Boulder Heights Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Boulder Heights Observatory clear sky chart from 2005-11-05 to 2017-10-06.

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
45%
16018
27%
47087
14%
15975
58%
15975
39%
25046

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
28%
899
30%
2506
11%
895
46%
895
37%
1284
January16th to endNight
26%
807
34%
2535
12%
807
50%
807
33%
1253
February1st to 15thNight
20%
698
24%
2262
6%
697
42%
697
27%
1209
February16th to endNight
23%
632
30%
1894
6%
632
48%
632
33%
1024
March1st to 15thNight
35%
720
28%
2105
10%
720
51%
720
40%
1106
March16th to endNight
37%
686
26%
2030
11%
686
52%
686
36%
1114
April1st to 15thNight
37%
539
23%
1798
12%
539
52%
539
34%
947
April16th to endNight
38%
540
23%
1800
14%
540
52%
540
30%
1010
May1st to 15thNight
45%
540
19%
1587
12%
540
53%
540
29%
995
May16th to endNight
59%
563
17%
1498
11%
561
64%
561
40%
879
June1st to 15thNight
67%
540
22%
1440
16%
540
71%
540
49%
772
June16th to endNight
79%
540
29%
1440
23%
540
82%
540
60%
714
July1st to 15thNight
75%
510
18%
1360
15%
510
78%
510
40%
795
July16th to endNight
82%
564
26%
1447
24%
531
82%
531
46%
787
August1st to 15thNight
80%
539
21%
1653
22%
536
82%
536
46%
834
August16th to endNight
77%
573
29%
1910
32%
573
79%
573
42%
956
September1st to 15thNight
69%
540
28%
1800
26%
540
75%
540
40%
912
September16th to endNight
68%
540
35%
1929
32%
540
77%
540
47%
864
October1st to 15thNight
49%
684
28%
2052
15%
684
59%
684
40%
1120
October16th to endNight
42%
729
32%
2137
14%
729
56%
729
39%
1132
November1st to 15thNight
40%
875
33%
2275
13%
875
53%
875
47%
1212
November16th to endNight
34%
900
34%
2421
12%
900
51%
900
49%
1232
December1st to 15thNight
26%
900
25%
2520
6%
900
42%
900
33%
1365
December16th to endNight
27%
960
26%
2688
7%
960
45%
960
30%
1530

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
5%4244245%6%9%50%
48127
Night
442332345%8%58%
47262
TransparencyDay
28%6%14%25%18%6%
47804
Night
23%5%13%28%21%7%
47087
SeeingDay
10%8%30%29%15%5%
5928
Night
9%9%30%31%16%3
16025

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
5%33423348%59%
1432
16th to endDay
133442245%7%61%
1701
February1st to 15thDay
6%25%5%24449%55%
1599
16th to endDay
6%25%42235%8%58%
1580
March1st to 15thDay
2425%5%245%6%8%52%
1854
16th to endDay
5%7%2432446%10%48%
2193
April1st to 15thDay
6%6%2332346%10%50%
2150
16th to endDay
10%8%25%425%5%6%7%40%
2160
May1st to 15thDay
11%8%245%35%6%5%8%38%
2359
16th to endDay
10%5%24446%6%7%9%39%
2616
June1st to 15thDay
5%213436%6%7%10%48%
2520
16th to endDay
2213325%5%8%9%54%
2520
July1st to 15thDay
7%4135%36%7%8%9%43%
2520
16th to endDay
43145%36%7%7%10%43%
2621
August1st to 15thDay
6%3246%45%7%8%10%41%
2298
16th to endDay
6%2135%35%6%7%9%48%
2292
September1st to 15thDay
6%41342445%8%54%
2160
16th to endDay
6%313323445%61%
2028
October1st to 15thDay
6%41333445%7%56%
1705
16th to endDay
45%12312346%62%
1724
November1st to 15thDay
131341336%9%60%
1583
16th to endDay
232331335%9%60%
1536
December1st to 15thDay
15%25%43445%9%54%
1440
16th to endDay
242432345%9%57%
1536
January1st to 15thNight
32432245%8%62%
2506
16th to endNight
1424323346%63%
2535
February1st to 15thNight
5%3442445%6%59%
2252
16th to endNight
7%24314446%59%
1894
March1st to 15thNight
241431245%10%58%
2105
16th to endNight
45%33323348%58%
2030
April1st to 15thNight
46%2332345%8%55%
1798
16th to endNight
11%7%14323346%51%
1800
May1st to 15thNight
12%6%143146%5%8%44%
1586
16th to endNight
8%5%1322445%8%53%
1497
June1st to 15thNight
421231446%8%60%
1440
16th to endNight
21121336%9%67%
1440
July1st to 15thNight
5%2134345%7%11%51%
1440
16th to endNight
42133345%6%9%55%
1545
August1st to 15thNight
321332346%10%56%
1662
16th to endNight
422333445%7%57%
1910
September1st to 15thNight
8%313323347%58%
1800
16th to endNight
5%212213346%65%
1929
October1st to 15thNight
6%5%1221335%6%59%
2052
16th to endNight
5%5%14323246%61%
2137
November1st to 15thNight
1313312347%65%
2275
16th to endNight
232221335%8%65%
2421
December1st to 15thNight
15%2442335%8%59%
2520
16th to endNight
1435%42346%9%54%
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
23%319%31%16%3
1433
16th to endDay
22%212%36%19%5%
1701
February1st to 15thDay
26%5%21%31%11%3
1600
16th to endDay
24%313%33%21%3
1580
March1st to 15thDay
27%414%30%20%3
1854
16th to endDay
30%5%13%29%15%4
2193
April1st to 15thDay
28%414%28%16%6%
2150
16th to endDay
39%5%15%23%13%2
2160
May1st to 15thDay
41%7%14%22%12%2
2359
16th to endDay
37%7%19%20%10%4
2620
June1st to 15thDay
27%9%16%20%18%9%
2520
16th to endDay
21%7%12%23%26%9%
2520
July1st to 15thDay
32%8%14%18%15%10%
2371
16th to endDay
29%8%15%25%13%7%
2456
August1st to 15thDay
31%9%15%19%15%8%
2283
16th to endDay
27%6%14%23%21%6%
2292
September1st to 15thDay
26%411%23%21%11%
2160
16th to endDay
23%38%26%32%4
2028
October1st to 15thDay
25%6%14%21%27%5%
1705
16th to endDay
21%212%28%27%6%
1724
November1st to 15thDay
20%415%26%22%9%
1583
16th to endDay
19%410%32%25%7%
1536
December1st to 15thDay
25%6%17%32%15%1
1440
16th to endDay
25%6%17%27%19%3
1536
January1st to 15thNight
19%416%32%22%4
2506
16th to endNight
22%310%32%23%6%
2535
February1st to 15thNight
26%6%15%32%16%3
2262
16th to endNight
25%5%9%30%22%6%
1894
March1st to 15thNight
21%5%11%30%25%5%
2105
16th to endNight
25%5%12%30%21%3
2030
April1st to 15thNight
26%5%13%27%20%6%
1798
16th to endNight
33%412%27%18%3
1800
May1st to 15thNight
36%7%15%22%15%2
1587
16th to endNight
27%7%22%24%13%5%
1498
June1st to 15thNight
19%6%17%27%15%12%
1440
16th to endNight
12%6%11%23%30%15%
1440
July1st to 15thNight
25%8%15%22%17%9%
1360
16th to endNight
22%6%16%29%15%9%
1447
August1st to 15thNight
21%5%20%23%19%8%
1653
16th to endNight
23%5%12%25%25%8%
1910
September1st to 15thNight
24%5%13%23%18%14%
1800
16th to endNight
18%311%26%31%7%
1929
October1st to 15thNight
24%6%12%21%27%7%
2052
16th to endNight
24%39%27%27%7%
2137
November1st to 15thNight
18%410%28%25%11%
2275
16th to endNight
17%311%30%28%8%
2421
December1st to 15thNight
23%5%17%31%17%4
2520
16th to endNight
26%6%16%29%18%2
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
10%6%33%27%13%8%
90
16th to endDay
6%8%41%35%8%
96
February1st to 15thDay
15%18%44%20%1
90
16th to endDay
12%19%29%32%41
81
March1st to 15thDay
9%19%41%23%41
144
16th to endDay
16%20%44%14%2
288
April1st to 15thDay
16%21%37%17%5%1
269
16th to endDay
21%16%36%18%5%1
270
May1st to 15thDay
16%9%34%27%10%2
418
16th to endDay
15%8%29%24%17%5%
517
June1st to 15thDay
5%5%27%31%23%7%
495
16th to endDay
3431%30%21%8%
495
July1st to 15thDay
9%218%32%25%10%
475
16th to endDay
6%316%34%30%9%
480
August1st to 15thDay
7%5%30%38%14%3
315
16th to endDay
5%425%41%18%3
332
September1st to 15thDay
8%7%33%30%14%5%
315
16th to endDay
8%6%25%36%15%6%
189
October1st to 15thDay
8%8%29%24%22%6%
107
16th to endDay
11%10%27%36%9%5%
96
November1st to 15thDay
7%321%34%23%10%
90
16th to endDay
13%11%47%27%
90
December1st to 15thDay
14%23%40%21%1
90
16th to endDay
311%44%35%5%
96
January1st to 15thNight
13%15%37%22%8%2
900
16th to endNight
12%16%40%22%6%1
807
February1st to 15thNight
11%16%44%21%5%
704
16th to endNight
10%14%46%23%5%
632
March1st to 15thNight
6%11%41%28%8%1
720
16th to endNight
10%10%37%34%5%1
686
April1st to 15thNight
10%8%38%33%7%
539
16th to endNight
14%9%32%29%13%1
540
May1st to 15thNight
16%5%26%34%15%2
540
16th to endNight
10%418%40%22%3
563
June1st to 15thNight
6%317%47%22%3
540
16th to endNight
2113%44%35%3
540
July1st to 15thNight
5%18%34%40%9%
510
16th to endNight
41433%47%9%
564
August1st to 15thNight
5%5%38%44%4
539
16th to endNight
6%17%38%36%10%
573
September1st to 15thNight
9%212%37%29%9%
540
16th to endNight
6%415%41%23%8%
540
October1st to 15thNight
10%6%30%32%15%4
684
16th to endNight
9%10%32%30%12%4
729
November1st to 15thNight
7%10%37%30%10%2
875
16th to endNight
7%11%44%29%7%
900
December1st to 15thNight
14%14%40%24%5%
900
16th to endNight
9%16%40%23%8%1
960
Page generated at 2017-10-07 12:07:48. Version ac04

Copyright 2017 A. Danko


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