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 2017-09-18.

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
70%
16190
35%
46988
29%
16150
75%
16150
51%
23527

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%
716
31%
2327
29%
716
69%
716
39%
1204
January16th to endNight
57%
768
34%
2325
27%
768
66%
768
36%
1311
February1st to 15thNight
62%
698
33%
2111
29%
698
69%
698
38%
1165
February16th to endNight
51%
632
29%
1895
28%
632
58%
632
30%
1161
March1st to 15thNight
58%
720
32%
2149
30%
720
66%
720
40%
1152
March16th to endNight
61%
768
32%
2058
25%
768
68%
768
44%
1158
April1st to 15thNight
52%
719
32%
1799
16%
719
60%
719
44%
1040
April16th to endNight
57%
720
34%
1800
16%
720
65%
720
54%
965
May1st to 15thNight
66%
560
35%
1640
23%
560
72%
560
54%
793
May16th to endNight
64%
562
35%
1685
24%
561
71%
561
56%
778
June1st to 15thNight
76%
540
36%
1620
28%
540
80%
540
72%
653
June16th to endNight
82%
540
38%
1620
31%
540
85%
540
81%
617
July1st to 15thNight
90%
510
32%
1530
28%
510
90%
510
69%
640
July16th to endNight
87%
597
33%
1624
27%
562
87%
562
60%
768
August1st to 15thNight
91%
717
37%
1790
24%
713
91%
713
75%
835
August16th to endNight
91%
764
44%
1910
30%
764
91%
764
74%
898
September1st to 15thNight
89%
720
39%
1883
32%
720
91%
720
72%
876
September16th to endNight
82%
667
47%
1847
41%
667
87%
667
75%
788
October1st to 15thNight
71%
660
40%
1815
34%
660
77%
660
56%
898
October16th to endNight
77%
704
41%
2109
40%
704
81%
704
55%
985
November1st to 15thNight
72%
700
35%
2275
35%
700
79%
700
51%
1048
November16th to endNight
69%
720
37%
2340
37%
720
75%
720
44%
1158
December1st to 15thNight
60%
720
32%
2340
31%
720
67%
720
36%
1258
December16th to endNight
56%
768
33%
2496
29%
768
64%
768
34%
1378

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%
47800
Night
2313323346%66%
47187
TransparencyDay
18%3313%27%32%
47499
Night
18%4313%26%33%
46990
SeeingDay
6%11%31%33%13%4
5878
Night
45%14%32%33%9%
16202

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%60%
1611
16th to endDay
7%6%2332345%5%55%
1896
February1st to 15thDay
5%423424436%58%
1751
16th to endDay
7%7%27%42345%7%48%
1579
March1st to 15thDay
5%412313348%61%
1809
16th to endDay
3323423347%61%
2164
April1st to 15thDay
4423324345%60%
2149
16th to endDay
2212212337%70%
2160
May1st to 15thDay
2212213237%70%
2310
16th to endDay
111112335%74%
2429
June1st to 15thDay
111212225%77%
2340
16th to endDay
1112286%
2340
July1st to 15thDay
2112312336%70%
2340
16th to endDay
121222446%6%62%
2431
August1st to 15thDay
111212335%75%
2160
16th to endDay
11221334472%
2292
September1st to 15thDay
2111213245%72%
2076
16th to endDay
1111222281%
1838
October1st to 15thDay
2214323235%69%
1815
16th to endDay
122323335%71%
1758
November1st to 15thDay
3312313235%68%
1584
16th to endDay
5%313313345%63%
1620
December1st to 15thDay
6%5%13425%35%8%53%
1620
16th to endDay
8%6%24324445%53%
1728
January1st to 15thNight
35%24323446%59%
2327
16th to endNight
6%6%245%23346%54%
2325
February1st to 15thNight
37%233245%46%57%
2101
16th to endNight
5%7%25%6%35%5%45%48%
1895
March1st to 15thNight
44224335%5%7%56%
2149
16th to endNight
25%124245%5%8%56%
2058
April1st to 15thNight
333231445%9%58%
1799
16th to endNight
2212223346%68%
1800
May1st to 15thNight
121221345%8%67%
1640
16th to endNight
111223337%72%
1684
June1st to 15thNight
1112136%79%
1620
16th to endNight
111188%
1620
July1st to 15thNight
112112345%75%
1620
16th to endNight
212323347%67%
1734
August1st to 15thNight
1212235%78%
1800
16th to endNight
11111122480%
1910
September1st to 15thNight
1221124478%
1883
16th to endNight
11122285%
1847
October1st to 15thNight
2112323346%69%
1815
16th to endNight
123323345%70%
2109
November1st to 15thNight
222332233470%
2275
16th to endNight
3414323445%62%
2340
December1st to 15thNight
5%5%15%32445%8%53%
2340
16th to endNight
7%6%25%433235%55%
2496

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
25%4413%26%25%
1612
16th to endDay
29%4413%22%25%
1896
February1st to 15thDay
26%5%214%26%25%
1751
16th to endDay
34%4415%26%15%
1579
March1st to 15thDay
20%3417%29%23%
1809
16th to endDay
23%45%19%30%17%
2164
April1st to 15thDay
24%4318%35%13%
2149
16th to endDay
14%3419%33%23%
2160
May1st to 15thDay
15%4314%33%28%
2310
16th to endDay
11%4416%39%23%
2432
June1st to 15thDay
10%3111%26%46%
2340
16th to endDay
7%1316%69%
2340
July1st to 15thDay
14%2311%21%46%
2201
16th to endDay
18%37%19%24%25%
2279
August1st to 15thDay
11%2212%25%45%
2146
16th to endDay
13%349%28%40%
2292
September1st to 15thDay
14%3310%25%43%
2076
16th to endDay
9%216%30%50%
1838
October1st to 15thDay
17%4213%29%33%
1815
16th to endDay
15%439%22%44%
1758
November1st to 15thDay
18%2413%30%30%
1584
16th to endDay
21%3410%29%30%
1620
December1st to 15thDay
28%36%16%20%23%
1620
16th to endDay
31%45%17%24%17%
1728
January1st to 15thNight
25%5%314%24%26%
2327
16th to endNight
30%4412%20%27%
2325
February1st to 15thNight
26%6%212%24%27%
2112
16th to endNight
34%7%214%23%17%
1895
March1st to 15thNight
23%7%316%26%23%
2149
16th to endNight
22%7%5%17%28%18%
2058
April1st to 15thNight
21%7%419%30%16%
1799
16th to endNight
17%5%416%30%25%
1800
May1st to 15thNight
12%7%414%30%30%
1641
16th to endNight
11%6%415%37%24%
1685
June1st to 15thNight
6%3210%25%50%
1620
16th to endNight
6%1413%73%
1620
July1st to 15thNight
9%337%22%53%
1530
16th to endNight
15%27%18%26%28%
1624
August1st to 15thNight
9%1114%26%45%
1790
16th to endNight
9%2210%29%46%
1910
September1st to 15thNight
10%2310%27%44%
1883
16th to endNight
6%36%30%51%
1847
October1st to 15thNight
15%5%212%31%32%
1815
16th to endNight
14%6%29%22%45%
2109
November1st to 15thNight
17%4310%30%33%
2275
16th to endNight
21%5%213%23%32%
2340
December1st to 15thNight
27%5%5%14%22%23%
2340
16th to endNight
31%45%15%24%19%
2496

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%15%28%33%6%
90
16th to endDay
15%18%29%27%7%1
264
February1st to 15thDay
6%16%34%28%11%1
266
16th to endDay
15%22%31%21%7%
238
March1st to 15thDay
12%17%31%22%12%2
270
16th to endDay
10%18%36%20%12%2
288
April1st to 15thDay
12%22%35%16%9%2
269
16th to endDay
8%22%40%18%6%2
270
May1st to 15thDay
7%17%36%28%6%3
288
16th to endDay
316%39%27%9%3
330
June1st to 15thDay
28%43%28%13%3
315
16th to endDay
2334%34%16%7%
315
July1st to 15thDay
1123%47%19%6%
305
16th to endDay
1216%48%20%11%
327
August1st to 15thDay
1126%43%15%11%
315
16th to endDay
2119%49%15%12%
332
September1st to 15thDay
2333%42%13%4
315
16th to endDay
48%29%40%13%3
264
October1st to 15thDay
6%11%38%33%9%
255
16th to endDay
49%29%29%24%2
196
November1st to 15thDay
5%12%13%35%24%8%
90
16th to endDay
12%13%22%33%15%3
90
December1st to 15thDay
5%6%21%45%17%3
90
16th to endDay
14%16%23%33%11%
96
January1st to 15thNight
5%6%16%36%23%11%
720
16th to endNight
9%8%15%32%27%6%
768
February1st to 15thNight
6%7%17%34%25%8%
704
16th to endNight
8%12%20%31%20%6%
632
March1st to 15thNight
6%7%21%34%23%5%
720
16th to endNight
6%7%20%31%26%7%
768
April1st to 15thNight
6%12%25%31%19%5%
719
16th to endNight
48%27%29%21%7%
720
May1st to 15thNight
27%19%41%23%4
561
16th to endNight
17%23%34%27%4
563
June1st to 15thNight
317%45%28%3
540
16th to endNight
113%42%35%5%
540
July1st to 15thNight
334%53%6%
510
16th to endNight
2228%55%10%
597
August1st to 15thNight
1326%54%14%
717
16th to endNight
2117%56%20%
764
September1st to 15thNight
5%25%53%14%
720
16th to endNight
111%31%40%14%
667
October1st to 15thNight
25%16%34%32%9%
660
16th to endNight
2312%31%34%16%
704
November1st to 15thNight
2415%31%34%12%
700
16th to endNight
5%5%13%30%29%15%
720
December1st to 15thNight
9%6%15%32%26%9%
720
16th to endNight
10%9%17%32%22%8%
768
Page generated at 2017-09-19 04:32:30. Version ac04

Copyright 2017 A. Danko


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