Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 231058
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
658 AM EDT Tue Apr 23 2019

.SYNOPSIS...
Low pressure east of Nantucket and Cape Cod before sunrise will
exit out to sea today providing a drying trend and sunshine
slowly developing this afternoon from west to east. A weak front
will bring a round of showers tonight into Wednesday morning,
followed by mainly dry weather. Thursday could be the pick of
the week with sunshine, light winds and mild temperatures. Low
pressure will then develop along a cold front as it approaches
the region, bringing another round of showers Friday into early
Saturday morning. A drying trend then develops Saturday
afternoon along with cool conditions. Scattered showers are
possible later Sunday followed by dry weather returning for
early next week along with moderating temperatures.

&&

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

645 am update ...

Vertically stacked low over eastern New England continuing to
provide showers and cool NNE flow into eastern MA and RI this
morning with temps only in the 40s. Subsidence on the backside
of this low providing back edge of the cloud shield to erode
across western CT/MA. Given the absence of precip and onshore
flow temps already near 60 degs in the CT river valley.

Progressive upper air pattern will support this clearing line to
slowly move east today, thanks to potent northern stream short
wave currently over the Great Lakes that will serve as a kicker
with this closed low moving offshore. Thus expecting sunshine to
develop from west to east today and temps warming into the 60s,
around 70 CT river valley and only in the 50s eastern MA.

&&

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

Tonight ...

Overnight scattered showers. Sweeping cold front with continental
tropical airmass. Decent tongue of theta-E, some weak elevated
instability, precipitable waters pushing slightly over 1-inch.
Greater confidence of outcomes N of the MA-Pike given supporting
lift / ascent associated with synoptics, stronger convergent flow
parent to the sweeping cold front. Likely PoPs mainly N of the MA-
pike. Rainfall amounts of around 0.25 inches, possibly upwards of
a half an inch closer to the N MA border given indications of a
moist environment and some measure of ascent through a moist
column.

Wednesday ...

Breezy, dry, seasonable. Pronounced cool, dry air following the cold
front. Boundary layer lapse rates steepen allowing the mix-down of
westerly momentum and drier air. Stepped-up westerly winds suggesting
gusts up to 30 mph across the high terrain while pushing surface
dewpoints lower as forecast model soundings highlight inverted-V
profiles. Scattered to broken stratocu around 4-5 kft beneath
cyclonic flow. Highs around the low 60s.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...

Highlights...

* Thu likely the pick of the week w/dry weather & highs 65-70
* Showers and cool weather return Friday into early Saturday
* Drying trend likely Saturday afternoon and into Sunday

Details...

Wednesday night and Thursday...

Dry cool northwest flow across the region as closed mid level low
over ME and its surface circulation over Nova Scotia at 00z Thu,
remain progressive and continue moving east. Thus dry and seasonable
weather expected Wed night. Thu should be the pick of the week in
response to short wave ridging and associated anticyclonic flow
overspreading the area and providing dry tranquil weather. Model
soundings indicate +3C at the top of the blyr around 875 mb. This
will support highs well into the 60s and possibly near 70 away from
the south coast, as modest NW winds in the morning shift to WSW in
the afternoon. Given full sun and light winds will make it feel even
warmer.

Friday / Fri night ...

Potent northern stream energy phases with southern stream moisture
yielding a high amplitude negative tilt trough over the northeast
heading towards 12z Sat. This results in low pres developing rapidly
along an approaching cold front. The combination of PWATs climbing
over 1.5 inches and strong jet dynamics (negative tilt trough and
RRQ of 110 kt upper level jet streak over SNE) will likely yield a
period of heavy rain, a few thunderstorms and strong winds. Greatest
impacts appear Fri night but still 3+ days away.

Saturday ...

Threat for rain early as negative tilt trough swings thru. Strong
post frontal winds possible as surface low bombs over ME with 984 mb
low east of Cape Ann 12z Sat deepens into the 970s as the low tracks
into ME. Good pres rise/fall couplet may enhance post frontal winds.
Nevertheless upper air pattern remains progressive so a drying trend
develops as the day progress but very windy and cool weather
follows.

Sunday / Monday ...

Signs of upper air pattern deamplifying somewhat with just a low
amplitude mid level trough over New England Sunday. However this
trough may be sufficient for a risk of scattered showers later
Sunday. Upper air pattern becomes more zonal by Monday so dry
weather likely returns along with temps moderating.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
Forecaster Confidence Levels...

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

Short Term /through Wednesday/...Moderate confidence.

11z update ...

IFR/LIFR conditions over eastern MA/RI slowly improve today.
Rain along the eastern MA coast slowly exits out to sea today. MVFR
in western MA/CT will slow lift to VFR today. North winds
slacken as the day progresses. Previous discussion below

=========================================================================

Tonight ...
SCT-BKN VFR becoming BKN-OVC VFR-MVFR with -SHRA mainly along
and N of the MA-pike. S winds becoming W. Generally 5 to 10 kts
with gusts up to 20 kts, strongest along the coast and over high
terrain.

Wednesday ...
Becoming SCT low-end VFR, CIGs 4-5 kft agl with breezy W winds
10 to 15 kts with gusts up to 25 kts.

KBOS terminal...
Expect -RA to dissipate early this morning, lingering as late as
16z. MVFR-IFR lifting, becoming VFR towards mid-afternoon.

KBDL terminal...
Conditions already VFR. SCT-BKN MVFR possible into early morning
with SCT -SHRA. Expect after sunrise that SCT-BKN low-end VFR
prevails with winds gradually turning S.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: VFR. Breezy.

Thursday: VFR.

Thursday Night: Mainly VFR, with areas MVFR possible. Chance
SHRA.

Friday: Mainly MVFR, with local IFR possible. Breezy. SHRA
likely.

Friday Night: Mainly VFR, with areas MVFR possible. Breezy.
Chance SHRA.

Saturday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Wednesday/...High confidence.

Small Craft Advisory conditions across Atlantic-exposed waters.
Initial 5 to 7 foot seas with 10 to 15 kt sustained with gusts
up to 25 kt northerly winds, especially over E waters. Gradually
diminishing late today into this evening out ahead of a sweeping
cold front into Wednesday morning. An opportunity for seas to
diminish, however behind the cold front westerly winds will be
breezy 10 to 15 kts with gusts up to 25 kts which will maintain
seas up around 4 to 6 feet. Small Craft Advisories for inner-
waters drop during the aforementioned lull will likely need to
be reissued for the Wednesday westerly wind burst.

Outlook /Wednesday Night through Saturday/...

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

Thursday: Winds less than 25 kt.

Thursday Night: Winds less than 25 kt. Chance of rain showers.

Friday: Winds less than 25 kt. Local rough seas. Rain showers
likely.

Friday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of rough seas. Chance of rain showers.
Local visibility 1 to 3 nm.

Saturday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Local rough seas. Slight chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 5 PM EDT this afternoon for ANZ235-
     237-256.
     Small Craft Advisory until noon EDT Wednesday for ANZ250.
     Small Craft Advisory until 11 PM EDT this evening for ANZ251.
     Small Craft Advisory until 8 PM EDT Wednesday for ANZ254-255.

&&

$$
SYNOPSIS...Nocera/Sipprell
NEAR TERM...Nocera/Sipprell
SHORT TERM...Sipprell
LONG TERM...Nocera
AVIATION...Nocera/Sipprell
MARINE...Nocera/Sipprell


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