ANNUAL CLIMATOLOGICAL SUMMARY
FT. SNELLING MN
The 1820 Ft. Snelling climatological record consists of fixed time temperature readings taken daily at or about 0700, 1400 and 2100 hours local solar time; single daily entries indicating the prevailing direction of the wind and the general condition of the sky; intermittent records of snowfall and/or snow cover; episodic records of phenological, hydrological, astronomical and/or other natural events (windstorms, prairie fires, etc.); descriptive entries indicating the general duration (and, in some instances, the intensity) of precipitation; precipitation type ; and special atmospheric phenomena (fog, smoke, etc.). So far as can be determined, observations were taken at Cantonment New Hope (a temporary camp consisting of log huts constructed in 1819 in the bottomlands adjacent to the St. Peter's [Minnesota] river) from January through much of May and from November through December 1820. During the remainder of the year, records may have been kept at Camp Coldwater, a temporary summer camp site on the upland prairie about one mile northwest of the site of the permanent fort enclosure. No temperature records and few records of any other meteorological occurrences were kept during the period 21-23 May and 5 October through 1 November 1820 (breaks probably attributable to the garrison's moves to and from the lower and upper camps).
Because they were obtained from instruments exposed in the Minnesota river bottomlands, temperatures recorded during the winter months of 1820 are undoubtedly significantly lower than values which would have been obtained (ceteris paribus) from thermometers located at the Ft. Snelling or Camp Coldwater sites (both of which are significantly higher than the Cantonment New Hope site). Analysis of the relationship between 0700, 1400 and 2100 readings further suggests that station thermometers -- at least during the summer months -- may have been exposed to the direct rays of the early morning and/or the mid-afternoon sun . Specifically, the average of 2100 hour readings taken during July and August were LOWER than the average of the 0700 hour readings, a pattern which, of course, is the reverse of the normal summer diurnal pattern. This suggests, in turn, that average temperatures during the summer of 1820 may have been significantly cooler than those indicated in the "official record" .
The foregoing 1820 temperature record includes both unadjusted (UNADJ) and adjusted (ADJ) mean temperatures. Unadjusted values are the averages of fixed time readings taken daily at 0700, 1400 and 2100 hours . Adjusted averages are from Charles J. Fisk's 1984 "Reconstruction of Daily 1820-1872 Minneapolis-St. Paul Temperature Observations". These values are based on statistically derived estimates of the daily maxima and minima that would have been recorded had the Ft. Snelling station been equipped with self-registering thermometers read and re-set at midnight . The foregoing 1820 record also includes both the monthly and annual extreme temperatures (highest daily minimum, lowest minimum, etc.) estimated by Fisk and the monthly extremes actually recorded/observed (OBSRV) by fort observers. All 1820 temperature distributions (e.g. days 90 F or higher, 32 F or lower, etc.) are based on Fisk's estimates of daily maxima and minima.
Although no quantitative precipitation records were kept at Ft. Snelling during 1820, extant records do, as noted, contain entries indicating precipitation type and, in some instances precipitation intensity (e.g. light snow, heavy rain, etc.). These records are the basis of the foregoing 1820 precipitation frequency record (e.g. number of days with snow, etc.) . Prevailing wind values, similarly, are based on entries indicating the predominate direction of the wind on each day of the month. Prevailing monthly winds indicate the direction most frequently observed/recorded during any given month.
Very cold and clear January: twenty three days during month described as "clear". Temperature of -30 F observed at 0700 hours on 30 January. Much illness and morbidity among garrison personnel during the month: many deaths from pneumonia and scurvy. Rapid warm-up after mid-February: 1400 readings of 41 F, 46 F and 46 F on 13, 22 and 25 February, respectively. Reading of 34 F at 0700 hours on 16 February. Thunderstorm with snow on 15 February. Cold early March: 0700 hour reading of -10 F on 8 March. Temperatures near 70 F on 22, 23 March. Heavy rain on 24 March. Wet, warm April with 1400 hour temperature of 79 F on 10 April. 82 F at 1400 hours on 19 April, 84 F on 23 April and 85 F on 24 April. Cold early April: readings of 10 F and 26 F at 0700 and 1400 hours, respectively on 1 April. Cantonment New Hope struck by a tornado "from the southwest" at about 0400 hours on 20 April: shingles torn from the barracks. Snow noted on 5, 6, 7 May following several days of rain. Station thermometer may have been moved to Camp Coldwater late in May. Dry late May. Clear (twenty one "clear" days) and dry June: low summer water levels prevented construction of a sawmill at Minnehaha Falls. Temperature of 81 F recorded at 0700 hours on 18 June. Heavy rains and cool early July: 64 F recorded at 1400 hours on 3 July. Twenty three "clear" days during month. Heavy rain on 3, 7, 22 July. Wet, cool August: heavy rains noted on 6, 29 August. Warm early September: temperatures probably reached the low 90's on 5 September. Heavy frost with 0700 temperature of 30 F on 19 September. Light frosts (probably in low lying areas only) on 17, 18 September. Heavy rain on 8, 9 September. Cornerstone for permanent fort laid on 10 September. Mid-October snowstorm: record indicates that eleven inches of snow had accumulated on 14 October, the last day of a three-day snowstorm. Snowy November: snow cover of seven inches on 24 November, snowfall of nine inches on 25 November. Snow preceded by warm temperatures: 54 F at 1400 hours on 23 November. Reading of -7 F at 0700 hours on 26 November. Snowy, very cold December. Heavy snowstorm on 26-27 December (records indicating amount of snowfall illegible) followed by extreme cold (-20 F at 0700 hours on 30 and 31 December).