NOAA Winter Outlook: Weak El Nino pattern with mild mountain weather in the mix

Posted at 6:00 PM, Oct 23, 2018
and last updated 2018-10-23 20:00:28-04

MISSOULA – The National Oceanic and Atmospheric Association released its 2018-2019 Winter Outlook and it’s a much different forecast than our two most recent winters.

If you’ve spent time outdoors over the last week, you’ve seen sunny days and clear nights, with an increase in valley haze. If the forecasted winter weather pattern holds, we’ll see more days like the last several than normal. The weak El Nino weather pattern that has developed favors milder mountain conditions.

“There is high confidence that we’re going to be seeing warm temperatures in the mountain areas,” said National Weather Service Meteorologist Alex Lukinbeal. “In the valleys, it tends to get a little more complicated. If we have long periods of valley inversions, we could actually see quite colder temperatures in the valleys.”

The key to these inversions is how often and how long ridges of high pressure settle over the Northern Rockies including western Montana. A week or more of high pressure inhibiting mixing of air will lead to cold highs and lows, and increased pollutants. As for precipitation, the jury is still out on what this forecasted El Nino will bring.

“There’s quite a bit of variability, there are actually weak El Ninos where we see above-average precipitation and weak El Ninos where we see below-average precipitation,” Lukinbeal said.

One interesting thing to keep in mind is the shift in precipitation during weak El Nino conditions over the last 100 years. Prior to 1980, many El Nino years were wetter than normal. Since 1980, every weak event has come with below normal precipitation, meaning the likelihood of less mountain and valley snow is the most likely scenario.

As is the case with every El Nino Winter, it is almost certain that, while the overall projection leads to drier and mild conditions, we’ll still have periods of snow and the occasional storm, just not as many as normal.

An increase in strong valley inversions also increases the chances for cold rain and freezing rain events.

— story by Russ Thomas – MTN News