670
FXUS61 KBOX 041629
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1229 PM EDT Sat May 4 2024

.SYNOPSIS...

High pressure off the Canadian Maritimes will continue to bring
dry weather with cool temperatures along the coast. A slow-
moving frontal boundary brings widespread showers Sunday into
early Monday. Then gradual clearing Monday afternoon along with
warming temperatures. Tuesday looks to be the pick of the week,
with abundant sunshine and highs in the 70s to near 80, although
significantly cooler near the coast with afternoon seabreezes.
Then lots of clouds Wed, Thu and Fri along with periodic showers
possible.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

9 AM Update

* Partly Sunny with some increasing clouds into the afternoon
* Highs lower 50s coast, 60+ inland and near 70 lower CT Rvr

Previous forecast is on track. High pressure across the Canadian
Maritimes will continue to generate a low level easterly flow of
air across southern New England. Therefore...we will have a
large range in temperatures across the region. Highs should
range from the lower 50s along the immediate coast...but 60+ not
too far inland and near 70 in the lower CT River Valley.

Dry weather with partly sunny skies are anticipated through the
afternoon with upper level ridging in control. We do expect
some lower clouds to invade areas near the coast and some higher
clouds to overspread the region from the west through the
afternoon.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...

Tonight

Overcast skies fill back in overnight as the boundary layer cools.
This will limit temperatures from falling to far, so expect
seasonable low temps in the low to mid 40s across much of the
region. High pressure drops to the southeast which will result in
easterly winds gradually shifting to the southeast as we approach
the dawn hours.

Tomorrow

Winds shift from southeast to south during the day tomorrow allowing
for a surge of moisture across the region. This will support
increasing moisture with PWATs rising close to an inch across the
region. Precip chances increase gradually from west to east across
the region as northern stream short wave energy traverses over The
Northeast. Latest suite of model guidance suggests shower chances
will peak during the mid-afternoon hours with the steadiest
precipitation taking place tomorrow night (see long-term AFD). Skies
will be overcast for much of the day tomorrow which will support
cooler temperature sin the mid to upper 50s across the region.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...

Highlights:

* Cool with rain Sunday into early Mon, then gradual clearing Monday
  afternoon, although clouds may linger over southeast MA

* Tue looks to be the pick of the week, with abundant sunshine and
  highs in the 70s to near 80, although much cooler at the coast

* Lots of clouds Wed, Thu & Fri along with the risk of periodic
  showers and cooler

Temperatures...

Warm westerly flow aloft Monday with 850 mb temps well above normal,
about +11C at 18z. Timing of clearing will be crucial to temp
forecast. Ensembles supporting 80-100% probability of 70+ highs
Monday in the CT River Valley and Merrimack River Valley. More
uncertainty southeast across RI and southeast MA given departure
timing of clouds. Not quite as warm aloft Tue, but still above
normal with +8C to +9C at 850 mb, but warmer blyr temps of +16 to
+17C at 925 mb, along with NW winds providing downslope flow. This
results in ensembles offering 90-100% probabilities of 70+ highs
away from the coastline, where afternoon seabreezes will yield
cooler temps. Farther inland, not out of the question a few towns
make a run at 80 degs! This combined with abundant sunshine, low dew
pts/low RH likely results in Tue being the pick of the week.

Not as warm Wed, Thu and Fri with frontal boundary getting hung up
over or near SNE, along with possible waves of low pressure tracking
south of the region. Highs likely in the 60s, except 50s along the
coast, including Cape Cod and the Islands.

Precipitation...

Height falls and associated cold front will combine with good
moisture advection (PWATs +2 sigma) to yield widespread showers
Sunday afternoon thru Monday morning across southeast MA. High
probability for 0.10 to 0.25 inches of rainfall during this time,
with low probs up to 0.50 inches. Clearing develops NW to SE during
Monday afternoon (last across SE MA) as the dry slot overspreads the
region. With diurnal heating, weak cyclonic flow aloft and surface
front lingering over the region, low probability of a few showers
and/or an isolated thunderstorm late in the day across the interior,
where duration of heating/sunshine will be greatest.

Dry weather Tuesday with PWATs only about 60% of normal. Then
becoming unsettled Wed, Thu and possibly Fri, along with a low
confidence forecast. Negative height anomaly downstream over
Newfoundland keeps a ridge axis with above normal heights from the
Mid Atlantic into New England. Meanwhile, a positive tilt trough over
the high plains ejects multiple plumes of moisture towards New
England. Models struggling with the large scale flow, specifically
how much of this moisture advects east into SNE, or dampens out
running into the ridge or is shunted southeast of New England?
Nonetheless, chance of showers both Wed, Thu and Fri. Although,
there will also be periods of dry weather during this time period.

&&

.AVIATION /16Z SATURDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:

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

18z TAF Update...

This afternoon and tonight...High Confidence in trends, but
more uncertainty in regards to specific timing.

MVFR ceilings along the coast this afternoon will gradually
spread westward tonight...eventually covering the entire region.
We also expect some IFR conditions to develop overnight with
even localized LIFR cigs/vsbys in the high terrain. Light E
winds.

Sunday...Moderate Confidence.

IFR/MVFR ceilings will trend to mainly MVFR thresholds with
some diurnal heating despite the cloudy skies. Some showers
will work into mainly interior MA & CT during the mid to late
afternoon hours. SE winds 5 to 10 knots.

Sunday night...Moderate Confidence.

Conditions should lower to mainly IFR with localized LIFR
cigs/vsbys given the cooling boundary layer Sunday night.
A round of widespread showers will overspread the region from
west to east Sunday night too. SE winds shift to more of a S
direction at 5 to 10 knots.

KBOS TAF...High confidence in trends but more uncertainty in
regards to specific timing.

KBDL TAF...High confidence in trends but more uncertainty in
regards to specific timing.

Outlook /Monday through Wednesday/...

Monday: Mainly VFR, with local IFR possible. Chance SHRA.

Monday Night through Tuesday: VFR. Slight chance SHRA.

Tuesday Night: VFR. Chance SHRA.

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

&&

.MARINE...
Forecaster Confidence Levels:

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

Marine


Today through Tomorrow

Conditions remain on the calm and quiet side across the coastal
waters through the weekend with high pressure largely in control.
Easterly winds today become more southeasterly overnight and
eventually southerly by Sunday. Seas generally in the 1 to 3 foot
range.

Outlook /Sunday Night through Wednesday/...

Sunday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Rain showers likely.

Monday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain showers.

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

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

Tuesday Night through Wednesday: Winds less than 25 kt. Chance
of rain showers.

&&

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

&&

$$

SYNOPSIS...Nocera/RM
NEAR TERM...Frank
SHORT TERM...RM
LONG TERM...Nocera
AVIATION...Frank/Nocera
MARINE...Nocera/RM