BOX issues Area Forecast Discussion (AFD) at Dec 26, 2:57 PM EST149
FXUS61 KBOX 261957
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
257 PM EST Thu Dec 26 2024
.SYNOPSIS...
Strong high pressure will continue to provide dry weather through
much of this weekend. Decreasing clouds early today in eastern
New England, although ocean effect cloud cover will continue
across Cape Cod and the Islands through early tonight. Gradual
warming temperatures are expected Friday and Saturday. An
approaching low pressure will bring the potential for mainly
rain late Sunday into Monday, with perhaps a bit of ice at the
onset across the interior.
&&
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Surface high pressure remains over the region tonight promoting dry
conditions and mainly clear skies. This will support another cooler
night with optimal conditions for radiational cooling. Low
temperatures drop into the teens across much of the interior with
single digits across the western MA. Areas closer to the coast drop
into the 20s.
&&
.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
Friday:
High pressure centers just south of the region Friday supporting
another dry day with light W/SW winds. Temperatures aloft warm 2-4
degrees from Thursday which usually would mean a decent warm up in
temperatures. However, model soundings show a rather shallow mixing
layer preventing the mixing down of the warmer temperatures aloft.
High temperatures will likely range in the upper 30s and low
40s.
Friday Night:
The area of high pressure once positioned to the south, will move
eastward off the coastline tomorrow night. A weak shortwave will
bring in our next chance precipitation arriving by early Saturday
morning. Overnight, temperatures at the surface should have time to
cool into the 20s across most spots. Warm air slowly advects in from
the south and moisture trends upward into the early morning hours
Saturday.
HREF guidance shows light precipitation arriving in the
interior 09-12z, continuing through the morning. Most model
guidance shows a signal for freezing rain potential Saturday
morning given the defined layer of WAA (850mb temperatures 4-5C)
over a shallow surface layer below freezing. Areas across the
interior especially the cooler spots like the Berkshires and
Worcester Hills will have a higher threat. Timing will play a
big role in the overall threat as we will need cold enough
surface temperatures paired with the onset of the precipitation
to support this potential. More details will be included in the
Long Term Discussion below.
&&
.LONG TERM /SATURDAY THROUGH THURSDAY/...
Key Messages
* Light icing and slippery travel possible early Saturday.
* Milder air follows with periods of rain Sat-Mon.
* More rain possible around New Year's Day followed by colder air.
Fairly active and overall mild pattern taking shape over weekend and
into New Year's Day as upper ridge remains parked offshore and mean
trough sets up to our west. A series of short waves will drive
several low pressure systems to our west, each accompanied by deep
southerly flow aloft and plentiful moisture.
Main concern deals with potential for light icing and slippery
travel early Sat as precipitation arrives ahead of warm front. Not a
great signal for cold air damming but light winds in place and
snowcover should help keep low level cold locked in, especially near
Berkshires, Litchfield Hills, and in Connecticut River Valley where
ensembles and pointing toward higher probabilities of light icing.
Model soundings show a classic freezing rain signal with a mid level
warm nose of 5-6C and a shallow subfreezing layer near the ground.
We did note that 12z HREF cuts off these probabilities sharply
farther east but that is due more to 48hr ending time of 12z Sat.
WPC ensemble probs do carry lower chances into BOS/PVD, which is
dependent upon how quickly precipitation arrives, but even for these
areas it's possible existing snow cover keeps low level cold trapped
for a few hours Sat morning.
Keep in mind these light icing events (light coating of a trace to a
few hundreths of an inch) can be the most dangerous for travel since
roads may look wet. Plan on some extra travel time Saturday morning
since you may need to exercise your winter driving skills.
Temperatures should warm up by midday Saturday ending the icing
threat.
Warmer air then floods SNE over the weekend and into early next
week, likely persisting through New Year's Day. Highs should reach
well into 50s Sun/Mon and settle back into 40s Tue/Wed. Two more
rounds of rain seem likely in Sun-Mon and Tue-Wed timeframes as next
low pressure systems track through region. After New Year's Day
ensembles are signaling toward a return to colder weather (highs in
20s/30s) as broad closed low takes hold over region.
&&
.AVIATION /20Z THURSDAY THROUGH TUESDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
18z TAF Update:
Today: High confidence.
Remaining stratus is expected to decrease in coverage to VFR
from west to east across Plymouth county and toward the
Cape/Islands. Through the evening, ceilings improve over the
Cape and Island and then scatter out. NW winds 5-8 kt today then
become more light WNW late in the day.
Tonight: High confidence.
Any leftover MVFR bases out over the Cape and Islands should
trend to VFR early. VFR elsewhere. Light WNW winds less than 8
kts. Can't rule out the low probability for patchy fog for E and
SE MA overnight.
Friday: High confidence.
VFR. Light W/WNW winds become SW around 5-8 kts. High clouds
arrive in the afternoon.
KBOS TAF...High confidence in TAF.
KBDL TAF...High confidence in TAF.
Outlook /Saturday through Tuesday/...
Saturday: Mainly VFR, with local IFR possible. Chance RA,
chance FZRA.
Saturday Night: MVFR/IFR conditions possible. RA likely.
Sunday: Mainly MVFR, with areas IFR possible. Breezy. RA
likely.
Sunday Night: Mainly MVFR, with local IFR possible. Breezy. RA.
Monday: Mainly VFR, with areas MVFR possible. Breezy. RA.
Monday Night: VFR. Breezy. Chance RA.
Tuesday: VFR.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
NNW winds today around 10-15 kt decrease and shift to light W
tonight and then become SW around 5-10 kt on Friday. Waves 2-4
ft for most zones overnight. Up to 5 ft for the outer waters off
the Cape/Islands through midnight.
Mainly dry weather is expected, although there could be patchy
freezing drizzle through mid morning today for vessels
traveling through Cape Cod Bay, Mass Bay and east of Cape Cod.
Outlook /Saturday through Tuesday/...
Saturday: Winds less than 25 kt. Chance of rain, slight chance
of freezing rain.
Saturday Night: Winds less than 25 kt. Rain likely.
Sunday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain.
Sunday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas up to 5 ft. Rain likely.
Monday: Moderate risk for Small Craft Advisory winds with gusts
up to 25 kt. Rough seas up to 8 ft. Rain.
Monday Night: Winds less than 25 kt. Areas of rough seas.
Chance of rain.
Tuesday: Winds less than 25 kt. Seas up to 5 ft.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 1 AM EST Friday for ANZ254-255.
&&
$$
SYNOPSIS...Mensch/JWD
NEAR TERM...Mensch
SHORT TERM...Mensch
LONG TERM...JWD
AVIATION...Mensch/JWD
MARINE...Mensch/JWD
Source:
BOX issues Area Forecast Discussion (AFD) at Dec 26, 2:57 PM EST----------------
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