947
FXUS61 KBOX 290304
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1104 PM EDT Fri Jun 28 2024

.SYNOPSIS...
Mainly dry weather continues on Saturday outside a few brief
spot showers across the distant interior. A slow moving frontal
system brings two potential rounds of scattered showers &
thunderstorms...mainly Saturday night into early Sunday morning
and then perhaps again later Sunday into Sunday night. Drier
weather with seasonable temperatures and comfortable humidity
levels returns early next week as high pressure builds in from
the west. This high pressure system will slide east of the
region late next week allowing very warm and humid weather to
return for the start of the long Holiday Weekend.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
No major changes to the forecast this evening. Still watching
showers across portions of NY state and PA. Some of these could
reach portions of NW MA towards daybreak. Minor tweaks to
temperatures to reflect observed trends and latest guidance.

650 PM Update...

* Increasing clouds overnight with lows in the 50 to near 60

Previous forecast is on track. Mainly clear skies early this
evening will give way to increasing mid-high clouds overnight.
This in response to high pressure moving off the coast coupled
with mid level warm front approaching. It will remain dry
though...just a low risk of a brief spot shower near daybreak in
far northwest MA. Overnight low temps will be in the 50s to
near 60.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
Surface warm front pushes through increasing humidity along with a
few nuisance showers and rumble of thunder, though most of the day
appears dry. Afternoon highs run a few degrees cooler than normal in
the upper 70s to 80F. WAA ushers in higher PWATs/dew points, with
dews returning to the low and middle 60s with PWATs around 1.5".
Though these values climb well over 2.0 inches Saturday night to
Sunday morning, which is impressive, per Sounding Climatology,
the daily max at CHH is 2.04". Plus, BUFKIT soundings indicate
the warm cloud layer is 10,000 FT to 12,000 FT - raises concerns
of heavy rains overnight and potential isolated flash flooding.


Steadiest rain arrives late, likely around 00z across the
western CWA getting to the Boston to Providence corridor closer
to 04z. Otherwise a mild night with lows only dipping into the
upper 60s to 70F.

In addition, there are fairly strong winds aloft, with a SW LLJ
increasing throughout the afternoon into the overnight hours. This
should promote a fairly consistent southwest wind with gusts
between 20 and 30 knots.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Key Points...

* Main concern is timing of showers & t-storms Sun/Sun night as well
  as assessing any severe weather & localized flooding potential

* Cooler/less humid Mon with seasonable temps Tue & Wed

* Warmer/Humid weather returns by Thu July 4th & into Holiday Weekend

Details...

Sunday and Sunday night...

Quite a complex forecast Sun into Sun night which we will break down
below. It appears that an initial round of scattered showers & t-
storms will be departing early Sun am in association with
shortwave/warm front. Otherwise...dry weather probably dominates the
region the rest of Sun morning into early afternoon. In
fact...southwest flow will result in a very warm and humid day.
Amount of solar insolation still somewhat uncertain...but thinking
there will be enough for highs in the upper 80s to near 90 away from
the south coast. A little bit of southwest breeze with gusts up to
25 mph. It also appears we may have an elevated risk of dangerous
rip currents on Sun especially near the south coast.

The main uncertainty revolves around the potential for scattered
showers & t-storms developing Sun PM from the approaching
shortwave/cold front. We should have moderate instability develop
with surface based Capes on the order of 1000 to 2000 J/KG. One
limiting factor will be poor mid level lapse rates...but 0 to 6 KM
shear values will be on the order of 40 to 50 knots which is quite
favorable. Timing of the front and other mesoscale processes will
ultimately determine the severe weather potential Sun PM. The CSU
Machine Learning guidance indicate some probs for severe weather
with the highest northwest of i-95. Appears the main threat will be
damaging wind gusts given steep low level lapse rates/strong jet
dynamics which is also supported by the CSU Machine learning
guidance. In addition...Pwats near 2 inches will support the
potential for torrential rainfall and a localized flood with any
thunderstorms.

Upcoming Work Week...

Significantly cooler and less humid air moves in behind the cold
front on Monday. High temps will only be in the upper 70s to near 80
with lowering humidity. Strong upper level trough/shortwave energy
should allow for plenty of CU and perhaps a few diurnally driven
showers...but the majority of the day will feature dry and pleasant
weather.

High pressure then builds into the region Tue and Wed bringing
dry/seasonable temperatures...but with tolerable humidity for this
time of year. Highs will mainly be in the 80s with the
warmer/slightly more humid day on Wed.

The high shifts east of the region by Thu, July 4th and into Fri.
This will result in very warm and humid weather returning. Low
confidence on timing any potential risk for scattered showers & t-
storms...but regardless plenty of dry weather expected over this
time too.

&&

.AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:

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

Tonight... High Confidence.

VFR with just increasing mid-high clouds overnight. Light SSW
winds.

Saturday...High Confidence.

VFR despite a fair amount of mid-high level cloudiness. S winds
increasing to between 10 and 15 knots with some gusts around 25
knots.

Saturday night... Moderate confidence in timing, higher
confidence in trends.

MVFR to eventually mainly IFR conditions overspread the region
from west to east Sat night. A round of scattered showers and
perhaps a few t-storms possible. S winds 10 to 15 knots with
gusts up to 25 knots.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Sunday through Wednesday/...

Sunday: Mainly MVFR, with local IFR possible. Breezy. Chance
SHRA, slight chance TSRA.

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

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

Monday Night through Tuesday Night: VFR.

Wednesday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels:

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

Tonight through Saturday Night... High confidence.

Tranquil boating conditions this afternoon and evening with
surface high pressure. Light winds will become south overnight
with stronger gusts expected on Saturday. Increasing southerly
winds to 15-20 kts by the afternoon. Will have some 20-30 kt
gusts, seas building 3-6 ft. Have opt to issue a Small Craft
Advisory, going into effect for all waters Saturday afternoon
for the northeast zones, while the rest of the ocean waters by
Saturday evening. Have included Boston Harbor and Narragansett
Bay during the overnight hours as well. All waters will remain
under a Small Craft Advisory though at least Sunday evening.

Areas of rain and thunder arrive late Saturday night into Sunday
morning.

Outlook /Sunday through Wednesday/...

Sunday: Moderate risk for Small Craft Advisory winds with gusts
up to 25 kt. Seas up to 5 ft. Rain showers likely, slight
chance of thunderstorms.

Sunday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain showers, slight chance of thunderstorms.

Monday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Slight chance of rain showers.

Monday Night through Wednesday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from midnight Saturday night to 7 PM EDT
     Sunday for ANZ230-236.
     Small Craft Advisory from 8 PM Saturday to 7 PM EDT Sunday for
     ANZ231>235-237-254>256.
     Small Craft Advisory from noon Saturday to 7 PM EDT Sunday for
     ANZ250-251.

&&

$$

SYNOPSIS...Frank/Dooley
NEAR TERM...Belk/Frank
SHORT TERM...Dooley
LONG TERM...Frank
AVIATION...Belk/Frank/Dooley
MARINE...Frank/Dooley