Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 221500 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 1000 AM EST THU JAN 22 2015 .SYNOPSIS... HIGH PRESSURE WILL BUILD INTO THE REGION TONIGHT AND LAST INTO FRIDAY. A COASTAL STORM WILL IMPACT MUCH OF THE REGION SATURDAY INTO SATURDAY NIGHT...BUT THE RAIN/SNOW LINE AND NORTHWEST EXTENT OF HEAVY PRECIPITATION REMAINS UNCERTAIN. DRY AND CHILLY WEATHER FOLLOWS SUNDAY. SOME SNOW IS POSSIBLE MONDAY IF LOW PRESSURE TRACKS CLOSE ENOUGH TO THE COAST...BUT EITHER WAY VERY COLD WEATHER FOLLOWS TUESDAY INTO WEDNESDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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10 AM UPDATE... AS HIGH PRES CONTINUES TO NOSE IN FROM THE W...NOTE A MORE NORTHERLY COMPONENT TO THE WIND. THIS CONTINUES TO ERODE MOST LIGHT SNOWS ACROSS THE S COAST. HOWEVER...IT HAS CONTINUED TO ENHANCE OCEAN ENHANCED ACTIVITY WITHIN AND NEAR MASS BAY TO CAPE COD BAY. THEREFORE...HAVE POPS DECREASING W...AND INCREASING TO CHANCE ACROSS THE EXTREME E.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... TONIGHT INTO FRIDAY... PRECIP SHOULD BE AT AN END BY TONIGHT. SECONDARY SHORTWAVE WILL PUSH THROUGH ALLOWING FOR CAA TO SPREAD ACROSS THE REGION. THIS SHORTWAVE MAY KEEP CLOUD AROUND DURING THE FIRST HALF OF THE NIGHT. 850 MB LLJ WILL ALSO BEING MOVING THROUGH BEHIND THE SHORTWAVE KEEPING WIND GUSTS UP TO 15-20 MPH. THIS WILL LIMIT ANY RADIATIONAL COOLING OVERNIGHT SO KEPT TEMPS CLOSE TO GUIDANCE RIGHT NOW. IF CONDITIONS DECOUPLE THEN TEMPS WILL NEED TO BE DROPPED INTO THE SINGLE DIGITS. HIGH PRESSURE WILL BUILD INTO THE MID-ATLANTIC ON FRIDAY. THIS WILL KEEP CONDITIONS DRY AND SKIES MOSTLY CLEAR. TEMPERATURES WILL WARM NEAR OR ABOVE THE FREEZING MARK. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... HIGHLIGHTS... * FAST MOVING COASTAL STORM SAT INTO SAT NIGHT * RAIN/WET SNOW LINE AND NORTHWEST EXTENT OF HEAVY PRECIP UNCERTAIN * NARROW BAND OF HEAVY WET SNOW POSSIBLE NEAR AND NORTHWEST OF I-95 * SOME SNOW POSS MON IF LOW TRACKS CLOSE ENOUGH TO OUR REGION * VERY COLD AIR EXPECTED MON THROUGH WED DETAILS... SATURDAY AND SATURDAY NIGHT... UPPER LEVEL ENERGY WILL MOVE TOWARDS THE GULF OF MEXICO ALONG WITH ITS ASSOCIATED LOW PRESSURE SYSTEM OVER THE NEXT 36 HOURS. SHORTWAVE ENERGY IS FAIRLY IMPRESSIVE AND WILL ALLOW THE SYSTEM TO INTENSIFY AS IT LIFTS NORTHEAST. IN FACT...THE LOW PRESSURE SYSTEM SHOULD BECOME A BOMB AS IT MOVES RAPIDLY NORTHEAST AND CROSSES SOMEWHERE NEAR THE BENCHMARK SATURDAY EVENING. THERE IS STILL SOME DISCREPANCY ON WHETHER THE STORM TRACKS A BIT INSIDE OR OUTSIDE THE BENCHMARK...WHICH WILL HAVE HUGE IMPACTS ON SPECIFIC OUTCOMES. THIS REMAIN A VERY DIFFICULT AND LOW CONFIDENCE FORECAST. THE MAIN ISSUE IS THAT WE DO NOT HAVE A HIGH PRESSURE SYSTEM OVER EASTERN CANADA...INSTEAD WE HAVE WEAK LOW PRESSURE. THEREFORE...THERMAL PROFILES ARE VERY MARGINAL BETWEEN RAIN AND HEAVY WET SNOW. THE OTHER PROBLEM IS THAT WITHOUT THE HIGH PRESSURE SYSTEM...BAROCLINICITY IS LESS THAN WE OFTEN SEE IN MANY WINTER STORM/S. THAT MEANS THE NORTHWEST EXTENT OF THE HEAVIER QPF MIGHT BE MORE LIMITED THEN WE TYPICALLY SEE FOR THE GIVEN TRACK...ESPECIALLY WITH A PROGRESSIVE PATTERN WITH NOT MUCH DOWNSTREAM BLOCKING. 1) RISK FOR NARROW BAND OF HEAVY WET SNOW THERE IS THE RISK FOR A NARROW BAND OF HEAVY WET SNOW. THE MOST LIKELY AREA IS NEAR AND NORTHWEST OF I-95 INTO THE WORCESTER HILLS AND EASTERN CT. IT WILL PROBABLY BE TOO WARM FOR ANY SIGNIFICANT SNOW FOR THE FAR SOUTHEAST NEW ENGLAND COAST. HOWEVER...EVEN THE SOUTHEAST NEW ENGLAND COAST MAY CHANGE TO SNOW AS STORM EXPLODES AND COLDER AIR WORKS INTO THE REGION. OF COURSE...THE TRACK IS NOT SET IN STONE SO RISK FOR HEAVY SNOW BAND STILL SUBJECT TO SHIFT EAST OR WEST. 2) TIMING OF PRECIPITATION/PTYPE: PRECIPITATION LOOKS TO OVERSPREAD THE REGION SATURDAY MORNING FROM SOUTH TO NORTH. THE HEAVIEST PRECIPITATION SHOULD FALL FROM SAT AFTERNOON INTO THE EVENING...BUT SHOULD QUICKLY COME TO AN END THEREAFTER AS STORM IS QUITE PROGRESSIVE. PTYPE STILL VERY DIFFICULT...BUT RIGHT NOW LOOKING AT BULK OF PRECIP TO BE SNOW NEAR AND NORTHWEST OF I-95 AND RAIN SOUTHEAST OF THAT REGION. EVEN AREAS SOUTHEAST OF I-95 SHOULD CHANGE TO SNOW AS COLDER AIR WRAPS INTO THE SYSTEM SAT EVENING. 3) STRONG WINDS ACROSS THE CAPE/ISLANDS: LOW PRESSURE WILL UNDERGO BOMBOGENESIS AS IT TRACKS NEAR THE BENCHMARK SATURDAY EVENING. THE SYSTEM DROPS 40 MB IN 24 HOURS AS IT WILL BE A SUB 970 MB ONCE IT PULLS AWAY FROM THE BENCHMARK. IF WE HAD A LARGE HIGH PRESSURE SYSTEM ACROSS EASTERN CANADA...WE PROBABLY WOULD BE TALKING ABOUT NEAR HURRICANE FORCE WIND GUSTS ALONG THE COAST. HOWEVER...THAT IS MISSING IN THIS CASE WHICH WILL LIMIT WIND POTENTIAL. NONETHELESS...RAPID PRESSURE FALLS WILL PROBABLY RESULT IN A PERIOD OF NORTH TO NORTHWEST WIND GUSTS OF 40 TO 55 MPH ACROSS THE CAPE AND ISLANDS. SUNDAY THROUGH WEDNESDAY... DRY AND BLUSTERY WEATHER FOLLOWS ON SUNDAY. LOW PRESSURE MAY BRING SOME SNOW TO THE REGION MON INTO MON NIGHT...IF THE GFS IS CORRECT. HOWEVER...ECMWF/GGEM TAKE THE NEXT LOW FURTHER SOUTH KEEPING US MAINLY DRY. A LOT OF UNCERTAINTY...BUT REGARDLESS IT SHOULD TURN VERY COLD TUE AND WED. HIGH OVER EASTERN CANADA WILL DELIVER SHALLOW COLD AIR ON NORTH WINDS...SO 850 TEMPS A BIT MISLEADING. PERHAPS EVEN A PERIOD OF SOME OCEAN EFFECT SNOW SHOWERS FOR THE SOUTHEAST NEW ENGLAND COAST. && .AVIATION /15Z THURSDAY 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/... TODAY...A BROKEN DECK OF MARGINAL MVFR TO VFR CIGS. MAINLY DRY ALTHOUGH A FEW LIGHT SNOW SHOWERS/FLURRIES POSSIBLE ACROSS CAPE AND NANTUCKET INTO EARLY AFTERNOON. TONIGHT AND TOMORROW...HIGH CONFIDENCE. VFR. KBOS TAF...HIGH CONFIDENCE IN TAF TRENDS. LOW CONFIDENCE ON OCEAN EFFECT SNOW SHOWER IMPACT ON TERMINAL. KBDL TAF...HIGH CONFIDENCE IN TAF. OUTLOOK /FRIDAY NIGHT THROUGH MONDAY/... FRIDAY NIGHT...HIGH CONFIDENCE IN VFR CONDITIONS FOR MOST OF THE NIGHT. SATURDAY AND SATURDAY NIGHT...MODERATE CONFIDENCE. A PERIOD OF MVFR- IFR CONDITIONS IN RAIN AND WET SNOW EXPECTED FOR MOST OF THE REGION. LOWEST CONDITIONS LIKELY ACROSS OUR EASTERN SECTIONS WHERE PRECIP IS THE HEAVIEST. BULK OF PRECIP PROBABLY RAIN SOUTHEAST OF I-95 AND SNOW NEAR AND NORTHWEST OF THAT REGION...BUT SUBJECT TO CHANGE. NORTH TO NORTHWEST WIND GUSTS OF 35 TO 45 KNOTS EXPECTED FOR CAPE/ISLANDS SAT NIGHT. SUNDAY...MODERATE TO HIGH CONFIDENCE IN VFR CONDITIONS. NORTHWEST WIND GUSTS OF 20 TO 30 KNOTS EXPECTED DURING THE DAYLIGHT HOURS. MONDAY...LOW CONFIDENCE. LOWERS CIGS/VSBYS ARE POSSIBLE IN SOME SNOW BUT ONLY IF LOW PRESSURE TRACKS CLOSE ENOUGH TO SOUTHERN NEW ENGLAND. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. .SHORT TERM /THROUGH THURSDAY NIGHT/...HIGH CONFIDENCE. COASTAL LOW WILL DEPART FROM THE REGION TODAY. THIS WILL SWITCH EASTERLY WINDS TO A MORE NORTHERLY DIRECTION. LIGHT OCEAN EFFECT SNOW SHOWERS ARE POSSIBLE ESP ACROSS THE EASTERN COASTAL REGIONS. CAA WILL MOVE OVER THE WATERS TONIGHT AND TOMORROW INCREASING GUSTS UP TO 20 KTS AND BUILDING SEAS TO NEAR 5 FEET. MARGINAL SCA HEADLINES MAY BE NEEDED LATER TONIGHT INTO FRI. OUTLOOK /FRIDAY NIGHT THROUGH MONDAY/... FRIDAY NIGHT...HIGH CONFIDENCE THAT WINDS/SEAS REMAIN BELOW SCA THRESHOLDS. SATURDAY AND SATURDAY NIGHT... MODERATE TO HIGH CONFIDENCE. LOW PRESSURE BOMBS OUT AS IT RAPIDLY MOVES NORTHEAST AND CROSSES NEAR THE BENCHMARK SAT EVENING. THIS WILL RESULT IN STRONG GALE FORCE WIND GUSTS FROM THE NORTH THAN THAN NORTHWEST. LOW RISK OF BRIEF STORM FORCE WIND GUSTS ACROSS THE WATERS EAST OF CAPE AND NANTUCKET. SEAS BUILD CLOSE TO 10 FEET ACROSS THE EASTERN OUTER-WATERS. SUNDAY...MODERATE TO HIGH CONFIDENCE. STRONG SCA TO MARGINAL GALE FORCE WIND GUSTS SUNDAY MORNING WILL DIMINISH SOME BY SUN AFTERNOON...BUT WILL REMAIN AT SMALL CRAFT LEVELS. MONDAY...LOW CONFIDENCE. WILL DEPEND ON WHERE LOW PRESSURE TRACKS WHICH IS VERY UNCERTAIN AT THIS TIME. && .TIDES/COASTAL FLOODING... TODAY: ASTRONOMICAL HIGH TIDE WILL OCCUR TODAY WITH BOS REACHING UP TO 12 FEET AROUND NOON. THE FLOW AT THE SURFACE WILL BE MORE NORTHERLY SO THE SURGE POTENTIAL WILL BE LOW. HOWEVER CANNOT RULE OUT THE POTENTIAL FOR MINOR SPLASHOVER ESP AT TYPICAL REGIONS. SATURDAY INTO SUNDAY: MAINLY JUST LOOKING AT THIS RISK FOR MINOR COASTAL FLOODING DURING THE VERY EARLY SUNDAY MORNING HIGH TIDE. AN 11.0 FOOT ASTRO HIGH TIDE OCCURS IN BOSTON AT 230 AM SUNDAY MORNING. THE STORM IS VERY PROGRESSIVE AND BY THEN SURFACE WINDS WILL BE FROM THE NORTHWEST AND SEAS WILL NOT BE BUILT UP AS HIGH AS WE OFTEN SEE WITH SLOWER COASTAL STORMS. ASTRO TIDES ARE FAIRLY HIGH THOUGH...SO MAY SEE SOME POCKETS OF MINOR COASTAL FLOODING. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...FRANK/DUNTEN NEAR TERM...DOODY SHORT TERM...DUNTEN LONG TERM...FRANK AVIATION...FRANK/DUNTEN MARINE...FRANK/DUNTEN TIDES/COASTAL FLOODING...

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