Sacramento
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sacramento clear sky chart from 2005-11-05 to 2018-02-14.

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
67%
15860
29%
48830
25%
15824
72%
15824
44%
25309

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
58%
776
17%
2651
17%
776
62%
776
29%
1560
January16th to endNight
60%
832
24%
2704
24%
832
64%
832
28%
1653
February1st to 15thNight
59%
752
26%
2463
25%
752
64%
752
29%
1468
February16th to endNight
56%
632
26%
1895
23%
632
63%
632
32%
1144
March1st to 15thNight
57%
720
17%
2043
16%
720
59%
720
29%
1314
March16th to endNight
53%
768
22%
2067
15%
768
59%
768
34%
1277
April1st to 15thNight
56%
719
23%
1799
12%
719
61%
719
37%
1148
April16th to endNight
62%
720
27%
1800
12%
720
67%
720
52%
999
May1st to 15thNight
68%
579
31%
1659
22%
579
73%
579
62%
755
May16th to endNight
70%
374
30%
1496
32%
374
76%
374
53%
565
June1st to 15thNight
71%
360
28%
1440
30%
360
80%
360
53%
553
June16th to endNight
81%
360
37%
1440
46%
360
87%
360
68%
467
July1st to 15thNight
89%
340
36%
1360
44%
340
93%
340
77%
408
July16th to endNight
88%
526
40%
1555
37%
493
90%
493
76%
584
August1st to 15thNight
81%
562
39%
1635
29%
559
84%
559
73%
665
August16th to endNight
86%
764
45%
1910
28%
764
88%
764
82%
856
September1st to 15thNight
86%
720
41%
1800
28%
720
89%
720
79%
815
September16th to endNight
81%
716
45%
1950
38%
716
86%
716
73%
861
October1st to 15thNight
73%
720
32%
2160
31%
720
79%
720
56%
1007
October16th to endNight
74%
768
38%
2304
38%
768
79%
768
52%
1113
November1st to 15thNight
68%
760
27%
2424
26%
760
73%
760
42%
1259
November16th to endNight
62%
780
25%
2633
26%
780
66%
780
33%
1451
December1st to 15thNight
58%
780
22%
2730
21%
780
64%
780
28%
1594
December16th to endNight
49%
832
22%
2912
19%
832
57%
832
24%
1793

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
8%313212336%62%
49250
Night
9%313212346%62%
49014
TransparencyDay
24%38%19%24%19%
48933
Night
24%49%19%23%18%
48831
SeeingDay
9%415%25%29%15%
6354
Night
10%215%39%29%3
15874

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%6%34424446%39%
1614
16th to endDay
17%8%25%424345%41%
1872
February1st to 15thDay
17%435%5%23336%44%
1700
16th to endDay
17%6%24423439%41%
1579
March1st to 15thDay
15%6%25%42446%7%40%
1915
16th to endDay
13%5%25%4245%5%6%43%
2157
April1st to 15thDay
13%5%244245%5%8%43%
2149
16th to endDay
7%311223245%63%
2160
May1st to 15thDay
332212336%71%
2289
16th to endDay
4313322346%63%
2615
June1st to 15thDay
432212245%69%
2520
16th to endDay
1111113483%
2520
July1st to 15thDay
1122386%
2520
16th to endDay
1112485%
2504
August1st to 15thDay
11111112483%
2313
16th to endDay
111112484%
2292
September1st to 15thDay
111123482%
2160
16th to endDay
221111225%76%
2007
October1st to 15thDay
3112213246%69%
1800
16th to endDay
7%32421334462%
1920
November1st to 15thDay
10%412324448%52%
1764
16th to endDay
13%6%25%42435%7%45%
1656
December1st to 15thDay
16%7%37%422336%41%
1560
16th to endDay
19%6%25%42345%6%39%
1664
January1st to 15thNight
15%5%25%323347%47%
2651
16th to endNight
15%414324447%46%
2704
February1st to 15thNight
15%4232235%46%48%
2451
16th to endNight
16%423323447%48%
1895
March1st to 15thNight
17%424323448%44%
2043
16th to endNight
14%423333347%50%
2067
April1st to 15thNight
9%425%42445%6%50%
1799
16th to endNight
7%212212347%64%
1800
May1st to 15thNight
311113237%71%
1659
16th to endNight
311213247%69%
1496
June1st to 15thNight
321112223475%
1440
16th to endNight
1111112384%
1440
July1st to 15thNight
11111288%
1440
16th to endNight
1111112484%
1662
August1st to 15thNight
11121122481%
1644
16th to endNight
111125%83%
1910
September1st to 15thNight
1111112483%
1800
16th to endNight
1121222480%
1950
October1st to 15thNight
5%112211246%70%
2160
16th to endNight
4213312347%66%
2304
November1st to 15thNight
9%31321235%8%57%
2424
16th to endNight
12%424222345%55%
2633
December1st to 15thNight
18%413322247%49%
2730
16th to endNight
20%5%14223446%44%
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
45%5%12%14%18%3
1614
16th to endDay
46%48%16%15%8%
1872
February1st to 15thDay
41%410%22%16%5%
1700
16th to endDay
41%5%11%25%13%3
1579
March1st to 15thDay
41%5%13%20%13%5%
1915
16th to endDay
40%6%14%18%17%3
2157
April1st to 15thDay
38%6%11%22%16%4
2149
16th to endDay
22%5%13%23%26%8%
2160
May1st to 15thDay
16%28%26%33%12%
2289
16th to endDay
20%412%27%24%9%
2619
June1st to 15thDay
18%39%23%24%20%
2520
16th to endDay
7%1415%37%33%
2520
July1st to 15thDay
5%1210%27%52%
2371
16th to endDay
6%1213%23%53%
2348
August1st to 15thDay
8%1312%31%43%
2297
16th to endDay
6%1215%36%37%
2292
September1st to 15thDay
8%1413%35%37%
2160
16th to endDay
12%26%20%36%21%
2007
October1st to 15thDay
15%39%20%27%23%
1800
16th to endDay
24%310%23%25%13%
1920
November1st to 15thDay
30%413%28%17%4
1764
16th to endDay
38%6%11%23%16%4
1656
December1st to 15thDay
45%49%17%18%5%
1560
16th to endDay
44%5%11%18%15%4
1664
January1st to 15thNight
37%414%20%16%6%
2651
16th to endNight
37%5%10%16%16%12%
2704
February1st to 15thNight
36%5%8%21%19%8%
2463
16th to endNight
34%5%10%25%19%3
1895
March1st to 15thNight
38%6%13%18%16%7%
2043
16th to endNight
33%5%11%21%20%6%
2067
April1st to 15thNight
33%5%12%22%18%6%
1799
16th to endNight
20%5%13%23%26%10%
1800
May1st to 15thNight
12%311%24%31%15%
1660
16th to endNight
14%314%33%22%12%
1496
June1st to 15thNight
14%311%25%25%20%
1440
16th to endNight
8%2313%33%38%
1440
July1st to 15thNight
6%28%28%54%
1360
16th to endNight
8%210%23%54%
1555
August1st to 15thNight
9%1213%27%46%
1635
16th to endNight
7%211%36%41%
1910
September1st to 15thNight
7%1411%34%39%
1800
16th to endNight
9%15%20%36%26%
1950
October1st to 15thNight
15%47%19%26%26%
2160
16th to endNight
18%38%22%27%19%
2304
November1st to 15thNight
24%413%27%20%8%
2424
16th to endNight
30%5%8%24%23%7%
2633
December1st to 15thNight
36%5%10%19%20%8%
2730
16th to endNight
41%410%18%18%6%
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
29%216%24%18%8%
152
16th to endDay
18%419%20%20%17%
304
February1st to 15thDay
19%5%15%16%27%15%
277
16th to endDay
19%8%16%23%19%12%
238
March1st to 15thDay
17%9%22%15%22%12%
270
16th to endDay
17%10%19%21%21%9%
288
April1st to 15thDay
16%10%22%23%14%12%
269
16th to endDay
7%12%20%28%20%11%
270
May1st to 15thDay
6%321%31%23%12%
288
16th to endDay
4416%24%30%18%
330
June1st to 15thDay
6%321%28%28%11%
315
16th to endDay
12%29%41%15%
315
July1st to 15thDay
7%34%41%15%
305
16th to endDay
9%31%40%17%
327
August1st to 15thDay
29%33%39%14%
315
16th to endDay
7%26%44%20%
332
September1st to 15thDay
18%28%39%22%
315
16th to endDay
2216%25%27%26%
315
October1st to 15thDay
46%18%23%25%20%
315
16th to endDay
8%311%22%29%22%
336
November1st to 15thDay
17%111%18%33%16%
180
16th to endDay
19%110%35%26%5%
112
December1st to 15thDay
22%7%10%20%24%15%
90
16th to endDay
15%413%27%30%9%
96
January1st to 15thNight
17%212%31%31%4
780
16th to endNight
18%211%34%27%5%
832
February1st to 15thNight
17%313%36%26%3
760
16th to endNight
16%5%17%35%21%3
632
March1st to 15thNight
16%415%33%27%2
720
16th to endNight
15%321%34%23%1
768
April1st to 15thNight
9%421%39%22%2
719
16th to endNight
7%324%36%25%2
720
May1st to 15thNight
422%46%23%2
580
16th to endNight
4121%46%25%
375
June1st to 15thNight
4120%51%22%
360
16th to endNight
113%54%29%
360
July1st to 15thNight
7%62%28%
340
16th to endNight
7%53%35%1
526
August1st to 15thNight
111%53%31%1
562
16th to endNight
19%47%40%1
764
September1st to 15thNight
18%41%45%2
720
16th to endNight
213%37%38%7%
716
October1st to 15thNight
5%213%41%30%6%
720
16th to endNight
5%112%33%36%9%
768
November1st to 15thNight
10%114%35%34%4
760
16th to endNight
13%215%38%25%5%
780
December1st to 15thNight
19%313%32%23%6%
780
16th to endNight
21%417%28%25%1
832
Page generated at 2018-02-15 07:58:47. Version ac04

Copyright 2018 A. Danko


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