Site "M"
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Site "M" clear sky chart from 2005-11-05 to 2017-09-18.

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
40%
15907
20%
46876
13%
15861
47%
15861
26%
30050

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
24%
900
17%
2506
7%
895
32%
895
22%
1724
January16th to endNight
21%
960
15%
2532
4%
960
29%
960
19%
1840
February1st to 15thNight
25%
842
13%
2250
4%
839
31%
839
20%
1615
February16th to endNight
26%
631
20%
1893
8%
631
36%
631
23%
1225
March1st to 15thNight
28%
678
18%
2118
9%
678
36%
678
20%
1442
March16th to endNight
29%
576
15%
2022
9%
576
37%
576
17%
1383
April1st to 15thNight
30%
539
19%
1797
12%
539
42%
539
23%
1121
April16th to endNight
37%
540
20%
1800
16%
540
45%
540
22%
1165
May1st to 15thNight
40%
540
18%
1596
11%
540
46%
540
24%
1083
May16th to endNight
51%
563
20%
1497
12%
561
56%
561
32%
981
June1st to 15thNight
60%
540
20%
1440
13%
540
63%
540
41%
856
June16th to endNight
53%
540
20%
1440
11%
540
58%
540
37%
885
July1st to 15thNight
67%
510
19%
1360
14%
510
68%
510
39%
823
July16th to endNight
74%
564
26%
1435
21%
531
76%
531
46%
807
August1st to 15thNight
78%
539
23%
1664
25%
536
78%
536
41%
880
August16th to endNight
72%
573
23%
1910
26%
573
76%
573
36%
1050
September1st to 15thNight
65%
540
29%
1800
31%
540
68%
540
36%
976
September16th to endNight
61%
622
31%
1801
22%
622
67%
622
38%
1029
October1st to 15thNight
50%
660
29%
1969
20%
660
58%
660
35%
1146
October16th to endNight
33%
704
24%
2156
14%
704
44%
704
29%
1292
November1st to 15thNight
35%
700
26%
2276
16%
700
48%
700
30%
1291
November16th to endNight
29%
786
20%
2406
12%
786
39%
786
24%
1534
December1st to 15thNight
23%
900
14%
2520
5%
900
30%
900
19%
1828
December16th to endNight
20%
960
13%
2688
4%
960
28%
960
14%
2074

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
12%7%35%5%35%45%7%39%
47922
Night
13%7%35%424446%43%
47047
Cloud CoverDay
12%7%35%5%3445%7%39%
47930
Night
13%7%35%424446%43%
47052
TransparencyDay
43%5%12%23%13%2
47610
Night
41%411%23%15%2
46877
SeeingDay
14%6%23%28%20%7%
5926
Night
16%7%28%31%13%1
15907

By Month

Percentage Cloud Cover NE (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
13%12%5%10%6%35%345%28%
1432
16th to endDay
13%13%5%8%6%34345%31%
1689
February1st to 15thDay
12%10%5%8%6%35%436%32%
1610
16th to endDay
11%9%48%6%35%348%33%
1580
March1st to 15thDay
14%11%46%6%3445%5%33%
1842
16th to endDay
15%10%47%5%35%45%7%30%
2202
April1st to 15thDay
16%7%45%5%24445%38%
2151
16th to endDay
18%6%36%5%35%45%6%34%
2160
May1st to 15thDay
19%7%25%5%35%46%7%31%
2352
16th to endDay
13%5%35%6%35%47%8%36%
2617
June1st to 15thDay
8%426%426%5%6%8%43%
2520
16th to endDay
8%425%6%35%5%5%8%42%
2520
July1st to 15thDay
7%4245%45%6%6%9%44%
2520
16th to endDay
5%314425%6%7%11%45%
2634
August1st to 15thDay
6%425%5%35%6%6%10%43%
2286
16th to endDay
8%4245%35%5%5%8%46%
2292
September1st to 15thDay
12%424434447%48%
2160
16th to endDay
8%6%245%3445%7%47%
1871
October1st to 15thDay
15%5%2442334448%
1658
16th to endDay
16%7%24423336%45%
1716
November1st to 15thDay
15%5%2432335%5%46%
1582
16th to endDay
16%8%5%6%5%13245%39%
1552
December1st to 15thDay
17%12%46%6%2345%6%29%
1440
16th to endDay
18%12%5%6%5%25%5%5%6%27%
1536
January1st to 15thNight
13%8%46%6%34445%38%
2506
16th to endNight
13%11%5%7%6%34345%33%
2532
February1st to 15thNight
14%10%5%6%6%34345%35%
2248
16th to endNight
14%8%37%323346%41%
1893
March1st to 15thNight
17%8%445%24445%38%
2105
16th to endNight
16%9%45%5%35%35%7%33%
2022
April1st to 15thNight
13%6%25%4345%47%41%
1797
16th to endNight
18%6%25%434446%39%
1800
May1st to 15thNight
17%5%35%42445%7%37%
1596
16th to endNight
9%6%26%425%5%5%8%43%
1496
June1st to 15thNight
8%4144235%5%8%51%
1440
16th to endNight
6%5%15%43347%8%47%
1440
July1st to 15thNight
6%4245%3445%9%49%
1440
16th to endNight
421342447%11%53%
1532
August1st to 15thNight
5%22232446%9%55%
1674
16th to endNight
7%2244245%48%53%
1910
September1st to 15thNight
11%423322345%55%
1800
16th to endNight
6%41342445%8%52%
1801
October1st to 15thNight
11%423424347%51%
1969
16th to endNight
16%5%2432335%449%
2156
November1st to 15thNight
10%6%24323245%52%
2276
16th to endNight
16%7%24423446%42%
2406
December1st to 15thNight
20%10%36%424345%32%
2520
16th to endNight
20%12%48%6%35%33428%
2688

Percentage Cloud Cover SE (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
13%12%5%10%6%35%345%29%
1432
16th to endDay
13%13%6%8%6%34335%31%
1689
February1st to 15thDay
12%10%6%7%6%35%436%32%
1610
16th to endDay
11%9%48%6%35%448%33%
1580
March1st to 15thDay
14%11%46%6%3445%5%33%
1852
16th to endDay
15%10%47%5%35%45%7%30%
2200
April1st to 15thDay
16%7%35%5%25%45%5%38%
2151
16th to endDay
18%6%26%5%345%5%6%34%
2160
May1st to 15thDay
20%6%35%5%35%45%7%31%
2352
16th to endDay
13%5%35%6%35%46%8%36%
2617
June1st to 15thDay
9%426%326%5%6%8%44%
2520
16th to endDay
8%425%6%35%5%5%8%43%
2520
July1st to 15thDay
7%4245%36%6%6%9%44%
2520
16th to endDay
5%324435%6%7%10%45%
2634
August1st to 15thDay
6%325%5%35%6%6%10%43%
2286
16th to endDay
8%4245%35%5%5%8%46%
2292
September1st to 15thDay
12%424434446%48%
2160
16th to endDay
8%6%345%2345%7%48%
1871
October1st to 15thDay
15%425%423345%48%
1658
16th to endDay
16%7%23423336%45%
1716
November1st to 15thDay
15%5%2431445%5%46%
1582
16th to endDay
16%8%47%5%23345%39%
1552
December1st to 15thDay
17%12%46%5%2345%7%29%
1440
16th to endDay
18%11%5%7%5%25%5%5%5%27%
1536
January1st to 15thNight
13%8%37%5%34445%38%
2506
16th to endNight
13%11%5%7%6%34345%33%
2532
February1st to 15thNight
14%10%5%6%7%24335%35%
2241
16th to endNight
14%8%26%423346%41%
1893
March1st to 15thNight
17%9%35%5%24345%37%
2118
16th to endNight
17%9%36%5%34447%33%
2022
April1st to 15thNight
13%6%25%5%3445%6%42%
1797
16th to endNight
18%7%24434446%39%
1800
May1st to 15thNight
17%5%35%5%15%45%8%37%
1595
16th to endNight
9%6%25%5%245%6%8%43%
1496
June1st to 15thNight
8%4144235%5%8%51%
1440
16th to endNight
7%5%25%5%3447%8%47%
1440
July1st to 15thNight
6%3245%3445%9%49%
1440
16th to endNight
421342447%10%53%
1532
August1st to 15thNight
5%21322446%9%55%
1674
16th to endNight
7%22342445%8%53%
1910
September1st to 15thNight
11%413323345%55%
1800
16th to endNight
6%423424348%52%
1801
October1st to 15thNight
11%423424347%51%
1969
16th to endNight
16%5%2432325%449%
2156
November1st to 15thNight
10%6%24322245%52%
2276
16th to endNight
16%7%24423446%42%
2406
December1st to 15thNight
20%10%37%424345%32%
2520
16th to endNight
19%11%48%6%3443428%
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
57%39%18%11%
1433
16th to endDay
56%413%18%6%
1689
February1st to 15thDay
53%314%21%6%
1612
16th to endDay
50%5%13%20%9%
1580
March1st to 15thDay
52%5%14%21%6%
1852
16th to endDay
52%5%14%19%6%1
2202
April1st to 15thDay
47%410%24%12%1
2151
16th to endDay
48%5%11%20%12%1
2160
May1st to 15thDay
50%6%13%20%9%
2352
16th to endDay
42%7%13%18%14%2
2621
June1st to 15thDay
35%6%13%25%17%2
2520
16th to endDay
37%7%12%22%17%3
2520
July1st to 15thDay
34%7%14%26%13%3
2371
16th to endDay
28%8%16%30%15%1
2468
August1st to 15thDay
33%8%13%26%16%1
2272
16th to endDay
33%7%11%24%17%4
2292
September1st to 15thDay
36%5%7%24%19%6%
2160
16th to endDay
34%48%31%19%2
1871
October1st to 15thDay
37%39%26%19%2
1658
16th to endDay
40%310%25%16%2
1716
November1st to 15thDay
39%311%22%19%3
1582
16th to endDay
47%312%24%10%
1552
December1st to 15thDay
55%415%17%8%
1440
16th to endDay
57%411%17%7%1
1536
January1st to 15thNight
47%412%22%13%
2506
16th to endNight
52%314%20%8%
2532
February1st to 15thNight
52%313%19%10%1
2250
16th to endNight
44%313%26%11%1
1893
March1st to 15thNight
48%49%23%11%1
2118
16th to endNight
50%412%21%9%1
2022
April1st to 15thNight
41%410%25%15%2
1797
16th to endNight
44%410%20%14%4
1800
May1st to 15thNight
45%5%12%21%14%
1596
16th to endNight
37%6%14%18%19%3
1498
June1st to 15thNight
29%5%14%27%19%3
1440
16th to endNight
32%6%12%23%20%4
1440
July1st to 15thNight
32%412%29%17%4
1360
16th to endNight
24%5%15%31%20%2
1435
August1st to 15thNight
23%7%14%30%21%3
1664
16th to endNight
28%7%10%26%21%5%
1910
September1st to 15thNight
31%38%26%23%7%
1800
16th to endNight
29%49%27%24%4
1801
October1st to 15thNight
32%38%26%22%5%
1969
16th to endNight
37%39%26%20%2
2156
November1st to 15thNight
34%311%24%19%6%
2276
16th to endNight
42%311%25%15%
2406
December1st to 15thNight
54%313%18%9%
2520
16th to endNight
60%410%16%7%1
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
30%11%37%14%5%1
90
16th to endDay
10%21%37%23%6%
96
February1st to 15thDay
15%17%38%20%7%
90
16th to endDay
12%16%35%27%7%1
81
March1st to 15thDay
31%14%37%14%2
90
16th to endDay
24%14%31%19%8%1
186
April1st to 15thDay
19%10%32%26%9%1
270
16th to endDay
20%5%28%29%12%3
270
May1st to 15thDay
20%13%27%26%10%2
348
16th to endDay
16%6%31%24%14%6%
517
June1st to 15thDay
10%321%33%23%7%
495
16th to endDay
9%5%28%31%17%7%
495
July1st to 15thDay
12%217%34%22%11%
475
16th to endDay
6%112%35%32%11%
515
August1st to 15thDay
7%110%35%31%14%
439
16th to endDay
9%112%27%37%11%
332
September1st to 15thDay
13%113%29%31%10%
315
16th to endDay
9%6%14%26%31%11%
262
October1st to 15thDay
11%8%18%34%18%9%
98
16th to endDay
21%433%33%7%
96
November1st to 15thDay
47%28%23%21%14%
90
16th to endDay
41%13%27%11%6%
90
December1st to 15thDay
18%15%33%23%6%2
90
16th to endDay
28%15%43%9%3
96
January1st to 15thNight
18%14%37%24%5%
900
16th to endNight
20%13%36%25%3
960
February1st to 15thNight
19%12%35%28%4
842
16th to endNight
19%11%37%28%3
631
March1st to 15thNight
22%10%33%27%4
678
16th to endNight
22%9%34%25%7%
576
April1st to 15thNight
16%13%35%27%7%
539
16th to endNight
22%6%30%30%10%
540
May1st to 15thNight
21%5%27%33%9%1
540
16th to endNight
10%427%38%17%2
563
June1st to 15thNight
11%219%47%17%1
540
16th to endNight
10%225%39%20%2
540
July1st to 15thNight
7%213%43%30%2
510
16th to endNight
5%12%40%37%3
564
August1st to 15thNight
7%7%45%33%5%
539
16th to endNight
7%11%35%41%3
573
September1st to 15thNight
11%312%36%30%5%
540
16th to endNight
9%5%17%34%27%6%
622
October1st to 15thNight
13%5%26%33%19%2
660
16th to endNight
20%8%34%27%9%
704
November1st to 15thNight
13%10%37%28%10%
700
16th to endNight
21%9%35%25%6%
786
December1st to 15thNight
25%10%35%22%5%
900
16th to endNight
26%11%34%23%3
960
Page generated at 2017-09-19 06:32:31. Version ac04

Copyright 2017 A. Danko


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