Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 210800
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
400 AM EDT Mon Oct 21 2019

.SYNOPSIS...
Low pressure well south of New England and its rain shield will
impact Cape Cod and the Islands early this morning. As the low
continues to move seaward, rain will exit and clouds will give
way to increasing sunshine later this morning into the
afternoon. However, some cloudiness may linger over Cape Cod and
the Islands. Dry weather tonight lingers into Tuesday morning.
Spotty light showers develop Tue afternoon, becoming widespread
Tue night ahead of an approaching cold front. Behind the front,
dry and seasonably mild conditions follow Wednesday afternoon
into Friday. Another cold front may bring a few showers Friday
afternoon and night. High pressure builds in for most of next
weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
340 AM update...

Back edge of rain shield associated with offshore low now moving
across coastal RI into Buzzards Bay and eastward to Cape Cod and the
Islands at 330 AM. Back edge of cloud shield over central MA/CT and
moving steadily eastward. Where skies have cleared over eastern NY
into Berkshire county MA, light winds and dew pts in the 40s has
resulted in patchy dense fog. Thus as the cloud shield advances east
and skies clear expected areas of fog to develop before sunrise
across central CT/MA which includes the Hartford area and the city
of Springfield. This may have some impact on the morning commute
depending how quickly skies clear. Also there could be enough blyr
mixing via light north winds to preclude fog from becoming too
widespread or dense. Something we will watch closely over the next
few hours.

As ocean storm departs short wave ridging develops across the area
with rain ending and clouds eroding/moving offshore. Thus increasing
sunshine later this morning into the afternoon from west to east.
Low level northeast flow may result in clouds lingering longer over
southeast especially Cape Cod and the Islands. Airmass relatively
mild with 925 mb temps around +9C by this afternoon. Model soundings
show mixing beyond 925 mb so expecting highs 60-65 this afternoon,
perhaps only upper 50s Cape Cod and Islands if clouds linger along
with cool northeast winds.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
340 AM update...

Tonight ...

Dry weather with short wave ridge over the area along with surface
ridge from Quebec into southern New England. This will provide
mostly clear conditions, light winds and with dew pts in the upper
30s to mid 40s expect radiational fog to develop.

Tuesday ...

Any possible breaks of sunshine early will quickly give way to
overcast conditions as return flow and associated SE low level jet
increase. Spotty light rain/drizzle may develop in the afternoon
with this increasing moist low level flow. Not a washout but could
get damp in the afternoon and especially late in the day. Cloud
cover and increasing onshore winds will limit highs to the mid and
upper 50s.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...

Highlights...

* Area of showers push across Tuesday night into early
  Wednesday
* Improving conditions and blustery winds Wednesday afternoon
* Dry and mild Thursday/Thursday night
* Another front brings scattered showers Friday afternoon into
  early Saturday
* Dry later Sat into Sunday morning, then another round of
  showers possible

Details...

Tuesday night through Wednesday...

Cutoff H5 low pres over S Ontario and the western Great Lakes
Tue evening lifts N-NE to Hudson Bay Wed. The steering flow
beneath the lifting low at the surface and aloft shifts from S
to W during Wed. This should allow the surface front to shift E
late Tue night and Wed.

00Z models also signaling a shift of the deep layer moisture
further E than previous model guidance with the increasing and
shifting deep layer wind flow. Models also showing the remnants
of Nestor well SE of Nantucket by 00Z Wed. This position, along
with an H5 short wave wrapping N across N Mass into northern New
England, will push the offshore moisture across Mass Bay then
the western edge clips E Mass early Tue night before shifting
into E NH/Maine. 00Z GFS also showing the PWAT moisture plume
(up to 2-3 SD above normal, or about 1.5 to 1.7 inches) moving
quickly up the eastern seaboard by 00Z Wed to near or E of Cape
Cod and SE coastal Mass before shifting to the Gulf of Maine by
around 06Z.

As the front crosses the region, the last of the showers push
offshore by midday Wed. Winds shift to W and become gusty,
upwards to around 20 kt during the afternoon. Clouds give way to
mostly sunny conditions Wed afternoon. Will see temps top off
in the mid- upper 50s across the higher inland terrain, ranging
to the lower-mid 60s across the coastal plain and the lower to
mid CT valley.

Thursday through Sunday...

Mid level steering flow remains rather fast, though noting
another digging H5 trough around Thursday, but will keep weather
systems steadily moving across the northeast. Will see dry
conditions and seasonably mild temperatures Thursday into early
Friday as high pressure ridge builds across. Fast moving short
wave and surface front.

The high flattens out as the center shifts off the mid Atlc
coast Thu night/Friday morning. Winds shift to S-SW, which will
allow moisture to work up the eastern seaboard as another cold
front approaches late Fri into Sat. Have CHC POPs across the
region, which should push offshore during Fri morning. Dry
conditions forecast for late Saturday into Sunday.

Noting widening model solution spread late Sunday into Monday,
with dry conditions offered by the GFS, while another short wave
moves across the Ohio Valley toward the region around the
Monday timeframe. Low forecast confidence. For now, have carried
CHC POPs from around mid Sunday through the remainder of the
day.

&&

.AVIATION /08Z MONDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...

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

Short Term /through Tuesday/...

06z update...

Thru 12z...High confidence on trends, lower on exact
timing/details

VFR for most of the region with light rain over RI and
southeast MA continuing to move east and should exit Cape Cod
and the Islands by 09z-12z. MVFR conditions will impact the
south coast of MA/RI including Cape Cod and the Islands. Other
area of concern is western MA/CT when skies clear patchy dense
ground fog is possible including BDL/BAF. Light winds.

After 12z...High confidence.

MVFR cigs may linger over Cape Cod and Islands into the
afternoon. Otherwise any patchy IFR/MVFR dense fog western MA/CT
lifts to VFR quickly. VFR elsewhere as well. Light NE winds,
bit higher Cape Cod and Islands.

Tonight...Moderate confidence, some uncertainty regarding areal
coverage of MVFR late.

VFR to start and dry. However MVFR cigs may come onshore late
and overspread much of the region.

Tuesday...High confidence on trends, lower on exact
timing/details

VFR/MVFR then trending IFR/MVFR in areas of low clouds and
drizzle in the afternoon and especially toward evening.

KBOS Terminal...
High confidence in TAF trends.

KBDL Terminal...
High confidence in TAF trends.

Outlook /Tuesday Night through Friday/...Moderate confidence.

Tuesday Night: Mainly IFR, with areas MVFR possible. Breezy. RA
likely, chance SHRA, patchy BR.

Wednesday: Mainly VFR, with local MVFR possible. Breezy. Slight
chance SHRA.

Wednesday Night: VFR. Breezy.

Thursday through Thursday Night: VFR.

Friday: Mainly VFR, with local MVFR possible. Breezy. Slight
chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Tuesday/...

340 AM update...

Today ...

Weak low pressure south of 40N/70W will provide NE winds 15-20
kt over the waters south of the Islands this morning, possibly
gusting up to 25 kt. Given the long fetch seas will increase 4
to 7 ft. Less wind and waves northward. Light rain before over
the southern waters exits offshore by or shortly after daybreak.
Northeast winds decrease this afternoon.

Tonight ...

East swells as wind diminishes with high pres from Quebec
building into New England. Dry weather and good vsby.

Tuesday ...

High pres moves into the maritimes with ESE winds strengthening
across New England. Vsby lowers in developing areas of
drizzle/rain.

Outlook /Tuesday Night through Friday/...Moderate confidence.

Tuesday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of rough seas. Rain likely, rain
showers likely, patchy fog. Areas of visibility 1 to 3 nm.

Wednesday: Low risk for Small Craft Advisory winds with gusts
up to 30 kt. Areas of rough seas. Chance of rain showers.

Wednesday Night through Thursday: Winds less than 25 kt. Seas
up to 5 ft.

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

Friday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Slight chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 6 AM EDT Tuesday for ANZ254>256.

&&

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


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