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 2005-11-05 to 2017-09-10.

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
37%
15189
20%
46819
11%
15150
48%
15150
24%
29545

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
21%
717
21%
2431
8%
716
38%
716
18%
1533
January16th to endNight
20%
768
22%
2496
6%
768
39%
768
21%
1539
February1st to 15thNight
21%
703
19%
2287
5%
701
38%
701
20%
1422
February16th to endNight
18%
631
24%
1913
6%
631
40%
631
21%
1212
March1st to 15thNight
25%
720
21%
2013
8%
720
38%
720
24%
1313
March16th to endNight
22%
768
20%
2082
7%
768
33%
768
24%
1408
April1st to 15thNight
24%
718
19%
1796
5%
718
33%
718
26%
1207
April16th to endNight
38%
720
19%
1800
7%
720
43%
720
30%
1220
May1st to 15thNight
36%
551
17%
1631
8%
551
43%
551
23%
1098
May16th to endNight
53%
374
17%
1497
15%
374
60%
374
23%
878
June1st to 15thNight
53%
360
18%
1440
16%
360
61%
360
24%
820
June16th to endNight
53%
360
17%
1440
17%
360
60%
360
24%
829
July1st to 15thNight
57%
340
12%
1360
14%
340
59%
340
18%
878
July16th to endNight
70%
533
16%
1564
12%
500
75%
500
36%
889
August1st to 15thNight
66%
539
18%
1609
14%
536
66%
536
30%
1009
August16th to endNight
62%
758
19%
1904
12%
758
63%
758
33%
1272
September1st to 15thNight
54%
700
24%
1750
14%
700
58%
700
34%
1154
September16th to endNight
52%
657
21%
1807
17%
657
55%
657
28%
1221
October1st to 15thNight
45%
660
24%
1980
21%
660
53%
660
26%
1269
October16th to endNight
36%
704
27%
2112
15%
704
51%
704
31%
1236
November1st to 15thNight
36%
700
25%
2233
14%
700
51%
700
27%
1330
November16th to endNight
30%
720
21%
2466
11%
720
45%
720
21%
1483
December1st to 15thNight
26%
720
18%
2520
7%
720
40%
720
17%
1618
December16th to endNight
22%
768
21%
2688
7%
768
39%
768
18%
1707

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%345%5%7%41%
47797
Night
14%5%2442445%7%43%
47001
Cloud CoverDay
14%5%25%4345%5%7%41%
47807
Night
14%5%2442445%7%43%
47005
TransparencyDay
40%7%12%22%15%2
47497
Night
38%6%11%22%16%3
46819
SeeingDay
17%9%25%25%15%6%
5653
Night
16%10%29%28%12%1
15194

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%6%2443445%7%40%
1505
16th to endDay
14%6%35%5%24446%42%
1728
February1st to 15thDay
14%5%35%5%346%5%6%39%
1575
16th to endDay
13%7%27%5%24445%41%
1560
March1st to 15thDay
15%6%35%5%23435%45%
1934
16th to endDay
16%6%36%5%2445%6%41%
2142
April1st to 15thDay
13%5%25%5%2345%7%44%
2152
16th to endDay
17%5%24423346%44%
2160
May1st to 15thDay
16%6%25%5%245%6%8%36%
2328
16th to endDay
15%5%25%5%345%6%8%37%
2618
June1st to 15thDay
11%4244445%7%8%41%
2520
16th to endDay
10%414435%5%6%9%42%
2520
July1st to 15thDay
9%5%246%45%6%7%9%39%
2520
16th to endDay
7%3245%46%7%7%10%37%
2495
August1st to 15thDay
11%6%26%5%46%6%6%7%35%
2331
16th to endDay
12%4145%35%6%7%7%40%
2292
September1st to 15thDay
13%424435%5%5%7%45%
2098
16th to endDay
16%6%25%42435%7%40%
1820
October1st to 15thDay
19%423323436%45%
1650
16th to endDay
14%424423446%47%
1760
November1st to 15thDay
14%5%2242445%6%46%
1622
16th to endDay
17%5%23424446%45%
1491
December1st to 15thDay
16%325%425%45%8%41%
1440
16th to endDay
17%6%25%424347%38%
1536
January1st to 15thNight
16%6%245%24447%41%
2431
16th to endNight
16%6%243245%46%43%
2496
February1st to 15thNight
14%6%2443345%5%44%
2285
16th to endNight
14%6%245%23346%44%
1913
March1st to 15thNight
16%5%23324446%44%
2001
16th to endNight
14%6%35%424446%41%
2082
April1st to 15thNight
13%6%25%4245%6%7%43%
1796
16th to endNight
16%5%244245%5%6%43%
1800
May1st to 15thNight
20%6%1432435%7%38%
1631
16th to endNight
13%5%143245%6%10%41%
1495
June1st to 15thNight
11%412435%5%7%10%43%
1440
16th to endNight
8%425%5%35%46%11%42%
1440
July1st to 15thNight
8%436%7%48%6%6%7%36%
1440
16th to endNight
5%2234347%8%12%45%
1671
August1st to 15thNight
10%4146%245%7%8%44%
1620
16th to endNight
10%5%25%4245%6%7%44%
1904
September1st to 15thNight
12%6%245%23447%46%
1750
16th to endNight
14%6%25%5%34447%42%
1807
October1st to 15thNight
18%5%23424335%45%
1980
16th to endNight
15%313323347%51%
2112
November1st to 15thNight
13%5%25%323345%50%
2233
16th to endNight
16%4145%2345%7%44%
2466
December1st to 15thNight
16%6%25%6%35%45%5%39%
2520
16th to endNight
16%5%35%424447%41%
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
16%6%243345%5%6%40%
1505
16th to endDay
14%6%25%434446%42%
1728
February1st to 15thDay
13%6%26%4445%6%6%39%
1575
16th to endDay
13%7%25%435%346%41%
1560
March1st to 15thDay
15%5%35%424345%45%
1945
16th to endDay
16%6%35%5%24346%40%
2141
April1st to 15thDay
13%5%25%5%34448%44%
2152
16th to endDay
17%5%235%23336%44%
2160
May1st to 15thDay
16%6%35%5%2446%8%36%
2328
16th to endDay
14%5%26%5%336%6%8%38%
2618
June1st to 15thDay
11%3245%35%5%7%9%40%
2520
16th to endDay
10%4245%35%5%7%10%41%
2520
July1st to 15thDay
9%426%6%36%6%6%10%37%
2520
16th to endDay
7%335%446%7%8%11%37%
2495
August1st to 15thDay
11%5%26%6%46%6%6%7%35%
2331
16th to endDay
12%5%145%36%6%6%7%40%
2292
September1st to 15thDay
13%414335%5%5%7%44%
2098
16th to endDay
15%7%25%43445%7%40%
1820
October1st to 15thDay
19%43432335%6%45%
1650
16th to endDay
14%42442435%6%47%
1760
November1st to 15thDay
14%5%223245%5%6%47%
1622
16th to endDay
17%5%2332345%5%45%
1491
December1st to 15thDay
16%425%3345%5%8%42%
1440
16th to endDay
18%6%25%42435%7%38%
1536
January1st to 15thNight
16%6%34423447%41%
2431
16th to endNight
16%6%23324446%43%
2496
February1st to 15thNight
14%6%2443445%6%44%
2278
16th to endNight
14%6%25%5%24346%45%
1913
March1st to 15thNight
16%424324446%44%
2013
16th to endNight
16%5%35%424447%41%
2082
April1st to 15thNight
13%5%25%425%5%5%7%43%
1796
16th to endNight
16%5%1442445%6%43%
1800
May1st to 15thNight
20%7%2432445%7%38%
1630
16th to endNight
13%5%143245%7%9%41%
1495
June1st to 15thNight
10%314325%6%6%10%44%
1440
16th to endNight
8%425%6%35%5%5%10%43%
1440
July1st to 15thNight
8%436%7%47%6%6%8%35%
1440
16th to endNight
6%214325%6%9%12%45%
1671
August1st to 15thNight
9%5%145%345%6%8%45%
1620
16th to endNight
10%425%5%345%5%8%43%
1904
September1st to 15thNight
13%5%2442445%6%46%
1750
16th to endNight
14%6%25%5%34447%41%
1807
October1st to 15thNight
18%42342334445%
1980
16th to endNight
15%312323347%51%
2112
November1st to 15thNight
13%5%15%423345%50%
2233
16th to endNight
16%41342446%7%44%
2466
December1st to 15thNight
17%5%25%6%3445%5%39%
2520
16th to endNight
17%5%25%433446%41%
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
41%7%13%21%12%3
1506
16th to endDay
41%5%11%24%13%3
1728
February1st to 15thDay
43%6%10%24%12%2
1577
16th to endDay
43%411%25%12%1
1560
March1st to 15thDay
41%411%23%15%2
1945
16th to endDay
44%5%11%18%17%2
2142
April1st to 15thDay
39%5%11%22%17%3
2152
16th to endDay
40%410%17%20%6%
2160
May1st to 15thDay
43%7%13%18%15%1
2328
16th to endDay
41%8%13%21%12%1
2622
June1st to 15thDay
37%10%12%25%13%
2520
16th to endDay
35%9%14%21%16%1
2520
July1st to 15thDay
39%9%14%19%14%2
2371
16th to endDay
35%10%15%23%13%2
2339
August1st to 15thDay
43%8%12%18%15%1
2318
16th to endDay
37%10%12%21%15%2
2292
September1st to 15thDay
36%7%13%18%20%2
2098
16th to endDay
42%5%10%21%19%1
1820
October1st to 15thDay
39%5%10%24%17%3
1650
16th to endDay
37%5%9%27%19%1
1760
November1st to 15thDay
35%6%11%22%17%5%
1622
16th to endDay
40%410%25%16%2
1491
December1st to 15thDay
39%6%15%23%12%2
1440
16th to endDay
45%411%24%13%1
1536
January1st to 15thNight
41%5%10%19%17%4
2431
16th to endNight
39%412%26%15%1
2496
February1st to 15thNight
39%5%12%23%15%2
2287
16th to endNight
40%49%25%17%2
1913
March1st to 15thNight
39%5%11%26%13%2
2013
16th to endNight
42%6%11%19%16%3
2082
April1st to 15thNight
38%6%11%19%19%3
1796
16th to endNight
39%6%10%19%17%7%
1800
May1st to 15thNight
44%5%11%21%13%2
1631
16th to endNight
35%8%18%19%14%2
1497
June1st to 15thNight
33%8%14%26%15%1
1440
16th to endNight
36%6%13%23%17%2
1440
July1st to 15thNight
43%9%15%16%11%4
1360
16th to endNight
26%9%19%24%17%2
1564
August1st to 15thNight
34%9%13%22%18%1
1609
16th to endNight
36%8%11%23%17%3
1904
September1st to 15thNight
37%5%11%21%20%4
1750
16th to endNight
41%6%8%18%20%3
1807
October1st to 15thNight
41%48%24%17%2
1980
16th to endNight
32%5%10%27%21%2
2112
November1st to 15thNight
36%48%22%20%7%
2233
16th to endNight
37%5%11%22%17%4
2466
December1st to 15thNight
44%6%11%22%13%2
2520
16th to endNight
43%5%12%23%12%1
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
24%27%32%12%11
73
16th to endDay
21%26%33%16%2
96
February1st to 15thDay
26%20%43%8%1
90
16th to endDay
16%20%41%20%1
219
March1st to 15thDay
19%19%30%24%5%
270
16th to endDay
20%15%35%20%5%2
288
April1st to 15thDay
17%16%32%21%10%1
270
16th to endDay
22%11%27%22%11%5%
270
May1st to 15thDay
25%19%22%17%9%4
288
16th to endDay
20%422%27%20%4
331
June1st to 15thDay
14%5%26%25%20%7%
315
16th to endDay
13%329%31%17%4
315
July1st to 15thDay
11%325%32%21%6%
305
16th to endDay
9%15%34%27%11%
326
August1st to 15thDay
14%117%29%24%12%
313
16th to endDay
10%11%34%27%16%
332
September1st to 15thDay
13%7%20%21%19%18%
294
16th to endDay
24%117%25%16%13%
254
October1st to 15thDay
23%5%17%25%22%5%
255
16th to endDay
15%13%26%29%12%1
272
November1st to 15thDay
18%11%26%23%17%3
242
16th to endDay
21%11%36%17%11%
111
December1st to 15thDay
18%26%28%11%11%3
60
16th to endDay
37%10%29%18%3
64
January1st to 15thNight
18%17%38%21%3
720
16th to endNight
20%17%39%21%1
768
February1st to 15thNight
18%16%37%25%1
704
16th to endNight
20%20%37%20%1
631
March1st to 15thNight
19%15%35%25%3
720
16th to endNight
18%13%41%19%5%1
768
April1st to 15thNight
16%17%37%22%4
718
16th to endNight
18%9%29%30%10%
720
May1st to 15thNight
23%7%28%29%11%
551
16th to endNight
16%5%19%38%18%1
375
June1st to 15thNight
10%227%35%22%
360
16th to endNight
9%124%48%15%
360
July1st to 15thNight
9%121%42%24%
340
16th to endNight
6%115%41%31%3
533
August1st to 15thNight
12%12%44%27%2
539
16th to endNight
12%114%37%28%4
758
September1st to 15thNight
14%322%29%27%3
700
16th to endNight
16%219%31%26%2
657
October1st to 15thNight
19%6%22%27%20%2
660
16th to endNight
17%11%32%27%11%
704
November1st to 15thNight
15%10%32%27%11%2
700
16th to endNight
19%16%29%25%8%
720
December1st to 15thNight
19%14%34%23%8%
720
16th to endNight
19%15%37%23%3
768
Page generated at 2017-09-11 19:35:30. Version ac04

Copyright 2017 A. Danko


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