Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 211503
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
1003 AM EST Sun Jan 21 2018

.SYNOPSIS...
A fast moving storm system will bring a period of heavy rain to
southern New England Tuesday along with strong winds on the
coast. This storm will be preceded by some mixed wintry precip
Monday and a risk of light icing across the interior Monday
night into early Tuesday morning. Blustery, dry and colder
weather follows Wednesday through Friday, before above normal
temperatures likely return next weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

High thin clouds across the region with a few thicker spots. Low
clouds show up over Northern VT and NH, but a westerly flow
should keep that to our north. Also low clouds over lower
Michigan, but the pattern generating those will remain well to
our west this afternoon. High pressure centered off the SE USA
coast will remain in place with dry weather in Southern New
England through the rest of the day, along with varying amounts
of filtered sunshine through the high clouds.

Temps at 950 mb this morning were between 0C and 5C, which
supports max sfc temps in the 40s.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
Tonight...
Clouds will be on the increase as a warm front starts to push
NE toward the region this evening as low pressure will push out
of the mid Mississippi valley toward the Great Lakes overnight.
Will remain in a general W flow aloft, but will start to turn to
a more SW flow toward daybreak.

Leading edge of the overrunning precip may approach overnight,
but precip may hold off for most areas until Monday. However,
could see some light precip reach into western areas and,
depending upon the low level temp profile, could see a wintry
mix at the onset as colder air damming sets up there. This may
occur around the start of the early morning commute in the
Hartford/Springfield area and along the I-91 corridor. Expect
temps to fall back to the mid-upper 20s from N Mass down the CT
valley, ranging to 30-35 across RI and SE Mass.

Monday...
With high pressure remaining across central Quebec, cold air
may continue push down across the interior through the mid to
late morning hours (at least). So, will see a mix of snow, sleet
and possibly some freezing rain as the precip pushes NE during
the morning.

Some question how quickly the temps will rise above freezing,
though it does look like it should be relatively quick as winds
shift to SE-S by around midday or so. The high should remain
well N of the region, allowing for slowly rising temps during
the day.

Looks like the biggest threat for a mix of snow and freezing
rain for most of the day will be along the Route 2 corridor of
N Mass. Expecting light QPF amounts, generally less than 0.1
inches, but the potential of lingering light freezing rain
across northern areas and the higher terrain will be a big
concern.

May see some precip taper off across south coastal areas toward
evening as the warm front lifts into central New England.

Expect temps to reach near seasonal levels for highs on Monday,
at least for now.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Highlights...

* Light icing risk Mon night across interior MA high terrain
* Heavy rain Tue with a period of strong winds SE New Eng
* Significant flooding issues are not expected Tuesday
* Dry/blustery and turning colder Wed and especially Thu/Fri

Monday night...

Main concern for Mon night continues to be a risk of light
icing over portions of the interior. Precip expected to be light
as some mid level drying moves in while best forcing remains to
the west. In fact, ice crystal growth region is drying which
suggests more in the way of drizzle. There is a cold air damming
signature with sfc ridging nosing down from the NE with low
level northerly ageostrophic flow. Leaned toward 3km NAM for
temps as higher resolution datasets should better capture
localized cold air damming and it targets higher terrain in
western and northern MA for near freezing temps, possibly down
to higher elevations in NW Hartford county. This is where the
greatest threat of some light freezing rain/drizzle exists with
potential for a light icing event. This also is supported by hi-
res ECMWF temps. Icy roads and walkways certainly a possibility
Mon night over the higher elevations.

Tuesday...

Potential for some light freezing rain lingering over higher
terrain on MA early, otherwise it`s all rain. Decent heavy rain
signal for Tue with PWAT anomaly +2SD and low level wind anomaly
up to +3SD. In addition, elevated instability at the nose of
the low level jet will likely result in some convective elements
with an isold t-storm possible. An area of heavy rain along the
pre-frontal low level jet will move west to east across SNE
with rain exiting the coast around evening. System is
progressive which should limit window of moderate to heavy
rainfall to about 6 hours. Rainfall amounts of 0.75 to 1.50
inches still looks reasonable with heaviest amounts in western
New Eng. Given that most of the rain will probably fall in a 6
hour window, expect typical minor urban and poor drainage street
flooding, but river flooding is not anticipated.

The other concern is a period of strong winds across RI and
eastern MA as 65-70 kt low level jet moves up along the coastal
plain. Low level lapse rates are near moist adiabatic which will
allow for some mixing, especially where temps climb into the
mid 50s across RI and SE MA and in the vicinity of any heavier
convective elements. In addition, models indicate impressive
pressure falls on the order of 9 mb in 3 hours which will
enhance isallobaric component of the wind. Potential exists for
wind gusts up to 50 mph for a few hours in the afternoon across
RI and SE MA. CIPS analogs also support this with fairly decent
probs of 40+ kts across SE MA.

Wednesday through Friday...

Turning colder and blustery behind the storm with brisk NW
flow. Temps near normal Wed, then trending below normal Thu/Fri
as core of coldest air aloft settles over the region. Decent
shot of cold air with -15C at 850 mb into SNE on Thu. Highs
likely in the 20s Thu and blustery winds will make it feel
considerably colder. Wind chills Thu night/early Fri morning
dropping into the single numbers with subzero wind chills over
higher terrain. Looks mainly dry during this period.

Saturday...

High pres moves off the coast with SE CONUS ridge building
north into New Eng leading to a moderating trend with above
normal temps likely. Dry weather.

&&

.AVIATION /15Z SUNDAY THROUGH THURSDAY/...
Forecaster Confidence Levels...

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

Short Term /through Monday/...

This afternoon...High confidence. VFR. W-NW winds around 10 kt
or less as pressure gradient relaxes.

Tonight...Moderate confidence in general trends, lower in timing
arrival of precip. Mainly VFR through midnight, then MVFR-IFR
CIGS move into central and western areas. Expect mixed
snow/sleet/freezing rain and patchy fog to move into the CT
valley during the early morning commute.

Monday...Moderate confidence.
MVFR CIGS lower to IFR by around midday, with LIFR across
southern areas in the afternoon. VSBYS lower to MVFR-IFR by
midday. Mixed -SN/-PE/-FZRA to start, then changes to -RA near
and S of the Mass Pike by midday, with mixed -RA/-SN across N
Mass. May see a mix with -FZRA toward sunset along the N Mass
border. Light/variable wind becomes E-SE during the day.

KBOS Terminal...Moderate to high confidence in TAF.

KBDL Terminal...Moderate to high confidence in TAF.

Outlook /Monday Night through Thursday/...

Monday Night: Mainly MVFR, with areas IFR possible. RA likely,
chance FZRA interior northern MA.

Tuesday: Mainly MVFR, with local IFR possible. Strong winds
with gusts to 40 kt RI and SE MA. RA. Pockets of FZRA early
interior northern MA.

Tuesday Night: Mainly VFR, with local MVFR possible. Windy with
gusts to 30 kt. Slight chance SHRA.

Wednesday: VFR. Windy with gusts to 30 kt.

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

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Monday/...High confidence.

This afternoon... W-NW winds diminish as high pressure passes S
of New England. Seas will also continue to subside.

Tonight...
Light and variable winds eventually shift to S-SW toward
daybreak as low pressure remains well W of the waters. Seas
remain below 5 ft. Some visibility restrictions across the
western waters toward daybreak as light rain moves in.

Monday...
Expect E-SE winds to increase during the afternoon, up to 10-15
kt with some gusts to 20 kt. Seas will build up to 3 ft on the
eastern outer waters late in the day. Visibility lowers to 1-3
NM by mid to late morning in rain along with a brief mix with
snow on the eastern waters.

Outlook /Monday Night through Thursday/...

Monday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain.

Tuesday: Low risk for gale force winds with gusts up to 40 kt.
Rough seas up to 13 ft. Rain.

Tuesday Night: Low risk for gale force winds with gusts up to
35 kt. Rough seas up to 10 ft. Chance of rain showers.

Wednesday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 10 ft.

Wednesday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Areas of rough seas.

Thursday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 10 ft.

&&

.HYDROLOGY...
A Flood Warning remains in effect for the Connecticut River at
Middle Haddam, where ice jams are causing river fluctuations.

Received new data from NERFC late Saturday night, so updated
the Flood Statement to provide the latest information. Not too
much change from the previous forecast.

For details on specific area rivers, including observed and
forecast river stages, please visit the Advanced Hydrologic
Prediction Service (AHPS) graphs on our website.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$
SYNOPSIS...KJC/EVT
NEAR TERM...WTB/EVT
SHORT TERM...EVT
LONG TERM...KJC
AVIATION...WTB/KJC/EVT
MARINE...WTB/KJC/EVT
HYDROLOGY...


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