D.A.R.C. Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the D.A.R.C. Observatory clear sky chart from 2005-11-05 to 2018-10-08.

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
75%
16851
33%
51070
29%
16814
79%
16814
52%
24489

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
68%
776
21%
2618
23%
776
70%
776
34%
1449
January16th to endNight
68%
832
26%
2704
27%
832
71%
832
34%
1512
February1st to 15thNight
67%
760
30%
2412
32%
759
71%
759
38%
1297
February16th to endNight
64%
684
28%
2051
25%
684
70%
684
40%
1120
March1st to 15thNight
65%
780
22%
2232
19%
780
69%
780
38%
1277
March16th to endNight
64%
832
25%
2223
18%
832
70%
832
43%
1258
April1st to 15thNight
58%
779
29%
1949
14%
779
64%
779
45%
1105
April16th to endNight
65%
772
30%
1930
13%
772
72%
772
62%
955
May1st to 15thNight
71%
747
32%
1917
19%
747
75%
747
67%
906
May16th to endNight
74%
406
36%
1624
35%
406
83%
406
63%
543
June1st to 15thNight
77%
390
36%
1560
37%
390
86%
390
60%
546
June16th to endNight
91%
390
41%
1560
49%
390
96%
390
87%
430
July1st to 15thNight
95%
370
38%
1480
47%
370
96%
370
76%
450
July16th to endNight
93%
612
39%
1737
35%
579
94%
579
75%
698
August1st to 15thNight
93%
665
42%
1810
30%
662
94%
662
83%
742
August16th to endNight
94%
828
45%
2070
29%
828
94%
828
86%
902
September1st to 15thNight
91%
780
47%
1950
34%
780
94%
780
82%
868
September16th to endNight
87%
776
48%
2091
42%
776
91%
776
81%
874
October1st to 15thNight
79%
752
33%
2256
34%
752
84%
752
57%
1025
October16th to endNight
81%
768
43%
2304
45%
768
85%
768
60%
1026
November1st to 15thNight
77%
760
33%
2414
33%
760
81%
760
50%
1125
November16th to endNight
73%
780
30%
2536
31%
780
77%
780
43%
1263
December1st to 15thNight
69%
780
25%
2730
26%
780
73%
780
32%
1507
December16th to endNight
60%
832
25%
2912
24%
832
67%
832
30%
1611

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
3212212335%68%
52067
Night
4212213346%68%
51259
TransparencyDay
18%37%20%27%22%
51751
Night
18%39%20%26%21%
51074
SeeingDay
5%6%16%29%29%12%
7350
Night
5%311%32%36%11%
16861

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
8%4245%25%6%6%9%45%
1648
16th to endDay
9%5%245%35%5%5%7%47%
1872
February1st to 15thDay
10%5%2431345%6%51%
1776
16th to endDay
9%6%245%3345%6%47%
1709
March1st to 15thDay
6%5%234335%6%10%47%
2057
16th to endDay
6%325%426%5%47%49%
2353
April1st to 15thDay
6%5%35%33435%6%52%
2329
16th to endDay
4212313335%66%
2305
May1st to 15thDay
112212346%72%
2359
16th to endDay
312212236%72%
2839
June1st to 15thDay
111111235%78%
2730
16th to endDay
1290%
2730
July1st to 15thDay
112287%
2727
16th to endDay
1111112385%
2676
August1st to 15thDay
11389%
2394
16th to endDay
112289%
2484
September1st to 15thDay
111289%
2340
16th to endDay
1111113483%
2197
October1st to 15thDay
212222335%72%
1873
16th to endDay
2211213435%70%
1920
November1st to 15thDay
5%213324346%61%
1773
16th to endDay
5%423334448%56%
1752
December1st to 15thDay
6%5%25%5%35%45%7%47%
1560
16th to endDay
7%425%5%445%5%8%45%
1664
January1st to 15thNight
7%5%245%2446%8%49%
2618
16th to endNight
8%424424448%51%
2704
February1st to 15thNight
7%41332335%9%53%
2404
16th to endNight
6%32332345%8%55%
2051
March1st to 15thNight
5%313425%45%7%54%
2232
16th to endNight
5%3133245%5%7%57%
2223
April1st to 15thNight
432332445%7%58%
1949
16th to endNight
21212336%73%
1930
May1st to 15thNight
1212236%76%
1917
16th to endNight
11121125%80%
1624
June1st to 15thNight
111233479%
1560
16th to endNight
1292%
1560
July1st to 15thNight
1121287%
1560
16th to endNight
1111111383%
1845
August1st to 15thNight
11289%
1819
16th to endNight
112289%
2070
September1st to 15thNight
11111288%
1950
16th to endNight
111121387%
2091
October1st to 15thNight
321212346%71%
2256
16th to endNight
311212245%73%
2304
November1st to 15thNight
4212213337%67%
2414
16th to endNight
5%31232445%8%58%
2536
December1st to 15thNight
6%42442445%8%51%
2730
16th to endNight
9%4234245%5%7%51%
2912

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
34%5%12%24%15%7%
1648
16th to endDay
36%5%10%18%21%7%
1872
February1st to 15thDay
33%39%24%21%7%
1776
16th to endDay
36%5%11%24%19%2
1709
March1st to 15thDay
31%5%14%25%18%5%
2057
16th to endDay
32%5%14%24%18%4
2353
April1st to 15thDay
32%49%26%21%5%
2329
16th to endDay
21%38%30%29%7%
2305
May1st to 15thDay
13%46%26%38%10%
2359
16th to endDay
15%37%29%33%10%
2843
June1st to 15thDay
10%27%18%33%26%
2730
16th to endDay
419%34%48%
2730
July1st to 15thDay
5%115%23%62%
2578
16th to endDay
8%1210%25%52%
2521
August1st to 15thDay
41110%29%52%
2378
16th to endDay
312%41%40%
2484
September1st to 15thDay
5%1111%37%42%
2340
16th to endDay
7%1221%40%26%
2197
October1st to 15thDay
15%37%23%27%23%
1873
16th to endDay
16%36%24%28%20%
1920
November1st to 15thDay
24%412%24%27%7%
1773
16th to endDay
26%5%10%26%25%6%
1752
December1st to 15thDay
34%6%10%17%20%10%
1560
16th to endDay
36%5%12%22%17%5%
1664
January1st to 15thNight
31%412%25%18%6%
2618
16th to endNight
31%412%16%22%11%
2704
February1st to 15thNight
27%49%25%24%8%
2415
16th to endNight
26%5%14%29%20%4
2051
March1st to 15thNight
28%6%16%22%18%7%
2232
16th to endNight
24%6%15%25%21%6%
2223
April1st to 15thNight
24%413%29%22%5%
1949
16th to endNight
12%314%30%29%9%
1930
May1st to 15thNight
10%37%23%38%16%
1918
16th to endNight
9%18%30%38%12%
1624
June1st to 15thNight
9%37%17%31%30%
1560
16th to endNight
2111%28%55%
1560
July1st to 15thNight
5%1420%66%
1480
16th to endNight
8%128%21%57%
1737
August1st to 15thNight
5%7%26%58%
1810
16th to endNight
49%33%51%
2070
September1st to 15thNight
6%119%28%52%
1950
16th to endNight
5%1117%40%33%
2091
October1st to 15thNight
15%37%21%26%26%
2256
16th to endNight
13%35%22%31%23%
2304
November1st to 15thNight
18%412%24%31%9%
2414
16th to endNight
22%5%11%24%28%8%
2536
December1st to 15thNight
31%5%10%20%20%11%
2730
16th to endNight
31%5%15%20%19%7%
2912

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%422%33%19%4
186
16th to endDay
11%5%20%29%27%5%
304
February1st to 15thDay
14%6%19%24%24%11%
298
16th to endDay
14%12%23%27%18%3
290
March1st to 15thDay
14%13%20%30%16%4
330
16th to endDay
11%12%25%33%14%2
352
April1st to 15thDay
10%17%28%23%17%2
329
16th to endDay
317%29%31%14%4
318
May1st to 15thDay
48%27%35%19%4
348
16th to endDay
5%9%19%32%24%8%
394
June1st to 15thDay
26%18%37%22%11%
375
16th to endDay
213%34%33%15%
375
July1st to 15thDay
17%27%42%20%
365
16th to endDay
428%44%21%
391
August1st to 15thDay
26%32%40%16%
359
16th to endDay
222%47%27%
396
September1st to 15thDay
6%29%43%19%
375
16th to endDay
1310%25%40%19%
375
October1st to 15thDay
2420%33%28%10%
345
16th to endDay
4315%25%37%13%
336
November1st to 15thDay
6%310%27%35%16%
189
16th to endDay
5%6%15%34%29%8%
134
December1st to 15thDay
7%418%25%31%12%
90
16th to endDay
5%11%12%29%25%16%
96
January1st to 15thNight
9%39%32%31%13%
780
16th to endNight
10%310%34%29%11%
832
February1st to 15thNight
10%410%31%32%11%
764
16th to endNight
8%7%15%36%24%7%
684
March1st to 15thNight
5%6%14%35%29%8%
780
16th to endNight
8%5%15%35%28%6%
832
April1st to 15thNight
5%8%20%34%25%5%
779
16th to endNight
46%20%30%27%9%
772
May1st to 15thNight
1419%38%29%7%
748
16th to endNight
15%15%37%35%4
407
June1st to 15thNight
1316%43%31%4
390
16th to endNight
6%45%39%7%
390
July1st to 15thNight
232%56%7%
370
16th to endNight
1121%55%19%
612
August1st to 15thNight
430%52%12%
665
16th to endNight
320%63%11%
828
September1st to 15thNight
5%27%52%13%
780
16th to endNight
118%27%45%16%
776
October1st to 15thNight
438%33%34%15%
752
16th to endNight
428%25%37%21%
768
November1st to 15thNight
4111%32%35%14%
760
16th to endNight
6%310%30%34%13%
780
December1st to 15thNight
9%310%37%30%9%
780
16th to endNight
11%6%13%34%26%6%
832
Page generated at 2018-10-09 07:39:12. Version ac04

Copyright 2018 A. Danko


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