BOX issues Area Forecast Discussion (AFD) at Dec 19, 4:34 PM EST791
FXUS61 KBOX 192134
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
434 PM EST Thu Dec 19 2024
.SYNOPSIS...
An offshore coastal storm is likely to bring light snow
accumulations late Friday into Saturday followed by very cold
weather into early next week. The weather pattern becomes unsettled
again as we head toward Christmas Day but temperatures will be
moderating.
&&
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
* Dry and quiet tonight with seasonably cold temperatures
High pressure passing to our north tonight will keep things quiet
and dry throughout with light winds. Given 925mb temps around -4C we
can expect lows generally in the mid to upper 20s, save for the Cape
and islands where low 30s are more likely thanks to the moderating
influence of the ocean.
&&
.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
Key Messages...
* Widely scattered ocean effect showers are possible during the day
on Friday with more light snow over the interior in the
evening/early overnight
As early as sunrise on Friday we should begin to see widely
scattered ocean effect snow (interior) and rain (immediate
coast/southeast MA). This, thanks to a surface low lifting north
from the mid Atlantic and deepening as it passes southeast of the
benchmark Friday night. The trajectory will keep the bulk of the
moisture and forcing (including the deep mid level trough) well
south of our region. Thus, not expecting much in the way of impacts
from this wintry system, more of a festive pre-Christmas snowfall
that will drop anywhere from a coating to an inch or two from Friday
into Saturday afternoon. New guidance today continues to keep most
of the QPF offshore in closer proximity to the low/forcing. Ensemble
clustering retains some spread in the speed of the low, but shows
higher confidence of a well offshore track. High pressure to our
north will help to keep temperatures down, highs limited to the mid
30s to low 40s (hence, the struggle to accumulate snow for many
locations). As the trough begins to move overhead this larger scale
forcing will bring more widespread light snow to the interior
overnight, but again, lack of moisture will be a big limiting factor
to us getting any more than a coating to an inch.
&&
.LONG TERM /SATURDAY THROUGH THURSDAY/...
Key Messages
* Dry this weekend but with very cold temperatures
* Temperatures trending back toward normal early next week
* Modest rain/snow event possible for Christmas Eve/Christmas day
Saturday through Monday night
A fairly deep low-pressure system off the east coast of southern New
England will continue to depart east on Saturday. A few lingering
snow showers may be possible during the day in a cold northwest
flow, but generally expecting dry/chilly conditions. Deep northwest
flow behind the departing low will advect a polar air mass over the
region on Saturday with 925 hPa temps dipping to -7 to -10 Celsius
by Saturday evening. This will support chilly temperatures Saturday
through Monday with high temperatures in the afternoon below the
freezing mark for most locations in southern New England. Low temps
will also be substantially below normal Saturday night through
Monday night with interior locations falling to single digit
temperatures. Elsewhere, low temps in the 10 to 20 degree range with
the milder temperatures focused near the immediate coast. Peak of
the cold will be Monday morning when some locations in western MA
may flirt with the 0F mark. This time period will be dominated by
surface high pressure, so expect dry conditions through Monday with
the exception of perhaps a few snow showers on Saturday.
Tuesday night through Thursday
As high pressure shifts east early Tuesday, short-wave energy digs
down from The Great Lakes, supporting a modest precipitation event
on Christmas Eve. The column should be cold enough to support
snowfall across the interior, but return flow from the south will
result in some temperatures above freezing across southeastern MA
and RI where rain will be more likely. Still some details to iron
out, but if we consult ensemble guidance we find that the model
exceedance probabilities for greater than 1 inch of snow on
Christmas Eve ranges from 20 to 40 percent for locations north of
CT/RI. Probabilites drop to 10 to 20 percent for RI and southeastern
MA. There is agreement among model guidance for this system to be
progressive and to be followed by surface high pressure which should
support a quiet Christmas Day and end of next week.
&&
.AVIATION /22Z THURSDAY THROUGH TUESDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
This afternoon: High confidence.
VFR. NW wind 10-20 kt with a few higher gusts.
Tonight: High confidence.
Mainly VFR, with some MVFR east toward 12z in light RA/SN.
Light N-NE wind.
Friday...Moderate confidence.
Lowering cigs to MVFR in light RA/SN, very scattered in the
morning, more widespread toward the evening especially over
southeast MA. Some minor accums possible west of I-95 and 128
in MA. NE wind 8-15 kt.
Friday night...Moderate Confidence.
MVFR/IFR in scattered RA/SN, mainly over SE MA and RI terminals.
Preciip exits toward 12Z with some improvement to VFR overnight
in the interior.
KBOS TAF...High confidence in trends.
KBDL TAF...High confidence in trends.
Outlook /Saturday through Tuesday/...
Saturday: Mainly VFR, with local MVFR possible. Breezy. Slight
chance SN.
Saturday Night through Sunday Night: VFR. Breezy.
Monday: VFR.
Monday Night: VFR. Slight chance SN.
Tuesday: Mainly VFR, with areas MVFR possible. Chance SN.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Key Messages:
* Small Craft Advisory issued for Friday afternoon through
Friday night.
Tonight: High confidence.
NW winds lighten and then shift to NE around 10-15 kt. Seas
between 2 and 4 feet.
Friday: Moderate confidence.
Surface low pressure system moves up the coast and remains out
to seas. Increasing east/northeast winds 15 to 20 knots with
gusts up to 30 knots on the outermost waters, nearshore waters
gusts are closer to 25 knots. Seas building 4 to 7 feet. Will
likely need to reissue a Small Craft Advisory for these
conditions.
Friday Night: Moderate confidence.
NE winds 25-30 kts with seas 6-9 feet.
Outlook /Saturday through Tuesday/...
Saturday: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Rough seas up to 10 ft. Chance of snow.
Saturday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 25 kt. Areas of rough seas. Chance of snow.
Sunday: Winds less than 25 kt. Local rough seas. Chance of
snow.
Sunday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of snow.
Monday: Winds less than 25 kt. Seas locally approaching 5 ft.
Monday Night: Winds less than 25 kt.
Tuesday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain, chance of snow.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 4 PM Friday to 7 AM EST Saturday for
ANZ231>235-237-251.
Small Craft Advisory from 1 PM Friday to 7 AM EST Saturday for
ANZ250-254>256.
&&
$$
SYNOPSIS...BW/RM
NEAR TERM...BW
SHORT TERM...BW
LONG TERM...RM
AVIATION...BW/RM
MARINE...BW/RM
Source:
BOX issues Area Forecast Discussion (AFD) at Dec 19, 4:34 PM EST----------------
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