Area Forecast Discussion
National Weather Service Boston/Norton MA
210 PM EDT Sat May 18 2024

.SYNOPSIS...
Unsettled and cool today with periods of rain. Trending drier 
with breaks of sunshine developing Sunday afternoon from 
northwest to southeast, as high pressure begins to nudge in from
the southwest. Early summerlike temperatures expected Monday 
through Wednesday, with the warmest days expected to be Tuesday 
and Wednesday. A cold front around Thursday offers the next 
chance at showers or thunderstorms, with temperatures then 
cooling to more seasonable levels by late in the week.

&&

.NEAR TERM /UNTIL 8 PM THIS EVENING/...

2 PM Update: 

Rain shield and its intensity slowly waning compared to a few
hours earlier, when ORH picked up 0.35 in an hour along with
0.22 at PVD. Low level easterly jet slowly slackens with time,
resulting in areal coverage and intensity of rain decreasing 
with time this afternoon. Otherwise cool conditions with clouds,
periods of rain and onshore flow with NE winds 10-20 mph (brisk
across eastern MA) limiting highs to 55-60 across eastern MA 
and RI. Meanwhile, drier weather across western MA/CT along with
a few breaks of sunshine supporting highs in the 60s to around 
70.


&&

.SHORT TERM /8 PM THIS EVENING THROUGH 6 PM SUNDAY/...

Pattern of persistence carries through this evening with little 
change in the synoptic setup through early tomorrow morning. 
Shortwave passing to our Northwest may renew shower activity 
between 00-06Z tonight. Widely scattered shower activity across 
the eastern half of the CWA will become increasingly sparse 
after the midnight hour, giving way to a more drizzle-stratus 
dominated environment by early morning. Temps will pretty much 
remain stagnant overnight given no change in the pattern with 
low sin the 50s.

While Sunday previously looked to be a much nicer day for southern 
New England, there are indications that the influence of onshore 
flow will persist through the better part of the day across eastern 
MA and RI, though conditions should improve across CT and western MA 
as weak high pressure is able to take better hold over the region. 
Fortunately, pesky mid level low tracks seaward, which will allow 
rain chances to decrease significantly by sunrise. As has been the 
case with many days this Spring, it's likely Sunday is another case 
of the "haves and have nots", as the CT River Valley breaks out into 
sunshine and temperatures warm into the low 70s while strong onshore 
flow pins stratus across eastern MA and much of RI where temps 
struggle to climb out of the 50s along the immediate coast. It's 
probably safe to say those in the Boston to Providence corridor are 
ready to shake this gloomy pattern, but fear not, the long term AFD 
highlights a significant pattern chance by mid week!

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...

Highlights: 

* Warming temperatures under partly to mostly sunny weather through 
  midweek, with the warmest days likely on Tuesday and Wednesday. 
  Could have our first 80 degree day in Boston Tuesday and/or 
  Wednesday, with 3 days of lower-mid 80s in Hartford.

* Our next chance for rains is around later Wednesday night or 
  Thursday with showers or thundershowers associated with a cold 
  front. 

* Cooling to more seasonable levels for late-week.

Details: 

While the general theme of a substantial warming trend to 
temperatures for the early to midweek period is still valid, today's 
00z guidance indicated more potential for continued cloud cover on 
Monday with higher RH in the 1000-850 mb layer, especially for 
eastern and southeast New England. Ended up bringing highs down from 
NBM by a couple degrees for Monday on the basis of this cloud cover, 
though the temperature forecast has obvious sensitivities to how 
long clouds linger/scatter out, and that is still a bit unclear. 
Kept highs in the mid 50s to mid 60s for the coasts and the coastal 
plain, but still think highs soar into the mid to upper 70s from 
central MA/eastern CT westward with less cloud cover. 

Warmest days look to be on Tuesday and Wednesday, with full 
sunshine, southwest breezes and continue dry weather. Relatively 
strong SW flow should keep sea breezes from making much of any 
intrusion landwards, so even sites such as Boston and the North and 
South Shore have a solid chance at reaching 80 degrees, having last 
occurred at Boston on October 28th of last year. Mid 80s inland seem 
reasonable on both days. Despite the breezes, both days should feel 
more reminiscent of early summer with dewpoint temps in the mid to 
upper 50s.  

Dry weather to prevail through Wednesday. Our next chance for 
showers or thundershowers isn't until a cold front arrives around 
Wednesday night or Thursday, but the timing and the strength of any 
thunderstorms are both uncertain. Latest guidance favors 
Thursday for frontal passage so favored the highest PoP around 
Thursday but only around 20-30 percent given the uncertainties 
in timing. Friday appears to be more entrenched in post-frontal 
colder air, with temps seemingly poised to return closer to 
late-May climatological levels.

&&

.AVIATION /18Z SATURDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:

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

18z TAF Update: 

Through 00z...Moderate confidence. Uncertainty on arrival time
of IFR/LIFR over Cape and Islands advancing northwestward. 

Rain shield and intensity will be on the decrease this
afternoon. NE winds continue 10-15 kt. IFR/LIFR across Cape Cod,
Islands and coastal Plymouth county slowly spread inland into RI
and eastern MA 21z-00z. Elsewhere MVFR/VFR continues across CT
into western-central MA. 

After 00z...Moderate confidence. Uncertainty in arrival time of
IFR/LIFR spreading inland.

IFR/LIFR advance inland into RI and eastern MA, with MVFR across
CT into western-central MA. Drizzle and fog most common across
RI and eastern MA. NE winds continue 10-15 kt. 

Sunday...Moderate Confidence. Uncertainty on timing of
conditions improving from LIFR/IFR in the morning to MVFR/VFR in
the afternoon. 

IFR/LIFR in the morning lifts to MVFR/VFR in the afternoon
across CT into western-central MA. Timing across RI into eastern
MA more uncertain.  NE winds 10-15 kt.

Sunday night...moderate confidence. Uncertainty on timing and
how conditions will lower across RI and eastern MA. 

MVFR at 00z across RI and eastern MA, with VFR westward into CT
and western-central MA. Uncertain how quickly and how far west IFR
across Cape and Islands at 00z traverses overnight. IFR possible
across much of RI and eastern MA, as NE winds continue. 

KBOS TAF...High confidence on trends but lower on exact arrival
time of IFR/LIFR this evening, then departure time of improving
conditions Sunday afternoon. 

KBDL TAF...High confidence in trends, but uncertainty on timing
and duration of lower conditions tonight, then uncertainty on
exact timing of improving conditions Sunday. 

Outlook /Monday through Wednesday/...

Monday Night through Tuesday Night: VFR. 

Wednesday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels:

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

Extended the SCA for the eastern outer waters through early
Monday morning for persistent seas. 

Saturday... High confidence.

Scattered light rain and drizzle across the waters. Will have
visibilities of 3-5 SM. Persistent 15-20 kts out of the NE with
gusts up to 20 kts. Seas 1-4 ft across the interior waters and
4-6 ft for the outer.

Saturday Night...Moderate confidence.

Scattered light rain and drizzle anticipated to persist. Will 
continue to see NE winds at 10-15 kts and gusts around 20 kts. 
Visibilities of 3-5 SM and seas 3-6 ft for the outer waters.

Sunday... High Confidence. 

Continued NE winds 10-15kt. Seas across the eastern outer
waters will remain above 5 feet through the period, but will 
fall below 5 ft elsewhere. Vsby reductions early Sunday morning 
should improve through the day. 

Outlook /Sunday Night through Wednesday/...

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

Monday through Monday Night: Winds less than 25 kt. Areas of
seas approaching 5 ft. 

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

Tuesday Night through Wednesday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 2 AM EDT Monday for ANZ250-254.
     Small Craft Advisory until 8 PM EDT this evening for ANZ255-
     256.

&&