NWS Forecast Discussion
957
FXUS61 KBOX 161824
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
224 PM EDT Fri May 16 2025
.SYNOPSIS...
Weakening low pressure will bring scattered showers or thunderstorms
at times through the end of the week as it reaches New England, but
a majority of the time will be dry. A cold front moves through
Saturday night behind the storms, drying and cooling the region.
Even with mostly dry conditions, scattered showers remain
possible Sunday with a cold pool aloft, then the pattern turns
unsettled again toward midweek.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Key Messages:
* Fog and stratus disperses around mid to late morning, but
lingers over the Cape and Islands most of the day.
* Scattered t-storms possible late in the day (after 3 PM) in
western New England, but severe weather is not expected.
Details:
Mild and moist early-morning across Southern New England, with
an extensive field of stratus blanketing a large portion of the
Northeast. Fog has developed in most locations as well, but so
far visibilities have been lowest along the coast, at times as
low as one-quarter mile but they`ve generally been at or around
half a mile. Coordinated with NWS New York City on special
weather statement for fog through 13z along the South
Coast/South Shore, Cape and Islands. Otherwise temps were in the
low 60s with similar dewpoints. On the larger scale, we`re in a
period of midlevel subsidence/weak geopotential height rises,
though that stands to change later this afternoon as we start to
feel increasing height falls associated with a seasonably
strong upper low over the Gt Lakes region.
Probably won`t see substantial improvement/scattering of fog and
stratus until mid-morning at earliest in western and northern
MA into CT, and around late morning to noontime for the Boston
to Providence corridor. Given the marine boundary layer, stratus
may linger for much of the day along the South Coast, Cape and
Islands.
Should be generally dry for most given the subsidence aloft;
however some threat for scattered showers and thunderstorms
still looks to materialize late in the day (probably not earlier
than 3 PM and tending to down-trend by sundown) and mainly west
of Fitchburg to Worcester to Willimantic with the onset of
geopotential height falls. In what still is best characterized
as a weakly-forced setup, the suite of convective-permitting
guidance has been all over the place as far as placement goes,
but looks like the greatest coverage of storms will be more to
our north and west, and we`ll have to watch to see if storms can
make it over the Berkshires/southern VT. Some instability
(around 1000-1200 J/kg) from diurnal heating should be present
in western portions of the CWA, but low to midlevel flow is
pretty weak and that limits shear magnitudes to less than 30
kt. Given this, probably not seeing much in the way of severe
weather potential with this activity but lightning and brief
downpours are still threats. Since this activity would stem
from last night`s round of severe weather in the Gt Lakes
region, any smaller- scale impulse from that activity could
modify that thinking, and that`s something to watch as we move
through today, but currently don`t see indication of that in obs
upstream.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
Key Messages:
* Fog and stratus develop again tonight, and it may linger for
quite a while into Saturday.
* Possible round of scattered t-storms Saturday morning in most
areas.
* Better chance at t-storms between 2-8 PM west of Worcester.
Some could become strong.
Details:
Tonight and Saturday:
Any showers or storms in western New England should
weaken/dissipate early tonight. We will end up seeing stratus
and fog return northward from the waters again tonight.
What will also be taking place in mid and upper levels late
tonight and into Saturday is the potent upper low over the
Great Lakes will continue to make eastward progress into the
eastern part of Michigan. This will induce greater height falls
and diffluent flow aloft to overspread much of the Northeast.
Given the moist airmass in place, it won`t take much heating or
much of a shortwave triggering mechanism at all to get showers
and t-storms going. What is also unclear is how today`s severe
weather setup in the Ohio Valley may influence shower/t-storm
coverage or development. There are unfortunately quite a bit of
uncertainties as it pertains to thunderstorm potential as we
move into Saturday, which is problematic given the number of
outdoor events happening, and makes it a difficult call as far
as timing and strength of storms goes. The potential exists for
a couple rounds of storms, possibly as early as the pre-
dawn/early-morning Saturday period in some model solutions; and
although this would not likely become strong, it could still be
capable of some lightning. There is some loose consensus on a
second round of scattered storms during the midafternoon to
early evening hours, and it`s this second round that may have
the better potential for severe weather mainly for interior
Southern New England near/west of Worcester. With this second
round, low and midlevel flow increases to the point where
forecast hodographs become pretty curved in a low-LCL setting,
As indicated in the machine-learning progs, potential for
locally strong winds and/or a tornado could develop in western
MA/CT if storms can root themselves at the surface. That leads
to the next source of uncertainty, in that we may still be
dealing with quite a bit of stratus and low clouds from the
overnight lingering even into the afternoon. The longer those
low clouds stick around, the less likely we`ll destabilize
enough.
Took the approach of keeping thunder probs low in the morning
hours, with an isolated mention of thunderstorms. Although I
still carry an isolated thunder mention in eastern MA and RI, I
opted to instead increase probs for thunder in western MA and CT
with the second round of possible storms. Felt uncertainties
that I described were too much to include any enhanced wording
but that might need to be considered later.
Those with outdoor plans on Saturday will want to keep a close
eye to the forecast and monitor for changes.
&&
.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
Key Messages:
* Cold front moves through Saturday night, drying and cooling the
region
* Unsettled weather makes a return later in the week
Details...
Any lingering showers or storms will clear out Saturday night as a
cold front passes through southern New England. Generally, the
timing for the end of these storms is still somewhat uncertain. Some
CAMs are hinting at a line moving through the region after 8 PM,
which will be something to monitor. This would depend on how much
energy and general instability is left following what moves through
in the afternoon/evening, though. Behind the front, drier and cooler
conditions with a cold pool settling in aloft that will likely
continue into the start of next week. Some scattered showers do
remain possible through Sunday as the mid-level low continues its
exit offshore into the Gulf of Maine and the cold pool lingers. High
temperatures will likely remain in the 60s and low 70s in some spots
with less cloud cover Monday, then as the cold pool lingers highs
through midweek will likely remain in the 60s.
Some brief mid-level ridging will shift towards southern New England
with surface high pressure to start the work week, but the pattern
turns unsettled once again towards midweek as another mid-level low
over the Great Lakes strengthens and an associated surface low
shifts to the northeast from the Ohio River Valley. Some guidance
indicates a surface low splitting off from this one in the OH River
Valley and moving along the east coast, which could end up impacting
southern New England in the form of increased cloud cover and rain
chances. However, it is still quite far out in time for any finer
details.
&&
.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
18z TAF Update:
This Afternoon: Moderate confidence.
MVFR-VFR cigs this afternoon. Low chance for an isolated
SHRA/TS mainly near and northwest of a BDL-ORH line after 19z
ending closer to or just after sundown. Light S winds with more
SE seabreeze at BOS.
Tonight: Moderate confidence.
IFR-LIFR ceilings and visibilities return from the coastal
waters mainly after 00z. Low chance of an isolated SHRA after
06z.
Saturday: Moderate confidence overall, but lower on timing both
sub-VFR improvement and on timing SHRA/TS.
IFR-LIFR stratus likely to begin Sat. Slow improvement late
morning through early afternoon with MVFR, improving over the
west terminals first then eastward. West terminals improve
toward VFR mid afternoon. Lower confidence in timing of further
improvements across the east terminals in the afternoon, likely
not until late afternoon if it does scatter out. Convective
showers/storms possible in the morning 13-16z, but will be
isolated- widely scattered. Another round for western airports
after 18z and closer to 00z. Timing lower confidence. Some
storms could become strong, with a better chance for strong
activity in the 2nd round of storms for BAF- BDL- ORH. Winds
mainly SE to S around 5-10 kt.
KBOS TAF...Moderate confidence. Seabreeze til 23z. IFR cigs
move in after 00z with lowering visibilities from BR. Slow
improvements in ceilings Saturday morning with MVFR cigs. Low
chance for convective showers 14-16z around the terminal. SE
winds 5-12 kts.
KBDL TAF...Moderate confidence. ISO SHRA/TS through 00z.
IFR/LIFR overnight. Gradual improvements after 15z toward MVFR
and VFR later in afternoon. Few rounds of thunderstorms possible
in the afternoon and early evening. Timing lower confidence. Few
stronger storms possible, more likely with the early evening
round of storms.
Outlook /Saturday Night through Wednesday/...
Saturday Night: VFR. Chance SHRA.
Sunday through Sunday Night: Mainly VFR, with local MVFR
possible. Breezy. Slight chance SHRA.
Monday through Tuesday: VFR. Breezy.
Tuesday Night: VFR. Slight chance SHRA.
Wednesday: Chance SHRA.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
High confidence overall.
Expect sub-SCA conditions to prevail on the waters. Fog and
reduced visibility will be the biggest potential hazard for
mariners today and tonight, with S winds around 10 kt and seas 4
ft or less. Risk for thunderstorms could develop as soon as
pre-dawn Saturday over the southern waters, with another round
of storms possible into Saturday afternoon.
Outlook /Saturday Night through Wednesday/...
Saturday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Chance of rain showers, isolated thunderstorms.
Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Sunday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of rain showers.
Monday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Monday Night through Tuesday: Winds less than 25 kt. Seas
locally approaching 5 ft.
Tuesday Night: Winds less than 25 kt.
Wednesday: Winds less than 25 kt. Seas up to 5 ft. Chance of
rain showers.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.
&&
$$
SYNOPSIS...Loconto/Hrencecin
NEAR TERM...Loconto
SHORT TERM...Loconto
LONG TERM...Hrencecin
AVIATION...Loconto/Hrencecin/Mensch
MARINE...Loconto/Hrencecin
NWS BOX Office Area Forecast Discussion
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