941
FXUS61 KLWX 180201
AFDLWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
901 PM EST TUE DEC 17 2024
SYNOPSIS
HIGH PRESSURE WILL BUILD INTO THE REGION TONIGHT. THE HIGH WILL
MOVE TO THE WESTERN ATLANTIC WEDNESDAY TO ALLOW ANOTHER LOW
PRESSURE SYSTEM TO IMPACT THE AREA WEDNESDAY INTO WEDNESDAY
EVENING. HIGH PRESSURE WILL CROSS THE AREA THURSDAY WITH ANOTHER
LOW APPROACHING THE GREAT LAKES BY FRIDAY.
NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/
A WEAK AREA OF LOW PRESSURE WAS MOVING FROM THE VA PIEDMONT TO S
MD THIS EVENING. LIGHT TO CALM WINDS, CLEARING SKIES AND HIGH
HUMIDITY IN THE LOW LEVELS HAS LED TO SOME PATCHY FOG JUST TO
THE NORTH OF THE LOW'S TRACK. LIGHT DRYING NW FLOW SHOULD SCOUR
OUT THIS FOG LATER THIS EVENING.
OTHERWISE, DRY CONDITIONS CONTINUE THIS EVENING INTO MUCH OF
THE OVERNIGHT WITH HIGH PRESSURE TAKING CONTROL OVERHEAD.
TEMPERATURES OVERNIGHT WILL BE NEARLY 10 DEGREES COLDER THAN
THEY WERE THIS MORNING WITH LOWS DROPPING INTO THE UPPER 20S TO
LOWER 30S IN PARTS OF WESTERN AND CENTRAL MARYLAND, EASTERN WEST
VIRGINIA AND THE APPALACHIANS. ELSEWHERE AND FURTHER EAST, LOWS
WILL DROP INTO THE MIDDLE TO UPPER 30S. IT IS THE AREAS THAT
ARE NEAR FREEZING OR BELOW FREEZING THAT WE NEED TO MONITOR FOR
ANY LIGHT ISOLATED MIXED PRECIPITATION LATE TONIGHT INTO EARLY
WEDNESDAY. HOWEVER, REGIONAL RAOBS AND ACARS SOUNDINGS INDICATED
ABUNDANT LOW-LEVEL DRY AIR WEST OF THE BLUE RIDGE/NORTH OF US-50,
SO PRECIP SHOULD HOLD OFF UNTIL SEVERAL HOURS AFTER DAYBREAK
WHEN IT IS WARMER.
SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/
TEMPERATURES WILL MODIFY THROUGH THE DAY WEDNESDAY WITH PLAIN
RAIN ANTICIPATED. THE LOW PRESSURE SYSTEM WILL IMPACT THE AREA
WEDNESDAY INTO WEDNESDAY NIGHT. RAINFALL AMOUNTS WITH THIS
SYSTEM WILL AVERAGE AROUND A QUARTER OF AN INCH NEAR THE METROS
TO UPWARDS OF THREE QUARTERS OF AN INCH NEAR WESTERN MARYLAND.
HIGHS WEDNESDAY WILL BE COOLER, BUT STILL SLIGHTLY ABOVE
AVERAGE FOR MID-DECEMBER. GUSTY WINDS, ESPECIALLY IN THE
MOUNTAINS, WILL OCCUR AS THE COLD FRONT CROSSES WEDNESDAY NIGHT.
FOR THE TYPICAL UPSLOPE AREAS OF THE ALLEGHENIES, PRECIPITATION
WILL CHANGE OVER TO A MIX OF LIGHT SNOW AND FREEZING RAIN OR
DRIZZLE AS SHALLOW MOISTURE AND AIR SEVERAL DEGREES BELOW
FREEZING INTERSECTS THE HIGHER TERRAIN.
COOLER THURSDAY WITH HIGH PRESSURE BUILDING IN BEHIND THE
DEPARTING STORM SYSTEM. HIGHS WILL BE CLOSE TO AVERAGE. LIGHT
PRECIP MAY LINGER INTO MID-MORNING ACROSS THE ALLEGHENIES, BUT
OTHERWISE DRY CONDITIONS ARE EXPECTED.
LONG TERM /FRIDAY THROUGH TUESDAY/
AN UPPER-LEVEL TROUGH AND ASSOCIATED CLIPPER LOW WILL MOVE
THROUGH THE AREA ON FRIDAY. THIS SYSTEM WILL BE RATHER MOISTURE
STARVED IN NATURE, BUT MAY PRODUCE A FEW MIXED RAIN AND SNOW
SHOWERS TO THE EAST OF THE MOUNTAINS. THE 12Z ECMWF-AI AS WELL
AS THE 12Z/18Z ICON AND ITS ENSEMBLES HINT AT AN INVERTED TROUGH
TYPE FEATURE FRIDAY NIGHT WHICH COULD RESULT IN SNOW SHOWERS
EAST OF THE MOUNTAINS. ALTHOUGH A LOWER PROBABILITY SCENARIO,
THERE ARE A FEW GEFS/EPS/SREF MEMBERS THAT HINT AT THIS, AS
WELL, SO IT BEARS MONITORING. FURTHER WEST, UPSLOPE SNOW
SHOWERS APPEAR LIKELY IN THE ALLEGHENIES DUE TO THE SHARP UPPER
TROUGH, DEEP MOISTURE, AND FAVORABLE TRAJECTORIES. THESE
UPSLOPE SNOW SHOWERS WILL CONTINUE ON AND OFF BEHIND THE SYSTEM
FRIDAY NIGHT INTO SATURDAY, WITH SEVERAL INCHES OF ACCUMULATION
APPEARING INCREASINGLY LIKELY IN THE MOUNTAINS.
NORTHWESTERLY FLOW BEHIND THIS SYSTEM WILL TRANSPORT A COLD AIRMASS
INTO THE REGION FOR THE WEEKEND. CONDITIONS WILL STAY DRY (WITH THE
EXCEPTION OF A FEW SNOW SHOWERS IN THE ALLEGHENIES ON SATURDAY), BUT
TEMPERATURES WILL BE WELL BELOW NORMAL. HIGHS WILL ONLY BE IN THE
20S AND 30S ON SATURDAY, AND MAY STRUGGLE TO REACH FREEZING AREAWIDE
BY SUNDAY. OVERNIGHT LOWS WILL GENERALLY BE IN THE TEENS.
HIGH PRESSURE WILL BUILD TO OUR NORTH ON MONDAY, LEADING TO SUNNY
SKIES. TEMPERATURES WILL REMAIN BELOW NORMAL, WITH DAYTIME HIGHS IN
THE UPPER 20S AND 30S.
AVIATION /00Z WEDNESDAY THROUGH SUNDAY/
VFR CONDITIONS THROUGH TONIGHT WITH HIGH PRESSURE MOVING
OVERHEAD, WITH FOG/LOW CIGS THIS EVENING LIKELY STAYING SOUTH OF
DCA/EAST OF CHO. MVFR OR IFR CONDITIONS POSSIBLE WEDNESDAY INTO
WEDNESDAY NIGHT AS ANOTHER LOW PRESSURE SYSTEM BRINGS RAIN TO
THE REGION. VFR CONDITIONS RETURN THURSDAY AND THURSDAY NIGHT
WITH THE NEXT HIGH PRESSURE CENTER BUILDING INTO THE REGION.
LIGHT NW FLOW TONIGHT BECOMES S WEDNESDAY THEN NW WEDNESDAY
NIGHT INTO THURSDAY WITH GUSTS TO 20 KNOTS.
PREVAILING VFR CONDITIONS AND LIGHT WINDS ARE EXPECTED ON FRIDAY. A
FEW RAIN OR SNOW SHOWERS MAY BE POSSIBLE, WHICH COULD BRIEFLY DROP
CONDITIONS TO SUB-VFR. VFR CONDITIONS AND NORTHWESTERLY WINDS ARE
EXPECTED FRIDAY NIGHT THROUGH SATURDAY.
MARINE
HIGH PRESSURE WILL BUILD OVERHEAD THROUGH TONIGHT. PATCHES OF
FOG REDUCING VISIBILITY TO OR BELOW 1 NM ARE POSSIBLE THROUGH
ABOUT MIDNIGHT. LOW PRESSURE WILL SPREAD SOME RAIN ACROSS THE
CWA WEDNESDAY INTO WEDNESDAY EVENING. BEHIND THE DEPARTING LOW
LATER WEDNESDAY NIGHT INTO THURSDAY, HIGH PRESSURE WILL BUILD IN
AND CAUSE NORTHWESTERLY WINDS TO INCREASE. SCA CONDITIONS COULD
START OVER ALL WATERS WEDNESDAY NIGHT AND INTO THURSDAY.
SUB-SCA WINDS ARE EXPECTED ON FRIDAY. WINDS TURN NORTHWESTERLY
FRIDAY NIGHT INTO SATURDAY. SCA CONDITIONS APPEAR LIKELY IN
NORTHWESTERLY FLOW FRIDAY NIGHT INTO SATURDAY.
LWX WATCHES/WARNINGS/ADVISORIES
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...NONE.
SYNOPSIS...CPB
NEAR TERM...KLW/DHOF/CPB
SHORT TERM...CPB
LONG TERM...KJP
AVIATION...KLW/DHOF/KJP
MARINE...KLW/DHOF/KJP
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