Growers in the southwest United States have become accustomed to the monsoon season, but what exactly is it and what does it mean for forage?
What is monsoon season?
The North American monsoon season is a large weather pattern similar to the monsoon season in Asia, although not as strong. It officially occurs from June 15 – September 30 with most storms occurring in July and August. This particular monsoon system effects northwest Mexico, Arizona, New Mexico, and parts of Utah and Colorado. It brings unpredictable weather patterns, strong winds, and precipitation. It is important to note that the word “monsoon” refers to a system not a storm. Many may see a thunderstorm coming and refer to this as a “monsoon” when the most appropriate term would be “storm” (as the result of a monsoon system).
Most of the southwestern US sits in heat for a large portion of the year. By the beginning of summer, the sun has warmed and dried the region causing an area of low pressure. Meanwhile, the sun is also heating the Gulf of Mexico and the Pacific Ocean, pulling moisture upward and creating an area of high pressure. As these systems collide the wind direction is changed from its normal westerly flow to southeasterly, bringing the moisture from the Gulf and Pacific to the dry desert. Monsoon season will last until the temperature difference between the land and the sea is reduced.
Some areas of North America receive about half of their annual rainfall during the monsoon. Precipitation varies greatly on a daily basis, and even within distances as short as a couple of miles. Patterns consist of bursts (periods of extremely heavy rainfall that are most often short in duration) and breaks (periods of no rainfall). Mountainous areas tend to receive the most rain and can even act as focal areas for thunderstorms as moist air rises and cools to the point of precipitation.
Moisture sources for North American monsoon.
Threatening weather is a hallmark of this weather pattern, for many reasons. The increased precipitation can cause flash floods and hail, and the wind shift often results in large dust storms called haboobs. The most lethal component of this extreme weather is lightening, which consistently burns hundreds of thousands of acres in the southwest every year. The risk is greatest during June and July, when excessive precipitation has not yet fallen and vegetation is still dry after nine months of heat and wind. It can take several days for fire fighters and monsoon precipitation to extinguish the flames.
What does this mean for growers?
Monsoon season is officially June 15 – September 30, peaking in the southwest in July and August. These dates are dictated by the National Weather Service (NWS) to make identifying and predicting the season easier for media and residents. By this point in the growing season, many farmers in this area are on their 3rd or 4th Alfalfa cutting. So what does this change in weather bring?
Growers will find themselves with the challenge of choosing the best days to cut and cure their hay. The unpredictable weather can make it difficult to find a good cutting window to allow windrows the adequate drying time without receiving any precipitation. On the other hand, vegetation flourishes during this time as ground water and basins are replenished and less irrigation is needed.
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