599
FXUS61 KBOX 221723
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
123 PM EDT Tue Apr 22 2025

.SYNOPSIS...
Rain showers then taper off this morning with decreasing cloudiness
in most areas and mild temperatures in the 60s to low 70s. Cloud
cover may linger into the afternoon for the southern coast with
cooler temperatures. Rather mild and dry with high pressure over New
England to round out the work week. While there is a low chance of a
passing shower late Thursday evening/night for northern
Massachusetts, majority of the region is dry. A system for Saturday
brings the next chance for widespread rainfall, though exact details
remain uncertainty. Drier conditions return late this weekend into
early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Key Messages...

* Rain ending Tuesday morning from west to east, becoming sunny
  shortly after the rain moves out, though the Cape and Islands may
  not escape the low clouds much of the day.

* Quite a bit warmer, with highs in the mid to upper 70s away from
  the cooler south coast.

Rain showers resulting from a frontal system crossing New England
this morning will continue off and on through the early morning
hours before a mid level cold front and accompanying dry air in the
upper/mid levels bring rain to an end from west to east. For
locations west of Worcester rain likely ends before sunrise with low
clouds clearing by late morning. Further east the bulk of the
precipitation should be out by 8am but the Cape and islands may hang
onto some scattered showers through the morning. Rapid clearing is
likely for southern New England, with sunny skies for everyone but
the Cape and islands by 1-2pm, though it will be filtered by high
clouds moving in in the afternoon. Guidance indicates a stubborn low
level inversion that`s hard to break over Cape Cod and the islands
which would not only keep clouds around all day, but while
temperatures inland reach well into the 70s, upper 50s to near 60
are more likely. A dry surface cold front drops through today,
likely stalling out for a time over southeast MA where that low
level moisture holds on longer. Eventually the cold front does fully
push through, dropping dewpoints from the upper 50s Tuesday to upper
30s after midnight. This will mean clearing skies by sunrise
Wednesday.

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
Key Messages...

* Dry and sunny.

Quiet, zonal flow continues on Wednesday with
surface high pressure building overhead. This brings quiet, if
cooler weather in the post frontal airmass. Even so, 925 mb temps
around 10-11C should result in highs warmer than average for late
April, in the upper 60s and low 70s; not a drastic temperature
gradient to the coast today given offshore flow.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Key Messages:

* Warm and mostly dry Thursday and Friday, outside of a stray shower
  in northern Massachusetts Thursday evening/night.

* The next chance for widespread rain comes in Saturday, but there
  are uncertainties with the exact timing.

* Drier conditions Sunday into early next week.

The Big Picture: Nearly zonal flow at 500mb across the CONUS
Thursday and Friday, a subtle 850mb shortwave may produce a couple
of spotty showers late Thursday evening into predawn Friday.
Otherwise, do think much of this time remains dry as surface high
pressure builds across New England. This feature moves northeast
towards Nova Scotia ahead of the only soaking chance of rain for
this part of the forecast, arriving Saturday, but confidence with
exact timing is low given the uncertainty amongst the guidance.
Behind the system, mid-level ridging, surface high pressure builds
in from the northwest with drier conditions Sunday into Monday of
next week.

Wednesday Night through Friday Night: Surface high pressure builds
across New England with a weak 850mb high centered off the Mid-
Atlantic coast. Will have drier air for part of Thursday and think it
will be the sunnier of the two days. Guidance has a shortwave riding
around the northern edge of the 850mb high, the better forcing is to
the north in Vermont and New Hampshire, cannot rule out spot rain in
northern Massachusetts. While the NBM did not show POPs during this
timeframe, did opt to use CONSALL, which gave 10-20 percent POPs for
locations along and north of Route 2. As for temperatures, will have
mild conditions both days as 850mb temperatures trend above normal,
around +10C across western/central Massachusetts and Connecticut and
+7/8C over eastern Massachusetts and Rhode Island. A quick look at
BUFKIT and GFS does show mixing Thursday afternoon to 850mb. Highs
Thursday afternoon reach the low to middle 70s, though at the coast
will likely have a seabreeze given the time of year, and there the
highs cooler in the 60s, perhaps upper 50s for the Islands and outer
Cape Cod. As for Friday, little change in the airmass, perhaps +1C
or +2C degrees warmer, would expect resulting highs for Friday to be
a few degrees warmer than the prior day. Overnight temperatures for
Thursday and Friday night are in the upper 40s and lower 50s.
Temperatures were inline with NBM and did not deviate.

Saturday: Low amplitude mid-level trough moves across the northeast
and development of a low-pressure system with a southerly LLJ. Will
have anomolous PWATs advect into southern New England, 1.2" to 1.5",
which is ~3 standard deviation above normal. There remains a good
amount of uncertainty with respect to the exact timing of the onset
and endtime the rain, but are increasing chances for a widespread
soaking rain during the daylight hours. Given the inherent
uncertainties due to the timeframe of day 5/6, did not deviate from
the NBM. Are modest probabilities for rainfall amounts greater than
0.5" across the region at 50 to 60 percent. Increase the potential
rainfall to 1.0" or greater will have probabilites between 20 and 30
percent. Will want to check back with us if you have outdoor plans
for Saturday.

Sunday and Monday: Mid-level ridging and surface high pressure will
result in drying conditions Sunday and Monday. North-northeast flow
Sunday lends a cooler day with highs in the upper-50s and low-60s.
The flow may become southwest by Monday and bring in slightly warmer
temperatures in the upper-60s.

&&

.AVIATION /17Z TUESDAY THROUGH SATURDAY/...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

18Z TAF Update:

Through 00Z: High Confidence

VFR across the interior with steady west winds around 10 knots
with some gusts to 20 knots. IFR/LIFR over The Cape Islands with
fog and low stratus. Sea-breeze at BOS may persist through
20-22Z. Confidence in sea-breeze activity is moderate at best.

Tonight: High Confidence

VFR. West/northwest winds 5-10 knots. IFR/MVFR cigs and vsbys
persist over The Cape/Islands through about 06Z before clearing
to VFR.

Tomorrow: High Confidence

VFR. West/northwest winds around 10 knots. About a 50/50 chance
for a sea-breeze at BOS, but likely would be after 18Z if it
develops.

Tomorrow Night: High Confidence

VFR. Light and variable winds.

KBOS TAF...High confidence in VFR. Lower confidence in sea-
breeze activity. Current onshore flow may persist through as
late as 22Z, but thinking closer to 20-21Z at this time.

KBDL TAF...High confidence in TAF.

Outlook /Thursday through Saturday/...

Wednesday Night through Thursday Night: VFR.

Friday: VFR. Slight chance SHRA.

Friday Night: Mainly VFR, with local MVFR possible. Breezy.
Chance SHRA.

Saturday: Mainly MVFR, with local IFR possible. Breezy. SHRA
likely.

&&

.MARINE...
Forecaster Confidence Levels:

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

Today through Wednesday: High confidence.

Generally tranquil boating conditions through the period. Winds S/SW
around 15-20 kt with passing rain showers early today. SW gusts
could reach near 25 kt over the far southeast offshore waters,
before becoming west late tonight.

Seas 2-4 ft overnight tonight, perhaps near 5 ft over the southern
offshore waters. Seas continue around that range through tonight.

Wednesday winds will be variable 5-10 kts, with seas of 1-3 ft.

Outlook /Thursday through Saturday/...

Wednesday Night through Friday: Winds less than 25 kt.

Friday Night: Winds less than 25 kt. Chance of rain showers.

Saturday: Low risk for Small Craft Advisory winds with gusts up
to 20 kt. Seas up to 5 ft. Rain showers likely.

&&

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

&&

$$

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