Bentsen-Rio Grande Valley State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bentsen-Rio Grande Valley State Park clear sky chart from 2005-11-06 to 2025-09-19.

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
Transparency	Day	33% 7% 14% 24% 15% 8%	130003
	Night	34% 7% 15% 22% 14% 8%	127404
Seeing	Day	10% 4 20% 34% 24% 9%	15435
	Night	13% 4 25% 39% 18% 1	25396

By Month

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	42% 6% 9% 17% 17% 10%	4078
	11th to 20th	Day	41% 4 8% 22% 17% 8%	4374
	21st to end	Day	48% 6% 8% 15% 16% 7%	4994
February	1st to 10th	Day	39% 4 8% 16% 19% 14%	2000
	11th to 20th	Day	38% 5% 10% 20% 18% 10%	1959
	21st to end	Day	36% 4 10% 20% 19% 11%	1652
March	1st to 10th	Day	34% 7% 11% 21% 10% 18%	4936
	11th to 20th	Day	37% 5% 6% 10% 23% 19%	4980
	21st to end	Day	29% 5% 9% 27% 17% 14%	5464
April	1st to 10th	Day	33% 6% 11% 21% 18% 12%	2200
	11th to 20th	Day	36% 7% 12% 20% 16% 9%	2176
	21st to end	Day	33% 7% 12% 20% 18% 10%	2288
May	1st to 10th	Day	37% 8% 15% 24% 11% 5%	5900
	11th to 20th	Day	23% 8% 14% 26% 19% 10%	5866
	21st to end	Day	28% 7% 11% 37% 15% 1	6447
June	1st to 10th	Day	22% 8% 13% 32% 21% 4	2600
	11th to 20th	Day	24% 6% 15% 24% 26% 5%	2600
	21st to end	Day	31% 10% 19% 27% 11% 2	2600
July	1st to 10th	Day	40% 8% 22% 25% 5%	5836
	11th to 20th	Day	29% 8% 28% 26% 9%	5831
	21st to end	Day	30% 7% 20% 34% 8%	6070
August	1st to 10th	Day	11% 5% 19% 47% 18% 1	3892
	11th to 20th	Day	21% 8% 33% 30% 6%	3882
	21st to end	Day	25% 9% 23% 31% 11% 1	4029
September	1st to 10th	Day	42% 10% 14% 19% 12% 2	2200
	11th to 20th	Day	42% 11% 17% 18% 9% 3	2178
	21st to end	Day	35% 9% 14% 22% 13% 7%	2090
October	1st to 10th	Day	24% 6% 7% 13% 27% 23%	3480
	11th to 20th	Day	25% 7% 9% 18% 22% 19%	3373
	21st to end	Day	22% 5% 7% 22% 31% 13%	3428
November	1st to 10th	Day	31% 7% 12% 22% 21% 7%	1958
	11th to 20th	Day	39% 5% 9% 18% 19% 10%	2000
	21st to end	Day	34% 6% 11% 19% 18% 11%	1825
December	1st to 10th	Day	58% 4 7% 16% 11% 5%	2940
	11th to 20th	Day	38% 7% 12% 19% 11% 12%	3389
	21st to end	Day	34% 5% 6% 23% 20% 12%	4488
January	1st to 10th	Night	42% 4 9% 15% 18% 11%	5888
	11th to 20th	Night	41% 4 11% 18% 17% 10%	5647
	21st to end	Night	54% 5% 9% 14% 12% 6%	5984
February	1st to 10th	Night	39% 5% 10% 17% 14% 15%	2400
	11th to 20th	Night	40% 7% 10% 18% 16% 8%	2338
	21st to end	Night	35% 6% 11% 18% 20% 10%	1975
March	1st to 10th	Night	38% 6% 11% 20% 12% 13%	4919
	11th to 20th	Night	38% 7% 8% 12% 16% 19%	4980
	21st to end	Night	33% 4 10% 22% 22% 9%	5467
April	1st to 10th	Night	35% 8% 16% 20% 13% 8%	2200
	11th to 20th	Night	38% 8% 13% 18% 14% 9%	2173
	21st to end	Night	42% 8% 12% 17% 13% 8%	2100
May	1st to 10th	Night	45% 10% 15% 18% 8% 4	4080
	11th to 20th	Night	30% 8% 14% 25% 15% 7%	4054
	21st to end	Night	36% 8% 17% 31% 7%	4452
June	1st to 10th	Night	19% 7% 19% 33% 20% 2	1800
	11th to 20th	Night	21% 8% 12% 34% 23% 3	1800
	21st to end	Night	25% 10% 25% 28% 11% 1	1800
July	1st to 10th	Night	39% 9% 26% 23% 3	4035
	11th to 20th	Night	31% 8% 31% 25% 5%	4026
	21st to end	Night	27% 7% 27% 30% 8%	4484
August	1st to 10th	Night	7% 5% 25% 53% 10%	3244
	11th to 20th	Night	20% 8% 39% 29% 3	3243
	21st to end	Night	16% 9% 31% 33% 10% 1	3867
September	1st to 10th	Night	30% 12% 22% 25% 10% 2	2200
	11th to 20th	Night	33% 10% 20% 25% 10% 2	2178
	21st to end	Night	27% 9% 17% 28% 14% 6%	2090
October	1st to 10th	Night	17% 5% 9% 18% 26% 25%	3480
	11th to 20th	Night	24% 6% 10% 19% 25% 17%	3513
	21st to end	Night	25% 5% 7% 22% 30% 11%	4120
November	1st to 10th	Night	29% 5% 13% 22% 24% 8%	2340
	11th to 20th	Night	37% 6% 10% 19% 18% 10%	2400
	21st to end	Night	37% 4 12% 21% 17% 10%	2570
December	1st to 10th	Night	59% 4 7% 12% 13% 5%	4250
	11th to 20th	Night	38% 5% 11% 22% 11% 12%	4817
	21st to end	Night	34% 6% 8% 18% 18% 15%	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	20% 9% 26% 28% 14% 3	300
	11th to 20th	Day	19% 6% 30% 33% 9% 3	300
	21st to end	Day	21% 7% 36% 23% 12% 1	330
February	1st to 10th	Day	16% 8% 29% 28% 18% 1	300
	11th to 20th	Day	20% 7% 36% 27% 8% 1	300
	21st to end	Day	16% 5% 34% 36% 8% 1	249
March	1st to 10th	Day	13% 9% 33% 32% 12%	300
	11th to 20th	Day	17% 5% 38% 31% 9%	300
	21st to end	Day	10% 9% 37% 38% 5% 1	330
April	1st to 10th	Day	13% 6% 37% 31% 11% 1	300
	11th to 20th	Day	8% 9% 33% 35% 14% 2	294
	21st to end	Day	9% 7% 39% 35% 9% 1	388
May	1st to 10th	Day	10% 7% 41% 30% 12% 1	703
	11th to 20th	Day	9% 5% 36% 37% 12% 2	725
	21st to end	Day	5% 4 31% 42% 17% 2	789
June	1st to 10th	Day	2 2 15% 42% 32% 7%	730
	11th to 20th	Day	3 2 13% 50% 26% 6%	730
	21st to end	Day	8% 1 10% 42% 28% 11%	730
July	1st to 10th	Day	7% 2 10% 39% 34% 8%	721
	11th to 20th	Day	4 1 6% 40% 40% 9%	718
	21st to end	Day	5% 1 5% 43% 37% 10%	722
August	1st to 10th	Day	1 5% 46% 33% 15%	527
	11th to 20th	Day	2 1 4 41% 35% 16%	517
	21st to end	Day	3 1 3 24% 38% 31%	418
September	1st to 10th	Day	11% 3 4 19% 41% 22%	330
	11th to 20th	Day	5% 1 4 18% 37% 36%	324
	21st to end	Day	4 1 7% 17% 41% 29%	300
October	1st to 10th	Day	6% 3 6% 20% 37% 27%	300
	11th to 20th	Day	11% 2 8% 23% 38% 18%	300
	21st to end	Day	13% 3 15% 33% 25% 10%	330
November	1st to 10th	Day	13% 3 12% 33% 33% 7%	300
	11th to 20th	Day	22% 5% 13% 21% 28% 11%	300
	21st to end	Day	23% 7% 24% 21% 15% 11%	300
December	1st to 10th	Day	23% 4 19% 24% 22% 8%	300
	11th to 20th	Day	18% 7% 22% 28% 18% 7%	300
	21st to end	Day	18% 5% 20% 35% 16% 5%	330
January	1st to 10th	Night	22% 6% 26% 34% 12%	1000
	11th to 20th	Night	20% 6% 28% 38% 8%	890
	21st to end	Night	22% 5% 27% 37% 8%	880
February	1st to 10th	Night	20% 5% 35% 32% 7%	800
	11th to 20th	Night	20% 7% 37% 31% 4	784
	21st to end	Night	18% 5% 45% 25% 7%	655
March	1st to 10th	Night	17% 9% 38% 32% 4	600
	11th to 20th	Night	12% 9% 46% 28% 4	600
	21st to end	Night	12% 8% 49% 28% 3	660
April	1st to 10th	Night	12% 8% 47% 30% 3	600
	11th to 20th	Night	13% 7% 45% 31% 4	593
	21st to end	Night	15% 9% 43% 30% 3	600
May	1st to 10th	Night	11% 9% 51% 27% 4	600
	11th to 20th	Night	10% 6% 41% 39% 4	591
	21st to end	Night	5% 5% 35% 44% 10%	650
June	1st to 10th	Night	3 2 16% 57% 21% 1	600
	11th to 20th	Night	4 2 19% 59% 15% 1	600
	21st to end	Night	5% 3 14% 49% 29% 1	600
July	1st to 10th	Night	8% 2 12% 51% 25% 1	585
	11th to 20th	Night	4 1 8% 56% 30% 1	582
	21st to end	Night	5% 1 6% 58% 29% 2	657
August	1st to 10th	Night	1 6% 57% 35% 1	597
	11th to 20th	Night	2 1 6% 53% 35% 3	594
	21st to end	Night	5% 6% 36% 47% 6%	660
September	1st to 10th	Night	9% 1 4 35% 45% 7%	600
	11th to 20th	Night	11% 1 5% 30% 47% 6%	594
	21st to end	Night	8% 1 6% 35% 43% 6%	570
October	1st to 10th	Night	4 2 7% 39% 43% 5%	570
	11th to 20th	Night	11% 2 13% 43% 30% 2	598
	21st to end	Night	9% 3 21% 43% 23% 1	836
November	1st to 10th	Night	10% 4 18% 43% 22% 2	780
	11th to 20th	Night	17% 3 20% 38% 21% 1	800
	21st to end	Night	19% 4 22% 38% 15% 1	970
December	1st to 10th	Night	20% 4 23% 36% 15% 1	1000
	11th to 20th	Night	21% 6% 25% 33% 14%	1000
	21st to end	Night	17% 6% 25% 39% 13%	1100

Page generated at 2025-09-16 00:49:16. Version ac07

Copyright © 2025 Attilla Danko.