Area Forecast Discussion
Issued by NWS Portland, ME-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KGYX 201040
Area Forecast Discussion
National Weather Service Gray ME
640 AM EDT SAT AUG 20 2016
High pressure will shift offshore this morning then remain anchored
off the coast through early Sunday. A cold front will approach
from the west late Sunday and slowly cross the region Sunday night
and early Monday. High pressure and drier air follows the front
late Monday through Thursday.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --638 AM...minor ESTF update to reflect current satellite trends and
to ingest the 10z mesonet into near term grids.
At 06z...a 1018 millibar surface ridge was draped across the
forecast area. A 1005 millibar low was over northern Quebec
province with a weak and diffuse warm/stationary front extending
southward through the eastern Great Lakes and mid Atlantic region
and a trailing cold front through the western Great Lakes. GOES
infrared imagery showed mainly clear skies across the forecast
area under the cresting surface ridge. However, the light winds
and clear skies were allowing patchy stratus and fog to develop
across our area most notably over interior valleys. For today, any
early morning stratus and fog will burn off quickly with a mainly
sunny start as the surface ridge retreats offshore. By afternoon,
a few clouds associated with the weak surface boundary should
spread northward into mainly southern and western New Hampshire
with a low chance for a late day shower/isolated thundershower
there. Highs today will be within a few degrees either side of
80F , with the exception of the immediate mid coast of Maine
which will be a few degrees cooler in developing onshore flow.
-- End Changed Discussion --
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
Little change tonight with the surface ridge parked offshore and
the weak surface boundary remaining to our south and west. There
will continue to be a few clouds across southern and western New
Hampshire along with the chance for an isolated shower. Otherwise, a
dry and partly cloudy night with more widespread stratus and fog
developing in the onshore flow. Lows tonight will range from the
mid 50s to the lower 60s. On Sunday, low clouds and fog should
gradually lift with partly sunny skies for much of our Maine zones
while we`ll see more clouds over New Hampshire ahead of the approaching
cold/occluded front. We`ll see an increasing chance for showers
and a few thunderstorms as we head through the day...with areas
vicinity of Penobscot Bay and the Kennebec valley staying dry for
the balance of the day. Sunday will be cooler then today given the
expected cloud cover and the persistent onshore flow. Highs
should range from the mid 70s to the lower 80s.
.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
All models remain in good agreement with the timing and evolution
of approaching surface cold front. As upper trough approaches New
England Sunday evening, surface cold front advects into eastern
New York. Ahead of the front, high precipitable water values will
surge northward from the mid Atlantic Region. Showers will cross
Maine and New Hampshire during the night. The atmosphere only
becomes modestly unstable with surface based CAPE values briefly
in the 200-300 J/KG range, bringing a minimal risk of
thunderstorms. Nevertheless, a brief period of locally heavy
rainfall remains a possibility through the daybreak hours on
Thereafter, cooler and drier air begins to filter into northern
New England as high pressure builds east from the Ohio River
Valley. There will still be a chance for a shower during the day
however as the upper level trough finally crosses our forecast
area by mid/late afternoon.
There will be a chill in the air by Tuesday morning as readings
fall into the mid 40s to lower 50s. Thereafter, dry and cool
conditions continue on Wednesday with patchy fog during the
overnight hours over the inland valleys.
A southwest flow (both at the surface and aloft) will advect
warmer temperatures into the region by late in the week as high
pressure slips off the Eastern Seaboard.
The next chance for precipitation will be Friday as a weakening
cold front passes through New England.
.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
Short Term /through Sunday/...Some IFR/LIFR conditions in areas
of valley stratus and fog through 13z...otw vfr today. Areas of
ifr/lifr developing tonight aft 04z Sunday in stratus, fog and
isolated -shra. Bcmg vfr aft 14z Sunday...with areas of mvfr
developing by afternoon over the Connecticut valley in
-shra/-tsra and gradually spreading eastward.
Long Term...VFR looks to prevail for much of the extended outside
of passing front Sun night. Along the front, SHRA/TSRA may create
local IFR or LIFR conditions. If coastal fog/stratus were to
develop...more widespread IFR conditions could occur from PSM thru
PWM...AUG...and RKD. By midweek high pres will bring VFR during
the day...but valley fog will be possible with LIFR conditions for
LEB and HIE especially.
Short Term /through Sunday/...quiet on the waters as a surface
ridge traverses the waters through tonight. On Sunday...increasing
southeast flow may brings winds and seas close to small craft
threshold outside the bays by evening.
Long Term...Ahead of approaching cold front late Sun seas may
build to near 5 ft on the outer waters. Will have to watch for
areas of coastal fog developing as a warm and moist air mass
briefly tries to work back into the area ahead of the front.