Peoria
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Peoria clear sky chart from 2005-11-06 to 2025-09-04.

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 7% 5% 5% 4 4 6% 7% 37%	126329
	Night	13% 10% 4 8% 4 4 4 3 5% 6% 39%	122655
Transparency	Day	44% 5% 12% 24% 14% 2	129849
	Night	44% 4 11% 24% 15% 2	127209
Seeing	Day	18% 12% 29% 24% 13% 4	16927
	Night	18% 10% 31% 29% 11% 1	26695

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	11% 13% 6% 15% 6% 6% 5% 3 5% 6% 24%	3617
	11th to 20th	Day	10% 11% 5% 13% 7% 7% 6% 4 7% 4 26%	3620
	21st to end	Day	16% 16% 8% 8% 7% 5% 4 3 4 5% 25%	4422
February	1st to 10th	Day	16% 12% 6% 10% 5% 5% 3 3 4 5% 30%	1800
	11th to 20th	Day	15% 10% 4 8% 7% 5% 5% 4 4 7% 32%	1928
	21st to end	Day	13% 14% 5% 9% 5% 4 4 3 4 6% 34%	1650
March	1st to 10th	Day	18% 14% 3 6% 3 3 2 2 3 4 41%	4480
	11th to 20th	Day	8% 7% 3 6% 5% 4 4 4 6% 8% 44%	4875
	21st to end	Day	19% 11% 4 10% 5% 5% 5% 3 5% 6% 28%	5869
April	1st to 10th	Day	16% 11% 4 8% 5% 4 4 3 5% 6% 36%	2400
	11th to 20th	Day	16% 10% 3 6% 5% 4 4 4 4 7% 37%	2374
	21st to end	Day	19% 8% 3 7% 5% 4 4 4 5% 6% 35%	2400
May	1st to 10th	Day	16% 8% 3 7% 5% 5% 4 4 6% 9% 33%	5849
	11th to 20th	Day	15% 7% 2 7% 4 4 4 3 5% 7% 42%	6314
	21st to end	Day	12% 7% 2 7% 5% 5% 5% 4 6% 8% 38%	6935
June	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 4 6% 9% 45%	2800
	11th to 20th	Day	8% 5% 2 7% 5% 5% 5% 4 6% 8% 46%	2800
	21st to end	Day	10% 7% 3 7% 5% 5% 5% 5% 6% 8% 41%	2800
July	1st to 10th	Day	9% 6% 3 6% 4 5% 5% 4 7% 11% 39%	6360
	11th to 20th	Day	9% 6% 3 7% 5% 5% 5% 4 7% 10% 39%	6360
	21st to end	Day	10% 7% 3 7% 5% 5% 5% 4 7% 10% 36%	6924
August	1st to 10th	Day	6% 5% 2 6% 5% 5% 5% 4 7% 10% 45%	4300
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 4 8% 9% 41%	3849
	21st to end	Day	5% 4 2 6% 4 5% 5% 4 7% 9% 49%	4312
September	1st to 10th	Day	11% 5% 2 5% 3 5% 4 3 5% 8% 49%	2316
	11th to 20th	Day	11% 4 2 5% 4 4 3 4 6% 7% 52%	2220
	21st to end	Day	9% 6% 3 6% 4 3 4 4 6% 8% 47%	2090
October	1st to 10th	Day	12% 6% 3 5% 3 4 4 3 5% 5% 51%	1947
	11th to 20th	Day	17% 8% 2 7% 4 4 3 2 4 6% 44%	1900
	21st to end	Day	20% 9% 3 6% 2 3 4 3 4 6% 39%	1971
November	1st to 10th	Day	11% 8% 2 6% 3 4 4 3 5% 8% 47%	1762
	11th to 20th	Day	17% 10% 3 7% 4 3 5% 3 4 6% 38%	1800
	21st to end	Day	17% 13% 3 8% 5% 4 4 2 4 5% 37%	1685
December	1st to 10th	Day	9% 8% 3 7% 5% 4 4 3 4 7% 46%	2610
	11th to 20th	Day	14% 16% 6% 11% 5% 6% 5% 3 5% 6% 23%	3008
	21st to end	Day	25% 22% 7% 12% 4 4 3 2 3 4 15%	3982
January	1st to 10th	Night	14% 14% 6% 12% 5% 4 3 3 4 5% 31%	6348
	11th to 20th	Night	11% 15% 6% 14% 7% 6% 5% 4 5% 4 24%	6360
	21st to end	Night	16% 14% 6% 10% 5% 4 3 2 3 5% 31%	6554
February	1st to 10th	Night	14% 13% 5% 9% 5% 5% 4 3 4 6% 31%	2600
	11th to 20th	Night	14% 12% 4 9% 4 4 4 2 4 6% 36%	2356
	21st to end	Night	16% 11% 4 7% 4 3 3 3 4 5% 39%	1980
March	1st to 10th	Night	17% 13% 4 6% 3 3 3 3 4 5% 39%	5373
	11th to 20th	Night	11% 8% 3 5% 4 4 4 3 4 7% 48%	5128
	21st to end	Night	17% 11% 5% 10% 5% 5% 4 3 5% 5% 29%	5059
April	1st to 10th	Night	15% 10% 2 6% 3 4 4 4 5% 6% 40%	2000
	11th to 20th	Night	15% 9% 2 6% 5% 4 4 3 4 6% 41%	1975
	21st to end	Night	18% 7% 3 7% 6% 4 4 3 5% 7% 37%	2000
May	1st to 10th	Night	18% 10% 3 8% 5% 4 4 3 5% 7% 33%	4043
	11th to 20th	Night	13% 6% 2 5% 4 4 5% 4 6% 9% 41%	3597
	21st to end	Night	13% 8% 3 8% 4 4 4 4 6% 7% 39%	3942
June	1st to 10th	Night	10% 5% 2 4 3 3 4 4 6% 8% 50%	1600
	11th to 20th	Night	7% 6% 2 6% 4 5% 4 4 5% 9% 47%	1600
	21st to end	Night	9% 5% 2 6% 5% 4 5% 4 7% 9% 45%	1600
July	1st to 10th	Night	9% 5% 2 7% 4 5% 5% 4 6% 11% 40%	3618
	11th to 20th	Night	5% 5% 2 7% 5% 4 5% 4 7% 9% 48%	3617
	21st to end	Night	10% 6% 2 7% 4 5% 5% 5% 6% 8% 41%	3947
August	1st to 10th	Night	6% 4 2 4 4 3 4 4 6% 10% 53%	2855
	11th to 20th	Night	5% 4 2 6% 4 4 5% 4 6% 9% 52%	3198
	21st to end	Night	5% 4 2 5% 3 4 4 4 6% 9% 53%	3586
September	1st to 10th	Night	10% 5% 2 5% 4 3 3 3 4 6% 57%	1930
	11th to 20th	Night	9% 4 2 4 4 3 4 3 5% 7% 55%	1940
	21st to end	Night	8% 6% 2 6% 4 4 4 4 6% 8% 48%	2090
October	1st to 10th	Night	10% 4 2 5% 3 4 4 3 4 6% 54%	2231
	11th to 20th	Night	15% 6% 2 4 3 3 3 3 5% 6% 49%	2280
	21st to end	Night	18% 9% 3 7% 4 4 4 3 5% 5% 39%	2627
November	1st to 10th	Night	12% 6% 3 4 4 3 4 3 4 6% 51%	2536
	11th to 20th	Night	13% 9% 3 7% 5% 4 4 4 4 6% 42%	2600
	21st to end	Night	17% 10% 4 7% 4 4 4 3 4 6% 37%	2710
December	1st to 10th	Night	10% 10% 3 7% 4 3 3 3 4 6% 46%	4580
	11th to 20th	Night	16% 12% 5% 9% 5% 4 4 3 4 5% 33%	5199
	21st to end	Night	25% 20% 7% 10% 5% 4 4 3 4 4 15%	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% 3 9% 19% 6% 1	3618
	11th to 20th	Day	59% 4 10% 12% 12% 3	3620
	21st to end	Day	63% 3 10% 17% 7% 1	4422
February	1st to 10th	Day	57% 3 13% 17% 7% 2	1800
	11th to 20th	Day	52% 5% 11% 21% 11% 1	1938
	21st to end	Day	53% 4 10% 22% 10% 2	1650
March	1st to 10th	Day	49% 2 8% 23% 16% 2	4480
	11th to 20th	Day	36% 5% 11% 32% 16% 1	4875
	21st to end	Day	57% 4 14% 19% 5% 1	5871
April	1st to 10th	Day	50% 4 11% 23% 12%	2400
	11th to 20th	Day	47% 4 10% 24% 13% 2	2374
	21st to end	Day	50% 5% 11% 20% 12% 2	2400
May	1st to 10th	Day	47% 5% 12% 21% 13% 1	5884
	11th to 20th	Day	42% 5% 11% 28% 12% 3	6318
	21st to end	Day	42% 6% 11% 23% 16% 2	6949
June	1st to 10th	Day	34% 6% 12% 29% 15% 3	2800
	11th to 20th	Day	35% 6% 10% 25% 21% 3	2800
	21st to end	Day	39% 7% 13% 22% 16% 3	2800
July	1st to 10th	Day	37% 5% 14% 27% 15% 2	6291
	11th to 20th	Day	39% 6% 15% 25% 14% 1	6285
	21st to end	Day	40% 7% 18% 22% 11% 2	6728
August	1st to 10th	Day	31% 6% 19% 31% 12% 1	4285
	11th to 20th	Day	37% 5% 15% 27% 15% 1	3885
	21st to end	Day	30% 6% 14% 31% 16% 4	4311
September	1st to 10th	Day	34% 5% 10% 25% 21% 5%	2316
	11th to 20th	Day	30% 4 11% 26% 24% 5%	2220
	21st to end	Day	34% 5% 10% 29% 21% 2	2090
October	1st to 10th	Day	23% 3 6% 27% 38% 3	3233
	11th to 20th	Day	29% 2 9% 22% 34% 4	3140
	21st to end	Day	42% 3 8% 25% 19% 3	3222
November	1st to 10th	Day	36% 4 15% 25% 16% 3	1762
	11th to 20th	Day	47% 3 11% 24% 13% 2	1800
	21st to end	Day	52% 3 12% 24% 10%	1685
December	1st to 10th	Day	40% 3 14% 34% 9%	2610
	11th to 20th	Day	61% 4 11% 18% 6% 1	3005
	21st to end	Day	75% 3 8% 9% 4	3982
January	1st to 10th	Night	56% 3 10% 23% 7%	6348
	11th to 20th	Night	64% 3 9% 12% 11% 1	6360
	21st to end	Night	58% 2 8% 20% 11% 1	6554
February	1st to 10th	Night	54% 4 11% 18% 11% 1	2600
	11th to 20th	Night	50% 4 11% 23% 11% 1	2357
	21st to end	Night	48% 3 9% 24% 14% 2	1980
March	1st to 10th	Night	48% 3 8% 25% 14% 3	5373
	11th to 20th	Night	38% 3 9% 29% 18% 4	5128
	21st to end	Night	56% 4 10% 21% 7% 1	5059
April	1st to 10th	Night	44% 4 11% 25% 14% 2	2000
	11th to 20th	Night	43% 4 8% 26% 14% 4	1975
	21st to end	Night	47% 5% 11% 22% 13% 3	2000
May	1st to 10th	Night	50% 5% 11% 20% 13% 2	4070
	11th to 20th	Night	39% 6% 14% 26% 12% 4	3598
	21st to end	Night	43% 5% 11% 23% 16% 2	3950
June	1st to 10th	Night	31% 5% 14% 27% 19% 4	1600
	11th to 20th	Night	33% 5% 12% 25% 21% 4	1600
	21st to end	Night	34% 6% 14% 24% 18% 3	1600
July	1st to 10th	Night	38% 5% 12% 29% 15% 2	3580
	11th to 20th	Night	31% 6% 14% 28% 20% 1	3572
	21st to end	Night	38% 8% 16% 21% 15% 3	3832
August	1st to 10th	Night	24% 6% 18% 32% 17% 2	2846
	11th to 20th	Night	30% 4 14% 33% 17% 1	3228
	21st to end	Night	26% 6% 14% 34% 16% 3	3586
September	1st to 10th	Night	29% 4 10% 28% 24% 5%	1930
	11th to 20th	Night	29% 4 10% 27% 25% 5%	1940
	21st to end	Night	33% 5% 10% 27% 21% 4	2090
October	1st to 10th	Night	23% 3 6% 28% 36% 4	3725
	11th to 20th	Night	25% 3 8% 24% 35% 5%	3779
	21st to end	Night	38% 3 10% 23% 22% 4	4326
November	1st to 10th	Night	34% 5% 11% 27% 19% 4	2536
	11th to 20th	Night	43% 3 12% 24% 16% 2	2600
	21st to end	Night	49% 3 9% 25% 13% 1	2710
December	1st to 10th	Night	40% 2 13% 32% 12% 1	4580
	11th to 20th	Night	54% 3 12% 22% 9%	5201
	21st to end	Night	73% 4 8% 11% 4	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	25% 21% 32% 18% 4	300
	11th to 20th	Day	29% 23% 36% 10% 2	300
	21st to end	Day	22% 27% 32% 15% 4	330
February	1st to 10th	Day	24% 21% 41% 12% 2	300
	11th to 20th	Day	25% 28% 30% 13% 4	300
	21st to end	Day	25% 22% 42% 9% 2	249
March	1st to 10th	Day	29% 26% 33% 10% 2	300
	11th to 20th	Day	29% 24% 33% 13% 2	300
	21st to end	Day	34% 15% 31% 14% 4 1	504
April	1st to 10th	Day	27% 15% 33% 21% 3 1	500
	11th to 20th	Day	24% 17% 31% 17% 10% 1	492
	21st to end	Day	26% 17% 32% 19% 5% 1	500
May	1st to 10th	Day	22% 14% 33% 21% 7% 2	503
	11th to 20th	Day	23% 12% 30% 23% 9% 3	720
	21st to end	Day	16% 11% 30% 24% 12% 7%	789
June	1st to 10th	Day	12% 6% 31% 28% 19% 4	730
	11th to 20th	Day	8% 8% 30% 34% 17% 3	730
	21st to end	Day	11% 9% 32% 31% 14% 4	730
July	1st to 10th	Day	11% 4 21% 32% 20% 13%	721
	11th to 20th	Day	11% 3 25% 32% 22% 7%	718
	21st to end	Day	11% 3 22% 36% 24% 4	794
August	1st to 10th	Day	7% 4 23% 35% 23% 8%	726
	11th to 20th	Day	11% 3 24% 26% 25% 12%	519
	21st to end	Day	7% 5% 19% 32% 29% 8%	583
September	1st to 10th	Day	12% 7% 20% 32% 25% 5%	502
	11th to 20th	Day	10% 4 18% 34% 26% 8%	490
	21st to end	Day	12% 12% 25% 24% 22% 5%	490
October	1st to 10th	Day	16% 12% 27% 28% 13% 4	347
	11th to 20th	Day	19% 22% 33% 18% 6% 1	300
	21st to end	Day	33% 15% 33% 15% 3	330
November	1st to 10th	Day	16% 16% 37% 21% 8% 2	300
	11th to 20th	Day	26% 19% 34% 15% 5% 1	300
	21st to end	Day	26% 13% 42% 18% 1	300
December	1st to 10th	Day	16% 26% 37% 15% 3 3	300
	11th to 20th	Day	25% 19% 36% 17% 3	300
	21st to end	Day	30% 27% 29% 13% 1	330
January	1st to 10th	Night	19% 16% 38% 22% 6%	1000
	11th to 20th	Night	21% 16% 38% 20% 5%	1000
	21st to end	Night	22% 15% 36% 24% 3	1100
February	1st to 10th	Night	23% 13% 38% 22% 4	1000
	11th to 20th	Night	22% 16% 35% 24% 3	801
	21st to end	Night	24% 17% 39% 18% 2	660
March	1st to 10th	Night	22% 14% 38% 22% 5%	800
	11th to 20th	Night	20% 13% 32% 29% 6%	670
	21st to end	Night	27% 11% 36% 20% 6%	660
April	1st to 10th	Night	21% 14% 36% 25% 5%	600
	11th to 20th	Night	21% 14% 30% 25% 9%	593
	21st to end	Night	22% 11% 31% 28% 7% 1	600
May	1st to 10th	Night	19% 8% 34% 30% 8% 1	600
	11th to 20th	Night	18% 6% 31% 35% 9% 1	591
	21st to end	Night	14% 5% 29% 34% 17% 2	650
June	1st to 10th	Night	12% 4 28% 43% 14% 1	600
	11th to 20th	Night	10% 3 28% 43% 15% 1	600
	21st to end	Night	10% 4 31% 39% 16% 1	600
July	1st to 10th	Night	10% 2 15% 38% 30% 4	585
	11th to 20th	Night	6% 3 21% 42% 26% 2	582
	21st to end	Night	8% 1 16% 45% 29% 1	657
August	1st to 10th	Night	8% 2 18% 43% 25% 5%	597
	11th to 20th	Night	7% 2 15% 42% 29% 5%	594
	21st to end	Night	7% 2 18% 40% 31% 2	660
September	1st to 10th	Night	12% 3 18% 37% 27% 2	579
	11th to 20th	Night	10% 3 18% 37% 26% 5%	610
	21st to end	Night	10% 9% 24% 33% 22% 2	760
October	1st to 10th	Night	12% 7% 29% 32% 18% 2	760
	11th to 20th	Night	19% 12% 29% 29% 11% 1	760
	21st to end	Night	24% 13% 34% 22% 7%	836
November	1st to 10th	Night	16% 11% 39% 25% 9% 1	780
	11th to 20th	Night	19% 16% 33% 25% 6%	800
	21st to end	Night	23% 14% 37% 22% 4	910
December	1st to 10th	Night	21% 14% 37% 23% 4	1000
	11th to 20th	Night	24% 13% 32% 26% 6%	1000
	21st to end	Night	32% 14% 30% 22% 2	1100

Page generated at 2025-09-01 00:51:02. Version ac07

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