Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 151415 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1015 AM EDT WED APR 15 2015 .SYNOPSIS... HIGH PRESSURE WILL BUILD ACROSS THE AREA TODAY...AND WILL BE NUDGED EAST THURSDAY AS AN UPPER LEVEL DISTURBANCE GLIDES TOWARD THE MID ATLANTIC. A WEAK COLD FRONT WILL CROSS THE REGION FRIDAY...FOLLOWED BY A SECOND COLD FRONT LATE SATURDAY INTO SUNDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... SURFACE HIGH PRESSURE WILLC ONTINUE TO BUILD TOWARD THE REGION FROM THE NORTH...BUT HIGH AND MID-LEVEL CLOUDS WILL CONTINUE TO SPREAD THROUGH THE AREA IN THE SOUTHWEST FLOW ALOFT WELL AHEAD OF AN UPPER-LEVEL TROUGH OVER THE CENTRAL CONUS. RAIN SHOULD STAY TO OUR SOUTH AND WEST WHERE OVERRUNNING WILL BE DEEPER FARTHER AWAY FROM THE CENTER OF THE HIGH. A PERIOD OF LIGHT RAIN CANNOT BE COMPLETELY RULED OUT ACROSS THE EXTREME SOUTHWESTERN PORTION OF THE CWA...BUT EVEN ACROSS THESE AREAS MOST OF THE TIME WILL BE DRY. LEFT THE PREVIOUS FORECAST FOR MAX TEMPS WHICH IS A BLEND OF ALL THE GUIDANCE. WOULD NORMALLY GO WITH THE WARMER GUIDANCE IN THIS SITUATION DUE TO A WELL MIXED BOUNDARY LAYER...BUT WITH A BKN TO OVC DECK OF MID-LEVEL CLOUDS TEMPS MAY BE A FEW DEGREES COOLER. THEREFORE...THE FORECAST FOR TEMPERATURES WAS NOT TWEAKED. MAX TEMPS ARE FORECAST TO RANGE FROM THE 50S IN THE MOUNTAINS TO THE MID AND UPPER 60S ACROSS MOST OTHER LOCATIONS. && .SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY NIGHT/... RDGG SHUD HV A FIRMER CONTROL OF WX TNGT...SO HV CLRD OUT SKIES JUST ABT AREAWIDE. THIS MAY BE WORDED AS PTCLDY FOR CENTRAL VA DUE TO THE CLOUDIER START AND POTL FOR A FEW LINGERING CLDS OVNGT. IN SPITE OF HIPRES...STILL BELIEVE WE WL HV A SLGT NELY DRAINING TAKING PLACE AND CONSEQUENTLY WL HV LGT FLOW IN WIND GRIDS. MIN-T WL BE ON THE COOL SIDE...LWR-MID 40S COMMON. WHILE THE SFC RIDGE AXIS WL HOLD INTO THU...RETURN FLOW WL COMMENCE. EXACTLY TO WHAT EXTENT STILL VERY MUCH IN DOUBT. A KEY DETERMINING FACTOR WL BE THE PRESENCE/STRENGTH/LOCATION OF DVLPG CSTL LOPRES. NAM DECIDEDLY FURTHER NW THAN THE REST /INLAND OVER ERN NC/ AND WAS NEGLECTED. HWVR...GEFS MEMBERS ALL OVER THE PLACE W OF THE APLCNS. WOULD THINK THAT WUD HV A DOWNSTREAM IMPACT AS WELL. RESULTANT FCST HAS SOMEWHAT LOW CONFIDENCE IN DETAILS. HWVR FROM A BIG PICTURE PERSPECTIVE...THERE IS AGREEMENT THAT MID LVL S/WVS WL HEAD TWD US...AND ELY/SELY SFC SLOW TRANSPORTING MARINE MSTR AND SLY/SWLY MID LVL FLOW ARE A RECIPE FOR POTL PCPN. USED A BLENDED APPROACH W/ HVY REPRESENTATION FROM SREF. CHOSE WX TYPE RA DUE TO THE OVERRUNNING NATURE OF SETUP. THU WL BE THE PD WHEN POPS RAMP UP THRU CHC TO LKLY IN THE MTNS...AND WL BE SPREADING EWD THU EVNG. USED A SILMR APPROACH TO TEMP FCST MAXT THU...AND WENT A BIT ON THE WARM SIDE OF THE BLEND FOR MIN-T THU NGT DUE TO SUSPECTED DEWPT ADVCTN. && .LONG TERM /FRIDAY THROUGH TUESDAY/... HIGH PRESSURE WILL BE OFF THE EAST COAST FRIDAY. A DISTURBANCE IS EXPECTED TO CROSS THE MID-ATLANTIC INTO FRIDAY AND RAIN SHOULD MOVE FROM WEST TO EAST FRIDAY MORNING WITH THE GREATEST CHANCE ACROSS THE NRN CWA. RAINFALL AMTS SHOULD BE LESS THAN A QUARTER INCH. WESTERLY FLOW BEHIND THE TROUGH AXIS SHOULD ADVECT DRIER AIR BY FRIDAY EVENING. A WEAK COLD FRONT MAY CAUSE LIGHT RAIN TO LINGER INTO FRIDAY NIGHT. A SECOND AREA OF HIGH PRESSURE WILL MOVE INTO THE REGION FRI NIGHT- SATURDAY. MODEL SPREAD EXISTS THIS WEEKEND AS A LARGE UPPER LEVEL LOW SPINS ACROSS THE CENTRAL PLAINS. RIDGING ACROSS THE MID-ATLANTIC SHOULD KEEP RAIN TO THE SOUTH AND WEST SATURDAY. MEANWHILE...LOW PRESSURE WILL BE INTENSIFYING ACROSS THE TN VALLEY TRACKING NORTHWARD. GFS/ECMWF ARE SHOWING ANOTHER WEDGE TO FORM SUNDAY. AT THIS TIME...CONFIDENCE IS LOW FOR THE ONSET OF RAIN AS MODEL SPREAD EXISTS. HOWEVER...RAIN IS EXPECTED TO MOVE INTO THE VA HIGHLANDS AND OHIO VALLEY BEFORE MOVING NORTHWARD ACROSS THE MID-ATLANTIC BY MONDAY MORNING. MODERATE TO HEAVY RAINFALL IS POSSIBLE INTO MONDAY MORNING. LOW PRESSURE WILL BECOME MORE ORGANIZED MONDAY. RAIN IS POSSIBLE THROUGH MONDAY. DRIER AIR WILL FILTER IN BEHIND THE SFC LOW TUESDAY. TEMPS SHOULD BE HIGHER THAN NORMAL FRIDAY AND SATURDAY THEN DIP TO NEAR NORMAL TOWARDS THE END OF THE LONG TERM. && .AVIATION /14Z WEDNESDAY THROUGH SUNDAY/... VFR CONDITIONS TODAY. NORTHERLY WINDS WILL GUST AROUND 15 KNOTS THIS AFTERNOON AND A BKN TO OVC DECK OF HIGH AND MID-LEVEL CLOUDS ARE EXPECTED. SKIES WL CLR OUT TNGT. AGN...THAT MAY SPELL PTCLDY FOR CHO. RETURN MOST WL OVERSPREAD TERMINALS THU-THU EVNG. CHO-MRB WL BE AFFECTED DURING THE AFTN...THE THE DC-BALT METROS WL SEE IT IN THE EVNG. MVFR PSBL ONCE PCPN ARRIVES...AND IT/LL BE LKLY THU EVNG/OVNGT. LOW CIGS/VSBYS RESULTING IN POSSIBLE FLIGHT RESTRICTIONS FRIDAY. && .MARINE... NORTHERLY WINDS ARE EXPECTED TODAY. A DEEPER MIXING LAYER WILL CAUSE WIND GUSTS AROUND 15 KNOTS. A FEW GUSTS MAY APPROACH SCA CRITERIA SINCE WINDS AT THE TOP OF THE MIXING LAYER WILL BE AROUND 20 KNOTS. HOWEVER...THE GRADIENT REMAINS WEAK AND THE WATERS ARE RELATIVELY COOLER...SO MOST AREAS SHOULD REMAIN BELOW SCA CRITERIA. ELY FLOW INCREASES THU...FEEDING PCPN WHICH WL BE SPREADING EAST. WHILE THERE IS CONSIDERABLE UNCERTAINTY IN SPECIFICS...GDNC DOES AGREE THAT MEAN MIXED LYR WINDS WL BE NEAR IF NOT EXCEEDING SCA THRESHOLDS. HV OPTED TO RAISE SCA STARTING AT 11AM THU...AND CONTG TO THE END OF THE THU PD. ONCE PCPN ARRIVES...WHICH WL BE LATE DAY OR ELY EVNG...FVRBL DOWNWARD TRANSPORT SHUD COME TO A RAPID END. LOW PRESSURE WILL MOVE SOUTH OF THE WATERS FRIDAY. HIGH PRESSURE MOVES IN SATURDAY. && .EQUIPMENT... NWR CHARLOTTESVILLE OPERATING IN DEGRADED MODE DUE TO TELCO ISSUES. TECHS ARE AWARE OF THE SITUATION. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 11 AM TO 6 PM EDT THURSDAY FOR ANZ530>543. && $$ SYNOPSIS...HTS NEAR TERM...BJL/HTS SHORT TERM...HTS LONG TERM...HAS AVIATION...BJL/HAS/HTS MARINE...BJL/HAS/HTS EQUIPMENT...BJL

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