Corvallis
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Corvallis clear sky chart from 2005-11-05 to 2018-02-14.

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
50%
15324
14%
48855
13%
15296
52%
15296
21%
33236

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
31%
776
7%
2716
7%
776
33%
776
9%
2202
January16th to endNight
39%
832
11%
2758
11%
832
41%
832
13%
2088
February1st to 15thNight
39%
752
8%
2470
8%
752
41%
752
12%
1946
February16th to endNight
37%
632
11%
2011
10%
632
40%
632
15%
1512
March1st to 15thNight
37%
720
5%
2016
5%
720
38%
720
13%
1626
March16th to endNight
36%
768
8%
2097
5%
768
37%
768
14%
1679
April1st to 15thNight
41%
719
7%
1799
4%
719
42%
719
17%
1413
April16th to endNight
52%
597
13%
1677
9%
597
54%
597
22%
1170
May1st to 15thNight
51%
422
14%
1502
13%
422
55%
422
25%
904
May16th to endNight
54%
375
11%
1496
14%
374
57%
374
19%
942
June1st to 15thNight
57%
360
10%
1440
13%
360
61%
360
21%
875
June16th to endNight
64%
360
15%
1440
23%
360
68%
360
31%
730
July1st to 15thNight
78%
340
21%
1360
31%
340
84%
340
52%
532
July16th to endNight
85%
406
30%
1444
40%
382
89%
382
65%
514
August1st to 15thNight
86%
538
28%
1611
26%
535
87%
535
62%
699
August16th to endNight
80%
651
36%
1797
25%
651
82%
651
60%
860
September1st to 15thNight
81%
720
32%
1800
21%
720
83%
720
62%
922
September16th to endNight
70%
716
27%
1985
23%
716
72%
716
41%
1138
October1st to 15thNight
59%
720
18%
2160
19%
720
62%
720
30%
1348
October16th to endNight
48%
768
15%
2304
15%
768
50%
768
21%
1611
November1st to 15thNight
40%
760
8%
2600
9%
760
41%
760
12%
2031
November16th to endNight
38%
780
7%
2730
7%
780
41%
780
14%
2015
December1st to 15thNight
42%
780
11%
2730
11%
780
44%
780
15%
2005
December16th to endNight
29%
832
6%
2912
7%
832
30%
832
7%
2474

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
16%8%37%6%34446%33%
49238
Night
16%7%36%5%34445%37%
49026
Cloud CoverDay
17%8%47%6%34446%33%
49238
Night
18%7%36%5%34445%36%
49030
TransparencyDay
51%312%18%10%2
48912
Night
49%313%19%10%2
48856
SeeingDay
19%416%25%22%10%
6121
Night
21%213%35%24%2
15337

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
27%11%6%11%8%4433314%
1552
16th to endDay
24%9%410%8%35%45%5%17%
1817
February1st to 15thDay
26%12%5%10%8%44345%14%
1694
16th to endDay
23%13%6%10%7%345%3417%
1462
March1st to 15thDay
26%13%410%7%45%45%5%12%
1941
16th to endDay
26%11%48%7%46%445%14%
2127
April1st to 15thDay
19%12%6%9%8%5%6%45%6%15%
2149
16th to endDay
19%10%37%7%35%6%6%7%23%
2281
May1st to 15thDay
15%8%47%5%24348%34%
2448
16th to endDay
17%7%37%6%36%6%5%7%27%
2615
June1st to 15thDay
17%7%47%5%35%35%6%31%
2520
16th to endDay
10%6%26%5%3445%8%42%
2520
July1st to 15thDay
4312212346%65%
2520
16th to endDay
6%212212225%69%
2624
August1st to 15thDay
221332345%8%62%
2340
16th to endDay
5%312323347%62%
2405
September1st to 15thDay
4413213237%64%
2160
16th to endDay
14%6%246%24447%42%
1973
October1st to 15thDay
14%7%37%6%345%5%6%34%
1800
16th to endDay
19%10%49%7%45%35%5%24%
1920
November1st to 15thDay
26%10%6%9%7%45%5%5%6%12%
1586
16th to endDay
22%11%5%10%8%45%345%16%
1560
December1st to 15thDay
22%11%5%9%8%3444420%
1560
16th to endDay
28%13%5%9%8%46%445%10%
1664
January1st to 15thNight
25%13%48%7%35%44417%
2716
16th to endNight
22%9%5%7%7%34445%24%
2758
February1st to 15thNight
21%11%47%7%36%5%5%5%21%
2458
16th to endNight
18%10%48%6%46%45%5%25%
2011
March1st to 15thNight
24%10%47%7%44445%22%
2016
16th to endNight
23%9%38%7%46%5%5%6%19%
2093
April1st to 15thNight
21%9%47%6%345%46%25%
1799
16th to endNight
14%5%36%6%35%5%47%36%
1677
May1st to 15thNight
10%6%25%6%3345%7%41%
1502
16th to endNight
13%7%35%5%3435%9%37%
1496
June1st to 15thNight
13%6%25%335%447%43%
1440
16th to endNight
7%5%245%23347%53%
1440
July1st to 15thNight
32122233473%
1440
16th to endNight
2111123480%
1542
August1st to 15thNight
211212336%73%
1620
16th to endNight
422212335%71%
1797
September1st to 15thNight
31131223473%
1800
16th to endNight
8%313424447%54%
1985
October1st to 15thNight
12%424434446%47%
2160
16th to endNight
17%8%26%6%34445%36%
2304
November1st to 15thNight
25%9%36%6%35%6%5%6%21%
2600
16th to endNight
20%9%37%7%45%445%26%
2730
December1st to 15thNight
22%9%47%5%3445%5%27%
2730
16th to endNight
25%12%411%7%5%45%4314%
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
29%13%6%11%7%3333314%
1552
16th to endDay
25%10%5%10%6%34446%16%
1817
February1st to 15thDay
27%12%5%10%7%45%335%14%
1694
16th to endDay
24%14%6%9%8%3443317%
1462
March1st to 15thDay
28%12%5%9%6%45%45%412%
1941
16th to endDay
26%10%5%7%7%46%5%45%15%
2127
April1st to 15thDay
20%12%6%9%8%45%5%45%16%
2149
16th to endDay
19%9%47%7%46%5%46%24%
2281
May1st to 15thDay
15%8%37%5%33447%35%
2448
16th to endDay
18%7%36%6%45%5%5%7%28%
2615
June1st to 15thDay
16%8%5%7%6%3445%6%31%
2520
16th to endDay
10%7%25%6%345%5%7%42%
2520
July1st to 15thDay
4313213245%66%
2520
16th to endDay
6%21231223469%
2624
August1st to 15thDay
221242345%8%63%
2340
16th to endDay
4312323346%62%
2405
September1st to 15thDay
4412312236%65%
2160
16th to endDay
14%6%346%34446%41%
1973
October1st to 15thDay
16%7%37%6%35%446%34%
1800
16th to endDay
20%11%5%8%6%45%44424%
1920
November1st to 15thDay
28%11%6%8%7%36%46%5%11%
1586
16th to endDay
24%11%6%9%9%35%345%16%
1560
December1st to 15thDay
23%10%7%10%8%3434418%
1560
16th to endDay
31%12%6%10%7%35%5%3410%
1664
January1st to 15thNight
28%12%5%8%6%35%34417%
2716
16th to endNight
23%9%5%7%6%34346%24%
2758
February1st to 15thNight
24%11%46%5%36%5%5%5%20%
2458
16th to endNight
21%9%48%6%35%5%45%25%
2011
March1st to 15thNight
25%10%5%8%6%3444421%
2016
16th to endNight
24%9%47%8%445%5%7%18%
2097
April1st to 15thNight
22%10%37%6%3445%5%25%
1799
16th to endNight
15%5%26%6%35%448%35%
1677
May1st to 15thNight
10%7%27%6%3345%6%41%
1502
16th to endNight
15%7%36%5%3435%9%35%
1496
June1st to 15thNight
13%6%35%42445%6%42%
1440
16th to endNight
7%5%245%1335%7%51%
1440
July1st to 15thNight
2212212235%72%
1440
16th to endNight
31111122480%
1542
August1st to 15thNight
211212337%72%
1620
16th to endNight
4212211235%71%
1797
September1st to 15thNight
32231233472%
1800
16th to endNight
9%313434347%53%
1985
October1st to 15thNight
13%5%25%434446%46%
2160
16th to endNight
19%8%25%5%34445%35%
2304
November1st to 15thNight
27%8%36%7%445%5%5%21%
2600
16th to endNight
23%9%37%7%35%345%25%
2730
December1st to 15thNight
24%10%46%5%3335%6%26%
2730
16th to endNight
27%12%5%10%7%35%43414%
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
75%37%9%31
1552
16th to endDay
69%39%11%42
1817
February1st to 15thDay
73%310%8%3
1694
16th to endDay
71%38%8%6%
1462
March1st to 15thDay
72%49%9%3
1941
16th to endDay
69%413%9%2
2127
April1st to 15thDay
67%414%11%2
2149
16th to endDay
57%5%16%15%41
2281
May1st to 15thDay
48%213%23%10%1
2448
16th to endDay
53%5%17%18%4
2619
June1st to 15thDay
52%317%20%5%
2520
16th to endDay
39%220%26%8%2
2520
July1st to 15thDay
20%212%31%24%7%
2371
16th to endDay
18%17%30%32%9%
2459
August1st to 15thDay
18%317%32%21%6%
2324
16th to endDay
21%212%32%24%4
2405
September1st to 15thDay
21%29%31%24%11%
2160
16th to endDay
42%413%24%12%3
1973
October1st to 15thDay
49%411%20%12%2
1800
16th to endDay
61%410%12%9%1
1920
November1st to 15thDay
71%411%9%2
1586
16th to endDay
71%38%7%8%
1560
December1st to 15thDay
67%48%10%7%
1560
16th to endDay
76%48%7%3
1664
January1st to 15thNight
69%410%9%5%1
2716
16th to endNight
62%210%12%9%2
2758
February1st to 15thNight
63%5%13%13%4
2470
16th to endNight
60%313%13%7%1
2011
March1st to 15thNight
64%412%13%4
2016
16th to endNight
63%414%12%3
2097
April1st to 15thNight
60%316%13%5%
1799
16th to endNight
48%5%18%20%42
1677
May1st to 15thNight
41%316%25%9%2
1503
16th to endNight
46%420%21%5%1
1496
June1st to 15thNight
42%5%18%26%6%
1440
16th to endNight
31%221%32%9%2
1440
July1st to 15thNight
16%114%31%26%8%
1360
16th to endNight
10%18%31%35%12%
1444
August1st to 15thNight
14%215%41%19%7%
1611
16th to endNight
15%311%37%24%7%
1797
September1st to 15thNight
16%211%30%26%12%
1800
16th to endNight
30%216%26%16%6%
1985
October1st to 15thNight
38%411%25%15%4
2160
16th to endNight
49%413%16%13%1
2304
November1st to 15thNight
62%5%12%14%4
2600
16th to endNight
60%213%10%10%1
2730
December1st to 15thNight
58%312%15%9%
2730
16th to endNight
74%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
35%410%21%24%4
90
16th to endDay
32%417%18%14%12%
249
February1st to 15thDay
33%415%20%19%5%
276
16th to endDay
29%8%19%25%13%4
219
March1st to 15thDay
39%8%21%21%6%2
270
16th to endDay
32%7%24%19%12%3
288
April1st to 15thDay
24%8%23%18%16%8%
269
16th to endDay
24%10%22%22%13%7%
270
May1st to 15thDay
18%6%25%25%17%6%
288
16th to endDay
14%5%14%20%22%22%
330
June1st to 15thDay
19%413%28%26%7%
315
16th to endDay
10%313%30%31%10%
315
July1st to 15thDay
6%110%33%31%16%
305
16th to endDay
4113%34%35%11%
327
August1st to 15thDay
310%30%30%24%
315
16th to endDay
5%19%28%35%19%
332
September1st to 15thDay
6%212%28%29%21%
315
16th to endDay
15%412%26%32%7%
315
October1st to 15thDay
20%320%25%21%7%
315
16th to endDay
27%418%21%20%7%
336
November1st to 15thDay
28%430%25%7%3
106
16th to endDay
31%232%13%13%7%
90
December1st to 15thDay
35%421%14%16%7%
90
16th to endDay
31%414%27%19%3
96
January1st to 15thNight
34%413%26%17%3
780
16th to endNight
27%313%31%20%3
832
February1st to 15thNight
27%312%32%22%2
760
16th to endNight
26%318%31%18%
632
March1st to 15thNight
29%417%32%15%
720
16th to endNight
29%217%32%16%1
768
April1st to 15thNight
26%413%33%20%
719
16th to endNight
19%113%41%23%
597
May1st to 15thNight
14%118%43%19%1
423
16th to endNight
18%39%37%27%3
375
June1st to 15thNight
16%310%43%24%2
360
16th to endNight
10%112%48%25%
360
July1st to 15thNight
428%48%35%1
340
16th to endNight
27%51%36%1
406
August1st to 15thNight
3438%47%5%
538
16th to endNight
5%6%41%43%2
651
September1st to 15thNight
47%42%39%5%
720
16th to endNight
11%19%39%36%2
716
October1st to 15thNight
15%114%40%25%2
720
16th to endNight
23%214%30%23%4
768
November1st to 15thNight
31%213%35%15%
760
16th to endNight
26%319%28%18%2
780
December1st to 15thNight
27%314%32%19%1
780
16th to endNight
33%417%27%16%1
832
Page generated at 2018-02-15 07:58:42. Version ac04

Copyright 2018 A. Danko


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