ANNUAL CLIMATOLOGICAL SUMMARY
FT. SNELLING MN
The 1838 Ft. Snelling climatological record consists of fixed time temperature readings taken daily at or about local sunrise (designated in the official record as the "AM" reading), 1400 hours local solar time (designated in the official record as the "PM" reading) and 2100 hours local solar time (designated in the official record as the "evening" reading); two daily entries indicating the prevailing direction of the wind and the general condition of the sky (expressed as "fair" or "cloudy"); a daily quantitative precipitation record (derived from measurements taken from the station's DeWitt rain gauge); 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 1838 observations were taken within the Ft. Snelling enclosure (on the bluffs overlooking the confluence of the Mississippi and Minnesota rivers) .
The foregoing 1838 temperature record includes both unadjusted (UNADJ) and adjusted (ADJ) mean temperatures. Unadjusted values are the averages of fixed time readings taken daily at sunrise and at or about 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 1838 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 1838 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.
The foregoing "precipitation days" record is derived from quantitative precipitation records kept by fort observers during 1838 and/or from notations entered in the remarks section of the 1838 record . The 1838 record contains few quantitative snowfall values: the foregoing monthly snowfall values, accordingly, are estimates (obtained for the most part from National Weather Service meltwater-snowfall conversion tables) . Prevailing monthly wind direction is based on the air movement observations taken by station observers twice daily during 1838: prevailing monthly winds indicate the direction most frequently observed/recorded during any given month. Sky cover distributions, similarly, are based on observations taken twice each day during 1838: fair days are those with "fair" conditions noted at both observations; cloudy days are those with "cloudy" conditions noted at both observations: and "mixed" days are those with fair conditions noted at one observation and cloudy conditions noted at one observation.
Ft. Snelling precipitation records for July and August 1838 contain several ambiguous/inaccurate entries. As a result, precipitation values for those months are problematic: correct values could be 11.11 and 3.08 inches for July and August, respectively.
Warm early January: readings of 38 F, 36 F, 36 F and 33 F at sunrise on 1, 2, 3, 4 January, respectively. Very cold late January: sunrise readings below zero on every day but two, 18-31 January. Mild early February followed by record setting cold at mid-month. "Mercury in the station thermometer "observed to stand at -40 F" at 0200 hours on 14 February: "believed to have been frozen" Readings of -32 F, -38 F and -29 F at sunrise on 13, 14, 15 February, respectively. So far as can be determined, January-February 1838 snowfall was light to moderate. Warm, sunny and very dry March: no measurable precipitation recorded, 8-31 March. Very warm late March: readings in the low to mid 70's F each day, 26-31 March. Sunrise readings of 48 F on 27, 31 March. Willow buds beginning to open on 26 March. Cool, cloudy and rainy April. Reading of 20 F at sunrise on 14 April. Heavy thunderstorm noted on 27 April. Cold, sunny May. Light snow on 4 May. Snow accompanied by "high" northwesterly winds during the afternoon of 21 May. Severe frost on 22 May: sunrise reading of 30 F on that date. Observer noted that a "piece of ice one inch in thickness" was seen on the morning of 22 May: ice did not melt until about 1100 hours. Very warm mid May: reading of 92 F at 1400 hours on 19 May. Warm June: reading of 96 F at 1400 on 21 June. Heavy rains, late June: 2.45 inches recorded, 28-29 June. Very warm and wet July. Readings of 100 F and 98 F at 1400 hours on 7, 15 July, respectively. Excessive rains on 9 July (5.1 inches) and 15-18 July (3.95 inches). Warm, sunny August. Reading of 96 F at 1400 on 26 August. Warm, sunny September. Light frost noted on 23, 24 September. Cold, cloudy and dry October. Snow with probable accumulation on 17 October. Reading of 21 F at sunrise on 12 October. Very cold November; sunrise readings of 7 F, 2 F, 2 F, -1 F on 8, 9, 14, 17 November, respectively. Reading of 16 F at 1400 on 9 November. Reading of -4 F at 2100 hours on 17 November. Mississippi river cover with ice on 9 November. Cold December but with alternating periods of warmth and cold. Reading of 46 F at 1400 on 11 December. So far as can be determined, snowfall during November and December 1838 was light to moderate.