836
FXUS61 KBOX 281945
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
345 PM EDT Tue Jul 28 2026

.WHAT HAS CHANGED...
Expanded the flood watch to include Worcester, Windham, and
Providence counties. Increased rainfall totals with a
widespread two to four inches expected for most areas, and up to
five to seven inches possible for the Berkshires and Worcester
Hills.

&&

.KEY MESSAGES...

- Prolonged period of heavy rain slowly overspreads the region
  from west to east overnight through Wednesday evening.
  Expecting areas of street and poor drainage flooding with the
  greatest risk across the interior where a Flood Watch remains
  in effect through 8pm Wednesday night.

- Improving conditions with nuisance showers Friday followed by
  a drier weekend, becoming unsettled late weekend into early
  next week.

&&

.DISCUSSION...
KEY MESSAGE 1...Prolonged period of heavy rain slowly
overspreads the region from west to east overnight through
Wednesday evening. Expecting areas of street and poor drainage
flooding with the greatest risk across the interior where a
Flood Watch remains in effect through 8pm Wednesday night.

Bottom line up front: expected rainfall totals have increased, and
in some areas, significantly so since the last update. We now expect
a widespread swath of 2 to 4 inches of rain with areas locally
seeing as much as 5 to 7 inches. The most likely locations to exceed
5 inches will be across the Berkshires and Worcester Hills with
orographic enhancement. In these areas, there may be some local
river/stream rises, otherwise, the main concern is for urban/poor
drainage flooding. Thus, we opted to expand the Flood Watch to
include Worcester, Windham, and Providence counties given recent
trends to increase QPF in those areas. To reiterate, if you live in
the hillier terrain of the Berkshires or Worcester Hills, or in an
urban/poor drainage area, this event will bring a significant risk
for potentially life-threatening flash flooding. Be sure to have a
way of receiving warnings especially at night when some of the
heaviest rain likely falls across western Massachusetts.

Anomalously deep mid level low that will be the main driver of our
upcoming heavy rain event continues to amplify over western NY this
afternoon. Eventually, there will be a response to this impulse at
the surface in the form of rapidly developing surface low. The
combination of favorable upper-level dynamics, and strong near-
surface flow advecting copious amounts of moisture over our CWA set
the stage for a prolonged, and in some localized instances, life-
threatening heavy rain event. Details on the exact placement of
heavy rain remain somewhat uncertain as even now, there are
differences in the evolution of the occlusion and surface low
between guidance. Global guidance has trended closer to the coast
with the surface low and thus puts the bulk of the heaviest QPF to
the north of the region. The CAMs continue to show a further
offshore solution with a secondary swath of high QPF along a W-E
oriented axis of frontogenesis across E central Massachusetts
Wednesday evening into Thursday. These changes reflect locally
stronger forcing across these areas as the surface low occludes
later Wednesday into Thursday. Guidance shows strong surface
convergence and east to west oriented axis of enhanced frontogenesis
developing as surface low pressure turns the flow more easterly in
these areas. Combine that with high PWATs and orographic enhancement
over the hillier terrain of Worcester County and eastern Connecticut
and there is the potential for flash flooding. Further to the west,
SE and E flow will serve to enhance upslope flow and rainfall totals
in the Berkshires as well. In this area, training storms
(continually moving over the same location) likely leads to
widespread flooding as the surface low slowly moves E. Timing for
the heaviest rain would begin as early as this evening for interior
SNE, while eastern MA is likely to stay dry until late tonight
night/Wednesday morning. Areas of heavy rain will move E over those
areas later Wednesday morning, with heavy rain increasing in
coverage through much of the afternoon as surface low pressure
approaches from the S. There will be plenty of instability for tall
convective cells as  MUCAPE increases to around 500 J/kg. Model
soundings show deep warm clouds with >90% saturation extending
through much of the column allowing the atmosphere to use ~90% of
the 1.5-2.0" PWATS for torrential rainfall. Unfortunately for
outdoor plans this appears to be a long duration event. Showers and
drizzle stick around through at least Friday. The good news is that
the heavy rain of Wednesday and early Thursday will wane as the low
becomes vertically stacked under an upper level low.

KEY MESSAGE 2...Improving conditions with nuisance showers Friday
followed by a drier weekend, becoming unsettled late weekend into
early next week.

Nuisance rain showers will continue on Friday with the vertically
stacked system remaining over southern New England. Despite a
saturated atmosphere with PWATs well above climatology, less
favorable jet dynamics will result in widely scattered light rain
showers rather than the tropical downpours experienced over the
previous two days. In a bit of better news, confidence continues to
increase that the mid-level ridge across the northwestern Atlantic
Ocean will de-amplify enough to allow this system to progress
eastward, with subtle mid-level ridging building in for the upcoming
weekend. This should lead to a drier weekend, albeit not as sunny as
the previous weekend. Nevertheless, flow will return to the south-
southwest, advecting warmer temperatures back into the region, which
will be a welcome relief after a few raw late July days. Highs
Friday will generally be in the upper 70s to around 80F. This
weekend trends a couple of degrees warmer, with seasonable
temperatures in the lower 80s. Late in the weekend into Monday and
Tuesday, the pattern becomes unsettled once again as our next chance
for rain arrives. Given the 5 to 6 day forecast horizon, additional
changes are likely.

&&

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

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

18z TAF Update:

Today...Moderate confidence.

Low-end VFR over the eastern terminals deteriorates to MVFR/IFR
generally after 18z at BDL, expanding east through 00z.
Sporadic, slow moving showers across western MA/CT through early
this evening. Low chance for embedded TSRA. Also seeing lower
probs that a shower could potentially brush the western part of
Boston, but confidence is too low that BOS would see impacts to
include in TAF at this time. SE winds 10-13 kt with gusts to 20
kt in the afternoon.

Tonight...Moderate confidence.

LIFR/IFR for most in periods of heavy rain. SE winds 5-10kt
with gusts to 20 kt possible.

Wednesday...Moderate confidence.

IFR/MVFR in continued periods of heavy rain. E winds 10-15 kts
with gusts to 25 kts possible.

KBOS Terminal...Moderate confidence. Lower confidence in
arrival time of rainfall.

KBDL Terminal...Moderate confidence. Lower confidence in
arrival time of rainfall, as well as how low visby`s could drop
during showers.

Outlook /Wednesday Night through Sunday/...

Thursday: Mainly VFR, with local IFR possible. Breezy. SHRA
likely, isolated TSRA.

Thursday Night: Mainly VFR, with local IFR possible. Chance
SHRA, isolated TSRA.

Friday: VFR. Slight chance SHRA, isolated TSRA.

Friday Night through Saturday Night: VFR.

Sunday: Mainly VFR, with local IFR possible. Slight chance
SHRA, slight chance TSRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Through Thursday...High confidence.

An anomalous midsummer low pressure system will bring a prolonged
period of unsettled weather to the southern New England coastal
waters beginning this evening and continuing through Thursday.
Periods of heavy rain, reduced visibilities, and embedded
thunderstorms are expected through much of the period. A Small Craft
Advisory remains in effect for all waters through Wednesday, and for
the outer coastal waters through Thursday. South to southeast winds
increase tonight, with gusts of 25 to 30 kt expected on Wednesday.
Seas build to 4 to 6 ft, highest across the outer waters. Wind
direction becomes more variable on Thursday as the surface low
tracks across the southern New England coastal waters. East to
northeast winds ahead of the low will shift to north to northwest in
its wake, although the eastern waters may remain northeasterly
longer before the system gradually departs Thursday night.

Outlook /Wednesday Night through Sunday/...

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

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

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

Saturday: Winds less than 25 kt. Seas locally approaching 5 ft.

Saturday Night through Sunday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Flood Watch through Wednesday evening for CTZ002>004.
MA...Flood Watch through Wednesday evening for MAZ002>004-008>012.
RI...Flood Watch through Wednesday evening for RIZ001-002.
MARINE...Small Craft Advisory from 2 AM to 8 PM EDT Wednesday for
     ANZ230-231-251.
     Small Craft Advisory from 8 PM this evening to 8 PM EDT
     Wednesday for ANZ232>237.
     Small Craft Advisory from 2 AM Wednesday to 8 AM EDT Thursday
     for ANZ250.
     Small Craft Advisory from 8 PM this evening to 8 AM EDT
     Thursday for ANZ254>256.

&&

$$

DISCUSSION...Dooley/FT
AVIATION...McMinn/FT
MARINE...Dooley/FT