Weather Blog

Arizona humidity so low, it's measured in milk fat terms

Arizona humidity so low, it's measured in milk fat terms

With the chilly spring mornings around here of late, you're probably well adept at dressing in layers.

Those in the hot Arizona desert are also being told to dress in layers... of lip balm.

A very strong thermal trough has been cooking the Desert Southwest this week, which in itself isn't too unusual, but temperatures have been above normal in California. The Los Angeles basin has been in the low 90s and the Bay Area has been in the mid 80s - at or a little above record levels.

And when the west coast gets the heat, it's typically accompanied by dry air as the offshore winds sink down the inland mountains and dry out.

But this past weekend, the weather pattern went into overdrive. Strong offshore flow became super dry as it sank and moved west.

At 6 p.m. on Saturday in Burbank, the temperature was 76 degrees but the dew point dropped to -15 degrees (yes, *minus* 15) during a strong northeast wind, making for a relative humidity of just 2%.

As the week progressed the ultra dry weather spread east. On Wednesday in Phoenix, Arizona, the temperature was 98 degrees, with a dew point of -2. That too made for a humidity of 2% -- tying the city's record all-time low humidity. (It was just the 14th time the city has recorded a 2% humidity in the 115 years the airport has been keeping records.)

Makes me wonder with the air so hot and dry, if swimming pools just spontaneously evaporate? :)

To compare, in the Northwest during our hot and sunny summer days, humidites are in the teens to 20% range.

(Thanks to Dr. Terry Kubar at the Jet Propulsion Lab for highlighting the statistics down in sunny California this week.)