Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 240920 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 420 AM EST SAT JAN 24 2015 .SYNOPSIS... A COASTAL STORM WILL IMPACT MUCH OF THE REGION TODAY AND THIS EVENING WITH HEAVY SNOW AND A WINTRY MIX ACROSS PARTS OF THE AREA. DRY AND SEASONABLE WEATHER EXPECTED ON SUNDAY. A WINTER STORM "MAY" BE BACK ON THE TABLE FOR SOME OF THE REGION LATE MONDAY INTO TUESDAY...BUT CONFIDENCE IS LOW. WHETHER OR NOT WE HAVE A WINTER STORM...IT WILL BE VERY COLD MONDAY THROUGH WEDNESDAY WITH MODERATING TEMPERATURES BY THE END OF THE WORK WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... **COASTAL STORM BRINGS MIXED PRECIP...WINDS AND COASTAL FLOODING** 4AM UPDATE... OVERRUNNING PRECIP IS ONGOING AHEAD OF DEVELOPING LOW PRESSURE SYSTEM IN THE CAROLINAS. MOST OF THE EASTERN SEABOARD IS IMPACTED RIGHT NOW WITH HEAVY SNOW. IN FACT PORTIONS OF NJ AND EASTERN PA HAS SEEN OVER 5 INCHES AS OF 330 AM. SNOW IS ALREADY STARTING TO FALL IN CT AND SOUTHERN RI AND EXPECT THE SNOW TO SPREAD RAPIDLY NORTHWARD. LATEST SREF GUIDANCE INDICATES THAT SNOW FALL RATES MAY BE AN INCH AN HOUR AT THE ONSET AND THIS SEEMS TO BE VERIFYING DOWNSTREAM. HI- RES GUIDANCE INCLUDING THE HRRR ARE PINPOINTING CT AND RI AS LOCATIONS THAT COULD SEE THIS SNOW BURST. VISIBILITIES WILL ALSO BE REDUCED VERY QUICKLY...DOWN TO HALF OF A MILE OR LESS IN SOME LOCATIONS. EXPECT A QUICK THUMP OF SNOW ONCE PRECIP MOVES IN WHICH COULD QUICKLY ADD UP TO 1-3 INCHES BEFORE ANY WINTRY MIX BEGINS. MORE DETAILS ON THE EVOLUTION OF THIS STORM BELOW: HIGHLIGHTS... * FAST MOVING COASTAL STORM TODAY. * NARROW BAND OF HEAVY WET SNOW POSSIBLE IN INTERIOR NORTHEAST MASS. * CHANCE OF FREEZING RAIN/SLEET POTENTIAL ALONG AND SOUTH OF THE PIKE. * STRONG WINDS FOR THE SOUTHEAST MA THIS EVENING. HEADLINES... NO MAJOR CHANGES TO HEADLINES AT THIS TIME AS SNOW AMOUNTS ARE FAIRLY SIMILAR TO PREV FORECASTERS. HAVE A LOW CONFIDENCE THAT ANYONE WILL SEE 10 INCHES DUE TO THE WET NATURE OF THE SNOW AND HOW PROGRESSIVE THIS SYSTEM IS. DID ADD COASTAL ESSEX COUNTY TO THE WARNING AS THERE COULD BE SOME DECENT ACCUMS ON THE BACKSIDE OF THIS SYSTEM DUE TO DECENT FGEN AND OMEGA IN THE SNOW GROWTH REGION. ALSO ADDED NEWPORT COUNTY IN RHODE ISLAND AND COASTAL PLYMOUTH TO THE ADVISORY AS THEY COULD SEE A QUICK 1-2 INCHES OF SNOW AT THE ONSET BUT WILL CHANGE TO SLEET/FREEZING RAIN MIX WHICH COULD MAKE THINGS SLICK BEFORE TRANSITIONING TO RAIN. OVERVIEW... DIGGING SHORTWAVE IN THE SOUTHEAST HAS DEVELOPED A SURFACE LOW OFF THE COAST OF THE CAROLINAS. THIS LOW WILL QUICKLY DEEPEN AND BOMB OUT AS IT MOVES TOWARDS THE GULF OF MAINE TODAY. 00Z GUIDANCE HAS COME INTO BETTER AGREEMENT THEN PREV RUNS HOWEVER THIS STILL SOME UNCERTAINTY SINCE THERMAL PROFILES ARE ISOTHERMAL...ONE DEGREE CAN ADD OR SUBTRACT SIGNIFICANTLY FROM SNOW AMOUNTS. FOR THIS FORECAST TRENDED TOWARDS THE 00Z NAM/EC/RGEM WHICH ARE ALL IN LINE WITH ONE ANOTHER. FEEL THE GFS QPF IS A LITTLE UNDERDONE. THE 06Z NAM CAME IN RATHER WARM THEN REST OF GUIDANCE AND ITS 00Z COUNTERPART. SO EVEN FORECAST GUIDANCE IS STILL FLIP-FLOPPING ON THERMAL FIELDS WITHIN 3-6 HOURS OF THIS EVENT. THE 00Z TREND IS ALSO FASTER SO HAVE SPEED THE SYSTEM UP WITHIN THE FORECAST BY AN HOUR OR TWO. APPEARS THAT TONIGHT WE MAY JUST SEE A FEW FLAKES ON THE CAPE AS THIS SYSTEM EXIT THE REGION QUICKLY. LASTLY...MODELS ARE ALSO INDICATING A GOOD COLD CONVEYOR BELT SET-UP ON THE BACKSIDE SO HAVE ADJUSTED SNOW TOTALS ACROSS EASTERN MASS WHICH COULD SEE DESCENT SNOW AMOUNTS LATE THIS AFTERNOON/EVENING HOURS. 1) TIMING AND PRECIPITATION TYPE... PRECIP HAS ALREADY ENTERED SOUTHERN NEW ENGLAND AND SHOULD OVER SPREAD TO THE REST OF THE REGION BY 7AM. AS NOTED BY PREV FORECASTERS...THIS SYSTEM IS VERY PROGRESSIVE DUE TO LACK OF BLOCKING UPSTREAM. SINCE GUIDANCE CONTINUES TO SPEED THE ONSET...EXPECT PRECIP TO COME TO AN END FROM WEST TO EAST BETWEEN 5- 9PM. P-TYPE ISSUES ARE TRICKY WITH THIS SYSTEM AS A DIFFERENCE OF ONE DEGREE CAN CAUSE CHANGES WITH P-TYPE. SNOW WILL START AREA WIDE INCLUDING THE CAPE AND THE ISLANDS THANKS TO OVERRUNNING FROM THE WAA. THERMAL PROFILES ARE STILL WAVY...SO BELIEVE THAT A MIX OF SNOW/SLEET/FREEZING RAIN WILL WORK ITS WAY INTO NORTHERN CT...RHODE ISLAND AND SOUTH OF THE MASS PIKE INTO BOS WHEN TEMPS BEGIN TO WARM AT 850MB. EXPECT MOSTLY RAIN AFTER THE INITIAL ONSET OF SNOW ACROSS THE CAPE AND ISLANDS. ALL SNOW WEST OF THE WORCESTER HILLS IN MASS. TOTAL SNOWFALL FOR THIS EVENT...WILL GENERALLY BE 3-6 INCHES WITH SOME 6 TO 9 INCH REPORTS ALONG THE WORCESTER HILLS AND INTO INTERIOR NORTHEAST MASS. 2) RISK FOR NARROW BAND OF HEAVY WET SNOW... THERE IS A RISK FOR A NARROW BAND OF HEAVY WET SNOW. THE MOST LIKELY AREA IS IN INTERIOR ESSEX COUNTY AND PORTIONS OF MIDDLESEX COUNTY THAT IS ALONG THE I-495 BELT. IT WILL PROBABLY BE TOO WARM FOR ANY SIGNIFICANT SNOW FOR THE FAR SOUTHEAST NEW ENGLAND COAST. ALSO THERMAL FIELDS SOUTH OF THE PIKE ARE TO MARGINAL AND WITH MIX MOVING IN...SNOWFALL AMOUNTS WILL BE LOWER. WHERE THIS HEAVY BAND SETS-UP THE RISK FOR POWER OUTAGES AND DOWN TREE LIMBS WILL BE A POSSIBILITY ESP IF SNOW TOTALS ARE 6+ INCHES. 3) STRONG WINDS ACROSS THE CAPE/ISLANDS... LOW PRESSURE WILL UNDERGO BOMBOGENESIS AS IT TRACKS NEAR THE BENCHMARK SATURDAY AFTERNOON. THE SYSTEM DROPS 40 MB IN 24 HOURS AS IT WILL BE A SUB 970 MB ONCE IT PULLS AWAY FROM THE BENCHMARK. WIND POTENTIAL IS LIMITED DUE TO PROGRESSIVE NATURE OF THIS SYSTEM. HOWEVER DUE TO THE STRONG PRESSURE FALLS BEHIND THIS SYSTEM WE COULD SEE WIND ADV CRITERIA ALONG THE CAPE AND THE ISLANDS. EXPECT NORTH TO NORTHWEST WIND GUSTS OF 40 TO 50 MPH ACROSS THE CAPE AND ISLANDS. NO CHANGES TO WIND HEADLINES AT THIS TIME. 4) COASTAL FLOODING... SEE COASTAL FLOODING SECTION BELOW. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/... TONIGHT... AFTER THE BRIEF BURST OF SNOW/WIND EXPECT A BREEZY AND COLD NIGHT BEHIND THE EXITING LOW PRES ESPECIALLY AFTER MIDNIGHT. DEPENDING ON HOW QUICKLY THE WINDS ARE ABLE TO DRY AREA ROADWAYS AND SIDEWALKS...MAY NEED TO WATCH FOR SOME LEFTOVER PATCHY BLACK ICE AS TEMPS FALL BACK INTO THE UPPER TEENS AND 20S BY DAYBREAK SUN. && .LONG TERM /SUNDAY THROUGH FRIDAY/... HIGHLIGHTS... * DRY AND SEASONABLE SUNDAY * WINTER STORM "MAY" BE BACK ON THE TABLE LATE MON/TUE - LOW CONFIDENCE * VERY COLD MON-WED WITH MODERATING TEMPS THU/FRI DETAILS... SUNDAY... RAPIDLY INTENSIFYING LOW PRESSURE WILL ALREADY HAVE LIFTED INTO THE CANADIAN MARITIMES EARLY SUN AM. IN ITS WAKE...DRY BUT BLUSTERY AND SEASONABLY CHILLY WEATHER EXPECTED. HIGHS MAINLY IN THE 30S...BUT IT WILL FEEL A BIT COLDER WITH NORTHWEST WIND GUSTS BETWEEN 20 AND 30 MPH. MONDAY AND TUESDAY... VERY LOW CONFIDENCE FORECAST. A FEW OF THE GFS ENSEMBLES AND PARTICULARLY THE 00Z OPERATIONAL ECMWF ARE NOW STRONGER WITH THE SHORTWAVE ENERGY DROPPING INTO THE SOUTHEAST STATES. THIS ALLOWS FOR A MORE AMPLIFIED UPPER LEVEL PATTERN...WHICH CAPTURES LOW PRESSURE ALLOWING A TRACK CLOSER TO THE COAST. FOR WHAT ITS WORTH...THE 00Z ECMWF SHOWS A MAJOR WINTER STORM FOR EASTERN NEW ENGLAND WITH HEAVY SNOW AND STRONG WINDS. KEEP IN MIND THIS IS JUST ONE OPERATIONAL MODEL RUN AND THE FIRST TO SHOW IT. MUCH OF THE 00Z GUIDANCE IS STILL WAY SOUTHEAST AND PRETTY MUCH A MISS FOR MOST OF THE REGION. WILL NEED TO SEE IF THIS WAS JUST A HICCUP OR IF THE ECMWF AND A FEW OF THE GEFS ARE ONTO SOMETHING IN THE NEXT 24 HOURS. REGARDLESS IF WE GET A WINTER STORM OR NOT...OCEAN EFFECT SNOW SHOWERS WILL LIKELY AFFECT SOUTHEAST MA/CAPE ISLANDS WITH VERY COLD NORTHEAST WINDS BLOWING OVER THE OCEAN. IT WILL ALSO BE QUITE COLD MON AND ESPECIALLY TUE...WHEN HIGHS MAY REMAIN IN THE TEENS FOR MUCH OF THE REGION. WEDNESDAY... IF WE DO END UP WITH THAT WINTER STORM...IT WOULD HAVE COME TO AN END BY EARLY WED. STILL WILL BE VERY COLD ACROSS THE REGION WITH SOME BELOW ZERO READINGS EXPECTED EARLY WED MORNING. THURSDAY AND FRIDAY... HIGH PRESSURE MOVES OFF THE COAST THURSDAY ALLOWING A RETURN FLOW OF SOMEWHAT MILDER AIR. SOME MODELS SHOWING LOW PRESSURE DEVELOPING OFF THE COAST BY FRI...BUT VERY LOW CONFIDENCE AT THIS TIME. && .AVIATION /09Z SATURDAY THROUGH WEDNESDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH TONIGHT/... TODAY...MODERATE CONFIDENCE. ALTHOUGH HAVE SOMEWHAT HIGH CONFIDENCE...LOWER CONFIDENCE IN EXACT TIMING OR WHERE THE RAIN/SNOW/MIX LINE ENDS UP. COASTAL LOW WILL PASS SE OF THE REGION. ANY VFR CONDITIONS WILL DROP TO IFR IN RAIN AND HEAVY WET SNOW. SNOW WILL ACCUMULATE ALONG THE RUNWAYS AS SNOWFALL RATES WILL BE CLOSE TO AN INCH AN HOUR AND VSBYS WILL DROP TO A QUICK 1/2SM AT THE ONSET. EXPECT MAINLY RAIN ON CAPE COD AND ISLANDS BY MID-MORNING BEFORE CHANGE TO SNOW THIS EVENING WHEN N/NW WINDS COULD GUST TO 45KT. A FEW SITES WILL SEE A WINTRY MIX DURING THE MID-MORNING HOURS...ESP BDL-ORH-BOS LINE SOUTHWARD. TOMORROW NIGHT...HIGH CONFIDENCE. CONDITIONS IMPROVE WITH WINDS SHIFTING NW. COULD BE A BURST OF SNOW AT CAPE COD TAF SITES BRIEFLY BEFORE ENDING WITH LOW VSBYS AND QUICK ACCUMS DURING THE EVENING. AFTER ENDING EXPECT RAPID IMPROVEMENT TO VFR BUT WITH WIND GUSTS 20-30KT OUT OF THE NW. KBOS TAF...HIGH CONFIDENCE IN TAF TRENDS...LOWER CONFIDENCE IN EXACT TIMING OF MIXING. KBDL TAF...HIGH CONFIDENCE IN TAF TRENDS...LOWER CONFIDENCE IN EXACT TIMING OF MIXING. OUTLOOK /SUNDAY THROUGH WEDNESDAY/... SUNDAY...HIGH CONFIDENCE. VFR. NW WIND GUSTS UP TO 25 KNOTS. MONDAY AND TUESDAY...LOW CONFIDENCE. MVFR-IFR CONDITIONS MAY DEVELOP IF COASTAL LOW PRESSURE TRACKS CLOSE ENOUGH TO OUR REGION LATE MON INTO TUE. HIGHEST RISK SOUTHEAST NEW ENGLAND COAST. STRONG NORTHEAST WINDS ARE ALSO POSSIBLE ON THE COAST DEPENDING ON TRACK OF THE STORM. WEDNESDAY...LOW TO MODERATE CONFIDENCE. WHAT EVER HAPPENS WITH THE STORM LATE MON INTO TUE...EXPECT CONDITIONS TO IMPROVE TO VFR FROM WEST TO EAST. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH TONIGHT/. TODAY AND TONIGHT...HIGH CONFIDENCE. STRENGTHEN COASTAL LOW WILL RAPIDLY MOVE INSIDE THE 70N/40W BENCHMARK THIS EVENING. THIS LOW WILL `BOMB` OUT...MEANING THAT INTENSE PRESSURE FALLS WILL BE ASSOCIATED WITH IT. THIS WILL ALLOW FOR A PERIOD OF STRONG GALE FORCE WINDS OUT OF THE N-NE...THEN SHIFTING TO THE NW BY LATE EVENING AS THE LOW MOVES OVER. EXPECT HEAVY RAIN AND FOG...POSSIBLY EVEN A LITTLE BIT OF SNOW CLOSER TO THE SHORE. THE GALES BEGIN DURING THE AFTERNOON. SEAS BUILD TO ABOUT 15 FT ON THE OUTER SE WATERS. OUTLOOK /SUNDAY THROUGH WEDNESDAY/... SUNDAY...HIGH CONFIDENCE. NORTHWEST SMALL CRAFT WIND GUSTS OF 20 TO 30 KNOTS EXPECTED IN THE COLD AIR ADVECTION PATTERN. MONDAY AND TUESDAY...LOW CONFIDENCE. LOW PRESSURE TO OUR SOUTHEAST WILL COMBINE WITH HIGH PRESSURE OVER EASTERN CANADA. HOW CLOSE THIS LOW TRACKS TO THE COAST REMAINS HIGHLY UNCERTAIN. REGARDLESS...SHOULD HAVE STRONG SCA TO NORTHEAST GALE GUSTS LATE MON/TUE WITH SEAS BUILDING TO 10+ FEET ACROSS OUR EASTERN WATERS. IF COASTAL LOW TRACKS FURTHER WEST LIKE THE 00Z ECMWF...SEAS OF 20+ FEET AND STORM FORCE WIND GUSTS WOULD BE POSSIBLE. WEDNESDAY...LOW CONFIDENCE. WIND SPEEDS AND SEAS WILL LIKELY BE DETERMINED BY TRACK OF THE COASTAL LOW LATE MON INTO TUE. MAY HAVE AT LEAST SOME LEFT OVER SMALL CRAFT ADVISORY WIND GUSTS FROM THE NORTHWEST. && .TIDES/COASTAL FLOODING... **POCKETS OF MINOR COASTAL FLOODING LIKELY ALONG THE EASTERN MA COAST DURING THE MID AFTERNOON HIGH TIDE CYCLE** GIVEN THE PROGRESSIVE NATURE OF THIS STORM AND LACK OF ONSHORE WIND/HIGH SEAS...WE ARE NOT EXPECTING A SIGNIFICANT COASTAL FLOOD EVENT. HOWEVER...EXPECT THAT WE WILL SEE SOME POCKETS OF MINOR COASTAL FLOODING ALONG THE EASTERN MA COAST DURING THE MID AFTERNOON HIGH TIDE CYCLE. BOSTON HAS AN ASTRO TIDE OF 11.4 FEET AT 230 PM THIS AFTERNOON. EXPECTING A 0.5 TO 1 FOOT STORM SURGE ALONG WITH FAIRLY RAPID PRESSURE FALLS. SO DESPITE THE LACK OF STRONG WINDS/HIGH SEAS...EXPECT SOME POCKETS OF MINOR COASTAL FLOODING. THERE IS A LOWER ASTRO HIGH TIDE OF 11.0 FEET IN BOSTON AT AROUND 230 AM SUNDAY MORNING. HOWEVER...BY THIS TIME WINDS WILL BE OFFSHORE SO WERE ONLY CONCERNED ABOUT THIS AFTERNOON/S HIGH TIDE. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...WINTER STORM WARNING UNTIL 7 PM EST THIS EVENING FOR CTZ002>004. MA...WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR MAZ002- 003-008-009-015>021. COASTAL FLOOD ADVISORY FROM 11 AM THIS MORNING TO 4 PM EST THIS AFTERNOON FOR MAZ007-015-016-019-022-024. WINTER STORM WARNING UNTIL 7 PM EST THIS EVENING FOR MAZ004>007-010>014-026. WIND ADVISORY FROM 3 PM THIS AFTERNOON TO MIDNIGHT EST TONIGHT FOR MAZ022-024. RI...WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR RIZ002>007. WINTER STORM WARNING UNTIL 7 PM EST THIS EVENING FOR RIZ001. MARINE...GALE WARNING FROM 1 PM THIS AFTERNOON TO 7 AM EST SUNDAY FOR ANZ231>235-237-250-251-254>256. SMALL CRAFT ADVISORY FROM 1 PM THIS AFTERNOON TO 7 AM EST SUNDAY FOR ANZ230-236. && $$ SYNOPSIS...FRANK/DUNTEN NEAR TERM...DUNTEN SHORT TERM...DUNTEN LONG TERM...FRANK AVIATION...FRANK/DUNTEN MARINE...FRANK/DUNTEN TIDES/COASTAL FLOODING...STAFF

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