Special Marine Warning 48, NWS Boston/Norton, MA

Area Forecast Discussion
National Weather Service Boston/Norton MA
947 PM EDT Wed Jul 21 2021

.SYNOPSIS...
A cold front moves offshore tonight pushing showers/thunder from
Southeast Mass to the offshore. High pressure moves in with
clearing skies and drier air tonight and Thursday. Scattered
shower and thunderstorms possible Friday afternoon into the
evening before drier weather returns on Saturday. Unsettled late
in the weekend into early next week with increasing heat and
humidity

&&

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

Cold front over the Cape and Islands at 9 PM with windshift
across Cape Cod Bay. South wind at Provincetown and Hyannis,
northwest wind at Marshfield and Boston. Dew points were in the
mid to upper 60s along and ahead of the front, with drier upper
50s to low 60s from Northeast Mass through Nrn Connecticut.
These lower dew points will trend east and southeast with the
front overnight.

Upper trough remains overhead during the night, then moves over
the Gulf of Maine by morning.

Satellite shows clouds moving offshore, although some additional
patchy clouds over the Central Hills moving east. As previously
noted, lower dew points will be moving across the region
overnight with values in the 50s, except low 60s Cape and
Islands. Expect min temps will be in a similar range by early
morning.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
High pressure building east from Ohio Valley will provide for
plenty of sunshine on Thursday, along with cooler temperatures.
Stayed close to NBM with highs in 70s to lower 80s and lower
humidity.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Highlights

*  Isolated to scattered showers/storms Friday. Better shot for more
   widespread precipitation Sunday into early next week.

* Drier weather on Saturday and mid next week.

* Upward trend for the heat and humidity Sunday into next week.

Thursday night through Friday night...

Cyclonic flow in place over southern New England through this
period. A shortwave trough will swing through southern New England
from the eastern Great Lakes during the day. A weak surface trough
will be over the region.

Dry and quiet weather expected Thursday night into early Friday with
cyclonic flow in place, but no lower level forcing in place. Does
appear that there will be better forcing in place during the day
into the early evening on Friday with the surface trough and
shortwave moving through. On top of this will have a decent cold
pool aloft with 500 hPa temperatures around -15 to -20 Celsius. Have
gone with isolated to scattered shower/thunderstorm activity.

Expecting drier air to be in place over southern New England on
Friday with northwesterly winds. Should see dewpoints generally in
the 50s. Deep layer shear is modest for organized convection being
in the 25-35 kt range with the highest values located along the
south coast. This may not be enough given current guidance shows
only a few hundred J/kg of MUCAPE in place. Usually need greater
instability to offset when the shear is somewhat lacking. Low level
lapse rates will be in the 7-9 degrees Celsius and decent mid level
lapse rates around 6-7 degrees Celsius, so this should aid in
sustaining thunderstorm updrafts. Not that a thunderstorm cannot
bring some heavy downpours, but not thinking there will be a
widespread risk given PWATs decrease to around 1 inch. This is just
below the 50th percentile for this time of year per SPC Sounding
Climatology for CHH. As previous shift mentioned soundings do have
an inverted-V profile, so am thinking that gusty winds will be a
risk with any storms that develop. Will be something we need to keep
a close eye on for future updates.

A bit cooler with northwest flow and 925 hPa temperatures in the 15-
18 degree Celsius range. The result are high temperatures ranging
from the 70s to low 80s.

Saturday through Wednesday...

Dry and quiet weather expected on Saturday as a ridge axis builds in
and a surface high moves over southern New England briefly. Get into
more of a zonal flow pattern late in the weekend into early next
week. Could have a few shortwaves sliding through bringing chances
of rainfall. Right now appears that the greatest risk for widespread
precipitation is on Sunday into Monday as a cold front moves
through. Still have kept slight chance to chances of precipitation
into early next week as a few shortwaves swing through. Though it is
definitely not looking like a washout as we head into the work week
next week. Aloft will have flow become more W and SW late on Sunday
into much of next week. This will bring increasing heat and
humidity. Expecting the warmest readings of the extended on Monday
with highs in the low to mid 80s across much of southern New England.

&&

.AVIATION /02Z THURSDAY THROUGH MONDAY/...
Forecaster Confidence Levels.

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

VFR across southern New England through the TAF period with
light northwest winds. May see some VCSH overnight with local
downpours over Southeast Mass including Cape Cod and Islands
through 2 AM.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Thursday Night through Monday/...

Thursday Night: VFR.

Friday: Mainly VFR, with areas MVFR possible. Scattered SHRA,
isolated TSRA.

Friday Night through Saturday: VFR.

Saturday Night: Mainly VFR, with local MVFR possible. Chance
SHRA.

Sunday: Mainly MVFR, with local VFR possible. Breezy. Chance
SHRA, isolated TSRA.

Sunday Night: Mainly MVFR, with local IFR possible. Breezy.
Chance SHRA, isolated TSRA.

Monday: Mainly VFR, with areas MVFR possible. Breezy. Slight
chance SHRA, isolated TSRA.

&&

.MARINE...
Forecaster Confidence Levels.

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

High confidence in forecast through Thursday.

A few lingering showers move off Southeast Mass into the
adjacent waters. Local downpours may bring brief vsbys 1 to 3
nm through 2 AM. Cold front moves over the waters overnight with
light winds shifting from the northwest. High pressure maintains
light northwest winds and seas 5 feet or less through Thursday.

/Outlook /Thursday Night through Monday/...

Thursday Night: Winds less than 25 kt.

Friday: Winds less than 25 kt. Isolated rain showers.

Friday Night through Saturday: Winds less than 25 kt.

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

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

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

Monday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain
showers, isolated thunderstorms.

&&

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

&&

SYNOPSIS...WTB/BL/JWD
NEAR TERM...WTB/RM
SHORT TERM...JWD
LONG TERM...BL
AVIATION...WTB/RM
MARINE...WTB/BL/JWD

Hazardous Weather Outlook
National Weather Service Boston/Norton MA
602 PM EDT Wed Jul 21 2021

CTZ002>004-MAZ002>024-026-RIZ001>008-222215-
Hartford CT-Tolland CT-Windham CT-Western Franklin MA-
Eastern Franklin MA-Northern Worcester MA-Central Middlesex MA-
Western Essex MA-Eastern Essex MA-Western Hampshire MA-
Western Hampden MA-Eastern Hampshire MA-Eastern Hampden MA-
Southern Worcester MA-Western Norfolk MA-Southeast Middlesex MA-
Suffolk MA-Eastern Norfolk MA-Northern Bristol MA-
Western Plymouth MA-Eastern Plymouth MA-Southern Bristol MA-
Southern Plymouth MA-Barnstable MA-Dukes MA-Nantucket MA-
Northern Middlesex MA-Northwest Providence RI-
Southeast Providence RI-Western Kent RI-Eastern Kent RI-Bristol RI-
Washington RI-Newport RI-Block Island RI-
602 PM EDT Wed Jul 21 2021

This Hazardous Weather Outlook is for northern Connecticut, all of
Massachusetts east of Berkshire County, and Rhode Island.

.DAY ONE...Tonight.

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

ANZ230>237-250-251-254>256-222215-
Boston Harbor-Cape Cod Bay-Nantucket Sound-Vineyard Sound-
Buzzards Bay-Rhode Island Sound-Narragansett Bay-Block Island Sound-
Coastal waters east of Ipswich Bay and the Stellwagen Bank National
Marine Sanctuary-Massachusetts Bay and Ipswich Bay-
Coastal waters from Provincetown MA to Chatham MA to Nantucket MA
out 20 nm-
Coastal Waters extending out to 25 nm South of Marthas Vineyard and
Nantucket-
Coastal Waters from Montauk NY to Marthas Vineyard extending out to
20 nm South of Block Island-
602 PM EDT Wed Jul 21 2021

This Hazardous Weather Outlook is for Massachusetts and Rhode
Island coastal waters.

.DAY ONE...Tonight.

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

For more information on upcoming hazardous weather, please see the
Area Forecast Discussion on our webpage for the latest forecast
thinking. There is also our Enhanced Hazardous Weather Outlook at
www.weather.gov/box/ehwo

For the latest updates...please visit our webpage at
www.weather.gov/boston

You can follow us on Facebook at
www.facebook.com/nwsboston

You can follow us on Twitter at
@NWSBoston

Special Weather Statement
National Weather Service Boston/Norton MA
750 PM EDT Wed Jul 21 2021

MAZ014>016-019-220030-
Eastern Plymouth MA-Suffolk MA-Eastern Norfolk MA-
Southeast Middlesex MA-
750 PM EDT Wed Jul 21 2021

...STRONG THUNDERSTORMS NEAR BOSTON HARBOR...

At 749 PM EDT, Doppler radar was tracking a strong thunderstorm over
Boston, moving east at 15 mph.

Pea size hail and winds in excess of 30 mph will accompany this
storm.

Locations impacted include...
Boston, Cambridge, Quincy, Malden, Weymouth, Revere, Everett,
Braintree, Chelsea, Milton, Hingham, Scituate, Winthrop, Norwell,
Hull and Cohasset.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Get indoors when this storm approaches. Winds may be strong enough to
produce minor damage, such as a few downed branches.

Frequent lightning was occurring. Lightning can strike far away from
the storm. Go inside a building or vehicle. Wait at least 30 minutes
until after the storm has passed to resume outdoor activities.

&&

LAT...LON 4239 7097 4237 7105 4232 7100 4230 7105
      4231 7097 4230 7100 4229 7102 4226 7097
      4230 7093 4225 7096 4225 7088 4233 7093
      4234 7088 4226 7087 4225 7077 4218 7071
      4217 7072 4224 7109 4242 7107
TIME...MOT...LOC 2349Z 262DEG 14KT 4233 7100

Chai

Special Weather Statement
National Weather Service Boston/Norton MA
820 PM EDT Wed Jul 21 2021

MAZ013-015-016-018-019-220100-
Eastern Plymouth MA-Suffolk MA-Western Norfolk MA-
Western Plymouth MA-Eastern Norfolk MA-
820 PM EDT Wed Jul 21 2021

...STRONG THUNDERSTORM OVER NORFOLK AND NORTHERN PLYMOUTH COUNTY...

At 819 PM EDT, Doppler radar was tracking a strong thunderstorm over
Randolph, moving east at 15 mph.

Penny size hail and winds in excess of 30 mph will accompany this
storm.

Locations impacted include...
Boston, Brockton, Quincy, Weymouth, Braintree, Randolph, Norwood,
Milton, Stoughton, Marshfield, Dedham, Hingham, Canton, Scituate,
Pembroke, Sharon, Rockland, Abington, Duxbury and Westwood.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Get indoors when this storm approaches. Winds may be strong enough to
produce minor damage, such as a few downed branches.

Frequent lightning was occurring. Lightning can strike far away from
the storm. Go inside a building or vehicle. Wait at least 30 minutes
until after the storm has passed to resume outdoor activities.

&&

LAT...LON 4201 7076 4214 7118 4226 7115 4226 7095
      4225 7096 4226 7090 4225 7088 4227 7088
      4226 7087 4227 7082 4224 7077 4225 7077
      4220 7073 4220 7071
TIME...MOT...LOC 0019Z 279DEG 13KT 4219 7108

Chai

Special Weather Statement
National Weather Service Boston/Norton MA
846 PM EDT Wed Jul 21 2021

MAZ013-017>019-220130-
Eastern Plymouth MA-Western Norfolk MA-Northern Bristol MA-
Western Plymouth MA-
846 PM EDT Wed Jul 21 2021

...STRONG THUNDERSTORMS DEVELOPING OVER NORTHERN BRISTOL AND
PLYMOUTH COUNTY...

At 846 PM EDT, Doppler radar was tracking a strong thunderstorm over
Foxborough, or near Stoughton, moving east at 15 mph.

Pea size hail and winds in excess of 30 mph will accompany this
storm.

Locations impacted include...
Brockton, Taunton, North Attleborough, Stoughton, Bridgewater,
Attleboro, Walpole, Mansfield, Middleborough, Easton, Canton, Norton,
Pembroke, Sharon, Rockland, Foxborough, Abington, Duxbury, Whitman
and Hanover.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Get indoors when this storm approaches. Winds may be strong enough to
produce minor damage, such as a few downed branches.

Frequent lightning was occurring. Lightning can strike far away from
the storm. Go inside a building or vehicle. Wait at least 30 minutes
until after the storm has passed to resume outdoor activities.

&&

LAT...LON 4199 7133 4216 7125 4207 7072 4182 7084
TIME...MOT...LOC 0046Z 288DEG 14KT 4205 7120

Chai

Special Weather Statement
National Weather Service Boston/Norton MA
929 PM EDT Wed Jul 21 2021

MAZ017>019-220215-
Eastern Plymouth MA-Northern Bristol MA-Western Plymouth MA-
929 PM EDT Wed Jul 21 2021

...STRONG THUNDERSTORMS PRODUCING TORRENTIAL RAINFALL IN BRISTOL
AND PLYMOUTH COUNTIES...

At 927 PM EDT, Doppler radar was tracking strong thunderstorms along
a line extending from near Marshfield to near Rehoboth. Movement was
east at 20 mph.

Pea size hail and winds in excess of 30 mph will accompany these
storms. Torrential rainfall could lead to localized poor drainage
flooding.

Locations impacted include...
Brockton, Plymouth, Taunton, Bridgewater, Marshfield, Attleboro,
Middleborough, Easton, Norton, Scituate, Pembroke, Rockland,
Abington, Duxbury, Whitman, Hanover, East Bridgewater, Seekonk,
Raynham and Kingston.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Get indoors when these storms approach. Winds may be strong enough
to produce minor damage, such as a few downed branches. Do not drive
through flooded roadways.

Frequent lightning was occurring. Lightning can strike far away from
the storm. Go inside a building or vehicle. Wait at least 30 minutes
until after the storm has passed to resume outdoor activities.

&&

LAT...LON 4199 7063 4201 7071 4198 7066 4198 7065
      4196 7066 4194 7062 4179 7094 4190 7133
      4219 7075 4219 7072 4209 7064 4205 7066
      4202 7062 4204 7065 4204 7066 4202 7068
      4200 7064 4201 7060
TIME...MOT...LOC 0127Z 272DEG 17KT 4213 7068 4187 7120

Chai