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Area forecast discussion
National Weather Service Boston/Norton Massachusetts
318 am EDT Thu Jun 20 2019

Synopsis...

Warm and humid air may bring a few showers or thunderstorms today.
Low pressure crossing southern New England tonight will bring more
widespread showers and thunderstorms, some with heavy rain. The low
will move offshore Friday morning followed by drier air in the
afternoon, although a brief shower or thunderstorm is still
possible. Dry and seasonable weather returns for the weekend.
Warmer weather arrives early next week with a few
showers/thunderstorms possible at times, but the majority of the
time will feature dry weather.



&&

Near term /until 6 PM this evening/...

Batch of showers and thunderstorms in eastern PA/New Jersey was lifting
NE early this morning. High-res models want to bring this
activity into southern New England before sunrise and it appears to be taking aim
on CT and South Coast. Airmass over southern New England is more stable so we do
think this activity will weaken as it reaches our area. Other
widely scattered showers should pop up during the day as deeper
moisture remains in place.

Once this activity clears the area later this morning, another round
of showers/storms is expected this afternoon, especially near
Berkshires where models show some limited instability (assuming we
can destabilize behind this morning's showers). Hrrr shows this
nicely with a line of convection in eastern New York 19-20z which could
reach western Massachusetts a couple of hours later. My partner in crime hf
points out that there is even a low risk for strong or perhaps
severe storms near the Berkshires, where there are decent
probabilities in the sig tornados (sref) and Max updraft helicity (href)
progs, although higher probabilities are focused farther SW.

Farther east, S/southeast flow will keep things stable with low clouds and
patchy fog for most of the day. Again, however, expect scattered
showers to pop up as deep moisture remains in place.

Meanwhile, most of the showers/storms today will be focused to our
north, closer to frontal boundary where better dynamics and moisture
convergence are located.

Highs should top out in 70s, warmest in Hartford/Springfield area
while along immediate coastline, temperatures may hold in 60s.
&&

Short term /6 PM this evening through 6 PM Friday/...

Showers will become more widespread later tonight as low pressure
crosses southern New England. Also have potential for thunder with models showing
some MUCAPE. Good setup for locally heavy rain with pwats over 2",
support from both upper and lower level jets, and larger scale lift
from approaching short wave. Forecast soundings show deep moist
profile with warm cloud depth of more than 12kft. Models, including
cams, are in good agreement that focus for heavier rainfall should
be near Berkshires, but there is also possibility that we see a
second axis somewhere near Hartford-Boston corridor.

Rainfall through tonight should average from as little as 0.25 to
0.50" on Cape Cod and the islands, to 0.50 to 1.00" elsewhere, with
as much as 1.50" in western Massachusetts.

Since there is a lot of uncertainty as to where this will occur, we
do not have enough confidence to issue flash flood watches at this
time. Certainly there is the potential for the usual minor urban and
poor drainage flooding. The lowest flash flood guidance values,
around 2"/hour, are located in western Massachusetts.

Interesting setup for Friday. Pattern looks more like something we
see in the cool season as opposed to late June, as models try
to close off 700 mb low which results in banding signature as
surface low heads offshore. With such an anomalously moist
airmass in place, there is once again the potential for a band
of heavy rain Friday morning, most likely in eastern Massachusetts. This
could be accompanied by brief drop in temperature, possibly into
50s before readings recover later in the morning.

Brief burst of 20-30 miles per hour gusts possible as low heads offshore.
Drying works into region Friday afternoon but enough moisture may
linger along with weak surface convergence to help a shower or storm
pop up in the afternoon, again mainly in eastern Massachusetts. Highs recover
into 70s.

&&

Long term /Friday night through Wednesday/...

Highlights...

* dry/seasonable this weekend with the warmer temps on sun

* Summer-like temps early next week with the risk for a few
showers/T-storms, but the majority of the time it will be dry

Details...

Friday night...

Drier air continues to work in behind the departing low pressure
system/cold front. Low temperatures by daybreak Saturday should be
mainly in the middle 50s to the lower 60s.

Saturday and Sunday...

Anomalous closed low over the Canadian Maritimes will result in
mainly a dry/beautiful weekend across southern New England. Its
associated cold pool aloft with 500t near -20c may result in the low
risk for a spot shower or two Sat. However, given dewpoints dropping
into the 40s that would probably be the worst case scenario and not
Worth inserting into the forecast at this point. Highs mainly in the
75 to 80 degree range on Sat and it will be quite breezy. BUFKIT
supporting west to northwest wind gusts of 25 to 35 mph by afternoon
with a very well mixed atmosphere.

The closed upper low lifts further north across the Canadian
Maritimes sun. This will allow for rising height fields and warmer
temperatures on sun. Highs will mainly be between 80 and 85 but
with with less wind then Sat along with continued comfortable
humidity levels.

Monday through Wednesday...

Closed low across the Canadian Maritimes weakens allowing for rising
height fields into southern New England. This should support highs
well up into the 80s for much of the first part of next week /away
from any localized marine influences/. There is the potential for
highs to approach 90 with perhaps the best chance for that on Tue,
but confidence not enough to forecast those readings. That would
depend upon whether we avoid any subtle backdoor cold fronts and we
see enough sunshine, which is quite uncertain this far out.

While it does look like the vast majority of the time will feature
dry weather, a few showers/T-storms will be possible. The main time
frame of concern would be Tue into Wed when an approaching shortwave
trough/frontal boundary may provide a focus for a few showers/T-
storms.

&&

Aviation /07z Thursday through Monday/...
forecaster confidence levels...

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

Short term /through Friday/... moderate confidence.

IFR/LIFR ceilings prevail along with fog, mainly near South
Coast. Showers and a few thunderstorms are possible toward
sunrise, mainly in western Massachusetts and CT. Should only have scattered
showers today before showers and thunderstorms become more
widespread tonight into Friday morning. Conditions gradually
improve to VFR from west to east Friday, although a pop-up shower or
thunderstorm could develop Friday afternoon.

Kbos terminal...moderate confidence in taf. Best chance of
showers is this afternoon and again late tonight, although a
brief shower may occur this morning.

Kbdl terminal...moderate confidence in taf. Brief shower or
storm possible through sunrise, then better chance of
showers/storms later today and tonight.

Outlook /Friday night through Monday/... moderate confidence.

Friday night through Sunday night: VFR. Breezy.

Monday: VFR.

&&

Marine...
forecaster confidence levels...

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

Short term /through Friday/... high confidence.

Light S/southeast winds and flat seas today along with scattered showers at
times. Seas on outer waters south and east of Cape Cod build today
and should reach 5-6 feet tonight and Friday, so small craft
advisories have been posted. Showers and scattered thunderstorms
expected tonight along with areas of fog.

Low pressure exits eastern Massachusetts coast Friday morning. May have brief
burst of 20-25kt gusts during morning, especially on waters north
and east of Cape Cod, before winds subside by early afternoon.

Outlook /Friday night through Monday/...moderate confidence.

Friday night: winds less than 25 kt. Local rough seas. Slight
chance of rain showers.

Saturday through Saturday night: winds less than 25 kt. Areas
of seas approaching 5 ft.

Sunday: low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of seas approaching 5 ft.

Sunday night: winds less than 25 kt. Seas locally approaching
5 ft.

Monday: winds less than 25 kt.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...Small Craft Advisory from 9 PM this evening to 6 PM EDT Friday
for anz254>256.

&&

$$
Synopsis...Frank/jwd

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