Big Bend Ranch State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Big Bend Ranch State Park clear sky chart from 2005-11-06 to 2026-08-15.

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	3 3 1 3 3 3 4 3 5% 7% 65%	150669
	Night	3 3 1 4 3 3 4 3 6% 8% 63%	148724
Transparency	Day	11% 35% 6% 14% 17% 17%	145783
	Night	12% 35% 6% 13% 17% 17%	144617
Seeing	Day	5% 7% 23% 35% 24% 6%	16618
	Night	5% 5% 25% 45% 18% 1	26856

By Month

Percentage Cloud Cover SW (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	1 3 1 3 2 2 2 2 4 6% 73%	5885
	11th to 20th	Day	3 3 1 3 2 2 3 3 4 5% 72%	5910
	21st to end	Day	3 5% 2 5% 3 3 4 3 4 6% 62%	6468
February	1st to 10th	Day	3 4 1 5% 3 3 3 3 4 5% 65%	2100
	11th to 20th	Day	4 5% 2 4 4 3 3 2 4 6% 62%	2049
	21st to end	Day	3 2 1 3 2 3 3 4 5% 6% 67%	1730
March	1st to 10th	Day	2 4 2 4 3 3 3 3 5% 7% 64%	4600
	11th to 20th	Day	2 2 1 4 3 3 3 3 4 6% 69%	4985
	21st to end	Day	2 4 1 4 2 3 3 4 5% 7% 64%	6046
April	1st to 10th	Day	3 3 1 3 3 2 3 3 5% 8% 66%	2520
	11th to 20th	Day	3 3 1 3 2 2 3 3 5% 5% 68%	2491
	21st to end	Day	3 3 1 3 3 2 3 3 4 5% 70%	2520
May	1st to 10th	Day	1 3 1 3 2 2 2 2 3 6% 75%	7057
	11th to 20th	Day	2 3 1 4 3 3 4 3 5% 7% 65%	7032
	21st to end	Day	2 2 1 3 2 3 4 4 5% 7% 68%	7826
June	1st to 10th	Day	1 1 2 2 3 4 3 6% 9% 69%	2730
	11th to 20th	Day	2 3 1 3 3 3 4 4 5% 9% 65%	2730
	21st to end	Day	2 2 1 4 3 4 4 5% 7% 8% 59%	2543
July	1st to 10th	Day	3 3 1 4 3 3 4 4 8% 11% 58%	7079
	11th to 20th	Day	5% 4 1 5% 4 5% 6% 5% 9% 10% 47%	7080
	21st to end	Day	1 2 1 3 3 3 5% 4 5% 9% 64%	7686
August	1st to 10th	Day	1 1 2 2 3 3 3 6% 10% 68%	5468
	11th to 20th	Day	2 2 1 3 3 5% 5% 5% 8% 11% 54%	5415
	21st to end	Day	2 2 1 3 3 4 5% 4 7% 10% 59%	5984
September	1st to 10th	Day	6% 5% 2 5% 5% 4 5% 4 7% 10% 45%	2400
	11th to 20th	Day	8% 5% 2 5% 4 4 5% 4 7% 8% 49%	2280
	21st to end	Day	4 4 2 4 3 3 5% 3 5% 6% 60%	2200
October	1st to 10th	Day	1 1 2 1 2 2 2 4 5% 80%	3590
	11th to 20th	Day	3 3 1 3 2 2 2 3 4 5% 74%	3382
	21st to end	Day	3 1 1 1 1 1 1 2 3 84%	3548
November	1st to 10th	Day	4 2 1 2 1 2 3 2 4 5% 74%	2059
	11th to 20th	Day	4 2 1 3 2 3 3 3 5% 5% 69%	1894
	21st to end	Day	4 4 2 5% 3 3 3 2 5% 6% 63%	1890
December	1st to 10th	Day	4 5% 2 6% 4 3 3 3 6% 8% 57%	3030
	11th to 20th	Day	1 3 2 4 3 3 3 3 4 6% 68%	3481
	21st to end	Day	2 2 1 3 2 2 3 3 5% 5% 74%	4981
January	1st to 10th	Night	2 2 1 3 2 2 3 2 4 6% 74%	7038
	11th to 20th	Night	4 2 1 3 2 2 2 3 4 5% 73%	7080
	21st to end	Night	5% 4 2 5% 3 3 4 3 6% 8% 57%	7746
February	1st to 10th	Night	4 4 1 4 3 2 4 3 5% 6% 64%	2520
	11th to 20th	Night	5% 4 2 5% 3 3 3 3 5% 7% 59%	2458
	21st to end	Night	4 4 1 2 3 3 3 4 6% 6% 64%	2076
March	1st to 10th	Night	3 3 1 4 3 3 3 3 5% 7% 63%	5494
	11th to 20th	Night	4 3 1 4 3 2 2 2 4 6% 68%	5211
	21st to end	Night	3 4 2 4 3 3 4 3 4 6% 65%	5149
April	1st to 10th	Night	4 4 1 3 2 4 4 3 6% 7% 62%	2100
	11th to 20th	Night	3 3 1 3 3 3 3 4 5% 7% 64%	2077
	21st to end	Night	3 3 1 4 3 3 3 3 4 5% 69%	2100
May	1st to 10th	Night	3 2 1 3 2 3 3 3 4 6% 70%	5890
	11th to 20th	Night	5% 3 1 5% 4 4 4 4 6% 7% 57%	5860
	21st to end	Night	4 2 1 4 3 4 4 4 6% 7% 61%	6344
June	1st to 10th	Night	2 2 1 4 4 4 5% 5% 9% 10% 54%	1890
	11th to 20th	Night	3 2 1 5% 4 5% 5% 5% 8% 11% 50%	1890
	21st to end	Night	3 3 2 5% 4 4 5% 5% 8% 9% 53%	2064
July	1st to 10th	Night	3 3 2 5% 4 4 5% 5% 9% 12% 48%	5910
	11th to 20th	Night	4 3 1 4 4 4 4 5% 9% 13% 49%	5910
	21st to end	Night	1 2 1 4 3 5% 5% 4 7% 10% 58%	6423
August	1st to 10th	Night	1 1 1 2 2 3 3 4 7% 12% 63%	4564
	11th to 20th	Night	2 2 1 4 3 4 5% 5% 9% 14% 51%	4523
	21st to end	Night	1 2 1 3 3 3 4 4 7% 13% 59%	4993
September	1st to 10th	Night	6% 4 2 6% 4 4 5% 4 8% 10% 47%	2000
	11th to 20th	Night	6% 4 2 7% 5% 5% 5% 5% 8% 10% 43%	2120
	21st to end	Night	4 4 2 5% 5% 5% 6% 5% 7% 9% 50%	2200
October	1st to 10th	Night	2 1 1 2 2 3 3 2 4 5% 75%	3590
	11th to 20th	Night	3 3 1 4 3 2 3 3 4 6% 68%	3756
	21st to end	Night	2 2 1 1 2 1 1 1 2 4 82%	4252
November	1st to 10th	Night	4 2 1 2 1 2 2 2 3 4 76%	2460
	11th to 20th	Night	3 3 1 4 2 2 2 3 5% 6% 69%	2701
	21st to end	Night	4 4 2 4 4 3 3 3 4 5% 66%	2730
December	1st to 10th	Night	3 4 2 8% 5% 4 4 4 6% 6% 52%	4380
	11th to 20th	Night	1 3 2 4 3 2 3 3 4 6% 70%	4946
	21st to end	Night	2 3 1 3 2 2 3 3 5% 5% 71%	6279

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	10% 21% 4 20% 25% 21%	5888
	11th to 20th	Day	12% 21% 3 11% 30% 22%	5910
	21st to end	Day	19% 23% 3 15% 25% 15%	6468
February	1st to 10th	Day	11% 58% 2 5% 9% 14%	2100
	11th to 20th	Day	10% 58% 3 8% 8% 14%	2059
	21st to end	Day	7% 58% 2 4 13% 15%	1730
March	1st to 10th	Day	14% 28% 3 7% 15% 34%	4600
	11th to 20th	Day	9% 29% 3 7% 15% 37%	4985
	21st to end	Day	13% 28% 4 6% 19% 30%	6046
April	1st to 10th	Day	7% 58% 3 5% 11% 15%	2520
	11th to 20th	Day	9% 60% 3 6% 8% 13%	2494
	21st to end	Day	7% 58% 2 6% 11% 15%	2520
May	1st to 10th	Day	8% 22% 4 11% 17% 38%	7057
	11th to 20th	Day	14% 23% 4 8% 19% 33%	7035
	21st to end	Day	11% 24% 6% 15% 18% 26%	7827
June	1st to 10th	Day	5% 59% 5% 12% 11% 7%	2730
	11th to 20th	Day	9% 59% 3 7% 13% 9%	2730
	21st to end	Day	8% 59% 6% 11% 10% 7%	2543
July	1st to 10th	Day	13% 25% 15% 26% 18% 4	7021
	11th to 20th	Day	23% 27% 16% 26% 7% 2	7017
	21st to end	Day	11% 23% 11% 24% 26% 5%	7516
August	1st to 10th	Day	8% 37% 7% 23% 22% 3	4012
	11th to 20th	Day	9% 38% 12% 25% 13% 2	3931
	21st to end	Day	9% 39% 12% 23% 14% 3	4311
September	1st to 10th	Day	12% 59% 6% 9% 7% 7%	2400
	11th to 20th	Day	11% 59% 8% 9% 10% 3	2280
	21st to end	Day	12% 58% 5% 11% 10% 4	2200
October	1st to 10th	Day	4 36% 4 7% 17% 32%	3590
	11th to 20th	Day	7% 36% 7% 12% 11% 26%	3382
	21st to end	Day	5% 34% 2 6% 35% 19%	3548
November	1st to 10th	Day	12% 53% 5% 7% 10% 12%	2059
	11th to 20th	Day	12% 55% 4 10% 10% 9%	1894
	21st to end	Day	11% 53% 4 10% 13% 9%	1890
December	1st to 10th	Day	17% 36% 5% 18% 15% 10%	3030
	11th to 20th	Day	12% 31% 3 17% 23% 15%	3479
	21st to end	Day	8% 26% 3 8% 29% 25%	4981
January	1st to 10th	Night	10% 20% 3 15% 30% 22%	7038
	11th to 20th	Night	11% 20% 2 9% 24% 34%	7080
	21st to end	Night	19% 23% 4 15% 22% 17%	7746
February	1st to 10th	Night	9% 58% 2 7% 11% 14%	2520
	11th to 20th	Night	9% 58% 3 7% 11% 12%	2458
	21st to end	Night	8% 59% 2 6% 11% 14%	2076
March	1st to 10th	Night	14% 28% 3 5% 15% 34%	5494
	11th to 20th	Night	10% 30% 4 8% 15% 34%	5211
	21st to end	Night	14% 29% 4 6% 15% 32%	5149
April	1st to 10th	Night	8% 59% 3 6% 8% 16%	2100
	11th to 20th	Night	8% 60% 4 8% 6% 13%	2077
	21st to end	Night	8% 59% 2 8% 11% 12%	2100
May	1st to 10th	Night	10% 24% 5% 12% 16% 32%	5888
	11th to 20th	Night	18% 25% 5% 11% 12% 30%	5861
	21st to end	Night	15% 25% 7% 17% 14% 22%	6346
June	1st to 10th	Night	10% 60% 5% 11% 11% 4	1890
	11th to 20th	Night	10% 60% 3 10% 12% 5%	1890
	21st to end	Night	9% 59% 8% 10% 9% 5%	2064
July	1st to 10th	Night	18% 25% 18% 23% 14% 1	5860
	11th to 20th	Night	20% 26% 20% 24% 8% 2	5850
	21st to end	Night	13% 24% 12% 22% 25% 3	6280
August	1st to 10th	Night	8% 36% 8% 27% 19% 2	3344
	11th to 20th	Night	9% 38% 16% 27% 9% 1	3283
	21st to end	Night	9% 39% 13% 25% 12% 2	3597
September	1st to 10th	Night	12% 59% 7% 10% 7% 6%	2000
	11th to 20th	Night	13% 60% 8% 8% 7% 4	2120
	21st to end	Night	13% 59% 7% 10% 8% 3	2200
October	1st to 10th	Night	6% 36% 5% 6% 17% 31%	3590
	11th to 20th	Night	8% 37% 7% 11% 10% 26%	3756
	21st to end	Night	6% 35% 2 7% 31% 19%	4252
November	1st to 10th	Night	11% 53% 5% 7% 11% 13%	2460
	11th to 20th	Night	10% 55% 4 10% 11% 10%	2701
	21st to end	Night	10% 54% 4 8% 13% 12%	2730
December	1st to 10th	Night	21% 36% 6% 14% 10% 13%	4380
	11th to 20th	Night	9% 31% 3 14% 26% 17%	4947
	21st to end	Night	9% 26% 4 8% 30% 23%	6279

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	9% 8% 33% 35% 14% 2	330
	11th to 20th	Day	5% 8% 31% 40% 15% 1	330
	21st to end	Day	7% 12% 32% 34% 13% 1	363
February	1st to 10th	Day	8% 10% 28% 31% 20% 4	330
	11th to 20th	Day	11% 14% 32% 30% 12% 1	330
	21st to end	Day	8% 15% 34% 36% 6% 2	273
March	1st to 10th	Day	9% 11% 38% 29% 11% 2	330
	11th to 20th	Day	10% 18% 33% 23% 12% 3	480
	21st to end	Day	8% 16% 32% 31% 10% 1	594
April	1st to 10th	Day	9% 15% 39% 30% 6% 1	540
	11th to 20th	Day	6% 17% 43% 27% 7% 1	532
	21st to end	Day	6% 13% 41% 34% 6%	540
May	1st to 10th	Day	3 12% 41% 32% 9% 2	543
	11th to 20th	Day	5% 11% 36% 35% 12% 1	568
	21st to end	Day	3 6% 33% 43% 15%	643
June	1st to 10th	Day	2 2 19% 44% 31% 3	780
	11th to 20th	Day	4 1 15% 42% 34% 3	780
	21st to end	Day	3 1 14% 40% 36% 6%	593
July	1st to 10th	Day	4 1 11% 34% 35% 15%	566
	11th to 20th	Day	3 8% 38% 40% 11%	564
	21st to end	Day	2 1 7% 40% 41% 9%	619
August	1st to 10th	Day	2 1 6% 32% 46% 12%	567
	11th to 20th	Day	6% 1 7% 33% 36% 16%	534
	21st to end	Day	3 2 8% 33% 39% 16%	583
September	1st to 10th	Day	7% 1 11% 37% 33% 11%	530
	11th to 20th	Day	6% 1 8% 32% 41% 12%	410
	21st to end	Day	6% 4 8% 29% 39% 15%	330
October	1st to 10th	Day	2 2 12% 34% 41% 8%	330
	11th to 20th	Day	8% 4 13% 36% 29% 10%	330
	21st to end	Day	7% 4 19% 32% 29% 9%	363
November	1st to 10th	Day	4 7% 20% 32% 30% 8%	330
	11th to 20th	Day	7% 9% 21% 28% 27% 8%	330
	21st to end	Day	8% 11% 30% 33% 16% 3	330
December	1st to 10th	Day	8% 6% 22% 36% 24% 4	330
	11th to 20th	Day	3 9% 28% 35% 21% 3	330
	21st to end	Day	5% 8% 26% 40% 15% 5%	363
January	1st to 10th	Night	7% 3 25% 48% 16% 1	840
	11th to 20th	Night	8% 6% 23% 45% 18%	840
	21st to end	Night	7% 7% 30% 43% 13% 1	924
February	1st to 10th	Night	5% 7% 27% 42% 18%	840
	11th to 20th	Night	9% 7% 32% 43% 10% 1	824
	21st to end	Night	6% 9% 36% 43% 6%	692
March	1st to 10th	Night	9% 8% 37% 37% 9% 1	840
	11th to 20th	Night	10% 10% 34% 34% 11% 1	840
	21st to end	Night	6% 7% 38% 39% 10% 1	722
April	1st to 10th	Night	4 12% 40% 37% 6%	630
	11th to 20th	Night	4 11% 43% 37% 5%	623
	21st to end	Night	4 12% 42% 36% 6%	630
May	1st to 10th	Night	6% 8% 41% 37% 7%	630
	11th to 20th	Night	5% 10% 33% 45% 6% 1	621
	21st to end	Night	4 6% 36% 47% 7%	683
June	1st to 10th	Night	2 4 31% 50% 12% 1	630
	11th to 20th	Night	3 2 29% 51% 15%	630
	21st to end	Night	4 3 23% 52% 18%	630
July	1st to 10th	Night	6% 1 20% 48% 23% 1	615
	11th to 20th	Night	4 1 12% 59% 23% 1	612
	21st to end	Night	2 1 13% 53% 29% 2	690
August	1st to 10th	Night	3 1 9% 51% 36% 1	627
	11th to 20th	Night	3 1 10% 41% 40% 4	606
	21st to end	Night	4 1 10% 48% 35% 2	660
September	1st to 10th	Night	6% 2 13% 48% 30% 1	600
	11th to 20th	Night	7% 1 15% 48% 28% 1	600
	21st to end	Night	5% 1 17% 50% 25% 2	600
October	1st to 10th	Night	3 2 17% 53% 24% 1	600
	11th to 20th	Night	7% 2 22% 45% 21% 2	710
	21st to end	Night	5% 4 16% 43% 28% 3	880
November	1st to 10th	Night	5% 3 18% 41% 31% 2	820
	11th to 20th	Night	4 5% 18% 49% 23% 1	1021
	21st to end	Night	5% 7% 25% 43% 17% 2	1050
December	1st to 10th	Night	7% 4 21% 48% 20% 1	1050
	11th to 20th	Night	5% 4 26% 46% 18% 1	1050
	21st to end	Night	5% 6% 23% 47% 19% 1	996

Page generated at 2026-08-12 02:37:16. Version ac07

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