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 2018-02-14.

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%
15497
18%
48770
7%
15465
38%
15465
20%
31879

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%
780
19%
2716
5%
776
32%
776
16%
1727
January16th to endNight
14%
832
19%
2912
4%
832
33%
832
15%
1864
February1st to 15thNight
14%
760
16%
2365
4%
757
29%
757
16%
1616
February16th to endNight
16%
631
22%
1893
6%
631
36%
631
18%
1250
March1st to 15thNight
17%
720
16%
2160
5%
720
31%
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
21%
597
18%
1677
4%
597
31%
597
19%
1149
May1st to 15thNight
22%
540
15%
1620
7%
540
30%
540
17%
1138
May16th to endNight
26%
408
11%
1530
7%
407
34%
407
15%
1033
June1st to 15thNight
30%
360
12%
1440
8%
360
42%
360
15%
969
June16th to endNight
33%
360
11%
1440
10%
360
43%
360
20%
886
July1st to 15thNight
43%
340
12%
1360
13%
340
49%
340
22%
828
July16th to endNight
46%
376
15%
1418
13%
354
53%
354
22%
854
August1st to 15thNight
44%
500
16%
1571
11%
498
49%
498
26%
982
August16th to endNight
51%
730
20%
1876
11%
730
54%
730
35%
1204
September1st to 15thNight
38%
720
19%
1857
9%
720
44%
720
31%
1206
September16th to endNight
45%
717
25%
1980
17%
717
53%
717
34%
1212
October1st to 15thNight
34%
720
22%
2007
11%
720
45%
720
26%
1290
October16th to endNight
24%
768
18%
2496
6%
768
39%
768
19%
1625
November1st to 15thNight
28%
760
20%
2472
10%
760
42%
760
21%
1597
November16th to endNight
24%
780
22%
2535
8%
780
40%
780
19%
1599
December1st to 15thNight
20%
780
17%
2714
5%
780
34%
780
16%
1762
December16th to endNight
14%
832
19%
2912
4%
832
31%
832
16%
1929

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%
49313
Night
16%6%24424446%41%
48940
Cloud CoverDay
17%6%25%424447%39%
49323
Night
16%6%25%424446%41%
48945
TransparencyDay
43%6%12%20%14%2
49001
Night
43%5%12%21%15%2
48770
SeeingDay
21%14%31%20%8%2
6307
Night
21%13%34%23%7%
15497

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%42%
1552
16th to endDay
16%6%24424447%42%
1664
February1st to 15thDay
17%7%35%435%46%7%33%
1796
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%8%38%
2367
16th to endDay
10%4245%36%46%7%44%
2324
September1st to 15thDay
13%5%24424447%45%
2103
16th to endDay
14%5%14323345%50%
1980
October1st to 15thDay
19%5%15%423346%43%
1949
16th to endDay
16%6%245%23446%43%
1728
November1st to 15thDay
20%7%3342334443%
1716
16th to endDay
16%5%2432435%5%44%
1755
December1st to 15thDay
17%6%35%5%24346%39%
1573
16th to endDay
23%6%25%424445%36%
1664
January1st to 15thNight
16%7%345%24345%41%
2716
16th to endNight
16%9%34433345%40%
2912
February1st to 15thNight
15%8%36%6%34445%38%
2364
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%44%
1581
16th to endNight
12%3144245%5%9%46%
1876
September1st to 15thNight
13%4245%1345%6%47%
1857
16th to endNight
14%5%13323446%51%
1980
October1st to 15thNight
18%5%23413346%45%
2007
16th to endNight
20%6%24423345%41%
2496
November1st to 15thNight
17%6%25%32335%444%
2472
16th to endNight
18%6%24424346%43%
2535
December1st to 15thNight
18%7%34433346%39%
2714
16th to endNight
17%8%35%32445%6%38%
2912

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%414445%42%
1552
16th to endDay
16%6%2442345%7%42%
1664
February1st to 15thDay
17%7%25%5%3445%8%33%
1796
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%38%
2367
16th to endDay
10%5%25%5%35%45%7%43%
2324
September1st to 15thDay
14%5%2442345%7%45%
2103
16th to endDay
14%5%23422335%50%
1980
October1st to 15thDay
19%5%14423346%43%
1949
16th to endDay
16%6%145%14447%43%
1728
November1st to 15thDay
20%6%34323335%43%
1716
16th to endDay
16%6%2442435%5%44%
1755
December1st to 15thDay
18%6%35%5%23446%39%
1573
16th to endDay
22%6%24424436%36%
1664
January1st to 15thNight
16%7%345%24335%41%
2716
16th to endNight
16%9%34433445%40%
2912
February1st to 15thNight
15%8%36%5%3445%5%37%
2357
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%44%
1581
16th to endNight
12%31443445%8%46%
1876
September1st to 15thNight
14%4245%2345%6%46%
1857
16th to endNight
14%5%23322446%51%
1980
October1st to 15thNight
18%5%23413446%45%
2007
16th to endNight
20%6%14423445%40%
2496
November1st to 15thNight
17%6%25%32335%5%44%
2472
16th to endNight
18%6%24323446%43%
2535
December1st to 15thNight
18%7%25%423346%38%
2714
16th to endNight
17%8%36%42445%6%38%
2912

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
43%5%10%24%12%3
1553
16th to endDay
40%6%13%24%13%1
1664
February1st to 15thDay
47%7%13%18%12%1
1799
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
42%7%14%22%12%1
2353
16th to endDay
37%7%12%24%16%1
2324
September1st to 15thDay
37%6%12%21%19%2
2103
16th to endDay
36%38%23%24%2
1980
October1st to 15thDay
43%410%24%14%3
1949
16th to endDay
40%6%12%23%15%1
1728
November1st to 15thDay
44%412%22%14%1
1716
16th to endDay
40%5%13%22%16%1
1755
December1st to 15thDay
44%416%16%16%
1573
16th to endDay
49%6%13%17%12%1
1664
January1st to 15thNight
45%412%21%14%2
2716
16th to endNight
45%412%19%15%2
2912
February1st to 15thNight
47%5%13%19%12%2
2365
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%15%1
1571
16th to endNight
33%7%13%27%17%
1876
September1st to 15thNight
37%6%13%22%18%
1857
16th to endNight
34%48%23%27%1
1980
October1st to 15thNight
39%5%12%22%15%3
2007
16th to endNight
44%413%23%13%
2496
November1st to 15thNight
42%6%11%20%17%2
2472
16th to endNight
42%412%23%14%2
2535
December1st to 15thNight
45%5%14%21%11%
2714
16th to endNight
46%5%11%21%13%
2912

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
22%31%27%16%2
90
16th to endDay
28%20%38%12%
96
February1st to 15thDay
26%21%36%12%2
264
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%9%32%28%14%2
313
16th to endDay
10%7%33%25%16%6%
332
September1st to 15thDay
19%7%32%22%13%5%
315
16th to endDay
20%6%25%21%13%13%
314
October1st to 15thDay
21%9%27%23%14%5%
314
16th to endDay
23%15%31%21%7%
288
November1st to 15thDay
25%14%30%19%8%2
280
16th to endDay
23%17%28%18%9%1
285
December1st to 15thDay
25%28%29%11%5%
103
16th to endDay
30%30%29%9%1
96
January1st to 15thNight
22%18%39%16%2
780
16th to endNight
22%19%37%17%2
832
February1st to 15thNight
21%18%41%17%1
760
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%
500
16th to endNight
13%325%39%16%1
730
September1st to 15thNight
16%5%34%30%12%
720
16th to endNight
18%5%26%25%20%3
717
October1st to 15thNight
21%10%28%25%11%2
720
16th to endNight
26%13%33%19%7%
768
November1st to 15thNight
21%12%33%22%9%1
760
16th to endNight
22%17%31%19%7%1
780
December1st to 15thNight
24%17%33%18%5%
780
16th to endNight
25%17%39%15%2
832
Page generated at 2018-02-15 10:58:43. Version ac04

Copyright 2018 A. Danko


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