Squirrel Valley Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Squirrel Valley Observatory clear sky chart from 2005-11-05 to 2017-09-20.

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
50%
15678
22%
46950
15%
15637
57%
15637
28%
29406

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
33%
719
25%
2327
12%
716
49%
716
25%
1365
January16th to endNight
33%
768
25%
2496
14%
768
48%
768
27%
1485
February1st to 15thNight
34%
702
25%
2190
13%
700
48%
700
30%
1257
February16th to endNight
29%
631
26%
1893
11%
631
44%
631
28%
1160
March1st to 15thNight
38%
720
26%
1995
16%
720
47%
720
30%
1252
March16th to endNight
37%
768
20%
2112
11%
768
44%
768
28%
1363
April1st to 15thNight
43%
718
23%
1961
13%
718
51%
718
34%
1179
April16th to endNight
50%
567
24%
1647
15%
567
56%
567
31%
1023
May1st to 15thNight
49%
540
16%
1620
9%
540
53%
540
25%
1067
May16th to endNight
61%
561
16%
1684
12%
561
63%
561
26%
1083
June1st to 15thNight
66%
540
12%
1620
10%
540
68%
540
25%
1094
June16th to endNight
71%
540
15%
1620
13%
540
72%
540
28%
1065
July1st to 15thNight
70%
510
10%
1530
8%
510
70%
510
23%
1044
July16th to endNight
73%
564
12%
1595
10%
531
75%
531
25%
1074
August1st to 15thNight
67%
539
12%
1609
12%
536
67%
536
23%
1119
August16th to endNight
66%
622
17%
1825
15%
622
67%
622
23%
1277
September1st to 15thNight
62%
720
18%
1980
16%
720
63%
720
27%
1350
September16th to endNight
54%
677
19%
1870
15%
677
57%
677
26%
1263
October1st to 15thNight
54%
660
31%
1900
26%
660
61%
660
34%
1154
October16th to endNight
54%
704
34%
2112
25%
704
67%
704
39%
1157
November1st to 15thNight
54%
700
29%
2188
24%
700
63%
700
36%
1212
November16th to endNight
44%
720
27%
2340
20%
720
55%
720
30%
1338
December1st to 15thNight
43%
720
24%
2340
16%
720
55%
720
26%
1412
December16th to endNight
38%
768
23%
2496
15%
768
48%
768
22%
1613

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
13%4244345%6%8%42%
47885
Night
13%42442445%7%45%
47147
TransparencyDay
37%7%12%20%16%4
47586
Night
37%6%11%19%19%5%
46950
SeeingDay
16%5%17%23%22%14%
5531
Night
16%5%20%30%22%4
15683

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
16%5%24412346%48%
1611
16th to endDay
14%41432335%5%49%
1728
February1st to 15thDay
14%42332335%6%48%
1669
16th to endDay
13%4244245%36%48%
1580
March1st to 15thDay
15%42332435%7%47%
1965
16th to endDay
18%5%13323447%44%
2111
April1st to 15thDay
12%4234245%47%49%
1985
16th to endDay
13%4245%35%45%6%44%
2322
May1st to 15thDay
12%4246%35%5%5%8%40%
2331
16th to endDay
11%5%24435%6%7%11%38%
2431
June1st to 15thDay
9%5%25%6%47%7%8%10%33%
2340
16th to endDay
6%314446%8%8%11%38%
2340
July1st to 15thDay
10%436%6%46%6%8%11%31%
2340
16th to endDay
6%3247%5%7%8%8%11%33%
2465
August1st to 15thDay
12%6%26%6%36%7%8%10%28%
2340
16th to endDay
12%425%7%36%6%7%11%31%
2360
September1st to 15thDay
10%426%5%35%6%6%7%40%
1980
16th to endDay
18%5%26%42446%7%39%
1859
October1st to 15thDay
17%312212235%56%
1730
16th to endDay
11%31342223361%
1760
November1st to 15thDay
10%413213346%58%
1670
16th to endDay
16%413322346%50%
1620
December1st to 15thDay
15%5%25%32446%6%45%
1620
16th to endDay
21%5%24313345%43%
1728
January1st to 15thNight
16%313223435%51%
2327
16th to endNight
15%423324445%48%
2496
February1st to 15thNight
13%41332344453%
2181
16th to endNight
11%424425%45%5%48%
1893
March1st to 15thNight
13%5%3332435%6%48%
1995
16th to endNight
15%5%24424345%45%
2112
April1st to 15thNight
13%414313447%50%
1961
16th to endNight
12%43442345%5%49%
1647
May1st to 15thNight
13%425%6%35%46%7%40%
1619
16th to endNight
10%415%6%36%6%5%9%40%
1682
June1st to 15thNight
9%4345%36%8%8%13%32%
1620
16th to endNight
8%424437%5%6%10%41%
1620
July1st to 15thNight
8%425%6%5%6%7%10%9%33%
1620
16th to endNight
6%325%5%47%7%9%14%31%
1703
August1st to 15thNight
13%5%25%5%35%6%7%11%33%
1620
16th to endNight
11%6%35%6%45%6%7%9%34%
1825
September1st to 15thNight
11%5%25%6%35%5%7%8%38%
1980
16th to endNight
18%5%24434347%39%
1870
October1st to 15thNight
16%42331233454%
1900
16th to endNight
11%31232333459%
2112
November1st to 15thNight
12%31332334457%
2188
16th to endNight
16%313323346%51%
2340
December1st to 15thNight
15%6%13324436%47%
2340
16th to endNight
21%5%24323436%41%
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
38%49%19%22%4
1612
16th to endDay
35%37%23%21%8%
1728
February1st to 15thDay
36%39%21%24%5%
1671
16th to endDay
36%5%10%23%17%6%
1580
March1st to 15thDay
36%5%8%23%20%6%
1965
16th to endDay
39%5%13%21%17%3
2112
April1st to 15thDay
33%410%23%21%5%
1985
16th to endDay
38%6%10%19%17%7%
2322
May1st to 15thDay
40%6%14%20%15%2
2331
16th to endDay
37%8%17%21%13%1
2435
June1st to 15thDay
40%10%18%21%7%1
2340
16th to endDay
33%12%19%19%13%2
2340
July1st to 15thDay
41%12%17%16%8%3
2201
16th to endDay
36%12%21%19%8%1
2310
August1st to 15thDay
45%11%15%18%8%
2327
16th to endDay
42%10%16%19%9%1
2360
September1st to 15thDay
39%10%11%18%15%3
1980
16th to endDay
43%6%11%17%17%4
1859
October1st to 15thDay
31%49%21%25%6%
1730
16th to endDay
29%26%20%29%10%
1760
November1st to 15thDay
28%39%19%29%10%
1670
16th to endDay
35%37%21%23%7%
1620
December1st to 15thDay
38%5%10%20%18%6%
1620
16th to endDay
44%39%18%17%6%
1728
January1st to 15thNight
36%49%17%24%7%
2327
16th to endNight
37%37%20%23%7%
2496
February1st to 15thNight
34%29%21%25%5%
2190
16th to endNight
36%49%21%23%3
1893
March1st to 15thNight
36%5%9%20%20%7%
1995
16th to endNight
39%5%11%21%18%4
2112
April1st to 15thNight
32%410%24%22%5%
1961
16th to endNight
35%5%10%19%20%7%
1647
May1st to 15thNight
41%6%13%20%15%1
1620
16th to endNight
38%7%13%25%11%2
1684
June1st to 15thNight
37%12%21%20%7%1
1620
16th to endNight
35%11%17%18%13%3
1620
July1st to 15thNight
40%11%20%16%8%2
1530
16th to endNight
36%13%21%17%7%2
1595
August1st to 15thNight
41%11%20%14%11%
1609
16th to endNight
42%10%16%19%9%1
1825
September1st to 15thNight
40%8%15%18%13%3
1980
16th to endNight
42%6%12%16%17%4
1870
October1st to 15thNight
34%47%22%24%5%
1900
16th to endNight
29%26%20%29%11%
2112
November1st to 15thNight
30%37%17%28%12%
2188
16th to endNight
35%36%19%26%8%
2340
December1st to 15thNight
38%410%19%20%7%
2340
16th to endNight
44%49%16%18%5%
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
18%16%35%20%8%
90
16th to endDay
14%17%45%16%5%
96
February1st to 15thDay
17%16%44%20%1
90
16th to endDay
17%12%43%18%8%
81
March1st to 15thDay
17%12%30%30%8%
255
16th to endDay
20%10%26%28%12%1
288
April1st to 15thDay
14%12%21%27%21%2
270
16th to endDay
19%321%25%19%10%
270
May1st to 15thDay
14%8%26%21%18%9%
288
16th to endDay
15%212%23%28%18%
331
June1st to 15thDay
13%211%20%27%24%
315
16th to endDay
11%113%24%24%25%
315
July1st to 15thDay
9%9%20%30%29%
305
16th to endDay
5%25%17%35%33%
326
August1st to 15thDay
22%7%20%23%24%
313
16th to endDay
15%6%17%30%29%
332
September1st to 15thDay
14%210%17%31%23%
315
16th to endDay
24%210%20%27%13%
270
October1st to 15thDay
22%314%28%21%8%
255
16th to endDay
15%413%36%23%6%
272
November1st to 15thDay
23%7%20%22%20%6%
178
16th to endDay
17%6%24%31%17%2
90
December1st to 15thDay
17%11%38%22%10%
90
16th to endDay
31%17%27%18%5%
96
January1st to 15thNight
18%12%30%30%7%
720
16th to endNight
18%10%34%33%3
768
February1st to 15thNight
16%11%35%34%2
704
16th to endNight
13%11%40%30%3
631
March1st to 15thNight
18%9%29%35%7%
720
16th to endNight
18%7%29%32%11%
768
April1st to 15thNight
16%9%27%31%14%
718
16th to endNight
15%5%22%34%20%1
567
May1st to 15thNight
16%421%33%22%1
540
16th to endNight
13%211%28%38%5%
563
June1st to 15thNight
10%110%29%37%9%
540
16th to endNight
8%19%25%42%12%
540
July1st to 15thNight
11%425%47%9%
510
16th to endNight
5%16%22%49%14%
564
August1st to 15thNight
16%424%44%9%
539
16th to endNight
14%1423%45%10%
622
September1st to 15thNight
14%18%25%40%9%
720
16th to endNight
20%113%27%31%5%
677
October1st to 15thNight
19%318%25%27%5%
660
16th to endNight
13%5%21%34%21%3
704
November1st to 15thNight
13%422%37%18%3
700
16th to endNight
17%9%24%30%17%1
720
December1st to 15thNight
19%6%24%37%11%
720
16th to endNight
25%6%26%33%8%
768
Page generated at 2017-09-21 07:18:15. Version ac04

Copyright 2017 A. Danko


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