Climate As you might expect from the fact that it is mostly desert, the weather tends to be hot and dry. In Presidio, on the Rio Grande River, the average high temperature varies from 68.4o F in January to 102.5o F in June. The highest recorded temperatures there exceed 115o F. The average low varies from 33.6o F in January to 72.9o F in July.
The average high in Alpine is only 60.6o F in January and 90.3o F in June. Alpine is over 2000 ft higher in elevation than Presidio. The highest recorded temperature there is 108o F.
The average annual rainfall in Presidio is 10.84 in, In Alpine it is 16.9 in. In both cases, the bulk of the rainfall occurs in July-Sept. Presidio recorded just 1.64 inches in 1956, the lowest ever in Texas, for the period 1873-1993.
One interesting feature of this region, that relates to rainfall, is the flash flood. Everywhere, you see stream beds which are almost always dry. However, a heavy shower anywhere in the drainage of one of these streams can cause the water to rise rather rapidly. This does not present a large risk for drowning, but it can cause a problem if you cross one of those dry stream beds, and need to be able to come back across it before dark. You may need an alternate plan.
Because of the heat, summer is the time of the least number of visitors in the region. However, I have been there in June, July, and September, and with minimal problems, but I am used to heat. Winters are mild there, however, and it is a popular tourist destination for Thanksgiving and Christmas. Avoid March, however, as it is packed.