Weather: A dry September often means a dry October
There doesn’t appear to be any type of normal weather pattern in our area or across the globe. It seems like it’s either feast or famine in terms of moisture.
For example, many areas across the Inland Northwest reported the wettest spring season in history. At Spokane International Airport, 4.56 inches of moisture fell in March, which was the most precipitation ever measured for the month of March. June was also a wet month with 2.86 inches of rain.
By extreme contrast, with the exception of a thunderstorm on Aug. 21, there hasn’t been any measurable moisture above a trace since July 20. September will likely go into the record books with no precipitation reported. There were two days with trace amounts of moisture. The only other years with no rain in September since 1889 were in 1990 and 1999. Because of the extreme dryness, fire danger levels have remained dangerously high. Air quality has been poor lately due to frequent smoky and hazy periods from wildfires.
Based on climatology, when September is very dry, most Octobers are drier than normal as well. However, in October 1990, a whopping 3.05 inches of moisture fell after a September with no measurable precipitation. In 1999, 0.89 inch fell in October. In September of 1987 and 1991, only 0.01 inch of moisture fell at the airport. The following Octobers were well below normal in terms of average rainfall.
The new moon cycle in mid-October should give us an idea of what the rest of the fall weather will be like across the Inland Northwest. This will be the time of a major pattern change.
If the same high pressure ridge that has been “blocking out” Pacific storm systems for two months backs up to a point some 800 miles west of Oregon’s coastline, then we should see one storm system after another move across the Inland Northwest. This would be almost identical to the soggy weather pattern of this past spring.
But if the strong ridge of high pressure continues to hold on, then the next six weeks will likely be drier than normal. Also, El Niño, the warmer than normal sea-surface temperature event in the south-central Pacific Ocean, has been weakening over the last few weeks. If ocean waters continue to cool in the next few months, then conditions could turn much wetter by December or January.
Remember, we’ve had a number of years with wetter than normal weather. In this cycle of wide weather extremes, our area may be due to flip to the drier side for an extended period of time.