Overview

December was a wet month in nearly all of Oregon (the only exceptions being a few locations in northern sections of the state). As is often the case during wet months, the average monthly temperatures were mostly above normal. A snow storm with very cold weather affected much of the state in the last week of the month (see story).

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			Snow	Stream Flow		SWSI
BASIN	(1)	(2)	(3)	(4)	(5)	(6)	(7)
OWYHEE	116	68	107	137	48	49	-1.7
MALHEUR	124	79	93	107	53	38	-1.7
GRAND RONDE, POWDER, BURNT	151	91	91	97	60	62	-1.4
UMATILLA, WALLA WALLA, WILLOW	182	101	96	94	84	79	+0.2
UPPER JOHN DAY	170	101	90	102	41	46	0.0
UPPER DESCHUTES, CROOKED	146	98	95	113	62	50	-0.3
LOWER DESCHUTES, HOOD RIVER	132	105	92	122	61	63	-0.7
WILLAMETTE	136	102	79	106	101	73	-0.7
ROGUE, UMPQUA	158	103	95	115	90	70	-0.5
KLAMATH	136	94	93	124	61	69	-2.0
LAKE COUNTY, GOOSE LAKE	106	67	89	116	37	44	-0.6
HARNEY	107	78	92	125	60	66	-0.8
NORTH COAST	105	94	n.a	n.a	80	77	-0.4
SOUTH COAST	154	107	n.a	n.a.	141	89	+0.9

n.a. Not available
(1) Percent of normal December 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 December 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 February-April 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 normal temperatures and above-normal precipitation for January-March. Since last summer we have been suggesting that we will experience one or more severe weather events this winter, and we have gotten them! More are expected in the next several months.

ENSO Update (from CPC)

Sea surface temperatures remained warmer than average across most of the equatorial Pacific Ocean during December, although departures from average decreased in all of the Niño index regions during the month. Equatorial ocean surface temperatures greater than +0.5°C (~1°F) above average were found between Indonesia and 170°W and in most of the eastern equatorial Pacific between 140°W and the South American coast. Departures greater than +1°C were found between 160°E and 180°W.

In spite of the slightly warmer-than-average oceanic temperatures, the monthly 850-hPa zonal wind indices, OLR index, 200-hPa zonal wind index, SOI and EQSOI do not indicate warm episode 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 equatorial Pacific.

A majority of the statistical and coupled model forecasts indicate near neutral conditions in the tropical Pacific (Niño 3.4 SST anomalies between -0.5°C and +0.5°C) through March 2004. Thereafter, the forecasts show increasing spread and greater uncertainty, during a time of the year when the skill level of all of the techniques is relatively low.

Snow and Ice Event, December 29-31

The largest snow storm in several years brought significant snowfall totals to most of Oregon in late December. A combination of cold air near the surface, and overrunning moist air from a Pacific weather system, was responsible for the snow. The National Weather Service (NWS) issued the following statement at 8:30 a.m. on 12/29:

"An upper level trough and surface low pressure area moving across the Oregon this morning have combined to pull cold moist air into the forecast area. This has produced areas of heavy snow. Several feet of snow have fallen in the Cascades over the past 24 hours with a foot of snow in the Salem area and 1 to 3 inches so far around the Portland area...heaviest near Oregon City and Wilsonville."

Earlier, NWS had issued warnings for many parts of the state. These were issued at 7:34 a.m.:

"Portland area: A heavy snow warning continues. The snow level has lowered to at or near valley floor this morning. Snow accumulations of 1 to 4 inches can be expected above 200 feet...and at the valley floor one to 3 inches of snow accumulation is likely in some areas before the snow ends later today.

Salem area: The snow level this morning has lowered to near valley floor in some areas. Reports this morning in the Salem area are 4 to 6 inches of new snow with 10 to 12 inches in the higher outlying areas above around 200 feet."

Near Corvallis, the Hyslop Experiment Station reported 3.8 inches of snow as of 8 a.m. This was a new daily record for December 29 (old record was 1.3 inches in 1971, and records go back to 1889), and the largest one-day event since 6" was reported in February, 1993. Even if no additional snow falls this year, 2003's annual total (currently 3.8 inches!) will be the largest since the 5.0 inch total in 1995.

East of the Cascades, snowfall totals were also unusually high. Some of the totals of new snowfall reported for the morning of 12/29 included:

Station	New snow (inches)
Meacham	8.0
Pendleton Airport	4.8
Bend	4.4
Condon	9.0
Elgin	9.0
Madras	8.0
Moro	5.5
Monument	6.0
Sunriver	5.0

Cascade totals were even higher:

Station	New snow (inches)
Government Camp	18.0
Marion Forks	10.0
Howard Prairie Dam	13.4
Odell Lake	7.0

In early January, the snow event turned into a major ice storm. Cold air remained over all of Oregon for the first week of the month. On January 5, a Pacific storm approached the Oregon coast. Rain began to fall in the southern Willamette Valley in the early hours of January 6. As the rain reached the ground, it generally froze on contact with objects (roads, cars, trees, and so on) that had been chilled by the cold temperatures -- the dreaded "freezing rain." Icy roads made driiving hazardous. Many trees were damaged or destroyed by large amounts of ice adhering to branches. Downed power lines (often due to falling trees) caused power outages.

Portland Airport saw many flights cancelled on the evening of January 6 and the morning of the 7th. The following was issued by the airport on January 7:
"Inclement Weather Notice
As of 9:30 a.m. on Wednesday, January 7, 188 flights have been cancelled in and out of Portland International Airport (PDX).
We continue to expect many cancellations, but the status of flights is dependent on the weather and determined by each individual airline. Please check the "Flight Search" Web page for more information, or contact your airline. For a list of airlines and their phone numbers, visit our "Airlines" page.
Airport Way is open, but very slippery from the I-205 interchange to the Terminal. All parking lots are open and the buses which serve the surface lots are running on schedule. Airport MAX, along with the total MAX system, is out of service. Travelers wishing to use public transportation can ride a bus to and from PDX, via the Gateway Transit Center for more information visit the Tri-Met Web site at www.trimet.org."

Roads were a mess. KGW-TV (Portland) reported the following road closures and problems on January 7:
-- I-84 remained closed between Troutdale and Hood River.
-- Highway 20 was closed east of Newport.
-- Oregon State Police required motorists on I-5 to use chains or traction devices between Wilsonville and Jefferson, south of Salem.
-- Motorists were urged to use chains for driving on all Portland-area freeways.
-- One lane of SR 14 was blocked by a snowslide near Bingen and WSDOT crews were trying to limit traffic to only local residents.
-- State Route 14 between Washougal and the Bridge of the Gods was completely closed.
-- Highway 224 remained closed near Carver.
-- Highway 35 south of Hood River was closed to trucks due to the weather.
-- The Astoria Bridge was closed.
-- A stuck car was blocking one lane of I-405 northbound at 4th Avenue.

More next month!

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