Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 220251
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
951 PM EST Sun Jan 21 2018

.SYNOPSIS...
A stalled frontal boundary across southern New England will
gradually lift north as a warm front late tonight through Monday
night. Low pressure will track northeast out of the Great Lakes
and into the St Lawrence Valley on Tuesday and will drive a cold
front through the region late in the day. Low pressure will
continue northeast into the maritimes Tuesday night. High
pressure will slowly build in from the west Wednesday through
Friday.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
950 pm Update: Previous forecast on track with no changes
needed at this time.

7 pm Update: Input latest mesonet data with only a few minor
tweaks needed. Previous forecast looks good going forward to the
overnight hours.

Previous Discussion:
Clouds will be on the increase overnight as weak over-running
sets up along a stalled frontal boundary draped across southern
New England. With the exception of a stray flurry in the
mountains...expect a dry night with lows dropping back into the
mid teens to mid 20s north and mid 20s to near 30 in the south.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
Frontal boundary will begin to lift north on Monday bringing
over-running precip into western zones in the afternoon.
Precipitation will likely be in the form of light rain or snow
in southern New Hampshire with occasional light snow elsewhere.
Expect little if any accumulation through evening with QPF
generally less than a tenth of an inch. Highs will range through
the 30s in the south and mid 20s to mid 30s north.

Warm front will continue to lift north Monday night producing
occasional light snow in northern zones and a mix of
sleet...snow and eventually freezing rain in southern sections.
Once again only looking for light amounts of QPF with just an
inch or two of accumulation in the north and light accumulations
of snow sleet and ice in the south. Southern New Hampshire will
hover around freezing overnight with the remainder of the
forecast area ranging through the 20s. With this generally being
a 3rd and 4th period event will let the mid shift decide on
timing and areal extent of any needed advisories.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
***Mixed precipitation expected Tuesday***

Focus of the extended remains on the Mon night/Tue system moving
out of the Great Lakes. 21.12z GFS and ECMWF remain insistent on
primary low pressure moving into Ontario...and weak secondary
development occurring and running thru the heart of New England.
There is not much climatological support for this type of
track...so I hesitate to warm the surface as much as those
models indicate. We are now in long ranges of some hi-res
guidance...which show a much colder and cold air dammed
scenario. I prefer this evolution...especially given the high
pressure building across the top of the advancing system. I
leaned heavily on the hi-res NAM 2 m temps for general pattern
Tue.

Aloft I used a multi-model blend for max wet bulb temp in order
to determine ptype. Relatively early on in the event...warmer
air aloft will be moving in from the SW. So I expect snow will
be rather brief outside of the Wrn ME mtns. Behind the mid level
warm front we end up in the warm sector without much precip
occurring. There could be some drizzle or freezing drizzle that
occurs at this time...but confidence is low. That warm air
aloft marches steadily NEwd...as the heavier precip arrives
around 12z. I expect a mix of snow in the mtns...sleet and
freezing rain S...and rain near the coast and parts of far Srn
and SWrn NH. The cold air damming signal lets up around 18z...so
I expect more of a transition to rain at that point and a mix in
the mtns. Overall no one winter ptype looks to amount to
significant accumulations...so in all likelihood a winter wx
advisory will handle it. The preference is to let the next shift
get another look at hi-res guidance...which will have a better
handle on low level temp fields.

It is still worth noting that 12z raobs across the Wrn CONUS
show H5 heights are higher than modeled ahead of the developing
wave. This has tended to favor stronger high pressure to the NE
of the storm in the ensemble systems. It is something to watch
for regarding cooling trends.

Also of concern is any run off going into area rivers. There
remain ice jams...and water levels rising may lead to renewed
flooding. A flood watch has been issued for the areas most at
risk for this.

Beyond the early week system...CAA midweek gradually gives way
to moderating and mild temps. The multi-model consensus blend
was used for this portion of the forecast...with the focus being
on the mixed precip event.

&&

.AVIATION /03Z MONDAY THROUGH FRIDAY/...
Short Term...VFR this evening with MVFR/IFR ceilings developing
after midnight. IFR/LIFR ceilings Monday through Monday with
IFR/LIFR ceilings/vsby Monday night.

Long Term...Widespread IFR conditions are likely as mid level
warm front moves thru and WAA continues aloft. Precip will
increase in intensity after 12z Tue...with some FZRA and PL
possible at all terminals. Coastal terminals are expected to
warm up first to RA...but it is possible that models are warming
the surface too quickly. Widespread LLWS is expected as
well...as LLJ increases to 50 kts around 2000 ft. Flow becomes
Wly Wed...returning S of the mtns to VFR. HIE will hang on to
MVFR CIGs and VCSH for much of the day.

&&

.MARINE...
Short Term...SCA`s may be needed late Monday afternoon and
Monday night.

Long Term...Gale force winds are possible Tue ahead of
approaching low pressure...especially outside of the bays. A
gale watch has been issued for the outer waters into Tue night.
SCA conditions likely for the bays. SCA conditions are expected
to continue for much of the rest of the week...in CAA Wly flow.

&&

.HYDROLOGY...
A flood watch has been issued as some run off and river rises
are expected and ice jams remain in place along several rivers.
This may lead to minor flooding as ice jams break up and reform
downstream.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Flood Watch from Tuesday morning through late Tuesday night
     for MEZ012-018>028.
NH...Flood Watch from Tuesday morning through late Tuesday night
     for NHZ003>015.
MARINE...Gale Watch from Tuesday morning through late Tuesday night for
     ANZ150-152-154.

&&

$$
Marine



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