Clarkson Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Clarkson Observatory clear sky chart from 2005-11-06 to 2024-01-31.

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
22%
22712
11%
74997
7%
22670
29%
22670
13%
56314

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
8%
760
7%
2649
2%
757
14%
757
5%
2261
January11th to 20thNight
12%
760
7%
2660
4%
760
16%
760
5%
2256
January21st to endNight
14%
835
8%
2866
4%
835
20%
835
8%
2313
February1st to 10thNight
8%
720
6%
2340
1%
720
14%
720
5%
1983
February11th to 20thNight
11%
703
10%
2219
3%
700
20%
700
9%
1782
February21st to endNight
13%
592
12%
1776
4%
592
22%
592
10%
1412
March1st to 10thNight
16%
720
12%
2160
7%
720
23%
720
11%
1707
March11th to 20thNight
16%
720
13%
2024
5%
720
23%
720
13%
1567
March21st to endNight
21%
792
18%
2030
7%
792
29%
792
16%
1544
April1st to 10thNight
17%
720
14%
1800
4%
720
23%
720
15%
1398
April11th to 20thNight
19%
711
14%
1775
3%
711
25%
711
17%
1359
April21st to endNight
19%
648
14%
1728
5%
648
25%
648
17%
1281
May1st to 10thNight
24%
370
13%
1450
8%
370
34%
370
14%
985
May11th to 20thNight
27%
354
19%
1416
12%
354
42%
354
17%
901
May21st to endNight
32%
388
13%
1551
11%
388
43%
388
19%
951
June1st to 10thNight
30%
360
10%
1440
9%
360
38%
360
14%
1006
June11th to 20thNight
35%
360
12%
1440
15%
360
43%
360
18%
911
June21st to endNight
30%
360
10%
1440
10%
360
38%
360
14%
978
July1st to 10thNight
40%
350
14%
1400
15%
350
51%
350
24%
792
July11th to 20thNight
42%
348
16%
1392
16%
348
52%
348
24%
817
July21st to endNight
40%
394
14%
1486
13%
372
45%
372
21%
914
August1st to 10thNight
45%
363
15%
1427
12%
361
51%
361
20%
870
August11th to 20thNight
45%
592
15%
1656
10%
592
49%
592
26%
1112
August21st to endNight
38%
792
16%
1980
6%
792
41%
792
28%
1370
September1st to 10thNight
40%
720
14%
1800
6%
720
42%
720
28%
1244
September11th to 20thNight
45%
720
21%
1831
12%
720
48%
720
32%
1191
September21st to endNight
38%
720
20%
1984
15%
720
42%
720
25%
1350
October1st to 10thNight
28%
720
14%
2160
11%
720
33%
720
17%
1548
October11th to 20thNight
24%
720
13%
2160
7%
720
32%
720
14%
1609
October21st to endNight
17%
792
10%
2546
5%
792
25%
792
11%
2011
November1st to 10thNight
19%
740
14%
2407
7%
740
28%
740
13%
1768
November11th to 20thNight
18%
760
14%
2578
9%
760
26%
760
11%
1919
November21st to endNight
14%
760
8%
2660
5%
760
19%
760
7%
2130
December1st to 10thNight
11%
760
5%
2660
2%
760
14%
760
4%
2309
December11th to 20thNight
12%
760
8%
3256
3%
759
18%
759
5%
2661
December21st to endNight
10%
828
3%
4850
1%
817
14%
817
2%
4104

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
19%11%47%6%3445%6%30%
74897
Night
19%13%5%8%6%34446%28%
75234
TransparencyDay
55%6%11%18%9%1
74602
Night
58%6%10%17%8%1
75063
SeeingDay
28%17%29%18%7%2
13499
Night
27%16%29%20%7%1
22721

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 10thDay
17%22%7%12%8%4444415%
1517
11th to 20thDay
18%20%6%12%7%4443416%
1520
21st to endDay
13%17%7%12%9%5%5%5%45%18%
1715
February1st to 10thDay
17%17%6%15%8%45%35%417%
1620
11th to 20thDay
16%15%8%12%8%44435%21%
1627
21st to endDay
19%19%6%9%8%44345%19%
1480
March1st to 10thDay
16%16%7%10%7%4444425%
1797
11th to 20thDay
19%15%5%7%7%34345%28%
1934
21st to endDay
22%13%46%5%33335%33%
2326
April1st to 10thDay
22%13%5%6%425%34431%
2160
11th to 20thDay
22%10%46%5%3434436%
2134
21st to endDay
25%11%45%434446%31%
2237
May1st to 10thDay
21%9%35%6%34446%33%
2520
11th to 20thDay
18%8%35%5%3445%6%39%
2478
21st to endDay
17%7%26%5%45%5%6%8%35%
2725
June1st to 10thDay
26%6%36%5%346%6%7%28%
2520
11th to 20thDay
20%5%25%6%25%6%7%8%34%
2520
21st to endDay
21%7%25%6%45%5%5%8%32%
2520
July1st to 10thDay
15%6%36%5%345%5%8%41%
2520
11th to 20thDay
15%5%35%6%45%6%7%8%35%
2520
21st to endDay
13%5%26%5%35%7%7%11%35%
2744
August1st to 10thDay
15%426%6%45%5%8%8%36%
2498
11th to 20thDay
13%6%36%5%46%6%7%9%36%
2226
21st to endDay
15%6%36%6%35%6%6%8%37%
2376
September1st to 10thDay
17%6%25%5%2446%7%41%
2160
11th to 20thDay
16%6%35%43446%7%45%
2129
21st to endDay
19%436%5%35%5%6%6%38%
1974
October1st to 10thDay
23%8%37%6%345%5%6%31%
1800
11th to 20thDay
21%12%48%6%45%5%46%25%
1800
21st to endDay
29%13%36%5%3435%5%24%
1810
November1st to 10thDay
17%12%48%7%445%46%29%
1671
11th to 20thDay
17%14%5%8%6%45%5%5%427%
1601
21st to endDay
20%19%5%11%6%35%435%19%
1520
December1st to 10thDay
24%20%7%11%7%3344412%
1520
11th to 20thDay
21%18%8%9%6%3444419%
1906
21st to endDay
24%20%5%11%6%4443316%
2772
January1st to 10thNight
18%22%7%13%7%4444414%
2649
11th to 20thNight
16%20%7%12%8%36%44416%
2660
21st to endNight
13%18%6%12%7%5%5%435%21%
2866
February1st to 10thNight
18%18%8%14%8%3444415%
2340
11th to 20thNight
16%15%8%10%8%45%345%23%
2217
21st to endNight
17%15%6%12%7%33445%24%
1776
March1st to 10thNight
17%18%6%9%7%3333426%
2150
11th to 20thNight
19%17%6%7%5%33435%29%
2023
21st to endNight
20%14%47%6%3333334%
2030
April1st to 10thNight
22%12%48%6%24345%30%
1800
11th to 20thNight
23%11%36%6%24436%33%
1775
21st to endNight
24%12%36%5%23345%33%
1728
May1st to 10thNight
25%8%3443445%7%32%
1450
11th to 20thNight
15%8%346%45%5%5%6%39%
1415
21st to endNight
15%6%36%5%35%45%9%40%
1550
June1st to 10thNight
23%6%35%6%35%5%5%8%30%
1440
11th to 20thNight
18%6%35%5%345%5%9%38%
1440
21st to endNight
19%6%35%6%36%7%5%7%31%
1440
July1st to 10thNight
13%4345%345%6%8%45%
1440
11th to 20thNight
11%5%26%5%46%5%6%10%41%
1440
21st to endNight
12%6%36%5%35%5%6%9%40%
1574
August1st to 10thNight
13%5%25%5%45%5%6%8%41%
1437
11th to 20thNight
16%6%36%5%3445%7%40%
1656
21st to endNight
15%7%35%5%3445%7%42%
1980
September1st to 10thNight
16%7%26%43445%6%43%
1800
11th to 20thNight
17%6%23423447%48%
1831
21st to endNight
17%8%35%5%345%5%7%39%
1984
October1st to 10thNight
22%7%36%5%35%45%6%33%
2160
11th to 20thNight
22%9%36%6%35%5%5%6%31%
2160
21st to endNight
28%12%37%6%34446%23%
2546
November1st to 10thNight
20%12%46%5%3445%5%31%
2407
11th to 20thNight
19%13%5%7%6%35%445%29%
2578
21st to endNight
22%16%6%9%6%34435%21%
2660
December1st to 10thNight
22%22%8%12%6%3434413%
2660
11th to 20thNight
22%19%6%10%5%3433322%
3288
21st to endNight
29%18%6%11%5%3333414%
4884

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
75%48%11%2
1518
11th to 20thDay
72%47%8%7%1
1520
21st to endDay
70%5%9%10%6%1
1715
February1st to 10thDay
72%5%6%13%31
1620
11th to 20thDay
67%49%13%6%1
1636
21st to endDay
68%6%7%11%7%1
1480
March1st to 10thDay
64%49%14%8%1
1800
11th to 20thDay
61%5%10%12%11%2
1934
21st to endDay
57%36%17%13%4
2326
April1st to 10thDay
58%47%19%10%2
2160
11th to 20thDay
53%47%19%14%2
2134
21st to endDay
55%410%14%13%3
2237
May1st to 10thDay
53%5%8%19%13%2
2520
11th to 20thDay
47%5%10%21%15%2
2482
21st to endDay
47%7%12%20%12%1
2725
June1st to 10thDay
53%8%11%17%11%1
2520
11th to 20thDay
46%7%12%24%10%2
2520
21st to endDay
51%9%10%20%10%1
2520
July1st to 10thDay
40%7%12%26%13%1
2450
11th to 20thDay
43%7%15%26%8%
2445
21st to endDay
41%9%17%23%9%
2591
August1st to 10thDay
43%9%15%24%8%
2484
11th to 20thDay
43%8%17%22%9%
2226
21st to endDay
44%7%14%24%11%
2376
September1st to 10thDay
42%6%14%25%12%1
2160
11th to 20thDay
39%5%11%30%14%1
2129
21st to endDay
45%7%13%25%9%
1974
October1st to 10thDay
55%5%11%19%10%1
1800
11th to 20thDay
60%7%13%14%6%1
1800
21st to endDay
64%6%10%13%6%1
1810
November1st to 10thDay
55%6%11%20%6%
1671
11th to 20thDay
60%7%9%14%7%2
1601
21st to endDay
69%6%12%9%5%
1520
December1st to 10thDay
76%5%9%8%2
1520
11th to 20thDay
70%7%10%11%3
1906
21st to endDay
74%5%7%12%2
2772
January1st to 10thNight
75%48%9%3
2649
11th to 20thNight
73%6%6%9%5%
2660
21st to endNight
68%5%8%12%6%1
2866
February1st to 10thNight
74%48%9%5%
2340
11th to 20thNight
66%5%8%15%6%
2219
21st to endNight
65%5%7%15%8%
1776
March1st to 10thNight
64%49%14%8%1
2160
11th to 20thNight
60%5%9%16%8%1
2024
21st to endNight
57%46%18%12%3
2030
April1st to 10thNight
58%5%8%18%10%1
1800
11th to 20thNight
55%5%8%18%13%1
1775
21st to endNight
55%49%17%12%3
1728
May1st to 10thNight
52%5%11%13%16%3
1450
11th to 20thNight
46%6%9%21%15%3
1416
21st to endNight
42%6%16%18%15%2
1551
June1st to 10thNight
51%8%13%18%10%1
1440
11th to 20thNight
44%7%14%19%16%1
1440
21st to endNight
49%8%13%20%10%
1440
July1st to 10thNight
35%7%15%26%16%1
1400
11th to 20thNight
36%8%14%29%12%
1392
21st to endNight
39%9%16%23%12%1
1486
August1st to 10thNight
40%8%18%23%11%
1427
11th to 20thNight
42%7%15%23%12%1
1656
21st to endNight
43%6%15%26%10%
1980
September1st to 10thNight
42%7%13%26%12%1
1800
11th to 20thNight
36%7%14%31%12%
1831
21st to endNight
44%6%11%27%11%1
1984
October1st to 10thNight
52%6%11%21%9%1
2160
11th to 20thNight
54%8%13%16%8%1
2160
21st to endNight
64%5%12%12%6%1
2546
November1st to 10thNight
55%6%13%16%8%1
2407
11th to 20thNight
59%412%15%6%3
2578
21st to endNight
67%5%11%11%4
2660
December1st to 10thNight
76%5%8%8%2
2660
11th to 20thNight
69%6%8%13%4
3288
21st to endNight
75%6%7%10%2
4884

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
34%16%31%14%5%
180
11th to 20thDay
32%24%29%12%31
180
21st to endDay
27%22%32%17%1
219
February1st to 10thDay
43%31%25%2
240
11th to 20thDay
33%29%34%4
294
21st to endDay
37%24%29%9%1
346
March1st to 10thDay
32%20%31%13%3
420
11th to 20thDay
35%22%28%11%31
420
21st to endDay
38%21%23%11%7%
462
April1st to 10thDay
36%20%28%12%4
420
11th to 20thDay
34%19%23%17%5%2
412
21st to endDay
37%18%28%10%5%1
420
May1st to 10thDay
32%16%29%16%6%1
423
11th to 20thDay
24%19%30%18%7%1
447
21st to endDay
21%16%29%24%9%
485
June1st to 10thDay
32%15%28%18%6%1
450
11th to 20thDay
20%15%34%21%7%3
450
21st to endDay
26%14%33%16%10%1
450
July1st to 10thDay
17%10%32%29%11%2
445
11th to 20thDay
15%13%33%29%8%2
444
21st to endDay
19%10%34%28%8%1
488
August1st to 10thDay
17%11%29%30%10%2
446
11th to 20thDay
18%10%27%29%14%4
439
21st to endDay
18%13%33%20%11%4
495
September1st to 10thDay
18%13%28%24%10%7%
450
11th to 20thDay
17%12%26%23%16%6%
450
21st to endDay
20%11%30%25%11%3
450
October1st to 10thDay
28%16%24%18%10%4
450
11th to 20thDay
29%20%30%13%6%1
450
21st to endDay
40%13%28%17%3
410
November1st to 10thDay
31%19%28%16%5%1
365
11th to 20thDay
32%23%28%10%6%1
261
21st to endDay
32%23%32%9%3
180
December1st to 10thDay
41%13%27%18%2
180
11th to 20thDay
33%27%33%7%1
180
21st to endDay
38%20%29%10%21
198
January1st to 10thNight
32%21%31%12%3
760
11th to 20thNight
32%22%27%16%31
760
21st to endNight
22%22%33%18%4
835
February1st to 10thNight
31%22%33%13%2
720
11th to 20thNight
28%22%35%14%2
703
21st to endNight
28%19%34%15%3
592
March1st to 10thNight
29%20%29%19%2
720
11th to 20thNight
30%20%31%15%3
720
21st to endNight
32%15%27%20%5%1
792
April1st to 10thNight
32%16%30%19%3
720
11th to 20thNight
32%17%28%17%6%
711
21st to endNight
33%14%30%17%6%
648
May1st to 10thNight
28%12%32%21%5%1
370
11th to 20thNight
22%9%37%25%6%1
354
21st to endNight
19%13%33%28%8%
389
June1st to 10thNight
26%10%27%31%5%1
360
11th to 20thNight
19%10%30%28%12%1
360
21st to endNight
19%9%36%26%9%1
360
July1st to 10thNight
11%9%33%38%8%1
350
11th to 20thNight
12%5%34%35%13%
348
21st to endNight
15%6%35%35%8%1
394
August1st to 10thNight
17%6%29%34%14%
363
11th to 20thNight
20%6%23%34%16%1
592
21st to endNight
17%8%32%30%11%2
792
September1st to 10thNight
18%10%28%30%13%1
720
11th to 20thNight
18%9%25%28%17%3
720
21st to endNight
20%13%26%25%15%1
720
October1st to 10thNight
27%13%29%19%12%
720
11th to 20thNight
29%16%26%22%6%1
720
21st to endNight
38%14%27%19%2
792
November1st to 10thNight
29%17%31%17%6%1
740
11th to 20thNight
30%20%28%14%8%1
760
21st to endNight
33%22%25%14%6%
760
December1st to 10thNight
38%20%24%15%2
760
11th to 20thNight
32%23%29%12%41
760
21st to endNight
36%18%29%14%3
836
Page generated at 2024-01-28 05:26:34. Version ac07

Copyright 2024 Attilla Danko


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