Lake Meade Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Meade Observatory clear sky chart from 2005-11-06 to 2026-02-16.

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% 2 6% 4 4 5% 4 6% 8% 40%	131076
	Night	14% 7% 2 6% 4 4 4 4 5% 7% 41%	129777
Transparency	Day	41% 6% 12% 23% 15% 3	134669
	Night	41% 5% 12% 24% 16% 3	134253
Seeing	Day	19% 12% 25% 23% 15% 6%	16455
	Night	17% 9% 29% 31% 12% 1	26006

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	13% 7% 3 9% 5% 5% 5% 3 4 5% 40%	4661
	11th to 20th	Day	11% 9% 3 9% 4 5% 4 3 4 6% 40%	5220
	21st to end	Day	13% 7% 3 7% 5% 5% 6% 4 5% 7% 39%	5780
February	1st to 10th	Day	14% 8% 3 8% 5% 4 5% 4 5% 6% 38%	1890
	11th to 20th	Day	14% 8% 3 9% 5% 4 5% 3 4 6% 38%	1843
	21st to end	Day	19% 8% 3 7% 5% 4 4 3 5% 5% 38%	1650
March	1st to 10th	Day	19% 6% 2 5% 3 4 4 3 4 6% 43%	4795
	11th to 20th	Day	11% 7% 2 6% 4 4 5% 3 6% 8% 44%	4980
	21st to end	Day	15% 8% 2 6% 4 4 5% 4 5% 6% 41%	5592
April	1st to 10th	Day	16% 8% 3 6% 6% 4 5% 4 5% 7% 37%	2400
	11th to 20th	Day	15% 7% 2 6% 5% 4 5% 3 5% 8% 41%	2374
	21st to end	Day	18% 7% 2 5% 4 3 5% 4 5% 7% 40%	2400
May	1st to 10th	Day	24% 7% 2 5% 5% 4 4 4 6% 9% 30%	5817
	11th to 20th	Day	24% 7% 3 6% 4 4 5% 3 6% 7% 31%	6306
	21st to end	Day	17% 5% 2 6% 4 5% 5% 4 6% 9% 37%	6934
June	1st to 10th	Day	12% 6% 2 5% 5% 5% 4 5% 8% 9% 40%	2800
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 4 7% 9% 39%	2800
	21st to end	Day	9% 4 2 5% 4 5% 4 5% 7% 10% 44%	2800
July	1st to 10th	Day	6% 5% 2 6% 5% 5% 5% 5% 7% 11% 43%	6360
	11th to 20th	Day	7% 7% 3 8% 5% 6% 7% 6% 8% 11% 33%	6360
	21st to end	Day	9% 6% 2 7% 5% 4 5% 4 7% 10% 41%	6426
August	1st to 10th	Day	16% 5% 2 7% 4 5% 6% 4 7% 9% 35%	4234
	11th to 20th	Day	12% 6% 2 5% 4 5% 5% 5% 7% 8% 40%	4019
	21st to end	Day	13% 5% 2 5% 3 3 4 3 5% 8% 49%	4312
September	1st to 10th	Day	15% 6% 2 5% 4 4 4 3 4 7% 47%	2400
	11th to 20th	Day	12% 5% 2 5% 3 3 4 4 5% 7% 50%	2400
	21st to end	Day	21% 8% 3 6% 4 3 4 3 5% 7% 37%	2110
October	1st to 10th	Day	16% 5% 2 6% 4 4 3 3 6% 7% 45%	2000
	11th to 20th	Day	16% 6% 2 5% 3 3 4 3 5% 7% 46%	2000
	21st to end	Day	14% 7% 2 6% 4 3 4 3 5% 6% 45%	2200
November	1st to 10th	Day	11% 6% 2 4 3 3 4 2 5% 7% 52%	1901
	11th to 20th	Day	14% 6% 2 5% 4 3 4 4 5% 6% 45%	1834
	21st to end	Day	14% 7% 3 6% 4 4 4 4 5% 6% 43%	1680
December	1st to 10th	Day	14% 6% 3 7% 4 4 4 3 7% 7% 39%	2680
	11th to 20th	Day	19% 9% 3 5% 4 4 4 3 5% 7% 37%	3070
	21st to end	Day	16% 9% 3 8% 6% 5% 5% 4 5% 7% 32%	4048
January	1st to 10th	Night	10% 8% 3 8% 5% 5% 5% 4 6% 8% 38%	8233
	11th to 20th	Night	11% 8% 3 6% 5% 4 4 3 5% 6% 44%	7723
	21st to end	Night	14% 7% 3 5% 4 3 4 3 5% 8% 44%	8401
February	1st to 10th	Night	15% 9% 2 6% 5% 4 5% 3 5% 7% 39%	2730
	11th to 20th	Night	16% 9% 3 8% 4 4 4 3 5% 7% 39%	2554
	21st to end	Night	16% 9% 3 7% 5% 4 4 4 4 5% 38%	1980
March	1st to 10th	Night	16% 7% 3 6% 4 3 3 3 4 6% 45%	5055
	11th to 20th	Night	10% 7% 2 6% 4 4 4 4 5% 6% 50%	4980
	21st to end	Night	12% 8% 2 6% 4 4 4 4 5% 6% 44%	5339
April	1st to 10th	Night	17% 8% 2 7% 5% 4 5% 4 6% 6% 35%	2000
	11th to 20th	Night	14% 6% 2 5% 4 4 4 4 5% 8% 43%	1975
	21st to end	Night	18% 6% 2 4 4 4 4 4 6% 7% 42%	2000
May	1st to 10th	Night	25% 7% 3 7% 4 4 4 4 6% 7% 29%	4108
	11th to 20th	Night	24% 8% 2 6% 4 4 4 3 6% 7% 32%	3585
	21st to end	Night	19% 6% 2 6% 4 4 4 4 6% 8% 35%	3920
June	1st to 10th	Night	13% 5% 2 5% 4 3 5% 4 6% 7% 46%	1600
	11th to 20th	Night	12% 5% 3 5% 5% 3 5% 6% 7% 9% 40%	1600
	21st to end	Night	9% 5% 2 6% 4 5% 5% 4 7% 10% 43%	1600
July	1st to 10th	Night	7% 6% 3 7% 5% 5% 6% 4 6% 11% 40%	3598
	11th to 20th	Night	9% 7% 4 9% 6% 6% 6% 5% 7% 10% 32%	3597
	21st to end	Night	10% 6% 2 6% 4 4 4 4 6% 9% 44%	4421
August	1st to 10th	Night	18% 5% 2 7% 4 4 5% 5% 6% 8% 36%	2915
	11th to 20th	Night	10% 7% 3 7% 5% 4 4 4 5% 8% 41%	2997
	21st to end	Night	13% 5% 2 5% 3 4 4 3 6% 8% 46%	3586
September	1st to 10th	Night	13% 6% 2 6% 4 4 4 3 5% 7% 47%	2000
	11th to 20th	Night	11% 6% 1 5% 4 4 4 3 4 7% 52%	2000
	21st to end	Night	21% 6% 3 5% 4 4 4 3 5% 6% 39%	2286
October	1st to 10th	Night	18% 7% 2 4 3 4 3 3 4 7% 46%	2400
	11th to 20th	Night	15% 5% 2 5% 4 3 3 3 5% 7% 49%	2400
	21st to end	Night	15% 6% 2 5% 3 3 4 3 6% 7% 47%	2640
November	1st to 10th	Night	11% 6% 2 5% 4 3 3 4 5% 5% 52%	2616
	11th to 20th	Night	14% 7% 2 5% 4 4 4 3 5% 7% 45%	2783
	21st to end	Night	13% 5% 2 6% 4 5% 5% 4 6% 6% 44%	2940
December	1st to 10th	Night	10% 5% 2 7% 5% 5% 4 5% 6% 7% 43%	4720
	11th to 20th	Night	21% 7% 2 6% 4 4 4 4 5% 6% 38%	5345
	21st to end	Night	17% 9% 3 8% 5% 5% 5% 4 6% 6% 31%	7150

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	45% 3 11% 23% 15% 2	4662
	11th to 20th	Day	45% 3 10% 18% 16% 8%	5220
	21st to end	Day	43% 4 13% 26% 12% 1	5780
February	1st to 10th	Day	46% 5% 12% 25% 11% 2	1890
	11th to 20th	Day	47% 5% 10% 24% 12% 2	1852
	21st to end	Day	48% 4 10% 21% 12% 4	1650
March	1st to 10th	Day	43% 4 9% 23% 15% 6%	4795
	11th to 20th	Day	37% 5% 11% 27% 14% 5%	4980
	21st to end	Day	43% 4 10% 19% 18% 5%	5592
April	1st to 10th	Day	46% 5% 11% 19% 15% 4	2400
	11th to 20th	Day	41% 5% 11% 22% 17% 4	2374
	21st to end	Day	43% 5% 10% 23% 17% 3	2400
May	1st to 10th	Day	50% 6% 12% 20% 10% 2	5851
	11th to 20th	Day	51% 7% 10% 22% 10% 1	6310
	21st to end	Day	42% 7% 13% 22% 15% 1	6949
June	1st to 10th	Day	38% 7% 14% 24% 16% 1	2800
	11th to 20th	Day	40% 8% 15% 23% 13% 2	2800
	21st to end	Day	33% 8% 14% 28% 16% 1	2800
July	1st to 10th	Day	35% 10% 13% 23% 17% 2	6290
	11th to 20th	Day	42% 9% 16% 22% 9% 1	6285
	21st to end	Day	37% 6% 11% 22% 22% 1	6241
August	1st to 10th	Day	45% 8% 13% 25% 9%	4221
	11th to 20th	Day	39% 7% 11% 28% 15% 1	4058
	21st to end	Day	34% 4 12% 29% 19% 2	4312
September	1st to 10th	Day	38% 5% 11% 21% 21% 4	2400
	11th to 20th	Day	33% 5% 9% 28% 21% 4	2400
	21st to end	Day	48% 5% 8% 18% 19% 2	2110
October	1st to 10th	Day	37% 4 7% 22% 25% 5%	3260
	11th to 20th	Day	28% 4 12% 29% 21% 6%	3240
	21st to end	Day	27% 3 11% 29% 28% 2	3538
November	1st to 10th	Day	32% 4 13% 25% 21% 4	1901
	11th to 20th	Day	38% 5% 11% 23% 19% 3	1834
	21st to end	Day	41% 4 12% 30% 11% 2	1680
December	1st to 10th	Day	42% 4 17% 26% 8% 3	2680
	11th to 20th	Day	48% 4 14% 25% 8% 1	3066
	21st to end	Day	50% 6% 16% 16% 10% 2	4048
January	1st to 10th	Night	43% 4 14% 24% 13% 2	8234
	11th to 20th	Night	39% 4 11% 21% 18% 6%	7723
	21st to end	Night	39% 3 10% 29% 17% 2	8401
February	1st to 10th	Night	45% 4 14% 24% 12% 1	2730
	11th to 20th	Night	45% 4 10% 22% 16% 3	2556
	21st to end	Night	47% 4 11% 20% 15% 4	1980
March	1st to 10th	Night	41% 4 9% 26% 12% 8%	5055
	11th to 20th	Night	35% 5% 13% 30% 13% 5%	4980
	21st to end	Night	40% 4 9% 20% 23% 3	5339
April	1st to 10th	Night	48% 4 10% 19% 15% 4	2000
	11th to 20th	Night	39% 6% 11% 21% 19% 4	1975
	21st to end	Night	39% 6% 10% 23% 18% 4	2000
May	1st to 10th	Night	55% 5% 9% 16% 11% 4	4135
	11th to 20th	Night	49% 6% 12% 21% 11% 1	3586
	21st to end	Night	45% 6% 11% 24% 11% 2	3927
June	1st to 10th	Night	35% 8% 11% 25% 19% 3	1600
	11th to 20th	Night	38% 7% 14% 23% 16% 2	1600
	21st to end	Night	35% 7% 13% 25% 18% 2	1600
July	1st to 10th	Night	38% 9% 14% 20% 16% 4	3560
	11th to 20th	Night	45% 9% 15% 18% 11% 1	3552
	21st to end	Night	36% 6% 13% 23% 21% 1	4292
August	1st to 10th	Night	44% 6% 18% 22% 9% 1	2904
	11th to 20th	Night	40% 6% 11% 26% 16% 1	3024
	21st to end	Night	36% 5% 11% 29% 17% 2	3586
September	1st to 10th	Night	37% 5% 12% 20% 22% 4	2000
	11th to 20th	Night	33% 5% 9% 27% 24% 3	2000
	21st to end	Night	45% 6% 9% 20% 18% 2	2286
October	1st to 10th	Night	40% 4 10% 22% 22% 2	3920
	11th to 20th	Night	27% 4 10% 28% 27% 4	3899
	21st to end	Night	26% 3 11% 34% 24% 3	4252
November	1st to 10th	Night	33% 5% 11% 25% 22% 4	2616
	11th to 20th	Night	38% 4 9% 25% 19% 5%	2783
	21st to end	Night	39% 4 13% 27% 15% 2	2940
December	1st to 10th	Night	39% 5% 14% 30% 11% 1	4720
	11th to 20th	Night	46% 4 14% 22% 13% 2	5348
	21st to end	Night	50% 6% 13% 18% 13% 1	7150

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	25% 24% 30% 16% 3 1	220
	11th to 20th	Day	26% 29% 32% 10% 3	319
	21st to end	Day	22% 27% 34% 12% 4 1	363
February	1st to 10th	Day	21% 25% 38% 14% 2 1	330
	11th to 20th	Day	28% 26% 34% 10% 1	360
	21st to end	Day	30% 16% 34% 17% 3	414
March	1st to 10th	Day	21% 20% 31% 23% 5%	500
	11th to 20th	Day	20% 22% 33% 18% 5% 1	500
	21st to end	Day	25% 18% 29% 20% 6% 1	550
April	1st to 10th	Day	26% 17% 31% 18% 7% 1	500
	11th to 20th	Day	20% 17% 29% 18% 12% 4	492
	21st to end	Day	25% 11% 28% 23% 9% 3	500
May	1st to 10th	Day	27% 11% 27% 22% 10% 3	503
	11th to 20th	Day	21% 12% 27% 23% 13% 5%	527
	21st to end	Day	20% 5% 19% 27% 22% 8%	573
June	1st to 10th	Day	16% 8% 26% 23% 19% 8%	530
	11th to 20th	Day	16% 7% 22% 27% 20% 7%	530
	21st to end	Day	11% 5% 24% 31% 20% 8%	530
July	1st to 10th	Day	12% 4 16% 29% 25% 14%	525
	11th to 20th	Day	6% 4 18% 30% 30% 13%	524
	21st to end	Day	12% 3 19% 32% 25% 8%	576
August	1st to 10th	Day	13% 3 15% 29% 31% 10%	526
	11th to 20th	Day	13% 5% 15% 30% 24% 12%	519
	21st to end	Day	12% 5% 15% 30% 24% 13%	583
September	1st to 10th	Day	17% 5% 17% 24% 23% 14%	530
	11th to 20th	Day	14% 3 14% 29% 26% 14%	530
	21st to end	Day	27% 7% 22% 24% 15% 5%	530
October	1st to 10th	Day	21% 6% 20% 25% 18% 10%	530
	11th to 20th	Day	16% 15% 27% 24% 16% 2	530
	21st to end	Day	16% 11% 37% 23% 10% 3	583
November	1st to 10th	Day	15% 13% 30% 27% 13% 2	452
	11th to 20th	Day	19% 16% 29% 25% 11% 1	374
	21st to end	Day	21% 22% 31% 18% 8%	220
December	1st to 10th	Day	25% 23% 30% 15% 6% 2	220
	11th to 20th	Day	24% 17% 33% 20% 5% 1	220
	21st to end	Day	23% 18% 30% 19% 9% 1	242
January	1st to 10th	Night	15% 16% 43% 23% 3	840
	11th to 20th	Night	20% 16% 33% 28% 3	840
	21st to end	Night	18% 13% 42% 25% 2	924
February	1st to 10th	Night	20% 15% 34% 28% 3	840
	11th to 20th	Night	21% 19% 41% 18% 1	804
	21st to end	Night	22% 15% 43% 18% 3	660
March	1st to 10th	Night	17% 15% 39% 24% 4	800
	11th to 20th	Night	22% 13% 36% 24% 6%	800
	21st to end	Night	20% 11% 39% 24% 5% 1	880
April	1st to 10th	Night	22% 15% 36% 22% 5%	800
	11th to 20th	Night	17% 11% 34% 29% 8% 1	791
	21st to end	Night	20% 9% 32% 31% 8%	800
May	1st to 10th	Night	22% 7% 26% 33% 12%	636
	11th to 20th	Night	21% 5% 26% 37% 11%	404
	21st to end	Night	16% 3 19% 45% 17% 1	433
June	1st to 10th	Night	13% 2 24% 40% 21% 1	400
	11th to 20th	Night	14% 3 22% 43% 18% 1	400
	21st to end	Night	11% 2 23% 49% 16% 1	400
July	1st to 10th	Night	11% 3 16% 41% 26% 2	390
	11th to 20th	Night	7% 1 12% 48% 29% 2	388
	21st to end	Night	10% 2 13% 45% 28% 1	651
August	1st to 10th	Night	12% 2 9% 46% 29% 2	597
	11th to 20th	Night	11% 3 11% 43% 28% 3	664
	21st to end	Night	14% 2 13% 39% 29% 3	880
September	1st to 10th	Night	15% 2 17% 37% 27% 3	800
	11th to 20th	Night	13% 3 13% 39% 29% 3	800
	21st to end	Night	24% 3 17% 35% 21% 2	800
October	1st to 10th	Night	21% 3 21% 31% 20% 4	800
	11th to 20th	Night	18% 7% 28% 33% 12% 1	800
	21st to end	Night	18% 6% 34% 31% 10% 1	880
November	1st to 10th	Night	14% 8% 32% 35% 10% 1	820
	11th to 20th	Night	17% 13% 33% 29% 8% 1	840
	21st to end	Night	16% 13% 35% 29% 7%	840
December	1st to 10th	Night	19% 13% 38% 23% 6%	840
	11th to 20th	Night	19% 9% 38% 29% 4	840
	21st to end	Night	20% 10% 37% 30% 3	924

Page generated at 2026-02-13 01:42:11. Version ac07

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