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 2024-11-05.

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% 12% 4 10% 6% 5% 5% 4 5% 7% 27%	101847
	Night	16% 14% 5% 11% 6% 5% 5% 4 5% 6% 24%	97263
Transparency	Day	56% 7% 11% 18% 7% 1	105318
	Night	60% 6% 10% 16% 7% 1	101882
Seeing	Day	22% 10% 29% 25% 11% 3	15223
	Night	23% 8% 29% 29% 10% 1	24127

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	13% 23% 8% 12% 5% 7% 7% 5% 5% 4 8%	2208
	11th to 20th	Day	9% 14% 6% 17% 11% 7% 6% 6% 6% 6% 12%	2210
	21st to end	Day	11% 23% 10% 14% 7% 6% 4 3 5% 5% 12%	2834
February	1st to 10th	Day	7% 15% 6% 11% 9% 9% 9% 5% 7% 6% 16%	1710
	11th to 20th	Day	9% 18% 6% 12% 8% 6% 7% 5% 5% 7% 17%	1663
	21st to end	Day	10% 14% 6% 15% 5% 6% 6% 5% 5% 7% 22%	1413
March	1st to 10th	Day	18% 15% 4 9% 5% 4 5% 4 5% 6% 25%	3321
	11th to 20th	Day	11% 18% 6% 16% 6% 4 4 3 3 4 26%	3480
	21st to end	Day	10% 14% 4 13% 7% 7% 6% 4 4 5% 25%	3836
April	1st to 10th	Day	17% 16% 6% 9% 5% 5% 4 4 5% 5% 24%	2280
	11th to 20th	Day	18% 12% 4 9% 5% 4 4 3 5% 5% 31%	2418
	21st to end	Day	19% 13% 4 9% 5% 4 4 3 4 5% 32%	2470
May	1st to 10th	Day	16% 11% 3 8% 5% 4 5% 4 6% 7% 30%	4414
	11th to 20th	Day	15% 9% 3 8% 5% 6% 6% 4 6% 7% 32%	4398
	21st to end	Day	18% 9% 3 7% 5% 4 4 4 6% 7% 35%	5018
June	1st to 10th	Day	20% 8% 3 7% 6% 4 4 5% 6% 8% 28%	2850
	11th to 20th	Day	15% 8% 3 7% 5% 5% 4 4 6% 8% 35%	2850
	21st to end	Day	19% 7% 2 7% 5% 5% 5% 4 6% 8% 32%	2850
July	1st to 10th	Day	17% 8% 3 8% 5% 5% 5% 4 7% 9% 29%	4760
	11th to 20th	Day	13% 8% 3 7% 5% 5% 5% 5% 6% 8% 35%	4760
	21st to end	Day	15% 8% 3 7% 5% 4 5% 4 7% 8% 34%	4986
August	1st to 10th	Day	14% 7% 3 7% 6% 6% 6% 5% 6% 9% 31%	4244
	11th to 20th	Day	16% 8% 3 8% 4 5% 5% 3 6% 7% 35%	4044
	21st to end	Day	13% 7% 3 7% 5% 4 5% 4 6% 9% 38%	4468
September	1st to 10th	Day	20% 8% 3 6% 4 4 5% 4 5% 7% 33%	2280
	11th to 20th	Day	21% 9% 3 7% 5% 4 5% 4 5% 7% 30%	2214
	21st to end	Day	21% 11% 5% 8% 5% 4 3 2 3 6% 31%	2026
October	1st to 10th	Day	23% 12% 2 8% 4 4 4 3 5% 5% 30%	1900
	11th to 20th	Day	29% 18% 5% 8% 4 3 3 3 4 4 18%	1900
	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%	1518
	11th to 20th	Day	21% 19% 7% 15% 6% 5% 4 4 4 4 12%	1520
	21st to end	Day	21% 26% 8% 12% 6% 5% 5% 2 3 3 9%	1520
December	1st to 10th	Day	16% 23% 7% 15% 8% 4 4 2 5% 5% 11%	1449
	11th to 20th	Day	14% 21% 6% 11% 7% 6% 6% 5% 4 6% 15%	1671
	21st to end	Day	16% 22% 9% 20% 8% 4 4 2 3 3 9%	2431
January	1st to 10th	Night	12% 18% 8% 16% 9% 7% 5% 4 5% 5% 12%	4748
	11th to 20th	Night	10% 16% 6% 16% 9% 7% 7% 5% 6% 5% 13%	4760
	21st to end	Night	9% 20% 10% 14% 7% 6% 5% 4 5% 5% 13%	4821
February	1st to 10th	Night	8% 15% 6% 11% 10% 8% 7% 4 6% 7% 16%	2470
	11th to 20th	Night	10% 17% 7% 13% 7% 7% 5% 4 5% 6% 19%	2403
	21st to end	Night	8% 17% 6% 13% 8% 7% 6% 5% 5% 6% 20%	2041
March	1st to 10th	Night	16% 13% 4 9% 6% 6% 5% 3 5% 5% 27%	3517
	11th to 20th	Night	12% 18% 6% 14% 9% 6% 4 3 4 5% 19%	3479
	21st to end	Night	12% 12% 6% 11% 6% 6% 4 3 5% 6% 28%	3796
April	1st to 10th	Night	18% 15% 5% 11% 6% 3 4 2 4 5% 28%	1900
	11th to 20th	Night	18% 11% 3 9% 5% 5% 5% 4 5% 5% 30%	1727
	21st to end	Night	20% 11% 4 8% 4 4 3 3 4 6% 33%	1710
May	1st to 10th	Night	18% 10% 3 8% 5% 6% 5% 4 4 5% 33%	2525
	11th to 20th	Night	15% 10% 2 6% 3 4 5% 4 6% 9% 36%	2495
	21st to end	Night	18% 7% 3 7% 5% 5% 5% 5% 8% 8% 30%	2560
June	1st to 10th	Night	21% 10% 3 8% 4 4 4 4 5% 6% 33%	1330
	11th to 20th	Night	16% 7% 3 7% 5% 3 3 4 5% 7% 39%	1330
	21st to end	Night	18% 6% 2 6% 5% 5% 5% 3 6% 7% 37%	1330
July	1st to 10th	Night	16% 8% 3 5% 5% 4 4 4 5% 7% 38%	2210
	11th to 20th	Night	16% 9% 3 7% 5% 4 4 4 6% 7% 33%	2210
	21st to end	Night	14% 7% 3 8% 4 5% 5% 4 6% 7% 37%	2572
August	1st to 10th	Night	8% 7% 3 8% 5% 6% 5% 4 7% 8% 39%	2683
	11th to 20th	Night	14% 7% 2 7% 4 4 4 3 5% 8% 40%	2785
	21st to end	Night	15% 7% 3 8% 4 3 3 3 4 6% 43%	3155
September	1st to 10th	Night	19% 6% 3 8% 5% 4 5% 3 6% 6% 35%	1900
	11th to 20th	Night	20% 8% 3 6% 4 4 3 3 5% 7% 37%	1962
	21st to end	Night	21% 9% 2 7% 5% 3 4 3 4 6% 37%	2153
October	1st to 10th	Night	20% 10% 3 8% 5% 4 5% 4 5% 7% 29%	2280
	11th to 20th	Night	25% 18% 4 11% 4 5% 3 3 4 5% 18%	2280
	21st to end	Night	21% 20% 5% 10% 4 5% 5% 3 5% 5% 18%	2662
November	1st to 10th	Night	20% 18% 6% 10% 5% 4 5% 3 4 5% 19%	2660
	11th to 20th	Night	20% 20% 6% 12% 7% 4 5% 4 4 4 15%	2660
	21st to end	Night	21% 21% 7% 13% 7% 5% 4 3 4 4 13%	2660
December	1st to 10th	Night	14% 22% 6% 15% 9% 6% 5% 4 4 4 10%	2727
	11th to 20th	Night	17% 19% 7% 13% 9% 6% 5% 4 4 5% 11%	3526
	21st to end	Night	19% 21% 9% 17% 8% 5% 3 3 4 4 9%	5236

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	77% 7% 8% 7% 1	2209
	11th to 20th	Day	70% 7% 7% 12% 4	2210
	21st to end	Day	74% 5% 6% 11% 4	2834
February	1st to 10th	Day	65% 7% 8% 12% 7%	1710
	11th to 20th	Day	64% 7% 9% 14% 6%	1672
	21st to end	Day	62% 5% 9% 17% 6% 1	1413
March	1st to 10th	Day	60% 6% 8% 18% 7%	3324
	11th to 20th	Day	63% 4 8% 16% 8% 1	3480
	21st to end	Day	58% 6% 8% 17% 9% 2	3836
April	1st to 10th	Day	61% 5% 9% 15% 9% 1	2280
	11th to 20th	Day	54% 5% 11% 18% 11% 1	2418
	21st to end	Day	55% 6% 9% 14% 14% 2	2470
May	1st to 10th	Day	47% 9% 13% 21% 9% 1	4428
	11th to 20th	Day	46% 10% 13% 21% 9% 1	4402
	21st to end	Day	47% 8% 10% 20% 14% 1	5018
June	1st to 10th	Day	51% 6% 12% 20% 10% 1	2850
	11th to 20th	Day	46% 8% 10% 22% 13% 1	2850
	21st to end	Day	49% 7% 12% 21% 10%	2850
July	1st to 10th	Day	49% 7% 15% 23% 5%	4686
	11th to 20th	Day	44% 7% 18% 21% 9% 1	4679
	21st to end	Day	45% 8% 13% 27% 6%	4828
August	1st to 10th	Day	46% 9% 17% 23% 4	4230
	11th to 20th	Day	48% 6% 15% 23% 7% 1	4083
	21st to end	Day	43% 6% 15% 27% 9%	4468
September	1st to 10th	Day	49% 8% 16% 20% 8%	2280
	11th to 20th	Day	52% 9% 16% 19% 4	2214
	21st to end	Day	57% 6% 10% 20% 7%	2026
October	1st to 10th	Day	61% 5% 12% 17% 5%	3160
	11th to 20th	Day	64% 5% 11% 16% 5%	3140
	21st to end	Day	72% 6% 10% 6% 6%	3161
November	1st to 10th	Day	72% 6% 10% 7% 4	1518
	11th to 20th	Day	77% 6% 8% 8% 2	1520
	21st to end	Day	82% 5% 7% 5% 1	1520
December	1st to 10th	Day	76% 5% 7% 9% 2	1449
	11th to 20th	Day	69% 7% 6% 14% 3	1671
	21st to end	Day	82% 4 6% 6% 1	2431
January	1st to 10th	Night	75% 7% 10% 7% 1	4748
	11th to 20th	Night	70% 7% 8% 12% 3	4760
	21st to end	Night	73% 5% 6% 11% 5%	4821
February	1st to 10th	Night	64% 6% 10% 11% 8%	2470
	11th to 20th	Night	65% 6% 9% 14% 6%	2405
	21st to end	Night	65% 5% 8% 15% 7% 1	2041
March	1st to 10th	Night	59% 6% 9% 14% 11% 2	3527
	11th to 20th	Night	67% 6% 8% 12% 5% 1	3480
	21st to end	Night	56% 7% 8% 14% 13% 2	3796
April	1st to 10th	Night	59% 4 7% 16% 13% 1	1900
	11th to 20th	Night	54% 7% 8% 17% 13% 1	1727
	21st to end	Night	52% 5% 8% 17% 16% 3	1710
May	1st to 10th	Night	49% 8% 13% 16% 12% 2	2531
	11th to 20th	Night	42% 9% 13% 23% 12% 1	2496
	21st to end	Night	46% 10% 13% 17% 12% 3	2561
June	1st to 10th	Night	51% 8% 9% 20% 12% 1	1330
	11th to 20th	Night	43% 6% 9% 22% 17% 2	1330
	21st to end	Night	45% 7% 11% 25% 10% 1	1330
July	1st to 10th	Night	44% 7% 12% 28% 9%	2175
	11th to 20th	Night	48% 7% 15% 20% 10% 1	2168
	21st to end	Night	46% 7% 12% 29% 6%	2490
August	1st to 10th	Night	41% 8% 15% 30% 6%	2673
	11th to 20th	Night	43% 6% 18% 27% 6%	2812
	21st to end	Night	44% 6% 14% 26% 10% 1	3155
September	1st to 10th	Night	48% 9% 14% 21% 8%	1900
	11th to 20th	Night	48% 7% 17% 22% 6%	1962
	21st to end	Night	49% 6% 14% 23% 7%	2153
October	1st to 10th	Night	55% 6% 12% 20% 7%	3800
	11th to 20th	Night	63% 5% 10% 19% 3	3779
	21st to end	Night	64% 6% 14% 11% 6%	4384
November	1st to 10th	Night	68% 7% 11% 11% 2	2660
	11th to 20th	Night	73% 7% 9% 8% 3	2660
	21st to end	Night	77% 7% 8% 7% 1	2660
December	1st to 10th	Night	79% 5% 7% 7% 2	2727
	11th to 20th	Night	75% 5% 7% 10% 3	3525
	21st to end	Night	80% 5% 6% 6% 3	5236

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% 36% 19% 7% 1	180
	11th to 20th	Day	16% 11% 34% 26% 10% 3	180
	21st to end	Day	18% 5% 29% 35% 12% 1	251
February	1st to 10th	Day	13% 16% 40% 23% 6% 1	270
	11th to 20th	Day	14% 11% 39% 29% 5% 2	270
	21st to end	Day	20% 16% 40% 20% 4	225
March	1st to 10th	Day	17% 11% 36% 26% 10%	431
	11th to 20th	Day	19% 12% 35% 25% 8% 2	460
	21st to end	Day	21% 12% 32% 25% 9% 1	506
April	1st to 10th	Day	21% 10% 32% 23% 10% 3	460
	11th to 20th	Day	22% 12% 29% 25% 10% 2	452
	21st to end	Day	24% 12% 26% 25% 11% 2	460
May	1st to 10th	Day	22% 7% 31% 24% 15% 2	463
	11th to 20th	Day	22% 10% 30% 23% 12% 4	487
	21st to end	Day	21% 10% 28% 28% 12% 1	632
June	1st to 10th	Day	23% 9% 27% 28% 11% 2	680
	11th to 20th	Day	19% 11% 32% 23% 12% 3	680
	21st to end	Day	19% 8% 24% 29% 16% 3	680
July	1st to 10th	Day	17% 9% 30% 29% 12% 3	671
	11th to 20th	Day	16% 10% 28% 28% 16% 2	668
	21st to end	Day	18% 5% 25% 32% 14% 5%	639
August	1st to 10th	Day	21% 8% 23% 27% 15% 6%	486
	11th to 20th	Day	18% 5% 21% 29% 18% 9%	479
	21st to end	Day	22% 9% 22% 23% 16% 7%	539
September	1st to 10th	Day	22% 11% 27% 24% 10% 6%	490
	11th to 20th	Day	23% 9% 23% 29% 13% 3	490
	21st to end	Day	24% 11% 26% 24% 11% 4	490
October	1st to 10th	Day	29% 12% 24% 23% 9% 3	490
	11th to 20th	Day	34% 15% 30% 15% 5% 1	490
	21st to end	Day	32% 14% 31% 18% 5% 1	418
November	1st to 10th	Day	33% 19% 29% 16% 3	188
	11th to 20th	Day	26% 19% 29% 19% 6% 1	180
	21st to end	Day	38% 13% 34% 10% 3 2	180
December	1st to 10th	Day	24% 13% 28% 21% 11% 3	180
	11th to 20th	Day	17% 17% 38% 18% 9% 1	180
	21st to end	Day	28% 10% 34% 16% 8% 4	198
January	1st to 10th	Night	23% 7% 32% 27% 9% 1	950
	11th to 20th	Night	24% 6% 31% 30% 7% 1	950
	21st to end	Night	16% 7% 26% 33% 16% 2	913
February	1st to 10th	Night	15% 9% 32% 33% 10% 1	760
	11th to 20th	Night	19% 9% 31% 31% 10% 1	743
	21st to end	Night	18% 10% 37% 26% 8% 1	628
March	1st to 10th	Night	17% 9% 33% 31% 9% 1	760
	11th to 20th	Night	22% 11% 30% 30% 7% 1	760
	21st to end	Night	18% 8% 33% 31% 9% 1	836
April	1st to 10th	Night	25% 11% 29% 27% 7% 1	760
	11th to 20th	Night	22% 9% 28% 29% 10% 1	603
	21st to end	Night	24% 9% 28% 29% 9% 1	570
May	1st to 10th	Night	20% 6% 29% 34% 11% 1	391
	11th to 20th	Night	22% 8% 29% 32% 8% 1	374
	21st to end	Night	20% 6% 33% 33% 8%	411
June	1st to 10th	Night	23% 7% 29% 31% 10% 1	380
	11th to 20th	Night	17% 9% 31% 32% 10% 1	380
	21st to end	Night	19% 5% 25% 36% 14% 1	380
July	1st to 10th	Night	18% 6% 25% 38% 13% 1	370
	11th to 20th	Night	17% 4 22% 43% 15%	368
	21st to end	Night	16% 3 22% 38% 19% 1	416
August	1st to 10th	Night	16% 4 26% 32% 20% 2	477
	11th to 20th	Night	16% 4 22% 35% 20% 3	564
	21st to end	Night	21% 6% 25% 30% 17% 2	645
September	1st to 10th	Night	22% 6% 25% 31% 14% 1	760
	11th to 20th	Night	25% 6% 25% 29% 12% 2	760
	21st to end	Night	26% 7% 23% 30% 12% 2	760
October	1st to 10th	Night	24% 9% 26% 30% 9% 1	760
	11th to 20th	Night	35% 10% 28% 19% 7% 1	760
	21st to end	Night	31% 12% 28% 22% 6% 1	836
November	1st to 10th	Night	30% 9% 33% 21% 6% 1	760
	11th to 20th	Night	29% 13% 30% 20% 8%	760
	21st to end	Night	32% 10% 34% 20% 4 1	760
December	1st to 10th	Night	27% 10% 29% 25% 8% 1	827
	11th to 20th	Night	25% 9% 30% 25% 9% 1	950
	21st to end	Night	28% 10% 26% 24% 9% 3	1045

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