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 2025-01-22.

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% 4 4 4 4 5% 7% 44%	104904
	Night	14% 6% 2 5% 4 4 4 3 5% 7% 46%	104547
Transparency	Day	37% 5% 11% 25% 18% 3	108563
	Night	36% 5% 10% 25% 20% 4	109029
Seeing	Day	15% 6% 22% 27% 21% 10%	15723
	Night	16% 5% 24% 34% 18% 2	25630

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	15% 9% 3 7% 4 4 4 3 4 5% 42%	2607
	11th to 20th	Day	16% 8% 3 6% 4 3 3 3 4 5% 46%	2839
	21st to end	Day	24% 10% 2 7% 3 3 3 2 4 5% 34%	3144
February	1st to 10th	Day	18% 10% 2 6% 3 3 4 4 5% 6% 38%	1803
	11th to 20th	Day	17% 9% 3 7% 4 4 3 3 5% 5% 40%	1848
	21st to end	Day	16% 10% 3 7% 5% 3 5% 4 5% 5% 36%	1570
March	1st to 10th	Day	20% 10% 3 8% 4 3 4 3 4 4 36%	3120
	11th to 20th	Day	14% 6% 2 5% 3 3 4 3 4 6% 50%	3435
	21st to end	Day	14% 7% 3 6% 5% 4 4 4 5% 6% 43%	4090
April	1st to 10th	Day	12% 6% 2 6% 4 4 4 3 6% 8% 46%	2280
	11th to 20th	Day	15% 7% 3 6% 5% 4 3 4 5% 7% 42%	2254
	21st to end	Day	18% 7% 2 6% 4 4 4 5% 5% 7% 39%	2280
May	1st to 10th	Day	14% 6% 2 7% 5% 5% 5% 4 8% 11% 34%	3877
	11th to 20th	Day	15% 7% 3 7% 4 5% 4 4 6% 8% 37%	4096
	21st to end	Day	10% 6% 3 7% 6% 5% 5% 4 5% 8% 40%	4824
June	1st to 10th	Day	8% 4 2 5% 5% 5% 5% 4 6% 9% 46%	2660
	11th to 20th	Day	5% 4 2 5% 5% 4 5% 5% 6% 9% 50%	2660
	21st to end	Day	4 3 2 5% 5% 4 6% 5% 8% 11% 46%	2660
July	1st to 10th	Day	8% 4 2 6% 5% 5% 6% 5% 8% 10% 41%	4440
	11th to 20th	Day	5% 3 1 5% 4 4 5% 5% 7% 9% 53%	4440
	21st to end	Day	7% 7% 3 9% 6% 6% 7% 5% 7% 9% 35%	4566
August	1st to 10th	Day	4 2 1 4 3 4 4 4 6% 11% 58%	3890
	11th to 20th	Day	10% 6% 2 6% 3 4 4 4 6% 9% 46%	3729
	21st to end	Day	5% 3 1 4 3 3 4 3 6% 8% 59%	4180
September	1st to 10th	Day	10% 5% 2 6% 4 4 5% 3 6% 7% 48%	2280
	11th to 20th	Day	10% 5% 2 7% 3 5% 4 3 5% 7% 48%	2209
	21st to end	Day	11% 5% 1 5% 3 3 3 4 3 8% 53%	2090
October	1st to 10th	Day	8% 4 2 4 3 3 4 3 5% 6% 60%	1984
	11th to 20th	Day	12% 6% 2 5% 3 3 3 4 5% 5% 54%	1900
	21st to end	Day	18% 6% 2 5% 3 3 3 3 4 5% 47%	2054
November	1st to 10th	Day	12% 5% 2 4 4 3 4 2 5% 5% 52%	1762
	11th to 20th	Day	14% 7% 2 5% 4 4 4 2 4 6% 48%	1800
	21st to end	Day	20% 8% 2 5% 3 3 4 3 4 5% 44%	1800
December	1st to 10th	Day	11% 8% 2 5% 3 3 4 4 4 5% 50%	2743
	11th to 20th	Day	16% 8% 2 7% 4 4 4 4 4 6% 41%	3008
	21st to end	Day	23% 13% 4 9% 4 4 3 2 4 5% 29%	3982
January	1st to 10th	Night	18% 7% 2 5% 4 4 4 4 6% 7% 40%	4568
	11th to 20th	Night	15% 7% 3 6% 4 5% 4 4 5% 7% 41%	4348
	21st to end	Night	24% 9% 2 6% 4 3 3 3 4 6% 37%	4546
February	1st to 10th	Night	19% 11% 3 6% 4 4 3 3 4 6% 37%	2375
	11th to 20th	Night	17% 8% 3 6% 4 3 3 3 4 5% 43%	2218
	21st to end	Night	18% 8% 2 6% 4 4 4 3 5% 5% 40%	1884
March	1st to 10th	Night	20% 9% 3 8% 4 3 4 3 4 5% 38%	3733
	11th to 20th	Night	13% 6% 2 6% 3 3 5% 3 4 5% 49%	3554
	21st to end	Night	13% 6% 3 6% 5% 4 5% 3 5% 6% 43%	3540
April	1st to 10th	Night	12% 6% 2 4 4 3 4 4 5% 7% 49%	1900
	11th to 20th	Night	15% 5% 2 6% 4 4 3 4 5% 8% 44%	1875
	21st to end	Night	18% 7% 2 5% 4 4 3 4 6% 7% 40%	1900
May	1st to 10th	Night	18% 6% 2 5% 3 4 4 3 5% 9% 42%	3016
	11th to 20th	Night	14% 7% 3 6% 5% 4 3 2 4 7% 44%	2794
	21st to end	Night	8% 6% 3 6% 5% 5% 6% 4 8% 8% 42%	2743
June	1st to 10th	Night	9% 5% 2 6% 5% 4 4 5% 8% 7% 46%	1520
	11th to 20th	Night	5% 3 1 4 3 3 5% 3 7% 9% 56%	1520
	21st to end	Night	3 2 1 4 3 4 4 5% 7% 12% 55%	1520
July	1st to 10th	Night	8% 4 2 4 4 4 5% 4 7% 9% 49%	2530
	11th to 20th	Night	4 4 1 4 3 4 4 4 6% 9% 57%	2530
	21st to end	Night	7% 7% 3 8% 5% 5% 5% 5% 7% 8% 40%	2993
August	1st to 10th	Night	3 3 1 4 3 3 4 4 6% 8% 62%	3039
	11th to 20th	Night	6% 4 1 5% 4 4 4 5% 6% 8% 52%	3100
	21st to end	Night	3 3 1 4 3 3 4 4 7% 10% 59%	3476
September	1st to 10th	Night	10% 6% 2 5% 4 3 3 3 4 6% 56%	1900
	11th to 20th	Night	8% 5% 3 6% 4 3 5% 3 5% 7% 52%	1952
	21st to end	Night	10% 5% 2 4 3 3 4 3 5% 6% 56%	2090
October	1st to 10th	Night	6% 4 1 4 3 3 4 2 4 6% 62%	2193
	11th to 20th	Night	12% 5% 2 4 3 2 3 3 5% 4 57%	2280
	21st to end	Night	17% 6% 2 5% 3 3 3 3 4 5% 49%	2541
November	1st to 10th	Night	12% 5% 2 4 3 3 3 2 5% 6% 56%	2536
	11th to 20th	Night	14% 5% 2 5% 4 3 4 2 5% 7% 51%	2600
	21st to end	Night	17% 6% 2 6% 4 4 3 2 4 6% 48%	2600
December	1st to 10th	Night	16% 7% 2 5% 3 4 3 3 4 5% 48%	4438
	11th to 20th	Night	18% 8% 2 5% 4 3 3 3 4 6% 45%	5199
	21st to end	Night	24% 9% 3 8% 5% 4 3 3 5% 5% 33%	6996

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	44% 4 10% 27% 13% 2	2608
	11th to 20th	Day	42% 5% 8% 26% 17% 3	2839
	21st to end	Day	53% 3 10% 19% 12% 2	3144
February	1st to 10th	Day	47% 4 11% 23% 14% 1	1803
	11th to 20th	Day	46% 4 11% 21% 13% 5%	1858
	21st to end	Day	49% 5% 9% 20% 12% 6%	1570
March	1st to 10th	Day	51% 4 6% 19% 13% 7%	3120
	11th to 20th	Day	37% 4 9% 27% 18% 5%	3435
	21st to end	Day	41% 5% 13% 24% 16% 1	4090
April	1st to 10th	Day	36% 5% 11% 28% 18% 2	2280
	11th to 20th	Day	42% 4 10% 22% 17% 4	2254
	21st to end	Day	44% 5% 10% 24% 15% 1	2280
May	1st to 10th	Day	41% 9% 14% 21% 13% 1	3912
	11th to 20th	Day	43% 7% 12% 24% 13% 1	4100
	21st to end	Day	40% 6% 11% 20% 21% 1	4837
June	1st to 10th	Day	33% 6% 14% 25% 20% 2	2660
	11th to 20th	Day	28% 8% 11% 29% 22% 3	2660
	21st to end	Day	28% 8% 16% 25% 18% 5%	2660
July	1st to 10th	Day	35% 7% 14% 25% 16% 3	4371
	11th to 20th	Day	25% 6% 12% 35% 19% 3	4365
	21st to end	Day	43% 8% 15% 25% 9% 1	4422
August	1st to 10th	Day	20% 6% 16% 32% 25% 1	3876
	11th to 20th	Day	34% 5% 12% 26% 19% 3	3765
	21st to end	Day	23% 5% 12% 39% 17% 3	4179
September	1st to 10th	Day	33% 6% 10% 26% 21% 4	2280
	11th to 20th	Day	35% 5% 9% 23% 25% 3	2209
	21st to end	Day	31% 5% 8% 25% 27% 4	2090
October	1st to 10th	Day	15% 2 6% 20% 43% 14%	3296
	11th to 20th	Day	23% 3 5% 22% 34% 13%	3140
	21st to end	Day	31% 3 4 28% 28% 6%	3368
November	1st to 10th	Day	33% 4 9% 25% 22% 6%	1762
	11th to 20th	Day	39% 2 7% 23% 24% 5%	1800
	21st to end	Day	44% 3 7% 26% 18% 2	1800
December	1st to 10th	Day	37% 4 8% 34% 16% 1	2743
	11th to 20th	Day	44% 4 10% 26% 14% 3	3005
	21st to end	Day	59% 4 11% 17% 9% 1	3982
January	1st to 10th	Night	41% 5% 9% 30% 14% 1	4568
	11th to 20th	Night	42% 5% 9% 26% 16% 3	4348
	21st to end	Night	48% 4 9% 24% 13% 1	4546
February	1st to 10th	Night	50% 3 8% 22% 16% 2	2375
	11th to 20th	Night	43% 4 9% 22% 18% 4	2219
	21st to end	Night	46% 4 9% 20% 17% 5%	1884
March	1st to 10th	Night	48% 5% 7% 17% 16% 7%	3733
	11th to 20th	Night	37% 5% 9% 23% 18% 8%	3554
	21st to end	Night	40% 5% 9% 32% 13% 1	3540
April	1st to 10th	Night	33% 5% 11% 26% 21% 4	1900
	11th to 20th	Night	37% 4 9% 23% 21% 6%	1875
	21st to end	Night	42% 5% 8% 25% 17% 3	1900
May	1st to 10th	Night	39% 8% 15% 26% 10% 1	3046
	11th to 20th	Night	40% 7% 14% 22% 17% 1	2795
	21st to end	Night	36% 8% 12% 25% 17% 2	2751
June	1st to 10th	Night	33% 6% 13% 23% 21% 3	1520
	11th to 20th	Night	22% 6% 13% 30% 23% 7%	1520
	21st to end	Night	20% 7% 18% 29% 18% 9%	1520
July	1st to 10th	Night	31% 6% 14% 29% 17% 4	2490
	11th to 20th	Night	22% 6% 12% 36% 19% 4	2482
	21st to end	Night	39% 8% 15% 24% 14% 1	2898
August	1st to 10th	Night	20% 5% 17% 34% 23% 1	3029
	11th to 20th	Night	29% 5% 15% 28% 18% 5%	3130
	21st to end	Night	20% 4 12% 37% 24% 4	3476
September	1st to 10th	Night	30% 4 8% 28% 23% 7%	1900
	11th to 20th	Night	31% 6% 8% 26% 24% 5%	1952
	21st to end	Night	30% 4 10% 23% 28% 6%	2090
October	1st to 10th	Night	15% 3 5% 17% 42% 19%	3661
	11th to 20th	Night	21% 2 5% 17% 43% 12%	3779
	21st to end	Night	28% 3 5% 25% 30% 8%	4177
November	1st to 10th	Night	31% 4 8% 27% 25% 6%	2536
	11th to 20th	Night	34% 3 6% 25% 24% 8%	2600
	21st to end	Night	39% 3 7% 26% 23% 3	2600
December	1st to 10th	Night	39% 4 7% 30% 19% 1	4438
	11th to 20th	Night	43% 3 10% 22% 20% 2	5201
	21st to end	Night	53% 4 10% 20% 11% 2	6996

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	26% 12% 32% 24% 6% 1	300
	11th to 20th	Day	22% 12% 46% 16% 4	300
	21st to end	Day	22% 9% 42% 23% 4	300
February	1st to 10th	Day	26% 11% 37% 20% 6% 1	270
	11th to 20th	Day	23% 17% 37% 17% 4 1	270
	21st to end	Day	30% 12% 36% 17% 5%	225
March	1st to 10th	Day	20% 12% 42% 19% 7%	270
	11th to 20th	Day	24% 13% 41% 17% 5% 1	270
	21st to end	Day	26% 11% 31% 23% 8%	457
April	1st to 10th	Day	19% 10% 33% 27% 11% 1	460
	11th to 20th	Day	19% 14% 29% 24% 12% 2	452
	21st to end	Day	19% 8% 32% 27% 11% 3	460
May	1st to 10th	Day	18% 9% 28% 28% 14% 3	463
	11th to 20th	Day	17% 4 20% 28% 21% 10%	489
	21st to end	Day	10% 4 24% 32% 21% 10%	734
June	1st to 10th	Day	11% 3 15% 27% 27% 17%	680
	11th to 20th	Day	6% 2 12% 38% 29% 13%	680
	21st to end	Day	5% 2 20% 37% 21% 14%	680
July	1st to 10th	Day	9% 1 9% 26% 30% 24%	671
	11th to 20th	Day	6% 1 11% 29% 35% 17%	668
	21st to end	Day	7% 2 9% 30% 34% 18%	739
August	1st to 10th	Day	8% 2 7% 31% 35% 17%	553
	11th to 20th	Day	14% 2 10% 27% 33% 15%	479
	21st to end	Day	9% 5% 24% 38% 24%	539
September	1st to 10th	Day	10% 2 9% 27% 36% 17%	490
	11th to 20th	Day	11% 2 8% 27% 35% 18%	490
	21st to end	Day	15% 4 17% 25% 28% 11%	490
October	1st to 10th	Day	9% 2 17% 34% 27% 11%	384
	11th to 20th	Day	15% 7% 32% 25% 14% 7%	300
	21st to end	Day	24% 10% 25% 27% 12% 2	330
November	1st to 10th	Day	16% 6% 30% 29% 14% 5%	300
	11th to 20th	Day	14% 10% 36% 24% 15% 2	300
	21st to end	Day	22% 11% 30% 25% 9% 2	300
December	1st to 10th	Day	17% 10% 36% 24% 11% 2	300
	11th to 20th	Day	25% 12% 30% 19% 14% 1	300
	21st to end	Day	27% 13% 34% 22% 5%	330
January	1st to 10th	Night	22% 8% 36% 29% 5%	1000
	11th to 20th	Night	23% 9% 37% 26% 5%	1000
	21st to end	Night	20% 8% 38% 32% 3	1051
February	1st to 10th	Night	24% 8% 36% 28% 4	855
	11th to 20th	Night	20% 10% 40% 28% 2	743
	21st to end	Night	22% 11% 38% 27% 3	628
March	1st to 10th	Night	20% 9% 34% 32% 5%	760
	11th to 20th	Night	21% 8% 34% 31% 6%	618
	21st to end	Night	22% 8% 29% 32% 8%	627
April	1st to 10th	Night	16% 6% 39% 32% 7%	570
	11th to 20th	Night	18% 8% 30% 32% 11% 1	563
	21st to end	Night	19% 6% 29% 35% 10% 1	570
May	1st to 10th	Night	17% 3 26% 39% 13% 2	570
	11th to 20th	Night	16% 2 22% 38% 19% 3	561
	21st to end	Night	10% 2 17% 41% 27% 4	617
June	1st to 10th	Night	12% 2 11% 39% 31% 4	570
	11th to 20th	Night	6% 1 8% 51% 32% 3	570
	21st to end	Night	4 12% 45% 35% 4	570
July	1st to 10th	Night	6% 2 6% 31% 45% 10%	555
	11th to 20th	Night	6% 1 6% 34% 44% 9%	552
	21st to end	Night	7% 1 8% 37% 39% 8%	624
August	1st to 10th	Night	5% 2 6% 36% 46% 6%	567
	11th to 20th	Night	9% 1 5% 35% 44% 7%	564
	21st to end	Night	6% 1 5% 32% 49% 7%	627
September	1st to 10th	Night	12% 3 6% 30% 41% 8%	570
	11th to 20th	Night	10% 2 8% 35% 39% 7%	622
	21st to end	Night	12% 3 16% 35% 30% 4	760
October	1st to 10th	Night	9% 2 16% 40% 29% 4	760
	11th to 20th	Night	15% 3 28% 33% 19% 2	760
	21st to end	Night	20% 5% 26% 36% 12% 1	836
November	1st to 10th	Night	14% 4 26% 39% 15% 1	780
	11th to 20th	Night	16% 5% 33% 35% 11%	800
	21st to end	Night	19% 7% 29% 34% 10% 1	800
December	1st to 10th	Night	21% 7% 30% 34% 7% 1	910
	11th to 20th	Night	24% 6% 29% 32% 8% 1	1000
	21st to end	Night	26% 8% 31% 30% 5%	1100

Page generated at 2025-01-19 02:06:44. Version ac07

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