Culpeper
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Culpeper clear sky chart from 2005-11-06 to 2026-03-03.

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	13% 6% 2 6% 4 4 5% 4 6% 8% 42%	131016
	Night	14% 6% 2 6% 4 4 4 4 5% 7% 44%	130171
Transparency	Day	37% 7% 12% 22% 17% 4	134617
	Night	37% 6% 11% 22% 18% 5%	134640
Seeing	Day	18% 12% 26% 24% 14% 5%	16648
	Night	17% 10% 29% 30% 13% 1	26403

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	14% 6% 2 5% 3 4 5% 4 5% 5% 47%	5117
	11th to 20th	Day	11% 8% 3 6% 3 3 3 3 4 3 52%	5280
	21st to end	Day	13% 5% 2 6% 5% 4 4 4 5% 5% 46%	5780
February	1st to 10th	Day	12% 8% 2 7% 4 4 4 3 5% 7% 43%	1890
	11th to 20th	Day	18% 7% 3 7% 4 3 3 4 5% 7% 41%	1861
	21st to end	Day	17% 8% 3 6% 4 5% 4 4 6% 5% 39%	1761
March	1st to 10th	Day	17% 5% 2 5% 4 4 4 3 5% 7% 43%	4957
	11th to 20th	Day	10% 6% 2 5% 3 4 4 3 5% 7% 51%	4980
	21st to end	Day	17% 7% 2 7% 4 4 4 4 5% 6% 40%	5465
April	1st to 10th	Day	12% 6% 2 5% 4 5% 4 3 5% 6% 46%	2393
	11th to 20th	Day	13% 6% 2 5% 4 4 4 3 5% 6% 48%	2374
	21st to end	Day	16% 7% 2 6% 5% 4 4 3 5% 7% 41%	2400
May	1st to 10th	Day	16% 7% 2 7% 5% 5% 6% 5% 7% 9% 32%	5862
	11th to 20th	Day	21% 6% 2 6% 4 5% 5% 4 6% 9% 31%	5902
	21st to end	Day	16% 5% 2 5% 4 5% 4 4 6% 9% 39%	6934
June	1st to 10th	Day	11% 5% 2 6% 5% 4 5% 5% 6% 10% 43%	2800
	11th to 20th	Day	11% 5% 2 6% 5% 5% 6% 4 7% 10% 40%	2800
	21st to end	Day	8% 4 1 5% 4 5% 5% 5% 7% 11% 44%	2800
July	1st to 10th	Day	7% 4 2 6% 5% 4 6% 5% 8% 11% 42%	6318
	11th to 20th	Day	8% 6% 2 7% 6% 6% 7% 7% 10% 13% 29%	5900
	21st to end	Day	8% 5% 2 7% 5% 5% 6% 5% 8% 10% 39%	6424
August	1st to 10th	Day	14% 5% 2 6% 4 5% 6% 5% 7% 12% 33%	4234
	11th to 20th	Day	9% 4 2 6% 5% 6% 6% 5% 8% 10% 39%	4052
	21st to end	Day	10% 4 1 5% 4 4 5% 4 6% 8% 49%	4312
September	1st to 10th	Day	13% 5% 2 6% 4 4 4 4 5% 7% 46%	2400
	11th to 20th	Day	12% 5% 2 6% 3 4 4 3 6% 8% 47%	2368
	21st to end	Day	22% 7% 3 5% 4 4 5% 4 5% 5% 37%	2103
October	1st to 10th	Day	15% 5% 2 5% 3 4 3 3 4 6% 49%	2000
	11th to 20th	Day	15% 5% 1 5% 3 4 4 4 5% 5% 50%	2000
	21st to end	Day	14% 5% 1 5% 3 4 4 3 4 6% 52%	2200
November	1st to 10th	Day	11% 5% 2 4 4 4 4 3 4 6% 54%	2041
	11th to 20th	Day	14% 5% 2 5% 4 3 4 4 5% 6% 50%	1830
	21st to end	Day	15% 5% 2 4 4 3 4 3 5% 5% 50%	1680
December	1st to 10th	Day	12% 5% 2 5% 3 3 3 3 5% 6% 52%	2680
	11th to 20th	Day	19% 7% 3 4 3 3 3 2 3 7% 46%	3070
	21st to end	Day	18% 7% 3 7% 4 4 4 4 5% 7% 38%	4048
January	1st to 10th	Night	11% 6% 2 4 3 3 5% 4 7% 7% 49%	7772
	11th to 20th	Night	12% 7% 2 5% 3 2 3 2 4 5% 54%	7680
	21st to end	Night	12% 6% 2 6% 3 3 3 3 4 5% 51%	8401
February	1st to 10th	Night	14% 7% 2 6% 5% 4 4 4 5% 6% 42%	2730
	11th to 20th	Night	19% 7% 2 6% 3 3 3 3 4 6% 43%	2643
	21st to end	Night	15% 7% 3 6% 3 4 4 3 5% 5% 44%	2043
March	1st to 10th	Night	16% 5% 2 5% 4 3 4 3 5% 5% 48%	4941
	11th to 20th	Night	11% 6% 2 4 3 3 4 4 5% 7% 51%	4980
	21st to end	Night	11% 6% 2 6% 4 4 4 4 6% 6% 46%	5467
April	1st to 10th	Night	14% 8% 2 5% 4 4 4 4 4 6% 43%	2006
	11th to 20th	Night	12% 5% 2 5% 5% 4 4 3 5% 7% 48%	1975
	21st to end	Night	15% 6% 2 5% 4 3 4 4 6% 6% 45%	2000
May	1st to 10th	Night	19% 9% 3 8% 4 4 4 4 6% 7% 31%	4061
	11th to 20th	Night	24% 6% 2 6% 4 4 4 4 6% 8% 30%	3987
	21st to end	Night	16% 6% 3 7% 5% 5% 4 4 6% 8% 37%	3920
June	1st to 10th	Night	11% 5% 2 5% 4 5% 4 4 7% 8% 45%	1600
	11th to 20th	Night	12% 5% 2 6% 5% 6% 4 4 6% 8% 42%	1600
	21st to end	Night	10% 4 1 5% 5% 5% 5% 5% 7% 9% 45%	1600
July	1st to 10th	Night	9% 5% 2 7% 5% 5% 6% 5% 8% 9% 38%	3634
	11th to 20th	Night	10% 7% 4 9% 6% 7% 6% 5% 8% 9% 28%	4057
	21st to end	Night	7% 6% 3 7% 5% 5% 6% 5% 7% 9% 38%	4427
August	1st to 10th	Night	15% 6% 3 7% 5% 6% 5% 5% 7% 10% 32%	2915
	11th to 20th	Night	11% 7% 3 9% 5% 5% 4 4 6% 8% 36%	2964
	21st to end	Night	12% 5% 2 6% 3 4 3 3 5% 8% 48%	3586
September	1st to 10th	Night	15% 6% 1 5% 3 4 5% 3 6% 7% 46%	2000
	11th to 20th	Night	12% 5% 2 6% 4 5% 4 3 5% 7% 48%	2028
	21st to end	Night	22% 7% 2 5% 5% 3 4 3 4 6% 38%	2295
October	1st to 10th	Night	18% 6% 2 6% 3 4 3 3 3 6% 46%	2400
	11th to 20th	Night	15% 5% 2 5% 3 3 4 3 5% 6% 50%	2400
	21st to end	Night	13% 5% 2 5% 3 3 3 3 6% 6% 51%	2640
November	1st to 10th	Night	12% 6% 3 5% 4 3 4 3 4 5% 53%	2476
	11th to 20th	Night	14% 6% 2 4 3 4 4 4 4 7% 48%	2788
	21st to end	Night	13% 5% 1 5% 4 4 4 4 4 7% 50%	2940
December	1st to 10th	Night	10% 5% 2 4 4 3 3 3 4 7% 54%	4720
	11th to 20th	Night	19% 6% 2 5% 4 3 4 3 4 5% 43%	5345
	21st to end	Night	16% 6% 2 6% 4 4 5% 4 5% 7% 41%	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	36% 5% 10% 23% 19% 7%	5118
	11th to 20th	Day	35% 4 6% 19% 22% 13%	5280
	21st to end	Day	39% 5% 8% 28% 16% 4	5780
February	1st to 10th	Day	41% 5% 12% 25% 15% 3	1890
	11th to 20th	Day	43% 4 10% 21% 18% 3	1870
	21st to end	Day	44% 6% 13% 17% 16% 4	1761
March	1st to 10th	Day	40% 6% 9% 19% 17% 9%	4957
	11th to 20th	Day	31% 5% 10% 24% 22% 7%	4980
	21st to end	Day	42% 6% 11% 17% 17% 7%	5465
April	1st to 10th	Day	37% 7% 12% 19% 17% 8%	2393
	11th to 20th	Day	36% 6% 11% 20% 21% 6%	2374
	21st to end	Day	42% 7% 10% 23% 14% 4	2400
May	1st to 10th	Day	44% 11% 15% 18% 11% 2	5897
	11th to 20th	Day	47% 8% 12% 22% 10% 1	5906
	21st to end	Day	38% 8% 16% 19% 17% 2	6949
June	1st to 10th	Day	35% 9% 14% 24% 16% 1	2800
	11th to 20th	Day	37% 10% 15% 23% 13% 2	2800
	21st to end	Day	31% 10% 17% 24% 17% 1	2800
July	1st to 10th	Day	32% 12% 19% 19% 13% 4	6248
	11th to 20th	Day	40% 14% 19% 21% 6% 1	5831
	21st to end	Day	37% 9% 12% 24% 18%	6240
August	1st to 10th	Day	41% 9% 18% 25% 7%	4221
	11th to 20th	Day	36% 10% 16% 24% 14% 1	4091
	21st to end	Day	31% 7% 16% 29% 16% 2	4312
September	1st to 10th	Day	38% 7% 12% 18% 20% 5%	2400
	11th to 20th	Day	35% 7% 8% 28% 20% 3	2368
	21st to end	Day	47% 7% 10% 18% 16% 2	2103
October	1st to 10th	Day	35% 5% 7% 18% 30% 5%	3260
	11th to 20th	Day	25% 4 8% 26% 27% 11%	3240
	21st to end	Day	21% 4 10% 29% 24% 12%	3538
November	1st to 10th	Day	32% 5% 10% 25% 24% 5%	2041
	11th to 20th	Day	35% 4 11% 22% 22% 7%	1830
	21st to end	Day	35% 5% 11% 24% 21% 3	1680
December	1st to 10th	Day	33% 5% 11% 25% 19% 6%	2680
	11th to 20th	Day	40% 3 14% 26% 13% 5%	3066
	21st to end	Day	42% 7% 14% 20% 15% 1	4048
January	1st to 10th	Night	32% 5% 11% 24% 23% 5%	7773
	11th to 20th	Night	33% 3 7% 21% 25% 11%	7680
	21st to end	Night	35% 5% 8% 28% 20% 4	8401
February	1st to 10th	Night	41% 6% 11% 23% 16% 3	2730
	11th to 20th	Night	43% 3 9% 21% 18% 6%	2645
	21st to end	Night	40% 6% 11% 20% 17% 6%	2043
March	1st to 10th	Night	36% 6% 8% 23% 19% 8%	4941
	11th to 20th	Night	29% 7% 10% 21% 25% 7%	4980
	21st to end	Night	36% 6% 10% 21% 20% 6%	5467
April	1st to 10th	Night	40% 6% 11% 18% 21% 5%	2006
	11th to 20th	Night	35% 6% 12% 22% 20% 5%	1975
	21st to end	Night	37% 7% 11% 25% 15% 5%	2000
May	1st to 10th	Night	49% 9% 14% 17% 8% 4	4088
	11th to 20th	Night	48% 9% 12% 20% 10% 1	3988
	21st to end	Night	43% 9% 14% 23% 10% 2	3927
June	1st to 10th	Night	33% 10% 14% 26% 16% 2	1600
	11th to 20th	Night	38% 9% 15% 22% 14% 1	1600
	21st to end	Night	33% 9% 16% 20% 19% 3	1600
July	1st to 10th	Night	39% 12% 18% 16% 14% 2	3596
	11th to 20th	Night	48% 12% 18% 15% 6% 1	4006
	21st to end	Night	37% 10% 15% 22% 15%	4297
August	1st to 10th	Night	45% 9% 16% 22% 7% 1	2904
	11th to 20th	Night	43% 9% 12% 22% 13% 1	2991
	21st to end	Night	34% 7% 14% 29% 16% 1	3586
September	1st to 10th	Night	37% 7% 12% 21% 17% 6%	2000
	11th to 20th	Night	35% 6% 9% 26% 20% 3	2028
	21st to end	Night	46% 6% 11% 18% 16% 3	2295
October	1st to 10th	Night	41% 5% 9% 20% 20% 6%	3920
	11th to 20th	Night	24% 4 10% 21% 31% 10%	3899
	21st to end	Night	21% 5% 9% 30% 27% 8%	4252
November	1st to 10th	Night	33% 4 9% 23% 24% 7%	2476
	11th to 20th	Night	36% 5% 7% 23% 22% 7%	2788
	21st to end	Night	34% 4 11% 24% 22% 5%	2940
December	1st to 10th	Night	30% 4 12% 28% 22% 4	4720
	11th to 20th	Night	43% 5% 11% 19% 17% 6%	5348
	21st to end	Night	39% 8% 14% 22% 16% 1	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	23% 25% 30% 17% 4	303
	11th to 20th	Day	25% 29% 28% 14% 3	330
	21st to end	Day	21% 25% 38% 12% 2 1	363
February	1st to 10th	Day	24% 25% 36% 13% 2	330
	11th to 20th	Day	36% 24% 28% 9% 1	348
	21st to end	Day	28% 20% 29% 21% 3	446
March	1st to 10th	Day	25% 19% 32% 20% 4	508
	11th to 20th	Day	23% 22% 31% 17% 6% 1	500
	21st to end	Day	24% 20% 34% 16% 5% 1	550
April	1st to 10th	Day	26% 22% 25% 20% 6% 1	500
	11th to 20th	Day	18% 19% 30% 20% 11% 3	492
	21st to end	Day	22% 12% 35% 19% 10% 1	500
May	1st to 10th	Day	22% 17% 28% 20% 11% 3	503
	11th to 20th	Day	21% 12% 28% 24% 11% 4	527
	21st to end	Day	19% 6% 26% 27% 16% 5%	573
June	1st to 10th	Day	12% 6% 27% 31% 19% 5%	530
	11th to 20th	Day	13% 7% 25% 28% 20% 7%	530
	21st to end	Day	10% 5% 25% 32% 22% 6%	530
July	1st to 10th	Day	10% 3 18% 32% 26% 11%	525
	11th to 20th	Day	5% 2 17% 35% 29% 13%	524
	21st to end	Day	11% 3 18% 30% 26% 11%	576
August	1st to 10th	Day	13% 4 16% 29% 27% 11%	526
	11th to 20th	Day	12% 3 18% 29% 27% 12%	519
	21st to end	Day	9% 3 19% 33% 22% 14%	583
September	1st to 10th	Day	15% 5% 20% 28% 19% 13%	530
	11th to 20th	Day	15% 3 20% 27% 24% 12%	530
	21st to end	Day	28% 10% 21% 25% 12% 4	530
October	1st to 10th	Day	18% 7% 22% 29% 16% 8%	530
	11th to 20th	Day	16% 14% 27% 24% 16% 2	530
	21st to end	Day	15% 15% 31% 27% 9% 3	583
November	1st to 10th	Day	14% 13% 32% 26% 12% 3	527
	11th to 20th	Day	20% 13% 32% 26% 8% 2	370
	21st to end	Day	22% 16% 32% 22% 7%	220
December	1st to 10th	Day	20% 19% 36% 17% 7%	220
	11th to 20th	Day	20% 16% 35% 20% 8%	220
	21st to end	Day	23% 22% 31% 17% 7%	242
January	1st to 10th	Night	19% 16% 40% 23% 3	840
	11th to 20th	Night	18% 16% 35% 26% 5%	840
	21st to end	Night	17% 15% 40% 26% 2	924
February	1st to 10th	Night	19% 13% 39% 26% 3	840
	11th to 20th	Night	25% 19% 36% 19% 1	823
	21st to end	Night	18% 19% 39% 22% 2	692
March	1st to 10th	Night	18% 18% 37% 24% 3	809
	11th to 20th	Night	21% 17% 34% 22% 5% 1	800
	21st to end	Night	17% 16% 39% 22% 6%	880
April	1st to 10th	Night	19% 18% 35% 24% 5%	800
	11th to 20th	Night	14% 13% 35% 28% 9% 1	791
	21st to end	Night	17% 11% 34% 31% 7% 1	800
May	1st to 10th	Night	20% 9% 28% 29% 13% 1	615
	11th to 20th	Night	21% 4 28% 31% 16%	572
	21st to end	Night	14% 3 21% 38% 22% 2	433
June	1st to 10th	Night	10% 5% 21% 43% 20% 2	400
	11th to 20th	Night	13% 4 19% 42% 22% 1	400
	21st to end	Night	10% 2 18% 47% 22% 2	400
July	1st to 10th	Night	11% 3 15% 39% 29% 3	400
	11th to 20th	Night	6% 1 13% 40% 35% 5%	582
	21st to end	Night	8% 3 15% 38% 32% 4	657
August	1st to 10th	Night	12% 2 12% 42% 29% 4	597
	11th to 20th	Night	12% 4 12% 39% 30% 3	644
	21st to end	Night	12% 3 14% 38% 29% 4	880
September	1st to 10th	Night	16% 3 15% 34% 29% 4	800
	11th to 20th	Night	13% 3 16% 35% 30% 3	800
	21st to end	Night	26% 4 19% 31% 19% 2	800
October	1st to 10th	Night	20% 5% 19% 30% 21% 4	800
	11th to 20th	Night	17% 8% 27% 32% 16% 1	800
	21st to end	Night	16% 8% 33% 30% 13% 1	880
November	1st to 10th	Night	15% 8% 33% 31% 12% 1	820
	11th to 20th	Night	16% 11% 34% 30% 8% 1	840
	21st to end	Night	14% 12% 36% 29% 9%	840
December	1st to 10th	Night	19% 11% 36% 27% 7%	840
	11th to 20th	Night	18% 9% 39% 30% 5%	840
	21st to end	Night	19% 11% 32% 33% 4	924

Page generated at 2026-02-28 01:40:23. Version ac07

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