Hampton Mountain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hampton Mountain clear sky chart from 2005-11-06 to 2025-11-18.

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	14% 6% 2 6% 4 4 5% 4 6% 8% 41%	126654
	Night	15% 6% 2 6% 4 4 4 4 5% 7% 43%	123726
Transparency	Day	39% 7% 11% 19% 18% 6%	130430
	Night	38% 6% 10% 19% 20% 6%	128019
Seeing	Day	18% 10% 23% 23% 17% 8%	16275
	Night	17% 10% 23% 28% 19% 3	26276

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	18% 10% 3 6% 2 3 3 2 4 4 47%	4056
	11th to 20th	Day	14% 6% 3 5% 3 3 3 3 4 4 53%	4060
	21st to end	Day	22% 10% 3 5% 3 3 3 2 4 4 41%	4581
February	1st to 10th	Day	18% 8% 2 6% 4 4 4 3 5% 6% 40%	2000
	11th to 20th	Day	25% 6% 2 5% 3 3 3 3 4 5% 41%	1948
	21st to end	Day	22% 7% 2 6% 4 3 3 3 4 5% 41%	1650
March	1st to 10th	Day	23% 7% 3 6% 4 4 4 4 5% 5% 36%	4653
	11th to 20th	Day	11% 6% 2 6% 3 4 3 3 4 7% 51%	4980
	21st to end	Day	17% 6% 2 6% 5% 4 3 3 4 5% 44%	5465
April	1st to 10th	Day	13% 5% 1 6% 4 4 5% 5% 6% 7% 43%	2240
	11th to 20th	Day	12% 6% 2 5% 5% 4 4 3 5% 7% 47%	2374
	21st to end	Day	12% 4 2 6% 3 4 4 4 5% 7% 48%	2581
May	1st to 10th	Day	15% 7% 3 7% 5% 4 5% 4 6% 8% 36%	5862
	11th to 20th	Day	20% 7% 3 7% 5% 5% 5% 5% 7% 8% 28%	5861
	21st to end	Day	15% 7% 2 7% 4 4 5% 4 6% 8% 39%	6433
June	1st to 10th	Day	10% 6% 2 7% 6% 6% 6% 5% 8% 11% 33%	2600
	11th to 20th	Day	6% 4 2 5% 6% 6% 6% 7% 8% 12% 38%	2600
	21st to end	Day	8% 4 2 5% 5% 6% 6% 6% 9% 11% 39%	2600
July	1st to 10th	Day	7% 4 2 6% 6% 6% 7% 6% 9% 12% 35%	5900
	11th to 20th	Day	6% 5% 2 6% 6% 6% 7% 6% 10% 14% 33%	5900
	21st to end	Day	9% 8% 3 9% 7% 7% 7% 6% 8% 10% 25%	6424
August	1st to 10th	Day	8% 6% 3 6% 4 6% 5% 6% 8% 11% 37%	4234
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 5% 8% 11% 40%	3976
	21st to end	Day	8% 5% 2 5% 4 5% 5% 4 6% 8% 48%	4297
September	1st to 10th	Day	11% 6% 3 7% 5% 4 5% 4 6% 8% 40%	2200
	11th to 20th	Day	15% 6% 2 6% 4 5% 4 4 5% 8% 40%	2200
	21st to end	Day	14% 5% 2 5% 4 4 5% 4 5% 7% 45%	2200
October	1st to 10th	Day	12% 5% 2 5% 3 3 3 3 5% 6% 54%	2200
	11th to 20th	Day	12% 5% 2 3 2 2 3 3 4 6% 58%	2070
	21st to end	Day	15% 5% 1 5% 3 3 3 3 4 4 55%	2200
November	1st to 10th	Day	13% 5% 2 4 4 3 3 2 4 5% 56%	1877
	11th to 20th	Day	15% 4 2 4 4 3 3 3 5% 6% 53%	1863
	21st to end	Day	15% 6% 2 5% 4 3 4 3 5% 6% 47%	1800
December	1st to 10th	Day	22% 5% 1 4 3 3 3 3 4 5% 47%	2930
	11th to 20th	Day	18% 8% 3 7% 4 4 4 3 4 4 40%	3373
	21st to end	Day	23% 6% 2 4 3 3 4 3 5% 7% 40%	4466
January	1st to 10th	Night	16% 7% 2 5% 3 3 3 2 4 6% 49%	5889
	11th to 20th	Night	15% 7% 3 6% 3 3 3 3 4 5% 48%	5900
	21st to end	Night	20% 9% 2 5% 3 3 3 2 3 4 44%	6372
February	1st to 10th	Night	16% 7% 3 6% 4 3 4 3 5% 6% 44%	2400
	11th to 20th	Night	23% 7% 2 6% 4 3 3 3 4 4 41%	2338
	21st to end	Night	20% 6% 2 6% 4 3 4 3 5% 6% 41%	1980
March	1st to 10th	Night	22% 8% 3 7% 4 4 4 3 5% 6% 35%	5199
	11th to 20th	Night	11% 4 2 4 3 3 4 3 6% 8% 52%	4980
	21st to end	Night	15% 7% 2 7% 4 4 3 3 5% 6% 45%	5467
April	1st to 10th	Night	12% 5% 2 5% 4 4 4 4 6% 7% 48%	2175
	11th to 20th	Night	13% 5% 2 5% 3 3 4 4 5% 6% 50%	1975
	21st to end	Night	10% 6% 2 6% 4 4 3 3 5% 7% 50%	1816
May	1st to 10th	Night	12% 7% 3 8% 6% 5% 5% 4 7% 8% 36%	4033
	11th to 20th	Night	20% 8% 3 6% 4 5% 5% 5% 6% 8% 30%	4032
	21st to end	Night	14% 6% 2 6% 4 4 5% 4 7% 9% 40%	4421
June	1st to 10th	Night	9% 5% 2 7% 7% 6% 6% 5% 8% 10% 36%	1800
	11th to 20th	Night	6% 5% 2 6% 5% 5% 6% 4 9% 12% 42%	1800
	21st to end	Night	7% 4 2 6% 5% 6% 5% 4 8% 10% 43%	1800
July	1st to 10th	Night	8% 6% 3 9% 6% 6% 6% 5% 8% 10% 33%	4058
	11th to 20th	Night	6% 5% 3 8% 5% 6% 7% 6% 8% 12% 33%	4057
	21st to end	Night	11% 8% 4 9% 6% 5% 6% 5% 7% 9% 29%	4427
August	1st to 10th	Night	10% 5% 2 7% 5% 5% 5% 4 8% 12% 37%	2915
	11th to 20th	Night	10% 7% 3 8% 4 4 4 4 5% 8% 43%	3068
	21st to end	Night	8% 6% 2 6% 4 4 4 4 5% 8% 50%	3586
September	1st to 10th	Night	9% 7% 2 7% 5% 5% 5% 4 6% 8% 41%	2180
	11th to 20th	Night	14% 6% 2 7% 4 5% 4 4 6% 8% 42%	2200
	21st to end	Night	14% 5% 2 5% 4 3 3 4 5% 7% 47%	2200
October	1st to 10th	Night	13% 5% 2 4 3 2 3 3 4 6% 55%	2200
	11th to 20th	Night	11% 4 2 5% 3 3 3 2 4 5% 58%	2328
	21st to end	Night	14% 4 2 4 3 3 3 3 4 5% 55%	2640
November	1st to 10th	Night	13% 5% 2 4 3 2 3 3 4 5% 54%	2636
	11th to 20th	Night	14% 6% 1 4 3 3 3 2 4 6% 54%	2692
	21st to end	Night	16% 5% 2 4 3 4 4 4 5% 6% 46%	2600
December	1st to 10th	Night	18% 6% 2 5% 3 3 3 3 4 5% 48%	4250
	11th to 20th	Night	20% 6% 2 5% 3 4 4 3 4 5% 43%	4822
	21st to end	Night	23% 6% 2 6% 3 3 3 3 4 5% 41%	6490

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	42% 3 4 20% 23% 8%	4057
	11th to 20th	Day	34% 3 6% 18% 28% 10%	4060
	21st to end	Day	48% 2 4 16% 21% 8%	4581
February	1st to 10th	Day	45% 4 8% 19% 20% 5%	2000
	11th to 20th	Day	45% 4 5% 20% 20% 6%	1958
	21st to end	Day	46% 4 7% 13% 21% 8%	1650
March	1st to 10th	Day	50% 3 7% 12% 18% 9%	4653
	11th to 20th	Day	34% 4 6% 14% 24% 18%	4980
	21st to end	Day	43% 3 7% 23% 20% 4	5465
April	1st to 10th	Day	38% 6% 10% 21% 20% 5%	2240
	11th to 20th	Day	37% 5% 8% 19% 23% 8%	2374
	21st to end	Day	33% 7% 12% 26% 19% 3	2581
May	1st to 10th	Day	43% 9% 13% 19% 15% 2	5897
	11th to 20th	Day	50% 9% 14% 18% 8% 1	5865
	21st to end	Day	41% 8% 11% 21% 18% 2	6447
June	1st to 10th	Day	41% 11% 16% 20% 9% 2	2600
	11th to 20th	Day	32% 12% 19% 25% 11% 1	2600
	21st to end	Day	35% 12% 16% 21% 13% 3	2600
July	1st to 10th	Day	36% 13% 19% 25% 7% 1	5835
	11th to 20th	Day	35% 14% 29% 17% 3 1	5831
	21st to end	Day	48% 13% 17% 17% 4	6240
August	1st to 10th	Day	37% 10% 13% 31% 9%	4221
	11th to 20th	Day	34% 10% 18% 23% 13% 3	4015
	21st to end	Day	32% 8% 13% 23% 21% 3	4297
September	1st to 10th	Day	39% 10% 14% 16% 18% 4	2200
	11th to 20th	Day	41% 8% 13% 18% 19% 2	2200
	21st to end	Day	37% 6% 13% 16% 21% 7%	2200
October	1st to 10th	Day	25% 4 7% 14% 38% 12%	3590
	11th to 20th	Day	20% 3 6% 14% 29% 28%	3349
	21st to end	Day	30% 4 5% 21% 28% 13%	3538
November	1st to 10th	Day	33% 4 7% 16% 31% 10%	1877
	11th to 20th	Day	33% 4 7% 20% 27% 10%	1863
	21st to end	Day	37% 5% 8% 17% 27% 7%	1800
December	1st to 10th	Day	40% 4 5% 17% 27% 8%	2930
	11th to 20th	Day	48% 3 7% 16% 20% 6%	3370
	21st to end	Day	44% 3 9% 25% 16% 2	4466
January	1st to 10th	Night	37% 3 6% 18% 30% 6%	5889
	11th to 20th	Night	39% 4 5% 19% 25% 9%	5900
	21st to end	Night	44% 2 5% 15% 27% 7%	6372
February	1st to 10th	Night	41% 4 9% 18% 21% 7%	2400
	11th to 20th	Night	47% 3 5% 18% 20% 7%	2339
	21st to end	Night	45% 4 8% 16% 20% 9%	1980
March	1st to 10th	Night	49% 4 8% 14% 20% 6%	5199
	11th to 20th	Night	30% 4 8% 15% 28% 16%	4980
	21st to end	Night	41% 4 6% 21% 20% 8%	5467
April	1st to 10th	Night	34% 6% 11% 20% 23% 6%	2175
	11th to 20th	Night	33% 5% 8% 21% 23% 10%	1975
	21st to end	Night	34% 6% 11% 26% 20% 4	1816
May	1st to 10th	Night	42% 9% 16% 20% 12% 1	4060
	11th to 20th	Night	50% 7% 16% 18% 9%	4033
	21st to end	Night	37% 8% 13% 24% 16% 2	4429
June	1st to 10th	Night	40% 10% 16% 20% 12% 2	1800
	11th to 20th	Night	32% 10% 20% 24% 13% 1	1800
	21st to end	Night	33% 11% 18% 22% 13% 4	1800
July	1st to 10th	Night	43% 11% 17% 23% 7%	4015
	11th to 20th	Night	38% 15% 26% 17% 4 1	4006
	21st to end	Night	49% 12% 18% 17% 4 1	4297
August	1st to 10th	Night	38% 9% 18% 28% 6%	2904
	11th to 20th	Night	38% 8% 17% 21% 15% 1	3095
	21st to end	Night	31% 7% 14% 22% 23% 2	3586
September	1st to 10th	Night	39% 9% 14% 17% 16% 4	2180
	11th to 20th	Night	38% 8% 14% 19% 19% 2	2200
	21st to end	Night	36% 8% 11% 18% 19% 8%	2200
October	1st to 10th	Night	25% 4 10% 14% 35% 11%	3590
	11th to 20th	Night	19% 2 5% 18% 32% 24%	3788
	21st to end	Night	26% 3 5% 23% 28% 17%	4252
November	1st to 10th	Night	32% 5% 7% 19% 26% 11%	2636
	11th to 20th	Night	32% 3 6% 18% 28% 12%	2692
	21st to end	Night	38% 4 6% 20% 25% 7%	2600
December	1st to 10th	Night	39% 3 5% 17% 28% 7%	4250
	11th to 20th	Night	42% 5% 8% 16% 23% 6%	4824
	21st to end	Night	46% 3 7% 26% 16% 2	6490

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% 25% 36% 10% 1	300
	11th to 20th	Day	30% 21% 29% 15% 5%	300
	21st to end	Day	29% 24% 35% 10% 2 1	330
February	1st to 10th	Day	25% 20% 34% 18% 2	300
	11th to 20th	Day	41% 23% 26% 10% 1	300
	21st to end	Day	34% 20% 33% 10% 2	249
March	1st to 10th	Day	26% 18% 29% 19% 7%	369
	11th to 20th	Day	23% 20% 32% 19% 5% 1	500
	21st to end	Day	23% 16% 35% 19% 5% 1	550
April	1st to 10th	Day	23% 15% 30% 21% 9% 1	500
	11th to 20th	Day	15% 17% 36% 20% 12% 1	492
	21st to end	Day	19% 11% 28% 25% 14% 3	500
May	1st to 10th	Day	17% 13% 30% 22% 13% 5%	503
	11th to 20th	Day	18% 8% 24% 27% 14% 9%	527
	21st to end	Day	17% 8% 19% 28% 18% 10%	573
June	1st to 10th	Day	14% 3 21% 30% 22% 11%	530
	11th to 20th	Day	6% 5% 17% 30% 25% 17%	530
	21st to end	Day	10% 3 17% 30% 26% 14%	530
July	1st to 10th	Day	10% 2 10% 27% 29% 21%	525
	11th to 20th	Day	8% 2 10% 22% 37% 20%	524
	21st to end	Day	7% 2 11% 26% 34% 20%	576
August	1st to 10th	Day	14% 3 15% 27% 23% 17%	526
	11th to 20th	Day	12% 4 12% 26% 30% 16%	519
	21st to end	Day	16% 3 11% 23% 28% 18%	583
September	1st to 10th	Day	11% 5% 12% 33% 27% 12%	530
	11th to 20th	Day	16% 5% 13% 25% 30% 11%	530
	21st to end	Day	15% 4 20% 26% 25% 10%	530
October	1st to 10th	Day	17% 4 23% 30% 18% 8%	530
	11th to 20th	Day	14% 11% 23% 26% 23% 4	530
	21st to end	Day	19% 10% 25% 28% 15% 3	583
November	1st to 10th	Day	23% 9% 28% 25% 14% 2	355
	11th to 20th	Day	18% 18% 36% 21% 7% 1	321
	21st to end	Day	14% 20% 35% 22% 8% 1	300
December	1st to 10th	Day	32% 20% 30% 15% 3	300
	11th to 20th	Day	25% 18% 32% 21% 4	300
	21st to end	Day	33% 17% 29% 15% 4 1	330
January	1st to 10th	Night	27% 20% 30% 20% 4	800
	11th to 20th	Night	23% 20% 29% 22% 6%	800
	21st to end	Night	22% 19% 35% 22% 2	880
February	1st to 10th	Night	20% 16% 32% 28% 5%	800
	11th to 20th	Night	28% 19% 30% 20% 3	783
	21st to end	Night	24% 18% 35% 21% 2	660
March	1st to 10th	Night	22% 16% 33% 26% 4	800
	11th to 20th	Night	18% 14% 34% 25% 8%	800
	21st to end	Night	20% 15% 28% 29% 8%	880
April	1st to 10th	Night	15% 17% 30% 28% 10%	775
	11th to 20th	Night	16% 12% 29% 31% 13% 1	593
	21st to end	Night	13% 8% 26% 33% 19% 1	600
May	1st to 10th	Night	13% 9% 24% 32% 22% 1	600
	11th to 20th	Night	15% 7% 22% 30% 22% 4	591
	21st to end	Night	15% 4 15% 30% 31% 6%	650
June	1st to 10th	Night	10% 2 16% 39% 29% 5%	600
	11th to 20th	Night	6% 2 15% 31% 33% 12%	600
	21st to end	Night	8% 1 13% 38% 33% 8%	600
July	1st to 10th	Night	11% 2 9% 24% 44% 11%	585
	11th to 20th	Night	9% 2 8% 24% 44% 12%	582
	21st to end	Night	9% 2 8% 29% 42% 10%	657
August	1st to 10th	Night	15% 3 10% 27% 36% 10%	597
	11th to 20th	Night	14% 3 8% 27% 39% 8%	594
	21st to end	Night	16% 3 10% 26% 35% 9%	660
September	1st to 10th	Night	11% 2 14% 31% 33% 8%	780
	11th to 20th	Night	16% 3 16% 27% 35% 3	800
	21st to end	Night	16% 4 16% 34% 28% 3	800
October	1st to 10th	Night	14% 4 21% 33% 22% 6%	800
	11th to 20th	Night	12% 7% 26% 32% 20% 3	800
	21st to end	Night	15% 11% 22% 32% 18% 2	880
November	1st to 10th	Night	17% 9% 24% 32% 18% 1	820
	11th to 20th	Night	17% 13% 29% 27% 13% 1	829
	21st to end	Night	19% 15% 26% 27% 12% 1	800
December	1st to 10th	Night	24% 17% 29% 23% 7% 1	800
	11th to 20th	Night	24% 13% 28% 26% 9% 1	800
	21st to end	Night	30% 14% 26% 25% 5%	880

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