Ashton Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ashton Observatory clear sky chart from 2005-11-05 to 2017-03-25.

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
38%
15483
19%
45336
11%
15436
45%
15436
26%
29224

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
30%
900
15%
2467
6%
895
37%
895
23%
1672
January16th to endNight
25%
960
17%
2496
5%
960
33%
960
21%
1799
February1st to 15thNight
25%
880
13%
2288
4%
876
30%
876
21%
1649
February16th to endNight
30%
720
20%
1982
7%
720
39%
720
26%
1313
March1st to 15thNight
33%
558
21%
1998
14%
558
44%
558
24%
1200
March16th to endNight
24%
558
11%
2041
6%
558
33%
558
15%
1396
April1st to 15thNight
29%
494
18%
1647
13%
494
39%
494
22%
1055
April16th to endNight
31%
495
17%
1587
10%
495
42%
495
21%
1072
May1st to 15thNight
36%
495
17%
1436
11%
495
43%
495
24%
975
May16th to endNight
44%
515
17%
1370
8%
513
50%
513
29%
919
June1st to 15thNight
53%
495
17%
1320
8%
495
57%
495
33%
841
June16th to endNight
56%
495
18%
1320
8%
495
59%
495
41%
780
July1st to 15thNight
71%
465
19%
1240
11%
465
72%
465
46%
700
July16th to endNight
72%
522
23%
1404
18%
489
74%
489
45%
752
August1st to 15thNight
69%
494
22%
1475
23%
491
70%
491
36%
849
August16th to endNight
64%
525
20%
1678
22%
525
67%
525
33%
975
September1st to 15thNight
58%
495
28%
1650
28%
495
64%
495
33%
910
September16th to endNight
51%
533
25%
1817
19%
533
60%
533
34%
992
October1st to 15thNight
41%
660
26%
1980
17%
660
48%
660
32%
1175
October16th to endNight
34%
704
21%
2112
10%
704
43%
704
28%
1306
November1st to 15thNight
36%
760
24%
2300
13%
760
47%
760
31%
1345
November16th to endNight
29%
900
17%
2520
8%
900
37%
900
25%
1668
December1st to 15thNight
22%
900
13%
2520
5%
900
30%
900
18%
1856
December16th to endNight
25%
960
15%
2688
6%
960
33%
960
16%
2025

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%7%35%5%2445%7%38%
45617
Night
12%7%35%424346%44%
45515
Cloud CoverDay
14%7%36%5%2445%7%38%
45626
Night
12%7%35%424446%44%
45519
TransparencyDay
44%6%13%22%11%1
45314
Night
40%5%13%24%14%2
45336
SeeingDay
16%7%26%29%16%4
5216
Night
15%7%31%31%11%
15483

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
9%9%5%8%7%45%446%34%
1469
16th to endDay
12%11%7%9%7%3445%6%26%
1728
February1st to 15thDay
11%13%5%7%435%45%5%32%
1575
16th to endDay
13%7%5%6%5%25%445%37%
1490
March1st to 15thDay
13%10%5%6%5%345%47%33%
1960
16th to endDay
18%11%46%423446%31%
2050
April1st to 15thDay
18%7%45%42345%5%36%
1971
16th to endDay
24%8%36%5%23445%31%
2040
May1st to 15thDay
20%7%35%6%35%45%6%30%
2185
16th to endDay
15%6%25%435%45%6%38%
2393
June1st to 15thDay
14%6%25%5%35%46%7%37%
2310
16th to endDay
9%4245%35%5%5%10%43%
2310
July1st to 15thDay
9%4234245%6%8%47%
2310
16th to endDay
8%3145%35%6%6%10%44%
2348
August1st to 15thDay
8%415%6%35%5%7%9%42%
2145
16th to endDay
12%5%15%424347%46%
2171
September1st to 15thDay
13%414313346%52%
1980
16th to endDay
12%4144235%47%49%
1800
October1st to 15thDay
13%7%25%423345%47%
1650
16th to endDay
17%8%25%323435%42%
1760
November1st to 15thDay
10%5%343235%5%7%47%
1556
16th to endDay
16%10%345%14347%38%
1440
December1st to 15thDay
18%12%5%7%425%446%28%
1440
16th to endDay
16%13%6%11%7%24345%23%
1536
January1st to 15thNight
11%8%36%5%35%447%38%
2467
16th to endNight
11%11%5%7%5%24346%35%
2496
February1st to 15thNight
12%11%47%5%24446%35%
2285
16th to endNight
13%7%35%424346%44%
1982
March1st to 15thNight
15%7%24313335%47%
1986
16th to endNight
16%8%36%6%35%45%7%33%
2041
April1st to 15thNight
15%6%35%424347%42%
1647
16th to endNight
19%6%35%5%24335%39%
1587
May1st to 15thNight
16%414436%5%5%8%38%
1436
16th to endNight
11%6%25%5%35%448%42%
1368
June1st to 15thNight
10%4245%25%45%9%46%
1320
16th to endNight
7%42432346%10%51%
1320
July1st to 15thNight
421322446%11%56%
1320
16th to endNight
421442446%8%56%
1510
August1st to 15thNight
5%325%3235%47%54%
1485
16th to endNight
9%42442445%5%53%
1678
September1st to 15thNight
10%414423346%55%
1650
16th to endNight
11%31422345%7%54%
1817
October1st to 15thNight
14%424413245%52%
1980
16th to endNight
14%7%34323245%47%
2112
November1st to 15thNight
12%5%24323347%51%
2300
16th to endNight
17%7%24424346%43%
2520
December1st to 15thNight
15%13%47%5%24445%32%
2520
16th to endNight
19%11%37%5%2444431%
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
9%9%5%9%6%45%447%33%
1469
16th to endDay
12%12%7%8%7%345%47%25%
1728
February1st to 15thDay
11%14%5%7%435%45%5%32%
1575
16th to endDay
13%8%5%6%6%25%446%37%
1490
March1st to 15thDay
13%10%5%6%5%445%47%32%
1971
16th to endDay
18%11%46%5%23446%31%
2048
April1st to 15thDay
18%7%45%42445%6%36%
1971
16th to endDay
24%8%36%5%24446%31%
2040
May1st to 15thDay
20%8%36%5%3445%7%30%
2185
16th to endDay
15%6%26%5%35%5%47%37%
2393
June1st to 15thDay
14%6%25%5%25%46%8%37%
2310
16th to endDay
9%4245%345%6%9%44%
2310
July1st to 15thDay
9%42343446%8%47%
2310
16th to endDay
8%3145%35%5%6%10%44%
2348
August1st to 15thDay
8%415%6%35%5%7%9%42%
2145
16th to endDay
12%425%424447%45%
2171
September1st to 15thDay
12%5%24323246%51%
1980
16th to endDay
12%325%423447%49%
1800
October1st to 15thDay
13%7%35%422345%47%
1650
16th to endDay
16%8%36%323345%42%
1760
November1st to 15thDay
10%6%344135%47%47%
1556
16th to endDay
16%10%345%23347%38%
1440
December1st to 15thDay
18%12%5%7%5%25%447%27%
1440
16th to endDay
17%13%6%10%8%24345%24%
1536
January1st to 15thNight
11%8%45%6%35%5%47%38%
2467
16th to endNight
11%11%5%8%5%24346%35%
2496
February1st to 15thNight
12%11%47%5%24347%34%
2278
16th to endNight
12%8%35%424336%44%
1982
March1st to 15thNight
15%7%34313336%47%
1998
16th to endNight
15%8%37%6%35%45%6%32%
2041
April1st to 15thNight
15%7%35%423347%42%
1647
16th to endNight
19%6%35%5%23435%39%
1587
May1st to 15thNight
16%424436%5%5%8%38%
1435
16th to endNight
10%7%25%6%34448%42%
1368
June1st to 15thNight
9%4245%2445%10%45%
1320
16th to endNight
7%42342446%10%51%
1320
July1st to 15thNight
41132245%6%11%56%
1320
16th to endNight
421442346%8%56%
1510
August1st to 15thNight
5%415%3335%48%54%
1485
16th to endNight
9%315%33445%5%53%
1678
September1st to 15thNight
10%423423336%55%
1650
16th to endNight
10%31422345%7%53%
1817
October1st to 15thNight
14%424322235%52%
1980
16th to endNight
14%7%34313335%47%
2112
November1st to 15thNight
12%5%24323346%51%
2300
16th to endNight
16%7%24414346%43%
2520
December1st to 15thNight
15%13%47%5%24445%32%
2520
16th to endNight
19%11%37%6%24435%30%
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
50%5%13%18%10%
1470
16th to endDay
57%6%14%15%5%
1728
February1st to 15thDay
52%5%14%20%6%
1576
16th to endDay
48%6%14%18%10%1
1490
March1st to 15thDay
50%6%15%18%9%
1971
16th to endDay
53%6%14%17%6%1
2050
April1st to 15thDay
47%5%10%27%8%
1971
16th to endDay
54%5%12%18%8%1
2040
May1st to 15thDay
53%6%13%18%7%
2185
16th to endDay
45%7%13%20%10%2
2397
June1st to 15thDay
43%7%15%20%12%
2310
16th to endDay
33%8%14%25%15%1
2310
July1st to 15thDay
34%7%16%24%13%3
2161
16th to endDay
31%8%17%24%16%1
2191
August1st to 15thDay
35%8%16%24%14%1
2131
16th to endDay
37%5%12%25%15%3
2171
September1st to 15thDay
33%5%13%24%21%2
1980
16th to endDay
33%6%12%31%15%
1800
October1st to 15thDay
38%310%25%18%2
1650
16th to endDay
44%312%25%12%1
1760
November1st to 15thDay
35%413%25%19%1
1556
16th to endDay
45%415%25%7%
1440
December1st to 15thDay
57%415%14%7%
1440
16th to endDay
63%5%11%12%6%
1536
January1st to 15thNight
44%5%17%18%13%
2467
16th to endNight
49%5%15%20%8%
2496
February1st to 15thNight
50%413%22%8%
2288
16th to endNight
41%5%13%24%13%1
1982
March1st to 15thNight
39%412%27%13%1
1998
16th to endNight
51%5%15%17%8%1
2041
April1st to 15thNight
42%410%25%14%2
1647
16th to endNight
47%412%20%12%2
1587
May1st to 15thNight
42%8%15%21%11%1
1436
16th to endNight
40%5%12%23%14%2
1370
June1st to 15thNight
35%5%17%25%12%2
1320
16th to endNight
27%6%13%26%21%4
1320
July1st to 15thNight
21%8%19%30%14%4
1240
16th to endNight
22%6%17%31%19%2
1404
August1st to 15thNight
27%8%12%32%16%2
1475
16th to endNight
32%6%11%23%19%7%
1678
September1st to 15thNight
30%5%8%26%24%3
1650
16th to endNight
29%5%11%32%19%2
1817
October1st to 15thNight
35%39%25%22%3
1980
16th to endNight
39%313%24%15%2
2112
November1st to 15thNight
33%412%26%19%3
2300
16th to endNight
43%314%26%11%
2520
December1st to 15thNight
53%5%12%19%8%
2520
16th to endNight
56%412%16%9%
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
23%10%41%20%23
90
16th to endDay
21%10%36%27%22
96
February1st to 15thDay
16%20%36%22%4
90
16th to endDay
20%9%41%17%7%2
81
March1st to 15thDay
17%21%38%20%11
90
16th to endDay
37%8%37%13%21
83
April1st to 15thDay
21%12%28%26%10%
210
16th to endDay
30%10%24%24%7%2
270
May1st to 15thDay
24%14%30%19%9%1
393
16th to endDay
17%7%30%27%15%2
437
June1st to 15thDay
14%6%27%32%14%5%
420
16th to endDay
8%429%35%17%5%
420
July1st to 15thDay
8%223%34%22%9%
400
16th to endDay
9%119%37%26%4
445
August1st to 15thDay
8%317%36%30%4
418
16th to endDay
13%413%36%25%6%
339
September1st to 15thDay
14%220%32%23%7%
255
16th to endDay
8%6%32%25%22%4
127
October1st to 15thDay
413%30%36%6%8%
90
16th to endDay
20%9%29%30%10%
96
November1st to 15thDay
5%433%33%17%5%
90
16th to endDay
40%11%36%8%3
90
December1st to 15thDay
22%16%34%18%7%
90
16th to endDay
30%16%39%11%2
96
January1st to 15thNight
14%11%37%27%8%
900
16th to endNight
16%10%37%29%5%
960
February1st to 15thNight
17%10%37%27%6%
880
16th to endNight
16%9%39%26%5%1
720
March1st to 15thNight
19%9%33%25%10%1
558
16th to endNight
18%11%39%23%6%
558
April1st to 15thNight
16%12%37%27%5%
494
16th to endNight
21%8%34%26%7%1
495
May1st to 15thNight
20%7%32%30%9%
495
16th to endNight
13%333%33%15%
515
June1st to 15thNight
12%324%47%10%
495
16th to endNight
8%129%44%15%
495
July1st to 15thNight
418%46%27%2
465
16th to endNight
5%15%47%28%2
522
August1st to 15thNight
6%113%48%27%1
494
16th to endNight
10%217%41%26%2
525
September1st to 15thNight
13%318%35%24%5%
495
16th to endNight
11%5%27%33%20%1
533
October1st to 15thNight
15%6%32%30%13%1
660
16th to endNight
17%9%33%28%10%
704
November1st to 15thNight
16%10%33%29%10%
760
16th to endNight
20%10%36%23%8%
900
December1st to 15thNight
21%12%35%25%4
900
16th to endNight
25%10%31%26%6%
960
Page generated at 2017-03-26 12:16:43. Version ac04

Copyright 2017 A. Danko


Ashton Observatory Clear Sky Chart | Charts Home