819
FXUS61 KBOX 181904
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
304 PM EDT Fri Apr 18 2025

.SYNOPSIS...
A warm front will bring increasing clouds but mainly dry weather
and southwest breezes tonight. Warm and breezy weather
conditions expected for Saturday, with scattered showers
arriving later Saturday afternoon into the evening. Drier and
mild behind the front Sunday. Weather pattern turns more
unsettled early next week.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
300 PM Update:

Key Messages:

* Warm front brings increased cloud cover tonight, but dry weather
  expected.

* Very mild lows for mid-April, in the mid 50s for many with upper
  40s Cape and Islands.

Details:

Although the one local exception is over the immediate south
coast and Cape Cod where SWly flow is keeping these locations a
little cooler (50s), it`s turned into a dry, breezy and mild
afternoon. Current temps are well into the 60s with SWly gusts
25-35 mph. The airmass is quite dry with current dewpoint
depressions some 35-40 degrees.

A warm front will be moving across Southern New England later
tonight and overnight. This will bring an increasing canopy of
mid to high clouds as we move through tonight. Regional radar
mosaic shows some echoes well to the west in western NY
associated with a plume of steeper lapse rates between 850-500
mb, but the airmass is still pretty dry not only at the surface
but also up to about 800 mb. In addition, strong SWly steering
flow should keep any shower activity to our northwest. These
factors seem too much to warrant to mention of showers so opted
for dry weather tonight. Influence of the mid-level overcast
combined with SWly winds around 15 mph should result in slower
cooling, with lows running around the 50s, with some cooler
upper 40s over Cape Cod.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
300 PM Update:

Key Messages:

* Very warm and breezy Saturday with temps well into the 70s to low
  80s, despite filtered sun.

* Cold front brings passing showers early Sat night, but with cooler
  conditions and gusty NW winds up to 45 mph for overnight.

Details:

Saturday:

Saturday is shaping up to be one of the warmest days thus far
in the year 2025, as the warm front passing to our north will
leave behind anomalously warm low-level temperatures by mid-
April standards. 925 mb temps tomorrow will be warming to around
+16-18C, with temps at 850 mb around +12-14C. Even though we`ll
still have a canopy of at least high clouds that may lead to
more of a filtered-sun look, temps should soar well into the 70s
to low 80s away from the South Coast/Cape and Islands (60s).
Quite a bit different than last Saturday when we were mired in
gray overcast and in the mid 30s to low 40s! The warm
temperatures will be met by continued SWly breezes, around 25-30
mph.

A cold front then arrives for late Saturday afternoon into the
early evening. This will bring a passing threat for isolated to
scattered showers from about 5-10 pm, given what looks to be
limited available instability with weak midlevel lapse rates and
the later time-of- day. Activity should be falling The cold
front`s passage will bring sharp cold advection (by 12z Sunday
our 925 temps will have dropped from +18C to +2C), along with
gusty NW winds around 25-40 mph with the highest gusts over the
higher terrain. Outside chance that NW gusts in the higher
terrain could get to around 45-50 mph. Lows then drop back into
the mid 40s to low 50s.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Key Messages:
* Breezy and Dry Sunday - monitoring for fire weather concerns
* Some showers Monday night/Tuesday and again Friday, but otherwise
  slightly above normal temperatures next week

Blended model guidance (NBM) again this afternoon looks pretty
reasonable for the long term, so the forecast reflects that blend.
Also, no significant changes from prior forecasts. Below are a few
notes to add to the key messages above:

Sunday: Compared to Saturday, a much cooler and drier airmass will
be in place. Model guidance is not much different from previous
runs, and forecast soundings show a very well mixed boundary layer
up to 6000 ft or so, and a very dry atmospheric column (precipitable
water values less than 1/4th inch). That well mixed boundary layer
will be efficient in bringing down stronger winds aloft associated
with a LLJ of 40-50kt at 850mb. However right now it looks like bulk
of the LLJ will be pushing offshore by the time daytime heating has
given us the deepest boundary layer, such that afternoon 850mb winds
will only be 25-30kt or so. Thus, although it will be breezy Sunday
afternoon, it won`t be excessively windy. In fact, the probability
of seeing gusts to 40 mph is less than 10% and is a significant
decrease from what guidance suggested yesterday. That deep mixing
will also lead to another situation of dewpoints running lower than
most guidance shows. Typical of sunny/dry spring days before green-
up. Did fold in the lowest 10th percentile dewpoints, which results
in RH values in the afternoon again dropping to lip cracking dry
values of around 20%. These conditions may result in additional
coordinated messaging with our MA/CT/RI state fire partners based on
what they are seeing for fuel conditions. Stay tuned.

Monday Night/Tuesday: Fast moving shortwave aloft will push across
the region. With the primary surface low remaining well to the north
across Quebec, there isn`t too much to the system. No instability to
work with, and a dry antecendant airmass. Thus QPF should be rather
light -- guidance only has a 10-20% chance of seeing more than 1/4".

Rest of the week: Pretty solid signal for overall warmer than normal
temperatures as zonal flow aloft persists. Certainly some
differences in the guidance, but in general the temperature spread
between the cooler (25th percentile) and warmer (75th percentile)
ensemble members is on the order of 5-10F, which isn`t too large.
Additionally each day there looks to be about a 10-20% chance of
seeing 75F or warmer across much of interior southern New England
and 10% or less for seeing temperatures not even making it to 60F
(exception of course the Cape/Islands).

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

18z TAF Update:

Rest of This Afternoon Through 12z Saturday: High confidence.

VFR, with increasing mid to high clouds. SW winds 10-15 kt with
gusts 20-25 kt through about 02z Sat, then to more sustained
SW winds 10-15 kt. Low level wind shear likely after midnight
with gusts easing and as a 35-50 kt SWly low level jet moves
across Southern New England.

Saturday: High confidence.

VFR for most airports, although some borderline MVFR/VFR
ceilings after 21z Sat for western airports as a cold front
approaches. SW winds 10-15 kt to start the morning, but gusts
25-30 kt develop by 13-15z.

Saturday Night: High confidence.

Mainly VFR, though borderline MVFR ceilings could accompany
cold front associated with isolated to widely scattered SHRA
thru 03z Sun. Cold front`s passage marked by rapid clearing but
also with NWly gusts 25-40 kt, strongest higher terrain airports
(BAF, ORH).

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Sunday through Wednesday/...

Sunday: VFR. Windy with gusts up to 35 kt.

Sunday Night through Monday: VFR.

Monday Night through Tuesday: Mainly VFR, with local IFR
possible. Breezy. Chance SHRA.

Tuesday Night: VFR. Breezy.

Wednesday: VFR.

&&

.MARINE...
Forecaster Confidence Levels:

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

Small Craft Advisories will be taking effect this afternoon and
continue into Saturday late afternoon, and may need to extend
the SCAs on the southern outer waters into Sunday with later
forecasts.

SW winds increasing to 15-25 kt this afternoon into tonight,
then with gusts 20-30 kt on Saturday. Winds then shift to NW
late Saturday evening into overnight at similar gust speeds.
Seas building to around 4-8 ft tonight into Saturday, higher on
southern offshore waters. Good visbys expected.

Outlook /Sunday through Wednesday/...

Sunday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Local rough seas.

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

Monday: Winds less than 25 kt.

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

Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Chance of rain showers.

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

Wednesday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 11 PM this evening to 7 PM EDT
     Saturday for ANZ231-233-235-254>256.
     Small Craft Advisory from 3 AM to 7 PM EDT Saturday for ANZ232-
     234-236-237.
     Small Craft Advisory from 6 PM this evening to 7 PM EDT
     Saturday for ANZ250.

&&

$$

SYNOPSIS...Loconto/Nash
NEAR TERM...Loconto/FT
SHORT TERM...Loconto/FT
LONG TERM...Nash
AVIATION...Loconto/FT/Nash
MARINE...Loconto/FT/Nash