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Eugene
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eugene clear sky chart from 2005-11-05 to 2017-05-24.

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
49%
14462
13%
45896
13%
14433
51%
14433
19%
32140

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
34%
716
8%
2506
9%
716
35%
716
9%
2007
January16th to endNight
40%
768
11%
2538
12%
768
41%
768
13%
1922
February1st to 15thNight
38%
699
7%
2288
8%
699
38%
699
10%
1862
February16th to endNight
39%
632
11%
2002
9%
632
41%
632
13%
1541
March1st to 15thNight
35%
720
5%
2019
4%
720
37%
720
13%
1642
March16th to endNight
34%
768
7%
2094
5%
768
35%
768
12%
1733
April1st to 15thNight
36%
719
7%
1799
4%
719
37%
719
14%
1476
April16th to endNight
49%
612
10%
1692
7%
612
49%
612
19%
1268
May1st to 15thNight
50%
425
11%
1505
12%
425
52%
425
20%
984
May16th to endNight
50%
361
9%
1440
12%
360
51%
360
13%
1007
June1st to 15thNight
54%
330
10%
1320
14%
330
58%
330
19%
842
June16th to endNight
62%
330
13%
1320
20%
330
66%
330
28%
703
July1st to 15thNight
73%
310
23%
1240
30%
310
81%
310
48%
506
July16th to endNight
75%
384
29%
1337
32%
359
85%
359
57%
524
August1st to 15thNight
82%
493
31%
1476
27%
490
85%
490
58%
672
August16th to endNight
77%
607
33%
1657
22%
607
81%
607
58%
820
September1st to 15thNight
77%
660
34%
1650
22%
660
79%
660
63%
841
September16th to endNight
68%
656
27%
1818
23%
656
69%
656
36%
1095
October1st to 15thNight
59%
660
17%
1980
17%
660
63%
660
29%
1262
October16th to endNight
48%
704
14%
2112
14%
704
49%
704
19%
1532
November1st to 15thNight
37%
700
8%
2375
8%
700
38%
700
10%
1885
November16th to endNight
40%
720
8%
2520
8%
720
41%
720
13%
1899
December1st to 15thNight
42%
720
10%
2520
11%
720
43%
720
14%
1862
December16th to endNight
29%
768
6%
2688
7%
768
30%
768
8%
2255

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
19%8%36%5%24446%34%
46392
Night
20%8%35%5%24445%35%
46068
Cloud CoverDay
21%7%35%5%24346%35%
46392
Night
22%7%35%423345%35%
46072
TransparencyDay
50%412%17%11%2
46067
Night
51%412%17%10%3
45897
SeeingDay
25%9%22%26%13%2
5262
Night
26%412%29%24%3
14472

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
31%11%37%7%35%445%14%
1432
16th to endDay
26%8%47%6%35%5%5%7%18%
1684
February1st to 15thDay
29%11%38%7%45%5%6%414%
1576
16th to endDay
26%14%6%9%6%2433418%
1472
March1st to 15thDay
27%13%5%8%6%35%435%15%
1938
16th to endDay
29%12%47%6%3445%5%15%
2130
April1st to 15thDay
24%12%5%8%7%45%435%18%
2149
16th to endDay
22%10%46%5%24446%26%
2265
May1st to 15thDay
17%8%37%42335%6%36%
2442
16th to endDay
22%9%37%5%25%45%7%26%
2514
June1st to 15thDay
19%9%47%5%34446%32%
2310
16th to endDay
14%6%35%424337%44%
2310
July1st to 15thDay
6%312312335%65%
2310
16th to endDay
7%31221222468%
2423
August1st to 15thDay
2312322347%65%
2145
16th to endDay
5%313312335%65%
2193
September1st to 15thDay
5%312312135%68%
1980
16th to endDay
14%6%36%5%24447%42%
1811
October1st to 15thDay
16%8%45%6%245%5%7%33%
1650
16th to endDay
22%10%46%7%25%46%6%23%
1760
November1st to 15thDay
32%10%38%6%33437%15%
1482
16th to endDay
26%9%5%8%6%35%5%6%6%15%
1440
December1st to 15thDay
25%12%47%7%345%5%5%17%
1440
16th to endDay
33%13%49%5%235%46%10%
1536
January1st to 15thNight
27%12%5%8%5%245%35%18%
2506
16th to endNight
24%10%48%6%34445%23%
2538
February1st to 15thNight
25%12%5%8%6%35%345%19%
2276
16th to endNight
23%11%5%7%6%34446%23%
2002
March1st to 15thNight
28%11%46%5%34346%21%
2019
16th to endNight
26%10%5%7%6%44445%19%
2090
April1st to 15thNight
23%13%47%5%3443424%
1799
16th to endNight
20%6%35%5%25%45%7%33%
1692
May1st to 15thNight
14%8%25%5%34345%40%
1505
16th to endNight
19%8%25%6%35%447%32%
1440
June1st to 15thNight
16%5%244235%5%7%41%
1320
16th to endNight
10%6%13314446%52%
1320
July1st to 15thNight
5%21121323471%
1320
16th to endNight
311111122378%
1436
August1st to 15thNight
2212212235%73%
1485
16th to endNight
421221223472%
1657
September1st to 15thNight
31221223474%
1650
16th to endNight
10%413423446%53%
1818
October1st to 15thNight
15%425%413346%47%
1980
16th to endNight
21%9%35%423446%32%
2112
November1st to 15thNight
31%7%46%6%25%45%5%19%
2375
16th to endNight
24%9%47%6%34445%25%
2520
December1st to 15thNight
26%9%45%5%23445%25%
2520
16th to endNight
32%12%5%9%5%3444414%
2688

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
33%10%45%6%45%345%16%
1432
16th to endDay
28%7%37%5%25%45%7%20%
1684
February1st to 15thDay
31%9%45%7%36%5%6%5%15%
1576
16th to endDay
29%12%5%8%6%2433319%
1472
March1st to 15thDay
31%12%48%5%3444416%
1938
16th to endDay
33%9%5%6%6%34445%16%
2130
April1st to 15thDay
26%11%5%8%7%35%43418%
2149
16th to endDay
24%8%46%5%2445%6%26%
2265
May1st to 15thDay
18%8%36%424346%36%
2442
16th to endDay
24%8%36%5%34447%26%
2514
June1st to 15thDay
21%8%47%5%24336%32%
2310
16th to endDay
14%7%25%433346%44%
2310
July1st to 15thDay
6%312312235%66%
2310
16th to endDay
7%31221222468%
2423
August1st to 15thDay
3312313346%66%
2145
16th to endDay
5%312312236%66%
2193
September1st to 15thDay
5%31222223469%
1980
16th to endDay
14%6%25%5%23346%44%
1811
October1st to 15thDay
18%7%26%5%24446%36%
1650
16th to endDay
25%8%26%6%4445%6%25%
1760
November1st to 15thDay
34%8%38%6%43345%18%
1482
16th to endDay
28%9%47%6%35%5%6%7%16%
1440
December1st to 15thDay
28%10%46%6%44347%19%
1440
16th to endDay
36%12%47%32345%7%12%
1536
January1st to 15thNight
31%10%46%6%24335%19%
2506
16th to endNight
26%10%37%5%345%45%24%
2538
February1st to 15thNight
30%10%47%5%34346%19%
2276
16th to endNight
25%10%46%5%34345%24%
2002
March1st to 15thNight
30%10%36%434445%21%
2019
16th to endNight
30%10%37%6%34345%19%
2094
April1st to 15thNight
26%12%47%42443424%
1799
16th to endNight
21%7%35%435%45%7%32%
1692
May1st to 15thNight
16%8%36%5%33345%39%
1505
16th to endNight
21%6%46%5%3435%7%30%
1440
June1st to 15thNight
17%6%245%235%47%40%
1320
16th to endNight
12%5%23322346%52%
1320
July1st to 15thNight
421121333471%
1320
16th to endNight
411111122378%
1436
August1st to 15thNight
2213212326%72%
1485
16th to endNight
421221223473%
1657
September1st to 15thNight
421111223374%
1650
16th to endNight
11%313414446%52%
1818
October1st to 15thNight
16%425%423345%47%
1980
16th to endNight
24%9%25%423446%33%
2112
November1st to 15thNight
33%7%36%5%345%5%419%
2375
16th to endNight
28%8%46%5%24435%26%
2520
December1st to 15thNight
29%8%35%42335%6%26%
2520
16th to endNight
35%10%47%5%3443415%
2688

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
68%310%9%6%1
1432
16th to endDay
60%49%12%8%4
1684
February1st to 15thDay
67%6%13%7%4
1576
16th to endDay
69%39%9%6%
1472
March1st to 15thDay
70%5%9%9%4
1938
16th to endDay
70%6%10%9%3
2130
April1st to 15thDay
69%5%12%10%2
2149
16th to endDay
58%7%14%12%5%
2265
May1st to 15thDay
49%416%19%8%1
2442
16th to endDay
58%6%14%16%2
2518
June1st to 15thDay
54%5%15%19%5%
2310
16th to endDay
41%319%24%9%1
2310
July1st to 15thDay
22%312%27%24%8%
2161
16th to endDay
20%25%26%33%10%
2259
August1st to 15thDay
18%414%34%21%6%
2129
16th to endDay
21%311%33%27%4
2193
September1st to 15thDay
19%28%31%24%12%
1980
16th to endDay
40%5%11%24%14%4
1811
October1st to 15thDay
48%5%12%16%14%3
1650
16th to endDay
56%6%12%15%8%1
1760
November1st to 15thDay
67%413%10%3
1482
16th to endDay
65%312%7%8%2
1440
December1st to 15thDay
64%5%10%11%7%
1440
16th to endDay
70%410%9%3
1536
January1st to 15thNight
67%49%9%7%1
2506
16th to endNight
61%49%11%8%4
2538
February1st to 15thNight
67%410%12%41
2288
16th to endNight
61%412%12%6%2
2002
March1st to 15thNight
64%5%11%12%5%
2019
16th to endNight
67%5%13%10%3
2094
April1st to 15thNight
64%5%13%11%4
1799
16th to endNight
52%7%17%15%42
1692
May1st to 15thNight
47%415%20%10%1
1506
16th to endNight
53%6%16%18%3
1440
June1st to 15thNight
43%8%17%24%6%
1320
16th to endNight
32%5%21%30%8%1
1320
July1st to 15thNight
17%313%30%24%10%
1240
16th to endNight
13%26%26%36%13%
1337
August1st to 15thNight
15%311%40%24%5%
1476
16th to endNight
16%310%34%26%8%
1657
September1st to 15thNight
15%39%31%26%13%
1650
16th to endNight
32%5%11%26%16%7%
1818
October1st to 15thNight
39%5%13%20%16%5%
1980
16th to endNight
53%5%12%15%11%2
2112
November1st to 15thNight
65%5%10%12%5%
2375
16th to endNight
60%410%10%10%3
2520
December1st to 15thNight
59%312%15%8%
2520
16th to endNight
72%410%9%3
2688

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
45%316%21%11%1
60
16th to endDay
30%7%18%19%19%4
212
February1st to 15thDay
38%7%17%22%12%
236
16th to endDay
38%11%20%21%7%
220
March1st to 15thDay
50%10%20%12%6%
270
16th to endDay
38%13%26%14%5%1
288
April1st to 15thDay
29%15%24%17%8%4
269
16th to endDay
34%13%22%20%43
270
May1st to 15thDay
25%15%21%24%10%2
288
16th to endDay
25%10%17%25%16%5%
301
June1st to 15thDay
20%10%22%29%14%2
255
16th to endDay
16%9%24%34%13%1
255
July1st to 15thDay
10%6%24%36%17%4
245
16th to endDay
5%5%29%38%15%4
271
August1st to 15thDay
3223%47%18%3
255
16th to endDay
5%5%26%30%23%7%
268
September1st to 15thDay
8%6%30%28%23%3
255
16th to endDay
19%6%23%32%15%2
255
October1st to 15thDay
23%9%23%27%14%1
255
16th to endDay
32%8%20%23%12%2
272
November1st to 15thDay
30%10%14%34%6%3
78
16th to endDay
40%10%20%11%16%1
60
December1st to 15thDay
56%18%11%11%1
60
16th to endDay
39%415%18%20%1
64
January1st to 15thNight
36%5%13%24%16%3
720
16th to endNight
31%311%27%20%5%
768
February1st to 15thNight
35%5%9%28%19%1
704
16th to endNight
31%8%13%28%17%
632
March1st to 15thNight
36%6%12%26%16%1
720
16th to endNight
34%6%14%26%16%1
768
April1st to 15thNight
32%7%14%24%20%1
719
16th to endNight
25%412%29%24%2
612
May1st to 15thNight
20%218%31%25%2
426
16th to endNight
26%110%28%30%3
361
June1st to 15thNight
19%315%35%23%3
330
16th to endNight
16%113%37%30%1
330
July1st to 15thNight
5%115%39%36%1
310
16th to endNight
4115%39%35%2
384
August1st to 15thNight
47%32%46%7%
493
16th to endNight
6%111%36%39%5%
607
September1st to 15thNight
5%112%33%40%6%
660
16th to endNight
13%19%34%36%3
656
October1st to 15thNight
17%311%35%26%5%
660
16th to endNight
30%29%27%23%5%
704
November1st to 15thNight
36%412%30%15%1
700
16th to endNight
33%7%11%25%18%3
720
December1st to 15thNight
33%410%28%20%2
720
16th to endNight
42%6%11%24%13%1
768
Page generated at 2017-05-25 10:27:33. Version ac04

Copyright 2017 A. Danko


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