Overview

May was a mild month throughput Oregon with overall near-normal precipitation. Several very powerful thunderstorms rumbled across eastern Oregon (see below) as a result of warm, humid air advecting into Oregon from the southwest. Water conditions continue to be excellent due to wet winter conditions and a remarkable snow pack. It has been a good year for water!

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 May 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 May 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 forecast for June-August (see maps below) suggests a higher-than average chance of above-normal temperatures. Precipitation odds slightly favor drier than normal conditions in eastern Oregon. Oregon Climate Service predicts average temperatures and precipitation during those months.

Water supply should deliver ‘banner year for irrigation’
Kathleen Ellyn, Silverton Appeal Tribune, June 7, 2006

Farmers and ranchers in Oregon shouldn’t worry about having enough water for irrigation this summer. Snowpack, soil moisture, stream flows and reservoir storage — key indicators of the statewide water picture — all point to a plentiful supply for agriculture and other water uses

“Water supplies are above normal all over the state, and reservoir levels are excellent at this time,” said Jim Johnson, the land-use and water-planning coordinator for the Oregon Department of Agriculture. “It looks like a banner year for irrigation in Oregon.”

Oregon does not normally receive the summer rain that the Midwest and other parts of the country get. Irrigation provides water necessary for much of the state’s agriculture during the growing season.

“Oregon has a reputation for being a wet state,” Johnson said. “However, irrigation is such a key in the summer months. Nearly 45 percent of all farms and ranches in the state do some type of irrigation totaling about 1.9 million acres.”

The sunny outlook for the summer is because of the cloudy, wet days of winter earlier this year. By December, the statewide snowpack in the mountains was 108 percent of average for that time of year. By mid-December, as the snow kept falling, that increased to 139 percent of average — the best statewide average of all Western states. As winter continued, the snowpack proceeded to build. Despite a dry February, the excellent conditions persisted as Oregon recorded above-average snowfall in March.

A Major Northeast Oregon – Southeast Washington Storm
May 19, 2006
George H. Taylor

Two weeks ago we had an amazing weather event in Oregon, with the strongest winds in over a decade. And I almost missed it.

The week of May 15 was a remarkable one. Early in the week we had an early heat wave, with a record-setting 93 degrees on the afternoon of the 15th. That day was also unusually humid, and I wrote about it in my last column.

But later in the week things really changed. A cool, moist storm system approached from the west, ending the heat wave. On the 18th, the afternoon high was 85 degrees. The next day, under the influence of the storm, temperatures only reached 67. Such big drops are not uncommon here during the warm season.

But east of the Cascades something very uncommon was taking place. As the storm approached, air moved into central and eastern Oregon from the south (as it usually does in advance of a storm). Warm, moist air from northern California (and offshore) mingled with dry eastern Oregon air and set off some big thunderstorms. I remember seeing the radar maps and thinking “Hmmm…some big storms over there.” Little did I know!

The thunderstorms on May 19 began forming in early afternoon over north central Oregon, east of The Dalles. Gradually they became stronger and stronger as more warm air was fed in. By 4 p.m. they had reached “severe” proportions.

Observers in Boardman were astonished to see a tornado approaching at around 4:00. Crossing farmlands south of the town, the twister snapped 31 power poles, overturned a dozen large circular irrigation systems, and carried several 1,300 pound hay bales 80 feet in the air. Hail from the storm destroyed 3,000 acres of crops (5 square miles!). Not far away, a tree farm (hybrid Poplars grown for paper pulp) sustained significant damage.

Approaching Boardman, the tornado passed very near the coal plant, causing extensive damage. The anemometer at the plant recorded sustained winds of 102 mph and a peak gust of 117 – the strongest measured wind in Oregon since the December, 1995 storm (which had a peak gust of 119 mph at Sea Lion Caves). 1.75 inches of rain fell in a very short period of time.

As it moved east, the tornado passed over I-84. A traveler watched in horror as a large semi truck was blown off the road. The witness escaped with only a bad scare.

To the east, security cameras at the Umatilla Weapons Depot captured the tornado on video. There was moderate damage to some buildings, and many trees downed. A wind gust reached 82 mph.

At that point, the tornado seems to have dissipated, but the thunderstorm that spawned it continued. Many observers reported hail, heavy rain, and strong winds in Oregon as well as southern Washington. A long-time observer in Benton County, Washington reported 60 mph winds, large hail, and “the heaviest downpour I can remember.” Others reported dime-sized hail or larger, lightning and thunder.

Mark Nelsen of KOIN-TV in Portland forwarded me a summary of “weather spotter” reports; if he hadn’t, I would have known very little about the storm. Since official weather stations in eastern Oregon are rather sparse, volunteer weather observers can be the difference between getting good information about a storm or missing it entirely. Fortunately, in this case we had solid reports and have a good picture of a remarkable storm.

Below are some of the spotter reports issued by the National Weather Service.

0400 PM     TSTM WND GST     BOARDMAN                45.84N 119.70W
 05/19/2006  M117 MPH         MORROW             OR   COUNTY OFFICIAL
             MEASURED AT COAL PLANT 102G117 MPH. EXTENSIVE DAMAGE
             AROUND PLANT.
 
400 PM     TORNADO          10 SW BOARDMAN          45.74N 119.85W
 05/19/2006                   MORROW             OR   PUBLIC         
             POSSIBLE TORNADO SNAPPED 31 POWER POLES OVERTURNED 12
             CIRCLE IRRIGATION SYSTEMS AND THREW SEVERAL 1300 LB HAY
             BAILS 80 FEET. HAIL DESTROYED 3000 ACRES OF CROPS. OWNER
             OF FARM ESTIMATES DAMAGE AT 1 MILLION.
 
 0400 PM     TSTM WND GST     N PROSSER               46.21N 119.77W
 05/19/2006  E56.00 MPH       BENTON             WA   AMATEUR RADIO   
             WIND GUST TO 56 MPH BETWEEN 4 AND 5 PM.
 
0400 PM     HAIL             10 SW BOARDMAN          45.74N 119.85W
 05/19/2006  E1.75 INCH       MORROW             OR   UTILITY COMPANY
             AT COAL PLANT
 
 0405 PM     HEAVY RAIN       N BOARDMAN              45.84N 119.70W
 05/19/2006  U0.00 INCH       MORROW             OR   TRAINED SPOTTER
             VERY HEAVY RAIN WITH VISIBILITY DOWN TO 1/8 MI. NO
             RAINGAGE. PEA SIZED HAIL AND WIND GUSTS TO 40 MPH.
 
 0405 PM     HEAVY RAIN       8 SW BOARDMAN           45.74N 119.80W
 05/19/2006  U0.00 INCH       MORROW             OR   TRAINED SPOTTER
             VERY HEAVY RAIN REPORTED ALONG WITH DIME SIZED HAIL AND
             WINDS IN EXCESS OF 40 MPH.
 
 0405 PM     TORNADO          2 E BOARDMAN            45.84N 119.66W
 05/19/2006                   MORROW             OR   PUBLIC         
             POSSIBLE TORNADO WITNESSED BY TRAVELER. FUNNEL CAME HALF
             WAY TO THE GROUND WITH DEBRIS. TRACTOR TRAILER BLOWN OFF
             I-84.
 
 0410 PM     TSTM WND GST     2 SW IRRIGON            45.88N 119.52W
 05/19/2006  M69.00 MPH       MORROW             OR   MESONET         
             SUSTAINED WIND 36 MPH WITH GUST TO 69 MPH.
 
 0414 PM     TORNADO          6 NW HERMISTON          45.89N 119.37W
 05/19/2006                   UMATILLA           OR   OTHER FEDERAL   
             POSSIBLE TORNADO AT THE UMATILLA DEPOT. DAMAGE TO
             BUILDINGS AND TREES DOWN. CAPTURED ON VIDEO BY SECURITY
             CAMERAS. POSSIBLE TORNADO MAY HAVE OCCURRED IN BOTH
             MORROW AND UMATILLA COUNTIES.