Wiarton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wiarton clear sky chart from 2005-11-06 to 2025-05-26.

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	15% 12% 5% 10% 5% 4 4 3 5% 6% 31%	113845
	Night	15% 14% 5% 12% 6% 5% 4 3 5% 5% 26%	115446
Transparency	Day	52% 7% 12% 18% 10% 1	117435
	Night	57% 7% 12% 15% 9% 1	120019
Seeing	Day	19% 11% 27% 26% 13% 4	15810
	Night	20% 12% 28% 26% 12% 2	25151

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	12% 20% 12% 18% 12% 5% 4 2 3 3 8%	3178
	11th to 20th	Day	10% 21% 12% 29% 9% 5% 3 2 2 1 4	3676
	21st to end	Day	13% 18% 11% 21% 7% 7% 4 3 3 3 9%	4466
February	1st to 10th	Day	12% 21% 7% 19% 9% 6% 4 3 4 4 11%	1800
	11th to 20th	Day	12% 17% 7% 14% 9% 5% 5% 4 5% 5% 16%	1753
	21st to end	Day	14% 18% 7% 12% 6% 6% 4 5% 5% 5% 18%	1605
March	1st to 10th	Day	16% 13% 5% 11% 5% 5% 5% 3 4 5% 28%	4789
	11th to 20th	Day	12% 16% 8% 10% 6% 5% 5% 4 5% 6% 24%	4980
	21st to end	Day	18% 15% 6% 9% 4 4 3 3 5% 5% 27%	5465
April	1st to 10th	Day	19% 12% 3 9% 5% 4 4 3 5% 7% 29%	2305
	11th to 20th	Day	19% 10% 2 7% 4 3 3 3 4 6% 38%	2572
	21st to end	Day	20% 9% 4 7% 3 3 4 3 5% 7% 35%	2600
May	1st to 10th	Day	16% 8% 2 6% 4 4 4 3 5% 7% 40%	4238
	11th to 20th	Day	14% 7% 2 6% 4 4 4 4 5% 7% 42%	4396
	21st to end	Day	15% 6% 2 5% 4 3 4 4 5% 8% 46%	4907
June	1st to 10th	Day	13% 8% 2 5% 4 4 5% 4 7% 8% 39%	2802
	11th to 20th	Day	11% 5% 2 5% 4 5% 5% 4 6% 8% 44%	2850
	21st to end	Day	15% 7% 2 5% 5% 3 4 4 6% 8% 42%	2850
July	1st to 10th	Day	14% 7% 2 6% 4 4 4 4 6% 8% 39%	4760
	11th to 20th	Day	11% 6% 1 5% 3 3 4 3 6% 8% 50%	4662
	21st to end	Day	9% 5% 2 5% 3 4 3 4 6% 9% 50%	4466
August	1st to 10th	Day	12% 6% 2 5% 4 4 5% 4 7% 8% 44%	4104
	11th to 20th	Day	16% 7% 2 5% 3 4 5% 3 6% 8% 41%	4044
	21st to end	Day	10% 5% 2 6% 4 5% 4 4 6% 9% 46%	4505
September	1st to 10th	Day	13% 6% 3 7% 4 4 4 4 5% 8% 41%	2256
	11th to 20th	Day	13% 6% 2 6% 4 4 4 4 5% 9% 44%	2090
	21st to end	Day	18% 7% 3 8% 4 5% 4 4 5% 6% 35%	2090
October	1st to 10th	Day	19% 9% 2 8% 5% 5% 5% 3 5% 6% 34%	1926
	11th to 20th	Day	23% 14% 3 10% 5% 5% 4 3 5% 5% 22%	1900
	21st to end	Day	29% 15% 4 10% 5% 3 4 2 4 5% 18%	2014
November	1st to 10th	Day	19% 18% 4 10% 6% 4 4 4 4 7% 21%	1717
	11th to 20th	Day	16% 21% 4 11% 6% 6% 5% 5% 4 5% 18%	1600
	21st to end	Day	20% 27% 7% 11% 5% 4 4 4 4 4 11%	1600
December	1st to 10th	Day	15% 30% 10% 13% 5% 4 4 3 3 4 9%	2600
	11th to 20th	Day	20% 25% 6% 16% 6% 4 3 2 3 5% 10%	2803
	21st to end	Day	27% 22% 6% 15% 5% 5% 4 2 3 3 8%	3476
January	1st to 10th	Night	12% 20% 10% 22% 8% 5% 4 2 3 3 10%	6785
	11th to 20th	Night	12% 19% 9% 23% 10% 6% 4 2 3 3 8%	6208
	21st to end	Night	12% 19% 10% 18% 7% 8% 5% 3 3 3 12%	6490
February	1st to 10th	Night	12% 20% 6% 16% 10% 6% 4 4 5% 3 13%	2600
	11th to 20th	Night	13% 16% 7% 15% 9% 5% 4 3 4 5% 18%	2533
	21st to end	Night	15% 14% 6% 11% 7% 5% 6% 4 5% 5% 22%	2020
March	1st to 10th	Night	14% 12% 5% 10% 5% 4 4 3 5% 6% 30%	5051
	11th to 20th	Night	10% 12% 6% 9% 6% 5% 5% 4 5% 7% 31%	4979
	21st to end	Night	20% 12% 5% 8% 4 4 4 3 4 5% 31%	5467
April	1st to 10th	Night	20% 11% 3 8% 5% 4 4 3 5% 6% 32%	2103
	11th to 20th	Night	18% 9% 3 7% 4 4 4 3 5% 6% 36%	1784
	21st to end	Night	20% 10% 3 8% 5% 4 4 4 5% 5% 33%	1800
May	1st to 10th	Night	15% 6% 3 8% 5% 5% 5% 3 5% 7% 39%	2923
	11th to 20th	Night	13% 7% 2 8% 5% 4 4 4 5% 7% 40%	2713
	21st to end	Night	12% 6% 2 7% 3 4 4 4 5% 7% 46%	2784
June	1st to 10th	Night	13% 8% 2 8% 5% 5% 4 3 6% 7% 39%	1373
	11th to 20th	Night	11% 5% 2 4 4 5% 5% 4 7% 10% 42%	1330
	21st to end	Night	14% 6% 3 6% 4 4 5% 4 6% 8% 40%	1330
July	1st to 10th	Night	12% 8% 3 6% 4 4 3 3 5% 7% 46%	2210
	11th to 20th	Night	12% 5% 2 5% 3 4 4 3 5% 7% 51%	2290
	21st to end	Night	7% 7% 3 5% 4 4 4 4 5% 7% 49%	3087
August	1st to 10th	Night	12% 7% 2 7% 4 4 4 4 6% 7% 43%	2825
	11th to 20th	Night	13% 7% 2 7% 4 5% 5% 4 5% 8% 41%	2785
	21st to end	Night	11% 6% 2 6% 4 4 4 4 5% 8% 46%	3124
September	1st to 10th	Night	11% 4 2 6% 4 3 4 5% 7% 7% 47%	1915
	11th to 20th	Night	11% 5% 2 6% 3 4 4 4 5% 7% 49%	2090
	21st to end	Night	17% 7% 2 8% 6% 5% 5% 3 4 6% 37%	2090
October	1st to 10th	Night	18% 8% 3 7% 5% 5% 4 3 6% 6% 35%	2253
	11th to 20th	Night	24% 11% 4 10% 5% 4 4 3 6% 6% 23%	2280
	21st to end	Night	26% 14% 4 10% 5% 4 5% 4 4 6% 20%	2581
November	1st to 10th	Night	19% 16% 4 9% 5% 4 4 3 5% 5% 25%	2581
	11th to 20th	Night	17% 19% 5% 10% 6% 6% 4 4 5% 6% 18%	2800
	21st to end	Night	23% 23% 5% 9% 6% 5% 4 3 4 5% 13%	2800
December	1st to 10th	Night	17% 26% 7% 13% 6% 5% 4 3 5% 5% 8%	4580
	11th to 20th	Night	15% 26% 9% 17% 6% 4 4 3 4 3 9%	5380
	21st to end	Night	23% 23% 7% 16% 7% 6% 3 2 3 3 8%	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	78% 7% 8% 4 2	3179
	11th to 20th	Day	88% 5% 3 3 1	3707
	21st to end	Day	78% 7% 9% 5% 1	4466
February	1st to 10th	Day	77% 6% 8% 7% 1	1800
	11th to 20th	Day	70% 8% 11% 7% 4	1762
	21st to end	Day	67% 6% 11% 12% 4	1605
March	1st to 10th	Day	58% 5% 15% 11% 10% 1	4792
	11th to 20th	Day	58% 6% 13% 16% 6% 1	4980
	21st to end	Day	57% 6% 13% 16% 8% 1	5465
April	1st to 10th	Day	55% 6% 11% 18% 10%	2305
	11th to 20th	Day	48% 4 8% 22% 16% 1	2572
	21st to end	Day	48% 6% 12% 19% 11% 3	2600
May	1st to 10th	Day	41% 7% 13% 19% 17% 2	4250
	11th to 20th	Day	39% 8% 16% 23% 13% 1	4400
	21st to end	Day	36% 7% 13% 20% 19% 5%	4907
June	1st to 10th	Day	40% 8% 11% 25% 15% 1	2802
	11th to 20th	Day	36% 7% 13% 25% 18% 1	2850
	21st to end	Day	40% 7% 12% 25% 14% 2	2850
July	1st to 10th	Day	41% 6% 16% 20% 14% 1	4686
	11th to 20th	Day	31% 6% 15% 35% 12% 1	4581
	21st to end	Day	31% 6% 12% 33% 17% 1	4324
August	1st to 10th	Day	35% 7% 16% 26% 14% 1	4091
	11th to 20th	Day	40% 7% 17% 25% 11%	4083
	21st to end	Day	33% 7% 15% 33% 11% 1	4505
September	1st to 10th	Day	40% 8% 13% 25% 13% 1	2256
	11th to 20th	Day	36% 8% 15% 28% 13%	2090
	21st to end	Day	49% 8% 12% 22% 9%	2090
October	1st to 10th	Day	41% 7% 14% 25% 12% 1	3199
	11th to 20th	Day	54% 6% 11% 20% 8%	3140
	21st to end	Day	60% 5% 14% 16% 4	3303
November	1st to 10th	Day	63% 7% 11% 14% 5%	1717
	11th to 20th	Day	66% 10% 12% 8% 5%	1600
	21st to end	Day	76% 9% 10% 5%	1600
December	1st to 10th	Day	78% 7% 10% 4 1	2600
	11th to 20th	Day	77% 8% 9% 6% 1	2802
	21st to end	Day	82% 5% 6% 5% 1	3476
January	1st to 10th	Night	75% 8% 9% 5% 2	6785
	11th to 20th	Night	79% 7% 6% 5% 2	6252
	21st to end	Night	76% 7% 10% 4 3	6490
February	1st to 10th	Night	73% 7% 9% 9% 2	2600
	11th to 20th	Night	68% 7% 11% 10% 4	2535
	21st to end	Night	61% 8% 13% 12% 6%	2020
March	1st to 10th	Night	52% 7% 15% 15% 11% 1	5061
	11th to 20th	Night	50% 7% 16% 17% 8% 1	4980
	21st to end	Night	55% 7% 10% 15% 12% 1	5467
April	1st to 10th	Night	53% 5% 10% 20% 11% 1	2103
	11th to 20th	Night	47% 5% 9% 20% 17% 1	1784
	21st to end	Night	51% 5% 10% 15% 16% 2	1800
May	1st to 10th	Night	42% 7% 13% 18% 17% 2	2930
	11th to 20th	Night	41% 8% 11% 21% 17% 2	2714
	21st to end	Night	37% 7% 11% 22% 19% 3	2785
June	1st to 10th	Night	42% 7% 11% 20% 18% 2	1373
	11th to 20th	Night	36% 6% 14% 24% 19% 2	1330
	21st to end	Night	40% 6% 12% 27% 13% 2	1330
July	1st to 10th	Night	38% 5% 13% 22% 17% 5%	2175
	11th to 20th	Night	33% 6% 10% 36% 15% 1	2248
	21st to end	Night	33% 7% 12% 25% 22% 1	2988
August	1st to 10th	Night	38% 5% 15% 25% 15% 1	2814
	11th to 20th	Night	40% 8% 18% 20% 14% 1	2812
	21st to end	Night	35% 7% 14% 31% 13% 1	3124
September	1st to 10th	Night	33% 9% 14% 28% 15% 1	1915
	11th to 20th	Night	34% 8% 15% 29% 14%	2090
	21st to end	Night	47% 8% 13% 23% 9%	2090
October	1st to 10th	Night	37% 8% 12% 27% 16%	3760
	11th to 20th	Night	52% 5% 14% 19% 10%	3779
	21st to end	Night	54% 8% 15% 18% 5%	4242
November	1st to 10th	Night	59% 7% 13% 16% 5%	2581
	11th to 20th	Night	65% 9% 14% 8% 3 1	2800
	21st to end	Night	72% 9% 11% 6% 1	2800
December	1st to 10th	Night	77% 7% 12% 3 1	4580
	11th to 20th	Night	77% 7% 9% 6% 1	5380
	21st to end	Night	83% 5% 8% 4 1	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	20% 21% 38% 14% 5% 1	205
	11th to 20th	Day	20% 17% 37% 18% 7% 1	300
	21st to end	Day	25% 17% 30% 21% 6% 1	330
February	1st to 10th	Day	22% 25% 33% 16% 4	300
	11th to 20th	Day	21% 21% 36% 18% 3	300
	21st to end	Day	19% 26% 37% 17% 1	249
March	1st to 10th	Day	23% 14% 33% 23% 6% 1	430
	11th to 20th	Day	21% 15% 32% 25% 7% 1	500
	21st to end	Day	24% 13% 30% 26% 6% 1	550
April	1st to 10th	Day	20% 15% 32% 22% 10% 1	500
	11th to 20th	Day	26% 13% 27% 18% 11% 5%	492
	21st to end	Day	25% 10% 30% 24% 10% 1	500
May	1st to 10th	Day	20% 8% 28% 29% 13% 2	503
	11th to 20th	Day	16% 8% 27% 28% 18% 4	527
	21st to end	Day	15% 6% 22% 32% 19% 5%	549
June	1st to 10th	Day	13% 6% 25% 36% 17% 2	632
	11th to 20th	Day	12% 5% 26% 37% 16% 4	680
	21st to end	Day	17% 5% 25% 33% 16% 4	680
July	1st to 10th	Day	11% 3 23% 36% 22% 5%	671
	11th to 20th	Day	13% 4 25% 33% 18% 7%	666
	21st to end	Day	11% 3 19% 40% 19% 7%	532
August	1st to 10th	Day	13% 5% 19% 30% 25% 8%	486
	11th to 20th	Day	14% 4 14% 33% 26% 9%	479
	21st to end	Day	15% 8% 22% 30% 19% 7%	539
September	1st to 10th	Day	14% 9% 21% 30% 19% 7%	490
	11th to 20th	Day	11% 8% 18% 26% 26% 13%	490
	21st to end	Day	18% 11% 20% 26% 20% 5%	490
October	1st to 10th	Day	22% 13% 25% 21% 16% 4	490
	11th to 20th	Day	22% 18% 31% 22% 6% 1	490
	21st to end	Day	33% 17% 26% 19% 4	463
November	1st to 10th	Day	26% 18% 30% 18% 7% 1	277
	11th to 20th	Day	25% 20% 34% 18% 4 2	200
	21st to end	Day	26% 20% 39% 15% 2	200
December	1st to 10th	Day	25% 25% 31% 15% 5%	200
	11th to 20th	Day	29% 23% 32% 12% 5%	200
	21st to end	Day	35% 18% 33% 11% 3	220
January	1st to 10th	Night	23% 18% 34% 20% 5% 1	1000
	11th to 20th	Night	26% 18% 31% 18% 6% 1	957
	21st to end	Night	20% 14% 33% 26% 6% 1	880
February	1st to 10th	Night	20% 18% 37% 21% 4	800
	11th to 20th	Night	18% 17% 34% 24% 7%	783
	21st to end	Night	20% 15% 37% 23% 4	660
March	1st to 10th	Night	17% 14% 37% 24% 7%	800
	11th to 20th	Night	18% 13% 37% 25% 7% 1	800
	21st to end	Night	20% 11% 29% 29% 11% 1	880
April	1st to 10th	Night	23% 11% 30% 29% 6% 1	800
	11th to 20th	Night	21% 8% 30% 27% 12% 3	600
	21st to end	Night	24% 8% 25% 29% 14% 1	600
May	1st to 10th	Night	17% 5% 23% 37% 17% 2	600
	11th to 20th	Night	17% 4 18% 38% 20% 1	480
	21st to end	Night	13% 4 22% 37% 21% 3	423
June	1st to 10th	Night	15% 4 26% 36% 16% 3	380
	11th to 20th	Night	11% 6% 23% 37% 22%	380
	21st to end	Night	13% 5% 21% 36% 23% 1	380
July	1st to 10th	Night	10% 2 16% 48% 22% 2	370
	11th to 20th	Night	10% 3 23% 31% 30% 3	409
	21st to end	Night	9% 3 18% 42% 25% 3	624
August	1st to 10th	Night	11% 2 20% 33% 31% 3	567
	11th to 20th	Night	10% 4 16% 33% 30% 7%	564
	21st to end	Night	14% 5% 19% 31% 26% 4	627
September	1st to 10th	Night	12% 6% 20% 35% 20% 7%	755
	11th to 20th	Night	13% 5% 19% 31% 25% 6%	760
	21st to end	Night	18% 8% 21% 26% 20% 7%	760
October	1st to 10th	Night	21% 9% 27% 26% 15% 3	760
	11th to 20th	Night	29% 15% 23% 23% 8% 2	760
	21st to end	Night	32% 15% 27% 21% 5%	836
November	1st to 10th	Night	27% 15% 28% 22% 7% 1	780
	11th to 20th	Night	25% 19% 30% 18% 7%	800
	21st to end	Night	32% 16% 30% 18% 3	800
December	1st to 10th	Night	28% 22% 32% 14% 4 1	800
	11th to 20th	Night	24% 20% 37% 15% 4	876
	21st to end	Night	33% 15% 32% 16% 4	1100

Page generated at 2025-05-23 09:21:00. Version ac07

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