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 2024-03-28.

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	4 7% 3 7% 6% 4 5% 5% 6% 8% 45%	78867
	Night	2 4 2 5% 5% 3 4 5% 6% 9% 57%	81192
Transparency	Day	34% 8% 10% 22% 19% 6%	78577
	Night	23% 7% 13% 27% 22% 7%	81004
Seeing	Day	14% 28% 29% 19% 8% 2	14640
	Night	9% 27% 29% 23% 11% 1	24866

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 4 6% 7% 4 6% 4 5% 10% 51%	2538
	11th to 20th	Day	2 3 8% 8% 5% 7% 7% 7% 8% 46%	2697
	21st to end	Day	5% 6% 9% 7% 3 4 4 5% 8% 49%	3146
February	1st to 10th	Day	3 4 7% 6% 4 4 5% 7% 11% 49%	1710
	11th to 20th	Day	3 2 6% 5% 4 5% 4 4 10% 56%	1795
	21st to end	Day	3 5% 8% 7% 4 5% 6% 5% 8% 51%	1570
March	1st to 10th	Day	1 7% 4 6% 6% 4 5% 4 5% 8% 49%	1914
	11th to 20th	Day	2 9% 5% 8% 6% 4 5% 4 6% 8% 43%	2090
	21st to end	Day	1 8% 5% 8% 8% 3 6% 5% 7% 9% 39%	2366
April	1st to 10th	Day	2 9% 3 6% 5% 4 6% 5% 6% 9% 46%	2160
	11th to 20th	Day	3 13% 5% 9% 7% 4 6% 4 5% 7% 37%	2131
	21st to end	Day	5% 12% 5% 8% 7% 3 5% 5% 6% 7% 36%	2160
May	1st to 10th	Day	6% 13% 5% 8% 6% 4 5% 6% 6% 7% 33%	2258
	11th to 20th	Day	8% 15% 4 8% 6% 4 5% 5% 6% 7% 32%	2478
	21st to end	Day	8% 10% 4 8% 7% 4 6% 5% 6% 7% 35%	2724
June	1st to 10th	Day	6% 5% 3 6% 6% 4 6% 6% 7% 8% 41%	2520
	11th to 20th	Day	7% 6% 3 6% 5% 4 5% 5% 5% 7% 47%	2520
	21st to end	Day	6% 5% 3 6% 6% 4 7% 7% 7% 8% 42%	2520
July	1st to 10th	Day	8% 7% 4 7% 8% 4 7% 7% 7% 7% 35%	2520
	11th to 20th	Day	7% 7% 3 7% 8% 4 7% 6% 6% 8% 36%	2520
	21st to end	Day	11% 8% 4 9% 9% 5% 6% 6% 7% 7% 29%	2643
August	1st to 10th	Day	13% 9% 4 9% 8% 4 6% 6% 6% 7% 29%	2328
	11th to 20th	Day	9% 7% 3 7% 7% 5% 6% 5% 5% 7% 39%	2151
	21st to end	Day	9% 8% 3 7% 6% 4 6% 6% 6% 6% 37%	2376
September	1st to 10th	Day	7% 7% 2 7% 6% 3 5% 4 5% 5% 49%	2160
	11th to 20th	Day	8% 6% 3 6% 6% 4 4 5% 5% 5% 49%	2160
	21st to end	Day	6% 6% 2 5% 4 3 3 4 4 6% 55%	1959
October	1st to 10th	Day	6% 7% 4 7% 5% 3 4 4 5% 5% 51%	1800
	11th to 20th	Day	4 4 2 3 3 2 3 4 5% 6% 62%	1800
	21st to end	Day	2 7% 2 6% 4 3 3 4 4 8% 56%	1949
November	1st to 10th	Day	1 3 2 3 4 2 3 4 5% 7% 66%	1673
	11th to 20th	Day	1 3 2 4 3 2 3 5% 5% 9% 64%	1710
	21st to end	Day	3 3 6% 5% 2 4 4 6% 9% 58%	1581
December	1st to 10th	Day	3 2 6% 7% 4 4 5% 5% 9% 55%	1520
	11th to 20th	Day	4 2 5% 5% 3 4 5% 6% 11% 55%	1926
	21st to end	Day	4 3 8% 7% 4 5% 5% 6% 10% 48%	2794
January	1st to 10th	Night	1 2 7% 9% 4 5% 5% 5% 8% 54%	4417
	11th to 20th	Night	2 1 4 7% 4 6% 6% 7% 7% 56%	4302
	21st to end	Night	4 3 7% 5% 3 4 4 5% 8% 58%	4521
February	1st to 10th	Night	2 3 6% 5% 3 4 4 5% 9% 60%	2470
	11th to 20th	Night	2 2 5% 5% 2 3 3 6% 9% 61%	2270
	21st to end	Night	3 2 5% 5% 3 4 5% 6% 8% 58%	1884
March	1st to 10th	Night	4 3 4 4 2 4 5% 6% 9% 59%	2261
	11th to 20th	Night	2 7% 3 6% 4 2 3 3 6% 9% 56%	2090
	21st to end	Night	2 4 4 5% 4 3 4 5% 5% 9% 54%	2144
April	1st to 10th	Night	1 5% 2 4 3 2 4 5% 5% 9% 60%	1800
	11th to 20th	Night	2 9% 3 6% 4 2 5% 5% 5% 8% 50%	1777
	21st to end	Night	4 9% 3 5% 4 3 3 4 5% 9% 52%	1800
May	1st to 10th	Night	5% 8% 3 5% 4 3 4 6% 7% 8% 47%	1697
	11th to 20th	Night	6% 10% 3 4 4 3 5% 6% 7% 8% 44%	1417
	21st to end	Night	5% 6% 2 4 5% 3 4 4 5% 10% 51%	1552
June	1st to 10th	Night	3 4 1 3 3 2 4 6% 7% 10% 57%	1440
	11th to 20th	Night	4 3 1 3 3 2 4 5% 6% 10% 59%	1440
	21st to end	Night	3 3 2 3 4 3 3 5% 7% 10% 58%	1440
July	1st to 10th	Night	5% 5% 2 4 4 4 5% 6% 7% 11% 47%	1440
	11th to 20th	Night	2 3 2 3 5% 4 6% 5% 7% 9% 54%	1440
	21st to end	Night	4 5% 3 4 5% 4 7% 6% 8% 12% 43%	1672
August	1st to 10th	Night	5% 6% 2 6% 5% 4 4 6% 6% 10% 47%	1611
	11th to 20th	Night	5% 4 2 4 4 3 5% 5% 6% 9% 53%	1748
	21st to end	Night	4 4 2 7% 5% 4 4 6% 6% 9% 49%	1980
September	1st to 10th	Night	5% 5% 1 4 4 2 5% 5% 6% 8% 55%	1800
	11th to 20th	Night	5% 3 2 4 4 3 4 5% 5% 7% 58%	1800
	21st to end	Night	4 4 2 4 3 3 4 5% 4 6% 61%	1997
October	1st to 10th	Night	5% 3 1 4 4 2 3 4 5% 7% 61%	2160
	11th to 20th	Night	2 2 1 3 2 2 2 3 5% 5% 73%	2160
	21st to end	Night	2 7% 2 4 4 2 3 4 4 7% 60%	2386
November	1st to 10th	Night	2 1 2 3 2 3 3 5% 8% 69%	2405
	11th to 20th	Night	3 1 3 3 2 3 3 6% 9% 66%	2470
	21st to end	Night	1 4 3 4 4 3 4 5% 6% 10% 58%	2597
December	1st to 10th	Night	2 1 4 5% 2 3 4 4 9% 64%	2660
	11th to 20th	Night	3 2 5% 5% 3 4 6% 7% 10% 56%	3271
	21st to end	Night	3 3 6% 7% 4 5% 5% 5% 9% 53%	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% 7% 9% 27% 22% 4	1914
	11th to 20th	Day	37% 7% 10% 25% 17% 4	2090
	21st to end	Day	39% 9% 9% 26% 14% 4	2366
April	1st to 10th	Day	33% 8% 11% 22% 18% 7%	2160
	11th to 20th	Day	45% 7% 9% 19% 17% 4	2134
	21st to end	Day	45% 7% 8% 25% 14% 2	2160
May	1st to 10th	Day	47% 8% 9% 21% 15% 1	2258
	11th to 20th	Day	50% 7% 12% 22% 9% 1	2482
	21st to end	Day	45% 8% 8% 20% 14% 4	2724
June	1st to 10th	Day	36% 8% 13% 19% 18% 6%	2520
	11th to 20th	Day	35% 7% 8% 18% 21% 11%	2520
	21st to end	Day	35% 8% 9% 19% 20% 9%	2520
July	1st to 10th	Day	41% 10% 9% 16% 16% 8%	2451
	11th to 20th	Day	40% 10% 10% 20% 13% 7%	2445
	21st to end	Day	47% 12% 13% 15% 9% 3	2496
August	1st to 10th	Day	50% 10% 11% 13% 13% 4	2313
	11th to 20th	Day	40% 10% 7% 18% 19% 7%	2151
	21st to end	Day	42% 9% 8% 19% 18% 5%	2376
September	1st to 10th	Day	34% 7% 5% 16% 25% 12%	2160
	11th to 20th	Day	32% 7% 7% 19% 25% 9%	2160
	21st to end	Day	27% 7% 5% 24% 28% 7%	1959
October	1st to 10th	Day	33% 7% 6% 20% 26% 8%	1800
	11th to 20th	Day	22% 6% 6% 26% 32% 8%	1800
	21st to end	Day	26% 7% 8% 26% 23% 9%	1949
November	1st to 10th	Day	18% 5% 13% 23% 32% 9%	1673
	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	22% 6% 11% 31% 26% 5%	2261
	11th to 20th	Night	26% 6% 11% 31% 20% 6%	2090
	21st to end	Night	27% 8% 13% 31% 20% 3	2144
April	1st to 10th	Night	21% 9% 13% 30% 22% 6%	1800
	11th to 20th	Night	30% 7% 12% 29% 19% 3	1777
	21st to end	Night	30% 5% 14% 30% 19% 1	1800
May	1st to 10th	Night	33% 6% 15% 28% 15% 3	1697
	11th to 20th	Night	35% 8% 19% 25% 12% 1	1418
	21st to end	Night	29% 6% 14% 27% 19% 4	1552
June	1st to 10th	Night	20% 8% 19% 30% 17% 7%	1440
	11th to 20th	Night	20% 7% 13% 23% 24% 15%	1440
	21st to end	Night	21% 6% 12% 25% 25% 11%	1440
July	1st to 10th	Night	30% 9% 12% 24% 17% 8%	1400
	11th to 20th	Night	22% 9% 16% 26% 20% 7%	1392
	21st to end	Night	30% 10% 25% 23% 10% 3	1579
August	1st to 10th	Night	32% 10% 19% 22% 13% 5%	1602
	11th to 20th	Night	26% 7% 15% 23% 23% 6%	1748
	21st to end	Night	30% 7% 11% 26% 21% 4	1980
September	1st to 10th	Night	26% 6% 11% 22% 26% 10%	1800
	11th to 20th	Night	23% 6% 10% 26% 24% 12%	1800
	21st to end	Night	23% 6% 8% 30% 27% 7%	1997
October	1st to 10th	Night	22% 6% 11% 26% 26% 9%	2160
	11th to 20th	Night	14% 4 10% 29% 32% 11%	2160
	21st to end	Night	24% 5% 10% 28% 25% 8%	2386
November	1st to 10th	Night	15% 6% 13% 25% 31% 10%	2405
	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	16% 43% 29% 11% 1	491
April	1st to 10th	Day	20% 36% 31% 10% 3	420
	11th to 20th	Day	24% 40% 27% 8% 1	412
	21st to end	Day	20% 35% 31% 10% 3 1	420
May	1st to 10th	Day	17% 32% 33% 15% 4 1	495
	11th to 20th	Day	20% 19% 31% 21% 7% 1	625
	21st to end	Day	16% 22% 28% 22% 11% 1	679
June	1st to 10th	Day	9% 19% 28% 28% 13% 3	630
	11th to 20th	Day	10% 20% 36% 22% 10% 2	630
	21st to end	Day	7% 18% 33% 25% 14% 2	630
July	1st to 10th	Day	10% 7% 27% 33% 19% 4	621
	11th to 20th	Day	7% 8% 26% 34% 20% 5%	618
	21st to end	Day	12% 11% 22% 32% 17% 5%	585
August	1st to 10th	Day	14% 15% 31% 27% 11% 2	447
	11th to 20th	Day	11% 13% 28% 31% 13% 4	437
	21st to end	Day	13% 14% 30% 29% 12% 2	495
September	1st to 10th	Day	13% 18% 30% 25% 11% 3	450
	11th to 20th	Day	10% 20% 38% 23% 9% 1	450
	21st to end	Day	10% 21% 31% 21% 13% 4	275
October	1st to 10th	Day	11% 27% 26% 19% 14% 3	270
	11th to 20th	Day	9% 40% 29% 15% 5% 2	270
	21st to end	Day	14% 40% 27% 14% 5% 1	297
November	1st to 10th	Day	13% 47% 21% 12% 7%	270
	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% 4 1	709
April	1st to 10th	Night	12% 28% 39% 19% 2	540
	11th to 20th	Night	11% 32% 34% 17% 6% 1	533
	21st to end	Night	9% 26% 37% 22% 6%	540
May	1st to 10th	Night	10% 17% 41% 22% 9% 1	540
	11th to 20th	Night	15% 11% 29% 34% 11% 1	531
	21st to end	Night	9% 13% 31% 30% 15% 2	584
June	1st to 10th	Night	6% 10% 28% 36% 19% 1	540
	11th to 20th	Night	6% 12% 32% 38% 11% 1	540
	21st to end	Night	4 6% 25% 40% 23% 2	540
July	1st to 10th	Night	7% 2 16% 41% 30% 4	525
	11th to 20th	Night	3 3 15% 39% 37% 3	522
	21st to end	Night	8% 2 11% 38% 36% 5%	591
August	1st to 10th	Night	9% 4 14% 44% 27% 2	537
	11th to 20th	Night	6% 3 19% 43% 25% 4	534
	21st to end	Night	5% 5% 19% 41% 26% 5%	594
September	1st to 10th	Night	6% 5% 23% 40% 22% 5%	540
	11th to 20th	Night	8% 8% 26% 37% 18% 3	540
	21st to end	Night	7% 11% 32% 30% 17% 2	562
October	1st to 10th	Night	8% 21% 33% 25% 12% 2	720
	11th to 20th	Night	6% 31% 30% 23% 9% 2	720
	21st to end	Night	10% 30% 33% 19% 7% 2	802
November	1st to 10th	Night	6% 36% 33% 17% 6% 1	925
	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

Page generated at 2024-03-24 21:37:02. Version ac07

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