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 2017-09-21.

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
51%
15431
26%
46992
18%
15385
58%
15385
34%
27304

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%
898
26%
2327
11%
895
47%
895
34%
1456
January16th to endNight
38%
897
29%
2433
14%
897
48%
897
33%
1503
February1st to 15thNight
35%
704
28%
2106
13%
698
47%
698
31%
1236
February16th to endNight
25%
632
28%
1894
9%
632
41%
632
30%
1111
March1st to 15thNight
34%
549
27%
1989
14%
549
49%
549
24%
1171
March16th to endNight
34%
576
23%
2112
16%
576
45%
576
25%
1220
April1st to 15thNight
31%
539
22%
1977
13%
539
46%
539
24%
1156
April16th to endNight
29%
540
25%
1769
13%
540
44%
540
25%
1095
May1st to 15thNight
37%
539
22%
1620
16%
539
46%
539
28%
1006
May16th to endNight
49%
562
25%
1684
21%
561
58%
561
33%
1003
June1st to 15thNight
69%
540
23%
1620
24%
540
74%
540
51%
806
June16th to endNight
68%
540
21%
1620
22%
540
73%
540
37%
941
July1st to 15thNight
78%
510
21%
1530
23%
510
81%
510
44%
832
July16th to endNight
82%
564
25%
1594
28%
531
85%
531
45%
843
August1st to 15thNight
89%
539
29%
1651
33%
536
90%
536
53%
779
August16th to endNight
76%
573
19%
1982
24%
573
77%
573
30%
1155
September1st to 15thNight
75%
540
20%
1980
24%
540
76%
540
32%
1101
September16th to endNight
71%
510
25%
1881
26%
510
73%
510
29%
1051
October1st to 15thNight
70%
509
33%
1829
33%
509
73%
509
38%
927
October16th to endNight
61%
704
35%
2112
24%
704
67%
704
48%
1069
November1st to 15thNight
52%
706
27%
2106
18%
706
58%
706
35%
1238
November16th to endNight
46%
900
29%
2340
15%
900
54%
900
37%
1410
December1st to 15thNight
41%
900
27%
2340
15%
900
47%
900
31%
1540
December16th to endNight
38%
960
24%
2496
11%
960
45%
960
29%
1655

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
12%5%2442445%7%45%
47860
Night
11%423323347%52%
47194
Cloud CoverDay
13%5%2442445%7%45%
47858
Night
12%423323347%52%
47194
TransparencyDay
37%5%10%18%18%9%
47558
Night
32%5%11%20%18%11%
46999
SeeingDay
12%317%29%28%8%
5396
Night
14%5%24%36%18%1
15435

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%324422235%49%
1611
16th to endDay
16%422313335%52%
1800
February1st to 15thDay
16%5%23313335%50%
1750
16th to endDay
17%6%13313335%49%
1580
March1st to 15thDay
20%7%23324245%43%
1970
16th to endDay
17%5%24313246%47%
2112
April1st to 15thDay
16%7%23424446%43%
1971
16th to endDay
15%6%35%424435%43%
2187
May1st to 15thDay
16%7%36%5%2445%6%36%
2331
16th to endDay
16%7%25%6%345%5%7%34%
2430
June1st to 15thDay
5%3246%36%46%10%45%
2340
16th to endDay
9%5%36%6%46%6%7%8%34%
2340
July1st to 15thDay
8%335%5%47%6%6%9%39%
2340
16th to endDay
7%3245%36%5%7%10%42%
2466
August1st to 15thDay
22123245%6%9%59%
2296
16th to endDay
7%415%6%36%7%6%10%38%
2220
September1st to 15thDay
10%5%25%6%45%5%6%6%40%
1980
16th to endDay
8%5%25%5%35%45%7%44%
1871
October1st to 15thDay
10%5%24423346%51%
1788
16th to endDay
8%213212346%63%
1760
November1st to 15thDay
11%7%345%24445%45%
1749
16th to endDay
15%5%2332322454%
1620
December1st to 15thDay
18%7%24313346%44%
1620
16th to endDay
15%6%25%424445%43%
1728
January1st to 15thNight
17%5%13313336%50%
2327
16th to endNight
17%42331334451%
2433
February1st to 15thNight
16%6%1321223453%
2102
16th to endNight
14%6%14323336%51%
1894
March1st to 15thNight
17%5%23324335%48%
1989
16th to endNight
15%5%24323446%48%
2112
April1st to 15thNight
14%5%25%323346%48%
1977
16th to endNight
16%5%34423346%45%
1769
May1st to 15thNight
13%5%25%414447%45%
1619
16th to endNight
10%4233245%7%10%46%
1683
June1st to 15thNight
41232335%9%63%
1620
16th to endNight
6%223325%5%5%10%52%
1620
July1st to 15thNight
5%21231445%12%54%
1620
16th to endNight
421341436%12%55%
1702
August1st to 15thNight
11121236%11%64%
1661
16th to endNight
7%314426%5%6%11%46%
1982
September1st to 15thNight
7%42343445%9%50%
1980
16th to endNight
8%4244335%5%7%48%
1881
October1st to 15thNight
10%313223346%59%
1829
16th to endNight
9%312212225%65%
2112
November1st to 15thNight
10%414423446%52%
2106
16th to endNight
14%5%1331223456%
2340
December1st to 15thNight
15%6%2442434447%
2340
16th to endNight
17%7%24323335%46%
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
17%414322235%50%
1611
16th to endDay
15%5%23223245%52%
1800
February1st to 15thDay
16%5%23312325%51%
1750
16th to endDay
18%6%23213335%49%
1580
March1st to 15thDay
21%6%24313335%44%
1970
16th to endDay
17%5%24313346%47%
2110
April1st to 15thDay
15%7%24324446%43%
1971
16th to endDay
16%5%35%424445%44%
2187
May1st to 15thDay
18%7%25%5%2435%6%37%
2331
16th to endDay
18%5%35%5%35%5%47%35%
2430
June1st to 15thDay
6%425%5%35%46%10%46%
2340
16th to endDay
11%5%35%6%45%6%7%8%35%
2340
July1st to 15thDay
9%3345%46%6%6%8%40%
2340
16th to endDay
9%3245%46%47%9%43%
2466
August1st to 15thDay
311332446%9%60%
2296
16th to endDay
8%425%5%46%6%7%10%39%
2220
September1st to 15thDay
11%5%35%6%35%45%8%40%
1980
16th to endDay
10%415%5%4445%7%45%
1871
October1st to 15thDay
11%423433347%51%
1788
16th to endDay
8%213212335%64%
1760
November1st to 15thDay
12%6%25%423445%46%
1749
16th to endDay
15%5%1332222455%
1620
December1st to 15thDay
18%7%24313336%44%
1620
16th to endDay
15%7%34424445%44%
1728
January1st to 15thNight
17%5%13323237%50%
2327
16th to endNight
17%413323335%51%
2433
February1st to 15thNight
16%5%2331223454%
2102
16th to endNight
14%5%23323236%51%
1894
March1st to 15thNight
17%5%14323335%49%
1989
16th to endNight
15%433313446%48%
2112
April1st to 15thNight
14%6%24413445%49%
1977
16th to endNight
17%434324345%45%
1769
May1st to 15thNight
13%5%25%41445%7%46%
1619
16th to endNight
11%4233235%6%9%47%
1683
June1st to 15thNight
41222235%10%63%
1620
16th to endNight
6%31333446%10%52%
1620
July1st to 15thNight
5%21231346%12%55%
1620
16th to endNight
5%21332337%11%55%
1702
August1st to 15thNight
21121236%10%65%
1661
16th to endNight
8%2235%345%6%11%46%
1982
September1st to 15thNight
8%41343445%8%50%
1980
16th to endNight
8%42442346%6%50%
1881
October1st to 15thNight
10%412213336%59%
1829
16th to endNight
9%312212235%65%
2112
November1st to 15thNight
11%41432345%6%53%
2106
16th to endNight
14%5%13312235%56%
2340
December1st to 15thNight
15%6%24424335%48%
2340
16th to endNight
17%6%24422335%47%
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
38%26%18%21%12%
1612
16th to endDay
34%35%15%25%15%
1800
February1st to 15thDay
37%37%14%21%16%
1751
16th to endDay
39%35%17%20%13%
1580
March1st to 15thDay
43%47%11%21%12%
1970
16th to endDay
39%47%16%21%10%
2112
April1st to 15thDay
41%5%7%14%17%12%
1971
16th to endDay
42%36%19%16%11%
2187
May1st to 15thDay
47%5%7%14%17%7%
2331
16th to endDay
47%5%10%16%15%3
2434
June1st to 15thDay
33%6%12%22%20%5%
2340
16th to endDay
44%8%10%19%14%2
2340
July1st to 15thDay
37%9%14%24%13%1
2201
16th to endDay
32%7%19%28%11%
2311
August1st to 15thDay
19%7%17%36%17%1
2282
16th to endDay
36%11%15%23%10%2
2220
September1st to 15thDay
40%8%10%18%15%5%
1980
16th to endDay
37%6%10%17%18%9%
1871
October1st to 15thDay
32%5%10%18%17%14%
1788
16th to endDay
23%36%16%29%20%
1760
November1st to 15thDay
38%5%8%18%17%10%
1749
16th to endDay
36%36%11%21%20%
1620
December1st to 15thDay
42%38%17%19%9%
1620
16th to endDay
41%49%15%17%10%
1728
January1st to 15thNight
36%36%17%19%17%
2327
16th to endNight
36%25%15%22%17%
2433
February1st to 15thNight
35%35%13%21%20%
2112
16th to endNight
35%36%16%20%16%
1894
March1st to 15thNight
39%48%12%20%14%
1989
16th to endNight
36%5%10%15%21%11%
2112
April1st to 15thNight
38%47%15%18%15%
1977
16th to endNight
40%5%9%17%15%11%
1769
May1st to 15thNight
38%411%19%16%9%
1620
16th to endNight
31%8%15%25%15%3
1685
June1st to 15thNight
18%5%15%28%28%4
1620
16th to endNight
27%8%17%27%15%2
1620
July1st to 15thNight
21%8%22%32%13%
1530
16th to endNight
20%8%26%34%9%
1594
August1st to 15thNight
13%7%23%37%16%1
1651
16th to endNight
29%10%20%26%9%3
1982
September1st to 15thNight
30%7%17%22%15%6%
1980
16th to endNight
31%8%15%19%16%9%
1881
October1st to 15thNight
26%411%23%19%14%
1829
16th to endNight
23%26%17%27%22%
2112
November1st to 15thNight
31%5%10%19%19%13%
2106
16th to endNight
32%37%13%20%22%
2340
December1st to 15thNight
40%37%17%19%10%
2340
16th to endNight
41%36%13%21%13%
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
16%6%35%30%10%1
90
16th to endDay
16%11%37%22%9%2
96
February1st to 15thDay
10%10%37%30%11%1
90
16th to endDay
20%9%44%19%4
81
March1st to 15thDay
30%10%30%15%13%1
90
16th to endDay
15%429%38%8%4
96
April1st to 15thDay
14%11%31%34%8%
90
16th to endDay
13%9%42%22%11%
297
May1st to 15thDay
17%7%36%28%8%
468
16th to endDay
21%5%23%32%16%1
517
June1st to 15thDay
8%10%43%31%7%
495
16th to endDay
10%19%34%33%10%
495
July1st to 15thDay
7%10%34%37%9%
475
16th to endDay
5%327%48%14%
515
August1st to 15thDay
5%223%51%16%
449
16th to endDay
13%15%27%30%20%
260
September1st to 15thDay
3215%51%25%
135
16th to endDay
8%115%41%32%
105
October1st to 15thDay
4426%47%16%
90
16th to endDay
20%18%27%37%5%
96
November1st to 15thDay
22%424%32%10%6%
90
16th to endDay
22%8%25%30%11%2
90
December1st to 15thDay
23%324%21%16%11%
90
16th to endDay
21%10%37%23%5%1
96
January1st to 15thNight
20%8%27%32%10%
900
16th to endNight
19%7%31%33%7%
897
February1st to 15thNight
20%10%30%31%6%
704
16th to endNight
18%9%44%25%2
632
March1st to 15thNight
18%8%34%32%5%
549
16th to endNight
15%10%37%32%3
576
April1st to 15thNight
17%8%39%32%2
539
16th to endNight
18%6%42%22%8%
540
May1st to 15thNight
17%8%33%32%7%
540
16th to endNight
12%330%37%16%
563
June1st to 15thNight
320%50%22%1
540
16th to endNight
5%117%48%23%3
540
July1st to 15thNight
6%10%49%31%2
510
16th to endNight
45%49%35%4
564
August1st to 15thNight
2349%38%5%
539
16th to endNight
8%341%41%4
573
September1st to 15thNight
8%7%34%42%5%
540
16th to endNight
10%8%32%44%4
510
October1st to 15thNight
10%113%38%30%5%
509
16th to endNight
10%321%33%27%2
704
November1st to 15thNight
13%424%35%20%1
706
16th to endNight
17%6%25%34%14%1
900
December1st to 15thNight
18%7%28%34%9%1
900
16th to endNight
21%7%28%32%9%
960
Page generated at 2017-09-22 06:35:33. Version ac04

Copyright 2017 A. Danko


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