textproduct: Boston / Norton

SYNOPSIS

Monday brings the return to drier, colder and blustery weather. Low pressure tracking south of New England brings accumulating snow to interior portions of CT and MA Tuesday and Tuesday night, with rain most likely in the lower elevations. Beyond that high pressure brings dry weather to end the week except for a moisture starved front Thursday.

NEAR TERM /THROUGH TONIGHT/

Key Message:

* Cold tonight with increasing clouds

High pres moves across New Eng this evening before shifting to the NE overnight. We should see a brief period of decent radiational cooling this evening with light winds and just some thin cirrus before clouds thicken and lower overnight. Low temps will be reached by midnight with lows ranging through the 20s with some upper teens possible across interior N MA. It will remain dry through the night as deeper moisture stays to the west through 12z.

SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/

225 PM Update:

Key Messages:

* Coastal storm system to bring a higher elevation accumulating snow with lower elevation mainly rain event to Southern New England.

* Accumulation of wet, dense snow in the interior will make for difficult travel during the afternoon and Tue PM commute, and significant accumulations of snow in the high terrain could lead to tree and powerline damage due to the weight of snow.

* Mainly rain for the majority of the event in lower elevations Tue, with 1 to 1.5 inches of rain; however bands of light-accumulating greasy snow are anticipated Tue night into early Wed AM in CT, eastern MA and RI.

Details:

A moisture-laden area of low pressure now organizing near the northern Gulf is expected to track ENE through the mid-Atlantic states and then continue along the New England coast on Tue, before pulling away into Nova Scotia late Tue night. This low pressure is expected to bring an accumulating wet/dense snowfall in the interior and higher terrain Tue into Tue night, with primarily rain in the lower elevations though ending as a period of light-accumulating snow Tue night due to wrap-around moisture as the storm exits.

While the exact track of the low pressure is still somewhat uncertain, today's forecast models have shown a loose consensus toward a track inside of the 40N/70W benchmark. This track will allow for above-freezing temps on easterly winds to advect inland enough to force a predominant precip type in the lower elevations as largely rain; higher-resolution guidance 2-m temps struggle to get the I-95 corridor down to near/below freezing levels until Tue night. The lack of a closed 700-500 mb circulation will also make it difficult to maintain or even sustain colder enough air in the lower elevations. In interior Southern New England, marginally cold enough air through the event to lead to accumulation of wet snow, and the higher elevations (Berkshires, eastern Franklin/northern Worcester and northwest Middlesex) could see significant accumulations to the point where we could have some downed trees/powerlines due to snow loading factors in those locations.

Snow accumulations and headlines are highly driven by elevation. We converted the Winter Storm Watch to Winter Storm Warnings in the Berkshires and into northern MA where forecast wet snow accumulations are in the 6 to 9 inch range. Besides just slippery road conditions and reduced visby with snow rates at or around 1 inch per hour, the potential exists for tree and powerline damage, and past storms producing significant wet snows have shown the potential for tree and powerline damage reports as snow totals start to exceed 4 inches. Winter Weather Advisories surround those areas with snow totals ranging from 3 to 6 inches. These headlines run from 7 AM Tue to 7 AM Wed. With the tendency in today's guidance to show a wrap-around band of snow as temperatures fall Tue night into the Merrimack Valley, Metrowest and part of northeast MA, we opted for a Winter Weather Advisory for those areas starting around 4 PM Tue until 7 AM Wed, and it's possible other areas may need to be added to this Advisory in later updates. Areas in this Winter Weather Advisory during the day on Tue should stay as rain during the daytime hours, which explains the difference in timing.

Precipitation is not expected to begin on Tue until the mid- morning to early afternoon, with steadier and heavier precip breaking out during the afternoon to mid-evening hours. Thus greater overall impacts to the Tuesday afternoon commute, and that's especially the case for interior Southern New England with sustained bands of moderate to at times heavy snow with reduced visbys. In lower elevations east and south of I-84 to I-495, moderate to heavy rains to the tune of 1-1.4 inches of rain are anticipated, with air temps in the upper 30s to the mid 40s. As low pressure pulls offshore Tue evening, colder air advancing southward on the backside of the system should allow for a changeover to wet snow, with potential for steadier light snowbands along the Merrimack Valley to the North Shore. Additional light, greasy snows southward into most of CT and RI and eastern MA for the overnight as colder air works southward and these wrap-around precip bands work through; this overnight band of snow offers the best chance for accumulating snows at around a half to 2 inches, and while not reaching Advisory levels they could make for some slippery spots for the overnight hours.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Key Messages:

* A few snow showers possible the second half of Thursday with the passage of an Arctic cold front, otherwise dry weather Wednesday through Friday. Turning unsettled for the upcoming weekend.

* Temperatures are trending well-below-average Wednesday through the upcoming weekend. An Arctic cold front Thursday night to bring the coldest air of the season, highs struggling to get above freezing by Friday afternoon.

Little in the way of precipitation between Wednesday and Friday with an area of high pressure building to the southwest of the region. A strong cold front, an Arctic Cold Front, brings a low chance for a few snow showers Thursday afternoon and evening. PWATs values are on the lower side 0.4 to 0.6", at this time do not expecting significant accumulations. Probabilities for 0.1" of new snow at this time are less than 20% for the Worcester Hills and less than 50% for the east slope of the Berkshires. The bigger story is the cold that follows the frontal passage. 925mb temperatures are lowering to -20C to -15C Thursday night, temperatures lower into the single digits and teens. But, a gusty northwest wind make it feel much colder as wind chills are below 0F across the higher terrain and single digits for the coastal plain. Friday afternoon, highs struggle to climb out of the 20s, "warmest" are south coast of RI/MA in the mid-30s.

Guidance trends are toward an active setup for the upcoming weekend, especially Saturday. Global ensembles continue to develop an area of low-pressure off the Mid Atlantic coast Saturday morning/afternoon. It is too soon to get into any details, but there is potential for another rain/snow/mixed event. Stay tuned!

AVIATION /19Z MONDAY THROUGH SATURDAY/

Forecaster Confidence Levels...

Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.

18Z update...

Through Tonight...High Confidence.

VFR. Lowering cigs late tonight. NW gusts to 25 kt, diminishing mid-late afternoon, then becoming light to calm tonight.

Tuesday...Moderate Confidence.

Lowering to IFR-LIFR as precip overspreads the region, 12-15z in west and 15-18z in the east. Ptype rain for coastal terminals, snow for BAF and ORH, and SN to RA-SN mix at BED and BDL. E-NE wind 5-15 kt. Minor accumulations at BDL-BAF-BED with more significant accums possible at ORH.

Tuesday night...Moderate confidence.

Widespread IFR-LIFR improving to VFR late from west to east. Interior snow in the evening may change to a period of snow along the I-95 corridor, including BOS and PVD for a few hours before ending around or just after midnight. Minor accum (up to an inch) possible at BOS. NE wind becoming N-NW with gusts to 25 kt developing, with 30-40 kt gusts possible for Cape/Islands.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...Moderate confidence in TAF. Lower confidence in timing of ptype changes.

Outlook /Wednesday through Friday/...

Tuesday Night: Mainly IFR, with local MVFR possible. Windy with gusts up to 35 kt. RA, chance SN.

Wednesday through Wednesday Night: VFR. Breezy.

Thursday: VFR. Windy with local gusts up to 30 kt. Slight chance SN.

Thursday Night: VFR. Windy with local gusts up to 30 kt.

Friday: VFR.

MARINE

Forecaster Confidence Levels...

Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.

Through Tuesday...High confidence.

W winds become NW through the day today with gusts 25-30 kt continuing. SCA for all waters. Winds quickly diminish through Mon afternoon as high pres builds in from the west. Light winds Mon evening becoming S-SE toward daybreak. Rough seas over southern waters will begin to subside during Mon and fall below 5 ft by Mon evening. Periods of rain ending tonight from W to E. Dry with good vsbys Mon and Mon night.

Tuesday rain overspreads the waters and SSE winds early increase and turn out of the east then northeast late as a low pressure system crosses the southern waters. This leads to gusts as strong as 25-30 kts by late Tuesday.

Outlook /Wednesday through Friday/...

Tuesday Night: Strong winds with gusts up to 35 kt. Rough seas up to 12 ft. Rain. Visibility 1 to 3 nm.

Wednesday: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 11 ft.

Wednesday Night: Winds less than 25 kt. Seas up to 5 ft.

Thursday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Slight chance of rain.

Thursday Night: Strong winds with gusts up to 40 kt. Areas of rough seas.

Friday: Winds less than 25 kt. Seas locally approaching 5 ft.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...Winter Storm Warning from 7 AM Tuesday to 7 AM EST Wednesday for MAZ002>004-008-009-026. Winter Weather Advisory from 4 PM Tuesday to 7 AM EST Wednesday for MAZ005-006. Winter Weather Advisory from 7 AM Tuesday to 7 AM EST Wednesday for MAZ010>012. RI...None. MARINE...Gale Warning from 7 PM Tuesday to 7 AM EST Wednesday for ANZ230. Gale Warning from 7 PM Tuesday to 1 PM EST Wednesday for ANZ231-232-250-251-254-255. Small Craft Advisory from 4 PM Tuesday to 7 PM EST Wednesday for ANZ233>235-237. Small Craft Advisory from 4 PM Tuesday to 7 AM EST Wednesday for ANZ236. Small Craft Advisory from 4 PM Tuesday to 1 AM EST Thursday for ANZ256.