Cooke Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cooke 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
57%
15857
21%
47009
16%
15816
62%
15816
29%
29505

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
42%
718
20%
2327
13%
716
51%
716
24%
1469
January16th to endNight
41%
768
23%
2404
16%
768
50%
768
26%
1509
February1st to 15thNight
43%
701
24%
2103
16%
698
52%
698
32%
1259
February16th to endNight
39%
631
23%
1872
12%
631
50%
631
29%
1163
March1st to 15thNight
44%
720
29%
1980
15%
720
56%
720
37%
1169
March16th to endNight
49%
768
27%
2112
19%
768
55%
768
38%
1225
April1st to 15thNight
50%
718
24%
1976
15%
718
57%
718
42%
1111
April16th to endNight
56%
682
26%
1842
17%
682
63%
682
41%
1069
May1st to 15thNight
69%
539
24%
1619
18%
539
74%
539
42%
886
May16th to endNight
72%
561
25%
1682
20%
561
75%
561
38%
970
June1st to 15thNight
67%
540
13%
1620
12%
540
67%
540
25%
1100
June16th to endNight
74%
540
9%
1620
8%
540
75%
540
23%
1134
July1st to 15thNight
76%
510
7%
1530
7%
510
76%
510
20%
1112
July16th to endNight
76%
564
5%
1595
6%
531
77%
531
20%
1170
August1st to 15thNight
74%
539
5%
1663
5%
536
75%
536
21%
1168
August16th to endNight
68%
681
10%
2018
11%
681
68%
681
20%
1446
September1st to 15thNight
65%
720
8%
1980
7%
720
66%
720
18%
1459
September16th to endNight
63%
685
15%
1892
14%
685
64%
685
21%
1359
October1st to 15thNight
67%
660
27%
1845
25%
660
70%
660
35%
1130
October16th to endNight
57%
704
29%
2112
26%
704
64%
704
34%
1229
November1st to 15thNight
57%
700
31%
2101
25%
700
66%
700
38%
1165
November16th to endNight
49%
720
28%
2280
21%
720
60%
720
33%
1308
December1st to 15thNight
46%
720
26%
2340
21%
720
55%
720
29%
1393
December16th to endNight
49%
768
23%
2496
21%
768
55%
768
28%
1502

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
8%425%6%36%6%7%9%38%
47858
Night
7%425%5%35%5%6%9%44%
47218
TransparencyDay
39%10%13%16%13%5%
47559
Night
34%9%15%19%15%5%
47021
SeeingDay
9%415%23%25%21%
5719
Night
9%420%31%25%8%
15865

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
11%5%25%5%25%5%5%10%40%
1611
16th to endDay
10%425%435%447%46%
1818
February1st to 15thDay
13%5%25%423446%45%
1750
16th to endDay
7%5%25%5%2435%6%50%
1601
March1st to 15thDay
7%315%32445%8%51%
1980
16th to endDay
7%5%24425%5%5%7%49%
2111
April1st to 15thDay
6%3235%37%46%8%48%
1972
16th to endDay
5%315%4345%6%8%50%
2125
May1st to 15thDay
5%224435%5%5%9%52%
2331
16th to endDay
6%2246%37%6%7%9%42%
2431
June1st to 15thDay
10%6%26%6%47%7%7%10%29%
2340
16th to endDay
7%5%26%7%48%8%10%10%28%
2340
July1st to 15thDay
8%5%36%8%5%9%10%9%11%21%
2340
16th to endDay
6%5%38%9%5%9%9%10%10%19%
2465
August1st to 15thDay
8%5%27%8%5%9%10%10%11%20%
2283
16th to endDay
9%6%37%7%5%8%7%9%10%24%
2172
September1st to 15thDay
8%5%36%9%6%9%7%9%10%23%
1980
16th to endDay
9%6%48%8%5%6%7%7%9%26%
1881
October1st to 15thDay
7%5%36%5%36%5%6%6%43%
1785
16th to endDay
7%435%42445%8%48%
1760
November1st to 15thDay
6%425%423447%53%
1757
16th to endDay
7%5%345%245%5%8%46%
1677
December1st to 15thDay
10%6%245%25%6%6%7%43%
1620
16th to endDay
7%5%245%35%6%5%9%44%
1728
January1st to 15thNight
11%7%25%425%5%5%9%39%
2327
16th to endNight
13%5%25%4245%5%7%43%
2404
February1st to 15thNight
11%6%2432435%6%49%
2103
16th to endNight
8%6%36%424447%46%
1872
March1st to 15thNight
6%5%2432446%6%53%
1980
16th to endNight
7%42432435%8%54%
2112
April1st to 15thNight
5%41332246%10%53%
1976
16th to endNight
6%314424447%55%
1842
May1st to 15thNight
43133345%5%9%55%
1619
16th to endNight
43145%246%6%9%52%
1682
June1st to 15thNight
9%5%25%5%35%7%7%9%37%
1620
16th to endNight
6%425%6%47%6%8%12%34%
1620
July1st to 15thNight
4435%6%47%7%10%14%31%
1620
16th to endNight
3435%7%5%9%9%10%13%27%
1703
August1st to 15thNight
5%426%6%5%6%7%10%14%30%
1674
16th to endNight
8%435%6%37%7%8%11%33%
2018
September1st to 15thNight
8%436%7%47%7%8%11%30%
1980
16th to endNight
8%5%27%7%46%7%8%10%31%
1892
October1st to 15thNight
6%415%5%3446%9%48%
1845
16th to endNight
9%425%423447%50%
2112
November1st to 15thNight
6%32432445%8%53%
2101
16th to endNight
6%435%425%35%8%49%
2280
December1st to 15thNight
10%5%2443445%8%46%
2340
16th to endNight
8%5%25%435%46%9%43%
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%6%10%18%19%6%
1612
16th to endDay
36%5%7%16%24%9%
1818
February1st to 15thDay
39%5%6%13%18%16%
1752
16th to endDay
33%7%10%16%21%11%
1601
March1st to 15thDay
30%5%11%22%22%8%
1980
16th to endDay
33%6%10%19%19%9%
2112
April1st to 15thDay
32%7%11%17%22%7%
1972
16th to endDay
29%7%11%19%23%7%
2125
May1st to 15thDay
28%6%14%22%19%8%
2331
16th to endDay
34%10%15%20%15%3
2435
June1st to 15thDay
47%12%17%18%4
2340
16th to endDay
47%16%18%13%3
2340
July1st to 15thDay
51%18%19%9%1
2201
16th to endDay
51%18%19%9%2
2310
August1st to 15thDay
49%18%23%8%
2270
16th to endDay
49%17%18%13%1
2172
September1st to 15thDay
52%16%15%11%3
1980
16th to endDay
50%12%14%14%6%2
1881
October1st to 15thDay
39%8%9%15%16%10%
1785
16th to endDay
34%5%9%15%21%12%
1760
November1st to 15thDay
29%5%9%23%21%10%
1757
16th to endDay
34%5%10%17%18%12%
1677
December1st to 15thDay
37%7%11%19%16%6%
1620
16th to endDay
35%7%11%20%16%8%
1728
January1st to 15thNight
40%5%12%18%16%5%
2327
16th to endNight
39%5%9%14%21%8%
2404
February1st to 15thNight
34%48%16%21%13%
2112
16th to endNight
36%6%11%16%21%7%
1872
March1st to 15thNight
28%6%11%25%20%7%
1980
16th to endNight
28%6%11%25%19%9%
2112
April1st to 15thNight
25%6%16%23%22%5%
1976
16th to endNight
28%414%24%22%6%
1842
May1st to 15thNight
24%6%16%25%18%7%
1620
16th to endNight
26%9%16%25%18%2
1684
June1st to 15thNight
38%12%22%20%5%
1620
16th to endNight
38%14%23%18%3
1620
July1st to 15thNight
38%19%30%9%1
1530
16th to endNight
38%20%29%10%1
1595
August1st to 15thNight
36%18%33%10%
1663
16th to endNight
39%17%23%17%2
2018
September1st to 15thNight
42%17%23%12%4
1980
16th to endNight
42%13%17%16%6%2
1892
October1st to 15thNight
30%8%11%20%19%8%
1845
16th to endNight
32%48%17%26%10%
2112
November1st to 15thNight
27%5%10%23%23%8%
2101
16th to endNight
31%5%11%20%17%13%
2280
December1st to 15thNight
35%6%10%25%16%5%
2340
16th to endNight
34%7%12%21%14%8%
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
14%11%42%14%15%2
90
16th to endDay
13%19%37%21%6%1
96
February1st to 15thDay
7%25%27%24%11%3
90
16th to endDay
8%13%34%31%11%
102
March1st to 15thDay
7%10%32%32%12%2
270
16th to endDay
10%10%23%27%22%4
288
April1st to 15thDay
9%9%24%28%22%5%
270
16th to endDay
7%5%16%32%30%8%
270
May1st to 15thDay
6%5%18%32%21%15%
288
16th to endDay
6%29%22%30%27%
331
June1st to 15thDay
14%25%16%31%28%
315
16th to endDay
8%5%12%29%43%
315
July1st to 15thDay
5%39%26%54%
305
16th to endDay
10%6%13%27%42%
326
August1st to 15thDay
11%311%27%45%
313
16th to endDay
10%6%14%29%38%
332
September1st to 15thDay
13%15%17%32%30%
315
16th to endDay
10%8%20%35%25%
278
October1st to 15thDay
8%116%32%30%10%
255
16th to endDay
9%224%30%25%7%
272
November1st to 15thDay
5%322%33%26%8%
265
16th to endDay
6%436%31%17%3
147
December1st to 15thDay
10%7%46%27%6%1
90
16th to endDay
5%428%42%18%1
96
January1st to 15thNight
15%9%27%33%14%
720
16th to endNight
16%10%28%33%11%
768
February1st to 15thNight
13%8%32%32%13%
704
16th to endNight
11%8%34%35%8%
631
March1st to 15thNight
8%8%34%35%11%
720
16th to endNight
9%6%31%36%15%1
768
April1st to 15thNight
7%5%31%38%16%
718
16th to endNight
8%326%39%21%
682
May1st to 15thNight
6%217%41%28%3
540
16th to endNight
6%11%40%33%8%
563
June1st to 15thNight
12%17%23%42%12%
540
16th to endNight
8%416%43%26%
540
July1st to 15thNight
6%213%40%36%
510
16th to endNight
4411%48%30%
564
August1st to 15thNight
6%210%48%32%
539
16th to endNight
11%5%18%37%27%
681
September1st to 15thNight
10%17%24%39%18%
720
16th to endNight
11%10%26%42%8%
685
October1st to 15thNight
8%114%41%30%4
660
16th to endNight
10%421%33%26%2
704
November1st to 15thNight
7%325%40%19%3
700
16th to endNight
6%6%30%39%16%
720
December1st to 15thNight
10%6%30%33%17%
720
16th to endNight
10%6%26%34%19%1
768
Page generated at 2017-09-23 05:43:39. Version ac04

Copyright 2017 A. Danko


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