An upper-level low pressure system along the Pacific Northwest coast created a push of marine air across the Cascades Mountains. The following figure shows the center of a low-pressure system located along the Washington coast. This location is ideal for creating lift along the east slopes of the Washington Cascades.

A cold front from the west brought marine air across the Cascades which converged with easterly flow flowing up-canyon on the east side of the Cascades. These converging surface winds, along with a moist, unstable air mass located east of the Cascades, helped anchor thunderstorms over elevated terrain along the Yakima River valley in southeast Kittitas County. Between about 2 and 3 pm a cluster of southward moving thunderstorms merged and stalled along and near Manastash Ridge. Over the next hour the thunderstorm remained anchored in place over Manastash ridge; an automated rain gauge on the northeast flank reported 2.99 inches. NWS Doppler Radar estimates showed up to 3.2 inches of rain in one hour across the red-shaded area in the figure below. An orchard on the north side of Manastash ridge reported small hail up to 5 inches deep and several other orchards reported fruit damage. The heavy rain saturated the ground allowing soil and rocks along steep slopes and ravines to flow and slide downhill. Rock and mudslides covered or washed out portions of a 17-mile stretch of Highway 821 (Canyon Road) between Yakima and Ellensburg. The following map outlines (red box) the area where the largest landslides occurred.

In a paper published in Washington Geology, Professor Martin Kaatz (Central Washington University) described one section of the landslides:

debris flows over-topped ditches and damaged irrigation canals and roads.roadside ditches overflowed, piling debris on roads.After the storm a landscape of scoured and scarred channels remained, commonly eroded to bedrockFresh percussion marks on rocks testified to the force with which some of the entrained rocks struck one anothersome flows had depths greater than 6 ft.

Ravines draining westward from the southwest flank of Manstash Ridge directly into the Yakima River Canyon discharged rocky debris that quickly buried portions of State Route (SR) 821. Major debris deposits covered SR 821 in eight separate places between mileposts 19 and 21Six reached well into the river. One of these buried the highway with debris more than 15 feet deep and continued more than 60% of the way across the river channel. Several motorists and a freight train were trapped by debris both north and south of their location, and close to 200 people had to be evacuated via boats on the Yakima River.

 

Following a month-long dry period, a cold front crossing the Columbia Basin on the morning of September 25, 1999 created strong winds gusting in the 50 to 60 mph range. The cold front produced strong wind gusts but almost no rain. The combination of these conditions led to clouds of blowing dust that in some locations changed conditions suddenly from clear skies to zero visibility. The following photograph taken on August, 12, 2005, illustrates how conditions can suddenly change from clear to zero visibility.


Figure 4 A dust cloud approaches highway 395 in Washington on Aug. 12, 2005.

Around 9:30 AM PST, blowing dust led to several chain reaction accidents on Interstate 84 along Reith Ridge, nine miles west of Pendleton. Six people died in the accidents and dozens were injured. A seventh fatality occurred later due to injuries incurred that day. More than 50 automobiles and semi-tractor trailer trucks on both the east and westbound lanes of I-84 were involved in accidents.


Figure 5 Dust and smoke obscure the scene as two motorists aid a seriously injured victim of the massive I-84 pileup on Sept. 25, 1999. (Photo and caption courtesy of East Oregonian.)

The Interstate was closed for 10 hours. A separate accident with a fatality occurred at 10:48 AM PST on I-84 at exit 216, six miles east of Pendleton. During the day, the Oregon Department of Transportation also closed State Highways 11 and 37 due to blowing dust.

 

 

 

A high-pressure ridge over the western U.S created a dangerous heat wave during July 2002. This heat wave was impressive because records were set for consecutive days of extreme temperatures across a broad area of eastern Oregon and Washington. Seneca, OR recorded 104 deg F on July 12, an all-time record high. Hanford, WA tied their all-time record high temperature of 113 deg F on July 13.
Enterprise, OR experienced their warmest 4-day stretch on record with high temperatures of 104, 105, 107, and 108 from July 10-13, respectively. Monument, OR experienced eight consecutive days greater than 99 deg F, from July 11-18. It was also Monuments warmest ever two-day stretch with high temperatures of 115 and 114 on July 12 and 13.
John Day, OR reported 110 deg F on July 12, their second highest temperature recorded, only 2 degrees less than their all-time record. John Day had their warmest overnight temperature on record, 70 degrees, on July 13. John Day also experienced a record four days in a row above 104 deg F: 109, 110, 109 and 105 deg F on July 11-14 respectively. The record high at Prosser, WA was set on July 14 and their second highest maximum temperature was set on July 13. Prosser had high temperatures of 107, 110, 111 on July 12-14, respectively, their warmest three-day stretch on record. The following tables list the five highest maximum temperatures recorded in John Day and in Prosser. Both lists are dominated by the heat wave of July 2002.
John Day, OR Top Five Maximum Temperatures on Record

Prosser, WA Top 5 Maximum Temperatures on Record

The long-duration high-pressure ridge over the western U.S. responsible for the widespread heat is shown next. Each chart shows the weather pattern at 5 pm PDT from July 9-13:

In addition to the extreme heat, two lightning-caused fires began on July 12. The Monument Complex burned 16,063 acres in Grant and Baker Counties and the Malheur Complex burned 19,367 acres in Grant County. Both fires were not controlled until 38 days later on August 19, 2002.

On Sunday afternoon, December 28, 2003, an Arctic cold front moved south out of Canada into the Columbia Basin. It reached as far as the southern border of Oregon overnight. Temperatures were generally in the 30s across eastern Washington and Oregon before the front arrived and then dropped into the 20s after the frontal passage. Throughout the 24-hour event, northerly surface flow out of Canada continued to reinforce this cool air. Meanwhile, a strong low-pressure weather system brought a Pineapple Express of moist sub-tropical air across the Pacific Ocean to the Pacific Northwest. Moist, warmer air was forced to rise over the dome of cold air in place across the interior Pacific Northwest. These conditions resulted in a long period of snow from the afternoon of the 28th through the afternoon of the 29th. The following satellite image shows the plume of upper-atmospheric water vapor (blue areas indicate higher water vapor) moving from the Pacific Ocean northeastward across the Pacific Northwest. Surface observations are also shown.

The weather system created a band of stronger rising motion over eastern Oregon which weakened somewhat as it moved northeastward into eastern Washington. Furthermore, during the event stronger upslope flow occurred along the Oregon foothills of the Blue Mountains and the Oregon portion of the Blue Mountains. As a result heavier snow amounts were observed across the Oregon foothills compared to the Washington foothills. For example, the Pendleton airport received 9.5 inches of snow while the Walla Walla airport received 5 inches.

Here are some of the larger storm-total snow amounts from various locations in the Pendleton forecast area:

John Day, OR received 9 inches of snow, the most on record for a 24-hour period. Seneca received 12 inches and Ukiah reported 15 inches; the second highest amounts on record over a 24-hour period for these two stations. Condon, OR received 15 inches and Meacham, OR reported 18 inches, the third highest amounts on record over a 24-hour period for these two stations. Two flights from the Redmond airport were canceled due to heavy snow.

 

Two wildfires, the Booth and the Bear Butte, started separately on August 19 about 15 miles west and northwest of Sisters, OR. Red areas on this map show the original locations of the two fires.

 

These two fires grew to become the B&B Complex, which burned 90, 769 acres over 39 days before it was contained on September 26, 2003. This map shows the approximate area burned (see red shading).


Figure 6 Topography map showing the area burned by the B&B Complex wildfire.

The next photo, taken by a member of the team fighting the fires, shows a high intensity burn on August 21, 2003. A heat low is an area of low pressure created by solar heating of the surface of the earth. The heat low moved from the west to the east side of the cascades which increased the heat and wind and led to extreme burn conditions.



The next figure is a visible satellite image showing the smoke plume created by the B&B complex on September 4, 2003. On this day the fire spread rapidly and Camp Sherman, OR was evacuated. The red spots indicate locations where the satellite detected heat.

Of the nearly 91,000 acres of the B&B complex, about 10% (8,865 acres) of the total burned at high intensity and an additional 30% burned at moderate intensity. A moderate intensity burn scorches the tops of trees and burns all the vegetation beneath; a high intensity burn consumes the trees and often leaves only charred ground behind. Over the course of 39-days fighting the B&B complex, 1,449 personnel were employed, and the total cost of the fire was over 33 million dollars.

On the afternoon and early evening of Friday, May 19th 2006 an extreme severe weather outbreak occurred across portions of Northern Oregon and Southeastern Washington. The storms formed in association with an upper level disturbance moving northward across the area. The region was in the midst of an early season heat wave with afternoon temperatures well into the 90s for several days leading up to the event. The hot temperatures coupled with abundant low level moisture (surface dewpoints in the 50s) led to an unusually unstable air mass for the Pacific Northwest. By early afternoon, thunderstorms developed over Jefferson County Oregon and became severe when entering Wasco County. The storms produced golf ball size hail in Maupin, OR and north of Ione, OR. As the storms moved northeast across Oregon they accelerated and took on bow shapes. These bow-shaped storms produced damaging winds through portions of Sherman, Gilliam, Morrow, and Umatilla Counties in Oregon and Benton, Franklin, Walla Walla, and Columbia Counties in Washington. This image shows a radar display of thunderstorms (the red and purple areas) with a bow shape as they approach the Tri-Cities, WA from the southwest.

 

The following photograph (courtesy of the Pacific Northwest National Laboratory Hanford Meteorological Station) shows the thunderstorms approaching the Tri cities.



Throughout the path of the storms, peak wind gusts were 60-75 mph, however there were at least 3 areas of winds exceeding 80 mph. The first area was 10-12 miles southwest of Boardman where a measured wind gust to 117 mph was recorded. The second area occurred at the Umatilla Chemical Depot in extreme northwest Umatilla County where peak wind gusts were measured at 86 mph. The third area of enhanced winds was estimated by a National Weather Service survey team near 90 mph about 5 miles east of Burbank in Walla Walla County.

These winds near 90 mph east of Burbank, WA, felled a large swath of Poplar trees at a tree farm; a portion of the tree fall is shown in this aerial photograph.

 

 

On January 4, 2008, a strong low-pressure system created areas of heavy precipitation and/or damaging winds at several areas in the western United States. The central sea-level pressure offshore was around 958 mb (28.29 inches of mercury), similar to the surface low of a category 2 hurricane. The Sierra Nevada Mountains in California were experiencing extreme blizzard conditions at the time of the infrared satellite image shown below (10 am PST on January 4).

 

On the morning of January 4th, the low-pressure system was strengthening offshore of the Pacific Northwest coast. A very strong low-level jet of southerly wind at around 10,000 feet MSL was crossing the Cascades into eastern Oregon.
For eastern Oregon and southeast Washington, the primary impact of the storm was damaging pre-frontal winds. A somewhat unusual aspect of this storm is that the strongest winds were not observed at higher elevations. Observations in the WFO Pendleton forecast area at elevations above 5000 feet reported peak wind gusts in the 40 to 60 mph range. (Round Mountain in central Oregon at elevation 5900 feet was the exception with a single gust to 70 mph.) Instead, the strongest winds were observed at relatively lower elevations. This is one indication that local terrain effects played an important role in the acceleration of wind during this event. The following table shows selected peak wind gusts from January 4.

 

Terrain effects were especially important during this event, and for the northern foothills of the Blue Mountains, local wind acceleration was created by a downslope wind storm. Downslope windstorms create a zone of higher wind speeds near the base of a mountain barrier on the downwind side. (These types of wind storms are more common along the front range of the Rocky Mountains, for example near Boulder, CO.) On January 4th the greatest density of damage in the Pendleton forecast area was from downslope winds over an area from Adams, Oregon, northeast into the Walla Walla Valley. The Veterans Affair Medical Center in Walla Walla, WA reported 28 structures, 4 vehicles and 50 trees damaged just on their campus alone. Over 5 trucks rolled over on I-84 on Cabbage Hill, and two trucks rolled-over on Highway 11 between Adams and Milton-Freewater (pictured below)


In summary, the January 4 wind storm in eastern Oregon and southeast Washington was attributable to a powerful low-pressure system leading to record low sea-level pressures, along with the interaction of a very strong low-level jet and local complex terrain. A downslope windstorm created a zone of damaging winds along the northern foothills of the Blue Mountains. Emergency managers estimate 3.9 million dollars damage in Umatilla County and 4.9 million in Walla Walla County. In the Walla Walla valley, 4 in 10 homes received damage from the storm. Much of the damage was due to falling trees, such as the one in this picture.

 

Cold arctic air that spread across the Columbia Basin in mid-January had modified over time and even rose above freezing at some mid-elevation locations. However, sub-freezing temperature air remained trapped in the Columbia Basin through the end of the month. This cold pool of air was in place as a warm front associated with a deep low-pressure system off the California coast moved across Oregon and Washington on January 26. The warm moist air from the California system moved northeastward over the cold air trapped in the Columbia Basin and led to freezing rain. A cold front then crossed the region on January 27. The infrared satellite image below shows a significant fetch of Pacific moisture ahead of the cold front as it merged with the warm front across the Columbia Basin the morning of the 27th.



Precipitation primarily fell as freezing rain and sleet across the Columbia River basin on January 26 then changed to heavy snow on January 27. Gusts up to 65 mph occurred in the mountains creating blizzard conditions at times especially across the Washington portion of the Blue Mountains and in Wallowa County. Joseph, OR reported a peak gust of 68 mph on the 26th and 68 mph on the 27th. The Ladd and Pyles Canyons area and the southern Grande Ronde Valley also experienced blizzard conditions at times. Union, OR recorded a peak gust of 57 mph during the event, and the La Grande airport, 51 mph.
I-84 through the Columbia River Gorge was closed between The Dalles and Corbett, OR, due to freezing rain the first day and because of snow on the second. This storm capped off 6 consecutive days of snow across the Washington Cascade mountains, and on both the 26th and 27th there were numerous avalanches in the mountains between Easton and Snoqualmie Pass.
The following storm reports were received on January 26.

The following are several storm reports received on January 27.

 

May 6, 2009 was a cool, cloudy day, the kind of day not typically conducive to severe thunderstorms. However, an isolated thunderstorm rapidly strengthened as it moved under a break in the clouds (which provided surface heat). As the thunderstorm strengthened, strong winds above the surface provided an environment in which the storm could rotate as a supercell thunderstorm. The storm moved eastward across Umatilla county just south of the Washington/Oregon border. Because the air mass instability was not strong, the thunderstorm was not tall compared to most severe storms. However, the strong winds aloft caused the storms updraft to be strongly tilted, a situation that allowed hail to grow large and is also conducive to tornado development. Hail up to 3/4 inch size covered the ground in Adams, OR and along highway 11 near Adams, and up to nickel-size hail covered the ground in Athena, OR. Up to golf ball size hail driven by strong thunderstorm winds punched holes in vinyl siding 4 miles southeast of Adams.
Four miles southeast of Adams a tornado traveled at least 1.6 miles due east towards the Blue Mountains. A National Weather Service survey team reported:

A TEAM FROM THE NATIONAL WEATHER SERVICE INVESTIGATED DAMAGE THAT
OCCURRED WEDNESDAY EVENING FROM A SUPERCELL THUNDERSTORM IN
NORTHEAST UMATILLA COUNTY. IT WAS DETERMINED THAT THE MOST INTENSE
DAMAGE OCCURRED FROM A TORNADO OF EF1 INTENSITY WITH ESTIMATED PEAK
WINDS OF 90 MPH. SOME MINOR STRAIGHT LINE WIND DAMAGE ALSO OCCURRED
ON THE PERIPHERY OF THE TORNADO.

THE TORNADO FIRST TOUCHED DOWN IN AN OPEN FIELD 4 MILES SOUTHEAST OF
ADAMS NEAR THE INTERSECTION OF TUBBS AND HOMILY ROADS. A NARROW BUT
WELL DEFINED PATH WITH EMBEDDED CYCLONIC SEMICIRCLES WAS EVIDENT IN
THE FIELD. THE TORNADO TRAVELED JUST NORTH OF DUE EAST AND STRUCK A
RANCH. THIS IS WHERE THE MOST DAMAGE OCCURRED. A 100 FOOT SECTION OF
A METAL ROOF FROM A WORKSHOP WAS TORN OFF AND THROWN...WITH SOME
PIECES LOFTED 1/2 MILE DOWNWIND. 50 GALLON DRUMS WERE ALSO TOSSED UP
TO 1/4 MILE. A TREE WAS UPROOTED AND NUMEROUS TREE LIMBS WERE DOWN.
ONE TREE LIMB WAS IMPLANTED SIX INCHES INTO THE GROUND. A LARGE
WOODEN PLANK WAS IMPALED INTO THE SIDE OF A WOODEN SHED.

THE TORNADO APPEARS TO HAVE DISSIPATED JUST EAST OF THE RANCH IN AN
OPEN FIELD ABOUT 5 MILES EAST SOUTHEAST OF ADAMS. TOTAL PATH LENGTH
WAS 1.6 MILES AND PATH WIDTH 40 YARDS.

The following photo shows damage caused by the tornado including a large wooden plank impaled into the side of a wooden shed.

The following radar imagery shows the characteristic hook echo signature typical of tornadic thunderstorms:



The hook echo signature is created by precipitation held aloft that wraps around the mid-level rotating mesocylone of the thunderstorm. The mesocyclone has counterclockwise winds and thus the radar reflectivity signature of a hook echo has a cyclonically shaped hook (see especially the upper-left quadrant above). The area free from reflectivity inside the hook is the updraft and inflow region of the thunderstorm. Not all hook echoes storms produce tornados, but in this case the hook echo radar signatures aligned precisely on the map with the path of the tornado.