Severe Thunderstorm Warning 73, NWS Boston/Norton, MA

004 
WWUS51 KBOX 231918 RRA
SVSBOX

Severe Weather Statement
National Weather Service Boston/Norton MA
318 PM EDT Thu Jul 23 2020

MAC011-017-027-231928-
/O.CAN.KBOX.SV.W.0073.000000T0000Z-200723T1945Z/
Worcester MA-Middlesex MA-Franklin MA-
318 PM EDT Thu Jul 23 2020

...THE SEVERE THUNDERSTORM WARNING FOR NORTHWESTERN WORCESTER...
NORTHWESTERN MIDDLESEX AND EAST CENTRAL FRANKLIN COUNTIES IS
CANCELLED...
        
The storm which prompted the warning has moved out of the area.
Therefore, the warning has been cancelled.

A Severe Thunderstorm Watch remains in effect until 800 PM EDT for
western, central and northeastern Massachusetts.

LAT...LON 4271 7203 4271 7188 4257 7184 4255 7229
      4265 7231 4272 7205
TIME...MOT...LOC 1917Z 259DEG 17KT 4265 7196 

$$

BL

Area Forecast Discussion
National Weather Service Boston/Norton MA
214 PM EDT Thu Jul 23 2020

.SYNOPSIS...

Scattered thunderstorms will continue into early evening ahead
of an approaching cold front. Some of the storms may produce
damaging winds and torrential rainfall/localized flooding.
Behind the front, not quite as hot or humid Friday along with
mainly dry weather, just a slight chance of an isolated shower
or thunderstorm across CT, RI and southeast MA. High pressure
over New England Saturday provides dry weather and seasonably
warm temperatures. The high moves offshore Sunday and Monday,
circulating hot and humid weather back into the region. A slow
moving cold front will likely result in scattered thunderstorms
Tuesday and Wednesday.

&&

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

210 PM Update...

* Severe Thunderstorm Watch into this evening for the entire
  region except for the Cape/Islands and the south coast of RI

* Localized flood threat exists too

Scattered to numerous thunderstorms have developed across the
northern half of MA at mid afternoon. Despite poor mid level
lapse rates...70 to 75 degree dewpoints have resulted in
surface capes between 2500 and 3000 J/KG. SPC Meso-analysis also
shows bulk effective shear has also increased to between 30 and
35 knots across much of the region, particularly across
northern MA.

As the shortwave and pre-frontal trough continue to press
southeast, scattered thunderstorms should develop further south
towards the Boston to Providence corridor and northern CT
through late afternoon. Despite the poor mid level lapse rates
and marginal shear, plenty of instability will result in some of
the storms becoming strong to severe. Therefore, a Severe
Thunderstorm Watch is in effect through 8 pm this evening for
all but the Cape/Islands and south coast of RI. We do think the
highest severe weather threat is across interior and northern
portions of MA and perhaps into northern CT. Somewhat better
shear/cape overlap exists in this region.

Lastly, given 70 to 75 dewpoints and marginal shear the
strongest thunderstorms will produce torrential rainfall. This
will result in a very localized flash flood threat, particularly
if a cluster of strong t-storms move over a vulnerable urban
center.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/...

Tonight...

The threat of severe storms shift south with the cold front but with
the loss of diurnal heating after sunset, severe storms coverage
will likely be more scattered in nature. Storms wind down by the pre-
dawn hours as the cold front clears the South Coast. It will still
remain very mild and muggy, however, with overnight lows in the mid
60s in the interior to low 70s in Eastern MA and RI.

Friday...

* Looks to be a mostly dry day but couldn't rule out afternoon
  thunderstorms, especially towards the S Coast.

By the early morning hours, a positively tilted upper level trough
lifts into Nova Scotia with rising H5 height fields. With light NW
flow aloft, initial signs are that Friday could be a mostly dry day.
The wildcard lies in the uncertainty of how far south the cold front
goes. There are signs that it could stall as a stationary front just
south of the south coast. Moreover, there are also indications of up
to 1000 J/kg of CAPE so have kept at least a slight chance of PoPs
for much of the interior and higher chances south of the MA Pike.
But K indices look to fall sharply behind the cold front from the
30s to the teens and even the single digits in the interior,
indicative of the intrusion of mid-level dry air. With mixing up to
850mb and 850mb temperatures between +13C to +15C, afternoon highs
should top out in the mid 80s. With dew points falling into the
upper 50s to mid 60s, it will feel quite comfortable.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...

323 am update...

Highlights...

* Dry weather Sat, Sun and possibly into Mon then an active
  convective pattern beginning Tue and continuing into at least mid
  week

* Seasonably warm/humid Saturday then possible three day heat wave
  Sunday, Monday and Tuesday

Temperatures...

Low amplitude mean trough over New England briefly erodes northern
periphery of subtropical ridge resulting in seasonable temps and
humidity for late July Fri night and Sat. With 1020 mb high pressure
over the region Friday night, sided with the slightly cooler MOS
guidance. In fact few places across western MA may dip into the
upper 50s! Saturday looks like the pick of the week especially after
a coolish Fri night then dry WNW flow aloft, seasonably warm with
highs in the mid to upper 80s and dew pts in the 60s. By Sunday,
excessive heat and humidity associated with subtropical ridge over
the central U.S. begins to advect eastward with ECENS warming 850 mb
temps to +19C over New England Sunday, then peaking to 20C Monday
before lowering to about +18C by Tuesday as high amplitude trough
enters the Great Lakes. These temps aloft may support a three day
heat wave for many locations in MA/RI/CT Sunday, Monday and Tuesday.
Good model agreement Monday will likely be the hottest day with
probability of 90+ temps between 90-100% and highs likely in the mid
90s. Highs likely fall back into the 80s Wed as approaching high
amplitude trough entering the Great Lakes begins to erode northern
periphery of subtropical ridge.

Precipitation...

Dry WNW flow aloft should yield mainly convective-free weather
Saturday, Sunday and possibly Monday. However by Tue and especially
Wed ECENS continuing to signal a fairly high amplitude trough (at
least by July standards) entering the Great Lakes Tue and edging
closer to New England Wed. This should yield a fairly active
convective pattern for New England beginning Tue and continuing at
least into Wed if not beyond.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...

18z Update...

Forecaster Confidence Levels...

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

This afternoon...High confidence in trends, but lower
confidence in trends. Scattered to numerous thunderstorms have
developed across northern MA. This activity will push southeast
towards the Boston to Providence through 21z-22z. So while VFR
conditions are expected outside the t-storms, IFR-LIFR along
with locally strong winds are expected within thunderstorms.

Tonight...High confidence in trends, but lower confidence in
timing. The scattered thunderstorm threat will end across much
of the region by 02z-03z, but persist a bit longer in parts of
RI/SE MA. Otherwise, VFR conditions dominate but IFR to even
LIFR conditions may develop across the Cape/Islands in lower
clouds and fog. More patchy fog may develop overnight in the
typically prone locations. Winds becoming light overnight.

Friday...High confidence. VFR with any remaining low clouds/fog
burning off during the morning across the Cape/Islands. Isolated
showers possible Fri afternoon mainly towards the south coast,
but the areal coverage will be limited. NE winds 5 to 10 knots.

KBOS Terminal...High confidence in TAF. Scattered thunderstorms
expected between 19z and 23z.

KBDL Terminal...High confidence in TAF. Scattered thunderstorms
expected between 19z and 23z.

Outlook /Saturday through Monday/...

Saturday through Saturday Night: VFR.

Sunday through Sunday Night: VFR. Breezy.

Monday: Mainly VFR, with local MVFR possible. Breezy. Slight
chance SHRA, slight chance TSRA.

&&

.MARINE...
340 AM Update...

Winds and seas remain below Small Craft Advisory criteria through
Friday night. A cold front on Thursday brings the risk for
thunderstorms, some of which may be strong Thursday afternoon
into evening.

Outlook /Saturday through Monday/...

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

Saturday through Sunday: Winds less than 25 kt.

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

&&

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

&&

SYNOPSIS...Nocera/Chai
NEAR TERM...Frank
SHORT TERM...Chai
LONG TERM...Nocera
AVIATION...Frank/Nocera
MARINE...Nocera/Chai

Hazardous Weather Outlook
National Weather Service Boston/Norton MA
505 AM EDT Thu Jul 23 2020

CTZ003-004-MAZ017>024-RIZ001>008-240915-
Tolland CT-Windham CT-Northern Bristol MA-Western Plymouth MA-
Eastern Plymouth MA-Southern Bristol MA-Southern Plymouth MA-
Barnstable MA-Dukes MA-Nantucket MA-Northwest Providence RI-
Southeast Providence RI-Western Kent RI-Eastern Kent RI-Bristol RI-
Washington RI-Newport RI-Block Island RI-
505 AM EDT Thu Jul 23 2020

This Hazardous Weather Outlook is for northern Connecticut,
southeastern Massachusetts, and Rhode Island.

.DAY ONE...Today and tonight.

Scattered strong to severe thunderstorms this afternoon into evening with
the potential for damaging winds, large hail, and heavy rainfall.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed.

ANZ230>237-250-251-254>256-240915-
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-
505 AM EDT Thu Jul 23 2020

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

.DAY ONE...Today and tonight.

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

CTZ002-MAZ002>016-026-240915-
Hartford 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 Middlesex MA-
505 AM EDT Thu Jul 23 2020

This Hazardous Weather Outlook is for northern Connecticut, central
Massachusetts, eastern Massachusetts, northeastern Massachusetts
and western Massachusetts.

.DAY ONE...Today and tonight.

Scattered strong to severe thunderstorms are expected this afternoon
into evening with the potential for damaging winds, large hail, and
heavy rainfall.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Hazardous weather is not expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will likely be needed.

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/us.nationalweatherservice.boston.gov

You can follow us on Twitter at
@NWSBoston

Special Weather Statement
National Weather Service Boston/Norton MA
133 PM EDT Thu Jul 23 2020

MAZ002-003-008-010-231815-
Western Franklin MA-Western Hampshire MA-Eastern Franklin MA-
Eastern Hampshire MA-
133 PM EDT Thu Jul 23 2020

...STRONG THUNDERSTORM...

At 133 PM EDT, Doppler radar was tracking a strong thunderstorm near
Goshen, or 10 miles north of Northampton, moving east at 25 mph.

Pea size hail and winds in excess of 40 mph will accompany this
storm.

Locations impacted include...
Amherst, Greenfield, Deerfield, Montague, Hadley, Sunderland,
Hatfield, Williamsburg, Conway, Shelburne, Leverett, Erving,
Shutesbury, Ashfield, Gill, Whately, Pelham, Goshen, New Salem and
Wendell.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 4263 7237 4237 7232 4240 7281 4253 7283
TIME...MOT...LOC 1733Z 268DEG 22KT 4246 7275

BW

Special Weather Statement
National Weather Service Boston/Norton MA
145 PM EDT Thu Jul 23 2020

MAZ006-007-231815-
Eastern Essex MA-Western Essex MA-
145 PM EDT Thu Jul 23 2020

...STRONG THUNDERSTORM OVER NORTHERN ESSEX COUNTY...

At 145 PM EDT, Doppler radar was tracking a strong thunderstorm over
Merrimac, or near Haverhill, moving east at 20 mph.

Pea size hail and winds in excess of 40 mph will accompany this
storm.

Locations impacted include...
Haverhill, Newburyport, Amesbury, Salisbury, Newbury, Merrimac and
West Newbury.

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.

&&

A Severe Thunderstorm Watch remains in effect until 800 PM EDT for
northeastern Massachusetts.

LAT...LON 4286 7085 4287 7082 4283 7081 4281 7087
      4280 7083 4282 7082 4277 7080 4279 7106
      4281 7107 4286 7103 4287 7097 4289 7093
      4289 7090
TIME...MOT...LOC 1744Z 256DEG 18KT 4284 7100

BL

Special Weather Statement
National Weather Service Boston/Norton MA
151 PM EDT Thu Jul 23 2020

MAZ002>004-008-010-231845-
Western Franklin MA-Western Hampshire MA-Eastern Franklin MA-
Northern Worcester MA-Eastern Hampshire MA-
151 PM EDT Thu Jul 23 2020

...LINE OF STRONG THUNDERSTORMS MOVING INTO CENTRAL MASSACHUSETTS...

At 151 PM EDT, Doppler radar was tracking strong thunderstorms along
a line extending from near Winchester to near Northampton. Movement
was northeast at 35 mph.

Pea size hail and winds in excess of 40 mph will accompany these
storms.

Locations impacted include...
Amherst, Northampton, Greenfield, Orange, Deerfield, Gardner,
Easthampton, Belchertown, Athol, Winchendon, Montague, Templeton,
Ashburnham, Barre, Hadley, Sunderland, Hatfield, Northfield, Hardwick
and Williamsburg.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Get indoors when these storms approach. 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 4271 7195 4241 7217 4226 7282 4273 7247
TIME...MOT...LOC 1751Z 246DEG 28KT 4273 7240 4236 7268

BW

Special Weather Statement
National Weather Service Boston/Norton MA
210 PM EDT Thu Jul 23 2020

MAZ004>007-014-231900-
Eastern Essex MA-Central Middlesex County MA-Western Essex MA-
Northern Worcester MA-Southeast Middlesex MA-
210 PM EDT Thu Jul 23 2020

...STRONG THUNDERSTORM...

At 210 PM EDT, Doppler radar was tracking a strong thunderstorm over
Acton, or 8 miles south of Chelmsford, moving northeast at 30 mph.

Pea size hail and winds in excess of 40 mph will accompany this
storm.

Locations impacted include...
Lowell, Lynn, Lawrence, Haverhill, Peabody, Salem, Billerica, Woburn,
Chelmsford, Andover, Lexington, Tewksbury, North Andover, Saugus,
Danvers, Wakefield, Reading, Burlington, Wilmington and Westford.

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.

&&

A Severe Thunderstorm Watch remains in effect until 800 PM EDT for
central and northeastern Massachusetts.

LAT...LON 4239 7152 4247 7159 4276 7107 4252 7090
TIME...MOT...LOC 1809Z 242DEG 25KT 4249 7143

BL

Special Weather Statement
National Weather Service Boston/Norton MA
215 PM EDT Thu Jul 23 2020

MAZ008>011-231900-
Western Hampshire MA-Western Hampden MA-Eastern Hampden MA-
Eastern Hampshire MA-
215 PM EDT Thu Jul 23 2020

...STRONG THUNDERSTORM MOVING INTO WESTERN HAMPDEN AND HAMPSHIRE
COUNTIES...

At 215 PM EDT, Doppler radar was tracking a strong thunderstorm over
Chester, or 15 miles northwest of Westfield, moving east at 25 mph.

Pea size hail and winds in excess of 40 mph will accompany this
storm.

Locations impacted include...
Chicopee, Westfield, Holyoke, Northampton, West Springfield, South
Hadley, Easthampton, Southampton, Hadley, Hatfield, Williamsburg,
Huntington, Russell, Westhampton, Chester, Blandford, Chesterfield,
Worthington, Montgomery and Middlefield.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 4240 7258 4214 7261 4218 7302 4227 7300
      4231 7300 4231 7303 4233 7306 4237 7307
TIME...MOT...LOC 1815Z 271DEG 21KT 4228 7298

BW