Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 220743 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 243 AM EST MON DEC 22 2014 .SYNOPSIS...
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SCATTERED SNOW/RAIN SHOWERS WILL CONTINUE TODAY THANKS TO THE ONSHORE FLOW. A WEAK LOW PRESSURE WILL MOVE ACROSS NEW ENGLAND BRINGING A PERIOD OF PRECIPITATION VERY LATE MONDAY NIGHT AND INTO TUESDAY. A MUCH STRONGER STORM PASSING WEST OF NEW ENGLAND WILL BRING HEAVY RAINFALL...GUSTY WINDS AND COASTAL FLOODING CONCERNS TO THE REGION WEDNESDAY AND WEDNESDAY NIGHT. DRY BUT VERY WINDY CONDITIONS FOLLOW FOR CHRISTMAS DAY. HIGH PRESSURE BRINGS DRY WEATHER FRIDAY. ANOTHER DEVELOPING SYSTEM MAY BRING RAIN AND SNOW NEXT SUNDAY.
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&& .NEAR TERM /THROUGH TODAY/...
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UPPER LEVEL RIDGE BUILDS AHEAD OF DIGGING MIDWEST TROUGH WITH HIGH PRESSURE REMAINING ANCHORED OVER THE CANADIAN MARITIMES THROUGH TONIGHT. EASTERLY FLOW WILL CONTINUE ONSHORE ALLOWING FOR THE PROFILE TO CONTINUE TO MOISTEN IN THE LOW LEVELS. IF THIS MOISTURE DEEPENS ENOUGH THEN WE COULD SEE LIGHT SHOWERS DEVELOP ESP ACROSS THE MASS EAST COASTLINE. OTHERWISE DRIZZLE MAY BE THE MAIN FACTOR AS THE UPPER LEVELS ARE FAIRLY DRY. OVERALL TODAY WILL BE A COOL AND CLOUDY DAY WITH HIGHS ONLY REACHING IN THE UPPER 30S TO LOW 40S AS CROSS SECTIONS ARE VERY MOIST IN THE LOW LEVELS.
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&& .SHORT TERM /TONIGHT THROUGH 6 PM TUESDAY/...
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TONIGHT INTO TOMORROW... *LIGHT FREEZING RAIN IS POSSIBLE ACROSS THE INTERIOR NORTHWEST AND NORTHERN WORCESTER HILLS* A WEAK AREA OF LOW PRESSURE DEVELOPS ALONG A WARM FRONT OFF THE MID ATLANTIC...DRIFTING NORTHWARD TOWARD THE AREA. THIS LOW REMAINS WEAK AS THE WARM FRONT MOVES SLOWLY NORTHWARD TONIGHT INTO TOMORROW. DECENT WARM ADVECTION AHEAD OF THIS WAVE WITH SEVERAL HI-RES GUIDANCE MODELS SHOWS A POTENTIAL FOR COLD AIR DAMMING ACROSS THE INTERIOR INTO TUESDAY MORNING. BIGGEST QUESTION WILL BE THE MOISTURE POTENTIAL...IS THERE ENOUGH TO DEVELOP PRECIP ESP TONIGHT? GUIDANCE DOES SHOW ENOUGH LIFT AHEAD OF APPROACHING SURFACE LOW PER THE GFS/EC SO ANTICIPATE PRECIP TO DEVELOP AND OVERSPREAD ACROSS SOUTHERN NEW ENGLAND. IF THIS PLAYS OUT WITH COLD AIR DAMMING AND WARM AIR ADVECTION...THEN WE COULD SEE FREEZING RAIN/DRIZZLE ACROSS THE INTERIOR NORTHWEST AND NORTHERN WORCESTER HILLS VERY LATE TONIGHT INTO TUESDAY MORNING. A WINTER WEATHER ADVISORY MAY BE NEEDED. AS SURFACE LOW CONTINUES TO MOVE NORTHWARD...AND HIGH PRESSURE OVER EASTERN CANADA...ANTICIPATE AN INCREASING LLJ. THIS SOUTHEASTERLY JET WILL CONTINUE TO FEED MOISTURE INTO THE REGION AND WITH SOUNDINGS SHOW A VERY SATURATED PROFILE COULD SEE NUMEROUS SHOWERS WITH PERHAPS A FEW HEAVY DOWNPOURS. NOTICED GUIDANCE HAS INCREASED THE QPF OVER THE PAST FEW DAYS. AS THE WEAK SURFACE LOW MOVES NORTH OF SOUTHERN NEW ENGLAND...WARM FRONT WILL LIFT NORTHWARD SO ALL PRECIP BY THE LATE MORNING WILL BE IN THE LIQUID FORM. WE COULD ALSO SEE SOME MINOR COASTAL FLOODING CONCERNS ON TUESDAY WITH DUE EASTERLY FLOW INCREASING TO ABOUT 20 TO 25 MPH. SEE BELOW FOR MORE DETAILS.
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&& .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
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BIG PICTURE... TUESDAY STARTS WITH UPPER RIDGES ON EACH COAST AND A DEEP UPPER TROUGH/CLOSED LOW OVER THE PLAINS. BY WEDNESDAY THE CLOSED LOW EJECTS NORTHEAST THROUGH LAKE SUPERIOR INTO CANADA. THIS SWEEPS THE TROUGH AXIS EAST AND PASSES ACROSS NEW ENGLAND CHRISTMAS DAY. ANOTHER SHORTWAVE MOVES ONSHORE IN THE PACIFIC NORTHWEST WEDNESDAY AND PHASES WITH A SECOND DROPPING SOUTH FROM NORTHERN CANADA. THIS REESTABLISHES THE UPPER TROUGH OVER THE NORTHERN PLAINS/GREAT LAKES SATURDAY. CONTOUR HEIGHTS WILL BE ABOVE NORMAL MIDWEEK...TRENDING BELOW NORMAL OVER THE WEEKEND AS THE SECOND UPPER TROUGH SHIFTS EAST. THIS POINTS TO A COOLING TREND AFTER CHRISTMAS. THE GFS AND ECMWF ARE SIMILAR IN HANDLING THE HOLIDAY STORM. THERE ARE DIFFERENCES BETWEEN THE MODELS IN HANDLING THE SUNDAY SYSTEM. WE USED A BLEND MOST OF THE LONG TERM PERIOD...BUT MANUALLY ADJUSTED POPS FOR SUNDAY WITH LOW CONFIDENCE IN MODEL VALUES. THE DAILIES... TUESDAY... HIGH PRESSURE OVER THE MARITIMES WITH RIDGING DOWN THE ATLANTIC COAST. COASTAL LOW PRESSURE WAVE DEVELOPS ALONG STALLED WARM FRONT AND MOVES NORTH. AS THE COASTAL LOW MOVES NORTH IT WILL RUN UP AGAINST THE MARITIME HIGH. THIS WILL INCREASE THE LOW LEVEL PRESSURE GRADIENT AND INCREASE THE LOW LEVEL SOUTHEAST WINDS. RESULT...A SOUTHEAST LOW LEVEL JET RUNS OVER THE RIDGING ALONG THE COASTAL PLAIN INDUCING LOW LEVEL LIFT. THE MOIST LAYER EXPANDS ABOVE 800 MB...NOT DEEP BUT DEEP ENOUGH FOR THE LIFT TO GENERATE LIGHT PCPN. PTYPE WILL BE RAIN MOST PLACES...BUT THERE COULD BE SPOTS OF LIGHT FREEZING RAIN IN NORTHWEST MASSACHUSETTS. WE WILL MAINTAIN CHANCE POPS BUT INCREASE TO AROUND 50 PCT...THE HIGH END OF THE CHANCE RANGE. LOW LEVEL SOUTH JET MOVES UP THE COAST TUESDAY NIGHT REACHING THE COOLER AIR OVER NEW ENGLAND AFTER MIDNIGHT AND BEFORE SUNRISE. THIS WILL GENERATE ADDITIONAL LIFT AS WELL AS INCREASING AND DEEPENING MOISTURE. THIS SUGGESTS INCREASING POPS OVERNIGHT. TEMPERATURES SHOULD REMAIN ABOVE FREEZING SO PTYPE SHOULD BE RAIN. WEDNESDAY-THURSDAY... SOUTH 40-50 KNOT LOW LEVEL JET MOVES OVER NEW ENGLAND WEDNESDAY GENERATING STRONG LIFT AND TRANSPORTING HIGH VALUES OF PRECIPITABLE WATER INTO THAT LIFT. THE MOISTURE VALUES ARE MORE THAN 3 STD DEVIATIONS ABOVE NORMAL FOR DECEMBER...AND ACTUALLY NEAR THE MAXIMUM PREVIOUSLY OBSERVED VALUE. THIS SUGGESTS RAIN WITH SOME HEAVY DOWNPOURS. COLD FRONT APPROACHES LATE WEDNESDAY NIGHT AND CROSSES SOUTHERN NEW ENGLAND CHRISTMAS MORNING. THE FRONT WILL HAVE DYNAMIC SUPPORT FROM A 140-150 KNOT UPPER JET. THE FOREWARD PROGRESS OF THE FRONT WILL SLOW BECAUSE MOST OF THE MOTION IN THE UPPER JET WILL BE PARALLEL TO THE FRONT. THIS WILL MEAN CONTINUED RAIN/HEAVY RAIN THROUGH THE NIGHT INTO THURSDAY MORNING. THE OBVIOUS CONCERN FOR THIS PERIOD WILL BE FLOODING FROM HEAVY RAINFALL. RAIN AMOUNTS OF 2 TO 3 INCHES ARE EXPECTED. THIS SHOULD BE SUFFICIENT FOR AT LEAST URBAN AND POOR DRAINAGE FLOODING. A FLOOD WATCH MAY BE NEEDED. A SECOND CONCERN WILL BE WIND. THE LOW LEVEL JET WEDNESDAY WILL BE SOUTH 40-50 KNOTS...AND INCREASE TO 55-65 KNOTS WEDNESDAY NIGHT. CONVENTIONAL MIXING WILL NOT BE DEEP...BUT HEAVY DOWNPOURS COULD CREATE A MOIST ADIABATIC CHANNEL THAT BRINGS DOWN SOME STRONGER WIND GUSTS. MODEL GRIDS ARE RATHER LIGHT ON WIND GUSTS...15 TO 30 KNOTS. WE WILL MANUALLY ADJUST THESE VALUES UP TO 25-35 KNOTS OVER LAND AND A LITTLE STRONGER OVER WATER. A THIRD CONCERN WILL BE COASTAL FLOODING. MORE DETAILS ON THIS IN THE TIDE/COASTAL FLOOD SECTION. WINDS SHIFT TO WEST BEHIND THE FRONT ON CHRISTMAS DAY. THIS WILL BRING DRIER AIR AND SO END THE RAINFALL. COLD ADVECTION WILL PROMOTE MIXING TO NEAR 850 MB IN THE AFTERNOON AND TAP 25-35 KNOT WIND GUSTS...POSSIBLY 40 KNOT GUSTS. A WIND ADVISORY MAY BE NEEDED FOR THESE WEST WINDS THURSDAY. FRIDAY THROUGH SUNDAY.... HIGH PRESSURE MOVES OVER THE REGION FRIDAY BRINGING DRY WEATHER. SHORTWAVE MOVING THROUGH THE GREAT LAKES SWINGS A COLD FRONT THROUGH NEW ENGLAND SATURDAY. THE SURFACE REFLECTION OF THE SHORTWAVE MOVES UP THE ST LAWRENCE VALLEY AND JET SUPPORT WILL MOSTLY BE NORTH OF THE BORDER...SO PCPN WILL BE LIMITED. QUESTION FOR SUNDAY WILL BE WHETHER A WAVE FORMS ON THE DEPARTING COLD FRONT...IF SO IT MIGHT BRING PCPN TO NEW ENGLAND. THE ECMWF THINKS SO BUT THE GFS DOES NOT. WE BROUGHT IN A CHANCE OF RAIN AND SNOW SHOWERS.
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&& .AVIATION /08Z MONDAY THROUGH FRIDAY/...
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FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH TUESDAY/... TODAY...HIGH CONFIDENCE. DRIZZLE OR A FEW FLURRIES POSSIBLE ACROSS EAST MASS TERMINALS. OTHERWISE ANY VFR CIGS WILL DROP TO MVFR CONDITIONS THROUGHOUT THE DAY. TONIGHT...MODERATE CONFIDENCE. MAINLY MVFR CONDITIONS CONTINUE IN SCATTERED LIGHT SNOW SHOWERS. LIGHT FZRA POSSIBLE LATE MONDAY NIGHT ACROSS NW MASSACHUSETTS. TUESDAY...MODERATE CONFIDENCE. MVFR CONDITIONS MAY DROP TO IFR WITHIN AND HEAVY RAIN FALL. VSBYS WILL BE REDUCED TO 5SM OR LESS AS WELL. KBOS TERMINAL...MODERATE CONFIDENCE. COULD SEE DRIZZLE LATER TODAY. KBDL TERMINAL...MODERATE CONFIDENCE. OUTLOOK...TUESDAY NIGHT THROUGH FRIDAY...MODERATE CONFIDENCE LATE TUESDAY NIGHT-WEDNESDAY-THURSDAY... CONDITIONS LOWERING TO IFR/LIFR IN RAIN/HEAVY RAIN. SOUTHEAST WINDS GUSTING 25 TO 35 KNOTS WEDNESDAY AND SOUTH WINDS SIMILAR SPEEDS WEDNESDAY NIGHT...EXCEPT 30 TO 40 KNOTS CAPE COD AND ISLANDS. WINDS AT 2000 FEET MAY REACH 55 TO 65 KNOTS BY WEDNESDAY NIGHT CREATING LOW LEVEL WIND SHEAR. ISOLATED THUNDERSTORMS WEDNESDAY AFTERNOON AND NIGHT. COLD FRONT SWINGS THROUGH ON THURSDAY MORNING BRINGING A WIND SHIFT TO WEST WITH GUSTS 30-40 KNOTS. CONDITIONS IMPROVE TO VFR AFTER THE WIND SHIFT. FRIDAY...VFR.
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&& .MARINE...
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FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH TUESDAY/...MODERATE TO HIGH CONFIDENCE. HIGH PRESSURE ACROSS QUEBEC AND THE MARITIMES WILL RESULT IN PERSISTENT NORTHEASTERLY TO EASTERLY WINDS ACROSS THE WATERS THROUGH TODAY. THIS WILL BUILD SEAS TO 5FT ON THE EASTERN WATERS DESPITE WIND GUSTS UP TO 20 KNOTS. HAVE CONTINUED SCA. APPROACHING SURFACE LOW PRESSURE FROM THE MID-ATLANTIC TONIGHT WILL HELP INCREASE AN EASTERLY LLJ OVER THE WATER TOMORROW. THIS WILL BUILD THE SEAS BETWEEN 5-8 FT. COULD SEE WIND GUSTS BETWEEN 20-30 KTS AS THE FRONT PASSES. SCA HAS BEEN EXPANDED ACCORDINGLY. OUTLOOK...TUESDAY NIGHT THROUGH FRIDAY...MODERATE CONFIDENCE WEDNESDAY-THURSDAY... SOUTH WINDS WITH FREQUENT GUSTS 35 TO 40 KNOTS BY WEDNESDAY AFTERNOON AND CONTINUING THROUGH THE NIGHT. WINDS SHIFT WEST THURSDAY MORNING WITH SIMILAR SPEEDS THROUGH THE AFTERNOON. SEAS WILL BUILD TO 7 TO 12 FEET ON THE EXPOSED WATERS BY WEDNESDAY NIGHT AND THURSDAY. A GALE WARNING MAY BE NEEDED. FRIDAY...WINDS DIMINISHING TO 25 KNOTS FRIDAY MORNING AND BELOW 25 KNOTS BY AFTERNOON. SEAS LINGERING AT 5 TO 7 FEET ON THE EXPOSED WATERS. A SMALL CRAFT ADVISORY MAY BE NEEDED.
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&& .TIDES/COASTAL FLOODING... HIGH ASTRONOMICAL TIDES WILL OCCUR TUESDAY THROUGH THURSDAY. TUESDAY...HIGH TIDE AT BOSTON WILL BE 11.6 FT. WINDS WILL BE FROM THE EAST...SO THERE WILL BE ONSHORE FLOW DURING THIS HIGH TIDE ALLOWING FOR MINOR SPLASHOVER. IF WINDS INCREASE THEN COULD SEE SOME POCKETS OF MINOR COASTAL FLOODING. WEDNESDAY...WINDS SHIFT TO A MORE SOUTHEASTERLY FLOW DURING THE DAY AND INCREASE QUICKLY AS AN APPROACHING SYSTEM BRINGS PRESSURE FALLS OF 1 MB/HR. THE WEDNESDAY AFTERNOON HIGH TIDE IN BOSTON IS 11.7 FT AND STRONG SOUTHEASTERLY WINDS WILL BE JUST OFFSHORE. RIGHT NOW BELIEVE MINOR COASTAL FLOODING IS POSSIBLE ALONG THE EAST COAST. WEDNESDAY EVENING...SOUTHERLY WINDS ARE EXPECTED AND ASTRONOMICAL TIDES INCREASE ALONG THE SOUTH COAST. HIGH TIDE IN PROVIDENCE WILL BE 5.2 FT. 925 MB LLJ STRENGTHENS TO 55-65 KTS WHICH COULD PUSH A DECENT SURGE UP ALONG THE SOUTH COAST DURING THE TIME OF HIGH TIDE. THINKING THAT MINOR COASTAL FLOODING COULD OCCUR BUT CANNOT RULE OUT MODERATE ALONG THE SOUTH COAST...ESPECIALLY IF LLJ CONTINUES TO STRENGTHEN. && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...NONE. MA...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 7 AM EST TUESDAY FOR ANZ250. SMALL CRAFT ADVISORY FROM 10 PM THIS EVENING TO 7 AM EST TUESDAY FOR ANZ251-255. SMALL CRAFT ADVISORY FROM 1 PM THIS AFTERNOON TO 7 AM EST TUESDAY FOR ANZ254.
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&& $$ SYNOPSIS...WTB/DUNTEN NEAR TERM...DUNTEN SHORT TERM...DUNTEN LONG TERM...WTB AVIATION...WTB/DUNTEN MARINE...WTB/DUNTEN TIDES/COASTAL FLOODING...

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