Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Medford or
343 am PST Monday Nov 30 2015
Discussion...radar imagery this morning is showing a band of
precipitation moving across the coast and into the coastal
ranges. This is several hours ahead of any model suite, as well as
the previous forecasts. Surface observations have also shown that
cold air remains well entrenched within the valleys, with teens
and twenties common in the Illinois, Coquille, rogue, and Umpqua
valleys. As if just to confirm suspicions, a spotter reported
light sleet in Myrtle Point earlier this morning as the band just
began to move overhead. Have therefore issued a Freezing Rain
Advisory, as any sleet in these areas will likely change to
freezing rain before finally becoming all rain, and up to a tenth
of an inch of ice is possible on area roadways. This os of
particular concern with the morning commute.
Aside from wintry conditions this morning, the front will produce
only light precipitation and little else as it pushes headfirst
into the blocking ridge overhead. This will be the sacrificial
system that punts The Block away, allowing the preferred
storm track to return to the Pacific northwest. The first of
these storms is due on Tuesday afternoon and evening, bringing a
round of rain and snow to the area, followed by showers into
Wednesday. Snow levels will rise with this system, mostly due to
the warmer maritime origins, so major passes and population
centers are expected to only receive rain.
The bigger, and much stronger, storm event is forecast for late
Wednesday night into Thursday. Models are producing a very sharp
negatively tilted upper level trough, with a deepening surface low
just offshore of the Oregon coast. These are the usual ingredients
we see producing strong wind storms for the region, particularly
along the coast, over the east side, and in the Shasta Valley,
and possibly even the Rogue Valley. There is also the potential
for a significant slug of precipitation with this system,
although there is little agreement in rainfall between the GFS and
European model (ecmwf). While there is some question as to the timing of this
system, the models have been producing similar solutions for over
24 hours now, so confidence is increasing. Will need to monitor
this event in future forecast cycles for the possibility of at
least wind headlines.
The trough should linger in the area into Friday and Saturday,
producing showers and cooler temperatures. Another wet and
potentially windy system is forecast to arrive over the weekend.
Temperatures throughout the week are expected to remain near
normal for this time of year. -Bpn
Aviation...for the 30/12z taf cycle...VFR conditions will prevail
through this morning...except for patchy LIFR ceilings/visibilities due
to freezing fog/low clouds in the Umpqua valley through around 15z. A
weak front will move onshore later today...and will bring some light
precipitation...mostly along the coast...Coast Range...and Umpqua
basin. There could be local light snow...sleet or freezing rain over
the west side valleys this morning. Areas of higher terrain will
become obscured from the Cascades west. The precipitation will
diminish this afternoon and evening...but higher terrain will remain
obscured. Isolated IFR ceiling/visibilities will develop tonight over some of
the west side valleys.
Marine...updated 200 am PST Monday 30 Nov 2015...a front now moving
through the waters is bringing Small Craft Advisory winds and seas
to the area. Moderate westerly swell will peak Monday evening. A
stronger front will move through the waters Tuesday night and this
will bring gale force winds and hazardous seas to the area. More
fronts will follow Wednesday into Thursday. South winds may approach
storm force Thursday afternoon and evening. Heavy westerly swell
will build Thursday night and subside Friday into Friday night.
or...Freezing Rain Advisory until 10 am PST this morning for
California...Freezing Rain Advisory until 10 am PST this morning for caz080.
Pacific coastal waters...Small Craft Advisory until 4 am PST Wednesday for pzz350-356.
Gale Warning from 1 PM Tuesday to 4 am PST Wednesday for
Small Craft Advisory until 1 PM PST Tuesday for pzz370-376.
Gale Warning from 7 am Tuesday to 4 am PST Wednesday for