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 2025-05-11.

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	16% 10% 3 8% 5% 4 4 4 5% 7% 33%	113992
	Night	16% 11% 4 8% 5% 4 4 4 5% 6% 32%	114938
Transparency	Day	50% 6% 12% 21% 11% 1	117570
	Night	51% 6% 12% 20% 11% 1	119524
Seeing	Day	24% 16% 31% 19% 8% 3	15040
	Night	22% 13% 30% 24% 9% 1	24386

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	12% 13% 4 10% 6% 4 4 4 6% 7% 30%	3597
	11th to 20th	Day	10% 19% 8% 14% 6% 6% 5% 3 4 4 21%	3570
	21st to end	Day	14% 17% 6% 17% 6% 6% 4 3 4 4 20%	4397
February	1st to 10th	Day	14% 16% 4 10% 7% 5% 5% 3 5% 6% 23%	1800
	11th to 20th	Day	13% 15% 4 12% 7% 5% 5% 3 4 4 28%	1753
	21st to end	Day	19% 13% 5% 9% 7% 6% 4 3 4 5% 24%	1601
March	1st to 10th	Day	20% 12% 4 10% 5% 4 3 3 4 6% 29%	4696
	11th to 20th	Day	11% 14% 4 9% 5% 5% 5% 4 5% 6% 32%	4980
	21st to end	Day	19% 12% 3 7% 4 3 3 2 4 5% 39%	5634
April	1st to 10th	Day	20% 13% 4 8% 5% 4 3 2 3 5% 32%	2400
	11th to 20th	Day	21% 9% 3 6% 4 4 3 3 5% 5% 37%	2374
	21st to end	Day	20% 11% 3 8% 5% 3 4 3 4 6% 33%	2550
May	1st to 10th	Day	20% 8% 2 7% 5% 4 5% 4 5% 6% 33%	4492
	11th to 20th	Day	16% 10% 3 8% 5% 5% 4 3 6% 8% 32%	4398
	21st to end	Day	13% 6% 2 6% 4 4 5% 4 5% 8% 42%	4837
June	1st to 10th	Day	19% 8% 3 7% 5% 5% 5% 5% 7% 7% 29%	2660
	11th to 20th	Day	15% 6% 2 5% 5% 5% 4 5% 7% 9% 37%	2660
	21st to end	Day	17% 8% 3 6% 5% 4 5% 4 6% 8% 34%	2660
July	1st to 10th	Day	11% 6% 2 7% 5% 5% 6% 4 7% 10% 36%	4440
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 5% 7% 10% 41%	4440
	21st to end	Day	8% 6% 2 7% 5% 5% 6% 4 7% 9% 41%	4814
August	1st to 10th	Day	16% 8% 3 7% 4 5% 5% 4 6% 8% 35%	4140
	11th to 20th	Day	17% 7% 2 7% 4 5% 4 4 7% 9% 35%	4044
	21st to end	Day	12% 6% 2 7% 4 4 5% 4 7% 9% 40%	4212
September	1st to 10th	Day	12% 7% 3 7% 4 4 5% 3 6% 8% 42%	2280
	11th to 20th	Day	11% 6% 2 6% 3 3 4 4 5% 8% 49%	2280
	21st to end	Day	18% 6% 2 6% 4 4 4 3 5% 8% 38%	1997
October	1st to 10th	Day	19% 9% 3 7% 4 4 4 3 5% 7% 35%	1900
	11th to 20th	Day	21% 9% 3 8% 4 5% 5% 4 5% 7% 29%	1900
	21st to end	Day	25% 11% 4 7% 5% 5% 5% 3 4 6% 26%	2024
November	1st to 10th	Day	15% 9% 3 8% 5% 5% 4 5% 6% 6% 34%	1716
	11th to 20th	Day	16% 13% 4 9% 5% 4 4 3 5% 6% 30%	1600
	21st to end	Day	22% 13% 5% 8% 5% 4 4 4 5% 6% 23%	1600
December	1st to 10th	Day	20% 16% 4 11% 5% 4 5% 4 5% 6% 19%	2600
	11th to 20th	Day	17% 20% 6% 11% 4 4 4 3 3 4 25%	2986
	21st to end	Day	24% 16% 4 9% 5% 4 3 2 3 5% 24%	3960
January	1st to 10th	Night	15% 14% 6% 12% 7% 5% 5% 3 5% 6% 24%	6349
	11th to 20th	Night	11% 15% 7% 14% 9% 6% 6% 4 6% 6% 18%	6315
	21st to end	Night	15% 15% 7% 13% 6% 5% 4 3 5% 5% 22%	6554
February	1st to 10th	Night	14% 15% 4 11% 6% 5% 5% 4 5% 5% 26%	2600
	11th to 20th	Night	13% 15% 6% 9% 6% 5% 4 4 5% 5% 28%	2533
	21st to end	Night	15% 12% 4 9% 5% 4 5% 4 6% 7% 29%	2028
March	1st to 10th	Night	19% 12% 3 9% 5% 5% 4 3 5% 4 30%	5140
	11th to 20th	Night	13% 12% 3 8% 5% 5% 5% 5% 6% 8% 31%	4979
	21st to end	Night	19% 10% 3 7% 4 4 3 3 5% 6% 36%	5297
April	1st to 10th	Night	19% 12% 3 8% 4 3 4 3 4 6% 33%	2000
	11th to 20th	Night	18% 9% 3 7% 4 4 5% 3 5% 5% 37%	1975
	21st to end	Night	18% 8% 3 7% 4 5% 4 3 6% 7% 34%	1867
May	1st to 10th	Night	22% 10% 3 6% 4 4 4 4 5% 7% 33%	2666
	11th to 20th	Night	17% 9% 2 7% 4 4 4 4 6% 6% 38%	2501
	21st to end	Night	12% 6% 2 6% 4 4 5% 4 4 7% 45%	2738
June	1st to 10th	Night	15% 7% 2 8% 6% 5% 5% 4 5% 8% 35%	1520
	11th to 20th	Night	12% 6% 2 6% 5% 4 4 4 5% 8% 44%	1520
	21st to end	Night	14% 7% 2 6% 5% 5% 3 4 6% 8% 39%	1520
July	1st to 10th	Night	9% 5% 2 7% 6% 6% 5% 5% 6% 8% 41%	2520
	11th to 20th	Night	13% 7% 2 5% 4 3 4 3 6% 8% 47%	2520
	21st to end	Night	10% 6% 2 5% 4 4 4 4 6% 8% 48%	2739
August	1st to 10th	Night	12% 6% 2 6% 4 4 5% 4 6% 7% 44%	2786
	11th to 20th	Night	14% 6% 2 5% 4 3 4 4 6% 7% 45%	2785
	21st to end	Night	10% 4 2 6% 4 4 6% 4 7% 10% 44%	3411
September	1st to 10th	Night	12% 6% 2 6% 4 3 5% 3 5% 7% 47%	1900
	11th to 20th	Night	12% 4 2 5% 4 4 3 4 5% 6% 52%	1900
	21st to end	Night	17% 6% 2 6% 5% 4 5% 4 5% 6% 43%	2180
October	1st to 10th	Night	15% 8% 2 7% 4 4 4 4 5% 7% 39%	2280
	11th to 20th	Night	20% 9% 3 8% 6% 5% 4 3 5% 6% 32%	2280
	21st to end	Night	22% 10% 3 8% 5% 5% 4 3 5% 6% 30%	2574
November	1st to 10th	Night	18% 10% 3 6% 4 5% 4 3 5% 7% 36%	2577
	11th to 20th	Night	18% 10% 4 8% 5% 4 5% 3 5% 6% 32%	2800
	21st to end	Night	20% 13% 4 9% 5% 5% 5% 4 6% 5% 26%	2800
December	1st to 10th	Night	20% 15% 4 10% 6% 5% 5% 4 6% 6% 19%	4580
	11th to 20th	Night	20% 16% 5% 9% 5% 4 4 3 4 5% 24%	5208
	21st to end	Night	26% 16% 4 9% 5% 4 4 3 4 5% 20%	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	52% 6% 12% 20% 9% 1	3598
	11th to 20th	Day	67% 4 10% 11% 7%	3600
	21st to end	Day	69% 4 7% 10% 9% 1	4397
February	1st to 10th	Day	61% 6% 11% 16% 6% 1	1800
	11th to 20th	Day	62% 4 9% 15% 10% 1	1762
	21st to end	Day	63% 5% 9% 11% 10% 1	1601
March	1st to 10th	Day	57% 3 11% 12% 15% 2	4699
	11th to 20th	Day	51% 4 18% 15% 10% 2	4980
	21st to end	Day	49% 3 7% 21% 17% 3	5634
April	1st to 10th	Day	55% 4 8% 18% 13% 3	2400
	11th to 20th	Day	49% 4 8% 22% 16% 2	2374
	21st to end	Day	54% 5% 7% 17% 14% 3	2550
May	1st to 10th	Day	51% 6% 9% 21% 11% 2	4506
	11th to 20th	Day	47% 9% 12% 20% 10% 2	4402
	21st to end	Day	38% 7% 13% 24% 15% 2	4837
June	1st to 10th	Day	49% 9% 11% 17% 13% 1	2660
	11th to 20th	Day	41% 8% 11% 24% 14% 2	2660
	21st to end	Day	45% 7% 14% 19% 13% 1	2660
July	1st to 10th	Day	41% 6% 14% 25% 13% 1	4370
	11th to 20th	Day	36% 7% 14% 33% 10%	4365
	21st to end	Day	38% 7% 14% 29% 11%	4661
August	1st to 10th	Day	45% 6% 15% 22% 12% 1	4126
	11th to 20th	Day	44% 6% 14% 27% 9% 1	4083
	21st to end	Day	40% 5% 13% 31% 10% 1	4212
September	1st to 10th	Day	38% 9% 12% 27% 12% 1	2280
	11th to 20th	Day	33% 6% 13% 31% 15% 1	2280
	21st to end	Day	44% 8% 12% 27% 10%	1997
October	1st to 10th	Day	43% 6% 11% 30% 10% 1	3160
	11th to 20th	Day	46% 5% 15% 24% 10% 1	3140
	21st to end	Day	53% 4 14% 21% 8%	3314
November	1st to 10th	Day	48% 7% 14% 21% 9% 1	1716
	11th to 20th	Day	54% 5% 12% 17% 11% 1	1600
	21st to end	Day	60% 8% 12% 12% 8%	1600
December	1st to 10th	Day	66% 5% 15% 9% 4	2600
	11th to 20th	Day	65% 4 10% 13% 8%	2986
	21st to end	Day	64% 4 8% 16% 8%	3960
January	1st to 10th	Night	60% 6% 10% 15% 8%	6349
	11th to 20th	Night	67% 7% 11% 11% 5%	6360
	21st to end	Night	64% 5% 8% 9% 12% 1	6554
February	1st to 10th	Night	58% 6% 11% 17% 6% 1	2600
	11th to 20th	Night	57% 4 11% 19% 9% 1	2535
	21st to end	Night	53% 6% 11% 19% 9% 1	2028
March	1st to 10th	Night	57% 4 6% 17% 12% 5%	5150
	11th to 20th	Night	48% 6% 18% 18% 8% 2	4980
	21st to end	Night	48% 3 10% 20% 16% 2	5297
April	1st to 10th	Night	52% 4 8% 20% 14% 2	2000
	11th to 20th	Night	48% 6% 9% 20% 16% 1	1975
	21st to end	Night	49% 6% 10% 17% 15% 3	1867
May	1st to 10th	Night	51% 5% 11% 18% 13% 3	2672
	11th to 20th	Night	44% 8% 12% 24% 10% 2	2502
	21st to end	Night	38% 7% 13% 20% 20% 2	2739
June	1st to 10th	Night	44% 8% 13% 22% 13% 1	1520
	11th to 20th	Night	38% 5% 13% 22% 20% 2	1520
	21st to end	Night	41% 8% 14% 22% 13% 2	1520
July	1st to 10th	Night	39% 6% 14% 23% 17% 2	2480
	11th to 20th	Night	37% 5% 12% 33% 13%	2472
	21st to end	Night	34% 6% 17% 30% 12% 1	2651
August	1st to 10th	Night	38% 6% 14% 28% 14% 1	2776
	11th to 20th	Night	38% 5% 15% 31% 11% 1	2812
	21st to end	Night	34% 7% 14% 33% 11% 1	3411
September	1st to 10th	Night	36% 7% 15% 27% 14% 1	1900
	11th to 20th	Night	31% 7% 14% 31% 16% 1	1900
	21st to end	Night	42% 7% 11% 28% 12% 1	2180
October	1st to 10th	Night	38% 6% 9% 28% 18%	3800
	11th to 20th	Night	44% 5% 15% 27% 9%	3779
	21st to end	Night	48% 5% 13% 25% 9%	4234
November	1st to 10th	Night	47% 5% 14% 22% 11% 1	2577
	11th to 20th	Night	51% 6% 11% 20% 10% 2	2800
	21st to end	Night	57% 8% 13% 16% 6%	2800
December	1st to 10th	Night	64% 5% 14% 14% 3	4580
	11th to 20th	Night	63% 5% 10% 13% 9%	5208
	21st to end	Night	67% 5% 8% 11% 9%	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	25% 24% 32% 17% 3 1	200
	11th to 20th	Day	27% 21% 33% 16% 4 1	200
	21st to end	Day	27% 23% 33% 13% 3	315
February	1st to 10th	Day	33% 26% 30% 9% 2	300
	11th to 20th	Day	31% 26% 35% 6% 1	300
	21st to end	Day	38% 18% 32% 10% 2	365
March	1st to 10th	Day	28% 18% 34% 14% 5%	500
	11th to 20th	Day	28% 21% 32% 14% 4 1	500
	21st to end	Day	35% 18% 27% 13% 6% 1	550
April	1st to 10th	Day	32% 19% 33% 12% 5% 1	500
	11th to 20th	Day	35% 20% 22% 13% 7% 3	492
	21st to end	Day	29% 20% 34% 10% 6% 1	500
May	1st to 10th	Day	26% 16% 30% 18% 7% 3	503
	11th to 20th	Day	20% 14% 34% 21% 8% 3	487
	21st to end	Day	16% 17% 34% 19% 10% 3	529
June	1st to 10th	Day	24% 13% 33% 22% 6% 2	490
	11th to 20th	Day	16% 15% 33% 23% 12% 2	490
	21st to end	Day	22% 13% 33% 19% 9% 3	490
July	1st to 10th	Day	13% 9% 30% 32% 13% 4	485
	11th to 20th	Day	15% 9% 29% 28% 14% 4	484
	21st to end	Day	13% 8% 37% 27% 12% 3	532
August	1st to 10th	Day	14% 10% 27% 29% 14% 6%	486
	11th to 20th	Day	13% 8% 27% 29% 17% 6%	479
	21st to end	Day	15% 10% 32% 23% 12% 8%	539
September	1st to 10th	Day	15% 12% 30% 24% 12% 7%	490
	11th to 20th	Day	13% 9% 23% 24% 19% 12%	490
	21st to end	Day	20% 11% 27% 24% 12% 5%	490
October	1st to 10th	Day	24% 18% 24% 18% 11% 6%	490
	11th to 20th	Day	26% 18% 31% 17% 7% 2	490
	21st to end	Day	30% 19% 30% 18% 4	504
November	1st to 10th	Day	30% 16% 28% 18% 8% 1	350
	11th to 20th	Day	31% 18% 34% 12% 5% 1	200
	21st to end	Day	28% 20% 34% 14% 3 2	200
December	1st to 10th	Day	31% 16% 36% 14% 3 1	200
	11th to 20th	Day	38% 20% 28% 11% 3 1	200
	21st to end	Day	35% 20% 30% 11% 3	220
January	1st to 10th	Night	28% 19% 31% 19% 4	800
	11th to 20th	Night	27% 17% 31% 20% 5%	800
	21st to end	Night	21% 15% 36% 24% 4 1	880
February	1st to 10th	Night	22% 20% 37% 20% 2	800
	11th to 20th	Night	24% 18% 37% 17% 4	783
	21st to end	Night	26% 19% 33% 20% 3	660
March	1st to 10th	Night	23% 18% 36% 20% 3	800
	11th to 20th	Night	25% 19% 31% 22% 3 1	800
	21st to end	Night	24% 14% 34% 20% 7% 1	880
April	1st to 10th	Night	26% 16% 33% 21% 4	800
	11th to 20th	Night	25% 19% 29% 18% 8% 1	791
	21st to end	Night	23% 13% 28% 24% 10%	667
May	1st to 10th	Night	25% 9% 28% 26% 9% 2	446
	11th to 20th	Night	16% 11% 32% 32% 9%	376
	21st to end	Night	13% 9% 34% 32% 11% 1	411
June	1st to 10th	Night	16% 8% 34% 32% 10%	380
	11th to 20th	Night	14% 7% 33% 34% 11% 1	380
	21st to end	Night	17% 6% 28% 38% 11% 1	380
July	1st to 10th	Night	6% 9% 29% 39% 16% 1	370
	11th to 20th	Night	13% 4 28% 35% 20% 1	368
	21st to end	Night	12% 3 26% 44% 14%	416
August	1st to 10th	Night	11% 4 27% 32% 24% 2	541
	11th to 20th	Night	11% 6% 21% 35% 24% 3	564
	21st to end	Night	12% 5% 29% 33% 18% 2	797
September	1st to 10th	Night	15% 6% 30% 30% 16% 3	760
	11th to 20th	Night	14% 6% 23% 26% 28% 4	760
	21st to end	Night	19% 9% 23% 28% 18% 3	760
October	1st to 10th	Night	19% 13% 26% 25% 16% 2	760
	11th to 20th	Night	25% 12% 30% 24% 9% 1	760
	21st to end	Night	28% 13% 30% 23% 6%	836
November	1st to 10th	Night	24% 13% 28% 25% 9%	780
	11th to 20th	Night	24% 16% 33% 19% 7% 1	800
	21st to end	Night	30% 16% 29% 20% 6%	800
December	1st to 10th	Night	31% 17% 31% 18% 3	800
	11th to 20th	Night	29% 17% 34% 17% 3 1	800
	21st to end	Night	36% 14% 29% 17% 3	880

Page generated at 2025-05-08 09:33:58. Version ac07

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