BOX issues Area Forecast Discussion (AFD) at Jan 19, 7:25 AM EST557
FXUS61 KBOX 191225
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
725 AM EST Sun Jan 19 2025
.SYNOPSIS...
Low pressure will bring a quick hitting snowstorm to most of the
region later today and especially tonight...which may begin as a
brief period of rain. An arctic airmass will bring frigid
temperatures and wind chills on the order of 5 to 15
below zero at times Monday night through Thursday
morning. Temperatures moderate a bit in the Thursday through
Saturday time frame...but they will remain below normal. Dry weather
will generally prevail...but a bit of light snow/flurries may clip
the southeast New England coast late Tuesday night into Wednesday
morning. Another wave of low pressure will bring the low risk for a
period of snow late Thursday night into Friday if the system tracks
close enough to the coast.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Key Messages...
* Areas of fog & patchy black ice early this morning
The first half of Sunday will be quiet with yesterday's system/rain
exited to the northeast. Early this morning, the main concerns
will be black ice and areas of fog. A combo of recent rainfall
and temperatures at or just above freezing by sunrise will
support areas of black ice, especially on bridges and overpasses.
If traveling, take caution. Surface observations and nighttime
microphysics satellite imagery indicate areas of fog across
parts of the CT River Valley, Cape Cod, and northeast MA. Some
locations have reported 2 miles to as low as 1/4 mile. A Dense
Advisory remains in effect through 9 AM this morning,
particularly for the areas mentioned above.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/...
Key Messages...
* Plowable snow late Sunday and through Sunday night.
* A Winter Storm Warning in effect for along and northwest of
Boston-Providence line. Winter Weather Advisory for areas
southeast of I-95
* Potential for bands of localized higher snow rates/amounts
setting up tonight. Low confidence on where they set up.
Temperatures rise into the upper 30s and low 40s today with
breaks of sun developing mid- morning. This improvement will be
short-lived as clouds increase by early afternoon ahead of the
incoming storm. This afternoon, our snowmaker of a storm will
track offshore of the mid-atlantic coast as a surface low ahead
of a broad upper trough. This surface low is expected to track
up the east coast Sunday night into Monday. The track of this
storm has come into better agreement among model and ensemble
guidance. However, there are still subtle differences that are
enough to create differing solutions in snowfall amounts.
Ingredients and features...
Ingredients are there to support a system capable of bringing
snow Sunday PM through Monday. Southern New England sits in an
optimal position for large scale ascent with respect to the
upper level jet. This will be coupled with ample moisture with
precipitable water values around 180-200% of normal. Despite
small differences in strength/track of the low, there is good
agreement among guidance for frontogenetical forcing extending
across portions of southern New England. Features to watch as
they will provide additional forcing/lift to help generate
higher rates within snow bands. HREF in particular indicates
these bands across north and central MA and another positioned
across SE MA along the coastal front. HREF means show potential
for 1-2" rates within these bands Sunday night(7pm- 1am). All
supported by the localized forcing and cold air advection for
higher ratios.
Storm track...
Deterministic and ensemble guidance has come into better and
consistent agreement on the track of the system. Still these
subtle differences in track and strength will have impacts on
expected totals and other details such as precipitation type at
the onset of the event. Some models have consistently showing
higher totals than others (e.g. GFS) while other models have
leaned lighter(ECMWF). There has also been some run to run
inconsistencies even this close to the event, particularly with
respect to banded snowfall amounts. Track will also influence
precipitation type with a more inland track meaning rain or
rain/snow for longer before switching to snow across areas
southeast of I-95. A blend of solutions support a start as rain
or a rain/snow mix for those areas. This seems realistic as high
resolution guidance shows the coastal front with ocean modified
air pushing into those areas Sunday afternoon while it's colder
to the north and west. The kicker will be how this coastal
front continues to position tonight as CAA works in from the
north as the low tracks across. As a result, areas generally
south and east of I-95 will hold a larger degree of uncertainty
in amounts.
Timing and Amounts...
There is sufficient confidence on the timing of onset for this event
with precipitation beginning in the 3-5pm timeframe for northern CT
and western MA and 4-6pm across central, east, southeast MA and RI.
Again, rain or a rain/snow mix is looking likely in areas at onset,
more likely across RI, east and SE MA before flipping to snow this
evening. Snow continues overnight with the most likely period for
banded, localized heavier snowfall falling in the 7pm-1am timeframe.
Snow decreases from west to east with snow diminishing by 7 am
Monday.
This is generally looking like a high end advisory to low end
warning event for areas north and west of I-95 with 6-8"
forecast. If banding does materialize, can't rule out the low
chance at localized amounts up to 10 inches (per HREF ens max).
Confidence is lower on the where these bands set up tonight. These
areas are under a Winter Storm Warning. For southeast of I-95,
there is greater uncertainty in how quickly it changes to snow
which will impact snow amounts. High resolution guidance has
hinted at the potential for a frontogenetical band positioning
in this area Sunday night and if cold enough could enhance snow
amounts with localized amounts near warning criteria. Given the
large amount of uncertainty, we put southern RI and MA
(southeast of I-95) in a Winter Weather Advisory for 3-6".
Impacts...
This storm will bring the usual impacts brought in with a
winter storm such as reduced visibilities and snow covered roads
making for hazardous in areas Sunday night. Snow will likely be
done by 7am for those who are participating in the AM commute.
Strong cold air pushes into the region, starting the streak of
frigid temperatures this week.
&&
.LONG TERM /MONDAY THROUGH SATURDAY/...
Key Points...
* Arctic Outbreak Mon PM through Thu AM
-Wind Chills 5 to 15 below zero and perhaps as low as -20 in spots
-Actual Lows in the single digits with some below zero
-Actual highs Tue & Wed mainly between 15 and 20
* Temps moderate a bit Thu/Fri/Sat but will remain below normal
* A period of light snow or flurries may clip southeast New England
esp the Cape/Islands late Tue night-Wed AM...Dependent on track
* Low risk for a period of snow late Thu night into Fri
Details...
Monday through Thursday morning...
All the model guidance continues to agree on an arctic outbreak in
the Mon through Thu am time frame. 850 MB temperatures will drop to
around -22C/-23C as arctic air pours into the region from the
northwest. Highs on Mon should reach the lower to middle 20s
for most locations with gusty NW winds. By Tue and Wed...expect
highs to mainly be in the 15 to 20 degree range. Overnight
low temps will be in the single digits with some below zero readings
at times...particularly Tue night when winds decouple. Wind Chills
will drop to between 5 and 15 below zero and perhaps as low as -20
in spots. Cold Weather Advisories will be needed.
The vast majority of this time will feature dry weather. We may see
a few brief spot snow showers Mon PM as the arctic air rushes into
the region. We may also see a period of light snow or flurries clip
the southeast New England coast late Tue night into Wed am from a
distant wave of low pressure. At this point...even if it happens
does not look to be a big impact. Nonetheless...some very minor
accumulations would be possible especially if winds can turn more
NNW which would result in some ocean effect/enhancement across the
Cape and Nantucket.
Thursday afternoon into Saturday...
The core of the coldest air begins to shift northeast and away from
our region. It still will be rather cold though with highs mainly in
the 20s Thu and perhaps 30 to 35 by Fri and Sat.
Also...we will be watching a low pressure system that will
bring snow/ice right down to portions of the Gulf Coast early this
week! This wave of low pressure will then track northeast...likely
passing southeast of the Benchmark. The majority of the GEFS/EPS/CMC
ensembles indicate this storm will miss us or just bring us a
glancing blow. That being said there are a few ensemble members that
are further northwest and would bring a better shot at snow to the
region...especially the coastal plain. We will likely need a few
more days to have a better idea on this risk.
Monday...High Confidence.
Mainly VFR outside a few brief spot snow showers that will be
possible. NW wind gusts of 20 to 30 knots.
KBOS TAF...Moderate Confidence in TAF. Heaviest of the snow
roughly between 00z and 05z. 1" per hour snowfall rates possible
at times.
KBDL TAF...Moderate Confidence in TAF. Heaviest of the snow
roughly between 22z and 03z. 1" per hour snowfall rates possible
at times.
IFR/MVFR this evening, becoming VFR overnight. VFR most of
Sunday. Light snow and MVFR CIGS move in between 21-23z.
Outlook /Monday through Thursday/...
Martin Luther King Jr Day: VFR. Windy with local gusts up to
30 kt. Slight chance SHSN.
Monday Night through Tuesday: VFR. Breezy.
Tuesday Night through Wednesday: VFR. Breezy. Slight chance
SHSN.
Wednesday Night through Thursday: VFR. Breezy.
&&
.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
12z TAF Update...
Today and tonight...Moderate Confidence.
Spotty/variable areas of shallow FG this morning in the valleys
and Cape early this morning including BDL, BAF, BED, and Cape
terminals. Areas of FG erode out by by 14z.
After the low clouds and fog burn off we should see a period of
mainly VFR conditions into a good portion of the afternoon.
Precipitation spreads across region from west to east between
20z and 23z with conditions lowering to MVFR/IFR.
Ptype will mainly be snow NW of I-95...but a period of rain may
occur near and especially southeast of I-95. Ptype should
transition to mainly snow northwest of the Cape Cod Canal by
00z/01z or so. Heavier snow rates will likely occur 00z through
04z/05z when IFR/LIFR conditions are expected. Snowfall rates of
1-2" per hour will be possible at times. Total snow
accumulations of 3-6"/4-8" will be common for much of the region
northwest of the Cape Cod Canal. Ptype probably changes to all
snow before ending even across the Cape. The last of the steady
snow should exit the coast by 09z/10z Mon. Conditions will
improve to VFR by daybreak Monday.
Winds should become N at 5 to 10 kts this afternoon. Winds
become more NW later tonight with gusts of 20-25 kts developing
and perhaps up to 30 kts at ORH and Cape terminals briefly.
Monday...High Confidence.
Mainly VFR outside a few brief spot snow showers that will be
possible. NW wind gusts of 20 to 30 knots.
KBOS TAF...Moderate Confidence in TAF. Heaviest of the snow
roughly between 00z and 05z. 1" per hour snowfall rates possible
at times.
KBDL TAF...Moderate Confidence in TAF. Heaviest of the snow
roughly between 22z and 03z. 1" per hour snowfall rates possible
at times.
IFR/MVFR this evening, becoming VFR overnight. VFR most of
Sunday. Light snow and MVFR CIGS move in between 21-23z.
Outlook /Monday Night through Thursday/...
Martin Luther King Jr Day through Tuesday: VFR. Breezy.
Tuesday Night: VFR. Slight chance SN.
Wednesday: VFR. Breezy. Slight chance SN.
Wednesday Night through Thursday: VFR. Breezy.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High- greater than 60 percent.
High confidence...
Sunday winds are light most of the day, increasing to 15-20 kts
Sunday night with gusts to 30 kts as a low pressure passes from
southwest to northeast. Gusts up to 35 kts possible for the
northern outer waters tonight through early Monday resulting in
a Gale Warning. Otherwise, expect SCAs generally from 00z
tonight through 12z Tuesday. Seas 4-9 ft.
Outlook /Monday through Thursday/...
Martin Luther King Jr Day: Moderate risk for Small Craft
Advisory winds with gusts up to 30 kt. Rough seas up to 9 ft.
Freezing spray, slight chance of snow showers.
Monday Night: Low risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of rough seas. Freezing spray, slight
chance of snow showers.
Tuesday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of seas approaching 5 ft. Freezing spray.
Tuesday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Freezing spray, chance of snow showers.
Wednesday: Low risk for Small Craft Advisory winds with gusts
up to 20 kt. Seas locally approaching 5 ft. Freezing spray,
chance of snow showers.
Wednesday Night: Winds less than 25 kt. Seas locally
approaching 5 ft. Freezing spray.
Thursday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Freezing spray.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Dense Fog Advisory until 9 AM EST this morning for CTZ002>004.
Winter Storm Warning from 1 PM this afternoon to 7 AM EST
Monday for CTZ002>004.
MA...Dense Fog Advisory until 9 AM EST this morning for MAZ002>012-
014-022>024-026.
Winter Storm Warning from 1 PM this afternoon to 7 AM EST
Monday for MAZ002>016-026.
Winter Weather Advisory from 1 PM this afternoon to 7 AM EST
Monday for MAZ017>021.
RI...Winter Storm Warning from 1 PM this afternoon to 7 AM EST
Monday for RIZ001-002.
Winter Weather Advisory from 1 PM this afternoon to 7 AM EST
Monday for RIZ003>007.
MARINE...Small Craft Advisory from 1 AM to 7 PM EST Monday for ANZ230-
236.
Small Craft Advisory from 10 PM this evening to 7 PM EST
Monday for ANZ231>235-237.
Gale Warning from 7 PM this evening to 7 AM EST Monday for
ANZ250.
Small Craft Advisory from 7 PM this evening to 7 AM EST
Tuesday for ANZ251.
Small Craft Advisory from 7 PM this evening to 3 PM EST
Tuesday for ANZ254>256.
&&
$$
SYNOPSIS...Frank/Mensch
NEAR TERM...Mensch
SHORT TERM...Mensch
LONG TERM...Frank
AVIATION...Frank/Mensch
MARINE...Frank/Mensch
Source:
BOX issues Area Forecast Discussion (AFD) at Jan 19, 7:25 AM EST----------------
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