Ashern
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ashern clear sky chart from 2005-11-06 to 2024-01-13.

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
38%
25170
12%
74662
7%
25119
42%
25119
20%
52257

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
31%
950
9%
2837
5%
946
35%
946
15%
2170
January11th to 20thNight
31%
915
9%
2743
6%
915
33%
915
14%
2129
January21st to endNight
30%
990
11%
2776
5%
990
35%
990
14%
2168
February1st to 10thNight
36%
900
12%
2507
7%
900
39%
900
19%
1831
February11th to 20thNight
41%
874
15%
2274
8%
874
45%
874
25%
1599
February21st to endNight
43%
659
19%
1843
11%
659
48%
659
24%
1275
March1st to 10thNight
40%
720
14%
2160
8%
720
45%
720
20%
1536
March11th to 20thNight
40%
545
18%
1985
13%
545
50%
545
22%
1247
March21st to endNight
38%
594
13%
2174
13%
594
43%
594
17%
1461
April1st to 10thNight
41%
540
19%
1729
17%
540
49%
540
25%
1081
April11th to 20thNight
41%
533
16%
1599
13%
533
47%
533
22%
1104
April21st to endNight
37%
540
13%
1620
8%
540
41%
540
24%
1080
May1st to 10thNight
38%
540
12%
1490
4%
540
40%
540
23%
1045
May11th to 20thNight
43%
531
14%
1241
6%
531
45%
531
31%
851
May21st to endNight
45%
584
6%
1358
4%
582
46%
582
26%
987
June1st to 10thNight
45%
540
3%
1260
3%
540
47%
540
28%
911
June11th to 20thNight
46%
540
1%
1260
1%
540
47%
540
32%
877
June21st to endNight
57%
540
0%
1260
1%
540
57%
540
30%
895
July1st to 10thNight
61%
525
3%
1225
4%
525
63%
525
46%
752
July11th to 20thNight
54%
522
5%
1218
3%
522
56%
522
42%
764
July21st to endNight
58%
591
12%
1325
7%
558
58%
558
41%
835
August1st to 10thNight
60%
537
15%
1424
6%
534
62%
534
37%
868
August11th to 20thNight
57%
534
16%
1591
9%
534
61%
534
36%
917
August21st to endNight
53%
594
19%
1782
17%
594
57%
594
33%
1070
September1st to 10thNight
50%
540
17%
1710
15%
540
56%
540
34%
962
September11th to 20thNight
46%
540
15%
1980
16%
540
51%
540
22%
1220
September21st to endNight
39%
540
19%
1980
16%
540
48%
540
22%
1218
October1st to 10thNight
35%
635
16%
2075
11%
635
40%
635
19%
1422
October11th to 20thNight
34%
828
16%
2268
9%
828
39%
828
21%
1650
October21st to endNight
27%
990
11%
2574
4%
990
31%
990
16%
1992
November1st to 10thNight
25%
925
9%
2554
3%
925
29%
925
13%
2030
November11th to 20thNight
25%
950
9%
2705
3%
950
30%
950
12%
2152
November21st to endNight
21%
950
7%
2850
2%
950
26%
950
11%
2256
December1st to 10thNight
33%
950
7%
2850
4%
950
36%
950
13%
2217
December11th to 20thNight
23%
950
11%
3457
4%
949
29%
949
10%
2565
December21st to endNight
29%
1034
7%
4978
6%
1026
34%
1026
9%
3120

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%47%6%45%5%6%8%35%
74640
Night
10%9%48%7%46%5%6%8%34%
75132
TransparencyDay
45%8%16%22%8%1
74323
Night
47%8%15%21%9%1
74968
SeeingDay
14%9%30%28%15%3
15102
Night
14%7%30%34%13%1
25186

By Month

Percentage Cloud Cover NW (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
8%12%7%10%8%6%8%7%7%7%21%
1329
11th to 20thDay
9%12%5%10%8%46%7%10%9%20%
1274
21st to endDay
9%13%7%12%8%5%7%7%7%8%17%
1579
February1st to 10thDay
8%11%5%9%11%5%7%6%7%7%23%
1452
11th to 20thDay
6%11%5%7%7%48%8%6%8%30%
1574
21st to endDay
7%8%410%9%47%8%7%7%30%
1430
March1st to 10thDay
13%9%5%9%8%46%6%6%7%27%
1800
11th to 20thDay
9%11%48%8%46%6%6%7%32%
1973
21st to endDay
10%10%47%7%36%5%6%7%35%
2182
April1st to 10thDay
9%9%37%6%46%5%5%8%38%
2231
11th to 20thDay
12%9%46%6%45%45%6%38%
2312
21st to endDay
13%7%47%5%45%5%6%8%38%
2340
May1st to 10thDay
14%8%35%5%35%5%6%7%40%
2465
11th to 20thDay
16%7%35%4345%5%7%42%
2655
21st to endDay
19%8%36%5%4446%7%36%
2918
June1st to 10thDay
15%7%46%6%345%6%8%37%
2700
11th to 20thDay
14%6%36%7%46%45%7%39%
2700
21st to endDay
12%6%25%6%36%6%7%9%38%
2700
July1st to 10thDay
8%4345%345%6%8%50%
2700
11th to 20thDay
11%426%435%5%7%9%44%
2700
21st to endDay
9%4244346%5%9%50%
2913
August1st to 10thDay
7%425%5%45%5%7%10%47%
2507
11th to 20thDay
12%5%26%5%35%46%8%44%
2310
21st to endDay
13%6%35%5%445%6%7%43%
2574
September1st to 10thDay
11%6%35%4245%6%7%45%
2247
11th to 20thDay
14%8%36%7%346%6%7%37%
1980
21st to endDay
13%6%27%5%445%8%9%37%
1980
October1st to 10thDay
18%11%47%6%345%6%8%30%
1866
11th to 20thDay
13%13%5%8%7%35%46%8%29%
1690
21st to endDay
15%14%8%10%7%35%5%5%6%22%
1782
November1st to 10thDay
17%15%6%10%8%335%46%24%
1523
11th to 20thDay
9%11%7%13%10%5%5%5%5%8%23%
1473
21st to endDay
12%14%5%9%8%47%45%7%25%
1330
December1st to 10thDay
6%13%6%13%11%6%7%6%5%7%19%
1330
11th to 20thDay
7%16%5%12%9%5%6%5%8%8%20%
1679
21st to endDay
7%8%48%8%36%7%6%7%35%
2442
January1st to 10thNight
7%11%6%11%9%5%7%7%7%8%23%
2837
11th to 20thNight
8%14%5%10%9%46%6%8%8%20%
2743
21st to endNight
10%11%411%8%5%7%8%7%10%19%
2776
February1st to 10thNight
8%10%5%10%8%46%7%7%8%28%
2507
11th to 20thNight
5%9%5%6%6%5%7%7%8%8%34%
2273
21st to endNight
6%8%6%10%7%46%5%5%7%36%
1843
March1st to 10thNight
11%10%5%7%8%35%5%6%8%33%
2160
11th to 20thNight
8%9%36%5%45%6%5%8%41%
1985
21st to endNight
11%11%47%7%35%5%6%6%35%
2174
April1st to 10thNight
8%8%36%6%45%6%6%8%40%
1729
11th to 20thNight
13%7%37%7%46%6%6%7%34%
1599
21st to endNight
11%7%48%6%36%5%5%8%38%
1620
May1st to 10thNight
16%8%36%5%36%5%5%6%36%
1490
11th to 20thNight
13%8%37%5%2435%7%43%
1241
21st to endNight
15%7%26%6%345%6%7%38%
1358
June1st to 10thNight
14%7%36%5%36%6%6%8%37%
1260
11th to 20thNight
15%4346%35%46%10%40%
1260
21st to endNight
11%426%437%7%8%8%41%
1260
July1st to 10thNight
6%313425%5%6%9%56%
1260
11th to 20thNight
7%425%4345%7%10%50%
1260
21st to endNight
6%424425%5%8%9%51%
1403
August1st to 10thNight
7%423435%5%7%8%53%
1432
11th to 20thNight
9%42443445%8%53%
1591
21st to endNight
13%5%25%33246%7%51%
1782
September1st to 10thNight
9%5%245%245%6%10%49%
1710
11th to 20thNight
12%6%35%6%245%6%7%44%
1980
21st to endNight
12%6%25%5%45%5%5%8%42%
1980
October1st to 10thNight
14%8%47%6%35%45%7%36%
2075
11th to 20thNight
13%10%48%7%35%5%5%7%33%
2268
21st to endNight
15%12%5%9%7%445%5%6%29%
2574
November1st to 10thNight
13%13%6%9%8%46%5%6%6%24%
2554
11th to 20thNight
9%13%6%11%8%5%6%46%6%26%
2705
21st to endNight
11%12%7%10%8%5%7%5%6%7%23%
2850
December1st to 10thNight
6%11%7%10%10%5%8%8%6%7%23%
2850
11th to 20thNight
8%13%7%12%8%46%6%6%7%24%
3518
21st to endNight
7%8%48%9%45%5%6%8%35%
5225

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
57%8%16%16%3
1329
11th to 20thDay
56%9%10%19%5%
1274
21st to endDay
63%7%8%14%8%
1579
February1st to 10thDay
56%8%13%15%7%1
1452
11th to 20thDay
49%9%16%18%8%
1583
21st to endDay
49%7%13%23%8%
1430
March1st to 10thDay
55%8%13%17%6%
1800
11th to 20thDay
50%8%14%21%7%1
1975
21st to endDay
47%9%14%20%9%1
2182
April1st to 10thDay
44%7%14%22%12%1
2231
11th to 20thDay
46%6%12%20%15%1
2312
21st to endDay
43%7%15%26%7%2
2340
May1st to 10thDay
42%7%13%24%13%1
2465
11th to 20thDay
41%7%12%25%14%2
2659
21st to endDay
47%8%11%21%12%1
2918
June1st to 10thDay
44%7%15%24%9%1
2700
11th to 20thDay
44%8%15%22%10%1
2700
21st to endDay
40%10%21%22%5%
2700
July1st to 10thDay
30%9%21%30%10%1
2626
11th to 20thDay
34%8%19%30%8%1
2619
21st to endDay
31%9%21%31%8%
2751
August1st to 10thDay
32%9%22%30%7%
2491
11th to 20thDay
37%9%23%27%5%
2310
21st to endDay
38%9%19%28%6%
2574
September1st to 10thDay
35%9%19%28%8%1
2247
11th to 20thDay
44%9%18%23%5%
1980
21st to endDay
42%9%19%23%7%
1980
October1st to 10thDay
51%8%17%20%3
1866
11th to 20thDay
53%9%17%18%31
1690
21st to endDay
61%9%14%11%4
1782
November1st to 10thDay
62%8%11%15%41
1523
11th to 20thDay
59%11%14%11%4
1473
21st to endDay
58%8%16%14%4
1330
December1st to 10thDay
63%7%14%11%4
1330
11th to 20thDay
58%9%16%14%4
1680
21st to endDay
44%9%15%17%14%1
2442
January1st to 10thNight
56%9%13%17%5%
2837
11th to 20thNight
59%8%11%17%5%
2743
21st to endNight
58%9%11%15%8%
2776
February1st to 10thNight
51%7%15%17%10%
2507
11th to 20thNight
42%9%17%22%9%
2274
21st to endNight
46%6%12%28%9%
1843
March1st to 10thNight
49%7%13%21%9%1
2160
11th to 20thNight
40%8%15%25%11%1
1985
21st to endNight
47%8%13%19%11%2
2174
April1st to 10thNight
40%6%13%21%17%3
1729
11th to 20thNight
47%7%9%18%17%3
1599
21st to endNight
42%7%13%24%11%2
1620
May1st to 10thNight
46%7%12%22%12%1
1490
11th to 20thNight
41%6%10%27%14%3
1241
21st to endNight
45%8%13%17%15%2
1358
June1st to 10thNight
43%8%15%23%10%1
1260
11th to 20thNight
39%8%18%22%11%3
1260
21st to endNight
36%12%19%26%5%1
1260
July1st to 10thNight
23%10%18%36%13%1
1225
11th to 20thNight
28%8%23%30%11%1
1218
21st to endNight
26%10%21%31%11%1
1325
August1st to 10thNight
27%11%17%34%11%
1424
11th to 20thNight
28%8%22%33%8%1
1591
21st to endNight
33%6%15%34%10%
1782
September1st to 10thNight
29%7%20%30%13%1
1710
11th to 20thNight
37%10%18%26%8%1
1980
21st to endNight
39%8%15%29%9%
1980
October1st to 10thNight
47%8%15%22%8%
2075
11th to 20thNight
50%7%15%23%5%
2268
21st to endNight
54%9%15%18%4
2574
November1st to 10thNight
59%9%14%12%5%1
2554
11th to 20thNight
58%10%16%12%4
2705
21st to endNight
60%9%14%13%4
2850
December1st to 10thNight
58%9%16%13%5%
2850
11th to 20thNight
56%8%15%14%7%
3516
21st to endNight
46%8%12%19%14%1
5225

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
10%9%36%34%9%3
270
11th to 20thDay
9%8%36%32%13%1
246
21st to endDay
15%8%31%29%15%2
264
February1st to 10thDay
13%8%38%33%7%2
240
11th to 20thDay
14%8%33%28%12%4
240
21st to endDay
410%34%31%20%1
198
March1st to 10thDay
15%8%33%28%15%2
240
11th to 20thDay
12%11%36%27%11%3
240
21st to endDay
14%10%29%29%16%1
268
April1st to 10thDay
15%10%33%30%10%2
491
11th to 20thDay
17%8%31%31%12%1
590
21st to endDay
14%11%32%31%11%1
600
May1st to 10thDay
14%10%32%30%13%2
603
11th to 20thDay
19%8%27%28%15%4
625
21st to endDay
19%10%25%24%19%2
679
June1st to 10thDay
16%10%29%25%14%6%
630
11th to 20thDay
15%10%31%26%14%4
630
21st to endDay
13%6%23%33%20%5%
630
July1st to 10thDay
10%7%29%31%20%5%
621
11th to 20thDay
11%7%29%31%17%6%
618
21st to endDay
9%7%26%29%21%8%
684
August1st to 10thDay
7%7%29%29%21%7%
626
11th to 20thDay
12%7%23%27%22%9%
615
21st to endDay
15%8%25%28%20%3
693
September1st to 10thDay
13%9%31%32%12%2
537
11th to 20thDay
20%9%34%22%13%1
270
21st to endDay
20%9%34%28%8%1
270
October1st to 10thDay
22%13%26%24%13%3
270
11th to 20thDay
20%12%33%25%9%1
270
21st to endDay
23%15%32%21%8%2
297
November1st to 10thDay
23%11%33%23%9%1
270
11th to 20thDay
14%13%38%24%9%2
270
21st to endDay
20%11%37%25%5%1
270
December1st to 10thDay
13%9%37%23%15%3
270
11th to 20thDay
15%11%37%27%8%2
270
21st to endDay
9%6%36%29%17%3
297
January1st to 10thNight
11%7%34%34%12%2
950
11th to 20thNight
15%7%33%33%11%1
915
21st to endNight
15%8%32%34%11%1
990
February1st to 10thNight
12%8%30%37%12%1
900
11th to 20thNight
10%6%32%33%17%2
879
21st to endNight
9%5%31%38%17%2
659
March1st to 10thNight
15%6%26%35%16%2
720
11th to 20thNight
11%7%36%34%11%1
545
21st to endNight
17%7%29%30%13%3
594
April1st to 10thNight
11%6%35%35%11%1
540
11th to 20thNight
16%5%30%36%13%1
533
21st to endNight
12%6%35%36%9%1
540
May1st to 10thNight
19%7%29%34%11%1
540
11th to 20thNight
17%8%27%34%13%2
531
21st to endNight
19%8%22%36%14%1
584
June1st to 10thNight
18%5%26%32%18%1
540
11th to 20thNight
16%427%37%15%1
540
21st to endNight
13%6%18%41%21%1
540
July1st to 10thNight
7%325%44%21%1
525
11th to 20thNight
9%5%28%38%19%2
522
21st to endNight
7%427%33%25%4
591
August1st to 10thNight
8%423%42%21%2
537
11th to 20thNight
10%425%37%20%5%
534
21st to endNight
16%424%36%19%2
594
September1st to 10thNight
11%6%29%36%17%2
540
11th to 20thNight
13%8%27%41%11%1
540
21st to endNight
14%5%34%34%12%1
540
October1st to 10thNight
19%9%30%33%9%
635
11th to 20thNight
19%7%30%31%12%1
828
21st to endNight
21%12%31%29%7%1
990
November1st to 10thNight
17%11%33%25%11%2
925
11th to 20thNight
15%12%35%27%8%3
950
21st to endNight
16%11%39%27%6%1
950
December1st to 10thNight
10%8%31%36%13%2
950
11th to 20thNight
14%9%37%30%9%1
950
21st to endNight
15%6%33%30%14%2
1045
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Copyright 2024 Attilla Danko


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