Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 201350

Area Forecast Discussion
National Weather Service Gray ME
950 AM EDT Thu Oct 20 2016

High pressure will exit into the Maritimes today as low pressure
developing over the Ohio Valley tracks northeast towards New
England by Friday. This system will intensify as it reaches the
southern New England coastline Friday night. A cold front pushes
through from the west on Saturday as the storm further strengthens
and moves through central New England. Cooler weather will arrive
on brisk northwest winds for the latter part of the weekend and
early next week.



950 13z...1027 millibar high was draped along the coastal
plain of eastern New England. The surface high will retreat
offshore by afternoon with clouds gradually increasing ahead of
the next disturbance over the Ohio valley and eastern Great Lakes.
NWS Doppler radar mosaic showed an area of showers and embedded
thunderstorms racing northeast towards western New England. This
activity and developing onshore flow will bring increasing pops as
we head into the afternoon and evening hours. Minor adjustments
were made to the near term grids to reflect the current mesonet as
well as satellite trends. Given the east to northeast flow off the
waters...I`m monitoring the afternoon high tide for any potential
splashover issues.

Prev disc...
645 am update...
High pressure overhead has begun shifting east this morning ahead
of an advancing cold front. VAD wind profile shows 25-30 kts at
1 kft. Temperatures and sky cover were the main elements adjusted
for this update.

Previous discussion...
Cirrus was spilling over into northern New England this morning
with near zonal flow and the jet stream in the area. At the
surface high pressure was centered over the New Hampshire and
Maine borders providing for calm to light winds and mostly clear
skies. Radiational cooling has helped temperatures drop into the
30s and 40s but likely won`t drop much more with dew points also
in a similar range. Valley fog was noted especially near the
Connecticut River Valley.

This airmass will support highs in the mid 50s to lower 60s
today. High pressure shifts offshore by midday allowing low
pressure to approach from the SW.


Rain will begin tonight in the west and spread to include all of
NH and western Maine after midnight tonight. There are signals
for moderate to even heavy rainfall at times with PW values
surging ahead of the slow moving frontal system. Overnight lows
tonight will drop into the 40s and 50s due to additional cloud
cover and winds that will not entirely decouple. On Friday the
warm front attempts to lift into the region as an upper level
cyclone pivots into the northeast and begins to close off.
Depending on where the warm front stalls...we could see some lower
70s over southern NH and SW Maine. Elsewhere readings in the 60s
are more likely.


A digging progressive long wave upper trough approaches New
England Friday night and becomes negatively tilted allowing a
secondary area of surface low pressure to develop off the mid
atlantic coast and then move north along the New England coast.
Very high PWATs and strong upward vertical motion will allow the
rain to be heavy at times Friday night into early Saturday. Models
generally give total QPF in the amounts of 1.5-2.5 inches with
some locally higher amounts possible in the higher terrain. It now
appears fairly certain some of the tropical moisture from the
system off the southeast U.S. will become entrained into the
system being the cause for the heavier rainfall. The system
becomes a large closed low over northern New England Saturday as
it slowly moves northeast and reaches the Canadian maritimes
Saturday night. With the large cyclonic flow plenty of clouds and
scattered showers will persist into Saturday night with most
occurring in the mountains and foothills. Much cooler air moves
across the area Saturday night changing some of the showers in the
mountains and foothills over to snow showers with some light
accumulations over the higher terrain possible.

A cold cyclonic flow aloft and at the surface will continue Sunday
and into midweek with cool temps and mostly cloudy conditions.
The cyclonic flow will continue the scattered rain and snow
showers over the mountains and foothills through midweek. Stayed
close to superblend guidance for temps and pops.


Short Term...VFR conditions today through much of today as high
pressure moves off to the east. Valley fog will lift this morning
which has brought some favored fog spots down to LIFR conditions.
Clouds will be increasing from west to east today, eventually
bringing MVFR conditions and showers to northern and western areas
this evening. Have added some LLWS in the TAFs with latest VAD
wind profiles from KGYX indicating 30 kts below 2 kft.

Showers will spread to all areas by Friday with some +RA possible
at times. Drizzle and fog will be possible closer to the coast
Friday as well.

Long Term...IFR to LIFR conditions expected Friday night 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...An easterly flow develops today, shifting to
southeasterly tonight. Although winds may stay below advisory
levels, the onshore fetch will allow wave heights to build above 5
FT by tonight. A SCA has been issued beginning tonight through
Friday night.

Long Term...The prolonged southeast fetch Friday night will allow
seas to increase mainly over the outer waters. The system exits to
the northeast on Saturday with a trailing cold front in its wake
with a west to northwesterly flow behind it which will likely gust
above 30 KT at times through the rest of the weekend.


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.


MARINE...Small Craft Advisory from 11 PM this evening to 8 AM EDT
     Saturday for ANZ150>154.


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