Baylor University
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Baylor University clear sky chart from 2005-11-06 to 2024-09-14.

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% 5% 2 5% 4 4 4 3 5% 7% 50%	100529
	Night	11% 5% 2 5% 3 3 3 3 5% 7% 54%	97454
Transparency	Day	34% 5% 11% 23% 20% 7%	100343
	Night	31% 5% 11% 22% 21% 10%	97311
Seeing	Day	12% 6% 21% 28% 24% 8%	14854
	Night	13% 7% 26% 36% 17% 2	24690

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	13% 6% 2 5% 3 2 2 2 4 6% 54%	2847
	11th to 20th	Day	14% 6% 1 3 2 2 2 2 5% 5% 57%	2850
	21st to end	Day	20% 10% 4 6% 2 2 2 2 3 5% 45%	3135
February	1st to 10th	Day	19% 8% 2 6% 3 3 2 3 3 5% 46%	1890
	11th to 20th	Day	16% 8% 4 6% 3 3 3 2 4 5% 46%	1849
	21st to end	Day	20% 6% 2 5% 3 3 3 2 4 4 50%	1594
March	1st to 10th	Day	16% 7% 2 6% 4 3 4 3 5% 6% 43%	3436
	11th to 20th	Day	20% 7% 2 7% 5% 4 4 3 5% 6% 37%	3480
	21st to end	Day	13% 7% 3 6% 4 4 4 3 6% 7% 42%	3814
April	1st to 10th	Day	14% 7% 3 5% 5% 3 4 4 5% 7% 44%	2090
	11th to 20th	Day	14% 8% 3 6% 4 5% 4 3 6% 7% 41%	2121
	21st to end	Day	13% 6% 2 5% 5% 4 3 3 5% 6% 49%	2399
May	1st to 10th	Day	20% 8% 3 7% 4 4 4 3 5% 7% 33%	4082
	11th to 20th	Day	14% 6% 2 6% 4 3 4 3 5% 6% 46%	4082
	21st to end	Day	13% 6% 2 7% 5% 5% 6% 5% 7% 9% 34%	4477
June	1st to 10th	Day	6% 4 1 4 4 4 5% 5% 6% 9% 52%	2470
	11th to 20th	Day	5% 4 1 5% 5% 4 5% 4 6% 9% 52%	2470
	21st to end	Day	6% 3 2 4 4 4 5% 5% 7% 9% 50%	2470
July	1st to 10th	Day	6% 4 1 5% 4 5% 5% 4 6% 8% 53%	4120
	11th to 20th	Day	4 2 1 3 4 4 4 3 6% 9% 59%	4120
	21st to end	Day	8% 7% 2 7% 5% 5% 5% 4 7% 9% 41%	4465
August	1st to 10th	Day	1 1 1 2 2 3 3 5% 8% 73%	4104
	11th to 20th	Day	4 2 1 3 2 2 3 3 5% 9% 66%	4026
	21st to end	Day	4 2 1 4 4 3 5% 4 7% 11% 55%	3932
September	1st to 10th	Day	9% 5% 2 6% 4 5% 6% 3 5% 6% 50%	2090
	11th to 20th	Day	11% 5% 2 6% 4 5% 5% 4 6% 6% 46%	2013
	21st to end	Day	8% 4 1 4 3 4 4 3 5% 6% 57%	1980
October	1st to 10th	Day	6% 3 2 4 3 3 3 3 5% 7% 60%	1961
	11th to 20th	Day	13% 4 1 5% 3 2 3 3 3 5% 58%	1800
	21st to end	Day	13% 4 2 5% 2 2 2 2 3 4 61%	1980
November	1st to 10th	Day	13% 6% 2 5% 3 3 3 3 4 6% 52%	1858
	11th to 20th	Day	8% 6% 2 5% 4 3 3 3 4 6% 55%	1808
	21st to end	Day	18% 6% 2 6% 3 3 3 2 4 6% 47%	1710
December	1st to 10th	Day	15% 5% 2 5% 4 4 3 3 5% 4 51%	1710
	11th to 20th	Day	15% 8% 3 6% 4 3 4 3 4 6% 45%	2161
	21st to end	Day	16% 7% 2 5% 3 3 3 2 4 4 51%	3135
January	1st to 10th	Night	16% 4 1 4 2 3 2 2 3 4 57%	4108
	11th to 20th	Night	13% 5% 1 3 2 2 2 2 3 3 63%	4120
	21st to end	Night	19% 6% 3 7% 3 3 3 2 4 5% 45%	4532
February	1st to 10th	Night	17% 7% 2 5% 3 3 3 3 4 5% 48%	2304
	11th to 20th	Night	18% 6% 2 5% 3 3 2 2 4 5% 49%	2218
	21st to end	Night	18% 6% 2 4 3 2 3 3 4 6% 50%	1859
March	1st to 10th	Night	15% 8% 2 6% 4 4 4 3 6% 6% 42%	3419
	11th to 20th	Night	17% 7% 3 6% 4 4 4 3 5% 7% 40%	3480
	21st to end	Night	13% 5% 3 6% 4 4 4 3 4 6% 47%	3817
April	1st to 10th	Night	10% 5% 1 4 4 4 3 4 5% 7% 52%	2090
	11th to 20th	Night	14% 5% 2 5% 4 3 4 3 5% 6% 48%	2005
	21st to end	Night	12% 5% 1 5% 4 3 3 3 6% 6% 51%	1777
May	1st to 10th	Night	21% 8% 2 6% 4 3 3 3 5% 7% 39%	2823
	11th to 20th	Night	10% 6% 2 7% 4 4 4 4 5% 7% 48%	2823
	21st to end	Night	10% 5% 3 5% 4 5% 5% 4 7% 8% 45%	3090
June	1st to 10th	Night	4 3 1 4 3 3 3 4 6% 11% 59%	1710
	11th to 20th	Night	3 3 1 4 2 3 3 3 6% 10% 62%	1710
	21st to end	Night	4 3 2 5% 4 3 4 4 5% 8% 57%	1710
July	1st to 10th	Night	4 3 1 4 3 3 3 4 6% 9% 60%	2850
	11th to 20th	Night	3 2 1 3 2 2 3 3 6% 10% 65%	2850
	21st to end	Night	6% 5% 2 6% 4 4 5% 4 7% 10% 46%	3098
August	1st to 10th	Night	1 1 1 1 2 2 4 7% 81%	2836
	11th to 20th	Night	3 3 1 3 2 2 3 3 6% 10% 64%	2798
	21st to end	Night	3 2 1 3 2 4 3 4 7% 10% 62%	3721
September	1st to 10th	Night	8% 3 2 5% 3 3 4 3 6% 9% 53%	2090
	11th to 20th	Night	9% 5% 2 6% 4 3 4 3 5% 8% 52%	2024
	21st to end	Night	7% 3 1 4 2 2 3 4 5% 8% 60%	1980
October	1st to 10th	Night	6% 3 1 2 2 3 3 3 5% 6% 66%	1980
	11th to 20th	Night	13% 3 1 4 3 3 3 3 4 5% 59%	2160
	21st to end	Night	15% 4 1 4 2 2 2 2 3 5% 60%	2376
November	1st to 10th	Night	11% 5% 1 5% 3 2 3 2 4 4 60%	2220
	11th to 20th	Night	8% 5% 2 6% 4 3 3 3 5% 5% 57%	2368
	21st to end	Night	18% 5% 2 5% 3 3 3 2 4 6% 50%	2470
December	1st to 10th	Night	14% 6% 1 4 2 2 3 3 5% 6% 54%	2470
	11th to 20th	Night	14% 8% 3 7% 3 3 3 2 4 5% 49%	3036
	21st to end	Night	18% 6% 2 4 2 2 2 2 3 4 54%	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	33% 4 5% 18% 29% 10%	2848
	11th to 20th	Day	30% 3 7% 21% 28% 11%	2850
	21st to end	Day	45% 3 5% 14% 23% 11%	3135
February	1st to 10th	Day	42% 4 5% 15% 21% 13%	1890
	11th to 20th	Day	42% 3 6% 17% 22% 10%	1859
	21st to end	Day	40% 3 5% 16% 19% 17%	1594
March	1st to 10th	Day	42% 4 7% 15% 22% 10%	3436
	11th to 20th	Day	49% 7% 10% 13% 16% 6%	3480
	21st to end	Day	40% 6% 11% 17% 20% 6%	3814
April	1st to 10th	Day	40% 5% 8% 18% 16% 12%	2090
	11th to 20th	Day	42% 5% 8% 15% 21% 9%	2121
	21st to end	Day	36% 5% 9% 19% 24% 7%	2399
May	1st to 10th	Day	50% 6% 10% 19% 11% 5%	4120
	11th to 20th	Day	39% 6% 8% 18% 27% 2	4086
	21st to end	Day	42% 9% 12% 21% 12% 3	4489
June	1st to 10th	Day	27% 8% 14% 28% 20% 3	2470
	11th to 20th	Day	28% 6% 11% 30% 18% 6%	2470
	21st to end	Day	29% 7% 14% 25% 21% 4	2470
July	1st to 10th	Day	29% 5% 21% 35% 9% 1	4056
	11th to 20th	Day	21% 5% 16% 38% 18% 3	4051
	21st to end	Day	37% 7% 15% 29% 12%	4325
August	1st to 10th	Day	11% 3 12% 38% 34% 2	4090
	11th to 20th	Day	16% 5% 19% 40% 18% 2	4065
	21st to end	Day	23% 7% 23% 29% 17% 2	3931
September	1st to 10th	Day	34% 6% 9% 21% 19% 11%	2090
	11th to 20th	Day	37% 8% 11% 18% 18% 8%	2013
	21st to end	Day	27% 4 8% 25% 22% 13%	1980
October	1st to 10th	Day	24% 5% 11% 23% 21% 16%	1961
	11th to 20th	Day	32% 3 6% 15% 26% 18%	1800
	21st to end	Day	30% 3 6% 16% 27% 18%	1980
November	1st to 10th	Day	35% 4 8% 21% 21% 11%	1858
	11th to 20th	Day	31% 5% 9% 18% 25% 13%	1808
	21st to end	Day	40% 4 5% 18% 21% 12%	1710
December	1st to 10th	Day	36% 4 9% 21% 21% 9%	1710
	11th to 20th	Day	41% 4 8% 13% 24% 11%	2159
	21st to end	Day	37% 2 6% 16% 26% 12%	3135
January	1st to 10th	Night	32% 3 5% 17% 30% 14%	4108
	11th to 20th	Night	28% 2 6% 16% 30% 18%	4120
	21st to end	Night	43% 3 5% 14% 23% 12%	4532
February	1st to 10th	Night	40% 3 7% 13% 21% 16%	2304
	11th to 20th	Night	39% 3 6% 15% 23% 13%	2218
	21st to end	Night	38% 3 7% 15% 20% 17%	1859
March	1st to 10th	Night	41% 5% 9% 14% 21% 11%	3419
	11th to 20th	Night	43% 6% 11% 17% 15% 7%	3480
	21st to end	Night	39% 5% 9% 17% 24% 7%	3817
April	1st to 10th	Night	31% 5% 11% 21% 17% 15%	2090
	11th to 20th	Night	36% 6% 10% 16% 18% 14%	2005
	21st to end	Night	33% 6% 11% 17% 25% 8%	1777
May	1st to 10th	Night	45% 5% 10% 19% 15% 6%	2850
	11th to 20th	Night	34% 8% 11% 20% 23% 4	2824
	21st to end	Night	35% 8% 13% 27% 11% 5%	3099
June	1st to 10th	Night	20% 8% 16% 31% 21% 4	1710
	11th to 20th	Night	19% 7% 14% 32% 21% 7%	1710
	21st to end	Night	25% 5% 14% 27% 24% 5%	1710
July	1st to 10th	Night	21% 5% 22% 42% 8% 1	2805
	11th to 20th	Night	16% 4 19% 40% 18% 2	2796
	21st to end	Night	32% 6% 21% 32% 10% 1	2999
August	1st to 10th	Night	5% 4 12% 37% 38% 4	2826
	11th to 20th	Night	17% 3 22% 37% 18% 3	2825
	21st to end	Night	18% 7% 24% 32% 16% 3	3721
September	1st to 10th	Night	28% 7% 13% 22% 19% 11%	2090
	11th to 20th	Night	32% 6% 15% 20% 19% 9%	2024
	21st to end	Night	23% 5% 11% 24% 22% 15%	1980
October	1st to 10th	Night	20% 5% 10% 26% 20% 19%	1980
	11th to 20th	Night	28% 4 7% 16% 24% 21%	2160
	21st to end	Night	30% 3 5% 17% 23% 23%	2376
November	1st to 10th	Night	29% 5% 7% 20% 25% 14%	2220
	11th to 20th	Night	30% 4 7% 19% 25% 15%	2368
	21st to end	Night	37% 4 8% 15% 22% 14%	2470
December	1st to 10th	Night	32% 4 8% 23% 21% 11%	2470
	11th to 20th	Night	40% 3 5% 13% 25% 14%	3037
	21st to end	Night	36% 2 5% 14% 28% 14%	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	19% 11% 37% 22% 10% 1	270
	11th to 20th	Day	21% 10% 34% 25% 8% 1	270
	21st to end	Day	20% 11% 38% 21% 10%	297
February	1st to 10th	Day	27% 14% 30% 20% 9%	270
	11th to 20th	Day	26% 11% 39% 20% 4	270
	21st to end	Day	25% 13% 41% 19% 2	225
March	1st to 10th	Day	21% 15% 37% 21% 6%	270
	11th to 20th	Day	20% 18% 35% 20% 6% 1	270
	21st to end	Day	15% 10% 47% 21% 6% 1	297
April	1st to 10th	Day	21% 17% 37% 19% 4	270
	11th to 20th	Day	18% 14% 35% 23% 9% 1	319
	21st to end	Day	17% 11% 36% 26% 8% 1	579
May	1st to 10th	Day	15% 12% 34% 30% 9% 1	653
	11th to 20th	Day	15% 7% 27% 32% 17% 3	675
	21st to end	Day	13% 6% 26% 31% 19% 4	734
June	1st to 10th	Day	5% 2 16% 40% 27% 10%	680
	11th to 20th	Day	6% 1 18% 42% 27% 7%	680
	21st to end	Day	5% 2 11% 34% 36% 12%	680
July	1st to 10th	Day	7% 1 7% 31% 39% 14%	671
	11th to 20th	Day	2 4 33% 47% 13%	668
	21st to end	Day	4 1 5% 32% 44% 16%	739
August	1st to 10th	Day	3 3 28% 48% 18%	676
	11th to 20th	Day	6% 1 3 29% 47% 15%	663
	21st to end	Day	6% 1 3 19% 38% 32%	395
September	1st to 10th	Day	8% 6% 21% 37% 28%	300
	11th to 20th	Day	5% 1 6% 21% 44% 23%	279
	21st to end	Day	11% 1 5% 26% 37% 20%	270
October	1st to 10th	Day	4 2 13% 29% 40% 12%	270
	11th to 20th	Day	12% 6% 22% 29% 24% 7%	270
	21st to end	Day	21% 12% 23% 21% 19% 5%	297
November	1st to 10th	Day	18% 6% 29% 29% 12% 6%	270
	11th to 20th	Day	16% 8% 25% 31% 19% 2	270
	21st to end	Day	17% 16% 30% 26% 10% 2	270
December	1st to 10th	Day	15% 7% 32% 27% 13% 5%	270
	11th to 20th	Day	19% 16% 32% 24% 8% 1	270
	21st to end	Day	21% 6% 40% 24% 9% 1	297
January	1st to 10th	Night	17% 10% 35% 30% 8%	950
	11th to 20th	Night	21% 11% 31% 30% 6% 1	950
	21st to end	Night	17% 10% 33% 34% 6%	1045
February	1st to 10th	Night	21% 12% 34% 28% 6%	784
	11th to 20th	Night	21% 11% 38% 27% 3	744
	21st to end	Night	20% 14% 43% 20% 2	603
March	1st to 10th	Night	19% 13% 36% 27% 5%	570
	11th to 20th	Night	15% 10% 40% 31% 5%	570
	21st to end	Night	12% 14% 43% 28% 4	627
April	1st to 10th	Night	11% 10% 44% 31% 4	570
	11th to 20th	Night	15% 12% 38% 27% 7%	563
	21st to end	Night	14% 9% 41% 27% 9%	570
May	1st to 10th	Night	11% 8% 42% 32% 6% 1	570
	11th to 20th	Night	11% 7% 34% 35% 13% 1	561
	21st to end	Night	10% 3 28% 42% 15% 2	617
June	1st to 10th	Night	4 3 18% 45% 28% 2	570
	11th to 20th	Night	5% 1 24% 51% 18% 1	570
	21st to end	Night	3 2 15% 43% 33% 4	570
July	1st to 10th	Night	5% 1 11% 44% 36% 3	555
	11th to 20th	Night	3 7% 52% 35% 3	552
	21st to end	Night	2 1 6% 50% 39% 2	624
August	1st to 10th	Night	2 4 50% 39% 4	567
	11th to 20th	Night	7% 1 5% 46% 36% 5%	564
	21st to end	Night	4 1 6% 39% 45% 6%	627
September	1st to 10th	Night	9% 1 6% 39% 39% 5%	570
	11th to 20th	Night	10% 1 6% 41% 39% 3	552
	21st to end	Night	8% 1 10% 38% 37% 6%	540
October	1st to 10th	Night	7% 1 13% 48% 25% 6%	540
	11th to 20th	Night	14% 4 22% 38% 20% 2	720
	21st to end	Night	14% 8% 28% 32% 17% 1	792
November	1st to 10th	Night	13% 3 26% 39% 18% 1	740
	11th to 20th	Night	9% 8% 28% 40% 14% 1	848
	21st to end	Night	20% 9% 29% 31% 10% 1	950
December	1st to 10th	Night	17% 7% 31% 35% 9% 1	950
	11th to 20th	Night	22% 8% 29% 33% 8%	950
	21st to end	Night	20% 8% 34% 30% 8%	1045

Page generated at 2024-09-11 09:00:06. Version ac07

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