Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 271147
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
647 AM EST Tue Feb 27 2024

.SYNOPSIS...
A warm front lifts north across our region today, bringing
unseasonably mild temperatures and increased cloud cover. A
potent cold front moving through Wednesday into Wednesday night
will bring soaking rains and strong wind gusts to southern New
England, followed by sharply falling temperatures late
Wednesday night. Windy with near seasonable temperatures on
Thursday before starting a warming trend again Friday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
7AM Update:

A SPS for locally dense fog has be hoisted for SE MA and RI.
Fog should burn off between 9am-noon, but could linger along
the east coast as any sea breeze that develops today could bring
clouds and fog back inland. Otherwise the forecast remains on
track.

Previous discussion.

Marine stratus finally developed across portions of southern RI
and southeast MA. These clouds are expected to linger a while
through this morning. An approaching warm front will lead to
increasing and thickening clouds across most of our region.
These clouds will complicate the temperature forecast quite a
bit today. While above normal temperatures will continue due to
the increasing southerly flow, if we can add on enough sunshine,
it`s possible that some of normally warmer spot approach high
temperatures near 60 degrees. For most locations though,
thinking the 50s is what will most likely happen. Just do not
have much confidence is prolonged periods of sunshine.

Most of today expected to be dry, with showers possibly arriving
along and west of the CT River very late this afternoon.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
This is the time period where the weather gets more unsettled. A
modest mid level shortwave and strong isentropic lift should
lead to a period of rainfall, which begins tonight and continues
into Wednesday. Not thinking that this will be a widespread
continuous rainfall, but more of a prolonged period of showers.
The heaviest rainfall still looks to be over RI and southeast
MA.

Still have concerns for wind potential tonight into Wednesday.
Model soundings showed a potent, but very shallow, inversion in
place over southern New England. Low level jet increases
dramatically tonight, and especially Wednesday. Peak speeds in
this low level jet of 65-75 kt are not out of the question by
Wednesday afternoon. Even stronger winds should precede the cold
front associated with this system Wednesday afternoon. With the
presence of the strong low level inversion, thinking a Wind
Advisory will be needed for portions of RI and MA from late
tonight into Wednesday.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Key Points

* Strong to damaging winds Wednesday night into Thursday

* Rapid drop in Temperatures Wednesday night into Thursday

* Warming up Friday through the weekend with more rain possible


Wednesday night

Potent northern stream trough and cold front come barreling through
southern New England overnight bringing strong to damaging wind
gusts and an extreme drop in temperature. Before that, a very strong
southerly LLJ ahead of the cold front will be over eastern MA. 925mb
winds are approaching 70-80 knots which is leading to the NAEFS and
ECMWF ensemble tables to have wind anomalies around +3 to +4. The
big question with a SE wind prior to the passage of the cold front
will be how much wind can be mixed down.  Bufkit soundings show a
strong inversion esspically near coastal areas due to cold ocean
temps around 40F. However, with strong WAA, temperatures will be
approaching the low to mid 50s during the peak of the LLJ. If
temperatures can warm into the mid 50s near the coasts, then we
could be looking at High Wind Warming (58mph) gusts.  If temps stay
in the low 50s, wind gusts likely only reach the advisory (46mph)
level. Given the uncertainty at this time range, will use the same
method as the previous shift which is to approximate the winds at
the surface by using 50% of the 925 mb winds which yields wind gusts
up to 50mph. Another uncertainty with this event is how will the
pressure falls to the north effect the wind potential. Strong
pressure falls to the north of a high wind area under a SSE jet
favors convergence with the wind rushing in towards the pressure
fall area. This is typically observed most in cases where the 3
hourly pressure falls are at least 6mb or more. The 00z GFS pressure
fields do show a 6-7mb pressure falls over Maine, but only 3-4mb
over New Hampshire. NBM probs for High Wind Warning criteria are
below 50% at this time, and given other uncertainties, decided to
hold off on a High Wind Watch for the Cape and Islands.

The potent cold front moves through the region late Wednesday night
into Thursday morning. 850mb temps quickly drop from +7C to -13C
while surface temperatures drop from the 50s into the 20s over the
course of 6-9 hours! The larger concern with the cold front however
will be the short period of enhanced winds. As the front passes
through, winds will turn to the NW, allowing for mixing up to 850mb
to occur. With 850mb winds near 55-65 knots, Very strong CAA, and
the possibility of a fine line of precipitation, gusts could
potentially reach 60mph at the surface. NBM probabilites for 58mph
gusts are also moderate to high at 50-80%. Given these factors, have
hoisted a High Wind Watch for the east slopes of the Berkshires.
further east, NBM probs for 58mph+ are low at 10% or less, however,
probs for 46mph+ are moderate at 30-60% meaning a wind advisory may
be needed for Thursday afternoon.

As for precipitation, A round of heavy windswept rain is likely with
the passage of the cold front. PWATS around 1.0-1.25 and very strong
forcing will allow for a wide spread 0.5 to 1.25 inches with a 10-
20% chance for 2+ inches of rain esspically across RI and SE MA.
Poor drainage and river flooding look to remain minimal at this time
with dry antecedent conditions. Behind the cold front, there may be
a quick back end thump of snow before dry air cuts off the precip.
Any snow that falls should be fast moving and short lived at any
given location. A quick coating to inch is possible especially
across the Berkshires and Worcester hills.

Thursday

Behind the front, gusty northwest winds and CAA continue much of the
day limiting highs to the low to mid 30s with wind chills in the
teens and 20s. Wind gusts during the day Thursday will likely
remains at 30-40 mph with 40-50mph for the Berkshires. With an
extremely dry airmass and high pressure overhead at this time, skies
will likely be sunny.

Friday and Beyond

Temps quickly rebound Friday as winds flip SE allowing WAA to kick
in. Highs warm into he upper 40s on Friday and low to mid 50s on
Saturday and Sunday. A weak shortwave disturbance moves through
Saturday afternoon, but uncertainty at this time remains high with
POPs staying below 50%.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
Forecast Confidence Levels:

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

Today...Low confidence.

IFR stratus across southern RI and southeast MA lingers past he
morning push. Status is already pushing into Boston and will
likely bring IFR CIGS through 14z and possibly later.
Otherwise, a tale of different conditions. VFR expected across
western MA with IFR fog burning off between 14z-17z for eastern
terminals. Low confidence forecast given due to the uncertainty
on how quickly fog will burn off and if a sea breeze will keep
pushing fog and low status onshore.

Tonight and Wednesday...Moderate confidence.

IFR conditions likely as rain overspreads the region, heaviest
across SE New England. Increasing S winds with 25-35 kt gusts
developing near the coast. LLWS developing, especially eastern
New England as low level jet strengthens across the region.

KBOS TAF...Lower confidence due to uncertainty in timing/extent
of fog and low status. Fog likely now until 14z, with more
uncertainty on if fog will burn off or stick around after 14z

KBDL TAF...Moderate confidence in TAF. It should remain VFR,
but will have to watch for some lower cigs possibly developing
later this morning. We did not include in TAF as confidence is
low.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: Mainly VFR, with local IFR possible. Strong
winds with gusts up to 50 kt. RA, chance SN.

Thursday: VFR. Strong winds with gusts up to 50 kt.

Thursday Night: VFR. Strong winds with areas of gusts up to
45 kt.

Friday: VFR. Windy with local gusts up to 30 kt.

Friday Night: Mainly VFR, with local MVFR possible. Windy with
local gusts up to 30 kt. Slight chance RA.

Saturday: Mainly VFR, with local IFR possible. Breezy. Chance
RA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Increasing south winds late today, and especially tonight into
Wednesday as a low level jet strengthens. Gusts will increase
to 35+ kt after midnight. Gale Warnings will be issued for the
waters. Reduced visibility in fog around the Cape and islands
this morning. More widespread reduced visibility in rain
tonight into Wednesday.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: gale force winds with gusts up to 45 kt. Rough
seas up to 16 ft. Rain, isolated thunderstorms. Local
visibility 1 to 3 nm.

Thursday: Strong winds with gusts up to 40 kt. Rough seas up to
14 ft.

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

Friday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Areas of seas approaching 5 ft.

Friday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of seas approaching 5 ft. Slight
chance of rain.

Saturday: Winds less than 25 kt. Chance of rain.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Wind Advisory from 3 PM Wednesday to 6 AM EST Thursday for
     CTZ003.
     Wind Advisory from noon Wednesday to 6 AM EST Thursday for
     CTZ004.
MA...Wind Advisory from 3 PM Wednesday to 6 AM EST Thursday for
     MAZ015.
     High Wind Watch from Wednesday evening through Thursday
     evening for MAZ002-003-008>011.
     Wind Advisory from 3 PM to 6 PM EST Wednesday for MAZ007.
     Wind Advisory from noon Wednesday to 1 AM EST Thursday for
     MAZ013.
     Wind Advisory from 3 PM Wednesday to 1 AM EST Thursday for
     MAZ014.
     Wind Advisory from 7 AM Wednesday to 1 AM EST Thursday for
     MAZ016>022.
     Wind Advisory from 7 AM Wednesday to 6 AM EST Thursday for
     MAZ023-024.
RI...Wind Advisory from noon Wednesday to 1 AM EST Thursday for
     RIZ001-002.
     Wind Advisory from 7 AM Wednesday to 1 AM EST Thursday for
     RIZ003>008.
MARINE...Gale Warning from 7 AM Wednesday to 7 PM EST Thursday for
     ANZ230-251.
     Gale Warning from 1 AM Wednesday to 1 PM EST Thursday for
     ANZ231>235-237.
     Gale Warning from 1 AM Wednesday to 10 AM EST Thursday for
     ANZ236.
     Gale Warning from 1 AM Wednesday to 7 PM EST Thursday for
     ANZ250.
     Gale Warning from midnight tonight to 7 PM EST Thursday for
     ANZ254>256.

&&

$$

SYNOPSIS...Belk/KP
NEAR TERM...Belk/KP
SHORT TERM...Belk
LONG TERM...KP
AVIATION...Belk/KP
MARINE...Belk/KP


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