Big Bird Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Big Bird Observatory clear sky chart from 2005-11-05 to 2017-12-02.

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
65%
15451
28%
47823
25%
15412
70%
15412
40%
25590

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
57%
719
19%
2479
18%
716
62%
716
28%
1451
January16th to endNight
52%
768
25%
2496
24%
768
58%
768
28%
1514
February1st to 15thNight
53%
697
23%
2288
21%
696
59%
696
26%
1407
February16th to endNight
53%
632
25%
1905
21%
632
59%
632
28%
1187
March1st to 15thNight
50%
720
16%
2046
13%
720
54%
720
26%
1362
March16th to endNight
47%
768
20%
2067
13%
768
52%
768
30%
1355
April1st to 15thNight
49%
719
21%
1799
11%
719
53%
719
31%
1202
April16th to endNight
62%
720
26%
1800
13%
720
66%
720
45%
1040
May1st to 15thNight
63%
520
28%
1600
20%
520
69%
520
49%
778
May16th to endNight
66%
375
25%
1496
28%
374
72%
374
38%
684
June1st to 15thNight
69%
360
25%
1440
31%
360
76%
360
43%
624
June16th to endNight
82%
360
35%
1440
45%
360
87%
360
60%
503
July1st to 15thNight
94%
340
34%
1360
47%
340
95%
340
75%
421
July16th to endNight
93%
488
41%
1519
42%
457
94%
457
80%
522
August1st to 15thNight
91%
541
39%
1614
33%
538
92%
538
73%
654
August16th to endNight
93%
764
45%
1910
29%
764
93%
764
84%
840
September1st to 15thNight
89%
720
43%
1800
29%
720
91%
720
79%
815
September16th to endNight
82%
716
44%
1953
37%
716
86%
716
72%
857
October1st to 15thNight
69%
720
32%
2160
31%
720
76%
720
52%
1032
October16th to endNight
74%
768
36%
2304
36%
768
78%
768
49%
1144
November1st to 15thNight
65%
760
25%
2443
24%
760
70%
760
35%
1363
November16th to endNight
57%
780
23%
2668
24%
780
60%
780
30%
1532
December1st to 15thNight
52%
728
21%
2548
19%
728
58%
728
24%
1573
December16th to endNight
45%
768
21%
2688
19%
768
51%
768
21%
1730

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%312212235%63%
48628
Night
12%312212335%59%
48005
TransparencyDay
24%38%18%24%20%
48309
Night
27%38%18%22%19%
47824
SeeingDay
12%8%23%31%19%4
6108
Night
13%312%31%33%5%
15460

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
21%314323245%46%
1456
16th to endDay
23%413223236%45%
1728
February1st to 15thDay
22%414223335%46%
1576
16th to endDay
22%6%22213447%41%
1568
March1st to 15thDay
24%5%24423345%40%
1911
16th to endDay
21%5%2341235%7%42%
2157
April1st to 15thDay
17%5%25%324447%42%
2149
16th to endDay
9%313213346%59%
2160
May1st to 15thDay
5%21321225%6%65%
2348
16th to endDay
6%213322446%61%
2615
June1st to 15thDay
5%212313345%64%
2520
16th to endDay
211112383%
2520
July1st to 15thDay
11112286%
2520
16th to endDay
1112288%
2542
August1st to 15thDay
11112286%
2334
16th to endDay
112288%
2292
September1st to 15thDay
1111112483%
2160
16th to endDay
31111225%77%
2004
October1st to 15thDay
5%21221233469%
1800
16th to endDay
11%312313345%59%
1920
November1st to 15thDay
14%31333345%7%48%
1746
16th to endDay
20%41432224449%
1618
December1st to 15thDay
22%5%2422434443%
1448
16th to endDay
27%5%23323235%40%
1536
January1st to 15thNight
18%5%22312347%47%
2479
16th to endNight
21%42332223449%
2496
February1st to 15thNight
20%5%23323347%43%
2276
16th to endNight
21%413223345%45%
1905
March1st to 15thNight
23%5%2331445%7%38%
2046
16th to endNight
19%5%24313335%46%
2067
April1st to 15thNight
14%5%25%33445%7%43%
1799
16th to endNight
9%313222346%60%
1800
May1st to 15thNight
5%22213346%66%
1600
16th to endNight
5%313314447%61%
1496
June1st to 15thNight
5%213212347%66%
1440
16th to endNight
21111223280%
1440
July1st to 15thNight
1121286%
1440
16th to endNight
111289%
1624
August1st to 15thNight
11111121383%
1623
16th to endNight
1123385%
1910
September1st to 15thNight
1111112385%
1800
16th to endNight
2111123480%
1953
October1st to 15thNight
7%11221223470%
2160
16th to endNight
9%211222345%64%
2304
November1st to 15thNight
14%31221346%6%53%
2443
16th to endNight
17%413412345%50%
2668
December1st to 15thNight
24%413323336%44%
2548
16th to endNight
27%413313335%42%
2688

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
41%211%20%17%8%
1456
16th to endDay
42%36%15%18%13%
1728
February1st to 15thDay
40%411%17%20%5%
1576
16th to endDay
41%311%25%14%2
1568
March1st to 15thDay
46%310%16%15%6%
1911
16th to endDay
42%5%13%18%15%4
2157
April1st to 15thDay
40%411%21%17%3
2149
16th to endDay
26%412%24%23%7%
2160
May1st to 15thDay
19%210%26%29%11%
2348
16th to endDay
23%5%13%27%22%8%
2619
June1st to 15thDay
20%5%10%19%22%21%
2520
16th to endDay
8%1415%35%33%
2520
July1st to 15thDay
6%129%29%50%
2371
16th to endDay
5%129%24%56%
2384
August1st to 15thDay
6%1211%32%44%
2318
16th to endDay
41111%36%43%
2292
September1st to 15thDay
7%1311%33%42%
2160
16th to endDay
11%16%22%33%24%
2004
October1st to 15thDay
18%37%19%27%23%
1800
16th to endDay
26%46%20%23%18%
1920
November1st to 15thDay
34%5%12%24%14%8%
1746
16th to endDay
39%39%19%19%8%
1618
December1st to 15thDay
44%38%16%21%5%
1448
16th to endDay
47%47%14%19%6%
1536
January1st to 15thNight
36%411%18%18%9%
2479
16th to endNight
40%28%14%18%16%
2496
February1st to 15thNight
41%39%18%17%10%
2288
16th to endNight
39%410%23%18%4
1905
March1st to 15thNight
43%412%15%16%7%
2046
16th to endNight
41%49%21%16%6%
2067
April1st to 15thNight
37%6%12%20%15%7%
1799
16th to endNight
25%5%11%21%28%8%
1800
May1st to 15thNight
19%49%22%30%13%
1601
16th to endNight
22%5%13%26%23%9%
1496
June1st to 15thNight
18%5%12%20%22%20%
1440
16th to endNight
11%2415%28%37%
1440
July1st to 15thNight
6%1211%23%54%
1360
16th to endNight
5%210%20%60%
1519
August1st to 15thNight
9%1113%30%43%
1614
16th to endNight
5%1313%30%45%
1910
September1st to 15thNight
7%1210%34%43%
1800
16th to endNight
9%25%17%37%28%
1953
October1st to 15thNight
18%25%19%27%26%
2160
16th to endNight
22%29%20%23%22%
2304
November1st to 15thNight
30%5%13%24%16%9%
2443
16th to endNight
35%48%22%19%10%
2668
December1st to 15thNight
41%49%16%20%7%
2548
16th to endNight
45%47%13%19%9%
2688

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
39%5%19%27%8%
84
16th to endDay
26%7%20%28%13%3
256
February1st to 15thDay
27%7%22%24%17%
236
16th to endDay
26%13%21%24%13%1
236
March1st to 15thDay
30%12%22%18%13%2
270
16th to endDay
26%14%23%22%12%
288
April1st to 15thDay
22%16%26%23%8%2
269
16th to endDay
12%19%30%28%6%2
270
May1st to 15thDay
9%12%35%28%11%2
288
16th to endDay
7%11%20%27%25%6%
330
June1st to 15thDay
6%14%26%31%16%4
315
16th to endDay
26%24%40%20%6%
315
July1st to 15thDay
1119%46%23%6%
305
16th to endDay
22%44%25%6%
327
August1st to 15thDay
1123%40%26%6%
315
16th to endDay
1121%38%28%9%
332
September1st to 15thDay
1320%39%28%6%
315
16th to endDay
39%21%33%28%2
315
October1st to 15thDay
6%12%26%29%21%3
315
16th to endDay
14%5%19%31%24%4
336
November1st to 15thDay
23%6%12%24%28%4
162
16th to endDay
21%421%37%12%1
103
December1st to 15thDay
43%332%19%1
62
16th to endDay
18%7%20%25%21%6%
64
January1st to 15thNight
20%213%41%18%3
720
16th to endNight
23%314%35%20%2
768
February1st to 15thNight
22%411%35%24%2
704
16th to endNight
23%5%14%32%21%3
632
March1st to 15thNight
24%6%11%28%25%3
720
16th to endNight
21%5%20%26%23%2
768
April1st to 15thNight
16%8%18%31%21%3
719
16th to endNight
11%6%15%34%26%6%
720
May1st to 15thNight
7%321%31%31%4
521
16th to endNight
5%417%26%40%5%
375
June1st to 15thNight
5%118%31%40%3
360
16th to endNight
3110%30%46%7%
360
July1st to 15thNight
224%65%7%
340
16th to endNight
422%63%9%
488
August1st to 15thNight
2326%57%9%
541
16th to endNight
5%28%56%8%
764
September1st to 15thNight
15%25%56%10%
720
16th to endNight
3110%30%39%14%
716
October1st to 15thNight
7%5%13%30%34%8%
720
16th to endNight
10%29%32%35%8%
768
November1st to 15thNight
16%213%32%29%5%
760
16th to endNight
17%314%36%23%3
780
December1st to 15thNight
25%311%36%21%1
728
16th to endNight
27%416%33%17%1
768
Page generated at 2017-12-03 08:16:43. Version ac04

Copyright 2017 A. Danko


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