Silverton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Silverton clear sky chart from 2005-11-05 to 2018-02-13.

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%
15278
12%
48827
12%
15251
47%
15251
17%
35352

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%
778
7%
2716
6%
776
33%
776
8%
2240
January16th to endNight
35%
832
10%
2788
10%
832
36%
832
11%
2191
February1st to 15thNight
34%
745
6%
2444
5%
745
35%
745
9%
2021
February16th to endNight
30%
632
10%
2002
6%
632
34%
632
11%
1581
March1st to 15thNight
31%
720
4%
2037
4%
720
31%
720
10%
1705
March16th to endNight
31%
768
6%
2083
4%
768
31%
768
9%
1781
April1st to 15thNight
32%
719
6%
1799
3%
719
33%
719
12%
1522
April16th to endNight
43%
608
8%
1688
6%
608
44%
608
16%
1291
May1st to 15thNight
47%
395
13%
1475
14%
395
51%
395
18%
975
May16th to endNight
48%
375
8%
1496
12%
374
48%
374
12%
1108
June1st to 15thNight
50%
360
8%
1440
11%
360
52%
360
14%
1012
June16th to endNight
56%
360
11%
1440
17%
360
59%
360
21%
873
July1st to 15thNight
77%
340
18%
1360
27%
340
80%
340
43%
585
July16th to endNight
82%
376
27%
1416
38%
354
87%
354
56%
528
August1st to 15thNight
84%
534
26%
1608
25%
532
85%
532
56%
737
August16th to endNight
76%
660
32%
1806
23%
660
78%
660
54%
929
September1st to 15thNight
76%
720
28%
1800
18%
720
76%
720
56%
972
September16th to endNight
66%
716
24%
1977
21%
716
67%
716
34%
1225
October1st to 15thNight
51%
720
16%
2160
16%
720
54%
720
25%
1449
October16th to endNight
43%
768
14%
2325
14%
768
44%
768
17%
1723
November1st to 15thNight
31%
760
7%
2595
7%
760
33%
760
9%
2145
November16th to endNight
37%
780
6%
2730
7%
780
37%
780
10%
2173
December1st to 15thNight
37%
780
10%
2730
10%
780
38%
780
12%
2093
December16th to endNight
28%
832
5%
2912
5%
832
29%
832
7%
2493

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%36%5%34446%33%
49233
Night
21%8%36%5%24445%34%
48995
Cloud CoverDay
20%8%36%5%34446%33%
49233
Night
21%8%36%5%24345%34%
48999
TransparencyDay
52%7%12%15%10%2
48904
Night
52%6%11%15%10%3
48828
SeeingDay
23%9%21%25%16%3
6065
Night
25%6%15%29%21%1
15288

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%11%48%7%3334314%
1552
16th to endDay
28%10%47%6%45%45%6%17%
1784
February1st to 15thDay
29%11%47%6%35%45%6%14%
1685
16th to endDay
26%12%6%8%6%44435%17%
1472
March1st to 15thDay
31%10%48%7%36%45%5%13%
1920
16th to endDay
28%12%5%9%6%26%445%14%
2140
April1st to 15thDay
25%11%48%7%45%45%5%17%
2149
16th to endDay
21%9%47%7%345%5%7%23%
2271
May1st to 15thDay
18%8%36%5%34346%35%
2475
16th to endDay
22%7%36%5%35%5%5%6%27%
2615
June1st to 15thDay
19%8%46%5%345%46%29%
2520
16th to endDay
12%7%35%5%35%446%41%
2520
July1st to 15thDay
4313322346%64%
2520
16th to endDay
6%31221233468%
2657
August1st to 15thDay
221322345%7%62%
2342
16th to endDay
5%313322347%61%
2396
September1st to 15thDay
5%313312347%63%
2160
16th to endDay
14%7%25%6%3445%6%40%
1980
October1st to 15thDay
19%6%36%6%2445%8%32%
1800
16th to endDay
22%10%46%6%3445%6%24%
1899
November1st to 15thDay
33%11%47%6%3346%6%12%
1592
16th to endDay
26%10%5%8%7%5%5%5%5%415%
1560
December1st to 15thDay
25%11%48%7%3445%5%19%
1560
16th to endDay
36%11%46%5%35%5%5%5%11%
1664
January1st to 15thNight
30%10%5%7%6%45%43417%
2716
16th to endNight
28%10%46%6%24345%23%
2788
February1st to 15thNight
26%11%5%6%7%2445%6%19%
2432
16th to endNight
25%11%46%5%33345%24%
2002
March1st to 15thNight
29%10%47%5%235%45%20%
2037
16th to endNight
26%11%48%6%34446%18%
2079
April1st to 15thNight
25%11%37%6%3445%5%21%
1799
16th to endNight
20%8%36%5%25%45%6%31%
1688
May1st to 15thNight
13%6%37%5%25%45%6%39%
1475
16th to endNight
20%7%36%6%35%45%8%29%
1496
June1st to 15thNight
17%7%36%5%24446%35%
1440
16th to endNight
9%7%27%5%24335%47%
1440
July1st to 15thNight
322313235%69%
1440
16th to endNight
3111111235%76%
1512
August1st to 15thNight
1312212327%70%
1616
16th to endNight
5%212213235%70%
1806
September1st to 15thNight
5%21232225%70%
1800
16th to endNight
11%41442345%7%50%
1977
October1st to 15thNight
15%7%25%5%23345%43%
2160
16th to endNight
22%8%26%5%23445%35%
2325
November1st to 15thNight
32%8%37%5%25%45%419%
2595
16th to endNight
27%9%37%6%33435%24%
2730
December1st to 15thNight
27%10%36%5%23436%25%
2730
16th to endNight
32%12%47%6%3433415%
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
33%10%48%7%35%33317%
1552
16th to endDay
29%9%36%5%36%447%19%
1784
February1st to 15thDay
28%12%47%6%45%45%5%15%
1685
16th to endDay
27%12%48%7%3444418%
1472
March1st to 15thDay
31%11%48%6%45%445%13%
1920
16th to endDay
30%12%5%8%5%35%44415%
2140
April1st to 15thDay
27%10%39%7%45%445%17%
2149
16th to endDay
23%10%37%6%4445%7%22%
2271
May1st to 15thDay
19%7%46%5%34336%35%
2475
16th to endDay
24%7%36%6%35%45%6%27%
2615
June1st to 15thDay
21%7%46%6%345%5%5%28%
2520
16th to endDay
13%8%25%5%35%35%6%40%
2520
July1st to 15thDay
4313312346%63%
2520
16th to endDay
6%312312235%68%
2657
August1st to 15thDay
3213224447%62%
2342
16th to endDay
5%31332335%6%61%
2396
September1st to 15thDay
6%313312337%62%
2160
16th to endDay
14%7%26%6%24346%40%
1980
October1st to 15thDay
20%6%36%5%345%5%7%34%
1800
16th to endDay
23%7%47%6%3445%6%25%
1899
November1st to 15thDay
33%10%5%6%5%2435%7%14%
1592
16th to endDay
27%10%48%7%36%45%416%
1560
December1st to 15thDay
25%11%37%7%3445%420%
1560
16th to endDay
35%12%37%5%2445%6%13%
1664
January1st to 15thNight
30%11%47%5%45%435%17%
2716
16th to endNight
28%9%37%5%24345%24%
2788
February1st to 15thNight
27%10%46%6%35%45%5%19%
2432
16th to endNight
25%12%47%6%23345%24%
2002
March1st to 15thNight
29%10%46%6%2345%5%20%
2037
16th to endNight
27%11%5%7%6%3445%5%17%
2083
April1st to 15thNight
26%10%47%6%33445%21%
1799
16th to endNight
22%10%35%425%446%30%
1688
May1st to 15thNight
14%7%36%425%45%6%38%
1475
16th to endNight
21%6%27%6%35%45%7%28%
1496
June1st to 15thNight
18%7%36%5%35%336%35%
1440
16th to endNight
10%8%36%5%3434446%
1440
July1st to 15thNight
4212313245%69%
1440
16th to endNight
311112235%75%
1512
August1st to 15thNight
2212212238%69%
1616
16th to endNight
4212212226%69%
1806
September1st to 15thNight
6%212212225%70%
1800
16th to endNight
12%41442335%7%50%
1977
October1st to 15thNight
16%6%36%423345%42%
2160
16th to endNight
23%7%35%423445%34%
2325
November1st to 15thNight
32%8%36%5%4444419%
2595
16th to endNight
28%8%36%6%25%44424%
2730
December1st to 15thNight
28%9%46%5%33336%25%
2730
16th to endNight
33%11%47%6%35%33416%
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
71%5%8%9%41
1552
16th to endDay
64%6%9%9%7%3
1784
February1st to 15thDay
69%9%9%7%4
1685
16th to endDay
69%8%6%8%6%
1472
March1st to 15thDay
72%7%8%6%3
1920
16th to endDay
74%6%9%7%2
2140
April1st to 15thDay
69%8%11%8%2
2149
16th to endDay
63%8%12%9%5%1
2271
May1st to 15thDay
51%5%13%19%8%
2475
16th to endDay
58%9%13%14%3
2619
June1st to 15thDay
57%7%15%14%4
2520
16th to endDay
44%7%17%20%6%2
2520
July1st to 15thDay
22%6%14%27%23%6%
2371
16th to endDay
19%410%26%32%7%
2490
August1st to 15thDay
20%6%18%29%19%5%
2325
16th to endDay
23%6%14%29%22%4
2396
September1st to 15thDay
22%5%14%24%22%11%
2160
16th to endDay
43%7%14%16%13%3
1980
October1st to 15thDay
48%8%13%16%9%3
1800
16th to endDay
57%9%11%9%11%1
1899
November1st to 15thDay
69%8%11%7%1
1592
16th to endDay
68%9%7%6%8%
1560
December1st to 15thDay
63%7%7%11%8%1
1560
16th to endDay
71%8%9%6%3
1664
January1st to 15thNight
68%6%8%8%5%1
2716
16th to endNight
63%5%7%9%8%4
2788
February1st to 15thNight
66%8%10%8%41
2444
16th to endNight
62%6%10%9%7%1
2002
March1st to 15thNight
65%8%9%10%4
2037
16th to endNight
68%8%9%10%3
2083
April1st to 15thNight
65%8%12%8%4
1799
16th to endNight
56%7%16%13%42
1688
May1st to 15thNight
48%5%13%20%8%3
1476
16th to endNight
55%9%14%14%41
1496
June1st to 15thNight
49%10%15%18%6%
1440
16th to endNight
40%6%18%23%8%2
1440
July1st to 15thNight
18%5%14%28%25%7%
1360
16th to endNight
12%312%28%31%10%
1416
August1st to 15thNight
16%316%36%18%7%
1608
16th to endNight
18%412%36%19%7%
1806
September1st to 15thNight
18%413%26%22%14%
1800
16th to endNight
34%6%15%22%14%7%
1977
October1st to 15thNight
44%5%10%19%15%4
2160
16th to endNight
52%8%9%11%15%2
2325
November1st to 15thNight
66%8%9%10%5%
2595
16th to endNight
63%7%7%7%10%2
2730
December1st to 15thNight
60%6%9%12%10%1
2730
16th to endNight
72%6%8%7%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%218%24%14%4
90
16th to endDay
36%12%16%16%16%2
216
February1st to 15thDay
38%10%19%17%11%1
273
16th to endDay
33%14%26%16%8%
220
March1st to 15thDay
44%15%20%15%21
270
16th to endDay
38%14%22%17%6%
288
April1st to 15thDay
30%17%24%14%10%3
269
16th to endDay
32%14%26%14%9%3
270
May1st to 15thDay
26%13%22%26%8%2
288
16th to endDay
22%7%20%22%22%4
330
June1st to 15thDay
20%11%20%25%18%2
315
16th to endDay
15%6%22%36%15%2
315
July1st to 15thDay
6%318%41%24%5%
305
16th to endDay
5%321%41%22%5%
327
August1st to 15thDay
5%315%38%28%8%
315
16th to endDay
45%19%34%27%8%
332
September1st to 15thDay
8%424%28%29%5%
315
16th to endDay
20%7%20%30%18%2
315
October1st to 15thDay
25%7%23%27%13%2
315
16th to endDay
29%9%20%23%12%5%
315
November1st to 15thDay
33%16%23%18%6%
106
16th to endDay
42%11%17%13%12%3
90
December1st to 15thDay
41%13%13%12%10%10%
90
16th to endDay
40%9%19%14%13%2
96
January1st to 15thNight
34%8%16%21%17%1
780
16th to endNight
31%9%13%25%17%2
832
February1st to 15thNight
32%6%17%26%16%1
752
16th to endNight
31%13%19%22%12%
632
March1st to 15thNight
34%13%15%24%11%1
720
16th to endNight
31%10%19%24%12%1
768
April1st to 15thNight
32%7%19%25%14%
719
16th to endNight
27%5%17%27%20%1
608
May1st to 15thNight
18%7%21%32%19%
396
16th to endNight
25%312%30%26%1
375
June1st to 15thNight
20%317%38%18%1
360
16th to endNight
16%217%41%21%
360
July1st to 15thNight
5%19%47%34%
340
16th to endNight
229%47%36%1
376
August1st to 15thNight
41434%49%5%
534
16th to endNight
6%111%36%38%4
660
September1st to 15thNight
6%111%37%38%4
720
16th to endNight
15%310%34%33%2
716
October1st to 15thNight
19%418%30%24%2
720
16th to endNight
27%6%14%25%21%4
768
November1st to 15thNight
35%10%16%28%10%
760
16th to endNight
31%12%12%25%15%1
780
December1st to 15thNight
33%6%17%25%15%1
780
16th to endNight
39%10%16%21%12%1
832
Page generated at 2018-02-13 17:46:03. Version ac04

Copyright 2018 A. Danko


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