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 2024-11-25.

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% 4 1 3 2 2 2 2 4 5% 66%	105363
	Night	10% 4 1 4 3 3 3 2 4 5% 62%	102852
Transparency	Day	22% 4 7% 18% 24% 25%	105118
	Night	25% 5% 8% 18% 22% 22%	102686
Seeing	Day	9% 6% 15% 25% 28% 17%	15249
	Night	10% 4 17% 37% 29% 3	24524

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% 10% 3 7% 4 4 4 3 4 5% 33%	2539
	11th to 20th	Day	23% 13% 3 9% 4 3 3 3 4 5% 32%	2825
	21st to end	Day	25% 9% 4 9% 4 5% 4 3 4 5% 29%	3146
February	1st to 10th	Day	18% 7% 2 4 3 3 3 4 5% 6% 45%	1710
	11th to 20th	Day	14% 5% 1 5% 4 3 4 4 5% 7% 47%	1750
	21st to end	Day	15% 5% 2 5% 3 4 4 3 5% 6% 49%	1570
March	1st to 10th	Day	17% 9% 3 8% 5% 5% 4 4 5% 6% 34%	3290
	11th to 20th	Day	12% 4 2 4 3 3 3 3 4 6% 57%	3490
	21st to end	Day	15% 7% 2 6% 5% 5% 4 4 6% 6% 40%	3938
April	1st to 10th	Day	11% 6% 2 5% 4 3 3 3 5% 7% 50%	2280
	11th to 20th	Day	9% 4 2 4 4 3 3 3 5% 6% 58%	2249
	21st to end	Day	4 4 1 3 2 3 3 2 4 8% 65%	2280
May	1st to 10th	Day	5% 2 2 1 1 2 2 3 5% 76%	3949
	11th to 20th	Day	2 2 1 2 2 1 2 1 3 5% 79%	4361
	21st to end	Day	2 2 1 2 1 2 2 2 3 5% 77%	4813
June	1st to 10th	Day	4 3 1 3 2 2 2 3 5% 7% 67%	2660
	11th to 20th	Day	1 1 2 1 2 1 1 4 5% 82%	2660
	21st to end	Day	2 1 1 1 1 1 2 3 3 85%	2660
July	1st to 10th	Day	1 1 1 1 1 1 2 93%	4420
	11th to 20th	Day	1 1 1 1 1 2 1 2 3 86%	4391
	21st to end	Day	1 1 1 1 1 2 4 88%	4455
August	1st to 10th	Day	2 2 1 2 1 2 2 2 4 5% 78%	4091
	11th to 20th	Day	1 1 1 1 1 1 1 2 3 90%	3841
	21st to end	Day	1 1 1 1 1 1 1 2 3 89%	4180
September	1st to 10th	Day	1 1 1 1 1 1 2 4 88%	2280
	11th to 20th	Day	2 1 1 3 2 2 2 1 2 6% 77%	2280
	21st to end	Day	3 2 1 2 1 1 1 1 3 5% 80%	2032
October	1st to 10th	Day	2 2 1 2 2 2 2 2 4 4 78%	3180
	11th to 20th	Day	5% 3 1 3 2 2 2 3 4 6% 70%	3161
	21st to end	Day	5% 3 1 3 3 4 4 3 5% 6% 63%	3448
November	1st to 10th	Day	10% 4 1 4 3 3 3 4 5% 9% 55%	1829
	11th to 20th	Day	13% 5% 2 6% 3 4 3 3 5% 7% 49%	1800
	21st to end	Day	12% 5% 1 5% 3 3 3 3 5% 5% 54%	1563
December	1st to 10th	Day	16% 6% 2 6% 4 3 3 2 5% 6% 46%	1520
	11th to 20th	Day	28% 9% 3 8% 4 4 4 3 5% 5% 29%	1928
	21st to end	Day	19% 8% 3 7% 4 5% 6% 3 6% 7% 32%	2794
January	1st to 10th	Night	16% 7% 3 8% 4 4 4 3 4 7% 39%	4406
	11th to 20th	Night	23% 8% 3 8% 4 4 4 4 4 4 35%	4141
	21st to end	Night	24% 9% 3 7% 4 4 4 3 4 5% 33%	4521
February	1st to 10th	Night	16% 5% 1 4 3 4 4 3 4 6% 49%	2470
	11th to 20th	Night	13% 4 2 4 3 3 4 4 6% 8% 50%	2315
	21st to end	Night	15% 4 1 4 4 2 3 3 5% 5% 53%	1884
March	1st to 10th	Night	18% 8% 3 7% 4 4 4 3 4 6% 39%	3581
	11th to 20th	Night	15% 5% 1 3 2 2 2 2 4 5% 58%	3490
	21st to end	Night	16% 6% 2 6% 4 5% 5% 4 5% 7% 42%	3715
April	1st to 10th	Night	8% 5% 2 5% 4 3 4 3 5% 6% 54%	1900
	11th to 20th	Night	9% 3 1 4 3 3 3 3 4 7% 60%	1879
	21st to end	Night	5% 2 1 3 2 2 3 3 4 7% 68%	1900
May	1st to 10th	Night	3 2 1 2 2 2 3 2 4 6% 74%	3022
	11th to 20th	Night	2 1 1 1 1 2 2 2 3 4 81%	2530
	21st to end	Night	2 2 1 2 1 1 2 2 4 5% 80%	2762
June	1st to 10th	Night	5% 2 1 3 2 2 3 3 4 6% 70%	1520
	11th to 20th	Night	1 1 1 2 2 2 3 6% 82%	1520
	21st to end	Night	1 1 1 2 2 2 1 2 3 3 83%	1520
July	1st to 10th	Night	1 1 1 1 1 94%	2540
	11th to 20th	Night	1 1 2 1 2 2 1 2 3 85%	2565
	21st to end	Night	1 1 1 1 1 1 2 4 88%	3109
August	1st to 10th	Night	3 3 1 2 2 2 2 2 3 4 77%	2848
	11th to 20th	Night	1 1 1 1 1 1 2 90%	3002
	21st to end	Night	2 1 1 1 1 1 1 1 1 2 89%	3498
September	1st to 10th	Night	1 1 1 1 1 1 1 1 3 89%	1900
	11th to 20th	Night	3 2 3 1 2 2 2 3 5% 77%	1900
	21st to end	Night	2 1 1 1 1 2 2 3 5% 82%	2143
October	1st to 10th	Night	2 2 1 2 2 2 2 2 3 3 79%	3800
	11th to 20th	Night	2 2 1 2 2 2 2 2 4 5% 77%	3777
	21st to end	Night	7% 2 1 2 3 3 3 3 4 7% 66%	4121
November	1st to 10th	Night	11% 3 1 4 3 3 4 3 5% 7% 58%	2468
	11th to 20th	Night	10% 3 1 4 3 3 4 3 6% 7% 56%	2600
	21st to end	Night	12% 5% 2 4 3 3 3 3 4 5% 56%	2707
December	1st to 10th	Night	17% 5% 2 5% 3 3 3 3 4 7% 49%	2660
	11th to 20th	Night	28% 7% 2 5% 4 3 3 3 6% 7% 33%	3276
	21st to end	Night	20% 7% 3 7% 6% 5% 5% 4 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	52% 7% 11% 22% 7% 2	2539
	11th to 20th	Day	56% 5% 9% 13% 11% 7%	2825
	21st to end	Day	55% 8% 10% 13% 11% 4	3146
February	1st to 10th	Day	39% 5% 10% 19% 19% 8%	1710
	11th to 20th	Day	35% 6% 11% 20% 21% 7%	1759
	21st to end	Day	36% 5% 10% 24% 18% 6%	1570
March	1st to 10th	Day	49% 9% 11% 14% 14% 4	3290
	11th to 20th	Day	29% 6% 10% 24% 19% 12%	3490
	21st to end	Day	41% 10% 13% 20% 14% 3	3938
April	1st to 10th	Day	34% 6% 10% 24% 18% 7%	2280
	11th to 20th	Day	27% 5% 12% 24% 23% 9%	2252
	21st to end	Day	19% 5% 13% 28% 27% 8%	2280
May	1st to 10th	Day	13% 4 9% 28% 25% 22%	3949
	11th to 20th	Day	10% 3 6% 24% 37% 20%	4364
	21st to end	Day	10% 4 11% 33% 29% 14%	4814
June	1st to 10th	Day	17% 4 11% 27% 27% 14%	2660
	11th to 20th	Day	8% 2 8% 21% 32% 29%	2660
	21st to end	Day	6% 2 4 12% 36% 40%	2660
July	1st to 10th	Day	3 1 2 5% 16% 73%	4351
	11th to 20th	Day	6% 1 2 7% 18% 66%	4316
	21st to end	Day	4 1 2 7% 25% 61%	4315
August	1st to 10th	Day	10% 2 2 8% 25% 53%	4076
	11th to 20th	Day	4 1 2 9% 40% 44%	3880
	21st to end	Day	6% 1 2 13% 39% 39%	4179
September	1st to 10th	Day	4 1 4 8% 28% 55%	2280
	11th to 20th	Day	13% 2 6% 22% 38% 20%	2280
	21st to end	Day	10% 2 5% 19% 32% 32%	2032
October	1st to 10th	Day	11% 3 4 12% 26% 44%	3180
	11th to 20th	Day	17% 3 6% 24% 29% 21%	3161
	21st to end	Day	23% 2 8% 22% 31% 14%	3448
November	1st to 10th	Day	26% 4 10% 26% 22% 12%	1829
	11th to 20th	Day	34% 5% 12% 24% 18% 7%	1800
	21st to end	Day	31% 6% 11% 21% 20% 10%	1563
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	41% 11% 14% 23% 8% 3	4406
	11th to 20th	Night	50% 9% 11% 11% 11% 8%	4141
	21st to end	Night	53% 6% 12% 12% 12% 5%	4521
February	1st to 10th	Night	36% 5% 9% 20% 19% 11%	2470
	11th to 20th	Night	32% 6% 10% 21% 22% 8%	2317
	21st to end	Night	32% 5% 9% 25% 20% 9%	1884
March	1st to 10th	Night	45% 9% 13% 15% 15% 3	3581
	11th to 20th	Night	28% 5% 8% 21% 24% 14%	3490
	21st to end	Night	39% 8% 15% 22% 12% 4	3715
April	1st to 10th	Night	30% 7% 12% 20% 22% 9%	1900
	11th to 20th	Night	25% 5% 12% 28% 19% 11%	1879
	21st to end	Night	17% 4 13% 29% 27% 8%	1900
May	1st to 10th	Night	12% 5% 12% 23% 28% 21%	3022
	11th to 20th	Night	9% 2 6% 24% 35% 23%	2530
	21st to end	Night	9% 3 11% 36% 26% 16%	2762
June	1st to 10th	Night	16% 4 12% 26% 29% 13%	1520
	11th to 20th	Night	8% 2 7% 21% 32% 30%	1520
	21st to end	Night	8% 2 4 11% 31% 44%	1520
July	1st to 10th	Night	3 1 1 6% 16% 74%	2500
	11th to 20th	Night	8% 1 1 7% 16% 67%	2517
	21st to end	Night	4 1 1 6% 25% 62%	3011
August	1st to 10th	Night	13% 1 1 8% 25% 52%	2839
	11th to 20th	Night	4 1 2 7% 40% 47%	3029
	21st to end	Night	7% 1 2 10% 36% 45%	3498
September	1st to 10th	Night	6% 1 2 7% 30% 55%	1900
	11th to 20th	Night	12% 2 5% 19% 37% 25%	1900
	21st to end	Night	7% 2 5% 17% 30% 38%	2143
October	1st to 10th	Night	12% 2 4 10% 20% 52%	3800
	11th to 20th	Night	12% 2 7% 27% 28% 24%	3777
	21st to end	Night	20% 3 5% 21% 30% 21%	4121
November	1st to 10th	Night	27% 5% 9% 23% 20% 15%	2468
	11th to 20th	Night	26% 6% 13% 25% 21% 9%	2600
	21st to end	Night	31% 5% 7% 22% 23% 13%	2707
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	22% 6% 21% 23% 19% 9%	348
	21st to end	Day	18% 6% 18% 23% 21% 13%	407
February	1st to 10th	Day	20% 11% 14% 20% 25% 11%	370
	11th to 20th	Day	19% 11% 23% 20% 18% 9%	405
	21st to end	Day	14% 13% 18% 29% 20% 7%	382
March	1st to 10th	Day	19% 14% 27% 23% 11% 6%	460
	11th to 20th	Day	20% 12% 17% 21% 17% 12%	460
	21st to end	Day	17% 13% 24% 25% 17% 4	506
April	1st to 10th	Day	15% 9% 22% 25% 18% 10%	460
	11th to 20th	Day	12% 9% 24% 26% 17% 13%	452
	21st to end	Day	5% 8% 19% 29% 24% 16%	460
May	1st to 10th	Day	6% 9% 26% 26% 23% 10%	463
	11th to 20th	Day	7% 5% 21% 25% 24% 18%	488
	21st to end	Day	5% 5% 16% 26% 26% 22%	529
June	1st to 10th	Day	3 4 16% 26% 32% 18%	490
	11th to 20th	Day	1 5% 17% 28% 36% 13%	490
	21st to end	Day	1 3 11% 28% 37% 20%	490
July	1st to 10th	Day	1 6% 31% 42% 20%	486
	11th to 20th	Day	5% 27% 43% 24%	484
	21st to end	Day	1 1 5% 27% 43% 24%	531
August	1st to 10th	Day	2 1 5% 28% 42% 22%	487
	11th to 20th	Day	1 2 7% 24% 40% 26%	477
	21st to end	Day	1 1 4 22% 41% 30%	539
September	1st to 10th	Day	1 1 7% 23% 43% 25%	490
	11th to 20th	Day	3 4 14% 24% 30% 25%	490
	21st to end	Day	2 3 15% 27% 30% 23%	490
October	1st to 10th	Day	3 6% 16% 21% 30% 24%	490
	11th to 20th	Day	6% 6% 15% 20% 30% 23%	490
	21st to end	Day	8% 9% 14% 22% 30% 16%	539
November	1st to 10th	Day	11% 8% 15% 22% 26% 18%	365
	11th to 20th	Day	14% 4 16% 26% 27% 13%	300
	21st to end	Day	14% 3 17% 27% 28% 10%	193
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% 14% 37% 22% 4	760
	21st to end	Night	19% 5% 15% 33% 24% 4	836
February	1st to 10th	Night	17% 6% 16% 34% 24% 3	760
	11th to 20th	Night	15% 5% 22% 33% 23% 3	744
	21st to end	Night	16% 8% 21% 35% 18% 2	628
March	1st to 10th	Night	18% 7% 21% 31% 21% 2	760
	11th to 20th	Night	17% 8% 18% 30% 26% 2	760
	21st to end	Night	16% 6% 24% 35% 18% 1	836
April	1st to 10th	Night	11% 5% 25% 36% 22% 2	760
	11th to 20th	Night	11% 6% 24% 32% 24% 4	751
	21st to end	Night	6% 5% 19% 40% 26% 3	760
May	1st to 10th	Night	6% 4 26% 38% 23% 3	667
	11th to 20th	Night	4 3 23% 44% 25% 1	388
	21st to end	Night	4 5% 19% 43% 28% 1	411
June	1st to 10th	Night	6% 2 23% 41% 26% 1	380
	11th to 20th	Night	1 3 26% 46% 23% 1	380
	21st to end	Night	2 2 21% 43% 32% 1	380
July	1st to 10th	Night	1 1 15% 52% 29% 1	370
	11th to 20th	Night	1 16% 56% 26% 1	380
	21st to end	Night	1 1 13% 44% 39% 2	624
August	1st to 10th	Night	2 1 18% 44% 33% 2	567
	11th to 20th	Night	1 1 12% 44% 39% 3	676
	21st to end	Night	1 1 8% 43% 46% 2	836
September	1st to 10th	Night	1 1 9% 36% 49% 4	760
	11th to 20th	Night	3 2 15% 35% 39% 5%	760
	21st to end	Night	3 2 15% 35% 39% 7%	760
October	1st to 10th	Night	4 3 14% 37% 35% 7%	760
	11th to 20th	Night	5% 4 13% 35% 38% 5%	760
	21st to end	Night	7% 5% 13% 35% 31% 9%	836
November	1st to 10th	Night	11% 5% 16% 31% 31% 7%	780
	11th to 20th	Night	11% 2 17% 38% 28% 4	800
	21st to end	Night	13% 4 15% 37% 27% 4	778
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 2024-11-22 05:02:28. Version ac07

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