BOX issues Area Forecast Discussion (AFD) at Jun 20, 1:13 PM EDT670
FXUS61 KBOX 201713
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
113 PM EDT Sat Jun 20 2026
.WHAT HAS CHANGED...
Tweaked timing of Small Craft Advisories for all waters today.
This included adding one for Narraganset Bay.
&&
.KEY MESSAGES...
- Cooler with westerly breezes this weekend. Risk of scattered
afternoon showers and possible thunderstorms through sundown
each day. However, the risk for severe weather is very low.
- Periods of heavy rain possible Monday into early Tuesday.
Drier air with seasonable temperatures expected midweek.
&&
.DISCUSSION...
KEY MESSAGE 1...Cooler with westerly breezes this weekend. Risk
of scattered afternoon showers and possible thunderstorms
through sundown each day. However, the risk for severe weather
is very low.
Cyclonic mid-level flow governs our weather across southern New
England this weekend. In that broader cyclonic flow aloft, a
series of mid level shortwaves will pass by at times. While not
particularly strong, these shortwaves are expected to be potent
enough to result in scattered diurnal showers each afternoon.
Not everyone will see these showers, with the greatest focus
across northern and eastern MA. There will be plenty of dry
hours for most locations this weekend.
Most unstable CAPE values are projected between 500-750 J/kg
today,and between 750-1,000 J/kg Sunday. These values suggest a
few thunderstorms are possible, but with not as much effective
bulk shear, severe weather is not likely.
Gusty west winds expected to continue through today with peak
gust speeds up to 40 MPH. All thing considered, not much
different from yesterday. Winds subside with sunset, and should
not be as gusty Sunday.
KEY MESSAGE 2...Periods of heavy rain possible Monday into early
Tuesday. Drier air with seasonable temperatures expected
midweek.
Latest guidance suite has narrowed some of the differences
between them. Have increased confidence in rainfall developing
Monday, falling most of Monday night, then drying out Tuesday.
This could be a substantial rainfall, with the probability of 1
inch or more of storm total rainfall between 70-80 percent
across southern New England. Even the probability for 2+ inches
of rainfall were about 20-40 percent, greatest across western MA
and CT.
Behind this system, high pressure and northwest flow will bring
rapidly drying conditions during the day Tuesday. Temperatures
are then expected to be pleasant midweek with seasonable highs
in the upper 70s to lower 80s. Only isolated rain chances
expected for Thursday as a low pressure approaches from the
west. A greater risk for showers is anticipated Friday.
&&
.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Today: High confidence.
VFR. WNW winds gusting up to 30 kts through sunset. Some risk
for diurnal SHRA with brief MVFR- VFR visibilities after 18Z,
mainly across eastern coastal terminals, including BOS. Not
impossible for a few TSRA also.
Tonight: High confidence.
VFR, any showers diminish post-sundown. WNW winds decrease to
5-10 kt.
Sunday...High confidence.
VFR. Relatively light west winds could lead to afternoon
seabreezes. Another risk for afternoon showers and TSRA.
KBOS Terminal...High confidence in shower activity and moderate
confidence in the exact timing. Westerly gusts 25-30 kt
continue through sundown.
KBDL Terminal...High confidence in TAF. Some diurnal showers
are possible, but there is lower confidence on how far west they
may reach. So, excluded these showers from the TAF.
Outlook /Monday through Thursday/...
Monday: Mainly VFR, with local IFR possible. Breezy. Chance
SHRA, slight chance TSRA.
Monday Night: MVFR/IFR conditions possible. Breezy. SHRA,
slight chance TSRA.
Tuesday: VFR. Breezy. Slight chance SHRA.
Tuesday Night through Wednesday Night: VFR.
Thursday: VFR. Slight chance SHRA, slight chance TSRA.
&&
.MARINE...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Small Craft Advisories remain in effect for MA and RI coastal
waters today. Could see a few gale force gusts as well, but not
thinking it will be prevalent enough to warrant an upgrade to
Gale Warnings. Risk for scattered showers and isolated
thunderstorms this evening, and again Sunday afternoon. Any
showers and thunderstorms should diminish after sunset.
Winds and seas should trend below SCA criteria tonight.
Outlook /Monday through Thursday/...
Monday: Low risk for Small Craft Advisory winds with local
gusts up to 30 kt. Chance of rain showers.
Monday Night: Moderate risk for Small Craft Advisory winds with
local gusts up to 30 kt. Areas of rough seas. Rain showers,
chance of thunderstorms.
Tuesday: Winds less than 25 kt. Areas of rough seas. Chance of
rain showers, slight chance of thunderstorms.
Tuesday Night: Winds less than 25 kt. Seas up to 5 ft.
Wednesday: Winds less than 25 kt. Seas locally approaching
5 ft.
Wednesday Night through Thursday: Winds less than 25 kt.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 7 PM EDT this evening for ANZ230-
232>235-237.
Small Craft Advisory until 4 PM EDT this afternoon for ANZ231-
236-250-251.
Small Craft Advisory until 1 AM EDT Sunday for ANZ254-256.
Small Craft Advisory until 4 AM EDT Sunday for ANZ255.
&&
$$
DISCUSSION...McMinn/Guest
AVIATION...McMinn
MARINE...McMinn
Source:
BOX issues Area Forecast Discussion (AFD) at Jun 20, 1:13 PM EDT----------------
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