La Prairie
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the La Prairie clear sky chart from 2005-11-06 to 2026-05-17.

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% 10% 3 8% 5% 5% 5% 4 5% 7% 31%	131932
	Night	17% 12% 4 9% 6% 5% 4 4 5% 6% 29%	130867
Transparency	Day	52% 4 12% 21% 10% 1	135389
	Night	56% 4 10% 19% 10% 1	135496
Seeing	Day	22% 12% 29% 23% 11% 3	16455
	Night	24% 9% 30% 27% 9% 1	25508

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	15% 18% 6% 14% 6% 5% 4 3 4 4 21%	4661
	11th to 20th	Day	12% 15% 6% 13% 7% 6% 4 3 5% 6% 21%	4650
	21st to end	Day	11% 13% 4 11% 8% 8% 6% 4 5% 6% 23%	5124
February	1st to 10th	Day	15% 15% 4 10% 7% 5% 5% 3 4 6% 25%	1833
	11th to 20th	Day	14% 11% 4 11% 7% 5% 5% 5% 5% 6% 26%	1966
	21st to end	Day	16% 17% 4 8% 6% 5% 4 4 4 6% 26%	1730
March	1st to 10th	Day	17% 13% 4 11% 7% 5% 5% 4 5% 5% 26%	4576
	11th to 20th	Day	13% 13% 4 10% 6% 5% 4 4 5% 6% 31%	4791
	21st to end	Day	18% 10% 4 9% 5% 5% 4 3 4 5% 33%	6102
April	1st to 10th	Day	22% 11% 3 7% 5% 4 4 3 4 6% 30%	2520
	11th to 20th	Day	21% 9% 3 6% 5% 4 3 3 5% 5% 36%	2494
	21st to end	Day	20% 10% 3 8% 5% 4 4 4 5% 6% 32%	2698
May	1st to 10th	Day	24% 11% 3 9% 5% 4 5% 3 5% 6% 22%	6345
	11th to 20th	Day	20% 8% 3 7% 5% 5% 4 4 5% 8% 31%	6402
	21st to end	Day	20% 8% 3 7% 4 4 5% 4 5% 8% 32%	6949
June	1st to 10th	Day	20% 8% 3 6% 5% 5% 5% 4 6% 7% 31%	2800
	11th to 20th	Day	14% 6% 3 6% 5% 4 4 3 6% 9% 39%	2800
	21st to end	Day	20% 7% 3 7% 5% 5% 5% 4 5% 7% 33%	2800
July	1st to 10th	Day	12% 7% 3 8% 6% 6% 6% 4 7% 9% 33%	6360
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 4 7% 9% 41%	6360
	21st to end	Day	11% 6% 2 5% 4 4 4 4 6% 9% 45%	6926
August	1st to 10th	Day	13% 6% 3 8% 4 5% 5% 5% 7% 9% 34%	4563
	11th to 20th	Day	13% 7% 2 7% 5% 4 5% 4 6% 9% 39%	4107
	21st to end	Day	15% 5% 2 7% 4 4 4 4 6% 9% 40%	4312
September	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 4 6% 8% 44%	2400
	11th to 20th	Day	13% 5% 2 5% 3 3 4 4 5% 7% 50%	2305
	21st to end	Day	15% 6% 3 6% 4 4 5% 4 6% 8% 41%	2200
October	1st to 10th	Day	18% 7% 3 7% 5% 5% 4 4 6% 6% 35%	2080
	11th to 20th	Day	17% 8% 3 8% 6% 5% 5% 3 6% 6% 31%	1946
	21st to end	Day	26% 9% 3 7% 4 4 4 3 4 6% 30%	1980
November	1st to 10th	Day	18% 12% 3 8% 5% 5% 4 4 5% 6% 31%	1851
	11th to 20th	Day	17% 11% 4 8% 6% 4 6% 4 5% 7% 28%	1827
	21st to end	Day	22% 13% 4 8% 6% 4 4 4 5% 6% 22%	1680
December	1st to 10th	Day	19% 20% 7% 11% 6% 4 4 3 4 5% 17%	2680
	11th to 20th	Day	19% 13% 4 10% 5% 4 5% 5% 6% 5% 24%	3066
	21st to end	Day	22% 13% 4 11% 6% 6% 6% 4 6% 5% 18%	4048
January	1st to 10th	Night	13% 19% 8% 14% 6% 4 4 3 4 4 21%	8234
	11th to 20th	Night	12% 16% 6% 16% 8% 6% 5% 4 5% 6% 16%	8235
	21st to end	Night	11% 14% 4 11% 9% 7% 6% 3 4 5% 25%	9057
February	1st to 10th	Night	14% 16% 6% 12% 7% 5% 4 3 5% 5% 22%	2782
	11th to 20th	Night	14% 11% 5% 9% 6% 5% 5% 4 5% 6% 27%	2538
	21st to end	Night	16% 14% 4 9% 5% 5% 4 3 4 4 32%	2076
March	1st to 10th	Night	21% 13% 3 8% 6% 4 4 3 4 5% 31%	5484
	11th to 20th	Night	15% 15% 3 8% 5% 5% 5% 4 6% 7% 30%	5383
	21st to end	Night	14% 13% 4 9% 6% 5% 5% 4 5% 4 31%	5072
April	1st to 10th	Night	24% 10% 3 7% 5% 4 4 3 5% 6% 30%	2100
	11th to 20th	Night	23% 9% 3 8% 4 3 4 3 5% 5% 33%	2075
	21st to end	Night	21% 9% 3 6% 4 5% 4 3 4 5% 35%	1921
May	1st to 10th	Night	25% 10% 3 9% 5% 4 4 4 5% 6% 25%	3846
	11th to 20th	Night	23% 9% 4 8% 5% 3 4 3 5% 6% 30%	3623
	21st to end	Night	18% 9% 4 8% 5% 5% 5% 3 5% 7% 32%	3926
June	1st to 10th	Night	22% 8% 3 8% 4 3 5% 4 6% 6% 32%	1600
	11th to 20th	Night	16% 6% 2 7% 4 4 4 5% 6% 7% 38%	1600
	21st to end	Night	18% 7% 3 7% 6% 4 5% 4 6% 7% 34%	1600
July	1st to 10th	Night	13% 7% 3 8% 5% 5% 5% 5% 7% 9% 34%	3600
	11th to 20th	Night	14% 6% 2 6% 5% 4 5% 4 6% 7% 40%	3600
	21st to end	Night	9% 6% 2 7% 5% 5% 5% 4 7% 9% 42%	3926
August	1st to 10th	Night	15% 8% 3 8% 4 5% 4 3 6% 7% 37%	2586
	11th to 20th	Night	15% 7% 3 8% 5% 5% 5% 3 5% 7% 38%	2879
	21st to end	Night	15% 6% 2 7% 4 5% 5% 4 5% 8% 39%	3586
September	1st to 10th	Night	12% 5% 3 8% 5% 4 5% 3 6% 7% 44%	2000
	11th to 20th	Night	14% 5% 2 5% 4 4 3 3 4 6% 50%	2095
	21st to end	Night	16% 7% 3 6% 4 4 4 3 5% 6% 42%	2200
October	1st to 10th	Night	17% 7% 3 7% 4 4 4 4 5% 6% 40%	2315
	11th to 20th	Night	21% 7% 3 7% 5% 5% 5% 3 5% 5% 34%	2452
	21st to end	Night	22% 9% 3 8% 4 4 5% 4 4 6% 30%	2860
November	1st to 10th	Night	20% 10% 4 7% 5% 5% 4 3 5% 6% 31%	2667
	11th to 20th	Night	19% 10% 3 9% 5% 4 4 3 5% 6% 32%	2791
	21st to end	Night	22% 14% 3 8% 5% 5% 4 4 5% 5% 24%	2940
December	1st to 10th	Night	18% 19% 7% 13% 6% 5% 4 3 4 5% 16%	4720
	11th to 20th	Night	22% 14% 4 9% 5% 4 4 3 5% 5% 24%	5348
	21st to end	Night	24% 16% 5% 9% 4 4 4 4 6% 6% 20%	7150

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	68% 4 9% 16% 3	4662
	11th to 20th	Day	66% 3 7% 13% 10% 1	4680
	21st to end	Day	62% 4 8% 13% 11% 1	5124
February	1st to 10th	Day	62% 3 9% 19% 6% 2	1833
	11th to 20th	Day	58% 5% 10% 19% 7% 1	1975
	21st to end	Day	60% 4 10% 16% 9% 1	1730
March	1st to 10th	Day	60% 5% 7% 15% 10% 3	4579
	11th to 20th	Day	53% 5% 16% 15% 10% 2	4791
	21st to end	Day	53% 5% 6% 18% 17% 1	6102
April	1st to 10th	Day	55% 5% 7% 19% 12% 2	2520
	11th to 20th	Day	50% 4 8% 22% 15% 1	2494
	21st to end	Day	52% 4 10% 19% 12% 3	2698
May	1st to 10th	Day	62% 5% 7% 18% 7% 1	6356
	11th to 20th	Day	52% 5% 14% 19% 9% 1	6406
	21st to end	Day	51% 5% 11% 20% 12% 1	6949
June	1st to 10th	Day	51% 5% 10% 20% 12% 2	2800
	11th to 20th	Day	42% 6% 10% 25% 14% 2	2800
	21st to end	Day	52% 4 11% 22% 10% 1	2800
July	1st to 10th	Day	48% 3 13% 26% 9%	6290
	11th to 20th	Day	39% 4 13% 31% 12%	6285
	21st to end	Day	37% 4 13% 38% 9%	6728
August	1st to 10th	Day	46% 4 17% 24% 9%	4549
	11th to 20th	Day	42% 4 18% 28% 7%	4148
	21st to end	Day	41% 3 18% 23% 14%	4312
September	1st to 10th	Day	37% 5% 14% 31% 12%	2400
	11th to 20th	Day	35% 4 12% 34% 14% 1	2305
	21st to end	Day	42% 5% 14% 27% 12% 1	2200
October	1st to 10th	Day	46% 3 13% 29% 9%	3392
	11th to 20th	Day	45% 4 17% 26% 7%	3149
	21st to end	Day	48% 2 17% 24% 8% 1	3180
November	1st to 10th	Day	53% 4 12% 21% 9% 1	1851
	11th to 20th	Day	56% 5% 10% 17% 12%	1827
	21st to end	Day	63% 6% 12% 14% 5%	1680
December	1st to 10th	Day	72% 3 8% 14% 2	2680
	11th to 20th	Day	62% 4 10% 16% 9%	3066
	21st to end	Day	68% 5% 9% 12% 6%	4048
January	1st to 10th	Night	68% 4 10% 13% 5%	8234
	11th to 20th	Night	70% 4 8% 12% 6%	8280
	21st to end	Night	63% 2 7% 14% 12%	9057
February	1st to 10th	Night	64% 4 9% 15% 7% 1	2782
	11th to 20th	Night	58% 4 11% 19% 9% 1	2540
	21st to end	Night	57% 3 8% 19% 12% 1	2076
March	1st to 10th	Night	58% 3 6% 16% 12% 4	5494
	11th to 20th	Night	55% 4 12% 16% 12% 1	5384
	21st to end	Night	56% 3 5% 22% 12% 2	5072
April	1st to 10th	Night	56% 3 7% 18% 14% 2	2100
	11th to 20th	Night	54% 4 8% 20% 13% 2	2075
	21st to end	Night	52% 3 8% 18% 15% 4	1921
May	1st to 10th	Night	61% 5% 8% 17% 7% 2	3852
	11th to 20th	Night	55% 4 9% 20% 10% 2	3624
	21st to end	Night	53% 4 9% 19% 14% 1	3927
June	1st to 10th	Night	51% 6% 9% 20% 13% 1	1600
	11th to 20th	Night	43% 6% 12% 22% 14% 3	1600
	21st to end	Night	49% 7% 10% 21% 13% 1	1600
July	1st to 10th	Night	47% 3 18% 22% 10%	3560
	11th to 20th	Night	41% 3 15% 28% 13%	3552
	21st to end	Night	41% 3 15% 28% 13%	3809
August	1st to 10th	Night	48% 4 13% 27% 9%	2576
	11th to 20th	Night	46% 4 18% 22% 9%	2903
	21st to end	Night	44% 3 13% 24% 15% 1	3586
September	1st to 10th	Night	40% 4 12% 28% 15% 1	2000
	11th to 20th	Night	37% 4 13% 32% 14% 1	2095
	21st to end	Night	43% 4 11% 25% 16% 1	2200
October	1st to 10th	Night	46% 2 13% 28% 10% 1	3783
	11th to 20th	Night	46% 3 11% 30% 10%	3988
	21st to end	Night	50% 3 14% 19% 13% 1	4610
November	1st to 10th	Night	54% 4 11% 22% 9% 1	2667
	11th to 20th	Night	54% 4 11% 19% 10% 1	2791
	21st to end	Night	63% 4 11% 17% 6%	2940
December	1st to 10th	Night	73% 2 11% 11% 3	4720
	11th to 20th	Night	63% 3 9% 14% 11%	5348
	21st to end	Night	66% 3 8% 14% 9%	7150

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	30% 14% 29% 18% 8% 1	220
	11th to 20th	Day	25% 17% 36% 17% 4 1	220
	21st to end	Day	22% 16% 32% 21% 7% 1	242
February	1st to 10th	Day	28% 19% 37% 14% 3	301
	11th to 20th	Day	22% 19% 36% 20% 2	454
	21st to end	Day	27% 15% 31% 24% 3	446
March	1st to 10th	Day	26% 13% 37% 18% 6%	540
	11th to 20th	Day	25% 16% 33% 19% 6% 1	540
	21st to end	Day	29% 15% 30% 17% 7% 2	594
April	1st to 10th	Day	33% 13% 29% 16% 7% 1	540
	11th to 20th	Day	31% 17% 26% 14% 9% 2	532
	21st to end	Day	27% 12% 32% 18% 9% 2	540
May	1st to 10th	Day	27% 11% 30% 21% 9% 2	543
	11th to 20th	Day	20% 10% 31% 25% 11% 3	551
	21st to end	Day	21% 11% 31% 24% 10% 2	573
June	1st to 10th	Day	24% 10% 28% 27% 9% 2	530
	11th to 20th	Day	15% 12% 28% 29% 14% 2	530
	21st to end	Day	21% 10% 31% 23% 12% 2	530
July	1st to 10th	Day	13% 8% 28% 29% 18% 4	525
	11th to 20th	Day	14% 7% 31% 31% 14% 4	524
	21st to end	Day	14% 7% 28% 30% 18% 3	576
August	1st to 10th	Day	14% 4 24% 33% 19% 5%	526
	11th to 20th	Day	13% 4 24% 33% 18% 9%	519
	21st to end	Day	15% 8% 24% 27% 16% 9%	583
September	1st to 10th	Day	13% 7% 28% 27% 17% 8%	530
	11th to 20th	Day	15% 7% 19% 25% 22% 12%	530
	21st to end	Day	17% 8% 28% 23% 17% 6%	530
October	1st to 10th	Day	19% 10% 31% 21% 14% 5%	530
	11th to 20th	Day	21% 15% 32% 20% 11% 1	500
	21st to end	Day	35% 11% 24% 23% 6%	462
November	1st to 10th	Day	31% 13% 26% 22% 7%	425
	11th to 20th	Day	24% 19% 32% 17% 7% 2	367
	21st to end	Day	32% 14% 32% 16% 5%	220
December	1st to 10th	Day	35% 10% 26% 21% 7% 1	220
	11th to 20th	Day	27% 20% 37% 11% 4	220
	21st to end	Day	28% 17% 30% 18% 4 2	242
January	1st to 10th	Night	28% 11% 35% 22% 5%	840
	11th to 20th	Night	27% 13% 34% 20% 6%	840
	21st to end	Night	20% 12% 36% 25% 7% 1	924
February	1st to 10th	Night	23% 11% 34% 27% 5% 1	840
	11th to 20th	Night	22% 12% 37% 24% 4	823
	21st to end	Night	26% 11% 34% 26% 4	692
March	1st to 10th	Night	27% 11% 33% 24% 5%	840
	11th to 20th	Night	29% 11% 32% 22% 6%	840
	21st to end	Night	26% 10% 32% 25% 7% 1	924
April	1st to 10th	Night	29% 12% 30% 25% 4	840
	11th to 20th	Night	29% 12% 29% 23% 6%	831
	21st to end	Night	26% 11% 30% 24% 9%	661
May	1st to 10th	Night	27% 7% 32% 24% 8% 1	501
	11th to 20th	Night	23% 8% 31% 29% 8% 1	406
	21st to end	Night	19% 9% 32% 30% 11%	433
June	1st to 10th	Night	27% 4 29% 31% 9% 1	400
	11th to 20th	Night	21% 5% 28% 34% 13%	400
	21st to end	Night	20% 5% 27% 34% 13% 1	400
July	1st to 10th	Night	15% 5% 26% 37% 16%	390
	11th to 20th	Night	11% 3 26% 44% 15% 2	388
	21st to end	Night	13% 4 22% 47% 14% 1	438
August	1st to 10th	Night	14% 4 15% 49% 17% 2	398
	11th to 20th	Night	13% 4 22% 35% 24% 2	595
	21st to end	Night	17% 3 21% 36% 20% 2	880
September	1st to 10th	Night	15% 3 25% 38% 17% 1	800
	11th to 20th	Night	17% 5% 18% 35% 22% 4	800
	21st to end	Night	20% 6% 28% 29% 16% 2	800
October	1st to 10th	Night	20% 8% 28% 28% 14% 1	800
	11th to 20th	Night	26% 8% 29% 28% 10%	800
	21st to end	Night	28% 11% 30% 26% 5%	880
November	1st to 10th	Night	27% 13% 30% 21% 8%	820
	11th to 20th	Night	26% 13% 30% 22% 9%	840
	21st to end	Night	30% 14% 29% 19% 8% 1	840
December	1st to 10th	Night	32% 11% 31% 21% 5%	840
	11th to 20th	Night	32% 13% 32% 17% 5% 1	840
	21st to end	Night	34% 13% 30% 19% 4 1	924

Page generated at 2026-05-14 01:58:57. Version ac07

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