PHOENIX -- The Valley is under another excessive heat warning today for temperatures that are expected to top out near 114 degrees today. The mercury hit 115 degrees yesterday, making it the hottest day we've had around here in about two years.
A common phrase during the summer in Phoenix is "But it's a dry heat!" But that's only true for the first part of our summer. Around the beginning of July, the humidity starts to increase thanks to the monsoon, and the phones in the 3TV weather department start ringing with questions about the dew point.
The dew point is a measure of moisture in the air, and folks with evaporative coolers or "swamp coolers" are especially interested in the dew points because they determine how well those swamp coolers will work. Because these coolers work using the evaporation process, the drier the air being pulled into your cooler, the better it will work. When the dew point gets into the 50s and especially 60s or higher, your swamp cooler won't work well at all.
For the most part, Valley dew points are forecast to stay in the 40s this week, but this weekend and into next week, forecast models are showing an increase in monsoon moisture pushing into the state.
The moisture may or may not be enough to bring us a little rain, but it's enough to push up humidity levels, and as humidity increases and those dew points surge. It will soon be time to shut off those swamp coolers and find another way to keep cool during our summer heat.