Area Forecast Discussion
Issued by NWS Boston, MA

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755 FXUS61 KBOX 211351 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 951 AM EDT Tue Mar 21 2017 .SYNOPSIS... High pressure will bring dry and mild conditions today. An arctic front will bring near record cold Wednesday into Thursday morning, along with bitterly cold wind chills. Milder weather returns Friday with the chance of a few rain showers. 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. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 925 am update... Considerable mid level cloudiness will continue to affect the region into the afternoon as depicted by model cross sections...but still expect partial sunshine at times. Mainly dry weather anticipated as shortwave with limited low level moisture passes to our north. It is possible we see a few brief sprinkles across northern MA late in the day/early in the evening...but nothing more than that. Despite considerable cloudiness at times...highs should reach well into the 50s given partial sunshine/light westerly flow and 850T between 0 and -2C. Weak gradient may allow sea breezes to develop this afternoon along the immediate coast...resulting in localized cooler temps. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... Tonight... Mid level trough expected to amplify as another shortwave crosses the Great Lakes late tonight. An arctic front should pass through most of our region tonight, too. Low level moisture is still rather limited, so not thinking a lot of showers will accompany this front. Gusty northwest winds develop behind the initial surge of the colder air. Given the timing of this front, am thinking min temperatures will be near to slightly below normal. Wednesday... Strong cold air advection continues. Late March sunshine should offset this cold advection to some degree. Max temperatures should be about 20 degrees lower than today, and about what our normal low temperatures should be. Drier air mass, so even less risk for precipitation. Excellent mixing should result in northwest wind gusts of 30 to 40 mph, resulting in wind chills dropping into the single digits and teens by late afternoon. Extremely well mixed atmosphere may yield a few 45+ mph gusts, so there remains a marginal risk for a Wind Advisory. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... 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 /14Z TUESDAY THROUGH SATURDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday/... Today...Moderate to high confidence. Mainly VFR cigs with a scattered to broken deck of mid level cloudiness. Some MVFR cigs may develop by mid to late afternoon. Tonight...High confidence. Mainly VFR. A few snow showers possible late along an arctic front, mainly over the Berkshires and western MA. Increasing NW winds with gusts to 20-30 kt developing 09-12z. Wednesday...High confidence. Low risk of brief MVFR cigs early, but otherwise VFR conditions. Northwest wind gusts of 25 to 35 knots expected with a few gusts to 40 knots possible. KBOS TAF...Moderate confidence in TAF. There is the potential for a few hours of sea breezes this afternoon. KBDL TAF...Moderate to high confidence in TAF. Outlook /Wednesday Night through Saturday/... 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. && .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/...High confidence. Today...Light NW winds becoming W/SW in the afternoon. A few gusts to 20 kt possible over south coastal waters but winds should remain below small craft thresholds. Lingering 5 foot seas may persist into the afternoon though across our eastern waters. Tonight...Increasing NW winds after midnight with gusts to 25-30 kt developing late as cold advection increases. Gale Warnings issued for most of the eastern coastal waters. Gale Watches continue for southern coastal waters, where confidence is not as high. Wednesday...Northwest wind gusts of 30 to 40 knots expected in the strong cold advection pattern. Areas of freezing spray are likely. Outlook /Wednesday Night through Saturday/... 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... CT...None. MA...None. RI...None. MARINE...Gale Watch from Wednesday morning through Wednesday evening for ANZ230>237. Gale Warning from 8 AM Wednesday to 2 AM EDT Thursday for ANZ250-251-254. Gale Watch from Wednesday morning through late Wednesday night for ANZ255-256. && $$ SYNOPSIS...Belk/Dunten NEAR TERM...Frank SHORT TERM...Belk LONG TERM...Dunten AVIATION...Frank/Belk/Dunten MARINE...Frank/Belk/Dunten CLIMATE...Staff

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