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 2026-09-29.

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	13% 9% 3 8% 5% 5% 5% 4 6% 8% 35%	148960
	Night	14% 9% 3 7% 4 4 4 4 5% 7% 36%	142459
Transparency	Day	46% 6% 13% 20% 13% 2	152658
	Night	46% 6% 11% 21% 13% 3	146833
Seeing	Day	19% 13% 22% 23% 16% 6%	17586
	Night	18% 11% 21% 31% 17% 2	27596

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	14% 18% 7% 10% 4 3 3 3 4 5% 29%	5258
	11th to 20th	Day	9% 16% 8% 11% 6% 4 3 2 3 3 35%	5280
	21st to end	Day	14% 15% 5% 11% 5% 3 3 2 4 5% 33%	5780
February	1st to 10th	Day	17% 12% 4 9% 5% 5% 4 3 5% 6% 31%	1940
	11th to 20th	Day	21% 14% 5% 8% 4 4 2 3 4 6% 29%	2048
	21st to end	Day	21% 12% 3 8% 4 4 2 3 4 5% 34%	1730
March	1st to 10th	Day	16% 14% 4 7% 4 4 4 3 4 5% 35%	4947
	11th to 20th	Day	12% 9% 3 5% 4 3 4 3 5% 6% 46%	5090
	21st to end	Day	16% 8% 2 6% 4 4 4 3 5% 7% 40%	5586
April	1st to 10th	Day	14% 9% 2 5% 5% 4 4 4 7% 8% 39%	2310
	11th to 20th	Day	15% 7% 2 5% 4 3 5% 4 5% 7% 42%	2541
	21st to end	Day	16% 7% 2 6% 5% 5% 5% 4 5% 6% 39%	2730
May	1st to 10th	Day	16% 8% 3 8% 6% 5% 5% 4 6% 8% 30%	7616
	11th to 20th	Day	14% 7% 3 8% 5% 6% 6% 4 6% 8% 33%	7626
	21st to end	Day	15% 7% 3 9% 7% 6% 6% 5% 7% 10% 26%	8391
June	1st to 10th	Day	12% 6% 2 6% 5% 5% 6% 5% 7% 8% 35%	2730
	11th to 20th	Day	9% 5% 2 8% 5% 7% 7% 5% 9% 10% 32%	2730
	21st to end	Day	11% 6% 2 6% 5% 5% 6% 6% 8% 9% 35%	2730
July	1st to 10th	Day	7% 5% 2 7% 5% 6% 6% 6% 9% 12% 35%	7680
	11th to 20th	Day	14% 7% 3 7% 6% 6% 6% 5% 7% 9% 30%	7680
	21st to end	Day	16% 9% 3 9% 7% 6% 7% 5% 8% 9% 21%	8340
August	1st to 10th	Day	11% 7% 3 9% 7% 7% 7% 6% 9% 11% 23%	6014
	11th to 20th	Day	11% 5% 2 7% 5% 6% 6% 5% 8% 12% 34%	5951
	21st to end	Day	6% 4 1 4 4 4 4 4 7% 8% 53%	6200
September	1st to 10th	Day	10% 5% 2 7% 5% 4 5% 5% 6% 7% 43%	2310
	11th to 20th	Day	14% 6% 2 6% 5% 5% 5% 3 6% 6% 41%	2310
	21st to end	Day	15% 6% 2 6% 5% 4 5% 5% 6% 8% 38%	2288
October	1st to 10th	Day	13% 5% 2 5% 3 3 4 3 4 7% 49%	2146
	11th to 20th	Day	15% 5% 2 4 3 3 3 3 5% 7% 50%	2000
	21st to end	Day	17% 9% 2 4 3 3 3 2 4 6% 46%	2200
November	1st to 10th	Day	12% 6% 3 5% 4 3 3 3 5% 6% 51%	1950
	11th to 20th	Day	11% 9% 3 5% 4 5% 4 4 5% 7% 44%	1890
	21st to end	Day	15% 9% 4 6% 4 3 3 4 5% 6% 41%	1890
December	1st to 10th	Day	13% 13% 3 10% 5% 4 4 3 4 5% 36%	3020
	11th to 20th	Day	17% 14% 4 9% 4 4 4 4 6% 7% 28%	3463
	21st to end	Day	12% 12% 6% 7% 5% 5% 5% 4 6% 7% 30%	4565
January	1st to 10th	Night	15% 16% 6% 11% 4 3 4 3 3 4 30%	7635
	11th to 20th	Night	13% 12% 4 10% 6% 4 4 2 3 3 38%	7680
	21st to end	Night	16% 11% 5% 10% 5% 4 4 3 4 5% 34%	8401
February	1st to 10th	Night	17% 12% 3 7% 3 4 5% 3 5% 6% 36%	2677
	11th to 20th	Night	20% 12% 4 9% 5% 3 4 3 4 5% 30%	2458
	21st to end	Night	20% 12% 3 10% 3 3 4 3 4 6% 32%	2076
March	1st to 10th	Night	20% 13% 3 6% 4 3 4 2 4 5% 36%	5124
	11th to 20th	Night	14% 5% 3 4 2 3 3 3 5% 7% 50%	5090
	21st to end	Night	12% 7% 2 5% 5% 5% 5% 4 6% 7% 41%	5588
April	1st to 10th	Night	14% 8% 3 5% 4 4 4 3 5% 8% 41%	2310
	11th to 20th	Night	14% 8% 2 5% 4 4 4 4 6% 6% 43%	2043
	21st to end	Night	14% 7% 3 6% 4 5% 4 3 5% 7% 41%	1890
May	1st to 10th	Night	17% 8% 3 8% 5% 5% 5% 5% 7% 9% 29%	5237
	11th to 20th	Night	14% 7% 3 8% 6% 5% 5% 4 6% 8% 35%	5234
	21st to end	Night	18% 10% 3 9% 5% 5% 5% 4 6% 7% 27%	5761
June	1st to 10th	Night	11% 6% 2 7% 6% 5% 5% 4 7% 10% 38%	1890
	11th to 20th	Night	8% 5% 2 7% 4 5% 6% 5% 9% 12% 39%	1890
	21st to end	Night	10% 5% 2 6% 5% 6% 5% 4 7% 11% 39%	1890
July	1st to 10th	Night	11% 6% 3 7% 5% 5% 6% 5% 8% 11% 32%	5278
	11th to 20th	Night	14% 8% 3 8% 5% 5% 6% 5% 7% 9% 31%	5277
	21st to end	Night	16% 10% 4 11% 7% 5% 5% 5% 7% 8% 22%	5736
August	1st to 10th	Night	11% 7% 3 9% 6% 6% 7% 5% 9% 11% 26%	4135
	11th to 20th	Night	12% 6% 2 6% 4 4 5% 4 7% 9% 40%	4095
	21st to end	Night	7% 4 2 5% 4 4 4 4 7% 11% 50%	4872
September	1st to 10th	Night	11% 6% 2 5% 5% 5% 4 3 5% 8% 46%	2310
	11th to 20th	Night	14% 5% 2 6% 4 4 4 4 6% 8% 44%	2310
	21st to end	Night	15% 6% 2 6% 4 4 4 2 5% 7% 46%	2289
October	1st to 10th	Night	15% 6% 2 5% 3 3 3 3 4 6% 50%	2252
	11th to 20th	Night	16% 7% 2 4 2 3 3 3 4 6% 50%	2400
	21st to end	Night	15% 8% 2 5% 3 2 4 3 4 6% 48%	2640
November	1st to 10th	Night	14% 8% 2 5% 3 3 4 3 5% 5% 49%	2566
	11th to 20th	Night	13% 9% 2 5% 4 4 3 3 5% 6% 45%	2730
	21st to end	Night	13% 11% 2 5% 3 3 4 3 5% 6% 45%	2730
December	1st to 10th	Night	14% 12% 5% 9% 4 4 3 3 4 6% 36%	4380
	11th to 20th	Night	18% 12% 5% 10% 4 4 4 3 4 5% 29%	4952
	21st to end	Night	13% 15% 6% 8% 5% 3 4 4 5% 8% 30%	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	58% 4 8% 20% 9% 1	5259
	11th to 20th	Day	55% 3 4 15% 20% 3	5280
	21st to end	Day	56% 3 7% 21% 13% 1	5780
February	1st to 10th	Day	55% 6% 7% 17% 14% 1	1940
	11th to 20th	Day	59% 4 7% 16% 13% 2	2058
	21st to end	Day	53% 4 8% 17% 14% 5%	1730
March	1st to 10th	Day	51% 5% 7% 15% 16% 7%	4947
	11th to 20th	Day	39% 4 6% 20% 24% 6%	5090
	21st to end	Day	43% 5% 8% 28% 14% 2	5586
April	1st to 10th	Day	42% 7% 13% 23% 13% 3	2310
	11th to 20th	Day	41% 6% 10% 21% 18% 4	2541
	21st to end	Day	45% 7% 10% 24% 11% 2	2730
May	1st to 10th	Day	50% 6% 12% 20% 11%	7651
	11th to 20th	Day	47% 6% 18% 21% 8% 1	7630
	21st to end	Day	50% 9% 14% 17% 9% 1	8405
June	1st to 10th	Day	42% 11% 16% 19% 11% 1	2730
	11th to 20th	Day	42% 12% 16% 17% 12% 1	2730
	21st to end	Day	41% 11% 16% 19% 12% 2	2730
July	1st to 10th	Day	38% 10% 22% 20% 9% 1	7615
	11th to 20th	Day	48% 7% 20% 20% 5% 1	7611
	21st to end	Day	55% 7% 14% 15% 9%	8156
August	1st to 10th	Day	50% 10% 20% 16% 4	6001
	11th to 20th	Day	41% 7% 23% 22% 7%	5990
	21st to end	Day	27% 5% 19% 36% 12% 1	6200
September	1st to 10th	Day	38% 10% 13% 20% 15% 4	2310
	11th to 20th	Day	42% 9% 11% 23% 14% 1	2310
	21st to end	Day	42% 8% 14% 18% 14% 4	2288
October	1st to 10th	Day	29% 4 7% 21% 31% 7%	3497
	11th to 20th	Day	27% 3 7% 27% 18% 17%	3240
	21st to end	Day	31% 3 5% 30% 19% 12%	3538
November	1st to 10th	Day	35% 5% 9% 20% 26% 5%	1950
	11th to 20th	Day	40% 4 8% 21% 22% 5%	1890
	21st to end	Day	44% 5% 8% 22% 18% 3	1890
December	1st to 10th	Day	51% 4 7% 16% 20% 1	3020
	11th to 20th	Day	56% 4 11% 16% 12% 2	3460
	21st to end	Day	51% 5% 15% 20% 9% 1	4565
January	1st to 10th	Night	57% 4 9% 20% 9% 1	7636
	11th to 20th	Night	50% 4 5% 17% 21% 3	7680
	21st to end	Night	54% 3 7% 19% 15% 2	8401
February	1st to 10th	Night	50% 5% 10% 19% 14% 1	2677
	11th to 20th	Night	56% 5% 8% 16% 11% 3	2459
	21st to end	Night	54% 5% 8% 17% 12% 4	2076
March	1st to 10th	Night	49% 5% 7% 19% 14% 5%	5124
	11th to 20th	Night	34% 5% 9% 20% 24% 9%	5090
	21st to end	Night	40% 6% 11% 27% 13% 2	5588
April	1st to 10th	Night	41% 7% 14% 21% 14% 3	2310
	11th to 20th	Night	39% 7% 10% 23% 17% 5%	2043
	21st to end	Night	43% 6% 13% 25% 12% 1	1890
May	1st to 10th	Night	50% 7% 14% 19% 9% 1	5264
	11th to 20th	Night	47% 7% 14% 23% 8%	5235
	21st to end	Night	53% 10% 12% 17% 8% 1	5771
June	1st to 10th	Night	40% 11% 17% 19% 12% 1	1890
	11th to 20th	Night	36% 12% 19% 22% 10% 1	1890
	21st to end	Night	37% 12% 16% 21% 12% 2	1890
July	1st to 10th	Night	44% 8% 18% 23% 7%	5235
	11th to 20th	Night	49% 8% 20% 18% 4 1	5226
	21st to end	Night	58% 7% 14% 12% 9% 1	5606
August	1st to 10th	Night	50% 11% 18% 17% 4	4124
	11th to 20th	Night	40% 6% 24% 23% 6%	4122
	21st to end	Night	29% 5% 17% 38% 10% 1	4872
September	1st to 10th	Night	37% 8% 15% 20% 16% 3	2310
	11th to 20th	Night	39% 8% 14% 22% 16% 1	2310
	21st to end	Night	39% 6% 13% 22% 17% 2	2289
October	1st to 10th	Night	36% 4 7% 20% 27% 6%	3681
	11th to 20th	Night	29% 4 7% 23% 22% 15%	3899
	21st to end	Night	27% 4 5% 30% 23% 11%	4252
November	1st to 10th	Night	37% 5% 10% 20% 23% 5%	2566
	11th to 20th	Night	40% 5% 7% 20% 22% 6%	2730
	21st to end	Night	41% 5% 7% 25% 19% 3	2730
December	1st to 10th	Night	52% 4 7% 20% 16% 1	4380
	11th to 20th	Night	58% 4 9% 16% 11% 2	4954
	21st to end	Night	51% 7% 12% 18% 11% 1	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	27% 29% 29% 13% 2	330
	11th to 20th	Day	32% 29% 24% 14% 2	330
	21st to end	Day	26% 30% 32% 10% 2	363
February	1st to 10th	Day	25% 23% 34% 14% 3	330
	11th to 20th	Day	39% 30% 23% 8% 1	330
	21st to end	Day	37% 19% 32% 10% 2	273
March	1st to 10th	Day	24% 22% 28% 19% 6% 1	490
	11th to 20th	Day	26% 25% 26% 19% 3 1	540
	21st to end	Day	25% 22% 26% 21% 7%	594
April	1st to 10th	Day	21% 20% 28% 19% 11% 2	540
	11th to 20th	Day	20% 17% 28% 23% 10% 2	532
	21st to end	Day	21% 14% 28% 20% 13% 4	540
May	1st to 10th	Day	21% 19% 28% 19% 10% 4	543
	11th to 20th	Day	18% 11% 23% 28% 15% 5%	567
	21st to end	Day	15% 9% 23% 23% 21% 9%	617
June	1st to 10th	Day	12% 6% 23% 28% 22% 8%	570
	11th to 20th	Day	9% 7% 20% 29% 24% 11%	570
	21st to end	Day	14% 7% 20% 24% 25% 10%	570
July	1st to 10th	Day	12% 5% 14% 24% 29% 16%	565
	11th to 20th	Day	10% 3 13% 31% 28% 14%	564
	21st to end	Day	15% 4 14% 29% 26% 13%	620
August	1st to 10th	Day	16% 4 16% 26% 24% 14%	566
	11th to 20th	Day	14% 3 16% 28% 28% 12%	559
	21st to end	Day	11% 3 11% 27% 29% 19%	627
September	1st to 10th	Day	9% 5% 14% 28% 30% 15%	570
	11th to 20th	Day	14% 4 12% 26% 30% 14%	570
	21st to end	Day	17% 7% 19% 30% 22% 6%	562
October	1st to 10th	Day	15% 7% 19% 28% 21% 9%	530
	11th to 20th	Day	14% 15% 21% 28% 19% 3	530
	21st to end	Day	22% 12% 21% 29% 13% 3	583
November	1st to 10th	Day	15% 17% 25% 28% 11% 3	428
	11th to 20th	Day	18% 23% 26% 25% 7%	330
	21st to end	Day	21% 20% 30% 22% 7% 1	330
December	1st to 10th	Day	27% 19% 35% 16% 2	330
	11th to 20th	Day	26% 17% 30% 22% 5%	330
	21st to end	Day	21% 23% 32% 15% 8%	363
January	1st to 10th	Night	24% 22% 27% 24% 3	840
	11th to 20th	Night	27% 19% 27% 24% 4	840
	21st to end	Night	22% 18% 35% 23% 2	924
February	1st to 10th	Night	22% 16% 30% 29% 3	840
	11th to 20th	Night	28% 21% 32% 18% 1	823
	21st to end	Night	25% 23% 29% 21% 2	692
March	1st to 10th	Night	23% 16% 30% 28% 4	840
	11th to 20th	Night	23% 19% 28% 22% 7%	840
	21st to end	Night	20% 13% 32% 28% 7%	924
April	1st to 10th	Night	18% 18% 26% 29% 9%	840
	11th to 20th	Night	16% 15% 28% 31% 11% 1	725
	21st to end	Night	17% 9% 27% 37% 10% 1	630
May	1st to 10th	Night	17% 10% 26% 32% 14% 1	630
	11th to 20th	Night	15% 6% 22% 36% 19% 2	621
	21st to end	Night	13% 3 17% 35% 29% 4	683
June	1st to 10th	Night	11% 3 12% 41% 29% 4	630
	11th to 20th	Night	8% 3 13% 42% 30% 4	630
	21st to end	Night	11% 3 10% 40% 33% 3	630
July	1st to 10th	Night	12% 3 7% 29% 43% 5%	615
	11th to 20th	Night	12% 3 7% 29% 43% 7%	612
	21st to end	Night	11% 4 6% 35% 36% 7%	690
August	1st to 10th	Night	11% 3 7% 34% 39% 5%	627
	11th to 20th	Night	12% 3 7% 36% 38% 4	624
	21st to end	Night	11% 2 7% 35% 38% 6%	749
September	1st to 10th	Night	13% 3 9% 34% 36% 6%	840
	11th to 20th	Night	15% 3 10% 30% 36% 5%	840
	21st to end	Night	17% 4 15% 36% 24% 2	833
October	1st to 10th	Night	16% 5% 16% 30% 27% 6%	800
	11th to 20th	Night	17% 8% 21% 35% 17% 2	800
	21st to end	Night	19% 11% 20% 35% 13% 2	880
November	1st to 10th	Night	17% 7% 21% 37% 15% 2	820
	11th to 20th	Night	18% 14% 22% 35% 10% 1	840
	21st to end	Night	19% 14% 26% 31% 10% 1	840
December	1st to 10th	Night	24% 15% 28% 28% 6%	840
	11th to 20th	Night	24% 13% 26% 30% 6% 1	840
	21st to end	Night	25% 16% 26% 29% 4	924

Page generated at 2026-09-26 04:18:39. Version ac07

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