Lake Louise
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Louise 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	7% 16% 6% 12% 7% 5% 5% 4 6% 6% 26%	131149
	Night	5% 15% 7% 14% 7% 6% 5% 4 6% 6% 25%	127224
Transparency	Day	34% 41% 9% 10% 5% 1	130863
	Night	35% 41% 9% 9% 5% 1	127088
Seeing	Day	16% 16% 29% 24% 12% 3	16687
	Night	10% 12% 32% 31% 13% 2	25387

By Month

Percentage Cloud Cover NW (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	1 17% 8% 23% 14% 10% 5% 4 4 3 11%	3179
	11th to 20th	Day	1 14% 6% 13% 8% 6% 6% 5% 4 6% 31%	3432
	21st to end	Day	3 20% 9% 13% 6% 5% 5% 3 5% 6% 25%	4004
February	1st to 10th	Day	2 14% 8% 19% 10% 9% 6% 4 4 6% 17%	1600
	11th to 20th	Day	1 15% 8% 22% 9% 6% 4 4 4 7% 19%	1691
	21st to end	Day	1 13% 10% 20% 13% 10% 5% 4 4 4 17%	1650
March	1st to 10th	Day	17% 9% 22% 9% 5% 4 4 5% 6% 20%	4518
	11th to 20th	Day	1 16% 10% 24% 7% 5% 4 2 3 4 23%	4771
	21st to end	Day	3 23% 13% 19% 7% 5% 4 4 5% 5% 13%	5808
April	1st to 10th	Day	4 22% 11% 20% 8% 6% 4 3 4 4 15%	2400
	11th to 20th	Day	4 24% 8% 16% 8% 5% 4 4 4 6% 17%	2550
	21st to end	Day	7% 26% 9% 13% 6% 5% 4 3 4 5% 18%	2618
May	1st to 10th	Day	7% 18% 5% 8% 4 4 5% 3 6% 8% 32%	6320
	11th to 20th	Day	9% 20% 6% 11% 7% 7% 5% 4 6% 7% 18%	6629
	21st to end	Day	9% 21% 4 9% 5% 4 4 3 5% 6% 28%	7405
June	1st to 10th	Day	16% 18% 5% 9% 6% 5% 5% 4 5% 7% 22%	3000
	11th to 20th	Day	19% 18% 5% 9% 7% 6% 6% 4 5% 5% 16%	3001
	21st to end	Day	13% 13% 4 10% 7% 6% 5% 4 7% 5% 26%	3200
July	1st to 10th	Day	8% 6% 2 6% 5% 5% 4 4 6% 7% 47%	6780
	11th to 20th	Day	10% 7% 3 7% 5% 5% 5% 4 6% 7% 41%	6780
	21st to end	Day	10% 7% 2 7% 6% 5% 6% 5% 8% 9% 35%	6965
August	1st to 10th	Day	7% 7% 2 7% 6% 5% 7% 5% 6% 9% 39%	4541
	11th to 20th	Day	10% 7% 3 8% 6% 6% 7% 5% 7% 7% 34%	4355
	21st to end	Day	11% 12% 3 8% 5% 5% 5% 4 6% 8% 34%	4642
September	1st to 10th	Day	12% 11% 3 8% 5% 4 4 3 5% 7% 38%	2400
	11th to 20th	Day	12% 15% 4 7% 4 4 4 3 5% 6% 36%	2265
	21st to end	Day	12% 18% 3 9% 5% 4 4 3 6% 5% 31%	2200
October	1st to 10th	Day	8% 21% 6% 9% 5% 4 4 4 6% 7% 25%	3466
	11th to 20th	Day	10% 19% 8% 8% 4 4 5% 4 6% 8% 24%	2914
	21st to end	Day	4 16% 8% 15% 5% 5% 6% 4 6% 7% 25%	3101
November	1st to 10th	Day	4 21% 7% 17% 8% 6% 6% 4 5% 5% 15%	1729
	11th to 20th	Day	2 16% 8% 16% 8% 7% 6% 5% 6% 6% 20%	1405
	21st to end	Day	3 16% 6% 17% 9% 6% 5% 5% 7% 7% 19%	1400
December	1st to 10th	Day	4 14% 5% 14% 9% 10% 7% 5% 6% 6% 20%	2290
	11th to 20th	Day	3 20% 11% 21% 10% 8% 5% 4 5% 3 10%	2642
	21st to end	Day	2 23% 8% 17% 8% 6% 5% 4 6% 7% 14%	3498
January	1st to 10th	Night	2 17% 10% 28% 13% 8% 5% 3 3 3 9%	6766
	11th to 20th	Night	2 13% 5% 16% 10% 8% 4 4 8% 6% 23%	6495
	21st to end	Night	5% 22% 7% 12% 7% 5% 5% 4 5% 6% 22%	6952
February	1st to 10th	Night	2 15% 9% 19% 11% 8% 6% 4 6% 6% 15%	2800
	11th to 20th	Night	3 14% 7% 21% 8% 7% 5% 4 5% 7% 19%	2590
	21st to end	Night	1 14% 9% 17% 10% 8% 6% 4 4 6% 20%	1980
March	1st to 10th	Night	1 15% 9% 16% 10% 7% 7% 5% 6% 6% 17%	5376
	11th to 20th	Night	1 12% 11% 23% 7% 5% 5% 4 6% 8% 18%	5227
	21st to end	Night	3 18% 13% 19% 6% 5% 5% 4 5% 7% 15%	5165
April	1st to 10th	Night	4 18% 8% 16% 7% 6% 5% 4 6% 8% 20%	2000
	11th to 20th	Night	2 15% 6% 13% 7% 6% 7% 5% 7% 8% 24%	1801
	21st to end	Night	4 17% 6% 11% 6% 7% 6% 5% 5% 7% 27%	1780
May	1st to 10th	Night	8% 15% 5% 9% 4 4 3 3 5% 6% 38%	3640
	11th to 20th	Night	8% 16% 5% 11% 6% 7% 6% 5% 7% 8% 22%	3262
	21st to end	Night	8% 19% 4 8% 4 4 4 3 4 6% 36%	3470
June	1st to 10th	Night	14% 14% 3 8% 5% 5% 5% 3 6% 5% 32%	1400
	11th to 20th	Night	13% 16% 3 8% 6% 6% 5% 5% 7% 7% 23%	1388
	21st to end	Night	8% 7% 2 6% 4 6% 6% 6% 8% 10% 37%	1200
July	1st to 10th	Night	8% 5% 1 4 3 4 4 4 6% 7% 53%	3170
	11th to 20th	Night	8% 8% 2 5% 4 3 4 3 6% 8% 48%	3180
	21st to end	Night	8% 9% 3 6% 3 3 4 3 5% 8% 47%	3874
August	1st to 10th	Night	9% 6% 3 6% 4 5% 5% 4 7% 9% 43%	2609
	11th to 20th	Night	10% 6% 2 6% 3 4 5% 3 7% 9% 45%	2695
	21st to end	Night	9% 9% 3 7% 4 4 4 3 5% 9% 42%	3267
September	1st to 10th	Night	8% 8% 3 6% 5% 5% 4 5% 5% 8% 43%	2000
	11th to 20th	Night	11% 12% 3 6% 4 4 4 3 7% 6% 40%	2135
	21st to end	Night	9% 15% 3 6% 4 4 4 5% 7% 7% 36%	2200
October	1st to 10th	Night	6% 16% 4 9% 6% 5% 5% 4 7% 8% 31%	3717
	11th to 20th	Night	6% 17% 8% 10% 5% 5% 4 3 5% 7% 30%	4190
	21st to end	Night	5% 19% 9% 12% 6% 5% 6% 4 6% 6% 23%	4457
November	1st to 10th	Night	5% 21% 9% 18% 9% 6% 5% 4 5% 5% 13%	2549
	11th to 20th	Night	2 17% 10% 18% 11% 7% 7% 4 4 5% 15%	2991
	21st to end	Night	2 16% 8% 20% 10% 7% 7% 5% 6% 5% 15%	3000
December	1st to 10th	Night	3 17% 6% 16% 10% 9% 8% 5% 6% 6% 14%	4890
	11th to 20th	Night	4 17% 12% 24% 11% 8% 6% 4 5% 3 6%	5550
	21st to end	Night	5% 21% 9% 17% 9% 7% 7% 4 5% 6% 11%	7458

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	55% 31% 6% 4 3 1	3179
	11th to 20th	Day	36% 30% 9% 9% 11% 5%	3456
	21st to end	Day	40% 34% 10% 11% 5%	4004
February	1st to 10th	Day	24% 64% 4 2 4 2	1600
	11th to 20th	Day	25% 62% 5% 4 4	1699
	21st to end	Day	26% 62% 3 4 4 1	1650
March	1st to 10th	Day	45% 31% 6% 7% 11% 1	4518
	11th to 20th	Day	44% 33% 11% 10% 2	4772
	21st to end	Day	49% 34% 5% 7% 4	5808
April	1st to 10th	Day	27% 63% 6% 3 1	2400
	11th to 20th	Day	24% 64% 6% 4 1	2550
	21st to end	Day	25% 63% 4 7% 1	2618
May	1st to 10th	Day	32% 32% 16% 15% 5%	6320
	11th to 20th	Day	45% 33% 10% 10% 3	6633
	21st to end	Day	35% 33% 19% 12% 2	7406
June	1st to 10th	Day	19% 64% 5% 9% 2	3000
	11th to 20th	Day	25% 63% 3 7% 3	3001
	21st to end	Day	25% 62% 4 6% 3	3200
July	1st to 10th	Day	22% 30% 10% 19% 18% 2	6706
	11th to 20th	Day	29% 29% 10% 17% 14% 1	6699
	21st to end	Day	33% 32% 12% 14% 9% 1	6770
August	1st to 10th	Day	23% 42% 8% 21% 6%	4524
	11th to 20th	Day	30% 43% 11% 15% 3	4397
	21st to end	Day	30% 40% 15% 11% 4	4641
September	1st to 10th	Day	21% 58% 8% 9% 4	2400
	11th to 20th	Day	24% 57% 4 11% 4	2265
	21st to end	Day	26% 58% 7% 8% 2	2200
October	1st to 10th	Day	39% 40% 11% 7% 3	3466
	11th to 20th	Day	37% 39% 11% 11% 1	2914
	21st to end	Day	34% 42% 10% 12% 3	3101
November	1st to 10th	Day	31% 59% 5% 3 2	1729
	11th to 20th	Day	25% 60% 7% 3 4	1405
	21st to end	Day	23% 62% 5% 5% 3 2	1400
December	1st to 10th	Day	40% 42% 12% 4 2	2290
	11th to 20th	Day	54% 36% 6% 2 2	2644
	21st to end	Day	47% 31% 9% 5% 6% 2	3498
January	1st to 10th	Night	60% 29% 4 5% 1 1	6766
	11th to 20th	Night	38% 30% 6% 6% 12% 7%	6533
	21st to end	Night	41% 32% 12% 10% 4	6952
February	1st to 10th	Night	26% 62% 3 3 5% 1	2800
	11th to 20th	Night	24% 62% 5% 4 4 1	2592
	21st to end	Night	22% 63% 4 5% 4 2	1980
March	1st to 10th	Night	40% 36% 8% 6% 9% 1	5376
	11th to 20th	Night	40% 35% 11% 11% 3	5227
	21st to end	Night	49% 33% 7% 7% 4	5165
April	1st to 10th	Night	19% 66% 8% 6% 2	2000
	11th to 20th	Night	18% 65% 8% 5% 3	1801
	21st to end	Night	21% 63% 6% 7% 3	1780
May	1st to 10th	Night	31% 30% 11% 23% 4 1	3637
	11th to 20th	Night	43% 35% 9% 10% 3	3262
	21st to end	Night	32% 31% 17% 17% 3	3470
June	1st to 10th	Night	14% 64% 5% 14% 3	1400
	11th to 20th	Night	20% 63% 5% 8% 4	1388
	21st to end	Night	15% 63% 6% 10% 5%	1200
July	1st to 10th	Night	21% 28% 11% 21% 17% 2	3135
	11th to 20th	Night	26% 28% 9% 22% 15% 1	3138
	21st to end	Night	29% 28% 16% 16% 10% 1	3765
August	1st to 10th	Night	23% 41% 9% 23% 5%	2601
	11th to 20th	Night	23% 40% 19% 16% 2	2719
	21st to end	Night	28% 38% 19% 11% 4	3267
September	1st to 10th	Night	18% 59% 9% 9% 4	2000
	11th to 20th	Night	21% 59% 6% 10% 4	2135
	21st to end	Night	21% 59% 9% 8% 2	2200
October	1st to 10th	Night	32% 43% 14% 7% 3	3717
	11th to 20th	Night	36% 39% 11% 12% 2 1	4190
	21st to end	Night	35% 42% 8% 12% 2	4457
November	1st to 10th	Night	32% 58% 4 4 2	2549
	11th to 20th	Night	29% 60% 5% 3 3 1	2991
	21st to end	Night	27% 60% 5% 4 2 2	3000
December	1st to 10th	Night	46% 42% 6% 3 3	4890
	11th to 20th	Night	54% 38% 4 3 1	5547
	21st to end	Night	48% 31% 11% 4 5% 1	7458

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	6% 20% 28% 29% 13% 5%	200
	11th to 20th	Day	5% 19% 37% 29% 10% 2	200
	21st to end	Day	9% 20% 38% 22% 8% 3	220
February	1st to 10th	Day	14% 21% 36% 20% 6% 4	200
	11th to 20th	Day	7% 18% 34% 28% 11% 2	289
	21st to end	Day	12% 21% 32% 24% 8% 1	414
March	1st to 10th	Day	13% 25% 31% 18% 10% 3	500
	11th to 20th	Day	11% 24% 34% 20% 8% 2	500
	21st to end	Day	14% 22% 29% 22% 10% 2	550
April	1st to 10th	Day	14% 23% 36% 19% 8%	500
	11th to 20th	Day	13% 24% 29% 22% 9% 3	492
	21st to end	Day	16% 21% 28% 22% 10% 3	500
May	1st to 10th	Day	18% 15% 30% 24% 10% 3	503
	11th to 20th	Day	13% 10% 24% 26% 20% 7%	672
	21st to end	Day	20% 10% 20% 27% 18% 5%	789
June	1st to 10th	Day	21% 12% 25% 25% 14% 2	730
	11th to 20th	Day	24% 12% 26% 23% 12% 3	731
	21st to end	Day	17% 11% 23% 28% 15% 6%	930
July	1st to 10th	Day	15% 10% 23% 27% 21% 4	721
	11th to 20th	Day	18% 9% 25% 27% 17% 4	718
	21st to end	Day	13% 11% 30% 24% 16% 6%	614
August	1st to 10th	Day	14% 12% 30% 27% 14% 3	527
	11th to 20th	Day	14% 18% 30% 24% 11% 3	517
	21st to end	Day	20% 15% 31% 21% 11% 3	583
September	1st to 10th	Day	23% 16% 27% 20% 12% 2	530
	11th to 20th	Day	21% 14% 29% 26% 9% 2	530
	21st to end	Day	32% 21% 24% 17% 5% 1	530
October	1st to 10th	Day	26% 17% 26% 20% 9% 3	520
	11th to 20th	Day	20% 20% 28% 21% 11% 1	324
	21st to end	Day	15% 21% 32% 23% 7% 2	330
November	1st to 10th	Day	12% 19% 38% 22% 7% 3	300
	11th to 20th	Day	16% 23% 37% 17% 5% 1	203
	21st to end	Day	7% 27% 33% 20% 8% 7%	200
December	1st to 10th	Day	8% 17% 33% 27% 9% 7%	200
	11th to 20th	Day	7% 20% 39% 26% 8% 1	200
	21st to end	Day	7% 13% 34% 29% 15% 2	220
January	1st to 10th	Night	8% 18% 39% 27% 6% 2	1000
	11th to 20th	Night	7% 16% 42% 28% 5% 2	896
	21st to end	Night	7% 15% 41% 29% 6% 2	880
February	1st to 10th	Night	8% 14% 38% 23% 12% 5%	800
	11th to 20th	Night	8% 12% 36% 31% 11% 2	784
	21st to end	Night	6% 11% 35% 30% 15% 3	660
March	1st to 10th	Night	6% 13% 39% 29% 13% 1	800
	11th to 20th	Night	6% 18% 34% 31% 10% 1	800
	21st to end	Night	6% 11% 32% 32% 14% 3	880
April	1st to 10th	Night	7% 13% 30% 33% 15% 2	800
	11th to 20th	Night	8% 10% 37% 32% 13% 1	613
	21st to end	Night	12% 12% 24% 34% 15% 2	580
May	1st to 10th	Night	11% 7% 23% 37% 20% 2	400
	11th to 20th	Night	10% 7% 19% 34% 26% 4	394
	21st to end	Night	15% 7% 20% 29% 25% 4	433
June	1st to 10th	Night	18% 8% 23% 32% 16% 3	400
	11th to 20th	Night	17% 9% 23% 33% 16% 2	400
	21st to end	Night	11% 5% 20% 33% 29% 3	400
July	1st to 10th	Night	11% 3 16% 43% 25% 2	390
	11th to 20th	Night	14% 4 18% 38% 24% 1	388
	21st to end	Night	7% 3 15% 45% 28% 2	438
August	1st to 10th	Night	10% 3 13% 41% 31% 3	398
	11th to 20th	Night	11% 6% 16% 42% 24% 2	462
	21st to end	Night	13% 5% 22% 41% 17% 1	669
September	1st to 10th	Night	14% 7% 23% 32% 20% 4	800
	11th to 20th	Night	16% 7% 19% 34% 20% 4	800
	21st to end	Night	19% 12% 27% 28% 13% 2	800
October	1st to 10th	Night	17% 9% 25% 34% 13% 2	800
	11th to 20th	Night	16% 10% 30% 33% 10% 2	792
	21st to end	Night	13% 15% 33% 28% 10% 1	836
November	1st to 10th	Night	13% 15% 38% 24% 8% 1	794
	11th to 20th	Night	11% 19% 40% 25% 4 1	1000
	21st to end	Night	8% 16% 41% 27% 7% 2	1000
December	1st to 10th	Night	7% 14% 40% 28% 9% 3	1000
	11th to 20th	Night	7% 14% 42% 28% 8% 2	1000
	21st to end	Night	6% 12% 43% 29% 8% 2	1100

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