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 2026-06-16.

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% 6% 2 5% 4 4 4 4 5% 7% 48%	137778
	Night	11% 6% 2 5% 3 3 4 3 5% 7% 52%	134615
Transparency	Day	33% 6% 10% 21% 19% 11%	141570
	Night	31% 6% 11% 20% 20% 13%	138890
Seeing	Day	12% 8% 24% 31% 20% 5%	16961
	Night	13% 7% 29% 36% 13% 1	26913

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% 7% 2 5% 4 3 3 2 4 5% 54%	5289
	11th to 20th	Day	13% 5% 1 4 3 2 2 3 5% 5% 56%	5310
	21st to end	Day	20% 7% 3 6% 4 4 2 2 3 5% 42%	6286
February	1st to 10th	Day	15% 7% 2 6% 3 3 4 2 4 6% 48%	2100
	11th to 20th	Day	15% 6% 2 6% 3 3 4 3 4 7% 47%	2049
	21st to end	Day	16% 5% 2 4 3 2 3 3 4 5% 52%	1730
March	1st to 10th	Day	11% 6% 3 6% 3 3 3 3 4 6% 52%	4948
	11th to 20th	Day	13% 5% 2 6% 3 3 3 3 4 4 53%	5090
	21st to end	Day	11% 6% 2 6% 3 4 4 3 5% 7% 48%	5583
April	1st to 10th	Day	12% 7% 3 6% 5% 4 3 3 5% 6% 44%	2310
	11th to 20th	Day	18% 7% 2 6% 4 4 3 3 5% 6% 42%	2323
	21st to end	Day	13% 6% 2 6% 5% 4 4 4 4 6% 45%	2662
May	1st to 10th	Day	18% 7% 2 6% 4 4 4 4 6% 8% 37%	7617
	11th to 20th	Day	10% 7% 2 7% 5% 5% 4 4 5% 8% 44%	7627
	21st to end	Day	12% 6% 3 7% 5% 5% 6% 5% 7% 9% 35%	8392
June	1st to 10th	Day	5% 3 2 5% 5% 5% 5% 6% 7% 10% 48%	2730
	11th to 20th	Day	7% 4 2 4 3 5% 5% 4 7% 9% 49%	2666
	21st to end	Day	7% 5% 1 5% 6% 5% 5% 5% 7% 10% 43%	2600
July	1st to 10th	Day	10% 7% 2 6% 5% 5% 5% 4 6% 9% 39%	5900
	11th to 20th	Day	4 3 2 4 4 4 6% 5% 9% 12% 48%	5900
	21st to end	Day	6% 4 2 6% 4 5% 5% 5% 8% 10% 46%	6422
August	1st to 10th	Day	1 1 1 2 2 3 3 3 4 8% 72%	4179
	11th to 20th	Day	3 2 1 4 3 3 4 4 6% 10% 61%	3846
	21st to end	Day	3 3 1 5% 4 5% 6% 5% 7% 11% 49%	4162
September	1st to 10th	Day	10% 6% 2 6% 4 4 5% 3 6% 6% 48%	2200
	11th to 20th	Day	10% 6% 2 6% 4 5% 5% 4 7% 9% 43%	2200
	21st to end	Day	8% 4 2 5% 4 4 5% 4 6% 7% 53%	2200
October	1st to 10th	Day	7% 4 1 3 3 4 4 4 4 6% 59%	2200
	11th to 20th	Day	11% 5% 1 4 3 3 4 3 4 6% 56%	2084
	21st to end	Day	10% 4 2 4 3 3 4 3 4 5% 59%	2200
November	1st to 10th	Day	13% 6% 2 5% 3 4 2 3 5% 6% 49%	2058
	11th to 20th	Day	9% 5% 2 6% 3 4 4 3 5% 6% 54%	1927
	21st to end	Day	14% 7% 2 6% 3 3 3 3 3 6% 48%	1890
December	1st to 10th	Day	22% 8% 3 6% 3 3 2 2 3 5% 42%	3030
	11th to 20th	Day	11% 8% 3 6% 5% 4 4 4 5% 6% 44%	3481
	21st to end	Day	10% 6% 2 4 3 3 3 2 3 4 59%	4587
January	1st to 10th	Night	12% 6% 2 4 3 3 3 2 3 5% 57%	7634
	11th to 20th	Night	9% 3 1 3 2 2 2 3 5% 5% 65%	7680
	21st to end	Night	23% 8% 3 6% 3 3 3 2 4 5% 40%	7972
February	1st to 10th	Night	13% 7% 2 5% 3 3 3 3 4 6% 51%	2520
	11th to 20th	Night	16% 6% 2 5% 3 2 3 3 4 6% 50%	2458
	21st to end	Night	15% 6% 2 6% 4 3 3 3 4 5% 50%	2076
March	1st to 10th	Night	10% 6% 2 6% 4 4 4 4 5% 8% 47%	5129
	11th to 20th	Night	13% 7% 2 4 3 4 3 3 4 5% 53%	5090
	21st to end	Night	12% 8% 2 6% 4 3 4 3 4 6% 48%	5588
April	1st to 10th	Night	9% 6% 2 5% 5% 5% 5% 3 6% 8% 47%	2310
	11th to 20th	Night	14% 6% 2 6% 4 5% 3 3 5% 6% 46%	2240
	21st to end	Night	14% 7% 2 5% 3 3 4 2 5% 6% 47%	1954
May	1st to 10th	Night	20% 8% 2 6% 4 3 4 3 5% 7% 38%	5266
	11th to 20th	Night	8% 6% 2 7% 4 4 5% 4 6% 7% 46%	5265
	21st to end	Night	12% 6% 2 6% 4 4 6% 4 7% 10% 38%	5793
June	1st to 10th	Night	4 3 2 3 3 3 4 3 6% 9% 60%	1890
	11th to 20th	Night	4 3 1 3 3 3 4 3 6% 10% 59%	1845
	21st to end	Night	6% 4 1 3 4 3 4 4 6% 10% 56%	1800
July	1st to 10th	Night	8% 5% 3 6% 4 4 4 4 7% 10% 44%	4078
	11th to 20th	Night	2 2 1 4 3 4 5% 5% 7% 11% 56%	4077
	21st to end	Night	4 4 2 5% 5% 4 5% 4 8% 10% 49%	4449
August	1st to 10th	Night	1 1 1 2 2 3 3 4 7% 76%	2975
	11th to 20th	Night	3 2 1 3 3 2 3 4 6% 10% 63%	3213
	21st to end	Night	4 3 1 4 3 3 4 4 6% 10% 57%	3741
September	1st to 10th	Night	8% 4 1 5% 3 4 4 4 5% 8% 53%	2200
	11th to 20th	Night	9% 5% 3 5% 4 4 4 4 6% 9% 48%	2200
	21st to end	Night	8% 3 2 4 4 3 4 4 6% 8% 55%	2200
October	1st to 10th	Night	5% 3 1 4 2 4 2 3 4 7% 66%	2200
	11th to 20th	Night	11% 4 1 4 3 3 3 3 5% 6% 58%	2295
	21st to end	Night	12% 4 1 4 3 2 2 2 3 4 61%	2640
November	1st to 10th	Night	12% 5% 2 5% 3 3 3 2 4 6% 56%	2460
	11th to 20th	Night	8% 6% 2 4 3 3 3 3 5% 6% 58%	2688
	21st to end	Night	15% 4 2 5% 3 4 4 3 4 6% 49%	2730
December	1st to 10th	Night	18% 8% 3 6% 4 3 4 3 4 5% 43%	4380
	11th to 20th	Night	13% 9% 3 7% 4 3 3 2 3 5% 48%	4946
	21st to end	Night	12% 6% 2 4 2 2 3 2 3 4 59%	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	33% 4 6% 23% 24% 10%	5290
	11th to 20th	Day	31% 2 4 15% 26% 21%	5310
	21st to end	Day	45% 4 5% 12% 23% 12%	6286
February	1st to 10th	Day	39% 4 5% 13% 21% 18%	2100
	11th to 20th	Day	37% 5% 8% 19% 18% 13%	2059
	21st to end	Day	35% 3 6% 16% 23% 16%	1730
March	1st to 10th	Day	33% 5% 5% 17% 17% 24%	4948
	11th to 20th	Day	34% 6% 5% 8% 14% 32%	5090
	21st to end	Day	35% 6% 8% 18% 21% 11%	5585
April	1st to 10th	Day	40% 5% 9% 17% 16% 13%	2310
	11th to 20th	Day	43% 5% 8% 15% 18% 11%	2323
	21st to end	Day	39% 6% 8% 20% 18% 9%	2662
May	1st to 10th	Day	43% 7% 11% 20% 16% 3	7655
	11th to 20th	Day	37% 6% 10% 17% 22% 8%	7631
	21st to end	Day	40% 9% 13% 24% 12% 2	8405
June	1st to 10th	Day	27% 10% 14% 28% 19% 3	2730
	11th to 20th	Day	29% 7% 14% 25% 19% 5%	2666
	21st to end	Day	33% 9% 13% 24% 17% 4	2600
July	1st to 10th	Day	40% 7% 18% 29% 5% 1	5836
	11th to 20th	Day	24% 9% 19% 31% 15% 2	5831
	21st to end	Day	29% 9% 17% 26% 18% 1	6240
August	1st to 10th	Day	12% 4 12% 39% 32% 1	4165
	11th to 20th	Day	20% 6% 22% 38% 11% 3	3882
	21st to end	Day	25% 11% 19% 26% 17% 2	4161
September	1st to 10th	Day	37% 6% 10% 20% 18% 9%	2200
	11th to 20th	Day	36% 9% 11% 20% 18% 6%	2200
	21st to end	Day	29% 6% 11% 22% 19% 14%	2200
October	1st to 10th	Day	15% 4 6% 13% 26% 36%	3590
	11th to 20th	Day	22% 4 7% 20% 25% 22%	3376
	21st to end	Day	23% 4 5% 18% 35% 14%	3538
November	1st to 10th	Day	35% 5% 8% 17% 21% 12%	2058
	11th to 20th	Day	32% 5% 8% 18% 22% 16%	1927
	21st to end	Day	39% 4 6% 16% 21% 14%	1890
December	1st to 10th	Day	46% 3 6% 17% 18% 10%	3030
	11th to 20th	Day	38% 6% 7% 12% 22% 14%	3479
	21st to end	Day	29% 3 5% 15% 27% 20%	4587
January	1st to 10th	Night	32% 3 6% 18% 27% 14%	7635
	11th to 20th	Night	22% 3 4 17% 30% 24%	7680
	21st to end	Night	47% 4 3 10% 21% 15%	7972
February	1st to 10th	Night	36% 4 7% 13% 22% 19%	2520
	11th to 20th	Night	36% 4 7% 18% 19% 16%	2458
	21st to end	Night	38% 4 6% 13% 21% 18%	2076
March	1st to 10th	Night	34% 7% 7% 18% 18% 16%	5129
	11th to 20th	Night	33% 6% 7% 10% 15% 28%	5090
	21st to end	Night	36% 6% 8% 18% 21% 12%	5588
April	1st to 10th	Night	35% 6% 10% 18% 16% 15%	2310
	11th to 20th	Night	40% 5% 10% 13% 17% 14%	2240
	21st to end	Night	39% 6% 9% 19% 18% 10%	1954
May	1st to 10th	Night	45% 6% 11% 18% 15% 6%	5293
	11th to 20th	Night	35% 7% 11% 17% 19% 10%	5266
	21st to end	Night	38% 9% 17% 26% 8% 3	5805
June	1st to 10th	Night	21% 8% 17% 31% 20% 3	1890
	11th to 20th	Night	20% 7% 17% 30% 22% 5%	1845
	21st to end	Night	24% 6% 20% 29% 17% 4	1800
July	1st to 10th	Night	35% 8% 24% 27% 5% 1	4035
	11th to 20th	Night	20% 9% 23% 34% 13% 1	4026
	21st to end	Night	26% 9% 23% 26% 13% 3	4320
August	1st to 10th	Night	9% 5% 15% 42% 29% 1	2965
	11th to 20th	Night	17% 7% 30% 33% 11% 2	3243
	21st to end	Night	22% 11% 21% 26% 18% 2	3741
September	1st to 10th	Night	29% 8% 13% 23% 19% 8%	2200
	11th to 20th	Night	33% 8% 14% 25% 15% 5%	2200
	21st to end	Night	26% 7% 14% 22% 19% 13%	2200
October	1st to 10th	Night	13% 4 8% 15% 22% 38%	3590
	11th to 20th	Night	20% 3 9% 17% 29% 21%	3729
	21st to end	Night	21% 3 7% 20% 34% 16%	4252
November	1st to 10th	Night	31% 5% 8% 18% 24% 14%	2460
	11th to 20th	Night	27% 4 9% 21% 21% 18%	2688
	21st to end	Night	36% 4 9% 16% 20% 15%	2730
December	1st to 10th	Night	45% 3 7% 16% 18% 12%	4380
	11th to 20th	Night	40% 3 6% 11% 22% 18%	4947
	21st to end	Night	31% 3 4 16% 28% 18%	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	19% 15% 38% 21% 6% 1	330
	11th to 20th	Day	22% 15% 31% 25% 6%	330
	21st to end	Day	18% 17% 39% 20% 6%	363
February	1st to 10th	Day	25% 14% 32% 22% 6% 1	330
	11th to 20th	Day	22% 19% 38% 19% 3	330
	21st to end	Day	22% 16% 41% 19% 2	273
March	1st to 10th	Day	20% 15% 42% 20% 3	330
	11th to 20th	Day	18% 18% 37% 21% 5%	330
	21st to end	Day	15% 16% 42% 20% 6% 1	363
April	1st to 10th	Day	16% 18% 42% 18% 5%	330
	11th to 20th	Day	22% 16% 35% 21% 5%	361
	21st to end	Day	17% 16% 40% 22% 5%	682
May	1st to 10th	Day	15% 13% 42% 24% 7%	753
	11th to 20th	Day	17% 10% 33% 29% 10% 1	775
	21st to end	Day	13% 9% 28% 36% 14% 1	844
June	1st to 10th	Day	6% 3 21% 43% 23% 4	780
	11th to 20th	Day	8% 2 18% 51% 19% 3	756
	21st to end	Day	7% 2 12% 41% 32% 7%	730
July	1st to 10th	Day	9% 3 11% 36% 32% 9%	721
	11th to 20th	Day	4 1 7% 42% 39% 7%	718
	21st to end	Day	3 1 5% 38% 42% 11%	794
August	1st to 10th	Day	2 4 39% 42% 13%	697
	11th to 20th	Day	6% 2 4 36% 38% 14%	517
	21st to end	Day	4 1 4 28% 40% 22%	498
September	1st to 10th	Day	10% 2 6% 26% 40% 17%	330
	11th to 20th	Day	6% 1 5% 29% 44% 16%	330
	21st to end	Day	10% 1 7% 33% 35% 13%	330
October	1st to 10th	Day	5% 2 15% 34% 33% 12%	330
	11th to 20th	Day	11% 3 24% 36% 21% 5%	330
	21st to end	Day	18% 9% 28% 27% 15% 4	363
November	1st to 10th	Day	19% 6% 26% 32% 12% 4	330
	11th to 20th	Day	16% 8% 28% 34% 10% 3	330
	21st to end	Day	21% 17% 31% 19% 9% 2	330
December	1st to 10th	Day	18% 10% 36% 25% 9% 2	330
	11th to 20th	Day	16% 15% 33% 24% 10% 2	330
	21st to end	Day	13% 14% 37% 28% 7% 1	363
January	1st to 10th	Night	17% 10% 35% 32% 6%	1050
	11th to 20th	Night	17% 12% 35% 30% 5%	1050
	21st to end	Night	21% 11% 34% 29% 6%	1007
February	1st to 10th	Night	19% 11% 36% 29% 6%	840
	11th to 20th	Night	20% 13% 40% 24% 3	824
	21st to end	Night	20% 13% 45% 22% 1	692
March	1st to 10th	Night	18% 13% 38% 28% 2	682
	11th to 20th	Night	17% 12% 38% 29% 4	630
	21st to end	Night	14% 12% 44% 27% 3	693
April	1st to 10th	Night	12% 11% 46% 28% 3	630
	11th to 20th	Night	16% 14% 42% 25% 3	623
	21st to end	Night	18% 11% 43% 23% 6%	630
May	1st to 10th	Night	15% 11% 41% 28% 4	630
	11th to 20th	Night	12% 8% 38% 31% 10%	621
	21st to end	Night	12% 6% 35% 37% 11%	683
June	1st to 10th	Night	4 3 26% 46% 20% 1	630
	11th to 20th	Night	5% 1 34% 47% 12% 1	615
	21st to end	Night	7% 19% 50% 22% 3	600
July	1st to 10th	Night	9% 2 12% 49% 25% 3	585
	11th to 20th	Night	4 12% 56% 25% 2	582
	21st to end	Night	4 1 8% 55% 28% 3	657
August	1st to 10th	Night	1 8% 57% 31% 3	597
	11th to 20th	Night	6% 1 7% 54% 29% 4	594
	21st to end	Night	6% 1 5% 46% 37% 6%	660
September	1st to 10th	Night	10% 2 8% 43% 33% 5%	600
	11th to 20th	Night	11% 2 8% 41% 35% 3	600
	21st to end	Night	10% 1 13% 42% 32% 3	600
October	1st to 10th	Night	5% 2 13% 46% 31% 3	600
	11th to 20th	Night	11% 4 23% 42% 18% 2	695
	21st to end	Night	13% 8% 30% 30% 18% 1	880
November	1st to 10th	Night	12% 6% 25% 41% 15% 1	820
	11th to 20th	Night	11% 7% 30% 38% 13% 1	1008
	21st to end	Night	17% 11% 32% 30% 10%	1050
December	1st to 10th	Night	17% 8% 30% 36% 8%	1050
	11th to 20th	Night	20% 9% 30% 34% 7%	1050
	21st to end	Night	16% 11% 32% 34% 7%	1155

Page generated at 2026-06-13 01:31:44. Version ac07

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