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 2026-07-31.

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 6% 4 4 4 3 5% 7% 45%	138361
	Night	16% 6% 2 5% 3 3 3 3 5% 6% 48%	135021
Transparency	Day	37% 5% 10% 20% 18% 10%	142140
	Night	36% 5% 11% 19% 18% 12%	139309
Seeing	Day	14% 7% 22% 29% 22% 6%	17145
	Night	17% 7% 25% 34% 16% 1	27001

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% 8% 3 5% 3 2 3 2 4 5% 51%	5289
	11th to 20th	Day	16% 4 2 5% 3 2 3 2 4 4 54%	5310
	21st to end	Day	26% 7% 2 5% 3 2 2 3 4 6% 40%	6211
February	1st to 10th	Day	22% 6% 2 6% 3 3 3 2 5% 4 45%	2100
	11th to 20th	Day	20% 7% 2 5% 3 3 3 3 4 5% 44%	2049
	21st to end	Day	19% 7% 2 5% 2 3 2 2 3 6% 49%	1730
March	1st to 10th	Day	15% 6% 2 6% 3 3 3 2 4 6% 51%	5016
	11th to 20th	Day	15% 7% 2 6% 4 3 3 2 3 4 50%	5090
	21st to end	Day	19% 7% 2 5% 3 3 3 3 4 5% 46%	5583
April	1st to 10th	Day	16% 8% 2 6% 5% 4 4 3 4 6% 42%	2310
	11th to 20th	Day	20% 6% 3 7% 4 4 4 3 4 5% 40%	2286
	21st to end	Day	17% 8% 2 6% 5% 4 4 3 4 7% 40%	2658
May	1st to 10th	Day	24% 8% 2 6% 4 3 4 3 5% 5% 35%	7617
	11th to 20th	Day	13% 7% 2 7% 4 4 4 3 5% 7% 43%	7627
	21st to end	Day	13% 7% 2 7% 5% 5% 6% 5% 7% 9% 33%	8392
June	1st to 10th	Day	8% 4 2 5% 3 5% 6% 5% 7% 10% 46%	2730
	11th to 20th	Day	8% 5% 2 6% 6% 5% 6% 5% 6% 9% 42%	2730
	21st to end	Day	7% 6% 2 7% 6% 6% 6% 5% 8% 10% 37%	2730
July	1st to 10th	Day	12% 7% 2 7% 6% 5% 5% 4 6% 8% 38%	6030
	11th to 20th	Day	6% 4 2 6% 5% 6% 6% 6% 8% 12% 39%	6030
	21st to end	Day	8% 5% 2 6% 5% 5% 6% 5% 7% 10% 40%	6553
August	1st to 10th	Day	1 2 1 3 3 2 3 3 5% 9% 69%	4234
	11th to 20th	Day	3 3 1 4 3 4 5% 4 7% 11% 56%	3852
	21st to end	Day	5% 3 2 5% 4 6% 6% 5% 7% 11% 47%	4114
September	1st to 10th	Day	9% 6% 2 8% 5% 5% 5% 4 5% 6% 43%	2200
	11th to 20th	Day	11% 6% 2 7% 5% 5% 5% 4 6% 8% 42%	2200
	21st to end	Day	8% 4 2 4 4 5% 6% 4 6% 8% 49%	2200
October	1st to 10th	Day	6% 4 2 5% 4 4 4 4 6% 7% 55%	2200
	11th to 20th	Day	12% 4 2 4 3 4 4 3 4 6% 53%	2060
	21st to end	Day	11% 4 1 5% 3 3 4 3 4 5% 57%	2200
November	1st to 10th	Day	14% 8% 2 6% 4 3 3 4 5% 5% 47%	2058
	11th to 20th	Day	13% 5% 2 5% 4 3 4 3 4 5% 52%	1984
	21st to end	Day	19% 7% 2 6% 4 4 3 2 4 5% 44%	1890
December	1st to 10th	Day	27% 8% 3 6% 3 3 3 2 4 5% 38%	3030
	11th to 20th	Day	19% 7% 2 6% 4 4 4 3 4 5% 43%	3481
	21st to end	Day	16% 6% 1 4 3 3 2 2 3 4 56%	4587
January	1st to 10th	Night	17% 7% 2 4 3 2 2 2 3 5% 52%	7634
	11th to 20th	Night	11% 3 1 3 2 2 3 3 4 4 63%	7680
	21st to end	Night	30% 5% 2 4 3 2 3 2 3 5% 40%	8045
February	1st to 10th	Night	19% 7% 2 4 3 3 3 2 5% 6% 47%	2520
	11th to 20th	Night	22% 7% 2 3 3 3 2 3 3 5% 48%	2458
	21st to end	Night	22% 6% 2 4 3 2 3 3 4 5% 45%	2076
March	1st to 10th	Night	20% 6% 2 5% 4 4 3 3 4 6% 44%	5058
	11th to 20th	Night	16% 8% 2 5% 3 3 3 3 4 5% 49%	5090
	21st to end	Night	22% 9% 2 5% 2 3 3 2 4 5% 43%	5588
April	1st to 10th	Night	17% 6% 2 5% 5% 3 3 3 5% 6% 44%	2310
	11th to 20th	Night	22% 7% 2 5% 3 3 4 2 4 6% 42%	2283
	21st to end	Night	22% 7% 3 5% 3 3 3 2 4 6% 43%	1955
May	1st to 10th	Night	28% 9% 3 5% 3 3 3 3 5% 6% 32%	5266
	11th to 20th	Night	14% 6% 2 5% 4 4 4 4 6% 8% 44%	5265
	21st to end	Night	17% 7% 3 6% 4 4 5% 4 6% 9% 36%	5793
June	1st to 10th	Night	8% 5% 1 4 3 3 3 3 5% 8% 57%	1890
	11th to 20th	Night	7% 4 2 4 4 3 3 3 6% 9% 54%	1890
	21st to end	Night	9% 5% 2 4 4 4 4 4 7% 8% 50%	1890
July	1st to 10th	Night	10% 6% 2 7% 4 4 4 4 6% 10% 42%	4168
	11th to 20th	Night	7% 4 1 5% 4 5% 5% 4 8% 12% 45%	4167
	21st to end	Night	9% 6% 2 5% 4 3 5% 4 7% 9% 44%	4539
August	1st to 10th	Night	2 1 1 2 2 2 3 2 5% 8% 74%	2926
	11th to 20th	Night	3 3 1 4 3 3 4 4 8% 10% 57%	3202
	21st to end	Night	6% 3 1 4 4 4 4 4 7% 10% 55%	3789
September	1st to 10th	Night	9% 5% 2 6% 4 4 4 3 6% 9% 48%	2200
	11th to 20th	Night	10% 6% 2 6% 4 4 4 4 6% 8% 46%	2200
	21st to end	Night	9% 5% 2 5% 3 4 4 3 6% 8% 52%	2200
October	1st to 10th	Night	7% 3 1 4 3 3 4 2 4 7% 61%	2200
	11th to 20th	Night	13% 5% 2 4 3 3 3 3 4 5% 55%	2320
	21st to end	Night	16% 4 2 4 2 2 2 2 3 4 60%	2640
November	1st to 10th	Night	15% 6% 2 5% 3 2 3 2 3 5% 54%	2460
	11th to 20th	Night	12% 5% 2 4 4 3 4 3 4 6% 55%	2630
	21st to end	Night	20% 6% 2 4 3 3 4 3 4 6% 46%	2730
December	1st to 10th	Night	24% 9% 2 6% 3 3 3 3 4 4 38%	4380
	11th to 20th	Night	23% 8% 2 5% 3 2 3 2 3 3 47%	4946
	21st to end	Night	20% 6% 2 3 2 2 2 2 3 4 55%	6633

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	38% 3 7% 20% 23% 10%	5290
	11th to 20th	Day	35% 2 4 14% 24% 21%	5310
	21st to end	Day	46% 3 5% 11% 24% 10%	6211
February	1st to 10th	Day	43% 4 6% 12% 20% 15%	2100
	11th to 20th	Day	43% 4 8% 16% 18% 11%	2059
	21st to end	Day	39% 4 7% 16% 20% 14%	1730
March	1st to 10th	Day	36% 4 6% 18% 16% 20%	5016
	11th to 20th	Day	38% 5% 4 8% 17% 28%	5090
	21st to end	Day	41% 5% 8% 18% 20% 9%	5585
April	1st to 10th	Day	44% 5% 7% 15% 16% 12%	2310
	11th to 20th	Day	45% 6% 8% 14% 17% 11%	2286
	21st to end	Day	44% 6% 7% 18% 17% 9%	2658
May	1st to 10th	Day	49% 6% 9% 19% 14% 3	7655
	11th to 20th	Day	39% 6% 10% 18% 20% 6%	7631
	21st to end	Day	42% 8% 13% 24% 11% 1	8405
June	1st to 10th	Day	30% 9% 15% 27% 17% 3	2730
	11th to 20th	Day	36% 8% 12% 23% 17% 4	2730
	21st to end	Day	38% 9% 13% 24% 14% 3	2730
July	1st to 10th	Day	43% 6% 17% 28% 4 1	5966
	11th to 20th	Day	35% 7% 19% 28% 11% 1	5961
	21st to end	Day	36% 6% 16% 25% 14% 3	6371
August	1st to 10th	Day	14% 5% 12% 42% 26% 1	4220
	11th to 20th	Day	20% 6% 23% 37% 11% 2	3888
	21st to end	Day	29% 9% 20% 24% 17% 1	4113
September	1st to 10th	Day	39% 8% 9% 20% 16% 8%	2200
	11th to 20th	Day	38% 8% 13% 19% 17% 5%	2200
	21st to end	Day	31% 8% 10% 21% 17% 13%	2200
October	1st to 10th	Day	17% 4 7% 12% 24% 36%	3590
	11th to 20th	Day	23% 4 9% 19% 26% 20%	3339
	21st to end	Day	27% 4 6% 18% 30% 15%	3538
November	1st to 10th	Day	38% 6% 8% 16% 20% 12%	2058
	11th to 20th	Day	34% 5% 8% 17% 21% 15%	1984
	21st to end	Day	43% 4 7% 15% 18% 13%	1890
December	1st to 10th	Day	51% 3 6% 16% 15% 9%	3030
	11th to 20th	Day	44% 5% 6% 11% 22% 13%	3479
	21st to end	Day	33% 3 5% 17% 27% 16%	4587
January	1st to 10th	Night	36% 3 6% 18% 22% 14%	7635
	11th to 20th	Night	26% 2 5% 17% 29% 21%	7680
	21st to end	Night	48% 3 3 12% 21% 13%	8045
February	1st to 10th	Night	39% 4 8% 12% 19% 18%	2520
	11th to 20th	Night	41% 4 6% 17% 18% 14%	2458
	21st to end	Night	41% 4 6% 15% 19% 15%	2076
March	1st to 10th	Night	41% 5% 6% 16% 16% 16%	5058
	11th to 20th	Night	38% 6% 7% 10% 14% 25%	5090
	21st to end	Night	44% 5% 7% 17% 17% 10%	5588
April	1st to 10th	Night	39% 6% 9% 17% 15% 14%	2310
	11th to 20th	Night	44% 5% 8% 14% 15% 14%	2283
	21st to end	Night	44% 5% 9% 18% 15% 9%	1955
May	1st to 10th	Night	52% 5% 9% 16% 13% 4	5293
	11th to 20th	Night	38% 7% 10% 19% 20% 7%	5266
	21st to end	Night	42% 7% 17% 25% 8% 1	5805
June	1st to 10th	Night	25% 6% 16% 29% 21% 2	1890
	11th to 20th	Night	26% 6% 16% 29% 18% 4	1890
	21st to end	Night	30% 9% 17% 27% 15% 2	1890
July	1st to 10th	Night	38% 8% 23% 27% 4	4125
	11th to 20th	Night	30% 7% 24% 29% 10%	4116
	21st to end	Night	34% 7% 20% 24% 12% 3	4410
August	1st to 10th	Night	11% 5% 17% 46% 21% 1	2916
	11th to 20th	Night	19% 8% 31% 31% 9% 1	3232
	21st to end	Night	24% 11% 22% 26% 15% 2	3789
September	1st to 10th	Night	33% 7% 16% 21% 15% 8%	2200
	11th to 20th	Night	35% 8% 15% 23% 14% 6%	2200
	21st to end	Night	29% 8% 14% 21% 16% 13%	2200
October	1st to 10th	Night	17% 4 8% 14% 21% 36%	3590
	11th to 20th	Night	21% 3 9% 17% 29% 20%	3767
	21st to end	Night	26% 4 5% 19% 29% 17%	4252
November	1st to 10th	Night	34% 5% 8% 17% 21% 14%	2460
	11th to 20th	Night	31% 6% 8% 17% 20% 17%	2630
	21st to end	Night	40% 4 8% 16% 18% 14%	2730
December	1st to 10th	Night	51% 3 7% 15% 15% 10%	4380
	11th to 20th	Night	44% 3 7% 8% 21% 17%	4947
	21st to end	Night	36% 3 4 14% 28% 16%	6633

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	25% 15% 32% 23% 5% 1	330
	11th to 20th	Day	26% 16% 27% 22% 8% 2	330
	21st to end	Day	21% 16% 35% 22% 5%	363
February	1st to 10th	Day	32% 10% 29% 21% 7%	330
	11th to 20th	Day	26% 17% 34% 19% 4	330
	21st to end	Day	23% 16% 42% 16% 2	273
March	1st to 10th	Day	26% 15% 37% 18% 4	330
	11th to 20th	Day	18% 18% 42% 18% 4 1	330
	21st to end	Day	21% 11% 35% 25% 8%	363
April	1st to 10th	Day	21% 14% 38% 23% 4	330
	11th to 20th	Day	21% 18% 33% 19% 9%	324
	21st to end	Day	22% 13% 36% 23% 6%	678
May	1st to 10th	Day	19% 12% 35% 25% 8%	753
	11th to 20th	Day	18% 9% 29% 31% 11% 2	775
	21st to end	Day	15% 6% 26% 35% 16% 2	844
June	1st to 10th	Day	10% 3 15% 40% 27% 6%	780
	11th to 20th	Day	9% 2 16% 43% 27% 3	780
	21st to end	Day	9% 2 14% 37% 27% 10%	780
July	1st to 10th	Day	10% 2 8% 36% 33% 10%	771
	11th to 20th	Day	7% 1 7% 32% 43% 9%	768
	21st to end	Day	6% 1 6% 34% 43% 11%	845
August	1st to 10th	Day	3 1 5% 28% 50% 13%	726
	11th to 20th	Day	4 1 5% 34% 44% 13%	523
	21st to end	Day	5% 1 5% 26% 39% 24%	463
September	1st to 10th	Day	10% 1 8% 28% 37% 16%	330
	11th to 20th	Day	7% 1 5% 27% 46% 15%	330
	21st to end	Day	8% 1 9% 31% 36% 15%	330
October	1st to 10th	Day	4 2 15% 33% 36% 10%	330
	11th to 20th	Day	10% 4 19% 37% 23% 6%	330
	21st to end	Day	18% 10% 25% 26% 16% 6%	363
November	1st to 10th	Day	18% 8% 28% 27% 17% 3	330
	11th to 20th	Day	18% 8% 28% 30% 15% 2	330
	21st to end	Day	20% 14% 35% 18% 12% 1	330
December	1st to 10th	Day	23% 7% 35% 24% 6% 5%	330
	11th to 20th	Day	22% 15% 27% 27% 9%	330
	21st to end	Day	21% 10% 35% 25% 8% 1	363
January	1st to 10th	Night	22% 10% 28% 32% 8% 1	1050
	11th to 20th	Night	20% 10% 32% 30% 7%	1050
	21st to end	Night	25% 10% 28% 30% 7%	1029
February	1st to 10th	Night	26% 10% 31% 28% 6%	840
	11th to 20th	Night	27% 11% 33% 25% 4	824
	21st to end	Night	25% 13% 38% 22% 2	692
March	1st to 10th	Night	26% 11% 34% 26% 3	646
	11th to 20th	Night	23% 10% 35% 27% 5%	630
	21st to end	Night	20% 9% 39% 29% 3	693
April	1st to 10th	Night	19% 9% 40% 28% 4	630
	11th to 20th	Night	22% 13% 36% 24% 5%	623
	21st to end	Night	24% 9% 36% 24% 7%	630
May	1st to 10th	Night	20% 10% 38% 27% 5%	630
	11th to 20th	Night	17% 8% 30% 35% 10%	621
	21st to end	Night	16% 4 32% 36% 13%	683
June	1st to 10th	Night	8% 3 20% 46% 21% 1	630
	11th to 20th	Night	6% 2 29% 47% 14% 1	630
	21st to end	Night	7% 2 19% 43% 25% 3	630
July	1st to 10th	Night	10% 1 10% 47% 30% 2	615
	11th to 20th	Night	6% 1 12% 47% 32% 2	612
	21st to end	Night	5% 1 10% 47% 34% 3	687
August	1st to 10th	Night	2 8% 48% 39% 4	597
	11th to 20th	Night	4 1 8% 50% 34% 4	594
	21st to end	Night	7% 1 6% 37% 45% 5%	660
September	1st to 10th	Night	8% 2 8% 39% 38% 5%	600
	11th to 20th	Night	11% 2 7% 37% 40% 3	600
	21st to end	Night	10% 1 13% 36% 38% 3	600
October	1st to 10th	Night	7% 1 10% 46% 32% 4	600
	11th to 20th	Night	13% 4 20% 38% 23% 2	720
	21st to end	Night	16% 8% 22% 33% 20% 2	880
November	1st to 10th	Night	15% 7% 20% 37% 21% 1	820
	11th to 20th	Night	14% 6% 25% 38% 15% 1	950
	21st to end	Night	22% 10% 26% 30% 12% 1	1050
December	1st to 10th	Night	21% 8% 28% 31% 10% 1	1050
	11th to 20th	Night	25% 10% 25% 32% 8%	1050
	21st to end	Night	23% 8% 28% 33% 8%	1155

Page generated at 2026-07-28 02:25:23. Version ac07

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