Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 241916
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
316 PM EDT Mon Jun 24 2019

.SYNOPSIS...
An approaching warm front will bring a period of widespread
showers and perhaps a few embedded thunderstorms Tuesday.
Summer-like warmth is expected Wednesday through Friday with a
few showers and thunderstorms possible at times, but dry weather
should dominate. A cold front sweeps south through Southern New
England Saturday bringing another chance of showers and
thunderstorms. Cooler weather then moves in Sunday.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Seabreezes finally developed late this morning, and should
remain well established into this evening. Tricky wind forecast
overnight. While seabreezes usually diminish, with winds turning
south or southwest, a warm front should be approaching from the
west late tonight. Thus, expecting winds to become light and
variable, then light southeast synoptically late tonight.

Tweaked temperatures through this afternoon into this evening
based on observed trends.

Increasing clouds late tonight, with a corresponding risk for
showers late. Thinking most of southern New England remains dry
through tonight.

Near normal temperatures tonight.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
Tuesday is the most likely period for showers to overspread our
region. Still some signs of elevated instability. Kept a mention
of thunderstorms in the forecast, but no thunderstorms should be
particularly strong. The peak of the showers should be about
early afternoon, then diminish from west to east into Tuesday
evening.

Precipitable water values projected to be 2-3 standard
deviations above normal, with 850 mb moisture flux about 3-4
standard deviations above normal. Thus, should be looking at
locally heavy rainfall, and the potential for poor drainage
flooding. Total rainfall should generally be one half to one
inch, locally higher up to about 1.5 inches.

Showers diminish Tuesday night as a cold front sweeps across
southern New England.

Lower temperatures Tuesday due to the clouds and showers. Below
normal for most areas. Low temperatures Tuesday night should be
near normal. It will be noticeably more humid Tuesday into
Tuesday night.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...

Big Picture...

Zonal flow over the Northeast USA through Friday. Broad upper ridge
over the Southern USA builds north through the Plains late in the
week, then shifts east early next week. Large closed low lingers
over the Pacific Coast through Friday, then ejects northeast into
Canada over the weekend. This ejecting low kicks another low away
from Hudsons Bay. The Hudsons Bay upper low sweeps southeast to New
England by Sunday and to our east Monday.

Contour heights from 500 mb will be above normal over our area for
most of the period. The exception will be Sunday-Monday as the upper
low noted above sweeps across New England bringing below-normal
heights. Expect above normal temperatures most of the period, except
cooling to near normal Sunday and/or Monday.

Forecast confidence is moderate-high. The various model mass fields
are similar through Monday, although showing the usual differences
in detail by Sunday and Monday.

Concerns...

Wednesday through Friday...

Multiple shortwaves move through the zonal flow during this period.
Moisture is limited, but concentrated in the 800-900 mb layer. PW
values vary from just under an inch up to 1.5 inches Wednesday night
and again Friday afternoon. So the deeper moisture varies, likely
tied into passage of shortwaves, but cloud-level moisture remains
present.

Expect the daytime heating to join with the shortwaves to generate
enough lift for clouds over our region along with scattered or
widely scattered showers mainly north of the Mass Pike. Otherwise
dry weather. Mixing will reach 800 mb and tap temps aloft of 10-
13C...supporting max sfc temps of 85-90. Warmest temperatures
Friday. Dew points remain in the low to mid 60s through the period,
so min temps are expected to be in the 60s.

Saturday...

Upper low from Hudsons Bay drives southeast, aided by a 100-kt upper
jet. This drives a cold front southeast across New England late
Saturday and Saturday night. The cold front provides a source of low-
level convergence, the upper jet provides dynamic support, and
daytime heating generates instability. CAPE of 1000-1500 J/Kg and
totals near 50 are forecast. So we expect showers/thunder to
develop. Mixing is not expected to go as deep as previous days, but
should still reach 850 mb, where temps will be around 16C. So max
temps will again be well into the 80s.

Sunday-Monday...

Surface cold front moves south of New England, while the upper
low/cold pool/cold pool moisture move south across Southern New
England. With the colder air moving in aloft, expect deep mixing to
800 mb or higher. The cold pool moisture should be enough to
generate clouds, and stability parameters support scattered
showers/thunder. Temps at 800 mb fall to 5-6C, which would support
max sfc temps 75 to 80F.

Conditions improve Monday as the upper low/cold pool move off to the
east. Lingering instability in Eastern Mass may continue to generate
scattered showers.

&&

.AVIATION /19Z MONDAY THROUGH SATURDAY/...
Forecaster Confidence Levels...

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

Short Term /through Tuesday Night/...High confidence.

Tonight...VFR to start. MVFR/IFR arrive after 10Z across CT and
western-central MA, possibly into RI. Low risk of showers
entering western MA/CT toward 12Z. Otherwise, remainder of the
region stays dry.

Tuesday...VFR possible early across eastern MA, otherwise
MVFR/IFR with spotty LIFR from late morning into the afternoon
accompanied by widespread showers with embedded thunder and
heavy rain. Southeast winds.

Tuesday Night...Conditions improving from west to east. Mainly
VFR across the western half of southern new England after
midnight, with MVFR/IFR farther east. Breezy. Patchy BR. SHRA
ending.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Wednesday through Saturday/...Moderate confidence.

Wednesday: Mainly VFR, with local MVFR possible. Slight chance
SHRA.

Wednesday Night: Mainly VFR, with local IFR possible. Slight
chance SHRA, patchy BR.

Thursday through Friday Night: VFR.

Saturday: Mainly VFR, with areas MVFR possible. Chance SHRA,
slight chance TSRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Tuesday Night/...High confidence.

Rather tranquil boating conditions tonight into Tuesday
morning. Showers and patchy fog arrive later in the day with
reduced visibility at times. A few thunderstorms with heavy
downpours are possible. These showers end from west to east
after midnight.

Winds generally remain less than 25 kt. There is a window for
some gusts possibly approaching 25 kt late Tuesday into Tuesday
night ahead of a cold front. Too marginal to issue Small Craft
Advisories at this time. However, this will need to be watched
over the next 24 hours.

Outlook /Wednesday through Saturday/...Moderate confidence.

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

Wednesday Night: Winds less than 25 kt. Seas less than 5 ft.
Patchy fog. Areas of visibility 1 to 3 nm.

Thursday through Friday Night: Winds less than 25 kt. Seas less
than 5 ft.

Saturday: Winds less than 25 kt. Seas less than 5 ft.Chance of
rain showers, slight chance of thunderstorms.

&&

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

&&

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



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