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 2017-09-20.

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%
15810
29%
46925
20%
15769
67%
15769
44%
24661

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%
825
29%
2434
23%
823
67%
823
53%
1192
January16th to endNight
59%
768
33%
2496
29%
768
67%
768
47%
1202
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
73%
515
36%
1815
33%
515
80%
515
49%
807
October1st to 15thNight
63%
660
34%
1980
22%
660
71%
660
51%
980
October16th to endNight
67%
704
38%
2112
24%
704
76%
704
56%
980
November1st to 15thNight
62%
836
38%
2236
22%
836
70%
836
63%
1055
November16th to endNight
56%
900
38%
2343
22%
900
65%
900
58%
1187
December1st to 15thNight
47%
900
29%
2520
14%
900
59%
900
49%
1307
December16th to endNight
48%
960
27%
2688
16%
960
57%
960
41%
1506

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%
47917
Night
231332445%8%61%
47111
TransparencyDay
22%7%13%26%22%7%
47603
Night
21%7%13%27%23%7%
46927
SeeingDay
5%10%25%29%22%7%
5693
Night
4426%41%20%1
15817

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
3233125%6%8%61%
1513
16th to endDay
12343245%6%9%56%
1728
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
121221335%6%67%
1911
October1st to 15thDay
32331346%7%63%
1650
16th to endDay
1212112235%72%
1760
November1st to 15thDay
12212346%73%
1611
16th to endDay
1223223336%67%
1615
December1st to 15thDay
32333346%11%58%
1440
16th to endDay
1423436%5%7%12%48%
1536
January1st to 15thNight
313322346%68%
2434
16th to endNight
1312223337%66%
2496
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
222213446%68%
1815
October1st to 15thNight
221321235%7%67%
1980
16th to endNight
32221234470%
2112
November1st to 15thNight
11112337%75%
2236
16th to endNight
132212245%71%
2343
December1st to 15thNight
1323213345%68%
2520
16th to endNight
1323324449%60%
2688

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
19%416%37%20%
1514
16th to endDay
23%5%13%33%20%2
1728
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
16%5%10%24%34%8%
1911
October1st to 15thDay
19%6%7%28%29%7%
1650
16th to endDay
14%47%29%38%6%
1760
November1st to 15thDay
12%411%31%33%7%
1611
16th to endDay
17%38%34%28%6%
1615
December1st to 15thDay
21%6%19%34%17%1
1440
16th to endDay
26%9%19%27%16%1
1536
January1st to 15thNight
17%417%32%24%2
2434
16th to endNight
19%5%12%34%24%3
2496
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
16%5%10%22%32%11%
1815
October1st to 15thNight
17%6%10%23%32%9%
1980
16th to endNight
15%47%26%39%6%
2112
November1st to 15thNight
10%5%10%30%36%7%
2236
16th to endNight
14%47%32%31%8%
2343
December1st to 15thNight
18%6%14%38%20%1
2520
16th to endNight
23%8%15%31%18%2
2688

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
7%13%22%37%14%4
90
16th to endDay
37%21%37%23%6%
96
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%324%30%29%6%
165
October1st to 15thDay
17%23%23%34%10%
90
16th to endDay
5%7%29%26%19%12%
96
November1st to 15thDay
1418%30%34%11%
90
16th to endDay
5%22%32%24%14%1
90
December1st to 15thDay
316%43%28%7%
90
16th to endDay
7%16%27%39%8%1
96
January1st to 15thNight
2427%47%16%1
828
16th to endNight
35%28%49%12%1
768
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
3216%45%29%2
515
October1st to 15thNight
3424%41%22%2
660
16th to endNight
5%221%43%23%3
704
November1st to 15thNight
16%27%44%19%
836
16th to endNight
5%6%30%40%17%1
900
December1st to 15thNight
48%38%38%10%
900
16th to endNight
38%35%41%9%
960
Page generated at 2017-09-21 05:18:11. Version ac04

Copyright 2017 A. Danko


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