Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 250204 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1004 PM EDT Sat Mar 24 2018 .SYNOPSIS... An upper level disturbance will sweep across Southern New England tonight and Sunday bringing chilly temperatures along with scattered snow showers. Brief snow accumulation is possible in these showers. Canadian high pressure builds across the region Monday through Wednesday bringing dry and somewhat milder temperatures, particularly across the interior. The chance for rain showers increase late next week as a cold front slowly approaches. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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10 pm update... * Scattered brief heavy snow showers overnight may result in slippery travel especially across portions of eastern MA Previous forecast is pretty much on track. Radar returns were beginning to increase late this evening as inverted trough was approaching from the northeast. Steep low level lapse rates in excess of 8 C/KM along coupled with deep moisture and a convergent zone were resulting in the development of scattered rain and snow showers. Ptype should be changing over to mainly snow showers though as temperatures are very cold aloft. interesting setup overnight into mid morning Sunday especially across eastern New England. Steep low level lapse rates along with a band of deep moisture and a convergent zone will set the stage for scattered snow showers...some of which will probably be briefly heavy. SPC meso-analysis page indicated 100 J/KG of MUCape just east of the coastline. NNE low level flow and the land/sea interface will help to tap some of the instability from the ocean as 850T fall below -10C. While the activity is progressive...brief bands of heavy snow showers may drop a quick inch or two of snow in some locations while other neighborhoods are spared. The prime area is across eastern MA given the added instability from the ocean. In fact...after the inverted trough passes we should see a couple bands of ocean effect snow showers especially in SE MA. This with NE flow and 850 to SST differentials of around 17C. Despite the mild temperatures today...areas that get under bands of heavy snow showers may see roads quickly become slippery along with brief poor visibility. Will go ahead and re- issue the special weather statement to highlight these concerns overnight into mid morning across eastern MA.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... Sunday... The upper trough and its cold core will move offshore Sunday morning. That should reduce support for snow showers during the day. However, lingering cold temperatures aloft along the Mass East Coast may maintain scattered to widely scattered snow showers during the morning. Moisture lingers below 750 mb much of the day, so while there may be breaks of sun late morning/midday, the overall character of the day will favor clouds. High pressure builds over Eastern Canada while a storm system races out to sea from the Carolinas. The pressure gradient between the two will build, bringing increasing northeast winds across Southern New England. Strongest winds will be near the coast in Eastern Massachusetts. Gusts to 30 knots/35 mph will be expected. The mixed layer should reach about 900 mb, with temperatures in that layer favoring max sfc temps in the 30s, possibly low 40s in the CT Valley. Sunday night... Drier air moves in, bringing at least partial clearing overnight. The winds will diminish inland, while remaining 25-34 knots south of Boston and favoring the Cape and Islands. Temperatures should fall to the 20s and lower 30s. && .LONG TERM /MONDAY THROUGH SATURDAY/... Highlights... * Dry weather for the first half of the work week * Moderating temperatures through the week, with Spring like weather returning by Thursday * On and off showers return by the end of the work week Overview... 12z guidance and its ensembles are in good agreement with the synoptic pattern into next week. Strong ridge will be in place over the eastern Pacific with digging trough into the desert southwest. Anomolous offshore ocean storm north of Bermuda will push southern New England in a ridge for the first half of the week. The ridge over the Northeast will begin to break down by Wednesday as Pacific ridge pushes onshore advancing the pattern forward. The southern trough will eject more northeastward late in the week and move into the region by Fri/Saturday. Overall a dry pattern will set up for the first half of the week, with increasing showers towards the end of the work week. Temperatures will moderate through the week. Details... Monday into Wednesday...Moderate confidence. Offshore 500 mb low will continue to push eastward early Monday as mid-level ridge and strong high pressure builds into the region. Despite building heights, flow will still be onshore resulting in below average temperatures on Monday. Moderating temperatures on Tuesday and Wednesday as 850mb temps begin to rise pushing in some WAA. Generally expect highs in the low 50s across the CT River Valley to the upper 40s across the interior. Locations along the MA east coast will remain in the mid to low 40s for each day thanks to northeast flow keeping the marine air onshore. Because the ridge begins to break down on Wednesday, there is the chance for a few showers across the west during the day. However, there are some model differences on the timing as well as uncertainty on whether we will be able to saturate the column. Thus will leave a chance of precip in the forecast for now. Thursday any beyond...Moderate confidence. Spring returns to the region as west to southwest flow filters into the area. High temps will warm above average for the end of March with a few spots potentially reaching to near 60F. However, mid- level ridge will begin to break down with several waves moving through the flow. This could result in a few rounds of precip during the late half of the week. Right now the EC has the heaviest precip moving in around late Friday into Saturday, with the GFS keeping the system offshore. Because of the uncertainty kept a chc of precip until guidance becomes more inline. && .AVIATION /02Z SUNDAY THROUGH THURSDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday Night/... Moderate to high confidence. VFR conditions early will lower to MVFR cigs/vsbys in snow showers during the first part of the night. Snow showers may bring accumulations on the ground, with the most favorable time would be 9 PM to 5 AM. Eastern Massachusetts will be most favored for snow, with 1-2 inches possible. Brief IFR cigs/vsbys possible in heavier snow showers in this area. Conditions will improve Sunday morning, returning to VFR during the morning. Northeast winds will increase with gusts to 30 knots possible along the coast and 20-25 knots inland. Clearing skies Sunday night with wind gusts 25 to 30 knots still possible. KBOS Terminal. High confidence in TAF. Most favorable time for snow showers will be 11 PM to 5 AM. An inch accumulation is possible. KBDL Terminal...High confidence in TAF. Outlook /Monday through Thursday/...Moderate Confidence. Monday: VFR. Windy with local gusts to 30 kt. Monday Night through Wednesday: VFR. Breezy. Wednesday Night: Mainly VFR, with areas MVFR possible. Slight chance SHRA. Thursday: Mainly VFR, with areas MVFR possible. Slight chance SHRA. && .MARINE... Short Term /through Sunday Night/... A weather disturbance sweeping south from Canada will cross the Massachusetts and RI waters later tonight and early Sunday. High pressure then builds over Eastern Canada. This will mean scattered rain and snow showers tonight, tapering off on Sunday. Northeast winds will increase tonight with gusts of 25 to 33 knots later tonight and Sunday. Brief marginal gale force gusts can not be ruled out across our far southeast waters...but felt strong small crafts were more representative. The strong northeast wind will also drive up seas a few feet. Existing model guidance seemed to underplay these effects, and so we manually bumped the higher-end values up a couple of feet. Outlook /Monday through Thursday/...Moderate Confidence. Monday through Monday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 12 ft. Tuesday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 15 ft. Tuesday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 16 ft. Wednesday: Winds less than 25 kt. Rough seas up to 15 ft. Wednesday Night: Winds less than 25 kt. Rough seas up to 11 ft. Thursday: Winds less than 25 kt. Areas of rough seas. && .EQUIPMENT... Due to our ongoing move to the new forecast office in Norton, MA. we are still trying to resolve some communication issues. The following NOAA Weather Radio transmitter is back on the air... Somers, CT transmitter........WXJ41.....162.475 MHz However, the following NOAA Weather Radio transmitters are not yet on the air... Johnston, RI transmitter......WXJ39.....162.400 MHz Gloucester, MA transmitter....WNG574....162.425 MHz Blue Hill, MA transmitter.....KHB35.....162.475 MHz Hyannis, MA transmitter.......KEC73.....162.550 MHz Paxton, MA transmitter........WXL93.....162.550 MHz && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 5 AM Sunday to 8 AM EDT Monday for ANZ231>235-237. Small Craft Advisory from 5 AM to 11 PM EDT Sunday for ANZ230- 236. Small Craft Advisory from 3 AM Sunday to 8 AM EDT Monday for ANZ250-251-254. Small Craft Advisory from 6 AM Sunday to 8 AM EDT Monday for ANZ255-256. && $$ SYNOPSIS...WTB/Dunten NEAR TERM...Frank SHORT TERM...WTB LONG TERM...Dunten AVIATION...WTB/Dunten MARINE...WTB/Dunten EQUIPMENT...Dunten is the U.S. government's official web portal to all federal, state and local government web resources and services.