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 2017-10-31.

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
72%
15420
28%
47394
27%
15385
74%
15385
43%
25003

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%
720
25%
1800
13%
720
70%
720
47%
1046
May1st to 15thNight
74%
575
29%
1655
22%
575
75%
575
55%
792
May16th to endNight
78%
375
26%
1496
32%
374
80%
374
45%
630
June1st to 15thNight
78%
360
27%
1440
35%
360
82%
360
50%
570
June16th to endNight
89%
360
37%
1440
51%
360
90%
360
66%
475
July1st to 15thNight
96%
340
35%
1360
48%
340
96%
340
75%
415
July16th to endNight
93%
491
39%
1522
41%
460
93%
460
72%
569
August1st to 15thNight
92%
583
38%
1656
30%
580
93%
580
75%
686
August16th to endNight
94%
764
45%
1910
29%
764
94%
764
82%
848
September1st to 15thNight
93%
720
43%
1800
31%
720
94%
720
81%
807
September16th to endNight
87%
716
45%
1938
40%
716
90%
716
72%
866
October1st to 15thNight
78%
720
31%
2160
33%
720
81%
720
53%
1040
October16th to endNight
77%
768
38%
2304
41%
768
80%
768
51%
1142
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%31221233464%
48359
Night
11%312212335%60%
47583
TransparencyDay
24%27%19%24%20%
48041
Night
26%28%19%22%19%
47401
SeeingDay
11%5%21%32%22%5%
6041
Night
13%17%33%34%9%
15432

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%312212336%60%
2160
May1st to 15thDay
5%212213335%68%
2291
16th to endDay
7%312322446%62%
2615
June1st to 15thDay
5%212212235%68%
2520
16th to endDay
211112384%
2520
July1st to 15thDay
1112286%
2520
16th to endDay
11111121285%
2539
August1st to 15thDay
11111286%
2295
16th to endDay
122287%
2292
September1st to 15thDay
111112384%
2160
16th to endDay
31121113478%
2020
October1st to 15thDay
6%12212346%68%
1800
16th to endDay
7%31332333462%
1918
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%
1800
May1st to 15thNight
6%21122336%68%
1655
16th to endNight
6%22212346%65%
1496
June1st to 15thNight
421221224470%
1440
16th to endNight
21111212284%
1440
July1st to 15thNight
111122286%
1440
16th to endNight
111111384%
1627
August1st to 15thNight
11121223381%
1665
16th to endNight
11112386%
1910
September1st to 15thNight
11112385%
1800
16th to endNight
11111223479%
1938
October1st to 15thNight
7%112212335%69%
2160
16th to endNight
7%212212336%65%
2304
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%24%6%
2160
May1st to 15thDay
19%29%29%30%8%
2291
16th to endDay
24%312%29%22%8%
2619
June1st to 15thDay
19%210%22%22%21%
2520
16th to endDay
8%315%35%37%
2520
July1st to 15thDay
7%118%26%55%
2371
16th to endDay
8%129%23%54%
2382
August1st to 15thDay
7%129%30%49%
2279
16th to endDay
5%1111%37%43%
2292
September1st to 15thDay
7%1313%33%41%
2160
16th to endDay
12%1422%35%23%
2020
October1st to 15thDay
17%36%24%26%22%
1800
16th to endDay
25%26%22%24%18%
1918
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
24%5%13%25%23%8%
1800
May1st to 15thNight
17%211%25%28%13%
1656
16th to endNight
18%316%31%20%9%
1496
June1st to 15thNight
17%211%25%23%20%
1440
16th to endNight
10%415%32%37%
1440
July1st to 15thNight
5%127%26%55%
1360
16th to endNight
9%129%23%54%
1522
August1st to 15thNight
8%1114%26%47%
1656
16th to endNight
6%1111%34%44%
1910
September1st to 15thNight
6%1411%37%38%
1800
16th to endNight
10%15%20%34%27%
1938
October1st to 15thNight
19%25%21%25%25%
2160
16th to endNight
20%35%22%26%20%
2304
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%13%25%25%16%3
270
May1st to 15thDay
8%8%29%32%15%4
288
16th to endDay
10%10%17%27%24%9%
330
June1st to 15thDay
7%6%29%34%16%5%
315
16th to endDay
322%38%25%8%
315
July1st to 15thDay
13%48%31%6%
305
16th to endDay
22%44%24%8%
327
August1st to 15thDay
323%40%23%7%
315
16th to endDay
15%43%25%13%
332
September1st to 15thDay
3116%45%26%6%
315
16th to endDay
3423%37%27%4
315
October1st to 15thDay
5%7%26%29%25%5%
315
16th to endDay
12%316%30%29%7%
336
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%9%
720
May1st to 15thNight
9%111%38%31%8%
576
16th to endNight
7%26%33%42%7%
375
June1st to 15thNight
6%9%34%44%5%
360
16th to endNight
2238%49%5%
360
July1st to 15thNight
130%61%6%
340
16th to endNight
1124%60%12%
491
August1st to 15thNight
2133%54%8%
583
16th to endNight
1232%55%8%
764
September1st to 15thNight
1227%57%11%
720
16th to endNight
27%32%41%14%
716
October1st to 15thNight
8%17%36%34%11%
720
16th to endNight
8%17%30%34%17%
768
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 2017-11-01 14:23:40. Version ac04

Copyright 2017 A. Danko


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