Champaign Star Gazers Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Champaign Star Gazers Observing Site clear sky chart from 2005-11-06 to 2026-06-16.

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	14% 10% 4 9% 5% 5% 5% 4 6% 7% 33%	137624
	Night	14% 10% 4 9% 5% 5% 4 4 5% 7% 34%	134435
Transparency	Day	47% 7% 12% 21% 12% 1	141249
	Night	47% 6% 11% 21% 13% 2	138882
Seeing	Day	17% 11% 27% 23% 15% 7%	17533
	Night	18% 10% 28% 29% 14% 2	27264

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% 16% 7% 16% 6% 5% 4 3 4 5% 17%	4691
	11th to 20th	Day	10% 14% 6% 15% 9% 8% 6% 4 3 4 20%	5139
	21st to end	Day	17% 13% 7% 12% 7% 6% 6% 4 5% 6% 17%	5780
February	1st to 10th	Day	17% 15% 6% 12% 6% 5% 5% 3 4 6% 21%	1932
	11th to 20th	Day	14% 12% 5% 15% 8% 4 4 4 5% 5% 23%	2048
	21st to end	Day	16% 13% 4 11% 5% 4 5% 3 4 6% 29%	1730
March	1st to 10th	Day	17% 14% 7% 12% 5% 4 4 3 4 4 26%	4670
	11th to 20th	Day	11% 10% 3 8% 5% 4 5% 3 5% 7% 38%	5090
	21st to end	Day	17% 12% 4 9% 6% 5% 4 3 5% 6% 30%	5586
April	1st to 10th	Day	14% 12% 4 9% 5% 5% 4 4 6% 7% 31%	2442
	11th to 20th	Day	16% 9% 3 8% 4 4 4 3 5% 7% 37%	2600
	21st to end	Day	17% 9% 3 7% 5% 5% 4 4 6% 7% 34%	2730
May	1st to 10th	Day	19% 10% 3 8% 5% 5% 5% 4 5% 6% 31%	7616
	11th to 20th	Day	16% 8% 3 6% 4 4 5% 4 6% 9% 35%	7626
	21st to end	Day	16% 8% 3 7% 5% 4 5% 4 7% 9% 32%	8391
June	1st to 10th	Day	13% 6% 2 7% 5% 5% 6% 4 6% 8% 39%	2745
	11th to 20th	Day	10% 6% 2 6% 6% 4 5% 4 8% 9% 39%	2871
	21st to end	Day	10% 5% 2 7% 4 4 5% 5% 7% 10% 40%	2800
July	1st to 10th	Day	9% 6% 3 7% 5% 4 5% 4 7% 9% 41%	6360
	11th to 20th	Day	9% 6% 2 7% 4 5% 6% 5% 7% 11% 38%	6141
	21st to end	Day	10% 6% 3 7% 5% 5% 6% 5% 8% 10% 35%	6424
August	1st to 10th	Day	7% 7% 3 7% 4 5% 5% 5% 7% 10% 42%	4234
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 4 7% 12% 41%	4174
	21st to end	Day	7% 4 2 7% 4 5% 5% 4 7% 9% 45%	4459
September	1st to 10th	Day	11% 5% 2 5% 4 4 4 4 4 6% 50%	2257
	11th to 20th	Day	8% 4 2 5% 5% 4 4 3 6% 8% 49%	2200
	21st to end	Day	17% 7% 2 6% 4 3 3 3 5% 7% 44%	2200
October	1st to 10th	Day	11% 7% 2 6% 4 3 4 3 5% 6% 47%	2191
	11th to 20th	Day	14% 8% 2 5% 4 4 4 4 5% 6% 44%	2000
	21st to end	Day	18% 9% 3 8% 5% 4 4 4 5% 8% 33%	2065
November	1st to 10th	Day	10% 9% 2 6% 4 4 4 3 5% 7% 45%	1852
	11th to 20th	Day	15% 12% 4 8% 4 4 4 3 5% 7% 33%	1890
	21st to end	Day	18% 14% 6% 11% 4 4 3 3 4 6% 28%	1890
December	1st to 10th	Day	15% 12% 4 10% 6% 4 5% 4 5% 5% 30%	3020
	11th to 20th	Day	19% 15% 6% 12% 5% 4 4 3 4 6% 21%	3463
	21st to end	Day	22% 19% 8% 11% 6% 5% 4 3 4 5% 13%	4317
January	1st to 10th	Night	12% 15% 7% 16% 8% 6% 5% 3 5% 5% 18%	8232
	11th to 20th	Night	9% 14% 8% 18% 8% 7% 6% 4 4 4 18%	7820
	21st to end	Night	17% 13% 5% 9% 5% 5% 4 3 5% 7% 26%	8401
February	1st to 10th	Night	18% 13% 3 9% 7% 6% 5% 4 4 5% 26%	2685
	11th to 20th	Night	15% 13% 4 10% 7% 4 3 3 5% 6% 30%	2458
	21st to end	Night	18% 12% 5% 12% 5% 4 4 3 5% 5% 27%	2076
March	1st to 10th	Night	18% 12% 5% 7% 4 4 4 3 3 5% 35%	5402
	11th to 20th	Night	12% 7% 3 7% 5% 5% 5% 3 5% 8% 40%	5090
	21st to end	Night	17% 9% 3 9% 5% 4 4 3 5% 6% 36%	5588
April	1st to 10th	Night	16% 10% 3 8% 5% 4 4 4 5% 7% 35%	2195
	11th to 20th	Night	14% 8% 3 7% 5% 4 5% 4 6% 7% 37%	1967
	21st to end	Night	16% 8% 3 7% 5% 4 4 3 6% 7% 37%	1890
May	1st to 10th	Night	21% 10% 3 7% 5% 4 4 4 5% 7% 29%	5237
	11th to 20th	Night	15% 7% 2 6% 4 4 5% 4 5% 8% 40%	5234
	21st to end	Night	14% 7% 2 7% 5% 5% 4 3 6% 9% 37%	5761
June	1st to 10th	Night	10% 6% 2 6% 4 4 5% 3 7% 7% 47%	1868
	11th to 20th	Night	8% 5% 2 6% 5% 4 4 3 7% 10% 46%	1640
	21st to end	Night	7% 4 2 5% 4 5% 5% 4 7% 10% 46%	1600
July	1st to 10th	Night	9% 6% 2 7% 4 4 5% 4 6% 8% 46%	3618
	11th to 20th	Night	7% 5% 2 7% 5% 4 5% 5% 6% 9% 44%	3810
	21st to end	Night	8% 7% 2 7% 5% 5% 5% 4 7% 9% 41%	4427
August	1st to 10th	Night	9% 7% 3 7% 4 4 5% 4 7% 9% 41%	2915
	11th to 20th	Night	7% 6% 3 7% 5% 5% 5% 3 6% 7% 46%	2875
	21st to end	Night	4 4 1 5% 4 5% 5% 5% 7% 10% 50%	3421
September	1st to 10th	Night	11% 5% 2 5% 4 3 4 3 5% 7% 52%	2121
	11th to 20th	Night	8% 4 2 4 3 3 3 3 6% 7% 57%	2200
	21st to end	Night	15% 6% 2 6% 3 4 4 3 5% 6% 46%	2200
October	1st to 10th	Night	9% 4 2 6% 4 4 4 4 5% 6% 53%	2208
	11th to 20th	Night	15% 8% 2 6% 4 4 4 3 5% 6% 43%	2400
	21st to end	Night	18% 8% 3 6% 5% 3 5% 4 5% 6% 38%	2770
November	1st to 10th	Night	12% 8% 3 6% 3 4 4 3 5% 7% 45%	2666
	11th to 20th	Night	16% 9% 4 8% 4 3 4 3 5% 7% 37%	2730
	21st to end	Night	18% 14% 5% 8% 6% 5% 4 4 5% 6% 27%	2730
December	1st to 10th	Night	15% 11% 4 9% 5% 5% 5% 4 5% 7% 30%	4380
	11th to 20th	Night	17% 16% 8% 13% 4 3 4 3 5% 5% 22%	4952
	21st to end	Night	22% 20% 8% 11% 5% 4 3 3 4 5% 15%	6868

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	69% 5% 10% 12% 4	4692
	11th to 20th	Day	68% 4 7% 8% 11% 1	5139
	21st to end	Day	67% 6% 10% 11% 6% 1	5780
February	1st to 10th	Day	64% 5% 10% 12% 8%	1932
	11th to 20th	Day	62% 6% 8% 15% 8%	2058
	21st to end	Day	56% 6% 13% 17% 7% 2	1730
March	1st to 10th	Day	60% 5% 8% 19% 7% 1	4670
	11th to 20th	Day	43% 6% 11% 28% 12% 1	5090
	21st to end	Day	53% 6% 12% 18% 8% 2	5586
April	1st to 10th	Day	51% 7% 12% 17% 12% 1	2442
	11th to 20th	Day	46% 6% 13% 20% 12% 2	2600
	21st to end	Day	48% 6% 13% 21% 11% 1	2730
May	1st to 10th	Day	51% 8% 11% 19% 11% 1	7651
	11th to 20th	Day	44% 7% 14% 24% 11%	7630
	21st to end	Day	45% 8% 11% 20% 12% 4	8405
June	1st to 10th	Day	42% 7% 11% 22% 15% 2	2745
	11th to 20th	Day	38% 8% 14% 23% 15% 1	2871
	21st to end	Day	38% 9% 16% 20% 15% 3	2800
July	1st to 10th	Day	37% 8% 10% 27% 16% 2	6291
	11th to 20th	Day	36% 10% 16% 23% 14% 1	6066
	21st to end	Day	39% 9% 14% 19% 16% 3	6240
August	1st to 10th	Day	33% 9% 18% 25% 14% 1	4221
	11th to 20th	Day	33% 8% 13% 32% 13% 1	4213
	21st to end	Day	31% 9% 13% 30% 13% 3	4458
September	1st to 10th	Day	34% 7% 11% 24% 21% 4	2257
	11th to 20th	Day	32% 5% 12% 25% 23% 3	2200
	21st to end	Day	40% 5% 10% 22% 22% 1	2200
October	1st to 10th	Day	25% 5% 11% 31% 27% 1	3568
	11th to 20th	Day	31% 6% 12% 27% 23% 2	3240
	21st to end	Day	39% 5% 10% 23% 20% 2	3315
November	1st to 10th	Day	38% 5% 12% 25% 17% 3	1852
	11th to 20th	Day	51% 5% 10% 21% 12% 2	1890
	21st to end	Day	57% 5% 10% 18% 8% 1	1890
December	1st to 10th	Day	53% 6% 14% 21% 6%	3020
	11th to 20th	Day	65% 5% 11% 15% 5%	3460
	21st to end	Day	74% 4 7% 10% 4	4317
January	1st to 10th	Night	67% 6% 9% 13% 5%	8233
	11th to 20th	Night	67% 5% 8% 10% 8% 1	7820
	21st to end	Night	57% 5% 12% 16% 7% 1	8401
February	1st to 10th	Night	60% 5% 11% 16% 8% 1	2685
	11th to 20th	Night	55% 5% 11% 17% 11% 1	2459
	21st to end	Night	58% 6% 10% 15% 9% 2	2076
March	1st to 10th	Night	51% 5% 8% 25% 10% 2	5402
	11th to 20th	Night	40% 7% 13% 28% 12% 1	5090
	21st to end	Night	48% 6% 9% 24% 12% 1	5588
April	1st to 10th	Night	46% 7% 12% 21% 13% 2	2195
	11th to 20th	Night	44% 7% 13% 17% 16% 4	1967
	21st to end	Night	45% 6% 12% 22% 13% 2	1890
May	1st to 10th	Night	51% 9% 10% 19% 9% 3	5264
	11th to 20th	Night	41% 8% 11% 25% 14% 1	5235
	21st to end	Night	41% 8% 12% 23% 12% 4	5771
June	1st to 10th	Night	34% 7% 12% 23% 23% 2	1868
	11th to 20th	Night	31% 9% 15% 26% 16% 3	1640
	21st to end	Night	30% 10% 16% 24% 16% 4	1600
July	1st to 10th	Night	35% 7% 12% 25% 17% 4	3580
	11th to 20th	Night	34% 10% 15% 26% 16% 1	3765
	21st to end	Night	36% 8% 14% 20% 18% 3	4297
August	1st to 10th	Night	36% 9% 16% 25% 13% 1	2904
	11th to 20th	Night	34% 7% 11% 28% 19% 1	2902
	21st to end	Night	26% 9% 16% 28% 19% 2	3421
September	1st to 10th	Night	32% 6% 12% 25% 20% 5%	2121
	11th to 20th	Night	25% 6% 10% 27% 27% 3	2200
	21st to end	Night	38% 6% 11% 20% 24% 2	2200
October	1st to 10th	Night	23% 4 8% 29% 34% 2	3611
	11th to 20th	Night	30% 4 10% 26% 27% 2	3899
	21st to end	Night	34% 5% 8% 27% 23% 4	4470
November	1st to 10th	Night	38% 5% 11% 24% 20% 2	2666
	11th to 20th	Night	46% 5% 9% 22% 15% 3	2730
	21st to end	Night	58% 4 11% 18% 8% 1	2730
December	1st to 10th	Night	53% 6% 13% 22% 6%	4380
	11th to 20th	Night	63% 5% 11% 14% 6%	4954
	21st to end	Night	72% 5% 8% 11% 3	6868

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	24% 18% 34% 18% 5%	330
	11th to 20th	Day	21% 22% 38% 15% 3	330
	21st to end	Day	29% 17% 31% 17% 5% 1	363
February	1st to 10th	Day	24% 15% 40% 15% 5%	330
	11th to 20th	Day	22% 23% 35% 16% 4	330
	21st to end	Day	22% 19% 46% 12% 1	273
March	1st to 10th	Day	24% 21% 34% 17% 4	368
	11th to 20th	Day	23% 16% 35% 20% 6% 1	540
	21st to end	Day	27% 16% 33% 19% 5%	594
April	1st to 10th	Day	19% 18% 33% 20% 7% 3	540
	11th to 20th	Day	18% 20% 30% 21% 8% 3	532
	21st to end	Day	19% 14% 34% 22% 10% 2	540
May	1st to 10th	Day	24% 13% 33% 20% 8% 3	543
	11th to 20th	Day	22% 8% 27% 24% 13% 7%	567
	21st to end	Day	15% 7% 25% 26% 17% 9%	617
June	1st to 10th	Day	13% 7% 23% 28% 21% 8%	585
	11th to 20th	Day	10% 7% 25% 31% 21% 7%	756
	21st to end	Day	11% 7% 25% 28% 20% 8%	730
July	1st to 10th	Day	12% 4 16% 25% 24% 18%	721
	11th to 20th	Day	9% 5% 20% 25% 26% 15%	629
	21st to end	Day	11% 2 15% 29% 27% 16%	576
August	1st to 10th	Day	10% 3 13% 26% 29% 19%	526
	11th to 20th	Day	11% 3 15% 29% 29% 13%	519
	21st to end	Day	8% 4 14% 27% 32% 15%	583
September	1st to 10th	Day	12% 4 15% 24% 32% 13%	530
	11th to 20th	Day	8% 3 12% 26% 32% 19%	530
	21st to end	Day	18% 9% 18% 25% 22% 8%	530
October	1st to 10th	Day	11% 6% 23% 27% 22% 11%	530
	11th to 20th	Day	14% 14% 30% 25% 15% 3	530
	21st to end	Day	22% 12% 37% 22% 6% 1	448
November	1st to 10th	Day	15% 14% 35% 23% 8% 4	330
	11th to 20th	Day	21% 18% 32% 18% 9% 2	330
	21st to end	Day	28% 14% 37% 18% 3	330
December	1st to 10th	Day	18% 21% 37% 17% 6% 1	330
	11th to 20th	Day	24% 15% 42% 16% 3	330
	21st to end	Day	33% 18% 31% 15% 4	363
January	1st to 10th	Night	21% 17% 35% 22% 4	1050
	11th to 20th	Night	24% 19% 36% 18% 4	889
	21st to end	Night	21% 17% 35% 23% 3	924
February	1st to 10th	Night	25% 12% 33% 28% 2	840
	11th to 20th	Night	22% 15% 36% 24% 2	823
	21st to end	Night	22% 15% 40% 21% 2	692
March	1st to 10th	Night	21% 13% 34% 25% 6%	840
	11th to 20th	Night	20% 15% 36% 23% 6%	840
	21st to end	Night	24% 13% 32% 25% 6% 1	924
April	1st to 10th	Night	21% 12% 34% 27% 5% 1	725
	11th to 20th	Night	17% 13% 34% 25% 10% 1	623
	21st to end	Night	18% 7% 39% 26% 9% 1	630
May	1st to 10th	Night	21% 9% 34% 25% 11%	630
	11th to 20th	Night	18% 5% 29% 33% 13% 2	621
	21st to end	Night	11% 4 23% 36% 23% 3	683
June	1st to 10th	Night	12% 2 24% 40% 21% 1	630
	11th to 20th	Night	11% 4 20% 39% 26% 1	615
	21st to end	Night	7% 2 22% 41% 26% 2	600
July	1st to 10th	Night	10% 3 13% 37% 32% 6%	585
	11th to 20th	Night	8% 3 15% 39% 30% 5%	582
	21st to end	Night	11% 3 11% 37% 36% 2	657
August	1st to 10th	Night	8% 2 10% 41% 34% 5%	597
	11th to 20th	Night	7% 2 11% 43% 32% 4	594
	21st to end	Night	6% 2 13% 37% 36% 6%	660
September	1st to 10th	Night	13% 4 14% 35% 30% 5%	721
	11th to 20th	Night	9% 3 13% 36% 34% 5%	800
	21st to end	Night	15% 5% 21% 35% 22% 3	800
October	1st to 10th	Night	11% 5% 24% 33% 22% 5%	800
	11th to 20th	Night	19% 9% 28% 31% 12% 1	800
	21st to end	Night	21% 11% 34% 25% 9%	880
November	1st to 10th	Night	16% 10% 31% 29% 13% 1	820
	11th to 20th	Night	19% 16% 32% 25% 7% 1	840
	21st to end	Night	25% 11% 33% 25% 6% 1	840
December	1st to 10th	Night	24% 13% 35% 23% 4	840
	11th to 20th	Night	24% 13% 35% 24% 5%	840
	21st to end	Night	28% 16% 32% 21% 3	1029

Page generated at 2026-06-13 02:31:45. Version ac07

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