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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KBOX 072356
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
756 PM EDT Tue Apr 7 2020

.SYNOPSIS...
High pressure in place will give way to a weak area of low
pressure moving in from the Great Lakes. This low pressure will
spread a period of rains later tonight into early Wednesday as
it moves into the waters south of Southern New England. Another
system moves in Thursday, bringing more rain and scattered
thunderstorms. Scattered showers are possible Thursday night
through Friday. Drier weather for this weekend before our next
wet weather system early next week.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
-- Changed Discussion --
Made some minor tweaks to the forecast this evening using the
latest high resolution guidance. Goal was to try to refine the
timing and location details. Have higher confidence in showers
and possible thunderstorms towards CT and southern RI.

Minor tweaks to temperatures to bring them back in line with
observed trends.

Previous Discussion...

The primary feature of interest for much of the night, however, is a
NW to SE oriented and rather well-defined warm front associated with
a low pressure area as of early this afternoon near northern
Michigan. The low and its related warm front will progress east-
southeast through the northern mid-Atlantic region into Southern New
England later tonight, with increasing clouds through midnight and
rains spreading east-northeastward especially for the overnight
hours.

Temperatures look to remain mild enough even across the terrain to
stay as rain. However worth noting the thermal contrast through the
warm front is fairly robust, and in addition to that, I did notice
on SPC`s mesoanalysis page a plume of weak mid-level instability
(700-500 mb lapse rates ~6-7 C/km) even on the north side of the
warm front. Some guidance - most notably the NAM and the RAP -
brings a sliver of this weak elevated instability into a part of
northern CT into central/southern RI and the south coastal waters
overnight tonight (roughly from a South Windsor to Putnam CT to
Coventry RI line). Though rain should predominate, I did opt to
include some isolated thunder (basically rumbles) along and south of
this line. Rains should continue into the Wednesday morning for
most. Model guidance QPF off today`s 12z guidance was a bit greater
than previous runs. Opted for rain totals thru 12z Wednesday from a
quarter to third of an inch for southern RI into the Hartford area,
then tapering to a tenth to two-tenths of an inch further north and
east.

Lows tonight mainly in the mid-upper 30s to the lower-mid 40s.
-- End Changed Discussion --

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
Wednesday:

Weak low pressure and attendant warm frontal-related showers pass
south of the coastal waters through the morning hours. As these
features pass to our south, likely to see a modest uptick in NE wind
speeds into the morning hrs and especially near the eastern MA coast
(indicated by the NAM 975 mb winds which tick up to around 25-kt
just offshore). Eventually these winds will lighten and shift to
easterly moving into the afternoon.

Some gradual improvement with rains coming to an end by late-
morning/early afternoon (latest towards Cape Cod and the offshore
waters), and skies trending mostly to partly cloudy. So the second
half of the day is looking somewhat better than the first half, but
with NE to E onshore flow and a shorter period of sun, I opted to
keep temperatures on the cooler side of guidance, into the upper 40s
to the mid 50s.

Wednesday Night:

Weak shortwave ridging/modest 500 mb height rises, ahead of a strong
frontal system to affect our area into Thursday, should allow for
dry conditions through the first part of the overnight. Model
guidance shows moisture levels starting to rise on SE flow into the
second half of the night, with increasing clouds spreading from west
to east. In addition, 500 mb height falls then spread into western
MA into northern CT into the early morning hrs. PoPs increasing to
chance type levels for these locations though most should stay dry.
Lows mainly into the upper 30s to mid 40s with modest SE breezes.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
* Widespread rain Thursday with scattered thunderstorms

* Lighter rain, and high elevation snow possible, on Friday with
  a few rumbles of thunder also possible

* Potential for minor coastal flooding Wednesday to Friday
  around high tide across the east and south coasts of MA and RI.
  See the Tides and Coastal Flooding section below for more
  details.

* Temperatures running near to below normal through Saturday,
  then a warm up

Thursday...

This still appears to be the most active weather day during
this portion of the forecast. Potent mid level low shifts over
northern New England, with a low pressure passing through our
region. Almost certainly looking at some rain for much of
southern New England, with some wet snow possible across the
higher terrain. Drier air rushes in behind the cold front of
this system, drying our the forecast into Friday.

As for thunderstorm potential, surface-based instability is not
the best. However, mid level lapse rates are better than moist
adiabatic with a strong low-level jet from the south. These
factors are enough to warrant at least a mention of isolated
thunderstorms. Still too early to say if any of these
thunderstorms could be severe.

Friday...

Low pressure continues to rotate away from our region. Still in
the cyclonic flow, so cannot dismiss the idea of a few showers
during the day, rain for most with snow possible across the
higher terrain.

Saturday through Sunday...

The weekend looks drier as a ridge of high pressure makes its way
east across the Mid Atlantic states. This should mean a warming
trend into Sunday.

Monday into Tuesday...

Another low pressure should move across the Great Lakes, leading
to another round of showers sometime from Monday afternoon into
Tuesday morning. Timing is not yet locked down. Looking warm
enough for all rain.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
-- Changed Discussion --
Forecaster Confidence Levels...

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

Tonight: High confidence in trends, moderate on timing.

Increasing/lowering clouds associated with a warm front which
will eventually spread rains across the TAFs. Initial VFR with
deterioration to MVFR ceilings (possible IFR ceilings south of
BDL to PVD to the Cape airports) after 08/05-07Z with VFR-MVFR
vsby rains spreading ESE through 08/08-12Z. Due to the dry air
around, timing is a bit uncertain but could be an hour or two
sooner than indicated in the TAFs.

Through midnight, mainly light/variable winds in the interior,
SE 5-8 kt towards the Cape and at BOS. After midnight through
08/12Z, winds to shift to NE around 5-10 kt as front slides S
of the coastal waters.

Wednesday: High confidence in trends, moderate on timing.

Initial MVFR, possible IFR with periods of rain to generally
taper off through the morning. Gradual improvement from
widespread MVFR to MVFR/VFR levels toward the afternoon. NE/ENE
winds 4-8 kt in the interior, around 7-10 kt with occasional
gusts to 20 kt coastal MA and the Cape.

Wednesday Night: Moderate to high confidence.

Increasing moisture levels on SE flow will result in VFR-MVFR
ceilings lowering to MVFR-IFR levels in the interior and across
the higher terrain. For the coastal plain into the Cape, initial
VFR to trend VFR/MVFR into the pre-dawn hrs. Rains should hold
off until the pre-dawn hrs in the CT Valley with dry conditions
elsewhere. SE winds 6-10 kt.

KBOS Terminal...High confidence in the TAF.

KBDL Terminal...High confidence in the TAF.

Outlook /Thursday through Sunday/...

Thursday: MVFR/IFR conditions possible. Windy with gusts up to
30 kt. Chance SHRA, isolated TSRA, patchy FG.

Thursday Night: VFR. Windy with gusts up to 35 kt.

Friday: VFR. Windy with gusts up to 30 kt. Slight chance SHRA.

Friday Night through Saturday: VFR. Breezy.

Saturday Night: VFR.

Sunday: VFR. Slight chance SHRA.
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
Winds and seas should remain below SCA thresholds through
Wednesday night.

A warm front will bring a period of steady rains for most of the
waters late tonight into Wednesday morning, with an outside/low
chance for a rumble or two of thunder across the southern offshore
waters overnight. Could see vsbys between 3-5 SM in rains,
likely lowest south coastal waters. Winds to become NE on Wed
AM, and could briefly reach marginal-SCA gusts with seas 3-4`
(near 5` per the SWAN guidance off the NAM) on the eastern
MA/Cape Cod waters. Wasn`t confident enough on criteria being
met to issue an SCA for these waters Wed AM, but may get close.

Winds lighten to under 20 kt and shift east later Wednesday and then
SE into Wednesday night. Seas mainly 2-3` Wednesday night, though
build to 2-4` by daybreak.

Outlook /Thursday through Sunday/...

Thursday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of rough seas. Chance of rain showers,
isolated thunderstorms, patchy fog. Local visibility 1 to 3 nm.

Thursday Night: Low risk for gale force winds with gusts up to
35 kt. Rough seas up to 10 ft.

Friday: Strong winds with gusts up to 30 kt. Rough seas up to
12 ft. Slight chance of rain showers.

Friday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 10 ft.

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

Saturday Night: Winds less than 25 kt. Seas locally approaching
5 ft.

Sunday: Winds less than 25 kt.
-- End Changed Discussion --

&&

.TIDES/COASTAL FLOODING...
418 PM Update:

Astronomical tides are on the rise over the next several days
(across multiple tidal cycles) due to the Supermoon. While the
overall threat is limited by poor wave action, due to the high astro
tides a number of tidal gages are forecast to be near flood stage or
into minor flooding categories per Stevens Institute guidance.

Appears the greater potential for minor coastal flooding later
tonight into Wednesday should exist for eastern coastal MA and Cape
Cod/Nantucket, especially around the period of high tides. By
Wednesday night into Thursday, stronger southerly winds ahead of a
strong frontal system will raise the coastal flood threat across
a larger area to include the South Coast and Narragansett Bay.
Coastal Flood Advisories have been posted thru Friday following
these general expectations.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
CT...None.
MA...Coastal Flood Advisory from 8 AM Wednesday to 8 AM EDT Friday
     for MAZ019-022.
     Coastal Flood Advisory from 8 PM Wednesday to 8 AM EDT Friday
     for MAZ015-016.
     Coastal Flood Advisory until 8 AM EDT Friday for MAZ007.
RI...Coastal Flood Advisory from 8 PM Wednesday to 8 AM EDT Friday
     for RIZ002-004>007.
MARINE...Gale Watch from Thursday afternoon through Friday afternoon
     for ANZ231-232-250-251-254-255.
-- End Changed Discussion --

&&

$$
SYNOPSIS...Belk/Loconto
NEAR TERM...Belk/Loconto
SHORT TERM...Loconto
LONG TERM...Belk
AVIATION...Belk/Loconto
MARINE...Belk/Loconto
TIDES/COASTAL FLOODING...Loconto