Holly Dome Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Holly Dome Observatory clear sky chart from 2005-11-05 to 2019-07-16.

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
34%
17503
20%
54180
10%
17469
44%
17469
23%
34473

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
22%
839
21%
2926
9%
836
39%
836
17%
1807
January16th to endNight
18%
896
22%
2935
6%
896
37%
896
19%
1822
February1st to 15thNight
17%
824
19%
2622
6%
821
33%
821
18%
1663
February16th to endNight
15%
735
24%
2205
6%
735
38%
735
18%
1416
March1st to 15thNight
21%
840
21%
2454
8%
840
37%
840
21%
1581
March16th to endNight
22%
896
21%
2362
8%
896
33%
896
25%
1570
April1st to 15thNight
21%
838
19%
2096
4%
838
29%
838
24%
1433
April16th to endNight
30%
831
17%
2077
5%
831
36%
831
26%
1427
May1st to 15thNight
30%
640
16%
1900
7%
640
37%
640
21%
1316
May16th to endNight
42%
438
13%
1753
10%
438
49%
438
17%
1132
June1st to 15thNight
48%
420
16%
1680
15%
420
56%
420
20%
1038
June16th to endNight
55%
420
16%
1680
18%
420
60%
420
24%
983
July1st to 15thNight
57%
400
14%
1600
16%
400
60%
400
20%
987
July16th to endNight
62%
452
15%
1593
15%
427
67%
427
27%
921
August1st to 15thNight
62%
641
17%
1781
11%
638
64%
638
30%
1143
August16th to endNight
60%
828
17%
2070
9%
828
62%
828
34%
1368
September1st to 15thNight
52%
780
23%
1950
13%
780
56%
780
32%
1302
September16th to endNight
50%
777
24%
2106
18%
777
55%
777
31%
1348
October1st to 15thNight
43%
780
21%
2324
16%
780
50%
780
26%
1487
October16th to endNight
33%
832
27%
2537
15%
832
48%
832
28%
1502
November1st to 15thNight
30%
820
22%
2667
12%
820
44%
820
22%
1665
November16th to endNight
29%
840
22%
2786
12%
840
43%
840
20%
1701
December1st to 15thNight
24%
840
18%
2940
7%
840
38%
840
17%
1894
December16th to endNight
20%
896
20%
3136
6%
896
38%
896
17%
1967

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
13%5%2442445%7%42%
55131
Night
14%6%2442445%7%43%
54354
Cloud CoverDay
13%5%2442445%7%42%
55140
Night
14%6%2442445%7%43%
54360
TransparencyDay
39%6%13%22%15%2
54823
Night
40%5%11%22%16%2
54180
SeeingDay
18%14%28%23%11%4
8119
Night
17%13%29%27%10%1
17505

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 15thDay
13%5%35%5%2445%7%43%
1672
16th to endDay
15%7%34423345%44%
1991
February1st to 15thDay
16%6%25%5%24447%41%
1898
16th to endDay
14%9%36%424446%39%
1840
March1st to 15thDay
15%5%25%325%347%43%
2153
16th to endDay
16%6%245%2435%5%43%
2565
April1st to 15thDay
16%6%2342445%6%43%
2512
16th to endDay
13%425%425%5%6%6%44%
2488
May1st to 15thDay
16%5%25%4345%5%7%39%
2721
16th to endDay
14%41443445%9%41%
3066
June1st to 15thDay
11%5%245%345%7%10%38%
2940
16th to endDay
9%4244246%8%10%43%
2940
July1st to 15thDay
7%5%245%35%5%7%9%43%
2940
16th to endDay
7%4246%36%6%9%9%38%
2837
August1st to 15thDay
10%4246%2447%8%42%
2406
16th to endDay
9%4245%45%5%8%8%41%
2484
September1st to 15thDay
13%6%245%3346%7%43%
2340
16th to endDay
14%6%35%5%35%45%6%40%
2183
October1st to 15thDay
17%5%25%32335%6%43%
1963
16th to endDay
15%415%323335%50%
2038
November1st to 15thDay
18%5%25%323446%44%
1851
16th to endDay
12%4235%24447%48%
1831
December1st to 15thDay
16%6%25%425%346%42%
1680
16th to endDay
18%7%2442335%8%40%
1792
January1st to 15thNight
17%5%24424446%42%
2926
16th to endNight
17%6%24323345%45%
2935
February1st to 15thNight
16%6%2442445%6%41%
2621
16th to endNight
17%6%24423445%45%
2205
March1st to 15thNight
16%6%24323336%45%
2441
16th to endNight
17%6%35%5%22336%44%
2362
April1st to 15thNight
14%7%25%5%23437%42%
2096
16th to endNight
16%425%33345%6%42%
2077
May1st to 15thNight
14%7%36%4345%6%8%36%
1900
16th to endNight
14%6%25%5%35%46%7%37%
1751
June1st to 15thNight
13%5%2443445%9%40%
1680
16th to endNight
7%425%6%25%5%7%10%42%
1680
July1st to 15thNight
7%435%6%36%6%6%9%41%
1680
16th to endNight
6%435%5%26%5%8%9%42%
1692
August1st to 15thNight
7%5%25%5%35%5%5%9%44%
1792
16th to endNight
9%425%5%25%5%6%7%45%
2070
September1st to 15thNight
12%5%25%5%34446%46%
1950
16th to endNight
14%5%13423448%44%
2106
October1st to 15thNight
16%6%1441335%6%44%
2324
16th to endNight
15%5%14323345%51%
2537
November1st to 15thNight
14%6%25%413345%46%
2667
16th to endNight
13%5%25%434447%44%
2786
December1st to 15thNight
17%7%35%42445%6%38%
2940
16th to endNight
17%5%2442445%6%42%
3136

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
13%5%35%5%2435%6%43%
1672
16th to endDay
15%6%35%323435%44%
1991
February1st to 15thDay
15%6%25%424446%42%
1898
16th to endDay
14%9%36%43345%5%40%
1840
March1st to 15thDay
15%5%25%32445%6%43%
2163
16th to endDay
16%6%24424345%43%
2564
April1st to 15thDay
15%6%2342435%6%44%
2512
16th to endDay
13%425%4245%5%7%44%
2488
May1st to 15thDay
15%5%25%5%25%45%8%38%
2721
16th to endDay
14%42443445%9%41%
3066
June1st to 15thDay
11%5%245%346%7%9%37%
2940
16th to endDay
8%4244245%7%11%43%
2940
July1st to 15thDay
7%5%24435%5%7%9%43%
2940
16th to endDay
7%425%5%36%7%9%9%37%
2837
August1st to 15thDay
10%5%25%5%245%7%8%42%
2406
16th to endDay
9%4245%45%5%7%9%41%
2484
September1st to 15thDay
12%6%2442446%7%43%
2340
16th to endDay
14%6%26%5%34448%39%
2183
October1st to 15thDay
16%5%25%42335%6%43%
1963
16th to endDay
15%424423335%50%
2038
November1st to 15thDay
17%5%25%323346%44%
1851
16th to endDay
13%423424347%48%
1831
December1st to 15thDay
16%6%25%325%35%6%41%
1680
16th to endDay
18%7%14423447%40%
1792
January1st to 15thNight
17%5%24424447%42%
2926
16th to endNight
17%7%24313445%45%
2935
February1st to 15thNight
15%7%2442435%6%41%
2614
16th to endNight
17%6%2442434444%
2205
March1st to 15thNight
16%6%24324336%45%
2454
16th to endNight
17%6%35%5%23236%44%
2362
April1st to 15thNight
14%7%26%434346%42%
2096
16th to endNight
16%5%2443445%6%41%
2077
May1st to 15thNight
14%7%36%5%3446%8%36%
1900
16th to endNight
13%6%35%426%5%5%8%37%
1751
June1st to 15thNight
13%5%335%25%45%9%40%
1680
16th to endNight
8%4245%35%5%7%9%42%
1680
July1st to 15thNight
7%425%6%45%6%6%9%41%
1680
16th to endNight
6%425%5%35%6%7%10%42%
1692
August1st to 15thNight
6%426%5%35%5%5%9%44%
1792
16th to endNight
10%4245%3446%7%45%
2070
September1st to 15thNight
12%5%245%34446%46%
1950
16th to endNight
13%6%24433449%44%
2106
October1st to 15thNight
16%6%24424446%44%
2324
16th to endNight
14%5%24323345%51%
2537
November1st to 15thNight
14%6%245%23345%46%
2667
16th to endNight
13%5%25%43445%6%44%
2786
December1st to 15thNight
17%7%25%32445%6%38%
2940
16th to endNight
17%5%2442445%6%41%
3136

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
40%5%14%20%14%4
1673
16th to endDay
41%5%11%23%14%3
1991
February1st to 15thDay
42%5%13%23%12%2
1901
16th to endDay
45%410%25%12%2
1840
March1st to 15thDay
40%5%12%22%16%2
2163
16th to endDay
41%5%9%21%17%3
2565
April1st to 15thDay
40%5%11%21%15%4
2512
16th to endDay
37%7%12%16%20%4
2488
May1st to 15thDay
42%7%14%20%13%2
2721
16th to endDay
38%7%16%23%11%1
3070
June1st to 15thDay
39%10%13%22%12%1
2940
16th to endDay
32%10%16%21%17%1
2940
July1st to 15thDay
35%8%14%23%17%2
2791
16th to endDay
36%10%16%23%12%1
2673
August1st to 15thDay
36%8%14%24%14%1
2393
16th to endDay
34%9%15%19%17%3
2484
September1st to 15thDay
38%6%13%20%19%2
2340
16th to endDay
42%6%10%17%20%2
2183
October1st to 15thDay
41%413%22%15%2
1963
16th to endDay
36%39%26%21%1
2038
November1st to 15thDay
41%412%22%16%2
1851
16th to endDay
36%412%27%16%2
1831
December1st to 15thDay
42%5%16%21%11%2
1680
16th to endDay
43%5%14%23%12%1
1792
January1st to 15thNight
42%411%20%16%4
2926
16th to endNight
41%410%25%16%1
2935
February1st to 15thNight
42%412%23%14%2
2622
16th to endNight
42%49%22%18%3
2205
March1st to 15thNight
41%411%23%16%3
2454
16th to endNight
42%310%19%19%4
2362
April1st to 15thNight
42%49%21%17%4
2096
16th to endNight
41%6%10%17%20%4
2077
May1st to 15thNight
45%7%10%19%14%2
1900
16th to endNight
43%9%14%17%13%1
1753
June1st to 15thNight
41%7%12%20%17%
1680
16th to endNight
35%8%13%24%15%2
1680
July1st to 15thNight
37%10%16%18%14%2
1600
16th to endNight
33%8%18%23%13%1
1593
August1st to 15thNight
35%8%15%21%17%1
1781
16th to endNight
35%8%13%21%19%2
2070
September1st to 15thNight
39%5%12%22%18%2
1950
16th to endNight
37%5%9%22%22%2
2106
October1st to 15thNight
40%5%11%23%16%2
2324
16th to endNight
35%49%28%19%2
2537
November1st to 15thNight
40%5%10%20%17%5%
2667
16th to endNight
38%5%11%23%17%2
2786
December1st to 15thNight
45%5%12%22%12%1
2940
16th to endNight
42%5%12%23%13%1
3136

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
15%34%28%15%5%
120
16th to endDay
26%28%29%15%
185
February1st to 15thDay
26%26%31%11%3
234
16th to endDay
22%25%37%11%1
343
March1st to 15thDay
19%28%29%18%4
390
16th to endDay
17%20%37%16%5%1
416
April1st to 15thDay
22%21%32%16%5%1
390
16th to endDay
18%14%37%17%10%2
379
May1st to 15thDay
27%14%28%20%7%1
408
16th to endDay
18%11%22%31%12%2
459
June1st to 15thDay
17%8%32%24%13%3
435
16th to endDay
9%9%30%32%15%3
435
July1st to 15thDay
10%223%34%22%6%
425
16th to endDay
8%324%35%21%6%
391
August1st to 15thDay
13%123%32%20%8%
358
16th to endDay
10%218%33%20%14%
396
September1st to 15thDay
17%6%23%21%19%11%
375
16th to endDay
21%5%24%25%12%10%
374
October1st to 15thDay
22%7%20%29%13%6%
375
16th to endDay
13%21%29%21%12%1
387
November1st to 15thDay
22%13%29%21%11%1
325
16th to endDay
14%24%31%18%9%1
271
December1st to 15thDay
25%25%27%10%11%
120
16th to endDay
28%26%25%18%
128
January1st to 15thNight
20%22%31%21%3
840
16th to endNight
21%22%34%20%1
896
February1st to 15thNight
20%20%37%19%1
824
16th to endNight
21%24%36%15%2
735
March1st to 15thNight
20%20%33%20%3
840
16th to endNight
20%15%36%19%6%1
896
April1st to 15thNight
18%19%37%20%4
838
16th to endNight
19%12%33%27%6%
831
May1st to 15thNight
18%9%36%27%7%
640
16th to endNight
16%5%28%35%13%
439
June1st to 15thNight
16%5%24%40%12%
420
16th to endNight
8%226%45%15%
420
July1st to 15thNight
9%220%46%20%1
400
16th to endNight
8%118%42%27%1
452
August1st to 15thNight
9%216%49%20%1
641
16th to endNight
12%117%38%26%3
828
September1st to 15thNight
15%321%35%20%3
780
16th to endNight
17%421%31%22%2
777
October1st to 15thNight
19%7%23%30%16%3
780
16th to endNight
18%14%30%23%11%
832
November1st to 15thNight
19%13%32%23%10%1
820
16th to endNight
16%20%30%22%9%
840
December1st to 15thNight
22%15%33%18%9%
840
16th to endNight
20%20%35%21%2
896
Page generated at 2019-07-17 08:53:05. Version ac04

Copyright 2019 A. Danko


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