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 2024-02-15.

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	14% 8% 4 7% 6% 3 5% 5% 5% 7% 36%	78324
	Night	13% 9% 4 7% 6% 3 4 4 5% 7% 38%	80804
Transparency	Day	47% 6% 13% 21% 11% 1	78029
	Night	45% 6% 13% 22% 13% 2	80619
Seeing	Day	16% 10% 30% 27% 14% 4	14816
	Night	16% 9% 32% 32% 11% 1	24884

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	8% 11% 10% 18% 9% 6% 5% 5% 4 5% 19%	2527
	11th to 20th	Day	10% 12% 4 10% 9% 6% 7% 6% 7% 6% 23%	2635
	21st to end	Day	14% 16% 8% 15% 8% 4 5% 5% 4 6% 15%	3135
February	1st to 10th	Day	10% 11% 6% 10% 8% 5% 5% 5% 5% 7% 27%	1710
	11th to 20th	Day	13% 11% 4 7% 6% 4 7% 5% 4 6% 33%	1610
	21st to end	Day	15% 11% 4 9% 7% 4 4 5% 5% 5% 30%	1453
March	1st to 10th	Day	15% 9% 6% 8% 6% 3 5% 4 5% 6% 32%	1916
	11th to 20th	Day	15% 8% 4 8% 6% 3 4 3 6% 9% 35%	1980
	21st to end	Day	20% 14% 4 7% 6% 3 4 5% 5% 7% 26%	2218
April	1st to 10th	Day	21% 10% 4 6% 5% 3 4 4 5% 7% 30%	2160
	11th to 20th	Day	18% 9% 3 7% 6% 4 4 4 4 7% 33%	2134
	21st to end	Day	23% 8% 3 6% 6% 3 4 4 5% 6% 33%	2241
May	1st to 10th	Day	19% 8% 3 6% 7% 3 5% 5% 6% 8% 29%	2404
	11th to 20th	Day	19% 8% 3 7% 5% 3 4 3 4 7% 36%	2479
	21st to end	Day	16% 6% 3 5% 6% 4 5% 5% 5% 8% 37%	2725
June	1st to 10th	Day	12% 5% 2 5% 4 3 5% 6% 6% 10% 43%	2520
	11th to 20th	Day	11% 5% 3 5% 5% 3 5% 4 5% 8% 45%	2520
	21st to end	Day	12% 4 3 6% 5% 4 6% 6% 6% 8% 39%	2520
July	1st to 10th	Day	9% 4 2 5% 4 3 4 4 7% 9% 49%	2520
	11th to 20th	Day	6% 5% 2 4 6% 3 5% 5% 6% 9% 48%	2520
	21st to end	Day	6% 4 2 4 5% 4 5% 6% 7% 10% 47%	2662
August	1st to 10th	Day	7% 5% 3 5% 5% 4 5% 7% 7% 9% 43%	2328
	11th to 20th	Day	11% 6% 2 5% 5% 3 5% 5% 6% 8% 44%	2301
	21st to end	Day	10% 5% 2 5% 5% 3 4 5% 5% 8% 49%	2390
September	1st to 10th	Day	13% 5% 2 4 4 2 3 4 5% 8% 50%	2160
	11th to 20th	Day	11% 4 3 4 4 3 4 5% 6% 8% 48%	2160
	21st to end	Day	14% 6% 3 4 4 3 3 5% 5% 7% 46%	1883
October	1st to 10th	Day	16% 6% 2 5% 5% 3 4 4 4 7% 43%	1800
	11th to 20th	Day	19% 7% 2 5% 5% 3 3 4 5% 7% 40%	1800
	21st to end	Day	18% 9% 3 5% 5% 2 4 4 4 5% 41%	1975
November	1st to 10th	Day	11% 7% 3 6% 4 3 4 5% 5% 7% 46%	1672
	11th to 20th	Day	14% 10% 5% 7% 7% 2 5% 5% 5% 6% 33%	1525
	21st to end	Day	15% 11% 4 5% 5% 3 4 3 5% 7% 38%	1520
December	1st to 10th	Day	12% 12% 4 11% 8% 4 6% 5% 4 7% 28%	1520
	11th to 20th	Day	13% 11% 5% 8% 7% 4 5% 5% 4 6% 31%	1918
	21st to end	Day	21% 18% 9% 12% 5% 3 3 3 3 5% 18%	2783
January	1st to 10th	Night	9% 12% 8% 18% 7% 3 4 4 4 5% 24%	4428
	11th to 20th	Night	10% 15% 5% 11% 8% 3 5% 7% 8% 6% 22%	4330
	21st to end	Night	15% 15% 7% 13% 8% 3 3 4 4 7% 20%	4532
February	1st to 10th	Night	9% 11% 6% 10% 9% 4 6% 4 5% 6% 30%	2470
	11th to 20th	Night	10% 9% 4 6% 6% 3 5% 5% 4 8% 40%	2332
	21st to end	Night	15% 8% 4 8% 7% 4 5% 4 5% 5% 37%	1803
March	1st to 10th	Night	16% 10% 4 5% 5% 2 4 4 5% 6% 40%	2060
	11th to 20th	Night	13% 8% 4 6% 5% 3 4 4 5% 8% 38%	1980
	21st to end	Night	18% 11% 5% 8% 6% 3 5% 5% 4 7% 29%	2137
April	1st to 10th	Night	15% 9% 3 7% 4 2 4 4 6% 6% 39%	1800
	11th to 20th	Night	18% 7% 3 6% 6% 3 5% 4 4 6% 38%	1775
	21st to end	Night	18% 6% 2 6% 4 2 3 5% 4 7% 42%	1715
May	1st to 10th	Night	17% 6% 3 6% 5% 3 5% 5% 6% 6% 39%	1553
	11th to 20th	Night	15% 6% 3 6% 5% 2 5% 4 5% 8% 40%	1416
	21st to end	Night	13% 6% 3 5% 5% 2 4 5% 6% 7% 44%	1551
June	1st to 10th	Night	8% 3 2 4 5% 3 5% 6% 6% 10% 46%	1440
	11th to 20th	Night	10% 5% 2 5% 4 4 5% 5% 7% 8% 45%	1440
	21st to end	Night	11% 4 2 4 4 2 4 4 5% 8% 51%	1440
July	1st to 10th	Night	5% 5% 1 3 4 3 5% 5% 5% 8% 56%	1440
	11th to 20th	Night	5% 3 2 3 3 2 4 5% 5% 10% 58%	1440
	21st to end	Night	5% 3 1 4 3 3 4 4 7% 9% 57%	1653
August	1st to 10th	Night	5% 3 2 4 5% 3 4 5% 7% 9% 51%	1611
	11th to 20th	Night	10% 4 3 4 3 2 3 4 5% 8% 54%	1600
	21st to end	Night	9% 4 2 5% 4 1 4 3 5% 7% 56%	1966
September	1st to 10th	Night	11% 4 2 6% 4 2 3 4 4 6% 54%	1800
	11th to 20th	Night	13% 5% 2 4 4 2 3 4 4 7% 55%	1800
	21st to end	Night	10% 4 2 3 4 2 3 4 4 7% 56%	2053
October	1st to 10th	Night	13% 5% 2 4 5% 3 3 4 4 7% 50%	2160
	11th to 20th	Night	17% 6% 3 6% 4 3 4 5% 4 6% 45%	2160
	21st to end	Night	17% 9% 3 5% 4 3 3 4 6% 6% 40%	2380
November	1st to 10th	Night	12% 7% 2 5% 4 2 4 3 5% 6% 50%	2406
	11th to 20th	Night	13% 9% 4 8% 6% 2 4 4 5% 6% 38%	2650
	21st to end	Night	15% 9% 4 6% 5% 3 4 4 5% 5% 41%	2660
December	1st to 10th	Night	11% 10% 4 9% 7% 4 5% 5% 6% 6% 31%	2660
	11th to 20th	Night	14% 11% 4 7% 8% 4 5% 4 5% 7% 32%	3279
	21st to end	Night	21% 16% 5% 11% 7% 3 4 4 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	67% 6% 11% 10% 5%	2528
	11th to 20th	Day	60% 4 12% 16% 7%	2635
	21st to end	Day	69% 5% 11% 11% 3	3135
February	1st to 10th	Day	55% 5% 14% 17% 8% 1	1710
	11th to 20th	Day	51% 5% 13% 22% 8% 1	1619
	21st to end	Day	55% 5% 11% 17% 9% 2	1453
March	1st to 10th	Day	52% 6% 15% 19% 7% 1	1916
	11th to 20th	Day	48% 6% 13% 23% 9% 1	1980
	21st to end	Day	57% 6% 11% 19% 6% 1	2218
April	1st to 10th	Day	54% 6% 12% 20% 7% 1	2160
	11th to 20th	Day	51% 5% 11% 20% 11% 1	2134
	21st to end	Day	51% 6% 11% 20% 10% 1	2241
May	1st to 10th	Day	51% 8% 15% 19% 7% 1	2404
	11th to 20th	Day	48% 5% 12% 23% 10% 1	2483
	21st to end	Day	46% 8% 12% 20% 13% 2	2725
June	1st to 10th	Day	36% 7% 16% 26% 14% 1	2520
	11th to 20th	Day	37% 7% 13% 22% 19% 2	2520
	21st to end	Day	40% 10% 13% 22% 13% 1	2520
July	1st to 10th	Day	31% 8% 15% 31% 13% 2	2451
	11th to 20th	Day	31% 9% 16% 25% 16% 2	2445
	21st to end	Day	28% 9% 19% 27% 15% 2	2514
August	1st to 10th	Day	35% 9% 14% 28% 11% 2	2314
	11th to 20th	Day	37% 8% 14% 27% 14% 1	2301
	21st to end	Day	33% 7% 10% 28% 20% 2	2390
September	1st to 10th	Day	34% 7% 13% 25% 19% 3	2160
	11th to 20th	Day	33% 7% 13% 33% 14%	2160
	21st to end	Day	37% 6% 12% 28% 16% 1	1883
October	1st to 10th	Day	40% 6% 12% 26% 16% 1	1800
	11th to 20th	Day	44% 4 13% 23% 14% 1	1800
	21st to end	Day	45% 5% 13% 23% 13% 1	1975
November	1st to 10th	Day	38% 6% 13% 25% 15% 3	1672
	11th to 20th	Day	51% 5% 14% 20% 10% 1	1525
	21st to end	Day	47% 5% 16% 23% 8% 1	1520
December	1st to 10th	Day	56% 6% 13% 16% 8% 2	1520
	11th to 20th	Day	55% 4 18% 15% 8% 1	1915
	21st to end	Day	71% 4 9% 11% 4	2783
January	1st to 10th	Night	62% 5% 12% 14% 7%	4428
	11th to 20th	Night	58% 5% 12% 17% 8%	4330
	21st to end	Night	65% 5% 10% 14% 5% 1	4532
February	1st to 10th	Night	54% 5% 11% 18% 11% 1	2470
	11th to 20th	Night	44% 6% 13% 24% 12% 2	2333
	21st to end	Night	49% 5% 11% 19% 13% 2	1803
March	1st to 10th	Night	46% 5% 13% 27% 9% 1	2060
	11th to 20th	Night	44% 6% 14% 21% 14% 1	1980
	21st to end	Night	56% 5% 13% 17% 8% 1	2137
April	1st to 10th	Night	45% 5% 12% 22% 13% 2	1800
	11th to 20th	Night	47% 5% 10% 21% 15% 3	1775
	21st to end	Night	42% 5% 12% 26% 13% 2	1715
May	1st to 10th	Night	44% 8% 12% 21% 14% 1	1553
	11th to 20th	Night	41% 8% 13% 24% 12% 1	1417
	21st to end	Night	38% 8% 13% 24% 15% 3	1552
June	1st to 10th	Night	30% 9% 17% 27% 15% 3	1440
	11th to 20th	Night	34% 8% 13% 19% 21% 5%	1440
	21st to end	Night	31% 7% 14% 28% 16% 3	1440
July	1st to 10th	Night	25% 8% 15% 32% 18% 3	1400
	11th to 20th	Night	22% 8% 18% 30% 18% 4	1392
	21st to end	Night	22% 8% 17% 30% 20% 3	1561
August	1st to 10th	Night	27% 7% 17% 30% 16% 2	1601
	11th to 20th	Night	29% 6% 15% 31% 17% 2	1600
	21st to end	Night	28% 6% 13% 26% 22% 5%	1966
September	1st to 10th	Night	31% 7% 9% 27% 24% 2	1800
	11th to 20th	Night	30% 5% 11% 34% 19% 1	1800
	21st to end	Night	29% 5% 11% 31% 22% 2	2053
October	1st to 10th	Night	34% 6% 11% 25% 21% 2	2160
	11th to 20th	Night	41% 5% 12% 23% 17% 2	2160
	21st to end	Night	44% 6% 12% 22% 15% 2	2380
November	1st to 10th	Night	36% 5% 14% 25% 18% 3	2406
	11th to 20th	Night	47% 5% 13% 23% 11% 1	2650
	21st to end	Night	45% 5% 13% 27% 9% 1	2660
December	1st to 10th	Night	52% 6% 14% 20% 8%	2660
	11th to 20th	Night	51% 6% 15% 21% 5% 1	3281
	21st to end	Night	67% 6% 9% 13% 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	17% 15% 35% 22% 9% 2	270
	11th to 20th	Day	23% 9% 39% 23% 5% 1	270
	21st to end	Day	19% 11% 39% 23% 7% 1	297
February	1st to 10th	Day	16% 16% 37% 26% 3 1	270
	11th to 20th	Day	18% 19% 33% 21% 8%	252
	21st to end	Day	22% 16% 36% 23% 4	198
March	1st to 10th	Day	15% 16% 47% 15% 6% 1	240
	11th to 20th	Day	22% 15% 31% 23% 8% 1	240
	21st to end	Day	32% 13% 31% 17% 5% 1	304
April	1st to 10th	Day	27% 15% 33% 20% 5% 1	420
	11th to 20th	Day	24% 19% 28% 21% 8% 1	412
	21st to end	Day	24% 14% 32% 20% 8% 2	501
May	1st to 10th	Day	23% 13% 32% 22% 8% 2	603
	11th to 20th	Day	22% 14% 27% 23% 10% 4	625
	21st to end	Day	16% 8% 29% 26% 17% 4	679
June	1st to 10th	Day	7% 7% 27% 35% 20% 4	630
	11th to 20th	Day	13% 6% 29% 35% 15% 3	630
	21st to end	Day	10% 7% 33% 29% 15% 5%	630
July	1st to 10th	Day	10% 3 18% 34% 24% 12%	621
	11th to 20th	Day	8% 4 25% 36% 22% 6%	618
	21st to end	Day	6% 2 27% 37% 22% 6%	684
August	1st to 10th	Day	8% 2 23% 33% 25% 8%	626
	11th to 20th	Day	13% 5% 17% 33% 25% 8%	615
	21st to end	Day	10% 5% 22% 36% 21% 6%	509
September	1st to 10th	Day	14% 7% 24% 28% 20% 6%	450
	11th to 20th	Day	8% 5% 28% 32% 22% 5%	450
	21st to end	Day	16% 11% 29% 27% 12% 4	288
October	1st to 10th	Day	20% 8% 29% 24% 16% 4	270
	11th to 20th	Day	23% 16% 38% 16% 7% 1	270
	21st to end	Day	25% 15% 32% 19% 7% 2	297
November	1st to 10th	Day	16% 13% 40% 22% 6% 3	270
	11th to 20th	Day	16% 23% 31% 21% 8% 1	270
	21st to end	Day	22% 13% 39% 22% 4	270
December	1st to 10th	Day	14% 12% 43% 21% 9% 1	270
	11th to 20th	Day	17% 11% 37% 23% 10% 1	270
	21st to end	Day	25% 17% 39% 15% 3	297
January	1st to 10th	Night	13% 13% 36% 29% 9%	950
	11th to 20th	Night	17% 11% 34% 31% 6%	950
	21st to end	Night	19% 11% 35% 29% 6%	1045
February	1st to 10th	Night	16% 11% 36% 31% 6% 1	950
	11th to 20th	Night	16% 11% 38% 28% 5% 1	902
	21st to end	Night	18% 13% 37% 25% 6% 1	619
March	1st to 10th	Night	20% 13% 33% 26% 7% 1	620
	11th to 20th	Night	16% 9% 36% 29% 9%	540
	21st to end	Night	23% 9% 37% 23% 6% 2	594
April	1st to 10th	Night	19% 12% 41% 24% 4	540
	11th to 20th	Night	22% 11% 32% 28% 8% 1	533
	21st to end	Night	21% 8% 34% 29% 7% 1	540
May	1st to 10th	Night	19% 8% 33% 29% 9% 1	540
	11th to 20th	Night	17% 8% 31% 34% 9% 1	531
	21st to end	Night	17% 6% 30% 32% 15% 1	584
June	1st to 10th	Night	10% 4 29% 41% 16% 1	540
	11th to 20th	Night	11% 4 29% 44% 12%	540
	21st to end	Night	11% 5% 28% 38% 18% 1	540
July	1st to 10th	Night	6% 2 14% 45% 30% 3	525
	11th to 20th	Night	5% 1 22% 44% 25% 2	522
	21st to end	Night	4 3 16% 53% 21% 3	591
August	1st to 10th	Night	5% 2 16% 48% 27% 1	537
	11th to 20th	Night	10% 4 18% 37% 27% 4	534
	21st to end	Night	10% 3 20% 40% 24% 2	594
September	1st to 10th	Night	12% 5% 19% 41% 19% 4	540
	11th to 20th	Night	14% 4 21% 38% 21% 2	540
	21st to end	Night	12% 8% 28% 35% 16% 1	636
October	1st to 10th	Night	15% 6% 33% 32% 14% 1	720
	11th to 20th	Night	20% 11% 30% 31% 7%	720
	21st to end	Night	21% 12% 31% 28% 8%	792
November	1st to 10th	Night	14% 9% 40% 30% 7% 1	740
	11th to 20th	Night	16% 15% 40% 24% 6%	940
	21st to end	Night	17% 12% 36% 26% 8%	950
December	1st to 10th	Night	17% 11% 40% 25% 6% 1	950
	11th to 20th	Night	23% 7% 33% 29% 7% 1	950
	21st to end	Night	24% 12% 35% 22% 6%	1045

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