Cat's Eye Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cat's Eye 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
47%
15494
27%
47173
17%
15447
57%
15447
35%
26667

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
34%
899
28%
2327
11%
895
45%
895
36%
1437
January16th to endNight
32%
843
33%
2379
12%
843
48%
843
35%
1390
February1st to 15thNight
33%
704
28%
2107
12%
698
46%
698
32%
1187
February16th to endNight
21%
632
30%
1894
8%
632
39%
632
32%
1063
March1st to 15thNight
30%
596
28%
2036
13%
596
47%
596
28%
1160
March16th to endNight
29%
576
26%
2112
15%
576
45%
576
29%
1148
April1st to 15thNight
24%
539
24%
1964
9%
539
44%
539
29%
1089
April16th to endNight
26%
540
27%
1746
14%
540
44%
540
29%
1041
May1st to 15thNight
30%
539
23%
1620
14%
539
43%
539
30%
971
May16th to endNight
43%
562
24%
1684
17%
561
56%
561
33%
1007
June1st to 15thNight
64%
540
22%
1620
20%
540
72%
540
50%
801
June16th to endNight
66%
540
23%
1620
24%
540
70%
540
41%
900
July1st to 15thNight
74%
510
21%
1530
22%
510
78%
510
40%
853
July16th to endNight
82%
564
26%
1594
30%
531
85%
531
47%
822
August1st to 15thNight
89%
539
28%
1733
34%
536
89%
536
51%
807
August16th to endNight
73%
573
21%
1934
25%
573
75%
573
31%
1124
September1st to 15thNight
77%
540
20%
1980
25%
540
78%
540
32%
1114
September16th to endNight
67%
537
24%
1980
25%
537
70%
537
28%
1165
October1st to 15thNight
65%
513
33%
1881
31%
513
71%
513
39%
924
October16th to endNight
54%
676
36%
2084
22%
676
63%
676
46%
1045
November1st to 15thNight
49%
772
30%
2172
15%
772
56%
772
41%
1215
November16th to endNight
44%
900
31%
2340
14%
900
53%
900
40%
1376
December1st to 15thNight
38%
900
30%
2340
14%
900
46%
900
34%
1459
December16th to endNight
35%
960
25%
2496
11%
960
43%
960
33%
1569

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
10%424424447%48%
48012
Night
8%424323347%54%
47374
Cloud CoverDay
10%5%24424447%48%
48010
Night
8%5%24323347%54%
47374
TransparencyDay
35%5%10%19%19%9%
47710
Night
29%5%11%20%20%12%
47179
SeeingDay
11%5%22%33%21%5%
5443
Night
10%7%30%35%14%1
15497

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
13%5%24312335%52%
1611
16th to endDay
12%422322335%55%
1854
February1st to 15thDay
12%423423346%54%
1750
16th to endDay
11%5%23314346%53%
1580
March1st to 15thDay
15%5%24323336%49%
1923
16th to endDay
12%5%24413335%51%
2112
April1st to 15thDay
12%425%323446%48%
1980
16th to endDay
11%5%35%5%24346%48%
2212
May1st to 15thDay
14%5%26%435%5%5%6%39%
2331
16th to endDay
16%5%35%5%25%5%5%6%39%
2430
June1st to 15thDay
4215%5%35%45%9%52%
2340
16th to endDay
8%425%5%35%6%7%9%40%
2340
July1st to 15thDay
7%436%5%35%5%5%8%41%
2340
16th to endDay
7%3245%45%5%5%10%45%
2466
August1st to 15thDay
1114435%5%5%9%56%
2214
16th to endDay
8%425%5%46%6%6%9%37%
2266
September1st to 15thDay
9%5%36%5%35%5%5%7%41%
1980
16th to endDay
12%325%5%35%46%6%43%
1980
October1st to 15thDay
8%425%5%23346%53%
1876
16th to endDay
7%313222335%64%
1776
November1st to 15thDay
11%425%424446%48%
1683
16th to endDay
10%424323225%57%
1620
December1st to 15thDay
15%8%24322236%48%
1620
16th to endDay
11%7%25%413346%48%
1728
January1st to 15thNight
14%5%23213335%52%
2327
16th to endNight
11%423323345%54%
2379
February1st to 15thNight
10%5%2432233357%
2102
16th to endNight
9%424323346%54%
1894
March1st to 15thNight
12%5%24423346%50%
2036
16th to endNight
8%5%34323437%53%
2112
April1st to 15thNight
8%5%25%424445%52%
1964
16th to endNight
9%5%24424447%50%
1746
May1st to 15thNight
11%5%34424447%49%
1619
16th to endNight
10%5%2332345%9%49%
1683
June1st to 15thNight
211221335%9%63%
1620
16th to endNight
5%2133245%6%9%55%
1620
July1st to 15thNight
42243345%5%11%52%
1620
16th to endNight
32142135%6%11%56%
1702
August1st to 15thNight
11221345%9%65%
1743
16th to endNight
6%4145%345%6%10%46%
1934
September1st to 15thNight
7%413435%46%8%50%
1980
16th to endNight
8%5%25%425%45%8%47%
1980
October1st to 15thNight
7%312323337%60%
1881
16th to endNight
7%21331223465%
2084
November1st to 15thNight
9%413322345%59%
2172
16th to endNight
10%413322236%58%
2340
December1st to 15thNight
12%6%24322346%51%
2340
16th to endNight
10%6%35%413336%50%
2496

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
12%6%24413235%52%
1611
16th to endDay
12%423422335%55%
1854
February1st to 15thDay
11%424423336%54%
1750
16th to endDay
11%5%23324336%52%
1580
March1st to 15thDay
15%6%14323236%49%
1923
16th to endDay
12%6%24423336%51%
2110
April1st to 15thDay
12%5%25%323446%48%
1980
16th to endDay
10%6%35%5%24346%48%
2212
May1st to 15thDay
14%6%35%435%45%6%39%
2331
16th to endDay
15%6%35%435%45%6%39%
2430
June1st to 15thDay
4225%5%3445%9%51%
2340
16th to endDay
8%4346%46%6%7%9%39%
2340
July1st to 15thDay
7%435%6%346%5%9%41%
2340
16th to endDay
7%324445%5%5%10%45%
2466
August1st to 15thDay
11134345%5%10%56%
2214
16th to endDay
8%425%6%47%7%6%9%37%
2266
September1st to 15thDay
9%6%37%6%345%5%6%41%
1980
16th to endDay
11%425%6%35%46%7%42%
1980
October1st to 15thDay
8%5%25%5%23346%53%
1876
16th to endDay
7%313222335%64%
1776
November1st to 15thDay
11%5%24424347%48%
1683
16th to endDay
10%5%24313225%57%
1620
December1st to 15thDay
15%8%24312235%48%
1620
16th to endDay
11%7%35%413346%48%
1728
January1st to 15thNight
13%6%23213335%52%
2327
16th to endNight
11%413323345%54%
2379
February1st to 15thNight
10%5%25%42333357%
2102
16th to endNight
9%424323346%54%
1894
March1st to 15thNight
12%5%24423346%50%
2036
16th to endNight
8%6%24323347%53%
2112
April1st to 15thNight
7%6%2442335%5%52%
1964
16th to endNight
9%6%24424447%50%
1746
May1st to 15thNight
10%5%34423447%49%
1619
16th to endNight
8%6%23323448%49%
1683
June1st to 15thNight
12321445%9%64%
1620
16th to endNight
5%31332446%9%55%
1620
July1st to 15thNight
43234345%5%11%52%
1620
16th to endNight
321321347%11%56%
1702
August1st to 15thNight
11132145%5%9%65%
1743
16th to endNight
5%4145%25%5%6%10%46%
1934
September1st to 15thNight
7%414426%46%8%49%
1980
16th to endNight
7%6%25%425%35%8%47%
1980
October1st to 15thNight
7%412323247%60%
1881
16th to endNight
6%313313235%65%
2084
November1st to 15thNight
8%5%13322245%59%
2172
16th to endNight
9%424313235%58%
2340
December1st to 15thNight
12%7%24322346%51%
2340
16th to endNight
10%7%34423336%50%
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
35%36%18%22%14%
1612
16th to endDay
31%36%13%26%17%
1854
February1st to 15thDay
31%37%15%22%19%
1751
16th to endDay
33%25%18%23%15%
1580
March1st to 15thDay
37%38%14%20%15%
1923
16th to endDay
36%47%17%22%11%
2112
April1st to 15thDay
37%49%14%19%15%
1980
16th to endDay
38%46%19%18%12%
2212
May1st to 15thDay
44%6%9%13%19%7%
2331
16th to endDay
44%6%9%16%18%4
2434
June1st to 15thDay
29%6%13%22%22%5%
2340
16th to endDay
39%8%11%19%16%4
2340
July1st to 15thDay
36%8%14%25%13%2
2201
16th to endDay
29%9%19%28%12%1
2311
August1st to 15thDay
23%5%15%36%17%1
2200
16th to endDay
39%9%14%23%9%2
2266
September1st to 15thDay
41%7%9%19%17%4
1980
16th to endDay
38%7%11%16%17%8%
1980
October1st to 15thDay
32%410%18%22%11%
1876
16th to endDay
22%45%16%30%20%
1776
November1st to 15thDay
36%48%18%20%11%
1683
16th to endDay
32%35%13%20%23%
1620
December1st to 15thDay
39%36%15%24%10%
1620
16th to endDay
37%38%15%23%11%
1728
January1st to 15thNight
34%35%17%20%19%
2327
16th to endNight
32%3415%24%19%
2379
February1st to 15thNight
31%37%11%22%23%
2112
16th to endNight
31%35%16%24%17%
1894
March1st to 15thNight
35%37%13%22%16%
2036
16th to endNight
32%410%18%20%13%
2112
April1st to 15thNight
34%39%17%17%18%
1964
16th to endNight
35%5%9%17%19%13%
1746
May1st to 15thNight
34%5%11%20%17%10%
1620
16th to endNight
33%6%14%25%16%4
1685
June1st to 15thNight
17%6%15%29%26%4
1620
16th to endNight
25%7%15%29%17%4
1620
July1st to 15thNight
24%8%18%32%14%1
1530
16th to endNight
18%8%25%31%14%1
1594
August1st to 15thNight
15%7%19%37%19%1
1733
16th to endNight
30%9%21%25%10%2
1934
September1st to 15thNight
30%7%14%23%17%5%
1980
16th to endNight
34%7%13%18%17%8%
1980
October1st to 15thNight
25%413%25%19%12%
1881
16th to endNight
22%36%17%28%21%
2084
November1st to 15thNight
27%37%24%22%13%
2172
16th to endNight
29%37%14%20%24%
2340
December1st to 15thNight
34%37%17%23%13%
2340
16th to endNight
36%37%15%21%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
18%10%38%24%7%
90
16th to endDay
15%11%46%20%5%
96
February1st to 15thDay
10%17%35%26%8%1
90
16th to endDay
14%8%50%20%4
81
March1st to 15thDay
20%12%38%20%8%
90
16th to endDay
13%7%39%28%11%
96
April1st to 15thDay
14%16%46%19%4
99
16th to endDay
13%17%41%22%6%
322
May1st to 15thDay
17%11%41%23%5%1
468
16th to endDay
21%8%31%27%10%
517
June1st to 15thDay
4120%48%23%2
495
16th to endDay
9%214%42%25%5%
495
July1st to 15thDay
5%213%44%28%6%
475
16th to endDay
5%15%41%35%10%
515
August1st to 15thDay
3339%39%13%
369
16th to endDay
13%8%33%29%13%
306
September1st to 15thDay
3426%43%21%
135
16th to endDay
17%225%42%12%
135
October1st to 15thDay
218%39%33%14%
107
16th to endDay
14%6%18%32%28%
96
November1st to 15thDay
35%6%26%16%8%5%
90
16th to endDay
25%14%27%21%7%3
90
December1st to 15thDay
24%225%32%10%5%
90
16th to endDay
20%17%38%21%1
96
January1st to 15thNight
16%10%35%29%7%
900
16th to endNight
13%9%40%28%7%
843
February1st to 15thNight
13%14%36%29%5%
704
16th to endNight
12%13%50%21%1
632
March1st to 15thNight
15%10%40%29%4
596
16th to endNight
9%13%46%26%3
576
April1st to 15thNight
9%12%52%22%2
539
16th to endNight
9%12%49%22%5%
540
May1st to 15thNight
11%11%45%27%4
540
16th to endNight
12%5%34%33%12%
563
June1st to 15thNight
2128%50%17%
540
16th to endNight
4221%48%21%1
540
July1st to 15thNight
412%53%26%1
510
16th to endNight
36%57%28%3
564
August1st to 15thNight
1348%40%5%
539
16th to endNight
6%17%45%35%3
573
September1st to 15thNight
9%6%43%34%5%
540
16th to endNight
10%112%42%31%2
537
October1st to 15thNight
8%219%41%25%2
513
16th to endNight
8%6%28%35%20%1
676
November1st to 15thNight
10%6%29%35%16%1
772
16th to endNight
11%8%32%34%11%1
900
December1st to 15thNight
17%9%32%32%7%
900
16th to endNight
14%11%35%31%6%
960
Page generated at 2017-10-07 13:07:51. Version ac04

Copyright 2017 A. Danko


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