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 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
74%
15479
32%
46910
28%
15442
79%
15442
51%
22591

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%
716
22%
2416
23%
716
71%
716
36%
1300
January16th to endNight
68%
768
27%
2496
28%
768
71%
768
34%
1396
February1st to 15thNight
65%
700
27%
2223
29%
699
69%
699
36%
1231
February16th to endNight
63%
632
26%
1895
23%
632
69%
632
38%
1059
March1st to 15thNight
66%
720
22%
2060
19%
720
70%
720
39%
1171
March16th to endNight
64%
768
25%
2052
18%
768
70%
768
43%
1157
April1st to 15thNight
57%
719
29%
1799
14%
719
64%
719
45%
1016
April16th to endNight
65%
720
30%
1800
14%
720
71%
720
60%
901
May1st to 15thNight
70%
690
31%
1770
18%
690
74%
690
67%
842
May16th to endNight
73%
374
37%
1496
35%
374
82%
374
63%
496
June1st to 15thNight
75%
360
33%
1440
34%
360
85%
360
58%
516
June16th to endNight
90%
360
42%
1440
50%
360
95%
360
86%
400
July1st to 15thNight
95%
340
37%
1360
46%
340
96%
340
77%
412
July16th to endNight
93%
564
40%
1593
35%
531
94%
531
76%
637
August1st to 15thNight
93%
625
41%
1698
29%
622
94%
622
83%
700
August16th to endNight
93%
764
46%
1910
30%
764
94%
764
86%
832
September1st to 15thNight
91%
720
45%
1800
32%
720
93%
720
81%
806
September16th to endNight
87%
667
49%
1798
43%
667
90%
667
80%
758
October1st to 15thNight
80%
660
34%
1980
35%
660
84%
660
55%
916
October16th to endNight
80%
704
41%
2112
43%
704
85%
704
59%
946
November1st to 15thNight
76%
700
35%
2223
35%
700
81%
700
51%
1031
November16th to endNight
73%
720
30%
2341
30%
720
77%
720
44%
1150
December1st to 15thNight
67%
720
24%
2520
25%
720
71%
720
30%
1435
December16th to endNight
60%
768
24%
2688
23%
768
66%
768
30%
1483

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
4212212335%68%
47887
Night
4212213346%67%
47099
TransparencyDay
19%37%20%27%22%
47571
Night
18%39%20%26%21%
46914
SeeingDay
5%6%17%30%28%10%
5972
Night
5%311%32%36%11%
15489

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
7%4235%25%5%5%8%48%
1520
16th to endDay
9%6%244345%5%7%47%
1728
February1st to 15thDay
10%6%24414446%49%
1635
16th to endDay
9%6%245%3345%6%45%
1579
March1st to 15thDay
6%5%234335%6%10%48%
1899
16th to endDay
6%424426%5%47%50%
2172
April1st to 15thDay
6%5%35%32435%7%52%
2149
16th to endDay
5%212313345%66%
2160
May1st to 15thDay
212212336%72%
2177
16th to endDay
312212236%72%
2615
June1st to 15thDay
121211235%77%
2520
16th to endDay
11290%
2520
July1st to 15thDay
112287%
2517
16th to endDay
1111112285%
2468
August1st to 15thDay
11288%
2253
16th to endDay
112290%
2292
September1st to 15thDay
1111388%
2160
16th to endDay
11111123482%
1886
October1st to 15thDay
222222345%71%
1650
16th to endDay
2211213335%70%
1760
November1st to 15thDay
5%213324246%62%
1634
16th to endDay
5%424334348%56%
1617
December1st to 15thDay
7%5%25%5%36%5%5%7%45%
1440
16th to endDay
8%5%25%5%45%5%5%8%45%
1536
January1st to 15thNight
6%4235%2445%8%51%
2416
16th to endNight
8%424324448%52%
2496
February1st to 15thNight
8%41342335%9%51%
2215
16th to endNight
6%3234335%5%9%53%
1895
March1st to 15thNight
5%3135%25%45%7%55%
2060
16th to endNight
5%212325%45%7%57%
2052
April1st to 15thNight
5%32332445%7%58%
1799
16th to endNight
311213346%71%
1800
May1st to 15thNight
1222236%76%
1770
16th to endNight
11111126%80%
1496
June1st to 15thNight
1111333478%
1440
16th to endNight
1292%
1440
July1st to 15thNight
1121288%
1440
16th to endNight
111111384%
1701
August1st to 15thNight
11289%
1707
16th to endNight
112289%
1910
September1st to 15thNight
11111288%
1800
16th to endNight
111121386%
1798
October1st to 15thNight
321212346%69%
1980
16th to endNight
312212245%72%
2112
November1st to 15thNight
4211212337%68%
2223
16th to endNight
431231445%8%59%
2341
December1st to 15thNight
7%5%24425%45%7%49%
2520
16th to endNight
9%42342345%7%51%
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
32%5%11%25%16%8%
1520
16th to endDay
37%5%9%17%21%8%
1728
February1st to 15thDay
35%39%24%19%6%
1635
16th to endDay
38%5%11%24%17%2
1579
March1st to 15thDay
30%5%15%23%19%5%
1899
16th to endDay
32%5%14%24%17%4
2172
April1st to 15thDay
32%410%26%20%5%
2149
16th to endDay
21%39%29%28%7%
2160
May1st to 15thDay
13%36%25%39%10%
2177
16th to endDay
15%37%28%34%11%
2619
June1st to 15thDay
11%28%20%31%26%
2520
16th to endDay
4110%34%47%
2520
July1st to 15thDay
5%115%21%64%
2368
16th to endDay
8%129%23%54%
2313
August1st to 15thDay
41111%29%51%
2237
16th to endDay
411%40%42%
2292
September1st to 15thDay
5%1112%36%41%
2160
16th to endDay
7%2222%40%24%
1886
October1st to 15thDay
15%37%24%28%20%
1650
16th to endDay
16%36%25%29%18%
1760
November1st to 15thDay
24%411%23%29%7%
1634
16th to endDay
27%49%25%25%6%
1617
December1st to 15thDay
36%6%11%18%21%5%
1440
16th to endDay
37%5%13%21%16%4
1536
January1st to 15thNight
29%412%25%19%7%
2416
16th to endNight
31%412%16%23%12%
2496
February1st to 15thNight
29%49%26%21%7%
2226
16th to endNight
27%5%15%28%19%3
1895
March1st to 15thNight
27%6%16%22%19%8%
2060
16th to endNight
24%6%16%25%21%7%
2052
April1st to 15thNight
24%414%29%22%5%
1799
16th to endNight
13%415%28%28%9%
1800
May1st to 15thNight
11%37%23%37%16%
1771
16th to endNight
8%18%27%40%12%
1496
June1st to 15thNight
10%38%17%28%30%
1440
16th to endNight
3111%28%54%
1440
July1st to 15thNight
5%1420%67%
1360
16th to endNight
8%127%21%59%
1593
August1st to 15thNight
5%7%28%56%
1698
16th to endNight
48%32%52%
1910
September1st to 15thNight
6%1210%28%50%
1800
16th to endNight
6%1117%42%31%
1798
October1st to 15thNight
16%37%23%26%22%
1980
16th to endNight
13%35%23%32%20%
2112
November1st to 15thNight
18%410%23%32%10%
2223
16th to endNight
21%411%24%28%8%
2341
December1st to 15thNight
33%5%10%20%21%7%
2520
16th to endNight
31%5%16%20%19%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
14%5%25%33%16%4
148
16th to endDay
12%6%21%29%24%5%
256
February1st to 15thDay
17%7%19%22%24%9%
247
16th to endDay
16%10%23%28%18%3
238
March1st to 15thDay
12%14%21%28%17%5%
270
16th to endDay
10%12%27%33%13%2
288
April1st to 15thDay
11%19%30%21%15%1
269
16th to endDay
419%30%32%11%1
270
May1st to 15thDay
49%27%37%16%4
288
16th to endDay
410%19%33%22%9%
330
June1st to 15thDay
37%21%41%18%7%
315
16th to endDay
214%37%31%13%
315
July1st to 15thDay
27%28%41%19%
305
16th to endDay
5%30%43%19%
327
August1st to 15thDay
27%34%41%13%
315
16th to endDay
322%46%26%
332
September1st to 15thDay
5%28%44%20%
315
16th to endDay
1310%24%39%20%
264
October1st to 15thDay
2418%34%29%10%
255
16th to endDay
4417%29%36%7%
272
November1st to 15thDay
6%410%20%37%20%
140
16th to endDay
6%8%17%39%22%4
89
December1st to 15thDay
11%6%21%31%28%
60
16th to endDay
7%10%14%34%21%10%
64
January1st to 15thNight
9%39%32%31%14%
720
16th to endNight
11%310%34%28%11%
768
February1st to 15thNight
11%411%31%30%11%
704
16th to endNight
8%7%15%37%23%7%
632
March1st to 15thNight
5%6%14%35%29%8%
720
16th to endNight
7%6%15%34%29%6%
768
April1st to 15thNight
5%8%21%33%24%5%
719
16th to endNight
46%20%30%28%9%
720
May1st to 15thNight
1420%38%28%7%
691
16th to endNight
15%16%38%34%4
375
June1st to 15thNight
1317%45%28%3
360
16th to endNight
7%45%38%8%
360
July1st to 15thNight
333%55%7%
340
16th to endNight
1121%54%20%
564
August1st to 15thNight
430%51%12%
625
16th to endNight
320%63%12%
764
September1st to 15thNight
5%25%53%14%
720
16th to endNight
18%24%46%17%
667
October1st to 15thNight
437%31%36%16%
660
16th to endNight
429%26%36%20%
704
November1st to 15thNight
4111%30%36%15%
700
16th to endNight
6%411%30%33%14%
720
December1st to 15thNight
9%410%37%28%9%
720
16th to endNight
11%7%14%35%25%6%
768
Page generated at 2017-09-19 04:32:27. Version ac04

Copyright 2017 A. Danko


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