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of the Figures in the original document were based on unpublished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revised and some have been replaced by new ones based on a longer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
siegmund@astro.washington.edu