Concordia College Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Concordia College Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	12% 8% 3 8% 5% 5% 5% 4 6% 7% 38%	105437
	Night	11% 9% 3 8% 5% 5% 5% 4 5% 7% 38%	102262
Transparency	Day	44% 6% 15% 25% 9% 1	105168
	Night	45% 6% 14% 23% 10% 1	102121
Seeing	Day	14% 9% 31% 29% 13% 3	16113
	Night	14% 8% 33% 33% 10% 1	26006

By Month

Percentage Cloud Cover SW (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	7% 13% 7% 13% 10% 8% 6% 4 6% 5% 20%	2218
	11th to 20th	Day	5% 9% 5% 13% 10% 11% 13% 6% 8% 6% 16%	2421
	21st to end	Day	7% 14% 10% 17% 7% 5% 4 4 4 5% 23%	2891
February	1st to 10th	Day	8% 14% 6% 10% 7% 6% 7% 5% 6% 5% 26%	1710
	11th to 20th	Day	6% 12% 5% 10% 8% 9% 7% 5% 7% 7% 25%	1664
	21st to end	Day	9% 13% 5% 12% 7% 7% 5% 4 7% 7% 23%	1522
March	1st to 10th	Day	12% 12% 3 9% 6% 6% 5% 3 5% 6% 34%	3271
	11th to 20th	Day	9% 10% 4 10% 6% 5% 5% 4 6% 9% 32%	3480
	21st to end	Day	17% 15% 5% 13% 6% 4 4 4 4 5% 24%	3814
April	1st to 10th	Day	14% 10% 3 8% 6% 4 4 3 5% 6% 35%	2239
	11th to 20th	Day	18% 11% 4 8% 4 4 4 3 5% 6% 32%	2439
	21st to end	Day	22% 9% 4 7% 4 4 4 4 6% 5% 33%	2470
May	1st to 10th	Day	17% 7% 2 7% 4 4 5% 4 5% 8% 38%	4120
	11th to 20th	Day	13% 6% 2 6% 5% 4 5% 5% 6% 8% 41%	4362
	21st to end	Day	18% 7% 2 7% 5% 4 5% 4 5% 7% 37%	5098
June	1st to 10th	Day	13% 5% 2 5% 4 4 5% 4 6% 9% 43%	2850
	11th to 20th	Day	14% 5% 2 5% 5% 4 4 4 6% 7% 43%	2850
	21st to end	Day	11% 5% 2 5% 4 4 5% 4 7% 10% 42%	2850
July	1st to 10th	Day	7% 4 2 6% 4 5% 6% 5% 7% 9% 45%	4750
	11th to 20th	Day	5% 3 1 4 3 4 4 4 6% 10% 56%	4750
	21st to end	Day	4 4 1 6% 4 5% 5% 5% 8% 9% 50%	4792
August	1st to 10th	Day	10% 4 1 5% 4 4 5% 5% 8% 9% 46%	4103
	11th to 20th	Day	13% 6% 2 6% 4 3 4 4 5% 8% 44%	4041
	21st to end	Day	10% 5% 2 6% 4 4 4 4 5% 7% 51%	4532
September	1st to 10th	Day	11% 4 2 5% 4 3 4 3 5% 8% 51%	2297
	11th to 20th	Day	12% 5% 2 6% 4 4 4 3 4 7% 48%	2090
	21st to end	Day	13% 6% 2 6% 4 3 4 3 6% 7% 46%	2090
October	1st to 10th	Day	11% 5% 2 5% 3 4 3 3 5% 7% 53%	3224
	11th to 20th	Day	14% 8% 3 6% 4 3 3 3 3 6% 49%	3140
	21st to end	Day	16% 9% 3 8% 4 5% 5% 3 6% 7% 35%	3162
November	1st to 10th	Day	14% 12% 4 11% 4 5% 4 3 4 5% 34%	1624
	11th to 20th	Day	10% 15% 5% 12% 8% 5% 4 2 4 5% 29%	1520
	21st to end	Day	10% 13% 5% 12% 7% 4 4 3 5% 5% 33%	1520
December	1st to 10th	Day	8% 16% 4 13% 8% 7% 5% 5% 5% 5% 24%	1408
	11th to 20th	Day	9% 13% 6% 13% 7% 5% 6% 4 6% 6% 25%	1683
	21st to end	Day	21% 13% 4 12% 8% 6% 4 3 3 4 23%	2442
January	1st to 10th	Night	7% 12% 5% 15% 9% 9% 8% 5% 5% 5% 20%	4737
	11th to 20th	Night	5% 11% 5% 13% 10% 11% 12% 7% 6% 6% 15%	4548
	21st to end	Night	8% 14% 8% 14% 6% 6% 6% 4 6% 5% 23%	4774
February	1st to 10th	Night	8% 11% 4 11% 6% 7% 5% 5% 6% 6% 31%	2470
	11th to 20th	Night	6% 11% 5% 10% 7% 7% 6% 6% 6% 6% 30%	2403
	21st to end	Night	9% 11% 4 10% 5% 6% 5% 5% 5% 6% 32%	1948
March	1st to 10th	Night	7% 9% 3 8% 5% 5% 4 4 6% 8% 40%	3588
	11th to 20th	Night	9% 11% 3 11% 6% 4 4 3 5% 6% 37%	3480
	21st to end	Night	17% 15% 4 9% 4 3 4 3 4 6% 30%	3817
April	1st to 10th	Night	13% 7% 3 7% 4 4 4 5% 6% 8% 39%	1936
	11th to 20th	Night	19% 10% 3 6% 4 4 4 4 5% 5% 36%	1689
	21st to end	Night	19% 9% 3 6% 6% 3 3 3 5% 7% 37%	1710
May	1st to 10th	Night	15% 9% 3 7% 5% 3 5% 4 6% 6% 38%	2850
	11th to 20th	Night	12% 6% 2 5% 4 4 4 4 7% 7% 44%	2541
	21st to end	Night	14% 7% 2 7% 4 4 4 4 5% 6% 44%	2487
June	1st to 10th	Night	10% 3 2 4 5% 4 3 4 7% 10% 47%	1330
	11th to 20th	Night	10% 5% 2 5% 3 5% 4 4 7% 8% 47%	1330
	21st to end	Night	6% 4 2 5% 4 4 5% 4 7% 10% 50%	1330
July	1st to 10th	Night	8% 4 2 5% 4 5% 6% 5% 7% 9% 44%	2220
	11th to 20th	Night	4 2 1 3 3 2 3 3 6% 8% 65%	2220
	21st to end	Night	5% 4 2 5% 4 4 5% 4 7% 10% 49%	2767
August	1st to 10th	Night	7% 4 1 5% 3 4 4 4 6% 7% 54%	2836
	11th to 20th	Night	12% 4 1 4 3 3 3 4 6% 9% 50%	2798
	21st to end	Night	10% 5% 2 5% 3 4 4 4 5% 7% 52%	3135
September	1st to 10th	Night	9% 3 1 4 3 4 4 3 6% 8% 56%	1878
	11th to 20th	Night	9% 5% 2 5% 3 4 4 3 4 7% 54%	2090
	21st to end	Night	13% 4 1 5% 3 3 3 3 5% 7% 53%	2090
October	1st to 10th	Night	9% 4 2 4 3 3 3 3 5% 6% 59%	3704
	11th to 20th	Night	13% 7% 2 5% 4 4 4 3 5% 7% 46%	3779
	21st to end	Night	15% 9% 3 7% 4 4 4 3 5% 6% 40%	4394
November	1st to 10th	Night	12% 11% 4 9% 5% 4 4 4 5% 7% 35%	2555
	11th to 20th	Night	11% 12% 5% 11% 6% 6% 5% 3 5% 6% 30%	2660
	21st to end	Night	11% 10% 3 8% 7% 5% 5% 3 6% 6% 35%	2660
December	1st to 10th	Night	8% 14% 5% 13% 8% 6% 5% 3 5% 5% 26%	2769
	11th to 20th	Night	10% 14% 6% 12% 7% 5% 5% 4 6% 5% 27%	3514
	21st to end	Night	19% 15% 5% 11% 7% 5% 4 3 4 4 24%	5225

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	65% 6% 12% 14% 3	2219
	11th to 20th	Day	65% 7% 14% 12% 3	2421
	21st to end	Day	64% 5% 10% 15% 6%	2891
February	1st to 10th	Day	57% 6% 12% 17% 7%	1710
	11th to 20th	Day	55% 6% 15% 18% 6% 1	1673
	21st to end	Day	57% 8% 14% 15% 6%	1522
March	1st to 10th	Day	51% 6% 11% 25% 6%	3271
	11th to 20th	Day	49% 5% 17% 24% 5%	3480
	21st to end	Day	63% 6% 12% 16% 4	3814
April	1st to 10th	Day	50% 6% 11% 22% 10% 1	2239
	11th to 20th	Day	52% 6% 12% 18% 11% 1	2442
	21st to end	Day	51% 7% 12% 22% 8% 1	2470
May	1st to 10th	Day	43% 6% 14% 24% 11% 1	4120
	11th to 20th	Day	39% 8% 14% 26% 10% 3	4366
	21st to end	Day	45% 7% 14% 25% 8% 1	5098
June	1st to 10th	Day	37% 7% 17% 28% 10% 1	2850
	11th to 20th	Day	39% 8% 16% 24% 12% 1	2850
	21st to end	Day	35% 9% 18% 26% 12%	2850
July	1st to 10th	Day	33% 8% 19% 28% 11% 1	4676
	11th to 20th	Day	23% 7% 18% 38% 13% 1	4669
	21st to end	Day	28% 7% 19% 35% 10% 1	4639
August	1st to 10th	Day	32% 6% 16% 32% 13% 1	4090
	11th to 20th	Day	38% 6% 16% 31% 8% 1	4080
	21st to end	Day	33% 5% 19% 32% 10% 1	4531
September	1st to 10th	Day	32% 6% 14% 36% 12% 1	2297
	11th to 20th	Day	36% 7% 17% 29% 10%	2090
	21st to end	Day	36% 7% 15% 31% 10% 1	2090
October	1st to 10th	Day	32% 4 9% 37% 16% 1	3224
	11th to 20th	Day	39% 4 9% 31% 16%	3140
	21st to end	Day	51% 4 15% 23% 8%	3162
November	1st to 10th	Day	53% 5% 14% 16% 11% 1	1624
	11th to 20th	Day	59% 6% 13% 16% 7%	1520
	21st to end	Day	55% 7% 15% 17% 6% 1	1520
December	1st to 10th	Day	62% 7% 12% 16% 3	1408
	11th to 20th	Day	57% 8% 17% 15% 3	1680
	21st to end	Day	67% 5% 8% 17% 3	2442
January	1st to 10th	Night	63% 8% 12% 13% 4	4737
	11th to 20th	Night	66% 8% 12% 10% 4	4548
	21st to end	Night	61% 6% 12% 16% 4	4774
February	1st to 10th	Night	50% 8% 15% 18% 8% 1	2470
	11th to 20th	Night	51% 7% 12% 20% 10%	2404
	21st to end	Night	51% 6% 13% 20% 9% 1	1948
March	1st to 10th	Night	41% 6% 18% 24% 11% 1	3588
	11th to 20th	Night	46% 5% 14% 25% 9%	3480
	21st to end	Night	55% 6% 13% 19% 6% 1	3817
April	1st to 10th	Night	42% 6% 14% 23% 13% 2	1936
	11th to 20th	Night	48% 5% 9% 23% 13% 2	1689
	21st to end	Night	48% 6% 10% 24% 10% 2	1710
May	1st to 10th	Night	43% 7% 14% 21% 12% 2	2850
	11th to 20th	Night	36% 8% 10% 26% 16% 3	2542
	21st to end	Night	40% 6% 12% 29% 12% 1	2488
June	1st to 10th	Night	30% 7% 17% 32% 11% 2	1330
	11th to 20th	Night	34% 7% 15% 25% 15% 5%	1330
	21st to end	Night	27% 9% 19% 30% 12% 2	1330
July	1st to 10th	Night	35% 9% 18% 24% 13% 1	2185
	11th to 20th	Night	17% 6% 14% 46% 15% 2	2178
	21st to end	Night	28% 6% 22% 32% 11% 2	2681
August	1st to 10th	Night	29% 6% 14% 33% 17% 2	2826
	11th to 20th	Night	31% 5% 16% 35% 12% 1	2825
	21st to end	Night	32% 6% 14% 32% 15% 1	3135
September	1st to 10th	Night	26% 6% 14% 37% 16% 1	1878
	11th to 20th	Night	31% 6% 17% 31% 14%	2090
	21st to end	Night	32% 5% 13% 32% 17% 1	2090
October	1st to 10th	Night	27% 4 9% 36% 19% 6%	3704
	11th to 20th	Night	38% 4 10% 28% 18% 2	3779
	21st to end	Night	46% 5% 12% 25% 12%	4394
November	1st to 10th	Night	48% 6% 11% 22% 11% 2	2555
	11th to 20th	Night	55% 7% 13% 16% 9% 1	2660
	21st to end	Night	48% 7% 19% 19% 7%	2660
December	1st to 10th	Night	59% 7% 16% 15% 4	2769
	11th to 20th	Night	58% 6% 16% 15% 4	3516
	21st to end	Night	65% 5% 12% 13% 5%	5225

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	10% 10% 35% 33% 10% 1	270
	11th to 20th	Day	13% 8% 39% 32% 8%	270
	21st to end	Day	19% 9% 31% 30% 9% 2	297
February	1st to 10th	Day	14% 16% 31% 32% 5%	270
	11th to 20th	Day	12% 13% 45% 22% 7% 1	270
	21st to end	Day	11% 7% 42% 34% 6%	225
March	1st to 10th	Day	13% 15% 37% 27% 7%	270
	11th to 20th	Day	17% 8% 36% 25% 9% 4	270
	21st to end	Day	18% 11% 28% 30% 11% 2	297
April	1st to 10th	Day	22% 15% 32% 22% 8%	419
	11th to 20th	Day	26% 13% 25% 27% 8% 1	640
	21st to end	Day	22% 11% 31% 23% 10% 2	650
May	1st to 10th	Day	20% 10% 31% 26% 12% 1	653
	11th to 20th	Day	17% 9% 30% 29% 12% 3	675
	21st to end	Day	17% 8% 28% 30% 14% 3	734
June	1st to 10th	Day	11% 9% 28% 32% 17% 3	680
	11th to 20th	Day	14% 9% 40% 23% 12% 2	680
	21st to end	Day	12% 7% 30% 32% 15% 4	680
July	1st to 10th	Day	7% 3 24% 34% 24% 7%	671
	11th to 20th	Day	9% 5% 29% 33% 19% 5%	668
	21st to end	Day	5% 3 28% 37% 21% 6%	739
August	1st to 10th	Day	8% 4 24% 36% 24% 4	676
	11th to 20th	Day	13% 5% 21% 32% 19% 9%	665
	21st to end	Day	9% 6% 28% 33% 20% 3	748
September	1st to 10th	Day	10% 6% 33% 30% 18% 3	507
	11th to 20th	Day	13% 7% 36% 30% 11% 2	300
	21st to end	Day	17% 14% 32% 25% 11% 2	300
October	1st to 10th	Day	18% 9% 31% 28% 11% 2	300
	11th to 20th	Day	18% 16% 32% 26% 8%	300
	21st to end	Day	22% 16% 34% 20% 7% 1	330
November	1st to 10th	Day	21% 11% 29% 32% 7% 1	282
	11th to 20th	Day	17% 14% 40% 23% 6% 1	270
	21st to end	Day	16% 16% 38% 27% 3	270
December	1st to 10th	Day	14% 6% 37% 31% 10% 1	270
	11th to 20th	Day	16% 11% 43% 26% 4	270
	21st to end	Day	21% 11% 34% 25% 7% 1	297
January	1st to 10th	Night	10% 9% 38% 32% 9% 2	950
	11th to 20th	Night	14% 9% 36% 34% 6%	950
	21st to end	Night	15% 9% 38% 30% 8% 1	1045
February	1st to 10th	Night	12% 10% 33% 35% 9% 1	950
	11th to 20th	Night	13% 10% 38% 30% 7% 2	929
	21st to end	Night	14% 9% 32% 30% 13% 1	692
March	1st to 10th	Night	15% 9% 35% 30% 9% 1	679
	11th to 20th	Night	14% 9% 39% 29% 8% 1	570
	21st to end	Night	17% 9% 31% 30% 11% 2	627
April	1st to 10th	Night	16% 11% 34% 31% 7%	570
	11th to 20th	Night	23% 10% 31% 26% 9% 1	563
	21st to end	Night	21% 10% 32% 26% 10%	570
May	1st to 10th	Night	18% 9% 32% 32% 8% 1	570
	11th to 20th	Night	15% 8% 34% 32% 11%	561
	21st to end	Night	13% 9% 35% 33% 10% 1	617
June	1st to 10th	Night	9% 7% 31% 40% 12%	570
	11th to 20th	Night	13% 5% 35% 39% 9%	570
	21st to end	Night	8% 4 27% 47% 13% 1	570
July	1st to 10th	Night	6% 2 23% 46% 21% 2	555
	11th to 20th	Night	6% 4 26% 47% 17% 1	552
	21st to end	Night	5% 3 24% 46% 21% 2	624
August	1st to 10th	Night	7% 3 21% 51% 17% 1	567
	11th to 20th	Night	9% 5% 22% 41% 21% 2	564
	21st to end	Night	9% 4 31% 37% 18% 1	627
September	1st to 10th	Night	9% 5% 31% 39% 14% 2	570
	11th to 20th	Night	9% 5% 30% 41% 14% 1	570
	21st to end	Night	15% 6% 34% 35% 10%	570
October	1st to 10th	Night	18% 9% 33% 31% 9%	703
	11th to 20th	Night	20% 9% 33% 29% 8%	760
	21st to end	Night	23% 10% 35% 26% 5%	996
November	1st to 10th	Night	17% 9% 33% 32% 8%	950
	11th to 20th	Night	17% 11% 36% 27% 8% 1	950
	21st to end	Night	15% 11% 40% 29% 5%	950
December	1st to 10th	Night	13% 9% 38% 30% 9% 1	950
	11th to 20th	Night	18% 9% 39% 28% 6% 1	950
	21st to end	Night	23% 8% 36% 26% 6%	1045

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