BOX issues Area Forecast Discussion (AFD) at Dec 23, 3:34 AM EST827
FXUS61 KBOX 230834
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
334 AM EST Mon Dec 23 2024
.SYNOPSIS...
Ocean effect snow showers come to an end this morning followed by a
dry and continued cold Monday, but temperatures moderate slightly. A
weak clipper system may bring very minor snow accumulations late
Monday night into Christmas Eve morning. Otherwise, dry weather
dominates the rest of the Holiday week into next weekend with
seasonably chilly temperatures.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Updated: 3:30 AM
Key Messages:
* Frigid morning with ongoing ocean effect snow from Cape Ann to
Cape Cod & coastal Plymouth County.
* Sunny and chilly this afternoon as the Arctic high centers over
the northeast.
This morning we are focused on two things; Arctic chill and ongoing
ocean effect snow. It's frigid this morning, many locations are
falling through the single digits, but the coast is a tad "warmer"
with temperatures in the teens and low 20s. And for those interested
what the daily record lows are for the region, see the climate
section of the AFD. This afternoon temperatures are slow to recover,
more on that in a moment.
During the overnight hours radar returns expanded over the ocean and
approaching Cape Ann and Cape Cod to coastal Plymouth County. There
is quite a bit of instability over the ocean as temps at the top of
the boundary layer around -14C to -15C leading to delta T of 22-23C
and ocean induced CAPES 400-500 J/kg.
Expect snow showers to continue and favorable low level trajectory
around 350 degrees will carry these snow showers to both Capes and
possibly portions of coastal Plymouth county as there may be some
low level convergence here from land-sea interface. Winds ease this
morning, ending the snow by mid morning. Current forecast stands, a
coating to an inch seems reasonable but low risk for localized
accums up to 2 inches over Cape Cod.
This afternoon the 1035mb high is over the northeast, leading to
another sunny day with light wind. 925mb temperatures begin to
moderate, -12C to -8C, while still chilly, highs are in the middle
to upper 20s, with far northwest Massachusetts still in the upper
teens to lower 20s. Clouds increase during the afternoon as a warm
front approaches ahead of a weak clipper system.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
Updated: 3:30 AM
Key Messages:
* Light snow late tonight into Tuesday morning from a weak clipper
system passing to our north.
* Berkshires and northern Worcester Hills have the best chance of
receiving more than an inch of new snow.
Weak clipper system tracks across northern New England overnight and
exits the northeast early Tuesday afternoon. A warm front approaches
late this evening, leading to light snow showers along and north of
the Mass Pike. Temperatures remain below freezing, so any precip
would come down as snow. With the passage of the warm front winds
become southwest, leading to a non-diurnal temperature trend
overnight into Tuesday morning. In fact, the coldest part of the
night could be between 10pm and 2am, with temperatures in the teens
and low 20s, and then followed by increasing temperatures through
sunrise. Many locations remain below freezing, but coastal
southeastern Massachusetts warms to the low to mid-30s by sunrise.
Trailing cold front pushes through the region from the predawn hours
and then exits eastern coastal Massachusetts early afternoon. Minor
snow accumulations for the northern Worcester Hills and Berkshires,
where one to two inches are possible, elsewhere the lower elevations
see a coating to an inch. Regardless, this system will not produce
much precipitation and ends by early afternoon. Highs recover into
the 30s, to as warm as 40 for Cape Cod and islands.
&&
.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Updated: 3:30 AM
Key Messages...
* Mainly dry conditions through the rest of the week and into next
weekend, but a low risk for some spotty light precip at times near
the coast Wed and Wed night
* Cold with below normal temps Wed, then slowly moderating temps for
the rest of the week into next weekend
* Potential for unsettled weather late Sun and/or next Mon
Details...
Tuesday night into Wednesday night...
Strong shortwave moves east from Maine developing into a closed Low
south of Nova Scotia which will bring a surge of low level colder
air southward into SNE with 925 mb temps dropping to -6 to -8C. Lows
Tue night will drop into the teens and low 20s with highs Christmas
Day upper 20s to mid 30s. The column also dries out considerably
with PWATs dropping to around 0.10". So overall a dry period with
clearing skies Tue night and lots of sunshine Wed. However, low
level northerly flow and shallow low level moisture may result in
considerable cloud cover over the Cape/Islands and coastal SE MA
through Wed night and can't rule out spotty ocean effect snow
showers. But given dry air aloft and potential for snow growth
region to dry out, there is some risk for patchy drizzle or freezing
drizzle. Both GEFS and EPS ensembles show high probs (60-90%) of QPF
> 0.01" through Wed night over Cape Cod.
Thursday through Sunday...
Mid level ridging gradually builds over New Eng, especially this
weekend before moving to the east toward the end of the weekend.
Meanwhile, strong high pres sets up over Quebec Thu-Fri before
shifting to the Maritimes next weekend. The column remains dry with
persistent N-NE flow so will have to watch for more cloud cover near
the coast, otherwise dry weather prevails into Sunday. However, as
mid level ridge moves to the east Sunday, next system will be
approaching from the west. Still lots of uncertainty with respect to
the timing and amplitude of next approaching trough and shortwave.
ECMWF and CMC have a more amplified system with some of its
ensembles bringing in precip as early as Sunday while GFS and its
ensembles are weaker and drier. Thermal profiles look to be warm
enough aloft for rain or some interior ice at the onset if low level
cold air is slow to erode. Temps will gradually moderate through the
period, from 30s on Thu-Fri with some 40s by the weekend in the
coastal plain and valleys.
&&
.AVIATION /09Z MONDAY THROUGH FRIDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
09z TAF Update...
Through 12z....
VFR, except for periods of MVFR-IFR in ocean effect snow showers
over Cape Cod into coastal Plymouth county. A coating to an
inch accum with localized 2 inch amounts possible.
Today...High confidence.
VFR, with areas of MVFR in ocean effect clouds and snow showers
ending on Cape Cod in the morning. Light N winds the AM,
turning light southerly in the PM.
Tonight...Moderate confidence.
VFR to start, then lowering to MVFR late as light snow
develops, mainly along and north of the MA Pike. SW wind 5-10
kt.
Tuesday...Moderate confidence.
A mix of VFR-MVFR cigs with some vsby restrictions in areas of
light snow showers, mainly in the morning. SW wind 5-10 kt
becoming NW in the afternoon.
KBOS TAF...High confidence in TAF.
KBDL TAF...High confidence in TAF.
Outlook /Tuesday Night through Friday/...
VFR.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Updated: 3:30 AM
Today and Tuesday...High confidence.
Cold and quiet through late afternoon, light northerly wind
becomes southwest this evening as an Arctic high pressure
system moves across the waters. Seas between 2 and 4 feet.
Tonight into Tuesday a weak clipper system moves across
northern New England, increasing southwest wind ahead of a cold
front on Tuesday leads to gusts of 20 knots. Cold front pushes
east of the waters Tuesday afternoon with light rain and snow
showers. Seas build slightly on the outermost southern waters,
but do remain below advisory criteria.
Outlook /Tuesday Night through Friday/...
Tuesday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of snow showers.
Christmas Day: Winds less than 25 kt. Local rough seas. Chance
of rain showers, chance of snow showers.
Wednesday Night: Winds less than 25 kt. Local rough seas.
Slight chance of rain showers.
Thursday through Friday: Winds less than 25 kt. Local rough
seas.
&&
.CLIMATE...
Record Lowest Minimum Temperature: 12/23
BOS: -12F (1883)
BDL: -5F (1989)
PVD: 2F (1989)
ORH: -2F (1989)
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 4 AM EST early this morning for
ANZ250-254.
&&
$$
SYNOPSIS...KJC/Dooley
NEAR TERM...Dooley
SHORT TERM...Dooley
LONG TERM...KJC
AVIATION...KJC/Dooley
MARINE...KJC/Dooley
CLIMATE...Dooley
Source:
BOX issues Area Forecast Discussion (AFD) at Dec 23, 3:34 AM EST----------------
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