Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 201841 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 241 PM EDT SUN JUL 20 2014 .SYNOPSIS...
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HIGH PRESSURE WILL REMAIN ALONG THE EASTERN SEABOARD THROUGH EARLY IN THE WEEK. TEMPERATURES WILL SLOWLY RISE THROUGH MIDWEEK AHEAD OF A COLD FRONT THAT IS EXPECTED TO MOVE INTO THE AREA THURSDAY. HIGH PRESSURE IS EXPECTED TO RETURN TO THE MID ATLANTIC STATES TO END THE WORKWEEK.
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&& .NEAR TERM /THROUGH MONDAY/...
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SURFACE HIGH REMAINS IN THE SAME GENERAL LOCATION AS IT HAS THE PAST COUPLE OF DAYS...FROM ALONG THE NEW ENGLAND COAST DOWN THROUGH THE MID-ATLANTIC STATES. MID LEVEL CLOUDS THINNED OUT A BIT DURING THE LATE MORNING...BUT CU/STRATOCU QUICKLY FILLED IN MAKING FOR A MOSTLY CLOUDY AFTERNOON. CWA IS SHOWER-FREE AT 18Z. STILL EXPECT A FEW SHOWERS TO POP UP BY MID-LATE AFTERNOON...MAINLY OVER THE POTOMAC HIGHLANDS/NEAR THE RIDGES AND ALSO CLOSE TO THE BAY. IN BETWEEN...CAN/T RULE OUT A STRAY SHOWER OR SPRINKLE...BUT MUCH OF THE TIME IT WILL LIKELY BE DRY INTO THE EVENING. ANY SHOWERS THAT DEVELOP SHOULD DISSIPATE AFTER DARK. THERE WILL CONTINUE TO BE PLENTY OF CLOUDS OVERNIGHT...BUT PATCHY FOG COULD STILL DEVELOP UNDER THE CLOUDS PARTICULARLY IN FOG PRONE AREAS OF THE SHENANDOAH VALLEY/POTOMAC HIGHLANDS. ONSHORE FLOW PERSISTS ON MONDAY...WITH MODELS SHOWING DEWPOINTS/PRECIPITABLE WATERS INCREASING A BIT. IN TANDEM WITH AN INCREASE IN MOISTURE WOULD BE SLIGHTLY BETTER INSTABILITY. EXPECT SCATTERED SHOWERS...ESPECIALLY WEST OF THE INTERSTATE 95 CORRIDOR PER SREFS. ISOLATED THUNDERSTORMS WILL ALSO BE POSSIBLE BUT NO SEVERE WEATHER IS EXPECTED. FOLLOWED A BLEND OF BIAS CORRECTED SREFS AND ADJMAV GUIDANCE THROUGH MONDAY.
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&& .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
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FLAT RIDGE BUILDS IN MONDAY NIGHT INTO TUESDAY...PROMOTING WARMER TEMPERATURES. EXPECT MORE IN THE WAY OF SUNSHINE AS WELL BY TUESDAY. A FEW DIURNAL THUNDERSTORMS WILL BE POSSIBLE ESPECIALLY NEAR THE RIDGES BUT FLAT RIDGE MAY LIMIT CONVECTIVE COVERAGE FOR TUESDAY. RIDGE STARTS TO GET SUPPRESSED TO THE SOUTH IN ADVANCE OF THE NEXT TROUGH ON WEDNESDAY...BUT IT WILL STILL BE A WARM DAY AND DAYTIME HEATING AND PRE-FRONTAL TROUGH MAY TRIGGER SCATTERED AFTERNOON THUNDERSTORMS.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
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UPPER LEVEL ENERGY WILL MOVE ACROSS THE EASTERN GREAT LAKES AND EASTERN OHIO VALLEY WEDNESDAY BEFORE SLIDING SOUTHEASTWARD INTO THE MID ATLANTIC WEDNESDAY NIGHT INTO THURSDAY. AN ASSOCIATED SURFACE COLD FRONT WILL MOVE PARALLEL TO THE OHIO VALLEY WEDNESDAY...BRINGING A CHANCE OF SHOWERS OR A THUNDERSTORM...MAINLY IN THE NORTHERN POTOMAC HIGHLANDS. THE CHANCE FOR SHOWERS AND THUNDERSTORMS LINGER WEDNESDAY NIGHT AS THE SURFACE FRONT MOVES INTO THE MID ATLANTIC REGION. MORE FREQUENT SHOWERS AND A COUPLE OF STRONGER THUNDERSTORMS MAY DEVELOP DURING THE DAY THURSDAY DUE TO A COMBINATION OF THE INGREDIENTS OF UPPER LEVEL ENERGY...A SURFACE COLD FRONT...ADDITIONAL MOISTURE AND DAYTIME HEATING. THE STRONGER THUNDERSTORMS COULD PRODUCE DAMAGING WINDS AND LOCALLY HEAVY RAIN. HIGH CAPE AND LOW TO MODERATE SHEAR COULD LEAD TO THE DAMAGING WINDS...WHILE PRECIPITABLE WATER VALUES OF AROUND 2 INCHES COULD INDICATE HEAVY RAIN WOULD BE A THREAT FROM THE STORMS. AS OF NOW...TIMING OF THE HEAVIEST ACTIVITY APPEARS TO BE LATE THURSDAY MORNING TO EARLY THURSDAY EVENING. A SURFACE COLD FRONT WILL FINALLY PUSH THROUGH OUR REGION THURSDAY NIGHT TO ALLOW FOR A RIDGE OF HIGH PRESSURE TO BUILD IN FROM THE NORTHWEST. THIS FRONT HAS THE POTENTIAL TO STALL NEAR THE VIRGINIA AND NORTH CAROLINA BORDER THURSDAY NIGHT INTO FRIDAY...THUS MAYBE KEEPING A SLIGHT CHANCE OF RAIN SHOWERS ACROSS THE SOUTHERN TWO-THIRDS OF THE CWA WITH A SLIGHT CHANCE OF THUNDERSTORMS ACROSS THE VIRGINIA PIEDMONT AND MAIN STEM CHESAPEAKE BAY. HIGH PRESSURE SHOULD GRADUALLY PUSH THE FRONT FARTHER SOUTH TO ALLOW COOLER AND DRIER AIR TO MOVE IN ACROSS THE CWA FRIDAY AFTERNOON THROUGH MIDDAY SATURDAY. THE HIGH IS EXPECTED TO MOVE OFFSHORE SATURDAY AFTERNOON AND SATURDAY NIGHT. AN ONSHORE FLOW DEVELOP DURING THE PERIOD...AIDING IN AN INCREASE IN LOW LEVEL MOISTURE. GIVEN THE UNCERTAINTY OF THE POSITION OF THE HIGH...NEAR LONG ISLAND OR THE TIDEWATER OF VIRGINIA...WE LEFT A CHANCE OF RAIN SHOWERS SATURDAY AND A SLIGHT CHANCE OF A SHOWER OR THUNDERSTORM SATURDAY NIGHT. DESPITE THE HIGH BEING THE FAVORITE...BOTH THE EURO AND GFS INDICATE A FEW RIPPLES IN THE UPPER LEVEL FLOW THAT MAY INDICATE A WEAK DISTURBANCE OR TWO MAY FIND ITS WAY ACROSS OUR CWA...HENCE THE CHANCE OF A SHOWER OR STORM. SUNDAY APPEARS TO BE A PRECURSOR OF WHAT IS TO COME OUR WAY DURING THE MIDDLE PART OF NEXT WEEK. SOME UPPER LEVEL ENERGY WILL TRY TO SQUEEZE AROUND THE PERIPHERY OF THE WEAK UPPER LEVEL HIGH AND PUSH INTO OUR NORTHWESTERN ZONES SUNDAY. THERE IS A CHANCE OF SHOWERS AND A THUNDERSTORM SUNDAY WITH THE BEST LIKELIHOOD IN THE POTOMAC HIGHLANDS.
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&& .AVIATION /18Z SUNDAY THROUGH FRIDAY/...
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STILL HAVE FEW-SCT CU AROUND 3K FT HANGING AROUND THIS AFTERNOON IN EASTERLY FLOW...BUT VFR GENERALLY EXPECTED THROUGH EVENING. THERE IS POTENTIAL FOR STRATUS DEVELOPMENT OVERNIGHT AND HAVE TRENDED CIGS INTO THE MVFR/IFR RANGE FOR LATE TONIGHT/MONDAY MORNING. MVFR COULD LINGER UNTIL AFTERNOON. SLIGHT CHANCE OF MAINLY AFTERNOON TSRA MON/TUE...THEN CHANCE OF TSRA INCREASES FOR WED. ANY SHOWERS OR ISOLATED THUNDERSTORMS THAT DEVELOP WEDNESDAY AND WEDNESDAY NIGHT COULD BRING MVFR CONDITIONS TO ANY OF THE TERMINALS. THERE IS A BETTER CHANCE OF IFR OR LIFR CONDITIONS AT ANY OF THE TERMINALS THURSDAY AS LOCALLY HEAVY RAINFALL AND GUSTY WINDS COULD ACCOMPANY THE SHOWERS AND THUNDERSTORMS.
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&& .MARINE...
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HIGH PRESSURE ALONG THE EASTERN SEABOARD WILL KEEP AN EASTERLY FLOW THROUGH EARLY WEEK...MAINLY 10 KT OR LESS THROUGH MONDAY. AS WINDS TURN SOUTHEAST...WINDS MAY INCREASE CLOSER TO 15 KT FOR TUESDAY. SMALL CRAFT ADVISORIES MAY BE NEEDED BY WEDNESDAY NIGHT AS SOUTH TO SOUTHWESTERLY WINDS INCREASE AHEAD OF AN APPROACHING SURFACE COLD FRONT.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...BPP/KLW NEAR TERM...BPP SHORT TERM...BPP LONG TERM...KLW AVIATION...BPP/KLW MARINE...BPP/KLW

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