Mark's Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mark's Observatory clear sky chart from 2005-11-05 to 2017-12-02.

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
64%
16511
19%
47829
16%
16474
67%
16474
30%
30403

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
56%
717
18%
2327
15%
716
62%
716
27%
1431
January16th to endNight
51%
768
25%
2481
21%
768
59%
768
32%
1422
February1st to 15thNight
51%
701
25%
2110
20%
701
58%
701
35%
1228
February16th to endNight
55%
631
29%
1738
18%
631
65%
631
39%
1007
March1st to 15thNight
58%
720
28%
1980
20%
720
65%
720
40%
1151
March16th to endNight
63%
768
27%
2112
21%
768
67%
768
43%
1182
April1st to 15thNight
67%
718
24%
1976
20%
718
70%
718
48%
1067
April16th to endNight
64%
720
26%
1802
16%
720
68%
720
42%
1096
May1st to 15thNight
69%
719
24%
1799
15%
719
72%
719
46%
1059
May16th to endNight
74%
577
18%
1698
16%
577
75%
577
30%
1097
June1st to 15thNight
66%
540
9%
1620
8%
540
66%
540
19%
1181
June16th to endNight
77%
540
10%
1620
9%
540
77%
540
24%
1135
July1st to 15thNight
72%
510
5%
1530
4%
510
72%
510
19%
1117
July16th to endNight
76%
564
8%
1595
8%
531
76%
531
25%
1097
August1st to 15thNight
77%
593
8%
1663
8%
590
77%
590
27%
1147
August16th to endNight
64%
764
6%
2012
5%
764
64%
764
20%
1512
September1st to 15thNight
65%
720
5%
1980
4%
720
65%
720
18%
1489
September16th to endNight
62%
717
6%
1980
7%
717
62%
717
16%
1529
October1st to 15thNight
69%
720
18%
2094
20%
720
70%
720
28%
1346
October16th to endNight
58%
768
21%
2304
20%
768
61%
768
27%
1495
November1st to 15thNight
64%
760
27%
2281
24%
760
70%
760
35%
1318
November16th to endNight
57%
780
27%
2340
23%
780
64%
780
29%
1463
December1st to 15thNight
62%
728
24%
2291
23%
728
67%
728
29%
1399
December16th to endNight
64%
768
23%
2496
23%
768
68%
768
32%
1435

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
8%6%37%8%5%7%6%7%8%29%
48607
Night
6%425%5%35%5%7%10%43%
48031
TransparencyDay
48%10%13%14%10%3
48308
Night
34%9%18%20%13%3
47834
SeeingDay
8%213%22%24%27%
6329
Night
7%214%31%31%11%
16520

By Month

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
9%5%37%6%46%6%7%8%35%
1611
16th to endDay
9%426%6%345%7%8%39%
1742
February1st to 15thDay
10%5%35%5%345%6%8%40%
1750
16th to endDay
6%5%35%5%36%46%9%43%
1733
March1st to 15thDay
4426%7%5%6%5%7%10%39%
1980
16th to endDay
7%5%36%7%36%6%7%8%39%
2111
April1st to 15thDay
6%4247%47%6%8%10%37%
1972
16th to endDay
6%5%26%6%48%5%6%9%37%
2157
May1st to 15thDay
3325%6%47%7%7%9%42%
2152
16th to endDay
8%6%49%9%5%8%7%7%8%23%
2423
June1st to 15thDay
12%9%49%9%5%8%7%7%8%17%
2340
16th to endDay
8%7%38%9%5%9%8%8%9%19%
2340
July1st to 15thDay
8%8%5%9%10%7%9%8%9%8%16%
2340
16th to endDay
8%8%410%11%6%8%8%7%8%18%
2465
August1st to 15thDay
7%7%48%10%5%9%8%8%10%18%
2273
16th to endDay
9%9%48%10%6%8%8%6%8%19%
2184
September1st to 15thDay
8%7%5%9%11%6%9%8%7%8%16%
1980
16th to endDay
10%9%5%10%11%5%9%8%6%7%15%
1980
October1st to 15thDay
7%6%38%9%5%7%7%8%10%25%
1866
16th to endDay
12%6%27%7%5%7%6%6%9%28%
1920
November1st to 15thDay
8%426%7%47%6%5%7%40%
1907
16th to endDay
8%5%36%6%5%6%5%6%7%38%
1950
December1st to 15thDay
10%7%36%7%35%5%6%7%36%
1703
16th to endDay
8%5%26%5%26%6%8%8%38%
1728
January1st to 15thNight
7%6%35%5%35%45%9%42%
2327
16th to endNight
6%4245%35%5%5%9%47%
2481
February1st to 15thNight
9%4234235%5%9%49%
2103
16th to endNight
5%3244245%6%9%51%
1738
March1st to 15thNight
32235%35%5%6%9%53%
1980
16th to endNight
42134145%6%10%54%
2112
April1st to 15thNight
32133235%6%9%58%
1976
16th to endNight
5%32442446%8%53%
1802
May1st to 15thNight
431342446%9%55%
1799
16th to endNight
6%4245%36%5%8%12%40%
1698
June1st to 15thNight
11%6%37%6%46%7%9%11%26%
1620
16th to endNight
4426%7%26%7%9%12%34%
1620
July1st to 15thNight
6%5%35%7%37%6%7%11%31%
1620
16th to endNight
5%326%7%36%6%8%11%37%
1703
August1st to 15thNight
5%425%5%46%6%7%14%36%
1674
16th to endNight
8%5%28%7%45%6%9%11%29%
2012
September1st to 15thNight
7%436%7%48%8%9%13%26%
1980
16th to endNight
7%6%38%8%48%7%9%11%23%
1980
October1st to 15thNight
7%415%5%45%6%7%11%39%
2094
16th to endNight
11%6%245%35%45%9%40%
2304
November1st to 15thNight
5%3145%35%46%9%49%
2281
16th to endNight
7%5%35%435%5%5%8%45%
2340
December1st to 15thNight
7%425%5%35%5%6%8%46%
2291
16th to endNight
6%5%245%345%6%9%47%
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
44%9%10%15%15%4
1612
16th to endDay
38%7%9%20%16%6%
1742
February1st to 15thDay
39%7%9%19%16%8%
1752
16th to endDay
36%5%11%22%16%7%
1733
March1st to 15thDay
37%7%11%23%16%3
1980
16th to endDay
39%6%12%20%14%6%
2112
April1st to 15thDay
36%7%15%20%15%3
1972
16th to endDay
41%7%11%19%17%3
2157
May1st to 15thDay
35%6%12%22%16%6%
2152
16th to endDay
54%9%12%15%8%
2427
June1st to 15thDay
60%10%13%11%3
2340
16th to endDay
55%13%18%10%1
2340
July1st to 15thDay
59%17%16%5%
2201
16th to endDay
57%13%19%9%
2310
August1st to 15thDay
53%15%21%8%
2260
16th to endDay
58%13%19%7%
2184
September1st to 15thDay
60%14%17%6%
1980
16th to endDay
64%12%12%8%1
1980
October1st to 15thDay
49%11%12%14%10%2
1866
16th to endDay
49%8%9%12%12%6%
1920
November1st to 15thDay
40%6%11%17%17%6%
1907
16th to endDay
42%7%8%15%18%7%
1950
December1st to 15thDay
45%7%10%16%15%4
1703
16th to endDay
38%8%10%20%16%5%
1728
January1st to 15thNight
36%6%16%21%14%3
2327
16th to endNight
32%5%12%26%16%5%
2481
February1st to 15thNight
32%410%23%20%8%
2112
16th to endNight
27%6%13%25%21%5%
1738
March1st to 15thNight
27%7%13%28%18%5%
1980
16th to endNight
24%6%15%25%21%5%
2112
April1st to 15thNight
20%6%19%30%18%3
1976
16th to endNight
27%7%13%24%21%4
1802
May1st to 15thNight
24%6%14%31%16%5%
1800
16th to endNight
34%10%17%27%9%
1700
June1st to 15thNight
46%12%21%15%4
1620
16th to endNight
36%16%28%16%1
1620
July1st to 15thNight
43%14%29%10%
1530
16th to endNight
35%15%32%15%1
1595
August1st to 15thNight
32%17%32%16%
1663
16th to endNight
44%15%28%10%
2012
September1st to 15thNight
42%18%26%10%1
1980
16th to endNight
47%16%20%11%2
1980
October1st to 15thNight
35%10%19%17%15%1
2094
16th to endNight
39%7%11%18%16%6%
2304
November1st to 15thNight
30%6%10%23%22%5%
2281
16th to endNight
36%6%9%17%20%8%
2340
December1st to 15thNight
35%7%12%22%17%4
2291
16th to endNight
31%6%15%23%18%4
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
13%8%36%26%12%2
90
16th to endDay
15%12%34%22%12%2
96
February1st to 15thDay
410%30%33%15%6%
90
16th to endDay
9%5%26%36%20%1
234
March1st to 15thDay
5%428%34%21%4
270
16th to endDay
6%424%30%25%7%
288
April1st to 15thDay
5%422%25%28%13%
270
16th to endDay
7%217%27%28%17%
270
May1st to 15thDay
3116%23%31%22%
288
16th to endDay
5%17%23%30%31%
331
June1st to 15thDay
12%18%19%21%35%
315
16th to endDay
5%49%25%53%
315
July1st to 15thDay
419%21%61%
305
16th to endDay
6%311%22%56%
326
August1st to 15thDay
7%210%22%55%
313
16th to endDay
9%7%10%21%49%
332
September1st to 15thDay
7%2413%21%50%
315
16th to endDay
11%1410%26%45%
314
October1st to 15thDay
10%28%27%33%18%
315
16th to endDay
14%223%25%22%11%
336
November1st to 15thDay
9%214%33%28%11%
325
16th to endDay
7%5%23%35%25%3
330
December1st to 15thDay
18%416%34%23%2
165
16th to endDay
5%6%12%46%21%7%
96
January1st to 15thNight
10%6%18%37%25%1
720
16th to endNight
7%6%27%41%16%
768
February1st to 15thNight
9%5%26%39%17%
704
16th to endNight
6%5%26%43%18%
631
March1st to 15thNight
5%427%42%19%1
720
16th to endNight
4422%45%22%
768
April1st to 15thNight
2320%45%25%2
718
16th to endNight
6%218%47%23%1
720
May1st to 15thNight
3215%46%29%2
720
16th to endNight
6%26%35%38%11%
579
June1st to 15thNight
12%1419%43%18%
540
16th to endNight
5%211%46%33%
540
July1st to 15thNight
7%147%46%32%
510
16th to endNight
5%36%45%38%
564
August1st to 15thNight
6%28%47%34%
593
16th to endNight
9%414%40%29%
764
September1st to 15thNight
9%15%10%41%31%
720
16th to endNight
10%1315%43%26%
717
October1st to 15thNight
10%6%33%38%9%
720
16th to endNight
14%214%32%29%7%
768
November1st to 15thNight
6%219%37%29%4
760
16th to endNight
8%321%37%25%2
780
December1st to 15thNight
7%317%40%28%2
728
16th to endNight
6%318%36%31%2
768
Page generated at 2017-12-03 11:16:39. Version ac04

Copyright 2017 A. Danko


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