171
FXUS61 KBOX 191410
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1010 AM EDT Sun May 19 2024

.SYNOPSIS...
One final day of unsettled conditions before a significant pattern
shift to drier and warmer weather on Monday. Very warm
temperatures are expected on Tuesday and Wednesday, with
temperatures reaching into the 80s, with an outside chance a few
locations see 90 degrees on Wednesday. Humidity levels will be
on the low side accompanying that midweek warmth. A cold front
arrives on Thursday with the potential for showers and
thunderstorms. A drier and more seasonable air mass then filters
in for late in the week into at least the early part of
Memorial Day Weekend.

&&

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

1015 AM Update:

KBOX radar and TBOS showing firehose of low level moisture
continuing to come off the ocean and onshore into eastern MA,
the Worcester Hills, into RI and southeast MA. Meanwhile, aloft,
short wave energy is diving southward from the ME coast into
eastern MA. This is firing convection ENE of PVC. More
importantly, this short wave energy is delaying height rises
that are currently occurring west of New England from advecting
eastward. Thus, we are stuck in this moist low level flow. As
the short wave energy moves offshore later today, the axis of
low level moisture will shift slowly southward. Therefore,
drizzle and low clouds may be confined to southeast MA later
today, with a drying trend elsewhere.

Already seeing breaks in the overcast across western MA into
northwest CT. Given the low level moisture axis is expected to
shift slightly southward later today, these breaks of sunshine
should spread eastward across CT, possibly to the RI border late
in the day. In MA, breaks of sunshine will advance eastward
from western MA into central MA, possibly into the Merrimack
Valley of northeast MA late in the day. Likely remaining
overcast with periods of drizzle for southeast MA, including
Cape Cod and the Islands. The only change to the forecast was to
add periods of drizzle where currently observed and lingering
into southeast MA through the day. Otherwise, all other forecast
parameters appear on track.

Most locations will see highs in the 60s, except low 70s across
western MA/CT given duration of partial, strong May sunshine.
The other exception will be across eastern MA, especially
southeast MA, where onshore flow with NE winds 15-20 mph
streaming across SSTs in the 50s, will yield highs only in the
50s.


&&

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

While the chance for showers drops significantly overnight, model
soundings suggest that stratus/drizzle will hang tough across SE
MA/Cape Cod, and fog, perhaps dense at times, will develop across
interior southern New England. It will be a seasonable night with
temperatures dropping into the upper 40s to low 50s.

Surface high nestles safely over southern New England Monday as mid
level ridging continues to build in intensity and 850mb temps climb
to between 12-14C by 00Z Tuesday. Given this, well deserved, shift
in the synoptic setup over southern New England, expecting much more
sunshine across the region as early morning fog/stratus/drizzle
dissipates quickly through 15Z; though may take until 18/20Z
across the Cape and Islands. Although temps remain mild aloft,
boundary layer mixing does not look overly impressive, perhaps
to ~925mb, so dropped temperatures from what was depicted by the
NBM (80s across the interior) to more conservative high
temperatures in the mid 70s away from the coast. While flow
shifts to the south gradually through the day, it will shift
latest, as late as 22Z, along the coast, so the "synoptic
seabreeze" will lead to another significant temperature gradient
along the immediate coast, where temperatures will struggle to
hit 60. In fact, temperatures may not climb out of the 50s on
the Cape all day!

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...

Highlights:

* Very warm temperatures Tuesday and Wednesday away from the
  southeast coast, with readings into the 80s. Warmest day is
  Wednesday, and a few locations in the Connecticut and Merrimack
  Valleys could see their first 90-degree temperature in 2024 on
  Wednesday! Humidity levels will be tolerable - a "dry heat".

* Cold front moves through sometime on Thursday. Timing of the front
  is still uncertain but the timing will influence how warm
  temperatures get and also the potential for thunderstorms, which
  could be strong.

* Drier with more seasonable temperatures for late in the week into
  the early Memorial Day Weekend.

Details:

00z ensembles continue to advertise a significant warm spell for at
least Tuesday and Wednesday for most of Southern New England. Full
sun and southwest downsloping breezes, combined with 850 mb temps
around +13 to +15C should be fairly common on Tuesday with 850 mb
temps rising about a degree or so on Wednesday. It is likely that
the Providence to Plymouth corridor on southward to Cape Cod and the
Islands would be the cooler locations given southwest flow off the
water, with values in the 70s to lower 80s and upper 60s-around 70
for Cape Cod. Very warm temperatures are expected further north and
west from there, with persistent SW flow keeping the eastern MA sea
breeze from developing. Of the two days, Wednesday projects as the
warmest. Highs on Tuesday away from the southern coast should reach
into the lower to mid 80s, with readings near 80 for the North Shore
into Greater Boston. Probabilistic maximum temperature data from the
NBM for Wednesday indicates 50-70% probs for highs reaching the 90-
degree mark in the CT and Merrimack Valleys! Mid to upper 80s
being common to the Providence-Plymouth corridor. Kept highs for
southeast coastal New England on Wednesday into the 70s to low
80s. Thus it is looking likely that we`ll see summerlike
temperatures making their first appearance in 2024 on Tuesday
and Wednesday for a large part of Southern New England, with
many likely not yet acclimatized to this warmth as yet. It`s
also more of the "toasty" heat versus the oppressive/muggy kind:
very warm ambient air temps but with tolerable humidity levels,
as dewpoints are expected in the mid to upper 50s.

A cold front then approaches sometime on Thursday, with increasing
cloud cover. The biggest question mark is on the timing of the
front, which will influence both how warm we get pre-frontal
passage and the potential potency of showers and t-storms along
and ahead of the front. Not out of the question that Thursday
could still be quite warm if we see a slower timing similar to
the ECMWF. Kept temps a little cooler than NBM but even with
clouds we should see highs reach the lower to mid 80s again for
most except southeast New England. Thursday could also feature
scattered strong to perhaps severe t-storms too if the timing of
the front coincides with peak daytime heating; GFS shows a
convective environment with about 1000 J/kg of CAPE with about
40-45 kt of wind shear in the 0-6 km layer for Thursday.
Machine-learning progs from Colorado State weren`t available
with the 00z guidance but the prior run hinted at the potential
for storms becoming severe in interior sections of New England.
Kept PoP around 30-50 percent, but those will need to be
adjusted pending the timing of the front. But Thursday should be
the next best chance for rains.

A more seasonable airmass then returns on NW flow for Friday and
Saturday, with drier weather also returning.

&&

.AVIATION /14Z SUNDAY THROUGH THURSDAY/...
Forecast Confidence Levels:

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

15z TAF Update:

Not much change from previous forecast. Not much change to
previous thinking. Axis of low clouds and drizzle may shift
slowly southward later today. Otherwise, some improvement with
dry weather and MVFR conditions lifting to VFR across CT and
western MA, possibly into central MA. Meanwhile, not much change
across eastern MA and RI. Possibly drier late today across
northern RI into interior NE MA. Earlier discussion below.

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

Today: High confidence in trends but lower to moderate on
vsbys and coverage of any showers.

IFR to periods LIFR ceilings from central MA and RI eastward,
with 3-6 SM vsby BR and intervals of drizzle or spotty rain
showers; categorical improvement is not expected. MVFR ceilings
for the western airports should trend to VFR by 17-19z. NE winds
around 10-12 kt for the coastline, and around 4-7 kt across the
interior.

Tonight...

Conditions deteriorate overnight with widespread fog, LIFR to
MVFR once again. Pockets of drizzle likely across eastern MA/RI
and the Cape and Islands. NE winds diminish to near calm across
the interior, leading to fog, and 15kt across the outer Cape.

Monday...

LIFR to MVFR and any fog that develops overnight will quickly
rebound to VFR for the duration of the day, though it may take
until 15Z or so to burn off on the Cape and Islands. Winds
generally less than 10kt and will finally begin to shift from
the E/NE to the S, shifting first across the interior and last
along the eastern coastline.

KBOS TAF...High confidence in TAF/trends but lower to moderate
on vsbys and rain coverage. IFR ceilings today and tonight,
areas of DZ/BR with vsbys around 3-6 SM. Vsbys probably trend
closer to 6SM by late this morning. Sub-VFR likely into at least
a part of Monday morning. NE winds around 10-12 kt today,
easing to around 4-8 kt tonight and Monday.

KBDL TAF...High confidence in TAF/trends but moderate on timing.
MVFR initially, although cloud bases lift to VFR around/after
18Z. Sub-VFR returns tonight. NE winds around 4-7 kt today and
tonight becoming more southerly on Monday.

Outlook /Monday Night through Thursday/...

Monday Night through Tuesday Night: VFR.

Wednesday through Wednesday Night: VFR. Breezy.

Thursday: VFR. Breezy. Chance SHRA, chance TSRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

3 AM update...

Sunday... High Confidence.

Offshore low and maritime high move very little, thus morning
low clouds, fog and spotty light rain and drizzle expected. Some
improvement in the afternoon. NE winds 10 to 20kt. Seas in
excess of 5ft across the outer waters.


Sunday night...High confidence.

More of the same weather given offshore low and maritime high
persist. Lighter winds and maritime high slowly advects over the
MA/RI waters. Small craft conditions continue for the eastern
outer waters with seas over 5 feet.

Monday... High confidence

Morning stratus/fog/drizzle will clear gradually though the day,
though may hang tough across the waters through 18Z/20Z. NE
winds gradually shift to the south late in the day, but high
pressure over New England will keep winds rather light, 5-10kt
with an occasional morning gust to 15kt. Small craft conditions
possible for the extreme outer waters with seas still around
5ft.

Outlook /Monday Night through Thursday/...

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

Tuesday through Wednesday Night: Winds less than 25 kt. Seas
locally approaching 5 ft.

Thursday: Winds less than 25 kt. Seas locally approaching 5 ft.
Slight chance of rain showers, isolated thunderstorms.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 2 AM EDT Monday for ANZ250.
     Small Craft Advisory until 2 PM EDT Monday for ANZ254.

&&

$$

SYNOPSIS...Loconto/KS
NEAR TERM...Loconto/Nocera/KS
SHORT TERM...KS
LONG TERM...Loconto
AVIATION...Loconto/Nocera/KS
MARINE...Loconto/KS