Wow! That Sounds Like It Ought To Be A Record. Oh, It Is.

Rain On Car Windshield | Photo by Tim Chuey

If this past month of September seemed inordinately wet you are right. I have a rain gauge in my yard and the National Weather Service has one (and other automated instruments), about a mile away from the airport runways. The best way to start off is to see what is considered to be “normal rainfall” for the month of September in Eugene.  According to the National Weather Service Forecast Office in Portland, the average (latest 30-year average) or “normal” September rainfall for Eugene is 1.29 inches.

Let’s get real and see how much rain actually fell in Eugene last month. The automated rain gauge near the airport registered 7.08 inches of rain for the month, which is 5.79 inches above average or normal.  For the month of September 2013, yes the same month I have been talking about, my rain gauge recorded only 5.27 inches of rain which is still 3.98 inches above that normal but is 1.81 inches below the record amount of rain that actually fell for the Weather Service measurement.

The best way to explain one of the reasons why my total is so much lower is to explain that rain does not fall from the clouds like water from a garden hose.

Watering The Lawn | Image Tim Chuey
Watering The Lawn | Image Tim Chuey

A hose can spray a particular area with exactly the same amount of water as an adjacent or even more distant area.  Not so with rainfall.  A particular plot of ground, for example, could have a series of clouds roll over it dropping varying amounts of rain from some of them and no rain from others, while another plot of ground receives a different amount of rainfall from those same clouds or even different clouds. Take two plots of land and separate them by miles and you can see an even more serious disparity in rainfall amounts.

Another way to see if the total for Eugene makes sense is to show how much rain fell in various locations in the area during the days of heaviest rainfall.  The two days of heaviest rainfall for the area, measured by the National Weather Service, were the 48 hours from 10:00 AM Friday September 27 through 10:00 AM Sunday September 28.

Automated Surface Observing Station |
Automated Surface Observing Station |

The National Weather Service ASOS, “Automated Surface Observing System”, (374 ft.) recorded 1.13 inches, 2 miles SW of Eugene (817 ft.) 1.91 inches, 2 miles SE of Springfield (489 ft.) 1.81 inches, Corvallis Municipal Airport 1.68 inches, and my rain gauge South Eugene (600 ft.) recorded 1.15 inches of rain for the two days Midnight to Midnight, not 10:00 AM-10:00 AM like the other readings. Those numbers show just how much the amount of rainfall, from a given event, can vary over relatively short distances.

There are other things to take into account; where the center of the storm was at the time, the elevation of each measuring station, and the direction in which each rain area was moving, to name just a few. We had a strong upper level low pressure area just offshore pumping moisture our way and then the remnants of Pacific Typhoon Pabuk added a second wave of moisture to the mix.

You might be wondering what is causing all of this rain?  It has been wetter than we’ve seen for years and as already mentioned, the greatest September rainfall total ever.  Some people have told me that they haven’t seen rain like this for 20 years.  Actually, that is about right.  It seems we are returning to a wetter cycle comparable to what we had some twenty years or so ago. Some will blame it on “Climate Change” or some other fancy term but I look at it as a return to the kind of weather Oregonians have been used to over the years past.  George Taylor, our former State Climatologist, explained to me years ago that we would be shifting back to a pattern of much wetter winters like Oregon used to have.

When looking for cause and effect I have found that too many people are willing to jump to some fantastic explanation as long as it satisfies their definition of the event.

Ockham's Razor | Image
Ockham’s Razor | Image

There is an old axiom called “Occam’s Razor” (also spelled Ockham) defined in the Free Dictionary by Farlex as “a principle in philosophy and science stating that assumptions introduced to explain a thing must not be multiplied beyond necessity, and hence the simplest of several hypotheses is always the best in accounting for unexplained facts.” Is the simple cyclical fluctuation of weather patterns from warm to cold and back (happening since the planet was born) the cause of the climate patterns we see now or a complicated man-made and man-caused explanation for our current circumstances?  I have found this question similar to my favorite definition of “faith” which is to a believer no proof is necessary and to a non believer no proof is enough.  The real answer will be found in the future.

Let me know what you would like me to talk about or explain. You can email me at: [email protected].


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