This page made possible by the sponsorship of: Clyde Miller.

CMiller Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the CMiller Observatory clear sky chart from 2005-11-05 to 2017-12-02.

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
36%
15199
15%
47657
10%
15163
41%
15163
19%
33003

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%
716
10%
2419
4%
716
22%
716
9%
1913
January16th to endNight
17%
768
11%
2496
4%
768
25%
768
10%
1958
February1st to 15thNight
17%
701
7%
2287
2%
701
24%
701
10%
1789
February16th to endNight
24%
631
11%
1988
4%
631
32%
631
13%
1469
March1st to 15thNight
25%
720
13%
1989
7%
720
30%
720
16%
1524
March16th to endNight
32%
768
20%
2112
11%
768
40%
768
23%
1457
April1st to 15thNight
28%
715
15%
1841
6%
715
34%
715
22%
1338
April16th to endNight
39%
540
21%
1620
10%
540
47%
540
26%
1041
May1st to 15thNight
43%
540
16%
1620
10%
540
48%
540
24%
1075
May16th to endNight
47%
379
17%
1502
16%
379
56%
379
25%
864
June1st to 15thNight
46%
360
13%
1440
12%
360
54%
360
21%
854
June16th to endNight
54%
360
15%
1297
17%
360
60%
360
25%
770
July1st to 15thNight
62%
340
18%
1292
21%
340
68%
340
35%
653
July16th to endNight
62%
555
15%
1586
14%
522
64%
522
33%
934
August1st to 15thNight
68%
539
18%
1609
14%
536
70%
536
35%
949
August16th to endNight
64%
606
23%
1752
16%
606
67%
606
36%
1030
September1st to 15thNight
56%
720
22%
1850
13%
720
59%
720
34%
1187
September16th to endNight
58%
717
23%
1980
17%
717
62%
717
33%
1226
October1st to 15thNight
42%
720
18%
2160
16%
720
47%
720
24%
1421
October16th to endNight
26%
768
16%
2304
10%
768
35%
768
17%
1676
November1st to 15thNight
35%
760
17%
2549
15%
760
41%
760
20%
1688
November16th to endNight
25%
780
12%
2730
6%
780
32%
780
12%
1979
December1st to 15thNight
15%
728
6%
2546
2%
728
19%
728
8%
2010
December16th to endNight
13%
768
7%
2688
2%
768
19%
768
7%
2198

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%8%37%6%35%5%5%7%31%
48781
Night
15%8%36%5%3445%7%35%
47838
Cloud CoverDay
14%8%36%6%35%5%5%7%31%
48791
Night
15%8%36%5%3445%7%35%
47842
TransparencyDay
50%7%13%18%9%
48480
Night
48%6%12%20%11%1
47657
SeeingDay
17%8%26%24%16%8%
5776
Night
18%8%28%28%13%1
15207

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
18%13%6%7%6%446%47%18%
1518
16th to endDay
13%16%7%12%8%35%445%16%
1728
February1st to 15thDay
15%14%7%10%7%44347%18%
1575
16th to endDay
16%12%5%9%8%46%435%22%
1482
March1st to 15thDay
15%12%6%9%6%4445%6%25%
1960
16th to endDay
15%10%5%7%6%35%446%32%
2112
April1st to 15thDay
20%9%47%5%3435%7%28%
2117
16th to endDay
18%7%36%424346%38%
2340
May1st to 15thDay
16%7%27%5%35%5%47%35%
2331
16th to endDay
12%5%35%6%3445%7%40%
2613
June1st to 15thDay
13%5%25%5%345%5%8%38%
2520
16th to endDay
12%4245%36%5%7%9%37%
2657
July1st to 15thDay
8%425%5%46%5%7%10%40%
2583
16th to endDay
9%426%5%35%7%7%9%36%
2473
August1st to 15thDay
8%5%25%6%45%7%7%8%37%
2340
16th to endDay
12%5%26%5%35%46%9%39%
2438
September1st to 15thDay
13%5%36%5%35%5%5%8%36%
2109
16th to endDay
13%5%25%5%345%5%7%40%
1980
October1st to 15thDay
19%6%36%5%3445%7%32%
1800
16th to endDay
23%10%37%6%35%5%5%5%24%
1920
November1st to 15thDay
13%9%36%6%345%6%7%33%
1638
16th to endDay
19%12%5%7%5%35%5%5%8%22%
1560
December1st to 15thDay
16%17%5%9%7%35%446%19%
1451
16th to endDay
20%15%7%10%7%35%5%45%13%
1536
January1st to 15thNight
20%12%5%9%6%34446%21%
2419
16th to endNight
14%14%7%10%7%25%45%5%21%
2496
February1st to 15thNight
15%13%5%9%7%45%5%45%23%
2285
16th to endNight
15%10%5%8%7%35%447%26%
1988
March1st to 15thNight
18%9%37%6%35%45%6%28%
1977
16th to endNight
15%9%36%423445%40%
2112
April1st to 15thNight
19%8%35%423447%35%
1841
16th to endNight
11%5%25%6%34447%42%
1620
May1st to 15thNight
15%6%26%43445%8%38%
1620
16th to endNight
11%4145%2445%8%46%
1500
June1st to 15thNight
11%415%436%5%7%8%41%
1440
16th to endNight
9%4145%25%6%5%7%45%
1297
July1st to 15thNight
5%31442345%9%56%
1371
16th to endNight
7%415%4345%6%8%48%
1693
August1st to 15thNight
6%2144445%6%9%49%
1620
16th to endNight
8%325%324347%52%
1752
September1st to 15thNight
11%424424347%48%
1850
16th to endNight
10%4245%3345%7%47%
1980
October1st to 15thNight
18%5%245%2335%6%41%
2160
16th to endNight
20%8%36%5%35%45%6%31%
2304
November1st to 15thNight
15%7%25%5%345%6%7%35%
2549
16th to endNight
20%9%36%5%35%5%5%8%27%
2730
December1st to 15thNight
20%14%5%7%6%345%5%6%20%
2546
16th to endNight
21%13%7%9%7%35%45%6%15%
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
19%13%5%8%6%35%6%47%19%
1518
16th to endDay
14%15%8%11%9%25%5%5%416%
1728
February1st to 15thDay
16%13%8%11%7%25%446%19%
1575
16th to endDay
17%12%5%9%8%45%5%46%22%
1482
March1st to 15thDay
16%12%6%9%6%45%45%6%24%
1971
16th to endDay
15%9%5%6%5%35%45%5%32%
2111
April1st to 15thDay
20%8%46%6%34347%29%
2117
16th to endDay
18%7%36%424445%38%
2340
May1st to 15thDay
15%7%26%6%34447%35%
2331
16th to endDay
13%5%35%5%35%5%47%40%
2613
June1st to 15thDay
13%5%25%5%35%5%6%8%37%
2520
16th to endDay
12%4146%36%5%7%9%37%
2657
July1st to 15thDay
8%5%245%45%5%7%10%40%
2583
16th to endDay
9%5%26%5%36%6%7%9%36%
2473
August1st to 15thDay
9%5%26%5%46%6%8%8%37%
2340
16th to endDay
11%5%25%5%35%5%6%8%39%
2438
September1st to 15thDay
13%6%35%6%35%5%5%8%36%
2109
16th to endDay
13%5%25%5%345%5%8%39%
1980
October1st to 15thDay
18%6%36%6%34447%33%
1800
16th to endDay
23%10%27%6%345%5%5%25%
1920
November1st to 15thDay
14%8%26%6%35%46%8%33%
1638
16th to endDay
19%13%37%6%245%6%7%23%
1560
December1st to 15thDay
16%15%6%8%8%35%346%20%
1451
16th to endDay
20%15%7%10%6%45%5%5%414%
1536
January1st to 15thNight
20%12%6%9%6%3445%5%21%
2419
16th to endNight
14%14%7%10%7%345%5%6%21%
2496
February1st to 15thNight
15%13%6%9%7%35%5%5%5%23%
2278
16th to endNight
16%10%5%8%7%35%35%6%27%
1988
March1st to 15thNight
20%8%36%6%345%46%28%
1989
16th to endNight
15%9%45%423446%40%
2112
April1st to 15thNight
19%8%35%434447%35%
1841
16th to endNight
11%5%36%5%34448%42%
1620
May1st to 15thNight
15%5%36%5%345%5%7%37%
1619
16th to endNight
12%425%43345%8%46%
1500
June1st to 15thNight
10%5%15%435%5%6%9%41%
1440
16th to endNight
10%3245%35%5%6%7%45%
1297
July1st to 15thNight
5%21442345%9%55%
1371
16th to endNight
7%4245%245%6%8%49%
1693
August1st to 15thNight
6%224326%48%9%48%
1620
16th to endNight
8%315%42435%7%53%
1752
September1st to 15thNight
11%5%24424447%48%
1850
16th to endNight
10%4235%3446%7%47%
1980
October1st to 15thNight
17%6%2442335%7%41%
2160
16th to endNight
20%7%46%43445%6%31%
2304
November1st to 15thNight
15%6%35%5%246%6%7%35%
2549
16th to endNight
20%9%45%5%345%5%8%27%
2730
December1st to 15thNight
21%13%5%7%5%25%45%6%21%
2546
16th to endNight
21%13%7%9%6%345%5%5%16%
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
64%6%10%12%5%
1519
16th to endDay
68%6%10%9%4
1728
February1st to 15thDay
65%6%10%12%3
1577
16th to endDay
63%5%11%13%4
1482
March1st to 15thDay
59%6%12%15%5%
1971
16th to endDay
52%5%11%18%9%1
2112
April1st to 15thDay
55%5%11%16%10%
2117
16th to endDay
47%5%10%20%13%2
2340
May1st to 15thDay
48%6%12%20%11%
2331
16th to endDay
42%6%13%22%13%1
2617
June1st to 15thDay
41%7%14%22%12%1
2520
16th to endDay
40%8%14%22%13%
2657
July1st to 15thDay
35%8%12%24%16%1
2433
16th to endDay
40%9%16%21%11%1
2317
August1st to 15thDay
39%9%15%20%12%1
2327
16th to endDay
39%8%14%24%11%1
2438
September1st to 15thDay
43%7%13%22%12%
2109
16th to endDay
41%7%14%26%10%
1980
October1st to 15thDay
50%6%12%17%10%1
1800
16th to endDay
58%7%13%14%5%
1920
November1st to 15thDay
47%8%15%20%8%
1638
16th to endDay
57%7%15%13%5%
1560
December1st to 15thDay
64%7%14%10%2
1451
16th to endDay
71%8%8%9%2
1536
January1st to 15thNight
64%5%10%10%7%
2419
16th to endNight
62%6%10%14%5%
2496
February1st to 15thNight
62%6%12%13%5%
2287
16th to endNight
56%5%12%16%7%
1988
March1st to 15thNight
55%7%11%18%6%
1989
16th to endNight
46%5%8%22%15%2
2112
April1st to 15thNight
50%5%10%20%13%
1841
16th to endNight
40%6%10%20%18%3
1620
May1st to 15thNight
44%5%11%24%12%2
1620
16th to endNight
35%7%14%24%14%3
1502
June1st to 15thNight
37%8%12%24%15%1
1440
16th to endNight
36%6%13%23%17%1
1297
July1st to 15thNight
26%6%12%27%24%3
1292
16th to endNight
31%7%14%25%17%3
1586
August1st to 15thNight
27%10%16%30%12%2
1609
16th to endNight
30%6%12%31%16%2
1752
September1st to 15thNight
35%6%12%27%16%1
1850
16th to endNight
34%5%13%29%15%1
1980
October1st to 15thNight
42%6%10%24%15%
2160
16th to endNight
51%7%11%19%8%
2304
November1st to 15thNight
44%7%14%19%12%1
2549
16th to endNight
54%6%15%16%6%
2730
December1st to 15thNight
62%7%13%11%3
2546
16th to endNight
68%6%11%10%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
18%22%41%5%10%1
75
16th to endDay
32%17%35%13%1
96
February1st to 15thDay
21%22%44%12%
90
16th to endDay
22%22%34%20%
81
March1st to 15thDay
24%9%32%25%7%
261
16th to endDay
25%5%33%24%9%2
288
April1st to 15thDay
23%11%31%21%9%1
270
16th to endDay
20%9%26%22%13%7%
270
May1st to 15thDay
19%7%25%25%13%7%
288
16th to endDay
14%8%26%26%15%8%
331
June1st to 15thDay
15%7%26%30%15%3
315
16th to endDay
13%7%27%30%14%5%
452
July1st to 15thDay
10%5%22%28%22%10%
367
16th to endDay
9%221%30%24%11%
326
August1st to 15thDay
10%117%26%26%16%
313
16th to endDay
12%317%20%23%21%
332
September1st to 15thDay
12%415%23%28%15%
315
16th to endDay
14%5%15%20%26%18%
314
October1st to 15thDay
21%6%25%23%16%7%
315
16th to endDay
25%9%31%23%8%1
336
November1st to 15thDay
20%12%29%22%11%3
124
16th to endDay
25%16%35%14%5%2
90
December1st to 15thDay
23%23%34%11%6%
63
16th to endDay
25%25%42%6%1
64
January1st to 15thNight
25%18%32%18%5%
720
16th to endNight
22%13%35%23%4
768
February1st to 15thNight
23%15%35%21%3
704
16th to endNight
22%12%33%26%5%
631
March1st to 15thNight
23%12%32%25%6%
720
16th to endNight
17%10%32%27%11%
768
April1st to 15thNight
23%11%30%27%6%
715
16th to endNight
12%7%33%33%12%1
540
May1st to 15thNight
16%330%32%15%1
540
16th to endNight
14%328%34%17%1
380
June1st to 15thNight
12%329%39%15%
360
16th to endNight
10%326%44%15%
360
July1st to 15thNight
5%25%46%21%1
340
16th to endNight
9%218%44%22%2
555
August1st to 15thNight
6%15%44%28%3
539
16th to endNight
9%216%35%33%2
606
September1st to 15thNight
13%419%32%25%5%
720
16th to endNight
12%318%29%28%7%
717
October1st to 15thNight
19%7%24%27%17%3
720
16th to endNight
25%10%31%26%5%
768
November1st to 15thNight
18%8%31%26%13%1
760
16th to endNight
25%13%29%22%8%
780
December1st to 15thNight
28%14%32%19%4
728
16th to endNight
27%13%35%19%4
768
Page generated at 2017-12-03 11:16:41. Version ac04

Copyright 2017 A. Danko


CMiller Observatory Clear Sky Chart |Charts Home