Area Forecast Discussion
National Weather Service Boston/Norton MA
1224 PM EDT Sat May 28 2022

.SYNOPSIS...
Showers lifting further offshore from the Cape this morning. 
Will have a bit of a lull in activity for a few hours with some
breaks of sunshine. A cold front moves in this afternoon into 
the evening bringing showers and thunderstorms especially across
the interior where a few strong to severe storms are possible. 
Turning warmer and dry with summer-like temperatures for the 
rest of the Memorial Day holiday weekend. Cooling trend Tuesday 
near the coast and for the rest of the region on Wednesday as a 
backdoor cold front moves through. Somewhat unsettled weather 
toward the end of the week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

...Mesoscale Update...
As of 1225 PM: Some limited breaks in overcast were taking 
place across western MA and into portions of western/west-
central CT. This was allowing for limited destabilization to 
take place with regional radar mosaic showing re-developing 
heavier showers across the I-91 corridor. Heavier thunderstorms 
were developing closer to a deamplifying upper low near the 
Poconos in eastern PA into NW NJ. One thunderstorm in particular
produced a half- inch of rain in 40 minutes time in western NJ.
Recent HRRR runs and the 12z NAM-3km convective permitting 
guidance shows coverage of showers and thunderstorms increasing 
in coverage between 17-22z into a broken linear structure then 
moving eastward towards the I-84/I-495/I-95 corridors. 
Instability profile is of the tall-skinny type with CAPEs under 
1500 J/kg, and lower to mid-level winds weaken as deamplifying 
low approaches. Presently think severe potential is pretty 
limited, but isn't zero: it make take cell mergers to briefly 
pulse storms to severe levels and be capable of 
isolated/localized wind damage. With slower NE storm motions and
humid, seasonably high PWAT values, local downpours appear to 
be the most apparent risk, with nuisance street flooding 
possible in areas that poorly drain or on city roads, but high 
flash-flood guidance (over 2 inches per hr) should by-and-large 
mitigate convective flooding risks. If you do have plans today, 
especially west of I-95/I-495, keep an eye to the sky especially
in the 1 to 6 PM timeframe. Has the look of a several-SPS sort 
of event with perhaps one pulsing to SVR levels. -AL/RC

Previous update:

10 AM UPDATE...

Forecast remains largely on track. Visible satellite shows
plenty of cloud cover this morning, with any transient gaps 
filled in quickly with the shower activity across the Berkshires
and to our south. Marine stratus is still hugging the coast, 
both across the south coast and on Cape Cod, where fog is 
locally dense. Actual cold front is still out across Central NY 
and PA, so the timing of 12-6 PM for thunderstorm activity still
looks good. SPC did continue with a marginal severe threat 
across much of our area. Given the current mesoanalysis, while 
severe threat couldn't be entirely ruled out, this could be an 
afternoon where SPS for gusty winds and small hail could suffice
for most of the convection, with a storm or two maybe requiring
a SVR with better chances generally west and along the I-84 
corridor. Any thunderstorms that develop will also be capable of
producing locally heavy downpours. Given the latest drought 
monitor, the rain will be welcome. 

Overall, the messaging remains the same. If you have outdoor
plans, be sure to stay weather aware. And when thunder roars, go
indoors. 

PREVIOUS DISCUSSION...

Highlights

* Any lingering showers/storms move offshore early this morning.

* Anticipate a bit of a lull/dry weather this morning before
  showers/storms fire across the interior as a cold front slides
  through. Could see a few strong to severe storms with the main
  risk being damaging wind gusts, but there may also be some
  small hail. 

A subtle shortwave lifts offshore this morning and a deeper
deamplifying trough lifts into southern New England from the Mid
Atlantic today. A cold front will slide into and through much of
southern New England today. 

Anticipating the initial round of showers/storms this morning to
push offshore as the 850 hPa low level jet moves offshore.
Thinking that any of the shower activity will linger the longest
across the Cape/Islands, but should be out by mid/late AM.
Leaned on the HREF/HRRRE guidance as it appears to be doing well
based on the latest observations. Should see a lull in activity
with dry and quiet weather expected for much of the morning with
some breaks of sunshine.

Main concern across southern New England today is the potential
for strong to severe storms as the cold front crosses the
region. Still some uncertainty with how much destabilization we
can get as it will depend on clearing skies. The deamplifying
trough lifts over the region bringing -10 to -15 degree Celsius
500 hPa air over us. The colder air along with some breaks in 
sunshine should allow for MLCAPEs in the 500-1000 J/kg range.
The low level lapse rates will be around 6-8 C/km with mid level
lapse rates around 6-7 C/km with the highest values across the
interior. Still have the muggy airmass in place, so low level
moisture will not be an issue. Deep layer shear in the 0-6 km
layer actually diminishes to around 20-30 kts ahead of the
front, which could be a limiting factor on top of how much
instability we can develop. Still think given these parameters
the SPC Day 1 Outlook of a marginal risk is fine across our
area. Anticipate marginally severe gusts and given there is
roughly 500 J/kg of CAPE within the hail growth region there
could be some small hail. Have added a mention of gusty winds
and small hail to the forecast in the latest update. Utilizing
the HREF it still pegs the highest updraft helicity probs of
10-20 percent across the interior, which actually lines up
pretty well with where the highest mid level lapse rates are.
Timing wise it still looks like 12-6 PM across the interior.
Should see the activity weaken as it moves eastward into RI/E MA
as the instability will wane. Thinking that the NSSL WRF/HRRR
has a pretty good handle on how things will evolve today.

Will be a bit cooler today in comparison to yesterday with highs
in the 70s across the region. Not completely out of the question
there are a few 80 degree readings in NE MA where there may be a
bit more clearing.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
4 AM Discussion...

Highlights 

* Any lingering showers/storms taper off this evening. More
  stratus/fog along the south coast until the front moves
  through.

* Pleasant on Sunday with increasing temperatures. 

Trough lifts offshore during the evening and a ridge builds into
the central Great Lakes behind it. The ridge axis amplifies as
it builds into the central/eastern Great Lakes on Sunday. The
surface cold front should finally exit the region this evening.
High pressure nudges in behind it tonight and south of the
region for Sunday.

Should see any lingering shower/storms taper off or move
offshore during the evening as the cold front exits. Should see
the thunder activity diminish/cease due to waning instability,
but there may still be a few showers around eastern areas. As
high pressure builds in will have skies becoming clear with
light NW winds. Did knock down lows to the 25th percentile of
guidance as we should see decent radiational cooling. Low
temperatures will generally be in the low/mid 50s, but there
could be a few upper 40 degree readings across the higher
terrain of the Berkshires.

High pressure remains in control on Sunday with a much more
comfortable airmass in place. Anticipate that we warm up nicely
as flow aloft becomes W/SW at 925 hPa advecting 15-18 degree
Celsius air overhead. The result will be upper 70 to low 80
degree temps for most. The only exception will be along the
coastal plain where local sea breezes keep temps in the 70s.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Memorial Day is looking to be quite warm, if not outright hot, 
across most of southern New England. Latest NBM 4.1 probability of 
high temperatures greater than 80 degrees is over 90 percent across 
all of southern New England west of the Cape Cod Canal. 
Significantly lower probabilities for high temperatures of 90 
degrees or higher. Generally about 30-40 percent across metro 
Boston, and 40-60 percent in the CT River Valley. Also expecting dry 
weather to prevail.

28/00Z guidance suite has come into better agreement on pushing a 
backdoor cold front into southern New England Tuesday. This will 
continue to complicate temperature forecasts, as much will depend on 
exact timing. Should this front arrive a few hours earlier than 
current expectations, that could make a 10-degree difference in high 
temperatures. A later timing would mean warmer conditions for the 
immediate east coast of southern New England. NBM probabilities for 
high temperatures of 80+ are less than 45 percent inside if I-495, 
but around 90 percent along and west of the CT River.

The trend should also be for less humidity during the day Tuesday. 
Not looking for many showers as our region is still under the 
influence of a mid level ridge, albeit a weakening one.

Showers look more likely sometime Wednesday into Friday, when a warm 
front returns, along with a pair of weak surface low pressures. The 
threat of showers continues into Friday, until a cold front can 
finally move east of our region. NBM forecast handled this 
reasonably, so saw little reason to deviate from it.

&&

.AVIATION /16Z SATURDAY THROUGH WEDNESDAY/...
Low - less than 30 percent. 
Medium - 30 to 60 percent. 
High - greater than 60 percent. 

Today...

IFR/LIFR to start with scattered showers exiting Cape/Islands. 
Will improve to MVFR and perhaps some SCT to VFR, but think
cloud bases remain in the 1.5-3 kft range. The only exception is  
the Cape/Islands where IFR/LIFR persists. Scattered to numerous 
showers and thunderstorms developing across the interior in the 
afternoon with a few strong storms possible. Risk for a stronger
storm or two highest for BDL/BAF/ORH. Should see this 
convection weaken as it moves toward the coast late in the day
as instability wanes. Still uncertain in the exact 
timing/location, so have kept a VCTS mention. SW wind gusts to 
15-20 kt, but winds shifting to the W as the front passes 
through.

Tonight...High confidence in trends, moderate on exact timing.

Any lingering showers/storms end during the evening. Will see 
conditions improving to VFR and winds shifting to the NW with 
speeds around 5 kts. IFR/LIFR cigs linger over the Cape/Islands
until the front slides through, this should fairly rapidly 
improve conditions to VFR with drier NW flow. Looks like this 
occurs at roughly 03-08Z. There is the possibility for some
patchy radiation fog across the interior, but uncertain on how
widespread it will be given the NW flow. Have only hinted at for
ORH/BED, but may be needed for other spots in future updates.

Sunday...High confidence.

VFR with light winds shifting to the SW. Local seabreezes 
developing around 14-16Z. 

KBOS TAF...High confidence in TAF, but moderate in specific
timing. Risk for storms in the 19-23Z window, but some 
uncertainty if the activity moving in from the west holds 
together. 

KBDL TAF...Moderate confidence in TAF. Showers/storms roughly
from 17-22Z, but still uncertain on coverage of thunder. Have
kept VCTS. Any stronger storm that moves through could bring 
gusty winds and perhaps some small hail.

Outlook /Sunday Night through Wednesday/... 

Sunday Night: VFR. Patchy BR.

Memorial Day: VFR. Breezy. Patchy BR.

Monday Night: VFR. Breezy. 

Tuesday: VFR. Breezy. Slight chance SHRA.

Tuesday Night: Mainly VFR, with local MVFR possible. Breezy.
Slight chance SHRA.

Wednesday: Mainly VFR, with local MVFR possible. Chance SHRA.

&&

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

Today...High confidence.

Modest low level jet still in place to start, but will move 
offshore this afternoon. Behind it a cold front will push and
and eventually across the waters this evening. Winds out of the
S/SSW with gusts of 25-30 kt to start diminishing to 20-25 kt 
this afternoon. Could perhaps see a few showers and an isolated
storm or two this afternoon/evening. Visibilities of 1/2 to 3 
NM. Seas 4-6 ft across the open waters.

Tonight...High confidence.

Cold front crosses the waters and high pressure builds in behind
it. Any showers/storms come to an end during the evening. 
Initially will still have low clouds/fog linger during the
evening with 1/4 to 3 NM of visby, but should dry out as winds
shift to the NW. Think there could still be some 1-3 NM visby
across the SE waters. W winds at 10-15 kts shift to the NW at
5-10 kts once the front passes through. Seas diminishing to 3-5
ft. Made no changes to the SCA as it looks good at this point.

Sunday...High confidence.

Dry and quiet weather could perhaps see some ocean stratus/fog
spreading into the south coast toward the evening. Light and
variable winds becoming southerly late in the day at 5-10 kts.
Seas 2-4 ft. 

Outlook /Sunday Night through Wednesday/... 

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

Sunday Night: Winds less than 25 kt. Patchy fog. 

Memorial Day: Winds less than 25 kt. Seas locally approaching
5 ft. Patchy fog. 

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

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

Wednesday: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 5 PM EDT this afternoon for ANZ232.
     Small Craft Advisory until 2 PM EDT this afternoon for ANZ231-
     233-234.
     Small Craft Advisory until 11 PM EDT this evening for ANZ235-
     237.
     Small Craft Advisory until 8 PM EDT this evening for ANZ250.
     Small Craft Advisory until 8 AM EDT Sunday for ANZ254>256.

&&