ANNUAL CLIMATOLOGICAL SUMMARY
FT. SNELLING MN
The 1833 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 1833 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 1833. Specifically, 1833 summer temperature records (May through August) include numerous 0700 readings exceeding or equaling 2100 readings (thereby reversing or nearly reversing normal summertime diurnal patterns). Such patterns obviously suggest that 1833's warm season average temperatures were elevated by direct exposure to early morning sunlight: the original record indicates, for example, that temperatures averaged about 74 F in July (as adjusted by Fisk, cited below), a value which, IF further adjusted for the probable effects of sun contamination , would be reduced to about 73 F.
The foregoing 1833 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 1833 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 1833 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 1833, 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 1833 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.
Warm, cloudy (nineteen cloudy days) January. Afternoon readings in the 40's F, 19-21 January. Readings of 34 F, 36 F, 36 F, 35 F and 34 F at 0700 hours on 2, 3, 4, 5, 23 January, respectively. Rain on 2, 3, 4 January. Warm February with afternoon temperatures near 50 F on 8, 14, 15 and 21 February. Rain on 4, 17 February. Readings of 35 F and 37 F at 0700 on 16, 17 February, respectively. Brief cold wave, late February - early March. Reading of -4 F at 1400 on 1 March: -20 F at 0700 on 2 March. Warm late March: reading of 70 F at 1400 on 18 March. Morning (0700) readings in the 50's F, 17-19 March. Twenty "fair" days during March. Warm April: many afternoon readings in the 70's F. Snow, reading of 33 F at 1400 hours on 11 April. Warm early May: afternoon temperatures near 90 F on 5 May. Reading of 75 F at 0700 on 5 May . Cool late May: reading of 50 F at 1400 on 26 May. Probable morning minima in the 30's F on 27, 28 May: light frost probable on those dates. Twenty two fair days during May. Cool early June: rainy, cool and windy on 1 June: 1400 hour reading of 54 F on that date. Minima in the high 30's F probable on 1, 2 June. Fifteen cloudy days during June. Warm, sunny (twenty three "fair" days) July. "Smoky atmosphere" noted on 14 July (probably attributable to forest or prairie fires north of the fort). Very warm (and probably humid) conditions, 16-28 July. Twenty "fair" days during August. Dry late August. Warm September. "Slight frost" noted on 11 September. Cold during the closing days of September: reading of 43 F at 1400 on 30 September. Cold, sunny (twenty "fair" days) October. Significant snowfall 16-17 October. Reading of 34 F at 1400 on 17 October. Snow on 27 October. Reading of 29 F at 1400 on 28 October. Mild, sunny (twenty "fair" days) November. Very little snow during November. Near record warm December. Twenty two cloudy days recorded. Above freezing readings recorded at 0700 hours each day, 1-15 December. Mississippi river closed by ice on 29 December. Afternoon readings in the high 30's and low 40's F each day, 1-15 December. Snow and cold during the closing days of December: -11 F at 2100 hours on 31 December.