Blazing Star Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blazing Star Observatory clear sky chart from 2005-11-05 to 2019-06-02.

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
55%
16632
17%
53839
15%
16604
59%
16604
25%
33811

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
36%
836
8%
2926
6%
836
39%
836
10%
2273
January16th to endNight
38%
896
8%
3136
7%
896
41%
896
11%
2437
February1st to 15thNight
45%
820
10%
2730
8%
816
49%
816
16%
1967
February16th to endNight
48%
736
14%
2276
11%
736
55%
736
21%
1560
March1st to 15thNight
48%
840
14%
2506
12%
840
52%
840
22%
1703
March16th to endNight
49%
896
16%
2343
9%
896
53%
896
27%
1591
April1st to 15thNight
52%
839
16%
2099
8%
839
54%
839
28%
1439
April16th to endNight
54%
647
19%
1895
13%
647
59%
647
33%
1105
May1st to 15thNight
65%
419
23%
1679
29%
419
71%
419
34%
812
May16th to endNight
67%
438
13%
1752
21%
438
71%
438
26%
968
June1st to 15thNight
68%
392
12%
1568
13%
392
71%
392
31%
801
June16th to endNight
67%
390
13%
1560
13%
390
70%
390
35%
740
July1st to 15thNight
81%
370
17%
1480
23%
370
84%
370
54%
560
July16th to endNight
82%
408
26%
1544
40%
386
88%
386
62%
524
August1st to 15thNight
88%
384
34%
1528
46%
382
91%
382
63%
524
August16th to endNight
77%
757
33%
1999
24%
757
79%
757
60%
988
September1st to 15thNight
75%
780
32%
1950
18%
780
78%
780
64%
981
September16th to endNight
69%
776
29%
2104
22%
776
72%
776
44%
1168
October1st to 15thNight
58%
780
22%
2340
20%
780
63%
780
31%
1395
October16th to endNight
56%
832
20%
2645
18%
832
62%
832
25%
1679
November1st to 15thNight
45%
820
12%
2763
11%
820
49%
820
19%
1871
November16th to endNight
42%
840
11%
2940
8%
840
47%
840
14%
2135
December1st to 15thNight
44%
840
12%
2940
10%
840
48%
840
13%
2157
December16th to endNight
37%
896
11%
3136
8%
896
41%
896
11%
2433

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
7%6%25%5%345%5%7%46%
54521
Night
8%7%35%5%3445%7%43%
54007
Cloud CoverDay
7%6%35%5%345%5%7%45%
54521
Night
9%7%36%5%3445%7%42%
54011
TransparencyDay
37%5%11%24%16%4
54192
Night
40%5%12%23%13%3
53840
SeeingDay
11%11%22%28%18%7%
7443
Night
13%5%14%38%24%3
16642

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 15thDay
13%15%5%10%7%445%5%6%20%
1672
16th to endDay
12%14%7%8%6%44346%27%
1792
February1st to 15thDay
11%13%37%7%35%5%6%7%28%
1793
16th to endDay
7%9%46%5%35%5%6%8%36%
1769
March1st to 15thDay
10%9%35%6%45%5%6%9%33%
2114
16th to endDay
7%7%36%6%47%6%7%8%35%
2584
April1st to 15thDay
9%6%36%7%46%7%6%8%34%
2509
16th to endDay
45%25%5%35%5%7%9%44%
2667
May1st to 15thDay
4314425%6%7%9%49%
2931
16th to endDay
8%5%26%6%45%5%6%8%40%
3063
June1st to 15thDay
7%4244345%5%8%48%
2746
16th to endDay
5%4144245%6%7%52%
2730
July1st to 15thDay
1112314346%68%
2730
16th to endDay
211121234473%
2881
August1st to 15thDay
11221235%6%72%
2676
16th to endDay
12232345%6%68%
2553
September1st to 15thDay
221222235%6%67%
2340
16th to endDay
6%31443445%6%56%
2185
October1st to 15thDay
7%5%345%245%5%7%48%
1950
16th to endDay
10%6%26%43446%7%44%
1931
November1st to 15thDay
10%10%37%6%345%5%7%35%
1753
16th to endDay
11%13%5%8%6%3446%7%29%
1680
December1st to 15thDay
11%12%5%10%6%35%45%6%28%
1680
16th to endDay
14%13%6%9%5%3436%6%27%
1792
January1st to 15thNight
13%15%5%10%6%35%45%7%22%
2926
16th to endNight
12%14%6%11%7%35%45%7%21%
3136
February1st to 15thNight
13%10%47%5%25%46%7%33%
2718
16th to endNight
8%8%36%6%35%5%7%8%36%
2276
March1st to 15thNight
11%7%26%5%345%7%10%36%
2506
16th to endNight
8%5%247%45%6%6%9%38%
2339
April1st to 15thNight
7%6%35%6%45%6%5%8%41%
2099
16th to endNight
6%6%145%3345%7%51%
1895
May1st to 15thNight
42245%1345%9%56%
1679
16th to endNight
8%323435%5%7%10%44%
1752
June1st to 15thNight
5%314325%46%6%54%
1568
16th to endNight
323425%5%5%6%58%
1560
July1st to 15thNight
111313246%73%
1560
16th to endNight
1111234478%
1640
August1st to 15thNight
11111346%77%
1536
16th to endNight
11231335%5%71%
1999
September1st to 15thNight
211212246%72%
1950
16th to endNight
5%21332345%7%58%
2104
October1st to 15thNight
7%6%2442435%6%50%
2340
16th to endNight
9%5%35%5%345%6%8%42%
2645
November1st to 15thNight
12%7%36%5%35%46%7%35%
2763
16th to endNight
12%13%5%6%5%3445%7%30%
2940
December1st to 15thNight
10%12%5%9%7%35%5%5%6%28%
2940
16th to endNight
15%13%6%10%6%3445%6%24%
3136

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
14%15%6%9%7%45%5%5%6%19%
1672
16th to endDay
13%15%6%10%6%34447%23%
1792
February1st to 15thDay
12%12%49%7%35%5%6%6%26%
1793
16th to endDay
8%10%47%5%45%46%8%33%
1769
March1st to 15thDay
11%10%36%6%36%5%6%9%30%
2114
16th to endDay
8%7%36%5%46%7%6%8%34%
2584
April1st to 15thDay
9%7%37%6%47%6%6%8%33%
2509
16th to endDay
5%5%26%5%35%6%7%9%43%
2667
May1st to 15thDay
44144346%7%9%48%
2931
16th to endDay
9%5%25%6%46%5%6%8%38%
3063
June1st to 15thDay
7%5%24425%5%6%8%46%
2746
16th to endDay
6%415%425%5%6%7%50%
2730
July1st to 15thDay
1111324346%68%
2730
16th to endDay
211212345%73%
2881
August1st to 15thDay
111312346%71%
2676
16th to endDay
211331345%7%66%
2553
September1st to 15thDay
2212222347%67%
2340
16th to endDay
6%314424447%55%
2185
October1st to 15thDay
7%5%25%5%25%5%6%7%46%
1950
16th to endDay
11%5%26%5%245%5%7%42%
1931
November1st to 15thDay
11%10%46%5%345%5%7%33%
1753
16th to endDay
12%13%6%9%5%3445%7%26%
1680
December1st to 15thDay
12%13%5%8%8%35%45%5%27%
1680
16th to endDay
15%15%7%7%6%3345%5%25%
1792
January1st to 15thNight
14%15%5%10%5%35%447%21%
2926
16th to endNight
13%15%6%11%7%35%45%6%20%
3136
February1st to 15thNight
13%12%36%5%35%5%5%7%31%
2718
16th to endNight
7%9%37%5%36%5%7%8%34%
2276
March1st to 15thNight
11%8%35%6%35%5%6%9%34%
2506
16th to endNight
9%5%25%7%36%6%6%9%36%
2343
April1st to 15thNight
7%6%36%6%35%5%5%8%39%
2099
16th to endNight
6%6%2443445%8%49%
1895
May1st to 15thNight
4425%31446%8%54%
1679
16th to endNight
8%424435%5%7%9%43%
1752
June1st to 15thNight
5%423435%446%53%
1568
16th to endNight
4313426%447%57%
1560
July1st to 15thNight
2122235%5%72%
1560
16th to endNight
11111234378%
1640
August1st to 15thNight
1212245%76%
1536
16th to endNight
2112313346%70%
1999
September1st to 15thNight
212212346%71%
1950
16th to endNight
5%32432445%7%57%
2104
October1st to 15thNight
8%5%25%4345%47%48%
2340
16th to endNight
10%7%26%425%5%6%7%41%
2645
November1st to 15thNight
14%7%36%6%246%7%6%34%
2763
16th to endNight
14%12%6%6%5%345%5%6%28%
2940
December1st to 15thNight
12%11%5%11%6%35%45%7%26%
2940
16th to endNight
16%14%6%9%7%34445%24%
3136

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
65%6%10%13%3
1672
16th to endDay
62%313%16%3
1792
February1st to 15thDay
57%7%14%15%4
1793
16th to endDay
47%6%16%22%6%
1769
March1st to 15thDay
49%6%14%21%8%
2114
16th to endDay
44%7%16%22%8%
2584
April1st to 15thDay
46%6%14%21%10%
2509
16th to endDay
35%5%14%26%14%3
2667
May1st to 15thDay
28%5%12%35%15%2
2931
16th to endDay
40%414%26%12%
3067
June1st to 15thDay
32%5%9%30%17%5%
2746
16th to endDay
30%48%29%22%4
2730
July1st to 15thDay
17%25%26%30%16%
2581
16th to endDay
14%2421%35%21%
2714
August1st to 15thDay
13%36%29%35%11%
2659
16th to endDay
17%28%31%30%8%
2553
September1st to 15thDay
16%28%31%30%9%
2340
16th to endDay
29%314%28%18%5%
2185
October1st to 15thDay
34%5%14%28%15%
1950
16th to endDay
41%5%15%26%10%
1931
November1st to 15thDay
48%6%14%17%9%2
1753
16th to endDay
57%5%14%15%6%
1680
December1st to 15thDay
58%6%13%14%6%
1680
16th to endDay
60%7%9%14%7%
1792
January1st to 15thNight
63%5%13%13%3
2926
16th to endNight
63%5%13%13%3
3136
February1st to 15thNight
51%8%17%16%5%
2730
16th to endNight
44%7%15%23%7%
2276
March1st to 15thNight
45%6%16%22%8%
2506
16th to endNight
42%5%16%26%8%
2343
April1st to 15thNight
41%6%13%25%12%
2099
16th to endNight
33%414%31%14%2
1895
May1st to 15thNight
27%310%35%18%4
1680
16th to endNight
34%5%16%30%12%
1752
June1st to 15thNight
29%5%10%29%20%4
1568
16th to endNight
25%411%33%22%3
1560
July1st to 15thNight
14%28%27%31%16%
1480
16th to endNight
9%2426%35%21%
1544
August1st to 15thNight
10%27%31%36%13%
1528
16th to endNight
15%37%29%34%9%
1999
September1st to 15thNight
14%28%29%33%11%
1950
16th to endNight
25%411%33%17%6%
2104
October1st to 15thNight
34%5%10%28%19%1
2340
16th to endNight
40%6%12%30%10%
2645
November1st to 15thNight
47%6%18%16%7%2
2763
16th to endNight
55%5%12%17%7%
2940
December1st to 15thNight
56%6%14%18%4
2940
16th to endNight
61%6%8%13%8%
3136

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
20%5%8%26%27%10%
120
16th to endDay
32%5%12%27%17%4
128
February1st to 15thDay
15%8%21%37%12%3
273
16th to endDay
16%10%24%29%17%2
322
March1st to 15thDay
16%15%22%27%15%2
390
16th to endDay
13%19%25%21%16%3
416
April1st to 15thDay
16%20%24%24%10%3
389
16th to endDay
10%17%29%20%13%7%
378
May1st to 15thDay
11%14%26%29%14%4
408
16th to endDay
13%8%17%26%23%11%
458
June1st to 15thDay
10%12%27%25%17%6%
380
16th to endDay
9%12%27%26%16%6%
375
July1st to 15thDay
48%25%34%21%5%
365
16th to endDay
27%25%32%23%8%
391
August1st to 15thDay
3421%33%22%13%
359
16th to endDay
48%20%30%23%11%
396
September1st to 15thDay
411%18%29%22%13%
375
16th to endDay
6%10%22%30%21%7%
375
October1st to 15thDay
13%13%22%27%18%4
375
16th to endDay
15%6%17%29%19%11%
251
November1st to 15thDay
19%15%18%27%17%1
151
16th to endDay
19%7%15%28%21%7%
120
December1st to 15thDay
19%213%29%22%13%
120
16th to endDay
21%311%46%13%3
128
January1st to 15thNight
22%7%11%32%21%3
840
16th to endNight
21%410%38%21%3
896
February1st to 15thNight
19%414%40%17%3
824
16th to endNight
13%6%20%36%19%3
736
March1st to 15thNight
16%5%18%39%18%2
840
16th to endNight
12%7%19%38%18%2
896
April1st to 15thNight
10%10%17%35%23%2
839
16th to endNight
9%7%19%38%21%3
647
May1st to 15thNight
6%5%16%40%27%3
420
16th to endNight
11%29%35%36%4
439
June1st to 15thNight
7%313%41%31%2
392
16th to endNight
45%15%46%26%2
390
July1st to 15thNight
2110%45%37%2
370
16th to endNight
2110%45%38%2
408
August1st to 15thNight
115%31%52%7%
384
16th to endNight
3212%36%37%7%
757
September1st to 15thNight
4312%33%35%10%
780
16th to endNight
7%312%37%31%7%
776
October1st to 15thNight
12%5%14%39%24%3
780
16th to endNight
15%412%38%24%4
832
November1st to 15thNight
19%7%17%42%12%1
820
16th to endNight
21%6%15%32%19%4
840
December1st to 15thNight
18%5%12%40%21%2
840
16th to endNight
23%6%12%44%12%1
896
Page generated at 2019-06-02 16:43:11. Version ac04

Copyright 2019 A. Danko


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