Desert Sky Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Desert Sky Observatory clear sky chart from 2005-11-05 to 2017-12-04.

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
77%
15916
37%
47846
33%
15877
81%
15877
54%
22687

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
67%
719
32%
2327
31%
716
73%
716
45%
1130
January16th to endNight
64%
768
36%
2496
33%
768
74%
768
41%
1271
February1st to 15thNight
69%
698
35%
2199
32%
698
78%
698
50%
1044
February16th to endNight
67%
632
37%
1865
37%
632
72%
632
46%
980
March1st to 15thNight
70%
720
40%
1980
33%
720
77%
720
57%
977
March16th to endNight
78%
768
39%
2112
32%
768
83%
768
62%
995
April1st to 15thNight
74%
695
34%
1954
26%
695
79%
695
56%
958
April16th to endNight
77%
540
45%
1727
40%
540
84%
540
70%
669
May1st to 15thNight
79%
539
40%
1619
34%
539
84%
539
69%
674
May16th to endNight
83%
561
41%
1684
35%
561
86%
561
73%
676
June1st to 15thNight
89%
540
35%
1620
31%
540
89%
540
69%
674
June16th to endNight
91%
540
35%
1620
31%
540
92%
540
73%
656
July1st to 15thNight
82%
510
24%
1530
20%
510
83%
510
47%
786
July16th to endNight
82%
564
26%
1593
22%
531
83%
531
40%
889
August1st to 15thNight
82%
539
30%
1611
27%
536
82%
536
46%
833
August16th to endNight
83%
615
33%
1859
32%
615
83%
615
43%
1003
September1st to 15thNight
80%
720
34%
1980
30%
720
81%
720
51%
1042
September16th to endNight
84%
716
44%
1980
35%
716
87%
716
65%
914
October1st to 15thNight
78%
720
41%
2076
34%
720
83%
720
66%
922
October16th to endNight
85%
768
47%
2304
42%
768
89%
768
69%
972
November1st to 15thNight
78%
760
41%
2287
36%
760
84%
760
61%
1028
November16th to endNight
74%
780
42%
2535
41%
780
79%
780
54%
1132
December1st to 15thNight
71%
736
37%
2392
39%
736
75%
736
47%
1156
December16th to endNight
68%
768
36%
2496
36%
768
72%
768
40%
1306

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
4212213346%67%
48641
Night
4212213346%67%
48042
TransparencyDay
18%1312%25%38%
48336
Night
19%1311%24%38%
47848
SeeingDay
5%316%34%28%9%
5680
Night
5%19%39%37%6%
15926

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
6%32221334464%
1611
16th to endDay
9%212313245%63%
1728
February1st to 15thDay
5%32323246%65%
1661
16th to endDay
9%313323246%59%
1607
March1st to 15thDay
5%312222345%66%
1980
16th to endDay
3213312345%68%
2112
April1st to 15thDay
312223247%69%
1994
16th to endDay
21111212479%
2230
May1st to 15thDay
111112236%77%
2331
16th to endDay
11111221382%
2429
June1st to 15thDay
1111222481%
2340
16th to endDay
1111122481%
2340
July1st to 15thDay
2214425%46%10%55%
2340
16th to endDay
5%2245%26%7%7%13%41%
2467
August1st to 15thDay
3213335%5%7%9%53%
2340
16th to endDay
3213435%45%9%56%
2339
September1st to 15thDay
421221346%7%63%
1980
16th to endDay
2111223479%
1980
October1st to 15thDay
211121234475%
1881
16th to endDay
11221113478%
1920
November1st to 15thDay
2211212246%72%
1899
16th to endDay
5%21331222471%
1755
December1st to 15thDay
9%312323336%60%
1649
16th to endDay
9%31331335%6%58%
1728
January1st to 15thNight
7%313224345%63%
2327
16th to endNight
10%313313335%61%
2496
February1st to 15thNight
5%313213345%66%
2188
16th to endNight
8%313323446%58%
1865
March1st to 15thNight
5%212212235%69%
1980
16th to endNight
3111212245%71%
2112
April1st to 15thNight
4122223335%67%
1954
16th to endNight
2111212381%
1727
May1st to 15thNight
111112246%75%
1619
16th to endNight
211212482%
1684
June1st to 15thNight
1111222479%
1620
16th to endNight
111123480%
1620
July1st to 15thNight
21144345%6%11%53%
1620
16th to endNight
3215%436%6%9%14%41%
1701
August1st to 15thNight
2314425%5%7%9%52%
1620
16th to endNight
23135%25%7%7%9%51%
1859
September1st to 15thNight
321331346%7%60%
1980
16th to endNight
21221233475%
1980
October1st to 15thNight
311121123475%
2076
16th to endNight
12111223379%
2304
November1st to 15thNight
3112212235%71%
2287
16th to endNight
421221222471%
2535
December1st to 15thNight
8%212312345%62%
2392
16th to endNight
10%313313345%57%
2496

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
23%1413%26%30%
1612
16th to endDay
24%1216%24%30%
1728
February1st to 15thDay
21%1416%26%30%
1661
16th to endDay
26%116%28%25%
1607
March1st to 15thDay
20%16%31%38%
1980
16th to endDay
19%18%32%36%
2112
April1st to 15thDay
16%117%36%37%
1994
16th to endDay
11%118%25%53%
2230
May1st to 15thDay
10%18%26%52%
2331
16th to endDay
10%6%24%56%
2432
June1st to 15thDay
10%1317%67%
2340
16th to endDay
9%11414%69%
2340
July1st to 15thDay
23%37%17%19%29%
2201
16th to endDay
31%415%24%17%6%
2312
August1st to 15thDay
23%48%19%18%25%
2325
16th to endDay
23%36%20%24%21%
2339
September1st to 15thDay
20%25%16%26%28%
1980
16th to endDay
10%16%29%50%
1980
October1st to 15thDay
13%129%25%47%
1881
16th to endDay
11%28%26%49%
1920
November1st to 15thDay
14%112%33%37%
1899
16th to endDay
18%119%25%43%
1755
December1st to 15thDay
25%1415%29%24%
1649
16th to endDay
26%1320%29%16%
1728
January1st to 15thNight
23%2310%26%32%
2327
16th to endNight
27%1113%26%29%
2496
February1st to 15thNight
21%1315%25%32%
2199
16th to endNight
26%115%27%28%
1865
March1st to 15thNight
18%218%27%42%
1980
16th to endNight
16%129%32%38%
2112
April1st to 15thNight
19%16%33%38%
1954
16th to endNight
9%116%24%57%
1727
May1st to 15thNight
10%116%29%50%
1620
16th to endNight
9%7%19%61%
1685
June1st to 15thNight
11%314%69%
1620
16th to endNight
9%12311%71%
1620
July1st to 15thNight
23%310%16%16%29%
1530
16th to endNight
28%414%22%21%8%
1593
August1st to 15thNight
23%49%20%15%26%
1611
16th to endNight
26%47%17%23%21%
1859
September1st to 15thNight
22%36%20%22%25%
1980
16th to endNight
12%216%27%49%
1980
October1st to 15thNight
13%1111%22%49%
2076
16th to endNight
11%119%21%54%
2304
November1st to 15thNight
16%1111%29%40%
2287
16th to endNight
18%119%24%44%
2535
December1st to 15thNight
23%1215%29%27%
2392
16th to endNight
28%1416%28%19%
2496

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
26%116%35%17%2
90
16th to endDay
9%315%39%19%12%
96
February1st to 15thDay
5%323%40%25%1
176
16th to endDay
11%6%26%37%15%1
238
March1st to 15thDay
5%10%25%34%18%4
270
16th to endDay
39%31%30%20%4
288
April1st to 15thDay
5%9%30%33%13%7%
269
16th to endDay
411%35%30%13%4
270
May1st to 15thDay
310%28%31%20%4
288
16th to endDay
2425%40%24%2
330
June1st to 15thDay
5%221%37%26%6%
315
16th to endDay
26%43%33%12%
315
July1st to 15thDay
38%35%37%15%
305
16th to endDay
4228%37%26%
327
August1st to 15thDay
3124%47%22%
315
16th to endDay
2424%45%22%
332
September1st to 15thDay
8%6%34%37%13%
315
16th to endDay
5%115%41%29%6%
315
October1st to 15thDay
4216%32%35%8%
216
16th to endDay
4334%41%15%
144
November1st to 15thDay
5%215%40%28%7%
135
16th to endDay
8%215%39%29%5%
135
December1st to 15thDay
10%16%41%36%6%
100
16th to endDay
22%317%37%17%1
96
January1st to 15thNight
8%214%45%23%5%
720
16th to endNight
11%213%42%24%4
768
February1st to 15thNight
7%213%46%26%3
704
16th to endNight
10%112%50%23%2
632
March1st to 15thNight
6%216%42%26%5%
720
16th to endNight
429%43%35%5%
768
April1st to 15thNight
4212%50%27%2
695
16th to endNight
2214%48%27%4
540
May1st to 15thNight
2213%45%31%5%
540
16th to endNight
229%41%37%6%
563
June1st to 15thNight
1444%45%2
540
16th to endNight
1231%57%6%
540
July1st to 15thNight
3323%58%9%
510
16th to endNight
4112%64%15%
564
August1st to 15thNight
3112%65%16%
539
16th to endNight
3119%60%14%
615
September1st to 15thNight
415%27%50%11%
720
16th to endNight
217%39%38%9%
716
October1st to 15thNight
411%41%36%5%
720
16th to endNight
27%40%39%9%
768
November1st to 15thNight
419%43%33%6%
760
16th to endNight
5%112%42%32%5%
780
December1st to 15thNight
10%19%43%31%3
736
16th to endNight
11%110%47%24%4
768
Page generated at 2017-12-05 08:19:03. Version ac04

Copyright 2017 A. Danko


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