Katy
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Katy clear sky chart from 2005-11-06 to 2025-12-18.

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 6% 8% 41%	127000
	Night	14% 6% 2 5% 4 3 4 3 5% 7% 46%	124287
Transparency	Day	42% 2 11% 21% 16% 8%	130675
	Night	38% 2 11% 21% 18% 9%	128675
Seeing	Day	12% 6% 18% 25% 25% 14%	16283
	Night	15% 5% 21% 34% 23% 3	26165

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% 11% 3 6% 3 4 3 2 3 4 41%	4077
	11th to 20th	Day	17% 6% 2 5% 4 3 3 2 3 5% 51%	4080
	21st to end	Day	31% 8% 3 5% 2 3 2 2 5% 5% 35%	4488
February	1st to 10th	Day	21% 8% 3 6% 5% 4 4 2 4 5% 38%	1940
	11th to 20th	Day	21% 9% 3 7% 4 3 3 3 4 5% 38%	1949
	21st to end	Day	20% 8% 2 6% 4 4 3 3 4 5% 41%	1802
March	1st to 10th	Day	14% 6% 3 7% 5% 5% 5% 4 5% 7% 39%	4936
	11th to 20th	Day	13% 6% 2 7% 5% 4 4 3 4 5% 47%	4980
	21st to end	Day	18% 7% 3 7% 4 4 4 3 5% 5% 40%	5462
April	1st to 10th	Day	14% 8% 3 9% 5% 5% 4 4 5% 5% 38%	2200
	11th to 20th	Day	17% 7% 2 7% 5% 4 4 3 5% 6% 39%	2298
	21st to end	Day	11% 7% 2 8% 5% 5% 5% 4 6% 6% 42%	2400
May	1st to 10th	Day	17% 8% 3 8% 5% 5% 5% 4 6% 7% 33%	5625
	11th to 20th	Day	10% 6% 2 7% 4 5% 5% 4 5% 8% 44%	5862
	21st to end	Day	10% 6% 3 7% 6% 5% 6% 5% 7% 10% 36%	6434
June	1st to 10th	Day	5% 4 2 6% 6% 4 6% 5% 7% 10% 45%	2600
	11th to 20th	Day	6% 4 1 5% 6% 6% 7% 6% 9% 10% 42%	2600
	21st to end	Day	5% 7% 3 8% 8% 8% 7% 6% 9% 10% 30%	2600
July	1st to 10th	Day	8% 5% 2 7% 6% 6% 7% 6% 9% 11% 32%	5900
	11th to 20th	Day	5% 6% 2 7% 6% 7% 7% 6% 10% 13% 30%	5900
	21st to end	Day	10% 7% 3 7% 5% 5% 6% 5% 8% 11% 35%	6422
August	1st to 10th	Day	2 2 1 4 3 4 4 5% 7% 10% 59%	4234
	11th to 20th	Day	3 2 1 4 4 5% 6% 5% 10% 14% 45%	4049
	21st to end	Day	6% 5% 2 7% 7% 5% 6% 6% 7% 10% 38%	4124
September	1st to 10th	Day	6% 6% 3 8% 6% 6% 6% 5% 7% 8% 39%	2200
	11th to 20th	Day	10% 7% 3 7% 6% 6% 6% 4 6% 8% 38%	2200
	21st to end	Day	7% 5% 2 6% 5% 4 5% 5% 7% 9% 47%	2200
October	1st to 10th	Day	6% 4 1 5% 4 4 3 4 6% 7% 57%	2108
	11th to 20th	Day	10% 4 2 6% 3 4 3 3 4 6% 54%	2000
	21st to end	Day	12% 5% 2 5% 4 3 3 3 4 6% 53%	2200
November	1st to 10th	Day	11% 6% 2 6% 4 4 4 3 5% 8% 47%	2058
	11th to 20th	Day	11% 6% 2 6% 4 3 4 4 5% 6% 48%	2100
	21st to end	Day	15% 7% 3 6% 6% 4 4 4 5% 5% 41%	2000
December	1st to 10th	Day	25% 8% 2 6% 4 3 3 2 4 7% 36%	3030
	11th to 20th	Day	14% 8% 3 7% 5% 4 4 3 5% 6% 42%	3454
	21st to end	Day	16% 6% 2 5% 4 4 3 3 4 6% 47%	4488
January	1st to 10th	Night	20% 7% 2 5% 4 4 2 2 4 6% 45%	5888
	11th to 20th	Night	16% 7% 2 4 3 3 3 2 4 5% 50%	5900
	21st to end	Night	30% 8% 2 5% 3 3 3 2 4 6% 35%	6490
February	1st to 10th	Night	20% 9% 4 7% 4 3 3 2 5% 5% 39%	2476
	11th to 20th	Night	21% 8% 3 5% 4 3 3 2 3 5% 44%	2338
	21st to end	Night	21% 8% 2 6% 4 3 4 3 4 5% 41%	1825
March	1st to 10th	Night	19% 9% 2 6% 3 3 4 3 5% 6% 39%	4919
	11th to 20th	Night	18% 8% 2 6% 4 3 3 3 4 5% 45%	4980
	21st to end	Night	19% 9% 2 6% 4 3 3 3 4 5% 42%	5467
April	1st to 10th	Night	14% 8% 3 5% 4 4 4 4 6% 7% 41%	2200
	11th to 20th	Night	16% 7% 3 5% 4 3 3 4 4 6% 44%	2050
	21st to end	Night	14% 7% 2 6% 4 4 4 4 4 7% 44%	2000
May	1st to 10th	Night	23% 9% 3 7% 4 4 4 3 5% 8% 30%	4274
	11th to 20th	Night	10% 6% 2 7% 5% 4 4 4 6% 9% 43%	4053
	21st to end	Night	10% 8% 3 8% 5% 5% 6% 5% 6% 10% 32%	4443
June	1st to 10th	Night	4 4 1 3 3 3 4 4 5% 11% 58%	1800
	11th to 20th	Night	5% 3 1 4 4 3 5% 4 6% 11% 55%	1800
	21st to end	Night	4 5% 2 5% 5% 3 6% 5% 8% 11% 46%	1800
July	1st to 10th	Night	6% 4 2 6% 4 4 5% 5% 9% 13% 42%	4078
	11th to 20th	Night	4 3 2 5% 4 4 6% 5% 7% 11% 49%	4077
	21st to end	Night	7% 5% 2 6% 4 4 5% 5% 6% 9% 46%	4449
August	1st to 10th	Night	1 1 1 3 2 2 2 3 5% 10% 72%	2926
	11th to 20th	Night	2 2 1 3 2 2 5% 3 8% 12% 60%	3002
	21st to end	Night	4 3 2 5% 4 5% 5% 5% 8% 12% 50%	3769
September	1st to 10th	Night	5% 5% 2 6% 5% 4 5% 4 8% 9% 47%	2200
	11th to 20th	Night	10% 5% 2 7% 4 4 5% 3 6% 8% 47%	2200
	21st to end	Night	7% 4 1 5% 3 3 4 3 7% 8% 55%	2200
October	1st to 10th	Night	4 3 1 4 3 3 3 3 4 8% 63%	2270
	11th to 20th	Night	10% 4 1 3 2 3 3 3 4 5% 62%	2400
	21st to end	Night	10% 5% 2 4 2 3 3 2 4 4 61%	2640
November	1st to 10th	Night	10% 6% 2 5% 3 3 3 3 4 6% 54%	2460
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 4 6% 53%	2520
	21st to end	Night	17% 7% 3 5% 3 3 4 3 5% 6% 46%	2615
December	1st to 10th	Night	23% 11% 4 7% 4 3 3 3 4 5% 34%	4380
	11th to 20th	Night	15% 9% 3 6% 4 3 3 3 4 5% 45%	4908
	21st to end	Night	15% 7% 2 5% 3 3 3 3 4 5% 50%	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	51% 1 3 20% 18% 7%	4078
	11th to 20th	Day	39% 1 4 20% 23% 14%	4080
	21st to end	Day	54% 1 2 12% 16% 15%	4488
February	1st to 10th	Day	50% 2 4 14% 17% 13%	1940
	11th to 20th	Day	51% 2 7% 14% 18% 9%	1959
	21st to end	Day	48% 2 7% 17% 16% 10%	1802
March	1st to 10th	Day	46% 1 7% 17% 16% 13%	4936
	11th to 20th	Day	41% 1 6% 11% 20% 21%	4980
	21st to end	Day	48% 1 6% 20% 19% 6%	5464
April	1st to 10th	Day	49% 2 6% 17% 16% 10%	2200
	11th to 20th	Day	46% 2 8% 17% 18% 10%	2298
	21st to end	Day	43% 3 7% 21% 20% 6%	2400
May	1st to 10th	Day	52% 1 9% 22% 12% 3	5660
	11th to 20th	Day	40% 2 10% 24% 21% 3	5866
	21st to end	Day	44% 2 10% 32% 11% 1	6447
June	1st to 10th	Day	34% 4 16% 26% 17% 1	2600
	11th to 20th	Day	35% 5% 14% 27% 17% 2	2600
	21st to end	Day	46% 7% 16% 22% 9% 1	2600
July	1st to 10th	Day	44% 3 31% 19% 3	5836
	11th to 20th	Day	44% 3 26% 22% 5%	5831
	21st to end	Day	44% 4 20% 25% 7% 1	6240
August	1st to 10th	Day	20% 4 15% 43% 17%	4220
	11th to 20th	Day	28% 5% 33% 28% 6% 1	4088
	21st to end	Day	41% 5% 16% 23% 13% 1	4123
September	1st to 10th	Day	40% 6% 15% 18% 16% 5%	2200
	11th to 20th	Day	44% 4 12% 20% 17% 4	2200
	21st to end	Day	34% 3 11% 21% 18% 13%	2200
October	1st to 10th	Day	21% 1 4 16% 20% 38%	3433
	11th to 20th	Day	23% 2 5% 18% 37% 16%	3240
	21st to end	Day	31% 1 3 18% 34% 13%	3538
November	1st to 10th	Day	37% 3 8% 19% 23% 10%	2058
	11th to 20th	Day	37% 3 8% 17% 22% 13%	2100
	21st to end	Day	46% 3 7% 17% 17% 11%	2000
December	1st to 10th	Day	51% 1 5% 18% 20% 5%	3030
	11th to 20th	Day	45% 1 6% 17% 22% 10%	3452
	21st to end	Day	42% 1 4 18% 23% 12%	4488
January	1st to 10th	Night	44% 1 4 21% 20% 10%	5888
	11th to 20th	Night	40% 1 3 20% 24% 12%	5900
	21st to end	Night	54% 1 2 14% 17% 12%	6490
February	1st to 10th	Night	49% 2 5% 13% 18% 14%	2476
	11th to 20th	Night	46% 1 7% 16% 18% 12%	2338
	21st to end	Night	47% 2 6% 15% 17% 12%	1825
March	1st to 10th	Night	49% 1 6% 16% 18% 10%	4919
	11th to 20th	Night	44% 1 6% 14% 17% 18%	4980
	21st to end	Night	47% 1 8% 15% 21% 8%	5467
April	1st to 10th	Night	43% 3 9% 19% 15% 10%	2200
	11th to 20th	Night	41% 2 10% 17% 16% 13%	2050
	21st to end	Night	42% 3 9% 21% 18% 7%	2000
May	1st to 10th	Night	56% 2 8% 21% 10% 4	4304
	11th to 20th	Night	40% 2 12% 24% 17% 5%	4054
	21st to end	Night	48% 2 15% 27% 7% 1	4452
June	1st to 10th	Night	23% 3 20% 35% 19% 1	1800
	11th to 20th	Night	24% 3 19% 32% 17% 4	1800
	21st to end	Night	31% 5% 25% 27% 12% 1	1800
July	1st to 10th	Night	34% 3 37% 22% 3	4035
	11th to 20th	Night	29% 4 29% 32% 6%	4026
	21st to end	Night	35% 6% 21% 30% 8%	4320
August	1st to 10th	Night	12% 2 18% 51% 17%	2916
	11th to 20th	Night	17% 4 37% 35% 6% 1	3029
	21st to end	Night	28% 11% 23% 27% 10% 1	3769
September	1st to 10th	Night	32% 6% 21% 20% 15% 5%	2200
	11th to 20th	Night	36% 4 14% 25% 16% 4	2200
	21st to end	Night	27% 4 15% 24% 18% 12%	2200
October	1st to 10th	Night	17% 1 7% 18% 18% 38%	3712
	11th to 20th	Night	17% 1 5% 24% 33% 19%	3899
	21st to end	Night	22% 1 4 20% 35% 17%	4252
November	1st to 10th	Night	33% 2 10% 22% 23% 10%	2460
	11th to 20th	Night	34% 3 9% 20% 21% 13%	2520
	21st to end	Night	41% 2 8% 20% 18% 11%	2615
December	1st to 10th	Night	56% 1 4 15% 17% 6%	4380
	11th to 20th	Night	44% 1 8% 12% 20% 14%	4909
	21st to end	Night	40% 1 5% 16% 29% 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	22% 13% 33% 25% 5% 2	300
	11th to 20th	Day	21% 14% 28% 27% 9% 1	300
	21st to end	Day	24% 13% 32% 22% 9% 1	330
February	1st to 10th	Day	26% 12% 27% 24% 10% 1	300
	11th to 20th	Day	26% 16% 30% 22% 5% 1	300
	21st to end	Day	24% 13% 38% 18% 6%	249
March	1st to 10th	Day	20% 16% 35% 20% 9%	300
	11th to 20th	Day	15% 14% 45% 20% 4 2	300
	21st to end	Day	19% 12% 35% 21% 12% 1	330
April	1st to 10th	Day	18% 12% 35% 25% 9%	300
	11th to 20th	Day	23% 12% 27% 25% 12% 1	416
	21st to end	Day	16% 9% 30% 30% 13% 2	500
May	1st to 10th	Day	15% 9% 33% 27% 16% 1	593
	11th to 20th	Day	13% 5% 25% 33% 21% 3	725
	21st to end	Day	8% 5% 22% 40% 21% 4	789
June	1st to 10th	Day	6% 2 8% 34% 35% 14%	730
	11th to 20th	Day	8% 2 9% 33% 37% 12%	730
	21st to end	Day	9% 2 7% 23% 36% 24%	730
July	1st to 10th	Day	8% 2 5% 21% 37% 26%	721
	11th to 20th	Day	4 2 3 17% 41% 33%	718
	21st to end	Day	6% 1 3 18% 41% 30%	794
August	1st to 10th	Day	3 1 3 17% 43% 33%	726
	11th to 20th	Day	5% 1 2 15% 41% 36%	645
	21st to end	Day	8% 2 5% 13% 33% 39%	473
September	1st to 10th	Day	9% 2 5% 19% 38% 28%	330
	11th to 20th	Day	8% 1 6% 20% 36% 28%	330
	21st to end	Day	8% 2 6% 22% 41% 21%	330
October	1st to 10th	Day	5% 2 7% 32% 42% 12%	330
	11th to 20th	Day	9% 3 13% 33% 27% 15%	330
	21st to end	Day	18% 6% 21% 22% 26% 7%	363
November	1st to 10th	Day	12% 5% 20% 33% 21% 10%	330
	11th to 20th	Day	13% 5% 23% 35% 20% 4	330
	21st to end	Day	18% 12% 32% 25% 11% 3	330
December	1st to 10th	Day	19% 9% 32% 22% 12% 5%	330
	11th to 20th	Day	21% 13% 26% 27% 10% 2	321
	21st to end	Day	19% 8% 34% 26% 10% 2	330
January	1st to 10th	Night	23% 8% 29% 31% 9%	1000
	11th to 20th	Night	23% 10% 27% 32% 8%	1000
	21st to end	Night	23% 9% 30% 33% 6%	1100
February	1st to 10th	Night	25% 9% 30% 31% 5%	876
	11th to 20th	Night	26% 8% 30% 30% 6%	784
	21st to end	Night	23% 11% 36% 26% 3	505
March	1st to 10th	Night	21% 9% 36% 29% 5%	600
	11th to 20th	Night	21% 9% 32% 32% 7%	600
	21st to end	Night	17% 8% 35% 33% 7% 1	660
April	1st to 10th	Night	17% 8% 34% 36% 5%	600
	11th to 20th	Night	19% 9% 30% 32% 10%	593
	21st to end	Night	18% 8% 32% 32% 10%	600
May	1st to 10th	Night	15% 6% 34% 38% 7%	600
	11th to 20th	Night	12% 4 28% 40% 13% 3	591
	21st to end	Night	8% 4 24% 41% 21% 2	650
June	1st to 10th	Night	5% 2 9% 47% 34% 3	600
	11th to 20th	Night	5% 2 10% 48% 33% 2	600
	21st to end	Night	6% 1 8% 32% 46% 7%	600
July	1st to 10th	Night	6% 4 31% 50% 9%	585
	11th to 20th	Night	4 2 2 25% 59% 8%	582
	21st to end	Night	2 1 3 31% 56% 7%	657
August	1st to 10th	Night	1 1 1 30% 60% 7%	597
	11th to 20th	Night	3 2 28% 59% 8%	594
	21st to end	Night	5% 1 4 22% 58% 11%	660
September	1st to 10th	Night	6% 1 3 28% 52% 9%	600
	11th to 20th	Night	13% 2 4 28% 49% 6%	600
	21st to end	Night	8% 1 8% 32% 45% 6%	600
October	1st to 10th	Night	5% 2 8% 37% 42% 6%	670
	11th to 20th	Night	10% 1 18% 44% 25% 2	800
	21st to end	Night	11% 6% 22% 37% 21% 3	880
November	1st to 10th	Night	12% 4 18% 40% 25% 2	820
	11th to 20th	Night	14% 6% 19% 39% 20% 1	840
	21st to end	Night	19% 6% 28% 33% 13% 1	935
December	1st to 10th	Night	23% 6% 25% 32% 14% 1	1050
	11th to 20th	Night	22% 7% 26% 35% 9% 1	1036
	21st to end	Night	22% 7% 29% 33% 9% 1	1100

Page generated at 2025-12-15 00:13:55. Version ac07

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