Flash Flood Warning 6, NWS Boston/Norton, MA

Area Forecast Discussion
National Weather Service Boston/Norton MA
253 AM EDT Mon Sep 5 2022

.SYNOPSIS...
A cold front moves into southern New England tonight then stalls
near the south coast Monday. The front moves south of the coast
Monday night into Tuesday as low pressure develops near the middle
Atlantic coast and persists into Wednesday. Multiple rounds of
showers are likely through Tuesday, with areas of heavy rainfall.
After a period of below normal temperatures Monday and Tuesday,
mainly dry weather with a warming trend follows for the end of the
week into next weekend as high pressure builds over the region.

&&

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

2am update...

Already seeing a line of stationary showers over Essex County
extending up into coastal New Hampshire at 2 AM. This is
clearly initiating along the boundary draped across the region
from northeast to southwest. Rainfall totals of 1.5 to 2 inches
are already being observed under the heaviest cells in northeast
MA for which an SPS has been issued. Flooding issues are
possible if this line of showers continues over the next few
hours.

Previous Discussion...

There is a cluster of showers and thunderstorms ongoing over
western CT at this hour. Hazards have been limited to lightning
and heavy rainfall thus far. Expect thunderstorm activity over
this area to wane in the next hour or two as instability wares
off and convective inhibition settles in. Made some slight
adjustments to the PoPs over the next couple of hours to reflect
radar observation. Otherwise the forecast remains on track.
Isolated to scattered showers will remain a possibility as we
head into the overnight hours.

Previous Discussion

A cold front sagging southward into New England this evening will
bring the onset of a prolonged period of wet weather. South of the
front, surface high pressure off the east coast is supporting
southwest winds and the transport of warm moist air into southern
New England. This will allow PWATs to rise to 1.75 to 2 inches
overnight. KBOX radar is already detecting a few isolated
showers/thunderstorms ahead of the front. Expect these showers to
expand in coverage as the front drops south during the evening .
hours. SPC mesoanalysis is revealing around 1000 J/kg of MLCAPE
across interior southern New England. Deep-layer shear is virtually
non-existent, thus not expecting any severe thunderstorms. However,
a few rumbles of thunder is possible. Mainly expect shower activity
this evening to be confined to the areas north and west of I-495.
Most of southeastern MA/RI should stay on the dry side.

Thunderstorm activity settles down after midnight and transitions to
scattered light showers as the frontal boundary become quasi-
stationary over southern New England. Where the boundary sets up
will have an influence on the overnight low temperatures. North of
the front, somewhere north of I90, lows will be in the low to mid
60s. South of the front overnight lows will range from the mid to
upper 60s.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM TUESDAY/...
Tomorrow through Tomorrow Night

Shower activity ramps back up tomorrow morning into tomorrow
afternoon. There won't be a lot of instability to work with,
therefore we're not expecting a lot of thunderstorm activity.
However, a deep warm cloud layer and high PWATs will help support
efficient rainfall processes which may lead to locally heavy
downpours. There is a slight risk for excessive rainfall over the
area, but it will be difficult to achieve the rainfall rates
necessary to support any widespread flash flooding. This will be
more of a long duration heavy rainfall event. Thus, expect any
flooding issues to be confined to small streams, urban areas, and
poor drainage areas.

Rainfall continues into tomorrow night and Tuesday as an area of low-
pressure approaches from the south. Rainfall totals by Tuesday
morning will range from 1 to 1.5 inches with higher amounts
possible. Additional rainfall is expected during the day Tuesday.
See long-term discussion for further details on Tuesday and beyond.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Highlights...

* Showers and localized downpours continue into Tue, especially
  south of the Mass Pike. Unseasonably cool
* Trending drier and milder Wed but still below normal
* Dry conditions with temps trending back above normal for the end
  of the week into next weekend

Tuesday into Tuesday night...

Global guidance is rather bullish on a period of heavy rainfall Tue,
especially south of the Mass Pike. Front settles south of New Eng
with moist easterly flow. While some drying is noted across northern
MA in the afternoon, anomalous PWAT plume 1.75-2.00" persists
further south. Mid level trough slides south across New Eng with a
surface low developing along mid Atlc coast. Large scale forcing
from right entrance region of upper jet acting on high PWATs will
likely bring some heavy rainfall to SNE. Additionally, warm cloud
depths around 12k ft is very supportive of warm rain processes and
enhanced rainfall rates. Latest guidance favors areas south of the
Pike through CT and RI but this will likely depend on location of
the stalled front. Potential for locally 1-2" rainfall on Tue where
heavy rainfall axis sets up but this could still shift north or
even south of New Eng. Instability is nil so not expecting any
thunder. Unseasonably cool day with easterly flow and cool low
levels holding temps in the 60s and possibly close to 60 over
higher terrain.

Drier air gradually pushes south through SNE Tue night as lower PWAT
air advects in from the north. Lingering showers will Tue evening
should be confined to CT/RI and SE MA then a gradual drying trend
expected overnight.

Wednesday...

High pres builds south into New Eng while low pres lingers off the
mid Atlc coast. While airmass is moderating, easterly low will slow
warming trend with highs ranging from upper 60s across east coastal
MA to mid 70s in the CT valley. Generally dry conditions but upper
trough is over New Eng so can't rule out a pop up shower, closer to
the south coast where moisture is greater.

Thursday through Sunday...

Upper trough gradually departs Thu with subtropical ridge building
into New Eng Fri through the weekend. High pres will be in control
at the surface with dry air in the column leading to dry weather and
mostly sunny skies. Temps moderating through the weekend with Thu
the transition day with near seasonable temps, then warming above
normal Fri-Sun with temps getting into the 80s away from the
coast.

&&

.AVIATION /07Z MONDAY THROUGH FRIDAY/...
Forecaster Confidence Levels:

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

06Z update...

This morning...high confidence.

Scattered showers redevelop after from west to east and in
northeast MA along a stationary front. VFR conditions will
trend toward MVFR/IFR through the morning. Light south-
southeast winds, possibly becoming N-NE across northern MA as
frontal boundary drifts southward.

Today...high confidence on trends, lower in timing and details.

VFR/MVFR southeast MA, MVFR/IFR elsewhere with LIFR possible
inland across the hilly terrain. Showers likely widespread along
with areas of fog. S-SE winds across RI and southeast MA, N-NE
winds elsewhere.

Tonight...High Confidence

IFR/LIFR across most of the interior with MVFR/IFR ceilings near
the east coast and southeast MA. Showers likely. Easterly winds
around 10 knots.

Tuesday...High Confidence.

IFR/LIFR for most of the interior again in continues SHRA
through 18-21Z. NE winds 8 to 10 kts.

KBOS Terminal..moderate confidence in TAFT. Uncertainty exists
in the arrival of MVFR/IFR ceilings associated with a prolonged
period of rainfall through tomorrow night.

KBDL Terminal...High confidence in TAF.

Outlook /Monday Night through

Tuesday: MVFR/IFR conditions possible. SHRA likely.

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

Wednesday: VFR. Breezy.

Wednesday Night through Friday: VFR.

&&

.MARINE...
Forecaster Confidence Levels:

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

Tonight through Tomorrow Night

Relatively benign conditions expected across the maritimes through
tomorrow night. Will see south/southeast winds become more easterly
tomorrow and tomorrow night as a surface front settles over the
region. Additionally expecting seas to rise to 2 to 4 feet through
tomorrow night as well. Moderate to heavy rainfall expected over the
coastal waters beginning late tomorrow morning and lasting through
Tuesday.

Outlook /Tuesday Night through Friday/...

Tuesday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain
showers.

Tuesday Night: Winds less than 25 kt. Seas up to 5 ft. Slight
chance of rain showers.

Wednesday: Winds less than 25 kt. Seas up to 5 ft.

Wednesday Night through Friday: Winds less than 25 kt. Areas of
seas approaching 5 ft.

&&

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

&&

SYNOPSIS...KJC/RM
NEAR TERM...BW/RM
SHORT TERM...RM
LONG TERM...KJC
AVIATION...KJC/BW/RM
MARINE...KJC/RM

Hazardous Weather Outlook
National Weather Service Boston/Norton MA
452 PM EDT Sun Sep 4 2022

CTZ002>004-MAZ002>024-026-RIZ001>008-052100-
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-
452 PM EDT Sun Sep 4 2022

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

.DAY ONE...Tonight.

Scattered showers and isolated thunderstorms with locally heavy
rainfall may result in areas of minor urban and poor drainage
flooding.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

Heavy rainfall will become more widespread Monday afternoon through
Tuesday with areas of urban and poor drainage flooding.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

ANZ230>237-250-251-254>256-052100-
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-
452 PM EDT Sun Sep 4 2022

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...Monday through Saturday.

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

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@NWSBoston

Special Weather Statement
National Weather Service Boston/Norton MA
245 AM EDT Mon Sep 5 2022

MAZ005>007-014-050745-
Eastern Essex MA-Central Middlesex County MA-Western Essex MA-
Southeast Middlesex MA-
245 AM EDT Mon Sep 5 2022

...Heavy showers with embedded thunder will impact portions of Essex
and northeastern Middlesex Counties through 345 AM EDT...

At 243 AM EDT, Doppler radar was tracking a cluster of heavy showers
and embedded thunderstorms containing very heavy rain over Lowell,
moving northeast at 15 mph.

HAZARD...Minor flooding.

SOURCE...Radar indicated.

IMPACT...Minor nuisance flooding of typically flood prone areas.

Locations impacted include...
Lowell, Lawrence, Haverhill, Peabody, Methuen, Billerica, Woburn,
Chelmsford, Andover, Lexington, Dracut, Tewksbury, North Andover,
Danvers, Wakefield, Reading, Burlington, Wilmington, Westford and
Acton.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Do not drive through flooded roads or underpasses. Avoid low lying
areas near small streams.

&&

LAT...LON 4287 7082 4283 7081 4281 7087 4280 7083
      4281 7081 4273 7078 4272 7079 4277 7082
      4271 7083 4271 7080 4268 7081 4245 7114
      4246 7144 4270 7132 4274 7124 4274 7118
      4281 7116 4281 7107 4286 7103 4289 7092
TIME...MOT...LOC 0643Z 192DEG 11KT 4262 7128

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...<30 MPH

Nocera