In the late afternoon today I could look to the east and see thunderstorm clouds boiling up behind the Rincons -- but I can tell the air is drying out. The forecast for the coming week is sunny skies, a few clouds, and temperatures rising to above 100 later in the week (104 on Thursday, and even hotter on the weekend). We will see how that plays out.
Whatever actually happens, I have had a taste of "the end", which gives hope after one of the longest and hottest summers I can ever remember. Drying out certainly plays a big part of it. Drier conditions will make for more dramatic night time cooling and may even allow me to resume sleeping out of doors. Lows the past 3 nights have dipped just below 70. The forecast for the rest of the week is for lows ranging from 67 to 72.
But now things are drying out and the evenings and mornings seem refreshingly cool again. One thing I noticed was the spiders. In my front yard I have large wolf spiders, and at night I enjoyed seeing the reflection of light from their eyes from a long ways away. But during the heat of summer, they were gone. Now with the weather cooling off they are back.
I was reading a book I have on Death Valley history. It mentions that one of the borax mines would cease operations from mid-June to mid-September due to heat. So mid-September (i.e. right now) marks a turning point from oppressive heat to something manageable. Even though temperatures in Tucson are forecast at 100 degrees for the following week, having dry conditions so it cools off nicely at night makes a big difference. And up at elevations like 5000 to 6000 feet (i.e. in the Santa Ritas) drops temperatures down to the 85-90 range, which I find entirely acceptable.
What can be said about all of this? August was simply nasty. There was no relief until early September, but even then things were still hot. But in September mornings and evenings are pleasant, which made for a significant change, especially psychologically.
This may sound hot, and it certainly is mid-day, but evenings are wonderful, and the mornings are great too. It is only after 10 AM or so and up to 5 PM that a person wouldn't want to be working outdoors. And in the mountains at only somewhat higher elevations (like 5000 to 6000 feet) it is just fine all day long, perhaps the best of temperatures for hiking.
I see all kinds of number quoted for the adiabatic lapse rate (how much the temperature drops as you go up in altitude). Everything from 3.3 to 5.4 degrees. The "official" rate is given as 9.8 degrees C per 1000 meter rise. If you work out the unit conversions, this is indeed 5.4 degrees F per 1000 feet.
So consider. My home is at 2400 feet. If I drive up to 5400 feet (an area I often explore in the Santa Rita mountains), this is a climb of 3000 feet and I should see a temperature drop of 16 degrees. So if we are having 103 degree high temperatures here in Tucson, the high at 5400 would be 87 degrees, which is ideal.
An interesting coincidence (or not?) that the weather has shifted on the very first of October. The forecast shows that it will warm up as the week progresses into highs around 95 degrees. Still no need for sweaters or light jackets, but I am shifting from wearing shorts every day to wearing pants regularly.
Tom's Weather Resources / [email protected]