Leon Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Leon Observing Site clear sky chart from 2005-11-06 to 2026-01-17.

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	15% 9% 3 8% 5% 5% 5% 4 6% 7% 34%	127459
	Night	15% 10% 3 8% 5% 4 4 3 5% 7% 35%	124251
Transparency	Day	47% 6% 10% 21% 14% 2	131131
	Night	47% 5% 10% 21% 14% 2	128648
Seeing	Day	22% 13% 26% 22% 13% 5%	16556
	Night	20% 10% 24% 29% 15% 2	26674

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	16% 20% 7% 12% 7% 4 3 3 4 5% 19%	4146
	11th to 20th	Day	16% 19% 8% 11% 6% 4 4 2 3 4 23%	4114
	21st to end	Day	19% 14% 5% 9% 6% 5% 4 3 5% 5% 24%	4466
February	1st to 10th	Day	22% 12% 5% 9% 5% 3 4 2 4 5% 29%	1800
	11th to 20th	Day	22% 13% 4 9% 5% 4 3 4 4 5% 27%	1896
	21st to end	Day	21% 14% 3 8% 4 3 3 3 3 6% 31%	1650
March	1st to 10th	Day	18% 13% 4 8% 4 4 4 3 4 6% 32%	4837
	11th to 20th	Day	14% 7% 2 6% 4 4 5% 4 5% 8% 42%	4980
	21st to end	Day	17% 9% 3 8% 5% 4 5% 4 6% 7% 32%	5465
April	1st to 10th	Day	16% 10% 3 7% 5% 5% 4 3 6% 6% 36%	2200
	11th to 20th	Day	16% 8% 3 7% 4 4 4 3 5% 7% 39%	2501
	21st to end	Day	18% 8% 2 7% 5% 5% 5% 4 6% 7% 35%	2600
May	1st to 10th	Day	17% 9% 3 9% 5% 6% 6% 5% 7% 7% 26%	5862
	11th to 20th	Day	18% 9% 3 8% 5% 5% 5% 4 6% 7% 31%	5861
	21st to end	Day	15% 6% 2 7% 5% 5% 6% 4 7% 8% 34%	6433
June	1st to 10th	Day	12% 5% 2 6% 5% 4 5% 5% 7% 10% 40%	2600
	11th to 20th	Day	9% 6% 2 7% 5% 5% 6% 5% 7% 10% 38%	2600
	21st to end	Day	10% 5% 2 5% 5% 6% 5% 5% 8% 10% 40%	2600
July	1st to 10th	Day	9% 5% 2 7% 6% 5% 4 4 6% 9% 44%	5900
	11th to 20th	Day	10% 6% 3 7% 5% 5% 6% 5% 8% 10% 33%	5900
	21st to end	Day	13% 8% 3 8% 6% 5% 6% 4 7% 8% 31%	6424
August	1st to 10th	Day	9% 6% 3 8% 5% 5% 6% 5% 8% 11% 35%	4234
	11th to 20th	Day	10% 6% 2 7% 5% 5% 6% 5% 7% 10% 38%	4174
	21st to end	Day	6% 4 1 5% 4 4 5% 4 6% 8% 53%	4576
September	1st to 10th	Day	13% 5% 2 5% 4 4 4 4 5% 7% 47%	2210
	11th to 20th	Day	10% 5% 2 6% 4 5% 4 4 5% 6% 48%	2200
	21st to end	Day	19% 7% 2 6% 4 4 5% 3 4 5% 40%	2200
October	1st to 10th	Day	13% 6% 2 5% 3 3 3 3 6% 7% 48%	2105
	11th to 20th	Day	14% 7% 3 5% 3 4 4 3 4 6% 46%	2000
	21st to end	Day	19% 7% 3 6% 5% 4 3 2 5% 6% 40%	2200
November	1st to 10th	Day	13% 7% 2 6% 4 3 3 3 4 6% 50%	1897
	11th to 20th	Day	16% 11% 2 7% 4 5% 4 3 4 5% 38%	1890
	21st to end	Day	17% 11% 3 7% 5% 5% 3 3 5% 5% 35%	1890
December	1st to 10th	Day	21% 13% 4 10% 6% 4 3 3 4 4 29%	3020
	11th to 20th	Day	24% 13% 5% 8% 4 3 4 4 4 5% 25%	3463
	21st to end	Day	18% 17% 4 11% 6% 5% 5% 3 5% 6% 20%	4565
January	1st to 10th	Night	16% 17% 6% 16% 5% 4 4 3 4 4 19%	6019
	11th to 20th	Night	19% 15% 6% 13% 6% 4 4 3 3 4 23%	5979
	21st to end	Night	21% 11% 4 8% 6% 4 3 3 4 5% 31%	6490
February	1st to 10th	Night	21% 14% 4 8% 5% 4 4 3 4 5% 29%	2600
	11th to 20th	Night	22% 12% 4 10% 5% 4 4 2 4 5% 27%	2388
	21st to end	Night	22% 14% 3 8% 4 4 4 3 5% 5% 29%	1980
March	1st to 10th	Night	19% 11% 2 6% 4 4 4 3 4 6% 37%	5016
	11th to 20th	Night	12% 9% 3 6% 4 3 4 3 6% 9% 42%	4980
	21st to end	Night	16% 10% 3 9% 6% 5% 5% 3 5% 5% 33%	5467
April	1st to 10th	Night	16% 10% 3 6% 5% 3 4 4 5% 6% 37%	2200
	11th to 20th	Night	14% 8% 3 6% 4 3 4 4 6% 7% 41%	1863
	21st to end	Night	16% 7% 3 6% 5% 5% 4 4 5% 6% 39%	1800
May	1st to 10th	Night	20% 10% 3 9% 5% 5% 5% 4 6% 7% 26%	4033
	11th to 20th	Night	16% 8% 3 8% 5% 5% 5% 4 6% 8% 33%	4032
	21st to end	Night	17% 7% 3 7% 5% 5% 5% 4 6% 8% 34%	4421
June	1st to 10th	Night	10% 6% 2 5% 5% 5% 4 4 6% 10% 44%	1800
	11th to 20th	Night	9% 5% 2 6% 5% 4 4 5% 7% 11% 42%	1800
	21st to end	Night	9% 5% 2 5% 4 4 5% 5% 7% 10% 44%	1800
July	1st to 10th	Night	9% 6% 3 7% 4 4 4 4 6% 9% 44%	4058
	11th to 20th	Night	11% 7% 3 7% 5% 5% 6% 4 7% 9% 36%	4057
	21st to end	Night	10% 7% 3 7% 5% 5% 6% 5% 7% 9% 36%	4427
August	1st to 10th	Night	10% 7% 2 8% 5% 6% 5% 5% 6% 9% 36%	2915
	11th to 20th	Night	11% 7% 3 7% 5% 4 4 4 7% 8% 42%	2875
	21st to end	Night	5% 3 1 6% 4 4 4 4 7% 10% 53%	3289
September	1st to 10th	Night	12% 4 1 5% 4 3 5% 4 5% 7% 50%	2186
	11th to 20th	Night	10% 4 1 5% 4 3 4 3 5% 6% 54%	2200
	21st to end	Night	16% 6% 2 6% 5% 4 4 4 5% 7% 42%	2200
October	1st to 10th	Night	11% 5% 2 5% 4 4 4 3 5% 7% 51%	2295
	11th to 20th	Night	14% 6% 2 6% 3 4 4 3 5% 7% 47%	2400
	21st to end	Night	20% 7% 2 5% 4 3 4 3 4 5% 42%	2640
November	1st to 10th	Night	11% 7% 2 6% 4 3 4 3 5% 6% 50%	2616
	11th to 20th	Night	17% 10% 3 6% 4 4 4 3 5% 6% 38%	2730
	21st to end	Night	19% 11% 4 7% 4 4 4 3 4 6% 36%	2730
December	1st to 10th	Night	18% 12% 4 11% 5% 4 4 3 4 5% 30%	4380
	11th to 20th	Night	19% 14% 6% 9% 4 4 4 3 4 5% 28%	4952
	21st to end	Night	18% 16% 4 10% 6% 5% 5% 4 5% 6% 21%	6633

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	69% 3 10% 13% 5%	4147
	11th to 20th	Day	67% 3 6% 14% 9% 1	4114
	21st to end	Day	62% 3 8% 18% 7% 1	4466
February	1st to 10th	Day	60% 3 10% 18% 9% 1	1800
	11th to 20th	Day	60% 4 9% 16% 10% 1	1906
	21st to end	Day	55% 5% 8% 20% 10% 1	1650
March	1st to 10th	Day	53% 4 7% 22% 10% 4	4837
	11th to 20th	Day	39% 4 9% 26% 19% 3	4980
	21st to end	Day	49% 5% 10% 21% 13% 2	5465
April	1st to 10th	Day	47% 6% 11% 20% 13% 3	2200
	11th to 20th	Day	44% 6% 9% 21% 17% 4	2501
	21st to end	Day	48% 6% 12% 20% 12% 3	2600
May	1st to 10th	Day	53% 7% 11% 16% 10% 2	5897
	11th to 20th	Day	51% 6% 10% 21% 10% 1	5865
	21st to end	Day	44% 7% 14% 19% 13% 3	6447
June	1st to 10th	Day	37% 8% 13% 24% 17% 1	2600
	11th to 20th	Day	39% 10% 14% 19% 16% 2	2600
	21st to end	Day	37% 10% 15% 23% 14% 3	2600
July	1st to 10th	Day	37% 7% 11% 26% 17% 2	5835
	11th to 20th	Day	42% 10% 13% 24% 10% 1	5831
	21st to end	Day	47% 7% 12% 17% 15% 1	6240
August	1st to 10th	Day	40% 9% 14% 27% 10%	4221
	11th to 20th	Day	40% 7% 10% 27% 16% 1	4213
	21st to end	Day	27% 7% 13% 29% 21% 2	4576
September	1st to 10th	Day	36% 6% 10% 20% 22% 6%	2210
	11th to 20th	Day	35% 6% 11% 25% 21% 3	2200
	21st to end	Day	45% 7% 8% 20% 19% 1	2200
October	1st to 10th	Day	27% 4 8% 24% 34% 3	3430
	11th to 20th	Day	30% 3 11% 28% 22% 5%	3240
	21st to end	Day	33% 3 10% 29% 22% 3	3538
November	1st to 10th	Day	37% 4 9% 27% 19% 3	1897
	11th to 20th	Day	48% 4 8% 20% 17% 3	1890
	21st to end	Day	51% 5% 9% 19% 15% 1	1890
December	1st to 10th	Day	60% 4 8% 22% 6%	3020
	11th to 20th	Day	61% 4 10% 17% 8%	3460
	21st to end	Day	65% 5% 10% 15% 5%	4565
January	1st to 10th	Night	68% 4 9% 14% 5% 1	6019
	11th to 20th	Night	65% 3 8% 14% 7% 2	5979
	21st to end	Night	57% 3 9% 21% 9% 1	6490
February	1st to 10th	Night	58% 4 10% 18% 10% 1	2600
	11th to 20th	Night	60% 4 7% 16% 12%	2389
	21st to end	Night	57% 4 9% 16% 10% 3	1980
March	1st to 10th	Night	49% 3 6% 24% 15% 3	5016
	11th to 20th	Night	38% 5% 8% 26% 21% 2	4980
	21st to end	Night	52% 4 7% 21% 14% 2	5467
April	1st to 10th	Night	46% 6% 9% 19% 16% 3	2200
	11th to 20th	Night	41% 6% 11% 21% 15% 6%	1863
	21st to end	Night	45% 6% 10% 20% 18% 2	1800
May	1st to 10th	Night	56% 7% 11% 13% 10% 3	4060
	11th to 20th	Night	47% 9% 12% 20% 11% 1	4033
	21st to end	Night	45% 8% 15% 20% 9% 3	4429
June	1st to 10th	Night	35% 8% 12% 24% 18% 3	1800
	11th to 20th	Night	35% 10% 16% 17% 21% 2	1800
	21st to end	Night	33% 9% 15% 22% 19% 2	1800
July	1st to 10th	Night	37% 8% 10% 24% 18% 3	4015
	11th to 20th	Night	42% 9% 16% 22% 10% 1	4006
	21st to end	Night	42% 8% 12% 22% 13% 3	4297
August	1st to 10th	Night	42% 9% 13% 25% 10% 1	2904
	11th to 20th	Night	38% 7% 9% 23% 21% 1	2902
	21st to end	Night	26% 6% 13% 29% 23% 2	3289
September	1st to 10th	Night	32% 8% 12% 21% 20% 7%	2186
	11th to 20th	Night	30% 6% 11% 24% 25% 4	2200
	21st to end	Night	41% 6% 10% 19% 22% 1	2200
October	1st to 10th	Night	29% 4 7% 25% 31% 4	3750
	11th to 20th	Night	30% 4 9% 24% 24% 9%	3899
	21st to end	Night	32% 3 7% 26% 26% 6%	4252
November	1st to 10th	Night	36% 4 9% 22% 23% 5%	2616
	11th to 20th	Night	47% 4 8% 19% 18% 4	2730
	21st to end	Night	50% 5% 8% 22% 13% 1	2730
December	1st to 10th	Night	57% 4 11% 22% 6% 1	4380
	11th to 20th	Night	59% 4 11% 19% 6% 1	4954
	21st to end	Night	63% 5% 10% 15% 7%	6633

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	32% 20% 33% 11% 4 1	330
	11th to 20th	Day	38% 25% 29% 7% 2	318
	21st to end	Day	32% 25% 30% 11% 3	330
February	1st to 10th	Day	34% 22% 30% 10% 4	300
	11th to 20th	Day	48% 21% 24% 5% 1 1	300
	21st to end	Day	37% 24% 31% 8%	249
March	1st to 10th	Day	30% 20% 28% 17% 4 1	450
	11th to 20th	Day	28% 20% 34% 12% 5% 1	500
	21st to end	Day	31% 18% 33% 14% 4	550
April	1st to 10th	Day	27% 21% 26% 16% 8%	500
	11th to 20th	Day	23% 18% 30% 19% 8% 2	492
	21st to end	Day	28% 13% 32% 18% 6% 2	500
May	1st to 10th	Day	25% 18% 28% 18% 7% 3	503
	11th to 20th	Day	22% 11% 29% 21% 13% 4	527
	21st to end	Day	15% 9% 24% 27% 17% 8%	573
June	1st to 10th	Day	12% 9% 26% 29% 18% 6%	530
	11th to 20th	Day	12% 6% 26% 29% 18% 9%	530
	21st to end	Day	10% 7% 29% 25% 22% 7%	530
July	1st to 10th	Day	15% 4 17% 26% 20% 18%	525
	11th to 20th	Day	10% 4 22% 34% 21% 9%	524
	21st to end	Day	15% 5% 18% 29% 24% 10%	576
August	1st to 10th	Day	11% 4 22% 31% 23% 10%	526
	11th to 20th	Day	15% 6% 15% 30% 23% 10%	519
	21st to end	Day	10% 3 18% 33% 23% 11%	583
September	1st to 10th	Day	14% 5% 17% 27% 25% 12%	530
	11th to 20th	Day	12% 3 15% 28% 30% 14%	530
	21st to end	Day	24% 8% 21% 27% 15% 5%	530
October	1st to 10th	Day	15% 7% 25% 28% 19% 6%	530
	11th to 20th	Day	17% 13% 29% 25% 13% 3	530
	21st to end	Day	25% 15% 27% 23% 9% 1	583
November	1st to 10th	Day	19% 16% 33% 22% 7% 2	375
	11th to 20th	Day	29% 17% 30% 17% 6% 1	330
	21st to end	Day	26% 19% 33% 18% 3	330
December	1st to 10th	Day	30% 22% 29% 14% 4 1	330
	11th to 20th	Day	30% 20% 31% 15% 3 1	330
	21st to end	Day	35% 19% 27% 14% 4	363
January	1st to 10th	Night	28% 18% 29% 21% 4	840
	11th to 20th	Night	33% 16% 29% 19% 2	825
	21st to end	Night	28% 16% 31% 22% 3	880
February	1st to 10th	Night	29% 14% 29% 26% 2	800
	11th to 20th	Night	32% 19% 29% 18% 2	783
	21st to end	Night	30% 15% 33% 20% 2	660
March	1st to 10th	Night	27% 15% 29% 26% 4	800
	11th to 20th	Night	25% 17% 29% 22% 7%	800
	21st to end	Night	24% 16% 29% 24% 6%	880
April	1st to 10th	Night	23% 16% 31% 23% 7%	800
	11th to 20th	Night	18% 12% 31% 28% 10% 1	666
	21st to end	Night	19% 9% 35% 31% 7% 1	600
May	1st to 10th	Night	19% 9% 30% 31% 12% 1	600
	11th to 20th	Night	20% 7% 26% 31% 15% 1	591
	21st to end	Night	14% 4 22% 31% 26% 3	650
June	1st to 10th	Night	12% 4 21% 38% 23% 3	600
	11th to 20th	Night	10% 2 21% 37% 26% 4	600
	21st to end	Night	10% 3 19% 38% 28% 3	600
July	1st to 10th	Night	11% 3 14% 34% 31% 6%	585
	11th to 20th	Night	9% 1 17% 35% 34% 4	582
	21st to end	Night	11% 2 13% 35% 32% 6%	657
August	1st to 10th	Night	11% 3 13% 37% 34% 3	597
	11th to 20th	Night	11% 3 11% 35% 32% 7%	594
	21st to end	Night	10% 1 14% 35% 33% 6%	700
September	1st to 10th	Night	14% 3 13% 33% 33% 5%	800
	11th to 20th	Night	11% 1 16% 33% 34% 5%	800
	21st to end	Night	18% 4 21% 32% 21% 3	800
October	1st to 10th	Night	12% 5% 22% 31% 28% 3	800
	11th to 20th	Night	17% 9% 27% 31% 16% 1	800
	21st to end	Night	22% 10% 24% 30% 12% 1	880
November	1st to 10th	Night	15% 10% 28% 32% 15% 1	820
	11th to 20th	Night	23% 16% 24% 27% 10%	840
	21st to end	Night	26% 11% 23% 32% 8% 1	840
December	1st to 10th	Night	29% 14% 28% 23% 5%	840
	11th to 20th	Night	27% 14% 28% 26% 5%	840
	21st to end	Night	30% 16% 25% 28% 2	924

Page generated at 2026-01-14 01:14:31. Version ac07

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