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 2024-11-11.

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% 40%	101071
	Night	13% 6% 2 5% 4 3 4 3 5% 7% 46%	98182
Transparency	Day	41% 3 11% 21% 17% 7%	104785
	Night	37% 3 12% 22% 18% 9%	102595
Seeing	Day	12% 6% 17% 25% 26% 14%	14841
	Night	15% 5% 21% 34% 23% 3	24695

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	18% 10% 2 5% 2 4 4 2 4 5% 43%	2847
	11th to 20th	Day	17% 7% 2 4 3 2 2 2 3 5% 52%	2850
	21st to end	Day	24% 8% 3 6% 3 3 3 2 6% 7% 35%	3135
February	1st to 10th	Day	22% 9% 3 6% 5% 4 4 2 4 5% 38%	1843
	11th to 20th	Day	20% 9% 3 7% 4 3 3 3 4 6% 38%	1849
	21st to end	Day	20% 8% 2 6% 4 4 3 3 4 5% 41%	1714
March	1st to 10th	Day	17% 7% 3 8% 6% 5% 6% 4 5% 7% 32%	3436
	11th to 20th	Day	19% 9% 3 9% 6% 5% 5% 4 5% 6% 30%	3480
	21st to end	Day	17% 6% 2 6% 4 4 4 3 6% 6% 42%	3814
April	1st to 10th	Day	14% 8% 3 9% 5% 5% 4 4 5% 5% 38%	2090
	11th to 20th	Day	18% 7% 2 7% 5% 4 4 3 5% 6% 39%	2182
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 4 6% 6% 43%	2280
May	1st to 10th	Day	16% 8% 3 9% 6% 5% 5% 4 6% 7% 32%	3915
	11th to 20th	Day	13% 7% 2 7% 5% 5% 4 4 5% 7% 40%	4082
	21st to end	Day	8% 6% 3 7% 6% 5% 6% 5% 7% 10% 36%	4477
June	1st to 10th	Day	5% 4 2 6% 6% 4 6% 5% 7% 10% 45%	2470
	11th to 20th	Day	5% 4 1 4 6% 6% 6% 6% 8% 9% 43%	2470
	21st to end	Day	6% 7% 3 8% 8% 8% 7% 7% 9% 10% 30%	2470
July	1st to 10th	Day	10% 4 2 5% 5% 5% 6% 6% 10% 11% 36%	4120
	11th to 20th	Day	6% 6% 3 8% 7% 7% 7% 6% 10% 11% 29%	4120
	21st to end	Day	14% 9% 3 8% 5% 5% 6% 5% 8% 10% 26%	4465
August	1st to 10th	Day	2 1 1 4 3 4 4 5% 7% 10% 60%	4104
	11th to 20th	Day	3 2 1 4 4 5% 6% 5% 10% 14% 46%	3923
	21st to end	Day	6% 5% 2 7% 7% 5% 6% 6% 7% 10% 38%	3998
September	1st to 10th	Day	6% 6% 3 8% 6% 6% 6% 5% 8% 8% 38%	2090
	11th to 20th	Day	10% 7% 3 7% 6% 6% 6% 4 6% 8% 36%	2090
	21st to end	Day	7% 5% 2 6% 5% 4 5% 5% 7% 9% 46%	2090
October	1st to 10th	Day	6% 4 1 5% 4 4 4 4 6% 7% 56%	2003
	11th to 20th	Day	10% 4 2 6% 4 4 4 3 4 6% 53%	1900
	21st to end	Day	12% 5% 2 5% 4 3 3 3 4 6% 53%	2090
November	1st to 10th	Day	12% 6% 3 6% 4 4 4 3 5% 8% 45%	1958
	11th to 20th	Day	12% 6% 2 6% 4 3 4 4 5% 6% 47%	1900
	21st to end	Day	16% 7% 3 6% 5% 4 4 4 5% 5% 41%	1810
December	1st to 10th	Day	16% 9% 3 6% 6% 4 3 3 4 7% 39%	1710
	11th to 20th	Day	15% 8% 3 6% 5% 5% 4 3 5% 5% 42%	2161
	21st to end	Day	16% 7% 3 6% 4 4 3 3 4 6% 45%	3135
January	1st to 10th	Night	19% 7% 2 5% 3 4 2 2 5% 6% 44%	4108
	11th to 20th	Night	19% 7% 2 4 3 2 2 2 3 5% 52%	4120
	21st to end	Night	23% 8% 3 5% 4 3 3 3 5% 7% 37%	4532
February	1st to 10th	Night	19% 9% 4 7% 4 3 3 2 5% 5% 39%	2353
	11th to 20th	Night	20% 8% 3 4 4 3 3 2 3 6% 45%	2218
	21st to end	Night	20% 9% 2 6% 4 3 3 3 4 5% 41%	1737
March	1st to 10th	Night	23% 11% 3 6% 4 3 4 3 6% 6% 32%	3419
	11th to 20th	Night	23% 9% 3 8% 5% 4 4 4 5% 6% 30%	3480
	21st to end	Night	13% 7% 2 6% 5% 4 4 3 4 6% 46%	3817
April	1st to 10th	Night	14% 8% 3 5% 4 4 4 4 7% 7% 40%	2090
	11th to 20th	Night	16% 7% 3 5% 4 3 3 4 4 6% 43%	1946
	21st to end	Night	14% 7% 2 6% 4 4 4 4 4 7% 44%	1900
May	1st to 10th	Night	22% 9% 3 7% 4 4 4 3 5% 7% 31%	2979
	11th to 20th	Night	13% 7% 3 7% 5% 4 4 4 5% 8% 42%	2823
	21st to end	Night	10% 7% 3 6% 4 5% 5% 5% 6% 11% 37%	3090
June	1st to 10th	Night	4 4 1 3 3 3 4 3 5% 10% 59%	1710
	11th to 20th	Night	5% 3 1 3 4 3 5% 4 5% 11% 55%	1710
	21st to end	Night	4 5% 2 5% 5% 3 6% 5% 8% 11% 46%	1710
July	1st to 10th	Night	6% 3 1 5% 4 3 4 4 8% 12% 50%	2850
	11th to 20th	Night	4 4 2 6% 5% 4 6% 5% 7% 11% 45%	2850
	21st to end	Night	9% 7% 3 7% 5% 5% 5% 5% 7% 9% 38%	3098
August	1st to 10th	Night	1 1 1 2 2 2 2 3 5% 10% 72%	2836
	11th to 20th	Night	2 2 1 3 2 3 5% 3 8% 12% 60%	2908
	21st to end	Night	4 3 2 5% 4 5% 5% 5% 8% 12% 50%	3654
September	1st to 10th	Night	5% 5% 2 6% 5% 4 5% 4 8% 9% 47%	2090
	11th to 20th	Night	11% 5% 2 7% 4 4 5% 3 6% 8% 46%	2090
	21st to end	Night	7% 4 1 5% 3 3 4 3 7% 9% 54%	2090
October	1st to 10th	Night	4 3 1 4 3 3 3 3 4 8% 63%	2156
	11th to 20th	Night	10% 4 1 3 2 3 4 3 4 5% 61%	2280
	21st to end	Night	10% 5% 2 4 3 3 3 2 4 4 61%	2508
November	1st to 10th	Night	11% 6% 2 5% 3 4 4 3 5% 6% 52%	2340
	11th to 20th	Night	13% 6% 2 5% 3 4 4 3 5% 6% 50%	2287
	21st to end	Night	17% 7% 3 5% 3 3 4 3 5% 6% 46%	2365
December	1st to 10th	Night	18% 8% 3 5% 4 3 3 3 5% 6% 42%	2470
	11th to 20th	Night	16% 9% 3 6% 4 4 4 3 5% 5% 41%	3036
	21st to end	Night	16% 7% 2 6% 4 3 3 3 4 5% 46%	4532

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% 1 4 18% 21% 10%	2848
	11th to 20th	Day	37% 1 5% 22% 24% 11%	2850
	21st to end	Day	51% 1 3 15% 19% 11%	3135
February	1st to 10th	Day	51% 2 4 14% 16% 12%	1843
	11th to 20th	Day	50% 2 7% 13% 19% 10%	1859
	21st to end	Day	48% 2 7% 17% 16% 11%	1714
March	1st to 10th	Day	54% 1 9% 16% 16% 4	3436
	11th to 20th	Day	56% 2 8% 13% 16% 6%	3480
	21st to end	Day	44% 1 7% 20% 22% 6%	3814
April	1st to 10th	Day	49% 2 6% 18% 16% 9%	2090
	11th to 20th	Day	47% 2 8% 17% 18% 9%	2182
	21st to end	Day	42% 3 7% 21% 21% 7%	2280
May	1st to 10th	Day	52% 2 10% 20% 11% 5%	3950
	11th to 20th	Day	45% 2 8% 19% 22% 4	4086
	21st to end	Day	43% 3 10% 33% 11% 1	4489
June	1st to 10th	Day	34% 4 16% 26% 17% 2	2470
	11th to 20th	Day	34% 5% 14% 27% 17% 3	2470
	21st to end	Day	46% 7% 15% 23% 9% 1	2470
July	1st to 10th	Day	39% 4 30% 23% 4	4056
	11th to 20th	Day	47% 4 20% 21% 8%	4051
	21st to end	Day	52% 5% 19% 20% 3 1	4325
August	1st to 10th	Day	20% 4 15% 43% 18%	4090
	11th to 20th	Day	28% 5% 33% 28% 6% 1	3962
	21st to end	Day	41% 5% 16% 23% 13% 1	3997
September	1st to 10th	Day	41% 6% 15% 18% 15% 5%	2090
	11th to 20th	Day	46% 4 12% 18% 17% 4	2090
	21st to end	Day	35% 3 12% 20% 18% 12%	2090
October	1st to 10th	Day	21% 2 4 16% 18% 39%	3328
	11th to 20th	Day	23% 2 5% 17% 36% 16%	3140
	21st to end	Day	31% 1 3 18% 34% 13%	3428
November	1st to 10th	Day	38% 3 8% 19% 22% 9%	1958
	11th to 20th	Day	39% 3 8% 16% 22% 12%	1900
	21st to end	Day	46% 3 6% 17% 17% 12%	1810
December	1st to 10th	Day	46% 2 7% 20% 18% 7%	1710
	11th to 20th	Day	46% 1 6% 15% 23% 10%	2159
	21st to end	Day	42% 2 5% 18% 22% 12%	3135
January	1st to 10th	Night	44% 1 5% 18% 18% 14%	4108
	11th to 20th	Night	40% 1 3 18% 26% 12%	4120
	21st to end	Night	50% 1 3 17% 19% 10%	4532
February	1st to 10th	Night	49% 2 5% 13% 17% 14%	2353
	11th to 20th	Night	44% 2 7% 16% 18% 13%	2218
	21st to end	Night	47% 2 6% 15% 17% 13%	1737
March	1st to 10th	Night	55% 1 8% 17% 14% 5%	3419
	11th to 20th	Night	57% 1 8% 15% 13% 5%	3480
	21st to end	Night	42% 2 10% 14% 25% 8%	3817
April	1st to 10th	Night	43% 3 9% 19% 15% 10%	2090
	11th to 20th	Night	42% 2 10% 16% 16% 13%	1946
	21st to end	Night	42% 3 8% 22% 18% 8%	1900
May	1st to 10th	Night	55% 2 9% 19% 10% 5%	3009
	11th to 20th	Night	42% 3 10% 19% 18% 7%	2824
	21st to end	Night	41% 3 17% 31% 7% 1	3099
June	1st to 10th	Night	22% 3 20% 34% 20% 1	1710
	11th to 20th	Night	24% 3 19% 33% 17% 4	1710
	21st to end	Night	31% 5% 23% 28% 12% 1	1710
July	1st to 10th	Night	29% 4 37% 27% 4	2805
	11th to 20th	Night	32% 5% 27% 28% 9%	2796
	21st to end	Night	41% 7% 22% 25% 4	2999
August	1st to 10th	Night	11% 2 19% 50% 17%	2826
	11th to 20th	Night	17% 4 37% 35% 6% 1	2935
	21st to end	Night	27% 11% 23% 28% 10% 1	3654
September	1st to 10th	Night	32% 6% 22% 20% 16% 4	2090
	11th to 20th	Night	37% 4 14% 24% 16% 4	2090
	21st to end	Night	27% 4 15% 23% 19% 12%	2090
October	1st to 10th	Night	17% 1 7% 18% 17% 39%	3598
	11th to 20th	Night	17% 1 5% 24% 33% 20%	3779
	21st to end	Night	22% 1 4 20% 36% 17%	4120
November	1st to 10th	Night	34% 2 10% 22% 22% 9%	2340
	11th to 20th	Night	36% 3 9% 20% 20% 12%	2287
	21st to end	Night	41% 2 8% 20% 18% 11%	2365
December	1st to 10th	Night	45% 2 7% 21% 15% 10%	2470
	11th to 20th	Night	46% 2 6% 12% 19% 14%	3037
	21st to end	Night	42% 2 6% 15% 27% 8%	4532

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% 11% 34% 26% 6% 3	270
	11th to 20th	Day	20% 12% 27% 29% 10% 1	270
	21st to end	Day	21% 14% 33% 23% 9% 1	297
February	1st to 10th	Day	27% 13% 29% 23% 9% 1	270
	11th to 20th	Day	24% 15% 31% 23% 5% 1	270
	21st to end	Day	23% 14% 40% 19% 4	225
March	1st to 10th	Day	21% 14% 35% 20% 10%	270
	11th to 20th	Day	17% 11% 44% 21% 4 3	270
	21st to end	Day	19% 13% 34% 22% 11% 1	297
April	1st to 10th	Day	18% 11% 37% 26% 9%	270
	11th to 20th	Day	24% 11% 28% 24% 12% 1	380
	21st to end	Day	14% 9% 30% 30% 14% 2	460
May	1st to 10th	Day	14% 9% 32% 28% 17% 1	548
	11th to 20th	Day	13% 4 24% 34% 22% 3	675
	21st to end	Day	8% 4 21% 39% 22% 5%	734
June	1st to 10th	Day	6% 2 8% 33% 36% 15%	680
	11th to 20th	Day	7% 1 8% 33% 37% 13%	680
	21st to end	Day	9% 1 8% 22% 36% 23%	680
July	1st to 10th	Day	7% 2 5% 22% 37% 28%	671
	11th to 20th	Day	5% 1 3 15% 40% 35%	668
	21st to end	Day	6% 1 4 18% 40% 31%	739
August	1st to 10th	Day	4 3 17% 42% 34%	676
	11th to 20th	Day	6% 1 2 15% 41% 36%	599
	21st to end	Day	8% 2 5% 13% 32% 40%	435
September	1st to 10th	Day	9% 2 5% 17% 38% 30%	300
	11th to 20th	Day	9% 1 6% 20% 35% 29%	300
	21st to end	Day	9% 2 5% 21% 41% 22%	300
October	1st to 10th	Day	6% 2 8% 32% 42% 11%	300
	11th to 20th	Day	9% 3 13% 34% 26% 15%	300
	21st to end	Day	19% 6% 22% 19% 25% 8%	330
November	1st to 10th	Day	12% 5% 19% 33% 21% 9%	300
	11th to 20th	Day	14% 6% 22% 35% 18% 4	270
	21st to end	Day	19% 13% 29% 26% 10% 4	270
December	1st to 10th	Day	16% 9% 29% 25% 15% 6%	270
	11th to 20th	Day	21% 15% 27% 28% 7% 2	270
	21st to end	Day	19% 8% 35% 26% 9% 2	297
January	1st to 10th	Night	22% 8% 29% 32% 9%	950
	11th to 20th	Night	23% 9% 26% 33% 8%	950
	21st to end	Night	21% 9% 30% 34% 7%	1045
February	1st to 10th	Night	24% 9% 30% 30% 6%	833
	11th to 20th	Night	25% 8% 30% 31% 6%	744
	21st to end	Night	23% 12% 37% 25% 3	481
March	1st to 10th	Night	22% 8% 36% 29% 5%	570
	11th to 20th	Night	21% 8% 31% 33% 7%	570
	21st to end	Night	16% 8% 35% 33% 7% 1	627
April	1st to 10th	Night	16% 8% 35% 36% 5%	570
	11th to 20th	Night	20% 9% 30% 31% 10%	563
	21st to end	Night	18% 7% 32% 32% 10%	570
May	1st to 10th	Night	15% 6% 33% 38% 7%	570
	11th to 20th	Night	12% 4 27% 41% 14% 3	561
	21st to end	Night	8% 4 23% 41% 22% 2	617
June	1st to 10th	Night	5% 1 9% 46% 35% 3	570
	11th to 20th	Night	5% 1 9% 48% 34% 2	570
	21st to end	Night	6% 1 8% 32% 45% 7%	570
July	1st to 10th	Night	6% 4 31% 50% 9%	555
	11th to 20th	Night	4 2 2 24% 59% 9%	552
	21st to end	Night	2 1 3 30% 56% 8%	624
August	1st to 10th	Night	1 1 1 30% 60% 7%	567
	11th to 20th	Night	3 2 28% 59% 8%	564
	21st to end	Night	4 1 4 22% 58% 10%	627
September	1st to 10th	Night	6% 1 3 27% 53% 9%	570
	11th to 20th	Night	13% 2 4 27% 49% 6%	570
	21st to end	Night	8% 8% 32% 44% 6%	570
October	1st to 10th	Night	5% 2 8% 36% 42% 6%	636
	11th to 20th	Night	11% 1 18% 44% 24% 2	760
	21st to end	Night	11% 6% 22% 37% 21% 3	836
November	1st to 10th	Night	13% 3 18% 40% 24% 2	780
	11th to 20th	Night	15% 7% 19% 38% 20% 1	763
	21st to end	Night	20% 5% 27% 33% 13% 2	845
December	1st to 10th	Night	21% 6% 25% 32% 15% 1	950
	11th to 20th	Night	22% 8% 26% 35% 9% 1	950
	21st to end	Night	22% 7% 29% 32% 9% 1	1045

Page generated at 2024-11-08 05:44:48. Version ac07

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