This page made possible by the sponsorship of: Dan & Reba Fischer.

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 2018-01-12.

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
52%
15946
27%
48343
19%
15899
59%
15899
35%
27721

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%
954
25%
2472
11%
951
45%
951
32%
1587
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%
540
20%
1980
25%
540
78%
540
31%
1111
September16th to endNight
73%
537
30%
1980
33%
537
75%
537
33%
1052
October1st to 15thNight
73%
609
33%
2049
31%
609
76%
609
43%
1009
October16th to endNight
59%
768
38%
2304
25%
768
67%
768
48%
1146
November1st to 15thNight
50%
760
27%
2280
17%
760
56%
760
35%
1330
November16th to endNight
46%
926
33%
2486
17%
926
55%
926
39%
1448
December1st to 15thNight
40%
975
27%
2535
14%
975
47%
975
30%
1679
December16th to endNight
37%
1040
24%
2704
11%
1040
44%
1040
28%
1803

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%
48974
Night
10%423323347%52%
48547
TransparencyDay
36%6%10%19%18%8%
48674
Night
31%5%11%21%19%11%
48352
SeeingDay
11%316%28%29%10%
5790
Night
12%5%24%35%19%1
15950

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%2332333450%
1710
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%5%35%5%6%8%43%
1980
16th to endDay
8%324435%5%5%8%48%
1980
October1st to 15thDay
9%5%1332335%6%54%
1896
16th to endDay
9%21222222465%
1920
November1st to 15thDay
11%5%24425%35%6%47%
1908
16th to endDay
12%424322335%54%
1800
December1st to 15thDay
18%6%24423346%42%
1755
16th to endDay
19%7%36%233346%38%
1872
January1st to 15thNight
17%5%24312325%50%
2472
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%50%
1980
16th to endNight
5%42442445%7%53%
1980
October1st to 15thNight
6%312223346%63%
2049
16th to endNight
9%212312235%66%
2304
November1st to 15thNight
9%414423346%53%
2280
16th to endNight
12%424312235%57%
2486
December1st to 15thNight
15%7%24423336%45%
2535
16th to endNight
17%8%34313336%44%
2704

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%26%19%20%12%
1711
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
37%7%11%21%15%6%
1980
16th to endDay
32%8%11%20%18%8%
1980
October1st to 15thDay
29%412%20%17%15%
1896
16th to endDay
23%3416%31%20%
1920
November1st to 15thDay
36%5%10%20%17%9%
1908
16th to endDay
34%36%14%24%17%
1800
December1st to 15thDay
43%39%15%17%9%
1755
16th to endDay
45%47%16%18%7%
1872
January1st to 15thNight
38%25%17%21%14%
2472
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%
1980
16th to endNight
28%6%13%22%19%9%
1980
October1st to 15thNight
22%411%25%20%15%
2049
16th to endNight
21%35%17%26%24%
2304
November1st to 15thNight
32%5%10%21%20%10%
2280
16th to endNight
31%26%15%24%19%
2486
December1st to 15thNight
41%37%19%18%10%
2535
16th to endNight
43%36%16%20%10%
2704

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
19%436%26%12%1
123
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
4214%40%37%
135
16th to endDay
2224%42%26%
135
October1st to 15thDay
3430%44%17%
135
16th to endDay
13%415%22%30%11%
144
November1st to 15thDay
24%217%36%14%4
135
16th to endDay
17%8%18%31%17%7%
135
December1st to 15thDay
27%5%19%26%12%8%
135
16th to endDay
31%11%27%20%7%
144
January1st to 15thNight
20%8%28%32%9%
956
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%
540
16th to endNight
8%9%32%42%6%
537
October1st to 15thNight
8%311%44%27%5%
609
16th to endNight
9%5%22%35%24%2
768
November1st to 15thNight
12%5%27%32%21%
760
16th to endNight
15%7%26%32%17%1
926
December1st to 15thNight
20%7%26%33%11%
975
16th to endNight
21%8%26%33%8%
1040
Page generated at 2018-01-12 21:01:28. Version ac04

Copyright 2018 A. Danko


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