486
FXUS61 KBOX 121935
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
335 PM EDT Mon Aug 12 2024

.SYNOPSIS...

Scattered brief showers and perhaps a few thunderstorms should
wind down during the first half of the evening. Otherwise...dry
and very pleasant weather is on tap for Tuesday and Wednesday.
Another round of scattered showers and perhaps a few
thunderstorms are possible Thursday. Mainly dry weather probably
returns for Friday...but a frontal system may bring some
unsettled weather by the latter half of the weekend.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...

335 PM Update...

* Scattered Showers/isolated t-storms end this evening
* Otherwise...dry & pleasant tonight with lows mainly in the 50s

Strong northern stream shortwave and cold pool aloft was
dropping southward into the region at mid-late afternoon.
Despite limited surface moisture...the cold pool aloft with 500T
dropping to -18C was resulting in 500 to 1000 J/KG of Cape. This
has allowed scattered brief showers to develop and we may also
see a few t-storms. Not expecting any severe weather...but we
may see small hail/graupel with a few of the stronger storms
given the cold pool aloft. Localized gusty winds are possible
too given a modest T/Td spread...but again not expecting severe
weather.

The scattered activity should wind down during the first half of
the evening with the loss of diurnal heating. Otherwise...a dry
and very pleasant night of weather is on tap. A ridge of high
pressure to our west will allow for skies to become mostly clear
and winds calm to light. This should yield a good night of
radiational cooling with lows by daybreak dropping mainly into
the 50s...but near 60/lower 60s expected in the Urban Heat
Islands of Boston/Providence. Very localized patchy ground fog
may develop in the typically most vulnerable low-lying spots
toward daybreak.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...

Key Points...

* Beautiful & mostly sunny Tue...Highs upper 70s/lower 80s
* Pleasant/Dry Tue night...lows 50s to the lower-middle 60s

Details...

Tuesday...

Upper level trough axis will be east of us on Tue. The result
will be dry/light northwest flow aloft and a very nice mid
August day. 850T on the order of +11C/+12C should result in high
temps in the upper 70s to the lower 80s. Most of the lower
elevations away from the immediate coast should be on the warmer
side of those numbers. However...dewpoints in the 50s will make
for very comfortable humidity levels for this time of year.

Tuesday night...

A ridge of high pressure to our west will remain in control of
our weather Tue night. This should allow for mostly clear skies
along with light to calm winds and another good night of
radiational cooling. Overnight lows should be in the 50s to the
lower to middle 60s in some of the urban centers. Very localized
patchy ground fog may develop in the typically most vulnerable
spots toward daybreak.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...

Key points:

* Work week continues to look dry with seasonable temperatures,
  aside from the chance of showers on Thursday

* Timing still not set for a frontal system moving through sometime
  this weekend/early next week, but starting to look more probable
  Saturday morning.

* Continuing to monitor Potential Tropical Cyclone 5 (PTC 5) for
  risk of high surf and rip currents this weekend. Please see the
  NHC Advisories for more information on this system.

Models continue to support the previous discussion`s assessment of
the rest of the work week; we continue to sit under cyclonic flow
aloft with high pressure at the surface. Expect to continue seeing
clouds move in and out during the day with high temperatures
remaining primarily in the upper 70s into the mid-80s and lower
relative humidities. Thursday still looks to have a good chance at
some showers this week. Some of the guidance is suggesting some
favorable mid-level lapse rates and slightly elevated CAPE values
for some more elevated convection, particularly in the Worcester
Hills and other higher terrain. PWATs look to be seasonably normal
and not indicative of any widespread downpours, so the main concern
is just some isolated thunderstorms over higher terrain areas on
Thursday afternoon into the evening.

This weekend into early next week continues to have a good chance at
more widespread showers with a strong frontal system coming in. The
12z GFS is starting to move more in agreement with the 12z runs for
the Canadian GEM and the ECMWF on timing for this front: the
international models favor Friday night for it to start going into
western MA and through central CT, and the GFS is favoring a couple
hours later into Saturday morning. Some disagreement about whether
or not this rain will continue into Monday, but most of the guidance
seems to favor rain continuing for most of the weekend. Did not put
PoPs higher than a chance for the time being through the weekend
into Monday.

We are continuing to monitor PTC 5 for a chance at seeing some
higher surf and strong rip currents, particularly along the South
Coast and the southern coastlines of the Islands. Both NBM and ECMWF
WAVE guidance seem to favor larger swells Sunday into Monday next
week. This storm is still forecast to stay well offshore and far
from southern New England, but it is still a bit early to get more
specific regarding any possible impacts for southern New England and
the forecast is very much subject to change. For more information
on the latest forecast for PTC 5, please check nhc.noaa.gov.

&&

.AVIATION /19Z MONDAY THROUGH SATURDAY/...

Forecast Confidence Levels:

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

18z TAF Update...

This afternoon...High Confidence.

VFR outside briefly lower conditions in scattered showers and
perhaps a few t-storms. W winds 5 to 15 knots.

Tonight...High Confidence.

Scattered showers should wind down quickly early this evening.
Otherwise...VFR with perhaps brief/very localized fog
developing toward daybreak in the typically lowest lying
locations. Calm/Light NW winds.

Tuesday...High Confidence.

VFR. NW winds 5 to 10 knots although winds should shift to more
of a SW direction late in the day near the I-95 corridor.

Tuesday night...High Confidence.

VFR with perhaps brief/very localized fog developing toward
daybreak in the typically lowest lying locations. Calm/Light NW
winds.

KBOS TAF...High Confidence.

KBDL TAF...High Confidence.

Outlook /Wednesday through Saturday/...

Wednesday through Wednesday Night: VFR.

Thursday: VFR. Chance SHRA, isolated TSRA.

Thursday Night: VFR. Slight chance SHRA.

Friday through Friday Night: VFR.

Saturday: VFR. Chance SHRA.

&&

.MARINE...

Forecaster Confidence Levels:

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

Tonight through Tuesday night...High Confidence.

A ridge of high pressure to our west will result in pleasant
boating weather winds/seas below small craft advisory thresholds
through Tuesday night. Vsbys should be quite good as well.

Outlook /Wednesday through Saturday/...

Wednesday through Wednesday Night: Winds less than 25 kt.

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

Thursday Night through Friday Night: Winds less than 25 kt.

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

&&

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

&&

$$

SYNOPSIS...Frank/CH
NEAR TERM...Frank
SHORT TERM...Frank
LONG TERM...CH
AVIATION...Frank/CH
MARINE...Frank/CH