Ashton Observatory at Johnson Farms
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ashton Observatory at Johnson Farms clear sky chart from 2005-11-06 to 2024-03-01.

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%
23602
20%
80169
11%
23501
47%
23501
22%
49609

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 10thNight
17%
752
23%
4298
7%
737
38%
737
13%
2359
January11th to 20thNight
22%
759
26%
3965
9%
740
38%
740
12%
2216
January21st to endNight
20%
830
16%
4450
8%
814
41%
814
13%
2699
February1st to 10thNight
25%
760
19%
2470
8%
760
38%
760
20%
1578
February11th to 20thNight
14%
742
19%
2344
3%
740
33%
740
18%
1493
February21st to endNight
17%
628
23%
1884
6%
628
37%
628
20%
1240
March1st to 10thNight
22%
723
24%
2037
8%
723
39%
723
25%
1266
March11th to 20thNight
22%
720
21%
1980
8%
720
35%
720
21%
1301
March21st to endNight
20%
792
20%
2134
6%
792
31%
792
23%
1451
April1st to 10thNight
21%
720
18%
1800
3%
720
31%
720
22%
1239
April11th to 20thNight
31%
711
20%
1775
6%
711
38%
711
30%
1169
April21st to endNight
31%
720
19%
1800
6%
720
38%
720
27%
1229
May1st to 10thNight
35%
606
17%
1686
8%
606
41%
606
24%
1128
May11th to 20thNight
38%
397
17%
1458
10%
397
48%
397
19%
942
May21st to endNight
52%
388
15%
1551
14%
388
58%
388
23%
909
June1st to 10thNight
51%
360
20%
1440
17%
360
59%
360
25%
812
June11th to 20thNight
48%
360
16%
1440
16%
360
54%
360
21%
873
June21st to endNight
53%
360
17%
1440
17%
360
60%
360
24%
826
July1st to 10thNight
60%
350
14%
1400
18%
350
62%
350
20%
895
July11th to 20thNight
68%
389
16%
1433
17%
389
70%
389
27%
805
July21st to endNight
63%
591
17%
1672
13%
558
67%
558
33%
1012
August1st to 10thNight
65%
537
15%
1600
12%
534
66%
534
27%
1051
August11th to 20thNight
60%
614
16%
1678
10%
614
62%
614
27%
1148
August21st to endNight
61%
792
19%
1980
11%
792
62%
792
33%
1322
September1st to 10thNight
53%
720
22%
1800
12%
720
58%
720
32%
1206
September11th to 20thNight
59%
720
30%
1800
21%
720
62%
720
37%
1145
September21st to endNight
45%
720
21%
2055
15%
720
51%
720
25%
1389
October1st to 10thNight
47%
720
19%
2160
17%
720
54%
720
27%
1386
October11th to 20thNight
41%
720
25%
2160
18%
720
53%
720
30%
1294
October21st to endNight
33%
792
26%
2376
15%
792
48%
792
28%
1449
November1st to 10thNight
38%
740
27%
2336
16%
740
53%
740
31%
1330
November11th to 20thNight
30%
760
26%
2479
13%
760
47%
760
24%
1469
November21st to endNight
31%
760
23%
2660
12%
760
47%
760
23%
1531
December1st to 10thNight
22%
760
19%
2660
7%
760
39%
760
18%
1681
December11th to 20thNight
24%
760
21%
3170
9%
759
39%
759
17%
1898
December21st to endNight
26%
829
14%
4798
10%
817
41%
817
11%
2868

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%6%25%5%35%5%6%7%42%
78513
Night
15%6%25%5%3445%7%44%
80897
TransparencyDay
40%7%12%23%16%3
78223
Night
39%6%12%23%16%3
80706
SeeingDay
19%13%28%24%13%4
13995
Night
17%11%30%29%11%1
23626

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 10thDay
17%42443445%6%47%
2551
11th to 20thDay
15%11%35%5%34345%41%
2840
21st to endDay
19%9%36%5%35%445%36%
3124
February1st to 10thDay
14%6%26%6%446%6%7%38%
1710
11th to 20thDay
18%7%25%43446%6%40%
1724
21st to endDay
18%8%26%5%35%445%40%
1570
March1st to 10thDay
14%5%25%42445%5%50%
1928
11th to 20thDay
17%6%35%6%2445%6%42%
1980
21st to endDay
17%6%46%6%3445%6%39%
2220
April1st to 10thDay
13%6%36%4345%5%8%43%
2160
11th to 20thDay
13%5%25%6%34447%47%
2134
21st to endDay
19%5%345%3345%8%40%
2160
May1st to 10thDay
15%7%26%6%345%6%9%38%
2289
11th to 20thDay
18%6%36%6%25%5%6%8%36%
2432
21st to endDay
13%6%36%5%346%6%9%40%
2725
June1st to 10thDay
12%4245%35%5%7%9%43%
2520
11th to 20thDay
12%5%36%5%45%5%7%9%40%
2520
21st to endDay
10%4245%36%6%8%10%43%
2520
July1st to 10thDay
10%426%6%45%6%6%10%41%
2520
11th to 20thDay
6%3245%46%7%8%11%43%
2475
21st to endDay
10%5%36%6%46%8%7%10%36%
2547
August1st to 10thDay
11%5%26%6%5%7%6%7%9%36%
2327
11th to 20thDay
12%5%26%6%46%6%7%8%38%
2203
21st to endDay
11%5%25%6%36%6%7%8%40%
2376
September1st to 10thDay
14%6%24445%5%5%6%45%
2160
11th to 20thDay
12%5%25%335%5%6%8%47%
2160
21st to endDay
18%8%26%5%3445%6%39%
1901
October1st to 10thDay
17%43443345%7%46%
1800
11th to 20thDay
19%32442346%6%47%
1800
21st to endDay
14%5%245%2445%6%47%
1980
November1st to 10thDay
13%5%2442445%7%52%
1739
11th to 20thDay
15%5%233235%6%6%50%
1696
21st to endDay
15%5%245%2445%5%48%
1520
December1st to 10thDay
16%6%35%435%5%6%8%40%
1520
11th to 20thDay
17%5%35%42345%8%44%
1910
21st to endDay
17%7%26%5%35%5%5%8%37%
2772
January1st to 10thNight
15%7%25%5%3445%7%44%
4393
11th to 20thNight
19%8%23423445%46%
4120
21st to endNight
21%9%25%323346%41%
4532
February1st to 10thNight
15%7%25%5%45%5%6%6%41%
2470
11th to 20thNight
18%7%25%5%2335%5%44%
2342
21st to endNight
17%7%35%5%34447%42%
1884
March1st to 10thNight
14%434435%5%5%6%49%
2037
11th to 20thNight
17%6%35%43445%7%43%
1980
21st to endNight
15%7%35%5%35%45%6%42%
2134
April1st to 10thNight
15%7%35%425%5%6%7%41%
1800
11th to 20thNight
14%5%26%5%3445%7%46%
1775
21st to endNight
18%5%245%245%6%8%41%
1800
May1st to 10thNight
18%6%25%5%245%6%8%39%
1686
11th to 20thNight
19%7%2443446%9%37%
1458
21st to endNight
13%5%15%435%48%11%41%
1550
June1st to 10thNight
11%325%5%345%7%10%45%
1440
11th to 20thNight
12%5%35%5%35%6%6%9%41%
1440
21st to endNight
10%4246%45%6%6%11%43%
1440
July1st to 10thNight
9%5%25%6%5%7%7%7%9%38%
1440
11th to 20thNight
6%425%5%36%7%7%9%45%
1481
21st to endNight
8%425%5%35%5%9%12%42%
1771
August1st to 10thNight
10%5%25%6%46%7%7%8%40%
1611
11th to 20thNight
10%6%37%5%35%5%6%8%41%
1678
21st to endNight
10%5%26%5%35%5%6%9%43%
1980
September1st to 10thNight
16%5%35%43445%7%45%
1800
11th to 20thNight
11%5%35%424447%51%
1800
21st to endNight
17%6%35%6%35%45%7%41%
2055
October1st to 10thNight
20%5%24423445%46%
2160
11th to 20thNight
16%424424345%52%
2160
21st to endNight
16%5%24424447%48%
2376
November1st to 10thNight
12%5%15%423346%54%
2336
11th to 20thNight
15%5%34423346%50%
2479
21st to endNight
14%4245%35%46%8%47%
2660
December1st to 10thNight
17%6%35%5%3446%6%41%
2660
11th to 20thNight
17%5%25%5%3445%7%43%
3285
21st to endNight
16%6%25%5%45%5%6%7%37%
4884

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 10thDay
37%5%9%31%14%4
2552
11th to 20thDay
46%5%11%20%15%4
2840
21st to endDay
48%6%11%22%11%2
3124
February1st to 10thDay
43%7%13%24%12%2
1710
11th to 20thDay
43%5%10%24%15%3
1733
21st to endDay
47%5%10%20%14%4
1570
March1st to 10thDay
36%5%13%25%20%2
1928
11th to 20thDay
43%5%10%18%18%5%
1980
21st to endDay
47%5%9%19%17%3
2220
April1st to 10thDay
38%6%12%21%18%5%
2160
11th to 20thDay
37%5%11%22%20%6%
2134
21st to endDay
42%5%12%20%18%4
2160
May1st to 10thDay
41%7%14%19%16%3
2289
11th to 20thDay
45%8%14%18%14%2
2436
21st to endDay
40%8%14%24%12%2
2725
June1st to 10thDay
36%9%14%24%15%1
2520
11th to 20thDay
39%11%12%22%14%2
2520
21st to endDay
33%10%15%24%17%2
2520
July1st to 10thDay
37%11%14%20%16%3
2450
11th to 20thDay
31%10%16%26%15%3
2400
21st to endDay
39%11%14%19%16%2
2405
August1st to 10thDay
41%10%15%22%12%1
2314
11th to 20thDay
40%9%14%19%16%2
2203
21st to endDay
37%10%13%23%13%3
2376
September1st to 10thDay
39%8%13%19%17%4
2160
11th to 20thDay
34%6%12%24%21%4
2160
21st to endDay
44%6%9%20%18%2
1901
October1st to 10thDay
39%6%10%24%18%3
1800
11th to 20thDay
36%6%10%23%21%3
1800
21st to endDay
37%5%9%26%21%2
1980
November1st to 10thDay
32%6%12%26%20%4
1739
11th to 20thDay
34%6%10%23%22%4
1696
21st to endDay
38%5%11%28%17%2
1520
December1st to 10thDay
41%7%14%24%12%2
1520
11th to 20thDay
38%413%31%11%2
1906
21st to endDay
45%6%15%22%11%1
2772
January1st to 10thNight
39%5%11%26%15%3
4393
11th to 20thNight
41%411%24%17%3
4120
21st to endNight
45%48%27%14%1
4532
February1st to 10thNight
42%6%12%24%14%1
2470
11th to 20thNight
43%49%22%17%4
2344
21st to endNight
43%5%11%22%15%5%
1884
March1st to 10thNight
36%5%11%27%18%3
2037
11th to 20thNight
41%6%12%20%18%4
1980
21st to endNight
42%6%10%19%16%6%
2134
April1st to 10thNight
41%7%10%18%19%4
1800
11th to 20thNight
38%5%13%20%18%6%
1775
21st to endNight
39%7%11%23%15%5%
1800
May1st to 10thNight
43%6%12%22%13%4
1686
11th to 20thNight
43%8%12%18%17%2
1459
21st to endNight
36%8%21%20%13%2
1551
June1st to 10thNight
33%8%13%26%17%2
1440
11th to 20thNight
38%9%14%23%13%3
1440
21st to endNight
35%8%14%22%18%2
1440
July1st to 10thNight
40%11%17%17%12%4
1400
11th to 20thNight
31%10%16%25%16%2
1433
21st to endNight
30%10%18%24%16%2
1672
August1st to 10thNight
37%11%16%21%15%1
1600
11th to 20thNight
39%10%14%21%14%2
1678
21st to endNight
36%8%14%24%15%4
1980
September1st to 10thNight
40%6%11%21%17%5%
1800
11th to 20thNight
34%5%10%26%22%4
1800
21st to endNight
43%7%10%18%18%4
2055
October1st to 10thNight
41%5%11%22%18%3
2160
11th to 20thNight
36%410%27%20%2
2160
21st to endNight
36%5%10%24%20%3
2376
November1st to 10thNight
33%5%10%26%21%5%
2336
11th to 20thNight
36%5%9%23%22%5%
2479
21st to endNight
35%5%12%25%19%3
2660
December1st to 10thNight
43%6%12%24%14%2
2660
11th to 20thNight
41%5%11%22%18%3
3288
21st to endNight
43%7%16%22%11%1
4884

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 10thDay
29%23%30%14%41
191
11th to 20thDay
30%24%31%13%2
270
21st to endDay
23%24%36%13%3
297
February1st to 10thDay
24%23%39%10%4
270
11th to 20thDay
31%21%39%6%2
331
21st to endDay
29%20%33%17%2
382
March1st to 10thDay
24%24%30%20%3
420
11th to 20thDay
25%21%32%17%32
420
21st to endDay
22%21%32%19%5%1
462
April1st to 10thDay
21%23%31%18%5%2
420
11th to 20thDay
18%17%33%19%10%3
412
21st to endDay
27%15%32%18%7%1
420
May1st to 10thDay
22%20%29%17%9%3
423
11th to 20thDay
21%13%29%25%10%2
447
21st to endDay
18%7%25%27%20%4
485
June1st to 10thDay
13%9%28%27%17%6%
450
11th to 20thDay
18%6%28%26%17%4
450
21st to endDay
9%6%30%32%18%5%
450
July1st to 10thDay
11%5%19%33%21%11%
445
11th to 20thDay
4321%35%28%9%
444
21st to endDay
13%324%33%22%6%
488
August1st to 10thDay
11%5%20%28%25%11%
446
11th to 20thDay
12%418%30%26%10%
439
21st to endDay
9%322%32%22%12%
495
September1st to 10thDay
16%6%20%24%20%13%
450
11th to 20thDay
14%422%31%18%11%
450
21st to endDay
23%10%24%28%12%4
450
October1st to 10thDay
23%6%22%24%19%6%
450
11th to 20thDay
18%14%27%26%13%2
450
21st to endDay
17%14%34%24%8%2
495
November1st to 10thDay
16%12%33%23%12%3
399
11th to 20thDay
18%14%35%22%10%1
356
21st to endDay
24%17%32%17%8%1
180
December1st to 10thDay
19%23%37%16%32
180
11th to 20thDay
24%22%29%18%7%
180
21st to endDay
25%16%33%19%6%
198
January1st to 10thNight
18%18%43%18%3
760
11th to 20thNight
22%17%34%24%3
760
21st to endNight
20%18%38%22%2
836
February1st to 10thNight
18%17%36%27%2
760
11th to 20thNight
25%21%37%16%1
743
21st to endNight
24%18%37%18%3
628
March1st to 10thNight
18%16%39%24%2
723
11th to 20thNight
23%18%35%19%5%1
720
21st to endNight
18%15%42%20%41
792
April1st to 10thNight
19%21%34%21%4
720
11th to 20thNight
15%15%35%27%7%
711
21st to endNight
21%10%34%28%7%
720
May1st to 10thNight
21%9%31%28%11%
606
11th to 20thNight
22%6%27%36%8%1
397
21st to endNight
15%6%20%40%17%2
389
June1st to 10thNight
11%328%36%21%1
360
11th to 20thNight
12%426%41%16%1
360
21st to endNight
11%224%47%16%
360
July1st to 10thNight
9%219%43%25%3
350
11th to 20thNight
5%216%42%33%2
389
21st to endNight
8%318%42%26%4
591
August1st to 10thNight
10%212%43%30%2
537
11th to 20thNight
11%414%43%25%3
614
21st to endNight
12%316%38%27%4
792
September1st to 10thNight
17%320%31%25%4
720
11th to 20thNight
10%417%36%28%4
720
21st to endNight
21%424%32%19%1
720
October1st to 10thNight
20%6%22%29%19%4
720
11th to 20thNight
18%9%28%31%14%1
720
21st to endNight
18%12%33%26%11%
792
November1st to 10thNight
15%8%34%32%9%2
740
11th to 20thNight
17%17%32%27%7%1
760
21st to endNight
17%15%32%28%8%1
760
December1st to 10thNight
20%17%35%20%7%1
760
11th to 20thNight
18%13%40%24%5%
760
21st to endNight
19%15%35%29%3
836
Page generated at 2024-02-27 06:30:16. Version ac07

Copyright © 2024 Attilla Danko.


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