Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 200133 AAA AFDLWX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 933 PM EDT FRI SEP 19 2014 .SYNOPSIS... HIGH PRESSURE WILL REMAIN OVERHEAD THROUGH SATURDAY. THE HIGH WILL MOVE OFF THE COAST SUNDAY AND A COLD FRONT WILL PASS THROUGH THE AREA SUNDAY NIGHT INTO MONDAY. HIGH PRESSURE WILL RETURN FOR THE MIDDLE PORTION OF NEXT WEEK. && .NEAR TERM /THROUGH SATURDAY/...
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A LITTLE WRINKLE IN THE UPPER FLOW WILL BRUSH PAST THE ERN HALF OF THE AREA OVERNIGHT. THIS FEATURE IS A WEAK UPPER TROUGH DRIFTING OFF THE NRN PERIPHERY OF A LARGE OFFSHORE UPPER SYSTEM OVER THE SRN ATLC. KDOX SHOWING A COASTAL FRONT DRIFTING ONSHORE AND OVER DELMARVA RECENTLY. ELY FLOW HAS BEEN ONGOING FROM THE AFTN HRS...W/ A DECENT STRENGTHENING OF IT OVER THE PAST FEW HRS. HIGH PRESSURE JUST OFF THE NEW ENGLAND COAST...W/ IT`S SRN PERIPHERY SQUEEZING DOWN INTO THE MID-ATLC IS PUSHING UP AGAIN THIS NRN TROUGH IS CAUSING THE ELY ONSHORE FLOW AND CONVERGENCE OF MOIST/DRY AIR. THE BREEZY CONDITIONS ARE MAKING THEIR WAY OVER THE WATERS OF THE CHES BAY BUT DISSIPATING OFF WELL OVER ERN MD/W OF THE BAY. A HANDFUL OF SHOWERS HAVE RESULTED FROM THE ONSHORE FLOW...ALONG W/ SOME LOW LEVEL MOISTURE BANKING INTO THE MTNS W/ SOME OVERRUNNING EFFECTS CREATING A DECENT STRATUS DECK OVER THE APLCNS. E OF THE BLUE RIDGE...MORE OF A SCT/BKN NATURE TO THIS DECK. THE RELATIVE INCREASE IN SFC MOISTURE OVER THE PIEDMONT/COASTAL AREAS WILL HELP MODERATE TEMPS OVER THESE AREAS AND THE DENSE CLOUD COVER WILL MODERATE LOWS OVER THE WEST. AFTER HITTING THE L-M40S OVER THE HIGHER TERRAIN LAST NIGHT...THESE AREAS WILL END UP ABOUT 10F DEG WARMER...WHILE THE ERN HALF OF THE CWA WILL BE CLOSER TO THEIR LOWS FROM LAST NIGHT. PREV DISC... THE SURFACE RIDGE WILL REMAIN IN PLACE FOR SATURDAY AND AN ONSHORE FLOW WILL CONTINUE. HOWEVER...THE SUBSIDENCE INVERSION SHOULD LOWER DUE TO RISING PRESSURES OVERHEAD BETWEEN A COLD FRONT OVER THE MIDWEST AND LOW PRESSURE DEVELOPING OFF THE SOUTH CAROLINA COAST. WITH A STRENGTHENING SUBSIDENCE INVERSION...THIS MEANS THAT ANY LOW CLOUDS AND FOG SATURDAY MORNING SHOULD GIVE WAY TO SUNSHINE. MAX TEMPS WILL RANGE FROM THE 70S IN THE MOUNTAINS TO NEAR 80 ACROSS THE WASHINGTON AND BALTIMORE METROPOLITAN AREAS.
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&& .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/... A COLD FRONT WILL APPROACH FROM THE GREAT LAKES/OHIO VALLEY DURING THE SECOND HALF OF THE WEEKEND. ABOVE AVERAGE TEMPERATURES WILL PRECEDE THE COLD FRONT...BUT MOISTURE RETURN FROM THE SOUTH WILL BE MEAGER. STILL...THE UPPER-LEVEL TROUGH FORCING THE COLD FRONT IS FORECAST TO BE PRETTY STRONG BY THE MODELS AND THAT SHOULD IN TURN FORCE NARROW BANDS OF SHOWERS AND THUNDERSTORMS. GUSTY OR PERHAPS SPOTTY DAMAGING WINDS ARE POSSIBLE MAINLY ACROSS WESTERN AREAS WHERE ADDED TERRAIN FORCING COULD RESULT IN BRIEFLY MORE ROBUST UPDRAFTS. SHOWERS AND THUNDERSTORMS WILL GRADUALLY WANE AS THEY PUSH EAST OF THE BLUE RIDGE AND TOWARDS THE CHESAPEAKE BAY DURING THE EVENING. THE COLD FRONT WILL MOVE OFFSHORE AS HIGH PRESSURE REBUILDS FROM CANADA RESULTING IN DRY AND COOLER THAN NORMAL TEMPERATURES TO START THE BEGINNING OF NEXT WEEK. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... A DRY AND FALL-LIKE WEEK IS FORECAST FOR MOST OF NEXT WEEK AS A LARGE AREA OF CANADIAN HIGH PRESSURE SLOWLY PUSHES ACROSS THE NORTHERN/EASTERN CONUS AND RIDGING PERSISTS ALOFT. WITH LIGHT WINDS AND MOSTLY CLEAR SKIES AND SHALLOW MOISTURE IN LIGHT EASTERLY FLOW...THE SETUP COULD BE IDEAL ON MORE THAN ONE OCCASION FOR LATE NIGHT/EARLY MORNING FOG OR STRATUS NEXT WEEK. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
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AN ONSHORE FLOW WILL CONTINUE THROUGH SATURDAY...W/ A BUILDING POTENTIAL FOR LOW CLOUDS TO DEVELOP ACROSS THE AREA - ESP ACROSS CENTRAL VIRGINIA/SPREADING NORTH AND EAST OVERNIGHT. MVFR CONDITIONS ARE FORECAST OVER THE TERMINALS TONIGHT INTO MID-MRNG SAT...BUT IFR CONDITIONS ARE POSSIBLE. IFR CONDITIONS ARE LIKELY AT KCHO DURING THIS TIME. ANY LOW CLOUDS AND FOG WILL BURN OFF LATER SATURDAY MORNING AND VFR CONDITIONS ARE EXPECTED IN THE AFTERNOON. SUB-VFR PSBL SUN IN SPARSE COVERAGE SHWRS/TSTMS IN AFTN/EVE. WINDS SW 10 KTS SUN. VFR LIKELY SUNDAY NIGHT THROUGH TUESDAY NIGHT BEHIND FRONT W/ W WINDS 10-15 KTS W/ GUSTS TO 20 KTS PSBL SUN NIGHT-MON...THEN N LESS 10 KTS OR LESS MON NIGHT-TUE NIGHT. MODERATELY HIGH CONFIDENCE FORECAST IN OVERALL SETUP AS MODELS ARE IN AGREEMENT WITH TYPICAL TIMING DIFFERENCES REVOLVING AROUND THE WIND SHIFT IMMEDIATELY FOLLOWING THE FRONT AND THE TIMING OF HIGHER GUSTS.
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&& .MARINE...
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AN ONSHORE FLOW WILL CONTINUE THROUGH SATURDAY AS HIGH PRESSURE REMAINS NEAR THE MID-ATLANTIC COAST. A PRESSURE SURGE WILL CAUSE WINDS TO INCREASE A BIT OVER THE WATERS TONIGHT. A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE MARYLAND CHESAPEAKE BAY AND LOWER TIDAL POTOMAC RIVER. WINDS SHOULD BE A BIT WEAKER SATURDAY AS THE GRADIENT SUBSIDES A BIT. S FLOW AROUND 10 KTS OR SO AHEAD OF COLD FRONT SAT NIGHT-SUN ALONG W/ CHC OF SHWRS/TSTMS WHICH COULD BE ACCOMPANIED BY GUSTY WINDS SUN EVE. FRONT AND PRECIP CLEARS THE COAST SUN NIGHT AND WINDS BECOME W OR NW 10-15 KTS GUSTS 20 KTS. WINDS BECOME N 10 KTS MON NIGHT-WED BEFORE VEERING AROUND TO THE E LATER IN THE WEEK AS HIGH PRESSURE SLOWLY MIGRATES TO THE NORTH OF THE REGION.
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&& .TIDES/COASTAL FLOODING...
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MOST LOCATIONS STILL SHOWING TIDAL ANOMALIES ARE AROUND ONE-HALF FOOT ABOVE NORMAL. THE SURFACE FLOW WILL STAY GENERALLY ELY OVER THE NEXT SEVERAL HRS...GUSTING IN THE 10-15KT RANGE WHICH WILL SHOULD CONTINUE TO PULL THOSE LEVELS UP. LOW PRESSURE WILL MOVE UP THE MID- ATLANTIC COAST SATURDAY NIGHT INTO SUNDAY...AND THIS MAY ENHANCE THE THREAT FOR ELEVATED WATER LEVELS. MINOR TIDAL FLOODING CANNOT BE RULED OUT WITH THE HIGH TIDE CYCLE LATE TONIGHT BUT UNLIKELY UNLESS WINDS STRENGTHEN FURTHER. THERE IS A BETTER CHANCE FOR MINOR TIDAL FLOODING WITH THE HIGH TIDE CYCLES LATER SATURDAY INTO SUNDAY.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 2 AM EDT SATURDAY FOR ANZ530>534- 537-539>541-543.
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&& $$ UPDATE...GMS PREV DISCUSSION...BJL/DFH

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