Prairie State College
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Prairie State College clear sky chart from 2005-11-06 to 2024-11-25.

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	13% 9% 3 7% 5% 4 5% 4 6% 7% 37%	101428
	Night	14% 10% 4 7% 5% 4 4 3 5% 6% 38%	98083
Transparency	Day	24% 47% 7% 13% 8% 1	105010
	Night	26% 47% 6% 12% 8% 1	102641
Seeing	Day	15% 9% 28% 28% 15% 5%	15840
	Night	18% 9% 30% 29% 12% 1	25689

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% 14% 7% 11% 5% 5% 5% 4 6% 5% 24%	2527
	11th to 20th	Day	14% 15% 7% 15% 5% 5% 5% 7% 7% 4 17%	2530
	21st to end	Day	21% 25% 6% 9% 4 3 3 2 3 5% 18%	2829
February	1st to 10th	Day	16% 14% 5% 9% 6% 5% 4 3 5% 7% 26%	1790
	11th to 20th	Day	13% 12% 4 8% 5% 6% 3 3 5% 6% 34%	1848
	21st to end	Day	15% 14% 5% 12% 4 4 5% 3 6% 6% 28%	1570
March	1st to 10th	Day	18% 14% 4 6% 5% 4 4 3 5% 5% 33%	3120
	11th to 20th	Day	10% 8% 4 7% 5% 5% 5% 4 6% 8% 38%	3259
	21st to end	Day	18% 12% 7% 11% 6% 6% 5% 4 5% 6% 21%	4165
April	1st to 10th	Day	16% 13% 3 8% 5% 4 5% 4 4 6% 31%	2280
	11th to 20th	Day	17% 9% 2 6% 6% 5% 4 4 5% 7% 35%	2254
	21st to end	Day	19% 9% 2 7% 5% 4 5% 4 5% 6% 33%	2399
May	1st to 10th	Day	17% 7% 3 6% 5% 5% 5% 4 6% 8% 34%	4082
	11th to 20th	Day	14% 7% 2 6% 4 4 4 4 5% 9% 40%	4207
	21st to end	Day	10% 6% 2 6% 4 4 5% 4 5% 8% 45%	4824
June	1st to 10th	Day	10% 5% 2 6% 5% 5% 4 4 6% 9% 44%	2660
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 5% 6% 9% 45%	2660
	21st to end	Day	10% 5% 2 7% 5% 6% 6% 5% 8% 9% 37%	2660
July	1st to 10th	Day	11% 7% 3 8% 5% 6% 6% 4 7% 9% 34%	4440
	11th to 20th	Day	7% 5% 2 5% 4 4 5% 4 7% 11% 47%	4440
	21st to end	Day	8% 6% 3 8% 5% 5% 5% 5% 7% 8% 41%	4813
August	1st to 10th	Day	8% 5% 2 6% 5% 4 5% 4 6% 8% 47%	4268
	11th to 20th	Day	9% 5% 2 7% 4 4 4 4 7% 9% 46%	3772
	21st to end	Day	6% 4 2 6% 4 4 5% 4 6% 9% 49%	4180
September	1st to 10th	Day	12% 5% 2 5% 4 5% 4 4 6% 8% 47%	2280
	11th to 20th	Day	11% 5% 2 4 3 3 4 3 6% 8% 50%	2138
	21st to end	Day	12% 5% 2 6% 4 4 5% 4 6% 9% 42%	2090
October	1st to 10th	Day	12% 7% 3 5% 4 4 5% 3 5% 7% 46%	2076
	11th to 20th	Day	18% 8% 3 6% 5% 4 5% 4 5% 7% 36%	1871
	21st to end	Day	19% 10% 3 7% 5% 3 4 4 6% 6% 33%	1881
November	1st to 10th	Day	13% 8% 2 6% 4 3 3 3 5% 7% 45%	1762
	11th to 20th	Day	16% 10% 3 9% 5% 4 4 3 5% 7% 35%	1800
	21st to end	Day	18% 11% 3 8% 5% 4 4 3 4 5% 34%	1732
December	1st to 10th	Day	16% 14% 5% 9% 4 4 5% 4 4 6% 28%	1520
	11th to 20th	Day	13% 13% 5% 11% 6% 5% 4 4 5% 6% 27%	1918
	21st to end	Day	20% 23% 8% 14% 5% 3 3 3 3 3 13%	2783
January	1st to 10th	Night	15% 16% 7% 11% 5% 4 3 3 4 5% 27%	4428
	11th to 20th	Night	15% 18% 8% 13% 5% 4 5% 5% 6% 3 17%	4440
	21st to end	Night	24% 17% 7% 9% 5% 4 3 2 4 4 21%	4823
February	1st to 10th	Night	16% 14% 4 9% 6% 4 4 3 4 5% 31%	2390
	11th to 20th	Night	14% 11% 4 8% 5% 5% 4 3 5% 6% 36%	2218
	21st to end	Night	18% 13% 4 8% 4 3 4 3 5% 5% 33%	1884
March	1st to 10th	Night	17% 12% 3 6% 4 4 3 3 4 5% 39%	3733
	11th to 20th	Night	10% 7% 2 6% 4 4 4 3 5% 6% 47%	3715
	21st to end	Night	18% 11% 8% 9% 5% 5% 4 3 4 5% 27%	3480
April	1st to 10th	Night	14% 9% 3 7% 4 5% 4 4 5% 7% 38%	1900
	11th to 20th	Night	18% 9% 3 7% 5% 4 3 3 5% 6% 39%	1875
	21st to end	Night	17% 8% 3 8% 5% 5% 4 3 5% 6% 36%	1780
May	1st to 10th	Night	17% 9% 2 7% 5% 4 4 4 6% 8% 35%	2813
	11th to 20th	Night	15% 7% 2 5% 4 4 4 4 6% 8% 40%	2675
	21st to end	Night	10% 7% 3 6% 5% 4 4 4 6% 7% 44%	2743
June	1st to 10th	Night	9% 5% 2 6% 4 4 4 3 5% 8% 49%	1520
	11th to 20th	Night	9% 6% 2 6% 4 4 4 4 7% 9% 46%	1520
	21st to end	Night	10% 7% 2 6% 6% 5% 6% 4 6% 8% 42%	1520
July	1st to 10th	Night	10% 5% 2 6% 5% 6% 6% 4 7% 8% 41%	2530
	11th to 20th	Night	7% 5% 2 5% 4 4 4 3 6% 8% 54%	2530
	21st to end	Night	4 5% 2 6% 5% 5% 6% 5% 7% 9% 46%	2750
August	1st to 10th	Night	7% 5% 2 6% 5% 4 5% 4 7% 9% 47%	2666
	11th to 20th	Night	8% 5% 2 5% 4 4 5% 4 5% 8% 51%	3040
	21st to end	Night	8% 4 2 5% 4 3 4 4 5% 9% 52%	3476
September	1st to 10th	Night	10% 7% 2 6% 3 3 3 3 5% 6% 52%	1900
	11th to 20th	Night	9% 4 2 5% 3 4 4 3 6% 8% 54%	2023
	21st to end	Night	10% 6% 3 7% 5% 4 5% 3 6% 7% 46%	2090
October	1st to 10th	Night	11% 5% 2 6% 4 3 4 3 4 6% 52%	2099
	11th to 20th	Night	17% 7% 2 6% 4 3 3 2 3 6% 46%	2308
	21st to end	Night	21% 9% 2 6% 4 3 4 3 5% 6% 37%	2717
November	1st to 10th	Night	13% 8% 2 6% 4 3 3 3 5% 7% 46%	2536
	11th to 20th	Night	14% 9% 4 9% 5% 4 4 3 5% 6% 36%	2600
	21st to end	Night	18% 11% 3 7% 4 4 4 3 4 6% 36%	2538
December	1st to 10th	Night	16% 11% 4 10% 5% 4 3 4 5% 6% 31%	2660
	11th to 20th	Night	15% 15% 4 8% 5% 4 4 3 4 5% 32%	3279
	21st to end	Night	24% 18% 6% 11% 5% 5% 3 3 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	39% 40% 8% 10% 3	2528
	11th to 20th	Day	44% 37% 6% 7% 5%	2530
	21st to end	Day	47% 40% 4 7% 2	2829
February	1st to 10th	Day	21% 64% 4 6% 5% 1	1790
	11th to 20th	Day	19% 64% 2 9% 5%	1858
	21st to end	Day	19% 65% 4 8% 2 2	1570
March	1st to 10th	Day	32% 41% 5% 13% 8% 2	3120
	11th to 20th	Day	23% 41% 8% 20% 8%	3259
	21st to end	Day	39% 45% 8% 7% 1	4165
April	1st to 10th	Day	21% 65% 3 7% 3	2280
	11th to 20th	Day	15% 66% 4 8% 4 2	2254
	21st to end	Day	17% 65% 4 6% 6% 2	2399
May	1st to 10th	Day	27% 43% 8% 15% 7%	4120
	11th to 20th	Day	23% 42% 8% 20% 7%	4211
	21st to end	Day	18% 41% 8% 15% 16% 2	4837
June	1st to 10th	Day	11% 66% 4 10% 8% 1	2660
	11th to 20th	Day	15% 66% 5% 9% 5% 1	2660
	21st to end	Day	14% 65% 5% 10% 5% 1	2660
July	1st to 10th	Day	32% 39% 9% 12% 7% 1	4371
	11th to 20th	Day	18% 38% 12% 21% 11%	4365
	21st to end	Day	24% 38% 10% 11% 15% 1	4662
August	1st to 10th	Day	21% 39% 11% 19% 10%	4253
	11th to 20th	Day	21% 39% 7% 23% 10%	3809
	21st to end	Day	21% 39% 9% 17% 13% 1	4179
September	1st to 10th	Day	15% 61% 5% 11% 8% 1	2280
	11th to 20th	Day	12% 61% 4 12% 10% 2	2138
	21st to end	Day	18% 60% 5% 10% 7% 1	2090
October	1st to 10th	Day	14% 37% 3 26% 19% 1	3453
	11th to 20th	Day	17% 39% 8% 17% 19%	3087
	21st to end	Day	27% 38% 6% 18% 10% 2	3081
November	1st to 10th	Day	20% 56% 8% 9% 6% 1	1762
	11th to 20th	Day	22% 57% 6% 9% 7% 1	1800
	21st to end	Day	25% 59% 6% 8% 3	1732
December	1st to 10th	Day	25% 59% 5% 6% 4	1520
	11th to 20th	Day	27% 48% 8% 13% 3	1915
	21st to end	Day	53% 37% 4 4 2	2783
January	1st to 10th	Night	41% 38% 7% 9% 5%	4428
	11th to 20th	Night	48% 37% 6% 6% 2	4440
	21st to end	Night	44% 40% 5% 8% 3	4823
February	1st to 10th	Night	19% 64% 4 6% 5% 1	2390
	11th to 20th	Night	17% 63% 3 11% 6%	2219
	21st to end	Night	18% 65% 3 7% 6% 1	1884
March	1st to 10th	Night	29% 41% 6% 15% 6% 3	3733
	11th to 20th	Night	20% 41% 5% 20% 13% 1	3715
	21st to end	Night	37% 42% 5% 12% 3	3480
April	1st to 10th	Night	18% 65% 4 9% 4 1	1900
	11th to 20th	Night	16% 65% 4 7% 6% 2	1875
	21st to end	Night	18% 65% 3 6% 7% 1	1780
May	1st to 10th	Night	29% 41% 7% 12% 8% 2	2840
	11th to 20th	Night	24% 43% 11% 18% 4	2676
	21st to end	Night	23% 41% 5% 11% 15% 4	2751
June	1st to 10th	Night	12% 65% 4 10% 8%	1520
	11th to 20th	Night	15% 66% 3 9% 7% 1	1520
	21st to end	Night	14% 64% 5% 9% 7%	1520
July	1st to 10th	Night	29% 38% 10% 13% 6% 4	2490
	11th to 20th	Night	17% 39% 9% 17% 17% 1	2482
	21st to end	Night	21% 38% 12% 11% 15% 3	2662
August	1st to 10th	Night	22% 41% 9% 18% 9%	2657
	11th to 20th	Night	20% 39% 9% 19% 13%	3068
	21st to end	Night	20% 39% 8% 21% 11% 1	3476
September	1st to 10th	Night	12% 60% 6% 11% 11% 1	1900
	11th to 20th	Night	10% 60% 4 13% 11% 1	2023
	21st to end	Night	18% 60% 4 12% 6% 1	2090
October	1st to 10th	Night	11% 36% 5% 27% 19% 2	3502
	11th to 20th	Night	20% 37% 5% 15% 21% 1	3831
	21st to end	Night	23% 37% 6% 16% 15% 3	4467
November	1st to 10th	Night	22% 57% 4 10% 6% 1	2536
	11th to 20th	Night	20% 57% 4 11% 7% 1	2600
	21st to end	Night	24% 58% 5% 9% 3	2538
December	1st to 10th	Night	24% 60% 3 8% 4 1	2660
	11th to 20th	Night	27% 49% 6% 11% 7% 1	3281
	21st to end	Night	47% 38% 7% 5% 3	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	21% 16% 34% 22% 6% 1	270
	11th to 20th	Day	22% 17% 33% 21% 6% 1	270
	21st to end	Day	23% 13% 36% 21% 6% 1	297
February	1st to 10th	Day	21% 17% 35% 24% 4	270
	11th to 20th	Day	22% 14% 38% 21% 4 1	270
	21st to end	Day	18% 15% 45% 18% 3	225
March	1st to 10th	Day	19% 14% 41% 22% 4	270
	11th to 20th	Day	20% 17% 32% 23% 8%	315
	21st to end	Day	23% 16% 31% 23% 7% 1	506
April	1st to 10th	Day	21% 13% 32% 27% 6%	460
	11th to 20th	Day	20% 13% 32% 22% 11% 2	452
	21st to end	Day	21% 12% 33% 23% 9% 2	460
May	1st to 10th	Day	22% 10% 29% 29% 8% 3	463
	11th to 20th	Day	19% 7% 30% 28% 13% 3	561
	21st to end	Day	12% 5% 28% 33% 17% 5%	734
June	1st to 10th	Day	10% 7% 26% 35% 18% 4	680
	11th to 20th	Day	11% 5% 28% 32% 20% 4	680
	21st to end	Day	13% 7% 28% 33% 16% 5%	680
July	1st to 10th	Day	8% 6% 20% 30% 23% 12%	671
	11th to 20th	Day	10% 3 21% 37% 19% 9%	668
	21st to end	Day	9% 2 22% 39% 23% 6%	739
August	1st to 10th	Day	7% 5% 13% 36% 28% 10%	586
	11th to 20th	Day	9% 5% 19% 30% 26% 11%	479
	21st to end	Day	7% 2 14% 38% 30% 9%	539
September	1st to 10th	Day	14% 5% 16% 32% 26% 7%	490
	11th to 20th	Day	10% 4 13% 33% 28% 12%	490
	21st to end	Day	15% 9% 24% 25% 18% 9%	490
October	1st to 10th	Day	17% 5% 25% 31% 17% 5%	476
	11th to 20th	Day	17% 17% 29% 26% 10%	300
	21st to end	Day	28% 14% 29% 23% 5%	330
November	1st to 10th	Day	16% 10% 34% 27% 10% 2	300
	11th to 20th	Day	20% 19% 35% 18% 7% 1	300
	21st to end	Day	22% 11% 40% 22% 5%	282
December	1st to 10th	Day	17% 19% 37% 20% 6% 1	270
	11th to 20th	Day	20% 13% 39% 23% 6%	270
	21st to end	Day	21% 19% 42% 16% 2	297
January	1st to 10th	Night	21% 16% 35% 24% 3	950
	11th to 20th	Night	23% 15% 38% 20% 4 1	950
	21st to end	Night	23% 12% 36% 25% 4	1045
February	1st to 10th	Night	24% 11% 39% 22% 4	870
	11th to 20th	Night	21% 12% 38% 26% 3	743
	21st to end	Night	25% 14% 37% 22% 3	628
March	1st to 10th	Night	20% 14% 37% 23% 6%	760
	11th to 20th	Night	16% 10% 40% 26% 7% 1	760
	21st to end	Night	23% 11% 31% 26% 8% 1	641
April	1st to 10th	Night	19% 12% 36% 26% 6% 1	570
	11th to 20th	Night	20% 10% 32% 28% 9% 1	563
	21st to end	Night	21% 8% 33% 29% 10% 1	570
May	1st to 10th	Night	21% 6% 30% 32% 11%	570
	11th to 20th	Night	19% 5% 25% 34% 16% 1	561
	21st to end	Night	13% 3 21% 39% 22% 2	617
June	1st to 10th	Night	9% 4 21% 45% 20% 1	570
	11th to 20th	Night	11% 3 28% 38% 19% 2	570
	21st to end	Night	11% 3 23% 40% 22% 2	570
July	1st to 10th	Night	7% 3 14% 44% 26% 6%	555
	11th to 20th	Night	8% 2 17% 39% 30% 5%	552
	21st to end	Night	5% 2 14% 48% 29% 3	624
August	1st to 10th	Night	6% 2 12% 46% 29% 6%	567
	11th to 20th	Night	8% 4 13% 37% 33% 6%	564
	21st to end	Night	9% 2 16% 38% 32% 4	627
September	1st to 10th	Night	12% 5% 15% 34% 30% 4	570
	11th to 20th	Night	9% 5% 14% 38% 29% 5%	693
	21st to end	Night	11% 5% 24% 31% 23% 4	760
October	1st to 10th	Night	13% 6% 24% 35% 20% 2	760
	11th to 20th	Night	21% 11% 32% 26% 9% 1	760
	21st to end	Night	25% 13% 31% 24% 7%	836
November	1st to 10th	Night	18% 10% 37% 24% 8% 1	780
	11th to 20th	Night	19% 18% 35% 23% 5%	800
	21st to end	Night	25% 12% 35% 23% 5%	788
December	1st to 10th	Night	24% 15% 36% 21% 4	950
	11th to 20th	Night	22% 14% 36% 24% 4	950
	21st to end	Night	28% 14% 35% 21% 2	1045

Page generated at 2024-11-22 07:02:24. Version ac07

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