ICStars Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the ICStars Ranch clear sky chart from 2005-11-05 to 2017-09-16.

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%
15871
22%
46923
14%
15824
51%
15824
30%
28681

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
29%
900
22%
2327
8%
895
39%
895
31%
1486
January16th to endNight
28%
960
23%
2496
8%
960
37%
960
30%
1610
February1st to 15thNight
23%
880
15%
2288
5%
876
29%
876
23%
1617
February16th to endNight
27%
672
23%
1934
7%
672
38%
672
28%
1222
March1st to 15thNight
33%
540
20%
1980
13%
540
43%
540
22%
1219
March16th to endNight
29%
576
14%
2112
9%
576
37%
576
17%
1424
April1st to 15thNight
35%
539
21%
1823
15%
539
46%
539
28%
1059
April16th to endNight
38%
540
21%
1761
16%
540
50%
540
24%
1126
May1st to 15thNight
44%
539
19%
1620
15%
539
51%
539
25%
1068
May16th to endNight
48%
563
20%
1577
15%
561
54%
561
30%
1006
June1st to 15thNight
67%
540
21%
1440
13%
540
71%
540
41%
839
June16th to endNight
64%
540
24%
1440
15%
540
68%
540
50%
784
July1st to 15thNight
69%
510
18%
1459
15%
510
70%
510
39%
852
July16th to endNight
77%
564
24%
1594
25%
531
79%
531
47%
816
August1st to 15thNight
79%
539
25%
1610
29%
536
80%
536
44%
857
August16th to endNight
72%
573
26%
1848
31%
573
75%
573
39%
993
September1st to 15thNight
64%
540
26%
1800
29%
540
67%
540
34%
997
September16th to endNight
63%
517
28%
1846
24%
517
70%
517
34%
978
October1st to 15thNight
50%
660
29%
1980
21%
660
55%
660
36%
1129
October16th to endNight
40%
704
27%
2112
15%
704
50%
704
34%
1225
November1st to 15thNight
41%
715
28%
2151
16%
715
53%
715
33%
1227
November16th to endNight
32%
900
23%
2520
10%
900
42%
900
30%
1578
December1st to 15thNight
28%
900
18%
2520
8%
900
37%
900
25%
1701
December16th to endNight
26%
960
19%
2685
7%
960
37%
960
22%
1868

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%42445%7%43%
47824
Night
12%5%24423447%48%
47116
TransparencyDay
39%6%13%24%14%2
47523
Night
35%5%12%26%17%3
46923
SeeingDay
13%5%23%29%21%6%
5902
Night
14%7%29%32%14%1
15872

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
12%5%36%5%24345%45%
1611
16th to endDay
13%9%45%5%24435%41%
1728
February1st to 15thDay
13%9%47%5%33346%37%
1575
16th to endDay
14%9%36%5%22346%39%
1548
March1st to 15thDay
13%11%45%6%33447%36%
1980
16th to endDay
22%9%46%5%24236%32%
2110
April1st to 15thDay
17%7%34433345%41%
2124
16th to endDay
20%6%36%5%34446%33%
2196
May1st to 15thDay
18%6%36%6%34446%36%
2331
16th to endDay
14%5%25%5%35%448%38%
2535
June1st to 15thDay
9%5%25%435%5%6%9%44%
2520
16th to endDay
5%314435%6%7%10%48%
2520
July1st to 15thDay
8%3245%245%7%10%45%
2409
16th to endDay
6%423426%5%7%8%47%
2466
August1st to 15thDay
8%415%5%245%6%9%46%
2340
16th to endDay
7%4145%35%5%5%8%48%
2353
September1st to 15thDay
11%42442445%6%50%
2160
16th to endDay
9%42342445%8%50%
1790
October1st to 15thDay
14%424323346%51%
1650
16th to endDay
13%5%34422235%51%
1760
November1st to 15thDay
11%6%1332335%6%52%
1702
16th to endDay
17%7%34223236%46%
1440
December1st to 15thDay
14%10%5%6%423347%38%
1440
16th to endDay
16%9%47%323435%39%
1536
January1st to 15thNight
11%6%25%333336%48%
2327
16th to endNight
10%6%36%423446%46%
2496
February1st to 15thNight
13%8%46%6%34446%38%
2278
16th to endNight
12%7%34323346%47%
1934
March1st to 15thNight
14%6%35%424345%44%
1980
16th to endNight
21%6%26%33445%6%35%
2112
April1st to 15thNight
12%7%24213347%49%
1823
16th to endNight
17%6%25%42335%6%42%
1761
May1st to 15thNight
14%5%245%2435%7%42%
1619
16th to endNight
12%42442436%7%45%
1575
June1st to 15thNight
6%212435%6%7%10%51%
1440
16th to endNight
321332346%11%55%
1440
July1st to 15thNight
8%3133245%6%9%51%
1547
16th to endNight
5%21331346%11%55%
1702
August1st to 15thNight
42133245%5%9%58%
1620
16th to endNight
6%313323447%57%
1848
September1st to 15thNight
11%31442335%7%52%
1800
16th to endNight
7%313434448%53%
1846
October1st to 15thNight
13%413323345%55%
1980
16th to endNight
11%41432333455%
2112
November1st to 15thNight
11%424323335%55%
2151
16th to endNight
15%6%23313335%50%
2520
December1st to 15thNight
17%8%24423345%42%
2520
16th to endNight
16%9%36%423335%39%
2685

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
40%5%12%24%16%
1612
16th to endDay
44%415%22%11%1
1728
February1st to 15thDay
47%415%22%9%
1576
16th to endDay
46%413%21%13%1
1548
March1st to 15thDay
48%5%11%23%9%1
1980
16th to endDay
55%5%11%18%8%
2112
April1st to 15thDay
44%5%10%23%13%1
2124
16th to endDay
51%412%18%11%
2196
May1st to 15thDay
49%6%11%23%9%
2331
16th to endDay
43%8%13%21%11%1
2539
June1st to 15thDay
35%8%12%28%13%1
2520
16th to endDay
27%8%17%28%14%2
2520
July1st to 15thDay
32%8%16%27%11%2
2269
16th to endDay
28%9%15%31%14%1
2311
August1st to 15thDay
32%8%15%26%15%1
2326
16th to endDay
31%7%12%23%18%5%
2353
September1st to 15thDay
34%6%11%24%19%4
2160
16th to endDay
30%6%12%30%18%2
1790
October1st to 15thDay
35%410%24%20%4
1650
16th to endDay
35%310%26%18%4
1760
November1st to 15thDay
32%5%12%24%20%5%
1702
16th to endDay
40%310%27%17%
1440
December1st to 15thDay
46%5%12%24%10%
1440
16th to endDay
47%414%20%10%2
1536
January1st to 15thNight
37%413%25%17%1
2327
16th to endNight
38%415%24%15%1
2496
February1st to 15thNight
47%5%11%21%12%2
2288
16th to endNight
38%5%12%23%18%2
1934
March1st to 15thNight
42%410%24%14%3
1980
16th to endNight
49%5%12%21%10%1
2112
April1st to 15thNight
35%49%26%20%3
1823
16th to endNight
42%5%9%25%15%1
1761
May1st to 15thNight
40%7%12%23%15%
1620
16th to endNight
36%7%15%25%13%1
1577
June1st to 15thNight
24%9%14%32%16%2
1440
16th to endNight
21%6%16%31%21%4
1440
July1st to 15thNight
29%6%12%32%15%3
1459
16th to endNight
20%6%16%36%18%1
1594
August1st to 15thNight
21%8%15%33%19%2
1610
16th to endNight
26%5%10%25%25%6%
1848
September1st to 15thNight
31%5%11%23%21%7%
1800
16th to endNight
28%5%10%30%21%3
1846
October1st to 15thNight
31%48%26%22%6%
1980
16th to endNight
32%48%27%20%5%
2112
November1st to 15thNight
31%411%22%22%7%
2151
16th to endNight
38%38%28%17%2
2520
December1st to 15thNight
44%413%23%12%
2520
16th to endNight
47%411%20%12%3
2685

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
24%12%41%18%3
90
16th to endDay
20%14%40%16%6%1
96
February1st to 15thDay
15%20%35%22%6%
90
16th to endDay
23%17%37%12%8%1
81
March1st to 15thDay
24%13%44%15%2
90
16th to endDay
28%14%32%14%10%
96
April1st to 15thDay
18%10%33%25%10%
243
16th to endDay
23%8%32%22%11%1
306
May1st to 15thDay
17%7%33%26%13%1
468
16th to endDay
18%6%29%25%15%4
517
June1st to 15thDay
9%324%34%22%7%
495
16th to endDay
7%327%34%20%6%
495
July1st to 15thDay
12%115%34%28%7%
475
16th to endDay
5%10%31%41%11%
515
August1st to 15thDay
7%10%34%37%8%
493
16th to endDay
8%11%34%34%10%
393
September1st to 15thDay
10%210%35%31%9%
315
16th to endDay
3323%35%19%14%
92
October1st to 15thDay
8%336%31%11%8%
90
16th to endDay
13%6%33%37%9%
96
November1st to 15thDay
8%323%34%15%14%
90
16th to endDay
36%17%20%18%5%1
90
December1st to 15thDay
20%10%40%18%6%4
90
16th to endDay
23%18%37%17%2
96
January1st to 15thNight
14%12%39%25%7%
900
16th to endNight
13%11%41%28%4
960
February1st to 15thNight
16%10%41%27%3
880
16th to endNight
16%11%41%26%3
672
March1st to 15thNight
17%11%35%29%6%
540
16th to endNight
22%8%35%26%6%
576
April1st to 15thNight
17%10%33%31%7%
539
16th to endNight
19%7%29%32%10%
540
May1st to 15thNight
15%429%36%12%1
540
16th to endNight
13%428%33%17%2
563
June1st to 15thNight
7%118%46%24%1
540
16th to endNight
4126%44%21%2
540
July1st to 15thNight
9%113%45%27%3
510
16th to endNight
7%9%40%41%2
564
August1st to 15thNight
38%43%42%1
539
16th to endNight
6%112%37%35%5%
573
September1st to 15thNight
12%114%40%26%4
540
16th to endNight
7%318%35%26%7%
517
October1st to 15thNight
15%425%31%19%3
660
16th to endNight
14%6%34%29%13%
704
November1st to 15thNight
13%8%33%31%13%
715
16th to endNight
17%10%36%26%7%
900
December1st to 15thNight
20%10%36%27%4
900
16th to endNight
21%10%35%29%3
960
Page generated at 2017-09-17 11:05:46. Version ac04

Copyright 2017 A. Danko


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