Buena Vista Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Buena Vista Observatory clear sky chart from 2005-11-05 to 2017-04-25.

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
71%
14836
28%
45614
27%
14801
73%
14801
42%
24298

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
64%
716
19%
2476
21%
716
66%
716
30%
1416
January16th to endNight
61%
768
24%
2496
26%
768
63%
768
28%
1522
February1st to 15thNight
58%
697
23%
2258
24%
697
62%
697
28%
1379
February16th to endNight
58%
632
25%
1895
25%
632
61%
632
30%
1190
March1st to 15thNight
54%
720
17%
2067
17%
720
56%
720
27%
1363
March16th to endNight
59%
768
20%
2050
16%
768
61%
768
30%
1348
April1st to 15thNight
59%
719
19%
1799
12%
719
61%
719
32%
1203
April16th to endNight
68%
700
24%
1750
13%
700
70%
700
47%
1017
May1st to 15thNight
73%
527
30%
1517
23%
527
75%
527
54%
732
May16th to endNight
78%
343
23%
1368
27%
342
79%
342
43%
584
June1st to 15thNight
79%
330
28%
1320
36%
330
82%
330
50%
523
June16th to endNight
88%
330
34%
1320
48%
330
90%
330
65%
441
July1st to 15thNight
95%
310
37%
1240
51%
310
96%
310
74%
382
July16th to endNight
92%
454
37%
1401
39%
423
92%
423
71%
529
August1st to 15thNight
93%
534
40%
1517
32%
531
94%
531
77%
618
August16th to endNight
94%
700
43%
1750
28%
700
94%
700
83%
775
September1st to 15thNight
93%
660
45%
1650
33%
660
94%
660
82%
732
September16th to endNight
87%
656
43%
1776
39%
656
90%
656
71%
801
October1st to 15thNight
77%
660
32%
1980
34%
660
80%
660
50%
980
October16th to endNight
76%
704
35%
2112
38%
704
78%
704
49%
1067
November1st to 15thNight
73%
700
28%
2256
32%
700
75%
700
42%
1165
November16th to endNight
65%
720
25%
2408
26%
720
69%
720
36%
1307
December1st to 15thNight
58%
720
21%
2520
22%
720
62%
720
26%
1516
December16th to endNight
50%
768
22%
2688
21%
768
55%
768
22%
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
10%31221233463%
46025
Night
12%312212335%60%
45803
TransparencyDay
25%28%19%24%19%
45707
Night
27%38%19%22%18%
45621
SeeingDay
12%6%22%33%20%4
5293
Night
13%17%33%34%9%
14848

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
19%423322435%48%
1461
16th to endDay
22%6%23323236%43%
1728
February1st to 15thDay
20%5%24223335%45%
1600
16th to endDay
24%6%24212446%41%
1579
March1st to 15thDay
20%6%2432445%6%40%
1890
16th to endDay
18%424424446%42%
2172
April1st to 15thDay
18%6%23324446%43%
2149
16th to endDay
12%312213336%60%
2098
May1st to 15thDay
6%212313335%68%
2099
16th to endDay
6%312322446%61%
2391
June1st to 15thDay
5%212212235%69%
2310
16th to endDay
21111112383%
2310
July1st to 15thDay
1112285%
2310
16th to endDay
11111121284%
2352
August1st to 15thDay
11111287%
2104
16th to endDay
122287%
2100
September1st to 15thDay
111112285%
1980
16th to endDay
31121113379%
1852
October1st to 15thDay
6%12213336%67%
1650
16th to endDay
8%31332323461%
1760
November1st to 15thDay
10%31222435%6%56%
1603
16th to endDay
14%424322335%52%
1551
December1st to 15thDay
21%5%2433343444%
1440
16th to endDay
24%5%23313346%40%
1536
January1st to 15thNight
17%41332235%8%46%
2476
16th to endNight
18%5%1342334447%
2496
February1st to 15thNight
20%41332335%6%44%
2253
16th to endNight
21%5%13312345%47%
1895
March1st to 15thNight
21%434323345%42%
2067
16th to endNight
19%6%22323345%47%
2050
April1st to 15thNight
14%5%34424446%44%
1799
16th to endNight
10%322312346%59%
1750
May1st to 15thNight
6%21222336%67%
1517
16th to endNight
6%22212447%63%
1368
June1st to 15thNight
4212212245%70%
1320
16th to endNight
21111212283%
1320
July1st to 15thNight
111121286%
1320
16th to endNight
111111383%
1506
August1st to 15thNight
111223383%
1526
16th to endNight
111112386%
1750
September1st to 15thNight
11112386%
1650
16th to endNight
11111223479%
1776
October1st to 15thNight
8%212312335%66%
1980
16th to endNight
7%212322336%64%
2112
November1st to 15thNight
11%412212345%59%
2256
16th to endNight
14%313323346%54%
2408
December1st to 15thNight
21%5%13313345%46%
2520
16th to endNight
26%5%23322335%41%
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
39%28%22%18%8%
1461
16th to endDay
45%37%15%16%12%
1728
February1st to 15thDay
41%39%20%18%6%
1600
16th to endDay
44%211%25%11%3
1579
March1st to 15thDay
44%312%18%15%5%
1890
16th to endDay
41%414%19%15%3
2172
April1st to 15thDay
40%411%24%14%4
2149
16th to endDay
26%313%27%23%5%
2098
May1st to 15thDay
20%28%28%31%9%
2099
16th to endDay
24%313%29%21%8%
2395
June1st to 15thDay
18%210%22%22%23%
2310
16th to endDay
8%315%36%34%
2310
July1st to 15thDay
7%119%28%52%
2161
16th to endDay
9%139%25%51%
2195
August1st to 15thDay
6%128%29%51%
2088
16th to endDay
6%1110%37%43%
2100
September1st to 15thDay
7%1210%34%43%
1980
16th to endDay
12%1321%35%25%
1852
October1st to 15thDay
18%37%25%27%17%
1650
16th to endDay
26%26%23%25%16%
1760
November1st to 15thDay
27%313%26%20%8%
1603
16th to endDay
35%39%22%24%5%
1551
December1st to 15thDay
44%28%19%20%3
1440
16th to endDay
45%310%16%17%6%
1536
January1st to 15thNight
36%311%20%16%10%
2476
16th to endNight
39%48%14%17%15%
2496
February1st to 15thNight
40%39%20%18%8%
2264
16th to endNight
39%39%26%16%4
1895
March1st to 15thNight
43%311%19%16%6%
2067
16th to endNight
39%5%10%19%17%6%
2050
April1st to 15thNight
40%413%20%14%5%
1799
16th to endNight
25%413%25%22%7%
1750
May1st to 15thNight
18%211%24%27%14%
1518
16th to endNight
19%417%30%19%9%
1368
June1st to 15thNight
16%212%24%21%21%
1320
16th to endNight
10%415%33%35%
1320
July1st to 15thNight
6%128%29%51%
1240
16th to endNight
9%129%25%51%
1401
August1st to 15thNight
7%1115%27%47%
1517
16th to endNight
6%1110%35%44%
1750
September1st to 15thNight
6%139%39%40%
1650
16th to endNight
11%15%19%33%28%
1776
October1st to 15thNight
21%26%22%27%19%
1980
16th to endNight
22%35%24%26%17%
2112
November1st to 15thNight
27%212%25%20%11%
2256
16th to endNight
31%29%24%23%8%
2408
December1st to 15thNight
41%211%18%18%7%
2520
16th to endNight
45%39%16%16%8%
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%6%16%20%13%3
89
16th to endDay
28%319%23%20%4
256
February1st to 15thDay
24%5%20%28%18%2
241
16th to endDay
27%9%21%26%14%
238
March1st to 15thDay
23%11%25%19%17%2
270
16th to endDay
21%9%25%26%15%1
288
April1st to 15thDay
25%11%28%19%11%2
269
16th to endDay
15%12%26%24%16%4
250
May1st to 15thDay
10%10%29%32%14%3
228
16th to endDay
10%11%20%29%21%7%
266
June1st to 15thDay
6%7%29%38%14%3
255
16th to endDay
1425%43%19%6%
255
July1st to 15thDay
15%48%30%4
245
16th to endDay
21%47%21%7%
271
August1st to 15thDay
2125%41%22%6%
255
16th to endDay
118%48%20%10%
268
September1st to 15thDay
3117%44%26%6%
255
16th to endDay
3321%36%29%5%
255
October1st to 15thDay
7%6%25%30%25%5%
255
16th to endDay
15%418%32%25%3
272
November1st to 15thDay
12%211%21%36%14%
109
16th to endDay
16%5%20%35%22%
79
December1st to 15thDay
31%323%26%11%3
60
16th to endDay
18%6%6%31%28%9%
64
January1st to 15thNight
17%36%32%28%11%
720
16th to endNight
22%26%33%23%12%
768
February1st to 15thNight
21%38%32%27%6%
704
16th to endNight
23%310%34%20%7%
632
March1st to 15thNight
23%38%30%26%7%
720
16th to endNight
21%211%34%24%5%
768
April1st to 15thNight
17%311%36%27%3
719
16th to endNight
11%210%35%29%10%
700
May1st to 15thNight
9%12%37%31%7%
528
16th to endNight
7%27%32%41%7%
343
June1st to 15thNight
5%9%35%44%4
330
16th to endNight
2240%48%5%
330
July1st to 15thNight
130%60%6%
310
16th to endNight
1124%61%11%
454
August1st to 15thNight
1135%53%8%
534
16th to endNight
1233%54%7%
700
September1st to 15thNight
1227%56%11%
660
16th to endNight
36%32%41%15%
656
October1st to 15thNight
9%17%35%34%12%
660
16th to endNight
9%18%32%33%15%
704
November1st to 15thNight
13%5%36%29%14%
700
16th to endNight
15%110%35%24%12%
720
December1st to 15thNight
23%27%34%23%8%
720
16th to endNight
29%210%30%20%5%
768
Page generated at 2017-04-26 14:21:47. Version ac04

Copyright 2017 A. Danko


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