Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 201932 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 232 PM EST SAT DEC 20 2014 .SYNOPSIS...
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HIGH PRESSURE WILL PERSIST THROUGH SUNDAY. LOW PRESSURE WILL TRACK UP THE MID-ATLANTIC COAST LATE MONDAY. A STRONG COLD FRONT WILL THEN PASS THROUGH THE AREA LATE WEDNESDAY INTO WEDNESDAY NIGHT.
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&& .NEAR TERM /THROUGH SUNDAY/...
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A SHORTWAVE WILL PASS THROUGH THE REGION THIS AFTERNOON...CAUSING HIGH AND MID-LEVEL CLOUDS WHILE SURFACE HIGH PRESSURE BUILDS OVERHEAD. SEASONABLY CHILLY CONDITIONS WILL CONTINUE...BUT THE DEEP MOISTURE FROM THIS SYSTEM IS EXPECTED TO REMAIN TO OUR SOUTH. THEREFORE...MOST AREAS WILL TURN OUT DRY. MAX TEMPS WILL RANGE FROM THE UPPER 20S TO LOWER 30S IN THE MOUNTAINS TO THE UPPER 30S/NEAR 40 IN WASHINGTON AND BALTIMORE. HIGH PRESSURE WILL REMAIN OVER THE REGION TONIGHT WHILE ANOTHER UPPER-LEVEL DISTURBANCE PASSES THROUGH THE AREA IN THE WESTERLY FLOW ALOFT. A BKN DECK OF MID-LEVEL CLOUDS IS EXPECTED...BUT MOISTURE WILL REMAIN TO OUR SOUTH SO DRY WEATHER IS EXPECTED. CLOUDS MAY BREAK OUT TOWARD MORNING BEHIND THE DISTURBANCE...AND WITH HIGH PRESSURE OVERHEAD THIS COULD LEAD RADIATIONAL COOLING. THEREFORE...MIN TEMPS HAVE BEEN TAKEN DOWN A FEW DEGREES CLOSER TO THE MAV GUIDANCE. MIN TEMPS WILL RANGE FROM THE LOWER AND MIDDLE 20S ACROSS MOST LOCATIONS TO THE LOWER AND MIDDLE 30S IN DOWNTOWN WASHINGTON AND BALTIMORE. HIGH PRESSURE WILL REMAIN OVER THE REGION FOR WEDNESDAY AND AN UPPER-LEVEL RIDGE WILL BUILD OVERHEAD BEHIND A DEPARTING DISTURBANCE. THIS WILL ALLOW FOR PLENTY OF SUNSHINE...BUT SEASONABLY CHILLY CONDITIONS WILL CONTINUE.
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&& .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
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UPPER TROUGH WILL BEGIN TO AMPLIFY OVER THE EASTERN U.S ON MONDAY. UPPER LEVEL JET/DYNAMICS SHIFT EAST TO THE COAST WHERE AN AREA OF LOW PRESSURE IS LIKELY TO DEVELOP OVER THE CAROLINAS AND TRACK SLOWLY NORTH INTO MONDAY NIGHT. TIMING OF PRECIPITATION IS STILL A BIT UNCERTAIN WITHIN THE NAM/GFS/EURO SOLUTIONS WITH THE NAM BEING THE MOST BULLISH AND QUICKEST TO ARRIVE VS THE SLOWER GFS AND EURO. EITHER WAY...TEMPERATURES WILL BE CRUCIAL WITH COLD HIGH PRESSURE OVER NEW ENGLAND PROVIDING CAD WEDGE OVER THE MIDDLE ATLANTIC TO START THE EVENT. IF PRECIPITATION BEGINS EARLIER IN THE DAY AS PER THE 12Z NAM THERE COULD BE MORE OF AN ZR/IP THREAT EVEN OVER SOME OF THE IMMEDIATE SUBURBS NORTH AND WEST OF DC/BWI THE FIRST PART OF MONDAY. IT IS TYPICAL FOR GUIDANCE TO ERODE THE CAD WEDGE TOO QUICKLY IN SITUATIONS LIKE THIS. HAVE UNDERCUT TEMPERATURES A FEW DEGREES FROM INHERITED NUMBERS AND EXPANDED ZR/IP A BIT EAST AS WELL. MILDER AIR WILL GRADUALLY CHANGE THE ICE TO RAIN EAST OF THE BLUE RIDGE BUT A LONGER PERIOD OF ZR/IP MAY OCCUR WEST OF THE BLUE RIDGE IN THE NORMALLY COLDER LOCALES. WILL CONTINUE TO HIGHLIGHT POTENTIAL IN THE HAZARDOUS WEATHER OUTLOOK. ENOUGH WARMER AIR SHOULD WORK IN AND CHANGE MUCH OF THE PRECIP TO RAIN MONDAY NIGHT ALTHOUGH THERE COULD STILL BE A FEW POCKETS OF ZR OVER THE HIGHER ELEVATIONS WITHIN THE HIGHLANDS.
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&& .LONG TERM /TUESDAY THROUGH SATURDAY/...
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A WARM FRONT WILL INCH ITS WAY NORTHWARD FROM THE CAROLINAS TO THE MID ATLANTIC COAST TUESDAY AND TUESDAY NIGHT. SOME STRATIFORM LIGHT TO MODERATE RAIN WILL PRECEDE THE WARM FRONT AND OVERRUN THE ENTIRE REGION. THROUGH THE DAY WEDNESDAY...AS THE WARM FRONT WORKS ITS WAY NORTH OF THE MASON-DIXON LINE...A POTENT STORM SYSTEM WILL BE PIVOTING NORTHEASTWARD FROM THE OHIO VALLEY INTO THE EASTERN GREAT LAKES REGION. ITS ASSOCIATED COLD FRONT WILL TRAIL SOUTHWARD AND POSSIBLY WORK INTO THE POTOMAC HIGHLANDS AND SHENANDOAH VALLEY BY LATER IN THE DAY WEDNESDAY. THIS COLD FRONT SHOULD MOVE ACROSS THE DELMARVA PENINSULA AND THEN OFFSHORE WEDNESDAY NIGHT. PROBABILITY OF RAIN REMAINS HIGH...NEAR 90 TO 100 PERCENT. THE RAIN EXPECTED LOOKS TO BE MORE CONVECTIVE IN NATURE AHEAD OF THE COLD FRONT AND POTENT STORM SYSTEM. HIGH TEMPERATURES WEDNESDAY WILL BE 15 TO 20 DEGREES ABOVE NORMAL AS WE ENCOUNTER MOST LOCATIONS REACHING NEAR 60 TO THE LOWER 60S...MAINLY EAST OF THE BLUE RIDGE MOUNTAINS. WE WILL LEAVE A CHANCE OF RAIN SHOWERS IN THE FORECAST FOR WEDNESDAY NIGHT CONSIDERING SOME UNCERTAINTY ON THE TIMING OF COLD FRONTAL PASSAGE. NONETHELESS...COLDER AND DRIER AIR WILL FILTER INTO THE REGION FROM WEST TO EAST WEDNESDAY NIGHT...ALLOWING FOR TEMPERATURES TO QUICKLY FALL THROUGH THE 50S INTO THE 40S. THERE IS A CHANCE FOR SOME SNOW SHOWERS IN THE HIGHER ELEVATIONS OF THE POTOMAC HIGHLANDS THURSDAY...PERHAPS ABOVE 2500 FEET. ALTHOUGH TEMPERATURES WILL BE SOME 10 TO 15 COOLER THAN WEDNESDAY...TEMPERATURES WILL STILL BE SLIGHTLY ABOVE NORMAL. DRY CONDITIONS FRIDAY WITH HIGH PRESSURE BUILDING JUST TO OUR SOUTH. HIGH TEMPERATURES MAY STILL BE SLIGHTLY ABOVE NORMAL WITH A GOOD BIT OF SUNSHINE. ANOTHER COLD FRONT COULD BRING A CHANCE FOR RAIN AND SNOW SHOWERS TO THE REGION FRIDAY NIGHT INTO SATURDAY.
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&& .AVIATION /18Z SATURDAY THROUGH THURSDAY/...
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HIGH PRESSURE WILL REMAIN OVER THE TERMINALS THROUGH SUNDAY...BRINGING VFR CONDITIONS. CLOUDS WILL INCREASE SUNDAY NIGHT AND SUBVFR CONDITIONS ARE POSSIBLE TOWARD MONDAY MORNING. CONDITIONS WILL DETERIORATE MONDAY INTO MONDAY NIGHT WITH SUB VFR CIGS AND VSBYS. PRECIPITATION TYPE IS A BIT UNCERTAIN ALTHOUGH EXPECTING MOSTLY LIQUID AT KDCA AND KBWI. NORTH AND WEST COULD SEE A WINTRY MIX OF FREEZING RAIN AND SLEET FOR PART OF MONDAY. ALL RAIN EXPECTED MONDAY NIGHT. IFR OR LIFR CONDITIONS ARE POSSIBLE TUESDAY AND TUESDAY NIGHT WITH LOW CLOUDS AND PERIODS OF RAIN. WINDS LIGHT AND VARIABLE. IFR OR LIFR CONDITIONS ARE POSSIBLE AGAIN WEDNESDAY WITH NUMEROUS GUSTY RAIN SHOWERS AHEAD OF A COLD FRONT. WINDS SOUTHEAST TO SOUTH 5 TO 10 KNOTS WEDNESDAY...INCREASING SOUTHWEST WEDNESDAY NIGHT.
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&& .MARINE...
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HIGH PRESSURE WILL REMAIN OVER THE WATERS THROUGH SUNDAY NIGHT. NO MARINE HAZARDS ARE EXPECTED DURING THIS TIME. WINDS COULD APPROACH SCA CRITERIA LATER MONDAY INTO EARLY TUESDAY AS LOW PRESSURE APPROACHES FROM THE SOUTH. NO MARINE HAZARDS TUESDAY AND TUESDAY NIGHT. SMALL CRAFT ADVISORIES MAY BE NEEDED WEDNESDAY WITH GUSTS TO 20 KNOTS.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...BJL/KRW LONG TERM...KLW AVIATION...BJL/KLW/KRW MARINE...BJL/KLW/KRW

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