Blanco State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blanco State Park clear sky chart from 2005-11-06 to 2026-05-17.

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	11% 6% 2 6% 4 4 4 3 5% 7% 47%	132323
	Night	13% 6% 2 5% 3 3 3 3 5% 6% 51%	130840
Transparency	Day	36% 3 9% 21% 20% 11%	136115
	Night	35% 3 9% 20% 20% 13%	135112
Seeing	Day	14% 9% 23% 30% 19% 5%	16790
	Night	16% 8% 26% 35% 14% 1	26803

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	11% 8% 2 5% 4 3 3 2 4 5% 53%	5289
	11th to 20th	Day	14% 6% 2 4 3 2 2 3 5% 5% 55%	5310
	21st to end	Day	21% 7% 3 6% 3 4 3 2 3 6% 42%	6321
February	1st to 10th	Day	17% 7% 2 6% 3 3 3 3 5% 5% 46%	2100
	11th to 20th	Day	15% 7% 3 5% 3 3 4 3 4 7% 46%	2049
	21st to end	Day	17% 6% 2 5% 3 2 3 3 4 4 52%	1730
March	1st to 10th	Day	12% 6% 2 5% 3 3 3 3 4 6% 53%	4948
	11th to 20th	Day	13% 7% 2 6% 4 3 3 2 3 5% 52%	5090
	21st to end	Day	13% 7% 3 6% 3 4 4 3 4 6% 47%	5583
April	1st to 10th	Day	13% 8% 3 6% 5% 4 4 3 4 6% 44%	2310
	11th to 20th	Day	19% 7% 2 5% 4 4 3 3 5% 6% 41%	2321
	21st to end	Day	15% 8% 2 6% 5% 4 4 3 4 6% 44%	2656
May	1st to 10th	Day	18% 8% 3 7% 4 4 4 4 6% 7% 35%	5992
	11th to 20th	Day	10% 6% 2 6% 4 4 4 3 6% 8% 46%	5941
	21st to end	Day	13% 7% 3 7% 5% 5% 6% 5% 7% 8% 34%	6434
June	1st to 10th	Day	5% 4 2 5% 5% 5% 6% 5% 7% 9% 48%	2600
	11th to 20th	Day	7% 6% 2 5% 5% 5% 5% 5% 6% 8% 47%	2600
	21st to end	Day	6% 6% 2 6% 6% 6% 6% 4 7% 10% 40%	2600
July	1st to 10th	Day	12% 7% 3 7% 6% 5% 5% 4 7% 8% 37%	5900
	11th to 20th	Day	4 4 1 5% 5% 5% 6% 5% 9% 10% 45%	5900
	21st to end	Day	6% 5% 2 6% 5% 5% 5% 5% 7% 10% 44%	6422
August	1st to 10th	Day	1 1 1 2 3 3 4 3 5% 9% 68%	4154
	11th to 20th	Day	3 3 1 4 3 3 4 4 6% 11% 58%	3846
	21st to end	Day	4 3 2 5% 5% 6% 6% 5% 7% 11% 46%	4161
September	1st to 10th	Day	10% 6% 3 7% 5% 5% 4 4 5% 6% 46%	2200
	11th to 20th	Day	10% 5% 2 6% 6% 5% 6% 4 7% 8% 41%	2200
	21st to end	Day	8% 4 2 6% 4 4 5% 4 6% 7% 50%	2200
October	1st to 10th	Day	6% 5% 2 4 3 4 5% 4 5% 6% 56%	2200
	11th to 20th	Day	11% 5% 2 4 4 3 3 4 4 6% 54%	2088
	21st to end	Day	11% 4 2 6% 4 3 3 2 4 5% 58%	2200
November	1st to 10th	Day	12% 8% 2 6% 4 3 3 3 5% 6% 47%	2058
	11th to 20th	Day	10% 5% 2 6% 4 4 3 4 5% 6% 52%	1932
	21st to end	Day	16% 6% 2 6% 4 2 4 3 4 6% 46%	1890
December	1st to 10th	Day	23% 8% 3 7% 3 3 3 2 4 4 40%	3030
	11th to 20th	Day	13% 9% 3 7% 4 4 4 3 5% 5% 44%	3481
	21st to end	Day	11% 6% 2 5% 3 2 3 2 3 4 59%	4587
January	1st to 10th	Night	13% 6% 3 4 2 3 3 2 3 5% 55%	7634
	11th to 20th	Night	9% 4 1 3 2 2 2 3 5% 4 64%	7680
	21st to end	Night	26% 6% 2 5% 3 3 3 2 4 5% 41%	7949
February	1st to 10th	Night	15% 8% 3 5% 2 3 3 2 4 5% 49%	2520
	11th to 20th	Night	16% 7% 2 5% 4 3 3 3 3 5% 49%	2458
	21st to end	Night	17% 7% 2 5% 3 3 3 2 4 5% 49%	2076
March	1st to 10th	Night	13% 8% 2 5% 4 4 3 3 5% 7% 46%	5129
	11th to 20th	Night	14% 8% 2 5% 3 3 3 2 4 5% 51%	5090
	21st to end	Night	15% 10% 2 5% 4 3 3 3 4 5% 45%	5588
April	1st to 10th	Night	11% 9% 3 6% 4 4 4 3 5% 6% 45%	2310
	11th to 20th	Night	17% 8% 2 7% 4 2 3 3 4 5% 45%	2243
	21st to end	Night	19% 8% 2 5% 4 3 3 3 3 5% 45%	1962
May	1st to 10th	Night	23% 10% 3 5% 3 3 3 3 4 6% 37%	4143
	11th to 20th	Night	8% 5% 2 6% 4 4 5% 3 6% 7% 49%	4107
	21st to end	Night	14% 7% 2 6% 4 4 5% 4 6% 9% 37%	4443
June	1st to 10th	Night	6% 4 1 3 3 4 3 3 6% 8% 59%	1800
	11th to 20th	Night	5% 4 2 3 3 4 4 3 6% 8% 58%	1800
	21st to end	Night	6% 5% 2 5% 4 3 5% 2 6% 10% 52%	1800
July	1st to 10th	Night	10% 7% 3 6% 5% 4 4 4 7% 9% 42%	4078
	11th to 20th	Night	3 4 1 5% 4 4 5% 4 7% 11% 50%	4077
	21st to end	Night	7% 7% 2 5% 4 4 4 4 6% 10% 46%	4449
August	1st to 10th	Night	1 1 1 2 2 2 3 3 4 8% 74%	2987
	11th to 20th	Night	3 2 1 3 3 3 4 3 7% 11% 60%	3213
	21st to end	Night	4 4 1 4 4 3 4 3 6% 10% 55%	3742
September	1st to 10th	Night	8% 5% 2 5% 4 4 4 3 6% 8% 51%	2200
	11th to 20th	Night	8% 6% 3 6% 4 4 5% 3 6% 8% 47%	2200
	21st to end	Night	7% 5% 2 4 4 4 4 3 7% 8% 52%	2200
October	1st to 10th	Night	5% 4 1 4 3 3 4 3 4 7% 62%	2200
	11th to 20th	Night	12% 5% 2 4 3 3 4 3 4 5% 56%	2290
	21st to end	Night	14% 5% 1 4 2 3 2 2 2 4 61%	2640
November	1st to 10th	Night	12% 7% 2 5% 3 3 2 2 4 5% 54%	2460
	11th to 20th	Night	9% 6% 2 5% 3 3 2 3 5% 6% 56%	2683
	21st to end	Night	16% 6% 2 5% 3 3 3 3 4 5% 48%	2730
December	1st to 10th	Night	20% 9% 3 6% 3 3 3 2 4 5% 41%	4380
	11th to 20th	Night	18% 11% 2 5% 3 3 2 2 3 4 47%	4946
	21st to end	Night	15% 7% 2 4 2 2 2 2 3 4 57%	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	35% 2 5% 22% 25% 10%	5290
	11th to 20th	Day	33% 1 4 14% 26% 21%	5310
	21st to end	Day	46% 2 5% 12% 24% 11%	6321
February	1st to 10th	Day	42% 3 3 13% 21% 17%	2100
	11th to 20th	Day	40% 3 6% 19% 19% 13%	2059
	21st to end	Day	38% 1 5% 18% 22% 16%	1730
March	1st to 10th	Day	36% 1 4 18% 18% 23%	4948
	11th to 20th	Day	39% 1 5% 9% 15% 31%	5090
	21st to end	Day	40% 2 8% 18% 21% 11%	5585
April	1st to 10th	Day	43% 2 7% 18% 17% 13%	2310
	11th to 20th	Day	46% 2 6% 16% 18% 11%	2321
	21st to end	Day	44% 3 5% 21% 17% 10%	2656
May	1st to 10th	Day	49% 3 8% 19% 17% 4	6030
	11th to 20th	Day	37% 3 11% 18% 22% 9%	5945
	21st to end	Day	46% 3 9% 27% 13% 2	6447
June	1st to 10th	Day	30% 4 13% 30% 19% 3	2600
	11th to 20th	Day	33% 4 11% 28% 19% 5%	2600
	21st to end	Day	38% 6% 11% 24% 17% 4	2600
July	1st to 10th	Day	43% 7% 16% 28% 5% 1	5836
	11th to 20th	Day	30% 7% 16% 30% 15% 2	5831
	21st to end	Day	34% 6% 16% 27% 17% 1	6240
August	1st to 10th	Day	14% 3 11% 41% 30% 1	4140
	11th to 20th	Day	20% 4 22% 39% 12% 2	3882
	21st to end	Day	29% 9% 16% 26% 18% 2	4160
September	1st to 10th	Day	40% 4 8% 21% 17% 9%	2200
	11th to 20th	Day	40% 5% 10% 21% 18% 5%	2200
	21st to end	Day	32% 4 9% 23% 19% 14%	2200
October	1st to 10th	Day	18% 2 6% 13% 25% 36%	3590
	11th to 20th	Day	24% 3 7% 20% 25% 22%	3380
	21st to end	Day	28% 2 4 18% 34% 14%	3538
November	1st to 10th	Day	40% 2 6% 19% 21% 13%	2058
	11th to 20th	Day	35% 3 6% 19% 22% 15%	1932
	21st to end	Day	42% 3 5% 16% 21% 14%	1890
December	1st to 10th	Day	49% 2 5% 17% 17% 10%	3030
	11th to 20th	Day	42% 4 7% 12% 22% 14%	3479
	21st to end	Day	32% 2 4 15% 28% 19%	4587
January	1st to 10th	Night	35% 2 5% 18% 26% 15%	7635
	11th to 20th	Night	24% 1 4 17% 30% 24%	7680
	21st to end	Night	49% 1 3 10% 22% 15%	7949
February	1st to 10th	Night	39% 2 5% 13% 22% 19%	2520
	11th to 20th	Night	40% 2 5% 18% 19% 15%	2458
	21st to end	Night	41% 3 4 15% 20% 17%	2076
March	1st to 10th	Night	41% 2 5% 19% 18% 16%	5129
	11th to 20th	Night	39% 1 7% 11% 15% 27%	5090
	21st to end	Night	43% 2 7% 17% 20% 11%	5588
April	1st to 10th	Night	40% 4 8% 17% 16% 15%	2310
	11th to 20th	Night	44% 3 8% 14% 17% 14%	2243
	21st to end	Night	44% 3 9% 19% 16% 9%	1962
May	1st to 10th	Night	52% 2 7% 17% 15% 7%	4170
	11th to 20th	Night	34% 3 11% 20% 19% 11%	4108
	21st to end	Night	44% 4 13% 27% 11% 3	4452
June	1st to 10th	Night	24% 4 15% 33% 21% 3	1800
	11th to 20th	Night	26% 4 13% 30% 22% 5%	1800
	21st to end	Night	29% 5% 17% 29% 16% 3	1800
July	1st to 10th	Night	37% 9% 23% 26% 4 1	4035
	11th to 20th	Night	26% 8% 21% 32% 12% 1	4026
	21st to end	Night	33% 6% 21% 24% 13% 3	4320
August	1st to 10th	Night	10% 4 15% 45% 25% 1	2977
	11th to 20th	Night	20% 4 31% 33% 10% 2	3243
	21st to end	Night	24% 9% 21% 26% 17% 2	3742
September	1st to 10th	Night	33% 6% 14% 22% 18% 8%	2200
	11th to 20th	Night	36% 5% 14% 24% 16% 5%	2200
	21st to end	Night	30% 4 13% 22% 19% 12%	2200
October	1st to 10th	Night	16% 2 7% 15% 22% 37%	3590
	11th to 20th	Night	22% 3 8% 18% 29% 20%	3724
	21st to end	Night	27% 1 5% 18% 33% 15%	4252
November	1st to 10th	Night	36% 3 6% 19% 24% 13%	2460
	11th to 20th	Night	31% 2 7% 21% 21% 17%	2683
	21st to end	Night	40% 2 7% 17% 19% 15%	2730
December	1st to 10th	Night	47% 2 6% 16% 17% 12%	4380
	11th to 20th	Night	45% 2 5% 10% 22% 18%	4947
	21st to end	Night	34% 2 3 15% 29% 17%	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	22% 14% 36% 24% 4 1	330
	11th to 20th	Day	24% 15% 32% 22% 7% 1	330
	21st to end	Day	20% 19% 36% 20% 5%	363
February	1st to 10th	Day	26% 15% 31% 23% 4	330
	11th to 20th	Day	23% 21% 36% 18% 2	330
	21st to end	Day	23% 16% 43% 16% 1	273
March	1st to 10th	Day	23% 18% 37% 20% 2	330
	11th to 20th	Day	18% 18% 40% 18% 5%	330
	21st to end	Day	16% 18% 38% 20% 6% 1	363
April	1st to 10th	Day	20% 17% 40% 20% 3	330
	11th to 20th	Day	21% 19% 35% 20% 4	359
	21st to end	Day	21% 15% 38% 21% 5%	676
May	1st to 10th	Day	16% 15% 38% 25% 5%	753
	11th to 20th	Day	18% 10% 32% 30% 8% 2	756
	21st to end	Day	16% 8% 29% 33% 13% 1	789
June	1st to 10th	Day	7% 3 20% 42% 23% 4	730
	11th to 20th	Day	10% 2 18% 47% 19% 3	730
	21st to end	Day	8% 3 13% 40% 30% 6%	730
July	1st to 10th	Day	10% 2 13% 35% 31% 8%	721
	11th to 20th	Day	6% 1 7% 37% 42% 6%	718
	21st to end	Day	5% 1 7% 36% 40% 10%	794
August	1st to 10th	Day	3 1 4 38% 42% 12%	685
	11th to 20th	Day	6% 1 4 38% 40% 10%	517
	21st to end	Day	4 1 5% 30% 41% 20%	497
September	1st to 10th	Day	11% 2 8% 28% 38% 13%	330
	11th to 20th	Day	5% 2 4 31% 42% 15%	330
	21st to end	Day	9% 2 9% 35% 34% 12%	330
October	1st to 10th	Day	5% 1 15% 38% 30% 10%	330
	11th to 20th	Day	9% 3 28% 36% 20% 4	330
	21st to end	Day	16% 13% 27% 26% 15% 3	363
November	1st to 10th	Day	19% 8% 25% 32% 12% 4	330
	11th to 20th	Day	20% 11% 25% 31% 12% 2	330
	21st to end	Day	23% 19% 30% 18% 9% 2	330
December	1st to 10th	Day	17% 12% 35% 26% 8% 2	330
	11th to 20th	Day	18% 16% 33% 23% 8% 1	330
	21st to end	Day	17% 13% 35% 26% 6% 1	363
January	1st to 10th	Night	19% 10% 33% 31% 7%	1050
	11th to 20th	Night	19% 12% 32% 30% 6%	1050
	21st to end	Night	23% 11% 31% 29% 6%	997
February	1st to 10th	Night	23% 12% 33% 26% 5%	840
	11th to 20th	Night	24% 13% 35% 25% 3	824
	21st to end	Night	23% 13% 41% 22% 1	692
March	1st to 10th	Night	23% 13% 34% 26% 3	682
	11th to 20th	Night	20% 13% 32% 30% 4	630
	21st to end	Night	19% 11% 40% 26% 4	693
April	1st to 10th	Night	15% 15% 40% 27% 3	630
	11th to 20th	Night	21% 13% 38% 26% 3	623
	21st to end	Night	22% 10% 38% 22% 7%	630
May	1st to 10th	Night	17% 13% 37% 28% 4	630
	11th to 20th	Night	14% 9% 36% 33% 8%	609
	21st to end	Night	15% 7% 33% 36% 10%	650
June	1st to 10th	Night	6% 3 24% 46% 20% 1	600
	11th to 20th	Night	7% 2 33% 45% 14% 1	600
	21st to end	Night	7% 4 16% 50% 20% 4	600
July	1st to 10th	Night	11% 3 11% 46% 25% 3	585
	11th to 20th	Night	4 1 10% 54% 28% 2	582
	21st to end	Night	7% 1 11% 49% 29% 3	657
August	1st to 10th	Night	1 1 9% 54% 33% 4	597
	11th to 20th	Night	6% 1 7% 52% 30% 5%	594
	21st to end	Night	6% 1 7% 44% 36% 5%	660
September	1st to 10th	Night	10% 2 9% 43% 32% 5%	600
	11th to 20th	Night	11% 2 11% 39% 34% 3	600
	21st to end	Night	11% 2 14% 37% 34% 3	600
October	1st to 10th	Night	7% 2 12% 46% 30% 3	600
	11th to 20th	Night	13% 4 21% 42% 19% 1	690
	21st to end	Night	15% 9% 25% 29% 20% 1	880
November	1st to 10th	Night	14% 7% 21% 40% 17% 1	820
	11th to 20th	Night	13% 8% 27% 37% 14% 1	1003
	21st to end	Night	20% 11% 29% 29% 10% 1	1050
December	1st to 10th	Night	20% 9% 29% 32% 9% 1	1050
	11th to 20th	Night	23% 10% 28% 32% 7%	1050
	21st to end	Night	19% 10% 30% 33% 7%	1155

Page generated at 2026-05-14 00:58:56. Version ac07

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