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 2025-06-10.

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	12% 6% 2 6% 4 4 4 4 6% 8% 44%	119794
	Night	14% 6% 2 5% 4 3 4 3 6% 8% 45%	118670
Transparency	Day	36% 8% 16% 22% 13% 6%	123589
	Night	36% 7% 15% 21% 15% 8%	123005
Seeing	Day	11% 3 11% 25% 34% 15%	15265
	Night	14% 4 14% 30% 32% 8%	25270

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	23% 9% 3 7% 3 3 3 3 5% 6% 34%	4077
	11th to 20th	Day	20% 8% 2 6% 4 4 3 3 5% 7% 40%	4080
	21st to end	Day	24% 8% 3 7% 5% 4 5% 3 4 4 33%	4838
February	1st to 10th	Day	21% 9% 2 6% 4 3 3 4 5% 5% 37%	2000
	11th to 20th	Day	21% 7% 3 6% 3 3 3 2 5% 7% 41%	1949
	21st to end	Day	18% 7% 3 5% 4 3 3 3 5% 5% 43%	1730
March	1st to 10th	Day	17% 9% 2 7% 4 4 4 3 5% 6% 41%	4936
	11th to 20th	Day	18% 7% 3 6% 4 3 3 2 4 5% 47%	4980
	21st to end	Day	16% 7% 2 7% 3 4 4 3 4 6% 44%	5462
April	1st to 10th	Day	13% 7% 2 5% 4 5% 4 3 6% 7% 43%	2200
	11th to 20th	Day	15% 6% 3 6% 5% 4 3 3 5% 7% 43%	2176
	21st to end	Day	12% 7% 2 6% 5% 4 4 4 6% 7% 45%	2375
May	1st to 10th	Day	17% 8% 3 7% 5% 4 5% 4 6% 9% 30%	5786
	11th to 20th	Day	9% 5% 2 6% 4 4 4 4 6% 8% 49%	5862
	21st to end	Day	8% 5% 2 7% 5% 6% 6% 5% 8% 11% 38%	6434
June	1st to 10th	Day	4 2 1 3 3 3 4 4 8% 13% 55%	2588
	11th to 20th	Day	3 3 1 3 4 4 4 4 8% 12% 54%	2470
	21st to end	Day	5% 4 1 4 5% 4 5% 5% 9% 14% 44%	2470
July	1st to 10th	Day	6% 4 2 6% 4 4 4 5% 7% 11% 47%	4120
	11th to 20th	Day	5% 5% 3 8% 6% 6% 7% 6% 8% 12% 34%	4120
	21st to end	Day	9% 6% 2 6% 4 5% 5% 4 7% 11% 42%	4465
August	1st to 10th	Day	1 1 2 2 2 2 3 5% 8% 74%	4104
	11th to 20th	Day	2 2 1 3 3 3 5% 5% 9% 15% 52%	3713
	21st to end	Day	4 2 1 4 4 5% 7% 5% 8% 14% 44%	3828
September	1st to 10th	Day	9% 6% 2 7% 5% 5% 6% 4 8% 10% 37%	2090
	11th to 20th	Day	10% 6% 2 6% 5% 5% 6% 4 6% 8% 42%	2090
	21st to end	Day	9% 4 2 5% 4 4 4 4 7% 10% 47%	2090
October	1st to 10th	Day	5% 4 1 5% 5% 4 4 4 5% 9% 54%	2090
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 4 7% 53%	1926
	21st to end	Day	10% 4 2 4 4 4 3 2 5% 7% 56%	2090
November	1st to 10th	Day	11% 5% 2 4 3 4 5% 4 6% 8% 47%	1958
	11th to 20th	Day	15% 6% 3 5% 4 3 4 3 5% 6% 47%	2000
	21st to end	Day	17% 7% 2 5% 4 4 3 3 4 6% 44%	1878
December	1st to 10th	Day	33% 10% 3 8% 3 3 3 3 4 5% 26%	2940
	11th to 20th	Day	11% 6% 2 7% 5% 5% 5% 4 6% 7% 41%	3391
	21st to end	Day	13% 7% 2 5% 3 3 4 3 5% 7% 48%	4488
January	1st to 10th	Night	24% 8% 2 6% 3 3 3 3 4 5% 38%	5888
	11th to 20th	Night	18% 7% 2 5% 3 3 4 4 6% 7% 42%	5900
	21st to end	Night	26% 8% 3 7% 4 3 3 3 6% 6% 30%	6169
February	1st to 10th	Night	18% 7% 3 5% 4 4 4 3 4 6% 42%	2400
	11th to 20th	Night	20% 6% 2 4 3 3 4 4 5% 6% 43%	2338
	21st to end	Night	19% 9% 2 5% 4 4 3 4 3 7% 42%	1898
March	1st to 10th	Night	18% 8% 2 6% 3 3 3 4 5% 7% 42%	4919
	11th to 20th	Night	15% 8% 3 6% 4 3 3 2 4 5% 46%	4980
	21st to end	Night	16% 6% 2 4 3 3 3 3 5% 6% 52%	5467
April	1st to 10th	Night	14% 8% 2 6% 4 4 4 3 6% 8% 40%	2200
	11th to 20th	Night	15% 7% 2 5% 4 4 4 2 5% 8% 43%	2173
	21st to end	Night	13% 8% 3 6% 5% 3 4 5% 6% 7% 40%	2024
May	1st to 10th	Night	23% 8% 2 6% 4 4 5% 4 5% 7% 30%	4107
	11th to 20th	Night	12% 5% 2 5% 3 3 3 4 6% 9% 48%	4053
	21st to end	Night	10% 7% 3 7% 5% 5% 5% 4 7% 11% 35%	4443
June	1st to 10th	Night	4 2 1 3 3 3 5% 4 9% 10% 54%	1796
	11th to 20th	Night	4 3 1 5% 3 4 5% 4 8% 14% 49%	1710
	21st to end	Night	6% 4 1 5% 4 4 5% 6% 7% 12% 46%	1710
July	1st to 10th	Night	5% 4 2 4 4 4 4 4 7% 10% 53%	2850
	11th to 20th	Night	3 4 2 6% 5% 6% 7% 5% 9% 13% 40%	2850
	21st to end	Night	6% 6% 2 5% 4 4 5% 4 7% 12% 45%	3098
August	1st to 10th	Night	1 1 1 2 2 2 4 9% 78%	2836
	11th to 20th	Night	2 2 1 3 3 3 4 4 8% 14% 55%	3120
	21st to end	Night	2 2 1 3 3 3 4 4 7% 13% 58%	3828
September	1st to 10th	Night	7% 5% 2 5% 4 5% 6% 5% 7% 10% 43%	2090
	11th to 20th	Night	9% 7% 2 5% 5% 4 4 4 5% 9% 43%	2090
	21st to end	Night	8% 3 2 5% 4 4 4 4 6% 9% 51%	2090
October	1st to 10th	Night	4 3 2 4 3 4 4 4 6% 8% 57%	2090
	11th to 20th	Night	9% 4 1 4 3 3 3 2 5% 7% 58%	2232
	21st to end	Night	10% 4 1 4 3 3 3 3 5% 6% 60%	2508
November	1st to 10th	Night	11% 4 1 4 4 3 3 4 5% 8% 53%	2340
	11th to 20th	Night	16% 5% 2 5% 4 3 3 2 4 5% 51%	2400
	21st to end	Night	17% 7% 2 6% 3 4 4 3 5% 6% 44%	2517
December	1st to 10th	Night	34% 11% 3 6% 3 3 2 2 3 4 30%	4250
	11th to 20th	Night	13% 7% 2 6% 4 4 4 3 5% 6% 45%	4816
	21st to end	Night	11% 6% 2 5% 3 3 4 3 5% 6% 51%	6490

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	49% 8% 10% 16% 10% 7%	4078
	11th to 20th	Day	45% 8% 9% 16% 15% 7%	4080
	21st to end	Day	54% 5% 7% 11% 15% 8%	4838
February	1st to 10th	Day	48% 7% 8% 13% 16% 9%	2000
	11th to 20th	Day	44% 5% 11% 17% 16% 7%	1959
	21st to end	Day	43% 6% 10% 20% 14% 7%	1730
March	1st to 10th	Day	44% 7% 11% 17% 7% 14%	4936
	11th to 20th	Day	40% 6% 8% 13% 19% 15%	4980
	21st to end	Day	39% 6% 12% 22% 14% 7%	5464
April	1st to 10th	Day	38% 7% 16% 18% 13% 8%	2200
	11th to 20th	Day	40% 7% 13% 18% 14% 8%	2176
	21st to end	Day	35% 9% 15% 23% 12% 7%	2375
May	1st to 10th	Day	45% 11% 16% 16% 9% 3	5824
	11th to 20th	Day	30% 9% 16% 24% 17% 5%	5866
	21st to end	Day	34% 10% 17% 32% 7%	6447
June	1st to 10th	Day	19% 9% 21% 36% 15%	2588
	11th to 20th	Day	20% 9% 19% 35% 15% 1	2470
	21st to end	Day	26% 12% 27% 27% 7% 1	2470
July	1st to 10th	Day	30% 9% 31% 27% 3	4056
	11th to 20th	Day	39% 13% 27% 17% 4	4051
	21st to end	Day	36% 10% 30% 22% 2	4325
August	1st to 10th	Day	10% 7% 26% 46% 11%	4090
	11th to 20th	Day	19% 10% 39% 29% 3	3749
	21st to end	Day	27% 13% 26% 27% 6% 1	3827
September	1st to 10th	Day	39% 13% 17% 20% 9% 2	2090
	11th to 20th	Day	37% 11% 16% 22% 12% 2	2090
	21st to end	Day	31% 11% 14% 25% 14% 6%	2090
October	1st to 10th	Day	21% 6% 9% 16% 27% 21%	3480
	11th to 20th	Day	29% 7% 12% 16% 28% 9%	3179
	21st to end	Day	25% 5% 9% 26% 27% 8%	3428
November	1st to 10th	Day	33% 8% 15% 23% 18% 4	1958
	11th to 20th	Day	39% 6% 11% 17% 18% 9%	2000
	21st to end	Day	42% 7% 11% 19% 14% 7%	1878
December	1st to 10th	Day	62% 4 8% 12% 11% 2	2940
	11th to 20th	Day	38% 8% 10% 20% 13% 10%	3389
	21st to end	Day	36% 6% 8% 23% 18% 8%	4488
January	1st to 10th	Night	47% 6% 8% 14% 14% 10%	5888
	11th to 20th	Night	41% 5% 10% 18% 18% 8%	5900
	21st to end	Night	55% 4 9% 11% 13% 8%	6169
February	1st to 10th	Night	43% 5% 10% 13% 16% 13%	2400
	11th to 20th	Night	42% 6% 12% 14% 19% 8%	2338
	21st to end	Night	43% 5% 7% 18% 18% 8%	1898
March	1st to 10th	Night	41% 6% 11% 19% 13% 11%	4919
	11th to 20th	Night	41% 6% 9% 10% 16% 18%	4980
	21st to end	Night	34% 5% 11% 23% 21% 7%	5467
April	1st to 10th	Night	42% 6% 13% 17% 14% 8%	2200
	11th to 20th	Night	40% 6% 11% 17% 16% 10%	2173
	21st to end	Night	40% 8% 13% 18% 13% 7%	2024
May	1st to 10th	Night	51% 7% 14% 16% 9% 4	4134
	11th to 20th	Night	31% 7% 15% 26% 16% 5%	4054
	21st to end	Night	38% 8% 20% 27% 7%	4452
June	1st to 10th	Night	20% 7% 20% 36% 16% 1	1796
	11th to 20th	Night	25% 8% 14% 33% 18% 1	1710
	21st to end	Night	28% 9% 25% 30% 7% 1	1710
July	1st to 10th	Night	27% 7% 29% 33% 4	2805
	11th to 20th	Night	31% 12% 33% 18% 5%	2796
	21st to end	Night	31% 9% 34% 23% 3	2999
August	1st to 10th	Night	6% 5% 25% 51% 12%	2826
	11th to 20th	Night	18% 10% 39% 31% 2	3150
	21st to end	Night	17% 11% 33% 30% 9% 1	3828
September	1st to 10th	Night	32% 13% 23% 19% 10% 3	2090
	11th to 20th	Night	37% 9% 16% 24% 12% 2	2090
	21st to end	Night	30% 8% 14% 25% 17% 6%	2090
October	1st to 10th	Night	19% 6% 9% 17% 23% 27%	3480
	11th to 20th	Night	22% 5% 13% 19% 28% 14%	3705
	21st to end	Night	21% 4 7% 26% 32% 10%	4120
November	1st to 10th	Night	30% 8% 13% 23% 20% 7%	2340
	11th to 20th	Night	38% 5% 11% 19% 19% 9%	2400
	21st to end	Night	41% 6% 10% 21% 14% 8%	2517
December	1st to 10th	Night	61% 4 7% 13% 12% 4	4250
	11th to 20th	Night	37% 7% 9% 22% 13% 12%	4817
	21st to end	Night	33% 7% 9% 22% 17% 13%	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	23% 6% 25% 28% 17% 1	300
	11th to 20th	Day	21% 6% 22% 33% 16% 2	300
	21st to end	Day	21% 8% 23% 35% 12% 1	330
February	1st to 10th	Day	25% 4 20% 34% 15% 2	300
	11th to 20th	Day	27% 7% 18% 29% 18% 1	300
	21st to end	Day	22% 4 22% 42% 8% 1	249
March	1st to 10th	Day	18% 6% 23% 39% 14%	300
	11th to 20th	Day	21% 6% 20% 41% 12%	300
	21st to end	Day	14% 6% 23% 44% 13%	330
April	1st to 10th	Day	14% 6% 27% 36% 16%	300
	11th to 20th	Day	16% 5% 23% 36% 18% 3	294
	21st to end	Day	13% 6% 23% 38% 19% 1	475
May	1st to 10th	Day	11% 5% 21% 46% 16% 1	666
	11th to 20th	Day	10% 3 13% 46% 25% 2	725
	21st to end	Day	5% 3 12% 38% 40% 3	789
June	1st to 10th	Day	5% 1 5% 24% 55% 10%	726
	11th to 20th	Day	5% 1 4 25% 54% 12%	680
	21st to end	Day	7% 1 3 18% 49% 21%	680
July	1st to 10th	Day	5% 1 3 16% 45% 30%	671
	11th to 20th	Day	4 1 6% 51% 36%	668
	21st to end	Day	5% 2 6% 55% 32%	739
August	1st to 10th	Day	1 1 6% 53% 39%	676
	11th to 20th	Day	3 1 1 6% 44% 45%	477
	21st to end	Day	7% 1 2 7% 31% 52%	330
September	1st to 10th	Day	11% 2 3 11% 40% 33%	300
	11th to 20th	Day	10% 2 9% 38% 40%	300
	21st to end	Day	7% 1 3 11% 45% 32%	300
October	1st to 10th	Day	8% 1 3 16% 54% 18%	300
	11th to 20th	Day	11% 2 5% 20% 46% 16%	300
	21st to end	Day	13% 3 15% 26% 34% 8%	330
November	1st to 10th	Day	14% 4 9% 23% 44% 6%	300
	11th to 20th	Day	23% 4 9% 26% 31% 7%	300
	21st to end	Day	25% 5% 18% 30% 18% 5%	300
December	1st to 10th	Day	27% 2 14% 29% 22% 6%	300
	11th to 20th	Day	18% 8% 17% 31% 25% 1	300
	21st to end	Day	18% 4 20% 37% 18% 3	330
January	1st to 10th	Night	24% 6% 20% 34% 15% 2	1000
	11th to 20th	Night	20% 6% 23% 36% 15% 1	1000
	21st to end	Night	23% 5% 24% 33% 15% 1	961
February	1st to 10th	Night	22% 6% 20% 36% 15% 1	800
	11th to 20th	Night	23% 8% 20% 35% 14% 1	784
	21st to end	Night	23% 7% 19% 40% 12%	578
March	1st to 10th	Night	17% 5% 22% 38% 17% 1	600
	11th to 20th	Night	16% 7% 22% 40% 15% 1	600
	21st to end	Night	14% 5% 19% 46% 15% 1	660
April	1st to 10th	Night	17% 4 21% 41% 16%	600
	11th to 20th	Night	17% 5% 21% 39% 18%	593
	21st to end	Night	15% 5% 21% 41% 18% 1	600
May	1st to 10th	Night	15% 5% 18% 44% 18%	600
	11th to 20th	Night	11% 2 15% 48% 22% 2	591
	21st to end	Night	7% 2 10% 40% 39% 2	650
June	1st to 10th	Night	4 1 3 30% 57% 6%	599
	11th to 20th	Night	4 1 3 33% 56% 3	570
	21st to end	Night	6% 1 5% 21% 51% 16%	570
July	1st to 10th	Night	5% 1 4 20% 51% 19%	555
	11th to 20th	Night	3 1 2 9% 59% 27%	552
	21st to end	Night	4 1 1 11% 61% 22%	624
August	1st to 10th	Night	1 7% 61% 30%	567
	11th to 20th	Night	2 1 1 7% 60% 29%	564
	21st to end	Night	5% 1 10% 49% 35%	627
September	1st to 10th	Night	7% 1 1 12% 54% 24%	570
	11th to 20th	Night	10% 1 4 14% 49% 22%	570
	21st to end	Night	9% 1 4 15% 54% 16%	570
October	1st to 10th	Night	5% 1 6% 18% 55% 15%	570
	11th to 20th	Night	10% 2 7% 28% 46% 7%	712
	21st to end	Night	11% 3 11% 34% 34% 6%	836
November	1st to 10th	Night	10% 2 11% 27% 43% 6%	780
	11th to 20th	Night	19% 3 14% 28% 34% 4	800
	21st to end	Night	18% 4 18% 32% 24% 3	917
December	1st to 10th	Night	22% 5% 18% 28% 23% 5%	1000
	11th to 20th	Night	20% 6% 19% 33% 20% 2	1000
	21st to end	Night	20% 6% 21% 33% 18% 2	1100

Page generated at 2025-06-07 09:28:18. Version ac07

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