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FXUS61 KBOX 170830
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
430 AM EDT Thu Oct 17 2019

.SYNOPSIS...
A powerful coastal storm over Rhode Island sound will continue
to strengthen and move north thru Rhode Island into
Massachusetts this morning and then into northern New England
this afternoon. Heavy rain and strong to damaging winds end
before sunrise and is replaced by scattered showers and gusty
west winds. Drier, though blustery and cooler weather follows
for Friday. Warming trend with dry weather for the weekend.
More active weather than looks to resume for early next week.

&&

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

430 AM Update:

Today...

Strong Winds ...

975 mb Low over eastern MA early this morning will slowly lift north
into NH and ME this afternoon. Low level jet associated with this
low over northeast MA will exit into NH/ME towards daybreak. Thus
winds briefly diminish but then shift to the NW on the backside and
with strong pressure rises NW winds will gusts to 40-50 mph later
this morning and into the afternoon. Gusts could will be a bit
higher up to 55 mph or so across Cape Cod and the Islands given
steeper lapse rates as WSW winds stream across relatively warm SST.
Low risk of a few gusts near 60 mph but confidence low on this
occurring so sided with a wind advisory vs high wind warning.

Rain ...

Dry slot moving across the region and has shifted very heavy
rainfall from overnight into northern New England. Thus a drying
trend early this morning along with some breaks of sunshine early.
However well defined comma-head already established over eastern NY
into western-central MA will expand eastward later this morning into
the afternoon. Moderate to heavy rain should be confined across
western-central MA within comma-head and therefore continuing flood
watch across this area. Elsewhere lighter scattered showers will
advance eastward later this morning and afternoon as comma-head
moisture wraps cyclonically around mid level low moving north of the
region.

Temps ...

Cool air advection today with 850 mb temps lowering to 0C to +1C
this afternoon. This combined with comma-head cloudiness
overspreading the region later this morning and early afternoon will
support highs in the low to mid 50s, upper 40s high terrain.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...

430 AM update:

Tonight...

Vertically stacked low along the ME coast this evening exits into
the maritimes. So any lingering isolated showers in the evening will
quickly give way to a drying trend along with NW winds diminishing
but still remaining somewhat gusty especially Cape Cod and the
Islands. Seasonably cool tonight with lows in the 40s.

Friday ...

Not as cool given rising heights/warming temps aloft. However with
cyclonic flow persisting expecting a fair amount of diurnal clouds.
Mid levels are dry so that should be sufficient to preclude any
diurnal showers. Highs 55-60 but low 50s high terrain and there will
be a cool WNW breeze as well given pgrad.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...

No updates to the extended given the active weather overnight.
Previous discussion below.

================================================================

Highlights...

* Blustery, cooler weather continues into Friday. Possible frost
Friday night?

* Warming trend and drier for the weekend.

* Active pattern resumes late weekend - early next week, though
with a high degree of uncertainty on which day(s) are more
unsettled than not.

Details...

Friday:

Cyclone to affect much of New England over the next 24-36 hrs
looks to be centered over northeast ME by early Friday per most
model guidance, weakening/filling as it does so. Cyclonic flow
aloft should be maintained though will also be steadily losing
overall influence as we the day. That being said, presence of
continued 925- 700 mb thermal trough amid lightening northwest
flow and residual shallow moisture ... it gives a continued
cool, blustery day looks likely for Friday. Northwest gusts
25-35 mph still look possible during the day as lapse rates
steepen, albeit through a smaller mixing depth. Look for
variable amounts of cloud cover - tending closer to mostly
cloudy further north and less so further south and east - and
there might still be enough moisture to wring out sprinkles
north of Route 2 but nothing significant. However, most areas
should see thinning cloud coverage later in the day. Highs in
the 50s.

By Friday night, we start to feel subsident effects of surface
ridging, with trends toward clearing skies and lightening NW
winds. Question remains on how quickly each of these occurs -
which will crucially affect lows. Though thermal advection
transitions toward neutral levels for the evening, could have
some frost/freeze concerns to contend with in areas where the
growing season is still declared as active (e.g. most areas
outside of the Pioneer Valley, northern Worcester and northern
Middlesex Counties). MOS-based guidance usually is the coldest
in such radiational situations, temps close to the MET-based MOS
would bring a widespread frost, with even some sub-freezing
lows in western/central MA and northern CT. Given uncertainty in
how quick NW gradient winds subside and on prospects for
clearing, will use a guidance blend as a starting point but give
some weight to some of the cooler MOS as well. Brings lows into
the mid/upper 30s to low 40s.

Saturday to Sunday:

Quiet weather pattern resumes for Saturday into a good part of
Sunday for most, with large surface ridge settling in and
eventually shifting east of the region. Warming trend to
temperatures as well with 850 mb temps rising to the upper
single digits Celsius.

Deterministic models, however, diverge on handling of energy
coming out of the Gulf of Mexico later Sunday/Sunday night. This
leads to questions/greater forecast uncertainty for the
remainder of the period. NHC has designated an area of disturbed
weather over the southwest Gulf of Mexico with some tropical
development potential. GFS/ECMWF/GEM develop a low from this
area into the northern Gulf early Saturday which takes a
decidedly Miller-A analog storm track from there into the
coastal Carolinas by Sunday. That's really about all that's
agreed upon, though, as the international guidance more or less
weakens and keeps the cyclone closer to the mid-Atlantic coast
thru the weekend. On the other hand the GFS pulls the system
well offshore to at least a well-developed gale south of the
40N/70W benchmark - which would bring greater impact to our
coastal/offshore waters with enhanced E/ENE flow and building
seas, with some showers toward the south coast, Cape and
Islands.

Will lean towards dry for the weekend until there's greater
consensus on the Gulf coast system.

Early Next Week:

Forecast uncertainty and spread in guidance for late Sunday
also affect the forecast into early next week.

Does look to be overall a pretty unsettled period, with an
amplified trough/ridge pattern across the eastern two-thirds of
CONUS. Strong mid-latitude cyclone over the northern Plains
Monday with a trailing cold front into the lower MS Valley
should progress E/NEward into southern New England either
Tuesday or Wednesday, though which day(s) may have higher
chances than others remains uncertain. Used a model consensus
blend in this period until better certainty and agreement in
details become more evident.

&&

.AVIATION /09Z THURSDAY THROUGH MONDAY/...
Forecaster Confidence Levels...

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

Short Term /through Friday/...

06z Update:

Thru 12z ... High confidence on trends, lower on exact timing

Very strong east winds up to 60 kt in gusts across eastern MA will
persist until 08z-09z and then lift northeast into NH/ME. WNW
winds then develop across the region from southwest to northeast
with WNW gusting up to 40 kt except up to 50 kt Cape Cod and
Islands. IFR/LIFR improving to VFR toward 12z except improving
to MVFR across the high terrain along with rain tapering off to
showers.

After 12z ... High confidence.

Marginal MVFR/VFR along with scattered showers. WNW winds
gusting up to 40 kt except up to 50 kt Cape Cod and the Islands.

Tonight ... High confidence.

VFR with any scattered showers ending. Modest WNW winds.

Friday ... high confidence.

VFR, dry weather and modest WNW winds continue.

KBOS Terminal...High confidence in TAF trends. Moderate
confidence in timing.

KBDL Terminal...High confidence in TAF trends. Moderate
confidence in timing.

Outlook /Friday Night through Monday/...Moderate confidence.

Friday Night: VFR. Breezy.

Saturday through Sunday Night: VFR.

Monday: Mainly VFR, with areas MVFR possible. Breezy. Slight
chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

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

430 AM update:

Today ...

975 mb low over northeast MA yielding Storm force SE winds across
the northern MA waters linger for a few more hours and then shift to
the WSW by daybreak at gale force. Elsewhere WSW 40-50 kt becoming
WNW later this morning and afternoon. Scattered showers but
improving vsby with the wind shift.

Tonight ...

Powerful low over ME moves slowly into the Maritimes. WNW gales but
dry weather and good vsby.

Friday ...

Gale Center over the Maritimes slowly weakens with subgale WNW winds
over the MA/RI waters. Dry weather and good vsby.

Outlook /Friday Night through Monday/...Moderate confidence.

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

Friday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Local rough seas.

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

Saturday Night: Winds less than 25 kt.

Sunday: Winds less than 25 kt. Slight chance of rain showers.

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

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Wind Advisory until 6 PM EDT this evening for CTZ002>004.
MA...Wind Advisory until 6 PM EDT this evening for MAZ002>006-
008>024-026.
Flood Watch until 7 AM EDT this morning for MAZ002>004-008>012-
026.
High Wind Warning until 7 AM EDT this morning for MAZ007.
RI...Wind Advisory until 6 PM EDT this evening for RIZ001>008.
MARINE...Storm Warning until 8 PM EDT this evening for ANZ232-233-
254>256.
Gale Warning until 9 PM EDT this evening for ANZ230.
Storm Warning until 5 PM EDT this afternoon for ANZ231.
Gale Warning until 8 PM EDT this evening for ANZ236.
Gale Warning until 4 AM EDT Friday for ANZ234-235-237.
Storm Warning until 8 AM EDT this morning for ANZ250-251.

&&

$$
SYNOPSIS...Nocera
NEAR TERM...Nocera
SHORT TERM...Nocera
LONG TERM...Loconto
AVIATION...Nocera/Loconto
MARINE...Nocera/Loconto
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