Johnson City
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Johnson City clear sky chart from 2005-11-06 to 2025-05-26.

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	14% 9% 3 7% 5% 5% 5% 4 6% 7% 36%	114540
	Night	14% 9% 3 7% 4 4 4 3 5% 7% 38%	114751
Transparency	Day	45% 7% 11% 20% 14% 3	118282
	Night	44% 7% 11% 21% 14% 3	119148
Seeing	Day	19% 14% 22% 23% 16% 6%	15739
	Night	18% 11% 21% 30% 17% 2	25863

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% 18% 8% 11% 4 3 3 3 4 4 28%	4056
	11th to 20th	Day	11% 18% 9% 10% 6% 4 3 2 3 4 31%	4060
	21st to end	Day	15% 15% 4 9% 4 3 4 2 4 5% 35%	4466
February	1st to 10th	Day	17% 12% 4 9% 5% 4 4 3 5% 6% 31%	1847
	11th to 20th	Day	21% 15% 5% 8% 4 4 2 3 4 5% 28%	1948
	21st to end	Day	21% 12% 3 7% 4 4 2 3 4 5% 35%	1650
March	1st to 10th	Day	16% 14% 4 7% 4 4 4 3 4 5% 35%	4839
	11th to 20th	Day	12% 9% 3 5% 4 3 4 3 5% 6% 47%	4980
	21st to end	Day	16% 8% 2 6% 4 4 4 3 5% 7% 39%	5465
April	1st to 10th	Day	14% 9% 2 5% 5% 4 4 4 7% 8% 38%	2200
	11th to 20th	Day	15% 8% 2 6% 4 3 5% 4 5% 6% 42%	2419
	21st to end	Day	16% 7% 2 6% 5% 5% 5% 4 5% 6% 38%	2600
May	1st to 10th	Day	20% 9% 3 8% 6% 5% 5% 4 6% 7% 29%	4212
	11th to 20th	Day	19% 8% 3 8% 5% 6% 5% 4 5% 6% 30%	4211
	21st to end	Day	11% 6% 2 6% 5% 5% 5% 4 8% 11% 37%	4541
June	1st to 10th	Day	12% 6% 2 6% 5% 6% 6% 5% 7% 8% 35%	2470
	11th to 20th	Day	9% 5% 2 8% 5% 7% 7% 5% 9% 10% 33%	2470
	21st to end	Day	11% 7% 2 6% 5% 5% 7% 6% 8% 9% 34%	2470
July	1st to 10th	Day	8% 4 2 6% 6% 6% 6% 6% 9% 12% 34%	4120
	11th to 20th	Day	12% 6% 3 6% 6% 5% 6% 5% 7% 9% 37%	4120
	21st to end	Day	18% 9% 4 10% 8% 7% 7% 5% 7% 7% 18%	4466
August	1st to 10th	Day	13% 6% 3 7% 6% 6% 7% 6% 8% 11% 28%	4104
	11th to 20th	Day	13% 5% 2 7% 5% 6% 6% 5% 8% 10% 33%	4044
	21st to end	Day	7% 4 1 4 4 4 4 5% 6% 7% 53%	4259
September	1st to 10th	Day	11% 5% 2 7% 5% 5% 5% 5% 6% 7% 42%	2090
	11th to 20th	Day	15% 6% 2 6% 5% 5% 5% 3 6% 6% 40%	2090
	21st to end	Day	15% 6% 2 5% 5% 4 5% 4 6% 8% 39%	2090
October	1st to 10th	Day	14% 5% 2 5% 4 3 4 3 4 7% 48%	2039
	11th to 20th	Day	15% 6% 2 4 3 3 3 3 5% 7% 49%	1900
	21st to end	Day	17% 9% 2 4 3 3 3 2 4 6% 47%	2090
November	1st to 10th	Day	12% 6% 2 5% 4 3 3 3 5% 6% 51%	1855
	11th to 20th	Day	11% 9% 3 6% 4 5% 4 4 5% 7% 43%	1800
	21st to end	Day	15% 9% 4 6% 4 3 3 4 5% 6% 42%	1800
December	1st to 10th	Day	13% 12% 3 11% 5% 3 4 3 4 5% 37%	2930
	11th to 20th	Day	18% 14% 4 9% 4 4 4 4 6% 7% 27%	3373
	21st to end	Day	12% 12% 6% 7% 5% 5% 5% 4 6% 7% 30%	4466
January	1st to 10th	Night	14% 16% 6% 12% 5% 3 4 3 3 4 28%	5889
	11th to 20th	Night	14% 14% 5% 11% 6% 4 4 2 4 4 32%	5900
	21st to end	Night	16% 10% 4 8% 5% 4 4 3 4 5% 38%	6490
February	1st to 10th	Night	17% 11% 3 7% 3 4 5% 3 5% 6% 36%	2550
	11th to 20th	Night	20% 12% 4 9% 5% 3 4 3 4 5% 30%	2338
	21st to end	Night	20% 12% 3 9% 3 3 3 3 5% 6% 33%	1980
March	1st to 10th	Night	20% 13% 3 5% 4 3 4 2 4 5% 36%	5012
	11th to 20th	Night	15% 6% 3 4 2 3 3 3 5% 7% 50%	4980
	21st to end	Night	12% 7% 2 5% 5% 5% 5% 4 6% 7% 41%	5467
April	1st to 10th	Night	15% 9% 3 5% 4 4 4 3 4 8% 41%	2200
	11th to 20th	Night	14% 8% 2 6% 4 4 4 4 6% 6% 43%	1944
	21st to end	Night	15% 7% 3 7% 5% 5% 4 3 5% 6% 41%	1800
May	1st to 10th	Night	18% 8% 3 8% 6% 5% 4 4 6% 8% 31%	2903
	11th to 20th	Night	20% 7% 3 7% 5% 5% 4 4 6% 8% 33%	2902
	21st to end	Night	13% 7% 2 6% 5% 5% 5% 4 7% 9% 38%	3130
June	1st to 10th	Night	11% 6% 2 7% 6% 5% 5% 4 7% 10% 38%	1710
	11th to 20th	Night	7% 5% 2 7% 5% 5% 6% 5% 9% 12% 39%	1710
	21st to end	Night	10% 6% 2 6% 5% 6% 5% 5% 7% 11% 38%	1710
July	1st to 10th	Night	11% 6% 3 6% 5% 5% 6% 6% 8% 12% 33%	2840
	11th to 20th	Night	9% 6% 3 6% 4 4 5% 5% 7% 10% 40%	2840
	21st to end	Night	14% 10% 5% 11% 7% 5% 5% 5% 7% 8% 22%	3087
August	1st to 10th	Night	12% 6% 3 7% 5% 5% 6% 5% 8% 11% 34%	2825
	11th to 20th	Night	14% 7% 3 6% 5% 5% 5% 4 6% 7% 38%	2785
	21st to end	Night	7% 3 1 4 3 4 4 4 8% 10% 52%	3359
September	1st to 10th	Night	12% 6% 2 6% 5% 5% 4 3 5% 7% 44%	2090
	11th to 20th	Night	16% 5% 2 6% 4 4 4 3 6% 8% 42%	2090
	21st to end	Night	14% 6% 2 5% 4 4 3 2 5% 6% 47%	2090
October	1st to 10th	Night	16% 6% 2 5% 3 3 3 3 4 6% 50%	2139
	11th to 20th	Night	16% 7% 2 4 2 3 3 3 4 6% 49%	2280
	21st to end	Night	15% 7% 2 5% 3 2 4 3 5% 7% 48%	2508
November	1st to 10th	Night	14% 7% 2 5% 3 3 4 3 5% 5% 49%	2441
	11th to 20th	Night	14% 10% 2 5% 4 4 3 3 6% 6% 44%	2600
	21st to end	Night	13% 11% 2 5% 3 3 4 3 5% 6% 45%	2600
December	1st to 10th	Night	14% 12% 5% 8% 4 4 3 3 4 6% 36%	4250
	11th to 20th	Night	19% 12% 5% 10% 4 4 4 3 4 5% 29%	4822
	21st to end	Night	13% 15% 6% 7% 5% 3 4 4 5% 8% 30%	6490

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	58% 5% 5% 20% 11% 2	4057
	11th to 20th	Day	58% 4 5% 14% 18% 1	4060
	21st to end	Day	53% 3 7% 21% 14% 1	4466
February	1st to 10th	Day	55% 6% 7% 17% 14% 1	1847
	11th to 20th	Day	60% 5% 7% 14% 13% 2	1958
	21st to end	Day	52% 4 8% 16% 15% 5%	1650
March	1st to 10th	Day	51% 5% 6% 15% 17% 7%	4839
	11th to 20th	Day	39% 4 6% 20% 25% 7%	4980
	21st to end	Day	44% 5% 8% 28% 14% 2	5465
April	1st to 10th	Day	42% 7% 12% 22% 14% 3	2200
	11th to 20th	Day	41% 6% 10% 19% 18% 5%	2419
	21st to end	Day	46% 8% 10% 23% 11% 2	2600
May	1st to 10th	Day	52% 10% 12% 18% 8% 1	4250
	11th to 20th	Day	52% 9% 12% 21% 5% 1	4215
	21st to end	Day	36% 12% 18% 20% 12% 2	4554
June	1st to 10th	Day	42% 12% 16% 18% 11% 1	2470
	11th to 20th	Day	42% 13% 15% 16% 13% 1	2470
	21st to end	Day	42% 11% 15% 18% 13% 2	2470
July	1st to 10th	Day	38% 12% 22% 18% 9% 1	4055
	11th to 20th	Day	42% 9% 18% 24% 6% 1	4051
	21st to end	Day	61% 10% 10% 12% 6%	4324
August	1st to 10th	Day	47% 9% 18% 20% 6%	4091
	11th to 20th	Day	42% 9% 17% 22% 9% 1	4083
	21st to end	Day	28% 7% 16% 36% 11% 1	4259
September	1st to 10th	Day	39% 11% 13% 19% 14% 4	2090
	11th to 20th	Day	42% 9% 10% 21% 15% 2	2090
	21st to end	Day	42% 8% 14% 18% 14% 4	2090
October	1st to 10th	Day	29% 4 7% 21% 31% 7%	3390
	11th to 20th	Day	27% 4 8% 26% 17% 18%	3140
	21st to end	Day	30% 3 5% 30% 19% 12%	3428
November	1st to 10th	Day	35% 5% 9% 19% 27% 5%	1855
	11th to 20th	Day	40% 4 8% 20% 22% 5%	1800
	21st to end	Day	43% 5% 8% 22% 19% 4	1800
December	1st to 10th	Day	51% 4 7% 16% 21% 1	2930
	11th to 20th	Day	56% 4 11% 16% 11% 2	3370
	21st to end	Day	51% 5% 15% 20% 9% 1	4466
January	1st to 10th	Night	58% 5% 6% 18% 11% 2	5889
	11th to 20th	Night	54% 5% 5% 15% 17% 3	5900
	21st to end	Night	49% 4 7% 21% 17% 2	6490
February	1st to 10th	Night	50% 5% 10% 19% 14% 1	2550
	11th to 20th	Night	57% 6% 8% 15% 11% 3	2339
	21st to end	Night	52% 6% 8% 17% 13% 4	1980
March	1st to 10th	Night	49% 5% 7% 19% 15% 5%	5012
	11th to 20th	Night	34% 5% 9% 19% 24% 9%	4980
	21st to end	Night	40% 6% 11% 27% 14% 2	5467
April	1st to 10th	Night	42% 7% 14% 20% 14% 3	2200
	11th to 20th	Night	40% 7% 10% 21% 17% 5%	1944
	21st to end	Night	44% 6% 13% 24% 12% 1	1800
May	1st to 10th	Night	50% 11% 13% 18% 7% 1	2930
	11th to 20th	Night	47% 11% 15% 22% 5% 1	2903
	21st to end	Night	36% 14% 18% 21% 10% 1	3138
June	1st to 10th	Night	39% 12% 17% 19% 12% 1	1710
	11th to 20th	Night	34% 13% 19% 22% 10% 1	1710
	21st to end	Night	38% 13% 15% 19% 12% 3	1710
July	1st to 10th	Night	42% 10% 20% 19% 8% 1	2795
	11th to 20th	Night	36% 9% 22% 25% 5% 2	2786
	21st to end	Night	56% 10% 13% 16% 5%	2988
August	1st to 10th	Night	43% 8% 21% 21% 5%	2814
	11th to 20th	Night	43% 7% 18% 24% 8%	2812
	21st to end	Night	26% 7% 15% 39% 11% 1	3359
September	1st to 10th	Night	39% 9% 14% 20% 15% 4	2090
	11th to 20th	Night	40% 9% 14% 20% 16% 1	2090
	21st to end	Night	38% 7% 13% 22% 18% 2	2090
October	1st to 10th	Night	37% 4 6% 19% 27% 6%	3568
	11th to 20th	Night	30% 4 7% 23% 22% 16%	3779
	21st to end	Night	26% 4 5% 31% 23% 12%	4120
November	1st to 10th	Night	37% 5% 10% 19% 23% 6%	2441
	11th to 20th	Night	40% 5% 7% 20% 22% 6%	2600
	21st to end	Night	40% 5% 7% 25% 19% 3	2600
December	1st to 10th	Night	52% 4 7% 20% 16% 2	4250
	11th to 20th	Night	58% 4 9% 16% 11% 2	4824
	21st to end	Night	51% 7% 12% 18% 11% 1	6490

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	27% 30% 28% 13% 2	300
	11th to 20th	Day	33% 28% 23% 14% 2	300
	21st to end	Day	24% 31% 32% 11% 2	330
February	1st to 10th	Day	26% 25% 33% 13% 3	300
	11th to 20th	Day	41% 31% 22% 6% 1	300
	21st to end	Day	38% 20% 31% 10% 2	249
March	1st to 10th	Day	25% 23% 27% 19% 6% 1	452
	11th to 20th	Day	25% 26% 26% 19% 3 1	500
	21st to end	Day	25% 23% 25% 19% 7%	550
April	1st to 10th	Day	22% 21% 28% 19% 9% 1	500
	11th to 20th	Day	21% 17% 28% 22% 10% 2	492
	21st to end	Day	22% 14% 28% 20% 13% 3	500
May	1st to 10th	Day	21% 19% 26% 19% 11% 4	503
	11th to 20th	Day	18% 11% 23% 27% 15% 5%	527
	21st to end	Day	14% 9% 21% 23% 21% 10%	549
June	1st to 10th	Day	13% 6% 23% 28% 22% 8%	490
	11th to 20th	Day	9% 7% 18% 29% 26% 11%	490
	21st to end	Day	14% 8% 21% 25% 23% 9%	490
July	1st to 10th	Day	12% 5% 15% 23% 29% 15%	485
	11th to 20th	Day	9% 4 14% 32% 28% 13%	484
	21st to end	Day	14% 4 14% 30% 26% 12%	532
August	1st to 10th	Day	15% 5% 17% 26% 24% 13%	486
	11th to 20th	Day	13% 3 17% 29% 26% 11%	479
	21st to end	Day	12% 3 10% 26% 29% 21%	539
September	1st to 10th	Day	9% 5% 14% 28% 30% 14%	490
	11th to 20th	Day	15% 4 14% 25% 30% 13%	490
	21st to end	Day	16% 8% 18% 29% 23% 5%	490
October	1st to 10th	Day	16% 7% 20% 29% 20% 8%	490
	11th to 20th	Day	15% 17% 20% 27% 18% 3	490
	21st to end	Day	20% 12% 21% 29% 14% 3	539
November	1st to 10th	Day	15% 18% 24% 28% 11% 4	393
	11th to 20th	Day	17% 24% 26% 26% 7%	300
	21st to end	Day	20% 19% 29% 24% 6% 1	300
December	1st to 10th	Day	26% 21% 36% 14% 3	300
	11th to 20th	Day	26% 17% 29% 21% 6%	300
	21st to end	Day	21% 23% 32% 15% 8%	330
January	1st to 10th	Night	24% 22% 26% 24% 3	800
	11th to 20th	Night	27% 19% 27% 24% 4	800
	21st to end	Night	22% 18% 35% 23% 3	880
February	1st to 10th	Night	22% 17% 30% 28% 3	800
	11th to 20th	Night	28% 22% 31% 18% 1	783
	21st to end	Night	25% 24% 29% 21% 2	660
March	1st to 10th	Night	23% 16% 30% 27% 4	800
	11th to 20th	Night	24% 19% 28% 22% 7% 1	800
	21st to end	Night	20% 13% 32% 27% 7%	880
April	1st to 10th	Night	19% 18% 27% 28% 8%	800
	11th to 20th	Night	16% 15% 28% 29% 11% 1	690
	21st to end	Night	17% 9% 27% 37% 9% 1	600
May	1st to 10th	Night	17% 10% 26% 31% 14% 1	600
	11th to 20th	Night	16% 7% 22% 34% 19% 2	591
	21st to end	Night	10% 3 17% 35% 30% 4	634
June	1st to 10th	Night	10% 4 13% 41% 29% 4	570
	11th to 20th	Night	6% 3 13% 42% 31% 4	570
	21st to end	Night	12% 3 11% 39% 32% 3	570
July	1st to 10th	Night	12% 3 8% 29% 43% 5%	555
	11th to 20th	Night	11% 2 7% 30% 42% 7%	552
	21st to end	Night	10% 4 6% 36% 36% 8%	624
August	1st to 10th	Night	10% 3 8% 34% 40% 5%	567
	11th to 20th	Night	12% 3 8% 36% 36% 4	564
	21st to end	Night	12% 2 7% 33% 39% 7%	677
September	1st to 10th	Night	13% 3 9% 34% 35% 6%	760
	11th to 20th	Night	16% 4 11% 30% 34% 5%	760
	21st to end	Night	16% 5% 16% 36% 25% 3	760
October	1st to 10th	Night	17% 5% 16% 30% 26% 6%	760
	11th to 20th	Night	18% 8% 21% 33% 16% 2	760
	21st to end	Night	18% 10% 20% 35% 14% 2	836
November	1st to 10th	Night	17% 7% 21% 37% 16% 2	780
	11th to 20th	Night	19% 13% 21% 35% 11% 1	800
	21st to end	Night	19% 14% 25% 31% 10% 1	800
December	1st to 10th	Night	24% 15% 27% 27% 6%	800
	11th to 20th	Night	25% 13% 26% 30% 6% 1	800
	21st to end	Night	25% 16% 25% 29% 4	880

Page generated at 2025-05-23 09:20:58. Version ac07

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