Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 240846 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 446 AM EDT Sat Mar 24 2018 .SYNOPSIS... A series of upper level disturbances will bring chilly temperatures this weekend along with scattered snow showers...mainly tonight into Sunday morning with the focus across eastern Massachusetts. Canadian high pressure builds into 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 PM THIS EVENING/... 415 am update... Upper trough/cold pool aloft overhead will result in an abundance of clouds today...particularly across eastern New England. Still should see some peeks of sunshine...particularly early in the day across western MA/northern CT. While much of the day will be dry...expect a few rain/snow showers to develop this afternoon. The focus of these will be across eastern MA where very steep 1000 to 700 mb lapse rates over 8C/KM along with deeper moisture will reside. High temperatures will reach into the lower to middle 40s in most locations. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... * Minor snow accumulations tonight/early Sun across eastern MA Tonight and Sunday... An impressive piece of shortwave energy will drop south out of Quebec tonight. The result will be an inverted trough swinging across the region...shifting the winds from north to northeast. There is a band of impressive forcing with the inverted trough along with a deep column of moisture. Low level lapse rates are quite steep too...resulting in total totals well into the 50s. This should result in scattered snow showers especially late tonight into Sunday morning. The scattered snow showers may begin as a brief period of rain showers given the initially warm boundary layer. However...cold temperatures aloft should quickly change an mixed precipitation over to snow showers. A brief period of snow showers may impact much of the region overnight/early Sunday as the inverted trough swings across the region. However...the focus for the snow showers will be across eastern MA. This is where moist low level NNE flow will tap some instability from the ocean and some enhancement via land/sea interface. The potential exists for an inch or two of snow across eastern MA with the low risk of 3 inch amounts. Climatology and pattern recognition would favor the north shore and/or portions of Plymouth county receiving the higher amounts. While the snow showers will be banded in nature...given the instability, moisture and lift they may be briefly heavy. So despite today/s mild temperatures snow accumulations on roadways are possible along with potential slippery travel overnight Sunday morning. Will go ahead and issue a special weather statement to highlight these concerns. The bulk of the snow showers will be later tonight into Sunday morning...but a few snow showers may linger into the afternoon across the eastern MA coast NNE flow and 850T below -10C. Otherwise...a chilly day with gusty northeast winds along the coast. High temperatures will be held into the middle to upper 30s across much of the region...but may see few locations in the lower CT river valley break 40. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Overview... 00Z model suite showing continued long, persistent NE wind fetch into east coastal areas into early next week as high pressure ridge at the surface and aloft slowly builds E. Winds will slowly diminish as the ridge builds across the region early next week. However, H5 cutoff low and its developing surface storm center, as forecast by the Ocean Prediction Center, sets up in the vicinity of about 37-38N/62-63W Mon through at least Tue, which will pretty much keep the ridge nearly stationary in the highly amplified mid level steering flow. Some question as to whether the northern portion of the ridge may try to break down toward the end of the long term, allowing lower H5 heights to move across the region toward the latter half of next week. This may allow the slow moving cold front to push close enough to the region to bring some moisture across, though uncertainty remains on the timing and track of the front with the blocking pattern across the western Atlantic in place. Details... Sunday night and Monday... Lingering snow showers across E Mass into portions of RI will tend to weaken as they move offshore Sunday evening. As high pressure ridge starts to gradually push S, with its 1044 hPa center across N Maine into eastern Quebec. Tight pressure gradient continues between the strong high to the N and a developing storm center well SE of Nantucket, so will continue to see NE winds gusting up to 25-35 mph across coastal areas mainly S of Boston, highest across Cape Cod and the islands. With the high to the north and low offshore nearly stationary, the winds will continue through Monday. Skies will become mainly clear across the CT valley and N central Mass, but scattered clouds will linger across coastal areas through through at least midday Monday. Temps will remain well below seasonal normals as H85 temps will range from -8C to -11C Sun night, then only recover to around -6C to -7C Monday. Expect overnight lows ranging from 20-25 across the higher inland terrain to 25-30 along the coast. Readings will recover especially across the CT valley and N central Mass on Monday, where there will be more sunshine and less effects from the cold onshore winds across coastal areas. Highs will range from the upper 30s to around 40 across E Mass into RI, up to the mid 40s across the mid and lower CT valley. Monday night through Wednesday... The high pressure will slowly sink south across New England during this timeframe, so expect mostly clear skies through at least Tuesday for most areas. Some clouds may linger across east coastal areas with the continued onshore winds. There will still be lingering cool temperatures along the coast with the persistent NE wind, but readings will reach close to seasonal levels inland. By Tuesday and Wednesday, highs will reach the lower-mid 50s, but will hold in the lower-mid 40s along the immediate E coastal areas. As the high settles across the region by about Wednesday, a cold front will start to slowly shift E out of the Great Lakes. This front looks to remain well W of the region at mid week. However, the coastal low may start to retrograde westward but should remain well offshore. This interaction may keep N-NE winds stirring especially near the coast. Wednesday night through Friday... Lower than average confidence during this timeframe, especially with a high amplitude long wave steering pattern in place, along with the mid level cutoff low and storm center spinning well SE of Cape Cod. With the low offshore and the high to the NW, timing the approach of the slow moving cold front is tough. Depending upon how far the ridge builds across, winds may try to shift to S-SW and will bring slowly moderating temperatures. May see some light rain showers move in during Thursday afternoon. If temps moderate, readings Thu night currently forecast to remain at or above freezing so the precip should remain all rain. Will be watching this aspect closely, though. Current forecast suggests temps running close to or a bit above seasonal levels. Again, not a whole lot of confidence for this timeframe. && .AVIATION /09Z SATURDAY THROUGH WEDNESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday/... Today...High confidence. Mainly VFR despite a scattered to broken deck of mid level cloudiness. A few rain/snow showers may develop this afternoon especially across eastern MA. Tonight and Sunday...Moderate to high confidence. Conditions should gradually deteriorate to MVFR /localized IFR conditions/ late tonight into Sunday morning in lower clouds and scattered snow showers. The snow showers will be most numerous across eastern MA where the best chance for IFR and perhaps even brief LIFR conditions will be possible. Some improvement expected Sunday afternoon across the interior...but MVFR conditions likely persist across eastern MA along with a few snow showers. NE wind gusts of 20 to 30 knots develop Sunday with the strongest of those across southeast New England. KBOS Terminal. High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Sunday Night through Wednesday/...Moderate Confidence. Sunday Night: Mainly VFR, with local MVFR possible. Windy with local gusts to 30 kt. Slight chance SHSN. Monday: VFR. Windy with local gusts to 30 kt. Monday Night through Wednesday: VFR. Breezy. && .MARINE... Short Term /through Sunday/... Today...High confidence. North winds of 10 to 15 knots but gusts/seas will remain below small craft advisory thresholds. Tonight and Sunday...High confidence. Strong high pressure building eastward into Quebec and northern New England will increase the pressure gradient. The result will be widespread northeast wind gusts of 25 to 30 knots developing toward daybreak and persisting Sunday. Brief marginal gale force gusts can not be ruled out across our far southeast waters...but felt strong small crafts were more representative. Seas will build to between 8 and 11 feet across our eastern outer waters. Outlook /Sunday Night through Wednesday/...Moderate Confidence. Sunday Night: Strong winds with local gusts up to 30 kt. Rough seas up to 12 ft. Slight chance of snow showers. Monday and Monday night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 12 ft. Seas may be higher S and E of Nantucket. 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 17 ft. Wednesday: Winds less than 25 kt. Rough seas up to 15 ft. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 6 AM Sunday to 8 AM EDT Monday for ANZ231>235-237-255-256. Small Craft Advisory from 6 AM to 6 PM EDT Sunday for ANZ230- 236. Small Craft Advisory from 3 AM Sunday to 8 AM EDT Monday for ANZ250-251-254. && $$ SYNOPSIS...Frank/EVT NEAR TERM...Frank SHORT TERM...Frank LONG TERM...EVT AVIATION...Frank/EVT MARINE...Frank/EVT is the U.S. government's official web portal to all federal, state and local government web resources and services.