Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 211951 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 351 PM EDT Tue Mar 21 2017 .SYNOPSIS...
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An arctic cold front crosses the region early Wednesday morning, followed by dry but windy and very cold temperatures into Thursday. Wind chills will drop to between 0 and 10 below zero Wednesday night into early Thursday morning. Milder weather returns Friday with the chance of a brief period of light precipitation. A cold front crosses the region Saturday with a period or two of rain/ice and/or snow possible into early next week, but confidence is low.
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&& .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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Departing shortwave to our north will allow skies to become mostly clear early this evening. The result will be dry and tranquil weather across southern New England for the majority of the night. An arctic cold front will sweep through the region toward daybreak. The very cold air will just be entering our areas towards 12z Wednesday...so expect temps to range form the middle 20s in northwest MA and lower to middle 30s across southeast MA at that time. Not much moisture associated with the arctic front...so expect mainly a dry passage other than perhaps a few brief passing flurries generally along the east slopes of the Berkshires.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
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***Windy and very cold Wednesday with wind chills dropping to between 0 and 10 below zero Wednesday night*** Wednesday... An anomalously cold airmass for late March will invade the region. 850T will drop to between -16C and -20C by mid to late Wednesday afternoon. Plenty of strong March sunshine will be fighting the strong cold advection into mid afternoon...so expect temps through early afternoon to be in the 20s across the interior to the lower 30s across southeast New England. The strong cold advection will begin to win out by late afternoon and by early evening temps should mainly be in the teens to lower 20s. Wind chills will have dropped into the single digits by early Wednesday evening...so quite a change from today`s mild weather. The other concern will be the strong winds that are expected. Super adiabatic low level lapse rates combined with lots of late March sunshine will probably allow winds to over achieve on Wednesday. Northwest wind gusts of 35 to 45 mph are anticipated with a few gusts up to 50 mph possible. Will hoist a wind advisory for central and eastern MA as well as Rhode Island. This may need to be expanded across our western zones, but will let later shifts examine more closely. Wednesday night... Strong northwest wind gusts will continue to usher very cold air into southern New England under mostly clear skies. Winds should start to gradually subside by late evening, but it still will be gusty well into the overnight hours. Low temps will range from 5 to 15 above. This will result in wind chills of 0 to 10 below zero, which is quite impressive for late March standards.
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&& .LONG TERM /THURSDAY THROUGH TUESDAY/... Highlights... * Cold and Blustery Wednesday night and Thursday * Milder Fri/Fri night with some rain showers possible * Low confidence next Sat-Mon with unsettled weather possible at times with some rain, ice and/or snow possible Pattern Overview... 00z models and ensembles are in agreement with the general synoptic pattern for the long term. Uncertainty increases in the extended as to mesoscale and thermal issues. Strong arctic airmass nearing 3 STD below normal will remain over the region Wednesday night. Temperatures will begin to moderate out on Thursday as high pressure from the west moves overhead. Mid-level ridge axis will move through the region on Friday as high pressure slides to the south. The initial closed 500 mb low is forecast over the Plains on Friday and will slowly move into the Ohio Valley over the weekend. The low comes into confluent flow and weakens into an open wave as it comes into the Mid-Atlantic. Due to the confluent flow aloft, high pressure persists over northern New England keeping the region cool, resulting in mixed precip at times for the weekend. The EC is a bit faster compared to the GFS/GEFS mean in the forward progression of the upper trough. Still a lot of uncertainty with this timeframe. Details... Wednesday night into Thursday...High confidence. Arctic airmass remains over the region Wednesday night resulting in lows in the single digits to teens. Urban locations will be a bit warmer with overnight lows in the low 20s. Surface high pressure will move overhead on Thursday resulting in dry weather. Could still be a bit gusty due to departing trough and approaching ridge from the west, NW winds near 20 MPH are possible. Temperatures will moderate into the mid to upper 30s on Thursday, but still below average for late March. Thursday night into Friday...Moderate confidence. Mid-level ridge will build overhead Thursday night allowing for WAA to develop. While overnight lows will fall, appears that they may hold steady during the later half of the night within the strong WAA pattern. Surface temperatures in the morning will determine p-type if precip begins to move into the region Friday morning. High pressure will move offshore on Friday as southwest flow returns increasing low level moisture. Warm front to the south and west of the region, with passing cold front to the east, appears to be enough lift to develop some overrunning precip on Friday. There is the potential that precip may start out as snow, but believe the dry air will be hard to overcome, so anticipate more rain than snow as precip will start later in the day. Widespread showers are not anticipated as precip with be light and spotty on Friday. Saturday into Monday...Low confidence. While guidance is in agreement synoptically, still a lot of details to work out for this portion of the forecast. Biggest uncertainties will be the placement of the upper level low and how quickly it will diffuse over the weekend. Also the location of the stalled front which will be the focus on where the precip will be orientated as well as the thermal profiles. Right now, 00z guidance shows stalled front draped across southern New England on Saturday with a few shortwaves moving through the flow. High pressure building in from the north has the potential to push the front farther southward, but the GFS is more pronounced than the EC. Diffusing closed low will become an open wave on Sunday and track through southern New England into Monday. Believe this is the timeframe where we will see the heaviest precip. As mentioned before, still a lot of uncertainty as to the thermal profiles. Looking at the latest EC, it has trended a bit cooler at the surface and with some warm air in the mid-levels, could see a mixed bag of precip. The GFS is a bit more pronounced with the potential for sleet/freezing rain but its surface temps are a bit warmer. Will continue the mentioning of snow, sleet, ice and/or rain for the forecast until thermal come better in alignment. && .AVIATION /20Z 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 Night/... Tonight...High confidence. VFR with mid level cloudiness dissipating through early evening. May see a brief band of marginal MVFR cigs in association with an arctic cold front toward daybreak Wednesday. Wednesday...High confidence. A few brief marginal MVFR cigs possible into mid morning, but otherwise VFR. Main story will be northwest wind gusts of 30 to 40 knots. Wednesday night...High confidence. VFR with gradually diminishing winds although it will remain gusty into the overnight hours. KBOS TAF...High confidence in TAF. Sea breeze comes to an end early this evening. KBDL TAF...High confidence in TAF. Outlook /Thursday through Sunday/... Thursday...High confidence in VFR conditions. Friday and Saturday...Low to moderate confidence. A period of two of showers along with some MVFR cigs are possible at times.
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&& .MARINE...
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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 Night/...High confidence. Tonight...Winds and seas will generally be below small craft advisory thresholds for most of the night. However...northwest winds should rapidly increase towards 12z Wednesday with gusts up to 30 knots behind an arctic cold front. Wednesday and Wednesday night...Northwest wind gusts of 30 to 40 knots expected under very strong cold advection. Strongest of those wind gusts will occur through Wed evening. Gale warnings are posted for all our waters. In addition...the anomalously cold airmass has prompted the issuance of freezing spray advisories for many of our waters Wed night into mid morning Thursday. Outlook /Thursday through Sunday/... Wednesday night...High confidence. Northwest wind gusts of 30 to 40 knots expected in the strong cold advection pattern. Gales will be needed. In addition...moderate freezing spray is expected across many waters Wed night into Thu am so freezing spray advisories will eventually be needed. Thursday...Moderate to high confidence. Freezing spray should diminish by mid morning. Otherwise...winds will gradually diminish but still expect small craft wind gusts for much of the day. Friday...Moderate confidence. Southwest wind gusts of 20 to 30 knots may develop ahead of frontal passage. Small craft headlines may be required. Saturday...Low confidence. Winds and seas highly uncertain depending on timing of a cold front.
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&& .CLIMATE... Record cold highs for Wednesday, March 22 are below: Boston (BOS) 24/1885 Hartford (BDL) 29/1960 Providence (PVD) 28/1914 Worcester (ORH) 25/2002 Record lows for Wednesday, March 22: Boston (BOS) 8/1885 Hartford (BDL) 12/1934 Providence (PVD) 15/1988 Worcester (ORH) 8/1988 Record lows for Thursday, March 23: Boston (BOS) 6/1934 Hartford (BDL) 9/1934 Providence (PVD) 8/1934 Worcester (ORH) 4/1934 && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...Wind Advisory from 8 AM to 8 PM EDT Wednesday for MAZ004>007- 012>024-026. RI...Wind Advisory from 8 AM to 8 PM EDT Wednesday for RIZ001>008. MARINE...Freezing Spray Advisory from 7 PM Wednesday to 9 AM EDT Thursday for ANZ231>235-250-251-254>256. Gale Warning from 8 AM Wednesday to midnight EDT Wednesday night for ANZ230>237. Gale Warning from 8 AM Wednesday to 2 AM EDT Thursday for ANZ250-251-254>256.
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&& $$ SYNOPSIS...Frank NEAR TERM...Frank SHORT TERM...Frank LONG TERM...Dunten AVIATION...Frank/Dunten MARINE...Frank/Dunten CLIMATE...Staff

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