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

2017-09-12
.

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%
15452
25%
46872
22%
15416
70%
15416
35%
26958

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
62%
716
20%
2360
20%
716
66%
716
32%
1353
January16th to endNight
62%
768
25%
2496
27%
768
64%
768
30%
1483
February1st to 15thNight
57%
698
22%
2281
23%
698
62%
698
26%
1415
February16th to endNight
54%
632
22%
1895
19%
632
60%
632
28%
1200
March1st to 15thNight
58%
720
19%
2001
17%
720
60%
720
29%
1305
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%
706
33%
1765
25%
706
86%
706
51%
994
September16th to endNight
83%
656
36%
1799
34%
656
84%
656
56%
909
October1st to 15thNight
73%
660
29%
1980
31%
660
76%
660
43%
1060
October16th to endNight
73%
704
32%
2112
34%
704
76%
704
39%
1169
November1st to 15thNight
71%
700
30%
2168
30%
700
74%
700
41%
1155
November16th to endNight
68%
720
25%
2409
27%
720
71%
720
35%
1311
December1st to 15thNight
57%
720
22%
2520
21%
720
64%
720
26%
1514
December16th to endNight
52%
768
21%
2688
20%
768
58%
768
26%
1614

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%
47786
Night
9%42332345%8%52%
47062
TransparencyDay
29%5%10%20%21%11%
47476
Night
31%410%19%20%12%
46873
SeeingDay
9%417%32%29%7%
6039
Night
11%210%28%35%11%
15464

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
14%41432435%6%48%
1575
16th to endDay
15%5%25%423347%45%
1728
February1st to 15thDay
17%435%414347%43%
1582
16th to endDay
18%5%36%424446%38%
1579
March1st to 15thDay
15%435%5%25%5%5%9%37%
1956
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%9%65%
2114
16th to endDay
3312213445%68%
1829
October1st to 15thDay
5%223423447%60%
1650
16th to endDay
8%313324436%57%
1760
November1st to 15thDay
8%32432346%7%52%
1690
16th to endDay
12%5%24323337%51%
1548
December1st to 15thDay
17%5%34423447%42%
1440
16th to endDay
17%5%2442335%8%41%
1536
January1st to 15thNight
13%42332445%7%48%
2360
16th to endNight
15%424323346%49%
2496
February1st to 15thNight
16%5%234245%5%6%43%
2269
16th to endNight
16%6%2332345%8%42%
1895
March1st to 15thNight
15%6%24423448%43%
2001
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%61%
1765
16th to endNight
3312212338%68%
1799
October1st to 15thNight
6%413322347%60%
1980
16th to endNight
6%414423347%58%
2112
November1st to 15thNight
8%412313348%58%
2168
16th to endNight
7%414423347%55%
2409
December1st to 15thNight
16%5%23423247%46%
2520
16th to endNight
19%42331425%5%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
34%6%13%20%15%10%
1575
16th to endDay
37%7%8%12%20%12%
1728
February1st to 15thDay
39%410%18%20%5%
1582
16th to endDay
43%7%8%23%11%4
1579
March1st to 15thDay
39%8%11%19%14%5%
1956
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%26%17%26%24%
2114
16th to endDay
18%37%23%29%17%
1829
October1st to 15thDay
22%411%19%24%17%
1650
16th to endDay
28%410%24%19%12%
1760
November1st to 15thDay
29%5%11%26%20%5%
1690
16th to endDay
32%5%11%18%25%6%
1548
December1st to 15thDay
41%5%12%16%18%6%
1440
16th to endDay
38%6%13%16%17%6%
1536
January1st to 15thNight
33%5%13%21%17%9%
2360
16th to endNight
36%5%11%13%16%16%
2496
February1st to 15thNight
39%5%10%17%17%8%
2281
16th to endNight
38%5%12%26%13%3
1895
March1st to 15thNight
39%5%12%20%15%6%
2001
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%12%27%27%
1765
16th to endNight
19%25%22%33%17%
1799
October1st to 15thNight
25%48%21%22%17%
1980
16th to endNight
29%37%23%21%15%
2112
November1st to 15thNight
26%412%25%23%7%
2168
16th to endNight
28%5%9%23%22%10%
2409
December1st to 15thNight
39%410%17%20%8%
2520
16th to endNight
37%5%14%17%17%7%
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
20%318%26%21%8%
204
16th to endDay
18%321%25%24%7%
256
February1st to 15thDay
18%5%20%25%22%7%
237
16th to endDay
17%10%21%27%18%4
238
March1st to 15thDay
18%7%22%25%22%5%
270
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
410%32%42%10%
300
16th to endDay
6%311%29%37%12%
255
October1st to 15thDay
5%318%32%30%8%
255
16th to endDay
12%317%31%26%8%
272
November1st to 15thDay
8%315%19%36%16%
196
16th to endDay
6%8%16%41%23%3
78
December1st to 15thDay
26%323%28%16%1
60
16th to endDay
12%10%12%23%32%7%
64
January1st to 15thNight
15%310%30%30%9%
720
16th to endNight
16%49%30%28%10%
768
February1st to 15thNight
17%5%11%27%30%7%
704
16th to endNight
19%415%34%20%6%
632
March1st to 15thNight
16%5%11%28%30%7%
720
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
4321%50%20%
706
16th to endNight
5%5%23%45%19%
656
October1st to 15thNight
8%36%28%37%16%
660
16th to endNight
9%17%26%35%19%
704
November1st to 15thNight
10%19%29%38%10%
700
16th to endNight
8%210%34%33%10%
720
December1st to 15thNight
17%411%31%27%8%
720
16th to endNight
18%5%16%33%21%4
768
Page generated at 2017-09-13 04:39:04. Version ac04

Copyright 2017 A. Danko


Baskin Engineering Observatory Clear Sky Chart | Charts Home