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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 2020-06-03.

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%
19067
22%
57854
15%
19025
54%
19025
26%
36469

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
24%
900
22%
2912
8%
896
40%
896
17%
1874
January16th to endNight
25%
960
26%
3063
11%
960
42%
960
21%
1946
February1st to 15thNight
28%
883
23%
2652
11%
881
40%
881
22%
1700
February16th to endNight
21%
791
21%
2373
7%
791
34%
791
19%
1609
March1st to 15thNight
27%
900
22%
2588
9%
900
37%
900
23%
1689
March16th to endNight
34%
960
20%
2640
11%
960
40%
960
26%
1720
April1st to 15thNight
40%
781
25%
2354
14%
781
51%
781
31%
1386
April16th to endNight
46%
669
26%
2105
17%
669
56%
669
29%
1245
May1st to 15thNight
52%
675
22%
2025
13%
675
58%
675
30%
1246
May16th to endNight
61%
705
19%
2115
14%
705
64%
705
29%
1335
June1st to 15thNight
68%
637
16%
1913
14%
637
70%
637
29%
1220
June16th to endNight
74%
630
16%
1890
13%
630
76%
630
32%
1151
July1st to 15thNight
67%
600
13%
1800
12%
600
68%
600
24%
1206
July16th to endNight
72%
660
15%
1883
12%
627
73%
627
26%
1237
August1st to 15thNight
70%
620
18%
1884
17%
617
70%
617
27%
1213
August16th to endNight
64%
669
18%
2230
19%
669
65%
669
22%
1488
September1st to 15thNight
62%
814
19%
2284
18%
814
64%
814
28%
1512
September16th to endNight
61%
837
26%
2310
20%
837
66%
837
34%
1438
October1st to 15thNight
54%
840
32%
2316
24%
840
61%
840
37%
1361
October16th to endNight
47%
896
32%
2688
24%
896
59%
896
34%
1535
November1st to 15thNight
47%
880
29%
2859
22%
880
57%
880
31%
1616
November16th to endNight
40%
900
27%
2925
18%
900
53%
900
27%
1706
December1st to 15thNight
30%
900
21%
2925
11%
900
43%
900
20%
1894
December16th to endNight
29%
960
19%
3120
13%
960
38%
960
17%
2142

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%5%25%5%35%5%5%7%39%
58554
Night
13%5%2442445%7%44%
58052
TransparencyDay
42%6%11%18%16%4
58255
Night
38%5%10%19%18%5%
57855
SeeingDay
20%8%20%22%17%10%
8906
Night
17%8%21%27%20%3
19070

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
20%7%1441334442%
2016
16th to endDay
18%6%24323335%44%
2215
February1st to 15thDay
21%7%24334346%37%
2200
16th to endDay
22%6%34424335%38%
1980
March1st to 15thDay
18%6%25%5%25%45%6%38%
2362
16th to endDay
16%5%25%5%2445%7%39%
2639
April1st to 15thDay
12%5%25%5%345%6%6%42%
2595
16th to endDay
12%5%2443445%7%46%
2787
May1st to 15thDay
11%5%25%5%34447%45%
2916
16th to endDay
10%5%26%6%35%5%6%8%38%
3055
June1st to 15thDay
9%5%26%7%46%6%7%10%34%
2756
16th to endDay
5%3246%37%7%9%10%39%
2730
July1st to 15thDay
9%5%36%7%48%7%7%11%27%
2730
16th to endDay
7%5%27%8%5%8%7%8%10%27%
2881
August1st to 15thDay
8%5%25%6%47%8%8%10%31%
2644
16th to endDay
12%7%36%7%5%6%7%7%7%27%
2676
September1st to 15thDay
11%6%26%6%45%5%5%8%37%
2321
16th to endDay
13%5%145%24447%44%
2310
October1st to 15thDay
12%413323436%52%
2304
16th to endDay
14%413312335%55%
2240
November1st to 15thDay
16%424313235%52%
1987
16th to endDay
14%423424445%48%
2025
December1st to 15thDay
21%6%2443335%6%39%
2025
16th to endDay
25%7%25%43434434%
2160
January1st to 15thNight
19%5%35%423345%41%
2912
16th to endNight
17%6%34423345%43%
3063
February1st to 15thNight
18%5%25%423346%42%
2643
16th to endNight
21%5%25%42444439%
2373
March1st to 15thNight
15%6%2443435%5%43%
2588
16th to endNight
13%5%25%5%24346%44%
2640
April1st to 15thNight
11%42341445%8%48%
2354
16th to endNight
9%425%42435%7%48%
2105
May1st to 15thNight
9%4245%35%45%8%46%
2024
16th to endNight
9%415%5%3445%10%43%
2114
June1st to 15thNight
6%4246%45%7%7%12%39%
1913
16th to endNight
4315%435%6%8%13%42%
1890
July1st to 15thNight
7%425%6%46%6%8%11%35%
1890
16th to endNight
5%325%6%46%7%8%12%36%
1991
August1st to 15thNight
7%425%5%36%5%7%12%39%
1895
16th to endNight
10%6%345%36%5%7%9%36%
2230
September1st to 15thNight
9%425%6%35%5%6%9%41%
2284
16th to endNight
10%415%4245%5%6%49%
2310
October1st to 15thNight
11%414313347%55%
2316
16th to endNight
12%5%23422235%55%
2688
November1st to 15thNight
14%423313336%53%
2859
16th to endNight
14%5%143235%45%49%
2925
December1st to 15thNight
18%7%26%423446%39%
2925
16th to endNight
23%7%25%5%24346%34%
3120

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%36%17%21%4
2017
16th to endDay
42%26%20%20%6%
2215
February1st to 15thDay
48%27%17%19%3
2202
16th to endDay
48%27%17%17%5%
1980
March1st to 15thDay
46%49%14%18%5%
2362
16th to endDay
44%412%20%15%3
2640
April1st to 15thDay
40%49%22%18%4
2595
16th to endDay
37%410%20%20%6%
2787
May1st to 15thDay
37%6%13%20%18%3
2916
16th to endDay
41%7%13%20%13%2
3059
June1st to 15thDay
42%9%16%20%9%1
2756
16th to endDay
33%10%18%22%12%1
2730
July1st to 15thDay
45%10%18%16%7%1
2591
16th to endDay
47%10%16%15%9%1
2726
August1st to 15thDay
42%10%17%18%8%1
2631
16th to endDay
51%9%13%14%8%2
2676
September1st to 15thDay
43%7%13%15%15%3
2321
16th to endDay
38%6%12%18%20%3
2310
October1st to 15thDay
33%49%19%24%7%
2304
16th to endDay
32%26%18%28%11%
2240
November1st to 15thDay
36%25%16%29%8%
1987
16th to endDay
38%37%16%26%7%
2025
December1st to 15thDay
45%38%18%16%6%
2025
16th to endDay
53%28%15%14%5%
2160
January1st to 15thNight
45%37%16%22%5%
2912
16th to endNight
43%25%19%22%5%
3063
February1st to 15thNight
43%38%19%19%6%
2652
16th to endNight
47%36%18%18%4
2373
March1st to 15thNight
42%48%17%18%7%
2588
16th to endNight
40%410%22%19%2
2640
April1st to 15thNight
34%411%24%21%5%
2354
16th to endNight
34%5%9%22%20%7%
2105
May1st to 15thNight
35%6%12%23%20%2
2025
16th to endNight
36%8%13%24%14%2
2116
June1st to 15thNight
34%10%18%23%10%1
1913
16th to endNight
30%10%20%22%13%2
1890
July1st to 15thNight
38%11%19%19%9%1
1800
16th to endNight
35%12%20%19%9%2
1883
August1st to 15thNight
36%10%17%22%11%1
1884
16th to endNight
41%10%16%16%13%2
2230
September1st to 15thNight
38%8%14%17%16%4
2284
16th to endNight
33%7%11%23%19%4
2310
October1st to 15thNight
30%5%11%20%25%7%
2316
16th to endNight
32%25%17%27%13%
2688
November1st to 15thNight
34%26%17%27%11%
2859
16th to endNight
36%37%19%25%8%
2925
December1st to 15thNight
45%39%18%17%6%
2925
16th to endNight
51%28%16%15%4
3120

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
37%12%33%13%2
225
16th to endDay
30%23%32%10%1
240
February1st to 15thDay
37%19%32%8%2
225
16th to endDay
43%17%28%8%1
201
March1st to 15thDay
36%16%25%16%3
337
16th to endDay
23%13%32%20%8%
480
April1st to 15thDay
24%11%29%22%10%1
450
16th to endDay
19%10%27%22%16%2
439
May1st to 15thDay
16%9%25%24%15%8%
468
16th to endDay
19%415%27%20%13%
523
June1st to 15thDay
13%215%24%26%18%
443
16th to endDay
9%214%25%25%21%
435
July1st to 15thDay
12%18%22%31%24%
425
16th to endDay
9%9%24%31%24%
454
August1st to 15thDay
14%110%23%27%22%
418
16th to endDay
17%110%20%30%19%
460
September1st to 15thDay
12%5%12%24%27%18%
435
16th to endDay
14%212%29%29%10%
434
October1st to 15thDay
17%321%29%18%8%
435
16th to endDay
19%9%21%27%17%4
464
November1st to 15thDay
31%14%21%24%7%
225
16th to endDay
16%13%35%24%9%1
225
December1st to 15thDay
36%15%28%18%2
225
16th to endDay
37%17%28%14%1
240
January1st to 15thNight
28%16%26%22%6%
900
16th to endNight
23%15%31%25%4
960
February1st to 15thNight
24%14%28%26%5%
884
16th to endNight
26%15%34%21%2
791
March1st to 15thNight
20%16%32%24%5%
900
16th to endNight
19%11%29%28%10%
960
April1st to 15thNight
17%11%27%29%13%
781
16th to endNight
13%8%26%33%17%1
669
May1st to 15thNight
10%6%24%31%24%2
675
16th to endNight
13%214%29%33%6%
707
June1st to 15thNight
8%111%33%34%10%
637
16th to endNight
49%33%40%11%
630
July1st to 15thNight
9%17%25%43%12%
600
16th to endNight
8%15%24%47%13%
660
August1st to 15thNight
10%18%25%44%10%
620
16th to endNight
13%110%24%40%11%
669
September1st to 15thNight
12%211%26%38%9%
814
16th to endNight
12%116%32%33%2
837
October1st to 15thNight
13%6%21%29%23%6%
840
16th to endNight
15%9%22%29%19%2
896
November1st to 15thNight
16%9%22%30%18%1
880
16th to endNight
18%13%24%28%14%
900
December1st to 15thNight
22%15%27%24%9%
900
16th to endNight
30%10%26%25%6%
960
Page generated at 2020-06-04 03:18:54. Version ac04

Copyright 2020 A. Danko


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