Walkerton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Walkerton clear sky chart from 2005-11-06 to 2025-11-18.

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	14% 12% 4 10% 5% 5% 4 4 5% 6% 30%	126990
	Night	14% 13% 5% 12% 6% 5% 4 3 5% 6% 27%	123429
Transparency	Day	53% 6% 11% 18% 10% 1	130539
	Night	57% 6% 10% 16% 9% 1	127954
Seeing	Day	19% 13% 29% 23% 11% 4	16479
	Night	21% 11% 29% 28% 10% 1	25665

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	11% 17% 9% 22% 11% 7% 5% 3 3 4 9%	3268
	11th to 20th	Day	9% 20% 11% 26% 14% 7% 4 2 2 2 4	3807
	21st to end	Day	13% 19% 9% 22% 8% 7% 5% 3 3 3 7%	4466
February	1st to 10th	Day	13% 20% 7% 19% 9% 7% 4 3 3 4 12%	1800
	11th to 20th	Day	12% 16% 9% 20% 10% 4 5% 3 5% 4 13%	1753
	21st to end	Day	15% 19% 7% 13% 7% 5% 4 4 4 4 17%	1619
March	1st to 10th	Day	15% 14% 6% 15% 8% 4 3 3 4 5% 24%	4794
	11th to 20th	Day	11% 15% 7% 11% 5% 4 4 4 5% 7% 26%	4980
	21st to end	Day	17% 16% 7% 12% 5% 4 3 3 4 5% 24%	5465
April	1st to 10th	Day	16% 17% 4 9% 5% 4 4 3 5% 5% 27%	2290
	11th to 20th	Day	18% 13% 2 6% 4 3 3 3 4 6% 36%	2571
	21st to end	Day	19% 12% 3 7% 4 4 4 3 5% 7% 32%	2600
May	1st to 10th	Day	17% 10% 3 7% 4 4 4 3 6% 6% 35%	5888
	11th to 20th	Day	14% 10% 3 7% 5% 4 4 3 5% 7% 36%	6041
	21st to end	Day	19% 9% 3 6% 4 4 3 3 5% 7% 38%	6949
June	1st to 10th	Day	14% 8% 2 7% 4 5% 4 4 6% 6% 39%	2893
	11th to 20th	Day	12% 5% 2 5% 5% 5% 5% 4 6% 8% 42%	3000
	21st to end	Day	16% 7% 2 6% 4 4 4 3 6% 8% 40%	3000
July	1st to 10th	Day	12% 6% 3 7% 4 5% 5% 4 6% 9% 40%	6819
	11th to 20th	Day	11% 6% 2 5% 3 4 5% 4 6% 8% 46%	6471
	21st to end	Day	8% 5% 2 5% 4 4 5% 4 6% 8% 48%	6424
August	1st to 10th	Day	12% 6% 2 7% 5% 6% 6% 5% 7% 8% 36%	4234
	11th to 20th	Day	13% 8% 2 7% 5% 5% 5% 4 7% 9% 34%	4174
	21st to end	Day	9% 5% 3 6% 4 4 5% 5% 7% 9% 42%	4625
September	1st to 10th	Day	12% 7% 2 7% 4 5% 5% 4 6% 8% 39%	2367
	11th to 20th	Day	13% 5% 2 5% 4 4 4 4 6% 7% 46%	2200
	21st to end	Day	16% 8% 3 7% 5% 5% 5% 5% 6% 7% 35%	2200
October	1st to 10th	Day	18% 9% 3 8% 4 4 4 3 5% 7% 34%	2030
	11th to 20th	Day	21% 14% 3 10% 5% 4 5% 3 5% 8% 21%	2000
	21st to end	Day	26% 15% 4 9% 6% 5% 5% 3 5% 4 18%	2135
November	1st to 10th	Day	15% 20% 4 10% 5% 5% 3 3 4 5% 25%	1831
	11th to 20th	Day	16% 19% 6% 12% 5% 5% 6% 4 4 6% 17%	1656
	21st to end	Day	17% 24% 9% 11% 6% 5% 4 4 4 5% 12%	1600
December	1st to 10th	Day	14% 29% 10% 17% 8% 5% 4 2 3 3 5%	2600
	11th to 20th	Day	17% 23% 7% 18% 6% 4 4 3 4 4 10%	2964
	21st to end	Day	24% 22% 7% 13% 6% 4 4 3 4 4 11%	3476
January	1st to 10th	Night	12% 17% 8% 22% 10% 6% 5% 3 4 4 7%	6694
	11th to 20th	Night	10% 16% 9% 24% 13% 9% 5% 3 4 3 5%	6072
	21st to end	Night	13% 16% 9% 21% 8% 6% 5% 3 4 5% 11%	6490
February	1st to 10th	Night	12% 22% 6% 16% 10% 6% 5% 4 4 4 13%	2600
	11th to 20th	Night	13% 16% 8% 17% 9% 5% 5% 3 3 5% 16%	2533
	21st to end	Night	14% 15% 6% 12% 8% 6% 5% 4 5% 5% 20%	2010
March	1st to 10th	Night	13% 14% 5% 11% 8% 5% 5% 3 5% 5% 26%	5045
	11th to 20th	Night	8% 13% 6% 10% 5% 4 5% 4 6% 7% 30%	4979
	21st to end	Night	17% 13% 5% 12% 5% 4 4 3 4 4 28%	5467
April	1st to 10th	Night	18% 15% 4 8% 5% 4 4 3 4 6% 28%	2110
	11th to 20th	Night	17% 10% 3 7% 4 5% 4 4 5% 6% 36%	1795
	21st to end	Night	16% 11% 4 8% 6% 5% 5% 4 5% 6% 32%	1800
May	1st to 10th	Night	17% 9% 3 6% 5% 4 4 3 5% 7% 37%	4053
	11th to 20th	Night	14% 7% 3 7% 4 5% 4 4 4 7% 41%	3850
	21st to end	Night	19% 7% 2 5% 3 3 4 3 5% 6% 43%	3926
June	1st to 10th	Night	13% 7% 2 7% 5% 5% 3 4 5% 8% 40%	1501
	11th to 20th	Night	11% 7% 2 7% 5% 4 5% 5% 6% 9% 40%	1400
	21st to end	Night	13% 6% 2 7% 4 4 6% 5% 5% 7% 43%	1400
July	1st to 10th	Night	10% 7% 3 8% 4 3 3 3 5% 8% 45%	3160
	11th to 20th	Night	12% 7% 2 5% 3 3 3 3 5% 7% 50%	3496
	21st to end	Night	9% 6% 2 6% 4 4 4 4 5% 8% 49%	4428
August	1st to 10th	Night	10% 7% 2 7% 4 5% 3 3 5% 6% 46%	2915
	11th to 20th	Night	14% 8% 3 7% 4 4 4 4 5% 9% 39%	2875
	21st to end	Night	12% 7% 2 5% 4 4 4 3 5% 6% 47%	3238
September	1st to 10th	Night	10% 6% 2 7% 4 5% 4 3 7% 7% 46%	2030
	11th to 20th	Night	12% 5% 2 4 4 4 4 3 5% 7% 51%	2200
	21st to end	Night	14% 8% 3 8% 5% 5% 4 3 5% 7% 38%	2200
October	1st to 10th	Night	17% 9% 2 7% 5% 4 4 3 5% 6% 38%	2369
	11th to 20th	Night	23% 11% 3 8% 5% 4 5% 4 5% 7% 25%	2400
	21st to end	Night	22% 15% 4 8% 6% 4 5% 3 5% 5% 23%	2700
November	1st to 10th	Night	16% 15% 3 8% 6% 5% 5% 4 5% 6% 27%	2686
	11th to 20th	Night	17% 18% 6% 10% 5% 5% 5% 4 6% 6% 18%	2899
	21st to end	Night	20% 20% 7% 11% 6% 4 4 3 4 6% 14%	2800
December	1st to 10th	Night	14% 24% 8% 15% 8% 6% 6% 4 5% 4 7%	4580
	11th to 20th	Night	12% 21% 10% 17% 7% 5% 4 4 5% 4 12%	5226
	21st to end	Night	20% 21% 8% 15% 6% 5% 4 3 4 4 11%	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	79% 6% 7% 5% 2	3269
	11th to 20th	Day	88% 4 4 2 2	3840
	21st to end	Day	80% 5% 7% 5% 2	4466
February	1st to 10th	Day	76% 6% 7% 10% 1	1800
	11th to 20th	Day	74% 7% 7% 8% 4	1762
	21st to end	Day	69% 7% 8% 11% 4	1619
March	1st to 10th	Day	63% 5% 14% 12% 6%	4797
	11th to 20th	Day	56% 6% 13% 18% 6% 2	4980
	21st to end	Day	60% 6% 10% 15% 8% 1	5465
April	1st to 10th	Day	58% 6% 10% 17% 9%	2290
	11th to 20th	Day	49% 6% 9% 21% 14% 1	2571
	21st to end	Day	51% 7% 11% 18% 12% 2	2600
May	1st to 10th	Day	45% 7% 12% 18% 13% 5%	5897
	11th to 20th	Day	46% 7% 11% 18% 17% 1	6045
	21st to end	Day	45% 6% 10% 20% 15% 5%	6949
June	1st to 10th	Day	42% 7% 12% 23% 15% 1	2893
	11th to 20th	Day	39% 7% 12% 25% 17% 1	3000
	21st to end	Day	42% 6% 13% 24% 13% 1	3000
July	1st to 10th	Day	40% 6% 13% 22% 18% 1	6746
	11th to 20th	Day	33% 6% 11% 31% 18% 1	6390
	21st to end	Day	32% 6% 13% 29% 19% 2	6240
August	1st to 10th	Day	40% 8% 14% 23% 14% 1	4221
	11th to 20th	Day	45% 7% 16% 23% 10%	4213
	21st to end	Day	36% 7% 15% 30% 12% 1	4625
September	1st to 10th	Day	41% 7% 14% 24% 11% 2	2367
	11th to 20th	Day	36% 7% 14% 28% 14%	2200
	21st to end	Day	46% 8% 14% 23% 8% 1	2200
October	1st to 10th	Day	45% 6% 12% 24% 12% 1	3303
	11th to 20th	Day	49% 6% 13% 22% 10%	3240
	21st to end	Day	61% 6% 12% 16% 5%	3424
November	1st to 10th	Day	61% 7% 9% 16% 6%	1831
	11th to 20th	Day	66% 9% 10% 8% 6% 1	1656
	21st to end	Day	76% 7% 9% 8% 1	1600
December	1st to 10th	Day	86% 5% 5% 3 1	2600
	11th to 20th	Day	78% 6% 7% 6% 2	2964
	21st to end	Day	78% 5% 7% 6% 4	3476
January	1st to 10th	Night	79% 7% 7% 6% 1	6694
	11th to 20th	Night	84% 7% 5% 3 2	6113
	21st to end	Night	75% 6% 8% 7% 4	6490
February	1st to 10th	Night	76% 5% 8% 9% 2	2600
	11th to 20th	Night	71% 6% 10% 10% 3	2535
	21st to end	Night	63% 7% 11% 13% 6%	2010
March	1st to 10th	Night	58% 6% 13% 15% 7% 1	5055
	11th to 20th	Night	50% 7% 16% 18% 8% 1	4980
	21st to end	Night	58% 6% 9% 15% 10% 1	5467
April	1st to 10th	Night	56% 6% 10% 16% 11% 1	2110
	11th to 20th	Night	49% 6% 8% 19% 16% 1	1795
	21st to end	Night	52% 7% 9% 16% 14% 2	1800
May	1st to 10th	Night	46% 6% 10% 17% 14% 7%	4060
	11th to 20th	Night	42% 9% 11% 21% 16% 1	3851
	21st to end	Night	42% 6% 9% 25% 16% 2	3927
June	1st to 10th	Night	41% 7% 10% 23% 17% 3	1501
	11th to 20th	Night	38% 8% 13% 24% 15% 2	1400
	21st to end	Night	39% 7% 12% 24% 17% 1	1400
July	1st to 10th	Night	38% 5% 12% 23% 18% 4	3125
	11th to 20th	Night	34% 5% 10% 30% 20% 1	3454
	21st to end	Night	33% 6% 12% 29% 19% 1	4297
August	1st to 10th	Night	38% 6% 11% 28% 16% 1	2904
	11th to 20th	Night	42% 8% 15% 22% 12% 1	2902
	21st to end	Night	37% 6% 11% 31% 13% 1	3238
September	1st to 10th	Night	36% 7% 13% 30% 13% 2	2030
	11th to 20th	Night	32% 7% 14% 30% 17%	2200
	21st to end	Night	45% 8% 12% 23% 11% 1	2200
October	1st to 10th	Night	38% 6% 9% 27% 19% 1	3876
	11th to 20th	Night	48% 6% 16% 18% 13%	3899
	21st to end	Night	53% 6% 15% 19% 7%	4348
November	1st to 10th	Night	57% 7% 11% 18% 6%	2686
	11th to 20th	Night	65% 8% 11% 11% 4 1	2899
	21st to end	Night	72% 7% 11% 8% 1	2800
December	1st to 10th	Night	80% 7% 9% 4 1	4580
	11th to 20th	Night	74% 7% 9% 8% 3	5226
	21st to end	Night	77% 6% 7% 8% 3	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	18% 21% 37% 17% 5% 1	223
	11th to 20th	Day	21% 21% 39% 13% 5% 1	300
	21st to end	Day	25% 18% 33% 21% 3 1	330
February	1st to 10th	Day	24% 25% 36% 10% 5%	300
	11th to 20th	Day	26% 20% 41% 11% 1	300
	21st to end	Day	27% 29% 29% 13% 1	249
March	1st to 10th	Day	23% 19% 37% 15% 6%	435
	11th to 20th	Day	22% 17% 33% 20% 6% 1	500
	21st to end	Day	28% 15% 31% 19% 6% 1	550
April	1st to 10th	Day	24% 17% 32% 20% 7% 1	500
	11th to 20th	Day	29% 15% 25% 16% 8% 5%	492
	21st to end	Day	24% 14% 27% 26% 6% 2	500
May	1st to 10th	Day	21% 12% 30% 24% 10% 2	503
	11th to 20th	Day	18% 11% 27% 24% 15% 4	527
	21st to end	Day	18% 9% 27% 26% 14% 7%	573
June	1st to 10th	Day	15% 11% 30% 27% 14% 3	623
	11th to 20th	Day	13% 10% 31% 30% 13% 3	730
	21st to end	Day	18% 8% 33% 27% 12% 2	730
July	1st to 10th	Day	10% 7% 28% 30% 21% 5%	721
	11th to 20th	Day	12% 7% 30% 29% 15% 7%	668
	21st to end	Day	10% 6% 28% 33% 16% 8%	576
August	1st to 10th	Day	10% 5% 24% 31% 19% 11%	526
	11th to 20th	Day	15% 6% 18% 28% 21% 12%	519
	21st to end	Day	13% 7% 22% 30% 19% 9%	583
September	1st to 10th	Day	14% 9% 24% 25% 19% 9%	530
	11th to 20th	Day	9% 6% 19% 26% 23% 17%	530
	21st to end	Day	16% 10% 28% 27% 13% 7%	530
October	1st to 10th	Day	21% 11% 26% 21% 16% 5%	530
	11th to 20th	Day	24% 19% 30% 21% 5% 1	530
	21st to end	Day	31% 20% 26% 18% 4	518
November	1st to 10th	Day	27% 20% 29% 17% 7%	319
	11th to 20th	Day	29% 20% 31% 15% 2 3	214
	21st to end	Day	29% 25% 31% 14% 2	200
December	1st to 10th	Day	27% 30% 29% 12% 4	200
	11th to 20th	Day	30% 22% 32% 14% 3 1	200
	21st to end	Day	37% 16% 31% 13% 2	220
January	1st to 10th	Night	23% 17% 35% 19% 6% 1	1000
	11th to 20th	Night	25% 17% 33% 20% 5% 1	896
	21st to end	Night	19% 13% 36% 26% 5% 1	880
February	1st to 10th	Night	22% 17% 37% 22% 3	800
	11th to 20th	Night	21% 16% 36% 23% 4	783
	21st to end	Night	22% 17% 37% 21% 3	660
March	1st to 10th	Night	19% 15% 36% 23% 7% 1	800
	11th to 20th	Night	18% 18% 35% 24% 5% 1	800
	21st to end	Night	24% 11% 30% 26% 8% 1	880
April	1st to 10th	Night	25% 15% 30% 26% 4	800
	11th to 20th	Night	21% 14% 28% 26% 9% 1	611
	21st to end	Night	22% 12% 27% 31% 9%	600
May	1st to 10th	Night	19% 6% 29% 34% 11% 1	600
	11th to 20th	Night	19% 6% 24% 39% 12% 1	513
	21st to end	Night	15% 3 25% 42% 15%	433
June	1st to 10th	Night	15% 7% 25% 41% 11% 1	400
	11th to 20th	Night	12% 8% 27% 41% 12%	400
	21st to end	Night	17% 4 24% 41% 13% 1	400
July	1st to 10th	Night	7% 4 20% 50% 18% 1	390
	11th to 20th	Night	11% 4 22% 39% 23% 1	475
	21st to end	Night	11% 4 19% 44% 22% 1	657
August	1st to 10th	Night	11% 3 15% 40% 29% 1	597
	11th to 20th	Night	12% 3 14% 37% 29% 4	594
	21st to end	Night	13% 4 20% 34% 26% 2	662
September	1st to 10th	Night	12% 6% 24% 35% 20% 5%	800
	11th to 20th	Night	13% 4 19% 36% 24% 4	800
	21st to end	Night	16% 9% 22% 32% 18% 3	800
October	1st to 10th	Night	19% 8% 27% 31% 14% 1	800
	11th to 20th	Night	27% 13% 25% 27% 7% 1	800
	21st to end	Night	30% 12% 31% 23% 3	880
November	1st to 10th	Night	26% 12% 30% 24% 8%	820
	11th to 20th	Night	26% 19% 29% 20% 6%	829
	21st to end	Night	29% 15% 32% 22% 3	800
December	1st to 10th	Night	31% 16% 31% 18% 4	800
	11th to 20th	Night	23% 18% 39% 16% 3	805
	21st to end	Night	32% 13% 34% 18% 3	1100

Page generated at 2025-11-15 00:55:56. Version ac07

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