Ashton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ashton clear sky chart from 2005-11-05 to 2018-02-13.

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
50%
16192
17%
48700
14%
16153
53%
16153
26%
31643

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
39%
870
8%
2809
7%
869
40%
869
14%
2148
January16th to endNight
39%
832
11%
2723
10%
832
40%
832
15%
2033
February1st to 15thNight
31%
747
8%
2444
8%
745
34%
745
13%
1885
February16th to endNight
32%
632
10%
1971
8%
632
36%
632
14%
1476
March1st to 15thNight
44%
720
11%
2025
10%
720
46%
720
21%
1451
March16th to endNight
42%
768
13%
2112
8%
768
45%
768
22%
1509
April1st to 15thNight
45%
611
14%
1810
9%
611
48%
611
23%
1221
April16th to endNight
44%
540
21%
1620
15%
540
47%
540
29%
1013
May1st to 15thNight
52%
539
18%
1619
15%
539
55%
539
31%
968
May16th to endNight
50%
561
15%
1523
11%
561
55%
561
30%
987
June1st to 15thNight
53%
404
15%
1304
12%
404
60%
404
31%
757
June16th to endNight
72%
360
27%
1260
29%
360
80%
360
53%
542
July1st to 15thNight
82%
340
26%
1201
31%
340
87%
340
56%
496
July16th to endNight
79%
520
28%
1549
30%
487
82%
487
59%
667
August1st to 15thNight
74%
539
28%
1611
25%
536
76%
536
51%
790
August16th to endNight
72%
573
38%
1719
30%
573
76%
573
56%
801
September1st to 15thNight
70%
633
29%
1887
23%
633
76%
633
48%
957
September16th to endNight
70%
716
32%
1980
25%
716
74%
716
46%
1065
October1st to 15thNight
57%
720
23%
2121
18%
720
60%
720
34%
1278
October16th to endNight
60%
768
25%
2352
21%
768
64%
768
33%
1396
November1st to 15thNight
45%
809
17%
2519
16%
809
47%
809
22%
1702
November16th to endNight
41%
975
13%
2730
9%
975
44%
975
22%
1921
December1st to 15thNight
35%
975
7%
2730
4%
975
37%
975
15%
2136
December16th to endNight
30%
1040
8%
3081
6%
1040
33%
1040
13%
2444

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
11%8%35%423446%44%
49345
Night
13%10%35%423446%41%
48875
TransparencyDay
40%310%21%15%7%
49019
Night
44%312%20%13%5%
48701
SeeingDay
16%8%23%26%19%5%
6271
Night
18%416%36%20%2
16204

By Month

Percentage Cloud Cover SW (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
22%16%5%8%5%23335%24%
1469
16th to endDay
20%16%6%7%5%2323328%
1849
February1st to 15thDay
21%14%5%6%423445%26%
1683
16th to endDay
14%15%5%9%7%33445%26%
1503
March1st to 15thDay
12%15%36%5%345%5%6%31%
1935
16th to endDay
13%13%48%6%4445%6%27%
2112
April1st to 15thDay
12%12%47%6%35%45%7%31%
2135
16th to endDay
11%9%36%6%3445%8%35%
2340
May1st to 15thDay
9%7%25%6%34448%44%
2331
16th to endDay
12%7%36%5%36%5%5%6%35%
2588
June1st to 15thDay
12%6%244345%7%8%40%
2653
16th to endDay
3212323346%65%
2700
July1st to 15thDay
221221345%8%64%
2685
16th to endDay
221231345%6%66%
2512
August1st to 15thDay
321332345%8%63%
2340
16th to endDay
3212323347%64%
2483
September1st to 15thDay
6%313413335%63%
2071
16th to endDay
9%413322347%57%
1980
October1st to 15thDay
13%6%244245%5%6%44%
1837
16th to endDay
13%6%24324346%47%
1871
November1st to 15thDay
20%10%34323335%38%
1656
16th to endDay
18%12%35%5%3243434%
1560
December1st to 15thDay
20%16%49%7%2323424%
1560
16th to endDay
22%16%5%8%5%2332423%
1492
January1st to 15thNight
21%16%5%7%5%2333427%
2809
16th to endNight
19%16%6%7%42333428%
2723
February1st to 15thNight
20%19%6%7%42323326%
2433
16th to endNight
15%16%6%8%6%34445%25%
1971
March1st to 15thNight
15%14%45%5%3435%7%32%
2025
16th to endNight
14%12%37%5%3445%7%31%
2112
April1st to 15thNight
11%10%46%5%345%5%8%33%
1810
16th to endNight
12%6%35%325%45%5%43%
1620
May1st to 15thNight
8%7%25%425%45%7%45%
1619
16th to endNight
10%8%25%425%6%6%9%37%
1522
June1st to 15thNight
10%5%24435%5%5%9%44%
1304
16th to endNight
412223348%66%
1260
July1st to 15thNight
11222346%12%62%
1272
16th to endNight
11232335%7%68%
1656
August1st to 15thNight
321331445%10%60%
1620
16th to endNight
3212223335%69%
1719
September1st to 15thNight
6%21322335%5%62%
1887
16th to endNight
8%3122235%46%58%
1980
October1st to 15thNight
13%6%24323345%50%
2121
16th to endNight
14%5%14323436%49%
2352
November1st to 15thNight
19%12%34323335%36%
2519
16th to endNight
16%12%46%423435%35%
2730
December1st to 15thNight
20%15%5%8%5%2432426%
2730
16th to endNight
22%18%6%8%5%1323323%
3081

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
63%413%12%5%1
1469
16th to endDay
60%314%15%41
1849
February1st to 15thDay
59%5%13%17%4
1683
16th to endDay
59%312%19%5%1
1503
March1st to 15thDay
51%5%16%20%5%1
1935
16th to endDay
56%312%20%6%
2112
April1st to 15thDay
51%413%21%9%
2135
16th to endDay
46%211%26%11%1
2340
May1st to 15thDay
37%28%33%16%1
2331
16th to endDay
46%212%25%10%1
2591
June1st to 15thDay
39%411%26%14%3
2653
16th to endDay
19%15%23%33%16%
2700
July1st to 15thDay
17%3421%30%22%
2527
16th to endDay
18%2314%27%32%
2356
August1st to 15thDay
18%35%19%29%23%
2325
16th to endDay
19%35%20%31%19%
2483
September1st to 15thDay
24%27%20%32%13%
2071
16th to endDay
27%210%29%22%8%
1980
October1st to 15thDay
37%413%31%9%3
1837
16th to endDay
38%316%26%14%
1871
November1st to 15thDay
49%415%21%7%2
1656
16th to endDay
53%319%17%5%
1560
December1st to 15thDay
64%311%16%3
1560
16th to endDay
66%314%11%31
1492
January1st to 15thNight
60%415%12%5%1
2809
16th to endNight
58%415%15%5%1
2723
February1st to 15thNight
62%413%15%4
2444
16th to endNight
60%213%17%41
1971
March1st to 15thNight
50%5%15%20%6%1
2025
16th to endNight
50%414%24%5%
2112
April1st to 15thNight
46%415%22%10%
1810
16th to endNight
40%312%30%13%
1620
May1st to 15thNight
36%39%32%16%1
1620
16th to endNight
40%315%23%15%1
1523
June1st to 15thNight
34%413%28%15%2
1304
16th to endNight
17%16%21%36%16%
1260
July1st to 15thNight
14%35%25%27%24%
1201
16th to endNight
13%3415%28%34%
1549
August1st to 15thNight
20%3421%24%25%
1611
16th to endNight
17%25%20%30%23%
1719
September1st to 15thNight
22%26%18%31%17%
1887
16th to endNight
25%39%28%26%8%
1980
October1st to 15thNight
36%212%31%13%3
2121
16th to endNight
36%213%28%17%
2352
November1st to 15thNight
48%313%24%6%2
2519
16th to endNight
50%318%17%8%1
2730
December1st to 15thNight
62%416%13%3
2730
16th to endNight
66%212%13%41
3081

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
33%16%25%25%7%
90
16th to endDay
30%215%30%16%5%
139
February1st to 15thDay
38%319%18%15%4
126
16th to endDay
22%16%29%22%9%
162
March1st to 15thDay
20%18%31%22%6%
270
16th to endDay
25%17%31%19%5%1
288
April1st to 15thDay
22%15%28%20%10%2
269
16th to endDay
21%14%30%20%11%2
270
May1st to 15thDay
14%11%32%19%18%3
288
16th to endDay
17%8%18%25%20%8%
489
June1st to 15thDay
16%9%17%28%22%5%
495
16th to endDay
47%26%29%25%6%
495
July1st to 15thDay
45%19%32%32%5%
461
16th to endDay
35%31%34%21%4
327
August1st to 15thDay
5%5%28%28%26%4
315
16th to endDay
47%18%30%24%13%
332
September1st to 15thDay
8%8%22%28%19%12%
315
16th to endDay
13%6%22%26%23%6%
315
October1st to 15thDay
19%6%24%22%22%4
172
16th to endDay
22%415%32%18%6%
144
November1st to 15thDay
29%114%28%14%10%
135
16th to endDay
29%322%34%8%
135
December1st to 15thDay
36%216%27%12%5%
135
16th to endDay
39%313%24%15%3
104
January1st to 15thNight
28%413%36%15%2
874
16th to endNight
29%214%32%17%2
832
February1st to 15thNight
30%5%16%33%12%2
752
16th to endNight
21%7%20%35%12%2
632
March1st to 15thNight
22%6%15%38%15%1
720
16th to endNight
21%7%20%35%14%1
768
April1st to 15thNight
17%6%20%37%15%2
611
16th to endNight
17%426%33%15%1
540
May1st to 15thNight
12%6%22%36%20%2
540
16th to endNight
14%7%18%34%22%2
563
June1st to 15thNight
12%5%21%37%22%1
404
16th to endNight
5%216%48%24%3
360
July1st to 15thNight
111%42%40%2
340
16th to endNight
2110%44%37%3
520
August1st to 15thNight
3212%41%37%2
539
16th to endNight
4215%37%35%4
573
September1st to 15thNight
8%113%38%30%6%
633
16th to endNight
10%213%31%32%9%
716
October1st to 15thNight
16%315%36%24%3
720
16th to endNight
17%212%40%21%4
768
November1st to 15thNight
25%5%15%34%16%1
809
16th to endNight
22%6%19%33%15%2
975
December1st to 15thNight
26%5%16%38%12%1
975
16th to endNight
31%415%34%11%2
1040
Page generated at 2018-02-13 18:46:03. Version ac04

Copyright 2018 A. Danko


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