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Published June 26, 2013
Monsoon Summary(data through 6/21/2013)
Data Source(s): Western Regional Climate Center
The monsoon storms historically begin in the first week of July in southern Arizona and New Mexico. However, the National Weather Service (NWS) announced that June 15 through September 30 would mark the official dates of the monsoon in order to more clearly communicate when monsoon risks, such as flash floods, are most likely to occur. Since June 15, there has been some precipitation in parts of the Southwest, but little rain has fallen throughout most of the region, which is typical (Figures 9a–c). Some places in the Tucson area received about 0.5 inches of rain on June 15, and parts of eastern New Mexico received 0.25 to 1.5 inches. While this rainfall did occur within the NWS defined monsoon period, it was not technically monsoon-driven as atmospheric circulation patterns characteristic of the monsoon are not yet in place. These include a monsoon high-pressure ridge over parts of Arizona and New Mexico that allows winds to blow from the south and southeast. The classic definition of the monsoon refers to a shift in prevailing wind direction by 120 degrees, which does occur in the Southwest.
This year, there are several indications that the monsoon will begin on time or slightly early. These include forecasts for the presence of a northward moving tropical storm in the eastern Pacific Ocean and the formation of a surface heat low near the border between California and Arizona. Both scenarios would help ferry moisture from the Gulf of California into the Southwest. Current conditions this year are similar to those of last year, and this summer may evolve similarly. Last year, substantial monsoon rains first fell at the Tucson International Airport around July 4. By July 15, nearly 66 percent of the season’s total rain had fallen. September 14 marked the final day of monsoon precipitation and the season tallied just under its long-term average.Notes:
The continuous color maps (figures above) are derived by taking measurements at individual meteorological stations and mathematically interpolating (estimating) values between known data points. Interpolation procedures can cause aberrant values in data-sparse regions.
Average refers to the arithmetic mean of annual data from 1971–2000. Percent of average precipitation is calculated by taking the ratio of current to average precipitation and multiplying by 100. Departure from average precipitation is calculated by subtracting the average from the current precipitation.
These data are obtained from the High Plains Regional Climate Center::
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.
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