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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 2022-11-11.

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%
22414
29%
66946
17%
22366
55%
22366
40%
36139

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%
1261
32%
3280
12%
1261
51%
1261
43%
1836
January16th to endNight
37%
1345
36%
3502
13%
1345
51%
1345
47%
1912
February1st to 15thNight
29%
1035
26%
3018
9%
1031
41%
1031
31%
1787
February16th to endNight
27%
889
31%
2664
12%
887
42%
887
34%
1467
March1st to 15thNight
33%
855
29%
2887
15%
855
47%
855
31%
1559
March16th to endNight
28%
813
23%
2980
12%
813
44%
813
27%
1611
April1st to 15thNight
25%
762
26%
2703
11%
762
46%
762
30%
1409
April16th to endNight
28%
747
27%
2280
12%
747
47%
747
32%
1301
May1st to 15thNight
29%
758
24%
2273
14%
758
46%
758
32%
1351
May16th to endNight
45%
778
25%
2329
20%
778
56%
778
38%
1300
June1st to 15thNight
51%
760
24%
2287
17%
758
60%
758
45%
1186
June16th to endNight
55%
752
27%
2280
19%
752
66%
752
52%
1106
July1st to 15thNight
71%
732
22%
2194
21%
732
75%
732
47%
1128
July16th to endNight
81%
794
30%
2266
33%
758
82%
758
51%
1119
August1st to 15thNight
73%
739
29%
2233
31%
736
78%
736
46%
1154
August16th to endNight
70%
810
26%
2616
27%
810
74%
810
42%
1350
September1st to 15thNight
63%
762
27%
2791
29%
762
68%
762
34%
1457
September16th to endNight
55%
756
32%
2786
27%
756
65%
756
37%
1375
October1st to 15thNight
45%
813
32%
2842
22%
813
57%
813
36%
1448
October16th to endNight
41%
1082
35%
3253
15%
1081
56%
1081
46%
1618
November1st to 15thNight
37%
1280
31%
3363
11%
1280
50%
1280
46%
1843
November16th to endNight
40%
1266
34%
3291
14%
1266
52%
1266
47%
1794
December1st to 15thNight
34%
1270
32%
3306
12%
1270
48%
1270
42%
1909
December16th to endNight
33%
1355
32%
3522
12%
1355
47%
1355
36%
2119

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%424323446%55%
67957
Night
7%413323346%58%
67183
TransparencyDay
29%410%25%22%7%
67671
Night
26%49%24%25%9%
66969
SeeingDay
10%8%28%31%18%3
12584
Night
9%8%34%34%12%
22422

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
7%5%1432343459%
2272
16th to endDay
6%424313346%57%
2404
February1st to 15thDay
8%8%3442322454%
2418
16th to endDay
8%7%35%323335%55%
2230
March1st to 15thDay
10%6%24424435%51%
2701
16th to endDay
11%6%25%32335%5%49%
2953
April1st to 15thDay
8%425%42345%6%52%
2856
16th to endDay
12%5%13423346%49%
3214
May1st to 15thDay
12%5%24424446%48%
3263
16th to endDay
9%42443445%7%48%
3374
June1st to 15thDay
5%31342445%8%55%
3315
16th to endDay
5%212324348%60%
3297
July1st to 15thDay
5%3133245%6%10%53%
3302
16th to endDay
431332445%9%56%
3463
August1st to 15thDay
5%4134335%6%9%51%
3188
16th to endDay
5%31342446%7%54%
3314
September1st to 15thDay
10%42442345%6%52%
2797
16th to endDay
6%413424436%58%
2792
October1st to 15thDay
10%42331323461%
2713
16th to endDay
8%32332222464%
2706
November1st to 15thDay
6%312322346%63%
2372
16th to endDay
7%423312235%63%
2272
December1st to 15thDay
8%5%24323346%55%
2294
16th to endDay
10%6%35%322246%52%
2447
January1st to 15thNight
6%423313346%60%
3279
16th to endNight
7%412212335%63%
3502
February1st to 15thNight
10%7%2442233453%
3010
16th to endNight
9%424322346%55%
2665
March1st to 15thNight
7%5%24423445%55%
2888
16th to endNight
10%5%2442435%6%51%
2978
April1st to 15thNight
9%423323347%55%
2706
16th to endNight
13%413313346%53%
2286
May1st to 15thNight
11%424323347%51%
2269
16th to endNight
6%3134245%5%9%52%
2328
June1st to 15thNight
421232445%9%58%
2295
16th to endNight
5%212233410%62%
2279
July1st to 15thNight
31133245%6%11%56%
2293
16th to endNight
41232345%9%61%
2383
August1st to 15thNight
221343446%9%56%
2243
16th to endNight
32133245%5%9%56%
2617
September1st to 15thNight
9%414323446%55%
2791
16th to endNight
6%41432235%6%58%
2787
October1st to 15thNight
9%413222346%59%
2842
16th to endNight
8%21331233367%
3255
November1st to 15thNight
7%313212236%63%
3363
16th to endNight
7%412212335%65%
3291
December1st to 15thNight
8%423313345%58%
3306
16th to endNight
9%6%24322235%55%
3527

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%26%26%6%
2275
16th to endDay
27%36%27%27%6%
2403
February1st to 15thDay
34%28%25%22%6%
2421
16th to endDay
33%36%24%23%8%
2230
March1st to 15thDay
34%48%20%20%11%
2700
16th to endDay
35%5%10%23%18%5%
2968
April1st to 15thDay
30%410%24%19%8%
2858
16th to endDay
35%5%9%24%20%4
3216
May1st to 15thDay
36%5%11%21%19%5%
3268
16th to endDay
34%6%12%27%16%2
3376
June1st to 15thDay
25%5%15%27%17%7%
3311
16th to endDay
21%6%13%25%25%7%
3300
July1st to 15thDay
24%7%13%27%22%4
3154
16th to endDay
23%5%11%31%23%4
3294
August1st to 15thDay
25%7%13%27%19%6%
3180
16th to endDay
25%7%13%27%19%5%
3316
September1st to 15thDay
31%5%10%22%21%8%
2799
16th to endDay
26%48%23%29%7%
2791
October1st to 15thDay
27%39%21%25%11%
2715
16th to endDay
25%26%24%27%13%
2705
November1st to 15thDay
23%37%25%28%11%
2372
16th to endDay
24%25%27%28%11%
2278
December1st to 15thDay
30%39%26%23%6%
2294
16th to endDay
34%39%21%26%6%
2447
January1st to 15thNight
25%28%25%29%8%
3281
16th to endNight
23%27%27%27%10%
3502
February1st to 15thNight
35%28%22%23%7%
3018
16th to endNight
29%36%23%23%12%
2665
March1st to 15thNight
29%47%21%23%13%
2887
16th to endNight
32%411%25%19%6%
2988
April1st to 15thNight
27%5%10%23%23%9%
2703
16th to endNight
31%410%26%19%7%
2286
May1st to 15thNight
32%5%12%20%21%6%
2273
16th to endNight
27%5%15%27%19%2
2330
June1st to 15thNight
21%5%15%29%20%5%
2287
16th to endNight
18%413%31%23%8%
2280
July1st to 15thNight
19%7%15%27%23%6%
2195
16th to endNight
19%411%30%29%5%
2268
August1st to 15thNight
21%6%14%27%22%7%
2235
16th to endNight
22%6%14%26%23%6%
2616
September1st to 15thNight
28%5%9%23%23%10%
2791
16th to endNight
24%5%7%22%29%9%
2786
October1st to 15thNight
26%49%21%23%14%
2843
16th to endNight
21%25%22%31%14%
3253
November1st to 15thNight
23%38%22%28%13%
3363
16th to endNight
23%26%24%29%14%
3291
December1st to 15thNight
27%310%25%24%8%
3306
16th to endNight
32%27%21%26%9%
3522

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
14%15%34%26%7%
315
16th to endDay
10%15%46%21%5%
333
February1st to 15thDay
14%14%43%23%3
315
16th to endDay
13%22%43%16%3
279
March1st to 15thDay
15%22%37%19%5%
315
16th to endDay
16%15%41%20%5%
336
April1st to 15thDay
13%22%36%21%5%
395
16th to endDay
15%17%37%21%5%1
761
May1st to 15thDay
13%10%40%25%8%1
836
16th to endDay
13%8%32%28%15%2
883
June1st to 15thDay
6%330%38%17%2
866
16th to endDay
6%125%39%22%4
864
July1st to 15thDay
5%13%37%32%9%
845
16th to endDay
5%5%41%38%8%
904
August1st to 15thDay
6%111%43%31%5%
828
16th to endDay
6%15%37%33%6%
728
September1st to 15thDay
7%11%38%34%7%
364
16th to endDay
8%321%37%23%5%
360
October1st to 15thDay
9%9%35%25%15%3
360
16th to endDay
16%10%30%27%12%2
384
November1st to 15thDay
13%7%38%30%8%2
347
16th to endDay
13%15%37%22%9%1
315
December1st to 15thDay
12%10%39%26%10%
315
16th to endDay
13%18%38%22%5%
336
January1st to 15thNight
9%13%36%34%5%
1262
16th to endNight
9%11%40%32%6%
1345
February1st to 15thNight
14%12%40%27%4
1036
16th to endNight
13%14%42%25%3
889
March1st to 15thNight
10%15%38%30%5%
855
16th to endNight
14%15%40%24%5%
813
April1st to 15thNight
11%16%44%22%4
762
16th to endNight
16%13%40%22%6%
749
May1st to 15thNight
13%10%43%25%6%
758
16th to endNight
7%7%35%34%13%1
779
June1st to 15thNight
5%334%41%13%
760
16th to endNight
4233%44%13%
752
July1st to 15thNight
319%45%28%1
732
16th to endNight
48%53%30%2
796
August1st to 15thNight
314%49%30%2
740
16th to endNight
5%117%43%30%2
810
September1st to 15thNight
10%219%40%25%2
762
16th to endNight
7%327%39%19%2
756
October1st to 15thNight
13%5%31%33%15%
813
16th to endNight
9%8%38%31%11%
1082
November1st to 15thNight
9%9%39%31%8%
1280
16th to endNight
10%10%35%32%9%
1266
December1st to 15thNight
11%11%39%29%7%
1270
16th to endNight
12%11%37%31%5%
1355
Page generated at 2022-11-12 13:12:29. Version ac05

Copyright 2022 A. Danko


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