Sunny Valley Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sunny Valley Observatory clear sky chart from 2005-11-05 to 2017-09-24.

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
44%
15134
9%
46756
6%
15108
47%
15108
17%
33632

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
34%
926
5%
2865
4%
925
35%
925
11%
2261
January16th to endNight
37%
928
12%
2976
9%
928
41%
928
14%
2199
February1st to 15thNight
46%
699
11%
2464
11%
698
49%
698
15%
1750
February16th to endNight
47%
632
9%
2069
10%
632
49%
632
16%
1510
March1st to 15thNight
42%
720
13%
2160
10%
720
45%
720
18%
1566
March16th to endNight
50%
768
16%
2020
10%
768
52%
768
25%
1443
April1st to 15thNight
44%
647
12%
1727
7%
647
47%
647
21%
1235
April16th to endNight
43%
397
9%
1477
12%
397
45%
397
15%
1010
May1st to 15thNight
53%
359
2%
1299
0%
359
53%
359
20%
845
May16th to endNight
55%
374
0%
1151
0%
374
55%
374
25%
750
June1st to 15thNight
52%
360
0%
1080
0%
360
52%
360
20%
756
June16th to endNight
58%
360
0%
1080
0%
360
58%
360
22%
741
July1st to 15thNight
55%
340
0%
1020
0%
340
55%
340
25%
675
July16th to endNight
64%
376
0%
1071
0%
354
65%
354
28%
667
August1st to 15thNight
70%
360
2%
1394
2%
358
70%
358
25%
810
August16th to endNight
52%
454
11%
1600
13%
454
55%
454
22%
1001
September1st to 15thNight
55%
693
12%
1773
8%
693
57%
693
30%
1178
September16th to endNight
43%
692
14%
1896
7%
692
47%
692
23%
1321
October1st to 15thNight
41%
660
12%
2030
8%
660
46%
660
18%
1451
October16th to endNight
36%
704
10%
2304
6%
704
42%
704
14%
1696
November1st to 15thNight
37%
856
13%
2606
10%
856
42%
856
18%
1860
November16th to endNight
37%
907
8%
2742
5%
907
40%
907
13%
2152
December1st to 15thNight
31%
930
6%
2880
4%
930
33%
930
9%
2386
December16th to endNight
37%
992
9%
3072
5%
992
41%
992
13%
2369

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
10%8%47%7%46%5%6%7%31%
48239
Night
9%10%48%7%46%5%6%7%30%
46878
TransparencyDay
49%8%16%19%5%
47866
Night
49%8%16%18%5%
46756
SeeingDay
14%8%23%29%17%5%
7029
Night
13%5%22%35%19%2
15145

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
9%11%6%10%9%5%7%46%7%21%
1074
16th to endDay
6%11%6%9%7%445%7%6%29%
1259
February1st to 15thDay
7%10%5%10%8%5%5%5%6%6%29%
1400
16th to endDay
6%11%410%9%5%8%6%7%6%24%
1405
March1st to 15thDay
6%11%6%10%8%47%7%5%7%25%
1800
16th to endDay
9%12%5%8%7%45%5%5%7%29%
2202
April1st to 15thDay
6%9%5%8%7%47%5%6%8%30%
2221
16th to endDay
11%11%47%7%45%46%5%30%
2481
May1st to 15thDay
10%7%36%7%46%5%5%7%35%
2652
16th to endDay
13%5%37%6%45%5%6%7%35%
2959
June1st to 15thDay
15%8%37%6%36%5%6%8%28%
2880
16th to endDay
14%5%25%6%46%6%6%8%31%
2880
July1st to 15thDay
12%6%36%6%36%5%6%8%34%
2880
16th to endDay
10%5%36%6%36%5%7%9%34%
3026
August1st to 15thDay
10%7%35%6%36%6%5%9%35%
2559
16th to endDay
12%5%26%7%36%5%8%7%33%
2602
September1st to 15thDay
10%6%245%346%6%8%40%
2184
16th to endDay
12%8%26%5%35%448%38%
1922
October1st to 15thDay
15%10%36%5%35%5%46%33%
1598
16th to endDay
13%14%48%5%2346%7%29%
1568
November1st to 15thDay
11%8%5%8%6%35%5%5%7%32%
1240
16th to endDay
7%12%7%11%10%5%6%345%25%
1215
December1st to 15thDay
9%16%5%9%11%48%6%5%5%17%
1080
16th to endDay
5%13%5%14%9%5%6%5%6%6%22%
1152
January1st to 15thNight
7%12%6%12%9%46%46%7%21%
2865
16th to endNight
8%12%5%9%6%46%45%7%27%
2976
February1st to 15thNight
6%10%6%8%8%46%6%6%7%29%
2452
16th to endNight
6%8%5%10%8%5%7%6%6%7%26%
2069
March1st to 15thNight
8%12%5%8%7%45%5%6%7%28%
2160
16th to endNight
5%12%47%5%36%5%6%7%35%
2016
April1st to 15thNight
8%10%46%6%36%6%6%7%33%
1727
16th to endNight
9%10%48%7%446%6%8%29%
1477
May1st to 15thNight
9%437%5%37%7%6%8%35%
1298
16th to endNight
11%6%35%435%5%6%9%38%
1151
June1st to 15thNight
14%6%36%5%35%5%8%9%30%
1080
16th to endNight
12%5%347%46%6%6%9%33%
1080
July1st to 15thNight
8%6%36%6%35%6%6%8%39%
1080
16th to endNight
10%4244246%7%10%42%
1143
August1st to 15thNight
7%4245%25%47%11%43%
1401
16th to endNight
11%5%245%245%8%9%39%
1600
September1st to 15thNight
10%5%25%445%46%8%42%
1773
16th to endNight
10%8%36%6%35%5%6%7%35%
1896
October1st to 15thNight
12%9%37%6%445%5%6%33%
2030
16th to endNight
11%13%47%6%25%5%5%7%29%
2304
November1st to 15thNight
10%12%47%5%35%5%5%7%32%
2606
16th to endNight
7%10%6%12%9%46%5%5%6%25%
2742
December1st to 15thNight
10%15%6%10%9%5%6%6%5%5%18%
2880
16th to endNight
5%13%6%11%8%5%6%5%5%7%24%
3072

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
61%8%14%10%4
1074
16th to endDay
51%8%15%17%5%1
1259
February1st to 15thDay
52%8%15%18%5%
1400
16th to endDay
55%8%16%16%2
1405
March1st to 15thDay
55%8%15%15%4
1800
16th to endDay
53%7%15%18%4
2202
April1st to 15thDay
49%7%14%18%8%1
2221
16th to endDay
53%6%12%19%7%1
2481
May1st to 15thDay
46%6%11%22%12%
2652
16th to endDay
46%6%12%20%12%1
2964
June1st to 15thDay
51%8%14%19%4
2880
16th to endDay
47%8%16%21%5%
2880
July1st to 15thDay
46%9%17%20%4
2711
16th to endDay
42%10%24%19%2
2835
August1st to 15thDay
43%10%23%19%2
2541
16th to endDay
45%10%21%19%3
2602
September1st to 15thDay
38%8%24%23%4
2184
16th to endDay
44%8%18%20%7%
1922
October1st to 15thDay
51%7%16%21%3
1598
16th to endDay
53%8%16%17%2
1568
November1st to 15thDay
49%8%14%23%3
1240
16th to endDay
61%5%12%16%21
1215
December1st to 15thDay
66%9%10%11%2
1080
16th to endDay
59%8%11%17%2
1152
January1st to 15thNight
60%8%15%11%3
2865
16th to endNight
54%8%15%14%5%1
2976
February1st to 15thNight
51%8%15%18%6%
2464
16th to endNight
53%7%17%16%4
2069
March1st to 15thNight
51%6%13%21%6%
2160
16th to endNight
45%7%14%23%8%
2020
April1st to 15thNight
46%7%12%18%13%1
1727
16th to endNight
49%7%11%20%10%1
1477
May1st to 15thNight
41%8%9%24%14%1
1299
16th to endNight
40%7%13%22%13%2
1151
June1st to 15thNight
45%9%15%22%6%
1080
16th to endNight
44%8%15%22%8%
1080
July1st to 15thNight
39%9%20%22%7%
1020
16th to endNight
34%9%29%23%2
1071
August1st to 15thNight
31%11%26%25%4
1394
16th to endNight
37%10%21%23%6%
1600
September1st to 15thNight
37%8%19%26%7%
1773
16th to endNight
44%7%19%20%7%
1896
October1st to 15thNight
48%8%16%21%4
2030
16th to endNight
52%9%17%16%3
2304
November1st to 15thNight
49%7%16%22%4
2606
16th to endNight
57%9%13%15%2
2742
December1st to 15thNight
65%8%11%11%2
2880
16th to endNight
58%7%15%15%3
3072

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
16%5%11%35%21%10%
60
16th to endDay
10%7%25%35%12%7%
64
February1st to 15thDay
18%6%21%36%8%8%
60
16th to endDay
10%6%29%32%19%1
145
March1st to 15thDay
11%13%33%28%10%2
270
16th to endDay
15%12%32%22%13%4
288
April1st to 15thDay
11%14%31%28%10%1
269
16th to endDay
17%19%23%23%13%2
270
May1st to 15thDay
14%12%24%24%18%5%
429
16th to endDay
13%7%19%31%20%6%
674
June1st to 15thDay
16%8%22%28%18%4
675
16th to endDay
14%418%30%23%8%
675
July1st to 15thDay
12%5%22%31%22%5%
645
16th to endDay
12%5%21%29%23%7%
694
August1st to 15thDay
12%419%35%20%7%
354
16th to endDay
18%12%30%28%8%1
332
September1st to 15thDay
18%7%23%29%15%5%
315
16th to endDay
14%18%25%28%9%3
288
October1st to 15thDay
27%10%24%25%10%2
185
16th to endDay
25%124%24%18%5%
93
November1st to 15thDay
11%11%43%21%11%
60
16th to endDay
8%8%28%28%18%8%
60
December1st to 15thDay
18%116%38%20%5%
60
16th to endDay
7%6%18%43%20%3
64
January1st to 15thNight
13%5%25%37%14%2
930
16th to endNight
14%8%24%38%11%
928
February1st to 15thNight
11%323%39%19%3
704
16th to endNight
9%222%39%23%2
632
March1st to 15thNight
12%7%25%38%14%2
720
16th to endNight
10%5%23%36%23%1
768
April1st to 15thNight
13%5%25%33%20%
647
16th to endNight
13%10%20%34%19%2
397
May1st to 15thNight
11%8%18%31%25%3
360
16th to endNight
12%420%36%24%2
375
June1st to 15thNight
18%414%30%30%1
360
16th to endNight
15%116%35%28%4
360
July1st to 15thNight
11%219%34%29%2
340
16th to endNight
10%313%31%36%4
376
August1st to 15thNight
9%19%31%40%6%
360
16th to endNight
14%320%38%20%2
454
September1st to 15thNight
14%318%31%29%3
693
16th to endNight
14%7%26%32%17%2
692
October1st to 15thNight
17%5%23%33%17%2
660
16th to endNight
18%6%25%33%13%2
704
November1st to 15thNight
16%7%27%33%13%2
856
16th to endNight
13%6%24%38%14%2
907
December1st to 15thNight
18%6%24%33%14%2
930
16th to endNight
12%6%21%37%18%3
992
Page generated at 2017-09-25 07:02:23. Version ac04

Copyright 2017 A. Danko


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