Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 240115

Area Forecast Discussion
National Weather Service Boston/Norton MA
915 PM EDT Thu May 23 2019

Scattered showers with embedded heavy downpours this evening followed
by a sweeping cold front overnight. Windy, seasonable conditions
Friday with light showers along the coast. Much of Saturday looks
dry with pleasant temperatures, but a fast moving disturbance will
probably bring a period of showers late Saturday into early Sunday.
The rest of Sunday into Memorial Day looks to be warm and mainly
dry, but an approaching warm front may bring some showers by Tuesday.


915 PM update...

Line of strong to severe storms along the cold front moving ESE
from central and eastern NY. Convection is firing within an
area of MUCAPES 500-1000 J/kg and 0-3km lapse rates 6.5-7 C/km.
Environment is much less favorable over New Eng. There will be
some elevated CAPE developing as the convection moves into SNE
but low level lapse rates are poor and surface instability is
nil so expect a weakening trend. 3km NAM handing the convection
reasonably well. Area of showers and sct t-storms expected to
sweep across SNE tonight, reaching NW MA 02-03z and rest of the
region 03-06z. A few strong storms are possible in NW MA but
activity will weaken as it approaches the coastal plain. Drying
trend overnight behind the cold front with partial clearing.


Friday into Friday night ...

Breezy, seasonable, dry conditions. Potent shortwave and mid-level
H5 trof digs out towards SE Canada promoting further cyclogenesis
that along the backside of which will amplify the low-level wind
profile and promote steep lapse rates to H8. Moisture lingering,
one of two things: 1.) Some light shower activity is possible
along E-coastal MA, and 2.) All of S New England will see breezy
N winds with gusts up as high as 40 mph but below WIND ADVISORY
thresholds. Scattered to broken cloud decks, more than likely
thicker further E. Highs around the upper 60s during the day.

Both clouds and winds dissipate going  into the evening and
overnight, but lingering enough to limit radiational cooling.
Lows down into the 40s.


As of 323 PM EDT Thursday...


* Memorial Day weekend will feature warmer than normal
  temperatures, with some showers mainly Saturday Night and
  early Sunday. Monday will be dry and comfortably warm -
  especially away from the coast.
* Several risks for showers/t-storms during the week. Could be
  warm for midweek.


Overall models from 00z & 12z are in decent agreement through
the holiday weekend, and then start to deviate after that. As
such, stuck with the model blend for most of next week with
little change to populate the forecast as confidence is lower in
any specific outcomes. A little more clarity/confidence for
this weekend`s weather. Comments regarding each day are below,
for those that want to get into some deeper technical reading...

looks like a pretty decent day. 925mb temperatures are around
15C, so that would support highs in the mid 70s inland. not a
strong pressure gradient, so sea breezes will develop by early
afternoon, keeping coastal areas to the 60s to maybe 70f. A
shortwave will approach late in the day, with at least
increasing clouds in western areas. Did hold back the chance for
any showers until evening, and even then just for mainly western
Mass. Overnight the shortwave will roll through. Some elevated
instability, so perhaps a rumble or two of thunder, mainly just
light showers. Liked the model blend with 60-70% PoPs and
roughly 0.1 to 0.2" total.

Sunday: More like summer, which is appropriate for the holiday
weekend to kick off summer. 925mb temperatures up around 20C,
which would suggest mid 80s for highs away from the coast. Upped
the model blends several degrees. Again, sea breezes keeping it
cooler at the coast. Dewpoints will be rising into the lower
60s, and along with the warm temperatures, we will have some
surface based instability. No strong forcing, but can`t rule out
a few showers or isolated t-storm that initiate along the sea
breeze and higher terrain. All in all most of us will see a
decent amount of sun and stay dry. So I`d say "it`s a go" for
those outdoor activities. Uncertainty for Sunday night as GFS
has a shortwave move through with perhaps a few showers. 12Z
Euro says dry. Have some low PoPs in the forecast, so we`ll see
if later model give more clarity.

Monday/Memorial Day: Flow turns northwest, with a building
ridge. Look for high and dry weather with lots of sun. 925mb
temperatures of 17-19C suggest highs in the 70s and approaching
80 in places like the CT River Valley. Sea breezes again.

Tuesday to Thursday: As mentioned above, confidence not all that
high for mid week. The general trend will be for high pressure
to move offshore, setting up southwest flow to bring in bring in
some warm air, which will then be pushed out with a cold front
sometime Wednesday night or Thursday. That warm air could
actually be pretty hot. 12z GFS has 925mb temperatures
approaching 25C on Wednesday. That would support temperatures
into the 90s across inland areas. The 00z Euro had a bunch of
clouds/showers and cooler conditions, but then the 12z Euro came
in looking more like the GFS and a hot day. Though the GFS has
been showing a hot day for a few runs, that`s not the case with
other models like FV3-GFS, Canadian, Euro. In fact, some show a
back door cold front slicing the area as well. Given that, stuck
with the model blend, which does feature highs into the lower
80s inland. Along with that, went with lots of 30-40% PoPs given
uncertainty in what will happen and exactly when.


Forecaster Confidence Levels...

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

Short Term /through Friday Night/...Moderate confidence.

915 PM update...

Timing of showers and sct t-storms 03-04z BDL/BAF/ORH and
BOS/PVD 04-05z, a bit faster than previous forecast suggested.

Previous discussion...
Mostly VFR across the region, though IFR with low ceilings
starting to move in along the south coast of RI and MA. Line of
thunderstorms out in western NY as of just before 00z will
quickly sweep southeast. Should be affecting BDL/BAF locations
about 02z, ORH about 03z and then BOS-PVD about 04z. Tried to
keep TEMPO groups to primary 2 hour window for the activity.
TSRA should be diminishing as things move across the region, so
kept mostly the "VCTS" aspect, and we can update later to better
indicate the details of the thunder portion. Expect IFR/MVFR
conditions as the showers push through. Some LLWS will persist
into the early overnight. A cold front will move through,
generally after 06z, with conditions improving to VFR area wide
by 12z. Gusty northwest surface winds tomorrow, with most TAF
locations seeing frequent gusts around 30kt from 15z through 20z
or so. Potential for isolated gusts near 40kt. Winds diminish
quickly Friday evening. VFR Friday night.

KBOS Terminal...Moderate confidence in TAF.

KBDL Terminal...Moderate confidence in TAF.

Outlook /Saturday through Tuesday/...

Saturday: VFR.

Saturday Night: MVFR/IFR conditions possible. Breezy. SHRA
likely, patchy BR.

Sunday: Mainly VFR, with local MVFR possible. Breezy. Slight
chance SHRA.

Sunday Night: VFR. Slight chance SHRA.

Memorial Day: VFR.

Monday Night through Tuesday: VFR. Chance SHRA.


Forecaster Confidence Levels...

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

Short Term /through Friday Night/...High confidence.

Rest of today ...
SW winds sustained around 10 to 15 kts, gusts around 20 to 25
kts will push seas 3 to 5 feet on the outer waters. SMALL CRAFT
ADVISORIES issued accordingly.

SW winds continue prior to a sweeping cold front during the early
morning hours. Will see sustained 10 to 15 kts with gusts around
20 to 25 kts throughout as the cold front sweeps through, SW winds
shifting W, waves building 5 to 7 feet on the outer waters. Lower
visibility with any heavy showers or thunderstorms that are forecast
ahead of the sweeping cold front. Heavy rain elements occurring
around midnight.

Friday into Friday night ...
Gales over the E waters by midday into afternoon with overcast
cloud decks and possible light showers. Winds dissipating into
evening and overnight. Waves on the outer waters possibly
pushing up as high as 8 to 10 feet peaking close to sunset then
dissipating thereafter.

Outlook /Saturday through Tuesday/...

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

Saturday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Rain showers likely, patchy fog.

Sunday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain
showers, patchy fog.

Sunday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers, patchy fog.

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

Monday Night through Tuesday: Winds less than 25 kt. Chance of
rain showers.


MARINE...Gale Watch from Friday afternoon through Friday evening for
     Small Craft Advisory until 5 AM EDT Friday for ANZ232>234.
     Small Craft Advisory until midnight EDT tonight for ANZ230.
     Small Craft Advisory until 2 AM EDT Friday for ANZ231-236-251.
     Small Craft Advisory until 11 PM EDT Friday for ANZ235-237.
     Small Craft Advisory until 2 PM EDT Friday for ANZ250-254>256.


SHORT TERM...Sipprell
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