BOX issues Area Forecast Discussion (AFD) at Dec 27, 6:52 AM EST466
FXUS61 KBOX 271152
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
652 AM EST Fri Dec 27 2024
.SYNOPSIS...
High pressure will maintain dry weather through Friday. Light
icing is possible early Saturday ahead of a warm front, that
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 PM THIS EVENING/...
345 AM Update:
A 1033 mb high pressure area was centered over northwest MA early
this morning. Clear skies and light to calm winds have resulted in
near optimal radiational cooling conditions. Many areas early this
morning were down in the mid teens, while a few locations in
northwest MA were in the low single digits! As is typical in strong
radiational cooling situations, elevated sites tend to be "warmer",
and the warmest readings are currently being observed at Worcester
Airport at this hour, in the upper 20s.
Tranquil weather conditions are expected for today under governing
high pressure. Light winds to gradually become light out of the SW.
Satellite shows a shield of high cloudiness which currently extends
across west-central NY, and this stream of high clouds is forecast
to advance eastward into Southern New England by late morning into
the afternoon. Still, expect a generous dose of sunshine today. For
temperatures...even though our 850 mb temps running around +4C today
would argue for warmer readings, forecast mixing is expected to be
quite shallow today and we won't mix to that depth. Still,
temperatures should rebound back into the mid 30s to lower 40s,
perhaps a few mid-40s.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/...
345 AM Update:
Key Messages:
* A light glaze of ice from freezing rain into interior Southern
New England mainly during the Saturday morning hours. Icing
may linger in lower-elevation interior areas (the
CT/Merrimack Valleys) into the early afternoon. Impacts from
ice accretion solely limited to travel. Winter Weather
Advisories issued.
* Light rain across RI and much of eastern/southeast MA.
* Rain becomes more intermittent/drizzly late afternoon to Saturday
evening.
Details...
Increasing cloudiness develops tonight in response to a warm
front associated with a frontal system now near the mid-MS
Valley region. This feature is expected to begin to spread light
precipitation by the Saturday pre-dawn hours timeframe in
interior western New England, and into early Saturday morning
for eastern portions of Southern New England. Before
precipitation arrives, we should see some initial period of
radiational cooling helping to drive temps into the mid- 20s by
early overnight. During the second half of the overnight,
increasing cloudiness and very light southerly flow should allow
for surface temps to very slowly rise into the upper 20s for
most, to around freezing for southeast New England.
Precip then begins to break out around 4-6 AM Saturday in western
New England, and into 5-8 AM Saturday for central and eastern
portions of Southern New England. Temperatures are quite warm aloft
with a pronounced warm nose and associated maximum temps in the warm
nose around +6C. Precip types will be one of either rain or freezing
rain, surface-temperature dependent, with no in-between. Greatest
risk for light ice accretions is in interior Southern New England
north and west of Interstate 95. Freezing rain should gradually
transition over to plain rain from south to north as temperatures
slowly warm above freezing. Model forecast soundings in lower
elevations in the CT valley and Merrimack Valley show very limited
mixing and a slower scour-out of sub-freezing air supporting a
somewhat longer duration of FZRA for those areas. In fact, more
elevated sites like the Berkshires and hills in northern
Worcester County could flip above freezing several hrs before
areas along the I-91 corridor would.
For RI and the Boston/Providence corridor south and east, there
could be some patchy slippery spots at onset as plain rain falls on
cold ground given the recent spell of below normal temperatures, but
felt the prevalence of freezing rain was unlikely enough to hold off
on extending winter weather advisories into these areas for now. It
would take an earlier arrival of precip before we would then become
more concerned about the potential for light accretions of ice for
the locations currently outside of the Advisory area, and that seems
to be a less likely outcome given recent trends in the NWP guidance.
In terms of QPF, this is a really light event. Only looking at
liquid-equivalent amts of a tenth to at worst two tenths of an inch,
and a fraction of that would be ice where freezing rain is expected.
Following recent science behind the Freezing Rain Accumulation
Methodology, very light winds and light precipitation rates with
this event are both meteorological factors which should allow ice to
accrete efficiently on surfaces where temps are cold enough for
freezing rain. But...it's just not a lot. A few hundredths of
icing is forecast in the Advisory areas, with totals no greater
than a tenth of an inch, and those higher totals more likely to
be observed in the CT Valley given the longer duration and
expected longer residence time of subfreezing air. Given the
expected increased traffic volume coming out of the recent
holidays, and that light freezing rain events often cause
greater travel impacts, coordination with neighboring offices
prompted issuance of Winter Weather Advisories which run from 4
AM til 1 PM Saturday.
Precipitation then starts to shift offshore by late in the day
into Saturday evening, as a dryslot moves in aloft. There is an
abundance of trapped low level moisture underneath the dryslot,
which is a classic pattern for drizzle and fog for Saturday
night/overnight as the warm front more or less either stalls or
washes out ahead of the next warm frontal surge slated for
Sunday. Lows should reach into the mid 30s to near 40.
&&
.LONG TERM /SUNDAY THROUGH THURSDAY/...
Key Messages
* Mild/unsettled weather expected between Sunday and the middle of
next week
* Two substantial precipitation events expected Sunday night/Monday
and Wednesday
* Trending colder/drier late next week
Sunday and Monday
Deep south/southwest flow continues to advect mild air into southern
New England with 925 hPa temps approaching 10 Celsius on Sunday
afternoon. Skies remain cloudy on Sunday, but nonetheless we're
still anticipating well above normal surface temperatures ranging
from the low to mid 50sF across the region. Continue to expect some
hit or miss warm advection driven showers early Sunday, but
precipitation coverage should become more steady as a frontal wave
approaches southern New England from the west Sunday afternoon. This
system will support wet/rainy conditions through Monday morning and
perhaps into early Monday afternoon. Not expecting any frozen
precipitation given the mild air mass that will be in place.
Tuesday through Thursday
A mid-level ridge and associated surface high pressure move over
southern New England on Tuesday supporting a lull in the
wet/unsettled pattern and another mild day with temperatures in the
upper 40s to low 50s. This lull will be short-lived as another low-
pressure system brings substantial precipitation to southern New
England on Wednesday. Ensemble probabilities for greater than 0.5
inches of liquid precipitation are currently hovering in the 50 to
60 percent range across the region. No signals for any snow or
frozen precipitation at this time, but there could be a risk for
some freezing rain across the interior Wednesday morning. We'll have
a better idea as the event draws nearer. Cool/dry conditions settle
in on Thursday as the cold front associated with the aforementioned
area of low-pressure moves through the region.
&&
.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
12Z TAF Update:
Today: High confidence.
VFR. Light WNW winds becoming SW around 5 kt.
Tonight and Saturday: Moderate confidence.
VFR for most airports through at least 06z, then we start to see
SCT-BKN MVFR stratus develop near the southern airports which
gradually expands north. Precipitation starts to break out
08-10z Sat for western New England TAFs, and around 10-13z Sat
in central and eastern TAFs, with ceilings going to MVFR/IFR
levels. Precip types will be either FZRA or RA, depending on
temperature and how quickly temps recover. Best chance icy
runways is at BDL, ORH and BED, though is possible at BOS if
precip arrives sooner. Most areas will have trended toward rain
by 16z. Rainy conditions then become more intermittent/drizzly
into by early Sat evening, with IFR/LIFR conditions.
KBOS TAF...High confidence in TAF. VFR through at least 10z Sat.
Possible MVFR stratus could intrude in by 10z Sat, with steady
light precip breaking out after 12z Sat. Should be in the form
of rain, but could fall as -FZRA if precip comes in earlier.
KBDL TAF...High confidence in TAF. Potential for light icing
from -FZRA (less than 0.10") early Sat.
Outlook /Sunday through Tuesday/...
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.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
High confidence for next several days.
High pressure over New England maintains light winds and light
seas into Sat night; winds shift SW today and continue into
Sat. A frontal system moves in on Saturday, however mainly light
rain is expected, which could be interspersed with fog as we
move into the Saturday afternoon/evening period.
Increasing S/SE winds later Sun into Mon should bring building
seas and periods of rain, when SCAs should be needed on most of
the waters.
Outlook /Sunday through Tuesday/...
Sunday: Winds less than 25 kt. Chance of rain.
Sunday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Seas up to 5 ft. Chance of rain.
Monday: Moderate risk for Small Craft Advisory winds with local
gusts up to 30 kt. Rough seas up to 9 ft. Rain.
Monday Night: Winds less than 25 kt. Areas of rough seas.
Chance of rain.
Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft.
&&
.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>006-008>012-026.
RI...None.
MARINE...None.
&&
$$
SYNOPSIS...Loconto/RM
NEAR TERM...Loconto
SHORT TERM...Loconto
LONG TERM...RM
AVIATION...Loconto/RM
MARINE...Loconto/RM
Source:
BOX issues Area Forecast Discussion (AFD) at Dec 27, 6:52 AM EST----------------
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