Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 310537 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1237 AM EST SAT JAN 31 2015 .SYNOPSIS... HIGH PRESSURE WILL BUILD ACROSS THE REGION FOR THE FIRST HALF OF THE WEEKEND. LOW PRESSURE WILL IMPACT THE AREA LATE SUNDAY INTO MONDAY. HIGH PRESSURE WILL RETURN FOR THE FIRST HALF OF NEXT WEEK. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... UPPER TROUGH HAS SWUNG EAST OF THE CWA WITH RIDGING BUILDING IN FROM THE WEST. FAIRLY WELL ALIGNED NORTHWEST WINDS ARE IN PLACE...THOUGH AS THE SFC HIGH BUILDS IN...PRESSURE GRADIENT WILL GRADUALLY WEAKEN...ALLOWING FOR THE WINDS TO CONTINUE TO SUBSIDE TONIGHT. WITH NO RECENT REPORTS OF ADVISORY LVL WINDS...AND THE TREND OF DECREASING...HAVE ALLOWED THE REMAINDER OF THE WIND ADVISORY TO EXPIRE. GOING WEST...WIND AND VERY COLD TEMPERATURES WILL ALLOW WIND CHILL VALUES TO DIP NEAR 10 BELOW OVER THE POTOMAC HIGHLANDS AND AS SUCH AM CONTINUING THE WIND CHILL ADVISORY THROUGH THE MORNING HOURS. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SUNDAY/... SAT HIGH PRES OVR THE AREA. E OF THE HIGHLANDS HIGHS SHOULD CLIMB INTO THE 30S. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... ZONAL FLOW WILL BE OVER THE AREA SATURDAY NIGHT AHEAD OF THE NEXT APPROACHING SHORTWAVE TROUGH IN THE PLAINS...WHILE SFC HIGH PRESSURE SLIDES OFF THE SE COAST. LITTLE OF NOTE OTHER THAN INCREASING MID AND HIGH LEVEL CLOUDS. LOWS GENERALLY IN THE 20S. THE LOW PRESSURE SYSTEM WILL TAKE SHAPE OVER THE OHIO VALLEY ON SUNDAY. ISENTROPIC LIFT MAY ALLOW SOME LIGHT SNOW TO BEGIN TO BREAK OUT...ESPECIALLY DURING THE AFTERNOON AND ALONG THE MD/PA BORDER. COLUMN ALOFT WILL BE COLD ENOUGH FOR SNOW...BUT SFC TEMPS WILL TRY TO EDGE ABOVE FREEZING AND IN FACT MAY RISE ABOVE 40 DEG SOUTH OF US-50...SO SOME RAIN MAY MIX IN WITH SOUTHERN EXTENT. QPF WILL BE VERY LIGHT THOUGH AND WHERE SNOW DOES FALL...AMOUNTS WOULD LIKELY BE LESS THAN AN INCH. 30.12Z MODEL SUITE HAS HELD SERVE WITH THE TRACK OF THE LOW PRESSURE SUNDAY NIGHT...WITH EVEN THE COLDER CANADIAN SOLUTION NOW ON THE NORTHWARD TREND. PER COLLAB WITH WPC...THIS SEEMS TO BE A STABLE TREND...AND IF ANYTHING MAY END UP BEING A BIT FURTHER NORTH. THIS SENDS THE TRACK OF THE SFC LOW RIGHT OVER THE HEART OF THE CWA AND DIMINISHES THE PROB OF A MORE SIGNIFICANT SNOW. THIS ALSO SEEMS REASONABLE SINCE THERE IS NOT A STRONG BLOCKING HIGH POSITIONED TO THE NORTH...RATHER AN EXTENSION OF A HIGH OVER THE PLAINS. TEMPERATURES LIKELY HOLD FAIRLY STEADY SUNDAY NIGHT. GREATEST CHANCE FOR ACCUMULATING SNOW WILL BE ALONG THE M-D LINE AND IN THE POTOMAC HIGHLANDS. SOUTHERN CWA MAY EVENTUALLY BECOME ALL RAIN. IN BETWEEN THE CONCERN WOULD BE FOR A LITTLE MIX OF EVERYTHING...AND WILL HAVE TO WATCH OUT FOR MODELS TRYING TO KEEP TEMPERATURES TOO WARM ON AN OVERNIGHT PRECIP EVENT WITH IN-SITU CAD/COLD AIR LOCKING IN PLACE IN THE CLIMO FAVORED AREAS. THIS COULD RESULT IN FZRA WHERE MODELS DEPICT IT BEING WARM ENOUGH FOR ONLY RAIN. DO HAVE SOME MINOR ICE ACCUMS FROM SHENANDOAH VALLEY UP TO AND ALONG THE M-D LINE...WHERE EVEN THEY WILL LIKELY MIX SOME AND LIMIT SNOW TOTALS. DC/BALT METROS ARE RIGHT ON THE EDGE...SO PLEASE KEEP TRACK OF THE LATEST FORECASTS AS THE EXACT TRACK OF THE LOW IS FINE TUNED. WILL HOLD OFF ON ISSUING ANY SORT OF WATCH ON THIS FORECAST ISSUANCE DUE TO THE LOW CONFIDENCE...LONG LEAD TIME...AND ONLY MARGINAL AMOUNTS FOR WARNING CRITERIA ON THE NORTHERN TIER OF THE CWA. A LOW PRESSURE SYSTEM NEAR METRO D.C. WILL QUICKLY MOVE OFFSHORE THE EAST COAST BY MIDDAY MONDAY. THE THREAT FOR A PERIOD OF ACCUMULATING SNOW OR PERHAPS A MIX OF RAIN AND SNOW EXISTS FOR THE REGION THROUGHOUT THE DAY...ESPECIALLY OVER THE EASTERN HALF. HIGH AND LOW TEMPERATURES MONDAY AND MONDAY NIGHT WILL AVERAGE 10 TO 15 DEGREES BELOW NORMAL...ESPECIALLY LATE MONDAY THROUGH MONDAY NIGHT WITH LOWS BOTTOMING OUT NEAR ZERO OR SINGLE DIGITS. AS FOR PRECIPITATION MONDAY NIGHT...THERE IS A CHANCE FOR SOME GOOD UPSLOPE SNOWFALL IN THE POTOMAC HIGHLANDS. HIGH PRESSURE WILL DOMINATE THE REGION TUESDAY AND TUESDAY NIGHT...BRINGING DRY CONDITIONS. TEMPERATURES WILL REMAIN NEARLY 10 DEGREES BELOW NORMAL. A COLD FRONT WILL SAG SOUTH OUT OF THE GREAT LAKES WEDNESDAY AND WEDNESDAY NIGHT BEFORE PUSHING ACROSS THE REGION THURSDAY. THERE IS A CHANCE OF SOME LIGHT SNOW OR A MIX OF SNOW AND RAIN...MAINLY WEDNESDAY NIGHT INTO THURSDAY. TEMPERATURES WEDNESDAY THROUGH THURSDAY WILL NOT BE AS COLD AS RECENT DAYS...BUT WILL STILL BE CHILLY. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... HIGH CONFIDENCE VFR CONDITIONS THROUGH SAT NIGHT. NW FLOW WILL GRADUALLY DIMINISH TONIGHT...THOUGH GUSTS INTO THE 20S STILL EXPECTED THRU DAYBREAK. IFR CONDITIONS POSSIBLE FROM SUNDAY AFTERNOON INTO SUNDAY NIGHT AS LOW PRESSURE CROSSES THE AREA. A MIX OF PRECIPITATION TYPES WILL BE LIKELY AT ALL TERMINALS. IFR OR LIFR CONDITIONS COULD START THE DAY MONDAY WITH PERIODS OF LIGHT SNOW ACROSS THE TERMINALS. THERE COULD BE A LITTLE RAIN MIX IN NEAR CHO. CONDITIONS SHOULD BECOME MVFR BY THE AFTERNOON BEFORE IMPROVING TO VFR LATE IN THE DAY. WINDS SW BECOMING NW LESS THAN 10 KNOTS EARLY MONDAY THEN INCREASING NW 15 KNOTS WITH GUSTS 20 TO 30 KNOTS MIDDAY MONDAY AND MONDAY AFTERNOON. VFR CONDITIONS MONDAY NIGHT AND TUESDAY. WINDS CONTINUING NW 15 KNOTS GUSTS 20 TO 30 KNOTS MONDAY BEFORE DIMINISHING N BECOMING S AT 5 TO 10 KNOTS TUESDAY. && .MARINE... GALES CONTINUE OVER THE WATERS THIS EVENING...WITH THE GALE WARNING CONTINUING OVERNIGHT. EVENTUALLY THIS WILL BE DOWNGRADED TO A SMALL CRAFT ADVISORY BUT THERE IS SOME UNCERTAINTY AS TO WHEN GALES WILL END. IT/S POSSIBLE THEY CONTINUE UNTIL SATURDAY MORNING...AT LEAST OVER THE LOWER MD BAY. IF THAT/S THE CASE THE GALE WOULD NEED TO BE EXTENDED. OTHERWISE...SCA CONDITIONS LIKELY SATURDAY. WINDS ARE FORECAST TO REMAIN BELOW SCA CRITERIA FROM SATURDAY NIGHT THROUGH SUNDAY NIGHT. LOW PRESSURE WILL BRING MIXED PRECIPITATION...ESPECIALLY THE UPPER POTOMAC AND NORTHERN BAY...SUNDAY AFTERNOON INTO SUNDAY NIGHT. SMALL CRAFT ADVISORIES ARE LIKELY MONDAY AFTERNOON THROUGH MONDAY NIGHT. NO MARINE HAZARDS EXPECTED TUESDAY. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...WIND CHILL ADVISORY UNTIL 9 AM EST THIS MORNING FOR MDZ501. VA...WIND CHILL ADVISORY UNTIL 9 AM EST THIS MORNING FOR VAZ503-504. WV...WIND CHILL ADVISORY UNTIL 9 AM EST THIS MORNING FOR WVZ501-503- 505-506. MARINE...GALE WARNING UNTIL 4 AM EST EARLY THIS MORNING FOR ANZ530>543. && $$

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