Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 160841 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 341 AM EST TUE DEC 16 2014 .SYNOPSIS...
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A WARM FRONT LIFTS NORTH THROUGH THE AREA THIS MORNING...FOLLOWED BY A COLD FRONTAL PASSAGE LATER TODAY. HIGH PRESSURE BUILDS IN THE WAKE OF THE FRONT THROUGH THE END OF THE WEEK. LOW PRESSURE WILL APPROACH FROM THE SOUTHWEST SATURDAY.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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OCCLUDED LOW PROGRESSING THROUGH THE MIDWEST EARLY THIS MORNING WITH THE ASSOCIATED WARM FRONT CURRENTLY EXTENDING SOUTH THROUGH CENTRAL KY...AND THE COLD FRONT DRAPED FURTHER TO THE SOUTH AND WEST. WATER VAPOR IMAGERY INDICATING CLOSED UPPER LVL LOW PIVOTING EASTWARD ACROSS THE MIDWEST. FIRST LINE OF PCPN MOVING INTO WESTERN PA/WV ASSOCIATED WITH SHORTWAVE ENERGY AHEAD OF THE LOW. THESE LIGHT RAIN SHOWERS ARE EXPECTED TO MOVE INTO OUR WESTERN CWA BY AROUND 12Z. DESPITE WINDS OVERALL BEING ON THE LIGHTER SIDE...ENOUGH OF AN SOUTHEASTERLY COMPONENT HAS ALLOWED FOR GOOD MOISTURE ADVECTION THROUGH THE NIGHT...RESULTING IN PATCHY FOG. HIGH CONFIDENCE IN RAIN SHOWERS TODAY AS THE WARM FRONT LIFTS THROUGH THIS MORNING...FOLLOWED THIS EVENING WITH THE ASSOCIATED COLD FRONT. 00Z MODEL CONSENSUS GENERALLY AGREEING ON LIGHT PCPN OVER FAR WESTERN AREAS FIRST PART OF THIS MORNING...SPREADING INTO CENTRAL VA BY MIDDAY...THEN IMPACTING EASTERN AREAS THIS AFTN/EVENING AS THE MAIN ENERGY ALOFT PIVOTS AROUND THE DOMINANT LOW OVER THE NORTHERN PLAINS. WESTERLY FLOW BEHIND THE FRONT WILL BE QUICK TO DRY THE AREA...BUT SLOW TO DROP THE TEMPS. AS SUCH...ONLY EXPECTING RAIN SHOWERS THROUGH 00Z THIS EVENING. WILL NOTE THAT SPC CONTINUING TO HAVE US IN A GENERAL TSTM MENTION WITH THE FRONTAL PASSAGE. WHILE THERE DOES LOOK TO BE WEAK ELEVATED INSTABILITY WITH STEEPENING MID LVL LAPSE RATES OVER SOUTHERN PORTIONS OF THE AREA...FEELING ANY DEVELOPMENT WOULD BE VERY...VERY ISOLATED IN NATURE AND HAVE TOO LITTLE CONFIDENCE AT TIME OF COVERAGE/OCCURRING TO INCLUDE IN FORECAST.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY NIGHT/...
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COLD FRONT QUICKLY EXITS TO THE EAST TONIGHT...TAKING ASSOCIATED PCPN TO THE EAST WITH IT. HAVE CHC POPS OVER AREAS SURROUNDING CHESAPEAKE BAY FOR THE EVENING...THEN DRYING OUT FOR THE REMAINDER OF THE NIGHT. TO THE WEST...MAINTAINING CHC POPS FOR THE ALLEGHENY FRONT AS A SFC TROUGH SWINGS THROUGH ON THE BACKSIDE OF THE LOW PRESSURE SYSTEM. THIS COULD GENERATE LIGHT RAIN SHOWERS. QPF TOTALS ARE ON THE LIGHTER SIDE...SO VERY WELL COULD END UP WITH AREAS DRY TONIGHT WITH THE PCPN MORE SCT IN NATURE. THE PCPN HERE DOES LOOK TO REMAIN IN LIQUID FORM AS THE CAA IS SLOW TO MOVE IN WITH A ZONAL FLOW TAKING HOLD ALOFT. THE ZONAL FLOW PERSISTS THROUGH WED...FINALLY WEAKENING ENOUGH WED NIGHT TO ALLOW THE CLOSED LOW POSITIONED JUST TO THE NORTH TO PUSH SOUTHWARD...FINALLY ADVECTING IN THE COLDER TEMPS. FOR WEDNESDAY...BROAD HIGH PRESSURE BUILDS IN AND WITH SUBSIDENCE INCREASING ALOFT...SHOULD SEE DRY WX AND CLEARING SKIES. PCPN CHC JUST REMAINS WED WEST OF THE ALLEGHENY FRONT. TAPERED POPS OFF IN THIS AREA FOR THE SECOND HALF OF WED NIGHT TO ACCOUNT FOR LOSS OF MOISTURE DESPITE THE CONTINUING UPSLOPE FLOW. DID INCLUDE A MENTION FOR PATCHY DRIZZLE/FREEZING DRIZZLE FOR THE ALLEGHENY FRONT RESULTING FROM ANY LINGERING PCPN STUCK IN THE LOWER LVLS UNDER THE INVERSION. FOR TEMPS THROUGH THIS PERIOD...LOWS TONIGHT AND HIGHS TOMORROW STILL ABV NORMAL. WITH THE CAA WED NIGHT...FINALLY TEMPS DROP TO AROUND NORMAL.
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&& .LONG TERM /THURSDAY THROUGH MONDAY/...
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HIPRES RDG XTNDG SEWD ACRS AREA WL BE KEY SYNOP FEATURE FOR THU-FRI. MEANWHILE...FLOW ALOFT WL BE ZONAL AND QUITE FAST...SO DO NOT XPCT TTLLY SUNNY SKIES. CLDS WL BE MORE NMRS IN THE MTNS...AS A DOWNSLOPE COMPONENT TO SFC FLOW WL PROVIDE SOME SUBSIDENCE. WIND FIELD BETTER THU. TEMPS WL BE SEASONABLE. WHILE ECMWF AND GFS STILL MILES APART WRT DVLPG STORM SAT...AM STARTING TO SEE A FEW SIGNS OF A CNVGNC OF FCST SOLN. LTST ECMWF A BIT MORE SURPRESSED...WHICH WUD BE LOGICAL FOR THE TIGHT FLAT HGT PTTN ALOFT. MEANWHILE...GFS FINALLY RECOGNIZING THAT THERE IS A DVLPG SRN STREAM WAVE. IMPLICATIONS LOCALLY INCL A DELAY OF THE PCPN START TIME TIL SAT AND A LWRG OF POPS ON SAT AS CORRIDOR OF LKLY PCPN WUD BE SHUNTED S. WHILE EXTENT OF COLD AIR MARGINAL...LTST TRACK WUD ALLOW FOR SOME POTL SNOW /OR SOMETHING OTHER THAN RAIN/... SPCLY SAT NGT. THIS CYCLE HAS A LOT MORE POTL OF JUST LGT RAIN IN LWR ELEVS THO...SPCLY DC SWD. STILL HV A CLSD LOW EMERGING OFF HAT...BUT NOW NOT TIL SUN...SO NEEDED TO ADD POPS INTO THAT DAYTIME PD. WINDS AND UPSLP SHSN FOLLOW. ECMWF STILL MUCH STRONGER IN CSTL DVPMNT...WHICH WUD LEAD TO A MUCH WINDIER SUN IF CORRECT. MID-RANGE POPS COMMON THRU THE WKND...AND WL BE TIL A WINNING SOLN CAN BE DETERMINED. HIPRES/CAA BLDS IN THE WAKE OF THIS SYSTEM...FOR A CHILLY BUT DRY MON.
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&& .AVIATION /09Z TUESDAY THROUGH SATURDAY/...
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GENERALLY VFR CONDITIONS THRU THIS MORNING...WITH MVFR CIGS/VIS EXPECTED AS THE RAIN SHOWERS MOVE IN MID MORNING AND THROUGH THE AFTN. ONLY EXCEPTION IS KBWI THIS MORNING WHERE STRATUS/FOG COMBO HAS KNOCKED CIGS AND VIS DOWN TO SUB-IFR. THESE CONDITIONS SHOULD IMPROVE BY 11Z TO VFR...THEN COME DOWN AGAIN LATE MORNING WITH THE PCPN. START TIME TO PCPN AT ALL SITES +/- 1 HOUR. HIGH CONFIDENCE ONLY RAIN...NO FROZEN PCPN EXPECTED. SUB-VFR CONDITIONS PERSIST UNTIL THIS EVENING AND POSSIBLY THRU THE FIRST HALF OF THE NIGHT...THEN IMPROVE THE LATTER HALF BEHIND THE COLD FRONT. MAINLY VFR CONDITIONS THEN EXPECTED THROUGH THE END OF THE WEEK. S WINDS TODAY GENERALLY LESS THAN 10 KTS. WIND SHIFT OCCURS LATE AFTN/EVENING TO A W FLOW. GUSTS MIX IN AFTR 12Z WED...WITH GUSTS UP TO 20 KTS PSBL DURING THE DAY WED. LIGHT WNW FLOW CONTINUES THROUGH FRIDAY. SAT...FLGT RESTRICTIONS /MVFR-IFR/ XPCTD AS LOPRES PASSES S OF TERMINALS. HOW FAR S...HOW STRONG THE STORM WL BE...AND THE EXTENT OF COLD AIR ALL STILL TBD.
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&& .MARINE...
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S FLOW TODAY WITH WINDS MAINLY 10 KTS OR LESS AND GUSTS 15 KTS OR LESS AS LOW LVL INVERSION KEEPS STRONGER WINDS ALOFT FROM MIXING TO THE SFC. WIND SHIFT OCCURS TONIGHT WITH INCREASING W FLOW BEHIND THE COLD FRONT. HAVE ISSUED A SCA FOR THE CHESAPEAKE BAY FOR LATE WED MORNING LASTING UNTIL WED EVENING TO ACCOUNT FOR GUSTS UP TO 20 KTS. THE SCA MAY NEED TO BE EXTENDED THROUGH WED NIGHT...BUT CONFIDENCE TOO LOW TO INCLUDE THE ADDITIONAL PERIODS AT THIS TIME. HIPRES SETTLES OVER THE WATERS THU-FRI. THERE WL STILL BE A GRADIENT THO. SCA LKLY W/ DIURNAL MIXING IN NW FLOW THU. WNDS WL BE LIGHTER FRI. STILL QUESTIONS SAT AS LOPRES PASSES S OF WATERS. STRENGTH/TRACK ISSUES REMAIN...WHICH ULTIMATELY WL AFFECT WIND FIELD.
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&& .TIDES/COASTAL FLOODING...
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CURRENT WATER LEVELS RUNNING OVER A FOOT ABV ASTRO NORMS. THIS WAS SUFFICIENT TO CAUSE ANNAPOLIS TO REACH CAUTION STAGE. OTHER SITES WERE ELEVATED AS WELL BUT UNDER ANY CRITICAL THRESHOLDS. DEPARTURES WILL BE SUSTAINED TODAY DUE TO SOUTH WINDS...BUT DO NOT BELIEVE THAT THEY WILL BE INCREASING MUCH FURTHER. AS A RESULT...THE HEIGHT OF THE DAYTIME TIDE CYCLE WL BE WITHIN A FEW INCHES OF THE OVERNIGHT HIGH TIDE. ANNAPOLIS MAY BE ON THE DOORSTEP OF AN ADVISORY...BUT DO NOT HAVE THE CONFIDENCE IN A THRESHOLD EVENT. AFTER THAN WINDS TURN WEST. DO NOT EXPECT A DRAMATIC DROP. RATHER...THERE SHOULD BE A SLIGHT EASING TO ANOMALIES.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 11 AM TO 6 PM EST WEDNESDAY FOR ANZ530>534-538>543.
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&& $$ SYNOPSIS...SEARS/HTS NEAR TERM...SEARS SHORT TERM...SEARS LONG TERM...HTS AVIATION...SEARS/HTS MARINE...SEARS/HTS TIDES/COASTAL FLOODING...HTS

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