Big Thicket Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Big Thicket Observatory clear sky chart from 2005-11-06 to 2025-10-04.

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	14% 6% 2 7% 5% 5% 5% 4 6% 8% 39%	126121
	Night	15% 7% 2 5% 4 3 4 3 5% 7% 44%	123494
Transparency	Day	42% 7% 11% 18% 16% 7%	129728
	Night	38% 6% 12% 19% 17% 8%	127950
Seeing	Day	14% 8% 21% 26% 21% 10%	16136
	Night	16% 6% 22% 31% 22% 3	25866

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% 10% 2 5% 3 3 3 2 4 4 41%	4077
	11th to 20th	Day	17% 5% 2 6% 4 4 3 2 3 5% 50%	4080
	21st to end	Day	28% 8% 3 6% 3 3 3 2 4 5% 35%	4488
February	1st to 10th	Day	22% 8% 3 6% 4 4 3 3 5% 6% 35%	1800
	11th to 20th	Day	24% 9% 3 6% 3 3 3 2 4 4 38%	2027
	21st to end	Day	24% 9% 3 6% 4 3 3 2 4 5% 37%	1815
March	1st to 10th	Day	23% 8% 3 6% 4 5% 4 4 5% 5% 34%	4936
	11th to 20th	Day	15% 6% 2 6% 5% 4 4 3 4 6% 45%	4980
	21st to end	Day	19% 8% 3 7% 5% 4 4 3 4 6% 38%	5462
April	1st to 10th	Day	16% 8% 3 7% 4 6% 5% 3 5% 6% 38%	2245
	11th to 20th	Day	17% 7% 3 6% 5% 4 4 4 5% 6% 38%	2374
	21st to end	Day	12% 6% 2 7% 5% 5% 4 4 6% 7% 41%	2400
May	1st to 10th	Day	19% 8% 3 8% 5% 5% 5% 5% 6% 7% 28%	5405
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 4 6% 8% 43%	5672
	21st to end	Day	10% 6% 3 8% 6% 6% 6% 5% 7% 10% 34%	6434
June	1st to 10th	Day	8% 5% 2 7% 6% 7% 7% 6% 8% 8% 35%	2600
	11th to 20th	Day	6% 6% 3 6% 6% 7% 9% 6% 9% 9% 34%	2600
	21st to end	Day	8% 6% 2 8% 7% 8% 8% 7% 9% 9% 29%	2600
July	1st to 10th	Day	8% 6% 2 7% 7% 7% 7% 6% 9% 12% 28%	5900
	11th to 20th	Day	7% 7% 3 9% 7% 6% 7% 6% 9% 12% 27%	5900
	21st to end	Day	12% 7% 3 7% 6% 6% 6% 5% 7% 10% 31%	6422
August	1st to 10th	Day	2 2 1 4 4 4 6% 3 7% 10% 56%	4234
	11th to 20th	Day	3 3 1 4 4 5% 7% 6% 9% 11% 45%	3858
	21st to end	Day	11% 6% 2 8% 6% 7% 7% 5% 7% 7% 35%	4312
September	1st to 10th	Day	10% 6% 2 8% 6% 5% 6% 5% 6% 9% 37%	2340
	11th to 20th	Day	14% 6% 2 7% 6% 5% 6% 5% 7% 8% 35%	2200
	21st to end	Day	11% 5% 1 6% 4 4 5% 4 6% 7% 46%	2197
October	1st to 10th	Day	7% 4 2 4 4 5% 4 4 5% 6% 55%	1930
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 6% 7% 52%	1900
	21st to end	Day	14% 5% 1 5% 3 3 3 3 4 6% 53%	2090
November	1st to 10th	Day	13% 6% 2 7% 5% 5% 4 4 6% 6% 44%	1958
	11th to 20th	Day	14% 5% 2 7% 3 4 3 4 5% 5% 49%	2000
	21st to end	Day	17% 7% 2 6% 5% 4 3 2 5% 4 45%	2000
December	1st to 10th	Day	23% 9% 2 5% 3 3 3 2 4 6% 40%	3006
	11th to 20th	Day	16% 8% 3 7% 5% 4 4 3 4 6% 40%	3391
	21st to end	Day	18% 6% 2 6% 3 3 3 3 5% 6% 45%	4488
January	1st to 10th	Night	19% 7% 2 5% 3 3 3 2 4 6% 46%	5888
	11th to 20th	Night	19% 8% 2 5% 3 2 2 2 3 5% 48%	5900
	21st to end	Night	30% 9% 2 6% 3 3 3 2 4 6% 32%	6490
February	1st to 10th	Night	21% 8% 3 5% 4 4 3 3 4 6% 39%	2600
	11th to 20th	Night	23% 9% 3 4 3 2 3 2 3 5% 42%	2274
	21st to end	Night	24% 9% 3 5% 4 3 3 3 4 5% 37%	1815
March	1st to 10th	Night	22% 12% 3 6% 3 3 3 3 4 4 37%	4919
	11th to 20th	Night	22% 7% 2 6% 4 3 3 2 4 5% 42%	4980
	21st to end	Night	21% 8% 3 5% 4 4 3 3 4 5% 41%	5467
April	1st to 10th	Night	18% 7% 3 6% 4 3 4 3 5% 7% 40%	2155
	11th to 20th	Night	19% 5% 1 5% 4 3 3 3 6% 8% 43%	1975
	21st to end	Night	15% 8% 2 5% 4 4 4 3 5% 6% 44%	2000
May	1st to 10th	Night	26% 9% 3 7% 4 4 4 4 6% 8% 26%	4490
	11th to 20th	Night	18% 6% 2 7% 4 4 4 3 5% 6% 41%	4229
	21st to end	Night	16% 7% 3 7% 4 5% 5% 5% 7% 10% 32%	4443
June	1st to 10th	Night	6% 5% 1 4 3 3 4 3 7% 10% 53%	1800
	11th to 20th	Night	5% 3 2 4 2 3 4 4 8% 13% 51%	1800
	21st to end	Night	7% 4 2 5% 3 5% 5% 5% 9% 12% 43%	1800
July	1st to 10th	Night	5% 5% 2 6% 5% 4 5% 5% 8% 14% 42%	4078
	11th to 20th	Night	4 4 2 6% 5% 5% 5% 4 7% 11% 47%	4077
	21st to end	Night	8% 6% 2 7% 5% 4 5% 4 6% 9% 43%	4449
August	1st to 10th	Night	2 2 1 2 3 3 3 3 6% 11% 64%	2926
	11th to 20th	Night	2 2 1 2 2 3 4 3 6% 12% 62%	3191
	21st to end	Night	7% 4 2 5% 4 4 6% 5% 8% 10% 44%	3586
September	1st to 10th	Night	7% 5% 2 5% 4 4 5% 5% 6% 11% 47%	2053
	11th to 20th	Night	11% 5% 2 6% 4 5% 5% 4 5% 8% 44%	2200
	21st to end	Night	9% 5% 2 4 3 3 4 3 4 7% 57%	2200
October	1st to 10th	Night	6% 3 1 4 3 3 3 4 5% 6% 61%	2297
	11th to 20th	Night	10% 4 1 4 2 3 3 3 5% 6% 60%	2280
	21st to end	Night	12% 6% 2 4 2 2 2 2 3 5% 60%	2508
November	1st to 10th	Night	12% 5% 1 5% 4 3 4 2 5% 6% 52%	2340
	11th to 20th	Night	12% 5% 1 5% 3 3 4 3 5% 6% 53%	2400
	21st to end	Night	15% 7% 3 6% 4 3 3 3 5% 6% 45%	2400
December	1st to 10th	Night	22% 9% 3 7% 4 3 3 3 4 5% 36%	4178
	11th to 20th	Night	16% 10% 3 6% 4 3 3 3 4 5% 43%	4816
	21st to end	Night	17% 7% 2 5% 3 3 3 3 4 5% 46%	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	47% 4 4 20% 18% 7%	4078
	11th to 20th	Day	39% 3 4 15% 27% 12%	4080
	21st to end	Day	53% 3 3 14% 15% 12%	4488
February	1st to 10th	Day	51% 4 6% 13% 16% 10%	1800
	11th to 20th	Day	50% 5% 6% 13% 17% 10%	2037
	21st to end	Day	51% 5% 6% 14% 16% 9%	1815
March	1st to 10th	Day	51% 5% 7% 10% 17% 10%	4936
	11th to 20th	Day	42% 4 7% 11% 20% 16%	4980
	21st to end	Day	48% 4 7% 19% 18% 4	5464
April	1st to 10th	Day	47% 6% 8% 14% 16% 9%	2245
	11th to 20th	Day	45% 6% 9% 14% 16% 10%	2374
	21st to end	Day	40% 7% 9% 16% 22% 5%	2400
May	1st to 10th	Day	52% 7% 9% 20% 9% 3	5440
	11th to 20th	Day	38% 6% 11% 22% 20% 2	5676
	21st to end	Day	41% 9% 12% 26% 10% 2	6447
June	1st to 10th	Day	41% 11% 14% 19% 14% 1	2600
	11th to 20th	Day	39% 11% 13% 21% 13% 2	2600
	21st to end	Day	45% 13% 17% 17% 8%	2600
July	1st to 10th	Day	44% 11% 26% 17% 3	5836
	11th to 20th	Day	45% 11% 24% 17% 3	5831
	21st to end	Day	45% 10% 16% 23% 5%	6240
August	1st to 10th	Day	22% 8% 13% 35% 22%	4220
	11th to 20th	Day	27% 10% 30% 27% 4 1	3894
	21st to end	Day	44% 11% 13% 16% 14% 1	4311
September	1st to 10th	Day	41% 12% 13% 16% 14% 4	2340
	11th to 20th	Day	44% 9% 13% 16% 14% 5%	2200
	21st to end	Day	36% 7% 12% 19% 15% 11%	2197
October	1st to 10th	Day	22% 4 7% 12% 17% 37%	3190
	11th to 20th	Day	20% 3 5% 18% 34% 20%	3140
	21st to end	Day	27% 4 4 12% 40% 13%	3428
November	1st to 10th	Day	40% 6% 8% 17% 19% 10%	1958
	11th to 20th	Day	38% 5% 7% 16% 21% 15%	2000
	21st to end	Day	43% 4 7% 18% 20% 9%	2000
December	1st to 10th	Day	47% 4 5% 17% 22% 5%	3006
	11th to 20th	Day	45% 5% 7% 13% 20% 11%	3389
	21st to end	Day	40% 4 5% 16% 25% 10%	4488
January	1st to 10th	Night	41% 3 6% 22% 21% 7%	5888
	11th to 20th	Night	41% 3 4 17% 26% 10%	5900
	21st to end	Night	55% 3 4 13% 15% 11%	6490
February	1st to 10th	Night	47% 5% 7% 12% 18% 12%	2600
	11th to 20th	Night	47% 4 6% 14% 19% 10%	2274
	21st to end	Night	50% 5% 6% 13% 14% 12%	1815
March	1st to 10th	Night	51% 4 5% 12% 18% 10%	4919
	11th to 20th	Night	46% 5% 7% 12% 14% 16%	4980
	21st to end	Night	47% 5% 8% 14% 19% 7%	5467
April	1st to 10th	Night	44% 6% 8% 17% 15% 10%	2155
	11th to 20th	Night	39% 6% 11% 17% 16% 12%	1975
	21st to end	Night	40% 5% 9% 20% 20% 6%	2000
May	1st to 10th	Night	55% 6% 11% 16% 9% 3	4520
	11th to 20th	Night	43% 5% 11% 19% 19% 3	4230
	21st to end	Night	43% 10% 18% 21% 8% 1	4452
June	1st to 10th	Night	24% 9% 20% 30% 16% 1	1800
	11th to 20th	Night	23% 9% 19% 31% 15% 2	1800
	21st to end	Night	30% 12% 23% 25% 9%	1800
July	1st to 10th	Night	32% 7% 38% 21% 2	4035
	11th to 20th	Night	30% 8% 33% 25% 3	4026
	21st to end	Night	37% 10% 19% 28% 6%	4320
August	1st to 10th	Night	14% 7% 19% 41% 18%	2916
	11th to 20th	Night	15% 8% 36% 35% 6%	3221
	21st to end	Night	33% 13% 20% 20% 12% 1	3586
September	1st to 10th	Night	29% 11% 21% 21% 14% 4	2053
	11th to 20th	Night	37% 8% 17% 19% 14% 5%	2200
	21st to end	Night	28% 6% 14% 23% 17% 12%	2200
October	1st to 10th	Night	18% 4 7% 16% 18% 37%	3804
	11th to 20th	Night	16% 4 4 24% 30% 22%	3779
	21st to end	Night	22% 2 5% 13% 40% 17%	4120
November	1st to 10th	Night	33% 4 12% 18% 22% 11%	2340
	11th to 20th	Night	32% 5% 10% 17% 23% 13%	2400
	21st to end	Night	40% 5% 9% 17% 19% 11%	2400
December	1st to 10th	Night	51% 4 6% 17% 17% 6%	4178
	11th to 20th	Night	44% 4 7% 11% 21% 12%	4817
	21st to end	Night	40% 5% 6% 14% 26% 9%	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	26% 15% 38% 14% 6% 1	300
	11th to 20th	Day	23% 16% 34% 20% 7% 1	300
	21st to end	Day	25% 21% 32% 16% 6%	330
February	1st to 10th	Day	26% 18% 34% 18% 4	300
	11th to 20th	Day	35% 17% 28% 18% 2	300
	21st to end	Day	29% 25% 31% 11% 2	249
March	1st to 10th	Day	28% 21% 30% 16% 5%	300
	11th to 20th	Day	19% 25% 40% 12% 4	300
	21st to end	Day	25% 16% 36% 18% 5%	330
April	1st to 10th	Day	20% 21% 31% 23% 5%	345
	11th to 20th	Day	22% 19% 27% 20% 11% 1	492
	21st to end	Day	17% 12% 31% 26% 12% 1	500
May	1st to 10th	Day	19% 14% 28% 25% 13% 1	503
	11th to 20th	Day	13% 8% 28% 32% 17% 3	639
	21st to end	Day	9% 7% 31% 31% 18% 4	789
June	1st to 10th	Day	7% 3 16% 36% 27% 11%	730
	11th to 20th	Day	8% 3 16% 35% 29% 8%	730
	21st to end	Day	9% 3 13% 28% 29% 18%	730
July	1st to 10th	Day	8% 2 7% 27% 36% 19%	721
	11th to 20th	Day	7% 3 7% 26% 35% 22%	718
	21st to end	Day	9% 2 6% 26% 34% 24%	794
August	1st to 10th	Day	4 1 4 27% 42% 23%	726
	11th to 20th	Day	5% 1 3 16% 45% 30%	528
	21st to end	Day	12% 3 6% 21% 32% 27%	583
September	1st to 10th	Day	10% 2 9% 25% 36% 19%	470
	11th to 20th	Day	12% 2 7% 32% 31% 17%	330
	21st to end	Day	15% 2 11% 29% 33% 10%	330
October	1st to 10th	Day	6% 3 19% 42% 23% 7%	309
	11th to 20th	Day	12% 3 19% 39% 19% 8%	300
	21st to end	Day	19% 8% 25% 30% 14% 5%	330
November	1st to 10th	Day	16% 9% 24% 31% 18% 2	300
	11th to 20th	Day	15% 11% 32% 32% 9% 2	300
	21st to end	Day	21% 18% 30% 20% 9% 2	300
December	1st to 10th	Day	23% 9% 33% 22% 11% 3	300
	11th to 20th	Day	16% 15% 40% 23% 5% 1	300
	21st to end	Day	22% 15% 37% 18% 6% 2	330
January	1st to 10th	Night	24% 10% 31% 27% 8%	1000
	11th to 20th	Night	23% 10% 31% 29% 7%	1000
	21st to end	Night	24% 11% 30% 30% 5%	1100
February	1st to 10th	Night	25% 11% 31% 29% 4	1000
	11th to 20th	Night	30% 9% 30% 25% 5%	719
	21st to end	Night	27% 10% 36% 25% 2	495
March	1st to 10th	Night	26% 10% 30% 31% 4	600
	11th to 20th	Night	22% 10% 35% 28% 6%	600
	21st to end	Night	22% 8% 33% 28% 9%	660
April	1st to 10th	Night	19% 11% 34% 30% 6%	600
	11th to 20th	Night	21% 10% 27% 31% 11%	593
	21st to end	Night	18% 8% 32% 32% 10%	600
May	1st to 10th	Night	17% 9% 28% 38% 9%	600
	11th to 20th	Night	14% 6% 26% 39% 15% 1	591
	21st to end	Night	8% 5% 22% 38% 24% 2	650
June	1st to 10th	Night	6% 2 10% 40% 39% 3	600
	11th to 20th	Night	5% 1 11% 44% 35% 4	600
	21st to end	Night	8% 3 9% 30% 44% 8%	600
July	1st to 10th	Night	6% 2 5% 30% 47% 10%	585
	11th to 20th	Night	3 1 5% 31% 48% 13%	582
	21st to end	Night	5% 1 3 30% 48% 12%	657
August	1st to 10th	Night	3 2 28% 57% 10%	597
	11th to 20th	Night	4 3 23% 56% 15%	594
	21st to end	Night	7% 2 4 25% 50% 12%	660
September	1st to 10th	Night	8% 2 7% 26% 48% 10%	600
	11th to 20th	Night	11% 2 6% 25% 50% 8%	600
	21st to end	Night	9% 1 9% 33% 41% 7%	600
October	1st to 10th	Night	7% 2 12% 35% 39% 5%	753
	11th to 20th	Night	11% 3 19% 40% 23% 3	760
	21st to end	Night	13% 6% 21% 35% 22% 3	836
November	1st to 10th	Night	13% 4 22% 37% 23% 2	780
	11th to 20th	Night	14% 8% 24% 38% 16%	800
	21st to end	Night	18% 8% 30% 30% 13% 1	800
December	1st to 10th	Night	22% 8% 27% 30% 12% 1	954
	11th to 20th	Night	24% 9% 29% 31% 8%	1000
	21st to end	Night	23% 9% 28% 31% 8%	1100

Page generated at 2025-10-01 00:39:09. Version ac07

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