Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 210900 CCA AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 400 AM EST SUN DEC 21 2014 .SYNOPSIS... HIGH PRESSURE WILL REMAIN WEDGED INTO THE MID-ATLANTIC THROUGH EARLY IN THE WEEK. LOW PRESSURE WILL TRACK UP THE MID-ATLANTIC COAST LATE MONDAY. A STRONG COLD FRONT WILL THEN PASS THROUGH THE AREA WEDNESDAY NIGHT. && .NEAR TERM /THROUGH TONIGHT/... THE WINTER SOLSTICE IS AT 603PM EST TODAY...SUNDAY DECEMBER 21 2014. THE SUN WILL BE AT THE LOWEST ANGLE OF THE YEAR WITH THE LEAST AMOUNT OF DAYLIGHT. SUNSETS WILL START GETTING LATER AFTER TODAY. A SHORTWAVE TROUGH WILL MOVE ACROSS THE NORTHERN MID-ATLANTIC WHILE HIGH PRESSURE CONTINUES AT THE SURFACE THIS MORNING. MOISTURE IN THE MID-LEVELS HAS MOVED NORTHWARD FROM THE SE US OVERNIGHT IN RESPONSE TO THE JET STREAM ACROSS THE CAROLINAS. BKN-OVC CONDITIONS ARE EXPECTED THIS MORNING AS THE CLOUD DECK STRETCHES BACK INTO THE OHIO VALLEY. RIDGING ALOFT WILL LEAD TO LITTLE FORCING TODAY AND ONCE MID-LEVEL MOISTURE MOVES EASTWARD BY AFTERNOON...THE SUN SHOULD START TO SHOW ON THE FIRST DAY OF WINTER. HIGH PRESSURE AT THE SFC WILL LEAD TO LIGHT NORTHERLY WINDS. FCST MAX TEMPS WILL REACH THE 30S IN THE MTNS AND LOW 40S ELSEWHERE. USED MET GUIDANCE SINCE IT HAS BEEN DOING THE BEST THE LAST FEW DAYS. HIGH PRESSURE WILL BEGIN TO WEDGE AGAINST THE APPALACHIAN REGION TONIGHT AS AN UPPER LEVEL TROUGH BEGINS TO AMPLIFY ACROSS THE CENTRAL US. THE JET STREAM ACROSS THE SE US WILL LEAD TO THE DEVELOPMENT OF LOW PRESSURE OFF THE CAROLINA COAST. MOISTURE ADVECTION INTO THE MID-ATLANTIC WILL LEAD TO PRECIPITATION MOVING INTO THE REGION FROM THE SOUTH LATE TONIGHT. WENT WITH THE SREF MEAN FOR PRECIP PROGRESSION. AT THIS TIME...MOISTURE SHOULD BE REACHING THE GROUND ACROSS THE CENTRAL FOOTHILLS...SHENANDOAH VALLEY...PIEDMONT EARLY MONDAY MORNING. HIGH PRESSURE WILL SERVE AS A SOURCE OF COLD AIR AT THE SFC WITH TEMPS REACHING THE UPPER 20S TO AROUND 30 BY MONDAY MORNING. 850-700MB THICKNESS VALUES AROUND 1550M UP TO I-66 AND 1000-850MB THICKNESS VALUES AROUND 1310 WOULD RESULT IN FZRA...SLEET MIXTURE EARLY MONDAY MORNING IF MOISTURE IS AVAILABLE. TEMPS ALONG AND WEST OF THE BLUE RIDGE ARE EXPECTED TO BE COLDER RESULTING IN A BETTER CHANCE FOR ICE ACCRETION. && .SHORT TERM /MONDAY THROUGH TUESDAY/... STILL HAVE SOME UNCERTAINTY REGARDING THE DETAILS OF MONDAY/MONDAY NIGHT. GENERAL IDEA IS THAT PRECIP WILL SPREAD NORTHWARD THROUGH THE CWA DURING THE DAY MONDAY...ALTHOUGH THE EXACT NORTH/NORTHWEST EXTENT REMAINS SOMEWHAT IN QUESTION. ALSO IN QUESTION WILL BE TIMING THE CHANGES TO THE THERMAL PROFILE THROUGH THE DAY...WHICH WILL DETERMINE P-TYPE. PREFER GENERAL IDEA FROM THE SREFS FOR POPS...ALTHOUGH POPS NOT QUITE AS HIGH FURTHER NORTH TOWARD THE MASON DIXON LINE. LEANED TOWARD SREFS FOR TEMPERATURE/PROFILE CONSIDERATIONS TOO. THIS SUGGESTS THAT INITIAL PRECIP MAY BE SLEET OR FREEZING RAIN...TRENDING TO JUST RAIN THROUGHOUT THE DAY ALTHOUGH WINTRY PRECIP COULD LINGER LONGER OVER THE POTOMAC HIGHLANDS. HIGHEST CONFIDENCE FOR ICING RESIDES ACROSS THE LOWER POTOMAC HIGHLANDS/SHENANDOAH VALLEY/CENTRAL VA FOOTHILLS. RISK OF FREEZING RAIN COULD CONTINUE OVER THE POTOMAC HIGHLANDS MONDAY NIGHT ASSUMING THERE IS PRECIPITATION FALLING...BUT THIS IS UNCERTAIN AS MODELS SUGGEST THE MAIN BATCH OF QPF LIFTS NORTHEAST IN TANDEM WITH WEAK LOW PRESSURE OFF THE COAST. WEDGE REMAINS IN PLACE TUESDAY. NOT SURE THERE/S A LOT OF MEASURABLE PRECIP GOING ON...IT MAY BE MORE DRIZZLE BUT CONTINUE CHANCE POPS FOR RAIN ACROSS THE CWA WITH GFS SHOWING BROAD LIGHT QPF. AM EXPECTING ANY PRECIPITATION TO BE IN LIQUID FORM DURING THE DAY TUESDAY. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... FOCUS THEN SHIFTS TO DEEP UPPER TROUGH/STRONG COLD FRONT OVER THE MIDWEST/OHIO VALLEY TUESDAY NIGHT. DECENT PLUME OF MOISTURE OVERRUNNING A WARM FRONT WILL BRING RAIN INTO THE MID-ATLANTIC TUESDAY NIGHT. AS LOW LEVEL JET STRENGTHENS ON WEDNESDAY...THIS SHOULD HELP TO PUSH THE WARM FRONT TO THE NORTH. PW/S MAY INCREASE NEAR 1.5 INCHES...LIKELY LEADING TO PERIODS OF MODERATE RAINFALL ON WEDNESDAY. INSTABILITY IS FORECAST TO BE WEAK SO NO THUNDER MENTIONED BUT POTENTIAL EXISTS FOR SOME GUSTY SHOWERS GIVEN WIND FIELDS OFF THE DECK. DESPITE CLOUDS/RAIN...MAXIMA SHOULD WARM WELL INTO THE 50S AND POSSIBLY ECLIPSE 60 IN SOME AREAS. STRONG COLD FRONT MOVES THROUGH WEDNESDAY NIGHT. SHOWERS END FROM WEST TO EAST...AND COLD ADVECTION/TIGHT PRESSURE GRADIENT WILL BRING A BLUSTERY AND COOLER DAY THURSDAY /MEX GUIDANCE LIKELY TOO WARM/. NEXT COLD FRONT APPROACHES FRIDAY NIGHT OR SATURDAY. && .AVIATION /09Z SUNDAY THROUGH THURSDAY/... VFR CONDITIONS EXPECTED TODAY AND TONIGHT. MID LEVEL MOISTURE WILL CONTINUE TO MOVE EASTWARD ACROSS THE REGION RESULTING IN BKN-OVC VFR CIGS. CLEARING IS EXPECTED BY THIS AFTERNOON WITH A SCT-BKN 5K FEET DECK EXPECTED INTO THE EVENING. CLOUDS WILL BUILD IN FROM THE SOUTH TONIGHT AS LOW PRESSURE DEVELOPS OFF THE EAST COAST. MVFR/IFR CIGS SHOULD REACH CHO BY MONDAY MORNING. LIGHT NRLY WINDS EXPECTED DURING THE TAF PERIOD. PRECIP SPREADS NORTH ON MONDAY...POSSIBLY BEGINNING AS A WINTRY MIX OF -IP/-ZR BEFORE TRANSITIONING TO -RA. MVFR CONDITIONS LIKELY ON MONDAY WITH PRECIP...DEGRADING INTO IFR/LIFR MONDAY NIGHT INTO TUESDAY. RESTRICTIONS CONTINUE INTO WEDNESDAY WITH SHOWERS AND POSSIBLE LLWS. COLD FRONT MOVES THROUGH WEDNESDAY NIGHT...WITH GUSTY SURFACE WINDS THURSDAY. && .MARINE... LIGHT NRLY WINDS EXPECTED ON THE WATERS TODAY AND TONIGHT. WINDS WILL REMAIN LIGHT BUT BECOME EASTERLY LATE TONIGHT AND INTO MONDAY MORNING. RAIN AND/OR SLEET SHOULD REACH THE SRN WATERS MONDAY MORNING BEFORE CHANGING TO ALL RAIN THROUGH MONDAY. SCA CONDITIONS ARE POSSIBLE IN SOUTHERLY FLOW AHEAD OF A COLD FRONT ON WEDNESDAY...THEN BEHIND THE FRONT FOR WEDNESDAY NIGHT AND THURSDAY. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...HAS/BPP NEAR TERM...HAS SHORT TERM...BPP LONG TERM...BPP AVIATION...HAS/BPP MARINE...HAS/BPP

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