Oregon Trail Overlook
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oregon Trail Overlook clear sky chart from 2005-11-05 to 2017-09-20.

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
58%
14885
23%
46841
18%
14858
63%
14858
34%
26543

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
48%
716
12%
2506
10%
716
52%
716
20%
1666
January16th to endNight
51%
768
12%
2667
11%
768
56%
768
23%
1684
February1st to 15thNight
52%
697
12%
2223
12%
697
55%
697
25%
1425
February16th to endNight
46%
632
18%
1895
13%
632
55%
632
28%
1183
March1st to 15thNight
49%
720
16%
2118
12%
720
56%
720
29%
1310
March16th to endNight
43%
768
19%
2097
11%
768
49%
768
29%
1360
April1st to 15thNight
48%
719
22%
1799
10%
719
55%
719
33%
1180
April16th to endNight
53%
543
28%
1623
16%
543
59%
543
39%
900
May1st to 15thNight
56%
539
26%
1619
19%
539
62%
539
42%
868
May16th to endNight
59%
469
20%
1592
20%
468
63%
468
34%
848
June1st to 15thNight
60%
360
20%
1440
25%
360
68%
360
32%
721
June16th to endNight
69%
360
30%
1440
37%
360
82%
360
57%
517
July1st to 15thNight
79%
340
25%
1360
32%
340
86%
340
49%
529
July16th to endNight
78%
394
33%
1433
41%
371
84%
371
55%
557
August1st to 15thNight
78%
539
31%
1611
26%
536
81%
536
54%
756
August16th to endNight
78%
654
41%
1800
27%
654
82%
654
61%
852
September1st to 15thNight
78%
720
34%
1887
23%
720
82%
720
62%
932
September16th to endNight
72%
675
37%
1869
30%
675
76%
675
51%
973
October1st to 15thNight
65%
660
33%
1851
27%
660
71%
660
48%
991
October16th to endNight
62%
704
29%
2260
24%
704
70%
704
39%
1195
November1st to 15thNight
55%
700
25%
2275
21%
700
62%
700
33%
1275
November16th to endNight
51%
720
20%
2340
13%
720
60%
720
30%
1372
December1st to 15thNight
47%
720
9%
2448
8%
720
50%
720
21%
1609
December16th to endNight
39%
768
13%
2688
9%
768
45%
768
18%
1840

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
5%42442445%7%54%
48014
Night
6%5%2442445%7%50%
47015
TransparencyDay
29%311%23%20%11%
47687
Night
32%413%23%16%10%
46842
SeeingDay
8%8%23%29%21%9%
5358
Night
9%419%40%23%2
14898

By Month

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
8%7%35%7%35%5%6%8%37%
1432
16th to endDay
9%8%246%46%5%6%8%36%
1554
February1st to 15thDay
6%8%35%5%35%47%9%41%
1637
16th to endDay
7%7%35%6%335%6%8%42%
1579
March1st to 15thDay
5%5%36%7%36%5%6%9%38%
1842
16th to endDay
8%7%36%6%35%46%8%39%
2124
April1st to 15thDay
6%6%25%5%345%6%9%43%
2149
16th to endDay
6%5%2432336%8%52%
2337
May1st to 15thDay
431342445%8%57%
2331
16th to endDay
44244245%6%8%49%
2520
June1st to 15thDay
6%313425%46%7%52%
2520
16th to endDay
2111211235%75%
2520
July1st to 15thDay
22231345%6%68%
2520
16th to endDay
2212213235%72%
2639
August1st to 15thDay
3212313345%67%
2340
16th to endDay
1112213345%73%
2399
September1st to 15thDay
22231234472%
2072
16th to endDay
5%213213335%66%
1860
October1st to 15thDay
5%324424447%57%
1779
16th to endDay
42145%3446%8%53%
1610
November1st to 15thDay
7%425%5%35%347%48%
1584
16th to endDay
6%7%26%6%35%5%7%9%39%
1620
December1st to 15thDay
11%8%26%6%45%5%45%37%
1510
16th to endDay
11%11%5%9%6%3446%6%29%
1536
January1st to 15thNight
8%8%37%6%35%5%6%8%35%
2506
16th to endNight
10%8%37%43445%7%41%
2667
February1st to 15thNight
8%7%36%6%35%5%5%7%40%
2212
16th to endNight
6%8%45%5%25%5%6%9%40%
1895
March1st to 15thNight
5%6%36%5%35%6%6%9%41%
2118
16th to endNight
8%6%36%6%35%45%8%41%
2097
April1st to 15thNight
7%6%26%5%35%45%6%45%
1799
16th to endNight
5%4244245%6%8%51%
1623
May1st to 15thNight
5%4133245%6%8%54%
1619
16th to endNight
6%425%5%3436%9%48%
1591
June1st to 15thNight
6%324335%45%8%52%
1440
16th to endNight
211112336%74%
1440
July1st to 15thNight
1232445%7%67%
1440
16th to endNight
2212212345%71%
1530
August1st to 15thNight
311232445%7%64%
1620
16th to endNight
1111223336%70%
1800
September1st to 15thNight
223213336%70%
1887
16th to endNight
4213323335%65%
1869
October1st to 15thNight
6%31332425%7%59%
1851
16th to endNight
6%31442445%8%54%
2260
November1st to 15thNight
8%425%5%2445%7%49%
2275
16th to endNight
6%5%26%5%36%5%5%7%45%
2340
December1st to 15thNight
10%8%36%6%35%5%5%8%35%
2448
16th to endNight
15%9%47%5%35%45%7%32%
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
43%8%23%20%2
1432
16th to endDay
43%7%24%18%5%
1554
February1st to 15thDay
38%7%24%23%5%
1637
16th to endDay
39%418%28%7%1
1579
March1st to 15thDay
40%417%27%7%1
1842
16th to endDay
40%415%26%11%1
2124
April1st to 15thDay
35%411%28%19%1
2149
16th to endDay
30%110%31%22%3
2337
May1st to 15thDay
25%27%30%27%6%
2331
16th to endDay
29%310%30%19%5%
2523
June1st to 15thDay
29%29%26%24%7%
2520
16th to endDay
13%1318%38%24%
2520
July1st to 15thDay
14%2214%32%33%
2371
16th to endDay
15%29%22%50%
2473
August1st to 15thDay
18%3313%27%33%
2325
16th to endDay
13%2217%36%28%
2399
September1st to 15thDay
15%1417%33%26%
2072
16th to endDay
21%15%26%33%11%
1860
October1st to 15thDay
28%211%32%19%5%
1779
16th to endDay
27%314%33%19%1
1610
November1st to 15thDay
35%416%30%10%1
1584
16th to endDay
40%320%28%7%
1620
December1st to 15thDay
47%6%22%19%4
1510
16th to endDay
53%422%15%4
1536
January1st to 15thNight
45%7%21%20%4
2506
16th to endNight
42%5%22%25%4
2667
February1st to 15thNight
40%6%23%23%5%
2223
16th to endNight
38%5%20%27%6%
1895
March1st to 15thNight
37%5%17%27%10%2
2118
16th to endNight
40%412%28%12%1
2097
April1st to 15thNight
38%310%28%16%2
1799
16th to endNight
28%49%28%25%3
1623
May1st to 15thNight
26%26%25%32%5%
1620
16th to endNight
31%28%26%24%5%
1592
June1st to 15thNight
30%28%22%27%8%
1440
16th to endNight
12%2417%34%29%
1440
July1st to 15thNight
16%3211%28%38%
1360
16th to endNight
14%217%19%54%
1433
August1st to 15thNight
17%3315%18%40%
1611
16th to endNight
15%2212%27%40%
1800
September1st to 15thNight
16%1413%33%30%
1887
16th to endNight
22%1320%32%18%
1869
October1st to 15thNight
25%27%32%23%8%
1851
16th to endNight
27%310%32%22%3
2260
November1st to 15thNight
32%314%29%16%2
2275
16th to endNight
36%319%29%9%
2340
December1st to 15thNight
45%5%26%17%4
2448
16th to endNight
50%419%21%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
13%6%21%31%15%11%
60
16th to endDay
16%422%26%26%2
67
February1st to 15thDay
11%431%21%25%4
152
16th to endDay
13%15%27%30%11%2
238
March1st to 15thDay
6%11%37%27%13%2
270
16th to endDay
10%18%35%26%8%
288
April1st to 15thDay
9%19%31%18%12%7%
269
16th to endDay
11%18%28%25%12%2
270
May1st to 15thDay
7%11%28%30%14%6%
288
16th to endDay
8%9%20%25%25%10%
330
June1st to 15thDay
6%9%28%30%19%6%
315
16th to endDay
36%25%31%22%11%
315
July1st to 15thDay
4218%30%30%14%
305
16th to endDay
3215%40%27%10%
327
August1st to 15thDay
6%220%31%28%9%
315
16th to endDay
1315%32%30%18%
332
September1st to 15thDay
5%5%18%24%25%21%
315
16th to endDay
7%5%15%29%27%14%
272
October1st to 15thDay
8%7%25%24%21%12%
219
16th to endDay
9%419%45%14%6%
96
November1st to 15thDay
12%444%33%5%
90
16th to endDay
17%17%24%26%11%2
90
December1st to 15thDay
33%221%30%9%1
71
16th to endDay
23%10%12%28%15%9%
64
January1st to 15thNight
13%320%42%19%1
720
16th to endNight
14%417%39%21%2
768
February1st to 15thNight
10%420%46%17%
704
16th to endNight
11%7%26%36%17%1
632
March1st to 15thNight
8%5%25%41%16%1
720
16th to endNight
11%8%29%37%12%1
768
April1st to 15thNight
10%9%23%37%16%2
719
16th to endNight
8%6%27%40%14%2
543
May1st to 15thNight
7%7%22%36%22%2
540
16th to endNight
8%419%30%31%4
470
June1st to 15thNight
8%418%39%28%
360
16th to endNight
4320%43%27%1
360
July1st to 15thNight
111%49%36%1
340
16th to endNight
1211%48%35%1
394
August1st to 15thNight
312%51%31%
539
16th to endNight
2112%47%33%2
654
September1st to 15thNight
3111%39%34%9%
720
16th to endNight
6%410%36%34%7%
675
October1st to 15thNight
8%317%38%28%4
660
16th to endNight
9%219%40%25%2
704
November1st to 15thNight
11%419%39%23%1
700
16th to endNight
9%5%24%38%18%3
720
December1st to 15thNight
14%5%20%41%16%1
720
16th to endNight
19%6%22%37%12%1
768
Page generated at 2017-09-21 05:18:13. Version ac04

Copyright 2017 A. Danko


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