BarC Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the BarC Observatory clear sky chart from 2005-11-05 to 2017-09-18.

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
59%
15011
23%
47106
19%
14968
64%
14968
31%
27997

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
42%
719
26%
2148
14%
716
53%
716
32%
1291
January16th to endNight
38%
768
26%
2304
15%
768
47%
768
27%
1458
February1st to 15thNight
42%
704
27%
2110
14%
700
53%
700
32%
1270
February16th to endNight
38%
631
23%
1893
12%
631
47%
631
27%
1209
March1st to 15thNight
43%
684
23%
2124
15%
684
50%
684
27%
1328
March16th to endNight
56%
576
25%
2003
21%
576
62%
576
32%
1092
April1st to 15thNight
53%
539
25%
1797
20%
539
62%
539
30%
1030
April16th to endNight
60%
540
28%
1800
27%
540
67%
540
39%
946
May1st to 15thNight
66%
539
22%
1799
23%
539
70%
539
34%
1007
May16th to endNight
74%
561
21%
1798
21%
561
77%
561
34%
1023
June1st to 15thNight
76%
540
14%
1620
15%
540
77%
540
32%
995
June16th to endNight
79%
540
14%
1653
16%
540
79%
540
30%
1019
July1st to 15thNight
81%
510
13%
1700
15%
510
81%
510
27%
1027
July16th to endNight
76%
564
10%
1772
13%
531
77%
531
25%
1116
August1st to 15thNight
82%
539
12%
1788
15%
536
82%
536
31%
1047
August16th to endNight
69%
573
12%
1910
14%
573
69%
573
23%
1249
September1st to 15thNight
70%
543
20%
1803
20%
543
72%
543
27%
1106
September16th to endNight
73%
669
26%
1848
22%
669
74%
669
36%
1124
October1st to 15thNight
73%
660
33%
1845
26%
660
76%
660
49%
976
October16th to endNight
63%
704
33%
2112
29%
704
68%
704
40%
1157
November1st to 15thNight
62%
700
33%
2172
30%
700
68%
700
37%
1216
November16th to endNight
55%
720
31%
2340
25%
720
63%
720
36%
1270
December1st to 15thNight
47%
720
24%
2340
20%
720
54%
720
27%
1413
December16th to endNight
38%
768
20%
2427
15%
768
44%
768
21%
1628

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%4245%35%5%6%9%42%
47645
Night
10%4244245%5%8%47%
47330
TransparencyDay
35%8%14%19%16%5%
47370
Night
33%6%14%19%17%7%
47110
SeeingDay
12%212%23%30%18%
4977
Night
11%316%28%28%10%
15015

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
11%5%35%425%447%44%
1790
16th to endDay
18%6%25%31333446%
1920
February1st to 15thDay
12%5%24433347%49%
1750
16th to endDay
14%6%25%5%2445%6%42%
1580
March1st to 15thDay
14%5%2442445%6%44%
1845
16th to endDay
10%5%2442445%8%47%
2218
April1st to 15thDay
10%5%235%345%5%9%43%
2151
16th to endDay
10%5%2433446%7%46%
2160
May1st to 15thDay
9%314435%5%6%8%45%
2151
16th to endDay
8%4145%345%6%10%44%
2311
June1st to 15thDay
6%426%5%37%7%9%11%35%
2340
16th to endDay
7%4246%5%6%8%9%13%32%
2300
July1st to 15thDay
7%426%7%48%8%8%12%28%
2160
16th to endDay
6%5%26%7%48%9%10%12%26%
2276
August1st to 15thDay
7%426%5%5%7%9%9%12%29%
2160
16th to endDay
11%435%6%47%7%9%11%29%
2292
September1st to 15thDay
9%4245%45%7%8%10%37%
2145
16th to endDay
7%424445%5%7%8%45%
1837
October1st to 15thDay
5%2134245%6%7%58%
1782
16th to endDay
7%313334346%58%
1760
November1st to 15thDay
9%312422447%55%
1683
16th to endDay
9%314313335%58%
1620
December1st to 15thDay
13%6%35%424346%46%
1620
16th to endDay
20%6%36%5%25%35%6%34%
1794
January1st to 15thNight
13%5%24323348%47%
2148
16th to endNight
18%5%2342342446%
2304
February1st to 15thNight
12%42442445%7%48%
2103
16th to endNight
15%6%25%433345%45%
1893
March1st to 15thNight
13%6%344245%5%7%43%
2124
16th to endNight
11%423323447%52%
2003
April1st to 15thNight
11%5%14325%447%49%
1797
16th to endNight
8%31332445%8%54%
1800
May1st to 15thNight
7%3145%245%6%10%47%
1799
16th to endNight
5%324425%6%7%10%48%
1797
June1st to 15thNight
6%315%5%26%7%8%11%40%
1620
16th to endNight
6%324436%6%8%13%39%
1653
July1st to 15thNight
4324436%6%8%12%41%
1800
16th to endNight
5%426%6%35%7%9%12%35%
1892
August1st to 15thNight
33244347%10%15%41%
1800
16th to endNight
8%426%6%36%5%8%11%35%
1910
September1st to 15thNight
7%4245%36%7%6%10%40%
1803
16th to endNight
8%4244245%6%9%47%
1848
October1st to 15thNight
4224224446%62%
1845
16th to endNight
9%313323345%59%
2112
November1st to 15thNight
8%314434345%55%
2172
16th to endNight
8%414333445%56%
2340
December1st to 15thNight
12%5%24424446%46%
2340
16th to endNight
19%8%25%42445%6%37%
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
39%5%7%16%22%9%
1791
16th to endDay
42%35%18%21%9%
1920
February1st to 15thDay
34%410%17%22%10%
1752
16th to endDay
41%5%6%18%20%8%
1580
March1st to 15thDay
38%5%7%22%18%6%
1845
16th to endDay
34%5%12%20%20%5%
2220
April1st to 15thDay
33%5%13%20%18%7%
2151
16th to endDay
32%5%13%24%18%5%
2160
May1st to 15thDay
31%8%14%22%16%6%
2151
16th to endDay
30%8%16%26%16%2
2315
June1st to 15thDay
34%10%19%25%9%
2340
16th to endDay
36%11%21%21%9%
2300
July1st to 15thDay
39%14%24%15%4
2031
16th to endDay
40%16%22%17%2
2133
August1st to 15thDay
37%14%26%15%5%
2148
16th to endDay
40%15%18%16%6%1
2292
September1st to 15thDay
35%10%19%18%10%4
2145
16th to endDay
31%11%13%19%17%6%
1837
October1st to 15thDay
22%413%20%25%14%
1782
16th to endDay
26%5%5%17%27%18%
1760
November1st to 15thDay
28%49%18%30%8%
1683
16th to endDay
27%47%19%26%14%
1620
December1st to 15thDay
39%49%22%18%6%
1620
16th to endDay
49%38%18%15%4
1794
January1st to 15thNight
36%310%16%22%10%
2148
16th to endNight
42%26%14%23%10%
2304
February1st to 15thNight
35%47%18%21%12%
2112
16th to endNight
41%45%17%19%11%
1893
March1st to 15thNight
38%6%9%16%22%6%
2124
16th to endNight
31%413%19%22%7%
2003
April1st to 15thNight
33%5%10%21%18%10%
1797
16th to endNight
26%5%11%28%20%7%
1800
May1st to 15thNight
29%6%13%24%19%5%
1800
16th to endNight
28%9%16%26%17%1
1799
June1st to 15thNight
32%8%21%25%10%
1620
16th to endNight
32%10%25%21%9%
1653
July1st to 15thNight
30%12%28%22%5%
1700
16th to endNight
33%12%30%20%2
1772
August1st to 15thNight
26%13%34%20%5%
1788
16th to endNight
38%11%25%15%5%2
1910
September1st to 15thNight
35%9%19%16%13%5%
1803
16th to endNight
31%7%17%19%16%7%
1848
October1st to 15thNight
22%412%20%22%17%
1845
16th to endNight
27%45%16%25%20%
2112
November1st to 15thNight
31%35%19%29%11%
2172
16th to endNight
30%35%19%23%17%
2340
December1st to 15thNight
38%410%21%19%6%
2340
16th to endNight
47%47%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
16%6%25%31%16%3
90
16th to endDay
22%6%41%20%8%
96
February1st to 15thDay
13%11%30%22%20%3
90
16th to endDay
9%7%39%29%13%
81
March1st to 15thDay
24%5%34%30%5%
90
16th to endDay
17%422%31%20%3
204
April1st to 15thDay
16%6%22%32%18%3
270
16th to endDay
14%215%35%25%5%
270
May1st to 15thDay
11%318%33%25%8%
288
16th to endDay
13%19%29%33%12%
331
June1st to 15thDay
10%5%22%37%23%
315
16th to endDay
9%1417%39%27%
315
July1st to 15thDay
9%111%35%41%
305
16th to endDay
7%114%38%37%
326
August1st to 15thDay
10%1111%41%32%
313
16th to endDay
9%15%12%37%34%
332
September1st to 15thDay
11%27%20%33%25%
315
16th to endDay
10%15%23%38%20%
262
October1st to 15thDay
414%25%38%16%
222
16th to endDay
13%10%38%21%15%
96
November1st to 15thDay
20%18%40%24%5%
90
16th to endDay
8%331%27%18%10%
90
December1st to 15thDay
17%5%22%38%13%2
90
16th to endDay
33%7%18%17%20%2
96
January1st to 15thNight
16%6%29%35%11%
720
16th to endNight
20%7%28%33%10%
768
February1st to 15thNight
15%5%31%32%13%
704
16th to endNight
18%6%31%32%10%
631
March1st to 15thNight
16%6%27%33%14%
684
16th to endNight
14%5%18%34%25%1
576
April1st to 15thNight
12%423%37%20%1
539
16th to endNight
11%221%33%28%2
540
May1st to 15thNight
10%113%38%32%3
540
16th to endNight
6%19%28%41%12%
563
June1st to 15thNight
7%320%50%16%
540
16th to endNight
6%1214%48%26%
540
July1st to 15thNight
5%19%46%35%
510
16th to endNight
41210%45%36%
564
August1st to 15thNight
328%45%39%
539
16th to endNight
10%212%42%29%
573
September1st to 15thNight
9%6%14%40%28%
543
16th to endNight
9%428%46%10%
669
October1st to 15thNight
5%112%33%39%6%
660
16th to endNight
11%316%31%29%7%
704
November1st to 15thNight
11%316%37%24%6%
700
16th to endNight
9%5%24%35%22%1
720
December1st to 15thNight
14%6%24%31%21%1
720
16th to endNight
22%7%25%30%12%1
768
Page generated at 2017-09-19 06:32:31. Version ac04

Copyright 2017 A. Danko


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