Area Forecast Discussion
Issued by NWS Boston, MA

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972
FXUS61 KBOX 250742
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
342 AM EDT Sat May 25 2019

.SYNOPSIS...
High pressure in control today with seasonably warm conditions.
A fast moving disturbance will bring a period of showers and
perhaps a few embedded thunderstorms tonight. The rest of the
holiday weekend looks warm and dry with just a low risk of an
isolated shower or thunderstorm Sunday afternoon. Showers and
cooler temperatures return Tuesday ahead of a warm front
approaching from the south. Scattered showers and storms are
expected Thursday as a cold front crosses the region.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
High pres in control today as it shifts south of New Eng with SW
flow developing. Expect lots of sunshine today, although some
increase in mid/high clouds during the afternoon ahead of next
shortwave. Highs should reach well into the mid 70s with light
winds for most locations, but developing sea breezes will hold
temps in the upper 60s along the immediate coast.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
Tonight...

A fast moving shortwave from the Gt Lakes will pass to the north
late tonight. Models all indicate a developing low level jet
tonight which will bring a decent instability burst as low
level theta-e ridge and increasing KI moves into the region.
Expect a period of showers developing from west to east late
evening into the overnight. A few t-storms are possible as well
as soundings indicate a conditionally unstable profile above the
inversion with marginal MUCAPES. Gusty SW winds will develop as
the low level jet moves into the region. Gusts 20-30 mph are
possible.

Sunday...

Shower activity will be exiting SE New Eng in the morning, with
areas of low clouds giving way to increasing sunshine as good
low and mid level drying develops. Clouds may linger over the
Cape/Islands through midday. It will be a warm day with
westerly winds and 850 mb temps 20-21C supporting highs into
the mid 80s with some upper 80s possible CT and Merrimack
valleys. Cooler 70s along the immediate south coast where winds
turn SW. Weak cold front moves into SNE in the afternoon and
models generating SBCAPEs 500-1000 J/kg. Limiting factor for
convection is the very dry air which moves in above 700 mb which
will limit any potential updrafts. Mainly dry weather in the
afternoon with just a low risk for a brief shower or perhaps a
low topped t-storm but coverage would be localized. Steep low
level lapse rates develop in the afternoon with deep mixed layer
supporting gusty west winds to 20-30 mph at times, especially
interior locations.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Updated 345 PM Friday.

Highlights...

* Warm and mainly dry Sun and Memorial Day.
* Cooler with showers likely Tue.
* Warmer later next week with scattered showers/storms Thu.

SNE should remain on the northern periphery of subtropical ridge
into next week as series of northern stream short waves move through
region bringing rounds of showers/storms every few days.
What looked to be a significant warmup by the middle of next week
now appears to be on hold as surface boundary remains south of
region and GEFS/EPS probabilities confine more significant heat and
humidity well to our south. Still looks seasonable for late May by
end of next week however.

Sunday...

Short wave moves offshore in morning which will take any lingering
showers and cloudiness with it. Sunshine will help temps reach low
to mid 80s inland which will result in decent instability Sunday
afternoon ahead of weak cold front. Depending on your model of choice,
CAPEs increase to 500-1500 J/kg, mid level lapse rates reach
6-7C/km, and 0-6km shear is strong at 40-50kt. However a
significant limiting factor is drying aloft which should prevent
widespread storm development. Our thinking is we may see a few
storms develop which could produce strong wind gusts.

Monday...

Front moves offshore with high pressure building north of region,
resulting in plenty of sunshine along with cooler temperatures and
low humidity. Expect highs to stay in 60s along immediate coast
where gradient should weaken enough to allow for coastal sea
breezes. Inland highs will reach 70s to near 80.

Tuesday Through Thursday...

Cooler/wet day Tuesday as warm front approaches and probably stays
SW of region with decent onshore flow in place. Keeping highs in 60s
per model consensus but it`s certainly possible for coastal
locations to hold in 50s. Although confidence decreases beyond
Tuesday due to timing issues with short waves, pattern favors warm
sector conditions Wednesday and Thursday, although cloudiness should
keep highs in 70s Wednesday and in 80s Thursday as main core of
heat/humidity remains well south of region. Cold front should bring
at least scattered showers/storms Thursday.

&&

.AVIATION /07Z 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/...

Today...High confidence. VFR. Coastal sea breezes developing by
afternoon.

Tonight...Moderate confidence. VFR in the evening, then a period
of showers and possibly a t-storm move through the region with
conditions lowering to MVFR after the showers begin. Localized
IFR cigs possible. Patchy fog developing along the south coast
late. SW gusts to 20-25 kt developing.

Sunday...High confidence in trends, lower confidence in timing.
MVFR/IFR early with showers ending SE New Eng. Then rapidly
improving to VFR during the morning, but lower cigs may linger
into the early afternoon over Cape/Islands. Low risk of an isold
shower/t-storm in the afternoon. West gusts to 20-25 kt.

KBOS Terminal...High confidence in TAF. Expect sea breeze to
develop by 16z.

KBDL Terminal...High confidence in TAF.

Outlook...

Sunday Night through Memorial Day: VFR.

Monday Night: VFR. Chance SHRA.

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

Wednesday: VFR.

&&

.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...Light winds becoming onshore over nearshore waters as
sea breezes develop around midday.

Tonight...Increasing SW winds as low level jet moves across the
waters. Gusts to 25 kt possible after midnight with building
seas and SCA may eventually be needed for some of the waters.
Showers move through late evening into the overnight with
reduced vsbys.

Sunday...Low level jet exits SE waters early with diminishing
winds. Another pulse of west gusts to 20-25 kt may develop in
the afternoon over Boston Harbor and Narragansett Bay. Patchy
fog may reduce vsbys in the morning with showers exiting SE
waters.

Outlook...

Sunday: Winds less than 25 kt. Seas up to 5 ft. Slight chance
of rain showers, slight chance of thunderstorms.

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

Memorial Day: Winds less than 25 kt. Seas locally approaching
5 ft.

Monday Night: Winds less than 25 kt. Slight chance of rain
showers.

Tuesday: Winds less than 25 kt. Chance of rain showers.

Wednesday: Winds less than 25 kt. Seas locally approaching 5 ft.

&&

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

&&

$$
SYNOPSIS...KJC
NEAR TERM...KJC
SHORT TERM...KJC
LONG TERM...JWD
AVIATION...KJC/JWD
MARINE...KJC/JWD



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