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 2024-02-10.

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 5% 5% 3 5% 5% 6% 8% 42%	78364
	Night	12% 6% 2 5% 5% 3 4 5% 5% 7% 45%	80595
Transparency	Day	40% 8% 12% 21% 15% 3	78085
	Night	38% 7% 12% 23% 17% 4	80393
Seeing	Day	18% 14% 24% 24% 14% 5%	13947
	Night	16% 11% 25% 31% 15% 2	23904

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% 5% 4 4 4 5% 6% 44%	2836
	11th to 20th	Day	13% 8% 3 6% 7% 3 5% 5% 5% 5% 40%	2840
	21st to end	Day	13% 9% 3 7% 6% 3 4 4 4 6% 40%	3124
February	1st to 10th	Day	11% 6% 3 7% 6% 3 6% 5% 5% 7% 42%	1701
	11th to 20th	Day	14% 7% 3 6% 5% 3 5% 5% 6% 6% 41%	1573
	21st to end	Day	14% 8% 3 5% 4 3 7% 4 5% 6% 41%	1544
March	1st to 10th	Day	12% 6% 2 4 4 3 4 4 5% 6% 51%	1980
	11th to 20th	Day	15% 7% 2 5% 4 4 5% 5% 7% 7% 39%	1980
	21st to end	Day	14% 8% 3 6% 6% 3 4 4 6% 7% 39%	2178
April	1st to 10th	Day	8% 6% 3 6% 4 4 5% 5% 6% 7% 48%	2100
	11th to 20th	Day	12% 5% 2 5% 4 3 5% 5% 5% 7% 47%	2134
	21st to end	Day	15% 6% 2 5% 5% 3 5% 4 5% 7% 42%	2232
May	1st to 10th	Day	14% 6% 3 5% 6% 4 5% 5% 7% 8% 37%	2340
	11th to 20th	Day	17% 7% 3 6% 5% 4 5% 5% 6% 8% 35%	2301
	21st to end	Day	14% 6% 2 5% 5% 4 5% 5% 6% 8% 39%	2592
June	1st to 10th	Day	11% 4 2 4 5% 4 6% 6% 6% 10% 43%	2520
	11th to 20th	Day	9% 5% 2 5% 6% 4 5% 7% 7% 11% 37%	2520
	21st to end	Day	7% 4 2 5% 7% 3 6% 6% 7% 11% 43%	2513
July	1st to 10th	Day	11% 5% 2 6% 6% 3 6% 6% 7% 9% 38%	2340
	11th to 20th	Day	6% 3 2 5% 6% 4 7% 8% 9% 12% 38%	2340
	21st to end	Day	10% 6% 2 6% 6% 5% 7% 7% 8% 10% 34%	2547
August	1st to 10th	Day	9% 6% 3 6% 7% 5% 7% 7% 7% 10% 34%	2327
	11th to 20th	Day	12% 6% 2 6% 7% 4 6% 7% 7% 10% 35%	2292
	21st to end	Day	11% 4 2 5% 5% 4 6% 6% 8% 9% 40%	2376
September	1st to 10th	Day	13% 6% 2 5% 5% 4 4 4 5% 5% 47%	2160
	11th to 20th	Day	12% 7% 3 5% 5% 4 4 4 5% 7% 44%	2040
	21st to end	Day	20% 6% 2 4 4 3 5% 4 6% 7% 39%	1944
October	1st to 10th	Day	15% 5% 2 5% 4 3 4 4 5% 6% 47%	1800
	11th to 20th	Day	15% 5% 2 5% 4 3 4 4 5% 6% 49%	1800
	21st to end	Day	12% 6% 2 5% 4 2 4 4 4 6% 51%	1980
November	1st to 10th	Day	11% 5% 2 4 4 2 4 3 4 6% 55%	1857
	11th to 20th	Day	11% 5% 3 4 4 3 4 5% 5% 6% 50%	1699
	21st to end	Day	12% 4 2 5% 5% 2 3 5% 4 7% 50%	1520
December	1st to 10th	Day	13% 7% 3 5% 6% 3 6% 5% 5% 6% 40%	1520
	11th to 20th	Day	13% 4 2 4 3 2 3 4 4 7% 53%	1910
	21st to end	Day	16% 7% 2 5% 5% 3 5% 6% 6% 8% 36%	2904
January	1st to 10th	Night	10% 7% 2 5% 5% 3 4 5% 5% 8% 47%	4109
	11th to 20th	Night	13% 8% 2 5% 4 3 4 4 4 6% 47%	4120
	21st to end	Night	14% 9% 3 6% 5% 3 4 4 4 6% 42%	4532
February	1st to 10th	Night	10% 7% 3 5% 4 3 5% 6% 5% 8% 45%	2464
	11th to 20th	Night	16% 7% 2 5% 4 3 5% 4 6% 6% 41%	2273
	21st to end	Night	13% 7% 2 5% 5% 2 4 5% 6% 8% 42%	1705
March	1st to 10th	Night	11% 5% 2 4 4 3 4 5% 5% 6% 52%	1980
	11th to 20th	Night	16% 6% 3 5% 4 3 5% 4 6% 6% 42%	1980
	21st to end	Night	14% 7% 3 5% 5% 3 4 4 5% 7% 43%	2178
April	1st to 10th	Night	11% 6% 3 6% 5% 3 4 5% 5% 8% 44%	1859
	11th to 20th	Night	10% 5% 2 4 4 3 4 5% 6% 8% 48%	1775
	21st to end	Night	16% 4 2 4 5% 3 4 5% 5% 7% 46%	1742
May	1st to 10th	Night	13% 6% 2 4 5% 4 4 5% 5% 8% 44%	1620
	11th to 20th	Night	16% 6% 3 5% 5% 3 5% 5% 6% 8% 38%	1592
	21st to end	Night	13% 4 2 5% 5% 3 5% 5% 6% 9% 42%	1678
June	1st to 10th	Night	10% 4 2 5% 4 3 4 5% 7% 11% 45%	1440
	11th to 20th	Night	9% 4 3 6% 5% 3 6% 5% 6% 8% 45%	1440
	21st to end	Night	8% 3 2 3 5% 3 5% 5% 6% 11% 48%	1441
July	1st to 10th	Night	9% 6% 3 6% 5% 3 5% 5% 7% 8% 44%	1620
	11th to 20th	Night	5% 3 1 4 6% 4 5% 6% 8% 12% 46%	1620
	21st to end	Night	7% 4 2 4 6% 3 7% 6% 8% 11% 42%	1771
August	1st to 10th	Night	9% 5% 2 6% 5% 4 5% 5% 8% 11% 39%	1611
	11th to 20th	Night	10% 6% 3 6% 5% 4 5% 6% 7% 8% 41%	1598
	21st to end	Night	10% 6% 2 6% 6% 3 5% 6% 7% 11% 39%	1970
September	1st to 10th	Night	12% 4 2 5% 5% 2 4 5% 5% 8% 49%	1800
	11th to 20th	Night	12% 6% 2 5% 4 3 4 4 5% 7% 47%	1916
	21st to end	Night	20% 7% 2 4 5% 2 4 4 4 6% 42%	2016
October	1st to 10th	Night	16% 5% 2 5% 4 3 4 3 5% 6% 47%	2160
	11th to 20th	Night	13% 5% 2 5% 4 2 4 4 5% 6% 50%	2160
	21st to end	Night	12% 4 2 5% 5% 3 3 4 4 7% 51%	2376
November	1st to 10th	Night	10% 6% 3 4 5% 2 3 4 4 5% 54%	2221
	11th to 20th	Night	11% 5% 2 4 5% 2 4 4 5% 6% 51%	2476
	21st to end	Night	12% 5% 2 4 5% 3 5% 4 5% 6% 50%	2660
December	1st to 10th	Night	13% 7% 3 5% 5% 4 5% 5% 5% 6% 43%	2660
	11th to 20th	Night	13% 6% 3 5% 5% 3 5% 4 5% 6% 46%	3285
	21st to end	Night	14% 6% 3 5% 5% 3 5% 6% 6% 8% 39%	4747

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% 4 10% 25% 16% 6%	2837
	11th to 20th	Day	45% 4 9% 18% 18% 6%	2840
	21st to end	Day	46% 5% 8% 22% 17% 3	3124
February	1st to 10th	Day	43% 6% 10% 22% 16% 3	1701
	11th to 20th	Day	42% 7% 10% 20% 17% 4	1582
	21st to end	Day	43% 7% 11% 17% 17% 6%	1544
March	1st to 10th	Day	36% 5% 11% 22% 22% 4	1980
	11th to 20th	Day	43% 8% 10% 17% 17% 6%	1980
	21st to end	Day	45% 8% 10% 20% 13% 5%	2178
April	1st to 10th	Day	35% 7% 11% 21% 18% 7%	2100
	11th to 20th	Day	36% 7% 11% 21% 20% 5%	2134
	21st to end	Day	44% 6% 12% 21% 13% 4	2232
May	1st to 10th	Day	43% 10% 15% 17% 13% 2	2340
	11th to 20th	Day	47% 9% 15% 19% 8% 2	2305
	21st to end	Day	42% 10% 15% 22% 10% 1	2592
June	1st to 10th	Day	37% 10% 15% 24% 13% 1	2520
	11th to 20th	Day	39% 12% 15% 19% 13% 2	2520
	21st to end	Day	33% 12% 17% 25% 12% 1	2513
July	1st to 10th	Day	40% 12% 13% 20% 13% 2	2275
	11th to 20th	Day	33% 14% 19% 21% 12% 1	2271
	21st to end	Day	41% 12% 13% 20% 12% 1	2405
August	1st to 10th	Day	42% 12% 17% 21% 8%	2314
	11th to 20th	Day	42% 12% 14% 21% 10% 1	2292
	21st to end	Day	38% 11% 19% 21% 10% 2	2376
September	1st to 10th	Day	39% 8% 15% 18% 18% 4	2160
	11th to 20th	Day	39% 7% 9% 24% 18% 3	2040
	21st to end	Day	45% 7% 10% 18% 17% 2	1944
October	1st to 10th	Day	38% 7% 11% 25% 15% 5%	1800
	11th to 20th	Day	36% 6% 11% 24% 20% 4	1800
	21st to end	Day	35% 5% 9% 26% 20% 6%	1980
November	1st to 10th	Day	32% 4 9% 24% 26% 5%	1857
	11th to 20th	Day	35% 6% 10% 20% 22% 8%	1699
	21st to end	Day	34% 5% 11% 24% 22% 3	1520
December	1st to 10th	Day	43% 7% 12% 20% 15% 3	1520
	11th to 20th	Day	33% 5% 9% 27% 19% 7%	1906
	21st to end	Day	43% 7% 13% 23% 13% 2	2904
January	1st to 10th	Night	35% 5% 11% 24% 22% 4	4109
	11th to 20th	Night	38% 5% 10% 22% 20% 5%	4120
	21st to end	Night	44% 5% 7% 23% 17% 4	4532
February	1st to 10th	Night	38% 8% 12% 24% 17% 2	2464
	11th to 20th	Night	44% 5% 9% 19% 16% 6%	2275
	21st to end	Night	40% 7% 12% 22% 14% 6%	1705
March	1st to 10th	Night	33% 7% 11% 25% 19% 5%	1980
	11th to 20th	Night	41% 7% 10% 21% 18% 3	1980
	21st to end	Night	41% 7% 12% 19% 16% 5%	2178
April	1st to 10th	Night	38% 8% 11% 19% 19% 5%	1859
	11th to 20th	Night	33% 8% 15% 19% 21% 5%	1775
	21st to end	Night	38% 6% 12% 25% 15% 3	1742
May	1st to 10th	Night	39% 9% 15% 21% 12% 3	1620
	11th to 20th	Night	44% 10% 15% 21% 10% 1	1593
	21st to end	Night	37% 12% 16% 25% 9% 1	1679
June	1st to 10th	Night	33% 10% 15% 29% 13%	1440
	11th to 20th	Night	35% 11% 18% 22% 12% 2	1440
	21st to end	Night	31% 11% 18% 21% 17% 2	1441
July	1st to 10th	Night	36% 11% 15% 21% 14% 3	1575
	11th to 20th	Night	28% 12% 20% 26% 12% 1	1566
	21st to end	Night	32% 12% 19% 26% 11%	1672
August	1st to 10th	Night	36% 13% 18% 23% 10% 1	1600
	11th to 20th	Night	38% 12% 14% 23% 12% 1	1598
	21st to end	Night	38% 11% 17% 22% 9% 3	1970
September	1st to 10th	Night	34% 9% 15% 20% 17% 4	1800
	11th to 20th	Night	36% 7% 12% 25% 18% 3	1916
	21st to end	Night	44% 7% 11% 20% 17% 3	2016
October	1st to 10th	Night	39% 6% 12% 24% 17% 3	2160
	11th to 20th	Night	35% 5% 10% 25% 21% 4	2160
	21st to end	Night	33% 5% 10% 23% 25% 5%	2376
November	1st to 10th	Night	34% 5% 9% 21% 24% 7%	2221
	11th to 20th	Night	34% 5% 8% 22% 24% 6%	2476
	21st to end	Night	36% 5% 10% 24% 21% 5%	2660
December	1st to 10th	Night	42% 6% 10% 23% 15% 4	2660
	11th to 20th	Night	39% 5% 9% 22% 20% 6%	3288
	21st to end	Night	40% 6% 12% 22% 18% 2	4747

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% 34% 24% 14% 3	270
	11th to 20th	Day	30% 31% 25% 12% 1	270
	21st to end	Day	26% 28% 32% 13% 1	297
February	1st to 10th	Day	23% 31% 32% 13% 1	267
	11th to 20th	Day	37% 29% 28% 6%	240
	21st to end	Day	32% 23% 25% 17% 4	307
March	1st to 10th	Day	20% 28% 29% 18% 5%	420
	11th to 20th	Day	24% 25% 27% 18% 4 2	420
	21st to end	Day	22% 21% 31% 20% 6% 1	462
April	1st to 10th	Day	21% 24% 25% 19% 10%	420
	11th to 20th	Day	20% 16% 26% 21% 13% 3	412
	21st to end	Day	23% 18% 29% 18% 9% 2	420
May	1st to 10th	Day	20% 21% 28% 21% 7% 4	423
	11th to 20th	Day	21% 11% 28% 23% 13% 4	447
	21st to end	Day	19% 6% 20% 27% 20% 8%	485
June	1st to 10th	Day	13% 7% 28% 27% 19% 6%	450
	11th to 20th	Day	12% 9% 24% 28% 17% 9%	450
	21st to end	Day	9% 6% 29% 32% 18% 6%	450
July	1st to 10th	Day	11% 4 17% 30% 28% 10%	445
	11th to 20th	Day	4 2 19% 36% 27% 12%	444
	21st to end	Day	10% 4 19% 32% 24% 11%	488
August	1st to 10th	Day	11% 5% 18% 28% 26% 12%	446
	11th to 20th	Day	13% 4 19% 25% 27% 13%	439
	21st to end	Day	11% 4 14% 33% 22% 16%	495
September	1st to 10th	Day	14% 5% 17% 25% 22% 16%	450
	11th to 20th	Day	14% 5% 15% 29% 27% 10%	450
	21st to end	Day	26% 9% 18% 23% 18% 5%	450
October	1st to 10th	Day	19% 7% 22% 28% 20% 5%	450
	11th to 20th	Day	17% 14% 24% 25% 17% 3	450
	21st to end	Day	17% 15% 32% 23% 10% 3	495
November	1st to 10th	Day	16% 13% 27% 28% 12% 3	455
	11th to 20th	Day	21% 15% 28% 24% 11% 1	304
	21st to end	Day	21% 18% 33% 21% 7% 1	180
December	1st to 10th	Day	23% 22% 35% 14% 5% 1	180
	11th to 20th	Day	23% 22% 26% 21% 8% 1	180
	21st to end	Day	20% 25% 32% 16% 6%	236
January	1st to 10th	Night	18% 21% 35% 22% 3	760
	11th to 20th	Night	19% 20% 30% 28% 3	760
	21st to end	Night	17% 20% 37% 24% 2	836
February	1st to 10th	Night	16% 20% 32% 29% 3	759
	11th to 20th	Night	24% 21% 35% 19% 1	703
	21st to end	Night	21% 17% 37% 22% 3	592
March	1st to 10th	Night	16% 20% 33% 27% 3	720
	11th to 20th	Night	24% 18% 30% 21% 6% 1	720
	21st to end	Night	20% 14% 32% 28% 6% 1	792
April	1st to 10th	Night	16% 19% 34% 25% 5%	720
	11th to 20th	Night	14% 16% 30% 28% 12% 1	711
	21st to end	Night	19% 9% 31% 32% 8% 1	662
May	1st to 10th	Night	18% 9% 27% 31% 14% 1	540
	11th to 20th	Night	19% 6% 23% 37% 15% 1	531
	21st to end	Night	15% 1 16% 40% 25% 3	518
June	1st to 10th	Night	10% 1 18% 48% 21% 2	360
	11th to 20th	Night	10% 3 17% 43% 26% 2	360
	21st to end	Night	7% 4 19% 45% 22% 2	361
July	1st to 10th	Night	10% 3 12% 34% 35% 6%	525
	11th to 20th	Night	5% 1 8% 38% 41% 7%	522
	21st to end	Night	6% 3 14% 39% 33% 6%	591
August	1st to 10th	Night	11% 2 10% 38% 35% 4	537
	11th to 20th	Night	13% 3 11% 37% 33% 4	534
	21st to end	Night	13% 2 12% 34% 35% 4	782
September	1st to 10th	Night	14% 3 10% 35% 32% 5%	720
	11th to 20th	Night	14% 3 14% 33% 31% 5%	720
	21st to end	Night	23% 4 19% 31% 20% 2	720
October	1st to 10th	Night	18% 6% 17% 33% 22% 4	720
	11th to 20th	Night	16% 11% 25% 32% 15% 1	720
	21st to end	Night	16% 11% 27% 33% 12% 1	792
November	1st to 10th	Night	15% 9% 26% 34% 13% 2	740
	11th to 20th	Night	15% 14% 29% 32% 9% 1	760
	21st to end	Night	15% 16% 27% 32% 9% 1	760
December	1st to 10th	Night	19% 15% 32% 27% 6%	760
	11th to 20th	Night	15% 14% 32% 33% 6%	760
	21st to end	Night	17% 14% 31% 34% 4	836

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