Robert Reeves Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Robert Reeves Observatory clear sky chart from 2005-11-06 to 2024-01-31.

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%
23793
25%
74568
17%
23738
55%
23738
31%
43172

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
38%
946
30%
2458
13%
946
48%
946
35%
1486
January11th to 20thNight
35%
903
27%
2423
12%
903
46%
903
31%
1475
January21st to endNight
35%
834
31%
2502
15%
834
48%
834
28%
1478
February1st to 10thNight
32%
720
29%
2160
12%
720
47%
720
30%
1231
February11th to 20thNight
30%
704
23%
2098
10%
700
41%
700
27%
1250
February21st to endNight
23%
592
27%
1776
8%
592
38%
592
26%
1051
March1st to 10thNight
28%
653
24%
2093
9%
653
42%
653
23%
1291
March11th to 20thNight
30%
540
23%
1980
14%
540
42%
540
22%
1186
March21st to endNight
26%
594
26%
2178
13%
594
43%
594
25%
1221
April1st to 10thNight
26%
540
25%
1980
12%
540
45%
540
25%
1115
April11th to 20thNight
22%
533
25%
1800
11%
533
40%
533
24%
1098
April21st to endNight
24%
540
27%
1777
13%
540
43%
540
26%
1083
May1st to 10thNight
28%
540
25%
1620
14%
540
41%
540
29%
990
May11th to 20thNight
35%
531
21%
1594
16%
531
45%
531
28%
1005
May21st to endNight
38%
583
20%
1745
13%
582
49%
582
26%
1115
June1st to 10thNight
61%
540
23%
1620
21%
540
69%
540
46%
840
June11th to 20thNight
50%
540
22%
1620
17%
540
60%
540
43%
868
June21st to endNight
56%
540
23%
1620
22%
540
61%
540
38%
925
July1st to 10thNight
64%
525
14%
1575
14%
525
66%
525
28%
997
July11th to 20thNight
73%
522
28%
1566
28%
522
79%
522
48%
806
July21st to endNight
78%
591
25%
1679
27%
558
83%
558
48%
862
August1st to 10thNight
81%
537
26%
1779
31%
534
84%
534
51%
819
August11th to 20thNight
78%
534
25%
1778
30%
534
81%
534
38%
954
August21st to endNight
72%
594
20%
1989
21%
594
75%
594
33%
1151
September1st to 10thNight
69%
540
19%
1980
22%
540
71%
540
28%
1160
September11th to 20thNight
65%
540
21%
1980
23%
540
68%
540
26%
1175
September21st to endNight
64%
540
25%
1980
26%
540
66%
540
29%
1112
October1st to 10thNight
68%
540
32%
1980
33%
540
70%
540
35%
1020
October11th to 20thNight
52%
540
32%
1980
26%
540
61%
540
31%
1076
October21st to endNight
48%
792
34%
2376
20%
792
57%
792
39%
1297
November1st to 10thNight
54%
787
28%
2267
17%
787
58%
787
35%
1341
November11th to 20thNight
49%
950
26%
2470
13%
950
55%
950
38%
1465
November21st to endNight
40%
950
28%
2470
13%
950
48%
950
31%
1573
December1st to 10thNight
44%
950
31%
2470
15%
950
52%
950
35%
1519
December11th to 20thNight
36%
949
27%
2902
12%
948
45%
948
25%
1837
December21st to endNight
39%
1039
18%
4303
13%
1026
47%
1026
24%
2300

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
14%5%2443445%7%48%
75015
Night
13%5%24323447%53%
75139
TransparencyDay
37%6%9%20%19%10%
74741
Night
33%5%11%20%19%13%
74933
SeeingDay
16%8%24%30%18%3
13692
Night
16%7%26%35%14%1
23805

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
13%7%24223336%55%
1707
11th to 20thDay
16%6%24432345%52%
1771
21st to endDay
14%5%14333447%53%
2080
February1st to 10thDay
15%7%245%2343451%
1800
11th to 20thDay
18%7%2442445%5%45%
1749
21st to endDay
16%5%23323446%53%
1480
March1st to 10thDay
19%7%25%433445%45%
1865
11th to 20thDay
17%8%35%333446%46%
1980
21st to endDay
18%6%24323346%49%
2178
April1st to 10thDay
16%7%3442345%7%45%
1980
11th to 20thDay
19%5%2442345%6%46%
2106
21st to endDay
17%5%35%423346%48%
2182
May1st to 10thDay
18%6%25%5%3446%6%42%
2340
11th to 20thDay
17%5%26%5%35%46%7%39%
2302
21st to endDay
19%6%25%6%45%5%7%7%35%
2531
June1st to 10thDay
8%4245%245%7%9%49%
2340
11th to 20thDay
10%5%25%5%35%5%5%9%46%
2340
21st to endDay
11%5%35%6%46%6%7%9%38%
2340
July1st to 10thDay
14%7%35%6%46%5%6%8%36%
2340
11th to 20thDay
8%323435%6%5%9%53%
2340
21st to endDay
7%3235%25%46%11%51%
2535
August1st to 10thDay
3313435%45%10%60%
2149
11th to 20thDay
7%424445%6%7%8%50%
2123
21st to endDay
7%5%25%6%45%6%6%8%45%
2364
September1st to 10thDay
13%6%36%7%46%5%5%7%39%
1980
11th to 20thDay
11%6%35%5%46%6%7%7%41%
1980
21st to endDay
11%425%6%446%5%7%46%
1980
October1st to 10thDay
9%425%5%35%45%7%52%
1980
11th to 20thDay
15%5%2432345%6%50%
1961
21st to endDay
15%5%24313335%56%
1980
November1st to 10thDay
16%7%25%423347%47%
1806
11th to 20thDay
13%7%25%42345%5%50%
1710
21st to endDay
18%5%34423345%48%
1710
December1st to 10thDay
15%7%34323446%50%
1710
11th to 20thDay
16%9%34434345%47%
2161
21st to endDay
15%6%2331234457%
3135
January1st to 10thNight
14%5%23423335%56%
2458
11th to 20thNight
15%6%23323345%53%
2423
21st to endNight
16%7%24323345%51%
2502
February1st to 10thNight
14%6%2322335%6%53%
2160
11th to 20thNight
17%6%23323446%51%
2098
21st to endNight
17%5%24423347%49%
1776
March1st to 10thNight
17%7%2433335%7%45%
2093
11th to 20thNight
17%6%245%34435%48%
1980
21st to endNight
15%6%23323446%52%
2178
April1st to 10thNight
11%6%25%42345%7%51%
1980
11th to 20thNight
18%425%324345%49%
1800
21st to endNight
18%5%24423346%50%
1777
May1st to 10thNight
14%5%2442445%7%48%
1620
11th to 20thNight
15%6%35%43435%7%46%
1593
21st to endNight
18%5%2442345%9%43%
1745
June1st to 10thNight
431322346%9%61%
1620
11th to 20thNight
7%32332445%8%59%
1620
21st to endNight
9%32442445%10%52%
1620
July1st to 10thNight
11%5%245%45%6%6%10%43%
1620
11th to 20thNight
432232446%9%62%
1620
21st to endNight
5%2233235%5%10%59%
1778
August1st to 10thNight
3213322348%68%
1790
11th to 20thNight
6%3135%235%7%10%55%
1778
21st to endNight
8%5%24435%5%7%11%48%
1989
September1st to 10thNight
10%5%34435%5%6%8%47%
1980
11th to 20thNight
12%6%35%5%2445%8%46%
1980
21st to endNight
10%5%15%5%3445%7%52%
1980
October1st to 10thNight
8%5%23323346%59%
1980
11th to 20thNight
16%423322347%54%
1980
21st to endNight
16%41321222463%
2376
November1st to 10thNight
14%6%24323246%55%
2267
11th to 20thNight
11%6%2332335%6%56%
2470
21st to endNight
18%5%2332345%6%48%
2470
December1st to 10thNight
14%6%23323347%54%
2470
11th to 20thNight
17%7%24423335%49%
3036
21st to endNight
18%6%22212236%54%
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
33%26%17%22%19%
1708
11th to 20thDay
38%25%16%22%18%
1771
21st to endDay
34%46%14%25%18%
2080
February1st to 10thDay
39%46%12%22%19%
1800
11th to 20thDay
42%36%16%19%14%
1759
21st to endDay
35%37%16%20%19%
1480
March1st to 10thDay
43%37%15%19%13%
1865
11th to 20thDay
42%46%14%16%18%
1980
21st to endDay
39%47%17%19%14%
2178
April1st to 10thDay
40%5%8%16%18%13%
1980
11th to 20thDay
39%5%7%18%18%14%
2106
21st to endDay
40%47%18%18%13%
2182
May1st to 10thDay
42%6%9%17%19%8%
2340
11th to 20thDay
43%7%8%19%18%4
2306
21st to endDay
47%7%10%19%15%2
2531
June1st to 10thDay
31%7%13%26%20%3
2340
11th to 20thDay
36%6%11%25%16%5%
2340
21st to endDay
40%8%11%22%15%4
2340
July1st to 10thDay
42%9%14%23%11%1
2276
11th to 20thDay
28%7%15%28%20%2
2271
21st to endDay
24%8%22%33%13%
2394
August1st to 10thDay
20%6%16%38%19%1
2136
11th to 20thDay
30%9%16%30%13%3
2123
21st to endDay
34%9%14%27%13%3
2364
September1st to 10thDay
44%7%10%18%16%5%
1980
11th to 20thDay
40%9%11%19%16%5%
1980
21st to endDay
37%6%9%19%19%9%
1980
October1st to 10thDay
33%5%10%22%23%7%
1980
11th to 20thDay
35%5%9%15%20%16%
1961
21st to endDay
32%4416%24%20%
1980
November1st to 10thDay
39%5%8%19%17%11%
1806
11th to 20thDay
38%46%17%19%16%
1710
21st to endDay
41%5%415%20%14%
1710
December1st to 10thDay
37%5%8%17%23%10%
1710
11th to 20thDay
42%45%11%21%17%
2159
21st to endDay
32%35%15%30%15%
3135
January1st to 10thNight
32%35%15%23%21%
2458
11th to 20thNight
36%36%16%22%18%
2423
21st to endNight
37%35%14%21%21%
2502
February1st to 10thNight
34%37%14%21%21%
2160
11th to 20thNight
36%36%16%20%18%
2098
21st to endNight
37%48%13%20%19%
1776
March1st to 10thNight
39%5%8%16%18%14%
2093
11th to 20thNight
40%5%7%12%17%19%
1980
21st to endNight
34%5%9%18%17%16%
2178
April1st to 10thNight
35%5%10%17%17%16%
1980
11th to 20thNight
38%5%8%14%17%17%
1800
21st to endNight
39%5%9%18%17%13%
1777
May1st to 10thNight
35%6%12%19%16%11%
1620
11th to 20thNight
39%6%9%25%16%5%
1594
21st to endNight
39%7%15%24%13%2
1746
June1st to 10thNight
19%8%18%31%21%3
1620
11th to 20thNight
24%6%15%28%21%5%
1620
21st to endNight
29%7%19%27%16%4
1620
July1st to 10thNight
36%9%19%25%9%1
1575
11th to 20thNight
18%8%18%31%22%2
1566
21st to endNight
18%8%26%36%12%1
1679
August1st to 10thNight
16%7%20%39%18%1
1779
11th to 20thNight
23%10%21%29%15%3
1778
21st to endNight
30%9%20%25%13%3
1989
September1st to 10thNight
35%7%14%22%17%6%
1980
11th to 20thNight
36%7%18%20%14%4
1980
21st to endNight
32%7%11%21%19%10%
1980
October1st to 10thNight
27%5%11%25%20%10%
1980
11th to 20thNight
33%410%17%21%16%
1980
21st to endNight
29%25%16%26%22%
2376
November1st to 10thNight
33%47%19%23%14%
2267
11th to 20thNight
31%48%19%20%17%
2470
21st to endNight
37%48%15%20%16%
2470
December1st to 10thNight
33%5%9%18%22%14%
2470
11th to 20thNight
39%45%14%16%22%
3037
21st to endNight
34%35%14%27%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
23%15%38%17%6%1
270
11th to 20thDay
27%12%33%20%6%1
270
21st to endDay
21%20%33%20%6%
294
February1st to 10thDay
30%12%32%19%7%
240
11th to 20thDay
30%15%33%16%5%
240
21st to endDay
27%21%35%14%3
198
March1st to 10thDay
25%19%42%13%1
240
11th to 20thDay
26%20%37%14%3
240
21st to endDay
23%17%44%14%11
264
April1st to 10thDay
27%15%38%19%1
240
11th to 20thDay
19%19%41%17%3
384
21st to endDay
18%15%44%18%4
442
May1st to 10thDay
23%10%40%22%6%
603
11th to 20thDay
21%8%34%29%7%1
625
21st to endDay
22%8%33%27%9%1
679
June1st to 10thDay
8%420%47%20%2
630
11th to 20thDay
11%322%46%16%2
630
21st to endDay
12%317%37%26%6%
630
July1st to 10thDay
14%411%36%30%5%
621
11th to 20thDay
7%7%44%36%6%
618
21st to endDay
6%27%42%37%6%
673
August1st to 10thDay
216%47%36%8%
447
11th to 20thDay
8%17%40%35%8%
437
21st to endDay
7%35%36%40%9%
483
September1st to 10thDay
11%19%29%40%10%
270
11th to 20thDay
7%17%34%45%7%
270
21st to endDay
11%310%33%38%5%
270
October1st to 10thDay
9%414%43%24%6%
270
11th to 20thDay
13%5%23%38%19%2
270
21st to endDay
25%12%25%24%12%2
297
November1st to 10thDay
21%6%35%26%11%1
270
11th to 20thDay
24%9%29%25%8%5%
270
21st to endDay
28%16%31%15%9%1
270
December1st to 10thDay
21%12%30%26%10%1
270
11th to 20thDay
26%16%30%21%7%
270
21st to endDay
21%12%35%24%6%1
297
January1st to 10thNight
18%11%28%34%8%1
950
11th to 20thNight
22%10%28%32%7%
903
21st to endNight
24%9%27%31%8%
834
February1st to 10thNight
23%11%31%29%7%1
720
11th to 20thNight
23%12%32%28%5%
704
21st to endNight
23%13%38%24%2
592
March1st to 10thNight
24%12%33%26%4
653
11th to 20thNight
22%10%34%29%5%
540
21st to endNight
19%11%42%23%5%
594
April1st to 10thNight
13%12%45%26%3
540
11th to 20thNight
20%14%43%21%2
533
21st to endNight
20%10%44%21%5%
540
May1st to 10thNight
15%13%43%25%4
540
11th to 20thNight
19%8%34%32%7%
531
21st to endNight
18%8%32%33%8%
584
June1st to 10thNight
6%228%48%16%
540
11th to 20thNight
8%236%45%9%
540
21st to endNight
10%326%42%19%1
540
July1st to 10thNight
11%314%50%21%2
525
11th to 20thNight
5%214%51%26%2
522
21st to endNight
6%110%53%29%2
591
August1st to 10thNight
319%52%33%2
537
11th to 20thNight
5%16%49%36%2
534
21st to endNight
7%29%43%35%4
594
September1st to 10thNight
9%28%42%36%3
540
11th to 20thNight
13%19%41%33%3
540
21st to endNight
10%313%37%32%4
540
October1st to 10thNight
9%314%44%28%2
540
11th to 20thNight
17%5%21%35%20%2
540
21st to endNight
17%8%25%27%21%2
792
November1st to 10thNight
18%5%19%37%18%2
787
11th to 20thNight
15%7%23%37%15%2
950
21st to endNight
22%10%23%33%11%1
950
December1st to 10thNight
19%7%26%35%12%1
950
11th to 20thNight
25%10%25%32%8%
950
21st to endNight
20%10%26%35%8%
1045
Page generated at 2024-01-28 04:26:32. Version ac07

Copyright 2024 Attilla Danko


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