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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 2018-02-22.

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%
15398
14%
48956
13%
15369
51%
15369
20%
34165

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%
776
8%
2716
9%
776
35%
776
9%
2189
January16th to endNight
36%
832
10%
2749
11%
832
38%
832
12%
2122
February1st to 15thNight
39%
759
8%
2483
8%
759
40%
759
11%
2001
February16th to endNight
37%
660
10%
2093
9%
660
40%
660
12%
1624
March1st to 15thNight
35%
720
5%
2019
4%
720
36%
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
52%
375
10%
1496
13%
374
54%
374
14%
1030
June1st to 15thNight
54%
360
10%
1440
13%
360
58%
360
18%
936
June16th to endNight
63%
360
15%
1440
23%
360
67%
360
30%
749
July1st to 15thNight
75%
340
22%
1360
29%
340
83%
340
49%
545
July16th to endNight
75%
415
31%
1452
35%
390
86%
390
58%
563
August1st to 15thNight
83%
538
29%
1611
26%
535
85%
535
57%
740
August16th to endNight
78%
663
35%
1809
24%
663
81%
663
59%
881
September1st to 15thNight
77%
720
33%
1800
21%
720
78%
720
61%
930
September16th to endNight
67%
716
26%
1983
23%
716
69%
716
36%
1196
October1st to 15thNight
60%
720
17%
2160
17%
720
63%
720
29%
1367
October16th to endNight
48%
768
15%
2304
16%
768
49%
768
20%
1652
November1st to 15thNight
35%
760
7%
2579
8%
760
36%
760
10%
2051
November16th to endNight
40%
780
8%
2730
8%
780
40%
780
13%
2068
December1st to 15thNight
43%
780
11%
2730
12%
780
43%
780
15%
1969
December16th to endNight
28%
832
6%
2912
6%
832
29%
832
8%
2449

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%
49310
Night
19%8%35%5%24445%36%
49128
Cloud CoverDay
20%7%35%424346%35%
49310
Night
22%7%35%423345%36%
49132
TransparencyDay
50%412%18%11%3
48985
Night
50%412%17%11%3
48957
SeeingDay
24%8%21%26%14%3
6162
Night
26%411%29%24%3
15408

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
30%10%37%7%45%445%14%
1552
16th to endDay
26%9%47%6%35%5%5%7%16%
1825
February1st to 15thDay
28%11%38%7%45%5%5%415%
1711
16th to endDay
26%15%6%8%6%2333418%
1527
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%36%5%35%45%7%27%
2615
June1st to 15thDay
19%8%47%6%34445%31%
2520
16th to endDay
13%6%25%424347%45%
2520
July1st to 15thDay
5%312312335%67%
2520
16th to endDay
6%31221222469%
2615
August1st to 15thDay
3312322347%65%
2340
16th to endDay
5%313312335%66%
2393
September1st to 15thDay
5%312212135%67%
2160
16th to endDay
14%6%36%5%24447%42%
1976
October1st to 15thDay
16%8%35%5%25%5%5%7%34%
1800
16th to endDay
22%10%36%6%25%46%6%25%
1920
November1st to 15thDay
31%10%38%6%34447%15%
1608
16th to endDay
27%10%5%8%6%35%5%6%6%14%
1560
December1st to 15thDay
23%12%47%7%345%6%6%19%
1560
16th to endDay
32%13%5%10%6%235%46%9%
1664
January1st to 15thNight
28%12%5%8%5%345%35%17%
2716
16th to endNight
24%10%48%6%34445%21%
2749
February1st to 15thNight
25%12%47%6%34346%20%
2471
16th to endNight
23%11%5%7%6%34446%23%
2093
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
18%8%25%6%35%447%34%
1496
June1st to 15thNight
17%6%24433447%40%
1440
16th to endNight
10%5%13313447%53%
1440
July1st to 15thNight
421121223472%
1440
16th to endNight
311111122378%
1551
August1st to 15thNight
2212212235%73%
1620
16th to endNight
32221223474%
1809
September1st to 15thNight
421221223473%
1800
16th to endNight
10%41332345%6%52%
1983
October1st to 15thNight
14%425%5%23346%47%
2160
16th to endNight
21%9%35%423446%34%
2304
November1st to 15thNight
30%8%46%6%35%5%5%5%19%
2579
16th to endNight
25%9%47%6%34445%25%
2730
December1st to 15thNight
25%9%45%5%2345%5%27%
2730
16th to endNight
31%12%5%9%5%3444414%
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
32%10%45%7%45%345%16%
1552
16th to endDay
28%8%47%6%35%45%7%19%
1825
February1st to 15thDay
30%9%45%6%35%5%5%5%16%
1711
16th to endDay
29%13%5%7%6%2433319%
1527
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%28%
2615
June1st to 15thDay
22%8%37%5%34336%31%
2520
16th to endDay
14%6%25%423346%45%
2520
July1st to 15thDay
5%312212235%67%
2520
16th to endDay
7%31221222470%
2615
August1st to 15thDay
331231235%6%66%
2340
16th to endDay
5%312312236%67%
2393
September1st to 15thDay
5%31222223468%
2160
16th to endDay
14%6%25%5%23346%43%
1976
October1st to 15thDay
18%6%26%5%34447%36%
1800
16th to endDay
25%8%26%5%45%35%7%27%
1920
November1st to 15thDay
34%8%37%5%43346%17%
1608
16th to endDay
29%9%47%6%345%6%7%15%
1560
December1st to 15thDay
26%10%36%5%4435%7%20%
1560
16th to endDay
35%12%47%43345%6%11%
1664
January1st to 15thNight
31%10%47%6%34335%18%
2716
16th to endNight
27%10%37%5%345%45%23%
2749
February1st to 15thNight
29%10%36%5%34346%20%
2471
16th to endNight
26%10%46%6%34345%23%
2093
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
20%6%46%6%3435%6%32%
1496
June1st to 15thNight
18%6%3442345%7%39%
1440
16th to endNight
11%5%23222346%53%
1440
July1st to 15thNight
42112233472%
1440
16th to endNight
311111122478%
1551
August1st to 15thNight
2213212325%72%
1620
16th to endNight
42121223374%
1809
September1st to 15thNight
421121223373%
1800
16th to endNight
12%31341445%6%51%
1983
October1st to 15thNight
15%425%423345%47%
2160
16th to endNight
23%8%24423446%34%
2304
November1st to 15thNight
32%7%36%5%445%5%419%
2579
16th to endNight
28%8%46%5%24435%26%
2730
December1st to 15thNight
28%7%35%42335%6%28%
2730
16th to endNight
35%11%47%5%3444415%
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
68%310%10%6%1
1552
16th to endDay
61%49%11%7%4
1825
February1st to 15thDay
66%7%13%8%4
1711
16th to endDay
70%39%9%6%
1527
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
57%6%14%17%3
2619
June1st to 15thDay
55%5%14%18%5%
2520
16th to endDay
39%318%25%9%2
2520
July1st to 15thDay
20%312%28%26%8%
2371
16th to endDay
19%25%27%34%10%
2451
August1st to 15thDay
18%415%32%21%7%
2324
16th to endDay
20%311%34%27%4
2393
September1st to 15thDay
19%38%31%25%12%
2160
16th to endDay
40%5%12%22%14%3
1976
October1st to 15thDay
47%5%11%16%15%3
1800
16th to endDay
55%6%11%15%9%1
1920
November1st to 15thDay
67%413%11%3
1608
16th to endDay
66%412%6%7%2
1560
December1st to 15thDay
62%5%10%12%8%
1560
16th to endDay
71%410%9%2
1664
January1st to 15thNight
68%49%9%6%1
2716
16th to endNight
63%48%11%8%4
2749
February1st to 15thNight
66%5%10%11%41
2483
16th to endNight
62%412%12%6%2
2093
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
52%6%16%19%4
1496
June1st to 15thNight
44%8%17%23%5%
1440
16th to endNight
31%5%20%30%9%2
1440
July1st to 15thNight
16%312%30%27%9%
1360
16th to endNight
13%26%27%38%12%
1452
August1st to 15thNight
15%311%38%23%7%
1611
16th to endNight
15%311%34%26%8%
1809
September1st to 15thNight
16%39%30%27%13%
1800
16th to endNight
32%5%13%26%15%6%
1983
October1st to 15thNight
38%5%12%21%16%5%
2160
16th to endNight
51%5%12%14%13%2
2304
November1st to 15thNight
65%5%10%11%5%
2579
16th to endNight
61%411%10%9%3
2730
December1st to 15thNight
56%312%16%10%
2730
16th to endNight
72%410%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
42%311%22%17%3
90
16th to endDay
33%9%17%18%17%3
257
February1st to 15thDay
37%7%19%22%12%1
281
16th to endDay
39%11%21%20%7%
239
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
24%10%16%24%17%6%
330
June1st to 15thDay
23%10%20%27%14%3
315
16th to endDay
15%7%23%35%15%2
315
July1st to 15thDay
8%5%21%40%18%4
305
16th to endDay
4428%39%17%5%
327
August1st to 15thDay
4219%43%23%6%
315
16th to endDay
5%5%23%32%26%7%
332
September1st to 15thDay
7%5%27%29%24%5%
315
16th to endDay
17%8%24%30%15%3
315
October1st to 15thDay
23%9%22%27%14%1
315
16th to endDay
31%7%18%22%16%4
336
November1st to 15thDay
34%13%18%26%5%2
114
16th to endDay
42%8%17%15%13%2
90
December1st to 15thDay
41%12%12%12%11%11%
90
16th to endDay
37%314%21%21%1
96
January1st to 15thNight
36%5%12%23%17%4
780
16th to endNight
32%312%27%18%4
832
February1st to 15thNight
34%49%28%20%1
764
16th to endNight
31%8%13%28%17%
660
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
25%110%28%31%3
375
June1st to 15thNight
20%314%34%24%2
360
16th to endNight
15%113%38%30%1
360
July1st to 15thNight
5%113%40%37%1
340
16th to endNight
4115%39%36%1
415
August1st to 15thNight
46%31%47%8%
538
16th to endNight
5%110%36%40%5%
663
September1st to 15thNight
5%111%32%41%7%
720
16th to endNight
14%18%35%35%3
716
October1st to 15thNight
17%311%36%26%5%
720
16th to endNight
29%29%26%24%6%
768
November1st to 15thNight
35%412%31%13%1
760
16th to endNight
33%6%11%26%18%3
780
December1st to 15thNight
32%410%26%23%2
780
16th to endNight
42%6%11%25%13%1
832
Page generated at 2018-02-23 08:21:36. Version ac04

Copyright 2018 A. Danko


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