ANNUAL CLIMATOLOGICAL SUMMARY
FT. SNELLING MN
The 1848 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 1848 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, 1848 Ft. Snelling temperature readings were taken from an instrument manufactured by George Tagliabue, New York City and precipitation observations were taken from a DeWitt rain gauge (which was probably mounted on a pole or post on the fort's parade ground). With the exception of many 0900 hour readings and October's 1500 and 2100 hour readings , fixed time temperature readings taken during 1848 are consistent with normal diurnal patterns. Unfortunately, however, contextual evidence suggests that, unlike most of the records compiled by Ft. Snelling observers from 1843-1847, the 1848 record (particularly the July-December portion) was sometimes poorly kept and/or poorly documented . Specific evidence of the deteriorating quality of late 1848 records includes an increased incidence of computational errors, an increased incidence of missing and/or problematic data (particularly wind speed and precipitation data), a decrease in the number and quality of explanatory remarks (e.g. descriptions of precipitation events, phenological notes, etc.) and an increasing incidence of illegible or semi-legible entries (suggesting that observational records may have been prepared carelessly and/or more hurriedly than in prior years). The most serious shortcoming of the 1848 record, however, is the problematic quality of October (and perhaps the early November) temperature data. Specifically, an inordinate number of the October temperature readings ostensibly taken at 2100 hours local time are HIGHER than those taken at 1500 hours. The result is a record in which the average (57.5 F) of observations taken at 2100 hours exceeds the average (55.6 F) of observations taken in mid-afternoon. Extant records provide no explicit explanation of this anomaly: it is probable, however, that it is the result of a temporary (but significant and unrecorded) shift in observation times (perhaps from a mid-afternoon and mid-evening to an early afternoon and late afternoon schedule). Or, alternatively, it may indicate that the station's "external" thermometer was, during the mid-evening hours, exposed to an artificial source of heat . Whatever the explanation, it is nonetheless obvious that this anomaly compromises the climatological value of both the October 1848 record and the estimated October 1848 data derived by Charles J. Fisk (op. cit.) in his 1984 analysis of early Twin Cities records.
All 1848 wind force values are expressed in terms of a quantified wind force value selected by the observer after noting the visual effect of 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) . In addition, 1848 records include notations indicating the total number of "fair" and the total number of "cloudy" days observed during each month of the year. Unfortunately, the terms "fair" and "cloudy" are nowhere defined: presumably, however, they refer to the general character of each day of the year, with "fair" probably indicating an essentially cloudless day and "cloudy" indicating an overcast or partially overcast day (thus probably including what, in modern terminology, would be recorded as "partly cloudy" days).
Unlike the 1848 daily sky cover record (which includes a complete set of daily entries), the force of wind record is sometimes incomplete: air movement records include a significant number of wind direction entries UNACCOMPANIED by corresponding Beaufort 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 or unable to expend the time and effort required to take consistent wind speed observations.
Like corresponding records from the years immediately preceding (and, as noted, perhaps even to a greater extent than), the 1848 Ft. Snelling record appears to understate the number of days with precipitation and/or measurable precipitation. This suggests that -- following the example of their predecessors -- Fort observers did not routinely/consistently measure and/or record small precipitation events, sometimes either ignoring less significant deposits of rain or snow (or. alternatively, using terms such as "inappreciable" or "slight" to denote small, but perhaps otherwise measurable, amounts of precipitation).
Although the 1848 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 1848 "snow days".
In addition to outdoor temperature, sky cover, precipitation and air movement data, the 1848 Ft. Snelling record includes four daily readings taken from the station's mercury barometer and from the "attached" thermometer (readings 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, 1848 barometric values are station pressures (i.e. readings which have not been adjusted to compensate for elevation above mean sea level).
The foregoing 1848 climatological record includes both unadjusted (UNADJ) and adjusted (ADJ) mean temperature values. Unadjusted values are the averages of the four fixed time readings taken each day during 1848 . 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 1848 record also includes both the monthly and annual extremes (highest daily minimum, lowest minimum, etc.) estimated by Fisk and the monthly extremes actually recorded by fort observers. All 1848 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 station's four daily numeric sky cover entries. The foregoing prevailing wind values are based on 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.
The amount of precipitation officially recorded during September and December 1848 may significantly understate the amount of moisture which actually fell during these months: both records include descriptive entries (e.g. showers) unaccompanied by any quantitative precipitation value.
Warm, cloudy (twenty three "cloudy" days recorded) January. Rain on several days during month. Reading of 46 F at 2100 hours on 2 January. Rain and hail followed by snow on 29-31 January. Prairie fires "burning west" on 29 January. Warm February. Thunderstorm on 15 February. Heavy rain on 18 February. Little snow during the month. Cold early March: -10 F recorded at sunrise on 5 March. Warm late March: sunrise reading of 46 F on 17 March. Prairie fires noted on 23, 26 March. Smoky conditions on 16, 17 March. Sunny and very dry April. Warm early April: afternoon readings of 72 F and 76 F on 6, 9 April, respectively. Prairie fires noted on 2, 8, 9 April. Warm, wet May: rain during the night, continuing throughout the day on 23 May (2.19 inches recorded). Mississippi and St. Peter's rivers noted as rising on 29 May. Cool early June: frost with "slight" damage noted on 6 June. Readings of 42 F and 57 F at sunrise and 1500 hours, respectively on 5 June. Thunderstorm with force seven winds on 16 June. Wet, cloudy (twenty two "cloudy" days) and very cool July: afternoon readings of 66 F, 68 F, 66 F, 67 F, 57 F and 66 F on 5, 6, 7, 8, 25, 26 July, respectively. Prolonged rain event from 1200 hours on 25 July until 0830 on 26 July. Cool, cloudy (twenty "cloudy" days) August. Afternoon readings of 60 F and 58 F on 14, 15 August, respectively. Prolonged rainfall event from 2040 hours on 12 August until 1500 on 13 August: 1.75 inches recorded. Smoky conditions on 1, 6 August. Foggy, very cool September. Afternoon reading of 45 F on 20 September. Warm, dry October. Prairie fires noted on 22, 23, 24, 25 October. Twenty four "cloudy" days recorded during October. Very dry November. Cold early November: sunrise reading of -1 F on 9 November. Afternoon readings of 15 F and 17 F on 8, 9 November, respectively. Windstorm on 24-25 November with force six and force seven winds recorded. Twenty seven "cloudy" days during November. Dry, cold, windy December. Force eight winds noted on 31 December. Severe windstorm during the night of 16-17 December. Sustained cold and frequent high winds, 19-27 December.