Benton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Benton clear sky chart from 2005-11-06 to 2024-01-12.

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	13% 7% 3 6% 6% 3 5% 5% 6% 8% 39%	74855
	Night	13% 7% 3 5% 5% 3 4 5% 5% 7% 42%	74869
Transparency	Day	42% 9% 11% 19% 16% 3	74578
	Night	40% 7% 11% 20% 17% 4	74665
Seeing	Day	17% 12% 23% 23% 18% 8%	13658
	Night	16% 10% 23% 29% 19% 3	23756

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	17% 9% 4 6% 6% 2 4 4 4 6% 39%	1706
	11th to 20th	Day	18% 11% 4 8% 5% 3 3 4 4 5% 35%	1629
	21st to end	Day	15% 9% 3 5% 5% 2 5% 4 4 7% 42%	1839
February	1st to 10th	Day	18% 10% 4 7% 5% 3 4 4 5% 6% 34%	1800
	11th to 20th	Day	22% 9% 3 7% 5% 3 3 4 5% 6% 33%	1748
	21st to end	Day	22% 10% 3 6% 5% 2 3 4 5% 5% 35%	1480
March	1st to 10th	Day	15% 7% 3 5% 5% 3 5% 4 5% 6% 41%	1823
	11th to 20th	Day	19% 7% 3 7% 6% 4 5% 4 5% 6% 34%	1980
	21st to end	Day	16% 9% 4 5% 5% 3 4 5% 5% 7% 36%	2178
April	1st to 10th	Day	11% 6% 2 4 5% 3 6% 6% 6% 7% 42%	2085
	11th to 20th	Day	14% 6% 3 6% 5% 2 4 4 5% 7% 44%	2134
	21st to end	Day	12% 6% 3 5% 5% 3 5% 5% 5% 7% 42%	2304
May	1st to 10th	Day	12% 5% 2 5% 5% 3 6% 4 6% 7% 44%	2340
	11th to 20th	Day	13% 5% 3 6% 6% 5% 6% 6% 6% 7% 38%	2301
	21st to end	Day	9% 5% 2 6% 6% 4 7% 6% 7% 8% 39%	2531
June	1st to 10th	Day	8% 6% 2 6% 6% 4 7% 6% 7% 10% 37%	2340
	11th to 20th	Day	5% 4 2 6% 6% 4 6% 7% 8% 10% 41%	2340
	21st to end	Day	7% 5% 2 6% 7% 4 6% 7% 7% 11% 38%	2340
July	1st to 10th	Day	9% 6% 3 6% 7% 5% 7% 7% 8% 11% 31%	2340
	11th to 20th	Day	9% 5% 3 6% 7% 4 8% 8% 9% 11% 30%	2340
	21st to end	Day	9% 5% 3 7% 7% 5% 8% 8% 8% 10% 29%	2547
August	1st to 10th	Day	8% 5% 2 7% 6% 5% 7% 8% 8% 11% 32%	2327
	11th to 20th	Day	10% 6% 3 6% 7% 4 7% 7% 7% 9% 34%	2170
	21st to end	Day	12% 6% 3 6% 6% 5% 7% 7% 7% 9% 32%	2376
September	1st to 10th	Day	11% 6% 2 7% 6% 3 5% 6% 6% 9% 39%	2020
	11th to 20th	Day	14% 5% 3 6% 6% 4 5% 5% 5% 7% 40%	1980
	21st to end	Day	12% 5% 2 5% 4 3 5% 4 5% 6% 48%	1980
October	1st to 10th	Day	11% 4 2 4 4 4 4 4 5% 6% 53%	1980
	11th to 20th	Day	12% 6% 2 4 3 2 3 3 3 6% 54%	1886
	21st to end	Day	13% 6% 2 4 4 2 4 4 5% 6% 52%	1932
November	1st to 10th	Day	13% 5% 2 3 4 3 4 3 4 5% 55%	1672
	11th to 20th	Day	12% 7% 2 4 4 3 4 3 5% 6% 49%	1710
	21st to end	Day	16% 7% 2 4 4 2 5% 4 5% 7% 45%	1710
December	1st to 10th	Day	19% 10% 3 6% 6% 3 4 5% 5% 5% 34%	1710
	11th to 20th	Day	16% 11% 4 6% 6% 3 4 4 4 4 37%	2153
	21st to end	Day	17% 13% 4 7% 5% 3 4 4 5% 7% 32%	3124
January	1st to 10th	Night	18% 10% 3 6% 5% 3 4 3 4 5% 39%	2459
	11th to 20th	Night	19% 10% 4 7% 5% 3 5% 4 5% 7% 33%	2360
	21st to end	Night	15% 10% 4 7% 4 3 4 4 4 5% 41%	2516
February	1st to 10th	Night	16% 9% 3 6% 5% 2 3 4 5% 6% 40%	2160
	11th to 20th	Night	21% 10% 4 5% 6% 3 4 4 3 4 36%	2098
	21st to end	Night	23% 9% 3 6% 5% 3 4 4 5% 6% 33%	1776
March	1st to 10th	Night	15% 7% 3 5% 4 3 5% 4 5% 6% 42%	2135
	11th to 20th	Night	17% 7% 3 6% 5% 3 4 4 5% 7% 38%	1980
	21st to end	Night	14% 9% 3 6% 5% 4 5% 5% 4 7% 39%	2178
April	1st to 10th	Night	13% 4 2 4 4 3 4 5% 5% 8% 49%	1890
	11th to 20th	Night	13% 6% 2 4 3 3 3 4 6% 7% 49%	1775
	21st to end	Night	14% 4 3 5% 5% 3 4 4 5% 8% 46%	1655
May	1st to 10th	Night	10% 5% 3 4 5% 3 4 5% 6% 8% 45%	1620
	11th to 20th	Night	11% 5% 3 5% 5% 4 5% 5% 7% 7% 42%	1592
	21st to end	Night	8% 6% 2 5% 6% 4 6% 6% 6% 10% 40%	1744
June	1st to 10th	Night	6% 5% 3 6% 7% 4 6% 6% 7% 11% 40%	1620
	11th to 20th	Night	4 3 2 4 5% 4 5% 6% 7% 12% 48%	1620
	21st to end	Night	4 5% 2 5% 5% 4 6% 5% 7% 11% 46%	1620
July	1st to 10th	Night	10% 4 3 6% 6% 4 6% 6% 7% 10% 37%	1620
	11th to 20th	Night	9% 4 1 5% 6% 5% 5% 7% 8% 13% 38%	1620
	21st to end	Night	7% 4 3 4 5% 4 8% 8% 10% 12% 36%	1771
August	1st to 10th	Night	8% 4 2 5% 6% 4 6% 7% 8% 11% 40%	1611
	11th to 20th	Night	8% 5% 2 5% 5% 5% 5% 6% 8% 11% 39%	1727
	21st to end	Night	10% 5% 2 5% 5% 4 6% 7% 7% 11% 37%	1980
September	1st to 10th	Night	10% 5% 2 6% 7% 4 5% 6% 6% 8% 41%	1921
	11th to 20th	Night	12% 6% 2 5% 6% 3 5% 5% 7% 8% 43%	1980
	21st to end	Night	10% 5% 3 4 4 3 5% 4 4 7% 51%	1980
October	1st to 10th	Night	12% 4 2 4 3 2 2 3 4 6% 58%	1980
	11th to 20th	Night	15% 4 2 4 4 3 4 3 4 4 53%	2071
	21st to end	Night	14% 6% 2 4 3 2 4 4 5% 5% 53%	2420
November	1st to 10th	Night	12% 6% 2 4 4 2 3 3 4 5% 54%	2406
	11th to 20th	Night	13% 6% 2 5% 4 2 3 4 4 6% 50%	2470
	21st to end	Night	14% 8% 3 4 5% 3 4 5% 4 6% 44%	2470
December	1st to 10th	Night	19% 9% 3 6% 6% 3 4 5% 5% 6% 35%	2470
	11th to 20th	Night	17% 10% 4 6% 4 2 3 3 4 6% 41%	3042
	21st to end	Night	16% 11% 4 7% 6% 3 5% 5% 5% 7% 30%	4532

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	48% 5% 7% 19% 18% 3	1707
	11th to 20th	Day	54% 5% 7% 16% 16% 2	1629
	21st to end	Day	44% 5% 8% 23% 17% 4	1839
February	1st to 10th	Day	52% 6% 7% 17% 16% 3	1800
	11th to 20th	Day	54% 5% 6% 17% 15% 3	1758
	21st to end	Day	52% 4 7% 12% 18% 6%	1480
March	1st to 10th	Day	43% 7% 8% 15% 20% 7%	1823
	11th to 20th	Day	51% 6% 10% 15% 15% 3	1980
	21st to end	Day	47% 7% 10% 22% 12% 1	2178
April	1st to 10th	Day	39% 9% 10% 21% 17% 4	2085
	11th to 20th	Day	40% 5% 8% 18% 23% 5%	2134
	21st to end	Day	41% 6% 11% 26% 14% 2	2304
May	1st to 10th	Day	38% 9% 13% 23% 15% 3	2340
	11th to 20th	Day	44% 11% 12% 19% 12% 1	2305
	21st to end	Day	39% 12% 13% 22% 12% 2	2531
June	1st to 10th	Day	39% 12% 16% 21% 10% 1	2340
	11th to 20th	Day	35% 12% 17% 23% 11% 2	2340
	21st to end	Day	37% 14% 17% 18% 12% 2	2340
July	1st to 10th	Day	44% 13% 15% 18% 8% 2	2275
	11th to 20th	Day	42% 16% 16% 13% 9% 3	2271
	21st to end	Day	44% 14% 17% 17% 7%	2405
August	1st to 10th	Day	40% 16% 19% 18% 6% 1	2314
	11th to 20th	Day	43% 13% 15% 17% 11% 1	2170
	21st to end	Day	47% 14% 13% 14% 10% 3	2376
September	1st to 10th	Day	41% 11% 13% 16% 15% 5%	2020
	11th to 20th	Day	43% 10% 11% 18% 17% 1	1980
	21st to end	Day	36% 8% 12% 17% 21% 6%	1980
October	1st to 10th	Day	32% 8% 9% 19% 26% 6%	1980
	11th to 20th	Day	32% 6% 9% 22% 23% 8%	1886
	21st to end	Day	33% 4 8% 23% 26% 6%	1932
November	1st to 10th	Day	32% 4 8% 18% 30% 7%	1672
	11th to 20th	Day	36% 5% 7% 20% 25% 7%	1710
	21st to end	Day	40% 5% 7% 19% 24% 4	1710
December	1st to 10th	Day	51% 7% 6% 17% 16% 3	1710
	11th to 20th	Day	48% 4 8% 15% 20% 4	2150
	21st to end	Day	50% 5% 9% 20% 14% 2	3124
January	1st to 10th	Night	50% 5% 8% 16% 17% 3	2459
	11th to 20th	Night	53% 6% 8% 15% 15% 3	2360
	21st to end	Night	47% 4 6% 21% 19% 3	2516
February	1st to 10th	Night	46% 5% 9% 18% 18% 3	2160
	11th to 20th	Night	53% 5% 6% 16% 15% 5%	2099
	21st to end	Night	53% 5% 7% 15% 15% 4	1776
March	1st to 10th	Night	44% 5% 8% 16% 19% 8%	2135
	11th to 20th	Night	45% 7% 10% 19% 16% 3	1980
	21st to end	Night	46% 6% 10% 22% 14% 1	2178
April	1st to 10th	Night	33% 7% 12% 22% 22% 4	1890
	11th to 20th	Night	35% 5% 10% 22% 21% 7%	1775
	21st to end	Night	36% 5% 12% 29% 16% 1	1655
May	1st to 10th	Night	35% 9% 13% 23% 18% 2	1620
	11th to 20th	Night	38% 11% 15% 23% 12% 1	1593
	21st to end	Night	35% 11% 14% 25% 13% 2	1745
June	1st to 10th	Night	36% 12% 17% 22% 11% 2	1620
	11th to 20th	Night	26% 12% 22% 28% 11% 2	1620
	21st to end	Night	31% 10% 21% 21% 13% 4	1620
July	1st to 10th	Night	38% 12% 18% 19% 11% 2	1575
	11th to 20th	Night	33% 12% 23% 17% 9% 5%	1566
	21st to end	Night	34% 14% 21% 22% 9% 1	1672
August	1st to 10th	Night	35% 13% 19% 24% 8% 1	1600
	11th to 20th	Night	35% 13% 20% 18% 13% 2	1727
	21st to end	Night	38% 13% 18% 20% 10% 2	1980
September	1st to 10th	Night	37% 11% 16% 18% 14% 4	1921
	11th to 20th	Night	38% 9% 15% 18% 20% 1	1980
	21st to end	Night	32% 7% 11% 21% 22% 6%	1980
October	1st to 10th	Night	28% 5% 11% 20% 27% 7%	1980
	11th to 20th	Night	35% 5% 9% 21% 23% 8%	2071
	21st to end	Night	34% 5% 5% 22% 26% 8%	2420
November	1st to 10th	Night	33% 5% 8% 21% 24% 9%	2406
	11th to 20th	Night	36% 5% 6% 20% 24% 9%	2470
	21st to end	Night	42% 5% 6% 21% 23% 4	2470
December	1st to 10th	Night	51% 7% 8% 16% 15% 3	2470
	11th to 20th	Night	45% 6% 7% 13% 26% 3	3044
	21st to end	Night	53% 5% 8% 20% 13% 1	4532

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% 24% 33% 13% 3	270
	11th to 20th	Day	27% 26% 29% 14% 5%	243
	21st to end	Day	22% 30% 37% 9% 2	264
February	1st to 10th	Day	26% 25% 33% 12% 3	240
	11th to 20th	Day	38% 28% 26% 8%	240
	21st to end	Day	39% 23% 31% 7%	198
March	1st to 10th	Day	26% 25% 30% 15% 5%	263
	11th to 20th	Day	25% 23% 30% 15% 6%	420
	21st to end	Day	26% 19% 32% 17% 6%	462
April	1st to 10th	Day	20% 18% 27% 21% 13% 1	420
	11th to 20th	Day	18% 20% 28% 22% 11% 1	412
	21st to end	Day	20% 14% 28% 24% 12% 3	420
May	1st to 10th	Day	15% 12% 33% 22% 12% 6%	423
	11th to 20th	Day	13% 6% 27% 29% 17% 9%	447
	21st to end	Day	11% 7% 19% 29% 20% 14%	485
June	1st to 10th	Day	9% 6% 21% 29% 24% 12%	450
	11th to 20th	Day	6% 5% 15% 30% 26% 17%	450
	21st to end	Day	9% 4 21% 29% 21% 16%	450
July	1st to 10th	Day	10% 4 15% 23% 27% 20%	445
	11th to 20th	Day	8% 3 10% 25% 35% 19%	444
	21st to end	Day	10% 3 8% 25% 33% 21%	488
August	1st to 10th	Day	11% 3 14% 25% 27% 20%	446
	11th to 20th	Day	10% 3 13% 30% 29% 14%	439
	21st to end	Day	14% 4 11% 23% 31% 17%	495
September	1st to 10th	Day	10% 3 13% 29% 29% 17%	450
	11th to 20th	Day	15% 4 12% 23% 30% 15%	450
	21st to end	Day	12% 6% 14% 30% 31% 7%	450
October	1st to 10th	Day	12% 8% 18% 32% 23% 8%	450
	11th to 20th	Day	13% 13% 26% 28% 19% 2	450
	21st to end	Day	19% 11% 24% 28% 16% 2	447
November	1st to 10th	Day	22% 10% 27% 24% 14% 2	270
	11th to 20th	Day	17% 15% 36% 25% 7%	270
	21st to end	Day	16% 17% 37% 21% 9% 1	270
December	1st to 10th	Day	26% 21% 31% 17% 4	270
	11th to 20th	Day	23% 19% 31% 20% 6% 1	270
	21st to end	Day	25% 21% 34% 15% 4	297
January	1st to 10th	Night	23% 21% 28% 23% 4	760
	11th to 20th	Night	24% 16% 30% 24% 5%	727
	21st to end	Night	21% 16% 34% 26% 3	792
February	1st to 10th	Night	20% 15% 35% 25% 5%	720
	11th to 20th	Night	27% 21% 32% 19% 2	703
	21st to end	Night	30% 19% 31% 18% 2	592
March	1st to 10th	Night	19% 15% 35% 26% 4	720
	11th to 20th	Night	21% 17% 31% 22% 7% 1	720
	21st to end	Night	20% 14% 32% 26% 8%	792
April	1st to 10th	Night	14% 17% 29% 30% 10%	630
	11th to 20th	Night	15% 13% 32% 28% 11% 1	533
	21st to end	Night	14% 9% 27% 35% 13% 1	540
May	1st to 10th	Night	11% 7% 29% 33% 18% 2	540
	11th to 20th	Night	13% 6% 20% 31% 25% 5%	531
	21st to end	Night	9% 3 14% 36% 32% 6%	584
June	1st to 10th	Night	7% 3 14% 36% 35% 4	540
	11th to 20th	Night	4 2 12% 35% 35% 12%	540
	21st to end	Night	6% 1 11% 34% 38% 9%	540
July	1st to 10th	Night	11% 3 9% 28% 40% 10%	525
	11th to 20th	Night	9% 2 6% 27% 45% 11%	522
	21st to end	Night	8% 1 9% 25% 46% 10%	591
August	1st to 10th	Night	9% 2 6% 25% 48% 9%	537
	11th to 20th	Night	9% 3 6% 34% 41% 7%	534
	21st to end	Night	11% 3 7% 29% 41% 9%	594
September	1st to 10th	Night	10% 3 10% 30% 41% 6%	661
	11th to 20th	Night	13% 3 12% 33% 34% 5%	720
	21st to end	Night	13% 3 15% 34% 32% 2	720
October	1st to 10th	Night	13% 5% 19% 28% 27% 7%	720
	11th to 20th	Night	16% 7% 25% 31% 20% 2	720
	21st to end	Night	17% 9% 21% 36% 16% 2	792
November	1st to 10th	Night	15% 8% 20% 37% 17% 3	740
	11th to 20th	Night	15% 13% 29% 32% 10% 1	760
	21st to end	Night	19% 12% 27% 31% 10%	760
December	1st to 10th	Night	24% 16% 25% 28% 7%	760
	11th to 20th	Night	22% 12% 31% 28% 7%	760
	21st to end	Night	23% 15% 27% 30% 5%	836

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