Joseph H. Rogers Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Joseph H. Rogers 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
34%
15956
12%
46695
8%
15912
37%
15912
18%
34401

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
16%
900
3%
2506
2%
895
18%
895
6%
2222
January16th to endNight
17%
960
6%
2688
3%
960
19%
960
7%
2351
February1st to 15thNight
19%
760
6%
2280
3%
758
22%
758
9%
1917
February16th to endNight
23%
631
9%
1893
5%
631
27%
631
10%
1545
March1st to 15thNight
31%
720
15%
2140
9%
720
35%
720
19%
1537
March16th to endNight
36%
720
18%
2064
13%
720
40%
720
22%
1434
April1st to 15thNight
29%
539
15%
1797
10%
539
37%
539
18%
1236
April16th to endNight
37%
540
20%
1623
11%
540
44%
540
25%
1068
May1st to 15thNight
37%
540
14%
1620
9%
540
44%
540
21%
1118
May16th to endNight
45%
562
15%
1499
8%
561
52%
561
31%
953
June1st to 15thNight
45%
540
13%
1440
7%
540
48%
540
29%
949
June16th to endNight
54%
540
13%
1440
8%
540
57%
540
34%
900
July1st to 15thNight
64%
510
16%
1360
11%
510
67%
510
43%
788
July16th to endNight
58%
564
17%
1417
11%
531
61%
531
39%
843
August1st to 15thNight
64%
527
21%
1518
16%
524
67%
524
37%
860
August16th to endNight
57%
525
18%
1646
16%
525
61%
525
31%
973
September1st to 15thNight
52%
550
18%
1705
15%
550
55%
550
29%
1049
September16th to endNight
52%
657
20%
1815
15%
657
54%
657
30%
1153
October1st to 15thNight
38%
660
18%
1871
12%
660
44%
660
22%
1326
October16th to endNight
26%
704
10%
2288
7%
704
30%
704
13%
1737
November1st to 15thNight
27%
700
15%
2276
12%
700
33%
700
15%
1667
November16th to endNight
20%
747
8%
2376
6%
747
23%
747
9%
1967
December1st to 15thNight
13%
900
2%
2700
1%
900
15%
900
6%
2411
December16th to endNight
13%
960
5%
2733
1%
960
16%
960
7%
2397

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%10%47%6%3445%6%31%
47278
Night
14%11%5%8%7%34446%28%
46863
Cloud CoverDay
14%10%47%6%3445%6%31%
47287
Night
14%11%5%8%7%34446%28%
46868
TransparencyDay
53%311%21%10%1
46964
Night
56%311%19%8%
46695
SeeingDay
18%7%26%27%15%4
5868
Night
20%7%27%31%11%1
15958

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%17%10%14%10%6%5%2448%
1432
16th to endDay
11%16%10%17%10%7%7%4337%
1536
February1st to 15thDay
11%14%8%12%14%6%8%33311%
1579
16th to endDay
11%15%9%13%11%5%6%44413%
1580
March1st to 15thDay
11%11%5%11%9%3445%6%26%
1809
16th to endDay
14%10%5%7%6%3445%6%30%
2169
April1st to 15thDay
19%13%3442435%5%32%
2151
16th to endDay
16%10%35%424446%34%
2337
May1st to 15thDay
17%7%36%6%34446%36%
2331
16th to endDay
10%6%25%435%46%7%43%
2615
June1st to 15thDay
13%5%25%5%3445%7%41%
2520
16th to endDay
11%5%25%6%25%46%9%40%
2520
July1st to 15thDay
10%41443445%8%47%
2520
16th to endDay
9%4244345%6%9%45%
2655
August1st to 15thDay
8%4245%446%6%8%43%
2345
16th to endDay
13%6%25%43335%7%43%
2204
September1st to 15thDay
15%5%25%5%3445%8%39%
1914
16th to endDay
15%5%34425%5%5%9%39%
1815
October1st to 15thDay
20%8%36%6%34446%31%
1758
16th to endDay
23%15%48%6%44346%17%
1584
November1st to 15thDay
14%16%5%7%6%3345%7%25%
1582
16th to endDay
16%23%8%10%7%3333413%
1576
December1st to 15thDay
15%20%11%16%12%333238%
1260
16th to endDay
17%22%12%11%7%443338%
1486
January1st to 15thNight
15%16%10%12%11%5%6%32311%
2506
16th to endNight
10%15%8%14%12%7%7%44410%
2688
February1st to 15thNight
11%15%8%11%13%5%6%43415%
2278
16th to endNight
12%14%7%16%8%35%44417%
1893
March1st to 15thNight
11%10%5%9%5%345%46%32%
2127
16th to endNight
13%9%5%6%6%24346%34%
2064
April1st to 15thNight
20%11%46%32345%6%32%
1797
16th to endNight
17%7%26%423445%40%
1623
May1st to 15thNight
15%6%27%6%45%6%6%7%32%
1620
16th to endNight
11%5%35%4245%5%8%42%
1497
June1st to 15thNight
13%6%25%5%345%5%7%40%
1440
16th to endNight
8%5%25%5%35%46%9%43%
1440
July1st to 15thNight
8%42332435%9%51%
1440
16th to endNight
7%424435%448%50%
1513
August1st to 15thNight
6%3245%345%6%9%48%
1527
16th to endNight
11%6%25%433347%47%
1646
September1st to 15thNight
13%6%245%33346%45%
1705
16th to endNight
15%5%25%42335%7%43%
1815
October1st to 15thNight
19%9%46%5%23346%34%
1871
16th to endNight
21%11%47%7%44446%23%
2288
November1st to 15thNight
14%14%5%6%7%34446%27%
2276
16th to endNight
17%19%7%10%6%45%446%14%
2376
December1st to 15thNight
15%19%11%14%10%45%3338%
2700
16th to endNight
16%19%10%12%9%4443410%
2733

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
14%18%10%14%10%5%5%3439%
1432
16th to endDay
11%17%9%15%11%6%8%4337%
1536
February1st to 15thDay
11%15%8%12%15%5%7%43411%
1579
16th to endDay
11%15%9%13%11%46%5%4413%
1580
March1st to 15thDay
11%11%410%9%445%5%5%26%
1819
16th to endDay
14%10%5%6%6%25%45%6%30%
2168
April1st to 15thDay
20%12%35%424445%31%
2151
16th to endDay
16%10%36%42435%6%34%
2337
May1st to 15thDay
17%7%36%6%34446%36%
2331
16th to endDay
11%6%2443445%7%43%
2615
June1st to 15thDay
13%6%25%4345%5%7%40%
2520
16th to endDay
11%5%25%5%345%6%9%39%
2520
July1st to 15thDay
11%4234345%5%9%46%
2520
16th to endDay
10%41442446%9%44%
2655
August1st to 15thDay
8%5%25%6%25%5%7%9%42%
2345
16th to endDay
13%7%15%5%2435%7%42%
2204
September1st to 15thDay
15%426%43345%8%39%
1914
16th to endDay
15%5%34435%5%6%8%37%
1815
October1st to 15thDay
20%8%46%5%34446%31%
1758
16th to endDay
24%14%39%7%3445%5%17%
1584
November1st to 15thDay
15%15%5%6%5%4435%7%25%
1582
16th to endDay
15%24%8%10%7%2333414%
1576
December1st to 15thDay
16%19%11%17%10%333228%
1260
16th to endDay
17%22%12%11%8%443338%
1486
January1st to 15thNight
15%17%10%14%10%45%42311%
2506
16th to endNight
10%15%8%13%12%6%7%44410%
2688
February1st to 15thNight
11%14%8%12%13%6%5%5%3315%
2271
16th to endNight
13%14%6%15%9%45%44417%
1893
March1st to 15thNight
12%10%5%7%6%35%445%32%
2140
16th to endNight
13%9%6%6%6%35%35%6%34%
2064
April1st to 15thNight
20%11%46%31445%6%31%
1797
16th to endNight
17%7%35%423346%41%
1623
May1st to 15thNight
14%6%26%6%36%6%5%7%32%
1619
16th to endNight
12%5%36%32445%9%42%
1497
June1st to 15thNight
13%5%25%5%25%5%5%7%40%
1440
16th to endNight
9%425%4345%6%10%42%
1440
July1st to 15thNight
8%5%23325%349%51%
1440
16th to endNight
7%3245%3445%8%49%
1513
August1st to 15thNight
6%315%5%345%6%8%48%
1527
16th to endNight
11%6%25%424347%47%
1646
September1st to 15thNight
14%6%345%24345%45%
1705
16th to endNight
15%6%245%33348%43%
1815
October1st to 15thNight
19%9%37%5%23346%34%
1871
16th to endNight
21%11%48%7%34346%23%
2288
November1st to 15thNight
14%14%5%7%6%35%346%27%
2276
16th to endNight
17%19%7%9%7%44445%14%
2376
December1st to 15thNight
15%20%10%14%10%45%3338%
2700
16th to endNight
15%20%10%13%9%4444410%
2733

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
80%36%7%1
1433
16th to endDay
82%25%7%1
1536
February1st to 15thDay
76%28%10%1
1581
16th to endDay
73%27%13%3
1580
March1st to 15thDay
57%411%17%6%
1819
16th to endDay
53%312%22%5%1
2169
April1st to 15thDay
53%29%22%10%
2151
16th to endDay
50%310%16%17%2
2337
May1st to 15thDay
49%38%25%10%2
2331
16th to endDay
38%312%27%15%1
2619
June1st to 15thDay
41%312%27%14%
2520
16th to endDay
40%414%25%13%1
2520
July1st to 15thDay
33%312%30%18%1
2371
16th to endDay
34%5%12%27%18%2
2488
August1st to 15thDay
35%5%12%32%13%
2330
16th to endDay
40%310%27%14%2
2204
September1st to 15thDay
42%311%28%12%
1914
16th to endDay
41%317%25%11%
1815
October1st to 15thDay
53%310%22%9%
1758
16th to endDay
68%312%11%3
1584
November1st to 15thDay
58%311%18%7%
1582
16th to endDay
75%211%9%1
1576
December1st to 15thDay
83%16%7%
1260
16th to endDay
81%18%6%1
1486
January1st to 15thNight
79%27%8%1
2506
16th to endNight
77%38%9%1
2688
February1st to 15thNight
72%27%13%2
2280
16th to endNight
69%210%13%3
1893
March1st to 15thNight
53%312%19%10%
2140
16th to endNight
50%212%23%9%
2064
April1st to 15thNight
52%28%22%11%1
1797
16th to endNight
46%210%21%16%2
1623
May1st to 15thNight
49%410%22%10%2
1620
16th to endNight
38%413%26%14%2
1499
June1st to 15thNight
41%413%25%14%1
1440
16th to endNight
36%416%25%15%1
1440
July1st to 15thNight
29%313%31%19%2
1360
16th to endNight
31%314%31%17%
1417
August1st to 15thNight
31%416%34%13%
1518
16th to endNight
37%214%28%15%1
1646
September1st to 15thNight
39%313%26%15%
1705
16th to endNight
40%315%31%9%
1815
October1st to 15thNight
52%28%24%11%
1871
16th to endNight
61%313%15%5%
2288
November1st to 15thNight
57%312%17%7%
2276
16th to endNight
72%211%10%2
2376
December1st to 15thNight
81%27%7%1
2700
16th to endNight
78%29%7%2
2733

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%10%38%26%6%
90
16th to endDay
34%325%28%8%1
96
February1st to 15thDay
16%18%43%17%3
90
16th to endDay
22%9%43%14%9%
81
March1st to 15thDay
20%16%26%24%11%
109
16th to endDay
26%5%20%31%13%1
288
April1st to 15thDay
30%5%25%27%7%3
270
16th to endDay
21%5%33%21%14%3
270
May1st to 15thDay
20%10%27%24%12%4
288
16th to endDay
14%9%33%25%13%4
515
June1st to 15thDay
17%5%32%27%14%3
495
16th to endDay
12%6%31%30%13%5%
495
July1st to 15thDay
12%5%23%32%19%6%
475
16th to endDay
10%5%25%32%18%7%
515
August1st to 15thDay
11%316%30%25%11%
354
16th to endDay
21%7%12%25%25%7%
268
September1st to 15thDay
17%120%25%22%12%
255
16th to endDay
16%5%16%34%20%6%
254
October1st to 15thDay
25%8%21%30%11%3
239
16th to endDay
21%10%41%21%4
96
November1st to 15thDay
17%12%27%28%10%3
90
16th to endDay
28%17%22%25%5%
87
December1st to 15thDay
30%26%26%13%3
60
16th to endDay
30%21%37%10%
88
January1st to 15thNight
24%10%31%25%7%
900
16th to endNight
18%10%35%27%7%1
960
February1st to 15thNight
20%8%33%30%6%
761
16th to endNight
22%11%27%30%7%
631
March1st to 15thNight
17%9%32%29%9%
720
16th to endNight
18%7%27%35%9%1
720
April1st to 15thNight
26%7%30%27%7%
539
16th to endNight
21%6%30%31%9%1
540
May1st to 15thNight
19%6%28%34%10%
540
16th to endNight
14%5%27%35%15%
563
June1st to 15thNight
16%5%23%37%15%1
540
16th to endNight
11%224%42%17%2
540
July1st to 15thNight
11%216%41%25%1
510
16th to endNight
8%121%40%24%2
564
August1st to 15thNight
8%116%44%26%3
527
16th to endNight
13%216%40%24%2
525
September1st to 15thNight
19%318%32%20%5%
550
16th to endNight
19%317%34%21%4
657
October1st to 15thNight
25%322%31%15%1
660
16th to endNight
29%10%25%26%6%
704
November1st to 15thNight
24%9%30%26%9%
700
16th to endNight
29%10%30%24%4
747
December1st to 15thNight
25%13%35%21%4
900
16th to endNight
25%8%34%25%41
960
Page generated at 2017-08-13 14:16:15. Version ac04

Copyright 2017 A. Danko


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