Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 191444
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
944 AM EST Sat Jan 19 2019

.SYNOPSIS...
Low pressure will move northeast through the Ohio Valley today
and will reach northern New Jersey by Sunday morning. Strong low
pressure will move northeast through the Gulf of Maine on Sunday
and into the Maritimes Sunday night. A strong cold northwest
flow will persist over the region Sunday night through monday
night as high pressure Gradually builds in from the west. High
pressure will crest over the region on Tuesday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
10am update.. just minor changes for today to sky cover and
temperatures to keep in line with observations. Will await 12Z
guidance before any big changes. Avalanche Watch has also been
issued for Southern Coos. See AVAGYX.

Update...Minor changes to reflect latest observational trends in
temps and sky cover.

Previous discussion...The real bitterly cold air mass is
working its way into Nrn zones at this hour...and is evident
across The County marked by a thin line of broken Cu dropping
Swd. This will continue to push slowly Swd thru the day...and
almost act a bit like a backdoor cold front by this evening.
This will be especially true as pressure fall to our S and the
gradient helps force this Nly drain.

That is pretty much the story for the day other than clouds
increasing thru the second half of the day as WAA begins to
ascend along the sloping warm front.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
MAJOR WINTER STORM TONIGHT INTO SUNDAY....

The overview has changed little overnight. Low pressure is
organizing quickly over the Mid Mississippi Valley...and
features significant convection at this late (early?) hour. Two
observations of note tonight that I found interesting were that
modeled H5 heights over the Nrn Rockies were lower than
observed raobs, and modeled temps at H8 over the OH Valley were
too warm compared to raobs. The H5 heights are interesting
because ensemble sensitivity was tied to heights in this region.
That uncertainty was both a low position and speed
difference...with lower heights in the Nrn stream tending to
favor a faster and farther N low pressure. If heights continue
to be higher than modeled...that could signal that low pressure
will trend SE. Put more simply...a deeper Nrn stream S/WV trof
is more likely to at least partially phase with the Srn stream
and allow it to amplify farther N. H8 temps are a little more
simple...in that WAA not penetrating as far N overnight will
help delay increasing temps downstream.

That brings me to changes in the forecast. Nothing major...but I
have trended to the colder side of guidance. This is especially
true at the surface where I think we have little chance to see
freezing in much if any of the forecast area. Aloft I also
trended cooler than the 00z guidance...which was all quite warm.
This still brings a sleet mixture to Srn NH and coastal Wrn
ME...and a little bit of freezing rain for Seacoast NH. Snowfall
forecasts were decreased slightly for a couple reasons. One is
that model guidance has been trending drier with successive
runs...and given the open wave aloft this makes sense. It is
difficult to sustain near 2 inch QPF amounts without a closed H7
low. Additionally I adjusted snow ratios down slightly which
also lowered snowfall amounts. With strong WAA and temps
increasing into the 0 to -5C range in the mid levels...we should
see some riming of flakes and ratios closer to climatological
mean values. This still results in widespread double digit
snowfall amounts...and in no way lessens the impact of this
storm.

Other details of the forecast include the continued strong
banding signature parallel to the storm track. This will lift
into the area late this evening...and then slide ENE poleward of
the track...most likely inland from the coast. Anywhere within
this band snowfall rates in excess of 1 to 2 inches per hour are
possible. This is supported by HREF 1 hr snow forecasts...as
well as time lagged hi-res guidance based ensembles. The focus
of the heaviest snow rates are Sun morning...a few hours either
side of 7 am. This will be the strongest WAA aloft...and likely
just on the leading edge of any sleet mix. It is during this
time that travel is discouraged and will be most treacherous.

Also continuing to watch the wind potential along the coast. At
this time it looks like there is only a partial overlap of
stronger gusts and heavy snow. So for now near-whiteout
conditions are possible...and I have mentioned this in the most
likely zones along with blowing snow.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
North winds will hamper cleanup efforts Sunday night as low
pressure pulls away into the maritimes. Expect considerable
blowing and drifting overnight with lingering snow showers
mainly confined to northern and eastern zones. Downsloping
should bring partial clearing downwind of the mountains.
Lows overnight will range from 5 below north to 5 above on
the coast. Will likely need wind chill advisories for the
mountains and Connecticut Valley for wind chills of 20 to 25
below.

Strong northerly winds will persist through the day Monday as
high pressure builds in from the west. Deepening upper low will
swing in from the west during the day with morning sun downwind
of the mountains giving way to clouds and snow showers. Expect
several more inches of accumulation in the usual favorable
upslope areas in the north and light and spotty accumulations
elsewhere. Highs will range through the single numbers north and
in the lower teens south.

Winds will continue to buffet the region Monday night as high
pressure continues to gradually build in from the west. Expect
gradual clearing through the evening hours with skies becoming
mostly clear after midnight. Lows will range from 5 to 15 below
in the north and 5 below to 5 above south. Wind chill values
will once again prompt advisories for the north where values of
20 to 30 below will be likely.

Winds will gradually subside on Tuesday as high pressure crests
over the area by late in the day. Weak over-running setting up
to the west will bring high clouds into the region in the
afternoon. Highs will range through the teens north and lower to
mid 20s south.

Models continue to diverge tonight at this point in the forecast
with big differences on timing and intensity of low pressure
moving through the Great Lakes. High pressure will shift
offshore Tuesday night as broad area of weak over-running shifts
in from the west ahead of afore mentioned low pressure. Looking
for increasing clouds overnight with a chance of snow showers
after midnight. Lows will range from 5 to 15 above.

Forecast confidence continues low on Wednesday as GFS takes low
pressure into southern Quebec while ECMWF quite a bit slower
keeping low pressure centered over the Great lakes by the end of
the day. Best guess at this point is for occasional light snow
mixing with sleet and possibly ending as a little light rain in
southern zones as warm advection passes to the east in the
afternoon. Highs will range through the 30s to lower 40s in the
south.

Picture remains uncertain for Wednesday night and Thursday as
models beginning to converge on low pressure moving up the east
coast but big differences in timing...track and intensity making
it difficult to say what form precip will take and how
much...but another round of mixed precip may be in the works for
Wednesday night and Thursday.

&&

.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
Short Term...VFR conditions expected for the early part of today
as Arctic high pressure and air mass move into the region.
Gradually this afternoon clouds will thicken and lower from SW
to NE as low pressure develops in the OH Valley. This evening
conditions quickly deteriorate to IFR and lower as SN breaks
out. Widespread LIFR is expected in +SN Sun morning into the
afternoon. PL may mix in across Srn NH and coastal Wrn ME Sun
morning around 12z as the warmest air makes it Nwd. With a
strong inversion in place...LLWS is a possibility at all
terminals...but especially coastal locations. +SN moves out
quickly Sun afternoon...but I expect lingering areas of IFR
with -SN/BS.

Long Term...MVFR/ifr ceilings/vsby Sunday evening...improving
to VFR with areas of MVFR ceilings in the mountains. MVFR
ceilings developing on Monday. Becoming VFR Monday night. VFR
Tuesday. MVFR/IFR ceilings/vsby developing Wednesday.

&&

.MARINE...
Short Term...Have upgraded gale watches to warning...as NE winds
are expected to increase ahead of and N of strong low pressure
moving thru the Gulf of ME. Strongest winds are expected Sun
morning...though gale force gusts will linger as flow becomes
off shore late Sun.

Long Term...Gales likely Sunday night through Monday night.

&&

.TIDES/COASTAL FLOODING...
With a strong storm moving through the Gulf of Maine Sunday,
northeasterly winds will increase and nearshore waves build to
around 10 ft. In combination with high astronomical tides during
the morning this may result in areas of minor to moderate
flooding. The highest threat is along the New Hampshire and
southwestern Maine coastline where the winds are most onshore
and highest surge values of around 1.5 ft are expected. A
coastal flood watch has been issued for this area. To the north
up through the midcoast the surge is expected to be lower, but
this area will also have to be monitored for possible minor
flooding.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Winter Storm Warning from 7 PM this evening to 1 AM EST Monday
     for MEZ012>014-018>028.
     Winter Storm Warning from 7 PM this evening to 7 AM EST Monday
     for MEZ007>009.
     Coastal Flood Watch from Sunday morning through Sunday
     afternoon for MEZ023-024.
NH...Winter Storm Warning from 7 PM this evening to 1 AM EST Monday
     for NHZ003>015.
     Winter Storm Warning from 7 PM this evening to 7 AM EST Monday
     for NHZ001-002.
     Coastal Flood Watch from Sunday morning through Sunday
     afternoon for NHZ014.
MARINE...Gale Warning from 7 AM to 7 PM EST Sunday for ANZ151-153.
     Gale Warning from 4 AM Sunday to 1 AM EST Monday for ANZ150-
     152-154.

&&

$$
SYNOPSIS...
NEAR TERM...Curtis
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...
TIDES/COASTAL FLOODING...


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