Holmes Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Holmes 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
67%
15482
26%
46985
23%
15446
71%
15446
36%
26623

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
60%
716
20%
2365
20%
716
64%
716
32%
1349
January16th to endNight
61%
768
25%
2496
26%
768
64%
768
30%
1475
February1st to 15thNight
57%
698
23%
2283
23%
698
62%
698
27%
1404
February16th to endNight
52%
632
22%
1895
18%
632
58%
632
29%
1190
March1st to 15thNight
56%
720
20%
2003
17%
720
59%
720
29%
1288
March16th to endNight
54%
768
20%
2089
15%
768
59%
768
32%
1323
April1st to 15thNight
52%
719
22%
1799
12%
719
56%
719
34%
1161
April16th to endNight
60%
720
25%
1800
11%
720
64%
720
43%
1054
May1st to 15thNight
70%
632
23%
1712
16%
632
72%
632
45%
945
May16th to endNight
70%
411
22%
1534
19%
411
75%
411
33%
787
June1st to 15thNight
75%
360
24%
1440
26%
360
81%
360
33%
727
June16th to endNight
90%
360
31%
1440
40%
360
91%
360
47%
604
July1st to 15thNight
89%
404
26%
1424
31%
404
90%
404
44%
660
July16th to endNight
82%
564
27%
1593
26%
531
83%
531
33%
922
August1st to 15thNight
78%
566
25%
1639
20%
563
79%
563
32%
982
August16th to endNight
84%
764
30%
1910
19%
764
84%
764
46%
1123
September1st to 15thNight
88%
720
34%
1800
26%
720
88%
720
54%
994
September16th to endNight
82%
688
40%
1879
36%
688
85%
688
59%
924
October1st to 15thNight
73%
660
29%
1980
31%
660
76%
660
44%
1040
October16th to endNight
73%
704
33%
2112
34%
704
77%
704
41%
1141
November1st to 15thNight
71%
700
29%
2172
29%
700
74%
700
43%
1130
November16th to endNight
65%
720
26%
2412
27%
720
69%
720
35%
1295
December1st to 15thNight
56%
720
23%
2520
20%
720
63%
720
27%
1503
December16th to endNight
50%
768
21%
2688
19%
768
57%
768
26%
1602

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
8%423323347%56%
47919
Night
8%32332445%7%53%
47174
TransparencyDay
29%39%20%23%13%
47609
Night
31%49%19%21%14%
46986
SeeingDay
10%5%19%34%25%6%
6075
Night
11%210%29%34%10%
15494

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
15%425%324448%45%
1571
16th to endDay
17%6%25%424345%44%
1728
February1st to 15thDay
19%5%34423347%41%
1582
16th to endDay
20%6%35%425%436%37%
1579
March1st to 15thDay
16%5%25%5%35%5%49%35%
1956
16th to endDay
14%5%35%5%35%446%41%
2133
April1st to 15thDay
15%6%24323348%43%
2149
16th to endDay
8%423323447%56%
2160
May1st to 15thDay
5%413224348%60%
2235
16th to endDay
5%5%25%323437%54%
2575
June1st to 15thDay
5%41322335%7%58%
2520
16th to endDay
111212236%73%
2520
July1st to 15thDay
111323247%70%
2448
16th to endDay
1112213148%71%
2468
August1st to 15thDay
1213323139%67%
2310
16th to endDay
12323238%71%
2292
September1st to 15thDay
1212212226%73%
2160
16th to endDay
4212212245%69%
1915
October1st to 15thDay
5%314323446%60%
1650
16th to endDay
8%413322346%58%
1760
November1st to 15thDay
9%424323447%52%
1687
16th to endDay
13%6%23323336%50%
1545
December1st to 15thDay
18%6%35%324445%41%
1440
16th to endDay
18%8%24423348%39%
1536
January1st to 15thNight
14%42442445%7%45%
2365
16th to endNight
16%5%233235%46%47%
2496
February1st to 15thNight
15%6%25%3245%5%6%42%
2271
16th to endNight
17%6%234235%5%8%40%
1895
March1st to 15thNight
16%6%3433345%7%42%
2003
16th to endNight
13%5%3443435%8%44%
2089
April1st to 15thNight
13%4235%33448%45%
1799
16th to endNight
6%32332435%9%56%
1800
May1st to 15thNight
3313424349%58%
1712
16th to endNight
33243225%6%9%55%
1533
June1st to 15thNight
2123325%5%6%8%58%
1440
16th to endNight
111223446%70%
1440
July1st to 15thNight
1232345%9%65%
1509
16th to endNight
115%5%35%5%6%9%56%
1701
August1st to 15thNight
3146%35%5%5%9%53%
1648
16th to endNight
114435%5%5%9%59%
1910
September1st to 15thNight
1112234349%65%
1800
16th to endNight
2212211247%70%
1879
October1st to 15thNight
5%413424237%61%
1980
16th to endNight
6%323323345%60%
2112
November1st to 15thNight
8%423223447%57%
2172
16th to endNight
8%324414447%53%
2412
December1st to 15thNight
16%6%23423346%45%
2520
16th to endNight
18%5%23324446%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
35%413%19%15%10%
1571
16th to endDay
39%49%12%20%13%
1728
February1st to 15thDay
41%29%19%20%6%
1582
16th to endDay
46%48%24%12%4
1579
March1st to 15thDay
41%5%11%21%14%5%
1956
16th to endDay
41%6%13%19%15%3
2133
April1st to 15thDay
37%5%14%20%20%2
2149
16th to endDay
28%413%26%19%7%
2160
May1st to 15thDay
23%312%28%25%6%
2235
16th to endDay
31%413%24%20%5%
2579
June1st to 15thDay
26%5%12%23%21%9%
2520
16th to endDay
16%36%20%33%20%
2520
July1st to 15thDay
21%2312%27%31%
2305
16th to endDay
19%3315%31%27%
2313
August1st to 15thDay
22%2316%29%24%
2294
16th to endDay
20%2421%27%23%
2292
September1st to 15thDay
19%25%17%28%26%
2160
16th to endDay
19%26%24%29%18%
1915
October1st to 15thDay
23%39%21%24%16%
1650
16th to endDay
28%210%24%21%13%
1760
November1st to 15thDay
30%310%28%20%6%
1687
16th to endDay
34%211%19%25%6%
1545
December1st to 15thDay
42%411%17%18%6%
1440
16th to endDay
41%314%15%18%6%
1536
January1st to 15thNight
34%312%22%17%9%
2365
16th to endNight
36%411%13%17%16%
2496
February1st to 15thNight
40%49%19%18%9%
2283
16th to endNight
39%413%26%13%3
1895
March1st to 15thNight
40%412%20%16%7%
2003
16th to endNight
37%413%20%18%5%
2089
April1st to 15thNight
36%414%23%17%3
1799
16th to endNight
25%5%12%27%20%8%
1800
May1st to 15thNight
26%311%20%27%11%
1713
16th to endNight
26%6%15%22%22%5%
1534
June1st to 15thNight
25%7%9%21%21%14%
1440
16th to endNight
17%45%14%31%26%
1440
July1st to 15thNight
19%5%211%22%37%
1424
16th to endNight
31%6%411%19%26%
1593
August1st to 15thNight
35%5%112%22%22%
1639
16th to endNight
27%4213%24%27%
1910
September1st to 15thNight
22%3413%26%30%
1800
16th to endNight
17%2323%34%18%
1879
October1st to 15thNight
24%39%21%22%18%
1980
16th to endNight
27%36%23%22%16%
2112
November1st to 15thNight
26%312%26%24%8%
2172
16th to endNight
29%39%22%22%10%
2412
December1st to 15thNight
39%310%18%20%8%
2520
16th to endNight
39%314%16%17%7%
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
23%5%19%28%18%5%
200
16th to endDay
20%322%25%21%6%
256
February1st to 15thDay
21%6%21%24%21%5%
237
16th to endDay
21%8%23%28%14%3
238
March1st to 15thDay
21%6%27%22%18%4
270
16th to endDay
15%10%25%32%13%2
288
April1st to 15thDay
16%13%28%28%10%2
269
16th to endDay
6%14%32%27%15%2
270
May1st to 15thDay
9%9%30%33%14%2
288
16th to endDay
8%9%19%33%23%5%
330
June1st to 15thDay
6%5%27%39%18%2
315
16th to endDay
1116%43%31%6%
315
July1st to 15thDay
38%40%38%7%
305
16th to endDay
16%44%37%10%
327
August1st to 15thDay
311%43%35%6%
315
16th to endDay
29%40%37%9%
332
September1st to 15thDay
6%11%39%33%9%
315
16th to endDay
5%415%31%33%9%
284
October1st to 15thDay
6%418%38%24%7%
255
16th to endDay
11%420%32%25%5%
272
November1st to 15thDay
9%314%25%31%15%
193
16th to endDay
11%6%14%41%24%1
77
December1st to 15thDay
28%10%21%25%15%
60
16th to endDay
12%15%9%23%31%7%
64
January1st to 15thNight
17%211%28%30%9%
720
16th to endNight
18%29%30%28%10%
768
February1st to 15thNight
19%410%28%30%6%
704
16th to endNight
21%316%32%20%6%
632
March1st to 15thNight
19%412%26%30%6%
720
16th to endNight
17%315%32%26%4
768
April1st to 15thNight
16%5%17%33%24%3
719
16th to endNight
9%6%19%30%26%7%
720
May1st to 15thNight
7%214%34%33%7%
633
16th to endNight
6%413%32%32%9%
412
June1st to 15thNight
414%37%37%5%
360
16th to endNight
2436%48%7%
360
July1st to 15thNight
3122%54%16%
404
16th to endNight
31320%50%21%
564
August1st to 15thNight
5%6%25%48%12%
566
16th to endNight
4323%52%14%
764
September1st to 15thNight
3325%48%17%
720
16th to endNight
416%26%43%17%
688
October1st to 15thNight
9%27%28%37%15%
660
16th to endNight
8%17%27%35%18%
704
November1st to 15thNight
11%10%29%36%11%
700
16th to endNight
9%310%33%32%10%
720
December1st to 15thNight
20%211%31%26%7%
720
16th to endNight
21%416%32%20%4
768
Page generated at 2017-09-24 06:15:49. Version ac04

Copyright 2017 A. Danko


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