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Clay Center Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Clay Center Observatory clear sky chart from 2005-11-05 to 2018-03-11.

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
26%
15607
18%
49066
7%
15575
38%
15575
20%
32253

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%
780
19%
2716
5%
776
32%
776
17%
1729
January16th to endNight
14%
832
18%
2912
3%
832
33%
832
14%
1898
February1st to 15thNight
16%
764
17%
2371
5%
761
31%
761
16%
1627
February16th to endNight
16%
683
22%
2049
6%
683
35%
683
17%
1382
March1st to 15thNight
16%
764
17%
2282
6%
764
31%
764
16%
1598
March16th to endNight
20%
768
23%
2040
7%
768
33%
768
22%
1389
April1st to 15thNight
20%
718
18%
1796
4%
718
29%
718
21%
1287
April16th to endNight
22%
585
18%
1665
4%
585
31%
585
19%
1138
May1st to 15thNight
22%
540
15%
1620
7%
540
30%
540
17%
1129
May16th to endNight
24%
428
11%
1550
7%
427
31%
427
16%
1044
June1st to 15thNight
28%
360
12%
1440
7%
360
39%
360
15%
980
June16th to endNight
31%
360
11%
1440
10%
360
40%
360
21%
877
July1st to 15thNight
39%
340
12%
1360
12%
340
46%
340
22%
824
July16th to endNight
42%
376
15%
1418
13%
354
50%
354
19%
895
August1st to 15thNight
40%
518
16%
1589
10%
516
45%
516
26%
1001
August16th to endNight
51%
714
21%
1860
12%
714
55%
714
33%
1188
September1st to 15thNight
39%
720
19%
1869
8%
720
46%
720
31%
1232
September16th to endNight
43%
717
25%
1980
16%
717
51%
717
32%
1229
October1st to 15thNight
34%
720
22%
2003
11%
720
44%
720
26%
1300
October16th to endNight
25%
768
18%
2496
7%
768
39%
768
20%
1609
November1st to 15thNight
28%
760
19%
2472
9%
760
41%
760
20%
1596
November16th to endNight
24%
780
22%
2535
8%
780
40%
780
19%
1605
December1st to 15thNight
20%
780
17%
2691
5%
780
36%
780
15%
1773
December16th to endNight
15%
832
19%
2912
4%
832
32%
832
15%
1923

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
17%6%2442445%7%40%
49570
Night
16%6%25%424446%40%
49236
Cloud CoverDay
17%6%2442445%7%40%
49580
Night
16%6%25%424446%41%
49241
TransparencyDay
43%6%11%21%15%2
49258
Night
43%5%11%21%15%2
49066
SeeingDay
23%14%32%19%8%2
6445
Night
21%13%34%23%7%
15607

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
15%8%25%3235%5%5%42%
1552
16th to endDay
16%6%26%42335%6%43%
1664
February1st to 15thDay
18%6%35%3345%47%36%
1819
16th to endDay
14%7%345%2445%7%40%
1710
March1st to 15thDay
20%8%2442445%7%34%
1905
16th to endDay
17%6%25%423445%42%
2181
April1st to 15thDay
17%8%25%5%24446%38%
2152
16th to endDay
17%5%24424447%41%
2294
May1st to 15thDay
24%8%35%423336%32%
2332
16th to endDay
16%5%25%5%2445%8%40%
2573
June1st to 15thDay
25%5%25%32445%8%32%
2520
16th to endDay
14%5%35%5%26%5%6%9%35%
2520
July1st to 15thDay
12%4245%46%5%6%10%37%
2520
16th to endDay
12%5%345%36%5%6%8%38%
2654
August1st to 15thDay
11%6%25%435%6%6%8%38%
2349
16th to endDay
11%4244345%6%8%43%
2339
September1st to 15thDay
14%414423347%47%
2091
16th to endDay
15%5%14323245%50%
1980
October1st to 15thDay
21%414433336%43%
1956
16th to endDay
16%6%34333446%43%
1728
November1st to 15thDay
20%6%2342343443%
1716
16th to endDay
16%5%24424447%43%
1755
December1st to 15thDay
18%6%35%424346%39%
1596
16th to endDay
22%8%24325%345%36%
1664
January1st to 15thNight
15%8%35%433345%42%
2716
16th to endNight
16%9%35%5%23345%40%
2912
February1st to 15thNight
16%8%25%5%34446%37%
2370
16th to endNight
17%8%34423445%41%
2049
March1st to 15thNight
18%7%245%34446%36%
2269
16th to endNight
15%8%35%41333443%
2040
April1st to 15thNight
16%8%25%43445%5%37%
1796
16th to endNight
21%5%25%424345%40%
1665
May1st to 15thNight
22%6%35%424446%36%
1620
16th to endNight
19%7%2442436%8%35%
1548
June1st to 15thNight
22%7%35%324437%34%
1440
16th to endNight
15%324425%5%5%8%41%
1440
July1st to 15thNight
11%5%26%6%245%6%9%39%
1440
16th to endNight
11%436%5%46%5%48%37%
1514
August1st to 15thNight
9%425%5%35%5%6%8%42%
1599
16th to endNight
12%4145%245%5%8%45%
1860
September1st to 15thNight
13%424435%45%6%46%
1869
16th to endNight
15%5%13313345%51%
1980
October1st to 15thNight
18%5%14323345%46%
2003
16th to endNight
18%5%24433447%41%
2496
November1st to 15thNight
16%6%25%433345%43%
2472
16th to endNight
17%6%25%414446%43%
2535
December1st to 15thNight
19%6%345%14446%38%
2691
16th to endNight
17%8%35%433446%37%
2912

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
15%8%2432345%5%43%
1552
16th to endDay
15%7%25%43335%5%43%
1664
February1st to 15thDay
18%6%35%335%447%37%
1819
16th to endDay
14%7%15%4245%46%41%
1710
March1st to 15thDay
20%8%2442445%7%34%
1915
16th to endDay
17%7%26%423445%42%
2181
April1st to 15thDay
17%7%35%5%3345%5%38%
2152
16th to endDay
18%42442345%7%41%
2294
May1st to 15thDay
24%7%36%423346%33%
2332
16th to endDay
16%5%245%24448%40%
2573
June1st to 15thDay
25%5%25%3245%5%7%33%
2520
16th to endDay
15%5%246%25%5%7%8%35%
2520
July1st to 15thDay
11%5%246%36%5%6%9%37%
2520
16th to endDay
12%4245%36%5%6%8%37%
2654
August1st to 15thDay
12%5%245%346%6%8%38%
2349
16th to endDay
12%4144345%5%9%43%
2339
September1st to 15thDay
13%5%24423347%47%
2091
16th to endDay
17%414224345%50%
1980
October1st to 15thDay
21%414433336%43%
1956
16th to endDay
16%6%24423446%44%
1728
November1st to 15thDay
21%7%2332343443%
1716
16th to endDay
17%5%24324347%43%
1755
December1st to 15thDay
17%7%26%433446%39%
1596
16th to endDay
22%9%23425%335%36%
1664
January1st to 15thNight
15%8%35%423345%41%
2716
16th to endNight
16%9%35%5%23345%40%
2912
February1st to 15thNight
16%8%25%5%34446%37%
2363
16th to endNight
16%9%34433445%41%
2049
March1st to 15thNight
19%7%35%5%34445%36%
2282
16th to endNight
16%8%36%42334443%
2039
April1st to 15thNight
16%7%35%5%34446%37%
1796
16th to endNight
21%5%25%5%24345%40%
1665
May1st to 15thNight
21%7%25%424346%35%
1620
16th to endNight
19%6%25%5%2245%8%35%
1548
June1st to 15thNight
23%6%3442445%6%34%
1440
16th to endNight
15%325%3346%5%7%41%
1440
July1st to 15thNight
11%5%26%5%35%5%6%8%40%
1440
16th to endNight
12%435%7%36%5%5%9%37%
1514
August1st to 15thNight
8%435%6%35%6%5%7%43%
1599
16th to endNight
12%41442445%8%46%
1860
September1st to 15thNight
13%4144245%5%6%46%
1869
16th to endNight
15%5%13323345%51%
1980
October1st to 15thNight
18%5%24323345%46%
2003
16th to endNight
18%5%24434446%41%
2496
November1st to 15thNight
16%6%25%423345%43%
2472
16th to endNight
17%6%25%324446%43%
2535
December1st to 15thNight
18%7%25%4245%45%39%
2691
16th to endNight
18%8%45%324446%37%
2912

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
42%6%9%24%13%3
1553
16th to endDay
42%5%11%25%14%1
1664
February1st to 15thDay
47%5%12%20%13%1
1822
16th to endDay
42%6%12%20%14%2
1710
March1st to 15thDay
48%6%11%20%10%2
1915
16th to endDay
43%5%9%20%14%5%
2181
April1st to 15thDay
46%5%10%19%15%3
2152
16th to endDay
41%5%9%21%17%4
2294
May1st to 15thDay
53%5%7%17%14%2
2332
16th to endDay
42%7%13%21%13%2
2577
June1st to 15thDay
50%6%11%19%9%1
2520
16th to endDay
42%7%14%19%14%1
2520
July1st to 15thDay
40%9%11%20%15%2
2371
16th to endDay
40%9%13%20%12%3
2487
August1st to 15thDay
40%9%12%22%14%1
2335
16th to endDay
35%8%10%25%18%1
2339
September1st to 15thDay
36%7%11%22%20%2
2091
16th to endDay
36%48%23%24%2
1980
October1st to 15thDay
43%48%25%14%3
1956
16th to endDay
41%5%12%22%16%2
1728
November1st to 15thDay
45%411%22%14%1
1716
16th to endDay
41%5%11%24%15%2
1755
December1st to 15thDay
46%414%15%17%
1596
16th to endDay
50%5%12%18%11%1
1664
January1st to 15thNight
44%412%21%14%1
2716
16th to endNight
46%5%10%19%15%2
2912
February1st to 15thNight
47%5%11%20%12%2
2371
16th to endNight
46%49%21%15%3
2049
March1st to 15thNight
48%5%9%19%13%3
2282
16th to endNight
45%37%18%20%4
2040
April1st to 15thNight
46%5%9%18%17%2
1796
16th to endNight
45%5%8%19%16%4
1665
May1st to 15thNight
49%5%9%17%14%3
1620
16th to endNight
46%8%14%18%9%2
1550
June1st to 15thNight
49%6%12%19%10%1
1440
16th to endNight
40%7%13%22%15%1
1440
July1st to 15thNight
39%7%12%25%14%
1360
16th to endNight
42%7%11%26%9%2
1418
August1st to 15thNight
37%8%13%23%14%2
1589
16th to endNight
34%7%11%26%19%
1860
September1st to 15thNight
36%7%11%23%19%1
1869
16th to endNight
34%5%7%23%26%2
1980
October1st to 15thNight
40%410%23%16%3
2003
16th to endNight
42%6%12%23%14%
2496
November1st to 15thNight
43%5%10%21%15%3
2472
16th to endNight
41%5%11%23%15%2
2535
December1st to 15thNight
46%5%13%20%12%
2691
16th to endNight
47%412%20%13%1
2912

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
26%28%25%15%3
90
16th to endDay
33%18%34%13%
96
February1st to 15thDay
28%21%36%11%1
287
16th to endDay
22%21%36%15%3
291
March1st to 15thDay
32%19%32%11%3
312
16th to endDay
21%26%31%9%9%1
288
April1st to 15thDay
26%17%32%15%7%
270
16th to endDay
23%16%32%21%42
270
May1st to 15thDay
37%17%23%13%6%1
288
16th to endDay
21%12%37%21%5%
331
June1st to 15thDay
28%10%36%17%6%
315
16th to endDay
15%11%41%24%5%2
315
July1st to 15thDay
18%7%36%27%8%
305
16th to endDay
13%7%33%30%12%2
326
August1st to 15thDay
13%10%30%31%12%1
313
16th to endDay
16%5%29%25%18%4
332
September1st to 15thDay
19%9%29%23%14%3
315
16th to endDay
25%427%18%12%11%
314
October1st to 15thDay
24%9%25%23%10%6%
312
16th to endDay
19%15%35%19%9%
288
November1st to 15thDay
26%15%30%16%8%3
280
16th to endDay
22%18%32%15%9%1
285
December1st to 15thDay
27%23%30%11%6%
126
16th to endDay
25%33%34%6%1
96
January1st to 15thNight
22%17%39%17%2
780
16th to endNight
24%18%37%17%2
832
February1st to 15thNight
22%17%38%19%1
764
16th to endNight
24%18%37%16%2
683
March1st to 15thNight
24%16%38%16%3
764
16th to endNight
22%17%35%19%5%
768
April1st to 15thNight
22%18%35%19%4
718
16th to endNight
24%15%34%20%4
585
May1st to 15thNight
26%15%33%20%4
540
16th to endNight
22%9%39%24%3
428
June1st to 15thNight
23%6%36%25%6%
360
16th to endNight
15%344%29%6%
360
July1st to 15thNight
13%238%35%9%
340
16th to endNight
12%234%39%11%
376
August1st to 15thNight
11%335%38%10%
518
16th to endNight
15%223%39%16%1
714
September1st to 15thNight
16%5%34%31%12%
720
16th to endNight
19%5%26%25%19%3
717
October1st to 15thNight
22%8%28%25%12%1
720
16th to endNight
22%14%34%19%8%
768
November1st to 15thNight
20%14%31%21%10%1
760
16th to endNight
21%17%31%20%7%
780
December1st to 15thNight
23%16%35%18%5%
780
16th to endNight
26%17%37%16%1
832
Page generated at 2018-03-12 13:28:01. Version ac04

Copyright 2018 A. Danko


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