Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Gray ME
559 am EDT Friday Aug 28 2015
high pressure centered over the northeastern United States will
bring seasonably mild weather through Saturday. A series of weak
cold fronts will move through the region Sunday and Monday with
a slight chance of a shower over the mountains. High pressure
south of the region next week will provide for increasing heat and
humidity...with little chance for precipitation through midweek.
Near term /through tonight/...
0600 am update...updated for current conditions. A very nice day
High pressure centered over western Pennsylvania this morning will
provide a mostly sunny day across the region today with
comfortable humidities and light northwest winds. Across the
mountains...partly cloudy skies can be expected. Any valley fog
should burn off quickly this morning with temperatures climbing to
the 70s to lower 80s across the region this afternoon. Coastal
areas will see a sea breeze develop during the afternoon.
Short term /Saturday/...
clear skies combined with dry air and light winds will lead to
another pleasant night tonight with temperatures dropping into
the 40s in the mountains and 50s elsewhere. With the cool
temperatures...fog will again develop in the colder valleys. The
ridge of high pressure will begin to move off the coast Saturday.
This will allow humidities to start to increase a bit late in the
day...especially across western New Hampshire. Afternoon sea breezes are
expected again along the coast.
Long term /Saturday night through Thursday/...
high impact weather potential: none.
Pattern summary: early morning water vapor imagery indicates a
general west northwest flow across much of noam between sprawling
ridge over the southwestern states and semi-permanent trough near
Hudson Bay. This trough axis remains centered near our
latitude...the result being a significantly drier and somewhat
cooler airmass than was overhead earlier in the week. Looking
ahead...primary controlling features for the long term forecast
period will be strengthening/broadening longwave trough along the
western coast of noam...with subsequent building of heights across
the eastern two thirds of noam west of ongoing blocking /-nao/
across the northern Atlantic. Pattern recognition would suggest
that the greatest chance for any sensible weather would have to come
earlier in the period...when the band of strongest westerlies aloft
is nearby...and before it is shunted north by developing ridging.
Beyond this...the primary weather story should be increasing warmth
as anomalous heat builds across central noam early in the
week...spilling east as the week progresses.
Guidance trends/confidence: longwave pattern agreement is rather
strong through the long term forecast period...having improved over
the past few days. Primary differences are focused around the
evolution of Erika as it moves northwestward towards the
southeastern United States. Regardless of these differences...the
vast majority of deterministic/ensemble members keep any impacts
from Erika /rain or otherwise/ well south of the region....which
fits well with dominant eastern noam ridging...which yields little
in the way of a path northward for such a system.
Best signal for precipitation potential comes right off The Bat as a
weak cool front settles through the region Saturday night/Sunday
Sunday in tandem with a poorly defined shortwave at 500 mb...but a
modest jet streak at h2. Moisture return ahead of this boundary is
not impressive. As mentioned in previous discussions...timing of
this frontal boundary may give the best clue as to whether it can
produce precipitation across the area...but this really does not
look like a widespread rain producer. 30-50 percent of sref members
produce precipitation...and the sref is typically a bit bullish...so
see little reason to stray much above 20-30 percent probability of precipitation for
northern areas...with downsloping south of this likely precluding
anything but some increased cloudiness reaching coastal areas.
Monday: northwest flow aloft will try to make one last stand on
Monday as impressive shortwave attempts to carve itself out over the
Canadian Maritimes. The GFS is much more aggressive with this
feature than the ggem/ECMWF...and is on the stronger side of the
gefs envelope. The European model (ecmwf) solution looks like a reasonable
compromise in this case...driving a weak cool front through the
region during the day Monday. The upper wave is more impressive
than the day previous...but moisture is again not terribly
impressive...and the dynamic forcing really gives only a glancing
blow...so will stick with 20-30 probability of precipitation for this period.
Deep-layer ridging looks to be in firm control of weather across the
region for Tuesday and Wednesday with little sensible weather to
speak of. With surface high pressure centered south/southwest of
the region will allow a modest return of llevel moisture...with
increasing humidity to go along with warming temperatures /see
There is some weak agreement in the guidance that as we reach the end
of this forecast period on Thursday...the sharpening ridge to the
west of the region may allow for energy to drop into northern New
England /Ridge rollers/ rather than remaining well north of the
area. Clearly there isn/T any skill timing this 7 days out...but
pattern recognition would suggest that probability of precipitation near climatology levels
/slight chance/ are likely warranted to end the period.
Temperatures: a warmer than normal forecast period is in
store...with t8s spending much of the week in the middle teens. This
supports highs well into the 80s outside of the mountains and
immediate Maine coast. Temperatures aloft appear to reach their warmest
levels toward the end of this forecast period with t8s +1-2
sigma...likely allowing the warmest spots to reach 90 at least once
during the week. Warmest day in the forecast is currently
Wednesday...as somewhat higher precipitation chances on Thursday
tempers confidence in readings continuing this warm through the end
of the week. Humidity will not be oppressive...but will be
increasingly noticeable during the week with no significant cooling
foreseen at least through next weekend.
Aviation /10z Friday through Tuesday/...
short term...mainly VFR conditions expected today and Saturday with
some IFR conditions expected in valley fog early this morning and
again tonight into Saturday morning.
Long term...no organized area of restrictions is expected through
the long term forecast period...with the greatest threat for any
rain showers activity coming on Sunday and Monday /coverage looks no greater
than widely scattered/. Outside of this...light winds and gradually
increasing boundary layer moisture suggest that valley fog at
hie/leb will be possible each morning.
short term...winds and seas expected to remain below Small Craft Advisory criteria
today through Saturday.
Long term...a period of generally light winds is expected through
the long term forecast period with high pressure anchored along the
East Coast...with both winds/waves remaining below Small Craft Advisory levels
through the period.