Oregon Climate Service, October 2004
Overview
October’s generally mild and wet conditions mirrored those in September, providing a good start to the Water Year. Eastern Oregon regions which have been especially hard-hit by drought conditions in recent years were the main recipients, with some stations receiving more than 300% of the October normal.
Table 1 is a summary of monthly
averages and totals at selected stations throughout the state. Table 2 lists
daily temperatures and precipitation for most of the locations listed
in Table
1. In Table 3, monthly and
seasonal precipitation totals throughout the state are listed.
Basin Summary
Here is a summary of precipitation, water supply, and snow pack as of the end of the month, by river basin:
|
|
|
|
||||
| BASIN |
|
|
|
|
|
|
| OWYHEE | 120 | 84 | 104 | 75 | 63 | -1.3 |
| MALHEUR | 107 | 103 | 102 | 57 | 42 | -0.7 |
| GRAND RONDE, POWDER, BURNT | 138 | 117 | 105 | 104 | 84 | -0.8 |
| UMATILLA, WALLA WALLA, WILLOW | 107 | 115 | 110 | 111 | 113 | 2.2 |
| UPPER JOHN DAY | 42 | 111 | 103 | 112 | 90 | 0.8 |
| UPPER DESCHUTES, CROOKED | 35 | 107 | 96 | 68 | 58 | 0.1 |
| LOWER DESCHUTES, HOOD RIVER | 121 | 102 | 97 | 130 | 78 | 0.9 |
| WILLAMETTE | 142 | 97 | 98 | 90 | 85 | 0.3 |
| ROGUE, UMPQUA | 87 | 97 | 99 | 102 | 83 | -0.2 |
| KLAMATH | 60 | 97 | 91 | 80 | 65 | -2.6 |
| LAKE COUNTY, GOOSE LAKE | 53 | 90 | 83 | 72 | 60 | -1.0 |
| HARNEY | 77 | 79 | 103 | 79 | 74 | -0.2 |
| NORTH COAST | 154 | 95 | n.a | 355 | 84 | 0.5 |
| SOUTH COAST | 163 | 99 | n.a | 54 | 86 | -0.7 |
n.a. Not available
(1) Percent of normal October precipitation, from NOAA Cooperative
sites
(2) Percent of normal seasonal precipitation (since Oct. 1), from
NOAA Cooperative sites
(3) Percent of normal seasonal precipitation, from Natural Resources
Conservation Service (NRCS) SNOTEL sites
(4) Percent of normal snow water equivalent, from NRCS SNOTEL
sites
(5) Percent of normal October stream flow, from U.S. Geological
Survey (USGS)
(6) Percent of normal seasonal stream flow (since Oct. 1), from
USGS
(7) Surface Water Supply Index, from NRCS (-4 = very dry, 0 =
normal, +4 = very wet)
Forecasts
The Climate Prediction Center’s (CPC) forecasts for November-January appear below. Temperatures for all of Oregon are likely to be above normal. Precipitation probabilities suggest an equal probability of below-, near-, or above-normal precipitation. CPC also says:
“
The outlook for NDJ 2004 is based on indications from warming trends in the
southwestern US... with above normal temperatures anticipated in the western
part of the US and also in southern Alaska... and also from composites associated
with weak El Niños. As the seasons progress through winter, the temperature
forecasts reflect El Niño composites in combination with trends and
indications from other tools”
Oregon Climate Service predicts above-normal precipitation and normal temperatures.
For the three-month period ending in January, we predict above-normal precipitation
and normal temperatures.
The “Fog Bowl”
A week ago the OSU football team faced a daunting obstacle: the USC Trojans,
top-ranked team in the country were coming to town. The Trojans are big,
fast, and really, really good. So how to slow them down?
Snow? Probably not. Though snow in the mid-valley has fallen as early as
October 31 (1935), it’s very rare this time of year. Rain? Well, maybe…but
how about taking away their ability to SEE the ball? Wouldn’t THAT slow
them down? Hey, how about dense fog?
And so it was, in what may be known as the Fog Bowl. The Beavers are good
enough that they probably didn’t need to fog to match up with USC, but it didn’t
hurt…except for the TV viewers and the fans in the “cheap seats,” who
had a hard time seeing things well. After the game, plenty of folks asked me
about the “valley fog,” as it has come to be known. Following are
my answers to the most common questions I hear.
What causes valley fog?
Fog is a cloud that is in contact with, or very close to, the ground. On cold,
calm nights, the coldest air settles into the lowest places, because it is
more dense than warm air. Cold air has less capacity to hold water vapor, and
if the temperature drops low enough the air will become saturated (this is
known as the “dew point”) and water vapor will condense into small
liquid droplets – a cloud! At these times, clouds are more likely where
temperatures are coolest, in the lowest elevations. In our locale, this is “valley
fog.”
Often after the sun comes up the temperature will rise, and if the temperature
is higher than the dew point the clouds will “melt away” as the
water droplets evaporate and turn back into water vapor. But fog is highly
reflective, and if it’s thick enough it will reflect much of the sun’s
rays and prevent them from reaching the ground and thus warm the low-level
air. In these cases, the fog may last all day (as it did on November 6, the
day of the USC game).
If winds are strong, they can stir up the air enough to keep the fog from forming
(by mixing the warm and cool air and prevent the really cold air from puddling
near the ground). Light winds, then, are pretty much essential for fog to form
and persist. Not surprisingly, November 6 has light winds.
When does valley fog occur?
Any time of year, but fall is the most likely time. The three foggiest months
at Eugene Airport (the nearest long-term measurement site) are October, November
and December. In an average year, about one day out of three during those months
has heavy fog, with visibility less than a quarter mile.
Does fog only occur in the valleys?
No, fog is not restricted to the valleys. Here’s a nice overview from
Dave Nicosia of the National Weather Service, Binghamton, New York – a
place that gets plenty of valley fog at about the same time we do:
“ Fog can form on our hilltops when very moist air is forced up the
hills by the wind. In this situation, fog will cover the hills and generally
not affect
the valleys. This most often occurs during or just after a rainstorm. Fog
can also affect both valley and hilltop. This typically occurs during a thaw
in
winter or early spring. When there is snow on the ground, the ground is cooled
by the snowpack. If warm and moist air moves over the snowpack, the air is
cooled to its dewpoint leading to fog formation. These two mechanisms for
fog formation do occur each year in our region, but are much less frequent
than
valley fog formation.”
I’m not enamored of fog, so I always hope for windy, rainy periods in
winter. And we’ve had our share of fog this season, so bring on the
storms!
Drought Update
Parts of Oregon are still officially in “drought” status. In
southeast Oregon the last 4 years has seen relatively low precipitation (last
winter
was pretty close to average, but insufficient to overcome a big deficit).
My friend Roger Pielke, Sr., the Colorado State Climatologist, said this about
drought:
“
In modern times "there's more to drought than simple lack of precipitation," adds
Roger Pielke Sr., a state climatologist for Colorado and a professor of atmospheric
sciences at Colorado State University. "You have to consider human factors
like the amount of water being drained from rivers for crop irrigation and
drinking water. In absolute terms, the ongoing dry spell is not yet as severe
as the Dust Bowl of the 1930s, but the impacts have been relatively severe
because the demands that people place on the water supply are so much greater
now than they were back then."
In the 30s, water supply recipients were primarily agriculture and domestic
users. Nowadays, in addition to supporting many more users due to increasing
population in the West, water suppliers have to worry about some additional
types of demand:
1. Recreation. Reservoirs are very popular recreation sites, and the public
demands full reservoirs for boating and other recreation pursuits. At the same
time, rivers are popular for recreation, and there is demand to keep them flowing
throughout the summer.
2. “In-stream” uses. Salmon and other aquatic species suffer
when water levels are low. There is increasing pressure to keep rivers, streams
and lakes full (and cool) to protect these species.
3. Industry. Water is an essential ingredient for most manufacturing processes.
One of the primary issues regarding water supply in the West involves the
supply-demand process. In many areas, demands for water far exceed supply.
Take Los Angeles,
for example. This is a megalopolis in a semi-arid area whose water inputs
(precipitation) are far smaller than the demands. Thus, Los Angeles has had
to import water
from other areas, some of them very far away. These include Northern California,
the Colorado River and (in years past) Owens Valley and Mono Lake. But increasing
demands in other states have led to some reallocations of water. One likely
victim will be the farming community of Imperial Valley, one of California’s
most productive agricultural areas. For decades, farmers there have relied
on Colorado River water for irrigation. But that may change for many growers
in the face of likely cutbacks in Imperial Valley water supplies later this
year.
Though it’s winter, let me reiterate what I say to Oregonians every year, whether we’re in a drought or not: water is and will continue to be a precious resource, Use it wisely, and conserve where possible. As my late mother was fond of saying: “Waste not, want not.”
Oregon Climate Service
George H. Taylor, Oregon State Climatologist
Wayne P. Gibson, Programmer/GIS mngr.
Eileen Kaspar, Research Assistant/Manager of Data Services
Melanie Mitchell, Undergraduate Assistant
Wolf Read, Undergraduate Assistant
Emily Gibson, Student Assistant
Cadee Hale, Publications Assistant
Kelsey Kuykendall, Undergraduate Assistant
Sara Joos, Student Assistant
Sean Daly, Student Assistant
Oregon Climate Service, Strand 326,Phone: (541) 737-5705 Oregon State University Fax: (541) 737-5710 Corvallis, Oregon 97331 E-mail: oregon@coas.orst.edu Web: http://www.ocs.oregonstate.edu