Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 222315 AFDAKQ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WAKEFIELD VA 715 PM EDT WED APR 22 2015 .SYNOPSIS... A COLD FRONT CROSSES THE MID ATLANTIC REGION THIS AFTERNOON AND EARLY EVENING. CANADIAN HIGH PRESSURE BUILDS INTO THE REGION FOR THURSDAY AND FRIDAY. LOW PRESSURE APPROACHES THE REGION FROM THE WEST ON SATURDAY...CROSSING THE REGION SATURDAY NIGHT INTO SUNDAY. HIGH PRESSURE RETURNS EARLY NEXT WEEK. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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UPDATE...CLOUD HEIGHTS HAVE DIMINISHED OVER THE PAST FEW HOURS AND LIGHT RAIN SHOWERS HAVE ZIPPED ACROSS THE AREA. BEST SHOWER ACTIVITY LEFTOVER AS OF 700 PM WILL BE EXITING THE COAST BY 800 PM THIS EVENING. HAVE REMOVED ANY MENTION OF THUNDER. BREEZY SW WINDS MAY EXPERIENCE A BRIEF LULL IN SPEEDS AS A COLD FRONT CROSSES THE REGION LATER THIS EVENING...BUT WILL VEER TO THE NW BEHIND THE FROPA AND BECOME BREEZY AGAIN FROM LATE EVENING THROUGH THE OVERNIGHT HOURS. GUSTS SHOULD AVERAGE 20-25 MPH. OTHERWISE...HIGH PRESSURE BUILDS IN FROM THE NW AFTER MIDNIGHT TONIGHT AND SKIES BECOME MOSTLY CLEAR. EXPECT OVERNIGHT LOWS FROM THE LOW 40S NW TO AROUND 50 SE.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
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UPPER/SFC LOW PRESSURE REMAINS VIC OF NEW ENGLAND THRU THE SHORT TERM PERIOD. CONFLUENCE OVER THE REGION WILL ALLOW WEAK HIGH PRESSURE TO BUILD INTO THE REGION THURSDAY...REMAINING OVER THE MID- ATLANTIC THRU FRIDAY NIGHT. ASSOCIATED AIRMASS WILL BE CANADIAN IN ORIGIN. THE RESULT WILL BE DRY CONDITIONS/LOW DEWPOINTS...MOSTLY CLEAR/SUNNY CONDITIONS AND BELOW NORMAL TEMPS. PER GEFS STD ANOMALIES...H85 TEMPS WILL RANGE FROM -1 TO -2 STD DEV THU AND FRI. HOWEVER...BREEZY WLY/DOWNSLOPE FLOW THU WILL HELP KEEP TEMPS IN THE LOW-MID 60S NORTH TO UPPER 60S SOUTH. TEMPS THU NIGHT FORECAST TO DROP INTO THE MID-UPPER 30S INLAND AND UPPER 30S-LOW 40S NEAR THE COAST. SHORTWAVE MOVING ACROSS THE MID-ATLANTIC THU- THU NIGHT WILL RESULT IN A PARTLY CLOUDY SKY ACROSS THE N-NERN LOCAL AREA...WHICH WILL LIKELY KEEP TEMPS SLIGHTLY WARMER. FEW LOCALS IN THE PIEDMONT MAY BE ABLE TO DROP INTO THE LOW 30S...BUT FROST IS NOT EXPECTED DUE TO THE DRY AIRMASS (DEWPOINTS IN THE 20S). COOLER FRI WITH HIGHS GENERALLY IN THE LOW-MID 60S. SFC HIGH PRESSURE SLIDES OFFSHORE SAT AS A SRN STREAM SYSTEM LIFTS FROM THE PLAINS INTO THE MIDWEST. ASSOCIATED SFC LOW LOCATES OVER THE MID MS VALLEY LATE SAT. MODELS IN GOOD AGREEMENT NOW WITH SFC LOW PLACEMENT. FRONTAL BOUNDARY OVER THE GULF STATES WILL BEGIN TO LIFT NWD IN AMPLIFYING FLOW AS MOISTURE INCREASES FROM THE GULF OF MEX. EXPECT BEST ISENTROPIC LIFT TO COMMENCE OVER THE REGION LATE SAT. BETTER UPPER LEVEL SUPPORT FROM THE UPPER WAVE ARRIVES SAT NIGHT...SO ONLY EXPECT LIGHT RAIN RICHMOND SOUTH AND WEST LATE SAT. CLOUDS ALSO INCREASE THRU THE DAY...RESULTING IN A MOSTLY CLOUDY SKY BY SAT AFTERNOON. COOL...WITH HIGHS GENERALLY IN THE LOW 60S (-1 STD DEV).
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&& .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... WEAKENING UPPER SHORTWAVE WILL PIVOT OFF THE CAROLINA COAST LATE SAT, WHICH WILL ALLOW FOR SCT SHRAS TO DEVELOP ACROSS THE AREA SATURDAY NIGHT. GREATEST COVERAGE EXPECTED ACROSS SE ZONES WHERE W-SW FLOW WILL BRING PW VALUES AOA 1" SAT NIGHT AND EARLY SUNDAY, SO WILL GO WITH HIGH END CHC IN THESE ZONES, 30-40% POP ACROSS THE NORTH, WITH A NARROW WINDOW OF SOME VERY SHALLOW LIFT SAT NIGHT SUNDAY MORNING. UPPER LOW AND PERTURBATIONS PINWHEELING AROUND IT WILL SERVE TO FLATTEN FLOW ALOFT SUNDAY AND ERY MON, THEREBY SUPPRESSING MOST OF THE ADDITIONAL WEAK DISTURBANCES RIDING ALONG THE WEAK/WAVY FRONTAL BOUNDARY TO THE SOUTH. DESPITE WHAT WILL LIKELY BE A COOL/CLOUDY DAY ON SUNDAY, WOULD EXPECT MUCH OF THE ACTIVITY WOULD REMAIN TO THE SOUTH. GIVEN SATURATED LLVLS WILL KEEP SLIGHT CHC POP IN PLACE EARLY IN THE DAY SUNDAY (THROUGH THE DAY SOUTH), WITH THE EXPECTATION OF LITTLE MORE THAN SOME PATCHY DRIZZLE/FEW SHRAS IN COOL W-NW FLOW. DID GO ABOUT A CATEGORY BELOW MOS GIVEN THIS MOIST SETUP...HIGHS IN THE L/M60S. ERY MORNING LOWS MONDAY IN THE 40S. DRY AND A BIT WARMER MONDAY AS HIGH PRESSURE TO THE NORTH OF THE REGION BUILDS A BIT FARTHER SOUTH. HIGHS 65-70. LOWS M40S-L50S. SHOULD REMAIN DRY THROUGH MONDAY NIGHT, BUT EXPECT INCREASING SLY FLOW/OVERRUNNING IN ASSOCIATION WITH NUMEROUS DISTURBANCES PUSHING EAST FROM DEEP UPPER LOW THAT WILL SET UP OVER THE CENTRAL/SOUTHERN PLAINS EARLY NEXT WEEK. THIS WILL SERVE TO KEEP UNSETTLED, COOL CONDITIONS IN PLACE ACROSS THE LOCAL AREA THROUGH MIDWEEK, WITH DAILY POP CHANCES IN THE SLIGHT TO LOW END CHC RANGE TO END THE PERIOD. DAYTIME HIGHS REMAIN IN THE 60S TO NR 70, WITH EARLY MORNING LOWS IN THE 40S TO AROUND 50. && .AVIATION /00Z THURSDAY THROUGH MONDAY/... BREEZY/WINDY S/SW WINDS THIS AFTN ACRS THE ENTIRE REGION AHEAD OF AN APPROACHING COLD FRONT. HAVE INCLUDED GUSTS TO 30 KT AT KRIC/KSBY...GENLY 25-30 KT ELSEWHERE THROUGH THE NEXT FEW HRS. RADAR SHOWS A LINE OF SHOWERS ENTERING CENTRAL VA AS OF 18Z...BUT THUS FAR UPSTREAM OBS SHOW LITTLE TO NONE OF THIS REACHING THE GROUND DUE TO DRY AIRMASS IN PLACE. FARTHER NORTH IN MD/FAR NRN VA ALONG THIS BROKEN LINE OF SHOWERS HAS EMBEDDED TSTMS AND PRECIP IS REACHING THE GROUND. HAVE INCLUDE "VCTS" AT KSBY AND "VCSH" AT KRIC AFTER 20Z...DID NOT INCLUDE THIS AT OTHER TERMINALS AS CONFIDENCE IS QUITE LOW THAT THIS LINE WILL HOLD TOGETHER AS SUPPORT WEAKENS FARTHER TO THE SE. MAIN IMPACTS WOULD BE ERRATIC/STRONG GUSTY WINDS WITH MINIMAL OR VERY BRIEF LOWERING OF CIGS/VSBYS. THIS EVENING...WINDS SHIFT TO THE W AND EVENTUALLY THE NW OVERNIGHT IN THE WAKE OF THE COLD FRONT. GENLY EXPECT WINDS TO DIMINISH TO 10-15 KT IN THE EVENING...BUT WITH A BRIEF INCREASE IN WIND SPEEDS/GUSTS TO 20-25 KT LIKELY AS WIND DIRECTIONS SHIFT FROM W TO NW BETWEEN 03-06Z. OTHERWISE DRY/VFR CONDS OVERNIGHT AND THROUGH THE NEXT SEVERAL DAYS AS HIGH PRESSURE BUILDS IN FROM THE WNW. WINDS REMAIN SOMEWHAT ELEVATED FROM THE W/NW THU AND FRI AFTN. CHANCE FOR RAIN LATER SAT INTO SUNDAY. && .MARINE...
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UPDATE...EXTENDED SCA FOR ERN VA RIVERS AND CURRITUCK SOUND UNTIL 1000 PM THIS EVENING. A SECONDARY SURGE IN SCA WINDS IS EXPECTED TO OCCUR WITH A COLD FRONTAL PASSAGE THIS EVENING. PREVIOUS DISCUSSION...LATEST OBS/BUOY REPORTS REFLECT PREFRONTAL S-SW FLOW 15-25 KT ACROSS THE MARINE AREA THIS AFTERNOON. PRES GRADIENT BETWEEN SFC HIGH PRESSURE TO THE SOUTH AND SFC TROUGH APPROACHING FROM THE WEST HAS TIGHTENED ENOUGH TO ALLOW INCREASING WINDS OVER THE PAST FEW HOURS, WITH GUSTS TO AROUND 30 KTS IN THE CENTRAL/LOWER BAY AND COASTAL ZONES. EXPECT A POST FRONTAL (NORTH) SURGE TONIGHT, AND THUS SCA FLAGS REMAIN IN EFFECT THROUGH LATE TONIGHT FOR THE BAY/NORTHERN COASTAL ZONES. WINDS VEER TO THE W-NW FOR THURSDAY/FRIDAY, WITH WINDS DIMINISHING SUB-SCA/SEAS SUBSIDING TO 2-4FT RANGE (HIGHEST OUT 20NM) AS HIGH PRESSURE BUILDS IN FROM THE WEST. SUB-SCA MARINE CONDITIONS CONTINUE ON SATURDAY, WITH WEAK FLOW PERSISTING AS SFC LOW PRESSURE DEVELOPS TO THE SOUTH AND MOVES OFFSHORE OF THE CAROLINA COAST BY MIDDAY SUNDAY. LIGHT SLY WINDS BACK TO THE E-NE BY EARLY SUNDAY. THERE IS A SLIGHT CHC THAT WINDS COULD INCREASE TO LOW END SCA ACROSS SOUTHERN ZONES BY SUNDAY MORNING, BUT EXPECT PREDOMINATE SUB-SCA CONDITIONS THROUGHOUT THIS PERIOD. FOR THAT REASON, HAVE FOLLOWED CLOSELY TO WAVEWATCH TROUGH THE WEEKEND.
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&& .FIRE WEATHER...
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A COOL AND DRY AIRMASS WILL SPREAD OVER THE REGION THU AND FRI AS CANADIAN HIGH PRESSURE BUILDS IN FROM THE WEST. MINIMUM RH VALUES ARE FORECAST TO RANGE FROM 20-30 PERCENT BOTH DAYS. A WEST WIND IS EXPECTED TO AVERAGE 10-15 MPH WITH GUSTS TO 20-25 MPH THU... DIMINISHING TO AROUND 10 MPH WITH GUSTS TO 20 MPH FRI. WHILE DRY/BREEZY CONDITIONS ARE EXPECTED...RECENT RAINFALL AND GREEN-UP WILL BE THE PRIMARY LIMITING FACTORS WITH RESPECT TO FIRE WEATHER CONCERNS.
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&& .AKQ WATCHES/WARNINGS/ADVISORIES...
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MD...NONE. NC...NONE. VA...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 10 PM EDT THIS EVENING FOR ANZ633- 635>638-650-652-654. SMALL CRAFT ADVISORY UNTIL 7 AM EDT THURSDAY FOR ANZ630>632- 634.
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&& $$ SYNOPSIS...AJZ/SAM NEAR TERM...BMD/SAM SHORT TERM...AJZ/SAM LONG TERM...MAM AVIATION...LKB MARINE...JEF/MAM FIRE WEATHER...AKQ

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