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 2005-11-05 to 2018-10-27.

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
71%
17700
36%
51366
29%
17660
76%
17660
51%
25644

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
63%
776
30%
2522
29%
776
68%
776
38%
1324
January16th to endNight
58%
832
35%
2519
29%
832
66%
832
37%
1398
February1st to 15thNight
64%
758
33%
2291
30%
758
71%
758
39%
1254
February16th to endNight
52%
684
30%
2051
28%
684
59%
684
31%
1236
March1st to 15thNight
58%
780
30%
2328
28%
780
66%
780
39%
1272
March16th to endNight
62%
832
31%
2229
24%
832
68%
832
44%
1259
April1st to 15thNight
53%
779
33%
1949
17%
779
61%
779
44%
1131
April16th to endNight
57%
772
34%
1930
16%
772
65%
772
54%
1035
May1st to 15thNight
66%
607
36%
1777
23%
607
71%
607
52%
873
May16th to endNight
66%
610
34%
1829
23%
609
71%
609
56%
853
June1st to 15thNight
77%
585
37%
1755
29%
585
81%
585
73%
701
June16th to endNight
83%
585
37%
1755
31%
585
86%
585
80%
668
July1st to 15thNight
90%
555
33%
1665
28%
555
90%
555
69%
694
July16th to endNight
88%
648
32%
1771
26%
613
88%
613
60%
832
August1st to 15thNight
91%
765
38%
1910
25%
761
92%
761
76%
889
August16th to endNight
91%
828
43%
2070
30%
828
91%
828
75%
969
September1st to 15thNight
90%
780
42%
2040
34%
780
91%
780
73%
936
September16th to endNight
84%
776
46%
2145
41%
776
89%
776
77%
908
October1st to 15thNight
73%
780
40%
2145
34%
780
79%
780
56%
1062
October16th to endNight
78%
816
42%
2441
41%
816
82%
816
57%
1122
November1st to 15thNight
72%
760
33%
2470
33%
760
78%
760
48%
1168
November16th to endNight
70%
780
38%
2535
39%
780
75%
780
44%
1255
December1st to 15thNight
61%
780
32%
2535
31%
780
67%
780
38%
1335
December16th to endNight
58%
832
34%
2704
30%
832
66%
832
35%
1470

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
3312313346%67%
52180
Night
2313323346%66%
51565
TransparencyDay
18%3413%27%32%
51879
Night
18%5%313%26%33%
51368
SeeingDay
5%10%29%32%15%5%
7379
Night
45%14%32%33%9%
17712

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
45%24323246%59%
1746
16th to endDay
7%6%2332245%6%56%
2054
February1st to 15thDay
4423324336%60%
1901
16th to endDay
6%7%26%32345%7%49%
1709
March1st to 15thDay
5%412313349%59%
1960
16th to endDay
3423333347%60%
2344
April1st to 15thDay
4423423346%60%
2329
16th to endDay
222212337%69%
2305
May1st to 15thDay
2212213237%70%
2503
16th to endDay
111112335%75%
2637
June1st to 15thDay
111212225%78%
2535
16th to endDay
1112287%
2535
July1st to 15thDay
2113313436%69%
2535
16th to endDay
121222446%7%62%
2636
August1st to 15thDay
111212335%76%
2293
16th to endDay
112213445%72%
2484
September1st to 15thDay
11121323474%
2249
16th to endDay
1111222382%
2145
October1st to 15thDay
221332323470%
2145
16th to endDay
122322235%73%
2034
November1st to 15thDay
3313313335%66%
1719
16th to endDay
5%313313345%63%
1755
December1st to 15thDay
5%5%13425%35%8%55%
1755
16th to endDay
7%6%24324445%54%
1872
January1st to 15thNight
45%24323447%57%
2522
16th to endNight
6%5%245%23346%55%
2519
February1st to 15thNight
27%233245%45%57%
2281
16th to endNight
5%7%25%5%35%445%50%
2051
March1st to 15thNight
44224335%5%8%54%
2328
16th to endNight
24134245%6%8%55%
2229
April1st to 15thNight
333232445%9%57%
1949
16th to endNight
2212223346%67%
1930
May1st to 15thNight
2122135%5%8%66%
1777
16th to endNight
112223347%70%
1828
June1st to 15thNight
112136%80%
1755
16th to endNight
112188%
1755
July1st to 15thNight
11112345%76%
1755
16th to endNight
212323347%68%
1881
August1st to 15thNight
212235%78%
1920
16th to endNight
11111122480%
2070
September1st to 15thNight
1211123480%
2040
16th to endNight
11122285%
2145
October1st to 15thNight
211222335%6%68%
2145
16th to endNight
11332234472%
2441
November1st to 15thNight
2223323335%67%
2470
16th to endNight
3314423446%61%
2535
December1st to 15thNight
5%5%1432445%8%54%
2535
16th to endNight
6%5%25%433235%56%
2704

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
26%4415%26%23%
1747
16th to endDay
27%4414%22%25%
2054
February1st to 15thDay
24%5%214%27%25%
1901
16th to endDay
33%4415%26%15%
1709
March1st to 15thDay
21%35%18%27%22%
1960
16th to endDay
23%45%18%30%16%
2344
April1st to 15thDay
23%4318%35%14%
2329
16th to endDay
14%3419%33%23%
2305
May1st to 15thDay
15%4314%32%28%
2503
16th to endDay
11%4417%39%23%
2640
June1st to 15thDay
9%3110%26%47%
2535
16th to endDay
6%1316%70%
2535
July1st to 15thDay
15%3312%20%45%
2396
16th to endDay
18%48%20%24%24%
2484
August1st to 15thDay
11%2312%25%45%
2279
16th to endDay
13%3411%29%38%
2484
September1st to 15thDay
13%329%24%46%
2249
16th to endDay
8%216%32%48%
2145
October1st to 15thDay
17%4212%28%35%
2145
16th to endDay
14%438%24%45%
2034
November1st to 15thDay
20%3413%29%29%
1719
16th to endDay
21%3410%28%30%
1755
December1st to 15thDay
26%36%16%20%26%
1755
16th to endDay
30%45%16%25%18%
1872
January1st to 15thNight
26%5%314%25%24%
2522
16th to endNight
29%4413%20%27%
2519
February1st to 15thNight
25%6%211%24%28%
2292
16th to endNight
33%6%214%25%17%
2051
March1st to 15thNight
24%7%317%25%22%
2328
16th to endNight
22%8%5%17%28%18%
2229
April1st to 15thNight
21%8%418%30%16%
1949
16th to endNight
17%5%416%30%25%
1930
May1st to 15thNight
13%8%413%29%30%
1778
16th to endNight
11%7%414%37%23%
1829
June1st to 15thNight
6%3210%25%52%
1755
16th to endNight
6%1412%74%
1755
July1st to 15thNight
9%339%22%52%
1665
16th to endNight
15%38%20%26%26%
1771
August1st to 15thNight
9%1213%27%45%
1910
16th to endNight
9%2212%29%43%
2070
September1st to 15thNight
9%239%26%47%
2040
16th to endNight
6%36%32%50%
2145
October1st to 15thNight
15%5%312%30%32%
2145
16th to endNight
13%5%19%22%47%
2441
November1st to 15thNight
18%4310%30%31%
2470
16th to endNight
21%5%212%24%33%
2535
December1st to 15thNight
26%5%5%14%21%26%
2535
16th to endNight
30%35%14%25%20%
2704

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
15%11%22%31%15%2
135
16th to endDay
13%16%26%28%12%3
326
February1st to 15thDay
5%15%31%28%13%5%
326
16th to endDay
15%21%29%22%10%
290
March1st to 15thDay
11%17%33%23%11%2
330
16th to endDay
9%17%37%21%12%1
352
April1st to 15thDay
10%20%34%20%10%2
329
16th to endDay
7%22%39%19%7%3
318
May1st to 15thDay
7%16%34%28%8%3
348
16th to endDay
215%41%27%10%3
394
June1st to 15thDay
27%39%29%14%5%
375
16th to endDay
2331%34%19%9%
375
July1st to 15thDay
2120%44%22%9%
365
16th to endDay
1114%46%24%11%
391
August1st to 15thDay
1124%42%18%12%
359
16th to endDay
1118%46%18%14%
396
September1st to 15thDay
2231%43%15%4
375
16th to endDay
37%28%40%17%3
375
October1st to 15thDay
5%11%37%34%10%1
375
16th to endDay
48%25%30%27%4
296
November1st to 15thDay
5%10%18%38%20%5%
135
16th to endDay
10%11%18%33%17%8%
135
December1st to 15thDay
38%22%40%21%2
135
16th to endDay
9%12%21%30%20%5%
144
January1st to 15thNight
6%6%15%36%23%11%
780
16th to endNight
8%8%15%32%28%6%
832
February1st to 15thNight
6%7%16%34%25%10%
764
16th to endNight
7%12%20%32%21%6%
684
March1st to 15thNight
6%8%20%36%23%4
780
16th to endNight
5%7%20%32%26%6%
832
April1st to 15thNight
5%11%24%32%20%5%
779
16th to endNight
48%26%30%22%7%
772
May1st to 15thNight
27%20%40%25%4
608
16th to endNight
17%22%36%27%4
611
June1st to 15thNight
316%44%29%4
585
16th to endNight
112%41%37%5%
585
July1st to 15thNight
332%54%7%
555
16th to endNight
2227%56%11%
648
August1st to 15thNight
1224%55%15%
765
16th to endNight
2117%56%21%
828
September1st to 15thNight
5%26%53%13%
780
16th to endNight
110%32%41%13%
776
October1st to 15thNight
2415%36%32%8%
780
16th to endNight
2312%30%35%16%
816
November1st to 15thNight
2414%35%31%11%
760
16th to endNight
5%413%30%31%15%
780
December1st to 15thNight
8%6%16%33%26%8%
780
16th to endNight
9%8%16%32%23%8%
832
Page generated at 2018-10-28 05:41:08. Version ac04

Copyright 2018 A. Danko


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