290
FXUS61 KBOX 041034
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
634 AM EDT Sat May 4 2024

.SYNOPSIS...
High pressure brings dry weather with cooler onshore breezes
Saturday. 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/...

630 AM Update:

Very pleasant conditions across the region early this morning,
with temps in the 40s, light winds and lots of sunshine. Only
caveat, is low clouds coming offshore of eastern MA this morning.
How far do these clouds travel over land before strong May
sunshine erodes cloudiness? Good model agreement that this low
level moisture begins to erode as it comes onshore, especially
later this morning and into the afternoon. Therefore, more
sunshine westward today across RI, CT and western-central MA.
Previous forecast handles this well, therefore no changes
planned with this update. Earlier discussion below.

---------------------------------------------------------------

Today

Almost a repeat of yesterday with high pressure just to the north
continuing to support a steady east/northeasterly flow over southern
New England. Expect similar temperature patterns today with cooler
high temps along the east coast in the mid to upper 50s with
gradually warmer temps to the west reaching the upper 60s in the CT
River Valley. Skies likely to be partly sunny with low-level
moisture coming off the ocean supporting SCT to BKN cloud cover for
much of the day.

&&

.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 /10Z SATURDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:

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

12z TAF Update:

Through 12Z: High confidence, only low confidence for the
immediate eastern MA coast, as low clouds come onshore this
morning. Thining marginal IFR/MVFR clouds will be confined to
the immediate coast, then lift to VFR cloud bases farther inland
away from the coast. Earlier discussion below.

-----------------------------------------------------------------

VFR conditions persist through 12Z with light and variable winds
becoming more steady out of the east/northeast by sunrise.

Today...Moderate confidence

MVFR level cloud bases move onshore this morning from the east,
but there is a bit of uncertainty with respect to sky cover.
Humidity in the low levels is choppy, so coverage may range from
SCT to BKN at times. So expect intermittent periods of MVFR
ceilings for the first half of the day until the skies fill into
BKN/OVC buy mid-afternoon/evening. Steady east/northeast winds
from 5 to 10 knots.

Tonight...High Confidence

MVFR/IFR ceilings return overnight with continued light easterly
winds. Winds becoming more east/southeasterly by 12Z Sunday.

Tomorrow...High Confidence

MVFR borderline IFR ceilings for most of the day tomorrow with
-RA spreading from west to east during the day. Southeast winds
 becoming more southerly by the afternoon.

KBOS TAF...Moderate Confidence

High confidence in MVFR cloud bases, but less confidence in
coverage. There may be intermittent periods of SCT/BKN VFR/MVFR
ceilings.

KBDL TAF...High confidence in TAF.

Outlook /Sunday Night through Wednesday/...

Sunday Night: MVFR/IFR conditions possible. SHRA likely.

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...Nocera/RM
SHORT TERM...RM
LONG TERM...Nocera
AVIATION...Nocera/RM
MARINE...Nocera/RM