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 2024-01-31.

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% 5% 2 4 4 3 4 4 5% 7% 47%	75023
	Night	14% 5% 2 4 4 2 3 4 4 7% 52%	75130
Transparency	Day	37% 5% 10% 20% 18% 10%	74748
	Night	33% 5% 11% 20% 19% 12%	74925
Seeing	Day	15% 7% 22% 30% 21% 4	13685
	Night	16% 6% 24% 37% 16% 1	23789

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	15% 6% 2 3 3 2 3 3 3 6% 54%	1707
	11th to 20th	Day	19% 5% 2 4 4 2 2 3 3 4 50%	1743
	21st to end	Day	15% 6% 2 3 3 2 3 3 4 6% 51%	2080
February	1st to 10th	Day	17% 6% 3 5% 4 2 3 3 3 5% 48%	1800
	11th to 20th	Day	21% 6% 2 5% 3 2 4 4 5% 5% 44%	1749
	21st to end	Day	18% 5% 2 4 3 1 4 3 3 6% 51%	1480
March	1st to 10th	Day	21% 7% 2 4 3 2 3 3 4 5% 44%	1890
	11th to 20th	Day	17% 6% 2 6% 4 2 4 4 4 5% 46%	1980
	21st to end	Day	20% 5% 2 4 3 2 3 3 3 6% 47%	2178
April	1st to 10th	Day	17% 7% 2 5% 4 2 4 4 4 7% 44%	1980
	11th to 20th	Day	20% 5% 2 4 4 2 4 4 4 6% 45%	2057
	21st to end	Day	18% 6% 2 5% 4 3 4 3 4 5% 45%	2209
May	1st to 10th	Day	19% 5% 3 4 5% 3 4 4 5% 7% 41%	2340
	11th to 20th	Day	17% 6% 3 6% 5% 3 5% 4 6% 7% 39%	2302
	21st to end	Day	19% 6% 2 5% 6% 4 5% 5% 6% 8% 35%	2531
June	1st to 10th	Day	8% 4 3 4 4 3 6% 5% 6% 9% 48%	2340
	11th to 20th	Day	9% 4 2 5% 5% 3 6% 6% 6% 9% 46%	2340
	21st to end	Day	11% 5% 3 5% 6% 4 6% 6% 6% 8% 39%	2340
July	1st to 10th	Day	14% 5% 3 6% 6% 4 6% 6% 6% 8% 36%	2340
	11th to 20th	Day	6% 3 2 4 5% 3 5% 5% 5% 9% 52%	2340
	21st to end	Day	6% 3 2 3 4 3 6% 5% 6% 10% 51%	2546
August	1st to 10th	Day	2 3 1 3 3 2 4 5% 5% 10% 60%	2178
	11th to 20th	Day	6% 3 2 5% 5% 4 5% 5% 5% 9% 50%	2123
	21st to end	Day	7% 5% 2 5% 5% 4 6% 5% 7% 9% 44%	2339
September	1st to 10th	Day	12% 5% 3 6% 6% 4 6% 4 6% 7% 40%	1980
	11th to 20th	Day	11% 6% 3 5% 6% 4 5% 6% 6% 7% 41%	1980
	21st to end	Day	10% 4 3 5% 6% 3 5% 5% 6% 7% 46%	1980
October	1st to 10th	Day	8% 5% 2 4 4 3 5% 4 5% 8% 52%	1980
	11th to 20th	Day	16% 4 2 4 3 3 4 4 4 5% 51%	1936
	21st to end	Day	14% 4 2 4 4 3 2 3 3 4 57%	1980
November	1st to 10th	Day	19% 8% 2 4 4 2 2 3 4 6% 45%	1849
	11th to 20th	Day	16% 6% 3 4 4 2 4 4 5% 5% 48%	1710
	21st to end	Day	19% 5% 3 5% 3 2 3 4 3 4 48%	1710
December	1st to 10th	Day	17% 7% 2 4 4 2 4 2 4 6% 48%	1710
	11th to 20th	Day	18% 7% 2 4 4 3 4 4 4 5% 46%	2161
	21st to end	Day	17% 5% 2 3 3 2 2 3 3 4 56%	3135
January	1st to 10th	Night	16% 4 2 3 3 2 3 3 4 6% 55%	2458
	11th to 20th	Night	16% 6% 3 4 3 2 2 3 3 5% 52%	2451
	21st to end	Night	18% 5% 2 4 3 2 3 3 4 5% 50%	2502
February	1st to 10th	Night	17% 5% 2 3 3 2 3 3 4 6% 52%	2160
	11th to 20th	Night	19% 6% 2 4 3 2 2 3 3 5% 51%	2098
	21st to end	Night	18% 5% 2 4 3 3 4 3 3 7% 48%	1776
March	1st to 10th	Night	18% 6% 3 5% 4 2 3 3 5% 7% 45%	2067
	11th to 20th	Night	18% 7% 2 4 4 2 3 4 4 4 48%	1980
	21st to end	Night	17% 5% 2 3 3 2 4 4 4 6% 51%	2178
April	1st to 10th	Night	15% 5% 2 4 4 2 3 5% 4 6% 49%	1980
	11th to 20th	Night	20% 5% 2 4 3 2 3 4 3 5% 49%	1848
	21st to end	Night	20% 4 3 4 4 2 3 3 3 5% 49%	1749
May	1st to 10th	Night	15% 4 3 3 5% 2 3 4 5% 8% 47%	1620
	11th to 20th	Night	15% 6% 2 4 5% 2 4 4 5% 8% 46%	1593
	21st to end	Night	18% 5% 2 4 4 2 4 3 5% 9% 44%	1745
June	1st to 10th	Night	6% 3 1 2 3 2 3 5% 6% 9% 60%	1620
	11th to 20th	Night	6% 3 2 3 4 2 4 5% 5% 8% 59%	1620
	21st to end	Night	9% 4 2 4 3 3 3 4 5% 11% 51%	1620
July	1st to 10th	Night	10% 5% 2 5% 6% 3 4 5% 7% 9% 44%	1620
	11th to 20th	Night	4 2 1 3 4 2 4 4 5% 9% 62%	1620
	21st to end	Night	5% 3 1 3 3 2 4 4 6% 10% 59%	1772
August	1st to 10th	Night	3 2 1 3 3 2 2 3 5% 8% 68%	1756
	11th to 20th	Night	6% 2 1 4 4 2 6% 5% 6% 9% 56%	1778
	21st to end	Night	7% 4 2 5% 5% 3 5% 5% 5% 10% 49%	2016
September	1st to 10th	Night	10% 5% 2 5% 5% 3 5% 4 5% 8% 47%	1980
	11th to 20th	Night	11% 7% 2 5% 4 3 5% 4 6% 8% 44%	1980
	21st to end	Night	9% 5% 2 5% 5% 3 4 5% 5% 8% 51%	1980
October	1st to 10th	Night	8% 4 2 4 4 2 4 3 5% 5% 60%	1980
	11th to 20th	Night	15% 4 1 3 4 2 3 3 5% 6% 53%	2004
	21st to end	Night	16% 4 2 2 2 1 2 2 3 4 62%	2376
November	1st to 10th	Night	15% 6% 2 4 3 2 2 3 4 6% 54%	2225
	11th to 20th	Night	12% 5% 2 3 3 2 3 3 5% 6% 55%	2470
	21st to end	Night	20% 4 1 3 4 2 3 3 5% 7% 48%	2470
December	1st to 10th	Night	16% 5% 2 3 3 2 4 3 4 6% 53%	2470
	11th to 20th	Night	19% 6% 3 4 4 2 3 3 3 5% 48%	3036
	21st to end	Night	20% 5% 2 3 2 1 3 2 3 6% 53%	4532

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	34% 4 4 18% 21% 19%	1708
	11th to 20th	Day	39% 3 5% 15% 21% 17%	1743
	21st to end	Day	36% 3 6% 14% 24% 17%	2080
February	1st to 10th	Day	41% 3 5% 12% 21% 17%	1800
	11th to 20th	Day	42% 4 6% 16% 18% 14%	1759
	21st to end	Day	37% 3 7% 17% 19% 17%	1480
March	1st to 10th	Day	43% 4 8% 14% 18% 12%	1890
	11th to 20th	Day	41% 4 6% 15% 16% 17%	1980
	21st to end	Day	40% 4 8% 17% 18% 13%	2178
April	1st to 10th	Day	41% 4 8% 16% 18% 12%	1980
	11th to 20th	Day	41% 5% 6% 17% 18% 13%	2057
	21st to end	Day	42% 4 6% 18% 17% 12%	2209
May	1st to 10th	Day	43% 6% 8% 17% 18% 8%	2340
	11th to 20th	Day	43% 6% 10% 19% 17% 5%	2306
	21st to end	Day	46% 6% 11% 20% 15% 2	2531
June	1st to 10th	Day	31% 8% 14% 25% 19% 4	2340
	11th to 20th	Day	35% 6% 12% 26% 16% 5%	2340
	21st to end	Day	40% 8% 11% 23% 14% 4	2340
July	1st to 10th	Day	42% 8% 15% 24% 11% 1	2276
	11th to 20th	Day	28% 7% 16% 28% 20% 2	2271
	21st to end	Day	24% 7% 22% 33% 13% 1	2405
August	1st to 10th	Day	19% 6% 17% 38% 19% 1	2164
	11th to 20th	Day	29% 9% 16% 30% 12% 3	2123
	21st to end	Day	34% 8% 16% 26% 13% 3	2339
September	1st to 10th	Day	42% 7% 10% 18% 16% 6%	1980
	11th to 20th	Day	39% 9% 11% 19% 17% 5%	1980
	21st to end	Day	35% 6% 10% 22% 18% 9%	1980
October	1st to 10th	Day	31% 6% 10% 21% 25% 8%	1980
	11th to 20th	Day	35% 5% 8% 17% 19% 16%	1936
	21st to end	Day	32% 4 5% 16% 24% 20%	1980
November	1st to 10th	Day	41% 4 8% 20% 17% 11%	1849
	11th to 20th	Day	39% 4 6% 17% 19% 16%	1710
	21st to end	Day	42% 3 5% 15% 20% 14%	1710
December	1st to 10th	Day	39% 4 8% 18% 21% 10%	1710
	11th to 20th	Day	41% 4 6% 10% 21% 16%	2159
	21st to end	Day	33% 3 5% 16% 29% 15%	3135
January	1st to 10th	Night	32% 4 5% 16% 22% 21%	2458
	11th to 20th	Night	37% 3 5% 16% 21% 18%	2451
	21st to end	Night	38% 3 5% 14% 21% 20%	2502
February	1st to 10th	Night	35% 4 7% 14% 21% 20%	2160
	11th to 20th	Night	38% 3 5% 16% 20% 17%	2098
	21st to end	Night	38% 4 6% 15% 19% 18%	1776
March	1st to 10th	Night	40% 4 9% 16% 18% 12%	2067
	11th to 20th	Night	41% 5% 7% 13% 16% 18%	1980
	21st to end	Night	36% 5% 11% 17% 17% 15%	2178
April	1st to 10th	Night	34% 5% 11% 18% 17% 15%	1980
	11th to 20th	Night	39% 4 9% 14% 17% 17%	1848
	21st to end	Night	39% 4 9% 19% 16% 12%	1749
May	1st to 10th	Night	36% 5% 13% 20% 15% 11%	1620
	11th to 20th	Night	38% 6% 10% 24% 16% 5%	1594
	21st to end	Night	39% 6% 16% 25% 13% 2	1746
June	1st to 10th	Night	21% 6% 19% 31% 21% 3	1620
	11th to 20th	Night	23% 6% 15% 29% 21% 5%	1620
	21st to end	Night	29% 7% 19% 27% 15% 3	1620
July	1st to 10th	Night	35% 8% 20% 28% 8% 1	1575
	11th to 20th	Night	19% 8% 20% 30% 21% 2	1566
	21st to end	Night	17% 9% 28% 35% 10% 1	1673
August	1st to 10th	Night	15% 6% 21% 40% 17% 1	1746
	11th to 20th	Night	24% 9% 22% 30% 13% 3	1778
	21st to end	Night	30% 8% 22% 25% 12% 3	2016
September	1st to 10th	Night	35% 7% 14% 22% 16% 6%	1980
	11th to 20th	Night	36% 8% 16% 21% 14% 4	1980
	21st to end	Night	31% 6% 13% 22% 18% 10%	1980
October	1st to 10th	Night	26% 4 12% 26% 21% 11%	1980
	11th to 20th	Night	32% 4 10% 17% 20% 16%	2004
	21st to end	Night	29% 3 6% 15% 25% 22%	2376
November	1st to 10th	Night	33% 4 7% 19% 22% 14%	2225
	11th to 20th	Night	31% 4 9% 19% 20% 16%	2470
	21st to end	Night	37% 4 8% 16% 19% 15%	2470
December	1st to 10th	Night	34% 4 8% 19% 22% 13%	2470
	11th to 20th	Night	40% 4 5% 14% 17% 20%	3037
	21st to end	Night	34% 4 5% 14% 27% 16%	4532

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% 13% 33% 25% 7%	270
	11th to 20th	Day	25% 15% 26% 25% 9%	270
	21st to end	Day	19% 16% 34% 24% 7%	294
February	1st to 10th	Day	30% 11% 27% 23% 9%	240
	11th to 20th	Day	29% 18% 30% 15% 7%	240
	21st to end	Day	25% 20% 32% 18% 5%	198
March	1st to 10th	Day	27% 13% 40% 18% 3	240
	11th to 20th	Day	20% 18% 42% 17% 4	240
	21st to end	Day	23% 16% 41% 17% 2	264
April	1st to 10th	Day	22% 16% 35% 23% 3	240
	11th to 20th	Day	17% 16% 38% 25% 4	335
	21st to end	Day	19% 12% 41% 23% 3	469
May	1st to 10th	Day	20% 10% 36% 28% 6%	603
	11th to 20th	Day	20% 7% 32% 32% 8% 2	625
	21st to end	Day	19% 6% 30% 33% 12% 1	679
June	1st to 10th	Day	7% 2 19% 44% 25% 3	630
	11th to 20th	Day	9% 1 19% 45% 23% 2	630
	21st to end	Day	11% 1 15% 38% 28% 7%	630
July	1st to 10th	Day	13% 2 11% 33% 34% 7%	621
	11th to 20th	Day	6% 1 6% 36% 45% 6%	618
	21st to end	Day	4 1 6% 34% 44% 11%	684
August	1st to 10th	Day	3 3 37% 44% 13%	476
	11th to 20th	Day	6% 2 5% 35% 40% 12%	437
	21st to end	Day	6% 1 7% 29% 41% 16%	458
September	1st to 10th	Day	11% 2 6% 26% 39% 16%	270
	11th to 20th	Day	9% 3 27% 45% 15%	270
	21st to end	Day	7% 1 11% 27% 43% 10%	270
October	1st to 10th	Day	8% 2 16% 35% 33% 6%	270
	11th to 20th	Day	13% 4 22% 38% 19% 4	270
	21st to end	Day	18% 15% 25% 26% 15% 1	297
November	1st to 10th	Day	21% 6% 28% 25% 16% 3	270
	11th to 20th	Day	24% 10% 24% 27% 12% 3	270
	21st to end	Day	25% 16% 32% 17% 9% 1	270
December	1st to 10th	Day	17% 13% 27% 28% 12% 3	270
	11th to 20th	Day	24% 15% 28% 24% 9%	270
	21st to end	Day	23% 11% 33% 25% 8%	297
January	1st to 10th	Night	19% 8% 26% 37% 10%	950
	11th to 20th	Night	21% 9% 29% 34% 8%	931
	21st to end	Night	23% 9% 26% 34% 8%	834
February	1st to 10th	Night	22% 11% 27% 31% 8%	720
	11th to 20th	Night	26% 10% 29% 29% 6%	704
	21st to end	Night	23% 11% 38% 27% 2	592
March	1st to 10th	Night	22% 11% 33% 28% 4 1	627
	11th to 20th	Night	20% 11% 33% 32% 4	540
	21st to end	Night	18% 11% 39% 27% 5%	594
April	1st to 10th	Night	14% 9% 43% 31% 3	540
	11th to 20th	Night	20% 10% 44% 24% 2	533
	21st to end	Night	20% 10% 40% 23% 6%	540
May	1st to 10th	Night	15% 10% 42% 28% 5%	540
	11th to 20th	Night	17% 6% 35% 34% 7% 1	531
	21st to end	Night	17% 6% 31% 36% 9%	584
June	1st to 10th	Night	6% 1 26% 47% 19% 1	540
	11th to 20th	Night	6% 1 32% 47% 14%	540
	21st to end	Night	7% 3 20% 47% 22% 1	540
July	1st to 10th	Night	9% 3 11% 47% 28% 1	525
	11th to 20th	Night	4 12% 52% 30% 2	522
	21st to end	Night	6% 1 8% 51% 33% 2	591
August	1st to 10th	Night	2 1 9% 48% 38% 2	537
	11th to 20th	Night	5% 7% 51% 33% 3	534
	21st to end	Night	7% 2 8% 38% 41% 4	594
September	1st to 10th	Night	10% 1 8% 42% 34% 5%	540
	11th to 20th	Night	12% 1 9% 41% 35% 2	540
	21st to end	Night	11% 2 12% 41% 30% 4	540
October	1st to 10th	Night	8% 2 13% 49% 26% 2	540
	11th to 20th	Night	16% 3 21% 40% 17% 3	564
	21st to end	Night	16% 7% 22% 30% 23% 2	792
November	1st to 10th	Night	14% 6% 19% 37% 21% 2	745
	11th to 20th	Night	15% 7% 19% 42% 16% 2	950
	21st to end	Night	22% 9% 23% 33% 13% 1	950
December	1st to 10th	Night	19% 7% 22% 38% 13% 1	950
	11th to 20th	Night	24% 10% 24% 32% 10%	950
	21st to end	Night	20% 8% 26% 37% 9% 1	1045

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