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Published June 26, 2013
Precipitation Outlook(July–December 2013)
Data Source(s): NOAA-Climate Prediction Center (CPC)
The seasonal precipitation outlooks issued by the NOAA-Climate Prediction Center (CPC) in June call for equal chances that precipitation during the July–September and August–October periods will be above, below, or near average across nearly all of New Mexico and Arizona (Figures 11a–b). However, decision support tools used to help guide forecasts show stronger signals this month for enhanced monsoon precipitation than in previous months. This reflects, in part, eight- to 14-day medium-range weather forecasts that indicate moisture will waft into the region and set the stage for a slightly early or on-time arrival of the monsoon. The monsoon usually begins around July 1 in southwest New Mexico and southeast Arizona.
While there is some indication monsoon rainfall will be above average, some climate models suggest the opposite, which provides forecasters with no clear signal for above- or below-average conditions. Moreover, dynamical models often are not accurate at forecasting the entire three-month monsoon. Nonetheless, there is also no indication that the monsoon will be a dud, which is good news for a region in the throes of widespread and intense drought. For the September–November and October–December periods, an equal chances forecast stems from uncertainty in the evolution of the El Niño–Southern Oscillation (ENSO; Figures 11c–d). ENSO usually develops in early winter and can have a substantial influence on precipitation in the Southwest.
These outlooks predict the likelihood (chance) of above-average, average, and below-average precipitation, but not the magnitude of such variation. The numbers on the maps do not refer to inches of precipitation.
The NOAA-CPC outlooks are a 3-category forecast. As a starting point, the 1981–2010 climate record is divided into 3 categories, each with a 33.3 percent chance of occurring (i.e., equal chances, EC). The forecast indicates the likelihood of one of the extremes—above-average (A) or below-average (B)—with a corresponding adjustment to the other extreme category; the “average” category is preserved at 33.3 likelihood, unless the forecast is very strong.
Thus, using the NOAA-CPC precipitation outlook, areas with light green shading display a 33.3–39.9 percent chance of above-average, a 33.3 percent chance of average, and a 26.7–33.3 percent chance of below-average precipitation. A shade darker green indicates a 40.0–50.0 percent chance of above-average, a 33.3 percent chance of average, and a 16.7–26.6 percent chance of below-average precipitation, and so on.
Equal Chances (EC) indicates areas where no forecast skill has been demonstrated or there is no clear climate signal; areas labeled EC suggest an equal likelihood of above-average, average, and below-average conditions, as a “default option” when forecast skill is poor.
Seasonal precipitation forecast downscaled to the local scale::
Southwest Climate Outlook Staff
- Michael Crimmins, UA Extension Specialist
- Stephanie Doster, Institute of the Environment Editor
- Gregg Garfin, Founding Editor, Institute of the Environment
- Zack Guido, Managing Editor, CLIMAS Associate Staff Scientist
- Nancy J. Selover, Arizona State Climatologist
- Jessica Dollin, CLIMAS Publications Assistant
- Dave Dubious, New Mexico State Climatologist
Please direct your Southwest Climate Outlook comments and suggestions to Zack Guido.
The CLIMAS Web site contains official and non-official forecasts, as well as other information. While we make every effort to verify this information, please understand that we do not warrant the accuracy of any of these materials.... Read full disclaimer