NWS Forecaster Discussion
BOX
Area Forecast Discussion National Weather Service Boston/Norton MA.
932
FXUS61 KBOX 151113
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
713 AM EDT Thu May 15 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. Scattered showers or
thunderstorms will be a possibility to start the weekend before
a cooling trend and drier conditions move into the region to
start next week.
&&
.NEAR TERM /THROUGH TONIGHT/...
330 AM Update:
Key Messages:
* Scattered showers early in the morning move offshore.
* Overcast and on the humid side.
* Isolated to widely scattered aftn showers/t-storms in the
interior if clouds can break, some which could be slow-moving
and be a localized heavy-downpour risk.
Details:
The axis of showers and embedded thunderstorms over interior
SNE will be gradually shifting eastward into eastern MA and RI
and Cape/Islands over the next couple hours. Could be some
localized downpours in some of this activity but it should just
make for difficult travel/reduced visby for morning commuters vs
yield any street flooding concerns. This axis of rain showers
continues moving offshore by mid-morning; in its wake is left a
rather cloudy and humid warm sector in an amorphous/weak/"blah"
sea-level pressure pattern. This occurs as an upper level
disturbance works its way northeast into eastern NY and opens up
as it does so.
The main forecast challenges for today are related to the extent
to which we can shake free of cloudiness, or if we can at all.
BUFKIT profiles from the RAP/HRRR suggest that cloudiness should
hang tough in eastern MA and RI, and it would also lead to more
convectively-stable thermo profiles. It wouldn`t take much mid-
May sun angle to disperse this layer of cloudiness but I`m more
pessimistic we`ll see much of any breaks in eastern New England.
There is more optimism we`ll scatter out during the afternoon in
interior Southern New England; and if that does occur then the
risk for diurnally-driven scattered showers and thunderstorms
could develop. There isn`t much in terms of a lifting source
given the above-described pressure pattern, other than weak
upslope convergence against the interior hills. CAPEs are
progged around 700-1200 J/kg from HFD-ORH-BED north and west
but would be of the tall, skinny type of CAPE profile with poor
mid- level lapse rates. Some of the convective-permitting model
output simulates some popup cells in that weakly unstable
airmass. Severe weather is not expected. But since mid-upper
flow weakens to under 20 kt thru a deep depth of atmosphere with
the approach of the upper disturbance, and that warm cloud
depths are around 10-11kft favoring precip efficiency, any storm
which develops would be slow moving and be capable of heavy
downpours and local heavy rain footprints, falling in an area
which has been soaked of late. Probabilistic HREF 3-hourly QPF
progs show some solid probs (up to 50%) of 1" rainfall in 3 hrs
from Worcester west. In a nutshell, could be some minor hydro
issues in slow moving cells but shouldn`t rise to the level of
significant/flash flooding.
Should see highs in the mid 60s coastal areas to the low-mid
70s, with better chance at mid 70s in the Berkshires and
interior SNE with sustained breaks in cloudiness.
&&
.SHORT TERM /FRIDAY/...
330 AM Update:
Key Messages:
* Stratus and areas of fog tonight, locally dense in some
locations.
* Should clear out Friday, and while generally dry, will watch
for possible scattered thunderstorms in western New England
late in the day. Better potential exists in NY.
Details:
Tonight:
Diurnally-driven showers or storms should dissipate by early
evening. Weak sea-level pressure pattern continues, with light
to calm winds, a humid airmass with recent rainfall having
occurred. Though I don`t have the strongest conviction in
ceiling/visby guidance of late, this is a favored setup for
development of areas of fog and stratus. There`s also been a
history of fog/stratus in the mid-Atlc states overnight tonight,
which is where our airmass is coming from. NBM visby progs
actually sock all of SNE in dense fog, so it`s possible later
shifts could consider doing fog statements or advisories if
needed. Rather mild, but generally dry and on the humid side
with lows in the mid 50s to lower to mid 60s.
Friday:
We probably will have quite a bit of stratus and fog to open
Friday. Background weak subsidence owing to 500 mb height rises
could lead to more uncertainty on when we can scatter out.
Tried to show some optimism in clearing during the mid to late
morning to a partly sunny look, and temps warming to well into
the 70s to a few spot 80 degree readings; if clearing is delayed
until the afternoon, we`ll probably struggle to reach 80.
Later in the day our western areas start to get into stronger
height falls with the approach of a midlevel warm front. This
front will really help steepen lapse rates in the 850-500 mb
layer, and there`s some potential for a few rumbles of thunder
during the late-afternoon stemming from a more active convection
pattern in the Gt Lakes. Think a better chance for more robust
convection develops in central/southern NY with weakening
activity if any here in SNE, and that`s the more likely outcome,
but a few solutions such as the high- res WRF windows offer
potential for scattered storms after 21z working over the
Berkshires.
&&
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Key Messages:
* Severe thunderstorms are a possibility on Saturday
* Drier and cooler to start next week
Details...
A warm front is expected to move through the region Saturday
morning, and we will be in the warm sector behind it before a cold
front moves through. Ensembles still showing some probs for some
elevated surface CAPE across western and central MA that would favor
some thunderstorms. Timing on the cold front`s passage could affect
just how favorable the environment could be for severe storms and
their mode. Even with some of the higher res guidance starting to
reach this period hinting at some more organized convection in the
evening hours Saturday, it`s still far enough out that this could
change. Probs for higher shear across the interior are soundly above
50 percent, so a high shear low CAPE environment could be what these
storms develop in. CSU ML guidance does indicate some slightly
higher chances for severe weather in southern New England, though,
so this will continue to be monitored.
A cold front moving through is expected to usher in a drier airmass
following the exit of the mid-level low. Mid-level ridging pushes
its way in heading into midweek with surface high pressure shifting
into southern New England, which should keep the region dry. Winds
shift more to the NW and N. Guidance shows temperatures aloft
cooling by around 10C from Saturday afternoon by Monday, continuing
into Wednesday. Saturday and Sunday highs are expected to be
primarily in the 70s, although Sunday is slightly cooler with the
highest temperatures in the low to mid 70s. Once the cold front
moves through, highs to start the week may settle more into the mid
to upper 60s.
&&
.AVIATION /11Z THURSDAY THROUGH MONDAY/...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
12z TAF Update:
Today: Moderate confidence.
Should see widespread MVFR-IFR cigs early with early-day
SHRA/embedded TS moving offshore. It looks like moisture gets
trapped and struggles to mix out east of ORH, and maintained at
least MVFR bases for most of the day. Wouldn`t rule out a SHRA
at times but majority of the time will be dry. For ORH, BAF and
BDL, there`s more optimism in bases lifting to VFR, but that
will increase the risk for SCT slow-moving SHRA/possible TS
indicated in TAFs with PROB30s from 17-23z. Although severe
weather not expected, lightning and downpours could affect these
western terminals if a direct hit occurs. Continued SE to S
winds around 5-10 kt.
Tonight: Moderate confidence.
Areas of IFR to LIFR fog and stratus develops after daytime
SHRA/TS eases after sundown. Showed most airports around 1/2 to
5SM, but fog could become locally dense and visbys could be as
low as 1/4SM, especially western airports. Light to calm winds.
Friday: High confidence in trends, but moderate on timing.
IFR-LIFR from overnight should start to improve to VFR 13-16z,
perhaps longer across the Cape/Islands. Some risk for SHRA/TS
possible west of ORH after 18z but stronger activity seems more
likely west of the Berkshires. Light S winds.
KBOS TAF...Moderate confidence. VFR for another couple hrs until
SHRA moves in around 08-09z with ceilings then trending to
MVFR/IFR. SHRA ends around 12z although MVFR ceilings likely
continue into early afternoon. Categories could trend MVFR-VFR
range during the afternoon, then start to lower again to IFR-
LIFR levels late-afternoon to tonight.
KBDL TAF...Moderate confidence. MVFR with 3-6 SM SHRA. SHRA ends
around 11z although MVFR-IFR bases continue into the early
afternoon. Scattering to VFR around early-midaftn, but
potential for slow-moving TS 17-23z. IFR-LIFR in fog/stratus
tonight, locally dense fog possible.
Outlook /Friday Night through Monday/...
Friday Night: Mainly VFR, with local IFR possible. Chance SHRA,
isolated TSRA.
Saturday: MVFR/IFR conditions possible. Chance SHRA, isolated
TSRA.
Saturday Night: VFR. Chance SHRA.
Sunday through Sunday Night: Mainly VFR, with local MVFR
possible. Breezy. Slight chance SHRA.
Monday: VFR. Breezy.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
330 AM Update:
High confidence overall.
E/SE winds remain below SCA levels Thu and Fri. Seas will be
building on the southern ocean waters where SCAs still continue.
Few showers or a thunderstorm possible early this morning, with
areas of marine fog developing tonight and could linger into a
good part of Fri.
Outlook /Friday Night through Monday/...
Friday Night: Winds less than 25 kt. Slight chance of rain
showers, isolated thunderstorms.
Saturday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain showers, isolated thunderstorms.
Saturday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Chance of rain showers.
Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Slight chance of rain showers.
Sunday Night through Monday: Winds less than 25 kt. Areas of
seas approaching 5 ft.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 4 PM EDT this afternoon for ANZ235-
237.
Small Craft Advisory until 1 AM EDT Friday for ANZ254>256.
&&
$$
SYNOPSIS...Loconto/Hrencecin
NEAR TERM...Loconto
SHORT TERM...Loconto
LONG TERM...Hrencecin
AVIATION...Loconto/Hrencecin
MARINE...Loconto/Hrencecin