NWS Technical Forecast Discussion

082
FXUS61 KBOX 241536
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1136 AM EDT Fri May 24 2019

.SYNOPSIS...
Windy and seasonable today, except for an abrupt change to much
cooler temperatures along the southeast New England 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. Showers and cool temperatures
return Tuesday as a warm front approaches from the south.
Unsettled weather pattern lingers into Thursday, but not a
washout.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

* Windy and turning significantly cooler along the southeast New
  England coast this afternoon

1130 am update...

Windy and mild at lunch time with current temperatures mainly in
the upper 60s to the lower 70s. This should set the stage for
an interesting afternoon. An amplifying shortwave east of the
Maritimes will result in an abrupt wind shift to the north
northeast this afternoon along the coast.

3 hour pressure rises on the order of 6 mb along the
southeast New England coast and steep low level lapse rates will
result in even windier conditions developing. Current
temperatures in the upper 60s to the lower 70s along the
southeast New England coast, should fall through the 50s this
afternoon as the winds come off the cold ocean. In
addition...rapid pressure rises with a strong NNE 925 mb LLJ
should result in 40 to 50 mph across the Cape/Nantucket as well
as the Plymouth county coast and Marthas Vineyard. Wind
Advisories have been posted for those locations. Can not rule
out a sprinkle or brief spot shower, but main idea is an abrupt
change to much cooler temperatures on strong northeast wind
gusts.

Further inland across the interior expect strato-cumulus clouds
with temperatures mainly in the upper 60s to lower 70s into the
afternoon. Expect 25 to 40 mph wind gusts in this region too,
but not as strong as along the southeast New England coast.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
Tonight...

Center of the stronger winds crosses the Cape and islands this
evening, so the gusty northerly winds will continue through
around midnight before diminishing as the core shifts S.
Otherwise, high pressure will build across the region through
the night, allowing winds to diminish.

With the lighter winds and mostly clear skies, expect temps to
fall back to the mid 40s to lower 50s, running close to or a
bit below seasonal levels.

Saturday...

With the fast mid level steering flow in place across the
northern tier, will see the low across New England push steadily
E. Winds shift around to light S-SW by midday, then will
increase to around 10-15 kt with some gusts up to around 20 kt
along the immediate S coast.

The question is timing the approach of the next system in the
fast steering flow. Clouds will increase from late morning
through the afternoon, though may hold off along the S coast
until evening. Leading edge of the precip looks to push into N
central and NW Mass during the mid and late afternoon, so most
areas should remain dry.

Expect highs to run from the 60s across Cape Cod and the islands
to the lower-mid 70s elsewhere.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Highlights...

* Period of showers Sat night, lingering into early Sun
  Cape/Islands
* Warm and mainly dry Sun/Mon with 80s Sun away from south
  coast
* Cool and potentially wet Tue
* Showery pattern may persist into Thu but not a washout

Overview...

Overall pattern features SNE on northern periphery of strong SE
CONUS subtropical ridge. As such, we will be vulnerable to
shortwaves and fronts moving through the region with periods of
showers from time to time, but warm and dry periods as well. Temps
in the extended period will be changeable and dependent on where
boundaries set up. Forecast confidence diminishes by Wed/Thu due to
uncertainty with location of shortwaves moving over the ridge and
placement of boundaries. The ridge will get pushed to the east by
Thu as trough approaches from the Lakes.

Saturday night into Sunday...

Fast moving shortwave approaches Sat night and guidance is
indicating an instability burst developing at the nose of a low
level jet as low level theta-e ridge moves into the region. This
will lead to some showers moving into SNE and can`t rule out a few t-
storms as marginal instability develops aloft. The showers may
linger into early Sun on the Cape/Islands, otherwise drying Sun with
westerly flow. Should see a fair amount of sunshine developing after
some early morning clouds, with warm temps. 925 mb temps around 20C
support highs in the low to mid 80s, except 70s along the south
coast. A weak cold front move into the region in the afternoon and
can`t rule out an isolated t-storm as marginal instability develops
in the afternoon.

Monday...

Front is offshore with high pres building to the north leading to a
mostly sunny day. Cooler temps aloft Mon but still a warm day with
highs in the 70s and possibly 80 CT valley. Sea-breezes expected to
develop keeping coastal communities a bit cooler.

Tuesday...

Could be a wet and cool day as warm front approaches and gets jammed
up to the southwest with moist onshore flow and cool high pres to
the east. Numerous showers expected along with a few t-storms
possible as instability aloft develops. Temps may end up cooler than
forecast with potential for 50s in some locations if it`s wet
with SE flow.

Wednesday into Thursday...

Low confidence for Wed. Earlier guidance was hinting at summer heat
moving into SNE for Wed but latest guidance has backed off on this
with boundary remaining near or south of New Eng. It all hinges on
positioning of shortwave riding over the ridge which models can`t
resolve at this time range.  It is still possible the front pushes
to the north with a hot day but this is very much uncertain and
temps could end up below normal.

Mid level trough approaches from the Lakes region Thu which will
lead to increasing risk of showers/t-storms. If the warm air doesn`t
get in here for Wed, the approaching trough and cold front should
push warm temps into SNE for Thu with potential for 80s.

&&

.AVIATION /16Z FRIDAY THROUGH TUESDAY/...
Forecaster Confidence Levels...

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

Short Term /through Saturday/...Moderate to high confidence.

Today...VFR despite a scattered to broken deck of cloudiness.
N-NW winds gusting up to 25-35 kt by mid to late morning,
highest across E coastal terminals. Winds shift to N-NE along
the coast during the afternoon with gusts between 40 and 45
knots across the Cape/Nantucket. Low risk for spotty showers
this afternoon across E Mass, possibly into RI, but should
remain VFR.

Tonight...VFR. N-NE winds gusting to 25-30 kt this evening
across Cape Cod and the islands, but will back to NW and
diminish by around 04Z.

Saturday...VFR. Light W-NW winds back to S-SW during the day,
increasing to 10-15 kt during the afternoon. Scattered showers
may reach into N central and NW Mass after 18Z with local MVFR
possible.

KBOS Terminal...Moderate to high confidence in TAF.

KBDL Terminal...Moderate to high confidence in TAF.

Outlook /Saturday Night through Tuesday/...

Saturday Night: Mainly MVFR, with areas VFR possible. Breezy.
SHRA likely, slight chance TSRA.

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

Sunday Night through Monday Night: VFR.

Tuesday: Mainly MVFR, with areas VFR possible. Chance SHRA,
slight chance TSRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Saturday/...High confidence.

* Significant impact this afternoon for Mariners with an abrupt
  wind shift to the northeast and gusts between 40 and 50
  knots.

Today...Gale Warnings all waters with short duration Storm
Warnings for Nantucket sounding and our southeast outer-waters.
Wind shift to the NNE this afternoon with strong pressure rises
and a rapid fall in temperatures along the coast should result
in a brief period of 40 to 50 knot wind gusts. Strongest across
the Cape/Nantucket and points east. A marine weather statement
has been issued to highlight the concern for recreational
boaters, especially those near shore with an abrupt wind
shift/strong wind gusts and rapid fall in temperatures.

Tonight...N-NE wind gusts up to 35 kt this evening near and E of
Cape Cod. Winds will become NW and diminish to around 10 kt by
around midnight. Seas 4 to 7 ft early tonight, then slowly
subside but may remain around 5 ft on the waters E of Nantucket.
Good visibility.

Saturday...Light NW winds in the morning back to S-SW and
increase to 10-15 kt with some gusts to 20 kt during the
afternoon. Seas 4 ft or less. Good visibility.

Outlook /Saturday Night through Tuesday/...

Saturday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Rain showers likely, slight chance of
thunderstorms.

Sunday: Winds less than 25 kt. Seas up to 5 ft. Slight chance
of rain showers.

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

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

Monday Night: Winds less than 25 kt.

Tuesday: Winds less than 25 kt. Chance of rain showers, slight
chance of thunderstorms.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Wind Advisory until 9 PM EDT this evening for MAZ019-022>024.
RI...None.
MARINE...Storm Warning until 8 PM EDT this evening for ANZ232-254-255.
     Gale Warning until 10 PM EDT this evening for ANZ231-233>235-
     250-251-256.
     Gale Warning until 9 PM EDT this evening for ANZ230-236.
     Gale Warning until 9 PM EDT this evening for ANZ237.

&&

$$
SYNOPSIS...Frank/EVT/KJC
NEAR TERM...Frank
SHORT TERM...EVT
LONG TERM...KJC
AVIATION...Frank/EVT/KJC
MARINE...Frank/EVT/KJC

NWS BOX Office Area Forecast Discussion

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