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 2024-04-25.

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	12% 8% 4 7% 6% 4 5% 5% 5% 7% 37%	82933
	Night	11% 9% 4 8% 7% 4 5% 5% 5% 6% 36%	86233
Transparency	Day	47% 7% 14% 23% 9% 1	82625
	Night	47% 7% 14% 22% 10% 1	86064
Seeing	Day	15% 9% 31% 30% 13% 3	15265
	Night	14% 8% 33% 33% 10% 1	25377

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% 12% 8% 11% 12% 6% 6% 6% 6% 5% 20%	2218
	11th to 20th	Day	5% 8% 5% 11% 12% 7% 14% 8% 8% 6% 16%	2421
	21st to end	Day	8% 13% 10% 16% 9% 4 5% 5% 4 5% 23%	2891
February	1st to 10th	Day	8% 13% 6% 9% 7% 5% 7% 7% 6% 6% 26%	1710
	11th to 20th	Day	6% 11% 6% 9% 9% 6% 8% 6% 7% 7% 25%	1664
	21st to end	Day	10% 11% 6% 10% 9% 5% 6% 5% 7% 8% 23%	1522
March	1st to 10th	Day	12% 11% 4 8% 7% 4 5% 4 4 6% 34%	3271
	11th to 20th	Day	10% 9% 5% 9% 7% 4 5% 5% 6% 9% 32%	3480
	21st to end	Day	17% 14% 5% 11% 8% 3 4 4 4 5% 24%	3814
April	1st to 10th	Day	15% 10% 3 7% 7% 3 5% 4 5% 6% 35%	2239
	11th to 20th	Day	18% 11% 4 7% 5% 3 4 4 5% 7% 33%	2439
	21st to end	Day	21% 8% 4 6% 5% 3 4 4 5% 6% 33%	2394
May	1st to 10th	Day	19% 8% 3 6% 6% 3 4 4 5% 6% 37%	2340
	11th to 20th	Day	14% 6% 2 5% 7% 3 5% 5% 5% 8% 40%	2456
	21st to end	Day	16% 6% 3 6% 6% 3 5% 4 5% 7% 39%	2869
June	1st to 10th	Day	14% 4 3 5% 5% 3 5% 5% 6% 9% 42%	2700
	11th to 20th	Day	14% 4 2 5% 5% 3 5% 5% 6% 8% 43%	2700
	21st to end	Day	10% 4 2 4 5% 3 5% 5% 7% 10% 43%	2700
July	1st to 10th	Day	7% 3 2 4 3 2 4 5% 7% 9% 54%	2700
	11th to 20th	Day	8% 3 1 5% 5% 3 4 5% 6% 10% 49%	2700
	21st to end	Day	5% 3 2 4 4 3 4 6% 7% 9% 54%	2740
August	1st to 10th	Day	7% 4 1 5% 5% 3 5% 6% 8% 9% 46%	2328
	11th to 20th	Day	13% 6% 2 5% 4 2 4 5% 4 7% 47%	2301
	21st to end	Day	9% 5% 1 5% 5% 3 4 4 4 7% 54%	2574
September	1st to 10th	Day	12% 4 2 4 5% 2 4 5% 5% 8% 51%	2177
	11th to 20th	Day	13% 5% 3 5% 5% 3 4 4 4 7% 47%	1980
	21st to end	Day	14% 5% 2 6% 5% 2 4 4 6% 8% 44%	1980
October	1st to 10th	Day	17% 7% 2 6% 6% 3 4 4 4 6% 41%	1836
	11th to 20th	Day	18% 10% 4 5% 5% 2 3 4 3 6% 41%	1800
	21st to end	Day	18% 11% 3 7% 5% 4 4 4 5% 6% 33%	1828
November	1st to 10th	Day	14% 10% 6% 10% 5% 4 5% 4 4 6% 35%	1588
	11th to 20th	Day	10% 14% 6% 11% 9% 4 4 3 4 5% 29%	1520
	21st to end	Day	10% 12% 6% 10% 9% 3 4 4 4 5% 33%	1520
December	1st to 10th	Day	8% 15% 5% 11% 9% 5% 6% 7% 5% 5% 24%	1408
	11th to 20th	Day	9% 12% 6% 12% 8% 5% 5% 6% 6% 6% 25%	1683
	21st to end	Day	21% 12% 5% 11% 9% 5% 5% 4 3 4 23%	2442
January	1st to 10th	Night	7% 11% 6% 12% 12% 7% 8% 7% 5% 5% 20%	4737
	11th to 20th	Night	5% 10% 5% 11% 12% 7% 14% 9% 6% 6% 16%	4548
	21st to end	Night	8% 14% 8% 13% 7% 4 7% 5% 6% 5% 23%	4774
February	1st to 10th	Night	8% 10% 5% 9% 7% 4 7% 6% 6% 6% 31%	2470
	11th to 20th	Night	6% 10% 5% 9% 8% 5% 7% 7% 6% 6% 30%	2403
	21st to end	Night	10% 10% 5% 9% 6% 5% 6% 6% 5% 6% 32%	1948
March	1st to 10th	Night	8% 8% 4 7% 6% 4 4 5% 5% 9% 40%	3588
	11th to 20th	Night	9% 10% 4 8% 8% 3 4 4 5% 6% 37%	3480
	21st to end	Night	17% 15% 5% 8% 5% 2 4 4 4 6% 31%	3817
April	1st to 10th	Night	13% 7% 4 6% 4 3 4 5% 5% 8% 40%	1936
	11th to 20th	Night	19% 10% 4 5% 4 3 4 5% 5% 5% 37%	1689
	21st to end	Night	19% 9% 4 5% 6% 2 4 4 5% 7% 38%	1665
May	1st to 10th	Night	15% 9% 4 6% 6% 2 5% 4 5% 5% 39%	1620
	11th to 20th	Night	15% 5% 2 3 5% 3 4 5% 7% 8% 44%	1437
	21st to end	Night	12% 5% 2 7% 4 3 5% 6% 6% 7% 44%	1405
June	1st to 10th	Night	10% 3 2 4 5% 3 3 5% 7% 11% 47%	1260
	11th to 20th	Night	9% 4 2 5% 4 3 5% 4 6% 9% 48%	1260
	21st to end	Night	6% 3 2 4 4 3 5% 5% 6% 10% 50%	1260
July	1st to 10th	Night	5% 2 2 4 3 3 5% 4 5% 8% 59%	1260
	11th to 20th	Night	4 3 1 3 4 2 3 5% 6% 9% 60%	1260
	21st to end	Night	4 3 2 3 4 2 4 4 6% 8% 59%	1574
August	1st to 10th	Night	6% 4 1 4 4 3 4 5% 7% 8% 54%	1611
	11th to 20th	Night	8% 5% 2 4 3 2 4 4 5% 7% 56%	1600
	21st to end	Night	8% 4 2 4 3 2 4 4 5% 6% 60%	1782
September	1st to 10th	Night	9% 3 2 3 3 3 4 4 5% 8% 56%	1778
	11th to 20th	Night	9% 4 2 4 4 3 5% 4 4 7% 54%	1980
	21st to end	Night	14% 4 1 4 4 2 3 4 5% 7% 52%	1980
October	1st to 10th	Night	15% 6% 3 5% 5% 3 4 5% 5% 7% 43%	2106
	11th to 20th	Night	16% 9% 3 5% 5% 3 4 3 5% 6% 41%	2160
	21st to end	Night	16% 10% 4 6% 5% 3 4 4 5% 6% 38%	2527
November	1st to 10th	Night	11% 10% 5% 8% 5% 3 5% 5% 6% 7% 35%	2490
	11th to 20th	Night	11% 11% 6% 10% 7% 4 5% 4 4 6% 31%	2660
	21st to end	Night	12% 9% 3 7% 7% 5% 5% 4 6% 7% 35%	2660
December	1st to 10th	Night	8% 12% 7% 12% 10% 5% 6% 5% 5% 6% 26%	2769
	11th to 20th	Night	11% 13% 6% 11% 8% 4 6% 5% 5% 5% 27%	3514
	21st to end	Night	19% 14% 5% 10% 8% 4 5% 4 3 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	50% 7% 12% 22% 8% 1	2394
May	1st to 10th	Day	48% 6% 12% 23% 10% 1	2340
	11th to 20th	Day	43% 7% 14% 25% 10% 1	2460
	21st to end	Day	45% 7% 13% 24% 10% 1	2869
June	1st to 10th	Day	38% 8% 16% 28% 9%	2700
	11th to 20th	Day	39% 8% 16% 24% 12% 1	2700
	21st to end	Day	34% 9% 18% 27% 11%	2700
July	1st to 10th	Day	25% 9% 17% 34% 14% 1	2626
	11th to 20th	Day	29% 9% 19% 28% 13% 2	2619
	21st to end	Day	25% 8% 16% 35% 15% 2	2587
August	1st to 10th	Day	30% 9% 17% 31% 10% 2	2314
	11th to 20th	Day	35% 8% 18% 27% 11% 1	2301
	21st to end	Day	29% 7% 13% 33% 15% 2	2574
September	1st to 10th	Day	32% 6% 15% 34% 12% 1	2177
	11th to 20th	Day	37% 7% 17% 29% 11%	1980
	21st to end	Day	38% 8% 14% 31% 8% 1	1980
October	1st to 10th	Day	45% 7% 13% 25% 10%	1836
	11th to 20th	Day	46% 5% 12% 25% 11% 1	1800
	21st to end	Day	53% 5% 15% 20% 7%	1828
November	1st to 10th	Day	52% 6% 14% 17% 11% 1	1588
	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% 11% 2	1665
May	1st to 10th	Night	46% 7% 11% 20% 14% 2	1620
	11th to 20th	Night	37% 7% 13% 23% 17% 3	1438
	21st to end	Night	38% 7% 14% 26% 14% 2	1406
June	1st to 10th	Night	30% 7% 17% 33% 10% 2	1260
	11th to 20th	Night	32% 7% 16% 26% 14% 5%	1260
	21st to end	Night	27% 10% 20% 30% 12% 2	1260
July	1st to 10th	Night	22% 8% 15% 32% 22% 1	1225
	11th to 20th	Night	20% 9% 16% 34% 18% 4	1218
	21st to end	Night	23% 6% 15% 34% 18% 3	1487
August	1st to 10th	Night	27% 8% 13% 33% 17% 3	1601
	11th to 20th	Night	28% 7% 16% 31% 16% 2	1600
	21st to end	Night	26% 6% 13% 32% 22% 1	1782
September	1st to 10th	Night	27% 7% 14% 35% 16% 1	1778
	11th to 20th	Night	30% 7% 16% 31% 15% 1	1980
	21st to end	Night	33% 6% 13% 33% 15% 1	1980
October	1st to 10th	Night	40% 6% 13% 27% 12% 2	2106
	11th to 20th	Night	43% 6% 12% 25% 13% 1	2160
	21st to end	Night	47% 6% 15% 23% 9%	2527
November	1st to 10th	Night	47% 6% 12% 22% 11% 2	2490
	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% 10% 32% 24% 10% 2	622
May	1st to 10th	Day	20% 9% 31% 27% 12% 1	603
	11th to 20th	Day	17% 9% 31% 27% 13% 3	625
	21st to end	Day	17% 9% 27% 30% 14% 3	679
June	1st to 10th	Day	11% 8% 27% 33% 18% 3	630
	11th to 20th	Day	14% 9% 39% 23% 13% 2	630
	21st to end	Day	11% 7% 30% 33% 15% 4	630
July	1st to 10th	Day	7% 3 25% 36% 24% 6%	621
	11th to 20th	Day	9% 5% 30% 33% 18% 4	618
	21st to end	Day	5% 3 28% 38% 21% 5%	684
August	1st to 10th	Day	7% 4 23% 37% 25% 4	626
	11th to 20th	Day	13% 5% 22% 33% 18% 9%	615
	21st to end	Day	10% 5% 28% 33% 21% 3	693
September	1st to 10th	Day	11% 6% 34% 30% 17% 3	467
	11th to 20th	Day	14% 8% 36% 29% 10% 2	270
	21st to end	Day	19% 14% 33% 23% 10% 2	270
October	1st to 10th	Day	20% 9% 30% 28% 11% 2	270
	11th to 20th	Day	19% 16% 31% 25% 9%	270
	21st to end	Day	22% 17% 34% 19% 6% 1	297
November	1st to 10th	Day	20% 10% 30% 31% 7% 1	270
	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%	555
May	1st to 10th	Night	18% 8% 33% 32% 8% 1	540
	11th to 20th	Night	15% 7% 34% 33% 11%	531
	21st to end	Night	13% 8% 35% 33% 10% 1	584
June	1st to 10th	Night	10% 6% 29% 41% 13%	540
	11th to 20th	Night	12% 5% 34% 40% 9%	540
	21st to end	Night	7% 4 27% 47% 14% 1	540
July	1st to 10th	Night	6% 2 24% 47% 20% 1	525
	11th to 20th	Night	6% 4 27% 47% 16% 1	522
	21st to end	Night	5% 3 23% 47% 20% 2	591
August	1st to 10th	Night	7% 2 20% 52% 17% 1	537
	11th to 20th	Night	9% 5% 22% 42% 20% 2	534
	21st to end	Night	10% 4 30% 37% 19% 1	594
September	1st to 10th	Night	10% 5% 30% 39% 14% 2	540
	11th to 20th	Night	10% 5% 29% 43% 13% 1	540
	21st to end	Night	15% 6% 34% 34% 10%	540
October	1st to 10th	Night	19% 9% 33% 30% 9%	666
	11th to 20th	Night	21% 9% 32% 29% 8%	720
	21st to end	Night	23% 11% 34% 26% 6%	943
November	1st to 10th	Night	17% 9% 34% 33% 7%	925
	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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