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 2025-01-22.

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 4 5% 7% 47%	105245
	Night	12% 7% 2 5% 3 3 3 3 4 6% 51%	104256
Transparency	Day	36% 3 9% 22% 20% 10%	109076
	Night	35% 3 10% 20% 20% 12%	108552
Seeing	Day	14% 8% 23% 31% 20% 5%	15062
	Night	15% 8% 26% 35% 14% 1	25112

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% 10% 2 4 3 3 3 2 4 5% 53%	2937
	11th to 20th	Day	16% 6% 1 3 3 2 2 3 4 5% 56%	2940
	21st to end	Day	15% 8% 2 5% 3 3 3 2 4 8% 46%	3405
February	1st to 10th	Day	18% 7% 3 6% 3 3 3 2 5% 5% 46%	1900
	11th to 20th	Day	15% 8% 3 5% 3 3 4 3 4 6% 46%	1849
	21st to end	Day	17% 6% 2 5% 3 2 3 3 4 4 51%	1570
March	1st to 10th	Day	15% 8% 2 7% 4 3 3 3 4 6% 44%	3367
	11th to 20th	Day	18% 11% 3 9% 5% 5% 4 3 4 5% 34%	3480
	21st to end	Day	13% 7% 2 6% 4 4 4 4 5% 7% 46%	3814
April	1st to 10th	Day	13% 8% 2 6% 5% 4 4 3 4 6% 45%	2090
	11th to 20th	Day	19% 7% 2 5% 4 4 3 3 5% 6% 42%	2097
	21st to end	Day	14% 7% 2 5% 4 4 4 3 4 6% 46%	2403
May	1st to 10th	Day	21% 9% 3 7% 4 4 4 4 5% 7% 32%	4082
	11th to 20th	Day	14% 7% 2 6% 5% 4 4 3 5% 6% 43%	4082
	21st to end	Day	11% 6% 2 7% 5% 5% 6% 5% 8% 9% 36%	4477
June	1st to 10th	Day	5% 4 2 5% 5% 5% 6% 5% 7% 9% 48%	2470
	11th to 20th	Day	7% 5% 2 5% 5% 5% 5% 5% 6% 8% 47%	2470
	21st to end	Day	6% 6% 2 7% 6% 6% 6% 4 7% 10% 40%	2470
July	1st to 10th	Day	6% 4 2 6% 5% 5% 5% 4 7% 8% 47%	4120
	11th to 20th	Day	4 3 1 4 4 5% 5% 4 8% 10% 50%	4120
	21st to end	Day	9% 6% 2 6% 4 5% 6% 6% 8% 10% 39%	4465
August	1st to 10th	Day	1 1 1 2 3 3 4 3 5% 9% 68%	4026
	11th to 20th	Day	3 3 1 4 3 3 4 4 6% 10% 59%	3726
	21st to end	Day	4 3 2 5% 5% 6% 6% 5% 8% 11% 46%	4034
September	1st to 10th	Day	10% 6% 3 8% 5% 5% 4 4 5% 6% 45%	2090
	11th to 20th	Day	11% 6% 2 7% 6% 5% 6% 4 7% 8% 40%	2090
	21st to end	Day	8% 4 2 6% 4 4 5% 4 6% 7% 50%	2090
October	1st to 10th	Day	6% 5% 2 4 3 4 5% 4 5% 6% 56%	2090
	11th to 20th	Day	12% 5% 2 4 4 3 3 4 4 7% 52%	1984
	21st to end	Day	11% 4 2 6% 4 3 3 2 4 5% 57%	2090
November	1st to 10th	Day	13% 8% 2 6% 4 3 4 3 5% 6% 45%	1958
	11th to 20th	Day	11% 5% 2 6% 4 4 3 4 5% 6% 52%	1840
	21st to end	Day	16% 6% 2 6% 4 2 4 3 4 6% 47%	1800
December	1st to 10th	Day	23% 8% 3 6% 3 3 3 2 4 4 40%	2940
	11th to 20th	Day	13% 9% 3 7% 4 4 4 3 5% 5% 44%	3391
	21st to end	Day	12% 6% 2 5% 3 2 3 2 3 4 59%	4488
January	1st to 10th	Night	17% 6% 3 4 1 2 2 2 4 5% 53%	4238
	11th to 20th	Night	12% 4 1 3 2 2 2 1 3 4 65%	4250
	21st to end	Night	19% 7% 2 7% 3 3 3 3 4 6% 43%	4313
February	1st to 10th	Night	16% 8% 3 6% 2 3 3 2 5% 5% 48%	2280
	11th to 20th	Night	16% 7% 2 5% 4 3 2 3 3 5% 50%	2218
	21st to end	Night	17% 7% 2 6% 3 3 3 2 4 5% 47%	1884
March	1st to 10th	Night	14% 9% 3 7% 5% 4 3 3 4 6% 42%	3489
	11th to 20th	Night	19% 12% 3 7% 4 4 4 3 4 6% 34%	3480
	21st to end	Night	14% 8% 2 6% 4 4 4 3 5% 5% 45%	3817
April	1st to 10th	Night	10% 9% 3 6% 3 4 4 3 6% 6% 47%	2090
	11th to 20th	Night	16% 8% 2 6% 4 2 3 3 4 6% 46%	2027
	21st to end	Night	17% 7% 2 5% 4 3 3 3 3 5% 47%	1776
May	1st to 10th	Night	24% 11% 2 5% 3 3 3 3 3 6% 37%	2823
	11th to 20th	Night	11% 7% 2 6% 4 3 4 3 5% 6% 49%	2823
	21st to end	Night	13% 6% 2 5% 4 3 4 4 6% 9% 43%	3090
June	1st to 10th	Night	5% 4 1 3 3 4 3 3 6% 8% 59%	1710
	11th to 20th	Night	5% 4 2 3 3 4 4 3 6% 9% 58%	1710
	21st to end	Night	6% 5% 2 5% 3 3 5% 3 6% 10% 52%	1710
July	1st to 10th	Night	6% 4 2 4 3 3 4 3 7% 10% 54%	2850
	11th to 20th	Night	3 3 1 4 3 3 5% 4 6% 10% 57%	2850
	21st to end	Night	9% 8% 3 6% 5% 4 4 4 6% 10% 42%	3098
August	1st to 10th	Night	1 1 1 2 2 2 3 3 4 8% 74%	2895
	11th to 20th	Night	3 2 1 3 3 3 4 3 6% 11% 61%	3113
	21st to end	Night	4 5% 2 4 4 3 5% 3 6% 10% 55%	3628
September	1st to 10th	Night	8% 5% 2 5% 4 4 4 3 6% 8% 51%	2090
	11th to 20th	Night	8% 6% 3 7% 4 4 5% 3 6% 8% 46%	2090
	21st to end	Night	7% 5% 2 5% 4 4 4 3 7% 8% 52%	2090
October	1st to 10th	Night	5% 4 1 4 3 3 4 3 4 7% 61%	2090
	11th to 20th	Night	12% 5% 2 4 3 3 4 3 5% 5% 54%	2175
	21st to end	Night	14% 5% 1 4 2 3 2 2 2 4 61%	2508
November	1st to 10th	Night	13% 8% 3 5% 3 3 3 2 4 6% 52%	2340
	11th to 20th	Night	9% 7% 2 5% 3 3 3 3 5% 6% 56%	2555
	21st to end	Night	16% 6% 2 5% 3 3 3 3 4 5% 49%	2600
December	1st to 10th	Night	20% 9% 3 6% 3 3 3 2 4 5% 41%	4250
	11th to 20th	Night	18% 11% 2 5% 3 3 2 2 3 4 47%	4816
	21st to end	Night	15% 7% 2 4 2 2 2 2 3 4 57%	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	37% 1 2 19% 26% 16%	2938
	11th to 20th	Day	33% 1 5% 14% 30% 16%	2940
	21st to end	Day	41% 2 4 12% 30% 12%	3405
February	1st to 10th	Day	43% 3 3 13% 21% 16%	1900
	11th to 20th	Day	41% 3 6% 18% 19% 14%	1859
	21st to end	Day	39% 1 5% 18% 20% 16%	1570
March	1st to 10th	Day	45% 1 5% 15% 22% 12%	3367
	11th to 20th	Day	56% 2 7% 10% 16% 9%	3480
	21st to end	Day	40% 2 8% 17% 20% 13%	3814
April	1st to 10th	Day	43% 2 7% 18% 17% 13%	2090
	11th to 20th	Day	45% 2 5% 17% 19% 11%	2097
	21st to end	Day	43% 3 4 22% 18% 10%	2403
May	1st to 10th	Day	55% 2 8% 15% 16% 5%	4120
	11th to 20th	Day	44% 2 7% 18% 22% 7%	4086
	21st to end	Day	44% 3 9% 31% 11% 2	4489
June	1st to 10th	Day	31% 4 12% 29% 20% 4	2470
	11th to 20th	Day	33% 4 10% 28% 19% 5%	2470
	21st to end	Day	39% 5% 10% 24% 18% 4	2470
July	1st to 10th	Day	32% 6% 16% 38% 7% 1	4056
	11th to 20th	Day	26% 6% 16% 32% 17% 2	4051
	21st to end	Day	37% 6% 17% 31% 10%	4325
August	1st to 10th	Day	14% 3 11% 41% 30% 1	4012
	11th to 20th	Day	20% 4 22% 40% 12% 2	3762
	21st to end	Day	29% 9% 17% 26% 17% 2	4033
September	1st to 10th	Day	40% 4 8% 21% 17% 9%	2090
	11th to 20th	Day	42% 5% 10% 20% 18% 6%	2090
	21st to end	Day	33% 4 9% 22% 19% 14%	2090
October	1st to 10th	Day	19% 2 6% 12% 25% 36%	3480
	11th to 20th	Day	24% 3 7% 19% 25% 23%	3276
	21st to end	Day	28% 2 4 18% 34% 14%	3428
November	1st to 10th	Day	41% 2 6% 20% 19% 12%	1958
	11th to 20th	Day	35% 3 6% 18% 22% 16%	1840
	21st to end	Day	41% 3 5% 17% 21% 14%	1800
December	1st to 10th	Day	49% 3 5% 18% 16% 10%	2940
	11th to 20th	Day	42% 4 7% 12% 21% 14%	3389
	21st to end	Day	32% 2 3 15% 28% 19%	4488
January	1st to 10th	Night	37% 1 3 15% 25% 19%	4238
	11th to 20th	Night	26% 2 3 18% 29% 23%	4250
	21st to end	Night	46% 1 3 12% 25% 14%	4313
February	1st to 10th	Night	41% 2 5% 13% 22% 18%	2280
	11th to 20th	Night	40% 2 5% 17% 20% 17%	2218
	21st to end	Night	42% 3 4 15% 19% 17%	1884
March	1st to 10th	Night	46% 2 5% 16% 20% 10%	3489
	11th to 20th	Night	54% 2 8% 11% 14% 10%	3480
	21st to end	Night	43% 2 8% 16% 20% 11%	3817
April	1st to 10th	Night	39% 4 8% 18% 17% 15%	2090
	11th to 20th	Night	43% 3 8% 14% 18% 15%	2027
	21st to end	Night	42% 3 8% 20% 18% 10%	1776
May	1st to 10th	Night	53% 2 6% 18% 14% 7%	2850
	11th to 20th	Night	37% 2 10% 24% 19% 8%	2824
	21st to end	Night	40% 3 13% 29% 11% 3	3099
June	1st to 10th	Night	23% 4 15% 33% 22% 3	1710
	11th to 20th	Night	25% 4 13% 30% 22% 5%	1710
	21st to end	Night	29% 5% 17% 30% 16% 3	1710
July	1st to 10th	Night	24% 8% 25% 36% 6% 1	2805
	11th to 20th	Night	23% 7% 20% 33% 16% 1	2796
	21st to end	Night	38% 6% 23% 27% 7%	2999
August	1st to 10th	Night	10% 4 16% 44% 26% 1	2885
	11th to 20th	Night	19% 4 30% 34% 10% 2	3143
	21st to end	Night	24% 9% 21% 26% 17% 2	3628
September	1st to 10th	Night	32% 6% 14% 22% 18% 8%	2090
	11th to 20th	Night	37% 5% 14% 23% 16% 5%	2090
	21st to end	Night	30% 4 13% 21% 19% 13%	2090
October	1st to 10th	Night	17% 2 7% 15% 21% 38%	3480
	11th to 20th	Night	23% 3 8% 17% 29% 20%	3609
	21st to end	Night	27% 1 5% 18% 33% 15%	4120
November	1st to 10th	Night	37% 3 6% 19% 22% 13%	2340
	11th to 20th	Night	31% 3 7% 21% 20% 18%	2555
	21st to end	Night	39% 2 7% 17% 19% 15%	2600
December	1st to 10th	Night	47% 2 6% 16% 17% 11%	4250
	11th to 20th	Night	45% 2 5% 10% 22% 18%	4817
	21st to end	Night	34% 1 3 15% 29% 18%	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	22% 15% 35% 24% 4 1	300
	11th to 20th	Day	25% 15% 31% 21% 7% 1	300
	21st to end	Day	18% 17% 36% 22% 6%	300
February	1st to 10th	Day	28% 17% 29% 22% 4	270
	11th to 20th	Day	24% 21% 35% 17% 3	270
	21st to end	Day	25% 17% 44% 14%	225
March	1st to 10th	Day	21% 19% 39% 19% 3	270
	11th to 20th	Day	20% 17% 39% 19% 6%	270
	21st to end	Day	18% 20% 41% 16% 4 1	297
April	1st to 10th	Day	19% 19% 41% 18% 3	270
	11th to 20th	Day	20% 20% 35% 20% 5%	295
	21st to end	Day	20% 15% 38% 22% 5%	583
May	1st to 10th	Day	16% 15% 37% 26% 6%	653
	11th to 20th	Day	20% 9% 30% 31% 8% 2	675
	21st to end	Day	16% 8% 28% 33% 14% 1	734
June	1st to 10th	Day	8% 3 19% 42% 24% 4	680
	11th to 20th	Day	10% 2 17% 48% 20% 3	680
	21st to end	Day	9% 3 12% 40% 30% 6%	680
July	1st to 10th	Day	8% 2 12% 36% 33% 9%	671
	11th to 20th	Day	5% 1 6% 37% 44% 7%	668
	21st to end	Day	4 1 7% 37% 40% 10%	739
August	1st to 10th	Day	3 1 4 38% 42% 12%	637
	11th to 20th	Day	7% 1 4 38% 40% 10%	477
	21st to end	Day	4 1 5% 29% 41% 19%	458
September	1st to 10th	Day	11% 2 8% 27% 38% 14%	300
	11th to 20th	Day	6% 2 4 30% 43% 16%	300
	21st to end	Day	10% 2 8% 34% 34% 12%	300
October	1st to 10th	Day	6% 1 16% 38% 28% 10%	300
	11th to 20th	Day	10% 3 27% 37% 19% 3	300
	21st to end	Day	17% 12% 28% 25% 14% 3	330
November	1st to 10th	Day	20% 8% 26% 33% 10% 4	300
	11th to 20th	Day	21% 12% 25% 27% 12% 2	300
	21st to end	Day	23% 18% 31% 18% 9% 2	300
December	1st to 10th	Day	17% 12% 34% 26% 8% 3	300
	11th to 20th	Day	18% 17% 33% 23% 7% 1	300
	21st to end	Day	18% 14% 35% 25% 6% 1	330
January	1st to 10th	Night	19% 10% 32% 31% 7% 1	1000
	11th to 20th	Night	20% 12% 31% 30% 6%	1000
	21st to end	Night	21% 10% 32% 30% 6%	909
February	1st to 10th	Night	23% 13% 33% 26% 6%	760
	11th to 20th	Night	24% 12% 36% 26% 2	744
	21st to end	Night	24% 13% 42% 20% 1	628
March	1st to 10th	Night	21% 12% 35% 28% 4	618
	11th to 20th	Night	21% 12% 32% 31% 4	570
	21st to end	Night	18% 12% 40% 25% 4	627
April	1st to 10th	Night	14% 15% 40% 27% 4	570
	11th to 20th	Night	20% 13% 38% 27% 2	563
	21st to end	Night	19% 10% 40% 23% 7% 1	570
May	1st to 10th	Night	16% 13% 38% 28% 4	570
	11th to 20th	Night	14% 7% 37% 34% 8% 1	561
	21st to end	Night	15% 6% 33% 35% 10%	617
June	1st to 10th	Night	5% 4 22% 47% 20% 1	570
	11th to 20th	Night	7% 1 31% 46% 14% 1	570
	21st to end	Night	7% 4 16% 49% 21% 4	570
July	1st to 10th	Night	10% 3 11% 46% 26% 4	555
	11th to 20th	Night	4 1 9% 55% 29% 2	552
	21st to end	Night	6% 1 10% 50% 29% 3	624
August	1st to 10th	Night	1 1 8% 53% 33% 4	567
	11th to 20th	Night	6% 1 6% 51% 30% 5%	564
	21st to end	Night	6% 1 7% 44% 36% 5%	627
September	1st to 10th	Night	10% 1 9% 43% 32% 5%	570
	11th to 20th	Night	12% 2 11% 37% 35% 3	570
	21st to end	Night	11% 1 14% 36% 35% 3	570
October	1st to 10th	Night	7% 2 13% 46% 29% 3	570
	11th to 20th	Night	13% 4 21% 42% 18% 2	655
	21st to end	Night	16% 9% 25% 28% 21% 2	836
November	1st to 10th	Night	15% 6% 22% 39% 16% 1	780
	11th to 20th	Night	13% 8% 27% 37% 14% 1	955
	21st to end	Night	20% 11% 30% 29% 10% 1	1000
December	1st to 10th	Night	20% 9% 28% 33% 9% 1	1000
	11th to 20th	Night	23% 10% 28% 32% 7%	1000
	21st to end	Night	20% 10% 30% 32% 7%	1100

Page generated at 2025-01-19 02:06:49. Version ac07

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