Staunton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Staunton clear sky chart from 2005-11-06 to 2025-03-12.

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	12% 6% 2 6% 5% 5% 5% 4 6% 8% 42%	108741
	Night	12% 6% 2 5% 4 4 4 4 6% 7% 46%	110260
Transparency	Day	38% 8% 12% 22% 16% 4	112391
	Night	36% 7% 12% 23% 18% 4	114749
Seeing	Day	18% 14% 25% 24% 14% 5%	15376
	Night	16% 11% 25% 31% 14% 2	25339

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	12% 6% 2 5% 4 5% 4 3 5% 5% 49%	4056
	11th to 20th	Day	12% 7% 2 6% 4 4 4 3 4 4 50%	4060
	21st to end	Day	12% 8% 3 6% 4 3 4 3 4 6% 47%	4466
February	1st to 10th	Day	11% 7% 2 8% 5% 4 5% 4 5% 7% 42%	1800
	11th to 20th	Day	15% 7% 3 7% 4 4 4 4 6% 7% 41%	1753
	21st to end	Day	14% 8% 3 6% 3 5% 5% 3 5% 6% 42%	1722
March	1st to 10th	Day	16% 10% 3 7% 4 5% 3 3 5% 6% 37%	3545
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 6% 7% 51%	3491
	21st to end	Day	14% 9% 3 7% 5% 5% 4 4 5% 6% 38%	3815
April	1st to 10th	Day	8% 7% 2 6% 4 5% 5% 4 6% 7% 47%	2217
	11th to 20th	Day	12% 6% 2 5% 4 4 4 4 6% 8% 46%	2254
	21st to end	Day	14% 7% 2 6% 5% 4 4 3 5% 6% 42%	2356
May	1st to 10th	Day	15% 6% 3 8% 6% 6% 6% 5% 8% 8% 31%	4082
	11th to 20th	Day	20% 8% 3 7% 4 5% 4 4 5% 7% 34%	4081
	21st to end	Day	9% 5% 2 6% 4 5% 5% 4 7% 10% 43%	4592
June	1st to 10th	Day	11% 4 2 5% 5% 6% 5% 5% 6% 10% 42%	2660
	11th to 20th	Day	9% 6% 2 6% 6% 5% 6% 5% 7% 10% 38%	2660
	21st to end	Day	7% 4 2 5% 6% 4 5% 5% 7% 11% 43%	2652
July	1st to 10th	Day	7% 4 2 5% 5% 5% 6% 5% 9% 10% 42%	4120
	11th to 20th	Day	9% 4 2 6% 5% 5% 6% 5% 8% 12% 37%	4120
	21st to end	Day	12% 7% 3 9% 6% 7% 6% 5% 7% 9% 30%	4466
August	1st to 10th	Day	12% 5% 2 7% 6% 6% 6% 5% 9% 10% 34%	4104
	11th to 20th	Day	9% 4 2 6% 6% 5% 6% 5% 7% 10% 39%	4019
	21st to end	Day	9% 3 2 5% 4 4 5% 4 7% 9% 47%	4180
September	1st to 10th	Day	12% 6% 2 6% 4 5% 4 3 5% 5% 48%	2280
	11th to 20th	Day	12% 8% 2 6% 4 5% 4 3 5% 7% 44%	2153
	21st to end	Day	22% 6% 2 5% 4 3 4 4 6% 6% 37%	2051
October	1st to 10th	Day	15% 5% 2 6% 3 4 4 3 4 6% 48%	1900
	11th to 20th	Day	14% 5% 2 5% 3 3 3 3 5% 6% 51%	1900
	21st to end	Day	11% 6% 2 5% 3 3 4 4 4 6% 52%	2090
November	1st to 10th	Day	11% 5% 2 4 3 3 4 3 5% 6% 55%	1957
	11th to 20th	Day	12% 5% 2 5% 3 4 4 3 6% 6% 50%	1787
	21st to end	Day	11% 5% 2 6% 4 3 3 4 5% 7% 49%	1600
December	1st to 10th	Day	9% 5% 2 4 4 4 4 4 5% 6% 53%	2600
	11th to 20th	Day	17% 6% 2 4 3 3 3 3 5% 7% 46%	2990
	21st to end	Day	17% 7% 2 6% 4 4 5% 4 5% 8% 37%	4162
January	1st to 10th	Night	9% 6% 2 5% 4 3 4 4 5% 6% 53%	5889
	11th to 20th	Night	11% 7% 2 5% 3 3 3 3 4 5% 54%	5900
	21st to end	Night	12% 7% 2 5% 3 3 3 3 4 5% 51%	6490
February	1st to 10th	Night	10% 8% 3 5% 4 4 4 4 6% 7% 44%	2600
	11th to 20th	Night	17% 8% 2 6% 4 4 4 3 5% 6% 41%	2533
	21st to end	Night	12% 8% 2 5% 5% 3 5% 4 6% 7% 43%	1901
March	1st to 10th	Night	18% 8% 3 6% 4 4 4 4 5% 6% 37%	3528
	11th to 20th	Night	10% 6% 2 5% 4 3 4 4 6% 7% 50%	3498
	21st to end	Night	14% 7% 2 5% 4 3 3 3 5% 6% 47%	3817
April	1st to 10th	Night	11% 6% 3 6% 5% 4 4 4 5% 8% 43%	1962
	11th to 20th	Night	10% 5% 2 5% 4 4 4 4 6% 8% 48%	1875
	21st to end	Night	15% 4 2 5% 4 4 5% 3 5% 6% 45%	1838
May	1st to 10th	Night	16% 7% 3 6% 5% 5% 4 5% 6% 8% 35%	2813
	11th to 20th	Night	22% 8% 3 5% 4 3 4 3 6% 6% 35%	2812
	21st to end	Night	9% 4 2 6% 4 4 5% 4 7% 10% 44%	2958
June	1st to 10th	Night	10% 5% 2 6% 4 4 4 3 7% 11% 45%	1520
	11th to 20th	Night	8% 4 2 7% 4 4 5% 5% 7% 9% 45%	1520
	21st to end	Night	8% 4 2 3 5% 4 5% 4 7% 11% 48%	1522
July	1st to 10th	Night	6% 4 2 5% 4 4 6% 5% 8% 10% 47%	2840
	11th to 20th	Night	8% 5% 2 6% 5% 6% 6% 5% 8% 10% 38%	2840
	21st to end	Night	11% 7% 3 8% 6% 6% 6% 4 7% 8% 34%	3087
August	1st to 10th	Night	14% 5% 2 6% 4 5% 5% 4 8% 10% 36%	2825
	11th to 20th	Night	9% 5% 3 8% 5% 5% 5% 5% 8% 8% 39%	2785
	21st to end	Night	10% 5% 2 6% 4 4 4 4 6% 9% 46%	3466
September	1st to 10th	Night	12% 5% 2 6% 4 3 4 4 5% 7% 49%	1900
	11th to 20th	Night	13% 6% 2 5% 4 4 5% 3 5% 7% 46%	2023
	21st to end	Night	21% 7% 2 5% 4 3 4 3 5% 5% 41%	2128
October	1st to 10th	Night	17% 5% 2 5% 4 4 4 2 5% 6% 47%	2280
	11th to 20th	Night	12% 5% 2 5% 3 4 4 3 5% 6% 51%	2280
	21st to end	Night	12% 4 2 5% 4 3 3 3 4 7% 53%	2508
November	1st to 10th	Night	10% 7% 2 5% 4 3 3 3 5% 5% 53%	2341
	11th to 20th	Night	11% 6% 2 5% 4 4 3 3 5% 6% 51%	2607
	21st to end	Night	11% 6% 2 5% 4 4 5% 3 5% 6% 50%	2800
December	1st to 10th	Night	8% 5% 2 5% 3 4 4 4 6% 6% 54%	4580
	11th to 20th	Night	15% 7% 2 5% 4 4 5% 4 5% 5% 42%	5205
	21st to end	Night	14% 7% 2 5% 4 4 5% 4 6% 8% 40%	6789

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% 3 8% 22% 22% 10%	4057
	11th to 20th	Day	37% 3 7% 17% 22% 12%	4060
	21st to end	Day	40% 4 7% 24% 21% 5%	4466
February	1st to 10th	Day	43% 6% 10% 22% 16% 3	1800
	11th to 20th	Day	42% 7% 10% 20% 17% 4	1762
	21st to end	Day	43% 7% 10% 18% 17% 6%	1722
March	1st to 10th	Day	47% 6% 9% 19% 13% 6%	3545
	11th to 20th	Day	31% 6% 9% 27% 20% 7%	3491
	21st to end	Day	46% 8% 9% 19% 14% 3	3815
April	1st to 10th	Day	35% 7% 11% 21% 18% 7%	2217
	11th to 20th	Day	36% 7% 12% 21% 20% 5%	2254
	21st to end	Day	43% 7% 12% 22% 13% 4	2356
May	1st to 10th	Day	47% 10% 13% 19% 10% 1	4120
	11th to 20th	Day	48% 8% 12% 21% 9% 1	4085
	21st to end	Day	32% 12% 17% 20% 17% 3	4606
June	1st to 10th	Day	37% 10% 15% 24% 13% 1	2660
	11th to 20th	Day	38% 12% 15% 20% 13% 1	2660
	21st to end	Day	33% 12% 17% 25% 13% 1	2652
July	1st to 10th	Day	33% 12% 20% 20% 9% 5%	4055
	11th to 20th	Day	36% 11% 19% 25% 8% 1	4051
	21st to end	Day	48% 10% 12% 19% 10% 1	4324
August	1st to 10th	Day	42% 10% 19% 22% 6%	4091
	11th to 20th	Day	36% 11% 14% 27% 11% 1	4058
	21st to end	Day	31% 10% 19% 26% 12% 1	4180
September	1st to 10th	Day	38% 8% 14% 17% 19% 4	2280
	11th to 20th	Day	40% 7% 9% 24% 18% 3	2153
	21st to end	Day	46% 7% 10% 18% 16% 2	2051
October	1st to 10th	Day	31% 5% 9% 20% 29% 6%	3160
	11th to 20th	Day	25% 4 9% 26% 23% 14%	3140
	21st to end	Day	21% 4 10% 31% 21% 13%	3428
November	1st to 10th	Day	32% 4 10% 24% 25% 4	1957
	11th to 20th	Day	34% 6% 10% 19% 22% 8%	1787
	21st to end	Day	35% 5% 11% 24% 22% 3	1600
December	1st to 10th	Day	32% 6% 11% 25% 20% 7%	2600
	11th to 20th	Day	38% 5% 13% 22% 17% 5%	2986
	21st to end	Day	44% 7% 14% 20% 15% 1	4162
January	1st to 10th	Night	31% 4 9% 22% 24% 10%	5889
	11th to 20th	Night	33% 4 8% 22% 24% 10%	5900
	21st to end	Night	37% 4 7% 26% 22% 5%	6490
February	1st to 10th	Night	38% 7% 11% 24% 16% 2	2600
	11th to 20th	Night	44% 5% 9% 19% 17% 6%	2535
	21st to end	Night	39% 7% 12% 22% 14% 6%	1901
March	1st to 10th	Night	46% 6% 10% 20% 13% 4	3528
	11th to 20th	Night	31% 5% 8% 25% 26% 5%	3498
	21st to end	Night	38% 6% 11% 22% 19% 4	3817
April	1st to 10th	Night	38% 8% 11% 19% 19% 5%	1962
	11th to 20th	Night	32% 8% 15% 20% 20% 5%	1875
	21st to end	Night	38% 7% 12% 25% 15% 3	1838
May	1st to 10th	Night	45% 10% 13% 19% 11% 2	2840
	11th to 20th	Night	48% 8% 12% 23% 8% 1	2813
	21st to end	Night	32% 12% 18% 25% 11% 3	2965
June	1st to 10th	Night	33% 10% 14% 28% 13% 1	1520
	11th to 20th	Night	34% 11% 18% 24% 12% 2	1520
	21st to end	Night	31% 11% 18% 21% 17% 2	1522
July	1st to 10th	Night	31% 12% 22% 19% 13% 3	2795
	11th to 20th	Night	37% 12% 19% 23% 9% 1	2786
	21st to end	Night	45% 12% 16% 20% 8%	2988
August	1st to 10th	Night	41% 10% 18% 24% 6% 1	2814
	11th to 20th	Night	39% 11% 15% 24% 11%	2812
	21st to end	Night	32% 9% 17% 31% 8% 2	3466
September	1st to 10th	Night	35% 9% 14% 20% 17% 5%	1900
	11th to 20th	Night	37% 7% 11% 25% 18% 3	2023
	21st to end	Night	45% 7% 10% 19% 16% 3	2128
October	1st to 10th	Night	40% 6% 11% 19% 19% 5%	3800
	11th to 20th	Night	25% 4 9% 22% 30% 9%	3779
	21st to end	Night	20% 3 10% 30% 28% 8%	4120
November	1st to 10th	Night	34% 5% 9% 22% 24% 6%	2341
	11th to 20th	Night	35% 5% 8% 21% 24% 6%	2607
	21st to end	Night	35% 5% 10% 24% 21% 5%	2800
December	1st to 10th	Night	30% 5% 12% 28% 23% 3	4580
	11th to 20th	Night	43% 5% 12% 18% 17% 6%	5208
	21st to end	Night	39% 6% 13% 22% 18% 1	6789

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% 36% 24% 13% 3	300
	11th to 20th	Day	28% 32% 26% 12% 2	300
	21st to end	Day	25% 29% 32% 13% 1	330
February	1st to 10th	Day	24% 31% 31% 12% 1	300
	11th to 20th	Day	40% 28% 25% 7%	300
	21st to end	Day	29% 23% 26% 18% 4	371
March	1st to 10th	Day	21% 27% 28% 19% 5%	500
	11th to 20th	Day	24% 25% 28% 17% 4 2	464
	21st to end	Day	22% 21% 31% 21% 5% 1	506
April	1st to 10th	Day	22% 25% 26% 18% 9%	460
	11th to 20th	Day	20% 17% 27% 21% 12% 3	452
	21st to end	Day	22% 18% 30% 19% 9% 2	460
May	1st to 10th	Day	19% 21% 28% 20% 8% 4	463
	11th to 20th	Day	22% 12% 26% 22% 14% 4	487
	21st to end	Day	18% 8% 22% 26% 19% 7%	529
June	1st to 10th	Day	12% 8% 28% 27% 18% 7%	490
	11th to 20th	Day	11% 8% 24% 29% 17% 10%	490
	21st to end	Day	8% 6% 29% 32% 18% 6%	490
July	1st to 10th	Day	11% 4 17% 30% 28% 10%	485
	11th to 20th	Day	5% 2 19% 36% 27% 11%	484
	21st to end	Day	10% 4 20% 31% 25% 10%	532
August	1st to 10th	Day	12% 5% 19% 27% 26% 12%	486
	11th to 20th	Day	11% 4 20% 26% 26% 12%	479
	21st to end	Day	10% 3 13% 34% 23% 17%	539
September	1st to 10th	Day	13% 5% 17% 26% 23% 16%	490
	11th to 20th	Day	14% 5% 15% 28% 27% 10%	490
	21st to end	Day	27% 10% 19% 23% 17% 4	490
October	1st to 10th	Day	19% 6% 22% 30% 19% 4	490
	11th to 20th	Day	16% 15% 24% 25% 17% 4	490
	21st to end	Day	15% 14% 31% 25% 12% 3	539
November	1st to 10th	Day	16% 13% 28% 29% 12% 3	495
	11th to 20th	Day	20% 14% 30% 25% 10% 1	332
	21st to end	Day	20% 21% 33% 20% 6% 1	200
December	1st to 10th	Day	22% 24% 35% 14% 6% 1	200
	11th to 20th	Day	23% 21% 26% 21% 9% 1	200
	21st to end	Day	20% 24% 32% 17% 7%	263
January	1st to 10th	Night	18% 21% 36% 22% 3	800
	11th to 20th	Night	18% 20% 31% 27% 3	800
	21st to end	Night	17% 19% 39% 24% 2	880
February	1st to 10th	Night	16% 19% 34% 28% 3	800
	11th to 20th	Night	24% 21% 35% 19% 1	783
	21st to end	Night	20% 17% 38% 23% 3	660
March	1st to 10th	Night	17% 19% 33% 27% 4	800
	11th to 20th	Night	23% 19% 29% 21% 6% 1	767
	21st to end	Night	20% 15% 32% 27% 5% 1	836
April	1st to 10th	Night	16% 20% 34% 24% 5%	760
	11th to 20th	Night	14% 16% 31% 28% 12% 1	751
	21st to end	Night	18% 10% 31% 32% 8% 1	698
May	1st to 10th	Night	18% 9% 26% 31% 14% 1	570
	11th to 20th	Night	19% 7% 23% 36% 15% 1	561
	21st to end	Night	15% 2 17% 39% 25% 2	547
June	1st to 10th	Night	10% 1 19% 48% 21% 2	380
	11th to 20th	Night	9% 3 17% 44% 25% 2	380
	21st to end	Night	7% 4 19% 46% 22% 2	382
July	1st to 10th	Night	10% 3 12% 35% 35% 5%	555
	11th to 20th	Night	5% 1 8% 38% 41% 7%	552
	21st to end	Night	7% 3 13% 40% 31% 6%	624
August	1st to 10th	Night	11% 2 10% 38% 35% 4	567
	11th to 20th	Night	12% 3 11% 39% 32% 4	564
	21st to end	Night	13% 2 11% 34% 36% 4	826
September	1st to 10th	Night	14% 3 10% 36% 32% 5%	760
	11th to 20th	Night	15% 3 13% 33% 31% 5%	760
	21st to end	Night	24% 5% 18% 31% 19% 2	760
October	1st to 10th	Night	18% 6% 17% 33% 22% 4	760
	11th to 20th	Night	15% 11% 25% 33% 15% 1	760
	21st to end	Night	15% 11% 26% 34% 13% 2	836
November	1st to 10th	Night	14% 9% 26% 36% 13% 2	780
	11th to 20th	Night	15% 14% 28% 33% 9% 1	800
	21st to end	Night	15% 16% 29% 31% 8% 1	800
December	1st to 10th	Night	19% 14% 34% 27% 6%	800
	11th to 20th	Night	16% 14% 31% 33% 6%	800
	21st to end	Night	17% 14% 30% 35% 4	880

Page generated at 2025-03-09 08:08:48. Version ac07

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