Lilly Bluff Overlook
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lilly Bluff Overlook clear sky chart from 2005-11-06 to 2024-01-16.

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	14% 7% 3 6% 6% 3 5% 5% 6% 7% 37%	74896
	Night	13% 7% 3 6% 5% 3 5% 5% 5% 7% 41%	74920
Transparency	Day	44% 7% 11% 20% 15% 3	74619
	Night	42% 6% 12% 21% 16% 3	74716
Seeing	Day	18% 13% 24% 22% 15% 7%	13633
	Night	16% 12% 23% 28% 18% 3	23740

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	17% 11% 4 7% 5% 3 5% 4 4 6% 34%	1706
	11th to 20th	Day	22% 11% 3 9% 6% 2 4 4 3 6% 30%	1665
	21st to end	Day	16% 9% 5% 6% 4 3 3 4 5% 6% 39%	1812
February	1st to 10th	Day	18% 11% 5% 7% 5% 3 4 4 4 6% 32%	1800
	11th to 20th	Day	22% 9% 4 8% 5% 3 4 5% 4 5% 31%	1748
	21st to end	Day	21% 9% 4 6% 5% 3 4 4 4 5% 35%	1480
March	1st to 10th	Day	15% 8% 3 6% 6% 3 5% 4 5% 7% 37%	1814
	11th to 20th	Day	21% 10% 3 7% 5% 4 4 4 4 6% 32%	1980
	21st to end	Day	16% 10% 3 7% 6% 3 5% 5% 4 6% 33%	2178
April	1st to 10th	Day	12% 8% 3 6% 5% 3 4 4 5% 7% 43%	2105
	11th to 20th	Day	15% 8% 3 5% 5% 3 3 4 5% 7% 43%	2134
	21st to end	Day	14% 7% 3 5% 5% 3 5% 5% 5% 6% 41%	2319
May	1st to 10th	Day	15% 7% 3 5% 4 3 6% 5% 6% 8% 39%	2340
	11th to 20th	Day	13% 8% 3 7% 6% 4 6% 4 6% 7% 35%	2301
	21st to end	Day	10% 6% 2 7% 6% 4 5% 6% 7% 10% 38%	2531
June	1st to 10th	Day	10% 6% 3 6% 5% 4 6% 7% 8% 9% 36%	2340
	11th to 20th	Day	6% 4 3 6% 7% 4 6% 7% 7% 10% 41%	2340
	21st to end	Day	7% 4 3 5% 7% 5% 6% 6% 8% 11% 38%	2340
July	1st to 10th	Day	10% 6% 3 7% 8% 6% 8% 7% 7% 10% 29%	2340
	11th to 20th	Day	11% 6% 3 7% 7% 5% 6% 9% 7% 10% 30%	2340
	21st to end	Day	10% 6% 3 7% 7% 5% 8% 7% 9% 10% 28%	2547
August	1st to 10th	Day	9% 7% 4 6% 7% 4 7% 7% 8% 10% 29%	2327
	11th to 20th	Day	10% 6% 3 7% 7% 5% 6% 7% 7% 10% 32%	2199
	21st to end	Day	11% 6% 3 7% 6% 4 7% 7% 8% 10% 33%	2376
September	1st to 10th	Day	14% 6% 3 6% 6% 4 5% 6% 6% 8% 37%	2032
	11th to 20th	Day	14% 6% 2 6% 6% 4 5% 5% 5% 8% 39%	1980
	21st to end	Day	14% 5% 2 5% 5% 4 4 4 5% 8% 46%	1980
October	1st to 10th	Day	11% 5% 1 5% 4 2 3 5% 5% 6% 52%	1980
	11th to 20th	Day	13% 5% 2 6% 3 2 3 4 5% 5% 52%	1879
	21st to end	Day	15% 6% 2 4 4 2 3 4 5% 7% 47%	1904
November	1st to 10th	Day	10% 5% 3 4 4 2 4 5% 5% 5% 55%	1672
	11th to 20th	Day	13% 6% 3 6% 5% 2 4 4 5% 6% 47%	1710
	21st to end	Day	16% 7% 4 5% 4 4 4 4 4 6% 44%	1710
December	1st to 10th	Day	19% 11% 4 8% 6% 3 4 4 4 5% 33%	1710
	11th to 20th	Day	14% 11% 4 6% 7% 3 4 5% 5% 6% 34%	2153
	21st to end	Day	18% 13% 4 6% 5% 3 5% 4 5% 7% 30%	3124
January	1st to 10th	Night	16% 9% 4 6% 6% 3 4 4 5% 6% 37%	2459
	11th to 20th	Night	18% 11% 4 8% 6% 4 4 4 6% 6% 29%	2417
	21st to end	Night	15% 9% 4 7% 5% 4 4 4 5% 4 38%	2542
February	1st to 10th	Night	18% 8% 3 7% 6% 3 5% 5% 5% 7% 34%	2160
	11th to 20th	Night	22% 8% 4 7% 6% 3 5% 4 3 5% 33%	2098
	21st to end	Night	21% 9% 5% 7% 6% 4 4 4 4 5% 31%	1776
March	1st to 10th	Night	14% 7% 3 6% 6% 4 5% 5% 5% 6% 40%	2143
	11th to 20th	Night	16% 9% 3 7% 6% 3 4 4 5% 6% 36%	1980
	21st to end	Night	15% 8% 3 6% 6% 3 6% 5% 5% 7% 37%	2178
April	1st to 10th	Night	12% 4 2 3 4 4 5% 5% 5% 8% 46%	1870
	11th to 20th	Night	13% 6% 2 5% 4 3 4 4 5% 6% 49%	1775
	21st to end	Night	12% 5% 2 6% 5% 4 4 5% 5% 8% 44%	1639
May	1st to 10th	Night	11% 7% 3 5% 5% 3 4 5% 5% 8% 44%	1620
	11th to 20th	Night	10% 6% 3 6% 5% 3 5% 5% 7% 8% 43%	1592
	21st to end	Night	5% 5% 3 7% 7% 3 6% 5% 7% 10% 40%	1744
June	1st to 10th	Night	6% 5% 3 5% 6% 3 5% 7% 6% 9% 43%	1620
	11th to 20th	Night	4 2 2 5% 4 3 5% 5% 7% 12% 51%	1620
	21st to end	Night	6% 4 2 5% 7% 4 5% 5% 7% 13% 42%	1620
July	1st to 10th	Night	9% 5% 2 6% 6% 5% 6% 7% 8% 10% 37%	1620
	11th to 20th	Night	7% 4 2 5% 5% 3 7% 7% 5% 12% 43%	1620
	21st to end	Night	6% 5% 3 6% 6% 3 8% 7% 7% 12% 37%	1771
August	1st to 10th	Night	7% 6% 2 5% 5% 3 6% 5% 7% 10% 43%	1611
	11th to 20th	Night	8% 6% 2 6% 6% 4 4 5% 7% 9% 43%	1698
	21st to end	Night	10% 5% 2 4 5% 3 5% 5% 7% 9% 44%	1980
September	1st to 10th	Night	11% 6% 2 6% 6% 4 5% 4 5% 7% 45%	1908
	11th to 20th	Night	11% 5% 2 6% 5% 3 4 5% 4 8% 46%	1980
	21st to end	Night	10% 5% 2 6% 4 2 4 3 4 6% 54%	1980
October	1st to 10th	Night	10% 5% 2 4 3 2 3 3 3 7% 58%	1980
	11th to 20th	Night	14% 5% 3 5% 4 2 3 4 4 6% 51%	2079
	21st to end	Night	13% 7% 3 5% 5% 2 4 3 3 6% 49%	2450
November	1st to 10th	Night	10% 5% 3 5% 5% 3 3 4 4 6% 52%	2406
	11th to 20th	Night	12% 7% 2 5% 4 2 5% 4 4 7% 47%	2470
	21st to end	Night	14% 8% 4 5% 4 2 4 5% 4 6% 43%	2470
December	1st to 10th	Night	19% 10% 4 7% 5% 3 4 3 5% 6% 32%	2470
	11th to 20th	Night	15% 10% 5% 8% 5% 3 4 3 4 5% 37%	3042
	21st to end	Night	17% 10% 6% 7% 6% 5% 6% 6% 6% 6% 25%	4532

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	52% 4 8% 19% 14% 3	1707
	11th to 20th	Day	57% 4 8% 16% 13% 2	1665
	21st to end	Day	45% 5% 10% 21% 17% 1	1812
February	1st to 10th	Day	54% 5% 7% 17% 15% 2	1800
	11th to 20th	Day	55% 5% 7% 18% 11% 3	1758
	21st to end	Day	52% 5% 9% 14% 15% 5%	1480
March	1st to 10th	Day	47% 5% 9% 18% 17% 5%	1814
	11th to 20th	Day	53% 5% 9% 17% 12% 3	1980
	21st to end	Day	50% 7% 11% 20% 12% 1	2178
April	1st to 10th	Day	41% 5% 12% 23% 16% 3	2105
	11th to 20th	Day	42% 5% 9% 17% 24% 3	2134
	21st to end	Day	43% 6% 11% 25% 14% 1	2319
May	1st to 10th	Day	42% 7% 12% 26% 12% 2	2340
	11th to 20th	Day	47% 10% 13% 19% 11% 1	2305
	21st to end	Day	40% 9% 15% 22% 11% 2	2531
June	1st to 10th	Day	41% 10% 15% 20% 13% 1	2340
	11th to 20th	Day	36% 11% 17% 21% 14% 2	2340
	21st to end	Day	37% 10% 17% 19% 12% 4	2340
July	1st to 10th	Day	45% 13% 12% 17% 11% 2	2275
	11th to 20th	Day	46% 10% 15% 15% 10% 3	2271
	21st to end	Day	45% 11% 14% 20% 8% 1	2405
August	1st to 10th	Day	45% 12% 16% 18% 8% 1	2314
	11th to 20th	Day	44% 11% 13% 17% 13% 1	2199
	21st to end	Day	42% 11% 15% 17% 12% 3	2376
September	1st to 10th	Day	43% 8% 12% 19% 15% 4	2032
	11th to 20th	Day	41% 8% 12% 20% 16% 2	1980
	21st to end	Day	37% 6% 10% 23% 19% 6%	1980
October	1st to 10th	Day	33% 5% 10% 22% 24% 6%	1980
	11th to 20th	Day	35% 5% 9% 21% 24% 7%	1879
	21st to end	Day	37% 4 9% 24% 22% 4	1904
November	1st to 10th	Day	32% 4 7% 24% 27% 5%	1672
	11th to 20th	Day	38% 4 6% 23% 23% 6%	1710
	21st to end	Day	42% 4 9% 22% 21% 3	1710
December	1st to 10th	Day	54% 4 5% 21% 13% 2	1710
	11th to 20th	Day	49% 5% 10% 17% 16% 2	2150
	21st to end	Day	52% 5% 11% 20% 11% 2	3124
January	1st to 10th	Night	47% 4 12% 19% 15% 3	2459
	11th to 20th	Night	54% 5% 10% 15% 13% 3	2417
	21st to end	Night	49% 4 10% 21% 15% 2	2542
February	1st to 10th	Night	50% 5% 10% 19% 14% 2	2160
	11th to 20th	Night	54% 4 7% 19% 12% 4	2099
	21st to end	Night	55% 6% 6% 15% 14% 4	1776
March	1st to 10th	Night	44% 5% 11% 15% 19% 6%	2143
	11th to 20th	Night	49% 6% 9% 20% 14% 3	1980
	21st to end	Night	47% 6% 11% 22% 12% 2	2178
April	1st to 10th	Night	35% 6% 12% 25% 20% 3	1870
	11th to 20th	Night	36% 5% 10% 20% 22% 7%	1775
	21st to end	Night	38% 6% 12% 29% 13% 1	1639
May	1st to 10th	Night	38% 7% 12% 27% 14% 3	1620
	11th to 20th	Night	37% 10% 17% 23% 12% 1	1593
	21st to end	Night	37% 11% 16% 23% 12% 1	1745
June	1st to 10th	Night	35% 10% 15% 26% 13% 2	1620
	11th to 20th	Night	25% 9% 22% 29% 14% 2	1620
	21st to end	Night	34% 11% 15% 24% 13% 4	1620
July	1st to 10th	Night	39% 12% 14% 19% 13% 2	1575
	11th to 20th	Night	32% 10% 20% 18% 14% 5%	1566
	21st to end	Night	34% 12% 19% 23% 10% 2	1672
August	1st to 10th	Night	34% 10% 18% 26% 11% 1	1600
	11th to 20th	Night	36% 11% 19% 19% 14% 2	1698
	21st to end	Night	35% 9% 16% 24% 14% 2	1980
September	1st to 10th	Night	37% 7% 13% 20% 17% 5%	1908
	11th to 20th	Night	36% 9% 11% 20% 22% 2	1980
	21st to end	Night	33% 6% 8% 24% 24% 5%	1980
October	1st to 10th	Night	29% 5% 9% 23% 27% 7%	1980
	11th to 20th	Night	35% 5% 10% 21% 21% 8%	2079
	21st to end	Night	37% 3 6% 22% 24% 7%	2450
November	1st to 10th	Night	34% 4 8% 21% 25% 8%	2406
	11th to 20th	Night	37% 4 7% 20% 24% 8%	2470
	21st to end	Night	43% 3 7% 24% 20% 3	2470
December	1st to 10th	Night	53% 5% 9% 19% 13% 3	2470
	11th to 20th	Night	49% 3 9% 19% 18% 3	3044
	21st to end	Night	55% 6% 12% 16% 11% 1	4532

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	28% 29% 30% 12% 1	270
	11th to 20th	Day	35% 28% 22% 12% 2 1	255
	21st to end	Day	24% 33% 31% 8% 3	264
February	1st to 10th	Day	33% 27% 29% 10% 1	240
	11th to 20th	Day	43% 28% 26% 3	240
	21st to end	Day	41% 25% 28% 4 1	198
March	1st to 10th	Day	28% 23% 37% 11% 1	254
	11th to 20th	Day	26% 28% 26% 15% 4	420
	21st to end	Day	25% 23% 30% 16% 6%	462
April	1st to 10th	Day	23% 20% 25% 21% 10% 1	420
	11th to 20th	Day	20% 18% 31% 19% 10% 1	412
	21st to end	Day	21% 15% 32% 17% 13% 1	420
May	1st to 10th	Day	19% 16% 34% 18% 9% 4	423
	11th to 20th	Day	14% 11% 27% 26% 14% 7%	447
	21st to end	Day	14% 8% 21% 28% 17% 12%	485
June	1st to 10th	Day	12% 7% 22% 28% 18% 13%	450
	11th to 20th	Day	5% 5% 18% 30% 28% 14%	450
	21st to end	Day	8% 5% 24% 30% 21% 12%	450
July	1st to 10th	Day	9% 4 15% 27% 24% 20%	445
	11th to 20th	Day	9% 7% 15% 26% 25% 18%	444
	21st to end	Day	11% 5% 13% 26% 30% 15%	488
August	1st to 10th	Day	14% 4 17% 26% 22% 15%	446
	11th to 20th	Day	11% 3 17% 32% 26% 11%	439
	21st to end	Day	12% 5% 11% 26% 30% 16%	495
September	1st to 10th	Day	11% 5% 15% 27% 30% 13%	450
	11th to 20th	Day	15% 4 14% 27% 29% 12%	450
	21st to end	Day	16% 5% 18% 29% 25% 8%	450
October	1st to 10th	Day	12% 9% 22% 25% 23% 8%	450
	11th to 20th	Day	16% 14% 28% 24% 14% 3	450
	21st to end	Day	21% 13% 30% 22% 12% 2	419
November	1st to 10th	Day	16% 13% 36% 26% 7% 2	270
	11th to 20th	Day	19% 17% 40% 21% 3	270
	21st to end	Day	18% 21% 37% 17% 6% 1	270
December	1st to 10th	Day	31% 21% 31% 12% 4	270
	11th to 20th	Day	25% 24% 27% 17% 6%	270
	21st to end	Day	31% 23% 33% 11% 2 1	297
January	1st to 10th	Night	21% 24% 31% 20% 4	760
	11th to 20th	Night	27% 23% 27% 19% 4	744
	21st to end	Night	21% 20% 37% 21% 2	792
February	1st to 10th	Night	22% 17% 35% 23% 3	720
	11th to 20th	Night	28% 21% 33% 18% 1	703
	21st to end	Night	29% 23% 28% 19% 1	592
March	1st to 10th	Night	20% 17% 34% 25% 3	720
	11th to 20th	Night	20% 20% 30% 23% 6% 1	720
	21st to end	Night	23% 15% 28% 26% 8%	792
April	1st to 10th	Night	15% 17% 29% 28% 11%	610
	11th to 20th	Night	16% 12% 30% 29% 13% 1	533
	21st to end	Night	13% 10% 31% 34% 11% 1	540
May	1st to 10th	Night	13% 11% 28% 32% 15% 2	540
	11th to 20th	Night	11% 8% 21% 35% 21% 4	531
	21st to end	Night	7% 4 17% 33% 33% 6%	584
June	1st to 10th	Night	7% 5% 14% 38% 31% 5%	540
	11th to 20th	Night	3 2 15% 36% 37% 7%	540
	21st to end	Night	6% 3 12% 39% 31% 8%	540
July	1st to 10th	Night	11% 2 6% 31% 40% 10%	525
	11th to 20th	Night	7% 4 8% 27% 43% 11%	522
	21st to end	Night	7% 2 9% 31% 42% 10%	591
August	1st to 10th	Night	9% 3 8% 28% 44% 8%	537
	11th to 20th	Night	8% 3 10% 33% 41% 5%	534
	21st to end	Night	10% 3 7% 29% 40% 11%	594
September	1st to 10th	Night	9% 3 11% 31% 38% 8%	648
	11th to 20th	Night	13% 2 12% 31% 35% 8%	720
	21st to end	Night	13% 4 17% 31% 32% 4	720
October	1st to 10th	Night	13% 7% 18% 26% 30% 7%	720
	11th to 20th	Night	16% 9% 25% 30% 18% 2	720
	21st to end	Night	15% 12% 26% 31% 14% 2	792
November	1st to 10th	Night	12% 11% 21% 36% 17% 3	740
	11th to 20th	Night	14% 18% 29% 27% 11% 1	760
	21st to end	Night	18% 17% 25% 29% 10%	760
December	1st to 10th	Night	24% 20% 27% 24% 6%	760
	11th to 20th	Night	20% 17% 28% 28% 6% 1	760
	21st to end	Night	27% 17% 27% 25% 4	836

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