Wartburg College Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wartburg College Observatory clear sky chart from 2005-11-06 to 2026-07-31.

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% 4 5% 4 6% 7% 38%	138835
	Night	12% 9% 3 9% 5% 4 4 4 5% 7% 40%	134518
Transparency	Day	44% 6% 13% 24% 13% 1	142415
	Night	43% 5% 12% 23% 14% 2	139017
Seeing	Day	16% 10% 30% 27% 13% 3	18315
	Night	16% 9% 32% 31% 11% 1	28127

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	7% 12% 8% 20% 9% 7% 5% 3 4 4 20%	4691
	11th to 20th	Day	6% 10% 5% 13% 8% 9% 7% 7% 6% 5% 25%	4927
	21st to end	Day	8% 12% 5% 12% 5% 6% 7% 4 5% 7% 28%	5812
February	1st to 10th	Day	9% 12% 6% 11% 7% 6% 5% 4 6% 7% 26%	1890
	11th to 20th	Day	11% 11% 4 8% 6% 5% 6% 5% 5% 6% 33%	1844
	21st to end	Day	13% 11% 4 9% 5% 5% 5% 4 5% 6% 33%	1699
March	1st to 10th	Day	16% 8% 4 6% 4 3 3 3 4 5% 46%	4898
	11th to 20th	Day	12% 6% 2 6% 4 4 4 3 5% 8% 47%	5090
	21st to end	Day	21% 14% 4 10% 5% 4 4 3 5% 6% 25%	5694
April	1st to 10th	Day	20% 11% 4 7% 4 4 4 4 5% 7% 30%	2520
	11th to 20th	Day	19% 9% 3 8% 5% 5% 4 4 5% 6% 33%	2494
	21st to end	Day	22% 9% 3 6% 5% 4 4 3 5% 6% 33%	2616
May	1st to 10th	Day	12% 6% 2 6% 4 4 4 4 6% 8% 41%	7847
	11th to 20th	Day	15% 7% 2 6% 3 3 4 3 5% 6% 46%	8222
	21st to end	Day	16% 7% 3 7% 5% 4 4 4 5% 7% 37%	9047
June	1st to 10th	Day	12% 6% 2 5% 4 4 4 5% 6% 10% 42%	2940
	11th to 20th	Day	12% 6% 2 7% 4 5% 4 4 6% 8% 43%	2940
	21st to end	Day	13% 6% 2 6% 5% 5% 6% 5% 7% 8% 39%	2940
July	1st to 10th	Day	8% 6% 3 7% 5% 4 6% 4 8% 9% 40%	6500
	11th to 20th	Day	8% 6% 2 6% 4 4 4 3 6% 7% 50%	6500
	21st to end	Day	8% 6% 2 6% 5% 5% 6% 5% 7% 10% 39%	6843
August	1st to 10th	Day	8% 6% 3 7% 4 5% 5% 5% 7% 8% 43%	4234
	11th to 20th	Day	11% 6% 2 6% 4 5% 5% 5% 7% 9% 40%	4171
	21st to end	Day	7% 5% 2 6% 4 4 4 4 6% 8% 49%	4327
September	1st to 10th	Day	12% 5% 2 6% 3 2 3 3 5% 8% 51%	2400
	11th to 20th	Day	10% 4 3 5% 4 4 4 5% 6% 8% 46%	2400
	21st to end	Day	13% 6% 2 5% 4 4 4 4 5% 8% 46%	2091
October	1st to 10th	Day	15% 6% 2 6% 4 4 4 3 4 6% 48%	2000
	11th to 20th	Day	18% 8% 2 6% 4 3 4 3 5% 7% 41%	2000
	21st to end	Day	17% 9% 3 6% 4 3 4 3 4 6% 42%	2193
November	1st to 10th	Day	11% 8% 3 6% 4 4 4 4 5% 7% 45%	1852
	11th to 20th	Day	14% 12% 4 9% 5% 4 4 4 5% 6% 33%	1685
	21st to end	Day	14% 12% 5% 7% 4 4 4 3 5% 7% 36%	1680
December	1st to 10th	Day	7% 9% 3 10% 6% 5% 5% 4 7% 8% 37%	2690
	11th to 20th	Day	14% 14% 5% 13% 7% 6% 5% 4 4 6% 23%	3088
	21st to end	Day	21% 21% 10% 13% 4 3 3 2 3 4 16%	4070
January	1st to 10th	Night	7% 12% 6% 19% 6% 6% 5% 4 5% 6% 24%	8232
	11th to 20th	Night	7% 12% 4 12% 7% 6% 7% 6% 7% 6% 25%	8058
	21st to end	Night	9% 11% 5% 11% 6% 4 4 4 5% 7% 34%	8402
February	1st to 10th	Night	9% 12% 5% 11% 8% 5% 5% 3 5% 6% 30%	2730
	11th to 20th	Night	10% 10% 3 8% 5% 5% 5% 3 4 7% 40%	2663
	21st to end	Night	13% 8% 3 9% 6% 5% 4 3 5% 5% 39%	2107
March	1st to 10th	Night	15% 8% 3 5% 3 2 3 3 4 5% 50%	5219
	11th to 20th	Night	9% 7% 3 6% 3 3 4 3 6% 8% 48%	5090
	21st to end	Night	22% 12% 4 10% 4 4 3 3 4 5% 29%	5462
April	1st to 10th	Night	16% 10% 3 7% 4 4 3 4 5% 5% 38%	2100
	11th to 20th	Night	17% 7% 3 7% 5% 4 5% 3 4 6% 39%	2075
	21st to end	Night	19% 7% 2 7% 3 4 3 4 4 6% 41%	2000
May	1st to 10th	Night	12% 5% 2 6% 3 4 5% 3 5% 7% 48%	5033
	11th to 20th	Night	12% 6% 2 6% 4 4 4 3 5% 6% 49%	4670
	21st to end	Night	15% 9% 3 7% 4 3 4 3 5% 7% 40%	5139
June	1st to 10th	Night	8% 4 2 6% 4 5% 5% 5% 6% 9% 46%	1680
	11th to 20th	Night	10% 5% 2 6% 4 5% 5% 4 7% 7% 44%	1680
	21st to end	Night	11% 5% 2 6% 4 3 4 4 5% 8% 48%	1680
July	1st to 10th	Night	8% 6% 1 5% 4 4 5% 4 6% 9% 48%	3698
	11th to 20th	Night	5% 5% 2 6% 4 4 4 4 5% 8% 54%	3697
	21st to end	Night	8% 4 2 6% 4 4 5% 4 7% 9% 47%	4245
August	1st to 10th	Night	6% 4 2 5% 4 5% 4 4 7% 9% 50%	2926
	11th to 20th	Night	11% 5% 3 5% 3 3 3 3 5% 8% 53%	2888
	21st to end	Night	9% 5% 2 5% 3 3 3 3 6% 7% 52%	3571
September	1st to 10th	Night	10% 4 2 6% 4 3 3 3 4 7% 55%	2000
	11th to 20th	Night	12% 5% 1 4 3 3 4 3 4 7% 53%	2000
	21st to end	Night	9% 5% 1 4 3 3 3 3 4 7% 57%	2283
October	1st to 10th	Night	13% 5% 2 5% 4 4 3 3 4 7% 51%	2400
	11th to 20th	Night	16% 7% 2 7% 3 3 4 3 4 6% 46%	2400
	21st to end	Night	17% 9% 3 6% 4 4 4 3 5% 6% 40%	2645
November	1st to 10th	Night	13% 7% 2 6% 3 3 4 3 5% 6% 48%	2666
	11th to 20th	Night	13% 11% 3 9% 5% 3 4 3 5% 6% 38%	2930
	21st to end	Night	14% 10% 4 8% 4 4 4 3 5% 5% 39%	2940
December	1st to 10th	Night	7% 8% 3 9% 6% 5% 5% 4 6% 7% 40%	4720
	11th to 20th	Night	14% 13% 5% 10% 5% 4 4 3 5% 6% 30%	5339
	21st to end	Night	21% 17% 7% 16% 5% 4 3 3 4 4 15%	7150

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	68% 5% 10% 13% 5%	4692
	11th to 20th	Day	58% 3 10% 15% 12%	4927
	21st to end	Day	55% 5% 13% 20% 7%	5812
February	1st to 10th	Day	56% 5% 14% 17% 8% 1	1890
	11th to 20th	Day	50% 6% 12% 23% 8% 2	1853
	21st to end	Day	51% 5% 13% 20% 9% 2	1699
March	1st to 10th	Day	42% 5% 12% 27% 11% 3	4898
	11th to 20th	Day	35% 5% 11% 33% 14% 1	5090
	21st to end	Day	59% 6% 14% 15% 6%	5696
April	1st to 10th	Day	54% 6% 12% 20% 8%	2520
	11th to 20th	Day	51% 6% 12% 20% 11% 1	2494
	21st to end	Day	51% 6% 11% 21% 11% 1	2616
May	1st to 10th	Day	38% 6% 11% 24% 21%	7885
	11th to 20th	Day	38% 5% 11% 29% 16% 2	8226
	21st to end	Day	44% 6% 11% 24% 13% 2	9061
June	1st to 10th	Day	36% 7% 15% 25% 15% 1	2940
	11th to 20th	Day	38% 7% 12% 23% 18% 2	2940
	21st to end	Day	40% 9% 14% 23% 13% 2	2940
July	1st to 10th	Day	38% 7% 15% 31% 9% 1	6431
	11th to 20th	Day	32% 6% 13% 31% 16% 1	6425
	21st to end	Day	37% 8% 18% 23% 14% 1	6652
August	1st to 10th	Day	37% 8% 14% 27% 12% 2	4220
	11th to 20th	Day	38% 7% 17% 25% 12% 1	4210
	21st to end	Day	32% 6% 14% 29% 17% 1	4326
September	1st to 10th	Day	32% 7% 14% 27% 19% 2	2400
	11th to 20th	Day	35% 7% 13% 31% 14%	2400
	21st to end	Day	36% 5% 11% 28% 18% 1	2091
October	1st to 10th	Day	24% 3 7% 36% 29% 1	3260
	11th to 20th	Day	31% 4 11% 29% 22% 3	3240
	21st to end	Day	41% 4 11% 30% 13% 2	3519
November	1st to 10th	Day	39% 6% 13% 25% 15% 2	1852
	11th to 20th	Day	51% 4 13% 21% 10%	1685
	21st to end	Day	50% 5% 15% 22% 7% 1	1680
December	1st to 10th	Day	43% 6% 13% 30% 6% 1	2690
	11th to 20th	Day	63% 4 13% 11% 8%	3085
	21st to end	Day	75% 3 8% 10% 3	4070
January	1st to 10th	Night	60% 5% 14% 15% 6%	8233
	11th to 20th	Night	56% 4 13% 15% 12% 1	8058
	21st to end	Night	49% 4 13% 23% 10% 1	8402
February	1st to 10th	Night	54% 5% 12% 18% 10% 1	2730
	11th to 20th	Night	44% 5% 13% 25% 12% 2	2664
	21st to end	Night	47% 5% 12% 20% 14% 2	2107
March	1st to 10th	Night	38% 4 9% 29% 17% 3	5219
	11th to 20th	Night	34% 4 11% 31% 18% 3	5090
	21st to end	Night	58% 5% 13% 15% 8% 1	5462
April	1st to 10th	Night	46% 5% 11% 22% 13% 2	2100
	11th to 20th	Night	45% 5% 11% 22% 15% 3	2075
	21st to end	Night	43% 5% 12% 25% 13% 2	2000
May	1st to 10th	Night	35% 6% 8% 24% 26% 1	5060
	11th to 20th	Night	36% 5% 10% 24% 19% 5%	4671
	21st to end	Night	44% 6% 9% 26% 13% 2	5149
June	1st to 10th	Night	31% 8% 16% 28% 15% 3	1680
	11th to 20th	Night	35% 7% 12% 19% 22% 4	1680
	21st to end	Night	34% 7% 14% 26% 16% 3	1680
July	1st to 10th	Night	32% 6% 17% 30% 14% 1	3660
	11th to 20th	Night	28% 6% 16% 32% 16% 2	3652
	21st to end	Night	32% 8% 18% 24% 16% 1	4125
August	1st to 10th	Night	29% 7% 16% 30% 17% 1	2916
	11th to 20th	Night	31% 6% 16% 33% 13% 1	2915
	21st to end	Night	31% 6% 14% 27% 19% 3	3571
September	1st to 10th	Night	29% 7% 10% 29% 23% 2	2000
	11th to 20th	Night	31% 5% 11% 34% 18% 1	2000
	21st to end	Night	28% 5% 11% 30% 24% 2	2283
October	1st to 10th	Night	23% 4 7% 31% 33% 2	3920
	11th to 20th	Night	28% 4 11% 25% 27% 5%	3899
	21st to end	Night	44% 4 10% 24% 15% 2	4269
November	1st to 10th	Night	37% 5% 14% 25% 17% 3	2666
	11th to 20th	Night	47% 5% 13% 23% 11% 1	2930
	21st to end	Night	48% 4 13% 26% 9% 1	2940
December	1st to 10th	Night	42% 5% 18% 26% 8%	4720
	11th to 20th	Night	54% 5% 14% 21% 4 1	5341
	21st to end	Night	73% 5% 9% 10% 4	7150

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	16% 15% 36% 23% 8% 2	330
	11th to 20th	Day	20% 11% 42% 22% 5% 1	330
	21st to end	Day	17% 14% 39% 22% 7% 1	363
February	1st to 10th	Day	16% 17% 38% 25% 3 2	330
	11th to 20th	Day	17% 21% 34% 21% 7%	330
	21st to end	Day	20% 14% 38% 24% 3	273
March	1st to 10th	Day	16% 15% 45% 18% 6% 1	330
	11th to 20th	Day	22% 18% 31% 22% 7% 1	330
	21st to end	Day	30% 16% 33% 17% 4 1	410
April	1st to 10th	Day	27% 17% 33% 18% 5% 1	540
	11th to 20th	Day	26% 19% 28% 20% 7% 1	532
	21st to end	Day	24% 14% 34% 19% 7% 2	636
May	1st to 10th	Day	21% 13% 32% 22% 10% 2	753
	11th to 20th	Day	22% 13% 28% 23% 11% 4	775
	21st to end	Day	16% 8% 30% 26% 16% 3	844
June	1st to 10th	Day	9% 9% 27% 33% 19% 3	780
	11th to 20th	Day	14% 7% 31% 32% 13% 2	780
	21st to end	Day	12% 7% 34% 29% 13% 4	780
July	1st to 10th	Day	10% 3 19% 33% 25% 10%	771
	11th to 20th	Day	8% 4 23% 35% 22% 8%	768
	21st to end	Day	7% 3 24% 39% 22% 6%	845
August	1st to 10th	Day	8% 3 24% 34% 25% 7%	726
	11th to 20th	Day	13% 5% 17% 33% 25% 7%	715
	21st to end	Day	9% 5% 22% 36% 22% 6%	598
September	1st to 10th	Day	12% 8% 23% 28% 22% 7%	530
	11th to 20th	Day	8% 6% 25% 34% 22% 4	530
	21st to end	Day	15% 10% 28% 28% 14% 5%	350
October	1st to 10th	Day	17% 8% 31% 24% 17% 4	330
	11th to 20th	Day	23% 15% 37% 18% 5% 1	330
	21st to end	Day	23% 15% 34% 20% 6% 2	363
November	1st to 10th	Day	16% 14% 42% 21% 5% 2	330
	11th to 20th	Day	19% 21% 33% 19% 7% 1	330
	21st to end	Day	22% 15% 37% 22% 4	330
December	1st to 10th	Day	14% 13% 44% 20% 8% 2	330
	11th to 20th	Day	19% 14% 37% 21% 9% 1	330
	21st to end	Day	27% 15% 38% 16% 3	363
January	1st to 10th	Night	13% 13% 36% 30% 8%	1050
	11th to 20th	Night	17% 13% 35% 30% 6%	1050
	21st to end	Night	18% 12% 36% 28% 6%	1155
February	1st to 10th	Night	16% 12% 36% 29% 6%	1050
	11th to 20th	Night	16% 12% 39% 28% 5% 1	1029
	21st to end	Night	17% 13% 39% 25% 6% 1	723
March	1st to 10th	Night	20% 13% 35% 25% 6% 1	722
	11th to 20th	Night	17% 10% 39% 27% 8%	630
	21st to end	Night	24% 11% 37% 22% 5% 1	693
April	1st to 10th	Night	20% 13% 40% 23% 4	630
	11th to 20th	Night	21% 13% 32% 27% 7%	623
	21st to end	Night	22% 9% 34% 28% 6% 1	630
May	1st to 10th	Night	18% 8% 34% 31% 9% 1	630
	11th to 20th	Night	17% 9% 31% 33% 9% 1	621
	21st to end	Night	17% 5% 31% 33% 13%	683
June	1st to 10th	Night	10% 4 31% 40% 15% 1	630
	11th to 20th	Night	13% 4 30% 42% 11%	630
	21st to end	Night	13% 6% 27% 37% 16% 1	630
July	1st to 10th	Night	7% 2 15% 45% 29% 3	615
	11th to 20th	Night	6% 1 20% 43% 27% 3	612
	21st to end	Night	6% 3 17% 50% 21% 3	687
August	1st to 10th	Night	5% 2 17% 48% 26% 1	597
	11th to 20th	Night	10% 4 18% 40% 25% 4	594
	21st to end	Night	10% 3 19% 40% 25% 2	660
September	1st to 10th	Night	11% 5% 20% 41% 19% 4	600
	11th to 20th	Night	14% 4 21% 40% 21% 2	600
	21st to end	Night	11% 8% 26% 37% 18% 1	708
October	1st to 10th	Night	15% 6% 32% 33% 14% 1	800
	11th to 20th	Night	20% 11% 32% 30% 7%	800
	21st to end	Night	21% 12% 31% 28% 7%	880
November	1st to 10th	Night	15% 9% 39% 30% 6% 1	820
	11th to 20th	Night	16% 15% 39% 24% 5%	1040
	21st to end	Night	18% 13% 36% 26% 7%	1050
December	1st to 10th	Night	17% 12% 40% 25% 6% 1	1050
	11th to 20th	Night	23% 9% 33% 27% 6% 1	1050
	21st to end	Night	25% 12% 35% 22% 6%	1155

Page generated at 2026-07-28 02:25:26. Version ac07

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