Yuba City Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Yuba City Astronomical Observatory clear sky chart from 2005-11-06 to 2024-01-14.

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 Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(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

By Month

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 Forecast	Data Points
Cloud Cover	Day	8% 3 1 3 3 2 3 3 4 6% 64%	74737
	Night	10% 3 1 3 3 2 3 3 4 6% 61%	75035
Transparency	Day	23% 4 9% 19% 24% 21%	74452
	Night	25% 5% 9% 19% 23% 20%	74841
Seeing	Day	9% 6% 15% 25% 29% 17%	14045
	Night	10% 4 17% 36% 29% 4	23433

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
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	23% 8% 3 6% 5% 2 4 4 5% 6% 33%	1519
	11th to 20th	Day	17% 7% 2 5% 4 2 3 4 4 6% 47%	1626
	21st to end	Day	17% 6% 3 6% 4 3 4 3 5% 7% 42%	1782
February	1st to 10th	Day	17% 6% 2 4 4 2 3 4 5% 6% 47%	1620
	11th to 20th	Day	13% 4 2 4 4 2 4 4 5% 8% 50%	1656
	21st to end	Day	16% 4 2 4 4 3 4 3 5% 6% 50%	1480
March	1st to 10th	Day	16% 6% 2 5% 5% 3 5% 4 5% 9% 41%	1887
	11th to 20th	Day	18% 6% 2 5% 4 3 4 4 5% 7% 43%	1980
	21st to end	Day	14% 5% 2 5% 5% 3 3 4 5% 7% 48%	2240
April	1st to 10th	Day	12% 5% 3 4 4 2 4 4 5% 8% 49%	2160
	11th to 20th	Day	9% 3 2 3 4 2 3 3 5% 6% 59%	2129
	21st to end	Day	5% 3 2 2 3 2 3 3 4 9% 65%	2160
May	1st to 10th	Day	5% 3 1 3 2 1 3 3 4 6% 69%	2244
	11th to 20th	Day	4 2 1 3 3 2 3 3 5% 8% 67%	2461
	21st to end	Day	4 2 1 2 3 2 3 4 5% 7% 68%	2723
June	1st to 10th	Day	5% 3 1 2 3 1 2 3 5% 7% 67%	2520
	11th to 20th	Day	1 1 2 2 1 2 2 4 5% 82%	2520
	21st to end	Day	2 1 1 1 1 1 2 3 4 85%	2520
July	1st to 10th	Day	1 1 1 1 1 2 4 88%	2520
	11th to 20th	Day	1 1 1 1 1 1 2 3 89%	2504
	21st to end	Day	1 1 1 1 1 1 2 2 4 86%	2546
August	1st to 10th	Day	2 1 1 1 1 1 2 1 2 4 84%	2328
	11th to 20th	Day	1 1 1 1 1 1 1 2 4 87%	2191
	21st to end	Day	1 1 1 1 1 1 1 2 3 90%	2376
September	1st to 10th	Day	1 1 1 1 1 1 2 4 88%	2160
	11th to 20th	Day	2 1 1 2 3 2 2 2 2 6% 77%	2160
	21st to end	Day	3 2 1 2 1 1 1 2 3 5% 79%	1926
October	1st to 10th	Day	3 2 1 2 2 2 2 3 4 5% 74%	1800
	11th to 20th	Day	6% 2 1 2 2 1 3 3 4 6% 70%	1800
	21st to end	Day	9% 2 1 3 3 2 3 3 4 6% 64%	1980
November	1st to 10th	Day	11% 4 1 4 3 3 3 4 5% 8% 54%	1736
	11th to 20th	Day	13% 5% 2 5% 4 3 3 4 5% 7% 50%	1710
	21st to end	Day	11% 5% 1 4 4 2 3 4 5% 6% 55%	1531
December	1st to 10th	Day	16% 6% 2 6% 5% 2 3 3 4 6% 46%	1520
	11th to 20th	Day	28% 8% 4 7% 5% 3 4 3 5% 5% 29%	1928
	21st to end	Day	19% 8% 3 6% 5% 4 5% 5% 5% 7% 32%	2794
January	1st to 10th	Night	19% 6% 2 5% 4 2 4 4 4 9% 41%	2646
	11th to 20th	Night	15% 5% 2 5% 4 2 4 5% 4 6% 48%	2409
	21st to end	Night	16% 5% 2 4 4 3 3 3 4 6% 49%	2574
February	1st to 10th	Night	16% 5% 1 3 4 3 4 3 4 6% 51%	2340
	11th to 20th	Night	12% 4 2 4 3 3 4 4 6% 8% 51%	2189
	21st to end	Night	16% 4 2 3 4 2 3 4 5% 5% 53%	1776
March	1st to 10th	Night	16% 6% 2 6% 5% 3 5% 4 4 6% 42%	2070
	11th to 20th	Night	16% 5% 2 4 4 2 4 4 5% 9% 46%	1980
	21st to end	Night	15% 4 1 3 3 3 4 4 4 6% 52%	2116
April	1st to 10th	Night	9% 5% 2 5% 4 2 5% 4 5% 6% 53%	1800
	11th to 20th	Night	9% 2 2 3 3 2 4 3 4 8% 60%	1779
	21st to end	Night	6% 2 1 2 2 2 3 3 4 8% 68%	1800
May	1st to 10th	Night	5% 2 1 2 3 1 3 4 4 7% 68%	1712
	11th to 20th	Night	4 2 1 2 3 2 3 3 5% 7% 69%	1430
	21st to end	Night	4 2 1 2 3 1 3 3 6% 7% 68%	1552
June	1st to 10th	Night	5% 2 1 2 2 1 3 4 4 6% 70%	1440
	11th to 20th	Night	1 1 1 1 2 2 3 6% 81%	1440
	21st to end	Night	1 1 1 1 2 1 2 2 3 3 83%	1440
July	1st to 10th	Night	1 1 2 1 2 2 90%	1440
	11th to 20th	Night	1 1 1 1 1 1 1 1 3 89%	1451
	21st to end	Night	1 1 1 1 1 1 1 1 3 4 86%	1773
August	1st to 10th	Night	2 2 1 1 2 1 2 1 2 3 82%	1611
	11th to 20th	Night	1 1 1 1 1 1 3 2 4 85%	1708
	21st to end	Night	1 1 1 1 1 1 1 2 3 88%	1980
September	1st to 10th	Night	1 1 1 1 1 1 1 1 3 89%	1800
	11th to 20th	Night	3 2 1 2 1 1 2 2 3 5% 78%	1800
	21st to end	Night	2 1 1 1 1 2 3 3 6% 81%	2029
October	1st to 10th	Night	4 2 1 2 3 1 2 3 3 4 76%	2160
	11th to 20th	Night	4 2 1 2 2 1 3 3 4 6% 72%	2160
	21st to end	Night	7% 2 1 2 3 2 2 3 3 6% 70%	2376
November	1st to 10th	Night	11% 3 2 3 3 2 4 3 5% 7% 58%	2341
	11th to 20th	Night	10% 3 2 3 4 2 4 4 6% 6% 57%	2470
	21st to end	Night	11% 4 2 4 4 2 4 4 4 6% 57%	2645
December	1st to 10th	Night	17% 5% 2 4 3 2 3 4 4 7% 49%	2660
	11th to 20th	Night	28% 6% 2 4 4 2 3 4 6% 7% 33%	3276
	21st to end	Night	20% 6% 3 6% 7% 4 5% 5% 5% 5% 33%	4862

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	53% 6% 11% 18% 9% 3	1519
	11th to 20th	Day	39% 5% 11% 15% 18% 11%	1626
	21st to end	Day	42% 6% 10% 16% 19% 7%	1782
February	1st to 10th	Day	38% 5% 10% 19% 19% 8%	1620
	11th to 20th	Day	33% 5% 11% 21% 22% 8%	1665
	21st to end	Day	37% 4 10% 23% 19% 7%	1480
March	1st to 10th	Day	42% 6% 13% 20% 15% 6%	1887
	11th to 20th	Day	42% 5% 10% 21% 16% 7%	1980
	21st to end	Day	37% 6% 13% 19% 20% 5%	2240
April	1st to 10th	Day	35% 6% 10% 23% 18% 8%	2160
	11th to 20th	Day	27% 5% 11% 24% 24% 10%	2132
	21st to end	Day	19% 5% 13% 28% 27% 8%	2160
May	1st to 10th	Day	17% 5% 11% 25% 29% 14%	2244
	11th to 20th	Day	18% 4 9% 28% 29% 12%	2464
	21st to end	Day	17% 5% 15% 30% 23% 10%	2724
June	1st to 10th	Day	17% 4 11% 27% 27% 14%	2520
	11th to 20th	Day	8% 2 9% 22% 31% 29%	2520
	21st to end	Day	6% 2 4 13% 36% 38%	2520
July	1st to 10th	Day	5% 2 4 9% 29% 52%	2451
	11th to 20th	Day	5% 1 3 12% 27% 52%	2429
	21st to end	Day	6% 2 3 9% 24% 56%	2405
August	1st to 10th	Day	8% 2 3 12% 31% 44%	2312
	11th to 20th	Day	6% 1 3 11% 33% 46%	2191
	21st to end	Day	4 1 3 13% 34% 45%	2376
September	1st to 10th	Day	5% 1 4 9% 27% 55%	2160
	11th to 20th	Day	12% 2 6% 21% 38% 21%	2160
	21st to end	Day	11% 2 5% 20% 31% 31%	1926
October	1st to 10th	Day	14% 4 6% 18% 30% 28%	1800
	11th to 20th	Day	17% 4 8% 20% 23% 28%	1800
	21st to end	Day	22% 3 8% 20% 27% 19%	1980
November	1st to 10th	Day	27% 5% 10% 25% 21% 12%	1736
	11th to 20th	Day	33% 5% 11% 24% 19% 7%	1710
	21st to end	Day	30% 6% 11% 22% 20% 11%	1531
December	1st to 10th	Day	38% 5% 9% 22% 18% 8%	1520
	11th to 20th	Day	58% 5% 9% 11% 14% 4	1928
	21st to end	Day	46% 12% 14% 16% 10% 3	2794
January	1st to 10th	Night	42% 6% 13% 23% 10% 6%	2646
	11th to 20th	Night	37% 7% 11% 16% 15% 13%	2409
	21st to end	Night	38% 4 12% 16% 21% 9%	2574
February	1st to 10th	Night	35% 5% 8% 20% 20% 12%	2340
	11th to 20th	Night	31% 6% 10% 21% 23% 9%	2191
	21st to end	Night	33% 5% 9% 24% 21% 9%	1776
March	1st to 10th	Night	43% 7% 11% 18% 17% 5%	2070
	11th to 20th	Night	36% 5% 10% 21% 19% 8%	1980
	21st to end	Night	33% 6% 13% 21% 19% 7%	2116
April	1st to 10th	Night	31% 7% 12% 18% 21% 9%	1800
	11th to 20th	Night	24% 5% 12% 27% 20% 12%	1779
	21st to end	Night	18% 5% 13% 28% 28% 8%	1800
May	1st to 10th	Night	16% 5% 10% 23% 31% 15%	1712
	11th to 20th	Night	17% 4 10% 30% 23% 15%	1430
	21st to end	Night	15% 5% 15% 28% 27% 10%	1552
June	1st to 10th	Night	16% 4 13% 25% 29% 13%	1440
	11th to 20th	Night	8% 2 7% 22% 30% 30%	1440
	21st to end	Night	9% 2 4 12% 31% 43%	1440
July	1st to 10th	Night	5% 1 2 10% 29% 53%	1400
	11th to 20th	Night	5% 1 3 11% 23% 57%	1403
	21st to end	Night	6% 2 2 10% 23% 58%	1674
August	1st to 10th	Night	11% 1 2 13% 29% 44%	1602
	11th to 20th	Night	6% 1 3 10% 32% 48%	1708
	21st to end	Night	5% 1 3 11% 32% 49%	1980
September	1st to 10th	Night	6% 1 2 7% 30% 54%	1800
	11th to 20th	Night	11% 3 5% 18% 37% 26%	1800
	21st to end	Night	8% 2 5% 18% 30% 37%	2029
October	1st to 10th	Night	14% 3 7% 16% 28% 31%	2160
	11th to 20th	Night	14% 3 8% 17% 28% 31%	2160
	21st to end	Night	18% 3 7% 20% 26% 25%	2376
November	1st to 10th	Night	27% 5% 9% 23% 20% 15%	2341
	11th to 20th	Night	26% 6% 12% 25% 22% 9%	2470
	21st to end	Night	29% 5% 8% 22% 23% 13%	2645
December	1st to 10th	Night	35% 7% 11% 18% 18% 10%	2660
	11th to 20th	Night	50% 5% 9% 15% 16% 4	3276
	21st to end	Night	48% 10% 12% 16% 11% 4	4862

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
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	42% 6% 16% 20% 16% 1	180
	11th to 20th	Day	23% 7% 19% 23% 20% 9%	328
	21st to end	Day	17% 6% 18% 24% 21% 14%	374
February	1st to 10th	Day	19% 11% 14% 19% 26% 11%	340
	11th to 20th	Day	18% 11% 23% 20% 19% 9%	371
	21st to end	Day	15% 13% 18% 27% 20% 6%	346
March	1st to 10th	Day	18% 13% 26% 25% 11% 6%	420
	11th to 20th	Day	22% 11% 17% 22% 17% 11%	420
	21st to end	Day	17% 13% 23% 24% 18% 5%	462
April	1st to 10th	Day	16% 9% 22% 26% 18% 9%	420
	11th to 20th	Day	12% 9% 25% 27% 15% 12%	412
	21st to end	Day	5% 8% 18% 29% 25% 14%	420
May	1st to 10th	Day	5% 8% 26% 25% 24% 11%	423
	11th to 20th	Day	7% 6% 23% 25% 23% 16%	448
	21st to end	Day	5% 6% 16% 24% 27% 22%	485
June	1st to 10th	Day	4 5% 16% 25% 32% 18%	450
	11th to 20th	Day	1 5% 16% 29% 35% 14%	450
	21st to end	Day	1 3 10% 28% 38% 20%	450
July	1st to 10th	Day	1 6% 32% 42% 18%	446
	11th to 20th	Day	5% 27% 43% 25%	444
	21st to end	Day	1 1 5% 26% 42% 25%	487
August	1st to 10th	Day	1 1 5% 29% 42% 22%	447
	11th to 20th	Day	1 1 7% 22% 42% 28%	437
	21st to end	Day	1 1 4 23% 42% 29%	495
September	1st to 10th	Day	2 1 7% 22% 44% 25%	450
	11th to 20th	Day	3 4 13% 23% 31% 25%	450
	21st to end	Day	2 3 16% 28% 30% 21%	450
October	1st to 10th	Day	3 6% 18% 21% 28% 24%	450
	11th to 20th	Day	5% 6% 14% 20% 31% 23%	450
	21st to end	Day	9% 9% 13% 22% 29% 18%	495
November	1st to 10th	Day	12% 7% 14% 22% 27% 18%	332
	11th to 20th	Day	13% 4 14% 25% 30% 14%	270
	21st to end	Day	12% 3 17% 28% 29% 11%	185
December	1st to 10th	Day	23% 7% 17% 19% 21% 13%	180
	11th to 20th	Day	19% 4 17% 29% 18% 13%	180
	21st to end	Day	23% 11% 18% 22% 23% 3	198
January	1st to 10th	Night	21% 3 17% 32% 22% 4	760
	11th to 20th	Night	17% 6% 15% 37% 22% 4	736
	21st to end	Night	18% 5% 15% 33% 25% 5%	792
February	1st to 10th	Night	17% 5% 15% 34% 25% 3	720
	11th to 20th	Night	14% 5% 22% 33% 23% 3	704
	21st to end	Night	17% 7% 21% 34% 18% 2	592
March	1st to 10th	Night	18% 7% 20% 31% 22% 3	720
	11th to 20th	Night	17% 7% 18% 30% 26% 2	720
	21st to end	Night	16% 6% 24% 34% 19% 1	792
April	1st to 10th	Night	11% 4 24% 37% 22% 2	720
	11th to 20th	Night	11% 5% 24% 32% 24% 4	711
	21st to end	Night	7% 5% 19% 40% 26% 3	720
May	1st to 10th	Night	6% 4 25% 38% 24% 3	632
	11th to 20th	Night	4 3 23% 42% 26% 1	368
	21st to end	Night	4 5% 19% 42% 29% 1	389
June	1st to 10th	Night	6% 2 22% 41% 27% 1	360
	11th to 20th	Night	1 2 25% 47% 24% 1	360
	21st to end	Night	2 2 19% 43% 33% 1	360
July	1st to 10th	Night	1 1 15% 51% 30% 1	350
	11th to 20th	Night	1 15% 57% 27% 1	359
	21st to end	Night	1 1 13% 43% 41% 2	591
August	1st to 10th	Night	2 1 17% 43% 34% 2	537
	11th to 20th	Night	1 11% 43% 42% 3	640
	21st to end	Night	1 7% 44% 47% 2	792
September	1st to 10th	Night	1 1 8% 36% 50% 4	720
	11th to 20th	Night	3 2 14% 35% 40% 6%	720
	21st to end	Night	3 2 15% 34% 39% 8%	720
October	1st to 10th	Night	4 3 15% 36% 34% 7%	720
	11th to 20th	Night	5% 3 13% 36% 38% 5%	720
	21st to end	Night	6% 5% 12% 35% 32% 9%	792
November	1st to 10th	Night	11% 4 16% 30% 32% 6%	740
	11th to 20th	Night	11% 1 16% 38% 30% 4	760
	21st to end	Night	11% 4 15% 38% 27% 4	760
December	1st to 10th	Night	18% 4 18% 32% 21% 7%	760
	11th to 20th	Night	26% 4 14% 29% 24% 3	760
	21st to end	Night	23% 5% 19% 31% 21% 2	836

Page generated at 2024-01-11 10:32:02. Version ac07

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