Area Forecast Discussion

FXUS61 KBOX 102339
Area Forecast Discussion
National Weather Service Taunton MA
639 PM EST Sun Dec 10 2017
Mainly dry and cool conditions are expected through Monday. Low
pressure will approach from the west late Monday night into 
Tuesday. This will likely bring a period of accumulating snow, 
mainly across interior northern Massachusetts, while any snow 
will quickly change to rain in the coastal plain. A shot of 
arctic air follows Wednesday and Thursday. Another low pressure
system may bring more snow to the region sometime in the 
Thursday night to Friday night timeframe.
635 PM update...
Mostly clear skies across SNE early this evening, but lots of
clouds just to the west will overspread the region as mid level
shortwave approaches from the west. Deepening moisture, modest 
forcing for ascent and steepening low level lapse rates over 
the ocean will increase risk of a few rain/snow showers near the
immediate south coast and islands after midnight given W/SW 
trajectory. Current forecast on track. 
Previous discussion...
Lake-effect clouds were spilling over the Berkshires into 
western and central MA. Expecting a mid level shortwave to 
arrive tonight, which will only spread more clouds from west to 
east across southern New England, especially after midnight. As 
such, not expecting good radiational cooling conditions. That 
said, min temperatures tonight should be below normal.
Fairly dry air below 800 mb, so dry weather will prevail for
much of the interior. A little different story towards the
coast, and coastal waters. The arrival of colder air over the
still relatively warm ocean will kickstart the ocean-effect
process. This will be mainly in the form of clouds, but cannot
dismiss the possibility for some showers around the Cape and
islands, including Block Island. A west wind direction would
place the greatest risk for any showers across the southern
coastal waters.
Mid level shortwave departs during Monday morning, followed by a
brief period of higher pressure. A nearly stationary front may
sag far enough south to reach portions of southern New England
late Monday into Monday night. Mainly dry with clearing sky once
any lingering morning showers move offshore. High temperatures 
remaining below normal.
A low pressure over the Great Lakes starts to exert more
influence on our weather late Monday Night. Another case of
increasing clouds after midnight, with a risk for some 
precipitation late. Given low temperatures below freezing 
across pretty much all of southern New England, light snow would
be expected over land, with the possibility of some rain over 
the ocean waters. 
Thinking around one inch or less across southern New England
through Monday night. It will all come down to timing. A faster
arrival would give more time for snow to accumulate before
daybreak. Slower timing would mean even less snow. At this
point, the majority of any precipitation from this low pressure
would occur after daybreak Tuesday. Some impact on the Tuesday
morning commute is expected, especially from Worcester county
* Accumulating snow Tue across interior N MA with any snow quickly 
  changing to rain in the coastal plain
* Arctic air and bitter cold wind chills follow Wed/Thu 
* More snow possible sometime Thu night to Fri night
Accumulating snow is the main forecast issue, but latest guidance 
suggests focus for appreciable snow accum will be confined to 
interior northern MA west of I495 and especially the Berkshires.
Amplifying northern stream trough across the Great Lakes will 
eventually become negatively tilted over the northeast. Primary low 
moves into the eastern Lakes while a secondary low is forecast to 
develop across SNE, but not in time to stop southerly low jet from 
advecting milder air north across SNE. Models all indicate rapid 
warming below 850 mb. Any snow early Tue will quickly change to rain 
across northern CT, RI and E MA as low level warming advances north. 
However, there could be an issue with a brief period of freezing 
rain south of the Mass Pike in the interior during the transition 
from snow to rain. 
Further into the interior, especially north of the Pike and west of 
I495, the snow will last through the morning but even here we expect 
an eventual changeover to rain in the afternoon. The exception may 
be across the east slopes of the Berkshires which may remain mostly 
snow. Preliminary snowfall forecast is for 2-5 inches across 
northern Worcester county to the Berkshires and possibly into the 
higher terrain in western Hartford county, but a few locations could 
reach 6 or 7 inches in the Berkshires, where decent omega in the 
snow growth region persists the longest. Any accum across RI and 
eastern MA will likely be limited to less than an inch. Winter 
weather advisories will likely be needed for interior northern MA, 
with a low probability for marginal warnings for the Berkshires. 
Wednesday and Thursday...
Behind the departing low pres, a surge of arctic air will invade the 
region with blustery NW winds as deep upper trough moves through. 
Temps well below normal with highs mostly in the 20s and lower 30s 
near the south coast. The gusty winds will make it feel much colder.
Mainly dry weather during this period, but can't rule out a few 
flurries Wed as the upper low moves across New Eng. 
Thursday night into Friday night...
Another amplifying northern stream trough approaches from the 
west with multiple shortwaves leading to the potential for some 
accumulating snow sometime during this period. However, low 
confidence on timing as models are struggling with resolving 
what will become the dominant shortwave. May have to watch the 
late Fri/Fri night period per ECWMF and EPS ensembles.
Saturday and Sunday...
Mainly cold and dry Sat then moderating temps Sun ahead of next 
upper trough approaching from the west as SW flow develops. 
Milder air may be accompanied by a few rain or snow showers.
Forecaster Confidence Levels...
Low - less than 30 percent. 
Moderate - 30 to 60 percent. 
High - greater than 60 percent.
Short Term /through Monday Night/...
Through Tonight...High confidence. Mainly VFR despite a broken 
deck of mid level cloudiness. Areas of low end VFR west of
KFIT=KORH-KIJD. Brief marginal MVFR conditions in a spot snow 
shower possible late.
Tomorrow...High confidence. Mainly VFR.
Tomorrow Night... High confidence. Mainly VFR, with local MVFR-
IFR possible toward daybreak as SN moves into the region, with 
some RN along the coastal plain.
KBOS Terminal...High confidence in TAF.
KBDL Terminal...High confidence in TAF. 
Outlook /Tuesday through Friday/...
Tuesday: MVFR/IFR conditions with snow changing to rain. 
Windy along the coast with areas gusts to 30 kt. 
Tuesday Night: Mainly VFR, with local MVFR possible. Breezy. 
Slight chance SHSN.
Wednesday: Mainly VFR, with local MVFR possible. Windy with
gusts to 35 kt. 
Wednesday Night: VFR. Windy with gusts 25-35 kt.
Thursday: VFR. Windy with local gusts to 30 kt. 
Thursday Night and Friday: MVFR/IFR conditions possible. Chance
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. 
Gusty west winds gradually diminish Monday afternoon. However,
rough seas will take longer to subside, especially across the
southern coastal waters, where the fetch will be longer. Therefore,
most Small Craft Advisories will continue into tomorrow.
Chance for showers, especially across the southern coastal 
waters tonight into Monday morning, then again late Monday 
Outlook /Tuesday through Friday/...
Tuesday: Low risk for gale force winds eastern waters with 
gusts up to 35 kt. Local rough seas. Rain likely. 
Tuesday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Rough seas up to 9 ft. Local visibility
1 to 3 nm.
Wednesday: Strong 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 15 ft. Local visibility 1 to
3 nm.
Thursday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of rough seas. 
Thursday Night and Friday: Winds less than 25 kt. Local rough 
seas. Chance of snow and rain. Visibility 1 to 3 nm.
MARINE...Small Craft Advisory until 1 PM EST Monday for ANZ231>234-250.
     Small Craft Advisory until 6 PM EST Monday for ANZ235-237.
     Small Craft Advisory until 7 AM EST Monday for ANZ251.
     Small Craft Advisory until midnight EST Monday night for