Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 171516

Area Forecast Discussion
National Weather Service Gray ME
1116 AM EDT Thu Aug 17 2017

High pressure settles into New England today with dry
weather and seasonable temperatures. On Friday night...a warm
front associated with low pressure over the Great Lakes will
bring an area of rainfall to the Northeast. The best chances for
a significant rainfall look to be farther south. Saturday should
bring a break in precipitation until the cold front swings
through the region. High pressure will build back into the
region Sunday into early next week with warming temperatures.


1100 AM Update...
Quick update to adjust temp/td/sky grids. Mainly scattered to
broken high clouds across the area late this morning along with
a fair amount of smoke from forest fires in Canada. Looking for
mostly sunny skies this afternoon with increasing high clouds in
the west late today. No major changes to current forecast
planned attm.

Prev Disc...
High pressure will move over the region today. Northwesterly
flow will continue this morning as the strong upper low to our
northeast provides a pressure gradient through the region. This
will prevent any seabreeze from forming along the coast.
Additionally a few gusts to 20mph are again possible.
Temperatures will remain seasonable with highs near 80 south.


Tonight look for the high pressure to begin to shift eastwards
as the next system moves out of the Great Lakes. Skies should
remain mostly clear overnight through the eastern portion of the
area with clouds approaching in the west. Increasing humidity
as a warm front lifts north will keep low temperatures milder.

Friday morning rain will move in as low pressure pushes
eastward. This rain will spread from west to east across the
area during the day on Friday. With southerly flow coming up out
of the tropics and high precipitable water values, heavy rain is
possible within the convective showers


Low pressure lifting into Canada will continue to push a warm
front towards Nrn New England Fri night. Model guidance suggests
this front will have trouble lifting thru the forecast
will tend towards more of an occlusion with time. The best LLJ
forcing and rainfall potential looks to be Fri night...where Srn
zones near the warm front could see a welcomed precip event. The
NAM forcing is a little more intense and sharper...leading to a
shorter duration rainfall. The GFS forecast soundings are longer
duration 25 kt SSW LLJ that bring over a half inch to coastal
zones. The GFS forecast resembles the latest ECMWF as
I will continue the heaviest precip near the coast overnight.

After the occlusion it will be warmer Sat as the low level
stable air is cleaned out. The initially clear dry slot will
give way to afternoon clouds and scattered showers or storms
ahead of the s/wv trof axis. The timing of the trof appears to
be favoring Sat not all that favorable for a focused
line of convection. So for now I will keep chance to slight
chance PoP in the forecast for Sat. I cannot rule out rain...but
it also does not look like a widespread rain.

After the trof passage a flat ridge looks to build into the
area...though deep SW flow will be feeding into it. This should
allow some warmer temps to work back into the region with time
heading into midweek. The next trof will cross the area around
the Wed time frame.


Short Term...VFR will continue across the area through late
tonight with just a chance for morning valley fog in the
Connecticut River valley. Increasing clouds ahead of the
approaching system will eventually result in ceilings decreasing
and MVFR conditions moving in from West to east during Friday
afternoon. Friday night IFR in rain and fog is possible.

Long Term...Areas of IFR conditions possible Fri night into Sat
as warm front/occlusion lifts into the forecast area. Into Sat
morning LLJ forcing will bring a round of steadier precip to
coastal zones...and this is probably the best window for IFR or
lower conditions. Until the cold front sweeps thru the region
late Sat...SHRA and/or an isolated TSRA are possible though
generally VFR conditions will prevail. VFR conditions continue
into Mon.


Short Term...Long period swell from Hurricane Gert is starting
to arrive in midcoast maine. Swell of 7-8ft with period around
12-14 seconds will provide a powerful pull and may result in
increased rip current risk. A high surf advisory remains in
effect through tonight for the midcoast and a small craft for
hazardous seas for the adjacent ocean waters. In the bays
sheltering will prevent any large swell while the southern Maine
and New Hampshire coast are too east facing to be affected by
the more southerly swell. After the swell decreases tonight
expect a period of calm conditions on the waters before seas and
winds begin to build as the next low moves through Friday night.

Long Term...Winds and seas build in response to a LLJ lifting
across the waters with the warm front. Given the WAA over the
relatively cooler water...wind gusts look to be marginally
close to SCA thresholds. More likely seas build to 5 ft on the
outer waters for a time Sat. The next chance for SCA conditions
will be closer to midweek...ahead of the next cold front.


ME...High Surf Advisory until 8 PM EDT this evening for MEZ025>027.
MARINE...Small Craft Advisory for hazardous seas until 8 PM EDT this
     evening for ANZ150-152.


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