DarkSights Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the DarkSights Observatory clear sky chart from 2005-11-05 to 2017-04-26.

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
64%
14957
25%
45644
23%
14921
67%
14921
37%
25550

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
61%
716
17%
2393
18%
716
64%
716
28%
1444
January16th to endNight
59%
768
24%
2496
25%
768
61%
768
26%
1546
February1st to 15thNight
55%
697
22%
2288
22%
697
60%
697
26%
1442
February16th to endNight
51%
632
22%
1895
19%
632
57%
632
26%
1232
March1st to 15thNight
53%
720
17%
2013
16%
720
56%
720
27%
1323
March16th to endNight
50%
768
20%
2085
14%
768
54%
768
29%
1351
April1st to 15thNight
51%
719
21%
1799
11%
719
54%
719
32%
1181
April16th to endNight
60%
704
24%
1760
12%
704
63%
704
45%
1023
May1st to 15thNight
67%
567
26%
1557
18%
567
70%
567
51%
811
May16th to endNight
66%
349
23%
1375
23%
349
71%
349
37%
646
June1st to 15thNight
69%
330
26%
1320
29%
330
75%
330
39%
611
June16th to endNight
83%
330
33%
1320
43%
330
86%
330
61%
464
July1st to 15thNight
88%
335
33%
1265
42%
335
88%
335
61%
471
July16th to endNight
75%
522
29%
1467
27%
489
76%
489
51%
700
August1st to 15thNight
74%
512
33%
1495
28%
509
74%
509
54%
712
August16th to endNight
81%
700
34%
1750
22%
700
81%
700
63%
891
September1st to 15thNight
82%
660
38%
1650
28%
660
82%
660
64%
833
September16th to endNight
77%
656
37%
1796
34%
656
79%
656
59%
875
October1st to 15thNight
73%
660
29%
1980
31%
660
76%
660
45%
1018
October16th to endNight
70%
704
32%
2112
35%
704
73%
704
43%
1123
November1st to 15thNight
68%
700
27%
2193
27%
700
72%
700
38%
1209
November16th to endNight
63%
720
24%
2427
25%
720
67%
720
32%
1361
December1st to 15thNight
55%
720
20%
2520
19%
720
60%
720
24%
1570
December16th to endNight
49%
768
19%
2688
18%
768
54%
768
22%
1713

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
7%424323346%57%
46018
Night
9%5%24423347%52%
45831
TransparencyDay
27%49%18%23%16%
45704
Night
29%49%18%21%16%
45645
SeeingDay
9%11%26%33%15%2
5433
Night
9%312%34%31%8%
14970

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
16%5%2442446%6%43%
1543
16th to endDay
17%7%25%433346%41%
1728
February1st to 15thDay
17%8%25%224446%41%
1576
16th to endDay
17%7%35%43335%7%38%
1579
March1st to 15thDay
14%6%35%5%25%46%9%36%
1944
16th to endDay
12%6%25%5%345%5%6%40%
2139
April1st to 15thDay
13%7%35%5%3445%6%42%
2149
16th to endDay
6%5%13323347%57%
2111
May1st to 15thDay
3313313337%63%
2062
16th to endDay
6%434312347%57%
2381
June1st to 15thDay
4423313447%60%
2310
16th to endDay
2112112235%75%
2310
July1st to 15thDay
212212336%73%
2280
16th to endDay
212212245%74%
2286
August1st to 15thDay
121331222474%
2126
16th to endDay
212212235%75%
2100
September1st to 15thDay
1212112225%76%
1980
16th to endDay
2313112236%71%
1832
October1st to 15thDay
4213313346%64%
1650
16th to endDay
7%313323245%60%
1760
November1st to 15thDay
8%4243145%47%51%
1666
16th to endDay
11%8%35%423336%48%
1530
December1st to 15thDay
16%8%35%42444441%
1440
16th to endDay
19%6%34413347%39%
1536
January1st to 15thNight
13%6%244245%5%8%43%
2393
16th to endNight
15%6%23423446%45%
2496
February1st to 15thNight
14%7%2443345%5%43%
2276
16th to endNight
15%7%14424447%42%
1895
March1st to 15thNight
16%6%25%433447%42%
2013
16th to endNight
13%6%45%433445%45%
2085
April1st to 15thNight
11%5%245%25%46%7%45%
1799
16th to endNight
6%323324347%58%
1760
May1st to 15thNight
343431335%7%58%
1557
16th to endNight
45%34333448%54%
1375
June1st to 15thNight
332441445%7%57%
1320
16th to endNight
122212335%73%
1320
July1st to 15thNight
312323347%67%
1347
16th to endNight
1336%424448%55%
1575
August1st to 15thNight
1336%5%33349%55%
1504
16th to endNight
314323349%62%
1750
September1st to 15thNight
1423422237%66%
1650
16th to endNight
2313313347%66%
1796
October1st to 15thNight
6%313322347%60%
1980
16th to endNight
6%424324345%57%
2112
November1st to 15thNight
8%5%2331335%8%54%
2193
16th to endNight
9%5%24423346%52%
2427
December1st to 15thNight
15%7%25%424445%43%
2520
16th to endNight
17%7%34323346%43%
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
37%7%12%18%16%7%
1543
16th to endDay
43%5%8%12%19%10%
1728
February1st to 15thDay
43%5%8%17%21%3
1576
16th to endDay
44%6%8%24%12%3
1579
March1st to 15thDay
44%5%11%18%15%5%
1944
16th to endDay
41%8%12%17%16%3
2139
April1st to 15thDay
40%6%13%18%18%2
2149
16th to endDay
25%5%12%25%23%7%
2111
May1st to 15thDay
19%410%25%31%8%
2062
16th to endDay
25%413%26%22%7%
2385
June1st to 15thDay
22%5%9%20%23%17%
2310
16th to endDay
11%15%16%33%31%
2310
July1st to 15thDay
11%249%25%46%
2133
16th to endDay
11%1410%27%44%
2131
August1st to 15thDay
13%312%28%39%
2110
16th to endDay
10%15%15%37%30%
2100
September1st to 15thDay
10%1415%32%35%
1980
16th to endDay
15%26%24%30%21%
1832
October1st to 15thDay
20%49%19%25%18%
1650
16th to endDay
24%5%10%22%23%13%
1760
November1st to 15thDay
31%6%11%26%16%7%
1666
16th to endDay
36%5%11%17%24%4
1530
December1st to 15thDay
44%6%9%16%18%3
1440
16th to endDay
44%5%13%16%16%4
1536
January1st to 15thNight
36%6%12%18%17%8%
2393
16th to endNight
38%6%10%12%17%15%
2496
February1st to 15thNight
40%5%10%18%17%7%
2288
16th to endNight
39%7%11%23%15%2
1895
March1st to 15thNight
41%5%12%19%14%6%
2013
16th to endNight
38%6%13%18%17%6%
2085
April1st to 15thNight
35%7%15%19%18%4
1799
16th to endNight
25%413%26%22%8%
1760
May1st to 15thNight
20%311%19%29%13%
1558
16th to endNight
24%414%24%23%7%
1375
June1st to 15thNight
23%410%19%20%21%
1320
16th to endNight
11%1413%32%37%
1320
July1st to 15thNight
13%139%23%50%
1265
16th to endNight
21%25%10%19%40%
1467
August1st to 15thNight
21%313%24%37%
1495
16th to endNight
17%1412%30%33%
1750
September1st to 15thNight
16%1310%27%40%
1650
16th to endNight
17%26%20%28%25%
1796
October1st to 15thNight
23%48%21%23%19%
1980
16th to endNight
25%38%22%24%15%
2112
November1st to 15thNight
28%5%12%27%17%8%
2193
16th to endNight
32%410%21%22%8%
2427
December1st to 15thNight
40%5%10%15%19%7%
2520
16th to endNight
42%6%11%15%17%6%
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
21%11%26%25%14%1
171
16th to endDay
19%9%19%28%20%2
256
February1st to 15thDay
19%14%20%25%20%
236
16th to endDay
18%15%27%23%13%1
238
March1st to 15thDay
16%17%29%19%14%2
270
16th to endDay
14%19%34%20%10%1
288
April1st to 15thDay
16%25%28%19%8%
269
16th to endDay
8%28%29%25%7%1
254
May1st to 15thDay
8%14%41%26%7%
228
16th to endDay
6%16%30%34%11%1
266
June1st to 15thDay
415%39%33%6%1
255
16th to endDay
16%29%42%16%2
255
July1st to 15thDay
26%53%17%1
245
16th to endDay
120%50%20%5%
271
August1st to 15thDay
2322%49%18%3
255
16th to endDay
1221%52%17%4
268
September1st to 15thDay
1316%48%22%7%
255
16th to endDay
37%21%37%21%7%
255
October1st to 15thDay
5%10%25%35%18%3
255
16th to endDay
11%7%29%29%20%1
272
November1st to 15thDay
10%422%25%30%6%
172
16th to endDay
8%14%25%32%20%
75
December1st to 15thDay
18%18%28%26%8%
60
16th to endDay
21%12%18%25%18%3
64
January1st to 15thNight
14%411%33%27%9%
720
16th to endNight
17%311%32%25%9%
768
February1st to 15thNight
16%412%32%26%6%
704
16th to endNight
15%6%16%34%20%5%
632
March1st to 15thNight
16%7%14%26%28%5%
720
16th to endNight
15%5%20%34%21%3
768
April1st to 15thNight
10%9%20%35%20%3
719
16th to endNight
6%5%20%36%23%6%
704
May1st to 15thNight
4213%44%29%5%
568
16th to endNight
4314%46%28%3
350
June1st to 15thNight
3113%51%26%3
330
16th to endNight
28%49%37%2
330
July1st to 15thNight
1241%47%6%
335
16th to endNight
2327%54%11%
522
August1st to 15thNight
35%36%44%9%
512
16th to endNight
1436%49%8%
700
September1st to 15thNight
3429%50%11%
660
16th to endNight
39%31%40%14%
656
October1st to 15thNight
7%28%37%33%10%
660
16th to endNight
7%29%33%32%14%
704
November1st to 15thNight
8%114%32%33%10%
700
16th to endNight
10%312%33%30%9%
720
December1st to 15thNight
17%5%13%32%24%6%
720
16th to endNight
18%5%17%34%19%4
768
Page generated at 2017-04-27 14:48:49. Version ac04

Copyright 2017 A. Danko


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