Eagle Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eagle Ridge Observatory clear sky chart from 2005-11-05 to 2018-03-21.

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
65%
16557
34%
49145
27%
16506
73%
16506
45%
24176

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
49%
780
29%
2635
23%
776
61%
776
32%
1323
January16th to endNight
47%
832
35%
2630
23%
832
64%
832
34%
1346
February1st to 15thNight
56%
760
37%
2281
30%
756
69%
756
40%
1166
February16th to endNight
54%
684
29%
2051
26%
684
63%
684
31%
1163
March1st to 15thNight
59%
780
28%
2332
23%
780
68%
780
39%
1197
March16th to endNight
63%
792
31%
2058
23%
792
68%
792
43%
1145
April1st to 15thNight
61%
719
31%
1799
18%
719
66%
719
45%
994
April16th to endNight
65%
720
32%
1800
16%
720
70%
720
50%
944
May1st to 15thNight
67%
662
27%
1742
17%
662
69%
662
44%
947
May16th to endNight
68%
561
31%
1685
21%
561
74%
561
49%
785
June1st to 15thNight
74%
391
29%
1471
27%
391
79%
391
37%
675
June16th to endNight
78%
360
35%
1440
38%
360
85%
360
50%
534
July1st to 15thNight
80%
340
34%
1360
37%
340
84%
340
47%
513
July16th to endNight
75%
619
32%
1642
23%
580
83%
580
52%
797
August1st to 15thNight
82%
717
33%
1790
22%
713
83%
713
60%
905
August16th to endNight
84%
764
40%
1910
24%
764
86%
764
62%
942
September1st to 15thNight
81%
720
36%
1800
28%
720
83%
720
57%
944
September16th to endNight
85%
716
43%
1980
38%
716
89%
716
64%
891
October1st to 15thNight
76%
720
35%
2044
35%
720
80%
720
56%
970
October16th to endNight
71%
768
43%
2304
39%
768
80%
768
53%
1052
November1st to 15thNight
66%
760
35%
2458
32%
760
74%
760
48%
1084
November16th to endNight
58%
780
39%
2535
32%
780
71%
780
43%
1162
December1st to 15thNight
51%
780
36%
2535
27%
780
64%
780
36%
1252
December16th to endNight
48%
832
33%
2863
25%
832
63%
832
32%
1445

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
4312213346%66%
49683
Night
4312213346%66%
49347
TransparencyDay
19%36%18%27%24%
49374
Night
19%46%17%26%25%
49157
SeeingDay
5%13%22%34%18%5%
6616
Night
5%15%8%25%34%11%
16564

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
7%413423236%60%
1630
16th to endDay
10%413212236%60%
1944
February1st to 15thDay
7%322212347%61%
1901
16th to endDay
10%314423235%57%
1709
March1st to 15thDay
5%323324446%58%
1956
16th to endDay
5%32232345%8%57%
2293
April1st to 15thDay
6%412213347%60%
2149
16th to endDay
4312212238%68%
2160
May1st to 15thDay
4412213348%63%
2205
16th to endDay
2312212349%67%
2429
June1st to 15thDay
45%13312348%59%
2484
16th to endDay
121112236%75%
2520
July1st to 15thDay
2211312346%69%
2520
16th to endDay
22221325%6%70%
2407
August1st to 15thDay
2211112235%74%
2160
16th to endDay
11112335%77%
2292
September1st to 15thDay
111112236%75%
2160
16th to endDay
121212235%77%
1980
October1st to 15thDay
422212235%71%
1914
16th to endDay
221221234470%
1920
November1st to 15thDay
3213223435%67%
1731
16th to endDay
4212413248%63%
1755
December1st to 15thDay
6%31232345%8%58%
1755
16th to endDay
9%313323347%57%
1709
January1st to 15thNight
7%5%1232335%6%57%
2635
16th to endNight
10%412312236%61%
2630
February1st to 15thNight
5%313323245%63%
2281
16th to endNight
12%313323335%56%
2051
March1st to 15thNight
5%31321445%6%59%
2332
16th to endNight
4322324447%60%
2058
April1st to 15thNight
6%313212245%65%
1799
16th to endNight
3312123247%68%
1800
May1st to 15thNight
431221335%6%65%
1742
16th to endNight
121221325%6%71%
1684
June1st to 15thNight
122212345%8%64%
1471
16th to endNight
11112237%75%
1440
July1st to 15thNight
221212238%71%
1440
16th to endNight
221111245%8%66%
1755
August1st to 15thNight
12112225%9%70%
1800
16th to endNight
1112347%74%
1910
September1st to 15thNight
2212212247%70%
1800
16th to endNight
1111225%5%77%
1980
October1st to 15thNight
2212212345%70%
2044
16th to endNight
432112236%71%
2304
November1st to 15thNight
3312212335%70%
2458
16th to endNight
4213213246%66%
2535
December1st to 15thNight
6%413313345%61%
2535
16th to endNight
10%312213335%60%
2863

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%38%14%23%24%
1630
16th to endDay
27%26%19%18%26%
1944
February1st to 15thDay
23%3415%27%25%
1901
16th to endDay
28%46%19%27%12%
1709
March1st to 15thDay
25%410%20%21%19%
1956
16th to endDay
22%5%12%25%19%13%
2293
April1st to 15thDay
22%312%26%24%10%
2149
16th to endDay
17%310%23%28%16%
2160
May1st to 15thDay
20%39%22%25%17%
2205
16th to endDay
16%311%30%28%9%
2432
June1st to 15thDay
25%38%16%31%14%
2484
16th to endDay
11%4410%35%34%
2520
July1st to 15thDay
15%4412%28%35%
2371
16th to endDay
15%47%20%30%21%
2258
August1st to 15thDay
13%3213%37%29%
2146
16th to endDay
9%4211%43%29%
2292
September1st to 15thDay
11%35%13%29%36%
2160
16th to endDay
11%2216%35%32%
1980
October1st to 15thDay
16%26%20%25%28%
1914
16th to endDay
17%3414%23%36%
1920
November1st to 15thDay
18%45%17%24%30%
1731
16th to endDay
20%27%15%21%32%
1755
December1st to 15thDay
23%47%16%22%25%
1755
16th to endDay
27%37%18%22%20%
1709
January1st to 15thNight
26%36%15%24%23%
2635
16th to endNight
26%26%16%17%31%
2630
February1st to 15thNight
23%2415%25%27%
2292
16th to endNight
31%35%16%25%16%
2051
March1st to 15thNight
23%39%20%25%17%
2332
16th to endNight
22%5%10%23%23%14%
2058
April1st to 15thNight
22%29%27%25%12%
1799
16th to endNight
16%48%24%27%19%
1800
May1st to 15thNight
20%5%9%21%26%15%
1743
16th to endNight
15%310%28%30%11%
1685
June1st to 15thNight
19%6%9%18%31%14%
1471
16th to endNight
9%6%412%34%33%
1440
July1st to 15thNight
11%4413%27%37%
1360
16th to endNight
14%5%8%21%26%22%
1642
August1st to 15thNight
11%6%5%11%34%30%
1790
16th to endNight
10%6%310%39%29%
1910
September1st to 15thNight
14%5%6%8%29%35%
1800
16th to endNight
8%5%213%34%35%
1980
October1st to 15thNight
15%35%18%27%29%
2044
16th to endNight
16%25%14%21%39%
2304
November1st to 15thNight
16%27%15%24%33%
2458
16th to endNight
18%2417%22%33%
2535
December1st to 15thNight
24%26%15%20%29%
2535
16th to endNight
26%37%16%23%22%
2863

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
13%12%37%26%8%1
168
16th to endDay
12%22%28%25%9%1
321
February1st to 15thDay
9%17%27%27%11%6%
326
16th to endDay
12%21%23%29%11%1
290
March1st to 15thDay
8%19%32%25%10%2
330
16th to endDay
7%16%27%34%10%1
311
April1st to 15thDay
6%20%31%25%10%5%
269
16th to endDay
322%34%28%7%2
270
May1st to 15thDay
6%19%25%30%13%3
288
16th to endDay
316%30%31%14%3
330
June1st to 15thDay
8%13%21%34%16%4
315
16th to endDay
19%10%40%26%11%
315
July1st to 15thDay
27%7%42%30%9%
305
16th to endDay
210%7%33%33%12%
327
August1st to 15thDay
35%7%49%26%7%
315
16th to endDay
5%8%40%34%10%
332
September1st to 15thDay
35%19%44%20%6%
315
16th to endDay
18%17%42%21%7%
315
October1st to 15thDay
312%26%38%18%1
315
16th to endDay
311%23%36%19%5%
336
November1st to 15thDay
46%22%35%16%15%
147
16th to endDay
411%25%25%25%8%
135
December1st to 15thDay
7%11%20%33%22%5%
135
16th to endDay
6%16%27%26%17%5%
106
January1st to 15thNight
8%18%15%34%17%5%
780
16th to endNight
10%20%14%30%20%2
832
February1st to 15thNight
6%17%12%33%22%7%
764
16th to endNight
11%17%9%33%23%3
684
March1st to 15thNight
6%18%9%36%25%5%
780
16th to endNight
5%17%7%31%31%5%
792
April1st to 15thNight
5%19%8%31%30%4
719
16th to endNight
419%7%28%32%8%
720
May1st to 15thNight
418%6%28%34%7%
663
16th to endNight
118%7%28%37%6%
563
June1st to 15thNight
117%223%44%10%
391
16th to endNight
116%15%55%10%
360
July1st to 15thNight
311%1454%25%
340
16th to endNight
216%1445%29%
619
August1st to 15thNight
19%19%54%22%
717
16th to endNight
18%18%48%31%
764
September1st to 15thNight
28%214%48%22%
720
16th to endNight
18%218%50%18%
716
October1st to 15thNight
39%5%28%42%9%
720
16th to endNight
5%8%8%27%36%12%
768
November1st to 15thNight
314%10%36%25%9%
760
16th to endNight
417%12%30%27%8%
780
December1st to 15thNight
7%19%14%31%22%5%
780
16th to endNight
12%20%13%29%19%3
832
Page generated at 2018-03-22 08:34:23. Version ac04

Copyright 2018 A. Danko


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