Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 031030 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 530 AM EST Sat Dec 3 2016 .SYNOPSIS... Low pressure over the maritimes will circulate a dry but chilly airmass into New England today on blustery northwest winds. Chilly and dry weather persist into Sunday. However, winds slacken as high pressure builds into the area from the west. A few brief snow or rain showers are possible Sunday night and Monday as a weak trough moves across the region. High pressure returns Monday night with mainly dry conditions into Tuesday. Low pressure off the mid Atlantic coast may bring some mixed light rain and/or snow into southern New England late Tuesday night into Wednesday night, though timing and track remain uncertain. A polar front crosses the region late next week resulting in a trend toward colder than normal temperatures. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 330 am Update... Potent northern stream short wave moving across Maine during the predawn hours. Some cloudiness associated with this feature along with a brief rain/snow shower. As this short wave exits eastward into the Gulf of Maine the main impacts for southern New England will be a reinforcing surge of colder air on gusty northwest winds. This will result in high temperatures about 5 degs cooler than Friday...with highs today about 40-45...except upper 30s for the high terrain. These temps are near normal however it will feel colder given gusty NW winds of 20 to 30 mph. Dry weather prevails today with cyclonic flow aloft and some lake effect influence yielding some cloudiness from time to time. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... 330 am update... Tonight... Cold air advection continues along with gusty northwest winds of 15 to 25 mph. However inland winds will drop off to less than 10 mph. Thus leaned toward the colder MOS guidance for low temperatures...20s for most locations...low 30s for the immediate coastline where winds will not decouple. Some cold advection strato-cu from time to time but dry weather will prevail. The only exception may be across the outer Cape as cold air advection on NNW winds will result in ocean effect clouds and snow showers. However hi res guid including the ARW and NMM keep the bulk of the ocean effect snow showers offshore as boundary layer winds may have enough westerly component...about 320 degs. Given this uncertainty will carry chance and slight chance pops for snow showers across the outer Cape. Sunday... Heights begin to rise a bit so probably more sunshine than today. However sunshine will be fairly ineffective given a cold airmass over the area and less blyr mixing as subsidence inversion lowers with approaching high pressure. Temps will be about 5 degs cooler than today with highs only in the upper 30s to lower 40s...mid 30s high terrain. These numbers are about 5 degs colder than normal. The good news these height rises will be accompanied by high pres building over the region. Thus pgradient will weaken resulting in winds not as gusty as today. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Highlights... * Temperatures running near to slightly below seasonal normals through mid week * Low pressure looks slowly move across the Ohio Valley and mid Atlantic states, which may bring some mixed rain and/or snow into the region Tuesday night into Wednesday night, but confidence remains low * A strong polar front approaches late next week, possibly bringing more unsettled conditions Sunday night through Monday...Moderate confidence. A weak mid level short wave and associated surface reflection looks to bring a band of scattered rain and/or snow showers across the region during this timeframe. 00Z model suite in better agreement in holding on to band of light QPF amounts as it crosses. Low probability that there might be some light snow accumulations /0.5 inches or less/ mainly across the higher inland terrain late Sunday night into Monday morning. Precip should push offshore during Monday afternoon. Have kept low CHC POPs in the forecast. Monday night...Moderate confidence. Dry conditions and mostly clear skies prevail Monday night with surface high pressure centered over southern Quebec...and upper level ridging...being the main influence on our weather. Tuesday and Wednesday...Low confidence. Models showing a bit better continuity with next approaching system during this timeframe. High pres ridge pushes into Quebec, with southern extent bringing E-NE winds. Some model timing issues in place on how quickly the leading edge of the overrunning precip pushes into the region. Seems the latest GFS is bringing precip shield NE a bit faster than the GGEM and ECMWF. Looks like best chance for light rain and/or snow will occur Tuesday night and Wednesday as low pressure moves slowly up to mid Atlantic coast, associated with H5 short wave moving NE in the SW flow behind to exiting long wave ridge that crosses the region Tue night. Still uncertainty as to exact track of the mid Atlantic low pressure, as well as moisture field to the W of the region with the second low. Noting a rather strong cutoff H5 low S of Hudson Bay, which looks to be digging a deep long wave trough across the western Great Lakes and Mississippi valley. Also seeing arctic airmass diving SE out of western Canada and Alaska late Wed/Wed night. Light precip could linger through Wed night, depending upon track of the coastal low as well as developing system in the central U.S. Thursday and Friday...Low confidence. Models continue to signal development of H5 long wave trough with arctic airmass diving into the Plains states. Timing and track differences remain on the 00Z model runs, along with how the sensible weather evolves. At this point, looks like the coastal low swings across the region sometime Thu, with another front swinging out of the Ohio Valley late Thu night or Fri. Again, timing in question with how quickly the second front swings eastward. Have continued chance POPs for this forecast. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 115 am update...high confidence thru Sunday Thru 12z... Mainly VFR with marginal MVFR across the higher terrain. Other than a brief sprinkle/flurry early this morning expecting mainly dry weather to prevail. WSW winds will become WNW with gusts up to 35 kt toward daybreak...highest gusts over high terrain and Cape Cod and islands. After 12z... More of the same...VFR and dry but gusty WNW winds up to 30-35 kt. Tonight... VFR and dry with gusty WNW winds up to 25 kt or so...strongest winds across the high terrain and Cape Cod and islands. Sunday... VFR and dry along with diminishing NNW winds. KBOS TAF...High confidence in TAF. Main impacts will be gusty WNW winds today and tonight with gusts up to 30 kt at times. KBDL TAF...High confidence in TAF. Main impacts will be gusty WNW winds today and tonight with gusts up to 30 kt at times. Outlook /Sunday night through Wednesday/... Sunday night and Monday...Moderate confidence. May see patchy MVFR conditions in scattered -SHRA/-SHSN Sunday night through midday Monday, then should be mainly VFR by Monday afternoon. Monday night...Moderate confidence. VFR. Tuesday and Wednesday...Moderate confidence for overall trends, lower on exact timing. Should be mainly VFR Tuesday morning. May see MVFR CIGS/VSBYS move into central and western areas Tuesday afternoon in mainly -RA, but may see mixed precipitation across the interior. MVFR to local IFR CIGS/VSBYS possible Tue night into Wed with chance of -RA and/or -SN. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday/... 330 am update... Today... WNW winds 20 to 30 kt. A few gusts to 35 kt possible but the majority of the time subgale winds will be observed. Any ocean effect snow showers should remain well offshore. Tonight... NNW winds 20-25 kt. Given more northerly wind direction ocean effect snow showers will track closer to the coast especially just east of Cape Cod. Sunday... NNW winds 20-25 kt early but then diminishing as high pressure builds over the area. Any ocean effect snow showers across eastern MA waters early will diminish by afternoon. Outlook /Sunday night through Wednesday/...Moderate confidence. Sunday night and Monday...Winds will remain below small craft criteria. Seas may briefly linger at around 5 ft on the outer waters E of Cape Cod, but should subside. Monday night through Tuesday night...Winds and seas remain below small craft criteria for most of the waters. NE winds shift to E and increase, gusting to around 20 kt Tuesday night across the southern outer waters. Wednesday...E winds will gusts to around 20 kt, possibly up to 25 kt on the southern outer waters. Seas forecast to build to 5-6 ft there as well. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 10 AM EST Sunday for ANZ230>237-250- 251-254>256. && $$ SYNOPSIS...Nocera/EVT NEAR TERM...Nocera SHORT TERM...Nocera LONG TERM...EVT AVIATION...Nocera/EVT MARINE...Nocera/EVT

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