AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 354 PM EDT THU JUL 7 2011 .SYNOPSIS... A FRONT WILL REMAIN STALLED ALONG THE SOUTH COAST OF NEW ENGLAND TONIGHT. WEAK HIGH PRESSURE WILL BUILD ACROSS NORTHERN NEW ENGLAND TONIGHT. LOW PRESSURE WILL MOVE ALONG THE FRONT AND PASS SOUTH OF NEW ENGLAND FRIDAY NIGHT AND EARLY SATURDAY. HIGH PRESSURE WILL FOLLOW SUNDAY THEN AN APPROACHING COLD FRONT WILL BRING A CHANCE OF SHOWERS AND THUNDERSTORMS MONDAY INTO TUESDAY. HIGH PRESSURE BUILDS BACK IN FOR WEDNESDAY && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... WIDELY SCATTERED SHOWERS ALONG THE CONNECTICUT AND RHODE ISLAND COASTLINE. MID AFTERNOON CAPE VALUES WERE AROUND 1000 J/KG IN THIS ZONE WITH A SHARP GRADIENT TO CONVECTIVE INHIBITION JUST OFFSHORE. BUT THE THREE HOUR TREND IS DOWN SHARPLY. EXPECT LINGERING SHOWERS THIS EVENING BUT DISSIPATING WITH SUNSET. NAM-GFS-GGEM SHOW INCREASING CLOUD LEVEL MOISTURE MOVING UP FROM PA TONIGHT. THIS IS CROSSING THE UPPER FLOW...ALTHOUGH THAT FLOW IS TURNING FROM WESTERLY TO SOUTHWESTERLY OVERNIGHT. WITH THE STALLED FRONT IN PLACE THERE IS AN EXISTING ZONE OF LOW LEVEL CONVERGENCE. SOME SEMBANCE OF 850 CONVERGENCE TEAMED WITH 250 MB DIVERGENCE OVER THE EASTERN LAKES...BUT THIS IS WEAK. MEANWHILE...CONVECTION OVER PA IS PRODUCING CLOUDS. THE LEFTOVERS FROM THIS CONVECTION COULD GENERATE MID LEVEL SKY COVER. WE WILL FORECAST INCREASING SKY COVER OVERNIGHT...BUT PRIMARILY MID AND HIGH LEVEL CLOUDS. THE AIRMASS IS SUFFICIENTLY DRY TO MAINTAIN POPS AT SLIGHT CHANCE OR LESS. DEWPOINT TEMPS HAVE DROPPED TO THE 50S NORTH OF THE FRONT BUT LINGER IN THE 60S ALONG THE COAST AND ISLANDS. THE INCREASING CLOUDS WILL SLOW TEMPS FROM FALLING ALL THE WAY TO DEWPOINT...BUT A RANGE OF 55-65 LOOKS REASONABLE. WE USED A BLEND OF MOS WHICH ACHIEVED THIS TARGET. WITH DEWPOINTS IN THE 60S ALONG THE SOUTH COAST...LINGERING CHANCE OF FOG IN THIS AREA. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... UPPER SHORTWAVE DIGS AS IT MOVES FROM THE GREAT LAKES ACROSS NEW YORK. THIS DRAWS MOISTURE NORTH...BUT CROSS-FRONT WIND IS SMALL SO NO A LOT OF MOTIVATION FOR THE STALLED FRONT TO MOVE NORTH ACROSS OUR AREA. THIS KEEPS US IN THE OVERRUNNING ZONE WITH AN EAST FLOW ACROSS SOUTHERN NEW ENGLAND AS A SOUTH TO SOUTHWEST FLOW MOVES UP ACROSS THE SOUTHERN OCEAN. THIS GENERATES A FAIR AMOUNT OF ISENTROPIC LIFT...ROUGHLY 7 MB PER HOUR IS FORECAST BETWEEN THE 300K AND 310K SURFACES. CONDENSATION PRESSURE DEFICITS ARE FORECAST AT 50-70 MB AT 300K /850 TO 900 MB/ ALTHOUGH A LITTLE MORE SATURATED AT 310K WHICH IS INTO THE MID-LEVEL CLOUD DECK. SHORTWAVE MOVES IN THE FLOW ALONG THE SURFACE FRONT LATER FRIDAY AND FRIDAY EVENING. THE MAIN SHORTWAVE ENTERS NEW ENGLAND LATE FRIDAY NIGHT. MOS VALUES BRING LIKELY POPS INTO OUR SOUTHERN AREAS FRIDAY AFTERNOON AND NIGHT. BASED ON THE LIFT AND RELATIVELY DRY AIR BELOW...WE ARE LESS CONFIDENT. AS SUCH WE WILL STAY WITH CHANCE POPS FRIDAY AND FRIDAY NIGHT WITH HIGHEST VALUES ALONG THE SOUTH COAST NEAREST THE STALLED FRONT. AN EAST SURFACE FLOW AND CLOUDS WILL LIMIT MIXING DEPTHS FRIDAY. WE USED TEMPS AT 925 MB TO ESTIMATE MAX TEMPS...AND GOT RESULTS IN THE 70S. WE USED A BLEND OF MOS TO GET THESE VALUES. && .LONG TERM /SATURDAY THROUGH THURSDAY/... MAIN POINTS... *HIGH PRES IN CONTROL FOR SATURDAY INTO SUNDAY *ANOTHER COLD FRONT SLIDES THRU THE REGION MONDAY INTO TUESDAY *DRY AND COOL WEATHER EXPECTED BY MIDWEEK INTO THE END OF THE WEEK OVERVIEW... OF CONCERN IS THE FACT THAT THE LATEST 0Z NAM IS REMAINING CONSISTENT WITH A TROPICAL WAVE DEVELOPING IN THE BAHAMAS AND LIFTING NWD TOWARDS THE MEAN FLOW AND THE S NEW ENGLAND SHORELINE BY THE WEEKEND. STILL THE OUTLIER...THE 21Z SREF HAS COME MORE IN-LINE WITH THE 0Z NAM SOLN. NEVERTHELESS STILL TRENDED MORESO TO THE CONSISTENT 12Z ECMWF WHICH FARED PRETTY WELL IN AGREEMENT WITH THE 0Z GFS...OF WHICH HAS BEEN GOOD ON HANDLING TRENDS CONSISTENTLY... BUT NOT SO MUCH WITH PARTICULARS. DETAILS... SATURDAY THRU SUNDAY NIGHT... RIDGE OF HIGH PRES WILL CONTROL THE RGNS WX LENDING TO A DRY PD. DIURNAL CU EXPECTED FOR SATURDAY WITH SEASONABLE HIGH TEMPS... CONSIDERABLY LESS MUGGY. WILL SEE INITIAL W/NW FLOW BECOME LGT/VRB INTO SUNDAY MORN...BY WHICH TIME SLIGHTLY COOLER AIR WILL HAVE SETTLED ACROSS THE RGN. WITH MOSTLY CLEAR SKIES AND CALM WINDS...MAY SEE UNSEASONABLY LOW TEMPS FOR SUNDAY MORN. INTO SUNDAY SFC WINDS WILL VEER OUT OF THE S/SW AND WILL SEE MUCH WARMER AIR OVERRUNS THE RGN ON THE WRN PERIPHERY OF THE DEPARTING SFC RIDGE OF HIGH PRES. ANTICIPATION OF MOSTLY CLEAR CONDITIONS COULD MAKE FOR A WARM DAY...POTENTIALLY MUGGY AS DEWPOINTS WILL ALSO BE ON THE REBOUND. MID-UPR LVL CLOUDS ON THE INCREASE INTO SUNDAY NIGHT AHEAD OF THE NEXT WX SYS. MONDAY THRU TUESDAY NIGHT... SOME DISCREPANCIES AMONGST MDL SOLNS CONCERNING DISTINCT OUTCOMES... YET THERE IS CONSISTENCY WITH THE OVERALL TREND. SFC COLD FRONT WILL SLIDE ACROSS THE RGN AROUND MIDDAY TUESDAY ALONG AND AHEAD OF WHICH MUCH WARMER AND MOIST AIR WILL BUILD LENDING TO A POTENTIALLY UNSTABLE ENVIRONMENT SUPPORTIVE OF SHOWERS/TSTORMS. MAY SEE AN INITIAL LEE TROF AHEAD OF THE SFC COLD FRONT FOR THE MONDAY AFTN INTO EVNG PD BRINGING CHC POPS FOR THE N/W FCST RGNS...SPREADING SEWD INTO TUE. MUCH COOLER AIR WILL SETTLE ACROSS THE RGN BEHIND THE FRONT AS S/SW WINDS...GUSTING AT TIMES AROUND 15 TO 20 KTS IMMEDIATELY ALONG AND AHEAD OF THE SFC COLD FRONT...SHIFT OUT OF THE W/NW. EXPECT MOST OF THE ACTIVITY TO BE OUT OF THE FCST RGN AFTER MIDNIGHT WEDNESDAY. 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. WILL SEE LGT/VRB NLY FLOW INITIALLY GRADUALLY VEER OUT OF THE S/SW BY FRIDAY. ANTICIPATE MOSTLY CLEAR CONDITIONS...PERHAPS DIURNAL CU DURING THE DAY WEDNESDAY... AND A GRADUAL WARMING TREND IN MAX/MIN TEMPS FOR THE PERIOD. && .AVIATION /19Z THURSDAY THROUGH TUESDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT MODERATE...30 PERCENT TO 60 PERCENT HIGH...GREATER THAN 60 PERCENT THIS EVENING... HIGH CONFIDENCE VFR. PRIMARY CONCERN IS WIND SHIFT TO NORTHEAST ESPECIALLY ALONG THE MASS EAST COAST. IT IS TAKING ITS TIME AS WEAK HIGH PRESSURE BUILDS TO OUR NORTH. EXPECT WINDS TO EVENTUALLY SHIFT TO NORTHEAST THIS EVENING OR EARLY TONIGHT. SECONDARY CONCERN IS THE CONVECTIVE POTENTIAL. WIDELY SCATTERED SHOWERS HAVE FORMED ALONG THE SOUTH COAST OF RI AND CT. THERE IS A POTENTIAL FOR WIDELY SCATTERED THUNDERSTORMS IN THIS AREA. POSSIBLE BRIEF MVFR CIGS/VSBYS IN ANY WIDELY SCATTERED SHOWERS. TONIGHT... HIGH CONFIDENCE VFR MOST AREAS. INCREASING MID TO HIGH CLOUDS OVERNIGHT. PATCHY FOG WITH IFR CEILINGS/VSBYS POSSIBLE ALONG THE SOUTH COAST. FRIDAY AND FRIDAY NIGHT... MEDIUM CONFIDENCE VFR MOST AREAS. POTENTIAL FOR LINGERING IFR IN FOG ALONG THE SOUTH COAST IN THE MORNING. SCATTERED SHOWERS/TSTMS ESPECIALLY IN THE AFTERNOON AND NIGHT WITH POTENTIAL FOR MVFR CEILINGS/VSBYS. KBOS TERMINAL... HIGH CONFIDENCE VFR. EXPECT THE SURFACE FLOW TO TURN NORTHEAST AND EAST TONIGHT. SCATTERED SHOWERS/TSTMS FRIDAY AFTERNOON AND NIGHT WITH POTENTIAL FOR MVFR CIGS/VSBYS. OUTLOOK...SATURDAY THROUGH MONDAY NIGHT... SATURDAY... MEDIUM CONFIDENCE VFR/MVFR. ANTICIPATE LOW CLOUDS AND POOR FLIGHT CONDITIONS FOR THE S TERMINALS...ESPECIALLY ALONG THE CAPE/ISLANDS... WITH THE POTENTIAL FOR IFR VSBY/CIG RESTRICTIONS...POTENTIALLY LIFR FOR ACK...WITH THE ANTICIPATION OF FOG DEVELOPMENT DURING THE MORNING HRS ON FRI. WILL SEE E/SE ONSHORE FLOW. SHRA/TSRA WILL BE PSBL WHICH WILL LEND FOR THE POTENTIAL OF TEMPO LOW CIGS/VSBYS. SATURDAY NIGHT INTO SUNDAY NIGHT... MEDIUM CONFIDENCE VFR. COULD SEE SOME LINGERING FOG IMPACTS FOR THE SE TERMINALS ALONG THE CAPE/ISLANDS...LOW CONFIDENCE AT THIS TIME. LGT/VRB WINDS GRADUALLY VEERING OUT OF THE S/SW INTO SUNDAY. MONDAY INTO MONDAY 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. S/SW FLOW GUSTING AT TIMES 15 TO 20 KTS PSBL. && .MARINE... WINDS AND SEAS EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY THRESHOLDS THROUGH FRIDAY NIGHT. AN AREA OF FOG AND LOW CLOUDS MAY REGENERATE TONIGHT WITH AREAS OF POOR VSBYS...MAINLY ON THE SOUTHERN WATERS. OUTLOOK...SATURDAY THROUGH MONDAY NIGHT... SATURDAY-SUNDAY... SEAS BUILDING TO AROUND 5 FEET WITH ELY SWELLS FOR THE S OPEN WATERS SAT INTO SUN IN PROXIMITY TO ENHANCED E FLOW ALONG A STALLED FRONTAL BOUNDARY S OF NEW ENGLAND. MAY SEE POTENTIAL GUSTS AROUND 15 KTS AS WELL. MONDAY... SEAS BUILDING TO AROUND 5 FEET ACROSS THE OPEN WATERS AS S/SW WINDS INCREASE...GUSTING AT TIMES 15 TO 20 KTS...ALONG AND AHEAD OF A SFC COLD FRONT ANTICIPATED TO SLIDE OVER THE WATERS LATE TUESDAY. CANT RULE OUT A GUST IN EXCESS OF 25 KTS. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...WTB/SIPPRELL