Graceland University Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Graceland University Observatory clear sky chart from 2005-11-06 to 2024-11-28.

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 7% 4 4 4 4 6% 7% 41%	101479
	Night	11% 8% 3 7% 4 4 4 3 5% 6% 45%	98119
Transparency	Day	23% 45% 7% 14% 9% 1	105122
	Night	23% 45% 6% 14% 11% 1	102616
Seeing	Day	15% 9% 29% 28% 15% 4	15850
	Night	15% 9% 33% 31% 12% 1	25713

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	12% 11% 5% 13% 6% 6% 5% 4 5% 7% 27%	2666
	11th to 20th	Day	10% 13% 5% 10% 6% 5% 8% 4 4 6% 30%	2850
	21st to end	Day	13% 15% 7% 16% 5% 5% 5% 3 4 5% 22%	3135
February	1st to 10th	Day	13% 12% 3 10% 8% 5% 5% 3 5% 6% 30%	1710
	11th to 20th	Day	11% 10% 4 8% 5% 5% 4 3 5% 8% 36%	1664
	21st to end	Day	14% 8% 2 7% 6% 4 4 3 6% 7% 39%	1556
March	1st to 10th	Day	17% 10% 3 7% 3 4 3 3 4 5% 42%	3436
	11th to 20th	Day	11% 8% 3 7% 4 4 4 3 6% 6% 45%	3480
	21st to end	Day	20% 15% 6% 8% 4 4 4 3 5% 7% 24%	3814
April	1st to 10th	Day	16% 9% 4 5% 5% 3 3 4 5% 7% 39%	2245
	11th to 20th	Day	15% 9% 2 7% 5% 4 4 3 5% 6% 38%	2254
	21st to end	Day	21% 8% 3 7% 4 4 3 3 4 6% 36%	2404
May	1st to 10th	Day	16% 7% 3 7% 5% 5% 5% 4 6% 8% 34%	4082
	11th to 20th	Day	15% 7% 3 7% 5% 5% 4 4 5% 7% 37%	4177
	21st to end	Day	13% 7% 2 5% 4 4 4 3 6% 7% 44%	4824
June	1st to 10th	Day	7% 5% 2 6% 4 5% 5% 5% 6% 8% 46%	2660
	11th to 20th	Day	8% 5% 1 5% 4 4 6% 4 7% 10% 46%	2660
	21st to end	Day	8% 5% 2 6% 5% 5% 6% 5% 7% 9% 43%	2660
July	1st to 10th	Day	10% 7% 2 7% 5% 5% 5% 5% 7% 9% 38%	4440
	11th to 20th	Day	6% 3 1 5% 4 3 4 4 6% 8% 54%	4198
	21st to end	Day	5% 3 2 5% 4 5% 6% 4 9% 11% 47%	4465
August	1st to 10th	Day	6% 4 2 5% 4 4 5% 5% 7% 11% 47%	4104
	11th to 20th	Day	13% 6% 2 6% 4 5% 4 4 6% 7% 43%	4041
	21st to end	Day	7% 5% 2 6% 4 4 5% 3 6% 9% 50%	4254
September	1st to 10th	Day	13% 4 2 4 3 3 4 3 4 6% 54%	2280
	11th to 20th	Day	10% 4 2 5% 4 4 4 4 5% 9% 51%	2184
	21st to end	Day	11% 4 1 6% 3 3 3 4 4 8% 52%	2036
October	1st to 10th	Day	14% 6% 2 5% 4 3 3 2 5% 6% 49%	1900
	11th to 20th	Day	13% 7% 2 5% 3 2 3 3 4 5% 52%	1900
	21st to end	Day	13% 8% 3 7% 5% 4 3 3 5% 5% 44%	2090
November	1st to 10th	Day	10% 6% 2 5% 3 3 5% 3 4 7% 51%	1913
	11th to 20th	Day	13% 9% 3 7% 4 2 4 3 5% 7% 44%	1600
	21st to end	Day	16% 11% 3 6% 4 3 3 2 5% 7% 40%	1576
December	1st to 10th	Day	11% 9% 3 8% 5% 5% 4 4 4 8% 39%	1520
	11th to 20th	Day	10% 10% 4 10% 5% 5% 3 4 6% 8% 35%	1918
	21st to end	Day	20% 14% 6% 13% 5% 4 4 3 4 5% 21%	2783
January	1st to 10th	Night	9% 9% 5% 19% 7% 4 4 4 4 5% 30%	4286
	11th to 20th	Night	10% 11% 5% 10% 4 5% 7% 4 7% 5% 30%	4120
	21st to end	Night	14% 15% 6% 12% 5% 4 4 3 4 5% 28%	4532
February	1st to 10th	Night	13% 11% 4 9% 5% 4 4 3 5% 6% 36%	2470
	11th to 20th	Night	11% 10% 4 7% 4 4 4 3 5% 6% 42%	2403
	21st to end	Night	12% 9% 3 7% 4 5% 4 3 4 5% 45%	1913
March	1st to 10th	Night	13% 8% 3 7% 4 4 4 3 4 4 47%	3419
	11th to 20th	Night	12% 8% 2 5% 3 3 3 3 3 5% 53%	3480
	21st to end	Night	18% 11% 5% 12% 5% 4 4 4 5% 6% 27%	3817
April	1st to 10th	Night	12% 6% 2 7% 4 3 3 4 5% 6% 48%	1934
	11th to 20th	Night	15% 7% 3 6% 4 3 5% 3 5% 5% 44%	1875
	21st to end	Night	17% 7% 3 5% 4 4 4 3 4 6% 42%	1772
May	1st to 10th	Night	16% 7% 3 6% 4 4 4 4 6% 7% 40%	2823
	11th to 20th	Night	13% 7% 3 6% 4 4 4 3 4 6% 45%	2710
	21st to end	Night	11% 5% 2 6% 4 4 4 3 5% 7% 47%	2743
June	1st to 10th	Night	6% 4 1 5% 3 3 3 4 7% 9% 54%	1520
	11th to 20th	Night	6% 5% 2 4 3 4 4 4 7% 12% 50%	1520
	21st to end	Night	5% 4 2 4 4 4 5% 4 7% 9% 52%	1520
July	1st to 10th	Night	11% 5% 2 5% 4 4 5% 4 5% 9% 47%	2530
	11th to 20th	Night	3 2 1 4 3 3 4 3 5% 8% 64%	2754
	21st to end	Night	6% 4 2 5% 4 4 5% 4 7% 9% 51%	3098
August	1st to 10th	Night	3 3 1 4 3 4 4 4 6% 9% 59%	2836
	11th to 20th	Night	12% 6% 1 4 3 3 3 3 5% 7% 52%	2798
	21st to end	Night	6% 4 2 4 3 3 4 3 5% 8% 58%	3404
September	1st to 10th	Night	10% 4 1 5% 3 2 3 3 5% 6% 58%	1900
	11th to 20th	Night	10% 5% 2 4 4 3 4 3 5% 7% 54%	1992
	21st to end	Night	8% 4 2 5% 3 3 3 3 5% 7% 57%	2123
October	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 4 5% 53%	2280
	11th to 20th	Night	12% 6% 2 6% 4 3 4 2 3 5% 53%	2280
	21st to end	Night	15% 9% 2 5% 4 3 3 3 3 5% 48%	2508
November	1st to 10th	Night	9% 4 2 5% 3 3 3 3 6% 7% 55%	2377
	11th to 20th	Night	11% 6% 2 6% 4 3 4 3 5% 7% 49%	2800
	21st to end	Night	15% 9% 3 5% 4 3 3 3 5% 6% 44%	2759
December	1st to 10th	Night	11% 10% 3 7% 5% 4 4 3 4 7% 41%	2660
	11th to 20th	Night	11% 9% 3 9% 5% 4 3 3 4 6% 42%	3279
	21st to end	Night	19% 16% 8% 11% 5% 3 3 3 4 4 24%	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	39% 37% 9% 10% 4 1	2667
	11th to 20th	Day	37% 36% 8% 14% 4	2850
	21st to end	Day	43% 39% 6% 8% 3	3135
February	1st to 10th	Day	22% 65% 3 6% 4	1710
	11th to 20th	Day	18% 63% 5% 7% 7%	1673
	21st to end	Day	15% 64% 3 9% 8% 2	1556
March	1st to 10th	Day	28% 41% 5% 12% 14% 1	3436
	11th to 20th	Day	19% 40% 7% 17% 15% 2	3480
	21st to end	Day	38% 41% 11% 8% 2	3814
April	1st to 10th	Day	18% 64% 4 9% 4	2245
	11th to 20th	Day	15% 65% 6% 8% 5%	2254
	21st to end	Day	19% 64% 3 9% 5%	2404
May	1st to 10th	Day	27% 42% 7% 14% 10% 1	4120
	11th to 20th	Day	29% 40% 6% 18% 7%	4181
	21st to end	Day	20% 40% 7% 18% 14% 1	4837
June	1st to 10th	Day	9% 65% 6% 11% 7% 2	2660
	11th to 20th	Day	12% 65% 5% 11% 6% 1	2660
	21st to end	Day	13% 63% 8% 10% 5%	2660
July	1st to 10th	Day	32% 35% 9% 16% 7% 1	4371
	11th to 20th	Day	17% 35% 9% 26% 13% 1	4126
	21st to end	Day	19% 35% 15% 21% 9% 1	4325
August	1st to 10th	Day	20% 36% 10% 23% 11%	4090
	11th to 20th	Day	29% 36% 8% 17% 10%	4080
	21st to end	Day	23% 37% 14% 19% 7% 1	4253
September	1st to 10th	Day	12% 59% 7% 12% 8% 1	2280
	11th to 20th	Day	12% 59% 6% 14% 9%	2184
	21st to end	Day	14% 59% 4 14% 8%	2036
October	1st to 10th	Day	12% 35% 2 10% 38% 2	3160
	11th to 20th	Day	9% 36% 4 20% 26% 7%	3140
	21st to end	Day	23% 35% 5% 21% 14% 2	3428
November	1st to 10th	Day	19% 55% 7% 9% 8% 1	1913
	11th to 20th	Day	19% 56% 4 11% 10%	1600
	21st to end	Day	21% 57% 4 12% 6%	1576
December	1st to 10th	Day	20% 59% 5% 10% 5% 1	1520
	11th to 20th	Day	22% 47% 10% 17% 3 1	1915
	21st to end	Day	48% 36% 5% 7% 3	2783
January	1st to 10th	Night	42% 37% 6% 10% 5% 1	4286
	11th to 20th	Night	37% 36% 8% 11% 9% 1	4120
	21st to end	Night	41% 39% 6% 9% 5% 1	4532
February	1st to 10th	Night	18% 64% 6% 8% 3 1	2470
	11th to 20th	Night	17% 63% 4 11% 6%	2404
	21st to end	Night	16% 64% 2 7% 9% 2	1913
March	1st to 10th	Night	27% 40% 5% 12% 14% 1	3419
	11th to 20th	Night	17% 40% 5% 22% 12% 5%	3480
	21st to end	Night	35% 40% 13% 9% 2	3817
April	1st to 10th	Night	15% 64% 5% 10% 5% 1	1934
	11th to 20th	Night	14% 65% 5% 10% 5% 1	1875
	21st to end	Night	15% 64% 3 9% 6% 2	1772
May	1st to 10th	Night	26% 41% 7% 13% 13%	2850
	11th to 20th	Night	25% 40% 6% 18% 10%	2711
	21st to end	Night	21% 40% 6% 15% 16% 1	2751
June	1st to 10th	Night	9% 64% 5% 12% 8% 2	1520
	11th to 20th	Night	10% 65% 4 13% 7% 2	1520
	21st to end	Night	10% 63% 8% 13% 5% 1	1520
July	1st to 10th	Night	27% 35% 7% 18% 10% 3	2490
	11th to 20th	Night	12% 35% 13% 24% 15% 1	2703
	21st to end	Night	20% 36% 16% 16% 12% 1	2999
August	1st to 10th	Night	14% 36% 10% 25% 14%	2826
	11th to 20th	Night	24% 36% 9% 17% 13% 1	2825
	21st to end	Night	18% 37% 13% 21% 9% 2	3404
September	1st to 10th	Night	12% 60% 5% 11% 9% 3	1900
	11th to 20th	Night	11% 59% 4 15% 9% 1	1992
	21st to end	Night	13% 59% 4 12% 10% 1	2123
October	1st to 10th	Night	13% 35% 2 9% 38% 2	3800
	11th to 20th	Night	12% 35% 4 18% 25% 6%	3779
	21st to end	Night	25% 35% 4 17% 16% 2	4120
November	1st to 10th	Night	15% 55% 7% 13% 10% 1	2377
	11th to 20th	Night	15% 56% 3 13% 11% 2	2800
	21st to end	Night	21% 56% 4 12% 6%	2759
December	1st to 10th	Night	19% 59% 4 11% 7%	2660
	11th to 20th	Night	20% 48% 5% 19% 7% 1	3281
	21st to end	Night	47% 36% 3 8% 4 1	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	23% 13% 31% 23% 8% 1	270
	11th to 20th	Day	21% 14% 39% 21% 4	270
	21st to end	Day	18% 12% 40% 27% 3	297
February	1st to 10th	Day	19% 17% 39% 20% 4 1	270
	11th to 20th	Day	18% 15% 40% 19% 7% 1	270
	21st to end	Day	19% 15% 44% 20% 3	225
March	1st to 10th	Day	20% 16% 44% 14% 5%	270
	11th to 20th	Day	23% 13% 36% 24% 4	270
	21st to end	Day	40% 19% 25% 13% 3	297
April	1st to 10th	Day	26% 16% 33% 19% 5% 1	425
	11th to 20th	Day	20% 15% 35% 22% 6% 1	452
	21st to end	Day	22% 18% 34% 19% 7% 1	584
May	1st to 10th	Day	21% 13% 32% 25% 7% 2	653
	11th to 20th	Day	21% 11% 30% 24% 11% 3	675
	21st to end	Day	17% 7% 29% 28% 15% 3	734
June	1st to 10th	Day	7% 6% 23% 33% 26% 7%	680
	11th to 20th	Day	9% 4 28% 37% 19% 4	680
	21st to end	Day	7% 8% 35% 33% 14% 3	680
July	1st to 10th	Day	9% 3 17% 33% 26% 12%	671
	11th to 20th	Day	7% 3 23% 38% 22% 8%	668
	21st to end	Day	7% 2 19% 40% 26% 5%	739
August	1st to 10th	Day	9% 3 19% 39% 24% 6%	676
	11th to 20th	Day	12% 3 18% 37% 25% 5%	665
	21st to end	Day	10% 3 18% 34% 28% 7%	587
September	1st to 10th	Day	13% 4 20% 29% 27% 8%	490
	11th to 20th	Day	10% 2 20% 36% 26% 6%	394
	21st to end	Day	15% 5% 30% 29% 14% 6%	300
October	1st to 10th	Day	18% 8% 29% 26% 15% 5%	300
	11th to 20th	Day	12% 21% 39% 19% 8% 1	300
	21st to end	Day	16% 19% 34% 21% 8% 2	330
November	1st to 10th	Day	18% 9% 42% 22% 7% 2	300
	11th to 20th	Day	21% 15% 38% 19% 7% 1	300
	21st to end	Day	24% 13% 33% 23% 7% 1	291
December	1st to 10th	Day	10% 16% 40% 23% 7% 3	270
	11th to 20th	Day	15% 15% 36% 28% 5% 1	270
	21st to end	Day	25% 18% 37% 18% 2	297
January	1st to 10th	Night	12% 13% 41% 25% 8%	950
	11th to 20th	Night	16% 14% 40% 23% 6%	950
	21st to end	Night	17% 12% 38% 28% 5%	1045
February	1st to 10th	Night	18% 11% 40% 25% 5%	950
	11th to 20th	Night	16% 13% 39% 26% 6%	929
	21st to end	Night	18% 16% 42% 21% 4 1	657
March	1st to 10th	Night	15% 14% 38% 26% 6%	570
	11th to 20th	Night	21% 10% 38% 26% 5%	570
	21st to end	Night	25% 13% 37% 20% 5%	627
April	1st to 10th	Night	15% 15% 41% 26% 4	570
	11th to 20th	Night	18% 13% 36% 26% 6%	563
	21st to end	Night	21% 8% 36% 27% 7% 1	570
May	1st to 10th	Night	16% 9% 34% 34% 6% 1	570
	11th to 20th	Night	16% 8% 30% 33% 12% 1	561
	21st to end	Night	14% 6% 29% 36% 15%	617
June	1st to 10th	Night	8% 3 26% 39% 23% 1	570
	11th to 20th	Night	8% 5% 26% 43% 17% 1	570
	21st to end	Night	7% 3 31% 42% 17%	570
July	1st to 10th	Night	7% 3 14% 41% 32% 3	555
	11th to 20th	Night	6% 1 18% 47% 26% 2	552
	21st to end	Night	6% 2 16% 48% 27% 1	624
August	1st to 10th	Night	5% 2 18% 47% 25% 2	567
	11th to 20th	Night	10% 3 14% 43% 27% 3	564
	21st to end	Night	9% 2 15% 42% 30% 2	627
September	1st to 10th	Night	12% 2 22% 34% 27% 4	570
	11th to 20th	Night	12% 2 22% 38% 24% 2	570
	21st to end	Night	9% 5% 30% 36% 20% 1	603
October	1st to 10th	Night	16% 6% 28% 34% 15% 2	760
	11th to 20th	Night	16% 10% 38% 28% 8%	760
	21st to end	Night	21% 11% 35% 26% 7% 1	836
November	1st to 10th	Night	10% 11% 39% 32% 8% 1	785
	11th to 20th	Night	15% 15% 40% 24% 7%	1000
	21st to end	Night	19% 13% 36% 26% 6%	986
December	1st to 10th	Night	16% 13% 38% 26% 6% 1	950
	11th to 20th	Night	18% 9% 37% 29% 6%	950
	21st to end	Night	22% 15% 36% 24% 4	1045

Page generated at 2024-11-24 23:22:17. Version ac07

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