BOX issues Area Forecast Discussion (AFD) at May 18, 12:50 PM EDT214
FXUS61 KBOX 181650
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
1250 PM EDT Sun May 18 2025
.SYNOPSIS...
An upper level low pressure will track across northern New
England today and into the Canadian Maritimes on Monday. This
will bring cooler and less humid conditions, but also generally
unsettled weather with cloud cover and hit or miss showers
mainly north of the Massachusetts Turnpike. A cooling trend
sets in Tuesday that will continue through the week. Unsettled
weather returns once again in the second half of the week into
the weekend.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Key Messages...
* Considerable clouds overspread the region from the west today
with highs mainly upper 60s/lower 70s and a bit of a breeze
* A few spot showers possible this afternoon mainly north of
I-90...but the vast majority of the day will remain dry
A closed upper level low across northern New England will result
in cyclonic flow across the region today. This will result in
broken deck of strato-cu overspreading the region from west to
east through the afternoon. The cold pool aloft coupled with
shortwave energy may trigger a few spot showers later
today...mainly north of I-90. However...the vast majority of the
day will be dry with the bulk of the showers in northern New
England closer to the closed upper level low.
High temps today will mainly be in the upper 60s to the lower
70s...although a few degrees cooler across the interior high
terrain. A westerly breeze of 20-25 mph and decreasing humidity
will make it feel cooler compared to the weather.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
230 AM Update:
Key Messages:
* Turns breezy and cooler, drier and much less humid tonight,
with partly cloudy skies. Lows mid 40s to low 50s.
* These conditions last into Monday, with less clouds south and
west and more north. Highs mainly in the 60s, but northwest
breezes could make it feel cooler.
Details:
The upper low will continue to pull into Maine tonight, then
slowly progress into the Maritimes on Monday. This will create a
strengthening NWly pressure gradient tonight which lasts into
Monday, along with strong cold and dry advection.
Expect any instability type showers to dissipate shortly after
sundown this evening. The real noticeable airmass change then
comes in as northwest winds pick up, with speeds 10-15 mph and
gusts in the 25-30 mph range. Dewpoints fall into the 40s, so it
should feel noticeably less humid compared to the last couple
days. Our 925 mb temps then turn unseasonably cool, falling to
around +3 to +5C by early Monday morning! Expect mostly clear to
partly cloudy skies, greatest north, but the strengthening
winds overnight should keep temps in the mid 40s to lower to
mid 50s.
Monday features variable amts of cloud cover, with less
cloudiness toward mostly sunny conditions south and west, and
quite a bit more across northern and northeast MA closer to the
upper level circulation. More sunshine will facilitate stronger
mixing too, with NWly gusts around 25-35 mph. Although the sun
should be enough to keep temps closer to the mid 60s - near 70,
temps could struggle to reach 60 degrees in northeast MA/North
Shore area, and the breezes could make it feel cooler than that.
&&
.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Key Messages:
* Cooling trend starts Tuesday and continues through the rest of the
week
* Another system will likely bring rain and gusty winds to southern
New England in the second half of the week
Details...
Not much has changed in the early part of this period. An upper
level low makes its exit offshore towards the Maritimes Monday
night. Northwest flow kicks in while cooler temperatures aloft
remain, which will help keep the region cooler and drier. Winds
shift to the northeast Tuesday into Tuesday night as the low
continues offshore. Highs Tuesday through Friday are expected to be
mostly in the 50s and low 60s.
A surface low is expected to move up along the east coast towards
southern New England. This late spring Nor'Easter could bring
significant rainfall and gusty winds starting sometime in the early
hours of Thursday through Friday. Timing is starting to get more
defined, with ensembles starting to agree on the low passing to the
southeast Thursday afternoon/evening. There is still significant
variance in its track though. The GEM tracks its center right over
SE MA, while the GFS and ECMWF track it to the southeast of
Nantucket (though the GFS keeps it further offshore). This is
uncertainty is also seen in the different ensembles' 24 hour QPF
values, where they range from around 0.35" across southern New
England (GEFS) up to an inch in some areas (ECMWF ENS). If the storm
remains closer to the coast, we can expect more rain and gustier
winds. Both decrease if the low tracks further offshore. NAEFS
guidance also signals PWATs about a standard deviation above normal
remaining well offshore. Even so, wetting rains can be expected. The
overall consensus is that the end of next week will be unsettled and
cool with continued broad cyclonic flow and cooler temperatures
aloft.
&&
.AVIATION /18Z SUNDAY THROUGH THURSDAY/...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
18z TAF Update...
This afternoon through Monday night...High Confidence.
A scattered to broken deck of mainly VFR clouds will continue to
impact the region through Monday night...particularly in
northern MA. We can not rule out some brief marginal MVFR
cigs...but overall thinking conditions will maintain VFR levels
the majority of the time. A few spot showers are possible at
times...mainly in northern MA but even in these locations the
vast majority of this period will feature dry weather. W winds
shift to the NW tonight continuing from that direction Mon into
Mon night. Gusts of 20 to 30 knots will be common right through
Mon night. Even a few brief gusts over 30 knots will be possible
at times in the high terrain.
KBOS TAF...High Confidence in TAF.
KBDL TAF...High Confidence in TAF.
Outlook /Tuesday through Thursday/...
Tuesday and Tuesday Night: Mainly VFR, with areas MVFR possible. Slight
chance SHRA.
Wednesday: MVFR/IFR conditions possible. Chance SHRA.
Wednesday Night: MVFR/IFR conditions possible. Breezy. SHRA
likely.
Thursday: Mainly MVFR, with areas IFR possible. Breezy. SHRA
likely.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Today through Monday: High Confidence.
An upper level low will track across northern New England today,
then move into the Gulf of Maine tonight and into Canadian
Maritimes Mon.
W wind gusts increase to around 20-25 kt on most waters this
afternoon, with a windshift to NW around 25-30 kt on most waters
tonight and into Monday. Offshore flow should limit wave heights
to around 3-5 ft, though some 6 footers possible on southern
waters. Small craft advisories remain posted.
Outlook /Monday Night through Thursday/...
Monday Night through Tuesday Night: Winds less than 25 kt.
Areas of seas approaching 5 ft.
Wednesday: Winds less than 25 kt. Seas up to 5 ft. Slight
chance of rain showers.
Wednesday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers.
Thursday: Strong winds with gusts up to 25 kt. Rough seas up to
10 ft. Rain showers likely.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 PM EDT Monday for ANZ230>237-250-
251-254>256.
&&
$$
SYNOPSIS...Loconto/Hrencecin
NEAR TERM...Frank
SHORT TERM...Loconto
LONG TERM...Hrencecin
AVIATION...Frank/Hrencecin
MARINE...Loconto/Hrencecin
Source:
BOX issues Area Forecast Discussion (AFD) at May 18, 12:50 PM EDT----------------
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