Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 181747 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 147 PM EDT MON AUG 18 2014 .SYNOPSIS... A FRONTAL BOUNDARY WILL STALL OVER VIRGINIA TODAY. A WAVE OF LOW PRESSURE WILL TRACK EASTWARD ALONG THE STALLED BOUNDARY TONIGHT BEFORE MOVING OFFSHORE TUESDAY. THE FRONTAL BOUNDARY SHOULD REMAIN NEARLY STATIONARY FROM THE GREAT LAKES TO THE SOUTHERN MID-ATLANTIC STATES WEDNESDAY AND THURSDAY WHILE A SERIES OF DISTURBANCES RIDE ALONG IT. THE FRONT WILL GRADUALLY SHIFT FARTHER SOUTH AND WEST OF THE AREA FRIDAY AND THIS WEEKEND AS HIGH PRESSURE WEDGES DOWN FROM EASTERN CANADA. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... LATEST WATER VAPOR AND 11-3.9 IR SHOW THE QUASI-STATIONARY FRONTAL BOUNDARY TO OUR SOUTH EXTENDING NORTHEAST INTO THE MARYLAND/WEST VIRGINIA PANHANDLE. DRY AIR WILL CONTINUE TO PRESS INTO THE REGION FROM THE NORTH THROUGH THE MORNING HOURS UNDER A LIGHT NORTHERLY FLOW. WINDS ARE EXPECTED TO VEER TOWARDS THE WEST-SOUTHWEST LATER THIS AFTERNOON AS THE FRONT WAVERS TO OUR SOUTH. A WEAK SURFACE LOW, CURRENTLY ACROSS THE MID-WEST, WILL RIDE ALONG THIS FRONTAL BOUNDARY LATER THIS AFTERNOON..STAYING TO THE SOUTH OF OUR CWA. BASED ON THE LATEST RAP AND HRRR WITH THE 12:30 PM UPDATE, PUSHED BACK ANY RAIN CHANCE TILL TONIGHT ACROSS THE SOUTHERN DELMARVA. ELSEWHERE, THE LOWER PWAT AIR IN PLACE WILL TAKE A WHILE TO MODIFY SO WE EXPECT A DRY DAY WITH SOME INCREASING CLOUD COVER LATE IN THE DAY. TEMPERATURES WILL RUN CLOSE TO NORMAL TODAY, LIKE THE PAST FEW DAYS. DID MAKE SOME MINOR ADJUSTMENTS ON THE TEMPERATURES WITH THE 12;30 PM UPDATE BASED ON THE 16Z METARS. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/... THE SURFACE WAVE ALONG THE FRONTAL BOUNDARY WILL PASS TO OUR SOUTH LATE TONIGHT. THIS SYSTEM OVER THE PAST SEVERAL DAYS HAS TRENDED TOWARDS A MORE SUPPRESSED, FASTER WEST-EAST MOVEMENT, AND A SOUTHEASTERN TRACK THAT WOULD ALLOW FOR LESS SIGNIFICANT RAINFALL THREAT THEN PREVIOUSLY THOUGHT...WE REMOVED THE MENTION FROM THE HWO AT THIS TIME. SURFACE FLOW BEGINS TO VEER TOWARDS THE EAST-SOUTHEAST BY THIS EVENING BRINGING MORE LOW-LEVEL INTO THE REGION...EVERYWHERE. NOT EXPECTING MUCH IN THE WAY OF RAIN CHANCES LATE TONIGHT, OUTSIDE OF THE DELMARVA, WITHOUT MUCH SYNOPTIC SCALE LIFT AND DON`T THINK THE SURFACE FLOW IS STRONG ENOUGH FOR UPGLIDE ACROSS OUR WESTERN ZONES, SO WE STAY MOSTLY DRY TONIGHT. TEMPERATURES, UNDER INCREASINGLY CLOUDY SKIES, WILL BE SEVERAL DEGREES WARMER THAN THE PAST FEW MORNINGS...BLEND OF THE MET/MAV LOOKS GOOD. && .LONG TERM /TUESDAY THROUGH SUNDAY/... WHILE OPPRESSIVE HEAT WILL BUILD ACROSS THE SOUTHERN CONUS IN ASSOCIATION WITH A STRENGTHENING ANTICYCLONE THIS WEEK, IT IS NOT EXPECTED TO REACH OUR AREA THROUGH THE NEXT 7 DAYS AS THE REGION WILL GENERALLY BE UNDER THE PRESENCE OF MEAN TROUGHING AND ONSHORE FLOW AT THE SFC. TEMPS THRU THE PERIOD SHOULD BE NEAR TO SLIGHTLY BELOW NORMAL FOR THIS TIME OF YEAR. LOPRES IS EXPECTED TO MOVE OFF THE SOUTHEAST VA COAST TUESDAY MORNING. MODELS CONTINUE THE TREND TOWARD A WEAKER, MORE PROGRESSIVE SYSTEM, WHICH WILL RESULT IN A EARLIER END TO THE SHOWERS ACROSS THE DELMARVA DURING THE MORNING. THERE MAY ALSO BE AN ISOLATED SHOWER THAT DEVELOPS ACROSS THE HIGHER ELEVATIONS OF PA LATE IN THE DAY, BUT THE BULK OF DIURNAL CONVECTION SHOULD BE CENTERED CLOSER TO THE SHARPENING LLVL THETA-E RIDGE, WHICH WILL RESIDE WEST OF THE AREA. OTHERWISE, DRY CONDITIONS PREVAIL. FCST MAX TEMPS RANGING FROM THE MID 70S IN THE POCONOS TO MID 80S ALONG THE I-95 CORRIDOR ARE CLOSE TO CLIMO. A WEAK RIDGE OF HIPRES BECOMES ESTABLISHED ACROSS THE COASTAL MID ATLANTIC TUESDAY NIGHT AND WEDNESDAY MORNING. ALTHOUGH MODEL GUIDANCE HASN`T JUMPED ON IT YET, WILL HAVE TO WATCH FOR THE POTENTIAL FOR FOG OR STRATUS DEVELOPMENT AS PERSISTENT ONSHORE FLOW IN THE BOUNDARY LAYER DRAWS MARINE AIR INLAND. THE NEXT SYSTEM TO IMPACT THE AREA WILL BE A WAVE OF LOPRES OVER THE GREAT LAKES THAT MOVES SOUTHEASTWARD ALONG THE STALLED FRONTAL BOUNDARY IN THE MID-ATLANTIC STATES WEDNESDAY AFTERNOON THROUGH THURSDAY. THE DISTURBANCE IS ALSO FORECAST TO WEAKEN AS THE UPPER LOW BECOMES AN OPEN WAVE BY THE TIME IT REACHES OUR AREA. THIS LOW OF PAC NW ORIGIN IS NOT EXPECTED TO TAP INTO APPRECIABLE GULF OF MEXICO MOISTURE DURING ITS CROSS-COUNTRY TREK. ACCORDINGLY, THE SETUP DOES NOT PARTICULARLY SUPPORT A HEAVY RAINFALL EVENT OR A WASHOUT, BUT THERE IS STILL A CHANCE FOR SHOWERS AND THUNDERSTORMS DURING THE SECOND HALF OF THE WORK WEEK. CHANCE POPS INITIALLY CONFINED TO WEST OF I-95 WEDNESDAY AFTERNOON, BEFORE THIS ACTIVITY WOULD TRY TO ADVANCE EASTWARD INTO THE REST OF THE CWA WEDNESDAY NIGHT. POPS THURSDAY HIGHEST CLOSER TO THE STATIONARY BOUNDARY OVER THE DELMARVA/NORTHEAST MD/SOUTHEAST PA. A RIDGE OF HIPRES OVER EASTERN CANADA IS EXPECTED TO NOSE DOWN INTO THE FORECAST AREA FRIDAY THROUGH THE WEEKEND. MODELS NOW SHOW THE HIGH BECOMING ESTABLISHED ALONG THE EASTERN SEABOARD SOONER THAN PREVIOUS GUIDANCE HAD INDICATED. TRENDED TOWARD A DRIER FORECAST FRIDAY INTO THE WEEKEND AS THE HIGH SHOULD ACT TO SHIFT THE OLD FRONTAL BOUNDARY AND STORM TRACK SOUTH AND WEST OF THE AREA. ONSHORE FLOW WOULD POSITION THE REGION IN COOLER, MORE STABLE AIRMASS REGIME. && .AVIATION /18Z MONDAY THROUGH SATURDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. SCATTERED MID LEVEL CLOUDS WILL CONTINUE TO MOVE EAST INTO THE REGION AHEAD OF A LOW PRESSURE SYSTEM PASSING TO OUR SOUTH THIS AFTERNOON. CEILINGS MAY LOWER TO AROUND 5000 FEET WITH THIS CLOUD COVER TONIGHT. PRECIPITATION LOOKS TO REMAIN SOUTH OF ALL TAF SITES. THE CLOUDS SHOULD BREAK UP AND BECOME MORE SCATTERED BY TOMORROW AFTERNOON. WINDS WILL BE VARIABLE THIS AFTERNOON WITH SOME UNCERTAINTY IN THE WIND DIRECTION BUT WINDS SHOULD REMAIN UNDER 10 KNOTS. A SLIGHT CHANCE FOR AN ISOLATED WIND GUST IS PRESENT THROUGH LATE AFTERNOON BUT SMALL ENOUGH NOT TO INCLUDE IN THE TAFS ATTM. LIGHT AND VARIABLE WINDS SHOULD TURN MORE OUT THE EAST ON TUESDAY AND REMAIN UNDER 10 KNOTS. OUTLOOK... TUESDAY NIGHT THROUGH WEDNESDAY MORNING...STRATUS OR FOG POSSIBLE AS ONSHORE FLOW DEVELOPS. BEST SETUP WOULD BE CLOSER TO THE COAST (ACY/MIV). WEDNESDAY AFTERNOON THROUGH THURSDAY NIGHT...CHANCE FOR SHRA/TSRA AS A SERIES OF DISTURBANCES MOVE THRU THE REGION. LOCAL/TEMPORARY FLIGHT RESTRICTIONS POSSIBLE. FRIDAY...VFR CONDITIONS.
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&& .MARINE... WE CONTINUE THE TRANQUIL SUB-SCA CONDITIONS TODAY AND TONIGHT. LIGHT NORTHERLY WINDS WILL BACK TOWARDS THE SOUTH-SOUTHEAST DURING THE COURSE OF THE DAY, AND REMAIN BELOW 10 KNOTS. SEAS WILL CONTINUE TO RUN AROUND 2 TO 3 FEET. WINDS THEN VEER TOWARDS THE EAST LATE TONIGHT AS A WEAK SURFACE LOW PRESSURE SLIDES EASTWARD TO OUR SOUTH. OUTLOOK... TUESDAY...LOPRES MOVES OFF THE VA COAST. A TIGHT PRESSURE GRADIENT TO THE NORTH OF THE LOW MAY PRODUCE EASTERLY WINDS 15-20 KT. SCA POTENTIAL LOW. WEDNESDAY THROUGH THURSDAY...ONSHORE FLOW CONTINUES BUT WILL WEAKEN OVER TIME. TSRA POSSIBLE IN SOUTHERN WATERS ON THURSDAY. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...KLEIN NEAR TERM...GAINES/HEAVENER SHORT TERM...HEAVENER LONG TERM...KLEIN AVIATION...GAINES/HEAVENER/KLEIN MARINE...HEAVENER/KLEIN

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