Area Forecast Discussion
Issued by NWS Boston, MA

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 300221

Area Forecast Discussion
National Weather Service Boston/Norton MA
1021 PM EDT Wed May 29 2024

Other than a few brief showers/thunderstorms this afternoon and
early evening, mainly dry, pleasant warm weather prevails. Low
pressure then brings a more widespread rain, moderate to heavy at
times later tonight into Thursday morning, then slowly dries out
Thursday afternoon from west to east. Drier weather with plentiful
sunshine for Friday. After a few days of temperatures at or slightly
cooler than normal, the weekend into Monday offers a warming trend
toward above normal temperatures and still tolerable humidity
levels. Drier weather should generally prevail this weekend into at
least Tuesday.


Update: 10:20PM

Clouds are increasing SW/NE with leading edge of moderate rain
out over western Long Island and Stamford, CT. These showers are
slow moving, storm motion and speed based off neighboring KOKX
radar is 220 degrees at 15 knots. It will take some time before
these showers to reach southwest Hartford County - thinking
between 12am and 2am. Few showers out ahead of the primary zone
are possible, but likely will take some time before bulk of the
rain to reach eastern areas of the CWA, between 4am and 7am.

Previous forecast discussion below...

3 PM update...

* More widespread rain after midnight into THU AM


Mainly dry this evening (after any diurnal showers/thunderstorms
dissipate), then bands of rain overspread the region later tonight
and become fairly widespread. This is in response to a potent s/wv
currently over southwest PA advects eastward. In fact, models are
suggesting this will take on more of a cool season rain event, as
s/wv is fairly baroclinic for late spring, with mid level Fgen
around 850 mb. In addition, models are hinting at some instability
above this layer and the response is for bands of moderate to heavy
rain. This already is present on radars across PA. Exact location of
these bands as they traverse SNE varies from model to model, ranging
from northern MA to the south coast. This instability may be
sufficient for isolated thunder, but more likely, enhancing rainfall
potential, with moderate to heavy rain at times late tonight and
towards Thu morning. Seasonably cool tonight with lows in the 50s.
Light and variable winds become NE toward morning and may become
gusty 15-20 mph towards morning, as surface wave develops along or
just offshore.


3 PM update...


* Bands of moderate to heavy rain THU AM
* Drying trend Thu PM from west to east
* Cooler given cold temps aloft


As mentioned in the short term section above, baroclinic s/wv and
attending surface low move across SNE Thu AM. 850 mb Fgen and weak
instability above this layer will yield bands of moderate to heavy
rain at times. Widespread rainfall totals of 0.25 to 0.75 inches,
with local amounts possibly 1+ inches. Could be a slow AM commute
given periods of moderate to heavy rain yielding minor
street/highway flooding.

Mid level trough axis moves east of the region after 18z along with
dry slot ovespreading the area. Thus, drying trends in the afternoon
from west to east, along with a breaks of sunshine possible,
especially late in the day. Much cooler tomorrow given cold pool
aloft, combined with NNE onshore flow along with precip in the AM.
Highs only in the 60s. Coolest along the eastern MA coastline,
especially with NNE winds 15-20 mph providing cool/damp/raw
conditions. Highs closer to 70 in the CT River Valley, including
Hartford and Springfield.

Thursday night...

Mainly dry weather, although clouds and spotty light rain/drizzle
may linger across the outer Cape to Nantucket given moist NNE flow.
Otherwise, dry and cool weather with lows 45-50 most of the region.
Given the cooler regime, we blended in some of the cooler MOS
guidance to derive min temps.


3 PM update...


* High pressure supports mostly dry/quiet weather through the
  middle of next week

* Temperatures gradually increasing through the middle of next week

Through Next Wednesday

The extended forecast looks to be very quiet from Friday forward as
a broad upper-level ridge builds in behind a departing short-wave
trough on Friday afternoon. This will support high pressure at the
surface that will support mainly dry/sunny conditions through at
least early next week. Temperatures will be on the uptick through
this time range as well with seasonable temperatures on Friday in
the low to mid 70s gradually increasing to the mid 80s by next
Tuesday. Low temps will follow a similar pattern with lows in the
upper 40s/low 50s Friday night increasing to the low 60s by
Wednesday morning. The upper level ridge supporting this pattern
looks to possibly breakdown mid to late next week with a potentially
robust upper trough digging down from The Great Lakes. This would be
the next possibility for any active/unsettled weather beyond Friday.


Forecast Confidence Levels:

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

00Z TAF Update: high confidence on trends, lower on exact
timing and details.

After 00z...high confidence, lower on exact timing of details.

VFR and mainly dry, then lowering conditions after midnight to MVFR
as a widespread rain overspreads the region. Light and variable
winds this evening becoming NNE overnight and increasing 10-20 kt.

Thursday...high confidence, lower on exact timing of details.

MVFR in widespread rain in the morning, low probability of IFR over
southeast MA.  Then rain shield slowly exits in the afternoon with
slow improvement to VFR from west to east. NNE winds 10-20 kt.

Thursday night...high confidence, lower on exact timing of details.

MVFR/IFR may linger across Cape Cod and Nantucket. Otherwise, VFR
prevails along with dry weather. NNE winds 10-15 kt.

KBOS TAF...Moderate confidence in TAF. Lowering conditions
after midnight to MVFR with large rain shield overspreading the
terminal. Periods of moderate to heavy rain from 06z to 18z Thu.
Drying trend and improvement for the late day push Thu.

KBDL TAF...Moderate confidence in TAF. MVFR with rain after 03z
and continuing until about 15z Thu. Then slow improvement

Outlook /Friday through Monday/...



Forecaster Confidence Levels:

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

3 PM update...

Tonight...mainly dry and good vsby this evening, then rain
overspreads the waters after midnight. Light onshore winds become
NNE overnight, 15-20 kt.

Thursday...weak/broad low pressure moves over or just offshore, with
NNE winds 15-20 kt across the MA/RI waters, along with reduced vsby
in rain in the morning.  Then slow improvement west to east in the

Thursday night...NNE winds 10-15 kt may yield spotty light
rain/drizzle across the eastern MA waters. Otherwise, dry weather
and good vsby for the RI waters.

Outlook /Friday through Monday/...

Friday through Sunday: Winds less than 25 kt.

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

Monday: Winds less than 25 kt.





NEAR TERM...Nocera/Dooley