Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 141354

Area Forecast Discussion
National Weather Service Gray ME
954 AM EDT Tue Aug 14 2018

A broad area of low pressure across the mid Atlantic region
will maintain an onshore flow across the region through
today. Much of the area will see clouds and a few showers along
with isolated thunderstorms. The moist flow will also produce
some areas of fog...especially near the coast. We`ll see some
improvement after a cold front crosses the area Wednesday. High
pressure builds over the region with fair and warm weather
Thursday. Another trough will approach from the west and bring
more unsettled weather toward the end of the week.


At 945 am a line of convective showers extended from PWM-IZG-HIE
moving slowly north. HRRR handling this line and its movement
well into the afternoon with a break in any pcpn south of that
axis over southern areas for next several hours. Adjusted POPs
to reflect the line of heavy showers moving north, and lack of
any pcpn south, on the HRRR/Radar/Sat imagery for forecast next
several hours. Areas of fog still lingering over some coastal
plain areas. Tweaked temps based on latest obs.

619 AM...minor ESTF update to reflect the current mesonet in
near term grids.

Prev disc...
At 06z...a weakening 1017 millibar ridge extending from northern
Maine across Nova Scotia with a broad weak area of low pressure
across the mid Atlantic region. The moist onshore flow continues
between these two features and is reflected by widespread clouds
along with areas of drizzle and fog. The upper low was situated
over eastern Pennsylvania on GOES water vapor imagery. a weak
impulse pivoting northward around this upper low was producing
scattered downpours across the region at moment. For today...the
upper low will wobble northward into eastern New York State by
early evening. Precipitable water values from the 00z raobs show
a plume of values at or above 1.75 inches across much of the
area. With approach of the upper low I`d expect convection to
increase in coverage over much of the western two- thirds of New
Hampshire northward to the international border area this
afternoon and evening. Showers and scattered thunderstorms with
tropical downpours and the potential for localized ponding of
water and drainage flooding. However...the best forcing and QPF
should remain to out west today in close proximity to the upper
low center.


The upper low will open up and become more progressive tonight
as it crosses the area. We`ll see scattered showers and
thunderstorms as the associated weak surface system crosses the
area along with areas of fog and drizzle near the coast. By
dawn...this system is sliding offshore. In its wake...broken
clouds followed by another round of showers and thunderstorms
across the higher terrain as another impulse and associated cold
front approach from Quebec. The forecast soundings suggest that
if we can see sufficient heating...CAPES of 1500 j/kg could
spawn scattered strong storms with wind the primary concern as
the activity crosses mountain sections during the mid and late
afternoon hours.


The cold front will be slipping slowly southward across the area
Wednesday night as it weakens and then stalls south of the region by
Thursday morning. Any showers or thunderstorms with the front
primarily over the mountains early Wednesday evening will dissipate
as front progresses southward.

A ridge of high pressure will build into the area Thursday leading
to sunshine and lower humidity across the area. The remnants of
the stalled front may lead to a bit more cloudiness across
southern New Hampshire and can`t rule out an afternoon shower or
thunderstorm for that area, although chances will be minimal.

Clouds will be on the increase across New Hampshire Thursday night
as the next weather system approaches from the west, but expecting
all areas to remain dry.  Models differ a bit on exact track of the
low pressure system crossing the area late Friday and Saturday with
the GFS farther south and faster than the European model.  This
leads to both timing differences in the associated precipitation and
differences in areal coverage for both Friday and Saturday.  For the
forecast, plan to bring the chance for showers into New Hampshire
during the morning hours Friday, and then chance to likely PoPs
across the region for showers and thunderstorms during Friday
afternoon. The greatest threat will be across the mountains.
Plan to continue the shower/possible thunderstorm threat into
Saturday as the upper trough swings through.

Both long-range models move the frontal boundary southeast of the
area for Sunday, although southern areas may still see some clouds
and a very minimal chance of a shower as weak disturbances move
along the frontal boundary well offshore.

A weak ridge of high pressure builds across the region for Monday
and Tuesday with minimal chances for any precipitation.


Short Term /through Wednesday/...IFR initially. We`ll see some
improvement to VFR at inland terminals by afternoon, but the
coastal plain will likely be stuck in IFR to MVFR at best for
today and tonight. Areas of MVFR on Wed in shra/tsra.

Long Term...MVFR to IFR conditions possible Wednesday evening in
scattered showers and thunderstorms improving to VFR Thursday.
MVFR to IFR conditions develop again Friday through Saturday in
showers, thunderstorms, and fog. VFR conditions expected Sunday.


Short Term /through Wednesday/...Winds and seas expected to
remain below SCA in persistent but light onshore flow.

Long Term...Winds and seas expected to be below SCA criteria.





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