Jul 252013

Last night storm movement took on a southerly direction. As a result, a few storms treated Flagstaff residents to a strong lightning show with a good dose of rain. From looking at the radar images in the middle of the night, I think the southerly flow provided the lift over the San Francisco Peaks to generate storms. It was enough to push me past the 5 inch level for precipitation at my house this month. A quick look at the weather record for Flagstaff shows that only 1964 and 1986 had precipitation totals for July of more than 5 inches. But, will it last. In 1964, the following August was drier, and closer to normal. In 1986, August was wetter with about 8 inches.

The drying trend out in the future is looking more likely as we move forward. Early next week it looks like drier air will move into the Northern Arizona area. Even if the rains stopped now, we would be close to an average monsoon season for rainfall. Persistent moisture in the area is responsible. It will be interesting to see how wet or dry we are in August. Here is the Flagstaff dewpoint temperature history for this summer from the National Weather Service office in Tucson.

Monsoon daily dewpoint tracker for Flagstaff from the National Weather Service in Tucson

Monsoon daily dewpoint tracker for Flagstaff from the National Weather Service in Tucson

I don’t remember such a sustained, above average dewpoint history. The red is the average dewpoint temperatures for 1962-2010. I thinks is fairly rare that we are above 50F. Yes, it has been wet and potentially uncomfortable when warm.

TR reminded me that the connection between dewpoint and humidity isn’t in the forefront of people’s minds. The dewpoint temperature is the temperature below which dew will form. This temperature is dependent on the moisture content of the air. Humidity is the water content of the air compared to how much water vapor the air can hold. As air warms, it can hold more water vapor, so the humidity for a given dewpoint temperature actually drops. If our dew point temperature is 55F, we would have 100% humidity at an air temperature of 55F. At an air temperature of 75F and a dewpoint of 55F, our humidity would be 50%. High temperature, same amount of water equals lower humidity.

The bottom line is that it has felt more like the East Coast than Arizona lately because it so wet.




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