349
FXUS61 KBOX 070802
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
402 AM EDT Tue May 7 2024

.SYNOPSIS...
Warm and dry conditions today with high pressure in control. A
warm front will bring a round of showers and isolated
thunderstorms very late tonight and Wednesday, with a low risk
for a few strong thunderstorms in western MA/CT Wednesday
afternoon. Unsettled pattern continues for the end of the week
into the weekend with the risk of occasional showers and cooler
temperatures.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
High pres in control today with subsidence and low PWATs bringing
abundant sunshine. However, fog and stratus may linger into the
start of the day for the Cape/Islands before clearing by late
morning. A warm day in store today as 925 mb temps 16-17C support
highs mid-upper 70s across much of SNE away from the coast, with a
few locations in CT valley possibly reaching 80. Light NW flow in
the boundary layer will allow sea breezes to develop which will keep
temps in the upper 60s along the immediate coast.

&&

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

Deamplifying upper ridge moves E from the Gt Lakes with weak
shortwave energy spilling into SNE late tonight, while more potent
trough and shortwave moves into the Gt Lakes. A warm front will
approach SNE from the SW with low level SW flow increasing moisture
transport into SNE as PWATs increase to 1-1.50" by 12z Wed.
Scattered showers may spill into western MA/CT toward daybreak in
response to the moisture increase. Lows will be mostly in the upper
40s and lower 50s. Patchy fog and stratus will redevelop over
Cape/Islands but should remain confined to this area.

Wednesday...

Key points...

* Showers and a few t-storms in the morning
* Low risk for a few strong to severs storms in western MA/CT during
  the afternoon

Deep moisture plume ahead of the warm front along with increasing
elevated instability will result in a round of showers moving across
SNE during the morning, with a few t-storms possible as well. Looks
like a wet morning, especially interior. Dry slot quickly moves in
from the west during the afternoon which should yield drying
conditions, but potent shortwave will be moving into New Eng during
the afternoon which will result in scattered showers and a few t-
storms developing ahead of the attendant cold front. Much of the
convection should be elevated but depending on location of warm
front and how far north and east it gets, surface based convection
is possible in a portion of SNE, especially western areas where
HREF highlighting max updrafts.

Increasing mid level winds will lead to a strongly sheared
environment with 0-6km shear 50-70 kt, but instability will be a
limiting factor as not expecting much sunshine. Steepening mid level
lapse rates will help to generate marginal SB instability with CAPES
around 500 J/kg. Best chance for a few strong to severe storms will
be in western MA/CT near the warm front. CSU ML probs and SPC SREF
highlight this area for a low risk for severe, and NCAR Neural
Network also indicating low probs for severe. SPC has western half
of SNE in a marginal risk. Severe risk will be dependent on
sufficient SB instability developing which is uncertain at this
time.

Temp forecast will be tricky due to the uncertainty in the location
of the warm front. Best chance of temps reaching 70+ will be in
western CT with 60s for rest of interior, while upper 50s more
likely across eastern MA.

&&

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

* Several disturbances will bring periods of rain Thursday through
  early next week.

* Timing, strength, and location of these disturbances remain highly
  uncertain.

After a nice start to the week weather wise, things begin to take a
turn off the deep end for the remainder of the week into the
weekend. An upper level trough begins to deepen on Thursday
eventually becoming a closed trough and stalling out over the region
through the weekend. This leaves the region under cyclonic flow
sending multiple rounds of shortwave energy through the region.
Deterministic and ensemble guidance remain very spread out and
confidence in any one model remains low for much of this time
period. The first round of precipitation looks to come through
sometime Thursday into Friday as a low pressure center passes nearby
the region. The GFS shows a wetter and slower moving system with a
stronger low to the north and a secondary low forming to the south.
The EURO is more progressive with less QPF and the primary low
passing just offshore to the south. Meanwhile, the NAM and Canadian
models have little to no precipitation Thursday with high pressure
dipping south from Canada pushing the low well offshore to the
south. Ensembles also remain very spread out which is why 24 hour
probs for 0.5 inches of rain are less then 50% despite PWATS around
1.1-1.3 inches and good forcing from the upper level trough.
Confidence in the forecast drops even further into the weekend as
guidance continues to struggle with placement and timing of a potent
surface low ejecting out of the Carolinas before moving north.
Latest guidance now keeps this low well offshore, however, there has
been little run to run consistency in this time range and will need
to be monitored closely.

The area of the forecast that is more certain is that temperatures
will be taking a dive off the deep end this week as the cold pool
from the closed low get stuck over the region. Highs Thursday remain
the most uncertain as flow becomes onshore, but timing of when
onshore flow begins is a bit more uncertain. If winds hold off from
turning ENE until late in the day Thursday, High temps could reach
the low to mid 70s esspically over the CT River Valley. However, if
winds turn ENE early in the day, highs likely remain in the mid to
upper 60s, with mid 50s near the coast. Friday is looking like the
coldest day of the week due to low cloud cover and onshore flow.
Highs on Friday possibly do not top 60F region wide. Surface winds
turn more southerly over the weekend which will allow high temps to
moderate a bit into the mid 60s.

&&

.AVIATION /08Z TUESDAY THROUGH SATURDAY/...
Forecast Confidence Levels:

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

Through 12z...

Areas of IFR-LIFR fog over Cape/Islands, otherwise mainly VFR.
But patchy radiation fog possible in the typical locations.

Today...High confidence away from the Cape/Islands. Moderate
confidence for the Cape/Islands.

VFR for most of the region. Stratus and fog Cape Cod and
Islands will lift with improvement to VFR 14-16z, but timing is
uncertain. ACK may only briefly break out to VFR for a few
hours after 18z before stratus and fog returns toward evening.
NW wind 5-10 kt with sea breezes developing along the coast.

Tonight...Moderate confidence.

Stratus and fog with IFR-LIFR redeveloping over Cape/Islands,
with mainly VFR elsewhere. Scattered showers moving into western
MA/CT 09-12z.

Wednesday...Moderate confidence.

MVFR-IFR expanding across all SNE as showers and isolated
t-storms move across the region through the morning. Decreasing
coverage of showers in the afternoon, but a few t-storms may
develop in the interior mid-late afternoon. S-SE wind 5-10 kt.

KBOS TAF...High confidence in TAF. VFR. Sea breeze developing
by 15z.

KBDL TAF...High Confidence in TAF. VFR.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: Mainly VFR, with local IFR possible. Breezy.
Slight chance SHRA.

Thursday: Mainly VFR, with local IFR possible. Chance RA.

Thursday Night through Friday Night: MVFR/IFR conditions
possible. Breezy. Chance RA.

Saturday: Mainly VFR, with local IFR possible. Breezy. Chance
RA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Through Wednesday...High Confidence

Winds and seas below SCA thresholds through the period. Onshore
winds developing today over the nearshore waters as sea breezes
develop. S-SE winds 10-15 kt Wed. Fog may reduce vsbys this morning,
then showers develop Wed morning.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: Winds less than 25 kt. Chance of rain showers.

Thursday: Winds less than 25 kt. Chance of rain.

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

Saturday: Winds less than 25 kt. Areas of rough seas. Slight
chance of rain.

&&

.TIDES/COASTAL FLOODING...
High astro tides this week and concern becomes late Thu into
Fri with potential frontal wave tracking south of New England,
generating onshore flow into eastern MA. Magnitude of potential
inundation and erosion will depend on strength and timing of
surface low. Too early for specifics with any certainty, but
given astro tides are already over 11 ft at Boston, it will only
take a 1 ft storm surge and modest wave action to yield minor
inundation and erosion. Stay tuned throughout the week for
updated information.

&&

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

&&

$$

SYNOPSIS...KJC/KP
NEAR TERM...KJC
SHORT TERM...KJC
LONG TERM...KP
AVIATION...KJC/KP
MARINE...KJC/KP
TIDES/COASTAL FLOODING...BL