-- Discussion containing changed information from previous version are highlighted. --
272
FXUS61 KBOX 121748
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
148 PM EDT Sun May 12 2024

.SYNOPSIS...
Widely scattered showers today along with cooler than normal
temperatures as an upper level low pressure moves over New
England. Chilly night tonight with dry weather, then turning
milder Monday with another round of scattered afternoon showers
possible across the interior. A frontal system may bring more
showers late Tuesday into Wednesday, then drying out for the
end of the week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Updated: 9:45AM

No whole sale changes to the forecast, made a slight change to
the sky cover to reflect the latest satellite trends. Forecast
discussion below remains valid, see for further details.

Previous discussion...

Mid level low and cold pool aloft move into New Eng today but better
moisture and forcing for ascent will be to the south as stronger
shortwave moves to the mid Atlc region. This is where the best
chance of showers will be today. However, steep low level lapse
rates with sufficient moisture in the column will support widely
scattered showers developing, especially in western New Eng where
850-700 mb moisture is greatest. Soundings show rather meager
instability with potential of 100-200 J/kg of CAPE and warm layer
around 700 mb will limit updrafts, so thunder risk is very low.
Another day with below normal temps as 850 mb temps 0 to -1C with
lots of clouds. Highs will range from the mid 50s to around 60.
Winds will be light with sea-breezes developing.

&&

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

Mid level trough axis moves east of New Eng this evening
followed by shortwave ridging and rising heights. Subsidence
and drying will result in partial clearing leading to another
chilly night with lows 40-45.

Monday...

Ridging aloft moves to the east followed by a modest mid level jet
approaching from the west which will increase warm advection.
Sunshine will give way to increasing afternoon clouds. Good moisture
transport and decreasing static stability at the nose of the jet
will result in a few showers moving into the interior during the
afternoon. However, no thunder expected as instability axis remains
well to the west. Warm advection and southerly flow will bring
milder temps into the mid-upper 60s, cooler near the south coast.
S-SW winds 10-20 mph are expected.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Tuesday

Upper level ridge axis begins to slide east as a shortwave trough
exits the Great Plains leaving the region in deep SW flow aloft. WAA
will bring 850 mb temps up from +8C to +12C on Tuesday. This will
help high temps rebound into the mid to upper 70s despite overcast
cloud cover. Precipitation chances remain low Tuesday despite the
WAA due to a couple dry layers in the mid levels. Better precip
chances arrives Tuesday night as better moisture and forcing arrives
from the shortwave.

Wednesday

Shortwave trough exits out of the Ohio River Valley and passes just
south of SNE.  With the best forcing to the south, this has caused
models to trend the associated surface low further south. This shift
south has been a trend with models in this time range over the last
week and wouldn`t be surprised if models keep shifting the low and
QPF south over the coming days. With the shift south, Ensemble QPF
probs for 1 and 2 inches have begun to decrease now showing 20-30%
chance for 1 inch and less then 10% for 2 inches. Depending on where
the surface low tracks, winds could be gusty on Wednesday up to 20-
30mph esspically near the coasts. High temps drop back into the mid
to upper 60s with 850mb temps dropping back to +8C along with rain
and thick cloud cover around much of the day.

Thursday and Friday

Guidance has trended slower kicking out the shortwave as it tries to
cutoff over the mid Atlantic coast. This has resulted in rain
chances lingering into Thursday before an abnormally dry airmass and
NW flow kick in for Thursday afternoon into Friday. High temps both
days should reach the low to mid 70s with mainly sunny conditions.
The only wrench in a nice pleasant end to the week is if the cutoff
stalls just south of the region which would cause NE onshore flow to
bring cooler temps and cloudier skies. This solution remains an
outlier though.

Next Weekend

Another shortwave trough exits the Ohio River Valley sometime
Saturday into Sunday. Guidance remains quite spread on the timing
and amplitude of this shortwave trough. There will likely be a wide
spread rain sometime over the weekend, but its too early to pin down
exact timing and how much will fall. Highs over the weekend look to
remain seasonable in the upper 60s to low 70s.

&&

.AVIATION /18Z SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --
Forecast Confidence Levels:

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


Through 00z...Moderate confidence.

VFR. Widely scattered showers developing across southern New
England, with the greatest concentration across western MA and
NW CT. Light winds S-SE in the afternoon with sea-breezes along
the coast.

Tonight...High confidence in CIGs, but low confidence in fog
formation.

VFR. Low probability for patchy fog possible in prone radiator
locations. Light SW winds.

Monday...Moderate confidence.

VFR cigs. Widely scattered showers possible across northern MA
and interior CT during the afternoon. S-SW wind 10-20 kt with
sea-breezes along the coast.

Monday Night...Moderate confidence.

VFR with localized MVFR possible. S-SW wind 10 kt.

KBOS TAF...High confidence in TAF.

Diurnal VFR cu this afternoon with a low probability of a spot
shower. Opt to leave out of the TAF due to low confidence in
this occurring. ESE wind will continue this afternoon, becoming
S around 00z. Overnight, light WSW wind, will have another sea-
breeze on Monday between 14z and 16z.

KBDL TAF...Moderate confidence in TAF.

Diurnal VFR cu this afternoon, CIGs are between 4-5 thousand
feet through 00z and 02z, during this time a brief light shower
is possible. Wind becomes calm overnight, potentially promoting
areas of fog, confidence in how widespread or dense remains low.
VFR again on Monday with CIGs 4-6 thousand feet. Showers
possible Monday afternoon.

Outlook /Tuesday through Thursday/...

Tuesday: VFR. Breezy. Chance SHRA.

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

Wednesday: Mainly MVFR, with areas IFR possible. Breezy. SHRA
likely.

Wednesday Night: Mainly VFR, with areas IFR possible. Breezy.
Chance SHRA.

Thursday: VFR. Breezy. Slight 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 Monday...

Light winds today but becoming onshore 10-15 kt over the nearshore
waters as sea-breezes develop. Modest SW-W winds tonight becoming S -
SW and increasing to 10-20 kt Mon. SCA will continue over SE waters
for marginal 5 ft seas today, otherwise seas will be below SCA
thresholds.

Outlook /Monday Night through Thursday/...

Monday Night: Winds less than 25 kt.

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

Tuesday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of seas approaching 5 ft. Chance of
rain showers.

Wednesday: Low risk for Small Craft Advisory winds with gusts
up to 25 kt. Local rough seas. Rain showers likely.

Wednesday Night through Thursday: Low risk for Small Craft
Advisory winds with gusts up to 25 kt. Areas of rough seas.
Chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ254-
     255.

&&

$$

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