R2 Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the R2 Observatory clear sky chart from 2005-11-05 to 2017-09-22.

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
28%
14823
14%
46672
7%
14785
35%
14785
17%
32338

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
8%
719
9%
2469
1%
716
17%
716
6%
1959
January16th to endNight
15%
768
10%
2496
3%
768
22%
768
8%
1953
February1st to 15thNight
11%
701
10%
2287
1%
701
22%
701
8%
1746
February16th to endNight
15%
631
13%
2015
4%
631
26%
631
11%
1480
March1st to 15thNight
18%
720
14%
1981
5%
720
25%
720
13%
1483
March16th to endNight
24%
768
21%
2112
8%
768
34%
768
22%
1412
April1st to 15thNight
19%
718
15%
1826
4%
718
25%
718
20%
1320
April16th to endNight
30%
543
20%
1623
8%
543
39%
543
24%
1060
May1st to 15thNight
38%
498
17%
1578
11%
498
46%
498
25%
1017
May16th to endNight
38%
374
17%
1497
13%
374
52%
374
26%
819
June1st to 15thNight
38%
360
13%
1437
10%
360
51%
360
20%
849
June16th to endNight
43%
360
15%
1260
13%
360
51%
360
28%
716
July1st to 15thNight
55%
340
17%
1262
19%
340
62%
340
33%
651
July16th to endNight
49%
495
16%
1527
13%
463
55%
463
32%
873
August1st to 15thNight
54%
539
18%
1609
10%
536
60%
536
36%
908
August16th to endNight
52%
612
23%
1758
12%
612
59%
612
36%
1025
September1st to 15thNight
47%
720
21%
1824
9%
720
53%
720
36%
1135
September16th to endNight
49%
685
22%
1906
15%
685
54%
685
33%
1179
October1st to 15thNight
32%
660
17%
1980
12%
660
40%
660
20%
1344
October16th to endNight
17%
704
11%
2112
3%
704
26%
704
12%
1605
November1st to 15thNight
27%
700
18%
2385
14%
700
34%
700
17%
1623
November16th to endNight
20%
720
11%
2520
6%
720
27%
720
10%
1896
December1st to 15thNight
12%
720
5%
2520
2%
720
16%
720
7%
2022
December16th to endNight
8%
768
6%
2688
1%
768
13%
768
5%
2263

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
15%9%47%6%35%45%7%30%
48200
Night
14%8%47%6%35%45%6%33%
46849
Cloud CoverDay
14%9%47%6%35%5%5%7%30%
48210
Night
14%9%47%6%35%45%6%33%
46853
TransparencyDay
52%412%19%10%
47895
Night
50%412%20%10%1
46672
SeeingDay
18%15%29%20%10%4
5608
Night
19%15%30%22%9%1
14828

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
14%15%7%10%8%46%45%5%17%
1468
16th to endDay
11%17%7%13%10%35%45%5%14%
1728
February1st to 15thDay
12%16%7%12%10%46%45%415%
1575
16th to endDay
17%14%6%9%5%445%45%23%
1455
March1st to 15thDay
13%11%5%9%9%34445%27%
1966
16th to endDay
13%11%47%6%25%33435%
2112
April1st to 15thDay
18%12%45%5%24447%30%
2127
16th to endDay
17%8%26%5%23446%37%
2340
May1st to 15thDay
16%7%36%5%245%47%35%
2373
16th to endDay
13%5%246%25%5%6%8%39%
2618
June1st to 15thDay
17%5%245%2447%9%35%
2520
16th to endDay
13%4146%35%5%6%9%36%
2698
July1st to 15thDay
9%425%6%36%5%6%9%39%
2619
16th to endDay
11%5%36%7%36%5%6%10%34%
2533
August1st to 15thDay
9%6%27%6%35%6%6%8%37%
2340
16th to endDay
12%5%25%5%36%6%6%8%36%
2432
September1st to 15thDay
16%6%26%5%4445%6%36%
2134
16th to endDay
15%5%26%6%35%448%36%
1867
October1st to 15thDay
20%7%37%7%35%345%32%
1650
16th to endDay
26%14%47%5%2435%5%20%
1760
November1st to 15thDay
13%12%47%5%26%45%6%29%
1469
16th to endDay
16%15%6%10%7%345%6%6%18%
1440
December1st to 15thDay
16%15%9%12%8%3446%413%
1440
16th to endDay
19%17%7%10%7%35%5%5%5%12%
1536
January1st to 15thNight
16%14%6%10%8%35%45%5%17%
2469
16th to endNight
11%11%6%12%10%5%6%5%5%6%18%
2496
February1st to 15thNight
13%12%5%8%9%45%5%5%7%22%
2285
16th to endNight
10%12%410%8%45%45%6%26%
2015
March1st to 15thNight
16%9%49%6%44335%31%
1969
16th to endNight
13%8%37%433345%41%
2112
April1st to 15thNight
17%9%36%5%2445%6%34%
1826
16th to endNight
12%9%35%5%3435%5%41%
1623
May1st to 15thNight
15%5%15%5%3445%8%39%
1578
16th to endNight
11%5%14324347%49%
1495
June1st to 15thNight
13%325%435%5%6%8%42%
1437
16th to endNight
10%335%4235%6%8%47%
1260
July1st to 15thNight
6%2245%24335%58%
1338
16th to endNight
8%3244345%7%7%48%
1633
August1st to 15thNight
6%314425%5%6%9%50%
1620
16th to endNight
9%41442435%7%51%
1758
September1st to 15thNight
12%4133235%6%6%49%
1824
16th to endNight
13%5%24423346%48%
1906
October1st to 15thNight
18%5%26%5%35%346%38%
1980
16th to endNight
21%11%36%5%45%6%5%6%24%
2112
November1st to 15thNight
16%9%35%5%35%5%5%7%33%
2385
16th to endNight
17%11%5%8%6%35%5%5%7%23%
2520
December1st to 15thNight
18%14%6%9%6%36%5%5%6%16%
2520
16th to endNight
19%13%10%12%7%45%45%412%
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%14%6%10%8%46%5%46%16%
1468
16th to endDay
11%16%8%12%9%45%5%5%5%14%
1728
February1st to 15thDay
13%15%7%11%10%5%6%44415%
1575
16th to endDay
16%15%5%9%6%35%5%45%23%
1455
March1st to 15thDay
14%11%5%10%8%35%345%26%
1977
16th to endDay
13%12%5%7%5%34335%35%
2111
April1st to 15thDay
18%12%46%425%45%6%29%
2127
16th to endDay
17%8%36%423446%38%
2340
May1st to 15thDay
16%7%36%5%35%446%36%
2373
16th to endDay
12%5%25%5%25%5%6%7%39%
2618
June1st to 15thDay
17%5%244345%7%9%35%
2520
16th to endDay
13%5%25%5%36%5%5%9%36%
2698
July1st to 15thDay
8%426%5%46%6%6%9%39%
2619
16th to endDay
10%5%36%6%46%6%6%9%34%
2533
August1st to 15thDay
8%6%37%5%35%5%7%9%37%
2340
16th to endDay
12%6%246%36%6%6%8%36%
2432
September1st to 15thDay
16%6%26%6%3445%7%36%
2134
16th to endDay
14%5%36%6%45%448%36%
1867
October1st to 15thDay
19%7%37%6%35%345%32%
1650
16th to endDay
25%14%47%7%33445%20%
1760
November1st to 15thDay
13%12%47%7%35%45%8%28%
1469
16th to endDay
16%14%7%10%7%445%5%6%17%
1440
December1st to 15thDay
17%16%8%12%7%35%5%4413%
1440
16th to endDay
19%14%8%10%7%35%5%5%5%12%
1536
January1st to 15thNight
17%15%6%11%7%35%445%17%
2469
16th to endNight
11%12%6%11%9%5%6%5%5%5%18%
2496
February1st to 15thNight
12%13%6%9%8%36%45%7%21%
2278
16th to endNight
12%12%5%10%7%45%5%5%7%25%
2015
March1st to 15thNight
16%10%5%8%7%34335%30%
1981
16th to endNight
12%9%46%5%33345%41%
2112
April1st to 15thNight
18%9%36%435%446%34%
1826
16th to endNight
13%9%36%424346%41%
1623
May1st to 15thNight
15%5%25%4345%5%8%39%
1577
16th to endNight
10%425%42335%7%50%
1495
June1st to 15thNight
13%3245%45%5%5%9%40%
1437
16th to endNight
9%326%3245%6%8%46%
1260
July1st to 15thNight
5%324434445%56%
1338
16th to endNight
7%3235%25%5%6%7%48%
1633
August1st to 15thNight
6%424325%6%6%9%49%
1620
16th to endNight
8%42342345%7%51%
1758
September1st to 15thNight
12%4234135%5%8%48%
1824
16th to endNight
12%5%245%2335%6%47%
1906
October1st to 15thNight
17%6%26%5%34346%37%
1980
16th to endNight
21%10%37%6%346%5%6%23%
2112
November1st to 15thNight
15%10%35%5%25%45%6%33%
2385
16th to endNight
17%11%5%8%7%345%5%6%23%
2520
December1st to 15thNight
18%15%6%8%7%35%5%5%5%16%
2520
16th to endNight
19%14%8%13%8%45%44412%
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
67%410%12%4
1469
16th to endDay
70%48%11%3
1728
February1st to 15thDay
70%47%14%2
1577
16th to endDay
62%49%15%7%1
1455
March1st to 15thDay
59%411%16%8%
1977
16th to endDay
52%39%18%14%1
2112
April1st to 15thDay
54%48%20%11%
2127
16th to endDay
46%310%22%14%1
2340
May1st to 15thDay
48%49%22%14%
2373
16th to endDay
41%5%14%22%14%2
2622
June1st to 15thDay
42%5%14%24%12%
2520
16th to endDay
41%5%14%24%13%
2698
July1st to 15thDay
38%6%13%25%15%1
2466
16th to endDay
44%5%13%23%10%1
2376
August1st to 15thDay
41%5%15%21%13%1
2327
16th to endDay
42%5%14%26%9%1
2432
September1st to 15thDay
45%412%25%10%1
2134
16th to endDay
47%311%26%9%
1867
October1st to 15thDay
54%49%20%10%
1650
16th to endDay
66%314%11%4
1760
November1st to 15thDay
53%5%14%16%8%
1469
16th to endDay
66%413%11%4
1440
December1st to 15thDay
72%412%8%1
1440
16th to endDay
71%410%10%2
1536
January1st to 15thNight
67%310%11%6%
2469
16th to endNight
64%412%14%3
2496
February1st to 15thNight
60%5%10%18%4
2287
16th to endNight
57%313%17%7%
2015
March1st to 15thNight
57%311%19%7%
1981
16th to endNight
45%310%22%16%2
2112
April1st to 15thNight
50%410%20%14%
1826
16th to endNight
43%311%20%17%2
1623
May1st to 15thNight
42%411%23%16%2
1578
16th to endNight
34%414%27%15%3
1497
June1st to 15thNight
40%5%11%24%16%1
1437
16th to endNight
34%5%14%29%16%
1260
July1st to 15thNight
29%411%29%23%2
1262
16th to endNight
31%6%14%28%16%2
1527
August1st to 15thNight
29%5%19%29%14%1
1609
16th to endNight
31%412%32%16%1
1758
September1st to 15thNight
33%415%30%13%1
1824
16th to endNight
35%413%33%12%
1906
October1st to 15thNight
47%410%23%12%1
1980
16th to endNight
58%5%13%16%6%
2112
November1st to 15thNight
50%413%21%9%1
2385
16th to endNight
59%5%14%16%3
2520
December1st to 15thNight
66%5%14%10%2
2520
16th to endNight
73%410%9%2
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
13%39%31%10%31
66
16th to endDay
30%30%28%10%1
96
February1st to 15thDay
23%38%28%7%1
90
16th to endDay
22%43%25%8%
81
March1st to 15thDay
20%27%29%15%6%
267
16th to endDay
24%18%31%17%7%1
288
April1st to 15thDay
24%18%32%14%8%1
270
16th to endDay
21%21%27%15%10%3
270
May1st to 15thDay
21%14%28%19%11%5%
288
16th to endDay
16%16%31%21%11%2
331
June1st to 15thDay
21%12%31%24%10%
315
16th to endDay
14%13%37%21%9%2
493
July1st to 15thDay
10%9%31%30%11%7%
400
16th to endDay
10%8%33%28%13%6%
326
August1st to 15thDay
8%6%30%25%17%11%
313
16th to endDay
13%9%21%25%17%12%
332
September1st to 15thDay
12%8%26%24%15%13%
315
16th to endDay
15%5%23%24%19%10%
278
October1st to 15thDay
19%13%30%18%12%5%
255
16th to endDay
33%20%26%15%2
272
November1st to 15thDay
12%17%38%24%32
78
16th to endDay
28%23%35%11%1
60
December1st to 15thDay
25%35%25%10%5%
60
16th to endDay
31%37%29%1
64
January1st to 15thNight
26%26%33%10%3
720
16th to endNight
17%20%35%20%5%
768
February1st to 15thNight
21%26%33%15%2
704
16th to endNight
21%21%35%18%3
631
March1st to 15thNight
23%24%30%19%2
720
16th to endNight
19%18%33%19%8%
768
April1st to 15thNight
24%17%34%19%3
718
16th to endNight
18%12%34%24%8%
543
May1st to 15thNight
17%8%27%31%12%2
498
16th to endNight
12%8%36%28%14%
375
June1st to 15thNight
14%9%30%33%11%
360
16th to endNight
10%6%33%34%15%
360
July1st to 15thNight
6%5%27%41%18%2
340
16th to endNight
9%6%29%35%17%2
495
August1st to 15thNight
6%426%37%22%2
539
16th to endNight
10%425%32%23%2
612
September1st to 15thNight
14%8%24%25%19%6%
720
16th to endNight
15%6%23%29%20%4
685
October1st to 15thNight
21%11%30%22%12%1
660
16th to endNight
26%19%30%17%5%
704
November1st to 15thNight
22%17%28%22%8%1
700
16th to endNight
24%21%27%20%5%
720
December1st to 15thNight
27%24%31%13%2
720
16th to endNight
27%23%31%14%3
768
Page generated at 2017-09-23 06:43:38. Version ac04

Copyright 2017 A. Danko


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