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 2017-10-06.

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%
15877
24%
47137
17%
15836
57%
15836
33%
27396

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
49%
748
26%
2358
20%
747
58%
747
36%
1263
January16th to endNight
46%
768
28%
2496
24%
768
54%
768
31%
1426
February1st to 15thNight
42%
698
23%
2288
18%
696
50%
696
31%
1309
February16th to endNight
34%
632
28%
1920
15%
632
49%
632
29%
1158
March1st to 15thNight
43%
720
27%
1980
16%
720
53%
720
37%
1162
March16th to endNight
41%
762
23%
2106
13%
762
49%
762
32%
1275
April1st to 15thNight
32%
539
18%
1798
12%
539
42%
539
23%
1096
April16th to endNight
36%
540
23%
1800
15%
540
48%
540
27%
1019
May1st to 15thNight
45%
540
21%
1662
14%
540
52%
540
30%
968
May16th to endNight
46%
563
22%
1545
14%
561
54%
561
35%
909
June1st to 15thNight
59%
540
28%
1440
17%
540
67%
540
50%
741
June16th to endNight
66%
540
29%
1440
22%
540
71%
540
50%
764
July1st to 15thNight
65%
510
15%
1432
13%
510
66%
510
26%
938
July16th to endNight
70%
564
13%
1593
12%
531
71%
531
25%
1053
August1st to 15thNight
69%
539
15%
1611
16%
536
69%
536
29%
990
August16th to endNight
69%
573
22%
1902
22%
573
71%
573
28%
1122
September1st to 15thNight
68%
540
24%
1800
24%
540
72%
540
31%
1051
September16th to endNight
60%
656
34%
1977
24%
656
69%
656
41%
1058
October1st to 15thNight
50%
684
27%
2052
18%
684
56%
684
37%
1153
October16th to endNight
57%
704
33%
2112
21%
704
66%
704
43%
1096
November1st to 15thNight
53%
757
30%
2157
20%
757
60%
757
41%
1186
November16th to endNight
50%
900
30%
2460
20%
900
56%
900
42%
1361
December1st to 15thNight
39%
900
19%
2520
11%
900
46%
900
32%
1545
December16th to endNight
37%
960
21%
2688
15%
960
43%
960
26%
1753

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
8%10%47%6%34345%41%
48052
Night
26%36%5%3445%6%50%
47328
TransparencyDay
44%39%20%16%4
47743
Night
32%411%24%20%6%
47138
SeeingDay
20%18%25%21%11%2
5711
Night
9%9%23%30%22%4
15886

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%6%9%43434450%
1590
16th to endDay
18%6%8%6%23345%49%
1728
February1st to 15thDay
8%7%12%6%34445%43%
1575
16th to endDay
18%7%12%9%345%4438%
1552
March1st to 15thDay
12%5%9%7%2335%6%42%
1977
16th to endDay
311%6%8%5%25%45%6%40%
2117
April1st to 15thDay
315%6%8%7%33345%38%
2150
16th to endDay
217%8%8%6%24345%36%
2160
May1st to 15thDay
5%16%5%7%6%345%5%5%33%
2286
16th to endDay
8%12%35%5%34346%41%
2565
June1st to 15thDay
7%5%245%23445%53%
2520
16th to endDay
5%426%5%34445%53%
2520
July1st to 15thDay
16%8%37%7%45%45%5%29%
2439
16th to endDay
20%11%5%9%8%37%445%19%
2467
August1st to 15thDay
23%10%48%7%45%34424%
2340
16th to endDay
17%11%48%8%445%4426%
2298
September1st to 15thDay
18%8%37%7%3433433%
2160
16th to endDay
13%9%25%42322448%
1980
October1st to 15thDay
12%12%2422323449%
1705
16th to endDay
5%9%34223235%58%
1760
November1st to 15thDay
28%35%42324359%
1690
16th to endDay
5%46%422235%61%
1497
December1st to 15thDay
19%5%10%5%45%345%45%
1440
16th to endDay
9%6%13%7%34345%39%
1536
January1st to 15thNight
5%46%5%26%447%52%
2358
16th to endNight
7%48%6%35%335%51%
2496
February1st to 15thNight
6%5%10%7%33347%47%
2277
16th to endNight
6%5%9%6%45%446%45%
1920
March1st to 15thNight
7%46%5%3445%7%50%
1980
16th to endNight
7%5%6%425%45%7%48%
2106
April1st to 15thNight
111%5%8%6%34446%42%
1798
16th to endNight
18%5%7%6%24345%49%
1800
May1st to 15thNight
29%35%425%45%6%49%
1661
16th to endNight
46%24425%45%7%51%
1545
June1st to 15thNight
321231445%6%64%
1440
16th to endNight
2213424446%63%
1440
July1st to 15thNight
5%5%25%6%47%6%7%8%40%
1518
16th to endNight
6%425%5%46%7%8%10%36%
1701
August1st to 15thNight
8%425%5%335%6%8%46%
1620
16th to endNight
7%5%24435%5%6%9%44%
1902
September1st to 15thNight
7%325%5%345%6%8%47%
1800
16th to endNight
5%5%1432233363%
1977
October1st to 15thNight
7%7%23223446%55%
2052
16th to endNight
26%2432334461%
2112
November1st to 15thNight
18%3442435%7%55%
2157
16th to endNight
5%5%5%3235%45%58%
2460
December1st to 15thNight
18%47%5%3445%6%48%
2520
16th to endNight
7%5%10%9%35%446%41%
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
35%216%27%15%3
1591
16th to endDay
35%311%24%18%6%
1728
February1st to 15thDay
41%314%20%13%5%
1575
16th to endDay
46%35%21%19%3
1552
March1st to 15thDay
41%210%25%15%3
1977
16th to endDay
42%310%25%14%3
2117
April1st to 15thDay
48%38%20%13%4
2150
16th to endDay
48%38%24%13%2
2160
May1st to 15thDay
50%38%24%11%
2286
16th to endDay
43%39%26%14%3
2568
June1st to 15thDay
32%38%23%23%8%
2520
16th to endDay
32%36%18%26%11%
2520
July1st to 15thDay
56%5%9%10%11%6%
2296
16th to endDay
66%5%12%8%7%
2312
August1st to 15thDay
65%37%9%10%3
2325
16th to endDay
60%49%12%11%2
2298
September1st to 15thDay
55%36%13%17%4
2160
16th to endDay
41%2323%23%5%
1980
October1st to 15thDay
39%2425%20%7%
1705
16th to endDay
29%26%28%27%5%
1760
November1st to 15thDay
28%39%24%24%9%
1690
16th to endDay
26%210%31%20%8%
1497
December1st to 15thDay
38%414%23%15%2
1440
16th to endDay
45%7%11%17%13%3
1536
January1st to 15thNight
28%313%26%20%6%
2358
16th to endNight
33%46%26%20%8%
2496
February1st to 15thNight
35%312%22%19%7%
2288
16th to endNight
37%36%25%22%5%
1920
March1st to 15thNight
32%212%27%21%4
1980
16th to endNight
33%312%26%19%3
2106
April1st to 15thNight
39%311%22%17%4
1798
16th to endNight
34%311%29%17%3
1800
May1st to 15thNight
33%413%31%16%1
1662
16th to endNight
31%314%29%17%3
1546
June1st to 15thNight
20%39%27%29%10%
1440
16th to endNight
21%36%20%34%13%
1440
July1st to 15thNight
39%8%12%14%16%8%
1432
16th to endNight
37%12%23%15%7%3
1593
August1st to 15thNight
35%7%18%18%15%5%
1611
16th to endNight
35%5%16%24%13%2
1902
September1st to 15thNight
34%5%15%19%20%5%
1800
16th to endNight
26%36%29%27%6%
1977
October1st to 15thNight
29%39%25%22%8%
2052
16th to endNight
24%37%29%31%5%
2112
November1st to 15thNight
26%310%21%26%10%
2157
16th to endNight
26%38%30%22%9%
2460
December1st to 15thNight
34%5%14%21%18%5%
2520
16th to endNight
40%5%11%22%14%5%
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
20%17%27%24%10%
90
16th to endDay
10%22%34%20%8%3
96
February1st to 15thDay
16%24%31%18%8%
90
16th to endDay
20%23%28%19%6%1
81
March1st to 15thDay
23%27%27%17%3
267
16th to endDay
27%29%28%11%3
288
April1st to 15thDay
24%28%27%14%21
269
16th to endDay
28%32%26%9%2
270
May1st to 15thDay
26%26%29%14%3
288
16th to endDay
22%21%21%21%9%3
466
June1st to 15thDay
11%14%27%24%19%3
495
16th to endDay
410%26%26%25%7%
495
July1st to 15thDay
18%11%18%25%20%6%
400
16th to endDay
29%7%18%25%16%2
327
August1st to 15thDay
26%7%22%28%10%4
315
16th to endDay
23%9%21%28%14%2
332
September1st to 15thDay
20%12%27%23%12%3
315
16th to endDay
26%13%28%20%7%3
258
October1st to 15thDay
20%21%21%16%15%3
107
16th to endDay
17%18%28%21%11%2
96
November1st to 15thDay
12%15%25%25%17%3
90
16th to endDay
21%27%28%17%4
90
December1st to 15thDay
16%34%31%16%1
90
16th to endDay
17%27%26%22%6%
96
January1st to 15thNight
6%10%29%31%16%3
751
16th to endNight
7%11%29%32%14%4
768
February1st to 15thNight
5%14%31%34%11%1
704
16th to endNight
10%11%38%27%10%
632
March1st to 15thNight
10%11%30%31%14%1
720
16th to endNight
8%17%27%29%14%1
762
April1st to 15thNight
13%19%29%25%11%
539
16th to endNight
10%14%33%26%13%2
540
May1st to 15thNight
9%11%27%32%16%3
540
16th to endNight
9%11%25%27%20%5%
563
June1st to 15thNight
5%7%25%30%27%4
540
16th to endNight
45%17%29%37%5%
540
July1st to 15thNight
8%17%32%42%7%
510
16th to endNight
8%2323%49%12%
564
August1st to 15thNight
10%4324%49%7%
539
16th to endNight
9%27%26%42%12%
573
September1st to 15thNight
8%38%34%38%7%
540
16th to endNight
10%7%14%28%28%10%
656
October1st to 15thNight
13%9%21%31%19%4
684
16th to endNight
7%8%21%32%23%6%
704
November1st to 15thNight
10%7%24%33%20%3
757
16th to endNight
9%11%25%31%16%5%
900
December1st to 15thNight
9%13%34%30%10%2
900
16th to endNight
12%11%33%30%11%1
960
Page generated at 2017-10-07 12:07:43. Version ac04

Copyright 2017 A. Danko


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