Great Hall, MU
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Great Hall, MU clear sky chart from 2005-11-06 to 2025-12-18.

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	16% 7% 2 6% 4 4 4 4 5% 7% 41%	127097
	Night	17% 8% 2 6% 4 4 4 3 5% 6% 43%	123921
Transparency	Day	41% 6% 12% 23% 16% 2	130637
	Night	41% 5% 11% 23% 17% 3	128468
Seeing	Day	18% 4 19% 33% 22% 5%	16470
	Night	19% 6% 26% 31% 15% 2	25666

By Month

Percentage Cloud Cover NE (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% 6% 2 3 3 2 3 2 4 6% 54%	3597
	11th to 20th	Day	14% 8% 2 5% 4 4 4 3 4 5% 46%	3570
	21st to end	Day	18% 10% 3 7% 4 4 4 2 3 5% 40%	4351
February	1st to 10th	Day	16% 9% 3 6% 4 4 4 3 5% 6% 41%	1830
	11th to 20th	Day	16% 9% 2 6% 4 3 4 3 5% 6% 43%	1948
	21st to end	Day	17% 8% 3 6% 4 4 3 4 5% 5% 41%	1650
March	1st to 10th	Day	21% 6% 2 4 2 3 3 2 4 5% 47%	4476
	11th to 20th	Day	11% 10% 3 6% 4 4 4 3 4 7% 43%	4768
	21st to end	Day	18% 6% 2 5% 4 4 4 3 5% 6% 44%	5924
April	1st to 10th	Day	18% 7% 2 6% 4 4 3 3 6% 7% 40%	2400
	11th to 20th	Day	16% 5% 2 5% 4 4 5% 4 5% 8% 41%	2374
	21st to end	Day	17% 6% 2 5% 4 4 4 5% 6% 8% 40%	2410
May	1st to 10th	Day	24% 9% 2 7% 4 4 5% 4 6% 7% 27%	5886
	11th to 20th	Day	24% 8% 3 5% 3 3 3 3 4 6% 37%	6212
	21st to end	Day	20% 6% 2 6% 4 4 4 3 5% 8% 37%	6949
June	1st to 10th	Day	15% 5% 2 5% 4 4 5% 4 8% 9% 38%	2800
	11th to 20th	Day	14% 6% 2 5% 4 4 5% 4 7% 9% 40%	2800
	21st to end	Day	10% 5% 2 5% 4 5% 5% 5% 7% 10% 42%	2800
July	1st to 10th	Day	8% 6% 2 7% 6% 7% 6% 4 6% 10% 37%	6360
	11th to 20th	Day	10% 8% 3 8% 5% 6% 7% 5% 8% 10% 31%	6360
	21st to end	Day	11% 6% 2 6% 4 4 5% 4 7% 9% 41%	6926
August	1st to 10th	Day	17% 5% 3 7% 5% 4 5% 4 7% 8% 35%	4223
	11th to 20th	Day	12% 6% 3 6% 4 5% 4 4 6% 8% 43%	3850
	21st to end	Day	9% 4 2 5% 3 3 4 4 7% 10% 49%	4312
September	1st to 10th	Day	14% 5% 2 6% 3 3 3 3 6% 7% 48%	2400
	11th to 20th	Day	12% 5% 2 4 3 3 4 3 5% 7% 51%	2310
	21st to end	Day	18% 7% 2 7% 4 4 5% 4 5% 6% 39%	2200
October	1st to 10th	Day	21% 5% 2 4 3 3 3 3 5% 7% 45%	2100
	11th to 20th	Day	16% 5% 2 5% 3 3 4 3 5% 7% 50%	2000
	21st to end	Day	17% 6% 2 5% 3 3 3 3 5% 7% 45%	2050
November	1st to 10th	Day	13% 6% 2 4 4 3 3 3 4 6% 52%	1851
	11th to 20th	Day	15% 6% 1 5% 4 3 4 4 5% 5% 48%	1890
	21st to end	Day	17% 6% 2 4 3 4 4 4 6% 6% 46%	1838
December	1st to 10th	Day	14% 6% 3 5% 3 3 4 4 6% 6% 46%	2680
	11th to 20th	Day	22% 9% 1 4 3 2 2 2 3 5% 47%	3042
	21st to end	Day	15% 7% 3 6% 4 5% 5% 4 4 7% 40%	3960
January	1st to 10th	Night	13% 6% 2 4 3 3 3 3 4 6% 52%	6349
	11th to 20th	Night	15% 8% 2 5% 3 3 3 3 4 4 50%	6315
	21st to end	Night	18% 10% 2 5% 3 3 4 3 5% 6% 40%	6600
February	1st to 10th	Night	17% 10% 2 5% 4 3 3 3 5% 6% 41%	2568
	11th to 20th	Night	18% 9% 2 6% 4 4 4 3 3 6% 42%	2338
	21st to end	Night	19% 8% 2 4 3 3 4 3 4 6% 42%	1980
March	1st to 10th	Night	18% 9% 3 6% 3 2 2 2 4 6% 46%	5364
	11th to 20th	Night	13% 13% 3 5% 3 3 3 2 4 5% 45%	5175
	21st to end	Night	19% 8% 2 7% 4 4 3 3 5% 5% 40%	4993
April	1st to 10th	Night	18% 8% 3 9% 3 4 4 3 4 6% 39%	2000
	11th to 20th	Night	17% 9% 2 6% 3 3 4 3 5% 7% 41%	1975
	21st to end	Night	18% 6% 2 5% 4 3 4 3 5% 8% 42%	1989
May	1st to 10th	Night	24% 9% 3 8% 5% 4 4 4 5% 8% 27%	4054
	11th to 20th	Night	25% 8% 3 6% 3 3 4 3 4 6% 34%	3723
	21st to end	Night	22% 8% 2 6% 3 4 4 4 5% 8% 34%	3926
June	1st to 10th	Night	17% 7% 2 5% 4 4 4 4 5% 8% 41%	1600
	11th to 20th	Night	15% 7% 2 5% 5% 4 5% 4 6% 9% 39%	1600
	21st to end	Night	10% 6% 3 6% 5% 5% 6% 4 7% 10% 40%	1600
July	1st to 10th	Night	8% 7% 3 9% 7% 6% 6% 5% 6% 9% 35%	3600
	11th to 20th	Night	12% 8% 3 8% 6% 5% 5% 5% 6% 10% 33%	3600
	21st to end	Night	13% 5% 2 7% 4 4 4 4 6% 8% 42%	3926
August	1st to 10th	Night	21% 7% 3 6% 4 4 5% 4 6% 8% 32%	2889
	11th to 20th	Night	12% 7% 3 7% 4 4 5% 4 6% 7% 41%	3197
	21st to end	Night	9% 5% 2 5% 4 3 4 3 5% 7% 53%	3586
September	1st to 10th	Night	14% 6% 2 6% 4 4 4 4 5% 6% 45%	2000
	11th to 20th	Night	13% 5% 2 5% 4 3 4 3 5% 6% 51%	2090
	21st to end	Night	20% 8% 3 6% 3 3 4 2 4 7% 40%	2200
October	1st to 10th	Night	20% 5% 2 5% 3 4 4 3 4 6% 43%	2297
	11th to 20th	Night	16% 4 1 4 4 4 3 3 4 6% 50%	2400
	21st to end	Night	19% 7% 3 6% 3 3 3 2 4 6% 45%	2790
November	1st to 10th	Night	12% 5% 2 5% 4 4 3 3 5% 6% 52%	2667
	11th to 20th	Night	16% 7% 2 5% 4 3 3 3 4 4 49%	2730
	21st to end	Night	14% 5% 2 5% 4 4 4 3 5% 7% 47%	2777
December	1st to 10th	Night	15% 7% 2 5% 3 3 3 3 4 5% 49%	4720
	11th to 20th	Night	24% 7% 2 4 3 2 3 3 4 5% 43%	5307
	21st to end	Night	17% 9% 3 6% 3 3 3 3 5% 5% 41%	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	32% 3 8% 32% 23% 2	3598
	11th to 20th	Day	40% 4 8% 24% 18% 5%	3600
	21st to end	Day	48% 4 9% 23% 13% 1	4351
February	1st to 10th	Day	44% 5% 13% 23% 14% 1	1830
	11th to 20th	Day	43% 4 9% 24% 17% 2	1957
	21st to end	Day	45% 5% 10% 22% 14% 4	1650
March	1st to 10th	Day	40% 3 11% 23% 16% 8%	4479
	11th to 20th	Day	40% 5% 10% 27% 14% 4	4768
	21st to end	Day	41% 5% 11% 15% 23% 5%	5924
April	1st to 10th	Day	43% 5% 11% 20% 16% 5%	2400
	11th to 20th	Day	40% 5% 13% 22% 17% 3	2374
	21st to end	Day	41% 5% 11% 20% 19% 4	2410
May	1st to 10th	Day	54% 8% 14% 14% 9% 1	5897
	11th to 20th	Day	50% 5% 10% 22% 13% 1	6216
	21st to end	Day	45% 5% 11% 23% 15% 1	6949
June	1st to 10th	Day	40% 8% 14% 22% 15% 2	2800
	11th to 20th	Day	39% 8% 14% 24% 12% 2	2800
	21st to end	Day	34% 9% 16% 23% 16% 1	2800
July	1st to 10th	Day	44% 9% 12% 20% 15% 1	6290
	11th to 20th	Day	45% 9% 18% 19% 9% 1	6285
	21st to end	Day	37% 7% 12% 23% 20% 1	6728
August	1st to 10th	Day	44% 8% 16% 23% 9% 1	4209
	11th to 20th	Day	37% 6% 14% 31% 11% 1	3886
	21st to end	Day	29% 6% 13% 30% 20% 2	4312
September	1st to 10th	Day	35% 6% 14% 23% 20% 2	2400
	11th to 20th	Day	32% 5% 12% 26% 24% 2	2310
	21st to end	Day	44% 6% 10% 18% 19% 2	2200
October	1st to 10th	Day	33% 5% 13% 23% 22% 5%	3425
	11th to 20th	Day	25% 4 11% 24% 32% 4	3240
	21st to end	Day	28% 3 15% 27% 24% 3	3288
November	1st to 10th	Day	35% 3 14% 26% 20% 2	1851
	11th to 20th	Day	39% 3 10% 24% 22% 3	1890
	21st to end	Day	39% 5% 13% 30% 12% 2	1838
December	1st to 10th	Day	38% 4 15% 28% 13% 2	2680
	11th to 20th	Day	43% 3 10% 29% 13% 3	3042
	21st to end	Day	43% 7% 11% 21% 16% 2	3960
January	1st to 10th	Night	34% 4 8% 26% 23% 5%	6349
	11th to 20th	Night	39% 3 11% 24% 16% 7%	6360
	21st to end	Night	46% 4 8% 22% 17% 3	6600
February	1st to 10th	Night	44% 4 14% 23% 12% 2	2568
	11th to 20th	Night	45% 4 9% 20% 19% 4	2340
	21st to end	Night	43% 4 8% 24% 17% 4	1980
March	1st to 10th	Night	43% 3 9% 23% 13% 9%	5374
	11th to 20th	Night	42% 4 11% 25% 13% 5%	5176
	21st to end	Night	47% 4 6% 15% 24% 5%	4993
April	1st to 10th	Night	46% 4 9% 19% 17% 4	2000
	11th to 20th	Night	43% 5% 10% 18% 22% 2	1975
	21st to end	Night	41% 5% 9% 20% 21% 5%	1989
May	1st to 10th	Night	55% 6% 12% 15% 9% 2	4060
	11th to 20th	Night	51% 5% 11% 17% 14% 1	3724
	21st to end	Night	47% 7% 11% 21% 12% 2	3927
June	1st to 10th	Night	43% 6% 10% 19% 21% 1	1600
	11th to 20th	Night	40% 8% 14% 26% 12% 1	1600
	21st to end	Night	38% 8% 15% 24% 15% 2	1600
July	1st to 10th	Night	46% 8% 11% 21% 13% 1	3560
	11th to 20th	Night	46% 7% 15% 22% 9% 1	3552
	21st to end	Night	38% 6% 14% 23% 17% 1	3809
August	1st to 10th	Night	49% 8% 18% 16% 9% 1	2879
	11th to 20th	Night	40% 7% 12% 29% 11% 1	3227
	21st to end	Night	30% 6% 11% 32% 20% 2	3586
September	1st to 10th	Night	40% 5% 11% 23% 19% 2	2000
	11th to 20th	Night	33% 4 11% 23% 24% 3	2090
	21st to end	Night	46% 4 8% 22% 19% 2	2200
October	1st to 10th	Night	38% 4 10% 23% 22% 3	3752
	11th to 20th	Night	25% 3 10% 26% 30% 5%	3899
	21st to end	Night	29% 4 11% 29% 23% 4	4502
November	1st to 10th	Night	35% 3 12% 25% 21% 4	2667
	11th to 20th	Night	40% 4 8% 23% 20% 5%	2730
	21st to end	Night	37% 5% 12% 27% 17% 1	2777
December	1st to 10th	Night	38% 4 12% 30% 14% 2	4720
	11th to 20th	Night	45% 3 9% 24% 15% 3	5307
	21st to end	Night	45% 5% 11% 21% 16% 3	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	17% 8% 39% 29% 8% 1	200
	11th to 20th	Day	17% 12% 38% 29% 4 1	200
	21st to end	Day	21% 6% 34% 29% 10% 1	305
February	1st to 10th	Day	24% 5% 28% 38% 6%	330
	11th to 20th	Day	22% 10% 35% 29% 4	496
	21st to end	Day	20% 7% 34% 32% 7%	414
March	1st to 10th	Day	18% 5% 34% 33% 9% 1	500
	11th to 20th	Day	18% 5% 31% 35% 10% 1	500
	21st to end	Day	23% 6% 25% 34% 10% 1	550
April	1st to 10th	Day	20% 5% 29% 36% 9% 1	500
	11th to 20th	Day	18% 4 23% 39% 14% 2	492
	21st to end	Day	20% 4 21% 40% 14% 1	500
May	1st to 10th	Day	25% 3 17% 36% 16% 3	503
	11th to 20th	Day	22% 1 13% 41% 19% 3	527
	21st to end	Day	22% 1 8% 29% 31% 9%	573
June	1st to 10th	Day	18% 2 10% 33% 30% 6%	530
	11th to 20th	Day	16% 1 9% 39% 28% 5%	530
	21st to end	Day	12% 4 7% 35% 34% 7%	530
July	1st to 10th	Day	11% 2 7% 30% 39% 11%	525
	11th to 20th	Day	9% 2 6% 27% 41% 14%	524
	21st to end	Day	11% 2 9% 34% 38% 6%	576
August	1st to 10th	Day	12% 2 4 34% 37% 11%	526
	11th to 20th	Day	13% 3 4 30% 39% 11%	519
	21st to end	Day	11% 2 6% 34% 35% 12%	583
September	1st to 10th	Day	17% 2 12% 30% 26% 13%	530
	11th to 20th	Day	15% 1 7% 32% 33% 12%	530
	21st to end	Day	24% 2 12% 32% 24% 5%	530
October	1st to 10th	Day	24% 2 13% 25% 27% 9%	530
	11th to 20th	Day	17% 4 22% 31% 22% 5%	530
	21st to end	Day	19% 6% 27% 27% 18% 4	500
November	1st to 10th	Day	14% 5% 23% 36% 18% 4	425
	11th to 20th	Day	16% 9% 34% 28% 13%	430
	21st to end	Day	18% 6% 31% 31% 12% 1	378
December	1st to 10th	Day	19% 5% 37% 28% 10% 1	220
	11th to 20th	Day	25% 9% 30% 24% 12%	214
	21st to end	Day	20% 8% 27% 30% 15%	220
January	1st to 10th	Night	20% 11% 40% 24% 5%	800
	11th to 20th	Night	23% 11% 34% 27% 5%	800
	21st to end	Night	20% 10% 43% 23% 3	880
February	1st to 10th	Night	22% 9% 38% 28% 3	800
	11th to 20th	Night	22% 11% 42% 23% 2	783
	21st to end	Night	22% 10% 35% 29% 4	660
March	1st to 10th	Night	19% 7% 40% 27% 8%	800
	11th to 20th	Night	20% 7% 34% 31% 7% 1	800
	21st to end	Night	20% 4 33% 33% 8% 1	880
April	1st to 10th	Night	20% 5% 32% 34% 8% 1	800
	11th to 20th	Night	20% 4 24% 40% 11%	791
	21st to end	Night	20% 3 27% 36% 13% 1	789
May	1st to 10th	Night	25% 4 18% 36% 15% 2	600
	11th to 20th	Night	25% 3 18% 38% 15% 1	464
	21st to end	Night	20% 2 10% 33% 30% 6%	433
June	1st to 10th	Night	20% 2 13% 36% 25% 4	400
	11th to 20th	Night	18% 2 7% 41% 30% 2	400
	21st to end	Night	10% 1 11% 46% 31% 2	400
July	1st to 10th	Night	12% 3 9% 36% 34% 6%	390
	11th to 20th	Night	14% 1 5% 35% 38% 6%	388
	21st to end	Night	11% 1 10% 39% 35% 3	438
August	1st to 10th	Night	13% 1 8% 39% 36% 4	571
	11th to 20th	Night	13% 2 8% 32% 37% 8%	790
	21st to end	Night	13% 2 11% 33% 33% 8%	880
September	1st to 10th	Night	16% 2 15% 33% 27% 8%	800
	11th to 20th	Night	16% 3 11% 32% 30% 8%	800
	21st to end	Night	23% 2 16% 32% 24% 4	800
October	1st to 10th	Night	22% 4 20% 26% 22% 6%	800
	11th to 20th	Night	18% 7% 24% 34% 16% 2	800
	21st to end	Night	23% 4 32% 29% 11% 1	880
November	1st to 10th	Night	15% 6% 31% 31% 15% 2	820
	11th to 20th	Night	20% 8% 33% 27% 11%	840
	21st to end	Night	15% 11% 37% 28% 9% 1	840
December	1st to 10th	Night	24% 10% 35% 22% 8% 1	840
	11th to 20th	Night	22% 8% 36% 29% 4	829
	21st to end	Night	21% 7% 41% 26% 5%	880

Page generated at 2025-12-15 01:13:56. Version ac07

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