Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 170009
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
809 PM EDT Mon Apr 16 2018

.SYNOPSIS...
Our wintry mix of precipitation will gradually transition to
rain across all but the far northern areas by this evening.
Strong gusty winds will continue into tonight as well,
especially on the coast. A broad area of weakening low pressure
will persist over the region Tuesday and will shift east on
Wednesday. Another area of low pressure will approach from the
west Wednesday night and will move east through the region on
Thursday. This could bring a round of rain or snow. Low pressure
will shift east into the maritimes Friday, followed by high
pressure building in for the weekend.

&&

.NEAR TERM /TONIGHT/...
8PM UPDATE...
Temperatures across the coastal plain of Maine have warmed to
freezing or above, so believe the freezing rain threat has ended
there and have let the advisory expire. Further north, the
threat remains as temperatures are still below freezing with
more substantial rain moving in. Expect temperatures here to
warm as well as heavier rain begins, though only to near
freezing until the low moves across tonight. Meanwhile, the band
of heavy rain moving through southwest Maine and northern New
Hampshire at this time has yielded storm total rainfall amounts
of 2.5 inches or so, and thus will need to watch the rivers for
potential flooding as this drains away. Until then, some
nuisance flooding of poor drainage areas could occur.

5PM UPDATE...
Have updated the forecast primarily to extend the Winter
Weather Advisory for Androscoggin, Kennebec, and Waldo Counties
as temperatures there remain near freezing or below, suggesting
icing is still occuring in spots. We are seeing the temperature
gradually warm closer to the coast as onshore flow increases in
response to the approaching surface low. To the north of the
surface low track, expect temperatures to hold near freezing
until the broader trough axis crosses the area overnight, at
which point the temperature will finally warm.

ORIGINAL DISCUSSION...
A very late season winter storm continues across the forecast
area. Temps are slowly continuing their climb thru the 30s...but
large areas of the interior remain at or below freezing.
Additionally very cold lower levels of the atmosphere are
allowing for continued snow grains and sleet...despite some
surface temps above freezing. I have left remaining winter wx
advisories in place...and extended the mtns and foothills until
8 PM. Untreated roads and elevated surfaces will remain icy into
this evening.

As temps rise above freezing precip will turn to heavy rain...as
the cold front sweeps NEwd tonight. Strong ESE LLJ will lift up
over the cold dome...producing strong isentropic lift across the
region. While there is some instability trying to work N...the
main surface front remains stuck across Srn New England and so
it will be a struggle to maintain that Nwd. A rumble or two of
thunder would not surprise me...but it probably is not worth
adding to an already complicated forecast. Precip rates will be
moderate to heavy at times...for about a 6 hour period and then
things taper off behind the front. Additional QPF around 1.5 to
1.75 inches is possible. At this time I am not too worried
about widespread flooding...but localized poor drainage flooding
is possible. Downsloping winds and colder temps will also
produce lighter rain and not much melting of snow in the
headwaters. As a result the forecasts for mainstem rivers is
generally action stage but not flooding.

Wind advisories remain in effect as well. Observations are a
little sparse...but what mesonet and spotter reports we have
received show that winds have been gusting in the 40 to 50 mph
range from EEN all the way N thru Pittsburg. That advisory will
remain in effect for downslope winds thru 8 PM...when LLJ moving
Ewd will weaken flow over the mtns. Along the coast of Wrn
ME...the LLJ sweeping N will continue to strengthen over the
next couple of hours. There is some uncertainty above how far
inland those stronger gusts will make it...but near the coast
will certainly see some 40 to 50 mph gusts. After midnight winds
along the coast will weaken as the core of the LLJ moves into
Downeast ME.

Finally astronomical tides will be high tonight...see the
coastal flooding section below for more information.

&&

.SHORT TERM /TUESDAY AND TUESDAY NIGHT/...
Large upper low gradually pinwheels across the region Tue.
Plenty of clouds and showers will linger as a result. With
gradual cooling aloft...mtns should see snow showers...while
rain showers persistent in the valleys and S of the high
terrain. Clouds will be slow to clear Tue night and so overnight
lows are on the mild side.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Pattern changes at 500 MB across North America and surrounding
areas, show a trend toward a less amplified flow later in the
period, which should allow temps to eventually moderate to
around normal, but not before a series of closing troughs moves
through late in the week, which will keep things unsettled.

Wednesday will see 500 mb closed low situated over the area
move east toward the maritimes. Will see a lot of clouds, and
likely some SHRASN, mainly in the mountains. Highs will mostly
be in the 40s, with some warmer spots on the coast and in srn NH
topping out around 50.

After that, confidence in the details of the forecast drops off
as two 500 MB waves move S_SE out of Canada, and interact Thu-
Fri, perhaps closing off into one low. Should see some precip in
this timeframe, probably centered around late Thu or Thu night,
but not convinced that the models are handling this interaction
well. I`d lean toward rain, or possibly non- accumulating snow,
outside the mountains, with snow in the mountains, although any
accums look to be at higher elevations. Highs will once again
be mostly mostly in the 40s, but mid to upper 30s in the
mountains.

Friday, may see some lingering showers associated with the
upper level low, but some downsloping should help temps warm a
bit outside the mtns. At this point the weekend looks dry as
sfc ridging holds beneath NW flow aloft. It`ll be a gradual
warming trend and temps could reach close to normal by Sunday,
but temps over the weekend will run in the mid to upper 40s N,
to the mid to upper 50s south.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
Short Term...Areas of IFR and LLWS will continue thru the early
evening as the heaviest precip moves NEwd across the forecast
area. Behind the cold front LLWS will diminish as winds shift to
SWly and weaken aloft. There are some indications that IFR CIGs
may linger...and that fog may develop underneath the upper low
pressure. I was not confident enough on fog to include in the
TAFs at this time however...but did keep CIGs on the low side.
Gradually moisture mixes out and CIGs lift to MVFR by Tue.

Long Term...Variable MVFR/VFR conditions expected on Wednesday,
with VFR Wed night. Flight restrictions possible in RA or SN
late Thu into Thu night. VFR Fri and Sat.

&&

.MARINE...
Short Term...Gale warnings remain in effect into the evening.
Behind the cold front winds will shift off shore and
diminish...though SCAs are likely needed especially outside of
the bays. Winds and seas gradually diminish thru Tue.

Long Term...There is a possibility of SCA late Thu and Thu night
as low passes to our southeast.

&&

.HYDROLOGY...
Heaviest precipitation is moving into the area now...with around
a 6 hour period of moderate to heavy precip expected. From here
on out around 1.5 to 1.75 inches of QPF is expected. This will
lead to rises on the majority of rivers...but only a handful are
forecast to go into action stage to go over flood stage. With
temps remaining mainly in the 30s over the headwaters...not much
snow melt is expected either. Will mainly be watching flashier
rivers...and localized poor drainage type flooding.

&&

.TIDES/COASTAL FLOODING...
High tide is forecast for 10.6 feet just after midnight tonight
at Portland Harbor. Strong Ely flow will help to build a storm
surge around 1.5 ft. This will put water levels right around
flood stage late this evening. Minor flooding is possible, but
beach erosion and splash over are likely. A coastal flood
advisory is in effect for all of the coast.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Wind Advisory until 2 AM EDT Tuesday for MEZ023>028.
     Coastal Flood Advisory until 2 AM EDT Tuesday for MEZ023>028.
     Winter Weather Advisory until midnight EDT tonight for
     MEZ007>009-012>014.
NH...Coastal Flood Advisory until 2 AM EDT Tuesday for NHZ014.
     Winter Weather Advisory until midnight EDT tonight for NHZ004.
MARINE...Gale Warning until midnight EDT tonight for ANZ150>154.

&&

$$

NEAR TERM UPDATE...Kimble
SHORT TERM...Legro
LONG TERM...Cempa



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