Area Forecast Discussion
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FXUS61 KGYX 202058
Area Forecast Discussion
National Weather Service Gray ME
458 PM EDT Thu Oct 20 2016
A slow moving frontal boundary and a developing low pressure
center will bring wet weather and cool onshore flow to the region
through Friday night. On Saturday...the low will gradually lift
north into Quebec. On the backside of this low...colder air will
arrive on brisk northwest winds for the latter part of the weekend
and early next week.
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Update...Have mainly adjusted PoP based on latest observations and
radar trends. Recent HRRR runs seem to have a fair handle on
precip trends tonight...and so I leaned the forecast in this
direction. That would mostly have rnfl coming in waves
tonight...with the first batch moving thru at this hour. The next
wave comes in from the S around midnight as onshore...Sly flow
increases...followed by the heaviest round Fri. The mtns should
see fairly continuous PoP until Fri morning...when warm front
lifts into Canada.
Previous discussion...At 18z...a 1027 millibar high was centered
near the Bay of Fundy. A cold front extended from western Quebec
southward through the eastern Great Lakes. A second boundary
extended from the mid Atlantic southward through the Mississippi
valley with a series of weak waves riding along it. For
tonight...the surface high will quickly exit into the maritimes.
Warm air advection clouds and light precipitation was entering the
forecast area from the west. Expect amounts will be light tonight
with strengthening onshore flow contributing some drizzle and fog
by later tonight. Rather uniform lows with onshore flow and cloud
cover with readings in the upper 40s to lower 50s.
.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
On Friday...digging shortwave energy with the upper trough going
negative tilt before closing off over the mid Atlantic states by
Saturday morning. At the surface...slow-moving cold front with strengthening
inflow off the Atlantic and a developing surface low tapping subtropical
moisture. Rain will increase in coverage and intensity as we head
through the day Friday with heaviest occurring late Friday into
Friday night. Highs Friday should be mainly in the lower and mid
60s. Steadier rain should taper to showers by Saturday morning as
the surface low meanders overhead. Lows Friday night will be in
the upper 40s and lower 50s.
.LONG TERM /SATURDAY THROUGH THURSDAY/...
Upcoming hazards: Potential for winds gusting into Wind Advisory
thresholds over the weekend. Locally heavy rainfall is possible.
12Z model suite gradually coming into somewhat of a consensus for
the track and evolution of upcoming strengthening storm. This
complex system will involve a hybrid tropical system in some
capacity, however the transfer and evolution of moisture into the
developing Nor`easter is still not totally clear. In any case,
models in good agreement that surface low pressure will begin to
undergo cyclogenesis off the Mid Atlantic coastline tomorrow
before heading northeast. Surface pressures continue to fall
Friday night as a negatively tilted, dynamic upper level trough
digs into the region. The question of the day is how far south can
the upper level low form and how progressive is this feature? This
will affect the outcome for rainfall totals across the region.
QPF: As of now it appears northern areas will be situated in the
best dynamics and for the longest period of time, thereby picking
up the most precipitation. Up to 2.5 inches of rainfall is
expected in the mountains with less to the south as surface low
develops overhead, shutting off the precipitation early with a dry
slot forming. There is an outlier with the Canadian model which
appears to bring a stripe of heavy rainfall to southern areas,
bringing up to 4 inches of rainfall to the Portland area. First
scenario appears more likely with heavy rainfall in the mountains.
Some of this moisture may be enhanced by the terrain with locally
higher amounts. Antecedent conditions are dry so flooding is not
expected at this time.
Very strong wind fields develop, possibly as early as late
Saturday over New Hampshire depending on the exact forecast track.
The strong wind gusts may be mainly diurnally driven and will
likely spread into Maine by Sunday morning. Winds may gust as high
as 45+ mph, leading to the possibility of some power outages. This
may be delayed until Sunday as this is dependent of the passage of
the upper level low in a strong tilted surface to upper level
area of low pressure.
A short wave will move through the fast flow on Sunday night
bringing more scattered showers to the region. Snow showers may
begin to develop in the mountains as boundary layer temperatures
begin to cool. Thereafter, gusty westerly winds and wet bulbing
effects will allow for areas of rain and snow showers in the
mountains with light accumulations of snow possible early next
.AVIATION /21Z THURSDAY THROUGH TUESDAY/...
Short Term /through Friday night/...VFR deteriorates to IFR and
LIFR tonight in rain...drizzle...and fog. We`ll likely see an
extended period of instrument flight rules as slow-moving low
pressure and an associated frontal system traverse the area.
IFR to LIFR conditions expected into early Saturday with the
expected rain. A cold front pushes east through the area Saturday,
allowing for partial clearing conditions to VFR over southern
areas while in the mountains and foothills MVFR conditions in
scattered showers will persist through much of the weekend and
into early next week.
Short Term /through Friday night/...Increasing and persistent
onshore flow will bring small craft conditions to the open waters
and marginal small crafts to the bays tonight through Friday
A strengthening area of low pressure moves through central New
England on Saturday with a trailing cold front in its wake. This
will set the state for a strong west to northwesterly flow behind
it which may gust into gales at times through the rest of the
The Friday 4 pm astronomical tide in Portland will be 10.6 feet.
A southeasterly flow ahead of the system may allow for building
storm tides during the day. This will be monitored as we move
through the workweek for possible advisory headlines for some
MARINE...Small Craft Advisory from 11 PM this evening to 8 AM EDT
Saturday for ANZ150>154.