055
FXUS61 KLWX 212009
AFDLWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
309 PM EST SAT DEC 21 2024
SYNOPSIS
STRONG CANADIAN HIGH PRESSURE WILL BUILD IN THROUGH MONDAY,
WITH DRY AND VERY COLD CONDITIONS. A WEAK LOW PRESSURE SYSTEM
WILL APPROACH MONDAY NIGHT INTO TUESDAY. HIGH PRESSURE WILL
BUILD NORTH OF THE AREA WEDNESDAY.
NEAR TERM /THROUGH TONIGHT/
LOW PRESSURE IS OVER THE CANADIAN MARITIMES WHILE ARCTIC HIGH
PRESSURE RESIDES OVER THE UPPER GREAT LAKES. THE UPPER LEVEL
TROUGH AXIS IS POSITIONED EAST OF THE AREA. STRONG NORTHWEST
FLOW EXISTS BETWEEN THESE FEATURES. MOISTURE IS STREAMING
SOUTHEAST FROM THE GREAT LAKES, WITH A SEMI-PERMANENT BAND FROM
NE OHIO TO SW PA. THIS BAND WAS PRODUCING NOTABLE SNOWFALL RATES
IN PA AND APPEARED TO BE POSITIONED TO AFFECT GARRETT COUNTY. A
WINTER WEATHER ADVISORY WAS ISSUED FOR THAT REASON. HOWEVER, THE
BAND HAS SINCE PIVOTED SLIGHTLY, WITH GENERALLY LOWER INTENSITY
(BUT STILL ACCUMULATING) SNOW SHOWERS REACHING OUR FORECAST
AREA. IT'S POSSIBLE THE ADVISORY WILL BE CANCELLED EARLY. WHILE
IT DOES APPEAR ROADWAY IMPACTS APPEAR MOST LIKELY IN GARRETT
COUNTY, SNOW COVERED ROADS HAVE BEEN NOTED AT TIMES FARTHER
SOUTH ALONG THE APPALACHIAN CREST IN WESTERN PENDLETON AND
HIGHLAND COUNTIES AS WELL. WHILE MOISTURE IS SPILLING EAST OF
THE CREST GIVEN HIGH FROUDE NUMBERS, THE MOISTURE DEPTH IS
RELATIVELY SHALLOW WITH A LOT OF DRY AIR IN THE BOUNDARY LAYER,
AND THE BEST PVA HAS EXITED THE AREA. SO FAR, ONLY SOME FLURRIES
HAVE BEEN NOTED THIS AFTERNOON, MAINLY WEST OF THE BLUE RIDGE.
TEMPERATURES ARE HOLDING STEADY IN THE 30S WITH WIND CHILLS IN
THE 20S.
THE HIGH WILL START BUILDING CLOSER TO THE AREA TONIGHT,
ALLOWING WINDS TO GRADUALLY DIMINISH. HOWEVER, THE LINGERING
GRADIENT WON'T ALLOW TEMPERATURES TO COMPLETELY CRASH, WITH LOWS
FORECAST IN THE MID TEENS TO MID 20S. WIND CHILL VALUES WILL BE
IN THE TEENS FOR MANY AREAS, ALTHOUGH NORTHERN MARYLAND COULD
DIP INTO THE SINGLE DIGITS ALONG WITH THE HIGHER ELEVATIONS.
WHILE THE HIGHEST PEAKS COULD HAVE VALUES BELOW 0, THERE DOESN'T
APPEAR TO BE A LARGE ENOUGH AREA REACHING -10 TO WARRANT COLD
ADVISORIES. ALLEGHENY SNOW SHOWERS WILL TAPER TO FLURRIES
OVERNIGHT. HOWEVER, NORTHWEST FLOW WILL CONTINUE TO ALLOW CLOUDS
TO SPILL ACROSS THE AREA.
SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/
STRONG CANADIAN HIGH CONTINUES ITS MARCH ACROSS THE EASTERN
U.S. SUNDAY AND MONDAY. WELL BELOW NORMAL TEMPERATURES ARE
FORECAST SUNDAY AS HIGH STRUGGLE TO REACH FREEZING DESPITE
INCREASING SUN. A LINGERING WIND OF 5-10 MPH WILL ALLOW FOR WIND
CHILL VALUES TO STAY IN THE TEENS TO MID 20S FOR MUCH OF THE
DAY. SUNDAY NIGHT WILL BE THE COLDEST OF THE STRETCH. KEPT THE
FORECAST BELOW NBM WITH WIDESPREAD TEENS OUTSIDE THE URBAN
CORES. SINGLE DIGITS AREN'T OUT OF THE QUESTION IN RURAL
VALLEYS. MONDAY IS NOT QUITE AS COLD, THOUGH STILL BELOW NORMAL
WITH HIGHS IN THE 30S.
A CLIPPER SYSTEM WILL WORK THROUGH THE GREAT LAKES MONDAY NIGHT
WITH TRAILING FRONTAL ZONES PUSHING TOWARD THE LOCAL AREA.
FORCING AND MOISTURE APPEAR TO BE LIMITED, BUT THERE IS SOME
MODEL CONSENSUS FOR SOME LIGHT PRECIPITATION, ESPECIALLY IN THE
ALLEGHENIES, BUT POTENTIALLY ANYWHERE ACROSS THE NORTHERN HALF
OF THE AREA. OVERNIGHT TEMPERATURES SHOULD BE BELOW FREEZING FOR
MOST LOCATIONS. SNOW APPEARS TO BE MOST FAVORED IF PRECIPITATION
WERE TO OCCUR, BUT SLIGHT WARM ADVECTION ALOFT COULD RESULT IN
MIXED PRECIPITATION TYPES. WILL CONTINUE TO MONITOR.
LONG TERM /TUESDAY THROUGH SATURDAY/
LOW PRESSURE TO THE NORTH ON TUESDAY MAY ALLOW FOR SOME
WEAK MOISTURE RETURN ACROSS THE NORTHERN PORTIONS OF THE LOCAL AREA.
A SLIGHT CHANCE FOR A FEW RAIN-SNOW SHOWERS IS POSSIBLE EARLY
TUESDAY MORNING BEFORE PROBABILITIES DIMINISH LATER IN THE DAY.
HIGHS WILL CLIMB INTO THE MID TO UPPER 40S FOR THE LOWER ELEVATIONS
WITH 30S ACROSS THE HIGHER TERRAIN. HIGH PRESSURE RETURNS ON
CHRISTMAS DAY WITH NOT MANY PRECIPITATION CHANCES OTHER THAN THE
ALLEGHENY FRONT IN THE UPSLOPE AREAS.
WEDNESDAY NIGHT WILL INTRODUCE ADDITIONAL CHANCES FOR A FEW RAIN-
SNOW SHOWERS. CANNOT RULE OUT SOME FREEZING RAIN ALONG THE NORTHERN
ZONES FOR A FEW HOURS. HIGH PRESSURE WILL SLOWLY MOVE FURTHER NORTH
AND EAST AND ALLOW THE NEXT LOW PRESSURE SYSTEM TO APPROACH FROM THE
WEST LATER IN THE WEEK. POPS INCREASE HEADING INTO THE REMAINDER OF
THE WORKWEEK WITH MAINLY A COLD RAIN EXPECTED EAST OF THE MOUNTAINS.
HIGHS WILL CONTINUE TO BE IN THE 40S FOR MOST AREAS EAST OF THE
ALLEGHENIES. OVERNIGHT LOWS WILL FLUCTUATE EARLY IN THE WEEK IN THE
UPPER 20S TO MORE 30S LATE IN THE WORK WEEK.
AVIATION /20Z SATURDAY THROUGH THURSDAY/
VFR CONDITIONS EXPECTED THROUGH MONDAY AS A STRONG CANADIAN
HIGH BUILDS ACROSS THE REGION (ALTHOUGH BROKEN CEILINGS MAY
CONTINUE INTO SUNDAY MORNING). THE MAIN AVIATION IMPACT THROUGH
THIS AFTERNOON IS FROM STRONG NORTHWEST WIND GUSTS UP TO 30 KT
(LOWER AT CHO). MOISTURE IS TENDING TO DRY UP EAST OF THE BLUE
RIDGE, BUT SOME VIRGA OR FLURRIES REMAIN POSSIBLE THROUGH EARLY
EVENING IN THE METROS. MRB STANDS THE BEST CHANCE FOR FLURRIES
OR PERHAPS EVEN A BRIEF SNOW SHOWER. WINDS WILL GRADUALLY
DIMINISH TONIGHT INTO SUNDAY.
BRIEF SUB-VFR CEILINGS WILL BE POSSIBLE LATE MONDAY NIGHT INTO
TUESDAY ALONG WITH A LOW CHANCE OF WINTRY PRECIPITATION TOWARD
SOME OF THE NORTHERN TERMINALS LIKE KMTN/KBWI/KMRB. WINDS WILL
LIKELY BE LESS THAN 10 KNOTS THROUGH CHRISTMAS DAY AS HIGH
PRESSURE BRIEFLY BUILDS IN ACROSS THE REGION.
MARINE
HAZARDOUS MARINE CONDITIONS CONTINUE AS A STRONG CANADIAN HIGH
PRESSURE BUILDS ACROSS THE REGION. PEAK WIND GUSTS ARE GENERALLY
AROUND 25-30 KNOTS ACROSS THE WATERS. SOME GUSTS NEAR GALE FORCE
HAVE BEEN OBSERVED SOUTH OF NORTH BEACH AND ON THE LOWER
POTOMAC, BUT THESE SHOULD BE MARGINAL AND BRIEF THROUGH LATE
THIS AFTERNOON. WINDS WILL SLOWLY DIMINISH THIS EVENING, BUT
REMAIN IN SCA LEVELS FOR PORTIONS OF THE THROUGH SUNDAY
AFTERNOON. NO CHANGES TO THE ADVISORY AT THIS TIME. WINDS ARE
FORECAST TO FALL BELOW 10 KNOTS SUNDAY NIGHT INTO MONDAY AS THEY
EVENTUALLY BECOME SOUTHERLY.
SUB-SCA WINDS ARE EXPECTED TUESDAY AND WEDNESDAY AS LOW
PRESSURE MOVES NORTH OF THE AREA AND BRINGS A FEW RAIN-SNOW
SHOWERS, ESPECIALLY FOR THE NORTHERN WATERS.
LWX WATCHES/WARNINGS/ADVISORIES
DC...NONE.
MD...SMALL CRAFT ADVISORY UNTIL 10 AM EST SUNDAY FOR MDZ008.
WINTER WEATHER ADVISORY UNTIL 10 PM EST THIS EVENING FOR
MDZ001.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 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 UNTIL 9 PM EST THIS EVENING FOR ANZ535.
SYNOPSIS...ADS
NEAR TERM...ADS
SHORT TERM...ADS
LONG TERM...ADM
AVIATION...ADS/ADM
MARINE...ADS/ADM
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