Will the upcoming fall turn wet?

September is here and so was a change in our weather pattern. Much-needed rain returned to the region last week as we entered the “full moon” lunar phase. This second full moon last month, also called a “Super Blue Moon,” was the biggest and brightest of the year. There is another supermoon in late September, but it will not be quite as spectacular as the one in late August.

On Aug. 30, Coeur d’Alene picked up an impressive 0.96 inches of rain, which broke the record for the date. The old record was back in 1926 with 0.42 inches. Other locations had over an inch of rain. For example, Hayden had 1.22 inches, North Idaho College reported 1.13 inches and Dalton Gardens picked up a whopping 1.40 inches of rain for the day.

The total August precipitation for Coeur d’Alene was an above-average 1.71 inches. The normal for August is 1.23 inches. At the Spokane International Airport, a total of 0.92 inches of rain was measured last month. This was also above their normal level of about a half-inch.

Despite the recent rainfall, the June through August period was drier than normal in Coeur d’Alene and other parts of the Inland Northwest. For the three months beginning June 1 and ending Aug. 31, a total of 2.92 inches of rainfall was recorded in Coeur d’Alene. The normal for this period is 4.07 inches.

In 2022, the June 1 through Aug. 31 period was wetter than normal with 5.87 inches of rainfall. However, the majority of the moisture arrived in the first two weeks of June as 4.83 inches fell. The rest of the summer was extremely dry as only 1.05 inches of rain was measured for the summer of 2022 in Coeur d’Alene which began June 21.

While most of us observe the fall season later this month, the “meteorological summer” season ended Aug. 31. Sept. 23 is the beginning of the “astronomical” fall in the northern hemisphere, which is based on the position of the Earth relative to the sun. In just over three weeks, the sun will be at 90 degrees, or directly overhead, at the equator. The next time the sun’s rays will be over the equator will be the first day of spring in 2024, which is called the vernal or spring equinox.

Although we base our seasons on the calendar, most meteorologists and climatologists break down the seasons into groups of three months. For example, the meteorological summer includes June, July and August. The meteorological fall begins Sept. 1 and ends Nov. 30. The meteorological winter is from December through February and the spring includes March, April and May.

As I’ve mentioned in previous articles, according to NOAA, the National Oceanic and Atmospheric Administration, meteorological seasons are primarily based on annual temperature cycles. For example, we really start to feel the chilly weather in December and the summer conditions in June. The spring and fall seasons are considered to be “transitional” periods. This system makes it easier for scientists and forecasters to calculate monthly and seasonal statistics. They were created for observing and forecasting weather patterns, which has proven useful for agriculture, commerce and other purposes.

In the southern hemisphere, Australia begins its spring season Sept. 1 as their seasons are the opposite of ours. Using the system of “astronomical seasons” that begin during the solstices or equinoxes, does not work very well for this country. For example, in northern Australia, where it’s very tropical, the year is divided into wet and dry seasons. Therefore, it was determined that spring begins Sept. 1, summer starts Dec. 1 and so on.

Since 2010, when Coeur d’Alene has a dry summer, the following fall is often wetter, in terms of percentages. Last year, after the long and dry summer season, the skies opened up and Coeur d’Alene picked up 9.74 inches of rain and melted snow for the fall of 2022. Over half of the moisture fell in November as 5.20 inches was measured at Cliff’s station in Coeur d’Alene.

The big difference between this year and 2022 is the sea-surface temperatures. Ocean waters near the Equatorial regions and other parts of the world are much warmer than average. Last year, there was a cooler La Niña event, but we now have an El Niño pattern. The Climate Prediction Center, and other forecasters, are indicating the upcoming fall season will have above-normal temperatures and below-normal precipitation for much of the northwestern U.S. Based on Coeur d’Alene’s climatology, I believe our fall season will be warmer with moisture totals near above average.

The early-to-mid portion of September does look dry across the Inland Northwest. However, we do believe there will be some wet periods over the next three months, especially near the new moon and full moon cycles. It’s very possible that the Inland Northwest may see another round of soaking rains at the end of September near the next supermoon.

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Contact Randy Mann at randy@longrangeweather.com.