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 2026-10-29.

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	9% 6% 2 7% 5% 5% 6% 5% 7% 9% 39%	148991
	Night	10% 7% 2 6% 4 4 5% 4 6% 9% 42%	143055
Transparency	Day	39% 7% 15% 18% 14% 7%	152728
	Night	38% 7% 14% 18% 16% 8%	147390
Seeing	Day	14% 8% 23% 25% 20% 9%	17997
	Night	13% 7% 23% 33% 21% 4	27991

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	8% 7% 2 6% 4 3 4 3 4 7% 51%	5258
	11th to 20th	Day	16% 8% 2 6% 3 4 4 3 5% 7% 41%	5280
	21st to end	Day	9% 7% 3 7% 4 4 4 4 6% 9% 44%	5900
February	1st to 10th	Day	14% 7% 2 6% 5% 3 4 3 5% 7% 44%	2100
	11th to 20th	Day	14% 6% 2 5% 4 4 4 4 5% 5% 47%	2048
	21st to end	Day	13% 6% 3 6% 5% 4 3 3 4 5% 48%	1747
March	1st to 10th	Day	16% 8% 3 7% 4 4 4 4 5% 7% 40%	5045
	11th to 20th	Day	7% 4 2 4 4 4 4 3 6% 8% 53%	5090
	21st to end	Day	12% 5% 2 5% 4 4 5% 4 5% 7% 47%	5586
April	1st to 10th	Day	9% 5% 2 5% 4 4 5% 4 6% 8% 47%	2310
	11th to 20th	Day	10% 5% 3 6% 5% 5% 4 4 5% 6% 47%	2316
	21st to end	Day	6% 4 2 5% 5% 5% 5% 4 6% 8% 51%	2673
May	1st to 10th	Day	11% 6% 2 8% 5% 5% 5% 4 6% 8% 38%	7616
	11th to 20th	Day	11% 6% 2 6% 4 4 4 4 7% 9% 42%	7626
	21st to end	Day	5% 5% 2 7% 5% 6% 7% 6% 9% 12% 38%	8391
June	1st to 10th	Day	10% 6% 3 9% 6% 6% 7% 6% 8% 10% 29%	2730
	11th to 20th	Day	6% 6% 2 8% 7% 8% 9% 6% 8% 11% 29%	2730
	21st to end	Day	7% 5% 3 9% 8% 7% 6% 6% 8% 10% 30%	2730
July	1st to 10th	Day	5% 6% 3 9% 8% 8% 8% 7% 9% 12% 24%	7680
	11th to 20th	Day	3 3 2 7% 7% 7% 8% 6% 10% 15% 32%	7680
	21st to end	Day	3 4 2 8% 7% 7% 8% 7% 11% 15% 29%	8340
August	1st to 10th	Day	13% 7% 4 9% 7% 7% 7% 6% 9% 11% 18%	6014
	11th to 20th	Day	4 4 2 7% 6% 7% 7% 6% 9% 12% 36%	5793
	21st to end	Day	9% 7% 3 9% 7% 7% 7% 6% 9% 12% 24%	5682
September	1st to 10th	Day	12% 8% 3 10% 7% 7% 6% 5% 8% 9% 26%	2310
	11th to 20th	Day	13% 9% 3 8% 6% 6% 6% 5% 7% 8% 29%	2310
	21st to end	Day	12% 6% 3 8% 5% 6% 5% 5% 6% 7% 38%	2310
October	1st to 10th	Day	14% 7% 3 8% 5% 4 4 4 5% 7% 39%	2310
	11th to 20th	Day	7% 5% 2 4 3 3 4 3 5% 6% 59%	2104
	21st to end	Day	9% 4 2 5% 4 4 4 4 5% 7% 52%	2280
November	1st to 10th	Day	9% 6% 2 6% 3 4 4 3 5% 6% 51%	2057
	11th to 20th	Day	10% 6% 2 5% 4 4 3 3 4 6% 54%	2007
	21st to end	Day	11% 7% 2 6% 4 4 4 4 5% 6% 47%	1890
December	1st to 10th	Day	7% 5% 2 6% 5% 4 4 4 5% 6% 53%	3020
	11th to 20th	Day	14% 8% 3 6% 4 4 4 3 5% 6% 43%	3463
	21st to end	Day	15% 10% 3 7% 4 4 4 2 4 5% 42%	4565
January	1st to 10th	Night	9% 7% 2 5% 3 3 3 3 5% 7% 53%	7635
	11th to 20th	Night	13% 7% 2 6% 4 5% 5% 4 6% 7% 41%	7680
	21st to end	Night	15% 8% 2 6% 4 4 4 3 5% 7% 44%	8263
February	1st to 10th	Night	14% 6% 2 5% 5% 4 4 3 5% 7% 46%	2520
	11th to 20th	Night	13% 7% 3 6% 4 4 3 4 4 6% 47%	2458
	21st to end	Night	12% 6% 2 5% 4 3 3 3 5% 8% 49%	2056
March	1st to 10th	Night	19% 9% 2 6% 3 3 3 2 4 6% 41%	5028
	11th to 20th	Night	7% 5% 2 4 3 3 3 3 7% 10% 54%	5090
	21st to end	Night	10% 6% 2 5% 3 4 4 3 5% 7% 51%	5588
April	1st to 10th	Night	10% 6% 2 4 4 4 4 4 6% 8% 48%	2310
	11th to 20th	Night	7% 5% 2 6% 4 3 4 2 5% 6% 55%	2252
	21st to end	Night	6% 4 2 4 4 4 4 4 5% 9% 54%	1962
May	1st to 10th	Night	8% 8% 3 8% 4 5% 5% 4 7% 8% 40%	5237
	11th to 20th	Night	12% 6% 2 6% 4 4 5% 4 7% 9% 42%	5234
	21st to end	Night	6% 6% 2 8% 5% 5% 6% 5% 7% 11% 39%	5761
June	1st to 10th	Night	9% 6% 2 8% 6% 6% 6% 6% 8% 10% 33%	1890
	11th to 20th	Night	6% 5% 2 8% 6% 6% 6% 6% 10% 11% 36%	1890
	21st to end	Night	6% 4 2 6% 6% 6% 6% 6% 8% 14% 36%	1890
July	1st to 10th	Night	6% 8% 3 9% 6% 7% 7% 6% 10% 13% 26%	5278
	11th to 20th	Night	5% 5% 3 8% 7% 7% 7% 8% 10% 12% 29%	5277
	21st to end	Night	4 6% 3 8% 6% 6% 7% 6% 9% 14% 32%	5736
August	1st to 10th	Night	12% 7% 4 9% 7% 6% 6% 6% 9% 11% 22%	4135
	11th to 20th	Night	3 4 2 6% 5% 6% 6% 6% 9% 15% 38%	4234
	21st to end	Night	8% 7% 3 9% 6% 6% 6% 5% 8% 12% 30%	5394
September	1st to 10th	Night	11% 8% 2 9% 6% 5% 5% 5% 8% 11% 30%	2310
	11th to 20th	Night	11% 7% 3 9% 6% 6% 6% 4 7% 8% 32%	2310
	21st to end	Night	8% 7% 2 7% 5% 5% 4 4 6% 9% 43%	2310
October	1st to 10th	Night	14% 6% 3 6% 4 5% 4 3 5% 7% 44%	2310
	11th to 20th	Night	7% 5% 2 5% 3 3 3 3 5% 6% 58%	2515
	21st to end	Night	7% 5% 2 6% 4 4 4 3 5% 7% 53%	2737
November	1st to 10th	Night	11% 5% 2 5% 3 4 4 4 5% 7% 51%	2461
	11th to 20th	Night	12% 6% 2 5% 4 3 4 2 3 6% 53%	2609
	21st to end	Night	11% 8% 2 5% 3 4 4 4 5% 7% 47%	2730
December	1st to 10th	Night	11% 5% 2 4 3 3 4 2 4 6% 54%	4380
	11th to 20th	Night	13% 10% 3 6% 4 3 3 3 4 5% 46%	4952
	21st to end	Night	14% 9% 3 7% 5% 4 4 3 5% 5% 42%	6633

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	34% 3 8% 15% 29% 10%	5259
	11th to 20th	Day	43% 3 5% 14% 18% 17%	5280
	21st to end	Day	37% 3 9% 20% 19% 11%	5900
February	1st to 10th	Day	40% 3 9% 16% 20% 11%	2100
	11th to 20th	Day	39% 5% 7% 17% 22% 12%	2058
	21st to end	Day	38% 3 7% 18% 19% 14%	1747
March	1st to 10th	Day	44% 3 9% 16% 18% 10%	5045
	11th to 20th	Day	29% 3 11% 17% 18% 22%	5090
	21st to end	Day	35% 5% 8% 21% 17% 13%	5586
April	1st to 10th	Day	34% 5% 10% 19% 19% 12%	2310
	11th to 20th	Day	37% 4 7% 17% 23% 12%	2316
	21st to end	Day	29% 6% 9% 25% 22% 9%	2673
May	1st to 10th	Day	42% 6% 12% 22% 14% 3	7651
	11th to 20th	Day	36% 6% 13% 29% 14% 2	7630
	21st to end	Day	35% 10% 20% 20% 15% 1	8405
June	1st to 10th	Day	45% 9% 16% 16% 12% 2	2730
	11th to 20th	Day	44% 11% 18% 20% 7%	2730
	21st to end	Day	45% 11% 21% 17% 6% 1	2730
July	1st to 10th	Day	47% 14% 26% 12% 2	7615
	11th to 20th	Day	36% 14% 34% 13% 2	7611
	21st to end	Day	37% 13% 25% 21% 4	8156
August	1st to 10th	Day	54% 12% 23% 11% 1	6001
	11th to 20th	Day	34% 12% 26% 21% 7%	5832
	21st to end	Day	47% 13% 19% 17% 3	5682
September	1st to 10th	Day	52% 9% 15% 14% 8% 2	2310
	11th to 20th	Day	50% 9% 13% 17% 8% 2	2310
	21st to end	Day	44% 6% 12% 18% 16% 4	2310
October	1st to 10th	Day	50% 4 7% 11% 14% 14%	3700
	11th to 20th	Day	18% 3 4 18% 34% 23%	3344
	21st to end	Day	23% 4 6% 17% 35% 15%	3618
November	1st to 10th	Day	33% 4 9% 18% 22% 14%	2057
	11th to 20th	Day	32% 4 7% 18% 26% 13%	2007
	21st to end	Day	37% 4 9% 18% 22% 10%	1890
December	1st to 10th	Day	32% 5% 9% 18% 24% 13%	3020
	11th to 20th	Day	42% 4 8% 19% 20% 7%	3460
	21st to end	Day	46% 3 6% 18% 22% 5%	4565
January	1st to 10th	Night	31% 3 9% 16% 31% 10%	7636
	11th to 20th	Night	42% 4 5% 14% 23% 13%	7680
	21st to end	Night	41% 4 8% 18% 20% 10%	8263
February	1st to 10th	Night	39% 4 8% 16% 21% 12%	2520
	11th to 20th	Night	39% 3 8% 18% 17% 13%	2459
	21st to end	Night	34% 4 10% 20% 18% 14%	2056
March	1st to 10th	Night	46% 3 10% 16% 15% 11%	5028
	11th to 20th	Night	26% 3 11% 20% 21% 19%	5090
	21st to end	Night	34% 4 9% 19% 21% 13%	5588
April	1st to 10th	Night	33% 6% 14% 18% 17% 11%	2310
	11th to 20th	Night	31% 4 8% 22% 24% 12%	2252
	21st to end	Night	27% 5% 13% 28% 20% 8%	1962
May	1st to 10th	Night	40% 7% 16% 21% 11% 4	5264
	11th to 20th	Night	37% 6% 19% 25% 10% 3	5235
	21st to end	Night	37% 10% 17% 22% 13% 1	5771
June	1st to 10th	Night	42% 9% 19% 18% 11% 1	1890
	11th to 20th	Night	36% 12% 23% 21% 7%	1890
	21st to end	Night	36% 12% 26% 19% 6% 1	1890
July	1st to 10th	Night	45% 14% 27% 13% 2	5235
	11th to 20th	Night	41% 16% 31% 11% 2	5226
	21st to end	Night	38% 14% 26% 20% 2	5606
August	1st to 10th	Night	51% 16% 24% 8% 1	4124
	11th to 20th	Night	30% 13% 31% 20% 6%	4261
	21st to end	Night	45% 12% 22% 19% 2	5394
September	1st to 10th	Night	44% 11% 21% 15% 7% 1	2310
	11th to 20th	Night	48% 11% 15% 17% 8% 1	2310
	21st to end	Night	36% 7% 16% 23% 14% 4	2310
October	1st to 10th	Night	48% 5% 9% 13% 15% 11%	3700
	11th to 20th	Night	19% 3 5% 17% 33% 22%	4014
	21st to end	Night	23% 4 6% 18% 34% 15%	4349
November	1st to 10th	Night	31% 5% 9% 21% 20% 14%	2461
	11th to 20th	Night	35% 3 7% 17% 25% 13%	2609
	21st to end	Night	36% 4 10% 20% 19% 11%	2730
December	1st to 10th	Night	33% 3 9% 18% 23% 16%	4380
	11th to 20th	Night	42% 5% 8% 18% 18% 9%	4954
	21st to end	Night	44% 4 9% 18% 22% 4	6633

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% 20% 43% 17% 5%	330
	11th to 20th	Day	19% 15% 41% 15% 8% 2	330
	21st to end	Day	24% 18% 41% 14% 3	363
February	1st to 10th	Day	21% 11% 41% 21% 5% 1	330
	11th to 20th	Day	22% 20% 38% 15% 4	330
	21st to end	Day	19% 18% 39% 21% 3	290
March	1st to 10th	Day	18% 16% 31% 24% 12%	540
	11th to 20th	Day	18% 15% 32% 22% 10% 2	540
	21st to end	Day	16% 12% 36% 24% 9% 2	594
April	1st to 10th	Day	19% 13% 30% 23% 14% 1	540
	11th to 20th	Day	14% 9% 31% 27% 14% 5%	532
	21st to end	Day	8% 8% 29% 30% 18% 7%	540
May	1st to 10th	Day	9% 10% 29% 26% 18% 8%	543
	11th to 20th	Day	9% 5% 25% 31% 20% 10%	567
	21st to end	Day	10% 4 16% 29% 29% 11%	617
June	1st to 10th	Day	13% 4 14% 31% 24% 14%	570
	11th to 20th	Day	9% 6% 14% 25% 28% 18%	570
	21st to end	Day	9% 2 9% 29% 31% 20%	570
July	1st to 10th	Day	7% 2 7% 24% 36% 25%	565
	11th to 20th	Day	6% 1 3 23% 42% 24%	564
	21st to end	Day	8% 3 8% 27% 35% 18%	620
August	1st to 10th	Day	14% 4 10% 20% 32% 21%	566
	11th to 20th	Day	9% 2 4 22% 38% 25%	559
	21st to end	Day	14% 4 11% 22% 31% 18%	627
September	1st to 10th	Day	15% 4 9% 25% 28% 18%	570
	11th to 20th	Day	14% 5% 14% 32% 25% 11%	570
	21st to end	Day	14% 3 13% 30% 28% 12%	570
October	1st to 10th	Day	20% 7% 25% 25% 16% 5%	570
	11th to 20th	Day	8% 6% 27% 34% 19% 6%	570
	21st to end	Day	13% 7% 30% 30% 16% 4	615
November	1st to 10th	Day	15% 8% 27% 29% 17% 4	535
	11th to 20th	Day	16% 8% 39% 25% 9% 3	447
	21st to end	Day	16% 14% 36% 25% 8% 1	330
December	1st to 10th	Day	18% 18% 33% 19% 11% 2	330
	11th to 20th	Day	21% 14% 33% 23% 8% 1	330
	21st to end	Day	18% 9% 36% 29% 7% 1	363
January	1st to 10th	Night	15% 14% 36% 29% 6%	840
	11th to 20th	Night	14% 12% 31% 33% 10% 1	840
	21st to end	Night	19% 14% 38% 25% 4	924
February	1st to 10th	Night	18% 11% 30% 32% 8%	840
	11th to 20th	Night	18% 14% 32% 30% 5%	823
	21st to end	Night	16% 14% 34% 33% 3	692
March	1st to 10th	Night	14% 12% 33% 34% 7%	840
	11th to 20th	Night	14% 11% 37% 27% 11% 1	840
	21st to end	Night	12% 11% 36% 31% 10%	924
April	1st to 10th	Night	14% 11% 31% 34% 10% 1	840
	11th to 20th	Night	10% 9% 34% 36% 10%	831
	21st to end	Night	8% 6% 27% 42% 16%	702
May	1st to 10th	Night	6% 5% 28% 44% 16% 1	630
	11th to 20th	Night	11% 3 21% 43% 20% 3	621
	21st to end	Night	9% 3 12% 41% 32% 4	683
June	1st to 10th	Night	11% 3 13% 39% 31% 3	630
	11th to 20th	Night	7% 3 10% 34% 34% 11%	630
	21st to end	Night	7% 1 9% 33% 40% 10%	630
July	1st to 10th	Night	8% 2 5% 30% 42% 13%	615
	11th to 20th	Night	8% 2 3 24% 48% 15%	612
	21st to end	Night	4 2 6% 32% 46% 11%	690
August	1st to 10th	Night	11% 1 4 26% 46% 11%	627
	11th to 20th	Night	5% 1 3 24% 51% 15%	624
	21st to end	Night	14% 3 8% 26% 37% 12%	846
September	1st to 10th	Night	13% 4 9% 28% 36% 10%	840
	11th to 20th	Night	13% 5% 12% 31% 34% 6%	840
	21st to end	Night	12% 3 14% 33% 34% 5%	840
October	1st to 10th	Night	17% 3 22% 33% 22% 3	840
	11th to 20th	Night	10% 5% 24% 36% 23% 2	840
	21st to end	Night	9% 6% 27% 35% 22% 1	913
November	1st to 10th	Night	12% 6% 26% 38% 17% 1	820
	11th to 20th	Night	14% 8% 28% 34% 14% 1	840
	21st to end	Night	15% 7% 31% 32% 14% 1	840
December	1st to 10th	Night	17% 8% 28% 33% 13%	840
	11th to 20th	Night	17% 9% 28% 31% 14% 1	840
	21st to end	Night	17% 11% 27% 32% 12%	924

Page generated at 2026-10-26 04:37:51. Version ac07

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