Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 262009
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
309 PM EST FRI DEC 26 2014

.SYNOPSIS...
HIGH PRESSURE OVER THE AREA TONIGHT WILL MOVE OFFSHORE SATURDAY. A
WEAK COLD FRONT WILL CROSS THE REGION SUNDAY. A LOW PRESSURE SYSTEM
WILL MOVE NORTHEAST ALONG THIS FRONTAL BOUNDARY ON MONDAY. COLDER
HIGH PRESSURE WILL FOLLOW FOR MID WEEK.
&&

.NEAR TERM /THROUGH SATURDAY/...
AMPLE SUN AND CALM CONDITIONS HAVE ALLOWED TEMPS TO CLIMB BACK INTO
THE 50S ACROSS MUCH OF THE AREA AFTER A NEAR SUB-FREEZING NIGHT.
LITTLE AIRMASS CHANGE BETWEEN NOW AND TONIGHT WILL HAVE US RIGHT
BACK IN THAT SAME RANGE OVERNIGHT BUT FOR THE AFTN PERIOD...WE
SHOULD PEAK IN THE M50S ACROSS MUCH OF THE MID-ATLC REGION. A
RELATIVELY WEAK BUT LARGE-SCALE REGIONAL HIGH PRESSURE AREA
CONTINUES TO ROLL ACROSS THE SOUTHEAST STATES...THE CENTER OF THE
HIGH CURRENTLY HANGING OVER THE I-95 CORRIDOR REGION OF THE
CAROLINAS - CLOSE TO THE COAST.

THE SOUTHEAST HIGH WILL CONTINUE TO PUT A LID ON THE SFC WINDS -
KEEPING THEM LIGHT/VARIABLE. MORE DECOUPLING AND CLEAR SKIES
OVERNIGHT WILL AGAIN TAKE TEMPS DOWN BACK TOWARD THE FREEZING MARK
AND TO SUB-FREEZING FOR SHELTERED VLYS/LOWLANDS. METRO DC/BALT AREAS
SHOULD STAY W/IN THE L-M30S RANGE - ABOUT WHERE THE CURRENT DEWPOINT
READINGS RESIDE.

THE SFC HIGH REMAIN PARKED OVER THE SRN ATLC STATES INTO EARLY
SAT...WHILE A DEEP UPPER TROUGH DIGS DOWN OVER THE ROCKIES AND INTO
THE CNTRL PLAINS. THE TROUGH WILL EVENTUALLY BREAK OFF INTO TWO
SEPARATE FEATURES THAT WILL AFFECT DIFFERENT PARTS OF THE EAST COAST
IN THE COMING DAYS. HIGHS TMRW WILL PEAK A FEW DEGREES HIGHER THAN
TODAY`S VALUES...AS A MORE CONCENTRATED/WARMER SLY WIND FLOW
DEVELOPS. SKIES WILL REMAIN GENERALLY CLEAR UNTIL LATER IN THE
AFTN/EVE WHEN THE CIRRUS/MID CLOUD DEBRIS FROM THE INCOMING LOW
PRESSURE WAVE ARRIVES FROM THE WEST.
&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
HIPRES RDG WL BE NUDGED OFFSHORE SAT NGT AS LOPRES TRACKS EWD ACRS
SRN CNDA. A WEAK CDFNT EXTENDS SWWD FM THIS LOW...WHICH PERHAPS WL
REACH THE PTMC HIGHLANDS BY DAWN. THE HGT FIELD ALOFT PACKED BUT
NOT-QUITE ZONAL. REGARDLESS...ALL SIGNS POINT TO A WEAK SYSTEM UP TO
THIS STAGE. WL HV ISENT UPGLIDE DURING THE OVNGT HRS...JUST AHD
OF THE FNT. HV CLDS INCRSG THRU THE NGT...AND LOWERING OVNGT.
CONFINED POPS TO WHERE THE LOWER CLDS RESIDE...MAINLY W OF BLURDG
AND ACRS NRN MD. ENUF WAA TO KEEP ALL TEMPS ABV FRZG. NO PTYPE
ISSUES. BLENDED MOS W/ PRVS FCST TO IRON OUT ANY DIFFS.

CDFNT WL SLIP THRU SLOWLY ON SUNDAY. MEANWHILE...WK LOPRES DVLPS
ALONG FNT INVOF GLFMEX CST AND HEADS NEWD. THAT SLUG OF MSTR SHUD
ARRIVE SUN NGT--A LTL QUICKER THAN PRVS FCST CYCLE. THEREFORE...POPS
RISE THRU THE DAY...AND HV THE WETTEST TIME FRAME LT SUN AFTN INTO
SUN EVNG. SINCE EVOLUTION A PINCH QUICKER...THAT PROVIDES THE
OPPORTUNITY FOR CAA PRIOR TO SUNRISE MON MRNG...ON THE BACK SIDE OF
THE LOW. DONT THINK THERE WL BE THAT MUCH RESIDUAL MSTR LEFT BY THAT
POINT /ONLY CHC POPS/...BUT ITS ENUF TO INTRODUCE WIDER CVRG OF
SHRA/SN...AND EVEN SOME SHSN IN THE APLCNS. LTL CONFIDENCE IN ACTUAL
SEEING MEASUREABLE SNW. LINGERING PCPN INTO MON AS LOW PULLS OUT AND
CDFNT INCHES SSEWD. IT/LL BE PARALLEL TO UPR FLOW...SO DONT SEE
RAPID IMPROVEMENT OCCURING.

NO BIG DISCREPANCIES IN MOS MAXT SUNDAY. HWVR...IF FROPA ANY SOONER
CUD NEED TO SHAVE OFF A CPL DEGF ACRS NRN MD AND THE PTMC HIGHLANDS.
A BIT MORE WIGGLE ROOM IN THE MIN-T SUN NGT. DID NOT GO AS COLD AS
SOME GDNC SUGGESTING. STRENGTH AND TIMING OF FNT WL BE DISCERNING
FACTORS. BASED ON MODEST CAA BHD SYSTEM...SHUD SEE A LTL DIURNAL
TEMP RISE...AND REFLECTED THAT IN MON MAXT. BUT IT WL CERTAINLY BE
TEMPERED BY NLY FLOW.
&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
THE COMBINATION OF AN UPSLOPE COMPONENT TO THE WIND AND SOME UPPER
LEVEL ENERGY FROM THE WEST WILL PROVIDE A CHANCE OF SOME LIGHT RAIN
OR SNOW IN THE POTOMAC HIGHLANDS AND PERHAPS THE HIGHEST TERRAIN OF
THE CENTRAL SHENANDOAH VALLEY MONDAY NIGHT. OTHERWISE...HIGH
PRESSURE WILL BUILD FROM THE WEST TO BRING A PROLONGED PERIOD OF DRY
CONDITIONS FROM TUESDAY THROUGH THURSDAY NIGHT. TEMPERATURES MAY
REMAIN ON THE COOL SIDE EACH PERIOD...AVERAGING 3 TO 5 DEGREES BELOW
NORMAL.

BOTH THE EUROPEAN AND GFS MODELS ARE HINTING OF SOME UPPER LEVEL
ENERGY ACCOMPANYING A DEVELOPING WARM FRONT THAT WILL MOVE FROM THE
TENNESSEE VALLEY TO THE MID ATLANTIC REGION. WITH SOME COLDER AIR IN
PLACE AHEAD OF THE WARM FRONT AND POSSIBLY TRAPPED IN SOME
VALLEYS...WE HAVE SLIGHT CHANCE TO CHANCE POPS OF EITHER SOME LIGHT
RAIN AND SNOW MIX OR PERHAPS ALL SNOW. OF COURSE...DIFFERENCES IN
THE TIMING AND MOVEMENT OF THE WARM FRONT LEADS TO LOW CONFIDENCE
FOR NOW. TEMPERATURES MAY TRY TO COME UP A FEW DEGREES FRIDAY AND
INTO FRIDAY NIGHT.
&&

.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
SOLID VFR CONDITIONS THRU THE CURRENT TAF PERIOD. SITES REPORTING
WINDS ARE GENERALLY OUT OF THE WEST...W/ A FEW SW AND S APPEARING.
HIGH PRESSURE TO OUR SOUTH WILL AGAIN CALM DOWN THE AREA OVERNIGHT...
ALONG W/ CLR SKIES. SAME STORY ON SAT W/ A BIT MORE DEFINED SLY
BREEZE BUT AOB 5KT.

OUTLOOK...
-SAT NGT...LWRG CIGS BUT SHUD STAY VFR.
-SUN-SUN NGT...MVFR-IFR IN LOW CLDS/RAIN. CFP DURING DAY. WINDS
SHUD STAY AOB 10 KT...BUT WL BE VEERING NLY.
-MON...CONTD CLDS..CHC SHRA INVOF FNT. PERHAPS A FEW SHSN NEAR MRB
TWD MRNG PUSH /LOW CONFIDENCE/. LKLY MVFR AT WORST.
-TUE...VFR.

&&

.MARINE...
LIGHT WINDS W/ VARIABLE DIRECTIONS OVER THE WATERS THIS AFTN. MOST
OBS AOB 10KT AND WILL DROP OFF FURTHER OVERNIGHT. HIGH PRESSURE
MOVING OFF THE CAROLINA COAST ON SAT WILL TURN THE WIND FIELD MORE
SLY AND POTENTIALLY INTRODUCE SOME MINOR SLY CHANNELING LATER IN THE
DAY BUT LOWER THAN SCA CRITERIA.

LGT WINDS THIS WKND AS PASSING CDFNT AND LOW PROVIDE STBL CONDS ON
THE WATER. NLY WINDS CUD PICK UP ON BACK SIDE OF SYSTEM MON. KEEPING
IT UNEVENTFUL FOR NOW.

&&

.EQUIPMENT...
KLWX 88D WILL REMAIN OUT OF SERVICE UNTIL SATURDAY...WHEN THE PARTS
TO REPAIR THE RADAR ARE EXPECTED TO ARRIVE.
&&

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

&&

$$
SYNOPSIS...HTS
NEAR TERM...GMS
SHORT TERM...HTS
LONG TERM...KLW
AVIATION...GMS/HTS
MARINE...GMS/HTS
EQUIPMENT...SMZ






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