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 2024-01-22.

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	13% 6% 3 5% 5% 3 4 5% 6% 8% 44%	74841
	Night	13% 6% 2 5% 5% 3 4 4 5% 7% 47%	75110
Transparency	Day	39% 6% 11% 24% 17% 3	74550
	Night	37% 5% 10% 25% 19% 4	74922
Seeing	Day	15% 6% 22% 27% 21% 10%	14353
	Night	16% 5% 24% 34% 18% 2	24296

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	20% 7% 3 5% 5% 3 4 4 4 4 42%	1517
	11th to 20th	Day	20% 8% 3 5% 5% 3 4 4 5% 5% 38%	1651
	21st to end	Day	14% 8% 3 7% 5% 3 4 3 5% 6% 43%	1791
February	1st to 10th	Day	18% 9% 3 6% 4 2 4 4 5% 6% 38%	1708
	11th to 20th	Day	18% 8% 3 6% 5% 3 4 4 5% 6% 38%	1748
	21st to end	Day	17% 10% 4 7% 5% 3 4 5% 4 5% 36%	1480
March	1st to 10th	Day	18% 6% 2 5% 5% 3 4 4 5% 5% 43%	1800
	11th to 20th	Day	21% 8% 3 6% 5% 3 4 4 4 6% 35%	1949
	21st to end	Day	19% 9% 3 6% 6% 3 5% 4 5% 6% 34%	2329
April	1st to 10th	Day	12% 5% 3 5% 4 3 4 4 6% 8% 47%	2160
	11th to 20th	Day	16% 6% 4 6% 6% 3 4 4 5% 7% 41%	2134
	21st to end	Day	18% 6% 2 6% 5% 3 5% 5% 5% 7% 39%	2160
May	1st to 10th	Day	16% 6% 3 6% 6% 3 5% 4 6% 9% 37%	2216
	11th to 20th	Day	13% 6% 3 6% 5% 4 4 5% 5% 7% 42%	2302
	21st to end	Day	9% 6% 3 7% 7% 4 6% 7% 6% 9% 36%	2725
June	1st to 10th	Day	8% 4 2 5% 6% 4 5% 6% 6% 9% 47%	2520
	11th to 20th	Day	5% 3 2 4 6% 3 5% 7% 6% 9% 50%	2520
	21st to end	Day	4 3 2 4 5% 3 6% 6% 8% 12% 47%	2520
July	1st to 10th	Day	7% 4 3 6% 6% 4 6% 7% 8% 10% 41%	2520
	11th to 20th	Day	5% 3 2 5% 5% 3 4 7% 8% 10% 49%	2520
	21st to end	Day	5% 4 2 5% 5% 3 6% 5% 8% 11% 46%	2605
August	1st to 10th	Day	6% 4 2 5% 6% 3 5% 6% 7% 12% 43%	2212
	11th to 20th	Day	9% 5% 3 5% 4 4 5% 5% 8% 10% 43%	2125
	21st to end	Day	7% 3 2 4 5% 3 5% 5% 7% 9% 48%	2376
September	1st to 10th	Day	10% 5% 2 5% 5% 3 5% 4 6% 8% 48%	2160
	11th to 20th	Day	10% 5% 2 6% 5% 3 4 4 5% 7% 49%	2093
	21st to end	Day	11% 4 1 4 4 3 3 4 3 8% 55%	1980
October	1st to 10th	Day	8% 4 2 3 3 2 4 4 5% 7% 58%	1880
	11th to 20th	Day	13% 6% 2 5% 4 2 3 4 4 5% 52%	1800
	21st to end	Day	19% 6% 2 4 4 2 3 3 4 5% 46%	1946
November	1st to 10th	Day	11% 4 2 3 5% 2 4 3 5% 6% 54%	1672
	11th to 20th	Day	14% 7% 2 5% 4 3 4 3 4 5% 48%	1710
	21st to end	Day	20% 7% 2 4 4 2 3 4 4 6% 44%	1710
December	1st to 10th	Day	16% 7% 3 5% 5% 3 4 5% 4 7% 41%	1601
	11th to 20th	Day	18% 7% 2 5% 6% 4 5% 5% 4 6% 38%	1918
	21st to end	Day	20% 11% 4 7% 5% 3 4 3 4 6% 33%	2783
January	1st to 10th	Night	18% 7% 3 5% 4 2 3 4 5% 6% 43%	2648
	11th to 20th	Night	20% 7% 3 6% 4 3 5% 4 4 6% 39%	2527
	21st to end	Night	15% 6% 2 6% 6% 3 4 4 5% 5% 44%	2600
February	1st to 10th	Night	20% 10% 3 5% 5% 3 4 4 4 6% 37%	2250
	11th to 20th	Night	18% 7% 3 5% 4 3 4 3 4 5% 43%	2098
	21st to end	Night	19% 8% 3 5% 5% 3 4 3 5% 5% 39%	1776
March	1st to 10th	Night	17% 7% 2 6% 5% 3 3 4 4 5% 44%	2160
	11th to 20th	Night	19% 7% 3 6% 4 2 5% 4 4 4 41%	2026
	21st to end	Night	19% 7% 3 6% 6% 3 5% 4 5% 6% 37%	2026
April	1st to 10th	Night	11% 6% 2 3 3 3 4 5% 5% 7% 50%	1800
	11th to 20th	Night	15% 5% 2 5% 4 3 3 5% 5% 9% 44%	1775
	21st to end	Night	18% 6% 3 4 5% 3 4 4 6% 8% 40%	1800
May	1st to 10th	Night	16% 5% 2 4 4 2 5% 4 5% 9% 45%	1742
	11th to 20th	Night	13% 6% 3 5% 6% 4 4 4 5% 7% 43%	1587
	21st to end	Night	7% 5% 3 6% 6% 3 5% 6% 7% 9% 42%	1551
June	1st to 10th	Night	9% 5% 2 5% 6% 3 4 5% 7% 8% 46%	1440
	11th to 20th	Night	5% 3 2 3 4 3 5% 4 7% 9% 57%	1440
	21st to end	Night	4 2 1 3 3 3 5% 5% 8% 12% 55%	1440
July	1st to 10th	Night	4 3 2 4 4 3 6% 5% 7% 10% 52%	1440
	11th to 20th	Night	5% 4 1 4 4 3 4 4 7% 10% 54%	1440
	21st to end	Night	5% 4 2 4 4 3 5% 5% 6% 9% 53%	1709
August	1st to 10th	Night	5% 4 2 4 5% 3 5% 6% 7% 11% 50%	1723
	11th to 20th	Night	7% 4 1 5% 5% 2 4 5% 6% 9% 53%	1776
	21st to end	Night	6% 4 2 5% 4 2 5% 5% 8% 9% 51%	1980
September	1st to 10th	Night	10% 5% 2 4 4 2 3 3 4 7% 55%	1800
	11th to 20th	Night	7% 4 2 5% 5% 2 5% 5% 5% 8% 52%	1849
	21st to end	Night	9% 4 2 3 4 2 4 3 4 6% 59%	1980
October	1st to 10th	Night	7% 4 1 4 4 2 3 4 4 6% 61%	2077
	11th to 20th	Night	13% 4 2 4 4 2 3 3 5% 4 56%	2160
	21st to end	Night	18% 6% 3 4 4 2 3 3 4 5% 49%	2407
November	1st to 10th	Night	11% 4 2 3 4 2 2 3 4 6% 58%	2406
	11th to 20th	Night	14% 4 2 4 4 2 3 3 4 7% 51%	2470
	21st to end	Night	17% 5% 2 5% 4 3 3 2 4 6% 48%	2470
December	1st to 10th	Night	18% 7% 3 5% 4 3 4 5% 4 5% 42%	2574
	11th to 20th	Night	18% 7% 3 4 5% 3 4 4 4 5% 43%	3279
	21st to end	Night	17% 9% 3 8% 7% 3 4 3 5% 5% 34%	4884

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	46% 4 8% 25% 14% 3	1518
	11th to 20th	Day	47% 5% 9% 25% 12% 1	1651
	21st to end	Day	42% 4 13% 25% 13% 2	1791
February	1st to 10th	Day	47% 4 11% 23% 14% 1	1708
	11th to 20th	Day	47% 4 11% 22% 11% 4	1758
	21st to end	Day	49% 5% 9% 21% 11% 5%	1480
March	1st to 10th	Day	43% 4 9% 24% 16% 4	1800
	11th to 20th	Day	51% 5% 10% 19% 13% 3	1949
	21st to end	Day	50% 6% 12% 21% 11% 1	2329
April	1st to 10th	Day	35% 4 11% 29% 18% 2	2160
	11th to 20th	Day	43% 4 10% 22% 17% 4	2134
	21st to end	Day	45% 5% 10% 24% 15% 1	2160
May	1st to 10th	Day	44% 6% 13% 23% 13% 1	2216
	11th to 20th	Day	42% 6% 14% 20% 16% 2	2306
	21st to end	Day	42% 8% 16% 22% 11% 2	2725
June	1st to 10th	Day	32% 6% 14% 26% 21% 1	2520
	11th to 20th	Day	28% 8% 11% 29% 21% 3	2520
	21st to end	Day	28% 8% 15% 26% 18% 5%	2520
July	1st to 10th	Day	35% 8% 16% 22% 15% 5%	2451
	11th to 20th	Day	27% 8% 16% 26% 18% 5%	2445
	21st to end	Day	30% 8% 16% 31% 13% 2	2460
August	1st to 10th	Day	31% 9% 15% 27% 16% 2	2198
	11th to 20th	Day	34% 7% 14% 27% 16% 2	2125
	21st to end	Day	30% 7% 15% 27% 16% 6%	2376
September	1st to 10th	Day	34% 5% 10% 28% 19% 4	2160
	11th to 20th	Day	34% 5% 9% 24% 26% 3	2093
	21st to end	Day	30% 4 8% 26% 28% 4	1980
October	1st to 10th	Day	25% 4 11% 27% 27% 6%	1880
	11th to 20th	Day	34% 4 6% 25% 23% 8%	1800
	21st to end	Day	41% 4 6% 26% 20% 5%	1946
November	1st to 10th	Day	32% 4 10% 25% 22% 7%	1672
	11th to 20th	Day	40% 2 7% 23% 24% 5%	1710
	21st to end	Day	44% 3 7% 25% 19% 2	1710
December	1st to 10th	Day	44% 4 10% 25% 14% 2	1601
	11th to 20th	Day	47% 5% 8% 24% 14% 2	1915
	21st to end	Day	53% 5% 11% 18% 11% 2	2783
January	1st to 10th	Night	42% 4 9% 25% 17% 2	2648
	11th to 20th	Night	47% 5% 9% 24% 14% 2	2527
	21st to end	Night	41% 4 10% 27% 16% 2	2600
February	1st to 10th	Night	50% 3 8% 22% 15% 2	2250
	11th to 20th	Night	44% 4 9% 22% 18% 3	2099
	21st to end	Night	47% 3 9% 21% 15% 5%	1776
March	1st to 10th	Night	43% 4 8% 18% 20% 7%	2160
	11th to 20th	Night	47% 4 11% 19% 15% 4	2026
	21st to end	Night	48% 5% 10% 24% 12% 2	2026
April	1st to 10th	Night	32% 5% 11% 26% 21% 4	1800
	11th to 20th	Night	37% 4 10% 23% 21% 6%	1775
	21st to end	Night	42% 5% 8% 25% 17% 3	1800
May	1st to 10th	Night	37% 6% 12% 26% 17% 2	1742
	11th to 20th	Night	41% 6% 12% 22% 17% 2	1588
	21st to end	Night	36% 7% 14% 25% 14% 3	1552
June	1st to 10th	Night	33% 6% 13% 24% 22% 2	1440
	11th to 20th	Night	22% 6% 14% 30% 22% 6%	1440
	21st to end	Night	20% 7% 18% 29% 17% 9%	1440
July	1st to 10th	Night	27% 7% 17% 28% 16% 5%	1400
	11th to 20th	Night	24% 7% 17% 28% 17% 7%	1392
	21st to end	Night	26% 7% 15% 33% 18% 1	1614
August	1st to 10th	Night	28% 7% 18% 29% 17% 1	1713
	11th to 20th	Night	28% 6% 14% 28% 21% 4	1776
	21st to end	Night	27% 6% 17% 25% 19% 6%	1980
September	1st to 10th	Night	31% 5% 9% 29% 21% 6%	1800
	11th to 20th	Night	30% 6% 9% 27% 24% 5%	1849
	21st to end	Night	27% 4 9% 24% 29% 6%	1980
October	1st to 10th	Night	25% 4 8% 27% 28% 8%	2077
	11th to 20th	Night	32% 3 7% 23% 28% 8%	2160
	21st to end	Night	39% 4 6% 24% 21% 7%	2407
November	1st to 10th	Night	29% 4 8% 28% 26% 6%	2406
	11th to 20th	Night	34% 3 6% 25% 23% 8%	2470
	21st to end	Night	39% 3 7% 25% 24% 3	2470
December	1st to 10th	Night	44% 4 10% 23% 16% 2	2574
	11th to 20th	Night	44% 4 8% 24% 19% 2	3281
	21st to end	Night	50% 5% 9% 19% 14% 2	4884

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% 12% 30% 24% 6% 1	270
	11th to 20th	Day	25% 11% 45% 15% 4	270
	21st to end	Day	19% 10% 43% 23% 4	267
February	1st to 10th	Day	26% 12% 38% 18% 5%	240
	11th to 20th	Day	25% 18% 38% 16% 4	240
	21st to end	Day	31% 10% 36% 18% 6%	198
March	1st to 10th	Day	20% 13% 42% 19% 6%	240
	11th to 20th	Day	26% 12% 39% 17% 5% 1	240
	21st to end	Day	28% 11% 29% 23% 8%	415
April	1st to 10th	Day	16% 10% 35% 27% 11% 1	420
	11th to 20th	Day	20% 12% 28% 25% 13% 2	412
	21st to end	Day	20% 9% 31% 28% 10% 3	420
May	1st to 10th	Day	19% 10% 28% 27% 13% 3	423
	11th to 20th	Day	18% 4 21% 28% 21% 9%	448
	21st to end	Day	9% 4 22% 33% 22% 11%	679
June	1st to 10th	Day	10% 3 14% 27% 29% 18%	630
	11th to 20th	Day	6% 2 13% 39% 29% 12%	630
	21st to end	Day	5% 2 21% 37% 20% 15%	630
July	1st to 10th	Day	10% 1 9% 24% 30% 26%	621
	11th to 20th	Day	7% 1 12% 28% 34% 19%	618
	21st to end	Day	7% 2 8% 29% 35% 19%	684
August	1st to 10th	Day	9% 2 6% 29% 37% 17%	510
	11th to 20th	Day	14% 2 9% 24% 35% 16%	439
	21st to end	Day	10% 5% 24% 38% 23%	495
September	1st to 10th	Day	10% 2 7% 26% 37% 17%	450
	11th to 20th	Day	10% 1 8% 28% 35% 18%	450
	21st to end	Day	14% 4 16% 25% 30% 12%	450
October	1st to 10th	Day	10% 2 18% 35% 26% 9%	350
	11th to 20th	Day	16% 8% 34% 26% 14% 3	270
	21st to end	Day	26% 11% 25% 27% 11% 1	297
November	1st to 10th	Day	16% 6% 30% 29% 14% 5%	270
	11th to 20th	Day	14% 11% 36% 23% 14% 2	270
	21st to end	Day	23% 11% 29% 26% 9% 2	270
December	1st to 10th	Day	16% 9% 37% 23% 12% 2	270
	11th to 20th	Day	26% 11% 29% 19% 14% 1	270
	21st to end	Day	27% 12% 35% 21% 5%	297
January	1st to 10th	Night	22% 8% 36% 28% 6%	950
	11th to 20th	Night	24% 9% 36% 26% 5%	950
	21st to end	Night	19% 8% 38% 32% 3	1000
February	1st to 10th	Night	25% 8% 36% 28% 4	810
	11th to 20th	Night	21% 10% 40% 28% 2	703
	21st to end	Night	23% 10% 37% 28% 3	592
March	1st to 10th	Night	21% 9% 34% 33% 4	720
	11th to 20th	Night	22% 8% 33% 31% 6%	586
	21st to end	Night	23% 8% 28% 32% 8%	594
April	1st to 10th	Night	15% 5% 39% 33% 7%	540
	11th to 20th	Night	18% 7% 29% 33% 11% 1	533
	21st to end	Night	20% 6% 28% 35% 10% 1	540
May	1st to 10th	Night	17% 3 26% 40% 13% 2	540
	11th to 20th	Night	16% 2 23% 38% 18% 2	531
	21st to end	Night	9% 2 16% 40% 28% 4	584
June	1st to 10th	Night	11% 2 11% 39% 32% 5%	540
	11th to 20th	Night	6% 1 8% 51% 32% 3	540
	21st to end	Night	4 13% 44% 35% 4	540
July	1st to 10th	Night	5% 2 5% 30% 47% 10%	525
	11th to 20th	Night	7% 1 6% 33% 44% 9%	522
	21st to end	Night	6% 1 8% 37% 41% 8%	591
August	1st to 10th	Night	5% 2 5% 36% 46% 6%	537
	11th to 20th	Night	8% 1 4 35% 45% 7%	534
	21st to end	Night	7% 1 5% 32% 48% 8%	594
September	1st to 10th	Night	11% 3 6% 29% 42% 8%	540
	11th to 20th	Night	9% 2 8% 34% 40% 7%	589
	21st to end	Night	11% 3 15% 35% 31% 5%	720
October	1st to 10th	Night	9% 2 17% 40% 28% 4	720
	11th to 20th	Night	15% 3 28% 34% 18% 2	720
	21st to end	Night	21% 5% 26% 35% 12% 1	792
November	1st to 10th	Night	14% 4 27% 39% 16% 1	740
	11th to 20th	Night	16% 5% 33% 35% 11%	760
	21st to end	Night	20% 7% 28% 34% 10% 1	760
December	1st to 10th	Night	22% 6% 30% 34% 8% 1	864
	11th to 20th	Night	24% 6% 28% 33% 9% 1	950
	21st to end	Night	25% 8% 31% 31% 4	1045

Page generated at 2024-01-19 08:28:34. Version ac07

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