Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 211320 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 920 AM EDT MON APR 21 2014 .SYNOPSIS...
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HIGH PRESSURE WILL REMAIN OVER THE AREA TODAY. HIGH PRESSURE WILL SLOWLY SLIDE EAST TONIGHT AND A COLD FRONT WILL PASS THROUGH THE AREA TUESDAY AFTERNOON AND EVENING. HIGH PRESSURE WILL RETURN FOR WEDNESDAY AND THURSDAY BEFORE MOVING OFF THE COAST FRIDAY. A COLD FRONT WILL PASS THROUGH THE AREA SATURDAY.
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&& .NEAR TERM /THROUGH TONIGHT/...
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THE CENTER OF SFC HIPRES HAS SHIFTED OFFSHORE AND SOUTH OF THE CANADIAN MARITIMES THIS MRNG WHILE SFC RIDGE AXIS CONTINUES TO EXTEND SW-WD ALONG THE ERN SEABOARD. THE CUTOFF LOW JUST OFF THE NC COAST YDA HAS DRIFTED FARTHER OFFSHORE TDA...ALLOWING FOR AN UPPER RIDGE TO BUILD UPSTREAM OF THE LOW AND OVER THE ERN CONUS. THE RESULTANT PATTERN WILL YIELD SUNNY SKIES AND SEASONABLE TEMPS. EVEN WITH A RELATIVELY COLD START TO THE DAY...TEMPS WILL RISE SHARPLY THIS MRNG AS THE STRONG BUT SHALLOW NOCTURNAL INVERSION MIXES OUT. THE 12Z IAD RAOB SOUNDING SUPPORTS RAISING MAX TEMP FCST BY SEVERAL DEGREES ACROSS INLAND AREAS WITH HIGHS TDA IN THE 70S. THERE WILL BE A ELY COMPONENT TO THE FLOW WHICH SHOULD KEEP LOCATIONS NEAR THE CHSPK BAY AND TIDAL POTOMAC COOLER AS WATER TEMPS ARE STILL IN THE MID 50S. HI CLOUDS AHEAD OF AN UPPER TROUGH APPROACHING FROM THE MIDWEST WILL INCREASE FROM WEST TO EAST LATE THIS AFTN AND TNGT. SFC LOPRES WILL STRENGTHEN WHILE MOVING EWD ACROSS THE GREAT LAKES TNGT. ATTENDANT COLD FRONT WILL ALSO APPROACH FROM THE WEST TNGT. THE INCREASING CLOUD COVER AND SLY FLOW AHEAD OF THE FRONT WILL CURB RADIATIONAL COOLING AND MITIGATE CONCERNS OF FROST/FREEZE. FCST MIN TEMPS ARE IN THE 40S AND LOWER 50S.
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&& .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/... WEAK HIGH PRESSURE WILL CONTINUE TO MOVE OFF THE COAST TUESDAY WHILE A COLD FRONT OVER THE OHIO VALLEY TUESDAY MORNING PASSES THROUGH OUR AREA TUESDAY AFTERNOON AND EVENING. A SOUTHERLY FLOW AHEAD OF THE FRONT WILL ALLOW FOR WARMER CONDITIONS...DESPITE CLOUD COVER ASSOCIATED WITH THE FRONTAL PASSAGE. MAX TEMPS WILL RANGE FROM THE LOWER 60S IN THE MOUNTAINS TO NEAR 80 IN THE VIRGINIA PIEDMONT. THE COMBINATION OF WARMER AIR AND INCREASING DEWPOINTS FROM THE SOUTHERLY FLOW WILL BE ENOUGH TO CAUSE AN UNSTABLE ATMOSPHERE. HOWEVER...INSTABILITY WILL BE LIMITED WITH DEEP MOISTURE REMAINING OFF TO OUR SOUTH. MOST OF THE DYNAMICS WITH THIS SYSTEM WILL BE TO OUR NORTH...BUT THERE SHOULD BE ENOUGH FORCING WITH THE FRONT TO COMBINE WITH THE INSTABILITY...CAUSING SOME SHOWERS ALONG AND AHEAD OF THE FRONT. A FEW THUNDERSTORMS CANNOT BE RULED OUT AS WELL. HOWEVER...ANY SEVERE THREAT WILL BE EXTREMELY LIMITED DUE TO THE LOW INSTABILITY. THE BEST CHANCE FOR SHOWERS AND THUNDERSTORMS WILL BE FROM MID-MORNING THROUGH EARLY AFTERNOON WEST OF THE BLUE RIDGE MOUNTAINS...AND DURING THE AFTERNOON HOURS EAST OF THE BLUE RIDGE MOUNTAINS. THE FRONT WILL MOVE OFF TO OUR EAST TUESDAY EVENING. ANY LEFTOVER SHOWERS ACROSS EXTREME SOUTHERN MARYLAND WILL END DURING THIS TIME. A NORTHWEST FLOW WILL USHER IN COOLER AND DRIER CONDITIONS FOR TUESDAY NIGHT. MIN TEMPS WILL RANGE FROM THE 20S ALONG THE RIDGE TOPS OF THE ALLEGHENY HIGHLANDS TO NEAR 50 IN DOWNTOWN WASHINGTON AND BALTIMORE. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... LOW PRESSURE WILL INTENSIFY NEAR NOVA SCOTIA WEDNESDAY WHILE HIGH PRESSURE BUILDS TOWARD THE REGION FROM THE GREAT LAKES. THE PRESSURE GRADIENT BETWEEN THESE SYSTEMS WILL CAUSE GUSTY NORTHWEST WINDS...AND MAX TEMPS WILL BE BELOW CLIMO DUE TO THE COLD ADVECTION ASSOCIATED WITH THE NORTHWEST FLOW. HIGH PRESSURE WILL BUILD OVERHEAD WEDNESDAY NIGHT...CAUSING DRY AND CHILLY CONDITIONS. HIGH PRESSURE WILL CONTINUE TO CONTROL THE WEATHER PATTERN THURSDAY BEFORE MOVING OF THE COAST FRIDAY. A RETURN FLOW AROUND THE HIGH WILL CAUSE WARMER CONDITIONS LATE IN THE WEEK BEFORE ANOTHER COLD FRONT PASSES THROUGH SATURDAY. CHILLIER CONDITIONS ARE EXPECTED BEHIND THIS BOUNDARY EARLY NEXT WEEK. && .AVIATION /13Z MONDAY THROUGH FRIDAY/...
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VFR TDA AND TNGT. ELY WINDS THIS MRNG WILL BECOME SELY THIS AFTN AND SLY TNGT. WIND SPEEDS WILL BE LGT /BELOW 10 KT/. VFR CONDITIONS ARE EXPECTED MOST OF THE TIME TUESDAY THROUGH FRIDAY. A FEW SHOWERS AND THUNDERSTORMS ARE POSSIBLE TUESDAY AND CIGS/VSBYS MAY BRIEFLY BE REDUCED IN ANY CONVECTION. NORTHWEST WINDS WILL INCREASE BEHIND A COLD FRONT TUESDAY NIGHT AND WEDNESDAY. THE STRONGEST WINDS ARE EXPECTED WEDNESDAY WITH GUSTS AROUND 30 KNOTS. HIGH PRESSURE WILL BUILD OVERHEAD WEDNESDAY NIGHT AND THURSDAY...CAUSING WINDS TO DECREASE. A SOUTHERLY FLOW IS EXPECTED FRIDAY AS THE HIGH MOVES OFF THE COAST.
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&& .MARINE...
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HIGH PRESSURE OVERHEAD WILL YIELD LIGHT WINDS FOR THE WATERS THRU TNGT. NELY WINDS THIS MRNG WILL BECOME ELY THIS AFTN AND SELY TNGT. WINDS WILL GENERALLY BE AOB 10 KT DURING THIS TIME BUT A FEW GUSTS TO 15 KT POSSIBLE IN THE MAIN STEM OF THE CHSPK BAY. A COLD FRONT WILL PASS THROUGH THE WATERS LATE TUESDAY AFTERNOON AND EVENING. A FEW SHOWERS AND THUNDERSTORMS ARE POSSIBLE AHEAD OF THE FRONT TUESDAY AFTERNOON AND EARLY EVENING. ANY THUNDERSTORMS THAT DO DEVELOP WILL BE CAPABLE OF PRODUCING GUSTY WINDS. NORTHWEST WINDS WILL INCREASE BEHIND THE COLD FRONT TUESDAY NIGHT. GUSTY NORTHWEST WINDS WILL CONTINUE INTO WEDNESDAY EVENING BEFORE GRADUALLY DECREASING WEDNESDAY NIGHT. A SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED FOR THE WATERS TUESDAY NIGHT INTO WEDNESDAY NIGHT. THE STRONGEST WINDS ARE EXPECTED WEDNESDAY WITH GUSTS AROUND 30 KNOTS. HIGH PRESSURE WILL BUILD OVERHEAD LATE WEDNESDAY NIGHT AND THURSDAY BEFORE MOVING OFF THE COAST FRIDAY.
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&& .TIDES/COASTAL FLOODING...
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LGT NE WINDS THIS MRNG WILL BECOME ELY THIS AFTN AND SELY TNGT. POSITIVE TIDAL ANOMALIES HAVE DEVELOPED THIS MRNG ALONG THE WRN SHORE OF THE MD CHSPK BAY AS A RESULT OF THIS ONSHORE FLOW AND ARE CURRENTLY ALMOST ONE-HALF FOOT. LATEST CBOFS GUIDANCE INDICATES ANOMALIES INCREASING TO ABOUT ONE FOOT BY TUE MRNG. THIS WOULD KEEP TIDAL LEVELS ABOUT ONE-QUARTER FOOT BELOW COASTAL FLOOD THRESHOLD AT ANNAPOLIS AND GREATER THAN ONE-HALF FOOT BELOW COASTAL FLOOD THRESHOLD AT BALTIMORE.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...JRK/BJL NEAR TERM...JRK SHORT TERM...BJL LONG TERM...BJL AVIATION...JRK/BJL MARINE...JRK/BJL TIDES/COASTAL FLOODING...JRK

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