Peotone
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Peotone clear sky chart from 2005-11-06 to 2025-06-10.

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	13% 9% 3 8% 5% 4 4 4 6% 7% 36%	119331
	Night	14% 10% 4 8% 5% 4 4 3 5% 6% 38%	119081
Transparency	Day	46% 3 11% 23% 14% 2	122911
	Night	47% 3 10% 23% 15% 2	123628
Seeing	Day	16% 10% 29% 25% 14% 5%	16526
	Night	18% 10% 30% 30% 12% 1	26452

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% 12% 7% 14% 6% 5% 4 4 5% 7% 23%	3617
	11th to 20th	Day	11% 13% 6% 14% 6% 6% 4 5% 6% 4 24%	3620
	21st to end	Day	16% 18% 5% 10% 4 3 3 3 4 6% 27%	4097
February	1st to 10th	Day	17% 12% 5% 9% 6% 5% 5% 4 5% 6% 25%	1880
	11th to 20th	Day	14% 12% 4 8% 7% 5% 4 3 5% 6% 32%	1948
	21st to end	Day	15% 13% 5% 10% 5% 4 4 4 5% 6% 29%	1650
March	1st to 10th	Day	19% 13% 4 7% 4 3 2 2 4 4 39%	4480
	11th to 20th	Day	8% 8% 3 7% 5% 4 5% 4 6% 9% 41%	4651
	21st to end	Day	19% 13% 6% 10% 6% 5% 4 4 4 6% 21%	5967
April	1st to 10th	Day	17% 13% 3 7% 5% 4 4 3 5% 7% 31%	2400
	11th to 20th	Day	16% 10% 3 6% 5% 5% 4 3 5% 7% 36%	2374
	21st to end	Day	19% 8% 3 7% 5% 5% 5% 4 5% 6% 34%	2512
May	1st to 10th	Day	19% 8% 2 7% 4 5% 5% 4 7% 9% 31%	5862
	11th to 20th	Day	14% 6% 2 7% 5% 5% 5% 4 6% 7% 39%	6057
	21st to end	Day	13% 7% 3 7% 5% 4 4 4 6% 9% 39%	6935
June	1st to 10th	Day	11% 6% 2 6% 4 4 4 5% 6% 8% 45%	2787
	11th to 20th	Day	9% 5% 1 6% 5% 4 5% 4 6% 9% 45%	2660
	21st to end	Day	10% 6% 2 6% 6% 6% 6% 5% 8% 8% 38%	2660
July	1st to 10th	Day	11% 7% 2 8% 5% 5% 6% 5% 7% 10% 33%	4440
	11th to 20th	Day	8% 4 2 5% 4 4 5% 5% 7% 10% 47%	4440
	21st to end	Day	9% 5% 2 7% 5% 5% 6% 5% 6% 9% 40%	4813
August	1st to 10th	Day	7% 5% 2 6% 4 4 5% 3 7% 9% 47%	4269
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 5% 7% 9% 44%	3743
	21st to end	Day	7% 4 2 6% 4 4 4 4 6% 9% 48%	4180
September	1st to 10th	Day	11% 5% 2 5% 4 4 5% 4 6% 7% 47%	2280
	11th to 20th	Day	12% 5% 2 4 3 4 4 4 5% 8% 51%	2142
	21st to end	Day	11% 5% 2 7% 5% 4 4 4 6% 9% 43%	2090
October	1st to 10th	Day	11% 6% 3 7% 4 3 4 3 5% 6% 47%	2068
	11th to 20th	Day	18% 8% 2 6% 4 4 4 3 6% 7% 38%	1881
	21st to end	Day	20% 8% 3 7% 4 4 4 3 5% 7% 33%	1881
November	1st to 10th	Day	13% 8% 2 4 4 3 3 4 5% 7% 46%	1762
	11th to 20th	Day	17% 10% 4 7% 5% 3 4 3 6% 6% 35%	1800
	21st to end	Day	18% 11% 3 10% 5% 3 4 3 4 6% 34%	1785
December	1st to 10th	Day	9% 11% 4 9% 5% 4 4 3 4 6% 42%	2610
	11th to 20th	Day	13% 16% 5% 11% 6% 5% 5% 4 6% 6% 23%	3008
	21st to end	Day	25% 22% 7% 12% 6% 4 3 3 4 3 10%	3982
January	1st to 10th	Night	14% 13% 7% 12% 5% 4 4 3 5% 5% 27%	6348
	11th to 20th	Night	13% 15% 7% 13% 7% 6% 5% 4 6% 4 20%	6360
	21st to end	Night	18% 14% 5% 9% 4 4 4 3 4 3 31%	6876
February	1st to 10th	Night	16% 15% 5% 8% 5% 5% 3 4 4 5% 31%	2518
	11th to 20th	Night	14% 11% 3 9% 5% 5% 4 4 4 7% 34%	2338
	21st to end	Night	18% 12% 3 9% 5% 4 3 2 5% 5% 34%	1980
March	1st to 10th	Night	17% 10% 4 7% 3 4 3 2 4 5% 40%	5373
	11th to 20th	Night	11% 6% 2 6% 4 4 5% 4 5% 7% 46%	5334
	21st to end	Night	17% 10% 5% 10% 6% 5% 5% 3 5% 5% 28%	4966
April	1st to 10th	Night	15% 8% 4 6% 4 4 4 4 5% 8% 40%	2000
	11th to 20th	Night	18% 8% 3 7% 4 4 4 3 4 6% 39%	1975
	21st to end	Night	17% 8% 3 7% 4 5% 5% 4 5% 6% 36%	1886
May	1st to 10th	Night	18% 9% 3 8% 5% 4 4 4 5% 7% 34%	4033
	11th to 20th	Night	12% 7% 3 6% 4 4 4 4 6% 9% 42%	3842
	21st to end	Night	14% 9% 3 7% 4 4 4 4 5% 7% 39%	3942
June	1st to 10th	Night	10% 5% 3 6% 4 4 3 4 6% 7% 50%	1597
	11th to 20th	Night	8% 5% 2 7% 4 5% 4 3 6% 9% 47%	1520
	21st to end	Night	9% 7% 2 5% 6% 4 5% 4 7% 8% 42%	1520
July	1st to 10th	Night	11% 5% 3 6% 5% 5% 5% 4 7% 9% 41%	2530
	11th to 20th	Night	6% 4 2 5% 4 4 4 4 5% 7% 56%	2530
	21st to end	Night	4 5% 3 7% 5% 5% 5% 5% 8% 8% 46%	2750
August	1st to 10th	Night	6% 4 2 6% 4 5% 5% 4 7% 9% 49%	2662
	11th to 20th	Night	8% 4 2 4 3 4 4 4 6% 8% 52%	3070
	21st to end	Night	8% 4 2 5% 3 4 4 3 5% 9% 52%	3476
September	1st to 10th	Night	10% 5% 1 6% 3 3 4 3 5% 7% 54%	1900
	11th to 20th	Night	8% 4 2 4 3 4 4 3 6% 8% 55%	2019
	21st to end	Night	9% 5% 2 6% 4 6% 5% 4 6% 8% 44%	2090
October	1st to 10th	Night	11% 5% 3 5% 3 4 4 3 4 7% 52%	2109
	11th to 20th	Night	15% 8% 2 6% 4 3 3 2 4 6% 47%	2299
	21st to end	Night	20% 8% 2 7% 4 4 3 2 4 6% 38%	2717
November	1st to 10th	Night	12% 8% 3 6% 4 4 3 3 5% 6% 47%	2536
	11th to 20th	Night	14% 9% 4 9% 4 4 5% 3 5% 6% 38%	2600
	21st to end	Night	17% 11% 4 7% 5% 5% 4 3 4 6% 36%	2610
December	1st to 10th	Night	12% 9% 3 7% 4 4 4 3 5% 6% 43%	4580
	11th to 20th	Night	18% 14% 4 9% 5% 4 4 3 4 5% 30%	5199
	21st to end	Night	24% 18% 6% 11% 6% 4 4 3 4 4 16%	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	62% 2 11% 17% 7% 1	3618
	11th to 20th	Day	62% 2 9% 10% 13% 4	3620
	21st to end	Day	61% 2 11% 17% 8%	4097
February	1st to 10th	Day	60% 2 11% 17% 9% 2	1880
	11th to 20th	Day	54% 2 9% 24% 9% 2	1958
	21st to end	Day	57% 2 10% 21% 8% 2	1650
March	1st to 10th	Day	51% 1 7% 25% 13% 3	4480
	11th to 20th	Day	41% 2 11% 34% 11% 1	4651
	21st to end	Day	65% 3 11% 14% 6% 1	5969
April	1st to 10th	Day	53% 3 10% 20% 14%	2400
	11th to 20th	Day	48% 3 11% 23% 12% 3	2374
	21st to end	Day	51% 3 13% 20% 12% 2	2512
May	1st to 10th	Day	50% 3 10% 23% 12% 2	5897
	11th to 20th	Day	44% 3 11% 27% 13% 2	6061
	21st to end	Day	43% 3 9% 25% 17% 3	6949
June	1st to 10th	Day	37% 4 11% 27% 19% 3	2787
	11th to 20th	Day	36% 3 11% 26% 21% 3	2660
	21st to end	Day	40% 5% 14% 23% 15% 3	2660
July	1st to 10th	Day	44% 5% 13% 22% 14% 2	4371
	11th to 20th	Day	31% 6% 16% 30% 16% 1	4365
	21st to end	Day	39% 6% 16% 18% 19% 3	4662
August	1st to 10th	Day	33% 5% 16% 31% 14% 1	4254
	11th to 20th	Day	34% 5% 12% 32% 16% 1	3779
	21st to end	Day	32% 5% 12% 28% 20% 3	4179
September	1st to 10th	Day	36% 4 11% 28% 17% 4	2280
	11th to 20th	Day	32% 3 10% 28% 22% 4	2142
	21st to end	Day	38% 4 8% 27% 21% 2	2090
October	1st to 10th	Day	26% 3 7% 31% 31% 2	3432
	11th to 20th	Day	35% 2 11% 25% 25% 1	3109
	21st to end	Day	43% 3 9% 25% 17% 2	3081
November	1st to 10th	Day	38% 2 15% 26% 16% 2	1762
	11th to 20th	Day	51% 2 12% 23% 12% 1	1800
	21st to end	Day	54% 3 10% 23% 11% 1	1785
December	1st to 10th	Day	46% 2 14% 28% 10%	2610
	11th to 20th	Day	61% 3 12% 17% 6% 1	3005
	21st to end	Day	80% 2 6% 8% 4	3982
January	1st to 10th	Night	61% 2 8% 18% 10%	6348
	11th to 20th	Night	67% 2 9% 9% 11% 2	6360
	21st to end	Night	61% 1 9% 18% 11% 1	6876
February	1st to 10th	Night	57% 2 10% 19% 10% 2	2518
	11th to 20th	Night	52% 2 9% 23% 13% 2	2339
	21st to end	Night	53% 3 9% 21% 11% 3	1980
March	1st to 10th	Night	49% 2 9% 27% 11% 3	5373
	11th to 20th	Night	39% 2 12% 28% 16% 3	5334
	21st to end	Night	59% 2 9% 21% 8% 1	4966
April	1st to 10th	Night	44% 3 12% 26% 14% 2	2000
	11th to 20th	Night	48% 2 7% 22% 17% 4	1975
	21st to end	Night	49% 4 10% 21% 14% 3	1886
May	1st to 10th	Night	51% 2 10% 17% 15% 4	4060
	11th to 20th	Night	40% 4 14% 27% 13% 3	3843
	21st to end	Night	45% 3 10% 21% 17% 4	3950
June	1st to 10th	Night	34% 2 12% 28% 21% 4	1597
	11th to 20th	Night	34% 3 11% 25% 23% 3	1520
	21st to end	Night	39% 4 15% 22% 15% 4	1520
July	1st to 10th	Night	40% 4 15% 24% 12% 6%	2490
	11th to 20th	Night	28% 4 13% 28% 25% 2	2482
	21st to end	Night	34% 5% 16% 20% 20% 5%	2662
August	1st to 10th	Night	31% 5% 18% 29% 17% 1	2653
	11th to 20th	Night	29% 5% 15% 30% 20% 1	3099
	21st to end	Night	29% 5% 11% 33% 18% 3	3476
September	1st to 10th	Night	31% 4 11% 26% 24% 5%	1900
	11th to 20th	Night	28% 3 8% 30% 27% 4	2019
	21st to end	Night	37% 4 8% 29% 18% 3	2090
October	1st to 10th	Night	22% 3 7% 34% 32% 3	3512
	11th to 20th	Night	33% 3 7% 26% 30% 2	3810
	21st to end	Night	40% 3 8% 25% 21% 4	4467
November	1st to 10th	Night	38% 3 9% 29% 19% 3	2536
	11th to 20th	Night	48% 2 11% 23% 15% 2	2600
	21st to end	Night	52% 2 10% 24% 12%	2610
December	1st to 10th	Night	43% 2 14% 28% 12% 1	4580
	11th to 20th	Night	58% 2 12% 17% 11% 1	5201
	21st to end	Night	73% 2 8% 11% 6%	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	21% 12% 35% 26% 6% 1	300
	11th to 20th	Day	24% 18% 37% 15% 5% 1	300
	21st to end	Day	22% 16% 36% 20% 5%	330
February	1st to 10th	Day	24% 19% 37% 16% 4	300
	11th to 20th	Day	24% 16% 37% 20% 4	300
	21st to end	Day	24% 19% 41% 12% 3	249
March	1st to 10th	Day	22% 21% 35% 20% 2	300
	11th to 20th	Day	21% 19% 34% 20% 6%	340
	21st to end	Day	30% 14% 31% 18% 5% 2	550
April	1st to 10th	Day	24% 13% 32% 22% 8% 1	500
	11th to 20th	Day	21% 17% 30% 19% 11% 3	492
	21st to end	Day	21% 16% 33% 20% 8% 2	500
May	1st to 10th	Day	22% 13% 31% 23% 9% 3	503
	11th to 20th	Day	20% 8% 32% 22% 14% 4	606
	21st to end	Day	14% 9% 33% 22% 15% 7%	789
June	1st to 10th	Day	10% 9% 30% 28% 18% 5%	726
	11th to 20th	Day	11% 5% 30% 31% 18% 5%	680
	21st to end	Day	13% 8% 30% 30% 14% 5%	680
July	1st to 10th	Day	9% 5% 21% 28% 22% 15%	671
	11th to 20th	Day	9% 5% 23% 31% 20% 11%	668
	21st to end	Day	8% 3 22% 35% 23% 9%	739
August	1st to 10th	Day	9% 3 16% 32% 27% 13%	587
	11th to 20th	Day	10% 4 19% 28% 24% 15%	479
	21st to end	Day	7% 2 17% 36% 25% 13%	539
September	1st to 10th	Day	11% 6% 20% 31% 23% 9%	490
	11th to 20th	Day	11% 5% 14% 27% 30% 12%	490
	21st to end	Day	13% 7% 26% 27% 19% 8%	490
October	1st to 10th	Day	13% 6% 29% 28% 19% 5%	468
	11th to 20th	Day	20% 18% 31% 21% 9% 1	300
	21st to end	Day	31% 12% 34% 18% 5%	330
November	1st to 10th	Day	16% 13% 35% 22% 8% 4	300
	11th to 20th	Day	23% 15% 36% 16% 9% 1	300
	21st to end	Day	23% 12% 37% 22% 6%	300
December	1st to 10th	Day	16% 19% 40% 17% 7% 1	300
	11th to 20th	Day	21% 16% 37% 20% 6%	300
	21st to end	Day	27% 20% 38% 13% 2	330
January	1st to 10th	Night	20% 14% 39% 23% 4	1000
	11th to 20th	Night	23% 14% 37% 21% 4	1000
	21st to end	Night	22% 13% 35% 26% 4	1100
February	1st to 10th	Night	24% 13% 38% 22% 3	918
	11th to 20th	Night	20% 14% 36% 26% 4	783
	21st to end	Night	23% 15% 38% 20% 3	660
March	1st to 10th	Night	22% 14% 35% 24% 5%	800
	11th to 20th	Night	18% 12% 39% 25% 6% 1	800
	21st to end	Night	26% 10% 35% 23% 7%	664
April	1st to 10th	Night	19% 10% 40% 25% 6% 1	600
	11th to 20th	Night	21% 12% 33% 25% 8%	593
	21st to end	Night	20% 11% 33% 28% 8% 1	600
May	1st to 10th	Night	19% 7% 34% 32% 9%	600
	11th to 20th	Night	16% 6% 30% 35% 13% 1	591
	21st to end	Night	11% 5% 28% 37% 18% 1	650
June	1st to 10th	Night	11% 4 27% 44% 14%	599
	11th to 20th	Night	10% 4 28% 42% 15% 2	570
	21st to end	Night	11% 4 27% 38% 18% 1	570
July	1st to 10th	Night	9% 2 16% 44% 26% 4	555
	11th to 20th	Night	7% 3 19% 40% 28% 3	552
	21st to end	Night	5% 1 18% 47% 28% 1	624
August	1st to 10th	Night	5% 2 11% 48% 31% 4	567
	11th to 20th	Night	8% 2 12% 41% 31% 5%	564
	21st to end	Night	8% 2 17% 38% 32% 3	627
September	1st to 10th	Night	11% 3 16% 40% 27% 4	570
	11th to 20th	Night	9% 4 16% 39% 28% 4	689
	21st to end	Night	12% 6% 24% 33% 22% 3	760
October	1st to 10th	Night	13% 6% 24% 36% 20% 1	760
	11th to 20th	Night	19% 13% 31% 27% 10%	760
	21st to end	Night	24% 13% 31% 24% 8%	836
November	1st to 10th	Night	16% 11% 38% 25% 9% 1	780
	11th to 20th	Night	19% 16% 34% 25% 6%	800
	21st to end	Night	22% 14% 35% 23% 7%	810
December	1st to 10th	Night	23% 13% 36% 24% 4	1000
	11th to 20th	Night	25% 11% 34% 25% 5%	1000
	21st to end	Night	29% 13% 33% 23% 2	1100

Page generated at 2025-06-07 09:28:13. Version ac07

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