Lafayette
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lafayette clear sky chart from 2005-11-06 to 2025-11-18.

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	11% 6% 3 7% 5% 5% 5% 4 7% 8% 39%	126259
	Night	12% 6% 2 6% 4 4 4 3 6% 8% 45%	124256
Transparency	Day	40% 8% 12% 18% 16% 7%	129868
	Night	36% 6% 13% 19% 17% 9%	128724
Seeing	Day	12% 6% 18% 24% 24% 15%	16235
	Night	13% 6% 20% 31% 25% 5%	25932

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	17% 8% 4 7% 4 3 4 3 5% 7% 38%	4077
	11th to 20th	Day	12% 8% 3 7% 4 3 3 3 4 5% 48%	4080
	21st to end	Day	22% 9% 3 8% 4 4 4 3 5% 5% 33%	4488
February	1st to 10th	Day	16% 9% 4 7% 4 4 4 3 5% 6% 37%	1940
	11th to 20th	Day	18% 9% 3 6% 4 4 5% 3 5% 6% 37%	1948
	21st to end	Day	17% 12% 4 7% 4 4 4 3 5% 6% 35%	1758
March	1st to 10th	Day	21% 9% 3 8% 5% 4 4 4 5% 7% 32%	4936
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 4 5% 7% 43%	4980
	21st to end	Day	13% 7% 3 8% 4 4 4 3 6% 8% 40%	5462
April	1st to 10th	Day	12% 7% 2 6% 4 5% 6% 4 6% 7% 40%	2391
	11th to 20th	Day	13% 7% 3 6% 5% 4 5% 4 7% 8% 39%	2374
	21st to end	Day	9% 5% 3 4 5% 6% 5% 5% 7% 9% 41%	2400
May	1st to 10th	Day	14% 7% 3 9% 6% 6% 6% 5% 7% 8% 31%	5405
	11th to 20th	Day	7% 5% 2 6% 4 5% 6% 4 7% 9% 45%	5404
	21st to end	Day	7% 4 2 7% 6% 6% 6% 5% 8% 11% 38%	6042
June	1st to 10th	Day	6% 5% 3 9% 7% 7% 6% 6% 7% 9% 36%	2600
	11th to 20th	Day	5% 5% 3 7% 7% 8% 8% 7% 8% 10% 33%	2600
	21st to end	Day	6% 6% 3 8% 9% 8% 8% 7% 10% 9% 25%	2600
July	1st to 10th	Day	6% 5% 3 8% 8% 8% 8% 7% 9% 11% 27%	5900
	11th to 20th	Day	6% 6% 3 8% 7% 7% 8% 7% 10% 13% 26%	5900
	21st to end	Day	9% 8% 3 9% 6% 6% 7% 5% 8% 12% 28%	6387
August	1st to 10th	Day	3 3 1 4 4 4 5% 5% 7% 11% 53%	3905
	11th to 20th	Day	5% 4 1 6% 5% 5% 7% 6% 10% 14% 37%	3849
	21st to end	Day	11% 7% 3 8% 7% 6% 6% 5% 6% 7% 33%	4312
September	1st to 10th	Day	10% 5% 2 7% 6% 5% 6% 5% 8% 9% 35%	2400
	11th to 20th	Day	11% 7% 2 7% 5% 5% 5% 4 7% 7% 38%	2400
	21st to end	Day	9% 5% 2 7% 5% 4 5% 4 6% 6% 47%	2116
October	1st to 10th	Day	7% 4 2 5% 4 4 4 3 5% 7% 57%	2000
	11th to 20th	Day	9% 4 2 6% 3 3 4 3 5% 6% 55%	2000
	21st to end	Day	11% 4 1 5% 4 3 4 3 4 6% 54%	2200
November	1st to 10th	Day	9% 5% 2 5% 4 4 4 4 5% 7% 50%	2058
	11th to 20th	Day	10% 6% 2 6% 4 4 2 3 5% 5% 53%	2070
	21st to end	Day	14% 6% 2 6% 4 4 4 3 6% 6% 45%	2000
December	1st to 10th	Day	18% 9% 3 7% 4 4 4 3 5% 6% 38%	3260
	11th to 20th	Day	10% 7% 3 6% 5% 4 4 4 5% 7% 45%	3529
	21st to end	Day	15% 7% 2 6% 4 3 4 3 5% 6% 45%	4488
January	1st to 10th	Night	18% 5% 3 5% 3 3 3 2 4 5% 47%	5888
	11th to 20th	Night	17% 7% 3 6% 3 3 3 2 4 5% 47%	5900
	21st to end	Night	24% 9% 3 6% 4 3 4 3 4 6% 34%	6490
February	1st to 10th	Night	15% 9% 3 7% 4 4 4 3 5% 6% 41%	2456
	11th to 20th	Night	19% 8% 2 6% 3 3 4 3 5% 5% 42%	2338
	21st to end	Night	19% 9% 3 6% 3 4 3 4 5% 6% 39%	1888
March	1st to 10th	Night	20% 9% 3 7% 4 3 4 3 4 5% 37%	4919
	11th to 20th	Night	16% 8% 2 6% 4 3 4 3 4 5% 45%	4980
	21st to end	Night	17% 7% 3 6% 4 3 4 3 5% 6% 42%	5467
April	1st to 10th	Night	13% 6% 2 5% 5% 4 4 3 6% 8% 43%	2007
	11th to 20th	Night	13% 6% 2 6% 4 3 4 3 4 7% 48%	1975
	21st to end	Night	7% 6% 2 5% 4 4 4 4 6% 7% 51%	2000
May	1st to 10th	Night	17% 7% 3 7% 4 4 4 4 6% 9% 33%	4490
	11th to 20th	Night	13% 6% 2 7% 4 4 4 4 6% 8% 42%	4489
	21st to end	Night	9% 5% 2 6% 4 4 5% 4 6% 11% 43%	4799
June	1st to 10th	Night	5% 4 2 5% 4 4 5% 5% 7% 11% 48%	1800
	11th to 20th	Night	4 4 1 4 5% 5% 5% 5% 7% 11% 48%	1800
	21st to end	Night	6% 5% 2 6% 6% 6% 6% 4 9% 11% 39%	1800
July	1st to 10th	Night	4 5% 2 6% 5% 5% 6% 5% 9% 13% 39%	4078
	11th to 20th	Night	4 3 2 5% 4 5% 6% 5% 9% 12% 46%	4077
	21st to end	Night	5% 5% 3 7% 5% 6% 5% 5% 8% 12% 39%	4465
August	1st to 10th	Night	2 2 1 3 3 3 4 4 6% 11% 61%	3244
	11th to 20th	Night	2 2 1 4 3 4 5% 4 9% 14% 52%	3200
	21st to end	Night	6% 6% 3 7% 5% 5% 5% 4 8% 9% 41%	3586
September	1st to 10th	Night	7% 4 2 6% 5% 5% 5% 5% 8% 11% 43%	2000
	11th to 20th	Night	7% 7% 3 6% 5% 5% 6% 4 8% 8% 40%	2000
	21st to end	Night	8% 4 2 5% 3 3 4 4 6% 8% 54%	2256
October	1st to 10th	Night	5% 4 2 5% 3 3 4 3 4 7% 59%	2400
	11th to 20th	Night	7% 4 2 4 3 3 3 3 5% 5% 60%	2400
	21st to end	Night	9% 5% 2 4 3 3 3 2 4 6% 58%	2640
November	1st to 10th	Night	8% 6% 2 6% 4 3 4 3 4 6% 54%	2460
	11th to 20th	Night	12% 4 2 5% 3 3 3 3 4 6% 56%	2485
	21st to end	Night	15% 6% 2 6% 3 4 3 3 5% 6% 48%	2400
December	1st to 10th	Night	18% 8% 3 7% 4 3 4 3 3 6% 40%	3920
	11th to 20th	Night	10% 7% 2 7% 4 4 4 3 5% 6% 47%	4669
	21st to end	Night	17% 9% 2 6% 4 3 3 2 3 5% 45%	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	44% 5% 6% 19% 20% 6%	4078
	11th to 20th	Day	40% 3 4 18% 26% 9%	4080
	21st to end	Day	53% 4 6% 12% 14% 11%	4488
February	1st to 10th	Day	47% 5% 7% 13% 18% 9%	1940
	11th to 20th	Day	47% 6% 7% 15% 17% 10%	1958
	21st to end	Day	49% 5% 8% 16% 17% 7%	1758
March	1st to 10th	Day	51% 5% 8% 12% 13% 10%	4936
	11th to 20th	Day	38% 7% 9% 13% 17% 16%	4980
	21st to end	Day	40% 6% 10% 19% 19% 7%	5464
April	1st to 10th	Day	40% 7% 11% 17% 17% 9%	2391
	11th to 20th	Day	40% 7% 10% 18% 15% 9%	2374
	21st to end	Day	34% 8% 12% 19% 22% 4	2400
May	1st to 10th	Day	47% 8% 11% 22% 9% 3	5440
	11th to 20th	Day	33% 7% 14% 25% 19% 3	5408
	21st to end	Day	34% 10% 16% 30% 10% 1	6055
June	1st to 10th	Day	40% 9% 14% 21% 14% 1	2600
	11th to 20th	Day	41% 10% 15% 21% 12% 1	2600
	21st to end	Day	47% 14% 16% 17% 6%	2600
July	1st to 10th	Day	43% 14% 25% 16% 2	5836
	11th to 20th	Day	43% 14% 28% 12% 1	5831
	21st to end	Day	46% 12% 19% 19% 3	6205
August	1st to 10th	Day	22% 9% 16% 32% 20%	3893
	11th to 20th	Day	33% 11% 24% 27% 4 1	3885
	21st to end	Day	49% 8% 13% 14% 14% 2	4311
September	1st to 10th	Day	40% 12% 16% 18% 11% 4	2400
	11th to 20th	Day	43% 8% 13% 16% 14% 5%	2400
	21st to end	Day	35% 6% 12% 20% 16% 10%	2116
October	1st to 10th	Day	25% 3 6% 12% 24% 30%	3260
	11th to 20th	Day	19% 3 4 20% 28% 25%	3240
	21st to end	Day	24% 4 4 12% 39% 17%	3538
November	1st to 10th	Day	32% 5% 9% 19% 24% 11%	2058
	11th to 20th	Day	32% 4 6% 17% 28% 13%	2070
	21st to end	Day	39% 5% 9% 17% 23% 9%	2000
December	1st to 10th	Day	47% 4 6% 15% 20% 7%	3260
	11th to 20th	Day	38% 5% 10% 16% 21% 10%	3527
	21st to end	Day	39% 5% 8% 17% 24% 7%	4488
January	1st to 10th	Night	39% 4 6% 20% 24% 7%	5888
	11th to 20th	Night	41% 3 4 15% 25% 11%	5900
	21st to end	Night	52% 4 6% 13% 14% 12%	6490
February	1st to 10th	Night	45% 4 6% 15% 19% 11%	2456
	11th to 20th	Night	44% 5% 7% 17% 16% 11%	2339
	21st to end	Night	46% 5% 10% 13% 15% 11%	1888
March	1st to 10th	Night	48% 4 8% 12% 15% 12%	4919
	11th to 20th	Night	40% 6% 8% 14% 16% 16%	4980
	21st to end	Night	42% 5% 9% 18% 18% 8%	5467
April	1st to 10th	Night	37% 7% 11% 17% 16% 11%	2007
	11th to 20th	Night	36% 5% 11% 19% 17% 12%	1975
	21st to end	Night	31% 7% 11% 23% 23% 6%	2000
May	1st to 10th	Night	46% 8% 12% 20% 10% 3	4520
	11th to 20th	Night	37% 7% 14% 22% 18% 1	4490
	21st to end	Night	33% 8% 20% 29% 10% 1	4808
June	1st to 10th	Night	26% 12% 20% 24% 17% 1	1800
	11th to 20th	Night	28% 10% 19% 27% 13% 2	1800
	21st to end	Night	36% 10% 23% 23% 7% 1	1800
July	1st to 10th	Night	33% 12% 34% 18% 3	4035
	11th to 20th	Night	28% 13% 42% 15% 2	4026
	21st to end	Night	36% 14% 21% 24% 5%	4336
August	1st to 10th	Night	17% 8% 20% 35% 21%	3232
	11th to 20th	Night	19% 10% 35% 31% 4	3230
	21st to end	Night	38% 11% 17% 18% 14% 2	3586
September	1st to 10th	Night	34% 10% 20% 21% 10% 6%	2000
	11th to 20th	Night	36% 11% 17% 17% 15% 4	2000
	21st to end	Night	29% 7% 13% 23% 16% 11%	2256
October	1st to 10th	Night	24% 4 8% 15% 19% 30%	3920
	11th to 20th	Night	16% 3 4 21% 30% 25%	3899
	21st to end	Night	20% 3 6% 12% 36% 24%	4252
November	1st to 10th	Night	31% 5% 9% 18% 25% 12%	2460
	11th to 20th	Night	31% 4 7% 17% 26% 16%	2485
	21st to end	Night	37% 5% 8% 19% 21% 11%	2400
December	1st to 10th	Night	48% 3 5% 17% 21% 6%	3920
	11th to 20th	Night	37% 5% 10% 18% 20% 11%	4670
	21st to end	Night	43% 4 7% 14% 23% 9%	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	21% 17% 37% 16% 7% 3	300
	11th to 20th	Day	15% 16% 36% 24% 8% 1	300
	21st to end	Day	23% 14% 40% 18% 5%	330
February	1st to 10th	Day	21% 11% 31% 28% 9%	300
	11th to 20th	Day	25% 18% 29% 19% 10%	300
	21st to end	Day	19% 18% 40% 17% 6%	249
March	1st to 10th	Day	21% 16% 32% 23% 8% 1	300
	11th to 20th	Day	22% 14% 35% 22% 6% 1	300
	21st to end	Day	14% 15% 37% 22% 9% 2	330
April	1st to 10th	Day	16% 14% 29% 28% 12% 1	491
	11th to 20th	Day	18% 11% 28% 25% 16% 2	492
	21st to end	Day	10% 7% 27% 34% 19% 3	500
May	1st to 10th	Day	15% 7% 24% 33% 18% 4	503
	11th to 20th	Day	10% 5% 22% 29% 25% 9%	527
	21st to end	Day	7% 2 18% 30% 30% 13%	618
June	1st to 10th	Day	7% 2 13% 30% 32% 17%	730
	11th to 20th	Day	7% 2 11% 29% 35% 16%	730
	21st to end	Day	8% 2 8% 25% 30% 27%	730
July	1st to 10th	Day	9% 3 5% 18% 36% 30%	721
	11th to 20th	Day	8% 1 4 16% 36% 35%	718
	21st to end	Day	9% 2 4 16% 38% 31%	784
August	1st to 10th	Day	3 1 3 13% 37% 43%	526
	11th to 20th	Day	7% 1 4 8% 30% 50%	519
	21st to end	Day	12% 2 6% 16% 32% 32%	583
September	1st to 10th	Day	12% 2 7% 22% 34% 25%	530
	11th to 20th	Day	9% 4 6% 19% 38% 24%	530
	21st to end	Day	9% 3 10% 23% 37% 17%	390
October	1st to 10th	Day	7% 3 18% 38% 25% 9%	330
	11th to 20th	Day	6% 4 18% 35% 25% 12%	330
	21st to end	Day	14% 10% 21% 27% 22% 6%	363
November	1st to 10th	Day	14% 6% 21% 29% 24% 6%	330
	11th to 20th	Day	14% 10% 25% 31% 17% 3	321
	21st to end	Day	18% 11% 30% 26% 12% 3	300
December	1st to 10th	Day	21% 7% 30% 25% 12% 5%	300
	11th to 20th	Day	19% 12% 33% 25% 11%	300
	21st to end	Day	22% 11% 32% 23% 11% 1	330
January	1st to 10th	Night	19% 9% 34% 30% 8%	1000
	11th to 20th	Night	19% 10% 30% 32% 9%	1000
	21st to end	Night	21% 10% 32% 31% 7%	1100
February	1st to 10th	Night	19% 10% 30% 35% 5%	856
	11th to 20th	Night	23% 10% 27% 32% 6%	783
	21st to end	Night	24% 13% 31% 28% 4	568
March	1st to 10th	Night	18% 9% 29% 36% 8%	600
	11th to 20th	Night	16% 9% 30% 37% 9%	600
	21st to end	Night	15% 6% 32% 34% 12%	660
April	1st to 10th	Night	16% 9% 30% 33% 11% 1	600
	11th to 20th	Night	13% 10% 30% 32% 14% 1	593
	21st to end	Night	8% 6% 26% 45% 14% 1	600
May	1st to 10th	Night	12% 5% 21% 47% 14% 1	600
	11th to 20th	Night	10% 3 19% 46% 20% 2	591
	21st to end	Night	7% 3 12% 38% 35% 5%	650
June	1st to 10th	Night	4 2 7% 37% 42% 8%	600
	11th to 20th	Night	4 1 7% 31% 49% 8%	600
	21st to end	Night	7% 2 5% 24% 46% 16%	600
July	1st to 10th	Night	5% 1 5% 16% 56% 17%	585
	11th to 20th	Night	4 1 3 11% 56% 25%	582
	21st to end	Night	4 1 3 17% 55% 19%	657
August	1st to 10th	Night	4 1 2 14% 57% 23%	597
	11th to 20th	Night	4 1 1 12% 56% 26%	594
	21st to end	Night	6% 2 3 18% 50% 20%	660
September	1st to 10th	Night	8% 1 6% 20% 48% 17%	600
	11th to 20th	Night	11% 3 5% 23% 49% 10%	600
	21st to end	Night	9% 2 7% 29% 46% 7%	722
October	1st to 10th	Night	6% 2 13% 37% 38% 5%	800
	11th to 20th	Night	8% 4 18% 40% 28% 3	800
	21st to end	Night	11% 7% 18% 39% 24% 2	880
November	1st to 10th	Night	10% 5% 19% 39% 25% 2	820
	11th to 20th	Night	13% 6% 23% 41% 16% 1	829
	21st to end	Night	15% 7% 28% 35% 14% 1	800
December	1st to 10th	Night	18% 9% 23% 34% 15%	800
	11th to 20th	Night	17% 8% 28% 34% 12%	905
	21st to end	Night	22% 8% 29% 30% 10%	1100

Page generated at 2025-11-14 23:55:59. Version ac07

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