Lake Zurich
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Zurich clear sky chart from 2005-11-06 to 2024-11-04.

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% 4 4 4 6% 7% 37%	101319
	Night	14% 10% 4 7% 4 4 4 4 5% 6% 38%	97774
Transparency	Day	45% 5% 12% 23% 14% 2	104887
	Night	45% 5% 11% 23% 15% 2	102347
Seeing	Day	18% 14% 30% 23% 11% 4	15831
	Night	18% 11% 30% 27% 12% 1	25665

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% 9% 10% 5% 4 4 3 4 4 29%	2527
	11th to 20th	Day	12% 14% 6% 15% 4 4 5% 8% 7% 5% 21%	2530
	21st to end	Day	18% 25% 8% 8% 4 3 3 2 3 5% 21%	2845
February	1st to 10th	Day	13% 16% 5% 8% 5% 6% 5% 4 5% 7% 28%	1740
	11th to 20th	Day	13% 12% 4 8% 5% 5% 4 3 5% 5% 37%	1848
	21st to end	Day	14% 13% 5% 11% 5% 4 3 3 5% 5% 31%	1570
March	1st to 10th	Day	14% 13% 4 8% 4 4 4 3 3 5% 37%	3120
	11th to 20th	Day	10% 7% 4 7% 5% 5% 5% 4 6% 8% 39%	3269
	21st to end	Day	20% 13% 5% 12% 5% 5% 4 3 5% 6% 21%	4165
April	1st to 10th	Day	18% 14% 3 7% 5% 4 4 3 5% 6% 31%	2280
	11th to 20th	Day	17% 10% 2 6% 5% 5% 4 3 6% 6% 34%	2254
	21st to end	Day	19% 9% 3 6% 5% 6% 3 4 5% 6% 33%	2390
May	1st to 10th	Day	16% 8% 3 7% 4 5% 5% 5% 5% 7% 36%	4082
	11th to 20th	Day	15% 7% 2 6% 4 4 4 4 6% 7% 42%	4325
	21st to end	Day	12% 6% 2 6% 4 4 4 4 6% 8% 42%	4824
June	1st to 10th	Day	10% 6% 2 6% 4 5% 4 4 6% 7% 45%	2660
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 4 7% 9% 44%	2660
	21st to end	Day	11% 7% 3 7% 5% 4 5% 4 8% 8% 38%	2660
July	1st to 10th	Day	12% 7% 3 7% 4 5% 6% 5% 7% 10% 33%	4440
	11th to 20th	Day	7% 4 2 5% 4 5% 5% 4 7% 9% 50%	4440
	21st to end	Day	9% 6% 2 7% 5% 6% 5% 4 7% 8% 42%	4813
August	1st to 10th	Day	11% 5% 2 6% 4 4 5% 4 7% 9% 42%	4342
	11th to 20th	Day	10% 5% 3 6% 4 4 5% 4 6% 9% 44%	3766
	21st to end	Day	8% 5% 3 6% 5% 4 4 4 5% 9% 48%	4180
September	1st to 10th	Day	12% 6% 2 5% 4 4 4 4 5% 7% 47%	2280
	11th to 20th	Day	12% 4 1 3 3 4 4 4 7% 7% 52%	2160
	21st to end	Day	12% 6% 2 6% 4 4 5% 4 6% 9% 42%	2090
October	1st to 10th	Day	13% 6% 3 6% 4 3 4 3 5% 6% 47%	2037
	11th to 20th	Day	18% 8% 3 7% 5% 4 4 4 5% 6% 36%	1881
	21st to end	Day	20% 10% 3 6% 4 4 3 3 5% 5% 37%	1881
November	1st to 10th	Day	12% 9% 3 6% 4 4 5% 3 4 6% 44%	1699
	11th to 20th	Day	15% 12% 3 9% 5% 4 4 4 5% 6% 34%	1710
	21st to end	Day	18% 12% 3 7% 4 4 4 3 3 6% 36%	1630
December	1st to 10th	Day	15% 13% 4 9% 5% 4 4 3 5% 6% 31%	1520
	11th to 20th	Day	12% 14% 5% 9% 4 5% 5% 4 6% 6% 29%	1918
	21st to end	Day	20% 24% 8% 11% 5% 3 3 3 3 4 15%	2783
January	1st to 10th	Night	14% 15% 8% 11% 5% 3 3 2 3 5% 31%	4428
	11th to 20th	Night	15% 17% 6% 14% 5% 4 4 6% 6% 4 19%	4440
	21st to end	Night	21% 18% 8% 10% 4 3 3 3 4 4 22%	4820
February	1st to 10th	Night	14% 14% 5% 9% 5% 4 4 3 4 5% 32%	2438
	11th to 20th	Night	13% 11% 4 8% 4 5% 5% 3 5% 6% 37%	2218
	21st to end	Night	18% 12% 3 8% 5% 3 4 3 4 5% 36%	1884
March	1st to 10th	Night	18% 11% 3 7% 3 3 4 3 4 5% 39%	3733
	11th to 20th	Night	9% 7% 3 6% 4 4 4 3 5% 7% 47%	3719
	21st to end	Night	22% 12% 5% 10% 5% 4 3 3 4 5% 28%	3466
April	1st to 10th	Night	16% 9% 3 6% 6% 4 5% 4 4 5% 38%	1900
	11th to 20th	Night	20% 8% 2 7% 4 4 4 3 4 5% 38%	1875
	21st to end	Night	19% 7% 3 7% 4 3 4 3 5% 6% 39%	1788
May	1st to 10th	Night	15% 7% 3 7% 5% 5% 4 4 6% 8% 35%	2813
	11th to 20th	Night	15% 7% 2 5% 4 4 4 5% 7% 9% 38%	2574
	21st to end	Night	12% 8% 3 7% 4 4 3 3 5% 6% 44%	2743
June	1st to 10th	Night	9% 5% 2 6% 4 5% 5% 4 6% 7% 47%	1520
	11th to 20th	Night	11% 5% 2 5% 5% 5% 4 4 6% 8% 47%	1520
	21st to end	Night	10% 6% 2 6% 5% 4 6% 3 7% 9% 42%	1520
July	1st to 10th	Night	12% 5% 2 7% 5% 5% 5% 4 7% 8% 39%	2530
	11th to 20th	Night	5% 4 1 4 4 5% 5% 4 6% 8% 54%	2530
	21st to end	Night	6% 4 2 5% 5% 5% 6% 5% 8% 8% 46%	2750
August	1st to 10th	Night	7% 5% 2 5% 4 4 5% 4 6% 9% 49%	2591
	11th to 20th	Night	9% 5% 2 6% 4 4 5% 3 6% 7% 51%	3061
	21st to end	Night	8% 4 2 5% 4 3 4 4 5% 9% 52%	3476
September	1st to 10th	Night	10% 6% 2 6% 3 4 3 3 4 6% 53%	1900
	11th to 20th	Night	10% 4 2 5% 3 3 3 3 4 7% 56%	2000
	21st to end	Night	12% 6% 2 5% 5% 4 4 4 5% 7% 47%	2090
October	1st to 10th	Night	12% 6% 2 5% 4 3 3 3 4 7% 51%	2141
	11th to 20th	Night	17% 7% 2 6% 4 3 4 3 4 5% 44%	2298
	21st to end	Night	20% 9% 3 6% 3 3 4 3 4 6% 38%	2717
November	1st to 10th	Night	11% 8% 3 7% 4 4 4 3 4 6% 48%	2452
	11th to 20th	Night	13% 11% 4 8% 5% 4 4 3 4 6% 36%	2470
	21st to end	Night	16% 10% 4 6% 5% 4 3 4 5% 5% 38%	2546
December	1st to 10th	Night	16% 12% 4 8% 5% 4 5% 4 5% 6% 32%	2660
	11th to 20th	Night	15% 13% 4 9% 4 3 4 4 5% 6% 32%	3279
	21st to end	Night	22% 18% 6% 10% 5% 4 4 3 4 5% 19%	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	60% 4 11% 18% 7%	2528
	11th to 20th	Day	60% 6% 12% 15% 7%	2530
	21st to end	Day	68% 3 7% 17% 5%	2845
February	1st to 10th	Day	56% 4 12% 15% 10% 1	1740
	11th to 20th	Day	49% 5% 10% 24% 10% 2	1858
	21st to end	Day	54% 6% 10% 18% 10% 2	1570
March	1st to 10th	Day	49% 5% 11% 21% 11% 3	3120
	11th to 20th	Day	41% 7% 11% 29% 11% 1	3269
	21st to end	Day	64% 6% 13% 13% 4 1	4165
April	1st to 10th	Day	55% 5% 10% 19% 12%	2280
	11th to 20th	Day	49% 6% 9% 21% 12% 4	2254
	21st to end	Day	51% 6% 12% 17% 13% 2	2390
May	1st to 10th	Day	45% 7% 11% 23% 13% 1	4120
	11th to 20th	Day	40% 7% 11% 27% 14% 1	4329
	21st to end	Day	37% 7% 13% 20% 18% 4	4837
June	1st to 10th	Day	36% 7% 12% 25% 18% 2	2660
	11th to 20th	Day	34% 8% 12% 23% 20% 3	2660
	21st to end	Day	40% 8% 13% 23% 14% 2	2660
July	1st to 10th	Day	45% 6% 12% 23% 11% 2	4371
	11th to 20th	Day	31% 4 16% 32% 16% 1	4365
	21st to end	Day	39% 5% 16% 17% 20% 3	4662
August	1st to 10th	Day	38% 5% 15% 29% 12% 1	4327
	11th to 20th	Day	37% 4 11% 33% 15% 1	3803
	21st to end	Day	34% 5% 13% 25% 21% 2	4179
September	1st to 10th	Day	35% 7% 12% 24% 18% 3	2280
	11th to 20th	Day	30% 6% 11% 31% 19% 3	2160
	21st to end	Day	39% 6% 10% 27% 18% 1	2090
October	1st to 10th	Day	26% 3 7% 38% 25% 1	3388
	11th to 20th	Day	36% 4 10% 27% 23% 1	3109
	21st to end	Day	45% 3 7% 28% 13% 4	3081
November	1st to 10th	Day	41% 4 13% 23% 17% 2	1699
	11th to 20th	Day	51% 5% 11% 22% 10% 1	1710
	21st to end	Day	52% 4 11% 24% 9%	1630
December	1st to 10th	Day	54% 5% 12% 20% 7% 1	1520
	11th to 20th	Day	54% 6% 14% 18% 7% 1	1915
	21st to end	Day	74% 3 9% 10% 4	2783
January	1st to 10th	Night	58% 4 9% 19% 9% 1	4428
	11th to 20th	Night	66% 4 10% 12% 8%	4440
	21st to end	Night	67% 4 9% 14% 6% 1	4820
February	1st to 10th	Night	55% 4 10% 17% 13% 2	2438
	11th to 20th	Night	48% 4 11% 21% 14% 1	2219
	21st to end	Night	51% 4 9% 21% 10% 4	1884
March	1st to 10th	Night	47% 5% 12% 24% 9% 3	3733
	11th to 20th	Night	36% 6% 11% 26% 18% 2	3719
	21st to end	Night	59% 6% 8% 18% 8% 1	3466
April	1st to 10th	Night	47% 6% 10% 22% 13% 1	1900
	11th to 20th	Night	47% 5% 7% 19% 17% 4	1875
	21st to end	Night	46% 5% 10% 22% 14% 2	1788
May	1st to 10th	Night	45% 7% 11% 20% 14% 3	2840
	11th to 20th	Night	39% 8% 15% 27% 11% 1	2575
	21st to end	Night	40% 7% 9% 18% 20% 6%	2751
June	1st to 10th	Night	33% 7% 13% 26% 19% 3	1520
	11th to 20th	Night	35% 6% 9% 26% 23% 2	1520
	21st to end	Night	38% 7% 15% 21% 17% 2	1520
July	1st to 10th	Night	42% 5% 15% 21% 12% 4	2490
	11th to 20th	Night	28% 4 14% 34% 17% 2	2482
	21st to end	Night	34% 6% 15% 18% 23% 3	2662
August	1st to 10th	Night	31% 5% 15% 29% 18% 1	2582
	11th to 20th	Night	32% 5% 13% 31% 18% 1	3090
	21st to end	Night	31% 4 12% 33% 17% 4	3476
September	1st to 10th	Night	33% 5% 10% 27% 24% 2	1900
	11th to 20th	Night	29% 5% 7% 33% 24% 2	2000
	21st to end	Night	37% 6% 10% 30% 16% 2	2090
October	1st to 10th	Night	23% 3 7% 39% 26% 2	3570
	11th to 20th	Night	37% 3 7% 24% 26% 2	3809
	21st to end	Night	42% 3 9% 25% 18% 3	4467
November	1st to 10th	Night	39% 5% 8% 27% 18% 3	2452
	11th to 20th	Night	48% 5% 11% 23% 12% 1	2470
	21st to end	Night	48% 4 13% 22% 12% 1	2546
December	1st to 10th	Night	52% 6% 10% 21% 9% 1	2660
	11th to 20th	Night	53% 5% 13% 19% 9% 1	3281
	21st to end	Night	68% 4 11% 12% 5%	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% 19% 36% 20% 3 1	270
	11th to 20th	Day	24% 24% 32% 17% 2 1	270
	21st to end	Day	27% 19% 34% 15% 5% 1	297
February	1st to 10th	Day	24% 20% 38% 15% 3	270
	11th to 20th	Day	27% 24% 34% 13% 2	270
	21st to end	Day	26% 25% 36% 8% 3 1	225
March	1st to 10th	Day	24% 26% 37% 11% 2	270
	11th to 20th	Day	29% 18% 35% 13% 5%	294
	21st to end	Day	28% 17% 29% 18% 7% 2	506
April	1st to 10th	Day	27% 18% 30% 20% 4	460
	11th to 20th	Day	24% 23% 23% 20% 7% 2	452
	21st to end	Day	25% 19% 28% 18% 10% 1	460
May	1st to 10th	Day	22% 16% 33% 19% 7% 3	463
	11th to 20th	Day	22% 12% 32% 22% 9% 3	627
	21st to end	Day	15% 13% 32% 23% 12% 6%	734
June	1st to 10th	Day	11% 12% 34% 26% 13% 3	680
	11th to 20th	Day	13% 10% 31% 30% 11% 4	680
	21st to end	Day	14% 9% 34% 28% 11% 4	680
July	1st to 10th	Day	9% 5% 28% 28% 19% 10%	671
	11th to 20th	Day	10% 7% 31% 30% 14% 8%	668
	21st to end	Day	7% 8% 28% 34% 16% 6%	739
August	1st to 10th	Day	11% 6% 24% 33% 18% 8%	634
	11th to 20th	Day	12% 5% 21% 32% 20% 10%	479
	21st to end	Day	8% 5% 24% 32% 22% 9%	539
September	1st to 10th	Day	15% 7% 24% 29% 20% 5%	490
	11th to 20th	Day	10% 5% 22% 30% 21% 11%	490
	21st to end	Day	17% 13% 25% 24% 15% 6%	490
October	1st to 10th	Day	16% 14% 25% 27% 14% 4	437
	11th to 20th	Day	23% 22% 30% 20% 5%	300
	21st to end	Day	34% 15% 33% 13% 5% 1	330
November	1st to 10th	Day	18% 18% 35% 20% 9% 1	279
	11th to 20th	Day	25% 23% 32% 16% 5%	270
	21st to end	Day	26% 14% 40% 17% 2 1	270
December	1st to 10th	Day	19% 23% 37% 16% 4 1	270
	11th to 20th	Day	19% 23% 38% 16% 4	270
	21st to end	Day	27% 24% 35% 12% 2	297
January	1st to 10th	Night	20% 18% 38% 21% 4	950
	11th to 20th	Night	23% 18% 35% 19% 4 1	950
	21st to end	Night	23% 13% 37% 22% 5%	1045
February	1st to 10th	Night	23% 14% 37% 20% 5%	918
	11th to 20th	Night	22% 17% 34% 24% 3	743
	21st to end	Night	26% 17% 35% 19% 3	628
March	1st to 10th	Night	20% 16% 36% 21% 7%	760
	11th to 20th	Night	17% 12% 39% 23% 7% 1	742
	21st to end	Night	24% 12% 29% 26% 9% 1	627
April	1st to 10th	Night	21% 14% 35% 24% 6% 1	570
	11th to 20th	Night	23% 15% 31% 22% 8% 1	563
	21st to end	Night	23% 13% 27% 29% 7% 1	570
May	1st to 10th	Night	17% 11% 34% 30% 8% 1	570
	11th to 20th	Night	20% 6% 27% 31% 14% 1	561
	21st to end	Night	14% 7% 25% 33% 19% 2	617
June	1st to 10th	Night	11% 5% 26% 39% 17% 1	570
	11th to 20th	Night	12% 6% 29% 38% 14% 1	570
	21st to end	Night	11% 5% 29% 33% 21% 1	570
July	1st to 10th	Night	9% 2 18% 38% 29% 3	555
	11th to 20th	Night	9% 4 22% 37% 24% 3	552
	21st to end	Night	6% 2 19% 45% 26% 2	624
August	1st to 10th	Night	6% 1 17% 45% 28% 4	567
	11th to 20th	Night	8% 3 15% 38% 31% 5%	564
	21st to end	Night	7% 3 19% 38% 29% 3	627
September	1st to 10th	Night	12% 6% 19% 32% 26% 4	570
	11th to 20th	Night	11% 4 21% 32% 27% 5%	670
	21st to end	Night	13% 9% 26% 28% 21% 4	760
October	1st to 10th	Night	15% 8% 24% 32% 19% 3	760
	11th to 20th	Night	21% 14% 31% 25% 9%	760
	21st to end	Night	26% 12% 31% 22% 8%	836
November	1st to 10th	Night	17% 15% 35% 23% 9% 1	755
	11th to 20th	Night	20% 19% 32% 23% 5% 1	760
	21st to end	Night	22% 13% 37% 21% 6%	836
December	1st to 10th	Night	22% 16% 35% 21% 5%	950
	11th to 20th	Night	24% 15% 34% 24% 3 1	950
	21st to end	Night	30% 16% 34% 18% 3	1045

Page generated at 2024-11-01 21:47:48. Version ac07

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