Lynchburg College Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lynchburg College Observatory clear sky chart from 2005-11-06 to 2026-04-17.

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% 42%	130945
	Night	14% 6% 2 5% 4 4 4 3 5% 7% 45%	131215
Transparency	Day	39% 3 12% 23% 17% 4	134550
	Night	38% 3 11% 24% 19% 5%	135680
Seeing	Day	20% 9% 24% 25% 16% 7%	16962
	Night	18% 7% 23% 33% 17% 2	27441

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	16% 5% 1 4 4 3 4 3 5% 6% 47%	5258
	11th to 20th	Day	12% 6% 2 5% 3 4 3 3 4 5% 53%	5280
	21st to end	Day	16% 6% 3 6% 3 4 4 3 3 4 47%	5780
February	1st to 10th	Day	11% 7% 2 7% 5% 5% 6% 4 6% 6% 40%	1890
	11th to 20th	Day	20% 6% 2 5% 4 4 4 3 4 7% 41%	1848
	21st to end	Day	19% 6% 3 7% 5% 4 4 3 5% 6% 39%	1841
March	1st to 10th	Day	17% 6% 2 6% 4 4 5% 4 6% 7% 39%	5045
	11th to 20th	Day	11% 5% 2 4 3 3 4 4 5% 7% 51%	5090
	21st to end	Day	15% 6% 3 7% 5% 4 4 4 5% 6% 41%	5586
April	1st to 10th	Day	12% 5% 2 5% 4 4 4 3 6% 7% 49%	2416
	11th to 20th	Day	14% 5% 2 4 4 4 4 4 6% 8% 46%	2446
	21st to end	Day	16% 6% 2 6% 5% 4 4 4 5% 7% 42%	2494
May	1st to 10th	Day	12% 6% 2 6% 5% 6% 7% 6% 8% 10% 33%	5862
	11th to 20th	Day	21% 7% 2 7% 5% 5% 4 5% 6% 8% 30%	5861
	21st to end	Day	14% 5% 2 5% 4 4 5% 4 7% 9% 41%	6433
June	1st to 10th	Day	10% 4 2 4 5% 5% 5% 5% 7% 10% 43%	2600
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 5% 8% 10% 40%	2600
	21st to end	Day	7% 4 2 6% 4 5% 6% 5% 8% 11% 42%	2600
July	1st to 10th	Day	6% 4 2 7% 5% 5% 5% 5% 9% 11% 40%	5900
	11th to 20th	Day	7% 5% 2 7% 6% 6% 7% 6% 9% 13% 31%	5900
	21st to end	Day	9% 6% 2 7% 5% 6% 7% 5% 8% 11% 32%	6424
August	1st to 10th	Day	14% 7% 2 7% 5% 5% 5% 5% 7% 12% 31%	4234
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 6% 7% 11% 38%	4174
	21st to end	Day	8% 4 2 5% 4 4 4 4 6% 10% 48%	4312
September	1st to 10th	Day	11% 5% 2 5% 4 4 4 4 5% 7% 49%	2400
	11th to 20th	Day	15% 6% 2 6% 4 4 4 3 6% 7% 43%	2213
	21st to end	Day	24% 7% 2 6% 4 4 4 3 5% 6% 35%	2185
October	1st to 10th	Day	16% 5% 1 4 4 3 3 2 4 6% 51%	2000
	11th to 20th	Day	15% 5% 2 4 3 2 3 2 5% 6% 54%	2000
	21st to end	Day	14% 6% 2 4 3 3 3 3 4 6% 52%	2200
November	1st to 10th	Day	12% 4 1 4 4 3 3 3 4 6% 55%	2057
	11th to 20th	Day	14% 5% 1 4 4 3 4 3 5% 7% 52%	1969
	21st to end	Day	14% 4 2 5% 4 3 3 4 5% 8% 47%	1714
December	1st to 10th	Day	14% 7% 2 5% 3 3 5% 3 6% 6% 46%	2680
	11th to 20th	Day	21% 5% 2 4 3 2 4 3 4 7% 45%	3088
	21st to end	Day	22% 7% 2 5% 4 4 4 4 7% 7% 35%	4565
January	1st to 10th	Night	13% 4 2 5% 3 3 3 3 5% 7% 52%	7635
	11th to 20th	Night	12% 5% 2 5% 3 3 3 2 4 5% 55%	7680
	21st to end	Night	17% 5% 2 5% 3 3 3 3 4 5% 50%	8401
February	1st to 10th	Night	14% 7% 3 6% 4 3 4 4 6% 7% 43%	2730
	11th to 20th	Night	20% 6% 2 6% 4 4 3 3 4 6% 41%	2655
	21st to end	Night	15% 7% 3 5% 5% 4 4 4 5% 7% 42%	1962
March	1st to 10th	Night	18% 6% 2 5% 3 3 4 3 5% 6% 44%	5028
	11th to 20th	Night	10% 3 1 4 3 4 4 3 5% 8% 55%	5090
	21st to end	Night	13% 6% 2 5% 4 4 4 4 6% 6% 44%	5588
April	1st to 10th	Night	15% 6% 2 5% 4 3 4 3 5% 8% 45%	2202
	11th to 20th	Night	13% 4 2 5% 3 4 4 4 5% 8% 49%	2036
	21st to end	Night	15% 5% 2 5% 4 3 5% 4 5% 8% 44%	1922
May	1st to 10th	Night	16% 7% 2 7% 4 4 4 4 6% 9% 36%	4033
	11th to 20th	Night	22% 8% 3 7% 4 4 4 3 5% 7% 32%	4032
	21st to end	Night	15% 5% 2 6% 4 4 4 3 6% 10% 41%	4421
June	1st to 10th	Night	9% 5% 2 5% 4 4 4 4 8% 11% 44%	1800
	11th to 20th	Night	11% 4 2 6% 4 4 4 4 7% 10% 44%	1800
	21st to end	Night	8% 4 2 4 4 5% 5% 5% 7% 11% 45%	1800
July	1st to 10th	Night	9% 6% 2 6% 5% 5% 5% 5% 8% 10% 39%	4058
	11th to 20th	Night	10% 7% 3 8% 6% 7% 6% 5% 8% 11% 29%	4057
	21st to end	Night	9% 7% 3 8% 7% 5% 6% 5% 8% 9% 32%	4427
August	1st to 10th	Night	16% 7% 3 7% 4 5% 5% 4 7% 11% 32%	2915
	11th to 20th	Night	9% 6% 2 6% 4 6% 6% 5% 7% 9% 39%	2875
	21st to end	Night	8% 5% 2 6% 5% 5% 5% 3 6% 9% 47%	3553
September	1st to 10th	Night	11% 6% 2 5% 4 5% 5% 3 5% 7% 48%	2000
	11th to 20th	Night	16% 5% 2 6% 5% 4 4 4 5% 6% 43%	2182
	21st to end	Night	23% 7% 3 7% 4 4 4 3 5% 5% 35%	2213
October	1st to 10th	Night	17% 5% 2 5% 4 3 3 3 4 6% 50%	2400
	11th to 20th	Night	14% 5% 2 5% 4 3 3 2 4 6% 52%	2400
	21st to end	Night	15% 3 2 4 2 2 3 3 4 6% 54%	2640
November	1st to 10th	Night	13% 6% 2 5% 3 3 4 2 4 5% 53%	2461
	11th to 20th	Night	13% 4 2 5% 4 3 4 3 4 5% 52%	2649
	21st to end	Night	13% 4 2 5% 4 4 4 3 5% 7% 50%	2900
December	1st to 10th	Night	12% 5% 2 5% 3 4 3 3 5% 6% 52%	4720
	11th to 20th	Night	19% 7% 2 5% 4 4 3 3 5% 6% 42%	5317
	21st to end	Night	18% 5% 1 4 4 4 4 3 6% 8% 42%	6633

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	39% 1 9% 21% 24% 5%	5259
	11th to 20th	Day	35% 2 4 18% 28% 13%	5280
	21st to end	Day	43% 1 5% 27% 19% 4	5780
February	1st to 10th	Day	42% 3 11% 23% 17% 3	1890
	11th to 20th	Day	45% 2 8% 23% 18% 4	1857
	21st to end	Day	47% 3 9% 19% 17% 5%	1841
March	1st to 10th	Day	43% 3 7% 20% 18% 9%	5045
	11th to 20th	Day	33% 2 8% 24% 22% 10%	5090
	21st to end	Day	44% 2 10% 19% 18% 6%	5586
April	1st to 10th	Day	35% 3 12% 24% 19% 8%	2416
	11th to 20th	Day	37% 2 12% 24% 19% 5%	2446
	21st to end	Day	43% 3 11% 25% 14% 4	2494
May	1st to 10th	Day	45% 4 14% 23% 12% 2	5897
	11th to 20th	Day	52% 3 11% 20% 12% 1	5865
	21st to end	Day	40% 4 15% 20% 18% 4	6447
June	1st to 10th	Day	34% 6% 17% 27% 15% 1	2600
	11th to 20th	Day	37% 6% 17% 22% 17% 1	2600
	21st to end	Day	33% 8% 16% 27% 15% 2	2600
July	1st to 10th	Day	36% 7% 21% 21% 11% 4	5835
	11th to 20th	Day	41% 7% 23% 21% 7%	5831
	21st to end	Day	44% 5% 16% 23% 11%	6240
August	1st to 10th	Day	46% 4 18% 25% 6%	4221
	11th to 20th	Day	38% 6% 15% 30% 11% 1	4213
	21st to end	Day	31% 4 21% 28% 15% 1	4312
September	1st to 10th	Day	34% 5% 14% 21% 21% 4	2400
	11th to 20th	Day	40% 4 9% 26% 19% 3	2213
	21st to end	Day	50% 3 9% 19% 17% 2	2185
October	1st to 10th	Day	34% 2 7% 21% 28% 7%	3260
	11th to 20th	Day	25% 1 8% 24% 29% 13%	3240
	21st to end	Day	24% 2 11% 28% 24% 11%	3538
November	1st to 10th	Day	32% 2 10% 23% 27% 6%	2057
	11th to 20th	Day	34% 3 8% 25% 23% 7%	1969
	21st to end	Day	35% 3 9% 26% 24% 4	1714
December	1st to 10th	Day	38% 2 9% 23% 21% 7%	2680
	11th to 20th	Day	40% 2 12% 21% 19% 5%	3084
	21st to end	Day	48% 2 10% 25% 14% 1	4565
January	1st to 10th	Night	34% 2 9% 24% 24% 8%	7636
	11th to 20th	Night	33% 2 5% 20% 31% 10%	7680
	21st to end	Night	39% 1 6% 28% 20% 6%	8401
February	1st to 10th	Night	39% 3 12% 24% 20% 3	2730
	11th to 20th	Night	45% 2 9% 19% 19% 5%	2657
	21st to end	Night	42% 3 9% 23% 17% 6%	1962
March	1st to 10th	Night	42% 2 6% 21% 21% 8%	5028
	11th to 20th	Night	29% 2 7% 22% 30% 10%	5090
	21st to end	Night	40% 2 9% 23% 20% 5%	5588
April	1st to 10th	Night	38% 3 12% 20% 22% 5%	2202
	11th to 20th	Night	34% 3 12% 25% 21% 5%	2036
	21st to end	Night	39% 4 11% 25% 17% 3	1922
May	1st to 10th	Night	45% 5% 16% 20% 12% 2	4060
	11th to 20th	Night	53% 4 10% 21% 12% 1	4033
	21st to end	Night	41% 3 16% 26% 12% 3	4429
June	1st to 10th	Night	33% 7% 16% 27% 16% 1	1800
	11th to 20th	Night	36% 6% 18% 22% 16% 2	1800
	21st to end	Night	31% 8% 17% 23% 18% 4	1800
July	1st to 10th	Night	40% 8% 18% 19% 13% 2	4015
	11th to 20th	Night	47% 7% 21% 17% 6% 1	4006
	21st to end	Night	47% 5% 15% 23% 10%	4297
August	1st to 10th	Night	47% 5% 18% 23% 7% 1	2904
	11th to 20th	Night	40% 5% 17% 27% 11% 1	2902
	21st to end	Night	34% 5% 15% 34% 11% 2	3553
September	1st to 10th	Night	36% 5% 13% 21% 18% 6%	2000
	11th to 20th	Night	41% 5% 8% 25% 19% 2	2182
	21st to end	Night	51% 4 8% 19% 15% 3	2213
October	1st to 10th	Night	38% 2 8% 20% 26% 7%	3920
	11th to 20th	Night	26% 2 7% 23% 29% 13%	3899
	21st to end	Night	21% 2 7% 30% 29% 12%	4252
November	1st to 10th	Night	35% 2 8% 23% 26% 6%	2461
	11th to 20th	Night	35% 2 8% 23% 25% 7%	2649
	21st to end	Night	35% 2 9% 27% 22% 6%	2900
December	1st to 10th	Night	35% 1 8% 29% 25% 3	4720
	11th to 20th	Night	45% 2 10% 20% 16% 6%	5320
	21st to end	Night	42% 2 11% 25% 18% 2	6633

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	33% 20% 26% 17% 3 1	330
	11th to 20th	Day	35% 17% 34% 13% 1	330
	21st to end	Day	28% 23% 34% 11% 4	363
February	1st to 10th	Day	24% 17% 40% 15% 4	330
	11th to 20th	Day	43% 17% 30% 8% 2	330
	21st to end	Day	29% 17% 33% 18% 3	384
March	1st to 10th	Day	26% 13% 33% 23% 4	540
	11th to 20th	Day	24% 19% 29% 21% 5% 1	540
	21st to end	Day	23% 13% 35% 21% 6% 1	594
April	1st to 10th	Day	22% 18% 28% 21% 8% 2	540
	11th to 20th	Day	20% 13% 29% 22% 12% 3	516
	21st to end	Day	23% 9% 31% 22% 13% 3	500
May	1st to 10th	Day	19% 12% 34% 22% 10% 3	503
	11th to 20th	Day	24% 7% 23% 25% 16% 5%	527
	21st to end	Day	21% 4 19% 27% 20% 9%	573
June	1st to 10th	Day	12% 4 25% 33% 18% 9%	530
	11th to 20th	Day	13% 5% 17% 32% 21% 12%	530
	21st to end	Day	10% 4 19% 32% 25% 10%	530
July	1st to 10th	Day	13% 1 14% 28% 28% 16%	525
	11th to 20th	Day	6% 1 12% 34% 30% 17%	524
	21st to end	Day	12% 2 15% 31% 26% 14%	576
August	1st to 10th	Day	16% 3 16% 25% 24% 15%	526
	11th to 20th	Day	13% 1 14% 31% 24% 16%	519
	21st to end	Day	11% 2 11% 30% 26% 21%	583
September	1st to 10th	Day	13% 3 13% 27% 28% 17%	530
	11th to 20th	Day	18% 3 10% 26% 29% 14%	530
	21st to end	Day	29% 6% 18% 23% 19% 6%	530
October	1st to 10th	Day	22% 4 16% 30% 22% 6%	530
	11th to 20th	Day	16% 11% 21% 28% 18% 5%	530
	21st to end	Day	18% 10% 27% 29% 13% 3	583
November	1st to 10th	Day	18% 8% 29% 30% 12% 3	535
	11th to 20th	Day	21% 15% 28% 24% 11% 1	409
	21st to end	Day	22% 19% 27% 20% 10% 2	236
December	1st to 10th	Day	27% 14% 36% 17% 6%	220
	11th to 20th	Day	26% 10% 32% 25% 5% 1	223
	21st to end	Day	29% 14% 30% 19% 7% 1	363
January	1st to 10th	Night	21% 14% 34% 28% 3	840
	11th to 20th	Night	20% 14% 33% 31% 2	840
	21st to end	Night	20% 11% 40% 27% 3	924
February	1st to 10th	Night	18% 12% 38% 28% 3	840
	11th to 20th	Night	28% 13% 34% 25% 1	823
	21st to end	Night	20% 14% 35% 28% 3	692
March	1st to 10th	Night	17% 13% 32% 33% 5%	840
	11th to 20th	Night	22% 12% 31% 27% 7% 1	840
	21st to end	Night	18% 11% 33% 32% 6%	924
April	1st to 10th	Night	17% 16% 32% 28% 7%	840
	11th to 20th	Night	16% 12% 29% 31% 12% 1	816
	21st to end	Night	18% 5% 27% 39% 11%	722
May	1st to 10th	Night	17% 7% 26% 34% 16% 1	600
	11th to 20th	Night	20% 5% 16% 38% 19% 2	591
	21st to end	Night	18% 2 10% 33% 32% 4	650
June	1st to 10th	Night	11% 1 13% 44% 30% 3	600
	11th to 20th	Night	13% 2 9% 35% 37% 4	600
	21st to end	Night	9% 2 9% 41% 33% 6%	600
July	1st to 10th	Night	11% 1 6% 33% 42% 6%	585
	11th to 20th	Night	7% 1 5% 30% 49% 8%	582
	21st to end	Night	11% 1 6% 39% 38% 5%	657
August	1st to 10th	Night	17% 2 6% 35% 36% 4	597
	11th to 20th	Night	14% 2 7% 31% 39% 5%	594
	21st to end	Night	12% 2 7% 35% 38% 7%	860
September	1st to 10th	Night	14% 2 8% 34% 37% 7%	800
	11th to 20th	Night	17% 2 9% 34% 33% 6%	800
	21st to end	Night	28% 4 14% 31% 23% 2	800
October	1st to 10th	Night	19% 4 16% 30% 27% 4	800
	11th to 20th	Night	16% 6% 22% 37% 17% 2	800
	21st to end	Night	17% 6% 22% 39% 14% 2	880
November	1st to 10th	Night	17% 7% 24% 37% 13% 2	820
	11th to 20th	Night	17% 9% 28% 34% 11% 1	840
	21st to end	Night	17% 9% 27% 36% 10% 1	840
December	1st to 10th	Night	23% 9% 33% 29% 6%	840
	11th to 20th	Night	19% 8% 34% 34% 5%	840
	21st to end	Night	23% 11% 29% 34% 4	924

Page generated at 2026-04-14 02:44:29. Version ac07

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