116
FXUS61 KLWX 180827
AFDLWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
327 AM EST WED DEC 18 2024
SYNOPSIS
LOW PRESSURE WILL BRING RAIN TO THE AREA TODAY. HIGH PRESSURE
WILL CROSS THE AREA THURSDAY WITH ANOTHER LOW APPROACHING THE
GREAT LAKES BY FRIDAY. ARTIC HIGH PRESSURE BUILDS BACK IN
SATURDAY INTO SUNDAY.
NEAR TERM /THROUGH TONIGHT/
KEY MESSAGES:
- RAIN CHANCES INCREASE NEAR MIDDAY
- FREEZING DRIZZLE IS POSSIBLE ACROSS THE HIGHER RIDGES OF THE ALLEGHENIES
TONIGHT
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AN AREA OF LOW PRESSURE WILL MOVE TOWARDS THE AREA TODAY
BRINGING WIDESPREAD RAIN. LATEST ACARS SOUNDINGS AND SATELLITE
WATER VAPOR CHANNELS INDICATED ABUNDANT LOW-LEVEL DRY AIR WEST
OF THE BLUE RIDGE/NORTH OF US-50, SO IT MAY TAKE A WHILE FOR
RAIN TO MAKE IT TO THE SURFACE. PRECIPITATION IS EXPECTED TO
START LATE ENOUGH THAT TEMPERATURE WILL MODERATE ENOUGH TO ALLOW
FOR PLAIN RAIN. 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. RAIN CHANCES DECREASE
OVERNIGHT, BUT REMNANT MOISTURE INTERACTING WITH TERRAIN IN NW
FLOW WILL ALLOW FOR WINTRY PRECIPITATION. MODELS SHOW FAVORABLE
SOUNDINGS FOR LIGHT FREEZING RAIN ACROSS THE HIGHER TERRAIN OF
THE ALLEGHENIES. SOME SNOW IS LIKELY TO MIX IN AS WELL. OVERALL
ACCUMULATIONS WILL BE LIGHT, BUT ANY ICE IS HAZARDOUS. WILL LET
FUTURE SHIFTS EVALUATE ICE POTENTIAL TO SEE IF A WINTER WEATHER
ADVISORY IS NECESSARY TONIGHT. IT WILL BE WINDY BEHIND THE FRONT
ASSOCIATED WITH THE LOW TONIGHT. GUSTS OF 20-30 MPH ARE
POSSIBLE.
A NOTABLE TEMPERATURE GRADIENT IS EXPECTED FROM N TO S ACROSS
THE CWA TODAY. MID 40S NEAR THE MASON-DIXON WITH MID-50S TO
NEAR 60 IN CENTRAL VA. COLDER TONIGHT WITH LOWS IN THE 20S TO
30S FOR MOST (NEAR 40 ALONG THE IMMEDIATE WATERS).
SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/
KEY MESSAGES:
- NOTABLY COLDER THURSDAY AND FRIDAY
- SEVERAL INCHES OF SNOW ARE POSSIBLE ACROSS THE ALLEGHENIES
FRIDAY INTO SATURDAY
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COLDER THURSDAY WITH HIGH PRESSURE BUILDING IN BEHIND THE
DEPARTING STORM SYSTEM. HIGHS WILL BE A TICK OR TWO BELOW
AVERAGE. LIGHT PRECIP MAY LINGER INTO MID-MORNING ACROSS THE
ALLEGHENIES, BUT OTHERWISE DRY CONDITIONS ARE EXPECTED.
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. MODELS HAVE TRENDED
TOWARDS A SHARPER TROUGH CLOSER TO THE COAST, BUT ALSO HINT AT
AN INVERTED NORLAN TROUGH FRIDAY NIGHT WHICH COULD RESULT IN
SNOW SHOWERS EAST OF THE MOUNTAINS. MODELS CONSENSUS FOR THIS
PHENOMENA IS FOCUSED TO OUR NORTH IN NJ, BUT SOME GUIDANCE CLIPS
NE MD. NOT THE BEST SFC CONVERGENCE ON MODEL GUIDANCE AT THIS
TIME, BUT THIS IS SOMETHING GLOBAL GUIDANCE TYPICALLY STRUGGLES
WITH. WILL BE INTERESTING TO SEE HOW THIS EVENT UNFOLDS OVER
THE NEXT FEW DAYS AS MESOSCALE GUIDANCE COMES INTO PLAY. FURTHER
WEST, UPSLOPE SNOW SHOWERS APPEAR LIKELY IN THE ALLEGHENIES DUE
TO THE SHARP UPPER TROUGH, DEEP MOISTURE, AND FAVORABLE
TRAJECTORIES. MODEL SOUNDINGS HAVE SATURATION THROUGH 700 MB
WITH FAVORABLE LIFT THROUGH THE DGZ FRIDAY INTO FRIDAY NIGHT
BEFORE DRYING OUT SATURDAY. 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. RATIOS BY FRIDAY NIGHT
WILL LIKELY BE APPROACHING 20:1 GIVEN THE COLD THERMALS ALOFT.
BELOW AVERAGE TEMPS ARE EXPECTED FRIDAY AND SATURDAY. HIGHS
30S/20S MTNS AND 40S ELSEWHERE. LOWS IN 20S TO UPPER TEENS
(MTNS).
LONG TERM /SATURDAY THROUGH TUESDAY/
THERE IS HIGH CONFIDENCE THAT A STRONG CANADIAN HIGH BUILDS SOUTH
ACROSS MUCH OF THE EASTERN CONUS THIS WEEKEND INTO EARLY NEXT WEEK.
A VERY COLD AIRMASS BRINGS WELL BELOW NORMAL TEMPERATURES SATURDAY
THROUGH MONDAY, THEN TEMPS RETURN CLOSER TO NORMAL TUESDAY. HIGHS
ARE FORECAST TO BE IN THE 30S EACH DAY, WITH 20S OR COLDER IN THE
MOUNTAINS. SUNDAY LOOKS TO BE THE COLDEST DAY, WHEN MOST OF THE AREA
COULD REMAIN AT OR BELOW FREEZING THROUGH THE DAY. OVERNIGHT LOWS IN
THE TEENS TO LOW 20S, WITH SUNDAY NIGHT BEING THE COLDEST WITH LOW
TO MID TEENS AREAWIDE, AND SINGLE DIGITS IN THE ALLEGHENIES.
BLUSTERY CONDITIONS SATURDAY AS NORTHWEST WINDS GUST AROUND 20-25
MPH IN THE AFTERNOON, KEEPING WIND CHILLS IN THE 20S. WINDS DECREASE
SUNDAY, BUT STILL COULD GUST AROUND 15-20 MPH. THE COLDER AIR TEMPS
AND SLIGHT WIND GUSTS RESULT IN WIND CHILLS IN THE TEENS TO 20S.
AVIATION /08Z WEDNESDAY THROUGH SUNDAY/
VFR CONDITIONS THROUGH DAYBREAK WITH HIGH PRESSURE MOVING
OVERHEAD, WITH FOG/LOW CIGS THIS EVENING LIKELY STAYING SOUTH OF
DCA/EAST OF CHO. MVFR OR IFR CONDITIONS POSSIBLE TODAY INTO
TONIGHT 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 ARE EXPECTED THIS WEEKEND. NORTHWEST WINDS GUSTING
AROUND 20-25 KNOTS SATURDAY LATE MORNING TO LATE AFTERNOON, THEN
WINDS BECOME LIGHT SATURDAY NIGHT INTO SUNDAY.
MARINE
HIGH PRESSURE WILL BUILD OVERHEAD THROUGH DAYBREAK. 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. HAVE ISSUED AN SCA FOR POST
FRONTAL WINDS TONIGHT INTO THURSDAY FOR ALL WATERS. SUB-SCA
WINDS ARE EXPECTED ON FRIDAY. WINDS TURN NORTHWESTERLY FRIDAY
NIGHT INTO SATURDAY.
SCA CONDITIONS ARE LIKELY ACROSS ALL THE WATERS SATURDAY INTO SUNDAY
MORNING, WITH GUSTS OF 20-25 KNOTS. WINDS BEGIN TO DECREASE SATURDAY
NIGHT, BUT COULD STILL GUST AROUND 18-20 KNOTS THROUGH SUNDAY
EVENING.
LWX WATCHES/WARNINGS/ADVISORIES
DC...NONE.
MD...SMALL CRAFT ADVISORY FROM 10 PM THIS EVENING TO 3 PM EST
THURSDAY FOR MDZ008.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 10 PM THIS EVENING TO 3 PM EST
THURSDAY FOR ANZ530>543.
SYNOPSIS...CPB
NEAR TERM...CPB
SHORT TERM...CPB
LONG TERM...KRR
AVIATION...CPB/KRR
MARINE...CPB/KRR
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