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 2018-01-20.

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%
16166
22%
48469
15%
16125
57%
16125
28%
30297

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%
779
24%
2522
12%
776
49%
776
26%
1476
January16th to endNight
34%
788
26%
2560
15%
788
49%
788
27%
1517
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
56%
717
20%
1980
17%
717
59%
717
27%
1325
October1st to 15thNight
55%
720
29%
2073
24%
720
61%
720
33%
1268
October16th to endNight
55%
768
35%
2304
27%
768
67%
768
39%
1255
November1st to 15thNight
54%
760
28%
2375
23%
760
62%
760
34%
1349
November16th to endNight
47%
780
29%
2535
22%
780
58%
780
31%
1421
December1st to 15thNight
42%
780
24%
2535
15%
780
55%
780
26%
1535
December16th to endNight
38%
832
24%
2704
15%
832
49%
832
22%
1744

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%5%8%43%
49055
Night
13%42442445%7%45%
48666
TransparencyDay
37%7%12%20%17%4
48756
Night
37%6%11%19%19%5%
48469
SeeingDay
16%5%17%23%22%14%
5948
Night
16%5%20%30%22%3
16171

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%24412336%48%
1746
16th to endDay
14%414323345%50%
1768
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
17%5%15%42446%7%40%
1980
October1st to 15thDay
17%312222235%56%
1887
16th to endDay
11%31332223361%
1920
November1st to 15thDay
12%413213346%55%
1813
16th to endDay
15%413322346%52%
1755
December1st to 15thDay
16%5%25%32335%6%45%
1755
16th to endDay
21%5%2431335%6%41%
1872
January1st to 15thNight
16%413223435%51%
2522
16th to endNight
15%5%23323445%48%
2560
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
17%5%2443435%7%40%
1980
October1st to 15thNight
16%42331233453%
2073
16th to endNight
11%31232333460%
2304
November1st to 15thNight
12%31332334455%
2375
16th to endNight
15%313323346%52%
2535
December1st to 15thNight
16%6%14324436%47%
2535
16th to endNight
20%5%24324437%41%
2704

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%5%
1747
16th to endDay
36%37%22%21%9%
1768
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
41%6%12%18%17%4
1980
October1st to 15thDay
32%49%21%25%6%
1887
16th to endDay
29%26%21%29%10%
1920
November1st to 15thDay
30%39%19%27%9%
1813
16th to endDay
33%37%20%25%8%
1755
December1st to 15thDay
38%49%21%18%5%
1755
16th to endDay
44%310%19%16%5%
1872
January1st to 15thNight
36%49%17%25%7%
2522
16th to endNight
37%37%20%23%7%
2560
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
41%6%12%16%18%4
1980
October1st to 15thNight
35%47%22%23%5%
2073
16th to endNight
28%26%20%29%11%
2304
November1st to 15thNight
32%37%18%26%11%
2375
16th to endNight
33%37%19%27%8%
2535
December1st to 15thNight
38%410%20%19%6%
2535
16th to endNight
44%410%17%17%5%
2704

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
19%17%32%21%9%
135
16th to endDay
14%16%43%18%7%
109
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
21%210%21%28%15%
314
October1st to 15thDay
22%213%27%25%7%
315
16th to endDay
14%5%13%35%22%8%
336
November1st to 15thDay
26%6%19%21%19%6%
231
16th to endDay
11%7%22%34%19%4
135
December1st to 15thDay
22%8%35%22%11%
135
16th to endDay
27%14%36%18%3
144
January1st to 15thNight
18%12%30%31%7%
780
16th to endNight
18%10%33%33%3
788
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
19%112%27%33%5%
717
October1st to 15thNight
19%318%24%29%5%
720
16th to endNight
13%5%22%33%23%3
768
November1st to 15thNight
14%421%37%18%3
760
16th to endNight
16%8%22%32%18%1
780
December1st to 15thNight
20%6%24%36%11%
780
16th to endNight
24%7%26%34%7%
832
Page generated at 2018-01-21 12:19:27. Version ac04

Copyright 2018 A. Danko


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