-- Discussion containing changed information from previous version are highlighted. --
340
FXUS61 KBOX 250505
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
105 AM EDT Wed Sep 25 2024

.SYNOPSIS...
Weak high pressure will remain across the region through
Wednesday. An approaching frontal system will bring showers
with some downpours to the region late Wednesday night into
Thursday. High pressure then building to our north will bring
dry and very pleasant early fall weather from Friday right
through Monday.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Surface and upper level ridging remain in place tonight. Weak
shortwave lifts northward and passes to the north and west late
tonight. While PWATs are increasing, deep moisture axis will
remain mostly to the west where best chance of showers will be
so expecting mainly dry weather tonight with mostly cloudy
skies. Exception will be across portions of eastern MA and RI
where a spot shower is possible as hi-res guidance continues to
indicate a few showers backing in from the ocean. Lows will
range from the upper 40s to mid 50s.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM THURSDAY/...
Wednesday...

Mid level shortwave moves to the north in the morning followed by
weak ridging and subsidence which should result in mainly dry
conditions for much of the day. But once again, can`t rule out a
spot shower in eastern MA as persistent easterly flow continues.
Mid level dry air holds on across eastern New Eng through the
day but deeper moisture begins to move into the west during the
afternoon. Can`t rule out a shower in western MA during the
afternoon, otherwise it should remain a dry day. Not much change
in low level temps so another day with highs mid-upper 60s

Wednesday night...

Fairly robust northern stream trough/upper low digs south across SE
Canada. Diffluent flow aloft ahead of this system and a modest low
level jet approaching from the west will result in increasing
forcing for ascent and decent moisture advection into New Eng.
Decent PWAT plume 1.5-1.75" moves into SNE. The increasing forcing
acting on this moisture will bring a period of showers to SNE from
NW to SE during the night, with greatest risk across northern MA.
Additionally, there is some marginal elevated instability
approaching from the west so can`t rule out a rumble of thunder or
locally heavy showers across northern and western MA toward
daybreak. Lows will be in the 50s.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Key Points...

* Showers Thu with some downpours along with the risk for an
  embedded t-storm or two

* Dry & very pleasant early fall weather Fri through Mon

Details...

A very dynamic closed upper level low pressure system will move
across Quebec/northern New England and into the Canadian Maritimes
late in the work week. The trailing shortwave energy and associated
cold front will move across the region Thu into Thu night. A brief
but modest PWAT plume...roughly between 1.50 and 1.80 inches will
move in ahead of this frontal system. There is a period of modest
forcing as well...with a southwest LLJ of 30-40 knots as well as a
bit of elevated instability. So in a nutshell...showers are expected
Thu into Thu evening with an embedded t-storm or two possible. We do
expect some downpours as well given the modest forcing and good Pwat
plume.

This frontal system is progressive and the dynamic closed upper low
will move east of the Maritimes this weekend. The result will be
some mid level ridging along building in from the west with a
surface high pressure system anchoring itself across Quebec and
northern New England into early next week. The result will be
generally dry and very pleasant early fall weather across the region
Fri right through Mon. Overnight lows generally will be in the
45 to 55 degree range with highs between 65 and 75. The warmest
day looks to be Friday with more of a northerly wind and many
locations may see highs in the middle 70s.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
-- Changed Discussion --
Forecast Confidence Levels:

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


Wednesday...Moderate confidence.

VFR/MVFR today with mid level clouds hanging around 3kft. Winds
remain out of the ESE today at 5-10 knots.

Wednesday night...Moderate Confidence

Rain and IFR/LIFR CIGS move from west to east overnight.
Showers overnight should remain light with the heavier rain
holding off until Thursday

Thursday...Moderate confidence

Moderate to heavy rain with IFR/LIFR Cigs. There could be
embedded thunder and a fine line of convection that crosses the
region from west to east in the late afternoon. CIGS clear
quickly to MVFR/VFR behind the fine line.

BOS TAF...Moderate Confidence in TAF.

VFR/MVFR again today with ESE winds.

BDL TAF...Moderate Confidence in TAF.

VFR/MVFR again today with ESE winds. Rain and IFR CIGs move in
overnight.

Outlook /Thursday Night through Sunday/...

Thursday: Mainly MVFR, with areas IFR possible. Breezy. Chance
SHRA, slight chance TSRA.

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

Friday: Mainly VFR, with local MVFR possible. Slight chance
SHRA.

Friday Night: Mainly VFR, with local MVFR possible.

Saturday: Mainly VFR, with local MVFR possible. Breezy.

Saturday Night through Sunday: VFR. Breezy.
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
Forecaster Confidence Levels:

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

Tonight through Wednesday night...High Confidence.

Persistent easterly swell will result in rough seas, 5-7 ft, across
the outer waters into Wed night. Have extended the SCA through Wed
night for outer waters. Persistent easterly winds 10-15 kt with
occasional gusts to 20 kt will diminish Wed night.

Rip Current Statement remains in effect for both the southern
and eastern coasts through this evening. Another rip current
statement for high risk of rip currents was issued for Wed for
the eastern MA coast.

Outlook /Thursday Night through Sunday/...

Thursday: Winds less than 25 kt. Areas of rough seas. Chance of
rain showers, isolated thunderstorms.

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

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

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

Sunday: Winds less than 25 kt. Seas up to 5 ft.
-- End Changed Discussion --

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
CT...None.
MA...High Risk for Rip Currents from 8 AM EDT this morning through this
     evening for MAZ007-019-022-024.
RI...None.
MARINE...Small Craft Advisory until 8 AM EDT Thursday for ANZ250-251-
     254>256.
-- End Changed Discussion --

&&

$$

SYNOPSIS...KJC/Frank
NEAR TERM...KJC/KP
SHORT TERM...KJC
LONG TERM...Frank
AVIATION...KP
MARINE...KJC/Frank