Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 311851 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 251 PM EDT FRI JUL 31 2015 .SYNOPSIS...
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A WEAKENING COLD FRONT WILL CROSS THE REGION SATURDAY. HIGH PRESSURE WILL REBUILD ACROSS THE REGION SUNDAY. ANOTHER COLD FRONT WILL APPROACH FROM THE NORTHWEST MONDAY AND THEN STALL IN THE REGION TUESDAY. THE STALLED FRONT WILL LINGER IN THE AREA THROUGH THURSDAY.
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&& .NEAR TERM /THROUGH SATURDAY/...
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MUCH DRIER AIR MASS NOW IN PLACE WITH DEW POINTS DOWN INTO THE UPPER 50S AND LOWER 60S. HIGH PRESSURE REMAINS CENTERED WELL TO THE WEST HOWEVER...WITH A FAIRLY FAST WEST TO NORTHWEST FLOW ALOFT OVER OUR REGION. WE SHOULD STAY MOSTLY CLEAR TONIGHT...SO RADIATIONAL COOLING WILL PROBABLY RESULT IN SOME PATCHY FOG IN THE MOST SHELTERED VALLEYS OF WEST-CENTRAL VIRGINIA AS TEMPS COOL TO THE DEW POINT. OTHERWISE...PLEASANT ACROSS THE REGION THROUGH TONIGHT. BROAD SHORTWAVE CROSSES THE REGION ON SATURDAY ACCOMPANIED BY A WEAKENING COLD FRONT. THIS FRONT IS BARELY IDENTIFIABLE...AND WILL HAVE LITTLE EFFECT ON OUR WEATHER. MOISTURE WILL BE LIMITED...AND AN INVERSION WILL CAP THE ATMOSPHERE ALOFT...WHILE THE WEAKNESS OF THE BOUNDARY SHOULD SEAL THE DEAL FOR A DRY DAY DESPITE A FEW PIECES OF GUIDANCE TO THE CONTRARY. WINDS MAY PICK UP A LITTLE BUT NOTHING UNUSUAL. HIGHS WILL AGAIN BE NEAR TO SLIGHTLY ABOVE NORMAL FOR EARLY AUGUST.
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&& .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
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SATURDAY NIGHT INTO SUNDAY THE FLOW ALOFT RELAXES A BIT IN THE WAKE OF SATURDAY`S TROUGH. AT THE SURFACE HIGH PRESSURE WILL FINALLY MOVE OVERHEAD LATER SUNDAY AND SUNDAY NIGHT. WHILE THE AIR MASS WILL REMAIN FAIRLY DRY...ANOTHER NIGHT OF DECENT RADIATIONAL COOLING SHOULD RESULT IN MORE PATCHY FOG ACROSS INLAND AREAS ON SATURDAY NIGHT...POSSIBLY EXTENDING AS FAR EAST AS THE OUTSKIRTS OF THE METRO. LOWS SATURDAY NIGHT WILL AGAIN BE COOL...WITH ANOTHER FAIRLY WARM/LOW END HOT DAY EXPECTED SUNDAY UNDER THE HIGH. NO PRECIPITATION IS EXPECTED. A 500 MB SHORTWAVE WILL PIVOT ACROSS THE REGION ON MONDAY. AT THE SAME TIME...A LEESIDE PRESSURE TROUGH WILL SHARPEN AS A COLD FRONT APPROACHES FROM THE OHIO VALLEY. NORMALLY THIS SETUP WOULD YIELD CONVECTION...BUT MONDAY WILL ALSO BE THE FIRST DAY OF APPRECIABLE LOW-LEVEL MOISTURE RETURN AS HIGH PRESSURE SHIFTS OFFSHORE. WITH THE AMOUNT OF MOISTURE IN QUESTION...INSTABILITY MAY REMAIN LOW ENOUGH TO PRECLUDE MORE WIDESPREAD SHOWERS AND THUNDERSTORMS. FOR NOW KEPT ISOLATED TO WIDELY-SCATTERED POPS MAINLY OVER THE NORTHWESTERN HALF OF THE CWA COINCIDENT WITH SUPPLEMENTAL TERRAIN FORCING.
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&& .LONG TERM /TUESDAY THROUGH FRIDAY/...
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UPPER-LEVEL JET STRENGTHENS TUESDAY AS THE FRONT MOVES INTO THE AREA AND STALLS. ANOTHER LEE SIDE TROUGH DEVELOPS TUESDAY AFTERNOON...BUT AGAIN INSTABILITY IS IN QUESTION DEPENDING ON THE POSITIONING OF THE FRONT AND CLOUD COVER. MOST GUIDANCE IS NOT HINTING AT MUCH IN THE WAY OF SYNOPTIC LIFT EITHER ON TUESDAY SO KEPT POPS VERY LOW /BUT STILL NON-ZERO/. TEMPERATURES WILL BE RUNNING A FEW DEGREES ABOVE NORMAL. MEAN TROUGHING WILL LINGER OVER THE EASTERN CONUS THROUGH THE MIDDLE AND LATTER PORTION OF NEXT WEEK. A BOUNDARY WILL REMAIN STALLED OVER THE AREA...AND GFS/ECMWF ARE BOTH HINTING AT A WAVE OF LOW PRESSURE RIDING ALONG THE FRONT WEDNESDAY NIGHT-THURSDAY WHICH WOULD ENHANCE SHOWER/THUNDERSTORM CHANCES...BUT THERE IS STILL PLENTY OF ENSEMBLE SPREAD IN TIMING/PLACEMENT. IF THE WAVE PASSES JUST SOUTH OF THE AREA AND/OR OVERNIGHT...SHOWERS WOULD INCREASE BUT THUNDERSTORM CHANCES WOULD REMAIN LOW. IF THE LOW PASSES TO THE NORTH AND DURING THE AFTERNOON...THUNDERSTORM CHANCES WOULD BE MUCH HIGHER. HIGH PRESSURE WILL TRY TO MAKE A COME BACK LATE NEXT WEEK BRINGING DRIER AND SEASONABLY WARM CONDITIONS.
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&& .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
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VFR CIGS AND VIS OVERALL THROUGH SATURDAY NIGHT. VERY SLIGHT CHANCE OF A SHOWER AS A VERY WEAK COLD FRONT PUSHES THROUGH SATURDAY...BUT RISK IS BELOW 15 PERCENT. ALSO POTENTIAL FOR SOME PATCHY FOG WITH IFR CIGS/VIS LATER TONIGHT...AND AGAIN LATER SATURDAY NIGHT...PRIMARILY AT INLAND TERMINALS CHO AND MRB. RIGHT NOW ODDS FAVOR SATURDAY NIGHT OVER TONIGHT SO HAVE KEPT OUT OF TAFS. WINDS MAY GUST UP TO 20 KNOTS SATURDAY FROM THE WEST. VFR EXPECTED SUN-WED. ANY CONVECTION SHOULD REMAIN VERY ISOLATED AND LIKELY CONFINED TO THE AFT/EVE HRS DURING THIS TIME. NLY FLOW AOB 10 KT BECOMES SLY AROUND 10 KT SUN...WITH GENERAL SWLY FLOW AROUND 10 KT MON-WED. WIND DIRECTION BECOMES SOMEWHAT UNCERTAIN TUE-WED AND DEPENDS ON POSITIONING OF THE FRONT.
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&& .MARINE...
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DRY CONDITIONS EXPECTED THROUGH SATURDAY NIGHT...THOUGH THERE IS THE SLIGHT CHANCE OF A SHOWER SATURDAY AS A VERY WEAK COLD FRONT PASSES. OF MORE PRESSING CONCERN IS POTENTIAL FOR WINDS TO REACH LOW END SCA SATURDAY AFTERNOON. IT LOOKS VERY BORDERLINE GIVEN THAT HIGHS ARE EXPECTED TO BE ABOVE THE WATER TEMPS WHICH SHOULD CREATE A LITTLE STABILITY DURING THE DAYLIGHT HOURS...SO HAVE NOT PULLED THE TRIGGER. THE UNIDIRECTIONAL FLOW MAY OVERWHELM THE LIMITED SURFACE STABILITY HOWEVER. HIGH PRESSURE PASSES OVER THE WATERS SUNDAY WITH SUB-SCA CONDITIONS EXPECTED. PRESSURE GRADIENT TIGHTENS A BIT AS A FRONT APPROACHES THE AREA AND STALLS MON-TUE...AND COULD RESULT IN SCA GUSTS DURING THIS TIME.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...RCM NEAR TERM...RCM SHORT TERM...RCM/DFH LONG TERM...DFH AVIATION...RCM/DFH MARINE...RCM/DFH

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