Lyndon B. Johnson National Grasslands
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lyndon B. Johnson National Grasslands clear sky chart from 2005-11-06 to 2024-11-04.

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	10% 5% 2 5% 3 3 4 3 5% 7% 54%	101111
	Night	9% 5% 2 4 3 3 3 3 4 7% 58%	98007
Transparency	Day	29% 5% 9% 25% 24% 8%	104880
	Night	26% 4 8% 24% 27% 11%	102365
Seeing	Day	11% 7% 24% 30% 22% 6%	15189
	Night	10% 8% 31% 35% 15% 1	25044

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	10% 6% 2 5% 3 3 3 2 4 6% 56%	2847
	11th to 20th	Day	8% 5% 2 3 2 2 3 2 3 5% 66%	2850
	21st to end	Day	19% 8% 3 6% 3 3 2 2 3 4 48%	3135
February	1st to 10th	Day	14% 7% 2 5% 3 3 3 2 4 6% 50%	1866
	11th to 20th	Day	14% 6% 2 5% 3 5% 3 3 4 5% 50%	1849
	21st to end	Day	18% 8% 3 4 3 2 3 1 3 3 54%	1570
March	1st to 10th	Day	15% 5% 1 4 2 3 3 3 5% 6% 53%	3397
	11th to 20th	Day	13% 6% 2 6% 4 3 3 3 5% 6% 48%	3480
	21st to end	Day	11% 7% 2 6% 4 3 4 4 7% 7% 44%	3814
April	1st to 10th	Day	10% 5% 2 5% 4 3 4 3 4 5% 54%	2090
	11th to 20th	Day	12% 5% 2 7% 3 4 3 3 5% 6% 50%	2161
	21st to end	Day	11% 5% 2 5% 4 4 4 4 5% 6% 51%	2470
May	1st to 10th	Day	15% 7% 3 6% 4 4 4 4 4 6% 43%	4082
	11th to 20th	Day	13% 6% 2 5% 3 3 4 3 5% 7% 48%	4082
	21st to end	Day	13% 7% 2 7% 4 5% 4 4 6% 7% 39%	4477
June	1st to 10th	Day	6% 4 2 5% 4 4 4 5% 7% 9% 52%	2470
	11th to 20th	Day	5% 4 1 4 4 4 5% 4 7% 8% 54%	2470
	21st to end	Day	5% 4 2 3 4 4 4 3 6% 9% 56%	2470
July	1st to 10th	Day	5% 4 1 5% 4 3 4 4 5% 9% 55%	4120
	11th to 20th	Day	3 2 1 3 3 4 4 3 6% 9% 62%	4120
	21st to end	Day	4 4 2 5% 4 5% 5% 4 7% 9% 51%	4465
August	1st to 10th	Day	2 2 1 3 3 4 4 3 5% 8% 66%	4104
	11th to 20th	Day	4 2 1 3 3 4 4 4 6% 9% 59%	4041
	21st to end	Day	3 2 1 4 3 4 4 5% 6% 9% 60%	4040
September	1st to 10th	Day	9% 4 2 5% 4 4 4 3 4 7% 55%	2090
	11th to 20th	Day	10% 5% 2 5% 4 5% 5% 4 6% 6% 48%	2090
	21st to end	Day	7% 3 1 5% 3 3 3 3 5% 7% 59%	2090
October	1st to 10th	Day	5% 3 1 4 3 3 3 3 5% 6% 63%	2080
	11th to 20th	Day	10% 3 2 4 2 2 2 2 4 5% 65%	1900
	21st to end	Day	13% 5% 1 3 2 2 3 2 2 3 63%	2090
November	1st to 10th	Day	11% 5% 2 4 3 3 3 2 3 6% 60%	1875
	11th to 20th	Day	6% 4 1 3 2 3 3 3 4 6% 65%	1710
	21st to end	Day	14% 5% 2 4 2 3 3 3 4 4 57%	1710
December	1st to 10th	Day	11% 6% 1 6% 3 3 3 4 5% 6% 52%	1710
	11th to 20th	Day	12% 8% 2 6% 5% 3 3 3 3 5% 49%	2161
	21st to end	Day	17% 5% 1 5% 2 3 4 3 4 5% 51%	3135
January	1st to 10th	Night	12% 4 2 4 2 2 3 3 5% 6% 57%	4108
	11th to 20th	Night	8% 5% 2 3 2 2 2 2 3 5% 66%	4120
	21st to end	Night	16% 8% 3 5% 3 3 2 2 3 4 50%	4532
February	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 4 5% 54%	2328
	11th to 20th	Night	13% 6% 2 4 3 3 4 3 4 6% 53%	2218
	21st to end	Night	14% 6% 2 4 3 3 2 2 3 4 56%	1884
March	1st to 10th	Night	11% 7% 2 6% 4 3 4 3 5% 6% 49%	3457
	11th to 20th	Night	11% 5% 2 4 3 3 3 3 5% 7% 54%	3480
	21st to end	Night	10% 6% 2 7% 4 3 4 3 4 6% 51%	3817
April	1st to 10th	Night	8% 5% 2 4 3 3 4 4 6% 7% 54%	2090
	11th to 20th	Night	10% 6% 3 5% 3 3 3 3 4 8% 53%	1962
	21st to end	Night	11% 4 1 5% 3 3 3 3 5% 7% 55%	1710
May	1st to 10th	Night	18% 8% 2 5% 4 3 4 3 4 5% 45%	2823
	11th to 20th	Night	11% 6% 3 5% 4 4 3 3 4 6% 51%	2823
	21st to end	Night	10% 5% 2 4 3 3 4 4 6% 8% 51%	3090
June	1st to 10th	Night	3 3 1 4 3 3 4 4 7% 10% 58%	1710
	11th to 20th	Night	3 2 1 3 2 3 4 4 5% 10% 63%	1710
	21st to end	Night	2 2 1 3 2 3 2 3 6% 8% 67%	1710
July	1st to 10th	Night	4 4 1 3 3 3 3 4 5% 10% 60%	2850
	11th to 20th	Night	2 1 1 2 2 2 3 2 4 9% 71%	2850
	21st to end	Night	3 3 1 3 3 4 3 3 5% 9% 62%	3098
August	1st to 10th	Night	2 1 2 2 2 3 2 5% 8% 73%	2836
	11th to 20th	Night	3 2 1 3 2 2 2 3 5% 10% 69%	2798
	21st to end	Night	2 2 1 3 2 3 3 3 5% 9% 67%	3615
September	1st to 10th	Night	6% 4 2 6% 4 3 3 3 4 7% 58%	2090
	11th to 20th	Night	9% 6% 2 6% 4 5% 3 3 5% 7% 52%	2090
	21st to end	Night	6% 2 1 2 2 3 3 4 5% 6% 64%	2090
October	1st to 10th	Night	5% 3 1 3 3 3 3 3 4 8% 65%	2090
	11th to 20th	Night	9% 3 2 3 2 2 2 2 3 4 66%	2270
	21st to end	Night	13% 4 1 3 2 2 2 2 3 4 64%	2508
November	1st to 10th	Night	10% 3 1 4 3 2 3 2 3 5% 63%	2272
	11th to 20th	Night	5% 4 1 4 2 3 3 3 5% 5% 64%	2470
	21st to end	Night	14% 5% 1 4 3 3 3 3 4 5% 55%	2470
December	1st to 10th	Night	11% 5% 2 4 2 3 3 3 4 6% 57%	2470
	11th to 20th	Night	11% 7% 2 5% 3 3 3 3 4 5% 53%	3036
	21st to end	Night	15% 6% 2 5% 2 2 2 2 3 5% 55%	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	31% 3 6% 20% 32% 7%	2848
	11th to 20th	Day	24% 2 8% 23% 35% 8%	2850
	21st to end	Day	43% 3 3 21% 23% 8%	3135
February	1st to 10th	Day	36% 4 6% 21% 24% 9%	1866
	11th to 20th	Day	38% 3 6% 20% 22% 10%	1859
	21st to end	Day	38% 2 3 14% 27% 15%	1570
March	1st to 10th	Day	32% 4 6% 16% 29% 13%	3397
	11th to 20th	Day	37% 6% 12% 24% 17% 4	3480
	21st to end	Day	36% 6% 11% 23% 18% 6%	3814
April	1st to 10th	Day	33% 4 8% 23% 19% 12%	2090
	11th to 20th	Day	35% 5% 9% 20% 20% 12%	2161
	21st to end	Day	33% 5% 9% 24% 24% 5%	2470
May	1st to 10th	Day	41% 5% 8% 21% 15% 9%	4120
	11th to 20th	Day	36% 5% 10% 25% 23% 1	4086
	21st to end	Day	41% 8% 12% 19% 14% 7%	4489
June	1st to 10th	Day	27% 6% 17% 29% 18% 3	2470
	11th to 20th	Day	25% 8% 12% 29% 22% 5%	2470
	21st to end	Day	24% 6% 11% 27% 26% 5%	2470
July	1st to 10th	Day	27% 6% 11% 39% 16% 2	4056
	11th to 20th	Day	18% 5% 10% 39% 26% 3	4051
	21st to end	Day	27% 6% 11% 35% 21% 1	4325
August	1st to 10th	Day	17% 5% 10% 26% 34% 8%	4090
	11th to 20th	Day	20% 4 13% 37% 23% 3	4080
	21st to end	Day	20% 5% 15% 38% 18% 3	4039
September	1st to 10th	Day	30% 5% 9% 21% 25% 11%	2090
	11th to 20th	Day	35% 7% 9% 19% 23% 7%	2090
	21st to end	Day	25% 5% 7% 23% 28% 12%	2090
October	1st to 10th	Day	14% 3 6% 14% 36% 27%	3457
	11th to 20th	Day	17% 2 5% 21% 40% 16%	3140
	21st to end	Day	22% 2 4 30% 30% 12%	3428
November	1st to 10th	Day	29% 3 8% 21% 27% 12%	1875
	11th to 20th	Day	21% 4 9% 22% 31% 13%	1710
	21st to end	Day	32% 3 5% 21% 27% 12%	1710
December	1st to 10th	Day	33% 4 7% 25% 24% 7%	1710
	11th to 20th	Day	39% 3 6% 16% 26% 11%	2159
	21st to end	Day	36% 4 4 23% 24% 9%	3135
January	1st to 10th	Night	28% 3 5% 21% 32% 9%	4108
	11th to 20th	Night	25% 2 8% 20% 33% 12%	4120
	21st to end	Night	39% 3 5% 17% 26% 10%	4532
February	1st to 10th	Night	33% 4 6% 21% 23% 13%	2328
	11th to 20th	Night	34% 4 7% 18% 26% 12%	2218
	21st to end	Night	34% 3 5% 16% 23% 19%	1884
March	1st to 10th	Night	35% 6% 5% 16% 24% 15%	3457
	11th to 20th	Night	30% 6% 9% 27% 21% 7%	3480
	21st to end	Night	35% 5% 8% 19% 28% 5%	3817
April	1st to 10th	Night	28% 5% 11% 20% 20% 16%	2090
	11th to 20th	Night	30% 5% 9% 20% 20% 15%	1962
	21st to end	Night	29% 5% 11% 24% 26% 5%	1710
May	1st to 10th	Night	42% 6% 7% 19% 18% 8%	2850
	11th to 20th	Night	35% 5% 11% 22% 25% 2	2824
	21st to end	Night	30% 7% 13% 26% 18% 7%	3099
June	1st to 10th	Night	19% 8% 15% 33% 20% 5%	1710
	11th to 20th	Night	17% 6% 13% 32% 25% 7%	1710
	21st to end	Night	16% 5% 14% 28% 30% 7%	1710
July	1st to 10th	Night	20% 6% 12% 43% 17% 3	2805
	11th to 20th	Night	13% 3 7% 43% 29% 5%	2796
	21st to end	Night	20% 4 13% 38% 24% 2	2999
August	1st to 10th	Night	11% 3 8% 30% 42% 7%	2826
	11th to 20th	Night	13% 3 13% 36% 28% 7%	2825
	21st to end	Night	16% 4 19% 36% 21% 4	3615
September	1st to 10th	Night	26% 5% 8% 22% 27% 12%	2090
	11th to 20th	Night	32% 5% 10% 19% 22% 11%	2090
	21st to end	Night	20% 4 8% 22% 29% 17%	2090
October	1st to 10th	Night	12% 3 6% 14% 33% 33%	3480
	11th to 20th	Night	16% 2 6% 18% 34% 24%	3769
	21st to end	Night	23% 2 4 26% 31% 14%	4120
November	1st to 10th	Night	25% 4 7% 21% 27% 16%	2272
	11th to 20th	Night	22% 4 7% 22% 30% 15%	2470
	21st to end	Night	33% 4 5% 16% 28% 13%	2470
December	1st to 10th	Night	28% 3 7% 23% 26% 12%	2470
	11th to 20th	Night	34% 3 5% 16% 29% 13%	3037
	21st to end	Night	33% 3 5% 19% 28% 12%	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	16% 13% 37% 27% 6%	270
	11th to 20th	Day	16% 15% 35% 25% 6% 2	270
	21st to end	Day	20% 12% 38% 21% 8% 1	297
February	1st to 10th	Day	21% 14% 37% 23% 5%	270
	11th to 20th	Day	20% 16% 41% 17% 5% 1	270
	21st to end	Day	26% 17% 40% 13% 4	225
March	1st to 10th	Day	20% 19% 33% 22% 6%	270
	11th to 20th	Day	19% 20% 39% 17% 5%	270
	21st to end	Day	15% 18% 45% 17% 4 1	297
April	1st to 10th	Day	15% 17% 37% 23% 7% 1	270
	11th to 20th	Day	13% 16% 44% 21% 6%	359
	21st to end	Day	14% 16% 38% 23% 8% 1	650
May	1st to 10th	Day	13% 11% 37% 30% 8% 1	653
	11th to 20th	Day	15% 8% 31% 31% 13% 2	675
	21st to end	Day	13% 9% 29% 30% 15% 4	734
June	1st to 10th	Day	6% 3 17% 41% 27% 7%	680
	11th to 20th	Day	6% 2 19% 42% 25% 6%	680
	21st to end	Day	4 2 13% 38% 34% 8%	680
July	1st to 10th	Day	6% 1 7% 37% 35% 13%	671
	11th to 20th	Day	3 1 7% 32% 45% 12%	668
	21st to end	Day	2 1 7% 31% 44% 15%	739
August	1st to 10th	Day	3 1 5% 36% 41% 14%	676
	11th to 20th	Day	7% 2 6% 34% 40% 11%	665
	21st to end	Day	4 1 5% 34% 36% 20%	464
September	1st to 10th	Day	9% 1 6% 23% 43% 19%	300
	11th to 20th	Day	4 2 9% 29% 38% 19%	300
	21st to end	Day	12% 2 10% 30% 33% 13%	300
October	1st to 10th	Day	3 2 21% 32% 31% 11%	300
	11th to 20th	Day	9% 8% 31% 32% 18% 1	300
	21st to end	Day	22% 9% 25% 27% 15% 3	330
November	1st to 10th	Day	15% 7% 34% 25% 14% 3	279
	11th to 20th	Day	11% 10% 30% 34% 9% 4	270
	21st to end	Day	18% 12% 37% 22% 10% 1	270
December	1st to 10th	Day	13% 11% 37% 26% 11% 2	270
	11th to 20th	Day	14% 11% 41% 26% 8%	270
	21st to end	Day	19% 11% 38% 23% 9%	297
January	1st to 10th	Night	12% 10% 38% 31% 8%	950
	11th to 20th	Night	13% 14% 35% 32% 6%	950
	21st to end	Night	13% 11% 35% 33% 7%	1045
February	1st to 10th	Night	14% 13% 40% 29% 4	808
	11th to 20th	Night	17% 12% 41% 28% 3	744
	21st to end	Night	17% 17% 43% 21% 2	628
March	1st to 10th	Night	14% 15% 39% 29% 4	597
	11th to 20th	Night	15% 11% 42% 28% 4	570
	21st to end	Night	12% 13% 43% 28% 4	627
April	1st to 10th	Night	11% 13% 46% 26% 4	570
	11th to 20th	Night	10% 15% 44% 26% 5%	563
	21st to end	Night	12% 12% 42% 27% 6% 1	570
May	1st to 10th	Night	10% 12% 42% 30% 6% 1	570
	11th to 20th	Night	10% 6% 40% 31% 12% 1	561
	21st to end	Night	7% 4 35% 38% 14% 2	617
June	1st to 10th	Night	3 2 22% 48% 21% 3	570
	11th to 20th	Night	3 1 28% 52% 16%	570
	21st to end	Night	2 1 19% 47% 28% 3	570
July	1st to 10th	Night	4 2 11% 48% 32% 4	555
	11th to 20th	Night	3 11% 47% 36% 3	552
	21st to end	Night	2 7% 48% 40% 3	624
August	1st to 10th	Night	2 1 8% 50% 36% 3	567
	11th to 20th	Night	7% 1 7% 46% 35% 4	564
	21st to end	Night	3 6% 46% 39% 5%	627
September	1st to 10th	Night	6% 1 11% 40% 39% 3	570
	11th to 20th	Night	10% 1 12% 43% 31% 3	570
	21st to end	Night	7% 1 16% 45% 29% 2	570
October	1st to 10th	Night	7% 2 22% 40% 26% 2	570
	11th to 20th	Night	11% 6% 29% 39% 14% 1	750
	21st to end	Night	15% 11% 29% 32% 12% 1	836
November	1st to 10th	Night	12% 4 34% 35% 14% 1	764
	11th to 20th	Night	8% 10% 34% 36% 11% 1	950
	21st to end	Night	17% 10% 36% 27% 9%	950
December	1st to 10th	Night	13% 10% 36% 35% 6%	950
	11th to 20th	Night	17% 10% 36% 31% 6%	950
	21st to end	Night	16% 11% 39% 29% 6%	1045

Page generated at 2024-11-01 21:47:42. Version ac07

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