Scientific Forecaster Discussion
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Area forecast discussion...updated
National Weather Service Gray ME
722 am EDT Sat may 27 2017
weak high pressure will build over the area today and will
shift offshore on Sunday...allowing US a window of dry weather.
The next system over the eastern Great Lakes will lift north
into Quebec Sunday night and will drag a front toward the region
on Monday with rain showers. That front will slowly cross the
area late Monday night and Tuesday with unsettled weather.
Near term /until 6 PM this evening/...
update...minor changes based on latest observational trends.
Previous discussion...trapped low level moisture and weak flow
will lead to very slow clearing today. In reality it will be
more like gradual lifting of the clouds with some breaks of sun.
Mid level temps are still forecast to be on the chilly
side...especially across the ern half of the forecast area...so
readings in the low 60s are most likely there. Warming temps in
the west at least give US an outside shot as a 70 degree reading in
the CT valley.
Short term /6 PM this evening through 6 PM Sunday/...
the stale air mass lingers over the area tonight into sun...with
little change expected. High pressure will try and nose into the
forecast area from the north...but never really quite makes it to
clear things out. What it will do as we head into early sun is
make an east-west pressure gradient and develop some onshore flow.
Lingering low level moisture plus that light upslope
flow...possibly aided by a passing S/WV trof...could lead to
some patchy drizzle across srn New Hampshire. This should dry up and lift
as daytime heating commences sun. The exception would be the NE
forecast area...where stalled boundary and passing S/WV may
spark some showers. More well defined S/WV ridging moving in
from the west and subsidence sun will allow for less cloud cover
and warmer temps...with a good chance at some 70s inland.
Long term /Sunday night through Friday/...
the deterministic models remain in decent agreement on the longwave
pattern through late next week. We begin the period with a weak
shortwave ridge cresting over the forecast area. This ridge is
quickly kicked offshore by Monday morning in response to a deepening
upper trough over the Great Lakes. The upper trough axis will
gradually shift eastward into the northeast Continental U.S....where it will
remain for the balance of the new work week. Temperatures this
period should average below normal as troughing dominates across
New England. In the dailies...a weak ridge of high pressure will
retreat well offshore on Monday. Low pressure centered north of
the Great Lakes will push a slow-moving occluded front across the
region Monday and Tuesday with onshore flow and the advancing
baroclinic zone providing a damp start to the new work week.
Behind this frontal system...the unsettled weather will continue
as an upper trough remains across the northeast and a series of
weak cold fronts or surface troughs cross the area.
Aviation /11z Saturday through Wednesday/...
short term...areas of MVFR continue as low level moisture is
very slowly eroding in the wake of low pressure. There have been
some local IFR conditions at times...but I feel that today will
trend towards MVFR or VFR. Especially with some afternoon
heating...I think VFR cigs will be most widespread. Tonight
across srn New Hampshire we will have to watch for a period of IFR cigs in
onshore flow and dz. Model forecast soundings suggest a 1 to 2
kft moist layer and weak S/WV trof providing some lift.
Confidence is too low to include in the tafs for psm and mht at
this time. Conditions will improve to VFR at all terminals sun.
Mon - Tue...MVFR in shra with LCL IFR in fog and drizzle.
Wed...areas of MVFR in -shra.
short term...some leftover swell continues north of Port Clyde this
morning. Small Craft Advisory for hazardous seas will continue at least into the
morning before seas diminish. Otherwise weak high pressure will
be in control of the waters thru the weekend...and Small Craft Advisory
conditions are not expected.
Mon - Tue...conditions could approach small craft outside the
the astronomical high tide in Portland is 11.9 feet MLLW at
119 am Sunday. Winds are expected to be light and seas low...but
high water conditions may require a coastal flood statement.