Mariposa Fairgrounds
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mariposa Fairgrounds clear sky chart from 2005-11-06 to 2024-01-15.

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 5% 65%	74790
	Night	9% 3 1 3 3 2 3 3 4 6% 63%	75015
Transparency	Day	22% 3 8% 19% 25% 23%	74503
	Night	23% 3 9% 20% 24% 20%	74824
Seeing	Day	10% 9% 27% 34% 14% 5%	14105
	Night	10% 2 12% 36% 31% 9%	23676

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	18% 7% 2 4 3 3 4 4 5% 8% 43%	1519
	11th to 20th	Day	14% 4 1 4 4 3 4 4 4 7% 51%	1593
	21st to end	Day	17% 6% 2 4 4 3 4 3 5% 7% 44%	1782
February	1st to 10th	Day	17% 5% 1 3 3 2 3 4 4 7% 51%	1670
	11th to 20th	Day	14% 5% 2 4 4 3 3 4 5% 7% 52%	1750
	21st to end	Day	18% 6% 2 5% 3 3 4 3 4 5% 46%	1480
March	1st to 10th	Day	17% 9% 3 6% 5% 3 3 5% 5% 8% 37%	1800
	11th to 20th	Day	16% 7% 2 4 4 3 4 4 5% 7% 43%	1961
	21st to end	Day	14% 5% 2 4 4 3 4 4 5% 7% 49%	2312
April	1st to 10th	Day	12% 5% 2 4 3 2 4 3 5% 6% 54%	2160
	11th to 20th	Day	11% 4 2 4 3 2 4 3 5% 6% 56%	2129
	21st to end	Day	8% 4 1 3 4 2 3 3 4 6% 62%	2160
May	1st to 10th	Day	4 4 2 3 3 2 3 3 3 7% 67%	2203
	11th to 20th	Day	5% 3 1 2 2 2 4 4 4 6% 67%	2355
	21st to end	Day	6% 3 1 3 3 2 3 5% 4 6% 63%	2723
June	1st to 10th	Day	4 3 1 2 2 2 3 2 4 6% 71%	2520
	11th to 20th	Day	1 1 1 2 1 2 2 2 4 85%	2520
	21st to end	Day	2 2 1 1 1 2 2 3 85%	2520
July	1st to 10th	Day	1 1 1 1 1 2 2 2 3 87%	2520
	11th to 20th	Day	1 1 1 1 2 1 2 2 2 4 83%	2520
	21st to end	Day	1 2 1 2 2 1 2 3 4 4 79%	2587
August	1st to 10th	Day	2 1 1 2 1 1 1 2 3 2 84%	2253
	11th to 20th	Day	1 1 1 1 1 2 2 2 3 86%	2122
	21st to end	Day	1 1 1 1 1 2 2 2 3 87%	2376
September	1st to 10th	Day	2 1 1 1 1 1 1 2 2 88%	2160
	11th to 20th	Day	2 2 1 1 1 1 1 2 3 3 82%	2129
	21st to end	Day	2 2 1 2 2 1 2 2 3 4 81%	1980
October	1st to 10th	Day	4 3 1 2 3 1 2 3 3 5% 72%	1843
	11th to 20th	Day	4 2 1 2 1 1 3 3 4 5% 73%	1800
	21st to end	Day	6% 2 1 2 3 2 3 3 4 5% 71%	1978
November	1st to 10th	Day	9% 4 2 2 4 2 4 4 4 7% 58%	1674
	11th to 20th	Day	8% 2 2 3 3 1 4 4 5% 7% 61%	1710
	21st to end	Day	11% 3 1 3 3 3 3 3 4 7% 57%	1710
December	1st to 10th	Day	14% 4 2 3 5% 3 3 3 4 6% 53%	1549
	11th to 20th	Day	26% 8% 2 5% 5% 3 3 3 3 5% 36%	1928
	21st to end	Day	13% 6% 4 5% 6% 4 5% 6% 5% 9% 38%	2794
January	1st to 10th	Night	17% 5% 2 4 4 2 3 4 5% 7% 46%	2646
	11th to 20th	Night	12% 4 2 3 4 2 4 5% 6% 7% 51%	2467
	21st to end	Night	15% 5% 2 4 4 2 3 4 4 7% 51%	2574
February	1st to 10th	Night	15% 5% 2 3 4 1 3 4 4 6% 53%	2289
	11th to 20th	Night	13% 5% 1 3 3 2 3 4 4 7% 56%	2098
	21st to end	Night	18% 7% 2 3 3 1 3 3 3 5% 51%	1776
March	1st to 10th	Night	18% 8% 2 4 4 2 3 4 3 7% 46%	2160
	11th to 20th	Night	16% 6% 2 3 4 3 3 5% 4 8% 47%	1996
	21st to end	Night	15% 5% 2 3 3 2 3 3 4 5% 56%	2043
April	1st to 10th	Night	12% 4 2 3 3 2 3 4 4 7% 57%	1800
	11th to 20th	Night	8% 3 2 3 3 2 4 4 3 5% 62%	1779
	21st to end	Night	6% 3 1 3 3 2 3 3 3 7% 66%	1800
May	1st to 10th	Night	5% 3 1 2 2 1 3 3 4 7% 69%	1756
	11th to 20th	Night	5% 1 1 2 2 1 2 2 4 7% 71%	1535
	21st to end	Night	4 2 1 3 3 2 3 3 4 5% 72%	1552
June	1st to 10th	Night	3 2 1 2 2 2 3 3 3 7% 72%	1440
	11th to 20th	Night	1 1 1 2 2 2 4 87%	1440
	21st to end	Night	1 1 1 1 1 2 2 2 3 86%	1440
July	1st to 10th	Night	1 1 1 1 2 3 90%	1440
	11th to 20th	Night	3 1 1 2 1 2 2 2 3 82%	1440
	21st to end	Night	2 2 2 2 3 1 3 2 4 4 75%	1727
August	1st to 10th	Night	2 2 1 1 1 1 2 1 2 3 84%	1686
	11th to 20th	Night	1 1 1 2 1 2 2 3 3 83%	1780
	21st to end	Night	1 1 1 1 1 1 1 3 2 88%	1980
September	1st to 10th	Night	1 1 1 1 1 2 2 2 89%	1800
	11th to 20th	Night	2 1 1 1 1 1 1 2 3 3 83%	1831
	21st to end	Night	2 1 1 2 1 1 1 2 3 4 82%	1980
October	1st to 10th	Night	4 2 1 2 3 1 2 2 3 4 74%	2114
	11th to 20th	Night	4 2 1 2 2 2 2 4 4 4 75%	2160
	21st to end	Night	5% 2 1 2 2 1 1 2 3 5% 77%	2376
November	1st to 10th	Night	10% 3 1 2 2 2 2 2 4 6% 65%	2405
	11th to 20th	Night	8% 3 1 3 2 1 3 4 4 7% 63%	2470
	21st to end	Night	11% 3 2 3 3 2 3 3 5% 6% 61%	2470
December	1st to 10th	Night	15% 4 2 4 4 1 3 3 4 7% 53%	2627
	11th to 20th	Night	25% 6% 3 4 4 2 3 3 5% 7% 38%	3276
	21st to end	Night	15% 6% 2 6% 6% 4 6% 6% 6% 7% 36%	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	40% 7% 13% 21% 15% 4	1519
	11th to 20th	Day	33% 6% 10% 21% 17% 13%	1593
	21st to end	Day	40% 6% 12% 19% 18% 6%	1782
February	1st to 10th	Day	35% 4 9% 26% 18% 9%	1670
	11th to 20th	Day	31% 3 11% 24% 23% 7%	1760
	21st to end	Day	39% 5% 10% 25% 20% 1	1480
March	1st to 10th	Day	44% 5% 11% 20% 17% 3	1800
	11th to 20th	Day	39% 5% 11% 20% 19% 5%	1961
	21st to end	Day	33% 5% 17% 26% 15% 4	2312
April	1st to 10th	Day	30% 4 13% 25% 20% 8%	2160
	11th to 20th	Day	29% 3 11% 27% 23% 8%	2132
	21st to end	Day	24% 4 10% 30% 27% 6%	2160
May	1st to 10th	Day	19% 3 10% 25% 33% 10%	2203
	11th to 20th	Day	17% 4 8% 26% 32% 13%	2358
	21st to end	Day	20% 3 10% 30% 28% 9%	2724
June	1st to 10th	Day	15% 3 10% 22% 31% 20%	2520
	11th to 20th	Day	7% 1 5% 17% 38% 32%	2520
	21st to end	Day	8% 1 2 8% 32% 49%	2520
July	1st to 10th	Day	6% 1 2 6% 23% 63%	2451
	11th to 20th	Day	8% 2 3 8% 23% 56%	2445
	21st to end	Day	10% 2 3 10% 25% 51%	2443
August	1st to 10th	Day	9% 1 2 9% 26% 53%	2237
	11th to 20th	Day	6% 1 2 7% 31% 53%	2122
	21st to end	Day	6% 1 2 8% 33% 50%	2376
September	1st to 10th	Day	7% 1 2 7% 27% 55%	2160
	11th to 20th	Day	8% 1 3 20% 37% 29%	2129
	21st to end	Day	10% 1 3 17% 37% 32%	1980
October	1st to 10th	Day	16% 3 6% 18% 28% 31%	1843
	11th to 20th	Day	13% 2 6% 21% 27% 29%	1800
	21st to end	Day	16% 2 6% 21% 31% 23%	1978
November	1st to 10th	Day	25% 4 11% 22% 23% 15%	1674
	11th to 20th	Day	24% 4 12% 24% 28% 8%	1710
	21st to end	Day	27% 5% 8% 20% 28% 12%	1710
December	1st to 10th	Day	34% 4 11% 21% 20% 10%	1549
	11th to 20th	Day	52% 3 9% 16% 14% 6%	1928
	21st to end	Day	43% 7% 15% 23% 9% 4	2794
January	1st to 10th	Night	38% 5% 14% 22% 17% 4	2646
	11th to 20th	Night	32% 6% 14% 20% 17% 12%	2467
	21st to end	Night	35% 4 12% 20% 21% 7%	2574
February	1st to 10th	Night	33% 3 10% 24% 20% 10%	2289
	11th to 20th	Night	28% 4 11% 27% 23% 7%	2099
	21st to end	Night	37% 2 11% 26% 18% 4	1776
March	1st to 10th	Night	40% 4 12% 19% 20% 4	2160
	11th to 20th	Night	35% 4 12% 23% 20% 6%	1996
	21st to end	Night	31% 4 16% 26% 18% 5%	2043
April	1st to 10th	Night	27% 4 16% 25% 19% 8%	1800
	11th to 20th	Night	23% 3 13% 28% 24% 8%	1779
	21st to end	Night	20% 3 12% 32% 28% 5%	1800
May	1st to 10th	Night	16% 4 10% 26% 34% 10%	1756
	11th to 20th	Night	15% 2 8% 30% 31% 14%	1536
	21st to end	Night	16% 3 10% 31% 30% 10%	1552
June	1st to 10th	Night	14% 3 12% 22% 31% 19%	1440
	11th to 20th	Night	5% 1 5% 19% 37% 32%	1440
	21st to end	Night	7% 1 3 9% 31% 50%	1440
July	1st to 10th	Night	4 1 1 5% 27% 63%	1400
	11th to 20th	Night	9% 2 2 7% 22% 59%	1392
	21st to end	Night	13% 2 2 7% 21% 54%	1631
August	1st to 10th	Night	9% 1 2 10% 24% 55%	1677
	11th to 20th	Night	8% 2 2 8% 29% 51%	1780
	21st to end	Night	6% 1 1 7% 32% 54%	1980
September	1st to 10th	Night	5% 1 2 6% 27% 59%	1800
	11th to 20th	Night	8% 2 4 15% 39% 31%	1831
	21st to end	Night	9% 1 3 14% 40% 33%	1980
October	1st to 10th	Night	16% 2 6% 16% 28% 32%	2114
	11th to 20th	Night	13% 2 7% 20% 28% 30%	2160
	21st to end	Night	12% 1 4 25% 32% 25%	2376
November	1st to 10th	Night	22% 3 9% 24% 22% 19%	2405
	11th to 20th	Night	21% 3 11% 27% 25% 13%	2470
	21st to end	Night	25% 3 8% 23% 29% 11%	2470
December	1st to 10th	Night	34% 4 10% 22% 19% 12%	2627
	11th to 20th	Night	46% 4 12% 17% 16% 6%	3276
	21st to end	Night	43% 7% 16% 21% 9% 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	32% 11% 16% 26% 12% 4	180
	11th to 20th	Day	22% 5% 23% 31% 14% 4	287
	21st to end	Day	18% 5% 25% 32% 17% 4	374
February	1st to 10th	Day	23% 10% 23% 23% 15% 6%	362
	11th to 20th	Day	18% 10% 33% 25% 12% 2	415
	21st to end	Day	20% 12% 34% 24% 9% 1	346
March	1st to 10th	Day	23% 13% 33% 22% 7% 1	420
	11th to 20th	Day	23% 15% 25% 23% 11% 2	420
	21st to end	Day	23% 13% 33% 23% 7%	462
April	1st to 10th	Day	17% 20% 30% 22% 10% 1	420
	11th to 20th	Day	16% 19% 30% 25% 7% 2	412
	21st to end	Day	8% 19% 30% 27% 12% 4	420
May	1st to 10th	Day	8% 18% 33% 27% 9% 5%	423
	11th to 20th	Day	9% 16% 31% 29% 9% 5%	448
	21st to end	Day	11% 12% 27% 32% 12% 6%	485
June	1st to 10th	Day	4 15% 29% 32% 12% 8%	450
	11th to 20th	Day	3 14% 31% 33% 11% 8%	450
	21st to end	Day	3 9% 30% 33% 16% 9%	450
July	1st to 10th	Day	1 3 28% 44% 15% 10%	446
	11th to 20th	Day	1 2 18% 54% 14% 12%	444
	21st to end	Day	2 1 24% 46% 17% 10%	487
August	1st to 10th	Day	4 3 31% 40% 13% 9%	447
	11th to 20th	Day	2 3 27% 44% 15% 8%	437
	21st to end	Day	1 2 23% 48% 17% 8%	495
September	1st to 10th	Day	2 4 25% 47% 17% 6%	450
	11th to 20th	Day	4 8% 33% 34% 18% 3	450
	21st to end	Day	4 7% 26% 45% 17% 2	450
October	1st to 10th	Day	3 12% 27% 37% 20% 1	450
	11th to 20th	Day	6% 8% 26% 35% 20% 4	450
	21st to end	Day	6% 9% 26% 36% 21% 3	493
November	1st to 10th	Day	10% 7% 22% 29% 24% 7%	270
	11th to 20th	Day	7% 6% 21% 40% 18% 8%	270
	21st to end	Day	11% 8% 23% 32% 20% 7%	270
December	1st to 10th	Day	18% 4 27% 25% 20% 7%	194
	11th to 20th	Day	16% 7% 26% 27% 17% 6%	180
	21st to end	Day	22% 7% 22% 26% 17% 6%	198
January	1st to 10th	Night	20% 2 17% 31% 21% 10%	760
	11th to 20th	Night	15% 3 14% 38% 22% 7%	740
	21st to end	Night	18% 2 14% 35% 22% 8%	792
February	1st to 10th	Night	18% 2 14% 37% 22% 7%	720
	11th to 20th	Night	15% 4 15% 33% 23% 9%	704
	21st to end	Night	21% 4 13% 40% 19% 4	592
March	1st to 10th	Night	22% 4 14% 36% 20% 5%	720
	11th to 20th	Night	17% 4 14% 30% 27% 7%	720
	21st to end	Night	19% 3 17% 36% 23% 3	792
April	1st to 10th	Night	13% 4 16% 37% 25% 4	720
	11th to 20th	Night	10% 5% 20% 36% 22% 7%	711
	21st to end	Night	7% 4 17% 38% 26% 8%	720
May	1st to 10th	Night	8% 5% 15% 39% 25% 7%	676
	11th to 20th	Night	6% 3 15% 38% 35% 3	473
	21st to end	Night	6% 3 12% 37% 35% 6%	389
June	1st to 10th	Night	4 4 8% 35% 43% 6%	360
	11th to 20th	Night	1 2 9% 38% 44% 5%	360
	21st to end	Night	1 7% 36% 48% 8%	360
July	1st to 10th	Night	3 37% 53% 7%	350
	11th to 20th	Night	3 1 33% 53% 10%	348
	21st to end	Night	2 1 2 26% 52% 17%	545
August	1st to 10th	Night	2 4 37% 44% 13%	612
	11th to 20th	Night	1 5% 38% 44% 11%	712
	21st to end	Night	1 3 33% 50% 13%	792
September	1st to 10th	Night	1 1 5% 33% 48% 12%	720
	11th to 20th	Night	2 1 6% 38% 41% 13%	720
	21st to end	Night	2 1 9% 34% 41% 12%	720
October	1st to 10th	Night	5% 1 8% 46% 30% 10%	720
	11th to 20th	Night	5% 2 10% 39% 33% 12%	720
	21st to end	Night	6% 1 12% 34% 31% 16%	792
November	1st to 10th	Night	12% 3 9% 34% 31% 12%	740
	11th to 20th	Night	10% 1 14% 39% 27% 9%	760
	21st to end	Night	11% 2 15% 38% 25% 8%	760
December	1st to 10th	Night	17% 2 13% 41% 20% 7%	760
	11th to 20th	Night	21% 1 14% 38% 20% 5%	760
	21st to end	Night	21% 3 17% 36% 18% 4	836

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