE FIRST PART OF MONDAY. A PERIOD OF SNOW/ZR/IP WILL BE POSSIBLE AT ALL THE TERMINAL SITES...ESPECIALLY KBWI/KMTN/KMRB AND KIAD. IMPROVING CONDITIONS WILL FOLLOW FROM WEST TO EAST LATER MONDAY. LOW PRESSURE AND ITS ASSOCIATED COLD FRONT WILL IMPACT THE TERMINALS LATER TUESDAY AND WEDNESDAY. && .MARINE... HIGH PRESSURE WILL BUILD OVER THE WATERS THROUGH SATURDAY. A SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR MUCH OF THE WATERS THIS EVENING...EXPECTED TO BE CANCELLED AROUND MIDNIGHT. WINDS WILL BE LIGHT SATURDAY AS HIGH PRESSURE BUILDS OVERHEAD. WINDS ARE EXPECTED TO REMAIN BELOW SCA LEVELS SATURDAY NIGHT THROUGH MONDAY. WINTRY PRECIPITATION WILL CAUSE REDUCED VISIBILITIES ON THE WATERS LATER SUNDAY INTO MONDAY. LOW PRESSURE AND ITS ASSOCIATED COLD FRONT WILL IMPACT THE WATERS DURING THE MIDDLE PORTION OF NEXT WEEK. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EST SATURDAY FOR ANZ531>534- 537-539>541-543. && $$ SYNOPSIS...BAJ/BJL NEAR TERM...BAJ/BJL SHORT TERM...BJL/KRW LONG TERM...CEM AVIATION...BAJ/BJL/KRW MARINE...BAJ/BJL/KRW

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