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 2024-04-03.

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 4 4 2 4 4 5% 7% 53%	79285
	Night	11% 4 2 3 3 2 3 4 4 7% 57%	80903
Transparency	Day	31% 6% 11% 23% 23% 7%	79010
	Night	28% 5% 10% 22% 25% 10%	80698
Seeing	Day	11% 6% 23% 27% 24% 9%	14299
	Night	11% 7% 29% 35% 16% 1	24370

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% 6% 2 4 4 2 2 3 5% 6% 54%	2847
	11th to 20th	Day	10% 5% 1 3 3 1 2 3 3 4 65%	2850
	21st to end	Day	20% 8% 3 5% 4 2 3 2 2 4 47%	3135
February	1st to 10th	Day	15% 7% 4 5% 4 2 3 3 4 5% 48%	1824
	11th to 20th	Day	16% 5% 2 5% 5% 2 3 3 4 5% 49%	1849
	21st to end	Day	21% 6% 2 3 4 1 2 3 3 3 52%	1575
March	1st to 10th	Day	17% 5% 2 4 3 2 4 4 4 6% 48%	2090
	11th to 20th	Day	17% 5% 2 4 4 2 4 3 4 5% 49%	2090
	21st to end	Day	14% 6% 2 4 4 2 3 5% 5% 6% 49%	2299
April	1st to 10th	Day	13% 5% 2 4 4 3 4 4 4 6% 51%	2002
	11th to 20th	Day	11% 5% 3 5% 5% 3 4 4 4 7% 49%	2044
	21st to end	Day	12% 5% 2 4 4 2 4 5% 5% 6% 50%	2324
May	1st to 10th	Day	12% 5% 2 5% 4 3 4 3 5% 7% 50%	2340
	11th to 20th	Day	13% 6% 1 5% 4 3 5% 4 5% 8% 46%	2302
	21st to end	Day	11% 6% 2 6% 6% 3 5% 5% 6% 9% 40%	2531
June	1st to 10th	Day	5% 4 2 4 4 3 4 6% 6% 9% 53%	2340
	11th to 20th	Day	6% 3 1 4 5% 3 4 6% 6% 7% 56%	2340
	21st to end	Day	5% 3 2 3 4 3 5% 5% 6% 9% 56%	2340
July	1st to 10th	Day	6% 3 1 4 5% 3 6% 6% 7% 11% 47%	2340
	11th to 20th	Day	3 2 1 2 3 3 4 5% 5% 9% 63%	2340
	21st to end	Day	3 2 1 3 4 3 6% 5% 8% 9% 54%	2546
August	1st to 10th	Day	3 2 1 3 3 3 4 5% 6% 9% 62%	2328
	11th to 20th	Day	7% 3 1 4 5% 3 5% 5% 6% 10% 51%	2301
	21st to end	Day	4 2 1 3 5% 3 5% 5% 7% 10% 53%	2334
September	1st to 10th	Day	9% 3 2 3 4 2 5% 3 5% 7% 57%	1980
	11th to 20th	Day	11% 4 2 4 5% 3 4 5% 6% 7% 48%	1980
	21st to end	Day	8% 3 1 3 3 3 4 4 5% 6% 61%	1980
October	1st to 10th	Day	7% 3 2 4 3 2 3 3 3 7% 61%	1940
	11th to 20th	Day	11% 3 2 3 3 1 2 3 4 6% 62%	1800
	21st to end	Day	15% 4 1 4 3 1 2 3 3 3 61%	1980
November	1st to 10th	Day	12% 4 2 3 4 2 3 3 4 6% 58%	1858
	11th to 20th	Day	8% 3 2 3 2 2 4 3 4 6% 64%	1740
	21st to end	Day	16% 5% 2 3 2 2 3 3 3 5% 56%	1710
December	1st to 10th	Day	13% 6% 2 4 4 2 3 4 5% 6% 51%	1710
	11th to 20th	Day	15% 7% 3 5% 5% 2 4 3 4 5% 47%	2161
	21st to end	Day	18% 5% 1 4 4 3 4 3 4 5% 49%	3135
January	1st to 10th	Night	13% 5% 2 3 3 2 4 4 4 5% 56%	4108
	11th to 20th	Night	10% 4 1 3 3 2 2 2 3 5% 65%	4120
	21st to end	Night	19% 6% 3 4 3 2 3 3 3 4 50%	4532
February	1st to 10th	Night	13% 6% 3 5% 5% 2 3 4 4 5% 51%	2371
	11th to 20th	Night	15% 7% 3 3 3 2 3 3 4 5% 51%	2218
	21st to end	Night	17% 5% 2 4 3 2 3 3 3 4 55%	1878
March	1st to 10th	Night	14% 4 2 4 4 2 3 4 5% 8% 48%	2090
	11th to 20th	Night	13% 6% 2 4 3 2 3 3 5% 8% 51%	2090
	21st to end	Night	11% 5% 2 4 3 2 4 3 4 7% 54%	2299
April	1st to 10th	Night	10% 5% 2 4 3 2 4 4 5% 8% 53%	2002
	11th to 20th	Night	13% 5% 2 4 3 2 3 3 4 7% 53%	1865
	21st to end	Night	11% 4 2 4 4 2 3 3 4 8% 56%	1632
May	1st to 10th	Night	11% 5% 2 3 4 2 3 4 5% 6% 53%	1620
	11th to 20th	Night	11% 4 2 4 4 2 5% 4 5% 8% 50%	1593
	21st to end	Night	8% 4 2 3 5% 3 4 5% 6% 11% 51%	1745
June	1st to 10th	Night	4 3 1 3 3 3 4 5% 6% 9% 59%	1620
	11th to 20th	Night	4 2 1 3 3 2 3 4 5% 10% 63%	1620
	21st to end	Night	3 2 1 2 3 2 3 5% 6% 9% 65%	1620
July	1st to 10th	Night	5% 2 2 3 5% 3 4 5% 5% 11% 55%	1620
	11th to 20th	Night	3 1 1 2 2 1 3 3 6% 10% 68%	1620
	21st to end	Night	1 2 1 3 4 3 4 5% 6% 10% 61%	1772
August	1st to 10th	Night	2 1 1 3 3 2 2 3 4 10% 69%	1611
	11th to 20th	Night	5% 3 2 3 3 2 4 4 7% 9% 59%	1600
	21st to end	Night	3 3 2 3 4 2 4 4 7% 10% 60%	2016
September	1st to 10th	Night	8% 3 1 4 4 3 3 4 4 7% 60%	1980
	11th to 20th	Night	9% 4 2 6% 4 3 4 4 5% 7% 53%	1980
	21st to end	Night	6% 2 1 3 2 2 3 4 5% 8% 64%	1980
October	1st to 10th	Night	6% 3 1 3 3 2 4 3 5% 6% 63%	2001
	11th to 20th	Night	10% 4 1 3 3 1 2 3 4 4 64%	2160
	21st to end	Night	16% 4 2 3 2 1 2 2 3 4 62%	2376
November	1st to 10th	Night	10% 3 1 3 3 2 3 3 4 5% 62%	2220
	11th to 20th	Night	7% 3 2 3 3 2 3 4 4 6% 62%	2436
	21st to end	Night	16% 5% 2 3 3 2 3 4 4 4 55%	2470
December	1st to 10th	Night	12% 5% 2 3 3 2 3 4 3 5% 57%	2470
	11th to 20th	Night	13% 5% 2 4 4 3 4 4 4 6% 51%	3036
	21st to end	Night	17% 6% 1 4 3 2 3 3 4 5% 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	30% 5% 9% 20% 31% 6%	2848
	11th to 20th	Day	25% 3 9% 22% 34% 7%	2850
	21st to end	Day	44% 3 5% 19% 22% 8%	3135
February	1st to 10th	Day	40% 4 8% 19% 21% 8%	1824
	11th to 20th	Day	39% 3 7% 22% 21% 9%	1859
	21st to end	Day	39% 3 4 15% 26% 13%	1575
March	1st to 10th	Day	37% 5% 8% 18% 21% 12%	2090
	11th to 20th	Day	38% 6% 9% 19% 22% 6%	2090
	21st to end	Day	36% 6% 11% 20% 20% 7%	2299
April	1st to 10th	Day	35% 6% 9% 22% 18% 10%	2002
	11th to 20th	Day	36% 6% 10% 18% 19% 10%	2044
	21st to end	Day	33% 7% 11% 23% 23% 4	2324
May	1st to 10th	Day	34% 6% 10% 22% 20% 7%	2340
	11th to 20th	Day	37% 7% 12% 24% 18% 2	2306
	21st to end	Day	40% 8% 13% 22% 15% 2	2531
June	1st to 10th	Day	26% 9% 18% 26% 17% 3	2340
	11th to 20th	Day	25% 8% 14% 29% 19% 5%	2340
	21st to end	Day	24% 7% 13% 26% 25% 5%	2340
July	1st to 10th	Day	28% 11% 19% 26% 15% 1	2276
	11th to 20th	Day	17% 7% 15% 34% 23% 4	2271
	21st to end	Day	21% 9% 18% 34% 18% 1	2405
August	1st to 10th	Day	17% 7% 16% 31% 26% 3	2314
	11th to 20th	Day	27% 8% 15% 27% 20% 3	2301
	21st to end	Day	23% 10% 15% 29% 19% 5%	2334
September	1st to 10th	Day	27% 6% 12% 22% 23% 10%	1980
	11th to 20th	Day	33% 9% 12% 18% 21% 7%	1980
	21st to end	Day	23% 6% 8% 23% 28% 12%	1980
October	1st to 10th	Day	24% 5% 11% 23% 21% 16%	1940
	11th to 20th	Day	26% 3 8% 16% 29% 17%	1800
	21st to end	Day	30% 3 7% 20% 26% 15%	1980
November	1st to 10th	Day	29% 5% 8% 22% 27% 10%	1858
	11th to 20th	Day	23% 5% 10% 21% 30% 11%	1740
	21st to end	Day	32% 4 6% 21% 26% 11%	1710
December	1st to 10th	Day	35% 4 7% 24% 24% 6%	1710
	11th to 20th	Day	40% 4 6% 15% 26% 9%	2159
	21st to end	Day	36% 4 7% 23% 23% 7%	3135
January	1st to 10th	Night	28% 4 9% 20% 30% 9%	4108
	11th to 20th	Night	25% 3 9% 21% 31% 11%	4120
	21st to end	Night	39% 4 6% 16% 25% 9%	4532
February	1st to 10th	Night	36% 4 9% 19% 22% 11%	2371
	11th to 20th	Night	36% 4 8% 18% 24% 10%	2218
	21st to end	Night	35% 3 7% 15% 23% 17%	1878
March	1st to 10th	Night	34% 6% 8% 17% 21% 14%	2090
	11th to 20th	Night	34% 5% 10% 18% 23% 9%	2090
	21st to end	Night	32% 5% 12% 21% 23% 7%	2299
April	1st to 10th	Night	29% 6% 11% 21% 19% 14%	2002
	11th to 20th	Night	32% 5% 10% 20% 19% 15%	1865
	21st to end	Night	29% 5% 11% 24% 25% 5%	1632
May	1st to 10th	Night	32% 6% 12% 21% 22% 8%	1620
	11th to 20th	Night	32% 7% 17% 21% 20% 3	1594
	21st to end	Night	27% 9% 17% 26% 18% 3	1746
June	1st to 10th	Night	21% 8% 14% 32% 20% 4	1620
	11th to 20th	Night	17% 6% 15% 32% 22% 7%	1620
	21st to end	Night	16% 8% 13% 28% 29% 6%	1620
July	1st to 10th	Night	22% 8% 17% 31% 19% 3	1575
	11th to 20th	Night	11% 6% 13% 34% 29% 7%	1566
	21st to end	Night	15% 8% 15% 35% 25% 2	1673
August	1st to 10th	Night	12% 5% 11% 36% 30% 7%	1601
	11th to 20th	Night	20% 7% 13% 30% 25% 5%	1600
	21st to end	Night	19% 7% 13% 30% 26% 5%	2016
September	1st to 10th	Night	24% 5% 11% 22% 27% 10%	1980
	11th to 20th	Night	31% 5% 12% 18% 22% 12%	1980
	21st to end	Night	19% 4 9% 24% 27% 17%	1980
October	1st to 10th	Night	22% 4 10% 24% 22% 18%	2001
	11th to 20th	Night	24% 4 9% 14% 28% 21%	2160
	21st to end	Night	28% 3 6% 17% 27% 19%	2376
November	1st to 10th	Night	25% 4 9% 20% 26% 16%	2220
	11th to 20th	Night	23% 5% 8% 21% 29% 14%	2436
	21st to end	Night	33% 4 6% 16% 28% 11%	2470
December	1st to 10th	Night	30% 4 8% 23% 24% 11%	2470
	11th to 20th	Night	34% 4 6% 16% 28% 12%	3037
	21st to end	Night	34% 3 7% 19% 26% 11%	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	17% 14% 32% 30% 7%	270
	11th to 20th	Day	20% 12% 36% 24% 7% 2	270
	21st to end	Day	18% 9% 39% 24% 9% 1	297
February	1st to 10th	Day	20% 10% 40% 21% 8%	270
	11th to 20th	Day	22% 15% 40% 17% 6%	270
	21st to end	Day	29% 13% 41% 13% 4	225
March	1st to 10th	Day	20% 15% 34% 24% 6%	270
	11th to 20th	Day	21% 17% 39% 16% 6% 1	270
	21st to end	Day	15% 13% 44% 20% 7% 1	297
April	1st to 10th	Day	16% 15% 37% 25% 7% 1	246
	11th to 20th	Day	16% 11% 39% 27% 7%	322
	21st to end	Day	13% 11% 42% 23% 9% 2	584
May	1st to 10th	Day	12% 9% 33% 33% 11% 1	603
	11th to 20th	Day	16% 5% 32% 28% 16% 3	625
	21st to end	Day	12% 6% 27% 32% 18% 5%	679
June	1st to 10th	Day	7% 1 12% 38% 33% 9%	630
	11th to 20th	Day	7% 1 17% 38% 29% 9%	630
	21st to end	Day	3 3 11% 35% 35% 13%	630
July	1st to 10th	Day	5% 2 7% 32% 36% 18%	621
	11th to 20th	Day	2 1 5% 29% 46% 18%	618
	21st to end	Day	3 1 4 24% 46% 22%	684
August	1st to 10th	Day	3 1 6% 27% 47% 17%	626
	11th to 20th	Day	8% 1 5% 29% 44% 14%	615
	21st to end	Day	5% 1 4 26% 40% 25%	453
September	1st to 10th	Day	6% 2 18% 41% 32%	270
	11th to 20th	Day	6% 2 8% 20% 43% 21%	270
	21st to end	Day	10% 3 9% 25% 35% 17%	270
October	1st to 10th	Day	3 1 19% 30% 35% 13%	270
	11th to 20th	Day	11% 7% 27% 30% 23% 3	270
	21st to end	Day	23% 11% 21% 23% 19% 3	297
November	1st to 10th	Day	16% 4 35% 26% 14% 5%	270
	11th to 20th	Day	10% 9% 35% 28% 15% 4	270
	21st to end	Day	17% 12% 36% 23% 10% 1	270
December	1st to 10th	Day	16% 8% 35% 27% 11% 3	270
	11th to 20th	Day	17% 10% 38% 26% 9%	270
	21st to end	Day	20% 12% 35% 26% 5% 1	297
January	1st to 10th	Night	14% 9% 37% 32% 8%	950
	11th to 20th	Night	16% 13% 34% 31% 5%	950
	21st to end	Night	15% 9% 36% 33% 6%	1045
February	1st to 10th	Night	16% 10% 40% 29% 4	851
	11th to 20th	Night	18% 11% 41% 27% 3	744
	21st to end	Night	21% 13% 43% 20% 3	622
March	1st to 10th	Night	16% 11% 37% 31% 4	570
	11th to 20th	Night	16% 9% 40% 30% 5%	570
	21st to end	Night	12% 11% 42% 30% 4	627
April	1st to 10th	Night	11% 11% 44% 29% 5%	546
	11th to 20th	Night	12% 13% 41% 28% 6%	533
	21st to end	Night	13% 7% 44% 26% 9% 1	540
May	1st to 10th	Night	11% 8% 37% 36% 7% 1	540
	11th to 20th	Night	9% 5% 37% 34% 14% 1	531
	21st to end	Night	8% 3 31% 39% 17% 2	584
June	1st to 10th	Night	4 2 17% 49% 26% 3	540
	11th to 20th	Night	3 1 21% 55% 19%	540
	21st to end	Night	2 1 16% 46% 31% 4	540
July	1st to 10th	Night	4 1 8% 44% 38% 6%	525
	11th to 20th	Night	3 7% 40% 47% 3	522
	21st to end	Night	1 5% 43% 47% 4	591
August	1st to 10th	Night	1 1 4 49% 41% 4	537
	11th to 20th	Night	5% 1 5% 42% 44% 4	534
	21st to end	Night	4 1 4 43% 42% 7%	594
September	1st to 10th	Night	7% 1 10% 37% 41% 4	540
	11th to 20th	Night	10% 1 10% 41% 35% 3	540
	21st to end	Night	6% 1 15% 43% 31% 4	540
October	1st to 10th	Night	6% 1 23% 40% 27% 3	561
	11th to 20th	Night	11% 7% 25% 41% 16% 1	720
	21st to end	Night	16% 9% 29% 31% 15% 1	792
November	1st to 10th	Night	10% 4 31% 39% 15% 1	740
	11th to 20th	Night	9% 8% 32% 38% 12%	916
	21st to end	Night	18% 9% 35% 28% 10%	950
December	1st to 10th	Night	14% 10% 35% 35% 6%	950
	11th to 20th	Night	19% 8% 35% 32% 5%	950
	21st to end	Night	17% 10% 37% 29% 7%	1045

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