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907
FXUS61 KBOX 091302
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
902 AM EDT Mon Sep 9 2024

.SYNOPSIS...

High pressure building south of New England will bring mainly dry
weather today with moderating temperatures, but a few showers are
possible late today and this evening, especially interior, as a
weak front moves into the region. High pressure will dominate
the weather for the rest of the week into next weekend with dry
conditions and warming temperatures above normal.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

-- Changed Discussion --
9 AM Update...

* Sunshine this morning gives way to a mixture of clouds and sun
  this afternoon with very pleasant highs in the middle 70s

* A few brief showers mainly across the interior toward evening

The previous forecast is on track. Upper trough and cold pool
aloft will allow sunny skies to give way to a mixture of diurnal
clouds and sunshine this afternoon. Good mixing on westerly flow
should allow for very pleasant afternoon high temperatures in
the middle 70s.

Despite limited surface moisture...we should muster a few
hundred J/KG of Cape toward evening with 500T near -18C. This
should also trigger a few brief showers toward evening...mainly
across the interior. Given cold pool aloft can not rule out a
touch of graupel with the low risk for a rumble of thunder.
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&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
Tonight...

The upper trough axis and shortwave moves across the region this
evening. Modest forcing along with cold pool aloft (500 mb temps
around -18C) acting on PWATs near 1 inch will bring a few showers
this evening, mainly interior locations. There is marginal
instability so can`t rule out a rumble of thunder, but risk is
pretty low. Any showers should diminish overnight as shortwave and
trough axis moves to the east. Lows will be mainly in the 50s.

Tuesday...

Upper trough moves offshore followed by rising heights, subsidence
and drying. Expect mostly sunny skies and near seasonable temps in
the mid-upper 70s, a bit cooler higher terrain. Winds will become NW
10-15 mph behind the weak front which moves offshore. Low humidity
levels as dewpoints in the 50s will drop into the 40s as mixing of a
dry boundary later occurs.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Highlights

* Dry weather through the week with high pressure in control. Cool
  Tue Night into Wed AM due to radiational cooling. Temperatures
  trending above seasonable late in the week and into the weekend.

Tuesday Night through Sunday...

A ridge axis builds from the OH Valley into central Ontario Tue
evening. The ridge will flatten out as it builds into Ontario/Quebec
and the eastern Great Lakes by later on Wed. A shortwave slides into
New England on Thu as a more amplified ridge builds across the Upper
Mississippi River Valley and the Great Lakes. The ridge firmly
builds into the central/eastern Great Lakes late in the week and
into the weekend. High pressure builds overhead Tue Night through
Wed. The high shifts offshore Wed Night into Thu. Another high
builds nearby/overhead for late in the week and through the weekend.

Dry and quiet weather through the extended with high pressure under
control. Main change made was to lower temps Tue Night into Wed AM
as the high is directly overhead. The result is clear skies and
light winds, which will bring strong radiational cooling. The NBM
tends to do quite poorly in these setups, so lowered temps to the
10th percentile of guidance. The result are widespread lows into the
40s across interior locations, but still should be in the low/mid
50s along the immediate coastline. Went with the 25th percentile of
guidance for Wed Night into Thu AM, as the high shifts offshore and
flow turns more southerly. Could see winds high enough where we
aren`t able to completely decouple. Lows range from the upper 40s to
mid 50s.

As for high temperatures throughout the extended will be gradually
warming up mid to late in the week and heading into the weekend.
Should see temperatures near to slightly warmer than seasonable on
Wed. By late in the week and into the weekend we run roughly 5-10
degrees warmer than normal. Should see several days where highs are
running into the 80s. The only exceptions are along the immediate
south coast where southerly flow will keep temps a bit cooler, and
localized seabreezes will keep temperatures cooler across eastern
coastal areas from time to time. Over past couple of shifts have
noticed that the peak heat has been trending later and later with
future updates. Now appears that the 925 hPa temps of 15-25 degrees
Celsius come somewhere in the Fri-Sun timeframe. In addition the
GEFS has backed away from low probs of 90+ degrees Celsius and
is in line with nil probs along with the EPS/GEPS.

&&

.AVIATION /13Z MONDAY THROUGH FRIDAY/...
Forecast Confidence Levels:

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

Today and Tonight...High confidence.

VFR. A period of BKN cigs 5-10kft developing this afternoon
into this evening, with a few light showers possible in the
interior as early as 19-21Z and ending around 04-06Z. At this
point have held off from including in any terminals, but may be
needed for BAF/BDL/ORH in future updates. Patchy MVFR to IFR fog
late night in the CT valley. W-SW wind 10-20 kt today,
diminishing tonight.

Tuesday...High confidence.

VFR. NW wind 8-15 kt.

KBOS TAF...High confidence.

VFR with WSW winds 10-15 kts. Should see gusts 15-20 kts
developing 14-16Z. Boundary layer decouples around 00Z and winds
turn to NW around 08-10Z.

KBDL TAF...High confidence.

VFR with WSW to W winds around 5-10 kts. Should see 15-20 kt
gusts developing around 15-17Z. Could have a spot shower around
19-21Z until roughly 02-04Z, but coverage too low to include in
latest update. If shower goes through then patchy fog risk will
increase for late tonight. Winds turn NWly roughly 12-14Z.

Outlook /Tuesday Night through Friday/...

VFR.

&&

.MARINE...
Forecaster Confidence Levels:

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

Today through Monday night...High confidence.

W-NW winds continue through tonight. Marginal SCA wind gusts
over the northern waters tonight. Monday winds become W-SW
10-20 kt. Seas below SCA thresholds tonight through Monday
night.

Outlook /Tuesday Night through Friday/...

Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None.
MA...None.
RI...None.
MARINE...None.
-- End Changed Discussion --

&&

$$

SYNOPSIS...KJC/BL
NEAR TERM...Frank
SHORT TERM...KJC
LONG TERM...BL
AVIATION...KJC/BL
MARINE...KJC/BL