BOX issues Area Forecast Discussion (AFD) at Sep 9, 3:02 PM EDT
950
FXUS61 KBOX 091902
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
302 PM EDT Mon Sep 9 2024
.SYNOPSIS...
A few brief spot showers tonight mainly this evening and focused
across the 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 /THROUGH TONIGHT/...
3 PM Update...
* A few brief spot showers tonight...mainly across the interior
* Overnight low temps mainly in the 50s
The latest SPC Meso-Analysis indicates 500T of -18C/-19C moving
in from the west with a vigorous upper level shortwave/cold
front. Despite limited surface moisture...the cold pool aloft
was enough to result in a few hundred J/KG of Cape. As the core
of this moves across the region this evening...thinking there is
enough there for a few brief showers with the focus for them
across the interior. Given the cold 500T...we can not rule out a
bit of graupel with a few of the showers and even the low risk
for a rumble of thunder. Not sure if any of this activity will
survive onto the coastal plain allowing for a brief spot shower
or two...but nothing more than that.
Areal coverage/duration of any showers will be quite limited
and regardless should wind down during the second half of the
night. Otherwise...overnight low temps should bottom out mainly
in the 50s to near 60 in the Urban Heat Island of Boston. A
touch of very localized patchy ground fog is possible late in
the typically most vulnerable locations...but this will not
impact most locations.
&&
.SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
Key Points...
* Sunny & Beautiful Tue with highs mainly middle-upper 70s
* Dry/Cool Tue night with lows mainly in the 40s and a few 50s
Details...
Tuesday...
A sunny & beautiful day is in store for Tue behind the
shortwave/cold frontal passage tonight. Plenty of sunshine &
good mixing with 850T near +9C should yield afternoon high temps
generally in the middle to upper 70s although a few degrees
cooler in the high terrain.
Tuesday night...
Large high pressure builds in from the west. This coupled with
light/calm winds and a relatively dry boundary layer should
allow overnight low temps to bottom out in the 40s across most
locations with some middle 50s in the urban centers of downtown
Boston/Providence and parts of the outer Cape/Nantucket.
Dewpoints in the 40s/lower 50s will result in a very
comfortable humidity too.
&&
.LONG TERM /WEDNESDAY 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 /19Z MONDAY THROUGH FRIDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
18z TAF Update...
This afternoon & tonight...High confidence.
VFR with just the risk of very localized patchy ground fog
toward daybreak in the typically most vulnerable low-lying
locations. A few brief spot showers expected mainly across the
interior this evening. W-SW winds 5 to 15 knots through tonight
with some gusts into the lower 20 knots this afternoon.
Tuesday...High confidence.
VFR. NW winds 5 to 15 knots with the low risk of a brief sea
breeze during the afternoon on the very immediate eastern MA
coast.
Tuesday night...High confidence.
VFR. Calm to light NW winds.
KBOS TAF...High confidence in TAF overall. Only uncertainty is a
few hours Tuesday afternoon....when a sea breeze may flirt with
the terminal for a few hours.
KBDL TAF...High confidence in TAF.
Outlook /Wednesday through Friday/...
VFR.
&&
.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.
W-SW winds of 10 to 15 knots will persist this evening and
shift the NW by Tue morning behind a cold frontal passage...but
below small craft advisory thresholds. Winds will then become
more variable in direction Tue PM...but winds/seas will remain
below small craft advisory thresholds as high pressure builds in
from the west.
Outlook /Wednesday through Friday/...
Winds less than 25 kt.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.
&&
$$
SYNOPSIS...Frank/BL
NEAR TERM...Frank
SHORT TERM...Frank
LONG TERM...BL
AVIATION...Frank/BL
MARINE...Frank/BL
Source: BOX issues Area Forecast Discussion (AFD) at Sep 9, 3:02 PM EDT (https://mesonet.agron.iastate.edu/p.php?pid=202409091902-KBOX-FXUS61-AFDBOX)
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