-- Discussion containing changed information from previous version are highlighted. --
362
FXUS61 KBOX 111055
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
655 AM EDT Sat May 11 2024

.SYNOPSIS...
A ridge of high pressure builds into New England today with dry but
cool conditions. An upper level low pressure may bring a few hit or
miss showers Sunday but a mostly dry day with below normal
temperatures. Milder next week with the risk for showers increasing
Tuesday into Wednesday, then mainly dry and seasonable toward the
end of next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Mid level trough will be exiting to the east by daybreak while
upstream trough moves through the Gt Lakes today. Subsidence and
weak ridging aloft between these 2 systems will result in a mainly
dry day today. Plenty of sunshine to start the day away from the
Cape/Islands, but lingering low level moisture and somewhat cooler
air aloft will result in diurnal cu developing this morning and
expanding across the region leading to mixed clouds and sun. Can`t
rule out a spot shower this afternoon in western New Eng where steep
low level lapse rates develop, but otherwise it`s a dry day. 850 mb
temps around 0C today so below normal temps with highs mid ranging
from mid 50s east coastal MA to low-mid 60s CT valley with E-NE
flow.

&&

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

The mid level trough over the Gt Lakes moves east and
approaches New Eng tonight with cooling temps aloft. Clouds
will increase ahead of the system and may see a few showers in
western New Eng late tonight, but otherwise a dry night. Lows
mostly between 40 and 45.

Sunday...

The mid level trough and cold pool moves overhead during Sun with
500 mb temps near -25C. Brunt of shortwave energy will be moving
from the Gt Lakes to mid Atlc region where best chance for showers.
This is where moisture and limited instability is greatest. There is
no instability in SNE and moisture is limited, but cold pool aloft
will help to generate a few showers, mainly in western New Eng, but
dry most of the time with mostly cloudy skies. Another cool day with
850 mb temps 0 to -1C. Highs will be mostly in the mid-upper 50s
with light winds and sea-breezes developing.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Key Points:

* Warming trend this week with more seasonable highs

* Dry much of Monday and Tuesday

* Next best chance for rain Tuesday night into Wednesday

Monday - Wednesday

Upper level closed low and cold pool finally move out of the region
to the NE while a weak ridge and high pressure extend north from the
Mid Atlantic. Some guidance shows low chances for showers late
Monday into Tuesday especially with warm air advection kicking in.
However, rising heights and dry mid levels should suppress rain
activity from becoming more then just an isolated shower. Better
moisture and forcing doesnt arrive until late Tuesday into Wednesday
as a decaying shortwave trough and associated surface low exits out
of the Ohio River Valley and passes just south of the region. Still
considerable uncertainty with how far north the track of the center
of low pressure goes with much of the shortwave forcing remaining
south of the region again. Even if the low stays south of the
region, thinking there will still be wide spread rain across the
region as the warm front stalls over the region. PWATS increase to
1.25-1.5 inches Tuesday night into Wednesday ahead of the shortwave
trough. Ensemble QPF remains rather spread due to the uncertainty in
the track of the low. 24 hour LREF 25th-75th percentiles show a
widespread 0.25-1.0 inches is possible with low probs up to 10% for
2 inches mainly along the south coast. Not too concerned about
convection or thunder chances at this time with models keeping
instability south of the surface low in its warm sector. High temps
Monday and Tuesday recover into the upper 60s to low 70s, but remain
more uncertain for Wednesday where temps could range from the upper
50s to upper 60s depending on how long rainfall lasts into
Wednesday.

Thursday and Friday

Upper level ridge and surface high pressure build in behind the
shortwave which should allow for dry conditions Thursday into Friday.
There is some considerable differences in the GFS and EURO due to
the EURO creating a cutoff low just south of the region. This cut
off could keep the very dry airmass from over southern Canada from
reaching into SNE. Either way, temps Thursday and Friday look to
reach the low to mid 70s.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
Forecast Confidence Levels:

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


Today...High confidence.

VFR cigs across the region, but MVFR persists at ACK and HYA.
Stratocumulus will form and may bring brief periods of MVFR
ceilings as they could form anywhere from 2000-4000ft. E-NE
winds 10-20 kt, gusts to 25 kt at ACK.

Tonight...Moderate confidence.

VFR cigs, but MVFR may develop across the CT valley and
Cape/Islands late tonight. Light winds.

Sunday...Moderate confidence.

Mainly VFR cigs, but areas of MVFR and scattered showers
possible across western MA/CT. SE wind 5-10 kt with sea breezes
developing.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Sunday Night through Wednesday/...

Sunday Night through Monday: VFR.

Monday Night: Mainly VFR, with local MVFR possible. Breezy.
Slight chance SHRA.

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

Tuesday Night: Mainly MVFR, with areas IFR possible. Breezy.
SHRA likely, isolated TSRA.

Wednesday: MVFR/IFR conditions possible. Breezy. Chance SHRA.
-- End Changed Discussion --

&&

.MARINE...
Forecaster Confidence Levels:

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

Through Sunday...

A brief period of 25 kt NE wind gusts possible this morning across
the SE waters as low pres makes its closest approach to the southern
waters. Otherwise NE winds 10-20 kt today diminishing and becoming
light tonight and Mon as weak high pres moves over the waters. Winds
will become onshore over the nearshore waters Sunday as sea-breezes
develop. SCA for SE waters through tonight for 25 kt gusts this
morning and 5 ft seas lingering into tonight.

Outlook /Sunday Night through Wednesday/...

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

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

Monday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers.

Tuesday: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of seas approaching 5 ft. Slight
chance of rain showers.

Tuesday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 25 kt. Seas up to 5 ft. Chance of rain
showers.

Wednesday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Seas up to 5 ft. Chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 AM EDT Sunday for ANZ254-255.
-- End Changed Discussion --

&&

$$

SYNOPSIS...KJC/KP
NEAR TERM...KJC/KP
SHORT TERM...KJC
LONG TERM...KP
AVIATION...KJC/KP
MARINE...KJC/KP