Minnesota (Fort Snelling) weather for the year 1840

Warm and Dry First Half, Cool and Wetter Second (graphic)

Contrasting thermal anomalies between the first and second halves along with modest precipitation marked 1840’s weather at Fort Snelling. Continuance of last year’s above normal temperature pattern, the winter to summer transition was very forward, March to June the second warmest such period in 21 years’ meteorological history. After July, however, a significant shift in temperature anomaly character took place. October tied for coolest on record with an unusually early and heavy snow the very first week, and November brought an unseasonably heavy snowstorm as well. Annual mean temperature (45 F) still finished as the second highest in six years, total precipitation finishing around 23 inches.

Mild, Snowless Winter – Mostly mild and dry, with the exception of a January cold term and several cold waves comprised 1840’s weather through the time of the spring breakup. January (mean temperature: 12 F) was unseasonably mild over the first half but unseasonably cold over the second. Snowfall was light, about 5 inches on six falls. Thanks to a long spell of south to southeasterly winds, the first and second weeks experienced almost daily afternoon temperatures in the 30’s to low 40’s, overnight readings remaining mostly in the 20’s. A sharp cold wave, one of three that would occur during this month and February, routed the mild pattern on the 14th, the mercury plummeting 40 F in 18 hours to minus 26 F by the following “A.M.”, -18 F and -22 F readings recorded on the next two mornings, the 16th and 17th. An even more intense blast set upon the Post about a week later, the mercury tumbling 43 F in 18 hours to -25 F at “A.M.” of the 23rd, a near all-time record -37 F read on the 24th, -32 F registered on the 25th. Near or below zero morning temperatures occurred regularly through the close, the coldest -18 F on the 31st. After some lingering early frigidity, February (mean temperature: 21 F) saw a return to mostly mild conditions. Total precipitation for the month was light, .12 inch of rain falling on two days and 2 inches of wet snow on another. Minus nineteen was recorded on the 1st, -13 F on the 3rd, but a marked warmup then ensued, afternoon 30’s and 40’s to be the rule through the third week. Another cold wave swept through on the 23rd with temperatures falling all day, but after a bitter -26 F observed next morning, conditions warmed dramatically, the mercury hitting 50 F on the 28th, the temperature range on Leap Year Day 40 F to 54 F. March (mean temperature: 36 F) was also very mild. Each of the first nine afternoons reached the 50’s, an unprecedented occurrence so early in the season based on the record-keeping experience so far. Fair skies and southerly winds predominated, nighttime temperatures over this mild period frequently remaining above 32 F. On the 3rd, the mercury reached 59 F, a highest-so-early-in-the-season mark. Afternoon readings from the 10th on were only slightly lower, mostly in the 40’s and 50’s. Following 1 to 2 inches’ snow on the 18th, a final, abbreviated arctic outbreak driven by “high” northwesterly winds dropped the mercury to 0 F on the morning on the 20th. By the 25th, however, the mercury was back to 55 F, and 59 F was read on the 28th. On the 31st, the Mississippi was still noted as “not open yet”, possibly reflecting the winter’s lack of an insulating snow cover and the several brief but intense arctic spells. Total snowfall for the ’39-’40 season was a paltry 15 inches, approximately, less than one-third the modern-day “normal” amount. The Mississippi breakup finally came on 3 April.

Warm, Dry Spring with Early Hot Weather – Mild to unseasonably warm temperatures along with more extended dry spells featured spring. April (mean temperature: 48 F) was mild, sunny, and almost rain-free through the first three weeks, afternoon temperatures with few exceptions reaching at least the 50’s and 60’s. Just .04 inch of precipitation was recorded. The 21st and 22nd brought a taste of early summer, 79 F and 78 F recorded at the “P. M.” observation time, overnight temperatures holding in the mid 50’s. Thunderstorms on the 23rd brought some needed moisture, 1.50 inches of rain left, and much cooler temperatures, afternoon readings in the high 40’s, prevailed on this day and the next two. Fair skies, southwesterly winds, and near 70 F readings, though, were back again before month-end. The season’s first two steamboats, the “Tennessee” and the “Omega” each arrived on the 27th. May (mean temperature: 64 F) tied 1836 for third warmest to date. Droughty weather was evident again over the first seventeen days, just .01 inch of rain falling. Mid-summer-like heat prevailed on five straight afternoons through the 18th with mid-to-upper 80’s occurring on four. Temporarily cooler and wetter weather followed, 1.70 inches’ rain falling over the 18th-20th, the latter only 58 F at mid-afternoon. But another even hotter spell then began to build as the month closed, temperatures of 92 F, 90 F, and 90 F recorded over the last three afternoons with overnight readings remaining in the mid-to-high 60’s. The 92 F reading on the 29th would be the year’s highest, distinguishing 1840 as the only year here locally until dust-bowl era 1934 in which the yearly maximum would be a May event. Premature heat continued over much of June (mean temperature: 71 F), roughly half the afternoons reaching the mid to upper 80’s. Numerous nights held in the 60’s, three sunrise temperatures noted at 70 F or higher. Rainfall picked up significantly over the first half, 2.70 inches measured through the 16th, .70 inches coming over the balance. Most afternoons during the last week approached 90 F, the highest (89 F) coming on the 24th, the next morning a sultry 78 F at sunrise.

Trend to Abnormal Coolness – Reminiscent of 1826 and 1829, May and June’s early warm buildup did not culminate with an oppressive balance of the summer. July (mean temperature: 72 F) was only seasonable, temperature-wise, August (mean temperature: 67 F) just 1 F warmer than 1836’s record coolest average. The former started with some unseasonable coolness, the 1st ranging from just 54 F to 63 F, the 4th 57 F to 70 F. Only a few hot days were experienced during the month, the warmest being five afternoons in the 88 F to 90 F range. Precipitation (2.89 inches’ total) was confined mostly to two several-day spells over the second week (1.62 inches), and during the third and fourth weeks (1.14 inches). August had only one 90 F afternoon, nine confined to the 60’s. Lowest morning temperature was 49 F. Rainfall was heavier and more evenly distributed than July’s, totaling 3.40 inches on eight days.

Cold Autumn With Early Snows – Cool and sunny weather made up September (mean temperature: 57 F). Overnight temperatures from the first week routinely dropped into the mid 40’s or cooler, the 10th and 11th 40 F, and 41 F, respectively. Not a single afternoon was a warm as 80 F at the “P.M.” observation time and just ten were as high as 70 F. Twenty days were “fair” at both the “A. M.” and “P. M.” observation times, rainfall totaling 2.35 inches on four falls. Following the season’s last thunderstorm on the 14th, dropping .85 inches, a cool outbreak brought 36 F on the 17th, lowest of the month. Just two days later, though, the month’s maximum, 78 F, was reached. Temperatures declined significantly in October, monthly mean temperature (41 F), tying for coldest in 22 years. The month began with winter-like cold and snow, three inches falling overnight of the 1st-2nd, the heaviest accumulation ever so early in the season here. Temperatures on the latter indicated 30 F, 31 F, and 28 F at the scheduled observation times. Afternoon readings over the ensuing days quickly recovered, 71 F reached on the 7th, but much colder weather then returned, the afternoon of the 8th no warmer than the low 40’s, 1.32 inches’ rain falling. Later in the month, a record-breaking cold snap set in, the 23rd-25th subfreezing continuously, the mercury dipping to 12 F on the 26th for the coldest October reading yet experienced here. Mild Indian Summer weather was back for Halloween, the mercury 58 F in the afternoon. November (mean temperature: 29 F) brought continued mild temperatures into the second week. Six of the first ten afternoons were in the 50’s, an equal number of nights dropping no lower than the 40’s. Three significant rains also dropped 1.80 inches. Thereafter, the trend was much colder again, just one day warmer than 32 F after the 13th, northerly winds predominating. Over the 20th-22nd, the second massive snowstorm in as many years buried the post with 14-15 inches (1.42 inches water content). The mercury dipped to minus 1 F on the 25th in the storm’s wake. December (mean temperature: 22 F) had mostly mild weather. Just two days of snow, totaling 1-2 inches fell, late November’s deep snowpack likely considerably dissolved by the close. Coldest weather came over the first few days, the monthly minimum, -6 F, coming on the 2nd. Almost every afternoon thereafter through mid-month was in the 30’s and 40’s, fair skies and south to southeasterly winds the rule. A spell of northwesterlies brought three successive mornings of just below zero temperatures late in the third week, but the remaining days were mostly mild again for the season with no subzero mornings and frequent thawing afternoons.