Area Forecast Discussion
Issued by NWS Boston, MA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS61 KBOX 262252

Area Forecast Discussion
National Weather Service Boston/Norton MA
652 PM EDT Tue May 26 2020

High pressure will move offshore tonight and will provide
summerlike warmth and mugginess away from the coast for the
rest of the work week. We end the week with showers and an
isolated chance for a thunderstorm or two on Friday as a cold
front crosses the region. High pressure will bring drier and
cooler weather for the second half of the weekend into early
next week.


7 PM Update: Forecast is on track.

* Dense Fog Develops on Cape Cod and the Islands Tonight

Satellite loop shows low clouds heading inland onto South Coast,
Cape Cod, and Islands this evening. High-res guidance slowly
advances this cloud deck inland tonight, mainly as far north as
Hartford, Providence, and Plymouth though it could make it into
Boston as well for a time.

Webcams indicate fog is still lurking offshore south of the
islands, but expect it to become more widespread near South
Coast this evening due to low temp/dewpoint spreads and light
S/SW winds. Cape Cod and Islands are typically favored for dense
fog in this pattern so we are continuing the Dense Fog Advisory
for tonight. It`s possible dense fog also makes it onto south
coastal RI and MA but still not confident enough to expand the
advisory just yet.

Lows in 50s and lower 60s look good.


* Very Warm & A Bit Humid Away From The South Coast Wednesday


The anomalous upper level ridge with height fields around 590 DM
will remain in control of our weather. 850T are bit milder than
today around +15C to +16C. This coupled with southwest flow should
yield afternoon high temps in the upper 80s to near 90 away from
cooling marine influence of the south coast. Unlike today, there
will not be a sea breeze in Boston so they will get in on the summer-
like warmth as well. It will be a bit muggy too with 60+ dewpoints,
but southwest wind gusts of 20 to 25 mph during the afternoon which
will help a bit. Dry weather will persist with the upper level ridge
in control.

Wednesday night...

Model cross sections indicate low clouds developing from south to
north Wednesday night. They will likely be more widespread, covering
most if not all of the region by daybreak. We may even see some
drizzle develop with some fog possible too especially near the south
coast. Overnight lows will only drop into the lower to middle 60s in
most locations with some 55 to 60 degree readings near the south



Morning fog likely to start off across coastal Rhode Island
through the south shore of Cape Cod. One of the biggest
questions for Thursday will be the extent to the cloud over.
Models show a decent swath of moisture between 925 and 850 mb...
especially across western MA/CT. PWATS range between 1.5 and
2.0 inches across the Mid Atlantic and up into southern New
York. With some weak forcing an isolated shower isn`t out of
the question. At 18z the 850mb temperatures climb to 14 degrees
(C), indicating afternoon highs could reach the mid-80s. Those
along the coast will have cooler afternoon highs in the upper
60s to low 70s. If clouds don`t erode those temperatures will be
difficult to produce, but, with a predominant southwesterly
flow we should be capable of mixing them out.


A cold front will spark scattered showers and possibly an isolated
thunderstorm. PWATS range from 1.5 to 2.0 inches across the Mid
Atlantic to Southern New England. Thunderstorms may develop NW of
our area where better instability is present and could move into
western Massachusetts during the mid-afternoon with locally heavy


Temperatures still remain rather warm on Saturday with 850 mb
temperatures between 8 and 10 degrees Celsius. A few morning
showers could linger depending on the speed the front moving
offshore. The greatest chance of seeing a shower will be in
eastern Massachusetts, the Cape, and Islands. Clouds clear from
west to east late in the day as drier and cooler air moves in
from Quebec.


An area of high pressure moves out of from the Great Lakes Region
Sunday into Monday with an upper-level through moves across New
England and eastern Quebec. The 500 mb temperatures above Southern
New England are -12 degrees Celsius! That will result in cooler
than normal temperatures in the middle and upper 60s.


Forecaster Confidence Levels...

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

00Z TAF Update: Moderate confidence.

CIGS steadily lower to IFR across much of CT, RI, and SE MA
tonight as well as near Berkshires, but conditions remain VFR
elsewhere. S/SW winds prevail as sea breezes subside.

IFR CIGS improve to VFR Wed morning as low clouds retreat
offshore, with process being the slowest across the Cape and
Islands. Otherwise, VFR conditions expected with SW wind gusts
into the lower 20 knots during the afternoon across the
southeast New England coast.

Low clouds return Wed night from south to north. Appears this
time the lower clouds will overspread most if not all of the
region. So expect mainly lower end MVFR to IFR conditions. LIFR
conditions with fog may impact the south coast, Cape, and

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Thursday through Sunday/...

Thursday: Mainly VFR, with local IFR possible. Slight chance

Thursday Night: Mainly VFR, with areas IFR possible. Breezy.
Chance SHRA, chance TSRA.

Friday through Friday Night: Mainly VFR, with local IFR
possible. Breezy. Chance SHRA, chance TSRA.

Saturday: Mainly VFR, with local MVFR possible. Breezy. Chance
SHRA, chance TSRA.

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

Sunday: VFR. Breezy.


Tonight through Wednesday night...High confidence. S to SW winds
will continue through Wed night, but winds/seas should generally
remain below SCA thresholds. Some choppy seas may develop Wednesday
afternoon though with some lower 20 knot wind gusts near shore.
The main issue will be for areas of fog that will be dense
especially during the overnight to mid morning hours.

Outlook /Thursday through Sunday/...

Thursday: Winds less than 25 kt. Slight chance of rain showers.

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

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

Friday Night: Winds less than 25 kt. Areas of rough seas.
Thunderstorms likely, chance of rain showers.

Saturday: Winds less than 25 kt. Local rough seas. Chance of
rain showers, chance of thunderstorms.

Saturday Night: Winds less than 25 kt. Local rough seas. Slight
chance of rain showers.

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


MA...Dense Fog Advisory until 8 AM EDT Wednesday for MAZ022>024.
RI...Dense Fog Advisory until 8 AM EDT Wednesday for RIZ008.


LONG TERM...Gaucher
MARINE...Frank/Gaucher is the U.S. government's official web portal to all federal, state and local government web resources and services.