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 2025-02-21.

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 5% 4 4 4 4 5% 7% 48%	109197
	Night	12% 5% 2 5% 3 3 3 3 5% 7% 53%	109624
Transparency	Day	33% 6% 10% 21% 20% 10%	113028
	Night	31% 6% 11% 20% 20% 13%	113920
Seeing	Day	13% 8% 23% 31% 20% 5%	15171
	Night	13% 7% 28% 36% 14% 1	25252

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	12% 9% 3 5% 4 3 3 2 3 5% 52%	4077
	11th to 20th	Day	15% 5% 1 3 3 2 2 3 5% 6% 55%	4080
	21st to end	Day	22% 7% 3 6% 3 3 2 2 3 5% 44%	4854
February	1st to 10th	Day	16% 7% 3 6% 3 3 4 2 4 6% 48%	2000
	11th to 20th	Day	15% 6% 2 6% 3 3 3 3 4 7% 47%	1949
	21st to end	Day	17% 5% 2 4 3 2 3 3 4 5% 51%	1570
March	1st to 10th	Day	14% 8% 3 8% 4 3 4 3 4 6% 44%	3367
	11th to 20th	Day	19% 7% 3 9% 5% 5% 5% 4 5% 5% 34%	3480
	21st to end	Day	12% 7% 2 6% 3 4 4 4 5% 7% 46%	3814
April	1st to 10th	Day	12% 7% 3 6% 5% 4 4 3 5% 7% 45%	2090
	11th to 20th	Day	18% 7% 2 5% 4 3 3 3 4 6% 44%	2099
	21st to end	Day	13% 6% 2 5% 4 4 4 4 4 6% 47%	2408
May	1st to 10th	Day	20% 7% 3 6% 5% 4 5% 4 6% 7% 33%	4082
	11th to 20th	Day	15% 7% 2 6% 4 4 3 3 4 6% 44%	4082
	21st to end	Day	11% 5% 2 6% 5% 6% 7% 6% 8% 9% 37%	4477
June	1st to 10th	Day	5% 3 2 5% 4 4 6% 5% 7% 9% 49%	2470
	11th to 20th	Day	7% 4 2 4 3 5% 5% 4 7% 10% 50%	2470
	21st to end	Day	7% 5% 1 5% 6% 5% 6% 5% 7% 10% 43%	2470
July	1st to 10th	Day	6% 4 1 5% 5% 5% 5% 4 6% 10% 49%	4120
	11th to 20th	Day	4 3 1 3 4 4 5% 4 7% 12% 54%	4120
	21st to end	Day	8% 5% 2 6% 4 5% 5% 5% 8% 10% 42%	4465
August	1st to 10th	Day	1 1 1 2 2 3 3 3 4 8% 72%	4051
	11th to 20th	Day	4 2 1 4 3 3 4 4 5% 10% 61%	3726
	21st to end	Day	3 3 1 5% 4 5% 6% 5% 7% 11% 49%	4034
September	1st to 10th	Day	10% 6% 2 6% 4 4 5% 3 6% 6% 47%	2090
	11th to 20th	Day	10% 6% 2 6% 4 5% 5% 4 6% 8% 42%	2090
	21st to end	Day	8% 4 2 5% 4 4 5% 4 6% 7% 53%	2090
October	1st to 10th	Day	7% 4 2 3 3 4 4 4 5% 6% 58%	2090
	11th to 20th	Day	11% 5% 2 4 3 3 4 3 4 6% 55%	1980
	21st to end	Day	10% 4 2 4 3 3 4 3 4 5% 58%	2090
November	1st to 10th	Day	14% 6% 2 6% 4 4 2 3 6% 6% 47%	1958
	11th to 20th	Day	9% 5% 2 6% 3 4 4 3 5% 6% 53%	1835
	21st to end	Day	14% 7% 2 5% 3 3 4 3 3 6% 49%	1800
December	1st to 10th	Day	22% 8% 3 6% 3 3 2 2 3 5% 41%	2940
	11th to 20th	Day	11% 8% 3 6% 5% 4 4 4 5% 6% 44%	3391
	21st to end	Day	11% 6% 2 4 3 3 3 2 3 4 60%	4488
January	1st to 10th	Night	16% 7% 2 4 2 2 2 2 3 5% 54%	5888
	11th to 20th	Night	11% 3 1 2 2 2 2 2 4 5% 66%	5900
	21st to end	Night	25% 7% 2 6% 3 3 3 2 4 5% 41%	6154
February	1st to 10th	Night	14% 7% 2 5% 3 3 3 3 4 6% 51%	2400
	11th to 20th	Night	16% 6% 2 5% 3 2 3 3 4 6% 50%	2338
	21st to end	Night	15% 6% 2 6% 4 3 3 3 4 5% 48%	1884
March	1st to 10th	Night	12% 7% 2 7% 5% 4 4 3 5% 7% 44%	3489
	11th to 20th	Night	19% 10% 2 6% 4 5% 4 4 5% 6% 36%	3480
	21st to end	Night	11% 7% 2 6% 4 4 5% 4 5% 6% 47%	3817
April	1st to 10th	Night	9% 6% 2 5% 5% 4 5% 3 6% 8% 48%	2090
	11th to 20th	Night	15% 5% 2 6% 4 5% 3 3 4 6% 46%	2024
	21st to end	Night	14% 7% 2 5% 3 3 4 2 5% 6% 50%	1768
May	1st to 10th	Night	22% 9% 2 5% 3 3 3 3 4 6% 40%	2823
	11th to 20th	Night	10% 6% 2 6% 4 3 4 3 4 6% 51%	2823
	21st to end	Night	11% 5% 2 5% 3 4 5% 4 7% 9% 45%	3090
June	1st to 10th	Night	4 3 2 3 3 3 3 3 5% 9% 62%	1710
	11th to 20th	Night	4 3 1 3 3 3 4 3 6% 10% 60%	1710
	21st to end	Night	6% 4 1 3 3 3 4 4 6% 10% 56%	1710
July	1st to 10th	Night	5% 3 2 3 3 3 4 4 6% 10% 57%	2850
	11th to 20th	Night	2 3 1 4 3 3 4 4 6% 9% 61%	2850
	21st to end	Night	4 5% 2 5% 5% 5% 6% 5% 8% 11% 45%	3098
August	1st to 10th	Night	1 1 1 2 2 2 3 4 7% 76%	2884
	11th to 20th	Night	3 2 1 3 3 2 3 4 6% 10% 63%	3113
	21st to end	Night	4 3 1 4 3 3 4 4 6% 10% 57%	3627
September	1st to 10th	Night	8% 4 1 4 3 4 4 4 5% 8% 54%	2090
	11th to 20th	Night	9% 5% 3 5% 4 5% 4 4 6% 8% 47%	2090
	21st to end	Night	8% 3 2 4 4 3 4 4 5% 8% 55%	2090
October	1st to 10th	Night	5% 3 1 4 2 4 2 3 4 6% 65%	2090
	11th to 20th	Night	11% 4 1 4 3 3 3 3 5% 6% 56%	2180
	21st to end	Night	12% 4 1 4 3 2 2 2 3 4 61%	2508
November	1st to 10th	Night	12% 5% 2 5% 3 3 3 2 4 6% 54%	2340
	11th to 20th	Night	8% 6% 2 4 3 3 3 3 5% 6% 57%	2560
	21st to end	Night	15% 4 2 5% 3 4 4 3 4 6% 50%	2600
December	1st to 10th	Night	18% 8% 3 6% 4 3 4 3 4 5% 43%	4250
	11th to 20th	Night	13% 9% 3 7% 4 3 3 2 3 5% 48%	4816
	21st to end	Night	12% 7% 2 4 2 2 3 2 3 4 59%	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	36% 5% 4 22% 22% 12%	4078
	11th to 20th	Day	31% 3 5% 16% 26% 19%	4080
	21st to end	Day	44% 4 4 9% 25% 15%	4854
February	1st to 10th	Day	40% 4 5% 13% 21% 18%	2000
	11th to 20th	Day	37% 4 7% 19% 18% 14%	1959
	21st to end	Day	36% 4 7% 16% 21% 16%	1570
March	1st to 10th	Day	40% 6% 7% 13% 20% 14%	3367
	11th to 20th	Day	49% 9% 7% 9% 16% 9%	3480
	21st to end	Day	34% 8% 10% 15% 20% 12%	3814
April	1st to 10th	Day	39% 5% 9% 17% 17% 13%	2090
	11th to 20th	Day	41% 5% 8% 15% 19% 11%	2099
	21st to end	Day	38% 6% 6% 21% 19% 10%	2408
May	1st to 10th	Day	47% 9% 10% 14% 15% 5%	4120
	11th to 20th	Day	40% 7% 8% 16% 22% 7%	4086
	21st to end	Day	36% 11% 14% 26% 11% 2	4489
June	1st to 10th	Day	27% 9% 13% 27% 20% 4	2470
	11th to 20th	Day	29% 7% 14% 26% 19% 6%	2470
	21st to end	Day	34% 9% 12% 23% 18% 4	2470
July	1st to 10th	Day	28% 7% 18% 38% 7% 1	4056
	11th to 20th	Day	22% 8% 17% 33% 18% 3	4051
	21st to end	Day	31% 10% 18% 30% 11% 1	4325
August	1st to 10th	Day	12% 4 12% 39% 32% 1	4037
	11th to 20th	Day	19% 6% 22% 38% 12% 3	3762
	21st to end	Day	25% 12% 19% 25% 17% 2	4033
September	1st to 10th	Day	37% 7% 10% 20% 17% 9%	2090
	11th to 20th	Day	37% 9% 11% 19% 18% 6%	2090
	21st to end	Day	30% 6% 11% 21% 19% 13%	2090
October	1st to 10th	Day	16% 4 6% 12% 25% 37%	3480
	11th to 20th	Day	22% 4 7% 19% 24% 23%	3272
	21st to end	Day	24% 4 5% 18% 35% 14%	3428
November	1st to 10th	Day	37% 6% 9% 18% 19% 12%	1958
	11th to 20th	Day	32% 5% 8% 17% 21% 16%	1835
	21st to end	Day	38% 4 7% 16% 21% 14%	1800
December	1st to 10th	Day	47% 3 6% 17% 17% 9%	2940
	11th to 20th	Day	39% 6% 7% 12% 22% 14%	3389
	21st to end	Day	29% 3 5% 15% 27% 20%	4488
January	1st to 10th	Night	34% 3 4 19% 26% 13%	5888
	11th to 20th	Night	23% 3 4 19% 29% 23%	5900
	21st to end	Night	45% 5% 3 10% 20% 17%	6154
February	1st to 10th	Night	37% 4 7% 13% 22% 19%	2400
	11th to 20th	Night	37% 4 7% 17% 19% 16%	2338
	21st to end	Night	39% 4 6% 13% 20% 18%	1884
March	1st to 10th	Night	38% 8% 8% 15% 20% 11%	3489
	11th to 20th	Night	46% 9% 9% 11% 14% 10%	3480
	21st to end	Night	36% 8% 9% 16% 20% 10%	3817
April	1st to 10th	Night	33% 6% 10% 18% 17% 15%	2090
	11th to 20th	Night	39% 6% 10% 13% 18% 15%	2024
	21st to end	Night	37% 6% 8% 20% 19% 10%	1768
May	1st to 10th	Night	45% 7% 9% 17% 14% 8%	2850
	11th to 20th	Night	32% 8% 11% 22% 19% 9%	2824
	21st to end	Night	33% 10% 15% 28% 11% 4	3099
June	1st to 10th	Night	19% 8% 17% 31% 22% 3	1710
	11th to 20th	Night	19% 6% 16% 31% 23% 5%	1710
	21st to end	Night	24% 6% 19% 30% 17% 4	1710
July	1st to 10th	Night	22% 8% 26% 37% 7% 1	2805
	11th to 20th	Night	20% 8% 20% 35% 17% 1	2796
	21st to end	Night	28% 9% 25% 29% 8%	2999
August	1st to 10th	Night	9% 5% 15% 42% 29% 1	2874
	11th to 20th	Night	17% 7% 30% 33% 12% 2	3143
	21st to end	Night	21% 11% 21% 26% 18% 2	3627
September	1st to 10th	Night	28% 8% 14% 23% 19% 8%	2090
	11th to 20th	Night	33% 8% 14% 23% 16% 5%	2090
	21st to end	Night	27% 7% 14% 20% 19% 13%	2090
October	1st to 10th	Night	13% 4 8% 15% 21% 39%	3480
	11th to 20th	Night	21% 4 10% 16% 29% 21%	3614
	21st to end	Night	21% 3 7% 20% 34% 16%	4120
November	1st to 10th	Night	32% 5% 9% 19% 22% 14%	2340
	11th to 20th	Night	28% 4 9% 21% 21% 18%	2560
	21st to end	Night	36% 5% 9% 16% 20% 16%	2600
December	1st to 10th	Night	45% 3 7% 16% 17% 11%	4250
	11th to 20th	Night	41% 4 6% 11% 22% 18%	4817
	21st to end	Night	31% 3 4 16% 28% 18%	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	19% 16% 38% 21% 5% 1	300
	11th to 20th	Day	23% 16% 30% 25% 6%	300
	21st to end	Day	18% 18% 37% 20% 7%	330
February	1st to 10th	Day	27% 14% 31% 22% 5%	300
	11th to 20th	Day	22% 20% 38% 18% 2	300
	21st to end	Day	24% 17% 42% 16%	225
March	1st to 10th	Day	19% 14% 44% 19% 3	270
	11th to 20th	Day	20% 17% 36% 22% 5%	270
	21st to end	Day	16% 17% 45% 17% 4	297
April	1st to 10th	Day	16% 19% 44% 16% 4	270
	11th to 20th	Day	23% 16% 36% 20% 6%	297
	21st to end	Day	16% 16% 40% 23% 5%	588
May	1st to 10th	Day	14% 13% 42% 24% 7%	653
	11th to 20th	Day	19% 8% 31% 31% 11% 1	675
	21st to end	Day	14% 8% 28% 35% 14% 1	734
June	1st to 10th	Day	5% 4 20% 43% 24% 4	680
	11th to 20th	Day	8% 1 18% 51% 19% 3	680
	21st to end	Day	7% 2 11% 42% 31% 7%	680
July	1st to 10th	Day	7% 3 10% 37% 33% 10%	671
	11th to 20th	Day	3 1 6% 42% 40% 7%	668
	21st to end	Day	4 1 5% 39% 42% 10%	739
August	1st to 10th	Day	2 4 40% 41% 12%	649
	11th to 20th	Day	7% 1 5% 36% 39% 12%	477
	21st to end	Day	4 1 4 29% 39% 22%	458
September	1st to 10th	Day	10% 1 6% 25% 40% 18%	300
	11th to 20th	Day	6% 1 5% 29% 43% 16%	300
	21st to end	Day	11% 1 6% 32% 36% 13%	300
October	1st to 10th	Day	6% 2 16% 34% 32% 11%	300
	11th to 20th	Day	12% 4 24% 37% 20% 4	300
	21st to end	Day	19% 8% 28% 26% 14% 5%	330
November	1st to 10th	Day	21% 5% 27% 33% 10% 3	300
	11th to 20th	Day	17% 8% 29% 31% 10% 4	300
	21st to end	Day	22% 17% 31% 18% 9% 3	300
December	1st to 10th	Day	18% 10% 34% 25% 10% 3	300
	11th to 20th	Day	17% 15% 34% 24% 9% 1	300
	21st to end	Day	14% 15% 38% 25% 6% 2	330
January	1st to 10th	Night	17% 10% 35% 31% 6% 1	1000
	11th to 20th	Night	18% 13% 34% 30% 5%	1000
	21st to end	Night	20% 10% 35% 29% 6%	959
February	1st to 10th	Night	20% 11% 36% 28% 6%	800
	11th to 20th	Night	21% 13% 39% 24% 3	784
	21st to end	Night	20% 13% 46% 20% 1	628
March	1st to 10th	Night	18% 11% 39% 28% 2	618
	11th to 20th	Night	18% 11% 38% 29% 4	570
	21st to end	Night	14% 13% 44% 26% 3	627
April	1st to 10th	Night	11% 12% 47% 28% 2	570
	11th to 20th	Night	16% 12% 43% 26% 3	563
	21st to end	Night	17% 9% 44% 23% 7%	570
May	1st to 10th	Night	14% 11% 42% 28% 5%	570
	11th to 20th	Night	12% 6% 38% 32% 10%	561
	21st to end	Night	12% 5% 36% 36% 10%	617
June	1st to 10th	Night	4 2 24% 48% 20% 1	570
	11th to 20th	Night	5% 2 33% 46% 13% 1	570
	21st to end	Night	7% 19% 48% 23% 3	570
July	1st to 10th	Night	8% 2 12% 50% 25% 3	555
	11th to 20th	Night	4 12% 56% 26% 3	552
	21st to end	Night	4 1 8% 56% 27% 3	624
August	1st to 10th	Night	1 8% 57% 31% 3	567
	11th to 20th	Night	6% 1 6% 54% 29% 4	564
	21st to end	Night	6% 1 5% 47% 36% 6%	627
September	1st to 10th	Night	10% 2 8% 43% 32% 6%	570
	11th to 20th	Night	11% 2 8% 39% 36% 4	570
	21st to end	Night	10% 1 12% 42% 32% 3	570
October	1st to 10th	Night	5% 2 14% 46% 30% 3	570
	11th to 20th	Night	12% 4 24% 41% 17% 2	660
	21st to end	Night	14% 8% 30% 30% 19% 1	836
November	1st to 10th	Night	12% 6% 25% 40% 15% 1	780
	11th to 20th	Night	12% 7% 30% 38% 13% 1	960
	21st to end	Night	16% 11% 33% 30% 10%	1000
December	1st to 10th	Night	17% 8% 30% 37% 9%	1000
	11th to 20th	Night	21% 9% 30% 34% 7%	1000
	21st to end	Night	17% 11% 32% 33% 7%	1100

Page generated at 2025-02-18 02:26:30. Version ac07

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