Corpus Christi
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Corpus Christi clear sky chart from 2005-11-06 to 2025-11-03.

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%	126688
	Night	14% 6% 2 5% 4 3 4 3 5% 8% 46%	123650
Transparency	Day	24% 40% 10% 14% 8% 4	130454
	Night	24% 39% 9% 14% 9% 5%	127947
Seeing	Day	11% 4 12% 30% 33% 10%	15852
	Night	14% 4 15% 32% 30% 5%	25745

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	22% 9% 3 6% 3 3 3 3 4 6% 37%	4077
	11th to 20th	Day	17% 6% 2 5% 3 3 3 4 5% 7% 45%	4080
	21st to end	Day	26% 8% 3 6% 3 3 4 4 5% 6% 32%	4879
February	1st to 10th	Day	20% 7% 3 6% 3 4 4 4 6% 5% 39%	2000
	11th to 20th	Day	19% 8% 3 6% 4 4 3 2 4 6% 41%	1949
	21st to end	Day	18% 7% 2 6% 4 4 3 3 5% 5% 43%	1710
March	1st to 10th	Day	16% 8% 2 5% 4 3 4 3 6% 7% 42%	4936
	11th to 20th	Day	18% 6% 3 6% 3 3 3 2 3 5% 46%	4980
	21st to end	Day	15% 7% 2 6% 4 4 4 3 5% 6% 43%	5462
April	1st to 10th	Day	12% 7% 2 6% 4 4 5% 3 6% 7% 43%	2200
	11th to 20th	Day	15% 7% 2 7% 4 4 3 3 5% 7% 41%	2176
	21st to end	Day	12% 7% 2 6% 5% 4 4 3 7% 8% 41%	2360
May	1st to 10th	Day	17% 7% 3 8% 6% 5% 6% 5% 7% 9% 27%	5862
	11th to 20th	Day	7% 4 2 5% 4 4 5% 4 7% 10% 48%	5862
	21st to end	Day	7% 4 2 5% 4 5% 6% 5% 9% 11% 41%	6434
June	1st to 10th	Day	4 2 1 4 3 4 4 4 8% 12% 55%	2600
	11th to 20th	Day	4 3 2 5% 5% 4 5% 4 7% 13% 48%	2600
	21st to end	Day	6% 4 2 4 4 5% 6% 5% 9% 13% 42%	2600
July	1st to 10th	Day	6% 6% 3 8% 5% 6% 6% 4 7% 10% 39%	5900
	11th to 20th	Day	4 5% 2 7% 5% 5% 6% 5% 8% 13% 41%	5900
	21st to end	Day	7% 5% 2 6% 4 4 5% 5% 7% 12% 43%	6422
August	1st to 10th	Day	1 1 2 2 2 2 3 5% 7% 74%	4205
	11th to 20th	Day	2 2 1 3 3 3 4 5% 9% 14% 53%	3846
	21st to end	Day	5% 3 1 5% 4 6% 6% 6% 8% 14% 42%	3959
September	1st to 10th	Day	8% 5% 2 7% 5% 5% 6% 6% 8% 11% 36%	2200
	11th to 20th	Day	10% 6% 3 7% 5% 5% 5% 4 7% 9% 41%	2200
	21st to end	Day	8% 4 1 5% 4 4 5% 4 8% 11% 47%	2200
October	1st to 10th	Day	6% 4 1 5% 4 4 5% 4 5% 8% 54%	2200
	11th to 20th	Day	9% 5% 1 5% 4 3 4 4 5% 7% 52%	2042
	21st to end	Day	8% 5% 1 5% 3 3 3 3 4 8% 58%	2200
November	1st to 10th	Day	9% 4 2 6% 4 5% 5% 4 6% 9% 46%	1978
	11th to 20th	Day	14% 6% 2 6% 4 3 4 3 4 7% 47%	2000
	21st to end	Day	17% 6% 2 6% 4 4 5% 4 5% 6% 42%	1850
December	1st to 10th	Day	26% 11% 4 8% 4 3 3 2 4 4 30%	2940
	11th to 20th	Day	11% 7% 2 7% 5% 5% 5% 5% 6% 7% 40%	3391
	21st to end	Day	13% 6% 2 6% 3 3 3 3 5% 7% 49%	4488
January	1st to 10th	Night	23% 8% 2 6% 3 3 3 2 4 5% 40%	5888
	11th to 20th	Night	15% 6% 2 6% 3 3 3 3 5% 7% 47%	5900
	21st to end	Night	29% 8% 3 6% 3 3 3 3 5% 6% 31%	6140
February	1st to 10th	Night	19% 8% 2 5% 3 4 4 3 5% 6% 41%	2400
	11th to 20th	Night	20% 7% 2 5% 3 3 3 3 5% 6% 43%	2338
	21st to end	Night	19% 9% 2 6% 4 3 3 2 4 6% 42%	1918
March	1st to 10th	Night	22% 8% 2 5% 3 3 4 3 5% 7% 40%	4919
	11th to 20th	Night	19% 8% 2 6% 4 3 3 3 3 4 45%	4980
	21st to end	Night	20% 6% 2 4 3 2 3 2 4 6% 49%	5467
April	1st to 10th	Night	15% 8% 3 7% 5% 4 4 3 5% 7% 39%	2200
	11th to 20th	Night	19% 6% 2 6% 4 4 3 3 4 8% 42%	2173
	21st to end	Night	17% 8% 2 7% 5% 4 4 3 5% 7% 38%	2033
May	1st to 10th	Night	29% 8% 3 6% 4 4 4 3 4 7% 27%	4053
	11th to 20th	Night	15% 6% 2 5% 4 4 3 3 6% 8% 45%	4053
	21st to end	Night	15% 8% 3 8% 4 5% 5% 4 6% 10% 32%	4443
June	1st to 10th	Night	4 3 2 4 3 3 5% 4 9% 10% 53%	1800
	11th to 20th	Night	4 4 1 5% 4 4 5% 5% 7% 13% 50%	1800
	21st to end	Night	5% 3 2 5% 4 5% 5% 5% 8% 11% 48%	1800
July	1st to 10th	Night	5% 5% 2 8% 5% 6% 5% 4 7% 10% 44%	4078
	11th to 20th	Night	3 3 2 5% 5% 5% 5% 5% 8% 13% 45%	4077
	21st to end	Night	7% 5% 2 6% 4 4 4 4 6% 11% 48%	4449
August	1st to 10th	Night	1 1 1 1 2 2 3 7% 81%	2949
	11th to 20th	Night	2 2 1 3 2 3 4 4 7% 13% 57%	3213
	21st to end	Night	2 2 1 3 3 2 4 4 6% 13% 59%	3938
September	1st to 10th	Night	6% 6% 2 7% 4 4 5% 5% 7% 10% 45%	2200
	11th to 20th	Night	8% 6% 2 6% 4 4 4 3 7% 10% 46%	2200
	21st to end	Night	6% 4 2 5% 3 4 4 3 5% 9% 55%	2200
October	1st to 10th	Night	4 3 1 3 3 4 4 3 5% 8% 62%	2200
	11th to 20th	Night	9% 4 1 4 3 3 3 2 5% 8% 59%	2335
	21st to end	Night	8% 3 1 4 3 3 2 2 4 7% 63%	2640
November	1st to 10th	Night	10% 5% 2 4 3 3 3 3 6% 7% 54%	2365
	11th to 20th	Night	15% 5% 2 6% 4 3 3 3 3 6% 52%	2400
	21st to end	Night	16% 7% 2 6% 4 4 3 3 5% 5% 45%	2545
December	1st to 10th	Night	30% 12% 3 7% 4 3 2 2 3 4 29%	4250
	11th to 20th	Night	13% 7% 3 7% 4 3 4 3 5% 7% 45%	4816
	21st to end	Night	10% 6% 2 5% 3 3 4 3 5% 6% 52%	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	39% 29% 6% 14% 8% 5%	4078
	11th to 20th	Day	30% 30% 7% 15% 13% 5%	4080
	21st to end	Day	41% 29% 4 8% 11% 8%	4879
February	1st to 10th	Day	21% 62% 3 3 5% 5%	2000
	11th to 20th	Day	17% 62% 4 8% 7% 2	1959
	21st to end	Day	19% 63% 3 6% 5% 3	1710
March	1st to 10th	Day	34% 32% 7% 12% 4 12%	4936
	11th to 20th	Day	29% 30% 4 10% 13% 14%	4980
	21st to end	Day	30% 31% 8% 16% 10% 5%	5464
April	1st to 10th	Day	15% 62% 4 6% 7% 6%	2200
	11th to 20th	Day	17% 63% 6% 6% 5% 4	2176
	21st to end	Day	15% 64% 5% 10% 5% 2	2360
May	1st to 10th	Day	39% 32% 12% 9% 6% 2	5900
	11th to 20th	Day	23% 31% 13% 16% 12% 5%	5866
	21st to end	Day	26% 36% 12% 24% 3	6447
June	1st to 10th	Day	7% 63% 10% 15% 5%	2600
	11th to 20th	Day	12% 65% 7% 11% 5% 1	2600
	21st to end	Day	11% 64% 11% 12% 2	2600
July	1st to 10th	Day	27% 30% 24% 18% 1	5836
	11th to 20th	Day	26% 30% 28% 13% 2	5831
	21st to end	Day	25% 29% 19% 21% 5%	6240
August	1st to 10th	Day	4 37% 14% 34% 12%	4191
	11th to 20th	Day	10% 40% 27% 21% 2	3882
	21st to end	Day	17% 41% 17% 20% 5% 1	3958
September	1st to 10th	Day	14% 63% 7% 9% 6% 1	2200
	11th to 20th	Day	14% 59% 8% 12% 6% 1	2200
	21st to end	Day	13% 60% 9% 13% 3 2	2200
October	1st to 10th	Day	12% 36% 5% 7% 20% 20%	3590
	11th to 20th	Day	18% 37% 7% 9% 22% 7%	3308
	21st to end	Day	15% 37% 5% 18% 20% 5%	3538
November	1st to 10th	Day	19% 59% 6% 9% 5% 2	1978
	11th to 20th	Day	21% 59% 4 7% 4 5%	2000
	21st to end	Day	22% 57% 4 7% 7% 2	1850
December	1st to 10th	Day	45% 36% 3 6% 9% 1	2940
	11th to 20th	Day	26% 34% 6% 16% 9% 9%	3389
	21st to end	Day	26% 28% 5% 19% 14% 9%	4488
January	1st to 10th	Night	39% 28% 4 11% 9% 9%	5888
	11th to 20th	Night	29% 28% 5% 17% 16% 6%	5900
	21st to end	Night	42% 29% 5% 8% 10% 6%	6140
February	1st to 10th	Night	20% 62% 3 4 6% 6%	2400
	11th to 20th	Night	17% 61% 5% 8% 6% 4	2338
	21st to end	Night	18% 62% 3 8% 6% 4	1918
March	1st to 10th	Night	36% 30% 7% 12% 7% 8%	4919
	11th to 20th	Night	32% 28% 5% 7% 11% 17%	4980
	21st to end	Night	26% 29% 7% 18% 16% 4	5467
April	1st to 10th	Night	17% 62% 4 6% 6% 5%	2200
	11th to 20th	Night	16% 62% 5% 6% 5% 5%	2173
	21st to end	Night	17% 62% 6% 7% 5% 2	2033
May	1st to 10th	Night	43% 29% 10% 9% 6% 2	4080
	11th to 20th	Night	24% 30% 10% 19% 11% 5%	4054
	21st to end	Night	33% 32% 14% 18% 2	4452
June	1st to 10th	Night	7% 62% 9% 16% 6%	1800
	11th to 20th	Night	13% 64% 4 12% 8%	1800
	21st to end	Night	12% 63% 11% 13% 2	1800
July	1st to 10th	Night	25% 29% 24% 20% 2	4035
	11th to 20th	Night	23% 31% 30% 15% 2	4026
	21st to end	Night	23% 28% 22% 20% 7% 1	4320
August	1st to 10th	Night	3 36% 12% 38% 11%	2939
	11th to 20th	Night	10% 38% 27% 23% 1	3243
	21st to end	Night	8% 40% 22% 24% 6% 1	3938
September	1st to 10th	Night	12% 59% 12% 8% 7% 2	2200
	11th to 20th	Night	12% 58% 8% 13% 7% 1	2200
	21st to end	Night	13% 60% 8% 15% 3 2	2200
October	1st to 10th	Night	10% 36% 6% 10% 16% 23%	3590
	11th to 20th	Night	11% 37% 7% 12% 23% 10%	3795
	21st to end	Night	13% 37% 5% 17% 23% 6%	4252
November	1st to 10th	Night	18% 58% 7% 9% 6% 3	2365
	11th to 20th	Night	22% 57% 5% 6% 6% 5%	2400
	21st to end	Night	21% 57% 4 7% 7% 3	2545
December	1st to 10th	Night	48% 35% 3 4 8% 3	4250
	11th to 20th	Night	24% 34% 5% 16% 10% 11%	4817
	21st to end	Night	25% 27% 7% 16% 13% 12%	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	21% 9% 23% 33% 14%	300
	11th to 20th	Day	19% 8% 20% 39% 12% 2	300
	21st to end	Day	23% 5% 28% 34% 11%	330
February	1st to 10th	Day	26% 7% 22% 31% 13% 1	300
	11th to 20th	Day	25% 7% 24% 33% 10%	300
	21st to end	Day	24% 5% 31% 33% 6%	249
March	1st to 10th	Day	21% 6% 24% 39% 10%	300
	11th to 20th	Day	23% 6% 28% 36% 7%	300
	21st to end	Day	17% 7% 30% 39% 7%	330
April	1st to 10th	Day	14% 6% 34% 36% 9% 1	300
	11th to 20th	Day	18% 9% 26% 31% 15% 1	294
	21st to end	Day	15% 6% 27% 38% 13%	460
May	1st to 10th	Day	13% 5% 26% 44% 11%	703
	11th to 20th	Day	10% 5% 19% 47% 17% 2	725
	21st to end	Day	7% 3 13% 46% 29% 1	789
June	1st to 10th	Day	5% 1 5% 36% 46% 7%	730
	11th to 20th	Day	6% 1 5% 37% 46% 6%	730
	21st to end	Day	7% 1 4 25% 48% 16%	730
July	1st to 10th	Day	6% 1 3 26% 49% 14%	721
	11th to 20th	Day	4 1 1 18% 58% 18%	718
	21st to end	Day	5% 2 1 16% 56% 20%	794
August	1st to 10th	Day	1 1 1 14% 57% 27%	710
	11th to 20th	Day	3 1 1 14% 61% 21%	517
	21st to end	Day	6% 1 2 10% 43% 39%	373
September	1st to 10th	Day	9% 1 3 14% 51% 21%	330
	11th to 20th	Day	8% 1 2 11% 50% 28%	330
	21st to end	Day	6% 2 4 13% 48% 26%	330
October	1st to 10th	Day	8% 4 3 22% 48% 15%	330
	11th to 20th	Day	12% 2 3 27% 43% 13%	330
	21st to end	Day	12% 2 16% 33% 31% 7%	363
November	1st to 10th	Day	12% 5% 9% 32% 39% 3	306
	11th to 20th	Day	20% 5% 11% 32% 27% 6%	300
	21st to end	Day	27% 6% 17% 30% 16% 4	300
December	1st to 10th	Day	23% 6% 16% 32% 20% 3	300
	11th to 20th	Day	21% 7% 19% 32% 19% 2	300
	21st to end	Day	20% 8% 18% 35% 15% 3	330
January	1st to 10th	Night	23% 7% 23% 34% 14% 1	1000
	11th to 20th	Night	21% 6% 23% 37% 12%	1000
	21st to end	Night	22% 6% 24% 36% 12%	945
February	1st to 10th	Night	24% 7% 22% 37% 10%	800
	11th to 20th	Night	24% 7% 23% 35% 10%	784
	21st to end	Night	25% 6% 27% 32% 10%	598
March	1st to 10th	Night	19% 6% 23% 38% 15%	600
	11th to 20th	Night	20% 7% 23% 41% 9%	600
	21st to end	Night	15% 5% 23% 44% 12% 1	660
April	1st to 10th	Night	18% 5% 27% 40% 11%	600
	11th to 20th	Night	21% 6% 23% 36% 15%	593
	21st to end	Night	18% 5% 22% 41% 14%	600
May	1st to 10th	Night	16% 4 22% 45% 13%	600
	11th to 20th	Night	13% 2 19% 48% 17% 2	591
	21st to end	Night	8% 2 14% 44% 31% 1	650
June	1st to 10th	Night	4 1 4 37% 50% 4	600
	11th to 20th	Night	5% 1 4 44% 44% 2	600
	21st to end	Night	5% 1 5% 29% 48% 12%	600
July	1st to 10th	Night	7% 2 2 29% 49% 11%	585
	11th to 20th	Night	3 1 2 19% 59% 16%	582
	21st to end	Night	5% 1 1 18% 63% 13%	657
August	1st to 10th	Night	1 1 13% 67% 18%	597
	11th to 20th	Night	4 1 1 11% 69% 15%	594
	21st to end	Night	4 1 2 13% 53% 27%	660
September	1st to 10th	Night	6% 2 3 18% 54% 18%	600
	11th to 20th	Night	10% 2 2 14% 53% 20%	600
	21st to end	Night	8% 1 3 21% 54% 14%	600
October	1st to 10th	Night	4 1 5% 23% 56% 11%	600
	11th to 20th	Night	10% 2 8% 33% 41% 6%	735
	21st to end	Night	9% 3 13% 37% 34% 4	880
November	1st to 10th	Night	11% 3 10% 35% 37% 5%	789
	11th to 20th	Night	17% 3 16% 34% 28% 3	800
	21st to end	Night	21% 6% 18% 34% 20% 3	945
December	1st to 10th	Night	22% 5% 17% 30% 21% 4	1000
	11th to 20th	Night	22% 6% 20% 35% 17% 1	1000
	21st to end	Night	20% 7% 23% 34% 15% 2	1100

Page generated at 2025-10-31 01:02:38. Version ac07

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