Ray Roberts Lake State Park - Johnson Branch Unit
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ray Roberts Lake State Park - Johnson Branch Unit clear sky chart from 2005-11-06 to 2026-10-29.

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%	149314
	Night	10% 4 2 4 3 3 3 3 4 7% 57%	143148
Transparency	Day	29% 5% 10% 25% 23% 7%	153018
	Night	27% 4 9% 23% 26% 10%	147511
Seeing	Day	11% 6% 22% 28% 24% 8%	17885
	Night	11% 7% 29% 36% 16% 1	27661

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	11% 5% 2 4 3 3 3 3 5% 6% 55%	5289
	11th to 20th	Day	6% 5% 2 3 3 2 2 3 4 6% 65%	5310
	21st to end	Day	20% 7% 3 6% 4 3 2 2 3 4 46%	5812
February	1st to 10th	Day	15% 8% 3 6% 3 3 3 2 4 5% 49%	2016
	11th to 20th	Day	16% 6% 3 6% 4 3 3 2 4 5% 48%	2049
	21st to end	Day	19% 6% 2 3 3 1 2 2 3 4 55%	1735
March	1st to 10th	Day	15% 5% 1 4 3 3 3 3 4 6% 53%	5046
	11th to 20th	Day	11% 4 1 4 3 3 3 3 4 5% 58%	5090
	21st to end	Day	12% 6% 2 6% 4 3 4 4 5% 6% 49%	5583
April	1st to 10th	Day	13% 6% 2 5% 3 4 3 3 5% 6% 50%	2310
	11th to 20th	Day	12% 6% 2 6% 4 4 3 3 4 6% 48%	2389
	21st to end	Day	15% 5% 2 5% 4 3 4 4 5% 6% 47%	2712
May	1st to 10th	Day	16% 7% 3 7% 4 4 4 3 5% 7% 40%	7617
	11th to 20th	Day	12% 6% 2 7% 4 4 4 3 5% 7% 46%	7627
	21st to end	Day	13% 7% 3 7% 5% 5% 5% 4 6% 8% 37%	8392
June	1st to 10th	Day	6% 4 2 5% 4 4 5% 5% 6% 9% 51%	2730
	11th to 20th	Day	6% 4 1 4 5% 4 4 5% 5% 8% 54%	2730
	21st to end	Day	5% 3 2 3 3 4 5% 3 6% 9% 58%	2730
July	1st to 10th	Day	6% 4 2 6% 4 4 5% 4 6% 9% 50%	7680
	11th to 20th	Day	3 2 1 4 3 4 5% 4 6% 10% 57%	7680
	21st to end	Day	3 2 1 3 3 3 3 3 6% 8% 64%	8337
August	1st to 10th	Day	1 1 1 2 2 3 3 3 5% 8% 72%	6014
	11th to 20th	Day	3 1 1 2 2 2 3 3 5% 7% 71%	5948
	21st to end	Day	3 2 1 3 3 3 4 3 6% 10% 62%	5947
September	1st to 10th	Day	9% 3 2 4 4 3 5% 3 5% 6% 57%	2310
	11th to 20th	Day	9% 4 2 5% 4 4 4 3 6% 7% 51%	2310
	21st to end	Day	7% 3 1 4 3 4 4 3 5% 7% 59%	2310
October	1st to 10th	Day	7% 4 1 4 2 3 3 2 3 7% 64%	2263
	11th to 20th	Day	10% 3 1 3 3 2 2 2 4 6% 63%	2100
	21st to end	Day	13% 4 1 4 3 2 3 2 3 4 62%	2280
November	1st to 10th	Day	13% 4 2 3 3 3 3 2 4 5% 58%	2058
	11th to 20th	Day	8% 3 2 3 2 3 3 2 4 5% 65%	1922
	21st to end	Day	15% 5% 1 4 2 3 2 3 3 6% 56%	1890
December	1st to 10th	Day	15% 8% 2 4 3 2 3 3 4 5% 52%	3030
	11th to 20th	Day	17% 7% 2 5% 4 3 3 3 4 4 48%	3481
	21st to end	Day	19% 7% 2 5% 3 3 3 2 4 4 50%	4587
January	1st to 10th	Night	12% 4 1 4 3 3 3 3 4 6% 57%	7634
	11th to 20th	Night	5% 3 1 2 2 2 2 2 3 5% 73%	7680
	21st to end	Night	23% 7% 2 5% 4 3 3 2 4 4 44%	8402
February	1st to 10th	Night	13% 6% 3 5% 4 3 3 3 4 5% 52%	2620
	11th to 20th	Night	16% 7% 3 4 3 2 3 2 4 5% 51%	2458
	21st to end	Night	16% 5% 2 4 2 3 2 3 3 4 57%	2069
March	1st to 10th	Night	16% 6% 2 5% 3 3 3 3 5% 6% 48%	5029
	11th to 20th	Night	9% 4 1 4 3 3 3 2 4 7% 59%	5090
	21st to end	Night	13% 5% 2 5% 3 4 4 3 4 6% 52%	5588
April	1st to 10th	Night	11% 5% 2 4 3 3 4 3 4 8% 52%	2310
	11th to 20th	Night	13% 5% 2 4 3 3 4 3 5% 7% 51%	2180
	21st to end	Night	12% 4 2 5% 3 3 3 3 4 8% 53%	1903
May	1st to 10th	Night	16% 7% 2 6% 4 4 4 4 5% 7% 41%	5266
	11th to 20th	Night	10% 5% 2 5% 3 4 5% 3 5% 7% 50%	5265
	21st to end	Night	11% 6% 2 6% 4 4 4 4 6% 9% 43%	5793
June	1st to 10th	Night	5% 4 1 4 3 3 5% 3 6% 9% 56%	1890
	11th to 20th	Night	4 3 1 4 3 3 3 3 5% 10% 62%	1890
	21st to end	Night	3 2 1 2 3 3 3 4 6% 9% 66%	1890
July	1st to 10th	Night	5% 3 2 5% 5% 4 4 3 6% 11% 51%	5308
	11th to 20th	Night	3 2 1 3 2 3 4 4 6% 9% 64%	5307
	21st to end	Night	2 2 1 3 2 3 3 3 4 7% 71%	5770
August	1st to 10th	Night	1 1 2 2 1 2 2 4 7% 78%	4156
	11th to 20th	Night	2 1 1 2 1 2 2 2 4 8% 75%	4118
	21st to end	Night	2 2 1 3 2 3 3 3 5% 8% 67%	5168
September	1st to 10th	Night	7% 4 1 4 3 3 3 3 5% 7% 60%	2310
	11th to 20th	Night	8% 4 2 6% 3 4 3 3 5% 6% 57%	2310
	21st to end	Night	6% 3 1 3 2 3 4 3 6% 8% 61%	2310
October	1st to 10th	Night	6% 4 1 3 2 2 4 2 4 6% 66%	2335
	11th to 20th	Night	10% 4 1 3 2 2 2 3 3 4 65%	2520
	21st to end	Night	14% 4 2 3 2 2 2 2 3 4 62%	2737
November	1st to 10th	Night	10% 4 1 3 3 3 2 2 4 5% 62%	2460
	11th to 20th	Night	7% 3 1 3 2 3 3 3 4 6% 64%	2693
	21st to end	Night	15% 5% 2 3 3 3 3 3 3 5% 56%	2730
December	1st to 10th	Night	13% 6% 2 4 2 3 3 3 4 5% 56%	4380
	11th to 20th	Night	17% 5% 2 5% 3 3 3 3 4 5% 51%	4946
	21st to end	Night	16% 6% 1 5% 3 2 2 2 4 5% 53%	6633

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	29% 4 9% 26% 28% 4	5290
	11th to 20th	Day	22% 3 6% 22% 39% 8%	5310
	21st to end	Day	44% 3 4 19% 20% 9%	5812
February	1st to 10th	Day	39% 4 7% 19% 21% 9%	2016
	11th to 20th	Day	39% 3 8% 22% 20% 8%	2059
	21st to end	Day	36% 3 4 16% 27% 14%	1735
March	1st to 10th	Day	33% 4 7% 15% 23% 18%	5046
	11th to 20th	Day	29% 6% 8% 19% 19% 20%	5090
	21st to end	Day	34% 6% 10% 23% 20% 6%	5585
April	1st to 10th	Day	35% 5% 9% 22% 19% 10%	2310
	11th to 20th	Day	37% 6% 9% 18% 20% 10%	2389
	21st to end	Day	36% 7% 10% 22% 21% 4	2712
May	1st to 10th	Day	43% 6% 11% 20% 16% 5%	7655
	11th to 20th	Day	38% 6% 9% 21% 23% 3	7631
	21st to end	Day	44% 8% 14% 19% 11% 5%	8405
June	1st to 10th	Day	27% 9% 17% 27% 17% 3	2730
	11th to 20th	Day	27% 8% 14% 28% 20% 4	2730
	21st to end	Day	23% 7% 15% 28% 24% 4	2730
July	1st to 10th	Day	30% 7% 13% 33% 16% 1	7616
	11th to 20th	Day	21% 6% 19% 33% 19% 2	7611
	21st to end	Day	17% 5% 13% 37% 26% 1	8155
August	1st to 10th	Day	11% 4 10% 31% 33% 11%	6000
	11th to 20th	Day	14% 4 12% 38% 30% 2	5987
	21st to end	Day	18% 7% 15% 36% 22% 2	5946
September	1st to 10th	Day	27% 6% 11% 23% 22% 11%	2310
	11th to 20th	Day	30% 8% 13% 22% 21% 7%	2310
	21st to end	Day	24% 6% 9% 24% 27% 11%	2310
October	1st to 10th	Day	15% 3 6% 14% 36% 26%	3614
	11th to 20th	Day	16% 3 6% 21% 35% 19%	3340
	21st to end	Day	24% 3 5% 31% 27% 10%	3618
November	1st to 10th	Day	29% 4 7% 21% 28% 10%	2058
	11th to 20th	Day	22% 4 10% 22% 30% 12%	1922
	21st to end	Day	31% 4 6% 22% 27% 10%	1890
December	1st to 10th	Day	37% 3 5% 29% 22% 4	3030
	11th to 20th	Day	40% 4 5% 12% 30% 9%	3479
	21st to end	Day	39% 3 5% 24% 21% 8%	4587
January	1st to 10th	Night	29% 3 8% 25% 29% 6%	7635
	11th to 20th	Night	16% 2 6% 21% 39% 15%	7680
	21st to end	Night	44% 4 5% 16% 21% 10%	8402
February	1st to 10th	Night	35% 4 8% 19% 23% 11%	2620
	11th to 20th	Night	36% 3 8% 19% 23% 10%	2458
	21st to end	Night	33% 3 7% 15% 25% 17%	2069
March	1st to 10th	Night	36% 5% 6% 13% 22% 18%	5029
	11th to 20th	Night	26% 5% 8% 19% 18% 24%	5090
	21st to end	Night	34% 5% 8% 17% 29% 6%	5588
April	1st to 10th	Night	31% 5% 10% 21% 20% 13%	2310
	11th to 20th	Night	33% 5% 10% 19% 19% 13%	2180
	21st to end	Night	32% 4 12% 23% 24% 5%	1903
May	1st to 10th	Night	41% 7% 14% 19% 15% 5%	5293
	11th to 20th	Night	33% 6% 11% 20% 24% 5%	5266
	21st to end	Night	35% 8% 17% 23% 10% 7%	5805
June	1st to 10th	Night	23% 9% 14% 31% 20% 4	1890
	11th to 20th	Night	19% 6% 15% 30% 23% 7%	1890
	21st to end	Night	15% 8% 14% 31% 27% 6%	1890
July	1st to 10th	Night	27% 6% 13% 33% 19% 2	5265
	11th to 20th	Night	16% 7% 17% 34% 23% 3	5256
	21st to end	Night	14% 5% 11% 36% 31% 3	5641
August	1st to 10th	Night	8% 3 7% 33% 37% 12%	4146
	11th to 20th	Night	9% 3 10% 38% 34% 5%	4145
	21st to end	Night	16% 5% 15% 33% 28% 4	5168
September	1st to 10th	Night	24% 5% 10% 23% 27% 10%	2310
	11th to 20th	Night	29% 5% 11% 23% 22% 11%	2310
	21st to end	Night	20% 4 10% 24% 26% 15%	2310
October	1st to 10th	Night	13% 3 5% 14% 34% 32%	3751
	11th to 20th	Night	15% 3 5% 19% 34% 24%	4019
	21st to end	Night	25% 3 5% 25% 28% 15%	4349
November	1st to 10th	Night	25% 4 8% 20% 27% 16%	2460
	11th to 20th	Night	22% 5% 8% 22% 28% 15%	2693
	21st to end	Night	33% 4 6% 18% 29% 11%	2730
December	1st to 10th	Night	32% 3 6% 24% 27% 8%	4380
	11th to 20th	Night	36% 3 5% 15% 26% 14%	4947
	21st to end	Night	35% 3 6% 21% 26% 10%	6633

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	17% 14% 32% 30% 7%	330
	11th to 20th	Day	18% 13% 36% 25% 7% 2	330
	21st to end	Day	18% 10% 38% 24% 8% 1	363
February	1st to 10th	Day	19% 9% 41% 22% 8%	330
	11th to 20th	Day	20% 16% 42% 16% 5%	330
	21st to end	Day	24% 12% 42% 17% 4 1	273
March	1st to 10th	Day	22% 16% 33% 23% 6%	330
	11th to 20th	Day	20% 16% 41% 17% 5% 1	330
	21st to end	Day	13% 12% 43% 24% 7% 1	363
April	1st to 10th	Day	16% 16% 34% 24% 8% 1	330
	11th to 20th	Day	17% 12% 40% 26% 6%	427
	21st to end	Day	17% 11% 40% 23% 8% 1	732
May	1st to 10th	Day	13% 10% 32% 34% 10% 1	753
	11th to 20th	Day	15% 8% 33% 26% 15% 3	775
	21st to end	Day	12% 7% 27% 32% 18% 4	844
June	1st to 10th	Day	8% 3 14% 37% 31% 8%	780
	11th to 20th	Day	8% 2 17% 38% 29% 7%	780
	21st to end	Day	3 2 11% 36% 36% 12%	780
July	1st to 10th	Day	5% 2 7% 32% 38% 16%	771
	11th to 20th	Day	2 1 5% 31% 44% 16%	768
	21st to end	Day	3 1 4 26% 44% 22%	849
August	1st to 10th	Day	3 1 5% 24% 49% 18%	776
	11th to 20th	Day	7% 1 4 28% 45% 15%	765
	21st to end	Day	5% 1 4 26% 40% 24%	576
September	1st to 10th	Day	6% 1 4 22% 40% 27%	360
	11th to 20th	Day	5% 2 6% 21% 44% 21%	360
	21st to end	Day	9% 4 11% 27% 33% 17%	360
October	1st to 10th	Day	4 1 15% 26% 37% 16%	360
	11th to 20th	Day	9% 6% 25% 31% 24% 5%	360
	21st to end	Day	20% 9% 20% 26% 21% 4	387
November	1st to 10th	Day	15% 5% 32% 28% 16% 4	330
	11th to 20th	Day	9% 9% 33% 29% 16% 4	330
	21st to end	Day	16% 11% 37% 24% 10% 2	330
December	1st to 10th	Day	16% 10% 35% 26% 11% 2	330
	11th to 20th	Day	16% 11% 36% 26% 9% 1	330
	21st to end	Day	20% 12% 33% 28% 6% 1	363
January	1st to 10th	Night	14% 9% 37% 32% 8%	1050
	11th to 20th	Night	14% 14% 36% 31% 5%	1050
	21st to end	Night	16% 10% 36% 32% 6%	1155
February	1st to 10th	Night	16% 9% 41% 29% 4	940
	11th to 20th	Night	19% 13% 39% 26% 3	824
	21st to end	Night	20% 12% 42% 23% 3	685
March	1st to 10th	Night	17% 12% 37% 30% 4	630
	11th to 20th	Night	16% 10% 40% 29% 4	630
	21st to end	Night	12% 10% 42% 32% 4	693
April	1st to 10th	Night	13% 12% 41% 29% 5%	630
	11th to 20th	Night	13% 14% 40% 27% 5%	623
	21st to end	Night	14% 7% 43% 27% 8% 1	630
May	1st to 10th	Night	12% 8% 37% 36% 6% 1	630
	11th to 20th	Night	9% 7% 37% 33% 14% 1	621
	21st to end	Night	8% 4 31% 40% 16% 2	683
June	1st to 10th	Night	6% 2 18% 48% 24% 3	630
	11th to 20th	Night	4 2 20% 56% 18%	630
	21st to end	Night	2 1 15% 47% 31% 4	630
July	1st to 10th	Night	4 1 8% 46% 36% 5%	615
	11th to 20th	Night	3 8% 41% 45% 2	612
	21st to end	Night	1 6% 43% 46% 4	690
August	1st to 10th	Night	1 5% 48% 42% 3	627
	11th to 20th	Night	4 1 4 44% 43% 4	624
	21st to end	Night	4 1 4 43% 41% 7%	693
September	1st to 10th	Night	7% 1 9% 39% 40% 4	630
	11th to 20th	Night	8% 1 9% 43% 36% 3	630
	21st to end	Night	7% 1 14% 46% 28% 3	630
October	1st to 10th	Night	7% 1 20% 40% 30% 2	655
	11th to 20th	Night	10% 6% 25% 42% 16% 1	840
	21st to end	Night	15% 9% 28% 32% 16%	913
November	1st to 10th	Night	10% 4 32% 39% 14% 1	820
	11th to 20th	Night	9% 8% 33% 38% 12%	1013
	21st to end	Night	17% 9% 35% 28% 10%	1050
December	1st to 10th	Night	14% 10% 36% 35% 5%	1050
	11th to 20th	Night	18% 8% 36% 32% 6%	1050
	21st to end	Night	17% 10% 37% 30% 6%	1155

Page generated at 2026-10-26 03:37:46. Version ac07

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