Lyons
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lyons clear sky chart from 2005-11-06 to 2026-05-17.

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% 11% 4 10% 6% 5% 5% 4 5% 7% 29%	132276
	Night	16% 12% 5% 11% 6% 5% 4 4 5% 6% 27%	130532
Transparency	Day	53% 7% 11% 19% 9% 1	135818
	Night	57% 6% 11% 17% 9% 1	135076
Seeing	Day	23% 17% 30% 19% 8% 3	16488
	Night	23% 16% 28% 23% 9% 1	25848

By Month

Percentage Cloud Cover NE (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	15% 19% 8% 21% 8% 5% 4 3 3 3 13%	4661
	11th to 20th	Day	12% 20% 8% 17% 10% 6% 4 4 5% 4 11%	4727
	21st to end	Day	13% 15% 6% 15% 13% 10% 5% 3 4 5% 11%	5780
February	1st to 10th	Day	15% 16% 7% 17% 10% 6% 5% 3 4 4 14%	1890
	11th to 20th	Day	15% 18% 8% 17% 7% 5% 5% 4 3 5% 14%	1843
	21st to end	Day	18% 16% 5% 15% 8% 4 5% 3 3 6% 17%	1718
March	1st to 10th	Day	17% 14% 5% 13% 7% 5% 3 3 3 4 26%	4804
	11th to 20th	Day	11% 17% 5% 9% 5% 4 4 4 5% 6% 31%	5090
	21st to end	Day	17% 13% 5% 11% 6% 5% 4 3 4 5% 27%	5762
April	1st to 10th	Day	19% 13% 5% 8% 5% 4 4 3 5% 6% 29%	2520
	11th to 20th	Day	20% 11% 3 7% 4 4 4 3 5% 6% 34%	2494
	21st to end	Day	20% 11% 4 7% 4 4 4 3 5% 6% 32%	2613
May	1st to 10th	Day	26% 10% 3 7% 4 5% 4 3 5% 6% 28%	6295
	11th to 20th	Day	14% 10% 4 9% 5% 5% 4 4 5% 7% 33%	6402
	21st to end	Day	19% 9% 2 7% 5% 5% 5% 4 6% 7% 33%	6949
June	1st to 10th	Day	17% 7% 3 6% 5% 4 6% 3 6% 8% 36%	2800
	11th to 20th	Day	13% 6% 2 7% 5% 4 5% 5% 7% 10% 36%	2800
	21st to end	Day	12% 6% 2 8% 6% 5% 5% 5% 7% 8% 37%	2800
July	1st to 10th	Day	9% 6% 2 7% 5% 5% 5% 4 7% 10% 40%	6360
	11th to 20th	Day	8% 6% 3 7% 5% 6% 6% 5% 8% 11% 36%	6360
	21st to end	Day	9% 5% 2 7% 5% 5% 5% 4 7% 8% 43%	6842
August	1st to 10th	Day	16% 6% 3 7% 4 5% 4 4 6% 7% 38%	4234
	11th to 20th	Day	13% 6% 3 8% 6% 6% 6% 4 6% 9% 34%	4127
	21st to end	Day	13% 7% 2 6% 5% 4 5% 4 6% 8% 41%	4312
September	1st to 10th	Day	13% 6% 2 5% 4 4 5% 5% 7% 8% 41%	2400
	11th to 20th	Day	13% 6% 2 5% 5% 4 4 3 5% 8% 44%	2400
	21st to end	Day	16% 8% 3 7% 5% 6% 5% 4 5% 7% 35%	2107
October	1st to 10th	Day	17% 7% 3 7% 5% 4 5% 3 5% 8% 36%	2000
	11th to 20th	Day	19% 10% 3 9% 6% 5% 4 3 5% 7% 30%	2000
	21st to end	Day	25% 13% 3 8% 4 5% 5% 3 5% 6% 23%	2155
November	1st to 10th	Day	14% 13% 4 9% 6% 5% 5% 4 5% 5% 31%	1851
	11th to 20th	Day	13% 16% 5% 11% 5% 4 5% 3 6% 7% 24%	1706
	21st to end	Day	20% 15% 4 11% 6% 4 5% 3 6% 6% 20%	1680
December	1st to 10th	Day	18% 17% 8% 16% 7% 6% 5% 3 4 5% 12%	2680
	11th to 20th	Day	18% 18% 6% 13% 6% 4 4 3 4 4 18%	3066
	21st to end	Day	21% 17% 6% 15% 8% 5% 4 3 4 6% 11%	4048
January	1st to 10th	Night	15% 19% 8% 24% 7% 4 4 3 3 3 11%	8234
	11th to 20th	Night	12% 20% 8% 18% 8% 6% 5% 3 5% 4 11%	8157
	21st to end	Night	13% 16% 6% 14% 10% 8% 5% 4 4 5% 14%	8401
February	1st to 10th	Night	16% 16% 5% 13% 7% 6% 5% 4 4 5% 19%	2730
	11th to 20th	Night	15% 15% 6% 14% 8% 5% 5% 4 5% 6% 17%	2663
	21st to end	Night	16% 13% 5% 15% 6% 5% 5% 3 5% 5% 20%	2087
March	1st to 10th	Night	16% 10% 7% 12% 7% 5% 4 4 5% 6% 25%	5254
	11th to 20th	Night	15% 16% 4 8% 4 4 4 3 5% 8% 30%	5089
	21st to end	Night	19% 10% 5% 12% 5% 4 5% 3 4 6% 27%	5412
April	1st to 10th	Night	19% 12% 4 9% 6% 5% 4 4 5% 6% 27%	2100
	11th to 20th	Night	20% 9% 2 8% 5% 5% 4 4 4 6% 34%	2075
	21st to end	Night	18% 8% 4 6% 4 4 5% 3 6% 7% 34%	2025
May	1st to 10th	Night	29% 10% 4 9% 5% 4 4 3 4 5% 25%	3866
	11th to 20th	Night	15% 8% 3 7% 4 5% 4 4 6% 8% 35%	3623
	21st to end	Night	19% 8% 3 6% 4 4 4 4 5% 7% 35%	3926
June	1st to 10th	Night	14% 9% 2 6% 4 4 5% 4 4 9% 37%	1600
	11th to 20th	Night	12% 7% 2 6% 5% 4 5% 4 7% 9% 39%	1600
	21st to end	Night	10% 7% 2 7% 5% 4 5% 3 6% 8% 41%	1600
July	1st to 10th	Night	11% 7% 3 6% 4 4 4 4 8% 10% 40%	3600
	11th to 20th	Night	10% 5% 2 7% 5% 4 5% 4 6% 8% 43%	3600
	21st to end	Night	10% 5% 2 6% 4 4 4 4 6% 8% 45%	4006
August	1st to 10th	Night	12% 7% 2 7% 4 4 4 4 7% 9% 40%	2915
	11th to 20th	Night	14% 7% 3 7% 4 4 5% 4 5% 7% 40%	2875
	21st to end	Night	7% 5% 2 6% 5% 5% 5% 4 7% 10% 45%	3586
September	1st to 10th	Night	13% 6% 2 6% 4 4 4 3 5% 7% 46%	2000
	11th to 20th	Night	13% 7% 2 5% 4 3 4 4 6% 7% 46%	2000
	21st to end	Night	16% 7% 2 7% 5% 5% 5% 4 7% 8% 36%	2289
October	1st to 10th	Night	19% 7% 2 8% 5% 5% 4 4 5% 6% 36%	2400
	11th to 20th	Night	21% 9% 2 7% 5% 5% 4 4 5% 7% 32%	2400
	21st to end	Night	25% 11% 3 8% 5% 5% 4 3 4 6% 26%	2683
November	1st to 10th	Night	17% 12% 4 8% 5% 4 4 4 5% 6% 32%	2667
	11th to 20th	Night	16% 14% 4 9% 5% 5% 4 5% 5% 7% 27%	2911
	21st to end	Night	19% 17% 5% 8% 5% 5% 4 4 5% 6% 22%	2940
December	1st to 10th	Night	17% 18% 8% 14% 7% 5% 5% 4 4 5% 13%	4720
	11th to 20th	Night	20% 16% 7% 12% 5% 5% 4 3 4 4 20%	5348
	21st to end	Night	25% 17% 5% 13% 6% 4 4 3 5% 5% 13%	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	76% 5% 10% 7% 2	4662
	11th to 20th	Day	74% 6% 9% 5% 4 1	4757
	21st to end	Day	75% 6% 9% 8% 2	5780
February	1st to 10th	Day	73% 5% 9% 11% 2	1890
	11th to 20th	Day	74% 6% 7% 11% 2	1852
	21st to end	Day	71% 4 9% 12% 4	1718
March	1st to 10th	Day	62% 5% 10% 16% 6%	4807
	11th to 20th	Day	54% 6% 18% 13% 9% 1	5090
	21st to end	Day	58% 5% 8% 18% 10% 1	5762
April	1st to 10th	Day	57% 5% 9% 16% 12% 2	2520
	11th to 20th	Day	51% 6% 9% 20% 14% 2	2494
	21st to end	Day	52% 5% 8% 19% 13% 2	2613
May	1st to 10th	Day	57% 6% 8% 16% 11% 2	6304
	11th to 20th	Day	49% 8% 9% 21% 12% 2	6406
	21st to end	Day	48% 8% 11% 21% 11% 2	6949
June	1st to 10th	Day	45% 7% 11% 20% 16% 1	2800
	11th to 20th	Day	40% 8% 13% 25% 13% 1	2800
	21st to end	Day	42% 8% 13% 21% 15% 1	2800
July	1st to 10th	Day	37% 8% 13% 27% 14% 1	6290
	11th to 20th	Day	37% 9% 16% 23% 14% 1	6285
	21st to end	Day	36% 8% 13% 29% 14%	6645
August	1st to 10th	Day	43% 7% 13% 21% 15% 1	4221
	11th to 20th	Day	44% 9% 15% 24% 7%	4166
	21st to end	Day	39% 8% 11% 35% 8% 1	4312
September	1st to 10th	Day	38% 8% 11% 30% 12% 1	2400
	11th to 20th	Day	38% 6% 13% 28% 15% 1	2400
	21st to end	Day	48% 6% 11% 23% 11%	2107
October	1st to 10th	Day	40% 6% 16% 26% 11%	3260
	11th to 20th	Day	47% 5% 15% 21% 12%	3240
	21st to end	Day	48% 8% 14% 23% 7%	3457
November	1st to 10th	Day	54% 7% 11% 17% 9% 1	1851
	11th to 20th	Day	58% 6% 13% 15% 7% 1	1706
	21st to end	Day	65% 6% 14% 14% 2	1680
December	1st to 10th	Day	76% 7% 9% 7% 1	2680
	11th to 20th	Day	68% 5% 12% 8% 6%	3066
	21st to end	Day	74% 6% 12% 6% 2	4048
January	1st to 10th	Night	80% 5% 7% 6% 2	8234
	11th to 20th	Night	74% 5% 8% 8% 5%	8202
	21st to end	Night	72% 5% 8% 9% 6%	8401
February	1st to 10th	Night	68% 5% 10% 12% 5%	2730
	11th to 20th	Night	68% 5% 10% 12% 4	2665
	21st to end	Night	65% 5% 12% 11% 7%	2087
March	1st to 10th	Night	59% 6% 13% 16% 6%	5264
	11th to 20th	Night	53% 5% 16% 16% 7% 3	5090
	21st to end	Night	57% 6% 7% 20% 9% 1	5412
April	1st to 10th	Night	58% 6% 9% 18% 7% 1	2100
	11th to 20th	Night	52% 5% 10% 17% 15% 1	2075
	21st to end	Night	47% 6% 10% 20% 14% 3	2025
May	1st to 10th	Night	62% 6% 7% 12% 10% 3	3873
	11th to 20th	Night	45% 8% 13% 21% 12% 1	3624
	21st to end	Night	46% 7% 13% 18% 15% 1	3927
June	1st to 10th	Night	43% 7% 10% 22% 16% 1	1600
	11th to 20th	Night	40% 7% 13% 22% 17% 2	1600
	21st to end	Night	40% 8% 11% 24% 16% 1	1600
July	1st to 10th	Night	38% 7% 14% 23% 16% 2	3560
	11th to 20th	Night	37% 8% 12% 25% 16% 2	3552
	21st to end	Night	34% 8% 12% 26% 19% 1	3888
August	1st to 10th	Night	39% 7% 14% 26% 13% 1	2904
	11th to 20th	Night	43% 7% 14% 27% 9%	2902
	21st to end	Night	32% 8% 13% 34% 11% 1	3586
September	1st to 10th	Night	37% 7% 13% 28% 13% 2	2000
	11th to 20th	Night	36% 6% 12% 29% 16% 1	2000
	21st to end	Night	45% 7% 12% 23% 13% 1	2289
October	1st to 10th	Night	46% 6% 10% 27% 11% 1	3920
	11th to 20th	Night	49% 6% 12% 20% 13% 1	3899
	21st to end	Night	48% 6% 13% 25% 7% 1	4331
November	1st to 10th	Night	53% 6% 11% 20% 8% 2	2667
	11th to 20th	Night	57% 6% 13% 15% 7% 1	2911
	21st to end	Night	63% 6% 14% 14% 3	2940
December	1st to 10th	Night	75% 6% 11% 7% 1	4720
	11th to 20th	Night	67% 5% 8% 12% 7% 1	5348
	21st to end	Night	72% 7% 9% 8% 3	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	32% 27% 30% 7% 4	220
	11th to 20th	Day	30% 29% 29% 9% 1	234
	21st to end	Day	29% 27% 31% 10% 2	363
February	1st to 10th	Day	30% 32% 29% 8% 1	330
	11th to 20th	Day	35% 27% 34% 5%	330
	21st to end	Day	35% 23% 30% 11% 1	434
March	1st to 10th	Day	24% 26% 33% 14% 3 1	540
	11th to 20th	Day	34% 22% 29% 12% 3	540
	21st to end	Day	34% 22% 28% 12% 3 1	594
April	1st to 10th	Day	31% 23% 30% 11% 4 1	540
	11th to 20th	Day	31% 23% 26% 12% 7% 2	532
	21st to end	Day	29% 20% 29% 16% 5% 1	540
May	1st to 10th	Day	26% 18% 32% 15% 7% 2	543
	11th to 20th	Day	18% 15% 32% 24% 9% 1	551
	21st to end	Day	17% 13% 33% 23% 12% 3	573
June	1st to 10th	Day	20% 16% 29% 27% 7% 2	530
	11th to 20th	Day	15% 13% 33% 26% 11% 2	530
	21st to end	Day	15% 14% 35% 25% 8% 2	530
July	1st to 10th	Day	12% 8% 28% 33% 16% 3	525
	11th to 20th	Day	13% 7% 29% 32% 17% 3	524
	21st to end	Day	11% 9% 36% 30% 12% 3	576
August	1st to 10th	Day	12% 6% 30% 28% 19% 6%	526
	11th to 20th	Day	13% 6% 32% 27% 14% 8%	519
	21st to end	Day	14% 9% 29% 27% 14% 7%	583
September	1st to 10th	Day	14% 13% 24% 27% 14% 8%	530
	11th to 20th	Day	12% 8% 23% 26% 20% 11%	530
	21st to end	Day	18% 13% 28% 24% 13% 4	530
October	1st to 10th	Day	20% 15% 28% 19% 13% 4	530
	11th to 20th	Day	25% 18% 32% 16% 7% 2	530
	21st to end	Day	32% 18% 31% 15% 4	558
November	1st to 10th	Day	26% 21% 28% 18% 7% 1	425
	11th to 20th	Day	26% 30% 26% 13% 4	246
	21st to end	Day	35% 25% 28% 10% 1	220
December	1st to 10th	Day	34% 20% 31% 11% 4	220
	11th to 20th	Day	35% 26% 27% 11% 1	220
	21st to end	Day	33% 26% 29% 11% 1	242
January	1st to 10th	Night	28% 28% 29% 13% 3	840
	11th to 20th	Night	31% 23% 29% 15% 2	840
	21st to end	Night	21% 27% 33% 17% 3	924
February	1st to 10th	Night	28% 24% 30% 17% 1	840
	11th to 20th	Night	27% 26% 32% 13% 2	823
	21st to end	Night	26% 25% 32% 15% 2	692
March	1st to 10th	Night	27% 21% 32% 17% 3	840
	11th to 20th	Night	29% 21% 27% 19% 4	840
	21st to end	Night	26% 19% 32% 18% 6% 1	924
April	1st to 10th	Night	27% 17% 32% 21% 3	840
	11th to 20th	Night	26% 17% 28% 23% 5% 1	831
	21st to end	Night	24% 13% 28% 26% 8%	765
May	1st to 10th	Night	27% 10% 22% 30% 10% 1	509
	11th to 20th	Night	15% 9% 31% 34% 9%	406
	21st to end	Night	12% 7% 33% 30% 18%	433
June	1st to 10th	Night	17% 8% 27% 33% 15% 1	400
	11th to 20th	Night	15% 9% 25% 35% 15% 1	400
	21st to end	Night	13% 7% 29% 40% 11% 1	400
July	1st to 10th	Night	9% 4 22% 41% 22% 2	390
	11th to 20th	Night	12% 3 21% 41% 22% 1	388
	21st to end	Night	13% 4 24% 41% 17% 2	468
August	1st to 10th	Night	10% 4 23% 38% 21% 3	597
	11th to 20th	Night	12% 5% 19% 35% 26% 3	594
	21st to end	Night	11% 7% 24% 33% 23% 2	880
September	1st to 10th	Night	16% 7% 23% 31% 20% 3	800
	11th to 20th	Night	16% 7% 17% 30% 27% 4	800
	21st to end	Night	19% 10% 21% 27% 20% 2	800
October	1st to 10th	Night	22% 11% 24% 23% 18% 2	800
	11th to 20th	Night	25% 16% 31% 21% 7% 1	800
	21st to end	Night	32% 13% 31% 20% 3	880
November	1st to 10th	Night	27% 16% 30% 21% 6%	820
	11th to 20th	Night	25% 22% 29% 16% 6% 1	840
	21st to end	Night	29% 21% 28% 16% 5%	840
December	1st to 10th	Night	32% 23% 29% 13% 3	840
	11th to 20th	Night	28% 25% 29% 15% 3	840
	21st to end	Night	35% 21% 28% 14% 1	924

Page generated at 2026-05-14 01:58:57. Version ac07

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