Area Forecast Discussion
Issued by NWS Boston, MA

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038
FXUS61 KBOX 241800
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
200 PM EDT Tue Apr 24 2018

.SYNOPSIS...
High pressure in control today will result in plenty of
sunshine and another mild afternoon. Low pressure approaching
from the southwest will bring a soaking rain to the region very
late tonight and Wednesday with localized heavy downpours. This
may result in some brief nuisance poor drainage street flooding.
Seasonable temperatures follow Thursday through Saturday with
mainly dry weather other than a few brief showers possible. A
brief cool down expected on Sunday, but this will be short lived
as unseasonably warm temperatures are possible by the middle of
next week.

&&

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

200 PM Update...

Dry weather and mostly clear skies remain across the region
today. High level cirrus is starting to stream up into
Connecticut and will continue to advance northeastward through
the day. Biggest change in the forecast was to increase wind
speeds as gusts around 20 MPH is ongoing and should linger into
the afternoon as we continue to mix.

Several locations have warmed into the upper 60s into low 70s
across the interior. South coastal regions have remained in the
mid to upper 50s thanks to onshore winds. Aside from a few minor
tweaks the forecast remains on track for this evening.

Previous Discussion...

Trends in the forecast remain on track for today. Strong high
pressure remains east of the region resulting in south/southwest
flow. Aloft, ridge axis remains over the region as moisture from
the Carolinas begins to stream into the area. This will
increase high level cloud cover, especially during the late
afternoon.

Temperatures have been on the rise early this morning with FIT
already coming in at 60F. Because mixing will increase moreso
then originally thought, believe that a run at the low 70`s is
possible esp across the Merrimack Valley. Gusts will increase
to near 20 MPH by the afternoon dropping RH values to below 25
percent (away from the coast). An SPS for fire weather interest
have been issued as a result.

&&

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

As the high shifts E, low pressure will develop near Chesapeake
Bay and the Delmarva peninsula. This will cause winds to back
to SE and start to increase. Noting a good low level moisture
feed setting up with the developing SE fetch from the western
Atlantic, which will moisten up the airmass.

Will see area of rain to lift NE into western areas by around
midnight, then steadily shifts E overnight. Swath of PWAT
moisture on the order of 1 to 1.2 inches works across the region
with the onshore flow. POPs approach categorical across most
areas by daybreak. Best lift remains S and W of the region, so
will see light rainfall, up to 0.2 inches across the lower CT
valley by 12Z.

With increasing clouds and dewpoints across the region, will see
temps only bottom out in the 40s.

Wednesday...

Low pressure will hug the NJ/DE coast during the day, keeping a
steady SE moisture feed working across the region. All models
signal a good slug of rainfall moving across, especially across
central and western areas. May see up to 0.5 to 1 inches of
rainfall, with a good shot of a bit more across the eastern
slopes of the Berkshires and Worcester Hills with a good
upslope feed.

Also noting very good instability axis crossing the region
during the day as the low approaches with K indices to the
lower 30s, LI values of zero to -1 and Total Totals around 50.
Have continued to mention isolated thunder. With the convection,
could see locally heavy downpours that may produce urban and
poor drainage flooding.

Rather strong SE low level jet, on order of 55-60 kt, but some
question how much of this will mix down. May see some of this
mix down along the S coast Wed afternoon, with gusts up to 25-35
kt possible.

&&

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

* Scattered showers Wed night with an isolated t-storm possible

* Mainly dry+seasonable Thu/Fri/Sat other than a few brief showers

* Dry and a bit cooler Sun with moderating temperatures by Mon

* Unseasonably warm temps may arrive by the middle of next week

Details...

Wednesday night...

The deeper moisture and forcing will push east of the region
Wednesday evening, bringing an end to the widespread rain.
However, upper level energy remaining west of the region coupled
with surface boundary will result in scattered showers
persisting well into the night. In fact...there is enough
elevated instability for an isolated thunderstorm or two. Low
temps will drop mainly into the upper 40s to around 50 and areas
of fog are also anticipated.

Thursday...

Drier mid level air will be working into the region from the west
allowing for partial sunshine.  Given the mild start high temps
should reach well into the 60s in most locales.  Mainly dry weather
anticipated...but shortwave/cold pool aloft will move across central
and northern New England. We should be on the southern fringe of its
main impacts...but given cold pool aloft a few brief showers are
possible with the greatest risk north of MA turnpike.

Friday and Saturday...

Overall...seasonable weather continues for late April.  While most
of this period will feature dry weather, it is possible a wave of
low pressure brings a brief period of showers late Friday if it
tracks close enough to the coast. Greatest risk for this will be
across southeast New England.  As for Sat...while most of the time
will be dry a cold front may bring a few passing showers Sat
afternoon and evening.  Highs Fri and Sat will mainly be in the 60s.

Sunday and Monday...

Dry weather behind the cold front with somewhat cooler weather Sun.
Still a pleasant day though with highs mainly in the 50s to perhaps
a few locales near 60 across southeast New England.  After a cool
start early Monday morning with many locales dipping down into the
30s...highs should recover into the 60s Monday afternoon as rising
height fields begin the warming trend.  In fact...much of our long
range guidance is showing the potential for unseasonable warmth by
the middle of next week with upper level ridging building over the
eastern U.S.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels...

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

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

Now til midnight...VFR. Southerly wind gusts near 25 kts
through the afternoon. Southerly winds gusts will subside as
winds begin to shift to the east/southeast.

After midnight into Wednesday...MVFR dropping to IFR towards
Wednesday morning. Rain will quickly overspread the region as
winds remain ESE. IFR/LIFR is possible during the late morning
into the afternoon with +RA and iso thunder. Low risk for 35 kt
gusts across the southeast coastal plain. Otherwise strong LLWS
through much of the day.

Wednesday night...IFR with possible LIFR across the area.
Improving to MVFR towards dawn on Thursday. +RA remains trending
towards showery weather after midnight. Could be low vsbys along
the south coast in Fog through much of the night.

KBOS Terminal...High confidence in TAF. Low risk for TSRA after
21z.

KBDL Terminal...High confidence in TAF. Morning rush could be
impacted with +RA.

Outlook /Wednesday Night through Saturday/...Moderate to High
confidence.

Wednesday Night: MVFR/IFR conditions possible. Windy with local
gusts to 30 kt across southeast New England coast during the
evening with some LLWS. SCT SHRA, areas BR, isolated TSRA.

Thursday: VFR. Slight chance SHRA.

Thursday Night: VFR.

Friday: VFR. Slight chance SHRA.

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

Saturday: VFR. 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 Wednesday/...

Today...High confidence.
S-SW wind increasing with gusts to 20 kt. Seas 3 feet or less.

Tonight...High confidence.
Winds shift to SE and gusts up to 25 kt. Small craft advisories
have been issued. Seas build to 5 ft on the southern outer
coastal waters late. Visibility restrictions in patchy fog.
Rain developing after midnight from W-E.

Wednesday...Moderate confidence.
SE winds gusting to 25-30 kt. Low risk of Gale force gusts on
the eastern outer waters Wed afternoon. Seas build to 6 to 12
feet, highest on the southern outer waters. Visibility
restrictions in areas of rain and fog. Isolated thunderstorms.

Outlook /Wednesday Night through Saturday/...Moderate to High
confidence.

Wednesday Night: Small Craft Advisory winds with gusts up to 30
kt and a low risk for a few 35 knot gusts early in the evening
across the southeast waters. Rough seas up to 13 ft. Chance of
rain showers, areas fog, isolated thunderstorms. Visibility 1 to
3 nm.

Thursday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Rough seas up to 10 ft. Slight chance of rain
showers.

Thursday Night: Winds less than 25 kt. Rough seas up to 9 ft.

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

Friday Night: Winds less than 25 kt. Local rough seas. Chance
of rain showers.

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

&&

.FIRE WEATHER...
Dry conditions with minimum RH values of 15 to 25 percent away
from the immediate coast are expected today. South to southwest
winds will gust up to 15 to 20 mph with some brief gusts up to
25 mph possible this afternoon.

&&

.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...None.
RI...None.
MARINE...Small Craft Advisory from 4 AM to 6 PM EDT Wednesday for
     ANZ231-232-235-237-254.
     Small Craft Advisory from 7 AM to 6 PM EDT Wednesday for
     ANZ233-234.
     Small Craft Advisory from 9 AM to 6 PM EDT Wednesday for
     ANZ236.
     Small Craft Advisory from 8 AM to 6 PM EDT Wednesday for
     ANZ250.
     Small Craft Advisory from 3 AM to 6 PM EDT Wednesday for
     ANZ255-256.

&&

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



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