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Federal forecasters issue the La Nina watch. What does this mean for next winter in Utah?


A map of a typical winter of La Nina. The National Weather Service’s Climate Prediction Center released a La Nina watch on Thursday, July 8, 2021. Forecasters say it looks like the trend will return this winter. (National Meteorological Service)

SALT LAKE CITY – The National Weather Service’s Climate Prediction Center released a La Nina watch on Thursday, indicating that trends show the oceanic event to emerge between September and November with a 66% chance that it will last all winter .

La Nina is the result of stronger Pacific trade winds that generally flow from South America to Asia. It pushes the warm ocean water with it westward, unlike its El Niño counterpart. This allows cooler ocean waters to replenish off the west coast of South America, according to the National Ocean Service, which is a division of the National Oceanic and Atmospheric Administration.

This is important because ocean trends impact weather conditions in the United States.

Based on an average of previous La Nina winters, La Nina’s models result in a polar jet model that provides wetter conditions in the Pacific Northwest and Great Lakes regions, as well. than colder air in the northern parts of the West and Midwest. This also results in warmer conditions in the southeast and drier in the southwest and southeast.

It differs from El Nino in that conditions during El Nino are generally wetter and cooler in the southern United States due to an extensive jet stream from the Pacific. This generally results in warmer conditions in the northern United States and Canada, as well as drier conditions in the Midwest.

Interestingly, neither model gives definite weather trends for most of Utah – at least historically speaking. This means it’s hard to tell if Utah is heading for a wet, dry, hot, or cold winter.

“Our signal is not very strong,” said Christine Kruse, chief meteorologist in the Salt Lake City office of the National Weather Service. “There are La Ninas where we might see more precipitation than normal), some average, some below normal. It just doesn’t have any consistency due to the way the jet stream is. installs with a typical La Nina. “

A typical La Nina might have a more negative impact on the southern tip of Utah, like St. George. The area is located just at the northern limit of where drier conditions normally emerge from the mid-polar jet stream.

Again, this dry area is based on the average winter of La Nina. Where the jet stream settles will ultimately determine whether Utah is heading for a desired wet, cold winter or a dreaded hot, dry winter due to the ongoing drought.

It also means meteorologists will have to wait for the jet stream to set in before they have a better idea of ​​what to expect this winter. Cruse said it usually starts to develop in the fall around the same time of September through November, when the Prediction Center expected La Nina to set in.

“(The jet stream) can change. You can start part of the winter with a particular storm path and a higher level ridge develops in a new location and things change,” she said. “But you’re starting to see a little bit of what winter can look like from late fall to early winter.”

The Climate Prediction Center typically publishes its outlook for the winter months beginning around mid-October.

This winter is already considered by state water experts to be a major winter due to the statewide drought. The US DroughtwMonitor currently lists about 98% of Utah in at least one extreme drought and nearly two-thirds in exceptional drought.

A large majority of Utah’s water comes from the snowpack during the winter, so experts say a strong winter is what is needed to help lift the state out of drought.

On a more regional scale, a La Nina event is good news for parts of the West, which is dry everywhere. The US Drought Monitor also lists 93.7% of the entire region – a collection of Utah, Arizona, California, Idaho, Montana, Nevada, New Mexico , Oregon and Washington – experiences at least moderate drought.

Almost 60% of the West is considered to be in extreme drought and just over a quarter of the region is in exceptional drought. Many areas of the Pacific Northwest, where a La Nina winter typically produces more rain, are currently in these more severe categories.

Conversely, a normal La Nina is potentially bad news for southwestern areas like Arizona and New Mexico, which are also covered by some of the more severe drought categories.

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Mary Cashion

The author Mary Cashion