Ag Weather Forum

Did Cold Pool Hype Atmospheric River?

Bryce Anderson
By  Bryce Anderson , DTN Senior Ag Meteorologist
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A large pool of anomalously cool water that developed over the northern Pacific Ocean has stayed around since fall 2016. (NOAA/NESDIS graphic)

One of the questions that I have fielded this winter on the farm show circuit has to do with the term "atmospheric river." This phrase has been a leading term in weather stories since the first of the year, when the western U.S. -- especially California -- took in the first of what has been seemingly wave after wave of very heavy rain and snow. The sourcing of the atmospheric river in the Pacific is the subject of a lot of inquiry. (NOTE -- I will also touch on this subject during my presentation Friday afternoon at Commodity Classic in San Antonio, Texas.)

The USDA Weekly Weather and Crop Bulletin dated Wednesday, February 22, has some interesting comments on this feature as well -- along with a review of the impact of this Brobdingnagian precipitation that has accumulated in the western U.S.

"La Nina faded in recent weeks, but the barrage of Pacific storms that headlined January's weather continued through the first three weeks of February. Although research has only begun, one area of interest has been a pool of anomalously cool water that developed last autumn over the northern Pacific Ocean. The Pacific "cool pool" may have helped to anchor the polar jet stream in such a way as to batter parts of the West with repeated storms over an extended period."

"The Sierra Nevada received more than its normal annual precipitation in less than two months to start 2017, suddenly pushing northern and central California into flood-control mode. In fact, drought concerns throughout the West have greatly diminished, except for lingering surface water and groundwater shortages in southern California and the Desert Southwest."

By February 15, 2017, most basins in the central one-third of the West, including the Sierra Nevada and the Wasatch Range, were reporting much above-normal snowpack for this time of year. In contrast, a few Southwestern basins have lost much of their snow due to recent and ongoing warmth. Meanwhile, many Northwestern basins have a near or slightly below-normal snowpack, due to early-season precipitation falling as rain and more recent storms delivering mostly powdery, rather than wet, snow accumulations."

In any event, the precipitation fortunes in the western U.S. have been substantial, as the Weather and Crop Bulletin report concludes:

"Season-to-date precipitation (October 1, 2016 through February 15, 2017) was near or above normal throughout the West. Amid an overall impressive Western winter wet season, precipitation totals have been truly exceptional (at least 150 to 200 percent of normal) in many watersheds stretching from the Sierra Nevada into western Wyoming. By February 1, 2017, projections for spring and summer streamflow were indicating the likelihood of near or above-normal runoff in most Western watersheds, except in northern areas. In particular, runoff in excess of 180 percent of average can be expected in many basins from the Sierra Nevada to the Wasatch Range. In contrast, runoff volumes of 70 to 90 percent of average should occur in numerous watersheds from the Cascades to the northern Rockies."

For agriculture, the bottom line is: Irrigation allocations are looking promising for crop year 2017.


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