HAPPY VALLEY, OREGON WEATHER: DECEMBER 2021
TEMPERATURES
Overall, Temperatures averaged slightly below Normal for December 2021. The month began quite mild, with the warmest day of the month being on the 1st (61.1°/49.4°) but quickly cooled as Maximum Temperatures remained ≤50° from the 3rd-17th (except for 52.6° on the 7th). The 18th saw 51.0° but every day following remained ≤50° through month’s end. The coldest weather waited until the last week beginning on Christmas Day as all Maximums remained ≤40° through the 31st, including a sub-freezing 31.6° on the 27th and a close-but-no-cigar 32.8° on the 29th.
Minimum Temperatures saw the same general decline through the month with only the 22nd remaining above 40° after the 11th. Overall, 8 days fell to ≤32° with 4 of those at ≤28°; the coldest reading of the month waiting until 2 minutes before midnight on New Year’s Eve when it dropped to 22.7°, the coldest December temperature since this station opened in May 2014.
Splitting the month in half, the following Max/Min/Mean Temperatures were observed: 1st-15th 46.9°/38.9°/42.9°; 16th-31st 40.5°/32.6°/36.5°. The coldest period of 25th-31st had Max/Min/Mean Temperatures of 35.3°/27.4°/31.3°.
The month’s largest diurnal range was 17.9° (51.0°/33.1°) on the 18th, the least was just 3.1° (38.8°/35.7°) on the 15th.
PRECIPITATION
“Nearly continuous” describes December 2021 as the only days without measurable precipitation were the 1st, 5th, and 14th. The monthly total of 9.31″ was 118% of the December Normal of 7.89″ for this location, which was also the 2nd highest December total since 2014 but far behind #1 when 17.65″ inundated the area in 2015. The 28 days of measurable precipitation tied this location’s December record (also in 2015) for most number of days. Of this month’s two heaviest periods of precipitation, the first began just after midnight on the 11th, continuing until late on the 13th, totaling over 2.00″; the second period began with rain late on the 17th, becoming the season’s first measurable snowfall late on the 18th (2.0″ by early on the 19th) before changing back to rain, finally ending late afternoon on the 19th with 3.34″ of liquid equivalent measured.
The first snowflakes of the season occurred just before noontime on the 9th when mixing with the rain, then again on the morning of the 15th. Though precipitation wasn’t very heavy from the 26th-31st, it was nearly all in the form of snowfall as 6-consecutive days of measurable snow occurred, totaling 9.0″ for the period, with the 26th-28th each recording ≥1.0″. The Maximum Snow Depth reached 3.5″ at the 07:00 AM Obs. time on the 28th.
≥0.25″: 11
≥0.50″: 5
≥1.00″: 2
OTHER OBSERVATIONS
Sky Cover:
1 Clear, 10 Partly Cloudy, and 20 Cloudy days.
Barometric Pressure:
Average Maximum/Minimum readings were 30.04″/29.81″, with the Highest Daily Value of 30.57” on the 5th, the Lowest Daily Reading of 29.34” on the 24th.
Relative Humidity:
Maximum/Minimum Averages were 98%/87%, having a Daily Maximum of 99% on the 7th; Daily Minimum of just 75% on the 11th, 14th, & 15th.
Dew Point:
Averages were a Maximum/Minimum of 42°/34°, with a Daily Maximum of 57° on the 1st, Daily Minimum of 18° on the 31st.
Wind:
The Daily Average Speed was 1.4 MPH and the highest Daily Average was 3.6 MPH on the 11th; the Daily Average Gust was 13.5 MPH and the Highest Gust reached 29 MPH from the SSW on the 11th.
HAPPY VALLEY MONTHLY WEATHER FORM: DECEMBER 2021 (click the month/year to link to the form).
Cover photo: Final Sunset of 2021 on Mt. Hood. 12/31/2021.