Sacramento Mountains Astronomy Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sacramento Mountains Astronomy Park 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
49%
15546
33%
47042
18%
15502
64%
15502
42%
23140

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
40%
720
32%
2327
16%
716
59%
716
37%
1108
January16th to endNight
36%
768
37%
2496
17%
768
61%
768
39%
1142
February1st to 15thNight
39%
703
36%
2115
15%
700
61%
700
46%
968
February16th to endNight
24%
632
40%
1894
11%
632
53%
632
38%
868
March1st to 15thNight
37%
720
36%
2049
14%
720
55%
720
41%
1006
March16th to endNight
36%
705
39%
2049
16%
705
57%
705
48%
945
April1st to 15thNight
29%
539
35%
1798
11%
539
58%
539
36%
814
April16th to endNight
30%
540
40%
1800
15%
540
64%
540
47%
714
May1st to 15thNight
36%
540
31%
1800
15%
540
59%
540
44%
801
May16th to endNight
46%
562
31%
1775
16%
561
66%
561
47%
826
June1st to 15thNight
64%
540
30%
1440
19%
540
72%
540
56%
722
June16th to endNight
69%
540
23%
1456
19%
540
71%
540
43%
838
July1st to 15thNight
76%
510
21%
1530
20%
510
76%
510
40%
854
July16th to endNight
80%
564
20%
1615
21%
531
81%
531
37%
927
August1st to 15thNight
77%
539
20%
1789
24%
536
77%
536
31%
1032
August16th to endNight
78%
573
20%
1910
23%
573
79%
573
32%
1091
September1st to 15thNight
72%
540
22%
1800
24%
540
74%
540
33%
1028
September16th to endNight
71%
519
34%
1862
34%
519
78%
519
42%
880
October1st to 15thNight
58%
637
36%
1957
23%
637
69%
637
45%
974
October16th to endNight
59%
704
39%
2112
23%
704
70%
704
56%
947
November1st to 15thNight
53%
739
41%
2139
20%
739
67%
739
55%
958
November16th to endNight
44%
900
39%
2340
17%
900
58%
900
46%
1201
December1st to 15thNight
39%
900
39%
2349
14%
900
57%
900
43%
1210
December16th to endNight
32%
912
34%
2640
14%
912
50%
912
37%
1286

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
431342445%7%58%
47864
Night
3212323447%63%
47241
Cloud CoverDay
431342445%7%57%
47862
Night
321232335%7%63%
47241
TransparencyDay
22%5%9%17%25%19%
47564
Night
18%5%9%17%27%20%
47043
SeeingDay
7%14%25%28%18%5%
5346
Night
5%15%25%28%21%4
15548

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
1212413445%66%
1611
16th to endDay
5%312323437%62%
1728
February1st to 15thDay
2312222336%68%
1744
16th to endDay
121233326%70%
1580
March1st to 15thDay
23123345%45%62%
1908
16th to endDay
1213313347%66%
2173
April1st to 15thDay
2212214346%67%
2150
16th to endDay
111112235%76%
2160
May1st to 15thDay
421332445%6%62%
2151
16th to endDay
4112313346%66%
2333
June1st to 15thDay
123245%6%8%63%
2520
16th to endDay
5%314436%6%7%9%48%
2499
July1st to 15thDay
10%425%6%48%6%7%10%33%
2340
16th to endDay
9%5%26%5%47%7%9%11%30%
2443
August1st to 15thDay
10%326%7%5%8%8%8%8%29%
2160
16th to endDay
8%435%8%46%6%8%9%34%
2292
September1st to 15thDay
13%5%25%5%345%6%7%39%
2160
16th to endDay
6%414324446%57%
1955
October1st to 15thDay
5%313223445%64%
1670
16th to endDay
222212235%75%
1760
November1st to 15thDay
211222236%74%
1706
16th to endDay
3211212335%70%
1620
December1st to 15thDay
2222135%5%8%65%
1608
16th to endDay
1312323447%64%
1593
January1st to 15thNight
131331444466%
2327
16th to endNight
4212213337%67%
2496
February1st to 15thNight
1211223347%68%
2105
16th to endNight
221123345%71%
1894
March1st to 15thNight
1212323447%65%
2049
16th to endNight
2112223235%73%
2049
April1st to 15thNight
3212224446%66%
1798
16th to endNight
111212235%76%
1800
May1st to 15thNight
3212213346%69%
1799
16th to endNight
422113446%66%
1774
June1st to 15thNight
11232447%8%63%
1440
16th to endNight
22135%37%6%6%9%51%
1456
July1st to 15thNight
7%323325%46%12%46%
1620
16th to endNight
5%214435%6%8%15%41%
1725
August1st to 15thNight
6%3145%346%9%13%40%
1800
16th to endNight
43145%35%5%7%12%45%
1910
September1st to 15thNight
9%4234345%5%10%46%
1800
16th to endNight
6%312313345%63%
1862
October1st to 15thNight
3212322346%66%
1957
16th to endNight
321121223474%
2112
November1st to 15thNight
212212237%72%
2139
16th to endNight
211331332471%
2340
December1st to 15thNight
3212223248%67%
2349
16th to endNight
221232345%6%66%
2640

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
1213323436%66%
1611
16th to endDay
4412224337%62%
1728
February1st to 15thDay
1313222336%68%
1744
16th to endDay
1212313335%71%
1580
March1st to 15thDay
23123345%46%61%
1908
16th to endDay
121332335%7%66%
2171
April1st to 15thDay
2212223346%67%
2150
16th to endDay
1111112235%76%
2160
May1st to 15thDay
321332435%6%61%
2151
16th to endDay
4112213346%65%
2333
June1st to 15thDay
11123245%7%8%62%
2520
16th to endDay
4224436%6%7%9%47%
2499
July1st to 15thDay
9%426%7%47%6%7%9%32%
2340
16th to endDay
9%5%36%6%47%8%10%9%29%
2443
August1st to 15thDay
9%5%26%8%5%8%7%8%8%28%
2160
16th to endDay
8%426%8%47%7%8%8%33%
2292
September1st to 15thDay
13%6%35%6%345%6%7%38%
2160
16th to endDay
6%314324346%57%
1955
October1st to 15thDay
5%213223345%64%
1670
16th to endDay
1212212325%75%
1760
November1st to 15thDay
211213235%75%
1706
16th to endDay
322212336%70%
1620
December1st to 15thDay
22232235%8%64%
1608
16th to endDay
1313224347%64%
1593
January1st to 15thNight
131322435%466%
2327
16th to endNight
3212222347%66%
2496
February1st to 15thNight
211214347%68%
2105
16th to endNight
2211113246%71%
1894
March1st to 15thNight
1312323447%65%
2049
16th to endNight
2111223225%73%
2049
April1st to 15thNight
2211224447%66%
1798
16th to endNight
11213245%76%
1800
May1st to 15thNight
2312213346%68%
1799
16th to endNight
42122345%6%67%
1774
June1st to 15thNight
111232447%8%63%
1440
16th to endNight
2213447%5%6%8%51%
1456
July1st to 15thNight
7%323425%46%11%47%
1620
16th to endNight
5%213435%7%9%14%41%
1725
August1st to 15thNight
6%3246%346%10%14%39%
1800
16th to endNight
43245%3448%13%45%
1910
September1st to 15thNight
8%5%2343447%10%45%
1800
16th to endNight
6%21221335%6%62%
1862
October1st to 15thNight
3212323346%66%
1957
16th to endNight
32221213474%
2112
November1st to 15thNight
2112212337%72%
2139
16th to endNight
221332332471%
2340
December1st to 15thNight
2212223348%66%
2349
16th to endNight
1312323447%66%
2640

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
17%37%17%31%21%
1612
16th to endDay
19%5%6%15%31%21%
1728
February1st to 15thDay
16%36%16%28%28%
1745
16th to endDay
15%25%14%36%26%
1580
March1st to 15thDay
19%5%7%16%29%22%
1908
16th to endDay
17%35%14%33%26%
2173
April1st to 15thDay
16%36%13%35%24%
2150
16th to endDay
10%2411%34%36%
2160
May1st to 15thDay
19%5%7%12%26%28%
2151
16th to endDay
16%47%16%26%28%
2336
June1st to 15thDay
14%5%10%14%24%30%
2520
16th to endDay
26%6%11%17%18%20%
2499
July1st to 15thDay
36%10%15%16%13%6%
2201
16th to endDay
35%13%20%19%10%
2290
August1st to 15thDay
38%12%18%20%7%2
2147
16th to endDay
38%10%14%21%12%2
2292
September1st to 15thDay
35%8%12%18%17%6%
2160
16th to endDay
23%5%9%21%27%12%
1955
October1st to 15thDay
20%48%17%26%22%
1670
16th to endDay
12%2419%34%26%
1760
November1st to 15thDay
12%35%21%33%23%
1706
16th to endDay
15%35%17%31%26%
1620
December1st to 15thDay
17%38%22%36%12%
1608
16th to endDay
17%5%11%19%32%13%
1593
January1st to 15thNight
19%48%14%30%21%
2327
16th to endNight
16%46%15%34%21%
2496
February1st to 15thNight
15%28%15%26%30%
2115
16th to endNight
15%2314%36%26%
1894
March1st to 15thNight
16%46%16%31%24%
2049
16th to endNight
14%35%13%36%27%
2049
April1st to 15thNight
17%46%11%37%22%
1798
16th to endNight
10%36%11%33%34%
1800
May1st to 15thNight
17%36%13%30%29%
1800
16th to endNight
16%47%16%26%28%
1776
June1st to 15thNight
14%6%9%15%21%32%
1440
16th to endNight
22%9%14%16%15%20%
1456
July1st to 15thNight
25%7%17%23%18%6%
1530
16th to endNight
25%10%25%23%13%1
1615
August1st to 15thNight
28%10%21%25%11%2
1789
16th to endNight
28%10%20%22%16%2
1910
September1st to 15thNight
29%8%17%19%16%8%
1800
16th to endNight
22%410%21%29%11%
1862
October1st to 15thNight
18%6%6%17%29%21%
1957
16th to endNight
13%2418%28%31%
2112
November1st to 15thNight
12%3419%34%25%
2139
16th to endNight
17%3415%30%29%
2340
December1st to 15thNight
17%46%20%32%19%
2349
16th to endNight
16%49%22%32%14%
2640

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
7%30%33%18%7%2
90
16th to endDay
8%39%19%21%9%1
96
February1st to 15thDay
8%14%30%32%14%
90
16th to endDay
6%29%33%19%7%3
81
March1st to 15thDay
7%28%44%15%31
198
16th to endDay
6%32%39%14%41
288
April1st to 15thDay
10%34%33%18%2
269
16th to endDay
9%40%35%11%21
270
May1st to 15thDay
5%30%43%15%4
288
16th to endDay
5%22%38%23%9%
396
June1st to 15thDay
25%29%34%24%3
495
16th to endDay
5%117%37%30%6%
474
July1st to 15thDay
8%11%45%25%8%
305
16th to endDay
218%28%43%14%
327
August1st to 15thDay
7%17%30%38%14%
315
16th to endDay
11%18%38%28%11%
332
September1st to 15thDay
13%113%43%21%6%
315
16th to endDay
5%326%44%16%4
165
October1st to 15thDay
17%6%26%28%13%6%
90
16th to endDay
5%6%28%31%18%10%
96
November1st to 15thDay
14%17%27%20%15%4
90
16th to endDay
11%30%34%15%6%2
90
December1st to 15thDay
7%21%38%23%6%2
90
16th to endDay
14%27%39%15%3
96
January1st to 15thNight
422%28%26%14%3
720
16th to endNight
5%26%29%24%11%2
768
February1st to 15thNight
320%35%25%10%4
704
16th to endNight
6%30%37%19%5%1
632
March1st to 15thNight
5%25%28%27%10%1
720
16th to endNight
320%37%27%9%
705
April1st to 15thNight
5%26%37%23%7%
539
16th to endNight
224%39%25%7%
540
May1st to 15thNight
5%16%40%30%6%
540
16th to endNight
411%34%31%16%1
563
June1st to 15thNight
2326%42%25%1
540
16th to endNight
3215%40%35%3
540
July1st to 15thNight
6%16%32%46%5%
510
16th to endNight
5%1221%54%14%
564
August1st to 15thNight
7%1316%50%20%
539
16th to endNight
4424%51%14%
573
September1st to 15thNight
9%26%28%45%7%
540
16th to endNight
9%311%36%33%5%
519
October1st to 15thNight
5%7%24%33%22%6%
637
16th to endNight
5%11%22%30%22%8%
704
November1st to 15thNight
216%25%29%18%7%
739
16th to endNight
5%19%26%27%15%5%
900
December1st to 15thNight
7%21%29%26%12%2
900
16th to endNight
6%27%30%23%8%2
912
Page generated at 2017-09-25 07:02:16. Version ac04

Copyright 2017 A. Danko


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