Mark's Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mark's Observing Site clear sky chart from 2005-11-06 to 2024-01-13.

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
44%
24432
27%
74391
16%
24376
54%
24376
37%
41358

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
37%
950
30%
2458
12%
946
50%
946
38%
1473
January11th to 20thNight
37%
915
30%
2379
12%
915
48%
915
40%
1403
January21st to endNight
36%
990
33%
2574
13%
990
48%
990
41%
1492
February1st to 10thNight
30%
866
23%
2306
8%
866
40%
866
33%
1442
February11th to 20thNight
32%
704
25%
2098
10%
700
42%
700
31%
1222
February21st to endNight
30%
592
32%
1776
11%
592
46%
592
34%
998
March1st to 10thNight
33%
638
28%
2078
12%
638
48%
638
35%
1110
March11th to 20thNight
35%
540
24%
1980
17%
540
47%
540
29%
1082
March21st to endNight
28%
594
21%
2178
10%
594
43%
594
23%
1321
April1st to 10thNight
32%
540
24%
1967
14%
540
49%
540
32%
1015
April11th to 20thNight
31%
533
24%
1681
13%
533
46%
533
29%
993
April21st to endNight
34%
540
24%
1620
15%
540
47%
540
29%
975
May1st to 10thNight
35%
540
20%
1620
14%
540
45%
540
27%
1028
May11th to 20thNight
47%
531
21%
1594
19%
531
53%
531
35%
908
May21st to endNight
48%
582
16%
1745
11%
582
55%
582
32%
1036
June1st to 10thNight
59%
540
21%
1620
14%
540
66%
540
45%
829
June11th to 20thNight
53%
540
22%
1620
12%
540
61%
540
44%
859
June21st to endNight
53%
540
24%
1620
15%
540
61%
540
48%
827
July1st to 10thNight
69%
525
20%
1575
17%
525
71%
525
43%
848
July11th to 20thNight
72%
522
25%
1566
21%
522
77%
522
53%
766
July21st to endNight
69%
591
23%
1673
24%
558
72%
558
39%
943
August1st to 10thNight
68%
537
24%
1601
24%
534
73%
534
43%
860
August11th to 20thNight
67%
534
28%
1600
30%
534
71%
534
40%
891
August21st to endNight
68%
594
30%
1885
31%
594
73%
594
47%
923
September1st to 10thNight
61%
540
26%
1966
26%
540
68%
540
37%
982
September11th to 20thNight
54%
540
30%
1980
27%
540
64%
540
36%
1018
September21st to endNight
57%
540
32%
1980
29%
540
64%
540
41%
939
October1st to 10thNight
49%
544
33%
1984
27%
544
59%
544
36%
1005
October11th to 20thNight
40%
720
34%
2160
15%
720
55%
720
46%
1081
October21st to endNight
43%
809
32%
2393
17%
809
53%
809
41%
1282
November1st to 10thNight
47%
925
33%
2405
13%
925
59%
925
52%
1275
November11th to 20thNight
39%
950
35%
2470
13%
950
52%
950
48%
1341
November21st to endNight
44%
950
30%
2470
15%
950
53%
950
42%
1430
December1st to 10thNight
41%
950
29%
2470
14%
950
51%
950
41%
1445
December11th to 20thNight
32%
948
32%
2870
12%
948
46%
948
33%
1625
December21st to endNight
34%
1038
20%
4429
13%
1026
47%
1026
22%
2691

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
9%5%2443445%7%53%
74914
Night
8%5%2442445%7%55%
74867
TransparencyDay
31%5%12%27%20%5%
74639
Night
29%411%27%22%6%
74662
SeeingDay
11%6%28%32%18%5%
14414
Night
11%7%33%37%12%1
24443

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 10thDay
5%6%25%5%23447%58%
1707
11th to 20thDay
9%6%35%42335%6%54%
1643
21st to endDay
6%6%36%42435%7%53%
1782
February1st to 10thDay
7%8%47%5%43346%48%
1670
11th to 20thDay
6%6%37%5%345%5%7%51%
1749
21st to endDay
7%6%25%42445%6%54%
1480
March1st to 10thDay
8%5%15%5%345%5%8%52%
1880
11th to 20thDay
15%8%24423346%50%
1980
21st to endDay
13%7%35%43445%7%46%
2178
April1st to 10thDay
10%5%2432445%7%54%
1988
11th to 20thDay
12%6%35%5%3445%7%47%
2230
21st to endDay
15%6%245%3445%7%45%
2340
May1st to 10thDay
14%7%35%5%3445%7%45%
2340
11th to 20thDay
11%6%244245%5%6%51%
2302
21st to endDay
12%5%35%5%46%5%6%9%41%
2531
June1st to 10thDay
5%3244345%5%8%57%
2340
11th to 20thDay
5%3245%25%5%5%8%56%
2340
21st to endDay
5%313325%5%6%9%57%
2340
July1st to 10thDay
7%4245%35%5%6%8%50%
2340
11th to 20thDay
3213425%5%6%10%58%
2340
21st to endDay
7%325%5%36%6%6%9%48%
2546
August1st to 10thDay
6%5%245%35%5%8%9%48%
2328
11th to 20thDay
7%4234245%7%8%54%
2301
21st to endDay
4324325%46%9%59%
2466
September1st to 10thDay
10%423424447%56%
1994
11th to 20thDay
9%424434447%55%
1980
21st to endDay
8%3245%23347%58%
1980
October1st to 10thDay
13%413423336%58%
1958
11th to 20thDay
10%324322236%64%
1800
21st to endDay
10%6%24322235%60%
1962
November1st to 10thDay
6%424324346%63%
1673
11th to 20thDay
7%424433346%61%
1710
21st to endDay
11%5%1342233462%
1710
December1st to 10thDay
7%5%25%43336%7%54%
1710
11th to 20thDay
9%6%35%423447%54%
2161
21st to endDay
9%9%48%6%3445%7%40%
3135
January1st to 10thNight
7%5%36%424446%55%
2458
11th to 20thNight
6%6%35%42444458%
2379
21st to endNight
7%5%35%324345%59%
2574
February1st to 10thNight
9%8%46%433446%49%
2306
11th to 20thNight
9%6%35%5%2446%7%50%
2098
21st to endNight
8%5%35%434347%55%
1776
March1st to 10thNight
7%5%24425%45%7%55%
2078
11th to 20thNight
12%6%24424447%51%
1980
21st to endNight
14%8%345%3445%7%43%
2178
April1st to 10thNight
10%41342345%9%54%
1967
11th to 20thNight
12%5%25%325%5%5%7%49%
1681
21st to endNight
14%5%24424447%49%
1620
May1st to 10thNight
15%6%345%3445%6%45%
1620
11th to 20thNight
12%5%134245%6%8%51%
1593
21st to endNight
10%4244345%6%11%46%
1745
June1st to 10thNight
6%3143225%6%9%59%
1620
11th to 20thNight
5%3134246%8%9%56%
1620
21st to endNight
422333447%10%59%
1620
July1st to 10thNight
6%3245%2436%10%55%
1620
11th to 20thNight
321222447%10%61%
1620
21st to endNight
6%324435%5%7%12%49%
1772
August1st to 10thNight
43135%35%5%7%11%53%
1611
11th to 20thNight
7%424425%45%8%54%
1600
21st to endNight
42244235%5%7%63%
1885
September1st to 10thNight
8%32343445%6%59%
1966
11th to 20thNight
7%4244245%46%58%
1980
21st to endNight
6%323324447%62%
1980
October1st to 10thNight
10%424423346%58%
1984
11th to 20thNight
9%212323335%67%
2160
21st to endNight
10%413422335%62%
2393
November1st to 10thNight
7%413312346%67%
2405
11th to 20thNight
7%423323346%64%
2470
21st to endNight
11%5%23213335%60%
2470
December1st to 10thNight
7%5%2443445%6%57%
2470
11th to 20thNight
9%5%24424346%57%
3036
21st to endNight
12%9%46%434347%44%
4532

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
27%412%31%23%2
1708
11th to 20thDay
32%314%29%19%4
1643
21st to endDay
32%314%31%17%3
1782
February1st to 10thDay
39%412%26%15%5%
1670
11th to 20thDay
33%5%14%26%17%6%
1759
21st to endDay
30%410%26%24%6%
1480
March1st to 10thDay
31%5%12%24%22%7%
1880
11th to 20thDay
37%310%22%23%5%
1980
21st to endDay
38%5%13%28%12%4
2178
April1st to 10thDay
31%5%12%26%20%6%
1988
11th to 20thDay
37%5%11%27%16%4
2230
21st to endDay
39%5%11%29%16%1
2340
May1st to 10thDay
40%6%12%21%18%4
2340
11th to 20thDay
34%6%14%30%15%1
2306
21st to endDay
39%7%16%26%10%2
2531
June1st to 10thDay
24%6%18%32%16%4
2340
11th to 20thDay
25%6%14%28%21%6%
2340
21st to endDay
23%6%13%26%25%8%
2340
July1st to 10thDay
30%6%13%27%20%4
2276
11th to 20thDay
19%7%16%28%24%6%
2271
21st to endDay
29%7%13%30%20%2
2405
August1st to 10thDay
28%8%16%28%16%4
2314
11th to 20thDay
27%6%13%30%18%6%
2301
21st to endDay
23%6%12%28%23%9%
2466
September1st to 10thDay
29%5%9%26%21%10%
1994
11th to 20thDay
29%49%27%26%5%
1980
21st to endDay
26%5%9%26%25%8%
1980
October1st to 10thDay
29%48%27%26%6%
1958
11th to 20thDay
25%38%26%30%10%
1800
21st to endDay
30%29%26%24%9%
1962
November1st to 10thDay
24%39%29%28%8%
1673
11th to 20thDay
26%39%27%28%7%
1710
21st to endDay
28%28%28%29%5%
1710
December1st to 10thDay
29%412%31%22%3
1710
11th to 20thDay
32%48%31%22%3
2159
21st to endDay
44%5%9%26%15%2
3135
January1st to 10thNight
31%49%30%22%4
2458
11th to 20thNight
30%310%28%25%4
2379
21st to endNight
29%411%31%22%4
2574
February1st to 10thNight
37%313%24%17%6%
2306
11th to 20thNight
34%411%26%19%6%
2098
21st to endNight
31%48%24%24%11%
1776
March1st to 10thNight
29%49%24%24%9%
2078
11th to 20thNight
33%410%25%22%6%
1980
21st to endNight
40%5%11%26%15%3
2178
April1st to 10thNight
28%412%25%24%7%
1967
11th to 20thNight
35%5%13%24%19%4
1681
21st to endNight
35%6%12%23%21%4
1620
May1st to 10thNight
40%5%13%20%19%3
1620
11th to 20thNight
29%6%17%30%16%1
1594
21st to endNight
31%8%21%27%10%2
1746
June1st to 10thNight
20%7%20%32%18%4
1620
11th to 20thNight
22%6%15%31%21%5%
1620
21st to endNight
20%6%14%30%23%8%
1620
July1st to 10thNight
25%5%14%28%23%4
1575
11th to 20thNight
17%6%15%29%26%7%
1566
21st to endNight
27%7%13%30%21%2
1673
August1st to 10thNight
24%7%16%34%15%4
1601
11th to 20thNight
27%6%11%32%19%4
1600
21st to endNight
21%5%13%27%24%10%
1885
September1st to 10thNight
26%5%11%23%24%11%
1966
11th to 20thNight
28%49%24%28%6%
1980
21st to endNight
23%410%23%31%9%
1980
October1st to 10thNight
28%410%22%29%8%
1984
11th to 20thNight
22%47%25%31%11%
2160
21st to endNight
27%38%23%27%11%
2393
November1st to 10thNight
21%39%28%29%11%
2405
11th to 20thNight
23%37%30%30%7%
2470
21st to endNight
28%38%26%25%9%
2470
December1st to 10thNight
29%312%28%22%5%
2470
11th to 20thNight
30%37%34%20%4
3037
21st to endNight
40%5%10%28%13%4
4532

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
10%8%40%26%13%2
270
11th to 20thDay
15%10%42%25%7%
248
21st to endDay
10%10%46%30%4
264
February1st to 10thDay
11%13%45%27%41
240
11th to 20thDay
13%9%46%24%8%
240
21st to endDay
9%15%51%20%5%1
198
March1st to 10thDay
10%10%46%27%6%1
240
11th to 20thDay
19%12%37%21%9%3
240
21st to endDay
18%12%43%23%31
264
April1st to 10thDay
11%14%40%27%8%
248
11th to 20thDay
14%12%40%30%3
508
21st to endDay
18%12%38%21%9%3
600
May1st to 10thDay
15%8%34%29%12%2
603
11th to 20thDay
16%8%26%29%17%4
625
21st to endDay
15%6%29%28%17%5%
679
June1st to 10thDay
5%422%37%23%10%
630
11th to 20thDay
6%428%40%19%4
630
21st to endDay
6%426%43%19%2
630
July1st to 10thDay
8%110%39%32%9%
621
11th to 20thDay
4213%43%30%8%
618
21st to endDay
8%111%36%33%11%
684
August1st to 10thDay
8%212%40%31%7%
626
11th to 20thDay
8%213%39%33%5%
615
21st to endDay
4214%39%33%8%
585
September1st to 10thDay
12%111%33%33%9%
284
11th to 20thDay
6%116%41%28%9%
270
21st to endDay
13%326%29%21%8%
270
October1st to 10thDay
14%6%30%23%17%10%
270
11th to 20thDay
9%8%36%31%13%3
270
21st to endDay
20%8%32%25%12%4
297
November1st to 10thDay
10%11%30%33%13%3
270
11th to 20thDay
12%9%41%24%11%3
270
21st to endDay
18%9%31%26%13%2
270
December1st to 10thDay
7%9%35%33%13%3
270
11th to 20thDay
12%11%38%30%9%1
270
21st to endDay
16%11%44%23%5%
297
January1st to 10thNight
9%9%38%36%7%
950
11th to 20thNight
9%10%38%33%8%1
915
21st to endNight
9%8%42%35%6%
990
February1st to 10thNight
12%11%42%31%41
866
11th to 20thNight
13%10%41%33%4
704
21st to endNight
10%12%43%30%4
592
March1st to 10thNight
10%12%41%32%4
638
11th to 20thNight
16%9%37%31%8%
540
21st to endNight
18%9%41%26%5%1
594
April1st to 10thNight
14%11%42%26%7%
540
11th to 20thNight
15%12%37%30%5%
533
21st to endNight
16%9%37%30%8%1
540
May1st to 10thNight
17%9%34%33%8%
540
11th to 20thNight
15%6%28%37%14%1
531
21st to endNight
13%6%28%36%15%2
584
June1st to 10thNight
6%426%41%21%2
540
11th to 20thNight
6%333%44%14%
540
21st to endNight
4235%44%14%
540
July1st to 10thNight
8%114%49%26%2
525
11th to 20thNight
5%119%51%24%1
522
21st to endNight
8%114%48%27%1
591
August1st to 10thNight
5%117%49%26%1
537
11th to 20thNight
8%214%51%23%1
534
21st to endNight
4118%44%30%3
594
September1st to 10thNight
8%123%47%20%2
540
11th to 20thNight
8%229%41%18%2
540
21st to endNight
7%5%28%41%18%1
540
October1st to 10thNight
12%5%29%34%19%1
544
11th to 20thNight
11%6%39%33%10%1
720
21st to endNight
14%6%34%34%11%1
809
November1st to 10thNight
8%5%35%37%14%1
925
11th to 20thNight
9%9%39%34%9%
950
21st to endNight
14%8%30%38%10%
950
December1st to 10thNight
10%8%36%36%8%
950
11th to 20thNight
14%9%40%34%4
950
21st to endNight
13%11%38%32%6%
1045
Page generated at 2024-01-10 18:35:19. Version ac07

Copyright 2024 Attilla Danko


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