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 2025-02-21.

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 8% 5% 5% 5% 4 6% 7% 33%	109156
	Night	14% 10% 4 9% 5% 4 4 3 5% 6% 34%	109451
Transparency	Day	47% 7% 12% 21% 12% 1	112825
	Night	47% 6% 11% 21% 13% 2	113921
Seeing	Day	17% 10% 27% 23% 16% 7%	15721
	Night	18% 9% 28% 29% 14% 2	25552

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	14% 16% 8% 18% 6% 6% 4 3 4 5% 17%	3617
	11th to 20th	Day	12% 15% 7% 14% 9% 6% 7% 4 3 3 19%	3945
	21st to end	Day	20% 15% 8% 11% 7% 5% 5% 3 4 5% 18%	4466
February	1st to 10th	Day	18% 15% 6% 12% 6% 5% 5% 3 4 5% 21%	1840
	11th to 20th	Day	15% 12% 5% 15% 8% 4 4 4 5% 5% 23%	1948
	21st to end	Day	17% 13% 4 10% 5% 4 5% 3 4 6% 28%	1570
March	1st to 10th	Day	21% 17% 5% 10% 5% 4 3 3 4 4 22%	3180
	11th to 20th	Day	13% 9% 3 8% 5% 4 5% 4 5% 6% 37%	3480
	21st to end	Day	19% 11% 4 9% 6% 4 4 3 5% 6% 29%	3815
April	1st to 10th	Day	14% 13% 4 9% 5% 4 4 4 5% 7% 31%	2209
	11th to 20th	Day	17% 10% 2 7% 4 4 4 3 5% 7% 37%	2350
	21st to end	Day	17% 9% 3 7% 5% 5% 4 4 5% 7% 33%	2470
May	1st to 10th	Day	20% 11% 3 7% 4 5% 5% 4 5% 6% 30%	4082
	11th to 20th	Day	20% 8% 3 6% 4 3 4 4 5% 8% 36%	4081
	21st to end	Day	11% 6% 2 7% 5% 5% 6% 5% 8% 10% 34%	4476
June	1st to 10th	Day	13% 6% 2 7% 5% 5% 6% 4 6% 8% 38%	2483
	11th to 20th	Day	10% 5% 2 6% 6% 4 5% 5% 8% 9% 40%	2660
	21st to end	Day	10% 5% 2 7% 5% 4 5% 5% 7% 10% 40%	2660
July	1st to 10th	Day	11% 7% 3 7% 5% 5% 5% 4 7% 10% 36%	4440
	11th to 20th	Day	8% 4 2 5% 4 4 5% 4 7% 12% 46%	4291
	21st to end	Day	9% 6% 3 6% 6% 5% 6% 4 8% 10% 37%	4466
August	1st to 10th	Day	7% 7% 3 7% 4 5% 5% 5% 7% 10% 42%	4104
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 4 7% 12% 41%	4044
	21st to end	Day	7% 4 2 6% 4 5% 5% 4 7% 9% 45%	4322
September	1st to 10th	Day	11% 5% 2 6% 5% 4 4 4 4 6% 49%	2144
	11th to 20th	Day	9% 5% 2 6% 5% 4 4 3 6% 8% 48%	2090
	21st to end	Day	17% 7% 2 6% 4 3 3 3 5% 7% 43%	2090
October	1st to 10th	Day	11% 7% 2 7% 4 4 4 3 5% 6% 46%	2082
	11th to 20th	Day	14% 8% 2 5% 4 4 4 4 5% 6% 43%	1900
	21st to end	Day	18% 10% 3 8% 4 4 4 4 5% 7% 32%	1962
November	1st to 10th	Day	10% 9% 2 6% 4 4 4 3 5% 7% 45%	1762
	11th to 20th	Day	15% 12% 5% 8% 5% 4 4 3 5% 6% 33%	1800
	21st to end	Day	18% 14% 5% 10% 4 4 3 3 4 6% 28%	1800
December	1st to 10th	Day	15% 12% 4 9% 6% 4 5% 4 5% 5% 31%	2930
	11th to 20th	Day	19% 15% 6% 12% 5% 4 4 3 4 6% 21%	3373
	21st to end	Day	23% 19% 8% 11% 6% 5% 4 3 4 5% 13%	4224
January	1st to 10th	Night	14% 16% 8% 16% 8% 5% 4 3 4 4 18%	6348
	11th to 20th	Night	11% 16% 8% 17% 8% 6% 6% 4 4 4 17%	6012
	21st to end	Night	20% 15% 6% 10% 5% 5% 4 3 4 5% 24%	6490
February	1st to 10th	Night	19% 13% 3 9% 7% 6% 5% 4 4 5% 25%	2557
	11th to 20th	Night	15% 13% 4 10% 7% 5% 3 3 5% 5% 29%	2338
	21st to end	Night	19% 13% 5% 12% 5% 4 4 3 4 5% 26%	1885
March	1st to 10th	Night	19% 13% 5% 7% 4 4 4 3 4 6% 33%	3672
	11th to 20th	Night	13% 7% 3 6% 5% 5% 4 3 5% 7% 42%	3480
	21st to end	Night	18% 9% 3 8% 5% 4 3 2 4 6% 38%	3817
April	1st to 10th	Night	15% 10% 3 8% 5% 4 4 4 6% 7% 36%	1986
	11th to 20th	Night	15% 8% 3 6% 5% 4 5% 4 6% 6% 37%	1777
	21st to end	Night	16% 8% 3 7% 5% 5% 4 3 6% 7% 36%	1710
May	1st to 10th	Night	22% 12% 3 7% 5% 4 4 4 4 7% 28%	2813
	11th to 20th	Night	18% 6% 3 6% 4 4 4 3 5% 7% 40%	2812
	21st to end	Night	9% 5% 2 5% 4 5% 5% 4 7% 11% 44%	3079
June	1st to 10th	Night	9% 6% 2 5% 4 5% 5% 3 7% 7% 48%	1690
	11th to 20th	Night	8% 4 1 6% 4 4 5% 3 6% 10% 47%	1520
	21st to end	Night	7% 4 2 5% 5% 5% 5% 4 7% 10% 46%	1520
July	1st to 10th	Night	11% 6% 2 7% 4 4 5% 3 6% 7% 45%	2530
	11th to 20th	Night	7% 4 2 5% 4 3 4 5% 6% 8% 53%	2671
	21st to end	Night	9% 7% 2 6% 4 5% 5% 4 7% 9% 41%	3087
August	1st to 10th	Night	10% 7% 3 7% 4 5% 5% 4 7% 9% 40%	2825
	11th to 20th	Night	7% 6% 3 7% 5% 5% 5% 3 6% 7% 46%	2785
	21st to end	Night	4 4 1 5% 4 4 5% 5% 7% 10% 50%	3316
September	1st to 10th	Night	11% 6% 2 5% 4 3 4 3 5% 7% 51%	2015
	11th to 20th	Night	8% 4 2 5% 3 3 3 3 5% 7% 57%	2090
	21st to end	Night	14% 6% 2 6% 3 3 4 3 5% 6% 46%	2090
October	1st to 10th	Night	9% 4 2 6% 4 4 4 4 5% 7% 52%	2097
	11th to 20th	Night	15% 8% 2 6% 4 4 4 3 5% 6% 42%	2280
	21st to end	Night	19% 8% 3 5% 5% 3 5% 4 5% 6% 38%	2631
November	1st to 10th	Night	12% 8% 3 6% 3 4 4 3 5% 7% 45%	2536
	11th to 20th	Night	16% 9% 4 9% 4 4 4 3 5% 7% 37%	2600
	21st to end	Night	17% 13% 5% 8% 6% 5% 4 4 5% 6% 27%	2600
December	1st to 10th	Night	16% 11% 4 8% 5% 5% 5% 4 5% 7% 30%	4250
	11th to 20th	Night	17% 16% 8% 13% 4 3 4 3 5% 5% 21%	4822
	21st to end	Night	22% 20% 8% 11% 5% 4 3 3 4 5% 15%	6720

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	70% 5% 7% 13% 6%	3618
	11th to 20th	Day	70% 4 8% 8% 10% 1	3945
	21st to end	Day	68% 6% 10% 8% 7% 1	4466
February	1st to 10th	Day	65% 5% 10% 11% 8%	1840
	11th to 20th	Day	63% 6% 8% 15% 8%	1958
	21st to end	Day	58% 6% 12% 16% 7% 2	1570
March	1st to 10th	Day	65% 5% 8% 16% 5%	3180
	11th to 20th	Day	44% 7% 10% 26% 11% 1	3480
	21st to end	Day	53% 7% 12% 20% 6%	3815
April	1st to 10th	Day	51% 7% 12% 17% 12% 1	2209
	11th to 20th	Day	46% 6% 13% 20% 13% 2	2350
	21st to end	Day	50% 6% 12% 19% 11% 2	2470
May	1st to 10th	Day	52% 8% 10% 21% 8% 1	4120
	11th to 20th	Day	46% 8% 13% 24% 8% 1	4085
	21st to end	Day	39% 11% 14% 21% 13% 2	4489
June	1st to 10th	Day	42% 7% 11% 23% 14% 2	2483
	11th to 20th	Day	37% 8% 14% 24% 15% 1	2660
	21st to end	Day	38% 9% 16% 20% 15% 3	2660
July	1st to 10th	Day	41% 8% 11% 21% 16% 3	4371
	11th to 20th	Day	29% 8% 15% 27% 19% 1	4216
	21st to end	Day	39% 9% 14% 18% 16% 3	4324
August	1st to 10th	Day	34% 9% 17% 25% 14% 1	4091
	11th to 20th	Day	33% 8% 13% 32% 14% 1	4083
	21st to end	Day	31% 9% 13% 30% 13% 3	4321
September	1st to 10th	Day	35% 7% 11% 22% 21% 4	2144
	11th to 20th	Day	33% 5% 12% 25% 22% 3	2090
	21st to end	Day	40% 5% 10% 23% 20% 1	2090
October	1st to 10th	Day	25% 5% 12% 31% 27% 1	3459
	11th to 20th	Day	31% 6% 12% 27% 23% 2	3140
	21st to end	Day	39% 5% 11% 23% 20% 2	3212
November	1st to 10th	Day	38% 5% 12% 25% 17% 3	1762
	11th to 20th	Day	51% 5% 10% 20% 12% 2	1800
	21st to end	Day	57% 5% 10% 18% 8% 1	1800
December	1st to 10th	Day	53% 6% 14% 21% 6%	2930
	11th to 20th	Day	65% 5% 11% 14% 5%	3370
	21st to end	Day	74% 4 7% 10% 4	4224
January	1st to 10th	Night	68% 6% 8% 13% 5%	6348
	11th to 20th	Night	70% 5% 8% 9% 7% 1	6012
	21st to end	Night	62% 5% 11% 14% 7% 2	6490
February	1st to 10th	Night	61% 5% 11% 16% 7% 1	2557
	11th to 20th	Night	56% 5% 10% 16% 11% 2	2339
	21st to end	Night	60% 6% 9% 14% 9% 2	1885
March	1st to 10th	Night	52% 6% 9% 23% 10% 1	3672
	11th to 20th	Night	40% 7% 12% 27% 12% 2	3480
	21st to end	Night	47% 6% 10% 27% 10% 1	3817
April	1st to 10th	Night	44% 7% 13% 22% 13% 2	1986
	11th to 20th	Night	44% 6% 12% 17% 17% 4	1777
	21st to end	Night	46% 6% 12% 21% 13% 2	1710
May	1st to 10th	Night	54% 8% 9% 20% 7% 2	2840
	11th to 20th	Night	41% 9% 13% 25% 10% 1	2813
	21st to end	Night	30% 10% 14% 28% 15% 2	3087
June	1st to 10th	Night	33% 8% 13% 23% 22% 2	1690
	11th to 20th	Night	30% 9% 15% 27% 16% 3	1520
	21st to end	Night	31% 9% 16% 24% 16% 4	1520
July	1st to 10th	Night	37% 7% 11% 24% 16% 5%	2490
	11th to 20th	Night	26% 8% 14% 30% 20% 1	2623
	21st to end	Night	37% 8% 15% 20% 16% 4	2988
August	1st to 10th	Night	37% 9% 16% 24% 13% 1	2814
	11th to 20th	Night	35% 8% 11% 27% 19% 1	2812
	21st to end	Night	27% 9% 16% 27% 19% 2	3316
September	1st to 10th	Night	32% 7% 12% 24% 19% 5%	2015
	11th to 20th	Night	26% 6% 11% 27% 26% 3	2090
	21st to end	Night	38% 6% 10% 21% 23% 2	2090
October	1st to 10th	Night	23% 4 8% 30% 33% 2	3500
	11th to 20th	Night	30% 4 10% 26% 27% 2	3779
	21st to end	Night	33% 5% 8% 26% 23% 4	4331
November	1st to 10th	Night	38% 5% 11% 23% 20% 3	2536
	11th to 20th	Night	47% 5% 9% 21% 15% 3	2600
	21st to end	Night	58% 5% 11% 19% 8% 1	2600
December	1st to 10th	Night	52% 6% 13% 22% 6%	4250
	11th to 20th	Night	64% 5% 11% 14% 6%	4824
	21st to end	Night	72% 5% 9% 11% 3	6720

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% 33% 19% 5%	300
	11th to 20th	Day	22% 18% 40% 16% 4	300
	21st to end	Day	30% 15% 33% 16% 5% 1	330
February	1st to 10th	Day	26% 17% 39% 15% 4	300
	11th to 20th	Day	22% 23% 36% 15% 3	300
	21st to end	Day	24% 17% 44% 12% 2	225
March	1st to 10th	Day	24% 21% 33% 18% 4	304
	11th to 20th	Day	22% 15% 35% 21% 6% 1	460
	21st to end	Day	28% 14% 33% 19% 5%	506
April	1st to 10th	Day	18% 17% 33% 21% 8% 3	460
	11th to 20th	Day	20% 19% 28% 21% 10% 4	452
	21st to end	Day	20% 15% 35% 20% 8% 2	460
May	1st to 10th	Day	25% 11% 32% 22% 8% 3	463
	11th to 20th	Day	22% 6% 26% 24% 14% 8%	487
	21st to end	Day	13% 5% 26% 26% 19% 11%	529
June	1st to 10th	Day	14% 6% 21% 30% 22% 8%	503
	11th to 20th	Day	10% 7% 23% 31% 22% 7%	680
	21st to end	Day	12% 7% 27% 28% 19% 8%	680
July	1st to 10th	Day	13% 4 17% 25% 22% 19%	671
	11th to 20th	Day	9% 5% 21% 24% 27% 15%	584
	21st to end	Day	11% 2 16% 28% 27% 16%	532
August	1st to 10th	Day	11% 3 13% 27% 27% 19%	486
	11th to 20th	Day	12% 3 16% 28% 28% 12%	479
	21st to end	Day	8% 4 13% 27% 32% 17%	539
September	1st to 10th	Day	12% 4 15% 25% 32% 12%	490
	11th to 20th	Day	9% 3 13% 26% 32% 18%	490
	21st to end	Day	18% 9% 19% 26% 20% 8%	490
October	1st to 10th	Day	11% 7% 24% 28% 21% 10%	490
	11th to 20th	Day	14% 14% 31% 22% 14% 4	490
	21st to end	Day	21% 12% 37% 22% 6% 1	411
November	1st to 10th	Day	15% 12% 36% 23% 9% 4	300
	11th to 20th	Day	20% 16% 31% 20% 10% 2	300
	21st to end	Day	27% 14% 37% 19% 3	300
December	1st to 10th	Day	20% 21% 35% 16% 7% 1	300
	11th to 20th	Day	24% 15% 42% 16% 3	300
	21st to end	Day	32% 17% 31% 15% 4	330
January	1st to 10th	Night	21% 18% 35% 21% 5%	1000
	11th to 20th	Night	25% 18% 35% 18% 4	847
	21st to end	Night	22% 16% 34% 24% 3	880
February	1st to 10th	Night	26% 12% 33% 26% 2	800
	11th to 20th	Night	22% 15% 36% 24% 2	783
	21st to end	Night	23% 14% 39% 20% 3	629
March	1st to 10th	Night	21% 13% 34% 26% 7%	760
	11th to 20th	Night	20% 15% 35% 24% 6% 1	760
	21st to end	Night	25% 11% 31% 26% 7% 1	836
April	1st to 10th	Night	20% 12% 34% 27% 5% 1	656
	11th to 20th	Night	18% 12% 33% 26% 11% 1	563
	21st to end	Night	18% 7% 39% 26% 8% 1	570
May	1st to 10th	Night	21% 8% 33% 25% 12% 1	570
	11th to 20th	Night	19% 4 28% 34% 14% 2	561
	21st to end	Night	9% 2 23% 37% 25% 4	617
June	1st to 10th	Night	11% 2 23% 41% 22% 1	570
	11th to 20th	Night	10% 3 20% 39% 26% 1	570
	21st to end	Night	8% 2 23% 41% 25% 2	570
July	1st to 10th	Night	10% 3 14% 37% 31% 6%	555
	11th to 20th	Night	7% 3 15% 39% 30% 5%	552
	21st to end	Night	12% 3 11% 38% 35% 2	624
August	1st to 10th	Night	8% 2 10% 40% 35% 5%	567
	11th to 20th	Night	8% 2 12% 44% 30% 5%	564
	21st to end	Night	7% 2 13% 36% 37% 6%	627
September	1st to 10th	Night	13% 4 14% 35% 29% 5%	685
	11th to 20th	Night	9% 3 13% 36% 33% 5%	760
	21st to end	Night	15% 5% 22% 35% 21% 3	760
October	1st to 10th	Night	11% 5% 25% 33% 21% 5%	760
	11th to 20th	Night	19% 9% 28% 30% 12% 1	760
	21st to end	Night	22% 11% 34% 24% 9%	836
November	1st to 10th	Night	16% 10% 30% 29% 13% 1	780
	11th to 20th	Night	20% 15% 32% 25% 7% 1	800
	21st to end	Night	25% 11% 33% 25% 6% 1	800
December	1st to 10th	Night	25% 13% 35% 23% 5%	800
	11th to 20th	Night	25% 13% 34% 24% 5% 1	800
	21st to end	Night	29% 15% 32% 22% 3	980

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