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Tom's Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tom's Ranch clear sky chart from 2005-11-06 to 2024-01-27.

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
46%
23834
27%
74522
17%
23779
57%
23779
36%
41141

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
36%
947
31%
2458
13%
946
48%
946
41%
1445
January11th to 20thNight
32%
908
29%
2428
10%
908
45%
908
37%
1425
January21st to endNight
30%
820
32%
2460
13%
820
47%
820
31%
1445
February1st to 10thNight
33%
720
29%
2160
12%
720
48%
720
34%
1214
February11th to 20thNight
28%
704
24%
2098
10%
700
41%
700
31%
1197
February21st to endNight
19%
592
29%
1776
6%
592
38%
592
30%
1021
March1st to 10thNight
22%
669
26%
2109
8%
669
40%
669
29%
1231
March11th to 20thNight
31%
540
24%
1980
13%
540
45%
540
25%
1139
March21st to endNight
22%
594
28%
2178
11%
594
45%
594
32%
1128
April1st to 10thNight
24%
540
27%
1967
12%
540
47%
540
31%
1045
April11th to 20thNight
20%
533
26%
1777
9%
533
40%
533
30%
1004
April21st to endNight
23%
540
29%
1778
13%
540
46%
540
34%
966
May1st to 10thNight
27%
540
27%
1620
13%
540
44%
540
35%
928
May11th to 20thNight
35%
531
21%
1593
16%
531
47%
531
31%
969
May21st to endNight
40%
583
21%
1745
12%
582
54%
582
33%
1045
June1st to 10thNight
61%
540
24%
1620
19%
540
72%
540
52%
789
June11th to 20thNight
57%
540
25%
1620
20%
540
68%
540
50%
811
June21st to endNight
67%
540
25%
1620
25%
540
71%
540
43%
877
July1st to 10thNight
74%
525
17%
1575
18%
525
76%
525
34%
944
July11th to 20thNight
83%
522
30%
1566
33%
522
87%
522
54%
754
July21st to endNight
83%
591
28%
1676
30%
558
88%
558
58%
777
August1st to 10thNight
88%
537
29%
1779
36%
534
89%
534
59%
754
August11th to 20thNight
79%
534
26%
1778
32%
534
80%
534
37%
969
August21st to endNight
79%
594
21%
1980
22%
594
81%
594
36%
1102
September1st to 10thNight
75%
540
21%
1971
25%
540
78%
540
33%
1073
September11th to 20thNight
70%
540
23%
1980
26%
540
73%
540
29%
1131
September21st to endNight
72%
540
27%
1980
27%
540
75%
540
34%
1047
October1st to 10thNight
71%
540
34%
1980
32%
540
77%
540
43%
928
October11th to 20thNight
55%
540
35%
1980
26%
540
65%
540
35%
1011
October21st to endNight
44%
787
33%
2371
17%
787
55%
787
40%
1285
November1st to 10thNight
51%
825
30%
2305
15%
825
59%
825
42%
1289
November11th to 20thNight
44%
950
27%
2470
11%
950
52%
950
43%
1419
November21st to endNight
38%
950
29%
2470
12%
950
47%
950
35%
1533
December1st to 10thNight
45%
950
32%
2470
15%
950
54%
950
39%
1485
December11th to 20thNight
34%
950
28%
2904
12%
949
45%
949
30%
1778
December21st to endNight
36%
1038
19%
4300
13%
1026
47%
1026
28%
2183

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%2443445%7%52%
74981
Night
8%42442345%7%57%
75095
TransparencyDay
32%6%11%20%21%11%
74707
Night
27%6%12%21%21%13%
74889
SeeingDay
9%7%25%33%20%5%
13737
Night
10%7%33%37%12%1
23845

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
10%5%34323336%58%
1707
11th to 20thDay
12%5%24323445%55%
1767
21st to endDay
10%4244345%35%56%
2040
February1st to 10thDay
11%5%2443445%5%55%
1800
11th to 20thDay
12%5%3442345%6%50%
1749
21st to endDay
12%41433345%6%56%
1480
March1st to 10thDay
12%7%25%5%3445%6%47%
1849
11th to 20thDay
11%6%25%43445%6%52%
1980
21st to endDay
9%5%245%34346%55%
2178
April1st to 10thDay
9%6%2442445%8%51%
1988
11th to 20thDay
10%6%35%5%2445%6%51%
2134
21st to endDay
9%5%245%34347%54%
2181
May1st to 10thDay
9%6%35%5%345%5%8%45%
2340
11th to 20thDay
10%6%36%5%36%5%5%7%45%
2302
21st to endDay
9%6%36%6%35%5%6%8%44%
2531
June1st to 10thDay
33245%345%6%10%56%
2340
11th to 20thDay
3224436%5%7%10%54%
2340
21st to endDay
5%3246%46%6%7%9%47%
2340
July1st to 10thDay
8%5%36%6%47%6%6%9%41%
2340
11th to 20thDay
4214435%45%9%59%
2340
21st to endDay
42134245%7%11%55%
2538
August1st to 10thDay
1113434449%66%
2149
11th to 20thDay
7%425%6%45%5%6%7%50%
2123
21st to endDay
5%425%6%45%46%10%48%
2376
September1st to 10thDay
10%425%5%35%5%6%9%45%
1987
11th to 20thDay
10%6%26%6%46%6%6%7%42%
1980
21st to endDay
9%5%245%3446%8%50%
1980
October1st to 10thDay
5%424435%45%8%57%
1980
11th to 20thDay
11%424424446%55%
1966
21st to endDay
10%424323335%61%
1980
November1st to 10thDay
11%5%25%32345%7%54%
1770
11th to 20thDay
7%5%23335%45%6%57%
1710
21st to endDay
10%6%26%423346%53%
1710
December1st to 10thDay
11%6%2432345%8%52%
1710
11th to 20thDay
10%6%26%5%3445%6%50%
2161
21st to endDay
10%5%2432334460%
3135
January1st to 10thNight
10%5%24313347%57%
2458
11th to 20thNight
11%5%2432335%6%56%
2428
21st to endNight
11%6%24424446%53%
2460
February1st to 10thNight
10%5%24423446%56%
2160
11th to 20thNight
12%5%2432335%5%55%
2098
21st to endNight
10%5%2442345%7%53%
1776
March1st to 10thNight
10%5%244245%6%8%49%
2109
11th to 20thNight
9%5%244345%5%6%51%
1980
21st to endNight
6%42442345%8%57%
2178
April1st to 10thNight
5%424425%5%6%8%55%
1967
11th to 20thNight
8%5%2443345%6%54%
1777
21st to endNight
9%32342345%7%59%
1778
May1st to 10thNight
7%423435%6%5%8%53%
1620
11th to 20thNight
8%5%244345%6%8%50%
1593
21st to endNight
7%42444446%11%51%
1745
June1st to 10thNight
211331246%13%63%
1620
11th to 20thNight
211232447%10%65%
1620
21st to endNight
43133345%7%10%58%
1620
July1st to 10thNight
5%324445%6%7%12%49%
1620
11th to 20thNight
211232336%8%68%
1620
21st to endNight
21123135%5%12%65%
1775
August1st to 10thNight
211112235%8%75%
1790
11th to 20thNight
4324435%5%7%9%54%
1778
21st to endNight
5%3244346%7%9%54%
1980
September1st to 10thNight
7%4244345%6%8%55%
1971
11th to 20thNight
9%425%5%3447%9%50%
1980
21st to endNight
8%31443446%8%55%
1980
October1st to 10thNight
421332445%8%65%
1980
11th to 20thNight
9%42432335%6%59%
1980
21st to endNight
10%41341333463%
2371
November1st to 10thNight
9%423423346%61%
2305
11th to 20thNight
7%41342345%7%60%
2470
21st to endNight
12%5%2442345%7%52%
2470
December1st to 10thNight
10%5%23323446%57%
2470
11th to 20thNight
9%7%25%5%24446%51%
3036
21st to endNight
10%5%24322336%59%
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
29%36%19%26%18%
1708
11th to 20thDay
32%45%16%25%18%
1767
21st to endDay
32%47%12%27%18%
2040
February1st to 10thDay
33%48%13%22%20%
1800
11th to 20thDay
35%47%17%20%17%
1759
21st to endDay
30%38%15%23%20%
1480
March1st to 10thDay
38%5%7%16%18%15%
1849
11th to 20thDay
35%5%9%16%17%19%
1980
21st to endDay
31%6%9%16%22%16%
2178
April1st to 10thDay
33%6%9%18%19%14%
1988
11th to 20thDay
35%5%8%16%21%15%
2134
21st to endDay
33%5%9%19%21%14%
2181
May1st to 10thDay
37%7%11%14%22%10%
2340
11th to 20thDay
38%8%11%19%20%4
2306
21st to endDay
40%8%11%21%18%3
2531
June1st to 10thDay
24%9%13%29%21%4
2340
11th to 20thDay
25%8%15%26%20%6%
2340
21st to endDay
33%9%13%22%18%5%
2340
July1st to 10thDay
37%12%15%25%10%1
2276
11th to 20thDay
22%8%16%28%22%3
2271
21st to endDay
20%9%24%33%13%1
2397
August1st to 10thDay
17%6%15%40%21%1
2136
11th to 20thDay
31%9%14%29%13%3
2123
21st to endDay
32%10%16%26%14%3
2376
September1st to 10thDay
37%8%12%19%17%7%
1987
11th to 20thDay
39%9%11%20%16%5%
1980
21st to endDay
32%6%12%20%19%10%
1980
October1st to 10thDay
26%7%11%23%24%9%
1980
11th to 20thDay
32%5%8%15%23%17%
1966
21st to endDay
29%45%16%27%20%
1980
November1st to 10thDay
32%5%10%20%21%12%
1770
11th to 20thDay
29%5%8%18%22%17%
1710
21st to endDay
34%46%17%23%15%
1710
December1st to 10thDay
33%5%8%17%26%11%
1710
11th to 20thDay
35%5%8%11%23%18%
2159
21st to endDay
29%45%16%27%20%
3135
January1st to 10thNight
29%46%14%25%22%
2458
11th to 20thNight
31%46%18%23%19%
2428
21st to endNight
33%5%6%13%23%20%
2460
February1st to 10thNight
30%5%10%12%22%21%
2160
11th to 20thNight
32%5%7%16%22%19%
2098
21st to endNight
32%5%7%13%22%21%
1776
March1st to 10thNight
32%7%10%17%21%13%
2109
11th to 20thNight
35%6%8%14%18%19%
1980
21st to endNight
28%6%11%19%19%17%
2178
April1st to 10thNight
29%6%11%19%17%18%
1967
11th to 20thNight
31%7%12%15%18%18%
1777
21st to endNight
28%6%11%22%21%13%
1778
May1st to 10thNight
29%6%13%20%19%11%
1620
11th to 20thNight
33%8%11%26%17%5%
1594
21st to endNight
31%8%16%27%15%3
1746
June1st to 10thNight
14%9%18%34%22%3
1620
11th to 20thNight
16%9%17%29%22%6%
1620
21st to endNight
23%8%18%28%18%5%
1620
July1st to 10thNight
26%14%21%27%10%2
1575
11th to 20thNight
14%8%18%32%25%3
1566
21st to endNight
12%7%27%38%15%1
1676
August1st to 10thNight
10%7%18%41%22%1
1779
11th to 20thNight
23%11%19%28%17%3
1778
21st to endNight
25%10%22%25%14%3
1980
September1st to 10thNight
27%9%15%23%19%7%
1971
11th to 20thNight
32%9%16%23%17%5%
1980
21st to endNight
27%8%13%23%19%11%
1980
October1st to 10thNight
19%7%15%26%21%12%
1980
11th to 20thNight
28%5%11%17%23%17%
1980
21st to endNight
28%37%16%23%23%
2371
November1st to 10thNight
27%5%9%20%25%14%
2305
11th to 20thNight
25%6%9%21%21%18%
2470
21st to endNight
34%5%9%15%22%16%
2470
December1st to 10thNight
30%5%10%17%24%14%
2470
11th to 20thNight
35%5%6%14%18%22%
3037
21st to endNight
29%45%15%29%18%
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
12%14%46%21%7%1
270
11th to 20thDay
17%13%34%28%7%2
270
21st to endDay
10%12%48%24%6%
282
February1st to 10thDay
17%13%41%18%11%
240
11th to 20thDay
24%12%40%20%3
240
21st to endDay
16%14%47%21%2
198
March1st to 10thDay
15%15%46%22%3
240
11th to 20thDay
13%15%42%20%10%
240
21st to endDay
13%15%47%18%6%
264
April1st to 10thDay
13%17%44%24%2
248
11th to 20thDay
11%17%43%24%4
412
21st to endDay
12%18%43%22%5%
441
May1st to 10thDay
10%10%45%30%5%
603
11th to 20thDay
15%7%32%33%11%2
625
21st to endDay
10%8%32%38%10%1
679
June1st to 10thDay
4222%48%22%2
630
11th to 20thDay
3124%48%22%2
630
21st to endDay
4215%46%29%5%
630
July1st to 10thDay
6%211%37%34%9%
621
11th to 20thDay
2447%39%8%
618
21st to endDay
25%40%39%13%
676
August1st to 10thDay
2438%44%13%
447
11th to 20thDay
7%15%33%39%15%
437
21st to endDay
6%15%29%41%17%
495
September1st to 10thDay
9%16%23%41%21%
277
11th to 20thDay
5%1326%46%19%
270
21st to endDay
13%16%28%38%14%
270
October1st to 10thDay
4414%37%36%6%
270
11th to 20thDay
10%5%22%39%21%3
270
21st to endDay
16%12%26%30%13%2
297
November1st to 10thDay
17%6%27%34%14%2
270
11th to 20thDay
16%11%29%26%13%6%
270
21st to endDay
15%20%37%19%7%2
270
December1st to 10thDay
14%9%31%31%11%3
270
11th to 20thDay
11%16%40%25%8%
270
21st to endDay
12%13%38%28%9%
297
January1st to 10thNight
13%10%38%31%8%1
950
11th to 20thNight
15%9%40%30%6%
908
21st to endNight
15%10%42%27%5%
820
February1st to 10thNight
13%13%40%28%6%
720
11th to 20thNight
14%14%41%28%3
704
21st to endNight
14%15%51%19%1
592
March1st to 10thNight
14%14%48%21%3
669
11th to 20thNight
14%9%43%30%4
540
21st to endNight
7%14%55%21%2
594
April1st to 10thNight
7%11%56%23%3
540
11th to 20thNight
9%13%56%20%2
533
21st to endNight
10%11%54%21%4
540
May1st to 10thNight
8%10%54%25%3
540
11th to 20thNight
10%7%44%30%10%
531
21st to endNight
7%7%43%34%8%
584
June1st to 10thNight
2131%51%14%
540
11th to 20thNight
1138%52%8%
540
21st to endNight
4123%51%20%1
540
July1st to 10thNight
5%113%55%24%2
525
11th to 20thNight
2110%63%23%1
522
21st to endNight
219%62%25%2
591
August1st to 10thNight
217%62%27%2
537
11th to 20thNight
417%55%31%2
534
21st to endNight
418%48%37%3
594
September1st to 10thNight
5%210%48%32%3
540
11th to 20thNight
10%110%46%32%2
540
21st to endNight
9%212%50%25%2
540
October1st to 10thNight
5%119%49%25%1
540
11th to 20thNight
10%6%26%42%16%1
540
21st to endNight
12%9%32%31%16%1
787
November1st to 10thNight
11%5%29%40%14%1
825
11th to 20thNight
9%6%36%34%13%2
950
21st to endNight
13%10%34%32%9%1
950
December1st to 10thNight
13%8%32%38%8%1
950
11th to 20thNight
15%10%38%32%5%
950
21st to endNight
12%12%37%32%7%
1045
Page generated at 2024-01-24 08:37:26. Version ac07

Copyright 2024 Attilla Danko


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