Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Medford or
315 am PST sun Nov 29 2015
Discussion...it is another cold morning in the Medford forecast
area, and in fact, looks very similar to the past couple of
mornings in that the skies remain clear for all but portions of
the Umpqua valley near Roseburg, which remains in fog yet again.
Also in a repeat of yesterday, this area will be slow to clear
out, and will therefore remain a bit cooler than the rest of the
west side valleys.
But there is change afoot! Beginning Monday, a series of system
will begin to push into the Pacific northwest, marking a return to
a wet and active pattern that will likely persist for at least the
next 10 days. The first of these systems will be a weak upper low,
which will be the kicker to finally shunt the blocking ridge away
from the West Coast. The associated surface system will weaken
considerably as it moves ashore, washing out before it crosses the
Cascades. Precipitation with this front will be light, but there
is a possible complication that may arrive in the form of ice.
With the timing of the front, cold air in the coastal range
valleys Sunday night, including the Camas and Illinois valleys,
may not warm quickly enough before precipitation begins, despite a
layer of warm air aloft. It is possible that there will be a brief
period of freezing rain in the colder valley locations Monday
morning, but if this does occur, only a light glazing is likely
before temperatures rise and precipitation becomes all rain. There
is very low confidence in the forecast for ice, and chances are,
precipitation will begin as rain and stay that way. However, those
in the affected areas should be prepared for the possibility of
slick roads for the morning commute.
The next system arrives Tuesday, and it is expected to be a much
wetter, and more typical, wet season event. However, the source of
this system is much warmer, and snow levels are forecast to rise
quite quickly to above 6000 feet. Thus, only the higher peaks and
ridges should receive much snow, while most areas get a good
Models beyond this point are consistent in solution, but do vary
more and more with timing as the time range extends further out.
One thing does appear quite apparent, however. The next system in
line, due into our region Thursday, has the potential to be a very
impactful storm. While models across the board are producing a
very vigorous and sharp upper level trough with a negative tilt, a
few are also producing a rapidly deepening low just offshore of
the Oregon coast. These are the primary ingredients for winds
storms in our area. We will need to keep an eye on this event as
it gets closer, as it could be one of the larger and stronger
storms of the season. After a brief one to two day break late in
the week, models solutions bring another storm into the forecast
area over the weekend. Confidence is high that we will remain in
an active pattern through the long term forecast, but is low in
the details such as timing and strength. Whatever the result, it
appears we will have an interesting weather week in store for
southern Oregon and northern California. -Bpn
Aviation...for the 29/12z taf cycle...VFR conditions will
prevail through Sunday night...except for areas of LIFR in
freezing fog/low clouds over the Umpqua basin...including
krbg...and patchy LIFR in freezing fog/low clouds over the
Illinois Valley and lower Klamath valley. The fog and low clouds
will clear by early Sunday afternoon...but will return to the same
areas Sunday night. -Jrs
Marine...updated 245 am PST Sunday 29 Nov 2015...a front will
move through the waters late Sunday night into Monday afternoon.
This will bring Small Craft Advisory winds and seas to the area. A
stronger front will move through the waters Tuesday into Tuesday
night with gales and hazardous seas possible. More fronts will
follow Wednesday into Thursday. South winds may approach storm
force Thursday. More fronts will follow into next weekend. -Jrs
or...frost advisory until 9 am PST this morning for orz021-022.
Freeze warning until 9 am PST this morning for orz021-022.
Pacific coastal waters...frost advisory until 9 am PST this morning for pzz350-356.
Freeze warning until 9 am PST this morning for pzz356.
Gale watch from Tuesday morning through Tuesday evening for
Small Craft Advisory from 7 PM this evening to 10 am PST Tuesday
Small Craft Advisory from 4 PM this afternoon to 10 am PST
Tuesday for pzz370-376.