La Sarre
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the La Sarre clear sky chart from 2005-11-06 to 2025-10-19.

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% 13% 4 10% 6% 5% 5% 4 5% 6% 26%	127152
	Night	15% 14% 6% 12% 6% 5% 5% 4 5% 5% 23%	122696
Transparency	Day	57% 6% 11% 18% 8% 1	130601
	Night	62% 6% 10% 15% 7% 1	127336
Seeing	Day	22% 11% 29% 24% 11% 3	16478
	Night	23% 8% 29% 28% 10% 1	25328

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	10% 23% 9% 19% 8% 7% 5% 3 4 3 7%	3158
	11th to 20th	Day	7% 18% 7% 17% 11% 6% 5% 5% 8% 5% 9%	3133
	21st to end	Day	8% 19% 9% 14% 7% 8% 7% 4 5% 6% 14%	4054
February	1st to 10th	Day	7% 15% 6% 12% 9% 9% 9% 5% 7% 6% 16%	1800
	11th to 20th	Day	9% 18% 6% 13% 8% 6% 7% 5% 5% 7% 17%	1753
	21st to end	Day	10% 14% 6% 15% 6% 6% 5% 4 4 7% 22%	1485
March	1st to 10th	Day	17% 16% 5% 10% 7% 5% 5% 4 5% 5% 21%	4779
	11th to 20th	Day	17% 17% 5% 13% 6% 5% 4 3 3 4 24%	4980
	21st to end	Day	11% 16% 5% 13% 6% 7% 5% 3 4 4 25%	5500
April	1st to 10th	Day	17% 15% 6% 10% 5% 5% 4 4 5% 5% 24%	2400
	11th to 20th	Day	19% 12% 4 8% 5% 4 4 3 5% 5% 31%	2547
	21st to end	Day	19% 13% 4 9% 5% 4 4 3 4 5% 31%	2600
May	1st to 10th	Day	15% 10% 3 8% 4 4 4 4 5% 6% 37%	6334
	11th to 20th	Day	13% 8% 3 8% 5% 5% 5% 4 6% 7% 35%	6318
	21st to end	Day	18% 11% 3 7% 4 4 3 3 5% 6% 36%	7214
June	1st to 10th	Day	20% 8% 3 7% 5% 4 4 5% 6% 8% 29%	3000
	11th to 20th	Day	15% 8% 3 7% 5% 5% 4 4 6% 7% 35%	3000
	21st to end	Day	20% 8% 3 7% 5% 5% 5% 4 6% 8% 32%	3000
July	1st to 10th	Day	14% 8% 3 8% 5% 5% 6% 5% 7% 10% 28%	6819
	11th to 20th	Day	15% 7% 2 6% 5% 5% 5% 5% 7% 9% 34%	6820
	21st to end	Day	17% 7% 3 7% 5% 5% 5% 4 7% 9% 31%	7182
August	1st to 10th	Day	14% 7% 3 7% 6% 6% 6% 5% 6% 9% 32%	4378
	11th to 20th	Day	15% 8% 3 8% 5% 5% 5% 3 6% 7% 35%	4174
	21st to end	Day	13% 7% 3 8% 5% 4 5% 4 6% 8% 37%	4609
September	1st to 10th	Day	20% 8% 3 7% 4 4 6% 4 5% 7% 32%	2400
	11th to 20th	Day	20% 9% 3 8% 5% 4 5% 4 5% 7% 31%	2330
	21st to end	Day	20% 11% 5% 8% 5% 4 3 3 4 6% 32%	2132
October	1st to 10th	Day	23% 11% 2 7% 4 4 4 4 5% 5% 31%	2000
	11th to 20th	Day	28% 18% 4 8% 4 4 3 3 4 4 19%	1980
	21st to end	Day	27% 18% 5% 10% 5% 5% 5% 3 4 5% 14%	1933
November	1st to 10th	Day	22% 18% 7% 11% 6% 4 4 3 4 5% 16%	1566
	11th to 20th	Day	21% 20% 7% 16% 6% 4 4 4 3 3 12%	1600
	21st to end	Day	21% 27% 8% 12% 6% 5% 4 2 3 2 9%	1600
December	1st to 10th	Day	12% 24% 12% 19% 10% 4 4 2 4 3 7%	2477
	11th to 20th	Day	11% 24% 7% 12% 8% 7% 4 4 3 4 16%	2621
	21st to end	Day	18% 22% 8% 15% 7% 5% 4 3 4 5% 8%	3476
January	1st to 10th	Night	9% 20% 10% 21% 9% 6% 4 3 4 4 10%	6808
	11th to 20th	Night	9% 16% 8% 19% 9% 6% 6% 5% 7% 4 10%	6772
	21st to end	Night	7% 17% 10% 15% 7% 6% 7% 6% 5% 5% 16%	6905
February	1st to 10th	Night	8% 15% 5% 10% 10% 9% 7% 4 7% 8% 16%	2600
	11th to 20th	Night	9% 17% 7% 14% 7% 7% 6% 4 5% 6% 18%	2533
	21st to end	Night	8% 17% 6% 13% 8% 7% 6% 5% 5% 6% 20%	2145
March	1st to 10th	Night	16% 16% 6% 11% 6% 5% 5% 4 4 4 23%	5059
	11th to 20th	Night	16% 18% 6% 14% 8% 6% 4 3 4 4 17%	4979
	21st to end	Night	12% 13% 5% 11% 7% 8% 4 3 5% 6% 25%	5432
April	1st to 10th	Night	18% 15% 5% 11% 6% 3 4 2 4 5% 28%	2000
	11th to 20th	Night	18% 11% 3 9% 5% 5% 5% 4 5% 5% 30%	1819
	21st to end	Night	20% 11% 4 8% 4 4 3 3 4 6% 33%	1800
May	1st to 10th	Night	16% 9% 3 9% 5% 5% 5% 4 4 6% 35%	3605
	11th to 20th	Night	13% 9% 3 6% 4 4 4 4 6% 8% 40%	3575
	21st to end	Night	18% 9% 3 7% 4 4 4 4 6% 7% 33%	3670
June	1st to 10th	Night	20% 10% 3 8% 4 5% 4 4 5% 7% 33%	1400
	11th to 20th	Night	16% 8% 3 7% 5% 4 3 4 5% 7% 39%	1400
	21st to end	Night	18% 6% 2 7% 4 5% 5% 4 6% 7% 36%	1400
July	1st to 10th	Night	17% 9% 3 7% 5% 4 4 4 5% 7% 38%	3160
	11th to 20th	Night	18% 8% 3 7% 5% 4 4 4 5% 7% 36%	3160
	21st to end	Night	13% 6% 2 7% 4 5% 5% 4 6% 8% 40%	3681
August	1st to 10th	Night	8% 7% 3 8% 5% 6% 5% 4 7% 8% 40%	2768
	11th to 20th	Night	14% 7% 2 7% 4 5% 4 3 5% 8% 40%	2875
	21st to end	Night	15% 7% 3 8% 4 3 3 3 4 6% 43%	3255
September	1st to 10th	Night	19% 7% 3 8% 5% 4 5% 3 5% 6% 34%	2000
	11th to 20th	Night	19% 8% 3 6% 4 4 3 3 5% 7% 38%	2066
	21st to end	Night	21% 9% 2 7% 5% 3 4 3 4 5% 38%	2267
October	1st to 10th	Night	20% 10% 3 8% 5% 4 5% 4 5% 7% 31%	2400
	11th to 20th	Night	25% 18% 4 11% 5% 5% 3 3 4 5% 19%	2377
	21st to end	Night	21% 20% 5% 10% 4 5% 5% 3 5% 5% 18%	2662
November	1st to 10th	Night	20% 19% 6% 10% 5% 4 5% 3 4 5% 19%	2732
	11th to 20th	Night	20% 20% 6% 13% 7% 4 5% 4 4 4 15%	2800
	21st to end	Night	20% 22% 7% 13% 7% 4 4 3 4 3 12%	2800
December	1st to 10th	Night	12% 23% 9% 19% 10% 6% 5% 3 4 3 7%	4703
	11th to 20th	Night	15% 19% 8% 13% 9% 9% 7% 4 4 4 10%	5586
	21st to end	Night	21% 21% 8% 13% 6% 4 4 3 5% 4 13%	7502

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	82% 5% 6% 5% 1	3159
	11th to 20th	Day	73% 5% 6% 11% 6%	3160
	21st to end	Day	70% 4 6% 14% 5%	4054
February	1st to 10th	Day	66% 7% 8% 12% 7%	1800
	11th to 20th	Day	65% 6% 8% 14% 6%	1762
	21st to end	Day	62% 5% 9% 17% 6% 1	1485
March	1st to 10th	Day	65% 5% 6% 14% 10% 1	4782
	11th to 20th	Day	65% 4 8% 14% 8% 1	4980
	21st to end	Day	61% 5% 7% 18% 7% 1	5500
April	1st to 10th	Day	61% 5% 9% 15% 10% 1	2400
	11th to 20th	Day	54% 5% 10% 19% 11% 1	2547
	21st to end	Day	56% 5% 9% 14% 14% 2	2600
May	1st to 10th	Day	45% 7% 9% 18% 19% 2	6345
	11th to 20th	Day	45% 8% 15% 19% 9% 3	6322
	21st to end	Day	48% 6% 8% 20% 15% 3	7214
June	1st to 10th	Day	51% 6% 12% 20% 10% 1	3000
	11th to 20th	Day	46% 8% 10% 21% 13% 1	3000
	21st to end	Day	49% 7% 12% 21% 10% 1	3000
July	1st to 10th	Day	48% 7% 16% 23% 6%	6746
	11th to 20th	Day	44% 7% 19% 23% 7% 1	6739
	21st to end	Day	47% 8% 14% 25% 6%	6977
August	1st to 10th	Day	46% 9% 18% 23% 4	4364
	11th to 20th	Day	48% 6% 15% 23% 7% 1	4213
	21st to end	Day	44% 6% 15% 27% 9%	4609
September	1st to 10th	Day	50% 8% 15% 20% 7%	2400
	11th to 20th	Day	51% 9% 15% 20% 4	2330
	21st to end	Day	55% 6% 10% 21% 7%	2132
October	1st to 10th	Day	60% 5% 12% 18% 6%	3260
	11th to 20th	Day	63% 5% 11% 16% 5%	3220
	21st to end	Day	72% 6% 10% 6% 6%	3161
November	1st to 10th	Day	72% 6% 10% 7% 4	1566
	11th to 20th	Day	77% 6% 8% 8% 2	1600
	21st to end	Day	83% 5% 7% 4 1	1600
December	1st to 10th	Day	83% 3 5% 6% 1	2477
	11th to 20th	Day	72% 5% 7% 14% 2	2621
	21st to end	Day	79% 4 6% 8% 3	3476
January	1st to 10th	Night	80% 5% 7% 6% 2	6808
	11th to 20th	Night	72% 6% 7% 9% 6%	6820
	21st to end	Night	69% 4 5% 15% 6%	6905
February	1st to 10th	Night	64% 6% 10% 12% 8%	2600
	11th to 20th	Night	66% 5% 9% 14% 6%	2535
	21st to end	Night	65% 5% 8% 15% 7% 1	2145
March	1st to 10th	Night	64% 4 6% 11% 10% 4	5069
	11th to 20th	Night	70% 6% 7% 10% 6% 1	4980
	21st to end	Night	60% 5% 6% 16% 10% 2	5432
April	1st to 10th	Night	59% 4 7% 16% 13% 1	2000
	11th to 20th	Night	54% 6% 8% 17% 14% 1	1819
	21st to end	Night	53% 5% 8% 17% 16% 2	1800
May	1st to 10th	Night	48% 7% 10% 16% 18% 1	3611
	11th to 20th	Night	41% 7% 14% 21% 13% 3	3576
	21st to end	Night	47% 7% 11% 17% 14% 4	3671
June	1st to 10th	Night	50% 7% 9% 20% 12% 1	1400
	11th to 20th	Night	44% 6% 9% 22% 17% 2	1400
	21st to end	Night	46% 7% 11% 24% 11% 1	1400
July	1st to 10th	Night	46% 5% 11% 28% 10%	3125
	11th to 20th	Night	47% 6% 13% 24% 9% 1	3118
	21st to end	Night	41% 7% 16% 31% 5%	3572
August	1st to 10th	Night	40% 8% 16% 30% 6%	2758
	11th to 20th	Night	43% 6% 17% 28% 6%	2902
	21st to end	Night	44% 6% 14% 26% 9% 1	3255
September	1st to 10th	Night	49% 9% 14% 21% 7%	2000
	11th to 20th	Night	47% 7% 17% 24% 6%	2066
	21st to end	Night	49% 6% 14% 25% 7%	2267
October	1st to 10th	Night	54% 6% 12% 21% 7%	3920
	11th to 20th	Night	63% 5% 10% 19% 3	3876
	21st to end	Night	64% 6% 14% 11% 6%	4384
November	1st to 10th	Night	68% 7% 11% 11% 2	2732
	11th to 20th	Night	73% 6% 9% 9% 3	2800
	21st to end	Night	79% 6% 8% 6% 1	2800
December	1st to 10th	Night	83% 4 6% 6% 1	4703
	11th to 20th	Night	78% 4 8% 8% 2	5585
	21st to end	Night	76% 4 6% 10% 4	7502

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	24% 13% 38% 18% 7% 1	200
	11th to 20th	Day	16% 11% 34% 26% 10% 4	200
	21st to end	Day	18% 6% 30% 33% 11% 1	279
February	1st to 10th	Day	13% 16% 43% 21% 6% 2	300
	11th to 20th	Day	14% 13% 38% 28% 5% 2	300
	21st to end	Day	19% 16% 40% 21% 4	249
March	1st to 10th	Day	17% 10% 38% 25% 9%	470
	11th to 20th	Day	20% 12% 35% 23% 8% 2	500
	21st to end	Day	21% 12% 32% 24% 9% 1	550
April	1st to 10th	Day	21% 11% 32% 22% 10% 3	500
	11th to 20th	Day	23% 12% 29% 24% 10% 2	492
	21st to end	Day	26% 11% 26% 24% 11% 2	500
May	1st to 10th	Day	22% 7% 31% 24% 15% 2	503
	11th to 20th	Day	21% 10% 30% 24% 11% 4	527
	21st to end	Day	21% 10% 27% 28% 12% 1	682
June	1st to 10th	Day	23% 11% 28% 26% 11% 2	730
	11th to 20th	Day	20% 11% 32% 23% 12% 2	730
	21st to end	Day	21% 9% 25% 28% 15% 3	730
July	1st to 10th	Day	17% 10% 30% 28% 12% 4	721
	11th to 20th	Day	16% 11% 29% 27% 15% 2	718
	21st to end	Day	18% 6% 26% 33% 13% 4	689
August	1st to 10th	Day	19% 8% 25% 27% 15% 7%	526
	11th to 20th	Day	17% 6% 23% 28% 18% 8%	519
	21st to end	Day	22% 9% 23% 23% 16% 7%	583
September	1st to 10th	Day	23% 11% 26% 24% 10% 6%	530
	11th to 20th	Day	22% 8% 23% 29% 14% 4	530
	21st to end	Day	23% 12% 25% 24% 12% 4	530
October	1st to 10th	Day	28% 12% 25% 23% 9% 3	530
	11th to 20th	Day	33% 14% 31% 16% 5% 1	522
	21st to end	Day	32% 14% 31% 18% 5% 1	418
November	1st to 10th	Day	34% 18% 30% 17% 3	200
	11th to 20th	Day	27% 19% 30% 19% 6% 1	200
	21st to end	Day	38% 14% 32% 11% 3 2	200
December	1st to 10th	Day	22% 13% 33% 20% 11% 3	200
	11th to 20th	Day	17% 17% 38% 19% 10% 1	200
	21st to end	Day	30% 10% 34% 15% 9% 4	220
January	1st to 10th	Night	23% 8% 33% 27% 9% 1	1000
	11th to 20th	Night	24% 6% 31% 31% 8% 1	1000
	21st to end	Night	16% 7% 27% 33% 15% 2	961
February	1st to 10th	Night	14% 10% 33% 32% 10% 1	800
	11th to 20th	Night	18% 9% 33% 30% 9% 1	783
	21st to end	Night	18% 10% 36% 27% 8% 1	660
March	1st to 10th	Night	18% 9% 33% 31% 8% 1	800
	11th to 20th	Night	23% 11% 31% 29% 7% 1	800
	21st to end	Night	18% 9% 34% 30% 9% 1	880
April	1st to 10th	Night	25% 12% 29% 26% 8% 1	800
	11th to 20th	Night	22% 9% 28% 28% 10% 2	635
	21st to end	Night	24% 9% 29% 28% 9% 1	600
May	1st to 10th	Night	20% 6% 29% 34% 11%	411
	11th to 20th	Night	21% 8% 29% 32% 8% 1	394
	21st to end	Night	21% 6% 32% 33% 9%	433
June	1st to 10th	Night	22% 7% 30% 30% 11% 1	400
	11th to 20th	Night	18% 10% 31% 32% 9% 1	400
	21st to end	Night	19% 5% 26% 36% 14% 1	400
July	1st to 10th	Night	18% 6% 25% 37% 13% 1	390
	11th to 20th	Night	17% 4 23% 42% 14%	388
	21st to end	Night	16% 3 23% 38% 18% 1	438
August	1st to 10th	Night	15% 4 26% 32% 21% 2	502
	11th to 20th	Night	16% 5% 22% 35% 19% 3	594
	21st to end	Night	21% 6% 25% 30% 17% 1	679
September	1st to 10th	Night	22% 8% 25% 30% 14% 1	800
	11th to 20th	Night	24% 6% 25% 30% 13% 2	800
	21st to end	Night	25% 8% 23% 30% 12% 2	800
October	1st to 10th	Night	24% 9% 27% 30% 9% 1	800
	11th to 20th	Night	35% 10% 28% 19% 7% 1	793
	21st to end	Night	31% 12% 28% 22% 6% 1	836
November	1st to 10th	Night	30% 10% 33% 21% 5% 1	780
	11th to 20th	Night	29% 13% 29% 20% 8%	800
	21st to end	Night	33% 10% 33% 20% 4 1	800
December	1st to 10th	Night	27% 10% 29% 25% 8% 1	871
	11th to 20th	Night	25% 9% 31% 25% 9% 1	1000
	21st to end	Night	28% 10% 26% 24% 9% 3	1100

Page generated at 2025-10-16 01:50:27. Version ac07

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