Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 261019
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
619 AM EDT Thu Apr 26 2018

.SYNOPSIS...

A weak high pressure ridge will bring a return to mainly dry
weather later this morning through tonight with seasonable
temperatures. Another fast moving low pressure system will bring
a period of widespread showers to the region Friday afternoon
and evening. Milder temperatures return Saturday, but a cold
front will bring a brief shot of cooler air to the region Sunday
into Monday. A significant warming trend will occur Tuesday
into Wednesday with dry weather expected.

&&

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

615 am update...

The bulk of the steady rain across eastern MA/RI should be
exiting the region over the next hour or two as drier mid level
air works in from the west. Otherwise...should see the fog and
low clouds dissipate from west to east this morning as that
drier air works into the region.  Still some localized dense fog
patches out there...but not widespread so will likely cancel the
Dense Fog Advisory shortly.

Skies will become partly to mostly sunny this afternoon for
most areas. It will be a more typical spring day as temperatures
rebound into the middle to upper 60s across much of the region.
As winds shift to SW to W during the day, may see wind gusts up
to around 25 mph mainly during the afternoon, possibly a bit
higher for a time along the immediate S coast.

&&

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

Tonight..

Weak high pressure crosses the region, so expect partly cloudy
skies on average. West winds will be briefly gusty this evening
mainly along the immediate S coast, but will become light by
around midnight.

Fast flow aloft continues as mid level long wave trough starts
to dig across the western Great Lakes. Noting another short wave
in this fast flow, with associated surface low pressure
shifting NE out of the Carolinas after midnight.

Expect dry conditions through the night, though mid and high
clouds will increase after midnight across western areas. Low
temps will range through the lower-mid 40s, typical for late
April.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...

Highlights...

* A period of widespread showers Fri afternoon/eve with localized
  brief heavy rainfall possible

* Mainly dry and milder during the day Sat with just few showers
  possible across the interior

* Scattered showers possible Sat night into Sun but not a washout

* Mainly dry and cool Sun night into Mon

* Dry with a significant warming trend Tue/Wed

Details...

Friday and Friday night...

While much of Friday morning may end up dry...shortwave energy
lifting northeastward will result in a period of widespread
showers focused Friday afternoon/evening. Despite the shortwave
energy gradually deamplifying a modest southerly LLJ/PWAT axis
will develop ahead of it. Guidance has trended stronger and
further west with the axis of the LLJ along with some elevated
instability. These ingredients should combined for a period of
widespread showers Friday afternoon/evening. Brief localized
heavy rainfall is possible and perhaps even an isolated t-storm
or two. Greatest risk for that will be across southeast New
England on the nose of the LLJ.

High temperatures may reach the lower to middle 60s for a time
during the late morning/early afternoon...but readings should
drop back into the 50s once the rain arrives and some fog should
develop. The bulk of the rain should come to an end after
midnight...but areas of fog may linger.

Saturday...

An approaching cold front will result in a milder southwest
flow of air into southern New England. Partial sunshine and good
mixing ahead of the front should allow afternoon high
temperatures to reach into the upper 60s to the lower 70s away
from the marine influence of the south coast. Mainly dry weather
expected Saturday...but enough forcing/marginal instability may
allow for a few showers to develop during the afternoon across
the interior.

Saturday night and Sunday...

The guidance has trended slower with the passage of the cold
frontal passage. While confidence is low...the slower movement
of the front may allow for a bit better moisture return and
perhaps a period of scattered showers Saturday night into Sun.
The main idea is that while it does not look like a washout...a
period of scattered showers is certainly possible. Highs Sun may
reach well into the 50s to the lower 60s given the slower
movement of the cold front.

Sunday night and Monday...

The latest model suite has slowed the departure of the deep
upper trough across the northeast. Therefore...cool weather is
on tap for Sunday night and Monday. Low temperatures Sun night
probably will bottom out well down into the 30s...so some frost
is possible. Highs on Monday should be mainly in the upper 50s
to around 60. Mainly dry weather expected...although a few spot
showers are possible on Mon given cold pool aloft overhead.

Tuesday and Wednesday...

A significant warmup is still in the cards for the region as
the upper trough quickly departs and is replaced by upper level
ridging. This should allow highs to probably break 70 across
much of the region Tue and perhaps 80+ in some locations by Wed.
Weak pressure gradient will likely allow for localized sea
breezes at times...resulting in cooler temperatures along the
immediate coast. Nonetheless...summerlike warmth is a good bet
by the middle of next week away from localized marine
influences. Dry weather is also anticipated Tue/Wed as upper
level ridge will result in little synoptic forcing for any
precipitation.

&&

.AVIATION /10Z THURSDAY THROUGH MONDAY/...
Forecaster Confidence Levels...

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

Short Term /through Tonight/...Moderate to High confidence.

Today...LIFR conditions dominated very early this morning...but
should see improvement to high end IFR-MVFR by mid morning and
mainly VFR by afternoon. High confidence in the improvement
given dry westerly flow mixing down...but uncertainty revolves
around the specific timing. W-SW winds will gust up to 20-25 kt
along the immediate S coast, Cape Cod and the islands as well as
the higher terrain.

Tonight...VFR conditions. W wind gusts up to around 20 kt. Mid
and high clouds increase after midnight across western areas.

KBOS Terminal...High confidence in TAF but lower confidence in
timing. LIFR conditions should improve to high end IFR-MVFR by
mid morning and mainly VFR this afternoon. Specific timing is
uncertain.

KBDL Terminal...High confidence in TAF but lower confidence in
timing. IFR conditions should improve to MVFR by mid morning and
then mainly VFR this afternoon.

Outlook /Friday through Monday/...Moderate to High confidence.

Friday: VFR in the morning will be replaced by MVFR-IFR
conditions form west to east during the afternoon/early evening
as rain showers move across the region with even the low risk of
an isolated t-storm.  Areas of fog also expected to develop
late.

Friday Night: Mainly MVFR-IFR conditions. SHRA mainly in the
evening, but areas of fog and low clouds may persist longer.

Saturday: VFR.

Saturday Night: VFR. Chance SHRA.

Sunday: VFR. Slight chance SHRA.

Sunday Night through Monday: VFR.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Tonight/...

Through 12Z...Moderate confidence.
Small Craft Advisories for all waters except Boston Harbor and
Cape Cod Bay. Expect E-SE winds gusting up to 25 kt. Rough seas
up to 10 to 12 ft. Rain showers along with areas of fog.
Visibility locally below 1 nm at times across the southern
waters.

Today...Moderate to high confidence.
S-SW winds gusting to 25-30 kt then will briefly diminish
around midday before shifting to W and gusting up to around 20
kt mainly on the outer waters. Seas will remain at 5 feet or
greater through the day across the open waters as well as the
south bays and sounds. Visibilities at or below 1 nm at times
through mid to late morning in patchy fog and showers, then
improving.

Tonight...High confidence.
W winds gusting to 25 kt early then diminishing. Seas will
slowly subside but remain at or above 5 ft. Good visibility.

Outlook /Friday through Monday/...Moderate to High confidence.

Friday: Winds less than 25 kt. Seas up to 5 ft. Rain showers
develop by late afternoon with an isolated t-storm or two
possible. Areas of fog. Local visibility 1 to 3 nm.

Friday Night: Winds less than 25 kt. Areas of rough seas.
Rain showers likely with perhaps isolated thunderstorm. Areas of
fog. Visibility 1 to 3 nm.

Saturday: Winds less than 25 kt. Seas up to 5 ft.

Saturday Night: Winds less than 25 kt. Seas up to 5 ft. Chance
of rain showers.

Sunday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas up to 5 ft. Chance of rain showers.

Sunday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas up to 5 ft.

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

&&

.EQUIPMENT...
The NOAA Weather Radio transmitter serving Providence is out of
service due to phone line problems. The phone company has
prioritized the issues and is working to get the weather
broadcast back on the air as soon as possible. The transmitter
serving Hyannis is back in service.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Dense Fog Advisory until 8 AM EDT this morning for MAZ020>024.
RI...Dense Fog Advisory until 8 AM EDT this morning for RIZ006>008.
MARINE...Small Craft Advisory until 10 PM EDT this evening for ANZ232.
     Small Craft Advisory until 1 AM EDT Friday for ANZ233-234.
     Small Craft Advisory until noon EDT today for ANZ236.
     Small Craft Advisory until 6 PM EDT Friday for ANZ235-237-250-
     254>256.
     Small Craft Advisory until 2 AM EDT Friday for ANZ251.

&&

$$
SYNOPSIS...EVT/Frank
NEAR TERM...Frank/EVT
SHORT TERM...EVT
LONG TERM...Frank
AVIATION...EVT/Frank
MARINE...EVT/Frank
EQUIPMENT...Staff



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