Area Forecast Discussion
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000 FXUS61 KBOX 271342 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 942 AM EDT SUN JUL 27 2014 .SYNOPSIS... PERIODS OF SHOWERS AND THUNDERSTORMS ARE EXPECTED TODAY THROUGH MONDAY AS LOW PRESSURE TRACKS FROM THE GREAT LAKES TO NEW ENGLAND AND EVENTUALLY PUSHES A COLD FRONT THROUGH THE REGION. A FEW STORMS COULD BE SEVERE ESPECIALLY MONDAY. THE COLD FRONT STALLS OVER THE MARITIMES AND NEW ENGLAND OFFSHORE WATERS FROM MIDWEEK THROUGH THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... 930 AM UPDATE... *** WIDESPREAD SEVERE WEATHER APPEARS LESS LIKELY THIS AFTERNOON/ EVENING...HOWEVER ISOLATED STRONG STORMS ARE POSSIBLE *** WARM FRONTAL CONVECTION CONTINUES TO PUSH EASTWARD FROM EASTERN NY INTO WESTERN NEW ENGLAND AT 930 AM. MODELS HANDLING THIS PRECIP FAIRLY WELL AND TRANSLATE THESE SHOWERS/TSTMS EASTWARD ACROSS THE REMAINDER OF SOUTHERN NEW ENGLAND THIS MORNING...REACHING EASTERN MA BETWEEN NOON AND 2 PM...THEN OFFSHORE BY MID AFTERNOON. AS THIS INITIAL SHORT WAVE TROUGH EXITS THE REGION EARLY THIS AFTERNOON ALL MODEL GUIDANCE THEN ADVECTS SHORT WAVE RIDGING FROM THE EASTERN LAKES AND WESTERN NY/PA INTO SOUTHERN NEW ENGLAND. AS THIS SHORT WAVE RIDGING ADVECTS INTO OUR REGION SO DOES MID LEVEL DRY WHICH GETS DEEPER WITH TIME LATER THIS AFTERNOON AND EVENING. THIS WILL ESSENTIALLY PROVIDE A SUBSIDENCE CAP WITH DEEPENING DRY AIR ALOFT CHOKING/MINIMIZING UPDRAFT POTENTIAL. IN FACT THIS DEEPENING MID LEVEL DRY AIR AND ASSOCIATED CAP WILL PRECLUDE SURFACE DEW PTS FROM MIXING OUT AND YIELDING FAIRLY HIGH SB CAPES VALUES LATER THIS AFTERNOON. HOWEVER LARGE SCALE SUBSIDENCE AND DEEPENING MID LEVEL DRY AIR SHOULD WIN OUT. NEVERTHELESS THERE WILL BE A VERY SMALL WINDOW OF OPPORTUNITY FOR STRONG STORMS TO DEVELOP AND THAT WILL OCCUR IMMEDIATELY BEHIND THE WARM FRONTAL PRECIP AND ONLY IF SURFACE HEATING CAN COMMENCE QUICKLY BEFORE SHORT WAVE RIDGING AND ASSOCIATED SUBSIDENCE/MID LEVEL DRY AIR ARRIVE FROM THE WEST. THUS THE RISK FOR WIDESPREAD STRONG STORMS IS VERY LOW WITH A SOMEWHAT HIGHER RISK FOR AN ISOLATED STRONG TSTM MID TO LATE THIS AFTERNOON ACROSS THE INTERIOR. OTHERWISE NO MAJOR CHANGES TO PREVIOUS FORECAST. EARLIER DISCUSSION BELOW. ================================================================== CLOUDS PUSHING INTO W NEW ENGLAND AHEAD OF SHORT WAVE MOVING OUT OF EASTERN GREAT LAKES. FEW LIGHT SHOWERS/SPRINKLES WEAKENED AS THEY REACHED BERKSHIRES...AND BULK OF SHOWERS WILL CONTINUE TO PASS TO OUR N THROUGH SUNRISE. MEANWHILE STORMS OVER ONTARIO WILL TRACK NE THIS MORNING AS ADDITIONAL ACTIVITY DEVELOPS ACROSS WESTERN NY PER HIGH-RES MODELS. FAVORABLE JET DYNAMICS COMBINED WITH APPROACHING SHORT WAVE WILL YIELD DECENT Q-VECTOR CONVERGENCE AND WILL RESULT IN BAND OF SHOWER/STORMS CROSSING SOUTHERN NEW ENGLAND THIS MORNING. BACK EDGE OF THIS ACTIVITY SHOULD REACH CT VALLEY BY MID MORNING AND E MA COAST BY EARLY AFTERNOON. CONFIDENCE IS THEN MODERATE AT BEST IN HOW THINGS EVOLVE. CONCERN IS WHETHER WE CAN DESTABILIZE ENOUGH BEHIND THIS SHORT WAVE TO PRODUCE A ROUND OF SEVERE STORMS. ON LARGER SCALE SUBSIDENCE BEHIND DEPARTING SHORT WAVE SHOULD BRING AT LEAST PARTIAL CLEARING...BUT WOULD ALSO MITIGATE ORGANIZED STORM THREAT. HOWEVER WITH PLENTY OF INSTABILITY AND LOW LEVEL MOISTURE /DEW POINTS NEAR 70/ WE THINK AT LEAST A FEW STORMS SHOULD BE ABLE TO DEVELOP...ALTHOUGH CONDITIONS ARE CERTAINLY MORE FAVORABLE WELL TO OUR S AND W. WE WILL MAINTAIN CHANCE POPS THIS AFTERNOON FOR SCATTERED STORMS. ENVIRONMENT SHOULD FEATURE MODERATE CAPE AND DECENT 0-3KM SHEAR AND MID LEVEL LAPSE RATES. SHOULD STORMS BE ABLE TO DEVELOP...MAIN THREATS WOULD BE DAMAGING WINDS AND HAIL. WE CANNOT RULE OUT AN ISOLATED TORNADO AS WELL IN W NEW ENGLAND WHERE FORECAST HODOGRAPHS SHOW PLENTY OF TURNING AT LOWER LEVELS. AGREE WITH SPC DAY 1 OUTLOOK. GIVEN UNCERTAINTY IN HOW MUCH CLEARING WE WILL SEE...LEANED ON BLEND OF GUIDANCE WHICH GIVES HIGHS IN 70S TO AROUND 80. CERTAINLY COULD REACH MID 80S SHOULD ENOUGH SUN BREAK OUT. && .SHORT TERM /MONDAY/... *** LOCALIZED FLASH FLOODING POSSIBLE TONIGHT *** *** FEW SEVERE STORMS POSSIBLE AGAIN MON *** CONCERN FOR TONIGHT IS POTENTIAL FOR LOCALIZED FLASH FLOODING AND PERHAPS STRONG TO SEVERE STORMS...BUT AGAIN CONFIDENCE REMAINS MODERATE AT BEST IN HOW THINGS EVOLVE. ONCE ANY STORMS DIMINISH THIS EVENING...ATTENTION TURNS TO POTENTIAL MCS DEVELOPMENT UPSTREAM ACROSS OHIO VALLEY. HIGHER-RES MODELS INCLUDING 00Z NAM ARE MORE INSISTENT THAT ITS REMNANTS WILL TRACK NEAR OR OVER SOUTHERN NEW ENGLAND TONIGHT...PROBABLY NEAR S COAST IF NOT A BIT FARTHER INLAND. 00Z GFS SEEMS TO BE STRUGGLING MORE WITH THIS FEATURE...PROBABLY DUE TO ITS COARSER RESOLUTION... BUT ALSO HINTS AT SOME SORT OF ORGANIZED CONVECTION. WILL MAINTAIN LIKELY POPS FOR MUCH OF REGION TONIGHT. OVERALL SEVERE THREAT TONIGHT IS QUESTIONABLE AS WE REMAIN UNSTABLE BUT 0-3KM SHEAR AND LAPSE RATES DROP OFF A BIT. CERTAINLY MAIN THREAT APPEARS TO BE HEAVY RAIN WITH PLENTIFUL LOW LEVEL MOISTURE. FLASH FLOOD THREAT DOES NOT APPEAR TO BE WIDESPREAD ENOUGH TO ISSUE ANY WATCHES AT THIS TIME...NOR DO WE HAVE CONFIDENCE IN GREATEST THREAT AREA. UPPER LOW CUTS OFF TO OUR W MON AS SURFACE LOW LIKELY PASSES JUST TO OUR W. THIS SHOULD FOCUS MOST OF SHOWERS/STORMS TO OUR W AND N WHERE BETTER LARGE SCALE FORCING RESIDES. WE MAY EVEN END UP WITH A DRY SLOT ACROSS SE NEW ENGLAND BUT PERSISTENT S/SW FLOW SHOULD MAINTAIN CLOUDINESS THERE. ONCE AGAIN THERE ARE QUESTIONS AS TO HOW MUCH CLEARING WE ACTUALLY SEE AND IF THAT GENERATES ENOUGH INSTABILITY FOR ADDITIONAL STORM DEVELOPMENT MON AFTERNOON. IF STORMS CAN DEVELOP...ENVIRONMENT WOULD FEATURE DECENT MID LEVEL LAPSE RATES AND STRONG 0-3KM SHEAR WHICH WOULD SUPPORT A FEW SEVERE STORMS. DUE TO CONTINUED UNCERTAINTY...USED BLEND OF GUIDANCE WHICH GIVES HIGHS IN 70S TO AROUND 80. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... BIG PICTURE... MODELS CONTINUE TO ADVERTISE A MERIDIONAL TYPE FLOW THROUGH THE UPCOMING WEEK. FOUR LOBES OF THIS FLOW ARE THE GULF OF ALASKA TROUGH...WESTERN NORTH AMERICA RIDGE...EASTERN NORTH AMERICA TROUGH...AND WEST ATLANTIC RIDGE. THE EFFECT OF THIS PATTERN WILL BE TO BRING SIMILAR WEATHER EACH DAY. MODELS CONTINUE TO SHOW THE CORE OF THE EASTERN NO-AM TROUGH EJECTING NORTH THROUGH QUEBEC FRIDAY AND SATURDAY. THIS MAY LEAVE ROOM FOR THE ATLANTIC RIDGE TO SHIFT WEST BY SATURDAY. THE SIMILARITY IN MODEL FIELDS FAVORS A BLEND OF AVAILABLE DATA. THE DAILIES... MONDAY NIGHT... SURFACE LOW PRESSURE LIFTS NORTH INTO CANADA...ALL THE WHILE SWINGING A COLD FRONT ACROSS THE REMAINDER OF SOUTHERN NEW ENGLAND AND THEN OFFSHORE. WINDS SHIFT TO WEST AND BECOME LIGHT. THE AIRMASS WILL STABILIZE AND FAVORABLE DYNAMICS WILL MOVE OFF. EVENING SHOWERS/THUNDERSTORMS WILL TAPER OFF AT NIGHT. SUFFICIENT AIRMASS DRYING IS INDICATED TO SUPPORT A CLEARING TREND OVERNIGHT. TUESDAY THROUGH FRIDAY... WITH THE UPPER TROUGH TO OUR WEST AND UPPER RIDGE TO OUR EAST...EXPECT THE UPPER FLOW TO REMAIN FROM THE SOUTHWEST. THE DEPARTED COLD FRONT WILL STALL OVER THE MARITIMES AND THE OFFSHORE WATERS. MEANWHILE COLD POOL INSTABILITY UNDER THE UPPER TROUGH WILL BE OVER NY AND ONTARIO WHILE NEW ENGLAND IS UNDER THE LEFT ENTRANCE REGION OF THE UPPER JET...A SUBSIDENT ZONE. SURFACE HIGH PRESSURE WILL BUILD OVER SOUTHERN NEW ENGLAND. THIS WILL MEAN A CHANCE OF SHOWERS WELL OFFSHORE AND OVER NY/ONTARIO WITH DRY WEATHER OVER SOUTHERN NEW ENGLAND. IF THE UPPER FEATURES SHIFT A LITTLE FURTHER EAST OR WEST...THEN IT IS POSSIBLE WE COULD HAVE A CHANCE OF SHOWERS IN PART OF SOUTHERN NEW ENGLAND. BUT DRY WEATHER IS THE LIKELY SCENARIO. SATURDAY... AS THE UPPER TROUGH LIFTS NORTH...EXPECT THE OFFSHORE FRONT TO SHIFT WEST CLOSER TO THE COAST. THIS SHOULD BRING AN INCREASE IN THE CHANCE OF SHOWERS...WITH THE BEST CHANCE ON THE CAPE AND ISLANDS. && .AVIATION /13Z SUNDAY THROUGH THURSDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. MODERATE CONFIDENCE THROUGH MON. 930 AM UPDATE... ONLY CHANGE TO PREVIOUS FORECAST IS AFTER LATE MORNING/EARLY AFTERNOON SHOWERS/TSTMS...WIDESPREAD STRONG STORMS LATE THIS AFTERNOON/EARLY EVENING APPEAR LESS LIKELY. OTHERWISE FORECAST REMAINS UNCHANGED. EARLIER DISCUSSION BELOW. =============================================================== ACTIVITY OVER ONTARIO AND W NY IS EXPECTED TO AFFECT MUCH OF REGION THIS MORNING. CIGS REMAIN VFR WITH THIS ACTIVITY BUT VSBYS SHOULD LOWER TO MVFR. BACK EDGE MOVES OUT OF CT VALLEY BY 15Z AND E MA COAST AROUND 18Z. VFR CIGS AOA 050 REMAIN IN ITS WAKE THIS AFTERNOON. POTENTIAL FOR ADDITIONAL SCATTERED SHOWERS/STORMS TO DEVELOP ESPECIALLY IN W NEW ENGLAND WITH BRIEF MVFR/IFR. IFR/LIFR CIGS/VSBYS BECOME MORE WIDESPREAD TONIGHT...FIRST ALONG S COAST...CAPE COD AND ISLANDS AROUND SUNSET BEFORE SPREADING INLAND. ALSO EXPECT NUMEROUS SHOWERS/STORMS WITH HEAVY RAINFALL. CONDITIONS SLOWLY IMPROVE AFTER 12Z MON AS FOCUS FOR SHOWERS/STORMS SHIFTS N AND W OF REGION. KBOS TAF...MODERATE CONFIDENCE. PREVAILING SW FLOW. SHOWERS/STORMS MOST LIKELY 15Z-18Z. KBDL TAF...MODERATE CONFIDENCE. SHOWERS/STORMS MOST LIKELY 13Z-15Z WITH SCATTERED STORMS POSSIBLE AFTER 19Z. OUTLOOK...MONDAY NIGHT THROUGH THURSDAY...MODERATE CONFIDENCE. MONDAY NIGHT...LINGERING AREAS OF MVFR/IFR IN THUNDERSTORMS. OTHERWISE VFR OR TRENDING TO VFR. WINDS SHIFT TO WEST AND DIMINISH. TUESDAY...VFR BUT WITH ISOLATED MVFR IN SHOWERS/TSTMS MAINLY SRN NEW HAMPSHIRE AND WESTERN/CENTRAL MASS IN THE AFTERNOON/EVENING. WEDNESDAY-THURSDAY...VFR. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. MODERATE CONFIDENCE TODAY THROUGH MON. SCA REMAINS POSTED TODAY FOR ALL WATERS DUE TO INCREASING SW FLOW WITH GUSTS TO 25 KT...ESPECIALLY NEAR SHORE. THIS WILL ALSO PRODUCE BUILDING SEAS TO 5 FT ON OUTER WATERS. SHOWERS AND STORMS EXPECTED LATER THIS MORNING WITH ADDITIONAL STORMS POSSIBLE DURING AFTERNOON. SW WINDS DROP OFF A BIT TONIGHT AND MON BUT SEAS CONTINUE TO BUILD ON OUTER WATERS TO 6 OR 7 FT. SHOWERS/STORMS SHOULD BECOME MORE WIDESPREAD WITH AREAS OF FOG TONIGHT...BEFORE CONDITIONS GRADUALLY IMPROVE MON. OUTLOOK...MONDAY NIGHT THROUGH THURSDAY...MODERATE CONFIDENCE. MONDAY NIGHT... COLD FRONT MOVES OVER THE WATERS. SOUTHWEST WINDS IN THE EVENING WILL GUST TO 25 KNOTS...BUT SHOULD DIMINISH AFTER THE COLD FRONT MOVES THROUGH AND WINDS SHIFT TO WEST. SEAS 5-7 FEET IN THE EVENING SHOULD SUBSIDE AFTER THE WIND SHIFT. TUESDAY...WINDS AND SEAS WILL CONTINUE TO SUBSIDE AS THE COLD FRONT SHIFTS EAST OF THE WATERS. SEAS AT 5 FEET MAY LINGER ON THE OUTER WATERS FOR PART OF THE DAY. WEDNESDAY-THURSDAY...LIGHTER WINDS AND SEAS AS HIGH PRESSURE BUILDS OVER THE WATERS. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY FROM 1 PM THIS AFTERNOON TO 8 PM EDT THIS EVENING FOR ANZ230>234-236-237-251. SMALL CRAFT ADVISORY FROM 1 PM THIS AFTERNOON TO 6 PM EDT MONDAY FOR ANZ235-250-254>256. && $$ SYNOPSIS...WTB/JWD NEAR TERM...WTB/NOCERA/JWD SHORT TERM...JWD LONG TERM...WTB AVIATION...WTB/JWD MARINE...WTB/JWD

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