Salem (OR)
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Salem (OR) clear sky chart from 2005-11-05 to 2017-12-20.

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
45%
15068
13%
48094
12%
15041
48%
15041
19%
33540

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
32%
717
8%
2506
7%
716
34%
716
9%
2052
January16th to endNight
39%
768
12%
2565
12%
768
40%
768
13%
1941
February1st to 15thNight
36%
697
7%
2288
7%
697
38%
697
11%
1837
February16th to endNight
33%
632
10%
2009
9%
632
36%
632
13%
1547
March1st to 15thNight
31%
720
5%
2028
4%
720
33%
720
12%
1657
March16th to endNight
32%
768
6%
2091
4%
768
33%
768
12%
1725
April1st to 15thNight
36%
719
7%
1799
4%
719
37%
719
16%
1441
April16th to endNight
44%
600
11%
1680
7%
600
46%
600
19%
1235
May1st to 15thNight
45%
404
14%
1484
12%
404
52%
404
23%
915
May16th to endNight
46%
375
9%
1496
11%
374
49%
374
15%
1016
June1st to 15thNight
45%
360
10%
1440
10%
360
51%
360
18%
928
June16th to endNight
55%
360
13%
1440
17%
360
61%
360
25%
813
July1st to 15thNight
68%
340
19%
1360
24%
340
77%
340
47%
546
July16th to endNight
72%
385
29%
1425
33%
363
84%
363
61%
503
August1st to 15thNight
79%
538
27%
1611
22%
535
84%
535
59%
728
August16th to endNight
72%
654
34%
1800
22%
654
77%
654
57%
896
September1st to 15thNight
72%
720
29%
1800
17%
720
75%
720
59%
947
September16th to endNight
64%
716
26%
1980
21%
716
67%
716
37%
1178
October1st to 15thNight
52%
720
17%
2160
17%
720
56%
720
27%
1390
October16th to endNight
44%
768
15%
2315
15%
768
47%
768
19%
1653
November1st to 15thNight
35%
760
8%
2603
9%
760
36%
760
11%
2072
November16th to endNight
38%
780
7%
2730
7%
780
39%
780
12%
2114
December1st to 15thNight
38%
780
10%
2730
11%
780
39%
780
13%
2064
December16th to endNight
27%
787
5%
2754
5%
787
28%
787
7%
2342

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%47%5%24446%33%
48764
Night
19%7%36%5%24345%36%
48263
Cloud CoverDay
19%7%37%5%34445%33%
48764
Night
20%7%36%5%24345%35%
48267
TransparencyDay
51%412%17%10%2
48436
Night
51%412%18%10%3
48095
SeeingDay
21%9%20%26%17%4
5950
Night
24%6%15%31%20%2
15079

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
33%12%6%11%5%3422313%
1432
16th to endDay
26%9%49%7%35%5%35%18%
1659
February1st to 15thDay
30%11%5%9%7%34335%14%
1576
16th to endDay
27%11%5%10%7%3444417%
1464
March1st to 15thDay
31%11%49%7%35%45%412%
1929
16th to endDay
29%11%6%8%7%34445%14%
2133
April1st to 15thDay
24%11%48%7%44446%16%
2149
16th to endDay
21%9%47%7%35%45%7%22%
2279
May1st to 15thDay
18%8%36%5%23347%35%
2464
16th to endDay
20%7%37%5%35%5%5%6%28%
2615
June1st to 15thDay
19%8%47%6%25%445%30%
2520
16th to endDay
11%6%35%5%35%45%7%41%
2520
July1st to 15thDay
4313322346%63%
2520
16th to endDay
7%212212235%68%
2646
August1st to 15thDay
331232435%7%61%
2340
16th to endDay
4313323347%61%
2402
September1st to 15thDay
5%413213237%62%
2160
16th to endDay
15%6%36%5%2345%5%40%
1977
October1st to 15thDay
18%8%46%6%25%446%31%
1800
16th to endDay
22%11%49%6%33346%24%
1908
November1st to 15thDay
30%13%6%10%6%345%3412%
1583
16th to endDay
26%10%5%10%7%35%34417%
1560
December1st to 15thDay
25%10%7%10%8%23345%18%
1560
16th to endDay
33%13%5%10%7%243449%
1568
January1st to 15thNight
30%11%47%5%3444418%
2506
16th to endNight
25%8%46%5%2445%6%24%
2565
February1st to 15thNight
25%11%47%6%35%436%20%
2276
16th to endNight
24%10%47%5%34445%25%
2009
March1st to 15thNight
26%10%48%5%34445%20%
2028
16th to endNight
26%10%48%6%35%46%5%19%
2087
April1st to 15thNight
23%10%47%6%3345%6%25%
1799
16th to endNight
19%6%25%5%35%448%34%
1680
May1st to 15thNight
12%5%36%5%345%46%42%
1484
16th to endNight
17%7%35%5%2446%7%34%
1496
June1st to 15thNight
16%6%45%425%346%40%
1440
16th to endNight
8%7%25%424345%51%
1440
July1st to 15thNight
3212213225%71%
1440
16th to endNight
31122479%
1521
August1st to 15thNight
2212212347%71%
1620
16th to endNight
5%22212235%70%
1800
September1st to 15thNight
4212212245%71%
1800
16th to endNight
10%31443335%6%52%
1980
October1st to 15thNight
14%6%24433445%45%
2160
16th to endNight
20%8%26%423445%35%
2315
November1st to 15thNight
29%7%37%6%35%5%5%6%19%
2603
16th to endNight
27%9%46%6%35%335%25%
2730
December1st to 15thNight
26%9%47%5%34335%24%
2730
16th to endNight
29%13%5%9%6%3443415%
2754

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
35%10%6%11%6%3432213%
1432
16th to endDay
27%9%49%8%45%345%17%
1659
February1st to 15thDay
29%11%5%9%8%24445%13%
1576
16th to endDay
26%11%5%9%7%3444416%
1464
March1st to 15thDay
31%11%48%7%35%45%412%
1929
16th to endDay
29%10%5%8%6%45%5%45%14%
2133
April1st to 15thDay
25%10%48%7%45%35%6%17%
2149
16th to endDay
21%8%47%6%45%45%6%24%
2279
May1st to 15thDay
18%7%36%424346%35%
2464
16th to endDay
21%7%36%6%35%5%5%7%28%
2615
June1st to 15thDay
20%7%37%5%245%5%5%30%
2520
16th to endDay
11%6%35%5%44446%41%
2520
July1st to 15thDay
5%313322346%64%
2520
16th to endDay
6%212212235%68%
2646
August1st to 15thDay
321342245%7%62%
2340
16th to endDay
5%313213346%61%
2402
September1st to 15thDay
5%313312346%63%
2160
16th to endDay
15%6%26%5%245%45%40%
1977
October1st to 15thDay
19%7%47%5%34446%31%
1800
16th to endDay
22%10%49%7%34345%24%
1908
November1st to 15thDay
31%12%5%9%7%25%445%12%
1583
16th to endDay
26%11%411%8%34435%16%
1560
December1st to 15thDay
26%11%5%10%6%33445%18%
1560
16th to endDay
35%11%5%7%7%26%5%3410%
1568
January1st to 15thNight
31%11%47%5%35%44417%
2506
16th to endNight
26%9%46%5%34346%24%
2565
February1st to 15thNight
26%11%48%5%35%346%20%
2276
16th to endNight
25%10%47%6%3334425%
2009
March1st to 15thNight
28%10%38%5%35%445%20%
2028
16th to endNight
26%10%48%7%2445%6%19%
2091
April1st to 15thNight
24%10%47%6%2435%5%23%
1799
16th to endNight
19%8%36%445%447%33%
1680
May1st to 15thNight
13%6%25%5%25%45%7%41%
1484
16th to endNight
19%6%346%25%5%7%8%30%
1496
June1st to 15thNight
16%7%36%5%33347%38%
1440
16th to endNight
9%7%26%5%24336%48%
1440
July1st to 15thNight
4212213335%70%
1440
16th to endNight
311111135%78%
1521
August1st to 15thNight
1212213236%71%
1620
16th to endNight
5%21221233470%
1800
September1st to 15thNight
4212212236%70%
1800
16th to endNight
11%324423347%52%
1980
October1st to 15thNight
15%6%15%5%24445%44%
2160
16th to endNight
21%8%36%5%23445%35%
2315
November1st to 15thNight
30%8%26%5%45%45%5%19%
2603
16th to endNight
27%8%47%6%2434425%
2730
December1st to 15thNight
28%10%37%5%34335%24%
2730
16th to endNight
30%12%5%8%6%3443414%
2754

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
77%26%8%41
1432
16th to endDay
65%39%10%7%2
1659
February1st to 15thDay
71%5%9%8%3
1576
16th to endDay
69%48%9%6%
1464
March1st to 15thDay
73%410%7%3
1929
16th to endDay
72%5%11%8%2
2133
April1st to 15thDay
67%5%13%10%2
2149
16th to endDay
59%6%15%12%5%1
2279
May1st to 15thDay
50%314%21%9%1
2464
16th to endDay
55%7%16%16%4
2619
June1st to 15thDay
54%5%16%17%5%
2520
16th to endDay
41%319%23%7%2
2520
July1st to 15thDay
21%313%29%24%7%
2371
16th to endDay
19%210%28%33%7%
2479
August1st to 15thDay
20%317%32%20%5%
2324
16th to endDay
22%313%32%23%4
2402
September1st to 15thDay
21%213%27%23%11%
2160
16th to endDay
44%413%20%13%3
1977
October1st to 15thDay
50%412%19%10%3
1800
16th to endDay
60%411%11%10%1
1908
November1st to 15thDay
71%5%11%8%2
1583
16th to endDay
70%48%7%8%
1560
December1st to 15thDay
66%48%11%8%
1560
16th to endDay
74%5%9%6%3
1568
January1st to 15thNight
70%38%9%5%2
2506
16th to endNight
61%48%12%9%3
2565
February1st to 15thNight
66%411%11%5%
2288
16th to endNight
62%311%12%7%1
2009
March1st to 15thNight
66%5%10%12%4
2028
16th to endNight
66%5%13%11%3
2091
April1st to 15thNight
61%415%12%6%
1799
16th to endNight
53%5%15%17%5%1
1680
May1st to 15thNight
43%315%25%8%3
1485
16th to endNight
50%7%18%17%5%1
1496
June1st to 15thNight
46%6%16%23%6%
1440
16th to endNight
38%318%28%8%2
1440
July1st to 15thNight
18%214%30%26%8%
1360
16th to endNight
11%111%31%33%10%
1425
August1st to 15thNight
15%315%38%19%6%
1611
16th to endNight
17%312%38%21%7%
1800
September1st to 15thNight
17%312%28%23%13%
1800
16th to endNight
32%415%24%15%7%
1980
October1st to 15thNight
41%410%23%15%4
2160
16th to endNight
51%5%11%14%14%2
2315
November1st to 15thNight
65%5%10%13%5%
2603
16th to endNight
63%49%9%10%2
2730
December1st to 15thNight
61%310%13%9%
2730
16th to endNight
73%5%8%8%3
2754

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
41%121%20%11%3
60
16th to endDay
29%9%17%19%18%5%
187
February1st to 15thDay
38%10%15%19%13%2
236
16th to endDay
32%11%24%20%7%2
219
March1st to 15thDay
44%14%18%16%41
270
16th to endDay
37%13%25%16%6%1
288
April1st to 15thDay
25%15%22%19%10%5%
269
16th to endDay
27%14%26%16%10%4
270
May1st to 15thDay
23%12%23%27%10%2
288
16th to endDay
21%7%16%20%25%7%
330
June1st to 15thDay
22%8%21%26%17%3
315
16th to endDay
11%8%23%36%18%1
315
July1st to 15thDay
5%5%18%40%21%8%
305
16th to endDay
5%221%42%24%4
327
August1st to 15thDay
5%315%39%27%9%
315
16th to endDay
46%18%31%31%7%
332
September1st to 15thDay
7%6%21%30%29%4
315
16th to endDay
17%8%20%30%19%3
315
October1st to 15thDay
22%8%22%27%16%2
315
16th to endDay
29%6%20%21%15%5%
324
November1st to 15thDay
35%16%23%14%6%2
103
16th to endDay
35%15%18%14%13%2
90
December1st to 15thDay
40%8%16%16%10%7%
90
16th to endDay
40%6%18%15%16%2
72
January1st to 15thNight
36%6%12%23%18%2
720
16th to endNight
31%6%10%25%21%3
768
February1st to 15thNight
30%9%12%25%19%2
704
16th to endNight
31%11%17%23%15%
632
March1st to 15thNight
33%11%16%25%12%
720
16th to endNight
30%9%17%27%13%
768
April1st to 15thNight
29%8%16%27%17%
719
16th to endNight
22%6%18%29%22%1
600
May1st to 15thNight
15%6%23%35%17%
405
16th to endNight
24%413%33%21%2
375
June1st to 15thNight
19%6%19%35%18%1
360
16th to endNight
12%420%46%15%
360
July1st to 15thNight
5%217%49%24%
340
16th to endNight
3118%54%20%1
385
August1st to 15thNight
411%39%37%5%
538
16th to endNight
7%114%44%30%2
654
September1st to 15thNight
6%115%39%31%5%
720
16th to endNight
13%411%37%30%2
716
October1st to 15thNight
17%5%17%34%22%2
720
16th to endNight
26%6%13%27%21%4
768
November1st to 15thNight
34%7%15%30%12%
760
16th to endNight
32%9%12%26%16%3
780
December1st to 15thNight
33%8%10%27%17%3
780
16th to endNight
36%10%15%22%14%1
787
Page generated at 2017-12-21 04:04:49. Version ac04

Copyright 2017 A. Danko


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