Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 181646
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1246 PM EDT Mon Mar 18 2024

.SYNOPSIS...
Seasonable temperatures for much of the work week with mainly
dry, gusty weather except for a few rain/snow showers possible
sometime Wednesday and/or Wednesday night. A period of unsettled
weather is also possible sometime this weekend...but confidence
is low at this time.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
10 AM Update...

Area of mid level status is beginning to break up over eastern
MA and move offshore. Skies will become clear briefly this
morning before more diurnal cumulus form early this afternoon.
Gusty winds have already started up across much of the northern
MA and will spread south and east today. expecting gusts to peak
early this afternoon, then slowly diminish into the evening.

320 AM Update...

* Partly sunny & breezy today with highs in the upper 40s/lower 50s

An approaching shortwave has backed the upper level flow a bit early
this morning. This has resulted in mid-high level cloudiness
overspreading much of the region. There is even the risk for a
brief sprinkle or two early this morning towards the southeast New
England coast...but not worth inserting into the forecast at this
time.

We do expect this band of mid-high level cloudiness to push east of
the region later this morning. This should result in skies
becoming partly sunny...but colder temps aloft moving in from the
west will allow a scattered to broken deck of CU to develop later
today. 925T around 0C/+1C with good mixing on westerly flow aloft
should allow for high temps to top off mainly in the upper 40s and
lower 50s. So it will be cooler than what we saw over the
weekend...but still a bit above normal for this time of year.

Bufkit soundings indicate westerly wind gusts of 20 to 25 mph by
late morning/early afternoon with a few gusts up to 30 mph
possible.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
Key Points...

* Dry/Seasonable tonight with lows in the upper 20s/lower 30s
* Partly sunny/breezy Tue with highs mainly in the middle-upper 40s

Details...

Tonight...

Low pressure over the Canadian Maritimes will generate a
seasonable westerly flow of air into southern New England. Although
the winds will likely not decouple in most places given a modest WNW
low level jet. Nonetheless...850T dropping to between -8C and -10C
will result in overnight low temps mainly in the upper 20s to the
lower 30s.

Tuesday...

Upper trough across the northeast will generate a cool west to
northwest flow of air aloft again on Tuesday. Cyclonic flow along
with the cold pool aloft should allow for a scattered to broken deck
of diurnal CU to develop again...yielding partly sunny skies later
in the day. Temperatures a few degrees colder aloft than today...so
expect Tue highs mainly in the middle to upper 40s. Bufkit indicates
westerly wind gusts of 20 to 25 mph with a few gusts up to 30 mph.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Highlights

* A quick moving front/system slides through Wed/Wed Night bringing
  light showers. Temps warmer than normal.

* Drier on Thu/Fri, but cooler and breezy.

* Could turn unsettled this weekend, but lots of uncertainty on how
  things evolve.

Tuesday Night through Wednesday Night...

Cyclonic flow in place through this period. A fast moving shortwave
trough digs from the western/central Great Lakes early on Wed into
the eastern Great Lakes by late in the day. The shortwave lifts into
the Gulf of Maine/northern New England Wed Night. A weak warm front
lifts into/through southern New England Tue Night into Wed. The
trailing cold front pushes through late Wed/Wed Night.

Still a tricky forecast in how wet it will be across the region,
especially earlier in the day. Due to this have generally stuck with
the NBM as it is mostly reasonable, but did bump up our PoPs a bit
as the stronger cold front slides through later on Wed into Wed
Night. The mitigating factors through this period for precip is we
are fairly dry with PWATs between 0.2-0.4 inches, which is between
the 25th to avg for this time of year per SPC sounding climo for
CHH. On top of this we are well mixed within the PBL per Bufkit
soundings, which should help mix down some drier dew points. For now
have kept more spotty showers before having better chances of precip
later in the day. High temps in the 40s across the higher terrain to
the upper 40s to low 50s elsewhere.

With the cold front and later in the day there is the better shot
for more widespread showers. For most this will be rain, but the
higher terrain has the potential for snow showers. There could even
be a bit of accumulation. Not out of the question lower elevations
see snow before things end. Right now there is discrepancy on how
much QPF we can ring out in this dry airmass. Given the uncertainty
stuck with the NBM. Best shot is across far northwestern MA for AOA
1 inch of snow over 24 hrs of mod to high (50-70+ percent chance)
and even some low probs (10-30 percent) for 3+ inches per the
GEFS/EPS guidance. The GEPS is essentially nil for the 3+ inch
probs. Further east along the Route 2 corridor probs are low to mod
(10-40 percent chance). Stay tuned for future updates.

Anticipating it to be breezy on Wed, but especially Wed Night in
wake of the cold front. Will have W to WNW flow with the LLJ
increasing to 25-35 kts. Stuck with the NBM for now as its higher
winds/gusts are reasonable given the cold air advection and LLJ in
place.

Thursday through Friday...

Flow somewhat cyclonic during this timeframe. A ridge axis will be
over the Low/Mid Mississippi River Valley early on Thu. This builds
into the TN Valley by late Thu. The ridge axis builds into the
Carolinas/Mid Atlantic on Fri, but flattens out a bit. High pressure
begins to nudge in from the OH Valley/Great Lakes on Thu and just
offshore of the Mid Atlantic on Fri.

Dry and quiet weather expected through this period as high pressure
nudges in. Anticipating gusty winds across southern New England on
Thu. Will be fairly well mixed with WNW to NW flow under cold air
advection and 925 hPa winds of 25-35 kts. Shouldn`t be terribly
difficult to mix down given the environment. So should have gusts of
35-40 mph through much of the day. Given the well mixed boundary
layer it won`t be tough to bring down -20 to -30 degree dew points
near the top of the PBL. Due to this lowered dew points/RH values to
the 15th percentile of guidance for now. Did bump up temps to the
75th percentile of guidance given the setup. Highs on Thu will be
right around normal for this time of year in the 40s.

Should still be a bit breezy on Fri, but the high will relax the
pressure gradient as it builds closer to our region. Temperatures
still right around seasonable levels.

This Weekend...

Considerable uncertainty for this upcoming weekend. A trough will be
located somewhere over the Southeastern US late on Fri. This lifts
northeastward toward our region on Sat and perhaps Sun depending on
how things evolve. Lot of uncertainty in if a coastal system slides
up our way.

Given the spread in guidance have stuck with the NBM for now for
this timeframe. Appears that it could be wet if the trough lifts up
into our area. There are some indications that the trough cuts off
to our south/southeast, which would keep us dry. At this point probs
are moderate (30-70 percent) of 24 hr QPF on both days AOA 0.1
inches. There are low probs of (10-30 percent) of 1+ inch of QPF
with the risk being highlighted over RI/SE MA. Can see the
uncertainty quite clearly via the large spread in MSLP low pressure
center tracks per the EPS/GEFS/GEPS. Temps still near to perhaps
slightly cooler than seasonable.

&&

.AVIATION /18Z MONDAY THROUGH FRIDAY/...
Forecast Confidence Levels:

Low - less than 30 percent.
Moderate - 30 to 60 percent.
High- greater than 60 percent.

Rest of Today...High confidence.

VFR. W winds 10 to 15 knots with gusts of 20-25 knots. Mid
level clouds linger with bases around 6-8 kft.

Tonight...High Confidence.

VFR. Gusty winds drop off across the interior but remain
sustained WNW at 5 to 15 knots. Gusty winds pick up over the
Cape and the Islands overnight.

Tuesday...High Confidence.

VFR. WNW 10 to 15 knots with gusts of 20 to 25 knots. Another
round of mid level CU with bases of 5-8 kft.

Tuesday Night...High Confidence

VFR. Decreasing winds turning south

KBOS TAF...High confidence in TAF.

VFR with gusty WNW winds

KBDL TAF...High confidence in TAF.

VFR with gusty west winds

Outlook /Tuesday Night through Friday/...

Tuesday Night: VFR. Breezy.

Wednesday: VFR. Breezy. Chance SHRA.

Wednesday Night: VFR. Strong winds with local gusts up to
40 kt. Chance SHRA.

Thursday: VFR. Windy with gusts up to 35 kt.

Thursday Night: VFR. Windy with gusts up to 30 kt.

Friday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels:

Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.

Today through Tuesday...High Confidence.

Upper trough over the northeast will generate a continued cool WNW
flow of air through Tuesday. Decent mixing should promote some 20 to
25 knot wind gusts at times...especially near shore during the
afternoon hours. It is very borderline small craft conditions...but
bulk of the time conditions will be below small craft criteria.
Therefore...only opted SCA headlines for  Tuesday across our
southern waters. This is for marginal 5 foot seas and 20 to 25 knot
wind gusts. Later shifts may need to consider additional marginal
small craft headlines for Tuesday...but confidence not high enough
to do that right now.

Outlook /Tuesday Night through Friday/...

Tuesday Night: Winds less than 25 kt. Areas of seas approaching
5 ft.

Wednesday: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of rain showers.

Wednesday Night: Low risk for gale force winds with gusts up to
35 kt. Local rough seas. Slight chance of rain showers.

Thursday: Moderate risk for gale force winds with gusts up to
40 kt. Areas of rough seas.

Thursday Night: Low risk for gale force winds with gusts up to
35 kt. Local rough seas.

Friday: Winds less than 25 kt. Seas locally approaching 5 ft.

&&

.FIRE WEATHER...
Today and Tuesday...

Minimum afternoon relative humidity values should drop into the 20
to 30 percent range today and Tuesday. West to northwest wind gusts
of 20 to 25 mph with a few gusts up to 30 mph are anticipated by
late morning/early afternoon on both days. In coordination with our
fire weather partners, we opted to issue a SPS for CT and RI due to
elevated fire weather concerns today and possibly again on Tuesday.

Thursday...

A cold front that will move through on Wednesday...will also
set the stage for the potential of elevated fire weather
concerns again on Thursday. Minimum relative humidity values of
20 to 40 percent are expected with WNW wind gusts of 30 to 40
mph.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 5 AM to 8 PM EDT Tuesday for
     ANZ254>256.

&&

$$

SYNOPSIS...Frank/BL
NEAR TERM...Frank/KP
SHORT TERM...Frank
LONG TERM...Frank/BL
AVIATION...KP
MARINE...Frank/BL
FIRE WEATHER...Frank


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