059
FXUS61 KLWX 201539
AFDLWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1039 AM EST FRI DEC 20 2024
SYNOPSIS
AN AREA OF LOW PRESSURE AND COLD FRONT WILL IMPACT THE AREA THIS
AFTERNOON INTO EARLY SATURDAY, BRINGING PERIODS OF LIGHT RAIN
AND SNOW. HIGH PRESSURE RETURNS LATE SATURDAY THROUGH MONDAY,
WITH DRY AND VERY COLD CONDITIONS. PRECIPITATION CHANCES
INCREASE AS ANOTHER FRONT APPROACHES DURING THE MIDDLE OF NEXT
WEEK.
NEAR TERM /THROUGH SATURDAY/
PREVIOUS DISCUSSION...
A STRONG UPPER TROUGH MOVES ACROSS THE REGION THIS AFTERNOON,
WITH A WEAK CLIPPER LOSING MOST OF ITS DEFINITION AFTER SLAMMING
INTO THE CENTRAL APPALACHIANS OUT AFTER IT SLAMS INTO THE
CENTRAL APPALACHIANS. HOWEVER, THIS IS EXPECTED TO BRING A
PERIOD OF SNOW SHOWERS TO THE ALLEGHENIES AND POTOMAC HIGHLANDS.
THE UPPER TROUGH INDUCES A SURFACE LOW TO DEVELOP OFF THE VA/NC
COAST, THAT BRINGS SOME MORNING RAIN ALONG PORTIONS OF THE I-95
CORRIDOR AND POINTS EAST. THE AREA BETWEEN I-95 AND US-15 IS
LIKELY TO BE WHERE THE RAIN/SNOW MIX LINE SETS UP.
MORNING SNOWFALL HAS SHIFTED TO THE EAST FROM THE APPALACHIANS
AND EASTERN WEST VIRGINIA TO ALONG AND EAST OF I-81 BUT NORTH
OF US 50 NEAR WASHINGTON DC AND PRINCE GEORGES COUNTY IN
MARYLAND. SOME RAIN IS ALSO MIXING WITH SNOWFALL. SNOW IN THESE
AREAS AREN'T EXPECTED TO GET MUCH MORE THAN A DUSTING TO AN INCH
WITH A QUICK 1.5 INCHES IN THE NORTHERN ZONES IN CENTRAL
MARYLAND. A LULL IN PRECIPITATION IS EXPECTED THIS AFTERNOON
BEFORE RETURNING THIS EVENING INTO TONIGHT, ESPECIALLY IN THE
ALLEGHENIES.
A LARGE CANADIAN HIGH BUILDS SOUTH INTO THE REGION, BRINGING VERY
COLD AND DRY CONDITIONS EAST OF THE MOUNTAINS. FOR THE ALLEGHENIES,
ADDITIONAL ACCUMULATING SNOWFALL IS LIKELY GIVEN FAVORABLE DYNAMICS
ALOFT, A SATURATED DGZ WITH SUFFICIENT LIFT. MOST OF THE
ACCUMULATING SNOW IS LIKELY TO COME FROM HEAVIER SNOW SHOWERS TO
SNOW SQUALLS. HOWEVER, THERE IS STILL UNCERTAINTY REGARDING THE
EXACT PLACEMENT, INTENSITY, AND DURATION OF ANY HEAVIER
SHOWERS/SQUALLS. THESE COULD SET UP AS STREAMERS, MEANING A LARGE
GRADIENT OF SNOW ACCUMULATIONS OVER SHORT DISTANCES. THE TOTAL SNOW
ACCUMULATION FROM FRIDAY NIGHT THROUGH SATURDAY EVENING WILL BE
AROUND 2-4", MAYBE UP TO 5" IN A WORST-CASE SCENARIO, FROM GARRETT
INTO WESTERN GRANT/WESTERN PENDLETON COUNTIES. DEPENDING ON HIGH RES
GUIDANCE LATER TODAY, WINTER WEATHER ADVISORIES MAY BE NEEDED.
BLUSTERY CONDITIONS EXPECTED SATURDAY AFTERNOON, AS WINDS GUST
AROUND 25-35 MPH, AND UP TO 40 MPH IN THE MOUNTAINS. COMBINED WITH
HIGHS IN THE 30S, THE RESULTING WIND CHILL VALUES DURING THE MIDDLE
OF THE DAY ARE LIKELY TO BE IN THE TEENS TO 20S, WITH SINGLE DIGITS
IN THE MOUNTAINS.
SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/
BRISK TO BLUSTERY CONDITIONS CONTINUE INTO SATURDAY NIGHT, AS LOWS
DROP TO THE 20S. GUSTY WINDS PRODUCE WIND CHILLS IN THE SINGLE
DIGITS TO LOW TEENS, WITH BELOW 0 VALUES IN THE ALLEGHENIES.
HIGHS REMAIN BELOW FREEZING FOR MOST OF THE AREA SUNDAY, WITH UPPER
20S TO LOW 30S, AND MID 30S IN CENTRAL VA. DOWNRIGHT COLD SUNDAY
NIGHT AS LOWS DIP TO THE LOW TEENS AREAWIDE, WITH SOME SINGLE DIGITS
IN THE MOUNTAINS AND ALONG THE MD/PA BORDER.
LONG TERM /MONDAY THROUGH THURSDAY/
DRY CONDITIONS CONTINUE MONDAY AS SURFACE HIGH PRESSURE REMAINS
OVERHEAD THROUGHOUT THE DAY. HIGH PRESSURE SHIFTS SOUTH ON TUESDAY
AS AN UPPER LEVEL TROUGH, PIVOTING OVER CANADA, PUSHES A LOW
PRESSURE SYSTEM AND ASSOCIATED COLD FRONT TOWARDS OUR AREA FROM THE
GREAT LAKES REGION. AS THE COLD FRONT APPROACHES FROM THE NORTH,
PRECIPITATION CHANCES RETURN TO THOSE IN THE ALLEGHENIES OVERNIGHT
MONDAY INTO TUESDAY. PRECIPITATION CHANCES SPREAD EASTWARD ALONG THE
MD/PA BORDER AND DOWN THE I-70 CORRIDOR TUESDAY AFTERNOON WITH A
SLIGHT CHANCE OF A RAIN/SNOW MIX. OVERNIGHT TUESDAY INTO WEDNESDAY,
PRECIPITATION CHANCES INCREASE AND SPREAD THROUGHOUT THE ENTIRE
FORECAST AREA AS THE COLD FRONT MOVES THROUGH. A SLIGHT CHANCE TO
CHANCE OF RAIN SHOWERS (SNOW AT HIGHER ELEVATIONS) PERSIST THROUGH
THURSDAY AS THE COLD FRONT STALLS SOUTH OF THE AREA.
TEMPERATURES GRADUALLY INCREASE EACH DAY WITH HIGHS IN THE 30S ON
MONDAY WARMING TO THE MID TO UPPER 40S ON THURSDAY. OVERNIGHT LOW
TEMPERATURES WILL WARM FROM THE 20S EARLIER IN THE WEEK TO MID TO
THE 30S ON THURSDAY NIGHT. LIGHT WINDS ARE EXPECTED THROUGHOUT THE
LONG TERM PERIOD.
AVIATION /16Z FRIDAY THROUGH TUESDAY/
PRECIPITATION MOVES ACROSS THE AREA LATE THIS MORNING INTO
TONIGHT, WITH PERIODS OF RAIN/SNOW SHOWERS POSSIBLE AT ALL
TERMINALS, EXCEPT CHO. OCCASIONAL SNOW SHOWER OR TWO COULD
VENTURE ACROSS MRB LATE THIS MORNING INTO EARLY AFTERNOON BEFORE
BECOMING MAINLY RAIN. ADDITIONAL SNOW SHOWERS ARE POSSIBLE
TONIGHT AT IAD, DCA, BWI, AND MTN, BUT CONFIDENCE IS CURRENTLY
LOW. ALSO, EXPECT LOW CLOUDS TO DEVELOP QUICKLY LATE MORNING,
AND LAST THROUGH LATE THIS EVENING.
A COLD FRONT MOVES THROUGH TONIGHT, WITH VFR CONDITIONS RETURNING
FOR SATURDAY AND SUNDAY. NORTHWEST WINDS INCREASE, GUSTING AROUND 23-
28 KNOTS SATURDAY AFTERNOON.
LIGHT WINDS BLOWING AROUND 5 KNOTS SHIFT FROM SOUTHERLY ON MONDAY TO
NORTHWESTERLY ON TUESDAY IN THE WAKE OF A COLD FRONT. VFR CONDITIONS
ARE EXPECTED MONDAY AND TUESDAY. AS PRECIPITATION CHANCES MOVE INTO
THE AREA, FLIGHT RESTRICTIONS ARE POSSIBLE AT KMRB AND KMTN
OVERNIGHT TUESDAY.
MARINE
NORTH WINDS BEGIN TO INCREASE THIS AFTERNOON, REACHING SCA LEVELS
ACROSS MOST OF THE WATERS BY THIS EVENING. NORTHERLY CHANNELING OVER
THE OPEN BAY WATERS WILL RESULT IN GUSTS UP TO 25 KNOTS TONIGHT.
WINDS TURN NORTHWEST SATURDAY WITH STRONGER GUSTS OF 25-30 KNOTS
EXPECTED ACROSS THE WATERS. WINDS DECREASE SATURDAY NIGHT, DROPPING
BELOW SCA LEVELS IN THE UPPER POTOMAC WATERS, BUT STILL GUSTING 20-
25 KNOTS OVER THE BAY. THESE ELEVATED WINDS CONTINUE THROUGH SUNDAY
AFTERNOON, BEFORE FINALLY DROPPING BELOW SCA LEVELS SUNDAY
EVENING.
SOUTHERLY WINDS ON MONDAY SHIFT TO NORTHWESTERLY ON TUESDAY AND ARE
EXPECTED TO STAY BELOW SCA CRITERIA.
LWX WATCHES/WARNINGS/ADVISORIES
DC...NONE.
MD...SMALL CRAFT ADVISORY FROM 7 PM THIS EVENING TO 10 AM EST
SUNDAY FOR MDZ008.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 7 PM THIS EVENING TO 10 AM EST
SUNDAY FOR ANZ530>532-536-538>540-542.
SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 4 PM EST
SUNDAY FOR ANZ533-534-537-541-543.
SMALL CRAFT ADVISORY FROM 6 AM TO 7 PM EST SATURDAY FOR ANZ535.
SYNOPSIS...KRR
NEAR TERM...KLW/KRR
SHORT TERM...KRR
LONG TERM...AVS
AVIATION...AVS/KLW
MARINE...AVS/KLW
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