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 2025-04-11.

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 3 3 5% 7% 67%	117800
	Night	3 3 1 4 3 3 3 3 5% 7% 64%	119352
Transparency	Day	9% 41% 5% 12% 16% 17%	117586
	Night	10% 41% 5% 11% 15% 18%	119155
Seeing	Day	5% 7% 22% 35% 25% 6%	14790
	Night	5% 5% 25% 45% 19% 1	25185

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	2 3 1 3 2 2 2 2 4 6% 73%	4537
	11th to 20th	Day	2 2 1 2 2 2 3 3 4 5% 74%	4540
	21st to end	Day	3 4 1 4 3 3 4 3 3 6% 66%	4994
February	1st to 10th	Day	3 4 1 4 3 3 3 3 4 4 66%	2000
	11th to 20th	Day	4 5% 2 4 4 3 3 2 4 6% 63%	1949
	21st to end	Day	3 2 1 3 2 3 3 4 6% 6% 66%	1650
March	1st to 10th	Day	2 4 2 4 3 3 3 3 5% 7% 64%	4500
	11th to 20th	Day	2 2 1 4 3 3 3 3 4 6% 69%	4878
	21st to end	Day	2 4 1 4 2 3 3 4 6% 7% 64%	5915
April	1st to 10th	Day	2 3 1 3 3 2 3 3 5% 8% 66%	2400
	11th to 20th	Day	2 3 1 3 3 3 3 3 5% 5% 70%	2252
	21st to end	Day	3 3 1 3 2 2 3 2 4 5% 71%	2280
May	1st to 10th	Day	1 2 1 2 2 2 2 2 3 6% 78%	3800
	11th to 20th	Day	1 2 1 3 3 2 3 3 5% 6% 71%	3765
	21st to end	Day	1 1 1 2 2 1 3 3 4 6% 77%	4191
June	1st to 10th	Day	1 1 2 2 3 4 3 6% 9% 69%	2470
	11th to 20th	Day	2 2 1 2 3 3 4 4 5% 9% 65%	2470
	21st to end	Day	2 2 1 4 3 3 4 5% 7% 8% 61%	2301
July	1st to 10th	Day	3 2 1 3 3 4 5% 5% 7% 9% 58%	3800
	11th to 20th	Day	2 2 1 2 3 3 5% 4 8% 10% 60%	3800
	21st to end	Day	3 3 1 4 3 4 5% 5% 6% 10% 55%	4118
August	1st to 10th	Day	2 1 3 2 4 4 4 7% 9% 64%	3784
	11th to 20th	Day	3 3 1 3 3 4 4 4 7% 8% 60%	3726
	21st to end	Day	2 2 1 4 3 4 5% 4 8% 10% 56%	4180
September	1st to 10th	Day	6% 5% 2 5% 5% 4 5% 4 7% 10% 46%	2280
	11th to 20th	Day	8% 5% 2 5% 4 4 5% 4 6% 8% 49%	2166
	21st to end	Day	4 4 2 4 4 3 5% 3 5% 6% 60%	2090
October	1st to 10th	Day	1 1 2 1 2 2 1 4 5% 80%	3480
	11th to 20th	Day	3 3 1 3 2 2 2 3 4 5% 74%	3278
	21st to end	Day	3 1 1 1 1 2 1 2 3 84%	3438
November	1st to 10th	Day	4 3 1 3 2 2 3 2 4 5% 73%	1959
	11th to 20th	Day	4 3 1 3 2 2 3 3 5% 5% 69%	1804
	21st to end	Day	4 4 2 5% 3 3 3 3 5% 6% 62%	1800
December	1st to 10th	Day	4 5% 2 6% 4 3 3 3 6% 8% 56%	2940
	11th to 20th	Day	1 3 2 4 3 3 3 3 4 6% 68%	3391
	21st to end	Day	2 2 1 3 2 2 3 3 5% 5% 74%	4874
January	1st to 10th	Night	3 2 1 3 1 2 3 2 4 6% 74%	5428
	11th to 20th	Night	3 2 1 3 2 2 2 3 4 4 75%	5440
	21st to end	Night	4 4 2 4 3 3 4 3 6% 8% 60%	5984
February	1st to 10th	Night	4 3 1 4 3 2 3 3 5% 6% 65%	2400
	11th to 20th	Night	5% 4 2 5% 3 3 4 3 5% 6% 59%	2338
	21st to end	Night	4 5% 1 2 3 3 3 4 6% 6% 63%	1980
March	1st to 10th	Night	3 3 1 5% 3 3 3 3 5% 7% 63%	5374
	11th to 20th	Night	4 3 1 4 3 2 2 2 4 6% 67%	5098
	21st to end	Night	3 4 2 4 3 3 4 3 5% 6% 65%	5038
April	1st to 10th	Night	4 3 1 3 2 4 3 3 5% 7% 63%	2000
	11th to 20th	Night	3 3 1 3 3 3 3 4 5% 7% 65%	1882
	21st to end	Night	3 3 1 4 3 3 3 3 3 5% 70%	1900
May	1st to 10th	Night	3 2 1 2 2 2 2 2 4 6% 75%	3170
	11th to 20th	Night	3 3 1 4 3 4 3 3 5% 5% 65%	3140
	21st to end	Night	3 2 1 3 3 3 4 3 5% 7% 67%	3387
June	1st to 10th	Night	2 2 1 4 4 4 5% 5% 10% 10% 53%	1710
	11th to 20th	Night	3 2 1 5% 4 5% 5% 5% 8% 12% 50%	1710
	21st to end	Night	3 3 1 3 3 4 5% 4 7% 9% 56%	1867
July	1st to 10th	Night	2 2 1 4 3 4 6% 6% 11% 11% 48%	3170
	11th to 20th	Night	2 1 1 2 3 2 3 4 7% 13% 62%	3170
	21st to end	Night	2 2 1 4 3 4 6% 4 8% 11% 55%	3445
August	1st to 10th	Night	2 2 1 3 3 3 4 6% 9% 13% 55%	3155
	11th to 20th	Night	2 2 1 3 3 4 5% 5% 8% 12% 55%	3113
	21st to end	Night	2 2 1 4 4 3 5% 4 7% 12% 55%	3487
September	1st to 10th	Night	5% 4 2 6% 4 4 5% 4 8% 10% 48%	1900
	11th to 20th	Night	6% 5% 2 7% 4 5% 5% 5% 7% 10% 44%	2014
	21st to end	Night	4 4 2 5% 5% 5% 6% 5% 7% 9% 50%	2090
October	1st to 10th	Night	2 1 1 3 2 3 3 2 4 5% 75%	3480
	11th to 20th	Night	3 3 1 4 3 2 3 3 4 6% 68%	3640
	21st to end	Night	2 2 1 1 1 1 1 1 2 4 82%	4120
November	1st to 10th	Night	4 2 1 2 1 2 2 3 4 4 75%	2340
	11th to 20th	Night	2 3 1 4 3 2 2 3 5% 6% 69%	2572
	21st to end	Night	4 4 2 4 4 3 3 3 4 5% 65%	2600
December	1st to 10th	Night	3 4 2 8% 5% 5% 4 4 7% 7% 52%	4250
	11th to 20th	Night	1 3 2 4 3 2 3 3 4 6% 69%	4816
	21st to end	Night	2 3 1 3 2 2 2 3 5% 5% 71%	6144

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	9% 26% 3 15% 23% 24%	4538
	11th to 20th	Day	8% 26% 3 12% 28% 21%	4540
	21st to end	Day	14% 29% 3 15% 24% 15%	4994
February	1st to 10th	Day	10% 61% 2 5% 8% 14%	2000
	11th to 20th	Day	9% 60% 3 7% 8% 13%	1959
	21st to end	Day	7% 61% 2 4 11% 15%	1650
March	1st to 10th	Day	14% 28% 3 7% 15% 33%	4500
	11th to 20th	Day	9% 30% 3 7% 15% 36%	4878
	21st to end	Day	13% 29% 4 5% 19% 30%	5915
April	1st to 10th	Day	6% 61% 2 4 10% 16%	2400
	11th to 20th	Day	7% 66% 3 5% 8% 12%	2255
	21st to end	Day	6% 64% 2 5% 10% 14%	2280
May	1st to 10th	Day	3 39% 2 7% 11% 38%	3800
	11th to 20th	Day	5% 40% 4 7% 14% 30%	3768
	21st to end	Day	4 39% 3 9% 12% 34%	4191
June	1st to 10th	Day	5% 65% 5% 10% 10% 6%	2470
	11th to 20th	Day	8% 65% 3 6% 11% 8%	2470
	21st to end	Day	6% 63% 5% 10% 10% 6%	2301
July	1st to 10th	Day	8% 38% 14% 24% 13% 3	3741
	11th to 20th	Day	8% 38% 14% 28% 10% 3	3737
	21st to end	Day	11% 37% 8% 20% 18% 6%	3988
August	1st to 10th	Day	8% 39% 7% 23% 21% 3	3772
	11th to 20th	Day	9% 39% 11% 26% 13% 2	3762
	21st to end	Day	9% 40% 12% 23% 14% 3	4179
September	1st to 10th	Day	11% 61% 6% 9% 7% 6%	2280
	11th to 20th	Day	11% 61% 6% 8% 10% 4	2166
	21st to end	Day	11% 61% 5% 11% 9% 4	2090
October	1st to 10th	Day	4 37% 4 6% 17% 32%	3480
	11th to 20th	Day	7% 37% 6% 12% 11% 26%	3278
	21st to end	Day	5% 35% 2 6% 35% 17%	3438
November	1st to 10th	Day	13% 56% 5% 8% 10% 9%	1959
	11th to 20th	Day	11% 57% 4 10% 10% 8%	1804
	21st to end	Day	11% 56% 3 9% 12% 9%	1800
December	1st to 10th	Day	17% 37% 5% 18% 14% 9%	2940
	11th to 20th	Day	12% 32% 3 17% 23% 14%	3389
	21st to end	Day	8% 26% 3 8% 30% 25%	4874
January	1st to 10th	Night	9% 25% 2 10% 30% 24%	5428
	11th to 20th	Night	8% 26% 3 10% 21% 33%	5440
	21st to end	Night	14% 29% 3 13% 22% 18%	5984
February	1st to 10th	Night	7% 61% 2 7% 9% 14%	2400
	11th to 20th	Night	8% 60% 3 7% 10% 11%	2338
	21st to end	Night	8% 61% 2 6% 10% 13%	1980
March	1st to 10th	Night	14% 28% 3 5% 15% 34%	5374
	11th to 20th	Night	10% 31% 4 8% 15% 33%	5098
	21st to end	Night	15% 29% 4 6% 15% 31%	5038
April	1st to 10th	Night	7% 62% 2 5% 8% 17%	2000
	11th to 20th	Night	7% 66% 3 7% 6% 12%	1882
	21st to end	Night	6% 64% 2 7% 9% 12%	1900
May	1st to 10th	Night	4 39% 1 5% 12% 38%	3170
	11th to 20th	Night	8% 42% 5% 9% 6% 31%	3141
	21st to end	Night	6% 41% 4 10% 10% 29%	3388
June	1st to 10th	Night	8% 65% 4 10% 10% 3	1710
	11th to 20th	Night	9% 66% 3 8% 11% 4	1710
	21st to end	Night	5% 64% 7% 10% 8% 6%	1867
July	1st to 10th	Night	11% 40% 18% 21% 9% 1	3120
	11th to 20th	Night	6% 37% 15% 31% 9% 2	3110
	21st to end	Night	9% 37% 10% 21% 20% 3	3336
August	1st to 10th	Night	8% 38% 8% 26% 18% 1	3144
	11th to 20th	Night	8% 39% 15% 27% 10% 1	3143
	21st to end	Night	9% 40% 13% 25% 11% 2	3487
September	1st to 10th	Night	10% 62% 7% 9% 7% 6%	1900
	11th to 20th	Night	12% 63% 7% 8% 7% 4	2014
	21st to end	Night	12% 62% 7% 10% 7% 3	2090
October	1st to 10th	Night	6% 37% 4 5% 16% 31%	3480
	11th to 20th	Night	7% 38% 7% 11% 10% 27%	3640
	21st to end	Night	5% 36% 2 7% 32% 18%	4120
November	1st to 10th	Night	11% 56% 5% 7% 11% 10%	2340
	11th to 20th	Night	10% 58% 4 10% 9% 9%	2572
	21st to end	Night	11% 57% 4 6% 11% 12%	2600
December	1st to 10th	Night	21% 37% 6% 14% 10% 12%	4250
	11th to 20th	Night	9% 32% 3 14% 26% 16%	4817
	21st to end	Night	9% 27% 3 7% 31% 23%	6144

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	10% 7% 33% 34% 15% 1	300
	11th to 20th	Day	4 9% 31% 40% 15% 1	300
	21st to end	Day	7% 13% 32% 35% 12% 2	330
February	1st to 10th	Day	8% 10% 26% 32% 20% 4	300
	11th to 20th	Day	11% 13% 33% 30% 13% 1	300
	21st to end	Day	8% 16% 35% 34% 5% 2	249
March	1st to 10th	Day	9% 11% 39% 29% 11% 1	300
	11th to 20th	Day	11% 19% 34% 23% 11% 3	443
	21st to end	Day	9% 18% 34% 30% 8% 1	550
April	1st to 10th	Day	9% 15% 39% 29% 7% 1	500
	11th to 20th	Day	5% 16% 45% 26% 8% 1	453
	21st to end	Day	5% 14% 38% 36% 7%	460
May	1st to 10th	Day	3 11% 38% 35% 10% 2	463
	11th to 20th	Day	4 10% 34% 38% 13% 1	488
	21st to end	Day	3 5% 30% 45% 16%	553
June	1st to 10th	Day	2 2 17% 44% 33% 3	680
	11th to 20th	Day	4 1 14% 42% 36% 3	680
	21st to end	Day	3 1 16% 40% 35% 5%	511
July	1st to 10th	Day	5% 1 10% 30% 37% 17%	486
	11th to 20th	Day	3 7% 38% 41% 11%	484
	21st to end	Day	3 1 7% 40% 40% 9%	531
August	1st to 10th	Day	2 1 6% 31% 47% 14%	487
	11th to 20th	Day	6% 1 7% 33% 35% 17%	477
	21st to end	Day	3 2 8% 33% 38% 16%	539
September	1st to 10th	Day	6% 1 10% 38% 33% 11%	490
	11th to 20th	Day	6% 1 7% 30% 42% 14%	376
	21st to end	Day	6% 3 8% 28% 40% 14%	300
October	1st to 10th	Day	2 3 12% 32% 42% 9%	300
	11th to 20th	Day	9% 4 13% 37% 27% 10%	300
	21st to end	Day	8% 5% 18% 31% 29% 9%	330
November	1st to 10th	Day	4 7% 20% 32% 30% 7%	300
	11th to 20th	Day	7% 10% 21% 29% 25% 8%	300
	21st to end	Day	9% 11% 27% 33% 17% 3	300
December	1st to 10th	Day	8% 6% 20% 36% 25% 4	300
	11th to 20th	Day	4 10% 28% 35% 20% 2	300
	21st to end	Day	5% 8% 28% 42% 15% 2	330
January	1st to 10th	Night	7% 3 25% 48% 17% 1	800
	11th to 20th	Night	8% 6% 22% 45% 18%	800
	21st to end	Night	7% 7% 30% 42% 14% 1	880
February	1st to 10th	Night	5% 7% 27% 42% 19%	800
	11th to 20th	Night	9% 7% 31% 43% 10% 1	784
	21st to end	Night	6% 9% 36% 43% 6%	660
March	1st to 10th	Night	9% 8% 37% 37% 9% 1	800
	11th to 20th	Night	10% 10% 34% 34% 11% 1	800
	21st to end	Night	6% 7% 39% 38% 9% 1	688
April	1st to 10th	Night	4 11% 41% 37% 7%	600
	11th to 20th	Night	4 11% 43% 36% 6%	565
	21st to end	Night	4 11% 40% 38% 6%	570
May	1st to 10th	Night	5% 6% 41% 40% 8%	570
	11th to 20th	Night	5% 9% 33% 45% 7% 1	561
	21st to end	Night	4 6% 34% 48% 8%	617
June	1st to 10th	Night	2 4 30% 51% 12% 1	570
	11th to 20th	Night	3 2 28% 51% 17%	570
	21st to end	Night	4 2 22% 53% 19%	570
July	1st to 10th	Night	5% 1 19% 49% 24% 1	555
	11th to 20th	Night	4 11% 60% 24% 1	552
	21st to end	Night	3 1 12% 53% 30% 2	624
August	1st to 10th	Night	3 1 8% 48% 39% 2	567
	11th to 20th	Night	4 1 10% 41% 40% 4	564
	21st to end	Night	4 1 10% 48% 35% 2	627
September	1st to 10th	Night	5% 2 11% 49% 31% 1	570
	11th to 20th	Night	8% 1 14% 47% 30% 1	570
	21st to end	Night	5% 1 17% 51% 25% 2	570
October	1st to 10th	Night	3 2 17% 52% 25% 1	570
	11th to 20th	Night	7% 3 23% 44% 21% 2	674
	21st to end	Night	6% 4 16% 43% 28% 3	836
November	1st to 10th	Night	6% 3 18% 41% 30% 3	780
	11th to 20th	Night	4 5% 18% 50% 22% 1	972
	21st to end	Night	6% 7% 25% 43% 18% 3	1000
December	1st to 10th	Night	7% 4 19% 48% 21% 1	1000
	11th to 20th	Night	5% 4 26% 46% 18% 1	1000
	21st to end	Night	5% 6% 24% 47% 17% 1	949

Page generated at 2025-04-08 08:17:25. Version ac07

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