910
FXUS61 KBOX 161441
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1041 AM EDT Thu May 16 2024

.SYNOPSIS...

Moderate to heavy rainfall gradually wanes this afternoon
giving way to a dry end to the week. Onshore flow will keep
temperatures in check along the coast. The weekend features
generally dry weather and onshore breezes, but still a good
amount of cloud cover. Warming trend then develops Monday
through Wednesday, and we could see a couple days of high
temperatures in the low 80s over interior sections of Southern
New England. After today, our next chance for rains may not
develop until later next week.

&&

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

1030 AM Update...

Made some adjustments to increase our wind speeds/gusts, QPF
amounts and PoPs in the latest update. Did this to better align
with current observations. Have leaned heavily toward the
latest HRRR/FV3 guidance as it is doing well based on
observations. Should see this mesoscale band gradually collapse
as we head into the afternoon as the low rotating south of our
region continues to push further offshore. Still have a 30-40 kt
easterly low level jet in place, which will bring some 25-30 mph
gusts into the afternoon. Should see those strongest gusts along
the immediate south coast/Nantucket.

710 AM Update:

Much of Southern New England seeing rain of varying intensity.
The heaviest seems to be centered in eastern CT, northern and
central RI into south coastal MA where a nearly stationary band
of rain, associated with strong moisture convergence, is
producing hourly rain rates of about a half-inch per hour. More
broadly speaking, most of Washington County RI saw rain totals
that were in excess of 3 inches over the last 12 hours, and
Westerly observed hourly rain rates nearly an inch an hour. It
looks like per pretty strong agreement in hi-res guidance that
this band of steady and at times heavy rains will remain quasi-
stationary over the next 2 to 3 hours, which has prompted an
areal flood warning mostly for urban and poor drainage hydro
problems particularly for the Providence, Fall River and New
Bedford areas. More or less just nowcasted the existing band of
steady rains in the zone forecast by bumping QPF upward in
eastern CT, northern and central RI and southeastern MA. We
should see this rain band fracture/fall apart as we move into
the early afternoon, with a general decrease in rain intensity
toward more intermittent showers elsewhere. Will continue to
monitor trends for possible additional areal flood warnings, but
we also will be considering river flood warnings for along-
river-channel flooding, particularly in the Pawtuxet, Pawcatuck,
Shetucket and Quinebaug basins.

Previous discussion:

Low pressure south of southern New England will continue to bring
widespread moderate, to at times heavy, rain to the region this
morning. Even in the immediate term, guidance remains quite jumpy in
the placement of the axis of heaviest precipitation as well as how
much additional rain can be expected to fall, with the hourly HRRR
forecast continuing to shift eastward with each subsequent run.
Overnight, the heaviest rain blossomed across Connecticut where, as
of 7Z, 6 hour QPF approached 1.5". Hi-res guidance continues to
depict a developing line of moderate to heavy rainfall that
will pivot from the south coast into southeast MA and RI through
the morning commute, with the beginning stages of this line,
capable of 1 inch per hour rainfall rates, already present on
radar, moving north from the Westerly/south Coast area early
this morning. The greatest period of concern for inch per hour
rainfall rates is from now through about 14Z, which, if located
over highly urbanized locations, could continue to heighten
concerns over minor urban and poor drainage flooding.
Fortunately, the heaviest rain overnight fell across more rural
parts of the region which combined with a lull in precip
intensity over much of RI and SE MA has mitigated flooding
threats thusfar. Some modest river rises have been observed on
small rivers and streams across far southern New England, but
all forecast points remain below action stage as of this
writing.

In terms of additional precipitation, additional QPF amounts will be
highly dependent convective elements making their way onshore,
with just isolated lightning pulses currently offshore, and
moisture enhancement along the the LLJ, generally draped south
of the I-90 corridor; with bets hedged towards the influence of
the latter being greater. Given higher than average uncertainty
in the hi- resolution guidance, heavily relied on ensemble
probabilities and mean HREF QPF to derive this morning`s
expected rainfall, with both pointing to an max of around 1-2",
locally higher pockets, of additional rainfall across SE MA/RI.
Much lower amounts will fall, to as little as a tenth of an inch
of additional QPF, across far northern MA.

Low pressure peaks in proximity to the region this morning before
gradually drawing southward through the afternoon, pulling the
precipitation shield along with it. Rain will become more showery in
nature after the lunch hour before coming to an end, from north to
south, through sunset this evening.

&&

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

Low pressure continues to work south and east of the region
overnight, which will yield clearing skies and dry conditions. Given
residual moisture and slackening winds, as LLJ accompanies the
departing low, some patchy fog is possible. We wont see much of an
airmass change, so dewpoints will remain the driving force in
keeping low temperatures seasonable for mid-May, in the low 50s
region wide.

Friday is shaping up to be a dry and pleasant day as mid level
ridging builds into southern New England. Any low cloud/stratus that
forms overnight will burn off, yielding a mix of clouds and sun.
High temperatures have a "boom or bust potential" given persistent
onshore flow and lackluster temps aloft, around 10-11C at 925mb.
There remains uncertainty in how far inland the "sea breeze", or
rather, synoptic E/ENE flow will influence afternoon temperatures,
but it will certainly be another significant temperature gradient
day with highs warming into the 70s across the CT River Valley and
struggling to warm into the 60s along the eastern coastline.

&&

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

Highlights:

* Other than a spot shower, mainly dry weather prevails with partly
  to mostly cloudy conditions, along with onshore breezes this
  weekend.

* Warming trend Mon through Wed, with less cloud cover. Could see a
  couple days of highs in the lower 80s inland.

Details:

Today`s global model ensembles from the 00z cycle have trended the
forecast in a more optimistic direction, as a closed upper level
circulation initially over the western Appalachians becomes parked
over the mid-Atlantic/Chesapeake Bay vicinity this weekend.
Surface ridge stretching from Nova Scotia southwestward through
Southern New England is progged to remain in place for several
days, at least into the early to midweek timeframe. In addition,
there continues to be indications of a warming trend to
temperatures by the early to mid next week period as 500 mb
shortwave ridge extends into Southern New England. These were
trends noted over the last day or two and there is now a greater
degree of agreement on this anticipated warming trend Monday
thru Wednesday. Other than a couple hit or miss showers, drier
weather looks to predominate; we may not see widespread rains
develop until late next week.

The Weekend:

Surface ridge of high pressure extending in from Atlantic Canada
will maintain onshore breezes. While generally dry, there should be
still a good amt of cloud cover around with partly to mostly cloudy
sky conditions. Expect high temperatures to be coolest near the
coast given the cooler onshore flow, in the upper 50s to lower 60s.
High temperatures further inland still project considerably warmer,
but how warm they get will depend on if we can see any cloudy
breaks/stronger heating; offered highs well into the 60s to the
lower 70s, but there is room for warmer temperatures if we see less
cloud cover than anticipated.

Monday through Wednesday:

High pressure still governs at the surface, but we`ll be adding 500
mb height rises. 850 mb temps warm to the +10 to +12C neighborhood
and with less cloud cover, highs inland could be pushing into the
lower 80s, with mid 60s to mid 70s in the coasts and the immediate
coastal plain with potential for seabreezes to develop.

&&

.AVIATION /15Z THURSDAY THROUGH MONDAY/...

Forecast Confidence Levels:

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

12z TAF Update:

Today: Moderate confidence.

Widespread rain, heavy at times south of the MA Turnpike through
at least the lunch hour with lingering showers through 00Z this
evening. Generally IFR with pockets of MVFR improving to MVFR
and VFR by late this afternoon and evening as rain comes to an
end; improvement occurring from north to south as low pressure
pulls south. Breezy conditions, especially for terminals in RI
and SE MA, with E/ENE winds gusting to as high as 25kt. LLWS
may be an issue for the Cape and Islands.

Tonight: Moderate confidence.

Latest guidance trends indicate ceilings either continuing or
returning to IFR levels with stratus, with more optimistic MVFR
type bases for BAF/BDL. Could also see fog/stratus although ENE
winds may keep visbys to no worse than 1 mile. Winds ENE around
5 to 10kt.

Friday...

Widespread VFR after any AM fog burns off. Dry, E/NE winds
gusting to around 15kt.

KBOS TAF...Moderate confidence in TAF. MVFR/intervals IFR
ceilings with MVFR visby RA thru 18z. NE winds around 15 kt.
Rain then turns more spotty/intermittent after 18z, although
latest indications are that stratus at IFR levels returns on
continued NE winds with speeds 5-10 kt. Little optimism for
improvement until Friday morning.

KBDL TAF...Moderate confidence in TAF. MVFR ceilings this
morning with light SHRA, then gradually improving to VFR this
evening. VFR persists through Friday once it develops with the
exception of perhaps some early am IFR due to Fog on Friday.
Rain, moderate to heavy at times, becoming more scattered after
16Z. E/ENE winds 15-20kt diminishing to around 5kt overnight.

Outlook /Friday Night through Monday/...

Friday: VFR. Breezy.

Friday Night through Sunday: VFR.

Sunday Night: Mainly VFR, with local IFR possible.

Monday: VFR.

&&

.MARINE...

Forecaster Confidence Levels:

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

2 AM Update...

Today...High confidence.

E/ENE winds 15-25 kts, gusts 20-30 kts possible. Areas of rough
seas with rain. Could still see some embedded thunderstorms
across the southern waters through the first half of the day.
Rain tapering off from north to south across the eastern waters
during the afternoon.

Tonight...High confidence. Rain tapering off across the
southern waters north to south as the night progresses. Winds
ENE to NE at 10-20 kts with gusts 15-20 kts gradually easing
through Friday morning. Winds should preclude widespread
fog/stratus formation but some pockets of fog may form by
sunrise.

Friday... High Confidence.

Any pockets of fog will burn off quickly Friday morning. Dry
with E/ENE winds gusting 15-20kt. Residual high seas resulted in
the extension of outer water small craft advisories through the
period.

Outlook /Friday Night through Monday/...

Friday: Winds less than 25 kt. Local rough seas.

Friday Night through Monday: Winds less than 25 kt. Seas up to
5 ft.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ231-
     233-234.
     Small Craft Advisory until 11 PM EDT this evening for ANZ232-
     235>237.
     Small Craft Advisory until 8 PM EDT Friday for ANZ254>256.

&&

$$

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