NOAA says warmer start to winter, but La Nina could bring cold, snow later
DULUTH — Seasonal weather experts at the National Climate Prediction Center on Thursday, Sept. 21, forecast a warmer-than-average start to the coming winter but said a developing La Nina cooling of the Pacific could bring colder weather here early in 2018.
The meteorologists said current trends show the Upper Midwest, Great Lakes, eastern states and the southwest U.S. have a better-than-average chance of seeing above-normal temperatures from October through December.
No portion of the U.S. is expected to see colder-than-normal temperatures through December.
The forecasters said there's no indication of any trend away from normal for Upper Midwest, Great Plains or Great Lakes rain and snow for late autumn and early winter.
But a La Nina cooling of equatorial water in the Pacific appears to be developing, with odds now at 62 percent that a full-blown La Nina will occur by mid-winter. If that happens, forecasters say the Upper Midwest and Great Lakes could see colder-than-normal temperatures and more snow early in 2018.
"Should La Nina fully develop we would forecast below-normal temperatures across the northern plains and above-normal snowfall," Matthew Rosencrans, seasonal forecaster for the Climate Prediction Center, told reporters in a conference call Thursday.
But that trend often doesn't hold true in this region. While El Nino Pacific warming events have a more pronounced warming impact on northern Minnesota, the impact of La Ninas on temperature here have been all over the board.
Last winter, a weak La Nina saw a much warmer winter than normal. January was up nearly 6 degrees in Duluth and February was 7.4 degrees warmer than normal. The National Weather Service in Duluth last year looked at climate records from the past 12 La Ninas and found "no strong climatological leanings in either temperatures or precipitation" in Duluth.
A strong La Nina in 1964-65 saw noticeably lower temperatures. A moderate-to-strong one in 1999-2000 saw much higher-than-normal temperatures, and a weaker La Nina in 2011-12 was among the warmest winters in recorded history for Duluth.
La Ninas do tend to bring more snow to northern Minnesota, however. Over the past 60 years, La Nina winters have averaged about 92 inches of snow in Duluth compared to 77 inches for non-La Nina winters. The 60-year average is 82 inches. Most of the extra snowfall in La Nina winters seems to come from February through April.
Half of the last 20 stronger La Nina winters produced snowfall in Duluth of 100 inches or more. But the connection isn't a sure thing. That moderate-to-strong La Nina in 1999-2000 saw just 60 inches of snow in Duluth, and last year's weak La Nina brought only 67 inches.
Drought continues in Dakotas
The climate experts, part of the National Oceanic and Atmospheric Administration that also includes the U.S. Weather Service, on Thursday said they expect that the current drought in Northwestern Minnesota will end by January but that the severe drought in the Dakotas and Montana will persist into winter.
August was third warmest
Earlier this week NOAA released climate data that shows the globally averaged temperature over land and ocean surfaces for August was the third-highest in the NOAA global temperature dataset, which dates back to 1880. The June-August seasonal global temperature was also third-highest on record, while the year-to-date global temperature is so far second-warmest in the 138-year record.
For 41 years now, Earth has not seen a single month where the temperature averaged colder than the 20th century average for that month. August 2017 marked the 41st consecutive August and the 392nd consecutive month with temperatures above the 20th century average.