Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 222330 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 630 PM EST MON DEC 22 2014 .SYNOPSIS... LOW PRESSURE MOVING UP THE COAST WILL BRING PERIODS OF RAIN TO NEW ENGLAND LATER TONIGHT INTO TUESDAY. THE RAIN MAY BEGIN AS A BRIEF PERIOD OF SNOW OR FREEZING RAIN ACROSS NORTHWEST AND NORTH CENTRAL MASSACHUSETTS. A MUCH STRONGER STORM PASSING WELL TO OUR WEST WED INTO CHRISTMAS MORNING WILL BRING HEAVY RAIN...GUSTY WINDS AND PROBABLY MINOR COASTAL FLOODING. DRY WEATHER WITH ABOVE NORMAL TEMPS EXPECTED CHRISTMAS AFTERNOON INTO SAT. UNSETTLED WEATHER MAY RETURN FOR SUN AND MON. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... 630 PM UPDATE...SCATTERED SHOWERS CONTINUE OVER EASTERN MASSACHUSETTS AND NORTHERN RHODE ISLAND. THESE ARE A RESULT OF LOW LEVEL EASTERLY FLOW. EXPECT THESE TO CONTINUE THROUGH THIS EVENING. MADE ONLY MINOR UPDATES TO THE FORECAST AS IT IS LARGELY ON TRACK. HIGH PRESSURE OVER THE MARITIMES WITH RIDGING SOUTHWEST ACROSS INTERIOR SOUTHERN NEW ENGLAND. THIS WILL HOLD ONTO SOME LINGERING COLDER AIR AT THE SURFACE. BUT THE AXIS OF THIS DRAINAGE IS FOCUSED MORE ON VT AND NY...AS PER LOW LEVEL AGEOSTROPHIC FLOW...AND THIS IS ALLOWING MODERATION OF THE AIR OVER SOUTHERN NEW ENGLAND. EAST FLOW AT THE SURFACE CONTINUES INTO EASTERN MASSACHUSETTS AND RHODE ISLAND...KEEPING CLOUDS AND SCATTERED SHOWERS OVER THIS REGION EARLY TONIGHT. LOW PRESSURE OFF NORTH CAROLINA MOVES UP THE COAST TONIGHT. THIS WILL TIGHTEN THE PRESSURE GRADIENT AS THE LOW RUNS UP AGAINST HIGH PRESSURE OVER THE MARITIMES...INCREASING THE EAST TO SOUTHEAST FLOW LEADING THE LOW AND APPROACHING SOUTHERN NEW ENGLAND OVERNIGHT. AS THE EAST SOUTHEAST FLOW MOVES OVER OUR AREA IT WILL FLOW OVER THE REMAINS OF THE INTERIOR COLD AIR PROMOTING LOW LEVEL LIFT. THIS SHOULD BRING AN INCREASED CHANCE OF SHOWERS FROM SOUTH TO NORTH OVERNIGHT. THE AIR OVER NORTHERN CT/WESTERN AND CENTRAL MASS MAY BE COLD ENOUGH FOR LIGHT SNOW OR SNOW/RAIN MIX. A BRIEF PERIOD OF FREEZING RAIN MAY TAKE PLACE IN SPOTS IN NORTHWEST MASS. BUT THE TREND WILL BE TOWARD RAIN ALL AREAS BY MORNING. THE CLOUDS AND EAST FLOW WILL KEEP TEMPS FROM FALLING MUCH THIS EVENING...AND MAY HELP A STEADY OR SLOWLY RISING TREND OVERNIGHT. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... TUESDAY... THE SOUTHEAST LOW LEVEL JET WILL MOVE ACROSS SOUTHERN NEW ENGLAND DURING THE DAY. THIS WILL FEED MOISTURE TO MAINTAIN A SATURATED AIRMASS THROUGH MOST OF THE COLUMN...AND BRING OUR BEST CHANCE OF RAIN. THE JET MOVES NORTH OF OUR AREA DURING THE AFTERNOON WHICH WILL BRING DIMINISHING CHANCE OF PCPN. AS WARMER AIR FILLS IN...TEMPERATURES WILL MODERATE FURTHER WITH VALUES MOSTLY IN THE 40S. THE STEADY SOUTHEAST FLOW WILL BE 15-25 MPH WITH SOME HIGHER GUSTS POSSIBLE. THIS WINDS COMES AFTER A STEADY EAST FLOW TODAY WHICH HAS PUSHED THE OCEAN TOWARD THE EAST MASS COAST. THIS SUGGESTS BUILDING OCEAN LEVELS NEARSHORE...WITH SOME MINOR COASTAL FLOODING CONCERNS ALONG THE EAST MASSACHUSETTS COAST. THE BEST CHANCE WOULD BE AROUND BOSTON HARBOR AND NEAR SCITUATE. TUESDAY NIGHT... THE SOUTHEAST JET MOVES OFF TO THE NORTH. WE WILL CONTINUE TO HAVE A MOIST AIRMASS WITH WARM ADVECTION AND LOW LEVEL LIFT. THE RESULT WILL BE LINGERING SHOWERS AND DRIZZLE TUESDAY NIGHT. LOW LEVEL SOUTH JET WILL MOVE UP THE ATLANTIC COAST OVERNIGHT AND REACH SOUTHERN NEW ENGLAND AFTER MIDNIGHT. THIS WILL BRING INCREASED LIFT WHICH WILL MEAN INCREASED COVERAGE OF SHOWERS LATE AT NIGHT. THIS SOUTH JET IS ALSO DRAWING AN ANOMALOUSLY HUMID AIRMASS NORTH WITH PRECIPITABLE WATER VALUES OVER 1.5 INCHES. SHOWERS DEVELOPING LATE TUESDAY NIGHT WILL LIKELY HAVE SOME EMBEDDED DOWNPOURS. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... HIGHLIGHTS... * PERIODS OF RAIN WEDNESDAY INTO CHRISTMAS MORNING WILL BE HEAVY AT TIMES * DRY BUT WINDY BY CHRISTMAS AFTERNOON * TEMPS AROUND 60 FOR SOME LATE WED INTO CHRISTMAS MORNING * DRY BUT ABOVE NORMAL TEMPS CONTINUE FRI AND SAT * UNSETTLED WEATHER MAY RETURN FOR SUN BUT CONFIDENCE IS LOW MODELS ARE IN DECENT AGREEMENT ON THE FIRST PART OF THE LONG TERM FORECAST. THERE HAS BEEN QUITE A BIT OF RUN TO RUN VARIABILITY ON THE TRACK OF THE STRONG SHORTWAVE AND SURFACE LOW EXPECTED TO MOVE THROUGH THE GREAT LAKES CHRISTMAS EVE. WHILE THE OVERALL PATTERN HAS BEEN WELL MODELED SINCE LAST WEEK...THIS VARIABILITY HAS LED TO SOME UNCERTAINTY...PARTICULARLY WITH THE WINDS AND THE QPF. BEYOND THE CHRISTMAS STORM...MODELS ARE IN FAIRLY GOOD AGREEMENT THROUGH THE FIRST PART OF THE WEEKEND. THEN ALL AGREEMENT GOES OUT THE WINDOW FOR THE LATTER PART OF THE WEEKEND INTO THE FIRST PART OF NEXT WEEK. THE ECMWF HAS A STRONG LOW PRESSURE SYSTEM DEVELOPING SOUTH OF THE AREA AND MOVING ALONG THE SOUTH COAST SUNDAY WHILE THE GFS HAS A STRONG HIGH PRESSURE RIGHT OVER SOUTHERN NEW ENGLAND. GIVEN THE HUGE DIFFERENCE HERE...OPTED FOR A BLEND AND MENTION OF THE VARIABILITY HERE. CHRISTMAS EVE AND DAY...STRONG SHORTWAVE MOVES THROUGH THE GREAT LAKES CHRISTMAS EVE AND INTO QUEBEC ON CHRISTMAS DAY. IN RESPONSE...LOW PRESSURE DEVELOPS AT THE SURFACE AND MOVES ACROSS THE GREAT LAKES INTO CANADA ON CHRISTMAS EVE. DEEP SOUTHERLY FLOW OVER SOUTHERN NEW ENGLAND WILL ALLOW SIGNIFICANTLY WARMER THAN NORMAL AIR TO MOVE OVER THE AREA RESULTING IN TEMPERATURES CLIMBING AS HIGH AS 60 ACROSS SOUTHEASTERN MASSACHUSETTS AND RHODE ISLAND FROM WEDNESDAY AFTERNOON THROUGH CHRISTMAS MORNING. IN ADDITION...RAIN WILL MOVE IN ACROSS SOUTHERN NEW ENGLAND FOR ALL OF WEDNESDAY INTO CHRISTMAS MORNING. WHILE QPF AMOUNTS FORECAST BY THE MODELS HAVE VARIED QUITE A BIT AS WE MOVE CLOSER TO THE EVENT...CAUSING GREATER UNCERTAINTY IN HOW MUCH RAIN WE ANTICIPATE...THE GEFS HAS BEEN VERY CONSISTENT IN FORECASTING PWAT VALUES 4 TO 5 STANDARD DEVIATIONS ABOVE NORMAL. THIS PRESENTS QUITE A CONCERN AS RAIN WILL BE QUITE HEAVY AT TIMES. AT THIS POINT...WE ARE LOOKING AT A WIDESPREAD 1 TO 3 INCH EVENT WITH HIGHER LOCALIZED AMOUNTS. THIS WOULD CERTAINLY BE ENOUGH TO PRODUCE TYPICAL NUISANCE STREET FLOODING. HOWEVER...WOULD NOT RULE OUT MORE WIDESPREAD FLOODING GIVEN THE HIGHLY ANOMALOUS PWATS THAT ARE FORECAST. WILL BE MONITORING OVER THE NEXT DAY OR SO FOR A POTENTIAL FLOOD WATCH. HAVE KEPT THE SLIGHT CHANCE OF THUNDER GIVEN K INDICES OVER 30 AND SHOWALTER INDICES NEAR ZERO. THE GREATEST CHANCE OF THIS IS SOUTH OF THE MASS PIKE THOUGH THERE IS POTENTIAL FOR SOME ISOLATED THUNDER ALONG THE EAST COAST WEDNESDAY AFTERNOON. IN ADDITION...HAVE ADDED GUSTY WINDS AND HEAVY RAINFALL WORDING EVERYWHERE. CONSERVATIVELY...A 50 TO 60 KT LOW LEVEL JET WILL BE OVER SOUTHERN NEW ENGLAND...ESPECIALLY LATE WEDNESDAY AFTERNOON AND WEDNESDAY NIGHT. WHILE AN INVERSION LOOKS TO KEEP THE STRONGEST OF THESE WINDS FROM REACHING THE SURFACE...THERE IS POTENTIAL FOR SOME OF THESE WINDS TO BE BROUGHT DOWN IN ANY STRONGER SHOWERS OR HEAVY RAINFALL. THE RAIN SHOULD COME TO AN END CHRISTMAS MORNING WHILE TEMPERATURES PEAK OUT AROUND 60 FOR MUCH OF THE REGION. DESPITE THE STRONGER LOW LEVEL JET WEDNESDAY NIGHT...THERE IS A MUCH BETTER CHANCE FOR THE WINDS TO MIX TO THE SURFACE CHRISTMAS AFTERNOON AND EVENING. BEHIND THE SYSTEM...THERE ARE STRONGER WESTERLY WINDS AND STEEPER MID LEVEL LAPSE RATES. ADVISORY LEVEL WIND GUSTS ARE FAIRLY CERTAIN... PARTICULARLY ACROSS SOUTHEASTERN MASSACHUSETTS...THE CAPE...AND ISLANDS WITH A LOW PROBABILITY OF HIGH WIND CRITERIA BEING MET. WILL BE WATCHING THIS FOR ANY HEADLINE ISSUANCE OVER THE NEXT DAY OR SO. FRIDAY AND SATURDAY...HIGH PRESSURE SLIDES SOUTH OF SOUTHERN NEW ENGLAND BRINGING DRY WEATHER...AND ABOVE NORMAL TEMPERATURES. SUNDAY AND MONDAY...LOW CONFIDENCE FORECAST AS MENTIONED ABOVE WITH WILDLY DIFFERENT SOLUTIONS FROM THE ECMWF AND THE GFS. HAVE OPTED FOR SLIGHT CHANCE TO CHANCE POPS FOR THE TIME BEING...RECOGNIZING THAT IF THE GFS IS CORRECT THESE WILL BE WAY TOO HIGH AND IF THE ECMWF IS CORRECT...WAY TOO LOW. POTENTIALLY UNSETTLED WEATHER DURING THIS TIME PERIOD AND DEFINITELY MUCH COOLER TEMPERATURES. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH TUESDAY/... TONIGHT...MODERATE CONFIDENCE. MAINLY MVFR CONDITIONS IN SCATTERED LIGHT RAIN AND SNOW SHOWERS. PATCHES OF LIGHT FREEZING RAIN POSSIBLE LATE TONIGHT ACROSS NW MASSACHUSETTS. TUESDAY...MODERATE CONFIDENCE. MVFR CONDITIONS MAY LOWER TO IFR IN SHOWERS. THE CORE OF THE SHOWERS WILL BE OVER OUR AREA DURING THE MORNING AND EARLY AFTERNOON...WITH VSBYS REDUCED TO 2-3SM IN THE HEAVIER SHOWERS. SHOWERS DIMINISH LATE IN THE DAY WITH VSBYS 5-6 MILES BUT CIGS LINGER AT 1000-1500 FEET. TUESDAY NIGHT...MODERATE CONFIDENCE. AFTER A SHORT PAUSE EARLY IN THE NIGHT...THE CHANCE OF SHOWERS WILL INCREASE AGAIN OVERNIGHT. CIGS WILL BE IFR OR LOW-END MVFR. VSBYS WILL BE 3-4 MILES WITH AREAS OF 2 MILE VSBYS. KBOS TERMINAL...MODERATE CONFIDENCE. KBDL TERMINAL...MODERATE CONFIDENCE. OUTLOOK...WEDNESDAY THROUGH SATURDAY... WEDNESDAY...HIGH CONFIDENCE. MVFR/IFR CONDITIONS IN WIDESPREAD -RA. LLWS IS LIKELY PARTICULARLY WEDNESDAY AFTERNOON AND EVENING AS WINDS AT THE SURFACE ARE LIKELY TO BE BELOW 10 KTS WHILE A SOUTHERLY LLJ SCREAMS OVERHEAD AT 50-60KTS. CHRISTMAS...MODERATE CONFIDENCE. CONDITIONS IMPROVE TO VFR AS SYSTEM CLEARS OUT. WESTERLY WINDS INCREASE DURING THE AFTERNOON GUSTING TO AROUND 40 KTS. FRIDAY AND SATURDAY...MODERATE CONFIDENCE. VFR. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH TUESDAY NIGHT/...MODERATE TO HIGH CONFIDENCE. HIGH PRESSURE ACROSS QUEBEC AND THE MARITIMES WILL RESULT IN PERSISTENT NORTHEASTERLY TO EASTERLY WINDS ACROSS THE WATERS TONIGHT. LOW PRESSURE MOVING UP THE ATLANTIC COAST WILL TIGHTEN THE PRESSURE GRADIENT A LITTLE TONIGHT...AND MAY ALLOW WINDS TO GUST AROUND 20 KNOTS OR IN THE LOW 20S. THE PERSISTENT ESE FLOW WILL ALLOW SEAS TO BUILD TO 5 FEET ON THE EASTERN OUTER WATERS...WITH 2-4 FEET MOST OTHER WATERS. SMALL CRAFT ADVISORY CONTINUES. APPROACHING SURFACE LOW PRESSURE FROM THE MID-ATLANTIC TONIGHT WILL HELP INCREASE AN EASTERLY LLJ OVER THE WATER TUESDAY. THIS WILL BUILD THE SEAS BETWEEN 5-8 FT. COULD SEE WIND GUSTS BETWEEN 20-30 KTS AS THE FRONT PASSES. THE SMALL CRAFT ADVISORY HAS BEEN EXPANDED ACCORDINGLY. SOUTHEAST WINDS WILL DIMINISH BUT MAINTAIN TRANSPORT OF OCEAN WATER TOWARD THE NEW ENGLAND COASTLINE ESPECIALLY ALONG EASTERN MASSACHUSETTS. EXPECT SEAS AT OR ABOVE 5 FEET ON MANY OF THE SOUTHERN NEW ENGLAND WATERS THROUGH THE NIGHT. WINDS SHOULD GENERALLY BE BELOW SMALL CRAFT THRESHOLDS. OUTLOOK...WEDNESDAY THROUGH SATURDAY...MODERATE CONFIDENCE SEAS INCREASE WEDNESDAY INTO CHRISTMAS MORNING AS A COLD FRONT APPROACHES AND THEN CROSSES THE WATERS. HIGH PRESSURE THEN BUILDS OVER THE WATERS FRIDAY AND SATURDAY ALLOWING SEAS TO SUBSIDE. SOUTHERLY GALES WEDNESDAY INTO CHRISTMAS MORNING WILL GIVE WAY TO WESTERLY GALES AS THE COLD FRONT MOVES ACROSS. VISIBILITIES WILL BE REDUCED WEDNESDAY INTO CHRISTMAS MORNING IN RAIN AND THERE IS A SLIGHT CHANCE OF THUNDER WEDNESDAY. && .TIDES/COASTAL FLOODING... HIGH ASTRONOMICAL TIDES OCCUR TUE AND WED. EAST MASSACHUSETTS COAST: TUESDAY...HIGH TIDE AT BOSTON WILL BE 11.6 FEET AT MIDDAY WITH A SURGE OF 1 TO 1.5 FEET. WINDS WILL BE FROM THE EAST AT 10 TO 15 KNOTS...SO THERE WILL BE ONSHORE FLOW DURING THIS HIGH TIDE. WHILE THIS IS NOTHING TOO STRONG...GIVEN THE HIGH ASTRO TIDE AND PERSISTENCE OF EAST WINDS WE EXPECT SOME SPLASH OVER/MINOR COASTAL FLOODING. CERTAINLY DO NOT EXPECT TO SEE ANY SIGNIFICANT ISSUES. A COASTAL FLOOD ADVISORY HAS BEEN ISSUED FOR THE EAST MASS COASTLINE FOR THIS MIDDAY HIGH TIDE. WEDNESDAY...HIGH TIDE AT BOSTON WILL BE AT 11.7 FEET AT MIDDAY WITH A SURGE OF 1 TO 1.5 FEET. WINDS WILL BE FROM THE SOUTHEAST NEAR 10 KNOTS BUT THERE WILL BE SOME PRESSURE FALLS WITH INTENSIFYING LOW PRESSURE TO OUR WEST. THIS SHOULD BE ENOUGH FOR MORE SPLASH OVER/MINOR COASTAL FLOODING WITH THE HIGH ASTRO TIDES. HOWEVER...DO NOT EXPECT ANY SIGNIFICANT PROBLEMS GIVEN WINDS/SEAS SHOULD BE HELD IN CHECK DURING THE TIME OF HIGH TIDE. SOUTH COAST: WEDNESDAY EVENING...SOUTHERLY WINDS ARE EXPECTED AND ASTRONOMICAL TIDES INCREASE ALONG THE SOUTH COAST. HIGH TIDE IN PROVIDENCE WILL BE 5.2 FEET WEDNESDAY EVENING. 925 MB LLJ STRENGTHENS TO 55-65 KTS WHICH COULD PUSH A 1 TO 2 FOOT SURGE UP ALONG THE SOUTH COAST DURING THE TIME OF HIGH TIDE. THE LOW LEVEL INVERSION WILL PROBABLY HOLD THE STRONGEST WINDS JUST ABOVE THE GROUND...SO THINKING THE RISK IS FOR SPLASH OVER AND MINOR COASTAL FLOODING. THERE STILL IS A LOW RISK FOR MODERATE COASTAL FLOODING...BUT THAT IS OFTEN HARD TO GET IN A NON-TROPICAL SYSTEM ALONG THE SOUTH COAST. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...COASTAL FLOOD ADVISORY FROM 9 AM TO 3 PM EST TUESDAY FOR MAZ007-015-016-019-022. RI...NONE. MARINE...SMALL CRAFT ADVISORY FROM 1 AM TO 7 PM EST TUESDAY FOR ANZ231- 232. SMALL CRAFT ADVISORY FROM 1 AM TO 10 AM EST TUESDAY FOR ANZ233- 234. SMALL CRAFT ADVISORY FROM 1 AM TUESDAY TO 6 AM EST WEDNESDAY FOR ANZ235-237-251-256. SMALL CRAFT ADVISORY UNTIL 6 AM EST WEDNESDAY FOR ANZ250-254. SMALL CRAFT ADVISORY FROM 10 PM THIS EVENING TO 6 AM EST WEDNESDAY FOR ANZ255. && $$ SYNOPSIS...WTB/RLG NEAR TERM...WTB/RLG SHORT TERM...WTB LONG TERM...RLG AVIATION...WTB/RLG MARINE...WTB/RLG TIDES/COASTAL FLOODING...

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