NWS Forecast Discussion

For Fremont, NH

000
FXUS61 KGYX 232334 AAA
AFDGYX

Area Forecast Discussion...UPDATED
National Weather Service Gray ME
634 PM EST Sat Feb 23 2019

.SYNOPSIS...
Low pressure organizing over the Plains and Mississippi Valley
will lift north and east into the Great Lakes on Sunday...with
an associated warm front bringing snow and mixed precipitation
to northern New England. A secondary low pressure system will
strengthen along the Maine coast and move into the Canadian
maritimes Sunday night and Monday...resulting in a period of
potentially damaging winds as Arctic air moves into the region.
Windy and cold weather will continue through Tuesday with high
pressure arriving from the west for the middle and latter
portion of next week...with temperatures remaining below normal.
Low pressure and more inclement weather will approach the
region by next weekend.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
630 PM Update...
Temperature forecast for the night is largely on track as upper
level cloudiness rotates out of the area briefly this evening
before WAA brings more back in. Readings are in the 20s and 30s
and continuing to drop with dew points below 20 still over a
good portion of the area. Timing of PoPs/impactful weather looks
good with it arriving in SW NH after midnight and into Maine
towards sunrise.


Previous discussion...
High Impact Weather Potential: Slick travel developing over
parts of southern New Hampshire towards daybreak.

Pattern: Early afternoon GOES 16 mid level water vapor imagery
shows an impressive shortwave trough lifting through the central
Plains with a broad area of warm advection-induced
moisture/cloudiness streaming into the northeastern United
States. This is resulting in an increase in upper level
cloudiness across our area as high pressure that crested over
the region this morning slowly settles into the Canadian
maritimes. Clearly the focus will be on the upstream
shortwave...with attendant surface low moving into the Great
Lakes tonight...reaching the Straits of Mackinac by daybreak
Sunday. To it/s east...ongoing moist warm advection will bring
precipitation to our doorstep by the end of this forecast period
daybreak Sunday.

Through this evening:  Relatively mild afternoon with quiet weather
across the region with varying amounts of high cloudiness.
Temperatures by 8pm will be in the 20s to around 30 in the
mountains...with lower/middle 30s along the coast and into the
foothills.

Tonight: Top down saturation continues through the night with
24-36 hour model trends suggesting a slight slowing to the
arrival of any precipitation. There has also been a reduction in
just how organized the precipitation shield is at first...with
one band of better forcing along the northward-lifting occluded
front to our west...and the other at the nose of the H8 low
level jet. This latter feature will largely be our
precipitation-maker...but this will take longer to arrive and
fits the delayed timing seen in the guidance.

Through daybreak...any precipitation that falls should take the
form of snow...and only occur over New Hampshire. Don/t foresee
more than an inch of accumulation through daybreak but
precipitation will be expanding...and becoming steadier and
heavier as we cross into the short term period Sunday morning.

Temperature forecast is a bit of a challenge given a later arrival
to precipitation. Simulated satellite imagery suggests a window
for radiational cooling through the first half of the night...
particularly over northern areas. Dewpoint depressions suggest
plenty of room for temperatures to drop...and will follow closer
to colder MET trends for the overnight...with teens north and
lower/middle 20s south favored.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
High Impact Weather Potential:

*Snow transitioning to mixed precipitation and rain with
 continued travel impacts.
*Southeasterly wind gusts may near advisory levels Sunday
 afternoon and evening along the Midcoast.
*Westerly winds begin to strengthen rapidly after midnight
 Sunday night all areas.

Sunday: Little in the way of significant change to the guidance
suite today as warm advection/LLJ driven precipitation shield
crosses the forecast area through the day. Guidance is also
consistent in the development of a triple point low during the
afternoon over southeastern New England that rides north and
east through the evening. NAM remains the warmest of the
guidance aloft...with the GFS significantly cooler. The RAP
provides a nice compromise...and helps produce a solution in
line with the HREF mean and was followed for this package. At
the surface...suspect that none of the guidance is quite cold
enough...particularly south of the mountains in the cold air
damming regime. Have followed close to the 3km NAM and MET
guidance...but even had to lower this in spots to slow the
temperature rise during the morning given southeasterly flow
which should favor persistent damming through the day.

PTYPE: Given the preferences above...expect precipitation to
begin as snow everywhere...but quickly transition to sleet and
freezing rain away from the coast over southern NH with a
transition to plain rain along the coast. Expect the transition
in PTYPE along the Maine coast to be more surface-layer
driven...with a change from snow to rain. Over the mountains and
foothills temperatures aloft may allow for sleet to mix in for
a time...but the back edge of the precipitation will probably
arrive before any significant icing.

QPF: Remain somewhat conservative given good agreement between
the HRRR/3km NAM and HREF in heavily favoring terrain
areas...with another max along the Midcoast focused along the
coastal front. QPF ranges from 0.25" in the downslope regime NW
of the Whites...to nearly 1 inch in the terrain and 0.75-1"
along the Maine coast.

Snow/Ice: Snow amounts have come down with this update...but we
remain around warning thresholds over the western Maine
mountains and foothills and will continue the warning. In these
areas 4-7" is likely...with 6-10" in the high terrain. 1-3"
appears likely over coastal Maine...with a coating to 2"
expected south of the Lakes region in NH. As for ice...do not
expect this to be a very significant ice maker with the greatest
accumulations likely over southwestern NH in areas of terrain
where 0.1-0.2" of ice is expected. At the valley bottom...little
to no ice is expected.

Headlines: No changes with this update. Do not have support to
add the coastal counties...and see no reason to transition any
of the advisory area to warnings.

Sunday Night: Secondary low south of Portland Sunday evening
will begin to strengthen rapidly as it lifts north and east
Sunday night...with pressure falls from around 990 mb 00Z Monday
to around 973-974 mb by daybreak. Precipitation shield will
exit rapidly during the evening with impressive cold advection
overspreading the region and taking T8s from above freezing over
much of the area Sunday evening to around -12C by daybreak.
Remaining precipitation will becoming increasingly confined to
upslope areas in the mountains and will take the form of snow as
temperatures fall through the column. Elsewhere...the story
will be developing winds as aforementioned cold advection
ensures deep mixing through the night. Isallobaric component
isn/t much help during the overnight...but with strengthening
llevel gradient...expect winds to increase after midnight with
gusts over 30mph likely by daybreak. More wind to come
Monday...see below.

Temperatures will fall through the night...but given that they
will be pretty mild in the evening Sunday...lows won/t be all
that cold...20s to around 30 from the mountains to the coast.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Ensemble and deterministic model solutions are in decent
agreement on the long wave pattern through late next week.
However...the block over the eastern Pacific and fast split flow
over the CONUS makes timing of individual shortwave impulses as
well as interaction/potential phasing between streams difficult.
The primary theme will be a mean trough over central and
eastern Canada and from the northern plains eastward across the
Great Lakes into the northeast CONUS. Below normal temperatures
can be expected with this pattern. Several shots of fresh arctic
air will spill into the forecast area over the next ten days
punctuated by brief warm ups with passing storm systems. In the
dailies...deep low pressure over the maritimes with cyclonic
flow producing lingering clouds and a few snow showers Monday
and Monday night along with strong westerly winds. High pressure
and arctic air builds east into the area for Tuesday through
Friday with temperatures averaging well below normal. The next
disturbance should arrive by next weekend preceded by moderating
temperatures and potential for yet another snow to mix
event...especially for coastal sections.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
Short Term...

Summary: High pressure will move east of the region allowing a
frontal system to arrive from the west early Sunday...with snow
and mixed precipitation as low pressure redevelops over the
Gulf of Maine and then moves into the Canadian maritimes Sunday
night and Monday. Behind this system...very strong westerly
winds will develop.

Restrictions:  VFR likely to persist all terminals through 9Z
Sunday. Beyond this...expect rapid deterioration to VLIFR/LIFR
in Snow...which will spread through all terminals from southwest
to northeast by 15Z Sunday. Precipitation will likely change to
rain PSM-PWM-RKD...with snow becoming a mix /including freezing
rain and sleet/ and possibly rain elsewhere during the day
Sunday. Conditions improve rapidly to VFR Sunday night as low
pressure and it/s associated precipitation pull east of the
area.

Winds: Light winds today go calm tonight before becoming east
and southeasterly around 10kts for the day on Sunday. Winds
along the ME coast /PWM-RKD/ will strengthen to 15G25kts with
gusts over 30KTS possible Sunday afternoon and evening. Winds
shift westerly Sunday night and increase to 15G25KTS by daybreak
Monday with much stronger winds expected into the day /see long
term discussion/.

LLWS: Southeasterly winds aloft strengthen on Sunday...with a
low level inversion suggesting the potential for LLWS by late
morning and through the afternoon. Best chance of LLWS before
18Z Sunday will be over southern NH...but values at this range
are too marginal to include in the TAF package. A better signal
exists in the 18Z-00Z timeframe and we/ll continue to assess in
future forecasts.

Long Term...

Mon - Mon Night...Sct MVFR -shsn.
                  Westerly sfc wind gusts to 45 kt.

Tue...NW sfc wind gusts to 30 kt.

&&

.MARINE...
Short Term...

After light winds tonight...southeasterly winds strengthen ahead
of a warm front...with gales likely by Sunday afternoon as low
pressure takes shape over southern New England...and tracks
northeast across the Gulf of Maine and into eastern Maine Sunday
night. A few gusts to near storm force are possible Sunday
afternoon in zone ANZ150 /Matinicus/...but the longer lasting
and greater wind threat will come on Monday.

Long Term...

Mon - Mon Night...Storms likely...especially outside the bays.

Tue - Wed...Gales likely.

Thu...SCAs likely.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Winter Weather Advisory from 3 AM to 7 PM EST Sunday for
     MEZ018>020.
     High Wind Watch from late Sunday night through Monday evening
     for MEZ007>009-012>014-018>028.
     Winter Storm Warning from 7 AM Sunday to midnight EST Sunday
     night for MEZ007>009-012>014.
     Winter Weather Advisory from 7 AM Sunday to midnight EST
     Sunday night for MEZ021-022.
NH...Winter Weather Advisory from 3 AM to 7 PM EST Sunday for
     NHZ005>013-015.
     High Wind Watch from late Sunday night through Monday evening
     for NHZ001>015.
     Winter Storm Warning from 7 AM Sunday to midnight EST Sunday
     night for NHZ004.
     Winter Weather Advisory from 3 AM Sunday to midnight EST
     Sunday night for NHZ001>003.
MARINE...Storm Watch from Monday morning through late Monday night for
     ANZ150>154.

&&

$$

NEAR TERM...Hanes
SHORT TERM...Arnott
LONG TERM...Schwibs

NWS GYX Office Area Forecast Discussion