Spring City Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Spring City Park clear sky chart from 2005-11-06 to 2025-03-12.

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% 7% 2 6% 5% 4 5% 4 6% 8% 40%	109174
	Night	14% 7% 2 6% 4 4 4 4 5% 7% 43%	109852
Transparency	Day	40% 7% 12% 22% 16% 3	112956
	Night	38% 6% 11% 23% 18% 4	114208
Seeing	Day	16% 10% 23% 23% 19% 9%	15124
	Night	16% 8% 24% 30% 19% 3	25262

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	15% 12% 3 7% 4 3 3 3 5% 5% 39%	4056
	11th to 20th	Day	15% 7% 5% 8% 4 4 4 2 4 5% 42%	4060
	21st to end	Day	20% 9% 3 5% 4 3 3 3 5% 7% 39%	4604
February	1st to 10th	Day	17% 10% 3 7% 4 4 4 3 5% 6% 36%	2000
	11th to 20th	Day	22% 9% 3 7% 5% 3 5% 3 4 5% 36%	1948
	21st to end	Day	20% 9% 2 6% 4 4 4 4 5% 6% 37%	1650
March	1st to 10th	Day	23% 12% 3 6% 4 4 4 3 4 6% 31%	3244
	11th to 20th	Day	15% 6% 2 6% 4 3 3 3 4 6% 49%	3491
	21st to end	Day	15% 7% 2 7% 4 5% 5% 4 5% 6% 39%	3815
April	1st to 10th	Day	11% 6% 2 7% 4 5% 5% 4 6% 7% 43%	2228
	11th to 20th	Day	14% 7% 3 6% 4 3 4 4 4 7% 44%	2254
	21st to end	Day	12% 6% 2 7% 5% 5% 4 3 6% 6% 44%	2432
May	1st to 10th	Day	15% 8% 3 8% 5% 5% 5% 4 5% 7% 36%	4082
	11th to 20th	Day	16% 7% 3 7% 5% 4 5% 4 6% 8% 35%	4081
	21st to end	Day	11% 6% 2 7% 4 4 5% 4 6% 9% 41%	4476
June	1st to 10th	Day	10% 6% 2 7% 5% 5% 6% 5% 7% 10% 38%	2470
	11th to 20th	Day	4 4 1 5% 5% 6% 6% 6% 9% 11% 43%	2470
	21st to end	Day	6% 5% 2 7% 6% 5% 6% 5% 8% 11% 39%	2470
July	1st to 10th	Day	6% 4 2 7% 5% 6% 7% 6% 10% 12% 35%	4120
	11th to 20th	Day	10% 5% 3 6% 6% 6% 6% 6% 7% 10% 34%	4120
	21st to end	Day	15% 11% 4 10% 7% 8% 7% 5% 7% 7% 19%	4466
August	1st to 10th	Day	5% 4 2 5% 5% 6% 6% 6% 9% 11% 40%	4104
	11th to 20th	Day	6% 4 2 6% 5% 5% 5% 6% 8% 12% 42%	3801
	21st to end	Day	7% 4 1 5% 4 4 5% 4 6% 8% 51%	4180
September	1st to 10th	Day	12% 5% 2 6% 5% 4 6% 5% 7% 8% 40%	2147
	11th to 20th	Day	14% 5% 2 6% 5% 5% 5% 4 7% 7% 41%	2090
	21st to end	Day	14% 5% 2 4 4 4 3 3 5% 6% 48%	2090
October	1st to 10th	Day	11% 5% 2 5% 2 4 3 3 4 6% 55%	2090
	11th to 20th	Day	12% 5% 2 5% 3 3 3 3 4 6% 55%	1995
	21st to end	Day	15% 4 2 4 3 3 3 3 5% 7% 49%	2009
November	1st to 10th	Day	12% 5% 1 5% 4 3 3 4 5% 5% 53%	1762
	11th to 20th	Day	13% 6% 2 7% 3 3 4 3 5% 7% 48%	1800
	21st to end	Day	14% 7% 2 5% 4 4 4 4 5% 6% 45%	1800
December	1st to 10th	Day	15% 6% 2 6% 5% 4 4 3 4 6% 45%	2930
	11th to 20th	Day	19% 13% 3 8% 5% 5% 4 3 4 6% 30%	3373
	21st to end	Day	20% 8% 3 6% 5% 4 4 4 5% 8% 33%	4466
January	1st to 10th	Night	16% 8% 3 8% 4 3 4 2 5% 6% 41%	5889
	11th to 20th	Night	18% 7% 2 5% 3 3 3 3 4 5% 45%	5900
	21st to end	Night	17% 9% 3 6% 4 3 4 3 4 6% 41%	6337
February	1st to 10th	Night	16% 7% 3 7% 5% 5% 4 4 5% 6% 39%	2400
	11th to 20th	Night	22% 8% 4 6% 5% 4 4 3 5% 4 36%	2338
	21st to end	Night	22% 9% 3 6% 5% 3 3 3 5% 6% 36%	1980
March	1st to 10th	Night	21% 9% 4 6% 5% 4 4 3 5% 7% 32%	3828
	11th to 20th	Night	9% 6% 2 5% 4 4 4 3 5% 7% 50%	3498
	21st to end	Night	13% 7% 2 7% 5% 4 4 4 5% 5% 41%	3817
April	1st to 10th	Night	12% 5% 2 5% 4 4 4 3 6% 7% 49%	1967
	11th to 20th	Night	13% 5% 2 6% 3 3 4 3 5% 7% 49%	1875
	21st to end	Night	11% 4 2 5% 4 4 5% 5% 5% 8% 47%	1748
May	1st to 10th	Night	13% 8% 3 7% 5% 4 5% 4 6% 8% 37%	2813
	11th to 20th	Night	16% 6% 2 6% 5% 4 4 4 6% 7% 39%	2812
	21st to end	Night	7% 6% 3 7% 5% 4 4 5% 7% 9% 43%	3079
June	1st to 10th	Night	7% 6% 3 6% 6% 6% 5% 5% 7% 9% 42%	1710
	11th to 20th	Night	4 4 1 4 4 4 5% 4 8% 12% 51%	1710
	21st to end	Night	6% 5% 2 6% 5% 6% 6% 5% 6% 11% 44%	1710
July	1st to 10th	Night	7% 5% 2 7% 6% 6% 6% 6% 8% 11% 35%	2840
	11th to 20th	Night	9% 5% 2 5% 4 4 5% 4 8% 10% 45%	2840
	21st to end	Night	12% 10% 4 10% 6% 6% 7% 5% 7% 10% 23%	3087
August	1st to 10th	Night	5% 3 1 5% 4 5% 5% 4 9% 11% 48%	2825
	11th to 20th	Night	6% 5% 2 5% 4 4 5% 3 6% 9% 50%	3024
	21st to end	Night	5% 4 1 4 4 3 4 4 6% 9% 55%	3476
September	1st to 10th	Night	9% 7% 3 6% 5% 4 5% 4 6% 8% 44%	2013
	11th to 20th	Night	12% 7% 2 6% 4 4 5% 4 5% 8% 43%	2090
	21st to end	Night	12% 5% 2 5% 4 4 4 3 4 6% 51%	2090
October	1st to 10th	Night	11% 4 2 4 3 3 3 3 3 6% 59%	2090
	11th to 20th	Night	13% 4 2 4 3 3 3 2 4 6% 54%	2182
	21st to end	Night	13% 5% 2 5% 3 3 3 3 4 5% 53%	2586
November	1st to 10th	Night	11% 5% 2 5% 4 3 3 3 4 6% 52%	2536
	11th to 20th	Night	12% 7% 2 6% 4 3 3 3 4 7% 49%	2600
	21st to end	Night	15% 7% 2 5% 4 4 4 4 5% 7% 43%	2600
December	1st to 10th	Night	18% 9% 2 6% 4 3 4 3 4 5% 41%	4250
	11th to 20th	Night	21% 9% 3 6% 4 4 4 3 4 5% 38%	4822
	21st to end	Night	19% 8% 3 6% 5% 5% 5% 4 6% 7% 31%	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	45% 5% 8% 23% 18% 1	4057
	11th to 20th	Day	44% 4 7% 20% 24% 1	4060
	21st to end	Day	46% 4 9% 24% 15% 2	4604
February	1st to 10th	Day	50% 4 9% 19% 16% 2	2000
	11th to 20th	Day	51% 5% 7% 18% 15% 3	1958
	21st to end	Day	47% 5% 8% 16% 18% 6%	1650
March	1st to 10th	Day	52% 7% 8% 14% 12% 7%	3244
	11th to 20th	Day	37% 5% 9% 24% 19% 6%	3491
	21st to end	Day	44% 6% 8% 28% 12% 2	3815
April	1st to 10th	Day	38% 7% 11% 23% 18% 3	2228
	11th to 20th	Day	38% 6% 9% 18% 24% 5%	2254
	21st to end	Day	39% 6% 11% 27% 15% 2	2432
May	1st to 10th	Day	45% 9% 10% 22% 12% 2	4120
	11th to 20th	Day	44% 9% 13% 24% 9% 1	4085
	21st to end	Day	37% 8% 13% 21% 19% 2	4489
June	1st to 10th	Day	38% 10% 15% 21% 14% 2	2470
	11th to 20th	Day	30% 11% 18% 24% 15% 2	2470
	21st to end	Day	35% 12% 19% 18% 13% 4	2470
July	1st to 10th	Day	35% 13% 22% 18% 11% 1	4055
	11th to 20th	Day	40% 10% 21% 21% 6% 2	4051
	21st to end	Day	60% 10% 12% 13% 5% 1	4324
August	1st to 10th	Day	31% 11% 17% 30% 10%	4091
	11th to 20th	Day	31% 9% 18% 26% 14% 2	3839
	21st to end	Day	30% 7% 14% 32% 16% 2	4179
September	1st to 10th	Day	38% 9% 14% 18% 16% 6%	2147
	11th to 20th	Day	39% 9% 12% 20% 17% 3	2090
	21st to end	Day	35% 6% 13% 21% 19% 7%	2090
October	1st to 10th	Day	22% 4 8% 20% 32% 13%	3480
	11th to 20th	Day	23% 3 6% 26% 32% 10%	3300
	21st to end	Day	28% 6% 9% 24% 25% 8%	3285
November	1st to 10th	Day	32% 5% 8% 23% 26% 6%	1762
	11th to 20th	Day	36% 4 7% 25% 23% 5%	1800
	21st to end	Day	40% 4 9% 24% 19% 4	1800
December	1st to 10th	Day	41% 5% 6% 25% 21% 2	2930
	11th to 20th	Day	55% 5% 8% 19% 11% 2	3370
	21st to end	Day	47% 5% 15% 23% 9% 1	4466
January	1st to 10th	Night	43% 5% 10% 23% 18% 1	5889
	11th to 20th	Night	41% 4 8% 19% 22% 5%	5900
	21st to end	Night	45% 3 7% 21% 18% 5%	6337
February	1st to 10th	Night	45% 5% 10% 21% 17% 3	2400
	11th to 20th	Night	51% 4 7% 18% 15% 5%	2339
	21st to end	Night	50% 4 8% 17% 17% 4	1980
March	1st to 10th	Night	50% 7% 10% 15% 15% 4	3828
	11th to 20th	Night	34% 5% 8% 25% 17% 11%	3498
	21st to end	Night	44% 5% 8% 24% 17% 2	3817
April	1st to 10th	Night	33% 5% 12% 25% 22% 3	1967
	11th to 20th	Night	35% 5% 9% 22% 23% 7%	1875
	21st to end	Night	34% 7% 13% 28% 17% 2	1748
May	1st to 10th	Night	42% 10% 12% 23% 12% 1	2840
	11th to 20th	Night	41% 8% 16% 21% 14%	2813
	21st to end	Night	32% 11% 14% 24% 17% 1	3087
June	1st to 10th	Night	36% 10% 15% 24% 13% 2	1710
	11th to 20th	Night	22% 9% 24% 27% 15% 2	1710
	21st to end	Night	33% 10% 15% 25% 13% 4	1710
July	1st to 10th	Night	38% 11% 20% 21% 8% 1	2795
	11th to 20th	Night	32% 9% 22% 27% 7% 3	2786
	21st to end	Night	54% 11% 13% 14% 6% 1	2988
August	1st to 10th	Night	27% 9% 17% 34% 12% 1	2814
	11th to 20th	Night	29% 8% 22% 26% 14% 1	3052
	21st to end	Night	24% 8% 15% 36% 16% 1	3476
September	1st to 10th	Night	36% 8% 16% 19% 15% 6%	2013
	11th to 20th	Night	39% 8% 13% 18% 21% 1	2090
	21st to end	Night	34% 6% 11% 21% 22% 5%	2090
October	1st to 10th	Night	22% 3 10% 20% 29% 15%	3480
	11th to 20th	Night	20% 3 6% 23% 33% 15%	3616
	21st to end	Night	26% 4 6% 27% 28% 10%	4260
November	1st to 10th	Night	34% 4 8% 22% 23% 8%	2536
	11th to 20th	Night	35% 4 7% 21% 26% 7%	2600
	21st to end	Night	41% 4 6% 25% 20% 4	2600
December	1st to 10th	Night	44% 5% 7% 20% 22% 2	4250
	11th to 20th	Night	48% 4 9% 21% 16% 1	4824
	21st to end	Night	48% 6% 14% 20% 10% 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	24% 23% 32% 17% 3 1	300
	11th to 20th	Day	25% 24% 34% 12% 3 2	300
	21st to end	Day	21% 23% 41% 12% 3	330
February	1st to 10th	Day	25% 22% 33% 16% 5%	300
	11th to 20th	Day	37% 18% 33% 9% 3	300
	21st to end	Day	32% 22% 34% 11% 1	249
March	1st to 10th	Day	24% 20% 35% 15% 5% 1	311
	11th to 20th	Day	23% 16% 33% 22% 5% 1	464
	21st to end	Day	23% 12% 36% 21% 7%	506
April	1st to 10th	Day	18% 18% 27% 24% 12% 2	460
	11th to 20th	Day	18% 15% 31% 23% 11% 2	452
	21st to end	Day	16% 10% 34% 25% 11% 4	460
May	1st to 10th	Day	15% 11% 32% 24% 14% 5%	463
	11th to 20th	Day	11% 8% 25% 26% 20% 9%	487
	21st to end	Day	14% 6% 20% 26% 20% 15%	529
June	1st to 10th	Day	12% 5% 19% 28% 24% 12%	490
	11th to 20th	Day	5% 4 15% 28% 30% 18%	490
	21st to end	Day	9% 2 18% 28% 25% 18%	490
July	1st to 10th	Day	9% 4 10% 23% 33% 22%	485
	11th to 20th	Day	10% 4 10% 24% 33% 20%	484
	21st to end	Day	11% 4 9% 23% 36% 18%	532
August	1st to 10th	Day	12% 3 10% 25% 33% 17%	486
	11th to 20th	Day	10% 5% 10% 33% 32% 11%	479
	21st to end	Day	14% 2 9% 21% 33% 21%	539
September	1st to 10th	Day	10% 4 9% 27% 33% 16%	490
	11th to 20th	Day	14% 3 10% 24% 33% 16%	490
	21st to end	Day	18% 4 15% 24% 30% 9%	490
October	1st to 10th	Day	13% 6% 18% 27% 26% 10%	490
	11th to 20th	Day	11% 11% 26% 27% 22% 3	490
	21st to end	Day	18% 8% 21% 31% 18% 4	458
November	1st to 10th	Day	19% 8% 27% 27% 15% 4	300
	11th to 20th	Day	13% 15% 35% 30% 7%	300
	21st to end	Day	14% 14% 35% 23% 12% 1	300
December	1st to 10th	Day	26% 17% 34% 17% 5% 1	300
	11th to 20th	Day	22% 16% 31% 23% 8%	300
	21st to end	Day	29% 14% 29% 21% 7% 1	330
January	1st to 10th	Night	23% 15% 36% 22% 4	800
	11th to 20th	Night	21% 17% 32% 24% 5%	800
	21st to end	Night	20% 15% 34% 30% 1	880
February	1st to 10th	Night	19% 14% 34% 29% 5%	800
	11th to 20th	Night	26% 16% 33% 22% 2	783
	21st to end	Night	27% 16% 32% 23% 2	660
March	1st to 10th	Night	19% 14% 33% 29% 4	800
	11th to 20th	Night	19% 13% 34% 26% 8% 1	767
	21st to end	Night	18% 12% 31% 31% 8%	836
April	1st to 10th	Night	14% 11% 32% 33% 9%	637
	11th to 20th	Night	15% 9% 32% 31% 12%	563
	21st to end	Night	13% 6% 31% 38% 11% 1	570
May	1st to 10th	Night	12% 7% 28% 35% 16% 2	570
	11th to 20th	Night	13% 5% 20% 34% 23% 4	561
	21st to end	Night	9% 4 14% 32% 35% 5%	617
June	1st to 10th	Night	9% 3 14% 36% 32% 6%	570
	11th to 20th	Night	5% 2 14% 32% 38% 9%	570
	21st to end	Night	8% 2 8% 36% 37% 10%	570
July	1st to 10th	Night	10% 2 8% 27% 40% 13%	555
	11th to 20th	Night	11% 3 6% 28% 41% 11%	552
	21st to end	Night	9% 2 8% 29% 41% 11%	624
August	1st to 10th	Night	8% 1 7% 28% 45% 11%	567
	11th to 20th	Night	9% 3 10% 33% 41% 4	564
	21st to end	Night	10% 2 8% 29% 42% 9%	627
September	1st to 10th	Night	9% 3 13% 30% 36% 8%	683
	11th to 20th	Night	14% 3 12% 29% 36% 5%	760
	21st to end	Night	14% 3 17% 33% 32% 2	760
October	1st to 10th	Night	11% 7% 17% 29% 29% 7%	760
	11th to 20th	Night	14% 7% 24% 33% 21% 2	760
	21st to end	Night	16% 7% 21% 38% 16% 2	836
November	1st to 10th	Night	14% 9% 23% 34% 18% 2	780
	11th to 20th	Night	14% 10% 34% 31% 10% 1	800
	21st to end	Night	18% 11% 28% 31% 11%	800
December	1st to 10th	Night	24% 14% 27% 28% 7%	800
	11th to 20th	Night	21% 10% 32% 30% 7%	800
	21st to end	Night	25% 12% 27% 31% 6%	880

Page generated at 2025-03-09 08:08:43. Version ac07

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