BOX issues Area Forecast Discussion (AFD) at Dec 14, 10:08 AM EST646
FXUS61 KBOX 141508
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
1008 AM EST Sat Dec 14 2024
.SYNOPSIS...
Strong high pressure will result in a dry but cold weekend. A
shift to a more unsettled weather pattern next week with
periods of precipitation possible. Temperatures trend above
normal Tuesday through Thursday. Potential for another late week
system; however, confidence is low in the details.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
* Sunny and cold today. Highs in the upper 20s to the mid 30s.
Near record high pressure just to our west, so quiet weather
will continue. Main changes this morning were to bring
temperatures and winds back in line with observed trends.
315 AM Update...
A very strong high pressure system nearing 1050 mb located near
the US/Quebec border will be in control of our weather today.
This will result in sunny skies with the exception across the
outer-Cape...where some ocean effect clouds may cross the region
at times with NNW winds.
Despite the sunny skies today...the low December sun angle
coupled with 925T near -9C will result in another cold day.
Afternoon high temperatures will range from the upper 20s in the
high terrain...to mainly the lower to middle 30s elsewhere.
These temps will be close to 10 degrees below normal for the
middle of December. Winds will be light/under 15 mph from a
northwesterly direction.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
Key Messages...
* Very cold tonight...lows in the teens with a few single digits
* Partly sunny on Sunday with highs in the 30s
Details...
Tonight...
The very strong high pressure system centered just to our north
will result in a very cold night with light/calm winds. Mostly
clear skies are expected other than perhaps some ocean effect
clouds across the Cape and Nantucket. Otherwise...tonight will
be ideal for radiational cooling especially with such a strong
high pressure system. Low temps will probably bottom out in the
single digits in the outlying locations of western MA with
mainly teens elsewhere. The Urban Heat Island of Boston will be
the mild spot with overnight lows in the lower 20s.
Sunday...
Large high pressure remains in control of our weather as it
slowly slides to our east on Sunday. Very light onshore flow
may result in some clouds moving in off the ocean and impacting
areas near the immediate coast at times...especially the Cape
and Islands. Model cross sections also indicate some mid-high
clouds may overspread the region from the west during the day.
So we are still looking at partial sunshine with more of the
clouds arriving for the second half of the day. High temps will
be a few degrees milder than today...but still remaining in the
30s and below normal for this time of year. Winds will be very
light on Sunday.
&&
.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Key Messages:
* Trend toward a more unsettled/active weather pattern next week.
* Weak system brings a round of light showers Monday (snow and rain)
with potential for areas of light freezing rain/drizzle
for the AM commute. Confidence low on location.
Sunday Night
Sunday night is the transition point as we trend towards a more
unsettled/active weather pattern that continues through the week
ahead. High pressure slowly shifts eastward across southern New
England as a shortwave trough approaches from the south/west.
Dry conditions to start, with high amounts of cloud cover
compared to the previous few nights. Although the coolest
airmass shifts off, it will still be a cooler night with
temperatures in the upper teens to low 20s.
Monday
Early Monday morning, as the shortwave trough approaches, moisture
gradually increases from the west accompanied by weak large scale
ascent. This will sufficient to support showers developing early
Monday morning. Precipitation type will be the main forecast
challenge. Although the high pressure/cooler airmass will to the
east, there should be sufficient residual cold air in the surface
layer to support light snow showers across the interior of MA. What
makes the precip type more of a challenge is the warm air advection.
Model guidance shows warm air subtly advecting in aloft from the
south and west. This combined with the shallow colder air could mean
potential for freezing rain/drizzle, but this will depend on both
the strength and how far north the WAA makes it. This will make the
location of these different precip types uncertain too. Models seem
to hint at low probabilities of freezing rain/drizzle in S MA/N CT
generally. Model soundings near Hartford depict a shallow cool layer
toward the surface coupled with upward motion and a noticeable
warm nose above it which would support freezing rain/drizzle if
a shower were to pass over that part of the region.
Precipitation amounts are low; however, this is something worth
monitoring because of its overlap with the AM commute. Light
snow and ice accumulations may lead to slick roads. To
summarize, there is potential for light snow showers and
freezing rain/drizzle early Monday morning.
Monday Night - Tuesday
Monday night into Tuesday a more substantial shortwave trough moves
across. This will be coupled with a LLJ jet helping transport a
plume of above normal moisture into the region (180-220% of normal).
This will bring more widespread chances for precipitation. For
amounts, ensembles are ranging from .25" to .50" mostly with low
potential for locally higher amounts closer to an inch. Temperatures
will be sufficiently above normal with highs into the 50s which keep
the precipitation type simple..rain.
Wednesday - Late Week
Conditions dry out into Wednesday with W/WSW flow aloft with
temperatures stay near to slightly above normal. Ensemble guidance
is hinting at potential for another late week system; however,
details are uncertain at this time (ie. timing, track, amount of
cold air). There is a general signal for cooler air to return to the
region for the weekend.
&&
.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Today...High Confidence.
VFR with just some scattered ocean-effect clouds at times
across the outer Cape. NW winds 5-10 knots.
Tonight and Sunday...High Confidence.
VFR outside some ocean effect clouds and some marginal MVFR
ceilings at times along portions of the immediate coast, mainly
the Cape and Islands. Light winds.
KBOS TAF...High Confidence in TAF.
KBDL TAF...High Confidence in TAF.
Outlook /Sunday Night through Wednesday/...
Sunday Night: Mainly VFR, with local MVFR possible. Slight
chance SN.
Monday: MVFR/IFR conditions possible. Chance RA, chance SN.
Monday Night: Mainly MVFR, with areas IFR possible. Breezy. RA
likely.
Tuesday: Mainly VFR, with areas MVFR possible. Breezy. RA.
Tuesday Night: VFR. Breezy. Slight chance RA.
Wednesday: VFR.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Today through Sunday...
A very strong high pressure system near 1050 mb located near the
Quebec/northern New England border will slowly drop southeast
over the waters Sunday afternoon. This will result in a weak
enough pressure gradient to keep winds and seas below small
craft advisory thresholds for the weekend.
Outlook /Sunday Night through Wednesday/...
Sunday Night: Winds less than 25 kt.
Monday: Winds less than 25 kt. Chance of rain.
Monday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of seas approaching 5 ft. Rain likely.
Tuesday: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of rough seas. Rain.
Tuesday Night: Winds less than 25 kt. Seas up to 5 ft. Chance
of rain.
Wednesday: Winds less than 25 kt. Seas locally approaching
5 ft.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.
&&
$$
SYNOPSIS...Frank/Mensch
NEAR TERM...Belk/Frank
SHORT TERM...Frank
LONG TERM...Mensch
AVIATION...Belk/Frank/Mensch
MARINE...Frank/Mensch
Source:
BOX issues Area Forecast Discussion (AFD) at Dec 14, 10:08 AM EST----------------
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