University of Arizona (UA) agricultural meteorologist Paul Brown says current long-range weather forecasts suggest a warm weather bias this summer along with a possible above-normal monsoon precipitation followed by a potentially wet El Niño winter in the West.
These forecasts could be wet answers to parched prayers for western farmers dealing with reduced surface water allocations and smaller-sized crops caused by extended drought.
If the wet predictions hold water, some growers may need to harvest crops either on time this fall or harvest their cornucopia earlier.
Brown says a wet monsoon season could distribute much needed moisture across much of Arizona and New Mexico, plus parts of Utah and Colorado. Arizona is in the 14th consecutive year of drought.
Turning to the wet El Niño forecast, Brown says federal weather watchers have issued an El Niño Watch which means conditions in the Pacific Ocean off South America are ripe for an El Niño to form.
Brown says there is a good chance for the West to have a strong and significant El Niño event this winter. In addition, El Niño rains could deliver much needed drought producers in West Texas.
Pacific Ocean waters have warmed quickly in recent months. Subsurface ocean temperatures are warming as much as 6 degrees Celsius above normal.
“If this system continues to develop into a full blown, strong El Niño this summer, there is a 70-80 percent chance of an above normal winter precipitation in the Southwest,” Brown said.
Some of the most recent winters with El Niño patterns failed to deliver a precipitation punch. Some of the climate science community suggests the system developing in the Pacific has a good chance to mirror the strong El Niño in 1997 which delivered good moisture.
Brown said, “El Niño moisture is a ‘coin toss’ around the San Francisco area but the chances of rain improve moving south into the San Joaquin Valley, southern California, and northern Mexico.”
He encourages western cotton growers to keep close tabs on the rapidly-building weather system.
“If subsequent forecast models call for rain in the early winter, cotton growers will need to make the hard decision in September and October whether to go for a top crop or harvest early due to anticipated rains.”
Brown added, “Let’s just hope the rain doesn’t arrive until Christmas.”
The UA farm meteorologist also shared good water expectations for water-storage reservoirs in Arizona – Lake Meade on the Arizona-Nevada border and upstream Lake Powell on the Arizona-Utah border which lie on the Colorado River. Meade and Powell are the two largest man-made reservoirs in the U.S., respectively.
The water level in Lake Meade has continued to sink in recent years – just above the 1,075 foot level. If the water depth on Jan. 1 of any year is 1,075 feet or lower, federal officials would declare a drought on the Colorado River which would reduce river water allocations.
The first reduction in river water deliveries would be farmers in central Arizona who receive water through the Central Arizona Project’s (CAP) 336-mile-long canal system. The CAP starts at Lake Havasu near Parker and moves south to the southern boundary of the San Xavier Indian Reservation southwest of Tucson.
Brown believes the El Niño system would likely deliver more water into Lake Mead.
“If we get a good El Niño winter and the Colorado Rockies get good snow then the water call on the Colorado River could be delayed for the short term,” Brown said.
Meanwhile, the water level in Lake Powell is actually rising from late spring snow melt in the Rockies. The water flow forecast from the Colorado River into the lake is currently 109 percent of normal flow; an additional 7.5 million acre feet of stored water.
Brown said, “This would be the best inflow into Lake Powell in several years.”
Lake Powell, in part, holds water for northern Arizona communities and farms and ranches.
Overall, Brown says this last winter and spring were extremely dry and warm in the West. In fact, last winter was one of the driest on record.
An important and key exception was the high elevation areas of Colorado where snowfall was plentiful which explains the good water flow forecast for the Colorado River. Temperatures since January have been among the warmest starts in history.
From Jan. 1 through April 24, temperatures along the Colorado River in western Arizona were 2-4 degrees above normal.
Brown said, “This doesn’t sound like a lot but from a meteorological perspective it is a big deal when it last for 120 days.”
Since Jan. 1, the University of Arizona weather station in Parker, located adjacent to California’s Mohave Desert, has recorded the warmest temperatures in more than 30 years. Heat unit (HU) accumulation in the Parker Valley from Jan. 1 through the end of April usually total about 1,000 HUs. The same period this year topped 1,275 HU’s – a mere 10 HU’s under the record.
As a result, the growing season in the Parker area is about 14 days ahead of normal, depending on the cropping system.
“It is an unprecedented year,” Brown concluded. “It’s been a very unique and dry spring.”
Information on HU’s and other Arizona agriculture weather information are available on the UA’s AZMET weather-crop website at http://ag.arizona.edu/azmet/.