Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 032356 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 656 PM EST TUE MAR 3 2015 .SYNOPSIS... A STORM SYSTEM MOVING FROM THE GREAT LAKES INTO CANADA WILL BRING A MIXTURE OF PRECIPITATION TONIGHT AND EARLY WEDNESDAY. WEAK LOW PRESSURE PASSING SOUTH OF NEW ENGLAND WILL BRING ANOTHER ROUND OF SNOW WEDNESDAY NIGHT AND THURSDAY.HIGH PRESSURE MOVES IN FOR FRIDAY THROUGH THIS WEEKEND...BRINGING DRY CONDITIONS...WITH COLDER THAN NORMAL TEMPERATURES. A WEAKENING FRONT MAY BRING SOME LIGHT SNOW SHOWERS ON MONDAY. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... SNOW IS MAKING A STEADY EASTWARD PROGRESSION INTO SOUTHERN NEW ENGLAND. VISIBILITY HAS BEEN LOWERING TO BELOW 2 MILES...IN SOME CASES BELOW 1 MILE. CURRENT FORECAST LOOKS ON TRACK...AND ONLY MINOR CHANGES MADE TO HOURLY TEMPS/DEWPOINTS TO REFLECT LATEST TRENDS. CONTINUED NON DIURNAL TREND ON TEMPERATURES. PREVIOUS DISCUSSION FOLLOWS... TONIGHT... HEAVIER PCPN LAGS THE LEADING EDGE BY 2-3 HOURS. EXPECT A HEAVIER BURST OF SNOW TO LEAVE SOME ACCUMULATION DURING THE FIRST PART OF THE NIGHT. QPF BASED ON HPC PROJECTIONS COMBINES WITH EXPECTED TEMPERATURES TO SUGGEST 1-3 INCHES ACCUMULATION...HEAVIEST IN THE WEST. OBSERVATIONS OF SLEET AND FREEZING RAIN IN CENTRAL PA POINT TO ADVANCING WARMER AIR ALOFT OF THE SURFACE LAYER. MODEL DATA SHOWS A 40 KNOT JET FROM THE OHIO VALLEY AND A 50 KNOT COASTAL JET AT 925 MB MOVING OVER THE REGION AND SUPPORTING THE WARM ADVECTION ALOFT. WITH NO COLD AIR DAMMING IN PLACE WE SHOULD EXPECT SLOWLY RISING TEMPS AT THE SURFACE OVERNIGHT...ALL OF WHICH SUPPORTS THE IDEA OF CHANGING PTYPE OVERNIGHT. WE USED A NON-DIURNAL TEMPERATURE TREND. BUFKIT SHOWS TEMPS IN THE 30S OVERNIGHT AROUND 925 MB AND A NEAR ISOTHERMAL LAYER TO THE SURFACE. SO OVERNIGHT TEMPERATURES SHOULD GO NO HIGHER THAN THE 30S. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... COLD FRONT MOVES THROUGH SOUTHERN NEW ENGLAND DURING THE MORNING. THAT SHOULD END MOST OF THE PCPN. THE BEST CHANCE OF PCPN WOULD BE ALONG THE SOUTH COAST...WITH TEMPS WARM ENOUGH FOR RAIN. UPPER FLOW WILL BE WEST-TO-EAST AHEAD OF ANOTHER UPPER TROUGH SWINGING ACROSS THE GREAT LAKES. THE WEDNESDAY COLD FRONT WILL LINE UP WITH THAT UPPER FLOW...STALLING THE FRONT SOUTH OF NEW ENGLAND. MEANWHILE THE UPPER JET IN THE FLOW MOVES ACROSS NEW ENGLAND AND PLACES US IN ITS RIGHT ENTRANCE REGION. THIS WILL GENERATE SUPPORT FOR A WAVE ON THE FRONT PUSHING PCPN NORTH AGAIN WEDNESDAY NIGHT. AT THE SAME TIME...WINDS SHIFTING TO NORTH WILL DRAW COLDER AIR SOUTH ACROSS THE REGION AGAIN. SO ANY DEVELOPING PCPN WOULD CHANGE TO FREEZING RAIN AND THEN SNOW. QUESTION REMAINS AS TO WHETHER THE COLD AIR WILL BE DRY ENOUGH TO SUPPRESS THE PCPN SHIELD FARTHER SOUTH. THIS MAY LIMIT ANY SIGNIFICANT PCPN TO THE SOUTH COAST OR EVEN JUST OFFSHORE. WE WILL GO WITH CATEGORICAL POPS ALONG THE SOUTH COAST...LIKELY POPS ACROSS CT-RI-SE MASS...AND CHANCE POPS FARTHER NORTH. BASED QPF ON HPC VALUES. DUE TO THE COMBINATION OF EXPECTED PCPN AND EXPECTED TEMPS...WE HAVE ISSUED A WINTER STORM WATCH ALONG THE SOUTH COAST INCLUDING CAPE COD AND ALL THE ISLANDS. THIS WILL ALSO INCLUDE KENT COUNTY RI. && .LONG TERM /THURSDAY THROUGH TUESDAY/... OVERVIEW... UPPER LEVEL PATTERN SHOWING A FEW SIGNS OF CHANGE WITH THE CHANGING SEASON...THOUGH DOES LOOK A COLD PATTERN REMAINS FOR MUCH OF THE NORTHEAST U.S. THROUGH A GOOD PORTION OF THIS LONG TERM TIMEFRAME. ONE NOTICEABLE CHANGE IS THE DRYING OF THE SAME PATTERN. USED A BLEND OF AVAILABLE GUIDANCE FOR THIS FORECAST...WHICH CONTINUED TO HAVE GOOD CONTINUITY TO THE PREVIOUS PACKAGE. DETAILS... THURSDAY... THE WINTER STORM WATCH CONTINUES INTO THURSDAY FOR SOUTHERN RI/BI AND SOUTH COASTAL MA INCLUDING THE CAPE AND ISLANDS. LOW PRESSURE ALONG THE SURFACE FRONT IS WELL SOUTH OF OUR AREA...12Z RUNS SHOWING IT OFF THE CAROLINA COAST...BUT PRECIPITATION SHOULD STILL GET INTO OUR AREA TO SOME EXTENT. FORECAST SURFACE TEMPS AND THICKNESSES INDICATE THE AIRMASS IN OUR AREA ON THURSDAY IS COLD ENOUGH FOR ALL SNOW. THERE MAY BE A FAIRLY SHARP CUTOFF WITHIN OR JUST SOUTH OF OUR AREA WITH RESPECT TO ACCUMULATING SNOWS VS. MORE MINIMAL SNOWFALL. AT THIS TIME THE BEST CHANCE FOR AN INCH OF SNOW OR GREATER DURING THURSDAY LOOKS TO BE IN THE VICINITY OF AND SOUTH OF THE MASS PIKE...WITH THE POTENTIAL FOR AN ADDITIONAL FEW INCHES OF SNOW IN SOUTHERN RI/FAR SOUTHEAST MA...IN THE WATCH AREA. THURSDAY NIGHT... UPPER TROUGH SHIFTS EAST...PUSHING THE FRONT FURTHER OFFSHORE. THERE MAY BE SOME LINGERING LIGHT SNOW EARLY THURSDAY EVENING IN EXTREME SOUTHEAST MA...BUT ANY SNOWFALL AT THIS TIME IS EXPECTED TO BE LESS THAN AN INCH. OTHERWISE ANOTHER SHOT OF ARCTIC AIR WORKS INTO SOUTHERN NEW ENGLAND...WITH WEAKENING WINDS AND CLEARING SKIES. SO ANOTHER NIGHT OF GOOD RADIATIONAL COOLING. OVERNIGHT LOWS IN TEH SINGLE DIGITS FOR MOST AREAS EXCEPT TEENS ALONG THE SOUTH COAST. CANT RULE OUT A FEW SUB-ZERO LOWS IN THE TYPICAL COLDER SPOTS OF THE FAR INTERIOR. FRIDAY THROUGH MONDAY... BROAD UPPER TROUGH PERSISTS ACROSS CENTRAL AND EASTERN CANADA... KEEPING THE REGION IN BELOW NORMAL TEMPS THROUGH THIS TIMEFRAME. FAST FLOW ALOFT ALSO BRINGS WEAK SYSTEMS TOWARD THE REGION...THOUGH LOOKS LIKE ONLY LIGHT PRECIP WITH W-NW FLOW IN PLACE WITH THESE CLIPPER TYPE SYSTEMS. AN AREA OF HIGH PRESSURE BUILDS TO THE SW OF OUR AREA ON FRIDAY. DAYTIME HIGHS IN THE 20S ARE EXPECTED...15 TO 20 DEGS BELOW NORMAL. AS THE HIGH SHIFTS S OF THE REGION SATURDAY AND SUNDAY...TEMPERATURES DO REBOUND A BIT. THEY LOOK REMAIN BELOW NORMAL BUT ANTICIPATING HIGHS IN THE 30S SAT AND SUN WITH WINDS FROM THE SW. A WEAK LOW/COLD FRONT PASSES NORTH OF OUR AREA LATE SAT INTO SUN... MOST OF THE ENERGY AND PRECIP LOOKS TO REMAIN ACROSS NORTHERN NEW ENGLAND. MIGHT SEE SOME CLOUDS OTHERWISE ANTICIPATING MAINLY DRY CONDITIONS FOR SOUTHERN NEW ENGLAND DURING THIS TIMEFRAME. ANOTHER CLIPPER SYSTEM QUICKLY MOVES N OF THE GREAT LAKES BY MONDAY MORNING...ONLY HAVE A SLIGHT CHANCE POPS FOR SNOW IN OUR AREA WITH THIS FEATURE. MAY SEE PRECIP MAY WASH OUT AS IT APPROACHES IN THE DRY W-NW FLOW. TUESDAY LOOKS UNCERTAIN WITH DIFFERENCES IN THE MODELS AS TO WHETHER HIGH PRESSURE KEEPS OUR AREA FAIRLY DRY...OR IF WE ARE CLIPPED BY A NORTHERN OR SOUTHERN STREAM LOW. AT THIS POINT HAVE DRY TO SLIGHT CHANCE POPS. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH WEDNESDAY/... 00Z TAF UPDATE... THIS EVENING INTO EARLY WEDNESDAY...MODERATE CONFIDENCE. ALTHOUGH THERE IS HIGH CONFIDENCE IN OVERALL TRENDS...THERE IS LOWER CONFIDENCE IN EXACT TIMING. CIGS LOWER TO MVFR/IFR EARLY THIS EVENING. SNOW HAD ALREADY OVERSPREAD INTERIOR TERMINALS BY 00Z...AND SNOW WILL OVERSPREAD EASTERN TERMINALS BY 01Z. ACCUMS RANGE FROM 1-3 INCHES WIDESPREAD ALTHOUGH SOME 4+ IS POSSIBLY IN THE HIGHER TERRAIN OF THE EAST SLOPES OF THE BERKSHIRES AND THE WORCESTER HILLS. IFR CONDITIONS AT TIMES LIKELY ESPECIALLY IN LOWER VSBYS. THE SNOW TRANSITIONS TO A PERIOD OF SLEET...TO FREEZING RAIN...TO STRAIGHT RAIN THROUGH THE OVERNIGHT HOURS FROM S-N. SOME ICE ACCUMS POSSIBLE...MAINLY IFR/MVFR CONDITIONS. STRONG LOW LEVEL JET BRINGS THE POTENTIAL FOR LOW LEVEL WIND SHEAR FOR SEVERAL HOURS AROUND AND AFTER MIDNIGHT. BEST CHANCE FOR THIS OCCURRING IS CENTRAL/EASTERN MA AND RI. WEDNESDAY...MODERATE CONFIDENCE. SOME GRADUAL IMPROVEMENT IS EXPECTED DURING THE MORNING HOURS FROM N-S ALTHOUGH IT/S LIKELY MVFR/IFR CONDITIONS LINGER CLOSER TO THE S COAST EVEN AS RAIN SLOWS AND FOG/DRIZZLE DEVELOPS. SOME VFR IS NOT OUT OF THE QUESTION DURING THE DAY INCLUDING CT VALLEY AND ALONG/NORTH OF THE MASS PIKE. WEDNESDAY NIGHT... EXPECT CONDITIONS TO DETERIORATE TO MVFR BY 05Z IN MIXED PRECIP CHANGING OVER TO SNOW FROM N-S. WILL VSBYS LOWER TO IFR-VLIFR ACROSS N CT/RI/SE MA IN PERIODS OF SN/+SN AFTER 06Z-08Z AND CONTINUE THROUGH THU MORNING. KBOS TAF...HIGH CONFIDENCE IN OVERALL TRENDS...LOWER CONFIDENCE IN EXACT TIMING. KBDL TAF...HIGH CONFIDENCE IN OVERALL TRENDS...LOWER CONFIDENCE IN EXACT TIMING. OUTLOOK...THURSDAY THROUGH SUNDAY... THURSDAY...MODERATE CONFIDENCE. EXPECT MVFR CONDITIONS OVERALL...LOCLAIZED CIGS/VSBYS LOWER TO IFR- VLIFR ACROSS N CT/RI/SE MA IN PERIODS OF SN/+SN THROUGH THU MORNING. CONDITIONS SHOULD SLOWLY IMPROVE FROM N-S DURING THU AFTERNOON...BUT LOWER CIGS/VSBYS CONTINUE ALONG S COAST INTO THU EVENING. NW WINDS COULD GUST TO 20-25 KT ALONG THE COAST. THURSDAY NIGHT...MODERATE CONFIDENCE. MAINLY VFR ACROSS MOST AREAS. RI/SE MA...IFR CONDITIONS EARLY IN LEFTOVER -SN...THEN IMPROVING TO VFR. N-NW GUSTING TO 20-25 KT ALONG THE COAST...DIMINISHING AFTER MIDNIGHT. FRIDAY THROUGH SUNDAY...MODERATE CONFIDENCE. EXPECT VFR CONDITIONS. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH WEDNESDAY/... TONIGHT... SOUTH-SOUTHWEST WINDS INCREASE AS A GREAT LAKES COLD FRONT APPROACHES. THE TIGHTENING PRESSURE GRADIENT SHOULD SUPPORT WINDS APPROACHING 25 KNOTS AT TIMES. THE WINDS WILL DRIVE HIGHER SEAS WITH 5 TO 8 FOOT VALUES ON THE EXPOSED WATERS BY LATE NIGHT. SMALL CRAFT ADVISORY IN EFFECT FOR ALL WATERS. WEDNESDAY... COLD FRONT CROSSES THE WATERS. THIS WILL SHIFT THE WIND OUT OF THE WEST. WINDS WILL CONTINUE TO GUST AT TIMES TO 25 KNOTS...AND SEAS WILL CONTINUE AT 5 TO 8 FEET ON THE EXPOSED WATERS. SMALL CRAFT ADVISORY CONTINUES BUT MAY BE DROPPED ON SOME NEAR SHORE WATERS. WEDNESDAY NIGHT...WINDS BECOME NORTHWEST AND PULL COLDER AIR ACROSS THE WATERS...GUSTING 20-25 KNOTS LATER AT NIGHT. SEAS WILL LINGER AROUND 5-6 FEET OVERNIGHT. OUTLOOK...THURSDAY THROUGH SUNDAY... THURSDAY-THURSDAY NIGHT... NW WIND THURSDAY EXPECTED TO GUST TO 25-30 KT BY LATE IN THE DAY...LASTING MUCH OF THURSDAY NIGHT. SEAS BUILD UP TO 4-6 FT ON THE OUTER WATERS. VSBYS REDUCED IN SNOW THURSDAY INTO THURSDAY NIGHT...BUT DIMINISHING THURSDAY NIGHT. LIGHT FREEZING SPRAY LIKELY THURSDAY NIGHT. FRIDAY AND SATURDAY... NW GUSTS TO AROUND 25 KT CONTINUE ON THE OPEN WATERS INTO FRIDAY...THEN BACK TO SW BUT WILL STILL GUST UP TO 25-30 KT DURING SAT. SEAS SUBSIDING ON FRIDAY BUT THEN BUILD TO 3 TO 5 FEET ON THE OUTER WATERS DURING SAT. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...WINTER WEATHER ADVISORY UNTIL 10 AM EST WEDNESDAY FOR CTZ002>004. MA...WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH THURSDAY EVENING FOR MAZ020>024. WINTER WEATHER ADVISORY UNTIL 10 AM EST WEDNESDAY FOR MAZ002>022-026. RI...WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH THURSDAY EVENING FOR RIZ003>008. WINTER WEATHER ADVISORY UNTIL 10 AM EST WEDNESDAY FOR RIZ001>007. MARINE...SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO NOON EST WEDNESDAY FOR ANZ231>234. SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 6 AM EST WEDNESDAY FOR ANZ230-236. SMALL CRAFT ADVISORY FROM 11 PM THIS EVENING TO 7 AM EST THURSDAY FOR ANZ235-237. SMALL CRAFT ADVISORY UNTIL 7 AM EST THURSDAY FOR ANZ250- 254>256. SMALL CRAFT ADVISORY UNTIL 1 PM EST WEDNESDAY FOR ANZ251. && $$ SYNOPSIS...WTB/NMB NEAR TERM...WTB/RLG/NMB SHORT TERM...WTB LONG TERM...NMB AVIATION...WTB/RLG/NMB MARINE...WTB/NMB

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