AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 400 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 SEMBLANCE 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/... HIGHLIGHTS... * HIGH PRES SAT AND SUN * A COLD FRONT WILL CROSS THE REGION MON NIGHT INTO TUE * HIGH PRES WITH DRY AND SEASONABLE CONDITIONS RETURN LATE NEXT WEEK OVERALL MODEL DISCUSSION... MODELS HAVE SOME SYNOPTIC AGREEMENT BUT ARE SPATIALLY DIFFERENT IN REGARDS TO SFC REFLECTION OF A SHORTWAVE DIVING INTO LONG WAVE TROF OVER QC SAT. WHILE ALL AGREE THAT THERE WILL BE A WEAK SFC LOW PRES SOMEWHERE IN THE VICINITY OF THE BENCHMARK...GFS AND EUROPEAN SUGGEST IT LAY GENERALLY E...WHILE MOST GEFS AND AND NAM KEEP IT JUST S OF THE BENCHMARK. THIS WILL ULTIMATELY DEFINE PRECIP CHANCES FOR EARLY SAT...BUT IN ANY CASE THE QUICK MOVING WAVE WILL USHER IN DRY CAA AS THE WAVE PIVOTS TO THE E. AFTER THAT...MODELS ARE IN GOOD AGREEMENT THAT DRY HIGH PRES WILL BUILD OVER THE REGION THROUGH SUN NIGHT AT THE EARLIEST. THEN...WHILE OVERALL SYNOPTIC TREND CONTINUES TO BE WELL AGREED UPON...THERE ARE FAIRLY SIGNIFICANT TIMING DIFFERENCES. A FAIRLY ROBUST LONGWAVE TROF WILL BEGIN TO DIVE INTO SRN ON AND QC WITH ATTENDANT SFC LOW AND COLD FRONT APPROACHING FROM THE NW. AT THIS POINT THE EUROPEAN IS AN OUTLIER IN SUGGESTING THERE IS AN ADVANCING SHORTWAVE FROM THE S. FOR NOW...WILL TEND TOWARD THE GEFS AND GFS AND PUSH THE COLD FRONT THROUGH DURING THE DAY TUE. THIS ALSO FITS PREVIOUS FORECAST. AFTER THIS FROPA...MODELS THEN AGAIN CONTINUE TO AGREE THAT FAIRLY COLD HIGH PRES PUSHES OVER SNE INTO LATTER PORTIONS OF THE WEEK. DETAILS... SAT... ELONGATED LOW PRES/FRONTAL SYSTEM S OF SNE WILL BEGIN TO SLOWLY PUSH E OF THE REGION DURING THE DAYLIGHT HOURS SAT. CURRENTLY...THE MODELS KEEP THE SFC LOW S/E OF THE BENCHMARK...SUGGESTING FRONTOGENETICAL FORCING REMAINS S OF THE AREA. THEREFORE...WITH SOME LEFT OVER MOISTURE TRAPPED AROUND A WELL MIXED BOUNDARY LAYER IN INCREASING SUNSHINE...DIURNAL CU WILL LIKELY DEVELOP AS THE MID LVLS CONTINUE TO COOL WITH INCREASING LLVL LAPSE RATES. ATTM...THERE MAY BE ENOUGH LLVL INSTABILITY TO INITIATE A SPOT LOW TOPPED -SHRA...BUT FEEL THAT IT WILL CONTINUE TO PROGRESSIVELY DRY WITH INCREASED SUBSIDENCE PROVIDING A CAP. THE GFS AND EUROPEAN SOUNDINGS FAVOR THIS DRIER SCENARIO...WHILE THE NAM REMAINS AN OUTLIER WITH MORE ROBUST CAPE FROM DWPTS THAT ARE LIKELY WELL TO HIGH GIVEN THE ENTRAINING AIRMASS. EVEN WITH WHAT WILL LIKELY BE A FAIR AMOUNT OF DIURNAL CU...WRN PORTIONS OF THE FA WILL LIKELY BE ABLE TO MIX TO AROUND H85 BY THE PEAK OF THE AFTERNOON. WITH H85 TEMPS AROUND THE 14C MARK...SOME AREAS THAT SEE ENOUGH SUNSHINE WILL LIKELY REACH INTO THE MID 80S. MAX TEMPS WILL LIKELY REMAIN COOLER TO THE E THANKS TO CLOUDS FOR MUCH OF THE DAY. SAT NIGHT THROUGH SUN NIGHT... FOLLOWING THE EXITING SFC LOW COOL CAA AND AND A FAIR AMOUNT OF SUBSIDENCE ALOFT WILL ALLOW SKIES TO CLEAR AND WINDS TO DROPOFF OVERNIGHT AS THE BL DECOUPLES SAT NIGHT. THEREFORE...WITH DWPTS DIPPING WELL INTO THE 50S...RAD COOLING WILL ALLOW TEMPS TO APPROACH THE UPPER 50S AS WELL. HIGH PRES WILL REMAIN IN CONTROL SUN AND WITH FULL MIXING TO H85 IF NOT H8... THE H85 TEMPS OF 14 TO 15C WILL BE REALIZED ACROSS THE BOARD...WHICH WILL YIELD TEMPS IN THE 80S. LIGHT FLOW SHOULD ALLOW SEA BREEZE DEVELOPMENT...KEEPING COASTAL LOCATIONS COOLER. THE HIGH PRES MOVES OFFSHORE ALLOWING RETURN FLOW TO DEVELOP OVER SNE SUN NIGHT. INCREASING UPPER LLVL CLOUD COVER AND WARMER DWPTS WILL KEEP MINS SLIGHTLY WARMER SUN NIGHT. TUE AND TUE NIGHT... A FAIRLY COOL AND ROBUST WAVE AND ATTENDANT LOW PRES WILL PUSH THROUGH QC INTO NRN NEW ENGLAND LATE TUE NIGHT. THE MOST LIKELY IMPACT ON SNE WILL BE FROM ITS TRAILING COLD FRONT SOMETIME IN THE MON NIGHT TO TUE PERIOD. THE EUROPEAN IS FASTER...SUGGESTING THE FRONT IS ALONG THE S COAST BY 12Z TUE...WHILE THE GFS AND GEFS AR SLOWER...PUSHING IT THROUGH WRN MA DURING THE MORNING...AND THEN STALLING IT OVER THE S COAST BY AFTERNOON. THIS WILL HAVE A BIG IMPACT ON FINAL PRECIP/TSTM CHANCES...AS TSTMS WILL BE DIFFICULT TO GENERATE OVERNIGHT WITH LITTLE ELEVATED INSTABILITY SUGGESTED. HOWEVER...THERE IS A FAIR AMOUNT OF CAPE AVAILABLE DURING THE DAY TUE...AND AS SUCH THE GFS/GEFS SOLN SUGGESTS MORE WIDESPREAD TSTM WITH MLCAPE APPROACHING 1000 J/KG. LIKE THE NIGHT CREWS ASSESSMENT IN LEAVING SOME POPS WITH ISOLD TS INTO THE DAY TUE. SO WILL TREND ANY CHANGES IN THE GRIDS TOWARD THIS SOLN. WED THROUGH LATE WEEK... FOLLOWING THE PASSAGE OF THIS FAIRLY ROBUST FRONT...COLD AIR WILL ABRUPTLY PUSH INTO THE REGION AS UNSEASONABLY STRONG HIGH PRES BEGINS TO MOVE OVER THE REGION. THEREFORE...WILL CONTINUE IN SUGGESTING A DRY AND SEASONABLE FORECAST FOR THE LATTER PORTIONS OF THE WEEK. && .AVIATION /20Z 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 TUESDAY... SAT THRU SUN NIGHT... LINGERING MVFR CIGS AND VSBYS OVER TERMINALS E OF ORH...AND THE CAPE AND ISLANDS WILL GRADUALLY LIFT TO VFR DURING THE MORNING SAT. OTHERWISE VFR THROUGH SAT NIGHT WITH HIGH PRES BUILDING OVER THE REGION. LIGHT AND VRB WINDS THROUGH MUCH OF THE PERIOD. MEDIUM TO HIGH CONFIDENCE. MON... MEDIUM CONFIDENCE VFR. HIGH PRES BEGINS TO SHIFT E WITH SW WINDS BUILDING OVER THE REGION. HIGH AND MID CLOUDS MAY BUILD OVER BY THE EVENING...BUT SUSPECT INLAND TERMINALS TO REMAIN VFR. LOW CONFIDENCE IN SOME FOG AND STRATUS WITH MVFR/IFR CIGS AND VSBYS ALONG CAPE AND ISLANDS ESPECIALLY LATE IN THE DAY. MON NIGHT INTO TUE... A SLOW MOVING COLD FRONT WILL BRING LOCALIZED MVFR/IFR CIGS AND VSBYS IN -SHRA/TSTMS LATE MON NIGHT INTO THE DAY TUE. BEST CHANCE FOR TSTMS WILL BE DURING DAYLIGHT HOURS TUE. OTHERWISE VFR INLAND. FOG AND STRATUS LIKELY TO CONTINUE OVER CAPE AND ISLANDS WITH MVFR/IFR CIGS AND VSBYS. MEDIUM CONFIDENCE IN OVERALL TREND...LOW CONFIDENCE IN TIMING. && .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... SAT INTO SUN... SLOW MOVING LOW PRES WILL EXIT WATERS TO THE E WITH DIMINISHING WINDS. HOWEVER...SEAS MAY REMAIN ABOVE 5 FT THRESHOLDS ESPECIALLY OVER SRN AND SERN OUTER WATERS. SCA MAY BE NEEDED TO COVER THIS THREAT. MON NIGHT... WINDS AND SEAS DROP BELOW SCA THRESHOLDS OVERNIGHT MON NIGHT. MON INTO TUE... A SLOW MOVING COLD FRONT WILL APPROACH THE WATERS FROM THE W. WINDS NEAR SHORE MONDAY MAY BRIEFLY GUST TO 25 KT DURING THE AFTERNOON. SW FETCH WILL ALLOW SEAS TO GRADUALLY BUILD...AND MAY REACH 5 FT BY TUE. OTHERWISE...-SHRA/TSTMS MAY AFFECT THE WATERS ESPECIALLY TUE AS THE FRONT CROSSES THE WATERS LATE IN THE DAY. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...WTB/DOODY