Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 231935
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
335 PM EDT Sat Jun 23 2018

.SYNOPSIS...
A warm front will slowly shift north, bringing showers and a
few thunderstorms this afternoon and tonight. Low pressure from
the Great Lakes moves across New England Sunday and will bring
showers and a few thunderstorms, especially during the afternoon
and evening. The activity may linger into Monday. Mainly dry
weather with seasonable temperatures anticipated Tuesday and
Wednesday with a ridge of high pressure in control. Summer heat
and humidity should return by the end of next week as this high
moves east of the region.

&&

.NEAR TERM /THROUGH TONIGHT/...

Tonight...

Radar shows showers upstream in PA. More showers/thunder over
VA. These trend to our area after 00Z and through the first half
of the night.

The first of two shortwaves will move over New England during
that time. This will motivate a warm front to move north of our
area, generating low level lift during passage and bringing
higher dew points/more humidity overnight. PW values remain
elevated, roughly 1.5 to 1.75 inches, which is 1-1.5 sd above
normal. Expect showers and scattered tstms to continue through
the first part of the night. Once the warm front moves through,
expect precip to diminish. Min temps will be near dew point,
roughly mid 50s to lower 60s.

&&

.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...

Another shortwave moves through the flow Sunday and Sunday
night. The shortwave will generate a wave on the warm front,
which then draws the warm front back to the south as a cold
front later in the day and early night. The upper temp field
features a small amount of cold advection, which will cause some
destabilization. The wind and divergence fields are enough to
generate adequate lift Sunday afternoon and early night.

With the high PW values, a few heavy downpours are possible. The
SPC HREF ensemble shows a 70-90 percent chance CAPE reaching
1000 Joules/Kg in Western CT and Western MA Sunday late
aftn/evening. We will mention a chance of strong gusts and
locally heavy downpours.

We will forecast showers and scattered thunder, with the
favored time from midday through evening. Temps in the mixed
layer reach an equiv of 10-12C, so with appreciable heating we
should reach the 70s with the interior in the upper 70s/low 80s.
Dew points will be in the 60s, so expect a warm muggy day. Min
temps Sunday night will be near the dew points, in the 60s.

&&

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

* Mainly dry/seasonable temps with comfortable humidity Tue and Wed
* Summer heat/humidity should return by the end of next week

Details...

Monday...

A vigorous shortwave/cold pool aloft will move across the
Northeast. Much of the 23/00Z guidance suite has come into
better agreement dropping 500 mb temperatures around -20C during
the afternoon and evening. While this should result in decent
lift, the atmospheric column is drying out fairly quickly. Its
looking like a race between the cold pool and moisture. Where
these coincide, scattered showers are expected to develop. At
this time, this appears to be mainly across the eastern half of
MA and points farther NE. This is a delicate balance between
features, and one which could easily change with later
forecasts over the next day or so.

Tuesday...

Mainly dry and pleasant early summer weather with a ridge of high
pressure in control.

Wednesday...

Mainly dry weather to start, with an increasing risk for showers
as a front approaches late in the day.

Thursday and Friday...

A pattern change to more summer-like warmth and humidity
expected as upper level ridging approaches our region. Dry weather
probably dominates much of this time, but a few showers or
thunderstorms cannot be ruled out at times, particularly Friday
with the expected passage of another cold front.

&&

.AVIATION /19Z SATURDAY 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/...High confidence through midday,
then moderate confidence.

Tonight...

Showers and a few thunderstorms developing upstream during the
afternoon will move through the region this evening and early
tonight. Meanwhile a warm front is moving north across the
region, and this is bringing lower cigs. IFR cigs will move
north, covering much of the region by this evening and linger
through the night. Showers will bring brief vsby reductions to
2-4 miles. Vsbys will go even lower in fog along the South
Coast with potential for 1/4 mile vsbys on Nantucket.

Sunday...

IFR cigs/vsbys early, but improving to VFR during the morning.
Low conditions may continue through the morning on the Islands,
but should improve to VFR around midday. Low pressure moves
across New England during the day, swinging a cold front through
the region during the afternoon/evening. This will bring showers
and a few thunderstorms. Overall conditions should be VFR from
midday through evening, but with brief lowering to MVFR during
showers/tstrms.

Sunday night...

Showers/scattered tstms end early. Any low conditions will
improve to VFR overnight. Winds trend NNW overnight bringing
drier air.

KBOS Terminal...High confidence in TAF trends. Moderate
confidence in timing.

KBDL Terminal...High confidence in TAF trends. Moderate
confidence in timing.

Outlook /Monday through Thursday/...Moderate confidence.

Monday: VFR. Breezy. Slight chance SHRA.

Monday Night: VFR. Breezy.

Tuesday through Tuesday Night: VFR.

Wednesday: Mainly VFR, with local MVFR possible. Breezy. 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 Sunday Night/...High confidence.

Tonight...

E-SE winds with gusts, but generally below 20 knots. Winds
become light with variable directions tonight. The outer edge of
the southern waters shows 5 foot seas. Showers and scattered
thunderstorms will swing across from the Mid Atlantic states
early tonight, then move off to the east after midnight.
Expect areas of fog with visibility 2 miles or less.

Sunday...

Winds shift out of the southwest during the day but remain
light. Seas will mostly be less than 5 feet, except for seas at
5 feet on the outer part of the southern outer waters. Much of
this is from a 5-6 foot swell south of our waters. Visibility 1
to 3 miles early in fog, improving by midday. Expect a chance
of showers and scattered thunderstorms, mostly during the
afternoon.

Sunday night...

Winds less than 25 knots, and seas mostly less than 5 feet.
Some lingering 5 foot seas in the southern part of our southern
waters. A cold front will move south across the waters early in
the night, and may continue to generate showers and a chance of
a thunderstorm. This should move out to sea overnight.

Outlook /Monday through Thursday/...Moderate confidence.

Monday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of seas approaching 5 ft. Slight chance of rain
showers.

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

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

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 2 AM to 6 PM EDT Sunday for
     ANZ254>256.

&&

$$
SYNOPSIS...WTB/Belk
NEAR TERM...WTB
SHORT TERM...WTB
LONG TERM...Belk
AVIATION...WTB/Belk
MARINE...WTB/Belk


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