Mammoth Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mammoth Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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
56%
23625
31%
74639
23%
23586
66%
23586
45%
35959

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 10thNight
44%
756
27%
2646
16%
756
60%
756
35%
1301
January11th to 20thNight
49%
744
27%
2559
21%
744
61%
744
40%
1196
January21st to endNight
48%
792
30%
2574
23%
792
60%
792
35%
1356
February1st to 10thNight
48%
720
32%
2223
23%
720
62%
720
40%
1146
February11th to 20thNight
47%
700
31%
2099
22%
700
60%
700
38%
1098
February21st to endNight
43%
592
29%
1776
18%
592
57%
592
36%
956
March1st to 10thNight
39%
720
24%
2160
14%
720
52%
720
34%
1153
March11th to 20thNight
44%
720
22%
2072
16%
720
52%
720
34%
1149
March21st to endNight
37%
792
24%
1995
9%
792
49%
792
38%
1155
April1st to 10thNight
41%
720
25%
1800
10%
720
50%
720
38%
1071
April11th to 20thNight
43%
711
26%
1779
9%
711
51%
711
40%
1002
April21st to endNight
47%
720
25%
1800
9%
720
54%
720
48%
979
May1st to 10thNight
49%
602
28%
1682
15%
602
55%
602
44%
870
May11th to 20thNight
51%
531
29%
1595
21%
531
57%
531
44%
783
May21st to endNight
59%
403
27%
1567
24%
403
68%
403
38%
709
June1st to 10thNight
66%
360
29%
1440
28%
360
77%
360
44%
588
June11th to 20thNight
66%
360
35%
1440
34%
360
80%
360
57%
493
June21st to endNight
73%
360
38%
1440
39%
360
85%
360
64%
483
July1st to 10thNight
79%
350
37%
1400
41%
350
87%
350
67%
456
July11th to 20thNight
76%
348
35%
1392
40%
348
82%
348
57%
512
July21st to endNight
81%
448
38%
1539
38%
423
85%
423
54%
641
August1st to 10thNight
72%
673
35%
1738
21%
670
76%
670
68%
817
August11th to 20thNight
77%
712
37%
1780
21%
712
79%
712
72%
849
August21st to endNight
77%
792
43%
1980
24%
792
81%
792
76%
914
September1st to 10thNight
76%
720
45%
1800
27%
720
82%
720
80%
797
September11th to 20thNight
70%
720
45%
1876
30%
720
79%
720
67%
862
September21st to endNight
69%
720
43%
1980
31%
720
82%
720
64%
874
October1st to 10thNight
64%
720
36%
2037
26%
720
77%
720
55%
982
October11th to 20thNight
69%
720
39%
2160
34%
720
79%
720
58%
955
October21st to endNight
63%
792
41%
2442
34%
792
77%
792
58%
1043
November1st to 10thNight
62%
740
33%
2405
29%
740
72%
740
50%
1064
November11th to 20thNight
55%
760
36%
2470
25%
760
70%
760
51%
1079
November21st to endNight
53%
760
35%
2470
26%
760
67%
760
44%
1163
December1st to 10thNight
47%
760
28%
2555
19%
760
60%
760
39%
1219
December11th to 20thNight
40%
760
23%
3205
18%
759
53%
759
24%
1771
December21st to endNight
38%
827
17%
4763
17%
817
52%
817
17%
2473

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
132432445%7%65%
74830
Night
121332345%8%67%
74995
TransparencyDay
22%5%10%20%26%18%
74537
Night
19%5%11%22%28%16%
74809
SeeingDay
10%20%31%23%12%4
14029
Night
5%11%25%31%22%6%
23643

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 10thDay
13143345%7%13%58%
1519
11th to 20thDay
115%425%5%5%8%61%
1524
21st to endDay
1435%435%5%7%9%52%
1782
February1st to 10thDay
132431445%9%64%
1735
11th to 20thDay
1225%6%145%6%10%57%
1750
21st to endDay
3245%35%6%6%7%57%
1480
March1st to 10thDay
335%5%36%6%8%10%51%
1800
11th to 20thDay
326%4346%8%11%51%
1885
21st to endDay
325%425%6%7%8%56%
2359
April1st to 10thDay
1335%5%345%6%9%56%
2160
11th to 20thDay
1425%42446%8%61%
2129
21st to endDay
24223235%6%7%63%
2160
May1st to 10thDay
2413425%46%7%61%
2276
11th to 20thDay
25%244345%6%6%60%
2301
21st to endDay
47%25%5%35%45%6%55%
2705
June1st to 10thDay
34133245%5%7%63%
2520
11th to 20thDay
2112212335%78%
2520
21st to endDay
231322334474%
2520
July1st to 10thDay
1113324446%72%
2520
11th to 20thDay
2213324345%69%
2520
21st to endDay
5%31443445%6%61%
2684
August1st to 10thDay
3213323435%71%
2190
11th to 20thDay
2212322346%73%
2122
21st to endDay
2213312245%77%
2376
September1st to 10thDay
2212323335%75%
2160
11th to 20thDay
221231233475%
2084
21st to endDay
1213212236%76%
1980
October1st to 10thDay
2413223245%71%
1920
11th to 20thDay
2213322346%72%
1800
21st to endDay
213113337%76%
1913
November1st to 10thDay
122431346%9%66%
1674
11th to 20thDay
11222245%10%71%
1710
21st to endDay
131232435%8%69%
1710
December1st to 10thDay
2222245%6%11%64%
1620
11th to 20thDay
13245%35%7%9%10%52%
1928
21st to endDay
5%36%5%35%6%7%11%50%
2794
January1st to 10thNight
13234345%8%10%59%
2646
11th to 20thNight
1124245%7%11%62%
2559
21st to endNight
13244346%6%10%58%
2574
February1st to 10thNight
2244245%5%9%63%
2223
11th to 20thNight
1225%4245%5%10%60%
2098
21st to endNight
3136%345%6%8%61%
1776
March1st to 10thNight
2235%35%6%8%11%56%
2160
11th to 20thNight
1325%4246%7%12%55%
2072
21st to endNight
133432445%7%64%
1995
April1st to 10thNight
1325%325%45%8%61%
1800
11th to 20thNight
1324425%35%8%64%
1779
21st to endNight
1423323446%69%
1800
May1st to 10thNight
1313423449%65%
1682
11th to 20thNight
2313323346%69%
1594
21st to endNight
45%12223236%68%
1567
June1st to 10thNight
12133235%5%8%67%
1440
11th to 20thNight
211212345%79%
1440
21st to endNight
111221122483%
1440
July1st to 10thNight
111212245%82%
1440
11th to 20thNight
1213322335%75%
1440
21st to endNight
2213223436%70%
1630
August1st to 10thNight
2112212235%79%
1747
11th to 20thNight
111221333380%
1780
21st to endNight
11111233483%
1980
September1st to 10thNight
11121122387%
1800
11th to 20thNight
111221223482%
1876
21st to endNight
111212335%80%
1980
October1st to 10thNight
241321233476%
2037
11th to 20thNight
1212213435%77%
2160
21st to endNight
1111122246%78%
2442
November1st to 10thNight
1132125%5%8%72%
2405
11th to 20thNight
1112213448%72%
2470
21st to endNight
31422345%9%68%
2470
December1st to 10thNight
1233235%6%10%65%
2555
11th to 20thNight
225%425%6%9%13%53%
3276
21st to endNight
5%37%6%35%6%7%11%46%
4862

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 10thDay
23%6%20%23%21%6%
1519
11th to 20thDay
24%7%13%24%22%11%
1524
21st to endDay
33%5%12%17%23%10%
1782
February1st to 10thDay
21%6%13%22%23%14%
1735
11th to 20thDay
28%310%25%25%9%
1760
21st to endDay
31%414%24%20%6%
1480
March1st to 10thDay
32%6%14%20%21%6%
1800
11th to 20thDay
33%7%14%21%18%7%
1885
21st to endDay
29%7%19%25%16%4
2359
April1st to 10thDay
29%6%16%24%17%8%
2160
11th to 20thDay
25%8%12%26%20%9%
2132
21st to endDay
24%6%17%31%19%4
2160
May1st to 10thDay
25%411%32%23%5%
2276
11th to 20thDay
25%6%12%29%24%5%
2304
21st to endDay
31%5%11%26%22%5%
2705
June1st to 10thDay
23%6%9%23%30%9%
2520
11th to 20thDay
11%47%21%35%22%
2520
21st to endDay
15%3413%36%29%
2520
July1st to 10thDay
15%3411%24%44%
2451
11th to 20thDay
18%26%14%26%35%
2445
21st to endDay
23%46%13%21%33%
2535
August1st to 10thDay
17%3411%24%42%
2174
11th to 20thDay
14%35%11%33%35%
2122
21st to endDay
13%2310%37%35%
2376
September1st to 10thDay
15%25%11%28%39%
2160
11th to 20thDay
14%27%17%31%29%
2084
21st to endDay
14%1419%36%26%
1980
October1st to 10thDay
20%27%16%30%25%
1920
11th to 20thDay
16%27%19%33%22%
1800
21st to endDay
13%47%21%35%20%
1913
November1st to 10thDay
19%312%21%28%16%
1674
11th to 20thDay
15%412%24%31%13%
1710
21st to endDay
20%310%22%30%15%
1710
December1st to 10thDay
20%7%13%22%25%14%
1620
11th to 20thDay
29%13%16%17%15%10%
1928
21st to endDay
28%8%15%19%21%10%
2794
January1st to 10thNight
22%6%16%26%21%8%
2646
11th to 20thNight
18%6%17%23%23%12%
2559
21st to endNight
28%413%20%23%13%
2574
February1st to 10thNight
21%7%11%24%22%14%
2223
11th to 20thNight
24%411%23%26%12%
2099
21st to endNight
25%5%12%24%26%8%
1776
March1st to 10thNight
25%6%17%21%22%9%
2160
11th to 20thNight
27%5%18%19%22%8%
2072
21st to endNight
25%5%21%28%17%4
1995
April1st to 10thNight
27%6%14%27%18%8%
1800
11th to 20thNight
23%415%26%22%10%
1779
21st to endNight
20%5%20%34%18%4
1800
May1st to 10thNight
21%5%13%32%25%5%
1682
11th to 20thNight
21%412%37%23%4
1595
21st to endNight
22%413%31%25%4
1567
June1st to 10thNight
17%5%13%27%32%7%
1440
11th to 20thNight
9%39%25%36%18%
1440
21st to endNight
10%2415%41%29%
1440
July1st to 10thNight
7%3413%31%42%
1400
11th to 20thNight
14%26%15%35%28%
1392
21st to endNight
16%38%16%31%27%
1539
August1st to 10thNight
11%26%13%29%38%
1738
11th to 20thNight
10%3417%37%29%
1780
21st to endNight
8%2314%39%34%
1980
September1st to 10thNight
6%2415%38%35%
1800
11th to 20thNight
9%35%21%39%22%
1876
21st to endNight
10%35%22%39%22%
1980
October1st to 10thNight
17%36%19%34%21%
2037
11th to 20thNight
13%37%20%36%21%
2160
21st to endNight
11%47%22%37%19%
2442
November1st to 10thNight
15%412%24%29%15%
2405
11th to 20thNight
14%411%23%33%14%
2470
21st to endNight
19%5%11%21%30%14%
2470
December1st to 10thNight
19%6%16%21%24%12%
2555
11th to 20thNight
25%13%15%19%19%9%
3276
21st to endNight
30%11%13%16%21%10%
4862

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 10thDay
16%31%25%17%7%3
180
11th to 20thDay
10%27%24%20%14%5%
212
21st to endDay
9%21%30%23%13%3
374
February1st to 10thDay
6%32%25%21%11%5%
392
11th to 20thDay
10%27%34%22%7%
415
21st to endDay
14%30%31%18%8%1
346
March1st to 10thDay
14%30%33%15%7%1
420
11th to 20thDay
17%25%28%18%10%2
420
21st to endDay
13%34%31%16%6%
462
April1st to 10thDay
14%28%31%18%7%2
420
11th to 20thDay
19%27%30%17%6%1
412
21st to endDay
12%23%35%17%10%4
420
May1st to 10thDay
15%21%33%17%11%3
423
11th to 20thDay
15%24%28%20%9%4
448
21st to endDay
16%17%26%21%16%4
485
June1st to 10thDay
8%19%33%21%13%6%
450
11th to 20thDay
11%21%32%19%12%6%
450
21st to endDay
6%14%39%26%10%6%
450
July1st to 10thDay
411%37%28%16%4
446
11th to 20thDay
49%34%32%15%6%
444
21st to endDay
7%10%34%28%15%7%
487
August1st to 10thDay
5%14%35%26%15%4
447
11th to 20thDay
6%12%32%25%19%7%
437
21st to endDay
310%40%27%13%7%
495
September1st to 10thDay
6%12%31%31%16%6%
450
11th to 20thDay
8%20%27%28%15%3
450
21st to endDay
6%15%36%28%12%3
450
October1st to 10thDay
7%20%31%24%15%2
450
11th to 20thDay
8%16%31%29%12%3
450
21st to endDay
9%19%30%24%14%4
428
November1st to 10thDay
11%21%21%18%23%6%
270
11th to 20thDay
7%23%23%25%15%7%
270
21st to endDay
6%20%26%27%19%3
270
December1st to 10thDay
11%23%29%21%13%4
228
11th to 20thDay
8%28%26%21%14%3
180
21st to endDay
18%22%29%17%10%5%
198
January1st to 10thNight
6%15%31%22%16%10%
760
11th to 20thNight
316%30%29%16%7%
744
21st to endNight
414%30%31%16%6%
792
February1st to 10thNight
214%30%31%17%5%
720
11th to 20thNight
6%14%28%28%16%6%
704
21st to endNight
8%17%29%30%11%5%
592
March1st to 10thNight
7%19%31%26%13%4
720
11th to 20thNight
6%17%27%26%18%6%
720
21st to endNight
421%33%26%13%2
792
April1st to 10thNight
5%15%34%26%17%3
720
11th to 20thNight
8%16%29%27%14%6%
711
21st to endNight
5%14%30%26%19%6%
720
May1st to 10thNight
7%12%29%31%18%4
602
11th to 20thNight
6%11%26%34%19%3
531
21st to endNight
9%8%21%31%26%5%
404
June1st to 10thNight
37%20%36%30%4
360
11th to 20thNight
47%20%38%27%4
360
21st to endNight
3319%42%31%3
360
July1st to 10thNight
1214%43%37%3
350
11th to 20thNight
316%41%36%4
348
21st to endNight
38%40%42%6%
448
August1st to 10thNight
2319%37%33%6%
673
11th to 20thNight
2216%40%34%6%
712
21st to endNight
2217%39%33%7%
792
September1st to 10thNight
2316%37%34%8%
720
11th to 20thNight
39%15%34%31%8%
720
21st to endNight
210%17%34%29%9%
720
October1st to 10thNight
48%21%36%25%7%
720
11th to 20thNight
5%8%17%37%27%8%
720
21st to endNight
49%22%28%25%12%
792
November1st to 10thNight
5%10%20%30%25%10%
740
11th to 20thNight
311%28%31%19%6%
760
21st to endNight
215%27%31%20%6%
760
December1st to 10thNight
6%15%28%30%15%6%
760
11th to 20thNight
6%19%31%27%14%3
760
21st to endNight
9%17%32%26%13%3
836
Page generated at 2024-01-13 16:28:30. Version ac07

Copyright 2024 Attilla Danko


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