BOX issues Area Forecast Discussion (AFD) at Apr 22, 7:18 PM EDT703
FXUS61 KBOX 222318
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
718 PM EDT Tue Apr 22 2025
.SYNOPSIS...
Warm and dry on Wednesday followed by a chilly Wednesday night
driven by radiational cooling. Thereafter, mainly dry and warm
conditions to round out the work week, then a frontal system
will bring widespread rainfall around Saturday although exact
details remain uncertain. Drying out and cooler Sunday behind
the system, then milder early next week.
&&
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Key Messages
* Dry cold frontal passages supports clearing overnight
Tonight
A cold front pushes through the region overnight and removes the
remaining fog/low stratus over The Cape/Islands region. Winds will
shift to the northwest around 10 knots. 925 hPa temps drop to around
5 Celsius. Although skies will be clear, steady northwest flow
should limit maximum radiational cooling. Thus, expect low temps in
the upper 40s to low 50s which is slightly above normal for mid-late
April.
&&
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
Short Term
Key Messages
* Warm/dry weather on Thursday with steady northwest winds
* Below normal low temperatures Wednesday night into Thursday with
lows in the upper 30s to low 40s
Tomorrow
Seasonable day tomorrow across southern New England. Quiet weather
with high pressure building in from the west. Gradient wind
continues to support steady northwest winds across the region from 5
to 10 mph. Expect efficient mixing in the afternoon that could
support a few 20 mph gusts, but nothing impactful. With 925 hPa
temps around 10C we can expect high temps in the upper 60s to low
70s. The coastal locations and especially The Cape/Islands will be
substantially cooler in the upper 50s to low 60s. There is a chance
for a sea-breeze tomorrow afternoon, mainly on the south shore. Model
guidance is less aggressive for a circulation developing from Boston
to Gloucester.
Tomorrow Night
Clear skies and light winds under high pressure should support a
strong radiational cooling night. Expect well below normal
temperatures on Thursday morning in the upper 30s to low 40s. The
urban heat islands may be more mid to upper 40s after a warm day
Wednesday.
&&
.LONG TERM /THURSDAY THROUGH TUESDAY/...
Key Messages:
* Warm and mostly dry Thursday and Friday, outside of a stray shower
in northern Massachusetts Thursday evening
* Potential for widespread rainfall around Saturday, but there is
uncertainty with the exact timing.
* Drier and cooler conditions Sunday
* Mainly dry and milder early next week
Details...
Broad ridging aloft Thu into Fri will bring mainly dry and warm
conditions for late April. A northern stream shortwave passage well
to the north with a plume of moisture north of a weak warm front
will impact mainly northern New Eng with some showers late Thu into
Thu night. A few of these showers could spill into northern MA Thu
evening, otherwise looking at dry conditions. Temps will average
well above normal with 70s away from the south coast. Warmest day
will be Friday where some CT valley locations could approach 80.
The next chance for appreciable rainfall will be sometime around
Saturday as amplifying northern stream trough moves through with a
cold front interacting with anomalous PWAT plume approaching 1.5
inches. There are timing differences among the global guidance with
GFS the most progressive with bulk of rainfall Fri night. Given the
progressive bias of the GFS, we leaned toward a slower solution
which is consistent with deterministic ECMWF as well as EPS
ensembles which have most of the rainfall on Saturday. The 25th to
75th percentile of the ensemble distribution from GEFS, EPS and CMC
is about 0.25 to 0.75" which is a reasonable first guess forecast of
expected rainfall. There is some elevated instability which could
lead to convective elements and locally heavier rainfall if
convection occurs.
Even the slower ECMWF has the cold front offshore by 12z Sun with
mainly dry and cooler conditions Sun which is supported by large
majority of EPS ensembles. Temps may be cooler than forecast,
especially eastern New Eng where cooler low level temps linger. Then
upper level ridging gradually builds eastward from the Gt Lakes Mon
and Tue with rising heights and milder temps returning as high pres
gradually shifts east of New Eng with SW flow developing.
&&
.AVIATION /23Z TUESDAY THROUGH SUNDAY/...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
00Z TAF Update:
Tonight: High Confidence
Areas of LIFR fog Cape/Islands and around BOS will linger this
evening until wind shift to NW clears it out 03-06z. Otherwise
VFR. Wind becoming NW 5-10 kt.
Tomorrow: High Confidence
VFR. West/northwest winds around 10 knots. About a 50/50 chance
for a sea-breeze at BOS, but likely would be after 18Z if it
develops.
Tomorrow Night: High Confidence
VFR. Light and variable winds.
KBOS TAF...High confidence in trends. LIFR fog lingers for a few
hours this evening and will improve to VFR around 03z as winds
shift to NW behind the cold front.
KBDL TAF...High confidence in TAF.
Outlook /Thursday through Sunday/...
Thursday through Friday: VFR.
Friday Night: Mainly VFR, with local MVFR possible. Breezy.
SHRA likely.
Saturday: Mainly MVFR, with local IFR possible. Breezy. SHRA,
isolated TSRA.
Saturday Night: VFR. Breezy. Chance SHRA.
Sunday: VFR. Breezy.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Tonight through Tomorrow Night
A cold front crosses the waters tonight resulting in a wind shift to
the northwest. This will also help usher out any remaining fog/low
stratus over the south coastal waters. High pressure builds in from
the west tomorrow and will support calm conditions over the coastal
waters through Thursday.
Outlook /Thursday through Sunday/...
Thursday through Friday: Winds less than 25 kt.
Friday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Chance of rain showers.
Saturday: Low risk for Small Craft Advisory winds with gusts up
to 20 kt. Seas up to 5 ft. Rain showers likely.
Saturday Night: Low risk for Small Craft Advisory winds with
gusts up to 20 kt. Seas up to 5 ft. Chance of rain showers.
Sunday: Winds less than 25 kt. Seas up to 5 ft.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.
&&
$$
SYNOPSIS...KJC/RM
NEAR TERM...RM
SHORT TERM...RM
LONG TERM...KJC
AVIATION...KJC/RM
MARINE...KJC/RM
Source:
BOX issues Area Forecast Discussion (AFD) at Apr 22, 7:18 PM EDT----------------
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