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 2024-11-03.

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% 5% 7% 9% 38%	100966
	Night	10% 7% 2 6% 5% 4 5% 4 6% 8% 42%	97959
Transparency	Day	41% 7% 14% 18% 14% 6%	100779
	Night	38% 7% 14% 18% 15% 7%	97816
Seeing	Day	14% 8% 23% 25% 21% 10%	15305
	Night	12% 7% 23% 33% 22% 4	25336

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% 8% 2 6% 4 3 4 2 5% 7% 47%	2836
	11th to 20th	Day	14% 8% 2 7% 4 4 4 4 5% 7% 42%	2840
	21st to end	Day	12% 7% 2 6% 4 4 4 4 6% 7% 44%	3188
February	1st to 10th	Day	15% 8% 2 6% 5% 3 4 3 5% 7% 42%	1900
	11th to 20th	Day	14% 6% 2 5% 4 4 4 4 5% 5% 48%	1848
	21st to end	Day	14% 6% 2 6% 5% 4 3 3 4 5% 47%	1585
March	1st to 10th	Day	15% 8% 3 8% 5% 5% 4 4 5% 7% 37%	3435
	11th to 20th	Day	7% 4 2 5% 5% 5% 5% 4 6% 8% 49%	3480
	21st to end	Day	15% 5% 2 5% 4 4 5% 4 6% 8% 44%	3815
April	1st to 10th	Day	9% 5% 2 6% 4 4 5% 4 6% 8% 47%	2090
	11th to 20th	Day	11% 5% 3 7% 5% 5% 5% 4 5% 6% 44%	2093
	21st to end	Day	6% 4 2 5% 5% 5% 5% 4 6% 7% 52%	2418
May	1st to 10th	Day	7% 4 2 5% 5% 6% 5% 4 6% 9% 47%	4082
	11th to 20th	Day	11% 7% 3 8% 6% 5% 6% 4 7% 8% 36%	4081
	21st to end	Day	5% 4 2 5% 5% 5% 6% 5% 8% 11% 45%	4476
June	1st to 10th	Day	11% 6% 3 9% 6% 6% 6% 6% 8% 10% 29%	2470
	11th to 20th	Day	6% 6% 2 8% 7% 8% 9% 6% 8% 10% 30%	2470
	21st to end	Day	8% 6% 3 10% 8% 7% 6% 6% 9% 9% 28%	2470
July	1st to 10th	Day	6% 7% 4 11% 9% 9% 9% 7% 9% 11% 19%	4120
	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	9% 6% 2 6% 3 4 4 3 6% 6% 52%	1877
	11th to 20th	Day	10% 6% 2 6% 4 4 3 3 4 7% 52%	1817
	21st to end	Day	11% 7% 2 5% 4 4 4 4 5% 6% 47%	1710
December	1st to 10th	Day	10% 6% 2 6% 5% 5% 4 4 6% 7% 43%	1710
	11th to 20th	Day	17% 7% 3 5% 5% 4 3 3 5% 6% 44%	2153
	21st to end	Day	16% 9% 4 7% 5% 4 4 2 3 5% 41%	3124
January	1st to 10th	Night	13% 8% 3 7% 4 4 4 3 5% 6% 43%	4109
	11th to 20th	Night	9% 8% 3 6% 4 5% 5% 4 6% 8% 42%	4120
	21st to end	Night	13% 8% 3 7% 5% 4 4 3 5% 6% 41%	4464
February	1st to 10th	Night	14% 7% 2 6% 5% 4 4 3 5% 7% 44%	2280
	11th to 20th	Night	13% 6% 3 6% 4 4 3 4 4 6% 47%	2218
	21st to end	Night	12% 6% 2 5% 4 4 3 3 5% 8% 48%	1866
March	1st to 10th	Night	20% 11% 3 7% 4 4 3 3 5% 6% 35%	3418
	11th to 20th	Night	8% 5% 2 4 3 4 4 3 7% 10% 50%	3480
	21st to end	Night	13% 6% 2 5% 4 4 4 3 4 6% 48%	3817
April	1st to 10th	Night	10% 6% 2 4 4 4 4 4 6% 8% 48%	2090
	11th to 20th	Night	8% 6% 2 7% 4 4 4 3 6% 6% 51%	2035
	21st to end	Night	6% 4 2 4 3 4 4 4 5% 9% 56%	1776
May	1st to 10th	Night	5% 5% 2 6% 3 5% 4 3 7% 9% 50%	2813
	11th to 20th	Night	12% 6% 2 5% 4 4 5% 4 6% 8% 42%	2812
	21st to end	Night	5% 3 1 5% 3 3 4 4 6% 11% 54%	3079
June	1st to 10th	Night	9% 5% 2 7% 6% 6% 6% 6% 8% 10% 33%	1710
	11th to 20th	Night	5% 4 2 7% 6% 5% 5% 6% 10% 11% 38%	1710
	21st to end	Night	6% 5% 2 6% 6% 6% 6% 5% 8% 14% 35%	1710
July	1st to 10th	Night	8% 9% 3 9% 8% 7% 8% 6% 9% 10% 22%	2840
	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 6% 7% 53%	2508
November	1st to 10th	Night	11% 5% 1 4 4 4 4 4 5% 7% 52%	2246
	11th to 20th	Night	12% 7% 2 5% 4 3 4 3 3 6% 52%	2360
	21st to end	Night	11% 8% 2 5% 3 5% 4 3 5% 7% 46%	2470
December	1st to 10th	Night	13% 6% 3 5% 4 4 4 3 6% 8% 45%	2470
	11th to 20th	Night	16% 7% 2 5% 4 3 3 3 5% 6% 47%	3042
	21st to end	Night	16% 8% 3 7% 5% 4 4 3 5% 5% 40%	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	38% 3 7% 16% 23% 12%	2837
	11th to 20th	Day	42% 4 6% 15% 18% 15%	2840
	21st to end	Day	38% 4 10% 14% 22% 12%	3188
February	1st to 10th	Day	43% 3 10% 15% 19% 10%	1900
	11th to 20th	Day	39% 4 6% 15% 23% 13%	1858
	21st to end	Day	39% 3 7% 17% 19% 14%	1585
March	1st to 10th	Day	47% 4 8% 19% 15% 6%	3435
	11th to 20th	Day	32% 4 13% 18% 17% 16%	3480
	21st to end	Day	37% 6% 9% 22% 16% 10%	3815
April	1st to 10th	Day	34% 5% 10% 18% 19% 13%	2090
	11th to 20th	Day	40% 5% 7% 17% 20% 11%	2093
	21st to end	Day	29% 6% 9% 24% 23% 9%	2418
May	1st to 10th	Day	32% 6% 12% 27% 17% 5%	4120
	11th to 20th	Day	43% 7% 12% 22% 15% 2	4085
	21st to end	Day	29% 7% 16% 28% 18% 2	4489
June	1st to 10th	Day	46% 9% 16% 17% 11% 1	2470
	11th to 20th	Day	43% 11% 17% 21% 8%	2470
	21st to end	Day	46% 11% 21% 15% 6% 1	2470
July	1st to 10th	Day	54% 14% 21% 9% 1	4055
	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	42% 5% 9% 16% 16% 12%	2090
	11th to 20th	Day	28% 5% 6% 22% 30% 10%	1904
	21st to end	Day	32% 5% 6% 18% 23% 16%	2090
November	1st to 10th	Day	33% 4 9% 18% 22% 14%	1877
	11th to 20th	Day	33% 4 7% 18% 25% 12%	1817
	21st to end	Day	38% 4 9% 19% 22% 9%	1710
December	1st to 10th	Day	39% 5% 11% 20% 16% 8%	1710
	11th to 20th	Day	42% 3 9% 17% 21% 8%	2150
	21st to end	Day	48% 3 5% 17% 20% 7%	3124
January	1st to 10th	Night	41% 4 6% 13% 22% 14%	4109
	11th to 20th	Night	40% 5% 6% 15% 23% 11%	4120
	21st to end	Night	43% 5% 9% 13% 19% 10%	4464
February	1st to 10th	Night	41% 4 8% 16% 19% 11%	2280
	11th to 20th	Night	39% 3 8% 17% 18% 14%	2219
	21st to end	Night	34% 5% 10% 20% 17% 14%	1866
March	1st to 10th	Night	50% 4 12% 14% 12% 8%	3418
	11th to 20th	Night	29% 4 13% 22% 18% 13%	3480
	21st to end	Night	37% 4 10% 19% 20% 10%	3817
April	1st to 10th	Night	33% 6% 14% 17% 18% 12%	2090
	11th to 20th	Night	33% 5% 9% 22% 21% 10%	2035
	21st to end	Night	26% 5% 12% 29% 21% 8%	1776
May	1st to 10th	Night	29% 8% 17% 26% 15% 6%	2840
	11th to 20th	Night	38% 8% 16% 24% 11% 3	2813
	21st to end	Night	23% 7% 16% 32% 20% 2	3087
June	1st to 10th	Night	41% 9% 19% 19% 11% 1	1710
	11th to 20th	Night	34% 12% 23% 23% 8%	1710
	21st to end	Night	36% 12% 27% 17% 6% 1	1710
July	1st to 10th	Night	51% 14% 24% 10% 2	2795
	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	37% 6% 12% 19% 16% 11%	2090
	11th to 20th	Night	27% 6% 7% 23% 28% 10%	2275
	21st to end	Night	31% 5% 8% 18% 23% 15%	2508
November	1st to 10th	Night	31% 5% 9% 22% 20% 14%	2246
	11th to 20th	Night	36% 3 8% 17% 25% 12%	2360
	21st to end	Night	38% 4 9% 21% 19% 9%	2470
December	1st to 10th	Night	37% 4 14% 21% 17% 7%	2470
	11th to 20th	Night	39% 5% 8% 17% 21% 9%	3044
	21st to end	Night	46% 4 10% 17% 19% 5%	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	16% 20% 41% 18% 5%	270
	11th to 20th	Day	16% 15% 40% 17% 9% 3	270
	21st to end	Day	24% 16% 44% 13% 2	297
February	1st to 10th	Day	24% 11% 41% 19% 5% 1	270
	11th to 20th	Day	19% 21% 38% 17% 5%	270
	21st to end	Day	17% 17% 41% 22% 4	240
March	1st to 10th	Day	17% 15% 31% 25% 11%	460
	11th to 20th	Day	17% 16% 32% 23% 10% 2	460
	21st to end	Day	18% 13% 35% 22% 11% 2	506
April	1st to 10th	Day	19% 13% 30% 22% 14% 1	460
	11th to 20th	Day	16% 9% 33% 25% 13% 4	452
	21st to end	Day	9% 9% 29% 29% 18% 6%	460
May	1st to 10th	Day	8% 10% 27% 25% 20% 9%	463
	11th to 20th	Day	8% 5% 24% 31% 21% 11%	487
	21st to end	Day	10% 3 15% 29% 30% 13%	529
June	1st to 10th	Day	14% 3 13% 29% 25% 15%	490
	11th to 20th	Day	9% 5% 13% 24% 29% 19%	490
	21st to end	Day	10% 2 9% 28% 32% 20%	490
July	1st to 10th	Day	7% 2 6% 23% 35% 27%	485
	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% 6% 27% 29% 17% 5%	463
	11th to 20th	Day	19% 8% 37% 24% 8% 3	377
	21st to end	Day	17% 11% 35% 27% 8% 1	270
December	1st to 10th	Day	16% 16% 33% 21% 12% 2	270
	11th to 20th	Day	23% 13% 33% 25% 6% 1	270
	21st to end	Day	19% 7% 38% 28% 7% 2	297
January	1st to 10th	Night	16% 13% 35% 29% 6% 1	760
	11th to 20th	Night	13% 12% 30% 33% 11% 1	760
	21st to end	Night	19% 14% 37% 25% 4	836
February	1st to 10th	Night	19% 11% 30% 31% 8%	760
	11th to 20th	Night	18% 13% 31% 32% 5%	743
	21st to end	Night	16% 12% 34% 35% 3	628
March	1st to 10th	Night	14% 12% 33% 34% 7%	760
	11th to 20th	Night	14% 10% 36% 27% 12% 1	760
	21st to end	Night	12% 12% 35% 31% 11%	836
April	1st to 10th	Night	14% 11% 30% 33% 10% 1	760
	11th to 20th	Night	11% 9% 33% 35% 11% 1	751
	21st to end	Night	8% 6% 28% 41% 16%	636
May	1st to 10th	Night	5% 5% 27% 45% 17% 1	570
	11th to 20th	Night	10% 4 19% 43% 22% 3	561
	21st to end	Night	8% 2 11% 42% 33% 3	617
June	1st to 10th	Night	11% 2 11% 39% 34% 3	570
	11th to 20th	Night	6% 3 11% 34% 34% 12%	570
	21st to end	Night	8% 1 9% 34% 39% 10%	570
July	1st to 10th	Night	7% 2 5% 30% 42% 14%	555
	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	9% 6% 26% 34% 23% 1	836
November	1st to 10th	Night	12% 6% 27% 36% 18% 1	749
	11th to 20th	Night	15% 9% 29% 33% 14% 1	760
	21st to end	Night	16% 6% 31% 32% 14% 1	760
December	1st to 10th	Night	16% 9% 27% 33% 15% 1	760
	11th to 20th	Night	18% 9% 28% 30% 15% 1	760
	21st to end	Night	17% 11% 27% 32% 12%	836

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