Starved Rock State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starved Rock State Park clear sky chart from 2005-11-06 to 2024-04-25.

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% 9% 4 7% 6% 3 5% 5% 5% 7% 36%	83267
	Night	14% 9% 4 7% 5% 3 4 4 5% 6% 38%	85896
Transparency	Day	46% 6% 12% 22% 12% 2	82968
	Night	46% 5% 12% 22% 13% 2	85716
Seeing	Day	17% 10% 28% 25% 15% 5%	14961
	Night	18% 10% 30% 30% 12% 1	24990

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	13% 11% 9% 12% 7% 4 5% 5% 4 5% 25%	2527
	11th to 20th	Day	13% 12% 6% 12% 10% 5% 6% 7% 8% 5% 18%	2530
	21st to end	Day	17% 21% 9% 11% 6% 2 3 4 4 4 17%	2982
February	1st to 10th	Day	17% 12% 5% 8% 6% 2 5% 5% 5% 6% 29%	1710
	11th to 20th	Day	14% 10% 5% 7% 7% 4 4 5% 4 6% 34%	1848
	21st to end	Day	15% 13% 7% 9% 5% 2 4 3 4 5% 31%	1570
March	1st to 10th	Day	16% 14% 4 7% 5% 3 3 4 4 4 36%	3120
	11th to 20th	Day	10% 7% 3 6% 5% 3 5% 5% 5% 8% 41%	3320
	21st to end	Day	21% 10% 6% 10% 6% 4 5% 5% 6% 6% 22%	4150
April	1st to 10th	Day	17% 11% 5% 7% 5% 3 5% 3 5% 6% 34%	2280
	11th to 20th	Day	16% 9% 4 6% 6% 3 4 4 4 6% 38%	2254
	21st to end	Day	20% 8% 3 5% 5% 3 5% 5% 4 6% 34%	2247
May	1st to 10th	Day	17% 8% 4 6% 6% 4 6% 5% 5% 7% 33%	2340
	11th to 20th	Day	19% 8% 3 6% 6% 4 5% 4 5% 7% 34%	2458
	21st to end	Day	15% 6% 3 6% 6% 4 5% 5% 6% 8% 36%	2725
June	1st to 10th	Day	10% 5% 3 4 5% 3 5% 5% 6% 9% 46%	2520
	11th to 20th	Day	9% 4 2 5% 5% 4 5% 5% 7% 9% 44%	2520
	21st to end	Day	10% 5% 3 6% 6% 4 6% 5% 7% 9% 39%	2520
July	1st to 10th	Day	7% 4 3 4 5% 3 5% 5% 7% 10% 46%	2520
	11th to 20th	Day	8% 4 2 4 5% 3 5% 6% 6% 10% 46%	2520
	21st to end	Day	7% 4 2 5% 5% 4 6% 6% 7% 10% 44%	2743
August	1st to 10th	Day	6% 4 2 5% 6% 3 6% 6% 7% 10% 44%	2422
	11th to 20th	Day	8% 5% 2 5% 5% 3 4 5% 6% 9% 47%	2125
	21st to end	Day	8% 4 2 4 4 3 4 5% 7% 9% 50%	2376
September	1st to 10th	Day	12% 4 2 5% 5% 3 4 4 6% 7% 47%	2160
	11th to 20th	Day	12% 4 2 3 4 3 3 4 6% 7% 53%	2080
	21st to end	Day	8% 6% 3 6% 5% 4 3 5% 6% 7% 47%	1980
October	1st to 10th	Day	11% 7% 2 6% 5% 2 3 4 5% 7% 47%	1880
	11th to 20th	Day	18% 7% 4 6% 5% 3 5% 4 4 5% 40%	1800
	21st to end	Day	20% 10% 3 5% 4 2 5% 4 4 7% 36%	1823
November	1st to 10th	Day	11% 7% 3 5% 4 2 4 4 6% 7% 47%	1672
	11th to 20th	Day	17% 9% 6% 7% 5% 2 4 4 4 7% 35%	1710
	21st to end	Day	19% 10% 5% 6% 5% 2 4 3 3 5% 37%	1614
December	1st to 10th	Day	15% 12% 5% 6% 7% 4 4 4 4 6% 34%	1520
	11th to 20th	Day	14% 14% 4 9% 7% 4 4 5% 5% 5% 29%	1918
	21st to end	Day	24% 17% 9% 11% 7% 3 3 3 3 5% 14%	2783
January	1st to 10th	Night	15% 14% 7% 9% 6% 3 4 4 4 5% 30%	4428
	11th to 20th	Night	13% 18% 7% 10% 8% 3 4 5% 6% 4 21%	4440
	21st to end	Night	21% 17% 7% 9% 6% 3 3 4 4 4 22%	4683
February	1st to 10th	Night	16% 12% 5% 7% 7% 3 4 4 5% 6% 32%	2469
	11th to 20th	Night	13% 10% 4 7% 6% 3 5% 4 5% 7% 37%	2218
	21st to end	Night	18% 10% 5% 8% 5% 3 4 3 4 6% 34%	1884
March	1st to 10th	Night	18% 11% 3 4 4 3 4 3 4 5% 40%	3733
	11th to 20th	Night	11% 5% 4 6% 5% 3 4 4 5% 6% 47%	3654
	21st to end	Night	21% 11% 6% 10% 6% 4 4 5% 4 5% 25%	3480
April	1st to 10th	Night	17% 10% 3 5% 5% 2 4 4 5% 7% 38%	1900
	11th to 20th	Night	18% 7% 2 6% 5% 2 4 3 3 6% 43%	1875
	21st to end	Night	18% 7% 2 6% 5% 3 4 5% 5% 8% 37%	1810
May	1st to 10th	Night	16% 8% 3 6% 5% 4 5% 4 6% 9% 34%	1620
	11th to 20th	Night	15% 6% 3 5% 5% 2 4 4 6% 9% 40%	1434
	21st to end	Night	12% 6% 3 6% 6% 4 4 5% 6% 9% 40%	1551
June	1st to 10th	Night	9% 5% 2 6% 4 2 4 5% 5% 7% 50%	1440
	11th to 20th	Night	8% 5% 3 5% 5% 3 4 5% 7% 10% 46%	1440
	21st to end	Night	9% 4 3 6% 5% 3 6% 5% 6% 8% 44%	1440
July	1st to 10th	Night	6% 5% 2 4 5% 3 4 4 6% 10% 50%	1440
	11th to 20th	Night	6% 3 2 4 3 3 5% 5% 6% 7% 56%	1440
	21st to end	Night	4 3 2 4 5% 3 5% 6% 8% 8% 52%	1575
August	1st to 10th	Night	4 5% 2 6% 3 3 6% 5% 6% 9% 51%	1512
	11th to 20th	Night	7% 3 2 5% 4 3 5% 4 7% 8% 52%	1776
	21st to end	Night	7% 4 2 4 4 2 4 4 5% 8% 56%	1980
September	1st to 10th	Night	10% 6% 2 4 5% 2 3 3 4 7% 54%	1800
	11th to 20th	Night	9% 5% 2 4 3 2 4 4 5% 7% 54%	1861
	21st to end	Night	8% 5% 3 5% 4 4 4 6% 6% 8% 49%	1980
October	1st to 10th	Night	11% 5% 3 5% 4 3 3 4 5% 5% 53%	2078
	11th to 20th	Night	17% 7% 2 5% 4 2 3 3 4 6% 46%	2160
	21st to end	Night	20% 8% 3 6% 4 2 4 4 5% 6% 38%	2531
November	1st to 10th	Night	11% 7% 3 4 5% 2 4 3 4 6% 51%	2406
	11th to 20th	Night	14% 9% 4 7% 6% 3 4 4 4 7% 39%	2470
	21st to end	Night	18% 8% 4 5% 5% 3 3 4 4 6% 39%	2565
December	1st to 10th	Night	16% 11% 4 8% 7% 3 4 4 5% 5% 34%	2660
	11th to 20th	Night	15% 12% 5% 9% 6% 3 3 3 4 5% 34%	3279
	21st to end	Night	23% 17% 7% 10% 7% 3 4 4 4 5% 16%	4884

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% 4 11% 17% 6%	2528
	11th to 20th	Day	63% 6% 10% 12% 8% 1	2530
	21st to end	Day	70% 4 9% 12% 5%	2982
February	1st to 10th	Day	56% 5% 13% 16% 7% 2	1710
	11th to 20th	Day	50% 5% 11% 22% 10% 1	1858
	21st to end	Day	56% 4 10% 21% 7% 2	1570
March	1st to 10th	Day	50% 5% 11% 20% 12% 2	3120
	11th to 20th	Day	39% 6% 14% 27% 13% 1	3320
	21st to end	Day	61% 7% 15% 14% 3 1	4150
April	1st to 10th	Day	51% 5% 11% 21% 11%	2280
	11th to 20th	Day	47% 4 11% 23% 11% 3	2254
	21st to end	Day	49% 6% 12% 18% 12% 2	2247
May	1st to 10th	Day	50% 6% 13% 22% 8%	2340
	11th to 20th	Day	49% 6% 10% 23% 12%	2462
	21st to end	Day	44% 7% 12% 19% 16% 2	2725
June	1st to 10th	Day	34% 7% 13% 27% 17% 2	2520
	11th to 20th	Day	34% 7% 11% 23% 22% 3	2520
	21st to end	Day	40% 7% 13% 24% 14% 2	2520
July	1st to 10th	Day	33% 6% 14% 29% 15% 3	2451
	11th to 20th	Day	31% 7% 15% 29% 16% 2	2445
	21st to end	Day	32% 7% 18% 26% 16% 2	2591
August	1st to 10th	Day	32% 7% 17% 29% 12% 2	2407
	11th to 20th	Day	33% 7% 15% 26% 18% 1	2125
	21st to end	Day	29% 7% 13% 28% 20% 4	2376
September	1st to 10th	Day	35% 6% 12% 24% 18% 5%	2160
	11th to 20th	Day	30% 4 12% 29% 21% 4	2080
	21st to end	Day	34% 5% 10% 28% 20% 2	1980
October	1st to 10th	Day	37% 5% 11% 26% 19% 1	1880
	11th to 20th	Day	47% 4 9% 24% 15% 2	1800
	21st to end	Day	48% 5% 11% 22% 10% 3	1823
November	1st to 10th	Day	36% 4 16% 25% 16% 3	1672
	11th to 20th	Day	50% 4 11% 23% 11% 1	1710
	21st to end	Day	51% 4 11% 23% 9%	1614
December	1st to 10th	Day	53% 4 13% 20% 9% 1	1520
	11th to 20th	Day	55% 5% 11% 20% 8% 1	1915
	21st to end	Day	75% 4 8% 9% 4	2783
January	1st to 10th	Night	56% 5% 12% 17% 9%	4428
	11th to 20th	Night	65% 4 12% 12% 8%	4440
	21st to end	Night	66% 4 10% 14% 6%	4683
February	1st to 10th	Night	54% 5% 10% 19% 11% 1	2469
	11th to 20th	Night	47% 4 12% 24% 13% 1	2219
	21st to end	Night	52% 4 9% 20% 11% 3	1884
March	1st to 10th	Night	47% 4 12% 23% 11% 2	3733
	11th to 20th	Night	37% 5% 11% 28% 18% 2	3654
	21st to end	Night	61% 5% 12% 17% 5% 1	3480
April	1st to 10th	Night	46% 5% 11% 22% 13% 2	1900
	11th to 20th	Night	43% 3 9% 24% 16% 5%	1875
	21st to end	Night	45% 5% 13% 22% 12% 3	1810
May	1st to 10th	Night	46% 5% 14% 23% 12% 1	1620
	11th to 20th	Night	41% 6% 13% 23% 15% 1	1435
	21st to end	Night	40% 7% 14% 20% 16% 3	1552
June	1st to 10th	Night	32% 6% 13% 26% 19% 4	1440
	11th to 20th	Night	33% 6% 13% 23% 23% 3	1440
	21st to end	Night	37% 8% 15% 22% 16% 3	1440
July	1st to 10th	Night	29% 6% 13% 30% 17% 5%	1400
	11th to 20th	Night	27% 6% 14% 29% 21% 3	1392
	21st to end	Night	25% 8% 17% 26% 20% 5%	1487
August	1st to 10th	Night	28% 7% 19% 28% 16% 2	1503
	11th to 20th	Night	28% 6% 15% 28% 21% 2	1776
	21st to end	Night	27% 5% 12% 29% 22% 5%	1980
September	1st to 10th	Night	31% 5% 11% 27% 22% 5%	1800
	11th to 20th	Night	29% 5% 10% 29% 24% 4	1861
	21st to end	Night	32% 5% 13% 28% 19% 3	1980
October	1st to 10th	Night	34% 4 10% 25% 23% 3	2078
	11th to 20th	Night	40% 4 8% 26% 20% 2	2160
	21st to end	Night	48% 4 10% 23% 14% 2	2531
November	1st to 10th	Night	35% 4 11% 28% 18% 4	2406
	11th to 20th	Night	46% 4 11% 23% 14% 2	2470
	21st to end	Night	47% 4 11% 24% 12% 1	2565
December	1st to 10th	Night	53% 4 12% 22% 8% 1	2660
	11th to 20th	Night	53% 4 12% 21% 9% 1	3281
	21st to end	Night	71% 5% 9% 11% 4	4884

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	23% 14% 34% 20% 8% 1	270
	11th to 20th	Day	24% 17% 37% 15% 6% 1	270
	21st to end	Day	23% 17% 34% 19% 6%	297
February	1st to 10th	Day	21% 17% 40% 19% 4	270
	11th to 20th	Day	21% 19% 37% 19% 5%	270
	21st to end	Day	23% 21% 38% 15% 3	225
March	1st to 10th	Day	24% 21% 36% 16% 2 1	270
	11th to 20th	Day	28% 17% 36% 14% 6%	270
	21st to end	Day	29% 16% 32% 16% 5% 2	491
April	1st to 10th	Day	27% 12% 34% 19% 7% 1	460
	11th to 20th	Day	20% 20% 28% 20% 10% 2	452
	21st to end	Day	24% 13% 31% 22% 8% 2	437
May	1st to 10th	Day	21% 12% 33% 22% 9% 3	423
	11th to 20th	Day	22% 11% 27% 26% 11% 3	604
	21st to end	Day	16% 8% 29% 23% 15% 9%	679
June	1st to 10th	Day	10% 6% 27% 30% 20% 6%	630
	11th to 20th	Day	10% 5% 29% 32% 19% 4	630
	21st to end	Day	12% 8% 31% 30% 15% 5%	630
July	1st to 10th	Day	8% 4 17% 29% 24% 17%	621
	11th to 20th	Day	11% 4 23% 31% 20% 11%	618
	21st to end	Day	6% 2 22% 35% 28% 6%	684
August	1st to 10th	Day	6% 4 18% 34% 27% 12%	612
	11th to 20th	Day	12% 4 14% 29% 28% 14%	439
	21st to end	Day	9% 2 18% 32% 28% 11%	495
September	1st to 10th	Day	15% 6% 17% 31% 26% 5%	450
	11th to 20th	Day	10% 5% 18% 28% 26% 12%	450
	21st to end	Day	10% 11% 27% 22% 22% 8%	450
October	1st to 10th	Day	15% 7% 27% 29% 17% 5%	350
	11th to 20th	Day	23% 20% 32% 20% 5% 1	270
	21st to end	Day	35% 13% 27% 22% 4	297
November	1st to 10th	Day	15% 13% 41% 19% 8% 4	270
	11th to 20th	Day	26% 16% 33% 19% 5% 2	270
	21st to end	Day	27% 7% 39% 22% 5%	270
December	1st to 10th	Day	19% 17% 37% 18% 7% 2	270
	11th to 20th	Day	19% 14% 39% 25% 4	270
	21st to end	Day	29% 20% 36% 13% 2	297
January	1st to 10th	Night	20% 14% 37% 24% 5% 1	950
	11th to 20th	Night	22% 15% 36% 21% 5%	950
	21st to end	Night	22% 12% 34% 27% 5%	1045
February	1st to 10th	Night	23% 12% 36% 24% 4	949
	11th to 20th	Night	18% 15% 37% 25% 4	743
	21st to end	Night	23% 15% 36% 22% 3	628
March	1st to 10th	Night	23% 14% 34% 23% 6%	760
	11th to 20th	Night	18% 12% 35% 30% 5% 1	679
	21st to end	Night	27% 11% 34% 22% 6% 1	627
April	1st to 10th	Night	22% 12% 36% 25% 5%	570
	11th to 20th	Night	23% 12% 31% 28% 6%	563
	21st to end	Night	22% 10% 33% 27% 8%	555
May	1st to 10th	Night	19% 9% 36% 27% 8% 1	540
	11th to 20th	Night	18% 7% 32% 32% 11%	531
	21st to end	Night	14% 5% 27% 36% 17% 1	584
June	1st to 10th	Night	10% 3 25% 46% 14% 1	540
	11th to 20th	Night	11% 6% 24% 42% 17%	540
	21st to end	Night	10% 4 28% 39% 19% 1	540
July	1st to 10th	Night	8% 2 14% 38% 33% 5%	525
	11th to 20th	Night	8% 2 19% 40% 27% 3	522
	21st to end	Night	4 3 15% 49% 28% 2	591
August	1st to 10th	Night	7% 2 14% 43% 30% 4	537
	11th to 20th	Night	8% 3 11% 40% 34% 5%	534
	21st to end	Night	8% 2 17% 40% 29% 3	594
September	1st to 10th	Night	14% 4 16% 36% 27% 3	540
	11th to 20th	Night	11% 3 19% 35% 29% 3	601
	21st to end	Night	12% 7% 24% 35% 21% 2	720
October	1st to 10th	Night	12% 7% 27% 34% 18% 2	720
	11th to 20th	Night	22% 12% 30% 26% 11%	720
	21st to end	Night	24% 12% 33% 25% 7%	792
November	1st to 10th	Night	14% 11% 39% 25% 11% 1	740
	11th to 20th	Night	21% 13% 34% 25% 7% 1	760
	21st to end	Night	22% 11% 34% 27% 6%	855
December	1st to 10th	Night	22% 12% 35% 25% 6%	950
	11th to 20th	Night	23% 11% 33% 27% 5% 1	950
	21st to end	Night	29% 15% 32% 21% 3	1045

Page generated at 2024-04-22 08:25:41. Version ac07

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