Oak Hills
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oak Hills clear sky chart from 2005-11-06 to 2026-09-14.

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% 10% 3 8% 5% 5% 5% 4 5% 7% 33%	149811
	Night	16% 11% 4 8% 5% 4 4 4 5% 6% 32%	141255
Transparency	Day	50% 5% 12% 21% 11% 1	153342
	Night	51% 5% 12% 20% 11% 1	145812
Seeing	Day	24% 16% 31% 19% 8% 3	16812
	Night	22% 13% 31% 24% 9% 1	25950

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	14% 13% 4 11% 6% 5% 5% 4 6% 6% 27%	4661
	11th to 20th	Day	11% 21% 8% 15% 7% 6% 4 2 3 4 18%	4650
	21st to end	Day	11% 15% 6% 17% 8% 8% 5% 3 4 4 19%	5697
February	1st to 10th	Day	14% 16% 4 10% 7% 5% 5% 3 5% 6% 24%	1890
	11th to 20th	Day	13% 15% 4 12% 7% 5% 5% 3 4 4 27%	1843
	21st to end	Day	19% 14% 6% 9% 7% 6% 4 3 4 5% 23%	1679
March	1st to 10th	Day	20% 12% 4 10% 5% 4 3 3 4 6% 29%	4800
	11th to 20th	Day	11% 14% 4 9% 5% 5% 5% 4 5% 6% 31%	5090
	21st to end	Day	19% 12% 3 7% 4 3 3 2 4 5% 38%	5758
April	1st to 10th	Day	20% 13% 4 8% 5% 4 3 2 3 5% 32%	2520
	11th to 20th	Day	22% 9% 3 6% 4 4 3 3 5% 5% 36%	2494
	21st to end	Day	20% 11% 3 8% 5% 3 4 3 4 6% 33%	2677
May	1st to 10th	Day	21% 8% 3 7% 5% 5% 5% 4 5% 6% 30%	8110
	11th to 20th	Day	16% 9% 3 8% 5% 5% 4 3 5% 7% 35%	8221
	21st to end	Day	18% 8% 2 6% 4 4 5% 4 5% 7% 36%	9060
June	1st to 10th	Day	18% 8% 3 7% 5% 5% 5% 5% 6% 7% 31%	2940
	11th to 20th	Day	15% 7% 2 5% 5% 5% 4 5% 7% 9% 36%	2940
	21st to end	Day	17% 8% 3 6% 5% 4 5% 4 6% 8% 34%	2940
July	1st to 10th	Day	11% 6% 2 7% 5% 5% 6% 4 7% 10% 37%	8280
	11th to 20th	Day	9% 5% 1 5% 4 4 4 4 7% 10% 47%	8280
	21st to end	Day	10% 5% 2 6% 4 5% 6% 4 7% 10% 41%	8993
August	1st to 10th	Day	17% 9% 3 7% 5% 4 5% 4 5% 7% 35%	6065
	11th to 20th	Day	14% 6% 2 7% 4 5% 5% 4 7% 9% 36%	5951
	21st to end	Day	12% 7% 3 7% 4 5% 5% 5% 8% 9% 35%	6126
September	1st to 10th	Day	12% 6% 2 7% 4 4 5% 4 6% 7% 42%	2520
	11th to 20th	Day	11% 5% 2 6% 3 3 4 4 5% 8% 50%	2436
	21st to end	Day	18% 6% 3 6% 4 4 4 3 5% 8% 38%	2102
October	1st to 10th	Day	19% 8% 3 7% 4 4 4 3 5% 7% 37%	2000
	11th to 20th	Day	20% 9% 3 8% 4 5% 5% 4 6% 7% 30%	2000
	21st to end	Day	25% 10% 4 7% 5% 5% 5% 3 4 6% 27%	2130
November	1st to 10th	Day	16% 9% 3 8% 5% 5% 4 5% 6% 6% 34%	1804
	11th to 20th	Day	16% 13% 4 9% 5% 4 4 3 5% 6% 30%	1680
	21st to end	Day	22% 14% 5% 8% 5% 4 4 4 5% 6% 23%	1680
December	1st to 10th	Day	20% 17% 5% 11% 5% 4 5% 4 5% 5% 19%	2680
	11th to 20th	Day	17% 20% 6% 11% 4 4 4 3 3 4 24%	3066
	21st to end	Day	24% 16% 4 9% 6% 4 3 2 3 5% 24%	4048
January	1st to 10th	Night	14% 14% 6% 13% 7% 5% 5% 3 5% 6% 22%	8234
	11th to 20th	Night	11% 18% 6% 14% 8% 6% 5% 3 5% 5% 16%	8235
	21st to end	Night	12% 14% 7% 12% 7% 5% 5% 3 5% 5% 25%	8479
February	1st to 10th	Night	13% 14% 4 11% 6% 5% 5% 4 5% 5% 26%	2730
	11th to 20th	Night	13% 15% 6% 10% 6% 5% 4 4 5% 5% 27%	2663
	21st to end	Night	15% 13% 4 9% 5% 4 5% 4 6% 7% 29%	2126
March	1st to 10th	Night	19% 12% 3 9% 5% 4 4 3 5% 4 30%	5255
	11th to 20th	Night	13% 12% 3 8% 5% 5% 5% 4 6% 8% 30%	5089
	21st to end	Night	19% 10% 3 7% 4 4 4 3 5% 6% 35%	5415
April	1st to 10th	Night	19% 12% 3 8% 4 3 4 3 4 6% 33%	2100
	11th to 20th	Night	18% 9% 3 7% 4 4 5% 3 5% 5% 37%	2075
	21st to end	Night	18% 8% 3 7% 5% 5% 5% 3 6% 7% 34%	1960
May	1st to 10th	Night	23% 9% 3 6% 4 4 4 4 5% 8% 30%	4786
	11th to 20th	Night	15% 8% 2 7% 4 4 4 4 5% 7% 41%	4639
	21st to end	Night	18% 6% 2 6% 4 4 4 4 5% 8% 39%	5114
June	1st to 10th	Night	15% 6% 2 8% 5% 5% 5% 4 5% 8% 37%	1680
	11th to 20th	Night	12% 6% 2 6% 5% 4 4 4 5% 9% 43%	1680
	21st to end	Night	14% 7% 2 7% 5% 4 3 4 5% 8% 39%	1680
July	1st to 10th	Night	8% 6% 3 7% 5% 5% 5% 5% 6% 10% 41%	4680
	11th to 20th	Night	9% 5% 2 5% 4 3 4 3 6% 9% 50%	4680
	21st to end	Night	10% 6% 2 5% 4 4 4 4 6% 8% 47%	5084
August	1st to 10th	Night	14% 7% 2 6% 4 5% 5% 4 6% 6% 40%	4081
	11th to 20th	Night	12% 5% 2 5% 4 3 4 4 5% 7% 48%	4095
	21st to end	Night	10% 5% 2 7% 5% 4 6% 4 7% 10% 41%	4952
September	1st to 10th	Night	12% 6% 2 6% 5% 3 4 3 5% 8% 48%	2100
	11th to 20th	Night	11% 4 2 5% 4 4 3 4 5% 7% 53%	2031
	21st to end	Night	17% 6% 2 6% 4 4 5% 4 5% 5% 42%	2295
October	1st to 10th	Night	15% 8% 2 7% 4 4 4 4 5% 7% 41%	2400
	11th to 20th	Night	20% 8% 3 8% 6% 5% 4 4 5% 6% 32%	2400
	21st to end	Night	21% 10% 3 7% 5% 5% 4 3 5% 6% 31%	2710
November	1st to 10th	Night	17% 10% 3 6% 4 4 4 4 5% 7% 36%	2709
	11th to 20th	Night	17% 11% 4 8% 5% 4 5% 3 5% 6% 32%	2940
	21st to end	Night	19% 14% 3 9% 5% 5% 5% 4 5% 5% 26%	2940
December	1st to 10th	Night	19% 15% 4 10% 6% 5% 5% 4 6% 7% 19%	4720
	11th to 20th	Night	20% 16% 5% 9% 5% 4 4 3 4 5% 24%	5348
	21st to end	Night	26% 16% 4 10% 5% 4 4 3 4 5% 20%	7150

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	57% 5% 12% 18% 7% 1	4662
	11th to 20th	Day	72% 3 8% 9% 7%	4680
	21st to end	Day	69% 3 8% 11% 9% 1	5697
February	1st to 10th	Day	60% 6% 11% 16% 7% 1	1890
	11th to 20th	Day	62% 4 9% 15% 10% 1	1852
	21st to end	Day	63% 5% 9% 12% 10% 1	1679
March	1st to 10th	Day	57% 3 11% 12% 15% 1	4803
	11th to 20th	Day	52% 4 17% 15% 10% 2	5090
	21st to end	Day	50% 3 7% 21% 16% 3	5758
April	1st to 10th	Day	56% 4 8% 17% 13% 2	2520
	11th to 20th	Day	50% 4 7% 21% 15% 2	2494
	21st to end	Day	54% 5% 8% 17% 14% 3	2677
May	1st to 10th	Day	54% 5% 9% 18% 12% 2	8121
	11th to 20th	Day	47% 6% 11% 20% 15% 1	8225
	21st to end	Day	47% 5% 10% 25% 12% 1	9061
June	1st to 10th	Day	49% 8% 10% 17% 14% 1	2940
	11th to 20th	Day	42% 7% 11% 25% 13% 2	2940
	21st to end	Day	45% 7% 14% 20% 13% 1	2940
July	1st to 10th	Day	41% 5% 16% 26% 12%	8210
	11th to 20th	Day	32% 5% 13% 33% 16% 1	8205
	21st to end	Day	37% 5% 15% 33% 9%	8795
August	1st to 10th	Day	48% 4 14% 18% 13% 3	6051
	11th to 20th	Day	42% 5% 17% 28% 7% 1	5990
	21st to end	Day	43% 5% 17% 27% 8%	6126
September	1st to 10th	Day	38% 8% 12% 29% 12% 1	2520
	11th to 20th	Day	32% 6% 13% 32% 16% 1	2436
	21st to end	Day	44% 8% 12% 26% 10%	2102
October	1st to 10th	Day	42% 6% 11% 31% 10%	3260
	11th to 20th	Day	46% 5% 15% 24% 10% 1	3240
	21st to end	Day	53% 4 13% 21% 8%	3420
November	1st to 10th	Day	49% 7% 14% 21% 9% 1	1804
	11th to 20th	Day	55% 5% 12% 17% 11% 1	1680
	21st to end	Day	60% 8% 12% 12% 8%	1680
December	1st to 10th	Day	66% 5% 15% 9% 5%	2680
	11th to 20th	Day	65% 4 10% 13% 8%	3066
	21st to end	Day	64% 4 8% 16% 8%	4048
January	1st to 10th	Night	63% 5% 10% 14% 7%	8234
	11th to 20th	Night	69% 6% 8% 10% 6%	8280
	21st to end	Night	60% 5% 8% 13% 13% 1	8479
February	1st to 10th	Night	58% 6% 11% 18% 7% 1	2730
	11th to 20th	Night	58% 4 10% 19% 8% 1	2665
	21st to end	Night	53% 6% 11% 19% 9% 1	2126
March	1st to 10th	Night	57% 4 6% 17% 12% 5%	5265
	11th to 20th	Night	49% 5% 18% 18% 8% 2	5090
	21st to end	Night	48% 3 10% 20% 16% 2	5415
April	1st to 10th	Night	52% 4 8% 20% 14% 2	2100
	11th to 20th	Night	48% 5% 9% 20% 16% 1	2075
	21st to end	Night	49% 5% 9% 18% 15% 3	1960
May	1st to 10th	Night	54% 4 9% 18% 12% 3	4792
	11th to 20th	Night	42% 6% 13% 23% 14% 1	4640
	21st to end	Night	44% 5% 12% 21% 17% 2	5115
June	1st to 10th	Night	43% 7% 12% 22% 15% 1	1680
	11th to 20th	Night	39% 5% 13% 22% 19% 2	1680
	21st to end	Night	41% 8% 14% 24% 12% 2	1680
July	1st to 10th	Night	39% 5% 19% 23% 15% 1	4640
	11th to 20th	Night	32% 4 13% 34% 16% 1	4632
	21st to end	Night	36% 5% 13% 31% 14%	4967
August	1st to 10th	Night	44% 4 14% 21% 13% 3	4071
	11th to 20th	Night	36% 4 16% 34% 10% 1	4122
	21st to end	Night	37% 6% 17% 30% 9% 1	4952
September	1st to 10th	Night	36% 6% 15% 29% 14% 1	2100
	11th to 20th	Night	31% 7% 13% 33% 16% 1	2031
	21st to end	Night	43% 7% 10% 27% 13% 1	2295
October	1st to 10th	Night	37% 5% 9% 29% 19% 1	3920
	11th to 20th	Night	44% 5% 15% 27% 9%	3899
	21st to end	Night	48% 5% 13% 25% 9%	4370
November	1st to 10th	Night	47% 5% 14% 22% 11% 1	2709
	11th to 20th	Night	51% 5% 12% 20% 10% 2	2940
	21st to end	Night	57% 8% 13% 16% 6%	2940
December	1st to 10th	Night	64% 5% 13% 14% 4	4720
	11th to 20th	Night	63% 5% 10% 14% 9%	5348
	21st to end	Night	67% 5% 8% 11% 9%	7150

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	25% 22% 33% 16% 3	220
	11th to 20th	Day	30% 21% 31% 15% 3	220
	21st to end	Day	27% 23% 33% 12% 4	347
February	1st to 10th	Day	32% 25% 29% 10% 3 1	330
	11th to 20th	Day	30% 25% 36% 7% 1	330
	21st to end	Day	37% 18% 33% 10% 2	395
March	1st to 10th	Day	28% 19% 35% 14% 4	540
	11th to 20th	Day	31% 21% 30% 14% 4 1	540
	21st to end	Day	35% 19% 27% 13% 5% 1	594
April	1st to 10th	Day	32% 20% 31% 11% 5% 1	540
	11th to 20th	Day	36% 20% 21% 13% 7% 2	532
	21st to end	Day	29% 19% 34% 11% 6% 1	540
May	1st to 10th	Day	26% 17% 30% 18% 7% 3	543
	11th to 20th	Day	20% 17% 35% 19% 8% 2	567
	21st to end	Day	19% 18% 33% 18% 9% 3	617
June	1st to 10th	Day	24% 14% 32% 22% 6% 2	570
	11th to 20th	Day	17% 16% 34% 21% 10% 2	570
	21st to end	Day	21% 13% 35% 19% 9% 2	570
July	1st to 10th	Day	13% 9% 31% 32% 12% 3	565
	11th to 20th	Day	16% 10% 29% 27% 14% 4	564
	21st to end	Day	13% 8% 37% 26% 12% 3	620
August	1st to 10th	Day	14% 10% 28% 29% 14% 5%	566
	11th to 20th	Day	12% 8% 29% 29% 16% 5%	559
	21st to end	Day	16% 10% 33% 22% 11% 7%	627
September	1st to 10th	Day	16% 12% 30% 24% 12% 6%	570
	11th to 20th	Day	12% 8% 23% 26% 19% 12%	542
	21st to end	Day	20% 11% 29% 24% 12% 5%	530
October	1st to 10th	Day	23% 17% 23% 19% 12% 6%	530
	11th to 20th	Day	25% 18% 33% 16% 6% 2	530
	21st to end	Day	29% 18% 31% 18% 3	544
November	1st to 10th	Day	31% 17% 28% 17% 7% 1	378
	11th to 20th	Day	30% 19% 34% 11% 5% 1	220
	21st to end	Day	30% 21% 33% 12% 3 1	220
December	1st to 10th	Day	31% 15% 37% 14% 3	220
	11th to 20th	Day	37% 20% 29% 10% 3 1	220
	21st to end	Day	37% 19% 31% 10% 3	242
January	1st to 10th	Night	27% 19% 31% 19% 3	840
	11th to 20th	Night	27% 17% 31% 20% 5%	840
	21st to end	Night	21% 15% 35% 23% 4 1	924
February	1st to 10th	Night	21% 19% 37% 21% 2	840
	11th to 20th	Night	23% 17% 37% 18% 4	823
	21st to end	Night	26% 19% 33% 19% 3	692
March	1st to 10th	Night	23% 18% 35% 21% 3	840
	11th to 20th	Night	25% 19% 30% 21% 3 1	840
	21st to end	Night	24% 14% 35% 19% 7% 1	924
April	1st to 10th	Night	27% 16% 32% 21% 4	840
	11th to 20th	Night	25% 19% 29% 19% 8%	831
	21st to end	Night	23% 13% 29% 24% 10%	700
May	1st to 10th	Night	24% 10% 28% 27% 10% 2	468
	11th to 20th	Night	16% 11% 34% 31% 8%	414
	21st to end	Night	15% 9% 35% 30% 10% 1	455
June	1st to 10th	Night	16% 8% 34% 33% 10%	420
	11th to 20th	Night	15% 8% 34% 32% 10% 1	420
	21st to end	Night	16% 6% 28% 39% 10% 1	420
July	1st to 10th	Night	6% 9% 30% 39% 15% 1	410
	11th to 20th	Night	12% 5% 28% 35% 19% 1	408
	21st to end	Night	12% 3 28% 43% 14%	460
August	1st to 10th	Night	12% 4 26% 33% 24% 2	599
	11th to 20th	Night	11% 5% 23% 35% 23% 3	624
	21st to end	Night	12% 6% 29% 34% 18% 2	881
September	1st to 10th	Night	15% 6% 30% 30% 16% 2	840
	11th to 20th	Night	13% 6% 23% 26% 28% 4	813
	21st to end	Night	20% 9% 23% 28% 18% 3	800
October	1st to 10th	Night	19% 12% 26% 25% 16% 2	800
	11th to 20th	Night	25% 12% 31% 23% 9% 1	800
	21st to end	Night	27% 13% 31% 23% 5%	880
November	1st to 10th	Night	25% 14% 28% 25% 9%	820
	11th to 20th	Night	24% 16% 33% 19% 7% 1	840
	21st to end	Night	30% 16% 28% 20% 5%	840
December	1st to 10th	Night	30% 17% 30% 19% 3	840
	11th to 20th	Night	29% 17% 34% 17% 3 1	840
	21st to end	Night	37% 14% 28% 17% 3	924

Page generated at 2026-09-11 04:11:55. Version ac07

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