Dense Fog Advisory 21, NWS Gray, ME

Area Forecast Discussion
National Weather Service Gray ME
948 PM EDT Mon Oct 23 2017

.SYNOPSIS...
High pressure will push east of the Gulf of Maine
tonight allowing a slow moving cold front will approach from the
west overnight and Tuesday. The front will slowly cross the region
Wednesday through Thursday. A ridge of high pressure will build over
the region on Friday and will shift offshore on Saturday before the
next low pressure system approaches from the southwest late in the
weekend.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
945 pm Update: Fog development now widespread along the coast
and working inland. Some patchy drizzle also beginning to
develop. Forecast looks good except tweaked temps based on
latest obs.

715 pm Update: Low clouds have once again moved onshore along
the ME/NH coast and parts of interior southeast NH. With the very
moist southeast low level flow, expecting fog and drizzle to
gradually develop,m m,ove further inland and overspread much of
southern and central areas of the forecast area. Input latest
mesonet data.

Previous Discussion:
Some clouds continue to move into srn NH from the south,a and
coastal stratus also continues to build up just offshore, but
heating is holding it there for now. The coastal stratus should
start moving inland during the late afternoon and early evening,
with clouds streaming in from the south and and west, and
clouding up most places by midnight. Lots of moisture will
stream in over the overnight inversion, so look for DZ to
develop, especially in SE upslope areas. Thinking that large
scale forcing will likely hold off until Tuesday, so for the
most part look for DZ/FG tonight. Temps will fall off a bit this
evening, but will likely start to rise after midnight, with
temps mostly in the mid to upper 50s.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
500 mb closed low over the gReat Lakes will move very slowly NE
on Tue and will see several a couple waves of energy move
through it, which will help it go thru two cycles of deepening,
which will keep sfc low and associated cold front over the GReat
Lakes and NY on Tue, with just some sct SHRA, and perhaps some
continued spotty DZ thru the day on Tue. Could see more
organized showers in the upslope areas of the Whites Tue
afternoon, but still nothing heavy until Tue night. Highs will
rise on increasing S-SE winds into the 60s. Mid to upper 60s
are expected in the CT valley, srn NH and SW ME, with low to mid
60s in central ME and the mid-coast. Dew points will also climb
into 60-65 range during the day, so it will start to feel humid
as well. Also those S winds will increase, and could see gusts
of 25-30 mph in the afternoon, especially on the coast and
across the hilltops.

Tue night will see the closed low over the GReat Lakes to start
making a little better progress to the NE, but it will still be
a slow go. This will push the sfc front ewd into NH after
midnight. Ahead of the front, expecting a line of convection to
form as strong low level jet will be in place just ahead of the
front. With the deep moisture ahead of the front, this
convection will produce heavy rain, and the possibility of TSRA.
Any TSRA could also help mix down the winds from the jet, and
good see some gusts approaching severe levels. Currently, this
line should be somewhere in the vicinity of the NH/ME border
around daybreak on Wed, and will continue across ME Wed morning.
This line will likely be responsible for a large part of the
rain that falls and could produce an inch to inch and a half in
several hours.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
A more active weather pattern is expected in the extended with
significant precipitation early and again late in the period.
In between expect a few more nice weather days.

On Wednesday a pronounced cold front will approach the area. Ahead
of the front sub tropical moisture will stream north over the
region. In addition there are indications of a wave forming on the
front. This would slow the eastward speed of the front and
potentially prolong  rainfall especially over eastern areas. Until
the front crosses the air mass remains unstable and could support
embedded thunder storms. Will include the chance of this through the
day on Wednesday.

The front will push east of the area late Wednesday Night over w
eastern areas and early on Thursday over eastern areas. A cyclonic
flow aloft as well as a cold pool aloft will help support showers on
Thursday. Rainfall amounts will be challenging. With subtropical
moisture involved and a slow moving pattern would favor significant
rainfall. On the other hand...models maybe somewhat overdone due to
convective elements embedded that models are trying to resolve.

A short wave Ridge will build over the region Friday into Saturday.
Allowing for drying and pleasant conditions. Low Pressure and an
associated cold front will approach from the Great Lakes Saturday
Night and Sunday. A secondary low may form along this front off the
Southeast Coast. This scenario would increase the threat of a
soaking rain late Sunday and into Monday. The GFS is about 12 hours
faster than the ECMWF with this feature...so the timing of this
event is in flux.

Temperatures will remain at or above normal through the period with
the warmest temperatures expected on Saturday when widespread 60s
for highs are expected south of the mountains.

&&

.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
Short Term...Any VFR breaks today will end early this evening as
low clouds move onshore or develop in moist southerly flow above
the diurnal inversion. Most places will see LIFR by after
midnight as FG/DZ will be added to the low clouds. Non-coastal
terminals will see improvement to IFR, and maybe MVFR for a bit
on Tue. Coastal terminals will probably be stuck with LIFR cigs
all day, although vis will improve at times. The only exception
will be KHIE, which will likely stay VFR in the southeast
downslope into Tue afternoon.

Long Term...
IFR to LIFR conditions possible ahead of approaching cold
front Wednesday and Wednesday Night. Rain with embedded
convection Wednesday with patchy fog Wednesday night. Winds
shift to west northwest Thursday resulting in improving
conditions. VFR conditions expected to return Friday and
Saturday.

&&

.MARINE...
Short Term...Will hold the flags as they are for now. SCA
confidence is very high, and will likely begin early Tue
morning. Gales are still a good bet, but timing is uncertain,
and they may only occur in a small time window late Tue night
into Wed morning. Seas will begin to push to around 10 ft by
early Wed morning.

Long Term...
Wednesday and into Thursday wind and waves at SCA levels and
possibly briefly reaching Gale conditions in strengthening
southerly flow ahead of approaching cold front. Winds shift to
west northwest Thursday resulting in subsiding waves. &&

.HYDROLOGY...
Overall, we are looking at 1-3" of rain across the area between
Tue and Thu, however, the bulk of the rain will fall Tue night
and Wed. Still, with river levels running very low, mainstream
flooding is not expected. However, could see a lot of rain in a
short period time as a line of heavy showers and/or
thunderstorms moves through late Tue night and Wed morning, and
this could lead to some poor drainage and minor urban flooding.

&&

.TIDES/COASTAL FLOODING...
A slow moving cold front will provide a prolonged period of
onshore flow. Seas will build to 10-12 ft in onshore flow, but
mostly away from shore. While this is a descent wind wave, all
other factors for coastal flooding remain low. We are at an
astronomical low point in the tidal cycle with high tide at
Portland in the 9ft range. Additionally all of the wave is in
the wind wave at around 8 seconds with no long period swell. The
low tide and short period means that even though there may be
around a foot of storm surge it will not be enough to cause
problems.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...Small Craft Advisory from 8 AM to 8 PM EDT Tuesday for
     ANZ150>154.
     Gale Watch from Tuesday evening through Wednesday evening for
     ANZ150>152-154.

&&

NEAR TERM...Marine

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