Overview

June’s cool, cloudy weather prevailed during the first half of July, but summer began in earnest by mid-month. The second half of July was sunny, warm and dry in most of Oregon.

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 water indicators at the end of the month, by river basin:

n.a. Not available
(1) Percent of normal July 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 July stream flow, from U.S. Geological Survey (USGS)
(5) Percent of normal seasonal stream flow (since Oct. 1), from USGS
(6) Surface Water Supply Index, from NRCS (-4 = very dry, 0 = normal, +4 = very wet)

Forecasts

The Climate Prediction Center’s (CPC) forecasts for August-October appear below. Temperatures for western Oregon are likely to be above normal. Precipitation probabilities suggest an equal chance of below-, near-, and above-normal rainfall.
Oregon Climate Service predicts normal temperatures and below-normal precipitation for the same three-month period.

El Niño update

The Australian Bureau of Meteorology (BOM) suggests that the chances of an El Niño event this year continue to decrease. Their August 3 update states:

Summary: Pacific likely to remain neutral.

Neutral conditions have persisted across the Pacific during the past fortnight, and all the available evidence suggests that this situation will continue for the remainder of the year.

The equatorial Pacific Ocean has continued to cool with most areas now being only marginally warmer than average. There are currently no obvious triggers that would reverse recent trends and boost the level of warmth to an El Niño state. Furthermore, the current patterns of Pacific cloud, wind and subsurface temperatures remain neutral, and the SOI has persisted in small positive values for the second successive month. This is a good sign against El Niño formation, as El Niños are associated with sustained negative SOI values.

Most international models, including the POAMA climate model run at the Bureau of Meteorology, clearly favour neutral conditions in the equatorial Pacific Ocean during the remainder of 2005.

NOAA’s Climate Prediction Center reported on July 7:

Synopsis: ENSO-neutral conditions are expected during the next 3-6 months.

According to CPC (July 21),

“ Sea surface temperatures (SSTs) in the equatorial Pacific are slightly above normal, with some changes from week to week. Subsurface ocean temperatures in the upper layers of the eastern Pacific are also quite close to normal... indicating that neutral ENSO conditions will likely persist for the next few months. There is modest consensus among both statistical and dynamical ENSO prediction models for neutral conditions to prevail through early 2006.”

A Really Hot Summer?
Q. Now that summer is here, I was wondering about which summer was the hottest in western Oregon. I guess it depends on how you define it, but what do you think?

A. When I received this e-mail, the first year that popped into my mind was 1967. It’s a legendary year for several reasons: the longest string of consecutive dry days (78 in a row in the mid-Valley), and a large number of hot days. But just to be safe, I ran the computer program that gives us statistics.

I used data from the local Hyslop Experiment Station, because it’s a long-term station that has seen very little land use change around it, and thus is considered representative of climate trends (locations whose surroundings are changing are often said to have their data “contaminated.”)

1. First, I defined “summer” as July-August only.

2. If you define “hottest summer” as the summer with the highest average temperature, the top five are 1958, 1941, 1917, 1942 and 1967. It’s interesting to see consecutive years on that list. The average temperature uses the daily high and low temperatures and averages them together.

3. On the other hand, if you define “hottest summer” as the summer with the highest average HIGH temperature, the top five are 1917, 1967, 1958, 1919, 1906. This considers only the daily highs and ignores the lows.

4. Or maybe what we care about are “hot days.” Typically, we define a hot day is one that reaches or exceeds 90 degrees. The top five in this category are 1917, 1919, 1967, 1972 and 1958.

5. If all we care about is the hottest day of the year, we’d list 1981 (108 degrees), 1946 (107), 1935 (106), and 1972 (105).

Note that 1967 appears on every list expect the last. So do 1958 and 1917. Those probably rank as my three hottest.

Some interesting things about 1967:

August of 1967 was the hottest month, overall, that was ever recorded here. The average high temperature was 88.9 degrees.

There were 21 days of 90 degrees or more, 16 of those in August.

The temperature never reached 100; the hottest day was 99 degrees.

Here’s a heat wave for you. High temperatures, beginning August 10, 1967: 99, 85, 90, 94, 96, 95, 96, 96, 95, 95, 97

A Wild Winter Shaping Up?
August 4, 2005

The Atlantic Ocean is active. Tropical Storm Harvey is the eighth named storm this season. This week prominent hurricane forecaster Bill Gray of Colorado State University predicted that there will be 20 named storms this year, 10 of which will be hurricanes. A “named storm” is a tropical storm or a hurricane, with sustained winds exceeding 34 mph (storm) or 74 mph (hurricane). The years with the most named storms were 1933 (21) and 1995 (19). Note that second year: 1995.

The Indian Ocean is active. The monsoon season has spread abundant rains into south Asia, culminating in the storm last week that dumped “an unprecedented deluge of up to 37 inches of rain -- the heaviest rainfall since India began keeping weather records in 1846. Much of it came over a few hours, transforming roads into fierce rivers and causing landslides that buried dozens of people and cut off villages.” (UPI).

The Pacific is rather quiet now. But watch out!

Forecasters are suggesting that this year’s “slight El Niño” conditions in the tropical Pacific will give way to a La Niña by late fall, and that suggests some pretty profound impacts for folks on or near the Pacific, such as:

1. Increased typhoons in the western Pacific
2. Drought in the southwestern U.S.
3. Wet, windy winter weather (the four W’s) for the Northwest

Both El Niño and La Niña involve sea surface temperatures in the tropical Pacific. On average, temperatures in the eastern Pacific (off South America) are rather cool (roughly 70 degrees F), while temperatures in the western region (near Indonesia) are much warmer (mid- to upper 80s). During an El Niño, the eastern waters warm up substantially, while the western waters cool, so the difference in temperature between east and west becomes rather small. El Niño produces climate extremes throughout the world; in the Northwest, our driest, mildest winters occur during El Niño events.

But sometimes the tables are turned and the cool eastern Pacific gets even cooler than average, while the warm western Pacific gets even warmer; in this case the large discrepancy in water across the Pacific becomes huge. We call this “La Niña.” Like her brother, La Niña produces climate extremes worldwide, and these are generally just opposite to El Niño’s. In the Northwest, our coolest, wettest winters are most likely to occur during La Niña conditions.

The reason is twofold. First, the jet stream is over us much of the time. The “jet” is the zone of strongest winds in the upper atmosphere, and it marks the approximate path of our winter storms; thus, the jet stream path is often called the “storm track.” Second, we’re more likely to receive the warm, wet, “subtropical jet streams” (commonly known as “Pineapple Express”) which are responsible for most of our winter flood events.

Both the Climate Prediction Center and the Climate Diagnostics Center are predicting major shifts toward La Niña in the coming months. Ominously, if the predictions are correct there will be a close match with the fall of 1995, that other bust hurricane year.

Ominous because the winter of 1995-96 was extreme and memorable: three major floods, a major wind storm, and two ice storms. I wrote about this last month, and the resemblance of this year to 1995 gets stronger and stronger.

This would be a really good time to weatherproof your house, before “ominous” turns into “wild and crazy.”

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

Sara Joos, Student Assistant

Sean Daly, Student Assistant

Kirk Borgerding, Undergraduate Assistant

Kelsey Kuykendall, Undergraduate 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