Peyto Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Peyto Lake clear sky chart from 2005-11-06 to 2025-07-21.

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	6% 16% 7% 14% 7% 5% 5% 4 5% 6% 25%	124639
	Night	4 14% 7% 17% 8% 6% 5% 4 6% 6% 23%	123142
Transparency	Day	58% 6% 12% 16% 7% 1	124393
	Night	60% 5% 12% 15% 7% 1	123032
Seeing	Day	16% 15% 28% 24% 13% 4	16592
	Night	10% 10% 28% 33% 15% 3	25063

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	9% 9% 26% 14% 11% 8% 4 4 5% 10%	3179
	11th to 20th	Day	1 12% 7% 18% 7% 6% 5% 4 6% 6% 29%	3432
	21st to end	Day	1 16% 10% 20% 7% 5% 4 3 5% 6% 24%	4004
February	1st to 10th	Day	2 15% 9% 20% 10% 8% 6% 4 6% 5% 16%	1600
	11th to 20th	Day	1 14% 8% 21% 10% 8% 6% 4 5% 7% 16%	1680
	21st to end	Day	1 11% 11% 22% 11% 10% 6% 4 5% 5% 14%	1650
March	1st to 10th	Day	1 15% 9% 20% 12% 7% 6% 4 5% 6% 16%	4518
	11th to 20th	Day	1 14% 9% 27% 10% 5% 4 2 3 4 20%	4735
	21st to end	Day	2 23% 11% 21% 9% 5% 4 3 5% 4 13%	5837
April	1st to 10th	Day	4 18% 11% 23% 10% 5% 4 3 4 5% 12%	2400
	11th to 20th	Day	4 23% 10% 16% 7% 6% 5% 4 5% 5% 16%	2540
	21st to end	Day	5% 24% 9% 15% 7% 6% 4 3 5% 6% 16%	2645
May	1st to 10th	Day	6% 18% 7% 9% 5% 5% 5% 4 6% 7% 29%	6320
	11th to 20th	Day	6% 21% 8% 12% 6% 5% 6% 5% 7% 7% 18%	6614
	21st to end	Day	8% 20% 6% 10% 4 4 4 4 5% 7% 28%	7405
June	1st to 10th	Day	14% 17% 4 9% 6% 5% 5% 4 6% 6% 24%	3000
	11th to 20th	Day	14% 18% 4 10% 6% 5% 5% 4 6% 7% 20%	3135
	21st to end	Day	11% 12% 3 9% 6% 6% 6% 5% 7% 8% 28%	3200
July	1st to 10th	Day	6% 9% 3 6% 5% 5% 5% 4 5% 5% 47%	5100
	11th to 20th	Day	7% 6% 2 6% 4 4 5% 4 6% 7% 50%	4890
	21st to end	Day	7% 9% 3 8% 5% 5% 4 5% 7% 8% 40%	4854
August	1st to 10th	Day	9% 8% 2 7% 6% 5% 6% 5% 7% 8% 38%	4401
	11th to 20th	Day	11% 8% 3 8% 6% 6% 6% 5% 6% 8% 33%	4250
	21st to end	Day	12% 15% 4 8% 5% 5% 5% 4 6% 7% 30%	4477
September	1st to 10th	Day	11% 15% 4 8% 5% 4 5% 4 5% 7% 34%	2280
	11th to 20th	Day	11% 18% 4 8% 4 4 4 4 4 6% 33%	2163
	21st to end	Day	11% 22% 5% 8% 5% 4 4 3 5% 5% 28%	2090
October	1st to 10th	Day	8% 26% 6% 9% 5% 4 4 3 5% 7% 23%	3353
	11th to 20th	Day	9% 24% 6% 12% 4 4 4 3 6% 7% 20%	2842
	21st to end	Day	3 20% 10% 17% 5% 4 4 3 4 5% 25%	3101
November	1st to 10th	Day	5% 21% 10% 21% 8% 6% 4 3 4 5% 14%	1714
	11th to 20th	Day	1 18% 8% 18% 10% 8% 6% 5% 5% 5% 17%	1400
	21st to end	Day	2 15% 7% 19% 12% 7% 5% 4 4 6% 18%	1400
December	1st to 10th	Day	1 15% 7% 16% 9% 9% 9% 4 5% 7% 18%	2290
	11th to 20th	Day	1 17% 9% 26% 11% 7% 5% 4 6% 5% 10%	2642
	21st to end	Day	1 14% 9% 22% 11% 6% 5% 3 5% 5% 19%	3498
January	1st to 10th	Night	1 9% 8% 30% 16% 9% 7% 4 4 3 9%	6766
	11th to 20th	Night	1 8% 6% 15% 11% 8% 8% 4 7% 8% 24%	6494
	21st to end	Night	1 19% 10% 15% 6% 5% 5% 4 5% 7% 23%	6952
February	1st to 10th	Night	1 14% 9% 20% 12% 6% 8% 4 5% 4 17%	2800
	11th to 20th	Night	2 14% 7% 20% 11% 6% 6% 5% 6% 6% 19%	2604
	21st to end	Night	11% 10% 19% 11% 10% 6% 4 6% 6% 18%	1980
March	1st to 10th	Night	1 13% 7% 20% 12% 9% 7% 5% 6% 6% 15%	5376
	11th to 20th	Night	1 10% 8% 26% 9% 5% 4 3 6% 7% 20%	5264
	21st to end	Night	1 17% 11% 25% 7% 6% 5% 4 5% 4 14%	5125
April	1st to 10th	Night	3 17% 9% 18% 8% 6% 6% 5% 6% 5% 17%	2000
	11th to 20th	Night	2 17% 7% 15% 9% 6% 6% 4 7% 6% 21%	1810
	21st to end	Night	4 17% 7% 12% 8% 8% 6% 4 6% 6% 23%	1753
May	1st to 10th	Night	7% 16% 6% 10% 5% 4 4 4 5% 7% 33%	3640
	11th to 20th	Night	6% 17% 7% 13% 7% 6% 5% 5% 8% 8% 20%	3279
	21st to end	Night	6% 17% 6% 9% 5% 5% 4 3 6% 6% 33%	3470
June	1st to 10th	Night	15% 16% 5% 8% 4 4 3 3 5% 7% 31%	1400
	11th to 20th	Night	12% 16% 5% 11% 6% 6% 7% 4 7% 6% 20%	1258
	21st to end	Night	7% 11% 3 8% 5% 6% 5% 5% 8% 9% 34%	1200
July	1st to 10th	Night	7% 7% 2 6% 4 3 4 3 5% 7% 51%	2076
	11th to 20th	Night	6% 6% 2 5% 3 4 4 4 6% 8% 55%	2290
	21st to end	Night	6% 10% 2 5% 4 3 4 4 5% 8% 49%	2696
August	1st to 10th	Night	9% 7% 3 6% 5% 5% 5% 4 7% 8% 42%	2529
	11th to 20th	Night	10% 7% 3 5% 4 4 5% 5% 8% 9% 42%	2579
	21st to end	Night	11% 12% 3 8% 5% 4 4 4 6% 7% 36%	3177
September	1st to 10th	Night	7% 12% 4 9% 5% 4 4 3 4 7% 40%	1900
	11th to 20th	Night	12% 13% 4 9% 4 4 4 3 4 7% 36%	2016
	21st to end	Night	9% 18% 4 8% 4 4 4 4 6% 5% 33%	2090
October	1st to 10th	Night	7% 19% 5% 9% 4 5% 5% 4 6% 7% 29%	3614
	11th to 20th	Night	7% 22% 5% 13% 4 4 5% 3 5% 7% 25%	4086
	21st to end	Night	3 17% 8% 19% 5% 4 4 3 5% 7% 24%	4457
November	1st to 10th	Night	4 22% 9% 18% 9% 6% 6% 4 5% 5% 11%	2563
	11th to 20th	Night	1 18% 9% 22% 10% 7% 5% 4 4 5% 15%	3000
	21st to end	Night	2 17% 7% 21% 10% 7% 5% 3 5% 7% 15%	3000
December	1st to 10th	Night	1 14% 9% 17% 12% 9% 7% 5% 5% 6% 15%	4890
	11th to 20th	Night	14% 9% 28% 12% 9% 7% 4 4 3 8%	5550
	21st to end	Night	1 14% 8% 23% 10% 7% 5% 4 5% 6% 15%	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	76% 4 7% 8% 5% 1	3179
	11th to 20th	Day	54% 5% 8% 12% 14% 7%	3456
	21st to end	Day	58% 6% 12% 14% 9%	4004
February	1st to 10th	Day	69% 4 8% 7% 8% 3	1600
	11th to 20th	Day	67% 5% 8% 12% 7% 2	1688
	21st to end	Day	70% 5% 8% 10% 5% 2	1650
March	1st to 10th	Day	67% 4 6% 11% 12% 2	4518
	11th to 20th	Day	66% 6% 10% 12% 5%	4736
	21st to end	Day	71% 7% 7% 9% 5% 1	5837
April	1st to 10th	Day	72% 8% 11% 7% 2	2400
	11th to 20th	Day	68% 8% 10% 11% 3 1	2540
	21st to end	Day	68% 8% 9% 12% 2 1	2645
May	1st to 10th	Day	53% 6% 16% 19% 6%	6320
	11th to 20th	Day	61% 9% 11% 16% 4	6618
	21st to end	Day	52% 10% 18% 16% 4	7406
June	1st to 10th	Day	58% 8% 13% 16% 4 1	3000
	11th to 20th	Day	61% 8% 12% 15% 4	3135
	21st to end	Day	51% 8% 17% 18% 5% 1	3200
July	1st to 10th	Day	39% 5% 9% 21% 23% 3	5024
	11th to 20th	Day	34% 4 11% 28% 22% 1	4809
	21st to end	Day	42% 4 12% 25% 16% 1	4701
August	1st to 10th	Day	43% 5% 9% 32% 10%	4384
	11th to 20th	Day	48% 5% 16% 24% 7%	4292
	21st to end	Day	53% 4 18% 20% 5% 1	4476
September	1st to 10th	Day	48% 6% 17% 20% 8%	2280
	11th to 20th	Day	51% 7% 12% 20% 9%	2163
	21st to end	Day	58% 6% 13% 16% 7%	2090
October	1st to 10th	Day	62% 4 15% 14% 5%	3353
	11th to 20th	Day	63% 5% 14% 16% 2	2842
	21st to end	Day	62% 5% 11% 17% 5%	3101
November	1st to 10th	Day	73% 5% 9% 9% 3 2	1714
	11th to 20th	Day	66% 8% 12% 7% 7% 1	1400
	21st to end	Day	64% 8% 13% 9% 5% 2	1400
December	1st to 10th	Day	66% 5% 14% 10% 4 1	2290
	11th to 20th	Day	76% 4 7% 8% 3 1	2644
	21st to end	Day	67% 4 8% 12% 7% 2	3498
January	1st to 10th	Night	79% 3 6% 8% 3 1	6766
	11th to 20th	Night	57% 3 7% 11% 14% 8%	6532
	21st to end	Night	59% 6% 13% 14% 8% 1	6952
February	1st to 10th	Night	68% 5% 7% 9% 7% 3	2800
	11th to 20th	Night	64% 6% 10% 10% 8% 2	2606
	21st to end	Night	65% 4 9% 13% 7% 3	1980
March	1st to 10th	Night	63% 7% 7% 11% 10% 2	5376
	11th to 20th	Night	62% 6% 11% 15% 5%	5264
	21st to end	Night	70% 5% 8% 9% 6% 1	5125
April	1st to 10th	Night	65% 8% 13% 12% 3	2000
	11th to 20th	Night	57% 9% 13% 13% 6% 1	1810
	21st to end	Night	57% 9% 11% 18% 5% 1	1753
May	1st to 10th	Night	50% 5% 13% 25% 5% 1	3637
	11th to 20th	Night	57% 7% 12% 19% 5%	3279
	21st to end	Night	47% 7% 19% 22% 5%	3470
June	1st to 10th	Night	52% 6% 13% 22% 5% 1	1400
	11th to 20th	Night	59% 10% 10% 15% 5%	1258
	21st to end	Night	41% 7% 19% 25% 7% 1	1200
July	1st to 10th	Night	33% 4 10% 29% 22% 2	2043
	11th to 20th	Night	27% 4 13% 31% 23% 2	2248
	21st to end	Night	34% 3 14% 30% 18% 1	2611
August	1st to 10th	Night	38% 5% 13% 36% 8%	2521
	11th to 20th	Night	36% 4 26% 28% 5%	2603
	21st to end	Night	46% 4 25% 21% 5%	3177
September	1st to 10th	Night	42% 7% 17% 24% 10% 1	1900
	11th to 20th	Night	48% 6% 17% 19% 10% 1	2016
	21st to end	Night	49% 9% 15% 19% 8%	2090
October	1st to 10th	Night	54% 7% 18% 16% 5%	3614
	11th to 20th	Night	59% 4 14% 19% 4	4086
	21st to end	Night	60% 4 13% 17% 4	4457
November	1st to 10th	Night	72% 6% 7% 7% 5% 2	2563
	11th to 20th	Night	71% 6% 8% 8% 6% 1	3000
	21st to end	Night	68% 6% 10% 8% 4 3	3000
December	1st to 10th	Night	69% 6% 11% 8% 6% 1	4890
	11th to 20th	Night	80% 5% 5% 7% 3	5547
	21st to end	Night	68% 5% 11% 9% 5% 2	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	4 25% 28% 26% 11% 7%	200
	11th to 20th	Day	8% 15% 40% 27% 9% 3	200
	21st to end	Day	8% 21% 38% 19% 10% 4	220
February	1st to 10th	Day	14% 19% 40% 17% 7% 5%	200
	11th to 20th	Day	8% 19% 34% 25% 12% 1	288
	21st to end	Day	14% 18% 31% 25% 9% 2	414
March	1st to 10th	Day	12% 23% 34% 18% 9% 3	500
	11th to 20th	Day	10% 22% 37% 20% 9% 2	500
	21st to end	Day	14% 20% 31% 22% 9% 3	550
April	1st to 10th	Day	13% 22% 36% 19% 9% 1	500
	11th to 20th	Day	13% 23% 33% 18% 10% 3	492
	21st to end	Day	17% 18% 28% 22% 12% 3	500
May	1st to 10th	Day	18% 17% 28% 22% 11% 4	503
	11th to 20th	Day	13% 10% 20% 29% 21% 7%	670
	21st to end	Day	17% 10% 21% 26% 19% 6%	789
June	1st to 10th	Day	20% 13% 26% 24% 15% 3	730
	11th to 20th	Day	19% 11% 25% 26% 14% 4	865
	21st to end	Day	15% 8% 21% 29% 21% 7%	930
July	1st to 10th	Day	13% 9% 21% 29% 22% 5%	851
	11th to 20th	Day	16% 9% 22% 29% 19% 5%	718
	21st to end	Day	12% 10% 26% 27% 19% 6%	569
August	1st to 10th	Day	12% 9% 28% 28% 18% 4	487
	11th to 20th	Day	13% 13% 31% 28% 11% 3	477
	21st to end	Day	21% 14% 29% 23% 11% 2	539
September	1st to 10th	Day	20% 20% 27% 22% 9% 2	490
	11th to 20th	Day	22% 15% 26% 27% 7% 3	490
	21st to end	Day	28% 22% 26% 16% 7% 2	490
October	1st to 10th	Day	26% 14% 27% 20% 11% 3	490
	11th to 20th	Day	22% 21% 24% 22% 10% 1	300
	21st to end	Day	18% 16% 34% 23% 8% 2	330
November	1st to 10th	Day	15% 19% 37% 18% 9% 2	290
	11th to 20th	Day	17% 21% 40% 14% 7% 2	200
	21st to end	Day	12% 23% 32% 20% 7% 8%	200
December	1st to 10th	Day	9% 18% 29% 30% 5% 10%	200
	11th to 20th	Day	5% 24% 38% 23% 10% 1	200
	21st to end	Day	8% 15% 29% 30% 15% 3	220
January	1st to 10th	Night	8% 16% 37% 31% 7% 1	1000
	11th to 20th	Night	8% 12% 38% 33% 7% 2	895
	21st to end	Night	5% 15% 36% 31% 9% 3	880
February	1st to 10th	Night	6% 13% 34% 28% 13% 5%	800
	11th to 20th	Night	7% 11% 31% 36% 12% 2	784
	21st to end	Night	6% 11% 27% 36% 16% 4	660
March	1st to 10th	Night	6% 13% 35% 30% 15% 2	800
	11th to 20th	Night	7% 14% 31% 34% 13% 2	800
	21st to end	Night	7% 10% 28% 33% 18% 4	880
April	1st to 10th	Night	9% 11% 29% 32% 17% 3	800
	11th to 20th	Night	7% 12% 32% 35% 14% 1	622
	21st to end	Night	11% 9% 25% 36% 17% 3	553
May	1st to 10th	Night	14% 6% 19% 37% 21% 3	400
	11th to 20th	Night	12% 4 16% 35% 27% 5%	394
	21st to end	Night	17% 9% 13% 28% 28% 4	433
June	1st to 10th	Night	23% 5% 15% 34% 18% 5%	400
	11th to 20th	Night	20% 5% 19% 32% 20% 3	400
	21st to end	Night	11% 4 14% 34% 32% 7%	400
July	1st to 10th	Night	12% 3 11% 40% 31% 3	390
	11th to 20th	Night	15% 4 12% 38% 28% 3	388
	21st to end	Night	6% 3 15% 39% 34% 4	416
August	1st to 10th	Night	9% 3 8% 35% 40% 5%	378
	11th to 20th	Night	13% 6% 12% 37% 28% 4	419
	21st to end	Night	14% 6% 17% 39% 21% 2	645
September	1st to 10th	Night	15% 6% 18% 34% 23% 5%	760
	11th to 20th	Night	17% 5% 15% 34% 22% 6%	760
	21st to end	Night	20% 11% 21% 31% 14% 4	760
October	1st to 10th	Night	16% 8% 21% 35% 16% 4	760
	11th to 20th	Night	16% 9% 26% 35% 11% 3	760
	21st to end	Night	13% 13% 31% 31% 11% 1	836
November	1st to 10th	Night	14% 12% 38% 26% 9% 2	790
	11th to 20th	Night	11% 19% 37% 27% 5% 1	1000
	21st to end	Night	10% 13% 38% 29% 8% 3	1000
December	1st to 10th	Night	8% 12% 36% 31% 10% 3	1000
	11th to 20th	Night	6% 12% 39% 32% 9% 3	1000
	21st to end	Night	5% 11% 39% 32% 11% 3	1100

Page generated at 2025-07-17 23:10:03. Version ac07

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