Area Forecast Discussion
Issued by NWS Portland, ME-- Highlight Changed Discussion --
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FXUS61 KGYX 181425
Area Forecast Discussion
National Weather Service Gray ME
1025 AM EDT Tue Oct 18 2016
A warm front will try to slowly lift northeast through the region
today. Temperatures will be very warm south of the warm front
today, but north of the front it will be cooler with showers
expected. As low pressure moves through Quebec, it will drag a
weak front into New England tonight and then move offshore. High
pressure with dry and very mild temperatures are expected
Wednesday. A trough of Low pressure will track across New England
Thursday and Friday and will bring some much needed rain to the
area. The system exits into the maritimes over the weekend with
breezy conditions and much cooler temperatures in its wake. Along
with the cool temperatures, clouds and even a few showers possible
in the mountains over the weekend.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --1020 AM...Winds have been more NE than SE this morning and this
allowing for stronger cold air damming to hold. Have adjusted sky
and temps to hold onto the clouds and cooler air longer across
the southern zones, and tweak maxes down in this areas as well.
Meso models do want to break the inversion in southern NH, the CT
valley and SW ME, but it will likely not happen until early to mid
afternoon, so highs will be limited to the mid to upper 60s in
many spots, with a few spots in the CT valley and maybe the
Merrimack valley making it to 70 or so. Also added patchy FG/DZ
to the coastal zones and the coastal plain of ME as the will see
more in the way of warm moisture advection above the inversion
630 AM Update: Only minor changes needed this hour with
shower activity essentially over as we find ourselves in a void
between activity north of the international border and more
showers off the Massachusetts coast...with H8 warm front moving
overhead with just a sprinkle or two. Adjusted to current
temperatures/dewpoints with very minor PoP tweaks...primarily to
lower them in the near term.
Previous discussion below...
High Impact Weather Potential: Splashover/minor coastal flood
potential /see Tides/Coastal Flood section below/.
Current Pattern: A look at early morning water vapor imagery reveals
decaying area of enhanced moisture associated with earlier MCS whose
remnants are now exiting my southern zones. Shortwave ridging is
now arriving from the west with next area of deep moisture
associated with developing surface low pressure system over northern
Michigan. Down at the surface...we can see a high pressure ridge
axis aligned over eastern Maine with building SLPs in a cold air
damming pattern setting up over coastal Maine into southern NH.
South and west of this feature is a stationary boundary separating
yesterday/s warmth from cooler air draining south with the high.
With aforementioned low pressure system continuing to lift north
and east...and shortwave ridging moving east of our longitude...
developing deep layer southwesterly flow will begin to nudge the
surface front north and east ahead of an approaching cold front
that we/ll discuss in the tonight forecast. Thus...forecast
concerns center around 1-precipitation potential in the
strengthening WAA regime and 2-surface temperatures and how the
surface front evolves.
Through Daybreak: Backdoor front continues to push south and
west...having cleared southern NH with surface pressures continuing
to rise. Last remnants of decaying MCS will exit my southern NH
zones through 5am...with nothing more than a few sprinkles noted
north of this. Expect this trend to continue...with a few light
showers/sprinkles along the leading edge of the moisture surge at H8
continuing over northern areas through 8am. Temperatures come down
another few degrees under the light northeasterly flow...in the
upper 40s to mid 50s.
Today: Deep southwesterly flow overspreads the region today well
ahead of deep low pressure that will reach near James Bay early this
afternoon...continuing northeast into this evening. Warm front at
H8 will depart my Maine zones this AM...taking any remaining light
shower activity with it. With surface low pressure so far removed
to our north and west...the surface boundary will struggle to make
northward progress today...with most recent renditions of high
resolution guidance continuing to bring the warm air to a smaller
and smaller portion of our forecast area. Will not go all the way
to the HRRR which indicates that the warm front does not arrive
during the daylight hours...but will trend afternoon highs back some
from inherited forecast. This brings Cheshire/Hillsborough/
Rockingham counties into the lower 70s...with 60s north and east
of this except northern Oxford/Franklin/Somerset in Maine where
mid 50s will likely be it. Certainly some bust potential vicinity
LEB/CON/PSM/SFM...but growing confidence that the warm air fails
to reach even southern Maine today.
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.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
High Impact Weather Potential: Minimal.
Pattern: Broad southwesterly flow will remain over the area through
the short term forecast period with just enough of an angle between
this flow and upstream surface front to push it through the region
tonight and offshore for Wednesday. Primary forecast concerns
center around precipitation potential along the front.
Tonight: Surface cold front will be just upstream of New England at
00Z...nearing the coastal plain by daybreak Wednesday. Llevel flow
largely veered ahead of the boundary with mid level shortwave energy
having bypassed the front to our north and east. Thus...while a +2-
3 sigma PWAT plume will pull overhead through the night...waning
instability and llevel convergence suggests a decaying band of
showers /embedded thunder?/ and forecast PoPs will follow this trend
with measurable precipitation rather unlikely along the coastal
plain. Clouds and warm airmass aloft will allow for another night
of mild low temperatures...with consensus lows in the 50s/lower 60s
Wednesday: Nice day expected on Wednesday with high pressure
building in behind departing cold front. Deep moisture plume will
be pushed offshore during the day...with very modest cold advection
behind this feature. Could see some residual clouds in the
mountains under modest northwesterly flow...but mostly sunny south
south and east of this. T8s remain around +10C with T9s +12-17C
north to south during the afternoon. Thus...expect highs to be well
above normal...60s north of the mountains with mid/upper 70s in the
foothills and points south. Enjoy it...as significant changes are
in store in the long term period below!
.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
A progressive digging upper trough will move across the Ohio
Valley and Great Lakes region Thursday and in advance first
spreading clouds and then the chance of rain in the afternoon
from west to east. The upper trough will continue to develop over
the eastern Great Lakes Thursday night and Friday becoming
vertically stacked and spawning surface cyclogenesis across the
St Lawrence Valley and upstate New York. A broad area of rain
will gradually develop by Friday afternoon. The upper trough will
continue to develop as it becomes negatively tilted and then
becomes a closed low by Friday night. As the system develops,
models are indicating a strong southeast flow will develop to its
east and will likely pick up some tropical moisture from a system
off the southeast coast of the U.S. This may bring some soaking
rains to the area late Friday and Friday night.
Models indicate the closed upper low is expected to move slowly north
and east into the maritimes Saturday and Sunday possibly allowing
some lingering showers mainly in the mountains due to the unstable
cyclonic flow. Much cooler temperatures will arrive behind the
system Saturday into Sunday.
Cool and dry weather is expected Monday as Canadian high
pressure builds across the region.
.AVIATION /14Z TUESDAY THROUGH SATURDAY/...
Short Term /through Wednesday/...
Summary: A warm front will slowly lift north through the area today
before a cold front moves in from the northwest tonight with high
pressure arriving for the day on Wednesday.
Restrictions: Conditions deteriorating attm with MVFR /and some
IFR/ cigs developing north of warm front. This trend will continue
through the morning before gradual improvement this afternoon and
evening. A few isolated showers are possible for ME terminals this
morning with dry conditions this afternoon. Tonight...a band of
showers will impact HIE/LEB before falling apart as it moves south
and east. Conditions overnight generally VFR except fog
development HIE/LEB and potentially CON/AUG. VFR for the day
Winds: Generally from the northeast 5-10kts today...shifting
south 10 kts this afternoon into this evening as the warm front
moves north. Southwesterly winds shift northwesterly for the day
on Wednesday 10-15kts.
LLWS: Impressive LLWS setup this evening as southwesterly flow
strengthens atop strong llevel inversion. Expecting 30-40kt winds
at 1-2kft all sites through the overnight.
Thunder: Very remote chance of a rumble this evening
HIE/LEB...otherwise no threat.
Long Term...Conditions deteriorate Thursday in an onshore flow
with increasing clouds and showers. IFR or LIFR conditions are
possible Thursday through Friday night. Could see an improvement
to VFR this weekend.
Short Term...Winds nearing SCA levels this morning...but bona-fide
SCA conditions hold off until tonight with strengthening southerly
winds/building seas. Winds/seas diminish behind departing cold
Long Term...An increasing south to southeast flow Friday and
Friday night may develop SCA conditions. Winds behind the system
over the weekend may be gusty from the west and northwest so SCA
conditions may continue.
Have issued coastal flood statement for this afternoon/s 1pm EDT
high tide given surge forecast of up to one half foot...which
would put both Portland and Fort Point right at FS early this
afternoon. Wave action does not look that impactful...only 2-3
feet at the coast. Will monitor the surge/winds this morning and
see if advisory is warranted.
Tides remain high for the next few days...but winds look to remain
light beyond today/s high tide. Will continue to monitor.
Tides at Portland the next few days follow below:
108 PM Tue 11.7 ft mllw
200 PM Wed 11.5 ft mllw
256 PM Thu 11.1 ft mllw
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MARINE...Small Craft Advisory until 8 AM EDT Wednesday for ANZ150>152-
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