Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 231149 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 650 AM EST FRI JAN 23 2015 .SYNOPSIS... HIGH PRESSURE WILL MOVE OFFSHORE TODAY. A COASTAL STORM WILL IMPACT MUCH OF THE REGION SATURDAY INTO SATURDAY NIGHT WITH THE POTENTIAL FOR HEAVY SNOW ACROSS PARTS OF THE AREA. LOW PRESSURE WILL PROBABLY PASS TOO FAR SOUTH OF THE REGION MONDAY AND MONDAY NIGHT TO RESULT IN MUCH ACCUMULATING SNOW. HIGH PRESSURE WILL THEN BUILD ACROSS EASTERN CANADA RESULTING IN VERY COLD WEATHER TUESDAY AND WEDNESDAY. && .NEAR TERM /THROUGH TONIGHT/... 650 AM UPDATE... CLEAR SKIES ACROSS THE REGION EARLY THIS MORNING...EXCEPT FOR SOME SCATTERED CLOUDS ALONG THE EAST SLOPES OF THE BERKSHIRES. HIGH PRES WILL PAST SOUTH OF THE REGION TODAY ALLOWING FOR DRY WEATHER TO CONTINUE. TEMPERATURES WILL BE SIMILAR TO YESTERDAY OR PERHAPS A TAD WARMER. LOTS OF DRY AIR ALOFT SO EXPECT PLENTY OF SUNSHINE. TONIGHT... INCREASING CLOUDS AHEAD OF DEVELOPING LOW PRES IN THE MID ATLANTIC. DUE TO LOW IN CANADA WINDS ALOFT WILL BE SW ALLOWING FOR SLIGHT WAA. THIS WILL KEEP MINS FROM FALLING OVERNIGHT. USED 2M TEMPS WITH LOWS DROPPING ONLY INTO THE UPPER 20S TO LOW 30S. && .SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/... HIGHLIGHTS... * FAST MOVING COASTAL STORM ON SAT * RAIN/WET SNOW LINE AND NORTHWEST EXTENT OF HEAVY PRECIP UNCERTAIN * NARROW BAND OF HEAVY WET SNOW POSSIBLE NEAR AND NORTHWEST OF I-495 * INCREASING CHANCE OF FREEZING RAIN/SLEET POTENTIAL SOUTH OF THE PIKE OVERVIEW... DIGGING SHORTWAVE ACROSS THE SOUTHERN PLAINS WILL MOVE ACROSS THE SOUTHEAST AND HEADS TOWARDS THE NORTHEAST BY SATURDAY. THIS DISTURBANCE COMBINED WITH THE NORTHERN STREAM WILL AID IN DEVELOPING A COASTAL STORM MOVING NEAR/JUST INSIDE THE BENCHMARK. THIS SHORTWAVE IS VERY ROBUST ALLOWING FOR THE LOW TO `BOMB` OUT AS IT PASSES CLOSE TO THE BENCHMARK. 00Z GUIDANCE CONTINUES TO SPEED THIS SYSTEM UP MAKING IT MORE OF A SATURDAY TIMEFRAME RATHER THAN A SATURDAY EVENING AS SHOWN A FEW RUNS AGO. EXTEND OF MOISTURE/QPF CONTINUES TO SHIFT SLIGHTLY WEST AS THE LOW PASSES. THIS IS A VERY PROGRESSIVE SYSTEM DUE TO THE LACK OF UPSTREAM BLOCKING...IE NO HIGH IN CANADA. THIS ALSO MAKES THERMAL PROFILES AND EVEN SURFACE TEMPS VERY TRICKY. OVERALL TREND LATELY IS JUST A TAD WARMER IN THERMAL PROFILES COMPARED TO 22.00Z MODEL RUN. DID A BLEND OF THE EC/GFS AND CANADIAN FOR THIS FORECAST. ALTHOUGH PORTIONS OF THE NAM LOOKS GOOD ITS OVERALL SPEED IN EXITING OFFSHORE SEEMS JUST A TAD TOO FAST COMPARED TO REMAINDER OF GUIDANCE SUITE. DESPITE GOOD MODEL AGREEMENT...FORECAST REMAINS VERY DIFFICULT AND CONFIDENCE IS LOWER THAN WE WOULD LIKE AT THIS TIME FRAME SINCE ANY WOBBLES IN TRACK HAS HUGE INFLUENCE IN PRECIPITATION TYPE AND SNOWFALL AMOUNTS. 1) TIMING AND PRECIPITATION TYPE... THIS SYSTEM CONTINUES TO SPEED UP WITH PRECIP MOVING FROM SOUTH TO NORTH. ENTERING CT/RI BEFORE 5AM AND THE REMAINDER OF THE REGION BY 8AM. THIS SYSTEM IS VERY PROGRESSIVE DUE TO LACK OF BLOCKING UPSTREAM SO PRECIP SHOULD BE COMING TO AN END FROM WEST TO EAST BETWEEN 8-11 PM. P-TYPE ISSUES ARE TRICKY WITH THIS SYSTEM AS A DIFFERENCE OF ONE DEGREE CAN CAUSE ISSUES WITH P-TYPE. ONCE PRECIP BEGINS...PROFILES WILL ISOTHERM SO THE SMALLEST CHANGE IN TEMPS CAN EITHER TURN P-TYPE TO SNOW OR RAIN. HOWEVER BIGGEST THING THAT MODELS ARE SHOWING COMPARED TO PREV RUNS IS THE POTENTIAL FOR FREEZING RAIN. APPEARS THAT SOUTHERLY WINDS AT 850MB WILL BE ENOUGH TO ALLOW FOR A 0.5-1C WARM NOSE WHICH COULD ADD FREEZING RAIN INTO THE WINTRY MIX. BOTH THE RGEM/NAM AND GFS HAVE INDICATED PERHAPS A FEW HOURS OF FREEZING RAIN DURING THE MID-MORNING TIMEFRAME ALONG THE MASS PIKE CORRIDOR. DO NOT EXPECT AMOUNTS TO BE A LOT...BUT COULD SEE UP TO 0.10 INCH OF ICE ACCRETION. AS PRECIP MOVES IN TEMPS WILL WET-BULB AT THE ONSET ALLOWING FOR A QUICK BURST OF SNOW...1-3 INCHES...ACROSS THE SOUTH COAST AND INTO RI. TEMPERATURES BEGIN TO WARM ALLOWING FOR A MIX OF SLEET/SNOW/FREEZING RAIN TO WORK ITS WAY UP TO THE MASS PIKE DURING THE LATE MORNING/EARLY AFTERNOON HOURS. BELIEVE TEMPS AND THERMAL PROFILES WILL BE COLD ENOUGH FOR ALL SNOW NORTH OF ROUTE 2. EXPECT ALL RAIN ACROSS THE CAPE AND THE ISLANDS FOR MUCH OF THIS EVENT. AS THE SYSTEM BEGINS TO DEPART...THERMAL PROFILES WILL COOL SIGNIFICANTLY ALLOWING FOR ALL SNOW ON THE BACKSIDE. CONTINUED THE WATCH FOR NOW DUE TO ISSUES WITH THE THERMAL PROFILES AND THE LACK OF CONSISTENCY FROM RUN TO RUN FROM THE MODELS. HAVE ADDED PORTIONS OF NW MASS INTO AN ADVISORY WHERE CONFIDENCE IS HIGHEST. LEFT NW FRANKLIN CO OUT DUE TO SHARP CUT-OFF IN QPF GRADIENT. DID NOT ISSUE ANYTHING SOUTH AND EAST OF THE WATCH AS THERMAL PROFILES ARE TO MARGINAL TO MAKE A CALL. WILL LET DAY SHIFT TAKE ANOTHER LOOK AND HOPEFULLY 12Z GUIDANCE WILL BE BETTER IN LINE. TOTAL SNOWFALL FOR THIS EVENT... WILL GENERALLY BE 2-5 INCHES WITH ISOLATED 6 TO 8 INCHES ALONG THE WORCESTER HILLS AND ALONG/NW OF I-495. 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 NEAR AND NORTHWEST OF I-495 INTO THE NORTHERN WORCESTER HILLS. 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. REGARDLESS...THE TRACK IS NOT SET IN STONE SO RISK FOR HEAVY SNOW BAND STILL SUBJECT TO SHIFT. 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. GREATEST CONCERN RIGHT NOW IS ALONG THE I-495 CORRIDOR NORTH OF I-90. 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. BELIEVE MODELS ARE UNDERDOING THE WINDS SOMEWHAT AND NOT ACCOUNTING FOR THE RAPID DEEPENING OF THE LOW. RIGHT NOW EXPECT NORTH TO NORTHWEST WIND GUSTS OF 40 TO 55 MPH ACROSS THE CAPE AND ISLANDS. 4) COASTAL FLOODING... SEE BELOW. && .LONG TERM /SUNDAY THROUGH THURSDAY/... HIGHLIGHTS... * DRY AND SEASONABLY CHILLY ON SUNDAY * NEXT SYSTEM PROBABLY GIVES US A GLANCING BLOW OR MISS MON/MON NIGHT * VERY COLD TUE/WED WITH WELL BELOW NORMAL TEMPS 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 MONDAY NIGHT... LOW PRESSURE ACROSS THE MIDWEST WILL MOVE EAST TOWARDS THE MID ATLANTIC COAST. THE MODELS ARE IN PRETTY GOOD AGREEMENT THAT THE LOW WILL SLIDE MORE EAST AS OPPOSED TO UP THE COAST...RESULTING A MISS OR A GLANCING BLOW FOR OUR REGION. THERE STILL IS A LOW PROBABILITY THAT THIS SYSTEM ENDS UP FURTHER NORTHWEST RESULTING IN A LARGER IMPACT...BUT MOST OF THE ENSEMBLES ARE PRETTY FAR SOUTH. RIGHT NOW JUST EXPECTING A ROUND OF LIGHT SNOW SHOWERS. WILL HAVE TO WATCH THE SOUTHEAST NEW ENGLAND COAST...WHERE SOME OCEAN ENHANCEMENT MAY OCCUR WITH NORTHEAST WINDS GIVING THEM A BETTER SHOT IN AT LEAST SOME LIGHT ACCUMULATIONS. TUESDAY AND WEDNESDAY... HIGH PRESSURE OVER EASTERN CANADA WILL SEND A VERY COLD AIRMASS INTO SOUTHERN NEW ENGLAND. THE VERY COLD AIR WILL BE DELIVERED ON NORTHERLY WINDS WHICH IS AN IDEAL TRAJECTORY FOR SOUTHERN NEW ENGLAND. THEREFORE...850 MB TEMPS ARE A BIT MISLEADING AND NEED TO LOOK LOWER IN THE ATMOSPHERE. HIGH TEMPS WILL LIKELY ONLY BE IN THE TEENS TO LOWER 20S BOTH DAYS. LOW TEMPS WILL BE IN THE SINGLE DIGITS TO BELOW ZERO EARLY TUE AND WED MORNING/S FOR MANY. DRY WEATHER FOR MOST TUE/WED...BUT WILL PROBABLY SEE A PERIOD OF SOME OCEAN EFFECT SNOW SHOWERS FOR THE SOUTHEAST NEW ENGLAND COAST GIVEN NORTHERLY WIND TRAJECTORIES. THURSDAY... HIGH PRESSURE MOVES OFF THE COAST THURSDAY ALLOWING A RETURN FLOW OF SOMEWHAT MILDER AIR. MAY SEE A FEW SNOW SHOWERS IN THE WARM AIR ADVECTION PATTERN...BUT NOTHING SIGNIFICANT IS EXPECTED. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH FRIDAY NIGHT/...HIGH CONFIDENCE. BEFORE 00Z...HIGH CONFIDENCE VFR. LOW PROB OF MVFR SCT DECK IN WESTERN MASS. TODAY AND TONIGHT...HIGH CONFIDENCE VFR. SATURDAY AND SATURDAY NIGHT...MODERATE CONFIDENCE. MVFR/IFR IN RAIN AND WET SNOW...MAINLY RAIN ON CAPE COD AND ISLANDS BEFORE CHANGE TO SNOW SAT EVENING WHEN N/NW WINDS COULD GUST TO 45KT. SNOW WILL ACCUMULATE ALONG THE RUNWAYS NORTH AND WEST OF I-95. A FEW SITES MAY EVEN SEE A WINTRY MIX DURING THE MID-MORNING HOURS...LOW CONFIDENCE ON EXACT LOCATION AT THIS TIME. KBOS TAF...HIGH CONFIDENCE IN TAF. KBDL TAF...HIGH CONFIDENCE IN TAF. OUTLOOK /SUNDAY THROUGH TUESDAY/... SUNDAY...HIGH CONFIDENCE. VFR. NW WIND GUSTS UP TO 25 KNOTS. MONDAY...LOW TO MODERATE CONFIDENCE. SOME MVFR CONDITIONS POSSIBLE IF A PERIOD SNOW SHOWERS MAKES INTO OUR REGION FROM A STORM PASSING TO OUR SOUTH. BEST SHOT SOUTHEAST NEW ENGLAND. TUESDAY...MODERATE CONFIDENCE. MAINLY VFR BUT SOME MVFR CIGS/VSBYS POSSIBLE ALONG THE SOUTHEAST NEW ENGLAND COAST IN OCEAN EFFECT SNOW SHOWERS. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH SATURDAY NIGHT/. TODAY AND TONIGHT...HIGH CONFIDENCE. A BUILDING SWELL ON THE E OUTER WATERS WILL BEGIN TO RELAX SEAS BELOW 5FT LATER TODAY AND ESP TONIGHT. CONTINUED SCA FOR NOW. SATURDAY AND SATURDAY NIGHT...MODERATE CONFIDENCE. LOW PRESSURE BOMBS OUT AS IT RAPIDLY MOVES NORTHEAST AND CROSSES NEAR 40/70 BENCHMARK SAT AFTERNOON. STRONGEST WINDS EXPECTED SAT AFTERNOON AND SAT NIGHT WITH N/NW GALES ON MOST OF WATERS. GALE WATCHES HAVE BEEN POSTED/CONTINUED. RAIN SAT SHOULD CHANGE TO SNOW SAT EVENING DECREASING VSBYS. GUIDANCE SEEMS TO BE UNDERDOING SEAS JUST A TAD DUE SO INCREASED THEM SLIGHTLY TO ACCOUNT FOR SIGNIFICANT PRESSURE FALLS. OUTLOOK /SUNDAY THROUGH TUESDAY/... SUNDAY...MODERATE TO HIGH CONFIDENCE. NORTHWEST SMALL CRAFT WIND GUSTS OF 20 TO 30 KNOTS EXPECTED IN THE COLD AIR ADVECTION PATTERN. MONDAY AND TUESDAY...LOW TO MODERATE CONFIDENCE. LOW PRESSURE TRACKS SOUTH OF NEW ENGLAND...BUT SHOULD COME CLOSE ENOUGH TO BRING INCREASING N/NE WINDS AND BUILDING SEAS. GALE FORCE WIND GUSTS POSSIBLE LATE MON INTO EARLY TUE ACROSS OUR SOUTHEAST WATERS. && .TIDES/COASTAL FLOODING... ...POCKETS OF MINOR COASTAL FLOODING LIKELY ALONG THE EASTERN MA COAST DURING THE SATURDAY MID AFTERNOON HIGH TIDE CYCLE... GIVEN THE PROGRESSIVE NATURE OF THIS STORM AND LACK OF HIGH PRESSURE OVER EASTERN CANADA 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 SAT AFTERNOON HIGH TIDE. BOSTON HAS AN ASTRO TIDE OF 11.4 FEET AT 230 PM. EXPECTING A 0.5 TO 1 FOOT STORM SURGE ALONG WITH FAIRLY RAPID PRESSURE FALLS. SO DESPITE THE LACK OF STRONG WINDS/HIGH SEAS...SEE POCKETS OF MINOR COASTAL FLOODING ALONG THE EASTERN MA COAST. A COASTAL FLOOD ADVISORY WILL LIKELY BE NEEDED. 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 PROBABLY JUST LOOKING AT SOME MINOR SPLASH OVER. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...WINTER STORM WATCH FROM LATE TONIGHT THROUGH SATURDAY EVENING FOR CTZ002>004. MA...WINTER STORM WATCH FROM LATE TONIGHT THROUGH SATURDAY EVENING FOR MAZ004>007-011>014-026. WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 7 PM EST SATURDAY FOR MAZ003-008>010. RI...WINTER STORM WATCH FROM LATE TONIGHT THROUGH SATURDAY EVENING FOR RIZ001. MARINE...GALE WATCH FROM SATURDAY AFTERNOON THROUGH SUNDAY MORNING FOR ANZ231>235-237-250-251-254>256. SMALL CRAFT ADVISORY UNTIL 7 PM EST THIS EVENING FOR ANZ250- 254. SMALL CRAFT ADVISORY UNTIL 7 AM EST THIS MORNING FOR ANZ255. && $$ SYNOPSIS...DUNTEN/FRANK NEAR TERM...FRANK/DUNTEN SHORT TERM...DUNTEN LONG TERM...FRANK AVIATION...FRANK/DUNTEN MARINE...DUNTEN/FRANK TIDES/COASTAL FLOODING...FRANK

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