Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 201943 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 343 PM EDT WED MAY 20 2015 .SYNOPSIS... A DRY AND COOL NIGHT WILL BE FOLLOWED BY A SEASONABLY MILD THURSDAY AFTERNOON. FAST MOVING LOW PRESSURE MAY BRING A BRIEF PERIOD OF RAIN SHOWERS TO THE SOUTHEAST NEW ENGLAND COAST THURSDAY NIGHT INTO FRIDAY. FROST AND MAYBE EVEN RECORD-BREAKING COLD IS POSSIBLE FOR SATURDAY MORNING. DRY AND SEASONABLE BENEATH HIGH PRESSURE FOR THE WEEKEND. POSSIBLE WET-WEATHER EARLY NEXT WEEK IS NOT OUT OF THE QUESTION. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... DIURNAL CUMULUS CLOUDS WILL DISSIPATE THIS EVENING WITH THE LOSS OF DAYTIME HEATING. GUSTY WINDS WILL ALSO DIMINISH THIS EVENING AND DECOUPLE ACROSS THE TYPICAL OUTLYING LOCATIONS AFTER MIDNIGHT. THIS SHOULD ALLOW THESE LOCATIONS TO DROP INTO THE 30S BY DAYBREAK. WHILE PATCHY FROST IS POSSIBLE ACROSS ALL OF THE NORMALLY COOLEST OUTLYING LOCATIONS...FELT IT WAS ONLY WORTH A FROST ADVISORY IN WESTERN MA WHERE IT WILL BE MORE WIDESPREAD. THIS IS MAINLY FOR TEMPS DROPPING INTO THE MIDDLE 30S...BUT SOME LOWER 30S IN THE NORMALLY COOLEST OUTLYING LOCATIONS CAN NOT BE RULED OUT. MEANWHILE...THE URBAN HEAT ISLAND OF BOSTON WILL ONLY SEE LOW TEMPS DROP INTO THE UPPER 40S. A CLASSIC NIGHT FOR RADIATIONAL COOLING WITH A WIDE VARIATION IN TEMPS BY DAYBREAK. THE ONLY FLY IN THE OINTMENT IS THE MODELS SHOW SOME MID/HIGH CLOUDINESS COMING INTO THE REGION AFTER MIDNIGHT FROM THE WEST. IF IT COMES IN EARLIER AND THICKER THAN EXPECTED...TEMPS WILL NOT GET AS COLD AS WHAT WE ARE CURRENTLY FORECASTING. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... THURSDAY... PARTLY TO MOSTLY SUNNY SKIES DESPITE SOME MID/HIGH LEVEL CLOUDINESS. SHOULD SEE HIGH TEMPS RECOVER TO THE UPPER 60S TO AROUND 70 IN THE AFTERNOON...WITH A FEW LOCATIONS POSSIBLY REACHING INTO THE LOWER 70S. IT WILL FEEL MORE COMFORTABLE THAN TODAY GIVEN LESS WIND. THURSDAY NIGHT... WEAK WAVE OF LOW PRESSURE TRACKS SOUTHEAST OF THE BENCHMARK THURSDAY NIGHT. ITS AN OPEN WAVE AND WILL BE MOVING FAIRLY QUICKLY...SO WILL NOT HAVE MUCH ATLANTIC INFLOW AND THE NORTHWEST EXTENT OF THE PRECIPITATION SHIELD WILL BE LIMITED. THERE IS UNCERTAINTY IN REGARDS TO HOW FAR NORTHWEST THE RAIN SHOWERS MAKE IT...SO LATER SHIFTS MAY CERTAINLY NEED TO MAKE ADJUSTMENTS. CURRENTLY IT LOOKS LIKE MOST OF THE MEASURABLE RAINFALL WILL LIKELY BE CONFINED TO SOUTHEAST NEW ENGLAND ESPECIALLY ACROSS THE CAPE AND NANTUCKET. EVEN IN THESE LOCATIONS...EXPECTING LESS THAN A QUARTER INCH OF RAIN AND ACTIVITY WILL BE SHORT LIVED. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... */ HIGHLIGHTS... - CHANCES FOR WET WEATHER INTO FRIDAY - TURNING COLD INTO SATURDAY MORNING - HIGH PRESSURE AND MODERATE TEMPERATURES OVER THE WEEKEND - POTENTIAL FOR WET WEATHER INTO EARLY NEXT WEEK OVERVIEW AND MODEL PREFERENCES... THERE IS STILL MODERATE AGREEMENT THROUGH THE WEEKEND IN THE SYNOPTIC PATTERN. HOWEVER A RECENT ADJUSTMENT IN THE LONGWAVE TROF AS A ROBUST VORTEX MOVES INTO IT/S BASE FOR FRI HAS LED TO A CHANGE IN THINKING FROM YESTERDAY...REGARDING SENSIBLE WX. THIS VORTEX WILL LEAD TO A TILT-SHIFT IN THE TROF FROM POSITIVE TO NEGATIVE...WHICH SHIFTS THE MAIN LEFT EXIT REGION OF THE UPPER JET IN BETTER POSITION TO SUPPORT LIFT IN THE NRN DEFORMATION BANDING OF THE COASTAL LOW PRES MOVING OFF THE MID ATLANTIC. THE APPROACHING COLD FRONT COULD STILL INITIATE SOME -SHRA ACTIVITY TO THE N...BUT IT APPEARS THAT MAINLY THE S COAST/CAPE/ISLANDS WILL HAVE THE BEST CHANCE AT SEEING SOME WETTING PRECIPITATION DUE TO THIS SHIFT. OTHERWISE...THE BREAKDOWN OF THE ROCKY MOUNTAIN RIDGE WILL LEAD TO SOME RIDGING ACROSS NEW ENGLAND FOR THE WEEKEND INTO EARLY NEXT WEEK. HOWEVER DISCREPANCIES IN THE ULTIMATE BREAKDOWN OF THIS RIDGE REMAINS A BIT OF QUESTION. ESPECIALLY THE APPROACH OF A WARM FRONT BY TUE. GIVEN THE TIMING DIFFERENCES ARE MOST EVIDENT BETWEEN THE OPERATIONAL GFS AND ECMWF...A BLEND OF THE ENSEMBLE GUIDANCE WILL YIELD A GOOD MIDDLE GROUND. DETAILS... FRI... TWO AREAS OF LIFT FOR PRECIP POTENTIAL. THE FIRST IS WITHIN THE NE AND NW QUAD OF LOW PRES MOVING S OF THE ISLANDS. THERE IS ENOUGH LIFT WITH AN UPPER LVL JET EXIT REGION AND TILTING TROF TO YIELD SOME RAINFALL MAINLY ALONG THE S COAST OF RI AND SE MA...UNTIL THE SYSTEM MOVES OUT TO SEA BY MID DAY. THE OTHER IS A STRONG COLD FRONT CROSSING THE REGION FROM THE NW. THE BETTER PWATS /NEAR AN INCH/ ARE ASSOCIATED WITH THE LOW PRES TO THE S...WHILE FURTHER N...THE TO P OUT AROUND 0.7 INCHES. THEREFORE...THIS FRONTAL PASSAGE...ALTHOUGH WITH DECENT F-GEN SUPPORT MAY BE ENTERING TOO DRY AN AIRMASS TO YIELD WIDESPREAD -SHRA. FEEL THE SLIGHT CHANCE POPS ARE STILL BEST GIVEN SEVERAL LOCATIONS ARE LIKELY TO REMAIN DRY. SAT THROUGH MON... HIGH PRES WILL REGAIN CONTROL BUT NOT WITHOUT SOME CONSEQUENCES INITIALLY. COLD ADVECTION BEHIND THE STRONG FRONT WILL ALLOW H85 TEMPS TO DROP TO -2C OR -4C...ALMOST 3 STD DEVIATIONS BELOW NORMAL. MODEL 2M TEMP ANOMALIES FOR FRI NIGHT AND SAT ARE ON THE ORDER OF -10F. THEREFORE...COOL WX WILL PREVAIL PARTICULARLY FRI NIGHT INTO SAT. MAY NEED TO WATCH FOR FROST...AS 2M TEMPS DIP WELL INTO THE MID 30S. THE ONE ISSUE REGARDING FROST PRODUCTION IS THE POSSIBILITY DECENT ISALLOBARIC COUPLET...WHICH COULD YIELD ENOUGH OF A NOCTURNAL BREEZE TO MITIGATE FROST DEVELOPMENT IN SPITE OF THE COLD TEMPERATURES...SHELTERED VALLEYS ARE MOST AT RISK. GRADUAL MODERATION IS EXPECTED SUN INTO MON...ALTHOUGH WITH A WEAKER PRES GRADIENT SUN NIGHT...ANOTHER /ALTHOUGH LOWER/ RISK FOR FROST WILL HAVE TO BE WATCHED. TEMPS NEAR TO SLIGHTLY ABOVE SEASONAL VALUES BY MON. TUE AND WED... ALTHOUGH THERE CONTINUE TO BE SOME ISSUES HERE REGARDING THE TIMING OF A WARM FRONTAL PASSAGE THROUGH THIS PERIOD. THE TRANSITION TO A MORE UNSETTLED PATTERN IS EXPECTED. INCREASING MOISTURE AND OVERALL WARM ADVECTION SUGGESTS MORE CLOUDS/SHRA CHANCES THROUGHOUT. GIVEN THIS IS A WARM FRONTAL APPROACH...IT/S FINAL LOCATION WILL MATTER SIGNIFICANTLY IN REGARDS TO TEMPS AND PRECIP CHANCES. ALSO...THIS LOCATION PROVIDES STEERING FLOW FOR UPSTREAM MCS. SOMETHING TO CONSIDER. && .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 NIGHT/... THIS AFTERNOON AND TONIGHT...HIGH CONFIDENCE IN VFR. WNW WIND GUSTS BETWEEN 25 AND 30 KNOTS DIMINISH THIS EVENING. THURSDAY...HIGH CONFIDENCE IN VFR CONDITIONS. THURSDAY NIGHT...HIGH CONFIDENCE IN MAINLY VFR CONDITIONS. A BRIEF BAND OF RAIN SHOWERS MAY CLIP PORTIONS OF SOUTHEAST NEW ENGLAND...PERHAPS BRINGING A BRIEF PERIOD OF OF MVFR CONDITIONS. HIGHEST RISK FOR THIS IS ACROSS NANTUCKET. KBOS TERMINAL...HIGH CONFIDENCE IN TAF. GUSTY WNW WINDS BETWEEN 25 AND 30 KNOTS DIMINISH BY 00Z. KBDL TERMINAL...HIGH CONFIDENCE IN TAF. GUSTY WNW WINDS BETWEEN 25 AND 30 KNOTS DIMINISH BY 00Z. OUTLOOK...FRIDAY THROUGH MONDAY... FRIDAY...MODERATE CONFIDENCE. MAINLY VFR...ALTHOUGH PERIODIC MVFR POSSIBLE ESPECIALLY ALONG THE SOUTH COAST WITH SOME LIGHT RAIN EARLY. WINDS SHIFT FROM W TO NW...WITH GUSTS APPROACHING 25 KT BY LATE DAY. SAT THROUGH MON...HIGH CONFIDENCE. VFR. GUSTY NW WINDS SAT AROUND 25 KT. SEA BREEZES POSSIBLE SUN. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/... TONIGHT...HIGH CONFIDENCE. NEAR SHORE WNW WIND GUSTS OF 25 KNOTS ACROSS BOSTON HARBOR/NARR BAY AND PORTIONS OF IMMEDIATE EASTERN MA COAST DIMINISH THIS EVENING. THESE LOCALIZED NEAR SHORE SMALL CRAFT HEADLINES WILL BE ALLOWED TO EXPIRE BY 7 PM. OTHERWISE...WINDS/SEAS BELOW SMALL CRAFT THRESHOLDS TONIGHT. THURSDAY AND THURSDAY NIGHT...HIGH CONFIDENCE. WEAK PRESSURE GRADIENT WILL KEEP WINDS/SEAS BELOW SMALL CRAFT ADVISORY THRESHOLDS. OUTLOOK...FRIDAY THROUGH MONDAY... FRI THROUGH SAT NIGHT...MODERATE CONFIDENCE. WITH A COLD FRONT CROSSING THE WATERS ON FRI EVENING. EXPECT WINDS TO SHIFT TO THE W-NW AND BEGIN GUSTING TO AROUND 25 KT. THIS WILL ALSO ALLOW FOR BUILDING SEAS...POSSIBLY REACHING 5-6 FT ON THE OCEAN WATERS ESPECIALLY. THESE CONDITIONS LINGER INTO THE DAY SAT...WITH WINDS DIMINISHING SAT EVENING AND SEAS DIMINISHING SAT NIGHT. SMALL CRAFT ADVISORIES LOOK LIKE THEY WILL BE NEEDED THROUGH THIS PERIOD. SUN AND MON...HIGH CONFIDENCE. MAINLY QUIET BOATING WEATHER THANKS TO HIGH PRES BUILDING OVER THE WATERS. && .FIRE WEATHER... THE NEXT CHANCE FOR MARGINAL FIRE WEATHER CONDITIONS APPEARS TO BE ON FRI. ALTHOUGH SOME PRECIPITATION IS POSSIBLE ESPECIALLY NEAR THE SOUTH COAST OF RI AND SOUTHEAST MA...ALONG WITH A SPOT SHOWER EVERYWHERE ELSE. MIN RH VALUES ARE EXPECTED TO DIP TO BETWEEN 20 AND 30 PERCENT. WINDS WILL SHIFT FROM W TO NW WITH GUSTS APPROACHING 25 MPH IN THE AFTERNOON. FIRE WEATHER CONDITIONS INCREASE ON SAT. THANKS TO LOW DEWPOINTS...RH VALUES FALL BACK INTO THE TEENS...WITH W-NW WIND GUSTS 25 TO 30 MPH AT TIMES. TEMPS NOT AS WARM...MAINLY IN THE 60S. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...FROST ADVISORY FROM 1 AM TO 8 AM EDT THURSDAY FOR MAZ002-003- 008>011. RI...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 7 PM EDT THIS EVENING FOR ANZ230- 236-251. && $$ SYNOPSIS...FRANK/DOODY NEAR TERM...FRANK SHORT TERM...NOCERA LONG TERM...DOODY AVIATION...FRANK/DOODY MARINE...FRANK/DOODY FIRE WEATHER...STAFF

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