Meyer-Womble Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Meyer-Womble Observatory clear sky chart from 2005-11-06 to 2025-09-04.

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	3 7% 3 8% 6% 5% 5% 4 6% 7% 44%	134883
	Night	1 4 2 6% 4 4 4 4 6% 8% 57%	131298
Transparency	Day	33% 8% 9% 21% 21% 8%	129829
	Night	22% 6% 12% 26% 24% 9%	127371
Seeing	Day	15% 28% 29% 19% 8% 2	16730
	Night	10% 26% 30% 23% 10% 1	26697

By Month

Percentage Cloud Cover SW (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	2 3 11% 5% 4 4 3 5% 7% 54%	3638
	11th to 20th	Day	2 2 7% 7% 7% 8% 4 7% 8% 48%	3867
	21st to end	Day	4 4 10% 5% 5% 4 3 5% 7% 54%	4510
February	1st to 10th	Day	3 3 8% 5% 5% 4 5% 7% 10% 50%	1800
	11th to 20th	Day	3 2 7% 5% 6% 4 3 5% 10% 55%	1893
	21st to end	Day	4 4 9% 6% 5% 5% 4 5% 7% 52%	1650
March	1st to 10th	Day	5% 5% 11% 5% 4 4 3 4 6% 53%	4541
	11th to 20th	Day	1 7% 6% 13% 7% 6% 5% 4 6% 8% 38%	5000
	21st to end	Day	7% 4 10% 7% 6% 5% 4 7% 8% 40%	5749
April	1st to 10th	Day	2 8% 3 7% 5% 5% 5% 4 6% 8% 47%	2400
	11th to 20th	Day	3 13% 5% 10% 6% 5% 5% 3 6% 6% 38%	2371
	21st to end	Day	3 13% 4 9% 6% 5% 5% 4 6% 7% 37%	2400
May	1st to 10th	Day	4 18% 5% 10% 6% 6% 5% 5% 6% 6% 29%	5702
	11th to 20th	Day	4 11% 3 9% 6% 5% 6% 5% 6% 7% 39%	6298
	21st to end	Day	5% 7% 3 7% 5% 5% 6% 5% 7% 8% 43%	6925
June	1st to 10th	Day	5% 6% 3 7% 6% 6% 6% 5% 7% 8% 41%	2800
	11th to 20th	Day	6% 6% 2 7% 4 5% 5% 4 6% 7% 46%	2800
	21st to end	Day	5% 6% 3 7% 6% 6% 6% 6% 8% 8% 41%	2800
July	1st to 10th	Day	4 5% 2 7% 6% 5% 6% 5% 6% 8% 45%	6339
	11th to 20th	Day	4 6% 3 9% 7% 7% 8% 6% 8% 9% 32%	6340
	21st to end	Day	9% 9% 4 10% 7% 6% 6% 5% 6% 6% 33%	6639
August	1st to 10th	Day	7% 6% 3 9% 6% 7% 6% 5% 9% 11% 31%	5779
	11th to 20th	Day	6% 7% 3 10% 7% 7% 6% 5% 6% 7% 37%	5419
	21st to end	Day	8% 9% 4 10% 7% 6% 6% 5% 7% 7% 31%	5981
September	1st to 10th	Day	7% 7% 2 8% 5% 4 5% 3 5% 5% 48%	2317
	11th to 20th	Day	7% 6% 2 7% 5% 5% 4 4 5% 5% 50%	2280
	21st to end	Day	6% 7% 2 6% 4 4 3 3 5% 6% 55%	2067
October	1st to 10th	Day	3 4 2 5% 4 3 3 3 4 5% 63%	3170
	11th to 20th	Day	4 6% 2 5% 5% 5% 5% 5% 7% 7% 48%	3150
	21st to end	Day	2 6% 2 6% 3 3 3 3 4 7% 62%	3381
November	1st to 10th	Day	1 4 2 5% 3 3 3 4 6% 6% 64%	1763
	11th to 20th	Day	1 3 2 4 3 3 3 3 6% 8% 64%	1800
	21st to end	Day	3 3 7% 4 3 5% 3 6% 8% 58%	1664
December	1st to 10th	Day	2 1 5% 4 3 4 3 4 6% 67%	2620
	11th to 20th	Day	3 1 4 4 3 4 3 6% 10% 62%	3026
	21st to end	Day	4 3 8% 5% 5% 4 3 6% 9% 51%	4004
January	1st to 10th	Night	1 2 10% 8% 5% 4 3 4 7% 56%	6327
	11th to 20th	Night	1 1 5% 6% 6% 6% 4 6% 6% 59%	6156
	21st to end	Night	3 3 6% 3 4 3 3 5% 8% 62%	6468
February	1st to 10th	Night	2 2 6% 4 4 4 4 6% 8% 60%	2600
	11th to 20th	Night	3 2 6% 5% 3 3 3 7% 9% 59%	2392
	21st to end	Night	3 2 6% 4 4 5% 4 6% 8% 59%	1980
March	1st to 10th	Night	5% 4 7% 4 4 4 3 5% 7% 57%	5330
	11th to 20th	Night	1 6% 4 9% 3 3 4 3 5% 8% 53%	5000
	21st to end	Night	1 5% 2 6% 4 4 5% 4 7% 10% 53%	5200
April	1st to 10th	Night	1 5% 2 5% 3 3 4 4 6% 9% 58%	2000
	11th to 20th	Night	2 10% 3 7% 3 4 5% 4 5% 8% 50%	1977
	21st to end	Night	3 10% 3 6% 3 3 3 3 5% 8% 52%	2000
May	1st to 10th	Night	2 12% 3 6% 4 4 5% 4 8% 9% 42%	4273
	11th to 20th	Night	3 7% 3 6% 4 5% 5% 5% 6% 8% 48%	3617
	21st to end	Night	2 5% 2 5% 3 3 4 3 5% 8% 59%	3972
June	1st to 10th	Night	3 5% 1 3 3 3 5% 5% 7% 10% 56%	1600
	11th to 20th	Night	4 3 1 3 3 4 4 4 6% 9% 60%	1600
	21st to end	Night	3 4 2 5% 4 4 3 3 7% 8% 57%	1600
July	1st to 10th	Night	2 4 2 4 3 4 5% 4 6% 9% 56%	3640
	11th to 20th	Night	1 2 1 4 4 5% 6% 6% 10% 12% 49%	3640
	21st to end	Night	3 4 2 5% 4 6% 6% 5% 8% 10% 49%	4231
August	1st to 10th	Night	3 5% 2 6% 4 4 4 5% 8% 11% 48%	4033
	11th to 20th	Night	2 3 1 5% 3 4 5% 4 7% 9% 55%	4415
	21st to end	Night	5% 5% 3 9% 6% 6% 6% 5% 7% 8% 41%	4993
September	1st to 10th	Night	5% 5% 1 4 3 4 4 4 6% 8% 56%	1930
	11th to 20th	Night	5% 3 2 4 4 3 4 4 5% 7% 59%	1900
	21st to end	Night	4 5% 2 4 3 4 3 3 4 6% 62%	2109
October	1st to 10th	Night	3 2 1 3 2 2 2 2 3 5% 73%	3800
	11th to 20th	Night	1 3 2 4 3 3 3 4 6% 7% 63%	3778
	21st to end	Night	1 5% 1 3 2 2 3 2 4 6% 70%	4143
November	1st to 10th	Night	3 1 3 3 3 3 3 5% 8% 67%	2535
	11th to 20th	Night	3 1 4 3 3 3 2 6% 9% 66%	2600
	21st to end	Night	1 4 2 5% 4 4 3 4 7% 9% 59%	2734
December	1st to 10th	Night	2 1 3 3 2 2 2 3 6% 77%	4570
	11th to 20th	Night	2 1 4 3 3 3 4 6% 8% 66%	5181
	21st to end	Night	4 3 8% 7% 5% 5% 4 6% 8% 50%	6974

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	26% 7% 11% 24% 23% 9%	3639
	11th to 20th	Day	28% 10% 14% 19% 20% 10%	3867
	21st to end	Day	27% 6% 8% 23% 21% 15%	4510
February	1st to 10th	Day	27% 8% 15% 24% 18% 9%	1800
	11th to 20th	Day	25% 8% 10% 26% 24% 7%	1903
	21st to end	Day	28% 8% 8% 20% 25% 10%	1650
March	1st to 10th	Day	30% 5% 6% 18% 28% 13%	4541
	11th to 20th	Day	40% 6% 9% 22% 20% 3	5000
	21st to end	Day	32% 10% 9% 32% 14% 2	5749
April	1st to 10th	Day	33% 8% 11% 23% 19% 7%	2400
	11th to 20th	Day	44% 7% 8% 18% 18% 5%	2374
	21st to end	Day	43% 7% 9% 25% 14% 1	2400
May	1st to 10th	Day	44% 12% 6% 19% 15% 3	5702
	11th to 20th	Day	37% 8% 9% 20% 20% 5%	6302
	21st to end	Day	32% 8% 7% 22% 26% 4	6926
June	1st to 10th	Day	36% 9% 12% 20% 18% 6%	2800
	11th to 20th	Day	34% 7% 8% 18% 22% 12%	2800
	21st to end	Day	35% 8% 9% 18% 20% 10%	2800
July	1st to 10th	Day	29% 7% 8% 14% 19% 22%	6271
	11th to 20th	Day	37% 11% 12% 20% 13% 7%	6265
	21st to end	Day	44% 9% 10% 12% 13% 11%	6448
August	1st to 10th	Day	45% 12% 13% 15% 12% 3	4208
	11th to 20th	Day	39% 10% 10% 13% 18% 10%	3923
	21st to end	Day	39% 10% 9% 15% 19% 8%	4311
September	1st to 10th	Day	35% 7% 5% 16% 25% 11%	2317
	11th to 20th	Day	32% 7% 7% 19% 26% 9%	2280
	21st to end	Day	27% 7% 6% 24% 29% 7%	2067
October	1st to 10th	Day	22% 4 7% 18% 33% 16%	3170
	11th to 20th	Day	29% 7% 9% 28% 23% 5%	3150
	21st to end	Day	21% 5% 6% 25% 35% 7%	3381
November	1st to 10th	Day	20% 5% 12% 23% 32% 9%	1763
	11th to 20th	Day	18% 5% 12% 30% 25% 10%	1800
	21st to end	Day	24% 5% 9% 28% 23% 11%	1664
December	1st to 10th	Day	19% 4 10% 34% 24% 9%	2620
	11th to 20th	Day	15% 7% 12% 33% 27% 6%	3024
	21st to end	Day	26% 7% 8% 23% 26% 10%	4004
January	1st to 10th	Night	25% 5% 9% 27% 26% 9%	6327
	11th to 20th	Night	19% 12% 12% 21% 20% 17%	6156
	21st to end	Night	20% 4 9% 25% 25% 16%	6468
February	1st to 10th	Night	21% 7% 14% 29% 21% 8%	2600
	11th to 20th	Night	20% 5% 11% 31% 26% 6%	2392
	21st to end	Night	22% 6% 8% 27% 25% 12%	1980
March	1st to 10th	Night	24% 5% 7% 18% 31% 15%	5330
	11th to 20th	Night	30% 3 8% 21% 26% 11%	5000
	21st to end	Night	23% 8% 15% 35% 17% 1	5200
April	1st to 10th	Night	21% 9% 12% 30% 22% 5%	2000
	11th to 20th	Night	31% 7% 11% 28% 20% 4	1977
	21st to end	Night	30% 5% 14% 31% 19% 1	2000
May	1st to 10th	Night	32% 10% 12% 27% 15% 4	4270
	11th to 20th	Night	30% 7% 12% 27% 23% 2	3618
	21st to end	Night	22% 6% 10% 30% 28% 3	3972
June	1st to 10th	Night	21% 8% 18% 30% 17% 6%	1600
	11th to 20th	Night	19% 7% 12% 23% 24% 16%	1600
	21st to end	Night	21% 6% 12% 25% 25% 12%	1600
July	1st to 10th	Night	22% 5% 8% 19% 24% 22%	3600
	11th to 20th	Night	19% 8% 21% 30% 17% 5%	3592
	21st to end	Night	25% 8% 20% 25% 11% 12%	4110
August	1st to 10th	Night	30% 10% 20% 21% 16% 3	2928
	11th to 20th	Night	23% 8% 23% 19% 19% 8%	3199
	21st to end	Night	32% 8% 13% 21% 22% 5%	3597
September	1st to 10th	Night	25% 6% 10% 24% 26% 9%	1930
	11th to 20th	Night	23% 6% 10% 26% 24% 12%	1900
	21st to end	Night	23% 5% 8% 29% 28% 7%	2109
October	1st to 10th	Night	14% 4 8% 25% 37% 12%	3800
	11th to 20th	Night	18% 5% 10% 38% 24% 6%	3778
	21st to end	Night	16% 3 7% 27% 34% 13%	4143
November	1st to 10th	Night	16% 5% 13% 25% 31% 10%	2535
	11th to 20th	Night	16% 5% 13% 30% 27% 10%	2600
	21st to end	Night	22% 6% 10% 28% 25% 10%	2734
December	1st to 10th	Night	12% 3 11% 33% 32% 8%	4570
	11th to 20th	Night	15% 5% 11% 29% 33% 7%	5182
	21st to end	Night	25% 7% 12% 19% 28% 9%	6974

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	18% 36% 25% 15% 6% 1	300
	11th to 20th	Day	15% 47% 23% 11% 4	300
	21st to end	Day	12% 45% 28% 11% 5%	330
February	1st to 10th	Day	22% 51% 20% 5% 1 1	300
	11th to 20th	Day	25% 45% 21% 7% 1	300
	21st to end	Day	29% 43% 22% 6%	249
March	1st to 10th	Day	19% 39% 26% 13% 3	315
	11th to 20th	Day	20% 33% 30% 15% 2	500
	21st to end	Day	19% 41% 29% 9% 1	550
April	1st to 10th	Day	21% 36% 30% 10% 3	500
	11th to 20th	Day	24% 39% 27% 7% 2 1	492
	21st to end	Day	21% 34% 33% 10% 2 1	500
May	1st to 10th	Day	20% 32% 30% 15% 3 1	583
	11th to 20th	Day	21% 20% 33% 19% 6% 1	725
	21st to end	Day	16% 23% 30% 21% 9% 1	789
June	1st to 10th	Day	9% 21% 30% 27% 12% 2	730
	11th to 20th	Day	10% 21% 36% 22% 9% 2	730
	21st to end	Day	9% 19% 33% 24% 13% 2	730
July	1st to 10th	Day	10% 10% 29% 31% 17% 3	721
	11th to 20th	Day	7% 9% 29% 32% 18% 4	718
	21st to end	Day	13% 12% 24% 32% 15% 4	683
August	1st to 10th	Day	13% 18% 31% 25% 10% 2	527
	11th to 20th	Day	11% 14% 29% 30% 12% 4	517
	21st to end	Day	13% 16% 30% 28% 11% 2	583
September	1st to 10th	Day	13% 18% 30% 25% 10% 3	503
	11th to 20th	Day	11% 20% 37% 22% 8% 1	490
	21st to end	Day	12% 19% 32% 21% 12% 4	305
October	1st to 10th	Day	10% 26% 28% 20% 13% 3	300
	11th to 20th	Day	10% 38% 30% 15% 5% 2	300
	21st to end	Day	15% 39% 28% 13% 4 1	330
November	1st to 10th	Day	15% 46% 21% 12% 6%	300
	11th to 20th	Day	16% 39% 28% 12% 3 1	300
	21st to end	Day	13% 39% 35% 9% 4	300
December	1st to 10th	Day	21% 36% 27% 10% 5% 1	300
	11th to 20th	Day	18% 49% 21% 8% 4	300
	21st to end	Day	22% 39% 26% 9% 2 1	330
January	1st to 10th	Night	12% 38% 26% 17% 6% 1	1000
	11th to 20th	Night	15% 40% 26% 12% 6% 1	920
	21st to end	Night	10% 37% 35% 14% 3	880
February	1st to 10th	Night	12% 45% 28% 10% 4	800
	11th to 20th	Night	13% 41% 30% 13% 3	784
	21st to end	Night	12% 41% 34% 12% 2	660
March	1st to 10th	Night	9% 37% 34% 15% 4 1	800
	11th to 20th	Night	9% 30% 34% 21% 5% 1	800
	21st to end	Night	12% 35% 35% 15% 3 1	759
April	1st to 10th	Night	12% 29% 39% 18% 2	600
	11th to 20th	Night	12% 32% 34% 16% 5% 1	593
	21st to end	Night	9% 26% 38% 21% 6%	600
May	1st to 10th	Night	12% 16% 41% 22% 8% 1	600
	11th to 20th	Night	15% 11% 31% 33% 10% 1	591
	21st to end	Night	9% 15% 32% 29% 14% 1	650
June	1st to 10th	Night	7% 11% 29% 36% 17% 1	600
	11th to 20th	Night	5% 12% 36% 36% 10% 1	600
	21st to end	Night	5% 7% 27% 39% 21% 2	600
July	1st to 10th	Night	7% 3 19% 40% 27% 3	585
	11th to 20th	Night	3 4 19% 39% 33% 3	582
	21st to end	Night	8% 3 15% 37% 32% 4	657
August	1st to 10th	Night	9% 5% 18% 42% 25% 2	597
	11th to 20th	Night	5% 3 22% 43% 23% 3	594
	21st to end	Night	5% 5% 20% 41% 24% 4	660
September	1st to 10th	Night	6% 5% 24% 40% 21% 4	579
	11th to 20th	Night	8% 9% 28% 36% 17% 3	570
	21st to end	Night	7% 11% 34% 30% 16% 2	594
October	1st to 10th	Night	7% 21% 35% 24% 11% 2	760
	11th to 20th	Night	6% 31% 31% 23% 8% 1	760
	21st to end	Night	10% 31% 33% 18% 7% 2	847
November	1st to 10th	Night	7% 36% 34% 17% 6% 1	975
	11th to 20th	Night	11% 39% 32% 13% 5% 1	1000
	21st to end	Night	7% 35% 36% 18% 4	1000
December	1st to 10th	Night	14% 35% 33% 15% 3	1000
	11th to 20th	Night	13% 41% 30% 13% 4	1000
	21st to end	Night	13% 38% 29% 15% 4	1100

Page generated at 2025-08-31 23:51:07. Version ac07

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