ANNUAL CLIMATOLOGICAL SUMMARY
FT. SNELLING MN
The 1831 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 1831 observations were taken within the Ft. Snelling enclosure (on the bluffs overlooking the confluence of the Mississippi and Minnesota 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 at least some portion of the late spring and summer months of 1831. Specifically, 1831 summer temperature records (late May through early August) include numerous 0700 readings exceeding or equalling 2100 readings (thereby reversing or nearly reversing normal summertime diurnal patterns). Such patterns obviously suggest that 1831's warm season average temperatures were elevated by direct exposure to early morning sunlight: the original record indicates, for example, that temperatures averaged about 69 F in June and about 73 F July 1831 (as adjusted by Fisk, cited below), values which, IF further adjusted for the probable effects of sun contamination , would be reduced to about 68 F and 72 F, respectively.
The foregoing 1831 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 by averaging 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 1831 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 1831 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 1831, 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 1831 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.
Cold, cloudy (eighteen cloudy days) January. Cold conditions prevailed during most of the month but without any notably low readings. Prevailing winds from the west or southwest on twenty one days during January. Cloudy (sixteen cloudy days) and dry February. Persistent cold during much of February with late winter thaw during the closing days of the month. Reading of 50 F at 1400 hours on 26 February: readings of 36 F, 40 F and 36 F at 0700 on 26, 27, 28 February, respectively. Heavy snowfall southeast of what is now Minnesota during the winter of 1830-31: Ft. Crawford WI reported snow cover of as much as 48 inches. At Ft. Snelling, the winter began with heavy December snowfall but appears to have produced only light to moderate snowfall during January and February. Mild conditions during early March and again during late March: mid-March cold with readings near 0 F on several days, 15-19 March. Thunderstorm on 3 March. Nineteen cloudy days during March. Cloudy (nineteen cloudy days) and cool April. Reading of 79 F at 1400 hours on 19 April followed by mid-day readings in the high 30's F, 19-21 April. Three inch snowfall on 21 April. Warm early May: readings of 88 F and 72 F at 1400 and 0700, respectively, on 10-11 May. Light frost noted on 22-23 May. No precipitation recorded between 21 April and 14 May. Near normal temperatures with probable droughty conditions during June. Warm, sunny (twenty clear days) July. Droughty conditions probably prevailed during much of July. Dry August (three days with rain and "very low" water levels on the Mississippi river). "Frost" noted on 4 August, a probable reference to an especially heavy early morning deposit of dew: temperatures on the date probably did not fall below 50 F. No rainfall noted, 27 July through 18 August. Cool, cloudy (seventeen cloudy days) September. Frost (probably light) noted on 2, 12, 17 September. Very cool conditions during the closing days of September. Cloudy (nineteen cloudy days) October. Mid-October warmth (82 F recorded at 1400 hours on 14 October and 61 F recorded at 0700 on 21 October). Cold late October: 19 F recorded at 0700 on 26 October. Warm early November with very cold conditions at the end of the month: -7 F recorded at 0700 on 29 November. Nineteen cloudy days during November. Near record cold December: 0700 hour readings near or below -20 F, 5-6 December and 11-15 December. Temperatures near -30 F probable on the morning of 14 December. Ice thick enough to permit skating reported at New Orleans during December: Mississippi river reportedly frozen 130 miles below the mouth of the Ohio river. Observer noted that 14 December 1831 was the coldest day recorded at the Ft. Snelling station since 31 January 1824. Moderating temperatures late December. Snowfall during November and December 1831 was probably light to moderate. Fourteen cloudy days during December.