This page made possible by the sponsorship of: Oregon Star Party Commitee.

Oregon Star Party
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oregon Star Party clear sky chart from 2005-11-05 to 2017-09-10.

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
52%
14693
17%
46778
15%
14668
55%
14668
24%
30475

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
38%
716
9%
2506
9%
716
41%
716
12%
1914
January16th to endNight
49%
768
13%
2649
13%
768
51%
768
17%
1849
February1st to 15thNight
41%
697
7%
2288
8%
696
42%
696
13%
1757
February16th to endNight
41%
632
13%
1915
12%
632
44%
632
16%
1427
March1st to 15thNight
39%
720
8%
2130
6%
720
41%
720
14%
1650
March16th to endNight
37%
768
9%
2016
5%
768
39%
768
16%
1552
April1st to 15thNight
40%
719
11%
1799
6%
719
41%
719
19%
1365
April16th to endNight
48%
681
16%
1761
9%
681
50%
681
27%
1204
May1st to 15thNight
54%
365
18%
1445
18%
365
59%
365
27%
791
May16th to endNight
57%
374
11%
1496
14%
374
61%
374
19%
926
June1st to 15thNight
59%
360
13%
1440
17%
360
65%
360
24%
828
June16th to endNight
61%
360
19%
1440
29%
360
68%
360
36%
678
July1st to 15thNight
81%
340
21%
1360
32%
340
85%
340
51%
534
July16th to endNight
77%
376
33%
1416
42%
354
86%
354
59%
512
August1st to 15thNight
83%
442
32%
1515
32%
440
86%
440
54%
649
August16th to endNight
78%
747
38%
1893
25%
747
80%
747
69%
908
September1st to 15thNight
78%
700
37%
1750
23%
700
81%
700
68%
858
September16th to endNight
68%
656
30%
1773
24%
656
71%
656
43%
1007
October1st to 15thNight
58%
660
21%
1980
20%
660
63%
660
32%
1188
October16th to endNight
53%
704
18%
2197
18%
704
56%
704
22%
1473
November1st to 15thNight
46%
700
13%
2281
15%
700
47%
700
16%
1674
November16th to endNight
42%
720
9%
2520
9%
720
44%
720
15%
1821
December1st to 15thNight
42%
720
9%
2520
8%
720
45%
720
14%
1857
December16th to endNight
35%
768
11%
2688
10%
768
37%
768
11%
2053

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
7%7%36%6%35%45%6%42%
47866
Night
6%7%36%6%35%5%5%7%42%
46946
Cloud CoverDay
7%7%36%6%35%5%5%6%43%
47866
Night
7%7%36%5%35%5%5%7%42%
46950
TransparencyDay
40%7%10%18%15%6%
47537
Night
39%8%12%19%14%5%
46779
SeeingDay
12%16%27%25%13%4
5519
Night
10%10%19%31%23%3
14706

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
10%10%410%8%5%6%5%5%9%22%
1432
16th to endDay
10%11%47%7%4447%9%27%
1572
February1st to 15thDay
7%12%6%10%7%47%6%6%7%23%
1576
16th to endDay
5%11%5%9%9%47%7%7%6%24%
1557
March1st to 15thDay
9%12%7%11%10%6%6%6%5%5%19%
1827
16th to endDay
9%14%5%10%9%47%446%23%
2208
April1st to 15thDay
8%12%7%9%8%45%5%5%5%26%
2149
16th to endDay
8%9%47%6%35%5%5%6%37%
2197
May1st to 15thDay
7%7%27%6%3445%6%42%
2504
16th to endDay
10%10%5%8%7%35%5%5%6%31%
2615
June1st to 15thDay
11%7%36%5%25%447%40%
2520
16th to endDay
5%425%423446%56%
2520
July1st to 15thDay
1112323346%68%
2520
16th to endDay
112212335%75%
2657
August1st to 15thDay
121222335%6%67%
2436
16th to endDay
21221223474%
2309
September1st to 15thDay
122312336%73%
2097
16th to endDay
5%5%25%42345%6%53%
1854
October1st to 15thDay
10%7%35%5%25%45%6%43%
1650
16th to endDay
10%7%47%7%36%5%45%37%
1675
November1st to 15thDay
10%11%47%8%45%45%8%29%
1575
16th to endDay
8%10%49%8%46%5%5%9%27%
1440
December1st to 15thDay
9%9%5%9%8%48%5%6%7%25%
1440
16th to endDay
11%14%5%10%9%5%7%6%5%7%16%
1536
January1st to 15thNight
7%10%5%9%8%46%7%6%8%26%
2506
16th to endNight
8%10%46%6%46%5%6%8%31%
2649
February1st to 15thNight
7%9%48%8%46%6%6%7%27%
2276
16th to endNight
7%9%48%6%47%6%7%9%29%
1915
March1st to 15thNight
10%9%5%9%7%47%5%6%9%24%
2130
16th to endNight
6%8%5%7%8%47%8%7%8%26%
2012
April1st to 15thNight
8%12%5%7%6%46%46%6%31%
1799
16th to endNight
5%8%46%5%25%5%5%7%43%
1761
May1st to 15thNight
5%6%245%3446%7%49%
1445
16th to endNight
7%5%26%6%35%5%6%8%40%
1496
June1st to 15thNight
8%43343445%7%49%
1440
16th to endNight
431342335%6%61%
1440
July1st to 15thNight
11222335%6%70%
1440
16th to endNight
1121233378%
1512
August1st to 15thNight
112312446%70%
1523
16th to endNight
11211223478%
1893
September1st to 15thNight
11222224475%
1750
16th to endNight
34243235%46%59%
1773
October1st to 15thNight
7%5%25%42445%6%51%
1980
16th to endNight
7%8%36%6%445%5%6%40%
2197
November1st to 15thNight
10%8%47%7%36%6%6%8%28%
2281
16th to endNight
8%10%48%7%5%6%6%5%7%31%
2520
December1st to 15thNight
9%9%410%7%46%5%5%7%30%
2520
16th to endNight
9%14%5%8%7%46%5%6%8%23%
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
10%10%410%8%46%6%6%7%23%
1432
16th to endDay
10%11%38%7%35%5%7%8%27%
1572
February1st to 15thDay
7%12%6%10%7%5%6%6%6%7%23%
1576
16th to endDay
5%11%49%8%47%8%6%7%24%
1557
March1st to 15thDay
8%12%6%11%10%5%8%5%5%420%
1827
16th to endDay
9%15%5%9%8%5%6%5%36%24%
2208
April1st to 15thDay
9%12%6%9%7%46%5%5%5%26%
2149
16th to endDay
8%9%38%6%345%5%6%37%
2197
May1st to 15thDay
7%7%27%5%35%5%47%43%
2504
16th to endDay
9%10%5%7%7%35%5%5%6%32%
2615
June1st to 15thDay
11%6%45%5%35%5%48%40%
2520
16th to endDay
5%415%423445%57%
2520
July1st to 15thDay
1112313346%69%
2520
16th to endDay
111121232476%
2657
August1st to 15thDay
121231345%7%67%
2436
16th to endDay
21221223474%
2309
September1st to 15thDay
1112222335%73%
2097
16th to endDay
6%5%25%5%1345%7%53%
1854
October1st to 15thDay
10%6%35%435%446%44%
1650
16th to endDay
10%7%37%7%3445%6%38%
1675
November1st to 15thDay
11%10%46%8%36%45%8%30%
1575
16th to endDay
8%10%49%8%35%6%6%9%26%
1440
December1st to 15thDay
9%10%49%8%46%6%6%6%25%
1440
16th to endDay
11%15%5%9%9%5%7%6%5%6%17%
1536
January1st to 15thNight
7%11%5%8%8%5%6%7%5%8%26%
2506
16th to endNight
8%10%45%6%46%6%6%8%32%
2649
February1st to 15thNight
8%10%48%9%46%7%6%8%26%
2276
16th to endNight
7%9%47%6%47%6%6%9%29%
1915
March1st to 15thNight
9%10%5%8%7%47%7%5%8%26%
2130
16th to endNight
7%8%47%7%36%8%8%9%27%
2016
April1st to 15thNight
10%11%5%6%6%35%5%6%6%32%
1799
16th to endNight
6%7%36%5%35%5%6%7%44%
1761
May1st to 15thNight
5%5%24425%46%7%50%
1445
16th to endNight
7%6%25%6%35%6%5%8%41%
1496
June1st to 15thNight
8%5%25%4235%5%7%50%
1440
16th to endNight
4313323347%61%
1440
July1st to 15thNight
1112223446%70%
1440
16th to endNight
11111233478%
1512
August1st to 15thNight
21221435%6%70%
1523
16th to endNight
11221222478%
1893
September1st to 15thNight
11221234475%
1750
16th to endNight
332332445%6%60%
1773
October1st to 15thNight
7%6%2443436%6%51%
1980
16th to endNight
8%7%37%6%45%5%47%40%
2197
November1st to 15thNight
11%8%46%6%46%6%6%8%29%
2281
16th to endNight
9%9%47%7%46%6%5%6%31%
2520
December1st to 15thNight
9%10%49%7%36%5%47%30%
2520
16th to endNight
10%14%5%8%7%35%6%5%9%22%
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
58%10%11%12%5%
1432
16th to endDay
52%8%15%12%7%3
1572
February1st to 15thDay
56%11%13%13%5%
1576
16th to endDay
54%14%13%13%3
1557
March1st to 15thDay
63%9%10%11%41
1827
16th to endDay
59%11%11%13%4
2208
April1st to 15thDay
55%9%12%15%5%
2149
16th to endDay
44%9%13%21%9%1
2197
May1st to 15thDay
39%7%13%25%12%1
2504
16th to endDay
51%9%10%18%9%1
2619
June1st to 15thDay
41%7%9%25%13%2
2520
16th to endDay
27%5%10%26%24%5%
2520
July1st to 15thDay
15%5%8%18%29%21%
2371
16th to endDay
12%35%12%34%30%
2490
August1st to 15thDay
16%48%21%30%18%
2419
16th to endDay
12%36%23%36%17%
2309
September1st to 15thDay
13%37%23%32%20%
2097
16th to endDay
30%6%9%22%23%7%
1854
October1st to 15thDay
39%9%11%18%15%5%
1650
16th to endDay
45%8%12%18%13%1
1675
November1st to 15thDay
51%11%12%17%7%
1575
16th to endDay
50%12%14%11%9%2
1440
December1st to 15thDay
56%11%12%14%4
1440
16th to endDay
65%8%9%11%4
1536
January1st to 15thNight
55%11%11%12%7%1
2506
16th to endNight
48%8%12%16%8%4
2649
February1st to 15thNight
54%11%14%11%7%
2288
16th to endNight
50%11%13%17%6%
1915
March1st to 15thNight
54%11%12%14%5%2
2130
16th to endNight
49%13%16%16%3
2016
April1st to 15thNight
50%9%14%19%6%
1799
16th to endNight
38%9%17%23%8%1
1761
May1st to 15thNight
30%8%14%30%14%1
1446
16th to endNight
38%10%17%24%8%1
1496
June1st to 15thNight
33%9%13%27%12%2
1440
16th to endNight
23%5%12%32%19%5%
1440
July1st to 15thNight
13%5%10%25%28%16%
1360
16th to endNight
10%45%16%37%26%
1416
August1st to 15thNight
13%5%7%26%31%15%
1515
16th to endNight
10%37%24%35%18%
1893
September1st to 15thNight
11%36%28%34%15%
1750
16th to endNight
23%7%9%23%21%12%
1773
October1st to 15thNight
32%7%13%21%19%5%
1980
16th to endNight
42%9%12%16%17%2
2197
November1st to 15thNight
49%11%12%15%10%
2281
16th to endNight
50%9%12%13%11%1
2520
December1st to 15thNight
52%10%15%15%6%
2520
16th to endNight
57%9%12%14%5%1
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
28%5%21%16%25%3
60
16th to endDay
22%19%19%28%8%4
100
February1st to 15thDay
17%22%26%24%8%
236
16th to endDay
14%27%34%17%6%
235
March1st to 15thDay
23%25%29%16%4
270
16th to endDay
20%28%29%17%3
288
April1st to 15thDay
15%25%28%17%8%4
269
16th to endDay
13%30%27%16%8%3
270
May1st to 15thDay
14%23%29%20%9%2
288
16th to endDay
14%16%22%26%14%5%
330
June1st to 15thDay
14%14%30%20%14%5%
315
16th to endDay
7%14%29%26%17%4
315
July1st to 15thDay
37%28%34%20%5%
305
16th to endDay
17%36%31%16%6%
327
August1st to 15thDay
16%28%34%16%12%
315
16th to endDay
39%20%32%23%11%
332
September1st to 15thDay
37%28%30%23%6%
294
16th to endDay
9%10%24%30%21%2
255
October1st to 15thDay
18%15%21%28%13%2
255
16th to endDay
17%16%24%27%12%1
187
November1st to 15thDay
12%15%25%35%10%
89
16th to endDay
16%21%28%15%16%1
60
December1st to 15thDay
26%31%25%15%1
60
16th to endDay
17%18%20%31%10%1
64
January1st to 15thNight
13%14%23%25%21%2
720
16th to endNight
15%12%16%26%23%4
768
February1st to 15thNight
11%12%22%30%19%2
704
16th to endNight
11%13%25%30%17%1
632
March1st to 15thNight
15%15%23%27%15%2
720
16th to endNight
10%18%26%26%16%
768
April1st to 15thNight
13%16%22%28%16%2
719
16th to endNight
9%14%23%28%19%3
681
May1st to 15thNight
8%7%25%31%23%2
366
16th to endNight
8%6%19%32%28%4
375
June1st to 15thNight
11%5%19%40%21%1
360
16th to endNight
46%21%40%25%1
360
July1st to 15thNight
1111%45%36%2
340
16th to endNight
1117%44%32%2
376
August1st to 15thNight
39%40%41%5%
442
16th to endNight
1214%38%38%5%
747
September1st to 15thNight
1215%35%37%7%
700
16th to endNight
46%16%31%35%6%
656
October1st to 15thNight
8%7%18%35%23%6%
660
16th to endNight
11%10%17%31%22%6%
704
November1st to 15thNight
14%13%20%35%16%1
700
16th to endNight
15%18%16%24%19%5%
720
December1st to 15thNight
15%11%21%31%17%2
720
16th to endNight
19%17%20%27%13%1
768
Page generated at 2017-09-11 16:35:14. Version ac04

Copyright 2017 A. Danko


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