Aubrie Le observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Aubrie Le observatory clear sky chart from 2005-11-06 to 2024-12-02.

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	10% 5% 2 5% 4 3 4 3 5% 7% 52%	101438
	Night	9% 5% 2 4 3 3 3 3 5% 7% 57%	98305
Transparency	Day	31% 4 10% 25% 23% 7%	105181
	Night	27% 4 9% 25% 26% 9%	102676
Seeing	Day	12% 9% 26% 30% 19% 5%	15426
	Night	11% 9% 31% 34% 14% 1	25329

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	10% 8% 2 6% 4 3 4 3 5% 7% 49%	2847
	11th to 20th	Day	8% 6% 2 3 3 2 3 2 4 5% 62%	2850
	21st to end	Day	16% 10% 4 6% 3 2 2 2 3 4 48%	3135
February	1st to 10th	Day	12% 7% 3 7% 4 3 3 2 5% 6% 47%	1795
	11th to 20th	Day	13% 6% 2 5% 3 4 4 2 5% 6% 51%	1849
	21st to end	Day	15% 8% 3 5% 3 3 4 2 3 5% 50%	1570
March	1st to 10th	Day	11% 7% 2 5% 3 3 3 2 4 6% 55%	3393
	11th to 20th	Day	10% 6% 2 6% 4 3 4 3 5% 6% 51%	3480
	21st to end	Day	15% 10% 3 7% 4 3 4 3 4 6% 40%	3814
April	1st to 10th	Day	10% 6% 2 5% 4 3 4 3 5% 7% 53%	2090
	11th to 20th	Day	14% 4 2 6% 4 3 4 3 5% 5% 49%	2224
	21st to end	Day	14% 6% 2 5% 4 4 4 3 5% 6% 47%	2470
May	1st to 10th	Day	17% 8% 2 6% 4 3 4 2 5% 5% 43%	4082
	11th to 20th	Day	11% 7% 2 6% 4 4 4 4 5% 6% 47%	4082
	21st to end	Day	15% 6% 2 6% 5% 4 4 4 5% 7% 41%	4477
June	1st to 10th	Day	8% 5% 2 6% 4 4 4 4 7% 8% 49%	2470
	11th to 20th	Day	6% 3 2 4 4 4 5% 4 5% 9% 53%	2470
	21st to end	Day	5% 3 1 4 3 3 4 5% 5% 8% 59%	2470
July	1st to 10th	Day	7% 4 2 5% 5% 4 5% 4 7% 9% 47%	4120
	11th to 20th	Day	5% 3 1 4 3 4 4 4 5% 8% 58%	4120
	21st to end	Day	4 3 2 4 4 4 5% 4 6% 9% 56%	4465
August	1st to 10th	Day	4 3 1 5% 4 4 4 3 6% 8% 58%	4104
	11th to 20th	Day	6% 3 2 4 3 3 5% 4 6% 9% 56%	4041
	21st to end	Day	3 2 1 4 3 4 4 4 6% 8% 62%	4195
September	1st to 10th	Day	9% 4 1 4 3 3 3 3 5% 7% 56%	2090
	11th to 20th	Day	12% 4 2 5% 3 3 3 3 6% 7% 51%	2090
	21st to end	Day	8% 4 2 4 3 3 3 3 4 6% 61%	2090
October	1st to 10th	Day	9% 4 1 5% 3 2 3 2 4 6% 61%	2051
	11th to 20th	Day	10% 3 1 3 2 2 2 2 3 4 66%	1900
	21st to end	Day	13% 5% 2 5% 3 3 2 2 3 4 59%	2090
November	1st to 10th	Day	10% 5% 1 3 4 3 2 3 4 7% 58%	1899
	11th to 20th	Day	8% 3 2 4 3 2 2 2 4 4 66%	1800
	21st to end	Day	13% 5% 1 3 3 2 3 2 3 5% 60%	1800
December	1st to 10th	Day	10% 5% 2 5% 3 3 4 3 5% 6% 53%	1719
	11th to 20th	Day	13% 7% 2 5% 3 3 4 3 4 6% 50%	2161
	21st to end	Day	15% 8% 2 5% 4 4 4 3 4 6% 43%	3135
January	1st to 10th	Night	11% 8% 2 5% 4 3 4 3 4 5% 51%	4108
	11th to 20th	Night	6% 4 2 4 3 3 3 3 4 7% 61%	4120
	21st to end	Night	17% 9% 2 5% 2 3 2 2 3 5% 51%	4532
February	1st to 10th	Night	12% 8% 3 5% 3 3 3 2 4 5% 51%	2399
	11th to 20th	Night	12% 8% 2 5% 3 2 2 2 4 6% 53%	2218
	21st to end	Night	11% 7% 3 5% 3 4 4 3 4 5% 52%	1884
March	1st to 10th	Night	11% 7% 3 5% 3 3 3 2 5% 6% 51%	3461
	11th to 20th	Night	10% 5% 2 4 2 2 2 3 4 6% 60%	3480
	21st to end	Night	12% 6% 2 5% 3 4 3 3 6% 6% 48%	3817
April	1st to 10th	Night	10% 5% 1 5% 3 3 3 2 4 7% 56%	2090
	11th to 20th	Night	13% 4 2 3 3 3 3 3 4 6% 55%	1899
	21st to end	Night	12% 5% 1 4 3 4 3 3 5% 7% 52%	1710
May	1st to 10th	Night	17% 7% 2 5% 3 3 3 2 5% 6% 46%	2823
	11th to 20th	Night	12% 5% 2 6% 3 4 3 4 6% 7% 48%	2823
	21st to end	Night	10% 5% 1 5% 4 3 4 3 5% 7% 52%	3090
June	1st to 10th	Night	5% 4 1 3 2 3 3 3 6% 11% 58%	1710
	11th to 20th	Night	4 4 2 4 3 3 3 4 6% 9% 58%	1710
	21st to end	Night	3 2 1 3 2 2 4 4 5% 9% 66%	1710
July	1st to 10th	Night	6% 4 1 6% 4 4 4 4 6% 9% 52%	2850
	11th to 20th	Night	2 1 1 2 2 3 3 3 5% 9% 69%	2850
	21st to end	Night	4 2 1 3 2 3 3 3 5% 9% 65%	3098
August	1st to 10th	Night	1 1 1 3 2 3 4 3 6% 8% 67%	2836
	11th to 20th	Night	4 2 1 3 3 4 4 4 7% 9% 59%	2798
	21st to end	Night	2 2 1 2 2 3 4 3 5% 9% 67%	3463
September	1st to 10th	Night	8% 3 2 4 2 3 4 3 4 6% 60%	2090
	11th to 20th	Night	10% 5% 2 5% 3 3 4 3 4 7% 53%	2090
	21st to end	Night	7% 4 2 3 2 2 4 3 5% 7% 61%	2090
October	1st to 10th	Night	7% 3 1 3 3 3 3 3 4 5% 64%	2109
	11th to 20th	Night	9% 4 2 3 3 3 3 2 3 4 65%	2280
	21st to end	Night	12% 4 2 4 2 2 2 2 4 4 62%	2508
November	1st to 10th	Night	9% 4 2 3 2 3 3 2 4 5% 63%	2395
	11th to 20th	Night	7% 4 2 5% 3 2 3 2 4 5% 63%	2600
	21st to end	Night	12% 5% 2 3 2 3 3 3 4 5% 58%	2600
December	1st to 10th	Night	9% 5% 2 4 3 3 3 2 5% 6% 58%	2496
	11th to 20th	Night	11% 6% 2 6% 4 3 3 3 3 4 54%	3036
	21st to end	Night	15% 6% 2 4 3 3 3 3 4 5% 51%	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	36% 3 9% 24% 24% 4	2848
	11th to 20th	Day	27% 2 12% 24% 32% 4	2850
	21st to end	Day	42% 2 5% 23% 23% 5%	3135
February	1st to 10th	Day	38% 3 8% 23% 23% 5%	1795
	11th to 20th	Day	35% 3 6% 27% 21% 7%	1859
	21st to end	Day	40% 2 5% 17% 26% 10%	1570
March	1st to 10th	Day	32% 3 5% 18% 25% 16%	3393
	11th to 20th	Day	35% 5% 10% 25% 20% 5%	3480
	21st to end	Day	45% 4 7% 23% 16% 4	3814
April	1st to 10th	Day	33% 4 9% 24% 21% 9%	2090
	11th to 20th	Day	37% 4 9% 22% 20% 8%	2224
	21st to end	Day	38% 4 9% 26% 19% 4	2470
May	1st to 10th	Day	44% 4 9% 20% 17% 6%	4120
	11th to 20th	Day	37% 5% 12% 27% 17% 2	4086
	21st to end	Day	42% 5% 12% 20% 14% 7%	4489
June	1st to 10th	Day	31% 6% 18% 27% 15% 3	2470
	11th to 20th	Day	27% 6% 13% 28% 22% 4	2470
	21st to end	Day	23% 6% 14% 29% 23% 6%	2470
July	1st to 10th	Day	30% 7% 14% 29% 16% 3	4056
	11th to 20th	Day	23% 5% 9% 34% 26% 3	4051
	21st to end	Day	23% 6% 15% 31% 24% 1	4325
August	1st to 10th	Day	23% 5% 10% 25% 26% 10%	4090
	11th to 20th	Day	24% 5% 15% 33% 19% 4	4080
	21st to end	Day	20% 6% 13% 43% 15% 3	4194
September	1st to 10th	Day	27% 5% 9% 24% 24% 11%	2090
	11th to 20th	Day	32% 7% 9% 21% 24% 7%	2090
	21st to end	Day	25% 4 8% 25% 30% 8%	2090
October	1st to 10th	Day	17% 2 5% 13% 42% 19%	3402
	11th to 20th	Day	18% 2 5% 24% 34% 17%	3140
	21st to end	Day	24% 2 7% 28% 30% 9%	3428
November	1st to 10th	Day	28% 3 7% 22% 29% 10%	1899
	11th to 20th	Day	23% 2 8% 27% 29% 11%	1800
	21st to end	Day	30% 2 5% 25% 28% 10%	1800
December	1st to 10th	Day	32% 4 10% 25% 25% 4	1719
	11th to 20th	Day	37% 3 6% 19% 28% 7%	2159
	21st to end	Day	41% 3 6% 22% 24% 3	3135
January	1st to 10th	Night	35% 3 6% 22% 28% 6%	4108
	11th to 20th	Night	24% 3 16% 22% 29% 7%	4120
	21st to end	Night	40% 2 6% 19% 27% 7%	4532
February	1st to 10th	Night	37% 3 8% 21% 24% 7%	2399
	11th to 20th	Night	34% 3 6% 25% 24% 8%	2218
	21st to end	Night	35% 4 5% 18% 23% 15%	1884
March	1st to 10th	Night	34% 4 5% 19% 23% 16%	3461
	11th to 20th	Night	26% 3 8% 33% 22% 8%	3480
	21st to end	Night	35% 4 10% 26% 22% 3	3817
April	1st to 10th	Night	29% 3 9% 22% 22% 14%	2090
	11th to 20th	Night	29% 4 10% 25% 19% 12%	1899
	21st to end	Night	32% 5% 11% 26% 22% 4	1710
May	1st to 10th	Night	40% 5% 9% 19% 20% 7%	2850
	11th to 20th	Night	35% 5% 14% 27% 17% 2	2824
	21st to end	Night	30% 6% 12% 24% 20% 7%	3099
June	1st to 10th	Night	21% 6% 17% 33% 19% 4	1710
	11th to 20th	Night	22% 5% 14% 29% 24% 5%	1710
	21st to end	Night	16% 4 13% 29% 30% 8%	1710
July	1st to 10th	Night	27% 6% 13% 33% 17% 4	2805
	11th to 20th	Night	12% 4 10% 42% 27% 4	2796
	21st to end	Night	17% 4 15% 36% 27% 2	2999
August	1st to 10th	Night	15% 5% 11% 26% 35% 9%	2826
	11th to 20th	Night	20% 5% 11% 35% 24% 4	2825
	21st to end	Night	14% 5% 14% 43% 20% 4	3463
September	1st to 10th	Night	25% 6% 8% 23% 27% 12%	2090
	11th to 20th	Night	32% 4 8% 21% 25% 10%	2090
	21st to end	Night	22% 4 7% 25% 30% 11%	2090
October	1st to 10th	Night	15% 3 6% 15% 37% 24%	3512
	11th to 20th	Night	18% 2 4 18% 38% 20%	3779
	21st to end	Night	21% 3 5% 29% 32% 10%	4120
November	1st to 10th	Night	24% 3 7% 23% 30% 13%	2395
	11th to 20th	Night	26% 3 6% 23% 30% 12%	2600
	21st to end	Night	30% 2 7% 21% 29% 11%	2600
December	1st to 10th	Night	28% 3 8% 27% 24% 9%	2496
	11th to 20th	Night	34% 3 6% 19% 30% 8%	3037
	21st to end	Night	35% 3 6% 23% 23% 9%	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	18% 14% 34% 27% 7%	270
	11th to 20th	Day	17% 19% 37% 22% 3 1	270
	21st to end	Day	14% 14% 39% 24% 8% 1	297
February	1st to 10th	Day	18% 17% 42% 18% 5%	270
	11th to 20th	Day	17% 22% 39% 19% 3	270
	21st to end	Day	24% 22% 37% 14% 3	225
March	1st to 10th	Day	19% 19% 37% 20% 5%	270
	11th to 20th	Day	19% 20% 39% 14% 7% 1	270
	21st to end	Day	19% 22% 37% 16% 6%	297
April	1st to 10th	Day	16% 22% 30% 26% 7%	270
	11th to 20th	Day	16% 19% 41% 21% 3	422
	21st to end	Day	18% 15% 36% 23% 7% 2	650
May	1st to 10th	Day	13% 13% 38% 29% 6% 1	653
	11th to 20th	Day	16% 8% 33% 26% 15% 2	675
	21st to end	Day	15% 6% 31% 29% 15% 4	734
June	1st to 10th	Day	8% 4 18% 37% 26% 6%	680
	11th to 20th	Day	6% 2 25% 42% 22% 4	680
	21st to end	Day	4 2 19% 41% 26% 7%	680
July	1st to 10th	Day	7% 1 12% 32% 34% 14%	671
	11th to 20th	Day	3 2 10% 39% 37% 9%	668
	21st to end	Day	4 1 6% 34% 40% 15%	739
August	1st to 10th	Day	4 1 9% 39% 39% 7%	676
	11th to 20th	Day	8% 2 12% 36% 34% 9%	665
	21st to end	Day	4 1 7% 33% 38% 16%	554
September	1st to 10th	Day	8% 1 8% 31% 35% 17%	300
	11th to 20th	Day	7% 2 13% 35% 31% 13%	300
	21st to end	Day	14% 4 13% 36% 23% 10%	300
October	1st to 10th	Day	7% 6% 26% 33% 19% 9%	300
	11th to 20th	Day	9% 10% 30% 39% 9% 2	300
	21st to end	Day	22% 9% 33% 21% 12% 2	330
November	1st to 10th	Day	17% 7% 41% 22% 12% 2	300
	11th to 20th	Day	15% 10% 36% 25% 11% 2	300
	21st to end	Day	18% 13% 39% 21% 8% 2	300
December	1st to 10th	Day	11% 13% 39% 25% 10% 2	273
	11th to 20th	Day	17% 16% 34% 27% 7%	270
	21st to end	Day	19% 17% 37% 22% 5%	297
January	1st to 10th	Night	11% 13% 38% 30% 7% 1	950
	11th to 20th	Night	13% 14% 35% 32% 6%	950
	21st to end	Night	12% 12% 37% 33% 6%	1045
February	1st to 10th	Night	16% 14% 39% 27% 4	879
	11th to 20th	Night	16% 15% 39% 26% 4	744
	21st to end	Night	16% 16% 41% 24% 3	628
March	1st to 10th	Night	14% 15% 34% 33% 3	601
	11th to 20th	Night	18% 14% 36% 29% 4	570
	21st to end	Night	15% 15% 42% 22% 6%	627
April	1st to 10th	Night	13% 16% 44% 22% 5%	570
	11th to 20th	Night	13% 14% 43% 25% 5%	563
	21st to end	Night	15% 11% 40% 26% 7% 1	570
May	1st to 10th	Night	10% 11% 43% 29% 7%	570
	11th to 20th	Night	13% 7% 35% 30% 14% 1	561
	21st to end	Night	9% 5% 33% 36% 16% 2	617
June	1st to 10th	Night	6% 3 21% 45% 23% 3	570
	11th to 20th	Night	6% 3 28% 51% 13%	570
	21st to end	Night	2 2 23% 49% 20% 3	570
July	1st to 10th	Night	5% 1 12% 47% 31% 4	555
	11th to 20th	Night	2 1 12% 50% 34% 2	552
	21st to end	Night	3 1 8% 49% 37% 2	624
August	1st to 10th	Night	2 10% 54% 31% 2	567
	11th to 20th	Night	5% 1 14% 44% 33% 2	564
	21st to end	Night	3 8% 45% 40% 4	627
September	1st to 10th	Night	9% 2 12% 43% 31% 3	570
	11th to 20th	Night	13% 1 19% 34% 30% 3	570
	21st to end	Night	9% 2 20% 42% 22% 5%	570
October	1st to 10th	Night	8% 3 29% 37% 22% 2	589
	11th to 20th	Night	11% 7% 34% 35% 12% 1	760
	21st to end	Night	15% 10% 31% 31% 12% 1	836
November	1st to 10th	Night	10% 7% 37% 32% 13% 1	835
	11th to 20th	Night	10% 12% 33% 35% 10% 1	1000
	21st to end	Night	15% 11% 37% 27% 10%	1000
December	1st to 10th	Night	12% 12% 36% 33% 8%	960
	11th to 20th	Night	18% 10% 36% 30% 6%	950
	21st to end	Night	16% 12% 36% 30% 7%	1045

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