Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 260429 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 1129 PM EST TUE NOV 25 2014 .SYNOPSIS... A STRONG NOREASTER WILL MOVE CLOSE TO THE 40N/70W BENCHMARK LATE TONIGHT INTO TOMORROW. THIS WINTER STORM WILL IMPACT THE REGION WEDNESDAY INTO WEDNESDAY NIGHT WITH SNOW...WIND AND COASTAL ISSUES. CONDITIONS WILL IMPROVE FOR THANKSGIVING DAY. HIGH PRESSURE BUILDS OVER NEW ENGLAND FRIDAY AND SHIFTS OFFSHORE OVER THE WEEKEND. A COLD FRONT SWINGS THROUGH NEW ENGLAND LATE SUNDAY NIGHT OR MONDAY. && .NEAR TERM /UNTIL 4 AM WEDNESDAY MORNING/...
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11 PM UPDATE... HIGH THIN CLOUDS CONTINUE TO STREAM ACROSS THE REGION. WINDS HAVE DIMINISHED INLAND TO LIGHT/VRBL OR CALM AT 04Z...WHICH HAS ALLOWED TEMPS TO FALL BACK TO THE LOWER-MID 30S MAINLY ACROSS N CENTRAL AND W MA/SW NH...WITH READINGS IN THE 40S TO LOWER 50S ACROSS E MA/RI WITH LIGHT W-NW WINDS. NOTING BAND OF LIGHT PRECIP ALONG THE S COAST...BUT NOT SEEING ANY PRECIP REACHING THE GROUND LIKELY DUE TO TEMP/DEWPT SPREADS FROM 7 TO 15 DEGREES ALONG THE S COAST. ANOTHER BAND OF STEADIER PRECIP WELL S OF THE REGION STREAMING NE. WOULD NOT BE SURPRISED TO SEE A LITTLE LIGHT RAIN REACH THE GROUND ACROSS THE OUTER CAPE AND NANTUCKET AFTER 1 OR 2 AM ONWARD. HAVE ADDED SLIGHT CHANCE POPS TO NANTUCKET FOR A TIME OVERNIGHT. OTHERWISE...UPDATED TEMPS/DEWPTS TO BRING CURRENT AND EXTENDED INTO NEAR TERM TRENDS AS WELL AS CLOUD COVER. PREVIOUS DISCUSSION... EXPECT A GOOD PORTION OF THE REGION TO REMAIN DRY FOR THE FIRST HALF OF THE NIGHT...UNTIL PRECIP WILL BLOSSOM FROM SOUTH TO NORTH NEAR 09Z. NOT A LOT OF COOL AIR ALOFT SO OVERNIGHT TEMPS WILL REMAIN MILD AS CLOUD COVER WILL LIMIT DIURNAL RADIATION. LOW OVERNIGHT WILL DROP IN THE MID 30S TO LOW 40S. HOWEVER ONCE PRECIP MOVES INTO THE REGION...AND DEPENDING ON INTENSITY TEMPS MAY WET BULB AND DROP AT OR BELOW FREEZING. HAVE NOTICED THAT THIS SYSTEM IS SPEEDING UP SO THE MORNING COMMUTE MAY BE IMPACTED FOR CT AND RI TOMORROW MORNING.
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&& .SHORT TERM /4 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
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WEDNESDAY INTO WEDNESDAY NIGHT... *** EARLY SEASON WINTER STORM TO IMPACT MUCH OF THE REGION WED/WED NIGHT *** IMPACTS... * HEAVY SNOW ACROSS MUCH OF THE INTERIOR IMPACTING WED TRAVEL * GUSTY WINDS ACROSS COASTAL PLYMOUTH CO AND THE ISLANDS * STRONG GALE FORCE WINDS ACROSS THE WATERS * MINOR BEACH EROSION AND SPLASHOVER FOR THE THU AM HIGH TIDE SYNOPTIC OVERVIEW... UPPER LEVEL TROUGH WILL CONTINUE TO DIG INTO THE SOUTHERN PLAINS. THIS HAS ALLOWED A GOOD PLUME OF MOISTURE TO MOVE UP THE EASTERN SEABOARD...TAPPING IN TROPICAL MOISTURE FROM BOTH THE GULF AS WELL AS THE BAHAMAS. FROM THIS SHORTWAVE...A WEAK WAVE WILL DEVELOP AND GENERATE A SURFACE LOW OFF THE CAROLINA COAST. THIS LOW WILL STRENGTHEN AS IT MOVES UP THE COAST AND DEVELOP AN EARLY SEASON NOR`EASTER FOR SOUTHERN NEW ENGLAND. THIS IS A VERY QUICK SYSTEM DUE TO THE LACK OF BLOCKING UPSTREAM. SURFACE LOW IS STILL TRACKING NEAR THE 40N/70W BENCHMARK...WITH H85 CIRCULATION MOVING ACROSS CAPE COD AND H7 LOW DEVELOPING AND TRACKING OVER BDL-MHT LINE. THIS SYSTEM WILL QUICKLY MOVE OUT OF THE REGION BY WED NIGHT AND PRECIP SHOULD BE WINDING DOWN BY DAY BREAK THURSDAY. GUIDANCE... GOOD GENERAL AGREEMENT AMONG THE MODELS FOR THE 12Z SUITE. BIGGEST THING IS THAT THE SYSTEM IS MOVING A FEW HOURS FASTER THEN ORIGINALLY THOUGHT. IT SHOULD BE NOTED THAT WHILE THE MODELS ARE IN GOOD AGREEMENT WITH RESPECT TO THE LARGER-SCALE FEATURES INCLUDING THE SURFACE LOW AND UPPER SHORTWAVE TROUGH...DIFFERENCES IN THE DETAILS REMAIN. APPEARS THAT THERE IS A 700 MB WARM-AIR INTRUSION/DRY SLOT IMPENDING UP NARRAGANSETT BAY AND UP INTO NORFOLK CO. NOTED THAT THE NAM/CMC WHERE THE COLDER SOLUTIONS COMPARED TO THE GFS/EC/SREF AND UKMET WHICH WERE SLIGHTLY WARMER IN THEIR TEMPS ALOFT. BECAUSE OF THIS GOOD CLUSTERING TRENDED THE FORECAST WITH THE GFS/EC/WPC IN TERMS OF THICKNESS AND QPF. PTYPE AND SNOWFALL... TRICKIEST PART OF THE FORECAST WAS DETERMINING SNOWFALL ACCUMS AND P- TYPES. BIGGEST REASON IS THE 700 MB WARM LAYER MOVING INTO THE REGION DURING THE LATE AFTERNOON HOURS. DEPENDING ON HOW FAR NORTHWARD THIS WARM LAYER MOVES INTO SOUTHERN NEW ENGLAND COULD PLAY ISSUES ON THE TOTAL SNOW ACCUMS. RIGHT NOW APPEARS THAT THIS WARM LAYER WILL MOVE INTO WELL INTO RI AND NORFOLK CO AND POINTS SOUTH AND EAST KEEPING BOSTON RIGHT ON THE FRINGE OF SUB-ZERO THERMAL PROFILE. AND WITH 925 MB TEMPS BELOW 0C WEST OF THE CANAL BELIEVE SLEET/WINTRY MIX WILL BE INTRODUCED. HOWEVER THE 18Z NAM CAME IN A LOT WARMER AT THE 700MB LEVEL...IF THIS TREND CONTINUES THROUGH THE REMAINDER OF THE GUIDANCE THIS SNOW TOTALS WILL BE TO HIGH. LASTLY A COASTAL FRONT WILL ALSO SET UP SOMEWHERE ALONG THE I-95 CORRIDOR...SO WILL NEED TO MONITOR WHERE IT DECIDES TO DEVELOP. AT THE ONSET...BECAUSE OF BOUNDARY LAYER TEMP ISSUES BELIEVE RAIN WILL START OVER A GOOD PORTION OF THE REGION WITH RAIN/SNOW MIX ACROSS HIGHER TERRAIN...NEAR DAY BREAK. AS PRECIP OVERSPREADS THE REGION AND THERMAL FIELDS ALOFT TIGHTEN...EXPECT A GOOD BANDING SIGNATURE TO DEVELOP...NEAR BDL TO ORH TO BED AT AROUND 15/18Z. PRECIP INTENSITY ASSOCIATED WITH THIS BAND SHOULD BE SUFFICIENT FOR A CHANGEOVER TO ALL SNOW ALONG WITH SNOW RATES OF 1-2" PER HOUR. DURING THE LATE MORNING HOURS BELIEVE THAT A COASTAL FRONT WILL SET UP AND KEEP MOST OF THE COASTAL REGION IN RAIN RATHER THAN SNOW. HOWEVER AS THE SURFACE WINDS BACK TO A NNE DIRECTION AS WELL EXPECT MORE LOW LEVEL COOLING WHICH WILL KEEP PRECIP TO ALL SNOW FOR A MAJORITY OF THE REGION...EXPECT ALONG THE 95 CORRIDOR WHERE A WINTRY MIX OF SNOW/SLEET/RAIN IS POSSIBLE. THE FRONTAL BAND WILL ALSO SWITCH TO A MORE NNE ASSOCIATION AS THE THERMAL FIELDS GET BACKED FROM THE MID-LEVEL WARM AIR MOVING INTO THE REGION. THIS WILL PUSH THE HEAVIER SNOWFALL OVER THE BERKS AND SOUTHERN NH. FINALLY AS THE STORM EXITS OUT...A MORE NORTHERLY FLOW WILL ALLOW FOR ALL PRECIP TO SWITCH TO SNOW AND ALLOW FOR A QUICK COUPLE OF INCHES OF ACCUMULATIONS. OVERALL HAVE EXPANDED THE CURRENT WINTER WEATHER WARNINGS TO ALL OF SOUTHERN NH...AND MOST OF MASS MINUS THE I-95 CORRIDOR AND NORTHERN CT. DECIDED TO GO WITH ADVISORY FOR PORTIONS OF RI UP TO COASTAL ESSEX INCLUDING THE CITIES OF PROVIDENCE AND BOSTON. ALTHOUGH AMOUNTS ARE UNDER ADVISORY FOR THE METRO REGIONS...BECAUSE OF THE HIGH IMPACT THIS EVENT CAN HAVE ON THE PRE-THANKSGIVING TRAVEL FELT THE ADVISORY WAS WARRANTED. ALSO WITH A SLIGHT SHIFT IN THE GUIDANCE OR IF TEMPS DROP JUST A DEGREE...ACCUMULATIONS COULD ADD UP. FOR NOW BELIEVE THAT AN INCH OR TWO OF SNOW IS POSSIBLE BUT ANOTHER COUPLE OF INCHES OF SLEET CANNOT BE RULED OUT. WINDS... A STRONG LOW LEVEL NORTHEAST JET WILL MOVE ACROSS THE SOUTH COAST OF RI AND MA INCLUDING CAPE COD AND THE ISLANDS WED AFTERNOON INTO THE OVERNIGHT HOURS. MODELS PROJECTING 45-50 KT JET AT 925 MB. THIS COUPLED WITH STRONG PRES FALLS AND RELATIVELY WARM OCEAN WATERS PROVIDING A WELL MIXED BLYR WILL YIELD A MODERATE RISK OF 50 MPH WIND GUSTS FROM SOUTH COASTAL PLYMOUTH COUNTY/CAPE COD AND THE ISLANDS. TIMING OF STRONGEST WINDS APPEAR 4 PM WED TIL 11 AM THU. BECAUSE THE JET DYNAMIC DOES NOT SEEM AS STRONG AS PREVIOUS RUNS HAVE DROPPED THE HIGH WIND WATCH TO A STRONG WIND ADVISORY FOR THIS AREA. IF THE COASTAL SYSTEM DOES DEEPEN MORE THEN FORECASTED...AND THE LLJ DOES STRENGTHEN THEN A HIGH WIND WARNING MAY BE NEEDED. COASTAL FLOODING... FORECAST TIDES OF 10 FEET ARE EXPECTED AT BOSTON SHORTLY AFTER MIDNIGHT THURSDAY. THIS SYSTEM IS VERY QUICK SO THE POTENTIAL FOR A LONG DURATION EASTERLY FETCH TO BUILD THE SEAS IS LOW. EVEN THE DURATION OF ONSHORE WINDS ARE SHORT PLUS WITH PRESSURES BEGINNING TO RISE TOWARD HIGH TIDE NOT EXPECTING MUCH IF ANY COASTAL FLOOD ISSUES INCLUDING EROSION. WORSE CAST...COULD SEE A SURGE NEAR 1.5 FEET WHICH MAY CAUSE SOME SPLASHOVER AND MINOR BEACH EROSION FOR TYPICAL PRONE AREAS.
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&& .LONG TERM /THURSDAY THROUGH TUESDAY/... BIG PICTURE... SOUTHERN STREAM TROUGH MOVES UP THE COAST ACROSS NEW ENGLAND THURSDAY. NORTHERN STREAM SHORTWAVE THEN MOVES ACROSS THE REGION FRIDAY. THE FLOW THEN TRANSITIONS TO ZONAL OVER THE WEEKEND. THE LONG RANGE MODELS SHOW GOOD AGREEMENT ON 500 MB HEIGHTS THROUGH MONDAY AND THEN SMALL DIVERGENCE TUESDAY. THE GFS IS FASTER/FARTHER EAST WITH A CLIPPER SYSTEM CROSSING CANADA OVER THE WEEKEND. BUT THE MODELS COME MORE IN LINE WITH THE TRAILING COLD FRONT IN NEW ENGLAND SUNDAY NIGHT. THIS MAINTAINS AT LEAST MODERATE CONFIDENCE IN THE FORECAST THROUGH THE WEEKEND WITH DIMINISHING CONFIDENCE BY NEXT TUESDAY/DAY SEVEN. THE DAILIES... THANKSGIVING DAY... SOUTHERN STREAM UPPER TROUGH TRAILS THE WEDNESDAY STORM...AND MOVES OVER SOUTHERN NEW ENGLAND DURING THE DAY. MODEL CROSS SECTIONS FROM THE GFS AND ECMWF SHOW A DEEP SUPPLY OF HIGH-RH AIR AND SOME WEAK LIFT AS THE TROUGH MOVES ACROSS THE REGION. WE WILL EXPECT MOSTLY CLOUDS AS WELL AS A CHANCE OF PCPN. TEMPERATURE PROFILES SUGGEST SCATTERED SNOW SHOWERS INLAND AND SCATTERED RAIN SHOWERS IN RI/SOUTHEAST MASS. TEMPERATURE PROFILES SUPPORT MAX TEMPS IN THE 30S...EXCEPT LOWER 40S CAPE AND ISLANDS. WE STAYED CLOSE TO GUIDANCE THURSDAY NIGHT WITH MIN TEMPS IN THE 20S EXCEPT LOWER 30S CAPE AND ISLANDS. ANY WET SURFACES FROM THE DAYTIME WILL REFREEZE IN MOST LOCATIONS RESULTING IN TRICKY POST- MEAL TRAVEL ON ANY UNTREATED SURFACES. FRIDAY... NORTHERN STREAM SHORTWAVE RACES ACROSS NEW ENGLAND IN THE MORNING WITH LINGERING AIRMASS MOISTURE BUT WEAK LIFT IF ANY. THIS COULD HOLD THE CLOUDS IN A LITTLE LONGER FRIDAY MORNING. BUT IT MOVES OUT QUICKLY AND SURFACE HIGH PRESSURE BUILDS IN. SO THE TREND WILL BE FOR CLEARING SKIES. MIXING DEPTH WITH THE SUNSHINE IS EXPECTED TO BE RATHER SHALLOW...AROUND 950 MB OR MAYBE A LITTLE HIGHER. THIS WILL SUPPORT MAX TEMPS IN THE 30S AND WINDS GUSTING TO 15-20 KNOTS. HIGH PRESSURE MOVES OVERHEAD FRIDAY NIGHT. THIS WILL ALLOW TEMPS TO INITIALLY FALL WITH MOSTLY CLEAR SKIES AND LIGHT WINDS. BUT MOISTURE FIELDS SUGGEST SOME MID AND HIGH CLOUDS OVERNIGHT...AND POSSIBLY LOW CLOUDS MOVING UP FROM THE OCEAN TOWARD CAPE COD AND THE ISLANDS. FORECAST TEMPS ARE CLOSE TO GUIDANCE WITH 14-23 EXCEPT 24-30 ALONG THE SOUTH COAST. SATURDAY-SUNDAY...CONTINUED FAIR WEATHER OVER THE WEEKEND AS A WARM FRONT SWEEPS NORTH ACROSS NEW ENGLAND AND HIGH PRESSURE BUILDS OFFSHORE. THE COMBINATION SUGGESTS A WARMING TREND OVER THE WEEKEND WITH A 12C INCREASED IN TEMPS ALOFT BETWEEN SATURDAY AND SUNDAY. THE WARM FRONT WILL BRING VARIABLE SKY COVER...AS NOTED BY RH FIELDS ALOFT IN THE MODELS. SOUTHWEST WINDS AT 925 MB INCREASE TO 30 KNOTS SATURDAY AFTERNOON AND 30-40 KNOTS SATURDAY NIGHT AND SUNDAY. EXPECT SOME GUSTINESS TO OUR SURFACE WINDS EACH DAY. BUT LOW-LEVEL MIXING WILL BE LESS THAN IDEAL EACH DAY WITH BETTER MIXING SATURDAY AND LESS SUNDAY. MONDAY-TUESDAY...SHORTWAVE IN THE ZONAL FLOW WILL PUSH A COLD FRONT THROUGH NEW ENGLAND EITHER LATE SUNDAY NIGHT OR MONDAY. TIMING OF THE SHORTWAVE IN A ZONAL FLOW THIS FAR OUT IS IN QUESTION BUT THAT/S OUR BEST SHOT AT THIS TIME. LIMITED MOISTURE ALOFT TOGETHER WITH FAVORABLE JET DYNAMICS FROM A 125 KNOT JET...SO WE HAVE CHANCE POPS FOR RAIN/SNOW SHOWERS. HIGH PRESSURE THEN BUILDS DRY WEATHER FOR THE REST OF MONDAY AND TUESDAY. && .AVIATION /04Z WEDNESDAY THROUGH SUNDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. .SHORT TERM /THROUGH TOMORROW NIGHT/...MODERATE CONFIDENCE. TONIGHT...EXPECT VFR CONDITIONS UP TO 09Z THEN CONDITIONS WILL BEGIN TO DETERIORATE FROM VFR TO IFR. TOMORROW AND TOMORROW NIGHT...COASTAL STORM ANTICIPATED. SIGNIFICANT ACCUMULATION SNOWS OVER INTERIOR TERMINALS IMMEDIATELY W OF THE I-95 CORRIDOR. +SN POSSIBLE ESPECIALLY BDL-ORH AND POSSIBLY FOR A TIME AT BOS AROUND 18Z THU. STRONG NE WINDS UP TO 45 KT AT HYA AND ACK AROUND 00Z THU. KBOS TERMINAL...MODERATE CONFIDENCE IN TAF. KBDL TERMINAL...MODERATE CONFIDENCE IN TAF. OUTLOOK...THURSDAY THROUGH SUNDAY...MODERATE CONFIDENCE THURSDAY...MVFR WITH SCATTERED RAIN/SNOW SHOWERS. DIMINISHING NORTHWEST WINDS. FRIDAY...VFR WITH NORTHWEST WINDS GUSTING 15-20 KNOTS. SATURDAY-SUNDAY...INCREASING SKY COVER BUT MAINLY VFR. LOW POTENTIAL FOR MVFR CIGS MOVING NORTH OFF THE OCEAN INTO CAPE COD AND ISLANDS. INCREASING WINDS AT 2000 FEET...REACHING SOUTHWEST 35-40 KNOTS...WITH LIGHTER SOUTHWEST WINDS AT SURFACE. && .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 TONIGHT/...MODERATE CONFIDENCE. OVERNIGHT...WESTERLY WINDS CONTINUE TO VEER AT 15 KT OR LESS. SEAS REMAIN AT 5-6 FT OVER THE OUTER WATERS. WED INTO WED NIGHT... NOR`EASTER ANTICIPATED TO PASS AROUND THE 40N/70W BENCHMARK 00Z THU. HIGH PROB OF NE GALES WITH A LOW RISK OF STORM FORCE GUSTS 21Z WED TO 06Z THU. HEAVY RAIN LENDING TO REDUCED VISIBILITIES AT TIMES. GALE WARNING IS OUT WITH HIGH END GUSTS ANTICIPATE. CANT RULE OUT A FEW STORM FORCE GUSTS. OUTLOOK...THURSDAY THROUGH SUNDAY...MODERATE CONFIDENCE. THURSDAY... NORTHWEST WINDS GUSTING TO 25 KNOTS IN THE MORNING BUT DIMINISHING. SEAS START THE DAY 5 TO 11 FEET ON THE EXPOSED WATERS AND SUBSIDE TO 5 TO 6 FEET BY THE END OF THE DAY. SMALL CRAFT ADVISORY WILL BE NEEDED ON MOST WATERS. FRIDAY... LINGERING 5 FOOT SEAS ON THE OUTER WATERS. NORTHWEST WINDS WILL GUST 20 TO 25 KNOTS. A SMALL CRAFT ADVISORY MAY BE NEEDED ON SOME OF THE WATERS. SATURDAY-SUNDAY... SOUTHWEST WINDS GUSTING TO 25 KNOTS AND SEAS BUILDING TO 5 TO 6 FEET ON THE EXPOSED WATERS. A SMALL CRAFT ADVISORY MAY BE NEEDED.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...WINTER STORM WARNING FROM 7 AM WEDNESDAY TO 7 AM EST THURSDAY FOR CTZ002>004. MA...WINTER STORM WARNING FROM 7 AM WEDNESDAY TO 7 AM EST THURSDAY FOR MAZ002>006-008>012-026. WIND ADVISORY FROM 2 PM WEDNESDAY TO 3 AM EST THURSDAY FOR MAZ019-022>024. WINTER WEATHER ADVISORY FROM 7 AM WEDNESDAY TO 7 AM EST THURSDAY FOR MAZ007-013>016. NH...WINTER STORM WARNING FROM 7 AM WEDNESDAY TO 7 AM EST THURSDAY FOR NHZ011-012-015. RI...WIND ADVISORY FROM 2 PM WEDNESDAY TO 3 AM EST THURSDAY FOR RIZ008. WINTER WEATHER ADVISORY FROM 7 AM WEDNESDAY TO 7 AM EST THURSDAY FOR RIZ001>003. MARINE...GALE WARNING FROM 3 PM WEDNESDAY TO 5 AM EST THURSDAY FOR ANZ230>237. GALE WARNING FROM 3 PM WEDNESDAY TO 7 AM EST THURSDAY FOR ANZ250-251-254>256. && $$ SYNOPSIS...WTB/DUNTEN NEAR TERM...WTB/EVT SHORT TERM...DUNTEN LONG TERM...WTB AVIATION...WTB/DUNTEN MARINE...WTB/DUNTEN/EVT

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