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 2024-01-22.

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	16% 10% 4 8% 7% 4 5% 5% 5% 7% 30%	74784
	Night	17% 11% 4 8% 6% 3 5% 5% 5% 6% 29%	75152
Transparency	Day	53% 7% 11% 18% 10% 1	74491
	Night	56% 6% 11% 17% 9% 1	74979
Seeing	Day	22% 17% 30% 20% 9% 3	13501
	Night	23% 16% 28% 23% 10% 1	22904

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	13% 18% 7% 13% 10% 5% 7% 5% 4 4 14%	1517
	11th to 20th	Day	18% 19% 8% 13% 10% 4 4 4 5% 4 11%	1542
	21st to end	Day	12% 17% 7% 14% 12% 5% 6% 5% 4 5% 11%	1791
February	1st to 10th	Day	17% 15% 8% 16% 10% 4 5% 4 3 4 14%	1620
	11th to 20th	Day	15% 15% 9% 15% 8% 4 6% 5% 3 5% 14%	1573
	21st to end	Day	20% 15% 5% 14% 9% 3 5% 4 3 6% 16%	1469
March	1st to 10th	Day	15% 13% 7% 14% 9% 4 5% 4 4 4 21%	1880
	11th to 20th	Day	15% 16% 6% 9% 7% 3 4 4 4 5% 27%	1980
	21st to end	Day	21% 12% 5% 7% 6% 3 4 4 4 6% 29%	2240
April	1st to 10th	Day	17% 13% 5% 8% 5% 3 5% 3 4 6% 30%	2160
	11th to 20th	Day	20% 9% 3 5% 5% 3 4 4 5% 6% 37%	2134
	21st to end	Day	21% 10% 4 6% 4 3 4 5% 5% 6% 32%	2239
May	1st to 10th	Day	16% 9% 4 7% 6% 4 5% 5% 5% 7% 33%	2443
	11th to 20th	Day	15% 7% 3 6% 6% 3 5% 5% 5% 7% 39%	2478
	21st to end	Day	12% 6% 2 5% 6% 3 5% 5% 6% 8% 41%	2725
June	1st to 10th	Day	17% 6% 3 5% 5% 3 5% 4 6% 7% 37%	2520
	11th to 20th	Day	14% 5% 2 5% 5% 3 5% 5% 7% 10% 38%	2520
	21st to end	Day	12% 6% 2 7% 7% 4 5% 6% 6% 8% 38%	2520
July	1st to 10th	Day	9% 6% 2 5% 6% 3 5% 5% 6% 9% 44%	2520
	11th to 20th	Day	11% 6% 3 5% 6% 4 5% 6% 7% 10% 39%	2520
	21st to end	Day	10% 5% 3 6% 6% 4 6% 6% 7% 8% 37%	2714
August	1st to 10th	Day	11% 4 2 6% 6% 4 5% 7% 8% 9% 38%	2327
	11th to 20th	Day	11% 6% 3 7% 7% 4 6% 6% 7% 10% 33%	2285
	21st to end	Day	14% 6% 3 5% 6% 4 5% 5% 7% 9% 36%	2376
September	1st to 10th	Day	14% 6% 3 4 5% 3 4 6% 7% 8% 39%	2160
	11th to 20th	Day	15% 6% 2 4 5% 3 5% 4 5% 8% 43%	2160
	21st to end	Day	15% 7% 4 6% 6% 4 6% 5% 5% 7% 36%	1898
October	1st to 10th	Day	18% 7% 4 6% 7% 4 4 5% 5% 7% 33%	1800
	11th to 20th	Day	20% 10% 3 7% 7% 3 5% 4 5% 7% 29%	1800
	21st to end	Day	27% 13% 4 6% 6% 4 5% 4 5% 5% 22%	1940
November	1st to 10th	Day	15% 12% 4 8% 7% 4 5% 5% 5% 5% 31%	1671
	11th to 20th	Day	14% 15% 6% 8% 7% 3 5% 4 6% 8% 25%	1544
	21st to end	Day	20% 14% 5% 10% 6% 3 6% 4 5% 6% 20%	1520
December	1st to 10th	Day	20% 18% 8% 11% 7% 4 5% 3 3 5% 16%	1520
	11th to 20th	Day	19% 17% 8% 13% 7% 3 4 4 4 5% 16%	1906
	21st to end	Day	27% 19% 6% 12% 8% 3 3 3 4 4 10%	2772
January	1st to 10th	Night	17% 18% 8% 14% 9% 4 5% 4 4 4 14%	2649
	11th to 20th	Night	17% 17% 7% 14% 9% 4 4 4 4 5% 13%	2637
	21st to end	Night	12% 15% 7% 15% 12% 5% 6% 4 4 5% 14%	2599
February	1st to 10th	Night	18% 15% 6% 13% 7% 4 6% 4 4 5% 18%	2340
	11th to 20th	Night	16% 14% 6% 13% 8% 4 5% 5% 4 6% 18%	2273
	21st to end	Night	18% 12% 6% 13% 8% 3 5% 4 5% 5% 21%	1786
March	1st to 10th	Night	16% 14% 7% 11% 8% 3 4 5% 4 6% 22%	2065
	11th to 20th	Night	18% 12% 6% 8% 6% 3 4 4 5% 6% 28%	1979
	21st to end	Night	19% 10% 4 8% 5% 3 5% 4 4 6% 32%	2116
April	1st to 10th	Night	19% 10% 4 7% 6% 3 5% 4 5% 6% 29%	1800
	11th to 20th	Night	19% 8% 2 7% 6% 4 5% 5% 4 6% 35%	1775
	21st to end	Night	18% 8% 4 6% 5% 3 5% 4 6% 7% 33%	1737
May	1st to 10th	Night	19% 8% 3 6% 7% 3 4 4 6% 6% 33%	1517
	11th to 20th	Night	13% 6% 3 5% 5% 4 4 5% 7% 10% 39%	1415
	21st to end	Night	10% 5% 3 5% 5% 3 5% 5% 5% 9% 45%	1550
June	1st to 10th	Night	14% 8% 3 5% 5% 4 5% 5% 5% 10% 37%	1440
	11th to 20th	Night	12% 7% 3 5% 5% 3 6% 4 7% 8% 41%	1440
	21st to end	Night	10% 6% 3 6% 6% 4 6% 5% 6% 8% 42%	1440
July	1st to 10th	Night	7% 5% 2 5% 5% 3 6% 5% 7% 8% 47%	1440
	11th to 20th	Night	11% 4 2 5% 5% 3 5% 4 6% 8% 47%	1440
	21st to end	Night	12% 4 2 5% 4 3 5% 5% 7% 10% 43%	1600
August	1st to 10th	Night	8% 5% 2 5% 5% 4 5% 4 7% 8% 46%	1611
	11th to 20th	Night	11% 6% 3 6% 6% 4 6% 5% 6% 8% 41%	1598
	21st to end	Night	9% 5% 2 5% 5% 3 5% 4 6% 9% 45%	1980
September	1st to 10th	Night	14% 5% 2 5% 5% 3 4 4 6% 7% 44%	1800
	11th to 20th	Night	14% 7% 3 5% 5% 2 3 5% 6% 7% 44%	1800
	21st to end	Night	15% 6% 2 6% 6% 3 5% 5% 7% 8% 39%	2059
October	1st to 10th	Night	20% 7% 2 7% 6% 4 4 4 5% 6% 33%	2160
	11th to 20th	Night	21% 9% 3 6% 6% 3 4 5% 5% 7% 31%	2160
	21st to end	Night	28% 12% 3 7% 5% 4 4 4 4 6% 24%	2414
November	1st to 10th	Night	17% 12% 4 6% 6% 3 4 5% 5% 6% 33%	2407
	11th to 20th	Night	17% 12% 4 8% 6% 4 5% 6% 5% 7% 27%	2633
	21st to end	Night	19% 16% 5% 7% 6% 3 5% 5% 4 6% 23%	2660
December	1st to 10th	Night	20% 17% 7% 9% 6% 3 5% 5% 5% 5% 17%	2660
	11th to 20th	Night	20% 15% 7% 11% 7% 3 5% 4 4 5% 19%	3288
	21st to end	Night	31% 16% 6% 9% 5% 3 4 4 5% 5% 12%	4884

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	74% 5% 9% 10% 3	1518
	11th to 20th	Day	77% 6% 8% 6% 2	1542
	21st to end	Day	74% 6% 10% 8% 2	1791
February	1st to 10th	Day	74% 5% 9% 10% 2	1620
	11th to 20th	Day	73% 6% 7% 11% 3	1582
	21st to end	Day	71% 4 9% 11% 4	1469
March	1st to 10th	Day	67% 5% 11% 13% 4 1	1883
	11th to 20th	Day	59% 6% 8% 15% 10% 1	1980
	21st to end	Day	56% 4 8% 17% 12% 2	2240
April	1st to 10th	Day	56% 5% 9% 16% 12% 2	2160
	11th to 20th	Day	48% 6% 9% 21% 14% 2	2134
	21st to end	Day	53% 5% 8% 19% 14% 2	2239
May	1st to 10th	Day	51% 5% 10% 19% 12% 2	2443
	11th to 20th	Day	44% 6% 10% 23% 14% 3	2482
	21st to end	Day	39% 8% 15% 23% 13% 1	2725
June	1st to 10th	Day	45% 7% 10% 21% 16% 1	2520
	11th to 20th	Day	39% 8% 12% 26% 14% 2	2520
	21st to end	Day	42% 8% 13% 22% 14% 1	2520
July	1st to 10th	Day	36% 8% 11% 28% 15% 2	2450
	11th to 20th	Day	38% 8% 15% 27% 12% 1	2445
	21st to end	Day	41% 9% 13% 22% 14% 1	2562
August	1st to 10th	Day	38% 10% 14% 24% 13% 1	2314
	11th to 20th	Day	43% 10% 14% 23% 10% 1	2285
	21st to end	Day	41% 9% 11% 26% 11% 1	2376
September	1st to 10th	Day	40% 9% 11% 28% 11% 1	2160
	11th to 20th	Day	40% 6% 13% 25% 15% 1	2160
	21st to end	Day	47% 6% 10% 24% 11% 1	1898
October	1st to 10th	Day	49% 6% 15% 19% 11% 1	1800
	11th to 20th	Day	55% 7% 14% 18% 7%	1800
	21st to end	Day	63% 6% 11% 13% 6% 1	1940
November	1st to 10th	Day	54% 7% 12% 17% 10% 1	1671
	11th to 20th	Day	58% 6% 13% 15% 7% 1	1544
	21st to end	Day	65% 6% 14% 14% 2	1520
December	1st to 10th	Day	73% 5% 10% 10% 1	1520
	11th to 20th	Day	71% 6% 13% 7% 3	1906
	21st to end	Day	78% 5% 9% 7% 1	2772
January	1st to 10th	Night	75% 5% 8% 8% 4	2649
	11th to 20th	Night	74% 6% 10% 7% 2	2637
	21st to end	Night	73% 4 9% 10% 3	2599
February	1st to 10th	Night	69% 5% 10% 11% 5%	2340
	11th to 20th	Night	68% 5% 10% 13% 4	2275
	21st to end	Night	66% 5% 11% 12% 6%	1786
March	1st to 10th	Night	64% 5% 11% 15% 5%	2075
	11th to 20th	Night	58% 5% 9% 18% 9% 1	1980
	21st to end	Night	55% 5% 9% 18% 11% 2	2116
April	1st to 10th	Night	57% 6% 10% 19% 8% 2	1800
	11th to 20th	Night	51% 5% 10% 17% 15% 1	1775
	21st to end	Night	49% 6% 10% 19% 14% 3	1737
May	1st to 10th	Night	51% 6% 8% 17% 14% 3	1517
	11th to 20th	Night	39% 8% 11% 24% 16% 3	1416
	21st to end	Night	36% 7% 16% 23% 16% 2	1551
June	1st to 10th	Night	43% 8% 11% 22% 16% 1	1440
	11th to 20th	Night	40% 7% 12% 21% 18% 2	1440
	21st to end	Night	39% 8% 11% 25% 16% 1	1440
July	1st to 10th	Night	32% 8% 14% 24% 19% 3	1400
	11th to 20th	Night	34% 7% 12% 29% 16% 1	1392
	21st to end	Night	35% 8% 14% 25% 16% 2	1511
August	1st to 10th	Night	35% 7% 15% 30% 13% 1	1600
	11th to 20th	Night	40% 8% 13% 29% 10%	1598
	21st to end	Night	34% 8% 13% 29% 13% 2	1980
September	1st to 10th	Night	39% 8% 13% 26% 12% 2	1800
	11th to 20th	Night	38% 5% 12% 27% 16% 1	1800
	21st to end	Night	43% 7% 12% 25% 12% 1	2059
October	1st to 10th	Night	51% 6% 11% 19% 12% 1	2160
	11th to 20th	Night	52% 6% 14% 18% 8% 1	2160
	21st to end	Night	63% 5% 12% 12% 7% 1	2414
November	1st to 10th	Night	53% 6% 11% 20% 8% 2	2407
	11th to 20th	Night	56% 6% 13% 16% 8% 1	2633
	21st to end	Night	62% 6% 14% 14% 3	2660
December	1st to 10th	Night	70% 6% 13% 9% 2	2660
	11th to 20th	Night	70% 6% 10% 12% 3	3288
	21st to end	Night	74% 6% 11% 8% 1	4884

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	27% 27% 33% 8% 5%	180
	11th to 20th	Day	30% 28% 30% 10% 2 1	191
	21st to end	Day	25% 28% 32% 12% 3	267
February	1st to 10th	Day	30% 34% 29% 6%	240
	11th to 20th	Day	32% 29% 35% 4	240
	21st to end	Day	35% 24% 27% 12% 1	335
March	1st to 10th	Day	22% 27% 33% 15% 3 1	420
	11th to 20th	Day	29% 24% 30% 14% 3	420
	21st to end	Day	32% 21% 27% 13% 4 1	462
April	1st to 10th	Day	26% 22% 34% 13% 5% 1	420
	11th to 20th	Day	29% 20% 25% 13% 9% 3	412
	21st to end	Day	30% 19% 29% 15% 6% 1	420
May	1st to 10th	Day	23% 18% 32% 17% 8% 2	423
	11th to 20th	Day	19% 13% 33% 25% 9% 1	447
	21st to end	Day	15% 13% 32% 24% 13% 4	485
June	1st to 10th	Day	21% 15% 28% 28% 6% 2	450
	11th to 20th	Day	17% 10% 32% 28% 11% 3	450
	21st to end	Day	14% 14% 33% 27% 9% 2	450
July	1st to 10th	Day	12% 8% 25% 34% 18% 4	445
	11th to 20th	Day	13% 6% 28% 32% 18% 3	444
	21st to end	Day	12% 8% 36% 28% 13% 3	488
August	1st to 10th	Day	11% 5% 31% 28% 19% 6%	446
	11th to 20th	Day	12% 6% 31% 27% 15% 8%	439
	21st to end	Day	15% 8% 28% 27% 14% 7%	495
September	1st to 10th	Day	14% 13% 24% 27% 13% 9%	450
	11th to 20th	Day	14% 10% 24% 26% 18% 9%	450
	21st to end	Day	17% 14% 27% 24% 13% 5%	450
October	1st to 10th	Day	23% 14% 30% 17% 13% 4	450
	11th to 20th	Day	24% 18% 33% 16% 7% 2	450
	21st to end	Day	34% 18% 30% 15% 4	475
November	1st to 10th	Day	24% 19% 28% 19% 8% 1	365
	11th to 20th	Day	25% 29% 28% 14% 4	204
	21st to end	Day	31% 26% 30% 12% 2	180
December	1st to 10th	Day	33% 19% 31% 12% 4 1	180
	11th to 20th	Day	32% 26% 29% 12% 2	180
	21st to end	Day	32% 27% 31% 9% 1	198
January	1st to 10th	Night	28% 27% 29% 13% 3	760
	11th to 20th	Night	29% 22% 30% 16% 2	760
	21st to end	Night	19% 26% 35% 17% 3	800
February	1st to 10th	Night	29% 24% 31% 14% 1	720
	11th to 20th	Night	25% 26% 33% 13% 3	703
	21st to end	Night	27% 25% 32% 15% 2	592
March	1st to 10th	Night	27% 20% 32% 18% 3	720
	11th to 20th	Night	28% 20% 28% 19% 4	720
	21st to end	Night	25% 17% 32% 19% 6% 1	792
April	1st to 10th	Night	25% 16% 33% 22% 4	720
	11th to 20th	Night	24% 16% 28% 24% 6% 1	711
	21st to end	Night	25% 13% 27% 26% 9%	657
May	1st to 10th	Night	27% 10% 20% 31% 11% 1	437
	11th to 20th	Night	15% 8% 32% 34% 10% 1	354
	21st to end	Night	10% 7% 33% 30% 19% 1	389
June	1st to 10th	Night	17% 7% 25% 34% 16% 1	360
	11th to 20th	Night	14% 9% 24% 36% 16% 1	360
	21st to end	Night	12% 8% 27% 41% 11% 1	360
July	1st to 10th	Night	8% 3 22% 43% 23% 2	350
	11th to 20th	Night	12% 3 20% 41% 23% 1	348
	21st to end	Night	13% 3 25% 39% 18% 2	420
August	1st to 10th	Night	11% 4 22% 38% 21% 3	537
	11th to 20th	Night	13% 5% 20% 35% 25% 3	534
	21st to end	Night	11% 7% 23% 33% 24% 2	792
September	1st to 10th	Night	16% 7% 22% 31% 21% 3	720
	11th to 20th	Night	17% 7% 18% 30% 24% 4	720
	21st to end	Night	17% 10% 22% 27% 21% 3	720
October	1st to 10th	Night	23% 12% 25% 21% 18% 2	720
	11th to 20th	Night	26% 15% 31% 22% 7% 1	720
	21st to end	Night	34% 13% 30% 20% 3	792
November	1st to 10th	Night	26% 15% 31% 22% 7%	740
	11th to 20th	Night	24% 22% 30% 16% 7% 1	760
	21st to end	Night	28% 21% 28% 17% 5%	760
December	1st to 10th	Night	33% 23% 28% 13% 3	760
	11th to 20th	Night	27% 24% 29% 16% 3	760
	21st to end	Night	34% 21% 30% 13% 1	836

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