Cassiopeia Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cassiopeia Observatory clear sky chart from 2005-11-05 to 2017-09-20.

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
71%
15564
35%
46935
29%
15526
77%
15526
49%
23207

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
67%
718
32%
2327
29%
716
75%
716
45%
1131
January16th to endNight
63%
768
35%
2496
32%
768
73%
768
37%
1313
February1st to 15thNight
66%
700
35%
2217
31%
700
77%
700
47%
1074
February16th to endNight
58%
632
37%
1832
31%
632
68%
632
43%
980
March1st to 15thNight
60%
720
38%
1980
28%
720
70%
720
49%
1033
March16th to endNight
67%
768
38%
2112
25%
768
77%
768
55%
1046
April1st to 15thNight
59%
677
33%
1936
21%
677
70%
677
50%
962
April16th to endNight
64%
540
45%
1786
34%
540
80%
540
66%
673
May1st to 15thNight
68%
539
39%
1619
28%
539
79%
539
62%
696
May16th to endNight
69%
561
41%
1684
30%
561
77%
561
67%
698
June1st to 15thNight
78%
540
34%
1620
28%
540
81%
540
66%
695
June16th to endNight
83%
540
31%
1620
26%
540
84%
540
57%
747
July1st to 15thNight
80%
510
20%
1530
17%
510
80%
510
39%
868
July16th to endNight
77%
564
17%
1593
15%
531
77%
531
30%
1009
August1st to 15thNight
85%
539
24%
1611
23%
536
85%
536
41%
904
August16th to endNight
84%
581
30%
1860
32%
581
84%
581
39%
1003
September1st to 15thNight
75%
720
29%
1980
25%
720
77%
720
42%
1158
September16th to endNight
79%
675
41%
1869
31%
675
84%
675
61%
897
October1st to 15thNight
73%
660
40%
1922
29%
660
81%
660
60%
891
October16th to endNight
81%
704
43%
2112
37%
704
86%
704
64%
921
November1st to 15thNight
75%
700
42%
2100
35%
700
82%
700
60%
937
November16th to endNight
69%
720
37%
2293
34%
720
75%
720
47%
1109
December1st to 15thNight
65%
720
36%
2340
35%
720
72%
720
45%
1143
December16th to endNight
59%
768
34%
2496
31%
768
67%
768
37%
1319

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
321332345%6%64%
47901
Night
2212323346%65%
47131
TransparencyDay
21%4412%28%28%
47596
Night
20%3414%28%28%
46937
SeeingDay
6%12%27%33%16%4
5402
Night
4414%35%33%7%
15573

By Month

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
3213424346%63%
1611
16th to endDay
5%214323345%62%
1728
February1st to 15thDay
4313212435%65%
1643
16th to endDay
431432345%5%60%
1642
March1st to 15thDay
3213423346%64%
1980
16th to endDay
2212212245%72%
2112
April1st to 15thDay
1112313345%70%
2012
16th to endDay
11111113480%
2171
May1st to 15thDay
11121333377%
2331
16th to endDay
11121222479%
2429
June1st to 15thDay
21221223477%
2340
16th to endDay
1111213346%72%
2340
July1st to 15thDay
43135%36%7%9%9%46%
2340
16th to endDay
7%426%6%47%8%8%10%33%
2467
August1st to 15thDay
6%3245%36%6%7%9%42%
2340
16th to endDay
4325%435%5%7%9%48%
2336
September1st to 15thDay
6%3135%45%6%7%6%49%
1980
16th to endDay
31122434470%
1860
October1st to 15thDay
2112312236%72%
1707
16th to endDay
22112335%75%
1760
November1st to 15thDay
112211346%74%
1759
16th to endDay
2212323335%69%
1665
December1st to 15thDay
4213422446%62%
1620
16th to endDay
431232447%7%58%
1728
January1st to 15thNight
333423445%65%
2327
16th to endNight
5%31342345%5%58%
2496
February1st to 15thNight
3312323345%65%
2206
16th to endNight
321332445%5%60%
1832
March1st to 15thNight
2213323345%66%
1980
16th to endNight
211223336%71%
2112
April1st to 15thNight
222323445%68%
1936
16th to endNight
1111122384%
1786
May1st to 15thNight
11112247%75%
1619
16th to endNight
212112382%
1684
June1st to 15thNight
1121222479%
1620
16th to endNight
112213335%73%
1620
July1st to 15thNight
33135%26%6%8%10%47%
1620
16th to endNight
44246%37%7%10%13%35%
1701
August1st to 15thNight
3212325%7%9%11%50%
1620
16th to endNight
2114435%5%8%10%51%
1860
September1st to 15thNight
33244245%5%8%54%
1980
16th to endNight
1212212335%73%
1869
October1st to 15thNight
11131233473%
1922
16th to endNight
121221223478%
2112
November1st to 15thNight
112222235%75%
2100
16th to endNight
411232334467%
2293
December1st to 15thNight
4212323347%62%
2340
16th to endNight
5%32442445%5%57%
2496

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
25%3311%31%24%
1612
16th to endDay
26%3216%27%23%
1728
February1st to 15thDay
22%3314%28%28%
1643
16th to endDay
24%4114%33%21%
1642
March1st to 15thDay
22%37%36%29%
1980
16th to endDay
17%2110%37%30%
2112
April1st to 15thDay
16%37%40%30%
2012
16th to endDay
11%119%30%45%
2171
May1st to 15thDay
13%218%30%43%
2331
16th to endDay
11%218%32%43%
2432
June1st to 15thDay
12%2424%55%
2340
16th to endDay
15%327%21%50%
2340
July1st to 15thDay
29%8%13%16%14%17%
2201
16th to endDay
40%9%18%21%8%1
2312
August1st to 15thDay
35%8%9%18%19%9%
2325
16th to endDay
31%7%11%17%21%11%
2336
September1st to 15thDay
33%5%7%19%18%15%
1980
16th to endDay
18%4110%35%29%
1860
October1st to 15thDay
16%3314%29%32%
1707
16th to endDay
12%339%31%39%
1760
November1st to 15thDay
13%2113%38%31%
1759
16th to endDay
19%3111%30%34%
1665
December1st to 15thDay
24%3318%31%19%
1620
16th to endDay
24%4420%32%12%
1728
January1st to 15thNight
22%4312%31%26%
2327
16th to endNight
28%3116%28%20%
2496
February1st to 15thNight
21%3315%26%29%
2217
16th to endNight
24%4214%33%20%
1832
March1st to 15thNight
20%3110%31%31%
1980
16th to endNight
17%3112%36%28%
2112
April1st to 15thNight
19%319%41%25%
1936
16th to endNight
8%210%33%44%
1786
May1st to 15thNight
10%3110%33%39%
1620
16th to endNight
10%119%28%48%
1685
June1st to 15thNight
11%215%20%59%
1620
16th to endNight
15%325%19%53%
1620
July1st to 15thNight
27%6%15%17%15%17%
1530
16th to endNight
35%8%21%22%8%2
1593
August1st to 15thNight
25%7%14%20%18%13%
1611
16th to endNight
26%6%14%18%21%13%
1860
September1st to 15thNight
27%6%8%22%20%15%
1980
16th to endNight
14%3213%36%29%
1869
October1st to 15thNight
15%2316%28%35%
1922
16th to endNight
12%2213%27%42%
2112
November1st to 15thNight
14%2114%35%31%
2100
16th to endNight
21%3312%23%36%
2293
December1st to 15thNight
23%2317%31%21%
2340
16th to endNight
28%35%18%28%15%
2496

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
8%12%31%40%6%1
90
16th to endDay
8%11%28%30%16%5%
96
February1st to 15thDay
8%10%25%39%13%1
158
16th to endDay
8%26%35%22%6%
238
March1st to 15thDay
8%24%32%18%13%2
270
16th to endDay
6%26%29%23%10%2
288
April1st to 15thDay
9%26%31%20%8%3
269
16th to endDay
7%26%38%19%5%1
270
May1st to 15thDay
6%19%43%17%11%2
288
16th to endDay
314%39%31%9%
330
June1st to 15thDay
49%40%29%12%3
315
16th to endDay
5%231%37%21%1
315
July1st to 15thDay
5%16%48%25%3
305
16th to endDay
9%13%38%26%11%
327
August1st to 15thDay
8%27%41%29%9%
315
16th to endDay
429%45%29%8%
332
September1st to 15thDay
9%319%43%18%6%
315
16th to endDay
5%8%27%39%15%4
272
October1st to 15thDay
6%10%30%32%16%4
147
16th to endDay
5%21%39%30%3
96
November1st to 15thDay
316%21%34%20%4
90
16th to endDay
217%33%33%13%
90
December1st to 15thDay
37%20%40%26%2
90
16th to endDay
7%19%27%37%7%1
96
January1st to 15thNight
5%317%44%24%4
720
16th to endNight
7%7%16%39%24%4
768
February1st to 15thNight
45%18%36%29%4
704
16th to endNight
5%9%23%40%19%2
632
March1st to 15thNight
5%9%21%35%22%5%
720
16th to endNight
36%19%36%27%5%
768
April1st to 15thNight
49%22%40%21%1
677
16th to endNight
29%23%38%22%3
540
May1st to 15thNight
26%20%39%27%3
540
16th to endNight
16%21%37%27%4
563
June1st to 15thNight
1213%44%33%3
540
16th to endNight
127%39%42%6%
540
July1st to 15thNight
4428%53%8%
510
16th to endNight
41319%54%16%
564
August1st to 15thNight
21216%60%17%
539
16th to endNight
2222%54%17%
581
September1st to 15thNight
5%27%24%46%13%
720
16th to endNight
2111%32%38%11%
675
October1st to 15thNight
1215%40%32%7%
660
16th to endNight
229%38%35%11%
704
November1st to 15thNight
1415%39%32%6%
700
16th to endNight
45%16%37%28%6%
720
December1st to 15thNight
7%5%16%35%30%4
720
16th to endNight
6%7%18%39%21%5%
768
Page generated at 2017-09-21 04:18:23. Version ac04

Copyright 2017 A. Danko


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