Half Hollow Hills
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Half Hollow Hills clear sky chart from 2005-11-06 to 2025-07-21.

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	17% 7% 2 6% 4 4 4 4 5% 7% 40%	119897
	Night	17% 8% 2 6% 4 4 4 3 5% 6% 42%	119218
Transparency	Day	41% 6% 13% 22% 16% 2	123482
	Night	42% 5% 11% 22% 16% 3	123794
Seeing	Day	21% 14% 32% 22% 9% 2	15938
	Night	21% 12% 31% 27% 9% 1	25017

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% 6% 1 5% 3 3 3 3 5% 6% 51%	3597
	11th to 20th	Day	14% 9% 3 6% 4 4 4 4 5% 5% 44%	3570
	21st to end	Day	18% 9% 4 8% 5% 4 4 2 4 4 39%	4209
February	1st to 10th	Day	17% 8% 2 6% 4 4 4 3 4 7% 40%	1858
	11th to 20th	Day	14% 7% 2 7% 5% 4 4 3 4 6% 44%	1948
	21st to end	Day	19% 9% 3 6% 4 4 4 3 5% 5% 39%	1650
March	1st to 10th	Day	21% 8% 2 5% 2 3 3 3 4 5% 42%	4476
	11th to 20th	Day	11% 8% 2 6% 4 4 5% 4 6% 8% 42%	4691
	21st to end	Day	18% 7% 3 6% 4 4 3 3 4 6% 42%	5970
April	1st to 10th	Day	19% 8% 3 6% 4 3 4 4 5% 8% 37%	2400
	11th to 20th	Day	17% 7% 2 6% 5% 4 4 3 5% 7% 41%	2374
	21st to end	Day	19% 6% 2 5% 4 3 4 3 5% 7% 41%	2465
May	1st to 10th	Day	28% 9% 2 5% 3 3 4 4 5% 8% 29%	5886
	11th to 20th	Day	23% 9% 3 6% 4 3 3 3 5% 6% 36%	6134
	21st to end	Day	20% 7% 2 5% 3 4 4 4 6% 8% 36%	6949
June	1st to 10th	Day	17% 5% 2 5% 5% 4 4 4 7% 9% 39%	2800
	11th to 20th	Day	15% 7% 2 5% 5% 4 5% 4 6% 8% 39%	2800
	21st to end	Day	11% 6% 3 5% 5% 4 5% 4 6% 9% 43%	2800
July	1st to 10th	Day	9% 7% 2 7% 5% 5% 6% 5% 7% 10% 36%	4580
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 5% 7% 10% 38%	4580
	21st to end	Day	15% 8% 3 7% 5% 5% 5% 5% 7% 8% 33%	4814
August	1st to 10th	Day	18% 7% 3 6% 5% 5% 5% 4 7% 9% 33%	4184
	11th to 20th	Day	11% 7% 2 6% 4 4 5% 4 6% 9% 42%	3730
	21st to end	Day	8% 5% 2 6% 4 4 4 4 6% 10% 47%	4180
September	1st to 10th	Day	14% 6% 1 6% 4 4 4 3 5% 8% 45%	2280
	11th to 20th	Day	12% 5% 2 5% 3 3 4 4 5% 7% 50%	2166
	21st to end	Day	19% 7% 3 6% 4 3 4 3 5% 6% 40%	2090
October	1st to 10th	Day	19% 7% 2 6% 3 3 4 3 5% 7% 41%	2036
	11th to 20th	Day	15% 5% 2 5% 4 4 4 4 5% 7% 47%	1900
	21st to end	Day	19% 6% 2 5% 4 4 4 3 5% 6% 42%	1901
November	1st to 10th	Day	14% 5% 2 6% 3 3 3 3 4 6% 51%	1761
	11th to 20th	Day	17% 7% 2 5% 2 3 3 2 4 7% 49%	1800
	21st to end	Day	15% 7% 2 5% 3 4 4 4 5% 7% 44%	1772
December	1st to 10th	Day	15% 6% 2 6% 4 4 3 3 6% 7% 44%	2600
	11th to 20th	Day	23% 8% 2 4 2 2 2 2 3 5% 47%	2986
	21st to end	Day	17% 9% 2 6% 4 4 4 3 5% 6% 39%	3960
January	1st to 10th	Night	14% 6% 2 5% 3 3 3 3 4 6% 51%	6349
	11th to 20th	Night	15% 7% 2 6% 4 3 3 3 4 5% 47%	6315
	21st to end	Night	17% 8% 3 7% 4 4 4 3 5% 6% 38%	6743
February	1st to 10th	Night	16% 10% 2 6% 4 3 5% 3 5% 5% 41%	2540
	11th to 20th	Night	19% 8% 3 5% 4 4 4 3 5% 6% 40%	2338
	21st to end	Night	19% 7% 3 5% 4 3 3 4 4 6% 42%	1980
March	1st to 10th	Night	19% 10% 2 5% 3 3 3 2 4 5% 43%	5364
	11th to 20th	Night	15% 9% 3 6% 4 4 4 3 5% 5% 43%	5263
	21st to end	Night	19% 9% 3 6% 4 4 4 3 5% 5% 38%	4962
April	1st to 10th	Night	19% 7% 2 6% 5% 4 5% 3 5% 6% 37%	2000
	11th to 20th	Night	19% 8% 3 5% 4 3 4 3 5% 6% 40%	1975
	21st to end	Night	18% 7% 3 6% 4 3 4 3 4 5% 42%	1934
May	1st to 10th	Night	25% 10% 4 8% 4 4 4 3 5% 7% 27%	4054
	11th to 20th	Night	22% 10% 3 7% 4 3 4 3 4 6% 34%	3788
	21st to end	Night	22% 8% 3 6% 4 4 4 3 5% 7% 35%	3926
June	1st to 10th	Night	17% 7% 2 5% 4 5% 3 4 5% 8% 39%	1600
	11th to 20th	Night	16% 7% 2 6% 4 4 4 4 6% 9% 39%	1600
	21st to end	Night	11% 6% 2 7% 5% 5% 6% 5% 8% 8% 39%	1600
July	1st to 10th	Night	11% 8% 4 9% 6% 6% 4 5% 7% 7% 34%	2600
	11th to 20th	Night	15% 7% 3 7% 4 4 5% 4 7% 9% 35%	2600
	21st to end	Night	18% 9% 3 6% 4 4 5% 4 6% 8% 33%	2739
August	1st to 10th	Night	23% 7% 3 6% 4 5% 4 4 6% 8% 31%	2709
	11th to 20th	Night	13% 7% 3 7% 4 4 5% 4 7% 8% 39%	3097
	21st to end	Night	8% 5% 2 4 4 4 4 4 5% 8% 52%	3476
September	1st to 10th	Night	13% 6% 2 6% 3 4 5% 4 6% 7% 43%	1900
	11th to 20th	Night	13% 5% 2 5% 3 4 4 3 4 6% 52%	2014
	21st to end	Night	18% 6% 2 6% 4 4 4 3 4 6% 41%	2090
October	1st to 10th	Night	19% 8% 2 7% 4 4 4 3 4 5% 41%	2141
	11th to 20th	Night	14% 5% 2 5% 3 3 3 3 5% 6% 50%	2280
	21st to end	Night	20% 6% 2 6% 4 3 3 3 5% 6% 42%	2695
November	1st to 10th	Night	12% 6% 2 5% 4 4 4 3 4 5% 51%	2537
	11th to 20th	Night	19% 6% 2 4 3 2 3 3 4 5% 48%	2600
	21st to end	Night	15% 5% 2 4 4 4 4 4 5% 6% 46%	2625
December	1st to 10th	Night	16% 7% 2 5% 3 4 3 3 4 5% 49%	4580
	11th to 20th	Night	25% 7% 2 5% 3 3 3 2 3 4 43%	5208
	21st to end	Night	18% 8% 3 7% 3 3 4 3 4 5% 42%	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	33% 4 8% 33% 20% 2	3598
	11th to 20th	Day	40% 4 11% 23% 17% 6%	3600
	21st to end	Day	47% 6% 10% 23% 14% 1	4209
February	1st to 10th	Day	44% 6% 14% 22% 13% 1	1858
	11th to 20th	Day	42% 4 11% 25% 17% 2	1957
	21st to end	Day	46% 5% 12% 21% 14% 3	1650
March	1st to 10th	Day	42% 5% 12% 18% 14% 9%	4479
	11th to 20th	Day	37% 6% 15% 27% 13% 2	4691
	21st to end	Day	44% 4 10% 14% 23% 5%	5970
April	1st to 10th	Day	44% 6% 10% 20% 16% 4	2400
	11th to 20th	Day	42% 5% 12% 21% 17% 3	2374
	21st to end	Day	41% 6% 10% 22% 17% 4	2465
May	1st to 10th	Day	53% 6% 17% 14% 10% 1	5897
	11th to 20th	Day	49% 5% 12% 19% 14% 2	6138
	21st to end	Day	44% 7% 13% 22% 13% 1	6949
June	1st to 10th	Day	41% 8% 13% 22% 15% 1	2800
	11th to 20th	Day	41% 8% 13% 24% 13% 1	2800
	21st to end	Day	37% 8% 16% 22% 15% 1	2800
July	1st to 10th	Day	43% 9% 13% 19% 15% 1	4510
	11th to 20th	Day	40% 6% 18% 22% 12% 1	4505
	21st to end	Day	46% 7% 14% 18% 14% 2	4661
August	1st to 10th	Day	46% 6% 17% 21% 9%	4170
	11th to 20th	Day	38% 6% 15% 32% 9% 1	3766
	21st to end	Day	31% 7% 14% 27% 20% 2	4180
September	1st to 10th	Day	37% 7% 14% 20% 20% 2	2280
	11th to 20th	Day	33% 5% 12% 24% 24% 2	2166
	21st to end	Day	45% 5% 11% 18% 19% 2	2090
October	1st to 10th	Day	36% 5% 11% 21% 22% 5%	3387
	11th to 20th	Day	26% 4 11% 22% 32% 5%	3140
	21st to end	Day	30% 4 15% 26% 23% 3	3113
November	1st to 10th	Day	36% 5% 14% 22% 21% 2	1761
	11th to 20th	Day	37% 5% 11% 23% 22% 3	1800
	21st to end	Day	40% 5% 15% 27% 11% 2	1772
December	1st to 10th	Day	39% 4 16% 27% 13% 1	2600
	11th to 20th	Day	42% 3 14% 21% 17% 3	2986
	21st to end	Day	45% 7% 9% 21% 15% 3	3960
January	1st to 10th	Night	35% 4 8% 26% 24% 3	6349
	11th to 20th	Night	40% 4 13% 22% 17% 5%	6360
	21st to end	Night	47% 4 9% 21% 16% 4	6743
February	1st to 10th	Night	44% 6% 13% 23% 12% 2	2540
	11th to 20th	Night	44% 5% 10% 20% 16% 4	2340
	21st to end	Night	44% 4 9% 23% 16% 4	1980
March	1st to 10th	Night	45% 3 11% 20% 14% 8%	5374
	11th to 20th	Night	43% 4 13% 24% 12% 4	5264
	21st to end	Night	48% 4 7% 13% 24% 5%	4962
April	1st to 10th	Night	47% 6% 10% 18% 16% 3	2000
	11th to 20th	Night	44% 6% 10% 18% 21% 2	1975
	21st to end	Night	44% 5% 9% 20% 17% 5%	1934
May	1st to 10th	Night	57% 5% 13% 13% 10% 1	4060
	11th to 20th	Night	52% 5% 14% 14% 13% 2	3789
	21st to end	Night	49% 5% 13% 21% 10% 1	3927
June	1st to 10th	Night	44% 6% 10% 20% 19% 1	1600
	11th to 20th	Night	41% 8% 13% 26% 12% 1	1600
	21st to end	Night	40% 8% 13% 24% 13% 2	1600
July	1st to 10th	Night	49% 7% 13% 18% 12% 1	2560
	11th to 20th	Night	45% 6% 14% 24% 10% 1	2552
	21st to end	Night	49% 6% 14% 15% 14% 1	2651
August	1st to 10th	Night	51% 7% 17% 16% 9% 1	2699
	11th to 20th	Night	41% 6% 14% 29% 9% 1	3127
	21st to end	Night	30% 5% 13% 33% 18% 1	3476
September	1st to 10th	Night	39% 7% 10% 24% 18% 1	1900
	11th to 20th	Night	34% 6% 11% 24% 22% 3	2014
	21st to end	Night	44% 6% 8% 20% 19% 3	2090
October	1st to 10th	Night	40% 4 11% 23% 19% 2	3570
	11th to 20th	Night	25% 3 11% 27% 31% 4	3779
	21st to end	Night	31% 4 14% 28% 21% 3	4433
November	1st to 10th	Night	35% 5% 13% 23% 20% 4	2537
	11th to 20th	Night	40% 4 10% 23% 19% 4	2600
	21st to end	Night	38% 5% 14% 29% 14% 1	2625
December	1st to 10th	Night	40% 3 13% 29% 13% 2	4580
	11th to 20th	Night	47% 3 9% 24% 15% 2	5208
	21st to end	Night	44% 4 11% 20% 17% 4	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	28% 24% 33% 13% 4	200
	11th to 20th	Day	24% 28% 32% 14% 3	200
	21st to end	Day	23% 20% 39% 12% 5% 1	274
February	1st to 10th	Day	28% 20% 37% 14% 2	358
	11th to 20th	Day	27% 21% 38% 14% 2	496
	21st to end	Day	28% 19% 36% 13% 4	414
March	1st to 10th	Day	24% 22% 33% 18% 3	500
	11th to 20th	Day	22% 21% 38% 16% 4 1	500
	21st to end	Day	28% 19% 34% 13% 5% 1	550
April	1st to 10th	Day	27% 22% 33% 13% 6% 1	500
	11th to 20th	Day	27% 18% 31% 18% 5% 1	492
	21st to end	Day	28% 16% 35% 16% 4 1	500
May	1st to 10th	Day	32% 17% 30% 16% 5% 1	503
	11th to 20th	Day	22% 15% 36% 20% 6% 1	527
	21st to end	Day	20% 8% 32% 24% 13% 2	573
June	1st to 10th	Day	21% 8% 31% 28% 10% 2	530
	11th to 20th	Day	18% 10% 35% 26% 9% 1	530
	21st to end	Day	14% 7% 36% 29% 11% 3	530
July	1st to 10th	Day	13% 7% 27% 34% 15% 4	525
	11th to 20th	Day	10% 6% 30% 36% 16% 3	524
	21st to end	Day	15% 9% 30% 30% 14% 2	532
August	1st to 10th	Day	15% 6% 28% 31% 16% 5%	486
	11th to 20th	Day	13% 6% 24% 36% 16% 3	479
	21st to end	Day	13% 6% 30% 32% 14% 6%	539
September	1st to 10th	Day	19% 7% 28% 24% 17% 4	490
	11th to 20th	Day	15% 7% 28% 26% 15% 10%	490
	21st to end	Day	23% 9% 29% 22% 13% 4	490
October	1st to 10th	Day	25% 8% 26% 21% 15% 4	490
	11th to 20th	Day	16% 15% 33% 23% 11% 2	490
	21st to end	Day	21% 13% 36% 18% 9% 2	439
November	1st to 10th	Day	15% 16% 30% 26% 10% 2	395
	11th to 20th	Day	22% 23% 29% 20% 6% 1	400
	21st to end	Day	21% 16% 32% 22% 7% 1	372
December	1st to 10th	Day	24% 22% 34% 16% 4 1	200
	11th to 20th	Day	35% 18% 34% 10% 4	200
	21st to end	Day	25% 16% 37% 15% 7%	220
January	1st to 10th	Night	21% 21% 36% 19% 3	800
	11th to 20th	Night	25% 20% 29% 24% 3	800
	21st to end	Night	21% 18% 38% 21% 2	880
February	1st to 10th	Night	22% 17% 37% 22% 2	800
	11th to 20th	Night	25% 20% 37% 16% 1	783
	21st to end	Night	24% 19% 36% 17% 4	660
March	1st to 10th	Night	23% 19% 33% 19% 5%	800
	11th to 20th	Night	22% 15% 39% 19% 5% 1	800
	21st to end	Night	23% 16% 36% 19% 4	880
April	1st to 10th	Night	24% 18% 35% 19% 5%	800
	11th to 20th	Night	25% 11% 35% 24% 5%	791
	21st to end	Night	22% 12% 36% 24% 5% 1	734
May	1st to 10th	Night	24% 11% 33% 24% 7% 1	600
	11th to 20th	Night	24% 11% 33% 27% 4	490
	21st to end	Night	23% 5% 24% 33% 14% 2	433
June	1st to 10th	Night	21% 6% 26% 35% 13%	400
	11th to 20th	Night	17% 4 25% 41% 14% 1	400
	21st to end	Night	13% 5% 26% 44% 12% 1	400
July	1st to 10th	Night	14% 2 23% 45% 15% 1	390
	11th to 20th	Night	14% 5% 22% 40% 17% 2	388
	21st to end	Night	14% 4 23% 41% 17%	416
August	1st to 10th	Night	11% 2 25% 43% 18% 1	490
	11th to 20th	Night	15% 3 21% 36% 22% 3	750
	21st to end	Night	14% 4 19% 38% 23% 3	836
September	1st to 10th	Night	16% 4 26% 35% 16% 3	760
	11th to 20th	Night	16% 5% 20% 34% 19% 6%	760
	21st to end	Night	21% 4 26% 30% 16% 2	760
October	1st to 10th	Night	24% 7% 24% 27% 15% 3	760
	11th to 20th	Night	17% 11% 29% 30% 12% 1	760
	21st to end	Night	24% 10% 32% 24% 9%	836
November	1st to 10th	Night	14% 12% 34% 27% 11% 2	780
	11th to 20th	Night	22% 15% 33% 22% 8%	800
	21st to end	Night	18% 18% 32% 24% 7% 1	800
December	1st to 10th	Night	25% 17% 33% 19% 5% 1	800
	11th to 20th	Night	25% 16% 34% 21% 4	800
	21st to end	Night	23% 15% 36% 22% 3	880

Page generated at 2025-07-18 01:10:02. Version ac07

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