Rockbottom Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rockbottom Observatory clear sky chart from 2005-11-05 to 2017-08-12.

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
26%
14757
18%
46455
7%
14725
38%
14725
20%
30435

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
15%
720
19%
2506
6%
716
32%
716
16%
1606
January16th to endNight
14%
768
19%
2688
4%
768
33%
768
15%
1708
February1st to 15thNight
14%
704
16%
2192
4%
701
29%
701
16%
1485
February16th to endNight
16%
631
23%
1893
6%
631
36%
631
18%
1250
March1st to 15thNight
16%
720
16%
2160
5%
720
30%
720
16%
1499
March16th to endNight
20%
768
22%
2023
7%
768
32%
768
21%
1376
April1st to 15thNight
20%
718
17%
1796
3%
718
29%
718
21%
1284
April16th to endNight
22%
597
18%
1677
4%
597
32%
597
19%
1149
May1st to 15thNight
22%
540
15%
1620
7%
540
31%
540
17%
1138
May16th to endNight
25%
408
11%
1530
7%
407
33%
407
15%
1033
June1st to 15thNight
30%
360
12%
1440
8%
360
41%
360
15%
969
June16th to endNight
33%
360
11%
1440
10%
360
43%
360
20%
886
July1st to 15thNight
42%
340
12%
1360
13%
340
48%
340
22%
828
July16th to endNight
45%
376
15%
1418
13%
354
52%
354
22%
854
August1st to 15thNight
44%
489
16%
1538
11%
487
49%
487
26%
959
August16th to endNight
50%
669
18%
1719
9%
669
53%
669
34%
1112
September1st to 15thNight
39%
660
20%
1702
9%
660
45%
660
31%
1112
September16th to endNight
45%
657
25%
1815
16%
657
53%
657
34%
1105
October1st to 15thNight
31%
660
22%
1840
10%
660
42%
660
25%
1199
October16th to endNight
24%
704
16%
2288
5%
704
38%
704
19%
1500
November1st to 15thNight
28%
700
21%
2277
10%
700
42%
700
22%
1457
November16th to endNight
24%
720
20%
2340
8%
720
38%
720
18%
1508
December1st to 15thNight
19%
720
17%
2505
5%
720
34%
720
16%
1621
December16th to endNight
14%
768
18%
2688
4%
768
31%
768
15%
1797

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
16%6%25%43445%7%39%
47525
Night
16%6%24424446%41%
46625
Cloud CoverDay
17%6%25%5%3445%7%39%
47535
Night
16%6%25%424446%41%
46630
TransparencyDay
43%6%12%20%14%2
47213
Night
43%6%12%21%14%2
46455
SeeingDay
21%14%31%21%8%2
5736
Night
21%13%34%23%6%
14757

By Month

Percentage Cloud Cover NE (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
15%7%35%425%345%41%
1432
16th to endDay
15%5%2443445%7%42%
1536
February1st to 15thDay
16%6%35%445%46%7%34%
1668
16th to endDay
14%8%36%5%35%335%40%
1580
March1st to 15thDay
21%8%2442445%6%35%
1790
16th to endDay
18%7%25%333337%40%
2197
April1st to 15thDay
18%7%35%5%33446%38%
2152
16th to endDay
18%4245%2445%6%40%
2283
May1st to 15thDay
24%8%34434446%32%
2332
16th to endDay
17%425%5%34348%39%
2594
June1st to 15thDay
25%5%24424447%33%
2520
16th to endDay
15%425%6%36%5%7%8%34%
2520
July1st to 15thDay
12%5%35%5%36%5%6%8%37%
2520
16th to endDay
11%5%25%5%36%5%5%9%38%
2654
August1st to 15thDay
11%5%25%6%45%5%5%9%38%
2315
16th to endDay
11%4245%36%5%5%7%42%
2129
September1st to 15thDay
13%5%34424447%45%
1928
16th to endDay
13%5%14323345%51%
1815
October1st to 15thDay
19%5%15%423346%42%
1787
16th to endDay
15%6%245%23446%42%
1584
November1st to 15thDay
20%6%33423235%44%
1581
16th to endDay
16%5%25%42435%5%43%
1620
December1st to 15thDay
17%6%35%5%24346%40%
1452
16th to endDay
23%6%25%4245%45%36%
1536
January1st to 15thNight
17%8%345%24335%40%
2506
16th to endNight
16%9%3443335%5%41%
2688
February1st to 15thNight
14%8%36%5%3445%5%38%
2191
16th to endNight
16%9%24433346%41%
1893
March1st to 15thNight
18%7%35%434446%36%
2147
16th to endNight
14%9%35%32434444%
2023
April1st to 15thNight
16%6%36%5%44446%37%
1796
16th to endNight
20%5%25%5%24345%40%
1677
May1st to 15thNight
21%6%15%5%23445%37%
1620
16th to endNight
17%6%246%3435%7%35%
1528
June1st to 15thNight
22%6%345%2435%7%34%
1440
16th to endNight
14%5%245%345%6%8%39%
1440
July1st to 15thNight
12%5%25%435%46%9%40%
1440
16th to endNight
11%435%5%3446%9%41%
1514
August1st to 15thNight
9%3245%35%5%6%7%45%
1548
16th to endNight
12%3144245%6%9%45%
1719
September1st to 15thNight
13%4245%1345%7%45%
1702
16th to endNight
13%5%13223446%52%
1815
October1st to 15thNight
19%5%23422346%44%
1840
16th to endNight
20%6%24423446%40%
2288
November1st to 15thNight
18%6%2432335%445%
2277
16th to endNight
19%6%24424446%41%
2340
December1st to 15thNight
18%7%345%33346%39%
2505
16th to endNight
18%9%36%32445%6%37%
2688

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
15%7%35%424445%41%
1432
16th to endDay
15%6%2442345%7%42%
1536
February1st to 15thDay
16%7%25%5%35%5%5%8%33%
1668
16th to endDay
14%8%36%5%34335%40%
1580
March1st to 15thDay
21%7%34424346%35%
1800
16th to endDay
18%6%34424337%40%
2197
April1st to 15thDay
18%7%35%424445%39%
2152
16th to endDay
18%4245%3445%6%40%
2283
May1st to 15thDay
24%8%34434345%32%
2332
16th to endDay
17%425%5%34348%39%
2594
June1st to 15thDay
25%5%2442445%7%33%
2520
16th to endDay
15%425%5%45%6%7%8%34%
2520
July1st to 15thDay
12%5%35%446%5%6%8%37%
2520
16th to endDay
11%5%25%6%36%5%5%8%38%
2654
August1st to 15thDay
12%5%25%6%45%5%5%8%39%
2315
16th to endDay
10%5%25%6%35%5%5%7%42%
2129
September1st to 15thDay
14%6%2442445%7%45%
1928
16th to endDay
14%5%23422335%51%
1815
October1st to 15thDay
20%5%14423346%42%
1787
16th to endDay
15%6%245%14447%42%
1584
November1st to 15thDay
21%6%33323335%43%
1581
16th to endDay
16%6%25%42445%5%43%
1620
December1st to 15thDay
18%6%35%5%23446%40%
1452
16th to endDay
23%7%24424436%36%
1536
January1st to 15thNight
17%8%345%24335%40%
2506
16th to endNight
16%9%34433345%41%
2688
February1st to 15thNight
14%8%36%5%3445%5%38%
2184
16th to endNight
16%9%3433435%5%41%
1893
March1st to 15thNight
18%8%35%425%446%36%
2160
16th to endNight
14%8%35%324335%44%
2022
April1st to 15thNight
16%7%36%5%34345%37%
1796
16th to endNight
21%5%25%433345%40%
1677
May1st to 15thNight
22%6%245%34345%37%
1620
16th to endNight
17%6%36%6%24448%35%
1528
June1st to 15thNight
22%6%345%2435%7%34%
1440
16th to endNight
14%5%245%25%5%6%8%39%
1440
July1st to 15thNight
13%425%5%3447%9%39%
1440
16th to endNight
12%5%25%5%35%46%9%40%
1514
August1st to 15thNight
9%325%5%25%5%6%7%45%
1548
16th to endNight
12%3144345%5%8%45%
1719
September1st to 15thNight
14%3245%2345%7%45%
1702
16th to endNight
13%5%23222446%51%
1815
October1st to 15thNight
19%5%23313346%44%
1840
16th to endNight
20%6%24423446%40%
2288
November1st to 15thNight
17%6%25%32335%5%44%
2277
16th to endNight
19%6%24423446%41%
2340
December1st to 15thNight
18%7%25%423346%39%
2505
16th to endNight
18%9%36%42445%6%36%
2688

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
44%5%11%24%11%3
1433
16th to endDay
39%6%12%25%13%1
1536
February1st to 15thDay
46%7%14%18%12%
1671
16th to endDay
46%49%22%13%3
1580
March1st to 15thDay
49%411%19%11%3
1800
16th to endDay
44%410%20%14%5%
2197
April1st to 15thDay
46%5%11%18%15%2
2152
16th to endDay
42%5%10%19%18%3
2283
May1st to 15thDay
54%5%8%17%12%2
2332
16th to endDay
44%7%12%20%12%2
2598
June1st to 15thDay
49%6%13%19%9%
2520
16th to endDay
43%9%12%18%13%
2520
July1st to 15thDay
42%8%11%20%14%1
2371
16th to endDay
40%9%14%19%12%3
2487
August1st to 15thDay
41%8%14%22%12%1
2301
16th to endDay
38%7%12%24%14%2
2129
September1st to 15thDay
37%6%12%21%19%1
1928
16th to endDay
35%38%23%25%2
1815
October1st to 15thDay
43%410%23%14%3
1787
16th to endDay
40%6%13%22%14%1
1584
November1st to 15thDay
44%413%22%14%1
1581
16th to endDay
41%5%13%21%16%1
1620
December1st to 15thDay
44%417%16%16%
1452
16th to endDay
49%6%13%17%11%
1536
January1st to 15thNight
46%412%21%13%2
2506
16th to endNight
44%412%20%15%2
2688
February1st to 15thNight
46%5%13%20%11%2
2192
16th to endNight
45%39%22%15%2
1893
March1st to 15thNight
47%5%10%19%12%3
2160
16th to endNight
43%49%17%19%5%
2023
April1st to 15thNight
47%5%10%18%16%2
1796
16th to endNight
45%5%9%18%16%4
1677
May1st to 15thNight
49%5%9%17%14%2
1620
16th to endNight
47%8%14%17%10%1
1530
June1st to 15thNight
48%7%12%20%9%1
1440
16th to endNight
39%8%13%22%14%1
1440
July1st to 15thNight
38%8%13%24%13%
1360
16th to endNight
38%8%15%24%10%2
1418
August1st to 15thNight
36%9%14%22%16%1
1538
16th to endNight
33%8%14%27%15%
1719
September1st to 15thNight
37%6%14%22%18%
1702
16th to endNight
33%5%8%23%27%1
1815
October1st to 15thNight
40%5%12%21%15%3
1840
16th to endNight
45%413%22%13%
2288
November1st to 15thNight
41%5%11%20%17%3
2277
16th to endNight
43%5%12%21%14%2
2340
December1st to 15thNight
45%5%14%22%12%
2505
16th to endNight
47%5%12%22%11%
2688

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
23%30%25%20%1
60
16th to endDay
26%18%43%10%
64
February1st to 15thDay
25%20%37%14%3
216
16th to endDay
21%23%30%18%4
239
March1st to 15thDay
30%20%31%14%2
270
16th to endDay
22%24%31%13%6%1
288
April1st to 15thDay
25%18%33%13%8%
270
16th to endDay
21%14%36%18%5%2
270
May1st to 15thDay
36%14%25%15%7%1
288
16th to endDay
20%12%36%22%7%
331
June1st to 15thDay
24%12%32%20%9%
315
16th to endDay
18%11%38%24%5%2
315
July1st to 15thDay
16%9%35%26%11%1
305
16th to endDay
12%9%30%31%11%3
326
August1st to 15thDay
12%8%31%29%15%3
297
16th to endDay
11%5%29%27%19%7%
268
September1st to 15thDay
19%6%28%25%14%5%
255
16th to endDay
17%5%27%23%12%12%
254
October1st to 15thDay
22%10%25%22%13%5%
254
16th to endDay
20%17%32%23%6%
240
November1st to 15thDay
27%12%28%19%8%2
235
16th to endDay
23%16%30%18%10%1
240
December1st to 15thDay
26%29%27%13%2
72
16th to endDay
34%25%28%10%1
64
January1st to 15thNight
23%18%38%17%2
720
16th to endNight
22%20%36%17%2
768
February1st to 15thNight
19%19%41%17%1
704
16th to endNight
23%19%35%17%2
631
March1st to 15thNight
23%20%36%16%3
720
16th to endNight
20%19%36%19%4
768
April1st to 15thNight
21%18%36%19%3
718
16th to endNight
21%17%34%18%6%
597
May1st to 15thNight
26%13%33%20%5%
540
16th to endNight
20%10%38%26%4
408
June1st to 15thNight
23%435%29%6%
360
16th to endNight
16%341%33%5%
360
July1st to 15thNight
12%334%37%10%
340
16th to endNight
12%231%40%12%
376
August1st to 15thNight
11%332%41%10%
489
16th to endNight
13%425%39%15%1
669
September1st to 15thNight
16%5%33%30%13%
660
16th to endNight
17%5%27%27%19%2
657
October1st to 15thNight
23%11%28%24%10%1
660
16th to endNight
26%13%33%20%5%
704
November1st to 15thNight
21%12%33%22%9%1
700
16th to endNight
23%17%30%19%7%1
720
December1st to 15thNight
24%17%34%18%4
720
16th to endNight
25%17%38%15%2
768
Page generated at 2017-08-13 14:16:25. Version ac04

Copyright 2017 A. Danko


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