Bayt Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bayt Observatory clear sky chart from 2005-11-05 to 2017-09-17.

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
75%
15385
31%
46861
29%
15351
78%
15351
48%
23557

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
66%
716
22%
2494
24%
716
70%
716
36%
1332
January16th to endNight
63%
768
27%
2496
29%
768
67%
768
33%
1428
February1st to 15thNight
64%
699
26%
2171
26%
697
68%
697
34%
1252
February16th to endNight
62%
632
24%
1895
26%
632
64%
632
32%
1151
March1st to 15thNight
65%
720
20%
2126
20%
720
67%
720
35%
1249
March16th to endNight
67%
768
23%
2011
18%
768
71%
768
41%
1189
April1st to 15thNight
66%
719
24%
1799
15%
719
67%
719
42%
1084
April16th to endNight
70%
720
26%
1800
15%
720
72%
720
50%
1011
May1st to 15thNight
74%
617
29%
1697
20%
617
76%
617
58%
823
May16th to endNight
77%
416
31%
1539
33%
416
80%
416
50%
646
June1st to 15thNight
85%
360
31%
1440
39%
360
87%
360
54%
540
June16th to endNight
94%
360
40%
1440
52%
360
95%
360
79%
425
July1st to 15thNight
95%
340
36%
1360
48%
340
95%
340
72%
428
July16th to endNight
89%
464
40%
1497
41%
435
90%
435
62%
597
August1st to 15thNight
91%
666
38%
1740
27%
663
91%
663
78%
771
August16th to endNight
94%
764
45%
1910
29%
764
94%
764
82%
856
September1st to 15thNight
93%
720
43%
1800
32%
720
93%
720
78%
820
September16th to endNight
89%
664
45%
1807
42%
664
90%
664
75%
790
October1st to 15thNight
81%
660
33%
1936
36%
660
82%
660
56%
922
October16th to endNight
82%
704
39%
2122
42%
704
85%
704
58%
975
November1st to 15thNight
78%
700
31%
2275
34%
700
81%
700
48%
1090
November16th to endNight
73%
720
31%
2340
33%
720
76%
720
42%
1198
December1st to 15thNight
66%
720
24%
2478
25%
720
68%
720
31%
1398
December16th to endNight
55%
768
24%
2688
22%
768
62%
768
27%
1582

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
8%312212335%64%
47910
Night
9%312212235%65%
47050
TransparencyDay
24%36%19%26%19%
47589
Night
23%29%21%25%17%
46871
SeeingDay
11%8%28%34%12%4
5844
Night
10%16%33%38%9%
15396

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
15%5%12213346%53%
1441
16th to endDay
18%6%24222336%46%
1728
February1st to 15thDay
16%6%23213445%49%
1682
16th to endDay
20%8%3432334443%
1579
March1st to 15thDay
16%6%2342445%7%41%
1833
16th to endDay
15%5%243235%46%44%
2212
April1st to 15thDay
14%7%33323336%48%
2149
16th to endDay
10%5%13313346%54%
2160
May1st to 15thDay
6%312212335%66%
2250
16th to endDay
7%313223346%60%
2571
June1st to 15thDay
3213312335%69%
2520
16th to endDay
111111386%
2520
July1st to 15thDay
11111112482%
2520
16th to endDay
21121222379%
2567
August1st to 15thDay
1111121286%
2210
16th to endDay
11111112383%
2292
September1st to 15thDay
21111121283%
2160
16th to endDay
221233478%
1857
October1st to 15thDay
6%21221345%465%
1691
16th to endDay
6%212222345%67%
1749
November1st to 15thDay
10%31232233459%
1584
16th to endDay
10%323323345%57%
1620
December1st to 15thDay
15%6%14323335%49%
1479
16th to endDay
18%5%34322335%45%
1536
January1st to 15thNight
13%313313246%54%
2494
16th to endNight
15%413323346%51%
2496
February1st to 15thNight
14%5%23313448%49%
2169
16th to endNight
19%6%12312346%48%
1895
March1st to 15thNight
14%423313446%52%
2126
16th to endNight
13%312313347%56%
2011
April1st to 15thNight
13%31221335%6%55%
1799
16th to endNight
7%31221323466%
1800
May1st to 15thNight
3113212235%71%
1697
16th to endNight
5%212112336%69%
1538
June1st to 15thNight
312213235%74%
1440
16th to endNight
1111389%
1440
July1st to 15thNight
1111221285%
1440
16th to endNight
221211212378%
1600
August1st to 15thNight
111112285%
1749
16th to endNight
1111386%
1910
September1st to 15thNight
1111222285%
1800
16th to endNight
11111112382%
1807
October1st to 15thNight
5%22122335%69%
1936
16th to endNight
6%11211335%72%
2122
November1st to 15thNight
9%212211246%66%
2275
16th to endNight
8%31331335%6%59%
2340
December1st to 15thNight
13%413313347%50%
2478
16th to endNight
20%413323246%47%
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
33%39%23%20%10%
1441
16th to endDay
41%38%16%16%13%
1728
February1st to 15thDay
37%39%23%18%6%
1682
16th to endDay
45%37%24%16%1
1579
March1st to 15thDay
41%411%18%16%6%
1833
16th to endDay
39%5%14%22%14%3
2212
April1st to 15thDay
38%39%25%18%4
2149
16th to endDay
30%310%28%22%4
2160
May1st to 15thDay
21%37%27%33%6%
2250
16th to endDay
24%47%31%25%5%
2575
June1st to 15thDay
18%37%20%29%19%
2520
16th to endDay
8%1111%40%37%
2520
July1st to 15thDay
8%217%25%54%
2371
16th to endDay
11%2310%24%48%
2407
August1st to 15thDay
6%1110%30%49%
2194
16th to endDay
8%111%39%37%
2292
September1st to 15thDay
9%2212%34%38%
2160
16th to endDay
10%3222%38%23%
1857
October1st to 15thDay
21%36%21%29%18%
1691
16th to endDay
20%25%25%29%16%
1749
November1st to 15thDay
28%39%21%24%12%
1584
16th to endDay
30%28%20%29%9%
1620
December1st to 15thDay
38%48%21%21%5%
1479
16th to endDay
41%411%19%15%8%
1536
January1st to 15thNight
31%211%22%23%8%
2494
16th to endNight
34%310%16%19%15%
2496
February1st to 15thNight
33%39%27%18%7%
2180
16th to endNight
37%213%27%15%3
1895
March1st to 15thNight
33%315%20%20%5%
2126
16th to endNight
29%416%26%17%5%
2011
April1st to 15thNight
30%316%28%16%4
1799
16th to endNight
23%414%27%24%6%
1800
May1st to 15thNight
17%29%28%31%10%
1698
16th to endNight
17%38%33%30%6%
1539
June1st to 15thNight
13%210%22%29%20%
1440
16th to endNight
5%213%37%40%
1440
July1st to 15thNight
6%116%29%53%
1360
16th to endNight
13%118%23%50%
1497
August1st to 15thNight
7%1112%28%48%
1740
16th to endNight
6%1110%39%40%
1910
September1st to 15thNight
8%1112%34%41%
1800
16th to endNight
9%1121%42%23%
1807
October1st to 15thNight
17%27%25%31%15%
1936
16th to endNight
16%26%25%28%19%
2122
November1st to 15thNight
21%211%23%26%13%
2275
16th to endNight
26%29%23%28%10%
2340
December1st to 15thNight
33%412%21%20%7%
2478
16th to endNight
39%312%18%16%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
46%120%15%8%7%
69
16th to endDay
26%423%25%16%4
256
February1st to 15thDay
25%7%23%23%14%4
255
16th to endDay
27%10%29%18%12%
238
March1st to 15thDay
21%11%27%22%14%2
270
16th to endDay
22%11%28%27%8%1
288
April1st to 15thDay
24%15%31%21%6%
269
16th to endDay
16%17%35%22%7%
270
May1st to 15thDay
12%13%34%28%5%4
288
16th to endDay
13%13%25%33%10%3
330
June1st to 15thDay
6%14%36%26%11%3
315
16th to endDay
15%30%42%10%8%
315
July1st to 15thDay
1123%51%11%9%
305
16th to endDay
1225%52%10%8%
327
August1st to 15thDay
2333%45%8%6%
315
16th to endDay
1226%46%15%7%
332
September1st to 15thDay
3332%40%16%3
315
16th to endDay
6%6%27%41%15%2
260
October1st to 15thDay
6%11%34%34%10%1
255
16th to endDay
8%8%30%33%18%1
261
November1st to 15thDay
11%27%30%35%13%
90
16th to endDay
14%10%24%33%15%2
90
December1st to 15thDay
17%132%26%19%1
67
16th to endDay
20%420%31%14%9%
64
January1st to 15thNight
15%19%40%23%10%
720
16th to endNight
19%19%36%25%8%
768
February1st to 15thNight
18%17%38%27%7%
704
16th to endNight
23%16%35%26%6%
632
March1st to 15thNight
15%28%38%26%7%
720
16th to endNight
15%27%37%31%5%
768
April1st to 15thNight
15%29%39%28%4
719
16th to endNight
8%310%37%33%6%
720
May1st to 15thNight
4213%38%36%6%
618
16th to endNight
7%9%29%44%7%
417
June1st to 15thNight
4433%50%6%
360
16th to endNight
1227%63%5%
360
July1st to 15thNight
19%68%10%
340
16th to endNight
215%62%18%
464
August1st to 15thNight
1225%59%10%
666
16th to endNight
118%64%14%
764
September1st to 15thNight
1129%52%15%
720
16th to endNight
1429%53%10%
664
October1st to 15thNight
7%5%37%38%9%
660
16th to endNight
7%5%29%40%16%
704
November1st to 15thNight
10%15%32%36%14%
700
16th to endNight
9%17%38%31%10%
720
December1st to 15thNight
16%16%42%26%6%
720
16th to endNight
22%112%37%20%5%
768
Page generated at 2017-09-18 05:38:21. Version ac04

Copyright 2017 A. Danko


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