Mayborn Planetarium
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mayborn Planetarium clear sky chart from 2005-11-06 to 2025-01-22.

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	11% 5% 2 5% 4 4 4 3 5% 7% 50%	105306
	Night	12% 5% 2 4 3 3 3 3 5% 6% 54%	104205
Transparency	Day	32% 5% 10% 22% 22% 9%	109101
	Night	30% 4 10% 21% 22% 12%	108537
Seeing	Day	12% 7% 22% 29% 22% 7%	15189
	Night	13% 6% 27% 36% 16% 1	25211

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% 8% 2 5% 2 2 3 3 4 6% 53%	2937
	11th to 20th	Day	16% 4 1 3 2 2 2 2 5% 6% 57%	2940
	21st to end	Day	18% 8% 3 5% 3 3 3 2 3 6% 47%	3249
February	1st to 10th	Day	18% 6% 2 6% 3 2 3 2 3 5% 50%	1900
	11th to 20th	Day	15% 7% 3 6% 3 3 2 3 4 5% 49%	1849
	21st to end	Day	18% 6% 2 4 3 2 3 2 4 5% 51%	1570
March	1st to 10th	Day	15% 8% 2 7% 4 4 4 3 5% 5% 44%	3419
	11th to 20th	Day	20% 6% 2 6% 5% 5% 5% 4 5% 7% 36%	3480
	21st to end	Day	10% 7% 3 7% 4 3 4 4 6% 6% 46%	3814
April	1st to 10th	Day	12% 8% 3 6% 4 4 3 3 6% 6% 45%	2090
	11th to 20th	Day	15% 7% 2 6% 5% 3 3 4 5% 6% 44%	2069
	21st to end	Day	13% 5% 2 5% 4 3 4 3 5% 6% 49%	2460
May	1st to 10th	Day	20% 8% 3 7% 4 4 5% 4 6% 6% 35%	4082
	11th to 20th	Day	14% 7% 2 6% 4 4 4 3 4 6% 46%	4082
	21st to end	Day	11% 6% 2 8% 5% 5% 6% 5% 7% 8% 35%	4477
June	1st to 10th	Day	5% 4 1 4 4 5% 5% 3 8% 9% 53%	2470
	11th to 20th	Day	5% 4 1 4 5% 4 5% 4 6% 9% 53%	2470
	21st to end	Day	6% 4 2 4 5% 5% 4 5% 6% 9% 49%	2470
July	1st to 10th	Day	6% 4 2 5% 4 5% 5% 4 6% 8% 52%	4120
	11th to 20th	Day	3 3 1 4 3 3 4 4 7% 9% 60%	4120
	21st to end	Day	7% 6% 2 6% 5% 4 5% 5% 7% 10% 44%	4465
August	1st to 10th	Day	1 1 2 2 3 3 3 4 7% 73%	4104
	11th to 20th	Day	4 2 1 3 2 3 3 3 5% 8% 65%	3859
	21st to end	Day	4 3 1 4 4 4 5% 5% 7% 10% 53%	3996
September	1st to 10th	Day	10% 4 2 5% 5% 6% 4 3 6% 7% 48%	2090
	11th to 20th	Day	10% 5% 3 6% 4 4 4 3 5% 7% 48%	2090
	21st to end	Day	7% 3 1 5% 4 4 4 3 5% 8% 55%	2090
October	1st to 10th	Day	6% 4 1 5% 3 4 3 3 5% 6% 61%	2090
	11th to 20th	Day	11% 5% 2 4 3 2 3 2 4 5% 60%	1929
	21st to end	Day	12% 4 1 4 2 2 3 2 3 4 61%	2090
November	1st to 10th	Day	15% 6% 2 5% 3 3 3 2 4 5% 51%	1958
	11th to 20th	Day	8% 5% 1 6% 3 3 3 3 4 6% 57%	1858
	21st to end	Day	16% 6% 3 5% 3 2 3 2 4 5% 50%	1800
December	1st to 10th	Day	20% 6% 2 5% 4 3 3 3 4 4 46%	2940
	11th to 20th	Day	16% 7% 3 6% 3 4 4 4 4 5% 45%	3391
	21st to end	Day	14% 6% 2 4 3 2 2 2 3 4 58%	4488
January	1st to 10th	Night	17% 5% 2 3 2 2 2 2 3 4 58%	4238
	11th to 20th	Night	12% 4 1 3 2 2 2 2 3 4 65%	4250
	21st to end	Night	18% 7% 3 7% 3 3 3 2 4 5% 45%	4470
February	1st to 10th	Night	15% 7% 3 5% 4 3 3 2 4 5% 51%	2280
	11th to 20th	Night	17% 6% 2 4 2 3 3 2 4 5% 52%	2218
	21st to end	Night	17% 5% 2 4 3 3 2 2 4 5% 50%	1884
March	1st to 10th	Night	14% 7% 2 6% 4 4 4 3 5% 6% 45%	3433
	11th to 20th	Night	17% 6% 3 6% 4 4 4 4 6% 7% 39%	3480
	21st to end	Night	11% 7% 2 6% 5% 4 4 3 5% 6% 48%	3817
April	1st to 10th	Night	10% 6% 2 5% 3 4 4 4 5% 6% 52%	2090
	11th to 20th	Night	14% 5% 3 5% 5% 4 4 4 4 6% 48%	2058
	21st to end	Night	13% 6% 2 4 3 4 3 2 5% 7% 51%	1714
May	1st to 10th	Night	23% 7% 2 4 3 3 3 3 4 6% 40%	2823
	11th to 20th	Night	10% 7% 2 6% 4 3 3 4 6% 8% 48%	2823
	21st to end	Night	12% 5% 2 5% 4 4 4 4 6% 8% 45%	3090
June	1st to 10th	Night	4 3 1 4 3 3 4 4 6% 8% 62%	1710
	11th to 20th	Night	4 3 1 3 4 3 3 3 6% 10% 61%	1710
	21st to end	Night	5% 4 1 4 4 4 4 4 6% 8% 56%	1710
July	1st to 10th	Night	4 3 1 3 3 3 3 4 6% 9% 61%	2850
	11th to 20th	Night	2 2 1 3 2 3 3 3 6% 10% 65%	2850
	21st to end	Night	4 6% 2 6% 4 4 4 4 7% 9% 49%	3098
August	1st to 10th	Night	1 1 1 1 1 2 2 4 7% 79%	2836
	11th to 20th	Night	3 3 1 3 2 3 3 3 5% 9% 64%	2975
	21st to end	Night	3 2 1 3 3 3 3 4 7% 11% 60%	3663
September	1st to 10th	Night	8% 4 2 4 4 4 4 4 6% 8% 53%	2090
	11th to 20th	Night	10% 5% 2 5% 4 4 4 3 6% 8% 49%	2090
	21st to end	Night	8% 3 2 3 3 3 3 4 6% 7% 60%	2090
October	1st to 10th	Night	6% 3 1 3 3 3 3 2 4 6% 67%	2090
	11th to 20th	Night	11% 3 1 4 3 2 3 3 3 6% 61%	2232
	21st to end	Night	13% 4 2 4 2 2 3 2 3 4 62%	2508
November	1st to 10th	Night	12% 6% 2 3 3 3 2 3 4 6% 57%	2340
	11th to 20th	Night	6% 6% 2 4 4 3 3 3 4 5% 60%	2539
	21st to end	Night	16% 6% 2 5% 3 3 3 3 4 6% 50%	2600
December	1st to 10th	Night	19% 6% 2 5% 3 3 3 2 5% 5% 47%	4250
	11th to 20th	Night	18% 7% 2 5% 3 3 3 2 3 5% 47%	4816
	21st to end	Night	15% 7% 2 4 2 2 2 2 3 3 59%	6490

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% 3 5% 19% 26% 12%	2938
	11th to 20th	Day	29% 3 7% 16% 30% 14%	2940
	21st to end	Day	42% 3 5% 12% 26% 12%	3249
February	1st to 10th	Day	40% 3 7% 13% 22% 15%	1900
	11th to 20th	Day	39% 3 6% 18% 21% 13%	1859
	21st to end	Day	38% 3 5% 16% 21% 17%	1570
March	1st to 10th	Day	41% 5% 7% 14% 21% 12%	3419
	11th to 20th	Day	46% 8% 12% 11% 16% 8%	3480
	21st to end	Day	37% 6% 11% 15% 23% 8%	3814
April	1st to 10th	Day	40% 5% 8% 18% 16% 14%	2090
	11th to 20th	Day	41% 4 8% 17% 18% 11%	2069
	21st to end	Day	35% 6% 8% 20% 23% 8%	2460
May	1st to 10th	Day	48% 7% 12% 16% 13% 4	4120
	11th to 20th	Day	38% 6% 8% 18% 26% 4	4086
	21st to end	Day	41% 10% 13% 22% 11% 3	4489
June	1st to 10th	Day	26% 7% 15% 26% 21% 4	2470
	11th to 20th	Day	28% 6% 13% 28% 19% 7%	2470
	21st to end	Day	30% 8% 13% 24% 22% 4	2470
July	1st to 10th	Day	29% 6% 18% 37% 10% 1	4056
	11th to 20th	Day	21% 5% 14% 37% 19% 4	4051
	21st to end	Day	35% 5% 15% 31% 13%	4325
August	1st to 10th	Day	12% 3 12% 35% 37% 2	4090
	11th to 20th	Day	16% 5% 18% 40% 17% 2	3898
	21st to end	Day	24% 7% 20% 28% 19% 2	3995
September	1st to 10th	Day	34% 6% 11% 21% 18% 11%	2090
	11th to 20th	Day	36% 7% 11% 20% 21% 6%	2090
	21st to end	Day	27% 5% 9% 22% 22% 15%	2090
October	1st to 10th	Day	15% 3 6% 13% 24% 39%	3480
	11th to 20th	Day	18% 3 6% 18% 34% 22%	3182
	21st to end	Day	24% 2 3 20% 38% 13%	3428
November	1st to 10th	Day	36% 4 8% 19% 23% 10%	1958
	11th to 20th	Day	30% 3 9% 17% 24% 16%	1858
	21st to end	Day	38% 4 5% 19% 21% 14%	1800
December	1st to 10th	Day	43% 3 6% 17% 22% 9%	2940
	11th to 20th	Day	42% 4 6% 12% 24% 13%	3389
	21st to end	Day	32% 2 4 18% 28% 16%	4488
January	1st to 10th	Night	32% 3 5% 18% 28% 16%	4238
	11th to 20th	Night	26% 2 5% 17% 29% 22%	4250
	21st to end	Night	42% 3 4 13% 24% 13%	4470
February	1st to 10th	Night	38% 4 6% 13% 22% 17%	2280
	11th to 20th	Night	37% 2 6% 17% 22% 15%	2218
	21st to end	Night	38% 4 6% 15% 20% 18%	1884
March	1st to 10th	Night	38% 6% 9% 13% 22% 12%	3433
	11th to 20th	Night	42% 8% 11% 15% 15% 9%	3480
	21st to end	Night	37% 7% 9% 17% 23% 8%	3817
April	1st to 10th	Night	33% 5% 9% 20% 17% 16%	2090
	11th to 20th	Night	38% 5% 11% 14% 19% 14%	2058
	21st to end	Night	34% 5% 10% 19% 23% 9%	1714
May	1st to 10th	Night	44% 6% 10% 19% 15% 7%	2850
	11th to 20th	Night	32% 7% 12% 22% 20% 7%	2824
	21st to end	Night	35% 8% 13% 28% 11% 5%	3099
June	1st to 10th	Night	19% 7% 16% 31% 22% 4	1710
	11th to 20th	Night	20% 6% 14% 32% 21% 7%	1710
	21st to end	Night	23% 8% 13% 28% 22% 5%	1710
July	1st to 10th	Night	21% 5% 22% 42% 9% 1	2805
	11th to 20th	Night	16% 4 18% 40% 19% 2	2796
	21st to end	Night	31% 5% 22% 32% 10% 1	2999
August	1st to 10th	Night	7% 4 12% 38% 37% 3	2826
	11th to 20th	Night	18% 4 23% 36% 17% 3	3002
	21st to end	Night	19% 8% 22% 31% 17% 3	3663
September	1st to 10th	Night	30% 6% 14% 23% 18% 11%	2090
	11th to 20th	Night	33% 6% 14% 21% 17% 7%	2090
	21st to end	Night	22% 5% 12% 25% 21% 15%	2090
October	1st to 10th	Night	13% 2 6% 15% 21% 42%	3480
	11th to 20th	Night	17% 2 8% 16% 32% 24%	3705
	21st to end	Night	24% 2 4 20% 34% 16%	4120
November	1st to 10th	Night	31% 4 7% 19% 24% 14%	2340
	11th to 20th	Night	27% 4 8% 19% 24% 18%	2539
	21st to end	Night	36% 4 7% 16% 21% 15%	2600
December	1st to 10th	Night	40% 3 5% 20% 22% 11%	4250
	11th to 20th	Night	42% 2 6% 10% 24% 16%	4817
	21st to end	Night	33% 2 4 16% 27% 18%	6490

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	21% 14% 35% 24% 5% 1	300
	11th to 20th	Day	21% 15% 34% 21% 7% 1	300
	21st to end	Day	18% 15% 37% 22% 7%	300
February	1st to 10th	Day	24% 16% 33% 22% 4	270
	11th to 20th	Day	21% 16% 40% 19% 3	270
	21st to end	Day	26% 19% 37% 16% 2	225
March	1st to 10th	Day	20% 19% 35% 23% 3	270
	11th to 20th	Day	21% 16% 37% 20% 5% 1	270
	21st to end	Day	17% 17% 38% 22% 6%	297
April	1st to 10th	Day	20% 18% 40% 18% 3	270
	11th to 20th	Day	19% 15% 39% 20% 6% 1	267
	21st to end	Day	15% 15% 38% 23% 8% 1	640
May	1st to 10th	Day	15% 11% 36% 28% 9%	653
	11th to 20th	Day	16% 5% 31% 32% 14% 3	675
	21st to end	Day	15% 6% 25% 34% 16% 4	734
June	1st to 10th	Day	6% 2 17% 39% 27% 9%	680
	11th to 20th	Day	6% 1 16% 47% 25% 5%	680
	21st to end	Day	6% 2 13% 36% 33% 10%	680
July	1st to 10th	Day	8% 1 10% 33% 34% 14%	671
	11th to 20th	Day	2 5% 35% 45% 12%	668
	21st to end	Day	3 1 5% 35% 43% 13%	739
August	1st to 10th	Day	2 1 5% 32% 46% 15%	676
	11th to 20th	Day	5% 1 4 33% 40% 16%	561
	21st to end	Day	5% 1 5% 23% 41% 26%	433
September	1st to 10th	Day	9% 2 3 24% 39% 23%	300
	11th to 20th	Day	6% 6% 22% 46% 19%	300
	21st to end	Day	12% 2 5% 31% 35% 15%	300
October	1st to 10th	Day	3 2 12% 38% 32% 13%	300
	11th to 20th	Day	11% 4 24% 31% 26% 4	300
	21st to end	Day	23% 10% 22% 21% 19% 4	330
November	1st to 10th	Day	20% 8% 30% 27% 11% 4	300
	11th to 20th	Day	14% 10% 30% 29% 12% 5%	300
	21st to end	Day	20% 13% 32% 21% 12% 2	300
December	1st to 10th	Day	19% 8% 31% 26% 12% 4	300
	11th to 20th	Day	19% 13% 37% 23% 8% 1	300
	21st to end	Day	20% 11% 38% 21% 9% 2	330
January	1st to 10th	Night	18% 8% 36% 31% 8%	1000
	11th to 20th	Night	18% 10% 33% 31% 7%	1000
	21st to end	Night	17% 11% 35% 30% 7%	1001
February	1st to 10th	Night	20% 12% 35% 29% 4	760
	11th to 20th	Night	20% 12% 37% 27% 3	744
	21st to end	Night	21% 12% 42% 21% 3	628
March	1st to 10th	Night	18% 11% 38% 28% 5%	584
	11th to 20th	Night	16% 9% 39% 30% 6%	570
	21st to end	Night	12% 12% 42% 30% 3	627
April	1st to 10th	Night	11% 9% 47% 29% 3	570
	11th to 20th	Night	16% 11% 41% 26% 5%	563
	21st to end	Night	14% 9% 44% 25% 8%	570
May	1st to 10th	Night	13% 9% 42% 30% 6%	570
	11th to 20th	Night	13% 5% 36% 33% 12% 1	561
	21st to end	Night	11% 4 34% 36% 14%	617
June	1st to 10th	Night	3 2 22% 46% 24% 3	570
	11th to 20th	Night	4 2 26% 51% 17% 1	570
	21st to end	Night	4 1 17% 47% 27% 3	570
July	1st to 10th	Night	5% 1 12% 46% 32% 3	555
	11th to 20th	Night	3 1 10% 53% 32% 2	552
	21st to end	Night	2 1 8% 53% 34% 3	624
August	1st to 10th	Night	1 5% 53% 37% 4	567
	11th to 20th	Night	7% 6% 48% 35% 5%	564
	21st to end	Night	5% 4 44% 40% 6%	627
September	1st to 10th	Night	10% 1 8% 41% 35% 5%	570
	11th to 20th	Night	13% 1 5% 40% 38% 3	570
	21st to end	Night	9% 1 11% 39% 37% 3	570
October	1st to 10th	Night	7% 12% 48% 28% 4	570
	11th to 20th	Night	12% 4 22% 41% 19% 2	712
	21st to end	Night	14% 8% 27% 32% 18% 1	836
November	1st to 10th	Night	15% 4 25% 40% 15% 1	780
	11th to 20th	Night	9% 8% 29% 38% 15% 1	939
	21st to end	Night	18% 9% 29% 31% 12% 1	1000
December	1st to 10th	Night	15% 8% 31% 36% 10% 1	1000
	11th to 20th	Night	20% 8% 30% 35% 7%	1000
	21st to end	Night	20% 8% 33% 32% 7%	1100

Page generated at 2025-01-19 02:06:43. Version ac07

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