Brazosport Planetarium
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brazosport Planetarium clear sky chart from 2005-11-06 to 2026-04-17.

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% 5% 5% 5% 4 7% 8% 39%	131561
	Night	14% 6% 2 6% 4 4 4 3 5% 8% 44%	130848
Transparency	Day	38% 8% 14% 21% 13% 6%	135222
	Night	37% 6% 13% 20% 15% 8%	135250
Seeing	Day	13% 6% 21% 29% 22% 9%	16553
	Night	15% 4 18% 31% 26% 5%	26539

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	20% 10% 3 7% 4 3 4 3 4 5% 39%	5289
	11th to 20th	Day	14% 7% 2 6% 3 3 3 3 4 6% 48%	5310
	21st to end	Day	26% 9% 3 8% 3 3 3 3 5% 6% 31%	5812
February	1st to 10th	Day	19% 8% 3 7% 4 4 5% 4 5% 5% 35%	2021
	11th to 20th	Day	21% 8% 3 6% 4 4 4 3 5% 6% 35%	2090
	21st to end	Day	19% 8% 3 6% 3 3 3 3 5% 7% 39%	1903
March	1st to 10th	Day	16% 7% 3 7% 4 4 4 4 6% 8% 38%	5046
	11th to 20th	Day	13% 6% 2 7% 5% 4 4 4 5% 6% 45%	5090
	21st to end	Day	17% 6% 2 7% 4 4 4 3 5% 6% 42%	5583
April	1st to 10th	Day	16% 8% 3 7% 5% 3 4 3 6% 8% 37%	2310
	11th to 20th	Day	16% 7% 2 6% 5% 4 5% 4 7% 8% 36%	2384
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 4 6% 7% 41%	2400
May	1st to 10th	Day	17% 8% 3 8% 6% 6% 6% 5% 7% 7% 27%	5405
	11th to 20th	Day	11% 5% 2 6% 4 4 4 4 6% 8% 45%	5861
	21st to end	Day	9% 5% 2 7% 5% 6% 6% 6% 9% 12% 32%	6434
June	1st to 10th	Day	5% 4 2 5% 5% 5% 6% 6% 8% 10% 44%	2600
	11th to 20th	Day	6% 4 1 6% 6% 6% 7% 6% 9% 11% 37%	2600
	21st to end	Day	7% 4 2 5% 7% 8% 7% 6% 10% 13% 31%	2600
July	1st to 10th	Day	6% 5% 2 7% 6% 6% 6% 5% 9% 12% 34%	5900
	11th to 20th	Day	5% 6% 3 8% 6% 7% 7% 6% 9% 12% 31%	5900
	21st to end	Day	9% 7% 2 7% 6% 5% 5% 5% 7% 10% 37%	6422
August	1st to 10th	Day	2 2 1 3 3 4 5% 5% 8% 12% 55%	4234
	11th to 20th	Day	2 2 1 5% 4 4 6% 6% 10% 15% 44%	3957
	21st to end	Day	6% 4 2 8% 5% 7% 7% 6% 9% 12% 34%	4185
September	1st to 10th	Day	9% 7% 3 7% 7% 6% 7% 6% 7% 8% 33%	2200
	11th to 20th	Day	13% 6% 3 7% 6% 6% 6% 4 8% 7% 33%	2200
	21st to end	Day	8% 5% 3 6% 4 6% 5% 4 5% 7% 46%	2200
October	1st to 10th	Day	5% 5% 2 4 4 5% 4 4 7% 8% 52%	2085
	11th to 20th	Day	9% 6% 2 5% 4 4 4 4 5% 6% 52%	2000
	21st to end	Day	10% 4 2 5% 4 3 3 3 4 7% 54%	2200
November	1st to 10th	Day	9% 6% 2 6% 4 5% 5% 5% 6% 8% 43%	2058
	11th to 20th	Day	15% 6% 2 4 5% 4 4 4 5% 6% 47%	2100
	21st to end	Day	16% 5% 3 7% 5% 5% 4 4 6% 6% 40%	2084
December	1st to 10th	Day	26% 8% 3 6% 3 4 3 3 5% 7% 32%	3030
	11th to 20th	Day	12% 6% 2 6% 4 4 4 4 7% 9% 42%	3481
	21st to end	Day	14% 6% 3 6% 4 4 4 3 5% 7% 44%	4587
January	1st to 10th	Night	18% 8% 3 7% 4 4 3 3 3 4 42%	7634
	11th to 20th	Night	16% 8% 2 7% 4 3 3 2 4 5% 46%	7680
	21st to end	Night	27% 9% 3 7% 4 3 3 3 4 6% 31%	8402
February	1st to 10th	Night	19% 9% 3 7% 4 4 3 3 4 6% 39%	2614
	11th to 20th	Night	19% 9% 3 5% 3 3 3 2 3 6% 42%	2416
	21st to end	Night	19% 8% 2 7% 5% 4 4 3 4 6% 39%	1903
March	1st to 10th	Night	22% 10% 3 6% 3 3 4 3 4 6% 37%	5029
	11th to 20th	Night	17% 8% 2 5% 4 3 4 3 4 5% 45%	5090
	21st to end	Night	17% 9% 2 6% 3 3 3 3 4 6% 45%	5588
April	1st to 10th	Night	15% 8% 3 6% 5% 4 4 4 5% 7% 41%	2310
	11th to 20th	Night	15% 5% 2 5% 4 3 4 3 5% 7% 46%	2094
	21st to end	Night	13% 6% 3 6% 5% 4 5% 4 5% 7% 43%	2000
May	1st to 10th	Night	27% 9% 3 7% 4 4 4 4 5% 7% 28%	4473
	11th to 20th	Night	14% 6% 2 5% 3 4 3 4 5% 8% 46%	4053
	21st to end	Night	17% 8% 3 6% 4 4 4 5% 7% 11% 31%	4443
June	1st to 10th	Night	6% 4 1 5% 3 3 3 3 6% 13% 54%	1800
	11th to 20th	Night	5% 4 1 4 3 4 4 4 8% 12% 50%	1800
	21st to end	Night	6% 4 1 5% 5% 4 6% 4 9% 13% 42%	1800
July	1st to 10th	Night	5% 4 2 6% 5% 4 5% 5% 7% 13% 44%	4078
	11th to 20th	Night	3 3 2 6% 5% 5% 6% 4 8% 13% 45%	4077
	21st to end	Night	6% 4 2 6% 5% 6% 5% 5% 7% 11% 45%	4449
August	1st to 10th	Night	1 1 1 2 2 3 2 5% 9% 73%	2926
	11th to 20th	Night	2 2 1 3 3 3 4 3 7% 14% 57%	3079
	21st to end	Night	4 3 1 5% 4 4 5% 5% 7% 12% 51%	3707
September	1st to 10th	Night	6% 4 2 7% 5% 5% 4 5% 8% 12% 43%	2200
	11th to 20th	Night	11% 6% 2 7% 5% 4 5% 4 5% 8% 44%	2200
	21st to end	Night	8% 4 2 5% 4 4 3 4 6% 9% 52%	2200
October	1st to 10th	Night	5% 4 2 4 3 3 4 3 4 8% 60%	2293
	11th to 20th	Night	8% 4 1 4 3 3 3 2 4 7% 62%	2400
	21st to end	Night	9% 3 2 5% 3 3 4 3 3 5% 60%	2640
November	1st to 10th	Night	9% 5% 1 5% 4 4 4 4 5% 7% 53%	2460
	11th to 20th	Night	12% 5% 2 5% 4 3 4 3 5% 6% 51%	2520
	21st to end	Night	14% 6% 2 7% 4 4 5% 4 5% 6% 45%	2531
December	1st to 10th	Night	26% 10% 3 8% 4 3 3 3 4 7% 29%	4380
	11th to 20th	Night	13% 8% 3 8% 4 4 4 3 5% 6% 42%	4946
	21st to end	Night	14% 6% 2 8% 4 3 3 2 4 5% 47%	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	48% 5% 7% 21% 12% 7%	5290
	11th to 20th	Day	38% 4 6% 22% 17% 11%	5310
	21st to end	Day	54% 4 5% 13% 15% 8%	5812
February	1st to 10th	Day	49% 6% 7% 14% 15% 10%	2021
	11th to 20th	Day	50% 5% 9% 14% 14% 7%	2100
	21st to end	Day	45% 7% 9% 15% 16% 8%	1903
March	1st to 10th	Day	42% 11% 10% 17% 9% 12%	5046
	11th to 20th	Day	39% 8% 8% 13% 19% 13%	5090
	21st to end	Day	41% 7% 9% 20% 19% 4	5585
April	1st to 10th	Day	44% 7% 11% 17% 14% 8%	2310
	11th to 20th	Day	42% 8% 11% 17% 14% 8%	2384
	21st to end	Day	38% 7% 12% 22% 16% 5%	2400
May	1st to 10th	Day	49% 12% 13% 15% 8% 2	5440
	11th to 20th	Day	34% 9% 14% 23% 16% 4	5865
	21st to end	Day	37% 13% 15% 27% 6%	6447
June	1st to 10th	Day	28% 9% 18% 31% 15%	2600
	11th to 20th	Day	32% 10% 16% 28% 13% 1	2600
	21st to end	Day	36% 12% 20% 26% 7%	2600
July	1st to 10th	Day	36% 10% 34% 18% 2	5836
	11th to 20th	Day	40% 11% 30% 16% 2	5831
	21st to end	Day	39% 10% 21% 25% 5%	6240
August	1st to 10th	Day	16% 9% 20% 47% 9%	4220
	11th to 20th	Day	22% 12% 36% 26% 3	3995
	21st to end	Day	37% 13% 18% 22% 8% 1	4184
September	1st to 10th	Day	43% 11% 14% 18% 13% 2	2200
	11th to 20th	Day	44% 10% 12% 19% 14% 1	2200
	21st to end	Day	35% 6% 13% 21% 17% 8%	2200
October	1st to 10th	Day	21% 5% 7% 16% 19% 31%	3397
	11th to 20th	Day	23% 5% 6% 24% 32% 11%	3240
	21st to end	Day	24% 5% 6% 21% 34% 11%	3538
November	1st to 10th	Day	35% 7% 11% 20% 21% 7%	2058
	11th to 20th	Day	37% 5% 9% 18% 18% 12%	2100
	21st to end	Day	43% 6% 10% 17% 15% 9%	2084
December	1st to 10th	Day	52% 5% 8% 19% 12% 3	3030
	11th to 20th	Day	35% 7% 10% 21% 17% 10%	3479
	21st to end	Day	39% 6% 7% 16% 20% 11%	4587
January	1st to 10th	Night	45% 6% 8% 16% 16% 9%	7635
	11th to 20th	Night	41% 3 5% 16% 22% 13%	7680
	21st to end	Night	54% 5% 5% 13% 15% 8%	8402
February	1st to 10th	Night	46% 5% 8% 10% 17% 14%	2614
	11th to 20th	Night	44% 4 8% 16% 17% 11%	2416
	21st to end	Night	46% 5% 8% 14% 19% 8%	1903
March	1st to 10th	Night	47% 5% 9% 16% 12% 10%	5029
	11th to 20th	Night	41% 6% 8% 14% 16% 16%	5090
	21st to end	Night	41% 5% 9% 17% 21% 7%	5588
April	1st to 10th	Night	42% 6% 10% 18% 15% 8%	2310
	11th to 20th	Night	37% 6% 11% 20% 14% 12%	2094
	21st to end	Night	39% 6% 11% 21% 16% 6%	2000
May	1st to 10th	Night	53% 8% 11% 16% 10% 3	4503
	11th to 20th	Night	34% 7% 12% 28% 14% 5%	4054
	21st to end	Night	42% 9% 19% 23% 6% 1	4452
June	1st to 10th	Night	24% 6% 20% 32% 18%	1800
	11th to 20th	Night	24% 8% 17% 33% 16% 2	1800
	21st to end	Night	30% 11% 25% 25% 9%	1800
July	1st to 10th	Night	31% 7% 36% 24% 2	4035
	11th to 20th	Night	28% 10% 36% 23% 3	4026
	21st to end	Night	33% 10% 24% 27% 5%	4320
August	1st to 10th	Night	10% 6% 18% 53% 14%	2916
	11th to 20th	Night	18% 8% 37% 34% 4	3106
	21st to end	Night	25% 14% 25% 25% 10% 1	3707
September	1st to 10th	Night	33% 11% 21% 20% 11% 4	2200
	11th to 20th	Night	38% 7% 14% 23% 16% 2	2200
	21st to end	Night	30% 7% 14% 23% 18% 8%	2200
October	1st to 10th	Night	19% 5% 8% 18% 19% 31%	3748
	11th to 20th	Night	16% 4 8% 25% 31% 15%	3899
	21st to end	Night	19% 4 6% 20% 35% 15%	4252
November	1st to 10th	Night	31% 6% 11% 22% 21% 9%	2460
	11th to 20th	Night	34% 4 12% 20% 19% 11%	2520
	21st to end	Night	40% 6% 9% 19% 17% 8%	2531
December	1st to 10th	Night	56% 5% 8% 17% 10% 5%	4380
	11th to 20th	Night	41% 6% 9% 16% 14% 14%	4947
	21st to end	Night	40% 5% 6% 16% 24% 9%	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	24% 10% 38% 20% 6% 2	330
	11th to 20th	Day	20% 12% 35% 26% 6% 1	330
	21st to end	Day	24% 13% 35% 20% 7%	363
February	1st to 10th	Day	24% 13% 34% 21% 8% 1	330
	11th to 20th	Day	25% 13% 34% 21% 6% 1	330
	21st to end	Day	22% 12% 45% 16% 5%	273
March	1st to 10th	Day	21% 14% 39% 22% 3	330
	11th to 20th	Day	16% 16% 45% 18% 3 1	330
	21st to end	Day	18% 13% 36% 27% 5% 1	363
April	1st to 10th	Day	20% 14% 39% 22% 5%	330
	11th to 20th	Day	21% 14% 30% 23% 11% 1	454
	21st to end	Day	18% 7% 35% 27% 12% 1	500
May	1st to 10th	Day	20% 6% 35% 27% 12% 1	503
	11th to 20th	Day	13% 4 32% 34% 14% 3	724
	21st to end	Day	9% 3 27% 41% 17% 3	789
June	1st to 10th	Day	6% 2 15% 42% 25% 8%	730
	11th to 20th	Day	8% 1 13% 44% 26% 8%	730
	21st to end	Day	9% 3 9% 36% 31% 13%	730
July	1st to 10th	Day	9% 2 6% 31% 33% 20%	721
	11th to 20th	Day	5% 2 2 31% 37% 23%	718
	21st to end	Day	7% 2 3 30% 38% 20%	794
August	1st to 10th	Day	3 2 2 24% 43% 26%	726
	11th to 20th	Day	4 2 1 18% 45% 31%	591
	21st to end	Day	10% 2 3 18% 38% 29%	508
September	1st to 10th	Day	13% 3 5% 27% 37% 15%	330
	11th to 20th	Day	10% 2 6% 29% 34% 18%	330
	21st to end	Day	9% 3 7% 32% 37% 13%	330
October	1st to 10th	Day	6% 2 10% 47% 27% 8%	330
	11th to 20th	Day	9% 2 15% 36% 27% 10%	330
	21st to end	Day	14% 6% 26% 33% 18% 3	363
November	1st to 10th	Day	12% 4 24% 39% 16% 5%	330
	11th to 20th	Day	18% 5% 25% 34% 14% 3	330
	21st to end	Day	19% 9% 38% 20% 11% 3	330
December	1st to 10th	Day	22% 6% 33% 25% 11% 2	330
	11th to 20th	Day	18% 10% 35% 26% 10% 1	330
	21st to end	Day	18% 8% 37% 23% 12% 2	363
January	1st to 10th	Night	23% 7% 29% 30% 11%	1050
	11th to 20th	Night	22% 7% 28% 34% 8% 1	1050
	21st to end	Night	24% 7% 30% 31% 8%	1155
February	1st to 10th	Night	24% 8% 27% 32% 8%	934
	11th to 20th	Night	23% 9% 27% 32% 9%	782
	21st to end	Night	22% 10% 33% 29% 7%	519
March	1st to 10th	Night	24% 7% 26% 33% 10%	630
	11th to 20th	Night	20% 6% 26% 38% 9% 1	630
	21st to end	Night	17% 5% 27% 36% 14% 1	693
April	1st to 10th	Night	18% 6% 30% 36% 10%	630
	11th to 20th	Night	18% 7% 27% 35% 12%	611
	21st to end	Night	17% 7% 25% 37% 14% 1	600
May	1st to 10th	Night	19% 3 27% 40% 11%	600
	11th to 20th	Night	12% 2 23% 43% 18% 2	591
	21st to end	Night	10% 3 18% 41% 27% 2	650
June	1st to 10th	Night	7% 1 5% 38% 44% 5%	600
	11th to 20th	Night	7% 1 5% 43% 40% 5%	600
	21st to end	Night	8% 1 5% 27% 46% 14%	600
July	1st to 10th	Night	7% 1 4 21% 52% 15%	585
	11th to 20th	Night	4 1 1 14% 59% 21%	582
	21st to end	Night	4 1 2 16% 61% 15%	657
August	1st to 10th	Night	1 1 12% 68% 18%	597
	11th to 20th	Night	5% 1 10% 66% 18%	594
	21st to end	Night	8% 2 1 15% 56% 19%	660
September	1st to 10th	Night	7% 2 3 16% 56% 17%	600
	11th to 20th	Night	14% 1 3 19% 51% 13%	600
	21st to end	Night	9% 1 4 25% 52% 10%	600
October	1st to 10th	Night	6% 1 7% 36% 40% 9%	693
	11th to 20th	Night	9% 2 13% 41% 31% 5%	800
	21st to end	Night	11% 4 16% 39% 26% 4	880
November	1st to 10th	Night	11% 3 16% 38% 28% 5%	820
	11th to 20th	Night	15% 3 19% 39% 22% 2	840
	21st to end	Night	17% 4 26% 34% 17% 2	851
December	1st to 10th	Night	22% 6% 22% 31% 17% 2	1050
	11th to 20th	Night	22% 6% 24% 34% 13%	1050
	21st to end	Night	20% 7% 28% 31% 12% 1	1155

Page generated at 2026-04-14 01:44:27. Version ac07

Copyright © 2026 Attilla Danko.