Ed Majden Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ed Majden Observatory clear sky chart from 2005-11-05 to 2017-10-31.

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
44%
14672
10%
47291
8%
14643
47%
14643
17%
33971

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
30%
750
9%
2686
8%
746
33%
746
10%
2148
January16th to endNight
36%
796
8%
2793
7%
796
38%
796
10%
2209
February1st to 15thNight
34%
698
7%
2288
6%
698
36%
698
11%
1827
February16th to endNight
41%
632
13%
2053
11%
632
44%
632
17%
1461
March1st to 15thNight
32%
720
7%
2045
3%
720
35%
720
14%
1604
March16th to endNight
38%
768
9%
2112
6%
768
40%
768
16%
1655
April1st to 15thNight
43%
647
10%
1733
5%
647
46%
647
20%
1284
April16th to endNight
44%
540
11%
1620
9%
540
47%
540
19%
1162
May1st to 15thNight
53%
371
12%
1451
16%
371
57%
371
17%
962
May16th to endNight
50%
375
6%
1362
6%
374
52%
374
16%
942
June1st to 15thNight
53%
360
2%
1260
2%
360
53%
360
19%
830
June16th to endNight
49%
360
4%
1260
1%
360
49%
360
18%
845
July1st to 15thNight
71%
340
6%
1190
4%
340
73%
340
32%
651
July16th to endNight
76%
376
12%
1247
16%
354
78%
354
40%
615
August1st to 15thNight
77%
487
13%
1561
16%
485
78%
485
37%
851
August16th to endNight
73%
573
18%
1719
16%
573
74%
573
36%
976
September1st to 15thNight
72%
706
22%
1792
14%
706
74%
706
45%
1050
September16th to endNight
51%
716
16%
1993
12%
716
53%
716
25%
1352
October1st to 15thNight
53%
720
11%
2160
11%
720
55%
720
25%
1419
October16th to endNight
39%
768
9%
2422
7%
768
43%
768
14%
1828
November1st to 15thNight
28%
700
6%
2450
3%
700
33%
700
9%
1970
November16th to endNight
32%
720
8%
2520
5%
720
36%
720
10%
1951
December1st to 15thNight
29%
749
7%
2694
4%
749
33%
749
9%
2119
December16th to endNight
26%
800
9%
2880
5%
800
32%
800
10%
2260

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
17%8%36%6%35%5%5%6%29%
48501
Night
18%9%36%5%35%5%5%6%29%
47437
Cloud CoverDay
18%7%36%5%35%5%5%7%32%
48501
Night
21%8%36%5%35%45%6%30%
47440
TransparencyDay
51%5%18%18%5%
48150
Night
54%416%17%6%
47292
SeeingDay
19%5%20%25%20%7%
6565
Night
24%313%28%23%6%
14679

By Month

Percentage Cloud Cover NW (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
25%15%45%6%45%445%17%
1253
16th to endDay
22%15%5%7%6%44346%18%
1429
February1st to 15thDay
26%14%46%6%35%5%46%17%
1576
16th to endDay
19%11%36%6%47%5%5%6%23%
1421
March1st to 15thDay
24%12%47%7%46%6%5%415%
1914
16th to endDay
20%12%49%9%46%6%45%17%
2112
April1st to 15thDay
19%10%48%7%47%6%5%6%18%
2212
16th to endDay
20%10%5%8%6%35%5%5%5%21%
2340
May1st to 15thDay
14%7%37%6%36%6%5%7%31%
2499
16th to endDay
17%7%47%7%46%5%6%7%23%
2748
June1st to 15thDay
14%8%38%8%46%5%5%7%26%
2700
16th to endDay
16%7%49%8%46%5%6%5%25%
2700
July1st to 15thDay
9%425%5%25%45%7%46%
2700
16th to endDay
8%324435%5%5%6%50%
2837
August1st to 15thDay
6%413425%5%5%7%51%
2389
16th to endDay
8%425%5%35%46%8%44%
2483
September1st to 15thDay
8%4145%3345%6%52%
2167
16th to endDay
18%6%36%6%35%45%7%32%
1966
October1st to 15thDay
21%8%36%6%35%44431%
1800
16th to endDay
27%9%37%5%25%45%6%22%
1798
November1st to 15thDay
27%10%46%6%36%5%5%418%
1408
16th to endDay
25%10%37%6%35%6%46%20%
1440
December1st to 15thDay
22%14%6%5%5%35%44423%
1265
16th to endDay
25%16%5%8%6%2444417%
1344
January1st to 15thNight
24%12%47%5%35%445%21%
2686
16th to endNight
23%12%47%6%36%5%5%5%19%
2793
February1st to 15thNight
23%13%38%5%35%6%46%18%
2276
16th to endNight
16%10%36%5%35%5%5%6%31%
2053
March1st to 15thNight
21%10%36%6%46%6%6%6%21%
2045
16th to endNight
16%9%47%8%5%7%5%6%6%20%
2108
April1st to 15thNight
16%11%36%7%45%5%7%7%26%
1733
16th to endNight
17%6%36%6%46%45%8%28%
1620
May1st to 15thNight
14%7%446%46%6%6%7%31%
1451
16th to endNight
12%8%48%7%45%5%6%7%28%
1362
June1st to 15thNight
14%6%27%5%46%45%8%33%
1260
16th to endNight
13%6%38%6%47%5%5%7%30%
1260
July1st to 15thNight
6%314445%6%6%6%49%
1260
16th to endNight
6%224325%348%56%
1331
August1st to 15thNight
7%4143345%46%54%
1569
16th to endNight
6%314425%5%7%8%48%
1719
September1st to 15thNight
7%313424447%56%
1792
16th to endNight
16%8%25%6%3345%6%37%
1993
October1st to 15thNight
17%6%246%3446%6%38%
2160
16th to endNight
26%9%36%434445%26%
2422
November1st to 15thNight
29%10%36%6%45%5%45%18%
2450
16th to endNight
22%10%46%5%46%445%23%
2520
December1st to 15thNight
23%14%5%7%5%35%44421%
2694
16th to endNight
25%12%37%436%445%21%
2880

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
30%13%5%6%5%34346%15%
1253
16th to endDay
27%14%5%6%5%46%5%46%14%
1429
February1st to 15thDay
29%12%38%5%335%45%19%
1576
16th to endDay
21%8%36%6%27%5%5%8%23%
1421
March1st to 15thDay
27%9%47%6%36%5%6%5%15%
1914
16th to endDay
21%9%47%8%46%6%5%5%19%
2112
April1st to 15thDay
18%9%37%6%46%6%7%7%22%
2212
16th to endDay
19%8%38%7%35%5%5%7%25%
2340
May1st to 15thDay
15%5%35%4346%6%8%35%
2499
16th to endDay
16%7%36%5%35%5%5%8%30%
2748
June1st to 15thDay
13%5%36%7%35%6%6%9%32%
2700
16th to endDay
14%6%37%6%46%5%6%7%30%
2700
July1st to 15thDay
8%42432445%8%52%
2700
16th to endDay
7%3133235%5%7%56%
2837
August1st to 15thDay
5%41232336%8%57%
2389
16th to endDay
8%4144345%6%8%48%
2483
September1st to 15thDay
8%31342435%7%55%
2167
16th to endDay
18%6%26%5%346%5%6%33%
1966
October1st to 15thDay
21%8%37%5%3444433%
1800
16th to endDay
27%8%36%6%45%445%21%
1798
November1st to 15thDay
30%8%48%5%35%44418%
1408
16th to endDay
29%9%35%5%27%5%45%19%
1440
December1st to 15thDay
26%12%48%5%3433423%
1265
16th to endDay
30%13%5%6%7%36%43315%
1344
January1st to 15thNight
27%12%46%6%3433420%
2685
16th to endNight
27%12%46%6%35%5%45%18%
2793
February1st to 15thNight
27%13%35%5%35%45%5%18%
2276
16th to endNight
20%8%26%5%345%46%30%
2053
March1st to 15thNight
25%7%46%7%46%6%5%5%20%
2045
16th to endNight
19%9%38%7%46%5%6%6%21%
2112
April1st to 15thNight
18%9%46%6%345%6%9%25%
1733
16th to endNight
18%7%36%6%36%5%5%9%29%
1620
May1st to 15thNight
16%7%26%6%36%5%6%7%33%
1451
16th to endNight
13%7%47%6%46%6%5%8%28%
1362
June1st to 15thNight
13%7%38%435%5%5%6%36%
1260
16th to endNight
13%7%38%6%36%45%7%32%
1260
July1st to 15thNight
6%423436%46%8%51%
1260
16th to endNight
7%313323447%57%
1331
August1st to 15thNight
7%413424446%56%
1569
16th to endNight
6%3244245%6%8%50%
1719
September1st to 15thNight
7%314324346%57%
1792
16th to endNight
18%8%26%42345%6%38%
1993
October1st to 15thNight
18%6%145%34446%40%
2160
16th to endNight
28%8%35%423446%27%
2422
November1st to 15thNight
33%8%35%6%35%44419%
2450
16th to endNight
25%11%36%5%35%5%45%22%
2520
December1st to 15thNight
28%11%47%5%2443421%
2694
16th to endNight
30%11%36%5%34445%20%
2880

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
70%410%9%4
1253
16th to endDay
70%410%9%21
1429
February1st to 15thDay
67%5%13%9%4
1576
16th to endDay
59%5%15%14%4
1421
March1st to 15thDay
67%5%13%10%2
1914
16th to endDay
65%5%12%14%1
2112
April1st to 15thDay
59%7%13%16%2
2212
16th to endDay
59%412%16%6%
2340
May1st to 15thDay
47%6%19%20%5%
2499
16th to endDay
52%6%20%18%2
2752
June1st to 15thDay
48%8%19%18%4
2700
16th to endDay
52%6%20%16%3
2700
July1st to 15thDay
32%5%24%26%10%1
2541
16th to endDay
26%5%26%30%9%
2658
August1st to 15thDay
26%6%25%29%9%1
2372
16th to endDay
32%5%29%24%6%1
2483
September1st to 15thDay
29%5%23%25%14%
2167
16th to endDay
48%5%17%19%7%
1966
October1st to 15thDay
55%416%14%7%
1800
16th to endDay
63%5%14%12%4
1798
November1st to 15thDay
66%5%12%11%3
1408
16th to endDay
66%412%11%31
1440
December1st to 15thDay
65%314%10%5%
1265
16th to endDay
71%39%10%21
1344
January1st to 15thNight
66%411%11%6%
2686
16th to endNight
65%411%12%31
2793
February1st to 15thNight
65%412%12%31
2288
16th to endNight
53%414%20%6%
2053
March1st to 15thNight
60%5%16%13%4
2045
16th to endNight
61%414%15%3
2112
April1st to 15thNight
52%6%15%19%5%
1733
16th to endNight
53%314%21%6%
1620
May1st to 15thNight
49%415%21%8%
1452
16th to endNight
51%5%19%18%4
1362
June1st to 15thNight
47%5%25%15%5%1
1260
16th to endNight
49%418%21%31
1260
July1st to 15thNight
31%5%23%25%11%2
1190
16th to endNight
24%5%28%31%9%1
1247
August1st to 15thNight
28%5%22%31%9%2
1561
16th to endNight
29%6%26%27%7%1
1719
September1st to 15thNight
27%417%30%18%1
1792
16th to endNight
46%318%20%8%2
1993
October1st to 15thNight
43%418%21%10%
2160
16th to endNight
58%5%17%13%4
2422
November1st to 15thNight
67%413%9%3
2450
16th to endNight
63%5%11%13%5%
2520
December1st to 15thNight
66%312%11%4
2694
16th to endNight
65%411%12%5%
2880

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
23%10%11%18%23%13%
60
16th to endDay
37%224%16%16%3
125
February1st to 15thDay
36%6%18%23%12%1
236
16th to endDay
26%7%21%24%15%5%
211
March1st to 15thDay
33%13%32%13%6%1
264
16th to endDay
31%10%26%18%9%4
288
April1st to 15thDay
20%10%27%22%13%5%
269
16th to endDay
24%10%26%22%12%3
270
May1st to 15thDay
20%6%20%27%19%5%
288
16th to endDay
17%417%29%22%8%
464
June1st to 15thDay
16%6%21%24%25%5%
495
16th to endDay
17%5%20%28%21%6%
495
July1st to 15thDay
8%318%30%29%9%
475
16th to endDay
6%416%30%28%13%
506
August1st to 15thDay
8%112%32%24%19%
315
16th to endDay
9%218%31%25%12%
332
September1st to 15thDay
9%221%27%25%13%
315
16th to endDay
20%6%22%24%19%6%
315
October1st to 15thDay
25%6%22%22%18%4
315
16th to endDay
32%7%19%22%12%6%
283
November1st to 15thDay
28%6%23%25%15%1
60
16th to endDay
33%5%11%11%13%25%
60
December1st to 15thDay
40%113%26%10%8%
60
16th to endDay
25%315%35%15%4
64
January1st to 15thNight
34%5%14%23%16%4
750
16th to endNight
32%312%26%19%7%
796
February1st to 15thNight
31%313%31%17%2
704
16th to endNight
23%416%32%18%4
632
March1st to 15thNight
28%7%20%25%14%3
720
16th to endNight
24%420%27%17%6%
768
April1st to 15thNight
20%5%14%32%22%4
647
16th to endNight
21%216%36%19%3
540
May1st to 15thNight
18%311%34%23%8%
372
16th to endNight
17%413%26%31%8%
375
June1st to 15thNight
14%312%33%29%6%
360
16th to endNight
18%312%34%25%6%
360
July1st to 15thNight
6%29%27%40%13%
340
16th to endNight
8%1326%43%16%
376
August1st to 15thNight
9%1121%48%17%
487
16th to endNight
9%6%28%46%8%
573
September1st to 15thNight
10%6%27%36%19%
706
16th to endNight
21%311%25%26%11%
716
October1st to 15thNight
21%310%32%25%7%
720
16th to endNight
30%213%27%18%6%
768
November1st to 15thNight
37%219%27%12%1
700
16th to endNight
30%416%26%16%4
720
December1st to 15thNight
34%5%12%26%17%3
749
16th to endNight
35%322%25%11%1
800
Page generated at 2017-11-01 14:23:37. Version ac04

Copyright 2017 A. Danko


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