Mammoth Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mammoth Observatory clear sky chart from 2005-11-05 to 2017-10-06.

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
60%
15420
30%
47069
23%
15392
68%
15392
45%
23536

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
55%
716
25%
2506
20%
716
66%
716
38%
1226
January16th to endNight
54%
768
27%
2526
24%
768
61%
768
34%
1350
February1st to 15thNight
51%
699
28%
2154
23%
699
60%
699
35%
1188
February16th to endNight
49%
632
26%
1895
21%
632
58%
632
33%
1082
March1st to 15thNight
49%
720
23%
2160
18%
720
57%
720
35%
1179
March16th to endNight
44%
768
23%
1989
12%
768
53%
768
37%
1177
April1st to 15thNight
44%
719
22%
1799
9%
719
51%
719
35%
1103
April16th to endNight
50%
720
22%
1800
9%
720
55%
720
43%
1022
May1st to 15thNight
55%
580
26%
1660
16%
580
60%
580
46%
845
May16th to endNight
57%
440
25%
1564
22%
440
63%
440
37%
761
June1st to 15thNight
65%
360
27%
1440
27%
360
76%
360
46%
584
June16th to endNight
78%
360
37%
1440
41%
360
87%
360
68%
465
July1st to 15thNight
88%
340
33%
1360
43%
340
90%
340
62%
477
July16th to endNight
84%
412
37%
1449
41%
387
86%
387
52%
596
August1st to 15thNight
78%
690
36%
1764
23%
687
80%
687
71%
824
August16th to endNight
83%
764
42%
1910
26%
764
85%
764
72%
906
September1st to 15thNight
81%
720
41%
1800
28%
720
84%
720
72%
851
September16th to endNight
74%
716
43%
1971
34%
716
82%
716
64%
892
October1st to 15thNight
65%
684
33%
1972
26%
684
74%
684
50%
980
October16th to endNight
67%
704
36%
2153
33%
704
77%
704
52%
996
November1st to 15thNight
65%
700
32%
2275
30%
700
71%
700
47%
1072
November16th to endNight
54%
720
33%
2340
26%
720
67%
720
43%
1120
December1st to 15thNight
48%
720
23%
2454
16%
720
58%
720
32%
1277
December16th to endNight
44%
768
24%
2688
19%
768
54%
768
26%
1563

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
121332345%7%63%
48141
Night
213313447%67%
47245
TransparencyDay
24%49%20%24%15%
47816
Night
20%5%11%23%26%12%
47070
SeeingDay
9%22%32%22%9%2
5858
Night
310%21%30%25%8%
15431

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
1422445%11%60%
1432
16th to endDay
1324425%5%6%9%52%
1695
February1st to 15thDay
313315%5%5%10%58%
1707
16th to endDay
325%5%25%6%7%8%52%
1579
March1st to 15thDay
2244345%8%11%53%
1800
16th to endDay
324425%6%7%9%53%
2231
April1st to 15thDay
1325%4245%6%9%53%
2149
16th to endDay
141332345%7%61%
2160
May1st to 15thDay
241342445%6%60%
2289
16th to endDay
37%25%5%34346%53%
2547
June1st to 15thDay
3312324446%63%
2520
16th to endDay
111211222478%
2520
July1st to 15thDay
2213324345%66%
2520
16th to endDay
421332333464%
2618
August1st to 15thDay
111221242473%
2187
16th to endDay
12331224473%
2292
September1st to 15thDay
2212313335%69%
2160
16th to endDay
1212212235%74%
1989
October1st to 15thDay
2313323236%66%
1784
16th to endDay
113213337%71%
1719
November1st to 15thDay
112331336%9%63%
1584
16th to endDay
2111345%8%69%
1620
December1st to 15thDay
2233135%5%9%61%
1503
16th to endDay
114425%7%8%10%52%
1536
January1st to 15thNight
21341347%8%62%
2506
16th to endNight
2133246%6%10%57%
2526
February1st to 15thNight
3144245%5%10%58%
2143
16th to endNight
3134335%6%9%57%
1895
March1st to 15thNight
2123245%7%9%59%
2160
16th to endNight
3242235%6%9%60%
1989
April1st to 15thNight
1225%326%448%57%
1799
16th to endNight
313313346%66%
1800
May1st to 15thNight
122313347%67%
1660
16th to endNight
3413223236%67%
1563
June1st to 15thNight
122222447%68%
1440
16th to endNight
11121385%
1440
July1st to 15thNight
11121345%77%
1440
16th to endNight
1213223225%72%
1548
August1st to 15thNight
1111122381%
1773
16th to endNight
11233380%
1910
September1st to 15thNight
1111222481%
1800
16th to endNight
11111335%78%
1971
October1st to 15thNight
1312212345%71%
1972
16th to endNight
111212245%74%
2153
November1st to 15thNight
122135%48%68%
2275
16th to endNight
2221335%9%68%
2340
December1st to 15thNight
1143135%6%10%60%
2454
16th to endNight
115%5%35%6%7%12%51%
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
23%6%15%25%21%7%
1432
16th to endDay
33%6%10%20%17%11%
1695
February1st to 15thDay
24%7%14%24%17%10%
1707
16th to endDay
34%5%11%24%20%3
1579
March1st to 15thDay
30%7%14%20%20%6%
1800
16th to endDay
33%8%15%25%13%3
2231
April1st to 15thDay
30%6%16%25%15%5%
2149
16th to endDay
26%7%15%28%16%5%
2160
May1st to 15thDay
26%5%11%32%20%2
2289
16th to endDay
34%410%24%20%4
2551
June1st to 15thDay
23%49%22%27%12%
2520
16th to endDay
13%1313%42%26%
2520
July1st to 15thDay
18%349%24%39%
2371
16th to endDay
22%35%10%20%37%
2454
August1st to 15thDay
14%2412%24%40%
2171
16th to endDay
16%2210%40%27%
2292
September1st to 15thDay
19%25%12%30%29%
2160
16th to endDay
15%25%25%30%20%
1989
October1st to 15thDay
22%26%21%32%14%
1784
16th to endDay
18%38%25%31%12%
1719
November1st to 15thDay
21%412%27%24%9%
1584
16th to endDay
20%311%24%33%5%
1620
December1st to 15thDay
27%7%14%25%19%5%
1503
16th to endDay
32%7%15%18%17%8%
1536
January1st to 15thNight
21%6%14%24%24%8%
2506
16th to endNight
27%5%12%20%20%13%
2526
February1st to 15thNight
25%8%11%25%18%10%
2154
16th to endNight
29%6%12%23%24%3
1895
March1st to 15thNight
25%6%15%20%21%9%
2160
16th to endNight
27%5%19%26%18%3
1989
April1st to 15thNight
30%5%14%28%16%5%
1799
16th to endNight
23%5%20%28%16%5%
1800
May1st to 15thNight
20%414%34%21%3
1661
16th to endNight
23%413%29%24%4
1564
June1st to 15thNight
16%412%26%31%9%
1440
16th to endNight
8%15%17%42%25%
1440
July1st to 15thNight
10%2414%33%34%
1360
16th to endNight
17%25%13%29%32%
1449
August1st to 15thNight
10%2316%31%36%
1764
16th to endNight
9%2318%42%23%
1910
September1st to 15thNight
9%3417%42%22%
1800
16th to endNight
10%36%28%33%17%
1971
October1st to 15thNight
19%37%24%34%10%
1972
16th to endNight
15%49%25%34%10%
2153
November1st to 15thNight
18%5%12%26%24%12%
2275
16th to endNight
19%410%25%31%8%
2340
December1st to 15thNight
24%7%18%21%22%4
2454
16th to endNight
33%7%11%19%18%8%
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
10%38%28%13%36%
60
16th to endDay
10%24%30%20%12%3
223
February1st to 15thDay
5%30%27%23%10%2
259
16th to endDay
10%34%30%19%5%
238
March1st to 15thDay
8%32%28%17%11%1
270
16th to endDay
10%36%32%15%5%
288
April1st to 15thDay
20%27%28%16%6%1
269
16th to endDay
15%31%34%13%4
270
May1st to 15thDay
14%20%34%20%6%3
288
16th to endDay
18%19%26%22%11%2
330
June1st to 15thDay
12%20%38%18%7%2
315
16th to endDay
6%15%41%21%10%4
315
July1st to 15thDay
6%10%36%29%14%3
305
16th to endDay
8%11%38%28%9%3
327
August1st to 15thDay
6%17%40%21%11%2
315
16th to endDay
313%35%27%12%7%
332
September1st to 15thDay
8%15%29%32%11%2
315
16th to endDay
7%18%31%28%12%1
315
October1st to 15thDay
10%23%34%22%7%1
278
16th to endDay
9%20%34%29%41
231
November1st to 15thDay
220%8%22%32%14%
90
16th to endDay
8%22%24%32%11%1
90
December1st to 15thDay
7%38%30%16%7%
71
16th to endDay
323%23%26%14%9%
64
January1st to 15thNight
311%25%25%21%12%
720
16th to endNight
213%25%31%17%9%
768
February1st to 15thNight
311%27%30%19%7%
704
16th to endNight
6%17%23%30%15%7%
632
March1st to 15thNight
316%26%27%19%7%
720
16th to endNight
318%29%26%17%4
768
April1st to 15thNight
415%30%26%18%4
719
16th to endNight
5%14%26%27%18%8%
720
May1st to 15thNight
5%9%27%31%22%4
581
16th to endNight
7%8%22%26%29%6%
441
June1st to 15thNight
4223%32%33%3
360
16th to endNight
2214%41%35%3
360
July1st to 15thNight
2344%44%4
340
16th to endNight
26%35%48%7%
412
August1st to 15thNight
1114%36%38%6%
690
16th to endNight
1110%34%40%10%
764
September1st to 15thNight
2110%35%38%11%
720
16th to endNight
17%14%30%33%12%
716
October1st to 15thNight
47%19%31%26%10%
684
16th to endNight
48%17%27%27%13%
704
November1st to 15thNight
27%22%28%27%11%
700
16th to endNight
214%25%27%21%9%
720
December1st to 15thNight
416%26%29%15%7%
720
16th to endNight
419%30%25%16%4
768
Page generated at 2017-10-07 11:07:42. Version ac04

Copyright 2017 A. Danko


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