245
FXUS61 KBOX 200211
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1011 PM EDT Fri Jul 19 2024

.SYNOPSIS...
High pressure will build southeastward tonight into early on
Saturday. While this will bring a modest increase in cloud cover
for Saturday, dry weather, seasonably warm temperatures and
lower humidity levels through the weekend. Pattern then turns
more active again next week, with humidity levels on the rise.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
10 PM Update...

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

200 PM Update:

Beautiful midsummer afternoon underway across Southern New
England under surface ridge of high pressure. Current temps are
in the upper 70s to the lower 80s under full sunshine, but also
with low humidity levels (dewpoints commonly in the 50s).

High pressure will continue to be in control for tonight as
well. Will have more of an increase in high clouds with some
higher level moisture advecting in from the SW late tonight and
overnight but dry weather is expected. Used MOS for nighttime
lows in the mid 50s to lower 60s for most, with mid 60s for the
Cape and Islands and the urban corridors.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
200 PM Update:

Saturday and Saturday Night:

High pressure to our south will bring a SWly flow to the region
for Saturday, with a passing cool front well to our north in
northern portions of VT/NH/ME for Saturday evening. The
increasing higher level cloud cover from tonight will continue
to increase further on Saturday as well, towards a filtered sun
or at worst a mix of clouds and sun. A few models were
generating some QPF in portions of western CT associated with a
low-amplitude 500 mb disturbance in the SW flow, one which is
also expected to shearing out and weaken; with drier air in the
lower atmosphere, opted for dry weather to prevail. Though cloud
cover decreases more into Saturday evening, still will be a
partly cloud evening. Dewpoints also start to rise back into the
mid 60s, so turning a touch more humid but nothing like we saw
for much of last week. Highs Saturday in the mid to mid/upper
80s (upper 70s to low 80s coasts), with lows in the mid 60s to
around 70.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Highlights

* Dry and quiet weather Sun and for much of Mon. Humidity levels
  beginning to climb on Mon.

* Active pattern returns Tue through Fri with opportunities for
  showers and thunderstorms. Humidity levels turning uncomfortable
  once again.

Sunday through Monday...

Not much of a change from 24 hours ago. Will initially have a ridge
axis extend from the Carolinas into the OH Valley and troughing over
Quebec. This keeps us under cyclonic flow. The ridge builds into the
Mid Atlantic/eastern Great Lakes by early Mon, but flattens out as
the day progresses as a shortwave rides on top of the ridge. A weak
surface trough/cold front slides through on Sun into Mon. A weak
high builds in behind this front on Mon.

Generally expect dry and quiet weather to prevail throughout this
timeframe. At this point haven`t deviated from the NBM as it looks
quite reasonable. There does appear to be an opportunity late on Mon
where portions of the interior could see an isolated shower/storm.
This is a result of the ridge breaking down and a weak shortwave
sliding in. Given the position of the high by later on Mon we will
see a return to southerly flow, which will bring more moisture into
our region. However, there really a lack of a trigger mechanism for
this activity other than perhaps diurnal heating as low level lapse
rates increase to 7-9 degrees Celsius. Thus the isolated
shower/thunder chance fine at this point. Not anticipating severe
weather as mid level lapse rates are very meh and MUCAPEs of a few
hundred J/kg. Though will be something to keep an eye on as deep
layer shear around 30-40 kts in the 0-6 km layer. Highs in the mid
to upper 80s on Sun. Still in the 80s on Mon, but should be a few
degrees cooler than Sun.

Tuesday through Friday...

More active pattern setting up during this timeframe. Will be stuck
under cyclonic flow with a couple of shortwaves sliding into/through
our region. Confidence in the specific timing of these waves is
somewhat uncertain and how things evolve convectively. Due to this
have stuck with the NBM at this point.

Unsettled with opportunities for showers and thunderstorms during
this period. Given the pattern will have a somewhat stalled out
frontal boundary nearby/overhead. Will continue to see moisture
levels increase with dew points climbing into the upper 60s and
lower 70s. Expect PWATs to increase to roughly 1-2 STD above model
climo per the NAEFS, while the EPS is a bit more juiced up as we
climb to roughly 1.5 to 2.5 STD. Could have PWATs of 1.5 to 2+
inches. Should have warm cloud layer depths of 2.5 to 4.5 km. Though
the higher warm cloud layer depths come mostly in the Wed-Fri
timeframe. Given this set up could have some heavy downpours. This
matches WPCs latest Day 5 ERO and CSU ML guidance UFVS in the Tue-
Wed period. Cannot rule out some stronger storms as well as will
have increasing deep layer shear and instability. Do have hints at
the risk with CSU ML guidance indicating low probs (5-15%) in the
Wed-Thu timeframe. Something to keep an eye on.

&&

.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:

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

Tonight through Saturday...High confidence.

VFR, with increasing mid to high clouds late tonight into
Saturday. Winds become light southerly tonight in all areas,
with SW speeds Saturday daytime around 5-10 kt (gusts 15-20 kt
Cape and Islands).

Saturday Night...High confidence, though moderate on fog
development.

VFR for most; PVD and the Cape/Islands could see patchy fog,
but uncertain if it develops. SW winds around 5 kt.

KBOS TAF...High confidence in TAF.

VFR thru the period. SE seabreezes to shift to light S winds by
00-01Z, then increasing to around 5-10 kt on Sat and shifting to
SW.

KBDL TAF...High confidence in TAF.

VFR thru the period. Variable winds shift to SW at 5-10 kts by
Sat afternoon.

Outlook /Sunday through Wednesday/...

Sunday through Monday: VFR.

Monday Night: VFR. Slight chance SHRA, isolated TSRA.

Tuesday: VFR. Chance SHRA, isolated TSRA.

Tuesday Night: Mainly VFR, with local IFR possible. Chance
SHRA.

Wednesday: Mainly VFR, with local IFR possible. SHRA likely,
isolated TSRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

200 PM Update:

Through Saturday Night: High confidence.

Favorable boating conditions for mariners with light north winds
early tonight becoming a light southerly (speeds 10 kt or less).
Will turn a little breezy on Saturday especially over the
nearshore waters, with SW speeds around 15-20 kt during the
daytime hrs; decreasing to 10 kt or less Saturday evening. Seas
3 ft or less all waters. Dry weather to prevail, although there
is a low chance for patchy fog Saturday evening on the southern
waters.

Outlook /Sunday through Wednesday/...

Sunday through Monday Night: Winds less than 25 kt.

Tuesday: Winds less than 25 kt. Slight chance of rain showers,
isolated thunderstorms.

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

Wednesday: Winds less than 25 kt. Seas locally approaching
5 ft. Chance of rain showers, isolated thunderstorms.

&&

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

&&

$$

SYNOPSIS...Loconto/BL
NEAR TERM...Loconto/BL/KP
SHORT TERM...Loconto
LONG TERM...BL
AVIATION...Loconto/BL
MARINE...Loconto/BL