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Area Forecast Discussion (AFD)

Issued by Boston / Norton, MA (BOX)

                            
250 
FXUS61 KBOX 260159
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
959 PM EDT Mon Mar 25 2019

.SYNOPSIS...

A coastal storm will track well out to sea tonight. High pressure
builds in from the west Tuesday into Wednesday with cool and dry
weather. A weak cold front may bring a few showers Thursday night,
otherwise moderating temperatures Thursday into Friday. Mild 
weather next weekend, but low pressure may bring a period of rain
sometime late Sunday into Monday with much cooler weather possible
by Monday.

&&

.NEAR TERM /THROUGH TUESDAY/...

10 pm update ...

Chilly. Light winds and a sharply-defined cloud shield SW-NE over
S New England presents opportunistic radiational cooling overnight.
However, mid-Atlantic low pressure emerging, isallobaric / gradient
wind response, N winds will pick up towards morning. Prior forecast
still in good agreement. Slight chance PoPs for the Islands with
the possibility of some sprinkles if that, whereas teens to low
20s N beneath light winds and clear conditions. 

&&

.SHORT TERM /TUESDAY NIGHT/...

Tuesday...

Mid level shortwave moves south across SNE, but airmass is bone
dry as high pres builds in from the west. PWATs dropping to less
than 0.1" with dewpoints down into the single numbers. Other 
than a few high clouds, a sunny day expected but chilly with 
temps 5-10 degrees below normal. High upper 30s to lower 40s.

Tuesday night...

High pres moves into New Eng setting the stage for a cold night
with clear skies and light winds. Lows away from the immediate
coast will drop into the teens, with 20s along the coast.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...

Highlights...

* Dry weather prevails much of this time period
* Gradual warming trend Wed & Thu then 60s possible Fri-Sun
* Low risk of showers Thu ngt/Fri AM then again Sat night/Sun

Wednesday...

Pleasant day on Wednesday as a 1034mb surface high moves over the 
region. Winds back to the southwest behind the low bringing 
moderating temperatures, into the mid-upper 40s (less along the 
south coast). Light winds and sunny skies will make it feel Spring 
like. 

Thursday and Friday...

Thursday the high exits to the east and we'll be sandwiched between 
it and a passing surface low/mid-level shortwave over southeast 
Canada. This increases the pressure gradient and makes for a breezy 
but warm day Thursday as southerly winds continue to advect warmer 
air northward. Highs should reach into the 50s save for the south 
coast/Cape Cod where strong onshore flow over the cold ocean waters 
keeps temps in the 40s. As this low moves east it drags a cold front 
across northern New England. Given the northward placement of the 
parent low and recent model trends, there looks to be less of a 
chance that we see the front hold together through much if any 
of southern New England. Thus, not expecting widespread rains, 
but more scattered shower chances Thursday night, best in NW 
Mass. Neither will we see much of a temperature drop; lows 
remain quite warm in the upper 30s to near 40. 

Friday attention turns to a low which forms in the lee of the 
Rockies early Friday and moves through the Ohio valley to the Great 
Lakes region by Saturday morning. We'll stay dry under a brief, weak 
high pressure, keeping the warming trend going. Highs on Friday 
reach into the upper 50s to near 60, except, again, along the south 
coast where onshore flow holds temps in the upper 40s/low 50s. 

Saturday and Sunday...

Strong WAA Friday night through at least Saturday. With 925mb temps 
approaching 12C, temps should reach well into the 60s, and even 
touch 70, especially in northeast MA. As the low approaches, the 
pressure gradient tightens and southwest winds will be breezy 
through the day. Good surface heating should make for a well mixed 
BL and with a 35-40kt LLJ we could see gusts 25-35 mph mixing down. 
Big question will be timing of the cold front/rain chances. Trending 
the forecast to the slower/EC solution which has been more 
consistently showing a late Sunday/early Monday passage. Overall the 
better of the two weekend days right now looks to be Saturday, with 
increasing rain chances during the day on Sunday ahead of that cold 
front. However, at this time period, still plenty of room for 
changes.

&&

.AVIATION /02Z TUESDAY THROUGH SATURDAY/...

Forecaster Confidence Levels...

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

Short Term /through Tuesday Night/...

VFR. BKN-OVC mid-high CIGs N to S, eroding S/E overnight into
Tuesday, becoming SKC. 

KBOS terminal...High confidence in TAF.

KBDL terminal...High confidence in TAF

Outlook /Wednesday through Saturday/...

Thursday: VFR. Breezy. 

Thursday Night through Friday: VFR. Breezy. Slight chance RA.

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

Saturday: VFR. Breezy. Slight chance RA.

Saturday Night: VFR. Breezy. Chance RA.

Sunday: Breezy. Chance RA.

&&

.MARINE...

Forecaster Confidence Levels...

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

Short Term /through Tuesday Night/...

A period of N gusts to 25 kt expected on the S-coastal waters 
late tonight into Tuesday morning as low pressure tracks well 
to the S. SCA for S coastal waters. Winds diminish Tuesday
afternoon and evening. Another period of marginal SCA northerly 
wind gusts possible late Tuesday night over E waters. A few 
showers possible this evening over the S outer waters, S of the
Islands.

Outlook /Wednesday through Saturday/...

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

Thursday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas up to 5 ft. Slight chance of rain. 

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

Friday Night: Winds less than 25 kt. Seas up to 5 ft. Slight
chance of rain. 

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

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

Sunday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of rough seas. Chance of rain. 

&&

.BOX WATCHES/WARNINGS/ADVISORIES...

CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 4 AM to 2 PM EDT Tuesday for ANZ255-
     256.
     Small Craft Advisory from 4 AM to 11 AM EDT Tuesday for ANZ235-
     237.

&&

$$

SYNOPSIS...KJC/BW
NEAR TERM...KJC/Sipprell/BW
SHORT TERM...KJC
LONG TERM...KJC
AVIATION...KJC/BW
MARINE...KJC/BW