Garden club talks Black Hills weather predictions

Dr. Adam French visited the Hill City Evergreen Garden Club March 27 to teach a seminar on climate change in the Black Hills and how it will affect gardens. French is with the Atmospheric and Environmental Sciences Program in the Department of Civil and Environmental Engineering at South Dakota School of Mines and Technology in Rapid City. 

In his presentation, French discussed changes in Black Hills weather, future projections and predictions for the coming growing season. 

French said here in the Hills temperatures ran two to four degrees above normal over the entire winter. In fact, French said this was the warmest winter on record for the contiguous United States. 

Some temperature observations from Custer showed that from December through February there were “45 days with a high temperature above normal, 43 days with low temperature above normal, 55 days with high temperature above freezing, four days with low temperature above freezing and two days with low temperature above normal high temperature,” said French. 

“We did obviously have that big cold snap back in January,” said French, “and we did set a couple record lows.” 

However, French said only one record high was set this winter.

“Precipitation-wise, we actually were right around normal,” said French. “We don’t get a lot of precipitation this time of the year anyway.” 

Winter tends to be dryer, and this year was about average for precipitation. French said the difference is the warm weather melted the snow, and the snowpack in the Black Hills is well below normal because of this. 

The driving weather pattern causing this is an El Niño, which French said is related to ocean temperatures and warm water piling up by South America. 

“Even though that’s a ways away, it has feedback all the way up through the weather system,” said French. Because of this, it is usually wetter in the south, dryer in the east and warmer in the northwest. 

French said the area is just now heading into the wet time of the year since most of the precipitation occurs between April and July with the majority falling in May.

“We average about 22 inches of precipitation, and over half of that falls in spring, early summer,” said French. “If we end up with a dry period during these next few months, that tells for the rest of the year.”

Based on data records, temperatures and precipitation have changed in the area over the last 80 years. For the Custer area, the average temperature between 1943-73 was 41 degrees Fahrenheit according to French. The average temperature between 1993 and 2023 was 44.5 degrees Fahrenheit. There has been a 3.5 degree increase in average temperatures, and “the cold years aren’t as cold,” said French. 

He did the same comparison for Rapid City and the increase was only about 0.5 degrees. 

With this data, French said the warmest temperatures of the year are actually trending down. Rather it is the coldest temperatures that are going up. 

“Nighttime cold temperatures are where we’re seeing a lot of the warming,” said French. “The idea is that we have more greenhouse gases trapping the heat. The ground heats up during the day, and all that heat is supposed to head off to outer space at night. So if we’re trapping more of that in, that keeps it from cooling as well at night. So it kind of fits with the physics of what we think is going on behind the scenes.” 

Along with this, the first and last frost dates shifted between 1943 and 2023 in the Custer area. Between 1943 and 1973, French said on average the last freeze was June 6, and the first freeze was Sept. 1. Between 1993 and 2023, the last freeze was May 25, and the first freeze was Sept. 22 on average. This adds a potential five weeks to the growing season, although French said there is “still a lot of year-to-year variation.” 

During the same time period, French said there has also been an increase in precipitation in the Custer area. Between 1943 and 1973, the average annual precipitation was 17.9 inches. Between 1993 and 2023, the average annual precipitation was 19.8 inches, which is a 1.9 inch increase. 

French said again there is year-to-year variation, but the wet years are likely getting wetter. 

An attendee asked French how certain he was that the tools used to gather data from 1943 going forward are as accurate as the tools used today. French said this is a challenge because the tools they have today are better, but this is taken into account when assessing the data. 

“The technology changes, but the basic data points are the same,” said French. 

Looking forward for Pennington County, French said the averages will likely get warmer overall in the summer, there will be warmer nighttime temperatures and there will be less days below freezing. The last one could be good for the growing season but could also be problematic for insects that usually die off in the winter. 

According to French, there were not a lot of differences between the predictions for Pennington County and Custer County. 

For average precipitation in Pennington County going forward, French said the annual total of precipitation is likely to increase by four percent, or one inch. 

The bigger thing French saw is “Where that increase is coming is in more of the heavy rain events.”

These potential thunderstorms or downpours could cause flooding and an increase in large hail. 

“If anything, some of the research seems to be suggesting that whether the storms become more frequent, we could definitely see some of the really destructive storms,” said French. 

Related to gardening and erosion, an attendee said, “There’s an imperative for gardeners to really be serious about their mulching and not to leave bare soil in the garden because the impact of heavy rain is exceedingly destructive.” 

Someone else suggested using rain barrels to collect the water from heavy rain events.

Along with this, French said the weather is also likely to be drier, and there will still be a wet year, dry year cycle. 

“If we are seeing those warmer temperatures, that ramps up the evaporation we can have out of the soil moisture,” he said. “If it’s warmer, you can get into drought or really dry conditions faster.” 

The cycle swings may become more dramatic, and there may be water resource challenges. This increases the risk of wildfires as well.

 Based on the National Weather Service Climate Prediction Center, French said the spring outlook seems to be similar temperature-wise with no clear indicators of whether it will be colder, warmer, wetter or drier. For the summer, French said there is a stronger signal for things drying out. 

“I think it’s really going to depend on, do we get some good precipitation in the next month or two,” said French. 

Information about the Hill City Evergreen Garden Club’s next seminar will be posted on their Facebook page.