For purists, monsoon has begun in Valley

All the dew point die-hards can stand down: The monsoon, under the old definition, has begun.

Saturday marked the third straight day of an average dew point of at least 55 degrees, so purists will note the monsoon's start came on July 3. Now comes the time of sticky conditions, anvil-head clouds building over the Mogollon Rim and evening thunderstorms rolling into the Valley.

For years, the 3-of-55 rule was used to determine when moisture-laden air had flowed into the state, key to the annual weather phenomenon known as the monsoon.

But this year, the National Weather Service handed down a dramatic change. Instead of a strict meteorological definition, "Arizona monsoon season" now begins on June 15, humid air or not - just as Atlantic hurricane season starts June 1, tropical cyclones or not.

Tony Haffer, meteorologist in charge of the Weather Service's Phoenix office, is responsible for this new season. He said the change was a good idea because people were concentrating too much on watching dew point readings (if they understood the dew point concept) rather than focusing on the monsoon's dangers, such as flash floods and lightning strikes.

Also, Haffer added, seasons with a specific start and end (Sept. 30) will aid in record-keeping and year-to-year comparisons.

For example, the Valley's official rain gauge recorded a trace of precipitation on June 25. The drops came from a thunderstorm that had all the hallmarks of one borne from the monsoon - but under the dew point definition, the monsoon hadn't started.

But that storm was still dangerous, as Haffer warned. A lightning strike in the West Valley is suspected of touching off the smoky Ethan fire, which charred 6,600 acres before it was contained.

The Valley's forecast for the rest of the week is typical for the monsoon: daytime highs ranging from 102 to 108 degrees, with a chance of afternoon/evening thunderstorms.