Minnesota (Fort Snelling) Weather for 1820

Severely Cold January - January provided an immediate introduction into the kind of prolonged intense cold possible in this remote locale, "severely felt" by the Army personnel in their hastily constructed log huts in the river bottomlands [Holcombe, 1908]. Twenty subzero morning temperatures were recorded by Surgeon Edward Purcell in the meteorological register, the monthly average temperature just 0 F, about twelve degrees below the modern-day average January figure for the Twin Cities area. Not until January 1856 would a colder month be experienced here average-wise. The mercury never got above 32 F, a gradually deepening cold taking hold that reached extreme levels after mid-month. On the 20th, climaxing

5 1/2 days of continuously below zero temperatures, -26 F was recorded at the scheduled 7AM observation time; on the 30^th an even more frigid –30 F was noted at the same hour. These being fixed-time observations and not self-registering instrument recordings, the absolute lowest the mercury sank to over the pre-dawn hours of these bone-chilling mornings was likely several degrees colder still. The bitter cold was a major complication to the deadly pneumonia and scorbutus (scurvy) that was already raging, some forty soldiers to ultimately perish before the winter was out. After the first week of February, though, the cold relaxed its grip, and thawing afternoon readings were the rule after the second week. Thunder and lightning was even recorded on the 15th, upper 40's 2PM temperatures reached on two afternoons during the last week. Mean temperature for the month finished at 20 F, about 2 F above the modern-day average. Down through the years, the first or second week of February have proven to be a favored times for interruptions of prolonged cold terms with establishment of interim or sometimes extended thawing spells. March (mean temperature: 26 F; -5 F departure), true to its name, was windy and changeable with abbreviated spells of both mid-winter-like cold and mid-spring-like warmth. Several days over the first half had "high" winds, those from the 15th on blowing "with some volume" almost every day. An arctic spell brought a return of subzero cold on several successive mornings, including -10 F at the start of the second week, but temperatures around the equinox soared to near 70 F on successive afternoons. On the 21st, the first "wild fowl" were observed returning from the south, and on the 24th the first precipitation in nearly a month, a "heavy rain" fell.

April Heat Followed by May Drought - April and May, not atypically as future years have demonstrated, displayed contrasting weather anomaly patterns, unseasonable warmth and early thunderstorms over much of the former, drought over nearly all of the latter. April (mean temperature: 53 F, +7 F departure) opened cold and blustery, the 1st a bitter 10 F at 7AM, still after an hour of elapsed daylight. Both it and the 2nd remained subfreezing all day. Conforming to the sub-monthly portion of the calendar year most naturally favored for extreme blustery episodes of this kind, "high" winds were noted on each of the first 12 days but one. "Verry high" levels were noted on the 4th, speeding the breakup of the St. Peter's (Minnesota) river onto the following day. Navigation was "free" in both the St. Peter's and Mississippi on the 8th, this of course, pertaining only to those portions within sight of the compound. A much more important opening, especially in the years to come, would be that of Lake Pepin, boat traffic from places below such as Fort Crawford (Prairie Du Chien) and St. Louis then becoming possible to St. Paul. On the 10th, a premature warm spell suddenly enveloped the area, conditions over the next two weeks occasionally more typical of early summer. Afternoon (2PM) temperatures frequently approached or topped 70 F, peaking with 85 F on the 23rd. Moist southeasterly or easterly winds prevailed on all but one day from the 10th through the 25th. Unseasonably early and frequent thunderstorm activity was an inevitable result, one on the 18th spawning a small tornado that ripped shingles from the barracks, a somewhat incredible happening considering that they were the only such buildings within several hundred miles. Cooler temperatures on the heels of "fresh" northwesterly winds (the "fresh" term probably derived from the Beaufort Scale, in this case indicating speeds between 20-25 miles per hour) finally moved in during the last week, and early May, an otherwise mild month overall (mean temperature: 59 F; 0 F departure) had a brief winter relapse -- snow falling on the morning of the 7th. During the month, plans were carried out to move the garrison to a higher and more sanitary area on upland prairie about a mile northwest of the future site of the fort. Located near a spring, it was named "Camp Coldwater", diary "remarks" for 21-23 May providing notes to that effect: "Moving from St. Peter's to Cold Water Camp." Another lengthy spell of anomalous weather had now set in -- drought. Over the 28-day period May 9th to June 6th, just a single light rain was recorded, this at a time when moist air is usually streaming in from the Gulf of Mexico, setting off the increasingly frequent and heavy rains that spur development of local vegetation and crops.

Cool First Summer - The first summer at Cantonment New Hope was relatively cool and clear, with slightly less than average rain frequencies. Combined June-August mean temperature (69 F) was 2 F degrees lower than the current climatic "normal", not to be surpassed for low average until 1835. Nine rain days were recorded in June, eleven in July, and nine in August. Unfortunately, no measured totals were included, readings of this kind not appear until July 1836 when the first official rain gauge began service atop the bluff at Fort Snelling. Relatively seasonable temperatures comprised June, monthly mean temperature (69 F) a degree above the modern-day normal figure. A welcome break in the drought came during the second week, five days in succession from the 7th having rains, six in all for the week. Accompanying the falls were cool to pleasant temperatures, most afternoons confined to the 70's. Drier and warmer weather made up the balance of the month, with just two rains recorded and five afternoons at 90 F or higher, including 93 F on the 17th, the warmest. The May/early-June lack of moisture had not prevented a "fine garden" planted in the St. Peter's (Minnesota) bottomlands from producing the first crop of garden peas, eaten on June 15th [Neill and Williams, 1881]. Low water, however, did delay a planned sawmill from being constructed at nearby Minnehaha Falls [Ford & Johnson, 1962], this project to be completed next year at St. Anthony Falls instead [Neill and Williams, 1881]. July (mean temperature: 70 F; -4 F departure) was cool, all of its 11 rains coming over the first 23 days. The afternoon of the 1st tied for summer's warmest with 93 F, but the 3rd was chilly with "heavy rain during the day" and the mercury just 64 F at 2PM. Except for the 21st-24th, which ranged from 84 F to 89 F, no warm spells of any note occurred, most afternoons in the low 80's or cooler. Afternoon temperatures over the 27th-30th were only in the 70's, this several-day calendar portion being the warmest of the year here climatologically (mid-afternoon figures at 83 F-84 F). Michigan Governor Lewis Cass, who visited the Post for three days starting with the 31st, noted that ninety acres were "planted with corn and potatoes and wheat", some "green corn" consumed on the 20th [Hansen, 1958]. August (mean temperature: 67 F; -4 F departure) was generally cool and sunny with 23 "clear" days, the rest "clear"/"cloudy" or "cloudy/clear". A few scattered warm afternoons were experienced over the first ten, including 89 F on 3rd and 92 F on 10th. The 8th was noted as “sultry”. Just four of the last nineteen reached as warm as 80 F, with an appreciable number confined to the low to mid-70's. Surgeon Purcell noted at month-end that "the thermometer was placed in the shade facing the Northwest". Work of the soldiers during this first summer "was pushed forward with all possible speed... procuring logs and other necessary materials" for construction of the Fort's buildings [Neill and Williams, 1881]. Colonel Josiah Snelling, after whom the Post would eventually be named in 1825, arrived this month, relieving Colonel Henry Leavenworth.

First Frosts, An Indian Summer Spell - September (mean temperature: 61 F; 0 F departure) provided a typical summer to fall transition. First, a late spell of mid-summer-like warmth set in, carrying over into the second week. Several afternoons approached 90 F. Then, successive cold fronts preceded by rains moved through. History was made on the 10th as the cornerstone of the Fort, to be called St. Anthony, was laid "with due ceremony" [Neill and Williams, 1881]. This was a day showing signs of change, with northerly winds, "rain and fair alternately", and a 2PM temperature of 69 F. Following the second front, the weather became distinctly more autumnal, the season's first frost coming on the 17th, additional visitations noted on the 18th, 19th and 20th. Finally, repeating a climatic script that is a trademark of autumnal weather in these parts (as well as most other areas of the eastern half of the United States), southwesterly winds around the back side of the southeastwardly drifting high pressure area set up a warming trend accompanied by a long run of Indian Summer days. This first recorded episode had clear skies and southwesterly winds prevailing almost each day from the 21st to the 30th, afternoon temperatures trending upward from the mid-50’s on the 21st to near 80 F by the 30th. Such fine weather would be touted by the State's first newspaper journalists a generation from now as "the most beautiful portion of the year" [St. Paul Pioneer, 1865].

Heavy October Snows and an Early Onset of Winter - With none of the post's buildings yet habitable, preparations now had to be made for a move back to Cantonment New Hope for the winter. Although weather observations had evidently remained in the river bottomlands for the summer, described from May on as being taken "at the mouth of the St. Peter's", perhaps this explains the incomplete October diary, temperature, wind, and "weather" observations missing with one exception after the 4th. The one exception was the noting of an extraordinarily early and heavy snowstorm -- 11 inches over the 11th-14th. More than 180 years aince, this still stands as the heaviest fall ever so early in the season in the now Minneapolis-St. Paul vicinity. While October 1820's largely absent data does not permit a full assessment of its character relative to September, pronounced anomaly shifts, both in temperature and precipitation have occasionally been displayed between these two seasonal transition months down through the years. Full meteorological record-keeping resumed on 2 November, much of the first half displaying some familiar weather for this month -- chilly afternoon temperatures in the 30's, frequent grey, dreary skies and light snowfalls, the "precursor to winter" as other future commentators would describe it [Rochester City News, 1867]. After mid-month, a last taste of Indian Summer occurred, predominantly clear skies and temperatures in the mid-50's recorded as late as the 23rd. The 24th and 25th, however, brought a sudden onset of winter, with a nine-inch snowstorm burying the Camp. In the storm's wake the mercury plunged to minus seven by the morning of the 26^th, the Mississippi now frozen over and the St. Peters 2/3rds closed. Future years would demonstrate this mid-to-late November calendar period as a preferred time for abrupt changeovers to wintry weather, five successive Novembers in the 1870's, for example, having such "crackdowns" (meriting an 1875 article in the Minneapolis press). November '20 finished with a 31 F mean temperature. Except for a few afternoons during the first week of December, the rest of the year would be continuously sub-freezing with numerous mornings near or below zero. Such premature arctic domination would be the norm for this and the next three Decembers. The last week of the year was stormy and severely cold, another major snowstorm passing through (amount obscured in the diary), and -20 F temperatures read on both the 30th and New Year's Eve Day. December's mean was 10 F, some 8 F below average.

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