Fox Run Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fox Run Observatory 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	15% 11% 4 9% 5% 5% 5% 4 6% 7% 30%	120725
	Night	14% 11% 4 10% 6% 5% 4 4 5% 6% 31%	118023
Transparency	Day	52% 6% 12% 19% 10% 1	124346
	Night	52% 6% 11% 19% 11% 1	122551
Seeing	Day	19% 12% 28% 24% 13% 5%	15718
	Night	19% 12% 30% 27% 11% 1	24714

By Month

Percentage Cloud Cover NE (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	11% 16% 8% 18% 7% 4 4 3 4 4 21%	3643
	11th to 20th	Day	10% 21% 9% 22% 9% 8% 5% 3 3 3 8%	4026
	21st to end	Day	15% 17% 7% 18% 8% 6% 5% 4 4 5% 12%	4466
February	1st to 10th	Day	15% 17% 7% 13% 9% 7% 5% 3 4 4 16%	1800
	11th to 20th	Day	14% 12% 7% 15% 8% 4 5% 4 6% 6% 18%	1753
	21st to end	Day	17% 16% 5% 11% 7% 5% 5% 3 5% 5% 20%	1581
March	1st to 10th	Day	19% 12% 5% 10% 6% 5% 3 3 4 5% 27%	4885
	11th to 20th	Day	12% 12% 6% 9% 5% 5% 5% 4 6% 8% 29%	4980
	21st to end	Day	18% 13% 4 8% 6% 5% 4 3 5% 5% 29%	5465
April	1st to 10th	Day	17% 14% 5% 9% 4 5% 4 3 6% 6% 27%	2320
	11th to 20th	Day	19% 11% 3 7% 4 4 4 4 5% 6% 34%	2507
	21st to end	Day	20% 11% 3 7% 5% 5% 3 3 5% 6% 32%	2600
May	1st to 10th	Day	18% 10% 3 7% 5% 4 4 3 5% 7% 34%	5888
	11th to 20th	Day	17% 10% 3 8% 5% 5% 5% 3 5% 6% 33%	6124
	21st to end	Day	18% 7% 2 6% 4 5% 4 3 5% 7% 38%	6949
June	1st to 10th	Day	14% 7% 2 6% 5% 5% 6% 5% 7% 8% 36%	2800
	11th to 20th	Day	11% 6% 2 7% 5% 5% 5% 5% 7% 8% 39%	2924
	21st to end	Day	14% 6% 2 6% 5% 5% 5% 4 6% 9% 38%	3000
July	1st to 10th	Day	10% 6% 2 6% 5% 5% 5% 5% 8% 10% 38%	4818
	11th to 20th	Day	10% 6% 2 5% 4 4 5% 5% 7% 10% 42%	4345
	21st to end	Day	8% 6% 2 6% 5% 5% 5% 4 7% 9% 42%	4466
August	1st to 10th	Day	15% 7% 2 6% 5% 5% 5% 4 6% 9% 35%	4104
	11th to 20th	Day	11% 8% 3 8% 5% 5% 5% 5% 8% 9% 32%	4044
	21st to end	Day	9% 5% 2 7% 5% 5% 6% 5% 7% 9% 40%	4418
September	1st to 10th	Day	11% 6% 3 6% 5% 5% 5% 4 5% 9% 40%	2280
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 4 6% 10% 43%	2104
	21st to end	Day	14% 8% 3 7% 4 6% 5% 4 7% 9% 34%	2090
October	1st to 10th	Day	18% 10% 3 7% 4 5% 5% 4 6% 6% 32%	1900
	11th to 20th	Day	22% 9% 3 9% 4 5% 3 4 5% 7% 29%	1900
	21st to end	Day	24% 13% 4 8% 5% 5% 5% 4 5% 7% 20%	2089
November	1st to 10th	Day	15% 12% 4 9% 5% 4 5% 4 6% 7% 29%	1710
	11th to 20th	Day	15% 15% 4 9% 6% 4 5% 4 6% 6% 24%	1600
	21st to end	Day	18% 17% 8% 13% 5% 5% 4 3 6% 6% 17%	1600
December	1st to 10th	Day	17% 24% 8% 14% 5% 5% 4 3 5% 5% 11%	2600
	11th to 20th	Day	20% 21% 5% 11% 6% 4 4 3 4 5% 16%	2986
	21st to end	Day	26% 18% 6% 13% 6% 5% 4 3 4 3 11%	3960
January	1st to 10th	Night	13% 14% 6% 15% 7% 6% 4 4 6% 5% 19%	6285
	11th to 20th	Night	12% 15% 7% 19% 12% 8% 6% 4 5% 4 9%	5859
	21st to end	Night	15% 14% 8% 15% 6% 5% 6% 4 5% 6% 15%	6490
February	1st to 10th	Night	14% 16% 5% 10% 9% 6% 5% 4 5% 6% 19%	2600
	11th to 20th	Night	14% 13% 6% 11% 7% 6% 5% 4 6% 7% 22%	2533
	21st to end	Night	15% 12% 5% 13% 6% 5% 5% 3 6% 6% 25%	2045
March	1st to 10th	Night	14% 10% 4 10% 6% 5% 5% 4 6% 6% 30%	4954
	11th to 20th	Night	9% 8% 4 9% 5% 4 5% 5% 7% 9% 35%	4979
	21st to end	Night	20% 10% 3 7% 4 4 4 3 5% 5% 35%	5467
April	1st to 10th	Night	19% 11% 3 7% 6% 4 4 4 4 6% 31%	2080
	11th to 20th	Night	16% 10% 3 7% 5% 4 4 4 5% 5% 37%	1857
	21st to end	Night	15% 8% 3 8% 5% 5% 4 3 6% 7% 35%	1800
May	1st to 10th	Night	17% 8% 3 6% 4 4 4 3 6% 6% 38%	4053
	11th to 20th	Night	13% 8% 3 8% 5% 4 4 3 5% 7% 38%	3769
	21st to end	Night	17% 6% 2 6% 4 4 3 3 5% 8% 44%	3926
June	1st to 10th	Night	12% 6% 2 5% 3 6% 4 4 7% 8% 43%	1600
	11th to 20th	Night	10% 5% 2 6% 4 5% 4 4 8% 9% 42%	1469
	21st to end	Night	12% 5% 2 5% 6% 5% 4 3 5% 8% 45%	1400
July	1st to 10th	Night	6% 4 2 5% 3 3 4 4 6% 9% 53%	2245
	11th to 20th	Night	10% 5% 2 5% 3 4 3 3 4 8% 53%	2611
	21st to end	Night	6% 5% 2 6% 4 5% 5% 4 6% 8% 49%	3087
August	1st to 10th	Night	11% 6% 3 6% 4 4 4 4 6% 7% 46%	2825
	11th to 20th	Night	11% 6% 2 6% 4 4 4 4 6% 9% 45%	2785
	21st to end	Night	11% 5% 2 6% 3 4 4 4 5% 8% 48%	3206
September	1st to 10th	Night	9% 5% 2 7% 4 4 5% 3 6% 7% 47%	1900
	11th to 20th	Night	11% 5% 2 4 3 3 3 4 6% 7% 53%	2071
	21st to end	Night	16% 7% 3 7% 4 5% 3 3 5% 7% 41%	2090
October	1st to 10th	Night	15% 7% 2 9% 5% 5% 4 3 5% 6% 40%	2280
	11th to 20th	Night	18% 9% 3 7% 5% 4 5% 3 4 6% 34%	2280
	21st to end	Night	20% 10% 3 8% 6% 5% 4 4 6% 7% 27%	2508
November	1st to 10th	Night	15% 10% 3 7% 5% 4 4 4 6% 7% 34%	2585
	11th to 20th	Night	15% 13% 4 10% 6% 5% 5% 4 6% 7% 25%	2800
	21st to end	Night	18% 14% 4 9% 7% 4 5% 4 6% 8% 23%	2800
December	1st to 10th	Night	15% 19% 8% 13% 6% 6% 5% 4 5% 5% 14%	4580
	11th to 20th	Night	15% 21% 7% 12% 7% 5% 4 3 4 4 17%	5208
	21st to end	Night	23% 19% 8% 12% 6% 5% 4 3 4 4 12%	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	64% 6% 9% 10% 10% 1	3644
	11th to 20th	Day	80% 7% 5% 5% 3	4060
	21st to end	Day	74% 5% 9% 7% 5%	4466
February	1st to 10th	Day	70% 6% 8% 12% 4 1	1800
	11th to 20th	Day	65% 6% 7% 13% 7% 2	1762
	21st to end	Day	65% 4 9% 14% 7% 1	1581
March	1st to 10th	Day	59% 4 13% 13% 9% 1	4888
	11th to 20th	Day	52% 5% 15% 19% 7% 3	4980
	21st to end	Day	56% 5% 9% 18% 10% 2	5465
April	1st to 10th	Day	56% 5% 9% 18% 11% 1	2320
	11th to 20th	Day	50% 5% 11% 21% 13% 1	2507
	21st to end	Day	52% 5% 10% 19% 11% 2	2600
May	1st to 10th	Day	49% 5% 12% 18% 10% 6%	5897
	11th to 20th	Day	50% 7% 11% 17% 14% 1	6128
	21st to end	Day	45% 5% 12% 20% 14% 4	6949
June	1st to 10th	Day	42% 8% 12% 21% 16% 1	2800
	11th to 20th	Day	39% 7% 14% 24% 14% 1	2924
	21st to end	Day	41% 7% 13% 25% 14%	3000
July	1st to 10th	Day	37% 6% 17% 23% 15% 2	4744
	11th to 20th	Day	34% 7% 14% 34% 11% 1	4270
	21st to end	Day	36% 7% 14% 22% 19% 1	4324
August	1st to 10th	Day	43% 7% 14% 23% 13% 1	4091
	11th to 20th	Day	44% 8% 16% 24% 9%	4083
	21st to end	Day	37% 7% 13% 31% 10% 1	4418
September	1st to 10th	Day	40% 7% 15% 26% 11% 1	2280
	11th to 20th	Day	35% 7% 14% 29% 14% 1	2104
	21st to end	Day	46% 6% 14% 24% 9%	2090
October	1st to 10th	Day	43% 7% 13% 22% 14% 1	3160
	11th to 20th	Day	43% 6% 13% 21% 17%	3140
	21st to end	Day	53% 6% 15% 19% 7%	3415
November	1st to 10th	Day	53% 7% 11% 20% 8% 1	1710
	11th to 20th	Day	58% 7% 12% 15% 8% 1	1600
	21st to end	Day	68% 6% 10% 12% 5%	1600
December	1st to 10th	Day	75% 5% 10% 8% 3	2600
	11th to 20th	Day	71% 5% 9% 9% 5%	2986
	21st to end	Day	78% 6% 5% 6% 6%	3960
January	1st to 10th	Night	62% 9% 8% 14% 7% 1	6285
	11th to 20th	Night	75% 6% 6% 8% 4	5900
	21st to end	Night	68% 5% 10% 11% 5% 1	6490
February	1st to 10th	Night	65% 6% 9% 16% 4 1	2600
	11th to 20th	Night	60% 6% 10% 16% 9% 1	2535
	21st to end	Night	59% 5% 11% 17% 8%	2045
March	1st to 10th	Night	52% 5% 15% 15% 11% 2	4964
	11th to 20th	Night	43% 6% 17% 21% 11% 2	4980
	21st to end	Night	50% 5% 8% 18% 16% 2	5467
April	1st to 10th	Night	54% 4 8% 18% 14% 1	2080
	11th to 20th	Night	48% 5% 8% 22% 16% 2	1857
	21st to end	Night	47% 5% 9% 21% 16% 2	1800
May	1st to 10th	Night	47% 5% 12% 15% 13% 8%	4060
	11th to 20th	Night	45% 7% 13% 19% 14% 2	3770
	21st to end	Night	39% 5% 13% 24% 16% 2	3927
June	1st to 10th	Night	37% 7% 11% 26% 17% 2	1600
	11th to 20th	Night	36% 6% 13% 26% 17% 2	1469
	21st to end	Night	36% 6% 14% 25% 17% 1	1400
July	1st to 10th	Night	28% 6% 14% 26% 21% 5%	2210
	11th to 20th	Night	31% 5% 12% 34% 18% 1	2563
	21st to end	Night	32% 8% 13% 28% 17% 2	2988
August	1st to 10th	Night	36% 6% 13% 26% 16% 2	2814
	11th to 20th	Night	36% 7% 16% 28% 13% 1	2812
	21st to end	Night	33% 7% 11% 33% 15% 1	3206
September	1st to 10th	Night	35% 8% 13% 28% 15% 1	1900
	11th to 20th	Night	29% 6% 12% 31% 20% 1	2071
	21st to end	Night	43% 5% 13% 27% 12%	2090
October	1st to 10th	Night	34% 5% 10% 27% 23% 1	3800
	11th to 20th	Night	45% 5% 12% 24% 15%	3779
	21st to end	Night	43% 5% 17% 26% 9%	4120
November	1st to 10th	Night	47% 7% 12% 21% 12% 1	2585
	11th to 20th	Night	56% 7% 12% 16% 7% 1	2800
	21st to end	Night	60% 6% 15% 13% 5% 1	2800
December	1st to 10th	Night	71% 6% 10% 11% 2	4580
	11th to 20th	Night	70% 4 9% 12% 5%	5208
	21st to end	Night	76% 4 8% 7% 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	23% 19% 33% 17% 7% 1	210
	11th to 20th	Day	22% 18% 39% 17% 3 1	300
	21st to end	Day	25% 18% 34% 18% 4	330
February	1st to 10th	Day	24% 23% 36% 14% 4	300
	11th to 20th	Day	24% 23% 35% 16% 2	300
	21st to end	Day	25% 27% 33% 14% 1	249
March	1st to 10th	Day	25% 14% 34% 21% 6%	477
	11th to 20th	Day	21% 17% 35% 20% 6% 1	500
	21st to end	Day	29% 12% 31% 20% 6% 1	550
April	1st to 10th	Day	22% 19% 29% 22% 7% 1	500
	11th to 20th	Day	27% 18% 25% 17% 10% 3	492
	21st to end	Day	25% 13% 31% 21% 9% 1	500
May	1st to 10th	Day	22% 12% 27% 26% 10% 4	503
	11th to 20th	Day	16% 10% 28% 23% 15% 6%	527
	21st to end	Day	16% 8% 28% 26% 16% 7%	573
June	1st to 10th	Day	14% 12% 29% 28% 14% 3	530
	11th to 20th	Day	13% 9% 28% 30% 17% 3	654
	21st to end	Day	15% 10% 27% 33% 12% 3	730
July	1st to 10th	Day	8% 8% 23% 30% 22% 8%	692
	11th to 20th	Day	13% 6% 23% 26% 23% 9%	484
	21st to end	Day	10% 4 23% 33% 20% 10%	532
August	1st to 10th	Day	12% 6% 20% 28% 22% 12%	486
	11th to 20th	Day	11% 6% 19% 25% 23% 15%	479
	21st to end	Day	14% 6% 21% 27% 21% 12%	539
September	1st to 10th	Day	10% 10% 23% 24% 19% 13%	490
	11th to 20th	Day	11% 5% 18% 25% 25% 16%	490
	21st to end	Day	17% 12% 22% 24% 18% 7%	490
October	1st to 10th	Day	21% 12% 25% 22% 13% 8%	490
	11th to 20th	Day	21% 15% 32% 22% 8% 2	490
	21st to end	Day	29% 14% 28% 22% 6% 1	538
November	1st to 10th	Day	22% 21% 30% 19% 7% 1	273
	11th to 20th	Day	25% 16% 36% 17% 5% 3	200
	21st to end	Day	27% 19% 33% 18% 4	200
December	1st to 10th	Day	30% 18% 31% 16% 6% 1	200
	11th to 20th	Day	30% 22% 27% 18% 4 1	200
	21st to end	Day	30% 20% 34% 11% 4	220
January	1st to 10th	Night	22% 19% 36% 17% 5% 1	800
	11th to 20th	Night	27% 17% 32% 20% 4	800
	21st to end	Night	20% 14% 38% 22% 6%	880
February	1st to 10th	Night	23% 18% 35% 22% 2	800
	11th to 20th	Night	22% 17% 37% 21% 4	783
	21st to end	Night	20% 19% 37% 21% 3	660
March	1st to 10th	Night	18% 17% 37% 23% 6%	800
	11th to 20th	Night	18% 17% 38% 21% 6%	800
	21st to end	Night	23% 12% 32% 24% 8% 1	880
April	1st to 10th	Night	23% 18% 31% 25% 5%	800
	11th to 20th	Night	21% 13% 33% 23% 9% 1	673
	21st to end	Night	17% 13% 31% 31% 8%	600
May	1st to 10th	Night	17% 7% 33% 29% 14% 1	600
	11th to 20th	Night	16% 5% 29% 37% 12% 1	484
	21st to end	Night	12% 4 29% 36% 18%	433
June	1st to 10th	Night	14% 5% 30% 40% 12%	400
	11th to 20th	Night	13% 7% 29% 40% 13%	400
	21st to end	Night	12% 6% 24% 43% 15% 1	400
July	1st to 10th	Night	6% 4 19% 49% 21% 1	380
	11th to 20th	Night	8% 4 25% 38% 24% 2	420
	21st to end	Night	10% 3 19% 46% 21% 1	624
August	1st to 10th	Night	8% 2 19% 42% 26% 3	567
	11th to 20th	Night	9% 4 16% 39% 29% 4	564
	21st to end	Night	14% 3 21% 33% 27% 2	670
September	1st to 10th	Night	11% 6% 21% 36% 21% 5%	760
	11th to 20th	Night	12% 5% 19% 32% 27% 5%	760
	21st to end	Night	19% 7% 20% 30% 19% 5%	760
October	1st to 10th	Night	18% 7% 28% 29% 15% 3	760
	11th to 20th	Night	22% 11% 28% 29% 9% 2	760
	21st to end	Night	25% 13% 30% 25% 6%	836
November	1st to 10th	Night	21% 12% 29% 28% 9% 1	780
	11th to 20th	Night	23% 15% 33% 21% 7% 1	800
	21st to end	Night	26% 15% 33% 22% 4	800
December	1st to 10th	Night	27% 17% 32% 19% 5%	800
	11th to 20th	Night	24% 19% 37% 16% 4	800
	21st to end	Night	30% 16% 33% 18% 3	880

Page generated at 2025-07-03 01:30:17. Version ac07

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