Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 120839 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 339 AM EST Tue Dec 12 2017 .SYNOPSIS... Strengthening low pressure in the Ohio Valley early this morning redevelops over northeast Massachusetts this evening and then intensifies into at least a Gale Center over New Brunswick Wed. This storm system will bring a wintry mix of snow and ice to the interior with mainly rain in the coastal plain today. A shot of arctic air follows Wednesday and Thursday with a period of strong winds and bitterly cold wind chills. Another low pressure system may bring more snow to the region sometime in the Thursday night to Friday night timeframe, if it tracks close enough to the coast. Somewhat milder weather will arrive by the end of the upcoming weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... *** A Wintry Mix Across The Interior This Morning *** 340 AM update... Low pressure currently over OH intensifies as significant trough amplification occurs today over the eastern Great Lakes with mid level trough taking on a negative tilt tonight and then closing off to a 506 dam low over western MA 12z Wed. For this morning a modest cold airmass in place over southern New England with temps below freezing inland and dew pts down to 16F at Worcester. 1020 mb high over Maine early this morning builds to about 1026 mb later today in response to upstream trough amplification. This will provide cold air damming into interior MA and possibly farther south into northern CT and northwest RI. Column is cold enough to support snow at the moment and is evident with light snow currently falling at BDL/ORH/ORE/PSF/AQW. However developing low level southeast jet provides strong WAA and will result in snow changing over to rain quickly in the coastal plain. However northwest MA will have the longest duration of snow and could be moderate to perhaps heavy for a time this morning toward 15z. In addition, mid level lapse rates approach 6.5-7C/KM combined with bulk of forcing for ascent occurring in the snow growth region yields the risk for a period of moderate to heavy snow 12z-15z. Thus this event could overperform a bit across northwest MA where a brief period of moderate to heavy snow could produce 1-3" snowfall amounts FROM 12Z- 15Z, possibly a few 4 or 5 inches in northwest Franklin county. Otherwise most locations will see snow quickly change to rain this morning as warm nose at 925 mb advects across the area. The issue will be across the interior (along and northwest of I-90 and I-495) where shallow cold air will be stubborn to dislodge. This will result in a period of freezing rain/ice. A shorter duration of freezing rain/ice is possible farther south across northern CT, northwest RI into the I-495 corridor. Given current temps remain below freezing across interior Essex county along with dew pts in the low 20s and winds calm, we`ll expand winter weather advisory to this region for a brief period of mixed wintry precip 7 am - 10 am. Keep in mind it doesn`t take much freezing rain/ice to result in slippery travel. Farther south into the coastal plain including Boston and Providence, any snow will quickly changeover to rain given increasing southeast winds. Rain will likely be heavy at times this afternoon given trough amplification/strong jet dynamics with LFQ of upper level jet streak overspreading the area, enhancing QG forcing. In addition some instability aloft with mid level lapse rates increasing to 6.5-7.0C/KM (TTs 50-55). This combined with fairly strong forcing may result in embedded convection, enhancing rainfall potential. It will become breezy along the eastern MA coast especially Cape Ann as low level jet increases as it departs offshore. This low level jet will warm the coastal plain to 45-50 degs this afternoon, this includes the Boston to Providence corridor. Meanwhile farther inland late day highs of 35-40. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/... 340 AM update... Vigorous negatively tilted short wave trough approaches from the southwest. Moisture is limited with this feature given attending dry slot. However could be sufficient low level moisture for a few low top rain/snow showers ahead of the dry slot. Behind this departing short wave arctic air blast across the region with very strong CAA as 925 temps crash from +7C over Cape Cod 7 pm to -7C by 12z Wed. Any standing water and/or slush will freeze. Thus this afternoon is your chance to remove any leftover snow/ice. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Wednesday... There is a chance of snow squalls continuing into Wednesday morning as an arctic front progresses across Southern New England. Very little snow accumulation is expected with these passing showers, likely up to an inch at most west of the Worcester Hills. Winds will pick up in the afternoon as there is an impressive upper level jet overhead. Models are in agreement with 40kts at 925mb mixing down to the surface Wednesday afternoon. The GFS suggests the strongest winds will be over the northern tip of the Cape and extend into Mass Bay. Wind gusts between 40 to 50 mph are not out of the question. Winds will likely peak by 00Z Thursday as the upper level jet sits directly over the region. Wednesday night temperatures will range in the teens due to the arctic airmass now over the region. With the combination of the arctic airmass and strong surface winds, wind chills are likely to hover near zero degrees overnight. With minimal cloud cover as well, radiational cooling will add to the low apparent temperatures. Thursday and Friday... Strong winds will continue into Thursday morning but begin to dissipate throughout the afternoon and evening. Both the ECMWF and NAM point towards a weak system that brings light snow to the islands and southern coast of New England Thursday afternoon. The system will likely not linger off the coast for very long, resulting in minimal snow accumulations, if any at all. The arctic airmass remains over the region through Thursday and Friday resulting in much below normal afternoon temperatures. With the winds diminishing by Thursday evening, wind chills should not be an issue, however overnight temperatures will continue to range in the teens across much of the region. Friday night and Saturday... A coastal low is expected to clip the region Friday/Saturday resulting in periods of heavy snow along the 95 corridor. Unfortunately, the models are not in agreement with timing or position for when it does make its way up to Southern New England. Going with guidance from the ECMWF and NAM, precipitation will push north across the region starting at 18z. As the low moves further northeast, east of the 95 corridor will likely see the most accumulation. The coastal low is expected to push offshore by Saturday afternoon. Sunday... A ridge builds in Sunday morning behind the coastal low. Winds will turn to the southwest, advecting warmer temperatures into the region by midday. Dry and seasonable temperatures will continue through early next week. && .AVIATION /08Z TUESDAY THROUGH SATURDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tonight/... 0730z update... Thru 12z...High Confidence. VFR with light snow/flurries across western portions of MA/CT. Increasing southeast wind along and near the coast. Light and variable inland. After 12...High confidence on trends but lower on exact details. MVFR except IFR across the far interior. Snow transitions to rain along the coast but freezing rain inland. Southeast winds increase along the coast. Tonight...high confidence on trends, lower on details. MVFR likely. Gusty NW winds develop. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Wednesday through Saturday/... Wednesday: Mainly VFR, with local IFR possible. Windy with gusts to 35 kt. Slight chance SHSN. Wednesday Night: VFR. Strong winds with local gusts to 40 kt. Thursday through Thursday Night: VFR. Breezy. Friday: Mainly VFR, with local IFR possible. Chance SN. Friday Night: Mainly VFR, with areas IFR possible. Breezy. Chance SN. Saturday: VFR. Breezy. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tonight/... 340 AM update... Today... Increasing southeast winds 20-30 kt with strongest winds across eastern MA waters. Snow to rain reduces vsby. Low pres moves from OH to northeast MA and intensifying as it does so. Tonight... Arctic cold front sweeps across the area with southeast winds shift to the west-southwest 20-30 kt. Vsby improves after evening rain/snow showers. Outlook /Wednesday through Saturday/... Wednesday: Moderate risk for gale force winds with gusts up to 40 kt. Rough seas up to 14 ft. Slight chance of snow showers. Visibility 1 to 3 nm. Wednesday Night: Moderate risk for gale force winds with gusts up to 40 kt. Rough seas up to 14 ft. Thursday: Moderate risk for Small Craft Advisory winds with local gusts up to 30 kt. Local rough seas. Local visibility 1 to 3 nm. Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Friday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of snow. Areas of visibility 1 to 3 nm. Friday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Chance of snow. Visibility 1 to 3 nm. Saturday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 10 ft. Local visibility 1 to 3 nm. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Winter Weather Advisory until 10 AM EST this morning for CTZ002>004. MA...Winter Weather Advisory until 1 PM EST this afternoon for MAZ005-010>012. Winter Weather Advisory until 4 PM EST this afternoon for MAZ002>004-008-009-026. RI...Winter Weather Advisory until 10 AM EST this morning for RIZ001. MARINE...Small Craft Advisory from 9 AM this morning to 6 AM EST Wednesday for ANZ231>234. Small Craft Advisory from 1 PM this afternoon to 7 PM EST this evening for ANZ230-236. Small Craft Advisory until 6 AM EST Wednesday for ANZ235-237- 255-256. Gale Warning from 10 AM this morning to 7 PM EST this evening for ANZ250-251-254. && $$ SYNOPSIS...Nocera NEAR TERM...Nocera SHORT TERM...Nocera LONG TERM...Correia AVIATION...Nocera/Correia MARINE...Nocera/Correia

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