Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 190157 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 857 PM EST THU DEC 18 2014 .SYNOPSIS... A WEAK UPPER-LEVEL TROUGH WILL CONTINUE TO PASS THROUGH THE REGION TONIGHT. HIGH PRESSURE WILL BUILD OVERHEAD THROUGH FRIDAY NIGHT...THEN PERSIST THROUGH SUNDAY. LOW PRESSURE WILL TRACK UP THE SOUTHEAST COAST SUNDAY NIGHT THROUGH MONDAY NIGHT...WITH A STRONGER LOW CROSSING THE MID-ATLANTIC WEDNESDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 01Z...994MB SFC LOW OVER CANADIAN MARITIMES AND A 1030MB SFC HIGH JUST WEST OF LAKE SUPERIOR (BOUNDARY WATERS). A WEAK UPR SHORTWAVE LOW IS MOVING EAST FROM WEST VIRGINIA. LIGHT ECHOES HAVE SPREAD EAST WITH SOME LIGHT SNOW REPORTED IN THE HARRISONBURG AREA. ADDED SOME FLURRIES TO THE FORECAST FOR ALL ELEVATIONS ABOVE 500 FT. WILL NEED TO MONITOR POSSIBLE EXPANSION OF FLURRY MENTION FOR ENTIRE BALTIMORE METRO (WHERE ECHOES ARE ABOVE ABOUT 1200 FT MSL AT 0148Z). OTHERWISE...THICK MID-LEVEL CLOUDS PERSIST THROUGH TONIGHT. MIN TEMPS MID TO UPR 20S WITH DEWPOINTS REMAINING IN THE LOW 20S. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... HIGH PRESSURE WILL BE IN CONTROL FOR FRIDAY AND FRIDAY NIGHT...LEADING TO TRANQUIL WEATHER AND LESS GUSTY WINDS. PERHAPS SOME PASSING CLOUDS BUT EVEN OVERNIGHT WITH THE MORE SUPPRESSED SOUTHERN STREAM SYSTEM...MOST OF THE CWA MAY ONLY SEE CIRRUS. NOT MUCH TEMPERATURE ADVECTION...HIGHS PERHAPS A TICK WARMER BUT STILL IN THE 40S...WITH OVERNIGHT LOWS BELOW FREEZING. SURFACE HIGH PRESSURE WILL BUILD OVER NEW ENGLAND AND THE RIDGE AXIS WILL EXTEND SOUTH INTO THE MID-ATLANTIC SATURDAY THROUGH SATURDAY NIGHT. THIS WILL ALLOW FOR SEASONABLY CHILLY CONDITIONS DURING THIS TIME. A COUPLE SHORTWAVES...ONE IN THE NORTHERN STREAM OF THE JET AND ONE IN THE SOUTHERN STREAM OF THE JET WILL PASS THROUGH OUR REGION SATURDAY AFTERNOON AND NIGHT. THESE SYSTEMS WILL NOT PHASE SO THE NORTHERN STREAM SHORTWAVE WILL REMAIN TO OUR NORTH AND THE SOUTHERN STREAM SHORTWAVE WILL REMAIN TO OUR SOUTH. MOST OF THE MOISTURE WILL REMAIN TO OUR SOUTH WITH THE SOUTHERN STREAM SYSTEM AS WELL. THEREFORE...MOST AREAS ARE EXPECTED TO REMAIN DRY DURING THIS TIME. HOWEVER...LIGHT PRECIPITATION MAY BRUSH PORTIONS OF THE POTOMAC HIGHLANDS AND CENTRAL VIRGINIA SATURDAY INTO SATURDAY NIGHT. THERE WILL BE ENOUGH COLD AIR FOR SNOW IF PRECIPITATION OCCURS...BUT LITTLE OR NO SNOW ACCUMULATION IS EXPECTED WITH MOST OF THE MOISTURE REMAINING TO THE SOUTH. MAX TEMPS SATURDAY WILL RANGE FROM THE 30S IN THE MOUNTAINS TO THE LOWER AND MIDDLE 40S ACROSS MOST OTHER LOCATIONS. MIN TEMPS SATURDAY NIGHT WILL BE IN THE MID TO UPPER 20S ACROSS MOST LOCATIONS...BUT LOWER AND MIDDLE 30S IN DOWNTOWN WASHINGTON AND BALTIMORE. && .LONG TERM /SUNDAY THROUGH THURSDAY/... UPPER LEVEL CUT-OFF LOW CENTERED OVER THE UPPER MISSISSIPPI VALLEY SUNDAY WILL SLOWLY DRIFT TO THE EAST AND FILL BY WEDNESDAY NIGHT. A SHORTWAVE MOVING THROUGH THE PATTERN WILL SUPPORT DEVELOPMENT OF A SURFACE LOW OVER EASTERN NORTH CAROLINA AND VIRGINIA WEDNESDAY. SURFACE LOW WILL MOVE ON TO NEW ENGLAND BY WEDNESDAY NIGHT. MOISTURE WILL INCREASE OVER MID ATLANTIC REGION WILL INCREASE ON SOUTHWEST WINDS DURING EARLY HALF OF PERIOD. MARGINAL 1000-500 MB THICKNESS VALUES AND AIR TEMPERATURES AROUND FREEZING MAY SUPPORT SNOW...OR WINTRY MIX. MORE MOISTURE WILL FOLLOW AT MID WEEK AHEAD OF LOW APPROACHING FROM THE MID WEST. TEMPERATURES SHOULD STAY HIGH ENOUGH THAT PRECIPITATION SHOULD BE RAIN. && .AVIATION /01Z FRIDAY THROUGH TUESDAY/... VFR MID LEVEL CIGS OVERNIGHT...VFR CONDITIONS EXPECTED THROUGH THE TAF PERIOD. NW FLOW 5-10 KT TONIGHT...10 TO 15 KT FRIDAY. VFR CONDITIONS ARE EXPECTED ACROSS MOST OF THE TERMINALS SATURDAY THROUGH SATURDAY NIGHT. A PERIOD OF LIGHT SNOW OR RAIN MAY IMPACT KCHO. SUBVFR CONDITIONS ARE POSSIBLE IF ANY PRECIPITATION DEVELOPS. HIGH PRESSURE WILL BUILD OVER THE TERMINALS SUNDAY...BUT LOW PRESSURE MAY IMPACT THE AREA TUESDAY AND WEDNESDAY WITH PRECIPITATION AND SUBVFR CONDITIONS. && .MARINE... HIGH PRESSURE BUILDS OVER THE WATERS THROUGH FRIDAY NIGHT. SCA RETURNS FOR ALL BUT WESTERN TRIBUTARIES FRIDAY MORNING INTO THE AFTERNOON AS THE GRADIENT REMAINS HIGH ENOUGH TO WARRANT 18 KT GUSTS. HIGH PRESSURE WILL REMAIN OVER THE WATERS SATURDAY THROUGH SUNDAY. DUAL LOW PRESSURE WILL IMPACT THE WATERS EARLY AND MIDDLE OF NEXT WEEK. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 6 AM TO 3 PM EST FRIDAY FOR ANZ531>534-537-539>541-543. && $$ SYNOPSIS...BAJ/BJL NEAR TERM...BAJ/ADS SHORT TERM...BJL/ADS LONG TERM...BJL/CEM AVIATION...BAJ/BJL/ADS MARINE...BAJ/BJL/ADS

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