BOX issues Area Forecast Discussion (AFD) at Jul 30, 3:10 PM EDT482
FXUS61 KBOX 301910
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
310 PM EDT Wed Jul 30 2025
.SYNOPSIS...
Stretch of high heat and humidity wraps up this afternoon.
Cloudy weather with much cooler conditions are expected Thursday
into Friday, with the potential for a flooding rainfall across
southern New England into northern Mid Atlantic region.
The location of heaviest rainfall remains unclear. An extended
stretch of dry weather then develops for this weekend into early
next week. Temperatures are seasonable with low humidity levels
this weekend, but with a warming trend for early next week.
&&
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Key Messages:
* Near record heat this afternoon with highs in the 90s and heat
indices 95-100+. Not as hot along the coast given seabreezes.
* Isolated severe thunderstorms possible mainly south of the
Mass Pike.
* Front passes through overnight with lowering dewpoints across
the interior.
THIS AFTERNOON:
A weak cold front continues to push south towards our CWA this
afternoon and will serve as a forcing mechanism for some widely
scattered showers and thunderstorms. There is a marginal risk of
severe convection today with MLCAPE values approaching 1000 J/kg
later this afternoon. 0-6 km shear of 35-40kts could aid in storm
organization, but diffuse and weak forcing will limit the areal
coverage of thunder activity. Storms should form mainly south of the
Mass Pike, where instability will be a bit more robust. There is a
chance for convection to fire along the seabreeze this afternoon
which is shown by the RRFS and HRRR CAMs respectively. Somewhat
meager midlevel lapse rates mean that shower and thunderstorm
activity will quickly wane with the loss of daytime heating this
evening.
Outside of the convective risk, the main story for the rest of the
afternoon will be the continued heat and humidity. Unfortunately we
are looking at another day of high temperatures in the lower to mid
90s across the interior with apparent temperatures rising to as high
as 95-102 degrees. As such, a heat advisory will remain in effect
for much of our CWA outside of the Cape and Islands through 00z
tonight.
Expecting high temperatures to come in just below record levels for
today, but it will be close. The record highs for today are as
follows:
BOS - 98F set in 1933
BDL - 98F set in 1988
PVD - 97F set in 1949
ORH - 95F set in 1949
TONIGHT:
The cold front pushes offshore overnight but doesn't make a lot of
southward progress. As a result, while inland areas, especially
along and north of the Mass Pike see some relief from higher
humidity the coast will likely still hold onto the near-70 degree
dewpoints. The cold front transitions to a stationary front as it
moves just offshore.
&&
.SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
Key Messages:
* Flood watch is in effect for northern Connecticut from 2pm
Thursday through 2pm Friday but may need to be expanded with
later forecast cycles.
Thursday morning should be mostly dry outside of a few widely
scattered showers. Should be a much cooler day than what we've seen
over the last several days with highs struggling into the upper 60s
and lower 70s. It will feel cooler with a stiff NE wind, especially
at the coast.
Attention turns to the potential for widespread heavy rainfall and
areas of flooding for Thursday night into Friday. Synoptically, the
event will be driven by a highly anomalous 130kt jet over northern
New England. Southern New England will be squarely in the right-
entrance region of the jet, under favorable upper divergence. Closer
to the surface, a vigorous baroclinic wave brings a robust axis of
low and mid-level frontogenesis to the region starting Thursday
evening. Mositure-wise, higher PWAT air will advect north ahead of
the amplifying disturbance Thursday afternoon. Guidance shows PWAT
values rising to 1.7-1.9 inches which is around 150 percent of
normal for this time of year. BUFKIT soundings show warm cloud
depths increasing to 12kft within the warmer, higher theta-e airmass
as it moves northward. The main forecast challenge is narrowing down
the corridor of highest QPF. Latest HREF PMM QPF guidance is
advertising two swaths of heavier rainfall. The heavier swath is
shown well to the south of our CWA across portions of the Mid
Atlantic and is directly associated with an 850mb circulation. The
second, associated with the mid-level frontogenesis maxima is
centered across much of northern Connecticut. In this area, the
forecast QPF from the HREF PMM is showing localized areas of 3-4
inches of rain. Outside of this maximum the NBM is showing a
widespread 1-2 inches of rainfall for just about everyone. There is
still some uncertainty as to where the heaviest axis of rain occurs,
but confidence is high enough for us to issue a flood watch for
northern Connecticut from 2pm Thursday through 2pm Friday. In
summary, the combination of cool-season upper dynamics and deep warm
cloud processes may result in areas of flooding with the highest
confidence across areas of northern Connecticut. Rainfall rates will
likely peak between 03 and 09z Thursday night during which time they
may approach 0.5 to 0.75 inches per hour. These rates could result in
areas of low-lying or poor drainage flooding and so it may be a good
idea to avoid unnecessary travel Thursday night.
&&
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Key Messages:
* Improving weather on Friday
* Seasonably cool weekend ahead
Rain begins to shift offshore Friday morning as high pressure
and dry air works its way south from northern New England.
Guidance is not in great agreement on the timing, with the GFS
being the quickest to dry things out by noon on Friday, while
the Euro, Nam, and Canadian are slower with precip lingering
into the evening commute. Friday will be an anomalously cool day
for the first day of August as rain and cloud cover, along with
NE flow, will likely hold high temperatures in the 60s to low
70s.
Saturday and Sunday
The weekend is shaping up to be nearly perfect weather-wise as high
pressure builds in from the north, ushering in dry and seasonable
conditions with mostly sunny skies. High temperatures on Saturday
warm into the mid-70s to low 80s with light northerly winds.
Dewpoints on Saturday range from the upper 40s inland to mid-50s
near the coast, making it feel very comfortable outside.
Temperatures warm slightly on Sunday into the low to mid 80s with
dewpoints in the mid to upper 50s.
Next week.
High pressure remains in control for the first half of next week.
High temperatures stay in the 80s with dewpoints around 60F. As
for precipitation, we are unlikely to see any until late in the week
as guidance hints at a shortwave exiting the Great Lakes.
&&
.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Today...Moderate confidence; some uncertainty if thunderstorms
develop and their coverage.
Isolated to widely scattered thunderstorms may develop between
19z and 22z. Low confidence on areal coverage, but if anything
does develop, it will likely remain towards western MA and
north- central CT. We handled this uncertainty with a PROB30
after 18Z for BDL and BAF. Low probability of a few robust
storms, with strong winds the main threat.
Tonight...High confidence.
VFR likely, except IFR/LIFR south coast, including Cape Cod and
islands in low clouds and fog. Light winds mainly W overnight
if they aren't calm.
Thursday...Moderate confidence, mainly due to timing issues.
VFR for most. Areas of MVFR possible in heavier rainfall. Timing
of lower conditions most likely in the mid to late afternoon,
but could hold off until Thursday night.
KBOS terminal...High confidence in TAF.
KBDL terminal...High confidence in TAF through 18z. Then some
uncertainty on development and coverage of showers and
thunderstorms today, though chances are diminishing.
Outlook /Friday through Monday/...
Friday: MVFR/IFR conditions possible. Breezy. SHRA likely.
Friday Night: VFR. Breezy. Slight chance SHRA.
Saturday: VFR. Breezy.
Saturday Night: VFR.
Sunday through Sunday Night: VFR. Breezy.
Monday:
&&
.MARINE...
Forecaster Confidence Levels...
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Through Thursday...High confidence on winds and seas, lower
confidence on timing and areal coverage of potential
thunderstorms.
Patchy dense fog possible early this morning around Nantucket,
and again tonight. Typical summer pattern with relatively light
winds and seas. Isolated to widely scattered thunderstorms
possible after 4-5 PM today. A cold front will provide a wind
shift to the NE toward Thu morning.
Outlook /Friday through Monday/...
Friday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Seas up to 5 ft. Rain showers likely. Local
visibility 1 to 3 nm.
Friday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Seas up to 5 ft. Chance of rain showers.
Saturday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of seas approaching 5 ft.
Saturday Night: Winds less than 25 kt. Seas locally approaching
5 ft.
Sunday through Monday: Winds less than 25 kt.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory until 8 PM EDT this evening for CTZ002>004.
Flood Watch from Thursday afternoon through Friday afternoon
for CTZ002>004.
MA...Heat Advisory until 8 PM EDT this evening for MAZ003>007-
010>021-026.
Air Quality Alert until 11 PM EDT this evening for MAZ020>024.
RI...Heat Advisory until 8 PM EDT this evening for RIZ001>007.
Air Quality Alert until 11 PM EDT this evening for RIZ006-007.
MARINE...None.
&&
$$
SYNOPSIS...Hrencecin/FT
NEAR TERM...FT/Nocera
SHORT TERM...FT/Nocera
LONG TERM...Loconto
AVIATION...Hrencecin/FT
MARINE...Belk/Loconto
Source:
BOX issues Area Forecast Discussion (AFD) at Jul 30, 3:10 PM EDT----------------
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