Silver Bell Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Silver Bell Observatory 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
57%
15723
22%
46870
17%
15684
63%
15684
30%
28932

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
41%
717
20%
2327
13%
716
50%
716
25%
1431
January16th to endNight
40%
768
23%
2418
16%
768
49%
768
25%
1528
February1st to 15thNight
39%
701
25%
2108
14%
699
51%
699
31%
1276
February16th to endNight
41%
631
24%
1893
14%
631
52%
631
30%
1157
March1st to 15thNight
46%
720
28%
1983
16%
720
56%
720
38%
1163
March16th to endNight
51%
768
25%
2112
16%
768
57%
768
37%
1234
April1st to 15thNight
52%
718
23%
1976
15%
718
58%
718
36%
1181
April16th to endNight
58%
627
29%
1785
20%
627
66%
627
42%
989
May1st to 15thNight
69%
539
26%
1619
20%
539
73%
539
43%
878
May16th to endNight
75%
561
24%
1682
21%
561
77%
561
40%
942
June1st to 15thNight
69%
540
16%
1620
14%
540
70%
540
27%
1057
June16th to endNight
77%
540
12%
1620
10%
540
77%
540
29%
1052
July1st to 15thNight
78%
510
10%
1530
10%
510
78%
510
26%
1025
July16th to endNight
77%
564
8%
1595
8%
531
78%
531
23%
1120
August1st to 15thNight
75%
539
8%
1654
8%
536
75%
536
24%
1135
August16th to endNight
69%
651
12%
1988
13%
651
69%
651
20%
1389
September1st to 15thNight
65%
700
11%
1925
11%
700
65%
700
21%
1380
September16th to endNight
58%
657
17%
1815
15%
657
60%
657
22%
1278
October1st to 15thNight
66%
660
28%
1840
26%
660
69%
660
34%
1124
October16th to endNight
60%
704
30%
2112
27%
704
67%
704
35%
1220
November1st to 15thNight
56%
700
31%
2101
26%
700
64%
700
38%
1172
November16th to endNight
50%
720
28%
2331
21%
720
62%
720
33%
1291
December1st to 15thNight
48%
720
27%
2340
24%
720
55%
720
30%
1382
December16th to endNight
49%
768
23%
2496
19%
768
57%
768
27%
1528

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
9%5%25%6%36%5%6%8%39%
47743
Night
8%4245%345%6%8%45%
47074
TransparencyDay
39%8%13%16%14%7%
47444
Night
34%8%14%19%15%8%
46877
SeeingDay
10%414%20%24%25%
5598
Night
10%419%32%26%6%
15732

By Month

Percentage Cloud Cover SE (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
12%7%345%2445%6%43%
1611
16th to endDay
14%434424345%46%
1804
February1st to 15thDay
16%5%2442234447%
1750
16th to endDay
13%5%34423335%50%
1580
March1st to 15thDay
8%41342345%8%52%
1976
16th to endDay
8%424425%45%7%51%
2111
April1st to 15thDay
9%325%5%3446%7%48%
1972
16th to endDay
6%3144345%5%8%50%
2182
May1st to 15thDay
6%323425%5%6%9%50%
2331
16th to endDay
6%425%7%45%6%6%8%42%
2431
June1st to 15thDay
8%5%27%8%5%7%8%8%10%27%
2340
16th to endDay
7%5%26%6%49%8%8%11%27%
2340
July1st to 15thDay
7%5%36%8%49%8%10%12%24%
2340
16th to endDay
8%5%47%7%6%9%9%8%10%21%
2465
August1st to 15thDay
11%428%8%5%9%7%9%11%20%
2292
16th to endDay
11%5%38%9%49%7%7%8%21%
2201
September1st to 15thDay
10%6%39%9%47%8%8%9%22%
1923
16th to endDay
13%7%48%7%46%6%6%6%28%
1815
October1st to 15thDay
9%5%26%5%245%5%6%42%
1788
16th to endDay
8%424334445%52%
1760
November1st to 15thDay
8%31442445%7%52%
1757
16th to endDay
10%5%24424445%51%
1626
December1st to 15thDay
11%5%25%5%3446%7%44%
1620
16th to endDay
11%6%345%245%5%8%41%
1728
January1st to 15thNight
12%5%35%5%24437%44%
2327
16th to endNight
14%5%35%5%2335%6%43%
2418
February1st to 15thNight
11%5%25%422245%52%
2103
16th to endNight
11%5%24434336%48%
1893
March1st to 15thNight
7%42442335%8%51%
1983
16th to endNight
8%424423436%55%
2112
April1st to 15thNight
7%5%3432445%6%52%
1976
16th to endNight
431442345%8%56%
1785
May1st to 15thNight
431332445%9%57%
1619
16th to endNight
431343446%9%54%
1682
June1st to 15thNight
8%4245%36%5%8%13%36%
1620
16th to endNight
5%325%5%35%7%9%14%36%
1620
July1st to 15thNight
5%424436%8%9%14%37%
1620
16th to endNight
3425%7%48%7%11%13%32%
1703
August1st to 15thNight
6%426%6%46%8%9%12%32%
1665
16th to endNight
7%5%35%6%37%6%8%10%34%
1988
September1st to 15thNight
8%5%36%6%5%6%7%8%11%31%
1925
16th to endNight
11%7%36%5%446%6%9%33%
1815
October1st to 15thNight
5%5%25%43445%7%50%
1840
16th to endNight
7%414434447%52%
2112
November1st to 15thNight
6%4235%34347%54%
2101
16th to endNight
8%5%1442435%6%52%
2331
December1st to 15thNight
11%5%35%424448%46%
2340
16th to endNight
10%6%35%43445%7%43%
2496

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
40%5%7%17%17%10%
1612
16th to endDay
39%47%16%21%10%
1804
February1st to 15thDay
40%36%14%19%16%
1752
16th to endDay
37%39%13%23%12%
1580
March1st to 15thDay
28%5%10%21%22%11%
1976
16th to endDay
31%6%10%20%19%11%
2112
April1st to 15thDay
32%6%9%18%22%10%
1972
16th to endDay
30%6%11%21%19%10%
2182
May1st to 15thDay
27%7%13%21%20%8%
2331
16th to endDay
34%10%13%20%16%3
2435
June1st to 15thDay
46%12%16%17%7%
2340
16th to endDay
44%13%18%17%6%
2340
July1st to 15thDay
44%15%24%13%1
2201
16th to endDay
49%14%21%11%2
2310
August1st to 15thDay
49%16%21%10%1
2279
16th to endDay
54%13%17%10%3
2201
September1st to 15thDay
52%12%16%10%5%1
1923
16th to endDay
52%8%11%15%8%4
1815
October1st to 15thDay
38%6%9%16%17%12%
1788
16th to endDay
31%5%8%14%24%15%
1760
November1st to 15thDay
29%49%20%22%13%
1757
16th to endDay
33%38%18%22%13%
1626
December1st to 15thDay
37%5%10%21%18%6%
1620
16th to endDay
38%6%10%22%12%8%
1728
January1st to 15thNight
39%5%9%17%18%10%
2327
16th to endNight
40%47%12%22%11%
2418
February1st to 15thNight
35%46%15%21%16%
2112
16th to endNight
36%48%16%20%12%
1893
March1st to 15thNight
30%412%22%20%10%
1983
16th to endNight
30%412%20%20%11%
2112
April1st to 15thNight
30%6%10%19%23%9%
1976
16th to endNight
24%6%11%26%21%8%
1785
May1st to 15thNight
23%7%14%26%19%9%
1620
16th to endNight
25%8%18%25%19%3
1684
June1st to 15thNight
36%10%21%25%5%
1620
16th to endNight
32%13%25%21%5%
1620
July1st to 15thNight
32%16%29%17%2
1530
16th to endNight
36%17%29%13%3
1595
August1st to 15thNight
35%16%30%14%2
1654
16th to endNight
40%14%24%15%4
1988
September1st to 15thNight
41%14%23%13%5%
1925
16th to endNight
44%10%15%17%10%3
1815
October1st to 15thNight
32%7%11%17%19%12%
1840
16th to endNight
31%47%16%24%14%
2112
November1st to 15thNight
28%48%21%24%11%
2101
16th to endNight
31%410%19%18%16%
2331
December1st to 15thNight
35%5%11%25%15%7%
2340
16th to endNight
38%5%10%21%14%8%
2496

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%15%42%14%7%6%
90
16th to endDay
15%18%37%16%11%
96
February1st to 15thDay
12%22%28%21%15%
90
16th to endDay
7%13%40%25%12%
81
March1st to 15thDay
10%10%28%30%17%3
266
16th to endDay
12%6%23%28%25%2
288
April1st to 15thDay
9%10%24%25%24%4
270
16th to endDay
5%218%29%28%14%
270
May1st to 15thDay
9%317%26%23%20%
288
16th to endDay
6%27%19%32%31%
331
June1st to 15thDay
12%18%10%26%40%
315
16th to endDay
9%1113%25%48%
315
July1st to 15thDay
418%23%60%
305
16th to endDay
7%48%26%51%
326
August1st to 15thDay
14%149%24%45%
313
16th to endDay
10%412%23%47%
332
September1st to 15thDay
15%15%18%25%34%
294
16th to endDay
18%17%18%31%22%
254
October1st to 15thDay
14%112%30%29%10%
255
16th to endDay
7%419%32%27%7%
272
November1st to 15thDay
12%219%35%22%7%
265
16th to endDay
5%438%28%17%6%
96
December1st to 15thDay
5%10%43%22%14%4
90
16th to endDay
13%10%26%33%12%4
96
January1st to 15thNight
15%8%28%33%13%
720
16th to endNight
16%10%26%35%10%
768
February1st to 15thNight
13%8%34%32%11%1
704
16th to endNight
15%9%30%38%6%
631
March1st to 15thNight
9%8%30%38%12%
720
16th to endNight
10%5%26%34%21%
768
April1st to 15thNight
9%428%38%18%
718
16th to endNight
6%424%37%25%1
627
May1st to 15thNight
6%217%45%26%2
540
16th to endNight
6%11%35%41%5%
563
June1st to 15thNight
11%7%27%40%12%
540
16th to endNight
6%421%45%21%
540
July1st to 15thNight
7%313%47%26%
510
16th to endNight
4214%54%23%
564
August1st to 15thNight
8%212%50%25%
539
16th to endNight
10%6%17%43%21%
651
September1st to 15thNight
11%16%23%41%16%
700
16th to endNight
16%19%31%35%5%
657
October1st to 15thNight
10%113%39%31%3
660
16th to endNight
8%320%39%26%1
704
November1st to 15thNight
9%224%39%22%1
700
16th to endNight
11%5%25%39%16%1
720
December1st to 15thNight
13%5%25%36%17%
720
16th to endNight
13%6%24%35%18%1
768
Page generated at 2017-09-11 19:35:18. Version ac04

Copyright 2017 A. Danko


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