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 2026-10-14.

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% 5% 5% 4 6% 8% 36%	149249
	Night	13% 9% 4 8% 5% 4 4 3 5% 6% 38%	142800
Transparency	Day	46% 4 11% 24% 14% 2	152784
	Night	46% 3 11% 23% 15% 2	147328
Seeing	Day	16% 11% 29% 25% 14% 5%	18463
	Night	17% 10% 30% 30% 12% 1	28209

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	13% 13% 6% 13% 6% 5% 5% 4 5% 7% 22%	4691
	11th to 20th	Day	9% 12% 6% 14% 7% 6% 6% 5% 6% 4 26%	4710
	21st to end	Day	13% 16% 5% 11% 6% 4 4 4 5% 6% 26%	5313
February	1st to 10th	Day	17% 12% 5% 10% 6% 5% 5% 4 5% 7% 25%	1974
	11th to 20th	Day	13% 12% 5% 8% 7% 5% 4 3 5% 6% 32%	2048
	21st to end	Day	14% 13% 5% 11% 5% 4 4 4 5% 6% 29%	1730
March	1st to 10th	Day	19% 13% 4 7% 4 3 2 2 4 4 39%	4580
	11th to 20th	Day	8% 8% 3 7% 5% 4 5% 4 6% 8% 41%	4754
	21st to end	Day	19% 13% 6% 10% 6% 6% 4 4 4 6% 22%	6099
April	1st to 10th	Day	18% 13% 3 7% 5% 4 4 3 5% 7% 31%	2520
	11th to 20th	Day	15% 10% 3 6% 5% 5% 4 4 5% 7% 36%	2494
	21st to end	Day	19% 8% 3 7% 5% 5% 5% 4 5% 6% 34%	2638
May	1st to 10th	Day	17% 8% 3 7% 5% 5% 5% 4 7% 8% 32%	7616
	11th to 20th	Day	13% 6% 2 7% 5% 5% 5% 4 6% 7% 38%	7878
	21st to end	Day	13% 7% 3 7% 5% 4 4 4 6% 9% 38%	9047
June	1st to 10th	Day	11% 6% 2 6% 4 5% 4 5% 6% 8% 44%	2940
	11th to 20th	Day	9% 5% 1 6% 5% 4 5% 4 6% 9% 45%	2940
	21st to end	Day	10% 6% 2 6% 6% 6% 6% 5% 8% 8% 39%	2940
July	1st to 10th	Day	8% 5% 2 7% 5% 5% 6% 5% 7% 11% 38%	8280
	11th to 20th	Day	7% 5% 2 6% 4 5% 5% 4 7% 10% 44%	8280
	21st to end	Day	10% 6% 2 7% 5% 5% 6% 5% 7% 9% 40%	8990
August	1st to 10th	Day	10% 6% 2 7% 5% 4 5% 4 6% 8% 43%	6254
	11th to 20th	Day	13% 7% 3 7% 4 5% 5% 5% 7% 9% 36%	5515
	21st to end	Day	5% 4 2 6% 4 4 5% 4 7% 10% 49%	6080
September	1st to 10th	Day	10% 5% 2 5% 4 3 5% 4 6% 8% 48%	2520
	11th to 20th	Day	12% 5% 2 4 4 4 3 4 5% 8% 50%	2368
	21st to end	Day	11% 5% 2 7% 5% 5% 5% 4 6% 8% 43%	2310
October	1st to 10th	Day	11% 6% 3 6% 4 4 4 3 5% 6% 48%	2286
	11th to 20th	Day	17% 8% 2 6% 4 4 4 3 5% 7% 38%	2010
	21st to end	Day	19% 8% 3 8% 4 4 4 3 5% 7% 34%	1980
November	1st to 10th	Day	13% 8% 2 5% 4 3 3 4 5% 7% 46%	1852
	11th to 20th	Day	17% 10% 4 7% 4 3 4 3 6% 6% 35%	1890
	21st to end	Day	18% 12% 3 10% 4 3 4 3 4 5% 34%	1874
December	1st to 10th	Day	9% 11% 4 9% 5% 4 4 3 4 6% 41%	2690
	11th to 20th	Day	13% 16% 5% 11% 6% 5% 5% 4 6% 6% 23%	3088
	21st to end	Day	25% 22% 7% 12% 6% 4 4 3 4 3 11%	4070
January	1st to 10th	Night	13% 13% 6% 12% 5% 5% 4 3 5% 5% 28%	8232
	11th to 20th	Night	11% 13% 6% 14% 8% 7% 6% 4 6% 5% 22%	8280
	21st to end	Night	15% 13% 5% 9% 4 5% 5% 4 4 4 31%	8896
February	1st to 10th	Night	15% 14% 5% 9% 5% 5% 3 3 4 5% 31%	2644
	11th to 20th	Night	14% 11% 3 9% 5% 5% 4 4 5% 7% 34%	2458
	21st to end	Night	17% 12% 4 10% 5% 4 3 2 5% 5% 34%	2076
March	1st to 10th	Night	16% 11% 4 7% 3 4 3 3 4 5% 39%	5493
	11th to 20th	Night	12% 7% 2 6% 4 4 5% 4 5% 7% 45%	5452
	21st to end	Night	17% 10% 4 10% 6% 5% 6% 3 5% 5% 28%	5076
April	1st to 10th	Night	15% 9% 4 7% 4 4 4 4 5% 7% 38%	2100
	11th to 20th	Night	18% 8% 3 7% 4 4 4 3 4 6% 39%	2075
	21st to end	Night	16% 8% 3 7% 4 5% 5% 4 5% 7% 36%	1980
May	1st to 10th	Night	17% 9% 3 7% 5% 4 4 3 5% 7% 37%	5237
	11th to 20th	Night	10% 5% 2 6% 4 4 4 4 7% 10% 44%	4992
	21st to end	Night	13% 8% 3 7% 4 4 5% 4 6% 8% 38%	5139
June	1st to 10th	Night	10% 5% 3 6% 3 4 3 4 5% 7% 49%	1680
	11th to 20th	Night	9% 5% 2 6% 5% 5% 4 3 6% 9% 46%	1680
	21st to end	Night	9% 6% 2 5% 6% 5% 5% 4 6% 9% 42%	1680
July	1st to 10th	Night	9% 6% 3 6% 5% 5% 5% 4 7% 9% 44%	4708
	11th to 20th	Night	6% 4 2 6% 4 4 4 4 5% 8% 51%	4707
	21st to end	Night	6% 5% 3 7% 5% 5% 5% 5% 7% 8% 45%	5117
August	1st to 10th	Night	12% 5% 2 5% 4 4 4 4 7% 8% 45%	3902
	11th to 20th	Night	12% 6% 3 6% 4 4 4 4 6% 8% 42%	4515
	21st to end	Night	7% 4 2 5% 3 4 4 4 5% 8% 54%	5046
September	1st to 10th	Night	9% 5% 1 6% 3 3 4 3 5% 7% 54%	2100
	11th to 20th	Night	8% 4 2 4 3 4 4 3 6% 8% 54%	2231
	21st to end	Night	9% 5% 2 7% 5% 6% 5% 4 6% 8% 44%	2310
October	1st to 10th	Night	11% 4 3 5% 3 4 4 3 4 6% 53%	2331
	11th to 20th	Night	14% 8% 2 6% 4 3 3 2 4 6% 47%	2457
	21st to end	Night	20% 8% 2 7% 4 4 4 2 4 6% 38%	2860
November	1st to 10th	Night	12% 8% 3 6% 4 4 3 3 5% 7% 46%	2666
	11th to 20th	Night	14% 9% 3 8% 4 4 5% 3 5% 6% 38%	2730
	21st to end	Night	17% 11% 4 7% 5% 4 4 3 4 6% 35%	2741
December	1st to 10th	Night	12% 9% 3 7% 4 4 4 3 5% 6% 42%	4720
	11th to 20th	Night	17% 14% 4 9% 5% 4 4 3 4 5% 30%	5339
	21st to end	Night	24% 18% 6% 11% 6% 4 4 3 4 4 16%	7150

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	63% 2 14% 15% 6% 1	4692
	11th to 20th	Day	60% 2 7% 14% 12% 3	4710
	21st to end	Day	60% 2 12% 18% 8% 1	5313
February	1st to 10th	Day	59% 2 12% 17% 8% 2	1974
	11th to 20th	Day	54% 2 9% 24% 9% 2	2058
	21st to end	Day	57% 2 10% 21% 7% 2	1730
March	1st to 10th	Day	51% 1 7% 25% 13% 3	4580
	11th to 20th	Day	41% 2 11% 34% 11% 1	4754
	21st to end	Day	65% 3 11% 15% 6% 1	6101
April	1st to 10th	Day	53% 3 10% 20% 13%	2520
	11th to 20th	Day	49% 3 11% 23% 12% 3	2494
	21st to end	Day	51% 3 12% 20% 12% 2	2638
May	1st to 10th	Day	49% 3 10% 24% 12% 1	7651
	11th to 20th	Day	45% 3 11% 24% 15% 1	7882
	21st to end	Day	44% 3 10% 22% 17% 4	9061
June	1st to 10th	Day	38% 4 11% 26% 19% 2	2940
	11th to 20th	Day	36% 3 10% 27% 21% 3	2940
	21st to end	Day	39% 5% 15% 23% 15% 3	2940
July	1st to 10th	Day	37% 6% 15% 25% 16% 1	8211
	11th to 20th	Day	33% 6% 14% 31% 15% 1	8205
	21st to end	Day	39% 6% 15% 24% 15% 2	8794
August	1st to 10th	Day	37% 5% 14% 28% 16% 1	6239
	11th to 20th	Day	43% 5% 13% 26% 12%	5551
	21st to end	Day	29% 5% 14% 33% 18% 2	6079
September	1st to 10th	Day	34% 4 11% 30% 17% 4	2520
	11th to 20th	Day	33% 3 10% 28% 22% 4	2368
	21st to end	Day	38% 4 8% 27% 21% 2	2310
October	1st to 10th	Day	26% 3 7% 31% 31% 2	3650
	11th to 20th	Day	35% 2 11% 25% 25% 2	3238
	21st to end	Day	43% 3 9% 25% 18% 2	3180
November	1st to 10th	Day	38% 3 14% 27% 16% 2	1852
	11th to 20th	Day	50% 2 12% 23% 12% 1	1890
	21st to end	Day	54% 3 9% 23% 10% 1	1874
December	1st to 10th	Day	46% 2 14% 28% 10%	2690
	11th to 20th	Day	61% 3 12% 18% 6% 1	3085
	21st to end	Day	80% 2 6% 8% 4	4070
January	1st to 10th	Night	59% 2 10% 19% 9%	8233
	11th to 20th	Night	63% 2 10% 12% 10% 2	8280
	21st to end	Night	58% 2 10% 21% 9% 1	8896
February	1st to 10th	Night	57% 2 10% 20% 10% 2	2644
	11th to 20th	Night	51% 2 9% 23% 13% 2	2459
	21st to end	Night	53% 3 10% 21% 11% 3	2076
March	1st to 10th	Night	49% 2 9% 27% 10% 3	5493
	11th to 20th	Night	40% 2 12% 28% 16% 3	5452
	21st to end	Night	58% 3 9% 22% 8% 1	5076
April	1st to 10th	Night	46% 3 12% 25% 13% 2	2100
	11th to 20th	Night	47% 3 8% 22% 17% 4	2075
	21st to end	Night	48% 4 10% 23% 14% 3	1980
May	1st to 10th	Night	49% 3 9% 21% 16% 3	5264
	11th to 20th	Night	36% 4 14% 26% 17% 2	4993
	21st to end	Night	44% 3 9% 19% 19% 6%	5149
June	1st to 10th	Night	35% 2 11% 27% 21% 4	1680
	11th to 20th	Night	35% 4 11% 25% 23% 3	1680
	21st to end	Night	39% 4 15% 23% 16% 3	1680
July	1st to 10th	Night	36% 5% 13% 26% 16% 3	4670
	11th to 20th	Night	31% 5% 12% 27% 23% 1	4662
	21st to end	Night	36% 6% 14% 23% 18% 4	5002
August	1st to 10th	Night	36% 4 15% 27% 17% 1	3893
	11th to 20th	Night	39% 6% 15% 24% 14% 1	4544
	21st to end	Night	28% 5% 11% 35% 18% 2	5046
September	1st to 10th	Night	31% 4 11% 27% 23% 4	2100
	11th to 20th	Night	29% 3 8% 29% 27% 4	2231
	21st to end	Night	37% 4 9% 28% 19% 3	2310
October	1st to 10th	Night	22% 3 7% 34% 32% 3	3734
	11th to 20th	Night	33% 3 7% 25% 30% 2	3968
	21st to end	Night	40% 3 8% 25% 21% 4	4610
November	1st to 10th	Night	38% 3 9% 28% 19% 3	2666
	11th to 20th	Night	47% 2 11% 23% 14% 2	2730
	21st to end	Night	52% 2 10% 24% 11%	2741
December	1st to 10th	Night	43% 2 14% 27% 12% 1	4720
	11th to 20th	Night	58% 2 11% 17% 11% 1	5341
	21st to end	Night	73% 2 8% 11% 6%	7150

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	22% 12% 35% 25% 6% 1	330
	11th to 20th	Day	23% 20% 38% 14% 4 1	330
	21st to end	Day	21% 18% 36% 20% 5%	363
February	1st to 10th	Day	22% 20% 36% 17% 5%	330
	11th to 20th	Day	23% 17% 37% 19% 3	330
	21st to end	Day	25% 19% 42% 11% 3	273
March	1st to 10th	Day	22% 21% 36% 18% 2	330
	11th to 20th	Day	23% 18% 33% 20% 5%	372
	21st to end	Day	28% 15% 33% 17% 5% 2	594
April	1st to 10th	Day	24% 15% 32% 21% 8% 1	540
	11th to 20th	Day	21% 18% 30% 19% 10% 2	532
	21st to end	Day	21% 15% 33% 21% 8% 2	540
May	1st to 10th	Day	22% 13% 31% 23% 9% 3	543
	11th to 20th	Day	19% 10% 33% 22% 13% 4	650
	21st to end	Day	14% 9% 33% 22% 16% 7%	844
June	1st to 10th	Day	10% 9% 31% 27% 18% 5%	780
	11th to 20th	Day	11% 6% 31% 31% 16% 4	780
	21st to end	Day	13% 8% 31% 30% 13% 5%	780
July	1st to 10th	Day	8% 5% 20% 30% 22% 14%	771
	11th to 20th	Day	9% 4 22% 32% 21% 11%	768
	21st to end	Day	8% 4 23% 34% 22% 8%	849
August	1st to 10th	Day	9% 3 16% 32% 27% 13%	677
	11th to 20th	Day	10% 4 19% 29% 24% 13%	559
	21st to end	Day	7% 2 18% 35% 25% 12%	627
September	1st to 10th	Day	10% 6% 21% 31% 23% 9%	570
	11th to 20th	Day	11% 5% 16% 26% 29% 13%	570
	21st to end	Day	13% 6% 26% 26% 20% 9%	570
October	1st to 10th	Day	12% 6% 29% 29% 19% 4	546
	11th to 20th	Day	19% 17% 30% 24% 9% 1	339
	21st to end	Day	30% 12% 35% 18% 5%	363
November	1st to 10th	Day	16% 14% 37% 21% 8% 4	330
	11th to 20th	Day	24% 16% 34% 16% 8% 1	330
	21st to end	Day	25% 12% 37% 20% 5%	330
December	1st to 10th	Day	15% 18% 41% 18% 7% 1	330
	11th to 20th	Day	22% 16% 37% 20% 5%	330
	21st to end	Day	28% 19% 38% 13% 2	363
January	1st to 10th	Night	20% 14% 39% 23% 4	1050
	11th to 20th	Night	22% 15% 38% 21% 4	1050
	21st to end	Night	21% 14% 36% 25% 4	1155
February	1st to 10th	Night	24% 13% 38% 23% 3	964
	11th to 20th	Night	20% 14% 37% 26% 4	823
	21st to end	Night	23% 15% 38% 20% 3	692
March	1st to 10th	Night	22% 15% 35% 23% 5%	840
	11th to 20th	Night	18% 12% 39% 25% 6% 1	840
	21st to end	Night	25% 10% 36% 22% 6%	697
April	1st to 10th	Night	19% 11% 39% 24% 5%	630
	11th to 20th	Night	21% 13% 33% 24% 8%	623
	21st to end	Night	19% 11% 33% 28% 8% 1	630
May	1st to 10th	Night	18% 7% 35% 31% 8%	630
	11th to 20th	Night	15% 7% 31% 34% 12% 1	621
	21st to end	Night	11% 5% 28% 36% 18% 1	683
June	1st to 10th	Night	12% 4 27% 43% 14%	630
	11th to 20th	Night	11% 5% 28% 42% 13% 1	630
	21st to end	Night	11% 4 28% 40% 17% 1	630
July	1st to 10th	Night	9% 2 16% 43% 26% 4	615
	11th to 20th	Night	7% 3 18% 40% 29% 3	612
	21st to end	Night	5% 2 18% 46% 28% 1	690
August	1st to 10th	Night	6% 2 11% 48% 30% 4	627
	11th to 20th	Night	8% 3 13% 41% 30% 4	624
	21st to end	Night	7% 2 16% 40% 31% 3	693
September	1st to 10th	Night	10% 3 16% 40% 27% 4	630
	11th to 20th	Night	9% 4 17% 39% 27% 4	761
	21st to end	Night	12% 6% 24% 33% 22% 3	840
October	1st to 10th	Night	13% 5% 25% 36% 20% 1	840
	11th to 20th	Night	19% 13% 31% 28% 10%	813
	21st to end	Night	23% 13% 31% 25% 7%	880
November	1st to 10th	Night	16% 11% 38% 25% 9% 1	820
	11th to 20th	Night	18% 16% 35% 25% 5%	840
	21st to end	Night	23% 14% 33% 23% 6%	851
December	1st to 10th	Night	23% 13% 36% 24% 4	1050
	11th to 20th	Night	24% 12% 35% 24% 5%	1050
	21st to end	Night	30% 14% 33% 23% 2	1155

Page generated at 2026-10-11 04:06:30. Version ac07

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