BOX issues Area Forecast Discussion (AFD) at Dec 10, 6:54 PM EST750
FXUS61 KBOX 102354
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
654 PM EST Tue Dec 10 2024
.SYNOPSIS...
Some showers begin to overspread the region later tonight with
periods of windswept heavy rain Wednesday into Wednesday night
ahead of a strong cold front. Strong to damaging wind gusts may
develop ahead of this cold front, along with the risk for some
river and urban flooding Wednesday into Wednesday night. Colder
than normal temperatures and dry conditions Thursday through
the first half of this weekend. The next chance for
precipitation comes Sunday night into early next week.
&&
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
7 PM update...
Weak surface wave over the Gulf of Maine continues to replenish
the shallow cold air over SNE via NNE winds. Despite temps
hovering around freezing from the Worcester Hills into northeast
MA, including Boston, patchy freezing fog doesn't appear to be
impacting road conditions per latest DOT websites and spotter
observations. Thinking road treatments from earlier today across
this region, combined with high volume traffic, is precluding
icy spots from developing. As a warm front approaches
overnight, winds will become southeast and temps will slowly
rise later tonight. In addition, as rain shield overspreads the
region from west to east, latent heat release from the precip
will also help temps rise a bit. Thus, not expecting any impacts
overnight, other than some patchy dense fog across the
Worcester Hills. Earlier discussion below.
------------------------------------------------------------------
Key Messages:
* Areas of freezing drizzle/black ice central and northeast MA
into this evening
Light north winds have maintained shallow cold air across
portions of northeast and north central MA. Will continue to
mention the risk of light freezing drizzle into the evening
commute there. Winds will need to turn east to southeast before
this particular threat will end. Latest 3km NAM still appeared
to have the best handle on temperature trends into this evening.
The main story tonight will be the widespread rainfall arriving
from the west. Much of this rainfall should be after midnight,
but did start ramping up rainfall chances from west to east this
evening. Further tweaks to this timing may be needed with later
forecasts. Generally expecting one quarter to one half inch of
rainfall, so not concerned about flooding overnight.
Low temperatures tonight should be early, with temperatures
slowly rising overnight as the south winds increase. Not
entirely sold on the timing, as that cold air has been stubborn
thus far. Will be watching trends this evening.
&&
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
Key Messages...
* Periods of rain will be heavy at times with a few embedded
thunderstorms possible too
* Some mainstem river and urban flooding is possible
* Strong to damaging wind gusts of 50-60 mph possible late
Wed into Wed night
* Temperatures surge to near 60+ later Wed
Details...
Quite the dynamic storm system will be impacting the region.
This will bring the potential for strong to damaging wind
gusts along with heavy rain and flooding. We will break it down
below.
Heavy Rain and Flooding Risk...
Strong southerly low-level jet will transport abundant moisture
into our region. Precipitable water values are projected to peak
out nearly 5 standard deviations above normal, a signal for a
rather rare event. Most of the rainfall for this event should
fall during the day Wednesday, but perhaps not all in a single
unbroken round. Still seeing signs there may be a brief break
during the mid to late morning, or at least a lightening of the
rainfall, before a more convective line arrives ahead of a
strong cold front during the afternoon into the evening.
With our current rainfall deficits, we should be able to
accommodate this rainfall as long as it does not fall too
quickly. The ground is at least partially frozen, so the soil
will simply not soak up the rain like it would in the summer.
This could lead to poor-drainage flooding. The Flood Watch
continues along the CT River, due to the risk of upstream
snowmelt and rainfall also contributing to the flood risk there.
Gave some thought to expanding the Flood Watch, but decided to
leave it focused where it is at this time.
Rainfall totals of 1-3 inches with locally higher amounts are
expected.
Strong to Damaging Winds...
A very powerful southerly LLJ will develop, peaking about 5
standard deviations above normal. Winds at 925 mb peak about
60-80 kt, which is not that common this time of year. Converted
the High Wind Watches to High Wind Warnings and Wind Advisories.
The southerly wind direction complicates things greatly.
Questions remain on the depth of the mixed layer farther inland,
as well as the impact of friction knocking down wind speeds as
well. Have the greatest confidence in high winds across southern
RI into eastern MA, then north along the immediate east coast of
MA. Much of the rest of southern New England converted to Wind
Advisories. Further tweaks to headlines may come with later
forecasts.
The heavy rain may exacerbate the risk for tree damage and power
outages.
Coastal Flooding...
We do not expect coastal flooding to be much of an issue with
this storm. Strong southerly wind gusts would make the south
coast most vulnerable, but it appears high tide will occur
before the peak winds arrive Wed evening. So other than perhaps
some splashover, the risk for any appreciable coastal flooding
remains low at this time.
&&
.LONG TERM /THURSDAY THROUGH TUESDAY/...
Key Messages:
* Colder than normal temperatures Thursday through Saturday, but
dry weather prevails
* Next chance for precipitation Sun night into early next week
Precipitation...
Strong column drying Thu behind departing cold front Wed night,
will yield a stretch of dry weather Thursday into much of the
weekend. Only exception could be some ocean effect rain/snow
showers along the south coast Thu via CAA on WSW winds across
the relatively mild ocean. Then the next chance of precipitation
is sometime Sun night into early next week, as a Pacific trough
approaches from the west. However, ensembles are trending
weaker with this trough, deamplifying with time as it approaches
SNE. Thus, low probs for widespread and meaningful
precipitation.
Temperatures...
Ensembles support strong post frontal CAA Thu and Fri, with
below normal temps. Highs in the upper 30s and lower 40s Thu,
but colder wind chills with WSW winds 15-25G30 mph possible.
Winds slacken Fri but core of cold air will be overhead, with
highs only in the 30s. Fri night/Sat morning will be the
coldest, with 1045+ mb high cresting over SNE, yielding
overnight lows in the teens most locations. The cold trough
finally departs over the weekend, with rising heights yielding
moderating temps, with highs 40-45 by Sunday and maybe 50
degrees early next week!
&&
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
00z TAFs...no major changes from previous TAFs. IFR/LIFR
conditions tonight, perhaps some improving trends to IFR/MVFR
toward 12z. Spotty light rain/drizzle this evening, becomes more
widespread later tonight, possibly heavy toward 12z across CT
into western-central MA. Temps around freezing across the
Worcester hills into northeast MA, should warm slowly overnight
as winds become SE along the coast. The precip will also result
in temps rising a few degs as well. Earlier discussion below.
--------------------------------------------------------------
Through Tonight...High Confidence.
LIFR/IFR conditions dominate with patchy drizzle into this
afternoon and evening. Latest observations continue to suggest
the risk for freezing drizzle across portions of north central
and northeast MA into this evening. Next batch of steadier
rainfall arrives between 00-06Z. Winds shift to the
south/southeast and gradually increase to 10 to 15 knots. Some
gusts to 20 knots develop over the south coast/Cape/Islands by
12Z.
Wednesday and Wednesday Night...High Confidence.
Generally IFR much of the time through 00Z. Could see some brief
period of MVFR, or even VFR towards far SE MA, during the day.
Strong cold front then returns with one last round of heavy
rainfall and IFR conditions. Improving to VFR from west to east
after midnight Thursday.
Strong S LLWS expected during the afternoon and evening,
especially towards southern RI and southeast MA. Winds up to
60 kt possible at FL020.
KBOS Terminal...High Confidence. Low risk for some spotty
freezing drizzle through about 22z with temperatures near 32F.
Marginal risk at Logan, with a greater concern just to the
northwest. Airport Weather Warnings due to strong winds likely
to be issued later tonight.
Outlook /Thursday through Sunday/...
Thursday: VFR. Windy with local gusts up to 30 kt. Patchy FZDZ.
Thursday Night: VFR. Breezy.
Friday through Saturday: VFR.
Saturday Night: VFR. Slight chance SN.
Sunday: VFR. Chance RA, chance SN.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Strong southerly winds develop late Wednesday into Wednesday
evening. Expecting storm-force gusts up to 50 kt for a time.
Converted the Storm Watches to Storm Warnings for most waters.
The exception will be Stellwagen Bank, where Small Craft
Advisories are still needed into this evening. Storm Warning
will be issued there, once the winds and seas diminish this
evening.
Outlook /Thursday through Sunday/...
Thursday: Strong winds with gusts up to 30 kt. Rough seas up to
14 ft. Slight chance of rain.
Thursday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of rough seas.
Friday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Friday Night through Saturday Night: Winds less than 25 kt.
Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Chance of rain.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Flood Watch from Wednesday afternoon through Thursday morning
for CTZ002-003.
Wind Advisory from 3 PM Wednesday to 1 AM EST Thursday for
CTZ002>004.
MA...Flood Watch from Wednesday afternoon through Thursday morning
for MAZ002-003-008>011.
Wind Advisory from 3 PM Wednesday to 1 AM EST Thursday for
MAZ004>006-010>014-026.
High Wind Warning from 3 PM Wednesday to 1 AM EST Thursday for
MAZ007-015>024.
RI...Wind Advisory from 3 PM Wednesday to 1 AM EST Thursday for
RIZ001-002.
High Wind Warning from 3 PM Wednesday to 1 AM EST Thursday for
RIZ003>008.
MARINE...Storm Warning from 7 PM Wednesday to 1 AM EST Thursday for
ANZ230.
Storm Warning from 4 PM Wednesday to 1 AM EST Thursday for
ANZ231>234-251-254>256.
Storm Warning from 4 PM to 11 PM EST Wednesday for ANZ235>237.
Small Craft Advisory until 7 PM EST this evening for ANZ250.
&&
$$
SYNOPSIS...Belk/Nocera
NEAR TERM...Belk/Nocera
SHORT TERM...Belk
LONG TERM...Nocera
AVIATION...Belk/Nocera
MARINE...Belk/Nocera
Source:
BOX issues Area Forecast Discussion (AFD) at Dec 10, 6:54 PM EST----------------
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