ANNUAL CLIMATOLOGICAL SUMMARY
FT. SNELLING MN
The 1825 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 1825 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 1825. Specifically, 1825 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 1825's warm season average temperatures were elevated by direct exposure to early morning sunlight: the original record indicates, for example, that May 1825 temperatures averaged about 60 F (as adjusted by Fisk, cited below), a value which, when further adjusted for the probable effects of sun contamination , is reduced approximately 0.5 F to 59.5 F.
The foregoing 1825 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 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 1825 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 1825 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 1825, 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 1825 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.
Cloudy (fourteen cloudy days), calm and relatively warm January. Three inch snowfall on 7 January. Rain on 15 January followed by snow on 16-17 January. Brief early February cold followed by generally warm conditions during the remainder of the month. Readings of 33 F at 0700 on 11 February; 36 F at 0700 on 25 February; 35 F at 0700 on 26 February; and 50 F at 1400 hours on 23, 27 February. Nineteen cloudy days during February. Six inches of snow noted on 20 February. Very warm and cloudy (eighteen cloudy days) March. No snow noted/recorded during March. Warmth of 1824-1825 winter season probably related to Pacific El Nino event. Frequent rain during March. Near record April warmth with nineteen days recorded as "clear". Morning (0700) readings of 55 F on 8 April, 57 F on 11 April, 58 F on 21 April, 63 F on 22 April, 64 F on 23 April. Highs near 80 F as early as 10 April. Dry late April. Cloudy (twenty cloudy days recorded) and rainy May. Morning (0700) readings in the 70's F, 27-30 May . High winds noted on 10, 21 May. Heavy rain on 27 May. Cloudy (twenty one cloudy days recorded), wet June with southerly winds on most days during month. "Falling" river levels noted in late June (suggesting high water levels with possible flooding earlier in the season). Cloudy (twenty three days recorded as "cloudy"), warm and humid July. Morning (0700) readings in the low 80's or high 70's F, 15-21 July. Heavy rain on 18, 21 July. Severe thunderstorm on 3 July. Southerly winds prevailing on most days during July. Cloudy (seventeen cloudy days) August. High winds on 14, 16, 31 August. Severe thunderstorm on 30 August. Heavy rain on 6 August. Relatively cloudy (fourteen cloudy days) and warm September. High winds on 17, 28, 29 September. High winds with rain on 25 September. No frost during September. Windy, cloudy (sixteen cloudy days) October. Heavy rain on 5, 9 October. Probable maxima in the low 80's F, 1-5 October. Cold late October: readings of 24 F and 26 F at 1400 hours on 27, 28 October, respectively. Warm early November: 64 F at 0700 and 69 F at 1400 on 6 November. Thunderstorms on 3, 5 November. Very warm late November: 69 F at 1400 hours on 29 November (with probable maximum of 70 F or higher on that date). Reading of 47 F at 0700 on 28 November. Cold, snowy December. Snow and high winds on 4, 7 December. "Extremely" severe blizzard in what is now Manitoba (and probably in much of what is now northern Minnesota) on 23 December. Snow and rain noted at Ft. Snelling on that date (following snow on 21-22 December). Twenty four days during month recorded as "clear".
Microfilm copies of July, August and September 1825 records are of poor quality: consequently, any transcription of records for these months is problematic/subject to unavoidable error.