Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Medford or
300 am PDT Wednesday Oct 26 2016
Discussion...26/00z NAM/GFS/ec in.
The northern hemispheric pattern shows a wave number of five
around the Globe. This is normally a progressive pattern, but with
a deep nearly cutoff trough off the West Coast, progress will be
That trough will remain in roughly the same location through at
least the rest of this week, as short waves diving down the back
side of it will force it to maintain its position. As long as it
remains out there, the Pacific northwest will remain under
southwest flow aloft, and short waves ejecting from the trough
will push fronts onshore through the period. It will remain
relatively wet, but high temperatures will be 5 to 15 degrees
above normal for the most part. The exception will be the coast
and Umpqua basin, where temperatures will be near normal to around
5 degrees above normal.
An incoming short wave is bringing precipitation and gusty winds
to the area at this time, and wind advisories are in effect for
the Shasta Valley and east side. Winds are currently gusting above
40 mph in those areas. The front associated with this weather will
progress very slowly inland due to the development of an upstream
system. So, the gusty winds may last a bit longer than previously
thought. The coast and Coast Range will also get a good soaking
with the front lingering overhead. Lesser amounts will fall
Yet another wave will move in Thursday. This one will come in from
the west and the energy is directed farther south. This will
reinforce the stationary front and this front will push inland
Thursday to the east side. Precipitation will move inland as
well, but there won't be a lot of it.
A split flow regime will affect the area beginning Friday. One
short wave will move up from the southwest into the east side
Friday, and another one coming in from the west will move onshore
Friday night. The first short wave will induce wave development
on the surface front, which will retrograde over the County Warning Area Friday
and then weaken. The front associated with the offshore wave will
move onshore with the wave Friday night, effective merging with
the other front.
More waves will follow Saturday as the pattern remains wet and
occasionally windy. Snow levels will remain well above pass
Long term discussion from the Tuesday afternoon afd...Saturday
through Tuesday night. The long term model solutions have a
general consensus that the pattern will be active and stormy with
a series of low pressure systems moving into the West Coast. The
trend was to adjust the probability of precipitation higher and
adjust temperatures lower. In line with lower temperatures, snow
levels were adjusted slightly lower. These look to be normal to
slightly warmer than normal fall systems with snow levels in the
ballpark of 5500 to 6500 feet. However, the model differences
quickly grow beginning on Saturday and have moderate to large
differences in timing, track, and strength of the individual
systems. As a result, there is a broad brush of mainly chance to
likely pops with the highest probability for Coos, Curry,
Josephine, and Siskiyou counties.
The long term looks to begin with a broad longwave upper trough
centered offshore from the Pacific northwest. The European model (ecmwf) and GFS each
indicate a split flow with one closed low near Vancouver Island and
another of similar strength far offshore from far northern
California around 40n 135w. The GFS is showing its typical bias of
being more progressive than the European model (ecmwf). It swings a cold front inland
on Saturday evening while the ec is nearly 12 hours slower. There
are differences in the extent to which our area is impacted by
either or both of the northern and southern branch of the trough.
The timing differences that grow with time lead to uncertainty in
whether our region will be in a stormy or Post-frontal showers
environment in any of the individual day/night periods early next
Aviation...26/06z taf cycle...a warm front moving north over
the area will bring steady rain across Douglas County, the coast and
the Coast Ranges tonight. Also expect moderate rain in The Mount
Shasta, kmhs, area tonight. MVFR/IFR is expected in the heavier rain
tonight, with terrain obscured west of the Cascades and in northern
California. The warm front will lift north in the early morning and
a cold front will approach the coast. Ahead of this front, southerly
winds will increase in the morning and conditions are expected to
improve to VFR for inland locations with VFR and areas of MVFR cigs
along the coast. Increasing winds aloft will also bring low level
wind shear to coastal locations and into krbg. Confidence is low on
the exact timing of IFR/MVFR conditions in western valleys tonight
into early Wednesday morning. East side of the Cascades, most
locations should remain VFR through tomorrow. -Cc
Note: the ceilometer at FAA site koth is out of service, so there
will be no ceiling observations available generally between the
hours of 04z and 14z.
Marine...updated 230 am PDT Wednesday, October 26, 2016...an area of
low pressure will lift north along 130w this morning bringing south
gales and very steep seas to a large portion of our coastal waters,
but the strongest winds and highest seas will be beyond 5 nm from
shore near Cape Blanco and beyond 10 nm from shore elsewhere.
The associated cold front will slowly push onshore this afternoon
and gales will subside, but seas will remain steep to very steep
through this evening. Winds and seas gradually subside Wednesday
night into Thursday with calmer conditions on Friday. The next front
will arrive Friday night into Saturday with increasing south winds
and steep seas. -Spilde
or...Wind Advisory until 2 PM PDT Thursday for orz029>031.
California...Wind Advisory until 2 PM PDT Thursday for caz083-085.
Wind Advisory until 5 PM PDT Wednesday for caz081.
Pacific coastal waters...Small Craft Advisory until 5 am PDT
Wednesday for pzz350-356-370-376.
Gale Warning from 5 am to 2 PM PDT Wednesday for pzz350-356.
Hazardous seas warning from 5 am to 11 PM PDT Wednesday for
Gale Warning until 2 PM PDT Wednesday for pzz370-376.