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 2024-11-04.

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	4 7% 3 8% 5% 5% 5% 4 6% 7% 45%	105176
	Night	2 4 2 6% 4 4 4 4 6% 8% 56%	102556
Transparency	Day	33% 9% 9% 21% 20% 8%	104923
	Night	23% 7% 12% 27% 23% 8%	102399
Seeing	Day	14% 28% 29% 19% 8% 2	15559
	Night	9% 26% 30% 23% 10% 1	25572

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	3 4 8% 6% 6% 5% 4 6% 9% 51%	2538
	11th to 20th	Day	2 2 9% 7% 6% 7% 5% 7% 8% 46%	2697
	21st to end	Day	6% 6% 11% 5% 5% 4 3 5% 7% 48%	3146
February	1st to 10th	Day	3 4 8% 5% 5% 4 5% 7% 10% 49%	1710
	11th to 20th	Day	3 2 6% 5% 5% 4 4 5% 10% 56%	1795
	21st to end	Day	4 4 9% 6% 5% 5% 4 5% 7% 51%	1570
March	1st to 10th	Day	6% 5% 10% 6% 5% 4 3 4 6% 50%	3157
	11th to 20th	Day	1 9% 8% 13% 6% 6% 4 3 6% 8% 37%	3490
	21st to end	Day	1 8% 5% 10% 7% 6% 6% 5% 8% 8% 37%	4010
April	1st to 10th	Day	2 9% 3 7% 5% 5% 5% 4 6% 8% 47%	2280
	11th to 20th	Day	3 13% 4 10% 6% 5% 5% 3 5% 6% 37%	2251
	21st to end	Day	4 14% 4 9% 6% 4 5% 4 6% 7% 37%	2280
May	1st to 10th	Day	4 16% 6% 10% 6% 6% 5% 6% 7% 6% 29%	3980
	11th to 20th	Day	5% 13% 3 8% 5% 5% 6% 5% 7% 8% 36%	4388
	21st to end	Day	5% 7% 2 6% 5% 5% 6% 5% 7% 8% 45%	4825
June	1st to 10th	Day	5% 6% 3 7% 6% 6% 6% 5% 7% 8% 41%	2660
	11th to 20th	Day	7% 6% 3 7% 4 5% 5% 4 6% 7% 46%	2660
	21st to end	Day	5% 6% 3 7% 6% 6% 6% 6% 8% 8% 41%	2660
July	1st to 10th	Day	5% 6% 2 7% 6% 5% 5% 4 6% 6% 47%	4430
	11th to 20th	Day	5% 6% 3 9% 7% 7% 7% 6% 8% 8% 35%	4430
	21st to end	Day	9% 8% 3 10% 7% 5% 5% 4 6% 6% 37%	4622
August	1st to 10th	Day	9% 8% 4 10% 7% 7% 6% 5% 8% 8% 27%	4092
	11th to 20th	Day	7% 7% 3 9% 6% 7% 6% 5% 6% 7% 38%	3766
	21st to end	Day	6% 7% 3 9% 6% 6% 7% 6% 7% 7% 36%	4180
September	1st to 10th	Day	8% 7% 2 8% 5% 4 5% 3 5% 5% 48%	2280
	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 1 4 3 3 3 4 6% 6% 66%	1700
	11th to 20th	Day	1 4 2 4 3 3 3 3 6% 8% 63%	1710
	21st to end	Day	3 3 7% 4 3 4 4 6% 8% 57%	1581
December	1st to 10th	Day	3 2 8% 6% 4 5% 4 5% 9% 55%	1520
	11th to 20th	Day	4 2 6% 5% 3 4 4 6% 11% 54%	1926
	21st to end	Day	4 3 9% 6% 6% 5% 4 6% 9% 48%	2794
January	1st to 10th	Night	1 1 9% 7% 5% 5% 4 5% 8% 54%	4417
	11th to 20th	Night	2 1 4 6% 5% 6% 5% 7% 7% 55%	4302
	21st to end	Night	4 3 8% 4 4 3 3 6% 8% 58%	4521
February	1st to 10th	Night	2 2 7% 4 4 4 4 6% 8% 59%	2470
	11th to 20th	Night	3 2 6% 4 3 3 3 6% 9% 60%	2270
	21st to end	Night	3 2 6% 5% 4 5% 4 6% 8% 58%	1884
March	1st to 10th	Night	5% 4 7% 4 4 4 3 5% 7% 57%	3703
	11th to 20th	Night	1 9% 6% 11% 3 3 3 2 5% 8% 50%	3490
	21st to end	Night	1 5% 3 6% 4 4 5% 5% 7% 9% 52%	3623
April	1st to 10th	Night	1 5% 2 5% 3 3 4 4 6% 9% 59%	1900
	11th to 20th	Night	2 10% 3 7% 3 4 5% 4 5% 8% 50%	1877
	21st to end	Night	3 10% 3 6% 3 3 3 3 5% 8% 51%	1900
May	1st to 10th	Night	3 10% 3 5% 4 4 4 4 8% 9% 46%	2985
	11th to 20th	Night	4 10% 3 5% 4 4 6% 5% 7% 8% 44%	2517
	21st to end	Night	3 5% 1 5% 3 3 4 3 5% 8% 58%	2762
June	1st to 10th	Night	3 4 1 3 3 3 5% 5% 7% 10% 57%	1520
	11th to 20th	Night	4 3 1 3 3 4 4 4 7% 9% 59%	1520
	21st to end	Night	3 3 2 4 4 4 3 4 7% 9% 57%	1520
July	1st to 10th	Night	3 5% 2 5% 4 4 4 3 6% 9% 56%	2540
	11th to 20th	Night	1 2 1 3 4 5% 5% 5% 9% 12% 53%	2540
	21st to end	Night	3 4 1 4 4 5% 5% 4 7% 9% 54%	2938
August	1st to 10th	Night	4 6% 3 7% 4 5% 5% 5% 9% 10% 43%	2847
	11th to 20th	Night	3 4 1 5% 4 4 5% 5% 8% 10% 51%	3071
	21st to end	Night	3 4 2 9% 6% 5% 6% 5% 7% 9% 45%	3487
September	1st to 10th	Night	5% 5% 1 4 3 4 4 4 6% 8% 55%	1900
	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	2 1 3 3 3 3 3 5% 8% 69%	2451
	11th to 20th	Night	3 1 4 3 3 3 3 6% 9% 66%	2470
	21st to end	Night	1 4 2 5% 4 4 3 4 7% 9% 58%	2597
December	1st to 10th	Night	3 1 5% 4 4 3 3 5% 9% 63%	2660
	11th to 20th	Night	3 2 5% 4 4 4 5% 7% 10% 55%	3271
	21st to end	Night	4 2 8% 6% 5% 5% 4 6% 8% 52%	4873

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	24% 10% 15% 22% 21% 7%	2539
	11th to 20th	Day	29% 13% 16% 25% 14% 4	2697
	21st to end	Day	31% 9% 9% 26% 18% 7%	3146
February	1st to 10th	Day	28% 8% 15% 24% 17% 7%	1710
	11th to 20th	Day	24% 8% 10% 26% 24% 7%	1805
	21st to end	Day	29% 9% 8% 21% 24% 9%	1570
March	1st to 10th	Day	32% 8% 5% 23% 25% 7%	3157
	11th to 20th	Day	42% 8% 10% 26% 12% 3	3490
	21st to end	Day	36% 13% 8% 26% 15% 2	4010
April	1st to 10th	Day	33% 8% 11% 23% 19% 7%	2280
	11th to 20th	Day	44% 7% 9% 19% 17% 4	2254
	21st to end	Day	43% 7% 9% 25% 14% 2	2280
May	1st to 10th	Day	43% 14% 6% 17% 17% 3	3980
	11th to 20th	Day	40% 9% 10% 24% 17% 1	4392
	21st to end	Day	32% 8% 7% 22% 26% 6%	4825
June	1st to 10th	Day	35% 8% 12% 20% 18% 6%	2660
	11th to 20th	Day	35% 7% 8% 18% 21% 11%	2660
	21st to end	Day	35% 8% 9% 19% 20% 9%	2660
July	1st to 10th	Day	31% 7% 7% 13% 17% 23%	4361
	11th to 20th	Day	37% 10% 10% 19% 16% 8%	4355
	21st to end	Day	40% 9% 10% 14% 13% 14%	4476
August	1st to 10th	Day	46% 12% 13% 15% 12% 3	4078
	11th to 20th	Day	39% 10% 10% 13% 17% 11%	3802
	21st to end	Day	38% 10% 9% 15% 19% 8%	4179
September	1st to 10th	Day	35% 7% 5% 16% 25% 11%	2280
	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	18% 5% 13% 24% 32% 9%	1700
	11th to 20th	Day	19% 5% 13% 31% 24% 8%	1710
	21st to end	Day	24% 5% 10% 28% 21% 12%	1581
December	1st to 10th	Day	25% 8% 15% 28% 19% 6%	1520
	11th to 20th	Day	20% 11% 12% 31% 22% 4	1924
	21st to end	Day	28% 9% 10% 21% 24% 9%	2794
January	1st to 10th	Night	26% 7% 11% 28% 21% 6%	4417
	11th to 20th	Night	18% 17% 14% 26% 17% 8%	4302
	21st to end	Night	25% 5% 12% 29% 22% 7%	4521
February	1st to 10th	Night	21% 7% 14% 31% 21% 6%	2470
	11th to 20th	Night	20% 6% 11% 31% 26% 6%	2270
	21st to end	Night	22% 7% 8% 28% 25% 10%	1884
March	1st to 10th	Night	24% 7% 7% 24% 29% 8%	3703
	11th to 20th	Night	33% 5% 9% 30% 18% 4	3490
	21st to end	Night	24% 10% 14% 32% 18% 2	3623
April	1st to 10th	Night	21% 9% 13% 29% 23% 5%	1900
	11th to 20th	Night	31% 7% 12% 28% 19% 4	1877
	21st to end	Night	31% 5% 14% 30% 19% 1	1900
May	1st to 10th	Night	29% 10% 11% 26% 17% 6%	2985
	11th to 20th	Night	33% 9% 14% 27% 16%	2518
	21st to end	Night	23% 6% 10% 32% 25% 4	2762
June	1st to 10th	Night	20% 8% 19% 30% 17% 7%	1520
	11th to 20th	Night	19% 7% 12% 23% 24% 15%	1520
	21st to end	Night	21% 6% 12% 25% 25% 11%	1520
July	1st to 10th	Night	24% 6% 9% 21% 20% 20%	2500
	11th to 20th	Night	19% 7% 16% 33% 18% 7%	2492
	21st to end	Night	21% 7% 17% 28% 10% 16%	2846
August	1st to 10th	Night	30% 10% 21% 21% 15% 3	2838
	11th to 20th	Night	23% 8% 23% 19% 19% 9%	3101
	21st to end	Night	32% 7% 12% 21% 23% 5%	3487
September	1st to 10th	Night	25% 6% 10% 23% 26% 9%	1900
	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	15% 5% 13% 25% 32% 10%	2451
	11th to 20th	Night	16% 5% 13% 32% 26% 8%	2470
	21st to end	Night	22% 6% 10% 28% 24% 10%	2597
December	1st to 10th	Night	19% 6% 18% 27% 22% 8%	2660
	11th to 20th	Night	21% 8% 15% 26% 24% 6%	3272
	21st to end	Night	25% 9% 11% 21% 23% 11%	4873

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	14% 36% 26% 16% 7% 1	270
	11th to 20th	Day	15% 49% 20% 12% 4	270
	21st to end	Day	8% 46% 29% 11% 5%	297
February	1st to 10th	Day	15% 56% 22% 6% 1 1	270
	11th to 20th	Day	22% 47% 21% 8% 1	270
	21st to end	Day	28% 46% 20% 7%	225
March	1st to 10th	Day	18% 40% 25% 14% 3	284
	11th to 20th	Day	18% 33% 32% 16% 2	460
	21st to end	Day	17% 43% 29% 10% 1	506
April	1st to 10th	Day	21% 36% 30% 10% 3	460
	11th to 20th	Day	23% 39% 28% 8% 2 1	452
	21st to end	Day	20% 34% 33% 10% 3 1	460
May	1st to 10th	Day	19% 31% 31% 14% 3 1	539
	11th to 20th	Day	19% 19% 34% 20% 7% 1	675
	21st to end	Day	16% 23% 28% 22% 10% 1	734
June	1st to 10th	Day	9% 19% 29% 28% 13% 2	680
	11th to 20th	Day	11% 21% 36% 21% 9% 2	680
	21st to end	Day	9% 19% 33% 24% 14% 2	680
July	1st to 10th	Day	10% 9% 28% 31% 18% 3	671
	11th to 20th	Day	7% 9% 28% 33% 19% 5%	668
	21st to end	Day	12% 12% 23% 32% 16% 5%	634
August	1st to 10th	Day	13% 16% 31% 27% 11% 2	487
	11th to 20th	Day	11% 14% 29% 30% 12% 4	477
	21st to end	Day	12% 15% 31% 29% 11% 2	539
September	1st to 10th	Day	13% 18% 30% 26% 11% 3	490
	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	13% 47% 21% 13% 6%	279
	11th to 20th	Day	14% 39% 30% 13% 3 1	270
	21st to end	Day	10% 40% 35% 10% 4	270
December	1st to 10th	Day	21% 39% 26% 9% 5% 1	270
	11th to 20th	Day	11% 53% 22% 9% 4	270
	21st to end	Day	20% 41% 25% 10% 2 1	297
January	1st to 10th	Night	11% 38% 26% 17% 6% 1	950
	11th to 20th	Night	15% 40% 26% 12% 6% 1	874
	21st to end	Night	9% 38% 35% 14% 3	836
February	1st to 10th	Night	9% 46% 29% 11% 4	760
	11th to 20th	Night	10% 42% 30% 14% 3	744
	21st to end	Night	12% 41% 33% 12% 2	628
March	1st to 10th	Night	8% 38% 34% 15% 5% 1	760
	11th to 20th	Night	8% 29% 35% 22% 5% 1	760
	21st to end	Night	10% 35% 35% 16% 3 1	721
April	1st to 10th	Night	12% 29% 38% 19% 2	570
	11th to 20th	Night	12% 32% 34% 17% 6% 1	563
	21st to end	Night	9% 27% 37% 21% 6%	570
May	1st to 10th	Night	12% 17% 41% 22% 8% 1	570
	11th to 20th	Night	15% 10% 30% 34% 10% 1	561
	21st to end	Night	10% 14% 30% 30% 14% 1	617
June	1st to 10th	Night	6% 10% 28% 36% 18% 1	570
	11th to 20th	Night	6% 12% 34% 37% 10% 1	570
	21st to end	Night	5% 6% 26% 39% 22% 2	570
July	1st to 10th	Night	7% 3 18% 40% 29% 3	555
	11th to 20th	Night	3 3 17% 39% 35% 3	552
	21st to end	Night	8% 2 13% 38% 34% 4	624
August	1st to 10th	Night	9% 4 15% 44% 26% 2	567
	11th to 20th	Night	5% 3 21% 43% 24% 4	564
	21st to end	Night	5% 5% 20% 41% 25% 4	627
September	1st to 10th	Night	6% 5% 24% 40% 21% 5%	570
	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	6% 36% 34% 17% 6% 1	943
	11th to 20th	Night	10% 39% 32% 13% 5% 1	950
	21st to end	Night	6% 35% 36% 19% 4	950
December	1st to 10th	Night	13% 37% 33% 14% 3	950
	11th to 20th	Night	10% 42% 30% 13% 4	950
	21st to end	Night	13% 39% 28% 16% 4	1045

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