Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 211122 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 722 AM EDT SUN SEP 21 2014 .SYNOPSIS... SHOWERS WITH LOCALLY HEAVY RAIN THIS MORNING MAINLY OVER CONNECTICUT...WESTERN-CENTRAL MASSACHUSETTS INTO SOUTHERN NEW HAMPSHIRE WILL BECOME LESS NUMEROUS THIS AFTERNOON FROM WEST TO EAST. WARM AND MUGGY CONDITIONS TODAY WILL BE REPLACED BY DRIER AND LESS HUMID WEATHER MONDAY AS A DRY COLD FRONT SWEEPS ACROSS THE REGION. HIGH PRESSURE DOMINATES THE WEEK AHEAD...WITH COOLER TEMPERATURES THE FIRST HALF...AND WARMER TEMPS THE LATTER. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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7 AM UPDATE... LEFTOVER CONVECTION CONTINUES TO DIMINISH IN A LINE FROM SW CT INTO SE NH. THIS AS THE OFFSHORE INVERTED TROF WEAKENS. THEREFORE...SUSPECT SHOWERS BECOME LESS WIDESPREAD THROUGH MORNING ALTHOUGH WILL NEED TO WATCH OFFSHORE CONVECTIVE ACTIVITY AS OFFSHORE LOW PRES DEVELOPS. THESE MAY SLIDE ACROSS SE MA LATE IN THE DAY. OTHERWISE...BULK OF CONVECTIVE ACTIVITY ASSOCIATED WITH A COLD FRONT REMAINS TO THE W THROUGH EVENING. MAY SEE BREAKS AS SUBSIDENCE DEVELOPS THROUGH THE AFTERNOON. PREVIOUS DISCUSSION... SURFACE OBSERVATIONS INDICATE PRONOUNCED INVERTED TROUGH ACROSS LONG ISLAND...NYC AND THEN DRAPED ALONG THE NJ COAST. THIS BOUNDARY IS THE FOCUS FOR SHOWERS WITH LOCALLY HEAVY RAINFALL AND ISOLATED TSTMS. THIS INVERTED TROUGH HAS ITS ROOTS IN A TROPICAL PLUME OF MOISTURE FROM OFF THE MID ATLC COAST NORTHWARD INTO SOUTHERN NEW ENGLAND WITH PWATS UP TO 1.6 INCHES...ABOUT +1 STD ABOVE CLIMO. MARGINAL INSTABILITY ALOFT WITH MID LEVEL LAPSE RATES ALMOST MOIST ADIABATIC AT 6C/KM. THIS IS RESULTING IN EMBEDDED TSTMS WITHIN THESE BANDS OF HEAVY RAIN. THE RAP13 HAS BEEN SIMULATING THESE RAIN BANDS THE BEST OF THE MODEL GUIDANCE INCLUDING THE HRRR. THE RAP13 SHOWS OVER AN INCH OF TOTAL RAINFALL POSSIBLE BY MIDDAY ACROSS CT INTO WESTERN-CENTRAL MA...WITH LESS ELSEWHERE. THE INVERTED TROUGH APPEARS TO WEAKEN THIS AFTERNOON ALONG WITH TROPICAL PLUME MOVING OFFSHORE AND BEING REPLACED BY MID LEVEL DRY SLOT AFTER 18Z. THUS THE FOCUS FOR SHOWERS WILL BE THIS MORNING. AS SOME SURFACE HEATING MATERIALIZES THIS AFTERNOON ALONG WITH DEW PTS CLIMBING TO 65-70 ALL MODEL GUIDANCE SUGGEST 750 TO 1500 J/KG OF CAPE POSSIBLE. HOWEVER DRY SLOT OVERSPREADS THE REGION AND THIS MAY PROVIDE A CAP AND RESULT IN SHOWERS BECOMING LESS NUMEROUS THIS AFTERNOON. AS FOR SEVERE WEATHER...THIS MORNING STRONGEST WIND FIELDS INCLUDING 0-1KM SHEAR ARE ACROSS NORTHERN MA AND SOUTHWEST NH. MEANWHILE BEST INSTABILITY REMAINS OFFSHORE. THUS SHEAR AND INSTABILITY ARE NOT COLOCATED. HENCE RISK OF STRONG TO SEVERE STORMS IS VERY LOW. AS FOR THIS AFTERNOON...MARGINAL SB INSTABILITY DEVELOPS OVER THE INTERIOR BUT DEEP LAYER SHEAR IS ALSO MARGINAL AT LESS THAN 30 KT. IN ADDITION DRY SLOT OVERSPREADING THE REGION SHOULD MINIMIZE THE RISK OF STRONG TO SEVERE TSTMS. THE MAIN RAIN SHIELD ASSOCIATED WITH THE MID ATLC TROUGH MAY CLIP CAPE COD AND THE ISLANDS THIS AFTERNOON. OTHERWISE EXPECT A SUMMER-ISH AFTERNOON WITH TEMPS WELL INTO THE 70S AND POSSIBLY NEARING 80 ALONG WITH DEW PTS 65 TO 70.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... TONIGHT... NORTHERN STREAM TROUGH AND COLD FRONT OVER THE GREAT LAKES THIS MORNING ZIPS ACROSS THE REGION TONIGHT. MOISTURE IS LIMITED SO AREAL COVERAGE OF SHOWERS WILL BE LIMITED AND CONFINED TO THE INTERIOR. OTHERWISE MAINLY DRY TONIGHT AND MILD AS FRONTAL PASSAGE DOESN/T OCCUR UNTIL MONDAY MORNING. MONDAY... COLD FRONT MOVES ACROSS THE AREA IN THE MORNING WITH A SECONDARY FRONT PASSING IN THE AFTERNOON. MOISTURE IS LIMITED SO JUST EXPECTING SOME CLOUDS MIXING WITH THE SUNSHINE. STILL MILD AS COOLER AIR DOESN`T ARRIVE UNTIL MON NIGHT. SO EXPECTING HIGHS MON WELL INTO THE 70S INCLUDING CAPE COD AND THE ISLANDS GIVEN WESTERLY WINDS. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... HIGHLIGHTS... * DRY WEATHER FOR MOST OF THE WEEK * COOL TEMPERATURES THROUGH WED...MODERATING BY THE WEEKEND OVERVIEW AND MODEL PREFERENCES... 21.00Z LONG RANGE MODEL GUIDANCE IS SHOWING FAIRLY GOOD AGREEMENT THROUGHOUT THE LONG TERM DESPITE THE VARIANCE IN OVERALL PATTERN LATE IN THE PERIOD. THIS VARIANCE IS APPARENT IN TELECONNECTIONS...WHERE ALTHOUGH AO/NAO ARE POSITIVE...HOW STRONGLY POSITIVE IT WILL BE REMAINS IN QUESTION. IN SPITE OF THIS...FAIRLY LOCKED PATTERN ACROSS THE CONUS IS FAVORED AS CUTOFF LOW PRES/LONGWAVE TROF IN THE E GIVES WAY TO BUILDING RIDGE. THIS RIDGE IS THE RESULT OF A COMBINATION OF A SRN STREAM RIDGE CURRENTLY ACROSS THE SW/TEXAS WHICH WILL COMBINE WITH THE PERSISTENT WRN ATLANTIC RIDGE. THEREFORE...AFTER A COOL AND DIURNALLY CLOUDY START TO THE WEEK...A GRADUAL WARMING TREND IS EXPECTED THROUGH THE WEEKEND. DRY WX PREVAILS THANKS TO STRONG 1035+ HIGH PRES ASSOCIATED WITH THE BUILDING UPPER RIDGE. GIVEN THE AGREEMENT HERE...A BLEND OF GUIDANCE WILL BE USED AS A BASELINE. DETAILS... MON NIGHT INTO WED... BAFFIN ISLAND CUTOFF IS CONNECTED TO LONGWAVE TROF WITH BASE THROUGH NEW ENGLAND. THIS WILL GRADUALLY SLIDE TO THE E THROUGH THE EARLY HALF OF THE WEEK. HOWEVER...GIVEN THE PERSISTENT COOL DRAW WITH N COMPONENT TO THE FLOW...SUSPECT THIS WILL BE THE COOLEST PORTION OF THE FORECAST WITH POTENTIAL FOR DIURNAL CLOUD COVER UNDER CYCLONIC FLOW. DAYTIME HIGH TEMPS ARE LIKELY TO COOL TUE AND MORESO ON WED THANKS TO A COOLER START. H85 TEMPS REMAIN CLOSE TO +6C EACH DAY...SO NOT QUITE AS COLD AS THE LATE WEEK COOL AIRMASS OF THIS PAST WEEK. HIGHS MAINLY IN THE LOW-UPPER 60S EACH DAY. REGARDING LOWS...TUE NIGHT IS LIKELY TO BE THE COOLER OF THE TWO THANKS TO CENTER OF HIGH PRES MORE DIRECTLY OVERHEAD YIELDING WEAK FLOW. ALTHOUGH WITH RADIATIONAL COOLING SOME FROST IS POSSIBLE EITHER NIGHT IN THE COOLER VALLEYS PARTICULARLY IN NW MA OR SW NH. THU INTO THE WEEKEND... HIGH PRES WILL BE SLOWLY CRESTING OVER THE REGION WITH TIME. LOW- MID LVL HEIGHTS CONTINUE TO RISE SUGGESTING INCREASING TEMPS THROUGH THE COLUMN...THEREFORE...MODERATE TEMPS ARE EXPECTED EACH DAY AS WELL. H85 TEMPS START ABOUT +9C THU...THEN MAY REACH BETWEEN +12C AND +14C BY SUN. WITH MODERATION EACH DAY SUSPECT THAT HIGHS WILL START NEAR NORMAL...INCREASING TO ABOVE NORMAL BY THE WEEKEND...AT WHICH POINT HIGHS IN THE UPPER 70S FOR THE WEEKEND. FOR WHAT IT/S WORTH...EVEN THOUGH THE BLOCKING PATTERN SUGGESTS THE DRY HIGH PRES AND ASSOCIATED SUBSIDENCE DOMINATES...THERE IS AN INVERTED TROF IN THE MID ATLANTIC WITH HIGHER MOISTURE WHICH MAY NEED TO BE WATCHED. WILL MAINTAIN A DRY FORECAST FOR NOW AS A DRY PATTERN SUCH AS THIS GENERALLY SUGGESTS POSITIVE FEEDBACK...MAINTAINING ITSELF. HOWEVER...WITH THE VARIANCE EVIDENT IN THE OVERALL FLOW PATTERN ALOFT LATE IN THE WEEK...MAY NEED TO MONITOR THIS INVERTED TROF AND SUBTROPICAL MOISTURE WHICH COULD YIELD A CHANGE IN THE FORECAST. INDIVIDUAL ENSEMBLE MEMBERS FROM BOTH THE GEFS AND ECENS DO BRING THIS TROF CLOSER TO NEW ENGLAND THAN DO OTHER MEMBERS AND THE OPERATIONAL MODELS. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/...
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FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH MONDAY/... 12Z UPDATE...MODERATE CONFIDENCE. MIX OF MVFR/IFR IN A LINE FROM CT THROUGH CENTRAL AND WESTERN MA INTO SRN NH. THIS WILL LINGER THROUGH THE MORNING UNTIL LEFTOVER SHOWERS COME TO AN END. OTHERWISE...MAINLY VFR ALTHOUGH SOME LOW CLOUDS MAY MOVE INTO SOUTHEAST MA LATE IN THE DAY. TONIGHT...MAINLY VFR EXCEPT MVFR/IFR CAPE COD AND THE ISLANDS EARLY HALF OF THE NIGHT. CHANCE OF A BROKEN LINE OF SHOWERS AROUND 06Z ESPECIALLY WESTERN- CENTRAL MA INTO NH. MONDAY...VFR. MODEST W WIND. DRY RUNWAYS. KBOS TERMINAL..MODERATE CONFIDENCE IN TAF ON TIMING BUT LOWER CONFIDENCE ON AREAL COVERAGE OF SHOWERS. KBDL TERMINAL...MODERATE CONFIDENCE IN TAF. OUTLOOK...MONDAY NIGHT THROUGH THURSDAY... HIGH CONFIDENCE. VFR DOMINATES THROUGH THE PERIOD. A FEW POCKETS OF EARLY MORNING FOG AT TYPICALLY PRONE TERMINALS EACH NIGHT.
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&& .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/... TODAY... MODEST S-SE WINDS WITH HEAVY SHOWERS ACROSS THE WESTERN WATERS. VSBY REDUCED IN HEAVY RAIN AND PATCHY FOG. TONIGHT... SHOWERS DIMINISH. SEAS BUILD ACROSS THE OCEAN WATERS THUS SCA IN EFFECT. SSW WINDS SHIFT TO WEST TOWARD SUNRISE. MONDAY... WEST WINDS YIELD GOOD VSBY AND DRY WEATHER. HOWEVER SEAS REMAIN ROUGH FROM LEFTOVER SOUTH SWELL COMBINED WITH DEVELOPING WEST WIND WAVES. OUTLOOK...MONDAY NIGHT THROUGH THURSDAY... HIGH CONFIDENCE... 5-8 FT SEAS AND WINDS BOTH DIMINISH MON NIGHT...SUCH THAT SMALL CRAFT ADVISORIES ARE LIKELY TO END. ALTHOUGH THE SWELL MAY LINGER A BIT INTO TUE...EVEN THESE SHOULD DROP BELOW SMALL CRAFT ADVISORY THRESHOLDS EARLY. OTHERWISE...MAINLY QUIET BOATING WEATHER FOR THE REMAINDER OF THE PERIOD UNDER HIGH PRES. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY FROM 7 PM THIS EVENING TO 7 PM EDT MONDAY FOR ANZ235-237-250-254>256. && $$ SYNOPSIS...NOCERA/DOODY NEAR TERM...NOCERA/DOODY SHORT TERM...NOCERA LONG TERM...DOODY AVIATION...NOCERA/DOODY MARINE...NOCERA/DOODY

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