Minnesota (Fort Snelling) weather for the year 1831
Droughty with Late & Early Frosts, Bitter December (graphic)
The Fort Snelling vicinity experienced a major cooling in 1831, the infrequent precipitation pattern persisting however. Annual mean temperature at the Post (42 F) was the lowest thus far in twelve years’ history, down 5 F from a year ago. Except for a mild and damp March that resulted in another opening of the rivers during this month, most of the year’s major weather events were cold and drought-related. Frosts were reported in late-May, early August, and early September, and the year finished with a bitterly cold December, almost equal in severity to 1822. Like 1830, entries appeared noting the low stage of the Mississippi.
Cold January/February, But Another March Breakup – The first six weeks of 1831 provided persistent, almost uninterrupted arctic cold at Fort Snelling. Twenty-nine of the first 45 days had at least one zero or colder temperature at the prescribed observation times, as low as minus 20. Thawing temperatures were recorded just twice, both of these 32 F. The main storm track having shifted southward, snowfall frequency was greatly diminished from December. Just six falls occurred in January (mean temperature: 8 F) and two in February (mean temperature: 14 F), but with so little melting, the deep blanket laid down in December remained likely very much intact. To the southeast in Illinois, the 1830-31 season would be remembered as the “Winter of Deep Snows”, Fort Crawford (Prairie du Chien), a short distance north of the border, measuring a 48-inch depth at one point [Ludlum, 1968]. Back at Snelling, the long cold pattern finally began to break down during the third week of February with a few scattered thawing days experienced. Snow-melting weather established itself for good over the last five, the 26th reaching the low 50’s with rain falling, the 27th remaining in the 40’s virtually all day with additional rain. More mild, cloudy, and damp weather during March (mean temperature: 32 F) resulted in the fifth (likely) consecutive breakup this month of the rivers within sight of the Post. Rain, sometimes mixed with snow, fell on eight days, ground conditions with all the snowmelt undoubtedly very sloppy and muddy. Afternoons over the first ten days were generally in the mid-30’s to upper 40’s with several rains, and a thunderstorm was even recorded on the 4th. A five-day subfreezing spell next set in on the 15th, diurnal temperature ranges confined to single digits for the mornings and teens/twenties for the afternoons, but a spell of much warmer weather came on the 21st, the mercury 58 F at 2PM. The Mississippi and St. Peter’s rivers each opened on the 25th.
Varied Spring Weather – April (mean temperature: 45 F) and May (mean temperature: 60 F) displayed an assortment of unseasonable weather — late snows, a long dry spell, early heat, and late frosts. Spring’s advance during April was slow, with numerous cloudy and cool days. Most afternoons over the first half only reached the low 40’s, several snows also falling. A brief surge of summery weather came on the 17th, 79 F recorded at 2PM with a thunderstorm occurring sometime during the day. But much colder weather followed, the 21st only in the high 30’s with a snowstorm “3 inches deep” blowing in. Droughty weather made up May, with just four days’ rain and extremes of both heat and cold. On the 10th, another early warm surge brought 88 F, hottest yet so early in the season here, the 11th almost as warm with 86 F. The first precipitation since the 3-inch snowstorm 22 days previous came as rain on the 14th, the mercury just in the low 50’s at mid-afternoon. On the 22nd and 23rd, the second episode of late-May frosts in as many years visited, tying 1822’s late-date record, but summery heat quickly followed, the last five afternoons all near or above 80 F, including two at 86 F.
Another Dry Summer – Summer ’31 was without last year’s prolonged heat, roughly seasonable in mean temperature, but it shared its infrequent falls of rain. Dry soil conditions likely contributed to a possible frost in early August. Just 16 days recorded rains, equaling 1829’s figure. June (mean temperature: 69 F) was quite pleasant with no extremes of heat. Most afternoons were confined to the 70’s, the warmest 84 F, seven days recording rain. July (mean temperature: 73 F), however, started out sweltering, four afternoons over the first week in the upper 80’s. Following “thunder & rain” on the evening of the 7th, though, cooler weather moved in, and except for the third week which had several afternoons in at least the mid-80’s including 92 F on the 21st, comfortable temperatures were the rule. August (mean temperature: 71 F) was relatively warm but dry, just three rainfalls seen all month, none over the first eighteen days. Cool weather prevailed early, most afternoons over the first week in the mid-to-low 70’s. On the 3rd, the second summertime frost in Post history was recorded, seventeen days earlier than the ’27 event. Notes did not disclose whether it was observed on the Fort grounds, the surrounding prairies, or the river bottomlands, and it should be mentioned that the observed 7AM temperature that morning in the enclosure was 56 F, at least raising the question as to whether it really was frost. If it was indeed genuine, though, the moisture-deficient ground and its greater tendency to radiate nighttime heat was certainly in part responsible. Further indicative of the summer’s absence of moisture, the Mississippi was reported “very low” on the 7th. Starting the second week, an extended two-week period of persistent southerly winds brought the summer’s longest warm spell. Twelve of thirteen days from the 7th had prevailing winds from this quarter, afternoon readings consistently reaching the mid-80’s, peaking with a tie for the summer’s highest with 92 F on the 16th. Thunder and rain on the 19th finally broke the spell, afternoon temperatures over the rest of the month back in the upper 70’s, predominantly.
September/October Contrasts, December Arctic Blasts- Temperatures declined sharply in September (mean temperature: 55 F), the month tying 1826 for coolest yet. Seventeen days were “cloudy” and six had rain. Autumn-like weather set in almost from the start, most afternoons over the first week only in the 60’s, frost reported on the 2nd. Much of the same made up the second week, afternoons principally in the 60’s, frost occurring again on the 12th. Following another frost on the 17th, a brief warm surge brought 80 F the very next day, warmest of the month. But thereafter, most afternoons were only in the 50’s, the last two mornings each 34 F. October was also relatively “cloudy” (19 days) but more seasonable in temperature (monthly mean: 48 F). Rain continued infrequent with just four falls. The first ten days remained cool, most afternoons in the 50’s, the 5th and 9th dropping to 32 F and 29 F, respectively, at 7AM. A strong warming then followed, balmy Indian Summer weather prevailing over the 12th-15th with successive afternoon readings of 76 F, 74 F, 82 F, and 78 F. Unseasonable warmth featured the 20th and 21st as well with 73 F and 72 F, respectively. But rain and snow mixed were seen on the 23rd, the mercury only 33 F at 2PM. The morning of the 26th was a chilly 19 F at 7AM. November (mean temperature: 31 F) featured a late arctic intrusion, prelude to another bitterly cold December. Precipitation continued infrequent, just two rains over the first sixteen days, four snows, apparently light, coming over the balance. Afternoon temperatures in the 40’s and 50’s comprised most days into the second week, the 8th and 9th in the 50’s all day with rains, but thereafter, the trademark cloudy/dark/chilly pattern took over, daily temperature ranges until the last few days typically in the 20’s for the mornings and the 30’s for the afternoons. Forerunner of another historically cold December, a rush of bitter arctic air brought falling temperatures all of the 28th: 11 F, 9 F, and 0 F recorded at the scheduled times, minus 7 recorded on the following morning. The Mississippi froze over for the winter on the 28th.
Near-Record Cold December – December belonged to the arctic, overall mean temperature (3 F) just one degree warmer than its’ 1822 namesake. This December’s frigidity, however, was more concentrated than 1822’s, confined mostly to the first half. Relatively moderate weather made up the first two days, afternoon temperatures around 20 F, mornings in single figures. But over the next three days, a fresh arctic surge invaded the region. Morning temperatures of –20 F, -20 F, and -16 F were recorded on the 5th-7th, respectively. Following a slight letup over the ensuing three, two additional cold pulses swept through, the result being successive morning readings of -22 F, -21 F, -18 F, -26 F, and -21 F on the 11th through 15th. The 14th was only -10 F at 2PM, helping earn it the distinction as the “coldest day since 31st January 1824” according to Surgeon Robert E. Wood. Minus 10 and minus 15 temperatures were recorded on the 17th and 19th, but the mercury then soared to 36 F on the 20th, first thawing reading in three weeks. Generally seasonable weather prevailed over the remaining days, a number of afternoons in the 20’s, several nights in the teens. The early December 1831 outbreaks apparently had been more far-reaching than those of 1822, contemporary accounts reporting the Mississippi to be frozen 130 miles below the mouth of the Ohio, ice at New Orleans thick enough to allow skating [Kendrew, 1937].