How soon till the monsoon?
Updated: Apr 25, 2020
Wondering when the highly anticipated monsoon season will begin? Currently, on-going drought, forest fires, and the dwindling water supply in our area make the arrival of the summer monsoon rains imperative.
Since the monsoons bring life-sustaining summer rainfall to most of the Desert Southwest, the arrival of the monsoon season is tracked at a handful of locations in our region by monitoring the dew point temperature. Dew point temperature is a way to quantify the amount of water vapor in the air. Air that is cooled to its dew point temperature has 100% relative humidity, which means water in the air will condense into dew (or frost). For reference, when the dew point is above 60 degrees Fahrenheit, it's uncomfortably muggy (click here for why you should pay attention to dew point instead of relative humidity).
Since warmer air can hold more water vapor than colder
air, as air is cooled, water vapor will eventually condense into dew (liquid water droplets). As shown in the glass of ice-water image, water in the air came in contact with the cold glass surface, which cooled it to its dew point, forming water droplets on the side of the glass. In the atmosphere, as warm air rises, it expands and cools to its dew point forming clouds.
The monsoon season officially starts when the mean daily dew point temperature exceeds a location-specific threshold for 3 consecutive days. The closest dew point tracking location
to the Southern San Juans is Albuquerque, NM. The monsoon season starts in Albuquerque when the mean daily dew point temperature stays above 47 degrees Fahrenheit (the green line on the graph) for 3 consecutive days, which historically doesn't occur until around July 10th (red line).
The blue line indicates how 2018 compares to the 1947-2017 historic average. As you can see, we've had below average moisture conditions during the 2nd half of June. We can thank the break-up of hurricane Bud for the spike on 6/16, which brought much needed rain to the region! This graphic is updated daily and I've linked it to the Albuquerque weather site.
The next closest dew point tracking location to the Southern San Juans is Flagstaff, AZ. The mean daily dew point temperature threshold for Flagstaff is 40 degrees Fahrenheit for 3 consecutive days. Since Flagstaff has a similar elevation as Pagosa Springs, our mean daily dew point threshold is probably close to 40 degrees Fahrenheit.
Unfortunately, Albuquerque and Flagstaff are a long ways from the Southern San Juans, but they can provide a glimpse of the regional moisture conditions. In case you're having trouble sleeping, here's a link to the riveting study that established the dew point thresholds for Albuquerque and Flagstaff: A METHOD FOR DEFINING MONSOON ONSET AND DEMISE IN THE SOUTHWESTERN USA.
So what did yesterday's dew point temperature indicate about the progression of the monsoon season in our area? Yesterday's dew point temperature in Pagosa Springs dipped to 8 degrees Fahrenheit, which means it was so dry today that you'd have to cool the air to 8 degrees Fahrenheit in order to squeeze any moisture out of the air, and at that temperature it would form frost! The mean dew point temperature for 7/4/18 was 20 degrees Fahrenheit. So we're going to need twice as much moisture than we had yesterday for 3 consecutive days in order to cross that 40 degrees Fahrenheit threshold. When that happens, we can declare that the monsoon season has officially arrived!
My next post will explain what a monsoon is, and how and why they bring moisture to our area. In the meantime, hopefully we'll have some physical rather than graphical evidence of the arrival of monsoon season. Let it rain!