Predicting the weather for winter many weeks before it begins is hard. If any season proved there is a long way to go in perfecting such long-term outlooks, this winter was it.
I am not aware of any outlet in the government, media or private sector that nailed the 2016-17 winter outlook. In fact, some forecasts predicted the opposite of what actually happened.
The National Weather Service and The Weather Company probably had the most accurage outlooks of those I reviewed, although they were far from perfect.
Across all of the various outlooks, the forecast errors were linked to a Pacific Ocean that did not behave as expected. Storms traveling across it were supposed to mostly pass to California’s north. Instead, time and time again they hit the Golden State head-on, unloading historic amounts of rain and snow, while flooding much of the rest of the nation with abnormally warm air.
Forecast groups presented two schools of thought for winter temperatures:
1) Warmer than normal air would dominate most of the country except for parts of the north as the jet stream hovered near the Canadian border.
2) The jet stream would dive south east of the Rockies, and colder than normal air would prevail over much of the northern and eastern parts of the country. The Southwest would be warm.
The first school proved closest to correct. Temperatures over the entire nation were warmer than normal except for the Pacific Northwest. It was the nation’s sixth-warmest winter on record.
The National Weather Weather Service and Weather Company (which operates Weather.com) fell into the first group, which best captured the winter’s temperature pattern, although their predictions missed some important details.
The Weather Service wrongly predicted below-normal temperatures in the Upper Midwest and didn’t capture the extent of the warm air in the eastern and central United States.
The Weather Company also missed the warmth that prevailed over the eastern third of the nation.
But the Weather Service and Weather Company forecasts were quite good compared to the Commodity Weather Group, Atmospheric Environmental Research, and WeatherBell Analytics, all of which called for a cold winter in much of northern and eastern United States — the opposite of what actually happened.
The precipitation forecasts I reviewed missed the onslaught of rain and snow that bombarded California, which turned out to be the winter’s biggest weather story.
The Weather Service confessed its California precipitation forecast was a “big dud.”
AccuWeather, the only other prominent group that offered a public precipitation outlook, wrongly said the southern two-thirds of California would be “dry.”
Why some forecasts were so bad
The Pacific Ocean firehose that blasted California not only messed up the precipitation forecast but also reflected a jet stream pattern that wreaked havoc with some of the temperature forecasts for the eastern United States.
Before winter began, forecasters expected a La Niqa event to develop and influence weather patterns. Typically, La Niqa produces a jet stream that keeps the storm track to the north of California, passing through Canada before dipping over the central and eastern United States, allowing Arctic air to spill south.
Often, California experiences drier than normal weather during La Niqa. But this La Niqa, which was weak and ultimately fizzled, didn’t behave like a typical La Niqa. Instead, a powerful Pacific jet stream frequently swept storms into California.
This same jet stream helped draw mild air eastward over the Lower 48, meaning substantially warmer than normal temperatures in most areas.
The raging Pacific jet formed from a configuration of sea surface temperatures that few forecasters anticipated. “ (the sea surface temperatures) were much colder in the Northeast Pacific than I thought and much warmer in the tropical eastern Pacific,” said Joe Bastardi, who produced WeatherBell Analytics’ outlook.
Judah Cohen, the author of Atmospheric Environmental Research’s outlook, traced the cold waters in the Northeast Pacific to frigid air that developed over Siberia in November. “The models missed that impressive buildup of cold air in Siberia … (that then) rapidly cooled the North Pacific sea surface temperatures,” Cohen said.
The contrast between the chilled North Pacific waters and much warmer waters in the tropical Pacific helped establish the rip-roaring jet stream that ultimately collided with the California coast. “Once that temperature gradient set up in the North Pacific, the jet (stream) really came alive,” Cohen said.
For Cohen, the strong Pacific jet stream was an unexpected consequence of the rapid advance of snow in Siberia during October, which then led to the cold November. His research has shown the fast build-up of autumn snow in this region is linked to cold winters in the eastern United States. “In an ironic twist, extensive Eurasian snow cover may have actually contributed to a milder North American winter, the opposite of what I have been preaching for much of my career,” he said.
Bastardi, who called his winter outlook “horrible,” stressed that many atmospheric factors converged to make the forecast a difficult one. The Pacific Ocean temperatures were “just the tip of the iceberg,” he said.
Matt Rogers of the Commodity Weather Group blamed “a complex interaction of variables” on the difficult forecast.
Tom Di Liberto, who analyzed the Weather Service’s outlook for Climate.gov, put it this way: “If this winter shows anything, it is that we aren’t kidding when we say that ENSO (El Niqo and La Niqa) is not the only game in town. Random weather and other climate factors can often override a La Niqa signal, especially when it is weak.”
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