As Of August 1st, NWS Makes It Official - Hotter, Drier Phoenix Valley Part Of The New Normal

[hatrack]

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On Aug. 1, the National Weather Service will turn the page in its book and begin using new numbers to describe normal weather conditions – the high and low temperatures, rainfall – in Phoenix and cities across the nation. Normal weather is based on the average of a 30-year period. The averages are updated every 10 years by climatologists at the Weather Service’s parent agency.

For the past 10 years, the average has been based on records for 1971-2000. Starting Aug. 1, records for the 1970s will drop out of the average and those from 2001 through 2010 will be added, creating a new 30-year time frame. The new average will show what many Valley residents have felt: Although Phoenix has always been hot, it’s a little hotter. The days get hotter earlier in the year and stay hotter longer, and the nights have grown warmer every month of the year.

The actual changes appear to be minor: The average temperature at Sky Harbor International Airport increased by less than 1 degree since 2001, and the average annual rainfall decreased by about one-quarter of an inch. But for meteorologists, the differences are significant.

And while tweaks to climate records might sound wonky, these normals are a touchstone for daily life. Scan a weather page or listen to a nightly forecast, and you’ll find constant references: “Today was 5 degrees above normal” or “Last night was 10 degrees below normal.” They’re also a point of reference to help understand climate conditions and a guidepost for what a city or region can expect during a specific period of time.

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http://tucsoncitizen.com/arizona-news/2011/07/24/phoenix-is-hotter-and-drier-a-new-normal-for-the-valley/