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 2024-10-20.

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% 5% 5% 4 6% 8% 39%	100791
	Night	13% 7% 2 6% 4 4 4 4 6% 7% 42%	97867
Transparency	Day	41% 7% 12% 22% 15% 3	100602
	Night	39% 7% 12% 22% 17% 3	97725
Seeing	Day	16% 10% 23% 24% 19% 9%	14686
	Night	16% 8% 23% 30% 19% 3	24690

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	16% 12% 3 7% 4 4 4 4 6% 6% 34%	2836
	11th to 20th	Day	19% 8% 4 9% 4 5% 5% 2 5% 5% 35%	2840
	21st to end	Day	23% 10% 3 6% 4 3 3 3 4 6% 35%	3220
February	1st to 10th	Day	18% 11% 3 7% 4 4 4 3 5% 5% 36%	1900
	11th to 20th	Day	21% 9% 3 7% 5% 3 5% 3 4 5% 36%	1848
	21st to end	Day	20% 9% 2 6% 4 4 4 4 5% 6% 35%	1570
March	1st to 10th	Day	23% 12% 3 7% 4 4 4 3 4 6% 31%	3143
	11th to 20th	Day	15% 6% 2 6% 4 3 3 3 4 6% 49%	3480
	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 7% 54%	1985
	21st to end	Day	16% 4 2 4 3 3 3 3 5% 7% 49%	1904
November	1st to 10th	Day	11% 5% 1 5% 3 3 3 4 5% 5% 55%	1672
	11th to 20th	Day	13% 6% 2 6% 3 3 4 3 5% 6% 49%	1710
	21st to end	Day	15% 7% 2 5% 3 4 3 4 5% 6% 45%	1710
December	1st to 10th	Day	22% 7% 3 7% 5% 4 4 4 5% 5% 35%	1710
	11th to 20th	Day	13% 9% 3 6% 4 6% 4 4 5% 7% 37%	2153
	21st to end	Day	19% 10% 3 7% 5% 4 4 4 5% 7% 32%	3124
January	1st to 10th	Night	18% 9% 3 6% 4 4 4 3 6% 7% 37%	4109
	11th to 20th	Night	19% 9% 3 6% 4 3 3 3 4 6% 39%	4120
	21st to end	Night	21% 12% 3 7% 4 3 5% 3 4 5% 33%	4435
February	1st to 10th	Night	16% 7% 3 7% 5% 5% 4 4 5% 6% 39%	2280
	11th to 20th	Night	21% 8% 3 6% 5% 4 4 3 5% 4 37%	2218
	21st to end	Night	23% 9% 3 6% 5% 3 3 3 5% 6% 34%	1884
March	1st to 10th	Night	22% 9% 4 6% 5% 4 4 3 5% 7% 32%	3709
	11th to 20th	Night	9% 6% 2 5% 4 4 4 3 5% 7% 50%	3480
	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%	2177
	21st to end	Night	14% 5% 2 5% 3 3 4 3 4 6% 52%	2449
November	1st to 10th	Night	11% 5% 2 5% 4 3 3 3 4 6% 53%	2406
	11th to 20th	Night	12% 7% 2 6% 4 3 3 3 4 7% 50%	2470
	21st to end	Night	16% 7% 2 5% 4 4 4 4 5% 7% 43%	2470
December	1st to 10th	Night	19% 9% 2 7% 4 4 5% 3 5% 6% 35%	2470
	11th to 20th	Night	16% 7% 3 6% 4 4 4 3 4 6% 43%	3042
	21st to end	Night	19% 8% 3 7% 5% 6% 6% 5% 7% 8% 27%	4532

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	49% 5% 7% 20% 17% 2	2837
	11th to 20th	Day	51% 4 8% 18% 18% 1	2840
	21st to end	Day	50% 4 8% 23% 14% 1	3220
February	1st to 10th	Day	50% 4 8% 18% 17% 2	1900
	11th to 20th	Day	51% 5% 7% 19% 15% 3	1858
	21st to end	Day	49% 5% 9% 15% 16% 6%	1570
March	1st to 10th	Day	53% 7% 8% 14% 11% 7%	3143
	11th to 20th	Day	37% 5% 9% 24% 19% 6%	3480
	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	30% 5% 9% 23% 25% 7%	2090
	11th to 20th	Day	31% 5% 8% 23% 26% 7%	1985
	21st to end	Day	34% 5% 8% 23% 26% 4	1904
November	1st to 10th	Day	31% 5% 8% 23% 27% 6%	1672
	11th to 20th	Day	35% 5% 7% 25% 24% 5%	1710
	21st to end	Day	40% 4 9% 24% 19% 4	1710
December	1st to 10th	Day	51% 5% 7% 22% 13% 3	1710
	11th to 20th	Day	46% 5% 10% 21% 16% 2	2150
	21st to end	Day	49% 5% 11% 22% 10% 2	3124
January	1st to 10th	Night	45% 5% 9% 23% 17% 2	4109
	11th to 20th	Night	46% 5% 9% 17% 18% 5%	4120
	21st to end	Night	52% 4 8% 18% 16% 1	4435
February	1st to 10th	Night	45% 5% 10% 21% 17% 3	2280
	11th to 20th	Night	50% 4 7% 18% 15% 5%	2219
	21st to end	Night	52% 4 8% 16% 16% 4	1884
March	1st to 10th	Night	50% 7% 10% 14% 15% 4	3709
	11th to 20th	Night	34% 5% 8% 25% 17% 10%	3480
	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	29% 4 9% 21% 28% 9%	2090
	11th to 20th	Night	31% 5% 9% 22% 25% 8%	2177
	21st to end	Night	35% 4 5% 23% 26% 8%	2449
November	1st to 10th	Night	33% 4 8% 22% 24% 9%	2406
	11th to 20th	Night	35% 4 7% 21% 25% 7%	2470
	21st to end	Night	41% 4 6% 24% 21% 3	2470
December	1st to 10th	Night	49% 5% 9% 21% 14% 3	2470
	11th to 20th	Night	41% 5% 9% 21% 22% 2	3044
	21st to end	Night	50% 7% 11% 18% 12% 1	4532

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	23% 24% 31% 19% 3 1	270
	11th to 20th	Day	27% 24% 32% 12% 4 2	270
	21st to end	Day	22% 22% 40% 12% 4	297
February	1st to 10th	Day	26% 21% 32% 15% 5%	270
	11th to 20th	Day	37% 17% 34% 9% 3	270
	21st to end	Day	34% 23% 33% 9% 1	225
March	1st to 10th	Day	24% 19% 35% 16% 6% 1	280
	11th to 20th	Day	23% 16% 33% 22% 5% 1	460
	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	486
	21st to end	Day	19% 9% 21% 29% 17% 4	419
November	1st to 10th	Day	19% 7% 27% 28% 14% 4	270
	11th to 20th	Day	11% 16% 36% 30% 7%	270
	21st to end	Day	14% 13% 36% 24% 12% 1	270
December	1st to 10th	Day	28% 15% 32% 18% 6% 1	270
	11th to 20th	Day	20% 16% 32% 23% 9%	270
	21st to end	Day	29% 14% 31% 21% 5% 1	297
January	1st to 10th	Night	23% 15% 35% 23% 4	760
	11th to 20th	Night	21% 17% 31% 24% 5%	760
	21st to end	Night	20% 15% 33% 30% 2	836
February	1st to 10th	Night	19% 13% 34% 29% 5%	760
	11th to 20th	Night	25% 15% 34% 23% 2	743
	21st to end	Night	28% 16% 32% 22% 2	628
March	1st to 10th	Night	19% 13% 34% 30% 4	760
	11th to 20th	Night	19% 13% 34% 26% 8% 1	760
	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	759
	21st to end	Night	16% 7% 21% 38% 15% 2	792
November	1st to 10th	Night	14% 9% 21% 35% 19% 3	740
	11th to 20th	Night	14% 10% 34% 31% 10% 1	760
	21st to end	Night	18% 11% 28% 32% 11%	760
December	1st to 10th	Night	24% 13% 27% 29% 7%	760
	11th to 20th	Night	20% 9% 32% 30% 8%	760
	21st to end	Night	25% 11% 27% 31% 6%	836

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