Joseph J. Casby Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Joseph J. Casby 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%
16131
16%
46897
9%
16085
43%
16085
24%
31773

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
29%
900
12%
2506
6%
895
35%
895
19%
1848
January16th to endNight
25%
960
11%
2562
4%
960
30%
960
17%
1964
February1st to 15thNight
30%
879
14%
2288
4%
875
36%
875
22%
1643
February16th to endNight
28%
738
15%
2000
4%
738
36%
738
22%
1416
March1st to 15thNight
31%
597
14%
2037
10%
597
37%
597
19%
1371
March16th to endNight
33%
576
15%
2085
12%
576
40%
576
17%
1432
April1st to 15thNight
31%
539
17%
1797
12%
539
41%
539
22%
1197
April16th to endNight
31%
540
16%
1689
11%
540
39%
540
18%
1218
May1st to 15thNight
33%
540
14%
1479
8%
540
38%
540
23%
1032
May16th to endNight
46%
562
15%
1498
6%
561
51%
561
28%
1007
June1st to 15thNight
48%
540
12%
1440
5%
540
51%
540
32%
930
June16th to endNight
57%
540
16%
1440
8%
540
60%
540
38%
878
July1st to 15thNight
61%
510
14%
1360
7%
510
63%
510
44%
791
July16th to endNight
66%
564
20%
1417
11%
531
69%
531
46%
804
August1st to 15thNight
66%
539
21%
1608
19%
536
68%
536
35%
945
August16th to endNight
57%
573
21%
1806
20%
573
63%
573
33%
1048
September1st to 15thNight
60%
540
23%
1800
22%
540
67%
540
35%
990
September16th to endNight
45%
556
18%
1848
13%
556
53%
556
29%
1090
October1st to 15thNight
41%
660
24%
1980
16%
660
48%
660
31%
1199
October16th to endNight
35%
704
15%
2139
9%
704
41%
704
21%
1451
November1st to 15thNight
34%
814
20%
2390
11%
814
41%
814
24%
1581
November16th to endNight
29%
900
14%
2520
8%
900
35%
900
18%
1843
December1st to 15thNight
23%
900
9%
2520
3%
900
28%
900
15%
1938
December16th to endNight
21%
960
10%
2688
3%
960
27%
960
12%
2157

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%3445%7%37%
47929
Night
13%8%36%5%24446%40%
47065
Cloud CoverDay
26%7%25%5%23446%32%
47940
Night
25%7%25%423335%35%
47069
Cloud CoverDay
13%8%36%5%3445%7%36%
47938
Night
12%8%46%5%34446%39%
47069
TransparencyDay
46%6%14%22%9%
47616
Night
44%5%13%23%11%1
46897
SeeingDay
17%7%28%27%14%3
6137
Night
16%7%30%32%11%1
16133

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
9%11%6%8%9%45%446%28%
1432
16th to endDay
9%15%5%10%7%45%5%5%8%21%
1661
February1st to 15thDay
8%10%7%10%7%45%45%5%30%
1575
16th to endDay
13%9%5%7%5%36%46%6%31%
1472
March1st to 15thDay
15%10%37%5%34447%33%
1921
16th to endDay
19%10%35%5%335%47%30%
2139
April1st to 15thDay
18%9%35%5%23346%37%
2151
16th to endDay
22%11%36%424446%28%
2268
May1st to 15thDay
20%8%35%6%24445%32%
2472
16th to endDay
14%6%246%345%48%38%
2617
June1st to 15thDay
17%5%15%4245%5%8%39%
2520
16th to endDay
10%425%5%35%6%6%9%39%
2520
July1st to 15thDay
8%32342446%9%48%
2520
16th to endDay
8%3244245%6%9%47%
2655
August1st to 15thDay
9%6%25%5%445%7%8%41%
2340
16th to endDay
12%41442445%6%47%
2396
September1st to 15thDay
11%5%1442445%8%46%
2160
16th to endDay
16%5%25%5%2345%6%41%
1843
October1st to 15thDay
16%7%23423346%45%
1650
16th to endDay
18%9%36%424326%37%
1733
November1st to 15thDay
11%11%5%6%5%34346%38%
1468
16th to endDay
16%9%47%6%24347%33%
1440
December1st to 15thDay
15%11%6%9%7%445%45%24%
1440
16th to endDay
19%15%7%10%7%3422420%
1536
January1st to 15thNight
11%8%6%7%7%46%44433%
2506
16th to endNight
12%11%6%9%6%25%5%46%28%
2562
February1st to 15thNight
8%10%5%9%5%35%445%37%
2285
16th to endNight
9%10%46%7%45%446%37%
2000
March1st to 15thNight
12%8%47%6%34345%39%
2025
16th to endNight
17%9%47%5%23347%35%
2085
April1st to 15thNight
19%8%35%423346%38%
1797
16th to endNight
23%7%27%424435%33%
1689
May1st to 15thNight
20%7%34324336%40%
1479
16th to endNight
10%6%25%5%35%5%6%7%41%
1496
June1st to 15thNight
13%4234245%5%7%45%
1440
16th to endNight
7%313435%5%5%7%53%
1440
July1st to 15thNight
42135%2345%10%55%
1440
16th to endNight
5%32322446%9%54%
1513
August1st to 15thNight
7%3143345%6%7%50%
1617
16th to endNight
9%414423446%53%
1806
September1st to 15thNight
9%324324337%55%
1800
16th to endNight
13%415%423346%50%
1848
October1st to 15thNight
16%6%23312336%49%
1980
16th to endNight
21%8%25%313246%40%
2139
November1st to 15thNight
13%8%35%42345%5%43%
2390
16th to endNight
14%10%47%5%34446%33%
2520
December1st to 15thNight
14%12%6%9%6%24335%29%
2520
16th to endNight
17%15%5%9%7%24435%22%
2688

Percentage Cloud Cover SW (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
23%9%46%7%45%345%25%
1432
16th to endDay
24%13%49%7%34446%18%
1661
February1st to 15thDay
23%9%5%8%6%3433426%
1575
16th to endDay
25%8%46%434445%26%
1472
March1st to 15thDay
27%8%37%422336%29%
1932
16th to endDay
31%9%25%423346%25%
2139
April1st to 15thDay
31%8%25%422235%31%
2151
16th to endDay
36%10%25%42333422%
2268
May1st to 15thDay
33%7%25%5%23345%26%
2472
16th to endDay
29%6%145%23346%31%
2617
June1st to 15thDay
31%5%13323446%31%
2520
16th to endDay
25%415%5%2445%7%32%
2520
July1st to 15thDay
23%31432335%7%39%
2520
16th to endDay
23%3143245%5%7%38%
2655
August1st to 15thDay
17%5%145%35%5%6%7%37%
2340
16th to endDay
18%5%1432345%6%44%
2396
September1st to 15thDay
18%41342335%7%43%
2160
16th to endDay
21%5%25%42345%5%39%
1843
October1st to 15thDay
24%6%23322345%42%
1650
16th to endDay
25%7%25%42333435%
1733
November1st to 15thDay
23%9%26%423335%34%
1468
16th to endDay
30%7%35%6%12335%29%
1440
December1st to 15thDay
30%10%5%8%6%3243320%
1440
16th to endDay
30%13%5%10%7%3222318%
1536
January1st to 15thNight
24%7%46%6%35%34428%
2506
16th to endNight
26%10%48%5%24435%23%
2562
February1st to 15thNight
22%10%47%42333432%
2278
16th to endNight
23%7%26%6%5%4435%31%
2000
March1st to 15thNight
24%7%35%5%32335%34%
2037
16th to endNight
31%7%26%322335%30%
2085
April1st to 15thNight
30%7%25%32234433%
1797
16th to endNight
36%8%25%423435%25%
1689
May1st to 15thNight
34%5%24223235%33%
1478
16th to endNight
26%5%25%5%33445%35%
1496
June1st to 15thNight
27%313423446%37%
1440
16th to endNight
22%212423346%44%
1440
July1st to 15thNight
21%113423338%46%
1440
16th to endNight
20%21332335%6%47%
1513
August1st to 15thNight
15%32432445%7%46%
1617
16th to endNight
16%313323345%51%
1806
September1st to 15thNight
15%214333346%51%
1800
16th to endNight
19%314433345%47%
1848
October1st to 15thNight
23%5%13322335%45%
1980
16th to endNight
27%8%24313235%36%
2139
November1st to 15thNight
24%8%2441243439%
2390
16th to endNight
27%9%36%5%23245%28%
2520
December1st to 15thNight
28%11%48%5%23235%24%
2520
16th to endNight
29%12%5%9%6%2333419%
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
9%12%6%8%8%46%446%27%
1432
16th to endDay
9%15%5%11%8%45%5%47%22%
1661
February1st to 15thDay
8%10%8%10%7%45%445%30%
1575
16th to endDay
12%9%5%7%6%45%5%5%6%31%
1472
March1st to 15thDay
14%10%48%5%24447%33%
1932
16th to endDay
18%10%45%5%24447%30%
2137
April1st to 15thDay
17%9%35%5%23446%36%
2151
16th to endDay
22%11%46%42445%5%28%
2268
May1st to 15thDay
20%8%36%5%3445%6%31%
2472
16th to endDay
14%7%246%35%45%7%37%
2617
June1st to 15thDay
16%6%24335%46%8%38%
2520
16th to endDay
9%5%25%6%35%5%6%10%38%
2520
July1st to 15thDay
7%424425%5%6%9%47%
2520
16th to endDay
7%324425%6%6%9%47%
2655
August1st to 15thDay
9%5%25%5%35%6%7%8%40%
2340
16th to endDay
12%5%2442445%6%47%
2396
September1st to 15thDay
11%5%145%2446%8%45%
2160
16th to endDay
14%6%25%5%235%5%6%40%
1843
October1st to 15thDay
16%7%23423345%45%
1650
16th to endDay
18%9%35%433335%37%
1733
November1st to 15thDay
11%11%47%5%24446%37%
1468
16th to endDay
16%9%46%7%24447%32%
1440
December1st to 15thDay
15%11%7%9%8%335%45%24%
1440
16th to endDay
17%17%7%10%8%2423420%
1536
January1st to 15thNight
11%9%6%7%7%46%445%32%
2506
16th to endNight
12%12%6%10%6%35%5%45%28%
2562
February1st to 15thNight
7%11%5%9%5%34446%36%
2278
16th to endNight
10%9%36%6%45%446%36%
2000
March1st to 15thNight
11%8%46%5%34445%39%
2037
16th to endNight
17%9%47%423347%34%
2085
April1st to 15thNight
18%9%35%423446%38%
1797
16th to endNight
22%9%35%424446%31%
1689
May1st to 15thNight
20%6%26%333346%39%
1478
16th to endNight
9%6%35%6%35%45%8%41%
1496
June1st to 15thNight
13%4245%2446%7%44%
1440
16th to endNight
6%323435%5%5%7%52%
1440
July1st to 15thNight
5%11342445%10%55%
1440
16th to endNight
4313325%47%8%54%
1513
August1st to 15thNight
7%3244245%6%7%50%
1617
16th to endNight
9%424423446%53%
1806
September1st to 15thNight
8%314333446%55%
1800
16th to endNight
12%32443435%6%49%
1848
October1st to 15thNight
15%5%24322336%49%
1980
16th to endNight
20%10%25%313336%39%
2139
November1st to 15thNight
13%8%35%423445%43%
2390
16th to endNight
13%11%47%6%34346%32%
2520
December1st to 15thNight
13%13%5%10%6%34345%28%
2520
16th to endNight
16%15%7%9%7%24345%22%
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
56%5%11%19%6%
1433
16th to endDay
60%7%13%14%4
1661
February1st to 15thDay
54%5%14%18%6%
1576
16th to endDay
52%7%11%23%5%
1472
March1st to 15thDay
51%5%15%19%7%
1932
16th to endDay
53%6%13%21%3
2139
April1st to 15thDay
48%412%21%10%1
2151
16th to endDay
56%6%12%15%9%
2268
May1st to 15thDay
52%5%13%20%6%
2472
16th to endDay
44%7%12%22%12%1
2621
June1st to 15thDay
41%7%14%25%9%
2520
16th to endDay
38%8%16%24%10%1
2520
July1st to 15thDay
31%7%16%28%14%1
2371
16th to endDay
31%9%17%24%15%2
2488
August1st to 15thDay
38%8%15%26%9%2
2326
16th to endDay
35%6%16%26%13%1
2396
September1st to 15thDay
35%6%15%30%11%
2160
16th to endDay
42%7%13%28%8%
1843
October1st to 15thDay
40%5%12%28%12%
1650
16th to endDay
49%5%14%22%7%
1733
November1st to 15thDay
47%5%12%20%12%1
1468
16th to endDay
51%7%19%14%6%
1440
December1st to 15thDay
61%6%14%13%4
1440
16th to endDay
69%49%12%4
1536
January1st to 15thNight
53%5%12%21%6%
2506
16th to endNight
56%5%15%16%5%
2562
February1st to 15thNight
48%5%14%23%8%
2288
16th to endNight
47%5%12%24%8%
2000
March1st to 15thNight
47%5%13%21%10%
2037
16th to endNight
50%5%12%22%7%
2085
April1st to 15thNight
46%48%24%14%1
1797
16th to endNight
52%6%9%17%11%2
1689
May1st to 15thNight
46%5%15%19%11%1
1479
16th to endNight
40%7%12%23%15%1
1498
June1st to 15thNight
36%6%16%25%13%1
1440
16th to endNight
29%7%13%29%17%2
1440
July1st to 15thNight
24%6%14%33%17%2
1360
16th to endNight
23%6%16%30%18%4
1417
August1st to 15thNight
30%7%13%28%16%3
1608
16th to endNight
31%6%14%28%15%3
1806
September1st to 15thNight
29%5%12%33%18%
1800
16th to endNight
35%5%15%29%14%
1848
October1st to 15thNight
36%411%30%15%2
1980
16th to endNight
46%5%13%21%12%
2139
November1st to 15thNight
43%5%11%23%15%
2390
16th to endNight
52%5%15%17%7%1
2520
December1st to 15thNight
58%6%13%17%4
2520
16th to endNight
64%5%12%13%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
21%8%36%25%6%1
90
16th to endDay
22%6%39%28%21
96
February1st to 15thDay
12%21%41%21%4
90
16th to endDay
22%11%37%27%11
81
March1st to 15thDay
17%12%44%20%5%
90
16th to endDay
30%8%31%21%6%1
123
April1st to 15thDay
24%10%27%28%8%1
270
16th to endDay
32%9%27%21%8%
378
May1st to 15thDay
23%13%29%22%9%1
468
16th to endDay
19%9%30%23%13%3
517
June1st to 15thDay
17%7%28%28%15%3
495
16th to endDay
10%8%33%27%15%3
495
July1st to 15thDay
9%227%29%21%9%
475
16th to endDay
6%326%32%23%6%
515
August1st to 15thDay
12%322%35%21%4
493
16th to endDay
17%319%33%21%5%
436
September1st to 15thDay
11%424%32%20%6%
315
16th to endDay
18%11%29%20%15%3
158
October1st to 15thDay
8%12%28%30%13%6%
90
16th to endDay
28%6%36%20%8%
96
November1st to 15thDay
10%434%34%14%2
90
16th to endDay
42%8%31%13%4
90
December1st to 15thDay
23%12%37%23%3
90
16th to endDay
41%14%32%10%1
96
January1st to 15thNight
15%10%35%30%8%1
900
16th to endNight
18%8%38%29%5%
960
February1st to 15thNight
14%10%36%28%8%1
880
16th to endNight
15%10%37%26%9%
738
March1st to 15thNight
15%8%36%28%9%
597
16th to endNight
20%11%29%25%11%1
576
April1st to 15thNight
22%8%32%29%6%
539
16th to endNight
25%6%31%27%7%
540
May1st to 15thNight
23%8%30%29%6%1
540
16th to endNight
13%5%29%35%14%1
563
June1st to 15thNight
15%427%41%12%
540
16th to endNight
8%327%47%13%
540
July1st to 15thNight
4126%40%24%1
510
16th to endNight
6%121%46%21%2
564
August1st to 15thNight
7%216%45%24%2
539
16th to endNight
10%223%37%24%2
573
September1st to 15thNight
8%322%40%19%5%
540
16th to endNight
14%6%28%30%18%1
556
October1st to 15thNight
19%8%28%28%13%1
660
16th to endNight
25%9%23%31%9%
704
November1st to 15thNight
18%8%32%28%9%1
814
16th to endNight
20%11%32%26%8%
900
December1st to 15thNight
19%8%38%26%6%
900
16th to endNight
23%8%33%28%6%
960
Page generated at 2017-09-20 03:49:57. Version ac04

Copyright 2017 A. Danko


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