Average Temperatures were fairly steady throughout the month with a difference between the Maximum and Minimum of only 8.2°. The Average Max/Min/Mean Temperatures December 1st-15th vs. 16th-31st: 44.7°/36.6°/40.6° vs. 43.6°/35.2°/39.4°. There was no unusual warmth or cold – the month only featured 5 days reaching Maxima ≥50° and most of those just barely, while Minima reached ≤32° on 9 days, including 7 in a row from 20th-26th. The greatest diurnal temperature range was just 12.9° (12th, 19th, 27th), the least only 3.0° (24th) during the only measurable snowfall of the month.
An extended dry period, unusual for December, occurred over much of the first half of the month, caused by persistent High Pressure off of the U.S. Pacific Northwest/Southwest British Columbia coasts. After receiving over 1/2″ of rain over the first few days to start the month, no rain fell from 5th-14th as skies stayed mostly clear as a steady north wind blew throughout the period. After the High influence finally abated, more seasonable moisture returned with more than 85% of the month’s precip. falling in the second half. The season’s first snowfalls occurred the days before Christmas, with nearly an inch accumulating on Christmas Eve, followed by some sleet and freezing rain, the latter sealing the snow depth for a rare White Christmas for this area. The freezing rain accreted to 0.2″ (24th), which remained for 3 days.
Freezing Rain: 3
There was an extended period of high Barometric Pressure beginning on the 3rd, with each day reaching at least 30.33″, not falling below 30.00″ until the 19th; the highest readings were 30.58″ on the 4th, 30.57″ on the 6th, and 30.56″ on 5th, 7th, and 8th.
The month saw 9 clear days, 10 partly cloudy days, and only 11 cloudy days. A total of 16 days with fog were observed, only 4 of which were heavy (<1/4 mile visibility).