Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 262124 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 424 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/... SFC ANLYS SHOWS HIGH PRES OVR THE SERN U.S. WHICH HAS BEEN RESPONSIBLE FOR QUITE A GORGEOUS BOXING DAY AS HIGH TEMPS CLIMBED TO 5+ DEGS ABV NRML. TNGT DECOUPLING AND CLEAR SKIES WILL TAKE TEMPS DOWN TOWARDS 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 /21Z FRIDAY THROUGH WEDNESDAY/... VFR CONDITIONS THRU THE CURRENT TAF PERIOD. SAME STORY SAT. 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 SRLY WINDS OVER THE WATERS WILL DROP OFF FURTHER OVERNIGHT. HIGH PRESSURE MOVING OFF THE CAROLINA COAST 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. && $$ UPDATE...WOODY! PRVS...GMS/HTS/KLW

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