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Why Not Here? It’s Time To Explain.

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Bermuda High air circulation | USA Today.com
Bermuda High air circulation | USA Today.com

Most people, especially native Oregonians, brag about all of the things Oregon has but in this discussion I will explain why all of the good things Oregon has can exist and the mechanisms that keep away the majority of the bad things that most of the rest of the US must endure.

Nature’s largest weather phenomenon the hurricane is where I will start. You will see what fuels these massive storms and what helps to control their movements. We need to look at the overall air circulation surrounding the North American continent.

The “Bermuda High” sits over the North Atlantic Ocean and with its clockwise rotation spins the airflow around to the east and then swings it to the southwest over Northeast South America, northwest into the Gulf of Mexico, then northeastward toward the US East Coast hugging the coast and continuing along the Southeast Coast of Canada.

Pacific High air circulation (shows sea level pressures) | USAToday.com
Pacific High air circulation (shows sea levelpressures)
| USAToday.com

Another High Pressure Center sits over the North Pacific Ocean and is called the “Pacific High.” Its clockwise circulation moves the airflow from the Northwest to the South and Southeast parallel to the West Coast of the US. If you take a look at these two Summer-time High Pressure centers you will see that the airflow would send hurricanes on the Atlantic side into the Gulf of Mexico and up the East Coast predominately. The airflow in the West also has the effect of keeping hurricanes moving westward away from the West Coast.

The Jet Stream has two branches that can cross the US. The Polar Jet Stream to the North bringing down colder air from the North and pushing it across the US and the Subtropical Jet Stream to the South which brings in warmer moist air and pushes it across the US. They help steer the surface storms across the North American continent. Their positions help determine whether we have surface storms moving through the Pacific Northwest.

There is another force that helps control hurricane development and the basic direction in which hurricanes travel. That force is sea surface currents. There is a basic pattern to the major ocean currents that effect the North American Continent. The most important thing to notice is how the currents flow in such a way to move hurricanes away from the Pacific Northwest.

Structure of a tropical cyclone, High pressure above returns airflow down
Structure of a tropical cyclone (High pressure above returns airflow down) | Compare Infobase Limited

Next we need to look at where hurricanes form. Many disturbances develop over Western Africa and move westward over the Atlantic Ocean. They start out as tropical waves and once they move over the ocean they can continue to grow as long as the water temperature is 85 degrees F or warmer. Also, there must be high pressure aloft to keep a cap over the tropical cyclone to force air back down into it. They then can move through the islands and swing more to the north into the Gulf of Mexico or along the US east coast. Occasionally one will cross Central America and end up in the Pacific Ocean where, if it has gained tropical storm status, it will be given a new name. Storms that develop in the eastern Pacific get pushed primarily to the West and don’t make it anywhere near Oregon. That briefly explains why hurricanes stay away from us.

Damage in Corvallis due to Columbus Day storm | OSU Archives
Damage in Corvallis due to Columbus Day storm |
OSU Archives

There was one remnant of a former Typhoon (Western and Central Pacific hurricane) that did hit Oregon with devastating effects and that was the Columbus Day storm of 1962. It was a dead Typhoon that came all the way across the Pacific Ocean and combined with a Gulf of Alaska storm and smashed through the Pacific Northwest. As many as 46 deaths and hundreds of injuries were attributed to the storm which produced wind gusts measured to 145 mph. It was the second deadliest storm in Oregon history according to Kathie Dello, director of the Oregon Climate Service at Oregon State University.

The continental US has the dubious distinction of being the tornado capitol of the world. Again the reason is location, location, location. The US is surrounded on three sides by water. The Pacific Ocean is to the West, the Atlantic Ocean to the East and the Gulf of Mexico to the South. They are the source of warm air and moisture. Add in the cold Arctic air that comes crashing down through Canada to meet the warm moist air. That is the perfect combination to produce thunderstorms and then tornadoes.

That should mean we get a lot of tornadoes too. Not so. Here is why. We, in western Oregon, live very close to the ocean and that gives us a Marine type climate. In order to form those large thunderstorms and tornadoes you need very warm moist air rising high up into the colder part of the atmosphere to give these powerful storms the energy they need. The very simplistic answer follows. When it gets very humid here it is usually already raining. The sun heats the surface air and it has to rise very high. It doesn’t get warm enough to rise into the higher part of the tropopause. Instead we have to wait for the cold air aloft to dive downward to meet what hot moist air we do have available to rise up. The higher the air rises the stronger the forces to produce a tornado. That distance is short enough to produce only weak and very infrequent tornadoes that are called “cold core” tornadoes.

From 1950 to 1995 only 50 tornadoes were recorded in the entire state of Oregon and no deaths or injuries have ever been recorded due to tornadoes. Over the history of record keeping the whole state of Oregon has an average of about 3 tornadoes per year. Compare that to the states in “Tornado Alley” and we are barely a blot on their record books. One of the strongest Oregon tornadoes was the EF2 (out of 5) tornado that struck Aumsville, OR in December 14, 2010.

Oregon Coast Lightning Strikes | Aaron Marineau
Oregon Coast Lightning Strikes | Aaron Marineau

Thunderstorms do occur over the ocean and along the coast, but they are much less frequent in the South Willamette Valley. From my 21 years of experience here we get most of our thunderstorms when there is a strong southerly airflow up the Cascades and foothills. The storms develop there and can start bouncing around and spreading to the Northwest and West into the Valley.

Snowstorms occur infrequently in the valleys of Western Oregon. The one everyone points to as the worst one (the best one according to the kids) was in 1969. That was a rare event for this area. The worst snow storm in my 21 years in Oregon occurred in 1996. We experienced heavy rains which caused serious flooding on the Mohawk River particularly. Then, after the rain-soaked ground helped loosen the roots of the trees, heavy wet snow fell toppling trees and cutting power lines throughout the area.

Because of our Marine climate we don’t see extreme cold Winter weather either. The record low for Eugene is -12 F recorded December 8, 1972. The coldest temperature at a location where I lived was -39 F in Eau Claire, WI in the mid 1970s which was the second coldest temperature ever recorded there. After a Winter cold front moved through bitter cold Arctic air swept in from the North.There were also high winds in Eau Claire that day producing a wind chill temperature of -85 F and we don’t see that kind of extreme cold in Western Oregon. The Marine climate also makes it more difficult to see extremely hot temperatures. The record highest temperature recorded in Eugene is 108 degrees F on August 9, 1981 and that was a very unusual event. That means our temperatures stay in a relatively comfortable range all year-round.

Cows stranded by flooding near Coquille River between Myrtle Point & Coquille | Jesse Higgins, The World
Cows stranded by flooding near Coquille River between Myrtle Point & Coquille | Jesse Higgins, The World

Flooding does occur occasionally in Western Oregon and it hits more often along the Mohawk, Siuslaw, and Coquille rivers among others. There used to be many more incidents of flooding until the dams were built. Controlling the flow of the rivers decreased the chance of massive severe flooding in Western Oregon. We have experienced record rainfall which caused flooding and particularly flash flooding in Western Oregon back in 1996 when Eugene set the all-time record rainfall of 74.18 in. of rain in the automated rain gauge and 101.93 in. in the old manual rain gauge at the old National Weather Service Office at the Eugene Airport. That year was an extremely rare one. This year, for example, Eugene experienced the driest first 5 months of the year ever with a total of only 8.57 in. of rain (37% of normal).

Oregonians have experienced volcanic eruptions as with the ash from Mt. St. Helens that managed to fall in the Willamette Valley, but not with devastating consequences. There is a bulge at the base of the South Sister which could eventually develop into something serious. An eruption from either of the Sisters could produce an ash cloud, but the predominant airflow over Western Oregon would push it away from us. Another major eruption of Mt. St. Helens could bring ash to us, but only if the airflow is from the Northwest, North, or Northeast. Airflow from any other direction would send an ash cloud away from us.

Wildfires are a big problem in the western US and even the Pacific Northwest. Fortunately those fires, for the most part, have missed the Eugene-Springfield area. There have been some minor fires in the Coburg Hills, but those have been discovered early and quickly extinguished.

Subduction Earthquake diagram | earthquake.usgs.gov
Subduction Earthquake diagram | earthquake.usgs.gov

Western Oregon has experienced earthquakes, but they have not been the powerful shakers like they get in California. That’s a good thing. We are now in a waiting game for the “Big One.” That’s a bad thing. It would be the subduction earthquake caused by the Pacific Ocean plate sinking below the Continental plate causing them to rub together. When the forces are strong enough the effect is an extremely powerful earthquake that could spread devastation from Southern Canada to Northern California depending on the location of its epicenter. That is potentially a life-changing event that is predicted to happen sooner than later by the experts.

So,we are very fortunate that, for the most part, really “bad” events just don’t happen here. When we do see a “serious” event it usually isn’t as bad as seen in other parts of the country and it doesn’t last very long. That makes Western Oregon a much more pleasant and relatively safer place to live. I’m really glad to call it my home and I hope you appreciate it as much as I do.

For any comments or questions you can email me at: tim.chuey@eugenedailynews.com

Tim Chuey is a Member of the American Meteorological Society and the National Weather Association and has been Awarded Seals of Approval for television weathercasting from both organizations.

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