Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 222103 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 503 PM EDT Wed Mar 22 2017 .SYNOPSIS...
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Blustery and very cold conditions will tonight will gradually moderate Thursday with less wind. High pressure will move off the eastern seaboard on Friday, bringing windy and milder conditions. A cold front will push south across the region Saturday, then stall south of New England early next week. Weak low pressure waves forecast to push along this front, with the potential for periods of rain and mixed precipitation.
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&& .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... Cold and very dry airmass across SNE with dewpoints in the single numbers below zero for much of the region. Gusty NW winds will continue in strong cold advection pattern with near dry adiabatic low level lapse rates promoting excellent momentum transfer with mixing likely to the top of the PBL. Soundings suggest peak of the wind will continue into early evening with gusts to 40-50 mph then gradually diminishing. However, winds will remain somewhat gusty through the night, especially along the coast as strong pressure gradient remains. Mid level trof axis moves east of New Eng this evening, as one last shortwave rotates through the NW flow. Column is very dry so mainly clear skies tonight and very cold. Used a blend of MOS and model temps for lows tonight which yields 5 to 15 degrees across much of SNE. Wind chills single numbers above and below zero. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... Thursday... Still some gusty winds in the morning along the coast but trend will be for diminishing wind in the afternoon as high pres builds east into New Eng. Under sunny skies, temps will moderate as low and mid level temps rise, with highs reaching mid/upper 30s which is still well below normal. Thursday night... High pres shifts south of New Eng with developing SW flow warm advection yielding increasing mid/high clouds. There should be a window for good radiational cooling in the evening before clouds thicken which will result in a cold night. Lows ranging from mid/upper teens to mid 20s across the region with temps stabilizing or slowly rising late. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/...
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Highlights... * Light snow early Friday changes to rain as temps rise to the lower-mid 40s * Mild temps on Saturday along with periods of light rain * Low confidence Sunday-Tuesday with unsettled weather possible at times with some rain, sleet and/or snow possible * Conditions may slowly improve during Wednesday, but low confidence continues Overview... 12Z model suite and ensembles continue to signal general agreement of a cold frontal passage during Saturday. Beyond this, a lot of questions, first where this front stalls as it becomes parallel to mid level northern stream steering flow. To complicate things, H5 cutoff low pressure over then central Mississippi valley late Saturday is forecast to open up and move along into the northern stream flow while large high pressure pushes along across central and eastern Canada keeping a cold air flow working southward. Much will depend how far N the front stalls, and the timing of weak low pressure waves that will move along this front. At this point, looks like we will see periods of rain this weekend, with some possible mixed precipitation during the nighttime hours as temps fall close to or below freezing. Best chance for any sleet/snow and/or freezing rain looks to occur main N of the Mass Pike each night. 12Z models signaling the best shot for better organized precip with be with the approaching open H5 wave late Mon into Tue. Models showing general agreement on features, but exact timing and track still very much in question. Could also see a better chance for mixed precip Mon night further S with the established E-NE wind flow, mainly for areas away from the coast. Lots of uncertainty continues. At this point, may see some improving conditions starting next Wednesday, but remains a difficult call this far out. Details... Friday...Moderate confidence. Surface high pressure shifts eastward resulting in warm/moist advection in the mid-levels. Tighten pressure gradient will result in gusty winds near 30 MPH. Ascent due to isentropic lift will eventually saturate the column, resulting in periods of precipitation during the day and into the night. A weak shortwave in the mid-levels will help increase precipitation chances. P-type will be dependent on timing of precip as well as mid-level warmth as surface temps will start out below freezing especially across the higher terrain. Model guidance and BUFKIT data shows warm nose inching in at 800 and 850 mb with cooling at 925mb. This will help support a transition from snow to sleet to eventually rain during the day on Friday. Low confidence on if freezing rain will occur, something to watching in the coming days. Saturday...Moderate confidence. A bit tricky forecast is in store for this timeframe. Used a non- diurnal trend in the Friday night into Sat morning forecast thanks to increasing WAA. 850 mb temps Saturday morning will be close to 8C but drop through the day. Surface temperatures will reach into the mid 50s, cannot rule out a few 60s if the mid-level ridge continues to build. Surface cold front will push through the region during the day. Could see a few rain showers but not expecting widespread rainfall as heights continue to build overhead. Sunday into Tuesday...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 into early next week. Already have seen a slower track and could see northern High pressure strengthen moreso leaning towards a slower precip time on Sunday. Right now, 00z guidance shows stalled boundary draped across southern New England on Sunday with a few shortwaves moving through the flow. High pressure building in from the north has the potential to push the front farther southward on Sunday which could leave the first half of it dry. Diffusing closed low will become an open wave and track through southern New England early next week with another wave right behind it. Believe timeframe where we will see the heaviest precip is when the open wave approaches Sunday night into Monday. As mentioned before, still a lot of uncertainty as to the thermal profiles. Looking at the latest EC, it has trended a warmer in the mid-levels versus the GFS with both models indicating surface temps near freezing. Believe that there could be a period where the region could see a mixed bag of precip. Still a lot of uncertainty with this timeframe as thermal profiles will change. Will continue the mentioning of snow, sleet, ice and/or rain for the forecast until thermals come better in alignment.
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&& .AVIATION /21Z WEDNESDAY THROUGH MONDAY/...
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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 Thursday Night/... High confidence. VFR. NW gusts to 30-40 kt into early evening will gradually diminish but still gusts to 25 kt overnight along the coast. NW wind gusts to 20 kt Thu becoming light Thu night. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Friday through Monday/... Friday...Moderate confidence. Mainly VFR. Patchy MVFR CIGS/VSBYS in -SN, changing over to -RA by around midday. May see some sleet early Fri across western terminals. Light rain ends from S-N Fri night, but may linger across E slopes of the Berkshires. SW winds gusting up to 25-30 kt, highest along the coast and higher terrain, lingering into Friday night across Cape Cod and the islands before diminishing around midnight. MVFR CIGS linger Fri night across higher terrain. Saturday and Sunday...Low to moderate confidence. Periods of light rain/showers through the weekend. May see mixed sleet/freezing rain push across portions of the region Saturday night into Sunday. Exact placement and timing in question. Sunday night-Monday...Low confidence. Depending upon how far S the colder air works in, could see areas of rain, sleet and freezing rain Sun night into Mon morning which may linger most of Mon across the higher terrain. Patchy MVFR CIGS/VSBYS mainly at night/early morning hours.
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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 Thursday Night/...High confidence. Tonight...NW gales continue into the evening before gradually diminishing from west to east. Freezing spray will also continue. Seas building to 12-15 ft over outer waters east of Cape Cod this evening before slowly subsiding. Thursday...Still gusty NW winds in the morning with gusts 25-30 kt diminishing a bit in the afternoon. Freezing spray will subside in the afternoon. Hazardous seas over outer waters but gradually subsiding. Thursday night...Diminishing NW winds becoming light SW overnight. Seas subsiding below 5 ft over outer waters. Outlook /Friday through Monday/... Friday...Moderate confidence. SW wind gusts up to 25-30 kt, shifting to W Fri night as cold front passes. Small crafts likely. Low chance for gale force gusts on the eastern outer waters Fri afternoon/evening prior to frontal passage. Visibility restrictions possible in patchy light rain Fri into Fri night. Saturday...Moderate confidence. Leftover small crafts as W winds gust to 25 kt early Sat, then should diminish. Light rain redevelops as cold front pushes off the coast with some visibility restrictions. May see mix of sleet and snow Sat night as colder air works in on NE winds. Sunday-Monday...Low confidence. Depending upon where the front stalls, may see more periods of rain during each day, possibly mixing with sleet and snow across the eastern waters Sun night. E-NE winds gusting to 25-30 kt so small crafts may be needed again.
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&& .CLIMATE... Record lows for Wednesday, March 22: Boston (BOS) 8/1885 Hartford (BDL) 12/1934 Providence (PVD) 15/1988 Worcester (ORH) 8/1988 Record cold highs for Wednesday, March 22: Boston (BOS) 24/1885 Hartford (BDL) 29/1960 Providence (PVD) 28/1914 Worcester (ORH) 25/2002 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...Wind Advisory until 6 PM EDT this evening for CTZ002>004. MA...Wind Advisory until 8 PM EDT this evening for MAZ004>007- 012>024-026. Wind Advisory until 6 PM EDT this evening for MAZ002-003- 008>011. RI...Wind Advisory until 8 PM EDT this evening for RIZ001>008. MARINE...Freezing Spray Advisory until 11 AM EDT Thursday for ANZ231>235-250-251-254>256. Gale Warning until 2 AM EDT Thursday for ANZ231-232-251-255- 256. Gale Warning until midnight EDT tonight for ANZ230-233>235-237. Gale Warning until 10 PM EDT this evening for ANZ236. Gale Warning until 5 AM EDT Thursday for ANZ250-254.
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&& $$ SYNOPSIS...KJC/EVT NEAR TERM...KJC SHORT TERM...KJC LONG TERM...EVT AVIATION...KJC/EVT MARINE...KJC/EVT CLIMATE...Staff

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