Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 031800 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 100 PM EST TUE MAR 3 2015 .SYNOPSIS... A STORM SYSTEM ACROSS SOUTHERN CANADA WITH A TRAILING COLD FRONT WILL BE THE FOCUS FOR WINTRY WEATHER LATE TODAY INTO EARLY TOMORROW. A WEAK WAVE OF LOW PRESSURE WILL MOVE ALONG A STALLED FRONT WED NIGHT AND THU...BRINGING ANOTHER ROUND OF SNOW. HIGH PRESSURE MOVES IN FOR FRIDAY THROUGH THIS WEEKEND...BRINGING DRY BUT COLD CONDITIONS. A WEAKENING FRONT MAY BRING SOME LIGHT SNOW SHOWERS ON MONDAY. && .NEAR TERM /UNTIL 3 PM THIS AFTERNOON/...
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1 PM UPDATE...WARM ADVECTION ALOFT IS BRINGING MID AND HIGH CLOUDS INTO THE REGION WITH THICKER SKY COVER STARTING TO CREEP EASTWARD TOWARDS SOUTHERN NEW ENGLAND. GROUND OBSERVATIONS OF SNOW ARE STILL BACK OVER EAST CENTRAL PENNSYLVANIA CURRENTLY. STILL LOOKING AT ROUGHLY AN ARRIVAL TIME IN THE BERKSHIRES AND CONNECTICUT VALLEY OF 4-5 PM. DEWPOINTS IN THE SINGLE DIGITS ACROSS MOST OF SOUTHERN NEW ENGLAND WILL ALLOW THE INITIAL SNOW TO EVAPORATE UNTIL THE LOWER LEVELS CAN MOISTEN UP. MORNING SOUNDINGS AT ALY AND CHH SHOW MIXING TO 900-925 MB. TEMPS AT THE TOP OF THIS MIXED LAYER WILL SUPPORT MAX TEMPS IN THE MID 20S TO NEAR 30.
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&& .SHORT TERM /3 PM THIS AFTERNOON THROUGH 6 PM WEDNESDAY/... ** MIXED WINTRY PRECIP EVENT BEGINS LATE TODAY ** HIGHLIGHTS... - SNOW BEGINS EVERYWHERE BY EVENING...1-4 INCHES EXPECTED. - SNOW CHANGES TO SLEET AND FREEZING RAIN OVERNIGHT. - ALL RAIN EXPECTED BY MORNING. OVERVIEW... LOW PRES WILL BE GRADUALLY SLIDING ACROSS SRN ONTARIO AND QUEBEC TONIGHT INTO TOMORROW MORNING. STRONG WARM ADVECTION ON THE LEADING EDGE...COINCIDENT WITH 50+ KT SLY LLJ AT H92 SUGGESTS STRONG OVERRUNNING EVENT AS SUBTROPICAL MOISTURE ASSOCIATED WITH THE SRN STREAM INITIATING WAVE SLIDES INTO THE AREA. WITH PWATS ABOUT 1-2 STD DEVIATIONS ABOVE NORMAL..THERE WILL BE PLENTY OF MOISTURE TO WORK WITH AS THE ISENTROPIC LIFT COMMENCES. INITIALLY THE COLUMN THROUGH ABOUT H8 IS COLD ENOUGH FOR SNOW...AND TIME/HEIGHT PROFILES SHOW A FAIR AMOUNT OF THE OMEGA BEGINS WITHIN THE DENDRITE ZONE. THEREFORE...MODERATE SNOWFALL IS EXPECTED AS THE PRECIP SHIELD MOVES IN LATE TODAY...WITH THE POSSIBILITY OF 1+ INCH/HOUR SNOWFALL RATES AT TIMES. GRADUALLY...MID LVL TEMPS WILL WARM THROUGH THE EVENING. WITH H92 TEMPS REACHING +4C AND H85 TEMPS +8C AT THE WARMEST DURING THE EARLY MORNING HOURS NEAR THE S COAST. THE WARMING IS EXPECTED TO BE MUCH FASTER ALOFT THANKS TO THE LLJ AND DEEP SNOWPACK ACROSS THE REGION...SLOWING THE SFC TEMP INCREASES. THEREFORE...EXPECT A TRANSITION FIRST TO SLEET...AS LOW LVL SOUNDINGS REMAIN COLD BENEATH THE INITIAL WARM LAYER...THEN A GRADUAL SHIFT TO FREEZING RAIN ESPECIALLY OVER THE INTERIOR. AS A TRANSITION TO STRAIGHT RAIN OCCURS FURTHER E AND AT THE COASTLINES THROUGH THE EARLY MORNING HOURS. 2M TEMPS WILL WARM...BUT IT/S LIKELY THAT SOME ICE ACCRETION WILL OCCUR AS SFC TEMPS AND SNOW REMAINS COLD...SO A LAYER OF LIGHT ICE CANNOT BE RULED OUT. TIMING... SNOW WILL BEGIN IN W MA AND CT BY LATE AFTERNOON...THEN BEGIN SHIFT E WITH TIME. EXPECT IT TO ARRIVE IN CENTRAL MA/RI AND E CT BY ABOUT 6PM...THEN SPREAD TO E MA WITHIN AN HOUR OR SO AFTER THAT. IT WILL REMAIN ALL SNOW...EVEN FOR THE CAPE AND ISLANDS OVER THE NEXT FEW HOURS...THEN A GRADUAL TRANSITION FROM 10PM THROUGH EARL MORNING WED TO SLEET AND FREEZING RAIN...TO ALL RAIN IS EXPECTED. FOR A TIME...IT WILL BE ALL RAIN DURING THE EARLY MORNING. THEN...DRIER AIR IS EXPECTED TO SPILL INTO THE NW AS A SFC COLD FRONT SLIDES ACROSS THE AREA...THIS WILL ALLOW PRECIP TO END GRADUALLY FROM NW TO SE AFTER SUNRISE...POSSIBLY ENDING ALMOST EVERYWHERE BY ABOUT MID MORNING. RECENT TREND IN HI-RES GUIDANCE SUGGESTS PRECIP COULD BE DONE ALMOST EVERYWHERE AWAY FROM THE S COAST BY 12Z...BUT WILL TAPER THIS SOMEWHAT. LOOKS LIKE AREAS S OF THE MASS PIKE MAY DEAL WITH SOME FOG OR POSSIBLY EVEN DRIZZLE AS THE DRY AIR COMES IN ALOFT FIRST...TRAPPING THE LOW LVL MOISTURE. THE LIGHT RAIN/DRIZZLE THREAT CONTINUES IN THIS AREA MUCH OF THE DAY. PRECIP TYPE/AMOUNTS... 0.2-0.4 OF THE TOTAL QPF THROUGHOUT WED WILL FALL IN THE REGIME COLD ENOUGH FOR SNOW. HOWEVER...WITH WARM AIR EXPECTED TO MOVE IN QUICKLY ALOFT...LIFTING THE DENDRITE ZONE AWAY FROM THE PEAK OMEGA...AGREE WITH PREVIOUS FORECASTER/S THINKING THAT 10-12 TO 1 SLR/S ARE ABOUT AS HIGH AS SLR/S WILL GET. THEREFORE...SOLID ADVISORY LVL SNOWFALL RANGING FROM 1-3 INCHES ACROSS THE AREA IS EXPECTED BEFORE TRANSITION THIS EVENING. MAYBE A BIT MORE IN THE E SLOPES OF THE BERKSHIRES WHERE ADDED LIFT COULD YIELD A FEW SPOTS OF 4+. AS THE WX TRANSITIONS TO SLEET AND FREEZING RAIN...GIVEN THE RAPID ADVANCEMENT OF WARM AIR ALOFT...AND WARMING 2M TEMPS...IT WILL BE DIFFICULT TO ACCRETE EXCEPT ON COLD SFCS...THEREFORE...SWATH OF A TRACE TO ABOUT A TENTH OF AN INCH OF ICE IS EXPECTED LATE TONIGHT AND EARLY TOMORROW MORNING BEFORE ALL RAIN IS EXPECTED FOR A TIME. TOTAL LIQUID AMOUNTS OF 0.5-0.75 INCHES IS EXPECTED...SO ABOUT A QUARTER OF AN INCH OF LIQUID RAIN IS LIKELY BY THE TIME IT ENDS. IMPACTS... THE SNOW THIS EVENING COULD BEGIN MID-COMMUTE FOR FOLKS IN WRN MA AND CT. AND TOWARD THE LATER HALF OF THE COMMUTE FOR AREAS FURTHER E. THIS WILL LEAD TO SLICK CONDITIONS INTO THE OVERNIGHT HOURS AS MODERATE ACCUMS OCCUR. FOLLOW THAT WITH SOME ICE...AND COLD SFC MAY DEVELOP A GLAZE ON TOP OF THE SNOW...EXACERBATING THE SLIPPERY CONDITIONS. AS THE TRANSITION TO RAIN OCCURS...THE COMBINATION OF NEW SNOW...SOME ICE...AND LIQUID WATER WILL CAUSE PROBLEMS ESPECIALLY ON UNCLEARED ROOFS ACROSS THE AREA AS THE WEIGHT WILL INCREASE QUITE RAPIDLY. WITH SOME SNOWMELT LIKELY AND RAIN...AREA DRAINS COULD BECOME CLOGGED...LEADING TO PONDING ON ROADWAYS AND SOME POOR DRAINAGE FLOODING LEADING INTO THE COMMUTE TOMORROW. HEADLINES/FINAL THOUGHTS... ADVISORIES LOOK SOLID...SO NO PLANS TO EXPAND OR UPGRADE. WILL BE BREAKING THEM UP INTO A FEW DISCRETE SECTIONS WHERE MORE SNOW...ICE OR LESS OF EITHER ARE EXPECTED. OTHERWISE...WILL SEE A GRADUAL END TO THE PRECIP EXCEPT FOR THE REMNANT DRIZZLE OR FOG THROUGH THE MORNING HOURS ON WED. ONE ISSUE OF NOTE IS IF THE SUN BREAKS OUT IN PARTS OF NRN MA ESPECIALLY...TEMPS COULD RISE QUITE RAPIDLY...SO HIGHS MAY BE A BIT TOO LOW. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... OVERVIEW... UPPER LEVEL PATTERN BEGINNING TO SHOW A FEW SIGNS OF CHANGE WITH THE CHANGING SEASON...THOUGH DOES LOOK LIKE SIMILAR 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. NE-SW ELONGATED LONG WAVE TROUGH WORKS E WED NIGHT...BUT WILL STAY IN SW FLOW ALOFT. BY THU...THOUGH...SHORT WAVE DIGS IN THIS GENERAL LONG WAVE PATTERN AND PUSHES E DURING THU. LONG WAVE TROUGH SHIFTS OFFSHORE LATE THU/THU NIGHT...SO EXPECT PRECIP TO END. FOR FRIDAY INTO THIS WEEKEND...UPPER PATTERN FLATTENS OUT ACROSS THE NORTHERN STREAM...SO EXPECT GENERALLY DRY CONDITIONS EXCEPT FOR A FEW QUICK MOVING CLIPPER TYPE SYSTEMS WHICH APPEAR TO KEEP MOST OF THEIR PRECIP N OF THE REGION. WILL STILL SEE COLDER THAN NORMAL TEMPS HOWEVER. USED A BLEND OF AVAILABLE GUIDANCE FOR THIS FORECAST...WHICH HAD GOOD CONTINUITY TO THE PREVIOUS PACKAGE. DETAILS... WEDNESDAY NIGHT-THURSDAY... STALLED FRONTAL SYSTEM JUST OFF THE SOUTHERN NEW ENGLAND COAST WILL KEEP PRECIP LINGERING ACROSS MOST OF THE REGION AS COLDER AIR RETURNS. MIXED PRECIP CHANGES BACK TO SNOW OVERNIGHT...THOUGH COULD SEE A PERIOD OF FREEZING RAIN/SLEET THROUGH ABOUT MIDNIGHT OR SO. GOOD BAROCLINIC ZONE REMAINS ESPECIALLY FROM THE MASS PIKE SOUTH DURING THIS TIMEFRAME ALONG WITH PRETTY GOOD MOISTURE CONVERGENCE AND OVERRUNNING RETURNS. SLIGHTLY HIGHER QPF FROM THE PREVIOUS FORECAST...RANGING FROM 0.2 TO 0.3 INCHES ACROSS N MA TO 0.5 TO 0.8 INCHES FROM N CT/RI/SE MA. SURFACE REFLECTION/WEAK WAVE WILL RIDE ALONG THE STALLED FRONT LATE WED NIGHT/THU. THIS...ALONG WITH COLDER AIR WORKING IN...WILL SEE SNOW PICK UP IN INTENSITY AFTER MIDNIGHT THROUGH THU MORNING WHERE THE BEST LIFT AND MOISTURE ARE LOCATED...GENERALLY S OF THE MASS PIKE. WILL LIKELY NEED HEADLINES FOR THIS EVENT...THOUGH HOLDING OFF CONSIDERING TODAY/S HEADLINES ALREADY IN PLACE. CONTINUE TO HIGHLIGHT IN THE HAZARDOUS WEATHER OUTLOOK. THURSDAY NIGHT... UPPER TROUGH SHIFTS E...PUSHING THE FRONT OFFSHORE OVERNIGHT. SOME MODEL TIMING DIFFERENCES THOUGH ALL DO TEND TO PUSH PRECIP OFFSHORE RATHER QUICKLY OVERNIGHT. ANOTHER SHOT OF ARCTIC AIR WORKS IN WITH OVERNIGHT LOWS IN THE SINGLE DIGITS FOR MOST AREAS EXCEPT THE TEENS ALONG THE S COAST. FRIDAY THROUGH MONDAY... A BROAD UPPER TROUGH CONTINUES 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. LARGE HIGH PRES BUILDS TO THE SW OF THE REGION FRI WITH TEMPS RUNNING 15 TO 20 DEGS BELOW THOUGH NOT CLOSE TO LOW MAX TEMP RECORDS EXCEPT FOR PROVIDENCE /VERY LOW MAX TEMP RECORDS FOR MARCH 6/. AS THE HIGH SHIFTS S OF THE REGION THIS WEEKEND...TEMPS REBOUND A BIT. THEY LOOK REMAIN BELOW NORMAL BUT WILL PROBABLY SEE HIGHS IN THE 30S AS WINDS BACK TO SW. A COLD FRONT APPROACHES LATE SAT/SAT NIGHT BUT MOST OF THE ENERGY AND PRECIP LOOKS TO REMAIN ACROSS NORTHERN NEW ENGLAND. WILL SEE SOME CLOUDS AND A WIND SHIFT TO W MOVES ACROSS BY SUNDAY MORNING AS THE FRONT WEAKENS. ANOTHER CLIPPER SYSTEM QUICKLY MOVES N OF THE GREAT LAKES BY MONDAY MORNING...WITH ANOTHER FRONT CROSSING LATE MON/MON NIGHT. CARRIED SLIGHT CHANCE POPS FOR MAINLY SNOW SHOWERS...BUT MAY SEE PRECIP MAY WASH OUT AS IT APPROACHES IN THE DRY W-NW FLOW. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/...
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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 WEDNESDAY/... 18Z TAF UPDATE... NO MAJOR ADJUSTMENTS. THROUGH ABOUT 22Z /5PM/...HIGH CONFIDENCE. MAINLY VFR CONDITIONS ACROSS THE AREA. WINDS SLOWLY SHIFT TO SOUTHERLY BUT LIGHT. THIS EVENING INTO EARLY TOMORROW...MODERATE CONFIDENCE. ALTHOUGH THERE IS HIGH CONFIDENCE IN OVERALL TRENDS...THERE IS LOWER CONFIDENCE IN EXACT TIMING. CIGS WILL LOWER TO MVFR THIS EVENING AND AREAS OF SNOW WILL DEVELOP FROM W-E FROM 21Z-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. TOMORROW...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 FOR TAF SITES N OF THE MASS PIKE. 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...WEDNESDAY NIGHT THROUGH SATURDAY... WEDNESDAY NIGHT AND THURSDAY...MODERATE CONFIDENCE. 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. CONDITIONS SHOULD SLOWLY IMPROVE FROM N-S DURING THU AFTERNOON...BUT LOWER CIGS/VSBYS CONTINUE ALONG S COAST INTO THU EVENING. NW WINDS GUSTING 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 25-30 KT FOR ALONG THE COAST...DIMINISHING AFTER MIDNIGHT. FRIDAY THROUGH SATURDAY...MODERATE CONFIDENCE. EXPECT VFR CONDITIONS.
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&& .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH WEDNESDAY/... THROUGH THIS EVENING...HIGH CONFIDENCE. HIGH PRES WILL CREST OVER THE WATERS ALLOWING SEAS AND WINDS TO DIMINISH RAPIDLY THIS MORNING. WINDS WILL SHIFT TO THE S...BUT REMAIN BELOW SMALL CRAFT THRESHOLDS UNTIL THIS EVENING. TONIGHT...MODERATE CONFIDENCE. S-SW WINDS INCREASE WITH A FEW GUSTS TO AROUND 25 KT EXPECTED. S SWELL ALSO BUILDS...REACHING ABOUT 8-10 FT BY TOMORROW MORNING. SMALL CRAFT ADVISORIES WILL BE ISSUED FOR ALL WATERS. TOMORROW...MODERATE CONFIDENCE. WINDS WILL SHIFT MORE TO THE W ESPECIALLY ON THE E COASTAL WATERS. A FEW GUSTS MAY STILL REACH 25 KT AT TIMES AND THE SWELL WILL LINGER SOME THROUGH THE DAY. THEREFORE...SMALL CRAFT ADVISORIES ARE LIKELY TO CONTINUE ON THE OCEAN WATERS...BUT MAY BE ABLE TO BE DROPPED FOR NEAR SHORE WATERS. OUTLOOK...WEDNESDAY NIGHT THROUGH SATURDAY... WEDNESDAY NIGHT-THURSDAY... W WIND WILL GUST UP TO 20 KT WED NIGHT...THEN SHIFT TO NW AND INCREASE DURING THU...GUSTING UP TO 25-30 KT BY LATE IN THE DAY. SEAS BUILD UP TO 5-6 FT ON THE OUTER WATERS. VSBYS REDUCED IN AREAS OF FOG AND PATCHY FOG. THURSDAY NIGHT... EXPECT N-NW WINDS GUSTING TO 25-30 KT THROUGH AROUND MIDNIGHT... HIGHEST ACROSS THE EASTERN WATERS...THEN WILL DIMINISH. SEAS WILL REMAIN AOA 5 FT OVER THE OPEN WATERS. REDUCED VSBYS EARLY THU NIGHT MAINLY FROM E OF CAPE COD SOUTHWARD THROUGH AROUND MIDNIGHT THEN SHOULD IMPROVE. FRIDAY AND SATURDAY... NW GUSTS TO AROUND 25 KT CONTINUE ON THE OPEN WATERS THROUGH FRI NIGHT...THEN BACK TO SW BUT WILL STILL GUST UP TO 25-30 KT DURING SAT. SEAS REMAIN AOA 5 FT THROUGH LATE FRI...THEN BRIEFLY SUBSIDE BEFORE BUILDING AGAIN ON THE SW WINDS DURING SAT. && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...WINTER WEATHER ADVISORY UNTIL 10 AM EST WEDNESDAY FOR CTZ002>004. MA...WINTER WEATHER ADVISORY UNTIL 10 AM EST WEDNESDAY FOR MAZ002>022-026. RI...WINTER WEATHER ADVISORY UNTIL 10 AM EST WEDNESDAY FOR RIZ001>007. MARINE...SMALL CRAFT ADVISORY FROM 7 PM THIS EVENING TO 4 AM EST WEDNESDAY FOR ANZ230>234-236. SMALL CRAFT ADVISORY FROM 7 PM THIS EVENING TO 7 PM EST WEDNESDAY FOR ANZ235-237-250-254>256. SMALL CRAFT ADVISORY FROM 7 PM THIS EVENING TO 1 PM EST WEDNESDAY FOR ANZ251.
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&& $$ SYNOPSIS...DOODY/EVT NEAR TERM...WTB/DOODY/RLG SHORT TERM...DOODY LONG TERM...EVT AVIATION...WTB/RLG/EVT MARINE...DOODY/EVT

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