Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 281525 AAA
AFDLWX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1025 AM EST SUN DEC 28 2014

.SYNOPSIS...
A COLD FRONT OVER OHIO WILL MOVE INTO THE AREA TODAY. LOW
PRESSURE WILL MOVE ALONG THE STALLED FRONT THIS AFTERNOON AND
EVENING... PUSHING THE FRONT SOUTH OF THE AREA. ANOTHER LOW
PRESSURE SYSTEM WILL MOVE ACROSS THE CAROLINAS MONDAY AND MONDAY
NIGHT. STRONG HIGH PRESSURE WILL BUILD OVER MUCH OF THE COUNTRY BY
TUESDAY...AND GRADUALLY PUSH EASTWARD DURING THE REST OF THE WORK
WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A COLD FRONT BEING DRAGGED ALONG BY AN EXITING LOW PRESSURE SYSTEM
NORTH OF NEW ENGLAND HAS YET TO ENTER THE NWRN CWA. STILL SLIDING
FROM CNTRL PA TO THE WINDWARD SIDE OF THE APLCNS...THE SFC
BOUNDARY - EVEN APPEARING ON REGIONAL RADAR SCANS - INCHING ITS
WAY ESE. PLENTY OF MID-LEVEL MOISTURE HAS BEEN STREAMING ACROSS
THE MID-ATLC FROM THE UPPER MIDWEST - BUT THE WLY COMPONENT TO THE
FLOW HAS ALLOWED THE APLCNS TO DO THEIR TYPICAL MOISTURE
ROBBING...PREVENTING MUCH MORE THAN DENSE MID CLOUDS TO MOVE EAST.

A MINOR KINK IN THE UPPER FLOW WILL ARRIVE FROM THE LOWER TENN
VLY IN THE COMING HRS...DEVELOPING A LOCALLY MORE ENHANCED AREA OF
PRECIP FROM THE BLUE RIDGE EWD. HI-RES DERIVATIVES LIKE THE HRRR
AND VARIOUS WRF RUNS SHOW THIS WELL...BUT STILL ONLY A LIGHT AND
SCATTERED NATURE TO THE INCOMING RAIN SHOWERS. TOTAL QPF VALUES
FROM THIS ACTIVITY THRU THE END OF THE DAY ONLY IN THE TRACE-FEW
HUNDREDTHS OF AN INCH...LOCALLY NEAR 0.1-0.2" ON THE HIGH- END.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
PERIODIC LIGHT RAIN WILL DRIFT SOUTH WITH THE FRONTAL BOUNDARY INTO
MONDAY. PERHAPS AN ADDITIONAL TENTH INCH RAIN...PARTICULARLY SOUTH
OF DC. NORTHWEST WINDS INCREASE TO AROUND 10 MPH TONIGHT WITH COLD
AIR ADVECTION RESULTING IN MIN TEMPS OF LOW 30S FOR NRN AND WESTERN
FRINGES...MID TO UPR 30S ELSEWHERE. RAIN ENDS AS SNOW FOR THESE
FRINGE AREAS NEAR THE MASON-DIXON LINE AND FOR RIDGES. NO SNOW
AMOUNTS WERE ADDED AS OF YET WITH LOW POPS...BUT THERE IS THE
POSSIBILITY OF A DUSTING...PARTICULARLY AT HIGH ELEVATIONS.

21Z SREF WAS EAGER TO HAVE HIGH POPS IN FOR MOST OF THE CWA THROUGH
MONDAY. HOWEVER...WENT WITH CONSENSUS OF NAM/GFS/ECMWF WITH HAVING
LIKELY POPS FOR RAIN LIMITED TO SRN MD MONDAY MORNING. LOW LEVEL
FLOW IS MORE NELY MONDAY AFTERNOON...WHICH WOULD PROMOTE CHANCE POPS
FOR RAIN/SNOW MIX OVER TERRAIN THE SWRN PART OF THE CWA. NO WINTRY
ACCUMULATION THERE EITHER WITH JUST CHANCE POPS.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
BASICALLY THE EXTENDED BOILS DOWN TO TWO PRECIP SYSTEMS AT THE
START AND END OF THE LONG TERM WITH COLD HIGH PRESSURE SANDWICHED
IN BETWEEN.

MON AND MON NIGHT...STILL SOME UNCERTAINTY BASED ON MODEL SPREAD
OF PRECIPITATION FOR MON. 00Z/NAM AND GFS SOLNS SHOW MOST OF THE
PRECIP SLIPPING SOUTH AND EAST OF THE CWA EARLY MONDAY AM. BUT
00Z/ECMWF LINGERS SOME MOISTURE ACROSS SRN TIER OF ZNS. KEPT
SLIGHT TO CHANCE POPS IN FOR MON OVER THE CWA...AND WITH TEMPS
COLD ALOFT BUT BOUNDARY TEMPS ABOVE FREEZING...MENTIONED
RAIN/SNOW MIX POSSIBLE. BY MON NIGHT...LINGERING MOISTURE ACROSS
SOUTHERN TIER OF ZONES WARRANT CHANCE POPS...WITH LIKELY POPS IN
FAR SW PORTION OF CWA ACROSS HIGHLAND COUNTY AND SRN PENDLETON
COUNTIES...AND COLD ENOUGH THERE FOR ACCUMULATING SNOW AROUND AN
INCH IN UPSLOPE AREAS.

TUE...COLD AIR LOFT IS A CERTAINTY AS THE LARGE POLAR AIR MASS
SETTLES OVER MUCH OF THE CONUS EAST OF THE ROCKIES. THE 00Z/NAM
AND 03Z/SREF ARE AGAIN SHOW BEING AGGRESSIVE WITH A WEAK
DISTURBANCE THAT THE 00Z/GFS/ECMWF/UKMO SOLNS SHOW A MUCH WEAKER
AND FLATTER SYSTEM THAT STAYS SOUTH. AT THIS POINT ANY PRECIP
AMOUNTS TUE WILL BE LIGHT BUT COULD BE IN FORM OF SNOW.

WED-FRI...HIGH PRESSURE DOMINATES WITH SEASONABLY COLD WEATHER AND
DRY CONDITIONS.

LATE FRI-SAT...NEXT SYSTEM WILL APPROACH FROM THE SOUTHWEST AS
MODELS SHOW A LARGE LOW PRESSURE SYSTEM MOVING FROM THE CENTRAL
PLAINS LATE FRI MOVING INTO THE UPPER GREAT LAKES ON SAT. THIS
SYSTEM LOOKS LIKE IT COULD BRING A WINTRY MIX INITIALLY FRIDAY
NIGHT WITH THE EXPECTED TRACK OF THE LOW NORTHWEST OF THE CWA...
LOTS OF WARM AIR WILL BE ADVECTED INTO THE AREA...CHANGING PRECIP
TO LIQUID BY SAT MORNING. OF COURSE...TIMING AND POSITION AND
TRACK OF THE LOW IS LOW CONFIDENCE AT THIS POINT.

&&

.AVIATION /14Z SUNDAY THROUGH THURSDAY/...
VFR CONDS THROUGH INTO THE EARLY AFTN...AS RAIN ASSOCIATED WITH A
COLD FRONT APPROACHES FROM THE OHIO VALLEY TODAY. MVFR CONDS THIS
AFTERNOON IN MAINLY LIGHT RAIN. FRONT STALLS/DRIFTS SOUTH
TONIGHT...SO CONDS CONTINUE TO LOWER WITH IFR POSSIBLE...BUT KEPT
06Z TAFS WITH MVFR CIGS. LIGHT WLY FLOW TODAY...NWLY FLOW UP TO 10
KT TONIGHT...NLY FLOW 10 KT MONDAY.

MVFR TO IFR CIGS/VSBYS MON AND MON EVENING. VFR CONDITIONS TUE
THROUGH THU...WITH POSSIBLE MVFR CIGS IN SNSH- ACTIVITY TUE.

&&

.MARINE...
LIGHT SWLY FLOW VEERS NWLY TODAY AS A COLD FRONT CROSSES THE WATERS
THIS AFTERNOON AND EVENING. COULD BE A NLY SURGE WITH GUSTS AROUND
18 KT LATE TONIGHT. DID NOT RAISE AN SCA DUE TO UNCERTAINTY...BUT
ONE OUT OF SANDY POINT IS POSSIBLE INTO MONDAY.

MON-WED...EXPECT WINDS TO REMAIN BELOW SCA LEVELS. PRECIP ON MON
PUSHES SOUTH AND EAST LATE MON. HIGH PRESSURE BUILDS IN TUE AND
CONTINUES THROUGH END OF THE WEEK.

&&

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

&&

$$
UPDATE...GMS
PREV DISCUSSION...BAJ/SMZ






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