Mustang Island State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mustang Island State Park clear sky chart from 2005-11-06 to 2026-10-14.

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	11% 6% 2 6% 4 4 4 4 6% 9% 44%	148821
	Night	13% 6% 2 5% 4 4 4 3 6% 8% 46%	143292
Transparency	Day	35% 8% 18% 22% 12% 5%	152574
	Night	35% 6% 16% 22% 14% 7%	147606
Seeing	Day	11% 3 11% 25% 35% 15%	17090
	Night	14% 4 13% 29% 32% 8%	26939

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	19% 8% 3 7% 3 3 3 3 4 6% 40%	5289
	11th to 20th	Day	17% 8% 2 7% 4 4 3 3 4 5% 42%	5310
	21st to end	Day	23% 8% 3 9% 5% 4 4 3 4 5% 32%	6270
February	1st to 10th	Day	20% 9% 2 6% 3 3 3 4 5% 5% 39%	2100
	11th to 20th	Day	20% 7% 3 6% 3 3 3 2 5% 7% 42%	2049
	21st to end	Day	18% 7% 3 5% 4 3 3 3 5% 5% 44%	1814
March	1st to 10th	Day	17% 9% 3 7% 4 4 4 3 5% 6% 40%	5046
	11th to 20th	Day	17% 7% 3 6% 3 3 3 2 4 5% 48%	5090
	21st to end	Day	16% 7% 2 7% 3 4 4 3 4 6% 45%	5583
April	1st to 10th	Day	13% 7% 2 6% 4 5% 5% 4 6% 7% 42%	2310
	11th to 20th	Day	15% 6% 3 6% 5% 4 3 3 6% 7% 42%	2286
	21st to end	Day	12% 7% 2 6% 5% 4 4 4 6% 7% 44%	2494
May	1st to 10th	Day	18% 8% 3 7% 5% 4 5% 4 6% 9% 30%	7513
	11th to 20th	Day	10% 6% 2 6% 4 4 5% 4 6% 8% 45%	7627
	21st to end	Day	9% 6% 3 8% 5% 6% 7% 5% 8% 10% 34%	8392
June	1st to 10th	Day	4 2 1 4 3 3 4 4 8% 13% 53%	2730
	11th to 20th	Day	4 3 1 3 4 4 5% 4 8% 12% 53%	2730
	21st to end	Day	5% 4 2 4 5% 4 5% 5% 9% 13% 45%	2730
July	1st to 10th	Day	5% 4 2 6% 4 5% 5% 5% 7% 10% 47%	7680
	11th to 20th	Day	4 6% 3 7% 5% 5% 7% 5% 8% 13% 36%	7680
	21st to end	Day	6% 4 2 5% 4 4 5% 4 6% 11% 50%	8337
August	1st to 10th	Day	1 1 2 2 3 3 3 6% 10% 68%	6014
	11th to 20th	Day	2 2 1 3 3 4 5% 5% 9% 15% 52%	5455
	21st to end	Day	3 2 1 3 4 4 6% 5% 8% 13% 52%	5566
September	1st to 10th	Day	8% 5% 2 7% 5% 5% 6% 4 8% 10% 39%	2310
	11th to 20th	Day	9% 5% 2 6% 4 5% 6% 4 7% 9% 44%	2310
	21st to end	Day	8% 4 2 4 4 4 4 4 8% 11% 47%	2310
October	1st to 10th	Day	6% 4 1 5% 5% 4 4 4 5% 8% 55%	2310
	11th to 20th	Day	9% 5% 2 4 3 3 4 3 4 7% 55%	2058
	21st to end	Day	9% 4 2 4 3 4 3 2 5% 7% 57%	2200
November	1st to 10th	Day	11% 5% 2 4 3 4 5% 4 6% 8% 49%	2058
	11th to 20th	Day	15% 6% 3 5% 4 3 4 3 5% 6% 48%	2100
	21st to end	Day	17% 7% 2 5% 4 5% 3 3 4 6% 43%	1972
December	1st to 10th	Day	33% 10% 2 7% 3 3 3 3 4 5% 26%	3030
	11th to 20th	Day	12% 6% 2 7% 5% 5% 4 4 6% 7% 41%	3481
	21st to end	Day	13% 7% 2 5% 3 3 4 3 5% 7% 48%	4587
January	1st to 10th	Night	19% 7% 2 6% 3 4 3 3 4 5% 45%	7634
	11th to 20th	Night	16% 7% 3 6% 3 3 4 3 5% 6% 44%	7680
	21st to end	Night	24% 9% 4 9% 4 4 4 3 5% 5% 29%	7987
February	1st to 10th	Night	17% 7% 3 5% 4 4 3 3 4 6% 43%	2520
	11th to 20th	Night	19% 6% 2 4 3 3 4 4 4 6% 44%	2458
	21st to end	Night	18% 8% 2 5% 4 3 3 3 3 7% 45%	1990
March	1st to 10th	Night	18% 8% 3 6% 3 3 3 4 5% 7% 41%	5029
	11th to 20th	Night	15% 8% 3 6% 4 3 3 2 4 5% 47%	5090
	21st to end	Night	15% 6% 2 4 3 3 3 3 5% 6% 52%	5588
April	1st to 10th	Night	15% 8% 3 6% 4 4 4 3 6% 8% 39%	2310
	11th to 20th	Night	15% 7% 2 5% 4 4 4 2 6% 7% 42%	2283
	21st to end	Night	13% 8% 3 6% 5% 3 4 5% 6% 7% 40%	2125
May	1st to 10th	Night	25% 8% 3 6% 4 4 5% 4 5% 7% 29%	5346
	11th to 20th	Night	12% 6% 2 5% 3 4 4 5% 7% 9% 44%	5265
	21st to end	Night	10% 7% 3 7% 5% 5% 5% 4 8% 11% 33%	5793
June	1st to 10th	Night	4 3 1 4 3 4 5% 4 9% 11% 52%	1890
	11th to 20th	Night	4 3 1 5% 3 4 5% 4 7% 14% 48%	1890
	21st to end	Night	6% 4 2 4 4 4 5% 6% 7% 11% 47%	1890
July	1st to 10th	Night	4 4 2 5% 4 5% 5% 4 7% 10% 49%	5308
	11th to 20th	Night	4 5% 2 6% 5% 5% 7% 5% 9% 13% 39%	5307
	21st to end	Night	5% 5% 2 5% 4 3 4 4 6% 11% 51%	5770
August	1st to 10th	Night	1 1 1 1 2 1 4 10% 79%	4156
	11th to 20th	Night	1 2 1 3 3 4 4 4 7% 14% 57%	4576
	21st to end	Night	2 1 1 2 2 2 4 4 7% 13% 62%	5560
September	1st to 10th	Night	6% 5% 2 5% 4 5% 6% 5% 7% 10% 44%	2310
	11th to 20th	Night	8% 6% 2 5% 5% 4 4 4 5% 10% 46%	2310
	21st to end	Night	7% 3 2 5% 4 4 4 4 6% 10% 51%	2310
October	1st to 10th	Night	5% 3 2 4 3 4 4 3 6% 8% 58%	2310
	11th to 20th	Night	9% 4 1 4 3 3 3 2 5% 7% 60%	2385
	21st to end	Night	9% 4 1 4 3 3 3 3 5% 6% 61%	2640
November	1st to 10th	Night	11% 4 1 4 3 3 3 3 5% 8% 55%	2460
	11th to 20th	Night	15% 5% 2 5% 3 2 3 3 4 5% 52%	2520
	21st to end	Night	16% 7% 2 6% 3 4 4 3 5% 7% 43%	2643
December	1st to 10th	Night	34% 10% 3 6% 3 3 2 2 3 4 30%	4380
	11th to 20th	Night	13% 7% 2 6% 4 4 4 3 5% 6% 45%	4946
	21st to end	Night	11% 6% 2 5% 3 3 4 3 5% 6% 51%	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	44% 7% 13% 20% 10% 6%	5290
	11th to 20th	Day	44% 6% 7% 15% 18% 9%	5310
	21st to end	Day	55% 5% 8% 10% 15% 6%	6270
February	1st to 10th	Day	47% 6% 9% 13% 16% 9%	2100
	11th to 20th	Day	44% 5% 12% 17% 16% 6%	2059
	21st to end	Day	41% 6% 10% 21% 15% 7%	1814
March	1st to 10th	Day	44% 7% 11% 17% 7% 13%	5046
	11th to 20th	Day	40% 6% 7% 13% 19% 15%	5090
	21st to end	Day	39% 6% 12% 22% 15% 7%	5585
April	1st to 10th	Day	39% 7% 16% 18% 12% 8%	2310
	11th to 20th	Day	41% 7% 14% 18% 13% 7%	2286
	21st to end	Day	36% 9% 16% 22% 11% 7%	2494
May	1st to 10th	Day	46% 10% 17% 17% 7% 2	7551
	11th to 20th	Day	34% 8% 16% 24% 14% 4	7631
	21st to end	Day	39% 9% 16% 29% 6%	8405
June	1st to 10th	Day	20% 9% 22% 34% 14%	2730
	11th to 20th	Day	23% 9% 20% 34% 14% 1	2730
	21st to end	Day	26% 11% 27% 28% 7% 1	2730
July	1st to 10th	Day	31% 9% 35% 23% 1	7616
	11th to 20th	Day	37% 11% 34% 15% 3	7611
	21st to end	Day	29% 8% 27% 31% 5%	8155
August	1st to 10th	Day	13% 9% 28% 43% 8%	6000
	11th to 20th	Day	19% 10% 40% 29% 2	5491
	21st to end	Day	22% 10% 29% 32% 6% 1	5565
September	1st to 10th	Day	37% 13% 19% 20% 9% 1	2310
	11th to 20th	Day	34% 11% 20% 23% 11% 2	2310
	21st to end	Day	30% 10% 14% 27% 13% 6%	2310
October	1st to 10th	Day	21% 6% 9% 17% 28% 20%	3700
	11th to 20th	Day	28% 6% 11% 17% 28% 9%	3311
	21st to end	Day	25% 5% 9% 26% 27% 8%	3538
November	1st to 10th	Day	32% 7% 14% 22% 20% 5%	2058
	11th to 20th	Day	38% 6% 11% 18% 18% 9%	2100
	21st to end	Day	43% 7% 11% 19% 14% 7%	1972
December	1st to 10th	Day	62% 4 8% 12% 12% 2	3030
	11th to 20th	Day	38% 8% 10% 20% 13% 10%	3479
	21st to end	Day	35% 6% 8% 24% 18% 8%	4587
January	1st to 10th	Night	41% 6% 10% 19% 16% 9%	7635
	11th to 20th	Night	41% 4 8% 18% 19% 10%	7680
	21st to end	Night	56% 4 9% 11% 12% 7%	7987
February	1st to 10th	Night	42% 5% 11% 13% 16% 13%	2520
	11th to 20th	Night	41% 6% 12% 15% 19% 8%	2458
	21st to end	Night	41% 5% 7% 19% 19% 8%	1990
March	1st to 10th	Night	41% 6% 11% 19% 12% 11%	5029
	11th to 20th	Night	41% 5% 9% 11% 16% 18%	5090
	21st to end	Night	33% 5% 11% 24% 21% 7%	5588
April	1st to 10th	Night	43% 6% 13% 17% 14% 8%	2310
	11th to 20th	Night	41% 6% 12% 17% 15% 10%	2283
	21st to end	Night	40% 9% 14% 18% 13% 7%	2125
May	1st to 10th	Night	53% 7% 15% 16% 7% 3	5373
	11th to 20th	Night	33% 9% 14% 26% 14% 4	5266
	21st to end	Night	40% 8% 20% 26% 6%	5805
June	1st to 10th	Night	22% 7% 21% 34% 15% 1	1890
	11th to 20th	Night	25% 8% 15% 33% 17% 1	1890
	21st to end	Night	28% 9% 26% 29% 8% 1	1890
July	1st to 10th	Night	30% 7% 32% 29% 2	5265
	11th to 20th	Night	34% 10% 37% 17% 3	5256
	21st to end	Night	26% 7% 27% 33% 7%	5641
August	1st to 10th	Night	5% 4 32% 48% 10%	4146
	11th to 20th	Night	17% 9% 39% 32% 2	4606
	21st to end	Night	14% 8% 33% 36% 8%	5560
September	1st to 10th	Night	31% 12% 24% 20% 10% 3	2310
	11th to 20th	Night	35% 8% 18% 24% 13% 1	2310
	21st to end	Night	28% 8% 15% 28% 16% 5%	2310
October	1st to 10th	Night	19% 6% 9% 17% 24% 25%	3700
	11th to 20th	Night	21% 5% 12% 21% 29% 13%	3858
	21st to end	Night	21% 4 7% 26% 32% 10%	4252
November	1st to 10th	Night	29% 7% 12% 22% 22% 8%	2460
	11th to 20th	Night	36% 5% 11% 20% 18% 9%	2520
	21st to end	Night	41% 6% 11% 21% 14% 8%	2643
December	1st to 10th	Night	61% 3 7% 13% 12% 4	4380
	11th to 20th	Night	38% 7% 9% 21% 14% 11%	4947
	21st to end	Night	33% 6% 8% 22% 18% 13%	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	21% 6% 25% 28% 19% 1	330
	11th to 20th	Day	20% 5% 22% 33% 17% 2	330
	21st to end	Day	21% 9% 23% 34% 13% 1	363
February	1st to 10th	Day	23% 4 19% 34% 18% 2	330
	11th to 20th	Day	26% 7% 17% 28% 20% 2	330
	21st to end	Day	20% 4 22% 42% 11% 1	273
March	1st to 10th	Day	19% 6% 22% 38% 15%	330
	11th to 20th	Day	19% 6% 19% 40% 15% 1	330
	21st to end	Day	13% 6% 21% 42% 17% 1	363
April	1st to 10th	Day	14% 6% 26% 36% 17%	330
	11th to 20th	Day	16% 5% 23% 36% 18% 2	324
	21st to end	Day	13% 6% 23% 38% 19% 1	514
May	1st to 10th	Day	12% 5% 20% 46% 16% 1	714
	11th to 20th	Day	11% 3 13% 46% 24% 2	775
	21st to end	Day	6% 3 11% 37% 40% 3	844
June	1st to 10th	Day	5% 1 5% 24% 54% 11%	780
	11th to 20th	Day	5% 2 4 25% 53% 11%	780
	21st to end	Day	7% 1 4 18% 49% 22%	780
July	1st to 10th	Day	5% 1 3 16% 47% 28%	771
	11th to 20th	Day	5% 1 1 7% 52% 34%	768
	21st to end	Day	6% 1 2 7% 53% 31%	849
August	1st to 10th	Day	1 1 6% 50% 42%	776
	11th to 20th	Day	3 1 1 7% 44% 45%	555
	21st to end	Day	6% 1 2 6% 31% 54%	396
September	1st to 10th	Day	9% 2 3 10% 41% 35%	360
	11th to 20th	Day	8% 2 8% 40% 42%	360
	21st to end	Day	6% 1 3 12% 47% 31%	360
October	1st to 10th	Day	8% 1 3 17% 52% 19%	360
	11th to 20th	Day	10% 2 5% 19% 47% 18%	339
	21st to end	Day	12% 3 15% 26% 36% 8%	363
November	1st to 10th	Day	13% 4 10% 23% 43% 8%	330
	11th to 20th	Day	21% 3 9% 26% 32% 8%	330
	21st to end	Day	24% 5% 19% 28% 19% 4	330
December	1st to 10th	Day	28% 2 14% 29% 22% 5%	330
	11th to 20th	Day	19% 7% 17% 31% 25% 1	330
	21st to end	Day	18% 4 19% 36% 19% 4	363
January	1st to 10th	Night	23% 6% 20% 34% 16% 2	1050
	11th to 20th	Night	19% 6% 22% 36% 15% 1	1050
	21st to end	Night	23% 5% 24% 33% 15% 1	1009
February	1st to 10th	Night	22% 6% 20% 37% 15%	840
	11th to 20th	Night	22% 7% 20% 36% 14% 1	824
	21st to end	Night	22% 6% 18% 40% 13%	606
March	1st to 10th	Night	18% 5% 21% 37% 18% 1	630
	11th to 20th	Night	15% 7% 22% 39% 16% 1	630
	21st to end	Night	13% 5% 18% 46% 16% 1	693
April	1st to 10th	Night	18% 4 21% 41% 16%	630
	11th to 20th	Night	17% 5% 20% 40% 17%	623
	21st to end	Night	15% 5% 21% 41% 18% 1	630
May	1st to 10th	Night	15% 4 18% 44% 18%	630
	11th to 20th	Night	11% 2 15% 48% 22% 2	621
	21st to end	Night	7% 2 10% 41% 39% 1	683
June	1st to 10th	Night	4 1 3 30% 56% 6%	630
	11th to 20th	Night	4 1 3 32% 55% 4	630
	21st to end	Night	6% 1 5% 21% 50% 16%	630
July	1st to 10th	Night	5% 1 4 19% 53% 18%	615
	11th to 20th	Night	3 1 2 10% 59% 25%	612
	21st to end	Night	4 1 2 11% 61% 22%	690
August	1st to 10th	Night	1 7% 60% 31%	627
	11th to 20th	Night	2 1 1 7% 61% 28%	624
	21st to end	Night	4 1 10% 48% 37%	693
September	1st to 10th	Night	7% 1 2 11% 55% 25%	630
	11th to 20th	Night	9% 1 4 13% 51% 23%	630
	21st to end	Night	8% 1 3 16% 55% 16%	630
October	1st to 10th	Night	5% 1 6% 18% 56% 15%	630
	11th to 20th	Night	9% 2 7% 28% 47% 8%	761
	21st to end	Night	11% 3 12% 34% 35% 6%	880
November	1st to 10th	Night	10% 3 11% 26% 44% 6%	820
	11th to 20th	Night	18% 2 13% 28% 35% 4	840
	21st to end	Night	18% 4 18% 33% 24% 3	963
December	1st to 10th	Night	23% 5% 17% 28% 22% 5%	1050
	11th to 20th	Night	20% 6% 19% 32% 21% 2	1050
	21st to end	Night	19% 6% 21% 32% 19% 3	1155

Page generated at 2026-10-11 04:06:33. Version ac07

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