Stillwaters Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stillwaters Observatory clear sky chart from 2005-11-05 to 2017-09-19.

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
38%
15884
16%
46824
11%
15841
43%
15841
21%
32335

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
16%
900
11%
2506
4%
895
22%
895
13%
1990
January16th to endNight
19%
922
11%
2650
4%
922
25%
922
13%
2073
February1st to 15thNight
20%
702
9%
2160
3%
701
26%
701
14%
1623
February16th to endNight
22%
631
14%
1893
6%
631
30%
631
15%
1406
March1st to 15thNight
27%
720
12%
2130
9%
720
31%
720
17%
1558
March16th to endNight
31%
738
16%
2082
7%
738
39%
738
20%
1471
April1st to 15thNight
30%
539
14%
1797
9%
539
37%
539
19%
1227
April16th to endNight
35%
540
21%
1662
12%
540
44%
540
23%
1100
May1st to 15thNight
36%
540
14%
1620
8%
540
41%
540
18%
1184
May16th to endNight
49%
562
16%
1623
11%
561
54%
561
29%
1042
June1st to 15thNight
55%
540
17%
1440
12%
540
59%
540
35%
906
June16th to endNight
54%
540
17%
1440
11%
540
59%
540
34%
923
July1st to 15thNight
63%
510
17%
1360
13%
510
65%
510
36%
838
July16th to endNight
70%
564
20%
1450
16%
531
72%
531
38%
860
August1st to 15thNight
70%
539
22%
1609
19%
536
73%
536
37%
922
August16th to endNight
68%
573
20%
1857
18%
573
70%
573
32%
1078
September1st to 15thNight
64%
618
27%
1878
24%
618
68%
618
36%
1068
September16th to endNight
60%
673
25%
1858
20%
673
63%
673
33%
1150
October1st to 15thNight
51%
660
27%
1833
21%
660
57%
660
34%
1119
October16th to endNight
30%
704
17%
2263
12%
704
38%
704
19%
1544
November1st to 15thNight
35%
700
23%
2276
16%
700
46%
700
25%
1404
November16th to endNight
26%
720
15%
2340
11%
720
33%
720
14%
1728
December1st to 15thNight
20%
789
8%
2409
4%
789
25%
789
11%
1885
December16th to endNight
14%
960
8%
2688
2%
960
20%
960
9%
2236

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
14%8%36%5%35%45%7%34%
47989
Night
15%8%36%5%34446%36%
46997
Cloud CoverDay
14%8%36%5%35%45%7%34%
47998
Night
15%8%36%5%34446%36%
47002
TransparencyDay
48%6%11%19%12%1
47680
Night
47%5%11%20%13%1
46824
SeeingDay
17%6%24%25%18%7%
5886
Night
19%7%28%29%14%1
15887

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
20%15%5%8%8%33446%20%
1432
16th to endDay
12%18%8%11%6%45%445%18%
1572
February1st to 15thDay
14%16%6%10%6%4445%5%20%
1699
16th to endDay
15%13%7%9%7%35%446%22%
1580
March1st to 15thDay
20%11%5%7%7%35%446%23%
1818
16th to endDay
20%8%37%6%44447%29%
2154
April1st to 15thDay
20%9%36%5%34446%31%
2151
16th to endDay
17%8%35%43445%6%35%
2298
May1st to 15thDay
20%8%35%5%35%45%6%30%
2331
16th to endDay
13%6%35%5%35%5%6%7%38%
2489
June1st to 15thDay
11%425%435%5%6%8%42%
2520
16th to endDay
10%426%5%35%6%7%8%38%
2520
July1st to 15thDay
7%5%25%5%35%46%8%43%
2520
16th to endDay
5%435%5%46%6%7%10%40%
2616
August1st to 15thDay
6%325%5%35%5%6%9%44%
2340
16th to endDay
9%425%5%35%5%6%9%41%
2343
September1st to 15thDay
11%425%5%35%5%46%43%
2070
16th to endDay
10%425%5%35%45%9%43%
1848
October1st to 15thDay
14%6%35%42445%7%42%
1796
16th to endDay
20%8%36%5%235%5%6%31%
1606
November1st to 15thDay
14%7%34333447%43%
1582
16th to endDay
20%12%5%7%5%24445%25%
1620
December1st to 15thDay
19%15%5%10%6%33336%21%
1548
16th to endDay
22%16%8%9%6%24335%16%
1536
January1st to 15thNight
20%14%5%7%6%33445%23%
2506
16th to endNight
15%14%6%9%6%34445%24%
2650
February1st to 15thNight
16%12%5%8%6%24447%27%
2158
16th to endNight
16%10%5%8%5%44445%28%
1893
March1st to 15thNight
17%10%46%6%35%35%5%32%
2117
16th to endNight
15%8%37%6%2446%7%34%
2082
April1st to 15thNight
17%7%345%35%6%5%6%34%
1797
16th to endNight
17%6%25%32345%7%40%
1662
May1st to 15thNight
19%7%46%5%4445%7%30%
1620
16th to endNight
13%434425%5%5%8%42%
1621
June1st to 15thNight
8%435%5%2435%8%49%
1440
16th to endNight
7%3345%35%5%5%9%45%
1440
July1st to 15thNight
6%3236%2445%8%51%
1440
16th to endNight
5%323425%5%7%9%49%
1549
August1st to 15thNight
4425%43446%10%49%
1620
16th to endNight
8%42443445%8%49%
1857
September1st to 15thNight
10%414424347%53%
1878
16th to endNight
11%5%24324446%50%
1858
October1st to 15thNight
11%6%14423346%49%
1833
16th to endNight
19%7%35%5%33345%37%
2263
November1st to 15thNight
13%7%35%5%23346%44%
2276
16th to endNight
20%10%47%5%24345%28%
2340
December1st to 15thNight
20%14%5%8%5%2445%423%
2409
16th to endNight
24%14%5%10%6%24345%17%
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
20%15%48%8%24446%20%
1432
16th to endDay
13%18%8%10%6%44445%18%
1572
February1st to 15thDay
15%16%6%10%7%3445%6%20%
1699
16th to endDay
15%13%7%9%6%35%446%23%
1580
March1st to 15thDay
20%11%47%7%34446%23%
1828
16th to endDay
20%8%37%6%35%347%28%
2153
April1st to 15thDay
20%9%35%5%25%446%31%
2151
16th to endDay
18%8%35%43435%7%35%
2298
May1st to 15thDay
20%8%35%6%35%45%6%30%
2331
16th to endDay
13%5%25%5%35%5%6%7%38%
2489
June1st to 15thDay
11%425%5%36%5%6%7%42%
2520
16th to endDay
10%426%5%35%6%7%8%38%
2520
July1st to 15thDay
7%5%25%5%25%5%6%8%43%
2520
16th to endDay
5%435%5%35%6%7%11%40%
2616
August1st to 15thDay
7%325%5%35%5%6%9%44%
2340
16th to endDay
9%425%5%25%5%5%9%42%
2343
September1st to 15thDay
11%434435%5%5%6%44%
2070
16th to endDay
10%425%5%345%5%8%43%
1848
October1st to 15thDay
14%6%35%42445%6%42%
1796
16th to endDay
20%8%36%5%3345%6%31%
1606
November1st to 15thDay
14%7%35%323346%44%
1582
16th to endDay
20%12%47%5%345%45%26%
1620
December1st to 15thDay
19%15%5%9%6%43435%22%
1548
16th to endDay
22%16%7%9%6%24335%16%
1536
January1st to 15thNight
21%14%5%7%6%33445%24%
2506
16th to endNight
16%14%6%9%6%44445%24%
2650
February1st to 15thNight
16%13%5%7%5%24447%28%
2151
16th to endNight
17%10%5%9%5%34445%29%
1893
March1st to 15thNight
18%10%36%5%35%345%32%
2130
16th to endNight
15%8%36%6%3446%6%34%
2082
April1st to 15thNight
18%7%34435%6%6%6%34%
1797
16th to endNight
18%6%35%32345%7%39%
1662
May1st to 15thNight
19%8%36%6%35%45%6%30%
1619
16th to endNight
13%5%24335%45%8%42%
1621
June1st to 15thNight
8%5%25%434347%49%
1440
16th to endNight
7%4345%35%5%5%10%45%
1440
July1st to 15thNight
6%425%5%2445%8%51%
1440
16th to endNight
4323435%5%7%9%50%
1549
August1st to 15thNight
5%325%43445%10%50%
1620
16th to endNight
8%3235%35%45%8%49%
1857
September1st to 15thNight
10%314324348%52%
1878
16th to endNight
12%424324446%50%
1858
October1st to 15thNight
12%5%1442345%6%50%
1833
16th to endNight
19%7%25%5%33345%37%
2263
November1st to 15thNight
13%7%25%5%23345%44%
2276
16th to endNight
21%11%46%6%24445%28%
2340
December1st to 15thNight
20%13%5%7%6%2445%424%
2409
16th to endNight
24%14%5%10%6%34435%17%
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
64%412%10%6%
1433
16th to endDay
67%5%11%10%5%
1572
February1st to 15thDay
65%410%13%5%
1701
16th to endDay
61%6%10%16%4
1580
March1st to 15thDay
61%411%14%7%
1828
16th to endDay
55%5%12%20%5%1
2154
April1st to 15thDay
53%6%9%19%11%
2151
16th to endDay
47%5%11%18%12%4
2298
May1st to 15thDay
53%7%10%19%8%
2331
16th to endDay
42%8%10%21%14%2
2493
June1st to 15thDay
37%7%11%24%17%1
2520
16th to endDay
38%9%13%19%17%1
2520
July1st to 15thDay
36%7%11%21%18%3
2371
16th to endDay
34%8%15%24%14%2
2452
August1st to 15thDay
33%8%14%25%16%2
2327
16th to endDay
36%6%13%21%16%3
2343
September1st to 15thDay
39%5%12%20%18%3
2070
16th to endDay
37%5%10%24%20%1
1848
October1st to 15thDay
41%5%10%23%17%1
1796
16th to endDay
51%5%12%19%10%
1606
November1st to 15thDay
40%5%9%24%17%2
1582
16th to endDay
58%6%10%18%6%
1620
December1st to 15thDay
64%411%15%4
1548
16th to endDay
70%5%10%9%3
1536
January1st to 15thNight
62%410%13%8%
2506
16th to endNight
61%5%12%16%4
2650
February1st to 15thNight
57%6%12%14%8%
2160
16th to endNight
56%411%18%7%
1893
March1st to 15thNight
53%5%11%17%9%1
2130
16th to endNight
48%6%11%22%8%2
2082
April1st to 15thNight
47%6%10%19%14%
1797
16th to endNight
43%6%9%20%16%3
1662
May1st to 15thNight
52%6%9%20%8%2
1620
16th to endNight
38%6%13%22%15%3
1623
June1st to 15thNight
33%6%10%27%20%1
1440
16th to endNight
34%7%16%23%15%2
1440
July1st to 15thNight
31%6%12%24%20%4
1360
16th to endNight
28%8%15%24%19%4
1450
August1st to 15thNight
28%6%12%27%21%2
1609
16th to endNight
31%7%12%21%21%5%
1857
September1st to 15thNight
30%411%25%21%5%
1878
16th to endNight
34%6%8%26%21%2
1858
October1st to 15thNight
34%48%28%22%
1833
16th to endNight
48%5%9%24%11%1
2263
November1st to 15thNight
41%39%24%18%2
2276
16th to endNight
57%410%19%7%
2340
December1st to 15thNight
61%5%9%15%6%
2409
16th to endNight
69%410%10%4
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
25%15%40%10%7%1
90
16th to endDay
26%16%34%19%3
96
February1st to 15thDay
22%23%37%16%
90
16th to endDay
19%13%35%22%8%
81
March1st to 15thDay
34%15%23%21%5%
118
16th to endDay
27%10%28%22%7%3
288
April1st to 15thDay
24%9%34%20%12%
270
16th to endDay
21%8%28%22%12%7%
270
May1st to 15thDay
28%8%23%23%11%4
288
16th to endDay
19%6%23%25%16%8%
389
June1st to 15thDay
13%5%25%34%15%6%
495
16th to endDay
13%5%31%24%19%5%
495
July1st to 15thDay
11%225%29%19%11%
475
16th to endDay
7%316%33%25%14%
476
August1st to 15thDay
10%13%26%30%19%
313
16th to endDay
16%112%21%32%15%
332
September1st to 15thDay
14%214%24%30%13%
315
16th to endDay
13%412%22%35%11%
266
October1st to 15thDay
18%7%16%28%20%8%
255
16th to endDay
26%10%29%30%3
118
November1st to 15thDay
8%10%26%30%17%6%
90
16th to endDay
27%15%41%12%3
90
December1st to 15thDay
25%17%37%12%6%
90
16th to endDay
26%25%40%7%1
96
January1st to 15thNight
28%12%34%19%4
900
16th to endNight
21%13%36%24%4
922
February1st to 15thNight
23%10%38%22%4
704
16th to endNight
21%12%37%23%4
631
March1st to 15thNight
22%10%32%25%7%
720
16th to endNight
19%9%33%29%7%1
738
April1st to 15thNight
21%9%35%26%7%
539
16th to endNight
20%5%34%27%11%1
540
May1st to 15thNight
23%5%28%32%10%
540
16th to endNight
15%325%34%19%1
563
June1st to 15thNight
10%123%46%17%
540
16th to endNight
9%124%37%24%1
540
July1st to 15thNight
9%17%45%25%1
510
16th to endNight
6%214%38%35%2
564
August1st to 15thNight
6%113%42%29%5%
539
16th to endNight
10%112%33%38%4
573
September1st to 15thNight
11%415%32%32%3
618
16th to endNight
14%414%33%29%3
673
October1st to 15thNight
14%6%22%32%20%3
660
16th to endNight
24%10%31%25%8%
704
November1st to 15thNight
17%9%32%27%12%1
700
16th to endNight
26%11%28%23%8%
720
December1st to 15thNight
28%13%31%21%5%
789
16th to endNight
31%12%32%19%4
960
Page generated at 2017-09-20 04:49:54. Version ac04

Copyright 2017 A. Danko


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