J. Stephen Schmidt Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the J. Stephen Schmidt Observatory clear sky chart from 2005-11-05 to 2017-10-06.

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
46%
15553
23%
47153
15%
15511
55%
15511
27%
29336

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
25%
720
22%
2327
9%
716
41%
716
18%
1478
January16th to endNight
25%
768
24%
2451
11%
768
41%
768
20%
1573
February1st to 15thNight
29%
703
25%
2112
10%
701
43%
701
25%
1281
February16th to endNight
22%
631
24%
1893
8%
631
37%
631
22%
1211
March1st to 15thNight
29%
720
22%
2070
11%
720
39%
720
24%
1331
March16th to endNight
37%
768
20%
2112
12%
768
43%
768
28%
1355
April1st to 15thNight
40%
625
25%
1883
14%
625
52%
625
32%
1092
April16th to endNight
47%
540
25%
1702
17%
540
56%
540
30%
998
May1st to 15thNight
49%
540
21%
1620
12%
540
57%
540
27%
1026
May16th to endNight
62%
561
20%
1683
14%
561
66%
561
32%
1029
June1st to 15thNight
69%
540
15%
1620
14%
540
70%
540
29%
1032
June16th to endNight
74%
540
18%
1620
15%
540
76%
540
32%
989
July1st to 15thNight
69%
510
13%
1530
12%
510
69%
510
26%
1006
July16th to endNight
73%
564
16%
1595
14%
531
74%
531
28%
1026
August1st to 15thNight
71%
539
19%
1639
18%
536
71%
536
28%
1035
August16th to endNight
63%
573
19%
1910
20%
573
65%
573
21%
1285
September1st to 15thNight
60%
698
18%
1958
17%
698
61%
698
27%
1311
September16th to endNight
59%
717
26%
1980
19%
717
64%
717
32%
1246
October1st to 15thNight
53%
684
33%
1886
24%
684
61%
684
39%
1081
October16th to endNight
50%
704
33%
2112
25%
704
61%
704
36%
1179
November1st to 15thNight
49%
700
30%
2274
24%
700
60%
700
34%
1225
November16th to endNight
38%
720
26%
2340
17%
720
51%
720
27%
1375
December1st to 15thNight
32%
720
22%
2340
12%
720
44%
720
22%
1478
December16th to endNight
29%
768
19%
2496
13%
768
38%
768
18%
1694

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
13%5%25%5%35%5%5%7%40%
48041
Night
12%5%2442445%7%45%
47351
TransparencyDay
41%6%11%18%17%4
47742
Night
37%5%11%20%19%5%
47154
SeeingDay
17%6%19%23%20%12%
5435
Night
15%8%22%27%21%3
15556

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
19%7%145%1334442%
1611
16th to endDay
18%5%24423336%43%
1772
February1st to 15thDay
18%6%2423445%7%40%
1750
16th to endDay
19%5%35%424435%42%
1580
March1st to 15thDay
17%6%2443445%7%39%
1890
16th to endDay
16%5%25%5%23447%41%
2111
April1st to 15thDay
13%5%25%5%345%5%6%43%
2074
16th to endDay
11%415%5%3445%7%46%
2256
May1st to 15thDay
11%5%25%5%3445%7%42%
2331
16th to endDay
9%5%16%6%36%5%6%9%38%
2431
June1st to 15thDay
8%5%26%7%37%6%7%10%33%
2340
16th to endDay
6%3235%36%7%9%10%40%
2340
July1st to 15thDay
9%5%36%7%48%7%7%11%28%
2340
16th to endDay
7%5%37%8%5%8%7%8%10%28%
2465
August1st to 15thDay
9%5%25%7%47%8%8%9%32%
2307
16th to endDay
13%7%27%8%5%6%7%8%7%25%
2292
September1st to 15thDay
12%6%36%6%35%6%5%9%35%
1989
16th to endDay
14%6%145%24447%43%
1980
October1st to 15thDay
12%413323335%55%
1872
16th to endDay
12%41331322458%
1760
November1st to 15thDay
14%323313335%55%
1582
16th to endDay
17%5%23413345%47%
1620
December1st to 15thDay
21%5%2443335%6%39%
1620
16th to endDay
26%7%2443334435%
1728
January1st to 15thNight
20%5%2432345%5%41%
2327
16th to endNight
17%6%345%2335%5%42%
2451
February1st to 15thNight
15%435%422346%46%
2103
16th to endNight
17%424424445%44%
1893
March1st to 15thNight
14%5%2443435%6%44%
2070
16th to endNight
12%5%25%5%24446%46%
2112
April1st to 15thNight
12%41341445%8%50%
1883
16th to endNight
8%425%42436%8%48%
1702
May1st to 15thNight
10%4245%35%46%8%43%
1619
16th to endNight
7%315%5%245%6%10%46%
1682
June1st to 15thNight
6%3246%35%7%7%11%40%
1620
16th to endNight
5%315%435%6%8%12%43%
1620
July1st to 15thNight
6%425%6%36%6%8%11%37%
1620
16th to endNight
6%225%6%36%7%8%12%38%
1703
August1st to 15thNight
6%425%5%36%47%12%40%
1650
16th to endNight
11%6%345%35%5%7%10%35%
1910
September1st to 15thNight
9%5%25%7%35%5%5%8%41%
1958
16th to endNight
12%4144245%5%7%47%
1980
October1st to 15thNight
10%414312237%57%
1886
16th to endNight
9%42442223458%
2112
November1st to 15thNight
11%413313336%56%
2274
16th to endNight
15%5%24323445%49%
2340
December1st to 15thNight
16%6%25%423346%42%
2340
16th to endNight
22%7%25%5%24346%35%
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
45%47%16%22%4
1612
16th to endDay
43%37%19%20%6%
1772
February1st to 15thDay
43%39%19%21%3
1752
16th to endDay
45%37%19%19%4
1580
March1st to 15thDay
43%49%16%19%5%
1890
16th to endDay
43%412%20%15%3
2112
April1st to 15thDay
39%49%21%19%4
2074
16th to endDay
37%410%21%20%5%
2256
May1st to 15thDay
40%6%13%19%17%3
2331
16th to endDay
40%7%14%20%13%2
2435
June1st to 15thDay
42%9%17%21%8%1
2340
16th to endDay
32%10%17%23%13%2
2340
July1st to 15thDay
46%9%18%17%7%1
2201
16th to endDay
46%10%16%16%8%1
2310
August1st to 15thDay
42%10%17%19%8%1
2294
16th to endDay
52%10%13%14%8%1
2292
September1st to 15thDay
44%7%13%16%14%3
1989
16th to endDay
39%5%12%17%20%4
1980
October1st to 15thDay
32%39%17%27%8%
1872
16th to endDay
31%25%19%29%11%
1760
November1st to 15thDay
32%25%16%32%9%
1582
16th to endDay
39%37%15%26%7%
1620
December1st to 15thDay
45%39%18%16%7%
1620
16th to endDay
51%38%16%15%4
1728
January1st to 15thNight
43%47%17%22%5%
2327
16th to endNight
44%35%18%21%5%
2451
February1st to 15thNight
39%28%20%21%8%
2112
16th to endNight
42%36%21%21%4
1893
March1st to 15thNight
40%49%19%18%7%
2070
16th to endNight
38%5%10%24%18%3
2112
April1st to 15thNight
32%411%23%21%5%
1883
16th to endNight
33%5%10%22%20%7%
1702
May1st to 15thNight
38%6%12%21%19%2
1620
16th to endNight
32%8%15%25%14%3
1684
June1st to 15thNight
33%11%20%23%9%1
1620
16th to endNight
30%10%18%23%14%2
1620
July1st to 15thNight
36%11%19%20%10%1
1530
16th to endNight
33%11%20%20%10%2
1595
August1st to 15thNight
34%10%17%23%12%1
1639
16th to endNight
42%10%15%17%13%1
1910
September1st to 15thNight
40%8%14%17%15%3
1958
16th to endNight
34%8%10%23%18%5%
1980
October1st to 15thNight
28%5%10%18%29%8%
1886
16th to endNight
31%25%18%29%12%
2112
November1st to 15thNight
31%25%17%30%13%
2274
16th to endNight
36%36%17%26%8%
2340
December1st to 15thNight
43%39%18%18%7%
2340
16th to endNight
50%38%16%17%4
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
28%13%36%16%4
90
16th to endDay
28%27%36%5%3
96
February1st to 15thDay
28%23%37%8%1
90
16th to endDay
30%24%34%7%2
81
March1st to 15thDay
31%13%27%18%6%1
180
16th to endDay
20%12%28%24%13%
288
April1st to 15thDay
22%10%27%23%13%2
270
16th to endDay
15%6%27%25%20%4
270
May1st to 15thDay
18%9%27%18%14%11%
288
16th to endDay
16%5%16%28%19%14%
331
June1st to 15thDay
11%14%23%26%23%
315
16th to endDay
10%115%25%23%23%
315
July1st to 15thDay
12%19%22%28%24%
305
16th to endDay
10%6%20%34%27%
326
August1st to 15thDay
15%19%24%24%23%
313
16th to endDay
15%111%22%29%18%
332
September1st to 15thDay
13%6%13%23%25%17%
315
16th to endDay
15%214%28%28%10%
314
October1st to 15thDay
15%423%30%18%6%
278
16th to endDay
14%8%18%26%25%5%
272
November1st to 15thDay
26%14%23%25%7%2
90
16th to endDay
22%12%33%21%8%2
90
December1st to 15thDay
30%12%34%21%2
90
16th to endDay
42%10%29%16%1
96
January1st to 15thNight
27%15%25%23%6%
720
16th to endNight
23%15%31%25%3
768
February1st to 15thNight
21%15%29%28%4
704
16th to endNight
22%17%35%22%3
631
March1st to 15thNight
19%15%33%25%6%
720
16th to endNight
17%12%27%29%11%
768
April1st to 15thNight
16%11%28%27%15%
625
16th to endNight
10%8%27%33%17%1
540
May1st to 15thNight
11%7%24%31%23%2
540
16th to endNight
11%215%30%34%5%
563
June1st to 15thNight
8%112%33%35%10%
540
16th to endNight
5%9%32%41%11%
540
July1st to 15thNight
7%18%25%44%12%
510
16th to endNight
7%6%23%48%12%
564
August1st to 15thNight
8%8%25%45%10%
539
16th to endNight
13%110%24%38%10%
573
September1st to 15thNight
13%212%25%36%9%
698
16th to endNight
13%118%33%30%2
717
October1st to 15thNight
13%6%22%30%22%4
684
16th to endNight
12%9%22%29%22%3
704
November1st to 15thNight
14%9%22%30%21%2
700
16th to endNight
19%14%25%25%14%
720
December1st to 15thNight
19%15%27%25%10%
720
16th to endNight
29%10%26%25%6%
768
Page generated at 2017-10-07 14:07:50. Version ac04

Copyright 2017 A. Danko


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