Baskin Engineering Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Baskin Engineering Observatory clear sky chart from 2005-11-05 to 2018-03-11.

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
67%
16174
25%
49142
23%
16138
70%
16138
35%
28169

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
61%
776
20%
2558
20%
776
64%
776
30%
1501
January16th to endNight
62%
832
24%
2704
25%
832
65%
832
29%
1615
February1st to 15thNight
59%
758
25%
2475
25%
758
65%
758
28%
1488
February16th to endNight
55%
684
24%
2051
20%
684
61%
684
29%
1273
March1st to 15thNight
57%
764
18%
2124
16%
764
59%
764
28%
1400
March16th to endNight
55%
768
20%
2091
15%
768
60%
768
32%
1344
April1st to 15thNight
54%
719
22%
1799
12%
719
57%
719
33%
1178
April16th to endNight
61%
720
24%
1800
11%
720
65%
720
44%
1053
May1st to 15thNight
71%
635
22%
1715
15%
635
72%
635
44%
951
May16th to endNight
68%
417
21%
1540
18%
417
73%
417
31%
813
June1st to 15thNight
72%
360
22%
1440
24%
360
76%
360
30%
757
June16th to endNight
87%
360
28%
1440
36%
360
89%
360
43%
629
July1st to 15thNight
85%
409
25%
1429
29%
409
85%
409
43%
672
July16th to endNight
75%
564
26%
1593
25%
531
75%
531
32%
935
August1st to 15thNight
71%
568
23%
1641
19%
565
72%
565
31%
999
August16th to endNight
78%
764
28%
1910
18%
764
78%
764
44%
1145
September1st to 15thNight
85%
720
33%
1800
25%
720
85%
720
51%
1017
September16th to endNight
83%
716
39%
1962
36%
716
85%
716
58%
975
October1st to 15thNight
74%
720
28%
2160
31%
720
77%
720
45%
1127
October16th to endNight
74%
768
34%
2304
37%
768
77%
768
41%
1255
November1st to 15thNight
71%
760
28%
2354
29%
760
73%
760
40%
1278
November16th to endNight
67%
780
26%
2610
27%
780
70%
780
34%
1437
December1st to 15thNight
60%
780
23%
2730
23%
780
65%
780
28%
1585
December16th to endNight
52%
832
22%
2912
21%
832
59%
832
26%
1742

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%42432345%8%53%
49484
Night
9%42332345%8%52%
49332
TransparencyDay
29%5%10%20%21%11%
49174
Night
31%410%19%20%13%
49143
SeeingDay
9%417%31%29%7%
6623
Night
11%210%29%35%11%
16186

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%415%43435%6%45%
1707
16th to endDay
15%5%25%423347%45%
1872
February1st to 15thDay
16%42441435%7%45%
1718
16th to endDay
17%5%35%4245%46%40%
1709
March1st to 15thDay
15%435%5%25%5%5%9%37%
2069
16th to endDay
11%6%25%5%35%5%48%41%
2133
April1st to 15thDay
12%5%3443345%8%44%
2149
16th to endDay
6%414313448%54%
2160
May1st to 15thDay
432331335%10%57%
2233
16th to endDay
5%5%25%5%2445%6%51%
2572
June1st to 15thDay
45%1442446%8%52%
2520
16th to endDay
1212222349%66%
2520
July1st to 15thDay
23133235%5%10%59%
2442
16th to endDay
131321446%9%61%
2468
August1st to 15thDay
142332345%9%60%
2310
16th to endDay
41321346%11%60%
2292
September1st to 15thDay
231221235%8%65%
2160
16th to endDay
3312213346%68%
1995
October1st to 15thDay
5%223323437%62%
1800
16th to endDay
7%313324436%57%
1920
November1st to 15thDay
8%41442346%7%52%
1834
16th to endDay
12%5%24323337%50%
1677
December1st to 15thDay
16%5%24413447%44%
1560
16th to endDay
16%6%2442345%8%41%
1664
January1st to 15thNight
14%5%2332445%7%46%
2558
16th to endNight
15%423323347%48%
2704
February1st to 15thNight
14%5%2332445%6%46%
2463
16th to endNight
15%5%2332445%8%44%
2051
March1st to 15thNight
15%7%2442345%8%41%
2124
16th to endNight
14%5%2342335%7%46%
2091
April1st to 15thNight
12%5%2343345%8%46%
1799
16th to endNight
7%313322349%58%
1800
May1st to 15thNight
35%1232445%9%57%
1715
16th to endNight
45%23425%45%9%53%
1539
June1st to 15thNight
23145%3346%8%55%
1440
16th to endNight
21222345%8%65%
1440
July1st to 15thNight
131333336%9%59%
1515
16th to endNight
5%26%5%35%5%5%11%46%
1701
August1st to 15thNight
17%36%5%25%5%5%10%47%
1650
16th to endNight
15%25%42445%9%53%
1910
September1st to 15thNight
13123245%5%7%60%
1800
16th to endNight
2311212338%69%
1962
October1st to 15thNight
5%413312336%63%
2160
16th to endNight
5%41342235%7%58%
2304
November1st to 15thNight
8%413313348%57%
2354
16th to endNight
8%414423347%53%
2610
December1st to 15thNight
15%5%23323248%48%
2730
16th to endNight
18%5%2331435%5%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
37%6%12%19%14%9%
1707
16th to endDay
37%7%9%13%20%11%
1872
February1st to 15thDay
37%410%19%21%7%
1718
16th to endDay
41%7%9%24%13%4
1709
March1st to 15thDay
40%8%11%19%14%5%
2069
16th to endDay
38%9%14%18%14%2
2133
April1st to 15thDay
35%8%13%22%18%2
2149
16th to endDay
28%6%14%25%18%7%
2160
May1st to 15thDay
22%6%13%27%23%6%
2233
16th to endDay
30%7%13%23%19%5%
2576
June1st to 15thDay
29%7%13%21%20%8%
2520
16th to endDay
19%29%20%31%16%
2520
July1st to 15thDay
24%16%15%26%26%
2299
16th to endDay
24%25%17%27%21%
2313
August1st to 15thDay
25%15%18%27%20%
2294
16th to endDay
25%16%22%26%18%
2292
September1st to 15thDay
21%27%17%26%24%
2160
16th to endDay
17%38%23%30%16%
1995
October1st to 15thDay
21%410%18%23%21%
1800
16th to endDay
27%310%23%19%14%
1920
November1st to 15thDay
29%5%12%27%20%5%
1834
16th to endDay
32%5%11%18%25%5%
1677
December1st to 15thDay
39%5%11%16%17%10%
1560
16th to endDay
38%6%12%16%19%6%
1664
January1st to 15thNight
35%5%13%21%16%8%
2558
16th to endNight
36%5%11%14%16%15%
2704
February1st to 15thNight
37%5%10%16%19%11%
2475
16th to endNight
37%5%12%27%13%4
2051
March1st to 15thNight
40%5%12%20%15%6%
2124
16th to endNight
37%6%13%19%18%5%
2091
April1st to 15thNight
35%7%13%24%16%3
1799
16th to endNight
25%6%14%27%20%7%
1800
May1st to 15thNight
25%5%12%21%25%10%
1716
16th to endNight
30%5%15%23%20%5%
1540
June1st to 15thNight
28%7%10%20%19%13%
1440
16th to endNight
20%37%14%30%23%
1440
July1st to 15thNight
24%2413%22%32%
1429
16th to endNight
35%45%14%17%22%
1593
August1st to 15thNight
38%2413%21%18%
1641
16th to endNight
30%25%13%24%24%
1910
September1st to 15thNight
24%25%13%27%26%
1800
16th to endNight
17%25%23%33%16%
1962
October1st to 15thNight
23%48%19%21%22%
2160
16th to endNight
28%37%22%21%17%
2304
November1st to 15thNight
27%412%25%23%7%
2354
16th to endNight
30%5%9%23%22%9%
2610
December1st to 15thNight
36%49%17%19%12%
2730
16th to endNight
37%5%13%16%18%7%
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
23%317%26%21%7%
246
16th to endDay
17%320%26%25%7%
304
February1st to 15thDay
15%419%25%24%10%
283
16th to endDay
15%11%23%27%18%4
290
March1st to 15thDay
20%7%21%26%20%4
312
16th to endDay
10%7%27%34%16%3
288
April1st to 15thDay
14%9%31%25%15%2
269
16th to endDay
6%11%31%29%18%2
270
May1st to 15thDay
10%7%25%31%21%3
288
16th to endDay
8%6%19%30%27%7%
330
June1st to 15thDay
6%323%41%22%2
315
16th to endDay
113%41%35%6%
315
July1st to 15thDay
5%7%34%42%10%
305
16th to endDay
3337%43%11%
327
August1st to 15thDay
47%39%41%6%
315
16th to endDay
35%37%42%9%
332
September1st to 15thDay
5%10%33%40%10%
315
16th to endDay
5%312%30%37%11%
315
October1st to 15thDay
4320%33%30%8%
315
16th to endDay
11%316%28%27%12%
336
November1st to 15thDay
10%314%26%32%13%
250
16th to endDay
10%5%13%38%27%4
117
December1st to 15thDay
17%318%21%30%8%
90
16th to endDay
9%11%11%23%29%14%
96
January1st to 15thNight
16%310%30%30%8%
780
16th to endNight
15%39%29%30%9%
832
February1st to 15thNight
16%5%11%27%30%9%
764
16th to endNight
18%5%15%34%21%5%
684
March1st to 15thNight
16%5%11%28%30%6%
764
16th to endNight
15%315%32%27%4
768
April1st to 15thNight
14%5%17%33%25%3
719
16th to endNight
8%5%19%31%27%8%
720
May1st to 15thNight
7%113%34%34%9%
636
16th to endNight
6%313%29%33%12%
418
June1st to 15thNight
6%11%37%36%7%
360
16th to endNight
2333%50%8%
360
July1st to 15thNight
7%118%52%20%
409
16th to endNight
7%220%46%23%
564
August1st to 15thNight
7%15%22%47%15%
568
16th to endNight
7%221%50%17%
764
September1st to 15thNight
5%321%49%20%
720
16th to endNight
46%24%45%18%
716
October1st to 15thNight
7%27%30%36%15%
720
16th to endNight
9%17%25%36%20%
768
November1st to 15thNight
10%19%31%37%10%
760
16th to endNight
9%29%33%33%10%
780
December1st to 15thNight
16%310%31%28%9%
780
16th to endNight
18%5%16%31%23%5%
832
Page generated at 2018-03-12 10:28:14. Version ac04

Copyright 2018 A. Danko


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