Dogstar Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dogstar Observatory clear sky chart from 2005-11-06 to 2024-10-25.

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
43%
24851
17%
96073
12%
24618
50%
24618
18%
61373

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%
755
21%
4008
10%
737
40%
737
13%
2250
January11th to 20thNight
22%
760
26%
3934
9%
740
34%
740
11%
2290
January21st to endNight
21%
832
15%
4464
10%
814
37%
814
12%
2791
February1st to 10thNight
31%
760
21%
2337
12%
760
41%
760
22%
1519
February11th to 20thNight
17%
743
18%
2218
7%
739
30%
739
16%
1552
February21st to endNight
20%
628
18%
1884
8%
628
29%
628
16%
1358
March1st to 10thNight
26%
758
14%
3531
11%
745
36%
745
12%
2432
March11th to 20thNight
27%
756
24%
3417
7%
740
36%
740
16%
1796
March21st to endNight
27%
832
12%
3703
6%
814
33%
814
13%
2335
April1st to 10thNight
31%
760
20%
2090
9%
760
40%
760
24%
1361
April11th to 20thNight
39%
609
22%
1860
13%
609
49%
609
26%
1157
April21st to endNight
46%
570
22%
1710
13%
570
53%
570
27%
1083
May1st to 10thNight
42%
565
14%
2795
8%
559
47%
559
13%
1921
May11th to 20thNight
48%
551
12%
2786
9%
541
51%
541
13%
1862
May21st to endNight
59%
607
12%
3043
11%
593
61%
593
16%
1771
June1st to 10thNight
58%
570
12%
1710
10%
570
60%
570
21%
1195
June11th to 20thNight
67%
570
11%
1710
8%
570
69%
570
29%
1088
June21st to endNight
68%
570
14%
1710
11%
570
69%
570
26%
1130
July1st to 10thNight
62%
542
10%
2736
8%
535
64%
535
12%
1845
July11th to 20thNight
66%
536
7%
2699
8%
533
66%
533
13%
1853
July21st to endNight
65%
614
6%
2984
9%
569
66%
569
11%
2399
August1st to 10thNight
63%
557
9%
2748
9%
545
64%
545
13%
1755
August11th to 20thNight
61%
556
9%
2699
15%
543
63%
543
13%
1819
August21st to endNight
62%
630
12%
3087
14%
627
63%
627
17%
1746
September1st to 10thNight
59%
760
15%
2090
14%
760
60%
760
22%
1471
September11th to 20thNight
53%
760
17%
2090
15%
760
54%
760
22%
1491
September21st to endNight
56%
760
20%
2090
16%
760
59%
760
26%
1398
October1st to 10thNight
51%
760
26%
2090
20%
760
56%
760
32%
1292
October11th to 20thNight
44%
760
24%
2280
19%
760
51%
760
29%
1378
October21st to endNight
51%
812
29%
2435
24%
812
59%
812
32%
1419
November1st to 10thNight
51%
740
25%
2339
21%
740
61%
740
30%
1360
November11th to 20thNight
40%
760
25%
2470
19%
760
52%
760
26%
1480
November21st to endNight
42%
760
24%
2470
18%
760
52%
760
24%
1511
December1st to 10thNight
31%
760
20%
2470
12%
760
41%
760
17%
1694
December11th to 20thNight
33%
759
23%
2945
15%
758
44%
758
19%
1758
December21st to endNight
27%
829
12%
4441
10%
817
36%
817
10%
2813

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
14%9%38%5%5%5%46%7%35%
100970
Night
14%9%37%44445%7%38%
97792
TransparencyDay
45%8%12%17%15%4
100783
Night
42%8%13%17%15%5%
97649
SeeingDay
21%13%23%22%14%7%
14949
Night
19%9%21%28%19%4
24979

By Month

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 10thDay
15%9%46%33446%6%40%
2836
11th to 20thDay
14%10%5%8%44433442%
2840
21st to endDay
21%11%35%33324441%
3124
February1st to 10thDay
16%10%47%44435%5%37%
1838
11th to 20thDay
17%12%36%5%32346%37%
1848
21st to endDay
20%11%27%444346%35%
1570
March1st to 10thDay
23%9%35%333346%38%
3308
11th to 20thDay
14%8%25%33334449%
3480
21st to endDay
17%9%36%44445%5%37%
3815
April1st to 10thDay
12%9%36%5%445%6%7%40%
2090
11th to 20thDay
14%10%37%445%45%6%39%
2284
21st to endDay
14%7%36%5%5%435%7%40%
2470
May1st to 10thDay
16%11%38%5%5%5%45%6%32%
4082
11th to 20thDay
19%10%48%5%46%45%6%28%
4081
21st to endDay
10%7%38%5%5%5%5%7%9%35%
4476
June1st to 10thDay
12%10%39%7%7%6%5%7%7%27%
2470
11th to 20thDay
8%7%310%6%7%8%6%9%8%28%
2470
21st to endDay
10%7%37%8%6%7%6%7%9%30%
2470
July1st to 10thDay
8%6%310%8%6%7%6%8%10%29%
4120
11th to 20thDay
10%8%410%7%7%7%6%8%8%26%
4120
21st to endDay
14%10%5%14%9%9%8%5%6%7%13%
4466
August1st to 10thDay
8%8%49%7%7%7%6%8%9%26%
4104
11th to 20thDay
11%6%38%6%7%7%5%8%11%29%
4044
21st to endDay
8%7%39%6%6%6%5%7%7%36%
4134
September1st to 10thDay
11%9%49%6%6%7%5%6%7%31%
2090
11th to 20thDay
15%9%410%6%6%5%46%8%29%
2090
21st to endDay
14%8%37%5%6%5%45%6%36%
2090
October1st to 10thDay
11%6%26%45%435%7%46%
2090
11th to 20thDay
11%7%25%333346%53%
1900
21st to endDay
13%7%14423246%53%
2027
November1st to 10thDay
10%6%2433445%5%54%
1736
11th to 20thDay
12%7%24335%35%6%50%
1710
21st to endDay
13%9%27%43435%6%44%
1710
December1st to 10thDay
22%10%35%444446%35%
1710
11th to 20thDay
15%9%35%43445%5%43%
2153
21st to endDay
15%9%5%8%5%44345%39%
3124
January1st to 10thNight
14%14%46%333245%41%
4109
11th to 20thNight
17%12%36%333345%42%
4120
21st to endNight
21%16%36%33323436%
4532
February1st to 10thNight
13%10%36%45%445%6%39%
2337
11th to 20thNight
19%12%37%444345%37%
2218
21st to endNight
20%10%48%5%4445%5%32%
1884
March1st to 10thNight
21%14%38%5%4435%5%28%
3543
11th to 20thNight
14%7%25%44445%8%44%
3480
21st to endNight
15%8%37%5%4445%7%37%
3817
April1st to 10thNight
13%9%37%445%35%6%42%
2090
11th to 20thNight
12%10%35%43436%7%43%
1860
21st to endNight
11%8%37%5%4435%7%45%
1710
May1st to 10thNight
17%12%38%445%35%7%31%
2813
11th to 20thNight
19%10%37%5%45%35%7%31%
2812
21st to endNight
8%7%37%6%5%6%5%8%10%36%
3079
June1st to 10thNight
10%8%37%5%5%5%6%8%11%32%
1710
11th to 20thNight
6%6%26%447%5%8%11%39%
1710
21st to endNight
9%6%25%45%6%6%9%11%37%
1710
July1st to 10thNight
9%7%28%6%6%7%6%8%12%29%
2840
11th to 20thNight
10%6%36%6%6%6%6%8%10%33%
2840
21st to endNight
17%11%410%7%7%6%5%7%8%20%
3087
August1st to 10thNight
8%6%38%6%5%7%5%8%12%32%
2825
11th to 20thNight
15%7%28%5%5%5%46%9%33%
2785
21st to endNight
8%6%25%445%47%10%45%
3483
September1st to 10thNight
10%7%38%5%6%6%5%8%8%35%
2090
11th to 20thNight
12%8%39%5%5%5%46%9%34%
2090
21st to endNight
13%8%26%45%445%7%42%
2090
October1st to 10thNight
12%6%25%44435%7%48%
2090
11th to 20thNight
12%7%26%444346%48%
2280
21st to endNight
12%8%14334345%52%
2435
November1st to 10thNight
12%7%25%44345%6%49%
2339
11th to 20thNight
12%10%36%433346%47%
2470
21st to endNight
14%9%26%344446%43%
2470
December1st to 10thNight
19%11%46%434445%34%
2470
11th to 20thNight
13%12%38%433345%43%
3042
21st to endNight
14%12%6%9%5%45%45%8%28%
4532

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
36%6%9%15%26%7%
2837
11th to 20thDay
40%8%8%12%27%6%
2840
21st to endDay
43%210%14%23%7%
3124
February1st to 10thDay
47%5%8%17%17%6%
1838
11th to 20thDay
48%46%16%19%6%
1858
21st to endDay
49%5%8%13%18%7%
1570
March1st to 10thDay
46%47%17%17%10%
3308
11th to 20thDay
37%5%7%17%22%12%
3480
21st to endDay
47%49%22%13%4
3815
April1st to 10thDay
41%6%11%20%19%5%
2090
11th to 20thDay
43%5%10%17%20%5%
2284
21st to endDay
42%6%11%24%15%2
2470
May1st to 10thDay
47%10%11%19%12%2
4120
11th to 20thDay
51%10%10%20%9%1
4085
21st to endDay
40%11%15%19%15%1
4489
June1st to 10thDay
51%10%15%17%6%1
2470
11th to 20thDay
45%11%17%15%10%1
2470
21st to endDay
46%11%15%16%10%2
2470
July1st to 10thDay
45%14%17%17%6%
4055
11th to 20thDay
50%15%19%11%41
4051
21st to endDay
66%11%10%8%4
4324
August1st to 10thDay
47%13%16%20%3
4091
11th to 20thDay
42%12%21%13%9%3
4083
21st to endDay
42%12%12%22%10%1
4134
September1st to 10thDay
48%9%11%16%13%3
2090
11th to 20thDay
52%6%11%16%14%2
2090
21st to endDay
46%7%12%15%14%5%
2090
October1st to 10thDay
36%7%9%18%24%7%
2090
11th to 20thDay
32%410%20%21%12%
1900
21st to endDay
33%48%20%24%11%
2027
November1st to 10thDay
32%48%17%28%12%
1736
11th to 20thDay
34%37%20%26%10%
1710
21st to endDay
39%47%18%25%7%
1710
December1st to 10thDay
50%47%17%15%6%
1710
11th to 20thDay
40%49%13%23%11%
2150
21st to endDay
43%413%19%18%4
3124
January1st to 10thNight
41%5%9%13%25%8%
4109
11th to 20thNight
42%6%6%13%24%9%
4120
21st to endNight
47%6%9%12%20%7%
4532
February1st to 10thNight
43%411%17%19%5%
2337
11th to 20thNight
48%7%6%17%18%5%
2219
21st to endNight
51%6%8%14%15%5%
1884
March1st to 10thNight
52%6%14%11%13%5%
3543
11th to 20thNight
35%6%10%22%17%10%
3480
21st to endNight
46%5%10%20%13%6%
3817
April1st to 10thNight
39%6%12%20%20%3
2090
11th to 20thNight
37%6%12%20%20%5%
1860
21st to endNight
37%8%13%26%15%1
1710
May1st to 10thNight
45%12%13%21%8%1
2840
11th to 20thNight
46%11%16%18%8%
2813
21st to endNight
33%15%19%25%9%
3087
June1st to 10thNight
41%14%18%19%7%1
1710
11th to 20thNight
33%12%25%22%7%1
1710
21st to endNight
35%14%18%20%11%3
1710
July1st to 10thNight
42%16%20%17%5%
2795
11th to 20thNight
39%19%25%13%31
2786
21st to endNight
58%13%15%10%31
2988
August1st to 10thNight
39%15%26%16%4
2814
11th to 20thNight
43%13%21%13%9%1
2812
21st to endNight
31%10%21%28%9%1
3483
September1st to 10thNight
41%12%15%17%12%2
2090
11th to 20thNight
46%9%12%18%14%1
2090
21st to endNight
40%8%13%19%15%4
2090
October1st to 10thNight
35%6%12%19%24%5%
2090
11th to 20thNight
36%5%11%20%19%9%
2280
21st to endNight
34%48%19%25%10%
2435
November1st to 10thNight
34%5%9%20%23%9%
2339
11th to 20thNight
37%5%7%16%24%11%
2470
21st to endNight
40%47%21%21%7%
2470
December1st to 10thNight
49%6%9%15%15%7%
2470
11th to 20thNight
40%5%9%13%25%8%
3044
21st to endNight
50%5%12%15%15%3
4532

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
34%21%31%13%1
270
11th to 20thDay
38%22%21%16%3
270
21st to endDay
32%28%27%10%3
297
February1st to 10thDay
34%20%33%10%3
270
11th to 20thDay
46%24%23%7%
270
21st to endDay
46%26%21%6%1
225
March1st to 10thDay
32%16%31%14%7%1
380
11th to 20thDay
29%23%28%14%41
460
21st to endDay
26%24%27%16%6%1
506
April1st to 10thDay
27%17%25%22%8%1
460
11th to 20thDay
22%22%21%22%11%2
452
21st to endDay
22%13%29%21%12%4
460
May1st to 10thDay
20%20%28%17%10%5%
463
11th to 20thDay
22%10%24%23%13%7%
487
21st to endDay
14%10%22%27%16%12%
529
June1st to 10thDay
17%7%22%28%17%11%
490
11th to 20thDay
9%6%22%25%25%13%
490
21st to endDay
14%7%27%21%18%13%
490
July1st to 10thDay
11%415%29%24%16%
485
11th to 20thDay
12%414%27%23%20%
484
21st to endDay
11%5%14%26%26%19%
532
August1st to 10thDay
17%6%18%23%19%17%
486
11th to 20thDay
13%5%17%25%27%12%
479
21st to endDay
14%413%24%26%19%
539
September1st to 10thDay
10%6%16%28%27%13%
490
11th to 20thDay
15%6%18%27%24%11%
490
21st to endDay
18%8%19%28%22%6%
490
October1st to 10thDay
18%8%21%27%18%9%
490
11th to 20thDay
14%14%26%27%16%3
490
21st to endDay
19%13%24%29%12%3
514
November1st to 10thDay
18%13%28%26%13%2
334
11th to 20thDay
23%18%31%23%5%
270
21st to endDay
19%18%36%20%6%1
270
December1st to 10thDay
35%18%28%15%3
270
11th to 20thDay
27%17%31%20%41
270
21st to endDay
31%18%35%13%4
297
January1st to 10thNight
28%13%30%24%5%
760
11th to 20thNight
27%16%30%21%6%
760
21st to endNight
23%14%36%24%4
836
February1st to 10thNight
21%13%31%31%4
760
11th to 20thNight
31%15%32%21%1
743
21st to endNight
32%18%28%19%3
628
March1st to 10thNight
25%14%30%25%5%
760
11th to 20thNight
26%14%26%24%8%1
760
21st to endNight
24%13%30%24%9%
836
April1st to 10thNight
23%16%25%25%9%1
760
11th to 20thNight
21%11%25%29%13%2
609
21st to endNight
15%11%22%35%16%1
570
May1st to 10thNight
16%10%23%31%18%2
570
11th to 20thNight
15%8%18%32%22%4
561
21st to endNight
14%313%30%32%7%
617
June1st to 10thNight
12%414%34%31%6%
570
11th to 20thNight
9%114%30%34%12%
570
21st to endNight
11%39%32%38%7%
570
July1st to 10thNight
12%29%24%45%9%
555
11th to 20thNight
10%27%25%42%13%
552
21st to endNight
9%36%23%45%12%
624
August1st to 10thNight
13%29%27%39%10%
567
11th to 20thNight
12%49%29%38%9%
564
21st to endNight
13%28%25%39%13%
649
September1st to 10thNight
12%410%29%37%9%
760
11th to 20thNight
16%413%28%30%8%
760
21st to endNight
17%5%13%34%27%4
760
October1st to 10thNight
16%7%18%25%26%8%
760
11th to 20thNight
16%9%24%31%18%3
760
21st to endNight
17%10%18%36%16%3
812
November1st to 10thNight
16%6%20%36%18%4
740
11th to 20thNight
20%11%23%33%11%3
760
21st to endNight
21%11%21%32%14%1
760
December1st to 10thNight
29%11%23%29%8%
760
11th to 20thNight
23%11%26%31%8%1
760
21st to endNight
27%12%25%31%4
836
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