Historical Data-in-Action: Less Predictable Winter Weather in Wisconsin

This Historical Data-in-Action article was prompted by my (perhaps fuzzy) recollection of the winter weather during my freshman year in college. My first collegiate winter (1977-1978) at Lawrence University of Wisconsin included a long period of cold weather. My memory was that Appleton set a record for consecutive days where the high temperature did not exceed 0 ºC (32º F or 273.15 K)–an interval I remembered as beginning in late November and ending in the first days of April.

The surface temperature data from the Global Land Data Assimilation System (GLDAS) Noah hydrologic model, available in the NASA Giovanni system, provide an opportunity to check the accuracy of this chilly memory. In addition, a comparison of the surface temperatures in the winter of 1977-1978 to the winter of 2018-2019 shows how winter weather has changed. The ability to examine the accuracy of our memories allows a “reality check” on what we think is changing in our world compared to what really is changing.

Winter 1977-1978 Surface Temperatures in the Appleton, WI Region

To recreate and simulate conditions in the winter of 1977-78, we turned to GLDAS 3-hourly, near-surface air temperature data. GLDAS provides several datasets that cover different time ranges. In particular, data for the 1977-1978 winter is available in Version 2.0, which extends from 1948 to 2014. For the winter of 2018-2019, Version 2.1 data (covering 2000-2026) was used.

For these plots, an area-averaged time series was generated in Giovanni. The time-series data were downloaded as a comma-separated-variable (CSV) file and imported into an Excel spreadsheet, which was used to make the plots shown here.

Figure 1a shows the near-surface air temperature plotted from October 1, 1977 to April 30, 1978. Figure 1b shows the bounding box used for this plot and for the data in Figure 2. I chose an area with Appleton in the northeast quadrant to reduce the potential influence of Lake Michigan. (GLDAS data have a spatial resolution of 0.25 degrees.)

Regarding the consecutive-days-below-freezing record for Appleton, the exact timeframe of my memory appears to be inaccurate. Temperatures began to stay consistently below the freezing mark (273.15 K) in late November 1977, but there were a couple of days in mid-December when temperatures rose slightly above freezing.

A stretch of days below freezing commenced on Christmas Eve 1977 and extended to February 28, 1978—a span of 67 days. So the below-freezing period does not appear to be as long as I remembered, but it definitely stayed “cold as ice” for awhile.

Winter 2018-2019 Surface Temperatures in the Appleton Region

GLDAS near-surface temperatures for the winter of 2018-2019 are plotted in Figure 2 below. One of the first observations that can be made from this plot is the increased temperature variability during this winter season—particularly in January and February 2019—compared to 1977 - 1978.

While there was a below-freezing period in early December 2018, the temperatures over the rest of that month and into early January commonly rose above freezing. Later in January there was a dramatic cold dive followed by a quick warmup, with temperatures rising above freezing briefly at the beginning of February. Temperatures generally remained below freezing for the rest of the month.

Comparison of Surface Temperatures for the Winters of 1977-1978 and 2018-2019

Figure 3 (below) was created in Excel to compare the near-surface temperatures for the winter of 1977-1978 to the winter of 2018- 2019. This comparison indicates that temperatures in 2018-2019 were generally warmer than in 1977-1978. This is most evident in December and early February. There are intervals where the 2018-2019 temperatures are notably colder than 1977-1978, especially at the end of January 2019 and the late February-early March period.

In addition to these differences, this plot indicates the increased variability of winter surface temperatures in 2018-2019. There are several potential causes of this different pattern, the full discussion of which is beyond the scope of this article. (One aspect that has been discussed is instability of the Arctic polar vortex.)

Meanwhile, in Green Bay

Although it was not possible to find detailed weather records for Appleton, the National Weather Service has a compendium of records for Green Bay, Wisconsin (Green Bay Weather Records). The city of Green Bay (home of the football Packers) is located about 40 miles north-northeast of Appleton, at the terminus of narrow Green Bay, which separates the Door Peninsula from Lake Michigan (see Figure 4 below and Figure 1b above).

The city is also where the Fox River–which arises west of Lake Winnebago, enters the lake at Oshkosh, and flows out of the lake through Appleton and then north–enters Green Bay. Lake Winnebago is not shown in the Figure 1b map, but the northern end lies between 44.1 and 44.2 degrees N latitude, which is within the bounding box.

In Green Bay Weather Records, a table lists the records for “Consecutive Days of High Temperatures Below 32 F.” The table shows that the longest period of freezing temperatures—2 days—occurred twice: December 15, 1892 to February 4, 1893, and December 31, 1978 to February 20, 1979. (I remember that my sophomore winter was cold, too, but with less snow than 1977-1978.)

The next line lists two 47-day below-freezing periods in the early 20th century. At “fifth place” is a 46 day long period occurring January 8 to February 22, 1978. That interval is consistent with my memory and with Figure 1a, and if Appleton is a bit colder than Green Bay (which could be influenced by the adjacent lake) the 67-day record for Appleton, indicated by the Giovanni time-series data, is not out of the question.

Potential Impact on Lake Winnebago and Fox River Watershed Sturgeon Fishing

One of the notable regional winter activities in this area is sturgeon spearing, a form of ice fishing. People set up ice shanties on the frozen lake surface, cut holes (usually square) in the ice, and then peer down into the water with a spear suspended above the hole.

Sturgeon are bottom feeders, subsisting on fly larvae (chironomids) and other benthic organisms, so they aren’t caught on a hook and line. When a sturgeon is spotted under the hole in the ice, the fisher plunges a multi-pronged spear down to spear the fish. The turbidity of the water and the snow cover atop the frozen lake affect the success of sturgeon spearing on Lake Winnebago; the latter influences how much light penetrates the shallow water.

The sturgeon fishery is strictly protected, with all catches reported daily and the state closing the season when catch limits are reached. The population of sturgeon in Lake Winnebago and the upriver lakes is estimated at about 40,0000 fish, roughly 25,000 males and 15,000 females. Furthermore, sturgeon spearing on the lake ice is the only way permitted to catch these remarkable fish. More information on sturgeon spearing is available on the Winsconsin Department of Natural Resources website.

Sturgeon spearing season typically occurs in February, which the temperature plots show is usually the coldest month of winter in this region. The lake ice must be thick enough to support the trucks that drive out on the lake ice with equipment for the shanties and for spearing.

The increased variability of winter temperatures and higher overall temperatures in recent years may thus impact the thickness of the lake ice and the length of the ice season. Indeed, there are recent videos showing what happens when sudden warming in spring causes a quick thaw and shifting ice, causing the spearing hole to open up and swallow a shanty. (Most of them are usually recovered.)

Changes to the hydrology of the Great Lakes, which are connected to numerous rivers and lakes in the Great Lake states of the U.S. Midwest (and also provinces of Canada), affect many different aspects of the ecology here. With regard to the lake sturgeon, the U.S. Geological Survey recently released a report on how such changes may specifically influence this unique resident of the region.