Dark Horse Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dark Horse Observatory clear sky chart from 2005-11-06 to 2024-03-28.

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
31%
23521
20%
80598
9%
23423
43%
23423
20%
50598

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 10thNight
16%
754
24%
4340
8%
737
36%
737
11%
2436
January11th to 20thNight
20%
760
24%
4232
7%
740
38%
740
10%
2446
January21st to endNight
17%
833
14%
4473
5%
814
38%
814
10%
2906
February1st to 10thNight
17%
760
19%
2470
7%
760
33%
760
17%
1600
February11th to 20thNight
10%
743
19%
2284
2%
740
30%
740
14%
1486
February21st to endNight
14%
628
23%
1884
6%
628
34%
628
17%
1235
March1st to 10thNight
19%
760
23%
2255
8%
760
38%
760
20%
1395
March11th to 20thNight
19%
760
22%
2090
7%
760
34%
760
20%
1392
March21st to endNight
19%
821
22%
2141
7%
821
32%
821
25%
1441
April1st to 10thNight
17%
720
18%
1800
3%
720
27%
720
21%
1236
April11th to 20thNight
26%
711
19%
1775
6%
711
32%
711
27%
1199
April21st to endNight
27%
720
19%
1800
5%
720
35%
720
25%
1235
May1st to 10thNight
27%
580
15%
1660
6%
580
33%
580
18%
1169
May11th to 20thNight
32%
354
18%
1416
11%
354
43%
354
16%
904
May21st to endNight
47%
388
15%
1551
14%
388
53%
388
20%
958
June1st to 10thNight
43%
360
18%
1440
16%
360
54%
360
22%
863
June11th to 20thNight
50%
360
15%
1440
14%
360
57%
360
21%
882
June21st to endNight
54%
360
17%
1440
19%
360
61%
360
24%
833
July1st to 10thNight
52%
350
13%
1400
14%
350
57%
350
19%
901
July11th to 20thNight
61%
348
17%
1392
18%
348
65%
348
25%
791
July21st to endNight
55%
455
17%
1544
15%
430
60%
430
26%
924
August1st to 10thNight
61%
537
16%
1600
11%
534
64%
534
28%
1026
August11th to 20thNight
53%
668
16%
1732
11%
668
55%
668
27%
1193
August21st to endNight
56%
792
17%
1980
8%
792
58%
792
32%
1314
September1st to 10thNight
45%
720
21%
1800
9%
720
51%
720
31%
1212
September11th to 20thNight
53%
720
29%
1813
19%
720
58%
720
38%
1132
September21st to endNight
44%
720
23%
1998
15%
720
52%
720
26%
1323
October1st to 10thNight
39%
720
16%
2160
12%
720
46%
720
24%
1416
October11th to 20thNight
38%
720
23%
2160
14%
720
50%
720
29%
1301
October21st to endNight
28%
792
26%
2420
13%
792
44%
792
25%
1497
November1st to 10thNight
34%
740
25%
2407
13%
740
51%
740
29%
1352
November11th to 20thNight
29%
760
25%
2470
13%
760
45%
760
21%
1518
November21st to endNight
25%
760
22%
2616
9%
760
43%
760
22%
1535
December1st to 10thNight
21%
760
18%
2660
6%
760
36%
760
16%
1725
December11th to 20thNight
21%
760
20%
3182
7%
759
38%
759
15%
1925
December21st to endNight
21%
827
13%
4773
8%
817
38%
817
10%
2897

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
15%6%35%5%35%5%5%7%40%
78743
Night
16%6%35%5%3445%7%42%
81244
TransparencyDay
42%6%11%23%15%3
78452
Night
41%6%11%23%16%3
81069
SeeingDay
23%15%28%21%10%3
14088
Night
20%14%30%26%10%1
23540

By Month

Percentage Cloud Cover NE (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 10thDay
15%8%25%434446%45%
2517
11th to 20thDay
14%10%39%6%3445%6%35%
2620
21st to endDay
20%8%36%6%35%445%35%
3124
February1st to 10thDay
16%6%36%5%345%5%7%39%
1710
11th to 20thDay
15%8%37%5%3445%5%40%
1782
21st to endDay
19%10%36%5%34446%38%
1570
March1st to 10thDay
15%5%35%5%34446%44%
1920
11th to 20thDay
15%6%25%6%45%5%48%39%
2090
21st to endDay
21%7%36%5%34436%40%
2370
April1st to 10thDay
14%7%36%5%3445%8%41%
2160
11th to 20thDay
14%7%35%5%25%5%5%7%43%
2134
21st to endDay
17%6%25%5%345%6%8%38%
2160
May1st to 10thDay
18%7%35%6%35%5%5%7%35%
2313
11th to 20thDay
19%6%36%5%25%5%5%8%35%
2478
21st to endDay
14%6%25%5%45%5%5%8%40%
2725
June1st to 10thDay
13%5%25%5%35%6%7%9%38%
2520
11th to 20thDay
13%6%36%6%46%6%6%8%37%
2520
21st to endDay
11%5%245%35%7%6%10%41%
2520
July1st to 10thDay
10%5%246%46%6%7%10%39%
2520
11th to 20thDay
7%425%5%35%6%9%11%43%
2520
21st to endDay
9%6%36%6%48%6%7%9%37%
2680
August1st to 10thDay
10%5%35%6%46%6%7%9%40%
2327
11th to 20thDay
11%6%25%6%46%5%7%10%39%
2148
21st to endDay
14%5%25%5%345%6%9%41%
2376
September1st to 10thDay
15%6%35%435%5%5%7%43%
2160
11th to 20thDay
14%5%2432345%8%51%
2146
21st to endDay
17%6%35%5%3445%6%39%
1958
October1st to 10thDay
18%5%26%42445%8%42%
1800
11th to 20thDay
16%5%245%3445%7%46%
1800
21st to endDay
20%6%2442445%6%43%
1934
November1st to 10thDay
13%6%34324437%51%
1671
11th to 20thDay
16%5%2432446%6%47%
1710
21st to endDay
15%5%244346%5%7%44%
1562
December1st to 10thDay
17%9%36%5%34446%38%
1520
11th to 20thDay
19%7%34433447%41%
1906
21st to endDay
16%7%36%6%46%5%6%6%35%
2772
January1st to 10thNight
15%6%35%5%35%446%44%
4429
11th to 20thNight
18%8%25%434446%43%
4338
21st to endNight
23%8%36%5%33345%37%
4532
February1st to 10thNight
16%9%35%43445%6%41%
2470
11th to 20thNight
17%8%26%5%3445%6%40%
2282
21st to endNight
18%7%35%4245%5%7%41%
1884
March1st to 10thNight
16%5%2443446%8%45%
2245
11th to 20thNight
17%7%25%434445%44%
2089
21st to endNight
17%8%26%423446%44%
2141
April1st to 10thNight
16%5%35%5%35%5%6%7%41%
1800
11th to 20thNight
15%6%35%5%25%45%8%42%
1775
21st to endNight
19%6%25%42346%7%43%
1800
May1st to 10thNight
19%7%36%5%35%5%5%6%36%
1660
11th to 20thNight
16%7%35%6%345%6%7%38%
1415
21st to endNight
14%6%35%5%25%45%10%41%
1550
June1st to 10thNight
15%5%36%5%3445%8%43%
1440
11th to 20thNight
11%6%245%5%5%6%7%9%40%
1440
21st to endNight
10%4246%35%5%7%9%44%
1440
July1st to 10thNight
10%5%36%6%46%6%6%8%39%
1440
11th to 20thNight
7%435%5%446%8%10%45%
1440
21st to endNight
9%5%35%6%25%6%8%11%42%
1635
August1st to 10thNight
9%5%25%6%36%7%6%10%42%
1611
11th to 20thNight
10%6%47%6%45%5%7%8%38%
1732
21st to endNight
13%5%35%5%35%5%6%8%42%
1980
September1st to 10thNight
15%6%35%5%24446%46%
1800
11th to 20thNight
12%5%25%323446%53%
1813
21st to endNight
16%7%245%345%5%6%43%
1998
October1st to 10thNight
19%6%35%5%34346%43%
2160
11th to 20thNight
16%5%24423446%49%
2160
21st to endNight
19%8%23423346%47%
2420
November1st to 10thNight
12%5%2442345%6%53%
2407
11th to 20thNight
17%6%24324445%48%
2470
21st to endNight
13%5%245%3445%8%46%
2616
December1st to 10thNight
19%6%35%5%35%45%6%38%
2660
11th to 20thNight
18%6%25%5%35%45%8%41%
3288
21st to endNight
18%7%36%5%3446%7%37%
4884

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 10thDay
40%313%27%13%4
2518
11th to 20thDay
49%5%10%20%13%3
2620
21st to endDay
50%6%10%22%10%2
3124
February1st to 10thDay
45%5%14%24%12%2
1710
11th to 20thDay
46%49%24%15%2
1791
21st to endDay
48%49%22%13%4
1570
March1st to 10thDay
41%411%26%15%2
1923
11th to 20thDay
44%5%10%22%15%4
2090
21st to endDay
47%48%20%18%3
2370
April1st to 10thDay
42%5%11%21%16%5%
2160
11th to 20thDay
40%6%11%22%17%4
2134
21st to endDay
44%6%11%18%17%4
2160
May1st to 10thDay
47%7%8%18%16%4
2313
11th to 20thDay
47%6%10%20%14%2
2482
21st to endDay
41%8%13%23%14%2
2725
June1st to 10thDay
40%7%13%24%14%1
2520
11th to 20thDay
42%8%14%22%11%3
2520
21st to endDay
37%7%14%25%16%1
2520
July1st to 10thDay
38%10%13%22%14%3
2450
11th to 20thDay
32%9%14%27%16%3
2445
21st to endDay
41%9%11%21%17%2
2530
August1st to 10thDay
39%10%13%23%15%1
2314
11th to 20thDay
39%7%14%23%16%2
2148
21st to endDay
38%8%11%22%18%3
2376
September1st to 10thDay
40%6%11%21%19%3
2160
11th to 20thDay
33%5%9%26%23%4
2146
21st to endDay
46%5%8%18%21%2
1958
October1st to 10thDay
41%6%11%23%18%1
1800
11th to 20thDay
38%410%24%21%2
1800
21st to endDay
41%410%26%17%2
1934
November1st to 10thDay
34%413%26%20%4
1671
11th to 20thDay
37%5%10%24%21%2
1710
21st to endDay
39%412%31%12%2
1562
December1st to 10thDay
46%415%20%13%1
1520
11th to 20thDay
43%414%27%11%1
1906
21st to endDay
46%6%14%21%12%1
2772
January1st to 10thNight
42%410%28%13%3
4429
11th to 20thNight
44%411%25%13%3
4338
21st to endNight
50%47%26%11%2
4532
February1st to 10thNight
45%412%25%12%2
2470
11th to 20thNight
46%39%20%18%4
2284
21st to endNight
44%5%8%23%16%5%
1884
March1st to 10thNight
38%411%25%18%3
2255
11th to 20thNight
42%5%9%23%17%4
2090
21st to endNight
43%49%20%20%5%
2141
April1st to 10thNight
42%5%11%20%17%4
1800
11th to 20thNight
41%5%10%20%20%4
1775
21st to endNight
41%6%9%20%18%5%
1800
May1st to 10thNight
48%7%10%16%16%3
1660
11th to 20thNight
45%7%11%16%18%3
1416
21st to endNight
41%8%15%19%15%3
1551
June1st to 10thNight
40%6%10%22%19%2
1440
11th to 20thNight
38%9%14%22%15%1
1440
21st to endNight
34%9%13%27%15%2
1440
July1st to 10thNight
40%12%13%18%14%3
1400
11th to 20thNight
32%11%15%25%15%3
1392
21st to endNight
34%9%16%23%16%2
1544
August1st to 10thNight
35%10%15%23%15%1
1600
11th to 20thNight
42%8%14%19%16%2
1732
21st to endNight
37%7%15%20%18%3
1980
September1st to 10thNight
39%7%11%20%20%3
1800
11th to 20thNight
32%6%9%23%26%4
1813
21st to endNight
41%6%8%21%22%2
1998
October1st to 10thNight
43%5%11%22%16%2
2160
11th to 20thNight
35%5%12%28%18%3
2160
21st to endNight
39%49%27%19%2
2420
November1st to 10thNight
33%412%26%19%5%
2407
11th to 20thNight
39%5%9%22%20%5%
2470
21st to endNight
37%413%28%16%2
2616
December1st to 10thNight
46%412%22%14%1
2660
11th to 20thNight
42%412%21%16%4
3288
21st to endNight
45%6%14%23%11%1
4884

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 10thDay
32%23%29%13%12
180
11th to 20thDay
36%26%29%8%1
209
21st to endDay
30%28%26%12%3
297
February1st to 10thDay
30%27%31%10%2
270
11th to 20thDay
32%27%32%9%1
390
21st to endDay
34%21%29%12%3
382
March1st to 10thDay
32%18%29%16%4
460
11th to 20thDay
30%26%28%12%31
460
21st to endDay
31%25%28%11%41
490
April1st to 10thDay
26%25%31%13%41
420
11th to 20thDay
25%22%27%17%7%2
412
21st to endDay
30%19%33%13%31
420
May1st to 10thDay
31%20%27%15%6%2
423
11th to 20thDay
26%14%33%19%7%1
447
21st to endDay
20%10%26%24%17%3
485
June1st to 10thDay
18%12%30%26%12%2
450
11th to 20thDay
18%11%31%25%13%2
450
21st to endDay
13%10%33%27%14%4
450
July1st to 10thDay
13%423%32%21%7%
445
11th to 20thDay
9%425%35%22%5%
444
21st to endDay
11%7%30%32%18%3
488
August1st to 10thDay
10%7%25%32%19%7%
446
11th to 20thDay
14%419%36%19%8%
439
21st to endDay
13%7%25%29%17%10%
495
September1st to 10thDay
19%10%20%26%16%8%
450
11th to 20thDay
16%6%29%24%15%10%
450
21st to endDay
22%14%23%24%13%4
450
October1st to 10thDay
25%8%27%22%13%5%
450
11th to 20thDay
19%18%27%24%12%2
450
21st to endDay
23%18%32%16%9%2
471
November1st to 10thDay
22%13%30%21%10%3
365
11th to 20thDay
23%20%32%19%6%1
370
21st to endDay
23%23%32%18%5%
222
December1st to 10thDay
32%26%28%9%6%
180
11th to 20thDay
34%23%28%12%3
180
21st to endDay
29%23%27%13%8%1
198
January1st to 10thNight
21%23%36%17%2
760
11th to 20thNight
27%18%31%22%3
760
21st to endNight
19%22%38%18%2
836
February1st to 10thNight
22%20%37%20%1
760
11th to 20thNight
28%25%34%13%1
743
21st to endNight
26%20%36%15%2
628
March1st to 10thNight
23%23%31%20%3
760
11th to 20thNight
24%23%31%17%5%
760
21st to endNight
21%16%40%18%5%
821
April1st to 10thNight
22%23%35%17%4
720
11th to 20thNight
19%14%38%23%6%
711
21st to endNight
23%16%32%24%6%
720
May1st to 10thNight
23%13%34%24%6%
580
11th to 20thNight
19%8%36%29%6%
354
21st to endNight
15%7%25%39%13%1
389
June1st to 10thNight
14%6%30%38%11%
360
11th to 20thNight
10%8%28%43%11%
360
21st to endNight
9%327%46%13%1
360
July1st to 10thNight
12%422%41%19%1
350
11th to 20thNight
7%321%41%27%1
348
21st to endNight
11%423%41%19%2
455
August1st to 10thNight
11%219%42%24%2
537
11th to 20thNight
14%417%37%26%2
668
21st to endNight
13%418%41%22%2
792
September1st to 10thNight
16%5%27%32%18%3
720
11th to 20thNight
14%5%22%33%23%3
720
21st to endNight
19%5%25%31%18%1
720
October1st to 10thNight
23%8%24%25%16%3
720
11th to 20thNight
19%11%29%29%11%
720
21st to endNight
25%13%31%23%8%
792
November1st to 10thNight
17%12%33%27%11%1
740
11th to 20thNight
23%17%26%26%8%
760
21st to endNight
18%17%35%22%7%1
760
December1st to 10thNight
26%19%30%19%6%1
760
11th to 20thNight
21%18%34%22%5%
760
21st to endNight
22%19%33%24%2
836
Page generated at 2024-03-24 23:36:59. Version ac07

Copyright © 2024 Attilla Danko.


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