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 2024-11-06.

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% 4 4 4 6% 7% 38%	101432
	Night	14% 9% 3 7% 4 4 4 4 5% 7% 39%	97578
Transparency	Day	43% 6% 10% 24% 15% 2	105148
	Night	42% 6% 9% 23% 17% 3	101988
Seeing	Day	18% 9% 25% 24% 16% 8%	15056
	Night	19% 7% 26% 29% 17% 2	24751

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% 12% 7% 8% 5% 4 5% 4 5% 7% 26%	2836
	11th to 20th	Day	17% 13% 5% 16% 4 5% 4 3 4 3 25%	2840
	21st to end	Day	26% 14% 9% 7% 4 3 3 3 3 5% 22%	3124
February	1st to 10th	Day	18% 12% 4 10% 5% 5% 4 3 4 5% 30%	1851
	11th to 20th	Day	19% 10% 3 7% 6% 4 4 3 5% 5% 32%	1848
	21st to end	Day	20% 11% 4 8% 5% 4 5% 3 6% 5% 30%	1570
March	1st to 10th	Day	24% 13% 4 7% 3 3 3 3 4 5% 30%	3148
	11th to 20th	Day	14% 6% 3 6% 4 3 4 3 5% 7% 45%	3480
	21st to end	Day	15% 8% 3 7% 5% 4 5% 4 5% 8% 37%	3815
April	1st to 10th	Day	14% 9% 3 8% 4 4 4 4 5% 7% 39%	2230
	11th to 20th	Day	16% 8% 3 6% 5% 4 4 3 6% 7% 39%	2282
	21st to end	Day	16% 8% 3 6% 5% 4 5% 4 5% 8% 37%	2470
May	1st to 10th	Day	19% 9% 3 8% 5% 5% 4 4 6% 7% 30%	4082
	11th to 20th	Day	18% 8% 3 7% 4 4 3 3 5% 6% 38%	4081
	21st to end	Day	11% 6% 2 7% 5% 5% 5% 5% 7% 10% 36%	4476
June	1st to 10th	Day	12% 6% 2 7% 5% 6% 5% 4 6% 6% 42%	2470
	11th to 20th	Day	8% 5% 2 6% 4 5% 6% 4 8% 9% 43%	2487
	21st to end	Day	9% 5% 2 6% 4 6% 5% 5% 7% 10% 41%	2660
July	1st to 10th	Day	11% 6% 2 7% 5% 5% 5% 5% 7% 9% 39%	4351
	11th to 20th	Day	8% 5% 1 6% 5% 5% 5% 5% 7% 10% 43%	4120
	21st to end	Day	16% 10% 4 9% 7% 6% 6% 4 7% 7% 25%	4466
August	1st to 10th	Day	8% 5% 2 5% 4 4 4 4 7% 10% 47%	4104
	11th to 20th	Day	9% 6% 2 6% 5% 5% 6% 4 9% 11% 38%	3995
	21st to end	Day	6% 4 2 6% 4 4 5% 4 5% 8% 54%	4180
September	1st to 10th	Day	13% 6% 2 6% 4 4 5% 5% 6% 7% 42%	2153
	11th to 20th	Day	12% 6% 2 5% 4 4 4 4 6% 7% 46%	2090
	21st to end	Day	15% 6% 3 6% 4 3 3 3 5% 6% 47%	2090
October	1st to 10th	Day	10% 5% 2 4 3 3 5% 3 4 6% 54%	2090
	11th to 20th	Day	12% 7% 1 6% 4 3 4 3 4 6% 49%	1948
	21st to end	Day	19% 6% 2 5% 4 3 4 3 4 6% 43%	1971
November	1st to 10th	Day	12% 6% 2 4 3 3 4 3 3 5% 55%	1717
	11th to 20th	Day	16% 8% 3 8% 4 3 3 3 5% 6% 43%	1710
	21st to end	Day	18% 9% 3 6% 5% 3 3 3 5% 6% 38%	1710
December	1st to 10th	Day	21% 13% 4 8% 4 4 4 3 4 4 30%	1710
	11th to 20th	Day	16% 14% 3 9% 5% 5% 4 3 5% 5% 32%	2153
	21st to end	Day	18% 16% 5% 9% 6% 5% 5% 4 5% 6% 21%	3124
January	1st to 10th	Night	16% 15% 5% 10% 6% 5% 4 4 5% 5% 26%	4109
	11th to 20th	Night	18% 14% 5% 11% 6% 4 4 3 3 4 28%	4120
	21st to end	Night	24% 14% 5% 7% 4 4 3 3 4 4 29%	4532
February	1st to 10th	Night	21% 10% 4 9% 4 4 3 3 5% 6% 29%	2327
	11th to 20th	Night	20% 10% 3 8% 5% 4 3 3 5% 5% 33%	2218
	21st to end	Night	22% 12% 4 8% 5% 4 4 4 4 4 29%	1884
March	1st to 10th	Night	21% 13% 3 7% 4 4 4 3 4 5% 32%	3702
	11th to 20th	Night	14% 6% 2 5% 3 3 4 3 4 6% 48%	3480
	21st to end	Night	14% 8% 3 7% 5% 4 4 3 6% 7% 39%	3817
April	1st to 10th	Night	12% 6% 3 6% 5% 5% 5% 4 6% 6% 42%	1966
	11th to 20th	Night	14% 8% 3 7% 5% 3 4 3 5% 7% 43%	1846
	21st to end	Night	15% 8% 3 6% 5% 5% 5% 4 5% 7% 39%	1710
May	1st to 10th	Night	20% 10% 3 8% 5% 5% 5% 4 6% 7% 27%	2813
	11th to 20th	Night	18% 7% 3 5% 4 4 4 4 6% 7% 38%	2812
	21st to end	Night	8% 5% 2 7% 5% 4 5% 4 7% 10% 42%	3079
June	1st to 10th	Night	9% 4 2 5% 4 4 4 5% 7% 10% 47%	1710
	11th to 20th	Night	5% 5% 2 5% 4 4 5% 5% 7% 10% 49%	1682
	21st to end	Night	7% 5% 1 4 6% 4 6% 3 8% 11% 45%	1520
July	1st to 10th	Night	7% 5% 2 7% 4 5% 5% 4 6% 11% 44%	2609
	11th to 20th	Night	7% 5% 2 5% 4 4 3 4 6% 9% 50%	2840
	21st to end	Night	14% 8% 3 8% 6% 5% 5% 5% 6% 9% 31%	3087
August	1st to 10th	Night	8% 5% 2 5% 4 4 4 4 6% 10% 49%	2825
	11th to 20th	Night	7% 6% 2 6% 5% 5% 6% 5% 6% 9% 43%	2817
	21st to end	Night	4 3 1 4 3 3 4 3 5% 8% 61%	3476
September	1st to 10th	Night	13% 4 2 5% 4 3 3 4 5% 8% 48%	2006
	11th to 20th	Night	10% 5% 2 5% 4 3 4 3 5% 7% 51%	2090
	21st to end	Night	13% 5% 2 5% 4 4 4 3 5% 6% 50%	2090
October	1st to 10th	Night	10% 4 2 4 3 3 3 3 4 7% 56%	2090
	11th to 20th	Night	14% 6% 2 4 3 4 3 3 4 7% 49%	2232
	21st to end	Night	17% 7% 2 5% 4 3 4 3 4 5% 45%	2622
November	1st to 10th	Night	12% 6% 3 6% 3 3 4 4 5% 5% 51%	2483
	11th to 20th	Night	15% 8% 3 5% 4 4 4 3 4 6% 44%	2470
	21st to end	Night	17% 10% 3 6% 4 4 3 4 4 6% 39%	2470
December	1st to 10th	Night	20% 12% 3 7% 4 4 4 3 5% 5% 33%	2470
	11th to 20th	Night	18% 11% 4 8% 4 3 4 3 5% 6% 34%	3042
	21st to end	Night	18% 15% 5% 10% 7% 6% 5% 4 5% 6% 21%	4532

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	57% 4 10% 18% 10% 1	2837
	11th to 20th	Day	64% 4 6% 18% 7% 1	2840
	21st to end	Day	65% 3 6% 20% 5% 1	3124
February	1st to 10th	Day	57% 4 7% 21% 9% 2	1851
	11th to 20th	Day	54% 4 7% 20% 12% 3	1858
	21st to end	Day	55% 4 7% 20% 10% 3	1570
March	1st to 10th	Day	56% 4 7% 18% 10% 4	3148
	11th to 20th	Day	39% 5% 11% 26% 18% 1	3480
	21st to end	Day	45% 6% 11% 26% 11% 1	3815
April	1st to 10th	Day	44% 5% 11% 24% 13% 3	2230
	11th to 20th	Day	44% 5% 9% 23% 16% 4	2282
	21st to end	Day	46% 6% 11% 24% 11% 2	2470
May	1st to 10th	Day	52% 7% 11% 21% 8% 1	4120
	11th to 20th	Day	48% 6% 11% 22% 13% 1	4085
	21st to end	Day	39% 9% 13% 19% 18% 2	4489
June	1st to 10th	Day	40% 7% 9% 27% 15% 2	2470
	11th to 20th	Day	34% 8% 14% 24% 17% 2	2487
	21st to end	Day	35% 9% 14% 21% 16% 4	2660
July	1st to 10th	Day	39% 7% 14% 23% 16% 1	4284
	11th to 20th	Day	34% 8% 12% 32% 13% 2	4051
	21st to end	Day	55% 7% 11% 16% 10% 1	4324
August	1st to 10th	Day	30% 9% 14% 35% 12% 1	4091
	11th to 20th	Day	37% 8% 12% 28% 14% 2	4034
	21st to end	Day	28% 7% 11% 32% 18% 3	4179
September	1st to 10th	Day	40% 6% 12% 18% 18% 5%	2153
	11th to 20th	Day	35% 6% 10% 24% 22% 3	2090
	21st to end	Day	39% 4 8% 25% 21% 3	2090
October	1st to 10th	Day	21% 4 7% 26% 40% 3	3480
	11th to 20th	Day	25% 3 10% 28% 32% 2	3214
	21st to end	Day	31% 4 8% 29% 21% 9%	3221
November	1st to 10th	Day	33% 3 9% 26% 24% 4	1717
	11th to 20th	Day	43% 3 8% 23% 19% 4	1710
	21st to end	Day	47% 3 8% 22% 18% 1	1710
December	1st to 10th	Day	58% 3 9% 20% 9% 1	1710
	11th to 20th	Day	54% 5% 9% 17% 14% 1	2150
	21st to end	Day	62% 5% 9% 17% 6% 1	3124
January	1st to 10th	Night	59% 6% 7% 17% 11% 1	4109
	11th to 20th	Night	61% 4 6% 19% 9% 2	4120
	21st to end	Night	59% 4 8% 19% 9% 1	4532
February	1st to 10th	Night	57% 3 10% 19% 10% 1	2327
	11th to 20th	Night	53% 4 7% 22% 12% 2	2219
	21st to end	Night	58% 4 9% 14% 11% 3	1884
March	1st to 10th	Night	54% 4 7% 21% 12% 2	3702
	11th to 20th	Night	36% 6% 9% 29% 17% 3	3480
	21st to end	Night	44% 5% 10% 24% 15% 1	3817
April	1st to 10th	Night	39% 6% 10% 23% 18% 3	1966
	11th to 20th	Night	41% 5% 9% 20% 19% 7%	1846
	21st to end	Night	44% 6% 11% 22% 13% 2	1710
May	1st to 10th	Night	53% 9% 9% 19% 7% 2	2840
	11th to 20th	Night	44% 8% 12% 25% 10% 1	2813
	21st to end	Night	34% 9% 13% 24% 17% 3	3087
June	1st to 10th	Night	31% 6% 16% 27% 16% 4	1710
	11th to 20th	Night	28% 8% 17% 24% 20% 3	1682
	21st to end	Night	31% 9% 17% 23% 15% 6%	1520
July	1st to 10th	Night	34% 9% 13% 25% 17% 3	2567
	11th to 20th	Night	30% 7% 13% 32% 16% 2	2786
	21st to end	Night	49% 7% 10% 21% 12% 1	2988
August	1st to 10th	Night	30% 9% 14% 32% 14% 1	2814
	11th to 20th	Night	35% 7% 11% 29% 16% 1	2844
	21st to end	Night	20% 7% 13% 34% 21% 4	3476
September	1st to 10th	Night	34% 6% 11% 22% 19% 7%	2006
	11th to 20th	Night	32% 5% 10% 25% 24% 3	2090
	21st to end	Night	36% 5% 7% 23% 24% 4	2090
October	1st to 10th	Night	21% 4 7% 24% 41% 3	3480
	11th to 20th	Night	25% 3 6% 27% 33% 5%	3705
	21st to end	Night	30% 3 6% 23% 29% 8%	4309
November	1st to 10th	Night	35% 4 7% 26% 23% 4	2483
	11th to 20th	Night	41% 4 7% 20% 22% 6%	2470
	21st to end	Night	46% 4 8% 24% 16% 2	2470
December	1st to 10th	Night	53% 4 10% 20% 12% 1	2470
	11th to 20th	Night	50% 4 8% 22% 14% 2	3044
	21st to end	Night	63% 7% 8% 14% 8%	4532

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	28% 14% 35% 16% 6% 1	270
	11th to 20th	Day	31% 20% 29% 16% 4	270
	21st to end	Day	24% 17% 41% 14% 4	297
February	1st to 10th	Day	27% 18% 36% 16% 3	270
	11th to 20th	Day	31% 20% 33% 12% 3 1	270
	21st to end	Day	31% 16% 40% 10% 3	225
March	1st to 10th	Day	28% 19% 36% 12% 5%	285
	11th to 20th	Day	22% 18% 37% 17% 5% 1	460
	21st to end	Day	28% 13% 33% 18% 7% 1	506
April	1st to 10th	Day	21% 16% 30% 20% 11% 2	460
	11th to 20th	Day	23% 14% 27% 23% 9% 4	452
	21st to end	Day	22% 11% 34% 22% 8% 3	460
May	1st to 10th	Day	22% 11% 30% 21% 12% 5%	463
	11th to 20th	Day	19% 7% 24% 25% 17% 7%	487
	21st to end	Day	14% 5% 21% 30% 18% 12%	529
June	1st to 10th	Day	15% 4 20% 25% 26% 10%	490
	11th to 20th	Day	8% 3 22% 31% 26% 11%	507
	21st to end	Day	9% 5% 22% 31% 20% 12%	680
July	1st to 10th	Day	16% 2 14% 26% 21% 22%	623
	11th to 20th	Day	10% 4 18% 24% 28% 17%	484
	21st to end	Day	14% 3 12% 30% 25% 16%	532
August	1st to 10th	Day	14% 3 14% 24% 27% 17%	486
	11th to 20th	Day	14% 4 13% 33% 25% 12%	479
	21st to end	Day	9% 2 12% 29% 31% 18%	539
September	1st to 10th	Day	13% 3 13% 30% 25% 16%	490
	11th to 20th	Day	14% 2 12% 28% 28% 16%	490
	21st to end	Day	19% 7% 18% 24% 22% 10%	490
October	1st to 10th	Day	12% 5% 18% 33% 23% 9%	490
	11th to 20th	Day	15% 11% 29% 27% 14% 5%	490
	21st to end	Day	20% 9% 33% 27% 11% 1	420
November	1st to 10th	Day	14% 8% 34% 27% 13% 3	285
	11th to 20th	Day	23% 16% 27% 25% 7% 2	270
	21st to end	Day	24% 11% 34% 25% 6%	270
December	1st to 10th	Day	24% 17% 30% 26% 3 1	270
	11th to 20th	Day	22% 13% 40% 18% 7%	270
	21st to end	Day	30% 16% 34% 17% 3	297
January	1st to 10th	Night	25% 14% 36% 20% 5%	760
	11th to 20th	Night	31% 14% 33% 18% 3	760
	21st to end	Night	25% 12% 38% 23% 2	836
February	1st to 10th	Night	28% 11% 36% 23% 3	760
	11th to 20th	Night	28% 13% 37% 21% 1	743
	21st to end	Night	30% 11% 38% 19% 2	628
March	1st to 10th	Night	25% 12% 32% 26% 6%	760
	11th to 20th	Night	24% 12% 35% 22% 7% 1	760
	21st to end	Night	21% 11% 32% 27% 8%	836
April	1st to 10th	Night	17% 10% 35% 30% 8%	636
	11th to 20th	Night	19% 9% 31% 29% 11% 1	563
	21st to end	Night	19% 4 37% 29% 9% 1	570
May	1st to 10th	Night	21% 4 32% 26% 14% 3	570
	11th to 20th	Night	18% 5% 19% 37% 19% 2	561
	21st to end	Night	10% 2 19% 34% 30% 5%	617
June	1st to 10th	Night	11% 1 18% 42% 24% 4	570
	11th to 20th	Night	8% 2 16% 40% 30% 4	570
	21st to end	Night	8% 3 18% 40% 28% 4	570
July	1st to 10th	Night	12% 1 13% 32% 31% 12%	555
	11th to 20th	Night	8% 1 12% 35% 38% 6%	552
	21st to end	Night	13% 2 9% 37% 33% 6%	624
August	1st to 10th	Night	10% 1 9% 33% 42% 5%	567
	11th to 20th	Night	10% 2 9% 39% 33% 7%	564
	21st to end	Night	8% 1 7% 33% 44% 6%	627
September	1st to 10th	Night	14% 2 9% 32% 35% 7%	676
	11th to 20th	Night	13% 2 13% 30% 36% 6%	760
	21st to end	Night	15% 3 19% 35% 24% 3	760
October	1st to 10th	Night	11% 3 18% 35% 28% 4	760
	11th to 20th	Night	18% 7% 26% 31% 17% 2	760
	21st to end	Night	22% 6% 32% 26% 12% 1	836
November	1st to 10th	Night	16% 7% 26% 32% 17% 2	764
	11th to 20th	Night	20% 9% 32% 28% 10% 1	760
	21st to end	Night	23% 10% 28% 28% 10% 1	760
December	1st to 10th	Night	27% 10% 31% 26% 6%	760
	11th to 20th	Night	27% 8% 33% 25% 6%	760
	21st to end	Night	29% 13% 30% 24% 5%	836

Page generated at 2024-11-03 13:18:59. Version ac07

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