Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 271958 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 258 PM EST FRI FEB 27 2015 .SYNOPSIS... HIGH PRESSURE WILL BUILD OVERHEAD THROUGH SATURDAY. THE HIGH WILL MOVE OFF THE COAST SUNDAY AND ANOTHER COLD FRONT WILL PASS THROUGH THE AREA SUNDAY NIGHT. A WARM FRONT AND LOW PRESSURE WILL CROSS THE AREA TUESDAY AND WEDNESDAY. && .NEAR TERM /THROUGH TONIGHT/... HIGH PRESSURE WILL APPROACH FROM THE OHIO VALLEY BEHIND THE COLD FRONT LATE THIS AFTERNOON. A NORTHWEST FLOW AHEAD OF THE HIGH WILL USHER IN COLD CONDITIONS. HIGH PRESSURE WILL BUILD OVERHEAD TONIGHT...BRINGING DRY AND COLD CONDITIONS. HIGH CLOUDS WILL INCREASE AS AN UPPER-LEVEL DISTURBANCE MOVES INTO THE AREA FROM THE SOUTHWEST. HOWEVER...THE CLOUD DECK SHOULD BE THIN ENOUGH TO ALLOW FOR RADIATIONAL COOLING. THEREFORE...THE MIN TEMP FORECAST LEANS TOWARD OR EVEN A LITTLE BELOW THE COLDEST GUIDANCE. MIN TEMPS ARE FORECAST TO RANGE FROM BELOW ZERO IN THE ALLEGHENY HIGHLANDS...TO THE SINGLE DIGITS AND LOWER TEENS ACROSS MOST OTHER LOCATIONS...TO THE MID AND UPPER TEENS IN WASHINGTON AND BALTIMORE. && .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 /19Z FRIDAY THROUGH WEDNESDAY/... VFR CONDITIONS ARE EXPECTED THROUGH SATURDAY. NORTHWEST WINDS WILL BECOME LIGHT AND VARIABLE TOWARD SUNSET. LIGHT WINDS WILL CONTINUE THROUGH SATURDAY. VFR CONDITIONS EXPECTED SATURDAY NIGHT INTO THE FIRST PART OF SUNDAY FOLLOWED BY 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 THE WATERS THIS AFTERNOON...BUT IT WILL BE MARGINAL ACROSS THE UPPER TIDAL POTOMAC RIVER AND NORTHERN PORTION OF THE BAY. THE SMALL CRAFT ADVISORY CONTINUES TONIGHT FOR THE MARYLAND CHESAPEAKE BAY SOUTH OF POOLES ISLAND AND THE LOWER TIDAL POTOMAC RIVER. NORTHERLY WINDS OVER THE RELATIVELY WARMER WATERS WILL INCREASE MIXING ACROSS THESE AREAS. 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. SMALL CRAFT ADVISORY UNTIL 6 PM EST THIS EVENING FOR ANZ530- 535-536-538-542. && $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...BJL/KRW LONG TERM...CEM AVIATION...BJL/KRW MARINE...BJL/KRW

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