BOX issues Area Forecast Discussion (AFD) at Dec 5, 12:41 PM EST
929
FXUS61 KBOX 051741
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
1241 PM EST Thu Dec 5 2024
.SYNOPSIS...
This morning's storm system will lift out today bringing an end to
widespread rain and snow by mid day. A strong cold front will then
bring a few snow squalls and strong winds in the afternoon. Gusty
conditions and below normal temperatures continue Friday into
Saturday with a low chance of an isolated snow shower or snow
squall. A weak clipper system passes through northern New England
early Sunday and brings a light snow shower to areas mainly north of
Route 2 in northern Massachusetts. Then the first-half of next week
features mild temperatures and a more active weather pattern.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
1045 AM Update:
Made several changes to the forecast. The first was to expire
the Winter Weather Advisory, as additional accumulations where
the Advisory was are no longer expected with steadier snow
having since ended/moved off the coast. See the latest Public
Information Statement for reported snowfall totals. A pretty
wide range in snowfall totals with most on grassy surfaces, and
the highest totals were by-and-large confined to elevations
above 700 ft.
For at least the next couple hours, we're looking at relative
downtime between the system from overnight/early this morning,
and an advancing strong cold front associated with much colder
air. Southwesterly winds should also be around 5-10 mph in this
period of time so on the modest side. These conditions should
last through the 12-2PM hours from west to east.
Focus then turns to the approaching strong cold front, now
marching through the Catskills of NY. A line of scattered heavy
snow showers and brief snow squalls, a couple of which had
observed lightning in northeast PA, are currently moving their
way into the Hudson Valley in NY. HRRR seems to have the best
handle on this activity, which looks to move into our interior
MA/CT counties between noon and 3 PM. Temperatures are hovering
in the mid 30s in western/central MA and northern CT although
similar temperature conditions were occurring in eastern PA, so
think there will still be potential for brief heavier snow
showers and possible snow squalls. Opted to bring awareness to
this potential through an SPS, and will then reassess radar and
observational trends for either SPSs or baseline snow squall
warnings if conditions develop into brief whiteouts.
Regarding the winds/wind gusts...we do have the Wind Advisory
across Cape Cod and the Islands currently active for SW gusts
overnight/earlier this morning, but winds have subsided and are
currently well below Advisory criteria. However passage of the
cold front late this afternoon and tonight will bring increased
NWly gusts, so am reluctant to drop the advisory even though
gusts over the Cape and Islands will fall well short for several
hours until the NWlys increase late this afternoon and tonight.
Previous discussion:
Rain and snow are ongoing this morning and will continue
through mid to late morning, exiting from mid morning (western
MA/CT) to late morning (eastern MA) as the parent low currently
over the eastern Great Lakes moves to northern Maine. A
particularly heavy band over RI/eastern MA has enough intensity
for dynamic cooling to overcome marginal temps (33-35F) and
bring some accumulating snow over the coastal plain of southeast
MA and RI as far south as Providence and east as Boston. Temps
should only be increasing on SW flow, but accumulations of up to
an inch or so will be possible even over southeast MA and
central Rhode Island which may be enough to cause minor issues
with the morning commute.
Later an impactful (to highway travel) period of scattered snow
squalls arriving in western MA/CT around noon accompanying the
passing cold front and deep mid level trough. Lingering low level
moisture combined with several favorable instability parameters
(steep 1000-700 mb lapse rates and several hundred J/kg of CAPE)
will set the stage for a few decent snow squalls. These will bring
the potential for rapid reduced visibility in blowing snow as well
as dropping a quick half inch to inch of snow. Boundary layer
temperatures will be more moderate along and east of the I-95
corridor so a rain/snow mix or plain rain showers are more likely in
the 2-5pm window.
Speaking of blowing snow, more widespread strong W/NW winds will
kick up over all of southern New England as cold advection leads to
good mixing of the boundary layer up to near 800 mb where we have a
~50 kt LLJ. The strongest winds (gusting 40-50 mph) are expected
over western/central MA, CT, and the Cape/Islands where a Wind
Advisory is in effect. However, it will be gusty over the rest of
SNE as well, more in the ballpark of 35-45 mph.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
Key Messages...
*Below normal temperatures and gusty winds Friday
Tonight we're placed between a low to our northeast and a high to
our southwest. The resultant tight pressure gradient leads to
continued gusty winds overnight, generally 30-40 mph. Post frontal
cold advection brings 925 mb temps down to -7 to -9C overnight which
results in lows as cold as the upper teens (high elevations) to
upper 20s (along the coast). However, given the gusty winds it will
feel more like the single digits to low 20s respectively. Friday not
much change in the synoptic pattern so winds remain elevated with a
much colder airmass overhead. Highs won't make it out of the 20s in
the high elevations and mid 30s elsewhere.
&&
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Key messages:
* Blustery and cold to start the weekend
* Chance for a snow shower, particularly in the Berkshires, Friday
night/early Saturday morning
* Milder, unsettled conditions to start the week
Friday and Saturday
The clipper system continues to move out of the region and high
pressure moves in to take its place. Between these systems, winds
are expected to continue to be gusty (up to 25 mph) primarily from
the west before high pressure fully takes over by the evening hours
Saturday. The latest guidance has a small chance for some
orographically-forced snow showers in the Berkshires, but that
chance remains low for the time being. There is not significant CAPE
in the models to indicate a strong signal for snow squalls, but a
small signal for some snow is present. Snow or not, it will be cold;
850 mb temps are still forecast to settle at and just below -15C as
an arctic airmass sinks in over southern New England. Friday and
Saturday night lows are very likely to be in the teens and 20s, and
highs Saturday are likely not getting out of the 30s.
Sunday onward
Winds die down considerably and shift more southerly, and
temperatures become more mild as the arctic airmass exits the
region. Another clipper system is expected to pass to the north and
the moisture associated with it is expected to remain there. Some
chances for snow showers, particularly in northern MA, may be
present, but the chances are low. High temperatures should increase
to the upper 30s/low 40s.
To start the work week, S to SW flow persists and a warming trend
takes hold. 850 mb temps climb out of the negatives and sit closer
to +5C by early Tuesday morning. Highs Monday through Wednesday are
expected to be more in the low to middle 50s. Ensembles still have a
signal for rain starting Monday afternoon going through Wednesday,
but it's important to note that this far out, timing is still very
likely to change.
&&
.AVIATION /18Z THURSDAY THROUGH MONDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
18z TAF Update:
Through 00z Friday: Moderate confidence.
Mix of borderline VFR/MVFR ceilings through 19-22z with SW
winds around 10-12 kt with gusts 20-25 kt. Strong cold front
moves west to east through the terminals 20-23z, bringing a
brief increase/surge in WNW gusts to 35-40 kt along with a brief
period of at least MVFR visby rain/snow. It is possible that
more intense activity could bring visbys to briefly IFR levels
and indicated this with TEMPOs.
Rapid clearing to VFR upon passage of the cold front, but with
increasing WNW speeds and gusts to 15-20 kt with gusts 35-40 kt;
highest gusts for the interior airports and over the Cape and
Islands.
Tonight: High confidence.
VFR, though could be some borderline MVFR ceilings in/around the
Berkshires. Strong WNW winds with gusts 35-40 kt thru 03z, with
slow decreases in WNW gusts 25-35 kt thru overnight.
Friday and Friday Night: High confidence.
VFR. Gusty WNW winds 25-35 kt during the morning, then gradually
decreasing to 25-30 kt thru the day. Gusts should ease into the
evening and overnight to sustained WNW/W winds around 5-10 kt.
KBOS Terminal...Moderate confidence in TAF. Borderline MVFR/VFR
with SW winds 10-15 kt with gusts 20-25 kt. Cold frontal passage
20-22z with TEMPO MVFR, possible IFR-visby RASN with increasing
WNW gusts to 40 kt briefly. Rapid improvement to VFR after 22z
with WNW gusts settling in around 35 kt, slowly decreasing to
around 30 kt early Fri AM.
KBDL Terminal...Moderate confidence in TAF. MVFR ceilings with
southerly winds around 10 kt. Cold frontal passage 19-21z with
TEMPO MVFR, possible IFR-visby RASN with increasing WNW gusts to
40 kt briefly. Rapid improvement to VFR after 22z with WNW
gusts settling in around 35-40 kt, slowly decreasing to around
30 kt early Fri AM.
Outlook /Friday Night through Monday/...
Friday Night through Saturday: VFR. Breezy.
Saturday Night: VFR. Slight chance SN.
Sunday: VFR. Breezy. Slight chance RA, slight chance SN.
Sunday Night: VFR.
Monday: MVFR/IFR conditions possible. RA likely.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
* Gale Warnings tonight through Thu night with 45 knot gusts
Today and tonight...
SSW wind gusts of 30 to 45 knots early this morning. The
strongest of those winds tonight are across the southern
waters.
A strong cold frontal passage crosses the region today. Winds
become westerly this afternoon, gusting 35 to 45 knots and
continuing through tonight. Gale Warnings are in effect on all
waters though this time and seas will be quite high and rough.
Friday...
Dry with gusty NW winds 25 to 35 kts. Seas 4-8 ft.
Outlook /Friday Night through Monday/...
Friday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas up to 5 ft. Chance of snow.
Saturday through Saturday Night: Winds less than 25 kt. Areas
of seas approaching 5 ft. Chance of rain, chance of snow.
Sunday: Winds less than 25 kt. Local rough seas. Chance of
rain.
Sunday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of rain.
Monday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Rain likely.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Wind Advisory until 10 PM EST this evening for CTZ002>004.
MA...Wind Advisory until 10 PM EST this evening for MAZ002>004-
008>012-022>024-026.
RI...Wind Advisory until 10 PM EST this evening for RIZ008.
MARINE...Gale Warning until 7 AM EST Friday for ANZ230>237-250-251-
254>256.
&&
$$
SYNOPSIS...BW/Hrencecin
NEAR TERM...Loconto/BW
SHORT TERM...BW
LONG TERM...Hrencecin
AVIATION...Frank/Loconto
MARINE...Frank/Loconto
Source: BOX issues Area Forecast Discussion (AFD) at Dec 5, 12:41 PM EST (https://mesonet.agron.iastate.edu/p.php?pid=202412051741-KBOX-FXUS61-AFDBOX)
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