More on the NWS Summer 2010 Forecast

The actual online NWS briefing for summer 2010 is available at the Tucson office webpage:

http://www.wrh.noaa.gov/twc/

and the link is under Top News of the Day. The briefing has eight components (i.e., clearly not designed for those with short attention spans): 1) Monsoon 2010 Forecast, 2) What is the Monsoon?, 3) Where are we now?, 4) El Nino/Southern Oscillation forecast, 5) Soil moisture and the Monsoon, 6) Official NWS forecast: July-September, 7) What could change?, and 8) Track the Monsoon with us! Shown above are the graphics used in parts 6 and 7. The official NWS CPC summer outlook is fairly typical and doesn't seem very enlightning - certainly not filled with information that people can easily understand or use to make decisions. Thus, I can easily understand reporter Beal's short-take, cynical overview. The full story that Beal has filed this morning follows:

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Conflicting signals about next monsoon

Tom Beal Arizona Daily Star Posted: Friday, May 21, 2010 12:00 am

It's going to be hot this summer, probably, and we'll have less rain or more rain than usual, according to the National Weather Service, which posted its first online monsoon briefing for 2010 on Thursday.

The North American Monsoon, a seasonal shift to southerly winds that brings moisture to the Southwest each summer from the the gulfs of California and Mexico, responds to a variety of atmospheric circumstances.

Generally, Southern Arizona receives less summer rain when the winter rains are above average, as they have been this year, said Erik Pytlak, monsoon researcher with the National Weather Service in Tucson.

That's because moist ground in the Plains states slows the heating needed to lure a high-pressure system northward from Mexico. The monsoon, which usually brings thunderstorms to Tucson by early July, won't start early and could be a little late, Pytlak said.

The monsoon could intensify later in the season, however, if the Pacific Ocean cools, a phenomenon known as La Niña - the flip-side of the El Niño warming that cut off last summer's monsoon prematurely.

Cooling oceans increase the contrast between temperatures over land and sea. As the sun warms the land, heat rises and cooler, moister air rushes in. The computer models are divided on whether the ocean-cooling phenomenon, known as La Niña, will occur.

Right now, most models call for average ocean temperatures, a condition the scientists call "El Niño neutral."

"In an El Niño-neutral year, the most likely thing to happen is near average rainfall," Pytlak said.

Officially, the National Weather Service forecasts "a 40 to 55 percent chance of above-average temperature" and "equal chances for above or below-average rainfall."

"There are conflicting signals out there now and quite a bit of uncertainty," Pytlak said.