It was a topsy-turvy month as the second half was actually warmer than the first half, not the usual steady decline as we move through Autumn. Splitting the month in two, the Average Max/Min/Mean Temperatures for Oct. 1st-15th vs. 16th-31st were thus: 61.7°/44.7°/53.2° vs. 61.9°/48.1°/55.0°. This was mainly due to a persistent end-of-month easterly wind that funneled in mild air through the Columbia River Gorge, especially elevating minimum temperatures. From the 22nd-29th, the Avg. Min. Temp. was 50.0°, well above the normal for late October, while only one Min. Temp. ≥50° occurred over the first half of the month (the warmest Minimum was 56.6° on the 27th). The average monthly diurnal temperature range was 15.3°, with the greatest day being 26.5° (4th), the least only 6.0° (20th). The season’s first frost occurred the morning of the 14th when the Minimum Temperature fell to 36.5°, the coldest reading here since 35.8° on 4/3/2017.
There were only two significant periods of rain this month, quite a contrast to the previous October when measurable rain (≥0.01″) fell on 30 of the 31 days; this month there was half that amount, 15 days. The first rainy period this month occurred from the 10th-13th, dropping a total of 1.44″. The more significant event impacted the area from the 18th-22nd when 4.35″ soaked this location. The two events combined for 95% of the October total.
The month saw 12 clear days, 15 partly cloudy days, and only 4 cloudy days, much less cloudier than normal. There were 15 days with Fog but only 2 of these were heavy (<1/4 mile visibility).
Featured cover photo is of Cumulus Congestus during the evening of 10/12/2017, Happy Valley, Oregon.
Double Rainbow, evening of 10/11/2017, Happy Valley, Oregon.
Colorful Autumn leaves, early evening 10/24/2017, Aurora, Oregon.
Spotted leaf, 10/27/2017, Happy Valley, Oregon.