075
FXUS61 KBOX 260207
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1007 PM EDT Wed Sep 25 2024

.SYNOPSIS...
An approaching frontal system will bring showers with moderate
heavy downpours and few embedded thunderstorms mainly Thursday
into Thursday evening. High pressure builds back in Friday
through Monday and will bring dry and very pleasant weather.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
10 PM Update...

Radar shows an area of showers moving east across western MA,
but seems like dry air is making it difficult for rain to reach
the ground. Any rain that does hit the ground tonight will be
light. Latest hi- res guidance seems to indicate a break in the
showers overnight before the next round moving in early tomorrow
morning.

Previous discussion:

A couple batches of showers pushing across southern New England
this evening. These will likely be scattered in coverage and
light. Added in shower chances a little further east to reflect
current trends. Overall nothing impactful. No other changes
needed to the forecast.

Surface high pressure over the Canadian Maritimes gradually
shifts northeast tonight. Moisture increases this evening with
precipitable water values increasing toward 1.3-1.4 inches. Weak
synoptic ascent and warm air advection will support the risk
for a few showers may increase across the distant interior this
evening. Elsewhere, expect cloudy skies overnight. Temperatures
drop into the mid to upper 50s.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY/...
Thursday:

Thursday, the strongest forcing arrives with the main upper
trough and coupled jet max. This will provide increased ascent
to support rainfall. Thursday morning through the afternoon,
light rain spreads west to east, becoming moderate to heavy by
late morning. HREF means show precipitable water values
increasing into the 1.5-1.75 inch range with high end potential
for values closer to 2 inches. A cold front is expected to
move across SNE late in the Thursday afternoon to early
evening time frame.

In this time frame, we will see our highest chances for moderate
to locally heavy rainfall with potential for embedded weak
thunderstorms/rumbles thunder. High-res guidance shows of
marginal instability with MUCAPE values < 500 J/kg. Most also
reflect the passage of a line of higher reflectivity close to
the frontal timing. Given weak instability and lapse rates as
well as cooler temperatures, severe weather low probability.
However, localized heavier rainfall is possible. Model soundings
show sufficient warm cloud depths combined with plentiful
moisture. The potential for brief heavier rain will accompany
the passage of the main line. Rainfall rates will generally stay
closer to .25"/hr with a low chance for localized .50"/hr or
greater, likely associated with the heavier more convective
showers. The HREF LPMM QPF continues to highlight potential for
higher amounts with a swath of 1-2" totals oriented across
north/central MA. Other areas, amounts are in the 0.5-1" range.

Thursday Night:

The main batch of rain/embedded storms moves offshore later
Thursday night as the main cold front moves through. Conditions
dry out behind it overnight.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Key Points...

* Dry & very pleasant weather Fri into early next week
* Next threat for some showers not until later Tue and/or Wed

Details...

Tranquil and generally dry weather is expected Friday into early
next week...although a few showers may linger into early Friday
morning towards the Cape/Islands but that would be short-lived.
This in response to closed low shifting east of the Canadian
Maritimes and a mid level ridge axis building to our northwest.
There will be a surface high pressure system moving across
Quebec coupled with a distant offshore low pressure system. So
we will need to watch for periods of clouds as we have seen of
late with the onshore flow.

Overall...expect pleasant cool nights and mild days from Friday into
early next week. Overnight low temps should bottom out mainly in the
upper 40s to the middle 50s with the coolest readings in the typical
low-lying locations. High temperatures will mainly be in the lower
to middle 70s except 65 to 70 degrees near the immediate coast and
parts of the high terrain.

Mid level ridge axis will keep our weather dry into early next week.
How quickly this mid level ridge axis shifts east of the
region...but there will be some shortwave energy approaching from
the west. This may bring us a period of showers...but not until
later Tue and/or Wed.

&&

.AVIATION /02Z THURSDAY THROUGH MONDAY/...
Forecast Confidence Levels:

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

Tonight...Moderate confidence.

Scattered showers around the terminals this evening. MVFR/IFR
CIGS move in from the west overnight into early Thursday
morning.

Thursday...Moderate confidence

Moderate to heavy rain with MVFR/IFR CIGS mainly. There could
be fine line of embedded convection (thunder) that crosses the
region from west to east in the late afternoon-early evening
time frame. Less confidence on exact timing of this line and
probability of thunder.

Thursday Night...High Confidence

CIGS will likely clear quickly to MVFR/VFR behind the line. A
cold front will push through in the 01-04Z time frame shifting
winds NW behind it.

BOS TAF...Moderate Confidence in TAF.

Tonight:
Few showers possible this evening. CIGS range around 030-035
dropping toward MVFR early Thursday morning.

Thursday:
MVFR with a few showers in the morning. SE winds becoming SSE in
the afternoon at 8-12 kts. Showers become more likely by the
afternoon. A line of rain and embedded convection moves through
late afternoon-early evening. Less certainty on exact timing,
but will more likely be in the 21-03Z time frame. Front arrives
01-03Z shifting winds NW.

BDL TAF...Moderate Confidence in TAF.

Tonight:
VFR/MVFR with showers possible tonight.

Thursday:
MVFR. SHRA in the morning. With increasing chances for rain and
embedded thunder by the afternoon. Front moves through in the
00-03Z timeframe shifting winds NW.


Outlook /Friday Night through Monday/...

VFR.

&&

.MARINE...
Forecaster Confidence Levels:

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

Today through Thursday...High Confidence.

Small Craft Advisories remain in effect for all outer open water
zones along with the northern near coastal waters for seas of 5-7
feet. Winds remain east at 10-15 knots, turning SSE overnight
into Thursday at 15-20 knots.

Rip Current Statement remains in effect through this 8 PM this
evening for eastern shorelines as large easterly swells
continue to pose a high risk for rip currents.

Outlook /Friday Night through Monday/...

Friday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers.

Saturday: Winds less than 25 kt. Slight chance of rain showers.

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

Sunday through Monday: Winds less than 25 kt. Areas of seas
approaching 5 ft.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 AM EDT Friday for ANZ250-254.
     Small Craft Advisory until 11 PM EDT Thursday for ANZ251.
     Small Craft Advisory until 8 PM EDT Thursday for ANZ255-256.

&&

$$

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