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 2024-01-31.

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	15% 9% 4 7% 6% 3 5% 5% 5% 7% 33%	75279
	Night	15% 9% 4 7% 6% 3 4 4 5% 7% 36%	74840
Transparency	Day	49% 7% 12% 20% 11% 2	74992
	Night	48% 6% 11% 20% 13% 2	74647
Seeing	Day	18% 10% 26% 23% 16% 7%	14294
	Night	18% 9% 28% 29% 14% 2	24141

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	17% 14% 6% 11% 9% 4 5% 5% 4 5% 19%	1517
	11th to 20th	Day	18% 15% 8% 13% 7% 4 5% 3 4 5% 18%	1657
	21st to end	Day	15% 17% 9% 11% 8% 4 4 4 5% 6% 17%	1872
February	1st to 10th	Day	19% 14% 7% 11% 7% 4 5% 4 4 5% 20%	1656
	11th to 20th	Day	15% 11% 5% 14% 10% 3 6% 4 4 6% 22%	1748
	21st to end	Day	18% 12% 5% 9% 6% 3 5% 4 4 6% 28%	1480
March	1st to 10th	Day	18% 11% 5% 8% 7% 4 3 4 5% 6% 29%	1832
	11th to 20th	Day	17% 11% 5% 8% 7% 3 4 4 5% 6% 29%	1980
	21st to end	Day	22% 12% 5% 8% 6% 3 3 3 4 6% 27%	2178
April	1st to 10th	Day	14% 11% 5% 8% 6% 3 4 5% 5% 7% 32%	2092
	11th to 20th	Day	18% 8% 2 7% 5% 3 4 4 5% 7% 37%	2224
	21st to end	Day	19% 9% 4 7% 6% 4 4 4 5% 7% 32%	2340
May	1st to 10th	Day	18% 10% 4 6% 5% 3 5% 5% 6% 6% 32%	2340
	11th to 20th	Day	20% 7% 4 6% 5% 3 4 6% 5% 7% 32%	2301
	21st to end	Day	10% 6% 3 6% 7% 4 6% 6% 8% 9% 35%	2531
June	1st to 10th	Day	13% 6% 3 6% 5% 4 6% 5% 5% 8% 39%	2352
	11th to 20th	Day	10% 5% 3 5% 7% 3 6% 6% 7% 9% 40%	2520
	21st to end	Day	11% 5% 3 5% 6% 3 6% 6% 6% 10% 39%	2520
July	1st to 10th	Day	11% 5% 2 5% 6% 4 6% 6% 7% 9% 39%	2520
	11th to 20th	Day	9% 4 2 5% 5% 3 5% 6% 6% 11% 43%	2441
	21st to end	Day	10% 5% 3 4 5% 3 7% 6% 7% 10% 40%	2547
August	1st to 10th	Day	8% 6% 3 5% 5% 4 5% 6% 7% 10% 42%	2327
	11th to 20th	Day	10% 5% 2 6% 7% 4 5% 6% 7% 11% 38%	2303
	21st to end	Day	9% 4 3 6% 5% 3 5% 6% 8% 10% 43%	2462
September	1st to 10th	Day	12% 5% 3 5% 6% 3 5% 4 4 7% 47%	2032
	11th to 20th	Day	9% 4 3 5% 6% 4 5% 4 6% 9% 47%	1980
	21st to end	Day	16% 5% 2 5% 5% 2 3 4 5% 8% 45%	1980
October	1st to 10th	Day	12% 7% 3 6% 5% 3 4 4 5% 7% 44%	1973
	11th to 20th	Day	15% 8% 2 5% 5% 3 4 4 5% 6% 42%	1800
	21st to end	Day	19% 10% 3 7% 6% 3 4 5% 5% 7% 31%	1859
November	1st to 10th	Day	10% 8% 3 5% 4 3 4 4 5% 7% 46%	1672
	11th to 20th	Day	15% 11% 5% 7% 5% 3 3 4 5% 7% 34%	1710
	21st to end	Day	18% 13% 6% 9% 5% 3 4 3 4 6% 29%	1710
December	1st to 10th	Day	18% 15% 7% 10% 7% 3 5% 5% 4 5% 21%	1710
	11th to 20th	Day	16% 14% 7% 11% 7% 3 5% 4 5% 6% 23%	2153
	21st to end	Day	22% 20% 10% 10% 7% 4 4 4 4 5% 10%	2960
January	1st to 10th	Night	16% 13% 7% 12% 7% 4 5% 5% 3 4 22%	2648
	11th to 20th	Night	18% 16% 7% 11% 8% 4 4 4 3 5% 21%	2515
	21st to end	Night	17% 16% 6% 10% 8% 3 4 4 4 5% 23%	2711
February	1st to 10th	Night	21% 14% 4 8% 8% 4 5% 4 3 5% 25%	2302
	11th to 20th	Night	15% 12% 5% 8% 8% 4 4 4 5% 6% 29%	2098
	21st to end	Night	19% 12% 6% 11% 6% 4 4 4 4 5% 26%	1776
March	1st to 10th	Night	16% 8% 5% 7% 6% 4 4 4 4 6% 35%	2127
	11th to 20th	Night	16% 9% 4 7% 6% 3 5% 4 5% 7% 36%	1980
	21st to end	Night	20% 10% 4 7% 5% 3 4 3 4 6% 33%	2178
April	1st to 10th	Night	14% 8% 3 7% 5% 3 4 5% 6% 8% 37%	1882
	11th to 20th	Night	15% 8% 3 5% 6% 3 5% 5% 6% 6% 38%	1683
	21st to end	Night	17% 7% 4 6% 6% 3 5% 4 6% 7% 36%	1620
May	1st to 10th	Night	18% 9% 3 7% 5% 3 4 6% 5% 8% 32%	1620
	11th to 20th	Night	17% 7% 3 5% 4 3 5% 4 5% 7% 39%	1592
	21st to end	Night	7% 5% 3 4 5% 4 5% 6% 7% 12% 42%	1744
June	1st to 10th	Night	8% 5% 2 5% 4 3 5% 4 7% 7% 49%	1602
	11th to 20th	Night	8% 4 2 5% 5% 3 4 5% 6% 10% 48%	1440
	21st to end	Night	8% 3 2 5% 5% 3 6% 5% 7% 10% 46%	1440
July	1st to 10th	Night	8% 5% 2 7% 6% 3 5% 4 6% 7% 47%	1440
	11th to 20th	Night	7% 4 2 5% 4 3 5% 6% 7% 9% 50%	1516
	21st to end	Night	9% 6% 2 4 4 3 5% 5% 6% 8% 48%	1771
August	1st to 10th	Night	6% 4 3 5% 6% 3 5% 7% 7% 10% 45%	1611
	11th to 20th	Night	7% 5% 2 5% 5% 3 6% 4 6% 8% 48%	1598
	21st to end	Night	6% 4 2 5% 5% 3 5% 6% 6% 9% 50%	1890
September	1st to 10th	Night	12% 5% 3 4 4 2 4 4 5% 7% 50%	1908
	11th to 20th	Night	9% 4 2 4 4 2 3 4 5% 7% 56%	1980
	21st to end	Night	13% 5% 2 5% 4 2 4 4 5% 6% 48%	1980
October	1st to 10th	Night	10% 5% 2 5% 5% 3 4 5% 5% 7% 51%	1986
	11th to 20th	Night	16% 8% 3 5% 5% 3 4 4 5% 6% 40%	2160
	21st to end	Night	20% 8% 3 5% 5% 2 4 5% 5% 6% 37%	2492
November	1st to 10th	Night	13% 7% 3 5% 4 3 4 4 5% 7% 45%	2406
	11th to 20th	Night	17% 9% 4 8% 4 2 4 3 4 7% 37%	2470
	21st to end	Night	18% 12% 5% 7% 6% 4 4 4 5% 6% 28%	2470
December	1st to 10th	Night	20% 12% 7% 9% 6% 3 5% 4 4 6% 24%	2470
	11th to 20th	Night	17% 12% 8% 9% 6% 3 4 4 4 7% 26%	3042
	21st to end	Night	22% 19% 9% 10% 6% 3 4 3 4 5% 15%	4692

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	66% 5% 8% 14% 6%	1518
	11th to 20th	Day	69% 6% 10% 11% 5%	1657
	21st to end	Day	69% 5% 10% 12% 4 1	1872
February	1st to 10th	Day	67% 5% 10% 11% 7%	1656
	11th to 20th	Day	64% 6% 9% 14% 7% 1	1758
	21st to end	Day	59% 6% 11% 16% 8% 2	1480
March	1st to 10th	Day	55% 6% 11% 20% 7% 1	1832
	11th to 20th	Day	55% 6% 11% 17% 10% 1	1980
	21st to end	Day	59% 5% 11% 19% 5% 1	2178
April	1st to 10th	Day	50% 7% 13% 18% 12% 1	2092
	11th to 20th	Day	47% 6% 13% 18% 13% 3	2224
	21st to end	Day	51% 6% 12% 19% 11% 2	2340
May	1st to 10th	Day	52% 7% 11% 19% 9% 1	2340
	11th to 20th	Day	50% 8% 12% 18% 10% 1	2305
	21st to end	Day	41% 11% 15% 21% 11% 1	2531
June	1st to 10th	Day	43% 7% 11% 23% 13% 2	2352
	11th to 20th	Day	38% 8% 14% 24% 15% 1	2520
	21st to end	Day	38% 9% 16% 20% 14% 3	2520
July	1st to 10th	Day	40% 10% 13% 20% 14% 3	2451
	11th to 20th	Day	33% 9% 14% 26% 16% 1	2366
	21st to end	Day	36% 9% 15% 24% 14% 2	2405
August	1st to 10th	Day	35% 9% 14% 26% 13% 2	2314
	11th to 20th	Day	38% 9% 13% 28% 12% 1	2303
	21st to end	Day	34% 9% 13% 24% 15% 5%	2462
September	1st to 10th	Day	36% 7% 12% 22% 19% 4	2032
	11th to 20th	Day	34% 5% 12% 25% 21% 2	1980
	21st to end	Day	38% 6% 10% 24% 21% 1	1980
October	1st to 10th	Day	39% 7% 10% 24% 17% 2	1973
	11th to 20th	Day	41% 6% 11% 24% 16% 3	1800
	21st to end	Day	51% 7% 12% 18% 10% 2	1859
November	1st to 10th	Day	37% 5% 12% 25% 18% 3	1672
	11th to 20th	Day	50% 5% 10% 21% 12% 2	1710
	21st to end	Day	56% 5% 10% 18% 9% 1	1710
December	1st to 10th	Day	65% 5% 10% 15% 4	1710
	11th to 20th	Day	61% 6% 9% 16% 7%	2150
	21st to end	Day	77% 5% 6% 7% 4	2960
January	1st to 10th	Night	65% 6% 7% 15% 7%	2648
	11th to 20th	Night	66% 5% 10% 14% 5%	2515
	21st to end	Night	64% 6% 9% 14% 7% 1	2711
February	1st to 10th	Night	63% 4 10% 15% 7% 1	2302
	11th to 20th	Night	56% 5% 11% 16% 10% 2	2099
	21st to end	Night	61% 5% 9% 15% 8% 2	1776
March	1st to 10th	Night	50% 6% 9% 21% 12% 2	2127
	11th to 20th	Night	48% 5% 12% 22% 10% 3	1980
	21st to end	Night	52% 5% 8% 23% 10% 1	2178
April	1st to 10th	Night	43% 7% 13% 22% 13% 2	1882
	11th to 20th	Night	44% 6% 13% 17% 17% 4	1683
	21st to end	Night	46% 6% 12% 21% 12% 2	1620
May	1st to 10th	Night	49% 8% 13% 18% 9% 3	1620
	11th to 20th	Night	44% 7% 12% 20% 14% 2	1593
	21st to end	Night	32% 10% 15% 27% 13% 3	1745
June	1st to 10th	Night	33% 8% 13% 24% 21% 2	1602
	11th to 20th	Night	31% 9% 15% 26% 15% 3	1440
	21st to end	Night	31% 9% 16% 24% 16% 4	1440
July	1st to 10th	Night	36% 8% 14% 20% 18% 4	1400
	11th to 20th	Night	29% 9% 13% 30% 18% 2	1468
	21st to end	Night	31% 8% 16% 27% 16% 3	1672
August	1st to 10th	Night	30% 9% 16% 27% 16% 1	1600
	11th to 20th	Night	32% 8% 14% 27% 19% 1	1598
	21st to end	Night	29% 8% 15% 22% 21% 4	1890
September	1st to 10th	Night	34% 6% 13% 24% 18% 5%	1908
	11th to 20th	Night	27% 7% 11% 27% 25% 3	1980
	21st to end	Night	35% 6% 11% 21% 24% 2	1980
October	1st to 10th	Night	33% 6% 12% 25% 23% 2	1986
	11th to 20th	Night	43% 5% 8% 24% 17% 2	2160
	21st to end	Night	47% 6% 9% 22% 14% 3	2492
November	1st to 10th	Night	38% 5% 11% 22% 20% 3	2406
	11th to 20th	Night	47% 5% 9% 21% 15% 3	2470
	21st to end	Night	56% 5% 11% 19% 8% 1	2470
December	1st to 10th	Night	62% 5% 9% 17% 7%	2470
	11th to 20th	Night	58% 6% 10% 19% 6% 1	3044
	21st to end	Night	72% 5% 8% 11% 4	4692

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% 17% 34% 19% 6%	270
	11th to 20th	Day	23% 17% 39% 17% 4	270
	21st to end	Day	33% 15% 30% 16% 5% 1	294
February	1st to 10th	Day	30% 17% 37% 14% 3	240
	11th to 20th	Day	23% 22% 40% 13% 3	240
	21st to end	Day	25% 18% 45% 11% 2	198
March	1st to 10th	Day	24% 21% 34% 17% 3	272
	11th to 20th	Day	23% 14% 36% 20% 6% 1	420
	21st to end	Day	30% 13% 33% 18% 5%	462
April	1st to 10th	Day	18% 15% 32% 22% 9% 3	420
	11th to 20th	Day	20% 18% 28% 20% 10% 4	412
	21st to end	Day	21% 15% 35% 20% 8% 2	420
May	1st to 10th	Day	25% 11% 31% 21% 8% 4	423
	11th to 20th	Day	22% 6% 28% 24% 14% 7%	447
	21st to end	Day	14% 5% 25% 25% 20% 11%	485
June	1st to 10th	Day	14% 5% 20% 31% 22% 8%	462
	11th to 20th	Day	10% 6% 23% 30% 22% 7%	630
	21st to end	Day	12% 7% 26% 28% 20% 8%	630
July	1st to 10th	Day	13% 3 16% 25% 23% 20%	621
	11th to 20th	Day	9% 4 19% 24% 26% 16%	539
	21st to end	Day	11% 2 15% 27% 27% 17%	488
August	1st to 10th	Day	11% 2 11% 27% 28% 20%	446
	11th to 20th	Day	12% 4 15% 26% 30% 13%	439
	21st to end	Day	8% 4 14% 27% 31% 16%	495
September	1st to 10th	Day	13% 3 16% 24% 32% 12%	450
	11th to 20th	Day	9% 3 13% 26% 31% 17%	450
	21st to end	Day	16% 9% 19% 26% 22% 8%	450
October	1st to 10th	Day	12% 7% 24% 27% 21% 9%	450
	11th to 20th	Day	15% 15% 32% 22% 14% 2	450
	21st to end	Day	23% 13% 37% 22% 5% 1	374
November	1st to 10th	Day	15% 13% 34% 24% 9% 5%	270
	11th to 20th	Day	21% 17% 29% 20% 11% 2	270
	21st to end	Day	26% 14% 37% 20% 3	270
December	1st to 10th	Day	20% 21% 34% 17% 7% 1	270
	11th to 20th	Day	23% 14% 42% 17% 4	270
	21st to end	Day	32% 18% 31% 15% 4	297
January	1st to 10th	Night	22% 17% 35% 21% 5%	950
	11th to 20th	Night	26% 17% 35% 19% 4	805
	21st to end	Night	23% 16% 34% 24% 4	835
February	1st to 10th	Night	29% 11% 33% 26% 2	720
	11th to 20th	Night	22% 15% 36% 25% 2	703
	21st to end	Night	24% 14% 40% 20% 3	592
March	1st to 10th	Night	21% 13% 33% 25% 7%	720
	11th to 20th	Night	20% 14% 34% 25% 6% 1	720
	21st to end	Night	26% 10% 31% 26% 7% 1	792
April	1st to 10th	Night	20% 11% 35% 28% 6% 1	622
	11th to 20th	Night	18% 12% 33% 26% 11% 1	533
	21st to end	Night	18% 7% 39% 26% 9% 1	540
May	1st to 10th	Night	22% 7% 34% 25% 12% 1	540
	11th to 20th	Night	19% 3 27% 34% 14% 2	531
	21st to end	Night	9% 2 22% 36% 26% 4	584
June	1st to 10th	Night	11% 2 23% 41% 23% 1	540
	11th to 20th	Night	10% 3 20% 38% 27% 1	540
	21st to end	Night	8% 2 21% 41% 25% 2	540
July	1st to 10th	Night	10% 2 12% 36% 33% 7%	525
	11th to 20th	Night	8% 3 14% 39% 30% 6%	522
	21st to end	Night	12% 3 11% 37% 35% 2	591
August	1st to 10th	Night	8% 2 9% 41% 35% 5%	537
	11th to 20th	Night	8% 2 12% 42% 32% 5%	534
	21st to end	Night	7% 2 13% 36% 36% 6%	594
September	1st to 10th	Night	14% 3 14% 34% 30% 5%	648
	11th to 20th	Night	10% 3 14% 34% 33% 6%	720
	21st to end	Night	13% 4 22% 35% 22% 3	720
October	1st to 10th	Night	12% 5% 25% 33% 21% 5%	720
	11th to 20th	Night	20% 9% 29% 30% 11% 1	720
	21st to end	Night	23% 11% 34% 24% 8%	792
November	1st to 10th	Night	16% 10% 30% 29% 14% 1	740
	11th to 20th	Night	20% 15% 32% 25% 7% 1	760
	21st to end	Night	24% 10% 34% 25% 6% 1	760
December	1st to 10th	Night	25% 13% 35% 23% 4	760
	11th to 20th	Night	24% 12% 34% 24% 5% 1	760
	21st to end	Night	28% 15% 32% 22% 3	931

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