BarCla Hill Private Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the BarCla Hill Private Observatory clear sky chart from 2005-11-05 to 2017-09-22.

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
55%
15016
23%
47004
18%
14972
61%
14972
30%
28079

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
37%
720
27%
2148
13%
716
50%
716
29%
1288
January16th to endNight
34%
768
27%
2304
13%
768
44%
768
25%
1467
February1st to 15thNight
35%
704
27%
2110
11%
700
48%
700
30%
1273
February16th to endNight
32%
631
23%
1893
11%
631
41%
631
24%
1222
March1st to 15thNight
37%
678
23%
2118
14%
678
45%
678
24%
1346
March16th to endNight
48%
576
25%
2007
19%
576
57%
576
32%
1102
April1st to 15thNight
46%
539
25%
1797
19%
539
56%
539
28%
1056
April16th to endNight
55%
540
28%
1800
24%
540
64%
540
36%
946
May1st to 15thNight
60%
539
21%
1799
20%
539
65%
539
32%
1026
May16th to endNight
69%
561
21%
1798
20%
561
72%
561
34%
1017
June1st to 15thNight
75%
540
13%
1620
14%
540
75%
540
31%
1005
June16th to endNight
78%
540
15%
1585
16%
540
78%
540
32%
983
July1st to 15thNight
81%
510
13%
1622
16%
510
82%
510
30%
987
July16th to endNight
77%
564
10%
1772
13%
531
77%
531
25%
1121
August1st to 15thNight
82%
539
11%
1788
14%
536
83%
536
30%
1065
August16th to endNight
73%
573
13%
1910
15%
573
73%
573
22%
1272
September1st to 15thNight
71%
540
21%
1800
21%
540
72%
540
27%
1106
September16th to endNight
71%
682
27%
1889
22%
682
72%
682
35%
1151
October1st to 15thNight
68%
660
33%
1853
26%
660
73%
660
48%
989
October16th to endNight
57%
704
36%
2112
29%
704
64%
704
42%
1123
November1st to 15thNight
58%
700
32%
2172
27%
700
65%
700
36%
1218
November16th to endNight
48%
720
31%
2340
24%
720
58%
720
34%
1276
December1st to 15thNight
42%
720
24%
2340
18%
720
50%
720
26%
1419
December16th to endNight
32%
768
20%
2427
12%
768
40%
768
21%
1621

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
11%5%25%6%35%5%6%8%38%
47812
Night
10%42442445%8%47%
47226
TransparencyDay
40%7%11%17%16%6%
47536
Night
34%6%13%19%17%8%
47008
SeeingDay
12%5%15%23%25%16%
5099
Night
12%5%18%29%25%7%
15019

By Month

Percentage Cloud Cover SE (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%5%25%433447%43%
1790
16th to endDay
20%5%2442333446%
1920
February1st to 15thDay
14%434424346%47%
1750
16th to endDay
17%5%25%43435%6%41%
1580
March1st to 15thDay
16%5%24424446%42%
1851
16th to endDay
12%5%25%425%45%6%44%
2215
April1st to 15thDay
13%5%245%246%6%7%40%
2151
16th to endDay
12%4235%245%7%9%42%
2160
May1st to 15thDay
11%425%5%35%5%5%8%41%
2151
16th to endDay
9%5%25%6%45%5%6%9%38%
2313
June1st to 15thDay
8%417%8%48%7%8%11%28%
2340
16th to endDay
7%5%36%8%5%8%7%7%12%26%
2355
July1st to 15thDay
8%5%48%8%5%8%8%7%10%24%
2226
16th to endDay
9%6%38%8%6%8%9%8%9%22%
2276
August1st to 15thDay
9%438%8%5%8%8%9%9%23%
2160
16th to endDay
11%6%47%7%6%7%7%6%8%26%
2292
September1st to 15thDay
10%6%36%7%47%6%6%7%33%
2149
16th to endDay
9%426%7%35%5%7%7%40%
1881
October1st to 15thDay
6%324434446%54%
1774
16th to endDay
7%314424346%55%
1760
November1st to 15thDay
10%424323346%54%
1684
16th to endDay
10%5%13313346%55%
1620
December1st to 15thDay
14%8%25%424346%44%
1620
16th to endDay
21%7%34434446%34%
1794
January1st to 15thNight
14%5%24314447%47%
2148
16th to endNight
19%5%2442343445%
2304
February1st to 15thNight
12%6%24423346%48%
2103
16th to endNight
16%7%35%422445%44%
1893
March1st to 15thNight
14%6%34425%446%42%
2118
16th to endNight
12%423213447%52%
2007
April1st to 15thNight
12%5%2442435%7%47%
1797
16th to endNight
9%31331335%9%54%
1800
May1st to 15thNight
9%3144245%6%8%49%
1799
16th to endNight
6%3244245%6%10%49%
1797
June1st to 15thNight
5%3145%35%8%7%12%41%
1620
16th to endNight
5%324425%7%9%11%42%
1585
July1st to 15thNight
5%324426%6%8%11%43%
1720
16th to endNight
4435%5%445%9%13%37%
1892
August1st to 15thNight
23245%448%10%13%41%
1800
16th to endNight
8%5%25%6%36%6%7%11%35%
1910
September1st to 15thNight
7%4245%35%6%7%10%41%
1800
16th to endNight
6%5%245%345%6%8%47%
1889
October1st to 15thNight
4313313346%62%
1853
16th to endNight
10%313212335%60%
2112
November1st to 15thNight
10%413424346%55%
2172
16th to endNight
9%42442333456%
2340
December1st to 15thNight
13%5%25%434347%45%
2340
16th to endNight
20%6%25%42445%6%36%
2427

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
40%46%15%22%10%
1791
16th to endDay
42%35%16%22%9%
1920
February1st to 15thDay
37%49%16%21%11%
1752
16th to endDay
42%46%18%20%8%
1580
March1st to 15thDay
41%47%20%18%7%
1851
16th to endDay
38%5%9%18%21%6%
2217
April1st to 15thDay
38%6%9%18%18%8%
2151
16th to endDay
35%6%11%23%18%5%
2160
May1st to 15thDay
38%7%11%20%16%7%
2151
16th to endDay
38%9%12%21%15%2
2317
June1st to 15thDay
42%11%14%21%9%1
2340
16th to endDay
44%10%18%17%8%
2355
July1st to 15thDay
46%14%19%14%4
2096
16th to endDay
49%13%18%15%2
2133
August1st to 15thDay
48%13%19%12%5%
2148
16th to endDay
49%13%15%13%5%2
2292
September1st to 15thDay
42%11%14%17%10%4
2149
16th to endDay
37%9%12%16%16%7%
1881
October1st to 15thDay
27%6%9%16%24%16%
1774
16th to endDay
28%35%14%27%19%
1760
November1st to 15thDay
30%47%17%30%9%
1684
16th to endDay
28%47%17%26%16%
1620
December1st to 15thDay
40%47%21%19%6%
1620
16th to endDay
49%5%7%17%16%4
1794
January1st to 15thNight
36%38%16%23%10%
2148
16th to endNight
42%35%14%23%10%
2304
February1st to 15thNight
36%37%18%21%12%
2112
16th to endNight
42%45%16%19%11%
1893
March1st to 15thNight
41%5%8%15%23%5%
2118
16th to endNight
32%312%20%22%7%
2007
April1st to 15thNight
36%410%21%16%10%
1797
16th to endNight
28%412%25%21%7%
1800
May1st to 15thNight
32%6%12%23%20%6%
1800
16th to endNight
29%7%16%26%17%2
1799
June1st to 15thNight
30%11%22%24%9%
1620
16th to endNight
31%9%25%22%9%
1585
July1st to 15thNight
28%13%29%22%5%
1622
16th to endNight
33%13%29%20%2
1772
August1st to 15thNight
27%14%33%19%5%
1788
16th to endNight
38%12%24%14%5%3
1910
September1st to 15thNight
34%9%18%17%13%6%
1800
16th to endNight
31%7%17%18%16%7%
1889
October1st to 15thNight
22%410%20%23%17%
1853
16th to endNight
27%25%16%26%21%
2112
November1st to 15thNight
30%46%17%28%12%
2172
16th to endNight
30%45%18%22%18%
2340
December1st to 15thNight
38%49%21%19%6%
2340
16th to endNight
46%5%7%19%14%6%
2427

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
21%8%34%24%7%3
90
16th to endDay
23%23%35%12%4
96
February1st to 15thDay
12%22%34%22%7%1
90
16th to endDay
13%19%38%22%6%
81
March1st to 15thDay
25%13%44%14%2
90
16th to endDay
19%7%25%28%17%1
201
April1st to 15thDay
18%11%25%23%18%2
270
16th to endDay
13%8%21%29%21%5%
270
May1st to 15thDay
12%8%23%25%23%7%
288
16th to endDay
13%416%29%22%12%
331
June1st to 15thDay
12%17%27%26%24%
315
16th to endDay
11%27%24%30%23%
367
July1st to 15thDay
8%423%33%29%
370
16th to endDay
7%2316%39%30%
326
August1st to 15thDay
10%5%15%37%30%
313
16th to endDay
11%16%16%34%30%
332
September1st to 15thDay
10%210%23%30%22%
315
16th to endDay
8%26%30%33%17%
278
October1st to 15thDay
3418%28%33%11%
214
16th to endDay
15%5%18%36%16%7%
96
November1st to 15thDay
22%325%33%14%1
90
16th to endDay
6%15%35%25%12%4
90
December1st to 15thDay
18%8%41%21%8%1
90
16th to endDay
35%11%21%19%10%1
96
January1st to 15thNight
17%10%30%32%8%
720
16th to endNight
21%11%28%30%7%
768
February1st to 15thNight
14%11%33%30%8%
704
16th to endNight
18%13%30%30%6%
631
March1st to 15thNight
17%11%29%32%10%
678
16th to endNight
14%6%25%33%18%1
576
April1st to 15thNight
14%7%27%31%17%1
539
16th to endNight
10%5%23%37%21%1
540
May1st to 15thNight
9%417%40%25%2
540
16th to endNight
7%112%32%39%6%
563
June1st to 15thNight
7%1428%44%12%
540
16th to endNight
6%322%45%20%
540
July1st to 15thNight
6%313%47%29%
510
16th to endNight
4315%44%31%
564
August1st to 15thNight
3212%51%30%
539
16th to endNight
9%1213%45%27%
573
September1st to 15thNight
8%17%19%39%23%
540
16th to endNight
8%17%33%41%8%
682
October1st to 15thNight
7%115%35%35%4
660
16th to endNight
12%419%32%25%4
704
November1st to 15thNight
11%5%18%36%22%4
700
16th to endNight
11%7%27%34%17%1
720
December1st to 15thNight
15%8%27%31%15%
720
16th to endNight
23%9%29%26%10%
768
Page generated at 2017-09-23 05:43:43. Version ac04

Copyright 2017 A. Danko


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