Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 222029

Area Forecast Discussion
National Weather Service Boston/Norton MA
429 PM EDT Tue May 22 2018

Rain showers will focus themselves to the south of the Massachusetts
turnpike this evening before moving offshore...but a few left
over showers will remain possible overnight ahead of a cold
front. Mainly dry weather with warm afternoons are anticipated
Wednesday, Thursday and Friday. Another cold front will drop
south and bring a chance for a period of unsettled weather
during the holiday weekend...but not expecting a washout.


310 pm update...

An approaching surface warm front/modest low level jet will
continue to generate some light rain showers into this evening.
The bulk of these showers will begin to focus themselves south
of the Pike and especially near the south coast...where stronger
forcing resides. While most of the showers will be light...some
briefly heavier showers may occur near the south coast with
even the low risk for a rumble of thunder.

Late this evening and into the overnight hours will feature
mainly dry weather as deeper forcing will have exited the
region. However...still expect a few showers overnight as a weak
cold front crosses the region.

The other concern will be for areas of fog developing overnight given
light southerly flow and increasing low level moisture. Main
focus for the more widespread fog will be along the south coast,
Cape and Islands. Overnight low temps should only drop into the
lower to middle 50s.



A beautiful day is in store for the region as drier air works in
behind the weak cold front. Partly to mostly sunny skies should
allow high temperatures to reach the lower 80s in many
locations away from localized coastal sea breezes. While dry
weather will dominate...a shortwave and a local sea breeze
boundary may be enough to trigger a few brief late
afternoon/early evening spot showers across eastern MA.

Wednesday night...

If a few brief spot showers are able to develop across eastern
MA...they should dissipate after sunset. Otherwise, dry and
tranquil weather anticipated as a weak ridge of high pressure
noses in from the west. Overnight lows should bottom out in the
upper 40s to middle 50s.




Broad mid level ridging continues across the norther tier
states into central Canada around 12Z Thursday as seen on 12Z
model suite and ensembles, which an H5 cutoff low sits off the
CA coast. The ridging does not last long, though, as H5 heights
signal a NW steering flow that gradually flattens out by the end
of the week. A mid level short wave and associated cold front
moves along in the flattening flow from southern Ontario late
this week into northern New England by the beginning of the
holiday weekend. Meanwhile, the western periphery of the
Bermuda high tries to extend toward the Carolina coast. Low
pressure in the Gulf of Mexico shifts slowly N while subtropical
moisture works N around the high across the southern
Appalachians. Limited moisture from the approaching front will
move south during Saturday, bringing scattered showers. May see
enough instability late Saturday into Sat evening to even see a
few thunderstorms.

The front becomes parallel to the mid level steering flow, so
it looks to stall near or just S of the region by Sunday. May
see a few weak waves move along this front, which will keep the
chance for showers through at least Saturday night. Some showers
may linger into Memorial Day mainly along S coastal areas.
Another short wave may approach sometime Tuesday with spotty

With H5 heights running in the 570-576 dm range late this week,
will see temps running well above seasonal normals especially
Friday and Saturday, then will fall back to near or a bit below
normal late this weekend into early next week.


Thursday through Saturday...

Large high pressure from the Great Lakes into New England will
bring dry but somewhat cool temps with sea breezes across
coastal areas. As the high moves offshore, winds shift to SW
and, as mid level heights rise, temps will as well Friday into
Saturday. Highs should run around 10 to 15 degrees above
seasonal levels away from the coast.

Clouds approach Friday night as cold front approaches from the
north. Will see chance for showers move into the Route 2 area by
late Sat morning. With the warm temps in place, along with
pretty good instability ahead of the front (SLIs around zero to
-1, K indices in the lower 30s and TQ values in the upper
teens), could see isolated thunderstorms develop.

Saturday night through Monday...

Cold front crosses the region Saturday night, with scattered
showers. Could also see isolated thunder Sat evening. Then, the
front will slow as it reaches the S coast Sunday. Some showers
will linger Sunday, then drier air moves in from Maine and N NH
as high pressure passes from Quebec into northern Maine during
Monday. Can not rule out some leftover showers especially along
the S coast during the day as the front lingers. Kept low chance
for showers mainly S of the Mass Pike.


Still can`t rule out a few spotty showers at this point, but
lower confidence during this timeframe with wide model solution


Forecaster Confidence Levels...

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

Short Term /through Wednesday Night/...

Tonight...Moderate to high confidence. Ceilings and
visibilities should gradually lower this evening and especially
after midnight. Timing uncertain but widespread MVFR conditions
should develop with locally IFR/LIFR focused across the south
coast, Cape and Islands where the greater risk is for lower
clouds and fog. Some showers mainly this evening focusing south
of the Pike with even the low risk for a rumble of thunder near
the south coast.

Wednesday...High confidence. Lingering lower cigs/vsbys should
improve to VFR by late morning/early afternoon in all locations.
These conditions will be slowest to improve across the Cape and
Islands. Low risk for an isolated late afternoon/early evening
shower or two across eastern MA.

Wednesday night...High confidence in VFR conditions.

KBOS Terminal...High confidence in TAF. Sea breeze should come
to an end early this evening.

KBDL Terminal...High confidence in TAF.

Outlook /Thursday through Sunday/...Moderate confidence.

Thursday: VFR.

Thursday Night through Friday Night: VFR. Breezy.

Saturday: Mainly VFR, with areas MVFR possible. Breezy. Chance
SHRA, isolated TSRA.

Saturday Night: Mainly MVFR, with local IFR possible. Chance
SHRA, isolated TSRA.

Sunday: Mainly MVFR, with local IFR possible. Chance SHRA.


Forecaster Confidence Levels...

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

Short Term /through Wednesday Night/...

Tonight through Wednesday night...High confidence. Weak pressure
gradient will keep winds and seas below small craft advisory
thresholds through Wednesday night. Showers this evening with a
low risk of an embedded t-storm across the southern waters. Main
concern will be areas of fog overnight into part of Wednesday
morning...which may be locally dense especially across our
southern waters.

Outlook /Thursday through Sunday/...Moderate confidence.

Thursday: Winds less than 25 kt.

Thursday Night: Winds less than 25 kt. Seas locally approaching
5 ft.

Friday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of seas approaching 5 ft.

Friday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of seas approaching 5 ft.

Saturday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of seas approaching 5 ft. Slight chance of rain

Saturday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Chance of rain showers, isolated thunderstorms, patchy
fog. Areas of visibility 1 to 3 nm.

Sunday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain showers.




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