662
FXUS61 KBOX 080022
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
722 PM EST Fri Feb 7 2025

.SYNOPSIS...

Winds diminish tonight with colder conditions into
Saturday. A snow storm is on tap later Saturday night into
Sunday morning, with perhaps some mixing at the end of the storm
near the outer-Islands. Drying out Sunday night through
Tuesday, with a period of cooler than normal temperatures and
limited if any snowmelt from the Saturday night storm. Our
weather pattern then becomes more active again with a coastal
low pressure passing to our south on Tuesday night into
Wednesday that may bring light snow, and monitoring a stronger
storm around late next week.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...

Winds gradually trend downward early this evening as the
pressure gradient relaxes and high pressure moves in. Quiet and
dry weather overnight with low temperatures dropping into the
middle teens to the lower 20s in most locations.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY/...

Key Messages:

* Snowstorm moves across southern New England Saturday night into
  Sunday morning.

* Medium confidence in snow totals with a mostly likely range of 4-
  8" across southern New England.

* Potential for freezing drizzle/snizzle on back end of storm Sunday
  AM.

Saturday:

Dry and less windy Saturday with surface high pressure in place
during the day. A colder airmass remains in place with 850mb
temperatures -9 to -13C. This will support highs in the low to mid
30s. Our next storm system approaches from the south with this
cooler airmass setting the stage for snowfall. Mid-level clouds
develop ahead of the system in the afternoon with increasing
moisture.

Saturday Night and Sunday:

A mid-level shortwave trough and a surface low tracking up east
coast will provide the favorable synoptic forcing for large-scale
precipitation. Latest model guidance hasn`t changed too much overall
with the track of the surface low across the 70/40 benchmark with
only some subtle northward trends in guidance. With plenty of cold
air to start, this puts us in a good place for snowfall.

In terms of timing we will see snow arriving generally from west to
east in the 6-10 PM timeframe. Other than large scale dynamics to
support lift for snow, we will also have frontogenetical forcing as
the warm front shifts across the region Saturday night. Model
soundings show a deep moisture coupled with positive omega fields in
the dendritic growth zone. All good signals for efficient snow
making which will lead to a period of moderate to heavy snow rates
late Saturday night through early Sunday morning (~10pm-3am). This
leave a 4-5 hour period for better snow rates to accumulate snow
quickly.

However, this is not a "slam dunk" warning criteria event. There are
some limiting factors here. As the surface low tracks northeast into
early Sunday morning, it brings a dry slot. This has been quite
evident in the mid and upper level RH fields. This will cut off the
deeper moisture, especially in the dendritic zone. As this dry slot
advances northward after 1-2 AM, the higher snow ratios and rates
will drop off. Model soundings reflect this issue with BUFKIT NAM
soundings showing warm air moving in aloft (close to slightly above
0C) and a layer of dry air above it. There is still omega in the
lower levels (not in DGZ) to support light precipitation. Depending
on how deep the below freezing layer is, this may support freezing
drizzle or snizzle on developing from south to north and the
backside of the storm early Sunday morning. If this moves in
quicker, this could impact snow totals. This is what wavers the
confidence in our snow totals. As the low lifts northeast, we will
get some wrap around across northern MA as winds transition north to
northwest 6-9 am. Could also get ocean enhancement as well given the
wind direction. Precipitation should come to and end from southwest
to northeast by early afternoon.

As for totals, ensemble mean QPF ranges from 0.4-0.7". Deterministic
models like the NAM are on the lighter end of guidance. Ensembles
have been interesting as far as highlighting potential areas for
higher totals with the ECMWF highlighting higher probabilities
(50- 70%) for 6"+ across the south coast and the SE MA while the
GEFS shows that axis for higher probabilities in north MA. The
ECMWF is likely hinting at a strong frontogenetical band owing
to potentially higher totals while the GEFS is highlighting the
combination of banding as well as an environment impacted by the
dry slotting less. A blend of guidance brings a general
widespread 4-8" across southern New England, so high-end
advisory to low end warning criteria. Given the uncertainty with
how this dry slot will impact totals, we decided to wait
another forecast cycle. A Winter Storm Watch is still in effect
for southern New England and there is a good chance that most
areas will be upgraded to a Warning.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...

Key Messages:

* Dry Sunday night through Tuesday, with slightly colder than normal
  temps. Some snowmelt possible but very limited if any at all.

* Monitoring low pressure moving off the mid-Atlantic coast Tue
  night for possible light snow, but the exact track and how much
  precip we could see, if any, is still uncertain.

* Stronger storm system around late in the week, but the exact track
  and precip amounts/types with this system are highly uncertain.

Details:

Sunday into Tuesday:

High pressure then builds back in for later Sun, with high pressure
remaining established into at least Tue. This area of high pressure
will bring a returning period of below-normal temperatures along
with sustained dry weather, in what is otherwise a rather active
weather pattern. Highs in this period only in the upper 20s to the
mid 30s, with lows in the teens (single digit lows Sun night). Thus,
although we should see a good amt of sunshine in this period of
time, temperatures will only support very limited if any melting of
snowpack.

Tuesday Night:

The active weather pattern then resumes for Tue night...as a
shortwave disturbance comes out of the central/southern Rockies Mon
and induces low pressure development in the southern Plains/mid-MS
Valley region and moves into the mid-Atlantic states Tue night.

It`s quite likely that temps would be cold enough to yield snow as
the dominant precip type. The exact track and how much precipitation
we receive from this system, if any, are both still uncertain. Prior
ECMWF and its parent EPS ensemble runs have been on the northern end
of the model-guidance envelope when it comes to precip this far
north into Southern New England. This is reflected in rather solid
(50-70%) EPS probs of 24-hr QPF at or above 0.1", with lower probs
(<30%) of 24-hr QPF of a half inch or greater. If the EPS/ECMWF
solutions are closer to correct, we could be looking at another
minor to perhaps moderate accumulating snow event. On the other hand
the GFS and Canadian are quite a bit less with several members being
dry; probs of 24-hr QPF of 0.1" or greater are less than 30% in both
ensemble systems, and would lead to little to no substantial impact
at all. Did note that the trend in current to previous ECMWF runs
have showed a decrease in QPF probabilities, indicating a possible
trend toward a somewhat drier/less robust outcome. With the
shortwave itself not looking strong, the wave itself being
progressive and a trend toward greater precip suppressed to the
south, the odds favoring a significant winter storm are pretty
long/unlikely with an offshore pass being a little more favored. But
given the spread in guidance, it is still too early to lock into any
singular outcome as yet.

Wednesday through Thursday Night:

We may get into brief high pressure behind the Tue night system for
Wed. But right on its heels is a stronger shortwave aloft which
comes out of the Rockies on Wed and induces a more robust area of
low pressure to come out of the mid-MS/OH Valley region Wed night
and into the Northeast on Thurs. The exact track and strength of
this system is also unclear at this time, but indications in the
ensembles is that a stronger wave allows for more downstream/SE
ridge amplification; that could introduce warmer air aloft coming in
from the south into the mix. Will leave PoP in the higher end of
Chance.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...

Forecast Confidence Levels:

Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

00z TAF Update...

Tonight & Saturday...High Confidence

VFR. W/WNW winds will continue to diminish tonight. W winds
5-10 knots on Sat shift to more of a SW direction by late
afternoon.

Saturday night and Sunday...High Confidence.

IFR/LIFR conditions rapidly develop Sat evening. This as snow
overspreads the region from southwest to northeast between 00z
and 03z Sun. The snow will fall heavy at times into the
overnight hours with 1-2" per hour rates at times. Brief change
over to rain/sleet is possible for mainly the Islands.

Snow winds down from west to east Sun morning...but will linger
longest across central and eastern MA. Improvement to VFR will
occur during the afternoon across western MA/CT...but lower cigs
may linger a bit longer across eastern MA with even a few left
over snow showers/flurries near the coast.

Light S winds Sat evening become NE at 5-10 knots by daybreak
Sun. Winds then shift to the NW Sun afternoon and speeds of 8-14
knots.


KBOS TAF...High Confidence in TAF. Snow arrives near 02z/03z Sun.


KBDL TAF...High Confidence in TAF. Snow arrives near 00z/01z
Sun.

Outlook /Sunday Night through Wednesday/...

Sunday Night through Monday Night: VFR.

Tuesday: VFR. Chance SN.

Tuesday Night: Mainly IFR, with local VFR possible. SN likely.

Wednesday: Chance SN.

&&

.MARINE...
Forecaster Confidence Levels:

Low - less than 30 percent.
Medium - 30 to 60 percent.
High- greater than 60 percent.

Overall high confidence through Saturday.

Gale warnings have been converted to Small Craft Advisories as
winds continues to decrease this evening. Winds and seas
subside tonight into Saturday as high pressure builds into
region from Great Lakes.

Outlook /Sunday Night through Wednesday/...

Sunday Night: Winds less than 25 kt. Seas up to 5 ft. Slight
chance of snow.

Monday: Winds less than 25 kt. Areas of seas approaching 5 ft.

Monday Night: Winds less than 25 kt. Seas locally approaching
5 ft.

Tuesday: Winds less than 25 kt. Chance of snow.

Tuesday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Snow likely. Visibility 1 nm or less.

Wednesday: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of snow, slight chance of rain.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Winter Storm Watch from Saturday evening through Sunday
     afternoon for CTZ002>004.
MA...Winter Storm Watch from Saturday evening through Sunday
     afternoon for MAZ002>024-026.
RI...Winter Storm Watch from Saturday evening through Sunday
     afternoon for RIZ001>007.
MARINE...Small Craft Advisory until 1 AM EST Saturday for ANZ230>237.
     Small Craft Advisory until 7 AM EST Saturday for ANZ250-251-
     254>256.

&&

$$

SYNOPSIS...Loconto/Mensch
NEAR TERM...Mensch
SHORT TERM...Mensch
LONG TERM...Loconto
AVIATION...Frank/Loconto/Mensch
MARINE...Loconto/Mensch