Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 042100 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 400 PM EST THU FEB 4 2016 .SYNOPSIS... COLD FRONT STALLING OFFSHORE WILL PROVIDE A FOCUS FOR LOW PRESSURE TO TRAVEL ALONG EARLY TOMORROW. THIS LOW PRESSURE WILL DELIVER A MIX OF RAIN CHANGING TO HEAVY SNOW ACROSS THE REGION. HIGH PRESSURE BRINGS DRY WEATHER OVER THE WEEKEND...ALTHOUGH A WEAK COLD FRONT SUNDAY MAY BRING A FEW CLOUDS. A COMPLEX COASTAL STORM SHOULD AFFECT THE REGION LATER MONDAY INTO TUESDAY. && .NEAR TERM /UNTIL MIDNIGHT TONIGHT/... OVERALL A RELATIVELY QUIET EVENING AS BRIEF MID/SFC RIDGING TAKES HOLD. THIS IS IN ADVANCE OF DEVELOPING COASTAL WAVE CURRENTLY DELIVERING PRECIP TO MUCH OF THE MID ATLANTIC REGION. TEMPS WILL NOT DROP SIGNIFICANTLY THANKS TO THE COLD AIR REMAINING TRAPPED MAINLY TO THE N AND W OF THE REGION. THIS MEANS THAT TEMPS ARE LIKELY ONLY TO DROP INTO THE UPPER 30S AND LOW 40S BEFORE PRECIP BEGINS TO START. MORE ON THE PRECIP/STORM BELOW. && .SHORT TERM /MIDNIGHT THROUGH 6 PM FRIDAY/... TONIGHT INTO TOMORROW... *** WINTER STORM WARNINGS FOR MUCH OF EASTERN MA...NORTHERN RI...AND NORTHEAST CT *** *** WINTER WEATHER ADVISORIES FOR NORTHERN CT...SOUTHERN RI AND SOUTHEAST MA...AS WELL AS WESTERN MA. OVERVIEW AND UNCERTAINTY IN THE FORECAST...INCLUDING TIMING... UPPER LVL SHORTWAVE WILL BE TAKING ON STRONG NEGATIVE TILT AS IT APPROACHES THE REGION DURING THE MORNING HOURS TOMORROW. THIS WILL COMBINE WITH EQUATORWARD ENTRANCE REGION OF STRONG UPPER JET TO DEVELOP COASTAL LOW PRES WAVE ALONG THE FRONTAL BOUNDARY JUST OFFSHORE. LATEST TRENDS ALL MAKE A MUCH CLOSER PASS WITH THIS WAVE THAN PREVIOUS FORECAST...AND GIVEN IT HAS A DIRECT CONNECTION TO BAY OF CAMPECHE AND GULF OF MEXICO MOISTURE...THE QPF FIELD IS EXPECTED TO SPREAD FURTHER W THAN PREVIOUS PROGS. QPF IS GENERALLY WELL AGREED UPON AT THIS POINT...AT ODDS ARE THE LOW LVL THERMAL PROFILES AND HOW QUICKLY/EFFICIENTLY THEY ARE ABLE TO COOL. WHILE TIMING OF THE TROWAL OVERHEAD IS WELL AGREED UPON...WITH PRECIP BEGINNING ALONG SE MA ROUND 10PM...THEN SPREADING NW THROUGH ABOUT 2-4AM. HOW QUICKLY IT CHANGES TO SNOW MAINLY AFTER 4AM IS THE PRIMARY QUESTION. SFC WET-BULBS ARE IN THE UPPER 20S TO LOW 30S...WHICH ARE MARGINAL. EXPECT GRADUAL CHANGE ACROSS WRN MA/CT BETWEEN 2-5AM...CENTRAL...NORTHEAST MA AND RI BETWEEN 4 AM AND 7AM...THEN BETWEEN 7 AM AND MID-DAY FOR SE MA. THE TIMING WILL HAVE MUCH TO DO WITH THE FINAL TOTALS...BUT GIVEN STRONG F-GEN ABOUT H6 YIELDING LIFT WITHIN THE SNOW GROWTH REGIME AROUND H5...HEAVY SNOWFALL RATES COULD LEAD TO ENOUGH DYNAMIC COOLING TO OVERCOME THE MARGINAL TEMPERATURES. HENCE THE RISK FOR HEAVY...WET SNOW DURING THE AM COMMUTE FOR MANY. QPF AND SNOWFALL... VERY HIGH PWAT AIRMASS REMAINS IN PLACE...THE SAME THAT BROUGHT THE PERIOD OF HEAVY RAIN LAST NIGHT. LOOKING AT 1.0-1.25 INCH PWATS /NEARLY 3 STD DEVIATIONS ABOVE NORMAL/ STRONG F-GEN COMBINED WITH MODERATE LLJ WILL YIELD QPF VALUES RANGING FROM THE 0.25 INCHES ACROSS WRN MA/CT TO AS MUCH AS AN INCH+ IN EASTERN MA. SNOWFALL BASED ON THIS QPF IS TRICKY FOR THE THERMAL REGIONS MENTIONED ABOVE. CHANGE-OVER TIMING AND LOW RATIOS ARE LIMITING THE POTENTIAL THIS STORM WOULD OTHERWISE HAVE. HIGHER RATIOS WILL BE WHERE LOWER QPF IS OBSERVED AND VICE-VERSA. THE PEAK OVERLAP IS FROM NE CT INTO NRN RI AND EASTERN MA...WHERE FINAL TOTALS OF 6-8 INCHES ARE POSSIBLE. 3-6 POSSIBLE MAINLY FOR CENTRAL MA/CT...SOUTHERN RI AND PORTIONS OF SE MA WITH LESS ON THE OUTER ARM OF CAPE COD AND THE ISLANDS DUE TO THE FACT THESE AREAS WILL REMAIN RAIN THE LONGEST. IMPACTS... DUE TO THE FACT THAT SNOW RATIOS WILL BE LOW WITH THIS STORM...AND BANDING WITH 1+ INCH/HR RATES ARE POSSIBLE...HEAVY WET SNOW MAY LEAD TO LOCALIZED POWER OUTAGES. THIS WILL BE EXACERBATED BY A LLJ AROUND 40 KT WITH THE POTENTIAL TO MIX DOWN SOME OF IT/S MOMENTUM. THEREFORE...THE COMBINATION OF WIND GUSTS 30-40 MPH AND HEAVY WET SNOW MAY INCREASE THE RISK. THE OTHER PRIMARY IMPACT IS THAT THE CHANGE-OVER AND HEAVIEST PRECIP/SNOW WILL BE OCCURRING DURING THE PEAK HOURS OF THE AM COMMUTE...WITH LOCALIZED VISIBILITY RESTRICTIONS AND SLIPPERY CONDITIONS POSSIBLE ON UNTREATED ROADWAYS. THE MORE DYNAMIC NATURE OF THIS SYSTEM IN RELATION TO PREVIOUS PROGS SUGGEST A SLOWER END AS WELL. ALTHOUGH THE NORTHERLY FLOW WILL BE DRYING THE LOW LEVELS...SO THERE COULD BE A LITTLE BIT OF SNOW LEFTOVER MID-LATE AFTERNOON ACROSS EASTERN MA BEFORE THINGS END BY EARLY EVENING. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... HIGHLIGHTS... * DRY WEATHER THIS WEEKEND * ANOTHER COASTAL STORM WILL AFFECT THE REGION MONDAY OR TUESDAY * DRY WEATHER RETURNS THE MIDDLE OF NEXT WEEK FRIDAY NIGHT INTO SUNDAY...MODERATE CONFIDENCE. HIGH PRESSURE BUILDS OVER REGION FRIDAY NIGHT INTO SATURDAY WITH DRY WEATHER EXPECTED. LOW PRESSURE TRACKING ACROSS EASTERN CANADA WILL SWING A COLD FRONT THROUGH SOUTHERN NEW ENGLAND SUNDAY...BUT THE BEST DYNAMICS/MOISTURE REMAIN FAR ENOUGH TO OUR N THAT WE SHOULD REMAIN DRY. HOWEVER...THE FRONT WILL BRING COLDER AIR INTO OUR REGION BY SUNDAY NIGHT WHICH SETS STAGE FOR POTENTIALLY STORMY WEATHER EARLY NEXT WEEK. MONDAY INTO TUESDAY...LOW CONFIDENCE. MODELS CONTINUE TO STRUGGLE WITH THE STORM POTENTIAL FOR EARLY NEXT WEEK. BOTH MODELS CONTINUE TO INDICATE A STORM OCCURRING DURING THIS TIME FRAME BUT DIFFER ON HOW THEY HANDLE THE STORM. EXPECT THIS STORM TO COME MORE INTO FOCUS IN THE NEXT DAY OR TWO AS THE SHORTWAVES MOVE ON TO THE WEST COAST AND ARE BETTER SAMPLED. HAVE HIGH CONFIDENCE IN SOME SORT OF STORM OCCURRING DURING THIS TIME FRAME. HOWEVER...THE DETAILS ARE STILL VERY UNCERTAIN. 12Z ECMWF PRODUCES TWO COASTAL STORMS...ONE OF WHICH WILL PASS WELL SOUTHEAST OF THE BENCHMARK ON MONDAY /WITH LITTLE EFFECT ON SOUTHERN NEW ENGLAND/...AND THE SECOND OF WHICH PASSES DIRECTLY OVER THE BENCHMARK ON TUESDAY. 12Z GFS PRODUCES A SINGLE COASTAL SYSTEM THAT DEVELOPS OVER THE TRI-STATE AREA AND MOVES OVER SOUTHERN NEW ENGLAND TUESDAY. THIS WOULD RESULT IN WIDELY DIFFERENT TEMPERATURE PROFILES THAN THE ECMWF. DUE TO THE WIDE VARIATIONS IN THESE DETERMINISTIC SOLUTIONS...WE ARE BASING FORECAST MORE ON ENSEMBLES AND WILL UTILIZE CONSENSUS BLEND TO WORK OUT DETAILS FOR NOW. THIS RESULTS IN SNOW DEVELOPING LATE MON INTO TUE...BUT DESPITE COLD TEMPERATURES ALOFT WE WILL PROBABLY BE DEALING WITH WARMTH IN BOUNDARY LAYER WHICH WILL GIVE US ISSUES WITH RAIN/SNOW MIX OR EVEN RAIN...PRIMARILY FROM PROVIDENCE AND BOSTON TO CAPE COD AND ISLANDS. SETUP RIGHT NOW FAVORS HIGHER SNOWFALL AMOUNTS ACROSS INTERIOR...BUT AGAIN...CONFIDENCE IS LOW AND THERE COULD BE SIGNIFICANT ADJUSTMENTS TO FORECAST IN COMING DAYS. FOR NOW...THE POTENTIAL IS THERE BUT WE NEED TO SEE HOW THESE TWO SHORT WAVES EVOLVE AS THEY ENTER WEST COAST AND WORK THEIR WAY ACROSS COUNTRY. WEDNESDAY...LOW CONFIDENCE. AGAIN MODEL SPREAD IS HIGH AT THIS TIME RANGE GIVEN UNCERTAINTIES IN HOW MON/TUE EVOLVES. BUT WE DO EXPECT TO SEE DRYING IN WAKE OF SYSTEM WITH SEASONABLE TEMPERATURES. THURSDAY...MODERATE CONFIDENCE. WHILE SOMEWHAT DEPENDENT ON HOW THE EARLY WEEK SYSTEM PLAYS OUT...THERE IS AGREEMENT AMONGST THE MODELS ON HIGH PRESSURE BUILDING INTO SOUTHERN NEW ENGLAND. EXPECT SEASONABLE TEMPERATURES. && .AVIATION /20Z THURSDAY THROUGH TUESDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH FRIDAY/... THROUGH 06Z...HIGH CONFIDENCE. MAINLY VFR...ESPECIALLY ONCE HYA/ACK CLEAR OUT LATER THIS AFTERNOON. EXPECT GRADUAL SPREAD OF ANOTHER SHIELD OF RAIN FROM S TO N MAINLY AFTER 00Z. LATE TONIGHT INTO 18Z TOMORROW...MODERATE CONFIDENCE. THE RAIN SHIELD CONTINUES TO EXPAND NORTHWEST...COVERING MOST OF SRN NEW ENGLAND BY ABOUT 10-12Z. THIS WILL ALSO BRING ABOUT MVFR/IFR CONDITIONS DUE TO LOW CIGS/VSBYS. THEN...AFTER 09Z ESPECIALLY THE RAIN WILL CHANGE TO SNOW FROM NW-SE UNTIL IT/S ALL SNOW AWAY FROM THE ISLANDS BY ABOUT 15Z. SOME ACCUMULATION IS POSSIBLE...ESPECIALLY ON GRASSY SFCS. HOWEVER RUNWAYS MAY RECEIVE A PLOWABLE AMOUNT MAINLY E OF AN IJD-ORH-BVY LINE. THIS WILL BE ACCOMPANIED BY MAINLY IFR CONDITIONS. AFTER 18Z TOMORROW...MODERATE CONFIDENCE. SNOWS/RAIN COME TO AN END AND VERY QUICK IMPROVEMENT TO VFR EXPECTED. KBOS TERMINAL...HIGH CONFIDENCE IN TRENDS...LOWER CONFIDENCE IN TIMING OF PRECIP AND CHANGE TO SNOW LATE TONIGHT/TOMORROW MORNING. KBDL TERMINAL...MODERATE CONFIDENCE IN TAF DUE TO UNCERTAINTY IN PRECIP TIMING. OUTLOOK /FRIDAY NIGHT THROUGH TUESDAY/... FRIDAY NIGHT THROUGH SUNDAY...HIGH CONFIDENCE. VFR. MONDAY AND TUESDAY...LOW CONFIDENCE. MVFR/IFR POSSIBLE IN RAIN OR SNOW...ESPECIALLY LATE. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH FRIDAY/...HIGH CONFIDENCE. THROUGH TONIGHT... WINDS GRADUALLY SHIFT MAINLY TO THE N THROUGH THE NIGHT...BUT WITH BOTH SEAS AND GUSTS BELOW SCA THRESHOLDS. THEREFORE...LEFTOVER SMALL CRAFT ADVISORIES WILL BE DROPPED BUT IN FAVOR OF A GALE WARNING...MORE ON THAT BELOW. TOMORROW... NORTHERLY WIND GUSTS PICK UP THROUGH THE MORNING...WITH GUSTS BETWEEN 30 AND 35 KT ALONG THE SOUTHERN WATERS...AND 35-45 KT ON THE EASTERN WATERS. GALE WARNINGS HAVE BEEN ISSUED FOR MUCH OF THE DAY. SEAS BECOME HIGH...MAINLY 8-10 FT ON THE SE OCEAN WATERS. OTHERWISE...EXPECT A PERIOD OF RAIN/FOG ACROSS THE WATERS WITH A POSSIBLE CHANGE TO SNOW NEAR THE EASTERN SHORELINES. OUTLOOK /FRIDAY NIGHT THROUGH MONDAY/...MODERATE CONFIDENCE... FRIDAY NIGHT...HIGH CONFIDENCE. WINDS AND SEAS DIMINISH AS HIGH PRESSURE STARTS TO BUILD OVER THE WATERS. SCA LIKELY NEEDED FOR LINGERING SEAS. SATURDAY INTO SUNDAY...MODERATE CONFIDENCE. WINDS AND SEAS MAINLY BELOW SCA. LINGERING 5 FOOT SEAS SATURDAY MORNING. MONDAY AND TUESDAY...LOW CONFIDENCE. EXPECT INCREASING N/NE WINDS AHEAD OF COASTAL LOW. SCA CONDITIONS LIKELY WITH 25-30KT GUSTS AND SEAS BUILDING TO 5 FT OR HIGHER. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...WINTER STORM WARNING FROM 1 AM TO 3 PM EST FRIDAY FOR CTZ004. WINTER WEATHER ADVISORY FROM 1 AM TO 1 PM EST FRIDAY FOR CTZ002-003. MA...WINTER WEATHER ADVISORY FROM 7 AM TO 3 PM EST FRIDAY FOR MAZ019>022. WINTER STORM WARNING FROM 1 AM TO 3 PM EST FRIDAY FOR MAZ004>007-012>018-026. WINTER WEATHER ADVISORY FROM 1 AM TO 1 PM EST FRIDAY FOR MAZ011. RI...WINTER WEATHER ADVISORY FROM 7 AM TO 3 PM EST FRIDAY FOR RIZ003-004-006-007. WINTER STORM WARNING FROM 1 AM TO 3 PM EST FRIDAY FOR RIZ001- 002. MARINE...GALE WARNING FROM 7 AM TO 7 PM EST FRIDAY FOR ANZ231>235-237- 250-254>256. SMALL CRAFT ADVISORY FROM 7 AM TO 7 PM EST FRIDAY FOR ANZ230- 236-251. SMALL CRAFT ADVISORY UNTIL 7 PM EST THIS EVENING FOR ANZ235- 237-250-254>256. && $$ SYNOPSIS...DOODY/RLG NEAR TERM...DOODY SHORT TERM...DOODY LONG TERM...RLG AVIATION...DOODY/RLG MARINE...DOODY/RLG

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