River Flood Warning 12, NWS Gray, ME

Area Forecast Discussion
National Weather Service Gray ME
810 PM EDT Sun Apr 16 2017

.SYNOPSIS...
A cold front will cross the region tonight and a trough of low
pressure will linger over the area on Monday. High pressure will
build south from Canada Monday night and Tuesday and will shift
east Tuesday night. Low pressure will weaken as it moves through
southern Quebec on Wednesday and a trailing cold front will
stall over the region Wednesday night. The front will lift north
on Thursday ahead of low pressure moving east from the Great
Lakes. Low pressure will slowly track east through the region
Friday through Saturday.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
805 pm...a line of showers now about to exit to the east
within the hour. Update based on latest POPS from radar. Used
HRRR for extrapolation for rest of the evening. Input latest obs
data to reflect current temps and trends for next few hours. No
other changes attm.

535 pm Update: Based on latest radar based pops have made
adjustments to timing of the line of showers/isold thunderstorms
to move across fa. Made adjustments to grids for the rest of the
afternoon into early evening for temps/dewpoints and RH based on
input obs data. See Marine discussion section below for
adjustments to SCA headlines for tonight.

Previous Discussion:
Cold front approaching from the west will sweep through the
region early this evening bringing an end to summer-like
weather. Line of convection getting organized at the eastern end
of Lake Ontario and will be heading east through late afternoon.
HRRR has a pretty good handle on this line and brings it into
the Connecticut Valley around 500 pm. Expect this line to
diminish as it continues east into eastern New Hampshire and
western Maine early this evening. SPC not looking for anything
severe in the CWA but damaging winds not out of the question in
isolated strong cells and the situation will be monitored
closely through the early evening. Behind the front expect
clearing downwind of the mountains overnight. Clouds and
occasional showers will persist overnight in the north. Lows
will bottom out in the 40s north and 50s south.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
A trough of low pressure will linger over the region on Monday
keeping clouds and occasional showers going in the mountains.
Farther south...a mix of sun and clouds will prevail in a
blustery northwest flow. Highs will range from the mid 40s to
mid 50s north and will range through the 60s south.

Clouds and rain or snow showers will persist in the mountains
Monday night and the remainder of the region will see variable
clouds as an upper trough swings through northern New England.
Lows will range from the mid 20s to mid 30s north and mid to
upper 30s south.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
High Impact Weather Potential:  Low potential for some wet snow
accumulations in the Wednesday night through Thursday night period
in the mountains.  However...confidence is low.

Pattern: A look at the flow pattern across North America early this
afternoon reveals a large scale southwest to northeast
orientation...due to large scale ridging over the southeastern
United States...with unorganized troughing off the west coast of
North America.  This is helping fuel today/s warmth...with little
blocking allowing fast moving systems to race across the country.  A
bit of a change is in the works through this long term forecast
period as the combination of cutoff low development over the western
Atlantic combines with developing ridging along the US West coast to
cause the flow to reorient to more of a WNW/ESE direction...pushing
more significant warmth to our south and eventually...towards /and
beyond/ the very end of this forecast period...slowing the pattern
down a bit.  With the jet aloft cutting across the CONUS for much of
the week...expect a series of impulses to maintain unsettled
conditions after initial high pressure on Tuesday pushes east.
Another respite is possible as we reach next weekend...although /as
discussed below/ confidence is shaky at this point.

Model trends/confidence: Spread in the deterministic/ensemble
guidance occurs rather quickly this coming week...which is not
surprising with a spring-like pattern featuring a number of cutoffs
which frequently cause predictability issues.  GEFS RMOP graphics
agree and paint a similar story to a comparison of deterministic
runs...showing good guidance agreement through Wednesday...with
rather large differences between guidance sources beyond
this...through the end of the forecast period on Sunday. Confidence
is thus high through the arrival of shortwave number one on
Wednesday...with confidence falling below average beyond this
/although unsettled late week conditions are generally agreed upon/
with confidence falling further for next weekend.

The Details....

Tuesday:  High pressure settles in over Atlantic Canada well north
and east of New England.  This feature should continue to build
south over our area during the day...but there has been a weak
signal for days that a lingering inverted trough Monday night will
leave some residual llevel moisture that may combined with the
easterly flow associated with the high to produce low clouds and
even a chance of drizzle all trapped beneath strengthening
subsidence inversion.  There has been a trend to a more
northeasterly /vs southeasterly/ flow at the surface over the past 2
days which would provide less support to maintaining the low level
moisture.  Will keep PoPs out of the forecast and begin the day with
low clouds that will break up with time as the deeper moisture thins
and is pushed west.  With an onshore component to the wind...do
expect a rather cool day with mid 40s to lower 50s /east to west/
being about all we can do.

Wednesday-Wednesday Night: We have seen increasing agreement that
next arriving low pressure system will be in a weakening phase as it
hits amplifying downstream ridge...with warm advection precipitation
arriving Wednesday afternoon. Trends have favored this system being
weaker...with a less impressive moisture plume.  This all suggests a
fairly unimpressive precip-maker.  Given the time of arrival...will
probably see all rain although temperatures will be marginal in the
mountains.  No doubt a chilly day with highs stuck in the 40s over
most spots...with some lower 50s over southern NH and near the CT
valley. Expect showers to continue into Wednesday night...with some
snow potentially mixing in over the mountains...but no significant
impacts expected.

Thursday-Friday: A bit of a lull arrives Thursday as weakening
shortwave continues to head east of the region.  Cold front will
stall south of the region...but remain a bit too close for comfort
to keep the forecast dry with a few rain showers possible and
another day of cool temperatures likely. Run to run and model to
model inconsistencies loom large for the next arriving shortwave for
Thursday night and Friday. The GFS/GGEM are much more amplified with
the wave...but lack support from many GEFS members.  The ECMWF is
much less amplified...with a secondary wave that becomes dominant
with time. These differences are important as the EC and many EC-EPS
members take surface low pressure south of New England...allowing
cool air associated with Canadian high pressure north of the region
to filter south...bringing ptype questions into play.  What is
likely is another precipitation event.  As for ptype...given poor
confidence...will paint a chance for rain/snow in the mountains on
Friday...with this mix potentially reaching further south
particularly Thursday night.  Again...high temperatures will remain
cool...at least 10F below seasonal norms.

Saturday-Sunday:  There is weak agreement that low pressure will
push east of the region for next weekend...with the level of drying
and cooling behind this system in question.  The overall pattern re-
orientation certainly favors highs below climatology on Saturday...
with less reason to depart from climatology for Sunday.
Precipitation chances likely higher in the mountains /again giving a
nod to climatology/ but no higher than slight or low chance given
the drying trend portrayed in both the deterministic and ensemble
suites.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
Short Term...MVFR/IFR ceilings in the mountains tonight with
MVFR ceilings Monday through Monday night. VFR south Tonight
through Monday night.

Long Term...Threat for MVFR stratus Tuesday morning with
improvement during the day continuing through Wednesday morning.
Arriving low pressure on Wednesday and Wednesday night will
bring a period of MVFR/IFR in SHRA with lingering
clouds...showers...and possibly drizzle and fog continuing
restrictions through Thursday. Another low pressure system will
likely maintain poor flying conditions to end the week Friday.

&&

.MARINE...
Short Term...Continuing SCA's through tonight over the outer
waters and allowing the SCA to expire at 8 pm in the bays. Gusty
west to southwest winds will subside in the bays this evening
but continue for a while over the outer waters...also seas will
remain near 5 ft over the outer waters through much of the
night so continued the SCA for those areas.

Long Term...Headline free conditions are generally expected
Tuesday-Tuesday night. Southeasterly winds ahead of low pressure
on Wednesday will likely bring a period of SCAs through early
Thursday. Uncertainty beyond this precludes much detail...but
SCAs are again possible to end the week Friday.

&&

.FIRE WEATHER...
Relative humidities will drop to between 30 and 35 percent
across portions of southern New Hampshire and southwest Maine
Monday afternoon. Although most areas will see some rain
overnight...winds will be strong and gusty on Monday and with
the low RH burning should be discouraged.

&&

.HYDROLOGY...
RFC still forecasting minor flooding on some area
rivers...mainly due to snow melt and the situation will be
closely watched overnight and Monday.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...Small Craft Advisory until 8 AM EDT Monday for ANZ150-152.
     Small Craft Advisory until 2 AM EDT Monday for ANZ154.

&&

NEAR TERM...Marine

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Special Weather Statement
National Weather Service Gray ME
646 PM EDT SUN APR 16 2017

MEZ007>009-012>014-018-019-NHZ002>006-008>010-012-013-015-162330-
Northern Oxford-Southern Oxford-Interior York-Interior
Cumberland-Southern Franklin-Southern Somerset-Northern
Franklin-Central Somerset-Strafford-Southern Coos-Northern
Carroll-Merrimack-Northern Grafton-Belknap-Western And Central
Hillsborough-Southern Carroll-Interior Rockingham-Eastern
Hillsborough-Southern Grafton-
646 PM EDT SUN APR 16 2017

...A LINE OF SHOWERS WILL AFFECT OXFORD...CENTRAL SOMERSET...
FRANKLIN...NORTHWESTERN YORK...NORTHWESTERN CUMBERLAND...WESTERN
ROCKINGHAM...SOUTHEASTERN COOS...WESTERN STRAFFORD...SOUTHEASTERN
GRAFTON...CENTRAL HILLSBOROUGH...BELKNAP...MERRIMACK AND CARROLL
COUNTIES...

At 645 PM EDT, radar indicated showers were located along a line
extending from near Eustis to Bennington. Movement was southeast at
45 mph.

Wind gusts up to 50 mph are possible with these showers.

Locations impacted include...
Manchester, Nashua, Concord, Derry, Rochester, Laconia, Conway,
Franklin, Farmington, Bridgton, Henniker, Fryeburg, Bethel, Eustis,
Merrimack, Moultonborough, Ossipee, Northwood, Rangeley and Naples.

To report severe weather, contact your nearest law enforcement
agency. They can relay your report to the National Weather Service
office in Gray Maine.

LAT...LON 4300 7203 4533 7058 4556 6974 4554 6977
      4553 6978 4532 6970 4273 7136
TIME...MOT...LOC 2245Z 297DEG 38KT 4524 7055 4304 7192

Marine