Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 261753
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
153 PM EDT Sun Jun 26 2022

.SYNOPSIS...
Hot and somewhat humid weather continues into Sunday with dry
weather prevailing. A cold front will bring a period of widespread
showers for Monday. Locally heavy rain is possible. Generally dry
and seasonable temperatures follow Tuesday and Wednesday.
Increasing temperatures late in the week with perhaps more
unsettled weather by the weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
955 AM update...

Stratus and patchy fog will flirt with Nantucket into this
afternoon, otherwise lots of sunshine and very warm to hot
conditions. Current forecast temps look good. Dewpoints
currently range though the 60s but expect them to drop into the
upper 50s to lower 60s away from the south coast this afternoon
as mixing increases within the deepening boundary layer.
Soundings show a shallow layer of low level moisture will
support diurnal CU developing, mainly in the interior. A few of
the CAMs have isolated showers developing in the interior this
afternoon. While there will be some SB instability, it is quite
dry above 800 mb which should preclude any showers.

Previous discussion...

Mild and dry early-morning underway across Southern New England
current temps in the mid 60s to low 70s at this hour. Surface high
anchored near Long Island early this morning is imparting a light
southerly flow. Areas of locally dense fog have overspread the
Islands per nighttime microphysics satellite imagery and is expected
to expand northward toward the immediate south coast toward
daybreak. While insolation and increasing southerly breezes should
disperse areas of fog during the morning, areas of stratus may still
linger over the adjacent waters.

Otherwise shaping up to be a very warm to hot day especially away
from the coast given 850 mb temps around +16 to 18C. Soundings show
full mixing which brings highs well into the 80s to the lower 90s;
cooler low 80s near the coasts. While dewpoints start off in the
lower to mid 60s, they do lower a few degrees given mixing. A few
convection-permitting solutions (NAM-3km, WRF-FV3) simulate shallow
convection across central/east-central MA toward mid to late
afternoon with modest CAPE (under 300 J/kg). However lots of dry air
aloft and background subsidence given mid-level ridge aloft should
prove hostile enough to mitigate any showers. Thus opted for a dry
forecast.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
300 AM Update:

Tonight:

Seasonably strong upper trough over the Gt Lakes moves into western
NY late tonight, with surface cold front marching eastward into
eastern NY/western MA by daybreak. At least through midnight, expect
dry weather to continue with south winds also continuing as well.
00z guidance seems a few hours slower with the front`s approach into
western New England and have tried to focus increasing PoPs into the
after-09z period. There is a modest increase in elevated instability
in western MA/CT toward dawn but still think the bulk of the rains
arrive on Monday. Expect increasing clouds, toward a mid-level
overcast further east and more of a lower cloud overcast west.

Monday:

Cold front then advances through Southern New England Monday. Air
mass is quite juiced with PWATs in the 1.8 to 2 inch neighborhood,
and while model soundings don`t depict much CAPE, very high warm-
cloud depths favoring heavy rain processes support continued mention
of heavy rain wording in the forecast. Thus, there may be a period
of downpours for a short period of time as the front trudges
eastward. While mid-level flow is a little weaker across CT/RI, in
general wind fields still are too strong (e.g. individual cell
motion is too fast resulting in short accumulating periods) to
produce high rainfall accumulations/footprints. While nuisance poor
drainage/street flooding issues could arise in a worst-case, the
only other projected impact may be a commute with brief low-
visibility rain, particularly in the Hartford-Springfield-
Worcester metro areas. Kept mention of isolated thunder going
but CAPE values are meager given the very warm profiles and
abundant cloud cover. Front should make it to the eastern MA
coast by the PM commute, with a wind shift to W and drier air
filtering in behind the front.

Highs in the 70s to near 80, but still rather humid until frontal
passage.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Highlights

* Showers tapering off as a cold front pushes offshore Mon night
  into early Tue.

* Generally dry and quiet for much of the coming week. Temps
  trending upward mid to late in the week.

* More unsettled late in the week and heading into the weekend.

Monday night into early Tuesday AM...

Trough over the Great Lakes lifts into northern New England by
Tuesday morning. Behind the trough a ridge builds into the Great
Lakes. In response to the trough a cold front will still be working
its way through central, but mainly eastern portions of the CWA.
High pressure will begin nudging into the region from the OH Valley.

Expecting shower to taper off as the cold front moves offshore and
cloud cover decreases as the night progresses from west to east.
Will feel much cooler heading into Tuesday with 850 hPa temps
diminishing to 5-10 degrees Celsius. The result will be lows
generally in the 50s, but there will be some low 60 degree readings
along the coastal plain.

Tuesday through Thursday...

Still caught up in somewhat cyclonic flow through much of this
period, but flow becomes more zonal by late Wednesday into Thursday.
High pressure builds into New England on Tuesday and offshore by
Wednesday and Thursday.

Will be much cooler on Tuesday in wake of the cold front. Will have
WNW/NW flow at 850 hPa with temps of 8-10 degrees Celsius. Bumped up
temps to the 75th percentile of guidance as there will be some
downsloping. Expect highs on Tuesday to range from the 70s to low
80s.

At this point still am anticipating dry and quiet weather through
Wednesday and Thursday. Will note there is a trough that lifts from
the Great Lakes into northern New England on Wednesday. Depending on
the exact timing this trough lifts in could have 500 hPa temps of -
10 to -18 degrees Celsius. This coupled with diurnal heating should
result in a fair amount of diurnal CU. The latest GFS shows some
light precip over our area, but the bulk of the ensemble guidance
keeps us dry. At this point 14 members bring some light precip to
our area, which are mostly GEFS members. This is a result of a
deeper trough over the eastern Great Lakes in comparison to the 86
other members. Did bump up precip chances to borderline isolated
showers given the conceptual model/experience, but may need to
increase further in future updates.

Generally appears that the dry weather prevails with high pressure
moving offshore. Will have SW to W flow bringing warmer air into
southern New England. On Wednesday will have 850 hPa temps increase
to 11-14 degrees Celsius. The result are highs in the mid 70s to the
mid 80s. As for Thursday will see 850 hPa temps of 12-16 degrees
Celsius. For both these periods went with the 75th percentile of
guidance. Highs top out on Thursday in the mid 70s to the upper 80s.

Friday and Saturday...

Next shot for more unsettled weather during this period. Could have
a shortwave or two lift into/through New England. Per WPC Cluster
Analysis most of uncertainty lies with the amplitude and positioning
of the trough. At this point confidence is highest in precipitation
chances on Saturday as all clusters show some sort of precip over
our region just varying amounts. Could see some thunder as there is
some instability in place and increasing deep layer shear.

Dialing back to Friday. At this point ensembles have a roughly 54 to
46 spread in if it will be wet versus dry. Have stuck with the NBM
at this point as it is difficult to push precip chances in any
specific direction. Expect the summer warmth to return on Friday and
could continue perhaps into Saturday. High temps on Friday range
from the mid 80s to the low 90s. At this point is a bit cooler on
Saturday with highs in the 80s.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
Forecaster Confidence Levels:

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

Tonight...Moderate confidence.

VFR for most with increasing mid/high clouds. Scattered showers
or an isolated t-storm possible across western New Eng 09-12z.
IFR/LIFR stratus and fog may redevelop over the Islands tonight
but confidence is lower.

Monday...Moderate confidence.

Cigs lower to MVFR with pockets of IFR as showers and isolated
t-storm move through. Focus for showers across western New Eng
in the morning shifting to the east during the afternoon. Brief
heavy rainfall possible. SW gusts increasing to 25 kt across
Cape/Islands and SE coastal MA as modest low level jet develops.
Wind shift to WNW across western MA during the afternoon as
cold front moves through.

Monday night...Moderate confidence.

MVFR/IFR conditions in showers and isolated thunder across SE
New Eng in the evening. Otherwise, VFR with clearing skies in
western New Eng spreading east overnight after post-frontal
wind shift to NW.

KBOS Terminal...High confidence in trends. Lower confidence in
specific details/timing.

KBDL Terminal...High confidence in trends. Lower confidence in
specific details/timing.

Outlook /Tuesday through Thursday/...

Tuesday through Tuesday Night: VFR.

Wednesday: VFR. Breezy.

Wednesday Night through Thursday: VFR.

&&

.MARINE...
Forecaster Confidence Levels:

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

Increasing southerly winds today to around 10-20 kt. A developing
low-level jet later tonight of around 25-30 kt could support gusts
tonight into Monday to levels near small craft criteria. Seas will
also build to around 3 to 4 ft, with borderline/5 ft seas later
tonight into Monday on the offshore waters. Given questions on
mixing of these stronger gusts through the marine boundary layer,
and with seas being borderline, didn`t have confidence as yet to
hoist any SCAs for Monday. It`s possible those may be needed in
later shifts but think conditions are still on the marginal side.

Areas of fog especially southern waters today that will reduce
visibility. Rain, heavy at times then overspreads the waters for
later Monday.

Outlook /Monday Night through Thursday/...

Monday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers.

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

Tuesday Night through Wednesday: Winds less than 25 kt.

Wednesday Night through Thursday: Winds less than 25 kt. Seas
locally approaching 5 ft.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Air Quality Alert until 11 PM EDT this evening for CTZ002.
MA...None.
RI...None.
MARINE...None.

&&

$$
SYNOPSIS...BL/Loconto
NEAR TERM...KJC
SHORT TERM...Loconto
LONG TERM...BL
AVIATION...KJC/BL
MARINE...BL/Loconto


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