Observatory Point
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatory Point clear sky chart from 2005-11-06 to 2024-01-12.

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
45%
22629
10%
74756
9%
22584
48%
22584
17%
53322

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
25%
846
6%
2836
4%
846
28%
846
7%
2392
January11th to 20thNight
35%
801
5%
2706
5%
801
36%
801
8%
2229
January21st to endNight
41%
792
8%
2682
7%
792
43%
792
11%
2099
February1st to 10thNight
30%
720
7%
2340
4%
720
34%
720
9%
1905
February11th to 20thNight
35%
700
9%
2274
8%
700
38%
700
13%
1738
February21st to endNight
31%
592
9%
1920
7%
592
35%
592
11%
1493
March1st to 10thNight
43%
720
11%
2057
9%
720
44%
720
16%
1558
March11th to 20thNight
38%
720
9%
1980
7%
720
39%
720
16%
1517
March21st to endNight
38%
792
7%
2152
5%
792
39%
792
14%
1716
April1st to 10thNight
39%
720
6%
1800
3%
720
41%
720
17%
1394
April11th to 20thNight
41%
610
12%
1678
8%
610
42%
610
20%
1202
April21st to endNight
40%
540
10%
1620
6%
540
43%
540
19%
1146
May1st to 10thNight
53%
363
12%
1443
16%
363
57%
363
22%
861
May11th to 20thNight
57%
354
12%
1416
17%
354
62%
354
20%
878
May21st to endNight
52%
389
8%
1530
11%
388
55%
388
20%
947
June1st to 10thNight
47%
360
8%
1260
6%
360
50%
360
22%
812
June11th to 20thNight
49%
360
6%
1260
5%
360
50%
360
25%
771
June21st to endNight
58%
360
10%
1260
8%
360
61%
360
35%
666
July1st to 10thNight
65%
350
10%
1225
10%
350
67%
350
37%
637
July11th to 20thNight
68%
348
18%
1218
18%
348
74%
348
43%
583
July21st to endNight
75%
394
21%
1459
29%
372
82%
372
56%
557
August1st to 10thNight
76%
448
19%
1514
21%
446
79%
446
45%
714
August11th to 20thNight
84%
534
24%
1602
23%
534
86%
534
52%
768
August21st to endNight
66%
642
23%
1830
16%
642
70%
642
42%
1009
September1st to 10thNight
72%
720
22%
1800
13%
720
74%
720
49%
1022
September11th to 20thNight
65%
720
19%
1836
12%
720
66%
720
32%
1219
September21st to endNight
58%
720
18%
2042
14%
720
60%
720
30%
1302
October1st to 10thNight
58%
720
11%
2160
11%
720
59%
720
24%
1442
October11th to 20thNight
51%
720
12%
2160
12%
720
53%
720
20%
1514
October21st to endNight
44%
792
13%
2472
11%
792
49%
792
17%
1777
November1st to 10thNight
35%
740
8%
2590
8%
740
38%
740
11%
2032
November11th to 20thNight
35%
760
7%
2660
6%
760
38%
760
10%
2070
November21st to endNight
33%
760
6%
2660
4%
760
36%
760
9%
2140
December1st to 10thNight
36%
760
7%
2660
6%
760
38%
760
10%
2094
December11th to 20thNight
30%
837
2%
3486
2%
837
31%
837
6%
2916
December21st to endNight
24%
925
3%
5168
3%
905
27%
905
4%
4202

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%8%38%7%46%6%6%8%34%
74737
Night
9%8%48%7%46%6%6%8%34%
74979
TransparencyDay
45%10%19%18%6%1
74427
Night
49%9%17%17%7%1
74807
SeeingDay
14%7%19%30%24%7%
14278
Night
18%8%18%30%21%5%
22648

By Month

Percentage Cloud Cover NW (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%13%7%10%10%5%6%7%8%7%15%
1329
11th to 20thDay
11%13%49%9%5%7%9%7%8%18%
1274
21st to endDay
11%13%5%10%10%5%6%9%7%8%17%
1673
February1st to 10thDay
13%12%411%7%5%8%7%7%9%17%
1620
11th to 20thDay
13%13%410%9%5%6%6%6%7%20%
1575
21st to endDay
11%13%5%12%10%5%8%8%5%6%16%
1335
March1st to 10thDay
8%12%5%10%9%5%7%7%7%7%22%
1898
11th to 20thDay
9%13%410%10%5%7%8%7%8%19%
1980
21st to endDay
10%14%5%11%10%6%7%7%6%7%17%
2204
April1st to 10thDay
11%13%49%9%5%8%8%7%8%18%
2160
11th to 20thDay
11%11%5%9%9%5%7%7%6%8%22%
2230
21st to endDay
13%9%49%9%5%7%5%7%8%24%
2340
May1st to 10thDay
10%8%47%7%5%7%6%6%7%33%
2515
11th to 20thDay
9%7%38%8%47%7%6%9%33%
2477
21st to endDay
13%8%37%6%36%6%7%7%33%
2741
June1st to 10thDay
12%7%48%7%45%5%6%7%34%
2700
11th to 20thDay
10%6%38%8%5%7%6%6%9%31%
2700
21st to endDay
8%5%35%6%36%6%6%7%45%
2700
July1st to 10thDay
9%415%43445%7%55%
2700
11th to 20thDay
7%3244245%47%59%
2700
21st to endDay
321321245%6%70%
2770
August1st to 10thDay
6%314423448%61%
2414
11th to 20thDay
5%31443446%8%60%
2298
21st to endDay
5%415%5%35%5%6%10%51%
2525
September1st to 10thDay
7%5%245%4345%8%55%
2160
11th to 20thDay
7%7%47%5%35%5%5%7%46%
2123
21st to endDay
8%6%36%6%46%6%5%8%43%
1918
October1st to 10thDay
12%6%36%6%36%6%7%9%36%
1800
11th to 20thDay
11%8%37%7%5%6%7%8%9%30%
1800
21st to endDay
13%8%38%8%46%6%6%8%31%
1881
November1st to 10thDay
12%12%6%11%9%48%6%7%7%18%
1488
11th to 20thDay
11%11%410%7%5%7%7%8%8%21%
1520
21st to endDay
14%11%5%7%8%47%8%8%7%20%
1520
December1st to 10thDay
10%13%6%9%9%5%6%6%6%7%24%
1520
11th to 20thDay
10%14%6%11%9%5%7%7%7%7%17%
1707
21st to endDay
12%14%6%12%10%5%7%6%7%7%14%
2442
January1st to 10thNight
12%12%5%10%10%5%8%7%7%7%18%
2836
11th to 20thNight
9%10%5%10%10%7%7%7%7%8%20%
2706
21st to endNight
12%10%49%8%5%7%7%8%9%20%
2682
February1st to 10thNight
13%11%6%10%9%5%7%5%7%8%21%
2340
11th to 20thNight
10%12%49%8%47%6%5%7%26%
2272
21st to endNight
13%12%411%10%5%7%7%7%6%20%
1920
March1st to 10thNight
7%8%38%9%5%7%7%9%9%27%
2057
11th to 20thNight
8%8%38%9%6%8%8%7%8%27%
1979
21st to endNight
9%10%5%10%10%5%9%7%7%7%22%
2152
April1st to 10thNight
11%11%48%8%5%7%6%6%9%25%
1800
11th to 20thNight
9%10%46%8%47%6%6%9%31%
1678
21st to endNight
10%9%47%8%45%6%6%9%32%
1620
May1st to 10thNight
7%5%45%5%5%5%5%6%9%45%
1443
11th to 20thNight
6%6%37%7%36%6%8%9%39%
1416
21st to endNight
10%426%7%35%5%6%9%43%
1530
June1st to 10thNight
10%5%38%7%445%46%44%
1260
11th to 20thNight
7%5%36%6%346%8%9%45%
1260
21st to endNight
5%3244345%7%9%55%
1260
July1st to 10thNight
4324423347%63%
1260
11th to 20thNight
341232345%6%68%
1260
21st to endNight
212212246%77%
1545
August1st to 10thNight
331331335%7%68%
1522
11th to 20thNight
321222345%8%69%
1602
21st to endNight
432433446%9%59%
1830
September1st to 10thNight
431432345%8%62%
1800
11th to 20thNight
9%426%5%45%46%7%48%
1836
21st to endNight
9%5%26%5%445%5%7%48%
2042
October1st to 10thNight
9%6%36%8%45%6%6%6%40%
2160
11th to 20thNight
11%7%37%7%46%6%6%8%35%
2160
21st to endNight
14%8%37%7%45%7%6%7%33%
2472
November1st to 10thNight
13%12%48%8%5%7%6%6%7%23%
2590
11th to 20thNight
13%9%5%8%8%48%7%7%8%23%
2660
21st to endNight
10%9%5%11%9%5%8%6%7%8%22%
2660
December1st to 10thNight
9%12%5%9%8%6%7%7%7%6%24%
2660
11th to 20thNight
9%12%5%11%9%5%7%8%8%8%17%
3495
21st to endNight
10%13%5%11%10%6%7%7%7%7%17%
5214

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
68%10%9%10%3
1329
11th to 20thDay
69%11%12%7%2
1274
21st to endDay
68%10%10%10%2
1673
February1st to 10thDay
65%10%12%8%4
1620
11th to 20thDay
61%9%13%13%4
1584
21st to endDay
59%10%14%13%31
1335
March1st to 10thDay
55%12%15%15%2
1898
11th to 20thDay
58%9%16%13%31
1980
21st to endDay
58%10%19%11%2
2204
April1st to 10thDay
54%12%20%12%2
2160
11th to 20thDay
50%11%17%15%6%1
2230
21st to endDay
47%11%19%18%41
2340
May1st to 10thDay
40%12%23%18%6%1
2515
11th to 20thDay
41%11%25%18%6%
2480
21st to endDay
43%9%25%20%4
2742
June1st to 10thDay
42%11%26%15%5%1
2700
11th to 20thDay
39%13%27%17%4
2700
21st to endDay
32%11%27%19%9%1
2700
July1st to 10thDay
27%10%21%28%13%2
2626
11th to 20thDay
23%8%25%31%13%1
2619
21st to endDay
12%8%24%38%15%3
2616
August1st to 10thDay
21%7%28%30%13%2
2397
11th to 20thDay
21%9%24%30%13%2
2298
21st to endDay
27%9%26%31%7%1
2525
September1st to 10thDay
29%8%23%25%14%2
2160
11th to 20thDay
38%9%17%20%14%1
2123
21st to endDay
39%9%21%20%10%1
1918
October1st to 10thDay
46%8%18%21%7%
1800
11th to 20thDay
52%11%20%13%4
1800
21st to endDay
53%11%15%13%7%
1881
November1st to 10thDay
66%8%13%10%21
1488
11th to 20thDay
62%8%12%12%41
1520
21st to endDay
63%12%9%12%4
1520
December1st to 10thDay
64%6%12%14%4
1520
11th to 20thDay
65%13%12%8%21
1710
21st to endDay
69%10%13%7%2
2442
January1st to 10thNight
67%11%10%8%4
2836
11th to 20thNight
66%8%12%8%31
2706
21st to endNight
60%9%12%14%41
2682
February1st to 10thNight
63%10%12%9%6%
2340
11th to 20thNight
56%10%14%14%6%
2274
21st to endNight
59%9%13%13%5%1
1920
March1st to 10thNight
52%10%16%17%5%
2057
11th to 20thNight
52%11%18%14%41
1980
21st to endNight
60%8%17%13%1
2152
April1st to 10thNight
52%11%19%15%4
1800
11th to 20thNight
47%9%18%19%6%2
1678
21st to endNight
48%9%19%15%9%1
1620
May1st to 10thNight
36%10%24%20%9%1
1443
11th to 20thNight
37%12%22%21%7%1
1416
21st to endNight
38%11%26%21%4
1530
June1st to 10thNight
43%7%20%22%6%2
1260
11th to 20thNight
34%12%30%21%4
1260
21st to endNight
24%9%31%24%9%3
1260
July1st to 10thNight
24%8%23%28%14%3
1225
11th to 20thNight
19%7%23%31%18%2
1218
21st to endNight
9%8%20%37%22%4
1459
August1st to 10thNight
19%6%24%31%16%3
1514
11th to 20thNight
15%8%25%32%15%6%
1602
21st to endNight
23%8%24%33%11%
1830
September1st to 10thNight
22%7%22%30%16%4
1800
11th to 20thNight
37%7%17%17%18%4
1836
21st to endNight
37%8%16%23%14%2
2042
October1st to 10thNight
44%6%16%22%11%
2160
11th to 20thNight
47%8%19%18%7%
2160
21st to endNight
51%7%14%18%9%
2472
November1st to 10thNight
61%8%14%12%4
2590
11th to 20thNight
59%9%16%9%5%2
2660
21st to endNight
62%11%12%10%6%
2660
December1st to 10thNight
60%10%12%13%5%
2660
11th to 20thNight
63%15%14%6%2
3491
21st to endNight
64%13%12%9%3
5214

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
29%11%24%23%13%
180
11th to 20thDay
28%9%20%27%16%
162
21st to endDay
29%5%22%28%13%3
265
February1st to 10thDay
27%15%26%23%10%
340
11th to 20thDay
24%13%18%29%15%
335
21st to endDay
19%17%21%28%14%1
282
March1st to 10thDay
17%12%20%30%18%3
420
11th to 20thDay
16%11%22%28%17%5%
420
21st to endDay
17%12%21%29%19%2
462
April1st to 10thDay
18%12%22%26%18%4
420
11th to 20thDay
15%10%16%32%20%7%
412
21st to endDay
17%6%25%27%21%4
420
May1st to 10thDay
11%7%17%32%29%4
423
11th to 20thDay
13%5%14%31%30%7%
448
21st to endDay
10%5%21%32%25%7%
503
June1st to 10thDay
13%7%23%31%22%4
630
11th to 20thDay
8%7%30%36%15%4
630
21st to endDay
6%423%33%24%10%
630
July1st to 10thDay
8%216%36%30%8%
621
11th to 20thDay
4320%33%30%8%
618
21st to endDay
2116%30%33%18%
516
August1st to 10thDay
5%213%25%38%18%
447
11th to 20thDay
219%27%42%19%
437
21st to endDay
6%413%32%33%12%
495
September1st to 10thDay
9%39%35%36%7%
450
11th to 20thDay
13%311%27%34%12%
450
21st to endDay
12%417%28%30%8%
450
October1st to 10thDay
17%6%13%28%26%10%
450
11th to 20thDay
23%9%11%28%24%5%
450
21st to endDay
20%11%23%28%14%3
414
November1st to 10thDay
29%9%23%25%14%
180
11th to 20thDay
23%8%23%23%21%2
180
21st to endDay
25%11%19%26%17%2
180
December1st to 10thDay
25%9%16%34%15%1
180
11th to 20thDay
24%14%21%29%11%1
180
21st to endDay
31%7%23%32%7%1
198
January1st to 10thNight
28%14%22%24%12%1
850
11th to 20thNight
24%14%15%27%18%1
801
21st to endNight
23%9%17%29%18%4
792
February1st to 10thNight
25%13%21%26%13%2
720
11th to 20thNight
21%12%18%30%17%3
704
21st to endNight
24%13%19%24%16%4
592
March1st to 10thNight
17%11%19%30%18%5%
720
11th to 20thNight
20%9%24%25%19%3
720
21st to endNight
16%10%22%30%18%4
792
April1st to 10thNight
22%7%21%27%20%4
720
11th to 20thNight
15%9%23%30%17%6%
610
21st to endNight
14%9%24%33%15%4
540
May1st to 10thNight
11%5%22%34%24%4
363
11th to 20thNight
10%418%34%27%6%
354
21st to endNight
10%6%19%37%26%2
389
June1st to 10thNight
12%6%23%34%22%3
360
11th to 20thNight
9%427%41%16%3
360
21st to endNight
6%425%31%28%8%
360
July1st to 10thNight
6%117%38%33%4
350
11th to 20thNight
3218%42%30%5%
348
21st to endNight
2117%38%33%9%
394
August1st to 10thNight
5%111%33%40%10%
448
11th to 20thNight
317%34%38%17%
534
21st to endNight
7%217%33%32%9%
642
September1st to 10thNight
8%213%34%32%13%
720
11th to 20thNight
10%310%27%32%16%
720
21st to endNight
13%316%30%28%11%
720
October1st to 10thNight
15%5%11%27%29%13%
720
11th to 20thNight
18%7%13%29%22%12%
720
21st to endNight
24%7%14%30%19%5%
792
November1st to 10thNight
27%8%19%29%16%2
740
11th to 20thNight
23%13%20%26%15%3
760
21st to endNight
24%11%21%24%16%4
760
December1st to 10thNight
25%10%18%28%18%2
760
11th to 20thNight
26%13%21%27%12%1
838
21st to endNight
27%13%25%25%9%1
935
Page generated at 2024-01-08 19:31:30. Version ac07

Copyright 2024 Attilla Danko


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