August 2017 : Monthly Weather Retrospective

John McGinley, Peak to Peak. I have been writing a weekly weather column for The Mountain-Ear for nearly 30 years. Owing to our frequent travels after retirement it has been more difficult to keep this up from remote locations. Still, with an automated weather station I can reliably collect weather data, and am able to share it with Mountain-Ear readers. Thus, we introduce this new weather column that will come out monthly to discuss weather data from the previous month, climate issues, extremes, and other interesting tidbits. The plan is to have the weather review appear in the first issue of The Mountain-Ear after the last day of the previous month.


August 2017 ended up being a wetter and cooler than normal month. This was welcomed after two dry months in June and July. The summer monsoon set up on the 7th and persisted to the 16th. Another monsoon episode went from the 21st to the 24th. We ended with a couple of rainy days the last two days of the month.


Rainfall: Total for the month was 2.43 inches of rain, 0.25 inches above normal. Rainiest day was the 3rd where 0.58 inches fell out of a thunderstorm. We had 15 days with thunderstorms.


Temperature: With an average high of 74F and an average low of 46F we found the average temperature 1 degree below normal. The high was a degree below normal as was the low. No real extremes in temperature with the highest high of 81F on the 2nd. A strong cold front coupled with monsoon moisture gave us our coolest day where the high only reached 53F on the 7th. The following morning brought our coolest day with a low of 40F on the 8th. This summer we only had one day where the temperature reached 90F, and that was in mid July.


Winds: August is typically not a very windy month, with less than one windy day (winds at or above 40mph) during a typical August. Winds this high are typically associated with thunderstorm outflows, the rain cooled air that spreads out beneath the storm. This August we had one windy day that was due to downslope flow, pretty rare.


Other features: An upper level ridge of high pressure with winds circulating in a clockwise manner brought smoky conditions from extensive fires in the Pacific Northwest and Northern Rockies. The mountains were quite hazy during the last two weeks. This high pressure system also harbors very warm temperatures at upper levels putting a cap on showers and sealing in other constituents like smoke. Sometimes patches of monsoon moisture will get injected in this system and rotate around bringing unexpected showers in this normally dry situation. A term used for this phenomenon is a “dirty ridge,” ”dirty” referring to the clouds that appear on satellite imagery and rotate clockwise around the gyre. This brought us our rain on the 30th and 31st.


Outlook for September: After a few days of fall-like temperatures we will return to warm and dry conditions for a couple of weeks as the ridge persists. Smoky conditions will hang in there. Mid-month we should see a break in this pattern bringing in our usual brilliant blue skies. We might see a brief return of the monsoon, the last gasp of the summer. The last part of the month will see the arrival of a series of weather systems that will cool thing off and bring in some precipitation. By then the aspens should be at their golden best.