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 2005-11-05 to 2017-10-06.

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
44%
15806
29%
47141
17%
15762
56%
15762
40%
25356

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
39%
900
33%
2327
13%
895
52%
895
45%
1273
January16th to endNight
38%
960
37%
2496
14%
960
52%
960
48%
1357
February1st to 15thNight
33%
739
26%
2148
10%
736
44%
736
33%
1247
February16th to endNight
30%
632
33%
1894
13%
632
45%
632
37%
1016
March1st to 15thNight
33%
606
27%
2046
14%
606
47%
606
32%
1112
March16th to endNight
29%
576
23%
2112
13%
576
43%
576
29%
1131
April1st to 15thNight
27%
539
24%
1917
11%
539
46%
539
31%
1003
April16th to endNight
29%
540
27%
1650
13%
540
47%
540
32%
950
May1st to 15thNight
31%
539
26%
1620
15%
539
48%
539
34%
943
May16th to endNight
47%
561
27%
1684
21%
561
58%
561
42%
900
June1st to 15thNight
50%
540
22%
1620
15%
540
59%
540
44%
849
June16th to endNight
57%
540
26%
1620
18%
540
66%
540
52%
789
July1st to 15thNight
71%
510
21%
1530
20%
510
74%
510
45%
801
July16th to endNight
82%
564
32%
1594
35%
531
83%
531
52%
783
August1st to 15thNight
75%
539
27%
1610
31%
536
77%
536
45%
851
August16th to endNight
73%
573
26%
1853
27%
573
78%
573
42%
963
September1st to 15thNight
62%
540
24%
1977
26%
540
67%
540
33%
1044
September16th to endNight
54%
537
33%
1980
26%
537
66%
537
35%
1008
October1st to 15thNight
47%
546
33%
1914
25%
546
57%
546
35%
995
October16th to endNight
44%
704
36%
2112
17%
704
58%
704
52%
1000
November1st to 15thNight
41%
861
32%
2261
11%
861
53%
861
49%
1208
November16th to endNight
39%
900
34%
2340
14%
900
50%
900
46%
1294
December1st to 15thNight
36%
900
30%
2340
11%
900
49%
900
42%
1350
December16th to endNight
35%
960
34%
2496
13%
960
49%
960
37%
1489

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%423323346%54%
48057
Night
7%313323346%58%
47337
Cloud CoverDay
8%424323446%54%
48055
Night
7%313323347%58%
47337
TransparencyDay
29%410%25%22%7%
47755
Night
26%49%25%25%9%
47142
SeeingDay
9%6%27%32%20%3
5796
Night
9%8%33%34%13%
15810

By Month

Percentage Cloud Cover SW (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
7%5%12323345%59%
1611
16th to endDay
7%423323346%58%
1728
February1st to 15thDay
9%6%3432322457%
1723
16th to endDay
9%6%2422323459%
1580
March1st to 15thDay
11%7%24315%346%49%
1914
16th to endDay
10%6%2442335%5%49%
2112
April1st to 15thDay
9%42442445%6%51%
2028
16th to endDay
13%5%23433346%48%
2309
May1st to 15thDay
13%424424345%49%
2331
16th to endDay
8%4246%345%5%7%47%
2430
June1st to 15thDay
6%3244235%48%54%
2340
16th to endDay
6%31232345%9%56%
2340
July1st to 15thDay
8%22332447%9%51%
2340
16th to endDay
431332435%9%57%
2466
August1st to 15thDay
5%324425%5%7%9%51%
2340
16th to endDay
5%3134345%5%8%54%
2347
September1st to 15thDay
11%424423447%51%
1983
16th to endDay
7%313324446%57%
1980
October1st to 15thDay
12%31332332459%
1832
16th to endDay
5%32322323466%
1760
November1st to 15thDay
6%213212237%65%
1595
16th to endDay
8%42321223464%
1620
December1st to 15thDay
9%5%24414246%54%
1620
16th to endDay
11%7%35%323235%53%
1728
January1st to 15thNight
6%413313345%62%
2327
16th to endNight
7%413212335%65%
2496
February1st to 15thNight
11%6%2442333455%
2138
16th to endNight
9%423323346%57%
1894
March1st to 15thNight
7%5%2432345%6%54%
2046
16th to endNight
10%423423446%53%
2112
April1st to 15thNight
9%41331335%7%55%
1917
16th to endNight
13%423323336%53%
1650
May1st to 15thNight
11%423213337%55%
1619
16th to endNight
6%323214449%56%
1683
June1st to 15thNight
5%21232445%9%58%
1620
16th to endNight
5%11231245%9%62%
1620
July1st to 15thNight
4213325%48%11%54%
1620
16th to endNight
32232345%9%62%
1702
August1st to 15thNight
22134345%6%9%54%
1620
16th to endNight
41133236%5%8%57%
1853
September1st to 15thNight
9%41442345%6%54%
1977
16th to endNight
7%41432335%7%55%
1980
October1st to 15thNight
10%423312336%56%
1914
16th to endNight
5%21221232470%
2112
November1st to 15thNight
6%313312246%64%
2261
16th to endNight
8%422312335%63%
2340
December1st to 15thNight
9%413213346%58%
2340
16th to endNight
10%5%34412235%56%
2496

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
7%413323345%60%
1611
16th to endDay
6%423313346%58%
1728
February1st to 15thDay
8%7%3432322457%
1723
16th to endDay
8%6%33222225%59%
1580
March1st to 15thDay
10%6%24324446%50%
1914
16th to endDay
10%6%25%42335%6%49%
2110
April1st to 15thDay
8%425%42345%6%52%
2028
16th to endDay
13%6%14423346%49%
2309
May1st to 15thDay
12%424434445%49%
2331
16th to endDay
8%424435%5%5%7%47%
2430
June1st to 15thDay
6%31342445%7%54%
2340
16th to endDay
5%31232445%9%57%
2340
July1st to 15thDay
7%313325%5%6%10%50%
2340
16th to endDay
431332445%9%57%
2466
August1st to 15thDay
43144246%7%9%50%
2340
16th to endDay
431343446%7%54%
2347
September1st to 15thDay
11%424423446%50%
1983
16th to endDay
7%423324436%56%
1980
October1st to 15thDay
11%41332332459%
1832
16th to endDay
5%223323225%65%
1760
November1st to 15thDay
6%213222246%65%
1595
16th to endDay
7%4233223464%
1620
December1st to 15thDay
9%5%24423245%54%
1620
16th to endDay
11%7%35%32223453%
1728
January1st to 15thNight
6%322313345%62%
2327
16th to endNight
7%412212335%64%
2496
February1st to 15thNight
10%6%23422335%55%
2138
16th to endNight
9%423323346%57%
1894
March1st to 15thNight
6%5%2442445%5%54%
2046
16th to endNight
10%424424346%53%
2112
April1st to 15thNight
9%32232335%7%55%
1917
16th to endNight
12%5%14313346%53%
1650
May1st to 15thNight
11%413312347%54%
1619
16th to endNight
6%312313449%56%
1683
June1st to 15thNight
421232445%9%57%
1620
16th to endNight
5%2122335%10%61%
1620
July1st to 15thNight
4113325%5%7%11%53%
1620
16th to endNight
412323449%62%
1702
August1st to 15thNight
22135%3446%10%53%
1620
16th to endNight
32133345%6%9%56%
1853
September1st to 15thNight
8%5%1432345%6%54%
1977
16th to endNight
6%42332345%7%56%
1980
October1st to 15thNight
11%323323336%56%
1914
16th to endNight
5%21231223371%
2112
November1st to 15thNight
5%313212336%64%
2261
16th to endNight
7%312212335%64%
2340
December1st to 15thNight
9%423313346%58%
2340
16th to endNight
10%6%24312245%56%
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
27%48%29%26%4
1612
16th to endDay
26%36%29%26%6%
1728
February1st to 15thDay
32%28%26%23%7%
1724
16th to endDay
30%25%29%23%8%
1580
March1st to 15thDay
35%410%21%20%8%
1914
16th to endDay
35%5%11%23%17%6%
2112
April1st to 15thDay
32%5%11%23%19%7%
2028
16th to endDay
36%49%23%22%4
2309
May1st to 15thDay
36%410%18%22%6%
2331
16th to endDay
34%6%12%25%17%3
2434
June1st to 15thDay
27%5%15%27%17%6%
2340
16th to endDay
23%6%15%22%24%8%
2340
July1st to 15thDay
27%6%12%27%21%4
2201
16th to endDay
22%5%12%29%25%5%
2311
August1st to 15thDay
26%7%14%25%18%7%
2326
16th to endDay
26%6%12%26%20%6%
2347
September1st to 15thDay
33%5%10%24%17%9%
1983
16th to endDay
27%5%8%24%27%6%
1980
October1st to 15thDay
29%310%22%25%8%
1832
16th to endDay
22%27%24%30%12%
1760
November1st to 15thDay
21%27%26%28%12%
1595
16th to endDay
25%25%26%29%10%
1620
December1st to 15thDay
32%310%27%22%3
1620
16th to endDay
35%29%22%23%5%
1728
January1st to 15thNight
23%27%28%29%7%
2327
16th to endNight
23%28%25%30%10%
2496
February1st to 15thNight
33%27%23%24%7%
2148
16th to endNight
27%26%25%25%11%
1894
March1st to 15thNight
29%48%23%22%11%
2046
16th to endNight
31%412%25%20%6%
2112
April1st to 15thNight
28%5%10%22%24%9%
1917
16th to endNight
33%39%24%20%8%
1650
May1st to 15thNight
30%5%10%20%23%8%
1620
16th to endNight
25%415%27%22%3
1685
June1st to 15thNight
22%5%14%30%21%4
1620
16th to endNight
18%414%28%24%10%
1620
July1st to 15thNight
21%6%14%27%24%5%
1530
16th to endNight
18%410%29%30%6%
1594
August1st to 15thNight
22%6%15%25%20%9%
1610
16th to endNight
23%6%12%25%23%7%
1853
September1st to 15thNight
29%5%10%24%19%10%
1977
16th to endNight
27%5%7%24%25%9%
1980
October1st to 15thNight
28%49%22%22%11%
1914
16th to endNight
18%26%23%35%13%
2112
November1st to 15thNight
22%27%22%30%13%
2261
16th to endNight
24%26%23%29%13%
2340
December1st to 15thNight
27%311%26%25%5%
2340
16th to endNight
32%27%22%25%9%
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
13%11%35%33%5%1
90
16th to endDay
5%13%54%20%5%1
96
February1st to 15thDay
8%11%42%34%3
90
16th to endDay
7%11%53%20%7%
81
March1st to 15thDay
14%22%42%20%1
90
16th to endDay
10%16%41%25%6%
96
April1st to 15thDay
10%23%29%30%5%
147
16th to endDay
15%14%40%23%41
419
May1st to 15thDay
11%10%41%25%9%1
468
16th to endDay
13%7%33%27%15%2
517
June1st to 15thDay
7%332%36%16%3
495
16th to endDay
7%226%36%22%4
495
July1st to 15thDay
8%116%41%26%5%
475
16th to endDay
5%5%39%41%7%
515
August1st to 15thDay
6%10%41%36%4
493
16th to endDay
6%17%37%32%5%
387
September1st to 15thDay
7%14%34%38%5%
138
16th to endDay
12%125%31%19%8%
135
October1st to 15thDay
10%8%31%28%15%5%
107
16th to endDay
8%334%37%13%3
96
November1st to 15thDay
13%336%25%17%3
90
16th to endDay
18%17%38%14%8%1
90
December1st to 15thDay
12%10%43%27%6%
90
16th to endDay
18%18%36%21%4
96
January1st to 15thNight
8%13%36%35%6%
900
16th to endNight
8%9%41%32%7%
960
February1st to 15thNight
12%11%37%31%5%
740
16th to endNight
11%13%43%27%4
632
March1st to 15thNight
9%12%41%30%6%
606
16th to endNight
13%13%41%25%5%
576
April1st to 15thNight
11%14%44%24%5%
539
16th to endNight
16%10%41%23%7%
540
May1st to 15thNight
12%10%42%24%8%1
540
16th to endNight
7%6%34%34%15%1
563
June1st to 15thNight
5%335%38%15%
540
16th to endNight
4330%43%16%1
540
July1st to 15thNight
418%48%25%1
510
16th to endNight
47%52%33%2
564
August1st to 15thNight
410%48%34%2
539
16th to endNight
5%113%42%33%2
573
September1st to 15thNight
9%220%37%26%3
540
16th to endNight
8%228%37%20%2
537
October1st to 15thNight
13%330%33%17%1
546
16th to endNight
6%7%38%31%14%
704
November1st to 15thNight
8%9%37%33%10%
861
16th to endNight
10%11%37%30%10%
900
December1st to 15thNight
12%10%38%29%8%
900
16th to endNight
13%10%36%32%7%
960
Page generated at 2017-10-07 13:07:47. Version ac04

Copyright 2017 A. Danko


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