BOX issues Area Forecast Discussion (AFD) at Dec 31, 9:14 PM EST781
FXUS61 KBOX 010214
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
914 PM EST Tue Dec 31 2024
.SYNOPSIS...
Our next system arrives tonight, bringing rainfall across
southern New England and possibly a few embedded thunderstorms
very late tonight into early Wednesday. Low pressure lifts
northeast of our region Wednesday morning...but a few showers
may linger into the afternoon and evening with one more day of
relatively mild temperatures. Temperatures will progressively
trend colder/below normal Thursday through the upcoming weekend.
A period of strong to damaging wind gusts are expected late
Wednesday and especially Thursday, as the initial surge of
colder air works into the region. Dry weather will generally
prevail Thursday through the weekend, outside of a brief spot
snow shower or two. We then will need to watch a storm system to
our south early next week. Odds currently favor a glancing
blow/miss early next week...but that is not set in stone.
&&
.NEAR TERM /THROUGH WEDNESDAY/...
Key Messages...
* A period of soaking rain with some embedded thunder possible
very late tonight into early Wednesday
Overall theme of the of the forecast continues. Did tweak the
rainfall timing into the overnight using the last several runs
of the HRRR, which appears to have a good handle on the timing.
Will need to monitor the threat of convection overnight, with
quite a bit of lightning observed off the NJ coast. Not
expecting severe weather, but mostly concerned about many people
being outdoors into the early morning hours.
Previous Discussion...
A shortwave trough over the midwest will induce deepening low
pressure over the Ohio valley while a secondary low pressure
forms along the frontal boundary to our southwest. This low will
deepen as it moves overhead by sunrise Wednesday bringing a
soaking rain to the region overnight. We have ample moisture
available with PWATs near 1" which is ~200% above normal for
late Dec. The low also induces a 35-45kt 925mb jet providing
ample forcing for ascent and these together will lead to 0.5 to
1 inch of rain across SNE by late Wed morning. Our relatively
mild airmass remains in place through Wednesday with 925mb temps
5-7C so all of this precipitation will fall as rain. The
exception will be over the high elevation of the Berkshires
Wednesday afternoon/evening when the trailing cold front swings
through and rain will flip over to snow, only amounting to a
coating or so by the time all is said and done. Something else
of note, we may even have some embedded thunderstorms
overnight/early Wed morning as a few hundred J/kg of instability
will be present; the best chance will be south of the MA pike.
While drier air will filter in by Wednesday late
morning/afternoon, mostly cloudy skies are likely to hold on
through much of the day, even as widespread rain comes to an end
by mid day. As the low lifts off things dry out but with the
lingering shortwave energy overhead scattered showers will
continue through the day, and may even expand for a time in the
evening.
&&
.SHORT TERM /WEDNESDAY NIGHT/...
Key Messages...
* Gusty to strong Winds develop Wednesday night
As the cold front moves through, colder air moves in in the mid
levels and lapse rates start to increase; we'll start to achieve
better mixing which will lead to mixing down of a 35 to 45 kt
925mb jet overnight into Thursday. Wind gusts of 45-55 mph are
possible; while the strongest winds are expected during the day
Thursday, locations like the Berkshires and Cape/Islands stand
the best chance of seeing these gusts as early as Wednesday
night.
&&
.LONG TERM /THURSDAY THROUGH TUESDAY/...
Key Messages...
* Strong-Damaging Wind Gusts Thu...Highs upper 30s-lower 40s
* Temps trending colder/below normal Fri through the weekend
* Mainly Dry Thu into the Weekend outside a brief spot snow shower
* Odds favor glancing blow/miss of snow Mon-Tue, but not set in stone
Details...
Thursday...
The main forecast concern on Thursday is the expected strong to
potentially damaging westerly wind gusts. A sub 985 mb low will
be lifting north into the Canadian Maritimes on Thu. This
combined with modest high pressure over the Ohio Valley will
increase the pressure gradient enough for a strong WNW low level
jet and impressive cold advection. We believe that NBM winds
are underdone given the very steep 1000-850 mb lapse rates and
excellent mixing Bufkit soundings support. Therefore...we opted
to issue a Wind Advisory for our entire region...based on fairly
high confidence that westerly winds will gust to between 45 and
55 mph. We also can not rule out a few 60+ mph wind gusts with
the best chance across western and central MA. This area is
favored because they are underneath the core of the low level
jet along with their high terrain as well as the downslope
potential into the valleys of western MA. At this time...we felt
that the Wind Advisories were more representative. But there is
some concern given what Bufkit is showing in the top of the
mixed layer. It is not out of the question that western/central
MA might need to be upgraded to a high wind warning...but
confidence was not high enough to do it at this point. Power
outages become more of a concern if those higher wind gusts do
materialize.
We do expect generally dry weather on Thu...but can not rule out a
brief flurry/snow shower or two especially towards the Berks from
remnant Lake moisture. High temps will mainly be in the upper 30s to
the lower 40s...but it will feel colder with the strong winds.
Friday/Saturday/Sunday...
All the model guidance continues to be in very good agreement in
deep closed upper level energy near the Quebec/Maine border.
This will carve out a deep trough with below normal heights
across the northeast. This results in temps trending
colder/below normal levels Friday through the Weekend. Highs
mainly in the 30s Fri and more like the upper 20s and lower 30s
by the Weekend. In fact...the high terrain will be a few degrees
colder with highs mainly in the lower to middle 20s for the
Weekend. It will also be be blustery with WNW wind gusts of 20
to 30 mph Fri into the Weekend with a few gusts up to 35 mph. So
Wind Chills probably in the single digits to middle teens
during the overnight and morning hours.
Generally dry weather will prevail over this time given the
trough axis is far enough east. However...we can not rule out
a brief spot flurry/snow shower at times especially towards the
Berks from shortwave energy and remnant Lake moisture on
westerly flow.
Monday and Tuesday...
We will need to watch low pressure which will be lifting
northeast from the southern Plains early next week. Most of
the guidance shunts this storm system to our south given the
vigorous closed upper level energy across the Canadian
Maritimes. Therefore...the most likely outcome at this point is
a miss or just a glancing blow of snow from this system.
However, this is still 6- 7 days in the future and if the closed
upper level energy can lift further northeast the risk for snow
would increase. In fact...while most EPS/CMC ensembles indicate
a miss/glancing blow there are a few that show a greater risk
for accumulating snow along with the UKMET model. Not much more
to say at this point...just something we will need to watch.
&&
.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Tonight...High confidence.
VFR conditions deteriorate to lower end MVFR-IFR conditions
after midnight from southwest to northeast. This in response to
a shield of heavy rain, and perhaps a few embedded thunderstorms
overnight. Winds becoming E at 5 to 15 knots with some gusts to
25 knots toward morning along the coast. LLWS will also become
an issue overnight
Wednesday and Wednesday night...High confidence in trends.
Moderate confidence in timing.
Steady rain exits the region by early-mid Wednesday morning,
but a few showers still possible especially Wednesday evening.
In fact, precipitation type will change to snow showers across
the higher terrain, but any real accumulations confined to the
Berks. As for the conditions, mainly IFR conditions early Wed
trend towards MVFR later Wed and eventually to mainly VFR
thresholds sometime Wed night. Winds shift to the W by Wed
afternoon at 10 to 15 knots with some 20-30 knot gusts
developing late. Westerly winds strengthen further Wed night
into the 15 to 25 knot range with gusts of 30-40 knots
developing.
KBOS TAF...High confidence in TAF.
KBDL TAF...High confidence in TAF.
Outlook /Thursday through Sunday/
Thursday: Mainly VFR, with local MVFR possible. Strong winds
with gusts up to 45 kt.
Thursday Night: VFR. Strong winds with gusts up to 45 kt.
Friday: VFR. Windy with local gusts up to 30 kt.
Friday Night: VFR. Breezy.
Saturday: VFR. Windy with gusts up to 30 kt.
Saturday Night: VFR. Breezy.
Sunday: VFR. Windy with local gusts up to 30 kt.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High- greater than 60 percent.
Tonight and Wednesday...
Winds and seas continue to diminish into this evening before
increasing SE winds develop tonight, then shift S for Wednesday.
Seas will build in response, especially across the outer coastal
waters.
Wednesday night...
W winds becoming increasingly gusty with building seas. Winds
sustained 25-35 kts with gusts 35-45 kts. Seas 10-12 ft on southern
waters, 6-9 ft on the eastern waters. Gale Warnings are in effect
for all waters.
Outlook /Thursday through Sunday/...
Thursday: Low risk for storm force winds with gusts up to
45 kt. Rough seas up to 15 ft.
Thursday Night: Moderate risk for gale force winds with gusts
up to 45 kt. Rough seas up to 12 ft.
Friday: Strong winds with gusts up to 35 kt. Areas of rough
seas.
Friday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Seas up to 5 ft.
Saturday: Strong winds with gusts up to 30 kt. Seas up to 5 ft.
Saturday Night: Strong winds with gusts up to 35 kt. Areas of
rough seas.
Sunday: Strong winds with gusts up to 30 kt. Areas of rough
seas.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Wind Advisory from 7 PM Wednesday to 10 PM EST Thursday for
CTZ002>004.
MA...Wind Advisory from 7 PM Wednesday to 10 PM EST Thursday for
MAZ002>024-026.
RI...Wind Advisory from 7 PM Wednesday to 10 PM EST Thursday for
RIZ001>008.
MARINE...Gale Warning from 7 PM Wednesday to 3 AM EST Friday for
ANZ230>237-251.
Gale Warning from 7 PM Wednesday to 7 AM EST Friday for ANZ250-
254.
Gale Warning from 1 PM Wednesday to 7 AM EST Friday for ANZ255-
256.
&&
$$
SYNOPSIS...Frank/BW
NEAR TERM...Belk/BW
SHORT TERM...BW
LONG TERM...Frank
AVIATION...Frank/BW
MARINE...Frank/BW
Source:
BOX issues Area Forecast Discussion (AFD) at Dec 31, 9:14 PM EST----------------
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