Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 012106 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 406 PM EST SUN MAR 1 2015 .SYNOPSIS...
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A FAST MOVING LOW PRESSURE SYSTEM WILL BRING ACCUMULATING SNOW LATER TODAY AND ESPECIALLY TONIGHT WITH THE HIGHEST AMOUNTS EXPECTED SOUTH OF THE MASSACHUSETTS TURNPIKE. HIGH PRESSURE BRINGS DRY COLD AIR FOR THE EARLY WEEK. LOW PRESSURE FROM NORTHERN CANADA AND ASSOCIATED LOW FORMING OVER THE PLAINS MONDAY WILL MERGE...THEN PASS WEST AND NORTH OF NEW ENGLAND. THIS WILL SWING A COLD FRONT ACROSS THE REGION ON WEDNESDAY. DRY AND COLD WEATHER RETURNS FOR THE END OF THE WEEK. ANOTHER COLD FRONT MOVES THROUGH ON SATURDAY.
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&& .NEAR TERM /UNTIL 5 PM THIS AFTERNOON/... 1 PM UPDATE... LIGHT SNOW IS WORKING ITS WAY INTO SOUTHERN NEW ENGLAND...BASED ON 18Z OBS LIGHT SNOW HAS MADE IT INTO THE SPRINGFIELD AREA AND LIGHT SNOW HAS EVEN STARTED AT PVD. THE SNOW WILL CONTINUE TO GRADUALLY OVERSPREAD THE REMAINDER OF OUR AREA AS THE AFTERNOON PROGRESSES...LIKELY REACHING BOSTON AROUND 20Z. AGAIN ONLY MINOR CHANGES MADE TO HOURLY TEMPS TO REFLECT LATEST OBS...FORECAST HIGHS CONTINUE TO LOOK ON TRACK. EARLY MORNING DISCUSSION... MID LEVEL CLOUDINESS WILL STREAM INTO SOUTHERN NEW ENGLAND AND THICKEN DURING THE MORNING HOURS IN ADVANCE OF APPROACHING LOW PRESSURE. SOUTHWEST FLOW ALOFT OVERRUNING THE COLD DOME AT THE SURFACE MAY ALLOW FOR SOME LIGHT SNOW/FLURRIES TO BREAK OUT ACROSS THE INTERIOR LATE THIS MORNING/EARLY AFTERNOON AND THEN FIND THEIR WAY TO THE COAST BY MID TO LATE AFTERNOON. THE LIFT THROUGH MID AFTERNOON IS FAIRLY WEAK...SO THE AREAS OF SNOW SHOULD BE RATHER LIGHT. ANY ACCUMULATIONS THAT OCCUR WILL PROBABLY BE A DUSTING TO LESS THAN 1 INCH THROUGH THAT THAT TIME. HIGH TEMPS WILL MAINLY BE IN THE UPPER 20S TO AROUND 30. && .SHORT TERM /5 PM THIS AFTERNOON THROUGH MONDAY NIGHT/... *** BULK OF THE ACCUMULATING SNOW OCCURS BETWEEN 3 PM AND 1 AM WITH THE HEAVIEST AMOUNTS SOUTH OF THE MA TURNPIKE *** 1) OVERVIEW AND TIMING: THE BULK OF THE ACCUMULATING SNOW WILL OCCUR BETWEEN 3 PM AND 1 AM ACROSS THE REGION. THE SNOW SHOULD TAPER OFF TO FLURRIES TOWARD DAYBREAK MONDAY. THE MODELS DO AGREE THAT THE BETTER FORCING WILL OCCUR TO THE SOUTH OF THE MA TURNPIKE. THIS A RESULT OF SECONDARY LOW PRESSURE NEAR THE SOUTH COAST...ALLOWING FOR SOME SURFACE CONVERGENCE AS WELL AS THE INTENSIFICATION OF THE LOW LEVEL JET. THE BIGGEST ISSUE IS THE MODELS ARE NOT IN AGREEMENT IN HOW INTENSE THE FORCING WILL BE ACROSS THE REGION THIS EVENING. THE RGEM/NAM ARE THE MOST ROBUST WITH QPF SOUTH OF THE MA TURNPIKE. THE NAM SHOWS A PERIOD OF FAIRLY STRONG LIFT OF 15 TO 20 MICROBARS PER SECOND WITHIN THE BEST SNOWGROWTH REGION THIS EVENING. THIS WOULD TRANSLATE TO A PERIOD OF 1+ INCH PER HOUR SNOWFALL RATES NEAR AND SOUTH OF THE MA PIKE. ON THE OTHER HAND...THE GFS ALSO HAS FAIRLY STRONG LIFT...BUT KEEPS IT SOUTHEAST OF OUR REGION OUT OVER THE OCEAN. THE SECONDARY LOW PRESSURE SYSTEM ON THE GFS IS WEAKER AND FURTHER SOUTHEAST...RESULTING IN THE LOW LEVEL JET BEING DISPLACED FURTHER EAST. THE ECMWF/UKMET SOLUTIONS SEEM TO BE THE MIDDLE GROUND WHICH WE WILL LEAN TOWARDS. 2) WINTER WEATHER HEADLINES AND SNOW ACCUMS: WITH THAT SAID...THE OTHER DILEMMA IS WHAT TO DO WITH THE CURRENT HEADLINES. THIS DOES NOT APPEAR TO BE THE TYPE OF SETUP WHERE WE ARE GOING TO RECEIVE WIDESPREAD WARNING SNOWFALL AMOUNTS. THE WINDOW FOR THE VERY STRONG LIFT/FORCING IS SHORT-LIVED AND REALLY WOULD LIKE TO SEE THE LOW LEVEL JET A BIT MORE BACKED TO TRANSPORT DEEPER MOISTURE NORTHWARD. THEREFORE...FEEL THAT FOR MOST OF THE REGION WINTER WEATHER ADVISORY/S FOR 3 TO 6 INCHES OF SNOW WILL COVER IT. HOWEVER...GIVEN THERE IS NICE OMEGA IN THE SNOW GROWTH REGION...WE MIGHT BE LOOKING AT SOME DECENT RATIOS. SO WE STILL CAN NOT RULE OUT THE LOW RISK OF REACHING WARNING AMOUNTS AND LATER SHIFTS WILL HAVE TO MONITOR CLOSELY...ESPECIALLY ACROSS NORTHERN CT AND NORTHWEST RI. WE DID UPGRADE A SMALL AREA FROM CENTRAL AND SOUTHERN RHODE ISLAND INTO SOUTHEAST MA INCLUDING THE SOUTH COAST TO A WINTER STORM WARNING. THE NOSE OF THE LOW LEVEL JET LOOKS TO TRANSPORT SOME DEEPER MOISTURE INTO THIS REGION. THERE ALSO COULD BE SOME ENHANCEMENT ALONG THE LAND/SEA INTERFACE AND A WEAK SURFACE BOUNDARY SO WENT WITH 4 TO 8 INCHES IN THIS REGION. 3) PTYPE AND IMPACTS: THE MODELS HAVE TRENDED COLDER OVER THE PAST 24 HOURS. THEREFORE...EXPECT THIS BE PRETTY MUCH A SNOW EVENT. IT DOES BECOME A VERY CLOSE CALL NEAR THE SOUTH COAST...BUT WERE LEANING TOWARDS IT STAYING MAINLY WET SNOW. IF PRECIPITATION LIGHTENS UP THAT MAY INCREASE THIS RISK WE SEE A BRIEF CHANGE OVER TO RAIN. MEANWHILE...WE WENT WITH A HIGH END WINTER WEATHER ADVISORY FOR THE CAPE BECAUSE THEY MAY CHANGE TO RAIN FOR A TIME...ESPECIALLY EAST OF HYANNIS. IF THE CHANGE OVER DOES NOT OCCUR...WE MAY NEED TO UPGRADE THEM TO A WINTER STORM WARNING ESPECIALLY NEAR THE CAPE COD CANAL GIVEN EXPECTED QPF. THE ONE THING WILL ALSO HAVE TO WATCH IS AREAS NEAR THE SOUTH COAST AND CAPE COD. LOOKS TO BE A WET SNOW DOWN THAT WAY AND ON GOING ROOF ISSUES MAY BE EXACERBATED...ESPECIALLY IF ANY AREAS THAT ARE ABLE TO EXCEED 6 INCHES OF WET SNOW. && .LONG TERM /TUESDAY THROUGH SUNDAY/...
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BIG PICTURE... THE BROAD UPPER FLOW CONTINUES TO FEATURE A TROUGH TRANSITING EAST ACROSS THE COUNTRY...REACHING THE EASTERN USA DURING THE LATE WEEK AND LINGERING THROUGH THE WEEKEND. MEANWHILE AN UPPER RIDGE SHIFTS FROM THE PACIFIC OCEAN BACK ASHORE ONTO THE WEST COAST. CONTOUR HEIGHTS IN THE TROUGH ARE LOWEST THURSDAY-FRIDAY AND NEAR NORMAL OVER THE WEEKEND. THIS MEANS A TREND TO COLDER TEMPS THURSDAY- FRIDAY FOLLOWED BY A TREND CLOSER TO NORMAL OVER THE WEEKEND. DAILIES... TUESDAY... HIGH PRESSURE OVER THE REGION MOVES OFFSHORE BY AFTERNOON WITH AIRFLOW SWINGING FROM NORTHWEST TO SOUTHWEST. THE SURFACE AIRMASS STARTS OUT QUITE DRY WITH DEW POINTS IN THE SINGLE NUMBERS BELOW ZERO TO START...CLIMBING TO 5-10 ABOVE BY EVENING. MODEL CROSS SECTIONS SHOW INCREASING MOISTURE MORNING AND AFTERNOON ABOVE 700 MB. THIS SUGGESTS INCREASING MID AND HIGH CLOUDS WHILE DRY BENEATH. LOW LEVEL JETS FROM THE CAROLINAS AND MIDWEST AND THE SURFACE PRESSURE GRADIENT ALL SUGGEST THE INFLOW AND ISENTROPIC LIFT WILL REMAIN TO OUR WEST THROUGH THE DAY...POSSIBLY ENTERING WESTERN MA/CT AT OR AFTER 21Z. SO WE EXPECT INCREASING CLOUDS TUESDAY BUT OTHERWISE DRY WEATHER THROUGH THE DAY. POSSIBLE LIGHT SNOW AROUND THE EVENING RUSH HOUR IN THE CT RIVER VALLEY. TEMPS SHOULD REACH THE MID 20S TO AROUND 30. TUESDAY NIGHT-WEDNESDAY... NORTHERN AND SOUTHERN STREAM SHORTWAVES MERGE OVER THE GREAT LAKES AND TRACK INTO CANADA. THIS BRINGS A MILD FLOW OF AIR UP OVER NEW ENGLAND. THE LEADING EDGE OF THIS AIR REACHES WESTERN SECTIONS TUESDAY EVENING AND EASTERN SECTIONS TUESDAY NIGHT. TEMPERATURE PROFILES SUPPORT AN INITIAL PERIOD OF SNOW CHANGING TO RAIN OR FREEZING RAIN OVERNIGHT. ACTUALLY...THE MODELS MAY NOT BE HANDLING WELL THE CHILLING MASS OF SNOW AND COLD GROUND /A.K.A. THE GIANT ICECUBE/ WHICH WOULD MEAN THE ACTUAL MAX SFC TEMPS WILL BE COOLER THAN MODEL FORECASTS. TEMPERATURES AT 925 AND 950 MB WILL BE IN THE 30S...SO EXPECT SURFACE TEMPS NO HIGHER THAN THE LOWER 40S. THE SURFACE LOW PRESSURE AREA PASSES WELL NORTH OF NEW ENGLAND WEDNESDAY AND SWINGS A COLD FRONT THROUGH THE REGION DURING THE AFTERNOON OR EVENING. MOISTURE CROSS SECTIONS SHOW DECREASING RH IN THE LIFT AND NUCLEATION ZONES ALOFT WEDNESDAY MORNING...SO THE TREND THROUGH THE DAY SHOULD BE TO DIMINISHING POPS. THURSDAY-FRIDAY... THE WEDNESDAY COLD FRONT WILL ALIGN WITH THE UPPER FLOW AS IT MOVES SOUTH OF NEW ENGLAND...SLOWING ITS OFFSHORE PROGRESS TO A CRAWL. MEANWHILE WE WILL BE UNDER THE RIGHT ENTRANCE REGION OF THE SUPPORTING UPPER JET...A SOURCE OF UPPER VENTING. THIS SHOULD SUPPORT LINGERING CLOUDS AND A CHANCE OF PCPN...WITH TEMPS SUPPORTIVE OF SNOW. BEST CHANCE SOUTH COAST...LESSER CHANCE FARTHER NORTH. THE JET AND SURFACE FRONT SWEEP OFFSHORE THURSDAY NIGHT. HIGH PRESSURE THEN MOVES OVER THE EASTERN USA FOR FRIDAY. TEMPS ALOFT SUPPORT MAX SFC TEMPS IN THE 20S. SATURDAY-SUNDAY... ANOTHER NORTHERN STREAM SHORTWAVE AND COLD FRONT SWINGS THROUGH THE FLOW SATURDAY. CROSS SECTIONS SHOW SOME MOISTURE ALOFT BUT MOST OF IT IS CONCENTRATED TO OUR NORTH. ALSO JUST LIMITED LIFT TO WORK ON THAT MOISTURE. WE WILL HAVE 25-50 PCT SKY COVER AND NIL POPS. HIGH PRESSURE THEN BUILDS FOR SUNDAY.
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&& .AVIATION /21Z SUNDAY 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 /TODAY AND TONIGHT/... 18Z UPDATE...MODERATE CONFIDENCE. THIS AFTERNOON...MVFR CIGS/VSBYS IN LIGHT SNOW AT BAF-BDL BUT MAINLY VFR TO THE EAST TO START...WITH CIGS AND/OR VSBYS LOWERING TO MVFR ACROSS THE REMAINDER OF SOUTHERN NEW ENGLAND TERMINALS BETWEEN 18Z AND 21Z IN LIGHT SNOW. TONIGHT...MODERATE CONFIDENCE. THE BULK OF THE MODERATE TO EVEN BRIEFLY HEAVY SNOW WILL OCCUR THIS EVENING WHEN WIDESPREAD IFR TO LIFR CONDITIONS OCCUR. THE LOWEST CONDITIONS WILL MOST LIKELY BE SOUTH OF THE MA TURNPIKE. PTYPE PRETTY MUCH ALL SNOW...EXCEPT FOR THE VERY IMMEDIATE SOUTH COAST/CAPE WHERE SNOW MAY MIX WITH OR CHANGE TO RAIN FOR A TIME. WHETHER OR NOT THAT HAPPENS IS UNCERTAIN...BUT WE DO THINK THAT AT LEAST THE ISLANDS WILL MIX OR CHANGE TO RAIN. BULK OF SNOW ENDS BY 8Z TO 9Z TONIGHT AND MUCH OF THE THE REGION SHOULD IMPROVE TO VFR CONDITIONS BY 12-13Z MONDAY. KBOS TAF...CONFIDENT IN OVERALL TRENDS BUT THERE IS UNCERTAINTY ON TIMING. SOME LIGHT SNOW IS EXPECTED DURING MID TO LATE AFTERNOON...BUT THE BULK OF ACCUMULATING SNOW WITH IFR TO LIFR CONDITIONS EXPECTED MAINLY THIS EVENING. KBDL TAF...CONFIDENT IN OVERALL TRENDS BUT THERE IS UNCERTAINTY ON TIMING. BULK OF ACCUMULATING SNOW WITH IFR TO LIFR CONDITIONS EXPECTED AFTER 3 OR 4 PM. OUTLOOK...TUESDAY THROUGH FRIDAY... TUESDAY...MODERATE CONFIDENCE. VFR DURING THE DAY WITH INCREASING SKY COVER. MVFR CIGS/VSBYS POSSIBLE LATE IN THE DAY CT RIVER VALLEY. TUESDAY NIGHT-WEDNESDAY...MODERATE CONFIDENCE. CONDITIONS LOWERING TO IFR/LIFR. INITIALLY SNOW BUT CHANGING TO SLEET/FREEZING RAIN DURING THE NIGHT AND RAIN IN THE COASTAL PLAIN OVERNIGHT. PCPN CHANGES TO RAIN ALL AREAS WEDNESDAY...BUT COLD SURFACES COULD MAINTAIN A FREEZING RAIN ELEMENT WEDNESDAY MORNING. COLDER AIR MOVES IN WEDNESDAY NIGHT CHANGING ANY RAIN TO SNOW. THURSDAY...LOW CONFIDENCE. VFR NORTH OF A HFD-BOS LINE. MVFR CIGS AND AREAS OF MVFR/IFR VSBYS IN SNOW...DIMINISHING BY EVENING. NORTHWEST WINDS GUSTING TO 20 KNOTS. FRIDAY...MODERATE CONFIDENCE. 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 /TODAY AND TONIGHT/...HIGH CONFIDENCE. A WEAK WAVE OF LOW PRESSURE MOVES ACROSS THE WATERS LATER TODAY AND TONIGHT. WEAK PRESSURE GRADIENT SHOULD KEEP WINDS/SEAS BELOW SMALL CRAFT THRESHOLDS TODAY AND TONIGHT. THE SYSTEM REALLY INTENSIFIES AS IT MOVES INTO THE CANADIAN MARITIMES NEAR DAYBREAK MONDAY...SO WESTERLY WIND GUSTS MAY REACH 20 TO 25 KNOTS NEAR 12Z MONDAY. OTHERWISE...RAIN AND SNOW LATE TODAY AND ESPECIALLY TONIGHT WILL REDUCE VISIBILITIES AT TIMES FOR MARINERS. OUTLOOK...TUESDAY THROUGH FRIDAY..MODERATE CONFIDENCE. TUESDAY... LINGERING 5 FOOT SEAS SOUTH AND EAST OF NANTUCKET IN THE MORNING BUT DIMINISHING. NORTHWEST WINDS DIMINISHING FROM 20 KNOTS. ANY SMALL CRAFT ADVISORY SHOULD END IN THE MORNING. TUESDAY NIGHT-WEDNESDAY...SOUTH TO SOUTHWEST WINDS WILL INCREASE TO 20-25 KNOTS. SEAS WILL BUILD 6 TO 10 FEET ON THE OUTER WATERS AND ON RI SOUND. REDUCED VSBYS...INITIALLY SNOW BUT CHANGING TO RAIN. A SMALL CRAFT ADVISORY MAY BE NEEDED. THURSDAY...NORTHWEST WIND GUSTING TO 25 KNOTS. SEAS 5 TO 8 FEET MAINLY ON THE OUTER WATERS...DIMINISHING LATE. A SMALL CRAFT ADVISORY MAY BE NEEDED. FRIDAY... SHIFTING WINDS LESS THAN 20 KNOTS. SEAS LESS THAN 5 FEET. QUIET WEATHER.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...WINTER WEATHER ADVISORY UNTIL 7 AM EST MONDAY FOR CTZ002>004. MA...WINTER STORM WARNING UNTIL 7 AM EST MONDAY FOR MAZ017>021. WINTER WEATHER ADVISORY UNTIL 7 AM EST MONDAY FOR MAZ002>016- 022>024-026. RI...WINTER STORM WARNING UNTIL 7 AM EST MONDAY FOR RIZ002>008. WINTER WEATHER ADVISORY UNTIL 7 AM EST MONDAY FOR RIZ001. MARINE...GALE WARNING FROM 11 AM MONDAY TO 4 AM EST TUESDAY FOR ANZ231- 232-250-251-254-255. GALE WARNING FROM 11 AM TO 11 PM EST MONDAY FOR ANZ233>235-237- 256. GALE WARNING FROM 11 AM TO 8 PM EST MONDAY FOR ANZ230-236.
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&& $$ SYNOPSIS...WTB/FRANK NEAR TERM...FRANK/DOODY/NMB SHORT TERM...FRANK LONG TERM...WTB AVIATION...WTB/FRANK/NMB MARINE...WTB/FRANK

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