San Marcos Baptist Academy
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the San Marcos Baptist Academy clear sky chart from 2005-11-06 to 2025-03-27.

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	14% 6% 2 5% 4 4 4 3 5% 7% 45%	109561
	Night	16% 6% 2 4 3 3 3 3 4 6% 49%	110013
Transparency	Day	36% 6% 10% 20% 18% 9%	113379
	Night	35% 6% 10% 19% 19% 12%	114322
Seeing	Day	14% 7% 21% 29% 23% 6%	15236
	Night	17% 7% 25% 35% 16% 1	25321

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	18% 8% 3 5% 3 2 2 2 4 5% 48%	4077
	11th to 20th	Day	18% 4 2 4 2 2 3 2 4 5% 53%	4080
	21st to end	Day	28% 7% 2 4 3 2 2 2 3 6% 40%	4792
February	1st to 10th	Day	22% 7% 2 6% 3 3 3 2 5% 4 44%	2000
	11th to 20th	Day	20% 8% 2 5% 3 3 3 3 4 5% 43%	1949
	21st to end	Day	19% 7% 2 5% 2 3 2 2 3 6% 47%	1650
March	1st to 10th	Day	17% 8% 2 7% 4 4 3 2 4 6% 43%	3529
	11th to 20th	Day	22% 9% 3 8% 5% 5% 4 3 3 4 34%	3590
	21st to end	Day	18% 7% 2 4 4 3 4 3 4 5% 47%	3880
April	1st to 10th	Day	16% 8% 2 6% 4 4 4 3 4 6% 42%	2090
	11th to 20th	Day	21% 5% 2 6% 4 4 4 3 4 5% 41%	2066
	21st to end	Day	16% 8% 2 6% 5% 4 4 3 4 7% 43%	2404
May	1st to 10th	Day	26% 9% 3 7% 5% 3 4 4 5% 5% 30%	4082
	11th to 20th	Day	16% 6% 2 6% 4 4 5% 3 5% 7% 42%	4082
	21st to end	Day	12% 6% 2 6% 5% 5% 6% 5% 8% 9% 37%	4477
June	1st to 10th	Day	7% 4 1 5% 4 5% 6% 4 7% 9% 47%	2470
	11th to 20th	Day	8% 5% 2 6% 6% 5% 5% 4 6% 9% 44%	2470
	21st to end	Day	8% 6% 2 7% 6% 6% 6% 6% 7% 10% 36%	2470
July	1st to 10th	Day	7% 5% 2 5% 5% 5% 6% 4 5% 8% 48%	4120
	11th to 20th	Day	5% 4 2 5% 4 5% 5% 6% 7% 11% 44%	4120
	21st to end	Day	10% 6% 2 6% 5% 6% 5% 5% 7% 10% 36%	4465
August	1st to 10th	Day	1 2 1 3 3 2 3 3 5% 8% 69%	4104
	11th to 20th	Day	3 3 1 3 3 3 5% 4 7% 11% 57%	3732
	21st to end	Day	5% 3 2 5% 4 6% 6% 5% 7% 11% 47%	3988
September	1st to 10th	Day	9% 6% 2 8% 6% 5% 5% 4 6% 6% 43%	2090
	11th to 20th	Day	12% 6% 2 7% 5% 5% 5% 4 6% 8% 41%	2090
	21st to end	Day	9% 4 2 4 4 5% 6% 5% 6% 8% 49%	2090
October	1st to 10th	Day	6% 4 2 5% 4 4 4 4 6% 7% 54%	2090
	11th to 20th	Day	12% 5% 2 4 4 4 4 3 4 7% 51%	1957
	21st to end	Day	12% 4 2 5% 3 3 3 3 4 5% 57%	2090
November	1st to 10th	Day	15% 8% 2 6% 4 3 3 4 5% 6% 44%	1958
	11th to 20th	Day	13% 5% 2 5% 4 3 4 3 4 5% 52%	1890
	21st to end	Day	18% 7% 2 5% 4 3 3 3 4 5% 45%	1800
December	1st to 10th	Day	27% 8% 3 6% 4 3 3 2 4 5% 37%	2940
	11th to 20th	Day	19% 7% 2 6% 4 4 4 3 4 5% 43%	3391
	21st to end	Day	16% 5% 1 4 3 3 2 2 3 4 57%	4488
January	1st to 10th	Night	21% 6% 2 4 2 2 2 2 3 6% 50%	5888
	11th to 20th	Night	13% 3 1 3 2 2 3 2 4 4 63%	5900
	21st to end	Night	30% 6% 2 5% 3 2 2 2 3 5% 40%	6214
February	1st to 10th	Night	20% 7% 2 5% 3 3 3 2 5% 5% 46%	2400
	11th to 20th	Night	22% 7% 2 3 3 3 2 3 3 5% 48%	2338
	21st to end	Night	23% 6% 2 4 3 2 3 3 4 5% 44%	1980
March	1st to 10th	Night	21% 8% 2 5% 4 4 3 3 4 6% 39%	3544
	11th to 20th	Night	23% 11% 3 7% 4 4 4 3 4 5% 33%	3590
	21st to end	Night	18% 7% 3 5% 3 3 4 3 4 6% 44%	3889
April	1st to 10th	Night	16% 7% 2 5% 5% 3 3 3 5% 7% 45%	2090
	11th to 20th	Night	21% 6% 2 5% 3 3 4 2 4 6% 43%	2063
	21st to end	Night	19% 8% 3 4 3 3 3 2 4 6% 46%	1769
May	1st to 10th	Night	29% 9% 3 4 3 3 3 3 4 5% 35%	2823
	11th to 20th	Night	15% 6% 1 5% 3 3 4 3 5% 7% 49%	2823
	21st to end	Night	15% 7% 2 4 3 3 4 4 6% 8% 43%	3090
June	1st to 10th	Night	7% 4 1 4 3 3 3 3 5% 8% 59%	1710
	11th to 20th	Night	5% 4 2 4 3 3 3 3 6% 10% 56%	1710
	21st to end	Night	8% 5% 2 4 4 4 4 4 7% 8% 49%	1710
July	1st to 10th	Night	6% 4 1 4 3 4 4 4 6% 10% 54%	2850
	11th to 20th	Night	5% 4 1 5% 4 4 5% 4 7% 11% 51%	2850
	21st to end	Night	12% 7% 2 6% 5% 4 5% 4 6% 9% 40%	3098
August	1st to 10th	Night	2 1 1 2 2 2 3 2 4 8% 74%	2836
	11th to 20th	Night	3 3 1 4 3 3 4 4 7% 10% 58%	3102
	21st to end	Night	5% 3 1 4 4 4 4 4 7% 10% 55%	3673
September	1st to 10th	Night	9% 5% 2 5% 4 4 4 3 6% 9% 49%	2090
	11th to 20th	Night	10% 6% 3 6% 4 4 5% 4 6% 8% 45%	2090
	21st to end	Night	9% 5% 2 5% 3 4 4 3 6% 8% 52%	2090
October	1st to 10th	Night	7% 3 1 4 3 3 4 2 4 7% 61%	2090
	11th to 20th	Night	13% 6% 2 4 3 3 3 3 4 5% 53%	2204
	21st to end	Night	16% 4 2 4 2 2 2 2 3 4 59%	2508
November	1st to 10th	Night	16% 7% 2 6% 3 2 3 2 4 5% 52%	2340
	11th to 20th	Night	12% 5% 2 4 4 3 4 3 4 6% 55%	2505
	21st to end	Night	19% 6% 2 4 3 3 4 3 4 6% 47%	2600
December	1st to 10th	Night	25% 9% 2 6% 3 3 3 3 4 4 38%	4250
	11th to 20th	Night	23% 8% 2 5% 3 2 3 2 3 3 46%	4816
	21st to end	Night	20% 6% 2 3 2 2 2 2 3 4 55%	6490

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% 4 5% 19% 22% 11%	4078
	11th to 20th	Day	35% 2 5% 16% 23% 19%	4080
	21st to end	Day	47% 3 4 9% 24% 13%	4792
February	1st to 10th	Day	44% 4 6% 12% 19% 15%	2000
	11th to 20th	Day	43% 4 8% 17% 17% 12%	1959
	21st to end	Day	40% 4 7% 15% 18% 15%	1650
March	1st to 10th	Day	42% 6% 8% 15% 19% 10%	3529
	11th to 20th	Day	52% 7% 6% 8% 16% 10%	3590
	21st to end	Day	38% 6% 9% 16% 21% 10%	3880
April	1st to 10th	Day	43% 6% 8% 16% 16% 12%	2090
	11th to 20th	Day	44% 6% 8% 15% 17% 11%	2066
	21st to end	Day	42% 6% 6% 19% 18% 9%	2404
May	1st to 10th	Day	52% 8% 9% 13% 13% 5%	4120
	11th to 20th	Day	39% 9% 9% 17% 19% 6%	4086
	21st to end	Day	36% 11% 15% 26% 11% 1	4489
June	1st to 10th	Day	29% 10% 14% 26% 18% 3	2470
	11th to 20th	Day	35% 8% 12% 25% 17% 4	2470
	21st to end	Day	40% 10% 12% 24% 13% 3	2470
July	1st to 10th	Day	32% 7% 17% 37% 6% 1	4056
	11th to 20th	Day	31% 7% 19% 28% 14% 2	4051
	21st to end	Day	40% 7% 18% 27% 8%	4325
August	1st to 10th	Day	14% 5% 12% 42% 26% 1	4090
	11th to 20th	Day	20% 6% 24% 37% 11% 2	3768
	21st to end	Day	29% 9% 20% 24% 17% 2	3987
September	1st to 10th	Day	40% 8% 9% 19% 16% 8%	2090
	11th to 20th	Day	39% 8% 12% 18% 17% 5%	2090
	21st to end	Day	31% 8% 10% 20% 17% 13%	2090
October	1st to 10th	Day	17% 4 7% 12% 23% 36%	3480
	11th to 20th	Day	23% 4 9% 18% 25% 20%	3236
	21st to end	Day	27% 4 6% 18% 30% 15%	3428
November	1st to 10th	Day	39% 7% 9% 17% 18% 11%	1958
	11th to 20th	Day	35% 5% 8% 17% 20% 15%	1890
	21st to end	Day	43% 4 7% 15% 18% 14%	1800
December	1st to 10th	Day	51% 3 6% 16% 15% 9%	2940
	11th to 20th	Day	44% 5% 6% 11% 21% 13%	3389
	21st to end	Day	33% 3 5% 17% 27% 16%	4488
January	1st to 10th	Night	38% 3 5% 18% 22% 14%	5888
	11th to 20th	Night	26% 2 5% 18% 30% 19%	5900
	21st to end	Night	48% 3 4 10% 20% 15%	6214
February	1st to 10th	Night	41% 4 7% 11% 19% 18%	2400
	11th to 20th	Night	41% 4 6% 16% 19% 15%	2338
	21st to end	Night	43% 4 6% 14% 18% 15%	1980
March	1st to 10th	Night	45% 7% 8% 15% 16% 10%	3544
	11th to 20th	Night	51% 8% 8% 10% 12% 10%	3590
	21st to end	Night	41% 6% 9% 15% 19% 10%	3889
April	1st to 10th	Night	38% 6% 9% 17% 15% 14%	2090
	11th to 20th	Night	43% 5% 8% 13% 16% 14%	2063
	21st to end	Night	41% 5% 9% 20% 16% 10%	1769
May	1st to 10th	Night	50% 7% 8% 15% 13% 6%	2850
	11th to 20th	Night	34% 9% 11% 21% 18% 7%	2824
	21st to end	Night	35% 9% 15% 28% 11% 1	3099
June	1st to 10th	Night	23% 7% 17% 28% 23% 3	1710
	11th to 20th	Night	24% 6% 16% 30% 19% 5%	1710
	21st to end	Night	29% 9% 17% 27% 14% 3	1710
July	1st to 10th	Night	26% 8% 23% 37% 5% 1	2805
	11th to 20th	Night	26% 9% 21% 29% 14% 1	2796
	21st to end	Night	39% 7% 23% 25% 6%	2999
August	1st to 10th	Night	11% 5% 17% 46% 21% 1	2826
	11th to 20th	Night	19% 9% 31% 31% 9% 1	3132
	21st to end	Night	24% 11% 22% 26% 15% 2	3673
September	1st to 10th	Night	33% 7% 16% 21% 15% 7%	2090
	11th to 20th	Night	36% 8% 14% 22% 14% 6%	2090
	21st to end	Night	29% 8% 14% 20% 16% 13%	2090
October	1st to 10th	Night	17% 4 8% 14% 20% 37%	3480
	11th to 20th	Night	22% 3 10% 17% 29% 20%	3651
	21st to end	Night	26% 4 6% 20% 29% 16%	4120
November	1st to 10th	Night	35% 6% 9% 18% 19% 14%	2340
	11th to 20th	Night	31% 6% 9% 17% 20% 17%	2505
	21st to end	Night	39% 4 8% 16% 18% 14%	2600
December	1st to 10th	Night	51% 3 7% 15% 15% 10%	4250
	11th to 20th	Night	44% 3 7% 8% 21% 17%	4817
	21st to end	Night	35% 3 3 13% 29% 16%	6490

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	24% 16% 33% 24% 3 1	300
	11th to 20th	Day	27% 16% 25% 23% 7% 2	300
	21st to end	Day	21% 15% 35% 23% 6%	330
February	1st to 10th	Day	33% 10% 29% 20% 7%	300
	11th to 20th	Day	27% 17% 33% 19% 4	300
	21st to end	Day	25% 16% 41% 16% 2	249
March	1st to 10th	Day	25% 15% 37% 18% 4	300
	11th to 20th	Day	19% 19% 41% 17% 4 1	300
	21st to end	Day	21% 13% 36% 23% 5%	315
April	1st to 10th	Day	21% 14% 37% 22% 4	270
	11th to 20th	Day	20% 18% 33% 19% 10%	264
	21st to end	Day	19% 13% 36% 26% 7%	584
May	1st to 10th	Day	18% 12% 34% 27% 9%	653
	11th to 20th	Day	18% 7% 27% 33% 13% 2	675
	21st to end	Day	16% 6% 24% 35% 17% 2	734
June	1st to 10th	Day	8% 2 13% 40% 30% 7%	680
	11th to 20th	Day	8% 2 14% 44% 29% 4	680
	21st to end	Day	10% 2 12% 36% 29% 11%	680
July	1st to 10th	Day	9% 2 9% 33% 35% 11%	671
	11th to 20th	Day	5% 1 6% 30% 48% 11%	668
	21st to end	Day	5% 1 5% 33% 43% 12%	739
August	1st to 10th	Day	3 1 5% 28% 50% 14%	676
	11th to 20th	Day	5% 1 5% 33% 44% 13%	483
	21st to end	Day	5% 1 5% 26% 38% 25%	425
September	1st to 10th	Day	10% 1 7% 27% 38% 17%	300
	11th to 20th	Day	7% 1 4 26% 46% 16%	300
	21st to end	Day	8% 1 9% 28% 38% 16%	300
October	1st to 10th	Day	5% 2 16% 33% 35% 10%	300
	11th to 20th	Day	11% 4 18% 38% 22% 6%	300
	21st to end	Day	18% 9% 25% 25% 16% 6%	330
November	1st to 10th	Day	19% 8% 28% 27% 15% 3	300
	11th to 20th	Day	19% 8% 28% 28% 15% 2	300
	21st to end	Day	20% 15% 35% 17% 12% 1	300
December	1st to 10th	Day	22% 7% 34% 26% 6% 5%	300
	11th to 20th	Day	23% 16% 27% 26% 9%	300
	21st to end	Day	21% 10% 36% 24% 8% 1	330
January	1st to 10th	Night	22% 9% 28% 31% 9% 1	1000
	11th to 20th	Night	21% 10% 31% 30% 8%	1000
	21st to end	Night	24% 9% 28% 31% 7%	980
February	1st to 10th	Night	26% 10% 30% 27% 6%	800
	11th to 20th	Night	27% 11% 33% 25% 4	784
	21st to end	Night	26% 13% 38% 21% 2	660
March	1st to 10th	Night	25% 11% 35% 27% 3	615
	11th to 20th	Night	23% 10% 35% 27% 5%	600
	21st to end	Night	20% 9% 39% 29% 3	647
April	1st to 10th	Night	18% 9% 41% 29% 4	570
	11th to 20th	Night	21% 12% 37% 25% 5%	563
	21st to end	Night	20% 10% 37% 25% 8%	570
May	1st to 10th	Night	19% 10% 38% 27% 6%	570
	11th to 20th	Night	17% 5% 30% 37% 11%	561
	21st to end	Night	15% 4 32% 36% 12%	617
June	1st to 10th	Night	7% 2 19% 48% 23% 1	570
	11th to 20th	Night	5% 2 28% 49% 14% 1	570
	21st to end	Night	6% 2 17% 43% 27% 4	570
July	1st to 10th	Night	9% 1 10% 46% 31% 3	555
	11th to 20th	Night	4 1 11% 48% 34% 2	552
	21st to end	Night	5% 1 9% 48% 34% 3	624
August	1st to 10th	Night	2 8% 48% 38% 4	567
	11th to 20th	Night	4 1 7% 50% 34% 3	564
	21st to end	Night	7% 1 6% 37% 45% 5%	627
September	1st to 10th	Night	8% 1 8% 39% 38% 5%	570
	11th to 20th	Night	12% 2 7% 36% 40% 3	570
	21st to end	Night	10% 1 12% 35% 38% 3	570
October	1st to 10th	Night	7% 1 11% 45% 32% 5%	570
	11th to 20th	Night	13% 4 20% 37% 22% 2	684
	21st to end	Night	16% 7% 22% 32% 20% 2	836
November	1st to 10th	Night	16% 6% 20% 36% 21% 1	780
	11th to 20th	Night	14% 6% 25% 38% 15% 2	905
	21st to end	Night	21% 10% 26% 30% 12% 1	1000
December	1st to 10th	Night	21% 8% 28% 32% 11% 1	1000
	11th to 20th	Night	25% 10% 25% 32% 8%	1000
	21st to end	Night	23% 7% 28% 33% 8%	1100

Page generated at 2025-03-24 08:04:29. Version ac07

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