Minnesota (Fort Snelling) weather for the year 1848

Abnormally Cold after Mid-Summer (graphic)

After a mixed progression of month-to-month temperature anomalies over 1848’s first half, thermal patterns over the second shifted decisively to unseasonable coolness, reminiscent of the extended cold terms scattered throughout 1842 to 1844. July-December 1848 still ranks as the coolest second half of the calendar year in the entire local climatic history down to the present. Annual mean temperature for the year finished at 42 F, a tie for second lowest since 1820. The ’47-’48 winter was another “open” one, although 1848’s growing season rains were quite ample. Total precipitation for the year was 23 inches.

Mild but Variable Winter, Heavy Rains – January and February exhibited strongly fluctuating temperature spells, alternating between short cold snaps and somewhat more protracted mild periods. Nearly 1 1/2 inches’ rain was recorded over the two months! January, a relatively mild 17 F in mean temperature, still managed two cold waves. Total precipitation, .62 inches, was about half from rain showers. The winter’s mildest temperature came on the 2nd, southwesterly to southeasterly winds all of the day sending the mercury to 46 F by 9PM. But just seven days later, on the 9th, the winter’s coldest reading was felt at sunrise (-24 F), the mercury no higher than -6 F at 3PM. Thawing temperatures were back by the end of the second week, 38 F read on the 14th at 9PM. Hours later, though, a vigorous cold wave plunged the temperature to minus 2 by the following sunrise, each of the next three days spending at least some time below zero. Steady mildness prevailed over the 19th to 29th, most of the afternoons in the mid-30’s to as warm as 40 F. But accompanied by a half-inch of rain, mist, hail, and snow late of the 30th and early of the 31st, another powerful cold wave with strong northwesterly winds drove the mercury down to minus 1 F by evening of the latter. February (mean temperature: 19 F), featured cold weather for the first and last weeks separated by a very mild interim. Several mornings over the first week were subzero, as low as -11 F, but a ten-day thawing spell set in beginning with the 12th. Temperatures held continuously in the 30’s to mid-40’s from mid-day of the 13th through the evening on the 19th. During the spell a thunderstorm dropped .36 inches of rain on the 15th. Then, on the 18th, an all-day storm left .77 more. These, remarkably, were February’s only measurable precipitation falls, the several other light snowfalls that occurred evidently being too insignificant to measure. Sharply colder weather then moved in on the night of the 21st, the remaining days similar to those preceding the thaw. The 29th’s range was only -5 F to 7 F. For the fifth straight year, February closed with the ground essentially bare of snow, just 8 inches (approximately) having fallen so far this winter.

Variable March, Dry April, Warm/Rainy May – Similar to ’47, February’s general mildness was not a precursor to a forward March, a slightly colder than average month (mean temperature: 28 F) the result with ice still in the river at month-end. Total precipitation was 1.71 inches, about six inches of this snow. Temperatures continued to show a strongly fluctuating pattern, the coldest and mildest weather occurring as abrupt, individual days’ events. Arctic cold predominated over part of the first week, the 5th minus 10 F, dustings of snow on several days contributing about 2 inches. The mercury then surged to 51 F on the 7th, but only the teens was reached the next afternoon, another arctic pulse dropping the mercury to 1 F on the 13th. Most afternoons after mid-month were only in the 30’s and 40’s, although 62 F was reached on the 17th, and the month’s warmest, 64 F, came on the 24th. The season’s last snowstorm left 3-4 inches over the 27th-28th, total snowfall for the ’47-’48 season finishing at a scanty 15 inches, approximately. April (mean temperature: 45 F) was very dry, with just two days’ precipitation totaling .15 inch. Very mild conditions prevailed over the first part, persistent southerly winds driving the mercury up to 68 F on the 2nd, 72 F on the 6th, and 76 F on the 9th. The Mississippi opposite the Post cleared of ice on the 5th, Lake Pepin opening on the 7th. After the 9th, prevailing winds were northwesterly with few afternoons warmer than the 60’s, most mornings near or below the freezing mark. No precipitation, rain or snow fell over the last thirteen days. May brought much heavier rainfall (5.16 inches on sixteen days) and a mean temperature (61 F) several degrees above normal. Daily temperatures over the first half typically ranged from the 40’s in the mornings to the 50’s or 60’s in the afternoons, although 80 F was reached on the 14th. Thereafter, most ranged from the 50’s to 60’s in the mornings to the 70’s to low 80’s in the afternoons. The 23rd had 2.09 inches of rain, temperatures hovering in the low 50’s most of the day.

Wet and Very Cool Summer – Summer was very cool and wet, reminiscent of the ’42, ’43, and ’44 threesome. June (mean temperature: 68 F) brought unseasonably cool weather early, daybreak of the 5th just 42 F with force 4 northwesterlies (25 miles per hour). The mercury was still only 57 F at 3PM. Frost followed overnight, affecting garden vegetables “slightly”, but a warming trend ensued, daily temperature ranges on the 14th and 15th 69 F to 90 F and 71 F to 90 F, respectively. Heavy thundershowers on the 16th ushered in much cooler weather again, most afternoons through month-end back in the 70’s, just two as warm as 84 F. The bulk of the month’s 2.83 inches’ rain also came over this period. July (mean temperature: 67 F) tied 1842 for coolest of the Snelling era, nearly half the afternoons in the low 70’s or cooler. Total rainfall was 4.60 inches. The 5th to 9th were much like early July ’42, with 1.50 inches of showers, brisk northwesterly to northeasterly winds and afternoon temperatures confined to the mid-to-upper 60’s. A gradual warming trend followed with some warm and humid afternoons in the mid-to-upper 80’s over the 13th to 19th and several mornings in the upper 60’s to low 70’s. But sharply cooler weather moved in again on the 21st behind force 4 northwesterlies (25 miles per hour). Average daily observational range for the last eleven days was just 57 F to 70 F. A 21-hour rainstorm over the 25th-26th drenched the Post with 2.20 inches, the mercury on the former only 57 F at 3PM. August (mean temperature: 67 F) was similarly cool and wet. A brief warm and humid spell prevailed into the second week, the 7th to 9th having daily ranges of 69 F to 86 F, 70 F to 85 F, and 67 F to 86 F, respectively. But much cooler weather then set in, just two afternoons as warm as 81 F registered through the close. Autumn-like coolness invaded around mid-month, daily range on the 15th just 48 F to 58 F. Most other diurnal temperature spreads over the last week in the high 50’s/low 60’s to low-to-mid 70’s. An 18-hour rainstorm dropped 1.75 inches over the 12th-13th, more than half the month’s 3.19 inches total. On the 10th, Surgeon George Turner reported “5 shooting stars observed at 8.30′ PM in ten minutes”, probably part of the annual Perseid shower.

Record-Tying Cold September, Mild October – Repeating the performance of July, September (mean temperature: 54 F) tied for coolest in 29 years. Week one had some warm and muggy weather, the 3rd’s observed daily range 68 F to 79 F with .75 inches’ rain left from thundershowers. Most other days’ readings varied from the mid-50’s in the morning to the mid-70’s in the afternoons. Steady autumnal-like weather prevailed thereafter, most mornings almost exclusively in the mid-30’s to the 40’s, afternoons in the 50’s to mid-60’s. No frost, however, was officially noted. Scattered showers, on seven days, dropped another 1.61 inches. October, not uncharacteristically, brought a thermal anomaly reversal, average temperature for the month (50 F) just 4 F cooler than September and several degrees warmer than the long-term average of Octobers up to this point in history. Total measurable precipitation was .78 inches on 5 days, all but .06 inch of this over the first sixteen. Afternoon temperatures trended upward over the first week, from the low 50’s on the first two days to 70 F by the 9th, the next six featuring observations at or near that level. Following .20 inches of rain accompanied by lightning on the evening of the 15th, though, a cooling set in, the season’s first frost (or at least mention of it) coming on the 17th, “slight snow” falling during the day. Most afternoons over the next ten were in the 40’s and 50’s, nights near freezing, prairie fires also noted for a couple of days. A last bit of Indian Summer weather returned for the 26th-27th, afternoon temperatures climbing to 63 F on each afternoon, but Halloween was only in the 30’s with an inch of snow falling.

Early Cold in November and December – The final two months each featured near record cold, about equal in combined intensity to that of 1838. November (mean temperature: 25 F), uniformly dull and chilly, had just a single day as warm as 40 F, with record early subzero weather felt during the second week. Exceptionally blustery weather opened the month, mid-afternoon of the 1st just 29 F with force 5 (35 miles per hour) north-northwesterlies. The 3rd was even more so with northeasterly winds as strong as force 7 (60 miles per hour) and temperatures confined to the 20’s. On the 9th, an early arctic outbreak brought minus 1 F at sunrise, earliest observed subzero reading in the Twin Cities vicinity until 1991. No notes regarding the state of the rivers appeared, although it’s likely they froze over on this date, and given the steady cold that was now to follow, quite possibly for the winter. Temperatures over the remaining days generally ranged from the teens or twenties in the mornings to the high 20’s or 30’s for the afternoons, a few very light snows falling. The 23rd brought the month’s warmest (44 F), the last thawing reading of the whole year, the earliest such date in the entire Twin Cities climatic record down to the present. Another spell of gale-force northwesterlies were felt over the 24th-25th, as temperatures held mostly in the 20’s. December saw deepening cold with the lowest mean temperature (7 F) for a month of this name since ’22 and ’31. Snowfall was light, about 2 inches. Afternoon temperatures through the 18th were generally confined to the teens and twenties, mornings occasionally subzero. But overnight of the 18th-19th, a “storm” brought the onset of a bitter eight-day arctic spell, including a stretch from sunrise on the 19th to mid-day on the 23rd with not a single observed temperatures above the zero mark. The 21st had especially dangerous windchills, north to northwesterly winds from force 4 (25 miles per hour) to force 5 (35 miles per hour), temperatures, however, displaying a curious rising, from –9 F at sunrise to zero by 9PM. Accompanied by lighter winds, morning readings were -15 F on the 23rd, -10 F on Christmas, and -12 F on the 27th.