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 2018-04-23.

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
42%
16772
22%
49588
14%
16725
50%
16725
30%
30362

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%
975
21%
2522
8%
970
39%
970
31%
1622
January16th to endNight
28%
1040
24%
2704
8%
1040
38%
1040
30%
1732
February1st to 15thNight
23%
955
15%
2483
5%
951
28%
951
23%
1752
February16th to endNight
26%
728
22%
2094
7%
728
37%
728
26%
1350
March1st to 15thNight
33%
585
21%
2145
13%
585
43%
585
23%
1298
March16th to endNight
28%
624
14%
2288
9%
624
36%
624
16%
1559
April1st to 15thNight
34%
584
22%
1975
15%
584
45%
584
27%
1156
April16th to endNight
38%
558
21%
1819
17%
558
50%
558
24%
1168
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
64%
561
29%
2002
26%
561
71%
561
35%
1058
October1st to 15thNight
48%
720
27%
2160
20%
720
53%
720
35%
1247
October16th to endNight
41%
768
29%
2304
17%
768
51%
768
35%
1314
November1st to 15thNight
39%
776
27%
2335
15%
776
51%
776
32%
1359
November16th to endNight
32%
975
25%
2730
11%
975
43%
975
31%
1692
December1st to 15thNight
29%
975
19%
2730
8%
975
38%
975
27%
1802
December16th to endNight
25%
1040
19%
2909
6%
1040
36%
1040
21%
2041

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%
49917
Night
12%5%24423447%48%
49781
TransparencyDay
39%6%13%24%14%2
49616
Night
36%5%12%25%17%3
49588
SeeingDay
14%6%25%28%20%5%
6568
Night
14%7%30%32%14%1
16773

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%26%5%34445%44%
1746
16th to endDay
12%9%45%5%24335%42%
1872
February1st to 15thDay
13%9%47%5%33346%36%
1710
16th to endDay
15%10%36%5%32346%38%
1675
March1st to 15thDay
13%11%45%5%2335%6%37%
2145
16th to endDay
23%9%47%424235%30%
2286
April1st to 15thDay
17%7%35%5%33345%40%
2302
16th to endDay
20%7%36%5%34446%33%
2252
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%51%
1944
October1st to 15thDay
15%424322346%50%
1800
16th to endDay
13%5%34422335%51%
1920
November1st to 15thDay
12%7%2332335%6%50%
1847
16th to endDay
17%6%34223236%47%
1560
December1st to 15thDay
13%9%45%423437%40%
1560
16th to endDay
15%9%47%323445%38%
1664
January1st to 15thNight
11%6%25%433336%48%
2522
16th to endNight
9%6%36%423346%46%
2704
February1st to 15thNight
13%8%46%6%3445%6%37%
2473
16th to endNight
14%8%34323346%45%
2094
March1st to 15thNight
13%6%35%424345%46%
2145
16th to endNight
22%7%26%334446%34%
2288
April1st to 15thNight
12%7%24223347%48%
1975
16th to endNight
17%6%25%42335%6%42%
1819
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%313433448%53%
2002
October1st to 15thNight
13%5%13313345%54%
2160
16th to endNight
11%41432333456%
2304
November1st to 15thNight
11%5%24323336%53%
2335
16th to endNight
14%6%23313335%50%
2730
December1st to 15thNight
15%7%24423345%44%
2730
16th to endNight
16%10%47%423335%38%
2909

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
41%5%12%23%16%
1747
16th to endDay
43%415%22%12%
1872
February1st to 15thDay
48%415%21%9%
1711
16th to endDay
47%412%20%13%1
1675
March1st to 15thDay
47%5%11%22%10%2
2145
16th to endDay
56%5%11%17%8%
2288
April1st to 15thDay
46%5%11%23%13%1
2302
16th to endDay
51%412%18%11%
2252
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%5%12%31%17%2
1944
October1st to 15thDay
35%49%24%20%5%
1800
16th to endDay
34%49%26%20%4
1920
November1st to 15thDay
34%412%23%19%4
1847
16th to endDay
39%39%28%18%
1560
December1st to 15thDay
44%5%12%25%11%
1560
16th to endDay
48%414%19%10%2
1664
January1st to 15thNight
37%414%25%16%1
2522
16th to endNight
38%415%25%15%1
2704
February1st to 15thNight
47%5%12%20%12%2
2483
16th to endNight
40%5%11%21%18%2
2094
March1st to 15thNight
40%410%24%15%4
2145
16th to endNight
50%5%12%20%10%1
2288
April1st to 15thNight
36%410%26%19%3
1975
16th to endNight
42%5%9%25%15%1
1819
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%31%20%2
2002
October1st to 15thNight
32%48%25%21%7%
2160
16th to endNight
31%48%27%22%5%
2304
November1st to 15thNight
33%411%22%21%6%
2335
16th to endNight
37%38%29%18%2
2730
December1st to 15thNight
42%413%24%13%
2730
16th to endNight
48%411%20%11%2
2909

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%12%38%18%7%
135
16th to endDay
17%11%43%21%4
144
February1st to 15thDay
17%20%38%18%4
135
16th to endDay
31%17%32%10%7%
120
March1st to 15thDay
21%11%48%17%1
135
16th to endDay
38%11%29%13%6%
144
April1st to 15thDay
20%12%35%21%8%
301
16th to endDay
24%8%31%22%11%1
325
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
7%219%38%21%11%
135
October1st to 15thDay
14%5%34%29%10%5%
135
16th to endDay
11%10%38%29%9%
144
November1st to 15thDay
13%234%28%11%9%
135
16th to endDay
28%14%24%22%8%
135
December1st to 15thDay
15%12%41%21%5%3
135
16th to endDay
22%18%39%18%2
144
January1st to 15thNight
13%12%39%25%7%
975
16th to endNight
13%11%41%28%4
1040
February1st to 15thNight
16%10%42%27%3
955
16th to endNight
18%12%40%25%3
728
March1st to 15thNight
16%10%36%29%6%
585
16th to endNight
24%8%34%26%5%
624
April1st to 15thNight
17%10%33%30%7%
584
16th to endNight
19%7%29%32%10%
558
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%36%26%7%
561
October1st to 15thNight
15%426%30%19%2
720
16th to endNight
13%7%34%30%13%
768
November1st to 15thNight
14%8%33%30%12%
776
16th to endNight
17%10%37%27%7%
975
December1st to 15thNight
19%11%36%27%5%
975
16th to endNight
21%10%37%27%3
1040
Page generated at 2018-04-24 09:03:02. Version ac04

Copyright 2018 A. Danko


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