Lexington
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lexington clear sky chart from 2005-11-06 to 2025-11-03.

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% 8% 3 7% 5% 5% 5% 4 6% 7% 37%	126985
	Night	14% 9% 3 7% 5% 4 4 4 5% 7% 38%	123053
Transparency	Day	44% 6% 10% 23% 15% 2	130657
	Night	44% 6% 9% 22% 16% 3	127437
Seeing	Day	18% 9% 25% 24% 16% 8%	16390
	Night	19% 7% 26% 29% 17% 2	26042

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% 13% 9% 9% 5% 4 4 3 5% 6% 26%	4056
	11th to 20th	Day	14% 12% 5% 16% 4 4 4 3 3 4 31%	4060
	21st to end	Day	20% 10% 7% 7% 5% 4 4 3 4 6% 29%	4466
February	1st to 10th	Day	18% 12% 5% 9% 5% 4 4 3 4 6% 30%	1949
	11th to 20th	Day	20% 10% 4 8% 6% 4 4 3 5% 5% 31%	1948
	21st to end	Day	19% 10% 4 8% 5% 4 4 3 6% 5% 31%	1650
March	1st to 10th	Day	18% 12% 5% 7% 4 4 4 3 4 5% 35%	4522
	11th to 20th	Day	13% 7% 3 6% 4 4 4 4 6% 8% 42%	4980
	21st to end	Day	15% 8% 3 7% 5% 4 5% 4 5% 8% 36%	5465
April	1st to 10th	Day	15% 9% 3 8% 4 4 4 4 5% 7% 38%	2348
	11th to 20th	Day	15% 8% 3 6% 5% 4 4 3 6% 7% 39%	2404
	21st to end	Day	16% 8% 3 6% 5% 5% 5% 4 5% 8% 36%	2600
May	1st to 10th	Day	19% 9% 3 9% 5% 5% 5% 5% 7% 8% 26%	5862
	11th to 20th	Day	18% 8% 3 8% 5% 5% 4 4 6% 7% 33%	5861
	21st to end	Day	14% 7% 2 6% 5% 5% 6% 5% 8% 10% 32%	6433
June	1st to 10th	Day	11% 6% 2 7% 5% 5% 6% 4 6% 6% 42%	2600
	11th to 20th	Day	8% 5% 2 6% 5% 5% 6% 4 7% 9% 41%	2618
	21st to end	Day	9% 5% 2 6% 4 6% 5% 5% 7% 10% 41%	2800
July	1st to 10th	Day	10% 6% 2 7% 4 5% 5% 4 6% 9% 42%	6229
	11th to 20th	Day	9% 6% 2 7% 6% 6% 6% 5% 8% 10% 34%	5900
	21st to end	Day	13% 8% 3 8% 7% 6% 6% 5% 7% 8% 28%	6424
August	1st to 10th	Day	8% 6% 2 5% 4 4 4 4 7% 10% 46%	4234
	11th to 20th	Day	8% 6% 2 6% 5% 5% 6% 5% 9% 11% 38%	4124
	21st to end	Day	5% 4 2 5% 4 4 5% 4 5% 8% 54%	4312
September	1st to 10th	Day	13% 6% 2 6% 4 4 5% 5% 6% 7% 42%	2266
	11th to 20th	Day	11% 6% 2 5% 4 4 4 4 6% 7% 47%	2200
	21st to end	Day	15% 6% 3 6% 4 3 3 3 5% 6% 47%	2200
October	1st to 10th	Day	10% 5% 2 4 3 3 4 3 4 6% 55%	2200
	11th to 20th	Day	12% 6% 1 5% 4 3 4 3 4 6% 50%	2050
	21st to end	Day	19% 7% 2 5% 4 3 4 3 4 6% 43%	2075
November	1st to 10th	Day	13% 6% 2 4 3 3 4 3 3 5% 53%	1780
	11th to 20th	Day	16% 9% 3 8% 4 3 3 3 5% 6% 42%	1800
	21st to end	Day	18% 10% 4 7% 5% 3 3 3 5% 6% 37%	1800
December	1st to 10th	Day	17% 10% 3 7% 5% 4 4 3 4 4 39%	2930
	11th to 20th	Day	19% 13% 4 10% 5% 5% 4 3 4 4 28%	3373
	21st to end	Day	19% 16% 5% 10% 6% 5% 4 4 5% 5% 22%	4466
January	1st to 10th	Night	15% 14% 5% 15% 7% 4 4 3 5% 6% 23%	5889
	11th to 20th	Night	17% 13% 6% 11% 6% 5% 4 3 3 4 28%	5900
	21st to end	Night	19% 10% 4 7% 4 4 3 3 4 5% 36%	6490
February	1st to 10th	Night	21% 11% 4 9% 4 4 4 3 5% 6% 29%	2449
	11th to 20th	Night	21% 10% 3 9% 5% 4 3 3 5% 5% 32%	2338
	21st to end	Night	21% 12% 4 8% 5% 4 4 4 4 4 31%	1980
March	1st to 10th	Night	18% 13% 3 6% 4 4 4 3 4 5% 36%	5328
	11th to 20th	Night	13% 6% 2 5% 4 4 4 4 5% 6% 47%	4980
	21st to end	Night	15% 9% 3 9% 6% 5% 4 4 6% 7% 34%	5467
April	1st to 10th	Night	14% 6% 3 6% 5% 5% 5% 4 6% 6% 41%	2069
	11th to 20th	Night	13% 8% 3 7% 5% 3 4 3 5% 7% 43%	1944
	21st to end	Night	15% 8% 3 6% 5% 5% 5% 4 6% 8% 38%	1800
May	1st to 10th	Night	19% 10% 3 8% 5% 5% 5% 4 6% 8% 26%	4033
	11th to 20th	Night	17% 8% 3 7% 5% 5% 5% 4 7% 8% 31%	4032
	21st to end	Night	12% 7% 3 7% 5% 5% 5% 4 6% 10% 37%	4421
June	1st to 10th	Night	9% 4 2 5% 4 4 4 5% 7% 10% 47%	1800
	11th to 20th	Night	6% 5% 2 5% 4 4 5% 5% 7% 10% 47%	1770
	21st to end	Night	6% 4 1 4 6% 4 6% 4 9% 11% 45%	1600
July	1st to 10th	Night	7% 5% 2 7% 4 5% 4 4 6% 9% 46%	3723
	11th to 20th	Night	8% 6% 2 7% 5% 5% 4 4 7% 10% 42%	4057
	21st to end	Night	12% 7% 3 7% 6% 5% 6% 5% 7% 10% 34%	4427
August	1st to 10th	Night	8% 5% 2 5% 4 4 4 4 6% 9% 49%	2915
	11th to 20th	Night	7% 6% 2 6% 5% 5% 6% 5% 6% 9% 43%	2908
	21st to end	Night	4 3 1 4 3 3 3 3 5% 8% 62%	3586
September	1st to 10th	Night	12% 4 2 5% 4 3 3 4 6% 8% 49%	2112
	11th to 20th	Night	10% 5% 2 5% 4 3 4 3 5% 7% 51%	2200
	21st to end	Night	13% 6% 2 5% 4 4 3 3 5% 6% 50%	2200
October	1st to 10th	Night	10% 4 2 4 3 3 3 3 4 7% 57%	2200
	11th to 20th	Night	13% 6% 2 4 3 4 3 3 4 7% 50%	2350
	21st to end	Night	18% 7% 2 5% 4 3 4 3 4 4 45%	2760
November	1st to 10th	Night	12% 6% 3 6% 3 3 4 4 5% 5% 50%	2563
	11th to 20th	Night	15% 8% 3 5% 4 4 4 3 4 7% 43%	2600
	21st to end	Night	17% 11% 3 6% 4 4 3 4 4 6% 38%	2600
December	1st to 10th	Night	17% 12% 3 8% 5% 3 4 2 4 4 38%	4250
	11th to 20th	Night	20% 11% 4 8% 4 3 4 3 4 6% 33%	4822
	21st to end	Night	18% 15% 6% 10% 6% 6% 5% 4 5% 5% 20%	6490

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	59% 4 8% 20% 8% 1	4057
	11th to 20th	Day	58% 4 5% 18% 13% 2	4060
	21st to end	Day	57% 4 8% 21% 8% 2	4466
February	1st to 10th	Day	56% 4 7% 21% 10% 2	1949
	11th to 20th	Day	56% 4 7% 19% 12% 3	1958
	21st to end	Day	54% 4 7% 21% 11% 3	1650
March	1st to 10th	Day	52% 4 6% 17% 15% 6%	4522
	11th to 20th	Day	39% 4 9% 26% 19% 2	4980
	21st to end	Day	46% 6% 11% 25% 12% 1	5465
April	1st to 10th	Day	44% 5% 11% 24% 13% 3	2348
	11th to 20th	Day	45% 5% 9% 23% 15% 4	2404
	21st to end	Day	46% 6% 11% 24% 11% 2	2600
May	1st to 10th	Day	53% 8% 11% 18% 9% 1	5897
	11th to 20th	Day	50% 6% 12% 20% 11%	5865
	21st to end	Day	42% 8% 15% 19% 14% 1	6447
June	1st to 10th	Day	40% 7% 9% 26% 16% 2	2600
	11th to 20th	Day	36% 8% 14% 23% 17% 2	2618
	21st to end	Day	35% 10% 15% 21% 16% 4	2800
July	1st to 10th	Day	38% 7% 12% 22% 19% 1	6162
	11th to 20th	Day	41% 10% 14% 25% 9% 1	5831
	21st to end	Day	50% 8% 12% 19% 10% 1	6240
August	1st to 10th	Day	31% 9% 14% 34% 12% 1	4221
	11th to 20th	Day	36% 8% 12% 28% 14% 2	4163
	21st to end	Day	27% 7% 11% 32% 19% 3	4311
September	1st to 10th	Day	39% 6% 12% 19% 18% 5%	2266
	11th to 20th	Day	34% 6% 10% 25% 23% 3	2200
	21st to end	Day	39% 4 8% 24% 22% 3	2200
October	1st to 10th	Day	21% 4 6% 26% 40% 3	3590
	11th to 20th	Day	25% 3 9% 28% 31% 3	3316
	21st to end	Day	32% 4 8% 28% 21% 8%	3325
November	1st to 10th	Day	35% 3 8% 26% 24% 4	1780
	11th to 20th	Day	44% 3 8% 22% 19% 4	1800
	21st to end	Day	48% 3 8% 21% 18% 1	1800
December	1st to 10th	Day	50% 3 7% 24% 16% 1	2930
	11th to 20th	Day	60% 4 8% 16% 11% 1	3370
	21st to end	Day	63% 5% 10% 16% 5% 1	4466
January	1st to 10th	Night	62% 5% 6% 17% 9% 1	5889
	11th to 20th	Night	60% 4 5% 17% 10% 4	5900
	21st to end	Night	51% 4 7% 22% 14% 2	6490
February	1st to 10th	Night	57% 3 10% 18% 10% 1	2449
	11th to 20th	Night	55% 4 7% 21% 12% 2	2339
	21st to end	Night	56% 4 8% 15% 12% 3	1980
March	1st to 10th	Night	51% 3 6% 22% 14% 4	5328
	11th to 20th	Night	36% 6% 8% 27% 21% 2	4980
	21st to end	Night	49% 5% 8% 23% 13% 1	5467
April	1st to 10th	Night	41% 6% 10% 23% 18% 3	2069
	11th to 20th	Night	40% 5% 9% 21% 19% 6%	1944
	21st to end	Night	44% 6% 11% 22% 14% 2	1800
May	1st to 10th	Night	53% 9% 10% 19% 8% 2	4060
	11th to 20th	Night	50% 8% 11% 21% 9% 1	4033
	21st to end	Night	40% 8% 15% 22% 13% 2	4429
June	1st to 10th	Night	31% 6% 16% 27% 17% 4	1800
	11th to 20th	Night	30% 8% 16% 24% 19% 3	1770
	21st to end	Night	30% 9% 17% 23% 16% 5%	1600
July	1st to 10th	Night	34% 9% 11% 25% 19% 2	3683
	11th to 20th	Night	35% 10% 17% 25% 12% 2	4006
	21st to end	Night	44% 9% 12% 21% 13% 1	4297
August	1st to 10th	Night	31% 9% 14% 32% 14% 1	2904
	11th to 20th	Night	35% 7% 12% 29% 16% 1	2935
	21st to end	Night	20% 7% 13% 34% 22% 4	3586
September	1st to 10th	Night	33% 6% 12% 22% 20% 6%	2112
	11th to 20th	Night	32% 5% 10% 25% 25% 3	2200
	21st to end	Night	37% 5% 7% 22% 25% 4	2200
October	1st to 10th	Night	21% 4 7% 24% 41% 3	3590
	11th to 20th	Night	25% 3 6% 26% 34% 6%	3823
	21st to end	Night	31% 3 6% 22% 29% 8%	4447
November	1st to 10th	Night	36% 4 7% 26% 23% 4	2563
	11th to 20th	Night	41% 4 7% 20% 22% 5%	2600
	21st to end	Night	47% 4 8% 24% 16% 2	2600
December	1st to 10th	Night	51% 3 9% 22% 14% 1	4250
	11th to 20th	Night	52% 4 10% 21% 13% 1	4824
	21st to end	Night	64% 6% 8% 15% 7%	6490

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	29% 16% 34% 15% 6% 1	300
	11th to 20th	Day	29% 22% 29% 17% 3	300
	21st to end	Day	23% 18% 41% 14% 3	330
February	1st to 10th	Day	28% 17% 37% 15% 3	300
	11th to 20th	Day	33% 21% 32% 11% 3 1	300
	21st to end	Day	29% 17% 39% 11% 3	249
March	1st to 10th	Day	28% 19% 35% 13% 5%	316
	11th to 20th	Day	23% 18% 37% 17% 4 1	500
	21st to end	Day	28% 15% 33% 17% 6% 1	550
April	1st to 10th	Day	22% 16% 31% 20% 10% 1	500
	11th to 20th	Day	23% 15% 29% 21% 8% 3	492
	21st to end	Day	22% 11% 33% 23% 8% 2	500
May	1st to 10th	Day	22% 11% 31% 21% 11% 4	503
	11th to 20th	Day	19% 9% 24% 25% 16% 7%	527
	21st to end	Day	16% 6% 22% 29% 17% 11%	573
June	1st to 10th	Day	15% 4 21% 25% 25% 10%	530
	11th to 20th	Day	9% 3 22% 31% 25% 10%	548
	21st to end	Day	9% 5% 21% 31% 22% 12%	730
July	1st to 10th	Day	15% 2 14% 26% 22% 21%	670
	11th to 20th	Day	10% 3 17% 26% 27% 17%	524
	21st to end	Day	14% 3 11% 29% 27% 16%	576
August	1st to 10th	Day	13% 3 15% 23% 28% 17%	526
	11th to 20th	Day	13% 4 13% 33% 26% 13%	519
	21st to end	Day	9% 2 13% 30% 30% 17%	583
September	1st to 10th	Day	13% 4 13% 30% 25% 15%	530
	11th to 20th	Day	13% 2 12% 27% 29% 17%	530
	21st to end	Day	18% 7% 18% 25% 22% 9%	530
October	1st to 10th	Day	12% 5% 18% 33% 23% 9%	530
	11th to 20th	Day	15% 10% 29% 28% 14% 5%	530
	21st to end	Day	22% 10% 31% 26% 10% 1	458
November	1st to 10th	Day	16% 8% 33% 27% 13% 3	306
	11th to 20th	Day	23% 17% 28% 24% 6% 2	300
	21st to end	Day	25% 12% 33% 24% 6%	300
December	1st to 10th	Day	24% 18% 31% 24% 3 1	300
	11th to 20th	Day	24% 13% 39% 18% 7%	300
	21st to end	Day	30% 16% 34% 17% 3	330
January	1st to 10th	Night	25% 14% 36% 20% 5%	800
	11th to 20th	Night	30% 15% 33% 18% 3	800
	21st to end	Night	25% 12% 39% 23% 2	880
February	1st to 10th	Night	28% 11% 36% 23% 2	800
	11th to 20th	Night	29% 13% 36% 20% 1	783
	21st to end	Night	29% 11% 38% 20% 2	660
March	1st to 10th	Night	25% 12% 32% 26% 6%	800
	11th to 20th	Night	24% 12% 35% 22% 7% 1	800
	21st to end	Night	21% 12% 33% 26% 8%	880
April	1st to 10th	Night	19% 10% 35% 28% 8%	669
	11th to 20th	Night	18% 10% 31% 29% 10% 1	593
	21st to end	Night	19% 4 37% 30% 9% 1	600
May	1st to 10th	Night	21% 5% 33% 26% 13% 3	600
	11th to 20th	Night	17% 6% 19% 37% 18% 2	591
	21st to end	Night	11% 3 20% 34% 28% 4	650
June	1st to 10th	Night	11% 1 19% 42% 24% 4	600
	11th to 20th	Night	9% 3 15% 40% 29% 4	600
	21st to end	Night	7% 3 17% 40% 29% 5%	600
July	1st to 10th	Night	11% 1 12% 32% 31% 11%	585
	11th to 20th	Night	8% 2 12% 35% 38% 5%	582
	21st to end	Night	13% 2 8% 36% 34% 6%	657
August	1st to 10th	Night	10% 2 10% 33% 42% 5%	597
	11th to 20th	Night	9% 2 9% 38% 34% 7%	594
	21st to end	Night	8% 1 8% 34% 42% 6%	660
September	1st to 10th	Night	13% 2 10% 33% 35% 7%	712
	11th to 20th	Night	13% 2 13% 30% 37% 6%	800
	21st to end	Night	15% 4 19% 35% 24% 3	800
October	1st to 10th	Night	11% 4 18% 35% 28% 4	800
	11th to 20th	Night	17% 7% 26% 33% 16% 2	800
	21st to end	Night	22% 7% 32% 25% 12% 1	880
November	1st to 10th	Night	17% 7% 26% 32% 17% 2	789
	11th to 20th	Night	20% 10% 32% 27% 10% 1	800
	21st to end	Night	24% 10% 28% 28% 10% 1	800
December	1st to 10th	Night	27% 11% 31% 25% 6%	800
	11th to 20th	Night	27% 9% 33% 25% 6%	800
	21st to end	Night	29% 13% 30% 24% 5%	880

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