Appomattox Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Appomattox Observatory clear sky chart from 2005-11-06 to 2024-12-02.

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 4 4 6% 8% 42%	101077
	Night	14% 6% 2 6% 4 4 4 4 5% 7% 44%	98474
Transparency	Day	38% 7% 12% 22% 17% 4	104727
	Night	38% 6% 11% 22% 18% 5%	102963
Seeing	Day	19% 11% 26% 24% 15% 5%	15189
	Night	17% 9% 27% 30% 15% 2	25136

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% 5% 1 4 3 3 3 3 4 5% 50%	2836
	11th to 20th	Day	15% 6% 2 6% 5% 4 3 4 4 6% 46%	2840
	21st to end	Day	21% 7% 3 6% 4 3 3 3 3 5% 40%	3124
February	1st to 10th	Day	12% 7% 2 6% 5% 5% 5% 4 6% 8% 42%	1710
	11th to 20th	Day	20% 6% 2 6% 3 4 4 3 5% 7% 43%	1663
	21st to end	Day	20% 8% 2 6% 5% 5% 4 3 6% 5% 38%	1664
March	1st to 10th	Day	21% 8% 2 6% 4 4 4 3 5% 6% 38%	3435
	11th to 20th	Day	10% 5% 2 4 4 4 4 3 5% 7% 52%	3480
	21st to end	Day	20% 6% 3 6% 5% 4 4 4 4 6% 38%	3815
April	1st to 10th	Day	10% 6% 2 4 4 4 4 4 6% 7% 51%	2221
	11th to 20th	Day	12% 6% 2 5% 4 4 4 3 5% 8% 48%	2254
	21st to end	Day	17% 5% 2 6% 5% 3 4 3 6% 6% 43%	2312
May	1st to 10th	Day	15% 7% 3 7% 5% 5% 6% 4 7% 9% 33%	4082
	11th to 20th	Day	20% 7% 2 6% 5% 4 4 4 6% 8% 34%	4081
	21st to end	Day	9% 4 2 6% 4 4 5% 4 7% 10% 46%	4497
June	1st to 10th	Day	10% 4 2 5% 4 5% 6% 4 6% 10% 44%	2660
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 11% 40%	2660
	21st to end	Day	8% 5% 2 6% 4 5% 6% 6% 8% 10% 41%	2582
July	1st to 10th	Day	6% 4 2 6% 5% 5% 6% 5% 8% 12% 40%	4120
	11th to 20th	Day	9% 6% 2 6% 5% 5% 6% 5% 8% 12% 35%	4120
	21st to end	Day	12% 8% 3 8% 6% 6% 6% 5% 8% 9% 29%	4466
August	1st to 10th	Day	15% 6% 3 6% 5% 5% 6% 5% 8% 11% 30%	4104
	11th to 20th	Day	8% 5% 2 6% 4 5% 6% 5% 8% 11% 39%	3965
	21st to end	Day	9% 5% 2 5% 3 4 4 4 6% 10% 49%	4180
September	1st to 10th	Day	12% 5% 2 6% 4 4 4 4 4 7% 48%	2280
	11th to 20th	Day	14% 6% 3 5% 5% 4 4 3 6% 7% 44%	2165
	21st to end	Day	23% 7% 2 6% 4 4 4 3 4 7% 36%	2043
October	1st to 10th	Day	14% 7% 2 5% 3 3 4 2 3 6% 51%	1900
	11th to 20th	Day	15% 4 1 4 4 3 3 3 3 5% 53%	1900
	21st to end	Day	13% 5% 2 6% 4 3 3 2 4 5% 54%	2090
November	1st to 10th	Day	12% 4 2 4 3 3 3 3 4 6% 55%	1957
	11th to 20th	Day	15% 5% 2 5% 3 4 4 3 4 6% 50%	1861
	21st to end	Day	14% 3 2 5% 3 2 4 3 5% 8% 51%	1600
December	1st to 10th	Day	17% 6% 2 6% 3 4 5% 5% 6% 7% 39%	1528
	11th to 20th	Day	16% 5% 2 4 4 3 2 2 4 5% 53%	1910
	21st to end	Day	19% 6% 2 5% 3 3 4 4 5% 8% 40%	2972
January	1st to 10th	Night	14% 6% 2 5% 4 4 4 3 5% 5% 49%	4109
	11th to 20th	Night	16% 7% 2 5% 3 3 4 2 4 5% 47%	4120
	21st to end	Night	21% 7% 2 6% 3 3 4 3 4 5% 43%	4532
February	1st to 10th	Night	14% 7% 2 5% 4 3 4 4 5% 8% 44%	2470
	11th to 20th	Night	19% 7% 3 5% 4 3 3 2 5% 6% 43%	2403
	21st to end	Night	15% 6% 2 6% 5% 3 4 3 5% 6% 44%	1785
March	1st to 10th	Night	20% 6% 3 7% 4 4 4 4 5% 6% 36%	3418
	11th to 20th	Night	12% 4 1 4 4 4 4 3 5% 7% 53%	3480
	21st to end	Night	16% 7% 2 5% 4 3 3 3 4 6% 46%	3817
April	1st to 10th	Night	14% 6% 2 6% 3 3 3 4 6% 6% 46%	1957
	11th to 20th	Night	12% 5% 2 4 3 4 4 4 6% 8% 48%	1875
	21st to end	Night	14% 5% 2 5% 4 4 4 4 7% 7% 44%	1883
May	1st to 10th	Night	17% 8% 3 7% 5% 4 5% 4 5% 8% 35%	2813
	11th to 20th	Night	24% 7% 2 5% 4 3 4 3 5% 5% 37%	2812
	21st to end	Night	11% 4 2 4 4 4 5% 4 7% 10% 45%	3053
June	1st to 10th	Night	9% 5% 2 5% 5% 5% 5% 4 7% 10% 42%	1520
	11th to 20th	Night	10% 6% 2 5% 4 6% 5% 4 6% 9% 43%	1520
	21st to end	Night	7% 5% 2 5% 4 4 5% 6% 6% 10% 46%	1588
July	1st to 10th	Night	6% 5% 2 7% 5% 6% 5% 5% 9% 9% 41%	2840
	11th to 20th	Night	9% 6% 3 7% 5% 5% 7% 5% 7% 10% 36%	2840
	21st to end	Night	12% 9% 3 9% 7% 6% 6% 5% 7% 8% 30%	3087
August	1st to 10th	Night	16% 7% 3 8% 6% 5% 5% 5% 6% 9% 31%	2825
	11th to 20th	Night	8% 6% 3 7% 5% 5% 6% 5% 8% 10% 37%	2817
	21st to end	Night	10% 5% 2 6% 4 5% 5% 4 6% 10% 44%	3476
September	1st to 10th	Night	12% 6% 2 7% 4 4 4 4 5% 7% 46%	1900
	11th to 20th	Night	14% 6% 2 6% 4 3 4 3 4 7% 45%	2010
	21st to end	Night	24% 8% 2 5% 4 3 4 3 5% 5% 37%	2136
October	1st to 10th	Night	17% 6% 2 5% 4 3 4 2 4 6% 48%	2280
	11th to 20th	Night	14% 4 2 4 4 4 3 3 5% 6% 51%	2280
	21st to end	Night	12% 4 2 4 3 3 4 3 4 6% 55%	2508
November	1st to 10th	Night	13% 6% 2 6% 4 3 3 3 4 4 53%	2341
	11th to 20th	Night	13% 5% 2 5% 4 3 4 4 5% 5% 50%	2530
	21st to end	Night	13% 3 2 5% 3 4 4 4 5% 7% 51%	2800
December	1st to 10th	Night	18% 7% 2 6% 4 4 4 3 4 5% 43%	2686
	11th to 20th	Night	16% 7% 2 4 4 3 3 3 4 6% 48%	3285
	21st to end	Night	17% 6% 2 6% 4 4 5% 4 6% 7% 40%	4678

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% 4 7% 30% 18% 5%	2837
	11th to 20th	Day	39% 4 8% 20% 24% 6%	2840
	21st to end	Day	46% 5% 6% 22% 17% 3	3124
February	1st to 10th	Day	39% 6% 11% 24% 16% 4	1710
	11th to 20th	Day	41% 4 8% 22% 20% 5%	1672
	21st to end	Day	47% 6% 10% 15% 17% 5%	1664
March	1st to 10th	Day	45% 6% 9% 19% 14% 7%	3435
	11th to 20th	Day	30% 7% 9% 24% 22% 9%	3480
	21st to end	Day	47% 6% 9% 18% 16% 3	3815
April	1st to 10th	Day	32% 6% 12% 23% 20% 8%	2221
	11th to 20th	Day	36% 5% 10% 23% 20% 6%	2254
	21st to end	Day	41% 6% 11% 22% 15% 5%	2312
May	1st to 10th	Day	45% 9% 13% 20% 11% 2	4120
	11th to 20th	Day	46% 8% 11% 23% 11% 1	4085
	21st to end	Day	30% 10% 16% 21% 20% 3	4511
June	1st to 10th	Day	34% 8% 16% 27% 15% 1	2660
	11th to 20th	Day	35% 9% 17% 22% 15% 2	2660
	21st to end	Day	34% 10% 17% 22% 15% 2	2582
July	1st to 10th	Day	34% 11% 22% 19% 10% 5%	4055
	11th to 20th	Day	38% 9% 20% 23% 9% 1	4051
	21st to end	Day	47% 9% 13% 19% 11%	4324
August	1st to 10th	Day	45% 8% 17% 23% 6% 1	4091
	11th to 20th	Day	36% 9% 18% 27% 10%	4004
	21st to end	Day	29% 8% 20% 27% 16% 1	4180
September	1st to 10th	Day	35% 8% 13% 18% 22% 4	2280
	11th to 20th	Day	40% 6% 10% 23% 19% 3	2165
	21st to end	Day	48% 5% 9% 17% 18% 2	2043
October	1st to 10th	Day	34% 3 8% 18% 30% 6%	3160
	11th to 20th	Day	25% 3 6% 23% 29% 14%	3140
	21st to end	Day	22% 3 12% 27% 25% 12%	3428
November	1st to 10th	Day	32% 4 9% 24% 26% 5%	1957
	11th to 20th	Day	36% 4 10% 22% 21% 8%	1861
	21st to end	Day	32% 5% 10% 24% 25% 4	1600
December	1st to 10th	Day	43% 7% 10% 21% 16% 4	1528
	11th to 20th	Day	34% 3 9% 25% 21% 8%	1906
	21st to end	Day	41% 6% 11% 25% 14% 2	2972
January	1st to 10th	Night	36% 5% 8% 23% 22% 5%	4109
	11th to 20th	Night	39% 4 7% 20% 24% 5%	4120
	21st to end	Night	46% 3 6% 23% 16% 6%	4532
February	1st to 10th	Night	38% 5% 11% 25% 18% 3	2470
	11th to 20th	Night	43% 3 8% 19% 20% 7%	2405
	21st to end	Night	41% 5% 10% 23% 16% 6%	1785
March	1st to 10th	Night	47% 6% 9% 18% 15% 4	3418
	11th to 20th	Night	31% 6% 7% 19% 28% 10%	3480
	21st to end	Night	38% 5% 9% 23% 19% 5%	3817
April	1st to 10th	Night	37% 6% 11% 18% 22% 6%	1957
	11th to 20th	Night	32% 6% 12% 23% 21% 6%	1875
	21st to end	Night	37% 8% 12% 22% 17% 4	1883
May	1st to 10th	Night	46% 8% 14% 19% 11% 2	2840
	11th to 20th	Night	47% 7% 10% 21% 12% 2	2813
	21st to end	Night	30% 9% 17% 26% 15% 3	3060
June	1st to 10th	Night	33% 11% 14% 26% 16% 1	1520
	11th to 20th	Night	36% 8% 18% 21% 16% 2	1520
	21st to end	Night	32% 11% 15% 21% 17% 4	1588
July	1st to 10th	Night	36% 12% 20% 17% 13% 3	2795
	11th to 20th	Night	40% 10% 21% 21% 7% 1	2786
	21st to end	Night	49% 10% 13% 19% 9%	2988
August	1st to 10th	Night	48% 9% 16% 20% 7%	2814
	11th to 20th	Night	38% 9% 17% 25% 11% 1	2844
	21st to end	Night	36% 7% 14% 32% 10% 2	3476
September	1st to 10th	Night	37% 8% 13% 19% 17% 6%	1900
	11th to 20th	Night	39% 8% 10% 20% 21% 2	2010
	21st to end	Night	49% 5% 8% 18% 16% 4	2136
October	1st to 10th	Night	39% 4 11% 18% 23% 5%	3800
	11th to 20th	Night	25% 4 7% 21% 29% 13%	3779
	21st to end	Night	20% 3 7% 31% 27% 13%	4120
November	1st to 10th	Night	36% 4 8% 20% 25% 7%	2341
	11th to 20th	Night	35% 5% 8% 19% 24% 9%	2530
	21st to end	Night	32% 5% 9% 25% 23% 7%	2800
December	1st to 10th	Night	43% 5% 7% 24% 17% 4	2686
	11th to 20th	Night	38% 4 9% 20% 21% 7%	3288
	21st to end	Night	40% 6% 10% 23% 17% 2	4678

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	27% 23% 31% 13% 4 1	270
	11th to 20th	Day	31% 23% 36% 9% 1	270
	21st to end	Day	28% 19% 39% 12% 2	297
February	1st to 10th	Day	23% 21% 40% 13% 3	270
	11th to 20th	Day	39% 24% 27% 7% 3	270
	21st to end	Day	33% 19% 30% 15% 3	366
March	1st to 10th	Day	25% 17% 34% 18% 5% 1	460
	11th to 20th	Day	22% 24% 31% 18% 4 1	460
	21st to end	Day	24% 16% 37% 16% 5% 1	506
April	1st to 10th	Day	22% 20% 31% 19% 7% 1	460
	11th to 20th	Day	20% 16% 29% 21% 10% 3	452
	21st to end	Day	22% 11% 35% 22% 9% 1	460
May	1st to 10th	Day	22% 12% 31% 23% 9% 3	463
	11th to 20th	Day	22% 9% 27% 24% 15% 4	487
	21st to end	Day	18% 6% 22% 28% 20% 7%	529
June	1st to 10th	Day	11% 6% 26% 30% 21% 6%	490
	11th to 20th	Day	11% 7% 23% 31% 20% 8%	490
	21st to end	Day	10% 5% 22% 34% 21% 7%	490
July	1st to 10th	Day	10% 3 18% 31% 27% 11%	485
	11th to 20th	Day	6% 2 17% 34% 29% 11%	484
	21st to end	Day	12% 3 20% 33% 22% 10%	532
August	1st to 10th	Day	15% 4 20% 26% 25% 11%	486
	11th to 20th	Day	11% 3 16% 31% 26% 12%	479
	21st to end	Day	10% 3 17% 29% 25% 17%	539
September	1st to 10th	Day	14% 4 15% 27% 23% 16%	490
	11th to 20th	Day	17% 4 15% 29% 23% 11%	490
	21st to end	Day	31% 6% 22% 24% 13% 4	490
October	1st to 10th	Day	19% 9% 20% 29% 17% 5%	490
	11th to 20th	Day	14% 13% 23% 27% 19% 3	490
	21st to end	Day	15% 12% 31% 29% 10% 4	539
November	1st to 10th	Day	16% 10% 32% 27% 11% 4	495
	11th to 20th	Day	19% 14% 33% 21% 13% 1	392
	21st to end	Day	23% 23% 25% 21% 8% 2	200
December	1st to 10th	Day	20% 26% 32% 15% 6% 1	182
	11th to 20th	Day	26% 16% 32% 22% 4 2	180
	21st to end	Day	29% 15% 33% 17% 5% 2	256
January	1st to 10th	Night	20% 18% 35% 23% 3	760
	11th to 20th	Night	20% 18% 34% 26% 2	760
	21st to end	Night	19% 16% 39% 24% 2	836
February	1st to 10th	Night	18% 15% 39% 25% 3	760
	11th to 20th	Night	25% 18% 38% 17% 1	743
	21st to end	Night	22% 15% 36% 23% 3	628
March	1st to 10th	Night	18% 17% 35% 26% 4	760
	11th to 20th	Night	24% 14% 34% 21% 7% 1	760
	21st to end	Night	19% 14% 37% 25% 5%	836
April	1st to 10th	Night	17% 18% 37% 23% 5%	760
	11th to 20th	Night	14% 14% 34% 28% 9% 1	751
	21st to end	Night	16% 8% 35% 33% 7% 1	743
May	1st to 10th	Night	16% 11% 32% 27% 12% 1	570
	11th to 20th	Night	21% 6% 24% 33% 14% 1	561
	21st to end	Night	16% 2 16% 36% 26% 3	603
June	1st to 10th	Night	9% 2 21% 41% 25% 2	380
	11th to 20th	Night	12% 2 17% 38% 27% 3	380
	21st to end	Night	7% 2 18% 47% 25% 2	448
July	1st to 10th	Night	12% 2 12% 37% 35% 4	555
	11th to 20th	Night	6% 1 11% 37% 39% 6%	552
	21st to end	Night	9% 2 15% 39% 30% 4	624
August	1st to 10th	Night	13% 3 12% 37% 31% 4	567
	11th to 20th	Night	13% 2 11% 38% 34% 3	583
	21st to end	Night	12% 2 12% 36% 33% 6%	836
September	1st to 10th	Night	14% 2 12% 34% 31% 7%	760
	11th to 20th	Night	17% 3 14% 34% 28% 5%	760
	21st to end	Night	27% 5% 18% 29% 20% 2	760
October	1st to 10th	Night	19% 5% 21% 26% 24% 5%	760
	11th to 20th	Night	15% 8% 25% 34% 17% 1	760
	21st to end	Night	16% 8% 28% 33% 14% 1	836
November	1st to 10th	Night	16% 8% 30% 31% 13% 2	780
	11th to 20th	Night	18% 11% 32% 28% 11%	800
	21st to end	Night	15% 11% 33% 30% 10% 1	800
December	1st to 10th	Night	23% 11% 34% 25% 7% 1	768
	11th to 20th	Night	19% 10% 36% 31% 5%	760
	21st to end	Night	22% 14% 30% 31% 4	836

Page generated at 2024-11-29 10:43:06. Version ac07

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