Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 222149 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 549 PM EDT Wed Mar 22 2017 .SYNOPSIS... 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. && .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. As large high pressure moves off the eastern seaboard Friday, expect SW winds to bring milder temperatures across the region. An approaching cold front will cause increasing pressure gradient, along with SW low level jet up to 40-45 kt from H95 thru H9 moves across. While best LL mixing is limited to 925 hPa, could still see some gusts up to around 30 kt during Fri afternoon, mainly from the Boston-Providence corridor SE to Cape Cod and the islands. Approaching cold front will bring the threat of light snow by mid to late morning Friday, then will quickly mixing with sleet and snow before changing to rain by early afternoon. With the good SW wind flow in place, should see temps rise quickly. At this point, freezing rain remains out of the forecast, but will continue to monitor this aspect carefully. Temps should reach the lower-mid 40s by late in the day, though a few spots across the higher terrain may remain below 40 but likely above freezing, at least at this point. By Friday night, most of the precip should dissipate or remain across northern New England, but still can not rule out the threat for spotty light rain. Noting a non-diurnal temp trend due to the milder air in place ahead of the approaching cold front. Looks like front should push into the region after 05Z- 06Z. Current thinking suggests that temps should remain in the 35-40 degree range through the night. Saturday-Saturday night...Moderate confidence. Will see mild temps on Sat, actually close to seasonal normals as warm air advection remains in place on W-SW winds. Looks like the front should push off the S coast between mid morning to midday on Saturday as winds start to shift to W-NW. Expect highs in the mid- upper 40s along the N Mass border, ranging to the mid 50s across N CT/RI/SE Mass, though would not be surprised to see readings a few degrees milder before beginning to fall during Sat afternoon. Short range models suggest that patchy light rain may redevelop during the day and continue into Sat night. Colder air works in Sat night as winds become light northerly. Weak low pres wave moves in, bringing another shot of light precip. As the colder air filters in, looks like a wintry mix could develop even as far S as the S coast after midnight. Lots of uncertainty remains due to timing of the colder air and the onset of precip, as well as how far south this will develop. Will monitor this closely. Sunday into Wednesday...Low confidence. General forecast agreement continues during this timeframe, but the big problem is the specific details for each day`s forecast. Will need to see how each piece of the puzzle fits in, such as the mid Mississippi upper low and how quickly it will weaken and move NE in the northern stream flow, plus timing the precip with each weak short wave. Another factor will be the high over eastern Canada and how it will interact with these lows as well as the intrusion of colder air affecting PTYPE during each night and whether it will linger into the daytime hours. A lot to consider, especially with the thermal patterns each day. At this point, could see mixed precip into Sunday morning, then again Sunday night into Monday. Have kept rather general mixed bag of precip each nighttime period for now, and possibly into the morning both Sunday and Monday. However, this could all change with the next forecast package.
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&& .AVIATION /22Z WEDNESDAY THROUGH MONDAY/... 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. && .MARINE... 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. && .CLIMATE...
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Just sent out the latest CLI messages for our four long term climate sites. Looks like the record mins and record cold max temps will remain intact for today. Record lows for today: Boston (BOS) 8/1885, forecast low of 20 Hartford (BDL) 12/1934, forecast low of 19 Providence (PVD) 15/1988, forecast low of 20 Worcester (ORH) 8/1988, forecast low of 14 Record cold highs for today: Boston (BOS) 24/1885, high was 43 set at 259 AM Hartford (BDL) 29/1960, high was 38 set at 251 AM Providence (PVD) 28/1914, high was 42 set at 1207 AM Worcester (ORH) 25/2002, high was 36 set at 1234 AM Record lows for Thursday, March 23: Boston (BOS) 6/1934 Hartford (BDL) 9/1934 Providence (PVD) 8/1934 Worcester (ORH) 4/1934
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&& .BOX WATCHES/WARNINGS/ADVISORIES... 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. && $$ SYNOPSIS...KJC/EVT NEAR TERM...KJC SHORT TERM...KJC LONG TERM...EVT AVIATION...KJC/EVT MARINE...KJC/EVT CLIMATE...Staff

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