Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 220855 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 355 AM EST MON DEC 22 2014 .SYNOPSIS...
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A WEAK AREA OF LOW PRESSURE WILL TRACK UP THE MID-ATLANTIC COAST TODAY INTO TUESDAY. STRONGER LOW PRESSURE WILL PUSH NORTH ALONG THE APPALACHIANS ON WEDNESDAY...SENDING A COLD FRONT EASTWARD WEDNESDAY NIGHT. BREEZY CONDITIONS WILL FOLLOW THE FRONT ON THURSDAY...THEN HIGH PRESSURE WILL BUILD BACK INTO THE REGION TO CLOSE OUT THE WEEK.
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&& .NEAR TERM /THROUGH TONIGHT/...
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CHALLENGING FORECAST EARLY THIS MORNING. CWA IS DRY ATTM...BUT RAIN HAS ALREADY PUSHED NORTHWARD INTO SOUTHERN VIRGINIA AT 08Z AND WILL CONTINUE TO SPREAD NORTHWARD THROUGH THE EARLY MORNING HOURS AS LOW PRESSURE DEVELOPS OFF THE SOUTHEAST COAST. TEMPERATURES ACROSS MUCH OF THE CWA WERE BELOW FREEZING...AND AS PRECIPITATION MOVES IN FROM THE SOUTH IT WILL ENCOUNTER THIS SUB-FREEZING AIR. A PERIOD OF SLEET IS POSSIBLE INITIALLY AS PRECIPITATION BEGINS OVER THE CWA...BUT PRIMARY P-TYPES TO CONTEND WITH OVER THE NEXT 12-24 HOURS WILL BE FREEZING RAIN OR RAIN DEPENDING ON SURFACE TEMPERATURES. CHALLENGES REVOLVE AROUND THE TIMING AND NORTH/NORTHWEST EXTENT OF PRECIPITATION TODAY AND ALSO HOW QUICKLY TEMPERATURES WILL BE ABLE TO CLIMB ABOVE FREEZING. TREND OF THE MODELS HAS BEEN TO SLOW DOWN THE BEGINNING OF PRECIP BY A LITTLE BIT. HAVE TRENDED THIS WAY...BUT PRECIP SHOULD STILL MAKE IT INTO THE VIRGINIA FOOTHILLS/PIEDMONT BY SUNRISE. WILL BE EXPANDING THE FREEZING RAIN ADVISORY A TIER EAST TO THE I-95 CORRIDOR AS LIGHT QPF IS EXPECTED TO FALL WHILE TEMPERATURES ARE NEAR FREEZING FROM SPOTSYLVANIA UP TO PRINCE WILLIAM COUNTY. TEMPERATURES IN THESE AREAS SHOULD RISE ABOVE FREEZING BY NOON. PRECIP IS ALSO LIKELY TO MAKE IT FURTHER NORTH INTO NORTHERN VIRGINIA DURING THE LATE MORNING/MIDDAY HOURS. SEVERAL SUITES OF GUIDANCE SUGGEST TEMPERATURES SITTING AROUND THE FREEZING MARK. THEREFORE HAVE EXPANDED ADVISORY A TIER NORTH AS WELL FOR AREAS OF FREEZING RAIN WHICH MAY CONTINUE INTO AFTERNOON. HAVE OPTED NOT TO EXPAND ADVISORY ALL THE WAY TO THE MASON DIXON LINE HOWEVER AS CONFIDENCE IS QUITE LOW IN PRECIP BEING ABLE TO MAKE IT THAT FAR NORTH THROUGH MID-AFTERNOON EVEN IF TEMPERATURES ARE COLD ENOUGH TO SUPPORT FZRA. FINALLY...EXPIRATION TIME OF EXISTING ADVISORY HAS BEEN EXTENDED FROM NOON TO 6 PM. AGAIN...SEVERAL SUITES OF GUIDANCE SUGGEST TEMPERATURES CONTINUING TO BE AT OR JUST BELOW FREEZING FOR AREAS NEAR/ALONG AND WEST OF THE BLUE RIDGE INTO THE AFTERNOON. WEAK LOW PRESSURE MOVES UP THE MID-ATLANTIC COAST TONIGHT. HIGHEST POPS WILL BE CLOSEST TO THE BAY...LOWER IN THE MOUNTAINS. MUCH OF THE CWA LOOKS WARM ENOUGH FOR PRIMARILY RAIN TONIGHT BUT THERE STILL MAY BE POCKETS OF SUB-FREEZING AIR WEST OF THE BLUE RIDGE AND ANY RAIN OR DRIZZLE MAY FREEZE AND ADVISORY MAY NEED TO BE EXTENDED INTO TONIGHT FOR THOSE AREAS.
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&& .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
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IN THE WAKE OF THE LOW...MID-ATLANTIC REMAINS IN A WEDGE/LIGHT FLOW REGIME ON TUESDAY THEREFORE CLOUDY SKIES AND THE CHANCE FOR LIGHT RAIN OR DRIZZLE WILL CONTINUE. TEMPERATURES SHOULD BE WARM ENOUGH FOR JUST LIQUID PRECIPITATION. WHILE THERE IS GENERAL SYNOPTIC AGREEMENT IN THE COMPUTER MODELS THROUGH THE MIDDLE OF THE WEEK...THERE IS STILL QUITE A BIT OF SPREAD IN THE SMALLER SCALE FEATURES. AMPLIFIED UPPER LEVEL PATTERN THROUGH THE MIDDLE PORTION OF THE WEEK. TROUGH OVER THE CENTRAL CONUS WILL LIFT EAST...INDUCING CYCLOGENESIS OVER THE WESTERN GULF OF MEXICO TUESDAY NIGHT. THIS LOW WILL RIDE UP THE WESTERN SIDE OF THE APPALACHIANS...REACHING CENTRAL QUEBEC BY THURSDAY. A STRONG LOW LEVEL JET AHEAD OF THE DEEPENING LOW WILL TRANSPORT MOISTURE UP THE EASTERN SEABOARD TUESDAY NIGHT...BRINGING INCREASING CHANCES OF RAIN. TEMPERATURES DROP LITTLE FROM TUESDAYS HIGHS...SO NO FROZEN PRECIP CONCERNS. WHILE PROBABLY NOT CONTINUOUSLY RAINY THROUGH THE PERIOD...90-100 POPS ARE WARRANTED...WITH MODERATE RAIN POSSIBLE AT TIMES. THE NATURE MAY BECOME MORE SHOWERY ON WEDNESDAY...BUT NOT A COMPELLING REASON TO BREAK THAT OUT AT THIS TIME. 00Z NAM/MET GUIDANCE MUCH COOLER FOR HIGHS ON WEDNESDAY...LIKELY DUE TO A MUCH WEAKER SFC LOW THAN THE GLOBAL MODELS...WHICH ALLOWS THE COLD POOL TO LINGER EAST OF THE MOUNTAINS. HOWEVER...THE OTHER GUIDANCE OF 60S MAY BE A BIT OVERDONE...EXCEPT PERHAPS EAST OF I-95. IF THIS OCCURS...WILL ALSO HAVE TO MONITOR FOR THE POTENTIAL OF STRONG WIND GUSTS IF CONVECTIVE ELEMENTS DEVELOP. THE COLD FRONT TRAILING THE LOW WILL PUSH THROUGH THURSDAY NIGHT...BRINGING AN END TO THE PRECIP EXCEPT SOME POSSIBLE UPSLOPE. HOWEVER WITH THE WARM START...IT WILL TAKE UNTIL LATE IN THE NIGHT FOR THE TEMPERATURES TO DROP COLD ENOUGH TO SUPPORT ANY SNOW. ALL TOLD...IMPRESSIVE PWAT VALUES AND A DYNAMIC SYSTEM COULD LEAD TO STORM TOTAL RAINFALL IN EXCESS OF AN INCH...ESPECIALLY EAST OF THE MOUNTAINS.
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&& .LONG TERM /THURSDAY THROUGH SUNDAY/...
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THURSDAY WILL BE BREEZY BEHIND THE FRONT. ANY UPSLOPE SNOW SHOWERS SHOULD GRADUALLY COME TO AN END. THERE WILL ONLY BE A GLANCING BLOW OF CAA...AS HIGH PRESSURE WILL BE BUILDING IN FROM THE SOUTHWEST. THIS HIGH WILL REMAIN OVER THE SE STATES THROUGH SATURDAY AND TEMPERATURES ARE EXPECTED TO REMAIN ABOVE NORMAL. THE NEXT CHANCE OF PRECIP WILL ARRIVE AS THE NEXT TROUGH APPROACHES SATURDAY INTO SUNDAY. MODEL SOLUTIONS STILL DIFFER QUITE A BIT...SO POPS REMAIN LOW. THERE WILL BE POTENTIAL FOR TEMPERATURES TO COOL BACK DOWN BEHIND THIS SYSTEM FOR THE SECOND PART OF THE WEEKEND.
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&& .AVIATION /09Z MONDAY THROUGH FRIDAY/...
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PRECIP IS EXPECTED TO SPREAD NORTH TODAY. PERIOD OF LIGHT FREEZING RAIN/SLEET IS MOST LIKELY AT CHO/IAD. MAY BE TOO WARM AT DCA/BWI FOR FREEZING RAIN...BUT INITIAL PERIOD OF SLEET CAN/T BE RULED OUT BEFORE TURNING TO RAIN. MODELS HAVE TRENDED A LITTLE SLOWER WITH ONSET OF PRECIP AND HAVE FOLLOWED SUIT IN TAFS. EXPECT CONDITIONS TO DROP INTO MVFR THIS AFTERNOON...THEN LIKELY IFR OR LIFR TONIGHT AND CONTINUING INTO TUESDAY. BELOW-VFR CIGS WILL LINGER THROUGH WEDNESDAY NIGHT. VSBY COULD DROP BELOW VFR IN HEAVIER RAIN/SHOWERS AT TIMES FROM TUESDAY NIGHT THROUGH WEDNESDAY NIGHT. WINDS WILL SHIFT FROM SOUTHERLY TO WESTERLY WEDNESDAY NIGHT AND COULD GUST ABOVE 25 KT ON THURSDAY. NO SIGNIFICANT WEATHER EXPECTED AFTER THURSDAY EVENING.
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&& .MARINE...
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WEAK LOW PRESSURE MOVES OFF THE MID-ATLANTIC COAST TONIGHT. MARGINAL SCA EXPECTED ON THE LOWER PORTIONS OF THE WATERS THIS AFTERNOON OTHERWISE WINDS BELOW SCA THROUGH TUESDAY. A STRONG LOW PRESSURE SYSTEM WILL MOVE THROUGH THE REGION BETWEEN TUESDAY AND WEDNESDAY NIGHT...BRING MODERATE RAIN AT TIMES OVER THE WATERS. A SCA IS LIKELY WEDNESDAY THROUGH THURSDAY...WITH THE STRONGEST GUSTS EXPECTED ON THURSDAY. WINDS WILL DIMINISH THURSDAY NIGHT AS HIGH PRESSURE BUILDS IN.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...NONE. VA...FREEZING RAIN ADVISORY UNTIL 6 PM EST THIS EVENING FOR VAZ025- 026-029-036>040-501-503-504-507-508. FREEZING RAIN ADVISORY UNTIL NOON EST TODAY FOR VAZ050>052-055- 056-502. FREEZING RAIN ADVISORY FROM 10 AM THIS MORNING TO 6 PM EST THIS EVENING FOR VAZ027-028-030-031-505-506. WV...FREEZING RAIN ADVISORY UNTIL 6 PM EST THIS EVENING FOR WVZ505- 506. FREEZING RAIN ADVISORY FROM 10 AM THIS MORNING TO 6 PM EST THIS EVENING FOR WVZ055. MARINE...SMALL CRAFT ADVISORY FROM 10 AM THIS MORNING TO 6 PM EST THIS EVENING FOR ANZ534-537-543.
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&& $$ SYNOPSIS...ADS NEAR TERM...BPP SHORT TERM...BPP/ADS LONG TERM...ADS AVIATION...ADS/BPP MARINE...ADS/BPP

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