The National Weather Service has released their Winter 2020 outlooks for both temperature and precipitation. Their current forecast has Wisconsin favored to have a wetter than average winter while temperatures have an equal chance to be above or below normal.
Noticeably, the southern half of the country is forecasted to be both dry and warm while the northwestern corner especially is favored to be wet and cold.
NWS Winter Temperature Outlook for 2020-2021
You might be skeptical about how they can forecast out this far and with what accuracy do they expect these conditions to land. One of the major ways they make these long-range forecasts are based on sea surface temperatures in the Pacific Ocean.
This winter the pacific ocean near the United States and South American will be cooler than average and is known as La Niña. Looking back at past La Niña patterns the National Weather Service can compare historical data with temperature and precipitation trends to determine how our own atmospheric setup translates to future weather.
NWS Winter Precipitation Outlook for 2020-2021
In their forecast, when it says we have an equal chance of both cooler than average or warmer than average conditions it means historically in a La Nina winter Wisconsin has had both scenarios occur. But also in La Nina years generally Wisconsin sees more precipitation than usual.
The atmosphere is very complex and a variety of variables have to come together for a simple 6 or 7-day forecast. But using historical data and ocean temperatures a broader and more generalized forecast is possible.