Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 012357 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 757 PM EDT MON SEP 1 2014 .SYNOPSIS... A BERMUDA HIGH WILL PERSIST THROUGH TUESDAY. A COLD FRONT WILL CROSS THE AREA TUESDAY NIGHT...FOLLOWED BY HIGH PRESSURE THROUGH THE REST OF THE WEEK. && .NEAR TERM /THROUGH TUESDAY/... SURFACE HIGH PRESSURE PERSISTS OFFSHORE. WATER VAPOR IMAGERY INDICATES A DISTURBANCE MOVING ACROSS WV...AND SOME ASSOCIATED SHOWER ACTIVITY APPROACHING EASTERN WV. THIS ACTIVITY HAS WEAKENED SOMEWHAT IN THE EARLY EVENING. LOSS OF SUNLIGHT WILL FOSTER A GRADUAL DECREASE IN INSTABILITY THIS EVENING...BUT WITH MOIST AIR IN PLACE...DEW POINTS IN THE UPPER 60S TO LOW 70S...FORECAST SOUNDINGS INDICATE IT WILL TAKE SEVERAL HOURS FOR SURFACE BASED CAPE TO DROP BELOW 1000 J/KG...ALONG WITH ELEVATED INSTABILITY ABOVE THE NOCTURNAL INVERSION THAT WILL SET UP. SCATTERED SHOWERS AND POSSIBLY THUNDERSTORMS REMAIN IN THE FORECAST FOR EASTERN WV AND PORTIONS OF WESTERN MD THIS EVENING...ALONG WITH POTENTIAL FOR ISOLATED ACTIVITY OVER PORTIONS OF WESTERN VA. WILL CONTINUE WITH POTENTIAL FOR ISOLATED ACTIVITY OVER THE HIGHLANDS OVERNIGHT AS THE UPPER DISTURBANCE AND A VORT MAX APPROACH FROM THE WEST. WILL HAVE POTENTIAL FOR FOG TONIGHT WITH MOIST AIRMASS IN PLACE...BUT IT MAY BE INHIBITED IN SOME SPOTS WITH APPROACHING CLOUDS FROM THE DISTURBANCE TO OUR WEST. LOWS GENERALLY IN THE UPPER 60S TO LOW 70S TONIGHT...AND SLIGHTLY COOLER IN ELEVATED AREAS. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... COLD FRONT WILL STILL BE LOCATED ACROSS THE OHIO VALLEY AT 12Z TUE. BUT FRONT WILL MARCH EASTWARD THROUGH THE DAY...MAKING IT TO THE POTOMAC HIGHLANDS BY LATE AFTERNOON. PRE-FRONTAL ENVIRONMENT WILL BE WARM AND MOIST...BUT CONVECTION LIKELY WAITS UNTIL THE FRONT GETS CLOSER TO THE CWA AND HAVE POPS EXPANDING EASTWARD WITH TIME HIGHEST IN THE EVENING ACROSS THE INTERSTATE 95 CORRIDOR. THERE IS THE RISK FOR A FEW STORMS TO BECOME SEVERE /DAMAGING WIND GUSTS/ TUESDAY...ESPECIALLY BEFORE DARK DUE TO THE COMBINATION OF INSTABILITY AND INCREASED SHEAR. CONFIDENCE IS LOWER FURTHER DOWNSTREAM ONCE THE SUN SETS. FRONT MOVES THROUGH AT NIGHT. POPS LOWER FROM WEST TO EAST. DRIER AIR MOVES IN FOR WEDNESDAY WITH THE RETURN OF SUNSHINE. WHILE DEWPOINTS ARE LOWER...DOWNSLOPING WILL SUPPORT ABOVE NORMAL TEMPERATURES WHICH STILL MAY BE NEAR 90. SAME TYPE OF SCENARIO ON THURSDAY. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... WEAK SURFACE TROUGH...MOISTURE AND WEAK PVA MAY BE ENOUGH TO SUPPLY A SLIGHT CHANCE OF SHOWERS/THUNDERSTORMS FRIDAY. INCREASED MOISTURE AND THE PASSAGE OF COLD FRONT WILL SUPPORT DEVELOPMENT OF STRONGER ACTIVITY OVER THE WEEKEND AND INTO MONDAY. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... PRIMARILY VFR CONDITIONS EXPECTED THIS EVENING INTO THE OVERNIGHT HOURS...ALTHOUGH A BRIEF SHOWER IS POSSIBLE AT KCHO. FOG MAY DEVELOP LATE TONIGHT WITH A MOIST AIRMASS IN PLACE. TSRA POSSIBLE AGAIN TUESDAY AFTERNOON/EVENING AHEAD OF A COLD FRONT. NO SIGNIFICANT WEATHER EXPECTED MID TO LATE WEEK. && .MARINE... SOME WIND GUSTS TO 15-17KT NOTED NEAR TANGIER SOUND THIS EVENING. THERE IS A LITTLE BIT OF A PRESSURE GRADIENT IN THIS AREA...BUT IT IS EXPECTED TO RELAX OVERNIGHT. FORECAST SOUNDINGS INDICATE WINDS IN THE UPPER TEENS AROUND 1-2KFT. NOT EXPECTING THIS TO MIX DOWN OVER THE OPEN COOLER WATERS...AND NEARSHORE GUSTS SHOULD DECREASE AS INSTABILITY OVER LAND DECREASES. ISOLATED SHOWER OR TSTM POSSIBLE THIS EVENING. APPROACHING COLD FRONT WILL LIKELY PRODUCE SCATTERED THUNDERSTORMS LATE TUESDAY AFTERNOON AND EVENING AS WELL...WITH GUSTY WINDS POSSIBLE. FRONT MOVES THROUGH TUESDAY NIGHT WITH HIGH PRESSURE BUILDING IN FOR WEDNESDAY. SOUTHERLY CHANNELLING/SCA CONDITIONS COULD BE POSSIBLE LATE FRIDAY. COLD FRONT EXPECTED TO MOVE THROUGH OVER THE WEEKEND. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...CEM/BPP NEAR TERM...BPP/KCS SHORT TERM...BPP LONG TERM...CEM AVIATION...CEM/KCS/BPP MARINE...CEM/BPP/KCS

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