516  
FXUS61 KLWX 151942  
AFDLWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC  
242 PM EST SUN DEC 15 2024  
   
SYNOPSIS  
 
A LIGHT WINTRY MIX LOOKS TO CONTINUE ALONG AND WEST OF THE BLUE  
RIDGE THROUGH THIS EVENING WITH A WEAKENING LOW PRESSURE SYSTEM  
PASSING OVER THE REGION. PRECIPITATION CHANCES DECREASE LATE TONIGHT  
INTO MONDAY BEFORE A COLD FRONT CROSSES THE REGION MONDAY NIGHT INTO  
EARLY TUESDAY. BRIEF HIGH PRESSURE AND MUCH WARMER TEMPERATURES  
RETURN TUESDAY INTO WEDNESDAY BEFORE ANOTHER LOW PRESSURE SYSTEM  
IMPACTS THE AREA MIDWEEK.  
 
 
   
NEAR TERM /THROUGH TONIGHT/  
 
THE BULK OF PRECIPITATION WITH THIS EVENT HAS ARRIVED AND IS  
CURRENTLY MOVING ACROSS THE BLUE RIDGE. THE TREND OBSERVED EARLY  
ON OF MOSTLY SLEET/FREEZING RAIN HAS GENERALLY CONTINUED, BUT  
SNOW HAS MIXED IN FOR SOME LOCATIONS NOW THAT 850MB WARM NOSE  
HAS RETREATED. AS A RESULT, MOST ACCUMULATION WILL BE SLEET/ICE,  
WITH SNOW TOTALS ON THE LOWER END. LOCATIONS IN COLDER SPOTS  
NEAR THE ALLEGHENIES HAVE ALREADY OBSERVED AROUND A QUARTER INCH  
OF ICE.  
 
SURFACE TEMPERATURES ALONG THE RIDGES TO THE SOUTH OF OUR AREAS  
HAVE RISEN ABOVE FREEZING AS THE CAD WEDGE SLOWLY ERODES FROM  
SOUTH TO NORTH. THE HIGHER RIDGES OF THE BLUE RIDGE IN OUR AREA  
LIKELY REMAIN NEAR OR BELOW FREEZING FOR AT LEAST A FEW MORE  
HOURS, IF NOT UNTIL AFTER SUNSET. HIGHER ELEVATIONS TO THE WEST  
(OUTSIDE OF THE COLD POCKET AROUND FROSTBURG/CUMBERLAND) WILL  
GRADUALLY WARM ABOVE FREEZING THROUGH THE NIGHT.  
 
AFTER THE BULK OF PRECIP CURRENTLY MOVING THROUGH, LIGHTER  
PRECIP IS EXPECTED LATER THIS AFTERNOON AND INTO TONIGHT. PRECIP  
TYPE WILL TRANSITION TO PURE RAIN FROM SOUTH TO NORTH AS WAA  
WINS OUT, THOUGH FREEZING RAIN COULD LINGER A BIT LONGER FOR THE  
HIGHEST RIDGES. PRECIP CHANCES WILL BE TAPERING OFF LATE  
TONIGHT. WITH WAA, TEMPERATURES WILL WARM THROUGH THE NIGHT  
NON-DIURNALLY, TO MID 30S AND LOW 40S IN THE LOWLANDS AND LOW  
30S AT HIGHER ELEVATIONS. FOG BECOMES A CONCERN AS PRECIP  
TERMINATES, AND COULD BECOME LOCALLY DENSE, ESPECIALLY IN AREAS  
EAST OF THE MOUNTAINS THAT CLEAR SOME CLOUDS WITH DOWNSLOPING.  
 
 
   
SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/  
 
AS THE SHORTWAVE MOVES NORTHEAST, PRECIP FROM THE FIRST SYSTEM  
IS EXPECTED TO END BY MONDAY AFTERNOON. HIGHER ELEVATIONS AND A  
COLD POCKET NEAR CUMBERLAND COULD STILL SEE FREEZING  
RAIN/DRIZZLE EARLY MONDAY MORNING.  
 
A TROUGH SWIFTLY APPROACHES FROM THE WEST TO BRING ANOTHER  
ROUND FOR MONDAY AFTERNOON INTO MONDAY NIGHT. THIS ROUND IS  
EXPECTED TO BE PURE RAIN WITH TEMPERATURES REBOUNDING TO THE 40S  
AND 50S. THOUGH HIGH PRESSURE TO OUR NORTHEAST WILL HAVE BEGUN  
TO MOVE OFF, THE CAD WEDGE LIKELY STILL LINGERS TO SOME DEGREE  
WITHOUT A FRONT TO SWEEP OUT THE MODIFIED COLD AIR MASS, SO  
TEMPS COULD RUN COOLER. THERE REMAINS SOME UNCERTAINTY WITH HOW  
FAR SOUTH THE SHOWERS WILL GET, WITH GUIDANCE DIFFERING ON THE  
AMPLITUDE OF THE UPPER TROUGH. CURRENTLY THE ALLEGHENIES AND  
NORTH-CENTRAL MARYLAND SEEM TO HAVE THE BEST SHOT AT PRECIP,  
WITH ABOUT 0.25-0.50 INCH QPF BETWEEN MONDAY AFTERNOON AND  
TUESDAY MORNING. SOUTHERLY WINDS PICK UP THROUGH THE DAY MONDAY  
AHEAD OF AN APPROACHING FRONT, RESULTING IN 15-20 MPH GUSTS AT  
THE HIGHER ELEVATIONS BY THE EVENING. OVERNIGHT, WINDS GUST  
15-20 MPH FOR MOST OF THE AREA, AND UP TO 40 MPH AT THE HIGHEST  
RIDGES.  
 
A WEAK FRONT MOVES THROUGH TUESDAY, BUT WITH STRONG ENOUGH W/NW  
FLOW TO HOPEFULLY FORCE OUT THE REMNANTS OF THE CAD WEDGE. AS A  
RESULT, TEMPERATURES ARE EXPECTED TO RAMP UP INTO THE 50S AND  
60S FOR MOST OF THE AREA, AND THE THE 40S IN THE MOUNTAINS.  
BRIEF HIGH PRESSURE WILL ALLOW OVERNIGHT TEMPS TO DROP INTO THE  
30S AND 40S BEFORE CLOUDS BEGIN TO INCREASE LATE IN THE NIGHT  
AHEAD OF THE NEXT SYSTEM.  
 
 
   
LONG TERM /WEDNESDAY THROUGH SATURDAY/  
 
SURFACE HIGH PRESSURE WILL REMAIN ACROSS THE NORTHERN MID-ATLANTIC  
AS ANOTHER TROUGH OF LOW PRESSURE AND COLD FRONT MOVE THROUGH THE  
REGION MIDWEEK. WARMER CONDITIONS ARE EXPECTED IN ADVANCE OF THIS  
STORM SYSTEM LEADING TO A PREDOMINANTLY RAIN EVENT. SURFACE LOW  
PRESSURE LOOKS TO TRACK NORTH AND EAST FROM THE MID-SOUTH WEDNESDAY  
MORNING SENDING A WARM FRONT NORTHWARD INTO THE AREA. THE SURFACE  
LOW PER THE LATEST 12Z GUIDANCE LOOKS TO WORK ACROSS THE CENTRAL  
APPALACHIANS AND OFF THE NEW ENGLAND COAST LATE WEDNESDAY INTO  
THURSDAY. AS THE LOW TRACKS NORTH AND EAST, IT'S ASSOCIATED COLD  
FRONT WILL SWING THROUGH THE AREA LATE WEDNESDAY INTO THURSDAY. HIGH  
TEMPERATURES AHEAD OF THIS BOUNDARY WILL PUSH INTO THE MID TO UPPER  
50S AND LOW 60S WITH UPPER 40S OVER THE MOUNTAINS. TEMPERATURES WILL  
FALL INTO THE UPPER 20S AND LOW TO MID 30S WEDNESDAY NIGHT AS POST  
FRONTAL NORTHWEST FLOW ENSUE.  
 
12Z DETERMINISTIC AND ENSEMBLE GUIDANCE CONTINUE TO SUGGESTS SOME  
SNOW MIXING IN AT THE TAIL END OF THE EVENT ACROSS THE NORTHWESTERN  
HALF OF THE FORECAST AREA. CONFIDENCE IN THIS IS LOW GIVEN HOW MUCH  
MOISTURE MAY LINGER. HIGHEST CONFIDENCE FOR ANY WINTRY PRECIPITATION  
LOOKS TO REMAIN WEST OF THE ALLEGHENIES MIDWEEK GIVEN THE POST  
FRONTAL NORTHWEST FLOW ALOFT AND SEVERAL PIECES OF WEAK SHORTWAVE  
INGER PIVOTING THROUGH IN THE WAKE OF THE DEPARTING TROUGH. A BRIEF  
LULL IS EXPECTED IN THE WAKE OF THE TROUGH THURSDAY AFTERNOON AND  
NIGHT BEFORE ANOTHER FRONT APPROACHES FRIDAY INTO THE START OF THE  
WEEKEND.  
 
THIS STORM SYSTEM LOOKS MORE LIKE A CLIPPER WITH LOW PRESSURE  
ANCHORED OVER THE EASTERN GREAT LAKES ADVANCING EASTWARD THROUGH  
SOUTHERN CANADA AND THE INTERIOR NORTHEAST REGION. MEANWHILE, LOW  
PRESSURE WILL SIT OFFSHORE WITH A SHORTWAVE TROUGH HUGGING THE COAST.  
THE TRAILING COLD FRONT WILL KEEP THE TROUGH OFFSHORE WHILE LENDING  
TO THE CONTINUATION OF UPSLOPE SNOW SHOWERS OVER THE MOUNTAINS. EVEN  
WITH THAT SAID, THE COMBINATION OF THE COASTAL TROUGH AND INCOMING  
COLD FRONT MAY LEAD TO A BRIEF PERIOD OF RAIN/SNOW SHOWERS OVER  
NORTHWESTERN PORTIONS OF THE FORECAST AREA FRIDAY. CONFIDENCE ONCE  
AGAIN IS LOW DUE TO SUBTLE MODEL DIFFERENCES.  
 
THE BIGGER STORY WITH THE LATE WEEK FRONT WILL BE THE COLD WITH WELL  
BELOW NORMAL TEMPERATURES EXPECTED THIS WEEKEND. HIGHS SUNDAY MAY  
BE THE COLDEST OF THE SEASON THUS FAR. SINGLE DIGIT TO TEENS WIND  
CHILLS POSSIBLE FRIDAY THROUGH SUNDAY, ESPECIALLY OVERNIGHT AND  
EARLY IN THE MORNING.  
 
 
   
AVIATION /18Z SUNDAY THROUGH FRIDAY/  
 
TERMINALS IAD AND EAST HAVE RETAINED VFR CONDITIONS THUS FAR  
TODAY, BUT AS THE BULK OF PRECIP IS NOW MOVING INTO IAD, CIGS  
AND VSBYS ARE EXPECTED TO DETERIORATE FROM WEST TO EAST. PRECIP  
TYPE FOR THESE TERMINALS IS EXPECTED TO BE MOSTLY RAIN BUT A FEW  
FLAKES AND PELLETS HAVE BEEN SEEN NEAR IAD. PRECIP OUTSIDE OF  
THE MAIN BAND HAS BEEN VERY LIGHT, SO VSBY RESTRICTIONS HAVEN'T  
BEEN AS LOW. HOWEVER, FOR MRB, THE MORE STEADY PRECIP HAS  
BROUGHT VSBYS TO 3/4 MI IN SNOW. EASTERN TERMINALS CAN EXPECT  
LOSSES IN VSBY, BUT MAYBE NOT QUITE AS LOW WITH RAIN RATHER THAN  
SNOW. WINTRY PRECIP IS MOST LIKELY FOR MRB OVER THE NEXT FEW  
HOURS, AND COULD BE OBSERVED AT CHO OFF AND ON BEFORE THE CAD  
WEDGE IS FORCED NORTH.  
 
ONCE SOCKED IN TONIGHT, IFR CONDITIONS LIKELY CONTINUE THROUGH  
SUNDAY NIGHT AND WELL INTO MONDAY AS COLD AIR DAMMING CONTINUES.  
SOUTHERLY FLOW INCREASES AHEAD OF AN APPROACHING FRONT MONDAY  
NIGHT, WITH GUSTS TO AROUND 20 KTS. THE FRONT MOVES THROUGH  
TUESDAY MORNING, FINALLY PUSHING OUT THE CAD WEDGE AND HOPEFULLY  
IMPROVING CONDITIONS. LIGHT W/NW FLOW FOLLOWS AS HIGH PRESSURE  
BRIEFLY BUILDS IN.  
 
SUB-VFR RESTRICTIONS ARE POSSIBLE WEDNESDAY AFTERNOON THROUGH  
THURSDAY MORNING AS ANOTHER LOW PRESSURE SYSTEM BRINGS RAIN TO THE  
REGION. VFR CONDITIONS ARE EXPECTED THURSDAY AFTERNOON THROUGH  
FRIDAY BEFORE ANOTHER PERIOD OF SUB-VFR CONDITIONS RETURN WITH A  
COLD FRONT LATER IN THE WEEK.  
 
 
   
MARINE  
 
EAST/NORTHEAST WINDS REMAIN LIGHT THROUGH TONIGHT. WINDS  
INCREASE OUT OF THE SOUTH ON MONDAY AHEAD OF AN APPROACHING COLD  
FRONT WHICH LIKELY NECESSITATE SCAS MONDAY NIGHT. BEHIND THE  
COLD FRONT, WINDS DIMINISH AND TURN W/SW ON TUESDAY.  
 
NO MARINE WIND HAZARDS ARE EXPECTED WEDNESDAY WITH SOUTHEASTERLY  
WINDS GUSTING LESS THAN 15 KNOTS. SCAS ARE POSSIBLE OVER THE WATERS  
THURSDAY IN POST-FRONTAL NORTHWEST FLOW. THE TIGHTENED GRADIENT BETWEEN  
THE DEPARTING LOW AND INCOMING FRONTAL BOUNDARY LATER THIS WEEK WILL  
LEAD TO A CONTINUATION OF SCAS FOR PORTIONS OF THE WATERS THROUGH  
THE START OF THE WEEKEND.  
 
 
   
LWX WATCHES/WARNINGS/ADVISORIES  
 
DC...NONE.  
MD...WINTER STORM WARNING UNTIL 7 AM EST MONDAY FOR MDZ001-501.  
WINTER WEATHER ADVISORY UNTIL 1 AM EST MONDAY FOR MDZ003-502.  
VA...WINTER WEATHER ADVISORY UNTIL 1 AM EST MONDAY FOR VAZ025>031-  
503-504-507-508.  
WINTER WEATHER ADVISORY UNTIL 3 PM EST THIS AFTERNOON FOR  
VAZ036.  
WV...WINTER STORM WARNING UNTIL 7 AM EST MONDAY FOR WVZ501-503-505.  
WINTER WEATHER ADVISORY UNTIL 1 AM EST MONDAY FOR WVZ050>053-  
055-502-504-506.  
MARINE...NONE.  
 
 
 
 
 
SYNOPSIS...EST  
NEAR TERM...CAS  
SHORT TERM...CAS/ADS  
LONG TERM...EST  
AVIATION...CAS/EST  
MARINE...CAS/EST  
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