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 2017-08-12.

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
50%
14589
14%
46527
13%
14561
52%
14561
21%
31615

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%
716
8%
2506
7%
716
32%
716
9%
2024
January16th to endNight
41%
768
11%
2546
12%
768
43%
768
14%
1889
February1st to 15thNight
38%
696
8%
2288
7%
696
39%
696
12%
1812
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%
526
29%
1575
26%
523
88%
523
63%
679
August16th to endNight
79%
596
33%
1646
24%
596
81%
596
58%
800
September1st to 15thNight
81%
660
33%
1650
22%
660
83%
660
64%
832
September16th to endNight
70%
656
28%
1819
23%
656
72%
656
41%
1042
October1st to 15thNight
59%
660
19%
1980
19%
660
62%
660
30%
1245
October16th to endNight
46%
704
13%
2112
13%
704
48%
704
20%
1497
November1st to 15thNight
40%
700
9%
2395
10%
700
41%
700
12%
1864
November16th to endNight
39%
720
7%
2520
7%
720
41%
720
14%
1844
December1st to 15thNight
39%
720
9%
2520
9%
720
41%
720
13%
1906
December16th to endNight
29%
768
6%
2688
7%
768
30%
768
7%
2284

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%
47464
Night
16%7%36%5%34445%37%
46698
Cloud CoverDay
17%8%47%6%34446%33%
47464
Night
18%7%36%5%34446%36%
46702
TransparencyDay
51%312%18%10%2
47138
Night
49%313%19%10%2
46528
SeeingDay
19%417%25%22%10%
5558
Night
21%213%35%24%2
14602

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
28%11%6%11%8%4333314%
1432
16th to endDay
24%9%49%8%345%5%5%18%
1677
February1st to 15thDay
27%13%5%10%8%44345%13%
1576
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%63%
2291
16th to endDay
5%313324347%60%
2204
September1st to 15thDay
4413212236%65%
1980
16th to endDay
14%6%246%24447%42%
1809
October1st to 15thDay
14%8%37%6%345%47%32%
1650
16th to endDay
19%10%49%7%45%45%5%22%
1760
November1st to 15thDay
26%10%6%9%7%45%5%5%6%12%
1462
16th to endDay
21%11%6%10%8%45%445%16%
1440
December1st to 15thDay
23%11%6%10%9%3444417%
1440
16th to endDay
27%12%5%9%8%46%445%10%
1536
January1st to 15thNight
25%14%48%6%35%44418%
2506
16th to endNight
21%9%5%7%6%34345%26%
2546
February1st to 15thNight
22%11%47%6%36%45%5%20%
2276
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%74%
1584
16th to endNight
422212335%69%
1646
September1st to 15thNight
311212235%75%
1650
16th to endNight
9%313424447%55%
1819
October1st to 15thNight
13%425%433446%46%
1980
16th to endNight
18%8%26%6%34445%34%
2112
November1st to 15thNight
26%8%36%6%35%6%5%6%22%
2395
16th to endNight
20%9%37%7%35%445%27%
2520
December1st to 15thNight
24%9%5%7%5%34345%24%
2520
16th to endNight
26%12%411%7%5%45%4314%
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
30%13%6%11%7%3333314%
1432
16th to endDay
24%10%5%10%6%34446%17%
1677
February1st to 15thDay
29%12%5%10%7%45%325%13%
1576
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
211242335%8%63%
2291
16th to endDay
5%312424346%61%
2204
September1st to 15thDay
5%413312236%65%
1980
16th to endDay
14%6%346%34346%41%
1809
October1st to 15thDay
16%8%37%6%35%446%32%
1650
16th to endDay
21%11%5%8%6%45%445%22%
1760
November1st to 15thDay
29%11%6%8%7%36%46%5%12%
1462
16th to endDay
23%12%5%9%9%45%34417%
1440
December1st to 15thDay
24%11%7%10%8%35%34416%
1440
16th to endDay
30%12%6%10%7%35%5%4410%
1536
January1st to 15thNight
28%12%5%8%6%3434418%
2506
16th to endNight
23%9%5%7%5%34446%25%
2546
February1st to 15thNight
25%11%47%5%36%45%5%20%
2276
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%73%
1584
16th to endNight
4212211346%69%
1646
September1st to 15thNight
22221233474%
1650
16th to endNight
9%313433347%54%
1819
October1st to 15thNight
13%5%25%333446%45%
1980
16th to endNight
19%8%36%6%34445%33%
2112
November1st to 15thNight
27%8%36%7%445%45%21%
2395
16th to endNight
22%9%37%7%35%445%26%
2520
December1st to 15thNight
25%10%5%7%5%34345%23%
2520
16th to endNight
28%12%5%10%6%3443414%
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
76%36%9%31
1432
16th to endDay
68%39%11%42
1677
February1st to 15thDay
75%39%8%3
1576
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
17%317%33%21%6%
2275
16th to endDay
23%212%31%24%4
2204
September1st to 15thDay
21%29%32%22%11%
1980
16th to endDay
42%412%24%12%3
1809
October1st to 15thDay
50%411%18%11%2
1650
16th to endDay
63%411%12%7%1
1760
November1st to 15thDay
71%411%9%2
1462
16th to endDay
70%38%8%8%
1440
December1st to 15thDay
70%48%9%6%
1440
16th to endDay
75%48%7%3
1536
January1st to 15thNight
69%39%10%5%1
2506
16th to endNight
60%211%13%10%2
2546
February1st to 15thNight
64%412%13%3
2288
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
13%215%41%20%7%
1575
16th to endNight
16%312%35%25%7%
1646
September1st to 15thNight
15%211%31%25%12%
1650
16th to endNight
30%215%27%17%7%
1819
October1st to 15thNight
39%411%25%14%4
1980
16th to endNight
51%413%16%12%1
2112
November1st to 15thNight
62%5%12%15%4
2395
16th to endNight
59%213%11%11%1
2520
December1st to 15thNight
61%412%14%7%
2520
16th to endNight
74%48%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
40%313%20%20%3
60
16th to endDay
31%414%19%16%14%
205
February1st to 15thDay
36%415%20%18%5%
236
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
3110%31%30%24%
300
16th to endDay
5%111%29%33%17%
268
September1st to 15thDay
6%214%29%25%20%
255
16th to endDay
14%411%29%34%6%
255
October1st to 15thDay
22%420%23%21%8%
255
16th to endDay
28%419%23%17%6%
272
November1st to 15thDay
27%425%30%6%5%
72
16th to endDay
28%333%8%16%10%
60
December1st to 15thDay
43%6%31%13%5%
60
16th to endDay
28%318%28%17%4
64
January1st to 15thNight
34%414%27%16%3
720
16th to endNight
26%311%31%22%3
768
February1st to 15thNight
28%312%31%22%2
704
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%
526
16th to endNight
6%7%40%43%1
596
September1st to 15thNight
47%43%38%5%
660
16th to endNight
11%18%39%35%2
656
October1st to 15thNight
15%113%40%26%2
660
16th to endNight
24%215%30%23%4
704
November1st to 15thNight
32%113%35%16%
700
16th to endNight
26%319%28%19%2
720
December1st to 15thNight
29%315%32%17%1
720
16th to endNight
33%417%25%16%1
768
Page generated at 2017-08-13 11:16:24. Version ac04

Copyright 2017 A. Danko


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