Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 190811 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 411 AM EDT Mon Mar 19 2018 .SYNOPSIS... Dry but unseasonably cold weather will continue through Tuesday. A coastal storm moves up from the Mid Atlantic coast Wednesday and then moves off to the east Thursday. High pressure brings drier weather Friday and early Saturday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... WV imagery shows the kicker shortwave currently moving across Maine this morning. While this is mostly without fanfare, there is a layer of moisture, narrow in perspective which is yielding a band of BKN-OVC SC shifting ESE through the S tier of the region this morning. Given very weak echos within this band, cannot rule out a few flurries. However, these are unlikely to measure, as even in these areas dwpt depressions are on the order of 5-10F with ceiling heights in the 5-8kft range. The band of SC will continue to shift offshore, such that most of the region currently under BKN/OVC conditions will be trending toward SKC shortly after sunrise. Otherwise, behind this wave, and ahead of converging N and S stream waves, H2 to H5 flow becomes confluent allowing the sfc high pres to ridge into New England from the NW. Sounding response yields dry/subsidence. Mostly sunny conditions are expected through the day. If anything H85 temps may increase slightly through the day, along with H92 temps which may be what mixing is limited too thanks to the strong subsidence inversion. Temps at this lvl avg around -6C. This will lead to highs in the low-mid 30s across NW MA, while coastal areas in the mid 30s to around 40 are expected. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... Overnight... Inverted ridging remains in control overnight. Increasing clouds expected, mainly in the form of advancing CI shield ahead of the first coastal storm development S of the Delmarva. Although winds should be weak, the increasing moisture aloft may limit the ability for radiational cooling a bit. Will allow mins to fall into the teens, but less so into the single digits as they had under clear skies previous nights. Tue... Although the first, dominant S stream wave continues to feature gradually deepening low pres well to the S, confluence aloft is dominant across New England and the bufkit continues to show strong subsidence as a result. Therefore, with all deterministic and ensemble guidance supporting the QPF shield remaining offshore, will follow suit, keeping Tue dry. Filtered sunshine (through increasing CI) should still allow BL to mix well especially as the subsidence inversion diminishes somewhat. Low lvl temps near the top of the mixed layer becomes nearly isothermal, about -4C to -6C. So a few more spots should reach the low 40s, while the remainder of the region holds in the 30s. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Big Picture... Southern stream crosses the southern USA. One shortwave digs in over the southeast USA Tuesday night, turning the upper flow up the coast over New England. Closed low within this trough moves up the coast, crossing New England Wednesday night and the Maritimes Thursday. Northern stream trough drops down from Canada over the weekend. Model solutions are similar through Saturday morning with differences in detail after that. However, run-to-run differences continue and so forecast confidence is low-moderate. Details... Tuesday night through Thursday... Upper flow turns from the south Tuesday night, supporting a scenario for increasing moisture flow toward Southern New England. Precipitable water values climb to between 0.5 and 0.75 inches, which is above average for the equinox but not excessively so. All models develop coastal low off North Carolina Tuesday afternoon and then move it northeast, passing near the benchmark either Wednesday or Wednesday night. The GFS and GGEM are similar in timing this passage late afternoon/evening, while the ECMWF is slower with passage Wednesday night. This track is about 70 miles farther north than previous model runs, which would push precip farther north with a better chance to affect Southern New England Wednesday. Temperatures Wednesday will be borderline for accumulation, even after accounting for wet bulb processes. Even so, the scenario as presented shows potential for some snow accumulation, with a 4-5 inch bullseye in Southeast Mass with amounts diminishing toward the Northwest. Strong low level jet on the north side of this storm, with winds 50- 60 knots aloft. This should support northeast wind gusts 35-40 knots at the surface. A wind advisory may be needed for parts of Eastern Mass, especially the Cape and Islands. The forecast brings likely pops into Southern RI and Southeast Mass Wednesday with chance pops southeast of Fitchburg to Springfield MA. The low moves off to the northeast Thursday, and northwest winds bring drier air into our area that should aid in partial clearing. Friday-Saturday... Upper cyclonic flow lingers over New England Friday. Otherwise dry weather with seasonably cool temperatures. Sunday... Northern stream trough dives south from Canada Saturday night and sweeps over New England Sunday. This by itself may be enough for some flurries or light snow showers. Another shortwave moving through the southern stream passes south of us Sunday. Either source would be good for chance pops for rain or snow. Forecast confidence is low. && .AVIATION /08Z MONDAY THROUGH FRIDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday/...High confidence. Through today... VFR. A few early AM SCT-BKN 040-070. NW winds with a few gusts 15-20 kt. Overnight... VFR. Weaker NW winds. Tue... VFR through the day with increasing high and mid clouds. Winds N-NE. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Tuesday Night through Friday/...Moderate Confidence. Tuesday Night: Mainly VFR, with local IFR possible. Windy with gusts to 35 kt. Slight chance SN. Wednesday: MVFR/IFR conditions possible. Strong winds with gusts to 45 kt, mostly in Eastern Mass. Chance SN. Wednesday Night: MVFR/IFR conditions possible. Strong winds with gusts to 50 kt, mostly in Eastern Mass. Chance SN. Thursday: Mainly VFR, with local MVFR possible. Strong winds with local gusts to 40 kt Thursday Night: VFR. Breezy. && .MARINE... Short Term /through Tuesday/...High confidence. Today into Tuesday... NW winds diminish today below the 25 kt threshold by about mid day. This will also allow the 5-6 ft wind driven waves to diminish. The small craft advisory on the E waters should be allowed to dissipate, along with the risk for further freezing spray. After these conditions subside, quiet boating weather continues into Monday. Outlook /Tuesday Night through Friday/...Moderate Confidence. Tuesday Night: Low risk for gale force winds with gusts up to 40 kt. Local rough seas. Chance of rain, slight chance of snow. Areas of visibility 1 to 3 nm. Wednesday: Moderate risk for gale force winds, and low risk for storm force winds. Gusts up to 50 kt. Rough seas up to 16 ft. Snow likely, rain likely. Visibility 1 to 3 nm. Wednesday Night: Low risk for storm force winds with gusts up to 50 kt. Rough seas up to 17 ft. Chance of snow, rain likely. Visibility 1 to 3 nm. Thursday: Moderate risk for gale force winds early with gusts up to 40 kt. Winds diminishing by afternoon. Rough seas up to 16 ft. Local visibility 1 to 3 nm. Thursday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Friday: Winds less than 25 kt. Seas locally approaching 5 ft. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Gale Watch from late Tuesday night through Wednesday evening for ANZ231>235-237-250-251-254>256. Small Craft Advisory until 2 PM EDT this afternoon for ANZ231- 251. Freezing Spray Advisory until 2 PM EDT this afternoon for ANZ231-250-251-254. Small Craft Advisory until 2 AM EDT Tuesday for ANZ250-254. && $$ SYNOPSIS...WTB/Doody NEAR TERM...Doody SHORT TERM...Doody LONG TERM...WTB AVIATION...WTB/Doody MARINE...WTB/Doody is the U.S. government's official web portal to all federal, state and local government web resources and services.