NWS Forecaster Discussion
BOX
Area Forecast Discussion National Weather Service Boston/Norton MA.
371
FXUS61 KBOX 300636
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
236 AM EDT Thu Apr 30 2026
.WHAT HAS CHANGED...
Extended the Small Craft Advisory for the outer waters through
8pm Friday.
&&
.KEY MESSAGES...
- Steady rain continues through much of the day giving way to a
clearing trend from west to east this afternoon.
- Cooler and mainly dry this weekend with a coastal storm passing
well offshore.
- Warmer albeit unsettled conditions return next week.
&&
.DISCUSSION...
KEY MESSAGE 1... Steady rain continues through much of the day
giving way to a clearing trend from west to east this afternoon.
Broad lift from approaching low pressure brings a shield of rain to
southern New England through much of the day today. Main area of low
pressure tracks through the St. Lawrence Valley. Weak secondary low
tracking from mid Atlantic will help enhance showers mainly across
eastern Mass and the Islands this afternoon into the early evening.
High-res guidance still shows some elevated instability developing
by the afternoon as the dry slot works its way overhead. Best chance
for any isolated thunder will be on the edge of the dry slot
focused near Cape Cod and Islands, but moreso offshore. Solid
rainfall event on the order of around 0.5" for most, but still
much needed given recent rainfall departures.
KEY MESSAGE 2...Cooler and mainly dry this weekend with a coastal
storm passing well offshore.
Amplified pattern over the weekend should feature a building ridge
of high pressure over central Canada which traps a closed 532
decimeter upper low over southern Ontario. There are still slight
differences among global guidance in the exact location and strength
of the ridge over Canada. The ECMWF shows a more southern solution
and thus a bit more in the way of shower activity later Saturday
afternoon. On the whole, southern New England should be far
enough removed from coldest air aloft to keep us mostly dry,
especially given W/NW flow, but pattern certainly favors diurnal
clouds and perhaps a few afternoon sprinkles over weekend.
Guidance continues to show a fairly weak low that may bring a few
showers or perhaps a period of light rain to the southern coast and
the Cape/Islands Saturday night into Sunday morning. Recent trends
still paint a weak unamplified picture with the majority of the EPS
and GEFS ensembles showing a further offshore track.
KEY MESSAGE 3... Warmer albeit unsettled conditions return next
week.
Pattern relaxes a bit early next week as closed low lifts farther
north, but we remain under broad cyclonic flow aloft. Eventually
longer range guidance shows closed low setting up near upper Great
Lakes, putting us in SW flow aloft. This could end up bringing more
moisture and warmer air into region by Tuesday/Wednesday as weak
front approaches resulting in scattered showers. Ensemble guidance
shows 850 mb temp anomalies climbing to +10F above climo Tuesday and
Wednesday of next week.
&&
.AVIATION /06Z THURSDAY THROUGH MONDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
06z TAF Update: Moderate confidence due to timing of flight
categories.
Widespread -SHRA thru 14z with IFR ceilings/visibilities.
Showers come to an end around midday today with gradual
improvement to MVFR ceilings, and possibly VFR later in day with
the exception of Cape Cod and Islands.
Quick improvements to VFR from W to E tonight with slower
improvements for the Cape and Islands.
KBOS Terminal...Moderate confidence. Reduced confidence in the
end time of IFR/LIFR this afternoon.
KBDL Terminal...High confidence in TAF.
Outlook /Friday Night through Monday/...
Friday Night: VFR.
Saturday through Saturday Night: VFR. Chance RA.
Sunday: VFR. Breezy. Slight chance RA.
Sunday Night: VFR.
Monday: VFR. Breezy.
&&
.MARINE...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
High confidence through the end of the week.
Pressure gradient between slow-moving low pressure SE of the 40/70
benchmark and high pressure over the Canadian Maritimes keeps E/NE
winds in play through the end of the week.
Main issue will be the long fetch of NE winds resulting in rough
seas of 5 to 8 feet on outer waters through Thu where SCA remains
posted. Areas of fog will persist through tonight along with
showers.
Outlook /Friday Night through Monday/...
Friday Night: Winds less than 25 kt. Seas up to 5 ft.
Saturday: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of rain.
Saturday Night through Sunday: Winds less than 25 kt. Seas
locally approaching 5 ft. Chance of rain.
Sunday Night: Winds less than 25 kt. Areas of seas approaching
5 ft.
Monday: Low risk for Small Craft Advisory winds with gusts up
to 30 kt. Seas up to 5 ft.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 AM EDT Friday for ANZ250.
Small Craft Advisory until 8 PM EDT Friday for ANZ254>256.
&&
$$
DISCUSSION...FT
AVIATION...FT
MARINE...FT