Fred's Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fred's Observatory clear sky chart from 2005-11-05 to 2017-10-31.

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
39%
15717
17%
47427
12%
15676
45%
15676
21%
32552

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
15%
720
11%
2327
5%
716
22%
716
9%
1870
January16th to endNight
18%
768
12%
2496
7%
768
26%
768
12%
1910
February1st to 15thNight
22%
701
11%
2261
5%
701
29%
701
13%
1691
February16th to endNight
17%
631
11%
1893
5%
631
23%
631
11%
1472
March1st to 15thNight
26%
720
16%
2031
9%
720
32%
720
18%
1475
March16th to endNight
28%
768
17%
2112
10%
768
34%
768
20%
1505
April1st to 15thNight
27%
668
14%
1878
6%
668
34%
668
22%
1299
April16th to endNight
35%
540
20%
1620
9%
540
43%
540
25%
1061
May1st to 15thNight
40%
540
13%
1620
8%
540
45%
540
19%
1156
May16th to endNight
55%
562
16%
1684
12%
561
59%
561
29%
1054
June1st to 15thNight
59%
540
16%
1620
12%
540
65%
540
33%
976
June16th to endNight
58%
540
16%
1620
12%
540
63%
540
31%
1005
July1st to 15thNight
58%
510
14%
1530
12%
510
60%
510
29%
981
July16th to endNight
71%
564
17%
1595
15%
531
73%
531
34%
954
August1st to 15thNight
70%
539
21%
1609
17%
536
73%
536
33%
973
August16th to endNight
71%
573
25%
1719
21%
573
72%
573
37%
987
September1st to 15thNight
63%
720
26%
1980
19%
720
66%
720
38%
1171
September16th to endNight
57%
717
27%
1980
22%
717
61%
717
33%
1243
October1st to 15thNight
50%
720
23%
2088
21%
720
54%
720
30%
1309
October16th to endNight
36%
768
23%
2312
17%
768
44%
768
23%
1553
November1st to 15thNight
43%
700
24%
2276
19%
700
50%
700
27%
1387
November16th to endNight
29%
720
14%
2340
11%
720
35%
720
15%
1683
December1st to 15thNight
20%
720
10%
2340
7%
720
26%
720
10%
1838
December16th to endNight
18%
768
9%
2496
4%
768
24%
768
9%
1999

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
16%8%36%5%3445%7%33%
48312
Night
15%8%35%5%3445%6%37%
47620
Cloud CoverDay
16%8%36%5%3445%7%33%
48322
Night
15%8%36%5%3445%6%36%
47624
TransparencyDay
49%6%11%19%11%1
48023
Night
46%6%11%20%13%1
47427
SeeingDay
19%9%23%21%16%8%
5563
Night
19%9%25%28%15%2
15721

By Month

Percentage Cloud Cover NE (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
22%14%6%10%6%34435%18%
1611
16th to endDay
17%16%6%11%5%43345%19%
1728
February1st to 15thDay
20%13%5%9%5%33335%25%
1600
16th to endDay
15%16%6%8%6%33336%26%
1580
March1st to 15thDay
21%11%5%6%5%34436%27%
1918
16th to endDay
21%9%36%5%24445%32%
2112
April1st to 15thDay
20%10%35%5%23345%34%
2080
16th to endDay
18%5%25%435%45%7%35%
2340
May1st to 15thDay
21%6%36%6%35%347%30%
2331
16th to endDay
13%326%5%445%6%9%37%
2431
June1st to 15thDay
11%5%25%435%5%7%9%38%
2340
16th to endDay
12%5%36%5%36%6%6%9%33%
2340
July1st to 15thDay
14%6%35%7%45%5%5%8%32%
2340
16th to endDay
10%425%5%47%6%7%9%36%
2465
August1st to 15thDay
8%426%6%45%7%8%9%36%
2340
16th to endDay
8%415%5%36%6%6%9%41%
2467
September1st to 15thDay
14%4245%3435%6%44%
1980
16th to endDay
17%6%25%423346%43%
1980
October1st to 15thDay
14%7%26%5%24447%40%
1871
16th to endDay
22%7%25%423245%39%
1908
November1st to 15thDay
12%7%35%42335%5%46%
1582
16th to endDay
21%12%45%433346%30%
1620
December1st to 15thDay
25%16%6%8%42334320%
1620
16th to endDay
22%17%6%8%5%24445%18%
1728
January1st to 15thNight
22%13%7%9%7%3433421%
2327
16th to endNight
17%14%5%8%6%3434426%
2496
February1st to 15thNight
19%11%46%6%3443429%
2259
16th to endNight
18%13%6%8%6%35%33425%
1893
March1st to 15thNight
18%9%36%425%45%6%32%
2019
16th to endNight
19%10%25%434347%35%
2112
April1st to 15thNight
16%7%26%42445%6%37%
1878
16th to endNight
13%6%25%6%3445%8%39%
1620
May1st to 15thNight
16%7%36%435%6%6%7%32%
1620
16th to endNight
9%5%25%425%6%6%8%42%
1682
June1st to 15thNight
6%3245%345%5%10%48%
1620
16th to endNight
10%4234345%6%9%44%
1620
July1st to 15thNight
8%5%35%5%245%6%7%45%
1620
16th to endNight
6%324425%6%7%10%45%
1703
August1st to 15thNight
5%325%5%36%5%6%10%46%
1620
16th to endNight
7%3234245%6%7%52%
1719
September1st to 15thNight
13%322313347%53%
1980
16th to endNight
13%424323446%49%
1980
October1st to 15thNight
12%5%25%43445%6%45%
2088
16th to endNight
19%5%25%4335%46%38%
2312
November1st to 15thNight
15%6%14423346%47%
2276
16th to endNight
20%10%36%435%45%5%30%
2340
December1st to 15thNight
24%12%6%7%5%23345%22%
2340
16th to endNight
22%15%6%7%5%33445%20%
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
22%15%6%10%5%44335%18%
1611
16th to endDay
17%16%7%10%5%4434419%
1728
February1st to 15thDay
19%13%6%9%5%33335%25%
1600
16th to endDay
15%15%6%9%5%33346%27%
1580
March1st to 15thDay
21%10%5%6%5%34436%27%
1929
16th to endDay
21%10%36%434345%32%
2111
April1st to 15thDay
19%10%36%5%23346%34%
2080
16th to endDay
17%5%25%435%45%7%35%
2340
May1st to 15thDay
21%7%37%5%35%35%7%29%
2331
16th to endDay
12%425%6%346%6%10%36%
2431
June1st to 15thDay
11%5%25%435%6%6%10%38%
2340
16th to endDay
12%5%36%5%35%6%7%9%32%
2340
July1st to 15thDay
13%7%36%6%46%5%5%8%32%
2340
16th to endDay
10%5%25%5%47%6%7%10%35%
2465
August1st to 15thDay
8%426%6%35%7%8%10%35%
2340
16th to endDay
8%416%436%6%7%9%41%
2467
September1st to 15thDay
14%5%146%2445%6%44%
1980
16th to endDay
16%6%25%433346%42%
1980
October1st to 15thDay
14%7%26%5%2445%6%40%
1871
16th to endDay
21%7%25%5%23245%39%
1908
November1st to 15thDay
11%7%35%42435%6%46%
1582
16th to endDay
21%11%45%424346%30%
1620
December1st to 15thDay
24%16%7%8%42434419%
1620
16th to endDay
21%18%5%9%5%24445%18%
1728
January1st to 15thNight
21%13%7%9%7%4433421%
2327
16th to endNight
17%14%6%8%6%34345%26%
2496
February1st to 15thNight
19%12%46%6%4344429%
2252
16th to endNight
18%13%6%9%5%35%43425%
1893
March1st to 15thNight
17%10%36%5%35%45%6%32%
2031
16th to endNight
19%9%35%424346%35%
2112
April1st to 15thNight
16%7%36%43445%7%36%
1878
16th to endNight
13%6%16%5%335%5%8%38%
1620
May1st to 15thNight
15%7%46%435%6%5%7%33%
1619
16th to endNight
8%5%34435%6%7%8%42%
1682
June1st to 15thNight
5%4245%25%5%5%10%48%
1620
16th to endNight
9%434335%5%6%9%44%
1620
July1st to 15thNight
8%5%35%5%25%5%6%7%44%
1620
16th to endNight
6%3244345%7%11%45%
1703
August1st to 15thNight
5%325%5%26%5%6%10%45%
1620
16th to endNight
6%3235%2446%8%51%
1719
September1st to 15thNight
13%323314347%52%
1980
16th to endNight
13%5%2442345%6%49%
1980
October1st to 15thNight
11%5%25%43445%6%45%
2088
16th to endNight
19%6%25%4335%47%38%
2312
November1st to 15thNight
15%6%14423345%47%
2276
16th to endNight
19%10%36%435%45%5%30%
2340
December1st to 15thNight
23%13%5%7%6%24345%22%
2340
16th to endNight
22%16%6%7%5%34445%20%
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
69%48%13%4
1612
16th to endDay
66%5%12%12%3
1728
February1st to 15thDay
62%411%13%7%
1602
16th to endDay
60%411%16%6%
1580
March1st to 15thDay
58%412%18%5%
1929
16th to endDay
54%5%10%21%7%
2112
April1st to 15thDay
51%5%10%19%11%2
2080
16th to endDay
46%6%10%18%12%5%
2340
May1st to 15thDay
53%6%12%17%9%1
2331
16th to endDay
40%10%13%21%12%1
2435
June1st to 15thDay
39%9%11%23%14%1
2340
16th to endDay
44%8%14%16%14%1
2340
July1st to 15thDay
48%7%10%18%13%1
2201
16th to endDay
39%10%15%21%12%
2310
August1st to 15thDay
38%10%13%23%12%1
2327
16th to endDay
35%8%14%23%13%4
2467
September1st to 15thDay
39%5%11%20%21%2
1980
16th to endDay
42%47%21%22%
1980
October1st to 15thDay
43%5%10%22%17%
1871
16th to endDay
47%311%24%11%1
1908
November1st to 15thDay
38%49%26%15%5%
1582
16th to endDay
54%5%11%18%9%
1620
December1st to 15thDay
68%410%11%5%
1620
16th to endDay
67%5%10%13%3
1728
January1st to 15thNight
67%39%12%6%
2327
16th to endNight
61%411%16%5%
2496
February1st to 15thNight
57%5%11%17%7%
2261
16th to endNight
62%5%9%16%6%
1893
March1st to 15thNight
51%6%10%22%7%1
2031
16th to endNight
50%5%10%22%10%1
2112
April1st to 15thNight
46%5%11%19%15%1
1878
16th to endNight
41%6%10%19%17%4
1620
May1st to 15thNight
47%8%12%19%9%1
1620
16th to endNight
35%8%16%22%14%3
1684
June1st to 15thNight
30%9%14%23%20%1
1620
16th to endNight
33%8%14%22%18%2
1620
July1st to 15thNight
36%9%11%19%20%3
1530
16th to endNight
29%9%16%26%15%2
1595
August1st to 15thNight
31%8%13%24%20%1
1609
16th to endNight
28%7%13%26%20%4
1719
September1st to 15thNight
30%5%12%21%24%5%
1980
16th to endNight
35%5%8%22%27%
1980
October1st to 15thNight
37%5%11%22%19%2
2088
16th to endNight
44%5%8%25%13%1
2312
November1st to 15thNight
38%410%22%18%4
2276
16th to endNight
53%5%11%18%10%1
2340
December1st to 15thNight
63%49%15%5%
2340
16th to endNight
65%5%10%13%4
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
31%23%33%6%41
90
16th to endDay
31%29%30%7%2
96
February1st to 15thDay
27%35%28%7%
90
16th to endDay
22%24%40%9%2
81
March1st to 15thDay
31%12%31%17%7%
219
16th to endDay
25%14%33%17%7%
288
April1st to 15thDay
26%12%27%20%11%1
270
16th to endDay
19%11%32%18%10%7%
270
May1st to 15thDay
28%14%23%17%10%6%
288
16th to endDay
16%7%27%24%13%9%
331
June1st to 15thDay
13%422%34%17%8%
315
16th to endDay
18%6%26%24%15%8%
315
July1st to 15thDay
19%322%19%22%11%
305
16th to endDay
12%212%25%26%21%
326
August1st to 15thDay
11%215%23%29%17%
313
16th to endDay
10%315%26%26%18%
332
September1st to 15thDay
16%414%20%28%15%
315
16th to endDay
18%414%17%29%14%
314
October1st to 15thDay
13%7%23%28%20%6%
315
16th to endDay
22%11%28%22%12%2
324
November1st to 15thDay
17%11%18%31%16%4
90
16th to endDay
27%23%34%7%6%
90
December1st to 15thDay
28%27%22%15%23
90
16th to endDay
33%28%30%8%
96
January1st to 15thNight
27%20%29%18%3
720
16th to endNight
24%17%34%21%2
768
February1st to 15thNight
26%15%30%25%1
704
16th to endNight
24%15%36%21%2
631
March1st to 15thNight
23%12%31%26%5%
720
16th to endNight
22%11%31%23%9%1
768
April1st to 15thNight
20%13%34%22%7%
668
16th to endNight
16%8%35%27%10%1
540
May1st to 15thNight
18%9%27%30%13%1
540
16th to endNight
11%423%32%24%3
563
June1st to 15thNight
8%124%42%21%1
540
16th to endNight
11%221%37%26%
540
July1st to 15thNight
12%117%35%28%4
510
16th to endNight
7%112%34%38%5%
564
August1st to 15thNight
6%111%38%35%5%
539
16th to endNight
8%211%34%35%7%
573
September1st to 15thNight
15%312%33%29%5%
720
16th to endNight
14%415%28%29%6%
717
October1st to 15thNight
15%5%23%31%21%3
720
16th to endNight
21%11%27%27%10%
768
November1st to 15thNight
18%9%24%29%15%1
700
16th to endNight
24%15%25%24%8%1
720
December1st to 15thNight
30%13%27%22%5%
720
16th to endNight
28%14%32%23%1
768
Page generated at 2017-11-01 17:23:34. Version ac04

Copyright 2017 A. Danko


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