BOX issues Area Forecast Discussion (AFD) at Sep 8, 1:19 PM EDT048
FXUS61 KBOX 081719
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
119 PM EDT Sun Sep 8 2024
.SYNOPSIS...
Breezy and cooler today with plenty of sunshine as high pressure
builds over the Ohio Valley. Slowly moderating temperatures
Monday with risk of spotty showers in the interior late in the
day and evening as a weak front approaches. Otherwise high
pressure dominates through the week with temperatures trending
warmer leading to unseasonably warm weather late in the week
into next weekend.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A breezy and cooler day in progress with morning with temps in
the low 60s and winds gusting 20 to 25 mph for many. No
significant changes to the forecast with the mid morning update.
Previous update...
Upper low lifts northward across Quebec as shortwave moves across
northern New England this afternoon. The shortwave may trigger a few
showers to the north and west, but lots of dry air in the column
across SNE with PWATs bottoming out around 0.30" this morning. This
will result in abundant sunshine today with just a few diurnal CU
developing across interior MA. Modest pressure gradient and deep and
well mixed boundary layer will lead to somewhat gusty W-NW winds
which will gust to 25 mph at times, especially interior. Cooler post-
frontal airmass with 850 mb temps down to 4-6C today will keep high
temps mostly in the mid-upper 60s, with lower 70s possible across SE
MA.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
Tonight...
Clear skies tonight with diminishing winds will result in good
radiational cooling. However, enough gradient for a modest breeze
which may limit how cool it gets. We leaned a bit higher than MOS
guidance with lows mid-upper 40s, except lower 50s near the coast.
Monday...
Mean upper trough axis sets up across New Eng as multiple shortwaves
rotate around the trough. Lots of sunshine in the morning, then
expect diurnal clouds to increase in the afternoon, especially
interior as increasing moisture in the 850-700 mb layer moves in
from the west assocd with the upper level trough. Cold pool aloft
with 500 mb temps falling to around -18C will contribute to limited
instability with SBCAPES 200-300 J/kg and decent mid level lapse
rates. This may lead to a few convective showers developing late in
the day in the interior. Low level temps are moderating slightly so
highs should reach the low-mid 70s, but a bit cooler higher terrain.
&&
.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Highlights
* Dry weather through the week with high pressure in control.
Temperatures trending above normal and moderating as the week
progresses. Will also see a couple of cool nights due to
radiational cooling.
Monday Night through Tuesday...
Will initially have cyclonic flow in place across the eastern Great
Lakes and New England Mon Night, while a ridge axis builds over the
Mississippi River Valley. A shortwave embedded within the cyclonic
flow will slide into New England during the evening and lift
offshore by early Tue. The cyclonic flow becomes more quasi-zonal
later on Tue as the ridge builds into the western/central Great
Lakes. A weak cold front slides into and through southern New
England Mon Night into early Tue. High pressure nudges in from the
eastern Great Lakes on Tue.
Have bumped up precipitation chances to slight chance for portions
of interior southern New England Mon Night into early Tue. Should
see PWATs climbing to roughly 0.75 to 1 inch. Deterministic guidance
showing a decent amount of mid level moisture in place (within the
700-500 hPa level), but not as much of a consensus in the lower
levels. The latest NAM/GDPS and RDPS are much more moisture laden in
the lower levels and have more widespread light showers. Latest
ensembles (GEPS/GEFS/EPS) all indicate mod to high probs (40-80+
percent) of measurable precip across western MA. Across the rest of
the region probs are low. As for probs AOA 0.10 inches they are nil,
so any showers that do move through will be light. Low temperatures
generally in the 50s.
Dry and quiet weather on Tuesday with high pressure nudging in from
the eastern Great Lakes. No impactful weather expected with highs
around seasonable levels.
Tuesday Night through Saturday...
Ridge axis initially over the western/central Great Lakes extends
into Ontario Tue Night. The ridge builds into the eastern Great
Lakes and Quebec on Wed. Another ridge axis builds across the Great
Lakes region late in the week and into the weekend. High pressure
builds overhead Tue Night through Wed. The high shifts offshore to
our east by late Wed into the weekend.
Tranquil weather through this timeframe with high pressure
dominating the weather. The high will be essentially overhead Tue
Night into Wed AM. This will allow for clear skies and light winds,
so have lowered temps to the 10th percentile of guidance as NBM
tends to do quite poorly in these setups. Lows generally in the 40s,
but still will have some readings in the 50s along the immediate
coastline.
The high shifts offshore to the E on Wed through the rest of the
extended. Given the position of the high will have flow turn more S
to SW. This will bring warmer temps into our region, so should see
above normal temperatures through the rest of the extended.
Will have continued ridging in place over the Great Lakes region
through this timeframe. The result is high pressure overhead on Wed,
but gradually shifting offshore to the SE/E by Thu/Fri. Will have
925 hPa temps of 15-20 degrees Celsius on Wed climb to 20-25 degrees
Celsius Thu/Fri/Sat. Should solidly be in the 80s for Thu-Sat (away
from the immediate south coast). Even have some low probs (10-20
percent) per the GEFS for 90+ degrees on Fri/Sat across portions of
the Merrimack Valley. Given that the EPS/GEPS is nil have not bumped
up at this point and think NBM looks reasonable at this time.
&&
.AVIATION /17Z SUNDAY THROUGH THURSDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
This afternoon through Monday night...High confidence.
VFR. W-NW wind 10-20 kt gusting to 25 kt this afternoon in the
interior. W winds diminish tonight then W-SW wind 10-20 kt
Monday, diminishing overnight.
KBOS TAF...High confidence.
VFR. Winds out of the W/WNW with gusts of 20-25 kts. Boundary
layer decouples around 00Z. Winds turn to WSW Mon AM.
KBDL TAF...High confidence.
VFR. Gusty WNW/W winds at 20-25 kt. Boundary layer decouples
around 23-01Z. Winds turning more WSW late tonight.
Outlook /Monday Night through Thursday/...
Monday Night: VFR. Breezy.
Tuesday through Thursday: VFR.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Today through Monday...High confidence.
W-NW winds 10-20 kt today and tonight with a few higher gusts this
afternoon. W-SW 10-20 kt Monday. Leftover easterly swell with 5-6 ft
seas over eastern waters will subside below 5 ft this afternoon.
Seas below SCA thresholds tonight and Monday.
Outlook /Monday Night through Thursday/...
Monday Night: Winds less than 25 kt. Seas locally approaching
5 ft.
Tuesday through Thursday: Winds less than 25 kt.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 2 PM EDT this afternoon for ANZ250-
254-255.
&&
$$
SYNOPSIS...KJC/BL
NEAR TERM...KJC/BW/BL
SHORT TERM...KJC
LONG TERM...BL
AVIATION...BW/BL
MARINE...BW/BL
Source:
BOX issues Area Forecast Discussion (AFD) at Sep 8, 1:19 PM EDT----------------
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