Area Forecast Discussion
Issued by NWS Boston, MA

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KBOX 130812 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 312 AM EST Wed Dec 13 2017 .SYNOPSIS...
-- Changed Discussion --
A gale center will move into the Maritimes today with windy and very cold conditions in its wake. A fast moving low pressure will track south of New England late tonight and early Thursday bringing a period of light snow to the south coast and especially the Islands. Another low pressure may bring some light snow around Friday night then cold and dry for Saturday. Somewhat milder temperatures return on Sunday.
-- End Changed Discussion --
&& .NEAR TERM /THROUGH TODAY/...
-- Changed Discussion --
Mid level low moves across New Eng this morning before lifting to the NE this afternoon. Cold pool aloft with 500 mb temps around -32C combined with some low and mid level moisture moving through will lead to a period of bkn cu and can`t rule out a few flurries, especially higher terrain. Clearing later afternoon. The main weather story for today will be wind and cold in the wake of the departing low pres moving into the Maritimes. 850 mb temps bottom out around -15 to -16C today so only expect minor recovery from morning lows. Highs will range through the 20s to near 30 outer Cape/Islands, with some upper teens in the Berkshires. Wind chills will be in the single numbers and teens. Well mixed boundary layer with steep low level lapse rates will promote excellent mixing with soundings suggesting peak gusts 40-50 mph, strongest mid/late afternoon especially over higher elevations. We expanded the wind advisory to include all of MA/RI.
-- End Changed Discussion --
&& .SHORT TERM /TONIGHT THROUGH 6 PM THURSDAY/...
-- Changed Discussion --
A period of clear skies expected this evening with gusty winds gradually diminishing overnight. However, clouds will quickly return as a rather robust mid level shortwave moves across the Ohio Valley to south of New Eng late tonight and early Mon. Low pres tracks south of the coast and attempts to spread some light snow north into portions of SNE late tonight into early Mon. Plenty of dry air initially to overcome which will limit northward extent of snowfall. Best chance for a period of light snow will be near the south coast and especially the Islands where better moisture and lift. Guidance indicating a brief period of modest omega in the DGZ over the Islands 09-12z with sharp decrease in omega to the north. Minor accum of a coating to an inch is possible for the south coast and especially the Islands with low prob for 2 inches BID-ACK. However, a sharp gradient is expected on the northern edge of the snow shield so if it shifts slightly south, little or no accum will be the result. Light snow may linger into Thu morning immediate south coast and especially Cape/Islands as low pres passes to the south. Otherwise, drier air and clearing skies behind the departing low pres will gradually move in from NW to SE but it may take until mid afternoon for clearing to reach far SE New Eng. A period of gusty NW winds will develop Thu afternoon with gusts 20-30 mph. Another unseasonably cold day with highs mid 20s to lower 30s.
-- End Changed Discussion --
&& .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... */ Highlights... - Skirting clipper low with light snow Thursday - Cold and dry Thursday night into Friday - Another shot of snow shower activity going into Friday night - Cold and dry again for Saturday - Potential wintry mix event for Sunday - Early on cold, light snow followed by a warmer trend next week */ Overview... Cold, active weather pattern persists into the weekend, beginning to relax into the following week. H5 trof pattern maintains over NE N America round which disturbances rotate, at times capturing S-stream energy, quickly escaping E with lesser downstream traffic. Looking at a series of clipper systems which will bring periods of wintry weather followed by gusty winds that aid in preserving the below- average temperature pattern we have seen as of late. Strength of individual disturbances is in question which will be broken down below, however their forecast quick movement and short residency, looking at brief impacts and leaning towards less impressive / deep storm development in vicinity of New England. Certain they`ll keep on reloading negative H85 temperature anomalies across the region. But perhaps a warming trend towards late December? The wave breaking over the NW Pacific as a stout jet of milder air pushes E into W N America, colder air is shunted back N as the H5 pattern across the CONUS relaxes, becoming more zonal. While still within the periphery of the polar jet, seemingly looking at a return of an ebb and flow pattern with a nod towards shots of cooler air out of the N rather than S-stream dominance. Continued confidence in operational forecast guidance out through 72-96 hours, thereafter preference to ensemble means. Wintry weather followed by cold and blustery themes into the weekend then a gradual warm-up into next week with potential for mixed precip events early on. */ Discussion... Thursday... Skirting clipper low, potential for wintry weather. Consensus of forecast guidance has a near-miss, the crux of the forcing offshore associated with positive differential vorticity advection, stronger ascent of greater moisture availability. However, evaluation along isentropes and the environment within the snow growth region, there are indications of weak lift and available moisture along decent SW to NE frontogenetical banding around H7-5. Can not rule out light snow chances spreading as far N/W of the MA/VT/NH border. Not sold on just saying zero based on synoptics. Consensus of guidance has the dry, subsiding wedge further N over N New England. Thus like to keep chance PoPs for all of S New England, likely along the S coast. Amounts light, thinking little impact. The EPS probabilities paint a decent picture of outcomes with respect to 24-hour 0.01 liquid. A mainly early-half of the day event, tapering into afternoon/eve. Nantucket having the best shot of seeing appreciable accumulation of precipitation. Late Thursday into Thursday night... Cold and dry. Initially blustery, storm system quickly steering out as high pressure builds in. Gales briefly on the waters, all else being good. Flirting with noteworthy wind chills yet seemingly prior to the crux of cold air with single digit lows into Friday morning. That being said any liquid from melt along roads will easily freeze. Friday into Friday night... Possible snow shower activity, otherwise maintained cold. Positively-tilted H5 trof axis quickly sweeping across the region yields little threat and impact to the region. Moisture present but lacking deep synoptic lift. Agree with the bulk of development across the better baroclinic zone well offshore as the H5 trof undergoes neutral tilt out across the Atlantic. Lack of mid-upper level curvature until further downstream. Chance PoPs with energy transfer from N-stream clipper to S-stream wave along the better baroclinic zone. Mainly snow showers and looking at light accumulations. Saturday into Saturday night... Blustery and cold. High pressure settling in behind exiting storm, would expect ocean-effect stratus / showers near the coast, perhaps some Lake effect snow shower activity getting into N/W MA before deeper subsidence and drier air builds in. Sunday into Sunday night... Potential mixed precip storm. Monitoring cold air damming as there is the possibility of over-running precipitation. Gradually warming as the warm front lifts N but also as the dry slot seemingly wraps in, looking at potential change overs before all is said and done. Too early to get on particulars but something to watch. Into next week... Some final clipper systems, shots of cold, then the warming trend begins as we get back into an ebb and flow pattern. With clipper and cold, the usual shot of snow shower activity enhanced by the Lakes, followed by blustery winds and the typical offshore ocean-effect stratus / shower activity. The H5 trof relaxing, we get back into S flow and a warmer trend. && .AVIATION /07Z WEDNESDAY THROUGH SUNDAY/...
-- Changed Discussion --
Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday/... Through 12z... Areas of MVFR cigs across the Cape/Islands will quickly improve to VFR. WNW gusts to 25-30 kt. Today...High confidence. VFR with sct-bkn050. Strong and gusty WNW winds peaking this afternoon with gusts 35-40 kt, locally 45 kt over the higher terrain. Tonight...Moderate confidence. Mainly VFR cigs, but lowering to MVFR over the islands and south coast after 06z as area of light snow spreads north. Low risk for brief IFR vsbys over the islands. Gusty winds to 35 kt in the evening, diminishing overnight. Thursday...High confidence. Areas of MVFR in lingering light snow in the morning Cape/Islands and south coast, otherwise VFR with gradual clearing from NW to SE. W/NW gusts to 25 kt in the afternoon. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Thursday Night through Sunday/... Thursday Night: VFR. Breezy. Friday: VFR. Friday Night: Mainly VFR, with areas MVFR possible. Breezy. Slight chance SHSN. Saturday: Mainly VFR, with local MVFR possible. Breezy. Slight chance SHSN. Saturday Night: VFR. Breezy. Sunday: VFR. Breezy. Chance SHSN.
-- End Changed Discussion --
&& .MARINE...
-- Changed Discussion --
Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday/...High confidence. Gale force WNW winds peaking this afternoon into early this evening with gusts 40-45 kt, then diminishing through tonight. Another pulse of WNW gusts to 25-30 kt developing Thu afternoon. Rough seas. Vsbys lowering in developing snow late tonight and early Thu over south coastal waters, improving in the afternoon. Outlook /Thursday Night through Sunday/... Thursday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Friday: Winds less than 25 kt. Areas of seas approaching 5 ft. Friday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of snow showers. Local visibility 1 to 3 nm. Saturday: Moderate risk for Small Craft Advisory winds with local gusts up to 30 kt. Local rough seas. Slight chance of snow showers. Saturday Night: Moderate risk for Small Craft Advisory winds with local gusts up to 30 kt. Local rough seas. Sunday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers.
-- End Changed Discussion --
&& .BOX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
CT...None. MA...Wind Advisory from noon today to 10 PM EST this evening for MAZ007-019-022>024. Wind Advisory from noon today to 8 PM EST this evening for MAZ002>006-008>018-020-021-026. RI...Wind Advisory from noon today to 10 PM EST this evening for RIZ008. Wind Advisory from noon today to 8 PM EST this evening for RIZ001>007. MARINE...Gale Warning from 6 AM this morning to 1 AM EST Thursday for ANZ232-235-237. Gale Warning from 8 AM this morning to 1 AM EST Thursday for ANZ233-234. Gale Warning from 10 AM this morning to 1 AM EST Thursday for ANZ230-231-251. Gale Warning from 10 AM this morning to 9 PM EST this evening for ANZ236. Gale Warning from 10 AM this morning to 3 AM EST Thursday for ANZ250-254. Gale Warning from 6 AM this morning to 3 AM EST Thursday for ANZ255-256.
-- End Changed Discussion --
&& $$ SYNOPSIS...KJC NEAR TERM...KJC SHORT TERM...KJC LONG TERM...Sipprell AVIATION...KJC/Sipprell MARINE...KJC/Sipprell

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.