Fox Park Public Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fox Park Public Observatory clear sky chart from 2005-11-06 to 2025-10-19.

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% 10% 4 9% 5% 5% 5% 4 5% 7% 34%	126344
	Night	14% 11% 4 9% 5% 5% 4 3 5% 6% 33%	123547
Transparency	Day	48% 6% 12% 21% 12% 1	129899
	Night	50% 5% 11% 20% 12% 1	128065
Seeing	Day	17% 12% 28% 24% 14% 6%	17096
	Night	19% 9% 30% 29% 12% 1	26886

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% 16% 7% 15% 7% 6% 4 4 4 5% 19%	3617
	11th to 20th	Day	13% 15% 7% 18% 9% 12% 6% 3 5% 4 8%	3620
	21st to end	Day	21% 18% 6% 13% 6% 4 6% 2 3 5% 16%	4095
February	1st to 10th	Day	13% 15% 5% 12% 9% 6% 4 4 5% 6% 20%	1820
	11th to 20th	Day	14% 13% 7% 14% 9% 5% 4 2 3 5% 24%	1948
	21st to end	Day	14% 16% 4 12% 6% 5% 5% 4 4 5% 25%	1650
March	1st to 10th	Day	14% 12% 4 11% 6% 4 4 3 5% 6% 32%	4480
	11th to 20th	Day	11% 11% 4 8% 6% 4 4 4 5% 7% 35%	4933
	21st to end	Day	17% 15% 5% 9% 5% 4 4 3 5% 6% 27%	5523
April	1st to 10th	Day	18% 14% 4 8% 5% 5% 4 4 5% 5% 30%	2400
	11th to 20th	Day	16% 10% 3 8% 4 5% 4 3 4 7% 36%	2472
	21st to end	Day	15% 9% 3 7% 5% 5% 5% 3 5% 8% 34%	2600
May	1st to 10th	Day	20% 9% 3 6% 4 4 4 3 5% 7% 35%	5862
	11th to 20th	Day	14% 9% 3 7% 5% 5% 4 4 6% 8% 35%	5861
	21st to end	Day	15% 7% 2 6% 4 4 4 3 5% 7% 42%	6725
June	1st to 10th	Day	10% 5% 2 6% 5% 5% 6% 5% 6% 8% 43%	2800
	11th to 20th	Day	11% 5% 2 7% 6% 4 4 4 6% 9% 42%	2800
	21st to end	Day	9% 5% 2 7% 5% 5% 5% 5% 8% 8% 40%	2800
July	1st to 10th	Day	10% 6% 2 6% 5% 5% 6% 5% 8% 10% 37%	6360
	11th to 20th	Day	7% 6% 2 6% 5% 4 5% 4 7% 9% 47%	6360
	21st to end	Day	7% 6% 2 6% 4 4 5% 4 7% 9% 46%	6799
August	1st to 10th	Day	11% 5% 2 5% 5% 4 5% 5% 7% 9% 42%	4234
	11th to 20th	Day	11% 6% 2 6% 5% 4 5% 4 6% 8% 43%	4174
	21st to end	Day	7% 6% 2 7% 5% 5% 5% 5% 7% 9% 42%	4458
September	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 4 6% 7% 42%	2325
	11th to 20th	Day	10% 5% 2 5% 4 3 5% 3 6% 8% 49%	2200
	21st to end	Day	13% 8% 3 7% 5% 4 5% 4 6% 8% 38%	2200
October	1st to 10th	Day	13% 7% 3 6% 4 5% 4 4 5% 7% 43%	2200
	11th to 20th	Day	17% 9% 4 9% 5% 4 5% 3 6% 6% 32%	1956
	21st to end	Day	21% 12% 3 7% 5% 5% 4 3 5% 7% 26%	1881
November	1st to 10th	Day	12% 12% 3 6% 5% 5% 4 4 4 6% 39%	1762
	11th to 20th	Day	14% 15% 5% 9% 7% 5% 5% 3 6% 6% 25%	1800
	21st to end	Day	18% 16% 5% 10% 5% 4 3 3 5% 5% 27%	1800
December	1st to 10th	Day	10% 16% 10% 16% 8% 6% 5% 4 5% 5% 17%	2839
	11th to 20th	Day	16% 21% 9% 13% 8% 5% 4 3 3 3 15%	3008
	21st to end	Day	23% 21% 7% 13% 4 4 4 3 4 4 12%	3982
January	1st to 10th	Night	12% 17% 7% 17% 7% 5% 5% 3 5% 5% 18%	6348
	11th to 20th	Night	12% 15% 8% 17% 8% 9% 5% 3 5% 5% 12%	6360
	21st to end	Night	17% 17% 8% 12% 5% 6% 5% 3 4 5% 17%	6876
February	1st to 10th	Night	14% 17% 5% 11% 9% 6% 5% 3 4 4 21%	2575
	11th to 20th	Night	12% 13% 5% 12% 7% 6% 5% 4 5% 4 25%	2338
	21st to end	Night	17% 12% 4 10% 5% 4 5% 4 6% 7% 27%	1980
March	1st to 10th	Night	14% 9% 4 9% 5% 4 4 3 5% 7% 37%	5373
	11th to 20th	Night	10% 8% 3 7% 4 4 4 4 5% 8% 43%	5026
	21st to end	Night	17% 11% 4 8% 4 4 4 3 4 6% 34%	5436
April	1st to 10th	Night	16% 11% 3 7% 5% 5% 4 4 4 6% 36%	2000
	11th to 20th	Night	18% 8% 3 7% 4 3 4 3 5% 6% 37%	1877
	21st to end	Night	17% 7% 4 6% 5% 4 4 4 5% 7% 37%	1800
May	1st to 10th	Night	18% 9% 3 8% 5% 4 4 3 5% 7% 33%	4033
	11th to 20th	Night	16% 9% 3 7% 4 4 3 3 4 7% 40%	4032
	21st to end	Night	15% 6% 3 7% 4 4 4 3 5% 7% 43%	4125
June	1st to 10th	Night	12% 5% 1 5% 4 4 4 4 6% 8% 46%	1600
	11th to 20th	Night	11% 6% 3 5% 4 4 4 3 7% 9% 44%	1600
	21st to end	Night	9% 5% 2 6% 4 4 4 4 7% 10% 46%	1600
July	1st to 10th	Night	8% 5% 1 5% 4 4 5% 4 8% 10% 46%	3618
	11th to 20th	Night	8% 5% 2 5% 4 4 4 4 6% 8% 51%	3617
	21st to end	Night	9% 6% 3 7% 4 4 3 4 6% 8% 47%	4067
August	1st to 10th	Night	9% 6% 2 5% 4 4 4 3 6% 9% 48%	2915
	11th to 20th	Night	11% 6% 2 5% 5% 4 4 4 6% 7% 46%	2875
	21st to end	Night	8% 7% 3 7% 5% 4 4 3 6% 8% 46%	3437
September	1st to 10th	Night	9% 5% 2 6% 5% 4 4 4 5% 8% 49%	2055
	11th to 20th	Night	9% 4 2 4 4 3 4 3 5% 7% 56%	2200
	21st to end	Night	14% 7% 2 7% 4 4 4 3 4 7% 44%	2200
October	1st to 10th	Night	15% 6% 3 5% 3 4 3 3 5% 7% 47%	2200
	11th to 20th	Night	17% 11% 3 7% 5% 5% 4 3 5% 5% 34%	2396
	21st to end	Night	21% 10% 3 8% 5% 4 4 3 5% 6% 31%	2717
November	1st to 10th	Night	14% 11% 3 7% 4 4 3 3 5% 5% 41%	2536
	11th to 20th	Night	14% 15% 4 9% 5% 5% 6% 4 5% 7% 27%	2600
	21st to end	Night	17% 16% 4 8% 4 4 4 4 5% 6% 27%	2600
December	1st to 10th	Night	12% 17% 8% 15% 6% 4 4 3 4 5% 20%	4340
	11th to 20th	Night	15% 21% 7% 15% 8% 5% 4 3 4 4 16%	5199
	21st to end	Night	24% 22% 6% 12% 5% 4 4 3 4 5% 13%	6996

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	67% 6% 11% 14% 3	3618
	11th to 20th	Day	80% 5% 8% 5% 3	3620
	21st to end	Day	73% 3 11% 9% 4	4095
February	1st to 10th	Day	64% 7% 10% 13% 6%	1820
	11th to 20th	Day	64% 4 8% 14% 8% 1	1958
	21st to end	Day	62% 5% 11% 14% 7% 2	1650
March	1st to 10th	Day	54% 5% 13% 18% 10% 1	4480
	11th to 20th	Day	46% 5% 17% 22% 9% 1	4933
	21st to end	Day	59% 5% 9% 15% 12% 1	5525
April	1st to 10th	Day	56% 4 11% 19% 10%	2400
	11th to 20th	Day	49% 5% 11% 20% 14% 2	2472
	21st to end	Day	47% 6% 11% 19% 14% 2	2600
May	1st to 10th	Day	49% 6% 11% 19% 15% 1	5897
	11th to 20th	Day	44% 8% 13% 21% 12% 1	5865
	21st to end	Day	41% 6% 9% 23% 19% 2	6739
June	1st to 10th	Day	36% 7% 12% 27% 16% 2	2800
	11th to 20th	Day	37% 7% 14% 23% 18% 2	2800
	21st to end	Day	38% 8% 13% 22% 16% 2	2800
July	1st to 10th	Day	39% 7% 13% 25% 15% 2	6291
	11th to 20th	Day	32% 6% 13% 28% 19% 1	6285
	21st to end	Day	32% 6% 15% 25% 20% 1	6604
August	1st to 10th	Day	36% 7% 13% 26% 16% 1	4221
	11th to 20th	Day	37% 6% 11% 31% 13% 1	4213
	21st to end	Day	36% 7% 13% 30% 12% 2	4457
September	1st to 10th	Day	38% 7% 13% 25% 15% 2	2325
	11th to 20th	Day	33% 5% 13% 30% 18% 1	2200
	21st to end	Day	43% 6% 12% 23% 16%	2200
October	1st to 10th	Day	30% 4 9% 36% 20% 1	3590
	11th to 20th	Day	41% 5% 10% 26% 17%	3172
	21st to end	Day	49% 5% 11% 24% 10% 1	3081
November	1st to 10th	Day	45% 7% 13% 21% 13% 1	1762
	11th to 20th	Day	59% 6% 11% 17% 7% 1	1800
	21st to end	Day	60% 5% 14% 15% 6% 1	1800
December	1st to 10th	Day	68% 7% 14% 8% 3	2839
	11th to 20th	Day	74% 4 8% 11% 2	3005
	21st to end	Day	77% 4 7% 9% 3	3982
January	1st to 10th	Night	66% 5% 9% 13% 6% 1	6348
	11th to 20th	Night	73% 4 10% 7% 6%	6360
	21st to end	Night	70% 4 11% 11% 4	6876
February	1st to 10th	Night	65% 6% 10% 13% 6% 1	2575
	11th to 20th	Night	60% 5% 9% 16% 8% 1	2339
	21st to end	Night	56% 6% 12% 16% 8% 2	1980
March	1st to 10th	Night	47% 5% 14% 24% 10% 1	5373
	11th to 20th	Night	37% 5% 15% 26% 15% 1	5026
	21st to end	Night	51% 5% 11% 19% 13% 2	5436
April	1st to 10th	Night	48% 6% 11% 21% 14% 1	2000
	11th to 20th	Night	46% 6% 11% 18% 17% 2	1877
	21st to end	Night	45% 5% 13% 21% 14% 3	1800
May	1st to 10th	Night	50% 7% 11% 16% 14% 2	4060
	11th to 20th	Night	45% 5% 9% 23% 14% 3	4033
	21st to end	Night	40% 5% 10% 23% 19% 3	4133
June	1st to 10th	Night	34% 5% 12% 28% 18% 2	1600
	11th to 20th	Night	36% 7% 14% 25% 17% 2	1600
	21st to end	Night	32% 8% 14% 25% 18% 2	1600
July	1st to 10th	Night	32% 6% 14% 27% 16% 5%	3580
	11th to 20th	Night	31% 5% 14% 29% 20% 1	3572
	21st to end	Night	35% 6% 14% 21% 23% 2	3950
August	1st to 10th	Night	32% 6% 13% 29% 18% 1	2904
	11th to 20th	Night	36% 6% 11% 32% 14% 1	2902
	21st to end	Night	35% 6% 11% 30% 16% 1	3437
September	1st to 10th	Night	33% 7% 11% 29% 19% 2	2055
	11th to 20th	Night	28% 5% 11% 33% 22% 2	2200
	21st to end	Night	40% 7% 12% 25% 16% 1	2200
October	1st to 10th	Night	26% 4 10% 36% 23% 1	3590
	11th to 20th	Night	45% 4 9% 21% 20% 1	3919
	21st to end	Night	41% 4 10% 30% 14% 1	4467
November	1st to 10th	Night	45% 6% 11% 24% 14% 1	2536
	11th to 20th	Night	55% 7% 13% 17% 8% 1	2600
	21st to end	Night	58% 6% 13% 18% 5%	2600
December	1st to 10th	Night	66% 5% 13% 13% 3	4340
	11th to 20th	Night	72% 4 10% 10% 4	5201
	21st to end	Night	74% 4 9% 8% 5%	6996

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	22% 15% 37% 19% 7% 1	300
	11th to 20th	Day	21% 17% 42% 15% 4 1	300
	21st to end	Day	27% 17% 35% 18% 4	330
February	1st to 10th	Day	24% 21% 33% 18% 3 1	300
	11th to 20th	Day	25% 18% 39% 16% 2	300
	21st to end	Day	27% 24% 34% 12% 2	249
March	1st to 10th	Day	21% 19% 44% 12% 4	300
	11th to 20th	Day	23% 15% 33% 23% 7%	479
	21st to end	Day	26% 16% 29% 23% 4 1	550
April	1st to 10th	Day	24% 13% 34% 22% 6% 1	500
	11th to 20th	Day	26% 18% 29% 17% 6% 5%	492
	21st to end	Day	19% 15% 30% 24% 11% 1	500
May	1st to 10th	Day	24% 15% 24% 24% 9% 3	503
	11th to 20th	Day	19% 11% 26% 24% 14% 6%	527
	21st to end	Day	16% 8% 26% 26% 17% 7%	696
June	1st to 10th	Day	12% 9% 28% 31% 15% 5%	730
	11th to 20th	Day	13% 6% 30% 30% 16% 5%	730
	21st to end	Day	12% 8% 28% 31% 16% 5%	730
July	1st to 10th	Day	8% 5% 20% 31% 21% 13%	721
	11th to 20th	Day	11% 7% 24% 28% 21% 9%	718
	21st to end	Day	8% 5% 23% 33% 23% 9%	744
August	1st to 10th	Day	9% 4 19% 28% 22% 19%	526
	11th to 20th	Day	13% 4 14% 30% 29% 10%	519
	21st to end	Day	11% 4 21% 26% 25% 13%	583
September	1st to 10th	Day	14% 7% 22% 23% 22% 12%	530
	11th to 20th	Day	10% 5% 15% 23% 30% 17%	530
	21st to end	Day	17% 11% 19% 24% 18% 10%	530
October	1st to 10th	Day	17% 8% 28% 24% 17% 7%	530
	11th to 20th	Day	19% 16% 26% 28% 9% 1	489
	21st to end	Day	27% 16% 34% 17% 4 1	330
November	1st to 10th	Day	17% 18% 35% 23% 6% 1	300
	11th to 20th	Day	24% 20% 35% 16% 5%	300
	21st to end	Day	26% 18% 38% 13% 5%	300
December	1st to 10th	Day	23% 26% 29% 14% 7% 1	300
	11th to 20th	Day	23% 22% 39% 13% 4	300
	21st to end	Day	27% 21% 34% 14% 4 1	330
January	1st to 10th	Night	21% 15% 35% 22% 6% 1	1000
	11th to 20th	Night	24% 14% 35% 22% 5% 1	1000
	21st to end	Night	20% 12% 35% 28% 5%	1045
February	1st to 10th	Night	24% 12% 38% 23% 3	800
	11th to 20th	Night	21% 16% 36% 24% 3	783
	21st to end	Night	22% 14% 41% 19% 3	660
March	1st to 10th	Night	20% 13% 36% 25% 6% 1	800
	11th to 20th	Night	17% 14% 37% 26% 5% 1	800
	21st to end	Night	22% 11% 33% 26% 8%	874
April	1st to 10th	Night	18% 13% 39% 25% 5% 1	600
	11th to 20th	Night	23% 11% 35% 23% 8% 1	593
	21st to end	Night	21% 7% 35% 29% 8% 1	600
May	1st to 10th	Night	20% 7% 32% 31% 9% 1	600
	11th to 20th	Night	21% 6% 31% 29% 11% 1	591
	21st to end	Night	12% 4 27% 35% 20% 2	650
June	1st to 10th	Night	13% 3 27% 43% 14% 1	600
	11th to 20th	Night	13% 4 26% 39% 18% 1	600
	21st to end	Night	9% 5% 22% 42% 21% 1	600
July	1st to 10th	Night	8% 2 18% 41% 26% 5%	585
	11th to 20th	Night	10% 3 18% 42% 24% 3	582
	21st to end	Night	7% 2 17% 47% 25% 2	657
August	1st to 10th	Night	8% 1 16% 44% 28% 3	597
	11th to 20th	Night	9% 1 18% 39% 28% 5%	594
	21st to end	Night	10% 3 18% 38% 28% 3	660
September	1st to 10th	Night	10% 4 19% 37% 26% 4	655
	11th to 20th	Night	11% 4 15% 36% 30% 4	800
	21st to end	Night	17% 6% 22% 28% 22% 5%	800
October	1st to 10th	Night	17% 6% 24% 33% 19% 1	800
	11th to 20th	Night	22% 12% 29% 28% 8% 1	793
	21st to end	Night	25% 11% 33% 24% 7%	836
November	1st to 10th	Night	21% 10% 30% 30% 9% 1	780
	11th to 20th	Night	22% 14% 35% 22% 6% 1	800
	21st to end	Night	25% 12% 34% 26% 4	800
December	1st to 10th	Night	24% 15% 34% 21% 6%	851
	11th to 20th	Night	23% 15% 36% 22% 4	1000
	21st to end	Night	32% 12% 34% 21% 2	1100

Page generated at 2025-10-16 01:50:28. Version ac07

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