HRH Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the HRH 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
65%
15900
20%
46984
17%
15861
68%
15861
30%
29447

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
55%
717
18%
2327
15%
716
60%
716
25%
1459
January16th to endNight
52%
768
24%
2373
20%
768
58%
768
30%
1436
February1st to 15thNight
50%
701
24%
2104
19%
699
57%
699
33%
1264
February16th to endNight
58%
631
25%
1857
17%
631
66%
631
37%
1077
March1st to 15thNight
58%
720
29%
1980
19%
720
67%
720
45%
1083
March16th to endNight
63%
768
27%
2112
21%
768
66%
768
41%
1205
April1st to 15thNight
68%
718
22%
1976
19%
718
70%
718
45%
1100
April16th to endNight
64%
720
27%
1896
19%
720
68%
720
42%
1122
May1st to 15thNight
78%
543
29%
1623
25%
543
81%
543
46%
860
May16th to endNight
78%
561
23%
1683
21%
561
78%
561
36%
1002
June1st to 15thNight
72%
540
10%
1620
10%
540
72%
540
25%
1111
June16th to endNight
81%
540
8%
1620
7%
540
82%
540
24%
1117
July1st to 15thNight
76%
510
6%
1530
5%
510
76%
510
20%
1142
July16th to endNight
77%
564
8%
1595
9%
531
77%
531
22%
1141
August1st to 15thNight
80%
539
4%
1699
5%
536
80%
536
23%
1179
August16th to endNight
67%
699
7%
2036
8%
699
67%
699
18%
1514
September1st to 15thNight
67%
720
7%
1980
7%
720
67%
720
18%
1475
September16th to endNight
63%
669
10%
1848
10%
669
64%
669
19%
1378
October1st to 15thNight
73%
660
24%
1838
25%
660
74%
660
35%
1129
October16th to endNight
59%
704
24%
2112
23%
704
63%
704
31%
1291
November1st to 15thNight
64%
700
30%
2101
27%
700
70%
700
37%
1208
November16th to endNight
57%
720
28%
2238
24%
720
64%
720
34%
1299
December1st to 15thNight
58%
720
24%
2340
23%
720
61%
720
28%
1419
December16th to endNight
61%
768
24%
2496
25%
768
64%
768
32%
1436

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
6%425%6%46%6%7%9%38%
47791
Night
6%425%5%35%5%7%10%43%
47191
TransparencyDay
39%9%15%17%13%4
47492
Night
33%9%17%19%14%5%
46994
SeeingDay
8%211%22%28%27%
5760
Night
8%214%32%30%11%
15909

By Month

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
9%6%25%435%6%8%9%38%
1611
16th to endDay
9%324435%5%5%7%46%
1848
February1st to 15thDay
9%5%35%43446%6%47%
1750
16th to endDay
6%42342445%8%53%
1616
March1st to 15thDay
421332446%8%56%
1980
16th to endDay
7%41442446%8%51%
2111
April1st to 15thDay
5%325%435%5%7%10%48%
1972
16th to endDay
5%314425%5%6%8%51%
2068
May1st to 15thDay
33133245%6%9%55%
2331
16th to endDay
5%435%5%46%6%7%9%39%
2431
June1st to 15thDay
9%6%27%7%47%7%9%11%24%
2340
16th to endDay
6%6%26%7%5%9%9%10%12%23%
2340
July1st to 15thDay
8%5%38%8%6%10%8%9%10%20%
2340
16th to endDay
6%5%28%9%6%10%8%9%13%19%
2465
August1st to 15thDay
5%427%8%6%11%10%10%11%21%
2246
16th to endDay
9%427%9%6%9%9%8%10%21%
2151
September1st to 15thDay
8%5%27%8%6%9%9%8%9%22%
1980
16th to endDay
7%7%38%8%5%8%7%9%11%23%
1837
October1st to 15thDay
5%426%8%46%5%7%8%39%
1790
16th to endDay
8%6%25%425%45%8%45%
1760
November1st to 15thDay
5%4245%36%46%9%49%
1757
16th to endDay
6%4345%345%6%7%47%
1719
December1st to 15thDay
7%5%26%6%36%5%6%8%41%
1620
16th to endDay
5%425%6%35%45%8%47%
1728
January1st to 15thNight
8%5%35%5%46%5%6%10%38%
2327
16th to endNight
10%5%25%435%5%6%8%42%
2373
February1st to 15thNight
10%425%424446%49%
2103
16th to endNight
5%5%24325%5%7%9%48%
1857
March1st to 15thNight
32133345%6%9%55%
1980
16th to endNight
5%31442445%8%54%
2112
April1st to 15thNight
4213425%5%6%8%55%
1976
16th to endNight
43244345%6%9%51%
1896
May1st to 15thNight
22342445%9%58%
1623
16th to endNight
4325%5%25%5%6%9%49%
1682
June1st to 15thNight
8%5%26%6%46%5%6%10%35%
1620
16th to endNight
4325%446%8%10%13%35%
1620
July1st to 15thNight
6%4346%46%7%10%13%31%
1620
16th to endNight
4326%6%48%8%10%13%30%
1703
August1st to 15thNight
4425%5%37%7%9%15%33%
1710
16th to endNight
8%436%7%37%7%8%13%29%
2036
September1st to 15thNight
5%5%36%8%47%8%10%11%27%
1980
16th to endNight
8%7%37%7%46%7%8%12%26%
1848
October1st to 15thNight
5%316%5%35%5%6%9%46%
1838
16th to endNight
8%6%25%5%2445%8%45%
2112
November1st to 15thNight
5%325%5%35%45%8%50%
2101
16th to endNight
7%4245%25%45%10%47%
2238
December1st to 15thNight
7%5%35%5%45%5%5%8%42%
2340
16th to endNight
6%4245%35%6%5%9%46%
2496

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
39%6%11%22%16%4
1612
16th to endDay
34%6%8%20%21%7%
1848
February1st to 15thDay
35%5%8%18%19%12%
1752
16th to endDay
29%5%13%18%22%9%
1616
March1st to 15thDay
24%5%12%26%22%8%
1980
16th to endDay
29%5%12%23%21%7%
2112
April1st to 15thDay
29%8%16%21%19%5%
1972
16th to endDay
29%7%14%19%24%5%
2068
May1st to 15thDay
23%7%16%25%19%6%
2331
16th to endDay
38%9%15%22%13%1
2435
June1st to 15thDay
49%10%21%15%2
2340
16th to endDay
47%16%22%11%1
2340
July1st to 15thDay
54%17%20%5%1
2201
16th to endDay
50%15%22%9%
2310
August1st to 15thDay
48%18%26%7%
2233
16th to endDay
53%17%20%8%
2151
September1st to 15thDay
51%15%21%9%1
1980
16th to endDay
50%14%16%12%41
1837
October1st to 15thDay
39%8%11%16%17%6%
1790
16th to endDay
35%5%10%17%20%10%
1760
November1st to 15thDay
30%5%10%22%21%8%
1757
16th to endDay
32%7%10%18%17%12%
1719
December1st to 15thDay
39%6%12%20%16%5%
1620
16th to endDay
33%5%13%21%18%6%
1728
January1st to 15thNight
39%6%12%23%13%3
2327
16th to endNight
36%5%10%20%19%6%
2373
February1st to 15thNight
34%47%18%21%12%
2112
16th to endNight
28%6%14%20%21%7%
1857
March1st to 15thNight
23%5%14%27%21%6%
1980
16th to endNight
27%5%13%24%22%7%
2112
April1st to 15thNight
23%6%19%25%18%5%
1976
16th to endNight
26%6%13%23%24%5%
1896
May1st to 15thNight
21%6%13%31%20%6%
1624
16th to endNight
29%8%17%26%17%1
1684
June1st to 15thNight
42%8%24%18%5%
1620
16th to endNight
33%18%26%16%4
1620
July1st to 15thNight
40%19%30%8%1
1530
16th to endNight
36%19%29%14%
1595
August1st to 15thNight
33%19%35%10%
1699
16th to endNight
43%16%26%11%1
2036
September1st to 15thNight
43%16%23%13%2
1980
16th to endNight
45%14%20%13%5%1
1848
October1st to 15thNight
31%8%16%17%19%7%
1838
16th to endNight
35%6%10%16%22%9%
2112
November1st to 15thNight
30%5%9%22%22%9%
2101
16th to endNight
31%6%12%21%16%12%
2238
December1st to 15thNight
37%5%13%22%15%5%
2340
16th to endNight
31%7%14%21%18%6%
2496

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
22%5%27%27%13%3
90
16th to endDay
8%13%38%27%10%2
96
February1st to 15thDay
11%11%28%27%15%5%
90
16th to endDay
11%133%35%17%
117
March1st to 15thDay
5%227%38%23%1
270
16th to endDay
10%322%33%25%5%
288
April1st to 15thDay
6%121%34%29%6%
270
16th to endDay
7%112%35%35%7%
270
May1st to 15thDay
6%112%26%33%19%
288
16th to endDay
6%6%21%33%32%
331
June1st to 15thDay
14%17%14%26%34%
315
16th to endDay
6%39%25%54%
315
July1st to 15thDay
6%424%63%
305
16th to endDay
11%129%19%54%
326
August1st to 15thDay
8%36%24%55%
313
16th to endDay
10%138%26%49%
332
September1st to 15thDay
9%2411%29%41%
315
16th to endDay
8%1314%40%32%
262
October1st to 15thDay
6%28%30%36%15%
255
16th to endDay
11%215%29%29%10%
272
November1st to 15thDay
7%111%34%34%10%
265
16th to endDay
7%224%32%26%5%
189
December1st to 15thDay
11%233%35%16%1
90
16th to endDay
7%212%33%37%7%
96
January1st to 15thNight
11%5%21%40%20%1
720
16th to endNight
12%6%23%41%16%
768
February1st to 15thNight
12%5%25%40%15%
704
16th to endNight
7%324%45%18%
631
March1st to 15thNight
5%327%45%17%1
720
16th to endNight
6%221%46%19%2
768
April1st to 15thNight
5%219%47%23%1
718
16th to endNight
6%220%44%25%
720
May1st to 15thNight
419%43%38%2
544
16th to endNight
6%6%33%43%9%
563
June1st to 15thNight
9%318%49%18%
540
16th to endNight
5%19%46%35%
540
July1st to 15thNight
7%2442%42%
510
16th to endNight
416%41%45%
564
August1st to 15thNight
5%7%41%44%
539
16th to endNight
12%410%38%34%
699
September1st to 15thNight
8%15%15%45%24%
720
16th to endNight
14%421%41%18%
669
October1st to 15thNight
6%17%39%36%7%
660
16th to endNight
13%116%32%31%4
704
November1st to 15thNight
6%119%44%24%3
700
16th to endNight
7%223%41%21%2
720
December1st to 15thNight
10%320%38%26%
720
16th to endNight
7%221%39%26%2
768
Page generated at 2017-09-19 07:32:27. Version ac04

Copyright 2017 A. Danko


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