Special Weather Statement, NWS Boston/Norton, MA

Area Forecast Discussion
National Weather Service Boston/Norton MA
309 PM EDT Tue Aug 23 2022

.SYNOPSIS...

Scattered thunderstorms with locally heavy rain come to an end this
evening. Then dry but warm weather follows Wednesday, with
slightly lower humidity Thursday. A cold front may trigger
scattered thunderstorms Friday afternoon/evening, along with
warm and humid conditions. High pressure will bring dry, lower
humidity and warm days but comfortably cool nights this weekend.
Heat and humidity likely return early next week.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...

An upper level low is in the process of slowly moving east through
southern New England today with a surface low and associated cold
front swinging through. This will continue to bring rounds of
convection to the region this afternoon into the early evening both
from the west ahead of the cold front and from the south as the
previously stationary front lifts north. This semi-stationary front
has lifted further north, dissecting RI and far southeast MA, and
this has helped to initiate the showers and thunderstorms generally
along the I-95 corridor from Hartford to Providence, moving north.
Plenty of instability for these storms to work with (mesoanalysis
indicates 1500-2000 J/kg of CAPE, maximized over southwest southern
New England thanks to the amount of sunshine they received earlier
in the day compared to southeast MA. Bulk shear is less robust, and
maximized (30 kt) over southeast MA, removed from the instability
maximum. Still, that is enough shear to get some rotation in these
storms. A waterspout was reported with a cell moving into New London
county, and many of these cells have had broad, mesocyclonic
rotation in them. Fortunately they have also been fairly vertical,
pulsing up and coming back down pretty quickly, and this should be
the theme of the afternoon. Can't rule out a severe storm or two but
it should be the exception rather than the rule. The main threat
would be from damaging winds associated with wet microbursts.
Secondary would be a chance for localized urban and poor drainage
flooding issues thanks to high PWATs and weak steering flow (slow
moving storms). Flash Flood Guidance is quite high thanks to our
ongoing drought, but if any location were to get a training storm
overhead they could have flooding issues. Sunset and loss of daytime
heating will significantly curtail our shower and thunderstorm
activity after 9 to 10 PM. The disturbance shifts east out of
southern New England leaving us with dry conditions for the rest of
the night.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...

Wednesday will be much quieter than the previous few days as the
trough further deamplifies and the surface low begins to be replaced
by high pressure. Low level flow veers to the W/NW pulling in a
marginally drier airmass and keeping showers out of the forecast for
most locations. The one exception may be portions of eastern MA
where a weak impulse rounding the base of the trough may be enough
to kick off a few scattered showers during the peak heating hours.
Though we won't have a significant change in airmass, mostly sunny
skies will allow for temps topping out about 5 degrees warmer than
today, in the mid to upper 80s.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...

Highlights...

* Overall dry and warm pattern continues into next week with best
  chance of showers/storms Fri and perhaps again Tue next week

* Warmer than normal Thu/Fri with highs 85-90 & dew pts in the 60s,
  not excessive heat/humidity but definitely a summer airmass

* Beautiful weather for the weekend, warm days & cool nights along
  with comfortable humidity away from the coastline

Thursday and Friday...

Short wave ridging will provide dry, pleasant weather and slightly
less humid conditions, with PWATs and dew pts in the upper 50s and
lower 60s away from the coastline. Above normal temps aloft combined
with WNW flow will yield a warm day with highs 85-90. Normal
high/low for late August is upper 70s/lower 80s and lows 60-65. Even
warmer and more humid Fri ahead of approaching short wave trough,
with highs in the upper 80s to lower 90s, and dew pts in the 60s to
near 70 along the south coast. Not record breaking or excessive, but
definitely feeling like summer Fri. Chance of afternoon/evening
storms with approaching short wave and associated cool front.
Ensembles indicate not an ideal setup for severe weather, with probs
of greater than 500 j/kg of CAPE over CT/RI and southeast MA.
Meanwhile highest probs of 40+ of wind at 500 mb across northern
portions of NY/VT/NH. Thus, not much overlap in shear and
instability. Then again, 3 days away and lots can change.

The Weekend & Early Next Week...

Refreshing post frontal airmass overspreads SNE this Saturday with
decreasing PWATs and dew pts lowering in the mid and upper 50s. This
will support warm days and cool nights this weekend. Highs 80-85
Sat, cooler along the coast with seabreezes. A comfortably cool
night Sat night/Sunday morning, in response to a 1025 mb high
cresting over SNE. This will yield lows in the 50s outside the urban
areas. Given this setup, sided with the cooler MOS datasets to
derive mins. Airmass slowly modifies each day with highs in the mid
to upper 80s Sunday and then approaching 90 by Monday, along with
increasing humidity as dew pts rising into the 60s by then. Likely
remaining dry Sun and Mon, but by Tuesday ensembles indicate the
next northern stream trough approaching. Thus, an increasing risk of
scattered showers/thunderstorms next Tue/Wed. Increasing heat and
humidity likely, as ensembles indicate subtropical ridge builds up
the east coast ahead of approaching Great Lakes trough.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels:

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

12Z TAF Update: Medium confidence.

Today...Medium confidence

Should see IFR/LIFR conditions improve after sunrise with fog
lifting and stratus becoming more BKN or perhaps SCT. MVFR or
VFR ceilings expected by this afternoon. Showers and
thunderstorms push through the region beginning early afternoon.

Tonight...Medium confidence

VFR across the interior. MVFR/IFR ceilings linger over the south
coast, Cape, and Islands.

Wednesday...High confidence

VFR. Light westerly winds becoming southwesterly.

KBOS...High confidence in TAF.

KBDL...High confidence in TAF.

Outlook /Thursday through Saturday/...

Wednesday Night through Thursday Night: VFR.

Friday: Mainly VFR, with areas MVFR possible. Breezy. Chance
SHRA, slight chance TSRA.

Friday Night: VFR. Chance SHRA, isolated TSRA.

Saturday: VFR.

&&

.MARINE...
Forecaster Confidence Levels:

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

This afternoon...

Southwesterly winds prevail over the southern waters while
southeasterly winds prevail over the eastern waters. Seas rise
to 3 to 4 feet over the southern waters and 2 to 3 feet over the
eastern waters outside of Boston Harbor.

Tonight...

Seas may approach SCY criteria over the outer zones of the south
coastal waters. Otherwise fairly quiet with modest southwest winds.

Wednesday...

Benign conditions over the coastal waters again on Wednesday with
diminishing winds and subsiding seas.

Wednesday night...

W winds 5-10 kts. Seas 3-4 ft.

Outlook /Thursday through Saturday/...

Thursday through Thursday Night: Winds less than 25 kt.

Friday: Winds less than 25 kt. Slight chance of rain showers.

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

Saturday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

SYNOPSIS...Nocera/BW
NEAR TERM...BW
SHORT TERM...BW
LONG TERM...Nocera
AVIATION...Nocera/BW
MARINE...Nocera/BW

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