The absence of snowfall during November is not too uncommon throughout the
midstate plateau. In Bend, where weather records date back to 1901, there have
been 30 years when there was no measurable snow in November and another 24
years when less than two inches were measured. However, one can usually count
on enough snow at higher elevations in the Cascades for Mt. Bachelor to open
before the Thanksgiving holiday period.
Although November started with winter-like weather, air masses whose origins
were from near Hawaii, streamed over Oregon during most of the month. This
situation was reminiscent of what occurred in December 1964 when widespread
floods occurred in the Pacific Northwest and Northern California.
The rains that fell in November helped restore the soil moisture before a
possible deep freeze that would make the soil impervious to infiltration by
future rains or melting snows.
What meteorological conditions accounted for the absence of mountain snows this
past month? George Taylor, State Climatologist in Corvallis, explained what had
occurred and ventured his snow forecast for the coming winter.
El Nino conditions (warm ocean current off Peru that causes some bizarre
weather throughout the world and drought conditions in parts of the Pacific
Northwest) have ended -- for now.
Taylor contends that under an El Nino episode the Aleutian Low (low pressure
system in the Gulf of Alaska) forms early and results in cool weather and early
snowfall to this region. Then a ridge of high pressure takes over and
essentially shuts off the moisture supply.
Thus, while winter sports get an early start, a paucity of renewed snowfalls
leads to some marginal ski conditions during parts of the winter season.
This November, according to George Taylor, there has been more convective
(heating) in the mid-Pacific and, as we now know, a stream of mild, moist air
was aimed at Washington State and Northern Oregon. California has been
exceptionally dry and warm and Sierra ski resorts received neither rain nor
snow.
Air which is "warm" has greater potential holding capabilities than air which
is "cold." For example, air at 70 degrees F. can contain four times as much
moisture as can air that is 30 degrees F.; hence, the heavy rainfalls in parts
of the Pacific Northwest.
Taylor predicts that this tropical moisture supply will be replaced by colder,
drier air. As the winter progresses, George forecasts the likelihood of more
storms whose origin is in the North Pacific and, as a result, there is the
strong likelihood of "normal snowfall." (Bend's average yearly snowfall is
about 34 inches; Sisters would be comparable).
From 95 years of weather records, I have identified the 20 mildest Novembers.
All but four occurred in the period 1901-49!
Snowfall the following winter and spring (it can and does snow in Central
Oregon during March and April and even in May!) ranged from a skimpy 4.7 inches
1933-34 to a prodigious 71.0 inches 1949-50.
The average "winter" snowfall was 28.6 inches, and most of it (an average of
18.2 inches fell) in the month of January.
In short, while this is not to be taken as a forecast, statistically the odds
are in favor of a normal Central Oregon winter and hopefully good conditions
for winter sports.
Raymond Hatton is author of "Sisters' Country Weather and Climate" and other
books.
