October has now come to a close and it was a dry and fairly mild month. It will go down in history as one of the driest October's in Reno history. We only got a trace of an inch of rain for the entire month of October, when average is a half inch. The past week has been extremely dry with relative humidity values in the teens and dewpoints well below zero. Dewpoints are the temperature the air has to cool down to in order for saturation to occur. The lower the dewpoint temperature the lower the moisture content is. Dry air also cools off easier than warm moist air. This Halloween was chilly with temperatures in the mid 50's during the day, which is comparable to 2016. Average high for this time of year is about 62 degrees.
All of the cold dry air moved in from Canada this past week behind a front. Whenever a front comes down from land opposed to the Pacific moisture levels are much lower. Dewpoints were 20 below zero in central Nevada on Halloween and a few degrees below zero in Reno Halloween night. If your skin and sinuses are extra dry, this is why. The bigger the gap between the dewpoint temperature and air temperature the lower the relative humidity will be. Historical data from weather balloon launches in Reno shows dewpoints below zero on multiple occasions. While this is uncommon especially this time of year, it is not unheard of. In the chart below the brown line shows the average dewpoint temperature. The red and blues lines are extremes. According to this chart dewpoints are usually in the 20’s and 30’s during the month of October in Reno. We’ve gotten to 20 below before too. The image below is from the Storm Prediction Center.
Compared to previous years, we’ve only seen a trace of an inch of rain during the month of October four times, and only once did we get nothing. This year will go down in history as one of the driest Octobers on record. 2010 was the wettest with 2.65 inches of rain.
September was a little bit better with around a quarter of an inch of rain falling in Reno. Average is closer to three tenths. While we could use the rain, it looks like we’ll stay dry through at least the middle of next week. Have a great weekend and enjoy the sunshine.
