Area Forecast Discussion
Issued by NWS Sterling, VA

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KLWX 180109 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 909 PM EDT SUN AUG 17 2014 .SYNOPSIS...
-- Changed Discussion --
A WEAK COLD FRONT AHEAD OF HIGH PRESSURE TO OUR NORTH WILL STALL OUT OVER THE REGION TONIGHT THROUGH MONDAY. LOW PRESSURE WILL RIDE ALONG THE BOUNDARY...PASSING THROUGH OUR AREA MONDAY NIGHT INTO TUESDAY. THE BOUNDARY WILL REMAIN STALLED OVER THE REGION DURING THE MIDDLE AND LATTER PORTIONS OF THE WEEK.
-- End Changed Discussion --
&& .NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
THIN STREAMER OF ISOLATED SHOWERS THAT FIRST MOVED INTO GARRETT COUNTY IN W MD EARLIER TODAY HAS SLOWLY PUSHED SOUTH ALONG THE FRONT THAT HAS EDGED INTO THE AREA FROM PA. THAT STREAMER HAS SLOWLY EXTENDED EAST AND PUSHED SOUTH. AT 9PM IT EXTENDS FROM NEAR PETERSBURG AND MOOREFIELD WV TO SOUTHERN MD. ACTIVITY HAS BEEN DIMINISHING AFTER SUNSET AND SHOULD CONTINUE TO DO SO. HAVE SCT SHOWERS IN THE FORECAST FOR THIS EVENING IN THAT ZONE IN THE HIGHER DEWPT AIR...BUT BY 10PM EXPECT THE SHOWER THREAT TO DISSIPATE FOR A FEW HOURS. NEXT UP IS SOME ISOLATED SHOWERS THAT COULD MOVE INTO OUR SW COUNTIES IN W CENTRAL VA IN THE EARLY MORNING HOURS OF MONDAY THRU DAWN. WINDS WHICH WERE GUSTY TODAY CONTINUE TO DIMINISH.
-- End Changed Discussion --
&& .SHORT TERM /MONDAY/...
-- Changed Discussion --
7AM MONDAY MORNING IS EXPECTED TO START OUT DRY FOR ALL EXCEPT W CENTRAL VA AND ADJACENT WV...BUT AS THE SHORT WAVE AND CLOSED SFC LOW APPROACHING FROM THE OH VALLEY MOVE IN...SCT SHOWERS AND TSTMS SHOULD DEVELOP ACROSS ALL BUT NE MD WHERE THE DRIER AIR WILL BE LAST TO MOVE OUT. BEST CHANCE OF STORMS DURING THE DAY MONDAY WILL BE OVER VA AND WV...PARTICULARLY WEST CENTRAL VA AND ADJACENT WV. TEMPS WILL BE SIMILAR TO SUNDAYS HIGHS. DO NOT ANTICIPATE A SVR THREAT MONDAY AS THE SFC LOW WILL BACK WINDS TO THE SOUTHEAST WITH SFC CAPES LESS THAN 1000 J/KG2 DURING THE DAY.
-- End Changed Discussion --
&& .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... GUIDANCE REMAINS CONSISTENT SHOWING A SHORT WAVE CROSSING A SURFACE BOUNDARY WHICH WILL BE ZONALLY BISECTING THE EASTERN US TO BEGIN THE WORKWEEK. THIS WILL BRING A FAIRLY COMPACT YET POTENT LOW THROUGH THE MID-ATLANTIC MONDAY NIGHT AND INTO TUESDAY MORNING. A RIBBON OF MID-LEVEL SUBTROPICAL MOISTURE WILL BRING PWATS NEAR 2 INCHES...ALLOWING FOR PERIODS OF HEAVY SHOWERS WITH THE PASSAGE OF THE LOW. THE PRIMARY UNCERTAINTY WITH THIS SYSTEMS REMAINS THE LOCATION OF THE HIGHEST RAINFALL AMOUNTS. GUIDANCE APPEARS TO BE FOCUSING IN ON SOUTHERN VIRGINIA UP TO THE MIDDLE PIEDMONT AND LOWER SHENANDOAH VALLEY REGIONS...SO POPS AND QPF WERE ADJUSTED ACCORDINGLY WITH HIGHEST VALUES AND LONGEVITY ACROSS THE SOUTHERN PORTION OF THE CWA. RELATIVELY DRIER AIR WILL WORK IN ON THE BACK SIDE OF THE LOW AND GREATLY REDUCE THE COVERAGE OF THE PRECIP BY TUESDAY AFTERNOON. THIS MAY ALLOW FOR SOME BREAKS IN THE CLOUDS AND ANY SOLAR HEATING THAT DOES OCCUR TUESDAY AFTERNOON COULD...IN CONJUNCTION WITH THE NORTHWEST FLOW ALOFT ON THE UPSTREAM SIDE OF THE SHORTWAVE COULD LEAD TO SOME MODEST INSTABILITY (AROUND 1000 J OF CAPE OR LESS). WITH THE SURFACE BOUNDARY IN THE AREA AND THE POTENTIAL FOR DIFFERENTIAL HEATING BOUNDARIES TO FORM IN THE AFTERNOON TO PROVIDE THE FORCING FOR CONVECTION...HAVE SCATTERED THUNDERSTORMS IN THE FORECAST FOR TUESDAY EVENING...THOUGH COVERAGE WILL LIKELY BE RATHER LIMITED AND SEVERE THREAT WILL BE LOW. ANY THUNDERSTORM ACTIVITY SHOULD DIMINISH SHORTLY AFTER SUNSET WITH THE LOSS OF SURFACE HEATING. GIVEN THE INCREASED SOIL MOISTURE FOLLOWING MONDAY NIGHTS RAINFALL AND THE CALM LOW LEVEL WINDS...FOG MAY BE A CONCERN LATE TUESDAY NIGHT/WEDNESDAY MORNING. THE REMAINDER OF THE LONG TERM WILL CONTINUE THE ACTIVE PATTERN...THOUGH CONFIDENCE IN TIMING AND LOCATION OF FEATURES IS LOWER AT THIS RANGE. A SERIES OF SHORT WAVES TRAVERSING THE LARGE SCALE TROUGH ACROSS THE EASTERN US AND WESTERN ATLANTIC WILL BRING PERIODS OF RAINFALL WEDNESDAY...THURSDAY AND FRIDAY. CONVECTIVE POTENTIAL AND STORM COVERAGE WILL LARGELY BE INFLUENCED BY THE TIMING OF THE SHORTWAVE PASSAGES IN RELATION TO THE ENHANCED INSTABILITY FROM DAYTIME HEATING. GUIDANCE CURRENTLY SHOWS THE FIRST SHORTWAVE ARRIVING WEDNESDAY AFTERNOON AND EVENING WITH THE STRONGEST LIFT FOCUSED ALONG THE MASON DIXON LINE. THUS MODERATE TO HIGH END CHANCE POPS AND THUNDERSTORMS FOCUSED ACROSS MARYLAND AND WEST VIRGINIA NORTH OF THE METRO AREAS FOR WEDNESDAY AND WEDNESDAY NIGHT. BEYOND WEDNESDAY CONFIDENCE IS LOW IN THE TIMING OF THE ARRIVAL OF SHORTWAVES...SO MODERATE TO LOW END POPS AND THUNDERSTORMS ARE IN THE FORECAST THROUGH THE END OF THE WEEK...WITH SLIGHTLY HIGHER POPS DURING THE EVENINGS. HIGH PRESSURE WILL NOSE DOWN THE EASTERN SEABOARD BEGINNING SATURDAY. THIS...WITH THE ASSISTANCE OF LOW PRESSURE WELL OFF THE MID-ATLANTIC COAST...WILL BRING A COOLER...MORE STABLE LOW LEVEL AIR MASS INTO THE AREA. EXPECT HIGHS IN THE MID 80S FOR THE MIDDLE AND END OF THE WORKWEEK TO GIVE WAY TO HIGHS NEAR 80 FOR THE WEEKEND AND MOSTLY CLOUDY SKIES GRADUALLY TRANSITION TO PARTLY CLOUDY TO MOSTLY SUNNY SKIES THROUGH THE SAME PERIOD. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/...
-- Changed Discussion --
MVFR CONDITIONS FOR VSBYS LATE TONIGHT FOR MRB AND MAYBE IAD. CURRENTLY HAVE THEM MVFR FOR AN HOUR BETWEEN 11 AND 12Z. CHO HAS THE BEST CHANCE OF FOG TONIGHT AND WENT IFR WITH VSBY DOWN TO 2SM BY 7Z. MONDAY WILL HAVE CHC OF TSTMS IN THE AFTERNOON ALL TAF LOCATIONS BUT AT A LOW PROBABILITY NOT TO HAVE IN TAF ATTM...EXCEPT CHO. IFR CONDITIONS ARE EXPECTED AS A WAVE OF LOW PRESSURE WILL BRING LOW CEILINGS AND VSBY TO THE AREA THROUGH THE NIGHT MONDAY AND INTO TUESDAY MORNING. A COOL MOIST MARINE AIRMASS AND LIGHT WINDS MAY COMBINE TO ENCOURAGE FOG FORMATION EARLY WEDNESDAY MORNING FOR THE NORTHEASTERN PORTION OF THE CWA INCLUDING IAD DCA BWI AND MTN. PERIODS OF SHOWERS AND THUNDERSTORMS MAY ALSO EFFECT AVIATION WEDNESDAY AFTERNOON AND EVENING.
-- End Changed Discussion --
&& .MARINE... NO MARINE HEADLINES EXPECTED THROUGH THE SHORT TERM. CHC TSTMS MON AFTERNOON AND LOWERING VSBYS MON NIGHT. CONFIDENCE IS LOW IN THE OCCURRENCE OF ANY MARINE HAZARDS THROUGH THE LONG TERM. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...STRONG NEAR TERM...STRONG SHORT TERM...STRONG LONG TERM...CEB AVIATION...STRONG/CEB MARINE...LEE/CEB

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.