Streator
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Streator clear sky chart from 2005-11-06 to 2025-07-21.

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	13% 9% 3 8% 5% 4 4 4 6% 7% 37%	120122
	Night	13% 10% 4 8% 5% 4 4 3 5% 6% 38%	119217
Transparency	Day	44% 6% 12% 23% 14% 2	123700
	Night	45% 6% 11% 22% 15% 2	123780
Seeing	Day	16% 10% 29% 26% 15% 5%	16741
	Night	17% 10% 31% 29% 12% 1	26578

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	12% 12% 7% 14% 7% 6% 6% 3 5% 6% 24%	3617
	11th to 20th	Day	10% 11% 6% 14% 7% 6% 6% 5% 7% 5% 25%	3620
	21st to end	Day	15% 16% 7% 9% 6% 4 4 3 4 6% 26%	4276
February	1st to 10th	Day	16% 13% 5% 9% 6% 5% 4 3 4 5% 28%	1816
	11th to 20th	Day	14% 10% 4 8% 6% 5% 4 4 5% 6% 32%	1948
	21st to end	Day	13% 14% 6% 10% 5% 3 4 3 4 6% 31%	1650
March	1st to 10th	Day	19% 13% 3 7% 3 3 3 2 3 4 40%	4480
	11th to 20th	Day	8% 7% 3 7% 4 5% 5% 4 6% 8% 43%	4740
	21st to end	Day	20% 11% 5% 10% 5% 5% 5% 3 5% 6% 25%	5957
April	1st to 10th	Day	17% 13% 4 8% 4 4 3 3 5% 5% 34%	2400
	11th to 20th	Day	16% 10% 3 7% 5% 5% 4 3 4 7% 37%	2374
	21st to end	Day	20% 8% 3 7% 5% 4 5% 3 5% 7% 33%	2445
May	1st to 10th	Day	17% 8% 3 7% 4 4 5% 4 6% 8% 34%	5862
	11th to 20th	Day	14% 7% 2 6% 4 5% 5% 4 5% 8% 40%	6222
	21st to end	Day	12% 7% 3 7% 4 4 5% 4 6% 9% 39%	6935
June	1st to 10th	Day	10% 5% 2 5% 4 4 5% 4 7% 8% 45%	2800
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 5% 6% 8% 45%	2800
	21st to end	Day	9% 6% 3 6% 6% 5% 5% 5% 6% 8% 41%	2800
July	1st to 10th	Day	10% 8% 3 7% 4 5% 6% 5% 8% 9% 34%	4580
	11th to 20th	Day	7% 5% 2 5% 4 4 5% 4 7% 11% 48%	4580
	21st to end	Day	8% 6% 2 7% 5% 5% 5% 5% 7% 9% 42%	4814
August	1st to 10th	Day	7% 5% 2 6% 4 5% 5% 4 7% 10% 45%	4242
	11th to 20th	Day	9% 6% 2 5% 4 4 5% 4 8% 10% 43%	3729
	21st to end	Day	6% 5% 2 6% 4 4 4 4 7% 10% 48%	4180
September	1st to 10th	Day	11% 5% 1 5% 4 4 4 4 5% 8% 49%	2280
	11th to 20th	Day	11% 4 1 4 3 3 4 5% 6% 7% 52%	2188
	21st to end	Day	9% 7% 3 6% 4 5% 4 3 6% 8% 45%	2090
October	1st to 10th	Day	11% 7% 2 6% 5% 4 4 3 5% 7% 48%	1996
	11th to 20th	Day	16% 8% 3 6% 4 3 4 3 4 6% 43%	1900
	21st to end	Day	19% 8% 3 7% 4 3 4 3 5% 5% 38%	1919
November	1st to 10th	Day	11% 8% 2 5% 4 4 3 3 5% 7% 47%	1762
	11th to 20th	Day	16% 12% 4 7% 5% 4 4 3 4 6% 36%	1800
	21st to end	Day	18% 11% 4 9% 5% 4 3 3 5% 4 35%	1720
December	1st to 10th	Day	9% 9% 4 9% 5% 4 4 3 5% 5% 45%	2610
	11th to 20th	Day	12% 15% 7% 12% 6% 5% 6% 3 6% 6% 22%	3008
	21st to end	Day	26% 20% 8% 13% 5% 4 3 2 3 4 12%	3982
January	1st to 10th	Night	13% 14% 6% 12% 5% 4 4 3 4 4 31%	6348
	11th to 20th	Night	12% 15% 7% 14% 8% 5% 5% 4 5% 3 22%	6360
	21st to end	Night	17% 14% 6% 9% 5% 4 4 3 3 4 31%	6697
February	1st to 10th	Night	16% 13% 4 10% 6% 4 4 2 4 6% 31%	2581
	11th to 20th	Night	14% 11% 3 9% 5% 5% 4 3 5% 6% 35%	2338
	21st to end	Night	17% 11% 5% 8% 4 4 3 3 4 6% 35%	1980
March	1st to 10th	Night	16% 12% 4 7% 4 3 3 3 4 5% 40%	5373
	11th to 20th	Night	11% 6% 3 7% 4 4 4 3 5% 7% 46%	5263
	21st to end	Night	18% 10% 5% 11% 6% 5% 4 4 5% 5% 27%	4971
April	1st to 10th	Night	15% 10% 3 6% 5% 3 4 3 5% 6% 38%	2000
	11th to 20th	Night	18% 8% 3 6% 4 4 4 3 5% 6% 42%	1975
	21st to end	Night	17% 7% 3 6% 4 4 4 4 6% 8% 37%	1952
May	1st to 10th	Night	18% 9% 4 7% 5% 4 4 3 6% 7% 33%	4033
	11th to 20th	Night	11% 6% 3 6% 4 4 5% 5% 7% 9% 41%	3684
	21st to end	Night	13% 8% 3 7% 5% 4 5% 4 6% 8% 38%	3942
June	1st to 10th	Night	10% 5% 2 5% 4 4 4 3 5% 9% 49%	1600
	11th to 20th	Night	8% 5% 2 6% 4 5% 4 4 7% 10% 44%	1600
	21st to end	Night	8% 5% 2 6% 5% 6% 5% 4 7% 8% 44%	1600
July	1st to 10th	Night	11% 6% 2 7% 5% 5% 5% 4 6% 9% 41%	2610
	11th to 20th	Night	5% 5% 2 4 3 4 5% 3 6% 7% 57%	2610
	21st to end	Night	5% 6% 3 7% 5% 4 5% 5% 7% 9% 46%	2750
August	1st to 10th	Night	6% 4 2 5% 4 4 5% 4 7% 9% 51%	2688
	11th to 20th	Night	6% 5% 2 5% 5% 4 5% 4 7% 9% 49%	3100
	21st to end	Night	6% 4 2 5% 4 3 4 3 6% 10% 53%	3476
September	1st to 10th	Night	11% 5% 2 4 4 3 3 2 3 8% 55%	1900
	11th to 20th	Night	8% 5% 1 4 3 4 4 3 6% 7% 55%	1971
	21st to end	Night	9% 5% 2 6% 4 5% 4 4 6% 8% 46%	2090
October	1st to 10th	Night	10% 5% 2 6% 4 4 4 3 4 6% 54%	2180
	11th to 20th	Night	15% 7% 2 6% 3 3 3 3 4 6% 48%	2280
	21st to end	Night	18% 9% 3 6% 4 4 3 3 5% 6% 39%	2677
November	1st to 10th	Night	11% 8% 2 5% 3 4 4 3 5% 6% 49%	2536
	11th to 20th	Night	13% 10% 3 8% 5% 4 4 3 5% 6% 39%	2600
	21st to end	Night	17% 9% 4 7% 5% 4 3 4 4 5% 38%	2677
December	1st to 10th	Night	11% 9% 3 7% 4 4 4 3 5% 6% 43%	4580
	11th to 20th	Night	16% 13% 5% 10% 5% 4 3 3 4 5% 32%	5199
	21st to end	Night	24% 19% 6% 10% 5% 4 4 3 4 4 16%	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	61% 4 11% 16% 7% 1	3618
	11th to 20th	Day	59% 4 9% 12% 13% 3	3620
	21st to end	Day	60% 3 12% 17% 7%	4276
February	1st to 10th	Day	58% 5% 12% 17% 7% 2	1816
	11th to 20th	Day	51% 5% 12% 21% 9% 1	1958
	21st to end	Day	54% 5% 11% 21% 8% 2	1650
March	1st to 10th	Day	49% 4 7% 24% 14% 3	4480
	11th to 20th	Day	37% 6% 11% 32% 13% 1	4740
	21st to end	Day	59% 7% 12% 15% 7% 1	5959
April	1st to 10th	Day	51% 5% 11% 20% 12%	2400
	11th to 20th	Day	48% 6% 9% 23% 11% 3	2374
	21st to end	Day	49% 6% 12% 19% 11% 2	2445
May	1st to 10th	Day	45% 8% 11% 22% 13% 1	5897
	11th to 20th	Day	41% 8% 10% 27% 12% 2	6226
	21st to end	Day	39% 8% 12% 23% 15% 3	6949
June	1st to 10th	Day	34% 8% 13% 26% 17% 3	2800
	11th to 20th	Day	35% 8% 10% 22% 22% 3	2800
	21st to end	Day	38% 8% 13% 22% 16% 3	2800
July	1st to 10th	Day	42% 7% 14% 24% 11% 2	4511
	11th to 20th	Day	28% 9% 16% 30% 16% 1	4505
	21st to end	Day	36% 9% 17% 18% 17% 3	4663
August	1st to 10th	Day	30% 8% 18% 28% 14% 1	4227
	11th to 20th	Day	33% 7% 15% 28% 16% 1	3765
	21st to end	Day	30% 7% 13% 29% 17% 3	4179
September	1st to 10th	Day	34% 5% 12% 24% 20% 5%	2280
	11th to 20th	Day	30% 6% 11% 28% 22% 4	2188
	21st to end	Day	36% 7% 10% 25% 20% 2	2090
October	1st to 10th	Day	25% 4 8% 27% 34% 2	3321
	11th to 20th	Day	29% 3 11% 23% 31% 2	3140
	21st to end	Day	41% 4 9% 24% 18% 3	3144
November	1st to 10th	Day	37% 5% 13% 26% 16% 3	1762
	11th to 20th	Day	50% 5% 10% 22% 12% 1	1800
	21st to end	Day	52% 5% 11% 22% 10%	1720
December	1st to 10th	Day	42% 4 13% 32% 9%	2610
	11th to 20th	Day	61% 6% 11% 17% 5% 1	3005
	21st to end	Day	77% 5% 7% 7% 4	3982
January	1st to 10th	Night	56% 5% 10% 20% 9%	6348
	11th to 20th	Night	65% 4 9% 9% 12% 1	6360
	21st to end	Night	58% 4 8% 18% 11% 1	6697
February	1st to 10th	Night	55% 4 11% 17% 11% 2	2581
	11th to 20th	Night	50% 4 11% 22% 12% 1	2339
	21st to end	Night	51% 4 11% 20% 12% 2	1980
March	1st to 10th	Night	47% 5% 9% 25% 11% 4	5373
	11th to 20th	Night	38% 6% 11% 26% 16% 3	5263
	21st to end	Night	57% 6% 10% 19% 7% 1	4971
April	1st to 10th	Night	45% 5% 11% 23% 13% 2	2000
	11th to 20th	Night	44% 4 9% 23% 15% 4	1975
	21st to end	Night	44% 7% 12% 22% 11% 3	1952
May	1st to 10th	Night	48% 7% 11% 17% 13% 3	4060
	11th to 20th	Night	36% 9% 13% 25% 13% 4	3685
	21st to end	Night	40% 8% 12% 22% 15% 3	3950
June	1st to 10th	Night	32% 8% 13% 25% 19% 4	1600
	11th to 20th	Night	33% 6% 14% 23% 21% 3	1600
	21st to end	Night	36% 9% 15% 22% 15% 4	1600
July	1st to 10th	Night	40% 7% 14% 22% 13% 3	2570
	11th to 20th	Night	25% 8% 13% 28% 25% 2	2562
	21st to end	Night	32% 9% 16% 18% 19% 5%	2662
August	1st to 10th	Night	26% 8% 19% 27% 18% 1	2679
	11th to 20th	Night	29% 8% 16% 28% 19% 1	3130
	21st to end	Night	28% 7% 12% 33% 18% 3	3476
September	1st to 10th	Night	30% 5% 10% 25% 24% 5%	1900
	11th to 20th	Night	28% 5% 10% 28% 25% 5%	1971
	21st to end	Night	35% 7% 11% 25% 19% 3	2090
October	1st to 10th	Night	21% 4 7% 32% 33% 3	3635
	11th to 20th	Night	28% 4 9% 23% 33% 3	3779
	21st to end	Night	38% 4 9% 25% 20% 4	4402
November	1st to 10th	Night	36% 6% 10% 27% 18% 4	2536
	11th to 20th	Night	46% 5% 12% 21% 15% 2	2600
	21st to end	Night	49% 5% 10% 24% 12% 1	2677
December	1st to 10th	Night	41% 4 14% 29% 10% 1	4580
	11th to 20th	Night	55% 4 11% 18% 11%	5201
	21st to end	Night	72% 5% 8% 10% 5%	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	21% 15% 32% 25% 6% 1	300
	11th to 20th	Day	23% 18% 39% 13% 6% 1	300
	21st to end	Day	18% 19% 35% 20% 7%	330
February	1st to 10th	Day	23% 13% 41% 19% 4	300
	11th to 20th	Day	22% 17% 38% 17% 6%	300
	21st to end	Day	20% 16% 47% 14% 3	249
March	1st to 10th	Day	25% 18% 38% 15% 3	300
	11th to 20th	Day	24% 18% 36% 16% 4 1	300
	21st to end	Day	27% 17% 35% 13% 6% 1	540
April	1st to 10th	Day	25% 14% 33% 22% 6% 1	500
	11th to 20th	Day	22% 18% 29% 19% 11% 2	492
	21st to end	Day	23% 13% 34% 22% 7% 1	500
May	1st to 10th	Day	20% 14% 32% 22% 9% 2	503
	11th to 20th	Day	21% 10% 26% 26% 13% 3	680
	21st to end	Day	15% 10% 30% 24% 14% 8%	789
June	1st to 10th	Day	10% 7% 27% 31% 19% 6%	730
	11th to 20th	Day	10% 5% 28% 34% 20% 4	730
	21st to end	Day	11% 8% 32% 30% 15% 4	730
July	1st to 10th	Day	9% 4 19% 31% 22% 15%	721
	11th to 20th	Day	10% 5% 21% 32% 23% 11%	718
	21st to end	Day	8% 3 19% 37% 24% 8%	740
August	1st to 10th	Day	7% 3 18% 36% 25% 11%	645
	11th to 20th	Day	10% 4 18% 28% 28% 12%	479
	21st to end	Day	6% 3 17% 33% 29% 12%	539
September	1st to 10th	Day	12% 5% 18% 31% 26% 7%	490
	11th to 20th	Day	10% 3 14% 30% 29% 13%	490
	21st to end	Day	12% 10% 25% 26% 20% 7%	490
October	1st to 10th	Day	16% 5% 27% 31% 18% 4	396
	11th to 20th	Day	16% 21% 31% 22% 8% 1	300
	21st to end	Day	31% 13% 30% 20% 5% 1	330
November	1st to 10th	Day	15% 14% 37% 22% 8% 4	300
	11th to 20th	Day	22% 18% 36% 16% 7% 1	300
	21st to end	Day	23% 13% 37% 22% 5%	300
December	1st to 10th	Day	15% 19% 41% 16% 7% 2	300
	11th to 20th	Day	18% 17% 37% 24% 4	300
	21st to end	Day	27% 20% 37% 14% 2	330
January	1st to 10th	Night	19% 13% 39% 23% 5%	1000
	11th to 20th	Night	21% 15% 41% 19% 5%	1000
	21st to end	Night	22% 13% 36% 26% 3	1100
February	1st to 10th	Night	22% 13% 39% 22% 3	981
	11th to 20th	Night	19% 14% 36% 26% 3	783
	21st to end	Night	23% 14% 39% 20% 4	660
March	1st to 10th	Night	20% 17% 36% 23% 5%	800
	11th to 20th	Night	17% 13% 38% 27% 5% 1	727
	21st to end	Night	25% 11% 37% 21% 6% 1	660
April	1st to 10th	Night	20% 14% 36% 25% 5%	600
	11th to 20th	Night	21% 13% 33% 27% 6%	593
	21st to end	Night	21% 11% 32% 28% 7% 1	600
May	1st to 10th	Night	20% 8% 35% 29% 8% 1	600
	11th to 20th	Night	17% 8% 31% 34% 10% 1	591
	21st to end	Night	13% 5% 30% 36% 15% 1	650
June	1st to 10th	Night	11% 4 27% 45% 13% 1	600
	11th to 20th	Night	11% 5% 26% 43% 14% 1	600
	21st to end	Night	9% 3 30% 40% 18%	600
July	1st to 10th	Night	8% 3 18% 37% 31% 4	585
	11th to 20th	Night	8% 2 18% 42% 27% 2	582
	21st to end	Night	4 1 15% 50% 27% 2	624
August	1st to 10th	Night	6% 2 15% 44% 29% 4	567
	11th to 20th	Night	8% 2 13% 40% 32% 4	564
	21st to end	Night	7% 2 16% 41% 32% 2	627
September	1st to 10th	Night	12% 4 19% 35% 28% 3	570
	11th to 20th	Night	9% 4 19% 38% 27% 4	641
	21st to end	Night	10% 8% 25% 34% 22% 1	760
October	1st to 10th	Night	11% 6% 27% 36% 18% 1	760
	11th to 20th	Night	18% 12% 33% 25% 12% 1	760
	21st to end	Night	23% 12% 33% 24% 7%	836
November	1st to 10th	Night	16% 11% 38% 25% 9% 1	780
	11th to 20th	Night	19% 14% 35% 25% 7%	800
	21st to end	Night	21% 12% 37% 24% 6%	877
December	1st to 10th	Night	21% 13% 40% 22% 5%	1000
	11th to 20th	Night	22% 13% 35% 26% 5%	1000
	21st to end	Night	30% 14% 34% 20% 2	1100

Page generated at 2025-07-18 00:10:02. Version ac07

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