Overview

The first half of October was a continuation of the last half of September: unusually cool and wet. But after the 20th the weather changed significantly, and the last 10 days were generally dry. The majority of stations reported below-average temperatures for the month, while precipitation was above average for all but a few stations.

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 precipitation totals throughout the state are listed. Figure 1 is a map showing the percentage of normal precipitation statewide for the month.

Basin Summary

Here is a summary of water indicators at the end of the month, by river basin:

*SWSI are as of October 1, 2007

n.a. Not available
(1) Percent of normal October precipitation, from NOAA Cooperative sites
(2) Percent of normal October precipitation, from Natural Resources Conservation Service (NRCS) SNOTEL sites
(3) Percent of normal October stream flow, from U.S. Geological Survey (USGS)
(4) 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. There is a higher likelihood of above-average precipitation in Oregon, and equal chances of above-, near-, and below-average temperatures.

Oregon Climate Service predicts normal temperatures and above-normal precipitation for the next three months.

ENSO Update

Australia Bureau of Meteorology (BOM), November 14, 2007

A La Niña event is well established in the Pacific, with further intensification evident during the past three weeks. The main characteristics of the event are colder than average temperatures along the equator both on and below the surface, stronger than average Trade Winds and reduced cloudiness. The Southern Oscillation Index (SOI) is the one ENSO indicator that is yet to show a typical La Niña signal: it remains neutral at about +6 for the past 30 days. Computer models forecast the La Niña to last until at least until the southern autumn of 2008.

Ocean temperatures immediately to the north and northwest of Australia (to near Sumatra) have been warming during October and November, although they remain somewhat cooler than would normally be observed during a La Niña. This would suggest an increased chance of a more typical La Niña rainfall pattern over Australia over the coming months.

NOAA’s Climate Prediction Center (CPC) agreed, saying (November 8):

La Niña continued to strengthen during October 2007, as equatorial sea surface temperature (SST) anomalies became increasingly negative from 170°E to the South American coast. The latest 4-week analysis shows the largest SST departures (-2ºC to -3ºC) located between 140oW and the South American coast, with departures of -0.5°C to -1°C observed near the Date Line (Fig. 2). All of the Niño region indices, except for Niño-4, remained lower than -1.0°C (Fig. 3) indicating that La Niña is approaching moderate-strength (3-month running mean value of the Niño 3.4 index below -1.0°C). The recent SST forecasts (dynamical and statistical models) for the Niño 3.4 region indicate a continuation of La Niña into early 2008.

A Big October Wind Event
George H. Taylor, November, 2007

Two weeks ago we had a near miss when a strong, fast-moving storm threatened to give us a rare October high-wind event. That one missed. Last week we had another, and this time it didn’t miss.

A week ago today the predictive models began suggesting that a major storm would be developing about Thursday. They also indicated that some leftover moisture from a Pacific typhoon (Lingling) would merge with the storm, causing it to intensify. The models were correct.

Thursday morning the winds began to increase along the coast. Highway 20 east of Newport was closed for awhile due to fallen trees on the roadway. Low-elevation winds near the coast routinely topped 60 mph, with the highest an 73 mph gust on the Yaquina Bay Bridge. Mt. Hebo, in the Coast Range, reached 83 mph.

As I mentioned, this was a rare event for October; we seldom get high wind events this early in the year. Of course, there was the legendary Columbus Day Storm (October 12, 1962), which stands head and shoulders above every other local wind storm, regardless of the time of year. But that storm was a FREAK! If the Columbus Day Storm were an ocean wave, it would be 90 feet tall. If it were a pumpkin, it would weigh 2,000 pounds. We may never see a storm like that again.

To find out how this storm compared with other (non-freaky) October storms, I consulted Wolf Read. Wolf is an OSU grad who moved away for awhile but is back in town temporarily. He is helping me write a paper on a history of big Northwest wind storms (he will be lead author). Wolf loves studying wind storms. He also loves studying trees. And he has combined these passions into a true expertise in “wind throw” events – wind storms that are so strong that they knock down trees. Wolf knows more about wind throw than anyone I know.

So when I asked him to compare the recent wind storm with other October blows, it didn’t take him long to come up with an answer: it was the biggest October wind storm in 25 years!

Wolf provided me with a list of other October wind storms

October 26, 1950: An intense 969 mb low tracks northward offshore, followed by a second high-wind-generating low that swept in from the west and across Vancouver Island. Winds were even higher inland than on the coast (Portland 66 mph gust, Salem 47, compared with 60 at Astoria and 55 at Newport).

October 12, 1962: The Freak. An intense 960 mb low tracked up the coast 50-75 miles offshore. Gusts: 145 mph at Cape Blanco, 138 at Newport, 127 at Corvallis, and an estimated 170 mph at Mt. Hebo (the anemometer disintegrated at 144). Hard to believe!

October 2, 1967: A deep (~977 mb) low moved over Astoria and tracked just north of Portland. Peak gusts 115 mph at Newport, 90 at Bandon, 77 at Corvallis and 78 at Portland. Winds in Washington comparatively light, due to being on the north side of the low center.

October 22, 1982: A strong (~984 mb) low moved into Vancouver Island with a well-developed cold front. Gusts: in excess of 90 mph at exposed headlands on the Oregon coast, 55 mph at Bellingham, 70 mph at Cape Flattery, WA. Many trees and powerlines went down in western Washington and on the Oregon coast.

October 18, 2007: A strong (~980 mb) low moved into Vancouver Island with weakly defined frontal systems and a relatively warm core. Tropical moisture helped the system intensify. Peak gusts:

40 mph Sexton Summit, OR (05:56).
55 mph North Bend, OR (08:35).
60 mph Astoria, OR (11:56).
64 mph Newport, OR (07:32).
68 mph Humbug Mt. St. Park, near Port Orford, OR (12:19, el 50 ft).
69 mph Garibaldi, OR (09:40).
70 mph Florence (Siuslaw Jetty), OR (08:35, with 59 mph avg wnd).
70 mph Lincoln City, OR (08:02).
73 mph Yaquina Bridge, Newport, OR (09:19 & 09:34).
83 mph Mt. Hebo, OR (10:49).

Not the biggest, but the biggest in a long time. It’s fun to watch history being made, isn’t it?

And it’s also great to have someone who understands history to put these events into perspective. That’s a big part of what I do.

And when it comes to wind events, there’s someone who does it much better: Wolf Read. I’m glad he was here to lend perspective and dig up statistics.