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 2018-08-29.

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
76%
16593
31%
50601
29%
16559
78%
16559
48%
25374

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%
776
22%
2703
25%
776
69%
776
35%
1465
January16th to endNight
65%
832
27%
2704
28%
832
68%
832
33%
1537
February1st to 15thNight
66%
759
28%
2356
29%
757
70%
757
36%
1325
February16th to endNight
62%
684
25%
2051
27%
684
64%
684
33%
1240
March1st to 15thNight
63%
780
19%
2303
20%
780
65%
780
33%
1381
March16th to endNight
66%
832
23%
2179
18%
832
70%
832
40%
1307
April1st to 15thNight
66%
779
24%
1949
15%
779
67%
779
42%
1179
April16th to endNight
71%
772
26%
1930
15%
772
72%
772
51%
1079
May1st to 15thNight
75%
669
30%
1839
21%
669
77%
669
58%
892
May16th to endNight
77%
452
31%
1671
33%
452
80%
452
51%
697
June1st to 15thNight
86%
390
33%
1560
42%
390
88%
390
57%
570
June16th to endNight
94%
390
39%
1560
52%
390
95%
390
80%
455
July1st to 15thNight
94%
370
37%
1480
49%
370
94%
370
70%
476
July16th to endNight
89%
503
39%
1632
41%
474
89%
474
61%
651
August1st to 15thNight
91%
710
39%
1856
28%
707
91%
707
78%
818
August16th to endNight
95%
819
44%
2049
29%
819
95%
819
83%
914
September1st to 15thNight
93%
720
43%
1800
32%
720
93%
720
78%
820
September16th to endNight
89%
716
46%
1950
43%
716
90%
716
75%
849
October1st to 15thNight
82%
720
33%
2112
35%
720
83%
720
58%
983
October16th to endNight
83%
768
41%
2315
44%
768
85%
768
59%
1061
November1st to 15thNight
77%
760
30%
2470
34%
760
80%
760
47%
1194
November16th to endNight
73%
780
32%
2535
34%
780
75%
780
41%
1307
December1st to 15thNight
68%
780
25%
2685
27%
780
70%
780
33%
1466
December16th to endNight
56%
832
25%
2912
23%
832
63%
832
27%
1708

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%
51646
Night
9%312212235%65%
50790
TransparencyDay
24%36%19%26%19%
51325
Night
22%28%21%25%18%
50611
SeeingDay
11%7%27%34%13%5%
7059
Night
10%16%33%38%9%
16604

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
16%5%12313346%50%
1562
16th to endDay
17%6%24223336%46%
1872
February1st to 15thDay
15%5%23213445%50%
1826
16th to endDay
19%8%3432334443%
1709
March1st to 15thDay
16%7%2342445%7%40%
1986
16th to endDay
16%5%244235%46%44%
2396
April1st to 15thDay
14%6%33323346%48%
2329
16th to endDay
10%5%13313346%55%
2305
May1st to 15thDay
6%313312335%65%
2438
16th to endDay
7%313223346%60%
2791
June1st to 15thDay
3112212335%71%
2730
16th to endDay
111111386%
2730
July1st to 15thDay
11111112482%
2730
16th to endDay
11121223379%
2783
August1st to 15thDay
111111286%
2347
16th to endDay
11111112383%
2450
September1st to 15thDay
21111121283%
2160
16th to endDay
211223479%
2009
October1st to 15thDay
5%21221235%467%
1845
16th to endDay
5%212223245%67%
1908
November1st to 15thDay
9%312423435%58%
1719
16th to endDay
10%323323336%57%
1755
December1st to 15thDay
14%5%14323336%51%
1602
16th to endDay
17%5%34423446%45%
1664
January1st to 15thNight
14%313314346%52%
2703
16th to endNight
15%412223347%50%
2704
February1st to 15thNight
12%423313348%51%
2354
16th to endNight
18%6%13312345%49%
2051
March1st to 15thNight
15%423323346%49%
2303
16th to endNight
14%412313237%55%
2179
April1st to 15thNight
13%41321335%6%54%
1949
16th to endNight
7%31221323466%
1930
May1st to 15thNight
3113212235%71%
1839
16th to endNight
5%212211336%70%
1670
June1st to 15thNight
21112235%76%
1560
16th to endNight
111389%
1560
July1st to 15thNight
11111222383%
1560
16th to endNight
121221222477%
1735
August1st to 15thNight
111112286%
1865
16th to endNight
1112386%
2049
September1st to 15thNight
1111222285%
1800
16th to endNight
1111112383%
1950
October1st to 15thNight
5%22112335%71%
2112
16th to endNight
5%11211335%72%
2315
November1st to 15thNight
9%212211246%65%
2470
16th to endNight
9%31321335%6%58%
2535
December1st to 15thNight
12%313313347%53%
2685
16th to endNight
19%413323346%47%
2912

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
34%39%22%19%9%
1562
16th to endDay
40%38%17%16%12%
1872
February1st to 15thDay
35%38%23%20%7%
1826
16th to endDay
45%37%24%17%1
1709
March1st to 15thDay
42%410%19%15%6%
1986
16th to endDay
40%5%13%23%14%2
2396
April1st to 15thDay
38%310%24%18%4
2329
16th to endDay
30%39%28%23%3
2305
May1st to 15thDay
22%36%29%31%6%
2438
16th to endDay
25%47%31%25%5%
2795
June1st to 15thDay
17%37%20%31%19%
2730
16th to endDay
7%1110%40%38%
2730
July1st to 15thDay
8%217%27%52%
2581
16th to endDay
11%2311%26%44%
2623
August1st to 15thDay
6%110%30%49%
2331
16th to endDay
8%110%41%36%
2450
September1st to 15thDay
9%2212%34%38%
2160
16th to endDay
10%2223%38%22%
2009
October1st to 15thDay
19%35%20%28%23%
1845
16th to endDay
19%25%24%27%20%
1908
November1st to 15thDay
28%39%23%22%12%
1719
16th to endDay
29%27%21%29%9%
1755
December1st to 15thDay
36%38%20%20%10%
1602
16th to endDay
40%410%18%16%9%
1664
January1st to 15thNight
32%210%23%22%8%
2703
16th to endNight
33%310%17%20%14%
2704
February1st to 15thNight
31%39%26%20%8%
2365
16th to endNight
37%212%27%16%2
2051
March1st to 15thNight
35%314%20%19%5%
2303
16th to endNight
31%415%27%17%4
2179
April1st to 15thNight
31%316%28%17%4
1949
16th to endNight
22%313%30%24%5%
1930
May1st to 15thNight
17%29%30%30%9%
1840
16th to endNight
17%38%35%29%6%
1671
June1st to 15thNight
12%210%21%31%21%
1560
16th to endNight
4213%37%41%
1560
July1st to 15thNight
7%117%28%52%
1480
16th to endNight
13%1111%24%46%
1632
August1st to 15thNight
7%1111%27%49%
1856
16th to endNight
6%1110%40%40%
2049
September1st to 15thNight
8%1112%34%41%
1800
16th to endNight
9%1221%43%22%
1950
October1st to 15thNight
16%26%23%30%20%
2112
16th to endNight
16%26%25%27%22%
2315
November1st to 15thNight
22%211%24%26%12%
2470
16th to endNight
26%38%23%28%9%
2535
December1st to 15thNight
31%411%20%20%11%
2685
16th to endNight
38%312%18%17%10%
2912

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
41%118%18%12%10%
100
16th to endDay
24%423%25%16%5%
304
February1st to 15thDay
21%7%22%24%18%4
309
16th to endDay
25%11%29%20%12%1
290
March1st to 15thDay
23%10%26%23%13%2
330
16th to endDay
24%10%28%25%9%1
352
April1st to 15thDay
24%14%28%23%8%
329
16th to endDay
16%16%33%22%9%1
318
May1st to 15thDay
12%12%33%29%7%4
348
16th to endDay
12%12%25%34%10%4
394
June1st to 15thDay
5%13%32%29%14%5%
375
16th to endDay
15%30%41%13%9%
375
July1st to 15thDay
1121%50%14%10%
365
16th to endDay
1221%52%12%10%
391
August1st to 15thDay
2330%45%9%7%
359
16th to endDay
1224%48%15%8%
385
September1st to 15thDay
3332%40%16%3
315
16th to endDay
5%6%31%39%15%2
315
October1st to 15thDay
5%11%34%34%11%2
315
16th to endDay
7%7%27%34%19%4
324
November1st to 15thDay
10%314%35%26%8%
135
16th to endDay
14%7%21%29%21%5%
135
December1st to 15thDay
13%131%23%26%6%
100
16th to endDay
15%5%19%26%18%14%
96
January1st to 15thNight
16%18%39%23%10%
780
16th to endNight
19%19%35%27%7%
832
February1st to 15thNight
16%17%37%28%8%
764
16th to endNight
23%17%35%26%6%
684
March1st to 15thNight
17%28%38%26%6%
780
16th to endNight
16%28%37%30%4
832
April1st to 15thNight
15%29%39%28%4
779
16th to endNight
8%310%36%32%7%
772
May1st to 15thNight
4212%38%35%6%
670
16th to endNight
6%9%29%44%7%
453
June1st to 15thNight
3431%52%7%
390
16th to endNight
1227%61%6%
390
July1st to 15thNight
118%67%12%
370
16th to endNight
213%63%19%
503
August1st to 15thNight
1224%58%12%
710
16th to endNight
117%65%15%
819
September1st to 15thNight
1129%52%15%
720
16th to endNight
1431%51%10%
716
October1st to 15thNight
6%6%38%38%9%
720
16th to endNight
7%5%28%40%18%
768
November1st to 15thNight
10%15%34%35%13%
760
16th to endNight
10%16%37%32%10%
780
December1st to 15thNight
15%16%41%27%7%
780
16th to endNight
21%112%36%21%6%
832
Page generated at 2018-08-30 02:34:23. Version ac04

Copyright 2018 A. Danko


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