BOX issues Area Forecast Discussion (AFD) at Jul 27, 3:39 AM EDT765
FXUS61 KBOX 270739
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
339 AM EDT Sat Jul 27 2024
.SYNOPSIS...
Dry and seasonably warm conditions will continue through the
weekend. Low pressure approaching from the ocean may bring scattered
showers and perhaps a thunderstorm Sunday night and Monday along
with cooler temperatures. It then turns warmer and much more humid
Tuesday through Friday, with daily chances at showers and
thunderstorms.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Today is essentially a copy-paste forecast from yesterday as surface
high continues to build over southern New England. Much weaker
pressure gradient will yield climatological seabreezes along the
coast; with development expected between 15-16z. Away from the
coast, weak north/northwest flow will persist. 850mb temperatures
between 13-15C continue to support highs in the low to mid 80s,
which combined with dewpoints in the mid 50s will yield a near
perfect summer day! Some diurnal cumulus development around 7000ft
is again expected due to persistent mid level cold pool centered to
our northwest.
Some smoke aloft was visible yesterday, but the HRRR shows the best
concentrations of smoke (>30-40 micrograms/m3) will be centered over
southern Quebec and norther New England. Thus, expect less of a
"hazy" appearance to the sky today, especially across SE MA and
RI.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
Tonight...
Surface high remains in place tonight as mid level
ridging continues to build northeast. Do expect decent radiational
cooling overnight with near calm winds, which will allow temps to
fall into the 50s/60s once again. With dewpoints acting as the lower
bound for temps, patchy fog is possible in our typically prone
locations. Will note that winds shift to the SE/S after sunset which
will cause dewpoints/PWATs to surge ever so slightly, to around 1"
along the south coast/Cape/Islands, between 00-06Z tonight. This may
result in more widespread fog development across our marine zones
and along the immediate coastline. The NAM, per usual, is very
aggressive in the development of marine stratus/reduced vsbys
overnight, so while the geographic extent of the fog may be overdone
by the model, it's worth mentioning the increased potential for our
south facing coast.
Sunday...
Weak mid level trough that generated scattered diurnal
cumulus on Friday and Saturday births a cutoff low centered south of
the benchmark between 00Z and 12Z tonight. surface low will begin to
retrograde towards the region during the day on Sunday, which will
increase clouds from southeast to northwest through the day; though
am wagering to bet that portions of NW MA remain mainly sunny until
late Sunday afternoon. The northwestern extent of the Sunday evening
rain shield will be highly dependent on the position of the low. At
present, the NAM and GFS forecast the center of the low to be well
east of the benchmark, which would delay the arrival of showers
until well after 00Z. Conversely, the Canadian and ECMWF forecast a
low center much closer to the benchmark around 21Z Sunday, which
would lead light showers prior to 00Z. Given model spread, can't
rule out a few showers between 5-8pm Sunday, but more clarity will
be gained over the next 36 hours. For reference, ECMWF probs of 0.1"
of QPF at ACK at 00Z Monday are around 20%, and near 0% on the GEFS.
All in all, Sunday looks to be a fine day for outdoor activities
with highs in the 80s and several hours of dry weather.
Will note that this system doesn't look overly impressive in its
precipitation potential given PWATs of around 1.5" (essentially the
climatological average for this time of year). More details
regarding the impacts from this approaching low can be found in the
long term discussion below.
&&
.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Key Points...
* Scattered showers developing in eastern New Eng Sun night,
expanding across rest of SNE Monday with low risk for thunder
* Much more humid with unsettled pattern Tue through Fri with daily
chances for showers and t-storms
Details...
Sunday night into Monday...
Quasi-stationary upper low will be meandering over the ocean south
of New Eng Sun night before drifting north into SNE during Mon. The
surface low is expected to the east of the benchmark Sun evening
then get pulled westward toward the eastern MA coast. The track of
the upper low and accompanying cold pool remains uncertain and this
will determine areal coverage of showers. It does appear showers
will be mostly confined to eastern half of New Eng Sun night as deep
moisture plume moves in from the east. Then expect risk for
scattered showers to expand across rest of SNE during Mon in the
vicinity of the cold pool, but areal coverage uncertain. Can't rule
out isolated thunder late Sun night and especially Mon as cooling
temps aloft help with destabilization, but favored location of
thunder will depend on the cold pool location. PWATs will be near
climatological normals so not expecting any significant rainfall.
Cooler temps likely Mon with extra cloud cover, with highs mostly in
the 70s in eastern New Eng and lower 80s further inland.
Tuesday through Friday...
The upper low will be lifting to the north on Tue followed by
another upper trough moving east from the Gt Lakes. Moist SW flow
aloft will result in increasing PWATs along with modest diurnal
instability leading to daily chances of showers and t-storms.
Pinning down the timing of convection will be very difficult in this
pattern but wet weather will be favored more so during the
afternoon/evening due to diurnal instability, and given increasing
PWATs there will be potential for locally heavy downpours. We
followed NBM PoPs which favor interior locations for best
chance of showers and t-storms.
Humidity levels will be on the rise through the week as PWATs
increase and likely looking at 70 degree dewpoints by Tue and into
the 70s Wed through Fri. Highs expected to be mostly in the 80s but
could reach 90 in a few locations away from the coast toward the end
of the week which would result in mid-upper 90s heat indices
developing.
&&
.AVIATION /07Z SATURDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
06Z TAF Update:
Through Sunday: High Confidence
VFR with light WNW/NW winds across interior southern New
England. Climatological coastal sea breezes very likely between
15-16Z as winds shift more easterly. Winds become SE to SSW
after sunset this evening.
Low probability of marine stratus/fog over the Islands after 06Z
tonight. VFR returns early Sunday morning. Tracking low pressure
that will advect increasing clouds over the region Sunday but
anticipate conditions will remain VFR. Winds will shift to the
east as low pressure approaches, any may gust as high as 25kt
across the Cape and Islands by 00Z Monday.
KBOS TAF...High confidence in TAF. VFR. Climatological seabreeze
likely today between 15-16Z. Winds shift to the SE after 00Z
tonight.
KBDL TAF...High confidence in TAF. VFR thru the period. Light
north/northwest winds. Winds shift more southerly after 00Z
Sunday.
Outlook /Sunday Night through Wednesday/...
Sunday Night: VFR. Breezy. Chance SHRA.
Monday through Monday Night: VFR. Chance SHRA, isolated TSRA.
Tuesday: VFR. Breezy. Chance SHRA, isolated TSRA.
Tuesday Night: VFR. Chance SHRA, isolated TSRA.
Wednesday: Mainly VFR, with local MVFR possible. Breezy. Chance
SHRA, isolated TSRA.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Overall high confidence through the weekend.
Ridge of high pressure will be across the region through
Saturday night. Thus winds should be 15kt or less, and in fact
barely over 10kts in many areas. There will be local onshore sea
breezes on Saturday. With the light winds and no significant
swell energy coming into the region, wave heights will remain 3
feet or less.
Low pressure develops near the benchmark and will bring showers
and increased easterly winds to the waters late Sunday
afternoon. Gusts to 25kt possible.
Outlook /Sunday Night through Wednesday/...
Sunday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Chance of rain showers.
Monday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain showers, isolated thunderstorms.
Monday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers, isolated thunderstorms.
Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Slight chance of rain showers, isolated thunderstorms.
Tuesday Night through Wednesday: Winds less than 25 kt. Seas
locally approaching 5 ft. Slight chance of rain showers,
isolated thunderstorms.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.
&&
$$
SYNOPSIS...KS/KC
NEAR TERM...KS
SHORT TERM...KS
LONG TERM...KJC
AVIATION...KS
MARINE...KJC/KS
Source:
BOX issues Area Forecast Discussion (AFD) at Jul 27, 3:39 AM EDT----------------
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