Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 030415 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 1115 PM EST MON MAR 2 2015 .SYNOPSIS... HIGH PRESSURE WILL BUILD ACROSS THE REGION OVERNIGHT...THEN WILL BEGIN TO MOVE OFFSHORE AHEAD TUESDAY. A STORM SYSTEM ACROSS SOUTHERN CANADA WITH A TRAILING COLD FRONT WILL BE THE FOCUS FOR WINTRY WEATHER LATE TUESDAY INTO WEDNESDAY. THIS FRONT WILL STALL SOUTH OF THE REGION WEDNESDAY NIGHT INTO THURSDAY RESULTING IN RENEWED WINTER WEATHER OUTCOMES. FROM THURSDAY NIGHT ONWARD... CONTINUED COLDER THAN NORMAL CONDITIONS WITH ADDITIONAL WEATHER DISTURBANCES. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... 1050 PM UPDATE... THIN BANDS OF LIGHT SNOW CONTINUE TO CROSS CENTRAL AND EASTERN AREAS AS SEEN ON LATEST KBOX 88D RADAR. MOVING RATHER QUICKLY IN THE NW FLOW THOUGH...SO NOT EXPECTING MUCH IF ANY ACCUMULATIONS EXCEPT MAYBE ON THE OUTER CAPE WHERE THE BANDS HOLD TOGETHER. SHOULD PUSH OFFSHORE AS WINDS DIMINISH. NW WINDS HAVE BEEN DIMINISHING OVER THE LAST COUPLE OF HOURS...BUT DID NOTE A BRIEF INCREASE AROUND 02Z ACROSS THE CT VALLEY. STILL SEE GUSTY WINDS UP TO 25-30 KT ON THE OUTER CAPE AND NANTUCKET AT 03Z. HOWEVER...AT 04Z...NOTING WINDS INLAND WINDS DOWN TO 5 TO AROUND 10 KT EXCEPT FOR A FEW SPOTS HOLDING AT 10-15 KT ACROSS N MA AROUND ROUTE 2 REGION. WINDS WILL CONTINUE TO DIMINISH OVERNIGHT AS HIGH PRES RIDGE BUILDS E OUT OF NY STATE. TEMPS WERE RUNNING A FEW DEGS ABOVE FORECASTED LEVELS AT 03Z...BUT SHOULD BEGIN TO DROP AS SKIES BECOME GENERALLY MOSTLY CLEAR AND WINDS CONTINUE TO DROP. SHOULD SEE RADIATIONAL COOLING IN PLACE AFTER MIDNIGHT ACROSS THE NORMALLY COLDER VALLEY LOCATIONS ACROSS INTERIOR E MA AND INTO THE CT VALLEY AND N CENTRAL/NE CT. HAVE UPDATED NEAR TERM FORECAST TO BRING CONDITIONS CURRENT. PREVIOUS DISCUSSION... BEST CHANCE FOR RADIATIONAL COOLING ONCE WINDS DECOUPLE...WILL BE ACROSS THE WESTERN HALF OF THE REGION. ACROSS THE EAST...IF WINDS GO LIGHT QUICKLY ENOUGH DURING THE LATER HALF OF THE NIGHT THEN RADIATIONAL COOLING WILL OCCUR. OTHERWISE EXPECT TEMPS TO REMAIN IN THE LOW TEENS OVERNIGHT. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... TUESDAY... HIGH PRESSURE WILL BEGIN TO PUSH EASTWARD DURING THE DAY TOMORROW AHEAD OF THE NEXT SYSTEM. EXPECT DRY WEATHER AND MOSTLY CLEAR SKIES INTO THE EARLY AFTERNOON HOURS. AS LOW PRESSURE SYSTEM APPROACHES HUDSON BAY...EXPECT PRECIP TO BEING TO OVERSPREAD THE REGION FROM SW TO NE DURING THE LATER AFTERNOON HOURS. TEMPS BOTH ALOFT AND AT THE SURFACE WILL REMAIN COLD ENOUGH FOR PRECIP TO START IN THE FORM OF SNOW AND QUICKLY ACCUMULATE ON SURFACES. THIS COULD MAKE THE EVENING COMMUTE ACROSS HARTFORD/SPRINGFIELD A BIT MESSY TOMORROW. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... */ LATE TUESDAY INTO WEDNESDAY MORNING... 1) HIGHLIGHTS... - PRECIP TRANSITION FROM SNOW TO RAIN WITH A WINTRY MIX BETWEEN - WINTER WEATHER ADVISORY IN EFFECT - IMPACTS ESPECIALLY TO THE TUESDAY AFTERNOON / EVENING COMMUTE 2) OVERVIEW... INSIDE-RUNNER EVENT WITH AN AREA OF LOW PRESSURE ACROSS SW CANADA AND A TRAILING COLD FRONT TOWARDS THE SW-CONUS AHEAD OF WHICH S-FLOW OF WARM-MOIST AIR ISENTROPICALLY ASCENDS ACROSS S NEW ENGLAND. AN OVER-RUNNING EVENT WITH A PUSH OF WARMER AIR N ALONG WITH INCREASING THICKNESSES...ANTICIPATING AN INITIAL SNOW EVENT TUESDAY EVENING TO TRANSITION SW-NE TO A WINTRY MIX BEFORE CHANGING TO RAIN /THOUGH PERHAPS NOT FOR ALL LOCATIONS/. TRICKY FORECAST IN NAILING DOWN TRANSITION TIMING WITH RESPECT TO THERMAL FIELDS. THIS IS NOT A PERFECT FORECAST BY ANY MEANS. LIKELY TO SEE SOME SLIGHT SHIFTS IN OUTCOMES. DETAILS ALONG WITH FORECAST THINKING HIGHLIGHTED IN THE DISCUSSION BELOW... 3) PRECIPITATION OUTLINE... VARIABILITY WITH RESPECT TO H925-85 THERMAL FIELDS AND H85-7/H100-85 THICKNESSES. PREFERENCE TO THE 02.12Z GFS AND REGIONAL CANADIAN WITH THE ECMWF NOT FAR BEHIND. THE 3 WILL SERVE AS THE FORECAST CONSENSUS FOR THE REMAINDER OF THIS DISCUSSION. BELIEVE THE NAM IS A TAD BIT TOO WARM AND AGGRESSIVE. H925-85 WINDS ARE THE STRONGEST. EVEN WITH THE PREVIOUS SNOW EVENT...NAM WAS THE WARMER/AGGRESSIVE OUTLIER. A FORECAST CONSENSUS AVERAGES AROUND A 0.3-0.5 TOTAL-PRECIP EVENT. SO LOOKING AT AN ADVISORY-LEVEL EVENT. SNOWS BEGINNING LATE TUESDAY AFTERNOON INTO THE EVENING HOURS WILL TRANSITION TO A WINTRY MIX SW- NE TOWARDS MIDNIGHT. WHILE INDICATIONS OF THE RAIN-LINE CREEPING N WITH ENHANCED ONSHORE S-FLOW...THE DEEP SNOWPACK AND SUB-FREEZING GROUND WILL LIKELY RESULT RAIN FREEZING ON THE SURFACE. THINKING A GOOD THRESHOLD IN WHERE WARM-RAIN WOULD OVERCOME THE COLDER GROUND IS AROUND 36-DEGREES. SHOULD SEE MOST OF THE AREA TRANSITION OVER TO RAIN AS WE GO TOWARDS WEDNESDAY MORNING...BUT IT IS PERHAPS THAT N MA LOCALES WILL STILL EXPERIENCING ICING WITH NEAR-FREEZING TEMPS AND REMNANT DEEP SNOWPACK. 4) SNOWFALL... MUCH OF THE SNOW OCCURRING FROM THE LATE AFTERNOON HOURS TUESDAY TOWARDS MIDNIGHT WEDNESDAY. PERHAPS INITIALLY FLUFFY...SNOW LIKELY TO MAINTAIN A WETTER CONSISTENCY WITH INFLUX OF WARMER AIR WITHIN THE LOW-LEVELS. THINKING 10:1 TO 12:1 SNOW-TO-LIQUID RATIOS. OVERALL DID NOT WANT TO BE CUTE WITH THE SNOWFALL AMOUNTS. LOOKING AN AVERAGE 2-3 INCH SNOWFALL EVENT FOR MOST OF THE AREA. SOME AREAS MAY SEE HIGHER AMOUNTS. WORTH NOTING...THIS IS SLIGHTLY LOWER THAN WHAT WAS PREVIOUSLY FORECAST. THE MOST SIGNIFICANT CHANGE IS ACROSS SE NEW ENGLAND. A FRONT-END THUMP IS TO BE ANTICIPATED OF SNOW INTO THE EVENING PERIOD PRIOR TO TRANSITION. A COMBINATION OF ONSHORE S- FLOW AND THINKING A WETTER SNOW WITH 1:10 RATIOS HAS LESSENED THE AMOUNTS ON THE ORDER OF 2-3 INCHES. 5) SLEET AND FREEZING RAIN... AGAIN...THE THRESHOLD FOR THE WINTRY MIX WILL BE SET AT 36-DEGREES. FEEL WITH THE LINGERING ARCTIC TUNDRA THAT SURFACES WILL REMAIN SUB- FREEZING FOR SLIGHTLY LONGER EVEN AS AIR TEMPERATURES WARM ABOVE THE FREEZING-MARK. LOOKING AT THE WINTRY-MIX TIMEFRAME AROUND MIDNIGHT WEDNESDAY INTO WEDNESDAY MORNING DURING WHICH TIME THERE WILL BE A S- N TRANSITION TO PLAIN RAIN AS WARMER AIR USHERS IN AND N ALOFT. PER A FORECAST CONSENSUS...EXPECT MORE SLEET THAN FREEZING RAIN... ESPECIALLY IN AREAS OF MODERATE PRECIPITATION WHERE THERE WOULD BE LIKELY LESS TIME RESIDING IN THE SHALLOW WARM-AIRMASS H9-7 ALOFT PER GFS BUFKIT PROFILES DURING THE OVERNIGHT HOURS. THOUGH THERE IS SOME CONCERN TOWARDS MORNING AS PRECIPITATION BEGINS TO BECOME LIGHTER THAT AREAS ACROSS THE INTERIOR AT OR BELOW 34 DEGREES WOULD RESULT IN SUB-FREEZING SURFACES TO FREEZE WITH THE PRESENCE OF RAIN. SO WHILE NOT BY DEFINITION FREEZING RAIN...ICING ISSUES LOOK TO DEVELOP BY MORNING ONCE THE WHOLE COLUMN WAS JUST ABOVE THE FREEZING- MARK KEEPING IN MIND THE SUB-FREEZING GROUND CONDITIONS AND DEEP SNOWPACK WE HAVE BEEN ENVELOPED. EXPECTING ICE ACCUMULATIONS UPWARDS OF A TENTH OF AN INCH. 6) HEADLINES AND IMPACTS... BASED ON THE FORECAST CONSENSUS...WILL BE GOING WITH AN ADVISORY FOR ALL AREAS OF RESPONSIBILITY EXCEPT THE ISLANDS AS IT IS ANTICIPATED THAT AREAS WILL SEE AT LEAST A TRACE OF A WINTRY MIX COMPRISED OF SLEET AND FREEZING RAIN. CONCERN FOR THE TUESDAY AFTERNOON AND EVENING COMMUTE AS SNOW WILL BE LIKELY BEGINNING. SLICK AND SLIPPERY TRAVEL CONDITIONS ALONG WITH SIGNIFICANTLY REDUCED VISIBILITIES. ALSO CONCERNS FOR WEDNESDAY MORN ESPECIALLY OVER THE INTERIOR WITH THE POTENTIAL FOR ICING. */ WEDNESDAY INTO LATE THURSDAY... 1) HIGHLIGHTS... - RENEWED OVER-RUNNING EVENT ALONG AN OFFSHORE COLD FRONT - PERIOD OF MODERATE SNOW...PERHAPS HEAVY? - GREATEST IMPACT S OF THE MASS-PIKE...ESPECIALLY S-COAST 2) OVERVIEW... COLD FRONT SWEEPING THE REGION WEDNESDAY WILL STALL S AND OFFSHORE FOR THE REMAINDER OF THE PERIOD BECOMING A FOCUS FOR AN ELONGATED AREA OF LOW PRESSURE AND ADDITIONAL MID-LEVEL IMPULSES ATTENDANT WITH LOW- TO MID-LEVEL CONVERGENT FLOW. DEEP-LAYER ASCENT COUPLED WITH UNDERCUTTING RETURN S-FLOW /AN ISENTROPIC RESPONSE/ YIELDS A MAINLY SNOW-EVENT ESPECIALLY FOCUSED ACROSS THE S-TIER OF THE FORECAST REGION...MORE SPECIFICALLY S OF MASS-PIKE. 3) PRECIPITATION OUTLINE... GFS IS THE COLDER SOLUTION OVER THE REGIONAL CANADIAN / ECMWF. THIS FAR OUT IN THE FORECAST TIMEFRAME /D3-4/ WILL GO WITH A BLEND OF THE FORECAST SOLUTIONS AND CONSIDER THIS TO BE THE FORECAST CONSENSUS. SO WITH THAT BEING SAID...RAIN COULD BE AN ISSUE WEDNESDAY AS THE COLD FRONT SWEEPS THE REGION...YET NEAR PARALLEL FLOW AND LACKING DYNAMICS RESULT IN A LULL ACROSS THE REGION. ALL MODELS INDICATE A PERIOD OF DRY-WEATHER FOR THE MOST PART. THE MAIN SHOW KICKS OFF TOWARDS EVENING. AS MID-LEVEL ENERGY AHEAD OF THE TROUGH PATTERN ALOFT DIGS ACROSS THE NE-CONUS ANTICIPATE AN ENHANCEMENT TO THE OFFSHORE ELONGATED LOW SUCH THAT ANOTHER OVERRUNNING EVENT MATERIALIZES. THE ISALLOBARIC RESPONSE OF THE WIND NETS A DRIVING NW-FLOW RESULTING IN UNDERCUTTING COLDER AIR TO THE OVER- RUNNING EVENT ALOFT. LOOKING AT A N-S TRANSITION OF RAIN TO SNOW LIKELY TO OCCUR MORE QUICKLY IN AREAS OF MODERATE PRECIPITATION THROUGH THE QUICKLY COOLING COLUMN ALOFT. IT MAY BE PERHAPS THAT SOME LOCATIONS START OFF AS SNOW. A SHARP N-S PRECIPITATION GRADIENT WITH LOCALES ALONG THE IMMEDIATE S-COAST / CAPE / ISLANDS SEEING THE MOST WITH AN AVERAGE OF 0.6-0.7 BASED ON THE FORECAST CONSENSUS. ALONG THE MASS- PIKE...AN AVERAGE 0.1-0.2 EVENT IS ADVERTISED...SO IN-BETWEEN A ROUGHLY 0.3-0.6 EVENT. SHARP GRADIENT AN OUTCOME OF BUILDING RIDGE OF HIGH PRESSURE REAR OF THE TROUGH PATTERN ALOFT AND ATTENDANT SUBSIDENCE. 4) SNOWFALL... SHOULD THE PRECIPITATION EVENT REMAIN AS MOSTLY ALL SNOW...COULD BE DISCUSSING WARNING-LEVEL SNOWS FOR THE IMMEDIATE S-COAST AND ISLANDS WITH ADVISORY LEVELS SNOWS N FROM THERE TO THE MASS-PIKE. THERE ARE WOBBLES WITH THE THERMAL FIELDS AND PRECIP AMOUNTS. EXACT STRENGTH AND MAGNITUDE OF THE OVER-RUNNING EVENT ARE SOMEWHAT IN QUESTION. SOME HINT PER SREF OF INCH PER HOUR SNOWFALL RATES. HEADLINES WILL NOT BE ISSUED AT THIS TIME...BUT WILL FOCUS ON THE IMPACTS WITHIN THE HAZARDOUS WEATHER OUTLOOK. */ THURSDAY NIGHT ONWARD... WILL PREVAIL WITH A DRY AND BELOW NORMAL TEMPERATURE FORECAST. THERE ARE SUBTLE HINTS OF CONTINUED WEATHER DISTURBANCES PREVAILING THRU THE CONTINUED CYCLONIC FLOW PATTERN ACROSS THE REGION. THIS ALONG WITH SHOTS OF COLDER AIR. WINTER DOES NOT LOOK LIKE IT IS GOING TO END ANY TIME SOON. && .AVIATION /04Z TUESDAY THROUGH SATURDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH TUESDAY/... OVERNIGHT...HIGH CONFIDENCE. VFR. NW GUSTS GUSTING TO 20-30 KT THROUGH 05Z-06Z ACROSS E MA WILL DIMINISH OVERNIGHT. SCT SHSN ACROSS E COASTAL MA WILL END BY 07Z. TUESDAY...MODERATE TO HIGH CONFIDENCE. VFR CONDITIONS THROUGH AT LEAST MID AFTERNOON. MVFR-IFR DEVELOP BY LATE TUESDAY AFTERNOON ACROSS WESTERN MA/NORTHERN CT AS LIGHT SNOW DEVELOPS. KBOS TAF...HIGH CONFIDENCE. KBDL TAF...HIGH CONFIDENCE. OUTLOOK...TUESDAY NIGHT THROUGH FRIDAY NIGHT... TUESDAY NIGHT INTO WEDNESDAY...MODERATE CONFIDENCE. IFR-VLIFR WITH SNOW. POSSIBLE VSBY IMPROVEMENT WITH TRANSITION TO RAIN...YET COULD TURN SOUPY WITH MILDER AIR OVER REMNANT SNOWPACK. BREEZY S/SW-WINDS WITH GUSTS UP TO 30 KTS POSSIBLE FOR COASTAL TERMINALS. SNOW ACCUMS ANTICIPATED FROM 21Z TUESDAY - 6Z WEDNESDAY. LOW CONFIDENCE ON INCH PER HOUR SNOWFALL RATES. WEDNESDAY...MODERATE CONFIDENCE. POTENTIAL IMPROVEMENT N-S AS A COLD FRONT SWEEPS THE TERMINALS. SHRA MAY LINGER. COULD POTENTIALLY BE DEALING WITH SOUPY CONDITIONS WITH WARMER AIR OVER THE SNOWPACK INITIALLY. WINDS BACK W WITH PASSAGE. WEDNESDAY NIGHT INTO THURSDAY MORNING...MODERATE CONFIDENCE. FOCUS ALONG THE MASS-PIKE S. DETERIORATING CONDITIONS. IFR-VLIFR WITH SNOW ESPECIALLY ALONG THE S-COAST WHERE +SN POSSIBLE. INCH PER HOUR SNOWFALL RATES WILL BE POSSIBLE. BREEZY N/NW-WINDS. THURSDAY INTO FRIDAY NIGHT...MODERATE CONFIDENCE. IMPROVING CONDITIONS TOWARDS VFR. CONTINUED W/NW WINDS DIMINISHING UNDER HIGH PRESSURE. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /TONIGHT THROUGH TUESDAY/... OVERNIGHT...HIGH CONFIDENCE. HAVE ENDED GALES ON ALL BUT THE EASTERN OUTER WATERS...WHICH SHOULD DIMINISH BY AROUND 06Z. EXTENDED SMALL CRAFTS OVERNIGHT... BUT WINDS WILL DIMINISH FURTHER AS HIGH PRES PUSHES E. WIDESPREAD LIGHT TO MODERATE FREEZING SPRAY WILL CONTINUE INTO THE EARLY MORNING BUT SHOULD END AS WINDS DROP OFF. FREEZING SPRAY ADVISORY CONTINUES. TUESDAY...HIGH CONFIDENCE. BOTH WINDS AND SEAS WILL RELAXED BELOW SMALL CRAFT ADVISORY THRESHOLDS BY EARLY MORNING AS HIGH PRESSURE BUILDS ACROSS THE WATERS. HOWEVER...LEFT OVER SWELL WILL KEEP SMALL CRAFT SEAS GOING ACROSS THE OUTER-WATERS UNTIL THE LATE MORNING HOURS. OUTLOOK...TUESDAY NIGHT THROUGH FRIDAY NIGHT... INITIAL DISTURBANCE TUESDAY NIGHT INTO WEDNESDAY WILL RESULT IN NEAR GALE-FORCE S/SW-WINDS. SEAS TO BUILD 6-8 FEET ON THE OUTER WATERS. VISIBILITY WILL BE RESTRICTED AT TIMES DUE TO SNOW INITIALLY TUESDAY NIGHT AND LIKELY FOG AS WARMER AIR PUSHES N OVER THE COLDER WATERS AS WE GO INTO WEDNESDAY. NOT THINKING GALE-FORCE WARNINGS AT THIS TIME...FEEL GALES WILL ONLY MANGE AN HOUR OR TWO BECOMING A LOW- RISK. VISIBILITIES WILL STILL BE ROUGH ALONG WITH SEAS. A COLD FRONT SWEEPS INTO THE WATERS WEDNESDAY...STALLING OVER THE S-WATERS WEDNESDAY NIGHT INTO THURSDAY BECOMING A FOCUS FOR SNOW. WILL SEE W/NW-WINDS INCREASE ALONG WITH THE LIKELIHOOD OF LIGHT FREEZING SPRAY. IMPROVEMENT BEGINS BY THURSDAY NIGHT AS WEATHER IS PUSHED OUT TO SEA BEHIND WHICH HIGH PRESSURE BUILDS INTO THE REGION TO ALLOW BOTH WINDS AND SEAS TO RELAX. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...WINTER WEATHER ADVISORY FROM 3 PM TUESDAY TO 10 AM EST WEDNESDAY FOR CTZ002>004. MA...WINTER WEATHER ADVISORY FROM 3 PM TUESDAY TO 10 AM EST WEDNESDAY FOR MAZ002>022-026. RI...WINTER WEATHER ADVISORY FROM 3 PM TUESDAY TO 10 AM EST WEDNESDAY FOR RIZ001>007. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EST TUESDAY FOR ANZ231-232. SMALL CRAFT ADVISORY UNTIL 3 AM EST TUESDAY FOR ANZ233-234. FREEZING SPRAY ADVISORY UNTIL 8 AM EST TUESDAY FOR ANZ231-250- 251. SMALL CRAFT ADVISORY UNTIL 5 AM EST TUESDAY FOR ANZ235-237-251. GALE WARNING UNTIL 1 AM EST TUESDAY FOR ANZ250-254. SMALL CRAFT ADVISORY UNTIL 11 AM EST TUESDAY FOR ANZ255. SMALL CRAFT ADVISORY UNTIL 7 AM EST TUESDAY FOR ANZ256. && $$ SYNOPSIS...DUNTEN/SIPPRELL NEAR TERM...DUNTEN/SIPPRELL/EVT SHORT TERM...DUNTEN LONG TERM...SIPPRELL AVIATION...DUNTEN/SIPPRELL MARINE...DUNTEN/SIPPRELL/EVT

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