BOX issues Area Forecast Discussion (AFD) at Dec 28, 12:19 AM EST
702
FXUS61 KBOX 280519
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
1219 AM EST Sat Dec 28 2024
.SYNOPSIS...
Light icing and hazardous travel is likely Saturday morning,
mainly northwest of I-95, as a warm front approaches the region.
This front will bring rain and milder air into the region over
the weekend and into early next week. Another low pressure
system may bring rain around New Years Day, then colder air
should follow for the first few days of 2025.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
600 PM Update:
Forecast for tonight is on track after reviewing latest guidance
including 18z runs and hourly HRRR. High clouds were spreading
across SNE this evening but are not thick enough to prevent
temps from dropping off, but they should level off overnight or
even climb slowly near coast. Current timing of onset of -FZRA
in western MA/CT looks good as well with arrival after 6-7 AM
Sat.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
205 PM Update:
Key Messages:
* A light glaze of ice from freezing rain Saturday morning, with
risk along and northwest of I-95, but highest probs in the CT &
Merrimack River Valleys. Ice accretion will impact travel. Winter
Weather Advisories remain posted.
* Light rain across much of RI and southeast MA and islands, with
above freezing temps.
* Rain becomes more intermittent/drizzly later afternoon/evening.
Details...
Saturday:
Short wave trough and attending warm front with WAA precip currently
moving across the OH valley, will arrive here Saturday morning. 1030
mb high lingering over eastern MA early Saturday, will trap low
level/shallow cold air along and northwest of I-95. This will yield
a period of light freezing rain across most of CT into northwest RI
and most of northern MA, including metro-west Boston. Current
thinking was to extend winter advisory eastward into northwest RI
and northeast MA, including Boston, given existing snowpack of 2-5"
in this region will enhance radiational cooling tonight and delay
erosion of shallow cold air and frozen ground until midday or so. In
addition, it only takes a trace of freezing rain to cause hazardous
travel. Although, probabilities for ice within the advisory area is
not uniform, with highest probs across the CT and Merrimack River
Valleys, where cold air will have the greatest depth and therefore
take the longest to scour out. Hence, longer duration of icing
likely in these areas. Precip is expected to arrive 6 to 9 AM across
CT into western-central MA, and 8-11 AM for RI and eastern MA. If
precip arrives earlier, more icing would occur. Conversely, if
precip arrives later, duration of icing will lessen. Nonetheless,
exercise caution if travailing Saturday morning and allow extra time
to reach your destination.
During the afternoon, temps will rise above freezing and ptype will
be just rain, with intensity fairly light. Highs by late Saturday
will climb into the 40s, except only mid to upper 30s across the CT
and Merrimack River Valleys. Light and variable winds in the
morning, will be light south in the afternoon.
Saturday night...
Spotty light rain/drizzle expected with warm front along or near the
south coast. Given the location of this boundary, areas of fog are
likely across the region. True warm sector air likely remains
offshore, yielding lows in the upper 30s and lower 40s across the
region, which is still above normal for late Dec.
&&
.LONG TERM /SUNDAY THROUGH FRIDAY/...
205 PM update...
Key Messages:
* Mild with two rounds of rainfall Sun night-Mon and New Year's Day.
* Cold returns later next week but mainly dry.
Overall pattern favors mild and wet weather to close out 2024 in
southern New England with upper ridge parked offshore and a series
of southern stream troughs lifting through Great Lakes. As we begin
the New Year, a return to a colder/drier pattern seems likely as
downstream blocking develops and carves out deep trough/closed low
over Great Lakes and Northeast.
First system brings widespread rainfall in the Sun night through Mon
timeframe. Deep southerly flow aloft will bring plenty of moisture
with precipitable water values climbing to 1.00-1.25". This time
temperatures are expected to be above freezing at onset so we do not
have any concerns for icing. Most of rain falls later Sun night into
Mon with approach of upper trough and cold front, with widespread
0.50" to 1.00" expected, perhaps as much as 1.50" in parts of
western MA and CT where ensemble probabilities favor these higher
totals. Not looking for any significant flooding issues on
rivers/streams per MMEFS and flash flood guidance, but certainly
minor flooding of places that tend to flood in heavier rainfall is
possible.
After a brief lull, next system follows quickly on its heels for New
Year's Day. This system should have somewhat less moisture to work
with, but there are also indications of secondary low development
near or just offshore of SNE which could bring some lower level cold
air into play and perhaps bring a rain/snow mix, or even some wet
snow, to the higher elevations near Berkshires and northern
Worcester County. Something to note for now but either way it
doesn't seem to be too impactful.
A return to colder and dry weather appears likely into the first
weekend of 2025 as deep trough takes up residence in the Great Lakes
and Northeast. High pressure building into northern Plains will keep
our area under cold NW flow.
&&
.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
06Z TAF Update: Moderate confidence
Through 12Z...Moderate Confidence
VFR gradually deteriorating to MVFR/IFR at the western
terminals with -FZRA between 09 and 12Z.
Today...Moderate Confidence
MVFR/IFR ceilings spread east this morning with -FZRA/-RA.
Terminals of concern for light icing are BDL/BED/BAF with lower
risks at BOS/PVD. Cape/Islands terminals should be warm enough
to avoid an -FZRA. IFR/LIFR ceilings develop between 18 and 00Z
with some IFR vsbys possible in BR/-RA. Light south/southwest
winds.
Tonight...Higher Confidence
IFR/LIFR vsbys and ceilings persist overnight with light
south/southwest winds.
Tomorrow
IFR/LIFR for the first half of the day, then possible some
improvements to MVFR, particularly over the south coast. Periods
of scattered -RA. LIght south winds to start increase to 10 to
15 knots out of the south/southeast after 18Z.
KBOS TAF...Overall high confidence. Low risk for some -FZRA
between roughly 10-12Z, but high confidence that would quickly
transition to rain after sunrise with temps rising above
freezing.
KBDL TAF...Overall high confidence. Main time frame for
-FZRA is 12z-16z since we should see light N winds maintaining
low level cold air, but that should erode around 16z.
Outlook /Sunday through Wednesday/...
Sunday: Mainly MVFR, with areas IFR possible. Breezy. RA
likely.
Sunday Night: Mainly MVFR, with areas IFR possible. Breezy. RA.
Monday: Mainly VFR, with areas MVFR possible. Breezy. RA.
Monday Night: VFR. Breezy. Slight chance RA.
Tuesday: VFR.
Wednesday: Mainly VFR, with areas MVFR possible. Breezy. RA
likely.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
205 PM update...
This evening/tonight...high confidence. High pressure over New
England provides dry weather and light winds.
Saturday...high confidence. Warm front approaches from the south,
yielding periods of light rain through the day. Light/variable winds
become light south.
Saturday night...high confidence. Warm front draped across the
waters, yielding areas of fog, drizzle and/or spotty light rain.
Light SSW winds.
Outlook /Sunday through Wednesday/...
Sunday: Winds less than 25 kt. Chance of rain.
Sunday Night: Low risk for Small Craft Advisory winds with
gusts up to 30 kt. Local rough seas. Chance of rain.
Monday: Moderate risk for Small Craft Advisory winds with local
gusts up to 30 kt. Rough seas up to 10 ft. Snow. Visibility
1 to 3 nm.
Monday Night: Winds less than 25 kt. Areas of rough seas.
Chance of rain.
Tuesday: Winds less than 25 kt. Local rough seas.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Winter Weather Advisory from 4 AM to 1 PM EST Saturday for
CTZ002>004.
MA...Winter Weather Advisory from 4 AM to 1 PM EST Saturday for
MAZ002>016-026.
RI...Winter Weather Advisory from 4 AM to 1 PM EST Saturday for
RIZ001.
MARINE...None.
&&
$$
SYNOPSIS...JWD/Nocera
NEAR TERM...Nocera
SHORT TERM...Nocera
LONG TERM...JWD
AVIATION...JWD/Nocera
MARINE...JWD/Nocera
Source: BOX issues Area Forecast Discussion (AFD) at Dec 28, 12:19 AM EST (https://mesonet.agron.iastate.edu/p.php?pid=202412280519-KBOX-FXUS61-AFDBOX)
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