This page made possible by the sponsorship of: Sonoma County Astronomical Society.

Santa Rosa
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Santa Rosa 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
61%
16016
26%
49145
23%
15979
66%
15979
34%
27965

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
57%
776
18%
2579
18%
776
61%
776
25%
1620
January16th to endNight
55%
832
24%
2704
23%
832
60%
832
27%
1668
February1st to 15thNight
55%
759
25%
2483
24%
758
61%
758
26%
1527
February16th to endNight
48%
684
23%
2089
17%
684
57%
684
27%
1292
March1st to 15thNight
49%
764
15%
2105
12%
764
52%
764
24%
1452
March16th to endNight
44%
768
21%
2106
14%
768
50%
768
29%
1359
April1st to 15thNight
45%
719
23%
1799
11%
719
50%
719
31%
1164
April16th to endNight
52%
720
26%
1800
12%
720
58%
720
42%
1049
May1st to 15thNight
59%
563
27%
1643
18%
563
65%
563
44%
861
May16th to endNight
62%
402
26%
1525
23%
402
69%
402
35%
731
June1st to 15thNight
62%
360
25%
1440
25%
360
70%
360
34%
676
June16th to endNight
79%
360
33%
1440
43%
360
84%
360
54%
543
July1st to 15thNight
86%
384
29%
1404
35%
384
87%
384
54%
560
July16th to endNight
78%
564
31%
1593
29%
531
78%
531
41%
831
August1st to 15thNight
75%
538
29%
1611
25%
535
76%
535
39%
846
August16th to endNight
77%
747
33%
1893
21%
747
78%
747
49%
1063
September1st to 15thNight
82%
720
36%
1800
24%
720
84%
720
55%
962
September16th to endNight
76%
716
39%
1979
34%
716
81%
716
56%
985
October1st to 15thNight
67%
720
29%
2160
29%
720
73%
720
46%
1102
October16th to endNight
69%
768
33%
2304
34%
768
73%
768
40%
1275
November1st to 15thNight
64%
760
25%
2358
25%
760
68%
760
35%
1346
November16th to endNight
58%
780
23%
2688
25%
780
62%
780
28%
1556
December1st to 15thNight
54%
780
21%
2730
20%
780
59%
780
23%
1692
December16th to endNight
49%
832
22%
2912
20%
832
55%
832
24%
1805

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
10%423323346%57%
49483
Night
11%424323346%54%
49333
TransparencyDay
30%38%20%23%13%
49171
Night
32%38%19%21%14%
49146
SeeingDay
12%9%24%30%17%5%
6570
Night
13%413%30%31%7%
16027

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
20%6%24323245%43%
1686
16th to endDay
16%7%35%425%245%42%
1872
February1st to 15thDay
18%5%24423335%46%
1711
16th to endDay
19%7%23423346%40%
1669
March1st to 15thDay
19%7%35%43445%6%35%
2088
16th to endDay
18%5%24434346%40%
2118
April1st to 15thDay
16%5%35%424446%41%
2149
16th to endDay
10%323312348%56%
2160
May1st to 15thDay
7%412213247%62%
2305
16th to endDay
7%5%23223347%58%
2586
June1st to 15thDay
6%413312246%61%
2520
16th to endDay
321112235%75%
2520
July1st to 15thDay
1212311235%74%
2468
16th to endDay
1312212235%73%
2468
August1st to 15thDay
1212312346%70%
2340
16th to endDay
1312312336%69%
2309
September1st to 15thDay
1312212236%70%
2160
16th to endDay
5%212211236%70%
1977
October1st to 15thDay
9%22213345%63%
1800
16th to endDay
10%5%13322336%58%
1920
November1st to 15thDay
11%3145%23347%51%
1831
16th to endDay
15%6%24423335%47%
1602
December1st to 15thDay
20%7%3242233444%
1560
16th to endDay
22%7%34323346%39%
1664
January1st to 15thNight
17%5%2342445%8%40%
2579
16th to endNight
19%424213436%46%
2704
February1st to 15thNight
17%5%24423346%45%
2471
16th to endNight
17%5%24324347%45%
2089
March1st to 15thNight
18%5%25%425%5%5%6%38%
2105
16th to endNight
17%6%24312345%47%
2106
April1st to 15thNight
12%433425%346%48%
1799
16th to endNight
8%423223335%60%
1800
May1st to 15thNight
4324412236%62%
1643
16th to endNight
4414333346%62%
1524
June1st to 15thNight
44233225%37%60%
1440
16th to endNight
32121123476%
1440
July1st to 15thNight
212312335%73%
1488
16th to endNight
241442345%7%60%
1701
August1st to 15thNight
1425%422437%60%
1620
16th to endNight
42441335%8%60%
1893
September1st to 15thNight
1312222247%67%
1800
16th to endNight
422212336%70%
1979
October1st to 15thNight
6%31331233465%
2160
16th to endNight
9%313423347%55%
2304
November1st to 15thNight
11%42432335%7%52%
2358
16th to endNight
15%414323345%50%
2688
December1st to 15thNight
21%5%23323346%43%
2730
16th to endNight
21%5%24323336%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
44%411%17%14%8%
1686
16th to endDay
45%37%14%17%10%
1872
February1st to 15thDay
41%37%20%20%5%
1711
16th to endDay
44%410%24%12%3
1669
March1st to 15thDay
48%5%11%18%12%4
2088
16th to endDay
44%5%12%20%14%2
2118
April1st to 15thDay
43%313%21%15%2
2149
16th to endDay
27%414%27%21%5%
2160
May1st to 15thDay
23%27%33%25%6%
2305
16th to endDay
27%413%29%20%5%
2590
June1st to 15thDay
25%311%23%24%11%
2520
16th to endDay
14%25%18%37%22%
2520
July1st to 15thDay
14%2310%30%37%
2323
16th to endDay
17%2410%28%36%
2313
August1st to 15thDay
17%4214%32%27%
2324
16th to endDay
18%3215%37%22%
2309
September1st to 15thDay
17%2316%32%27%
2160
16th to endDay
17%25%26%30%17%
1977
October1st to 15thDay
24%27%19%26%19%
1800
16th to endDay
29%47%24%22%11%
1920
November1st to 15thDay
32%6%9%30%12%7%
1831
16th to endDay
42%48%20%17%6%
1602
December1st to 15thDay
44%38%15%20%7%
1560
16th to endDay
47%310%16%14%6%
1664
January1st to 15thNight
41%5%12%18%14%8%
2579
16th to endNight
40%310%13%17%13%
2704
February1st to 15thNight
41%37%19%18%9%
2483
16th to endNight
38%412%23%16%3
2089
March1st to 15thNight
46%413%15%15%4
2105
16th to endNight
40%311%21%18%4
2106
April1st to 15thNight
36%414%21%18%4
1799
16th to endNight
27%310%28%21%8%
1800
May1st to 15thNight
25%36%23%30%11%
1644
16th to endNight
24%5%10%30%21%7%
1525
June1st to 15thNight
24%5%9%22%23%14%
1440
16th to endNight
14%25%15%37%25%
1440
July1st to 15thNight
15%227%31%39%
1404
16th to endNight
26%347%22%35%
1593
August1st to 15thNight
27%4311%25%27%
1611
16th to endNight
25%3311%29%27%
1893
September1st to 15thNight
19%3310%31%30%
1800
16th to endNight
18%2323%30%21%
1979
October1st to 15thNight
24%27%19%23%23%
2160
16th to endNight
28%36%21%24%14%
2304
November1st to 15thNight
32%412%29%14%6%
2358
16th to endNight
36%48%22%20%8%
2688
December1st to 15thNight
42%37%16%19%9%
2730
16th to endNight
42%310%16%19%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
33%8%20%19%14%2
224
16th to endDay
19%9%22%26%17%3
304
February1st to 15thDay
20%6%26%22%20%3
281
16th to endDay
19%14%28%22%13%1
281
March1st to 15thDay
26%13%27%17%11%3
312
16th to endDay
20%17%33%20%6%1
288
April1st to 15thDay
18%23%28%20%5%2
269
16th to endDay
15%23%27%22%8%2
270
May1st to 15thDay
11%17%30%28%10%1
288
16th to endDay
12%11%22%29%17%6%
330
June1st to 15thDay
9%14%28%33%10%3
315
16th to endDay
3427%38%21%5%
315
July1st to 15thDay
3218%44%23%7%
305
16th to endDay
1115%51%21%9%
327
August1st to 15thDay
2322%43%21%5%
315
16th to endDay
3123%40%24%6%
332
September1st to 15thDay
4223%41%18%9%
315
16th to endDay
5%8%21%30%24%9%
315
October1st to 15thDay
8%8%26%32%17%6%
315
16th to endDay
14%8%19%28%22%6%
336
November1st to 15thDay
13%7%19%24%27%7%
247
16th to endDay
16%10%29%21%21%3
100
December1st to 15thDay
26%12%16%13%20%11%
90
16th to endDay
16%14%12%23%28%4
96
January1st to 15thNight
18%310%33%26%6%
780
16th to endNight
21%312%29%26%6%
832
February1st to 15thNight
19%5%11%32%26%4
764
16th to endNight
19%7%18%30%20%4
684
March1st to 15thNight
20%6%14%27%26%4
764
16th to endNight
19%6%21%28%20%3
768
April1st to 15thNight
13%10%21%29%20%4
719
16th to endNight
10%10%21%25%25%6%
720
May1st to 15thNight
6%320%32%33%4
564
16th to endNight
7%5%17%31%30%7%
403
June1st to 15thNight
7%5%16%36%32%2
360
16th to endNight
4111%39%39%3
360
July1st to 15thNight
3426%56%8%
384
16th to endNight
5%5%23%51%13%
564
August1st to 15thNight
5%6%26%49%11%
538
16th to endNight
5%8%30%46%8%
747
September1st to 15thNight
37%26%49%11%
720
16th to endNight
5%28%30%39%13%
716
October1st to 15thNight
8%312%33%31%10%
720
16th to endNight
11%28%29%33%14%
768
November1st to 15thNight
14%112%31%31%9%
760
16th to endNight
16%413%28%28%8%
780
December1st to 15thNight
23%411%29%23%7%
780
16th to endNight
24%416%31%20%2
832
Page generated at 2018-03-12 10:28:15. Version ac04

Copyright 2018 A. Danko


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