Sycamore Stars Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sycamore Stars Observatory clear sky chart from 2005-11-05 to 2017-09-22.

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
35%
15977
14%
46870
9%
15935
39%
15935
19%
33554

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
14%
900
6%
2506
2%
895
17%
895
8%
2133
January16th to endNight
16%
960
5%
2688
2%
960
18%
960
7%
2348
February1st to 15thNight
18%
707
8%
2187
3%
707
22%
707
9%
1769
February16th to endNight
25%
631
12%
1893
7%
631
30%
631
12%
1462
March1st to 15thNight
29%
720
14%
2139
9%
720
33%
720
18%
1529
March16th to endNight
30%
726
17%
2070
9%
726
38%
726
21%
1441
April1st to 15thNight
29%
539
13%
1797
9%
539
35%
539
18%
1243
April16th to endNight
33%
540
20%
1650
10%
540
43%
540
23%
1089
May1st to 15thNight
33%
540
13%
1620
7%
540
40%
540
21%
1118
May16th to endNight
44%
562
15%
1566
9%
561
49%
561
28%
1029
June1st to 15thNight
50%
540
16%
1440
10%
540
55%
540
35%
893
June16th to endNight
55%
540
15%
1440
10%
540
59%
540
33%
915
July1st to 15thNight
61%
510
16%
1360
11%
510
64%
510
40%
793
July16th to endNight
67%
564
21%
1417
16%
531
69%
531
39%
841
August1st to 15thNight
66%
539
21%
1604
17%
536
70%
536
38%
889
August16th to endNight
64%
573
21%
1839
19%
573
67%
573
32%
1067
September1st to 15thNight
62%
608
26%
1868
23%
608
65%
608
35%
1077
September16th to endNight
55%
685
23%
1892
17%
685
57%
685
31%
1194
October1st to 15thNight
47%
660
24%
1839
18%
660
52%
660
27%
1213
October16th to endNight
25%
704
14%
2282
8%
704
34%
704
15%
1627
November1st to 15thNight
31%
700
18%
2276
14%
700
38%
700
19%
1552
November16th to endNight
22%
720
12%
2340
8%
720
28%
720
11%
1833
December1st to 15thNight
14%
849
5%
2469
2%
849
16%
849
7%
2133
December16th to endNight
12%
960
5%
2688
1%
960
16%
960
6%
2366

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%9%47%5%34447%33%
48021
Night
15%10%47%5%34446%33%
47039
Cloud CoverDay
14%9%47%5%3445%7%33%
48030
Night
15%10%47%5%34446%33%
47044
TransparencyDay
50%5%11%20%11%1
47708
Night
52%411%19%11%1
46870
SeeingDay
17%9%27%24%15%6%
5975
Night
20%9%27%29%12%1
15981

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
18%17%7%11%9%345%3412%
1432
16th to endDay
13%22%9%13%11%4422410%
1536
February1st to 15thDay
12%16%9%15%10%45%42315%
1672
16th to endDay
15%14%7%14%6%44435%18%
1580
March1st to 15thDay
14%13%5%8%7%3445%7%25%
1811
16th to endDay
17%11%46%5%33346%33%
2166
April1st to 15thDay
19%14%46%423335%31%
2151
16th to endDay
18%8%24423447%38%
2310
May1st to 15thDay
18%8%35%435%46%6%33%
2331
16th to endDay
12%5%35%5%35%5%5%7%41%
2547
June1st to 15thDay
10%5%35%5%35%45%8%42%
2520
16th to endDay
10%425%6%36%6%6%9%39%
2520
July1st to 15thDay
7%415%5%245%6%9%46%
2520
16th to endDay
8%425%435%5%6%10%44%
2655
August1st to 15thDay
8%425%6%35%6%6%8%42%
2346
16th to endDay
12%5%25%425%45%8%41%
2361
September1st to 15thDay
13%426%435%45%9%41%
2079
16th to endDay
12%5%35%5%25%45%9%40%
1881
October1st to 15thDay
18%6%25%5%24445%38%
1790
16th to endDay
26%9%36%434446%26%
1587
November1st to 15thDay
15%11%36%425%445%36%
1582
16th to endDay
19%18%6%9%5%24335%19%
1620
December1st to 15thDay
17%20%12%12%6%3422314%
1488
16th to endDay
21%20%11%11%6%2333411%
1536
January1st to 15thNight
20%15%7%12%8%3433316%
2506
16th to endNight
14%15%11%13%10%4443412%
2688
February1st to 15thNight
13%17%7%11%8%3433420%
2185
16th to endNight
15%13%7%9%7%45%345%24%
1893
March1st to 15thNight
17%11%38%423346%33%
2126
16th to endNight
15%8%46%5%3445%7%34%
2070
April1st to 15thNight
18%10%35%434447%33%
1797
16th to endNight
17%6%35%424436%40%
1650
May1st to 15thNight
18%6%36%5%34347%34%
1620
16th to endNight
12%6%2443446%8%41%
1564
June1st to 15thNight
11%4235%2445%8%47%
1440
16th to endNight
8%4145%36%5%6%9%44%
1440
July1st to 15thNight
6%42442445%9%52%
1440
16th to endNight
6%31442447%9%51%
1513
August1st to 15thNight
5%3144345%7%8%51%
1614
16th to endNight
8%5%245%24346%50%
1839
September1st to 15thNight
12%413324446%52%
1868
16th to endNight
11%6%244245%46%47%
1892
October1st to 15thNight
17%6%2442345%6%42%
1839
16th to endNight
25%8%37%423345%32%
2282
November1st to 15thNight
16%11%36%423445%36%
2276
16th to endNight
21%16%5%8%5%34335%22%
2340
December1st to 15thNight
21%20%10%9%6%2433413%
2469
16th to endNight
22%18%9%11%6%3443411%
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
19%17%6%12%9%45%5%35%12%
1432
16th to endDay
13%21%10%12%10%35%33410%
1536
February1st to 15thDay
12%16%9%14%9%35%43315%
1672
16th to endDay
15%14%8%12%6%45%445%17%
1580
March1st to 15thDay
15%12%5%8%7%245%5%7%25%
1821
16th to endDay
17%11%46%5%33346%33%
2165
April1st to 15thDay
20%14%35%424345%31%
2151
16th to endDay
17%8%34423446%39%
2310
May1st to 15thDay
18%7%35%5%35%5%5%7%32%
2331
16th to endDay
11%5%35%5%35%5%6%7%40%
2547
June1st to 15thDay
10%5%26%5%35%45%7%42%
2520
16th to endDay
9%415%6%36%5%7%8%39%
2520
July1st to 15thDay
7%4145%345%6%9%46%
2520
16th to endDay
8%424445%5%7%9%43%
2655
August1st to 15thDay
8%425%6%35%5%6%8%42%
2346
16th to endDay
13%425%5%25%46%8%41%
2361
September1st to 15thDay
12%426%5%25%45%9%41%
2079
16th to endDay
12%5%25%5%25%45%9%40%
1881
October1st to 15thDay
17%6%35%5%3435%5%38%
1790
16th to endDay
26%10%26%5%34446%26%
1587
November1st to 15thDay
16%11%35%425%445%36%
1582
16th to endDay
19%18%6%9%5%24345%19%
1620
December1st to 15thDay
17%19%12%12%6%2332315%
1488
16th to endDay
21%20%10%11%6%2233411%
1536
January1st to 15thNight
20%15%8%12%8%3333316%
2506
16th to endNight
14%15%11%13%11%4444412%
2688
February1st to 15thNight
14%17%8%10%8%4433420%
2178
16th to endNight
16%12%7%9%6%44435%24%
1893
March1st to 15thNight
17%11%37%423346%33%
2139
16th to endNight
15%7%46%5%3345%8%34%
2070
April1st to 15thNight
18%10%44435%5%47%32%
1797
16th to endNight
17%7%25%425%436%40%
1650
May1st to 15thNight
18%7%35%5%4435%7%35%
1619
16th to endNight
13%6%24435%35%9%41%
1564
June1st to 15thNight
11%4235%3345%8%47%
1440
16th to endNight
8%4235%36%5%5%10%44%
1440
July1st to 15thNight
6%42442446%7%53%
1440
16th to endNight
6%314425%46%9%51%
1513
August1st to 15thNight
5%3144245%6%8%51%
1614
16th to endNight
9%4245%23446%50%
1839
September1st to 15thNight
12%413424347%51%
1868
16th to endNight
10%6%245%24446%47%
1892
October1st to 15thNight
17%5%24424347%42%
1839
16th to endNight
25%8%37%423345%31%
2282
November1st to 15thNight
16%11%36%424445%36%
2276
16th to endNight
21%15%5%7%5%24445%22%
2340
December1st to 15thNight
21%19%10%9%6%3333414%
2469
16th to endNight
22%17%9%11%6%3443411%
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
73%5%10%7%2
1433
16th to endDay
78%38%7%2
1536
February1st to 15thDay
73%46%11%4
1674
16th to endDay
69%410%11%4
1580
March1st to 15thDay
58%5%12%15%7%
1821
16th to endDay
53%310%24%6%1
2166
April1st to 15thDay
55%48%18%13%
2151
16th to endDay
46%412%19%14%3
2310
May1st to 15thDay
49%5%12%22%9%
2331
16th to endDay
40%6%13%26%12%1
2551
June1st to 15thDay
39%5%11%25%17%
2520
16th to endDay
38%6%14%21%16%1
2520
July1st to 15thDay
33%5%11%25%20%3
2371
16th to endDay
33%6%14%25%17%2
2488
August1st to 15thDay
35%7%11%28%13%2
2332
16th to endDay
38%5%13%26%14%2
2361
September1st to 15thDay
38%5%11%25%17%2
2079
16th to endDay
40%5%11%26%15%
1881
October1st to 15thDay
47%49%24%13%
1790
16th to endDay
58%412%17%6%
1587
November1st to 15thDay
49%5%9%22%11%1
1582
16th to endDay
67%49%14%2
1620
December1st to 15thDay
75%37%10%2
1488
16th to endDay
77%39%7%2
1536
January1st to 15thNight
72%48%10%3
2506
16th to endNight
75%5%10%6%2
2688
February1st to 15thNight
68%48%13%4
2187
16th to endNight
62%310%17%41
1893
March1st to 15thNight
53%313%18%9%1
2139
16th to endNight
48%413%22%8%1
2070
April1st to 15thNight
51%49%19%14%1
1797
16th to endNight
45%410%19%16%3
1650
May1st to 15thNight
49%312%21%10%2
1620
16th to endNight
39%7%13%23%14%2
1566
June1st to 15thNight
34%5%12%28%18%1
1440
16th to endNight
33%8%17%22%16%1
1440
July1st to 15thNight
28%5%14%27%20%3
1360
16th to endNight
28%6%14%25%20%3
1417
August1st to 15thNight
28%414%29%20%1
1604
16th to endNight
34%410%26%19%4
1839
September1st to 15thNight
31%410%29%20%2
1868
16th to endNight
37%410%28%17%1
1892
October1st to 15thNight
42%48%25%17%
1839
16th to endNight
54%312%19%9%
2282
November1st to 15thNight
50%410%21%12%1
2276
16th to endNight
64%411%17%2
2340
December1st to 15thNight
75%47%8%3
2469
16th to endNight
76%49%7%1
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
21%20%37%17%3
90
16th to endDay
26%15%31%20%5%1
96
February1st to 15thDay
20%26%34%14%4
90
16th to endDay
18%18%32%23%6%1
81
March1st to 15thDay
29%16%28%18%7%
111
16th to endDay
28%11%26%23%7%2
288
April1st to 15thDay
29%8%31%21%8%
270
16th to endDay
22%12%28%19%11%4
270
May1st to 15thDay
24%11%26%23%9%5%
288
16th to endDay
15%9%31%26%11%5%
447
June1st to 15thDay
13%8%36%25%12%3
495
16th to endDay
12%10%31%25%15%4
495
July1st to 15thDay
9%430%27%17%9%
475
16th to endDay
9%426%30%20%9%
515
August1st to 15thDay
8%117%28%25%18%
319
16th to endDay
17%414%24%27%11%
332
September1st to 15thDay
12%315%28%25%13%
315
16th to endDay
15%414%26%28%9%
278
October1st to 15thDay
19%8%20%32%16%3
255
16th to endDay
27%16%35%21%
99
November1st to 15thDay
8%18%26%27%15%2
90
16th to endDay
35%21%31%7%4
90
December1st to 15thDay
32%27%22%14%3
90
16th to endDay
27%30%38%31
96
January1st to 15thNight
28%14%32%18%6%
900
16th to endNight
20%12%33%30%3
960
February1st to 15thNight
22%14%34%23%5%
710
16th to endNight
20%14%32%26%6%
631
March1st to 15thNight
22%12%29%26%8%
720
16th to endNight
17%11%34%27%8%
726
April1st to 15thNight
22%10%33%27%6%
539
16th to endNight
20%8%33%27%7%1
540
May1st to 15thNight
20%7%31%30%8%1
540
16th to endNight
15%5%28%33%15%
563
June1st to 15thNight
12%425%41%15%
540
16th to endNight
9%325%40%20%1
540
July1st to 15thNight
9%118%44%22%3
510
16th to endNight
7%215%44%28%2
564
August1st to 15thNight
8%12%46%27%4
539
16th to endNight
11%113%35%32%5%
573
September1st to 15thNight
13%5%13%35%28%4
608
16th to endNight
13%6%18%30%25%4
685
October1st to 15thNight
20%5%21%32%18%1
660
16th to endNight
28%13%27%21%8%
704
November1st to 15thNight
21%10%30%26%10%1
700
16th to endNight
29%13%27%22%6%
720
December1st to 15thNight
29%13%30%21%3
849
16th to endNight
31%13%33%18%2
960
Page generated at 2017-09-23 06:43:46. Version ac04

Copyright 2017 A. Danko


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