Eagle Rock Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eagle Rock Observatory clear sky chart from 2005-11-05 to 2017-09-16.

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
51%
15497
19%
46740
16%
15458
55%
15458
28%
29547

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
39%
755
10%
2545
9%
755
41%
755
15%
1861
January16th to endNight
42%
768
12%
2514
12%
768
45%
768
17%
1816
February1st to 15thNight
41%
700
9%
2288
10%
697
43%
697
17%
1655
February16th to endNight
39%
632
12%
1944
11%
632
42%
632
19%
1395
March1st to 15thNight
44%
720
13%
2034
10%
720
48%
720
22%
1456
March16th to endNight
40%
768
16%
2112
9%
768
44%
768
24%
1476
April1st to 15thNight
43%
629
16%
1815
10%
629
48%
629
25%
1207
April16th to endNight
47%
540
21%
1620
16%
540
50%
540
28%
1017
May1st to 15thNight
52%
539
19%
1619
16%
539
55%
539
33%
970
May16th to endNight
55%
561
17%
1571
15%
561
57%
561
31%
1008
June1st to 15thNight
56%
408
18%
1308
15%
408
62%
408
34%
729
June16th to endNight
69%
360
30%
1260
32%
360
78%
360
54%
530
July1st to 15thNight
80%
340
25%
1256
31%
340
86%
340
52%
518
July16th to endNight
78%
520
30%
1549
32%
487
81%
487
59%
680
August1st to 15thNight
76%
539
29%
1611
25%
536
79%
536
50%
798
August16th to endNight
73%
573
39%
1719
31%
573
77%
573
55%
804
September1st to 15thNight
69%
658
30%
1905
23%
658
75%
658
49%
981
September16th to endNight
69%
660
33%
1826
26%
660
73%
660
47%
989
October1st to 15thNight
59%
660
27%
1930
20%
660
64%
660
38%
1091
October16th to endNight
58%
704
25%
2161
21%
704
63%
704
32%
1297
November1st to 15thNight
49%
703
20%
2278
20%
703
51%
703
25%
1445
November16th to endNight
42%
900
15%
2520
10%
900
46%
900
24%
1718
December1st to 15thNight
35%
900
8%
2520
5%
900
38%
900
17%
1898
December16th to endNight
33%
960
9%
2835
6%
960
36%
960
14%
2208

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%7%35%424446%47%
48013
Night
10%8%35%42445%6%44%
46920
TransparencyDay
37%410%21%17%8%
47692
Night
40%412%21%14%7%
46741
SeeingDay
11%11%24%27%18%5%
5776
Night
14%5%19%35%20%3
15508

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
14%13%47%5%23446%29%
1404
16th to endDay
16%14%5%7%423435%31%
1708
February1st to 15thDay
13%13%5%8%6%24445%30%
1575
16th to endDay
9%12%5%9%6%35%35%7%31%
1527
March1st to 15thDay
8%12%5%8%6%25%45%8%32%
1925
16th to endDay
11%12%6%7%6%35%5%5%6%29%
2112
April1st to 15thDay
9%12%36%435%5%5%7%35%
2131
16th to endDay
9%9%35%5%345%5%6%41%
2340
May1st to 15thDay
7%6%25%5%25%5%5%7%46%
2331
16th to endDay
11%8%26%5%26%5%6%7%37%
2542
June1st to 15thDay
9%425%425%6%5%7%45%
2648
16th to endDay
222213346%69%
2700
July1st to 15thDay
221231345%8%65%
2625
16th to endDay
3212223336%67%
2509
August1st to 15thDay
3213314247%65%
2340
16th to endDay
2213312345%67%
2483
September1st to 15thDay
5%31322235%5%65%
2052
16th to endDay
6%313222347%63%
1823
October1st to 15thDay
12%6%14424446%49%
1699
16th to endDay
9%6%25%6%34447%44%
1708
November1st to 15thDay
13%10%44424336%42%
1566
16th to endDay
12%10%47%5%24346%38%
1440
December1st to 15thDay
15%12%6%9%7%2435%5%27%
1440
16th to endDay
15%14%5%9%6%35%445%26%
1385
January1st to 15thNight
16%14%47%5%23347%30%
2545
16th to endNight
16%15%5%6%5%13345%32%
2514
February1st to 15thNight
14%12%5%7%5%25%35%5%31%
2277
16th to endNight
11%12%5%7%6%345%5%6%31%
1944
March1st to 15thNight
8%11%47%6%445%5%7%33%
2034
16th to endNight
10%10%37%6%245%5%7%35%
2112
April1st to 15thNight
9%8%36%6%35%5%5%7%38%
1815
16th to endNight
10%9%245%23446%45%
1620
May1st to 15thNight
6%7%25%5%3446%8%46%
1619
16th to endNight
10%7%24435%46%7%43%
1570
June1st to 15thNight
8%5%143245%7%8%48%
1308
16th to endNight
3112213247%68%
1260
July1st to 15thNight
11121447%11%62%
1332
16th to endNight
111131245%6%68%
1656
August1st to 15thNight
32242345%8%62%
1620
16th to endNight
2212313347%67%
1719
September1st to 15thNight
5%213313336%63%
1905
16th to endNight
6%213323346%60%
1826
October1st to 15thNight
10%5%14324445%54%
1930
16th to endNight
10%6%24423446%48%
2161
November1st to 15thNight
13%9%34423346%44%
2278
16th to endNight
9%11%46%5%2435%6%38%
2520
December1st to 15thNight
15%12%48%7%3335%6%29%
2520
16th to endNight
18%18%5%7%5%2433426%
2835

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
55%5%19%13%5%
1404
16th to endDay
55%5%14%18%41
1708
February1st to 15thDay
56%5%15%18%5%
1575
16th to endDay
53%6%12%20%5%
1527
March1st to 15thDay
51%5%14%21%6%1
1925
16th to endDay
54%411%20%7%
2112
April1st to 15thDay
46%6%14%20%11%
2131
16th to endDay
42%5%10%27%13%1
2340
May1st to 15thDay
36%5%7%29%18%1
2331
16th to endDay
43%6%10%25%12%1
2545
June1st to 15thDay
37%49%27%17%3
2648
16th to endDay
16%3421%37%17%
2700
July1st to 15thDay
17%3419%32%23%
2472
16th to endDay
19%2313%24%36%
2353
August1st to 15thDay
20%3314%30%27%
2325
16th to endDay
19%3320%32%21%
2483
September1st to 15thDay
20%37%20%32%15%
2052
16th to endDay
22%39%28%27%8%
1823
October1st to 15thDay
36%313%31%10%3
1699
16th to endDay
39%314%26%15%
1708
November1st to 15thDay
44%415%22%9%2
1566
16th to endDay
47%219%21%6%1
1440
December1st to 15thDay
59%5%13%16%4
1440
16th to endDay
61%5%16%12%3
1385
January1st to 15thNight
55%6%17%15%41
2545
16th to endNight
54%414%18%5%1
2514
February1st to 15thNight
54%5%16%17%5%
2288
16th to endNight
51%5%15%19%5%1
1944
March1st to 15thNight
49%5%13%22%7%1
2034
16th to endNight
47%5%13%24%8%
2112
April1st to 15thNight
43%5%15%23%10%1
1815
16th to endNight
39%411%27%16%
1620
May1st to 15thNight
35%49%29%20%2
1620
16th to endNight
38%411%26%15%2
1571
June1st to 15thNight
30%5%12%24%23%4
1308
16th to endNight
16%25%16%37%22%
1260
July1st to 15thNight
15%45%19%27%28%
1256
16th to endNight
14%2313%26%39%
1549
August1st to 15thNight
20%3416%25%29%
1611
16th to endNight
18%2417%29%28%
1719
September1st to 15thNight
22%35%15%33%20%
1905
16th to endNight
24%36%27%28%10%
1826
October1st to 15thNight
32%213%31%16%3
1930
16th to endNight
35%410%29%17%2
2161
November1st to 15thNight
42%413%25%11%3
2278
16th to endNight
46%416%21%9%1
2520
December1st to 15thNight
55%5%19%14%4
2520
16th to endNight
62%314%14%3
2835

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
31%5%8%30%20%5%
60
16th to endDay
27%217%31%18%3
93
February1st to 15thDay
25%12%18%16%21%5%
90
16th to endDay
17%21%30%18%9%2
186
March1st to 15thDay
17%27%27%22%6%
270
16th to endDay
20%24%32%15%6%
288
April1st to 15thDay
15%23%26%19%11%3
269
16th to endDay
17%15%32%21%10%1
270
May1st to 15thDay
10%12%32%25%13%4
288
16th to endDay
16%6%19%29%19%8%
443
June1st to 15thDay
10%11%22%29%19%5%
495
16th to endDay
5%7%25%30%24%7%
495
July1st to 15thDay
45%16%33%33%6%
406
16th to endDay
35%25%40%22%3
327
August1st to 15thDay
6%427%31%25%4
315
16th to endDay
36%24%30%23%11%
332
September1st to 15thDay
6%6%24%27%24%10%
315
16th to endDay
7%8%26%28%20%7%
258
October1st to 15thDay
15%12%18%24%23%5%
139
16th to endDay
17%15%18%20%20%6%
96
November1st to 15thDay
13%118%23%25%17%
90
16th to endDay
22%11%31%27%6%1
90
December1st to 15thDay
27%13%25%27%5%
90
16th to endDay
23%126%32%7%8%
71
January1st to 15thNight
23%6%18%30%18%2
759
16th to endNight
24%5%14%33%19%3
768
February1st to 15thNight
21%6%19%33%17%2
704
16th to endNight
16%9%25%31%13%3
632
March1st to 15thNight
13%8%24%35%14%3
720
16th to endNight
14%9%26%35%12%1
768
April1st to 15thNight
13%8%26%33%15%2
629
16th to endNight
15%8%22%35%16%2
540
May1st to 15thNight
10%5%23%35%22%2
540
16th to endNight
12%6%17%36%23%4
563
June1st to 15thNight
10%5%24%34%23%2
408
16th to endNight
4319%38%27%6%
360
July1st to 15thNight
212%41%36%6%
340
16th to endNight
2112%43%34%5%
520
August1st to 15thNight
6%110%44%34%2
539
16th to endNight
3215%40%33%5%
573
September1st to 15thNight
6%215%34%33%7%
658
16th to endNight
8%115%34%29%10%
660
October1st to 15thNight
12%5%17%37%23%4
660
16th to endNight
13%415%40%20%5%
704
November1st to 15thNight
17%6%21%32%19%2
703
16th to endNight
14%9%23%32%17%2
900
December1st to 15thNight
22%7%22%34%12%1
900
16th to endNight
28%8%18%29%13%2
960
Page generated at 2017-09-17 10:05:42. Version ac04

Copyright 2017 A. Danko


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