Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 281902

Area Forecast Discussion
National Weather Service Boston/Norton MA
302 PM EDT Sun May 28 2023


A sunny and warm afternoon and evening is in store today. We then
have a brief cool down Monday, especially across eastern MA as
a backdoor front sweeps across the area. Warming trend begins
Tuesday, with potential for 90 degree temperatures Thursday
into Friday. A cold front brings the next chance for showers
with a few thunderstorms Friday night into early Saturday,
although soaking rains are not likely. Temperatures then trend
cooler than normal for next weekend with a period of cooler
onshore flow.



Tonight clear and quiet weather continues under high pressure.
However, across northern and especially northeastern MA the first
half of the night will be quite a bit milder than the second half
thanks to initial warm air advection (925 mb temps jump to +20C)
followed by a backdoor cold front. This will keep surface temps in
the mid to upper 60s through around midnight before dropping into
the upper 50s/low 60s along with gusty winds behind the front. The
front is starved of moisture so not expecting any rain to accompany
it but we will see a brief period of increased cloudcover.



Thus, Monday will be quite a bit cooler than Sunday, especially the
closer you get to the eastern MA coast as onshore northeasterly flow
over the ocean with SSTs in the low to mid 50s keeps temps limited
to the upper 60s. Further inland highs make it into the mid 70s
while western MA and CT will see highs in the upper 70s and low 80s
in the CT valley. The day will start gusty as the shortwave dropping
through helps to induce a 25 to 35 kt 925 mb jet which should mix
down enough to see wind gusts in the 20 to 25 mph range, even to 30
mph over Cape Cod and the islands. The jet then moves off and winds
diminish by sunset. Overnight Monday the high continues to expand
overhead leaving clear skies and light winds. Lows in the post
frontal airmass will be 5 to 10 degrees cooler than the night
previous, in the 40s.




* Warm and dry weather with potential for 90-degree temps Thurs and
  Fri. Low humidity levels.

* Sct showers/storms Fri night into early Sat, but not a washout.

* Cold front moves in either Fri or Fri night, bringing our next
  chance for rain with a few t-storms also possible.


Ensembles remain in good agreement on the mid-level pattern through
Thurs, as a higher geopotential height-over-lower geopotential
height (Rex block) pattern dominates the pattern. As the upper ridge
of higher heights aloft moves into New England Wed and Thurs,
increasing subsidence will maintain a dry weather pattern but also
result in significant warmup towards temperatures resembling
summerlike values, albeit without the humidity we often see in the
summer months. Given the recent and persistent spell of dry weather
along with rather deep mixing, temperatures may end up overachieving
guidance especially in the interior.

The warmup begins on Tues with highs back into the 70s (mid 60s near
the coastlines), and continuing into the lower to mid 80s Wed (upper
60s/low 70s South coastal areas). While high temperatures into Thurs
and Fri should reach into the mid 80s to lower 90s, low humidity
levels (dewpoints 40s to 50s) mean the thresholds for significant
heat/Heat Advisory criteria are unlikely to be met. Nonetheless
still very warm to hot. Coolest lows Tue night in the 40s to lower
50s, though these also steadily increase each night with 50s in the
forecast for Wed and low to mid 60s lows for many on Thurs.

Models continue to advertise a cold front moving southward from
Canada around the later Fri to early Sat timeframe, a little later
than prior guidance was indicating. This front will also offer our
next chance for showers with a few t-storms also possible, although
not likely to be a washout or put much of a dent into the spell of
dry weather given the progressive nature to the front and a shorter
duration of related showers/storms. Kept lower end PoP in the
forecast for Fri late-day into early Sat AM, better albeit low probs
for thunder around or just after sundown.

Fairly good agreement on the early part of next weekend featuring a
break from the very warm temps, as a pronounced shortwave trough
disturbance aloft digs into ME/Nova Scotia vicinity, with cooler NE
onshore flow returning for Sat.


Tuesday through Thursday:

The brief cooldown on Memorial Day looks to be a distant memory,
with a multi-day warm-up with summerlike temps in the forecast for
Wed and especially Thurs. This occurs as a midlevel ridge associated
with a Rex block builds in aloft over SNE, with sfc high pressure
remaining anchored over or just to our south.

Expect several days of warm and dry days and warming nighttime
temps. Highs should reach the 70s to perhaps a few low 80s Tues,
then warm up further into the low-mid 80s (cooler low-mid 70s near
the southern coast). Warmest low-level air (850 mb temps around +16
to +18C) builds in on Thurs, which is expected to be the warmest
day. Moderate (around 30-50%) EPS/Canadian ensemble probabilities
for 2-m temps of 90 degrees or greater are still apparent in the
RI/MA coastal plain, Merrimack and into the CT Valleys; pretty
notable ensemble-probabilistic signal at this time horizon for
temps at or around 90+ degrees.


A bit of uncertainty on Fri regarding the timing of a cold front
which moves southward from Quebec and northern New England; its
possible that Fri could be at least as warm if not a couple degs
warmer than Thurs if a slower frontal timing verifies (e.g. such as
depicted in the 12z Canadian GEM). With 500 mb flow perpendicular to
the E-W frontal zone, suspect the front will be more progressive.

In a protracted dry spell, this front should also bring our next
chance for showers and thunderstorms too; however the front`s timing
will be critical on the coverage and how strong any showers/storms
may become.


Forecaster Confidence Levels:

Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.

18Z TAF Update: High confidence.

VFR through Monday night. SW winds will diminish toward sunset
then veer briefly to the NW then NE by 10Z with a backdoor cold
front. This front drops through generally arriving between
6-12Z from NE to SW. This front will bring a brief period of
gusty winds, to 20 kt between 09 and 18Z then diminishing.
Monday night winds will be light and remain out of the east or

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday through Thursday/...

Monday Night: VFR. Breezy.

Tuesday through Thursday: VFR.


Forecaster Confidence Levels:

Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.

This afternoon and tonight...High Confidence.

* SCA headlines near south coast for SW Wind Gusts up to 25 kts

Southwest winds continue to blow to 10 to 15 knots ahead of a
backdoor cold front. Good mixing over the land should result in
some nearshore gusts around 25 knots near the south coast
leading to some choppy seas. Gusts will diminish after sunset
and then shift to the NE after midnight behind the backdoor cold
front. Gusts of 20 to 25 knots will develop again across the
waters by daybreak.

Monday...High Confidence.

* ENE Wind Gusts of 25 kts & Rough Seas Monday

A strong backdoor cold front for this time of year will result
in a period of ENE wind gusts around 25 knots for all waters on
Monday. We will need to hoist small craft headlines for all
waters and seas will be choppy.

Monday night...High Confidence.

Winds out of the east/northeast diminish through the night, 5 to
10 kt. Seas 3-4 ft.

Outlook /Tuesday through Thursday/...

Monday Night: Winds less than 25 kt. Areas of seas approaching
5 ft.

Tuesday: Winds less than 25 kt. Seas locally approaching 5 ft.

Tuesday Night through Thursday: Winds less than 25 kt.


MARINE...Small Craft Advisory until 7 PM EDT this evening for


LONG TERM...Loconto
MARINE...Loconto/BW is the U.S. government's official web portal to all federal, state and local government web resources and services.