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 2017-09-10.

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
39%
15984
19%
46823
11%
15937
46%
15937
27%
30074

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%
576
11%
2106
6%
576
32%
576
15%
1458
April1st to 15thNight
28%
539
16%
1797
12%
539
38%
539
22%
1162
April16th to endNight
32%
540
18%
1731
11%
540
43%
540
21%
1170
May1st to 15thNight
38%
540
17%
1566
10%
540
45%
540
26%
1040
May16th to endNight
43%
563
18%
1498
9%
561
50%
561
29%
1002
June1st to 15thNight
55%
540
16%
1440
8%
540
58%
540
36%
894
June16th to endNight
55%
540
19%
1440
9%
540
58%
540
41%
849
July1st to 15thNight
71%
510
18%
1360
11%
510
72%
510
47%
762
July16th to endNight
72%
564
24%
1525
19%
531
75%
531
46%
812
August1st to 15thNight
69%
539
21%
1610
23%
536
71%
536
37%
914
August16th to endNight
64%
573
22%
1832
24%
573
67%
573
34%
1052
September1st to 15thNight
58%
525
27%
1750
27%
525
64%
525
34%
959
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
13%7%35%5%2445%7%39%
47802
Night
12%7%35%424346%44%
47002
Cloud CoverDay
13%7%35%5%2445%7%39%
47811
Night
12%7%35%424447%44%
47006
TransparencyDay
44%6%13%22%12%1
47499
Night
40%5%13%24%14%2
46823
SeeingDay
15%7%27%29%16%4
5995
Night
15%7%31%31%12%1
15984

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
19%11%46%423446%30%
2118
April1st to 15thDay
19%7%45%42345%6%35%
2151
16th to endDay
24%8%36%5%23446%30%
2226
May1st to 15thDay
19%7%35%5%3445%7%32%
2385
16th to endDay
16%6%25%5%35%45%6%38%
2617
June1st to 15thDay
13%5%25%5%35%45%8%41%
2520
16th to endDay
9%4245%35%5%6%10%44%
2520
July1st to 15thDay
8%4234245%6%9%48%
2520
16th to endDay
7%3145%35%6%6%10%45%
2535
August1st to 15thDay
7%415%5%35%5%7%9%43%
2340
16th to endDay
11%5%15%5%24347%45%
2369
September1st to 15thDay
12%414313346%53%
2097
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%46%6%35%446%32%
2106
April1st to 15thNight
15%7%35%424347%41%
1797
16th to endNight
19%6%35%5%23335%39%
1731
May1st to 15thNight
15%414435%45%8%40%
1566
16th to endNight
11%6%25%5%35%348%42%
1496
June1st to 15thNight
9%32442445%9%48%
1440
16th to endNight
7%32432346%10%51%
1440
July1st to 15thNight
321322445%11%57%
1440
16th to endNight
421442446%8%57%
1631
August1st to 15thNight
5%3243235%5%7%55%
1620
16th to endNight
9%32442345%5%54%
1832
September1st to 15thNight
10%414423345%56%
1750
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
19%12%46%5%23436%30%
2116
April1st to 15thDay
19%7%45%42445%6%35%
2151
16th to endDay
24%8%36%5%14446%30%
2226
May1st to 15thDay
19%7%35%5%3445%7%32%
2385
16th to endDay
15%6%26%5%35%5%47%37%
2617
June1st to 15thDay
13%5%25%5%2445%8%41%
2520
16th to endDay
9%3245%35%5%6%10%44%
2520
July1st to 15thDay
8%42343446%9%48%
2520
16th to endDay
7%3145%25%5%6%10%45%
2535
August1st to 15thDay
7%415%6%35%5%7%9%43%
2340
16th to endDay
11%425%5%24447%45%
2369
September1st to 15thDay
12%424313247%52%
2097
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
16%9%37%6%35%45%6%31%
2106
April1st to 15thNight
15%7%35%433347%41%
1797
16th to endNight
19%6%35%5%23436%39%
1731
May1st to 15thNight
15%424435%5%5%8%40%
1565
16th to endNight
10%6%25%5%34448%42%
1496
June1st to 15thNight
9%4245%2445%10%47%
1440
16th to endNight
7%4234145%6%10%51%
1440
July1st to 15thNight
311322446%11%57%
1440
16th to endNight
4244235%6%8%56%
1631
August1st to 15thNight
5%325%3335%5%8%54%
1620
16th to endNight
9%31433445%5%53%
1832
September1st to 15thNight
9%424423336%56%
1750
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
54%5%14%16%6%
2118
April1st to 15thDay
48%5%11%26%8%
2151
16th to endDay
54%5%11%17%9%
2226
May1st to 15thDay
51%6%13%20%8%
2385
16th to endDay
45%7%13%20%11%2
2621
June1st to 15thDay
40%7%14%21%14%
2520
16th to endDay
33%8%14%25%15%1
2520
July1st to 15thDay
33%8%16%25%13%3
2371
16th to endDay
30%8%17%25%17%1
2378
August1st to 15thDay
34%8%16%24%14%1
2326
16th to endDay
37%5%12%25%15%3
2369
September1st to 15thDay
32%5%13%25%21%2
2097
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
52%5%15%17%8%1
2106
April1st to 15thNight
43%5%10%25%13%2
1797
16th to endNight
47%412%20%12%2
1731
May1st to 15thNight
40%7%15%22%13%
1566
16th to endNight
40%5%12%23%15%2
1498
June1st to 15thNight
33%5%16%25%14%3
1440
16th to endNight
27%7%13%25%22%4
1440
July1st to 15thNight
21%8%18%31%15%4
1360
16th to endNight
22%6%17%31%20%1
1525
August1st to 15thNight
26%8%12%33%15%2
1610
16th to endNight
30%6%11%24%19%6%
1832
September1st to 15thNight
29%5%8%27%24%3
1750
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
41%9%34%10%2
102
April1st to 15thDay
23%10%31%24%10%
270
16th to endDay
32%11%25%21%7%1
336
May1st to 15thDay
22%12%31%21%10%1
468
16th to endDay
17%8%30%26%13%2
517
June1st to 15thDay
12%5%26%32%17%5%
495
16th to endDay
8%5%32%33%15%4
495
July1st to 15thDay
7%224%33%24%9%
475
16th to endDay
8%119%38%27%4
515
August1st to 15thDay
7%318%37%28%5%
493
16th to endDay
12%415%34%24%7%
409
September1st to 15thDay
12%221%32%23%7%
294
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
19%10%39%23%6%
576
April1st to 15thNight
17%12%37%27%5%
539
16th to endNight
21%8%32%27%7%1
540
May1st to 15thNight
18%7%32%32%9%
540
16th to endNight
13%433%33%15%
563
June1st to 15thNight
11%324%46%12%
540
16th to endNight
8%130%43%14%
540
July1st to 15thNight
318%47%26%2
510
16th to endNight
5%15%48%27%2
564
August1st to 15thNight
5%214%47%27%2
539
16th to endNight
10%117%41%26%2
573
September1st to 15thNight
12%319%36%23%4
525
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 2017-09-11 18:35:14. Version ac04

Copyright 2017 A. Danko


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