Rattle Snake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rattle Snake Observatory clear sky chart from 2005-11-06 to 2024-01-15.

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
37%
24447
22%
74756
13%
24383
46%
24383
27%
46835

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
23%
950
19%
2501
6%
946
34%
946
24%
1684
January11th to 20thNight
18%
923
20%
2399
6%
923
28%
923
22%
1681
January21st to endNight
21%
990
20%
2574
6%
990
30%
990
23%
1804
February1st to 10thNight
19%
900
15%
2340
4%
900
26%
900
20%
1689
February11th to 20thNight
20%
871
17%
2266
5%
867
28%
867
23%
1556
February21st to endNight
16%
575
22%
1759
6%
575
30%
575
20%
1158
March1st to 10thNight
23%
540
23%
1980
10%
540
39%
540
22%
1182
March11th to 20thNight
27%
540
18%
1980
11%
540
37%
540
17%
1313
March21st to endNight
21%
594
11%
2178
6%
594
29%
594
12%
1559
April1st to 10thNight
28%
540
22%
1810
13%
540
43%
540
26%
1063
April11th to 20thNight
32%
533
22%
1775
17%
533
43%
533
23%
1108
April21st to endNight
28%
540
18%
1800
10%
540
42%
540
22%
1175
May1st to 10thNight
35%
540
18%
1620
12%
540
44%
540
24%
1064
May11th to 20thNight
44%
531
18%
1577
14%
531
50%
531
26%
1012
May21st to endNight
46%
584
19%
1552
11%
582
52%
582
28%
1036
June1st to 10thNight
66%
540
22%
1440
16%
540
69%
540
44%
819
June11th to 20thNight
60%
540
25%
1440
16%
540
63%
540
41%
849
June21st to endNight
61%
540
27%
1440
15%
540
67%
540
51%
785
July1st to 10thNight
69%
525
19%
1409
16%
525
70%
525
41%
831
July11th to 20thNight
70%
522
22%
1566
20%
522
73%
522
46%
813
July21st to endNight
67%
591
25%
1673
24%
558
72%
558
41%
922
August1st to 10thNight
69%
537
22%
1601
23%
534
73%
534
39%
900
August11th to 20thNight
70%
534
28%
1636
30%
534
75%
534
41%
882
August21st to endNight
74%
594
28%
1980
32%
594
76%
594
42%
1005
September1st to 10thNight
62%
540
26%
1800
27%
540
66%
540
38%
953
September11th to 20thNight
63%
540
31%
1834
29%
540
69%
540
35%
990
September21st to endNight
56%
603
30%
2043
23%
603
65%
603
38%
1062
October1st to 10thNight
51%
720
28%
2160
20%
720
56%
720
39%
1188
October11th to 20thNight
32%
720
27%
2160
15%
720
43%
720
30%
1281
October21st to endNight
30%
792
25%
2376
12%
792
41%
792
26%
1477
November1st to 10thNight
36%
740
30%
2230
16%
740
50%
740
34%
1238
November11th to 20thNight
28%
826
26%
2536
12%
826
42%
826
28%
1499
November21st to endNight
25%
950
22%
2660
8%
950
37%
950
27%
1710
December1st to 10thNight
24%
950
20%
2660
6%
950
36%
950
24%
1779
December11th to 20thNight
23%
949
20%
3154
7%
948
32%
948
20%
2042
December21st to endNight
18%
1043
11%
4847
6%
1026
30%
1026
10%
3726

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
13%7%35%5%3445%7%43%
74673
Night
12%7%35%43445%7%46%
75118
TransparencyDay
40%6%12%24%15%2
74391
Night
38%6%11%25%17%3
74920
SeeingDay
17%12%28%26%15%3
14483
Night
16%11%32%29%12%1
24450

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
11%9%46%5%345%5%6%42%
1659
11th to 20thDay
14%12%5%8%5%34445%36%
1656
21st to endDay
11%11%47%5%34446%40%
1782
February1st to 10thDay
16%11%5%7%5%24446%35%
1620
11th to 20thDay
14%9%46%6%34447%39%
1580
21st to endDay
17%11%45%5%34446%38%
1511
March1st to 10thDay
13%10%47%5%3445%5%41%
1980
11th to 20thDay
21%10%46%424346%34%
1980
21st to endDay
21%13%37%6%34446%30%
2178
April1st to 10thDay
13%6%46%5%245%5%7%43%
2150
11th to 20thDay
18%9%244245%5%6%40%
2134
21st to endDay
20%7%36%7%34446%35%
2160
May1st to 10thDay
19%7%35%5%345%5%7%36%
2336
11th to 20thDay
17%6%36%5%35%46%6%39%
2315
21st to endDay
12%6%36%6%46%5%7%9%35%
2725
June1st to 10thDay
7%425%5%35%5%7%10%46%
2520
11th to 20thDay
8%425%5%35%6%7%8%47%
2520
21st to endDay
7%313435%5%7%10%51%
2520
July1st to 10thDay
10%4245%35%6%7%10%43%
2505
11th to 20thDay
44145%46%6%7%10%51%
2340
21st to endDay
9%5%25%5%36%5%7%9%44%
2546
August1st to 10thDay
7%5%26%5%35%6%8%11%43%
2328
11th to 20thDay
10%425%5%35%5%7%8%45%
2265
21st to endDay
8%42442445%8%54%
2376
September1st to 10thDay
11%5%245%245%5%7%50%
2160
11th to 20thDay
10%5%244335%5%6%53%
2123
21st to endDay
8%5%25%4235%5%6%55%
1898
October1st to 10thDay
12%5%245%24346%54%
1800
11th to 20thDay
15%6%34322336%53%
1800
21st to endDay
18%8%26%423335%45%
1980
November1st to 10thDay
11%6%24323447%54%
1844
11th to 20thDay
15%6%24424347%49%
1641
21st to endDay
16%9%46%325%237%46%
1520
December1st to 10thDay
12%9%5%5%5%33447%43%
1520
11th to 20thDay
13%10%5%7%5%23345%42%
1918
21st to endDay
16%16%6%10%5%34445%25%
2783
January1st to 10thNight
10%10%46%435%345%44%
2501
11th to 20thNight
14%8%48%7%34345%39%
2399
21st to endNight
11%11%5%7%5%35%45%5%40%
2574
February1st to 10thNight
14%11%5%7%6%35%446%36%
2340
11th to 20thNight
14%8%46%5%35%446%42%
2265
21st to endNight
15%10%37%4235%45%42%
1759
March1st to 10thNight
15%8%34424346%47%
1980
11th to 20thNight
18%9%36%425%45%6%38%
1980
21st to endNight
21%10%46%5%45%5%5%6%30%
2178
April1st to 10thNight
11%6%35%5%24447%50%
1810
11th to 20thNight
14%8%35%42345%7%44%
1775
21st to endNight
17%6%35%5%3445%6%42%
1800
May1st to 10thNight
15%5%35%5%35%5%5%9%42%
1620
11th to 20thNight
14%5%25%5%3445%7%45%
1576
21st to endNight
11%6%36%5%345%6%10%42%
1551
June1st to 10thNight
5%2234345%6%10%56%
1440
11th to 20thNight
6%42442447%12%52%
1440
21st to endNight
3212425%37%9%60%
1440
July1st to 10thNight
10%3243335%6%9%53%
1449
11th to 20thNight
32144235%5%11%59%
1620
21st to endNight
7%424325%5%7%9%53%
1772
August1st to 10thNight
5%3245%345%6%10%53%
1611
11th to 20thNight
6%314425%45%7%58%
1636
21st to endNight
6%21343446%7%59%
1980
September1st to 10thNight
11%424323348%57%
1800
11th to 20thNight
9%4243245%6%7%53%
1834
21st to endNight
8%32443335%7%58%
2043
October1st to 10thNight
9%41432445%6%58%
2160
11th to 20thNight
15%4245%33445%52%
2160
21st to endNight
16%7%245%23345%50%
2376
November1st to 10thNight
11%5%23333435%58%
2230
11th to 20thNight
11%7%35%423446%51%
2536
21st to endNight
15%9%35%323345%48%
2660
December1st to 10thNight
13%10%45%5%3445%6%41%
2660
11th to 20thNight
14%10%47%424446%42%
3279
21st to endNight
17%17%6%9%6%33435%27%
4884

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
42%5%11%24%17%1
1660
11th to 20thDay
51%5%11%23%10%
1656
21st to endDay
46%414%24%11%2
1782
February1st to 10thDay
52%5%11%20%11%1
1620
11th to 20thDay
47%5%12%20%12%3
1589
21st to endDay
48%49%22%14%3
1511
March1st to 10thDay
44%5%10%23%14%4
1980
11th to 20thDay
52%5%9%19%11%3
1980
21st to endDay
56%6%13%18%7%1
2178
April1st to 10thDay
41%6%12%24%16%2
2150
11th to 20thDay
44%5%13%23%13%2
2134
21st to endDay
50%6%11%21%11%1
2160
May1st to 10thDay
47%7%13%21%11%1
2336
11th to 20thDay
44%9%11%22%13%1
2319
21st to endDay
44%10%13%20%11%2
2725
June1st to 10thDay
31%9%16%29%15%1
2520
11th to 20thDay
32%9%14%26%16%3
2520
21st to endDay
27%8%16%31%14%5%
2520
July1st to 10thDay
34%9%15%25%14%3
2436
11th to 20thDay
27%9%16%26%19%3
2271
21st to endDay
34%7%13%32%12%1
2405
August1st to 10thDay
32%10%19%25%13%1
2314
11th to 20thDay
34%8%12%30%14%1
2265
21st to endDay
27%8%13%25%21%6%
2376
September1st to 10thDay
34%6%11%28%16%5%
2160
11th to 20thDay
30%6%9%26%26%3
2123
21st to endDay
28%6%12%27%24%4
1898
October1st to 10thDay
32%5%11%25%23%4
1800
11th to 20thDay
35%48%27%22%5%
1800
21st to endDay
43%48%22%19%4
1980
November1st to 10thDay
31%5%13%25%20%5%
1844
11th to 20thDay
36%411%23%22%3
1641
21st to endDay
43%48%28%16%1
1520
December1st to 10thDay
42%411%29%13%1
1520
11th to 20thDay
45%412%25%11%2
1915
21st to endDay
61%5%10%14%9%1
2783
January1st to 10thNight
43%5%11%23%17%1
2501
11th to 20thNight
47%412%23%13%1
2399
21st to endNight
46%5%13%22%13%1
2574
February1st to 10thNight
50%5%11%20%12%2
2340
11th to 20thNight
44%5%11%20%16%3
2266
21st to endNight
45%5%10%21%15%4
1759
March1st to 10thNight
39%5%10%24%18%4
1980
11th to 20thNight
48%6%9%21%13%3
1980
21st to endNight
55%6%12%18%8%1
2178
April1st to 10thNight
35%6%10%25%20%4
1810
11th to 20thNight
39%7%8%26%16%5%
1775
21st to endNight
44%5%10%23%16%1
1800
May1st to 10thNight
40%8%11%23%16%1
1620
11th to 20thNight
37%9%14%23%16%1
1577
21st to endNight
39%8%15%23%13%2
1552
June1st to 10thNight
23%8%16%33%16%3
1440
11th to 20thNight
25%9%13%27%23%4
1440
21st to endNight
19%8%16%32%20%6%
1440
July1st to 10thNight
27%7%15%31%16%3
1409
11th to 20thNight
20%8%14%31%23%4
1566
21st to endNight
25%7%13%37%16%2
1673
August1st to 10thNight
25%9%18%32%14%2
1601
11th to 20thNight
25%6%11%34%22%2
1636
21st to endNight
22%7%12%27%24%7%
1980
September1st to 10thNight
27%6%13%26%23%7%
1800
11th to 20thNight
28%7%11%24%26%4
1834
21st to endNight
26%5%9%29%27%4
2043
October1st to 10thNight
27%5%9%26%26%6%
2160
11th to 20thNight
35%5%7%26%21%7%
2160
21st to endNight
39%48%22%22%4
2376
November1st to 10thNight
28%6%12%28%21%6%
2230
11th to 20thNight
35%48%25%24%4
2536
21st to endNight
41%49%27%17%3
2660
December1st to 10thNight
43%5%11%25%15%1
2660
11th to 20thNight
43%5%10%27%13%1
3281
21st to endNight
61%6%8%15%8%2
4884

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
23%23%34%16%3
270
11th to 20thDay
30%21%39%9%1
252
21st to endDay
18%25%44%11%2
264
February1st to 10thDay
28%28%32%11%2
240
11th to 20thDay
23%29%35%10%3
240
21st to endDay
33%28%29%9%2
198
March1st to 10thDay
20%26%44%10%1
240
11th to 20thDay
35%15%33%16%1
240
21st to endDay
39%22%27%9%3
264
April1st to 10thDay
19%16%40%18%5%1
410
11th to 20thDay
22%20%32%20%6%
412
21st to endDay
28%13%32%21%6%
420
May1st to 10thDay
21%15%34%22%7%
599
11th to 20thDay
21%14%26%27%11%1
625
21st to endDay
15%10%31%26%13%5%
679
June1st to 10thDay
7%6%21%36%25%6%
630
11th to 20thDay
10%425%39%19%3
630
21st to endDay
7%7%31%36%15%3
630
July1st to 10thDay
12%314%31%30%10%
621
11th to 20thDay
5%324%34%28%6%
618
21st to endDay
10%317%34%31%6%
684
August1st to 10thDay
8%319%39%26%4
626
11th to 20thDay
10%319%36%27%6%
579
21st to endDay
9%216%32%33%8%
495
September1st to 10thDay
14%317%35%25%5%
450
11th to 20thDay
8%221%38%25%6%
413
21st to endDay
10%11%25%34%16%4
270
October1st to 10thDay
16%8%33%27%12%4
270
11th to 20thDay
19%23%35%20%3
270
21st to endDay
31%20%31%16%11
297
November1st to 10thDay
16%17%36%21%7%2
270
11th to 20thDay
21%19%33%20%41
270
21st to endDay
28%19%29%21%3
270
December1st to 10thDay
18%23%34%18%7%1
270
11th to 20thDay
23%20%36%19%21
270
21st to endDay
25%30%36%9%
297
January1st to 10thNight
17%17%39%21%6%
950
11th to 20thNight
20%20%37%18%41
923
21st to endNight
17%18%40%22%2
990
February1st to 10thNight
20%16%41%20%3
900
11th to 20thNight
21%17%38%23%2
871
21st to endNight
23%18%40%16%3
575
March1st to 10thNight
19%15%40%22%4
540
11th to 20thNight
22%14%32%28%4
540
21st to endNight
26%16%35%20%4
594
April1st to 10thNight
14%17%38%26%41
540
11th to 20thNight
20%13%32%26%9%1
533
21st to endNight
20%9%39%24%8%
540
May1st to 10thNight
17%7%35%32%9%
540
11th to 20thNight
17%7%27%34%14%1
531
21st to endNight
12%8%27%32%19%2
584
June1st to 10thNight
6%219%45%26%1
540
11th to 20thNight
7%324%44%20%2
540
21st to endNight
3330%44%19%2
540
July1st to 10thNight
11%211%41%30%5%
525
11th to 20thNight
4218%42%33%2
522
21st to endNight
9%117%40%30%2
591
August1st to 10thNight
6%215%42%33%2
537
11th to 20thNight
6%115%45%29%4
534
21st to endNight
6%214%38%37%3
594
September1st to 10thNight
12%218%39%25%4
540
11th to 20thNight
11%319%36%26%5%
540
21st to endNight
8%5%24%38%21%3
603
October1st to 10thNight
10%7%28%31%21%3
720
11th to 20thNight
17%10%39%26%8%
720
21st to endNight
20%13%34%25%8%
792
November1st to 10thNight
12%12%37%30%8%
740
11th to 20thNight
15%16%37%25%7%
826
21st to endNight
21%15%36%23%5%
950
December1st to 10thNight
20%13%39%22%6%
950
11th to 20thNight
22%13%38%23%4
950
21st to endNight
22%19%38%19%2
1045
Page generated at 2024-01-12 06:31:48. Version ac07

Copyright 2024 Attilla Danko


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