NWS Forecast Discussion - Boston Area

Forecast Discussion for BOX NWS Office
000
FXUS61 KBOX 181958
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
358 PM EDT Tue Sep 18 2018

.SYNOPSIS...
Showers and thunderstorms exit the south coast early this
evening followed by a drying trend and slightly cooler less
humid air behind the frontal passage. Northeast winds bring low
clouds, spotty light rain/drizzle and patchy fog Wednesday
morning which slowly gives way to breaks of afternoon sunshine
from west to east. High pressure builds into New England Wed
night and Thu yielding dry cool weather. Warmer Friday ahead of
an approaching cold front then turning cooler over the weekend
as high pressure builds into the area from the Great lakes.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...

4 PM Update...

Showers and T-storms associated with frontal boundary now along the
south coast at 330 pm. Front is progressive so convection will move
offshore shortly.  However not much of an airmass change with the
wind shift behind this frontal boundary. Dew pts still 65-70
northward into central New England. Thus patchy fog possible
overnight especially given amount of standing water still exist
especially in areas that experienced 5-6 inches of rain in Worcester
and Middlesex counties (see PNS for details).

Despite rain ending across much of the region will continue with
Flood headlines as rivers and streams continue to rise and may be
issuing river flood warnings in the very near future.

Later tonight and especially toward morning low pressure develops on
the departing front south of New England. This enhances the NE winds
across the region especially over eastern MA. Much of the model
guidance has some spotty low top showers and/or drizzle and fog
developing in this NE flow from the Gulf of Maine late tonight over
eastern MA, possibly into RI as well.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...

Wednesday...

As frontal wave south of New England strengthens northeast flow
increase across the area during the morning. Much of the guidance
has low clouds and low top showers and/or spotty drizzle and patchy
fog in this flow off the Gulf of Maine especially into RI and
eastern MA. Clouds may struggle to get into the CT river valley so
at least partial sunshine may prevail here along with milder
temperatures of 70-75.

NE winds increasing up to around 25 mph will result in a cooler and
breezy day across Cape Cod and Islands.

However as heights rise during the afternoon temps warm aloft and NE
winds ease as ocean low tracks farther offshore, breaks of sunshine
should develop all areas from west to east during the afternoon,
perhaps waiting until just before sunset across the Cape and
Islands.

Turning less humid with dew pts eventually falling into the upper
50s late in the day.

Wednesday night...

Dry along with partial clearing as 1024 mb surface high over the
maritimes builds southward into New England. Cooler with dew pts in
the 50s. Given light winds, drier airmass and at least partly cloudy
have leaned toward the cooler MOS guidance for mins.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...

Highlights...

* Fast wind flow aloft will bring changeable conditions into
  next weekend
* A warm front pushes north Thu night, followed by a cold front
  late Fri night into early Sat
* Below normal temperatures through mid week, then briefly mild
  late week before a return to cool readings

Overview...

H5 short wave will push E through around midday Wednesday.
There may be a few leftover showers or some spotty drizzle
during the morning, then conditions should improve though it
will remain cool with a gusty northeasterly wind. Mid level
ridging builds across the Great Lakes into south central
Canada, keeping a general W-NW steering flow in place across
the northeast through most of this period. High pressure builds
across through mid week, bringing dry conditions but a
persistent onshore wind flow that will keep temperatures below
normal.

A short wave rides eastward in the fast flow aloft by late this
week, with a warm front approaching Thu night into Fri. A few
showers may push into NW Mass Thu night with the front, but most
of the precip looks to remain out of the region. Winds will
shift to southerly by around daybreak Friday. Dewpoints will
increase as well, so there could be some patchy fog developing
during the early morning hours Fri. Will see mild temps, with
readings topping off in the 70-75 degree range Fri afternoon.
However, with the mid level ridge pushing across the region,
will see another cold front approach Fri night, bringing
scattered showers and possibly a few thunderstorms.

The front pushes offshore Sat morning, with another large high
building out of central Canada. This will bring another shot of
dry but cool conditions through the upcoming weekend into early
next week.

&&

.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels...

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

Short Term /through Wednesday Night/...

18z update...

Thru 00z...moderate confidence.

Line of showers and T-storms across southern RI and southeast MA
moves offshore 21z-23z with wind shift from SSW to NNE. Across
CT and western MA MVFR trending VFR while in the east across RI
and eastern MA. IFR trending MVFR.

Tonight...Moderate confidence.

VFR CT and western-central MA but MVFR-IFR stubborn to exit RI
and eastern MA. Drying trend this evening but low top showers,
drizzle and patchy fog may develop across eastern MA possibly
into RI late tonight as NE winds increase.

Wednesday...moderate confidence.

VFR western CT/MA, MVFR-IFR across RI and eastern MA in low
clouds, drizzle, patchy fog and few low top showers. However
conditions lift/improve in the afternoon to MVFR-VFR all
terminals.

Wednesday night...moderate confidence.

VFR but trending toward MVFR in lower clouds and areas of fog
late.

KBOS Terminal...improving trends this evening but later tonight
toward sunrise Wed low clouds, drizzle, patchy fog and few low
top showers may come onshore in NE flow.

KBDL Terminal...Improving trend this evening and overnight with
VFR Wed and dry runways.

Outlook /Thursday through Sunday/...

Thursday: Mainly VFR, with local MVFR possible. Breezy.

Thursday Night through Friday: Mainly VFR, with local MVFR
possible. Breezy. Slight chance SHRA.

Friday Night: Mainly VFR, with local MVFR possible. Breezy.
Slight chance SHRA, isolated TSRA.

Saturday: VFR. Breezy.

Saturday Night: VFR.

Sunday: VFR. Slight chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Wednesday Night/...

Tonight...

Frontal boundary slips north to south across the New England waters
with wind shift from SSW to NNE. Toward morning NNE winds 15-20 kt
with gusts up to 25 kt are possible. Shower and T-storms with
torrential downpours early this evening before exiting. Vsby may
lower late in patchy fog and drizzle especially eastern MA waters.

Wednesday...

NNE winds 15-20 kt with gusts up to 25 kt especially eastern and
southern waters of MA. Vsby may lower in spotty light rain/drizzle
and patchy fog in the morning but improving in the afternoon.

Wed night...

1024 mb high over Maritimes builds southward into New England
resulting in diminishing winds and seas. Vsby should be good.

Outlook /Thursday through Sunday/...

Thursday: Winds less than 25 kt. Local rough seas.

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

Friday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Seas up to 5 ft.

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

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

Saturday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft.

Sunday: Winds less than 25 kt. Seas locally approaching 5 ft.
Slight chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Flash Flood Watch until 2 AM EDT Wednesday for CTZ004.
MA...Flash Flood Watch until 2 AM EDT Wednesday for MAZ005>007-
     012>019-026.
RI...Flash Flood Watch until 2 AM EDT Wednesday for RIZ001>004.
MARINE...Small Craft Advisory until 8 AM EDT Wednesday for ANZ231>235-
     237.
     Small Craft Advisory from 6 AM to 6 PM EDT Wednesday for
     ANZ250.
     Small Craft Advisory until 6 PM EDT Wednesday for ANZ254>256.

&&

$$
SYNOPSIS...Nocera
NEAR TERM...Nocera
SHORT TERM...Nocera
LONG TERM...EVT
AVIATION...Nocera/EVT
MARINE...Nocera/EVT

NWS BOX Office Area Forecast Discussion