Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 051922 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 322 PM EDT TUE MAY 5 2015 .SYNOPSIS... A COLD FRONT WILL SLOWLY MOVE THROUGH OUR REGION TONIGHT AND WEDNESDAY. HIGH PRESSURE WILL THEN MOVE INTO THE AREA FROM THE NORTH AND EAST ON THURSDAY THROUGH THE WEEKEND. ANOTHER SLOW MOVING COLD FRONT WILL APPROACH OUR AREA EARLY NEXT WEEK...AND MOVE THROUGH THE REGION BY MID WEEK. && .NEAR TERM /THROUGH TONIGHT/... THE COLD FRONT HAS MADE ITS WAY ACROSS MUCH OF THE AREA, AND IS DRAPED ACROSS FAR SOUTHEASTERN PENNSYLVANIA, SOUTHERN NEW JERSEY, AND THE DELMARVA. IT WILL CONTINUE TO SLOWLY SAG SOUTHWARD THROUGH TONIGHT, BUT HAVE A HARD TIME CLEARING THE ENTIRE AREA OVERNIGHT. MEANWHILE, SEVERAL SHORT WAVE/VORTICITY IMPULSES ARE FORECAST TO AFFECT THE AREA OVERNIGHT. THE FIRST IS MOVING THROUGH LATE THIS AFTERNOON, WHICH HAS ALREADY CREATED SOME SHOWER ACTIVITY MOVING THROUGH NOW. THE SECOND IS EXPECTED TO APPROACH THE AREA EARLY THIS EVENING, WHICH SHOULD ENHANCE SHOWER POTENTIAL FOR THIS EVENING. THIS WILL PASS TO OUR EAST OVERNIGHT, WHILE ANOTHER IMPULSE APPROACHES AND PASSES ACROSS THE NORTHERN TIER OF THE AREA OVERNIGHT TOWARD DAYBREAK. WHILE THE SHOWER ACTIVITY ACROSS THE SOUTH MAY DIMINISH OVERNIGHT, SHOWERS COULD CONTINUE ACROSS THE NORTHERN AREAS WITH THE IMPULSE AFFECTING THEM. OVERALL COVERAGE IS NOT EXPECTED TO BE WIDESPREAD, SO WE WILL CARRY SCATTERED SHOWERS FOR NOW. THERE REMAINS SOME INSTABILITY THIS AFTERNOON, SO THERE IS THE POTENTIAL FOR ISOLATED THUNDERSTORMS LATE THIS AFTERNOON INTO THIS EVENING, SO WE KEEP THE MENTION OF ISOLATED THUNDERSTORMS. IF ANY STORMS DID DEVELOP, WITH PW VALUES AROUND 1.0-1.5 INCHES, THEY COULD PRODUCE LOCALLY BRIEF HEAVY RAIN; LOCALLY GUSTY WINDS ARE POSSIBLE AS WELL. && .SHORT TERM /WEDNESDAY/... THE FRONT IS EXPECTED TO HAVE PASSED TO OUR SOUTH BUY WEDNESDAY MORNING, BUT MAY HANG AROUND THE VERY FAR SOUTHERN DELMARVA UNTIL MID-LATE MORNING. THERE ARE A COUPLE OF MORE VORTICITY IMPULSES THAT ARE FORECAST TO SLIDE ACROSS THE AREA WEDNESDAY. THERE WILL REMAIN DECENT MOISTURE AROUND BEHIND THE FRONT, WITH PW VALUES NEAR 1.0-1.25 INCHES, SO WE WILL KEEP ISOLATED/SCATTERED SHOWERS IN THE FORECAST THROUGH THE DAY WEDNESDAY. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... OVERVIEW... MID-LEVEL RIDGE SLOWLY MOVES OVER THE NORTHEAST CONUS THU THRU SAT...WITH WEAK S/WV DISTURBANCES TRAVERSING IT. MEANWHILE...A CUT-OFF LOW DEVELOPS INVOF THE SOUTHEAST US COAST...AND THIS MAY ACQUIRE SUBTROPICAL CHARACTERISTICS DURING THIS TIME FRAME. OVERALL...THERE WILL BE A GENERAL BLOCKING PATTERN ALONG THE EAST COAST WHICH MAY BECOME REX-LIKE ATTMS. THIS WILL LEAD TO A RIDGE OF HIGH PRES AT THE SURFACE THROUGH THE WEEKEND...AND GRADUALLY GIVE WAY TO A COOL FRONT APPROACHING FROM THE NW BY EARLY NEXT WEEK. GENERALLY FAIR WX EXPECTED THRU THE WEEKEND... WITH AN INCREASING CHANCE OF SHRA/TSRA WITH THE APPROACH OF COOL FRONT SUN THROUGH EARLY NEXT WEEK. MAX TEMPERATURES WILL BE NEAR AVERAGE THRU THE PERIOD...COOLER NEAR THE COAST THU THROUGH SAT WITH ONSHORE FLOW. BY SUNDAY...THE AIRMASS MAY TURN INCREASINGLY HUMID. DAILIES... WEDNESDAY NIGHT...A WEAK S/WV WILL MOVE THROUGH THE REGION WITH FAVORABLE JET DYNAMICS. THIS WILL LEAD TO SOME OVERRUNNING ALONG A SLOW MOVING FRONTAL BOUNDARY JUST TO OUR SOUTH. WEAK LIFT AND LIMITED MOISTURE MAY SUPPORT SOME -SHRA OVER THE SOUTHWEST CWA. THURSDAY AND FRIDAY...BOTH DAYS WILL FEATURE A WEAK S/WV MOVING THRU THE REGION DURING THE AFTERNOON TIME FRAME. THIS INDUCES A WEAK SFC TROF...WITH A SEA-BREEZE ALONG THE COAST...WHICH WILL ENHANCE SFC CONVERGENCE. THERE WILL BE MORE MOISTURE AVAILABLE ON THURSDAY...SO -SHRA ARE POSSIBLE...MAINLY NORTHWEST OF THE I-95 CORRIDOR. STABILITY INDICES DO NOT SUPPORT THUNDER ATTM. ALSO...THERE MAY BE SOME PATCHY FOG FRI AM...MAINLY OVER THE NORTHWEST INTERIOR...PER SYNOPTIC PATTERN AND MODEL SOUNDINGS. SATURDAY AND SUNDAY...RIDGE BUILDS SURFACE AND ALOFT ON SAT... AND GRADUALLY MOVES SOUTHEAST ON SUNDAY. SFC FLOW GRADUALLY VEERS FROM THE SOUTHEAST ON SATURDAY TO SOUTHWEST ON SUNDAY. A COOL FRONT WILL APPROACH THE SAINT LAWRENCE VALLEY BY 00Z SUNDAY...WITH THE GFS MUCH MORE PROGRESSIVE THAN THE EURO THEREAFTER WITH THE SOUTHWARD PROGRESSION OF THE FRONT. GIVEN THE BLOCKING PATTERN ALONG THE EAST COAST...AND THE RIDGE ANCHORED OVER THE MID-ATLANTIC...FAVOR THE SLOWER SOLUTION. FEEL GENERAL SUBSIDENCE WILL KEEP THE COLUMN DRY/CAPPED ACROSS THE CWA...BUT CANNOT RULE OUT -SHRA/TSRA MAKING IT INTO THE NW PORTION OF THE CWA ON SUN AFTN. MONDAY AND TUESDAY...AS THE COOL FRONT APPROACHES...THERE WILL BE GREATER MOISTURE, LIFT, AND INSTABILITY AVAILABLE. GIVEN A SLOW FRONTAL PASSAGE WITH AMPLE GULF/SUBTROPICAL MOISTURE, AND FAVORABLE JET DYNAMICS...HEAVY RAINFALL IS POSSIBLE DURING THIS TIME FRAME. && .AVIATION /19Z TUESDAY THROUGH SUNDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. WE CONTINUE A VFR FORECAST THROUGH THE TAF PERIOD. THERE REMAINS THE CHANCE FOR SCATTERED SHOWERS LATE THIS AFTERNOON INTO THE EVENING HOURS, BEFORE A SHOWER-LESS PERIOD EXPECTED OVERNIGHT. HOWEVER, SCATTERED SHOWERS ARE ONCE AGAIN POSSIBLE ON WEDNESDAY. THERE IS ALSO THE POSSIBILITY FOR THUNDERSTORMS THIS AFTERNOON INTO THE EARLY EVENING, BUT WE KEPT THEM OUT OF THE TAFS AS CONFIDENCE IN OCCURRENCE IS LOW. IF ANY HEAVY SHOWERS/THUNDERSTORM DID AFFECT A TAF SITE, THEY COULD BRIEFLY REDUCE CIGS AND/OR VSBYS, BUT AGAIN CONFIDENCE WAS LOW IN THIS HAPPENING, SO WE HAVE AS LOW AS 6SM FORECAST. GUIDANCE EARLIER WAS SHOWING THE POTENTIAL FOR MVFR CIGS/VSBYS AROUND DAYBREAK WEDNESDAY INTO THE DAY, BUT HAS NOW BACKED OFF OF THIS POTENTIAL. FOR NOW WE ONLY HAVE A SCATTERED DECK AROUND 2,000-2,500 FEET IN THE FORECAST. WINDS BEHIND THE FRONT WILL START OUT WEST-NORTHWEST, THEN EVENTUALLY BECOME NORTHEAST OVERNIGHT INTO WEDNESDAY MORNING. OUTLOOK...00Z THU THRU 00Z MON WED NIGHT AND THU...GENERALLY VFR...EXCEPT MVFR POSSIBLE IN -SHRA... MAINLY CONFINED TO PHL, PNE, ILG, ABE, RDG. FRI THRU SAT NIGHT...VFR CONDITIONS EXPECTED. SUN...VFR CONDITIONS MAY DETERIORATE TO MVFR OVER THE INTERIOR IN AFTN SHRA/TSRA. && .MARINE... SUB-SMALL CRAFT ADVISORY CONDITIONS ARE EXPECTED TONIGHT INTO WEDNESDAY. SEAS WILL REMAIN 3-4 FEET, AND SOUTH-SOUTHWEST WINDS MAY GUST AROUND 20 KNOTS AT TIMES AHEAD OF THE COLD FRONT. HOWEVER, AS THE FRONT PASSES THROUGH, WINDS WILL DIMINISH AND BECOME NORTHEAST, STARTING FROM NORTH TO SOUTH DURING WEDNESDAY. OUTLOOK...00Z THU THRU 00Z MON THU THRU SAT...PERSISTENT ONSHORE OUT OF THE SOUTHEAST. WINDS ARE EXPECTED TO REMAIN BELOW SCA CRITERIA. HOWEVER...THERE IS A LOW PROBABILITY THAT SEAS MAY APPROACH SCA LEVELS BY SATURDAY. SUN...SUB-SCA CONDITIONS EXPECTED. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...FRANCK NEAR TERM...ROBERTSON SHORT TERM...ROBERTSON LONG TERM...FRANCK AVIATION...FRANCK/ROBERTSON MARINE...FRANCK/ROBERTSON

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