22 Hills Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the 22 Hills Site clear sky chart from 2005-11-05 to

2017-09-12
.

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
51%
15434
26%
46859
19%
15387
59%
15387
35%
26870

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
37%
898
25%
2327
11%
895
45%
895
31%
1497
January16th to endNight
36%
960
29%
2496
11%
960
46%
960
33%
1560
February1st to 15thNight
34%
722
27%
2123
11%
715
45%
715
29%
1284
February16th to endNight
25%
593
29%
1855
10%
593
41%
593
28%
1083
March1st to 15thNight
33%
540
26%
1980
15%
540
47%
540
24%
1178
March16th to endNight
36%
576
24%
2112
16%
576
48%
576
28%
1176
April1st to 15thNight
33%
539
24%
1977
12%
539
49%
539
27%
1101
April16th to endNight
35%
540
25%
1780
16%
540
50%
540
30%
1037
May1st to 15thNight
38%
539
21%
1619
15%
539
47%
539
30%
982
May16th to endNight
55%
562
27%
1684
22%
561
65%
561
40%
937
June1st to 15thNight
74%
540
23%
1620
24%
540
78%
540
52%
796
June16th to endNight
75%
540
23%
1620
25%
540
79%
540
43%
874
July1st to 15thNight
79%
510
23%
1530
26%
510
82%
510
45%
812
July16th to endNight
83%
564
23%
1594
27%
531
86%
531
45%
842
August1st to 15thNight
90%
539
31%
1610
37%
536
90%
536
57%
758
August16th to endNight
76%
573
20%
1953
25%
573
77%
573
31%
1136
September1st to 15thNight
76%
530
20%
1943
24%
530
78%
530
31%
1092
September16th to endNight
73%
492
30%
1815
32%
492
75%
492
34%
956
October1st to 15thNight
71%
558
34%
1878
31%
558
75%
558
42%
938
October16th to endNight
59%
704
36%
2112
24%
704
66%
704
47%
1061
November1st to 15thNight
49%
700
29%
2100
19%
700
57%
700
35%
1220
November16th to endNight
45%
855
31%
2295
16%
855
53%
855
37%
1362
December1st to 15thNight
40%
900
27%
2340
14%
900
46%
900
30%
1552
December16th to endNight
38%
960
24%
2496
11%
960
45%
960
30%
1636

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
11%42443445%7%45%
47781
Night
10%423323347%52%
47063
TransparencyDay
36%6%10%19%18%8%
47481
Night
31%5%11%21%19%11%
46868
SeeingDay
11%316%28%29%10%
5424
Night
12%5%24%35%19%1
15438

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
17%5%2331333451%
1611
16th to endDay
16%5%34212335%50%
1728
February1st to 15thDay
17%5%24312325%49%
1743
16th to endDay
17%6%24322336%46%
1616
March1st to 15thDay
21%7%24323345%41%
1980
16th to endDay
16%5%35%413345%46%
2110
April1st to 15thDay
12%5%35%5%2345%7%42%
1971
16th to endDay
13%5%35%5%2445%6%43%
2175
May1st to 15thDay
12%5%36%5%45%5%5%7%38%
2331
16th to endDay
10%5%35%6%446%6%9%37%
2430
June1st to 15thDay
43145%35%6%7%10%46%
2340
16th to endDay
6%425%6%46%7%7%11%38%
2340
July1st to 15thDay
6%4246%45%6%8%10%40%
2340
16th to endDay
5%3246%47%6%7%10%41%
2466
August1st to 15thDay
41123245%5%9%58%
2340
16th to endDay
7%325%6%45%7%7%10%38%
2243
September1st to 15thDay
9%426%435%5%6%8%43%
1936
16th to endDay
8%323435%5%5%8%50%
1815
October1st to 15thDay
9%5%1332335%6%53%
1738
16th to endDay
10%21222222465%
1760
November1st to 15thDay
10%5%34425%35%6%49%
1758
16th to endDay
13%5%24322335%52%
1662
December1st to 15thDay
17%7%25%413346%42%
1620
16th to endDay
17%6%35%233446%40%
1728
January1st to 15thNight
18%5%23322325%50%
2327
16th to endNight
16%42332235%5%50%
2496
February1st to 15thNight
14%6%24322235%52%
2120
16th to endNight
14%423323336%51%
1855
March1st to 15thNight
16%5%24323346%46%
1980
16th to endNight
10%425%424346%52%
2112
April1st to 15thNight
8%424425%45%7%50%
1977
16th to endNight
11%5%34423347%49%
1780
May1st to 15thNight
8%5%245%2445%9%47%
1619
16th to endNight
5%2133245%7%11%50%
1683
June1st to 15thNight
211321435%10%62%
1620
16th to endNight
42133145%6%11%54%
1620
July1st to 15thNight
421222446%10%57%
1620
16th to endNight
42133145%8%11%53%
1702
August1st to 15thNight
2121245%12%65%
1620
16th to endNight
5%415%5%345%7%12%44%
1953
September1st to 15thNight
8%313325%5%6%8%49%
1943
16th to endNight
6%42432445%7%54%
1815
October1st to 15thNight
6%312323346%62%
1878
16th to endNight
9%21231223466%
2112
November1st to 15thNight
9%424423346%54%
2100
16th to endNight
13%5%24312235%56%
2295
December1st to 15thNight
15%7%25%423335%46%
2340
16th to endNight
15%8%34313335%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
38%26%19%20%12%
1612
16th to endDay
37%36%14%23%14%
1728
February1st to 15thDay
39%35%14%23%13%
1744
16th to endDay
40%4417%19%12%
1616
March1st to 15thDay
45%47%12%20%9%
1980
16th to endDay
40%46%16%24%7%
2112
April1st to 15thDay
40%5%9%16%16%11%
1971
16th to endDay
40%5%8%16%19%9%
2175
May1st to 15thDay
43%6%10%15%15%8%
2331
16th to endDay
41%7%12%18%16%2
2434
June1st to 15thDay
30%8%13%24%18%4
2340
16th to endDay
38%10%12%22%13%2
2340
July1st to 15thDay
34%10%16%26%10%1
2201
16th to endDay
33%8%20%25%11%
2311
August1st to 15thDay
20%8%17%34%17%1
2326
16th to endDay
36%10%15%24%10%2
2243
September1st to 15thDay
38%7%11%21%14%5%
1936
16th to endDay
31%7%10%20%20%9%
1815
October1st to 15thDay
30%411%18%17%16%
1738
16th to endDay
24%3417%32%19%
1760
November1st to 15thDay
35%410%20%18%10%
1758
16th to endDay
35%36%12%23%18%
1662
December1st to 15thDay
43%39%16%17%8%
1620
16th to endDay
43%47%16%19%8%
1728
January1st to 15thNight
38%2416%20%15%
2327
16th to endNight
36%35%14%23%16%
2496
February1st to 15thNight
37%35%13%23%18%
2130
16th to endNight
35%36%18%19%16%
1855
March1st to 15thNight
39%47%13%21%12%
1980
16th to endNight
33%411%16%23%9%
2112
April1st to 15thNight
32%5%9%18%18%13%
1977
16th to endNight
35%410%20%18%11%
1780
May1st to 15thNight
34%6%12%20%17%8%
1620
16th to endNight
25%7%16%28%17%3
1685
June1st to 15thNight
17%5%15%31%25%4
1620
16th to endNight
22%8%18%29%18%3
1620
July1st to 15thNight
21%7%21%34%14%
1530
16th to endNight
19%9%26%32%11%
1594
August1st to 15thNight
12%7%21%36%19%2
1610
16th to endNight
29%10%21%27%8%2
1953
September1st to 15thNight
30%8%16%23%13%7%
1943
16th to endNight
27%6%13%21%19%10%
1815
October1st to 15thNight
23%410%23%20%16%
1878
16th to endNight
22%35%18%26%23%
2112
November1st to 15thNight
31%48%21%21%11%
2100
16th to endNight
33%26%13%23%21%
2295
December1st to 15thNight
41%37%19%18%9%
2340
16th to endNight
41%36%16%21%11%
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
16%5%40%27%8%1
90
16th to endDay
15%11%43%19%9%
96
February1st to 15thDay
13%11%37%27%10%
90
16th to endDay
18%14%38%20%7%
81
March1st to 15thDay
28%12%28%17%10%2
90
16th to endDay
7%7%31%35%14%4
96
April1st to 15thDay
10%11%40%26%8%3
90
16th to endDay
20%5%31%29%12%1
285
May1st to 15thDay
14%7%34%30%11%1
468
16th to endDay
14%426%33%16%3
517
June1st to 15thDay
6%10%39%34%8%
495
16th to endDay
8%110%29%38%11%
495
July1st to 15thDay
5%5%33%41%13%
475
16th to endDay
4324%48%17%
515
August1st to 15thDay
4121%51%20%
493
16th to endDay
12%7%24%34%20%
283
September1st to 15thDay
4313%40%39%
123
16th to endDay
3116%41%37%
90
October1st to 15thDay
2334%51%8%
90
16th to endDay
18%111%21%37%9%
96
November1st to 15thDay
24%220%34%14%4
90
16th to endDay
24%10%17%27%13%6%
90
December1st to 15thDay
27%5%17%25%13%10%
90
16th to endDay
22%12%33%20%9%1
96
January1st to 15thNight
20%8%28%32%9%
900
16th to endNight
18%10%32%31%7%
960
February1st to 15thNight
18%11%32%31%6%
722
16th to endNight
19%10%43%23%3
593
March1st to 15thNight
19%6%36%29%7%
540
16th to endNight
11%9%38%34%5%
576
April1st to 15thNight
8%9%45%32%4
539
16th to endNight
14%6%37%29%11%
540
May1st to 15thNight
9%8%41%34%6%
540
16th to endNight
6%230%40%18%1
563
June1st to 15thNight
2117%50%25%2
540
16th to endNight
411%48%30%3
540
July1st to 15thNight
6%6%46%36%3
510
16th to endNight
35%45%42%3
564
August1st to 15thNight
3245%43%4
539
16th to endNight
6%15%39%40%6%
573
September1st to 15thNight
8%15%33%45%5%
530
16th to endNight
8%9%31%42%6%
492
October1st to 15thNight
8%312%46%25%4
558
16th to endNight
10%5%22%34%24%2
704
November1st to 15thNight
11%5%27%31%22%1
700
16th to endNight
16%7%26%32%15%1
855
December1st to 15thNight
19%7%27%33%11%
900
16th to endNight
20%9%27%33%9%
960
Page generated at 2017-09-13 06:39:25. Version ac04

Copyright 2017 A. Danko


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