921
FXUS61 KBOX 300537
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
137 AM EDT Tue Apr 30 2024

.SYNOPSIS...
A backdoor cold front will bring much cooler conditions,
clouds, and spot showers tonight and Tuesday morning.
Unsettled mid to late in the week due to a backdoor cold front
nearby. This could bring spotty showers and keep us a bit
cooler, but there is a significant amount of uncertainty with
the fronts location. Better shot for more widespread showers
late Saturday into Sunday as a frontal system slides through.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
730 PM Update...

Forecast remains on track. No changes in the latest update.

Previous discussion...

Backdoor front across SNE will move south and west of the region by
early this evening with cooler airmass continuing to advect into the
region. The front will stall to the west across eastern NY and while
there will be no surface instability, the cool air is relatively
shallow and higher 850 mb theta-e air will support marginal elevated
instability in western New Eng tonight. Expect a few showers
developing in western MA and northern CT in the vicinity of the low
level boundary, and can`t rule out an isolated t-storm given MUCAPES
200-500 J/kg. Lows will be mostly in the 40s, but close to 50 in the
CT valley.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM WEDNESDAY/...
Tuesday...

We may see a few lingering showers across the interior in the
morning and perhaps an isolated t-storm in western MA and northern
CT, otherwise it should be a mainly dry day as somewhat drier air
advects in from the SW. However, plenty of low level moisture in
place with easterly BL flow will result in lots of clouds. Much
cooler day with highs generally in the 50s, ranging from around 50
across east coastal MA to perhaps the lower 60s in the lower CT
valley from Hartford to Springfield.

Tuesday night...

Mid level shortwave will move across New England Tue evening and
will likely result in a period of showers as weakening convection
moves in from the west. CAMs are rather active with showers and
storms developing across central and eastern NY Tue afternoon which
will weaken as they move into stable environment in SNE during Tue
night. Otherwise, moist boundary layer will support stratus and
perhaps some patchy fog. Lows will be in the 40s.

&&

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

* Low confidence in the extended with a frontal boundary lingering
  nearby Wed through Fri. Generally think it will be dry, but light
  spotty showers cannot be ruled out. Temps near to below normal.

* Unsettled, especially late this weekend as a frontal system slides
  in. This brings a better shot for heavier showers.

Wednesday through Friday...

Mostly will have ridging in place to our west through much of this
timeframe. Initially starting off with a shortwave ridge over the
eastern Great Lakes early on Fri. The ridge builds into Northern New
England, while another ridge builds into the OH Valley/Great Lakes
region by Wed night. The second ridge over the OH Valley/Great Lakes
builds into the eastern Great Lakes on Thu, but a shortwave slides
across Quebec into northern New England late on Thu. The ridge
continues to build over the eastern Great Lakes/Mid Atlantic on Fri,
while the trough digs across the Gulf of ME/Nova Scotia. A frontal
boundary will be nearby/over the region through the vast majority of
this timeframe.

Confidence in the forecast quite low at this point in time given the
details are mostly in the mesoscale. The exact location of the front
will be key in determining precip chances along with temps we
realize. Leaned heavily on probabilistic guidance at this point
where the GEFS/EPS and GEPS guidance indicate mod to high (40-90%+)
probs of precip AOA 0.01 inches. The best chance is on Wed with
essentially 100% probs. Probs are lower at 40-70% on Thu/Fri where
the high may be more overhead, but am leery to jump on it being dry
with a front nearby/sliding through. Deterministic guidance also a
bit all over the place, but shows the best shot on Thu as that
shortwave is sliding through. Uncertain, so have stuck with the NBM
at this point.

Due to uncertainty with the position of the front have also stuck
with the NBM for temperatures through this period. If we can get
into westerly flow temps could climb into the 70s, especially across
the interior on Thu. The GEPS/GEFS/EPS guidance are low to mod (10-
50 % chance) of temps AOA 70 degrees on Wed-Fri. Best shot is across
the interior on Thu with little to no shot on Wed/Fri.

Saturday through Sunday...

Ridge axis in place over the eastern Great Lakes/Upstate NY on Sat.
Will have a the ridge building offshore on Sun. During this
timeframe a shortwave may ride the ridge later on Sat into Sun. A
deeper trough may lift in later on Sun, but there is a lot of
uncertainty in its timing/intensity and placement.

Appears that it could be drier for a good part of Sat before the
frontal system works its way in from the west into Sun. At this
point think that Sat could be dry with the showers returning Sun,
but just too much uncertainty given not sure how things will evolve
even in the previous period. Should note that PWATS are elevated for
the BOX area per NAEFS/EPS situational awareness tables. Values are
around 1-1.5 STD above model climo. This in combination with the
frontal system sliding through could bring some heavier showers.
Again have stuck with the NBM for now. Temperatures will be near to
below seasonable.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
Forecast Confidence Levels:

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

06Z TAF Update

Through 12Z... high confidence in flight categories, moderate
confidence in precipitation potential.

VFR for locations east of ORH continue through morning with MVFR
at and west of ORH. Generally light easterly winds at the
terminals. A few showers with perhaps VCTS is possible at and
west of ORH but confidence is low as and thunderstorms should be
isolated in nature. Have only mentioned VCSH in the 06Z TAFs.

Today... High confidence.

MVFR ceilings continue to stay focused generally west of the
I-495 corridor. Persistent easterly winds. East of I-495 expect
mid-level clouds around 050 for the day with some possible
breaks above 10 thousand feet during the afternoon over The
Cape/Islands terminals.

Tonight.. Moderate confidence.

IFR/MVFR ceilings overspread the rest of southern New England
overnight. Winds persist out of the east through about 06Z
before shifting northeast between 06 and 12Z. Expect periods of
SHRA between 00 and 06Z.

Tomorrow... Moderate confidence

MVFR/IFR conditions should persist through late morning with
some improvements to VFR possibly during the early to mid
afternoon hours. Northeast winds become more easterly by the
evening hours.


KBOS TAF...High confidence in VFR, moderate confidence on
afternoon cloud bases.

Generally onshore flow prevails through the TAF period with a
steady sea-breeze settling in by 15Z. High confidence in VFR
ceilings. While cloud bases are generally expected to persist
around 5000 feet, there is expected to be a region of higher
bases over east/southeast MA this afternoon. Not expecting the
higher bases to extend north over BOS, but can`t rule out the
possibility of higher cloud bases up to 10000 feet after 18Z
before falling back to MVFR/IFR tonight.

KBDL TAF...High confidence in TAF.

MVFR persists today before possible deterioration to IFR
overnight. Some showers and a rumble of thunder possible over
the next couple of hours (06-09Z).

Outlook /Wednesday Night through Saturday/...

Wednesday: Mainly VFR, with local IFR possible. Chance SHRA.

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

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

Thursday Night: VFR. Slight chance SHRA.

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

Friday Night: Mainly VFR, with areas MVFR possible. Breezy.
Chance SHRA.

Saturday: Mainly VFR, with local MVFR possible. Chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Through Tuesday night... High confidence.

Easterly flow develops tonight and continues into Tue night with
speeds 10-15 kt and gusts to 20 kt at times. Seas below SCA
thresholds.

Outlook /Wednesday Night through Saturday/...

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

Wednesday Night through Friday: Winds less than 25 kt. Slight
chance of rain showers.

Friday Night through Saturday: Winds less than 25 kt. Chance of
rain showers.

&&

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

&&

$$

SYNOPSIS...KJC/BL
NEAR TERM...KJC/BL
SHORT TERM...KJC
LONG TERM...BL
AVIATION...BL/RM
MARINE...KJC/BL