510
FXUS61 KLWX 202002
AFDLWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
302 PM 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 TONIGHT/
AN UPPER LEVEL TROUGH OF LOW PRESSURE WILL SWING ACROSS THE
REGION LATER THIS AFTERNOON. SOME EXITING RAIN AND SNOW SHOWERS
OVER NORTHEAST MD WILL GIVE WAY TO A LULL IN PRECIPITATION EARLY
THIS EVENING. A PIECE OF ENERGY WILL QUICKLY PIVOT WITHIN THE
UPPER LEVEL TROUGH TO BRING A RETURN AND ENHANCED THREAT OF A
FEW RAIN SHOWERS AND SNOW SHOWERS MIX IN NORTHEAST MD AND
PERHAPS CENTRAL MD. THIS SAME ENERGY WILL USHER IN COLDER AIR
AND ALLOW FOR AN UPSLOPE WIND TO ENHANCE SNOW SHOWERS OVER THE
APPALACHIANS THIS EVENING AND INTO THE OVERNIGHT. SNOW AMOUNTS
WILL BE LIGHT ACROSS CENTRAL AND NORTHEAST MD TO THE AMOUNT OF A
TRACE OR COATING TO PERHAPS AN INCH WITH ISOLATED UP TO 2 INCHES
CLOSER TO THE MASON-DIXON LINE. MOST ACCUMULATING SNOW TONIGHT
IN THE APPALACHIANS WILL BE LATER TONIGHT AS THE TROUGH AXIS
SWINGS THROUGH.
SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/
A LARGE HIGH WILL BUILD SOUTH INTO THE REGION BEHIND THE
DEPARTING UPPER LEVEL STORM SYSTEM. THIS HIGH WILL CIRCULATE
MORE ARCTIC AIR SOUTHEAST AND SOUTHWARD. WHILE CONDITIONS LOOK
DRY TO THE EAST OF THE MOUNTAINS, AN ADDITIONAL INCH OR 2 COULD
ACCUMULATE. MOST OF THE ACCUMULATING SNOW IS LIKELY TO COME
FROM HEAVIER SNOW SHOWERS TO SNOW SQUALLS. 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. TOTAL SNOW ACCUMULATION THROUGH SATURDAY EVENING WILL
BE AROUND 2 TO 4 INCHES WITH ISOLATED 5 INCH IN A WORST- CASE
SCENARIO, FROM GARRETT INTO WESTERN GRANT/WESTERN PENDLETON
COUNTIES.
BLUSTERY CONDITIONS EXPECTED SATURDAY AFTERNOON, AS WINDS GUST
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.
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 FRIDAY/
ARCTIC AIR WILL RELEASE IT'S GRIP UPON OUR REGION MONDAY WITH
MODERATING TEMPERATURES THROUGHOUT THE HOLIDAY WEEK. OVERALL THE
UPPER LEVEL FLOW WILL BECOME MORE ZONAL WITH A FAIRLY ACTIVE
NORTHERN AND SOUTHERN JETSTREAM. SEVERAL PIECES OF SHORTWAVE ENERGY
WILL TRAVERSE THE SOUTHERN JETSTREAM EJECTING OUT OF THE SOUTHERN
U.S INTO THE MID-SOUTH AND MID-ATLANTIC WITH SUBTROPICAL RIDGING OFF
THE SOUTHEAST U.S COAST.
COLD AND DRY CONDITIONS LOOK TO CONTINUE THROUGH MONDAY AS STRONG
CANADIAN HIGH PRESSURE MAINTAINS IT'S PRESENCE OVER THE REGION. HIGH
PRESSURE WILL PUSH OFFSHORE LATE MONDAY INTO TUESDAY AS A NORTHERN
STREAM LOW PRESSURE SYSTEM RACES EAST FROM THE CENTRAL GREAT LAKES
REGION. THIS LOW PRESSURE SYSTEM COULD BRING RENEWED SNOW SHOWER
CHANCES TO THE ALLEGHENIES AS EARLY AS MONDAY NIGHT. ANY WIDESPREAD
PRECIPITATION LOOKS TO HOLD OFF UNTIL TUESDAY AND WEDNESDAY AS THE
LOW PRESSURE SYSTEM TRACKS NORTH OF THE AREA. SOME UNCERTAINTY
REMAINS AMONGST BOTH THE DETERMINISTIC AND ENSEMBLE GUIDANCE OF WHAT
THE MAIN PRECIPITATION TYPE WILL BE DURING THE TUESDAY AND WEDNESDAY
TIMEFRAME. AS IT STANDS NOW, IT LOOKS AS IF TEMPERATURES APPEAR COLD
ENOUGH AT ONSET FOR A LIGHT WINTRY MIX TUESDAY AFTERNOON INTO EARLY
WEDNESDAY MORNING (CHRISTMAS EVE/CHRISTMAS DAY) ESPECIALLY IN
LOCATIONS ALONG AND NORTH OF I-66/US-50. BEYOND THIS POINT,
UNCERTAINTY REMAINS TO HOW MUCH COLD AIR WILL BE LEFTOVER CHRISTMAS
DAY, AS THE BULK OF THE 12Z GUIDANCE SUGGESTS A WARMER SOLUTION
AHEAD OF THE SLOW MOVING COLD FRONTAL BOUNDARY. ANY RESIDUAL FROZEN
PRECIPITATION CHRISTMAS MORNING WILL LIKELY CHANGE OVER TO PLAIN
RAIN OUTSIDE THE MOUNTAINS WHICH COULD HOLD ONTO THE COLD AIR
LONGER. OVERALL THE PROBABILITY FOR A WHITE CHRISTMAS ACROSS THE
AREA REMAINS LOW, BUT NOT ZERO ESPECIALLY FOR THOSE WEST OF THE
ALLEGHENIES. A SLIGHT CHANCE OF RAIN SHOWERS (SNOW AT HIGHER
ELEVATIONS) PERSIST THROUGH THURSDAY AS THE COLD FRONT STALLS JUST
SOUTH OF THE AREA.
BELOW NORMAL TEMPERATURES LOOK TO CONTINUE THROUGH MONDAY BEFORE
TRENDING BACK TOWARD NORMAL FOR THE MIDDLE OF THE UPCOMING HOLIDAY
WEEK. HIGHS WILL GENERALLY REMAIN IN THE 30S AND 40S WITH LOWS IN
THE 20S AND 30S. BY FRIDAY, SOME LOCATIONS COULD PUSH 50 DEGREES.
AVIATION /20Z FRIDAY THROUGH WEDNESDAY/
A LIGHT MIX OF RAIN AND SNOW SHOWERS WILL EXIT NORTHEAST MD IN
THE EARLY EVENING HOURS. MTN AND BWI WILL HAVE IFR CONDITIONS
THROUGH THE PERIOD WITH THIS PRECIPITATION. A LULL IN
PRECIPITATION WILL ALLOW FOR CEILINGS TO BECOME MVFR OR VFR
LATER THIS EVENING AND OVERNIGHT. A COLD FRONT MOVES THROUGH
TONIGHT, WITH VFR CONDITIONS RETURNING FOR SATURDAY AND SUNDAY
FOR ALL SITES. NORTHWEST WINDS INCREASE, GUSTING AROUND 25 TO 35
KNOTS SATURDAY AFTERNOON.
VFR CONDITIONS CONTINUE THROUGH TUESDAY AS HIGH PRESSURE REMAINS
NEARBY. THE NEXT CHANCE FOR SUB-VFR CONDITIONS ARRIVES TUESDAY
EVENING (CHRISTMAS EVE) AND WEDNESDAY (CHRISTMAS DAY) AS AN AREA OF
LOW PRESSURE AND FRONT CROSS THE REGION. VFR CONDITIONS RETURN WITH
BRIEF HIGH PRESSURE THURSDAY BEFORE ANOTHER WAVE OF LOW PRESSURE
CROSSES FRIDAY.
MARINE
SCA IN EFFECT THROUGH EARLY SUNDAY DUE TO THE EXPECTATIONS OF
GUSTY NORTHWEST TO NORTH WINDS THROUGHOUT MUCH OF THE PERIOD.
GUSTS COLD REACH 30 KNOTS ACROSS THE WATERS SATURDAY. WINDS
DECREASE SATURDAY NIGHT, DROPPING BELOW SCA LEVELS IN THE UPPER
POTOMAC WATERS, BUT STILL GUSTING UP TO 25 KNOTS OVER THE BAY.
THESE ELEVATED WINDS CONTINUE THROUGH SUNDAY AFTERNOON, BEFORE
FINALLY DROPPING BELOW SCA LEVELS SUNDAY EVENING.
SUB-SCA LEVEL WINDS ARE EXPECTED MONDAY AND TUESDAY. SOUTHERLY WINDS
LESS THAN 15 KTS MONDAY WILL SHIFT TO THE NORTHWESTERLY DIRECTION
TUESDAY. SHOWER CHANCES LOOK TO RETURN TO THE WATERS DURING THIS
TIME AND CONTINUE THROUGH THE WEDNESDAY (CHRISTMAS) HOLIDAY.
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 UNTIL 4 PM EST SUNDAY FOR ANZ533-534-537-
541-543.
SMALL CRAFT ADVISORY FROM 6 AM TO 7 PM EST SATURDAY FOR ANZ535.
SYNOPSIS...KLW
NEAR TERM...KLW
SHORT TERM...KLW
LONG TERM...EST
AVIATION...KLW/EST
MARINE...KLW/EST
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