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Evans Above Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Evans Above Observatory clear sky chart from 2005-11-05 to 2018-01-12.

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
38%
15100
12%
48311
10%
15071
42%
15071
16%
34140

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
29%
763
8%
2661
8%
760
32%
760
9%
2139
January16th to endNight
31%
768
11%
2596
10%
768
35%
768
11%
1965
February1st to 15thNight
29%
700
7%
2288
6%
700
30%
700
9%
1845
February16th to endNight
30%
632
10%
2005
7%
632
35%
632
11%
1552
March1st to 15thNight
28%
720
6%
2046
5%
720
29%
720
10%
1702
March16th to endNight
27%
768
6%
2079
4%
768
28%
768
10%
1737
April1st to 15thNight
29%
719
7%
1799
3%
719
30%
719
14%
1473
April16th to endNight
33%
600
11%
1680
5%
600
37%
600
16%
1263
May1st to 15thNight
36%
378
14%
1457
12%
377
43%
377
17%
889
May16th to endNight
38%
375
8%
1496
9%
374
43%
374
13%
1015
June1st to 15thNight
37%
360
8%
1440
8%
360
43%
360
15%
941
June16th to endNight
39%
360
13%
1352
11%
360
50%
360
22%
776
July1st to 15thNight
61%
340
17%
1360
20%
340
70%
340
41%
570
July16th to endNight
57%
376
26%
1416
26%
354
77%
354
50%
532
August1st to 15thNight
70%
510
23%
1584
19%
508
77%
508
54%
685
August16th to endNight
64%
655
31%
1801
18%
655
72%
655
49%
913
September1st to 15thNight
63%
720
27%
1800
14%
720
67%
720
52%
962
September16th to endNight
53%
716
23%
1976
15%
716
59%
716
30%
1223
October1st to 15thNight
45%
720
17%
2160
16%
720
49%
720
24%
1418
October16th to endNight
38%
768
14%
2337
12%
768
42%
768
16%
1698
November1st to 15thNight
30%
760
7%
2606
7%
760
32%
760
8%
2154
November16th to endNight
29%
780
6%
2730
5%
780
32%
780
9%
2131
December1st to 15thNight
29%
780
9%
2730
9%
780
31%
780
10%
2094
December16th to endNight
22%
832
6%
2912
5%
832
24%
832
6%
2463

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
24%7%36%5%34345%32%
49013
Night
24%7%25%423345%35%
48479
Cloud CoverDay
23%8%36%5%24345%31%
49013
Night
24%7%35%423335%34%
48483
TransparencyDay
55%411%16%9%2
48684
Night
52%412%18%9%2
48312
SeeingDay
22%13%17%23%16%5%
5998
Night
23%16%13%30%15%1
15105

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
40%9%48%5%3323315%
1520
16th to endDay
33%8%48%5%3324421%
1626
February1st to 15thDay
32%13%5%6%5%235%4415%
1576
16th to endDay
34%11%47%6%2323419%
1468
March1st to 15thDay
37%12%38%5%3434411%
1912
16th to endDay
36%10%37%6%4444413%
2145
April1st to 15thDay
29%10%48%6%34446%16%
2149
16th to endDay
25%9%48%6%345%46%21%
2277
May1st to 15thDay
20%6%35%5%34346%35%
2491
16th to endDay
26%6%35%5%45%447%24%
2615
June1st to 15thDay
24%7%5%6%6%34346%26%
2520
16th to endDay
16%6%35%435%45%7%38%
2578
July1st to 15thDay
8%312223345%61%
2520
16th to endDay
8%313223236%62%
2657
August1st to 15thDay
5%41341335%6%59%
2367
16th to endDay
8%423423237%57%
2399
September1st to 15thDay
7%323424335%58%
2160
16th to endDay
18%6%35%5%33446%38%
1983
October1st to 15thDay
23%9%36%424345%31%
1800
16th to endDay
31%9%37%5%2334424%
1885
November1st to 15thDay
37%10%48%5%35%34313%
1581
16th to endDay
33%11%47%43434419%
1560
December1st to 15thDay
32%11%47%6%2324420%
1560
16th to endDay
41%10%48%5%2223413%
1664
January1st to 15thNight
36%9%26%5%24445%19%
2661
16th to endNight
31%7%36%5%23345%26%
2596
February1st to 15thNight
29%9%46%5%34335%22%
2276
16th to endNight
30%8%35%6%34345%24%
2005
March1st to 15thNight
33%10%46%43444419%
2046
16th to endNight
30%8%47%6%25%446%18%
2075
April1st to 15thNight
27%10%47%6%35%335%22%
1799
16th to endNight
25%7%35%5%23347%31%
1680
May1st to 15thNight
16%5%245%145%5%6%41%
1457
16th to endNight
18%7%346%345%6%7%32%
1496
June1st to 15thNight
17%6%36%6%33335%38%
1440
16th to endNight
14%6%24323335%49%
1352
July1st to 15thNight
422213235%69%
1440
16th to endNight
41111122477%
1512
August1st to 15thNight
2111212237%72%
1592
16th to endNight
5%21221223469%
1801
September1st to 15thNight
6%31221223471%
1800
16th to endNight
12%4145%24446%49%
1976
October1st to 15thNight
19%5%33423335%44%
2160
16th to endNight
25%6%35%5%23346%32%
2337
November1st to 15thNight
35%7%35%5%345%35%18%
2606
16th to endNight
32%8%36%5%2443424%
2730
December1st to 15thNight
30%10%36%423346%24%
2730
16th to endNight
37%12%46%5%2433316%
2912

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
42%10%37%5%2332315%
1520
16th to endDay
34%9%36%5%23335%21%
1626
February1st to 15thDay
35%11%5%7%5%33345%15%
1576
16th to endDay
34%12%46%5%3322320%
1468
March1st to 15thDay
38%13%48%5%2333412%
1912
16th to endDay
36%12%39%6%3434412%
2145
April1st to 15thDay
28%12%48%6%35%345%16%
2149
16th to endDay
24%10%47%7%35%5%45%22%
2277
May1st to 15thDay
18%7%47%6%34345%35%
2491
16th to endDay
25%8%37%5%45%347%24%
2615
June1st to 15thDay
23%8%47%6%35%45%6%25%
2520
16th to endDay
14%7%36%5%36%346%38%
2578
July1st to 15thDay
7%313323346%60%
2520
16th to endDay
7%323313336%60%
2657
August1st to 15thDay
5%42442235%6%58%
2367
16th to endDay
8%414423436%56%
2399
September1st to 15thDay
7%424314445%57%
2160
16th to endDay
18%6%26%6%24346%37%
1983
October1st to 15thDay
25%7%27%5%2445%5%30%
1800
16th to endDay
32%8%36%5%3323425%
1885
November1st to 15thDay
38%11%48%5%2433412%
1581
16th to endDay
35%10%47%5%2333418%
1560
December1st to 15thDay
33%12%45%5%3334320%
1560
16th to endDay
42%11%45%5%3423313%
1664
January1st to 15thNight
37%9%36%5%2434419%
2661
16th to endNight
31%9%36%423335%26%
2596
February1st to 15thNight
31%9%36%6%34335%22%
2276
16th to endNight
30%9%46%5%23435%23%
2005
March1st to 15thNight
35%10%45%425%42419%
2046
16th to endNight
31%11%47%6%24445%17%
2079
April1st to 15thNight
26%11%47%6%34345%21%
1799
16th to endNight
24%7%46%433337%30%
1680
May1st to 15thNight
16%6%35%5%13447%40%
1457
16th to endNight
17%7%37%5%345%5%7%31%
1496
June1st to 15thNight
19%6%46%7%3432438%
1440
16th to endNight
11%7%26%423336%48%
1352
July1st to 15thNight
421222323469%
1440
16th to endNight
41111122476%
1512
August1st to 15thNight
212213247%71%
1592
16th to endNight
5%22212235%68%
1801
September1st to 15thNight
6%21221223470%
1800
16th to endNight
13%324433446%47%
1976
October1st to 15thNight
19%5%34423335%43%
2160
16th to endNight
26%7%26%5%23346%31%
2337
November1st to 15thNight
36%9%35%5%34435%17%
2606
16th to endNight
34%7%36%5%2343424%
2730
December1st to 15thNight
31%9%35%423345%25%
2730
16th to endNight
38%12%36%42433415%
2912

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
74%36%8%6%
1520
16th to endDay
66%48%10%7%2
1626
February1st to 15thDay
71%5%8%10%3
1576
16th to endDay
71%38%10%5%
1468
March1st to 15thDay
76%37%8%3
1912
16th to endDay
75%39%9%1
2145
April1st to 15thDay
70%411%12%1
2149
16th to endDay
64%5%12%11%5%1
2277
May1st to 15thDay
50%314%20%8%1
2491
16th to endDay
59%6%15%14%3
2619
June1st to 15thDay
58%5%17%12%5%
2520
16th to endDay
46%5%17%21%7%2
2578
July1st to 15thDay
26%415%27%21%5%
2371
16th to endDay
23%313%27%26%5%
2490
August1st to 15thDay
26%415%32%16%5%
2350
16th to endDay
29%413%28%18%4
2399
September1st to 15thDay
28%412%22%20%11%
2160
16th to endDay
47%413%17%12%3
1983
October1st to 15thDay
55%49%19%8%3
1800
16th to endDay
63%210%11%10%
1885
November1st to 15thDay
75%38%8%3
1581
16th to endDay
70%38%9%7%
1560
December1st to 15thDay
69%37%12%6%
1560
16th to endDay
76%36%9%3
1664
January1st to 15thNight
68%310%10%5%1
2661
16th to endNight
61%39%12%9%2
2596
February1st to 15thNight
65%5%10%12%4
2288
16th to endNight
62%311%12%7%
2005
March1st to 15thNight
68%5%10%12%3
2046
16th to endNight
68%5%12%11%2
2079
April1st to 15thNight
65%313%12%4
1799
16th to endNight
54%6%13%17%5%1
1680
May1st to 15thNight
42%417%23%8%2
1458
16th to endNight
48%8%20%16%5%1
1496
June1st to 15thNight
49%416%22%6%
1440
16th to endNight
38%321%26%7%2
1352
July1st to 15thNight
18%316%31%23%6%
1360
16th to endNight
13%212%34%27%8%
1416
August1st to 15thNight
13%320%38%17%6%
1584
16th to endNight
19%315%36%17%6%
1801
September1st to 15thNight
19%215%29%20%12%
1800
16th to endNight
35%5%16%22%14%5%
1976
October1st to 15thNight
43%310%23%14%3
2160
16th to endNight
53%5%11%15%12%2
2337
November1st to 15thNight
69%5%8%12%3
2606
16th to endNight
64%49%10%9%1
2730
December1st to 15thNight
61%5%10%13%7%
2730
16th to endNight
73%48%9%3
2912

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
37%36%20%23%8%
82
16th to endDay
34%13%12%18%11%10%
154
February1st to 15thDay
41%15%12%15%13%2
236
16th to endDay
37%16%16%19%7%1
219
March1st to 15thDay
44%21%16%13%21
270
16th to endDay
33%19%24%14%5%2
288
April1st to 15thDay
24%17%19%20%10%7%
269
16th to endDay
27%17%21%22%7%3
270
May1st to 15thDay
23%20%21%14%17%3
288
16th to endDay
22%16%10%18%23%9%
330
June1st to 15thDay
20%16%18%23%17%4
315
16th to endDay
9%15%25%28%16%3
373
July1st to 15thDay
6%10%17%31%24%8%
305
16th to endDay
5%12%15%31%28%6%
327
August1st to 15thDay
7%7%15%30%25%13%
315
16th to endDay
6%9%15%28%26%12%
332
September1st to 15thDay
7%8%18%35%21%8%
315
16th to endDay
18%8%19%28%21%3
315
October1st to 15thDay
25%10%17%26%15%3
315
16th to endDay
32%8%15%23%12%7%
301
November1st to 15thDay
39%5%22%21%8%1
103
16th to endDay
42%322%12%15%4
90
December1st to 15thDay
44%116%12%16%8%
90
16th to endDay
43%411%20%17%2
96
January1st to 15thNight
34%18%8%23%14%1
764
16th to endNight
29%18%8%25%16%1
768
February1st to 15thNight
29%19%13%21%15%1
704
16th to endNight
27%18%14%26%12%
632
March1st to 15thNight
33%19%10%25%10%
720
16th to endNight
27%20%15%24%11%
768
April1st to 15thNight
25%20%13%23%16%1
719
16th to endNight
26%18%13%29%11%1
600
May1st to 15thNight
16%19%20%31%12%
378
16th to endNight
18%18%12%35%15%
375
June1st to 15thNight
16%18%15%38%11%
360
16th to endNight
11%17%23%38%8%
360
July1st to 15thNight
412%16%50%14%
340
16th to endNight
316%19%46%13%
376
August1st to 15thNight
39%10%43%29%2
510
16th to endNight
6%10%13%42%25%1
655
September1st to 15thNight
7%9%14%39%25%3
720
16th to endNight
14%9%14%37%23%1
716
October1st to 15thNight
21%10%15%30%19%2
720
16th to endNight
28%10%13%27%17%2
768
November1st to 15thNight
33%15%11%27%11%
760
16th to endNight
32%17%11%25%12%
780
December1st to 15thNight
32%17%10%25%12%1
780
16th to endNight
36%19%12%21%10%
832
Page generated at 2018-01-12 19:01:32. Version ac04

Copyright 2018 A. Danko


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