The Friedman Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Friedman Observatory clear sky chart from 2005-11-06 to 2024-02-25.

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
30%
23240
15%
80508
8%
23141
38%
23141
16%
55427

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 10thNight
12%
755
15%
4372
4%
737
25%
737
6%
2893
January11th to 20thNight
18%
760
12%
4324
5%
740
28%
740
6%
3133
January21st to endNight
14%
832
9%
4514
5%
814
26%
814
6%
3516
February1st to 10thNight
15%
760
14%
2470
6%
760
26%
760
13%
1746
February11th to 20thNight
9%
743
13%
2331
2%
740
23%
740
11%
1694
February21st to endNight
14%
611
17%
1831
6%
611
27%
611
13%
1338
March1st to 10thNight
17%
720
17%
2117
7%
720
29%
720
16%
1478
March11th to 20thNight
18%
720
18%
1980
5%
720
31%
720
18%
1397
March21st to endNight
18%
792
18%
2082
5%
792
29%
792
17%
1474
April1st to 10thNight
17%
720
13%
1800
3%
720
24%
720
17%
1345
April11th to 20thNight
25%
711
16%
1775
5%
711
31%
711
23%
1258
April21st to endNight
26%
720
16%
1800
5%
720
31%
720
22%
1271
May1st to 10thNight
31%
495
15%
1575
9%
495
36%
495
17%
1123
May11th to 20thNight
33%
354
19%
1416
12%
354
47%
354
16%
912
May21st to endNight
44%
388
14%
1551
14%
388
49%
388
17%
989
June1st to 10thNight
46%
360
17%
1440
17%
360
56%
360
21%
880
June11th to 20thNight
45%
360
14%
1440
13%
360
53%
360
20%
883
June21st to endNight
51%
360
15%
1440
17%
360
59%
360
25%
837
July1st to 10thNight
55%
350
14%
1400
17%
350
60%
350
22%
863
July11th to 20thNight
59%
348
16%
1392
19%
348
63%
348
22%
822
July21st to endNight
52%
433
15%
1523
15%
409
56%
409
23%
923
August1st to 10thNight
59%
537
15%
1600
12%
534
61%
534
27%
1024
August11th to 20thNight
56%
618
14%
1682
9%
618
58%
618
26%
1153
August21st to endNight
53%
792
18%
1980
9%
792
55%
792
30%
1340
September1st to 10thNight
47%
720
18%
1800
8%
720
52%
720
28%
1234
September11th to 20thNight
49%
720
27%
1800
16%
720
54%
720
34%
1159
September21st to endNight
44%
720
23%
2029
17%
720
50%
720
27%
1335
October1st to 10thNight
41%
720
16%
2160
13%
720
46%
720
23%
1432
October11th to 20thNight
34%
720
17%
2160
10%
720
44%
720
22%
1426
October21st to endNight
25%
792
17%
2424
10%
792
35%
792
18%
1708
November1st to 10thNight
30%
740
20%
2407
11%
740
42%
740
23%
1503
November11th to 20thNight
23%
760
18%
2505
10%
760
35%
760
16%
1685
November21st to endNight
22%
760
16%
2660
7%
760
35%
760
16%
1792
December1st to 10thNight
16%
760
11%
2660
5%
760
25%
760
10%
1966
December11th to 20thNight
19%
760
12%
3230
5%
759
29%
759
9%
2315
December21st to endNight
15%
829
8%
4838
4%
817
26%
817
6%
3580

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%47%6%45%5%5%7%34%
78381
Night
16%8%37%6%35%5%5%7%36%
80909
TransparencyDay
49%8%12%19%11%1
78089
Night
47%8%13%20%11%1
80735
SeeingDay
23%19%28%18%9%3
13821
Night
21%16%29%24%9%1
23257

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 10thDay
13%14%6%8%7%4444432%
2517
11th to 20thDay
13%14%7%13%8%44445%23%
2584
21st to endDay
18%15%6%9%8%35%345%23%
3124
February1st to 10thDay
16%11%5%8%7%46%5%7%5%27%
1710
11th to 20thDay
13%10%6%7%7%45%36%7%32%
1735
21st to endDay
19%10%39%6%446%46%29%
1520
March1st to 10thDay
13%9%5%8%8%3445%7%33%
1837
11th to 20thDay
15%9%47%7%4446%6%33%
1980
21st to endDay
19%10%37%6%34446%34%
2272
April1st to 10thDay
16%10%5%6%6%45%45%6%34%
2160
11th to 20thDay
18%8%36%5%35%5%5%6%37%
2134
21st to endDay
17%6%37%6%35%46%7%36%
2160
May1st to 10thDay
20%7%36%6%35%45%7%33%
2400
11th to 20thDay
19%6%36%6%45%5%5%7%33%
2478
21st to endDay
16%6%26%5%35%5%5%8%39%
2725
June1st to 10thDay
16%5%27%7%36%6%6%9%34%
2520
11th to 20thDay
14%6%36%6%46%6%6%8%35%
2520
21st to endDay
13%5%35%5%35%6%7%9%38%
2520
July1st to 10thDay
10%5%37%7%47%6%7%9%35%
2520
11th to 20thDay
9%5%26%5%446%7%10%41%
2520
21st to endDay
11%6%27%6%47%7%6%8%36%
2702
August1st to 10thDay
11%6%35%7%5%8%6%8%8%35%
2327
11th to 20thDay
14%7%26%8%46%6%5%8%34%
2201
21st to endDay
15%6%36%6%45%5%6%9%36%
2376
September1st to 10thDay
17%5%35%5%35%5%5%7%40%
2160
11th to 20thDay
13%6%25%5%345%5%6%46%
2160
21st to endDay
18%7%36%5%35%45%7%38%
1927
October1st to 10thDay
18%6%26%5%245%6%8%38%
1800
11th to 20thDay
18%7%35%6%35%5%5%7%37%
1800
21st to endDay
22%9%26%6%445%5%7%31%
1931
November1st to 10thDay
13%8%46%5%2345%6%44%
1671
11th to 20thDay
16%10%37%6%34447%37%
1672
21st to endDay
17%10%45%6%45%45%8%33%
1520
December1st to 10thDay
18%13%6%6%6%45%45%5%28%
1520
11th to 20thDay
22%11%5%7%43445%5%31%
1906
21st to endDay
20%15%6%9%7%5%5%44421%
2772
January1st to 10thNight
15%10%49%7%35%45%6%32%
4429
11th to 20thNight
15%10%5%13%7%35%5%5%6%27%
4372
21st to endNight
21%12%5%9%8%445%45%23%
4532
February1st to 10thNight
15%10%47%6%35%45%6%34%
2470
11th to 20thNight
14%9%48%8%36%6%5%6%31%
2329
21st to endNight
16%10%48%7%45%445%33%
1831
March1st to 10thNight
15%8%47%5%45%5%6%8%35%
2107
11th to 20thNight
15%8%46%445%5%5%6%38%
1979
21st to endNight
16%8%36%7%445%5%6%37%
2082
April1st to 10thNight
15%11%47%6%45%5%6%5%33%
1800
11th to 20thNight
16%6%35%5%345%5%8%40%
1775
21st to endNight
19%7%26%5%3445%5%41%
1800
May1st to 10thNight
19%8%38%5%44445%35%
1575
11th to 20thNight
17%5%26%436%5%6%7%39%
1415
21st to endNight
13%5%36%6%35%5%6%7%41%
1550
June1st to 10thNight
15%435%5%3446%10%40%
1440
11th to 20thNight
13%5%36%5%35%7%6%9%39%
1440
21st to endNight
13%4244335%7%10%45%
1440
July1st to 10thNight
10%6%26%5%35%5%7%9%42%
1440
11th to 20thNight
9%5%35%5%45%6%7%11%40%
1440
21st to endNight
12%6%15%6%445%7%9%42%
1613
August1st to 10thNight
10%6%25%5%36%5%8%9%42%
1611
11th to 20thNight
13%6%35%5%46%5%7%8%38%
1682
21st to endNight
13%425%5%345%5%7%44%
1980
September1st to 10thNight
16%6%24435%5%6%7%42%
1800
11th to 20thNight
13%5%35%42446%7%49%
1800
21st to endNight
17%6%25%43335%7%43%
2029
October1st to 10thNight
21%6%24334446%43%
2160
11th to 20thNight
17%7%35%43445%6%43%
2160
21st to endNight
22%7%35%5%35%5%5%6%34%
2424
November1st to 10thNight
11%7%36%5%3445%6%46%
2407
11th to 20thNight
18%8%35%5%35%446%38%
2505
21st to endNight
14%8%36%5%35%5%6%7%38%
2660
December1st to 10thNight
18%10%5%7%5%45%5%6%6%28%
2660
11th to 20thNight
19%11%37%7%35%447%31%
3288
21st to endNight
21%13%48%7%34446%26%
4884

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 10thDay
54%7%13%20%5%1
2518
11th to 20thDay
64%6%10%14%5%1
2584
21st to endDay
62%7%9%16%5%1
3124
February1st to 10thDay
57%6%12%15%9%1
1710
11th to 20thDay
52%6%11%21%9%1
1744
21st to endDay
55%5%11%19%7%2
1520
March1st to 10thDay
51%6%12%20%9%2
1840
11th to 20thDay
51%6%11%20%11%2
1980
21st to endDay
53%6%9%17%14%3
2272
April1st to 10thDay
51%6%10%19%11%3
2160
11th to 20thDay
47%7%11%20%13%2
2134
21st to endDay
45%8%10%21%13%4
2160
May1st to 10thDay
51%7%10%18%11%3
2400
11th to 20thDay
49%8%10%19%12%2
2482
21st to endDay
43%9%15%19%12%2
2725
June1st to 10thDay
45%10%13%19%12%1
2520
11th to 20thDay
45%9%14%20%11%1
2520
21st to endDay
39%10%15%25%11%
2520
July1st to 10thDay
42%11%14%20%13%1
2450
11th to 20thDay
35%10%18%23%13%1
2445
21st to endDay
42%10%14%20%14%1
2551
August1st to 10thDay
42%12%14%20%11%
2314
11th to 20thDay
46%9%15%20%10%
2201
21st to endDay
42%8%12%21%13%2
2376
September1st to 10thDay
44%8%12%21%14%2
2160
11th to 20thDay
38%6%12%22%21%2
2160
21st to endDay
45%7%11%20%16%2
1927
October1st to 10thDay
43%8%14%21%13%2
1800
11th to 20thDay
45%8%11%25%11%
1800
21st to endDay
53%6%13%17%9%2
1931
November1st to 10thDay
41%6%14%22%15%2
1671
11th to 20thDay
48%6%12%19%12%2
1672
21st to endDay
50%8%14%21%7%1
1520
December1st to 10thDay
58%7%14%13%7%1
1520
11th to 20thDay
56%6%15%17%5%
1906
21st to endDay
66%8%9%13%4
2772
January1st to 10thNight
51%8%15%19%6%1
4429
11th to 20thNight
58%7%12%16%6%1
4372
21st to endNight
61%9%9%15%6%
4532
February1st to 10thNight
51%7%13%20%8%1
2470
11th to 20thNight
54%7%11%18%9%1
2331
21st to endNight
54%5%10%18%11%2
1831
March1st to 10thNight
47%7%14%21%9%2
2117
11th to 20thNight
46%7%13%21%11%2
1980
21st to endNight
47%6%12%15%16%3
2082
April1st to 10thNight
52%6%12%18%11%2
1800
11th to 20thNight
43%9%11%21%16%1
1775
21st to endNight
45%6%11%21%14%3
1800
May1st to 10thNight
52%6%10%20%10%3
1575
11th to 20thNight
43%9%11%20%14%2
1416
21st to endNight
41%11%15%18%12%2
1551
June1st to 10thNight
39%8%11%26%14%
1440
11th to 20thNight
39%10%16%23%11%1
1440
21st to endNight
33%10%15%29%12%1
1440
July1st to 10thNight
36%11%15%23%13%2
1400
11th to 20thNight
35%11%16%26%12%2
1392
21st to endNight
36%10%18%20%14%1
1523
August1st to 10thNight
34%12%16%26%12%1
1600
11th to 20thNight
41%9%16%20%13%1
1682
21st to endNight
37%9%13%22%18%1
1980
September1st to 10thNight
40%8%13%24%14%2
1800
11th to 20thNight
34%7%11%25%21%2
1800
21st to endNight
41%6%11%24%18%1
2029
October1st to 10thNight
42%8%13%22%14%1
2160
11th to 20thNight
42%7%14%24%12%2
2160
21st to endNight
49%7%13%21%10%1
2424
November1st to 10thNight
39%6%15%21%16%2
2407
11th to 20thNight
47%5%13%21%10%2
2505
21st to endNight
45%8%14%23%9%1
2660
December1st to 10thNight
55%9%13%17%6%
2660
11th to 20thNight
54%7%13%17%8%1
3288
21st to endNight
59%8%12%18%3
4884

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 10thDay
31%25%32%9%31
180
11th to 20thDay
37%27%27%8%1
198
21st to endDay
28%31%28%8%41
297
February1st to 10thDay
34%30%27%7%1
270
11th to 20thDay
35%27%30%6%1
342
21st to endDay
33%28%29%9%2
362
March1st to 10thDay
29%25%31%12%3
420
11th to 20thDay
30%27%27%12%31
420
21st to endDay
30%28%25%11%42
462
April1st to 10thDay
31%25%26%14%5%
420
11th to 20thDay
26%28%25%12%7%2
412
21st to endDay
25%25%30%14%5%2
420
May1st to 10thDay
29%23%28%9%8%2
423
11th to 20thDay
23%20%32%15%9%2
447
21st to endDay
20%12%29%22%15%3
485
June1st to 10thDay
18%16%31%22%11%2
450
11th to 20thDay
17%20%23%27%11%2
450
21st to endDay
16%14%32%27%11%1
450
July1st to 10thDay
11%11%29%28%17%5%
445
11th to 20thDay
9%9%31%30%18%4
444
21st to endDay
13%11%33%27%13%3
488
August1st to 10thDay
14%8%27%25%19%7%
446
11th to 20thDay
14%8%28%26%17%7%
439
21st to endDay
14%13%27%24%13%9%
495
September1st to 10thDay
20%12%22%22%18%7%
450
11th to 20thDay
14%10%28%22%17%9%
450
21st to endDay
24%11%26%22%13%4
450
October1st to 10thDay
23%15%22%20%15%4
450
11th to 20thDay
21%21%28%22%7%1
450
21st to endDay
29%18%28%19%5%1
471
November1st to 10thDay
22%21%25%22%9%2
365
11th to 20thDay
26%26%27%16%5%1
332
21st to endDay
32%24%33%8%3
180
December1st to 10thDay
33%26%28%8%31
180
11th to 20thDay
36%25%28%11%1
180
21st to endDay
29%26%35%9%2
198
January1st to 10thNight
23%25%36%14%3
760
11th to 20thNight
25%21%32%20%2
760
21st to endNight
19%27%35%18%2
836
February1st to 10thNight
25%24%32%18%2
760
11th to 20thNight
26%25%37%11%1
743
21st to endNight
28%23%33%13%3
611
March1st to 10thNight
27%22%32%17%2
720
11th to 20thNight
25%22%32%15%5%
720
21st to endNight
22%24%32%16%5%1
792
April1st to 10thNight
23%23%33%18%4
720
11th to 20thNight
21%18%33%20%7%
711
21st to endNight
22%17%30%25%5%
720
May1st to 10thNight
22%17%25%26%9%1
495
11th to 20thNight
14%12%35%32%6%1
354
21st to endNight
15%9%24%37%15%
389
June1st to 10thNight
16%6%24%36%16%
360
11th to 20thNight
13%7%29%38%13%
360
21st to endNight
11%6%27%45%12%
360
July1st to 10thNight
10%5%25%38%20%1
350
11th to 20thNight
10%421%45%17%2
348
21st to endNight
13%6%22%40%18%2
433
August1st to 10thNight
13%317%44%21%2
537
11th to 20thNight
14%5%15%36%27%3
618
21st to endNight
13%7%20%34%24%1
792
September1st to 10thNight
18%5%23%33%19%2
720
11th to 20thNight
14%7%24%26%24%5%
720
21st to endNight
19%10%21%31%17%2
720
October1st to 10thNight
22%10%23%26%17%2
720
11th to 20thNight
19%16%26%31%7%1
720
21st to endNight
26%15%30%24%5%
792
November1st to 10thNight
17%16%32%25%9%1
740
11th to 20thNight
24%19%29%20%6%1
760
21st to endNight
21%21%32%20%5%
760
December1st to 10thNight
26%23%32%16%4
760
11th to 20thNight
24%22%31%19%3
760
21st to endNight
25%20%35%18%2
836
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Copyright 2024 Attilla Danko


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