Hill Country State Natural Area
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hill Country State Natural Area clear sky chart from 2005-11-06 to 2026-06-16.

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% 47%	137807
	Night	15% 6% 2 4 3 3 3 3 4 6% 51%	134579
Transparency	Day	36% 5% 10% 20% 18% 11%	141638
	Night	34% 5% 10% 19% 19% 13%	138815
Seeing	Day	15% 8% 24% 30% 20% 4	16863
	Night	16% 7% 24% 36% 15% 1	26840

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	13% 7% 2 4 2 2 3 2 3 5% 56%	5289
	11th to 20th	Day	15% 5% 2 4 3 2 2 2 4 4 56%	5412
	21st to end	Day	23% 9% 2 3 2 2 2 2 4 6% 44%	6468
February	1st to 10th	Day	17% 7% 2 6% 3 3 3 3 4 4 47%	2100
	11th to 20th	Day	19% 7% 2 5% 3 3 3 3 5% 5% 45%	2049
	21st to end	Day	17% 5% 2 4 2 2 3 2 4 6% 52%	1730
March	1st to 10th	Day	15% 6% 2 4 2 3 3 2 4 5% 55%	4838
	11th to 20th	Day	16% 6% 2 6% 3 3 3 2 3 4 52%	5090
	21st to end	Day	19% 7% 2 4 2 3 3 2 4 6% 47%	5583
April	1st to 10th	Day	16% 8% 2 6% 4 3 4 3 5% 6% 44%	2310
	11th to 20th	Day	21% 5% 2 5% 4 4 4 4 5% 6% 42%	2405
	21st to end	Day	18% 7% 2 6% 4 4 4 3 4 6% 42%	2578
May	1st to 10th	Day	23% 7% 2 6% 3 4 4 3 5% 7% 36%	7617
	11th to 20th	Day	15% 5% 2 5% 3 4 4 4 6% 9% 44%	7627
	21st to end	Day	15% 8% 2 7% 4 5% 5% 4 7% 8% 34%	8392
June	1st to 10th	Day	8% 5% 2 5% 4 5% 5% 4 6% 9% 46%	2730
	11th to 20th	Day	9% 5% 2 6% 5% 4 6% 5% 6% 9% 45%	2666
	21st to end	Day	9% 6% 2 6% 6% 6% 6% 5% 6% 9% 40%	2600
July	1st to 10th	Day	15% 8% 2 6% 5% 4 5% 4 6% 7% 37%	5900
	11th to 20th	Day	8% 5% 2 7% 5% 6% 5% 4 7% 9% 43%	5900
	21st to end	Day	7% 5% 2 6% 4 5% 6% 5% 7% 9% 44%	6422
August	1st to 10th	Day	2 2 1 3 3 2 3 4 5% 9% 68%	3949
	11th to 20th	Day	3 2 1 4 3 4 4 3 6% 10% 59%	3846
	21st to end	Day	5% 4 1 5% 5% 5% 5% 4 7% 10% 48%	4231
September	1st to 10th	Day	12% 6% 3 7% 5% 6% 5% 4 6% 7% 40%	2200
	11th to 20th	Day	10% 6% 2 6% 5% 5% 5% 5% 6% 7% 43%	2200
	21st to end	Day	9% 5% 3 5% 5% 4 5% 4 6% 7% 48%	2200
October	1st to 10th	Day	7% 5% 2 4 3 4 4 3 5% 7% 55%	2200
	11th to 20th	Day	15% 4 2 4 3 3 4 3 4 5% 53%	2150
	21st to end	Day	13% 4 2 4 4 3 3 2 3 4 58%	2200
November	1st to 10th	Day	18% 8% 2 5% 3 3 3 2 4 6% 47%	2047
	11th to 20th	Day	14% 7% 2 4 3 3 4 2 5% 5% 50%	1890
	21st to end	Day	19% 7% 2 6% 3 2 4 3 3 4 47%	1890
December	1st to 10th	Day	26% 9% 3 6% 3 2 2 2 3 5% 38%	3030
	11th to 20th	Day	18% 8% 2 6% 3 3 4 3 4 5% 44%	3481
	21st to end	Day	15% 6% 2 3 2 2 2 2 3 4 58%	4587
January	1st to 10th	Night	13% 5% 1 4 2 2 3 2 4 6% 57%	7634
	11th to 20th	Night	11% 4 1 3 2 2 3 3 4 5% 64%	7620
	21st to end	Night	28% 5% 2 4 2 2 2 2 3 4 44%	7746
February	1st to 10th	Night	16% 6% 1 4 3 2 2 2 5% 5% 53%	2520
	11th to 20th	Night	19% 6% 1 4 3 2 2 2 4 5% 51%	2458
	21st to end	Night	17% 5% 2 4 3 3 4 2 4 7% 50%	2076
March	1st to 10th	Night	17% 7% 2 5% 3 3 3 3 4 6% 47%	5242
	11th to 20th	Night	15% 7% 2 5% 3 3 3 2 3 4 54%	5090
	21st to end	Night	19% 8% 2 4 3 2 4 2 5% 5% 47%	5588
April	1st to 10th	Night	15% 6% 2 5% 4 3 3 4 4 6% 48%	2310
	11th to 20th	Night	21% 6% 2 5% 3 2 3 3 3 5% 46%	2159
	21st to end	Night	23% 6% 2 5% 3 3 3 3 3 5% 45%	2040
May	1st to 10th	Night	25% 9% 2 6% 3 3 3 2 4 5% 37%	5266
	11th to 20th	Night	13% 5% 2 5% 4 4 4 4 5% 8% 46%	5265
	21st to end	Night	16% 7% 2 5% 4 4 4 4 6% 11% 37%	5793
June	1st to 10th	Night	7% 4 1 3 3 3 4 4 6% 9% 57%	1890
	11th to 20th	Night	7% 4 2 4 4 3 4 4 5% 8% 56%	1845
	21st to end	Night	8% 6% 1 4 3 4 3 4 5% 11% 51%	1800
July	1st to 10th	Night	13% 6% 2 6% 5% 4 4 4 6% 9% 41%	4078
	11th to 20th	Night	6% 5% 2 5% 4 4 5% 4 7% 10% 49%	4077
	21st to end	Night	9% 7% 2 6% 4 4 4 4 6% 8% 47%	4449
August	1st to 10th	Night	2 2 1 3 2 2 2 2 5% 8% 71%	3205
	11th to 20th	Night	4 2 1 3 3 3 4 3 6% 9% 61%	3213
	21st to end	Night	5% 4 1 4 3 4 4 3 6% 10% 54%	3661
September	1st to 10th	Night	10% 6% 2 6% 4 5% 4 3 5% 8% 47%	2200
	11th to 20th	Night	10% 7% 2 6% 3 4 4 4 7% 8% 45%	2200
	21st to end	Night	8% 5% 2 6% 3 4 4 4 5% 8% 51%	2200
October	1st to 10th	Night	7% 4 1 4 3 3 3 3 5% 5% 61%	2200
	11th to 20th	Night	14% 4 1 4 3 3 3 2 4 6% 56%	2228
	21st to end	Night	15% 4 2 3 2 2 2 1 3 4 63%	2640
November	1st to 10th	Night	15% 6% 2 4 3 3 2 2 3 6% 54%	2467
	11th to 20th	Night	12% 5% 2 4 3 2 3 2 4 6% 56%	2730
	21st to end	Night	19% 5% 1 4 3 3 3 3 5% 6% 48%	2730
December	1st to 10th	Night	26% 8% 2 4 3 3 3 2 4 5% 39%	4380
	11th to 20th	Night	22% 7% 2 4 3 2 3 2 3 4 48%	4946
	21st to end	Night	18% 5% 2 3 2 2 2 2 3 5% 56%	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	32% 4 5% 20% 25% 14%	5290
	11th to 20th	Day	34% 2 3 14% 25% 23%	5412
	21st to end	Day	42% 3 5% 14% 25% 11%	6468
February	1st to 10th	Day	41% 3 5% 12% 21% 18%	2100
	11th to 20th	Day	41% 4 7% 17% 19% 13%	2059
	21st to end	Day	35% 3 6% 17% 22% 17%	1730
March	1st to 10th	Day	33% 3 5% 16% 18% 25%	4838
	11th to 20th	Day	37% 3 4 9% 15% 32%	5090
	21st to end	Day	38% 5% 8% 18% 19% 13%	5585
April	1st to 10th	Day	42% 4 8% 15% 17% 14%	2310
	11th to 20th	Day	42% 6% 7% 16% 16% 13%	2405
	21st to end	Day	44% 5% 8% 17% 15% 11%	2578
May	1st to 10th	Day	46% 6% 10% 19% 14% 5%	7655
	11th to 20th	Day	36% 6% 11% 19% 21% 8%	7631
	21st to end	Day	43% 8% 12% 25% 11% 1	8405
June	1st to 10th	Day	31% 8% 15% 26% 18% 3	2730
	11th to 20th	Day	35% 6% 12% 24% 17% 5%	2666
	21st to end	Day	38% 8% 12% 24% 13% 4	2600
July	1st to 10th	Day	44% 7% 15% 28% 5% 1	5836
	11th to 20th	Day	35% 7% 16% 29% 12% 1	5831
	21st to end	Day	32% 8% 17% 25% 16% 2	6240
August	1st to 10th	Day	14% 5% 11% 43% 26% 1	3935
	11th to 20th	Day	20% 7% 23% 38% 11% 2	3882
	21st to end	Day	29% 9% 18% 24% 19% 2	4230
September	1st to 10th	Day	42% 7% 10% 17% 17% 7%	2200
	11th to 20th	Day	37% 8% 12% 21% 17% 5%	2200
	21st to end	Day	34% 6% 10% 22% 17% 12%	2200
October	1st to 10th	Day	18% 4 6% 13% 25% 34%	3590
	11th to 20th	Day	27% 4 8% 18% 22% 21%	3481
	21st to end	Day	28% 4 6% 15% 34% 14%	3538
November	1st to 10th	Day	39% 4 7% 18% 19% 12%	2047
	11th to 20th	Day	37% 4 6% 17% 19% 18%	1890
	21st to end	Day	42% 3 5% 16% 20% 13%	1890
December	1st to 10th	Day	51% 3 5% 16% 15% 11%	3030
	11th to 20th	Day	41% 5% 7% 14% 19% 14%	3479
	21st to end	Day	31% 3 4 16% 28% 18%	4587
January	1st to 10th	Night	29% 4 7% 18% 26% 16%	7635
	11th to 20th	Night	25% 2 4 16% 28% 25%	7620
	21st to end	Night	46% 2 3 11% 23% 15%	7746
February	1st to 10th	Night	34% 4 7% 14% 21% 21%	2520
	11th to 20th	Night	38% 3 6% 18% 20% 16%	2458
	21st to end	Night	36% 4 6% 15% 21% 18%	2076
March	1st to 10th	Night	38% 4 6% 17% 17% 18%	5242
	11th to 20th	Night	35% 5% 5% 12% 15% 28%	5090
	21st to end	Night	39% 5% 9% 18% 17% 13%	5588
April	1st to 10th	Night	36% 5% 11% 16% 16% 16%	2310
	11th to 20th	Night	42% 5% 9% 13% 16% 16%	2159
	21st to end	Night	43% 4 9% 17% 15% 11%	2040
May	1st to 10th	Night	48% 6% 9% 17% 13% 7%	5293
	11th to 20th	Night	35% 6% 11% 18% 20% 10%	5266
	21st to end	Night	41% 7% 17% 24% 9% 2	5805
June	1st to 10th	Night	23% 6% 19% 31% 19% 2	1890
	11th to 20th	Night	25% 6% 15% 28% 21% 5%	1845
	21st to end	Night	29% 7% 20% 27% 15% 3	1800
July	1st to 10th	Night	39% 8% 22% 26% 4	4035
	11th to 20th	Night	28% 9% 22% 28% 12% 1	4026
	21st to end	Night	33% 8% 21% 24% 12% 3	4320
August	1st to 10th	Night	13% 5% 15% 44% 21%	3195
	11th to 20th	Night	19% 7% 29% 36% 8% 1	3243
	21st to end	Night	25% 11% 21% 25% 17% 2	3661
September	1st to 10th	Night	35% 6% 14% 21% 16% 7%	2200
	11th to 20th	Night	34% 8% 16% 22% 14% 5%	2200
	21st to end	Night	30% 6% 13% 22% 18% 12%	2200
October	1st to 10th	Night	17% 3 7% 15% 22% 35%	3590
	11th to 20th	Night	24% 3 9% 15% 29% 19%	3623
	21st to end	Night	25% 3 6% 17% 34% 15%	4252
November	1st to 10th	Night	33% 4 7% 18% 23% 15%	2467
	11th to 20th	Night	30% 4 8% 19% 21% 18%	2730
	21st to end	Night	37% 4 8% 16% 19% 15%	2730
December	1st to 10th	Night	48% 4 7% 14% 14% 13%	4380
	11th to 20th	Night	42% 3 5% 11% 21% 18%	4947
	21st to end	Night	32% 3 4 14% 28% 18%	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	24% 12% 33% 24% 6%	330
	11th to 20th	Day	24% 17% 28% 24% 8%	330
	21st to end	Day	23% 17% 32% 21% 7%	363
February	1st to 10th	Day	28% 13% 25% 24% 9%	330
	11th to 20th	Day	25% 19% 32% 18% 5%	330
	21st to end	Day	23% 16% 38% 18% 5%	273
March	1st to 10th	Day	27% 16% 38% 16% 2	330
	11th to 20th	Day	18% 19% 42% 18% 4	330
	21st to end	Day	21% 17% 39% 19% 5%	363
April	1st to 10th	Day	24% 17% 32% 24% 3	330
	11th to 20th	Day	21% 17% 37% 21% 3	443
	21st to end	Day	20% 15% 40% 21% 3	598
May	1st to 10th	Day	22% 12% 37% 24% 5%	753
	11th to 20th	Day	18% 9% 36% 29% 7% 1	775
	21st to end	Day	18% 7% 32% 30% 11% 1	844
June	1st to 10th	Day	8% 4 22% 42% 22% 2	780
	11th to 20th	Day	10% 3 21% 43% 21% 2	756
	21st to end	Day	10% 1 17% 38% 28% 6%	730
July	1st to 10th	Day	14% 2 11% 34% 32% 7%	721
	11th to 20th	Day	8% 1 7% 36% 42% 6%	718
	21st to end	Day	5% 2 9% 34% 41% 10%	794
August	1st to 10th	Day	3 4 37% 44% 12%	558
	11th to 20th	Day	5% 2 6% 37% 40% 11%	517
	21st to end	Day	6% 2 7% 30% 41% 14%	541
September	1st to 10th	Day	11% 3 9% 28% 35% 13%	330
	11th to 20th	Day	7% 1 4 32% 43% 13%	330
	21st to end	Day	7% 2 12% 31% 40% 9%	330
October	1st to 10th	Day	6% 2 14% 37% 34% 7%	330
	11th to 20th	Day	12% 4 21% 40% 20% 4	330
	21st to end	Day	15% 14% 25% 30% 15% 2	363
November	1st to 10th	Day	21% 7% 27% 26% 15% 3	330
	11th to 20th	Day	22% 9% 25% 29% 12% 3	330
	21st to end	Day	26% 15% 32% 18% 10% 1	330
December	1st to 10th	Day	20% 12% 29% 25% 11% 2	330
	11th to 20th	Day	23% 14% 27% 26% 10%	330
	21st to end	Day	23% 10% 31% 27% 9%	363
January	1st to 10th	Night	19% 8% 26% 36% 10%	1050
	11th to 20th	Night	20% 10% 29% 34% 7%	1029
	21st to end	Night	25% 9% 26% 33% 7%	924
February	1st to 10th	Night	22% 12% 26% 32% 8%	840
	11th to 20th	Night	27% 10% 30% 28% 6%	824
	21st to end	Night	21% 10% 37% 29% 2	692
March	1st to 10th	Night	25% 12% 32% 27% 3 1	731
	11th to 20th	Night	20% 12% 33% 31% 4	630
	21st to end	Night	19% 12% 38% 27% 5%	693
April	1st to 10th	Night	15% 13% 41% 29% 2	630
	11th to 20th	Night	22% 13% 41% 23% 2	623
	21st to end	Night	23% 12% 37% 22% 5%	630
May	1st to 10th	Night	18% 10% 41% 26% 4	630
	11th to 20th	Night	17% 8% 36% 32% 7%	621
	21st to end	Night	17% 8% 33% 34% 8%	683
June	1st to 10th	Night	8% 3 27% 44% 17%	630
	11th to 20th	Night	7% 3 33% 44% 13%	615
	21st to end	Night	7% 4 20% 47% 21% 1	600
July	1st to 10th	Night	11% 3 12% 46% 27% 1	585
	11th to 20th	Night	4 1 14% 51% 29% 1	582
	21st to end	Night	7% 2 10% 49% 31% 2	657
August	1st to 10th	Night	2 1 9% 48% 38% 2	597
	11th to 20th	Night	5% 1 8% 52% 32% 3	594
	21st to end	Night	6% 2 8% 39% 41% 4	660
September	1st to 10th	Night	10% 2 10% 42% 32% 4	600
	11th to 20th	Night	11% 1 9% 43% 34% 2	600
	21st to end	Night	10% 2 13% 42% 30% 4	600
October	1st to 10th	Night	7% 2 12% 49% 27% 2	600
	11th to 20th	Night	14% 3 21% 40% 18% 3	628
	21st to end	Night	16% 7% 22% 31% 22% 2	880
November	1st to 10th	Night	14% 7% 20% 37% 20% 2	827
	11th to 20th	Night	15% 7% 20% 42% 16% 2	1050
	21st to end	Night	22% 10% 22% 33% 12% 1	1050
December	1st to 10th	Night	21% 8% 22% 36% 12% 1	1050
	11th to 20th	Night	24% 9% 24% 32% 10%	1050
	21st to end	Night	20% 8% 25% 37% 9% 1	1155

Page generated at 2026-06-13 01:31:41. Version ac07

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