San Antonio
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the San Antonio clear sky chart from 2005-11-06 to 2024-11-03.

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	13% 6% 2 5% 4 4 4 4 5% 7% 45%	100968
	Night	14% 5% 2 5% 3 3 3 3 5% 7% 50%	98129
Transparency	Day	36% 5% 11% 22% 18% 8%	100779
	Night	34% 5% 12% 21% 18% 10%	97989
Seeing	Day	13% 7% 20% 30% 24% 7%	14736
	Night	15% 6% 24% 37% 17% 1	24646

By Month

Percentage Cloud Cover SE (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	16% 7% 2 4 3 3 3 3 4 6% 51%	2847
	11th to 20th	Day	18% 5% 1 3 3 2 2 2 4 5% 55%	2850
	21st to end	Day	20% 8% 2 4 3 3 3 3 5% 8% 42%	3456
February	1st to 10th	Day	21% 7% 3 5% 3 3 3 3 3 5% 45%	1900
	11th to 20th	Day	20% 7% 2 5% 3 2 3 3 5% 6% 44%	1849
	21st to end	Day	19% 6% 2 4 3 2 4 2 4 6% 48%	1570
March	1st to 10th	Day	17% 8% 2 7% 4 4 4 3 4 6% 42%	3369
	11th to 20th	Day	23% 9% 3 8% 5% 5% 4 3 4 4 33%	3480
	21st to end	Day	18% 7% 2 5% 3 3 3 2 5% 6% 46%	3814
April	1st to 10th	Day	16% 7% 3 6% 4 4 4 3 5% 5% 43%	2090
	11th to 20th	Day	20% 6% 2 5% 4 4 4 3 5% 5% 42%	2083
	21st to end	Day	17% 7% 2 6% 4 3 4 3 4 5% 44%	2382
May	1st to 10th	Day	23% 8% 3 7% 5% 4 4 3 5% 6% 32%	4082
	11th to 20th	Day	13% 6% 2 6% 4 5% 4 4 5% 7% 42%	4082
	21st to end	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 9% 40%	4477
June	1st to 10th	Day	6% 3 2 5% 4 5% 6% 5% 7% 10% 46%	2470
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 4 7% 10% 45%	2470
	21st to end	Day	8% 6% 2 7% 6% 6% 5% 5% 8% 9% 37%	2470
July	1st to 10th	Day	8% 5% 2 5% 4 5% 5% 4 6% 9% 46%	4120
	11th to 20th	Day	6% 4 2 6% 5% 5% 5% 5% 8% 11% 43%	4120
	21st to end	Day	9% 5% 2 7% 5% 5% 6% 4 8% 11% 36%	4465
August	1st to 10th	Day	1 2 1 2 2 3 3 3 5% 8% 68%	3958
	11th to 20th	Day	3 2 1 4 3 3 5% 5% 8% 11% 55%	3726
	21st to end	Day	5% 4 2 5% 4 5% 5% 5% 7% 12% 47%	4025
September	1st to 10th	Day	9% 6% 3 6% 5% 5% 6% 5% 7% 7% 41%	2090
	11th to 20th	Day	10% 6% 2 7% 5% 5% 5% 5% 7% 8% 39%	2090
	21st to end	Day	9% 4 2 5% 5% 5% 4 4 6% 9% 48%	2090
October	1st to 10th	Day	8% 4 1 4 4 4 4 5% 6% 7% 54%	2090
	11th to 20th	Day	14% 5% 2 5% 4 4 4 3 5% 5% 51%	1997
	21st to end	Day	11% 5% 2 5% 3 2 3 3 3 5% 58%	2090
November	1st to 10th	Day	17% 9% 3 5% 4 4 3 3 5% 5% 43%	1878
	11th to 20th	Day	15% 6% 2 5% 4 3 3 4 4 6% 48%	1772
	21st to end	Day	21% 6% 2 5% 3 3 3 3 4 4 45%	1710
December	1st to 10th	Day	18% 6% 3 5% 4 3 3 3 5% 7% 44%	1710
	11th to 20th	Day	17% 8% 2 5% 4 4 4 3 4 5% 44%	2161
	21st to end	Day	16% 6% 2 5% 3 3 3 2 3 5% 53%	3135
January	1st to 10th	Night	19% 6% 1 3 2 3 2 2 4 6% 51%	4108
	11th to 20th	Night	14% 4 1 3 2 2 2 2 2 4 65%	4120
	21st to end	Night	23% 6% 2 6% 3 2 2 2 4 6% 43%	4240
February	1st to 10th	Night	19% 6% 1 4 3 3 3 3 5% 6% 47%	2280
	11th to 20th	Night	21% 7% 1 4 3 3 2 2 4 5% 49%	2218
	21st to end	Night	20% 6% 2 5% 3 3 3 3 5% 6% 46%	1884
March	1st to 10th	Night	21% 8% 2 5% 5% 3 3 3 4 5% 41%	3484
	11th to 20th	Night	23% 8% 3 8% 5% 4 4 3 4 5% 34%	3480
	21st to end	Night	19% 7% 2 4 3 3 3 3 5% 5% 46%	3817
April	1st to 10th	Night	14% 6% 2 6% 3 4 3 3 5% 7% 46%	2090
	11th to 20th	Night	20% 6% 2 5% 4 3 3 3 4 6% 45%	2040
	21st to end	Night	19% 7% 2 5% 4 3 3 3 4 5% 44%	1796
May	1st to 10th	Night	24% 8% 2 5% 3 3 3 3 4 5% 39%	2823
	11th to 20th	Night	15% 5% 2 5% 3 3 4 3 4 8% 48%	2823
	21st to end	Night	13% 6% 2 6% 4 5% 3 3 5% 8% 45%	3090
June	1st to 10th	Night	6% 4 2 3 2 3 3 3 6% 7% 59%	1710
	11th to 20th	Night	6% 4 1 3 3 4 3 4 6% 10% 56%	1710
	21st to end	Night	7% 4 2 5% 4 4 4 4 6% 10% 49%	1710
July	1st to 10th	Night	6% 5% 2 5% 4 3 4 5% 6% 11% 51%	2850
	11th to 20th	Night	4 4 2 5% 4 5% 6% 5% 7% 10% 49%	2850
	21st to end	Night	10% 6% 2 7% 4 4 5% 4 7% 10% 42%	3098
August	1st to 10th	Night	1 1 2 2 2 3 3 4 8% 73%	2977
	11th to 20th	Night	3 2 1 4 3 4 4 4 7% 12% 57%	3113
	21st to end	Night	6% 3 2 4 3 4 4 3 6% 10% 54%	3633
September	1st to 10th	Night	9% 5% 2 5% 4 5% 5% 4 6% 8% 47%	2090
	11th to 20th	Night	11% 6% 2 6% 4 4 4 4 6% 8% 46%	2090
	21st to end	Night	8% 4 2 6% 4 4 4 4 6% 7% 51%	2090
October	1st to 10th	Night	6% 4 1 4 3 3 4 4 5% 8% 59%	2090
	11th to 20th	Night	13% 5% 1 4 2 2 4 2 4 6% 55%	2161
	21st to end	Night	15% 4 2 3 2 2 2 2 2 4 62%	2508
November	1st to 10th	Night	14% 6% 3 5% 3 3 2 2 4 5% 53%	2245
	11th to 20th	Night	11% 6% 2 4 2 3 3 3 4 6% 54%	2403
	21st to end	Night	20% 6% 2 5% 3 3 3 2 4 6% 47%	2470
December	1st to 10th	Night	18% 6% 2 4 3 2 3 3 4 6% 50%	2470
	11th to 20th	Night	20% 6% 2 6% 3 3 3 2 3 5% 46%	3036
	21st to end	Night	19% 6% 1 4 2 2 2 2 3 6% 52%	4532

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	36% 2 5% 15% 26% 16%	2848
	11th to 20th	Day	33% 2 5% 17% 23% 19%	2850
	21st to end	Day	42% 3 5% 13% 28% 9%	3456
February	1st to 10th	Day	44% 3 5% 13% 19% 16%	1900
	11th to 20th	Day	42% 3 6% 17% 19% 13%	1859
	21st to end	Day	38% 4 8% 16% 18% 15%	1570
March	1st to 10th	Day	45% 4 7% 17% 18% 9%	3369
	11th to 20th	Day	54% 5% 6% 10% 16% 9%	3480
	21st to end	Day	38% 4 8% 18% 18% 14%	3814
April	1st to 10th	Day	41% 5% 9% 16% 17% 13%	2090
	11th to 20th	Day	43% 4 6% 17% 17% 12%	2083
	21st to end	Day	41% 5% 6% 20% 17% 11%	2382
May	1st to 10th	Day	50% 6% 10% 16% 12% 6%	4120
	11th to 20th	Day	38% 7% 9% 20% 18% 7%	4086
	21st to end	Day	34% 8% 12% 34% 12% 1	4489
June	1st to 10th	Day	28% 9% 14% 28% 19% 3	2470
	11th to 20th	Day	32% 6% 14% 26% 18% 5%	2470
	21st to end	Day	39% 8% 14% 24% 12% 3	2470
July	1st to 10th	Day	33% 5% 16% 37% 7% 1	4056
	11th to 20th	Day	34% 6% 18% 27% 14% 1	4051
	21st to end	Day	38% 8% 18% 28% 9%	4325
August	1st to 10th	Day	15% 4 11% 44% 25% 1	3944
	11th to 20th	Day	21% 6% 23% 36% 11% 2	3762
	21st to end	Day	30% 8% 19% 23% 18% 2	4024
September	1st to 10th	Day	40% 8% 10% 18% 16% 7%	2090
	11th to 20th	Day	39% 8% 10% 20% 18% 5%	2090
	21st to end	Day	32% 7% 11% 21% 17% 13%	2090
October	1st to 10th	Day	28% 6% 10% 19% 26% 12%	2090
	11th to 20th	Day	35% 5% 9% 17% 19% 16%	1997
	21st to end	Day	29% 3 6% 17% 25% 21%	2090
November	1st to 10th	Day	42% 4 8% 18% 17% 11%	1878
	11th to 20th	Day	36% 5% 9% 16% 20% 14%	1772
	21st to end	Day	43% 3 7% 15% 19% 13%	1710
December	1st to 10th	Day	42% 5% 6% 19% 19% 10%	1710
	11th to 20th	Day	42% 5% 7% 10% 21% 14%	2159
	21st to end	Day	37% 2 5% 19% 26% 12%	3135
January	1st to 10th	Night	35% 3 6% 15% 19% 22%	4108
	11th to 20th	Night	27% 1 5% 17% 27% 22%	4120
	21st to end	Night	45% 3 4 12% 25% 11%	4240
February	1st to 10th	Night	39% 4 8% 13% 19% 18%	2280
	11th to 20th	Night	39% 3 6% 17% 19% 15%	2218
	21st to end	Night	39% 4 6% 17% 18% 15%	1884
March	1st to 10th	Night	44% 4 9% 17% 16% 9%	3484
	11th to 20th	Night	51% 5% 9% 12% 12% 10%	3480
	21st to end	Night	37% 4 12% 16% 20% 11%	3817
April	1st to 10th	Night	35% 6% 11% 19% 16% 14%	2090
	11th to 20th	Night	41% 4 10% 14% 16% 16%	2040
	21st to end	Night	41% 6% 8% 18% 15% 11%	1796
May	1st to 10th	Night	46% 6% 10% 18% 14% 8%	2850
	11th to 20th	Night	35% 7% 10% 22% 19% 8%	2824
	21st to end	Night	34% 8% 15% 30% 12% 1	3099
June	1st to 10th	Night	21% 6% 18% 31% 23% 2	1710
	11th to 20th	Night	22% 4 14% 32% 22% 5%	1710
	21st to end	Night	30% 6% 18% 30% 14% 2	1710
July	1st to 10th	Night	27% 7% 24% 36% 6% 1	2805
	11th to 20th	Night	28% 7% 22% 27% 14% 1	2796
	21st to end	Night	35% 7% 23% 26% 7%	2999
August	1st to 10th	Night	11% 5% 16% 47% 21%	2967
	11th to 20th	Night	19% 7% 32% 34% 7% 1	3143
	21st to end	Night	24% 10% 24% 26% 15% 2	3633
September	1st to 10th	Night	33% 7% 18% 20% 15% 7%	2090
	11th to 20th	Night	35% 8% 14% 23% 15% 5%	2090
	21st to end	Night	27% 7% 15% 23% 17% 12%	2090
October	1st to 10th	Night	22% 5% 11% 27% 20% 14%	2090
	11th to 20th	Night	29% 4 10% 20% 20% 18%	2161
	21st to end	Night	28% 3 6% 17% 25% 21%	2508
November	1st to 10th	Night	34% 4 8% 20% 20% 13%	2245
	11th to 20th	Night	31% 5% 11% 18% 20% 15%	2403
	21st to end	Night	39% 4 8% 16% 19% 13%	2470
December	1st to 10th	Night	36% 4 9% 20% 19% 13%	2470
	11th to 20th	Night	42% 3 6% 13% 17% 19%	3037
	21st to end	Night	34% 4 6% 14% 28% 13%	4532

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	23% 10% 36% 23% 7% 1	270
	11th to 20th	Day	23% 12% 31% 26% 7% 1	270
	21st to end	Day	18% 13% 33% 26% 10%	297
February	1st to 10th	Day	29% 14% 26% 21% 9%	270
	11th to 20th	Day	26% 16% 31% 18% 7% 1	270
	21st to end	Day	23% 14% 41% 19% 2	225
March	1st to 10th	Day	20% 14% 38% 24% 4	270
	11th to 20th	Day	15% 14% 44% 21% 5%	270
	21st to end	Day	18% 15% 38% 25% 4	297
April	1st to 10th	Day	20% 13% 37% 24% 6%	270
	11th to 20th	Day	16% 16% 36% 24% 8%	281
	21st to end	Day	16% 13% 37% 28% 6% 1	562
May	1st to 10th	Day	18% 11% 33% 30% 9%	653
	11th to 20th	Day	14% 10% 28% 34% 12% 1	675
	21st to end	Day	14% 6% 27% 37% 15% 1	734
June	1st to 10th	Day	6% 3 13% 42% 32% 5%	680
	11th to 20th	Day	7% 2 12% 46% 29% 5%	680
	21st to end	Day	9% 2 11% 34% 34% 10%	680
July	1st to 10th	Day	9% 3 8% 30% 40% 11%	671
	11th to 20th	Day	5% 1 7% 26% 46% 13%	668
	21st to end	Day	6% 1 6% 29% 44% 14%	739
August	1st to 10th	Day	2 1 3 30% 46% 17%	595
	11th to 20th	Day	5% 1 4 34% 41% 15%	477
	21st to end	Day	5% 2 6% 25% 40% 22%	449
September	1st to 10th	Day	9% 1 9% 24% 37% 19%	300
	11th to 20th	Day	5% 1 6% 26% 42% 20%	300
	21st to end	Day	10% 2 8% 25% 40% 16%	300
October	1st to 10th	Day	7% 2 13% 32% 37% 9%	300
	11th to 20th	Day	11% 4 14% 40% 26% 5%	300
	21st to end	Day	18% 11% 20% 27% 20% 5%	330
November	1st to 10th	Day	19% 9% 18% 33% 16% 5%	276
	11th to 20th	Day	22% 7% 22% 29% 16% 4	270
	21st to end	Day	24% 13% 34% 19% 9% 1	270
December	1st to 10th	Day	18% 9% 28% 28% 14% 3	270
	11th to 20th	Day	23% 16% 26% 27% 7% 1	270
	21st to end	Day	18% 8% 34% 31% 8% 1	297
January	1st to 10th	Night	21% 5% 27% 36% 11% 1	950
	11th to 20th	Night	21% 8% 27% 35% 9%	950
	21st to end	Night	23% 7% 28% 34% 8%	870
February	1st to 10th	Night	23% 9% 30% 32% 7%	760
	11th to 20th	Night	27% 8% 30% 30% 5%	744
	21st to end	Night	24% 12% 34% 28% 3	628
March	1st to 10th	Night	22% 10% 35% 29% 3 1	613
	11th to 20th	Night	21% 9% 33% 33% 4	570
	21st to end	Night	17% 11% 40% 27% 4	627
April	1st to 10th	Night	15% 9% 44% 29% 4	570
	11th to 20th	Night	23% 10% 36% 27% 4	563
	21st to end	Night	21% 9% 39% 25% 6%	570
May	1st to 10th	Night	17% 9% 41% 28% 4	570
	11th to 20th	Night	15% 6% 35% 36% 7%	561
	21st to end	Night	13% 6% 37% 34% 10%	617
June	1st to 10th	Night	5% 2 23% 48% 21% 1	570
	11th to 20th	Night	6% 2 29% 49% 13% 1	570
	21st to end	Night	6% 2 19% 45% 25% 2	570
July	1st to 10th	Night	8% 3 13% 47% 26% 2	555
	11th to 20th	Night	4 1 10% 50% 33% 2	552
	21st to end	Night	5% 2 10% 47% 34% 1	624
August	1st to 10th	Night	1 1 9% 50% 38% 2	567
	11th to 20th	Night	5% 1 9% 51% 31% 4	564
	21st to end	Night	6% 1 6% 42% 41% 4	627
September	1st to 10th	Night	10% 2 8% 41% 36% 4	570
	11th to 20th	Night	12% 1 9% 39% 36% 4	570
	21st to end	Night	7% 1 12% 41% 37% 3	570
October	1st to 10th	Night	6% 2 13% 47% 31% 2	570
	11th to 20th	Night	14% 3 17% 42% 22% 2	641
	21st to end	Night	13% 7% 23% 35% 20% 2	836
November	1st to 10th	Night	15% 5% 18% 38% 22% 1	749
	11th to 20th	Night	13% 4 23% 41% 18% 2	883
	21st to end	Night	22% 6% 24% 32% 15% 1	950
December	1st to 10th	Night	19% 7% 21% 37% 15% 1	950
	11th to 20th	Night	24% 8% 23% 33% 11%	950
	21st to end	Night	20% 6% 26% 37% 11%	1045

Page generated at 2024-10-31 02:39:22. Version ac07

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