The Williams' Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Williams' Ranch 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
59%
23773
33%
74503
23%
23717
70%
23717
46%
36372

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
51%
760
35%
2457
23%
756
67%
756
46%
1167
January11th to 20thNight
51%
740
35%
2405
23%
740
66%
740
49%
1110
January21st to endNight
48%
792
38%
2520
22%
792
68%
792
46%
1196
February1st to 10thNight
52%
720
38%
2160
23%
720
69%
720
55%
993
February11th to 20thNight
43%
703
32%
2098
18%
700
58%
700
46%
1041
February21st to endNight
33%
592
38%
1776
15%
592
56%
592
51%
826
March1st to 10thNight
43%
720
35%
2075
15%
720
59%
720
46%
1047
March11th to 20thNight
47%
720
34%
1980
17%
720
60%
720
46%
1040
March21st to endNight
42%
700
41%
2086
18%
700
64%
700
56%
928
April1st to 10thNight
38%
540
40%
1800
19%
540
63%
540
51%
771
April11th to 20thNight
37%
533
37%
1777
17%
533
63%
533
50%
780
April21st to endNight
42%
540
42%
1800
24%
540
71%
540
56%
722
May1st to 10thNight
44%
540
35%
1800
22%
540
66%
540
54%
771
May11th to 20thNight
55%
531
30%
1770
24%
531
68%
531
50%
797
May21st to endNight
60%
583
31%
1939
25%
582
73%
582
54%
852
June1st to 10thNight
68%
540
29%
1490
23%
540
73%
540
49%
805
June11th to 20thNight
73%
540
37%
1440
28%
540
79%
540
59%
715
June21st to endNight
76%
540
24%
1600
23%
540
78%
540
42%
888
July1st to 10thNight
78%
525
21%
1575
21%
525
79%
525
38%
900
July11th to 20thNight
81%
522
24%
1566
25%
522
82%
522
38%
871
July21st to endNight
80%
591
22%
1759
24%
558
80%
558
34%
1030
August1st to 10thNight
79%
537
21%
1779
25%
534
79%
534
30%
1045
August11th to 20thNight
77%
534
24%
1778
29%
534
78%
534
33%
1011
August21st to endNight
79%
594
22%
1980
25%
594
80%
594
32%
1153
September1st to 10thNight
81%
540
26%
1800
30%
540
81%
540
35%
987
September11th to 20thNight
75%
540
31%
1816
34%
540
76%
540
35%
1001
September21st to endNight
75%
540
34%
1980
35%
540
79%
540
41%
932
October1st to 10thNight
70%
666
32%
2106
27%
666
73%
666
45%
1069
October11th to 20thNight
63%
720
38%
2160
23%
720
72%
720
52%
1038
October21st to endNight
68%
792
42%
2376
28%
792
77%
792
59%
1074
November1st to 10thNight
66%
740
42%
2220
27%
740
76%
740
62%
978
November11th to 20thNight
64%
864
39%
2384
23%
864
73%
864
60%
1142
November21st to endNight
56%
950
39%
2470
21%
950
65%
950
53%
1282
December1st to 10thNight
54%
950
38%
2470
21%
950
63%
950
48%
1354
December11th to 20thNight
49%
948
36%
2935
18%
948
64%
948
46%
1498
December21st to endNight
50%
886
25%
4376
23%
874
66%
874
39%
1558

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
421332445%7%64%
74680
Night
431332445%7%63%
75092
TransparencyDay
19%5%8%17%26%25%
74413
Night
20%5%8%16%26%26%
74881
SeeingDay
5%7%21%29%24%14%
13363
Night
5%5%26%38%23%2
23784

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 10thDay
441332435%7%64%
1708
11th to 20thDay
231222345%6%70%
1665
21st to endDay
5%423323445%65%
1832
February1st to 10thDay
3313323447%69%
1800
11th to 20thDay
4423424446%64%
1749
21st to endDay
2312323345%73%
1480
March1st to 10thDay
3215%415%5%6%8%60%
1880
11th to 20thDay
4424323346%65%
1980
21st to endDay
2213324447%69%
2268
April1st to 10thDay
2213223347%71%
2160
11th to 20thDay
321221233476%
2131
21st to endDay
211221234478%
2160
May1st to 10thDay
3211213345%75%
2160
11th to 20thDay
3112224346%71%
2125
21st to endDay
2112212247%76%
2337
June1st to 10thDay
211232345%7%70%
2451
11th to 20thDay
111232335%6%73%
2520
21st to endDay
4213425%5%7%9%60%
2347
July1st to 10thDay
5%315%6%5%5%6%8%10%46%
2340
11th to 20thDay
4314435%6%7%11%51%
2340
21st to endDay
5%3245%47%7%8%11%45%
2451
August1st to 10thDay
4313436%6%8%11%52%
2149
11th to 20thDay
5%325%6%5%6%6%8%11%43%
2123
21st to endDay
5%3246%45%6%7%11%47%
2376
September1st to 10thDay
9%41442445%8%56%
2160
11th to 20thDay
8%4245%3445%7%54%
2142
21st to endDay
4122323347%68%
1980
October1st to 10thDay
5%213423448%66%
1850
11th to 20thDay
5%31332234470%
1800
21st to endDay
121231232478%
1980
November1st to 10thDay
421231235%6%72%
1859
11th to 20thDay
221332435%5%71%
1772
21st to endDay
5%3133235%46%65%
1710
December1st to 10thDay
5%32432445%7%62%
1710
11th to 20thDay
2225%5%35%45%7%60%
2121
21st to endDay
321322346%7%67%
3064
January1st to 10thNight
5%42232335%5%66%
2457
11th to 20thNight
442332335%6%66%
2405
21st to endNight
5%313324346%66%
2520
February1st to 10thNight
3312213347%69%
2160
11th to 20thNight
4314334446%64%
2098
21st to endNight
432322235%6%69%
1776
March1st to 10thNight
441332445%8%62%
2075
11th to 20thNight
4324333347%64%
1980
21st to endNight
221222335%8%69%
2086
April1st to 10thNight
3212323447%69%
1800
11th to 20thNight
4212223345%72%
1777
21st to endNight
2112313245%76%
1800
May1st to 10thNight
4311223335%73%
1800
11th to 20thNight
421232345%6%68%
1770
21st to endNight
311332345%7%69%
1939
June1st to 10thNight
2223435%5%7%9%59%
1490
11th to 20thNight
321233336%7%67%
1440
21st to endNight
44245%35%5%7%10%53%
1600
July1st to 10thNight
34245%36%6%6%11%49%
1620
11th to 20thNight
3324437%7%7%11%49%
1620
21st to endNight
4225%5%47%7%8%10%46%
1863
August1st to 10thNight
44246%47%8%8%12%41%
1790
11th to 20thNight
4425%6%45%6%8%13%44%
1778
21st to endNight
44245%36%7%7%12%46%
1980
September1st to 10thNight
5%424435%6%5%9%53%
1800
11th to 20thNight
7%324435%5%5%8%53%
1816
21st to endNight
6%31442446%6%62%
1980
October1st to 10thNight
5%323434448%61%
2106
11th to 20thNight
5%313313335%69%
2160
21st to endNight
421221223475%
2376
November1st to 10thNight
4212212336%74%
2220
11th to 20thNight
2313323445%72%
2384
21st to endNight
7%21222335%6%66%
2470
December1st to 10thNight
5%424324347%63%
2470
11th to 20thNight
332442335%7%63%
3069
21st to endNight
4313223345%72%
4617

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
20%35%20%34%17%
1709
11th to 20thDay
16%46%16%36%23%
1665
21st to endDay
23%35%13%33%24%
1832
February1st to 10thDay
16%37%15%27%32%
1800
11th to 20thDay
22%46%15%27%26%
1759
21st to endDay
15%2411%30%37%
1480
March1st to 10thDay
21%47%13%29%25%
1880
11th to 20thDay
22%3412%24%34%
1980
21st to endDay
16%26%12%30%35%
2268
April1st to 10thDay
14%25%13%31%36%
2160
11th to 20thDay
13%349%27%44%
2134
21st to endDay
10%35%11%28%43%
2160
May1st to 10thDay
12%35%8%23%49%
2160
11th to 20thDay
15%47%14%25%36%
2128
21st to endDay
10%36%16%21%44%
2337
June1st to 10thDay
13%48%17%27%31%
2451
11th to 20thDay
12%35%12%25%43%
2520
21st to endDay
19%6%11%17%22%25%
2347
July1st to 10thDay
30%11%13%19%17%10%
2276
11th to 20thDay
23%9%16%21%22%10%
2271
21st to endDay
27%13%18%26%14%3
2315
August1st to 10thDay
22%11%13%29%20%5%
2136
11th to 20thDay
31%10%15%24%15%4
2123
21st to endDay
30%9%14%24%17%6%
2376
September1st to 10thDay
27%7%12%18%20%16%
2160
11th to 20thDay
28%6%10%17%24%15%
2142
21st to endDay
17%5%7%22%31%18%
1980
October1st to 10thDay
19%5%8%16%28%24%
1850
11th to 20thDay
18%47%12%27%33%
1800
21st to endDay
11%2415%38%29%
1980
November1st to 10thDay
15%35%20%31%26%
1859
11th to 20thDay
15%36%20%30%25%
1772
21st to endDay
20%36%18%32%20%
1710
December1st to 10thDay
22%48%23%30%14%
1710
11th to 20thDay
23%5%9%19%30%15%
2119
21st to endDay
15%37%17%35%23%
3064
January1st to 10thNight
20%46%17%32%21%
2457
11th to 20thNight
19%36%15%34%23%
2405
21st to endNight
21%25%16%33%23%
2520
February1st to 10thNight
16%27%16%25%34%
2160
11th to 20thNight
22%37%12%27%29%
2098
21st to endNight
18%25%9%27%39%
1776
March1st to 10thNight
21%35%14%26%31%
2075
11th to 20thNight
22%45%13%25%32%
1980
21st to endNight
14%36%13%28%36%
2086
April1st to 10thNight
16%26%9%32%35%
1800
11th to 20thNight
16%36%11%23%41%
1777
21st to endNight
12%3412%27%42%
1800
May1st to 10thNight
15%348%22%48%
1800
11th to 20thNight
17%48%14%23%34%
1771
21st to endNight
15%5%8%12%21%39%
1940
June1st to 10thNight
21%6%9%15%21%29%
1490
11th to 20thNight
15%5%7%11%20%41%
1440
21st to endNight
26%7%14%14%17%23%
1600
July1st to 10thNight
26%9%15%23%18%9%
1575
11th to 20thNight
24%10%15%20%21%10%
1566
21st to endNight
29%10%16%23%18%4
1759
August1st to 10thNight
30%11%16%23%15%6%
1779
11th to 20thNight
29%8%17%26%15%4
1778
21st to endNight
29%10%14%20%18%9%
1980
September1st to 10thNight
27%8%13%17%18%16%
1800
11th to 20thNight
28%8%12%19%16%17%
1816
21st to endNight
22%5%9%17%28%19%
1980
October1st to 10thNight
22%6%10%14%24%25%
2106
11th to 20thNight
19%35%14%25%34%
2160
21st to endNight
15%2413%30%35%
2376
November1st to 10thNight
14%25%16%33%30%
2220
11th to 20thNight
15%35%18%33%27%
2384
21st to endNight
19%36%17%32%23%
2470
December1st to 10thNight
23%45%20%30%18%
2470
11th to 20thNight
21%47%21%29%19%
3070
21st to endNight
16%35%16%39%22%
4617

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
10%12%33%26%17%3
270
11th to 20thDay
6%11%31%31%18%3
255
21st to endDay
49%34%33%14%6%
264
February1st to 10thDay
5%7%32%33%17%7%
240
11th to 20thDay
11%12%37%27%12%2
240
21st to endDay
10%16%33%30%9%3
198
March1st to 10thDay
9%15%33%31%11%1
320
11th to 20thDay
11%13%32%27%12%4
420
21st to endDay
7%20%37%25%8%3
462
April1st to 10thDay
5%14%40%26%12%2
420
11th to 20thDay
6%18%36%27%11%2
412
21st to endDay
5%16%37%29%11%2
420
May1st to 10thDay
312%36%31%15%3
423
11th to 20thDay
18%31%36%19%5%
448
21st to endDay
26%28%41%21%3
485
June1st to 10thDay
3217%40%29%8%
607
11th to 20thDay
2214%39%38%6%
630
21st to endDay
4111%32%33%20%
457
July1st to 10thDay
416%22%38%30%
446
11th to 20thDay
5%1322%34%35%
444
21st to endDay
21421%37%35%
487
August1st to 10thDay
4215%33%45%
447
11th to 20thDay
6%5%21%38%30%
437
21st to endDay
6%6%19%34%35%
495
September1st to 10thDay
8%16%24%33%28%
450
11th to 20thDay
6%16%25%35%25%
432
21st to endDay
417%26%34%28%
270
October1st to 10thDay
10%112%28%31%18%
270
11th to 20thDay
5%316%32%31%13%
270
21st to endDay
48%20%28%23%16%
297
November1st to 10thDay
6%7%21%31%26%9%
270
11th to 20thDay
36%19%30%32%10%
270
21st to endDay
10%13%28%27%16%6%
270
December1st to 10thDay
9%7%26%29%24%6%
270
11th to 20thDay
410%28%39%17%2
270
21st to endDay
8%11%30%35%12%3
297
January1st to 10thNight
7%5%34%39%13%2
760
11th to 20thNight
6%8%32%38%15%2
740
21st to endNight
6%9%34%36%15%1
792
February1st to 10thNight
48%33%38%15%1
720
11th to 20thNight
7%7%40%36%10%1
704
21st to endNight
5%10%48%30%6%1
592
March1st to 10thNight
6%12%37%35%10%1
720
11th to 20thNight
6%11%32%39%12%1
720
21st to endNight
39%44%36%8%
700
April1st to 10thNight
410%45%31%8%
540
11th to 20thNight
5%10%46%28%10%
533
21st to endNight
211%42%34%10%
540
May1st to 10thNight
47%43%38%8%
540
11th to 20thNight
36%32%45%13%1
531
21st to endNight
3428%52%13%
584
June1st to 10thNight
4222%49%23%1
540
11th to 20thNight
3118%54%24%1
540
21st to endNight
4211%47%35%2
540
July1st to 10thNight
417%39%48%2
525
11th to 20thNight
35%31%56%4
522
21st to endNight
41430%55%7%
591
August1st to 10thNight
5%5%25%58%7%
537
11th to 20thNight
316%26%55%10%
534
21st to endNight
5%1427%58%5%
594
September1st to 10thNight
6%15%37%47%4
540
11th to 20thNight
9%5%42%41%3
540
21st to endNight
7%111%44%35%3
540
October1st to 10thNight
6%217%44%29%3
666
11th to 20thNight
6%323%41%24%3
720
21st to endNight
5%5%19%42%24%4
792
November1st to 10thNight
5%224%39%28%3
740
11th to 20thNight
3326%43%24%1
864
21st to endNight
7%7%26%39%19%2
950
December1st to 10thNight
7%6%28%40%17%1
950
11th to 20thNight
5%7%34%41%12%1
950
21st to endNight
5%9%31%41%12%1
893
Page generated at 2024-01-12 23:38:09. Version ac07

Copyright 2024 Attilla Danko


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