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Area forecast discussion
National Weather Service Boston/Norton Massachusetts
733 am EDT Sat Jun 23 2018

Synopsis...
high pressure will slowly push east of the region this morning.
Low pressure and an associated warm front will slowly shift
north, bringing showers and a few thunderstorms through tonight.
Another weak disturbance may bring scattered showers and a few
thunderstorms during Sunday. 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 /until 6 PM this evening/...

Increased rainfall chances for the next 12 hrs based on the
latest runs of the hrrr. Regional radars showing rain right on
the doorstep for some portions of southern New England already.
Still not thinking it will rain all the time over the next 12
hours, just that there is a greater risk for measurable rainfall
during that window. Temperatures are not likely to increase
much during today, which previous forecast handled well.
Otherwise, just brought the forecast back in line with observed
trends.

Previous discussion...

A band of showers across central and western areas at 08z will
push NE this morning, with another band moving toward the region
in the SW flow aloft.

Weak low pressure across the central Great Lakes with a warm
front extending east to southern New Jersey will shift slow north during the
day as the ridge across the region shifts east to the Maritimes.
00z model suite signaling that the cutoff low associated with
the surface feature will flatten out during the day. Leftover
mid level energy will trigger the development of more showers
through the day.

Noting good instability, with k indices in the mid-upper 30s,
tq values in the upper teens and slis below zero. The cool ocean
waters may limit the convection, but have put in isolated
thunder. Precipitable water moisture plume works up the coast as well, up to
1.9 to 2 inches across most of the region, so could also see
some locally heavy rainfall.

With the onshore flow in place and the cloud cover, temps will
only rise to the 60s.

&&

Short term /6 PM this evening through 6 PM Sunday/...
tonight...

Will see showers through most of the night as another weak low
moves across along the warm front that tries to push toward the
S coast. Another weak wave may move along the front through
around midnight, which could be a trigger for a few more
thunderstorms along with locally heavy rainfall.

Drier air moves east after midnight as the precipitable water moisture plume
moves offshore. With the high moisture in place, fog will
redevelop, locally dense at times along portions of the S coast,
Cape Cod and the islands. Winds will shift to west-SW as the low
moves to the Gulf of Maine. Temps will bottom out from the mid
50s to around 60.

Sunday...

Another weak 500 mb low will move east out of New York state, which could be
another trigger for convection to develop from mid morning
through the afternoon. Looks like the best shot for
showers/isold thunder will occur across the interior where
likely pops are in place, with chance pops for most of the coastal
plain. With dewpoints in the lower-mid 60s, expect a mild and
muggy day. Highs will be close to seasonal normals.

&&

Long term /Sunday night through Friday/...
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
Massachusetts 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 /12z Saturday through Wednesday/...
forecaster confidence levels...

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

Short term /through Sunday/...high confidence through midday,
then moderate confidence.

Today...bands of rain showers across the region, with isolated thunderstorms and rain and
locally heavy rainfall. Expect conditions to lower to MVFR-IFR
across the region, then mainly IFR-LIFR ceilings/visibilities with lowest
conditions across S Rhode Island/S coastal mass.

Tonight...mainly IFR with some LIFR conditions in areas of
showers and fog. Isolated thunderstorms and rain and locally heavy rainfall.

Sunday...IFR conditions early improving to VFR by midday. Local
MVFR ceilings/visibilities may develop across the interior with the best
chance for showers/isold thunderstorms and rain. Scattered rain showers and a few thunderstorms and rain
across most of the coastal plain.

Kbos terminal...high confidence in taf trends. Moderate
confidence in timing.

Kbdl terminal...high confidence in taf trends. Moderate
confidence in timing.

Outlook /Sunday night through Wednesday/...moderate confidence.

Sunday: mainly VFR, with local IFR possible. Chance shra,
isolated thunderstorms and rain.

Sunday night: mainly VFR, with local MVFR possible. Chance
shra, slight chance tsra, patchy br.

Monday: VFR. Breezy. Slight chance rain showers.

Monday night: VFR. Breezy.

Tuesday through Tuesday night: VFR.

Wednesday: mainly VFR, with local MVFR possible. Breezy. Slight
chance rain showers.

&&

Marine...
forecaster confidence levels...

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

Short term /through Sunday/...high confidence.

Today...S-se winds will back to east during the day. May see a few
gusts approaching 25 kt across portions of the waters around
midday. Visibility will lower in showers and areas of fog, below
1 nm across the waters east and S of Cape Cod by evening. Showers
moving in from S-N, with isolated thunderstorms from late
morning through the afternoon.

Tonight...E-se winds gusting up to around 20 kt, shift to west-SW
after midnight. Seas up to 5 ft on the southern outer waters,
where small craft advisories have been issued. Areas of fog with
visibility 2 nm or less, at or below 1 nm on the southern
waters. Showers likely with isolated thunder, which should shift
east after midnight.

Sunday...W-NW winds 10-15 kt shift to S-SW during the day. Seas
remain around 5 ft on the southern outer waters. Visibility 1 to 3
nm early, improving by midday.

Outlook /Sunday night through Wednesday/...moderate confidence.

Sunday: winds less than 25 kt. Areas of seas approaching 5 ft.
Slight chance of rain showers, isolated thunderstorms, patchy
fog. Local visibility 1 nm or less.

Sunday night: winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain showers, isolated thunderstorms, patchy
fog. Local visibility 1 to 3 nm.

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.
Massachusetts...none.
Rhode Island...none.
Marine...Small Craft Advisory from 2 am to 6 PM EDT Sunday for
anz254>256.

&&

$$
Synopsis...Belk/evt

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