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 2017-05-24.

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
35%
14586
14%
45724
9%
14550
41%
14550
19%
31802

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
25%
701
10%
1789
February16th to endNight
23%
631
11%
1988
4%
631
31%
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
29%
715
15%
1841
6%
715
34%
715
22%
1338
April16th to endNight
40%
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
48%
365
17%
1446
15%
365
57%
365
25%
825
June1st to 15thNight
46%
330
14%
1320
13%
330
55%
330
21%
780
June16th to endNight
54%
330
15%
1189
17%
330
59%
330
26%
698
July1st to 15thNight
64%
310
19%
1178
22%
310
70%
310
36%
591
July16th to endNight
62%
514
14%
1461
12%
481
64%
481
33%
859
August1st to 15thNight
67%
494
18%
1474
14%
491
70%
491
34%
881
August16th to endNight
63%
555
21%
1605
15%
555
66%
555
36%
949
September1st to 15thNight
55%
660
22%
1696
14%
660
58%
660
33%
1097
September16th to endNight
57%
657
20%
1815
15%
657
61%
657
32%
1136
October1st to 15thNight
42%
660
19%
1980
16%
660
48%
660
25%
1298
October16th to endNight
25%
704
14%
2112
8%
704
33%
704
16%
1556
November1st to 15thNight
35%
700
18%
2348
15%
700
41%
700
21%
1533
November16th to endNight
25%
720
11%
2520
7%
720
32%
720
12%
1851
December1st to 15thNight
15%
720
6%
2520
2%
720
19%
720
8%
1986
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
15%8%47%6%35%5%5%7%31%
46541
Night
15%8%36%5%3445%7%34%
45905
Cloud CoverDay
15%8%46%6%35%5%5%7%31%
46551
Night
15%8%46%5%3445%7%34%
45909
TransparencyDay
50%7%13%18%9%
46240
Night
48%6%12%19%11%1
45724
SeeingDay
17%8%26%24%15%7%
5054
Night
18%9%29%28%12%1
14594

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%246%3445%7%41%
2512
June1st to 15thDay
14%5%25%6%345%5%8%37%
2310
16th to endDay
12%4235%36%5%7%9%38%
2435
July1st to 15thDay
8%425%5%46%5%7%10%40%
2368
16th to endDay
9%425%5%35%7%7%9%37%
2291
August1st to 15thDay
8%5%25%6%45%6%7%8%37%
2145
16th to endDay
12%5%26%5%35%46%9%38%
2234
September1st to 15thDay
14%6%36%5%35%5%5%8%35%
1933
16th to endDay
14%5%25%5%345%6%7%38%
1815
October1st to 15thDay
18%6%36%5%345%5%7%33%
1650
16th to endDay
24%10%38%6%25%5%5%5%23%
1760
November1st to 15thDay
13%9%36%6%345%5%7%33%
1509
16th to endDay
19%12%5%8%5%245%5%9%20%
1440
December1st to 15thDay
16%17%5%9%7%35%446%19%
1440
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%7%47%
1444
June1st to 15thNight
12%414436%5%7%9%41%
1320
16th to endNight
9%4145%25%6%5%7%46%
1189
July1st to 15thNight
431442345%9%56%
1257
16th to endNight
6%415%43446%9%48%
1568
August1st to 15thNight
6%2144445%7%9%48%
1485
16th to endNight
8%325%324347%52%
1605
September1st to 15thNight
11%5%24424347%48%
1696
16th to endNight
11%4245%3345%7%45%
1815
October1st to 15thNight
17%5%25%5%2335%6%41%
1980
16th to endNight
21%8%36%5%35%45%6%29%
2112
November1st to 15thNight
15%6%25%5%245%6%8%36%
2348
16th to endNight
21%9%37%5%3445%8%26%
2520
December1st to 15thNight
20%14%5%7%6%345%5%6%21%
2520
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
12%435%5%35%5%47%41%
2512
June1st to 15thDay
14%5%25%6%35%5%6%8%36%
2310
16th to endDay
12%4146%36%5%6%9%38%
2435
July1st to 15thDay
8%424446%5%7%10%40%
2368
16th to endDay
9%5%25%5%46%6%7%9%36%
2291
August1st to 15thDay
9%426%5%46%6%8%8%37%
2145
16th to endDay
11%5%25%5%345%6%9%39%
2234
September1st to 15thDay
13%6%35%6%35%5%5%8%35%
1933
16th to endDay
14%5%25%5%345%5%8%37%
1815
October1st to 15thDay
17%6%36%6%35%5%47%33%
1650
16th to endDay
24%10%27%6%345%5%5%24%
1760
November1st to 15thDay
14%8%26%6%35%46%7%33%
1509
16th to endDay
20%13%37%6%245%5%8%21%
1440
December1st to 15thDay
16%16%6%8%8%35%346%19%
1440
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
11%32443345%7%47%
1444
June1st to 15thNight
11%5%15%435%5%7%9%41%
1320
16th to endNight
9%3245%245%6%7%46%
1189
July1st to 15thNight
421442345%9%56%
1257
16th to endNight
6%3245%245%5%9%49%
1568
August1st to 15thNight
6%324325%48%9%47%
1485
16th to endNight
8%316%42435%7%52%
1605
September1st to 15thNight
11%5%24424446%48%
1696
16th to endNight
11%4235%3446%7%45%
1815
October1st to 15thNight
17%6%2442335%7%41%
1980
16th to endNight
21%7%46%43445%6%29%
2112
November1st to 15thNight
15%6%35%4246%6%8%36%
2348
16th to endNight
21%9%45%5%345%5%8%26%
2520
December1st to 15thNight
21%13%5%7%5%25%45%6%21%
2520
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
41%6%13%22%13%1
2516
June1st to 15thDay
42%7%15%21%11%1
2310
16th to endDay
40%8%14%22%13%
2435
July1st to 15thDay
35%8%12%24%16%1
2218
16th to endDay
40%9%16%20%11%2
2135
August1st to 15thDay
40%9%15%19%12%1
2132
16th to endDay
39%8%15%24%11%1
2234
September1st to 15thDay
44%7%14%22%11%
1933
16th to endDay
42%7%14%25%9%
1815
October1st to 15thDay
49%6%13%17%11%1
1650
16th to endDay
60%7%13%13%4
1760
November1st to 15thDay
47%8%15%19%8%
1509
16th to endDay
58%7%15%13%5%
1440
December1st to 15thDay
64%7%14%10%2
1440
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%25%15%3
1446
June1st to 15thNight
38%7%11%24%15%1
1320
16th to endNight
35%6%14%23%17%1
1189
July1st to 15thNight
26%5%12%27%25%3
1178
16th to endNight
31%7%15%24%17%3
1461
August1st to 15thNight
28%10%16%28%13%2
1474
16th to endNight
31%6%12%30%16%2
1605
September1st to 15thNight
36%6%12%27%15%1
1696
16th to endNight
35%5%14%29%13%1
1815
October1st to 15thNight
41%6%11%24%15%
1980
16th to endNight
52%7%12%19%7%
2112
November1st to 15thNight
43%7%15%19%13%1
2348
16th to endNight
56%6%14%16%6%
2520
December1st to 15thNight
62%7%14%11%3
2520
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
12%7%26%28%16%8%
302
June1st to 15thDay
16%8%27%27%15%3
255
16th to endDay
12%6%25%32%17%6%
380
July1st to 15thDay
9%423%28%22%11%
302
16th to endDay
10%220%30%25%11%
270
August1st to 15thDay
9%118%24%26%18%
253
16th to endDay
11%413%22%23%23%
268
September1st to 15thDay
13%314%23%29%16%
255
16th to endDay
16%5%15%22%23%15%
254
October1st to 15thDay
18%6%26%24%18%6%
255
16th to endDay
27%7%30%25%7%
272
November1st to 15thDay
16%16%27%25%9%4
85
16th to endDay
30%15%30%16%5%3
60
December1st to 15thDay
25%25%36%8%5%
60
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
13%329%33%17%1
366
June1st to 15thNight
13%328%38%16%
330
16th to endNight
10%325%43%16%
330
July1st to 15thNight
425%46%21%1
310
16th to endNight
9%219%44%22%2
514
August1st to 15thNight
7%115%44%28%3
494
16th to endNight
9%215%35%33%2
555
September1st to 15thNight
13%419%31%24%5%
660
16th to endNight
13%319%30%28%5%
657
October1st to 15thNight
19%8%24%28%17%3
660
16th to endNight
26%9%32%26%4
704
November1st to 15thNight
17%8%33%25%13%2
700
16th to endNight
26%12%28%23%8%
720
December1st to 15thNight
29%14%32%19%4
720
16th to endNight
27%13%35%19%4
768
Page generated at 2017-05-25 13:27:40. Version ac04

Copyright 2017 A. Danko


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