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 2026-09-29.

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% 11% 4 9% 5% 4 4 3 5% 7% 33%	149575
	Night	15% 14% 5% 11% 6% 5% 4 3 5% 6% 27%	141894
Transparency	Day	50% 6% 12% 20% 10% 1	153122
	Night	56% 6% 11% 16% 9% 1	146435
Seeing	Day	19% 12% 27% 26% 13% 3	17679
	Night	20% 12% 28% 26% 12% 2	26787

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	13% 20% 11% 18% 10% 5% 4 2 3 4 10%	4128
	11th to 20th	Day	10% 22% 12% 28% 11% 5% 3 2 2 1 4	4792
	21st to end	Day	11% 16% 10% 21% 10% 9% 5% 3 3 3 8%	5780
February	1st to 10th	Day	12% 21% 7% 19% 9% 6% 4 3 3 4 12%	1890
	11th to 20th	Day	13% 17% 7% 14% 9% 6% 5% 4 5% 5% 16%	1843
	21st to end	Day	14% 18% 7% 13% 7% 6% 5% 4 4 5% 18%	1683
March	1st to 10th	Day	16% 13% 5% 11% 5% 5% 5% 3 4 5% 28%	4895
	11th to 20th	Day	13% 16% 8% 10% 6% 5% 5% 4 5% 6% 23%	5090
	21st to end	Day	18% 15% 6% 9% 4 4 4 3 5% 5% 27%	5586
April	1st to 10th	Day	19% 12% 3 9% 5% 4 4 3 5% 7% 28%	2420
	11th to 20th	Day	20% 10% 2 7% 4 3 3 3 4 6% 38%	2702
	21st to end	Day	20% 9% 4 7% 3 3 4 3 5% 7% 35%	2730
May	1st to 10th	Day	14% 8% 2 7% 4 4 5% 4 5% 8% 40%	7642
	11th to 20th	Day	14% 9% 3 7% 4 4 4 3 5% 7% 40%	7973
	21st to end	Day	18% 8% 2 5% 3 3 3 3 4 7% 44%	9060
June	1st to 10th	Day	13% 8% 2 5% 4 4 5% 4 7% 7% 40%	3098
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 4 6% 9% 42%	3150
	21st to end	Day	15% 7% 2 6% 4 3 4 4 6% 8% 41%	3150
July	1st to 10th	Day	13% 8% 2 5% 4 4 4 3 6% 8% 41%	8879
	11th to 20th	Day	11% 5% 1 4 3 3 4 3 5% 9% 52%	8712
	21st to end	Day	9% 6% 2 5% 3 4 4 4 5% 8% 51%	8340
August	1st to 10th	Day	16% 6% 3 5% 4 4 4 3 6% 7% 43%	6014
	11th to 20th	Day	14% 6% 2 5% 3 3 4 3 6% 9% 45%	5951
	21st to end	Day	15% 7% 3 6% 4 4 4 4 6% 8% 39%	6552
September	1st to 10th	Day	13% 6% 3 7% 4 4 5% 4 5% 8% 41%	2494
	11th to 20th	Day	12% 5% 2 6% 4 4 4 4 5% 9% 45%	2310
	21st to end	Day	18% 7% 3 7% 4 5% 4 4 5% 6% 37%	2288
October	1st to 10th	Day	19% 8% 2 8% 4 5% 4 3 4 6% 36%	2027
	11th to 20th	Day	23% 14% 4 10% 5% 5% 4 3 5% 6% 22%	2000
	21st to end	Day	28% 15% 4 10% 5% 4 4 2 4 5% 19%	2120
November	1st to 10th	Day	19% 18% 4 10% 5% 4 4 4 5% 7% 21%	1804
	11th to 20th	Day	16% 21% 5% 11% 6% 6% 4 4 4 5% 18%	1680
	21st to end	Day	20% 27% 7% 11% 5% 4 4 4 4 4 10%	1680
December	1st to 10th	Day	15% 30% 10% 13% 5% 4 4 3 3 4 9%	2680
	11th to 20th	Day	20% 25% 7% 16% 6% 4 3 2 3 5% 10%	2879
	21st to end	Day	27% 22% 6% 15% 5% 5% 4 2 3 3 8%	3553
January	1st to 10th	Night	13% 19% 11% 21% 7% 5% 4 3 3 3 11%	8794
	11th to 20th	Night	11% 23% 10% 22% 10% 5% 4 2 3 3 7%	8100
	21st to end	Night	10% 17% 9% 19% 10% 9% 5% 3 3 3 12%	8401
February	1st to 10th	Night	12% 20% 5% 16% 9% 6% 5% 4 5% 3 15%	2730
	11th to 20th	Night	13% 16% 7% 15% 9% 5% 4 3 4 5% 19%	2663
	21st to end	Night	15% 15% 6% 11% 7% 5% 5% 4 5% 5% 22%	2118
March	1st to 10th	Night	14% 12% 5% 10% 5% 4 4 3 5% 6% 30%	5164
	11th to 20th	Night	11% 12% 5% 10% 6% 5% 5% 4 5% 7% 30%	5089
	21st to end	Night	20% 12% 5% 8% 4 4 4 3 4 5% 30%	5588
April	1st to 10th	Night	20% 11% 3 8% 5% 5% 4 3 5% 6% 31%	2208
	11th to 20th	Night	18% 9% 3 7% 4 4 5% 3 5% 6% 36%	1874
	21st to end	Night	19% 9% 3 8% 5% 4 4 4 5% 5% 33%	1890
May	1st to 10th	Night	14% 7% 3 8% 5% 5% 4 3 6% 7% 37%	5257
	11th to 20th	Night	16% 7% 2 7% 5% 4 4 3 5% 6% 41%	4883
	21st to end	Night	18% 6% 2 6% 3 3 3 3 5% 7% 43%	5114
June	1st to 10th	Night	13% 8% 2 7% 5% 4 4 3 6% 7% 41%	1517
	11th to 20th	Night	11% 5% 3 5% 4 5% 5% 4 7% 9% 41%	1470
	21st to end	Night	14% 7% 3 6% 4 4 5% 4 6% 8% 40%	1470
July	1st to 10th	Night	12% 8% 3 6% 4 4 4 3 5% 8% 42%	4110
	11th to 20th	Night	11% 5% 2 5% 4 4 4 3 6% 8% 50%	4246
	21st to end	Night	10% 7% 2 5% 4 4 4 3 6% 8% 48%	5737
August	1st to 10th	Night	14% 8% 2 7% 4 4 3 3 5% 7% 42%	4135
	11th to 20th	Night	13% 6% 2 5% 3 4 4 3 4 7% 47%	4095
	21st to end	Night	15% 9% 3 7% 4 4 4 4 5% 7% 39%	4532
September	1st to 10th	Night	11% 4 2 6% 4 3 4 5% 7% 7% 47%	2117
	11th to 20th	Night	11% 5% 2 6% 3 5% 4 4 5% 7% 49%	2310
	21st to end	Night	16% 7% 2 8% 5% 5% 5% 3 4 6% 38%	2289
October	1st to 10th	Night	17% 7% 3 7% 5% 5% 4 3 6% 6% 36%	2372
	11th to 20th	Night	24% 11% 4 10% 5% 4 4 3 6% 5% 24%	2400
	21st to end	Night	25% 13% 4 10% 5% 4 5% 4 4 6% 21%	2717
November	1st to 10th	Night	18% 16% 4 10% 5% 5% 4 3 4 5% 24%	2713
	11th to 20th	Night	17% 20% 5% 10% 6% 6% 4 4 5% 6% 18%	2940
	21st to end	Night	23% 24% 5% 9% 6% 4 4 3 4 5% 13%	2940
December	1st to 10th	Night	16% 26% 8% 14% 6% 5% 4 3 5% 5% 8%	4720
	11th to 20th	Night	15% 26% 9% 17% 6% 4 4 3 4 3 9%	5524
	21st to end	Night	23% 23% 7% 16% 7% 6% 3 2 3 3 8%	7667

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	77% 6% 8% 6% 2	4129
	11th to 20th	Day	89% 4 3 2 1	4823
	21st to end	Day	78% 7% 8% 4 2	5780
February	1st to 10th	Day	76% 6% 8% 8% 2	1890
	11th to 20th	Day	70% 8% 11% 7% 4	1852
	21st to end	Day	68% 5% 11% 12% 4	1683
March	1st to 10th	Day	57% 5% 15% 12% 10% 1	4898
	11th to 20th	Day	59% 6% 13% 15% 6% 1	5090
	21st to end	Day	57% 6% 13% 16% 8% 1	5586
April	1st to 10th	Day	55% 5% 10% 18% 10%	2420
	11th to 20th	Day	49% 4 8% 22% 16% 1	2702
	21st to end	Day	48% 6% 12% 20% 11% 3	2730
May	1st to 10th	Day	41% 6% 14% 22% 14% 3	7651
	11th to 20th	Day	42% 7% 12% 21% 17% 1	7977
	21st to end	Day	41% 5% 10% 25% 16% 3	9061
June	1st to 10th	Day	40% 8% 10% 25% 16% 1	3098
	11th to 20th	Day	37% 6% 13% 25% 17% 1	3150
	21st to end	Day	40% 7% 12% 25% 13% 2	3150
July	1st to 10th	Day	39% 5% 17% 24% 13% 1	8806
	11th to 20th	Day	29% 4 13% 39% 14% 1	8631
	21st to end	Day	31% 5% 14% 34% 15% 1	8156
August	1st to 10th	Day	39% 6% 16% 23% 15% 2	6001
	11th to 20th	Day	36% 6% 20% 29% 9%	5990
	21st to end	Day	41% 6% 17% 27% 8% 1	6552
September	1st to 10th	Day	40% 8% 14% 25% 12% 1	2494
	11th to 20th	Day	35% 7% 15% 30% 12%	2310
	21st to end	Day	48% 7% 12% 21% 11% 1	2288
October	1st to 10th	Day	41% 7% 14% 26% 12% 1	3300
	11th to 20th	Day	54% 6% 11% 20% 9%	3240
	21st to end	Day	60% 5% 14% 16% 5%	3409
November	1st to 10th	Day	63% 7% 11% 14% 5%	1804
	11th to 20th	Day	66% 10% 12% 8% 5%	1680
	21st to end	Day	76% 8% 10% 6%	1680
December	1st to 10th	Day	78% 7% 10% 4 1	2680
	11th to 20th	Day	77% 8% 8% 6% 1	2878
	21st to end	Day	82% 6% 6% 5% 1	3553
January	1st to 10th	Night	75% 7% 9% 6% 2	8794
	11th to 20th	Night	81% 6% 5% 5% 2	8144
	21st to end	Night	75% 6% 9% 6% 4	8401
February	1st to 10th	Night	72% 6% 9% 10% 3	2730
	11th to 20th	Night	67% 7% 11% 11% 4	2665
	21st to end	Night	61% 8% 13% 12% 6%	2118
March	1st to 10th	Night	52% 7% 15% 15% 10% 1	5174
	11th to 20th	Night	51% 7% 16% 17% 8% 1	5090
	21st to end	Night	55% 7% 10% 15% 12% 1	5588
April	1st to 10th	Night	53% 5% 10% 20% 10% 1	2208
	11th to 20th	Night	48% 5% 9% 21% 16% 1	1874
	21st to end	Night	51% 5% 11% 16% 15% 2	1890
May	1st to 10th	Night	44% 6% 9% 21% 16% 4	5264
	11th to 20th	Night	42% 6% 9% 22% 19% 1	4884
	21st to end	Night	41% 5% 8% 26% 17% 2	5115
June	1st to 10th	Night	40% 6% 11% 20% 20% 3	1517
	11th to 20th	Night	37% 6% 13% 24% 18% 1	1470
	21st to end	Night	41% 6% 12% 27% 13% 2	1470
July	1st to 10th	Night	38% 5% 17% 23% 15% 3	4075
	11th to 20th	Night	31% 5% 11% 35% 16% 1	4204
	21st to end	Night	34% 5% 11% 31% 19% 1	5606
August	1st to 10th	Night	41% 5% 13% 23% 17% 1	4124
	11th to 20th	Night	36% 6% 18% 29% 10% 1	4122
	21st to end	Night	43% 6% 12% 27% 10% 1	4532
September	1st to 10th	Night	32% 9% 15% 29% 14% 1	2117
	11th to 20th	Night	33% 7% 15% 30% 14%	2310
	21st to end	Night	46% 7% 12% 22% 11% 1	2289
October	1st to 10th	Night	36% 8% 12% 27% 16%	3879
	11th to 20th	Night	52% 5% 14% 19% 10%	3899
	21st to end	Night	53% 8% 15% 18% 5%	4378
November	1st to 10th	Night	59% 7% 13% 16% 5%	2713
	11th to 20th	Night	65% 8% 14% 8% 4 1	2940
	21st to end	Night	73% 9% 11% 6% 1	2940
December	1st to 10th	Night	77% 7% 12% 3 1	4720
	11th to 20th	Night	77% 7% 9% 6% 2	5524
	21st to end	Night	83% 5% 8% 4 1	7667

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	23% 22% 37% 13% 4 1	226
	11th to 20th	Day	21% 19% 36% 17% 6% 1	330
	21st to end	Day	26% 18% 30% 21% 5% 1	363
February	1st to 10th	Day	20% 25% 34% 17% 4	330
	11th to 20th	Day	23% 20% 36% 18% 3	330
	21st to end	Day	20% 25% 37% 17% 1	273
March	1st to 10th	Day	24% 16% 32% 22% 5% 1	466
	11th to 20th	Day	23% 16% 31% 23% 6% 1	540
	21st to end	Day	25% 14% 29% 25% 6% 1	594
April	1st to 10th	Day	22% 15% 32% 21% 9% 1	540
	11th to 20th	Day	27% 14% 27% 18% 11% 4	532
	21st to end	Day	25% 11% 30% 23% 10% 1	540
May	1st to 10th	Day	20% 9% 30% 27% 12% 2	543
	11th to 20th	Day	16% 9% 28% 27% 17% 4	567
	21st to end	Day	15% 8% 24% 30% 18% 4	617
June	1st to 10th	Day	13% 8% 27% 34% 16% 2	728
	11th to 20th	Day	13% 7% 28% 34% 14% 3	780
	21st to end	Day	17% 6% 28% 30% 15% 4	780
July	1st to 10th	Day	11% 4 25% 35% 20% 4	771
	11th to 20th	Day	13% 6% 26% 32% 17% 6%	766
	21st to end	Day	11% 4 23% 39% 17% 6%	620
August	1st to 10th	Day	13% 4 22% 31% 24% 7%	566
	11th to 20th	Day	14% 4 18% 32% 23% 7%	559
	21st to end	Day	16% 8% 22% 30% 18% 7%	627
September	1st to 10th	Day	15% 10% 21% 30% 18% 6%	570
	11th to 20th	Day	10% 7% 20% 27% 24% 12%	570
	21st to end	Day	18% 10% 20% 27% 20% 4	562
October	1st to 10th	Day	21% 12% 25% 22% 15% 4	530
	11th to 20th	Day	22% 18% 32% 21% 5% 1	530
	21st to end	Day	31% 18% 27% 19% 4	503
November	1st to 10th	Day	28% 19% 28% 17% 7% 1	304
	11th to 20th	Day	24% 21% 33% 17% 3 1	220
	21st to end	Day	27% 20% 39% 13% 1	220
December	1st to 10th	Day	26% 25% 30% 14% 4	220
	11th to 20th	Day	31% 22% 30% 12% 4	220
	21st to end	Day	37% 18% 32% 10% 3	242
January	1st to 10th	Night	23% 18% 34% 20% 5%	1050
	11th to 20th	Night	27% 19% 31% 18% 6%	1005
	21st to end	Night	20% 15% 33% 25% 6% 1	924
February	1st to 10th	Night	20% 18% 36% 21% 5%	840
	11th to 20th	Night	18% 17% 34% 24% 7%	823
	21st to end	Night	21% 15% 37% 23% 4	692
March	1st to 10th	Night	18% 14% 37% 24% 7%	840
	11th to 20th	Night	20% 13% 36% 24% 6% 1	840
	21st to end	Night	20% 12% 29% 28% 10% 1	924
April	1st to 10th	Night	24% 12% 29% 28% 6% 1	840
	11th to 20th	Night	21% 9% 30% 27% 11% 3	630
	21st to end	Night	23% 8% 25% 29% 14% 1	630
May	1st to 10th	Night	16% 6% 23% 37% 16% 2	630
	11th to 20th	Night	18% 5% 19% 37% 20% 1	504
	21st to end	Night	14% 4 24% 36% 20% 3	455
June	1st to 10th	Night	15% 4 26% 36% 16% 3	420
	11th to 20th	Night	11% 8% 24% 36% 20%	420
	21st to end	Night	14% 5% 22% 37% 21% 1	420
July	1st to 10th	Night	10% 3 18% 47% 20% 2	410
	11th to 20th	Night	10% 3 23% 32% 28% 3	453
	21st to end	Night	9% 3 19% 42% 24% 3	690
August	1st to 10th	Night	11% 3 20% 34% 29% 3	627
	11th to 20th	Night	11% 4 17% 35% 28% 6%	624
	21st to end	Night	14% 6% 19% 31% 26% 4	693
September	1st to 10th	Night	12% 7% 20% 35% 20% 6%	835
	11th to 20th	Night	12% 5% 20% 32% 25% 6%	840
	21st to end	Night	17% 8% 21% 27% 20% 6%	833
October	1st to 10th	Night	20% 8% 27% 27% 16% 2	800
	11th to 20th	Night	29% 15% 23% 23% 8% 2	800
	21st to end	Night	31% 14% 27% 22% 5%	880
November	1st to 10th	Night	27% 15% 29% 21% 7% 1	820
	11th to 20th	Night	25% 19% 30% 18% 8%	840
	21st to end	Night	33% 17% 30% 17% 3	840
December	1st to 10th	Night	27% 23% 32% 14% 4	840
	11th to 20th	Night	24% 21% 37% 14% 4	920
	21st to end	Night	33% 17% 31% 15% 4	1155

Page generated at 2026-09-26 04:18:38. Version ac07

Copyright © 2026 Attilla Danko.