Area Forecast Discussion
Issued by NWS Boston, MA

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675
FXUS61 KBOX 222308
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
708 PM EDT Fri Jun 22 2018

.SYNOPSIS...
High pressure continues to move offshore tonight, but it will
remain dry. Scattered showers and a few thunderstorms are
expected at times this weekend...but it is uncertain if any
activity will linger into Monday. Mainly dry weather with
seasonable temperatures anticipated Tuesday and Wednesday with a
ridge of high pressure in control. Summer heat and humidity
should return by the end of next week as this high moves east of
the region.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...

7 pm update...

The center of high pressure will continue to gradually slide
east of our region. Mainly expect increasing/thickening
cloudiness across our area overnight with dry weather
prevailing. May see a few spot showers arrive near
daybreak...but there is initially some dry air to overcome. Low
temperatures will mainly be in the middle to upper 50s.

Also...we did update Saturday to include categorical pops and
the potential for localized heavy rainfall. While the entire
day will not be a washout...most locations should see a period
of two of rainfall with isolated t-storms possible.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...

Saturday...

A warm front lifts NE-ward during the day, and may reach the south
coast of New England around 00Z. Increasing moisture is
expected throughout southern New England, with precipitable
water increasing to 1.5 inches or higher. The approach of the
front will provide lift, allowing for the development of showers
across our area. Planning on going with likely pops. While it
doesn`t look to be a washout for the full day, hi-res guidance
is in agreement on areas of showers moving thru the region.

Model thermal profiles show a low level inversion which makes sense
given warm front to the S, and an onshore/E wind providing a cooler
marine influence near the surface. However some elevated instability
is anticipated, which should yield isolated thunderstorms and
the potential for brief locally heavy rainfall. Plan to go with
likely pops and considerable cloudiness. High temps will be on
the low side, only reaching into the 60s. A few spots might
reach 70.

Saturday night...

Warm front lingers in our vicinity Sat night, accompanied by a 30-40
kt low level jet. This will continue to provide a lifting mechanism
for showers. Precipitable water values remain at or above 1.5
inches, so brief locally heavy rainfall is possible. Model
soundings showing continued elevated instability. Will continue
with likely pops, with isolated thunderstorms. Best chance for
thunder is probably along south coastal MA/RI, closer to the low
level jet. Areas of fog developing.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...

Highlights...

* Warmer with scattered showers and t-storms on Sunday
* Mainly dry/seasonable temps with comfortable humidity Tue and Wed
* Summer heat/humidity should return by the end of next week

Details...

Sunday...

The warm front will lift north of most locations Sunday
morning...allowing a warmer and more humid airmass to move into the
region.  High temps should reach into the upper 70s and lower 80s
despite potential for a fair amount of clouds.  We may see a period
of partial sunshine though and if that does occur a few middle 80s
would be possible.

The main concern will be Sun afternoon/evening when a pre-frontal
trough/cold front approach from the west.  There probably should be
enough instability for scattered showers and a few thunderstorms
during that time.  If we can muster 1000 J/KG of MLCape...which is
dependent on solar insolation and amount of low level moisture
return a few strong thunderstorms would be possible. 0 to 6 km shear
is on the order of 30 to 40 knots...but mid level lapse rates are
weak and we will not have the anomalous environment that we saw last
Monday. Nonetheless...a few strong thunderstorms with gusty winds
and heavy rainfall are possible if enough instability can be
realized.

Monday...

A vigorous shortwave/cold pool aloft will drop southeast into the
Northeast on Monday.  The GFS is most aggressive showing the
anomalous cold pool dropping furthest south into our region with
500T dropping below -20C.  This scenario would likely produce
scattered showers and thunderstorms along with some hail given such
cold temperatures aloft.  While this solution is possible, appears
to be a low probability at this time given the rest of the guidance
is further north and east with the cold pool...resulting in mainly
dry weather.  Therefore...will just include some low pops for now
and see how the models trend over the next 24 hours.

Tuesday and Wednesday...

Mainly dry and pleasant early summer weather with a ridge of high
pressure in control.  High temperatures will mainly be in the upper
70s to the middle 80s along with comfortable humidity levels.

Thursday and Friday...

A pattern change to more summerlike warmth and humidity expected Thu
and Fri as upper level ridging builds to sour south...resulting in
rising height fields in southern New England.  Highs should be well
up into the 80s to perhaps over 90...but specific details this far
out remain uncertain.  Dry weather probably dominates...but a few
showers/t-storms can not be ruled out.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
Forecaster Confidence Levels...

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

Short Term /through Saturday Night/...High confidence thru
tonight, then moderate confidence.

Tonight...VFR conditions continue despite thickening mid level
cloudiness overnight.

Saturday...Bands of SHRA across the region, with isolated TSRA
and localized heavy rainfall. VFR in most locations at
12z...but MVFR-IFR overspread the region from south to north
later in the morning through the afternoon.

Saturday night...Mainly IFR with even some LIFR conditions in
areas of showers and fog. Isolated TSRA.

KBOS Terminal...High confidence in TAF thru tonight, then
moderate confidence. VFR thru tonight, deteriorating to MVFR
Sat morning then IFR during the afternoon.

KBDL Terminal...High confidence in TAF thru tonight, then
moderate confidence. VFR thru tonight, deteriorating to MVFR
Sat morning then IFR during the afternoon. Locally lower
conditions may occur earlier in heavier showers.

Outlook /Sunday through Wednesday/...Moderate confidence.

Sunday: Mainly VFR, with local MVFR-IFR possible. Chance SHRA,
isolated TSRA.

Sunday Night: Mainly VFR, with local MVFR possible. Chance
SHRA, slight chance TSRA, patchy BR.

Monday: Mainly VFR, with local MVFR possible. Slight chance
SHRA, isolated TSRA.

Monday Night: VFR.

Tuesday through Wednesday: VFR.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Saturday Night/...High confidence.

Tonight and Saturday...E-SE winds in place. A few gusts approaching
25 kt on the southern outer waters late tonight into early Saturday.
Visibility restriction in areas of fog along the southern waters
late tonight, then in showers and areas of fog moving in from S-N
during Sat. Isolated thunderstorms possible during Sat.

Saturday Night...SW winds less than 25 kt. Seas approaching 5 ft on
the southern outer coastal waters. Showers likely with isolated
thunderstorms. Areas of fog visibility 2-3 nm or less.

Outlook /Sunday through Wednesday/...Moderate confidence.

Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Slight chance of rain showers, isolated thunderstorms, patchy
fog.

Sunday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of rain showers, isolated thunderstorms,
patchy fog. Local visibility 1 to 3 nm.

Monday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas up to 5 ft. Slight chance of rain showers,
isolated thunderstorms.

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

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

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

Wednesday: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas up to 5 ft.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$
SYNOPSIS...NMB/Frank
NEAR TERM...Frank/NMB
SHORT TERM...NMB
LONG TERM...Frank
AVIATION...NMB/Frank
MARINE...NMB/Frank



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