815
FXUS61 KLWX 151516
AFDLWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1016 AM EST SUN DEC 15 2024
SYNOPSIS
A WEAKENING LOW PRESSURE SYSTEM WILL AFFECT THE AREA THROUGH
TONIGHT AS STRONG HIGH PRESSURE REMAINS POSITIONED TO THE
NORTHEAST. AS A SECOND, STRONGER AREA OF LOW PRESSURE MOVES
NORTH OF THE GREAT LAKES MONDAY, THE TRAILING COLD FRONT WILL
CROSS THE AREA EARLY TUESDAY. AFTER BRIEF HIGH PRESSURE, ANOTHER
LOW PRESSURE SYSTEM MAY AFFECT THE AREA WEDNESDAY INTO EARLY
THURSDAY.
NEAR TERM /THROUGH TONIGHT/
MID-MORNING UPDATE...
NOW THAT THE WINTRY MIX EVENT HAS BEGUN IN THE AREA, WE'RE ABLE
TO OBSERVE THE RESULTS OF THE ACTUAL THERMAL PROFILE. WHILE
RECENT GUIDANCE HAS TRENDED COLDER, THUS FAR OBSERVATIONS FROM
SPOTTERS AND WEBCAMS INDICATE THE COLD LAYER IS VERY SHALLOW,
WITH ONLY SLEET AND FREEZING RAIN REPORTS COMING IN. THIS
MORNING'S 12Z IAD AND RNK SOUNDINGS BOTH SHOW A WARM NOSE ABOVE
0C AROUND 900-850MB. 14Z SPC MESOANALYSIS FOR 850MB AND 900MB
SHOW THE 0C ISOTHERM BANKING UP AGAINST THE MOUNTAINS, BUT THE
COLD AIR AT 850MB HAS BEEN MORE ERODED BY WAA. SOME COOLING AT
850MB IS POSSIBLE LATE THIS MORNING/EARLY THIS AFTERNOON AS THE
SHORTWAVE AND BULK OF THE PRECIP SHIELD ADVANCE EAST, WITH THE
COLD LAYER ~925MB STILL EXPECTED TO LINGER (PRIMARILY OVER
WESTERN MD AND EASTERN WV), WHICH COULD ALLOW FOR A THICKER COLD
LAYER, BUT AT THAT POINT SURFACE TEMPERATURES OUTSIDE OF THE
HIGHER ELEVATIONS ARE EXPECTED TO BE ABOVE FREEZING. BASED ON
THESE OBSERVATIONS AND ANALYSES, IT SEEMS THE WINDOW OF
OPPORTUNITY FOR SNOW ACCUMULATION HAS SHRUNK, WITH SLEET AND
FREEZING RAIN BECOMING THE DOMINANT PRECIP TYPE. AREAS WHERE
COLD AIR CAN HANG AROUND LONGER THROUGH THE WHOLE TEMPERATURE
PROFILE, LIKE HIGHER ELEVATIONS AND THE COLD POCKET NEAR
FROSTBURG AND CUMBERLAND WOULD HAVE THE BEST CHANCE FOR SNOW.
GRANTED, A LIGHTER BAND OF PRECIP LED AHEAD OF THE MORE STEADY
PRECIP, SO NOW THAT THE STEADIER PRECIP IS ARRIVING, MORE
OBSERVATIONS WILL BE COMING IN. WE'LL CONTINUE TO WATCH THE
FINER DETAILS AS THE EVENT UNFOLDS THIS MORNING AND SEE WHAT
THERMAL PROFILE ACTUALLY RESULTS BY THIS AFTERNOON.
AN SPS HAS BEEN ISSUED FOR AREAS WITH COLD AIR BANKED AGAINST
THE EASTERN SLOPES OF THE BLUE RIDGE/CATOCTINS, WHICH COULD SEE
BRIEF FREEZING RAIN AND/OR SLEET THIS MORNING INTO EARLY THIS
AFTERNOON.
PREVIOUS DISCUSSION FOLLOWS....
A COMPACT CLOSED UPPER LOW IS LOCATED OVER ILLINOIS EARLY THIS
MORNING WHILE STRONG 1045 MB HIGH PRESSURE IS LOCATED OVER NEW
ENGLAND. THE SURFACE REFLECTION OF THE INCOMING SYSTEM IS WEAK,
BUT THERE IS PLENTY OF LIFT ALOFT ALONG WITH WARM/MOIST
ADVECTION OVER TOP OF THE COLD AIR DAMMING WEDGE POSITIONED EAST
OF THE APPALACHIANS. PRECIPITATION IS ADVANCING EASTWARD FROM
THE MID OHIO VALLEY AT THIS TIME. ONE TREND FROM PREVIOUS
FORECASTS IS THAT THERE HAS BEEN SOME CONSOLIDATION TOWARD
COLDER THERMAL PROFILES, ESPECIALLY WITH NORTHERN EXTENT. THIS
COULD RESULT IN HIGHER SNOW TOTALS UNLESS THERE IS ENOUGH WARM
ADVECTION TO TRANSITION TO SLEET (IT WOULDN'T TAKE MUCH AND IS
SUGGESTED BY SOME GUIDANCE). THE RISK FOR A QUARTER INCH OF ICE
REMAINS GREATEST ALONG THE CONTINENTAL DIVIDE WHERE WARM AIR
FROM THE WEST WILL INFLUENCE THE PROFILE ALOFT. HAVE ADDED THE
REMAINDER OF AREAS WEST OF THE BLUE RIDGE TO THE ADVISORY SINCE
THERE COULD BE SOME SNOW/ICE ACCUMULATIONS, ESPECIALLY ON THE
RIDGES. ALSO ADDED NELSON COUNTY WHERE THE EARLIER ONSET AND
MORE VARIED TERRAIN COULD RESULT IN SOME MINOR ACCUMULATIONS
BEFORE CHANGING TO RAIN THIS AFTERNOON. WILL NEED TO MONITOR THE
REMAINING COUNTIES ON THE EAST SLOPE OF THE BLUE RIDGE, WITH
WESTERN FREDERICK MD (CATOCTIN/SOUTH MTN) BEING MOST LIKELY TO
HAVE WINTRY ACCUMULATIONS. FURTHER TO THE EAST, TEMPERATURES
SHOULD WARM ENOUGH PRIOR TO PRECIPITATION ONSET (WHICH ISN'T
EXPECTED UNTIL THIS AFTERNOON) TO PREVENT ACCUMULATION, EVEN IF
THERE IS A BRIEF PERIOD OF SNOW OR SLEET.
TONIGHT, PRECIPITATION WILL GRADUALLY MOVE EAST COINCIDENT WITH
THE UPPER TROUGH. HOWEVER, SOME LIGHT RAIN OR DRIZZLE MAY LINGER
IN ITS WAKE DUE TO CONTINUED WEAK LIFT OVER THE CAD WEDGE. SOME
OF THE RIDGES, ESPECIALLY IN THE COLD POCKET NEAR CUMBERLAND,
MAY REMAIN BELOW FREEZING THROUGH THE NIGHT. LOCALLY DENSE FOG
COULD DEVELOP AS WARM ADVECTION ATTEMPTS TO TAKE PLACE AMONGST
THE SATURATED LOW LEVELS. TEMPERATURES REMAIN FAIRLY STEADY OR
PERHAPS RISE A BIT THROUGH THE NIGHT.
SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/
SHORTWAVE RIDGING WILL MOVE OVERHEAD MONDAY, BUT THE MODIFIED
CAD AIRMASS WILL RESULT IN CLOUDY SKIES (WITH A SMALL CHANCE OF
BREAKS WEST OF THE BLUE RIDGE). HAVE TEMPERATURES IN THE MID 40S
TO MID 50S, BUT EXPECT THE LOWER END OF THE RANGE FOR LOCATIONS
THAT KEEP LOW CLOUDS.
A TROUGH SWIFTLY APPROACHES FROM THE WEST TO BRING ANOTHER
ROUND OF SHOWERS LATE MONDAY AFTERNOON INTO MONDAY NIGHT. THIS
ROUND IS EXPECTED TO BE PURE RAIN WITH TEMPERATURES REMAINING
WELL ABOVE FREEZING. THERE REMAINS SOME UNCERTAINTY WITH HOW FAR
SOUTH THE SHOWERS WILL GET GIVEN THE BETTER FORCING SKIMS BY TO
THE NORTH. OVERNIGHT, SOUTHERLY WINDS GUST 15-20 MPH FOR MOST
OF THE AREA, AND UP TO 40 MPH AT THE HIGHEST RIDGES.
BRIEF HIGH PRESSURE, CLEARING SKIES, AND WESTERLY DOWNSLOPING
WINDS WILL PUSH TEMPERATURES WELL ABOVE NORMAL TUESDAY. CLOUDS
WILL INCREASE TUESDAY NIGHT AS THE NEXT LOW PRESSURE SYSTEM
QUICKLY APPROACHES FROM THE OHIO VALLEY. THERE IS A LOW CHANCE
PRECIPITATION ARRIVES TOWARD DAWN.
LONG TERM /WEDNESDAY THROUGH SATURDAY/
SFC HIGH PRESSURE BUILDS IN AHEAD OF A STRONG TROUGH THAT WILL BRING
PRECIPITATION TO THE AREA LATER WEDNESDAY INTO THURSDAY. AT THIS
TIME, RAIN LOOKS TO BE FAVORED FOR MOST OF THE CWA. THERE MAY BE
SOME MIXING OF SNOW AT THE END OF THE EVENT ACROSS THE NW CWA AS
COLDER AIR RUSHES IN. NW FLOW ALOFT AND A FEW EMBEDDED DISTURBANCES
BRING THE POTENTIAL FOR UPSLOPE SNOW SHOWERS THURSDAY THROUGH THE
WEEKEND. OVERALL PREDICTABILITY WRT TIMING IS LOW DUE TO MODEL
DIFFERENCES. BEST CHANCE FOR ACCUMULATING SNOW IS ACROSS THE
ALLEGHENIES. NON-ZERO CHANCE FURTHER EAST, BUT LOW INDEED.
ABOVE NORMAL TEMPS WEDNESDAY BEFORE A COOLING TREND TO WELL BELOW
AVERAGE HEADING INTO THE 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 /14Z SUNDAY THROUGH THURSDAY/
AN MVFR DECK STRADDLES THE AREA THIS MORNING, ALTHOUGH IT MAY
BRIEFLY RETREAT FROM IAD AND MRB. OTHERWISE, EXPECT GRADUALLY
LOWERING CEILINGS THROUGH THE DAY AS THE NEXT SYSTEM APPROACHES.
WINTRY PRECIP IS POSSIBLE FOR MRB AND CHO BY MID TO LATE MORNING.
WINTRY WEATHER AT CHO SHOULD BE BRIEF, BUT A MORE SUSTAINED
PERIOD OF SNOW COULD OCCUR AT MRB BEFORE TRANSITIONING TO RAIN
LATE IN THE DAY. SOME SNOWFLAKES OR SLEET PELLETS COULD MIX IN
FOR IAD IN THE EARLY AFTERNOON, BUT TEMPERATURES ARE EXPECTED TO
BE ABOVE FREEZING BY THEN. RAIN MAY NOT REACH DCA/BWI/MTN UNTIL
SUNSET. EXPECT IFR TO LIFR CONDITIONS TO DEVELOP TONIGHT AS RAIN
GRADUALLY PUSHES TO THE EAST. AS IT DOES SO, LOCALLY DENSE FOG
IS POSSIBLE, BUT CONDFIDENCE IS LOW.
SUB-VFR CEILINGS LIKELY PERSIST THROUGH MONDAY ALTHOUGH RAIN
SHOULD END (PERHAPS SOME OCCASIONAL DRIZZLE). THE NEXT SYSTEM
WILL BRING A CHANCE OF SHOWERS MONDAY NIGHT. SOUTHERLY WINDS
COULD GUST TO 20 KT AHEAD OF THIS FRONT, THEN SHIFT TO THE WEST
EARLY TUESDAY. FLIGHT CONDITIONS WILL IMPROVE BEHIND THE FRONT.
CIG/VSBY RESTRICTIONS POSSIBLE LATE WEDNESDAY INTO THURSDAY AS THE
NEXT SYSTEM BRINGS RAIN TO THE AREA. RESTRICTIONS SHOULD LIFT
THURSDAY AS THE SYSTEM MOVES EAST.
MARINE
WINDS ENHANCED OVER THE MIDDLE BAY EARLIER IN THE NIGHT BUT SEEM
TO BE WEAKENING. A SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR
THIS AREA UNTIL 6 AM. AFTERWARD, EAST/NORTHEAST WINDS REMAIN
LIGHT THROUGH MONDAY.
WINDS INCREASE OUT OF THE SOUTH ON MONDAY AHEAD OF AN APPROACHING
COLD FRONT WHICH LIKELY NECESSITATE SCAS MONDAY NIGHT. PORTIONS
OF THE WATERS MAY NEED ADVISORIES WITH WESTERLY POSTFRONTAL FLOW
INTO TUESDAY. WINDS WILL LESSEN BY LATE TUESDAY WITH BRIEF HIGH
PRESSURE.
NO MARINE WIND HAZARDS EXPECTED WEDNESDAY. SCA CONDITIONS ARE
POSSIBLE ACROSS ALL WATERS THURSDAY AS THE SYSTEM DEPARTS WITH A
REMNANT GRADIENT LEFT BEHIND OVER THE WATERS.
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...ADS
NEAR TERM...ADS/CAS
SHORT TERM...ADS
LONG TERM...CPB
AVIATION...ADS/CPB
MARINE...ADS/CPB
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