Flash Flood Warning 28, NWS Boston/Norton, MA

092 
WGUS71 KBOX 211832
FFSBOX

Flash Flood Statement
National Weather Service Boston/Norton MA
232 PM EDT Fri Jul 21 2023

MAC011-015-212115-
/O.CON.KBOX.FF.W.0028.000000T0000Z-230721T2115Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Franklin MA-Hampshire MA-
232 PM EDT Fri Jul 21 2023

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 515 PM EDT THIS 
AFTERNOON FOR CENTRAL FRANKLIN AND NORTH CENTRAL HAMPSHIRE 
COUNTIES...

At 232 PM EDT, local law enforcement reported thunderstorms 
producing heavy rain across the warned area. Between 2 and 4.5 
inches of rain have fallen. The expected rainfall rate is 1 to 3 
inches in 1 hour. Additional rainfall amounts of 1 to 3 inches are 
possible in the warned area. Flash flooding is already occurring.

HAZARD...Life threatening flash flooding. Thunderstorms producing
         flash flooding.

SOURCE...Fire departments in Conway reported several flooded
         basements in the town of Conway, along with significant
         street flooding on Main Poland Rd in Conway. In
         addition, significant street flooding was reported in
         Greenfield on High Street and Hastings Road.

IMPACT...Life threatening flash flooding of urbanized areas,
         highways, streets and underpasses. Sharp rises on
         streams and creeks to over bankfull.

Some locations that will experience flash flooding include...
  Greenfield, Deerfield, Montague, Williamsburg, Bernardston, 
  Buckland, Conway, Shelburne, Ashfield, Gill, Whately, 
  Chesterfield, Goshen, Cummington and Leyden.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Turn around, don't drown when encountering flooded roads. Most flood 
deaths occur in vehicles.

Move to higher ground now. Act quickly to protect your life.

In hilly terrain there are hundreds of low water crossings which are 
potentially dangerous in heavy rain. Do not attempt to cross flooded 
roads. Find an alternate route.

Flooding is occurring or is imminent. It is important to know where 
you are relative to streams, rivers, or creeks which can become 
killers in heavy rains. Campers and hikers should avoid streams or 
creeks.

&&

LAT...LON 4252 7286 4261 7274 4263 7265 4268 7251
      4262 7251 4260 7251 4256 7255 4251 7259
      4244 7271 4241 7278 4241 7285 4240 7287
      4243 7287

FLASH FLOOD...OBSERVED
FLASH FLOOD DAMAGE THREAT...CONSIDERABLE
EXPECTED RAINFALL RATE...1-3 INCHES IN 1 HOUR

$$

AL

423 
WGUS71 KBOX 211926
FFSBOX

Flash Flood Statement
National Weather Service Boston/Norton MA
326 PM EDT Fri Jul 21 2023

MAC011-015-212115-
/O.CON.KBOX.FF.W.0028.000000T0000Z-230721T2115Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Franklin MA-Hampshire MA-
326 PM EDT Fri Jul 21 2023

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 515 PM EDT THIS 
AFTERNOON FOR CENTRAL FRANKLIN AND NORTH CENTRAL HAMPSHIRE 
COUNTIES...

At 326 PM EDT, local law enforcement reported thunderstorms 
producing heavy rain across the warned area. Between 3 and 5.5 
inches of rain have fallen. The expected rainfall rate is 1 to 2 
inches in 1 hour. Additional rainfall amounts of 1 to 2 inches are 
possible in the warned area. Flash flooding is already occurring.

HAZARD...Life threatening flash flooding. Thunderstorms producing
         flash flooding.

SOURCE...There are multiple reports of flooded homes and
         basements in Conway, along with multiple road closures
         in Conway, Greenfield and Deerfield as reported by
         police and fire department. Route 116 and Route 5 in
         Conway are closed due to flooding. In addition, some
         roads in Conway have experienced washouts.

IMPACT...Life threatening flash flooding of urbanized areas,
         highways, streets and underpasses. Sharp rises on
         streams and creeks to over bankfull.

Some locations that will experience flash flooding include...
  Greenfield, Deerfield, Montague, Williamsburg, Bernardston, 
  Buckland, Conway, Shelburne, Ashfield, Gill, Whately, 
  Chesterfield, Goshen, Cummington and Leyden.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Turn around, don't drown when encountering flooded roads. Most flood 
deaths occur in vehicles.

Move to higher ground now. Act quickly to protect your life.

In hilly terrain there are hundreds of low water crossings which are 
potentially dangerous in heavy rain. Do not attempt to cross flooded 
roads. Find an alternate route.

Flooding is occurring or is imminent. It is important to know where 
you are relative to streams, rivers, or creeks which can become 
killers in heavy rains. Campers and hikers should avoid streams or 
creeks.

&&

LAT...LON 4252 7286 4261 7274 4263 7265 4268 7251
      4262 7251 4260 7251 4256 7255 4251 7259
      4244 7271 4241 7278 4241 7285 4240 7287
      4243 7287

FLASH FLOOD...OBSERVED
FLASH FLOOD DAMAGE THREAT...CONSIDERABLE
EXPECTED RAINFALL RATE...1-2 INCHES IN 1 HOUR

$$

AL

796 
WGUS71 KBOX 212107
FFSBOX

Flash Flood Statement
National Weather Service Boston/Norton MA
507 PM EDT Fri Jul 21 2023

MAC011-015-212117-
/O.CAN.KBOX.FF.W.0028.000000T0000Z-230721T2115Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Franklin MA-Hampshire MA-
507 PM EDT Fri Jul 21 2023

...FLASH FLOOD WARNING FOR CENTRAL FRANKLIN AND NORTH CENTRAL 
HAMPSHIRE COUNTIES HAS BEEN REPLACED WITH A FLOOD WARNING...

Excessive rainfall has ended, although flooding impacts continue. 
Given that excessive rain has ended, the Flash FLood Warning will be 
replaced with an areal flood warning to address continued flooding.

LAT...LON 4252 7286 4261 7274 4263 7265 4268 7251
      4262 7251 4260 7251 4256 7255 4251 7259
      4244 7271 4241 7278 4241 7285 4240 7287
      4243 7287

$$

AL

Area Forecast Discussion
National Weather Service Boston/Norton MA
203 PM EDT Fri Jul 21 2023

.SYNOPSIS...
Showers and thunderstorms, especially across western portions
of Massachusetts and Connecticut may have strong wind gusts and
heavy rain. Drying trend begins late tonight into Saturday from
west to east. Otherwise, mainly dry weather prevails. Gorgeous
midsummer weather for Sunday with mostly sunny skies, low
humidity and seasonably warm temperatures. Then a gradual
increase in heat and humidity next week, with scattered
showers and thunderstorms possible Tuesday and again late next
week.

&&

.NEAR TERM /UNTIL 7 PM THIS EVENING/...
145 pm update...only minor tweaks to the foreacst. With
coordination with SPC, a Severe T-Storm Watch has been raised
for CT and Western MA (Worcester County westward). As indicated
previously, not a clear cut severe weather day. Mid level lapse
rates are rather poor, but we do have enough instability and
bulk shear that could sustain a more robust convective cell. We
will all know the answer by late this evening

1025 am update...

made modest tweaks to the grids based on latest radar/satellite
trends and the initial output from the newest hi-res CAMs. SPC
has increased the threat level for severe weather to the Slight
category across western portions of southern New England. Looks
reasonable, and in typical New England style, nothing is clear
cut for how things are going to unfold. Certainly, as previous
shift indicated, good signals for instability, shear and even
low level helicity. The latest CAMs are all similar in that they
show a broken line of convection to develop but otherwise they
are all over the place in timing and location. FV3 came in more
agressive than NAM3km and the recent HRRR runs. Perhaps it's on
to something given we already have convective development in
western CT at this time. Also some suggestion we have one batch
of convection early/mid afternoon, with a second line developing
later in the afternoon and getting into western sections after
6pm. In any case, as is typical with convection, we are just
going to have to roll with the punches and respond to whatever
Mother Nature decides to give us.

7 AM update...

Lots of low clouds and patchy fog across the region, except here
in eastern MA, partial sunshine with mid/high WAA clouds
approaching from the west. Warm frontal showers and
thunderstorms occurring across NYC into southwest CT. This
activity will weaken as low/mid level jet shears off to the
northeast into upstate NY and VT. Warm front will stall this
afternoon somewhere across eastern CT into central MA, with warm
sector airmass westward across central-western MA/CT, with
MUCAPE 1000-1500 j/kg, then lowering dramatically eastward into
RI and eastern MA. Best deep layer shear (around 30 kt) and CAPE
profiles overlap across eastern NY into western-central CT/MA.
This is where storms are expected to be most numerous and
intense based on HREF UH swaths. If stronger storms form
vicinity of warm front, could be sufficient low level turning
for an isolated tornado. SPC has a 2% TOR prob eastward into the
CT River Valley of MA/CT. PWATs up to 1.5 inches combined with
rivers and streams 7 day flows greater than 90th percentile will
yield low risk of flash flooding. Storm potential for 1 inch per
hourly rainfall rates and isolated storm totals of 1-3 inches
across western-central MA/RI.

Otherwise, typical summer day with highs in the upper 70s to
lower 80s and dew pts 65-70. True warm sector airmass focused
across CT into western-central MA. SSE winds becoming SSW in CT
and western-central MA this afternoon with arrival of warm
sector.

&&

.SHORT TERM /7 PM THIS EVENING THROUGH 6 PM SATURDAY/...
A cold front should slowly cross southern New England tonight,
before moving offshore after daybreak Saturday morning.
Weakening thunderstorms and scattered showers cross our region
tonight, with showers lingering along the east coast Saturday
morning. A marked drying trend from W to E during the late
morning and afternoon hours.

More sunshine should produce slightly higher max temperatures
Saturday.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Key Points:

* Not as warm and less humid Sat night

* Pick of the weekend is Sunday with sunny and seasonably warm
  weather, but comfortable humidity

* Chance of showers/t-storms next Tue and Fri. Otherwise mainly
  dry weather with a gradual increase in heat & humidity, with
  90s possible late next week.

Short wave trough over southeast Quebec deamplifies and lifts
northeast away from the region. In its wake, NW flow aloft
streaming across SNE with 850 mb ensemble temp anomalies
slightly cooler than normal into MA/CT/RI. This combined with
light winds, decreasing clouds and dew pts falling into the mid
and upper 50s, low to mid 60s for the coastline, will result in
a very comfortable Sat night for late July.

Departing short wave over southeast Quebec yields rising
heights across SNE, supporting dry weather & sunshine. Post
frontal airmass with 850 mb temps at or slightly cooler than
normal will yield very pleasant conditions, with seasonably warm
temps (highs in the low to mid 80s), but accompanied by dew pts
in the 50s, except low to mid 60s for the coastline as
afternoon seabreezes advect higher dew pts onshore.

Next week, western Atlantic subtropical ridge begins to
retrograde towards the east coast. Rising heights across SNE
should support another mainly dry weather Monday. A warm day
with highs in the 80s but humidity tolerable, with dew pts in
the upper 50s to lower 60s, except mid to upper 60s along the
south coast. Mean trough over the Great Lakes/OH Valley and its
attending moisture plume advects eastward into New England Tue,
but with trough deamplifying, not expecting sufficient forcing
for ascent to warrant widespread showers/thunderstorms. Should
be more widely scattered. Hence, not a washout Tuesday with many
hours of dry weather likely. Continued warm Tue but more humid,
with dew pts creeping up to 65-70. Deamplifying mean trough
moves offshore Wed, with rising heights into SNE Thu, supporting
mainly dry weather. Ensembles have 591 heights over SNE by Thu,
signaling warmer (85-90) and increasing humidity with
developing SW flow.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
Forecast Confidence
Levels:

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

18z update.

Confidence overall is moderate.

Tricky forecast, as it always is with convection. As of just
prior to 18z, scattered thunderstorms are forming across western
CT and MA. They should progress eastward during the afternoon
and into the evening, but questions about how well they maintain
intensity. That has big ramifications for the forecast for BOS
in particular. Have added in TEMPO groups for best guess on
timing for TSRA at BAF, BDL and ORH. However as the storms move
further east, they should be weakening, so only went with TEMPO
SHRA for BOS, BED and PVD, though did include VCTS in the body
of the TAF. There may be another weakening line of showers and
t-storms, that are currently across central NY, coming into the
area during the mid evening into overnight hours. Low
confidence, so a lot of VCSH in the forecast. That second line
of convection will actually mark the passage of a weak cold
front. Winds will shift to SW/W after that passage during the
overnight hours. Expect a mix of VFR and MVFR ceilings today,
with IFR expected, especially along the east coast, Cape and
Islands. Eventually we break out into VFR area wide starting
Saturday morning.

KBOS TAF...Moderate confidence in TAF. Expect additional TAF
amendments to fine tune timing of TSRA later this afternoon.
Some low ceilings over the adjacent waters are expected to move
in this evening for MVFR, perhaps IFR conditions.

KBDL TAF...Moderate confidence in TAF. Expect additional TAF
amendments to fine tune timing of TSRA. Potenial for IFR
conditions after 04z with fog forming in the CT River Valley.
Low confidence, so not in the forecast at this time.

Outlook /Saturday Night through Tuesday/...

Saturday Night through Monday Night: VFR.

Tuesday: VFR. Slight chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

High confidence overall. Lower confidence on coverage of fog
across the waters.

Rather tranquil boating conditions expected across the waters
through Saturday. Areas of fog with visibility reduced less than
1 nm expected this morning across the eastern MA coastal
waters, including those around the Cape and islands. After some
improvement during the day today, should see a period this
evening with reduced visibility once more. Visibility finally
improves late tonight into Saturday as a cold front moves
offshore, bringing drier air over the coastal waters.

Outlook /Saturday Night through Tuesday/...

Winds less than 25 kt.

&&

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

&&

SYNOPSIS...Belk/Nocera/Nash
NEAR TERM...Nocera/Nash
SHORT TERM...Belk
LONG TERM...Nocera
AVIATION...Nash
MARINE...Belk/Nocera

Hazardous Weather Outlook
National Weather Service Boston/Norton MA
419 AM EDT Fri Jul 21 2023

CTZ004-MAZ004>007-012>024-026-RIZ001>008-220830-
Windham CT-Northern Worcester MA-Central Middlesex MA-
Western Essex MA-Eastern Essex 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-
419 AM EDT Fri Jul 21 2023

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

.DAY ONE...Today and tonight.

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

ANZ230>237-250-251-254>256-220830-
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-
419 AM EDT Fri Jul 21 2023

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...Saturday through Thursday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

CTZ002-003-MAZ002-003-008>011-220830-
Hartford CT-Tolland CT-Western Franklin MA-Eastern Franklin MA-
Western Hampshire MA-Western Hampden MA-Eastern Hampshire MA-
Eastern Hampden MA-
419 AM EDT Fri Jul 21 2023

This Hazardous Weather Outlook is for northern Connecticut and
western Massachusetts.

.DAY ONE...Today and tonight.

A few strong to severe thunderstorms are possible this afternoon and
early evening. The main threats are damaging winds, flash flooding
and large hail.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

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/NWSBoston

You can follow us on Twitter at
@NWSBoston

Special Weather Statement
National Weather Service Boston/Norton MA
1256 PM EDT Fri Jul 21 2023

MAZ002-003-008-211800-
Western Franklin MA-Western Hampshire MA-Eastern Franklin MA-
1256 PM EDT Fri Jul 21 2023

...A strong thunderstorm will impact portions of northwestern
Hampshire and central Franklin Counties through 200 PM EDT...

At 1256 PM EDT, Doppler radar was tracking a strong thunderstorm over
Goshen, or 11 miles northwest of Northampton, moving northeast at 15
mph.

HAZARD...Winds in excess of 30 mph and pea size hail.

SOURCE...Radar indicated.

IMPACT...Strong winds could cause minor damage such as downed
         branches. Little to no impact from hail is expected.

Locations impacted include...
Greenfield, Orange, Deerfield, Montague, Sunderland, Northfield,
Williamsburg, Bernardston, Buckland, Conway, Shelburne, Leverett,
Erving, Ashfield, Colrain, Gill, Whately, Charlemont, Chesterfield
and Worthington.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Get indoors when you hear thunder. Do not resume outdoor activities
until at least 30 minutes after the storm has passed.

&&

LAT...LON 4260 7285 4273 7255 4257 7229 4237 7293
TIME...MOT...LOC 1656Z 240DEG 13KT 4245 7283

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH

BW

Special Weather Statement
National Weather Service Boston/Norton MA
155 PM EDT Fri Jul 21 2023

CTZ002-003-MAZ009>011-211900-
Hartford CT-Tolland CT-Western Hampden MA-Eastern Hampden MA-
Eastern Hampshire MA-
155 PM EDT Fri Jul 21 2023

...A strong thunderstorm will impact portions of northwestern
Tolland, northern Hartford, southeastern Hampshire and south central
Hampden Counties through 300 PM EDT...

At 155 PM EDT, Doppler radar was tracking a strong thunderstorm over
Canton, or 12 miles west of Windsor, moving northeast at 25 mph.

HAZARD...Winds in excess of 40 mph and penny size hail.

SOURCE...Radar indicated.

IMPACT...Strong winds could cause minor damage such as downed
         branches. Minor damage to outdoor objects is possible.

Locations impacted include...
Springfield, Hartford, West Hartford, Bristol, Chicopee, Enfield,
Westfield, Holyoke, Windsor, Agawam, West Springfield, South Windsor,
Farmington, Simsbury, Bloomfield, Avon, South Hadley, Longmeadow,
Suffield and East Longmeadow.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Get indoors when you hear thunder. Do not resume outdoor activities
until at least 30 minutes after the storm has passed.

A Severe Thunderstorm Watch remains in effect until 800 PM EDT for
northern Connecticut...and western Massachusetts.

&&

LAT...LON 4181 7295 4184 7294 4185 7295 4189 7294
      4190 7291 4197 7289 4197 7297 4223 7256
      4196 7237 4167 7299 4180 7302
TIME...MOT...LOC 1755Z 231DEG 23KT 4190 7291

MAX HAIL SIZE...0.75 IN
MAX WIND GUST...40 MPH

BW