380
FXUS61 KBOX 171328
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
928 AM EDT Sat May 17 2025

.SYNOPSIS...
An upper level low pressure over Michigan will be responsible
for scattered showers and thunderstorms. Some storms this
afternoon in interior Southern New England could become severe.
Turning cooler and drier tonight, with blustery conditions also
developing on Sunday. Dry to start the week, and a cooling
trend sets in Tuesday that will continue through the week.
Unsettled weather returns once again in the second half of the
week into the weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

Key Messages...

* A few severe storms possible across western MA/CT after 4-5 pm
  today but greater areal coverage across northern New England

* Much of today may end up dry with partial clearing and highs
  well up into the 70s to near 80 with some humidity too

Details...

A complex forecast into this evening...which we will explain
below. Low clouds covered much of region at mid-morning...but
enough diurnal heating with the strong May sun angle should
allow for partial sunshine to develop through the afternoon.
Highs should be well into the 70s to near 80 with modest
humidity too.

The main concern revolves around the convective threat today.
The latest guidance is fairly limited with the threat of
elevated activity through mid afternoon with better forcing and
moisture to our northwest. While a few isolated showers and
perhaps an isolated t-storm can not be ruled out...thinking
dry weather may prevail across much of the region through mid
afternoon.

We do expect a modest amount of instability to develop
across the interior with MLCapes rising into the 1500-2000 J/KG
range. There also will be a fair amount of effective shear on
the order of 35 to 45 knots. At the same time...a relatively
strong shortwave will be lifting into northern New England.
Although we expect a fair amount of instability/shear we will be
on the edge of the stronger forcing. So that may keep any
activity that develops across our region isolated to scattered
with better coverage in northern New England. However...given
the amount of instability and shear and storm that develops in
western MA/northern CT will be capable of becoming severe with
the main threats being localized damaging wind gusts and hail.
This also looks to be a rather late show...mainly after 4-5 pm
across western MA/CT. This is supported by the CAMs and machine
learning guidance tend do have some severe probs into this
region...but hint at a better chance to our north.

What ever activity develops should weaken this evening...as it
out runs better instability/forcing. So while a rumble or two of
thunder may survive onto the I-95 corridor...the severe weather
threat appears low in this region.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
Key Messages:

* Drier and much less humid tonight, although still some cloud
  cover around.

* Partly to mostly cloudy Sunday, breezy with generally
  seasonable temps. Hit or miss shower possible north of the
  Mass Pike.
likely
Details:

Our weather pattern for tonight into Sunday then becomes more
strongly governed by the upper level low over Michigan. This
looks to be accompanied by below-average 850 mb temps and still
quite a bit of low to midlevel RH. So while we do clear out
tonight and trend dry, there could still be at least partly
cloudy skies tonight but not the low clouds we`ve had the last
couple nights. The biggest change though is that dewpoints will
plummet back into the 40s to low 50s, so a considerably less
humid airmass.

Sunday is looking partly to mostly cloudy and rather breezy
with WNW winds around 10-15 mph with gusts to 20 mph. Couldn`t
rule out a hit or miss shower north of the Mass Pike Sunday but
probably not widespread or capable of washouts. It`s possible
that adiabatic downsloping could boost areas such as metrowest
Boston to around 70 degrees, but highs could struggle to reach
the low to mid 60s in interior Southern New England.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Key Messages:

* Dry and seasonable Monday

* Cooling trend returns Tuesday through the rest of the week

* Another system may bring significant rain and gusty winds to
  southern New England midweek

Details...

An upper level low makes its exit offshore towards the Maritimes
Monday night. Northwest flow kicks in in its place while the cooler
temperatures aloft remain, which will help keep the region cooler
and drier; highs Tuesday through Thursday will remain mostly in the
50s and low 60s.

Towards the second half of the week, another upper level low is
expected to dig into the Great Lakes. An associated surface low is
then expected to move up along the east coast towards southern New
England. The late spring Nor`Easter would likely bring significant
rainfall and gusty winds sometime Wednesday evening through Friday,
however, timing still varies greatly in the guidance. Deterministic
guidance also still varies significantly on the track of the low`s
center, and the GEM generally has the system approaching slightly
later than the other models do and moves it further to the south of
the region. This would keep most of the rain to the south and glance
the south coast. Generally, though, the consensus is that the end of
next week will be unsettled and cool with continued broad cyclonic
flow and cooler temperatures aloft.

&&

.AVIATION /13Z SATURDAY THROUGH WEDNESDAY/...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

12Z TAF Update:

Today: Moderate confidence.

An active, complicated aviation forecast period, with continued
stratus/fog and then two potential rounds of TS.

IFR-LIFR likely at most airports at onset of this period, and
categories unlikely to change significantly thru the AM hrs.
First potential round of SHRA/TSRA looks to move in between
12-17z. This activity would be capable of downpours and
lightning, although it is still uncertain on how widespread it
may be, which lead to handling this first potential round with
PROB30s until its areal coverage becomes more clear.

After ~17z, some improvement in most areas to something closer
to a SCT-BKN VFR BDL-BAF-ORH with MVFR/perhaps still lingering
IFR eastern airports (best chance IFR Cape and Islands). SCT
TSRA, some of which could become strong to severe, then begins
to develop or work in from eastern NY between 17-00z, likely as
a broken line of storms. Better chc at strong t-storms for BAF
and BDL and ORH, and opted to indicate 2-3 SM TSRA in PROB30s
where the potential for stg/severe storms would lie. Unlikely
storms would survive past BED/PVD but this will need to be
monitored today.

Light south winds, which could become ESE near the eastern coast
thru mid/late afternoon, then a windshift to SW very late in
the day to around 10 kt.

Tonight: High confidence.

Any SHRA/TS threat should dissipate after 01z. Rapid improvement
to SCT-interior BKN VFR clouds takes place tonight, along with a
windshift to W/NW around 10-14 kt.

Sunday: High confidence.

VFR / VFR-MVFR ceilings interior airports (bases 020-040). Hit
or miss SHRA mainly N and W of ORH. W/NW winds 10-15 kt with
gusts to 20-25 kt.

KBOS TAF...Moderate confidence. Initial MVFR bases should go to
IFR by 08z, then remain in IFR-MVFR range into most of the AM
hrs. Possible SHRA/TS between 14-17z (indicated with PROB30s)
but it`s unclear how widespread any TS may be. Gradual
improvement to MVFR-VFR after 17z. Less of an afternoon TSRA
risk but it is not zero and will need to be monitored. S winds 5
kt or less become SE by late morning, then flip to SW 23-00z.

KBDL TAF...Moderate confidence. IFR ceilings to begin. Initial
round of SHRA/TS in the 12-15z timeframe, and while its
coverage is still uncertain, it would not likely become strong.
Ceilings then lift to BKN VFR after 17z, with second risk for
SCT TSRA 17-00z, and its these which could become strong to
severe. S winds under 10 kt become briefly SE this aftn then
flip to W around 10-12 kt late in the day.

Outlook /Sunday Night through Wednesday/...

Sunday Night: Mainly VFR, with local MVFR possible. Windy with
local gusts up to 30 kt.

Monday: VFR. Windy with local gusts up to 30 kt.

Monday Night: VFR. Breezy.

Tuesday: Mainly VFR, with areas MVFR possible. Breezy.

Tuesday Night: Mainly VFR, with local IFR possible.

Wednesday: MVFR/IFR conditions possible. Chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

High confidence overall.

Winds and seas remain below SCA levels through tonight. However
fog is a concern for boaters this morning, and there could be
thunderstorms over the southern waters late this morning to
early afternoon.

West to northwest winds increase tonight and especially on
Sunday to around 20-25 kt, with seas increasing to 3 to 5 ft.
Small craft advisories have been hoisted for Sunday and into
Sunday night for the southern waters. Conditions look borderline
on the eastern waters for SCAs but could be considered in later
updates.

Outlook /Sunday Night through Wednesday/...

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

Monday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of rain showers.

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. Slight
chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 8 AM Sunday to 8 AM EDT Monday for
     ANZ232>235-237-254>256.

&&

$$

SYNOPSIS...Loconto
NEAR TERM...Frank
SHORT TERM...Loconto
LONG TERM...Hrencecin
AVIATION...Loconto/Hrencecin
MARINE...Loconto/Hrencecin