Area Forecast Discussion
Issued by NWS Boston, MA

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020
FXUS61 KBOX 210224
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1024 PM EDT Sun May 20 2018

.SYNOPSIS...
After a few showers with a cold frontal passage this evening,
drier weather returns through Monday night. Cooler with passing
showers Tuesday afternoon into Tuesday evening as a warm front
approaches. Mainly dry weather for the rest of the week into
Saturday with temperatures averaging above normal. The risk for
showers increases by Sunday.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
1024 PM update...

Cold front and its associated band of showers had moved just
south of Nantucket about 10 PM. The front and these showers
will continue to move southward overnight. Expecting areas of
fog to dissipate with clearing skies as drier air arrives
behind this front. Winds will shift to the NW. Forecast mainly
on track, just tweaked a few things to reflect observed trends,
especially visibility and timing of fog dissipation.

Previous Discussion...

NW drier flow should lead to clearing through the overnight,
pres rises are relatively meager. Therefore, could be a cool
morning with the possibility of localized decoupling, mins in
the upper 40s to mid 50s.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
Tomorrow...
1025mb high pres noses in from the W through the day as modest
mid lvl ridging returns. Dry wx prevails with some diurnal CU
possible. H85 temps near +10C, but mixing may well exceed this
value, therefore expecting widespread mid-high 70s for highs.
A few exceptions, W downsloping should allow typical downslope
locations like the CT and Merrimack valleys to reach around 80,
and sea breezes are possible along the immediate coastlines,
holding highs in the lower 70s. Comfortable with low, well mixed
dwpts.

Tomorrow night...
Mainly dry as high pres slips E. Only issue will be incoming
mid and high clouds during the AM hours. However, the precip
shield from a remnant MCS should hold off until the daylight
hours. Mins in the 50s most locations.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Highlights...

* Cooler with passing showers Tue into Tue night
* Mainly dry weather with above normal temps Wed through Sat,
  coolest Thursday
* Risk of showers increases by Sunday

Overview...

Zonal flow with weak shortwave passage Tue, then northern stream
trough will amplify to the north and east Wed into Thu which will
push a cold front through the region. Rising heights and shortwave
ridging follow Fri into Sat then next northern stream trough
approaches Sunday.

Precipitation...

Main focus for wet weather this week will be Tue into Tue night as
shortwave passage with weak warm front approaching from the SW and
moistening column will likely bring some showers during this time
period. Best chance appears to be in the afternoon/evening. No
surface instability but marginal elevated instability may support an
isold t-storm late late Tue and Tue evening. Looks dry Wed into Sat.
We have a cold front moving through Wed, but limited moisture and
low level convergence will likely result in a dry fropa. Increasing
risk of showers by Sunday with approach of next northern stream
trough, but confidence is low due to timing uncertainty.

Temperatures...

Coolest day of the week will likely be Tue as SNE will be influenced
by clouds and some shower activity on cool side of frontal boundary,
but temps close to seasonable normals. Warmer air returns Wed ahead
of a cold front then a bit cooler post-frontal airmass Thu.
Potential for summer warmth with temps into the 80s interior Fri-Sun.

&&

.AVIATION /02Z MONDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...

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

Short Term /through Monday Night/...

Through 06z...Areas of MVFR/IFR Cape Cod and islands will
improve to VFR. Winds shift to NW Cape/Islands.

Overnight into Monday...High confidence. VFR. Clearing skies.

Monday night...High confidence. Mainly VFR. Light W Winds.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday through Friday/...Moderate confidence.

Tuesday: VFR. Chance SHRA.

Tuesday Night: Mainly VFR, with local MVFR possible. Chance
SHRA.

Wednesday: VFR. Slight chance SHRA.

Wednesday Night through Thursday Night: VFR.

Friday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels...

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

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

Winds will gradually be shifting to the NW all waters, if they
haven`t already at the time of this writing. Winds remain below
Small Craft Advisory thresholds through tomorrow night. Seas
however were running about 5-7 ft on the SE ocean waters, so
will continue Small Craft Advisory into tomorrow for these seas,
at which point they too should drop below thresholds.

A few showers cross the waters through the early evening hours.
Otherwise, lingering fog possible mainly across the SE waters,
these too should lift during the overnight.

Outlook /Tuesday through Friday/...Moderate confidence.

Tuesday through Tuesday Night: Winds less than 25 kt. Chance of
rain showers.

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

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

Thursday Night: Winds less than 25 kt.

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

&&

.FIRE WEATHER...
Spotty locations received as much as 0.5 inches of precipitation
this weekend, but several locations received less. Given fuels
were dry, this may not have been enough to fully moisten them.
RH values Monday will drop as low as 15-25 percent inland, but
winds should remain light out of the NW, around 10mph most of
the day.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 1 PM EDT Monday for ANZ254>256.
     Small Craft Advisory until 6 AM EDT Monday for ANZ235-237.

&&

$$
SYNOPSIS...KJC/Doody
NEAR TERM...Belk/Doody
SHORT TERM...Doody
LONG TERM...KJC
AVIATION...Belk/KJC/Doody
MARINE...Belk/KJC/Doody
FIRE WEATHER...Staff



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