DAS Dark Sky Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the DAS Dark Sky Site clear sky chart from 2005-11-05 to 2018-02-22.

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
50%
16640
27%
48892
17%
16598
59%
16598
39%
27396

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
50%
974
28%
2716
18%
970
59%
970
43%
1505
January16th to endNight
47%
926
33%
2798
21%
926
60%
926
42%
1485
February1st to 15thNight
42%
760
23%
2383
15%
759
52%
759
34%
1362
February16th to endNight
40%
660
32%
1978
16%
660
55%
660
37%
1095
March1st to 15thNight
44%
720
27%
2160
15%
720
54%
720
39%
1203
March16th to endNight
39%
644
26%
1997
14%
644
52%
644
35%
1128
April1st to 15thNight
32%
539
22%
1798
11%
539
47%
539
31%
1014
April16th to endNight
39%
540
19%
1800
14%
540
49%
540
25%
1108
May1st to 15thNight
41%
540
20%
1620
15%
540
48%
540
28%
1022
May16th to endNight
44%
562
17%
1502
10%
561
49%
561
33%
939
June1st to 15thNight
51%
540
17%
1440
10%
540
57%
540
41%
838
June16th to endNight
60%
540
24%
1440
16%
540
65%
540
47%
786
July1st to 15thNight
61%
510
16%
1360
10%
510
65%
510
36%
853
July16th to endNight
69%
564
23%
1416
17%
531
72%
531
38%
852
August1st to 15thNight
61%
539
16%
1688
15%
536
64%
536
30%
1022
August16th to endNight
63%
573
25%
1910
25%
573
70%
573
38%
1010
September1st to 15thNight
60%
540
27%
1800
23%
540
69%
540
39%
949
September16th to endNight
62%
537
34%
1968
30%
537
72%
537
43%
916
October1st to 15thNight
47%
651
30%
2091
19%
651
57%
651
37%
1124
October16th to endNight
59%
841
37%
2377
22%
841
67%
841
51%
1215
November1st to 15thNight
53%
950
33%
2470
17%
950
61%
950
53%
1312
November16th to endNight
53%
975
36%
2538
21%
975
62%
975
50%
1388
December1st to 15thNight
45%
975
25%
2730
13%
975
55%
975
41%
1547
December16th to endNight
44%
1040
28%
2912
15%
1040
53%
1040
36%
1723

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
5%41332445%7%55%
49377
Night
5%42442445%7%54%
49064
Cloud CoverDay
5%41332445%7%55%
49375
Night
5%42432445%7%54%
49064
TransparencyDay
26%5%11%25%22%8%
49051
Night
27%5%12%25%21%7%
48892
SeeingDay
9%7%26%31%19%6%
6350
Night
7%431%41%13%1
16646

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
35%34413346%59%
1552
16th to endDay
35%23423447%60%
1791
February1st to 15thDay
37%25%334436%55%
1807
16th to endDay
36%24323346%58%
1642
March1st to 15thDay
3424424347%58%
1800
16th to endDay
8%6%2432346%7%51%
2225
April1st to 15thDay
8%5%2432445%7%52%
2150
16th to endDay
11%6%1432346%6%47%
2160
May1st to 15thDay
9%6%24425%5%6%8%44%
2331
16th to endDay
9%31442446%9%48%
2611
June1st to 15thDay
7%2133245%6%8%52%
2520
16th to endDay
21222446%8%62%
2520
July1st to 15thDay
6%214325%5%6%10%50%
2520
16th to endDay
4223425%6%7%9%51%
2656
August1st to 15thDay
4212435%6%7%11%50%
2259
16th to endDay
42123245%6%9%56%
2292
September1st to 15thDay
6%21242435%6%59%
2160
16th to endDay
5%21221235%6%65%
1992
October1st to 15thDay
7%313323346%61%
1866
16th to endDay
6%312222246%65%
1833
November1st to 15thDay
3414314346%61%
1718
16th to endDay
3423212346%65%
1748
December1st to 15thDay
37%23324346%57%
1560
16th to endDay
45%36%423447%52%
1664
January1st to 15thNight
25%2432445%7%57%
2716
16th to endNight
45%24423335%60%
2798
February1st to 15thNight
37%35%424448%50%
2373
16th to endNight
37%25%324446%56%
1978
March1st to 15thNight
45%2432445%7%55%
2160
16th to endNight
6%6%2332345%9%52%
1997
April1st to 15thNight
8%6%234245%5%7%49%
1798
16th to endNight
15%6%24433447%43%
1800
May1st to 15thNight
12%4245%3445%8%44%
1619
16th to endNight
10%4144235%48%49%
1501
June1st to 15thNight
5%313325%5%6%9%53%
1440
16th to endNight
321232448%10%56%
1440
July1st to 15thNight
6%3135%36%6%8%9%45%
1440
16th to endNight
32135%37%6%6%9%49%
1512
August1st to 15thNight
5%325%6%45%6%7%9%44%
1696
16th to endNight
6%3134245%6%8%54%
1910
September1st to 15thNight
7%3133245%6%8%54%
1800
16th to endNight
5%21332325%7%62%
1968
October1st to 15thNight
9%413322346%58%
2091
16th to endNight
5%312212346%64%
2377
November1st to 15thNight
221322325%8%61%
2470
16th to endNight
45%1231245%7%60%
2538
December1st to 15thNight
36%25%324346%56%
2730
16th to endNight
47%35%42445%6%51%
2912

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
45%34322345%60%
1552
16th to endDay
35%23323347%59%
1791
February1st to 15thDay
36%35%434447%53%
1807
16th to endDay
36%34324346%58%
1642
March1st to 15thDay
3424433447%57%
1800
16th to endDay
7%6%2432345%7%51%
2223
April1st to 15thDay
7%6%2332345%8%51%
2150
16th to endDay
11%6%2442345%7%46%
2160
May1st to 15thDay
9%6%2433447%8%44%
2331
16th to endDay
9%3133245%7%10%47%
2611
June1st to 15thDay
7%3133245%6%9%52%
2520
16th to endDay
211232445%8%62%
2520
July1st to 15thDay
5%214425%47%10%51%
2520
16th to endDay
32133345%8%10%51%
2656
August1st to 15thDay
4212435%5%7%10%51%
2259
16th to endDay
43123245%6%8%57%
2292
September1st to 15thDay
6%313324446%60%
2160
16th to endDay
5%21231235%6%64%
1992
October1st to 15thDay
7%312323345%61%
1866
16th to endDay
6%41222235%465%
1833
November1st to 15thDay
341332345%6%61%
1718
16th to endDay
2423213346%65%
1748
December1st to 15thDay
37%2432445%6%57%
1560
16th to endDay
45%35%5%14447%52%
1664
January1st to 15thNight
25%2442445%7%56%
2716
16th to endNight
45%2442334460%
2798
February1st to 15thNight
37%25%5%2446%6%50%
2373
16th to endNight
37%24323446%54%
1978
March1st to 15thNight
45%243235%5%7%55%
2160
16th to endNight
6%6%2441445%7%52%
1997
April1st to 15thNight
8%6%14434447%50%
1798
16th to endNight
15%6%23433447%43%
1800
May1st to 15thNight
11%5%24435%5%5%8%43%
1619
16th to endNight
10%41432445%9%49%
1501
June1st to 15thNight
5%223315%5%6%10%52%
1440
16th to endNight
221333445%11%56%
1440
July1st to 15thNight
6%214435%6%7%10%45%
1440
16th to endNight
4213436%6%7%9%48%
1512
August1st to 15thNight
4325%6%347%7%9%44%
1696
16th to endNight
5%41343445%8%54%
1910
September1st to 15thNight
7%3133245%7%8%53%
1800
16th to endNight
5%213324347%62%
1968
October1st to 15thNight
9%41331335%5%58%
2091
16th to endNight
6%312222346%64%
2377
November1st to 15thNight
321322335%7%62%
2470
16th to endNight
45%1221345%7%60%
2538
December1st to 15thNight
36%25%32435%6%56%
2730
16th to endNight
47%35%423447%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
25%311%30%23%5%
1553
16th to endDay
23%49%30%24%7%
1791
February1st to 15thDay
30%5%12%33%13%4
1808
16th to endDay
26%38%30%24%6%
1642
March1st to 15thDay
25%411%24%25%8%
1800
16th to endDay
31%414%22%20%6%
2225
April1st to 15thDay
29%5%11%26%20%7%
2150
16th to endDay
35%5%12%23%18%4
2160
May1st to 15thDay
35%8%11%25%15%3
2331
16th to endDay
29%7%17%24%15%5%
2615
June1st to 15thDay
26%7%14%22%19%10%
2520
16th to endDay
18%5%10%25%27%13%
2520
July1st to 15thDay
27%7%11%22%20%11%
2371
16th to endDay
25%7%12%28%19%6%
2489
August1st to 15thDay
25%7%14%24%17%9%
2243
16th to endDay
22%6%11%22%26%9%
2292
September1st to 15thDay
23%5%8%24%23%14%
2160
16th to endDay
19%37%23%35%9%
1992
October1st to 15thDay
23%49%22%27%11%
1866
16th to endDay
21%38%26%27%13%
1833
November1st to 15thDay
22%39%27%25%12%
1718
16th to endDay
20%37%25%32%11%
1748
December1st to 15thDay
27%48%32%21%5%
1560
16th to endDay
31%5%12%27%18%5%
1664
January1st to 15thNight
25%410%29%25%4
2716
16th to endNight
25%48%27%25%8%
2798
February1st to 15thNight
31%5%14%29%15%3
2383
16th to endNight
29%38%27%22%8%
1978
March1st to 15thNight
27%410%23%25%7%
2160
16th to endNight
28%6%12%22%24%5%
1997
April1st to 15thNight
31%5%12%24%18%6%
1798
16th to endNight
38%6%12%22%16%4
1800
May1st to 15thNight
36%7%13%25%12%4
1620
16th to endNight
33%7%20%19%11%6%
1502
June1st to 15thNight
25%8%20%21%14%9%
1440
16th to endNight
21%7%13%27%21%9%
1440
July1st to 15thNight
32%7%13%22%14%9%
1360
16th to endNight
27%9%16%22%19%4
1416
August1st to 15thNight
31%10%17%20%13%6%
1688
16th to endNight
26%6%11%27%20%7%
1910
September1st to 15thNight
25%6%14%20%21%11%
1800
16th to endNight
21%5%8%28%27%8%
1968
October1st to 15thNight
27%5%10%20%26%10%
2091
16th to endNight
20%48%26%27%13%
2377
November1st to 15thNight
19%39%26%26%14%
2470
16th to endNight
22%38%26%28%10%
2538
December1st to 15thNight
27%5%12%28%19%6%
2730
16th to endNight
31%412%27%20%3
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
8%5%19%45%15%4
135
16th to endDay
9%431%33%18%3
144
February1st to 15thDay
8%10%44%30%5%
135
16th to endDay
314%38%31%11%3
100
March1st to 15thDay
410%32%33%20%
90
16th to endDay
14%21%30%22%8%1
278
April1st to 15thDay
12%18%36%21%8%2
269
16th to endDay
23%18%31%17%7%1
270
May1st to 15thDay
14%10%28%31%11%4
468
16th to endDay
15%8%24%29%17%4
517
June1st to 15thDay
9%6%22%31%20%8%
495
16th to endDay
2424%37%24%5%
495
July1st to 15thDay
10%315%30%29%10%
475
16th to endDay
5%113%36%32%10%
515
August1st to 15thDay
6%224%33%25%7%
342
16th to endDay
5%224%36%22%8%
332
September1st to 15thDay
7%327%33%18%10%
315
16th to endDay
12%426%24%19%12%
147
October1st to 15thDay
7%7%21%29%18%15%
135
16th to endDay
6%5%31%23%27%5%
144
November1st to 15thDay
25%25%36%24%5%
135
16th to endDay
8%7%37%31%13%1
135
December1st to 15thDay
8%10%36%32%11%
135
16th to endDay
45%29%47%12%
144
January1st to 15thNight
45%33%42%11%1
975
16th to endNight
7%434%41%11%1
926
February1st to 15thNight
6%5%39%42%6%
764
16th to endNight
5%8%41%38%5%
660
March1st to 15thNight
5%6%38%39%9%
720
16th to endNight
10%7%38%36%6%
644
April1st to 15thNight
12%7%44%31%3
539
16th to endNight
18%6%32%35%7%
540
May1st to 15thNight
15%5%32%34%11%
540
16th to endNight
12%6%31%36%12%
563
June1st to 15thNight
7%334%40%14%
540
16th to endNight
3228%48%17%
540
July1st to 15thNight
7%119%45%23%1
510
16th to endNight
4115%46%28%2
564
August1st to 15thNight
6%20%46%24%1
539
16th to endNight
8%120%48%18%2
573
September1st to 15thNight
8%125%45%15%3
540
16th to endNight
6%225%42%22%1
537
October1st to 15thNight
12%5%31%34%14%1
651
16th to endNight
8%224%43%17%2
841
November1st to 15thNight
35%33%42%13%1
950
16th to endNight
7%6%29%42%12%1
975
December1st to 15thNight
5%5%36%40%9%1
975
16th to endNight
7%6%34%39%10%1
1040
Page generated at 2018-02-23 09:21:35. Version ac04

Copyright 2018 A. Danko


DAS Dark Sky Site Clear Sky Chart |Charts Home