BOX issues Area Forecast Discussion (AFD) at Jan 22, 10:13 PM EST777
FXUS61 KBOX 230313
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
1013 PM EST Wed Jan 22 2025
.SYNOPSIS...
An arctic airmass will persist through tonight with moderating
temperatures Thursday into the weekend although still below
normal. Other than passing snow showers associated with a
Clipper low pressure area Sunday, mainly dry weather will govern
the latter part of this workweek through early next week.
Temperatures cool off to slightly below normal levels Friday and
Saturday, then rebounding to near to slightly above normal
levels for Sunday into early next week.
&&
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
1010 PM update...
Mid-high clouds overspreading SNE which has prevented a sharp
temp drop. However, may see some partial clearing develop
overnight with a small window for a further cooling. Looking at
lows mostly zero to 10 above, with teens outer Cape/ACK and
Boston metro.
The risk for black ice development for Cape/Islands appears low
at this time. Dewpoints expected to remain in the single numbers
here tonight, rising into the mid teens toward daybreak at ACK
and outer Cape where temps expected rise into lower 20s. T/Td
depressions should remain large enough to preclude any
condensation developing and freezing on area roadways.
Previous discussion...
Key Messages:
* Dry, though with increasing mid to high clouds.
* Outside chance at black ice for southeast New England?
Generally tranquil/dry conditions tonight, and while still
colder than normal we're not expecting conditions to be nearly
as cold as the last few nights. An expanding layer of mid to
high clouds now starting to advect in from the west will help
facilitate that. Although we will see an early period of
cooling, the coverage of cloudiness should be widespread enough
to stunt further cooling. Still looking at lows in the single
digits to the lower to mid teens though.
What is less clear is the potential for some patchy slippery
spots, mainly over southeast MA/RI, in response to increasing
moisture levels. Very dry over most of interior New England
(e.g. dewpoints down to 5 to 10 below), with little recovery
anticipated. However the one area to watch for possible slippery
spots is in southeast New England, with the vast majority of
models showing dewpoints rising into the lower to perhaps mid
teens on increased light southerly flow. Forecast dewpoints are
near current temps. We've seen instances where condensation
occurs as dewpoints rise coming out of frigid, Arctic airmasses
and leaves a shallow layer of moisture on cold pavement which
could become slippery. Not a good sense if we see this
development or what the coverage could be, but it wouldn't
surprise me if there was patchy instances of black ice over
southern RI, southeast MA and the Cape and Islands as dewpoints
start to rise/recover as winds become southerly.
Previous discussion:
High pressure and mid level ridge move offshore to the east tonight,
with weak shortwave energy and mid level warm front moving through.
Increased moisture is expected with the warm front, but with little
to no upper level support, noting more then increased mid to high
level cloud cover is expected tonight. With little to no wind
and cold air still in place, low temperatures should bottom out
in the single digits again across the interior, and low teens
near the coasts.
&&
.SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
Better upper level forcing arrives Thursday in the form of a weak
short wave, but by this time, the better mid level moisture will
have moved off to the north east. With drying mid levels, not
expecting any precip inland, but a weak low spinning up offshore
could bring some light snow to the Cape and Islands tomorrow. Most
guidance keeps the snow offshore tomorrow, but a couple of the hi-
res guidance sources do show 1-2 inches possible on the Cape and
Islands. Given the shallow moisture profiles, I think these values
are a bit bullish, but a 1/2 inch seems more likely if it ends up
snowing. With warming 850mb temps to -10C, and SW surface
winds, high temperatures will be able to warm into the upper 20s
to low 30s.
High pressure builds back overnight, allowing for clearing
skies and calm winds. With good radiational cooling conditions,
overnight low will again drop into the single digits to low
teens.
&&
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Key Messages:
* Rather benign weather in the offing for late January standards
this forecast period; other than a passing Clipper system Sun
which could bring passing snow showers, dry weather prevails into
early next week.
* Fri and Sat feature colder than normal temperatures before
rebounding back to near/slightly above normal levels for Sunday.
* Early next week outlook favors continued dry weather with
temperatures around normal.
Details:
Overall no substantive change to the forecast and messaging in this
portion of the forecast. Southern New England will be entrenched in
what is climatologically the coldest portion of the calendar year
during this forecast period.
This forecast period will continue be governed by the northern
stream of a split-flow pattern at 500 mb, with mean troughing over
the central and northeastern US and a trough/closed low feature over
the southwest CONUS. Other than passing snow showers in
association with a Clipper low moving in on Sunday, dry weather
looks to be the theme.
Will see a period of colder than normal temps Fri and on Sat, highs
mid 20s to around freezing with lows in the single digits Fri night.
But this shot of cold air does not look to be nearly as stout as the
colder airmass working its way over Southern New England today.
Warmest day of this period then takes place on Sunday with highs in
the low to mid 30s with some sunshine ahead of the 2nd clipper
system Sunday, which then cools us off to around seasonable
temperatures into Mon and Tue.
&&
.AVIATION /03Z THURSDAY THROUGH MONDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
00z TAF Update:
Tonight: High confidence.
Mainly VFR; though a limited risk for MVFR decks could develop
over the Cape and Islands after 08z or so in a shallow moisture
return regime. Light SW winds, 5-8 kt.
Thursday...High confidence.
VFR cigs with patchy MVFR possible over Cape/Islands. SW wind
around 10 kt. Low chance for a light snow across the Cape and
Islands
Thursday night...High confidence
VFR with light and variable winds 5 knots or less.
KBOS TAF...High Confidence in TAF.
VFR with light and variable winds
KBDL TAF...High Confidence in TAF.
VFR with light and variable winds
Outlook /Friday through Monday/...
Friday through Saturday: VFR.
Saturday Night through Sunday Night: VFR. Breezy.
Monday: Breezy.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High- greater than 60 percent.
Tonight:
Light and variable winds overnight less then 10 knots, except
for extreme northern waters where winds will be SW at 10-15
knots.
Thursday...
Increasing WSW winds, at 10-15 knots. Low risk for a 25 knot
gust in the northern waters, but confidence was not high enough
to issue SCAs.
Thursday Night.
West winds continue at 10-15 knots.
Outlook /Friday through Monday/...
Friday through Friday Night: Winds less than 25 kt.
Saturday: Winds less than 25 kt. Seas locally approaching 5 ft.
Saturday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Local rough seas.
Sunday: Moderate risk for Small Craft Advisory winds with gusts
up to 25 kt. Areas of rough seas.
Sunday Night through Monday: Low risk for Small Craft Advisory
winds with gusts up to 25 kt. Local rough seas.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.
&&
$$
SYNOPSIS...Loconto/KP
NEAR TERM...KJC/Loconto/KP
SHORT TERM...KP
LONG TERM...Loconto
AVIATION...Loconto/KP
MARINE...Loconto/KP
Source:
BOX issues Area Forecast Discussion (AFD) at Jan 22, 10:13 PM EST----------------
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