Overview
November began with very cold temperatures, as an early-season
Arctic outbreak dropped into the U.S. from Canada. Some daily
record low temperature records were set, especially in eastern
Oregon. In the last week of the month, wet, mild weather prevailed,
but generally rainfall was below normal for the month, while monthly
temperatures were below normal statewide.
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.
Figure 1 shows the percentage of seasonal precipitation statewide.
Basin Summary
Here is a summary of precipitation, water supply, and snow pack as of the end of the month, by river basin:
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Snow |
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| BASIN |
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| OWYHEE | 47 | 79 | 71 | 103 | 47 | 50 | -2.4 |
| MALHEUR | 164 | 79 | 70 | 73 | 46 | 29 | -2.1 |
| GRAND RONDE, POWDER, BURNT | 82 | 62 | 76 | 88 | 58 | 64 | -1.8 |
| UMATILLA, WALLA WALLA, WILLOW | 63 | 61 | 78 | 84 | 63 | 71 | +0.1 |
| UPPER JOHN DAY | 71 | 60 | 65 | 68 | 45 | 51 | -0.6 |
| UPPER DESCHUTES, CROOKED | 56 | 80 | 77 | 89 | 43 | 43 | -0.8 |
| LOWER DESCHUTES, HOOD RIVER | 96 | 80 | 86 | 109 | 55 | 66 | -1.2 |
| WILLAMETTE | 95 | 77 | 78 | 15 | 34 | 42 | -1.5 |
| ROGUE, UMPQUA | 91 | 80 | 81 | 96 | 31 | 41 | -1.0 |
| KLAMATH | 65 | 87 | 59 | 76 | 71 | 75 | -2.5 |
| LAKE COUNTY, GOOSE LAKE | 63 | 51 | 63 | 78 | 41 | 41 | -0.9 |
| HARNEY | 76 | 82 | 53 | 77 | 67 | 70 | -1.2 |
| NORTH COAST | 100 | 81 | n.a | n.a | 72 | 74 | -0.9 |
| SOUTH COAST | 68 | 84 | n.a | n.a. | 21 | 21 | +1.4 |
Forecasts
The Climate Prediction Center's (CPC) forecasts for December-February appear below. Temperatures for Oregon (and all of the West) are likely to be above normal, while precipitation probabilities are above normal for northern Oregon and near normal for the southern half.
Oregon Climate Service predicts near-normal temperatures and above-normal precipitation for the next three months. Since last summer we have been suggesting that we will experience one or more severe weather events this winter, most likely either a major wind storm or intense rainfall event.
ENSO Update (from CPC, December 11, 2003)
Surface and subsurface temperatures remained warmer than average across most of the equatorial Pacific Ocean during November. Equatorial ocean surface temperatures greater than +0.5°C (~1°F) above average were found in most areas between Indonesia and the South American coast. Departures greater than +1°C were found between 150°E and 170°W. Positive SST anomalies were observed in all four Niño index regions for the second consecutive month. However, the 850-hPa zonal wind indices, OLR index, 200-hPa zonal wind index, SOI and EQSOI all indicate ENSO-neutral conditions. Over the past few months these atmospheric indices have not shown any significant trends that would support either additional large-scale increases or any substantial decreases of SST anomalies in the equatorial Pacific.
A majority of the statistical and coupled model forecasts indicate near-average conditions in the tropical Pacific (Niño 3.4 SST anomalies between -0.5°C and +0.5°C) through Northern Hemisphere winter 2003-2004. However, some forecasts indicate that weak warm episode conditions will develop during the winter, which is consistent with observed trends in SST anomalies, particularly in the vicinity of the date line.
The three-month (September-November) average SST anomaly in the Niño 3.4 region (+0.4°C) is just below the threshold (+0.5°C) required for NOAA to declare a weak Pacific warm episode (El Niño). It is likely that the October-December 2003 average will reach that threshold and that borderline weak El Niño / ENSO-neutral conditions will persist through the Northern Hemisphere winter of 2003-04. However, it seems unlikely that classical El Niño conditions will develop along the west coast of South America.
Two questions from readers:
Q. Do volcanoes affect the earth's climate? In what way? Paul V., Corvallis
A. Sometimes volcanoes produce a very significant effect on climate, regionally as well as globally. The biggest direct effect is usually a cooling, due to dust from a volcanic eruption reflecting some of the sun's radiation before it reaches us (in much the same way that a cloud reduces sunlight on a summer day). If an eruption is violent enough, dust smoke will travel high up into the atmosphere, and be dispersed widely in the upper atmosphere. Dust from a tropical eruption can reach the polar latitudes, and vice-versa. If the quantity of material is large, the dust cloud can be rather thick and last for many months.
The biggest recent eruption of this type was Mt. Pinatubo in the Philippines in June, 1991. Pinatubo rose about 5725 ft ( 1745 m) above sea level before the eruption. This means almost 500 ft (150 m) of the volcano was blasted away by the eruption. The dust remained in the atmosphere for several years (causing spectacular sunrises and sunsets). Global temperatures dropped noticeably. NASA scientists found that the reduced sunlight and cooling temperatures caused the earth's vegetation to grow more slowly differences in greenness before and after Pinatubo were rather striking when measured from space.
But as volcanoes go, Pinatubo was medium-sized. Vulcanologists
believe that the biggest dust-producing eruptions of the last
10,000 years were Tambora (Indonesia) in 1815 A.D. and Taupo (New
Zealand) in 186 A.D. Both emitted an estimated 24 cubic miles
of material. In contrast, Pinatubo emitted less than 3 cubic miles
and St. Helens (1980) only about one-fourth of a cubic mile. According
to www.volcanolive.com, "1816
became the year without a summer as the global climate effects
were felt. Aerosols from the Tambora eruption blocked out sunlight
and reduced global temperatures by 3 deg C. Europe missed a summer,
and India had crop failures following the Tambora eruption."
Tambora's cooling was about 6 times as great as Pinatubo's, and
led to the legendary "summer without a summer" in Europe
and the Americas.
But there's more. A new study by scientists at the University
of Virginia and the National Center for Atmospheric Research (NCAR)
suggests that explosive volcanic eruptions in the tropics may
increase the probability of an El Niño event occurring
during the winter following the eruption. The study results appear
in the Nov. 20 issue of the journal Nature.
The cooling influence of a large volcano, especially one erupting in the tropics, alters the interaction between the oceans and atmosphere, "possibly encouraging a warming response in the Pacific Ocean as the massive body of water attempts to restore an initial equilibrium," according to the study authors.
"The El Nino-Southern Oscillation (ENSO) is the dominant mode of interannual climate variability on the planet," says NCAR scientist and coauthor Caspar Ammann. "When thinking about long-term climate, we must ask whether this system itself undergoes changes, perhaps in response to changes in radiative forcing or in the background climate itself. Our findings, based on two reconstructions, suggest that it indeed might."
And since ENSO exerts a large influence on our weather, climate,
ocean conditions, and salmon populations, anything that affects
ENSO affects us even a tropical volcano halfway around the
world.
Q. Is there an effect of cities on the weather or the climate?
In what way? Mike, Madras
A. For many years, we've known about a phenomenon called the
"urban heat island effect," or UHI. The first large-scale
study of UHI tookplace near St. Louis in the early 1970s, a project
known as Metromex. The city warmed the air compared with rural
locations, and as the warmer air rose, it created thunderstorms
and enhanced rainfall downwind.
Other studies have shown similar patterns in many other locations,
including Atlanta, Salt Lake City, and Los Angeles. Now scientists
are turning to better, more sophisticated tools to understand
UHI.
New evidence from satellites, models, and ground observations
reveal urban areas, with all their asphalt, buildings, and aerosols,
are impacting local and possibly global climate processes. This
is according to some of the world's top scientists convening in
a special session at the Fall Meeting of the American Geophysical
Union in San Francisco.
According to a NASA press release on December 11, Dr. J. Marshall
Shepherd of NASA's Goddard Space Flight Center, Greenbelt, Md.,
and Steve Burian of the University of Utah, Salt Lake City, used
the world's first space-based rain radar to study urban impact
on local rainfall. Instruments aboard the Tropical Rainfall Measuring
Mission (TRMM) satellite, and dense rain gauge networks on land,
were used to determine that higher rainfall rates occur during
the summer months downwind of large cities like Houston and Atlanta.
Burian and Shepherd offer new evidence that rainfall patterns
and daily precipitation trends have changed in regions downwind
of Houston from a period of pre-urban growth, 1940 to 1958, to
a post-urban growth period, 1984 to 1999.
In related work, Dr. Daniel Rosenfeld, an atmospheric scientist
at Hebrew University, Jerusalem, reveals the increased amount
of aerosols, tiny air particles, added by human activity to those
naturally occurring also alter local rainfall rates around cities.
Rosenfeld suggests the particles provide many surfaces upon which
water can collect, preventing droplets from condensing into larger
drops and slowing conversion of cloud water into precipitation.
In summer, rain and thunder increases downwind of big cities,
as rising air from urban heat islands combines with 'delayed'
rainfall resulting from the presence of aerosols, creating bigger
clouds and heavier rain.
According to Shepherd and Burian, UHI temperature enhancement
is significant; cities are one to 10 degrees F warmer than surrounding
suburbs and rural areas. Warming from urban heat islands, the
varied heights of urban structures that alter winds, and interactions
with sea breezes are believed to be the primary causes for the
findings in a coastal city like Houston.
It's true in Oregon as well. 50 years ago, temperatures at our
local Hyslop Experiment station (a rural location on the Experiment
Station between Corvallis and Albany) and Portland Airport (PDX)
were nearly identical. Over the years, the area around PDX grew
more traffic, more blacktop and concrete, more buildings,
more aircraft while Hyslop remained about the same. The
result: PDX has slowly gotten warmer and warmer than Hyslop, and
is now consistently 3-4 degrees F warmer. Similar warming is seen
in other urban areas, such as Hillsboro. Similar contrasts exist
in Washington, between urban sites like Seattle and Bellingham
and rural stations such as Long Beach and Cedar Lake. I've posted
charts of trends at these stations at http://www.ocs.orst.edu/pub/climate_data/trends/
Oregon Climate Service
George H. Taylor, Oregon State Climatologist
Wayne P. Gibson, Programmer/GIS mngr.
Mandy Matzke, 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
Oregon Climate Service, Strand 316,Phone: (541) 737-5705 Oregon State University Fax: (541) 737-5710 Corvallis, Oregon 97331 E-mail: oregon@oce.orst.edu Web: http://www.ocs.oregonstate.edu