BOX issues Area Forecast Discussion (AFD) at Dec 31, 3:17 PM EST
803
FXUS61 KBOX 312017
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
317 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
Pleasant weather continues the rest of the day under the influence
of shortwave ridging. Clear skies have already begun to fill in as
warm advection begins ahead of tonight's storm system. Thus, we'll
see clouds thickening and lowering now through late evening.
Tonight, 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 then 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 with 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 /20Z TUESDAY 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 early this evening deteriorate to lower end
MVFR-IFR conditions after midnight from west to east. This in
response to a shield of heavy rain, and perhaps a few embedded
thunderstorms overnight. Winds becoming E at 5 to 15 knots.
Wednesday...High confidence in trends. Moderate confidence in
timing.
Rainfall comes to an end, with IFR conditions trending to MVFR
into the afternoon.
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...BW/Frank
NEAR TERM...BW
SHORT TERM...BW
LONG TERM...Frank
AVIATION...BW/Frank
MARINE...BW/Frank
Source: BOX issues Area Forecast Discussion (AFD) at Dec 31, 3:17 PM EST (https://mesonet.agron.iastate.edu/p.php?pid=202412312017-KBOX-FXUS61-AFDBOX)
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