Erickson Observatory Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Erickson Observatory Site 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
67%
24880
35%
74472
29%
24831
74%
24831
48%
37690

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
57%
756
31%
2457
26%
756
64%
756
35%
1320
January11th to 20thNight
61%
728
36%
2308
32%
728
69%
728
40%
1208
January21st to endNight
52%
792
37%
2376
27%
792
64%
792
35%
1345
February1st to 10thNight
58%
720
35%
2160
29%
720
68%
720
40%
1166
February11th to 20thNight
53%
700
32%
2099
26%
700
63%
700
35%
1184
February21st to endNight
50%
592
30%
1776
27%
592
58%
592
32%
1056
March1st to 10thNight
49%
720
26%
2160
24%
720
56%
720
30%
1288
March11th to 20thNight
58%
720
29%
2054
25%
720
65%
720
40%
1159
March21st to endNight
54%
792
30%
2097
20%
792
62%
792
39%
1245
April1st to 10thNight
51%
720
32%
1800
16%
720
60%
720
43%
1058
April11th to 20thNight
54%
711
36%
1779
19%
711
62%
711
49%
975
April21st to endNight
56%
720
35%
1800
17%
720
64%
720
52%
985
May1st to 10thNight
58%
572
36%
1652
21%
572
66%
572
49%
839
May11th to 20thNight
66%
531
37%
1595
25%
531
70%
531
54%
748
May21st to endNight
61%
583
36%
1746
23%
582
69%
582
55%
809
June1st to 10thNight
75%
540
38%
1620
29%
540
79%
540
68%
672
June11th to 20thNight
74%
540
39%
1620
30%
540
79%
540
75%
643
June21st to endNight
77%
540
37%
1620
29%
540
81%
540
72%
653
July1st to 10thNight
88%
525
36%
1575
31%
525
88%
525
77%
615
July11th to 20thNight
86%
522
36%
1566
30%
522
87%
522
69%
654
July21st to endNight
87%
640
34%
1721
26%
605
88%
605
59%
828
August1st to 10thNight
87%
716
36%
1780
23%
712
88%
712
74%
842
August11th to 20thNight
92%
712
41%
1780
26%
712
92%
712
77%
823
August21st to endNight
90%
792
44%
1980
32%
792
91%
792
75%
929
September1st to 10thNight
89%
720
42%
1834
33%
720
90%
720
73%
862
September11th to 20thNight
86%
720
45%
1980
39%
720
90%
720
75%
854
September21st to endNight
80%
720
45%
1980
38%
720
86%
720
72%
872
October1st to 10thNight
73%
720
39%
1980
33%
720
80%
720
57%
977
October11th to 20thNight
78%
720
46%
1980
40%
720
83%
720
64%
908
October21st to endNight
71%
792
41%
2461
40%
792
78%
792
56%
1112
November1st to 10thNight
72%
740
37%
2405
37%
740
79%
740
51%
1106
November11th to 20thNight
73%
760
38%
2470
37%
760
79%
760
51%
1136
November21st to endNight
61%
760
34%
2470
33%
760
69%
760
37%
1307
December1st to 10thNight
58%
760
31%
2470
29%
760
65%
760
35%
1345
December11th to 20thNight
56%
760
31%
2937
30%
758
64%
758
26%
1692
December21st to endNight
53%
824
20%
4384
27%
817
62%
817
20%
2475

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
3313323346%68%
74847
Night
3423323346%65%
74921
TransparencyDay
17%5%413%27%34%
74578
Night
18%7%312%25%34%
74713
SeeingDay
7%11%29%32%15%5%
14498
Night
5%6%17%34%31%8%
24901

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
6%6%24424348%57%
1708
11th to 20thDay
5%5%2332446%6%59%
1693
21st to endDay
7%7%235%23445%56%
1980
February1st to 10thDay
5%5%23424345%61%
1800
11th to 20thDay
46%35%3235%5%7%57%
1750
21st to endDay
6%9%35%434446%53%
1480
March1st to 10thDay
5%5%244345%5%9%54%
1800
11th to 20thDay
5%5%2443435%8%57%
1904
21st to endDay
3423334446%63%
2255
April1st to 10thDay
5%42342445%7%60%
2160
11th to 20thDay
2223314446%70%
2129
21st to endDay
3312323347%70%
2160
May1st to 10thDay
2323324347%68%
2308
11th to 20thDay
1212212247%77%
2301
21st to endDay
2212213346%75%
2530
June1st to 10thDay
2211212336%78%
2340
11th to 20thDay
121222486%
2340
21st to endDay
211121222383%
2340
July1st to 10thDay
1112212335%77%
2340
11th to 20thDay
221332345%7%69%
2340
21st to endDay
2312335%6%7%8%61%
2491
August1st to 10thDay
2112213335%76%
2149
11th to 20thDay
112213446%75%
2122
21st to endDay
2112213345%75%
2376
September1st to 10thDay
3212224345%72%
2124
11th to 20thDay
11111122387%
1980
21st to endDay
21221333480%
1980
October1st to 10thDay
2213323346%70%
1980
11th to 20thDay
111322333477%
1980
21st to endDay
1212322325%77%
1888
November1st to 10thDay
3422313336%71%
1674
11th to 20thDay
3313423346%69%
1710
21st to endDay
5%42341445%6%61%
1710
December1st to 10thDay
5%6%24425%36%8%56%
1710
11th to 20thDay
8%6%245%36%5%6%8%45%
2169
21st to endDay
5%6%36%6%5%7%6%5%5%46%
3146
January1st to 10thNight
5%6%2443445%8%55%
2457
11th to 20thNight
46%24433446%60%
2308
21st to endNight
6%7%35%5%23346%55%
2376
February1st to 10thNight
48%243245%5%6%59%
2160
11th to 20thNight
37%345%35%44458%
2098
21st to endNight
410%25%5%25%5%47%51%
1776
March1st to 10thNight
5%6%345%45%5%6%9%47%
2160
11th to 20thNight
47%343235%5%7%56%
2054
21st to endNight
36%235%25%5%6%8%55%
2097
April1st to 10thNight
45%334345%5%9%56%
1800
11th to 20thNight
2423323248%66%
1779
21st to endNight
221333445%7%66%
1800
May1st to 10thNight
14133235%5%8%66%
1652
11th to 20thNight
111332245%8%70%
1594
21st to endNight
1212223348%72%
1746
June1st to 10thNight
112222137%79%
1620
11th to 20thNight
121222386%
1620
21st to endNight
211121113384%
1620
July1st to 10thNight
111111223483%
1620
11th to 20thNight
112213346%76%
1620
21st to endNight
221333345%8%66%
1822
August1st to 10thNight
1111312335%80%
1790
11th to 20thNight
111113336%80%
1780
21st to endNight
211122222481%
1980
September1st to 10thNight
12221224480%
1834
11th to 20thNight
111121122385%
1980
21st to endNight
211121223383%
1980
October1st to 10thNight
221232335%6%69%
1980
11th to 20thNight
111211324479%
1980
21st to endNight
121342234474%
2461
November1st to 10thNight
2323323435%70%
2405
11th to 20thNight
3323423345%68%
2470
21st to endNight
35%35%43345%6%57%
2470
December1st to 10thNight
5%7%25%435%45%7%54%
2470
11th to 20thNight
6%7%35%5%35%5%6%9%46%
3041
21st to endNight
5%9%47%6%35%45%6%47%
4521

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
25%6%417%26%21%
1709
11th to 20thDay
24%6%5%13%29%24%
1693
21st to endDay
29%6%413%23%26%
1980
February1st to 10thDay
26%5%312%25%29%
1800
11th to 20thDay
25%6%313%27%26%
1760
21st to endDay
29%8%314%24%22%
1480
March1st to 10thDay
25%6%5%17%26%22%
1800
11th to 20thDay
24%6%5%14%30%21%
1904
21st to endDay
20%7%6%20%31%16%
2255
April1st to 10thDay
23%5%5%20%33%14%
2160
11th to 20thDay
15%5%317%35%26%
2132
21st to endDay
15%4417%39%20%
2160
May1st to 10thDay
16%6%416%32%27%
2308
11th to 20thDay
9%5%314%40%29%
2304
21st to endDay
11%5%418%40%22%
2530
June1st to 10thDay
10%3213%35%37%
2340
11th to 20thDay
5%327%24%59%
2340
21st to endDay
9%21417%67%
2340
July1st to 10thDay
11%238%18%59%
2276
11th to 20thDay
14%45%20%25%32%
2271
21st to endDay
19%5%8%19%25%23%
2353
August1st to 10thDay
11%2411%23%49%
2135
11th to 20thDay
11%3413%24%44%
2122
21st to endDay
12%3410%29%42%
2376
September1st to 10thDay
15%439%19%49%
2124
11th to 20thDay
6%216%29%55%
1980
21st to endDay
10%429%28%47%
1980
October1st to 10thDay
15%5%312%26%39%
1980
11th to 20thDay
11%5%210%26%47%
1980
21st to endDay
12%328%24%50%
1888
November1st to 10thDay
16%4212%30%36%
1674
11th to 20thDay
16%45%10%29%37%
1710
21st to endDay
23%5%410%26%32%
1710
December1st to 10thDay
26%46%16%22%26%
1710
11th to 20thDay
32%8%8%14%22%17%
2168
21st to endDay
33%11%317%22%14%
3146
January1st to 10thNight
26%8%316%25%23%
2457
11th to 20thNight
24%7%413%27%26%
2308
21st to endNight
30%5%412%21%28%
2376
February1st to 10thNight
25%6%212%23%32%
2160
11th to 20thNight
28%7%310%24%28%
2099
21st to endNight
28%11%113%22%24%
1776
March1st to 10thNight
27%13%315%20%22%
2160
11th to 20thNight
23%10%5%13%30%20%
2054
21st to endNight
22%12%5%18%27%17%
2097
April1st to 10thNight
23%8%418%29%18%
1800
11th to 20thNight
17%8%315%29%27%
1779
21st to endNight
15%10%414%34%23%
1800
May1st to 10thNight
13%11%413%28%31%
1652
11th to 20thNight
11%8%414%30%32%
1595
21st to endNight
10%8%415%39%23%
1746
June1st to 10thNight
7%5%211%31%44%
1620
11th to 20thNight
45%17%20%63%
1620
21st to endNight
8%31415%69%
1620
July1st to 10thNight
6%225%19%65%
1575
11th to 20thNight
10%35%18%28%36%
1566
21st to endNight
17%38%21%25%26%
1721
August1st to 10thNight
9%2311%26%48%
1780
11th to 20thNight
7%3315%26%46%
1780
21st to endNight
9%229%28%50%
1980
September1st to 10thNight
9%339%22%52%
1834
11th to 20thNight
6%426%24%58%
1980
21st to endNight
8%428%30%48%
1980
October1st to 10thNight
14%6%312%28%37%
1980
11th to 20thNight
9%5%29%26%48%
1980
21st to endNight
13%7%18%21%50%
2461
November1st to 10thNight
15%7%28%29%38%
2405
11th to 20thNight
17%5%310%26%39%
2470
21st to endNight
25%7%212%22%31%
2470
December1st to 10thNight
27%8%412%20%29%
2470
11th to 20thNight
30%10%5%14%23%19%
3041
21st to endNight
29%14%416%23%14%
4521

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
13%12%32%33%9%1
270
11th to 20thDay
12%12%22%38%14%2
301
21st to endDay
13%19%29%27%11%2
462
February1st to 10thDay
8%16%34%27%11%4
420
11th to 20thDay
14%21%32%23%10%
415
21st to endDay
18%21%33%20%7%1
346
March1st to 10thDay
15%23%33%21%6%1
420
11th to 20thDay
15%16%37%20%11%2
420
21st to endDay
16%19%37%19%9%1
462
April1st to 10thDay
11%19%34%24%10%2
420
11th to 20thDay
8%23%39%18%9%2
412
21st to endDay
8%18%32%24%12%6%
420
May1st to 10thDay
8%17%36%25%11%4
423
11th to 20thDay
6%13%38%28%11%4
448
21st to endDay
6%16%34%26%14%4
485
June1st to 10thDay
310%33%30%18%6%
450
11th to 20thDay
17%36%32%16%7%
450
21st to endDay
26%33%34%17%8%
450
July1st to 10thDay
1223%46%20%9%
446
11th to 20thDay
1118%42%26%12%
444
21st to endDay
1214%44%24%14%
487
August1st to 10thDay
1225%40%20%12%
447
11th to 20thDay
2118%41%23%14%
437
21st to endDay
1117%46%19%15%
495
September1st to 10thDay
4227%42%18%8%
450
11th to 20thDay
26%34%36%18%5%
450
21st to endDay
48%28%35%19%7%
450
October1st to 10thDay
5%10%30%37%14%4
450
11th to 20thDay
211%31%36%18%2
450
21st to endDay
5%8%29%30%23%4
371
November1st to 10thDay
9%10%21%39%19%3
270
11th to 20thDay
5%10%25%37%19%4
270
21st to endDay
10%16%25%30%14%6%
270
December1st to 10thDay
7%13%30%30%17%3
270
11th to 20thDay
5%11%28%36%18%2
270
21st to endDay
16%18%25%26%12%2
297
January1st to 10thNight
9%8%19%34%22%9%
760
11th to 20thNight
7%6%19%38%24%7%
728
21st to endNight
10%10%20%34%22%3
792
February1st to 10thNight
7%8%20%35%22%7%
720
11th to 20thNight
7%12%23%31%20%6%
704
21st to endNight
9%14%22%32%19%5%
592
March1st to 10thNight
9%12%23%35%17%3
720
11th to 20thNight
8%9%20%33%23%7%
720
21st to endNight
7%11%23%32%22%4
792
April1st to 10thNight
7%11%27%32%21%4
720
11th to 20thNight
6%13%24%33%20%4
711
21st to endNight
5%9%28%28%24%7%
720
May1st to 10thNight
410%25%34%24%3
572
11th to 20thNight
17%22%37%28%5%
531
21st to endNight
29%26%35%25%3
584
June1st to 10thNight
15%17%45%29%4
540
11th to 20thNight
1221%44%29%3
540
21st to endNight
1216%39%36%5%
540
July1st to 10thNight
17%38%46%7%
525
11th to 20thNight
18%35%50%6%
522
21st to endNight
21231%54%10%
640
August1st to 10thNight
116%32%48%12%
716
11th to 20thNight
2325%55%16%
712
21st to endNight
2322%56%17%
792
September1st to 10thNight
115%28%54%12%
720
11th to 20thNight
1110%35%43%10%
720
21st to endNight
2213%33%38%12%
720
October1st to 10thNight
3415%38%33%6%
720
11th to 20thNight
25%13%38%32%10%
720
21st to endNight
35%16%32%32%13%
792
November1st to 10thNight
45%14%39%28%10%
740
11th to 20thNight
4215%38%31%11%
760
21st to endNight
5%10%17%35%25%8%
760
December1st to 10thNight
8%8%20%34%24%7%
760
11th to 20thNight
10%8%17%37%22%5%
760
21st to endNight
9%8%24%34%18%7%
836
Page generated at 2024-01-09 22:25:02. Version ac07

Copyright 2024 Attilla Danko


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