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SDSS Engineering

A Twenty-Year Summary of Sacramento Peak Weather: August 1954 Through July 1974

Sloan Digital Sky Survey Telescope Technical Note 19970822

 

Howard L. DeMastus

Contents

This document was originally released by the United States Air Force Geophysics Laboratory, on May 3, 1976. The report number is AFGL-TR-76-0096. The Air Force Geophysics Laboratory is located at Hanscom AFB, Massachusetts 01731. Text in red italics through this document are notes made by the editor. Some of the Figures in the original document were based on unpublished data and were not reproduced herein.

Introduction

A General Summary of Sacramento Peak Weather, GRD Research Notes No. 82, May 1962 (hereafter called the 1962 summary) by this author describes and summarizes the meteorological conditions observed at the Sacramento Peak Observatory during the period August 1954 through December 1961.

This report summarizes and discusses newly derived means for the period August 1954 through July 1974. All statistics have been revised and some have been replaced by new ones based on a longer series of observations. In some cases the latest means differ so little from the old that changes seemed unnecessary. Even though the twenty years of data presented in this summary may help more accurately to support a climatological study over those contained in the 1962 summary, a 20-year period of data still lacks the statistical significance one would desire.

Briefly to review some of the introductory remarks in the 1962 summary, part of the meteorological program at the Sacramento Peak Observatory was supported by contract funds until such contracts were terminated in 1967 and 1968.

The equipment and procedures described in the 1962 summary are those still in use. The instrumentation, privately owned and maintained by the author includes a Bendix-Friez Microbarograph, two Wallace and Tiernan precision high-altitude barometers, Bendix-Friez Aerovane wind indicating and strip-chart recording systems, separate Belfort/Casella wind direction and speed transmitters for remote digital readout, Bendix-Friez dual-traverse weighing and recording rain and snow gauge, M.R.I. heated tipping-bucked moisture gauge with remote indicator, Brown electronic strip-chart temperature recorder, Bendix-Friez recording hygrometer and a mercurial barometer.

All equipment is periodically checked for proper calibration. All original records are on permanent file at the observatory with the exception of the wind speed and direction charts. Due to a growing lack of storage facilities only the current years' records are kept.

It may be questioned whether or not a weather station is of first importance to a solar observatory. During DeMastus' earlier years at Sacramento Peak there were relatively few outside requests for such data and even fewer-in house requests. Since then, however, the situation has changed dramatically. Many of the construction programs both here at the observatory and in the local area, and a number of research programs at the observatory are making use of the readily available information.

Since there are relatively very few meteorological stations at higher altitudes and the fact that there is information readily available both on a daily basis as well as from a body of data extending over the past 20-year period, DeMastus is now providing information to an increased number of users.

The Sacramento Peak Observatory is situated in south-central New Mexico near the southern end of the Sacramento mountain range. The Observatory proper is located 32 °47 ' 16" north latitude, 105 °49' 13" west longitude (+ 07h 03m 16.6s), elevation 9240 feet above mean sea level.

Temperature

The two most important elements that combine to form climate are temperature and rainfall (or snowfall). These have perhaps been more constantly and carefully observed throughout the world than the other elements, namely wind, humidity, pressure and percentage of sunshine which are by no means unimportant.

The temperature at Sacramento Peak is continuously graphed by a single-pen, strip-chart recorder whose total range is -40 °F to +140 °F, with a full-scale accuracy of ± 0.25 °F. The time resolution and instrumental time constants are such that even the greatest rate of change that would be experienced is easily readable. The sensing device for the remote recorder is in a properly exposed housing approximately 6 ft above ground level. From this strip-chart the daily maximum and minimum temperatures are read and recorded onto a separate graph.

The mean temperature for any day is usually taken to be the mean of the highest and lowest temperatures of that day. In reviewing the many requests for our data, most are for either average maximum (or minimum) temperature for a given month instead of the mean between maximum and minimum temperatures. Therefore, the values of each day's maximum (and minimum) temperature for each month have been averaged over the 20-year period and are illustrated by the two curves in Figure 1.

Figure 1: Mean monthly maximum and minimum temperatures (August 1954 - August 1974).

The curves in Figures 2a through 5c illustrate the departures of individual monthly means (both maximum and minimum) from the 20-year means.

Table 1 lists the monthly average maximum and average minimum temperatures for each of the years 1954 through 1974. Table 2 gives the extreme temperatures observed each month for the same period.

In world climatological investigations the duration of time where soil temperatures are higher than 43 °F is called the "vegetative period" since that is about the lower temperature limit of seed germination. In this paper we will discuss the freeze-free period or the length of time between the last and the first killing frosts since no soil temperature data are available.

At Sacramento Peak the freeze-free period is on the average, 143 days. The dates of the average last and first freeze are 17 May and 7 October, respectively.

Figure 2a: January departures from 20-year means.

Figure 2b: February departures from 20-year means.

Figure 2c: March departures from 20-year means.

Figure 3a: April departures from 20-year means.

Figure 3b: May departures from 20-year means.

Figure 3c: June departures from 20-year means.

Figure 4a: July departures from 20-year means.

Figure 4b: August departures from 20-year means.

Figure 4c: September departures from 20-year means.

Figure 5a: October departures from 20-year means.

Figure 5b: November departures from 20-year means.

Figure 5c: December departures from 20-year means.

Table 1: Mean Maximum (and Minimum) Temperatures, August 1954 - July 1974. The first line associated with each year gives the average high temperature for each month. The second line associated with each year gives the mean low temperature for each month. Presented here is a summary of the full table.

Mean

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

max

38.7

40.3

46.7

55.5

66.3

74

71.8

68.9

65.7

57.2

46.7

40.6

min

21.5

20.6

24.6

31

39.4

46.9

50.3

48.6

44.9

36.2

27.4

22.7

diff

17.2

19.7

22.1

24.5

26.9

27.1

21.5

20.3

20.8

21

19.3

17.9

Table 2: Extreme Temperatures for Each Month, September 1954 - August 1974. The first line associated with each year gives the high temperature for each month. The second line associated with each year gives the low temperature for each month.

The dates of the first and last freeze for each of the years 1954 through 1974 are shown in Table 3.

The record high and low temperatures observed at Sacramento Peak since 1954 were:

93°F 18 June 1970

-23°F 10 January 1962

The second record high and low temperatures were:

91.2°F 29 June 1960

-12°F 11 January 1962

The record highest minimum temperature was 62 °F, 7 August 1962, and the record lowest maximum was -4 °F, 10 January 1962. The extreme temperatures observed for any given month are shown in Table 4.

Table 3: Dates of First and Last Freeze, 1954-1974.

Year

First

Last

1954

Oct. 15

--

1955

Oct. 6

May 26

1956

Oct. 9

May 15

1957

Oct. 11

May 18

1958

Oct. 19

May 14

1959

Oct. 4

May 21

1960

Oct. 12

May 21

1961

*Sept. 4

May 15

1962

Oct. 20

May 28

1963

Nov. 1

April 27

1964

Oct. 13

May 31

1965

Sept. 20

May 14

1966

Oct. 14

April 24

1967

Sept. 27

May 15

1968

Oct. 16

May 7

1969

Oct. 23

May 9

1970

Sept. 25

*June 1

1971

Sept. 20

May 24

1972

Sept. 22

May 16

1973

Sept. 26

May 15

1974

--

May 21 

Average number of days between first and last freeze = 143.

Average last freeze 17 May.

Average first freeze 7 October.

* Record early and late freeze, respectively.

Table 4: Extreme temperatures for any given month.

Max

Min

Date

Year

Temp

Date

Year

Temp

Jan. 27

1967

63

Jan. 10

1962

-23

Feb. 4

1967

60

Feb. 2

1956

-7

Feb. 7

1963

60

Mar. 4

1966

-2

Mar. 30

1969

71

Apr. 8

1973

5

Apr. 22

1965

79

May 1

1970

20

May 31

1969

83

May 9

1967

20

June 18

1970

93

June 1

1970

31

July 5

1969

91

July 21

1974

41

Aug. 16

1969

87

Aug. 3

1957

41

Aug. 28

1970

41

Aug. 31

1968

41

Sept. 16

1956

79

Sept. 26

1970

28

Sept. 28

1970

28

Oct. 9

1965

78

Oct. 31

1972

11

Nov. 14

1967

69

Nov. 22

1957

3

Dec. 5

1965

66

Dec. 22

1968

-2

Precipitation

The nature of precipitation is important as a climatological element. A mere statement of the mean annual rainfall (or snowfall) at any given place is not sufficient. The significance of seasonal distribution can be of fundamental importance and this distribution is independent of the annual total.

The pattern, or regime of precipitation may be divided into five or six distinct categories when considering world-wide patterns. These general patterns can be modified due to more localized effects. Mountains, for instance, cause a local modification of the rainfall regime and the kind of modification is dependent upon the locations of the observer.

Sacramento Peak receives its precipitation during two distinct periods throughout the year. The late spring and summer thunderstorm season is responsible for nearly two-thirds of the annual mean. Of the five months, May through September, July and August contribute the greater part, on the average 41 percent of the annual mean. While early May, June and late September are also considered to be part of the thunderstorm season, the average contribution by convective thunderstorms to the annual total is usually negligible. Intrusion of weak cyclonic depressions during the early fall, and cyclonic systems lasting into late spring may bring light to moderate rains to the desert southwest. The balance, or one-third of the annual precipitation, is in the form of snow and is received from well-developed wave systems which develop either in the southwestern United States or invade the continent from the Pacific Ocean. This regime is in effect generally from October through March or April.

At Sacramento Peak the mean annual precipitation is 23".45 with a maximum monthly mean of 5".2 in July, and a minimum monthly mean of 0".31 in April. The distribution of the annual mean is illustrated in Figure 6 and Table 5, gives the water equivalent for each month during the period 1955 through 1974. The annual water equivalent as expressed in percent of normal is shown in Figure 7.

Figure 6: Distribution of Mean Annual Precipitation, Sacramento Peak.

 

Table 5: Monthly Precipitation, Water Equivalent, August 1954 - July 1974
             
             
             
            Record rainfall rates. 
            Most rain in 1 hour:             1.66         15 July 1974
            Most rain in 12 hours:           3.06         1 September 1969            
            Most rain in 24 hours:           3.54         31 August- 1 September 1969
            Most rain in 1 calendar week:    8.17         25 August- 1 September 1969
             

Figure 7: Percent normal precipitation, 1955 through 1973.

 

As inspection of the curve in Figure 7 might indicate a gradual increase in the average annual precipitation at Sacramento Peak at least for the period shown. As a curiosity we have plotted the percent normal precipitation curves shown in Figure 8 for El Paso, Texas, 85 miles SSW of Sacramento Peak, elevation 3900 ft MSL; Alamogordo, New Mexico, 12 miles NY of Sacramento Peak, elevation 4335 ft MSL; Mountain Park, New Mexico, 11 miles NNW of Sacramento Peak, elevation 6720 ft MSL, and Sacramento Peak. There seems to be no significant increase in the annual mean precipitation at these additional three sites.

The family of curves in Figure 9 compares the distribution of mean annual precipitation for Alamogordo, Mountain Park and Sacramento Peak.

As previously indicated, approximately two-thirds of the annual mean is contributed by the thunderstorm season. The balance, or approximately one-third of the annual mean is from snowfall. In general, the snowfall season extends from October through April with residual amounts occurring in September and May. The mean seasonal snowfall is 71".8 and the seasonal distribution is illustrated in Figure 10. The four-month period December through March contributes about 85 percent of the seasonal total and the monthly totals during this four-month period are nearly equally divided with the exception of a slight decrease during February.

Figure 8: Percent Normal Precipitation. Data is unavailable.

Figure 9: Distribution of Mean Annual Precipitation, Sacramento Peak; Mount Peak; and Alamogordo, New Mexico. Data is unavailable.

Figure 10: Distribution of mean seasonal snowfall.

The actual snowfall in inches per month for the period 1956 through 1974 is shown in Table 6. The individual monthly totals for the period October 1954 through December 1955 are not available.

Table 7 shows the total seasonal snowfall in inches with the dates of first and last occurrence. The average first and last seasonal snowfalls are 28 October and 18 April, respectively.

At Sacramento Peak the snow depth is measured at frequent intervals especially during high rates of accumulation or during particularly high moisture content snows. A foot of new snow can settle several inches within a few hours. The greatest accumulated depth of snow on the ground at any given time was 46".5 in mid-January 1960

Table 6: Inches of snowfall per month for each snow season.

Table 7: Dates of first and last seasonal snowfall.

Season

First

Last

Season Total

1954-55

Nov. 3

Mar. 26

34

1955-56

Nov. 7

Apr. 2

40

1956-57

Oct. 17

May 10

50

1957-58

Oct. 11

Mar. 4

119

1958-59

Oct. 28

May 5

24

1959-60

Oct. 4

Mar. 30

117.5

1960-61

Oct. 17

Apr. 27

63.25

1961-62

Nov. 2

Feb. 21

104.75

1962-63

Nov. 17

Feb. 21

54.5

1963-64

Nov. 7

Apr. 4

47.75

1964-65

Oct. 26

Apr. 26

73.5

1965-66

Oct. 17

Apr. 25

79

1966-67

Nov. 8

Apr. 13

24.5

1967-68

Oct. 29

Apr. 23

120.5

1968-69

Nov. 2

May 8

86.75

1969-1970

Oct. 29

May 2

78.5

1970-71

Sept. 27

May 12

33.75

1971-72

*Sept. 19

May 14

77.75

1972-73

Oct. 21

Apr. 8

*142.5

1973-74

Nov. 19

Mar. 24

64

Average first seasonal snow October 28

Average last seasonal snow April 20

* Record earliest and latest snowfall and season, respectively.

Since there is a direct relation between measured depth and weight, any form of precipitation can therefore be weighted and converted into inches of water. This report does not discuss the moisture content of individual snowfalls, however, the overall ratio of snow depth to equivalent inches of water is approximately 10.9 to 1.0.

Barometric Pressure

The first weather record keeping in the area that was to be the future location of the Sacramento Peak Observatory was that of the site survey team in 1947 and 1948. Among a variety of observations, records of temperature and barometric pressure were kept. Most of the pressure records have survived but unfortunately nearly all of the temperature records have been lost.

Atmospheric pressure observations were made using a high-altitude mercurial barometer which, incidentally is still in use. According to standard practice, corrections for temperature, instrument error, etc., were made. One unfortunate fact, however, remains. No mention is made in any of the extant records at which of the two observing sites the barometer was located, therefore, it is impossible to determine the absolute values of recorded station pressure and in another instance, impossible to determine the absolute value of the record maximum pressure. While all of this may be of academic interest only, it should be mentioned for some future Observatory historian.

All observations of atmospheric pressure subsequent to 1952 have been made in terms of the local bench mark altitude of 9240 ft MSL. It is assumed that the 1948 through 1951 observations were made at one of the two sites mentioned above and also that such readings were not made in terms of the bench mark altitude and are therefore not compatible with all later readings. However, the maximum observed pressure of 21".91 (-0".028, -0".049) Hg, 1 July 1949 will remain as the record value since any contending values subsequent to 1952 do not equal or exceed the 21".91 value with its attendant correction.

The record minimum pressure of 20".799 was observed on two separate occasions, 9 February 1960 and 17 December 1967.

The mean barometric pressure at Sacramento Peak has been computed for each of the individual months for the period 1954 through 1974 and the smoothed curve is illustrated in Figure 11. At the Observatory the mean pressure for each four-day interval is computed and compared with the standard smoothed curve. An example is shown in Figure 12. Since these analyses are of little interest, the complete history is not presented in this report.

Figure 11: Mean Monthly Atmospheric Pressure (inches of Hg). Data is unavailable.

Figure 12: Four-day Pressure Mean, 1973. Data is unavailable.

Wind Behavior

Both wind speed and direction are continuously recorded at the Observatory. the equipment is so arranged as to provide both speed averages as well as peak gusts as a graph on a strip-chart recorder. The sensing device is located atop a 110 ft water tower, essentially exposed to free-air flow and not subject to turbulence created either by trees or man-made objects. The water tower is situated approximately 300 yards east of an escarpment and no doubt there is some turbulence due to this nearby geographical feature.

Subsequent to the publication of the 1962 summary this author has had the opportunity to measure wind speeds at the top of the solar vacuum tower, located approximately 600 yards south-southwest of the water tower and situated just at the edge of the escarpment. The top of the vacuum tower is approximately 120 ft above that of the water tower.

Table 8 (and the graph in Figure 13) gives the total non-consecutive hours per month where the average wind speed maintains values from 30 mph to 50 mph by 5-mile increments. Also shown in Table 8 are averages of the peak gusts for any given month.

Table 8: Average Number of Non-Consecutive Hours of Given Wind Speeds by 5-mph increments, 1954-1974

Month

30-35

35-40

40-45

45-50

Avg. Gust

Jan.

17.5

2.8

0.5

0.3

72

Feb.

26

6.5

4.8

1.4

81

Mar.

14.2

7.9

5.1

0.8

60

Apr.

17.1

3.1

0.5

*

67

May

6.1

4.1

0.8

0

54

June

3.8

3.5

0.2

0

55

July

4.1

1.5

0.9

0.2

42

Aug.

2.9

0.9

0.2

0

31

Sept.

6

1.5

0.3

*

41

Oct.

11.2

4.2

1.8

0.2

46

Nov.

16

6.8

4

1.9

74

Dec.

26.4

4.9

4.1

1.1

61

Some notable wind speeds observed at Sacramento Peak were gusts of 113 mph, February 1960, and 103 mph, November 1958.

To construct the wind rose diagrams in Figure 14, we have plotted the percentage frequencies of wind direction. The total number of hours per month of average wind from each of eight 45-deg sectors is expressed as a percent of the total possible time. The year is divided into two seasons, summer extending from April through September, and winter from October through March. During both seasons the wind direction has a predominately higher westerly index (west to east). There is a considerable increase in the easterly component during the summer months with which is associated the local mountain thunderstorm season.

Figure 13: Non-consecutive Hours of Given Wind Speed.

 

Figure 14a: Percentage Frequencies of Wind Direction - Winter. This drawing is based on the figure in the original text. No data was available for exact duplication.

 

Figure 14b: Percentage Frequencies of Wind Direction - Summer. This drawing is based on the figure in the original text. No data was available for exact duplication.

Relative Humidity

The relative humidity can be one of the more noticeable of the climatological elements especially during extended periods of time when both the humidity and temperature are high.

Only recently have we begun keeping humidity records at the Observatory. Figure 15 illustrates the average monthly relative humidity computed from nearly nine years of data, 1955 through 1974. Again the affect of the summer thunderstorm season is a striking feature. While the average humidity is 70 percent during July and August, there can be periods of several days during which it will not fall below 90 percent.

Figure 15: Average Monthly relative Humidity. Data is unavailable.

Conclusions

While climatological conditions at the Sacramento Peak Observatory are in general not unlike those encountered elsewhere at similar elevations through the mountain range, they do vary markedly from those encountered in such places as Alamogordo or Mountain Park.

About the only reasonable conclusions that may be made from a study of this sort is that even though some of the recently derived means differ so little from those presented in the 1962 summary, observations made during a 20-year period are still not entirely statistically significant, but a reasonable indication of the climate can be shown.

Postscript

This document was converted to .html format and edited by Elaine Cabuang and Matt Buffaloe. 

Date created: 8/29/1997
            Last modified: 8/29/1997
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