Overview

For the first time in quite awhile, Oregon experienced a cooler than average September. In particular, high temperatures were unusually mild due to frequent cloud cover.

Much of the state was wetter than normal, as autumn rains came early. Stations in the northern half of Oregon were mostly wet, with southern stations generally drier than average.

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:

	Precipitation			Stream Flow		SWSI
BASIN	(1)	(2)	(3)	(4)	(5)	(6)
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 September 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 September 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 October-December 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 OND (Oct.-Dec.) 2004 is based on indications from warming trends in the Southwestern U.S., with above normal temperatures anticipated along the U.S. West coast and in coastal Alaska primarily due to abnormally warm SSTs in the eastern North Pacific Ocean and Gulf of Alaska. As the seasons progress into winter... the temperature forecasts reflect El Niño composites in combination with trends and indications from other tools... especially the newly operational NCEP CFS model and the IRI multi-model forecasts.”

Oregon Climate Service predicts above-normal precipitation and normal temperatures. For the three-month period ending in December, we predict above-normal precipitation and below-normal temperatures.

Regarding ENSO, CPC says:

Positive sea surface temperature (SST) anomalies greater than +0.5°C persisted in the central and western equatorial Pacific, and expanded eastward into the eastern equatorial Pacific during September 2004. By the end of the month, positive SST anomalies greater than +0.5°C (~1°F) were found between 155°E and 110°W, with anomalies greater than +1°C extending from 160°E eastward to 120°W. The increase and eastward expansion of the area of anomalous warmth in the central equatorial Pacific during July-September indicate the early stages of a warm (El Niño) episode. Through the end of September conditions were not yet indicative of a basin-wide El Niño, particularly due to the presence of below-average SSTs in the far eastern equatorial Pacific between 95°W and the South American coast.

NOAA U.S. WINTER OUTLOOK

Oct. 6, 2004 — NOAA scientists today announced that a number of climate conditions will influence the winter weather across the United States from December through February. The NOAA 2004-2005 Winter Outlook calls for above-average temperatures in Alaska, much of the West and the northern and central Great Plains. Below average temperatures are expected across the Gulf Coast states, the Southeast and the mid-Atlantic region of the U.S. There are equal chances of warmer, cooler or near-normal temperatures this winter in the Northeast, Midwest and parts of Southwest. (See NOAA winter temperature forecast for USA, below.)

The precipitation outlook (above) calls for wetter-than-average conditions in parts of California, the extreme Southwest and across the Southern U.S.—from Texas to Florida. Drier-than-average conditions are expected in the Midwest, northern Plains and Pacific Northwest.

The winter outlook indicates some improvement in drought conditions in the West, but long-term drought is expected to persist through the winter in many areas.

The winter outlook reflects a blend of impacts associated with weak-to-moderate El Niño events in the central equatorial Pacific Ocean and is based on the likelihood that these conditions will persist through early 2005. El Niño influences the winter weather patterns by affecting the jet stream and the track storms take across the eastern Pacific and North America. NOAA scientists do not expect this El Niño to reach the strength of the1997-1998 El Niño event.

" Our winter forecast factors in the effects of a weak El Niño that may strengthen into a moderate event during the winter months," said retired Navy Vice Adm. Conrad C. Lautenbacher, Ph.D., undersecretary of commerce for oceans and atmosphere and NOAA administrator. "But we'll keep our eye on other climate features in the Pacific and the North Atlantic that play an important role on the week-to-week variability in our winter weather. These patterns influence the position of the jet stream and dictate where and how winter storms will move."

During weak to moderate El Niño events, shifts in the jet stream change the patterns of storminess over the eastern North Pacific and North America. "In particular, NOAA anticipates enhanced storminess near the Aleutian Islands and in the Southeast U.S., and warmer, drier conditions over western North America," said Jim Laver, director, NOAA Climate Prediction Center. (See NOAA forecast for USA winter jet stream, temperature and precipitation, below.)

Also, the climate system called the North Atlantic Oscillation plays an important role in modulating the winter weather over the eastern half of the U.S. The NAO is a climate pattern that influences the position of the jet stream over the North Atlantic, affecting winter weather over the Northeast.

" To a large extent, our forecast of equal chances of above or below normal temperatures and precipitation over the northeastern U.S. is based on the NAO, which is only confidently predicted one to two weeks in advance," said Ed O'Lenic, meteorologist at the NOAA Climate Prediction Center. Impacts from the NAO are included in the NOAA Climate Prediction Center's 8-14 day and 6-10 day outlooks and U.S. Hazards Assessment.

NOAA continues to improve climate forecasting and push the envelope in understanding the Earth's climate system. For the first time, NOAA's new Climate Forecast System is being used as a tool for this outlook. The Climate Forecast System is a coupled ocean-atmosphere model, which complements other NOAA models and gives increased confidence of probable climate events before they happen.

" NOAA's progress in climate forecasting is based on ongoing research and collaboration with our partners, advancements in our understanding of the global climate system, upgrades to the weather and climate supercomputer, and improvements in the state-of-the-art atmospheric and oceanic modeling applications. The knowledge and understanding NOAA gains is allowing us to begin a new era in climate prediction," said Louis W. Uccellini, director of the NOAA National Centers for Environmental Prediction.

NOAA is dedicated to enhancing economic security and national safety through the prediction and research of weather and climate-related events and providing environmental stewardship of the nation’s coastal and marine resources. NOAA is part of the U.S. Department of Commerce.

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