Stephen C. Foster State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stephen C. Foster State Park clear sky chart from 2005-11-06 to 2025-07-06.

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	10% 6% 2 7% 5% 5% 5% 4 6% 8% 40%	120076
	Night	10% 7% 2 6% 4 4 4 4 6% 8% 44%	118696
Transparency	Day	39% 7% 13% 18% 16% 8%	123855
	Night	37% 6% 13% 18% 17% 8%	123054
Seeing	Day	14% 8% 23% 25% 20% 10%	16181
	Night	13% 7% 23% 32% 21% 4	26242

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	9% 6% 2 5% 3 3 3 2 4 6% 56%	4056
	11th to 20th	Day	17% 8% 2 6% 4 4 4 3 4 6% 42%	4060
	21st to end	Day	10% 6% 3 6% 4 4 4 4 5% 8% 46%	4558
February	1st to 10th	Day	15% 8% 2 6% 5% 3 4 3 5% 7% 43%	2000
	11th to 20th	Day	14% 6% 2 5% 4 4 4 3 5% 5% 48%	1948
	21st to end	Day	14% 6% 2 6% 5% 4 3 3 4 5% 48%	1666
March	1st to 10th	Day	16% 8% 3 7% 4 4 4 4 5% 7% 39%	4935
	11th to 20th	Day	7% 4 2 4 4 4 4 3 6% 8% 53%	4980
	21st to end	Day	12% 5% 2 5% 4 4 4 4 5% 7% 47%	5465
April	1st to 10th	Day	9% 5% 2 5% 4 4 4 4 6% 8% 48%	2200
	11th to 20th	Day	10% 5% 3 6% 5% 5% 5% 4 5% 6% 46%	2205
	21st to end	Day	6% 4 2 5% 5% 5% 5% 4 6% 7% 51%	2546
May	1st to 10th	Day	8% 5% 2 7% 5% 6% 5% 4 7% 9% 41%	5862
	11th to 20th	Day	11% 7% 2 7% 5% 4 4 4 6% 9% 42%	5861
	21st to end	Day	4 3 2 5% 5% 5% 6% 5% 8% 11% 45%	6433
June	1st to 10th	Day	10% 6% 3 9% 7% 6% 6% 6% 8% 10% 29%	2600
	11th to 20th	Day	6% 6% 2 8% 7% 8% 9% 6% 9% 11% 30%	2600
	21st to end	Day	7% 5% 3 10% 8% 7% 7% 6% 8% 10% 29%	2600
July	1st to 10th	Day	7% 7% 4 11% 9% 9% 9% 7% 9% 11% 18%	4185
	11th to 20th	Day	5% 4 2 7% 7% 7% 8% 6% 9% 14% 31%	4120
	21st to end	Day	5% 6% 3 10% 8% 9% 8% 6% 9% 13% 24%	4466
August	1st to 10th	Day	14% 6% 4 8% 7% 7% 7% 6% 9% 11% 21%	4104
	11th to 20th	Day	6% 5% 2 8% 6% 6% 6% 6% 8% 11% 35%	3931
	21st to end	Day	11% 7% 3 9% 7% 7% 7% 6% 8% 11% 25%	3903
September	1st to 10th	Day	12% 8% 3 10% 7% 7% 6% 5% 8% 9% 26%	2090
	11th to 20th	Day	14% 9% 3 9% 6% 6% 6% 5% 7% 7% 27%	2090
	21st to end	Day	12% 6% 3 7% 5% 6% 5% 5% 5% 7% 38%	2090
October	1st to 10th	Day	12% 6% 3 8% 5% 4 4 4 5% 7% 41%	2090
	11th to 20th	Day	7% 5% 2 4 3 4 4 3 5% 6% 57%	1904
	21st to end	Day	9% 4 2 5% 4 4 4 4 6% 6% 51%	2090
November	1st to 10th	Day	10% 6% 2 6% 3 4 4 3 5% 6% 51%	1957
	11th to 20th	Day	10% 6% 2 5% 4 4 3 3 4 7% 52%	1912
	21st to end	Day	11% 7% 2 6% 4 4 4 4 5% 6% 48%	1800
December	1st to 10th	Day	6% 4 2 6% 5% 4 4 4 5% 6% 54%	2930
	11th to 20th	Day	14% 8% 3 6% 4 4 4 3 5% 6% 42%	3373
	21st to end	Day	15% 10% 3 7% 4 4 4 2 3 5% 41%	4466
January	1st to 10th	Night	9% 6% 2 5% 3 3 3 3 5% 5% 57%	5889
	11th to 20th	Night	14% 7% 2 6% 4 5% 5% 4 6% 7% 38%	5900
	21st to end	Night	14% 7% 2 6% 4 4 4 3 5% 7% 45%	6380
February	1st to 10th	Night	14% 6% 2 6% 5% 4 4 3 5% 7% 45%	2400
	11th to 20th	Night	14% 7% 3 6% 4 4 3 4 4 6% 47%	2338
	21st to end	Night	12% 6% 2 5% 4 3 3 3 5% 8% 49%	1961
March	1st to 10th	Night	20% 9% 2 6% 3 3 3 2 4 6% 40%	4918
	11th to 20th	Night	7% 5% 2 4 3 3 3 3 7% 10% 54%	4980
	21st to end	Night	10% 6% 2 5% 4 4 4 3 5% 7% 51%	5467
April	1st to 10th	Night	10% 6% 2 4 4 4 3 5% 6% 8% 49%	2200
	11th to 20th	Night	8% 6% 2 6% 4 3 4 3 5% 6% 53%	2143
	21st to end	Night	6% 4 2 4 3 4 4 4 5% 9% 55%	1869
May	1st to 10th	Night	6% 6% 3 8% 4 5% 5% 4 7% 9% 44%	4033
	11th to 20th	Night	12% 6% 2 5% 4 4 5% 4 7% 9% 42%	4032
	21st to end	Night	5% 4 2 6% 4 4 5% 5% 7% 12% 48%	4421
June	1st to 10th	Night	9% 6% 2 7% 6% 6% 6% 6% 8% 10% 33%	1800
	11th to 20th	Night	5% 5% 2 7% 6% 6% 6% 6% 10% 11% 37%	1800
	21st to end	Night	6% 5% 2 6% 6% 6% 6% 5% 8% 14% 36%	1800
July	1st to 10th	Night	8% 9% 3 9% 8% 7% 8% 6% 9% 10% 22%	2885
	11th to 20th	Night	5% 6% 3 8% 6% 6% 6% 8% 11% 13% 27%	2840
	21st to end	Night	6% 7% 3 9% 6% 6% 8% 6% 10% 14% 24%	3087
August	1st to 10th	Night	12% 5% 3 8% 6% 6% 6% 6% 8% 12% 27%	2825
	11th to 20th	Night	4 4 2 6% 5% 5% 6% 5% 8% 13% 41%	2879
	21st to end	Night	9% 7% 3 8% 5% 5% 5% 5% 7% 12% 35%	3718
September	1st to 10th	Night	12% 8% 2 9% 6% 5% 5% 4 9% 11% 29%	2090
	11th to 20th	Night	12% 8% 3 10% 7% 6% 6% 4 7% 7% 30%	2090
	21st to end	Night	9% 7% 3 7% 5% 4 4 4 6% 9% 44%	2090
October	1st to 10th	Night	11% 6% 3 6% 4 4 4 4 5% 7% 47%	2090
	11th to 20th	Night	7% 5% 2 5% 3 3 3 3 5% 6% 57%	2275
	21st to end	Night	6% 5% 2 6% 5% 4 4 3 5% 7% 53%	2508
November	1st to 10th	Night	11% 5% 2 5% 3 4 4 4 5% 7% 50%	2341
	11th to 20th	Night	12% 7% 2 5% 4 3 4 2 3 6% 51%	2485
	21st to end	Night	11% 8% 2 5% 4 4 3 3 5% 7% 47%	2600
December	1st to 10th	Night	11% 5% 2 4 3 3 4 2 4 6% 55%	4250
	11th to 20th	Night	14% 10% 3 6% 4 3 3 3 4 5% 45%	4822
	21st to end	Night	15% 9% 3 7% 5% 4 4 3 5% 5% 42%	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	31% 3 6% 14% 33% 13%	4057
	11th to 20th	Day	44% 3 5% 13% 20% 15%	4060
	21st to end	Day	36% 4 9% 20% 21% 11%	4558
February	1st to 10th	Day	41% 3 10% 16% 20% 10%	2000
	11th to 20th	Day	39% 4 6% 16% 22% 12%	1958
	21st to end	Day	39% 3 7% 18% 19% 14%	1666
March	1st to 10th	Day	45% 3 9% 15% 18% 10%	4935
	11th to 20th	Day	29% 3 11% 17% 18% 23%	4980
	21st to end	Day	35% 5% 8% 21% 17% 13%	5465
April	1st to 10th	Day	33% 5% 10% 20% 20% 12%	2200
	11th to 20th	Day	39% 4 7% 17% 21% 12%	2205
	21st to end	Day	29% 6% 9% 25% 22% 9%	2546
May	1st to 10th	Day	38% 7% 13% 25% 13% 4	5897
	11th to 20th	Day	38% 5% 13% 29% 12% 2	5865
	21st to end	Day	28% 7% 19% 25% 19% 2	6447
June	1st to 10th	Day	46% 9% 16% 17% 11% 1	2600
	11th to 20th	Day	43% 11% 18% 20% 7%	2600
	21st to end	Day	46% 11% 21% 16% 6% 1	2600
July	1st to 10th	Day	54% 15% 21% 9% 1	4120
	11th to 20th	Day	39% 13% 34% 11% 3	4051
	21st to end	Day	46% 16% 26% 11% 2	4324
August	1st to 10th	Day	52% 12% 22% 13% 1	4091
	11th to 20th	Day	38% 11% 19% 22% 9%	3970
	21st to end	Day	49% 12% 17% 20% 2 1	3903
September	1st to 10th	Day	52% 9% 16% 13% 7% 2	2090
	11th to 20th	Day	53% 9% 14% 15% 7% 2	2090
	21st to end	Day	44% 6% 12% 17% 16% 4	2090
October	1st to 10th	Day	48% 4 7% 11% 14% 15%	3480
	11th to 20th	Day	18% 3 4 19% 34% 22%	3144
	21st to end	Day	23% 4 6% 17% 35% 15%	3428
November	1st to 10th	Day	34% 4 9% 18% 21% 13%	1957
	11th to 20th	Day	33% 4 7% 18% 25% 13%	1912
	21st to end	Day	37% 4 9% 18% 22% 10%	1800
December	1st to 10th	Day	31% 5% 9% 18% 24% 14%	2930
	11th to 20th	Day	42% 4 9% 19% 19% 7%	3370
	21st to end	Day	47% 3 6% 18% 22% 5%	4466
January	1st to 10th	Night	30% 3 6% 13% 36% 13%	5889
	11th to 20th	Night	45% 4 5% 15% 23% 9%	5900
	21st to end	Night	39% 4 9% 17% 20% 10%	6380
February	1st to 10th	Night	40% 4 8% 17% 21% 11%	2400
	11th to 20th	Night	39% 3 8% 18% 18% 14%	2339
	21st to end	Night	34% 4 9% 20% 18% 14%	1961
March	1st to 10th	Night	46% 3 9% 15% 15% 11%	4918
	11th to 20th	Night	26% 3 11% 20% 20% 20%	4980
	21st to end	Night	34% 4 9% 18% 21% 13%	5467
April	1st to 10th	Night	33% 6% 14% 18% 18% 12%	2200
	11th to 20th	Night	31% 4 8% 22% 22% 12%	2143
	21st to end	Night	26% 5% 13% 28% 20% 8%	1869
May	1st to 10th	Night	34% 7% 18% 25% 11% 4	4060
	11th to 20th	Night	37% 7% 19% 26% 9% 2	4033
	21st to end	Night	27% 8% 18% 29% 17% 2	4429
June	1st to 10th	Night	41% 9% 19% 18% 11% 1	1800
	11th to 20th	Night	35% 12% 23% 22% 8%	1800
	21st to end	Night	36% 12% 26% 19% 6% 1	1800
July	1st to 10th	Night	51% 14% 24% 10% 2	2840
	11th to 20th	Night	42% 17% 29% 9% 3	2786
	21st to end	Night	46% 16% 24% 12% 2	2988
August	1st to 10th	Night	46% 14% 28% 11% 1	2814
	11th to 20th	Night	30% 12% 27% 22% 8%	2906
	21st to end	Night	40% 11% 24% 23% 2	3718
September	1st to 10th	Night	45% 11% 21% 14% 7% 2	2090
	11th to 20th	Night	50% 11% 15% 16% 7% 1	2090
	21st to end	Night	36% 7% 17% 22% 14% 4	2090
October	1st to 10th	Night	46% 5% 9% 13% 15% 12%	3480
	11th to 20th	Night	19% 3 5% 18% 33% 22%	3774
	21st to end	Night	23% 4 7% 18% 35% 14%	4120
November	1st to 10th	Night	32% 5% 9% 21% 19% 13%	2341
	11th to 20th	Night	36% 3 8% 16% 25% 12%	2485
	21st to end	Night	37% 4 9% 20% 20% 10%	2600
December	1st to 10th	Night	32% 3 9% 18% 23% 16%	4250
	11th to 20th	Night	42% 5% 9% 18% 18% 9%	4824
	21st to end	Night	44% 4 9% 17% 22% 4	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	15% 22% 42% 16% 5%	300
	11th to 20th	Day	17% 15% 41% 16% 8% 2	300
	21st to end	Day	23% 18% 43% 13% 3	330
February	1st to 10th	Day	22% 10% 42% 21% 5% 1	300
	11th to 20th	Day	22% 20% 38% 16% 5%	300
	21st to end	Day	17% 17% 40% 23% 4	265
March	1st to 10th	Day	19% 16% 31% 24% 10%	500
	11th to 20th	Day	18% 15% 32% 22% 10% 2	500
	21st to end	Day	17% 13% 36% 23% 10% 1	550
April	1st to 10th	Day	18% 13% 31% 23% 13% 1	500
	11th to 20th	Day	15% 9% 32% 27% 13% 4	492
	21st to end	Day	8% 8% 27% 30% 19% 7%	500
May	1st to 10th	Day	8% 9% 29% 26% 19% 9%	503
	11th to 20th	Day	8% 5% 25% 31% 20% 11%	527
	21st to end	Day	10% 4 17% 29% 29% 12%	573
June	1st to 10th	Day	14% 4 14% 30% 24% 14%	530
	11th to 20th	Day	8% 5% 13% 25% 30% 19%	530
	21st to end	Day	9% 2 8% 29% 31% 21%	530
July	1st to 10th	Day	8% 2 7% 23% 35% 26%	505
	11th to 20th	Day	7% 1 3 20% 40% 27%	484
	21st to end	Day	9% 3 6% 26% 36% 19%	532
August	1st to 10th	Day	14% 3 9% 19% 32% 22%	486
	11th to 20th	Day	9% 2 4 21% 38% 26%	479
	21st to end	Day	14% 3 10% 22% 32% 19%	539
September	1st to 10th	Day	16% 4 7% 24% 28% 21%	490
	11th to 20th	Day	16% 6% 12% 32% 24% 10%	490
	21st to end	Day	15% 2 12% 30% 29% 13%	490
October	1st to 10th	Day	17% 7% 26% 27% 18% 6%	490
	11th to 20th	Day	8% 6% 27% 34% 19% 6%	490
	21st to end	Day	13% 7% 27% 31% 18% 4	539
November	1st to 10th	Day	16% 7% 27% 29% 16% 4	495
	11th to 20th	Day	17% 8% 39% 23% 8% 3	412
	21st to end	Day	17% 13% 36% 25% 8% 1	300
December	1st to 10th	Day	15% 18% 34% 20% 12% 2	300
	11th to 20th	Day	23% 12% 34% 24% 6% 1	300
	21st to end	Day	19% 9% 37% 28% 6% 2	330
January	1st to 10th	Night	15% 14% 36% 28% 6% 1	800
	11th to 20th	Night	14% 12% 30% 33% 10% 1	800
	21st to end	Night	19% 14% 38% 25% 4	880
February	1st to 10th	Night	18% 11% 30% 32% 8%	800
	11th to 20th	Night	19% 14% 32% 31% 5%	783
	21st to end	Night	16% 13% 34% 35% 3	660
March	1st to 10th	Night	14% 12% 33% 33% 7%	800
	11th to 20th	Night	14% 10% 37% 27% 11% 1	800
	21st to end	Night	12% 12% 35% 31% 10%	880
April	1st to 10th	Night	14% 11% 31% 33% 10% 1	800
	11th to 20th	Night	11% 9% 34% 35% 10% 1	791
	21st to end	Night	8% 6% 28% 42% 16%	669
May	1st to 10th	Night	5% 5% 27% 45% 16% 1	600
	11th to 20th	Night	10% 3 21% 42% 21% 3	591
	21st to end	Night	8% 3 12% 41% 33% 3	650
June	1st to 10th	Night	11% 3 13% 39% 32% 3	600
	11th to 20th	Night	6% 3 11% 34% 35% 12%	600
	21st to end	Night	8% 1 9% 34% 39% 10%	600
July	1st to 10th	Night	8% 2 5% 29% 42% 14%	570
	11th to 20th	Night	8% 3 3 23% 47% 16%	552
	21st to end	Night	4 2 5% 32% 47% 11%	624
August	1st to 10th	Night	10% 1 4 28% 47% 11%	567
	11th to 20th	Night	6% 1 3 23% 50% 16%	564
	21st to end	Night	14% 3 7% 24% 39% 13%	765
September	1st to 10th	Night	14% 4 8% 27% 38% 10%	760
	11th to 20th	Night	14% 5% 11% 31% 34% 5%	760
	21st to end	Night	12% 3 14% 34% 33% 4	760
October	1st to 10th	Night	14% 3 21% 35% 24% 3	760
	11th to 20th	Night	9% 6% 24% 35% 23% 2	760
	21st to end	Night	8% 6% 26% 34% 23% 1	836
November	1st to 10th	Night	12% 6% 27% 37% 17% 1	780
	11th to 20th	Night	15% 9% 29% 33% 14% 2	800
	21st to end	Night	16% 7% 30% 32% 15% 1	800
December	1st to 10th	Night	16% 9% 28% 34% 14% 1	800
	11th to 20th	Night	18% 9% 28% 31% 15% 1	800
	21st to end	Night	18% 11% 28% 31% 12%	880

Page generated at 2025-07-03 01:30:14. Version ac07

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