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 2017-09-23.

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
65%
15395
26%
46970
23%
15359
68%
15359
38%
26148

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%
720
25%
1800
12%
720
63%
720
46%
1045
May1st to 15thNight
67%
618
26%
1698
18%
618
70%
618
52%
879
May16th to endNight
66%
382
25%
1504
25%
382
71%
382
36%
712
June1st to 15thNight
70%
360
24%
1440
27%
360
75%
360
39%
658
June16th to endNight
83%
360
35%
1440
45%
360
86%
360
61%
503
July1st to 15thNight
88%
368
32%
1388
39%
368
89%
368
63%
508
July16th to endNight
76%
564
31%
1593
29%
531
78%
531
52%
748
August1st to 15thNight
73%
559
31%
1632
26%
556
73%
556
52%
789
August16th to endNight
81%
764
36%
1910
23%
764
82%
764
63%
970
September1st to 15thNight
80%
720
36%
1800
27%
720
81%
720
64%
914
September16th to endNight
77%
688
39%
1876
35%
688
80%
688
60%
909
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%58%
47938
Night
8%5%24423347%53%
47157
TransparencyDay
26%49%18%23%17%
47624
Night
29%49%18%21%16%
46971
SeeingDay
8%10%26%33%17%3
6022
Night
9%312%34%31%8%
15408

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%58%
2160
May1st to 15thDay
3313313347%64%
2250
16th to endDay
5%5%34312347%58%
2604
June1st to 15thDay
442331345%6%60%
2520
16th to endDay
1112212235%75%
2520
July1st to 15thDay
212212235%74%
2487
16th to endDay
212212245%75%
2468
August1st to 15thDay
121331222473%
2319
16th to endDay
112212235%75%
2292
September1st to 15thDay
1213212235%75%
2160
16th to endDay
2313112236%70%
1918
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%
1800
May1st to 15thNight
3424323347%59%
1698
16th to endNight
45%45%333448%54%
1504
June1st to 15thNight
432441335%7%58%
1440
16th to endNight
132212325%73%
1440
July1st to 15thNight
212222348%68%
1470
16th to endNight
1326%423448%57%
1701
August1st to 15thNight
1435%6%33349%54%
1641
16th to endNight
214423349%62%
1910
September1st to 15thNight
1423422236%66%
1800
16th to endNight
2313313247%67%
1876
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%24%23%7%
2160
May1st to 15thDay
18%410%27%31%8%
2250
16th to endDay
25%413%25%23%7%
2608
June1st to 15thDay
22%5%9%21%23%17%
2520
16th to endDay
11%1416%32%33%
2520
July1st to 15thDay
10%139%24%50%
2340
16th to endDay
11%149%25%47%
2313
August1st to 15thDay
14%312%29%38%
2303
16th to endDay
10%15%15%36%31%
2292
September1st to 15thDay
11%15%16%31%33%
2160
16th to endDay
15%26%25%29%20%
1918
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%412%25%22%9%
1800
May1st to 15thNight
20%311%21%29%13%
1699
16th to endNight
25%413%25%23%7%
1504
June1st to 15thNight
23%49%20%22%20%
1440
16th to endNight
11%1313%31%38%
1440
July1st to 15thNight
12%129%21%53%
1388
16th to endNight
20%15%10%18%43%
1593
August1st to 15thNight
22%312%24%36%
1632
16th to endNight
17%1412%30%34%
1910
September1st to 15thNight
16%1412%26%38%
1800
16th to endNight
16%26%22%28%24%
1876
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%28%25%7%1
270
May1st to 15thDay
6%14%41%27%8%
288
16th to endDay
5%14%29%34%13%2
330
June1st to 15thDay
5%15%36%31%8%1
315
16th to endDay
15%26%41%21%4
315
July1st to 15thDay
22%51%20%3
305
16th to endDay
120%48%20%8%
327
August1st to 15thDay
2320%47%20%5%
315
16th to endDay
1118%46%25%6%
332
September1st to 15thDay
2317%46%24%6%
315
16th to endDay
38%23%37%21%7%
284
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%21%36%23%6%
720
May1st to 15thNight
4214%43%29%5%
619
16th to endNight
5%213%44%29%3
383
June1st to 15thNight
4113%50%27%2
360
16th to endNight
28%47%39%2
360
July1st to 15thNight
1239%50%6%
368
16th to endNight
2329%52%12%
564
August1st to 15thNight
45%34%44%10%
559
16th to endNight
1436%48%9%
764
September1st to 15thNight
35%30%48%11%
720
16th to endNight
319%31%39%13%
688
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 2017-09-24 06:15:55. Version ac04

Copyright 2017 A. Danko


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