Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 232018 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 418 PM EDT WED JUL 23 2014 .SYNOPSIS... A COLD FRONT WILL APPROACH THE REGION TONIGHT TRIGGERING SCATTERED SHOWERS AND THUNDERSTORMS. A FEW STRONG THUNDERSTORMS ARE POSSIBLE WEST OF THE CENTRAL HILLS. SHOWERS WILL LIKELY LINGER INTO THURSDAY SOUTHEAST OF THE BOSTON TO PROVIDENCE CORRIDOR. HIGH PRESSURE BUILDS WITH DRIER WEATHER FOR FRIDAY AND SATURDAY. AN APPROACHING WARM FRONT SUNDAY WILL BRING MORE HUMID UNSETTLED WEATHER FOR THE EARLY PART OF NEXT WEEK. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... * A FEW STRONG TO SEVERE STORMS POSSIBLE LATE THIS AFTERNOON INTO THE EVENING HOURS * 415 PM MESO-UPDATE... CONTINUING TO MONITOR FOR THE POTENTIAL FOR STRONG TO SEVERE THUNDERSTORMS LATE THIS AFTERNOON INTO THE EVENING HOURS. CURRENTLY THE COLD FRONT HAS JUST PUSHED THROUGH ITHACA NY UP TO MONTPELIER VT...AND WILL CONTINUE A EASTWARD PROGRESSION TOWARDS SOUTHERN NEW ENGLAND THROUGH THE REMAINDER OF THE DAY. OVER THE NEXT FEW HOURS...BELIEVE A FEW ISOLATED SHOWERS AND THUNDERSTORMS WILL POP- UP /JUST LIKE THEY ARE IN MOHAWK VALLEY REGION/. THEN EXPECT A MORE BROKEN LINE SEGMENT TO MOVE THROUGH BY THE EVENING HOURS AS THE FRONT MOVES CLOSER TO THE REGION. LOOKING AT SPC MESO ANALYSIS...SB CAPE VALUES HAVE REACHED TO 2500 J/KG WITH NOT MUCH IN THE TERMS OF EFFECTIVE SHEAR FOR SOUTHERN NEW ENGLAND. RAP 0-6 KM BULK SHEAR VALUES HAVE INCREASED SLIGHTLY...AND ARE NOW 15-20 KTS. AS OF 20Z...THE STRONGER WIND SHEAR AND UPPER LEVEL JET DYNAMICS ARE STILL SITUATED ACROSS UPSTATE NEW YORK WHICH IS ALSO WHERE THE DEEP LAYER MOISTURE IS LOCATED PER THE K-INDEX. HENCE WHY THE STORMS ARE SUSTAINING THEMSELVES. OVERVIEW AND INTO TONIGHT... A COLD FRONT WILL PASS ACROSS THE NORTHEAST EARLY THIS EVENING AND INTO THE EARLY OVERNIGHT HOURS. ALTHOUGH WE ARE CURRENTLY LACKING MOISTURE AND SHEAR AS MENTIONED ABOVE...RAP GUIDANCE SHOWS THAT BOTH OF THESE PARAMETERS WILL INCREASE CLOSER TO 00Z. THEREFORE BELIEVE THAT SHOWERS AND STRONGER THUNDERSTORMS WILL DEVELOP AND OVERSPREAD THE REGION AS THE FRONT PUSHES CLOSER TO SOUTHERN NEW ENGLAND. THROUGHOUT THE EVENING HOURS...THE MAIN CONCERN IS THE AMOUNT OF INSTABILITY WITH LACK OF SOLAR HEATING BY THE LATE EVENING HOURS. CURRENT THINKING THOUGH IS THAT SINCE THE ATMOSPHERE HAS NOT BEEN WORKED OVER AND THE GUIDANCE SHOWS LINGER ELEVATED INSTABILITY OVERNIGHT BELIEVE THAT THE THUNDERSTORM POTENTIAL WILL LINGER TIL ABOUT MIDNIGHT. BY THEN THE STORMS WILL ENTER THE THE EASTERN PORTION OF THE AREA WHICH IS BEING INFLUENCED BY THE ADVECTING MARITIME AIR FROM TODAYS GUSTY SOUTHWEST WINDS. STILL CANNOT RULE OUT THE POTENTIAL FOR SEVERE WEATHER BUT HAVE INCREASING CONFIDENCE THAT AT LEAST STRONG STORMS WILL DEVELOP LATE THIS AFTERNOON INTO THE EVENING HOURS. AFTER DISCUSSING WITH SPC DECIDED TO ISSUE A WATCH FOR THE LOCATIONS THAT HAVE THE BEST POTENTIAL TO SEE THE BEST MOISTURE/INSTABILITY AND SHEAR OVERLAPPING ONE ANOTHER. THE MAIN THREATS ARE DAMAGING WINDS AND LOCALIZED FLOODING AS PWATS CONTINUE TO INCREASE ABOVE 1.8 INCHES. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/... THURSDAY... COLD FRONT WILL SLOW DOWN DURING ITS PASSAGE ACROSS SOUTHERN NEW ENGLAND THURSDAY MORNING. BOTH THE EC AND NAM SHOW A WAVE DEVELOPING ALONG THE FRONT ALLOWING FOR THE SLOW DOWN WHILE THE GFS SEEMS TO BE THE OUTLIER ON PUSHING THE FRONT THOUGH BY 12Z. IN FACT THE UPPER LEVEL TROUGH AXIS IS STILL ACROSS UPSTATE NY BY 12/15Z RESULTING IN CLOUDS AND THE CONFIDENCE THAT PRECIP WILL LINGER ESP FOR AREAS SOUTH AND EAST OF THE BOS-PVD CORRIDOR. BELIEVE THAT BY 00Z THE FRONT AND THE BULK OF THE PRECIP WILL BE OFFSHORE BUT CANNOT RULE OUT A FEW LINGERING SHOWERS ESP FOR THE CAPE AND THE ISLANDS. BECAUSE OF THE SLOW DOWN AND THE POTENTIAL WAVE DEVELOPMENT...CANT RULE OUT THE POTENTIAL FOR EMBEDDED THUNDERSTORMS DURING THE DAY. DRIER AIR WILL WORK ITS WAY IN BEHIND THE FRONT RESULTING IN A COOLER DAY WITH HIGHS WELL BELOW AVERAGE AND CLOSE TO 15 DEGREES COOLER THEN TODAY. ASIDE FROM THE CLOUDS AND LINGERING PRECIP CHANCES...SHOULD BE A PLEASANT DAY. && .LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/... */ HIGHLIGHTS... - DRY AND SEASONABLE INTO FRIDAY - RETURN OF WARM AND MUGGIER CONDITIONS FOR SATURDAY - SIGNIFICANT WEATHER SATURDAY NIGHT INTO EARLY NEXT WEEK - A RETURN OF DRY AND SEASONABLE WEATHER BY MIDWEEK */ OVERVIEW AND MODEL PREFERENCE... SURPRISING PATTERN AS WE CLOSE OUT THE MONTH OF JULY! AS PRESENT NW PACIFIC IMPULSE EJECTS E IT COUPLES WITH AN UPPER-LEVEL LOW PARKED OVER NE CANADA RESULTING IN TROUGH ENHANCEMENT THROUGH THE GREAT LAKES REGION. SUBSEQUENT DOWNSTREAM RIDGING OVER THE N-ATLANTIC AND RIDGE STRENGTHENING OVER THE W-CONUS AHEAD OF A PACIFIC IMPULSE BOTTLED IN THE GULF OF ALASKA...THE ATMOSPHERIC PATTERN BUCKLES. WITH THE STAGNANT PATTERN IN PLACE...ANOMALOUS CONDITIONS PREVAIL AS DECENT AGREEMENT AMONG ENSEMBLE MEMBERS SIGNAL A -3 TO -4 SD IN HEIGHTS/TEMPERATURE/HUMIDITY. BUT A NOTE OF CAUTION: SIMILAR ENSEMBLE MEMBERS OUT TO D8 AND INTO EARLY AUGUST ARE EXHIBITING CONSIDERABLE SPREAD WITHIN NAO/PNA TRENDS. IT IS WITH NO CERTAINTY AS TO HOW THIS PATTERN WILL EVOLVE. THIS MAKES THE FORECAST OVER THE NE-CONUS DIFFICULT FURTHER OUT IN TIME AS NEW ENGLAND ESPECIALLY FINDS ITSELF WITHIN THE E-PERIPHERY OF THE AFOREMENTIONED TROUGH. JUST A SLIGHT WOBBLE OF THE OVERALL BUCKLED PATTERN E OR W CAN RESULT IN CONSIDERABLE CHANGES IN THE FORECAST. FEEL THE DECENT AGREEMENT BETWEEN DETERMINISTIC AND ENSEMBLE MEMBERS WARRANTS A BLEND OF MODEL GUIDANCE TOWARDS THE FORECAST. WILL HIT ON THE MAIN POINTS ALONG WITH ANY PREFERRED GUIDANCE IN THE DAILIES BELOW. */ DAY-TO-DAY DETAILS... THURSDAY NIGHT THROUGH SATURDAY... THINKING A DRY FORECAST PERIOD WITH THE RRQ OF THE UPPER-LEVEL JET SHIFTING SE. FEEL THE COLD FRONT AND ATTENDANT WAVE LOW WILL REMAIN OVER THE WATERS. SHOWERS DISSIPATING /IF ANY/ TOWARDS MIDNIGHT AS DYNAMICS ARE SHUNTED OUT OF THE REGION. OTHERWISE...HIGH PRESSURE AND LIGHT NW-FLOW SWEEPS ACROSS NEW ENGLAND FRIDAY /SEA-BREEZES ALONG THE SHORES/ FOLLOWED BY RETURN BREEZY S/SW-FLOW FOR THE REMAINDER OF THE PERIOD AS THE HIGH SLIDES E/SE AND LOW PRESSURE BEGINS TO BUILD IN FROM THE W. SEASONABLE WX INITIALLY...BUT EXPECT THE RETURN OF WARMER/MUGGIER CONDITIONS BY SATURDAY. LOOKING CLEAR FOR FRIDAY...DIURNAL CUMULUS FOR SATURDAY. SATURDAY NIGHT INTO EARLY NEXT WEEK... THE EVOLUTION OF THE TROUGH AND THE PROXIMITY OF ITS E-PERIPHERY ARE KEYS TO THE FORECAST /AS IS THE OFFSHORE ENHACING RIDGE ACROSS THE N- ATLANTIC/. THE TRACK TIMING AND MORPHOLOGY OF INDIVIDUAL IMPULSES THROUGH THE CYCLONIC FLOW WILL ULTIMATELY DETERMINE THE POTENTIAL OUTCOMES FOR THE REGION. FOR SATURDAY NIGHT INTO SUNDAY...SEEMINGLY AN INITIAL IMPULSE IS A FOCUS FOR CONVECTIVE ACTIVITY /PERHAPS A MCS/ WHERE THERMAL/MOIST AXES AND SUBSEQUENT INSTABILITY CONVERGE AT THE SURFACE AND ALONG THE NOSE OF A LLJ REAR OF AN ATTENDANT WARM-FRONT. THE MORE ZONAL REGIME ADVECTS THIS ACTIVITY W-TO-E. NEARLY UNI-DIRECTIONAL SHEAR PRESENTS A THREAT OF DAMAGING WIND. BUT EARLY IN TIME AND LIKELY ABUNDANCE OF CLOUD COVER...THREAT MAY BE LIMITED. HINTS OF MID-LEVEL DRYING AND WAKE SUBSIDENCE? JUST A HUGE MESS. MAY BE LOOKING AT MORE WIDESPREAD STRATIFORM WITH EMBEDDED THUNDERSTORMS. WHO KNOWS...JUST A FIRST GUESS. BIGGEST CONCERN IS THE PLUME OF PWATS EXCEEDING 1.5 INCHES AND A POSSIBLE RISK OF FLASH FLOODING. SOME CONFIDENCE OF THAT AT LEAST. INTO MONDAY...THE LOW DEEPENS AS IT OCCLUDES OVER THE GREAT LAKES. ALONG AND AHEAD OF THE COLD FRONT WITHIN WARM/MUGGY/UNSTABLE CONDITIONS...CONVECTION IS LIKELY WITHIN AN ENVIRONMENT OF DEEP- LAYER FORCING...BUT IT IS JUST TOO EARLY TO GO INTO DETAIL. MANY QUESTIONS AS TO WHETHER THE ENVIRONMENT WILL DESTABILIZE BENEATH STRONG SW-NE UNI-DIRECTIONAL SHEAR. APPEARS ACTIVITY MAY OCCUR IN THE MORNING ONCE AGAIN FOLLOWED BY MID-LEVEL DRYING AND SUBSIDENCE. YEESH. AGAIN...LOTS OF UNCERTAINTY. ONLY CONFIDENCE IS WITH SURGING PWATS IN EXCESS OF 2-INCHES CONINTUING THE POSSIBLE RISK OF FLASH FLOODING. A FINAL NOTE...EVALUATING THE 23.0Z AND 23.12Z CIPS ANALOGS...BOTH PING UPON POTENTIAL CONVECTIVE THREATS SUNDAY AND MONDAY. THE PROBABILITIES OF SEVERE WEATHER IMPACTS HAVE SLIGHTLY INCREASED WITH THE 23.12Z ANALOGS /UP TO 70-PERCENT/. SO WHILE THE ABOVE DISCUSSION CONTAINS A FAIR AMOUNT OF UNCERTAINTY...THE FORECAST STILL WARRANTS CLOSE MONITORING. AT SOME POINT THE COLD FRONT SHOULD PUSH E BEHIND WHICH DRIER AND COOLER AIR WRAPPING INTO THE OCCULUSION SHOULD PREVAIL RESULTING IN SEASONABLE CONDITIONS FOR THE REGION. WHETHER THIS OCCURS ON TUESDAY OR WEDNESDAY...JUST TOO UNCERTAIN. && .AVIATION /20Z WEDNESDAY THROUGH MONDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH THURSDAY/... GENERALLY MODERATE CONFIDENCE ON FORECAST. THROUGH 22Z...GENERALLY VFR. AFTER 22Z INTO TONIGHT...MVFR CIGS AND VSBYS IN VICINITY OF SCT TSTMS AHEAD OF A COLD FRONT. A FEW TSTMS MAY BRIEFLY LOWER CIGS/VSBYS TO IFR LEVELS. ALSO...A FEW TSRA MAY PRODUCE STRONG WIND GUSTS. THERE IS ALSO A MODERATE POTENTIAL FOR IFR CIGS FORMING TONIGHT ACROSS THE CAPE AND ISLANDS. THURSDAY...GENERALLY MVFR CIGS AND VSBYS TO START IN ANTICIPATED RAIN OR SHOWERS. CONDITIONS WILL BE IMPROVING FROM NW TO SE THROUGH MUCH OF THE DAY. EXCEPT ALONG AND SE OF A PYM-UUU LINE WHICH MAY STAY IN LOWER CLOUDS THROUGH MUCH OF THURSDAY...IMPROVING LATE. KBOS TAF...HIGH CONFIDENCE. VFR THROUGH MOST OF THE DAY. TSTMS POSSIBLE AFT 00Z TO THE N AND W OF BOS AND CLOSER TO THE AIRFIELD ITSELF BY 03Z. KBDL TAF...HIGH CONFIDENCE IN TAF. TSTMS POSSIBLE AFT 22Z. ANY TSTMS COULD CONTAIN STRONG WIND GUSTS. OUTLOOK...THURSDAY NIGHT THROUGH MONDAY... THURSDAY NIGHT THROUGH SATURDAY...HIGH CONFIDENCE. VFR. -RA MOVES OUT THURSDAY NIGHT UNDER NW FLOW. LIGHT WINDS AND MOSTLY CLEAR ON FRIDAY /SEA-BREEZES ALONG THE SHORES/. SCT-BKN 5 KFT CIGS SATURDAY WITH BREEZY S/SW WINDS. SATURDAY NIGHT THROUGH MONDAY...LOW CONFIDENCE. PERIODS OF RA/TSRA. MIX OF MVFR-IFR CONDITIONS...WORST OF WHICH ANTICIPATED DURING OVERNIGHT PERIODS AND +RA. CONTINUED BLUSTERY S/SW WINDS. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH THURSDAY/...MODERATE CONFIDENCE. THE SW FLOW WILL STRENGTHEN AHEAD OF A COLD FRONT TO PRODUCE GUSTS APPROACHING 25 KT ACROSS MANY OF THE NEAR SHORE WATERS...THEREFORESCA IS STILL IN EFFECT. SEAS MAY APPROACH 5 FEET EAST OF CAPE ANN THIS EVENING. OTHERWISE WILL NEED TO MONITOR FOR AREAS OF FOG THAT MAY DEVELOP ALONG THE SOUTH COASTAL WATERS TONIGHT. OUTLOOK...THURSDAY NIGHT THROUGH MONDAY... THURSDAY NIGHT THROUGH SATURDAY...HIGH CONFIDENCE. TRANQUIL BOATING WEATHER. SOME SHOWERS MAY LINGER ALONG THE SE OUTER- WATERS THURSDAY NIGHT...BUT SHOULD BE GOOD AFTER MIDNIGHT. HIGH PRESSURE AND LIGHT NW-FLOW FRIDAY /SEA-BREEZES ALONG THE SHORES/. WINDS VEER S/SW OVERNIGHT AND BECOME BREEZY DURING THE DAY SATURDAY. SATURDAY NIGHT THROUGH MONDAY...LOW CONFIDENCE. WEATHER TURNING SOUR. INCREASE S/SW WINDS AHEAD OF A STRONG LOW OVER THE GREAT LAKES REGION WILL RESULT IN SIGNIFICANT WAVE HEIGHTS OVER THE S-WATERS ESPECIALLY. SHOWERS/THUNDERSTORMS ANTICIPATED SOME OF WHICH COULD BE STRONG. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR ANZ230>237-251. SMALL CRAFT ADVISORY UNTIL 8 AM EDT THURSDAY FOR ANZ250-254. && $$ SYNOPSIS...DUNTEN/SIPPRELL NEAR TERM...DUNTEN/SIPPRELL SHORT TERM...DUNTEN LONG TERM...SIPPRELL AVIATION...DUNTEN/SIPPRELL MARINE...DUNTEN/SIPPRELL

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