Area Forecast Discussion
Issued by NWS Boston, MA

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587 FXUS61 KBOX 190203 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1003 PM EDT Sun Mar 18 2018 .SYNOPSIS... Dry but unseasonably cold weather will continue through tomorrow. High pressure brings dry weather 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 AM MONDAY MORNING/...
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10pm update... Yet another weak and progressive shortwave will rotate through N New England this evening. However, outside of the SCT CU where Great Lake moisture is available, and a slight increase in CI mainly SKC conditions should continue. OBS already showing several locations have decoupled within the last couple of hours so have leaned most heavily on cold MOS guidance for overnight mins. Otherwise, the forecast is on track this evening.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... Monday into Monday night... High pressure centered over south-central Canada will continue to influence our weather into Monday night, with dry conditions and cool temperatures persisting. Temperatures will be slightly warmer than today, with highs in the mid to upper 30s. Cannot rule out a 40F but the overall trend is still below normal. A weak shortwave will pass well east of the region, which will tighten the pressure gradient. Thus gusty winds near 25 MPH is possible across northern and eastern MA. Temperatures overnight will be slightly warmer as WAA begins to advance into the region ahead of VA/NC developing cyclone. Cloud cover will also be on the increase during the overnight hours which will limit any diurnal cooling. && .LONG TERM /TUESDAY THROUGH SUNDAY/... */ Highlights... - Tuesday, keep it cold and dry, N winds, skirting S-coastal snow - Wednesday into Thursday, monitoring potential storm - Friday into the weekend, keep cool, dry pattern for now - Pass on any later potential weather features into next week */ Overview and discussion (Tuesday through Thursday)... Continued evaluation of possible midweek wintry-weather. Suppressing SE Canadian gyre against W-E Pacific energy train. With an upstream N-Pacific pattern ridge amplification, downstream H5 trof-ridge-trof sharpens, preferred NE CONUS H5 troughing, however neighbored W by a forward leaning H5 ridge / mild SW Pacific-punch while E a wide-open N Atlantic now with +NAO. While progressive pattern preferred, there are still wildcards: morphology of 1.) suppressive SE Canadian gyre, and 2.) upstream central N American H5 ridging. Likely more but both implicative as to sharpness of E CONUS H5 trof and mid-level feature potency. Could give longer residency towards low maturation, backed further N/W to our coast, subsequent bigger impacts, outcomes ... that is if the H5 ridge upstream highly amplifies while suppression N/E lessens, the opportunity for N-stream energy to cascade rearward within the E CONUS H5 trof. Flat and fast versus sharp and slower. Evaluating isentropes, subsiding S split flow, Canada into E Great Lakes split towards OH River Valley and NE CONUS initially. Dry. Beneath mid-level confluence along pressure surfaces, lessening while pushing E. Can see W-E stacked frontogenesis with height S-N Tuesday with the first passing low. But moisture present, and lift, especially in the dendritic growth zone? And to what intensity is lift, precipitation, especially with consideration of timing (i.e., daytime), low-level thermal profiles? Low PoPs, skirting S-coastal snow for Tuesday, light accumulation if any. Then late Wednesday into Thursday, the second low, SW-NE fronto- genetical banding re-emerging. Stronger synoptics, deeper lift and pull back beneath mid-level features, N/E suppressive wave lesser. Conveyor belt motions amplified, some concern with a cold, dry belt wrap around along the isentropes, but expect moisture present along with lift, especially within the dendritic growth zone, a measure of trowaling. But to what intensity is lift, precipitation, especially noting timing (i.e., daytime), low-level thermal profiles? Far too much spread to get into specific details, and yes, even considering the latest 18.12z EC. It`s just one model run, prefer consistency before jumping on it. Keep in mind, a lot of moving parts, chaotic, so expect adjustments in later forecasts. Focus Tuesday through Thursday. Preference to ensemble means / WPC forecasts over operational guidance. A nod to SREF / CIPS analog probabilistics (though with CIPS, not favoring 60 hr NAM-derived forecast guidance, while the 84 hr GFS-derived looks reasonable). Recognize SE New England at higher risk with latest 12z guidance and probabilistics. Light snow around late Tuesday, if any, along the S-coast. A better chance of light to moderate snow late Wednesday into Thursday. As to amounts ... still too early to say. Winds an issue during the latter period, gusts of 30-40 mph, initial guess. Roughly 10.6 foot Boston tide 315a on Thursday potentially during strongest winds. Can`t rule out coastal flood issues for E-coastal MA. An first-cut 72-hour snowfall grid is published with highest amounts of 2-4 inches S-coastal New England, Cape and Islands, but take this as a first-guess with low confidence. Forecasts will change. Continued advice, stay informed, keep tuned to later forecasts. && .AVIATION /02Z MONDAY THROUGH FRIDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday Night/...High confidence. VFR. NW winds, diminishing over time, can`t rule out gusts upwards of around 20 kts at times. Mainly SKC other than SCT-BKN 4-6 kft CIGs over SW New England around 7-9z tonight. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Tuesday through Friday/...Moderate Confidence. Tuesday: VFR. Tuesday Night: VFR. Windy with areas gusts to 30 kt. Wednesday: Mainly VFR, with local MVFR possible. Strong winds with local gusts to 40 kt. Slight chance SN. Wednesday Night: Mainly VFR, with areas MVFR possible. Strong winds with gusts to 40 kt. Slight chance SN. Thursday: Mainly VFR, with local MVFR possible. Strong winds with local gusts to 40 kt. Slight chance SN. Thursday Night: VFR. Breezy. Friday: Breezy. && .MARINE... Short Term /through Monday Night/...High confidence. Progressive northwest flow across the waters will lead to seas at or near 5 feet through tonight. SCA will linger into tomorrow, especially for the eastern waters, as winds will pick back up to around 20-25 kts by the afternoon. Conditions should begin to subside by the overnight hours. Very cold airmass in place combined with gusty winds will result in some freezing spray across the eastern waters. A freezing spray adv has been issued. Outlook /Tuesday through Friday/...Moderate Confidence. Tuesday: Winds less than 25 kt. Tuesday Night: Low risk for gale force winds with gusts up to 35 kt. Seas locally approaching 5 ft. Slight chance of rain, slight chance of snow. Wednesday: Moderate risk for gale force winds with gusts up to 40 kt. Rough seas up to 13 ft. Chance of snow, chance of rain. Local visibility 1 nm or less. Wednesday Night: Moderate risk for gale force winds with gusts up to 45 kt. Rough seas up to 18 ft. Snow likely, rain likely. Local visibility 1 to 3 nm. Thursday: Low risk for gale force winds with gusts up to 40 kt. Rough seas up to 18 ft. Chance of snow. Thursday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Friday: Winds less than 25 kt. Local rough seas. && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 2 AM EDT Monday for ANZ232>235-237- 255-256. Small Craft Advisory until 2 PM EDT Monday for ANZ231-251. Freezing Spray Advisory until 2 PM EDT Monday for ANZ231-250- 251-254. Small Craft Advisory until 2 AM EDT Tuesday for ANZ250-254.
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&& $$ SYNOPSIS...Dunten/Sipprell NEAR TERM...Doody SHORT TERM...Dunten LONG TERM...Sipprell AVIATION...Dunten/Sipprell MARINE...Dunten/Sipprell is the U.S. government's official web portal to all federal, state and local government web resources and services.