Area Forecast Discussion
Issued by NWS Boston, MA

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348
FXUS61 KBOX 200222
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1022 PM EDT Tue Jun 19 2018

.SYNOPSIS...
Dry weather is expected tonight and Wednesday as high pressure
builds over New England. Showers are likely Wednesday night,
especially south of the Mass Pike, as low pressure passes
offshore. High pressure from Canada brings dry weather
Thursday and Friday. A cold front them brings a chance of
showers over the weekend, followed by dry weather early next
week.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
10 PM UPDATE...
High clouds are spilling into the region moving SE, stretching
from the Berkshires to the RI coast. Clouds will continue to
move into the area, likely becoming more widespread over the
next couple hours.

Lowered min temps for tonight given that we should stay mostly
clear overnight and sites will have the chance to radiate across
the region. Temps in the upper 40s are possible tonight,
especially in upper Connecticut River Valley along the 495
corridor.

Otherwise, previous forecast remains on track.

Previous Discussion...
Any lingering diurnal clouds will dissipate toward sunset,
giving way to clear skies and diminishing winds tonight. This
will allow for good radiational cooling away from coast. Sided
closer to cooler MOS guidance which gives lows in upper 40s to
mid 50s. Airmass remains dry enough to preclude mention of
patchy fog.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
High pressure over SNE heads offshore in afternoon, resulting in
S/SW flow across region. Airmass remains dry as seen in model cross
sections so just expect some diurnal clouds to form, but overall
plenty of sunshine. Highs should run a few degrees cooler than
today, ranging from mid 70s on South Coast, Cape, and Islands to the
mid 80s inland.

Models in good agreement on arrival of showers Wednesday night as
short wave passes and weak surface low pass south of New England.
Main issue is how far north do the showers extend into SNE. Right
now we are most confident for CT, RI, and SE MA which come under
influence of best theta-e advection and lower level convergence/
moisture transport. Blended in high-res ARW WRF which gives as much
as 0.50 to 0.75" of rain. Farther north, it will be a battle with
dry air pushing down from northern New England, so it`s possible
areas along and north of Mass Pike remain dry.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Highlights...

* Lingering showers, south coast on Thursday
* Dry and seasonable on Friday
* Unsettled weather for the weekend

Overview...

12z models show good agreement with the flow pattern evolution
during the long term increasing forecaster confidence. Northern
stream flow will feature a persistent upper ridge over central
Canada with a couple of frontal waves moving across the central U.S.
New England will remain on the edge of an upper level trough over
the Maritimes keeping the region in northwest flow. Passing wave
from the Midwest will impact southern New England over the weekend
before northwest flow returns for next week. As an FYI, the Canadian
model indicates the formation of a nor`easter early next week but
this is not supported by its own ensemble mean nor the GFS and ECMWF
solutions.

Details...

A few lingering showers on Thursday morning thanks to passing wave
to the south. Conditions will improve in the afternoon with
seasonable temperatures. High pressure on Friday will lead to dry
weather and temperatures near normal. Sea breeze potential possible.

Unsettled weather returns for the weekend as a low pressure from the
Great Lakes passing through northern New England. Associated warm
and cold front will sweep through resulting in a warm frontal
showers on Saturday followed by showers and thunderstorms on Sunday
with approaching cold front from the west. Still some timing issues
but appears precip will impact this upcoming weekend, luckily not a
washout.

Canadian high pressure will move in behind the front on Monday
lasting into the work week resulting in dry weather.

&&

.AVIATION /02Z WEDNESDAY 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/... High confidence.

VFR. N/NW winds gust to 20-25 kt through late afternoon before
diminishing and becoming light/variable tonight. SW winds
prevail Wednesday and Wednesday night. Showers likely across CT,
RI, and SE MA Wednesday night with areas of MVFR or perhaps IFR
ceilings.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Thursday through Sunday/...Moderate confidence.

Thursday through Friday Night: VFR.

Saturday: Mainly VFR, with local MVFR possible. Chance SHRA.

Saturday Night: Mainly VFR, with areas IFR possible. Chance
SHRA, isolated TSRA.

Sunday: Mainly VFR, with local MVFR possible. Chance SHRA,
isolated TSRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Wednesday Night/...

High confidence.

Diminishing N/NE winds and seas tonight as high pressure builds over
SNE. SW flow develops Wednesday and Wednesday night as the high
becomes centered offshore. Winds and seas remain below 25 kt and 5
ft respectively, but recreational boaters should be aware of 15-20
kt gusts and locally choppy seas of 2 or 3 ft on Narragansett Bay
and south coastal sounds Wednesday afternoon.

Reduced visibility in showers and patchy fog Wednesday night,
especially on south coastal waters.

Outlook /Thursday through Sunday/...Moderate confidence.

Thursday: Winds less than 25 kt. Slight chance of rain showers,
patchy fog.

Thursday Night through Friday Night: Winds less than 25 kt.

Saturday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain showers.

Saturday Night: Winds less than 25 kt. Local rough seas. Chance
of rain showers, isolated thunderstorms.

Sunday: Winds less than 25 kt. Areas of rough seas. Chance of
rain showers, isolated thunderstorms.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$
SYNOPSIS...Dunten/JWD
NEAR TERM...Correia/JWD
SHORT TERM...JWD
LONG TERM...Dunten
AVIATION...Dunten/Correia/JWD
MARINE...Belk/Dunten/JWD



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