Morgan County Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Morgan County Observatory clear sky chart from 2005-11-06 to 2026-01-17.

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% 6% 2 6% 5% 5% 5% 4 6% 8% 39%	127283
	Night	14% 6% 2 6% 4 4 5% 4 6% 8% 41%	124417
Transparency	Day	26% 39% 8% 15% 10% 2	130881
	Night	26% 39% 8% 16% 10% 2	128888
Seeing	Day	23% 13% 25% 21% 13% 5%	16368
	Night	20% 12% 25% 29% 13% 1	26035

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	13% 7% 2 8% 6% 5% 5% 4 6% 6% 37%	3930
	11th to 20th	Day	12% 9% 3 9% 6% 5% 5% 4 6% 7% 34%	4114
	21st to end	Day	14% 7% 3 7% 5% 5% 5% 4 6% 6% 38%	4466
February	1st to 10th	Day	14% 11% 4 7% 4 4 4 4 5% 6% 37%	1800
	11th to 20th	Day	15% 9% 2 7% 7% 5% 4 4 5% 6% 37%	1753
	21st to end	Day	15% 9% 4 8% 5% 4 4 3 5% 5% 38%	1663
March	1st to 10th	Day	17% 8% 3 6% 4 4 4 3 4 6% 40%	4935
	11th to 20th	Day	10% 7% 2 6% 4 5% 4 4 6% 8% 45%	4980
	21st to end	Day	13% 8% 3 7% 5% 5% 5% 4 6% 6% 38%	5465
April	1st to 10th	Day	14% 9% 2 7% 6% 5% 5% 3 5% 8% 36%	2390
	11th to 20th	Day	13% 7% 3 5% 5% 4 5% 4 5% 7% 42%	2374
	21st to end	Day	18% 6% 2 6% 4 4 5% 3 5% 5% 40%	2456
May	1st to 10th	Day	18% 7% 3 7% 5% 5% 5% 5% 7% 8% 30%	5862
	11th to 20th	Day	23% 7% 2 6% 4 4 5% 4 6% 9% 30%	5998
	21st to end	Day	15% 6% 2 6% 5% 5% 5% 4 6% 9% 36%	6934
June	1st to 10th	Day	13% 6% 1 5% 4 4 5% 5% 7% 10% 41%	2800
	11th to 20th	Day	11% 6% 2 7% 5% 5% 6% 4 8% 9% 38%	2800
	21st to end	Day	10% 4 2 5% 5% 5% 5% 4 7% 11% 43%	2800
July	1st to 10th	Day	5% 4 2 7% 5% 5% 6% 5% 8% 10% 45%	6360
	11th to 20th	Day	7% 5% 2 7% 5% 6% 6% 5% 9% 12% 34%	5995
	21st to end	Day	8% 6% 3 6% 5% 5% 5% 4 7% 9% 40%	6424
August	1st to 10th	Day	17% 5% 2 6% 5% 5% 5% 5% 6% 9% 34%	4234
	11th to 20th	Day	9% 5% 2 7% 4 5% 6% 5% 7% 9% 41%	4114
	21st to end	Day	12% 4 2 5% 4 4 5% 4 6% 7% 48%	4312
September	1st to 10th	Day	15% 6% 2 5% 3 4 4 4 5% 7% 45%	2400
	11th to 20th	Day	12% 5% 2 6% 4 3 4 3 5% 8% 47%	2352
	21st to end	Day	21% 8% 2 6% 4 4 4 4 5% 6% 37%	2112
October	1st to 10th	Day	15% 6% 2 5% 3 4 4 3 5% 7% 47%	2000
	11th to 20th	Day	15% 5% 1 5% 3 4 4 4 5% 7% 46%	2000
	21st to end	Day	14% 5% 2 5% 4 4 3 4 6% 6% 47%	2200
November	1st to 10th	Day	10% 5% 2 4 3 3 4 3 5% 7% 52%	2013
	11th to 20th	Day	15% 6% 2 5% 4 3 4 3 6% 7% 44%	1769
	21st to end	Day	15% 6% 2 5% 5% 5% 5% 4 6% 7% 40%	1680
December	1st to 10th	Day	13% 6% 2 6% 5% 5% 5% 5% 7% 7% 40%	2680
	11th to 20th	Day	19% 9% 3 6% 4 4 4 3 5% 6% 37%	3070
	21st to end	Day	16% 8% 4 7% 5% 5% 5% 5% 8% 8% 29%	4048
January	1st to 10th	Night	10% 7% 3 8% 5% 5% 5% 4 6% 8% 41%	6233
	11th to 20th	Night	13% 8% 3 6% 4 4 4 4 5% 7% 42%	5979
	21st to end	Night	14% 8% 3 6% 4 4 4 4 5% 6% 42%	6490
February	1st to 10th	Night	14% 8% 3 6% 5% 4 4 4 7% 7% 39%	2600
	11th to 20th	Night	16% 9% 3 7% 5% 5% 5% 4 6% 6% 36%	2533
	21st to end	Night	15% 10% 3 7% 5% 4 4 4 5% 7% 36%	1965
March	1st to 10th	Night	15% 7% 2 5% 4 4 4 3 4 6% 45%	4918
	11th to 20th	Night	9% 5% 2 6% 5% 5% 4 4 6% 7% 47%	4980
	21st to end	Night	10% 6% 3 7% 4 5% 5% 4 6% 7% 44%	5467
April	1st to 10th	Night	17% 8% 3 5% 5% 5% 4 5% 5% 6% 37%	2010
	11th to 20th	Night	13% 6% 3 6% 5% 4 5% 4 6% 8% 41%	1975
	21st to end	Night	17% 5% 2 5% 3 4 4 4 6% 7% 43%	1960
May	1st to 10th	Night	22% 8% 3 8% 5% 5% 5% 4 6% 8% 28%	4033
	11th to 20th	Night	27% 7% 2 5% 4 4 4 4 5% 8% 31%	3895
	21st to end	Night	17% 6% 2 6% 4 4 5% 4 7% 9% 35%	3920
June	1st to 10th	Night	11% 4 2 5% 3 5% 4 5% 7% 8% 46%	1600
	11th to 20th	Night	12% 5% 3 5% 5% 4 6% 4 6% 10% 41%	1600
	21st to end	Night	9% 5% 2 5% 4 5% 4 5% 7% 12% 43%	1600
July	1st to 10th	Night	7% 6% 2 7% 5% 6% 6% 5% 6% 9% 42%	3598
	11th to 20th	Night	6% 6% 4 10% 7% 7% 7% 6% 8% 10% 30%	3957
	21st to end	Night	8% 5% 2 6% 5% 5% 6% 5% 8% 10% 40%	4427
August	1st to 10th	Night	16% 5% 3 7% 5% 5% 6% 4 7% 9% 34%	2915
	11th to 20th	Night	10% 5% 2 6% 4 5% 4 4 6% 8% 44%	2900
	21st to end	Night	14% 4 1 4 4 4 4 4 6% 8% 46%	3586
September	1st to 10th	Night	15% 5% 2 5% 4 4 4 4 5% 7% 47%	2000
	11th to 20th	Night	11% 7% 3 6% 3 4 3 3 4 8% 51%	2044
	21st to end	Night	22% 5% 2 6% 4 5% 4 3 4 6% 39%	2287
October	1st to 10th	Night	19% 6% 2 4 3 3 3 3 4 6% 47%	2400
	11th to 20th	Night	14% 4 1 5% 3 3 4 3 5% 6% 50%	2400
	21st to end	Night	15% 5% 2 4 3 3 3 3 5% 6% 50%	2640
November	1st to 10th	Night	10% 6% 1 5% 4 3 4 3 5% 7% 52%	2503
	11th to 20th	Night	14% 7% 2 5% 4 4 3 3 4 7% 45%	2847
	21st to end	Night	13% 6% 3 7% 5% 5% 5% 4 6% 7% 41%	2940
December	1st to 10th	Night	10% 5% 2 5% 4 5% 5% 4 6% 9% 46%	4720
	11th to 20th	Night	18% 8% 2 6% 4 4 5% 4 6% 7% 35%	5345
	21st to end	Night	16% 7% 3 7% 5% 5% 6% 5% 7% 9% 29%	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	34% 27% 7% 17% 11% 4	3931
	11th to 20th	Day	35% 27% 7% 12% 15% 4	4114
	21st to end	Day	31% 30% 8% 18% 10% 2	4466
February	1st to 10th	Day	20% 62% 5% 8% 4 1	1800
	11th to 20th	Day	19% 61% 4 8% 7% 1	1762
	21st to end	Day	18% 62% 5% 9% 6% 1	1663
March	1st to 10th	Day	35% 30% 6% 14% 9% 6%	4935
	11th to 20th	Day	23% 30% 8% 22% 12% 4	4980
	21st to end	Day	31% 31% 7% 14% 14% 3	5465
April	1st to 10th	Day	21% 62% 4 6% 6% 1	2390
	11th to 20th	Day	15% 63% 5% 11% 6% 1	2374
	21st to end	Day	18% 62% 4 10% 6%	2456
May	1st to 10th	Day	36% 32% 9% 15% 6% 2	5897
	11th to 20th	Day	36% 32% 7% 20% 4	6002
	21st to end	Day	30% 32% 10% 15% 11% 1	6949
June	1st to 10th	Day	16% 63% 4 10% 7%	2800
	11th to 20th	Day	16% 64% 4 10% 6% 1	2800
	21st to end	Day	14% 62% 6% 11% 8%	2800
July	1st to 10th	Day	25% 31% 11% 19% 12% 2	6290
	11th to 20th	Day	31% 31% 14% 18% 6%	5923
	21st to end	Day	27% 28% 8% 19% 17% 1	6240
August	1st to 10th	Day	31% 39% 9% 17% 5%	4221
	11th to 20th	Day	22% 39% 9% 21% 9%	4153
	21st to end	Day	21% 38% 9% 20% 13%	4312
September	1st to 10th	Day	16% 58% 6% 10% 9% 1	2400
	11th to 20th	Day	15% 57% 4 13% 9% 1	2352
	21st to end	Day	24% 58% 5% 8% 5%	2112
October	1st to 10th	Day	22% 36% 5% 15% 20% 4	3260
	11th to 20th	Day	14% 37% 8% 20% 14% 7%	3240
	21st to end	Day	13% 35% 9% 21% 20% 2	3538
November	1st to 10th	Day	17% 54% 7% 11% 10% 2	2013
	11th to 20th	Day	15% 54% 6% 11% 13% 1	1769
	21st to end	Day	19% 55% 6% 14% 5% 1	1680
December	1st to 10th	Day	27% 36% 11% 18% 5% 4	2680
	11th to 20th	Day	34% 31% 11% 16% 6% 1	3066
	21st to end	Day	37% 30% 13% 10% 10% 1	4048
January	1st to 10th	Night	28% 27% 7% 21% 15% 2	6233
	11th to 20th	Night	29% 27% 8% 17% 13% 5%	5979
	21st to end	Night	29% 30% 8% 20% 12% 2	6490
February	1st to 10th	Night	17% 62% 7% 11% 3 1	2600
	11th to 20th	Night	19% 60% 4 9% 7% 1	2535
	21st to end	Night	17% 62% 5% 8% 5% 3	1965
March	1st to 10th	Night	30% 30% 6% 19% 8% 6%	4918
	11th to 20th	Night	23% 30% 10% 24% 10% 4	4980
	21st to end	Night	26% 31% 9% 16% 15% 3	5467
April	1st to 10th	Night	18% 62% 5% 9% 6%	2010
	11th to 20th	Night	16% 63% 5% 10% 5% 1	1975
	21st to end	Night	15% 63% 4 11% 6% 1	1960
May	1st to 10th	Night	43% 31% 8% 10% 6% 3	4060
	11th to 20th	Night	37% 31% 8% 18% 5%	3896
	21st to end	Night	35% 32% 9% 18% 4 2	3927
June	1st to 10th	Night	16% 63% 4 9% 8% 1	1600
	11th to 20th	Night	16% 63% 4 11% 6%	1600
	21st to end	Night	13% 62% 6% 10% 8%	1600
July	1st to 10th	Night	29% 30% 13% 14% 11% 3	3560
	11th to 20th	Night	37% 31% 12% 13% 7%	3909
	21st to end	Night	29% 28% 8% 19% 15% 1	4297
August	1st to 10th	Night	32% 39% 11% 13% 4	2904
	11th to 20th	Night	23% 39% 8% 19% 10%	2927
	21st to end	Night	21% 37% 9% 22% 11%	3586
September	1st to 10th	Night	16% 58% 6% 11% 8% 1	2000
	11th to 20th	Night	16% 57% 4 13% 10% 1	2044
	21st to end	Night	24% 57% 4 10% 5%	2287
October	1st to 10th	Night	23% 36% 7% 16% 17% 2	3920
	11th to 20th	Night	13% 36% 7% 15% 22% 6%	3899
	21st to end	Night	12% 35% 8% 22% 19% 3	4252
November	1st to 10th	Night	17% 54% 7% 12% 9% 2	2503
	11th to 20th	Night	17% 54% 4 11% 12% 2	2847
	21st to end	Night	19% 55% 6% 12% 7% 1	2940
December	1st to 10th	Night	21% 37% 12% 23% 8% 1	4720
	11th to 20th	Night	34% 31% 9% 15% 9% 2	5348
	21st to end	Night	38% 30% 11% 12% 9%	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	42% 22% 24% 8% 4	278
	11th to 20th	Day	39% 21% 27% 11% 2	318
	21st to end	Day	32% 27% 27% 10% 4	330
February	1st to 10th	Day	34% 25% 28% 10% 3	300
	11th to 20th	Day	45% 22% 27% 5%	300
	21st to end	Day	34% 19% 27% 17% 3	399
March	1st to 10th	Day	33% 21% 25% 18% 4	500
	11th to 20th	Day	30% 24% 25% 15% 5% 2	500
	21st to end	Day	28% 22% 30% 14% 5% 1	550
April	1st to 10th	Day	29% 23% 23% 17% 6% 1	500
	11th to 20th	Day	23% 19% 27% 17% 9% 4	492
	21st to end	Day	31% 15% 27% 17% 9% 2	500
May	1st to 10th	Day	27% 15% 29% 15% 10% 3	503
	11th to 20th	Day	26% 15% 25% 17% 12% 4	527
	21st to end	Day	20% 11% 24% 22% 16% 8%	573
June	1st to 10th	Day	16% 11% 30% 19% 18% 6%	530
	11th to 20th	Day	16% 9% 29% 25% 16% 5%	530
	21st to end	Day	13% 9% 27% 28% 15% 8%	530
July	1st to 10th	Day	13% 5% 20% 30% 22% 11%	525
	11th to 20th	Day	6% 4 24% 28% 25% 12%	524
	21st to end	Day	15% 5% 19% 34% 19% 9%	576
August	1st to 10th	Day	16% 5% 20% 25% 21% 12%	526
	11th to 20th	Day	13% 3 22% 30% 22% 10%	519
	21st to end	Day	10% 4 22% 28% 24% 12%	583
September	1st to 10th	Day	18% 9% 18% 24% 22% 10%	530
	11th to 20th	Day	16% 5% 17% 28% 26% 9%	530
	21st to end	Day	29% 9% 22% 21% 15% 4	530
October	1st to 10th	Day	22% 6% 20% 29% 18% 6%	530
	11th to 20th	Day	22% 13% 25% 23% 14% 3	530
	21st to end	Day	20% 15% 31% 21% 11% 2	583
November	1st to 10th	Day	20% 12% 29% 23% 13% 3	511
	11th to 20th	Day	25% 17% 29% 21% 8% 1	309
	21st to end	Day	29% 19% 30% 15% 7% 1	220
December	1st to 10th	Day	31% 22% 29% 14% 4	220
	11th to 20th	Day	30% 20% 26% 20% 5%	220
	21st to end	Day	28% 19% 29% 15% 8%	242
January	1st to 10th	Night	22% 21% 32% 21% 3	840
	11th to 20th	Night	26% 16% 31% 25% 2	825
	21st to end	Night	22% 21% 32% 22% 2	880
February	1st to 10th	Night	23% 19% 30% 26% 2	800
	11th to 20th	Night	28% 24% 29% 17% 2	783
	21st to end	Night	28% 17% 32% 20% 2	660
March	1st to 10th	Night	24% 18% 33% 21% 4	800
	11th to 20th	Night	27% 19% 27% 22% 5%	800
	21st to end	Night	21% 17% 36% 21% 5% 1	880
April	1st to 10th	Night	26% 18% 30% 21% 6%	800
	11th to 20th	Night	19% 14% 32% 26% 9% 1	791
	21st to end	Night	21% 13% 26% 32% 7%	760
May	1st to 10th	Night	24% 7% 23% 32% 14% 2	600
	11th to 20th	Night	24% 7% 24% 31% 13%	532
	21st to end	Night	16% 5% 21% 35% 20% 2	433
June	1st to 10th	Night	12% 5% 25% 34% 25%	400
	11th to 20th	Night	13% 6% 18% 40% 21% 2	400
	21st to end	Night	10% 2 24% 42% 21% 1	400
July	1st to 10th	Night	12% 4 14% 37% 31% 3	390
	11th to 20th	Night	7% 4 10% 41% 34% 5%	537
	21st to end	Night	10% 2 16% 39% 31% 3	657
August	1st to 10th	Night	13% 2 13% 41% 29% 3	597
	11th to 20th	Night	12% 2 12% 40% 30% 5%	606
	21st to end	Night	14% 3 14% 36% 29% 4	880
September	1st to 10th	Night	17% 3 16% 34% 27% 4	800
	11th to 20th	Night	14% 4 15% 34% 29% 4	800
	21st to end	Night	23% 6% 18% 32% 19% 2	800
October	1st to 10th	Night	22% 6% 18% 30% 21% 3	800
	11th to 20th	Night	17% 12% 24% 33% 13% 1	800
	21st to end	Night	20% 12% 26% 31% 11%	880
November	1st to 10th	Night	16% 10% 29% 33% 11% 1	820
	11th to 20th	Night	22% 17% 24% 29% 8% 1	840
	21st to end	Night	20% 17% 27% 29% 6%	840
December	1st to 10th	Night	21% 18% 30% 25% 6%	840
	11th to 20th	Night	23% 14% 30% 29% 3	840
	21st to end	Night	20% 17% 27% 33% 3	924

Page generated at 2026-01-14 01:14:25. Version ac07

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