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 2025-03-27.

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% 8% 3 8% 5% 4 4 4 6% 7% 37%	109239
	Night	12% 9% 3 9% 5% 4 4 3 5% 6% 39%	110322
Transparency	Day	44% 6% 13% 23% 13% 1	112860
	Night	44% 5% 12% 23% 14% 2	114841
Seeing	Day	16% 10% 30% 27% 13% 4	16328
	Night	16% 9% 32% 31% 11% 1	26392

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	6% 12% 8% 21% 10% 7% 5% 3 4 4 20%	3617
	11th to 20th	Day	7% 10% 5% 12% 7% 9% 7% 7% 6% 5% 26%	3781
	21st to end	Day	10% 14% 6% 13% 5% 5% 6% 3 4 6% 27%	4488
February	1st to 10th	Day	10% 12% 6% 11% 7% 6% 5% 4 6% 7% 26%	1800
	11th to 20th	Day	11% 11% 4 8% 6% 6% 6% 5% 5% 6% 32%	1754
	21st to end	Day	14% 10% 4 9% 5% 5% 5% 4 5% 6% 33%	1620
March	1st to 10th	Day	16% 7% 4 7% 4 3 3 3 4 5% 43%	3441
	11th to 20th	Day	12% 6% 2 7% 4 4 4 3 6% 7% 45%	3590
	21st to end	Day	22% 15% 5% 11% 5% 4 4 3 5% 6% 20%	3961
April	1st to 10th	Day	21% 11% 3 7% 4 4 3 4 5% 7% 30%	2280
	11th to 20th	Day	18% 9% 3 8% 5% 5% 4 3 5% 6% 34%	2254
	21st to end	Day	22% 8% 3 7% 5% 4 4 4 5% 6% 33%	2366
May	1st to 10th	Day	20% 8% 3 7% 5% 4 4 4 6% 8% 32%	4202
	11th to 20th	Day	15% 8% 2 6% 4 3 4 3 5% 7% 42%	4399
	21st to end	Day	17% 6% 3 6% 5% 5% 4 4 5% 7% 40%	4824
June	1st to 10th	Day	12% 6% 2 5% 4 4 4 5% 6% 9% 43%	2660
	11th to 20th	Day	11% 6% 2 7% 4 5% 4 4 6% 8% 43%	2660
	21st to end	Day	13% 5% 2 7% 5% 5% 6% 5% 7% 8% 39%	2660
July	1st to 10th	Day	10% 6% 3 7% 5% 5% 6% 5% 8% 9% 36%	4440
	11th to 20th	Day	5% 4 2 4 4 4 4 4 6% 8% 55%	4440
	21st to end	Day	5% 4 2 6% 5% 5% 6% 5% 8% 11% 42%	4665
August	1st to 10th	Day	8% 6% 3 7% 4 5% 5% 5% 7% 8% 43%	4104
	11th to 20th	Day	11% 6% 2 6% 4 5% 5% 5% 7% 9% 40%	4041
	21st to end	Day	7% 5% 2 6% 4 4 4 4 6% 8% 49%	4194
September	1st to 10th	Day	12% 5% 2 5% 3 2 3 3 5% 8% 51%	2280
	11th to 20th	Day	11% 4 3 5% 4 4 4 4 6% 8% 48%	2280
	21st to end	Day	13% 6% 2 5% 4 3 3 4 5% 8% 46%	1987
October	1st to 10th	Day	15% 6% 2 6% 4 4 4 3 4 6% 46%	1900
	11th to 20th	Day	18% 8% 2 5% 4 3 3 3 5% 7% 42%	1900
	21st to end	Day	17% 9% 3 6% 4 3 4 3 4 6% 41%	2084
November	1st to 10th	Day	12% 8% 3 6% 4 4 4 4 5% 7% 44%	1762
	11th to 20th	Day	14% 12% 4 9% 5% 4 5% 4 5% 6% 32%	1605
	21st to end	Day	14% 11% 5% 7% 4 4 4 3 5% 7% 37%	1600
December	1st to 10th	Day	7% 8% 3 10% 5% 5% 5% 4 7% 8% 38%	2610
	11th to 20th	Day	14% 14% 5% 13% 7% 6% 5% 4 4 6% 23%	3008
	21st to end	Day	21% 21% 10% 14% 4 3 3 2 3 4 16%	3982
January	1st to 10th	Night	6% 11% 7% 21% 6% 6% 5% 3 5% 6% 24%	6348
	11th to 20th	Night	9% 13% 4 11% 7% 6% 6% 6% 8% 7% 24%	6194
	21st to end	Night	11% 12% 5% 12% 6% 4 3 3 4 6% 32%	6490
February	1st to 10th	Night	9% 12% 5% 11% 8% 5% 5% 3 5% 6% 30%	2600
	11th to 20th	Night	10% 10% 4 8% 5% 5% 5% 3 4 7% 39%	2533
	21st to end	Night	14% 8% 3 9% 6% 5% 4 3 5% 5% 39%	2010
March	1st to 10th	Night	14% 8% 3 6% 3 3 3 3 5% 6% 46%	3663
	11th to 20th	Night	10% 7% 3 6% 4 3 3 3 6% 8% 48%	3590
	21st to end	Night	26% 12% 4 11% 4 4 3 3 4 5% 26%	3807
April	1st to 10th	Night	15% 10% 3 7% 4 3 3 4 6% 5% 39%	1900
	11th to 20th	Night	17% 7% 3 7% 5% 4 5% 4 4 6% 38%	1875
	21st to end	Night	18% 6% 2 7% 4 3 3 4 4 6% 42%	1810
May	1st to 10th	Night	17% 7% 3 6% 4 4 5% 3 6% 5% 41%	2700
	11th to 20th	Night	12% 6% 2 6% 4 4 4 3 5% 6% 47%	2506
	21st to end	Night	11% 6% 2 5% 4 3 4 4 5% 8% 46%	2743
June	1st to 10th	Night	8% 4 2 5% 4 5% 5% 5% 6% 9% 47%	1520
	11th to 20th	Night	10% 5% 2 5% 4 5% 5% 4 7% 7% 44%	1520
	21st to end	Night	11% 5% 2 6% 4 3 4 3 5% 8% 49%	1520
July	1st to 10th	Night	9% 6% 2 5% 4 4 5% 4 6% 9% 46%	2530
	11th to 20th	Night	4 3 1 4 3 3 4 4 5% 9% 58%	2530
	21st to end	Night	5% 4 2 6% 4 4 5% 4 8% 9% 50%	2895
August	1st to 10th	Night	6% 4 2 5% 4 5% 4 4 7% 9% 50%	2836
	11th to 20th	Night	11% 5% 3 5% 3 3 3 2 5% 8% 53%	2798
	21st to end	Night	9% 5% 2 5% 3 3 3 3 6% 7% 52%	3462
September	1st to 10th	Night	10% 4 2 6% 4 2 4 3 4 6% 55%	1900
	11th to 20th	Night	13% 5% 1 4 3 3 3 3 4 7% 54%	1900
	21st to end	Night	10% 5% 1 4 3 3 3 3 4 7% 56%	2168
October	1st to 10th	Night	13% 5% 2 5% 4 4 3 3 4 6% 51%	2280
	11th to 20th	Night	16% 6% 2 6% 3 3 4 4 4 5% 46%	2280
	21st to end	Night	17% 9% 3 6% 4 4 4 3 6% 6% 39%	2513
November	1st to 10th	Night	13% 7% 2 6% 3 3 4 3 5% 6% 49%	2536
	11th to 20th	Night	13% 11% 4 9% 5% 3 4 3 5% 6% 38%	2790
	21st to end	Night	14% 10% 3 8% 4 4 4 3 5% 5% 40%	2800
December	1st to 10th	Night	7% 7% 3 9% 6% 5% 5% 4 6% 7% 40%	4580
	11th to 20th	Night	14% 14% 5% 10% 5% 4 4 3 5% 6% 30%	5199
	21st to end	Night	21% 18% 7% 16% 5% 4 3 3 4 4 15%	6996

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	67% 5% 9% 14% 4	3618
	11th to 20th	Day	58% 3 12% 12% 14% 1	3781
	21st to end	Day	58% 5% 13% 16% 7%	4488
February	1st to 10th	Day	56% 5% 14% 17% 8% 1	1800
	11th to 20th	Day	50% 6% 12% 22% 9% 1	1763
	21st to end	Day	51% 5% 12% 20% 10% 2	1620
March	1st to 10th	Day	44% 6% 11% 24% 13% 2	3441
	11th to 20th	Day	37% 6% 11% 31% 13% 1	3590
	21st to end	Day	64% 7% 12% 13% 4 1	3961
April	1st to 10th	Day	53% 6% 12% 21% 8%	2280
	11th to 20th	Day	50% 6% 11% 20% 11% 1	2254
	21st to end	Day	50% 6% 11% 20% 11% 1	2366
May	1st to 10th	Day	48% 8% 14% 18% 12% 1	4240
	11th to 20th	Day	40% 7% 12% 30% 11% 1	4403
	21st to end	Day	42% 7% 11% 24% 15% 1	4837
June	1st to 10th	Day	35% 7% 16% 25% 15% 2	2660
	11th to 20th	Day	38% 7% 12% 22% 19% 2	2660
	21st to end	Day	40% 10% 13% 22% 13% 2	2660
July	1st to 10th	Day	41% 8% 16% 26% 8% 1	4371
	11th to 20th	Day	26% 7% 15% 32% 19% 1	4365
	21st to end	Day	32% 10% 19% 21% 17% 1	4518
August	1st to 10th	Day	36% 8% 14% 27% 13% 2	4090
	11th to 20th	Day	38% 7% 16% 25% 12% 1	4080
	21st to end	Day	33% 6% 14% 28% 17% 1	4193
September	1st to 10th	Day	33% 7% 13% 26% 20% 2	2280
	11th to 20th	Day	34% 7% 13% 33% 14%	2280
	21st to end	Day	36% 5% 12% 29% 17% 1	1987
October	1st to 10th	Day	24% 3 7% 36% 29% 1	3160
	11th to 20th	Day	31% 4 11% 29% 22% 3	3140
	21st to end	Day	41% 4 11% 30% 13% 2	3410
November	1st to 10th	Day	40% 6% 13% 25% 14% 2	1762
	11th to 20th	Day	52% 4 13% 20% 10%	1605
	21st to end	Day	49% 5% 15% 23% 8% 1	1600
December	1st to 10th	Day	43% 6% 13% 31% 6% 1	2610
	11th to 20th	Day	63% 4 13% 11% 9%	3005
	21st to end	Day	75% 3 8% 10% 3	3982
January	1st to 10th	Night	60% 4 12% 16% 7% 1	6348
	11th to 20th	Night	56% 4 13% 14% 12% 1	6194
	21st to end	Night	53% 5% 12% 20% 10% 1	6490
February	1st to 10th	Night	54% 5% 11% 18% 11% 1	2600
	11th to 20th	Night	45% 5% 12% 24% 12% 1	2534
	21st to end	Night	46% 5% 12% 20% 15% 2	2010
March	1st to 10th	Night	40% 5% 10% 28% 16% 2	3663
	11th to 20th	Night	34% 5% 11% 31% 17% 2	3590
	21st to end	Night	62% 5% 12% 14% 5% 1	3807
April	1st to 10th	Night	45% 6% 12% 23% 13% 2	1900
	11th to 20th	Night	46% 5% 10% 21% 15% 3	1875
	21st to end	Night	42% 5% 12% 26% 13% 2	1810
May	1st to 10th	Night	42% 8% 10% 17% 21% 2	2727
	11th to 20th	Night	37% 7% 10% 27% 16% 4	2507
	21st to end	Night	34% 8% 13% 27% 16% 2	2751
June	1st to 10th	Night	30% 9% 16% 27% 15% 3	1520
	11th to 20th	Night	35% 8% 13% 19% 21% 4	1520
	21st to end	Night	33% 7% 14% 27% 17% 3	1520
July	1st to 10th	Night	35% 6% 18% 27% 12% 1	2490
	11th to 20th	Night	22% 7% 18% 35% 16% 2	2482
	21st to end	Night	27% 9% 17% 24% 21% 2	2803
August	1st to 10th	Night	29% 7% 15% 30% 17% 1	2826
	11th to 20th	Night	31% 6% 16% 33% 13% 1	2825
	21st to end	Night	31% 6% 14% 26% 19% 3	3462
September	1st to 10th	Night	29% 7% 9% 28% 24% 2	1900
	11th to 20th	Night	31% 5% 11% 34% 18% 1	1900
	21st to end	Night	28% 5% 11% 31% 23% 2	2168
October	1st to 10th	Night	23% 4 7% 31% 34% 2	3800
	11th to 20th	Night	27% 4 11% 25% 27% 5%	3779
	21st to end	Night	44% 5% 10% 24% 15% 2	4137
November	1st to 10th	Night	37% 4 14% 24% 18% 3	2536
	11th to 20th	Night	47% 5% 13% 23% 11% 2	2790
	21st to end	Night	47% 4 13% 26% 9% 1	2800
December	1st to 10th	Night	41% 5% 18% 27% 9%	4580
	11th to 20th	Night	54% 5% 14% 21% 4 1	5201
	21st to end	Night	73% 5% 8% 10% 4	6996

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% 22% 9% 2	300
	11th to 20th	Day	21% 10% 41% 22% 5% 1	300
	21st to end	Day	18% 12% 40% 22% 6% 1	330
February	1st to 10th	Day	17% 16% 38% 24% 3 1	300
	11th to 20th	Day	17% 22% 34% 20% 7%	300
	21st to end	Day	20% 15% 38% 24% 4	249
March	1st to 10th	Day	16% 14% 47% 17% 5% 1	300
	11th to 20th	Day	21% 17% 32% 22% 7% 1	300
	21st to end	Day	31% 14% 32% 17% 4 1	358
April	1st to 10th	Day	28% 15% 33% 18% 5% 1	460
	11th to 20th	Day	24% 20% 27% 21% 7% 1	452
	21st to end	Day	25% 15% 32% 19% 7% 2	546
May	1st to 10th	Day	23% 14% 32% 21% 9% 2	653
	11th to 20th	Day	21% 13% 28% 24% 10% 4	675
	21st to end	Day	16% 9% 29% 26% 16% 4	734
June	1st to 10th	Day	8% 8% 27% 34% 19% 4	680
	11th to 20th	Day	13% 6% 30% 34% 14% 3	680
	21st to end	Day	11% 7% 33% 29% 14% 5%	680
July	1st to 10th	Day	10% 3 18% 34% 24% 11%	671
	11th to 20th	Day	8% 4 24% 36% 21% 7%	668
	21st to end	Day	6% 2 25% 38% 22% 6%	739
August	1st to 10th	Day	8% 3 23% 34% 24% 7%	676
	11th to 20th	Day	13% 5% 18% 33% 24% 8%	665
	21st to end	Day	10% 5% 22% 37% 21% 6%	553
September	1st to 10th	Day	13% 7% 23% 28% 22% 7%	490
	11th to 20th	Day	8% 6% 26% 33% 22% 4	490
	21st to end	Day	16% 11% 29% 28% 13% 4	319
October	1st to 10th	Day	18% 8% 30% 23% 17% 4	300
	11th to 20th	Day	22% 14% 38% 19% 6% 1	300
	21st to end	Day	25% 15% 34% 18% 7% 2	330
November	1st to 10th	Day	17% 12% 41% 22% 6% 2	300
	11th to 20th	Day	19% 22% 31% 20% 8% 1	300
	21st to end	Day	21% 14% 39% 22% 4	300
December	1st to 10th	Day	13% 12% 45% 20% 8% 1	300
	11th to 20th	Day	19% 13% 37% 21% 9% 1	300
	21st to end	Day	26% 16% 38% 16% 4	330
January	1st to 10th	Night	13% 13% 36% 30% 8%	1000
	11th to 20th	Night	17% 13% 34% 30% 6%	1000
	21st to end	Night	19% 11% 36% 28% 6%	1100
February	1st to 10th	Night	16% 12% 37% 29% 5% 1	1000
	11th to 20th	Night	16% 13% 39% 27% 5% 1	979
	21st to end	Night	18% 12% 38% 25% 6% 1	690
March	1st to 10th	Night	20% 13% 35% 25% 6% 1	688
	11th to 20th	Night	16% 10% 39% 28% 8%	600
	21st to end	Night	24% 10% 36% 22% 6% 1	647
April	1st to 10th	Night	19% 12% 40% 24% 4	570
	11th to 20th	Night	21% 12% 33% 27% 7% 1	563
	21st to end	Night	21% 9% 34% 28% 7% 1	570
May	1st to 10th	Night	19% 8% 33% 30% 9% 1	570
	11th to 20th	Night	16% 9% 31% 34% 9% 1	561
	21st to end	Night	16% 6% 31% 32% 14%	617
June	1st to 10th	Night	10% 4 30% 40% 15% 1	570
	11th to 20th	Night	12% 4 29% 43% 12%	570
	21st to end	Night	12% 6% 27% 37% 17% 1	570
July	1st to 10th	Night	6% 2 15% 45% 29% 3	555
	11th to 20th	Night	5% 1 22% 43% 26% 3	552
	21st to end	Night	5% 3 16% 52% 21% 3	624
August	1st to 10th	Night	5% 2 17% 48% 26% 1	567
	11th to 20th	Night	10% 4 18% 39% 25% 4	564
	21st to end	Night	10% 3 19% 41% 25% 2	627
September	1st to 10th	Night	12% 5% 19% 41% 19% 4	570
	11th to 20th	Night	14% 4 21% 39% 20% 2	570
	21st to end	Night	12% 8% 27% 36% 17% 1	672
October	1st to 10th	Night	15% 6% 32% 32% 14% 1	760
	11th to 20th	Night	19% 11% 32% 31% 7%	760
	21st to end	Night	21% 13% 31% 28% 8%	836
November	1st to 10th	Night	16% 8% 39% 30% 7% 1	780
	11th to 20th	Night	16% 15% 40% 23% 6%	990
	21st to end	Night	18% 13% 36% 26% 7%	1000
December	1st to 10th	Night	16% 12% 40% 25% 6% 1	1000
	11th to 20th	Night	23% 8% 33% 28% 7% 1	1000
	21st to end	Night	24% 12% 35% 22% 6%	1100

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