Cossatot Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cossatot Observatory clear sky chart from 2005-11-05 to 2017-10-06.

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
43%
15704
26%
47087
16%
15658
52%
15658
31%
28011

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
27%
898
28%
2327
9%
895
41%
895
29%
1457
January16th to endNight
25%
960
30%
2496
9%
960
38%
960
29%
1564
February1st to 15thNight
25%
880
21%
2285
5%
875
34%
875
27%
1480
February16th to endNight
22%
558
27%
1820
10%
558
38%
558
25%
1076
March1st to 15thNight
26%
540
22%
1980
12%
540
38%
540
21%
1230
March16th to endNight
28%
576
20%
2112
13%
576
39%
576
21%
1310
April1st to 15thNight
27%
539
24%
1863
12%
539
44%
539
25%
1069
April16th to endNight
35%
540
24%
1800
17%
540
49%
540
28%
1049
May1st to 15thNight
36%
540
21%
1662
13%
540
48%
540
25%
1062
May16th to endNight
47%
563
22%
1684
18%
561
55%
561
31%
1044
June1st to 15thNight
63%
540
22%
1620
21%
540
68%
540
40%
903
June16th to endNight
70%
540
25%
1620
24%
540
74%
540
43%
869
July1st to 15thNight
72%
510
19%
1530
18%
510
75%
510
38%
862
July16th to endNight
81%
564
26%
1594
31%
531
83%
531
44%
854
August1st to 15thNight
82%
539
26%
1610
30%
536
83%
536
47%
841
August16th to endNight
70%
573
23%
1893
29%
573
71%
573
31%
1114
September1st to 15thNight
67%
540
25%
1852
26%
540
69%
540
32%
1037
September16th to endNight
66%
537
34%
1980
34%
537
72%
537
35%
1019
October1st to 15thNight
50%
684
29%
2052
19%
684
56%
684
34%
1198
October16th to endNight
44%
704
35%
2112
19%
704
56%
704
40%
1127
November1st to 15thNight
42%
700
30%
2100
17%
700
54%
700
33%
1190
November16th to endNight
33%
819
30%
2259
14%
819
45%
819
27%
1427
December1st to 15thNight
29%
900
24%
2340
9%
900
39%
900
27%
1559
December16th to endNight
27%
960
24%
2496
10%
960
37%
960
25%
1670

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
15%5%24424446%42%
48104
Night
13%424323346%50%
47286
TransparencyDay
41%5%9%20%17%4
47804
Night
34%49%22%22%7%
47091
SeeingDay
15%6%22%28%21%5%
5743
Night
16%9%26%28%17%2
15706

By Month

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
17%7%1332233449%
1611
16th to endDay
18%5%2432332448%
1728
February1st to 15thDay
20%5%23323235%45%
1575
16th to endDay
22%7%35%322235%41%
1661
March1st to 15thDay
22%6%15%32333442%
1980
16th to endDay
22%7%35%5%24435%37%
2110
April1st to 15thDay
20%5%34414336%43%
2085
16th to endDay
21%6%25%5%24445%38%
2160
May1st to 15thDay
19%7%345%34346%36%
2286
16th to endDay
14%6%35%6%45%5%5%7%34%
2430
June1st to 15thDay
10%6%36%435%45%8%40%
2340
16th to endDay
7%5%25%5%46%6%6%7%41%
2340
July1st to 15thDay
10%5%35%7%46%6%7%10%32%
2340
16th to endDay
7%3245%47%6%7%10%40%
2466
August1st to 15thDay
6%2146%45%7%7%11%41%
2340
16th to endDay
10%5%25%5%47%6%8%7%35%
2308
September1st to 15thDay
13%6%245%24447%43%
2106
16th to endDay
9%32343445%6%52%
1968
October1st to 15thDay
16%6%24423335%48%
1706
16th to endDay
15%313212235%57%
1760
November1st to 15thDay
16%413313346%51%
1758
16th to endDay
20%6%2331222450%
1698
December1st to 15thDay
19%7%24312445%44%
1620
16th to endDay
22%9%3221332443%
1728
January1st to 15thNight
16%6%13213245%52%
2327
16th to endNight
15%5%33313235%52%
2496
February1st to 15thNight
16%5%24313335%48%
2278
16th to endNight
16%5%24322345%49%
1820
March1st to 15thNight
20%5%25%423336%42%
1980
16th to endNight
16%6%345%23346%44%
2112
April1st to 15thNight
14%42442345%5%49%
1863
16th to endNight
13%5%24322346%50%
1800
May1st to 15thNight
14%5%25%424446%44%
1661
16th to endNight
10%43442445%9%45%
1683
June1st to 15thNight
6%424323348%56%
1620
16th to endNight
6%21331446%8%57%
1620
July1st to 15thNight
5%314425%5%8%12%46%
1620
16th to endNight
411332447%12%53%
1702
August1st to 15thNight
32123245%8%11%55%
1620
16th to endNight
7%4145%35%5%7%10%44%
1893
September1st to 15thNight
9%41442335%8%51%
1852
16th to endNight
8%314324446%57%
1980
October1st to 15thNight
13%424313346%52%
2052
16th to endNight
12%31321123462%
2112
November1st to 15thNight
11%423323245%56%
2100
16th to endNight
19%6%2331322450%
2259
December1st to 15thNight
20%6%2432235%5%45%
2340
16th to endNight
19%6%24413335%44%
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
39%36%23%20%6%
1612
16th to endDay
41%3422%23%5%
1728
February1st to 15thDay
43%37%21%18%5%
1576
16th to endDay
48%25%17%19%6%
1661
March1st to 15thDay
45%38%18%18%6%
1980
16th to endDay
51%47%19%14%2
2112
April1st to 15thDay
43%38%21%17%5%
2085
16th to endDay
47%47%18%18%3
2160
May1st to 15thDay
48%5%8%15%17%3
2286
16th to endDay
46%7%11%20%13%
2434
June1st to 15thDay
40%6%11%24%15%1
2340
16th to endDay
38%6%12%22%17%1
2340
July1st to 15thDay
42%8%14%23%11%
2201
16th to endDay
35%9%15%25%13%
2311
August1st to 15thDay
33%9%13%26%16%1
2326
16th to endDay
43%8%14%20%10%3
2308
September1st to 15thDay
41%5%10%17%15%8%
2106
16th to endDay
31%5%10%23%21%7%
1968
October1st to 15thDay
39%37%16%21%11%
1706
16th to endDay
31%26%18%27%12%
1760
November1st to 15thDay
34%37%22%23%7%
1758
16th to endDay
40%2319%25%8%
1698
December1st to 15thDay
43%38%20%18%5%
1620
16th to endDay
46%25%21%18%4
1728
January1st to 15thNight
36%36%19%29%5%
2327
16th to endNight
37%25%21%26%7%
2496
February1st to 15thNight
39%38%22%19%7%
2288
16th to endNight
36%36%24%20%7%
1820
March1st to 15thNight
44%37%16%19%8%
1980
16th to endNight
42%48%20%20%3
2112
April1st to 15thNight
36%39%19%20%9%
1863
16th to endNight
36%48%21%25%4
1800
May1st to 15thNight
40%5%8%19%17%7%
1662
16th to endNight
35%6%16%25%14%1
1685
June1st to 15thNight
28%410%31%21%3
1620
16th to endNight
24%5%11%27%26%3
1620
July1st to 15thNight
26%7%18%29%16%1
1530
16th to endNight
21%8%16%33%18%
1594
August1st to 15thNight
20%6%18%31%20%3
1610
16th to endNight
33%7%13%25%17%3
1893
September1st to 15thNight
30%6%10%20%22%9%
1852
16th to endNight
28%47%24%25%9%
1980
October1st to 15thNight
33%48%18%20%14%
2052
16th to endNight
27%35%18%30%14%
2112
November1st to 15thNight
31%37%22%24%11%
2100
16th to endNight
39%2417%27%8%
2259
December1st to 15thNight
42%38%17%20%7%
2340
16th to endNight
43%36%20%18%7%
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
22%17%37%21%1
90
16th to endDay
19%30%33%11%5%
96
February1st to 15thDay
21%21%44%10%3
90
16th to endDay
34%20%30%12%1
81
March1st to 15thDay
36%12%40%10%1
90
16th to endDay
18%23%33%21%2
96
April1st to 15thDay
28%16%26%18%8%1
204
16th to endDay
31%12%25%17%10%2
270
May1st to 15thDay
18%12%34%22%9%
423
16th to endDay
18%7%32%26%11%3
517
June1st to 15thDay
13%317%37%22%5%
495
16th to endDay
7%225%33%24%7%
495
July1st to 15thDay
9%118%34%29%6%
475
16th to endDay
4431%43%15%
515
August1st to 15thDay
8%19%36%34%9%
493
16th to endDay
16%16%32%31%10%
348
September1st to 15thDay
9%110%32%39%6%
261
16th to endDay
5%216%44%25%4
135
October1st to 15thDay
8%5%36%30%14%4
107
16th to endDay
19%334%32%8%2
96
November1st to 15thDay
16%15%22%32%10%3
90
16th to endDay
36%13%28%14%42
90
December1st to 15thDay
20%17%37%17%42
90
16th to endDay
31%21%36%6%4
96
January1st to 15thNight
22%16%31%24%4
900
16th to endNight
19%17%36%23%3
960
February1st to 15thNight
21%18%32%23%3
880
16th to endNight
21%15%38%19%4
558
March1st to 15thNight
23%11%35%24%5%
540
16th to endNight
19%11%36%23%6%1
576
April1st to 15thNight
15%15%38%22%7%
539
16th to endNight
16%11%33%26%10%1
540
May1st to 15thNight
17%7%32%29%11%1
540
16th to endNight
11%5%31%30%19%2
563
June1st to 15thNight
7%117%41%27%2
540
16th to endNight
6%15%34%37%4
540
July1st to 15thNight
6%12%37%39%4
510
16th to endNight
35%29%50%10%
564
August1st to 15thNight
5%5%35%43%10%
539
16th to endNight
9%9%32%40%6%
573
September1st to 15thNight
10%112%36%34%4
540
16th to endNight
9%115%34%35%4
537
October1st to 15thNight
15%424%32%19%3
684
16th to endNight
14%9%29%26%18%1
704
November1st to 15thNight
14%11%28%32%12%1
700
16th to endNight
24%13%26%24%10%
819
December1st to 15thNight
26%10%30%25%6%
900
16th to endNight
24%13%31%24%6%
960
Page generated at 2017-10-07 13:07:51. Version ac04

Copyright 2017 A. Danko


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