Robinson Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Robinson Observatory clear sky chart from 2005-11-05 to 2017-03-25.

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
59%
15413
20%
45233
16%
15371
64%
15371
29%
28752

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
46%
719
20%
2327
15%
716
54%
716
25%
1455
January16th to endNight
45%
768
23%
2481
18%
768
54%
768
28%
1509
February1st to 15thNight
42%
701
24%
2103
15%
698
52%
698
33%
1240
February16th to endNight
44%
631
26%
1806
14%
631
55%
631
34%
1071
March1st to 15thNight
52%
720
29%
1980
18%
720
62%
720
43%
1102
March16th to endNight
54%
744
24%
2046
17%
744
60%
744
39%
1191
April1st to 15thNight
55%
658
24%
1811
18%
658
60%
658
39%
1049
April16th to endNight
58%
660
24%
1664
16%
660
62%
660
41%
1013
May1st to 15thNight
68%
557
27%
1547
20%
557
71%
557
41%
899
May16th to endNight
74%
513
19%
1538
16%
513
75%
513
31%
967
June1st to 15thNight
70%
495
15%
1485
12%
495
70%
495
24%
1017
June16th to endNight
71%
495
8%
1485
8%
495
71%
495
23%
1050
July1st to 15thNight
70%
465
7%
1395
6%
465
70%
465
17%
1052
July16th to endNight
76%
522
9%
1469
8%
489
78%
489
21%
1037
August1st to 15thNight
83%
494
8%
1474
8%
491
83%
491
26%
996
August16th to endNight
65%
682
8%
1846
7%
682
65%
682
19%
1369
September1st to 15thNight
66%
660
9%
1815
8%
660
66%
660
19%
1338
September16th to endNight
59%
657
11%
1815
11%
657
60%
657
17%
1375
October1st to 15thNight
69%
660
25%
1898
25%
660
71%
660
31%
1203
October16th to endNight
62%
704
26%
2112
25%
704
67%
704
31%
1308
November1st to 15thNight
60%
700
28%
2101
24%
700
67%
700
33%
1246
November16th to endNight
55%
720
29%
2199
22%
720
64%
720
32%
1321
December1st to 15thNight
51%
720
25%
2340
22%
720
59%
720
28%
1433
December16th to endNight
52%
768
22%
2496
20%
768
58%
768
28%
1511

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
9%5%36%7%46%6%6%8%34%
45701
Night
8%425%5%35%5%6%8%43%
45442
TransparencyDay
45%8%13%15%12%5%
45402
Night
36%8%15%19%14%6%
45245
SeeingDay
9%213%22%24%27%
5152
Night
9%217%32%28%8%
15420

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 15thDay
11%6%35%5%45%45%9%38%
1611
16th to endDay
11%5%345%2336%7%45%
1740
February1st to 15thDay
10%5%26%6%3435%5%44%
1750
16th to endDay
8%5%35%6%45%5%5%6%44%
1665
March1st to 15thDay
5%425%5%35%5%5%8%48%
1980
16th to endDay
8%425%5%45%448%45%
2045
April1st to 15thDay
7%425%7%46%46%9%41%
1807
16th to endDay
6%426%5%36%5%6%8%42%
1964
May1st to 15thDay
6%3245%36%6%6%7%46%
2081
16th to endDay
8%436%7%5%8%7%7%8%31%
2223
June1st to 15thDay
10%6%26%8%5%8%7%7%10%26%
2145
16th to endDay
9%5%38%8%5%9%7%8%9%24%
2145
July1st to 15thDay
10%7%48%9%5%9%8%7%8%20%
2145
16th to endDay
8%5%49%10%6%8%8%6%9%21%
2283
August1st to 15thDay
5%5%38%10%7%8%7%9%10%22%
2145
16th to endDay
9%7%49%9%5%7%8%7%8%20%
1989
September1st to 15thDay
9%7%38%10%5%8%7%8%8%22%
1815
16th to endDay
12%9%49%8%5%7%6%7%7%19%
1815
October1st to 15thDay
10%7%37%7%46%6%5%7%33%
1730
16th to endDay
10%5%25%6%45%45%7%43%
1760
November1st to 15thDay
6%425%337%5%6%8%45%
1757
16th to endDay
9%6%27%5%36%45%7%39%
1758
December1st to 15thDay
10%7%36%5%45%47%8%37%
1620
16th to endDay
8%426%6%35%6%6%7%41%
1728
January1st to 15thNight
10%5%35%5%36%45%7%42%
2327
16th to endNight
12%5%25%3245%6%6%45%
2481
February1st to 15thNight
10%5%25%423445%51%
2103
16th to endNight
8%3245%3335%7%51%
1806
March1st to 15thNight
6%2133235%5%8%56%
1980
16th to endNight
5%324424447%55%
2046
April1st to 15thNight
6%32442345%9%52%
1811
16th to endNight
6%42442345%8%52%
1664
May1st to 15thNight
5%214425%45%7%55%
1547
16th to endNight
6%315%5%36%6%6%9%45%
1538
June1st to 15thNight
7%6%26%6%26%7%9%9%34%
1485
16th to endNight
7%5%36%6%46%6%8%11%32%
1485
July1st to 15thNight
7%6%36%6%47%8%8%11%29%
1485
16th to endNight
6%5%35%6%48%8%8%11%32%
1577
August1st to 15thNight
3415%6%47%7%9%13%36%
1485
16th to endNight
9%6%36%6%46%7%7%10%30%
1846
September1st to 15thNight
6%436%7%47%6%8%9%33%
1815
16th to endNight
9%7%39%7%5%6%6%7%10%25%
1815
October1st to 15thNight
7%5%15%5%346%6%9%44%
1898
16th to endNight
10%4245%34448%47%
2112
November1st to 15thNight
6%325%5%35%5%5%7%48%
2101
16th to endNight
8%4245%35%45%8%48%
2199
December1st to 15thNight
9%4346%35%5%5%8%44%
2340
16th to endNight
8%5%25%426%5%6%8%43%
2496

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
42%5%8%18%17%7%
1612
16th to endDay
37%48%17%20%10%
1740
February1st to 15thDay
40%47%13%20%12%
1752
16th to endDay
39%6%9%14%20%9%
1665
March1st to 15thDay
33%6%10%24%17%7%
1980
16th to endDay
37%411%17%20%7%
2046
April1st to 15thDay
39%6%9%19%18%6%
1807
16th to endDay
37%6%11%17%19%8%
1964
May1st to 15thDay
33%8%12%20%18%6%
2081
16th to endDay
45%8%14%16%13%1
2227
June1st to 15thDay
50%10%16%18%3
2145
16th to endDay
52%12%20%11%3
2145
July1st to 15thDay
58%13%16%10%1
2006
16th to endDay
55%12%17%12%1
2128
August1st to 15thDay
50%14%24%9%1
2132
16th to endDay
57%13%17%8%1
1989
September1st to 15thDay
54%11%18%10%4
1815
16th to endDay
60%9%13%9%5%1
1815
October1st to 15thDay
47%6%10%13%14%7%
1730
16th to endDay
40%5%8%14%21%10%
1760
November1st to 15thDay
34%49%21%22%7%
1757
16th to endDay
42%5%6%16%18%10%
1758
December1st to 15thDay
43%8%10%17%15%5%
1620
16th to endDay
39%5%13%18%14%7%
1728
January1st to 15thNight
40%5%10%20%15%7%
2327
16th to endNight
38%49%18%19%9%
2481
February1st to 15thNight
34%310%16%19%14%
2112
16th to endNight
32%5%13%19%20%8%
1806
March1st to 15thNight
25%414%29%19%6%
1980
16th to endNight
27%6%13%22%20%9%
2046
April1st to 15thNight
28%6%16%22%17%8%
1811
16th to endNight
29%5%12%22%21%7%
1664
May1st to 15thNight
28%5%15%26%16%7%
1548
16th to endNight
32%10%16%24%15%
1540
June1st to 15thNight
40%11%18%25%4
1485
16th to endNight
41%12%22%18%3
1485
July1st to 15thNight
43%18%23%12%2
1395
16th to endNight
40%14%27%15%1
1469
August1st to 15thNight
32%16%36%13%1
1474
16th to endNight
44%14%25%13%1
1846
September1st to 15thNight
44%14%21%15%4
1815
16th to endNight
51%10%16%14%41
1815
October1st to 15thNight
36%7%11%19%18%6%
1898
16th to endNight
36%5%8%16%23%9%
2112
November1st to 15thNight
33%5%10%21%21%7%
2101
16th to endNight
34%5%8%20%19%11%
2199
December1st to 15thNight
37%5%12%23%13%6%
2340
16th to endNight
36%6%13%22%13%7%
2496

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
17%12%27%26%11%4
90
16th to endDay
13%13%32%21%14%4
96
February1st to 15thDay
415%26%26%18%7%
90
16th to endDay
12%9%33%30%13%
166
March1st to 15thDay
5%7%28%34%21%3
270
16th to endDay
11%424%25%26%6%
264
April1st to 15thDay
8%420%27%26%12%
210
16th to endDay
6%218%25%26%20%
210
May1st to 15thDay
7%111%25%30%23%
228
16th to endDay
7%10%17%28%34%
267
June1st to 15thDay
12%420%20%41%
255
16th to endDay
7%213%22%54%
255
July1st to 15thDay
7%18%21%61%
245
16th to endDay
7%5%11%21%54%
270
August1st to 15thDay
416%14%22%50%
253
16th to endDay
10%411%18%54%
268
September1st to 15thDay
11%412%21%49%
255
16th to endDay
14%315%25%40%
254
October1st to 15thDay
12%28%26%35%14%
255
16th to endDay
10%221%25%28%11%
272
November1st to 15thDay
6%116%32%33%9%
265
16th to endDay
10%420%36%24%3
228
December1st to 15thDay
10%434%38%11%1
90
16th to endDay
7%217%41%25%6%
96
January1st to 15thNight
12%5%29%34%16%1
720
16th to endNight
14%6%27%38%11%
768
February1st to 15thNight
13%433%34%13%
704
16th to endNight
10%6%33%40%9%
631
March1st to 15thNight
7%5%29%41%14%1
720
16th to endNight
7%427%39%19%1
744
April1st to 15thNight
6%327%41%20%1
658
16th to endNight
8%323%42%20%1
660
May1st to 15thNight
6%113%45%28%3
558
16th to endNight
8%8%33%41%8%
515
June1st to 15thNight
10%1423%47%11%
495
16th to endNight
10%318%42%24%
495
July1st to 15thNight
9%1313%45%26%
465
16th to endNight
6%112%50%28%
522
August1st to 15thNight
4114%52%27%
494
16th to endNight
11%417%40%25%
682
September1st to 15thNight
11%419%41%22%
660
16th to endNight
11%6%25%42%13%
657
October1st to 15thNight
10%18%32%40%6%
660
16th to endNight
13%213%32%32%5%
704
November1st to 15thNight
8%121%35%29%3
700
16th to endNight
10%323%41%19%1
720
December1st to 15thNight
9%324%37%23%2
720
16th to endNight
10%425%35%22%1
768
Page generated at 2017-03-26 13:16:41. Version ac04

Copyright 2017 A. Danko


Robinson Observatory Clear Sky Chart | Charts Home