Arthur
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Arthur clear sky chart from 2005-11-06 to 2024-03-01.

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%
24868
23%
80048
12%
24777
50%
24777
32%
45694

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
33%
938
24%
4355
10%
926
46%
926
21%
2468
January11th to 20thNight
30%
946
24%
4340
12%
930
43%
930
23%
2265
January21st to endNight
29%
1034
17%
4595
8%
1023
41%
1023
22%
2473
February1st to 10thNight
26%
801
20%
2365
7%
801
37%
801
26%
1521
February11th to 20thNight
25%
743
21%
2218
7%
740
38%
740
29%
1354
February21st to endNight
29%
628
24%
1884
8%
628
43%
628
33%
1080
March1st to 10thNight
35%
722
24%
2166
9%
722
46%
722
33%
1242
March11th to 20thNight
34%
636
24%
2076
13%
636
46%
636
33%
1169
March21st to endNight
33%
594
17%
2054
10%
594
43%
594
22%
1289
April1st to 10thNight
28%
540
18%
1800
9%
540
41%
540
24%
1082
April11th to 20thNight
26%
533
19%
1777
9%
533
42%
533
24%
1073
April21st to endNight
36%
540
18%
1638
15%
540
44%
540
25%
1043
May1st to 10thNight
38%
540
17%
1620
12%
540
46%
540
27%
1038
May11th to 20thNight
38%
531
16%
1587
11%
531
44%
531
28%
1013
May21st to endNight
37%
582
14%
1552
6%
582
42%
582
25%
1080
June1st to 10thNight
49%
540
16%
1440
7%
540
52%
540
38%
869
June11th to 20thNight
40%
540
17%
1440
6%
540
46%
540
35%
897
June21st to endNight
56%
540
18%
1440
9%
540
59%
540
39%
862
July1st to 10thNight
54%
525
16%
1400
8%
525
57%
525
39%
840
July11th to 20thNight
62%
522
24%
1392
15%
522
65%
522
44%
792
July21st to endNight
60%
591
23%
1488
16%
558
64%
558
42%
873
August1st to 10thNight
56%
537
18%
1566
14%
534
60%
534
32%
958
August11th to 20thNight
57%
534
25%
1676
22%
534
65%
534
42%
892
August21st to endNight
55%
594
27%
1980
24%
594
66%
594
40%
1007
September1st to 10thNight
49%
540
28%
1800
21%
540
63%
540
39%
921
September11th to 20thNight
51%
540
29%
1957
25%
540
63%
540
37%
974
September21st to endNight
48%
540
31%
1980
25%
540
60%
540
38%
956
October1st to 10thNight
46%
540
31%
1980
24%
540
57%
540
32%
1044
October11th to 20thNight
46%
725
31%
2165
16%
725
57%
725
41%
1138
October21st to endNight
41%
990
29%
2574
13%
990
49%
990
40%
1504
November1st to 10thNight
43%
925
31%
2405
13%
925
52%
925
46%
1353
November11th to 20thNight
37%
950
32%
2470
12%
950
50%
950
41%
1427
November21st to endNight
44%
950
30%
2470
14%
950
54%
950
44%
1418
December1st to 10thNight
31%
950
26%
2603
9%
950
44%
950
37%
1495
December11th to 20thNight
34%
949
28%
3079
12%
948
46%
948
34%
1600
December21st to endNight
31%
1038
17%
4716
8%
1026
45%
1026
20%
2684

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
8%5%2443445%7%53%
78453
Night
7%6%25%43445%7%52%
81010
TransparencyDay
30%6%13%28%19%5%
78157
Night
31%6%13%27%18%4
80828
SeeingDay
10%9%31%31%16%3
14755
Night
10%9%37%35%9%
24906

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 10thDay
48%37%42335%5%55%
2538
11th to 20thDay
5%8%35%5%35%6%6%7%48%
2540
21st to endDay
4425%4345%6%7%56%
2794
February1st to 10thDay
6%8%47%6%5%5%46%6%42%
1829
11th to 20thDay
7%5%47%6%35%446%49%
1849
21st to endDay
6%8%25%424346%55%
1570
March1st to 10thDay
7%6%24433348%56%
1800
11th to 20thDay
8%7%35%435%35%7%51%
1883
21st to endDay
10%10%36%6%35%5%5%7%41%
2299
April1st to 10thDay
11%6%35%323438%52%
2160
11th to 20thDay
14%6%35%5%3445%6%45%
2131
21st to endDay
13%6%345%2445%7%46%
2322
May1st to 10thDay
13%6%35%5%3445%8%45%
2340
11th to 20thDay
15%6%25%4345%5%7%45%
2306
21st to endDay
12%6%25%4345%6%8%45%
2724
June1st to 10thDay
6%41332446%10%57%
2520
11th to 20thDay
7%5%1443345%8%56%
2520
21st to endDay
42133335%6%9%61%
2520
July1st to 10thDay
7%3134245%7%8%55%
2520
11th to 20thDay
42134245%6%8%60%
2520
21st to endDay
5%324445%6%6%9%52%
2742
August1st to 10thDay
7%414436%6%8%9%48%
2364
11th to 20thDay
5%325%4335%5%8%58%
2222
21st to endDay
6%42432335%7%61%
2376
September1st to 10thDay
8%41332336%6%61%
2160
11th to 20thDay
7%413324348%61%
2003
21st to endDay
8%423433345%63%
1980
October1st to 10thDay
12%5%23323346%58%
1980
11th to 20thDay
9%424323445%61%
1773
21st to endDay
9%6%24422348%56%
1782
November1st to 10thDay
44244345%6%8%57%
1673
11th to 20thDay
45%24334447%61%
1710
21st to endDay
7%6%2442335%6%58%
1710
December1st to 10thDay
5%6%35%5%34448%52%
1573
11th to 20thDay
5%5%25%5%23447%59%
1926
21st to endDay
10%11%36%434346%46%
2794
January1st to 10thNight
5%9%37%7%2445%8%45%
4417
11th to 20thNight
37%47%5%3445%8%51%
4430
21st to endNight
35%36%7%45%46%7%51%
4873
February1st to 10thNight
7%9%46%5%35%5%6%6%44%
2365
11th to 20thNight
5%7%46%5%35%5%5%7%47%
2218
21st to endNight
47%36%43446%6%52%
1884
March1st to 10thNight
6%7%35%43345%6%53%
2166
11th to 20thNight
8%6%3442345%7%53%
2076
21st to endNight
9%8%45%5%36%5%6%8%41%
2054
April1st to 10thNight
11%7%25%43445%8%46%
1800
11th to 20thNight
13%6%3433445%6%48%
1777
21st to endNight
13%6%246%35%45%7%45%
1638
May1st to 10thNight
11%5%345%35%7%5%8%44%
1620
11th to 20thNight
14%7%245%335%6%6%46%
1586
21st to endNight
15%6%246%346%5%9%39%
1552
June1st to 10thNight
8%3244345%6%9%52%
1440
11th to 20thNight
10%424435%5%7%9%48%
1440
21st to endNight
5%3245%46%6%8%10%48%
1440
July1st to 10thNight
7%334435%5%6%10%50%
1440
11th to 20thNight
43234345%5%9%57%
1440
21st to endNight
5%324435%6%8%10%50%
1576
August1st to 10thNight
7%425%5%446%8%9%45%
1574
11th to 20thNight
5%423425%46%7%58%
1676
21st to endNight
442432345%8%60%
1980
September1st to 10thNight
8%414423447%59%
1800
11th to 20thNight
7%42333335%6%60%
1957
21st to endNight
9%323223445%63%
1980
October1st to 10thNight
13%5%13323346%57%
1980
11th to 20thNight
8%5%13322447%60%
2165
21st to endNight
8%6%24422346%59%
2574
November1st to 10thNight
5%42332445%8%59%
2405
11th to 20thNight
44244345%6%7%56%
2470
21st to endNight
6%6%2432445%7%57%
2470
December1st to 10thNight
5%5%35%43345%7%55%
2603
11th to 20thNight
45%25%42446%7%57%
3271
21st to endNight
10%11%35%32345%7%47%
4873

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
31%411%33%20%1
2539
11th to 20thDay
34%8%12%27%17%3
2540
21st to endDay
26%8%19%30%14%4
2794
February1st to 10thDay
41%6%14%22%13%4
1829
11th to 20thDay
36%413%25%18%5%
1859
21st to endDay
30%413%30%17%6%
1570
March1st to 10thDay
28%413%28%22%4
1800
11th to 20thDay
34%5%13%23%19%4
1883
21st to endDay
43%6%15%22%12%2
2299
April1st to 10thDay
33%5%15%27%15%4
2160
11th to 20thDay
39%5%15%22%15%4
2134
21st to endDay
37%6%14%25%18%1
2322
May1st to 10thDay
37%6%14%30%13%
2340
11th to 20thDay
38%7%18%26%10%1
2310
21st to endDay
37%8%16%24%12%2
2724
June1st to 10thDay
24%7%20%32%15%2
2520
11th to 20thDay
27%7%14%27%19%7%
2520
21st to endDay
18%6%13%33%25%5%
2520
July1st to 10thDay
25%7%13%30%21%4
2451
11th to 20thDay
21%7%11%26%26%9%
2445
21st to endDay
25%9%13%28%21%4
2590
August1st to 10thDay
30%9%16%25%15%5%
2348
11th to 20thDay
25%6%13%28%22%6%
2222
21st to endDay
24%5%9%25%26%11%
2376
September1st to 10thDay
24%49%27%23%13%
2160
11th to 20thDay
22%5%9%29%27%8%
2003
21st to endDay
24%47%31%28%5%
1980
October1st to 10thDay
30%310%26%26%5%
1980
11th to 20thDay
26%5%9%29%23%8%
1773
21st to endDay
30%312%29%20%7%
1782
November1st to 10thDay
25%5%15%28%21%6%
1673
11th to 20thDay
24%412%29%26%5%
1710
21st to endDay
28%412%30%22%5%
1710
December1st to 10thDay
31%6%11%30%18%3
1573
11th to 20thDay
26%5%15%37%16%2
1924
21st to endDay
40%410%29%14%2
2794
January1st to 10thNight
37%6%13%27%16%1
4417
11th to 20thNight
31%6%18%25%18%2
4430
21st to endNight
31%7%14%30%17%1
4873
February1st to 10thNight
39%7%13%25%14%3
2365
11th to 20thNight
35%6%14%27%14%3
2218
21st to endNight
31%5%13%26%20%6%
1884
March1st to 10thNight
31%5%12%27%21%4
2166
11th to 20thNight
31%5%11%26%23%4
2076
21st to endNight
40%8%14%24%12%1
2054
April1st to 10thNight
36%7%14%22%16%5%
1800
11th to 20thNight
37%6%13%25%16%3
1777
21st to endNight
38%8%13%27%13%2
1638
May1st to 10thNight
37%9%16%24%14%1
1620
11th to 20thNight
37%8%18%26%11%1
1587
21st to endNight
41%10%18%19%9%2
1552
June1st to 10thNight
28%8%22%27%12%2
1440
11th to 20thNight
31%9%18%23%14%6%
1440
21st to endNight
28%8%17%26%20%2
1440
July1st to 10thNight
29%7%17%30%14%3
1400
11th to 20thNight
24%8%12%29%22%6%
1392
21st to endNight
26%8%17%28%18%3
1488
August1st to 10thNight
31%10%19%25%11%4
1566
11th to 20thNight
24%7%15%31%18%4
1676
21st to endNight
23%7%10%28%23%9%
1980
September1st to 10thNight
26%5%10%24%27%9%
1800
11th to 20thNight
25%6%11%26%24%8%
1957
21st to endNight
24%5%7%29%28%6%
1980
October1st to 10thNight
30%5%8%26%26%5%
1980
11th to 20thNight
25%410%29%23%10%
2165
21st to endNight
28%411%25%23%8%
2574
November1st to 10thNight
23%5%12%29%24%7%
2405
11th to 20thNight
26%6%12%26%24%6%
2470
21st to endNight
26%411%29%23%5%
2470
December1st to 10thNight
28%5%14%29%19%4
2603
11th to 20thNight
26%413%37%19%2
3272
21st to endNight
38%411%31%14%2
4873

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%10%41%25%13%2
270
11th to 20thDay
12%13%36%33%41
270
21st to endDay
9%12%49%20%7%3
297
February1st to 10thDay
10%14%52%21%3
270
11th to 20thDay
6%15%48%23%6%1
270
21st to endDay
12%20%44%20%4
225
March1st to 10thDay
11%11%40%28%9%1
240
11th to 20thDay
12%11%31%34%10%2
240
21st to endDay
16%12%40%21%9%1
385
April1st to 10thDay
14%18%39%21%8%1
420
11th to 20thDay
17%21%32%24%5%1
412
21st to endDay
18%14%30%25%11%2
582
May1st to 10thDay
15%10%30%28%13%2
603
11th to 20thDay
19%7%30%28%14%2
625
21st to endDay
16%10%30%27%15%2
679
June1st to 10thDay
8%425%31%26%6%
630
11th to 20thDay
8%8%33%32%16%2
630
21st to endDay
45%30%37%21%2
630
July1st to 10thDay
8%324%39%23%3
621
11th to 20thDay
4422%43%24%4
618
21st to endDay
7%218%44%25%4
684
August1st to 10thDay
8%220%39%25%4
626
11th to 20thDay
5%426%39%24%2
536
21st to endDay
4128%39%22%6%
495
September1st to 10thDay
6%424%41%18%6%
450
11th to 20thDay
3419%43%22%9%
293
21st to endDay
11%11%24%31%19%3
270
October1st to 10thDay
16%8%21%29%22%4
270
11th to 20thDay
10%15%33%26%15%1
270
21st to endDay
13%16%27%29%12%3
297
November1st to 10thDay
414%40%23%16%3
270
11th to 20thDay
9%12%36%32%10%1
270
21st to endDay
12%7%40%29%9%3
270
December1st to 10thDay
9%10%47%27%6%1
270
11th to 20thDay
10%13%42%26%7%1
270
21st to endDay
15%16%40%24%5%1
297
January1st to 10thNight
8%12%40%31%9%
950
11th to 20thNight
8%15%41%28%7%1
950
21st to endNight
7%11%45%30%6%
1045
February1st to 10thNight
11%12%45%27%5%
801
11th to 20thNight
10%10%49%26%5%
744
21st to endNight
8%11%48%29%3
628
March1st to 10thNight
10%11%40%33%6%
722
11th to 20thNight
12%9%41%31%7%
636
21st to endNight
12%9%40%31%7%
594
April1st to 10thNight
15%14%38%29%4
540
11th to 20thNight
16%14%41%26%3
533
21st to endNight
16%13%30%34%6%
540
May1st to 10thNight
13%8%37%34%8%
540
11th to 20thNight
18%6%33%32%11%
531
21st to endNight
17%8%34%30%11%1
584
June1st to 10thNight
11%433%36%14%2
540
11th to 20thNight
11%6%39%36%8%1
540
21st to endNight
5%428%50%12%
540
July1st to 10thNight
7%231%43%16%1
525
11th to 20thNight
4327%54%11%1
522
21st to endNight
7%225%50%16%
591
August1st to 10thNight
9%124%49%17%1
537
11th to 20thNight
8%127%51%13%
534
21st to endNight
5%5%31%45%14%
594
September1st to 10thNight
8%5%32%40%14%
540
11th to 20thNight
8%5%32%38%16%1
540
21st to endNight
11%5%33%39%11%1
540
October1st to 10thNight
15%7%29%38%11%
540
11th to 20thNight
12%9%30%37%11%1
725
21st to endNight
11%11%34%34%9%1
990
November1st to 10thNight
7%7%38%38%8%1
925
11th to 20thNight
6%11%42%33%7%
950
21st to endNight
9%8%36%36%10%
950
December1st to 10thNight
8%13%43%29%6%
950
11th to 20thNight
8%11%42%32%7%
950
21st to endNight
13%13%38%31%5%
1045
Page generated at 2024-02-27 04:30:19. Version ac07

Copyright © 2024 Attilla Danko.


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