Folsom Lake State Recration Area
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Folsom Lake State Recration Area clear sky chart from 2005-11-05 to 2018-03-11.

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
71%
15934
28%
49118
27%
15899
73%
15899
42%
26060

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
63%
776
18%
2677
20%
776
65%
776
28%
1601
January16th to endNight
60%
832
22%
2704
24%
832
62%
832
27%
1685
February1st to 15thNight
62%
756
26%
2462
27%
756
66%
756
30%
1466
February16th to endNight
58%
684
26%
2051
26%
684
62%
684
31%
1263
March1st to 15thNight
57%
764
17%
2189
17%
764
58%
764
26%
1460
March16th to endNight
57%
768
20%
2055
16%
768
60%
768
31%
1341
April1st to 15thNight
58%
719
20%
1799
12%
719
61%
719
32%
1203
April16th to endNight
66%
720
25%
1800
13%
720
69%
720
49%
1032
May1st to 15thNight
71%
569
29%
1649
22%
569
74%
569
56%
783
May16th to endNight
77%
374
27%
1496
32%
374
80%
374
47%
611
June1st to 15thNight
74%
360
27%
1440
33%
360
79%
360
49%
579
June16th to endNight
87%
360
36%
1440
49%
360
90%
360
67%
473
July1st to 15thNight
94%
340
35%
1360
48%
340
95%
340
77%
408
July16th to endNight
92%
498
39%
1528
40%
466
92%
466
76%
560
August1st to 15thNight
90%
574
37%
1647
29%
571
90%
571
75%
677
August16th to endNight
94%
764
45%
1910
29%
764
94%
764
84%
837
September1st to 15thNight
92%
720
42%
1800
30%
720
93%
720
80%
816
September16th to endNight
85%
716
45%
1942
39%
716
88%
716
73%
865
October1st to 15thNight
75%
720
31%
2160
32%
720
79%
720
53%
1030
October16th to endNight
78%
768
37%
2304
39%
768
80%
768
50%
1149
November1st to 15thNight
72%
760
26%
2443
29%
760
74%
760
40%
1304
November16th to endNight
65%
780
24%
2620
25%
780
68%
780
34%
1446
December1st to 15thNight
60%
780
21%
2730
21%
780
64%
780
28%
1606
December16th to endNight
50%
832
22%
2912
21%
832
56%
832
22%
1865

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%212212335%64%
49512
Night
11%312212335%61%
49303
TransparencyDay
24%48%19%24%19%
49194
Night
26%49%19%22%18%
49120
SeeingDay
10%416%29%29%9%
6418
Night
12%19%35%34%6%
15948

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
18%5%2342435%5%44%
1590
16th to endDay
19%5%25%423446%41%
1872
February1st to 15thDay
19%324323336%46%
1729
16th to endDay
19%5%24322345%45%
1709
March1st to 15thDay
19%5%24425%446%40%
2005
16th to endDay
16%424424446%43%
2168
April1st to 15thDay
16%6%23414446%44%
2149
16th to endDay
10%212212345%62%
2160
May1st to 15thDay
5%21213235%71%
2296
16th to endDay
5%213312345%64%
2615
June1st to 15thDay
5%212212335%68%
2520
16th to endDay
21112484%
2520
July1st to 15thDay
11112287%
2520
16th to endDay
111112286%
2533
August1st to 15thDay
1112287%
2303
16th to endDay
111388%
2292
September1st to 15thDay
1122384%
2160
16th to endDay
31111122378%
2013
October1st to 15thDay
5%12112335%70%
1800
16th to endDay
8%31331333463%
1920
November1st to 15thDay
11%313323446%55%
1746
16th to endDay
16%313314346%50%
1668
December1st to 15thDay
18%5%34323235%46%
1560
16th to endDay
21%5%2332345%6%40%
1664
January1st to 15thNight
18%413323448%45%
2677
16th to endNight
18%5%13324346%45%
2704
February1st to 15thNight
17%423323346%48%
2452
16th to endNight
18%313312345%49%
2051
March1st to 15thNight
19%5%24424345%42%
2189
16th to endNight
18%413224336%48%
2055
April1st to 15thNight
14%315%43445%6%45%
1799
16th to endNight
9%313111446%62%
1800
May1st to 15thNight
5%212212245%71%
1649
16th to endNight
5%21212348%66%
1496
June1st to 15thNight
4212212235%71%
1440
16th to endNight
1211111383%
1440
July1st to 15thNight
11112188%
1440
16th to endNight
11111386%
1634
August1st to 15thNight
1111113382%
1656
16th to endNight
112386%
1910
September1st to 15thNight
111112385%
1800
16th to endNight
11111223479%
1942
October1st to 15thNight
6%21212325%70%
2160
16th to endNight
6%212322236%66%
2304
November1st to 15thNight
12%312213346%57%
2443
16th to endNight
14%313313346%54%
2620
December1st to 15thNight
19%423222336%49%
2730
16th to endNight
22%5%24322336%43%
2912

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
41%6%12%17%17%4
1590
16th to endDay
44%6%9%15%14%9%
1872
February1st to 15thDay
40%5%9%19%19%6%
1729
16th to endDay
40%6%12%24%13%3
1709
March1st to 15thDay
44%6%10%18%14%4
2005
16th to endDay
41%7%12%18%17%2
2168
April1st to 15thDay
39%6%10%24%14%4
2149
16th to endDay
23%5%12%25%25%6%
2160
May1st to 15thDay
17%39%28%31%9%
2296
16th to endDay
21%5%12%28%24%8%
2619
June1st to 15thDay
18%410%22%23%20%
2520
16th to endDay
7%1315%37%34%
2520
July1st to 15thDay
6%1210%25%53%
2371
16th to endDay
7%49%23%53%
2376
August1st to 15thDay
6%311%30%47%
2287
16th to endDay
5%212%38%40%
2292
September1st to 15thDay
6%1313%34%39%
2160
16th to endDay
12%25%21%35%22%
2013
October1st to 15thDay
15%48%21%26%23%
1800
16th to endDay
24%48%21%25%15%
1920
November1st to 15thDay
29%5%13%26%18%6%
1746
16th to endDay
35%7%11%21%18%4
1668
December1st to 15thDay
42%411%16%18%6%
1560
16th to endDay
43%7%10%17%16%4
1664
January1st to 15thNight
37%5%12%20%15%8%
2677
16th to endNight
39%5%9%14%16%14%
2704
February1st to 15thNight
37%39%20%20%8%
2463
16th to endNight
36%5%9%25%19%3
2051
March1st to 15thNight
42%5%10%18%16%5%
2189
16th to endNight
38%6%10%18%19%7%
2055
April1st to 15thNight
38%6%12%20%14%6%
1799
16th to endNight
23%5%14%23%24%8%
1800
May1st to 15thNight
16%411%25%28%14%
1650
16th to endNight
16%416%32%19%10%
1496
June1st to 15thNight
16%411%25%22%19%
1440
16th to endNight
9%1414%32%38%
1440
July1st to 15thNight
5%138%27%54%
1360
16th to endNight
7%1310%23%53%
1528
August1st to 15thNight
8%1413%27%45%
1647
16th to endNight
5%211%35%43%
1910
September1st to 15thNight
6%2411%36%39%
1800
16th to endNight
9%26%19%33%28%
1942
October1st to 15thNight
18%36%20%25%25%
2160
16th to endNight
20%37%21%26%20%
2304
November1st to 15thNight
27%413%26%18%9%
2443
16th to endNight
32%39%23%22%7%
2620
December1st to 15thNight
37%411%16%20%9%
2730
16th to endNight
43%5%8%16%18%7%
2912

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
30%310%26%22%5%
128
16th to endDay
23%316%26%21%7%
304
February1st to 15thDay
20%5%15%26%24%8%
286
16th to endDay
22%8%22%24%18%4
290
March1st to 15thDay
21%11%22%20%18%5%
312
16th to endDay
18%10%19%27%19%4
288
April1st to 15thDay
20%11%25%20%16%5%
269
16th to endDay
11%10%25%27%17%6%
270
May1st to 15thDay
6%6%26%30%22%8%
288
16th to endDay
7%5%20%24%30%11%
330
June1st to 15thDay
6%5%22%31%26%6%
315
16th to endDay
1113%33%41%8%
315
July1st to 15thDay
6%36%48%7%
305
16th to endDay
11%36%39%12%
327
August1st to 15thDay
311%39%38%6%
315
16th to endDay
9%30%44%14%
332
September1st to 15thDay
27%38%37%12%
315
16th to endDay
3119%33%30%11%
315
October1st to 15thDay
5%6%20%31%25%11%
315
16th to endDay
11%311%27%31%14%
336
November1st to 15thDay
19%38%27%30%11%
162
16th to endDay
16%213%32%32%2
115
December1st to 15thDay
21%6%14%25%20%12%
90
16th to endDay
13%6%14%27%27%11%
96
January1st to 15thNight
19%27%32%29%9%
780
16th to endNight
20%28%34%25%9%
832
February1st to 15thNight
19%29%34%27%5%
764
16th to endNight
19%215%35%22%5%
684
March1st to 15thNight
20%310%31%27%5%
764
16th to endNight
19%214%33%25%3
768
April1st to 15thNight
13%415%35%26%3
719
16th to endNight
9%315%34%30%6%
720
May1st to 15thNight
6%117%37%32%4
570
16th to endNight
6%19%37%41%2
375
June1st to 15thNight
5%13%42%35%1
360
16th to endNight
25%42%46%1
360
July1st to 15thNight
144%50%2
340
16th to endNight
1235%55%5%
498
August1st to 15thNight
2343%47%3
574
16th to endNight
1238%53%4
764
September1st to 15thNight
2332%55%6%
720
16th to endNight
29%32%41%12%
716
October1st to 15thNight
7%111%36%34%9%
720
16th to endNight
7%19%31%36%14%
768
November1st to 15thNight
13%8%35%32%8%
760
16th to endNight
15%111%35%26%9%
780
December1st to 15thNight
20%29%33%24%9%
780
16th to endNight
25%313%29%23%4
832
Page generated at 2018-03-12 10:28:04. Version ac04

Copyright 2018 A. Danko


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