Friendship Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Friendship 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
50%
17716
25%
53912
18%
17670
57%
17670
33%
31717

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
40%
1048
28%
2717
12%
1045
48%
1045
34%
1694
January16th to endNight
38%
1047
28%
2839
13%
1047
47%
1047
33%
1767
February1st to 15thNight
32%
824
25%
2466
12%
818
43%
818
27%
1516
February16th to endNight
23%
736
25%
2206
8%
736
37%
736
26%
1367
March1st to 15thNight
31%
641
26%
2321
14%
641
46%
641
23%
1402
March16th to endNight
34%
672
22%
2464
15%
672
44%
672
25%
1439
April1st to 15thNight
32%
629
23%
2307
14%
629
46%
629
25%
1344
April16th to endNight
30%
624
24%
2040
14%
624
45%
624
26%
1241
May1st to 15thNight
39%
629
23%
1890
18%
629
47%
629
27%
1188
May16th to endNight
49%
658
24%
1972
19%
657
60%
657
35%
1151
June1st to 15thNight
69%
612
25%
1836
25%
612
75%
612
52%
906
June16th to endNight
68%
585
20%
1755
21%
585
72%
585
37%
1022
July1st to 15thNight
78%
555
20%
1665
22%
555
81%
555
43%
906
July16th to endNight
82%
612
26%
1738
28%
579
85%
579
46%
903
August1st to 15thNight
89%
575
28%
1761
32%
572
90%
572
53%
832
August16th to endNight
78%
621
19%
2148
23%
621
79%
621
32%
1219
September1st to 15thNight
73%
585
19%
2145
22%
585
74%
585
28%
1247
September16th to endNight
70%
582
23%
2145
25%
582
71%
582
27%
1250
October1st to 15thNight
71%
602
32%
2162
32%
602
74%
602
37%
1115
October16th to endNight
59%
832
34%
2496
23%
832
65%
832
45%
1305
November1st to 15thNight
52%
827
26%
2467
18%
827
57%
827
32%
1497
November16th to endNight
47%
1050
30%
2730
15%
1050
54%
1050
37%
1649
December1st to 15thNight
40%
1050
28%
2730
15%
1050
47%
1050
31%
1787
December16th to endNight
36%
1120
22%
2912
10%
1120
42%
1120
28%
1970

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
13%5%245%2445%7%44%
54588
Night
12%423323347%51%
54114
Cloud CoverDay
13%5%2443445%7%45%
54586
Night
12%423323347%51%
54114
TransparencyDay
38%5%9%19%18%8%
54286
Night
33%5%11%20%18%10%
53919
SeeingDay
14%419%28%25%8%
7584
Night
14%5%24%35%17%1
17720

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
17%424422245%48%
1881
16th to endDay
16%423313336%51%
2100
February1st to 15thDay
19%6%24323335%46%
2050
16th to endDay
20%6%24313335%44%
1840
March1st to 15thDay
19%7%24324345%41%
2298
16th to endDay
16%6%24323346%46%
2464
April1st to 15thDay
15%6%23424446%43%
2301
16th to endDay
15%6%35%424445%43%
2519
May1st to 15thDay
16%7%36%6%2445%6%36%
2721
16th to endDay
14%6%25%6%35%5%5%7%36%
2846
June1st to 15thDay
5%3246%36%5%6%9%46%
2653
16th to endDay
10%5%36%6%46%7%7%8%34%
2535
July1st to 15thDay
8%325%5%47%5%6%9%40%
2535
16th to endDay
7%3245%36%5%6%9%45%
2674
August1st to 15thDay
22123245%6%9%58%
2439
16th to endDay
6%415%6%36%7%6%10%41%
2406
September1st to 15thDay
12%6%25%7%45%5%6%6%37%
2145
16th to endDay
10%5%26%6%35%45%7%41%
2145
October1st to 15thDay
10%5%245%24447%49%
2113
16th to endDay
10%313213235%61%
2080
November1st to 15thDay
12%7%35%5%24445%43%
2047
16th to endDay
13%5%23323235%54%
1890
December1st to 15thDay
18%6%24423346%43%
1890
16th to endDay
17%7%24424445%41%
2016
January1st to 15thNight
17%5%13213336%50%
2717
16th to endNight
16%5%23323345%50%
2839
February1st to 15thNight
18%6%2431223449%
2462
16th to endNight
16%6%24323336%46%
2206
March1st to 15thNight
17%6%24324336%45%
2321
16th to endNight
14%5%24323447%46%
2464
April1st to 15thNight
13%5%24323346%48%
2307
16th to endNight
15%5%34323346%46%
2040
May1st to 15thNight
13%5%25%424447%44%
1889
16th to endNight
9%4233245%6%11%47%
1971
June1st to 15thNight
31232335%10%63%
1836
16th to endNight
6%323325%45%10%52%
1755
July1st to 15thNight
5%2122145%5%13%54%
1755
16th to endNight
421341436%11%57%
1846
August1st to 15thNight
12121235%11%64%
1771
16th to endNight
6%314426%46%11%48%
2148
September1st to 15thNight
9%42343445%8%47%
2145
16th to endNight
9%5%25%5%345%5%7%46%
2145
October1st to 15thNight
9%313223347%57%
2162
16th to endNight
11%312212235%63%
2496
November1st to 15thNight
11%5%24423446%50%
2467
16th to endNight
12%5%13322235%55%
2730
December1st to 15thNight
16%5%2442324448%
2730
16th to endNight
19%7%2432333444%
2912

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%414422235%49%
1881
16th to endDay
15%5%23222246%51%
2100
February1st to 15thDay
19%5%24322325%47%
2050
16th to endDay
20%6%23313336%44%
1840
March1st to 15thDay
20%6%24323445%42%
2298
16th to endDay
16%5%24323346%46%
2462
April1st to 15thDay
15%7%24323446%43%
2301
16th to endDay
15%5%25%424445%44%
2519
May1st to 15thDay
18%6%26%5%34346%37%
2721
16th to endDay
16%5%35%5%35%5%47%37%
2846
June1st to 15thDay
5%3245%35%5%6%10%47%
2653
16th to endDay
11%5%35%6%45%6%7%8%35%
2535
July1st to 15thDay
8%3345%46%6%6%9%40%
2535
16th to endDay
8%323435%46%9%47%
2674
August1st to 15thDay
311332445%9%59%
2439
16th to endDay
7%4145%45%6%7%10%41%
2406
September1st to 15thDay
13%5%35%7%35%45%7%38%
2145
16th to endDay
11%5%25%6%4445%7%42%
2145
October1st to 15thDay
11%5%23433447%50%
2113
16th to endDay
11%213223335%61%
2080
November1st to 15thDay
14%6%25%423445%44%
2047
16th to endDay
14%42332233454%
1890
December1st to 15thDay
18%7%24323336%44%
1890
16th to endDay
18%6%2442444443%
2016
January1st to 15thNight
17%413213336%51%
2717
16th to endNight
17%414223335%50%
2839
February1st to 15thNight
19%6%23312335%49%
2462
16th to endNight
17%6%24323236%46%
2206
March1st to 15thNight
18%5%14323435%46%
2321
16th to endNight
14%434423446%47%
2464
April1st to 15thNight
13%5%24413445%49%
2307
16th to endNight
15%434324346%46%
2040
May1st to 15thNight
14%5%25%424446%45%
1889
16th to endNight
9%3233235%6%10%48%
1971
June1st to 15thNight
41222235%10%63%
1836
16th to endNight
7%31343446%9%52%
1755
July1st to 15thNight
5%21231446%12%55%
1755
16th to endNight
421332336%11%57%
1846
August1st to 15thNight
21121236%10%64%
1771
16th to endNight
7%2234345%6%12%48%
2148
September1st to 15thNight
10%42343445%8%47%
2145
16th to endNight
10%425%5%3446%6%47%
2145
October1st to 15thNight
10%412223436%58%
2162
16th to endNight
11%312212235%63%
2496
November1st to 15thNight
12%42432345%6%50%
2467
16th to endNight
13%5%13323235%55%
2730
December1st to 15thNight
16%6%24423335%48%
2730
16th to endNight
19%7%2442233444%
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
39%26%18%20%12%
1882
16th to endDay
35%35%15%25%14%
2100
February1st to 15thDay
41%37%13%19%14%
2051
16th to endDay
43%46%15%18%12%
1840
March1st to 15thDay
44%47%11%19%11%
2298
16th to endDay
39%48%17%20%9%
2464
April1st to 15thDay
41%5%7%15%18%11%
2301
16th to endDay
42%46%19%17%9%
2519
May1st to 15thDay
48%6%7%14%17%6%
2721
16th to endDay
45%6%10%18%16%3
2850
June1st to 15thDay
31%6%12%24%19%5%
2653
16th to endDay
43%8%10%19%14%2
2535
July1st to 15thDay
36%9%15%23%14%1
2396
16th to endDay
30%7%18%29%13%
2519
August1st to 15thDay
20%7%16%35%17%1
2425
16th to endDay
34%11%15%24%11%2
2406
September1st to 15thDay
44%8%10%17%14%5%
2145
16th to endDay
40%7%10%17%16%8%
2145
October1st to 15thDay
33%5%12%18%16%12%
2113
16th to endDay
26%36%15%28%20%
2080
November1st to 15thDay
40%5%9%18%16%9%
2047
16th to endDay
34%36%15%22%18%
1890
December1st to 15thDay
43%37%16%20%9%
1890
16th to endDay
43%49%14%18%9%
2016
January1st to 15thNight
35%36%17%19%17%
2717
16th to endNight
37%25%14%22%16%
2839
February1st to 15thNight
39%36%13%19%18%
2472
16th to endNight
40%36%15%18%14%
2206
March1st to 15thNight
40%48%13%18%13%
2321
16th to endNight
37%5%10%16%20%9%
2464
April1st to 15thNight
37%5%7%16%18%14%
2307
16th to endNight
38%5%9%18%16%11%
2040
May1st to 15thNight
39%410%20%16%7%
1890
16th to endNight
29%7%14%29%14%3
1973
June1st to 15thNight
17%5%16%29%27%4
1836
16th to endNight
27%8%16%28%15%2
1755
July1st to 15thNight
21%9%23%30%14%
1665
16th to endNight
19%7%24%36%10%
1738
August1st to 15thNight
14%7%23%36%16%1
1761
16th to endNight
27%10%21%26%10%3
2148
September1st to 15thNight
33%7%17%21%14%5%
2145
16th to endNight
34%8%14%19%15%8%
2145
October1st to 15thNight
27%5%13%23%18%12%
2162
16th to endNight
25%26%16%26%22%
2496
November1st to 15thNight
33%6%10%19%17%11%
2467
16th to endNight
32%36%16%21%19%
2730
December1st to 15thNight
40%37%18%19%10%
2730
16th to endNight
44%35%13%21%12%
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
17%8%32%27%12%1
180
16th to endDay
21%9%32%27%8%1
192
February1st to 15thDay
25%10%30%24%8%
180
16th to endDay
30%8%40%16%3
159
March1st to 15thDay
25%13%34%17%7%
180
16th to endDay
17%430%37%7%2
192
April1st to 15thDay
12%11%39%27%8%
180
16th to endDay
13%9%39%25%11%
411
May1st to 15thDay
19%7%32%30%10%
618
16th to endDay
16%5%24%33%17%2
677
June1st to 15thDay
7%10%44%31%6%
616
16th to endDay
10%18%36%32%10%
570
July1st to 15thDay
7%8%31%38%13%
550
16th to endDay
5%325%49%15%
595
August1st to 15thDay
4225%50%15%
502
16th to endDay
11%423%34%24%
318
September1st to 15thDay
11%5%14%41%27%
180
16th to endDay
15%5%18%38%22%
180
October1st to 15thDay
7%27%23%35%23%
180
16th to endDay
25%315%23%26%6%
192
November1st to 15thDay
25%422%30%13%3
180
16th to endDay
13%10%28%28%15%3
180
December1st to 15thDay
23%6%31%18%13%6%
180
16th to endDay
29%9%32%20%7%
192
January1st to 15thNight
20%8%26%32%11%
1050
16th to endNight
19%7%30%33%8%
1047
February1st to 15thNight
23%9%30%29%6%
824
16th to endNight
21%9%43%23%2
736
March1st to 15thNight
19%7%37%30%4
641
16th to endNight
14%9%38%33%3
672
April1st to 15thNight
16%8%39%31%3
629
16th to endNight
16%7%42%23%8%
624
May1st to 15thNight
17%7%32%33%8%
630
16th to endNight
10%332%37%15%
659
June1st to 15thNight
320%51%21%1
612
16th to endNight
6%117%49%21%3
585
July1st to 15thNight
5%9%48%32%3
555
16th to endNight
4450%35%3
612
August1st to 15thNight
2450%37%5%
575
16th to endNight
7%343%39%4
621
September1st to 15thNight
10%6%32%42%6%
585
16th to endNight
12%8%32%42%4
582
October1st to 15thNight
9%12%36%33%5%
602
16th to endNight
13%321%33%26%2
832
November1st to 15thNight
14%423%36%19%1
827
16th to endNight
16%6%25%34%15%1
1050
December1st to 15thNight
19%7%28%34%9%
1050
16th to endNight
23%7%28%31%8%
1120
Page generated at 2019-06-10 18:29:47. Version ac04

Copyright 2019 A. Danko


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