Minnesota (Fort Snelling) weather for the year 1846

Warmest Recorded Year of Nineteenth Century

     Completing a great three-year rise in annual mean temperature, 1846 brought the warmest year (49 F) of the Snelling era, 11 F above record-cold 1843. A higher annual average would not be recorded in the Minneapolis-St. Paul vicinity until 1931, the official figure for that year: 51 F. Winter was exceptionally mild and almost snowless, a near-record early breakup of the rivers followed in March, and July/August were each warm and humid with generous rains. Autumn and early winter were also unseasonably mild. Precipitation for the year totaled about 26 inches.

Record Warmth in January and March – January (mean temperature: 29 F) made up for the early season’s bitter weather with the warmest month of its name ever recorded in Twin Cities area weather history. Not a single subzero morning was felt (coldest +8 F), a feat not repeated again until 1990 and 2006. The absence of snow continued, just one inch falling, and nearly all of the month’s .52 inches’ precipitation came as rain. The first 2 1/2 weeks were mild enough, but the 19th to 29th was a consummate “January thaw” with every afternoon but one in the 40’s or higher. On the 24th, the mercury touched 59 F at 3PM, highest January temperature ever recorded locally, accompanied by light south-southwesterly winds and a “smoky” atmosphere. The 25th hit 49 F, the 28th 50 F (to go with .23 inches of rain during the day), and the 29th hovered in the mid-to-high 40’s all day with dense fog, “occasional mist” and an additional .13 inch of rain. A first hand impression of the month’s weather before the big thaw was offered by William R. Brown of St. Croix County, who commented in his dairy on the 17th: “Weather continues pleasant. No snow on the ground. I have not seen such a winter in this country, such fine weather and no snow.” [Ludlum, 1968]. February (mean temperature: 19 F) was similarly mild over the first half but with a short bitter cold snap late in the month. The 4th and 6th rose to 48 F and 52 F, respectively, and several other afternoons through the second week reached the 40’s , but thereafter the trend was decidedly colder. On the 20th, a brief but intense arctic spell suddenly set in, the next six days reminiscent of last November, with frigid temperatures and cutting west-northwesterly winds. Sunrise temperatures on the 24th-26th were -14 F, -15 F, and -16 F, respectively, the 24th especially bitter at that hour with force 4 winds (about 25 miles per hour); the 25th was just 0 F at 3PM. A welcome wind shift finally set in on the morning of the 26th, Surgeon Turner, probably the most competent and thorough of all the Fort Snelling observers, making a precise note of it: “Change of wind to south at 10.15’AM.”. No precipitation was triggered by the late cold outbreak and February’s monthly total finished at a meager .02 inches. Conditions quickly surged back to unseasonable mildness again at the start of March, monthly mean temperature for the month (39 F) equaling 1838 for warmest in 27 years. Every day reached at least the 30’s, the monthly maximum, a comparatively moderate 64 F, registered on the 17th. No sunrise temperatures below 20 F were observed all month. The first ten days were like Indian Summer in October, a “smoky atmosphere” observed on each, the mercury reaching the low 60’s four times. A heavy rainstorm moved in over the 10th-12th, dropping 1.19 inches, and setting the ice moving in both the Mississippi and St. Peters. Both were “about free” on the 16th, one of the earliest dates in the historical experience. Three other measurable precipitation falls totaling about one-half inch melted occurred before the close, including 3 inches of wet snow on the 22nd. This modest accumulation virtually doubled the season’s meager total thus far, roughly 7 inches now having been received. On the 31st, Lake Pepin opened for boat traffic.

Steady Warming after mid-April – April (mean temperature: 46 F), about seasonable in temperature overall, had 2.90 inches’ precipitation on 14 days. Spring’s advance stalled a bit over the first two weeks as some unseasonably cold days were felt. Four of the first five afternoons reached the relatively balmy 50’s and one having a .75 inch thunderstorm. But the 7th-10th were raw and blustery, afternoon temperatures confined to the 20’s and 30’s. The latter day, with the mercury just 25 F at 3PM accompanied by force 4 northerlies, was colder and more bitter than any day during March. Six inches of wet snow also fell over the night of the 13th-14th, the heaviest storm of the entire ’45-’46 season. Thereafter a strong warming trend developed, the 20th having a mid-summer-like 85 F read at 3PM. Five days later a partial eclipse of the sun was also noted. Anomalous warmth prevailed over much of May (mean temperature: 64 F), afternoon temperatures from the very first week consistently reaching the 70’s and low 80’s. Just five nights all month were as cool as the 40’s, though frost did occur on the 15th, “affecting garden vegetables slightly.” Total recorded rainfall for the month was 2.00 inches on 9 days.

Mild June; Warm, Muggy, and Wet July/August – June (mean temperature: 67 F) brought relatively infrequent, light rains. The early part was quite cool, the first four days no warmer than 60 F at 3PM, the 5th 44 F at sunrise. But within a week, mid-80’s temperatures were recorded, conditions likely sultry as indicated by persistent southeasterly winds and overnight readings just under 70 F. Generally cooler weather prevailed for the remaining days, but the last several were warm and humid again, diurnal temperatures ranging from the low 70’s to the mid-to-upper 80’s. Three storms over the 14th to 18th, dropping nearly 2 1/2 inches’ rain, comprised most of the month’s 3.10 inch total. July (mean temperature: 74 F) was warm, with a few hot afternoons but numerous warm and likely uncomfortable nights. Rain fell on 8 days to a total of 4.85 inches, some 2.87 inches of this coming on the 3rd. Afternoon temperatures reached the 90’s four times, including 90 F, 95 F, and 92 F on the 7th-9th, respectively. Sunrise readings for those days, also, indicated oppressive sleeping weather (74 F, 74 F, and 77 F, respectively). Humid nights were scattered all through the month, average sunrise temperature from the 22nd to 29th, inclusive, a muggy 70 F. Surgeon Turner noted at month-end that “the Mississippi for the past month has been remarkably high and steamboat navigation has crossed above the mouth of the St. Croix, 35 miles below this post”. August was also warm, humid, and hazy, monthly mean temperature (74 F) making it the hottest August since 1821. Like July, predominating winds continued mostly light and south to southeasterly, not a single northwesterly noted all month. The summer’s most prolonged oppressive spell came over the 3rd to 11th, afternoons reaching 90 F to 94 F on eight out of the nine days, sunrise readings either 74 F or 75 F on six straight mornings over the 3rd through 8th. A heavy thunderstorm dropped 1.70 inches in one hour on the afternoon of the 8th. Cooler and more variable temperatures characterized the next two weeks, with a mixture of 70’s to low 80’s, but the last days were increasingly warm and humid again, diurnal ranges in the 60’s to mid-80’s. Another 1.70 inches of rain fell on the 25th, bringing the final monthly total 4.20 inches.

Summery September, Mild November and December – September (mean temperature: 63 F) was the warmest month of its name to date. Warm and muggy weather extended well into the second week, six of the first 13 afternoons reaching the 80’s. Observed temperature ranges on the 2nd and 13th were 70 F to 87 F and 64 F to 89 F, respectively. Four rains over the 3rd to 10th also dropped 2.07 inches, all but 0.16 inches of the month’s total. The remaining days were somewhat cooler, the majority of the afternoons in the 60’s to low 70’s but with a few 80’s also. The nights of the 24th to 27th each dropped into the low to mid-40’s, and the season’s first frost was noted on the 26th. October (mean temperature: 46 F) was the year’s coolest month, relative to average. A warming trend developed over the first week, the 6th almost summer-like with 64 F at sunrise and 76 F at 3PM, but a rainier/cooler pattern then followed, 2.22 inches falling over the next nine days. Afternoon temperatures over the 14th-20th barely reached 40 F on most days, and the 17th brought the season’s first hard freeze, the mercury 20 F at sunrise. The first snow (“inappreciable”) also fell on the 19th. Generally warmer afternoons characterized the remaining days, several afternoons approaching or surpassing 60 F, most mornings, though, still freezing or nearly so. Just .23 inch precipitation fell over the last 16 days, a few smoky days and prairie fires also noted. November was very mild (mean temperature: 40 F – second warmest since ’19) and cloudy (average clearness of the sky: 2.6). Precipitation, nearly all of it rain, totaled 2.10 inches on 10 days. Thanks to persistent, light easterly and southeasterly winds and frequent overcast skies, no freezing temperatures were felt over the first eighteen days. Afternoon temperatures reached the high 50’s to low 60’s every day but one from the 3rd to 12th. The prolonged moist flow pattern also brought three appreciable rains over the period, totaling 2.02 inches. Thereafter, gradually colder conditions set in, the mercury continuously subfreezing over the 24th-26th. A wintry 7 F was noted on the latter, ice also seen running in the Mississippi this day. Much warmer weather returned again to close the month, the mercury hitting 48 F on the 28th, the rivers reopening and showing rises. December (mean temperature: 22 F) was uniformly mild, cloudy, and dry. No subzero mornings were recorded, average clearness of the sky (2.2). Just .21 inches’ precipitation fell, including about an inch of snow. Prevailing winds were from some aspect of east on 24 days, resulting in many mild, overcast nights with readings remaining in the 20’s. Thirteen afternoons reached the 30’s or higher, the warmest 42 F on the 26th. The Mississippi closed with ice on the night of the 3rd-4th.