AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 432 AM EDT FRI JUL 8 2011 .SYNOPSIS... A FRONT WILL REMAIN STALLED ALONG THE SOUTH COAST OF NEW ENGLAND TODAY. A LOW PRESSURE WILL MOVE ALONG THIS FRONT AND PASS SOUTH OF NEW ENGLAND TONIGHT AND EARLY SATURDAY. HIGH PRESSURE RETURNS BRIEFLY FOR SATURDAY NIGHT INTO EARLY MONDAY. A COLD FRONT SHOULD GRADUALLY SLIDE THROUGH THE REGION THROUGH TUESDAY...BRINGING A CHANCE OF SHOWERS AND THUNDERSTORMS. HIGH PRESSURE RETURNS WEDNESDAY INTO THE END OF THE WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... MID-LEVEL INSTABILITY HAS INCREASED...AND STARTING TO SEE SIGNS OF GOOD MOISTURE LOW-LEVEL MOISTURE TRANSPORT. DEW POINTS ALONG THE SOUTH COAST...WHICH IS WHERE A STALLED FRONT WAS LOCATED EARLY THIS MORNING...HAVE CLIMBED TO NEAR 70F. LATEST MESOANALYSIS FROM SPC SHOWING 20 KTS OF EFFECTIVE BULK SHEAR...WHICH HAS TURNED OUT TO PROVIDE ENOUGH ORGANIZATION TO GENERATE ISOLATED SHOWERS AND THUNDERSTORMS THIS MORNING. GIVEN THE CONVECTIVE NATURE OF THE PRECIPITATION THIS MORNING... HAVE LOW CONFIDENCE IN TIMING AND COVERAGE FOR ANY SPECIFIC LOCATION...ESPECIALLY THIS MORNING. WILL SLOWLY RAMP UP RAINFALL CHANCES IN THIS FORECAST TO LIKELY AROUND NOON...MAINLY SOUTH OF THE MASS PIKE. TEMPERATURES WILL BE SIGNIFICANTLY LOWER TODAY COMPARED TO THE PAST SEVERAL...BUT THE COMBINATION OF ELEVATED INSTABILITY AND PROXIMITY OF A STALLED FRONT...SHOULD BE SUFFICIENT TO TRIGGER CONVECTION LATER TODAY. USED A BLEND OF THE GUIDANCE FOR TEMPERATURES...BUT MODIFIED GUIDANCE DEW POINTS TO BRING THEM UP QUICKER. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/... A MID-LEVEL SHORTWAVE CROSS OUR REGION THIS EVENING...AND WILL LIKELY GENERATE A WEAK SURFACE WAVE ALONG THE FRONTAL BOUNDARY AS IT MOVES BY. NOT VERY CONFIDENT IN THE DETAILS OF SUCH A WEAK FEATURE. AS SUCH...USED A BLEND OF THE GFS AND NAM TO PROVIDE SOME TIMING. DRIER WEATHER RETURNS FOR SATURDAY AS A HIGH PRESSURE ARRIVES FROM SOUTHERN CANADA AND FINALLY PUSHES THIS FRONT OFFSHORE. USED A BLEND OF THE GUIDANCE FOR TEMPERATURES. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... MAIN POINTS... *COOLER AND DRIER WEATHER ASSOC WITH HIGH PRES FOR SUNDAY *COLD FRONT WITH SHOWERS AND THUNDERSTORMS MONDAY INTO TUESDAY *UNSEASONABLY COOL WEATHER BEGINNING WEDNESDAY INTO THE END OF THE WEEK *ANOTHER WET WEATHER SYSTEM POSSIBLE INTO THE WEEKEND OVERVIEW... 0Z NAM HAS FINALLY COME INTO CONSENSUS WITH MDL SOLNS...MORESO WITH THE OUTCOMES FCST BY THE GFS FOR THE LAST SEVERAL DAYS CONCERNING SHRTWV ENERGY THRU THE SRN BRANCH OF THE MID-LVL TROF INTO THE END OF THIS WEEK USHERING CYCLOGENESIS OFF THE SHORELINE OF THE DELMARVA PENINSULA AND ELONGATING ALONG THE STALLED QUASI-STATIONARY FRONTAL BOUNDARY S OF NEW ENGLAND. AS SUCH FOR THE EXTENDED PD PLACED GREATER WEIGHT UPON THE 0Z GFS...WHILE TAKING INTO CONSIDERATION THE CONSISTENT NATURE OF THE ECMWF. WEIGHTED MORESO WITH BIAS-CORRECTED MAV GUIDANCE TRANSITIONING TO THE BIAS-CORRECTED MOS GUIDANCE. DETAILS... SATURDAY NIGHT THRU SUNDAY NIGHT... SFC HIGH PRES SETTLES ACROSS THE RGN SATURDAY NIGHT INTO SUNDAY MORNING...GRADUALLY PROGRESSING E INTO SUNDAY NIGHT...ALLOWING FOR A PERIOD OF SEASONABLY/DRY WX. LGT/VRB SFC FLOW COUPLED WITH NVA- SUBSIDENCE AND MUCH DRIER /SLIGHTLY COOLER/ AIR WILL MAKE FOR A GOOD CASE OF NOCTURNAL COOLING AT THE SFC FOR SUNDAY MORNING LOWS. EXPECTING LOW SFC DEWPOINTS ATTENDANT WITH THE SFC HIGH PRES WILL ALLOW FOR MINS TO FALL INTO THE MID-UPR 50S ACROSS THE N/W NH AND MA...INTO THE LOW 60S FURTHER S AND CLOSER TO SHORE. SUNDAY WILL SEE RETURN ONSHORE SFC SLY FLOW AS THE SFC HIGH SHUNTS E...WITH SW FLOW AT MID-LVLS ADVECTING WARM AND MOIST AIR OVER THE RGN. SFC S FLOW MAY BE LIGHT ENOUGH TO ALLOW SEA-BREEZES ALONG THE E SHORELINE. OTHERWISE EXPECT WITH THE MOISTURE RETURN FOR SOME CU DVLPMNT TOWARDS THE AFTN...YET ANTICYCLONIC FLOW WILL STILL BE PREVALENT EXPECT SCT /RATHER THAN BKN/ CU MIXING UP TO H85/5-7 KFT... ESPECIALLY ALONG W SLOPES OF TERRAIN WHERE MID-LVL MOIST AND Q-VECT CONV MAY BE BETTER DEFINED. RETURN OF H925 TEMPS TO +18-20C SHOULD ALLOW SFC TEMPS TO REBOUND INTO THE UPR 70S/LOW 80S. SUNDAY NIGHT WILL CONTINUE TO SEE CONTINUED WARMING/MOISTENING AT MID-LVLS AIDED BY W/SW FLOW ALOFT. SHOULD BE A SLIGHTLY WARMER NIGHT IN TERMS OF MINS AS MID-UPR LVL CLOUDS WILL LIKELY BE STREAMING ACROSS THE RGN ALONG THE MEAN LYR FLOW AHEAD OF THE NEXT SYS FOR THE BEGINNING OF THE WEEK. MONDAY THRU TUESDAY NIGHT... MATURATION PHASE OF LOW PRES ACROSS ERN CANADA WILL AMPLIFY THE E-W THERMAL AXIS/H3 JET STREAK IN PROXIMITY OF THE N GRT LKS RGN INTO N NEW ENGLAND THEREBY AMPLIFYING ATTENDANT SHRTWV DISTURBANCES ALONG THE MEAN LYR FLOW. ALTHO MDL DISCREPANCIES EXIST AMONGST THE GFS/ ECMWF IN HANDLING THE AFOREMENTIONED FEATURES...THERE IS AGREEMENT UPON A GENERAL TREND IN WHERE SHRTWV DISTURBANCES SHOULD AT LEAST PROVIDE ENHANCED ASCENT OF AVAILABLE MOISTURE/INSTABILITY THAT HAS BEEN PUMPED ACROSS THE RGN ALONG THE WRN PERIPHERY OF THE DEPARTING SFC HIGH PRES...WITH BETTER DYNAMICS CONFINED TO N NEW ENGLAND MONDAY NIGHT INTO TUESDAY. HAVE GREATER CONFIDENCE IN 0Z GFS OUTCOME...AMPLIFICATION OF SHRTWV ENERGY THRU N NEW ENGLAND SHOULD DRAG COOLER AIR SEWD ALONG AND BEHIND A COLD FRONT...ESPECIALLY AT MID-LVLS...WHICH SHOULD PROVIDE ENOUGH FRONTOGENETICAL FORCING OF WARM/MOIST UNSTABLE AIR ALONG AND AHEAD. TIMING OF THIS FRONTAL BOUNDARY REMAINS STILL IN QUESTION...AND WHETHER INSTABILITY ALONG AND AHEAD WILL BE SFC BASED. SHOULD CONVECTION FIRE IN THE VICINITY OF THE E GRT LKS AND PROGRESS E WITH THE COLD FRONT MON AFTN CONTINUING INTO TUE...NOT CERTAIN IF SFC DESTABILIZATION WILL OCCUR WITH POTENTIAL CLOUD COVER OVERSPREADING THE RGN FROM THE W. DETAILS ARE STILL SKETCHY AT THIS TIME...NEVERTHELESS FEEL BEST POP CHS FOR SHOWERS/THUNDERSTORMS WILL BE ON TUESDAY INTO TUESDAY NIGHT AS WARM/MOIST UNSTABLE AIR...AIDED BY STRONG AND POTENTIALLY GUSTY SW FLOW...WILL BE READILY AVAILABLE ALONG AND AHEAD OF THE EXPECTED COLD FRONT. WEDNESDAY INTO THE END OF THE WEEK... MDL SOLNS CONTINUE TO HIGHLIGHT A STRONG SFC HIGH PRES RIDGE IN CONTROL OF THE RGNS WX BRINGING COOLER AND MUCH DRIER CONDITIONS TO THE RGN. INITIALLY MODEST N/NW FLOW...WITH GUSTS 20-25 KTS...BEHIND THE EXITING SYS WILL USHER SOME VERY COOL MID-LVL AIR SEWD WITH H925 TEMPS AS +10C. WILL SEE MIN TEMPS FALL INTO THE LOW TO MID 50S... WARMER ALONG THE SHORE. SOME AREAS REPORTING UPR 40S FOR MINS WED/THURS MORN IS NOT OUT OF THE QUESTION. MAX TEMPS FOR THESE TWO DAYS WILL RANGE IN THE LOW TO MID 70S...COOLER ALONG THE SHORE. VERY UNSEASONABLE WX! WILL SEE LGT/VRB NLY FLOW ON THURS GRADUALLY VEER OUT OF THE S/SW BY FRIDAY...SO THEREAFTER EXPECT A GRADUAL WARMING TREND ALONG AND AHEAD OF ANOTHER WET WX SYS FOR THE WEEKEND. ANTICIPATE MOSTLY CLEAR CONDITIONS FOR MUCH OF THE TIMEFRAME... PERHAPS DIURNAL CU DURING THE DAY WEDNESDAY...WITH INCREASING CLOUDS RETURNING INTO LATE FRI INTO SAT. && .AVIATION /08Z FRIDAY THROUGH TUESDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT MODERATE...30 PERCENT TO 60 PERCENT HIGH...GREATER THAN 60 PERCENT THROUGH 12Z...HIGH CONFIDENCE VFR FOR MOST TERMINALS. IFR CONDITIONS ACROSS THE ISLANDS FROM KBID-KMVY-KACK AND IMMEDIATE SOUTH COAST. AREAS OF MVFR ACROSS COASTAL PLAINS OF SOUTHEAST MA AND SOUTHERN RI. TODAY AND TONIGHT...MEDIUM CONFIDENCE VFR FOR MAINLAND TERMINALS. LOW CONFIDENCE IN OCCASIONAL -SHRA/TSRA OVER ANY GIVEN TERMINAL. GREATEST RISK FOR ANY SHRA/TSRA WOULD BE TOWARD CAPE COD AND NANTUCKET. LOCALIZED MVFR/IFR IN THESE -SHRA/TSRA. CAPE AND ESPECIALLY KACK MAY SEE MVFR/IFR IN FOG AND STRATUS CONTINUE THROUGH MOST OF THIS MORNING. SATURDAY...HIGH CONFIDENCE VFR DEVELOPS BY MID-MORNING MOST LOCATIONS. EXCEPT MAY BE ACROSS CAPE COD AND NANTUCKET WHERE PATCHY FOG MAY LINGER A BIT LONGER. EXPECTING VFR ALL AREAS BY AFTERNOON. KBOS TERMINAL...HIGH CONFIDENCE VFR. SCATTERED SHRA/TSRA... ESPECIALLY THIS AFTERNOON AND EVENING...COULD RESULT IN MVFR CIGS/VSBYS. OUTLOOK...SATURDAY NIGHT THROUGH TUESDAY... SATURDAY NIGHT INTO SUNDAY NIGHT... MEDIUM CONFIDENCE VFR. N/NW FLOW SATURDAY NIGHT IN WAKE OF THE DEPARTING COLD FRONT BECOMING LGT AND VRB INTO SUNDAY MORNING AND SLOWLY VEERING OUT OF THE S/SW INTO SUNDAY NIGHT. COULD STILL SEE SOME RESIDUAL FOG THRU THE OVRNGT HRS FOR THE WEEKEND ALONG THE SE TERMINALS OUT ALONG THE CAPE/ISLANDS. LOW CONFIDENCE AT THIS TIME. MONDAY INTO TUESDAY NIGHT... MEDIUM CONFIDENCE VFR/MVFR. ANOTHER COLD FRONT APPROACHING THE TERMINALS ALONG AND AHEAD OF WHICH SHRA/TSRA WILL DEVELOP. FEEL LOW VSBY/CIG IMPACTS WILL BE PRIMARILY SUITED FOR THE N/W TERMINALS MONDAY...TRANSITIONING SEWD TOWARDS SE NEW ENGLAND INTO TUESDAY. S/SW FLOW GUSTING AT TIMES 15 TO 20 KTS PSBL. ANY TSRA IMPACTING THE TERMINALS WILL LIKELY RESULT IN TEMPO IFR/LIFR VSBYS AND CIGS. SIGNIFICANT WEATHER SHOULD BE THRU THE TERMINALS BY TUESDAY NIGHT. && .MARINE... WINDS AND SEAS EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY THRESHOLDS THROUGH TONIGHT. AREAS OF FOG AND LOW CLOUDS WILL RESULT IN POOR VSBYS...MAINLY ACROSS THE SOUTHERN COASTAL WATERS FOR A PORTION OF THIS MORNING. THE PASSAGE OF A WEAK SURFACE LOW AND THE ARRIVAL OF A STRONG SOUTHERLY SWELL SATURDAY IS EXPECTED TO BUILD SEAS TOWARDS 5 FT ACROSS THE OUTER SOUTHERN COASTAL WATERS. OUTLOOK...SATURDAY NIGHT THROUGH TUESDAY NIGHT... SATURDAY NIGHT INTO SUNDAY NIGHT... SEAS OF AROUND 5 TO 6 FEET WILL CONTINUE ACROSS THE S OPEN WATERS AS A RESULT OF SWELL GENERATED BY SLY WINDS S OF A STATIONARY FRONTAL BOUNDARY DRAPED S OF NEW ENGLAND. ANTICIPATE SEAS BELOW SCA THRESHOLDS BY SUNDAY. MONDAY INTO TUESDAY NIGHT... A COLD FRONT APPROACHES THE REGION ALONG AND AHEAD OF WHICH S/SW WINDS WILL INCREASE...WITH GUSTS UP TO 25 KTS POSSIBLE PRIMARILY FOR TUESDAY. WILL SEE SEAS BUILD IN CONCERT WITH STRONG AND GUSTY SW WINDS UP TO 5 TO 6 FEET FOR THE OPEN WATERS AND PERHAPS FOR SOME OF THE WATERS ALONG THE S AND CLOSE TO SHORE. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...WTB/SIPPRELL