Cheddar Ranch Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cheddar Ranch Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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
42%
24280
29%
74359
16%
24221
55%
24221
39%
40021

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 10thNight
37%
950
31%
2458
12%
946
51%
946
43%
1386
January11th to 20thNight
34%
930
33%
2418
13%
930
47%
930
42%
1347
January21st to endNight
36%
990
36%
2574
13%
990
51%
990
45%
1424
February1st to 10thNight
28%
774
26%
2214
9%
774
41%
774
32%
1320
February11th to 20thNight
27%
703
26%
2098
10%
700
40%
700
32%
1198
February21st to endNight
26%
592
32%
1776
12%
592
42%
592
32%
997
March1st to 10thNight
32%
640
28%
2080
13%
640
46%
640
33%
1126
March11th to 20thNight
30%
540
27%
1980
15%
540
47%
540
28%
1067
March21st to endNight
26%
594
24%
2178
11%
594
44%
594
27%
1162
April1st to 10thNight
27%
540
27%
1979
12%
540
48%
540
34%
960
April11th to 20thNight
22%
533
25%
1734
9%
533
42%
533
27%
988
April21st to endNight
30%
540
28%
1620
13%
540
50%
540
33%
920
May1st to 10thNight
29%
540
25%
1620
13%
540
46%
540
32%
964
May11th to 20thNight
41%
531
22%
1594
18%
531
51%
531
34%
932
May21st to endNight
45%
582
24%
1745
17%
582
56%
582
39%
958
June1st to 10thNight
56%
540
23%
1620
18%
540
64%
540
44%
847
June11th to 20thNight
47%
540
25%
1620
15%
540
59%
540
47%
830
June21st to endNight
56%
540
28%
1620
20%
540
66%
540
55%
776
July1st to 10thNight
72%
525
20%
1575
20%
525
76%
525
45%
828
July11th to 20thNight
74%
522
28%
1566
28%
522
78%
522
52%
767
July21st to endNight
80%
591
30%
1673
34%
558
82%
558
50%
834
August1st to 10thNight
73%
537
29%
1601
31%
534
78%
534
50%
794
August11th to 20thNight
67%
534
29%
1602
30%
534
72%
534
41%
891
August21st to endNight
74%
594
27%
1980
29%
594
77%
594
45%
961
September1st to 10thNight
66%
540
27%
1975
28%
540
72%
540
39%
964
September11th to 20thNight
56%
540
28%
1980
26%
540
63%
540
30%
1089
September21st to endNight
54%
540
34%
1980
28%
540
66%
540
40%
948
October1st to 10thNight
52%
540
33%
1980
26%
540
62%
540
38%
958
October11th to 20thNight
39%
684
36%
2124
16%
684
55%
684
43%
1065
October21st to endNight
38%
792
34%
2376
15%
792
53%
792
43%
1225
November1st to 10thNight
41%
902
34%
2382
12%
902
55%
902
50%
1268
November11th to 20thNight
36%
950
32%
2470
12%
950
49%
950
48%
1338
November21st to endNight
38%
950
32%
2470
14%
950
49%
950
43%
1402
December1st to 10thNight
36%
950
33%
2470
12%
950
50%
950
43%
1406
December11th to 20thNight
29%
950
32%
2860
10%
948
44%
948
33%
1652
December21st to endNight
33%
1040
21%
4367
12%
1026
48%
1026
24%
2429

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
8%5%2442445%7%55%
74934
Night
8%42442345%7%58%
74907
TransparencyDay
29%5%10%25%23%7%
74659
Night
27%410%25%25%9%
74702
SeeingDay
10%9%29%31%18%4
14251
Night
10%9%35%34%12%1
24288

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 10thDay
6%5%25%42445%5%60%
1707
11th to 20thDay
9%6%24323436%57%
1665
21st to endDay
7%5%24423447%57%
1782
February1st to 10thDay
9%11%45%42323454%
1760
11th to 20thDay
8%6%25%5%34335%55%
1749
21st to endDay
9%8%35%334435%54%
1480
March1st to 10thDay
9%6%25%5%34446%51%
1880
11th to 20thDay
14%7%24323445%53%
1980
21st to endDay
9%7%36%43446%6%48%
2178
April1st to 10thDay
7%425%43345%7%55%
1980
11th to 20thDay
13%6%25%43345%7%48%
2172
21st to endDay
13%5%2443345%6%52%
2340
May1st to 10thDay
13%6%34434446%47%
2340
11th to 20thDay
11%5%2442445%7%52%
2302
21st to endDay
10%5%25%5%45%5%6%8%44%
2531
June1st to 10thDay
6%3244345%6%9%53%
2340
11th to 20thDay
6%32342445%8%58%
2340
21st to endDay
6%21332445%8%61%
2340
July1st to 10thDay
7%424425%5%7%11%49%
2340
11th to 20thDay
43133245%5%9%61%
2340
21st to endDay
5%3234245%5%11%55%
2546
August1st to 10thDay
44145%346%7%9%54%
2328
11th to 20thDay
7%5%245%445%7%9%49%
2296
21st to endDay
43144245%6%7%60%
2376
September1st to 10thDay
10%42432335%6%58%
1985
11th to 20thDay
10%5%245%35%6%46%51%
1980
21st to endDay
7%324424447%59%
1980
October1st to 10thDay
9%424324335%60%
1980
11th to 20thDay
10%21332223469%
1818
21st to endDay
11%42432332462%
1980
November1st to 10thDay
7%323323346%65%
1693
11th to 20thDay
6%423312335%66%
1710
21st to endDay
10%5%2431325%6%59%
1710
December1st to 10thDay
6%5%25%42445%7%56%
1710
11th to 20thDay
9%5%35%32435%5%56%
2161
21st to endDay
8%9%47%6%35%5%47%44%
3135
January1st to 10thNight
6%42442345%6%60%
2458
11th to 20thNight
8%5%23313446%61%
2418
21st to endNight
8%5%23323345%63%
2574
February1st to 10thNight
11%8%3442343453%
2214
11th to 20thNight
11%5%23433346%54%
2098
21st to endNight
9%5%35%423446%55%
1776
March1st to 10thNight
5%5%345%345%5%6%55%
2080
11th to 20thNight
14%6%24313335%55%
1980
21st to endNight
9%5%25%42446%7%51%
2178
April1st to 10thNight
7%32332345%7%60%
1979
11th to 20thNight
13%5%23323447%52%
1734
21st to endNight
13%424323447%54%
1620
May1st to 10thNight
11%5%24423447%52%
1620
11th to 20thNight
9%4244346%6%9%50%
1593
21st to endNight
8%4234245%5%10%53%
1745
June1st to 10thNight
5%313335%5%5%10%57%
1620
11th to 20thNight
6%31332346%10%59%
1620
21st to endNight
6%21132435%9%64%
1620
July1st to 10thNight
42243245%6%11%55%
1620
11th to 20thNight
421332446%11%60%
1620
21st to endNight
41134345%5%10%60%
1772
August1st to 10thNight
2213435%6%6%10%57%
1611
11th to 20thNight
5%3245%35%5%5%8%55%
1602
21st to endNight
32133345%6%11%59%
1980
September1st to 10thNight
8%42332345%6%60%
1975
11th to 20thNight
10%6%2433445%7%52%
1980
21st to endNight
5%32442345%6%61%
1980
October1st to 10thNight
8%41332345%8%59%
1980
11th to 20thNight
9%32332232467%
2124
21st to endNight
10%32332233365%
2376
November1st to 10thNight
8%413222346%66%
2382
11th to 20thNight
5%423423235%66%
2470
21st to endNight
10%423312346%61%
2470
December1st to 10thNight
8%5%23323446%60%
2470
11th to 20thNight
8%6%35%423245%57%
3036
21st to endNight
12%7%25%434446%50%
4532

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 10thDay
26%5%8%30%24%6%
1708
11th to 20thDay
30%48%22%30%6%
1665
21st to endDay
28%46%29%27%6%
1782
February1st to 10thDay
36%29%24%23%6%
1760
11th to 20thDay
34%38%25%23%8%
1759
21st to endDay
34%35%23%24%10%
1480
March1st to 10thDay
35%49%21%20%12%
1880
11th to 20thDay
35%5%9%23%19%9%
1980
21st to endDay
36%6%11%24%18%5%
2178
April1st to 10thDay
28%411%26%21%9%
1980
11th to 20thDay
36%5%9%23%19%8%
2172
21st to endDay
33%5%11%26%22%3
2340
May1st to 10thDay
38%5%11%18%21%7%
2340
11th to 20thDay
32%6%13%30%17%2
2306
21st to endDay
37%6%13%26%14%3
2531
June1st to 10thDay
27%7%18%28%14%6%
2340
11th to 20thDay
24%6%13%27%23%7%
2340
21st to endDay
21%6%14%25%26%8%
2340
July1st to 10thDay
28%8%15%27%19%3
2276
11th to 20thDay
20%6%11%29%27%7%
2271
21st to endDay
24%6%13%31%24%3
2405
August1st to 10thDay
23%8%13%31%19%6%
2314
11th to 20thDay
30%7%15%25%20%3
2296
21st to endDay
23%6%12%28%23%8%
2376
September1st to 10thDay
27%5%10%23%23%12%
1985
11th to 20thDay
33%6%9%22%24%6%
1980
21st to endDay
25%5%9%24%29%8%
1980
October1st to 10thDay
28%410%22%27%9%
1980
11th to 20thDay
23%36%21%31%16%
1818
21st to endDay
28%37%25%25%12%
1980
November1st to 10thDay
22%37%24%31%12%
1693
11th to 20thDay
23%26%28%30%11%
1710
21st to endDay
28%35%27%26%11%
1710
December1st to 10thDay
29%410%30%24%5%
1710
11th to 20thDay
32%310%20%29%7%
2159
21st to endDay
40%48%21%21%5%
3135
January1st to 10thNight
25%410%26%28%7%
2458
11th to 20thNight
26%38%25%30%8%
2418
21st to endNight
25%36%27%28%11%
2574
February1st to 10thNight
36%38%22%24%7%
2214
11th to 20thNight
33%48%24%22%10%
2098
21st to endNight
30%47%20%24%14%
1776
March1st to 10thNight
29%5%8%21%25%13%
2080
11th to 20thNight
33%48%25%21%10%
1980
21st to endNight
31%5%13%25%19%6%
2178
April1st to 10thNight
24%5%10%23%25%12%
1979
11th to 20thNight
32%6%9%25%19%9%
1734
21st to endNight
32%311%28%21%5%
1620
May1st to 10thNight
32%6%12%19%24%6%
1620
11th to 20thNight
31%6%15%24%19%5%
1594
21st to endNight
27%5%18%29%17%3
1746
June1st to 10thNight
22%6%19%31%18%5%
1620
11th to 20thNight
21%6%14%30%24%6%
1620
21st to endNight
18%413%30%24%11%
1620
July1st to 10thNight
21%7%19%28%21%3
1575
11th to 20thNight
18%6%10%27%30%10%
1566
21st to endNight
20%5%13%31%29%4
1673
August1st to 10thNight
19%6%16%30%23%7%
1601
11th to 20thNight
27%6%13%24%24%7%
1602
21st to endNight
20%7%14%27%25%8%
1980
September1st to 10thNight
24%5%8%26%25%12%
1975
11th to 20thNight
32%6%10%18%25%9%
1980
21st to endNight
23%5%7%25%30%10%
1980
October1st to 10thNight
24%5%12%22%25%12%
1980
11th to 20thNight
24%35%19%32%17%
2124
21st to endNight
25%36%24%29%14%
2376
November1st to 10thNight
22%38%23%30%14%
2382
11th to 20thNight
22%36%26%31%11%
2470
21st to endNight
26%37%22%28%13%
2470
December1st to 10thNight
26%410%26%26%8%
2470
11th to 20thNight
31%36%22%30%8%
3037
21st to endNight
35%38%22%24%8%
4532

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 10thDay
11%16%40%25%7%1
270
11th to 20thDay
18%19%35%23%5%
255
21st to endDay
9%16%50%19%5%
264
February1st to 10thDay
14%15%42%26%3
240
11th to 20thDay
15%20%43%18%4
240
21st to endDay
15%22%44%15%5%
198
March1st to 10thDay
14%19%40%21%5%
240
11th to 20thDay
20%19%37%18%5%1
240
21st to endDay
16%17%44%17%5%
264
April1st to 10thDay
13%20%36%23%8%
240
11th to 20thDay
15%20%42%20%3
450
21st to endDay
16%18%36%22%6%2
600
May1st to 10thDay
13%11%44%24%7%1
603
11th to 20thDay
15%9%32%28%14%2
625
21st to endDay
13%7%31%30%16%3
679
June1st to 10thDay
7%424%38%23%4
630
11th to 20thDay
7%332%40%15%3
630
21st to endDay
5%128%40%21%5%
630
July1st to 10thDay
7%112%36%34%10%
621
11th to 20thDay
3112%45%33%6%
618
21st to endDay
7%16%38%39%9%
684
August1st to 10thDay
5%113%46%30%5%
626
11th to 20thDay
7%215%36%34%6%
610
21st to endDay
5%12%37%37%9%
495
September1st to 10thDay
8%9%41%34%8%
275
11th to 20thDay
7%317%40%29%4
270
21st to endDay
10%423%32%23%7%
270
October1st to 10thDay
9%8%31%29%19%5%
270
11th to 20thDay
10%12%37%29%11%1
270
21st to endDay
20%12%33%22%11%2
297
November1st to 10thDay
11%7%39%34%7%2
270
11th to 20thDay
13%14%36%24%11%2
270
21st to endDay
17%13%37%23%9%1
270
December1st to 10thDay
9%12%42%26%11%
270
11th to 20thDay
12%15%39%26%9%
270
21st to endDay
14%22%40%20%4
297
January1st to 10thNight
8%12%39%34%6%
950
11th to 20thNight
12%15%36%32%5%
930
21st to endNight
10%11%41%31%7%
990
February1st to 10thNight
15%12%40%28%5%
774
11th to 20thNight
14%15%42%26%4
704
21st to endNight
13%16%43%24%4
592
March1st to 10thNight
6%18%41%30%5%
640
11th to 20thNight
18%11%38%27%6%
540
21st to endNight
12%18%41%24%5%
594
April1st to 10thNight
9%15%46%23%7%
540
11th to 20thNight
15%16%44%22%3
533
21st to endNight
16%13%39%23%7%
540
May1st to 10thNight
12%11%45%28%4
540
11th to 20thNight
11%8%35%32%13%1
531
21st to endNight
8%6%37%35%13%2
584
June1st to 10thNight
6%429%42%18%1
540
11th to 20thNight
6%438%43%9%
540
21st to endNight
4233%44%16%1
540
July1st to 10thNight
4117%45%29%3
525
11th to 20thNight
4117%49%28%1
522
21st to endNight
419%56%28%2
591
August1st to 10thNight
3115%52%28%1
537
11th to 20thNight
6%116%48%27%2
534
21st to endNight
4116%41%36%3
594
September1st to 10thNight
9%218%43%26%2
540
11th to 20thNight
12%224%36%23%2
540
21st to endNight
6%429%41%17%2
540
October1st to 10thNight
9%5%29%37%18%1
540
11th to 20thNight
12%7%40%34%8%
684
21st to endNight
11%11%37%28%13%1
792
November1st to 10thNight
10%7%39%34%9%1
902
11th to 20thNight
7%12%41%33%7%1
950
21st to endNight
13%13%34%31%9%
950
December1st to 10thNight
11%11%39%30%8%1
950
11th to 20thNight
14%11%42%28%5%
950
21st to endNight
12%13%38%31%5%
1045
Page generated at 2024-01-13 08:37:54. Version ac07

Copyright 2024 Attilla Danko


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