Clarkson Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Clarkson Observatory clear sky chart from 2005-11-05 to 2017-09-14.

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
24%
14689
11%
46819
6%
14658
29%
14658
13%
35147

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
8%
720
5%
2506
2%
716
13%
716
5%
2135
January16th to endNight
13%
768
7%
2655
4%
768
18%
768
6%
2167
February1st to 15thNight
9%
704
6%
2287
2%
701
15%
701
6%
1931
February16th to endNight
14%
631
10%
1915
4%
631
21%
631
9%
1561
March1st to 15thNight
16%
720
12%
2129
7%
720
23%
720
12%
1659
March16th to endNight
24%
768
17%
2013
7%
768
31%
768
17%
1511
April1st to 15thNight
18%
718
14%
1796
4%
718
24%
718
16%
1396
April16th to endNight
23%
672
16%
1752
5%
672
30%
672
20%
1258
May1st to 15thNight
26%
366
15%
1446
11%
366
38%
366
15%
960
May16th to endNight
31%
374
12%
1497
9%
374
42%
374
16%
969
June1st to 15thNight
30%
360
9%
1440
8%
360
38%
360
13%
1024
June16th to endNight
34%
360
9%
1440
10%
360
41%
360
18%
928
July1st to 15thNight
44%
340
12%
1360
14%
340
52%
340
24%
779
July16th to endNight
45%
376
13%
1418
13%
354
50%
354
24%
847
August1st to 15thNight
43%
423
12%
1494
8%
421
48%
421
19%
963
August16th to endNight
44%
744
19%
1890
9%
744
48%
744
33%
1236
September1st to 15thNight
40%
716
15%
1790
7%
716
42%
716
28%
1239
September16th to endNight
41%
657
20%
1782
12%
657
45%
657
28%
1168
October1st to 15thNight
28%
660
15%
1980
11%
660
34%
660
17%
1429
October16th to endNight
19%
704
7%
2216
4%
704
24%
704
9%
1796
November1st to 15thNight
21%
700
14%
2285
9%
700
28%
700
13%
1692
November16th to endNight
18%
720
10%
2520
8%
720
23%
720
8%
2003
December1st to 15thNight
11%
720
4%
2520
1%
720
14%
720
5%
2158
December16th to endNight
9%
768
6%
2688
2%
768
14%
768
4%
2338

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%10%37%5%34446%29%
47910
Night
19%12%47%5%34445%28%
46988
Cloud CoverDay
19%10%47%5%34446%29%
47919
Night
19%12%47%5%34445%28%
46994
TransparencyDay
55%5%10%17%8%1
47597
Night
58%5%10%16%8%
46819
SeeingDay
26%14%28%19%8%2
5540
Night
27%14%29%20%7%
14690

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
19%19%6%11%7%4443415%
1432
16th to endDay
14%18%6%10%7%45%445%17%
1569
February1st to 15thDay
15%15%7%13%9%46%33416%
1575
16th to endDay
18%17%6%10%7%33335%21%
1557
March1st to 15thDay
18%16%6%8%6%3423324%
1820
16th to endDay
19%11%45%423335%35%
2211
April1st to 15thDay
23%12%5%5%32323431%
2152
16th to endDay
20%9%35%42335%5%35%
2212
May1st to 15thDay
20%8%35%5%34445%33%
2511
16th to endDay
19%6%26%435%45%7%34%
2618
June1st to 15thDay
27%5%25%5%345%5%7%28%
2520
16th to endDay
21%5%25%5%35%5%6%8%30%
2520
July1st to 15thDay
16%5%25%5%345%6%7%37%
2520
16th to endDay
14%5%25%6%35%6%6%9%33%
2654
August1st to 15thDay
15%5%26%6%45%5%7%8%31%
2454
16th to endDay
13%4345%35%6%6%8%38%
2298
September1st to 15thDay
20%5%25%424347%39%
2146
16th to endDay
18%42443445%5%42%
1847
October1st to 15thDay
23%7%36%444446%30%
1650
16th to endDay
29%13%36%5%24245%21%
1656
November1st to 15thDay
15%11%47%6%445%46%29%
1572
16th to endDay
21%16%5%9%5%2433324%
1440
December1st to 15thDay
24%18%6%9%7%2343414%
1440
16th to endDay
25%21%6%9%5%3433313%
1536
January1st to 15thNight
18%20%6%12%6%3433414%
2506
16th to endNight
13%19%6%10%8%45%42420%
2655
February1st to 15thNight
15%19%7%12%8%3433317%
2285
16th to endNight
17%14%7%11%7%3334420%
1915
March1st to 15thNight
19%15%5%8%6%3332428%
2116
16th to endNight
20%12%45%5%2233435%
2013
April1st to 15thNight
24%11%45%5%13335%30%
1796
16th to endNight
22%8%245%23345%37%
1752
May1st to 15thNight
21%7%34334447%33%
1446
16th to endNight
17%6%25%5%25%448%35%
1495
June1st to 15thNight
25%6%25%5%245%47%29%
1440
16th to endNight
18%424426%6%6%8%34%
1440
July1st to 15thNight
12%324435%45%10%41%
1440
16th to endNight
10%425%435%5%6%9%42%
1514
August1st to 15thNight
14%6%35%5%345%6%8%36%
1504
16th to endNight
14%42442345%7%46%
1890
September1st to 15thNight
18%6%25%424346%42%
1790
16th to endNight
17%5%244235%47%43%
1782
October1st to 15thNight
22%7%35%424346%33%
1980
16th to endNight
30%11%26%6%34345%21%
2216
November1st to 15thNight
21%10%45%5%3445%5%29%
2285
16th to endNight
22%14%6%7%6%2433423%
2520
December1st to 15thNight
22%21%6%9%5%3333316%
2520
16th to endNight
23%21%7%9%5%3433314%
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
18%19%6%11%7%36%43315%
1432
16th to endDay
14%18%6%11%7%45%446%17%
1569
February1st to 15thDay
15%15%7%13%9%5%5%33415%
1575
16th to endDay
18%17%7%10%7%23335%20%
1557
March1st to 15thDay
18%16%6%9%6%3422423%
1830
16th to endDay
20%11%45%42233435%
2210
April1st to 15thDay
23%12%5%5%31433431%
2152
16th to endDay
20%10%35%42335%6%34%
2212
May1st to 15thDay
20%8%35%5%3445%5%32%
2511
16th to endDay
19%6%26%435%45%7%34%
2618
June1st to 15thDay
26%6%25%5%3445%6%28%
2520
16th to endDay
21%5%25%5%35%5%6%8%29%
2520
July1st to 15thDay
16%6%26%5%345%6%8%36%
2520
16th to endDay
14%5%26%5%36%6%6%9%32%
2654
August1st to 15thDay
15%5%27%6%45%6%7%8%31%
2454
16th to endDay
13%5%25%5%35%5%5%9%37%
2298
September1st to 15thDay
20%6%25%423348%38%
2146
16th to endDay
18%5%25%33435%6%41%
1847
October1st to 15thDay
23%8%26%435%446%30%
1650
16th to endDay
28%13%46%5%33345%20%
1656
November1st to 15thDay
15%12%37%7%3445%5%29%
1572
16th to endDay
20%16%5%10%5%2442323%
1440
December1st to 15thDay
23%19%6%10%7%2443313%
1440
16th to endDay
25%20%7%9%6%2333313%
1536
January1st to 15thNight
17%20%7%13%6%35%33414%
2506
16th to endNight
13%19%6%11%8%36%33419%
2655
February1st to 15thNight
15%18%8%13%8%3433317%
2278
16th to endNight
16%15%7%10%8%3435%5%19%
1915
March1st to 15thNight
19%16%5%8%6%3222428%
2129
16th to endNight
20%13%46%5%2333335%
2013
April1st to 15thNight
24%12%35%5%2433430%
1796
16th to endNight
22%8%25%423335%37%
1752
May1st to 15thNight
21%7%34425%45%8%32%
1446
16th to endNight
17%6%25%5%245%5%7%35%
1495
June1st to 15thNight
25%6%35%5%335%5%7%28%
1440
16th to endNight
17%325%435%6%6%9%34%
1440
July1st to 15thNight
12%4245%35%46%10%41%
1440
16th to endNight
10%425%5%25%5%7%9%42%
1514
August1st to 15thNight
14%6%25%6%2446%8%36%
1504
16th to endNight
13%5%25%42345%7%45%
1890
September1st to 15thNight
18%6%25%424346%42%
1790
16th to endNight
17%5%15%423447%43%
1782
October1st to 15thNight
22%8%26%5%24446%32%
1980
16th to endNight
30%11%36%5%3434421%
2216
November1st to 15thNight
20%11%35%5%3445%5%29%
2285
16th to endNight
21%15%5%7%6%3433423%
2520
December1st to 15thNight
22%21%7%10%6%2332315%
2520
16th to endNight
22%21%7%10%5%3433314%
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
74%36%10%3
1433
16th to endDay
68%410%9%5%
1569
February1st to 15thDay
73%46%13%2
1577
16th to endDay
67%47%11%7%1
1557
March1st to 15thDay
67%39%12%6%1
1830
16th to endDay
54%37%15%15%4
2211
April1st to 15thDay
58%36%18%11%1
2152
16th to endDay
50%39%18%14%3
2212
May1st to 15thDay
53%5%8%18%12%1
2511
16th to endDay
49%6%11%19%11%1
2622
June1st to 15thDay
54%6%11%17%8%
2520
16th to endDay
50%7%10%20%9%
2520
July1st to 15thDay
42%6%13%25%10%
2371
16th to endDay
45%8%17%20%8%
2487
August1st to 15thDay
48%8%14%20%7%
2440
16th to endDay
41%6%16%24%10%
2298
September1st to 15thDay
44%5%11%24%12%
2146
16th to endDay
43%5%10%28%11%
1847
October1st to 15thDay
55%5%11%18%8%
1650
16th to endDay
66%6%11%10%5%
1656
November1st to 15thDay
55%6%11%18%6%1
1572
16th to endDay
65%5%8%13%6%
1440
December1st to 15thDay
73%6%9%9%1
1440
16th to endDay
77%46%8%3
1536
January1st to 15thNight
74%5%8%8%3
2506
16th to endNight
69%5%7%11%5%
2655
February1st to 15thNight
73%38%10%2
2287
16th to endNight
67%47%12%7%
1915
March1st to 15thNight
62%39%17%6%
2129
16th to endNight
55%37%16%12%3
2013
April1st to 15thNight
57%47%17%11%
1796
16th to endNight
49%48%19%14%2
1752
May1st to 15thNight
50%5%11%15%15%2
1446
16th to endNight
46%6%14%19%12%1
1497
June1st to 15thNight
53%6%13%16%9%
1440
16th to endNight
44%7%15%20%12%
1440
July1st to 15thNight
35%7%15%27%13%
1360
16th to endNight
37%7%16%23%13%1
1418
August1st to 15thNight
43%7%18%19%10%
1494
16th to endNight
37%5%14%29%12%
1890
September1st to 15thNight
43%5%12%27%11%
1790
16th to endNight
40%410%30%12%
1782
October1st to 15thNight
52%5%11%20%9%
1980
16th to endNight
66%5%12%11%3
2216
November1st to 15thNight
56%6%13%13%8%2
2285
16th to endNight
66%5%9%12%5%1
2520
December1st to 15thNight
74%5%9%9%1
2520
16th to endNight
76%5%7%7%2
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
28%23%25%16%6%
60
16th to endDay
37%17%31%11%1
69
February1st to 15thDay
44%25%28%1
90
16th to endDay
33%24%28%11%1
216
March1st to 15thDay
30%19%30%14%4
270
16th to endDay
31%20%25%13%8%1
288
April1st to 15thDay
32%21%28%13%4
270
16th to endDay
31%14%27%15%7%3
270
May1st to 15thDay
31%12%28%15%9%1
288
16th to endDay
22%17%31%18%9%
331
June1st to 15thDay
31%11%30%19%6%
315
16th to endDay
22%13%33%21%6%1
315
July1st to 15thDay
18%9%30%29%9%3
305
16th to endDay
18%8%30%28%11%2
326
August1st to 15thDay
20%7%27%28%12%3
313
16th to endDay
16%9%28%25%13%7%
332
September1st to 15thDay
20%10%24%21%12%10%
310
16th to endDay
19%12%27%23%12%5%
254
October1st to 15thDay
25%13%26%16%13%3
255
16th to endDay
45%11%25%14%2
253
November1st to 15thDay
23%15%32%17%8%1
226
16th to endDay
36%15%30%13%5%
60
December1st to 15thDay
40%16%26%16%
60
16th to endDay
46%23%26%3
64
January1st to 15thNight
30%21%32%12%2
720
16th to endNight
24%23%30%16%4
768
February1st to 15thNight
27%19%35%14%1
704
16th to endNight
25%18%35%16%3
631
March1st to 15thNight
30%18%30%17%2
720
16th to endNight
29%16%25%20%5%1
768
April1st to 15thNight
32%14%32%17%3
718
16th to endNight
31%13%28%18%7%
672
May1st to 15thNight
26%9%33%22%5%1
366
16th to endNight
21%12%32%26%8%
375
June1st to 15thNight
28%8%27%27%7%
360
16th to endNight
17%7%36%27%10%1
360
July1st to 15thNight
11%7%31%36%12%
340
16th to endNight
13%433%34%11%1
376
August1st to 15thNight
20%427%30%15%1
423
16th to endNight
15%6%28%32%14%2
744
September1st to 15thNight
20%8%27%27%15%1
716
16th to endNight
18%10%26%24%17%1
657
October1st to 15thNight
28%12%27%20%11%
660
16th to endNight
39%14%21%20%3
704
November1st to 15thNight
27%15%30%17%8%1
700
16th to endNight
32%20%22%14%9%
720
December1st to 15thNight
36%22%25%13%2
720
16th to endNight
36%18%29%11%3
768
Page generated at 2017-09-15 10:29:57. Version ac04

Copyright 2017 A. Danko


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