Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 280640 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 140 AM EST FRI NOV 28 2014 .SYNOPSIS... A WEAK SHORTWAVE MOVING UP THE COAST MAY PRODUCE ACCUMULATING SNOW ACROSS EASTERN MA INCLUDING THE BOSTON AREA TODAY. HIGH PRESSURE MOVES OVER NEW ENGLAND TONIGHT AND SHIFTS OFFSHORE OVER THE WEEKEND. A WARM FRONT MOVES ACROSS THE REGION LATE SATURDAY NIGHT AND EARLY SUNDAY. A COLD FRONT THEN SWINGS THROUGH NEW ENGLAND MONDAY. ANOTHER WARM FRONT/COLD FRONT COMBINATION WILL MOVE THROUGH THE REGION WEDNESDAY AND WEDNESDAY NIGHT. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... 1 AM UPDATE... BAND OF RAIN/SNOW DEVELOPING AS SEEN ON LAST FEW SHORT RANGE MODEL RUNS COMING TOGETHER ACROSS E MA INTO SE NH. LOOKS LIKE INVERTED TROUGH SETTING UP IN A NNW-SSE ORIENTATION FROM NEAR KMHT-KGHG-KCQX AS SEEN ON LATEST NE REGIONAL 88D RADAR TRENDS. IR SATELLITE ALSO SHOWING THE DEVELOPING LOW PRES SE OF NANTUCKET WHICH THIS TROUGH IS EMANATING...AND ALSO SHOWING THE TROUGH EXTENDING FROM S CENTRAL NH SE TO CAPE COD AT 05Z. INTERESTING NOTE...TEMP AT KFMH AT 32 WITH LIGHT NW WIND WHILE LIGHT N WIND CONTINUE AT KPVC WITH A TEMP OF 41...SO GOOD BAROCLINIC ZONE SETTING UP. PLUS...JUST CAUGHT THE LATEST WEBCAM LOOP FROM MANCHESTER NH...ROADWAYS WENT FROM WET TO WHITE OVER THE LAST FEW HOURS. VSBYS ARE DROPPING IN SOME OF THE STEADIER SNOW ACROSS NE MA/S CENTRAL NH AS WELL AS ALONG THE IMMEDIATE E COAST. WILL CONTINUE TO SEE THIS TREND DOWNWARD AS AREA OF PRECIP BECOMES BETTER ORGANIZED. WHERE THE BACK EDGE OF THIS PRECIP SETS UP STILL IN QUESTION...WILL MONITOR THIS ASPECT AND ADJUST TRENDS ACCORDINGLY. HAVE INCREASED POPS ALONG THE E COAST TO CATEGORICAL...AND LIKELY AS FAR W AS S CENTRAL NH AND ALONG THE I-495 BELTWAY. CUT OFF THE PRECIP SHARPLY FURTHER W AFTER 07Z-08Z AS LEFTOVER PRECIP FROM FIRST SHORT WAVE ENDS. WILL KEEP AN EYE ON INCREASING INTENSITY OF PRECIP OVER THE NEXT FEW HOURS AND DECIDE WHETHER EXTENSION OF THE ADVISORY A BIT FURTHER TO THE W MAY BE NECESSARY. REMAINDER OF GRIDS WERE PRETTY GOOD BUT DID UPDATE TO BRING CURRENT. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/... *** ACCUMULATING SNOW THROUGH MIDDAY ACROSS EASTERN MA FROM CAPE ANN TO BOSTON TO PORTIONS OF CAPE COD...POSSIBLY INTO S CENTRAL NH *** INVERTED TROUGH LOOKS TO PRODUCE MOD TO HVY SNOW FOR A TIME AFTER SUNRISE THROUGH LATE MORNING...THEN SHOULD PUSH BEGIN TO PUSH OFFSHORE BY AROUND MIDDAY. SHORT RANGE MODELS HAVE DONE RATHER WELL WITH THIS TIMING...BUT STILL SOME QUESTION AS TO HOW FAR W OR E THIS WILL ULTIMATELY SET UP. STILL NOTING IMPRESSIVE TOTAL TOTALS...ON ORDER OF 50-55 ON THE 00Z NAM RUN THROUGH 15Z-18Z THEN SHIFTS OFFSHORE. WILL NEED TO EXAMINE 00Z GFS BEFORE DECIDING UPON ADDING ANY ZONES TO THE CURRENT ADVISORY. FOR NOW...WILL ISSUE SPECIAL WEATHER STATEMENT FOR THE AREAS FROM S CENTRAL NH AND MOST OF E MA. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... BIG PICTURE... ZONAL FLOW THIS WEEKEND WITH 500 MB HEIGHTS BUILDING OVER NEW ENGLAND WHILE A SHORTWAVE TROUGH DROPS THROUGH WESTERN CANADA INTO THE PACIFIC NORTHWEST. THE SHORTWAVE THEN RACES EAST TO CROSS NEW ENGLAND MONDAY NIGHT. ANOTHER SHORTWAVE RACES EAST ACROSS THE NORTHERN TIER DURING THE WEEK. THERE ARE DIFFERENCES BETWEEN THE ECMWF AND GFS REGARDING THE AMPLITUDE AND SPEED OF THIS SHORTWAVE WITH THE GFS FASTER/LESS AMPLIFIED. WE FAVOR A MODEL BLEND FOR MOST OF THE LONG TERM. MOVEMENT OF SHORTWAVES THROUGH ZONAL FLOW LEADS TO QUESTIONS ON TIMING SO CONFIDENCE IS AT BEST MODERATE. LATE IN THE LONG TERM WE TEND CLOSER TOWARD THE ECMWF. AS NOTED BY HPC...THE GREATER AMPLITUDE TROUGH SHOWN BY THE ECMWF IS MORE REASONABLE DUE TO DEEP LOW PRESSURE IN THE BERING SEA AND RESULTING BUILDING OF A RIDGE ALONG THE PACIFIC COAST. THE DAILIES... FRIDAY NIGHT-SATURDAY... HIGH PRESSURE BUILDS OVER NEW ENGLAND WITH DRY CHILLY WEATHER. CROSS SECTIONS SHOW INCREASING MID AND HIGH LEVEL MOISTURE SATURDAY AS THE HIGH SHIFTS EAST AND WARMER AIR STARTS MOVING IN OVER THE TOP OF THE COLDER AIR. SO WE EXPECT MOSTLY CLEAR SKIES FRIDAY NIGHT AND INCREASING SKY COVER ON SATURDAY. WE STAYED CLOSE TO A COMPOSITE OF GUIDANCE FOR TEMPS BOTH PERIODS. SATURDAY NIGHT THROUGH MONDAY... A WARM FRONT APPROACHES SATURDAY NIGHT. THIS WILL MAINTAIN CLOUDS OVER THE REGION. LOW LEVEL PROFILES LOOK RATHER DRY AND LIFT IS WEAK. SO ANY PCPN SHOULD BE LIMITED. WE SHOWED SLIGHT CHANCE POPS MAINLY ALONG AND NORTH OF THE MASS PIKE SATURDAY NIGHT AND IN SRN NH SUNDAY MORNING. THE WARM FRONT LIFTS NORTH ON SUNDAY ALLOWING FOR MILDER TEMPS AND DEWPOINTS AS WELL AS A GENERALLY DRY DAY. THE MODELS SHOW DIFFERENCES IN TIMING THE PASSAGE OF THE COLD FRONT. THIS IS NOT A SURPRISE AS WE WILL BE IN A ZONAL FLOW. THE GFS IS FASTEST WITH PASSAGE MONDAY MORNING. THE ECMWF IS SLOWER WITH PASSAGE MONDAY EVENING. WE USED A BLEND OF THIS DATA WITH CHANCE POPS IN THE WEST IN THE MORNING...SLIGHT CHANCE ALL AREAS AFTN...AND CHANCE ALL AREAS EARLY MONDAY NIGHT. AT BEST MODERATE CONFIDENCE IN THIS TIMING. TUESDAY... HIGH PRESSURE BUILDS OVER THE REGION WITH COLDER AIR. MIXING WILL BE LIMITED TO 925 OR 950 MB...AND TEMPS AT THAT LEVEL SUPPORT MAX TEMPS IN THE UPPER 20S AND 30S. WEDNESDAY-THURSDAY... SHORTWAVE MOVES OUT OF THE PACIFIC NORTHWEST AND PUSHES A COLD FRONT ACROSS THE NORTHERN TIER OF STATES TUESDAY- WEDNESDAY. THIS WILL DRAW A SOUTHWEST LOW LEVEL JET OF 40-45 KNOTS LEADING THE COLD FRONT UP TO OUR AREA BY WEDNESDAY. THIS JET WILL SUPPLY MOISTURE AND GENERATE SUFFICIENT LIFT FOR CLOUDS AND A CHANCE OF PCPN. CONFIDENCE IN TIMING IS LOW BUT AS NOTED ABOVE WE FAVORED THE TIMING SHOWN BY THE ECMWF FOR ONSET OF CLOUDS AND ANY PCPN. LOW LEVEL TEMPERATURES WILL DETERMINE PCPN TYPE...BUT TREND SHOULD BE FROM SNOW TO RAIN EARLY WEDNESDAY AND WEDNESDAY MORNING. LINGERING COLD AIR AT THE SURFACE MAY SUPPORT A PERIOD OF SLEET OR FREEZING RAIN DURING THE TRANSITION DURING THE MORNING...THEN TEMPS SHOULD BE WARM ENOUGH FOR PCPN TO FALL AS RAIN ANY OTHER TIME OF THE DAY. TIMING OF THE COLD FRONT PER THE ECMWF WOULD BE LATE WEDNESDAY OR EARLY WEDNESDAY NIGHT. HIGH PRESSURE BRINGS DRIER WEATHER ON THURSDAY. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. .SHORT TERM /THROUGH TONIGHT/...MODERATE CONFIDENCE. THROUGH 12Z...MVFR-IFR CIGS HAVE STARTED TO DEVELOP ACROSS S CENTRAL NH INTO NE MA AND SHOULD LOWER AS PRECIP BECOMES BETTER ORGANIZED BY 08Z-10Z ACROSS MOST OF E MA...POSSIBLY AS FAR W AS KFIT-KSFZ-KUUU. VSBYS ALSO DROPPING FROM KMHT-KLWM TO IFR. WILL ALSO TREND CIGS/VSBYS DOWNWARD ACROSS E MA/E RI TERMINALS OVERNIGHT. ACROSS CENTRAL-W AREAS...MAINLY VFR WITH LOCAL MVFR CIGS/VSBYS IN LOCAL SNOW SHOWERS MAINLY ACROSS SW NH/N CENTRAL MA. TODAY...EXPECT AREA OF MAINLY SNOW...SOME OF WHICH MAY FALL MODERATELY AT TIMES...ACROSS S CENTRAL NH/E MA INTO E RI. VSBYS MAY BRIEFLY LOWER TO LIFR IN BRIEF PERIODS OF MOD-HVY SNOW. WILL SEE MIXED RAIN/SNOW ALONG COAST S OF BOSTON TO CAPE COD AND ISLANDS. CONDITIONS SHOULD BEGIN TO IMPROVE FROM W-E AROUND 16Z- 18Z AS TROUGH MOVES OFFSHORE. FURTHER INLAND...EXPECT MAINLY VFR. TONIGHT...MAY SEE LEFTOVER MVFR CONDITIONS ALONG E COAST WHICH SHOULD IMPROVE BY 02Z-03Z...OTHERWISE VFR. KBOS TERMINAL...MODERATE CONFIDENCE MAINLY FOR TIMING OF MVFR-IFR CONDITIONS THROUGH MIDDAY...THEN WHEN IMPROVING CONDITIONS MOVE IN. HIGH CONFIDENCE TONIGHT. KBDL TERMINAL...HIGH CONFIDENCE. OUTLOOK...SATURDAY THROUGH TUESDAY...MODERATE CONFIDENCE. SATURDAY...VFR. INCREASING SKY COVER FROM W-E. NORTHWEST WINDS BECOME SOUTHWEST BUT REMAIN LIGHT. SATURDAY NIGHT-SUNDAY...LOWERING CLOUDS SATURDAY NIGHT WITH POTENTIAL FOR MVFR CIGS/VSBYS IN WIDELY SCATTERED PCPN LATE AT NIGHT AND SUNDAY MORNING. LOW LEVEL WINDS...AROUND 2000 FEET...WILL INCREASE OVERNIGHT AND SUNDAY TO 40-45 KNOTS AND MAY CREATE LOW LEVEL WIND SHEAR. MONDAY...VFR WITH SCATTERED SHOWERS AS A COLD FRONT MOVES THROUGH. SOUTHWEST WINDS AHEAD OF THE COLD FRONT WILL SWITCH TO NORTHWEST AFTER THE FRONT MOVES THROUGH. TUESDAY...VFR WITH NORTH TO NORTHEAST WINDS. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. .SHORT TERM /TODAY/...HIGH CONFIDENCE. OVERNIGHT...STILL NOTING SEAS UP TO 7 FT ON THE EASTERN WATERS AT 02Z...BUT APPEAR TO BE SUBSIDING. HAVE KEPT SMALL CRAFTS GOING. OTHERWISE CONTINUED TRENDS FROM PREVIOUS FORECAST WITH SEAS SUBSIDING EARLY...THEN BEGINNING TO BUILD AGAIN LATE AS LOW PRES PASSES S OF THE WATERS. WILL ALSO SEE N-NW WINDS THAT MAY BECOME NE ALONG THE COAST BUT REMAIN LIGHT THOUGH GUSTS INCREASE TOWARD DAYBREAK. TODAY...WINDS INCREASE...GUSTING TO NEAR 25 KTS. HAVE SMALL CRAFT ADVISORIES UP FOR MOST OF THE COASTAL WATERS FOR EITHER SEAS...GUSTY WINDS OR BOTH. OUTLOOK...TONIGHT THROUGH TUESDAY...MODERATE CONFIDENCE. TONIGHT...DIMINISHING WINDS AND SEAS. LINGERING 5 FOOT SEAS ON THE OUTER WATERS BEFORE MIDNIGHT MAY REQUIRE A SMALL CRAFT ADVISORY. SATURDAY...WINDS AND SEAS SHOULD REMAIN BELOW SMALL CRAFT THRESHOLDS. SUNDAY...SOUTHWEST WINDS INCREASE TO 25 KNOTS AND SEAS BUILD TO 5-7 FEET. A SMALL CRAFT ADVISORY MAY BE NEEDED ON MOST WATERS. MONDAY...A COLD FRONT MOVES THROUGH DURING THE AFTERNOON OR EVENING. SOUTHWEST WINDS SHIFT TO NORTHWEST LATER IN THE DAY...WITH SPEEDS 20 TO 25 KNOTS. SEAS DIMINISH A LITTLE BUT REMAIN AT OR ABOVE 5 FEET ON THE EXPOSED WATERS. A SMALL CRAFT ADVISORY MAY STILL BE NEEDED. TUESDAY...NORTH WINDS BECOME NORTHEAST WITH GUSTS AROUND 25 KNOTS. SEAS LINGER AT 5 TO 6 FEET ON THE OUTER WATERS. A SMALL CRAFT ADVISORY MAY BE NEEDED. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...WINTER WEATHER ADVISORY UNTIL NOON EST TODAY FOR MAZ007-015- 016-019. NH...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EST THIS EVENING FOR ANZ235- 237-250-251-254>256. && $$ SYNOPSIS...WTB/RLG NEAR TERM...EVT SHORT TERM...RLG LONG TERM...WTB AVIATION...WTB/RLG/EVT MARINE...RLG/EVT

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