ANNUAL CLIMATOLOGICAL SUMMARY
FT. SNELLING MN
The 1845 Ft. Snelling climatological record consists of: four daily fixed time readings taken from the station's "detached" thermometer; daily precipitation values; four daily fixed time sky cover observations; four daily fixed time observations of wind "force" and wind direction; two daily fixed time wet bulb readings; four daily barometric readings; and four daily readings from the station's "attached" thermometer (i.e. from an indoor thermometer used to adjust barometric readings for the effects of temperature on the station's mercury barometer) . Temperature, sky cover, wind direction/force and barometric observations were taken at or about local sunrise, at or about 0900 hours, at or about 1500 hours and at or about 2100 hours local solar time. Wet bulb readings were taken at local sunrise and at 1500 hours local time. Although extant records give no indication of the time at which 1845 precipitation observations were taken, contextual evidence suggests either a 2100-2100 schedule and/or an early morning (probably "sunrise") schedule (which, in at least in some instances, may have entailed "shifting" of precipitation values from the date on which the observation was actually made to the day immediately preceding).
So far as can be determined, all 1845 temperature observations were taken from a thermometer manufactured by George Tagliabue, New York City and all precipitation observations were taken from a DeWitt rain gauge (which was probably mounted on a pole or post on the fort's parade ground). All 1845 wind force values are expressed in terms of a quantified wind force value selected by the observer after noting the effect of the wind on flags, trees, signs and other easily movable objects . The degree of cloudiness was similarly quantified, using a scale of zero (complete overcast) to ten (a totally cloudless sky) . Although the 1845 daily sky cover record includes a complete set of daily entries, monthly force of wind records, in contrast, are incomplete: daily air movement records include a significant number of wind direction entries UNACCOMPANIED by corresponding wind speed indicators. Extant records give no explanation for these lapses: perhaps the missing entries indicate a force of wind value of more than zero but less than one or, alternatively, that fort personnel, for whatever reason, were unwilling to expend the time and effort required to take consistent wind speed observations.
Comparison of sunrise, 0900 and 1500 hour readings taken during 1845 suggest (in contrast to 1843 and, to a lesser extent, 1844) that the station thermometer(s) was exposed in a properly shaded location: so far as can be determined, fixed time readings taken during 1845 are consistent with "normal" diurnal temperature patterns (indicating, of course, that the station thermometer had been re-located and/or sheltered as necessary to protect it from the early morning, mid-morning and/or afternoon sun). Extant evidence similarly indicates that 1845 Ft. Snelling precipitation records are, on balance, more complete and reliable than their pre-1843 counterparts. When compared with modern records they do, nevertheless, appear to significantly understate the number of days with precipitation and/or measurable precipitation. This suggests that the Fort's 1845 observers -- following the example of their predecessors -- did not routinely/consistently measure and/or record small amounts of precipitation, sometimes either ignoring small rainfall or snowfall events or, alternatively, using the term "inappreciable" to indicate small, but otherwise measurable, amounts of precipitation.
Although the 1845 Fort Snelling record includes daily liquid/melted precipitation values and a record of the TYPE of precipitation observed, it includes NO QUANTITATIVE snowfall values (whether of fresh snowfall or accumulated snow cover). Any snowfall values contained in the foregoing compilation, therefore, are estimates obtained by applying the National Weather Service meltwater-snowfall conversion matrix to the meltwater values recorded by Ft. Snelling observers on 1845 "snow days".
In addition to outdoor temperature, sky cover, precipitation and air movement data, the 1845 Ft. Snelling record includes four daily readings taken from the station's mercury barometer and from the "attached" thermometer (readings from which, as noted above, were probably used to correct barometric readings for the effects of temperature on the mercury in the station barometer). So far as can be determined, 1845 barometric values are station pressures (i.e. readings which have not been adjusted to compensate for elevation above mean sea level.
The foregoing 1845 climatological record includes both unadjusted (UNADJ) and adjusted (ADJ) mean temperature values. Unadjusted values are the averages of the four fixed time readings taken daily during 1845 . 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 which would have been recorded had the Ft. Snelling station been equipped with self-registering thermometers read and re-set at midnight . The foregoing 1845 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 1845 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.
All foregoing monthly mean cloudiness values are the simple average of the numeric "clearness" values derived from the station's four daily visual sky cover observations. The foregoing monthly prevailing wind values are derived from daily entries indicating the direction of the wind at sunrise/0900/1500/2100: prevailing/predominate winds are those most frequently observed/recorded during any given month.
Extant evidence suggests that the Ft. Snelling precipitation record for January, February and March 1845 may be incomplete: remarks entered in the station's 1845 meteorological registers indicate that observers failed to measure and/or record small amounts of precipitation which fell on one or more days during these months. The record further indicates that a substantial portion of the September 1845 precipitation record is incomplete, the result of high winds which "blew the station rain gauge from its stand" during a heavy thunder shower on 6 September.
Warm, sunny January: sunrise reading of 36 F on 2 January. Partial wind force records suggest that winds during January were generally light. January snowfall was probably light to moderate with only one substantial snowfall during the month. Very warm February: sunrise readings of 34 F, 36 F, 40 F, 38 F, 36 F, 34 F on 11, 18, 19, 20, 21, 22 February, respectively. Heavy snow on 13-14 February. Readings of 48 F, 52 F and 49 F at 1500 hours on 18, 19, 24 February, respectively. Rain and hail accompanied by force seven winds during the night of 19-20 February. Mild, sunny March. Little precipitation until the closing days of the month: 2.6 inches of precipitation recorded, 28-31 March. Sunrise readings of 47 F and 48 F on 26, 27 March, respectively. Readings of 79 F at 1500 on 26 March and 80 F at an "off-schedule" observation at 1730 hours on 28 March. Massive outbreak of prairie fires during March: fires and/or smoky conditions noted on 10, 12, 17, 19, 22, 25, 26, 28 March. Force five winds with fires "raging furiously" on 28 March. Thunderstorm with hail and force six winds on 30 March. Dry early April followed by rainy conditions after mid-month. Very cold day, 7 April: readings of 15 F and 22 F at sunrise and 1500 hours, respectively. Prairie fires noted on 6 April. Mississippi and St. Peter's rivers "rising rapidly" on 25 April. Reading of 82 F at 1500 on 12 April. Warm, dry, sunny May. Very warm, 8-11 May: sunrise readings of 68 F and 69 F on 11, 12 May, respectively. Wet, cloudy June: 3.1 inches of rain, 5-7 June. Four foot rise in the Mississippi and St. Peter's rivers noted, 1-7 June. Warm July with frequent thunderstorms but only moderate amounts of rain. Foggy conditions noted on many July mornings. Heat wave, 9-15 July. Reading of 64 F at 1500 on 29 July. Thunderstorm with force eight winds on 19 August. Smoky conditions noted on 10-11 August. Heavy rain with hail and force eight winds on 6 September: station rain gauge blown from its stand on that date. Much morning fog during September. "Hoarfrost" on 21 September, light frost on 23 September. Dry but cloudy October. Smoky conditions noted on 6, 16, 17, 18, 20, 23, 24, 25, 26 October. Massive outbreak of prairie fires during month. Sunrise reading of 18 F on 15 October. Readings of 36 F at 1500 hours on 13, 14 October. Warm late October, sunrise readings in the 50's F each day, 26-30 October. Afternoon readings of 70 F, 70 F, 72 F, 68 F on 25, 26, 27, 28 October, respectively. Prairie fires noted on 1, 9, 16 November. Very cold late November: afternoon readings of 10 F, 2 F, 5 F, 2 F and 5 F on 26, 27, 28, 29, 30 November, respectively. Sunrise readings of -12 F, -7 F, -7 F and -10 F on 27, 28, 29, 30 November, respectively. Cloudy, very dry and cold December. Very little snow during November and December. Warm during the closing days of December.