BOX issues Area Forecast Discussion (AFD) at Sep 3, 1:48 PM EDT299
FXUS61 KBOX 031748
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
148 PM EDT Tue Sep 3 2024
.SYNOPSIS...
Dry and very pleasant weather persist through the end of the
work week, with seasonably warm days but cool nights. Shower
chances increase this weekend, but no washouts anticipated at
this point.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
10 AM Update...
Satellite shows a clear picture this morning. Not a cloud in the
sky. Cool start to the day keeping the forecast on track for a
cooler day overall with highs in the upper 60s and low/mid 70s.
No changes were needed to the previous forecast.
Previous discussion...
Strong subsidence behind departing northern stream shortwave along
with very dry airmass will lead to abundant sunshine today with
hardly a cloud in the sky. PWATs bottom out around 0.30" this
morning before slowly recovering this afternoon. This dry air in the
column will result in dewpoints dropping into the upper 30s today.
Temps will average 5-7 degrees below normal with highs low-mid 70s,
except upper 60s higher terrain with an early autumn feel today.
Diminishing N-NW wind as large high pres builds in from the
west with weakening pressure gradient will lead to afternoon sea
breezes developing.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
Tonight...
Large high pres builds over New Eng delivering clear skies and light
to calm winds. This will lead to excellent radiational cooling with
lows ranging through the 40s, as cool as lower 40s in the typically
colder locations, but low-mid 50s in the urban centers and outer
Cape and Nantucket. Used a blend of the colder MOS guidance to
derive low temps.
Wednesday...
Large high pres remains control as it gradually moves east of New
Eng during the afternoon. Weak shortwave moves into the region from
the Gt Lakes in the afternoon but column remains dry so another
mostly sunny day with just a few clouds. Moderating low level temps
will lead to warmer temps reaching the mid-upper 70s as winds turn
southerly in the afternoon. Humidity levels will be low with
dewpoints in the upper 40s to lower 50s.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Highlights...
* Dry and quiet weather late this week and heading into the weekend.
Temperatures near to slightly cooler than seasonable.
* Next shot for showers comes over the weekend, but there is
uncertainty on timing and intensity of a front moving in. Turning
drier early next week.
Wednesday Night through Friday...
A ridge axis initially builds over the central Great Lakes Wed
Night, while a weak shortwave lingers over New England. The ridge
builds into the eastern Great Lakes by late Thu, while the shortwave
cuts off/meanders over New England. The ridge builds into New
England by late Fri, while the shortwave lifts into northern New
England/Nova Scotia. An amplified trough digs into western/central
Great Lakes toward the end of this timeframe. High pressure builds
overhead Wed Night, but will gradually build further offshore by Thu
and Fri.
Tranquil weather anticipated through this timeframe with high
pressure in control. Expect strong radiational cool Wed Night into
Thu morning with clear skies and light winds. The NBM tends to
perform quite poorly in these situations, so have nudged down lows
to the 10th percentile of guidance. Lows range from the upper 40s
across the interior and typical radiators, to the low/mid 50s
elsewhere. Should be a bit milder the next two nights with increased
cloudiness and slightly stronger winds. Temps rebound nicely on
Thu/Fri with highs near to slightly cooler than seasonable.
Will note that latest deterministic guidance indicating some light
precip on Fri with prolonged onshore flow. Forcing looks quite weak
and there isn't a lot of moisture to work with, PWATs around 1 STD
above/below climo per NAEFS/EPS. Wondering if this is hinting more
at stratus/drizzle given the high RH values in the lowest 1000-850
hPa. Have kept forecast dry for now.
Saturday through Sunday...
The trough over the western/central Great Lakes late on Fri will dig
and cutoff over the central Great Lakes/Ontario by Sat. A shortwave
rotates around the cutoff into/through the Mid Atlantic on Sat. The
cutoff meanders slightly further east on Sun with another
shortwave/cutoff lifting into western portions of New England.
Somewhat complex surface pattern with several lows nearby, but a
cold front slides through the eastern Great Lakes on Sat and perhaps
into portions of southern New England on Sun.
Next potential opportunity for more widespread showers across
southern New England. Big questions at this point is timing the
front sliding in and its intensity. Could be a situation where the
upper forcing is a bit too far removed where we receive widespread
rains and remains more confined to interior New England. Did dial
back NBM precip chances slightly due to uncertainty. This matched up
fairly well with latest EPS/GEFS guidance decreasing probs from run
to run of QPF AOA 0.10 inches (was roughly 50-90% in previous and
has lowered to 40-80% in current). Could be something to keep an eye
on as we could tap into some higher moisture values from prolonged
southerly flow, though is only 1-1.5 STD above model climo per
NAEFS/EPS at this point. High temps in the low to mid 70s through
the weekend.
Early next week...
Cutoff low over the Great Lakes region continues to rotate
nearby/overhead. Guidance indicating at this point that dry slot
punches in/through, which will keep our weather dry. Though at this
point confidence quite low as models tend to progress cutoffs
through a bit too quickly based on past experience. For now have
stuck with the NBM, which keeps us dry with highs near seasonable
values.
&&
.AVIATION /18Z TUESDAY THROUGH SATURDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Today through Wednesday Night...High confidence.
VFR. N-NW wind 5-10 kt today becoming light to calm tonight.
Winds sea breeze along the coast Wednesday afternoon. Calms
winds Wednesday night.
KBOS TAF...Moderate confidence for much of TAF.
VFR through forecast. Sea breeze is not likely this afternoon
with NW winds 8-10 kts. There is a low chance the sea breeze
kicks in for a few hours this afternoon. Higher confidence in
sea breeze late tomorrow morning.
KBDL TAF...High confidence in TAF.
VFR through forecast. Light NW winds becoming light/variable
tonight.
Outlook /Wednesday Night through Saturday/...
Wednesday Night through Thursday Night: VFR.
Friday: VFR. Breezy.
Friday Night: Mainly VFR, with local MVFR possible. Breezy.
Saturday: Mainly VFR, with local MVFR possible. Breezy. Chance
SHRA.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Today...High confidence.
Gusty N-NW winds to 20-25 kt early this morning will diminish before
12z, becoming light in the afternoon. This will leading to onshore
winds developing over nearshore waters as sea breezes develop.
Tonight and Wednesday...High Confidence.
Light winds and seas as high pres builds over the waters. Winds
turning southerly Wed afternoon.
Outlook /Wednesday Night through Saturday/...
Wednesday Night through Thursday: Winds less than 25 kt.
Thursday Night: Winds less than 25 kt. Seas locally approaching
5 ft.
Friday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Friday Night: Winds less than 25 kt. Local rough seas.
Saturday: Winds less than 25 kt. Rough seas up to 8 ft. Chance
of rain showers.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.
&&
$$
SYNOPSIS...KJC/BL
NEAR TERM...KJC/BL/Mensch
SHORT TERM...KJC
LONG TERM...BL
AVIATION...BL/Mensch
MARINE...KJC/BL
Source:
BOX issues Area Forecast Discussion (AFD) at Sep 3, 1:48 PM EDT----------------
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