Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 250215 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 1015 PM EDT FRI APR 24 2015 .SYNOPSIS... UNSEASONABLY COOL WEATHER CONTINUES THROUGH THIS WEEKEND WITH SPOTTY SHOWERS OR SPRINKLES. PERIODS OF UNSETTLED WEATHER AND BELOW NORMAL TEMPERATURES WILL CONTINUE THROUGH MOST OF NEXT WEEK AS WELL. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... 1015 PM UPDATE... LATEST SATELLITE DATA CONTINUES TO SHOW A SLOW EROSION OF THE SOUTHERN EDGE OF THE CLOUDS ASSOCIATED WITH THE COLD POOL ALOFT. LIKE LAST NIGHT...THIS WILL BE KEY TO LOW TEMPERATURES SATURDAY MORNING. LIKE LAST NIGHT...DEW POINTS ARE LINGERING AROUND 20. IF WE CAN KEEP THE SKIES CLEAR FOR LONG ENOUGH...THEN FREEZING TEMPERATURES WILL LIKELY BE REALIZED. HAVE MODERATE CONFIDENCE IN THE CURRENT FREEZE WARNING AT THIS TIME ACROSS NORTHERN CT. LESS CLOUDS OVER RI...SO SLIGHTLY GREATER CONFIDENCE THERE. WE STILL EXPECT DRY CONDITIONS WITH DIMINISHING WINDS OVERNIGHT. COLD POOL ALOFT ALONG WITH LIGHT WINDS AND CLEARING SKIES /MAINLY AROUND OR AFTER MIDNIGHT/ WILL ALLOW TEMPERATURES TO EVENTUALLY FALL. HAVE UPDATED NEAR TERM CONDITIONS TO REFLECT LATEST OBSERVED TRENDS. PREVIOUS DISCUSSION... TONIGHT... LINGERING CLOUD SHIELD UNDER THE UPPER LOW AND COLD POOL...BUT THIS SHOULD START TO LIFT OUT TO THE NORTH AND EAST SOMEWHAT. SO WE EXPECT AT LEAST PARTIAL CLEARING TONIGHT WITH THE BEST CHANCE OVER CONNECTICUT. PRESSURE GRADIENT STAYS ENOUGH TO KEEP THE AIR MOVING...SO FROST IS NOT LIKELY EXCEPT POSSIBLY IN THE MOST SHELTERED OF LOCATIONS THAT CLEAR. ON THE OTHER HAND TEMPERATURES WILL BE SIMILAR TO LAST NIGHT OR PERHAPS A DEGREE OR TWO COOLER. EXPECTED RANGE IS IN THE UPPER 20S AND 30S...AND FREEZING TEMPS IN PARTS OF THE ACTIVE GROWING ZONE /CT-RI-SOUTHEAST MA/. WE PLAN ON CONVERTING THE EXISTING FREEZE WATCH TO A FREEZE WARNING FOR NORTHERN CT AND NORTHWEST RI. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... SATURDAY...UPPER CLOUD SHIELD AND COLD POOL WILL BE FOCUSED OVER NORTHERN NEW ENGLAND BUT CLOSE ENOUGH TO AFFECT US. DAYTIME HEATING AND A SHORTWAVE CYCLING AROUND THE LOW MAY PUSH CLOUDS BACK OUR WAY DURING THE DAY. THE SURFACE LAYER WILL BE DRIER...SO MOST ATTEMPTS AT PRECIPITATION SHOULD EVAPORATE ON THE WAY DOWN. TEMPS AT 850 MB ARE FORECAST AROUND -2C...WHICH SUPPORTS MAX SFC TEMPS IN THE 50S. WINDS ALOFT IN THE MIXED LAYER REACH 20 KNOTS...SO EXPECT ANOTHER DAY OF GUSTS EITHER SIDE OF 20. SATURDAY NIGHT... WEAK RIDGE BUILDS OVER SOUTHERN NEW ENGLAND PROVIDING CLEARING SKIES AND LIGHT WINDS. RADIATIONAL COOLING WITH DEW POINTS IN THE 30S...SO MIN SFC TEMPS SHOULD BE IN THE 30S. && .LONG TERM /SUNDAY THROUGH FRIDAY/... HIGHLIGHTS... * BELOW NORMAL TEMPERATURES THROUGH AT LEAST THE MIDDLE OF NEXT WEEK * SCATTERED DIURNAL SHOWERS THIS WEEKEND INTO MID-NEXT WEEK * LOW CONFIDENCE ON COASTAL SYSTEM THU OR FRI OVERVIEW AND MODEL PREFERENCES... PERSISTENT UPPER LEVEL BLOCKING PATTERN REMAINS IN PLACE ACROSS THE LOWER 48 WITH FEW CHANGES EXPECTED INTO THE MIDDLE OF NEXT WEEK. HOWEVER...NOTING SOME SUBTLE CHANGES TOWARD NEXT THU/FRI WHICH ARE SHOWING UP AT LEAST ON THE LAST COUPLE OF MEDIUM RANGE OPERATIONAL RUNS OF BOTH THE GFS AND ECMWF THAT ARE STARTING TO SIGNAL THE BREAKING DOWN OF THE UPPER TROUGH PATTERN. THE GEFS AND EC ENSEMBLES CONTINUE TO KEEP SLOW PROGRESSION OF SYSTEMS...SO STILL QUITE A BIT OF TIMING AND TRACK ISSUES TO CONTEND WITH THIS FORECAST CYCLE. NEGATIVE NAO/AO PATTERN REMAINS IN PLACE...KEEPING BELOW NORMAL TEMPS AND PERIODS OF UNSETTLED WEATHER THROUGH AT LEAST THE MIDDLE OF NEXT WEEK AS CUTOFF H5 LOW PRES CONTINUES TO SIT AND SPIN ACROSS THE NORTHEAST INTO EASTERN QUEBEC AND THE MARITIMES. MODELS SIGNALING A STRONGER SHORT WAVE THAT WILL DROP S ACROSS THE REGION OUT OF EASTERN CANADA IN THE UPPER FLOW WILL DROP ACROSS THE REGION BRINGING A BETTER CHANCE FOR SHOWERS ALONG WITH AN ENHANCED N-NE WIND FLOW. ONCE THIS SHORT WAVE MOVES S...THE UPPER SYSTEM MAY START TO SHIFT E BUT TIMING IS STILL VERY MUCH IN QUESTION DUE TO WIDE MODEL SOLUTION SPREAD BEYOND TUESDAY. ANOTHER QUESTION AT THIS POINT IS THE POTENTIAL COASTAL SYSTEM THAT WORKS OFF THE SE U.S. COAST LATE WED OR THU. THE 12Z MODEL RUNS CONTINUE TO KEEP THE BLOCKING ACROSS THE NORTHEAST WHICH MAY ACTUALLY SHUNT THE COASTAL SYSTEM S OF THE REGION. NOTING A RATHER STRONG SYSTEM ON THE 12Z ECMWF...WHICH TENDS TO DEVELOP AND SLOW THE SYSTEM AS IT PASSES S OF NEW ENGLAND THU NIGHT OR FRIDAY... WHILE THE GFS IS A MORE OPEN WAVE BUT STILL PUSHES OFFSHORE. WILL STILL NEED TO WATCH FUTURE MODEL TRENDS BEFORE WRITING THIS ONE OFF FOR NOW. USED A BLEND OF AVAILABLE GUIDANCE INTO TUESDAY...WHICH SHOWED GOOD CONSISTENCY WITH THE PREVIOUS FORECAST...THEN TRANSITIONED OVER TO ENSEMBLE GUIDANCE THROUGH THE REMAINDER OF NEXT WEEK. DETAILS... * SUNDAY...HIGH CONFIDENCE. WHILE THE UPPER LOW CONTINUES TO BRING A FEW DIURNAL SHOWERS WITH THE COLD POOL ALOFT WHICH ACTUALLY LOOKS TO SLOWLY SHIFT E LATER IN THE DAY. SO...AS HAS BEEN THE CASE OVER THE LAST SEVERAL DAYS...SKIES SHOULD START OFF PARTLY TO MOSTLY SUNNY THEN CLOUDS DEVELOP ALONG WITH A FEW SPOTTY SHOWERS ESPECIALLY NEAR AND N OF THE MASS PIKE CLOSER TO THE SHORT WAVE THAT BEGINS TO SHIFT OUT OF NORTHERN NEW ENGLAND LATE IN THE DAY. EXPECT TEMPS TO TOP OFF MAINLY IN THE 50S...BUT IF A LITTLE MORE SUN WORKS THROUGH THE CLOUDS ACROSS THE LOWER CT VALLEY...READINGS MAY TOUCH 60 IN A FEW SPOTS. * MONDAY THROUGH TUESDAY NIGHT...MODERATE CONFIDENCE. RATHER POTENT H5 SHORT WAVE AND ASSOCIATED BACKDOOR /OF SORTS/ SURFACE REFLECTION ROTATE SW ACROSS THE REGION DURING THIS TIMEFRAME. LOOKS LIKE THE BEST ENERGY AND PRECIP CHANCES WILL PUSH ACROSS MON NIGHT THROUGH INTO TUESDAY NIGHT. WINDS ALSO SHIFT TO N-NE AND INCREASE. GUSTS UP TO AROUND 25 KT POSSIBLE MAINLY ALONG E COASTAL AREAS. MAY SEE SOME APPRECIABLE RAINFALL WITH QPF OF 0.2 TO 0.3 INCHES ALONG THE E COAST AS LOW LEVEL MOISTURE INCREASES WITH THE ONSHORE WIND. * WEDNESDAY THROUGH FRIDAY...LOW CONFIDENCE. STILL QUITE A BIT OF UNCERTAINTY WITH SOUTHERN STREAM SYSTEM THAT MAY MAKE THE TURN UP THE EASTERN SEABOARD. HOWEVER...12Z MODEL TRENDS ARE TENDING TO KEEP THIS SYSTEM TO THE S THANKS TO THE UPPER LEVEL LOW THAT MAY PUSH THE SOUTHERN SYSTEM OFFSHORE. THIS THIS WAS A RECENT TREND THOUGH...DID KEEP CHANCE POPS GOING FROM THU AFTERNOON THROUGH A GOOD PORTION OF FRIDAY DUE TO THE MODEL/S HANDLING OF THE SOUTHERN STREAM UPPER LEVEL SYSTEM. TEMPS ARE ALSO TRYING TO CREEP BACK CLOSER TO SEASONAL LEVELS DURING THIS TIMEFRAME AS WELL. && .AVIATION /02Z SATURDAY THROUGH WEDNESDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. .SHORT TERM /THROUGH SATURDAY NIGHT/... TONIGHT...HIGH CONFIDENCE. VFR. LEFTOVER W-NW WIND GUSTING TO 20 KT TOWARD THE COASTS...DIMINISHING LATE. SATURDAY...HIGH CONFIDENCE. VFR. POSSIBLE BRIEF MVFR IN SPOTTY SHOWERS DURING THE DAY SATURDAY. NORTHWEST WINDS GUSTING AROUND 20 KNOTS. SATURDAY NIGHT...HIGH CONFIDENCE. VFR WITH LIGHT WIND. KBOS TAF...HIGH CONFIDENCE IN OVERALL TAF. KBDL TAF...HIGH CONFIDENCE IN OVERALL TAF. OUTLOOK...SUNDAY THROUGH WEDNESDAY... MODERATE CONFIDENCE SUNDAY THROUGH TUESDAY...LOW CONFIDENCE WEDNESDAY. SUNDAY...MAINLY VFR. MAY SEE BRIEF MVFR CONDITIONS IN SCT SHOWERS. SEA BREEZE DEVELOPMENT POSSIBLE ALONG E COAST. MONDAY-TUESDAY...AREAS OF MVFR CIGS/VSBYS POSSIBLE WITH BETTER CHANCE FOR SHOWERS. N-NE WINDS INCREASE ESPECIALLY ALONG E COAST. MAY SEE GUSTS TO 20-25 KT FROM PLYMOUTH COUNTY S TO CAPE COD AND THE ISLANDS MAINLY MON NIGHT AND TUE. WEDNESDAY...VFR WITH MAINLY DRY CONDITIONS. LIGHT N-NW WINDS. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/... WEST-NORTHWEST WINDS GUST 20 TO 25 KNOTS...WITH STRONGEST GUSTS OFFSHORE. SEAS LINGER NEAR 5 FEET ON THE OUTER WATERS THROUGH SATURDAY...THEN SUBSIDE. SEAS BELOW 5 FEET ALL OTHER WATERS THROUGH THE PERIOD. CANCELLED THE SMALL CRAFT ADVISORY FOR THE SOUNDS OF RI THIS EVENING...WHERE WINDS HAVE DIMINISHED TO LESS THAN 25 KT. SMALL CRAFT ADVISORY LINGERS ON THE OUTER WATERS THROUGH SATURDAY MORNING DUE TO SEAS AND OCCASIONAL GUSTS TO 25 KNOTS. SCA ALSO LINGERS ON RI AND BLOCK ISLAND SOUNDS TONIGHT MOSTLY DUE TO WINDS AT OR NEAR 25 KNOTS. OUTLOOK...SUNDAY THROUGH WEDNESDAY...HIGH CONFIDENCE. SUNDAY...WINDS AND SEAS BELOW SMALL CRAFT CRITERIA. EXPECT NW WINDS TO SHIFT TO NE BUT REMAIN BELOW 15 KT. SEA BREEZES POSSIBLE ALONG E COAST. MONDAY...N-NW WINDS INCREASE BUT REMAIN BELOW SMALL CRAFT. SEAS REMAIN BELOW 5 FT. MONDAY NIGHT THROUGH TUESDAY NIGHT...N-NE WINDS INCREASE...GUSTING TO 25-30 KT. SEAS BUILD UP TO 5-7 FT...HIGHEST ON THE EASTERN OUTER WATERS DURING TUE. MODERATE PROBABILITY FOR SMALL CRAFT. WEDNESDAY...WINDS BECOME NW AND DIMINISH. MAY SEE LEFTOVER GUSTS TO 25 KT EARLY. SEAS WILL REMAIN AOA 5 FT MAINLY ON THE OUTER WATERS. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...FREEZE WARNING FROM 2 AM TO 8 AM EDT SATURDAY FOR CTZ002>004. MA...NONE. RI...FREEZE WARNING FROM 2 AM TO 8 AM EDT SATURDAY FOR RIZ001-003. MARINE...SMALL CRAFT ADVISORY UNTIL NOON EDT SATURDAY FOR ANZ250- 254>256. && $$ SYNOPSIS...WTB/EVT NEAR TERM...WTB/BELK/EVT SHORT TERM...WTB LONG TERM...EVT AVIATION...WTB/BELK/EVT MARINE...WTB/BELK/EVT

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