ANNUAL CLIMATOLOGICAL SUMMARY
FT. SNELLING MN
The 1824 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, all 1824 observations were taken within the Ft. Snelling enclosure (on the bluffs overlooking the confluence of the Mississippi and Minnesota [then the St. Peters] rivers) .
Analysis of the relationship between 0700, 1400 and 2100 readings indicates that the station thermometer was probably exposed to direct morning and/or afternoon sunlight during the warm months of 1824. Specifically, 1824 summer temperature records (late May through early August) include numerous 0700 readings exceeding or equaling 2100 readings (thereby reversing or nearly reversing normal summertime diurnal patterns). Such patterns obviously suggest that 1824's warm season average temperatures are significantly elevated by direct exposure to early morning sunlight: the original record indicates, for example, that May 1824 and July 1824 temperatures averaged about 55 F and 72 F, respectively (as adjusted by Fisk, cited below), values which, when further adjusted for the probable effects of sun contamination , are reduced approximately 1 F to 54 F and 71 F, respectively.
The foregoing 1824 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". Adjusted averages were obtained from 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 1824 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 1824 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 1824, 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 1824 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.
Sunny (twenty four clear days noted), dry January with much "calm" weather noted. Warm late January (37 F at 0700 on 23 January) but with severe cold wave during the closing days of January and the first day of February. Readings of -24 F at 0700 hours on 31 January and -27 F at 0700 hours on 1 February; -14 F at 1400 hours on 31 January. Sunny (twenty three clear days) but cold February. Four inches of snow noted on 17 February, probably the first significant snowfall of the winter. Cold March: readings of -10 F at 0700 on 13 March and -1 F at 0700 on 20 March. Four inch snowfall during the night of 19-20 March. Cloudy (sixteen cloudy days recorded), cool April. Heavy precipitation, 21-23 April. One inch snowfall on 28 April. Very cold early May: minimum temperatures near 20 F probable on 3, 4 and 5 May. Afternoon temperatures in the low 40's F recorded on 1, 2, 3 May. Warm conditions at the end of May. Windy, cloudy (sixteen cloudy days) and cool June. Heavy rains during late June. Readings of 60 F at 1400 hours on 11, 12 June: 58 F at 1400 hours on 18 June. Cloudy (fourteen cloudy days recorded) and rainy July. Heavy rains on 9, 16 July. Windy August. Heavy rains on 17, 26 August. Twelve cloudy days during August. Light frost noted on 6, 7 September. Heavy rain on 18 September. Thirteen cloudy days during September. Warm mid-September. Cold, cloudy (eighteen cloudy days recorded) October. Dry early October: no precipitation noted prior to 19 October. Very cloudy (twenty two cloudy days) November. Mid-November cold wave: -1 F at 0700 hours on 18 November. Warm Late November. Thunderstorm on 30 November: readings of 46 F at 0700 hours and 57 F at 2100 hours on that date. Cloudy (twenty one cloudy days) but relatively warm December. Records indicate that December snowfall was probably light. Readings of 35 F at 0700 on 10, 12 December. Probable maximum in the 50's F during the early morning hours of 1 December: 39 F recorded at 0700 hours on that date.