BOX issues Area Forecast Discussion (AFD) at Mar 19, 4:49 AM EDT
071
FXUS61 KBOX 190849
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
449 AM EDT Wed Mar 19 2025
.SYNOPSIS...
Dry weather with mild afternoon temperatures are on tap for the
interior Wednesday and Thursday...but it will be considerably cooler
on the coast particularly on Wednesday with onshore flow. A system
and accompanying cold front will bring rain Thursday night into
early Friday. A transition to light snow is possible behind
cold front early Friday for the higher elevations of the
interior. Windy conditions are expected Friday with highs around
or slightly below normal. Warmer temperatures for the weekend.
Another round of precipitation early next week possible with
even the chance at a light Spring snow in spots.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Key Messages...
* Cold start this morning thanks to good radiational cooling.
* Big range in high temperatures from eastern MA to western MA/CT.
* Largely sunny for most, though mid/high clouds move in late from
the west while low clouds move in from the east.
Today sunny skies returns for much of the day under the influence of
a high pressure ridge between low pressure centers over the western
Atlantic and the Midwest. This brings well above normal high
temperatures for portions of the region (namely western MA and much
of CT) thanks to 925 mb temps rising toward +10C. On the contrary,
cool, onshore flow at the surface will keep temperatures down in the
upper 40s and low 50s along the immediate MA east coast. Thus, quite
the gradient in high temperatures expected across southern New
England.
As onshore flow increases in the mid to late afternoon low level
moisture (below 2,000 ft) advects inland leading to a deck of low
stratus invading the east coast which will be accompanied by periods
of fog and drizzle. BUFKIT soundings indicate potential for these
low clouds moving into the Cape and islands as early at 7-9am, then
there is some uncertainty as to how quickly these clouds expand
west. Most likely reaching the immediate south shore of MA (Plymouth
county area) by late morning and expanding well into eastern MA/RI
toward sunset.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
Key Messages...
* Low clouds and drizzle expanding overnight.
* Cloudy on Thursday with periods of drizzle but largely dry.
Thursday SNE is downstream of a shortwave which will eventually
bring widespread rain overnight. Guidance has slowed down the
progression of this system in the last 24 hours so the appreciable
rain doesn't move in until well into the overnight hours on
Thursday. Even so, given the saturated low levels periods of drizzle
will be possible through the day. Increased cloudcover coupled with
925mb temps decreasing to near 7C will mean highs topping out in the
mid to upper 50s (cooler along the immediate coast).
&&
.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Key Messages:
* System brings rain Thursday night through Friday. Higher
elevations of the interiors may transition to light snow early
Friday morning.
* Light snow accumulation possible for high elevations such as
Berkshires, but more likely less than an inch.
* Windy Friday with gusts 30-40 mph for most areas, locally higher
gusts possible.
Thursday Night - Friday:
A shortwave trough moves across the region Thursday into Friday with
an attendant front and surface low. There is high confidence that
this will bring our next chance for widespread precipitation across
southern New England Thursday night through Friday. There is
sufficient lift with the front/surface low and a plume of anomalous
moisture (160-200% of normal).
However, deterministic and ensemble solutions are not in strong
agreement with the details of this system. Particularly with respect
to the track and speed/timing of the system. One of the notable
differences is between GFS and ECMWF solutions. The ECMWF portrays
this system as a more progressive open wave in the mid-levels as it
moves across southern New England. This would push the
system/precipitation through quicker resulting in less precipitation
overall. The GFS solutions show a closed off low at 500mb with the
surface low tracking to the south and east of southern New England.
This will support slower movement and as solutions show, higher QPF.
In addition to model to model difference, there also has been
difference from run to run with the models. The main takeaway is
that there is lower confidence on how much liquid this system will
bring.
Overall, we will see precipitation chances increase late Thursday
night as the system and cold front approaches with rain spreading
from west to east. The cold front likely moves through early Friday
morning, with gusty NW winds and colder air working in behind it.
There is still agreement with the potential for a transition to
light snow across the interior, mainly for the higher elevation
spots like the Berkshires and higher Worcester Hills. As noted
earlier, the speed of the system is low certain, but means show the
system exiting by later Friday afternoon with showers decreasing
from west to east.
The uncertainty in the track and speed of the system will play into
the QPF for this event. GEFS means show a range of 0.30-1" while the
ECMWF ensemble mean is drier with a range of .30-.60" of total QPF.
There are individual members and deterministic solutions in the GFS
suite that a notable outliers with a couple values > 1.5". Settling
on a range from .30-1.00 for now with the chances for seeing the
higher end of that range further west of the Berkshires with help
from the upslope component. For snow amounts, the highest
probabilities for seeing >1" are confined to the Berkshires (30-
60%). Worcester Hills north of the Mass Pike has lower probabilities
and will more likely see a dusting to 1/2" if it does stick. Overall
minimal impacts. Overall, minor accumulations in the high elevation
spots at most.
Post-front it will be cooler during the day Friday with highs in the
40s. With a LLJ moving across and CAA, this will likely support a
windy day with gusts 30-40 mph. There is still potential for
localized higher gusts around 45 mph for the higher elevation spots,
especially Friday afternoon. The surface low may be an additional
source of high winds as well as it tracks offshore of New England on
Friday. Adjustments will be better made to the offshore wind
forecast as the finer details (low track) come into better
agreement.
The Weekend:
Mid-level ridging moves in for the weekend with dry conditions.
Warming 850mb temperatures and breezy downslope winds will support
temperatures rebounding back into the 50s Saturday. Ensemble
guidance shows a shortwave trough moving across late Saturday into
Sunday. With limited forcing and moisture, this will be more likely
result in some scattered showers Saturday evening. Temperatures
trend cooler on Sunday in the 40s.
Early Next Week:
There is good overall agreement among ensemble guidance with the
passage of an upper level trough early next week. Guidance depicts
New England in the left exit region of the upper jet coupled with
anomalous moisture. This will bring another round of precipitation
to the region. Despite notable differences in the track of the
system and available cold air, ensemble means signal the potential
for a light Spring snow in the Monday-Tuesday timeframe. Ensembles
have highlighted the higher probabilities north of the Mass Pike for
light snow accumuation. Details will become more available as we get
closer. A lot can change with the details of this system this far
out...
&&
.AVIATION /09Z WEDNESDAY THROUGH SUNDAY/...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
06z TAF Update:
Through 12Z...High confidence.
VFR, with SCT-BKN high clouds. Lower borderline VFR/MVFR deck
possible just offshore of ACK but will stay away from the
terminals. NE winds 4-8 kt, though stronger (10-15 kt / gusts
20-25 kt) Cape and Islands.
Today...High confidence overall, moderate late in the day.
VFR for the majority of SNE; however MVFR marine stratus may
try to return to the Cape and Islands during the morning/early
afternoon, and could get into BOS as soon as 18z, but think more
likely after sundown as moisture is shallow and prone to being
mixed out. NE winds around 4-8 kt with stronger winds Cape and
Islands, though winds will become E/ESE late in the day.
Tonight...High Confidence in trends, moderate confidence in
timing.
Light/moist onshore flow coupled with a cooling boundary layer
will allow low clouds and fog to back in off the ocean as the
night wears along. IFR/LIFR conditions dominate by daybreak
Thu. In addition...areas of drizzle will also likely develop
late Wed night.
Thursday...High Confidence.
IFR to start, with some improvement to MVFR during the day. SE
winds 5-10 kts.
KBOS TAF...High Confidence in TAF.
KBDL TAF...High Confidence in TAF.
Outlook /Thursday Night through Sunday/...
Thursday Night: MVFR/IFR conditions possible. Breezy. RA.
Friday: MVFR/IFR conditions possible. Windy with gusts up to
30 kt. Chance RA.
Friday Night: VFR. Windy with local gusts up to 30 kt.
Saturday through Saturday Night: VFR. Breezy.
Sunday: Breezy.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Today through Thursday...High Confidence.
Mid-level ridging remains overhead today allowing for quiet and dry
weather. This will keep wind gusts below small craft advisory
criteria through Wed night. However...lingering easterly swell will
result in the need for small craft advisories for seas to persist
across the outer-waters through Thursday. Areas of fog will develop
late Wed and especially Wed night which will reduce vsbys for
mariners.
Outlook /Thursday Night through Sunday/...
Thursday Night: Winds less than 25 kt. Seas up to 5 ft. Chance
of rain.
Friday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Rough seas up to 8 ft. Chance of rain.
Friday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 9 ft. Slight chance of
rain.
Saturday: Winds less than 25 kt. Seas up to 5 ft.
Saturday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft.
Sunday: Winds less than 25 kt. Seas up to 5 ft.
&&
.HYDROLOGY...
In response to Monday's rainfall and some contributions from
snowmelt upriver along the Connecticut River basin, river flood
warnings for minor flooding are active on portions of the
Connecticut River.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 AM EDT Thursday for ANZ250-
254>256.
&&
$$
SYNOPSIS...BW/Mensch
NEAR TERM...BW
SHORT TERM...BW
LONG TERM...Mensch
AVIATION...BW/Mensch
MARINE...BW/Mensch
HYDROLOGY...BW
Source: BOX issues Area Forecast Discussion (AFD) at Mar 19, 4:49 AM EDT (https://mesonet.agron.iastate.edu/p.php?pid=202503190849-KBOX-FXUS61-AFDBOX)
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