Milwaukee and southeast Wisconsin got an early taste of Winter this week. It could be the start of a potentially wetter-than-average cold season, according to NOAA.
A weak La Niña is forecast to develop in the next few weeks - potentially influencing the jet stream and prevailing weather patterns in the Northern Hemisphere. Drier and warmer conditions are expected across the Southern U.S. while colder-than-average weather is projected in the Pacific Northwest.
A WEAK LA NIÑA
Sea-surface temperatures in the equatorial Pacific have trended cooler in the last several weeks. Meteorologists and climate scientists have been closely monitoring the El Niño Southern Oscillation (ENSO). While ENSO-neutral conditions have been observed in the Fall, forecasters expect a transition to a weak La Niña phase.
The El Nino Southern Oscillation (ENSO) is a cyclic climate pattern primarily driven by the trade winds in the Pacific Ocean near the Equator. Faster trade winds (blowing East to West) over the Pacific push warm ocean waters farther West. Colder water gradually moves up from the below leading to cooler-than-average sea surface temperatures off the West coast of South America. This pool of cooler water influences the jet stream and prevailing weather patterns across the Northern Hemisphere.
A La Niña drives the polar jet stream farther North and weakens the Pacific jet stream. This leads to colder and wetter conditions across the northern U.S. and Canada. Meanwhile, the southern U.S. trends drier and warmer.
Given the weaker nature of this season's La Niña, the effects may be more variable.
Periods of colder weather are possible as the polar jet stream is nudged farther North. But we may also encounter near-normal conditions as well.
WHAT THIS MEANS FOR MILWAUKEE
The city of Milwaukee averages 48.7" of snow each cold season. This is based on 30 years of snowfall data (1990-2020).
37.1" (or about 76%) of the average seasonal snow falls between December and February.
During the Winter of 2022-2023, only 26.4" of snow fell in Milwaukee. This was during the last weak La Niña. That's about 10.7" below the average snowfall during the December-February timeframe. However, the total precipitation topped out at 8.61". This is 3.18" above normal for this time period.
Each Winter is unique and seasonal weather predictions are difficult to make. Milwaukee's temperatures and snowfall are influenced by much more than a La Niña or an El Niño. But they can certainly make their mark. Last Winter, the city only received 19.5" of snowfall during one of the strongest El Niño's in recent years.
Storm Team 4's projection falls in line with the NOAA outlook. Given the weak La Niña, a variable polar jet stream allows for equal chances of above & below-average temperatures throughout the Winter Season in Wisconsin. Additional moisture may lead to more precipitation across the region.
