Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Medford or
441 am PDT sun Sep 25 2016
Aviation...25/12z taf cycle...VFR conditions are expected through
the next 24 hours over most of the area. Along the north coast,
including koth, patchy fog and stratus this morning will burn off
to VFR. Stratus and fog return this evening and will likely be
more widespread and persistent along the coast tonight through
Monday morning. -Wright
Previous discussion... /issued 323 am PDT sun Sep 25 2016/
skies are clear across the forecast area this morning as high
pressure continues to build into the Pacific northwest. East winds
across the ridges and a dry and drying air mass have developed a
strong inversion this morning. For example, relative humidities
across the ridges of western Siskiyou County and Curry County are
currently a mere 10 to 30 percent with winds gusting around 20
mph. Current temperatures in those same areas are in the 60s to
lower 70s, while sheltered valleys dip into the 30s and 40s.
Temperatures will climb 40 to as much as 50 degrees from morning
lows today to this afternoon's highs across the interior portions
of the area due clear skies and the very dry air mass in place.
This will result in plenty of 80s and 90s in the interior valleys
today which will be several degrees short of calendar day record
The warm and dry air mass will reach its warmest on Monday, still
a few degrees short of record highs. Temperatures will remain 10
degrees or more above normal Tuesday and Wednesday for interior
locations, as well. The marine layer is likely to return to
the coast and Umpqua basin Monday night with some marine layer
type of light rain and drizzle possible.
The GFS based guidance drops temperatures by 9 degrees for highs
on Thursday, whereas the European model (ecmwf) is slower to bring them back down
to normals for the date. Have leaned toward consensus from the
last 3 days, which would bring them down by about 10 degrees.
Numerical models and ensembles are very well agreed on a large
trough of low pressure moving in Thursday through Friday, with
numerous small scale impulses moving through this broader scale
trough this weekend through early next week. We expect that the
most likely result from this trough will be cooler than normal
temperatures and near to above average precipitation across the
area, even in our northern California areas. Showers and,
possibly, isolated thunderstorms will be possible along and east
of the Cascades Thursday afternoon and evening. For now have left
thunder out due to marginal instability. West side rain chances
for next Saturday are in the "likely" category and valley highs
are expected to be mostly in the upper 50s to lower 60s. Wetting
rainfall appears likely for the west side Friday through next
Wednesday and possible for much of the rest of the area. Snow
levels will come back down to around 6kft, so there could be
accumulating snow again the mountains. Btl
Marine...updated 215 am PDT Sunday 25 September 2016...a thermal
trough will keep moderate north winds and wind driven seas going
over most of the area through tonight. The trough will weaken
briefly tomorrow with lower winds and seas...but it will redevelop
Tuesday into Wednesday after a weak front moves onshore. Strong
north winds will return...possibly reaching gale force by midweek
south of Cape Blanco. Winds will weaken again Wednesday night into
Thursday as another weak front approaches the coast. -Wright
Fire weather...updated 210 am PDT Sunday 25 September 2016...
offshore flow continues as forecast over the mountains, and it is
drying out rapidly. Humidity recoveries occurred last evening in
many mountain locations, and humidities continue to fall this
morning. Winds aren't quite as strong as expected yet, but typically
they peak around dawn, so the red flag warnings look well on their
way to verifying this morning.
With an upper ridge and surface thermal trough in place, the pattern
will be hot and very dry through Monday. Winds are expected to peak
this morning, and then humidities bottom out today through Monday.
Recoveries in many mountain locations may not get out of the teens
tonight, but with diminishing winds, red flag criteria are not
expected to be met except in isolated locations. Nevertheless,
conditions will be near critical over most of the area today and
Monday and over the mountains again tonight.
The thermal trough moves inland Tuesday, at which point humidities
creep up and temperatures begin to cool. This gradual cooling trend
continues through Wednesday, then temperatures fall off a cliff
Thursday and Friday as an upper low and frontal system move in. This
system may bring a wetting to many areas late this week and next
weekend. It is too early to know exactly how much rain falls or
where it falls, but confidence is fairly high that the pattern will
shift to a much cooler wetter one later this week. -Wright
or...red flag warning until 10 am PDT this morning for orz618-619.
California...red flag warning until 10 am PDT this morning for caz280.
Pacific coastal waters...Small Craft Advisory for hazardous seas until
5 am PDT Monday for pzz350-356-370-376.
Small Craft Advisory until 5 am PDT Monday for pzz376.