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Area forecast discussion
National Weather Service Taunton Massachusetts
1054 PM EST Sat Jan 20 2018

Synopsis...
a fast moving storm system will bring the potential for heavy
rain and a period of strong winds on the coast Tuesday, but this
will be preceded by a risk of a light wintry mix/ice across the
interior Monday 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 am Sunday morning/...

1020 PM update...

Streams of high clouds continue to push across the region as
seen on latest GOES-16 nighttime microphysics rgb composite and
fog imagery has show. A nearly zonal wind flow remains in place
tonight as low pres moves across the Maritimes and west-east elongated
high pressure remains across the southeast states.

Even with the high clouds in place, temps have been falling
steadily across some of the colder inland valley spots with
light/variable or calm winds, while readings were milder toward
the coastal plain. Temps ranged from the upper 20s to mid 30s
across the CT valley and NE CT/north central mass, up to around 40
from central and S Rhode Island to Cape Cod and the islands at 03z.

Expect light/variable (mainly west-nw) winds to continue through
the remainder of the night. Not many changes to the previous
forecast, though updated to bring conditions current. Temps
should bottom out in the 20-25 degree range across the normally
colder valley locations up to 30-35 along the immediate coast.

&&

Short term /6 am Sunday morning through Sunday night/...

High pressure in place Sunday with fair skies and light wind.
Moisture fields do show some increasing mid and high level moisture,
so expect some increasing clouds mostly in the afternoon/evening.
With mixing to 950 mb, expect Max temps in the mid to upper 40s, a
few spots around 50.

The clouds increase Sunday night. A cold front in northern New
England dips south and may slip through southern New England. But
with the upper flow west-east we do not expect a lot of push to it,
and potential that it stalls either over or near US. The net change
in the airmass is nil, so min temps Sunday night should be similar
to tonight.

Low level southerly winds reach only to western New York/PA by 12z
Monday...still west winds over US at that time...which means little
lift to be generated Sunday night. So the probability of precip
should be low. If the precipitation were to move in faster,
low level temperatures would support a mix with sleet and
freezing rain. But that scenario looks unlikely at this time.

Our forecast shows slight chance pops in western Massachusetts/CT by 12z
Monday, and that may be overplaying the likelihood.

&&

Long term /Monday through Saturday/...
highlights...

* light icing risk Mon/early Tue across interior W/focus high terrain

* heavy rain Tue with a period of strong winds possible on the coast

* significant flooding issues are not expected Tuesday

* dry/blustery but turning colder Wed and especially by Thu/Fri

Details...

Monday and Monday night...

Main concern Mon into Mon night will be the potential for a period of
light icing across parts of interior southern New England with
the main focus being the Worcester Hills and east slopes of the
Berkshires.

A cold air damming pattern appears to be setting up with Canadian high
pressure in place. Meanwhile...enough warm advection aloft
should result in light precipitation breaking out across the
region. Timing uncertain...but potential increases Monday
afternoon and night although can not rule out some light
precipitation arriving Monday morning. The bulk of the
precipitation that falls into Monday night should be light as
stronger synoptic scale forcing/deeper moisture will remain to
our west. Mainly just light rain showers expected on the coastal
plain. The focus will be across interior southern New England
with the main area of concern the high terrain of the Worcester
Hills and east slopes of the Berkshires. Some very minor light
snow/sleet accums are possible at the onset, but main issue will
be light freezing rain/light icing potential.

How much of the interior is impacted by a period of icing remains
uncertain. Most of the guidance indicates the surface high
fairly far north in Canada and it is not really nosing down into
southern New England. Plus the fact that were dealing with an
unseasonably mild airmass currently in place for January that
needs to depart. Therefore...the main concern will be the high
terrain of the northern Worcester Hills and east slopes of the
Berkshires. Temps likely to be a few degrees colder in this
region and most of the high resolution guidance including the
sref probabilities is targeting this region for the potential of
light icing. Icy roads and walkways certainly a possibility
especially later Monday into Monday night.

Tuesday...

The main surface low will be lifting across the Great Lakes. This
will induce a southerly low level jet 3+ Standard deviations above normal
with pwats 2+ above normal. While some lingering freezing rain
can not be ruled out across the high terrain of Massachusetts early Tue
am, any left over ice should change to rain. The main story will
then be a period of heavy rain given the anomalous ingredients
in place. As previous forecaster mentioned...there may even be
an isolated T-storm or two as showalter indices drop below zero.

In addition...potent southerly low level jet may result in a
period of 40 to 50 mph wind gusts along the coastal plain. This
is especially true if high temps climb well into the 50s and
any convective elements are able to tap the stronger winds
aloft.

The fortunate thing is this system looks fairly progressive...so
most of the heavy rain will be ending Tuesday evening. Rainfall
amounts on the order of 0.75 to 1.50 inches seem
reasonable...which may lead to typical nuisance/poor drainage
street given much of this probably falls in a 6 hour period.
However, the northeast river forecast center indicates that
while a few rivers may rise to action stage they are not
expecting any significant problems.

Wednesday through Friday...

Transient trough sets up over the northeast allowing
colder weather to work back into the region...but it should be
dry as high pressure builds in from the west. High temps Wed
will be well up into the 30s to the lower 40s on the coastal plain
although a bit windy. Colder Thu and Fri with highs mainly in
the upper 20s to the lower 30s.

Saturday...

The high pressure system moves off the coast which should allow a
return flow of milder air into the region. Above normal temps
look to return and right now it looks like any forcing/deeper
moisture will be to the west of our region. Therefore...will
maintain a dry forecast for the first part of next weekend.

&&

Aviation /04z Sunday through Thursday/...
forecaster confidence levels...

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

Short term /through Sunday night/...

Overnight...high confidence. VFR with just a low risk of
marginal MVFR cigs near daybreak across far western Massachusetts.

Sunday...high confidence. VFR. West-northwest winds around 10 kt or less
as pressure gradient relaxes.

Sunday night... moderate confidence.

VFR. Increasing sky cover late at night.

Kbos terminal...high confidence in taf.

Kbdl terminal...high confidence in taf.

Outlook /Monday through Thursday/...

Monday: MVFR/IFR conditions possible. Chance -shra, chance -fzra
across the interior high terrain.

Monday night: mainly MVFR, with areas IFR possible. Breezy.
-Shra. Pockets of -fzra possible across the interior with the
focus in the high terrain of Massachusetts.

Tuesday: MVFR/IFR conditions possible. Strong winds with gusts
to 40 kt. Rain.

Tuesday night: mainly VFR, with local MVFR possible. Windy with
local gusts to 30 kt. Slight chance rain showers.

Wednesday through Wednesday night: VFR. Windy with gusts to
35 kt.

Thursday: VFR. Windy with 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 Sunday night/...high confidence.

Overnight...

Winds have diminished below small craft levels across the near
shore waters so the Small Craft Advisory ended at 10 PM. Still
noting some gusts up to 20-25 kt and seas up to 5-6 ft over the
open waters which will subside through the remainder of the
night.

Sunday and Sunday night...

High pressure over the waters should provide fair weather with light
winds and seas below 5 feet. Clouds will increase overnight, but
support for any precipitation will remain well to our west during
the night.

Outlook /Monday through Thursday/...

Monday: winds less than 25 kt. Chance of rain showers.

Monday night: winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain showers.

Tuesday: risk for gale force winds with gusts up to 40 kt.
Rough seas up to 12 ft. Rain. Areas of visibility 1 to 3 nm.

Tuesday night: risk for gale force winds with gusts up to 35
kt. Rough seas up to 11 ft. Chance of rain showers.

Wednesday: moderate risk for gale force winds with gusts up to
35 kt. Areas of rough seas.

Wednesday night: low risk for gale force winds with gusts up to
35 kt. Areas of rough seas. Freezing spray.

Thursday: moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Local rough seas. Freezing spray.

&&

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 tonight 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.
Massachusetts...none.
Rhode Island...none.
Marine...Small Craft Advisory until 6 am EST Sunday for anz250-254>256.

&&

$$
Synopsis...wtb/Frank
near term...Frank/evt

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