Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 210900
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
400 AM EST SUN DEC 21 2014

.SYNOPSIS...
HIGH PRESSURE WILL REMAIN WEDGES INTO THE MID-ATLANTIC THROUGH
EARLY IN THE WEEK. LOW PRESSURE WILL TRACK UP THE MID-ATLANTIC
COAST LATE MONDAY. A STRONG COLD FRONT WILL THEN PASS THROUGH THE
AREA WEDNESDAY NIGHT.

&&

.NEAR TERM /THROUGH TONIGHT/...
THE WINTER SOLSTICE IS AT 603PM EST TODAY...SUNDAY DECEMBER 21 2014.
THE SUN WILL BE AT THE LOWEST ANGLE OF THE YEAR WITH THE LEAST
AMOUNT OF DAYLIGHT. SUNSETS WILL START GETTING LATER AFTER TODAY.

A SHORTWAVE TROUGH WILL MOVE ACROSS THE NORTHERN MID-ATLANTIC WHILE
HIGH PRESSURE CONTINUES AT THE SURFACE THIS MORNING. MOISTURE IN THE
MID-LEVELS HAS MOVED NORTHWARD FROM THE SE US OVERNIGHT IN RESPONSE
TO THE JET STREAM ACROSS THE CAROLINAS. BKN-OVC CONDITIONS ARE
EXPECTED THIS MORNING AS THE CLOUD DECK STRETCHES BACK INTO
THE OHIO VALLEY. RIDGING ALOFT WILL LEAD TO LITTLE FORCING TODAY AND
ONCE MID-LEVEL MOISTURE MOVES EASTWARD BY AFTERNOON...THE SUN SHOULD
START TO SHOW ON THE FIRST DAY OF WINTER. HIGH PRESSURE AT THE SFC
WILL LEAD TO LIGHT NORTHERLY WINDS. FCST MAX TEMPS WILL REACH THE
30S IN THE MTNS AND LOW 40S ELSEWHERE. USED MET GUIDANCE SINCE IT
HAS BEEN DOING THE BEST THE LAST FEW DAYS.

HIGH PRESSURE WILL BEGIN TO WEDGE AGAINST THE APPALACHIAN REGION
TONIGHT AS AN UPPER LEVEL TROUGH BEGINS TO AMPLIFY ACROSS THE
CENTRAL US. THE JET STREAM ACROSS THE SE US WILL LEAD TO THE
DEVELOPMENT OF LOW PRESSURE OFF THE CAROLINA COAST. MOISTURE
ADVECTION INTO THE MID-ATLANTIC WILL LEAD TO PRECIPITATION MOVING
INTO THE REGION FROM THE SOUTH LATE TONIGHT. WENT WITH THE SREF MEAN
FOR PRECIP PROGRESSION. AT THIS TIME...MOISTURE SHOULD BE REACHING
THE GROUND ACROSS THE CENTRAL FOOTHILLS...SHENANDOAH
VALLEY...PIEDMONT EARLY MONDAY MORNING. HIGH PRESSURE WILL SERVE AS
A SOURCE OF COLD AIR AT THE SFC WITH TEMPS REACHING THE UPPER 20S TO
AROUND 30 BY MONDAY MORNING. 850-700MB THICKNESS VALUES AROUND 1550M
UP TO I-66 AND 1000-850MB THICKNESS VALUES AROUND 1310 WOULD RESULT
IN FZRA...SLEET MIXTURE EARLY MONDAY MORNING IF MOISTURE IS
AVAILABLE. TEMPS ALONG AND WEST OF THE BLUE RIDGE ARE EXPECTED TO BE
COLDER RESULTING IN A BETTER CHANCE FOR ICE ACCRETION.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY/...
STILL HAVE SOME UNCERTAINTY REGARDING THE DETAILS OF MONDAY/MONDAY
NIGHT. GENERAL IDEA IS THAT PRECIP WILL SPREAD NORTHWARD THROUGH THE
CWA DURING THE DAY MONDAY...ALTHOUGH THE EXACT NORTH/NORTHWEST
EXTENT REMAINS SOMEWHAT IN QUESTION. ALSO IN QUESTION WILL BE TIMING
THE CHANGES TO THE THERMAL PROFILE THROUGH THE DAY...WHICH WILL
DETERMINE P-TYPE.

PREFER GENERAL IDEA FROM THE SREFS FOR POPS...ALTHOUGH POPS NOT
QUITE AS HIGH FURTHER NORTH TOWARD THE MASON DIXON LINE. LEANED
TOWARD SREFS FOR TEMPERATURE/PROFILE CONSIDERATIONS TOO. THIS
SUGGESTS THAT INITIAL PRECIP MAY BE SLEET OR FREEZING
RAIN...TRENDING TO JUST RAIN THROUGHOUT THE DAY ALTHOUGH WINTRY
PRECIP COULD LINGER LONGER OVER THE POTOMAC HIGHLANDS. HIGHEST
CONFIDENCE FOR ICING RESIDES ACROSS THE LOWER POTOMAC
HIGHLANDS/SHENANDOAH VALLEY/CENTRAL VA FOOTHILLS.

RISK OF FREEZING RAIN COULD CONTINUE OVER THE POTOMAC HIGHLANDS
MONDAY NIGHT ASSUMING THERE IS PRECIPITATION FALLING...BUT THIS IS
UNCERTAIN AS MODELS SUGGEST THE MAIN BATCH OF QPF LIFTS NORTHEAST IN
TANDEM WITH WEAK LOW PRESSURE OFF THE COAST.

WEDGE REMAINS IN PLACE TUESDAY. NOT SURE THERE/S A LOT OF MEASURABLE
PRECIP GOING ON...IT MAY BE MORE DRIZZLE BUT CONTINUE CHANCE POPS
FOR RAIN ACROSS THE CWA WITH GFS SHOWING BROAD LIGHT QPF. AM
EXPECTING ANY PRECIPITATION TO BE IN LIQUID FORM DURING THE DAY
TUESDAY.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
FOCUS THEN SHIFTS TO DEEP UPPER TROUGH/STRONG COLD FRONT OVER THE
MIDWEST/OHIO VALLEY TUESDAY NIGHT. DECENT PLUME OF MOISTURE
OVERRUNNING A WARM FRONT WILL BRING RAIN INTO THE MID-ATLANTIC
TUESDAY NIGHT.

AS LOW LEVEL JET STRENGTHENS ON WEDNESDAY...THIS SHOULD HELP TO PUSH
THE WARM FRONT TO THE NORTH. PW/S MAY INCREASE NEAR 1.5
INCHES...LIKELY LEADING TO PERIODS OF MODERATE RAINFALL ON
WEDNESDAY. INSTABILITY IS FORECAST TO BE WEAK SO NO THUNDER
MENTIONED BUT POTENTIAL EXISTS FOR SOME GUSTY SHOWERS GIVEN WIND
FIELDS OFF THE DECK. DESPITE CLOUDS/RAIN...MAXIMA SHOULD WARM WELL
INTO THE 50S AND POSSIBLY ECLIPSE 60 IN SOME AREAS.

STRONG COLD FRONT MOVES THROUGH WEDNESDAY NIGHT. SHOWERS END FROM
WEST TO EAST...AND COLD ADVECTION/TIGHT PRESSURE GRADIENT WILL BRING
A BLUSTERY AND COOLER DAY THURSDAY /MEX GUIDANCE LIKELY TOO WARM/.
NEXT COLD FRONT APPROACHES FRIDAY NIGHT OR SATURDAY.

&&

.AVIATION /09Z SUNDAY THROUGH THURSDAY/...
VFR CONDITIONS EXPECTED TODAY AND TONIGHT. MID LEVEL MOISTURE WILL
CONTINUE TO MOVE EASTWARD ACROSS THE REGION RESULTING IN BKN-OVC VFR
CIGS. CLEARING IS EXPECTED BY THIS AFTERNOON WITH A SCT-BKN 5K FEET
DECK EXPECTED INTO THE EVENING. CLOUDS WILL BUILD IN FROM THE SOUTH
TONIGHT AS LOW PRESSURE DEVELOPS OFF THE EAST COAST. MVFR/IFR CIGS
SHOULD REACH CHO BY MONDAY MORNING. LIGHT NRLY WINDS EXPECTED DURING
THE TAF PERIOD.

PRECIP SPREADS NORTH ON MONDAY...POSSIBLY BEGINNING AS A WINTRY MIX
OF -IP/-ZR BEFORE TRANSITIONING TO -RA. MVFR CONDITIONS LIKELY ON
MONDAY WITH PRECIP...DEGRADING INTO IFR/LIFR MONDAY NIGHT INTO
TUESDAY. RESTRICTIONS CONTINUE INTO WEDNESDAY WITH SHOWERS AND
POSSIBLE LLWS. COLD FRONT MOVES THROUGH WEDNESDAY NIGHT...WITH GUSTY
SURFACE WINDS THURSDAY.

&&

.MARINE...
LIGHT NRLY WINDS EXPECTED ON THE WATERS TODAY AND TONIGHT. WINDS
WILL REMAIN LIGHT BUT BECOME EASTERLY LATE TONIGHT AND INTO MONDAY
MORNING. RAIN AND/OR SLEET SHOULD REACH THE SRN WATERS MONDAY
MORNING BEFORE CHANGING TO ALL RAIN THROUGH MONDAY.

SCA CONDITIONS ARE POSSIBLE IN SOUTHERLY FLOW AHEAD OF A COLD FRONT
ON WEDNESDAY...THEN BEHIND THE FRONT FOR WEDNESDAY NIGHT AND
THURSDAY.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...HAS/BPP
NEAR TERM...HAS
SHORT TERM...BPP
LONG TERM...BPP
AVIATION...HAS/BPP
MARINE...HAS/BPP






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