Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 012346 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 646 PM EST SUN MAR 1 2015 .SYNOPSIS... A FAST MOVING LOW PRESSURE SYSTEM WILL BRING ACCUMULATING SNOW THIS EVENING AND 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. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... 7 PM UPDATE...SNOW HAS MOVED ACROSS THE REGION. LOWEST VSBYS ARE ACROSS CONNECTICUT/RI/SOUTHEAST MASS. EXPECT THIS TO REMAIN IN PLACE THROUGH MIDNIGHT BUT CAN/T RULE OUT A WOBBLE NORTH THAT BRINGS BRIEFLY HEAVIER SNOW RATES NEAR THE MASS PIKE CORRIDOR. NO SIGNIFICANT CHANGES MADE...THE 4 PM FORECAST HANDLES IT QUITE WELL. PREVIOUS DISCUSSION... LOW PRESSURE EMERGING FROM THE MID ATLANTIC COASTLINE IS EXPECTED TO PASS SOUTHEAST OF NANTUCKET TONIGHT...BRINGING A WIDESPREAD SNOW TO SOUTHERN NEW ENGLAND. SURFACE OBS AS OF 21Z INDICATE THAT SNOW HAS OVERSPREAD THE ENTIRE AREA. THE STRONGEST RADAR RETURNS AT 21Z WERE NEAR THE SOUTH COAST OF CT INTO RI...AND TO THE SOUTHWEST. THE BETTER FORCING FROM THIS EVENT IS EXPECTED TO OCCUR TO THE SOUTH OF THE MA TURNPIKE. 12Z MODELS WERE IN DECENT AGREEMENT ON PLACING THE HIGHEST QPF IN THAT AREA. BECAUSE OF THE QUICK HITTING NATURE OF THIS SYSTEM WITH A SHORT LIVED WINDOW FOR VERY STRONG LIFT/FORCING...CONTINUE TO THINK THAT FOR MOST OF THE REGION WINTER WEATHER ADVISORY/S FOR 3 TO 6 INCHES OF SNOW WILL COVER THIS EVENT. 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...ESPECIALLY ACROSS NORTHERN CT AND NORTHWEST RI. WE DID UPGRADED BLOCK ISLAND TO A WINTER STORM WARNING FOR THE LATE AFTERNOON FORECAST PACKAGE. THERE MAY BE SOME MIXING WITH RAIN IN THIS AREA AT TIMES. EXPECT THIS TO BE A SNOW EVENT FOR THE VAST MAJORITY OF SOUTHERN NEW ENGLAND. IT DOES BECOME A VERY CLOSE CALL NEAR THE SOUTH COAST...BUT WERE LEANING TOWARDS IT STAYING MAINLY WET SNOW. CONTINUED THE 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...SNOWFALL TOTALS MAY BE SOMEWHAT HIGHER. THE PRECIPITATION IS EXPECTED TO COME TO AN END ACROSS THE MAJORITY OF THE AREA BY DAYBREAK MONDAY. && .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... MONDAY... PRECIPITATION WILL HAVE LARGELY COME TO AN END FOR DAYBREAK MONDAY WITH THE LOW PRESSURE RAPIDLY PULLING AWAY INTO THE CANADIAN MARITIMES AND DRIER AIR/HIGH PRESSRUE MOVING IN FROM THE WEST. INCREASING SUNSHINE EXPECTEED DURING THE DAY...WITH TEMPS TOPPING OUT IN THE UPPER 20S TO MID 30S. HOWEVER AS WE GET TOWARDS MIDDAY/AFTERNOON TIGHTENING GRADIENT WILL ALLOW NORTHWEST FLOW TO BECOME BLUSTERY...WITH GUSTS OF 25 TO 30 MPH...25 TO 35 MPH ON THE CAPE AND ISLANDS. MONDAY NIGHT... HIGH PRESSURE SETTLES OVER THE AREA WITH CLEAR SKIES EXPECTED. GIVEN OUR SNOWPACK IN PLACE AND LIGHT WINDS...SHOULD BE ANOTHER NIGHT FOR EXCELLENT RADIATIONAL COOLING. BECAUSE OF THIS DID GENERALLY GO BELOW MODEL GUIDANCE FOR MIN TEMPS...LOOKING TO ANTICIPATED SURFACE DEWPOINTS FOR A GUIDELINE ON HOW LOW WE CAN GO. MAY SEE SOME SPOTS IN THE INTERIOR DROP BELOW ZERO. && .LONG TERM /TUESDAY THROUGH SUNDAY/... 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. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/... TONIGHT...MODERATE CONFIDENCE. MVFR CIGS WITH PATCHES OF IFR VALUES. VSBYS MOSTLY 1 TO 3 MILES WITH A ZONE FROM SOUTHERN CT THROUGH RI AND SE MASS WHERE VSBYS ARE LIFR AT 1/2 MILE TO 1 MILE. EXPECT THESE CONDITIONS TO LINGER THROUGH MIDNIGHT. THE ZONE OF LOWER VSBYS AND SNOWFALL RATES COULD WOBBLE NORTH A FEW MILES AND BRIEFLY APPROACH BOSTON BUT SHOULD PRIMARILY REMAIN TO THE SOUTH. SOUTH FLOW BRINGS ENOUGH MILDER AIR NORTH TO MIX OR CHANGE THE PCPN TO RAIN ON NANTUCKET AND PARTS OF THE OUTER CAPE. BULK OF THE SNOW SHOULD ENDS 06Z WEST TO 10Z EAST /LATE TONIGHT AND EARLY MONDAY/ MUCH OF THE REGION SHOULD IMPROVE TO VFR CONDITIONS BY 12-13Z MONDAY. KBOS TAF...CONFIDENT IN OVERALL TRENDS BUT THERE IS UNCERTAINTY ON TIMING. VSBYS BELOW 1 MILE SHOULD REMAIN TO THE SOUTH BUT COULD BRIEFLY VISIT THE AIRPORT EARLY TONIGHT. THE BULK OF ACCUMULATING SNOW IS EXPECTED BY MIDNIGHT. KBDL TAF...CONFIDENT IN OVERALL TRENDS BUT THERE IS UNCERTAINTY ON TIMING. BULK OF ACCUMULATING SNOW WITH IFR TO LIFR CONDITIONS EXPECTED BY MIDNIGHT. MONDAY AND MONDAY NIGHT...HIGH CONFIDENCE VFR. NORTHWEST WINDS GUSTING TO 25 TO 30 MPH ACROSS MUCH OF THE AREA DURING MONDAY AFTERNOON...25 TO 35 MPH GUSTS CAPE/ISLANDS. WINDS DIMINISHING TOWARDS SUNSET. 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. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/...HIGH CONFIDENCE. A WEAK WAVE OF LOW PRESSURE MOVES ACROSS THE WATERS TONIGHT. THIS 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 THIS EVENING AND TONIGHT WILL REDUCE VISIBILITIES AT TIMES FOR MARINERS. MONDAY...AS THE LOW PRESSURE GOING INTO THE CANADIAN MARITIMES INTENSFIES...INCREASING NORTHWEST WINDS ARE EXPECTED OVER THE SOUTHERN NEW ENGLAND COASTAL WATERS...WITH GALE FORCE GUSTS EXPECTED. GALE WARNINGS HAVE BEEN HOISTED FOR ALL COASTAL WATERS FROM MIDDAY MONDAY INTO MONDAY NIGHT. 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. && .BOX WATCHES/WARNINGS/ADVISORIES... 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. && $$ SYNOPSIS...WTB/NMB NEAR TERM...WTB/NMB SHORT TERM...NMB LONG TERM...WTB AVIATION...WTB/NMB MARINE...WTB/NMB

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