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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 2021-11-10.

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%
21271
29%
63470
17%
21227
55%
21227
39%
34393

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
38%
1200
32%
3107
13%
1195
51%
1195
42%
1751
January16th to endNight
36%
1280
36%
3328
13%
1280
51%
1280
46%
1831
February1st to 15thNight
29%
991
25%
2880
9%
988
41%
988
30%
1728
February16th to endNight
28%
844
31%
2530
12%
844
42%
844
34%
1405
March1st to 15thNight
32%
808
28%
2728
14%
808
46%
808
31%
1491
March16th to endNight
27%
768
23%
2816
12%
768
43%
768
27%
1526
April1st to 15thNight
25%
719
26%
2557
11%
719
47%
719
30%
1335
April16th to endNight
29%
714
26%
2180
13%
714
47%
714
32%
1248
May1st to 15thNight
30%
719
24%
2160
14%
719
46%
719
32%
1290
May16th to endNight
46%
753
25%
2260
20%
753
56%
753
38%
1257
June1st to 15thNight
52%
720
25%
2160
18%
720
62%
720
46%
1112
June16th to endNight
54%
720
26%
2160
18%
720
64%
720
52%
1050
July1st to 15thNight
71%
690
21%
2070
20%
690
75%
690
46%
1077
July16th to endNight
81%
756
30%
2170
33%
723
83%
723
52%
1065
August1st to 15thNight
73%
710
29%
2122
32%
707
78%
707
47%
1100
August16th to endNight
70%
765
26%
2473
27%
765
75%
765
43%
1257
September1st to 15thNight
62%
720
27%
2636
29%
720
67%
720
33%
1397
September16th to endNight
54%
717
30%
2640
25%
717
64%
717
36%
1324
October1st to 15thNight
44%
768
33%
2688
22%
768
57%
768
36%
1368
October16th to endNight
41%
1024
35%
3072
15%
1024
56%
1024
47%
1516
November1st to 15thNight
39%
1205
32%
3165
11%
1205
52%
1205
46%
1731
November16th to endNight
40%
1200
35%
3120
14%
1200
52%
1200
47%
1717
December1st to 15thNight
35%
1200
31%
3120
12%
1200
48%
1200
41%
1808
December16th to endNight
34%
1280
33%
3328
12%
1280
48%
1280
36%
2009

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%424323346%54%
64501
Night
7%413323346%57%
63666
Cloud CoverDay
8%424323446%54%
64499
Night
7%413323347%57%
63666
TransparencyDay
29%410%25%22%7%
64199
Night
26%410%25%24%9%
63471
SeeingDay
10%7%28%31%18%3
11319
Night
10%8%34%33%12%
21275

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%13323445%58%
2151
16th to endDay
7%5%24313346%57%
2304
February1st to 15thDay
9%7%35%423325%52%
2314
16th to endDay
9%7%3431323455%
2110
March1st to 15thDay
10%7%24314345%50%
2552
16th to endDay
11%7%25%42345%5%48%
2816
April1st to 15thDay
9%42432445%7%51%
2707
16th to endDay
13%5%23423446%48%
3043
May1st to 15thDay
12%424434346%48%
3111
16th to endDay
9%4246%345%48%46%
3262
June1st to 15thDay
5%31332345%9%55%
3120
16th to endDay
6%31232345%9%58%
3120
July1st to 15thDay
6%22332446%9%52%
3120
16th to endDay
431332435%9%57%
3298
August1st to 15thDay
5%3244245%6%9%51%
3071
16th to endDay
5%3134345%5%8%55%
3134
September1st to 15thDay
11%424423446%51%
2644
16th to endDay
7%313424446%57%
2640
October1st to 15thDay
11%31322222461%
2576
16th to endDay
8%32322222465%
2560
November1st to 15thDay
7%312313336%64%
2224
16th to endDay
8%423312235%63%
2160
December1st to 15thDay
9%5%24414246%54%
2160
16th to endDay
10%7%25%323246%51%
2304
January1st to 15thNight
6%5%13312446%59%
3107
16th to endNight
7%413212335%63%
3328
February1st to 15thNight
11%6%25%42333452%
2870
16th to endNight
10%5%24323336%55%
2530
March1st to 15thNight
8%5%2432335%6%54%
2728
16th to endNight
11%5%24323446%52%
2816
April1st to 15thNight
9%413313347%54%
2557
16th to endNight
13%413323336%53%
2180
May1st to 15thNight
11%423323447%51%
2159
16th to endNight
6%3243245%5%9%53%
2259
June1st to 15thNight
421232346%9%59%
2160
16th to endNight
5%12312349%63%
2160
July1st to 15thNight
321332448%10%55%
2160
16th to endNight
31233335%10%61%
2278
August1st to 15thNight
2213425%5%6%10%55%
2132
16th to endNight
41133235%5%8%59%
2473
September1st to 15thNight
9%5%13323446%54%
2636
16th to endNight
6%41432335%6%57%
2640
October1st to 15thNight
10%423312345%59%
2688
16th to endNight
7%21222233467%
3072
November1st to 15thNight
6%313322235%63%
3165
16th to endNight
8%412212235%64%
3120
December1st to 15thNight
8%413323345%58%
3120
16th to endNight
10%6%24422235%55%
3328

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%1332343458%
2151
16th to endDay
7%424313346%57%
2304
February1st to 15thDay
8%8%35%42323452%
2314
16th to endDay
8%7%35%323325%55%
2110
March1st to 15thDay
10%6%25%424445%50%
2552
16th to endDay
11%6%25%42335%5%48%
2814
April1st to 15thDay
8%425%42345%6%52%
2707
16th to endDay
13%5%13423346%49%
3043
May1st to 15thDay
12%5%24434446%47%
3111
16th to endDay
9%4244345%5%7%47%
3262
June1st to 15thDay
5%31342445%8%56%
3120
16th to endDay
6%21232445%8%59%
3120
July1st to 15thDay
6%3133245%6%10%52%
3120
16th to endDay
431332445%9%57%
3298
August1st to 15thDay
5%4134245%6%9%51%
3071
16th to endDay
431342446%7%55%
3134
September1st to 15thDay
11%42442345%6%50%
2644
16th to endDay
7%413424436%57%
2640
October1st to 15thDay
11%42321222461%
2576
16th to endDay
8%32332222465%
2560
November1st to 15thDay
6%323312346%63%
2224
16th to endDay
7%42332235%63%
2160
December1st to 15thDay
9%5%24423246%54%
2160
16th to endDay
10%6%35%322246%51%
2304
January1st to 15thNight
6%423313346%59%
3107
16th to endNight
7%412212335%63%
3328
February1st to 15thNight
10%7%245%22335%52%
2870
16th to endNight
10%424323346%55%
2530
March1st to 15thNight
7%5%24423345%54%
2728
16th to endNight
11%5%24424346%51%
2816
April1st to 15thNight
9%42232335%7%55%
2557
16th to endNight
13%414323346%53%
2180
May1st to 15thNight
11%5%24323448%50%
2159
16th to endNight
6%3134245%5%9%53%
2259
June1st to 15thNight
431232445%10%58%
2160
16th to endNight
5%2122335%10%62%
2160
July1st to 15thNight
31133245%6%11%54%
2160
16th to endNight
31232345%9%61%
2278
August1st to 15thNight
2213435%46%10%55%
2132
16th to endNight
32133245%5%9%57%
2473
September1st to 15thNight
9%414323446%54%
2636
16th to endNight
6%42432235%6%57%
2640
October1st to 15thNight
10%413222336%59%
2688
16th to endNight
7%21231223368%
3072
November1st to 15thNight
6%313212336%63%
3165
16th to endNight
8%412212335%64%
3120
December1st to 15thNight
8%423323345%58%
3120
16th to endNight
9%6%24322235%55%
3328

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
28%48%27%25%5%
2152
16th to endDay
28%37%27%27%5%
2304
February1st to 15thDay
36%29%24%20%6%
2315
16th to endDay
34%26%25%22%7%
2110
March1st to 15thDay
34%48%21%20%10%
2552
16th to endDay
36%5%11%24%17%6%
2816
April1st to 15thDay
31%5%11%24%19%7%
2707
16th to endDay
35%49%24%20%4
3043
May1st to 15thDay
37%5%11%21%19%5%
3111
16th to endDay
35%6%12%25%16%2
3266
June1st to 15thDay
24%5%15%28%18%7%
3120
16th to endDay
22%6%14%25%24%7%
3120
July1st to 15thDay
25%7%13%28%20%4
2981
16th to endDay
22%5%12%31%23%4
3143
August1st to 15thDay
26%7%14%28%17%6%
3057
16th to endDay
25%6%13%27%20%5%
3134
September1st to 15thDay
32%5%10%22%20%8%
2644
16th to endDay
27%5%8%23%27%7%
2640
October1st to 15thDay
27%39%21%25%12%
2576
16th to endDay
25%26%24%27%13%
2560
November1st to 15thDay
23%37%25%29%12%
2224
16th to endDay
25%25%27%28%10%
2160
December1st to 15thDay
31%39%27%22%5%
2160
16th to endDay
35%29%21%24%6%
2304
January1st to 15thNight
26%28%25%29%7%
3107
16th to endNight
24%27%27%28%9%
3328
February1st to 15thNight
36%38%22%22%6%
2880
16th to endNight
29%37%24%23%11%
2530
March1st to 15thNight
30%47%21%22%12%
2728
16th to endNight
32%411%25%19%6%
2816
April1st to 15thNight
28%5%10%23%23%8%
2557
16th to endNight
32%410%26%19%7%
2180
May1st to 15thNight
32%6%12%20%21%6%
2160
16th to endNight
27%5%15%28%19%3
2261
June1st to 15thNight
21%5%14%30%21%6%
2160
16th to endNight
18%414%31%23%8%
2160
July1st to 15thNight
20%7%16%27%23%4
2070
16th to endNight
18%411%31%28%5%
2170
August1st to 15thNight
21%5%15%27%21%7%
2122
16th to endNight
22%6%13%27%23%6%
2473
September1st to 15thNight
29%5%9%23%22%9%
2636
16th to endNight
26%5%7%23%27%9%
2640
October1st to 15thNight
27%49%21%22%14%
2688
16th to endNight
21%25%23%31%15%
3072
November1st to 15thNight
23%28%21%29%13%
3165
16th to endNight
24%26%24%29%13%
3120
December1st to 15thNight
27%310%25%24%8%
3120
16th to endNight
33%27%21%25%9%
3328

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
15%14%35%26%8%
270
16th to endDay
11%15%49%18%4
288
February1st to 15thDay
15%14%45%22%2
270
16th to endDay
14%20%45%15%4
240
March1st to 15thDay
15%23%38%18%3
270
16th to endDay
15%15%41%19%6%1
288
April1st to 15thDay
13%21%36%23%5%
346
16th to endDay
16%16%37%22%6%1
695
May1st to 15thDay
13%10%41%24%8%1
768
16th to endDay
13%7%32%28%15%2
837
June1st to 15thDay
6%330%38%17%3
795
16th to endDay
7%127%39%20%4
795
July1st to 15thDay
6%14%36%31%9%
775
16th to endDay
5%5%39%39%8%
835
August1st to 15thDay
6%111%44%31%4
774
16th to endDay
5%16%37%32%6%
662
September1st to 15thDay
9%11%37%33%8%
319
16th to endDay
9%321%37%22%6%
315
October1st to 15thDay
10%10%35%26%14%2
315
16th to endDay
16%10%31%26%13%2
336
November1st to 15thDay
13%6%37%31%8%2
298
16th to endDay
15%13%38%21%9%1
270
December1st to 15thDay
12%11%38%28%9%
270
16th to endDay
15%19%36%22%6%
288
January1st to 15thNight
9%13%36%34%6%
1200
16th to endNight
10%11%40%31%6%
1280
February1st to 15thNight
14%12%40%27%4
992
16th to endNight
13%13%42%25%4
844
March1st to 15thNight
10%14%39%29%5%
808
16th to endNight
14%14%40%24%5%
768
April1st to 15thNight
11%15%44%22%5%
719
16th to endNight
16%12%40%23%7%
714
May1st to 15thNight
13%10%42%25%7%
720
16th to endNight
7%6%35%34%14%1
755
June1st to 15thNight
5%333%41%14%
720
16th to endNight
5%234%43%13%
720
July1st to 15thNight
418%45%28%2
690
16th to endNight
47%53%31%2
756
August1st to 15thNight
313%50%29%1
710
16th to endNight
5%117%43%30%2
765
September1st to 15thNight
10%219%40%24%2
720
16th to endNight
8%328%37%19%2
717
October1st to 15thNight
14%5%31%32%14%1
768
16th to endNight
9%8%38%31%11%
1024
November1st to 15thNight
9%9%39%32%8%
1205
16th to endNight
11%10%35%32%9%
1200
December1st to 15thNight
11%10%39%29%7%
1200
16th to endNight
13%11%37%32%5%
1280
Page generated at 2021-11-11 17:33:37. Version ac04

Copyright 2021 A. Danko


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