Pegasus Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pegasus Observatory clear sky chart from 2005-11-05 to 2019-06-10.

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
48%
17929
19%
53902
13%
17888
54%
17888
23%
35420

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
30%
840
19%
2717
11%
836
41%
836
16%
1824
January16th to endNight
29%
896
20%
2912
11%
896
41%
896
18%
1906
February1st to 15thNight
30%
822
20%
2549
11%
821
40%
821
20%
1660
February16th to endNight
24%
735
20%
2205
9%
735
35%
735
18%
1504
March1st to 15thNight
29%
840
20%
2349
11%
840
37%
840
20%
1601
March16th to endNight
33%
896
15%
2464
8%
896
38%
896
22%
1694
April1st to 15thNight
38%
832
20%
2297
11%
832
45%
832
27%
1462
April16th to endNight
48%
624
20%
1870
13%
624
55%
624
26%
1191
May1st to 15thNight
52%
630
15%
1890
9%
630
56%
630
25%
1237
May16th to endNight
63%
657
15%
1972
11%
657
65%
657
25%
1287
June1st to 15thNight
68%
612
12%
1836
10%
612
70%
612
27%
1196
June16th to endNight
74%
585
14%
1755
12%
585
75%
585
32%
1079
July1st to 15thNight
72%
555
11%
1665
10%
555
73%
555
24%
1162
July16th to endNight
72%
612
12%
1739
10%
579
73%
579
25%
1166
August1st to 15thNight
70%
575
13%
1715
13%
572
71%
572
23%
1186
August16th to endNight
70%
653
15%
1979
15%
653
70%
653
23%
1353
September1st to 15thNight
61%
780
16%
2145
14%
780
62%
780
21%
1524
September16th to endNight
59%
777
21%
2145
18%
777
60%
777
27%
1430
October1st to 15thNight
55%
780
26%
2232
22%
780
60%
780
29%
1394
October16th to endNight
50%
832
30%
2496
23%
832
60%
832
32%
1459
November1st to 15thNight
52%
820
26%
2598
22%
820
60%
820
28%
1573
November16th to endNight
45%
840
25%
2730
18%
840
55%
840
25%
1644
December1st to 15thNight
36%
840
19%
2730
14%
840
45%
840
18%
1830
December16th to endNight
32%
896
18%
2912
12%
896
41%
896
15%
2058

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%6%36%6%36%5%6%8%36%
54608
Night
9%6%35%5%35%5%6%8%40%
54099
TransparencyDay
43%8%13%18%13%3
54309
Night
39%8%13%19%15%3
53902
SeeingDay
17%11%19%21%18%11%
7732
Night
15%10%18%30%20%3
17933

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
10%6%36%5%46%6%5%7%36%
1881
16th to endDay
10%6%37%43445%7%41%
2016
February1st to 15thDay
11%6%36%5%246%6%6%38%
1969
16th to endDay
11%7%37%5%35%45%7%38%
1840
March1st to 15thDay
13%7%35%5%35%45%6%38%
2271
16th to endDay
11%8%46%5%35%5%5%7%36%
2463
April1st to 15thDay
10%5%345%35%5%5%9%41%
2321
16th to endDay
11%6%36%5%2445%7%41%
2695
May1st to 15thDay
9%6%36%7%35%6%5%9%35%
2721
16th to endDay
9%5%27%5%46%7%6%9%34%
2847
June1st to 15thDay
8%6%36%7%5%8%7%7%9%30%
2652
16th to endDay
6%425%7%48%8%8%10%32%
2535
July1st to 15thDay
10%7%37%8%5%8%7%7%10%24%
2535
16th to endDay
7%6%26%8%48%8%8%10%27%
2673
August1st to 15thDay
9%7%37%6%47%7%9%10%25%
2487
16th to endDay
10%6%37%7%5%8%7%7%10%27%
2560
September1st to 15thDay
11%7%47%7%5%6%6%7%7%30%
2145
16th to endDay
13%7%25%6%45%5%5%8%34%
2145
October1st to 15thDay
11%5%24424346%50%
2057
16th to endDay
10%5%3442333453%
2080
November1st to 15thDay
9%6%25%4235%5%6%49%
1919
16th to endDay
10%6%35%33335%6%47%
1890
December1st to 15thDay
11%6%37%6%36%5%5%6%37%
1890
16th to endDay
12%8%47%6%45%45%6%34%
2016
January1st to 15thNight
10%6%36%6%46%5%5%6%37%
2717
16th to endNight
11%7%37%5%4445%6%39%
2912
February1st to 15thNight
10%7%46%5%25%46%6%39%
2540
16th to endNight
11%7%35%6%45%5%5%6%36%
2205
March1st to 15thNight
11%7%46%425%6%6%6%38%
2349
16th to endNight
9%7%36%6%45%5%5%9%37%
2464
April1st to 15thNight
9%6%345%3445%8%45%
2297
16th to endNight
8%5%26%5%3445%7%45%
1870
May1st to 15thNight
9%435%6%345%7%9%40%
1889
16th to endNight
5%425%6%36%6%7%9%41%
1970
June1st to 15thNight
45%25%5%26%6%9%14%37%
1836
16th to endNight
5%424435%5%8%11%43%
1755
July1st to 15thNight
6%425%6%47%6%7%11%35%
1755
16th to endNight
5%426%6%46%6%8%11%37%
1847
August1st to 15thNight
7%425%6%36%7%8%11%37%
1726
16th to endNight
6%5%25%6%46%7%8%9%36%
1979
September1st to 15thNight
8%6%36%7%46%6%6%8%37%
2145
16th to endNight
11%6%25%5%2435%5%45%
2145
October1st to 15thNight
10%5%244245%6%7%47%
2232
16th to endNight
8%5%25%42344454%
2496
November1st to 15thNight
10%6%243235%5%6%48%
2598
16th to endNight
9%6%25%4245%5%6%47%
2730
December1st to 15thNight
11%8%36%6%35%6%6%6%36%
2730
16th to endNight
12%9%47%6%36%46%7%30%
2912

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
42%8%11%17%15%4
1882
16th to endDay
39%6%9%21%17%4
2016
February1st to 15thDay
43%7%11%18%17%2
1971
16th to endDay
44%6%12%19%15%2
1840
March1st to 15thDay
45%5%9%18%16%5%
2271
16th to endDay
45%7%12%19%13%1
2464
April1st to 15thDay
38%6%13%23%15%3
2321
16th to endDay
42%5%10%21%15%4
2695
May1st to 15thDay
44%9%14%19%11%1
2721
16th to endDay
43%10%14%19%10%1
2851
June1st to 15thDay
46%11%20%15%6%
2652
16th to endDay
42%10%15%17%12%1
2535
July1st to 15thDay
51%10%15%13%7%
2396
16th to endDay
44%12%19%14%7%1
2518
August1st to 15thDay
49%11%16%14%6%1
2474
16th to endDay
47%12%15%16%6%1
2560
September1st to 15thDay
48%9%13%14%9%3
2145
16th to endDay
45%7%13%16%15%2
2145
October1st to 15thDay
35%5%12%19%21%4
2057
16th to endDay
33%46%23%23%8%
2080
November1st to 15thDay
34%5%8%19%24%7%
1919
16th to endDay
36%48%21%22%5%
1890
December1st to 15thDay
45%5%10%18%15%3
1890
16th to endDay
49%5%11%16%13%3
2016
January1st to 15thNight
43%9%9%16%17%3
2717
16th to endNight
44%5%8%18%19%3
2912
February1st to 15thNight
42%5%11%21%15%3
2549
16th to endNight
45%6%11%19%14%2
2205
March1st to 15thNight
43%7%11%16%16%4
2349
16th to endNight
43%7%13%21%12%1
2464
April1st to 15thNight
36%6%14%24%16%2
2297
16th to endNight
37%6%13%20%17%3
1870
May1st to 15thNight
39%8%16%23%10%1
1890
16th to endNight
36%12%17%23%9%1
1972
June1st to 15thNight
34%12%24%20%6%
1836
16th to endNight
31%9%24%20%12%1
1755
July1st to 15thNight
39%13%18%18%8%1
1665
16th to endNight
36%13%23%17%8%1
1739
August1st to 15thNight
35%16%19%15%11%
1715
16th to endNight
39%12%18%21%6%1
1979
September1st to 15thNight
43%12%13%17%10%2
2145
16th to endNight
40%7%12%19%18%1
2145
October1st to 15thNight
35%6%13%21%19%3
2232
16th to endNight
32%5%6%22%25%6%
2496
November1st to 15thNight
35%6%8%19%23%7%
2598
16th to endNight
36%5%8%22%21%5%
2730
December1st to 15thNight
44%8%12%16%15%3
2730
16th to endNight
50%6%10%16%13%2
2912

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
27%21%33%14%21
180
16th to endDay
26%31%25%11%4
192
February1st to 15thDay
25%28%27%14%3
180
16th to endDay
34%28%27%8%1
159
March1st to 15thDay
26%21%24%20%5%
351
16th to endDay
20%19%27%22%8%1
416
April1st to 15thDay
19%15%25%23%12%3
390
16th to endDay
17%10%25%21%19%5%
379
May1st to 15thDay
15%15%18%24%17%9%
408
16th to endDay
15%5%20%24%18%16%
459
June1st to 15thDay
12%418%25%23%17%
411
16th to endDay
8%5%19%20%24%22%
375
July1st to 15thDay
10%14%20%27%26%
365
16th to endDay
7%110%24%29%26%
390
August1st to 15thDay
16%210%24%19%26%
358
16th to endDay
10%9%22%26%30%
396
September1st to 15thDay
13%48%22%30%20%
375
16th to endDay
15%115%26%28%12%
374
October1st to 15thDay
16%7%16%23%25%10%
375
16th to endDay
17%14%15%29%17%5%
400
November1st to 15thDay
20%10%27%24%12%3
247
16th to endDay
13%21%30%17%14%2
180
December1st to 15thDay
26%22%32%13%3
180
16th to endDay
28%21%32%13%3
192
January1st to 15thNight
23%17%24%28%6%
840
16th to endNight
21%16%26%30%4
896
February1st to 15thNight
21%16%26%30%4
824
16th to endNight
20%23%29%24%2
735
March1st to 15thNight
19%18%29%28%4
840
16th to endNight
16%15%28%27%11%
896
April1st to 15thNight
17%16%24%30%10%
832
16th to endNight
14%11%19%37%15%1
624
May1st to 15thNight
13%5%20%34%23%2
630
16th to endNight
9%213%34%35%6%
659
June1st to 15thNight
6%112%34%33%11%
612
16th to endNight
5%18%29%43%11%
585
July1st to 15thNight
7%15%28%46%10%
555
16th to endNight
7%1223%48%15%
612
August1st to 15thNight
8%6%29%44%9%
575
16th to endNight
10%326%47%11%
653
September1st to 15thNight
10%39%28%39%7%
780
16th to endNight
15%312%29%33%5%
777
October1st to 15thNight
13%8%16%29%24%6%
780
16th to endNight
13%12%19%33%18%2
832
November1st to 15thNight
16%8%16%36%19%2
820
16th to endNight
17%13%20%32%14%
840
December1st to 15thNight
19%15%22%33%8%
840
16th to endNight
22%15%24%31%5%
896
Page generated at 2019-06-10 19:29:46. Version ac04

Copyright 2019 A. Danko


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