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Published September 20, 2011
Monsoon Summary(data through 9/12/2011)
Data Source(s): Western Regional Climate Center
The monsoon season is ending like it began: with a bang. Between September 9 and 16, a low pressure system parked over the region and brought cool air high in the atmosphere. This created atmospheric instability that combined with ample moisture to generate widespread and intense monsoon storms—many parts of both states received more than 200 percent of average during this period. The recent storms helped southeast Arizona experience its wettest September on record. Despite this activity, however, total monsoon rainfall has been below average for most of the rest of Arizona and New Mexico (Figures 8a–c). This has been especially true for southeast New Mexico, where moisture incursions from the south were blocked by the persistence of a high pressure ridge centered over Oklahoma and Texas—too far east to continuously funnel moisture into the region. The position of the ridge is both a cause and consequence of the exceptionally dry conditions in Texas and southeast New Mexico. The lack of rain also contributed to soaring temperatures. Both Arizona and New Mexico posted their warmest August on record. Temperatures that month were about 6–10 degrees above average in southwest New Mexico and between 2 and 6 degrees F above average in Arizona.
Precipitation in the Southwest has not been sufficient to improve drought conditions. Since the monsoon began on June 15, drought in Arizona has expanded and intensified in all regions except the southeast corner, where storms have been most vigorous. In New Mexico, drought conditions have remained virtually the same since the monsoon began (see page 9).
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 National Climatic Data 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 Dubois, New Mexico State Climatologist
Please direct your Southwest Climate Outlook comments and suggestions to Zack Guido.
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