Area Forecast Discussion
National Weather Service Boston/Norton MA
703 PM EDT Mon May 25 2020

.SYNOPSIS...
Surface warm front approaches the region from the southwest tonight 
with low clouds, patchy fog and drizzle moving back onshore 
impacting the area. Then the warm front lifts thru the region 
Tuesday afternoon followed by a stretch of summer warmth and 
humidity for the remainder of the workweek, but cooler near the
south coast. A cold front then approaches the region Friday and
then moves across the area Saturday. Both days will feature a 
risk of scattered showers and thunderstorms. Cooler, drier and 
less humid conditions follow next Sunday and Monday.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
7 PM update...

Stratus along east coastal MA and over the Islands will 
gradually move inland this evening as boundary layer cools with
light E/SE flow. With dew pts in the 55-60 range, about 5-10 
degs above normal for late May, expect areas of fog and drizzle 
to develop overnight, especially as warm front approaches from 
the southwest. These relatively higher dew pts will result in 
mild temps overnight with lows in the 50s.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
Tuesday ... 

Anomalous 588 dam ridge builds over New England providing dry 
weather with a touch of summer heat and humidity. At the surface, 
warm front lifts north of the region by midday with morning clouds, 
patchy fog and drizzle giving way to increasing afternoon sunshine 
and much warmer temps. Model soundings indicate mixing to at or 
above 850 mb away from the coast. With 850 temps warming to +12C to 
+13C, expecting highs 80-85 away from the coast with a few 86/87 
possible well inland. Closer to the coast SSW winds will limit highs 
to the 70s, 65-70 for the outer Cape and Islands. A touch of summer 
humidity as well with dew pts in the low 60s. 

Tuesday night ...

588 dam ridge continues to provide dry weather to the region. 
Surface ridge remains along the south coast so the combination of 
light winds and more humid conditions will yield patchy fog but also 
mild temps with lows in the upper 50s to low 60s.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Highlights... 

* Summer-like temperatures and increasing humidity Wed through Fri 
  but cooler south coast
* Increasing risk of showers/t-storms Fri into Sat
* Cooler and drier Sun/Mon with below normal temps

Wednesday into Thursday...

Anomalous mid level ridge over New Eng with near record 500 mb 
heights for May. This will bring summer like warmth with highs well 
into the 80s in the interior but cooler along the south coast with 
southerly flow. Increasing humidity levels will be felt as dewpoints 
rise into the 60s. The higher dewpoints over the cooler SST will 
result in late night and morning stratus and patchy fog along the 
south coast which will also have some impact on temps near the south 
coast. Other than patchy drizzle near the coast, mainly dry weather 
expected. As the mid level ridge slides to the east on Thu and 
deeper SW flow develops, higher PWATs up to 1.75" will move into 
SNE. No instability across SNE but can't rule out a few showers Thu 
along with more cloud cover as leading edge of deeper moisture 
moves into region. 

Friday into Saturday...

Mid level ridge moves to the east as northern stream trough 
approaches from the Gt Lakes. Risk of showers/t-storms increases Fri 
in the interior as some instability develops but cold front still 
well back to the west near the Gt Lakes so only expecting sct 
activity. Better chance for showers/t-storms later Fri night and Sat 
as the front moves into the region. Modest instability and 
increasing wind field as the trough approaches may result in a few 
strong storms depending on the timing of the front. Heavy rainfall 
also a threat in high PWAT airmass. Faster timing of the front would 
limit risk on Sat but if slower trend continues t-storm risk would 
increase. 

Sunday and Monday... 

Mid level trough across New Eng with post frontal airmass resulting 
in cooler and drier conditions. Model differences on the amplitude 
of this trough will impact magnitude of cooler air but trend will be 
for below normal temps.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
Forecaster Confidence Levels...

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

00z update ... 

Tonight ... high confidence on trends, lower on exact timing.

IFR/LIFR stratus and fog along the immediate coast will spread 
inland tonight. Light SE winds. Low risk for spotty light 
drizzle. 

Tuesday ... high confidence on trends, lower on exact timing.

IFR/LIFR in the morning low clouds, fog and spotty drizzle lifts
to VFR all terminals in the afternoon, although may be delayed 
until late in the day along south coast including Cape Cod and 
Islands. South winds 5-10 kt.

Tuesday night ... high confidence.

Most likely, VFR, dry conditions with SSW winds 5-15 kt.

KBOS Terminal...High confidence in trends, lower on exact timing.

KBDL Terminal...High confidence in trends, lower on exact
timing.

Outlook /Wednesday through Saturday/...

Wednesday: VFR. Breezy. 

Wednesday Night: Mainly VFR, with local IFR possible. 

Thursday: Mainly VFR, with areas MVFR possible. Breezy. Slight
chance SHRA.

Thursday Night: Mainly MVFR, with local IFR possible. Chance
SHRA.

Friday: Mainly MVFR, with local IFR possible. Breezy. Chance
SHRA, slight chance TSRA.

Friday Night: Mainly MVFR, with areas IFR possible. Breezy.
Chance SHRA, slight chance TSRA.

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

&&

.MARINE...
Tonight ... light SE winds with patchy fog and drizzle 
developing overnight. 

Tuesday ... Patchy morning fog and drizzle gives way to dry 
weather in the afternoon along with improving vsby. SE winds 
become SSW in the afternoon as warm front lifts north of the 
area. 

Tuesday night ... Surface ridge over the waters which will 
translate to light winds. Although patchy fog likely develops 
overnight and reduces vsby at times.

Outlook /Wednesday through Saturday/...

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

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

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

Friday Night: Winds less than 25 kt. Areas of rough seas.
Chance of rain showers, slight chance of thunderstorms. 

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&