Halfmoon Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Halfmoon 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
43%
15665
22%
46834
15%
15621
51%
15621
27%
29409

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
23%
900
19%
2506
8%
895
33%
895
20%
1736
January16th to endNight
23%
906
20%
2508
8%
906
32%
906
22%
1719
February1st to 15thNight
20%
704
17%
2112
7%
701
28%
701
18%
1476
February16th to endNight
19%
631
19%
1893
7%
631
29%
631
19%
1298
March1st to 15thNight
26%
720
18%
2160
9%
720
33%
720
21%
1453
March16th to endNight
33%
649
17%
2020
10%
649
39%
649
21%
1362
April1st to 15thNight
37%
539
24%
1797
14%
539
51%
539
29%
1023
April16th to endNight
42%
540
23%
1794
17%
540
51%
540
28%
1069
May1st to 15thNight
39%
539
18%
1619
11%
539
47%
539
25%
1066
May16th to endNight
61%
561
20%
1674
15%
561
65%
561
31%
1035
June1st to 15thNight
65%
540
22%
1440
16%
540
68%
540
41%
855
June16th to endNight
72%
540
24%
1440
18%
540
75%
540
42%
842
July1st to 15thNight
69%
510
18%
1360
14%
510
71%
510
36%
845
July16th to endNight
75%
564
23%
1473
19%
531
78%
531
41%
851
August1st to 15thNight
75%
539
23%
1761
26%
536
76%
536
36%
969
August16th to endNight
75%
573
26%
1910
31%
573
77%
573
35%
1036
September1st to 15thNight
63%
574
26%
1834
24%
574
67%
574
32%
1060
September16th to endNight
59%
669
27%
1848
21%
669
63%
669
36%
1117
October1st to 15thNight
56%
660
33%
1833
25%
660
61%
660
37%
1080
October16th to endNight
43%
704
28%
2205
20%
704
52%
704
31%
1314
November1st to 15thNight
45%
700
30%
2276
24%
700
56%
700
33%
1274
November16th to endNight
33%
720
25%
2340
17%
720
44%
720
26%
1409
December1st to 15thNight
28%
723
17%
2343
11%
723
35%
723
18%
1598
December16th to endNight
23%
960
18%
2688
7%
960
33%
960
19%
1922

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
12%6%25%5%3445%7%40%
47964
Night
13%6%2442445%6%44%
47016
TransparencyDay
41%5%11%23%15%2
47648
Night
39%410%23%17%3
46836
SeeingDay
14%7%21%25%20%10%
5710
Night
17%8%24%28%18%2
15668

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
20%7%38%424445%34%
1432
16th to endDay
14%7%37%6%34345%39%
1711
February1st to 15thDay
14%11%47%5%23345%38%
1750
16th to endDay
15%10%37%5%34446%34%
1580
March1st to 15thDay
21%8%36%5%22445%35%
1800
16th to endDay
17%8%37%5%24446%34%
2213
April1st to 15thDay
14%5%25%6%33447%41%
2151
16th to endDay
15%6%25%5%2435%7%40%
2166
May1st to 15thDay
17%6%26%5%35%45%6%35%
2331
16th to endDay
9%5%36%7%35%5%7%8%36%
2437
June1st to 15thDay
7%4245%25%6%6%8%45%
2520
16th to endDay
5%3246%36%6%7%10%43%
2520
July1st to 15thDay
9%5%25%6%46%6%5%9%37%
2520
16th to endDay
5%425%6%46%6%7%11%39%
2592
August1st to 15thDay
6%425%6%36%5%6%9%41%
2186
16th to endDay
7%425%6%36%5%6%11%41%
2292
September1st to 15thDay
11%425%6%35%6%5%8%39%
2112
16th to endDay
11%6%15%423346%48%
1837
October1st to 15thDay
12%5%24423337%51%
1796
16th to endDay
16%5%1432234451%
1667
November1st to 15thDay
12%5%2432334453%
1582
16th to endDay
18%6%24313446%45%
1620
December1st to 15thDay
20%11%345%23445%35%
1613
16th to endDay
18%10%45%42343436%
1536
January1st to 15thNight
17%10%36%424345%37%
2506
16th to endNight
16%9%37%42335%5%38%
2508
February1st to 15thNight
19%9%46%5%24335%35%
2103
16th to endNight
16%8%36%5%2444437%
1893
March1st to 15thNight
17%8%34423345%40%
2160
16th to endNight
16%7%36%5%23446%38%
2020
April1st to 15thNight
12%5%2432345%7%48%
1797
16th to endNight
13%5%3442445%7%44%
1794
May1st to 15thNight
16%5%345%25%35%6%41%
1619
16th to endNight
6%4145%45%5%7%10%43%
1673
June1st to 15thNight
7%415%32346%8%50%
1440
16th to endNight
32135%35%5%8%11%49%
1440
July1st to 15thNight
8%3245%25%5%6%11%45%
1440
16th to endNight
6%313325%5%6%10%50%
1574
August1st to 15thNight
5%42442346%9%51%
1772
16th to endNight
6%31442446%10%50%
1910
September1st to 15thNight
12%42342345%7%49%
1834
16th to endNight
10%5%24424446%50%
1848
October1st to 15thNight
10%5%24323235%55%
1833
16th to endNight
16%6%1332333450%
2205
November1st to 15thNight
13%5%13422345%53%
2276
16th to endNight
17%6%23323345%47%
2340
December1st to 15thNight
21%10%35%423345%35%
2343
16th to endNight
22%9%35%42433435%
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
51%37%24%11%1
1433
16th to endDay
47%310%27%9%1
1711
February1st to 15thDay
49%29%25%11%2
1752
16th to endDay
50%311%18%13%1
1580
March1st to 15thDay
51%38%21%12%2
1800
16th to endDay
50%411%24%7%
2214
April1st to 15thDay
42%49%21%20%2
2151
16th to endDay
43%49%26%13%2
2166
May1st to 15thDay
47%6%11%20%12%1
2331
16th to endDay
41%8%14%20%12%2
2441
June1st to 15thDay
32%7%13%25%18%2
2520
16th to endDay
33%7%13%21%19%4
2520
July1st to 15thDay
41%8%11%21%12%4
2371
16th to endDay
34%6%19%24%12%1
2430
August1st to 15thDay
36%6%12%25%16%2
2173
16th to endDay
36%7%12%22%17%4
2292
September1st to 15thDay
40%6%11%21%16%3
2112
16th to endDay
37%47%21%24%5%
1837
October1st to 15thDay
33%48%24%23%5%
1796
16th to endDay
36%35%26%22%5%
1667
November1st to 15thDay
34%28%22%23%7%
1582
16th to endDay
40%37%28%15%3
1620
December1st to 15thDay
51%311%18%11%2
1613
16th to endDay
51%411%22%9%1
1536
January1st to 15thNight
50%28%21%16%1
2506
16th to endNight
47%310%23%13%1
2508
February1st to 15thNight
52%28%22%11%1
2112
16th to endNight
49%310%22%12%2
1893
March1st to 15thNight
46%49%19%15%4
2160
16th to endNight
46%5%12%23%11%1
2020
April1st to 15thNight
33%411%25%19%5%
1797
16th to endNight
38%38%26%19%3
1794
May1st to 15thNight
44%411%24%14%1
1620
16th to endNight
33%8%15%21%16%3
1675
June1st to 15thNight
29%5%15%25%21%2
1440
16th to endNight
25%8%15%25%20%5%
1440
July1st to 15thNight
31%7%14%26%14%5%
1360
16th to endNight
26%7%17%30%16%2
1473
August1st to 15thNight
28%6%13%25%23%2
1761
16th to endNight
27%7%12%27%21%4
1910
September1st to 15thNight
33%5%9%26%20%5%
1834
16th to endNight
33%48%19%25%8%
1848
October1st to 15thNight
32%37%21%29%6%
1833
16th to endNight
38%25%24%23%6%
2205
November1st to 15thNight
33%26%23%24%8%
2276
16th to endNight
39%38%25%19%3
2340
December1st to 15thNight
51%310%18%13%2
2343
16th to endNight
52%39%19%12%1
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
35%21%27%6%8%
90
16th to endDay
11%32%44%10%1
96
February1st to 15thDay
23%34%30%10%2
90
16th to endDay
25%22%35%13%2
81
March1st to 15thDay
30%25%33%8%2
90
16th to endDay
18%14%34%23%9%
261
April1st to 15thDay
13%17%30%25%10%2
270
16th to endDay
20%9%24%27%14%4
270
May1st to 15thDay
20%12%24%26%9%6%
288
16th to endDay
13%6%22%30%15%11%
337
June1st to 15thDay
9%318%27%27%14%
495
16th to endDay
6%321%35%21%10%
495
July1st to 15thDay
13%120%28%24%12%
475
16th to endDay
6%17%27%32%24%
452
August1st to 15thDay
15%17%26%29%20%
313
16th to endDay
13%17%22%39%15%
332
September1st to 15thDay
13%211%22%32%18%
315
16th to endDay
17%212%23%27%16%
262
October1st to 15thDay
12%326%25%22%10%
236
16th to endDay
15%10%27%30%14%2
96
November1st to 15thDay
13%7%31%27%15%4
90
16th to endDay
25%18%30%16%7%1
90
December1st to 15thDay
16%16%40%17%6%2
90
16th to endDay
23%22%41%9%2
96
January1st to 15thNight
25%16%32%22%3
900
16th to endNight
22%16%35%22%2
906
February1st to 15thNight
24%17%33%22%2
704
16th to endNight
22%16%38%20%1
631
March1st to 15thNight
22%14%33%24%4
720
16th to endNight
21%11%29%28%8%
649
April1st to 15thNight
14%12%34%26%11%
539
16th to endNight
17%6%30%30%14%
540
May1st to 15thNight
20%5%28%28%14%3
540
16th to endNight
9%319%34%30%3
563
June1st to 15thNight
9%16%38%31%4
540
16th to endNight
4114%40%37%3
540
July1st to 15thNight
10%9%33%38%6%
510
16th to endNight
7%8%29%41%11%
564
August1st to 15thNight
9%7%30%43%9%
539
16th to endNight
8%7%36%41%5%
573
September1st to 15thNight
14%112%24%37%8%
574
16th to endNight
13%315%28%31%7%
669
October1st to 15thNight
13%5%17%31%25%6%
660
16th to endNight
21%5%26%29%15%1
704
November1st to 15thNight
14%9%27%30%17%1
700
16th to endNight
22%11%30%24%10%
720
December1st to 15thNight
28%11%28%23%8%
723
16th to endNight
29%10%32%23%4
960
Page generated at 2017-09-19 06:32:23. Version ac04

Copyright 2017 A. Danko


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