Comments on Soil Moisture Recharge

Comments on Soil Moisture Recharge:

I have heard from many MPR listeners in recent weeks about their concern for the dryness this autumn season and its potential negative effects for gardens and agricultural soils. Indeed, the precipitation during the autumn season is one of the most critical features of our climate in terms of maintaining adequate soil moisture for gardens and for agricultural crops.

Numerous studies over the decades by respected scientists like Donald Baker and Wally Nelson have shown that on average 50 to 60 percent of the total autumn precipitation across Minnesota is stored by the soil, the highest fractional storage of moisture for any season of the year. This relatively higher value of soil moisture storage for this time of year is due to several reasons.

Most vegetation has died or is in the process of going dormant and using little soil moisture; surface evaporation is reduced because of the lower air temperatures, sun angle and declining daylength; and rainfall rates more closely match the infiltration rates of our soils (0.25 to 0.35 inches per hour), meaning that less is lost to runoff. For individual autumn storms, storage efficiency can be as high as 80 percent, so that for every inch of rainfall, approximately 0.80 inches can be stored in the soil in many areas of the state.

Average autumn (September 1 to November 30) precipitation across the state ranges from 6 inches to 8 inches for most areas of the state. So far in the autumn of 2024 rainfall has been mixed across the state, with abundant amounts (2-4 inches) in northern counties and some southeastern areas (1 to 3 inches), but less than 1 inch over most of the rest of the state. Many important agricultural counties in the state have measured less than half an inch of rainfall. As of this week according to the U.S. Drought Monitor, 86 percent of the Minnesota landscape was in at least Moderate Drought, and 43 percent was in Severe Drought.

Despite recent rainfalls of 0.25 to 0.50 inches (Thursday), it is looking less likely that soil moisture recharge will be near average this autumn, even if soils remain unfrozen and absorb a good portion of both November and December precipitation. This situation means that soil moisture recharge in the early spring of 2025 will be very critical to both the 2025 gardening season as well as the 2025 crop season in Minnesota. For most gardeners, supplemental water this fall will be good for the yard and garden, but most farmers don’t have this option. Hopefully we will have a wet spring in 2025 so we can be more optimistic about the next crop season.

Weekly Weather Potpourri:

The Weather Underground reported this week that Hurricane Milton spawned a record number of tornadoes across Florida according to data from the Southeast Regional Climate Center. From just before midnight on October 8 to October 9, there were 46 tornado reports across Florida, most across south-central areas. This is a record daily number at least going back to 1950. The tornadoes amplified the total damages from Milton, still be tabulated.

The Weather Underground also featured a good article about the expected change in the polar jet stream across North America next week. The Jetstream pattern is expected to transition from Zonal to Amplified, meaning that low pressure systems may be coming to Minnesota from the southwest, perhaps bring more heat, but more moisture as well. This could mean more general rains next week to conclude a dry month of October. The rains would be most welcome.

MPR listener question:

You and Cathy Wurzer have spoken so much this year about the winds, especially the frequency of high wind speeds. We wondered if we have had any perfectly calm days in the Twin Cities this year? And if we have, is this pretty rare?

Answer:

No, we have not recorded an entire day of calm this year in the Twin Cities. The closest we came to this was on February 21st, when 14 of the 24 hours that day showed calm. But the average wind speed that day was 1.8 mph. A completely calm day is quite rare historically. Most years it does not occur. Speaking of wind, November is climatologically the 2nd windiest month of the year in Minnesota, so expect more wind in the coming weeks.

Twin Cities Almanac for October 25th:

The average MSP high temperature for this date is 53 degrees F (plus or minus 12 degrees F standard deviation), while the average low is 37 degrees F (plus or minus 8 degrees F standard deviation).

MSP Local Records for October 25th:

MSP records for this date: highest daily maximum temperature of 82 degrees F in 1989; lowest daily maximum temperature of 29 degrees F in 2020; lowest daily minimum temperature of 12 degrees F in 1887; highest daily minimum temperature of 62 degrees F in 2000, and record precipitation of 0.75 inches in 2012. Record snowfall is 0.4 inches in 2020.

Average dew point for October 25th is 35°F; the maximum dew point on this date is 65°F in 1971 and the minimum dew point on this date is 9 degrees F in 1972.

All-time state records for October 25th:

The state record high temperature for this date is 87 degrees F at New Ulm 2S (Brown County) in 1927. The state record low temperature for this date is -10 degrees F at St Vincent (Kittson County) in 1887. The state record precipitation for this date is 4.17 inches at Winona Dam (Winona County) in 2023. The statewide snowfall record for this date is 15.0 inches at Sandy Lake Dam (Aitkin County) in 1942.

Past Weather:

One of the coldest October weather patterns in history was gripping the state on October 25 of 1887. Several climate stations reported morning lows in the single digits and some reported subzero readings. The daytime high only reached 21°F at Rochester, a typical high temperature for the month of January.

A warm spell of weather encompassed the state on October 25 of 1927. Many areas, even on the Iron Range saw daytime highs reach the 70s F. Fourteen counties reported afternoon high temperatures of 80°F or greater.

An early season winter storm brought heavy snow to the northern third of Minnesota over October 24-25 of 1942. Many areas reported 4 to 8 inches of snow, while a few climate stations in north-central and northeastern Minnesota reported over 10 inches of snowfall.

Outlook:

Mostly sunny over the weekend with warmer than normal temperatures. Then very warm for Monday and Tuesday with increasing cloudiness on Tuesday and a chance for showers later in the day. Chances for showers continue on Wednesday and early Thursday of next week, with temperatures running closer to normal.