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 071720 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1220 PM EST Wed Dec 7 2016 .SYNOPSIS... Light snow and rain will impact the region early this morning, giving way to drying by later today. A cold front crosses the region Thursday, with little more than a brief passing rain/snow shower or two. Mainly dry but unseasonably cold temperatures follow Friday and Saturday. Low pressure brings wintry precipitation to the region Sunday into Monday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 10 AM update... WV imagery shows layer of dry air moving in aloft and latest LAPS/RTMA soundings across portions of W New England suggest this to be the case. Mainly dry air building in from about H6 and downward. This trend will continue through the morning as a subsidence inversion takes hold under reinforced ridging. Therefore, expect the low-lvl moisture to become trapped until sfc winds have veered to the W for long enough that some mixing can occur. Will be increasing daytime skycover, and thereby lowering daytime temps across the board. Although the drizzle lingering along and within the I-495 corridor should gradually subside, the skies will likely remain predominantly BKN-OVC. These will be the primary changes with the mid morning update, as the overall late afternoon/evening drying currently forecast still looks reasonable based on trends. Previous discussion... Not really a terrific setup for accumulating snow, with marginal temperatures, and persistent low level dry air, limiting snow growth across much of southern New England. Expecting to lose active ice nuclei in the dendritic snow growth region from west to east between 4 AM and 7AM. Should precipitation linger longer than expected, we could be looking at either drizzle or freezing drizzle, depending on temperatures at the time. Drier air should overspread all of southern New England by midday, behind a cold front, ending the precipitation risk. Plenty of clouds should remain, even after precipitation has ended. Expecting seasonable temperatures. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Another low pressure should stay over southeast Canada tonight and Thursday, while weak high pressure lingers over the central Appalachians. This combination will produce a persistent west flow for our region. Mostly cloudy skies should prevail through this period, along with mainly dry weather. Cannot completely rule out a few sprinkles or flurries, especially across western MA. However, west winds are not a favored direction for both lake- effect and ocean-effect processes in southern New England. Another surge of colder air should arrive late in the day, Thursday. Seasonable temperatures expected prior to its arrival. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... * Unseasonably cold but mainly dry Friday and Saturday * Wintry precipitation possible Sunday into Monday * Unseasonable cold returns Tuesday Models and ensemble members are in generally good agreement on much of the long term, particularly with the synoptic pattern. A couple of shortwaves will move through southern New England throughout the period. The first one ushers in unseasonably cold air into the region for Friday and Saturday. The second one will follow a weak upper level ridge and bring a period of wintry precipitation to the area. This is followed by another round of unseasonably cold temperatures. As usual, confidence decreases towards the end of the forecast period. Thursday night through Saturday...Northwesterly flow will usher in unseasonably cold air into Southern New England. High temperatures during this period will have trouble getting above freezing. Most areas will be below freezing for most of this time. The south coast may see high temperatures just above freezing both days. Low temperatures should fall into the 20s Thursday night and into the teens Friday and Saturday nights. Otherwise, high pressure will keep dry weather in the area. Sunday and Monday...Much of the day Sunday should be fairly dry as weak upper ridging moves over southern New England. Then a shortwave will move through the upper level flow over the area. This, along with a potential secondary low pressure developing south of Long Island from a parent low in the Great Lakes, will bring a period of wintry precipitation to the region. At this point, thermal profiles indicate that while the coastal plain may see a quick period of snow at the start, temperatures will warm enough for a change to rain. Across the interior, cold air remains and a period of snow is more likely, particularly if the secondary low develops. Confidence is relatively high for a precipitation event to occur, however, confidence is low in the details. Tuesday...While confidence is not high this far out, all indications are that another period of unseasonably cold weather is expected beginning Tuesday. && .AVIATION /17Z WEDNESDAY THROUGH SUNDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short term...through Thursday night. Remainder of today...High confidence in trends, lower confidence in timing. Mix of IFR/MVFR conditions will give way to lower end VFR conditions through 20Z - 00Z this evening. This will come as a result of fog lifting and CIGS increasing in height before some breaks are observed. Timing in TAF may be off by a bit. Otherwise, winds gradually shift around to the W, but remain relatively weak. Overnight...High confidence. Mainly VFR once the last of the low clouds lift out. Winds out of the W, but may increase during the early morning hours to around 10 kt after being light most of the overnight. Tomorrow and tomorrow night...High confidence. Mainly VFR. Some MVFR possible in higher terrain due to lower CIGS and even a low risk for light snowfall late in the day. W winds increase, with gusts 15-20 kt at times by late afternoon, continuing into the overnight. Some gusts +20kt along the immediate coast. KBOS TAF...High confidence in overall trends. Lower confidence in exact timing. Expect IFR CIGS/MVFR vsbys to linger through 20Z then slowly attempt to lift out to low end VFR later this afternoon and this evening as NW flow becomes predominantly W. KBDL TAF...Moderate confidence in TAF, mainly due to timing issues. Outlook /Thursday Night through Sunday/... Thursday night through Saturday...High confidence. Mainly VFR conditions expected. A period of lower clouds Friday may result in some MVFR conditions. Sunday...Moderate confidence. VFR conditions to start. Conditions may lower to MVFR/IFR later Sunday afternoon and Sunday night in rain and/or snow. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday/... High Confidence. Winds and seas generally remain below Small Craft Advisory levels through Thursday morning. There are a couple of exceptions. Marginal 5 foot seas could develop across the outermost RI coastal waters early this morning. Rough seas and gusty west winds should develop Thursday afternoon. Not enough confidence to issue Small Craft Advisories this morning. Small Craft Advisories will likely be needed sometime Thursday afternoon. Outlook /Thursday Night through Sunday/... Thursday night and Friday...High confidence. Small craft advisories are likely with winds gusting over 25 knots and seas on the outer waters 5 to 6 feet. There is a low probability of NW gales. Saturday...Moderate confidence. Winds and seas slowly diminish, but generally remain above SCA criteria until late Saturday night. Sunday...Moderate confidence. Seas below 5 feet will slowly increase once again from the south as low pressure approaches the waters. Winds increase as well, with small craft advisories likely. There is a low probability of S-SW gales. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Belk/RLG NEAR TERM...Belk/Doody SHORT TERM...Belk LONG TERM...RLG AVIATION...Doody/RLG MARINE...Belk/RLG is the U.S. government's official web portal to all federal, state and local government web resources and services.