7500 Foot Desert Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the 7500 Foot Desert Observatory clear sky chart from 2005-11-05 to 2018-01-20.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.
Observation TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(no limit)Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
58%
16356
29%
48498
20%
16315
67%
16315
45%
25359

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 15thNight
60%
894
29%
2638
23%
892
67%
892
54%
1276
January16th to endNight
60%
788
34%
2561
30%
788
68%
788
48%
1224
February1st to 15thNight
51%
701
26%
2225
19%
700
61%
700
46%
1117
February16th to endNight
43%
632
34%
1894
20%
632
58%
632
44%
979
March1st to 15thNight
51%
720
30%
2070
18%
720
62%
720
48%
1076
March16th to endNight
48%
702
32%
2046
17%
702
61%
702
47%
1060
April1st to 15thNight
39%
539
27%
1798
15%
539
57%
539
39%
895
April16th to endNight
44%
540
30%
1800
20%
540
60%
540
37%
945
May1st to 15thNight
51%
540
24%
1753
17%
539
63%
539
38%
906
May16th to endNight
54%
562
28%
1497
15%
561
65%
561
45%
819
June1st to 15thNight
65%
540
27%
1440
17%
540
72%
540
54%
739
June16th to endNight
73%
540
25%
1440
21%
540
76%
540
52%
749
July1st to 15thNight
68%
510
16%
1360
13%
510
69%
510
29%
901
July16th to endNight
78%
564
13%
1570
13%
531
79%
531
27%
987
August1st to 15thNight
72%
539
13%
1698
14%
536
73%
536
26%
1072
August16th to endNight
74%
573
19%
1910
22%
573
75%
573
28%
1160
September1st to 15thNight
70%
540
23%
1800
23%
540
73%
540
32%
1040
September16th to endNight
71%
546
37%
1926
33%
546
78%
546
47%
875
October1st to 15thNight
61%
720
33%
2160
21%
720
70%
720
53%
1054
October16th to endNight
68%
768
40%
2304
26%
768
77%
768
57%
1060
November1st to 15thNight
59%
908
38%
2428
21%
908
68%
908
64%
1148
November16th to endNight
57%
975
40%
2538
23%
975
66%
975
60%
1270
December1st to 15thNight
48%
975
29%
2730
15%
975
60%
975
50%
1407
December16th to endNight
48%
1040
29%
2912
17%
1040
58%
1040
43%
1600

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

Occurrence of each ForecastData
Points
Cloud CoverDay
23133245%6%9%57%
49031
Night
231332345%8%61%
48684
TransparencyDay
22%7%13%26%23%7%
48717
Night
20%6%13%27%24%7%
48500
SeeingDay
5%9%25%29%22%7%
6060
Night
4427%41%20%1
16363

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
2233125%6%9%62%
1640
16th to endDay
12243245%6%9%57%
1766
February1st to 15thDay
22341436%11%58%
1636
16th to endDay
31332345%8%61%
1580
March1st to 15thDay
22342446%8%60%
1887
16th to endDay
131432445%7%60%
2178
April1st to 15thDay
231232446%8%60%
2150
16th to endDay
36%13323448%58%
2160
May1st to 15thDay
231342446%8%57%
2193
16th to endDay
121332446%8%60%
2616
June1st to 15thDay
11122245%6%9%62%
2520
16th to endDay
1122245%6%9%63%
2520
July1st to 15thDay
3224436%7%9%12%43%
2520
16th to endDay
33145%47%9%10%12%37%
2488
August1st to 15thDay
3325%6%46%6%8%9%42%
2253
16th to endDay
3324435%6%8%11%45%
2292
September1st to 15thDay
4315%5%246%7%10%47%
2160
16th to endDay
221321335%6%66%
2031
October1st to 15thDay
32231345%6%65%
1800
16th to endDay
1212212235%73%
1920
November1st to 15thDay
12212346%73%
1748
16th to endDay
1213223337%68%
1749
December1st to 15thDay
21332345%11%60%
1560
16th to endDay
1323436%5%7%12%50%
1664
January1st to 15thNight
313312346%68%
2638
16th to endNight
1312223337%67%
2561
February1st to 15thNight
424323249%63%
2215
16th to endNight
141321345%7%63%
1894
March1st to 15thNight
2423313347%62%
2070
16th to endNight
2313313336%66%
2046
April1st to 15thNight
25%133235%5%8%58%
1798
16th to endNight
44243245%5%6%57%
1800
May1st to 15thNight
331332446%7%58%
1753
16th to endNight
221432337%8%60%
1497
June1st to 15thNight
11231435%9%64%
1440
16th to endNight
1123245%8%9%59%
1440
July1st to 15thNight
5%425%5%5%7%6%7%10%40%
1440
16th to endNight
3414437%7%9%13%39%
1677
August1st to 15thNight
44246%26%7%9%10%42%
1707
16th to endNight
4325%436%6%8%11%42%
1910
September1st to 15thNight
5%324426%5%8%11%46%
1800
16th to endNight
322313446%67%
1926
October1st to 15thNight
2112212346%68%
2160
16th to endNight
22221234471%
2304
November1st to 15thNight
111112337%75%
2428
16th to endNight
132212246%72%
2538
December1st to 15thNight
1322213245%68%
2730
16th to endNight
1323324348%61%
2912

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
18%416%37%22%1
1641
16th to endDay
23%5%13%34%20%2
1766
February1st to 15thDay
20%7%16%33%18%3
1637
16th to endDay
20%6%10%29%27%5%
1580
March1st to 15thDay
21%5%12%27%29%4
1887
16th to endDay
23%5%9%31%26%3
2178
April1st to 15thDay
20%6%9%32%24%7%
2150
16th to endDay
24%410%27%24%7%
2160
May1st to 15thDay
24%7%12%24%25%5%
2193
16th to endDay
20%5%13%22%25%11%
2620
June1st to 15thDay
16%6%11%20%21%22%
2520
16th to endDay
15%5%11%21%25%20%
2520
July1st to 15thDay
29%11%18%16%14%9%
2371
16th to endDay
31%13%24%20%7%2
2332
August1st to 15thDay
34%12%16%16%13%6%
2238
16th to endDay
28%9%17%24%15%4
2292
September1st to 15thDay
29%8%15%23%15%7%
2160
16th to endDay
17%5%10%24%34%8%
2031
October1st to 15thDay
18%6%7%27%30%9%
1800
16th to endDay
13%48%29%38%5%
1920
November1st to 15thDay
12%411%32%33%6%
1748
16th to endDay
17%38%34%28%6%
1749
December1st to 15thDay
20%6%18%32%18%3
1560
16th to endDay
25%8%18%28%17%2
1664
January1st to 15thNight
17%416%33%25%3
2638
16th to endNight
18%5%12%35%24%3
2561
February1st to 15thNight
21%5%16%32%19%4
2225
16th to endNight
19%7%10%29%27%5%
1894
March1st to 15thNight
21%411%30%29%3
2070
16th to endNight
20%5%8%28%30%5%
2046
April1st to 15thNight
23%5%11%29%23%7%
1798
16th to endNight
25%6%10%27%23%7%
1800
May1st to 15thNight
23%7%12%25%24%7%
1754
16th to endNight
20%7%15%20%22%13%
1498
June1st to 15thNight
16%6%14%17%19%25%
1440
16th to endNight
17%7%14%18%22%19%
1440
July1st to 15thNight
35%11%16%15%10%10%
1360
16th to endNight
29%15%25%20%7%1
1570
August1st to 15thNight
31%14%20%16%11%6%
1698
16th to endNight
31%12%19%20%12%4
1910
September1st to 15thNight
29%9%18%20%13%7%
1800
16th to endNight
17%5%10%22%32%11%
1926
October1st to 15thNight
16%5%10%22%33%11%
2160
16th to endNight
14%47%26%39%7%
2304
November1st to 15thNight
10%49%30%36%7%
2428
16th to endNight
13%47%33%31%8%
2538
December1st to 15thNight
18%5%14%37%21%1
2730
16th to endNight
21%7%15%31%21%2
2912

Seeing (when cloud cover <= 80%)
Color Meanings:
Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
5%8%26%38%17%2
135
16th to endDay
26%20%36%25%8%
109
February1st to 15thDay
1436%43%13%1
90
16th to endDay
8%17%23%30%19%
81
March1st to 15thDay
316%35%27%14%2
177
16th to endDay
9%23%36%21%7%1
288
April1st to 15thDay
5%25%38%18%10%1
269
16th to endDay
11%27%36%17%5%1
270
May1st to 15thDay
7%16%37%24%12%1
324
16th to endDay
411%29%31%18%4
517
June1st to 15thDay
27%23%33%26%6%
495
16th to endDay
2319%30%33%10%
495
July1st to 15thDay
6%212%27%39%11%
475
16th to endDay
8%311%25%34%17%
347
August1st to 15thDay
9%111%36%30%11%
315
16th to endDay
6%315%36%26%12%
332
September1st to 15thDay
4427%30%20%12%
315
16th to endDay
5%6%27%29%26%5%
198
October1st to 15thDay
211%28%20%28%8%
135
16th to endDay
36%23%29%24%12%
144
November1st to 15thDay
27%29%28%24%8%
135
16th to endDay
5%16%31%28%15%2
135
December1st to 15thDay
211%37%35%9%3
135
16th to endDay
5%13%28%41%8%2
144
January1st to 15thNight
2427%48%16%1
897
16th to endNight
35%28%48%13%1
788
February1st to 15thNight
3336%46%9%
704
16th to endNight
5%7%40%40%6%
632
March1st to 15thNight
46%32%43%11%
720
16th to endNight
36%38%39%10%
702
April1st to 15thNight
6%11%41%33%7%
539
16th to endNight
7%6%37%37%10%
540
May1st to 15thNight
5%6%31%42%13%
540
16th to endNight
46%28%39%19%1
563
June1st to 15thNight
2124%47%22%
540
16th to endNight
1117%44%34%1
540
July1st to 15thNight
7%110%34%42%2
510
16th to endNight
41328%53%8%
564
August1st to 15thNight
8%434%45%7%
539
16th to endNight
6%17%36%42%5%
573
September1st to 15thNight
7%112%42%33%3
540
16th to endNight
4217%45%28%2
546
October1st to 15thNight
3427%41%20%2
720
16th to endNight
4121%43%23%3
768
November1st to 15thNight
16%30%42%18%
908
16th to endNight
46%29%41%16%1
975
December1st to 15thNight
37%37%39%10%
975
16th to endNight
38%35%41%10%
1040
Page generated at 2018-01-21 10:19:31. Version ac04

Copyright 2018 A. Danko


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