Orillia
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Orillia clear sky chart from 2005-11-06 to 2026-08-30.

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% 10% 4 9% 5% 5% 5% 4 5% 7% 33%	145298
	Night	14% 11% 4 10% 6% 5% 5% 4 5% 6% 30%	136920
Transparency	Day	49% 6% 12% 21% 10% 1	148886
	Night	52% 7% 12% 18% 10% 1	141422
Seeing	Day	18% 11% 28% 26% 12% 3	17164
	Night	20% 11% 30% 28% 11% 1	25933

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% 14% 6% 12% 7% 6% 6% 4 5% 5% 23%	4661
	11th to 20th	Day	8% 18% 8% 17% 10% 9% 6% 4 4 4 11%	4961
	21st to end	Day	10% 16% 7% 15% 8% 7% 5% 4 5% 6% 17%	5780
February	1st to 10th	Day	13% 17% 7% 15% 9% 5% 4 4 5% 4 19%	1890
	11th to 20th	Day	12% 14% 7% 12% 7% 7% 3 4 5% 6% 23%	1843
	21st to end	Day	16% 15% 6% 13% 7% 6% 4 3 3 5% 22%	1590
March	1st to 10th	Day	18% 11% 4 10% 6% 5% 4 3 4 5% 30%	5042
	11th to 20th	Day	11% 12% 6% 10% 6% 6% 6% 4 6% 7% 27%	5090
	21st to end	Day	18% 12% 4 10% 5% 3 4 3 4 5% 32%	5586
April	1st to 10th	Day	18% 12% 4 9% 5% 5% 5% 3 4 5% 29%	2488
	11th to 20th	Day	20% 11% 2 6% 4 3 4 3 5% 6% 35%	2592
	21st to end	Day	20% 10% 3 7% 5% 4 4 3 4 6% 34%	2730
May	1st to 10th	Day	16% 7% 3 7% 4 4 4 4 6% 7% 38%	7716
	11th to 20th	Day	14% 8% 3 8% 5% 4 4 3 5% 7% 38%	8221
	21st to end	Day	18% 7% 2 7% 3 4 4 3 5% 6% 41%	9060
June	1st to 10th	Day	16% 7% 2 6% 5% 5% 4 4 6% 7% 38%	2940
	11th to 20th	Day	12% 5% 2 6% 5% 5% 5% 4 8% 9% 39%	3063
	21st to end	Day	15% 6% 3 6% 5% 5% 4 4 6% 9% 38%	3150
July	1st to 10th	Day	11% 6% 2 7% 5% 5% 5% 4 6% 10% 39%	8819
	11th to 20th	Day	8% 4 2 6% 4 4 4 4 6% 9% 50%	8280
	21st to end	Day	8% 5% 2 6% 4 5% 5% 4 7% 9% 46%	8579
August	1st to 10th	Day	14% 7% 2 6% 4 4 4 4 6% 9% 39%	4364
	11th to 20th	Day	13% 6% 3 6% 4 4 5% 4 7% 10% 38%	4304
	21st to end	Day	7% 6% 2 7% 4 4 5% 4 6% 8% 45%	4629
September	1st to 10th	Day	13% 6% 2 8% 4 5% 4 3 5% 8% 41%	2400
	11th to 20th	Day	11% 5% 1 6% 4 4 5% 3 5% 7% 47%	2291
	21st to end	Day	16% 6% 3 7% 5% 5% 5% 5% 6% 6% 37%	2154
October	1st to 10th	Day	17% 9% 3 7% 5% 4 5% 3 6% 7% 35%	2000
	11th to 20th	Day	21% 10% 4 8% 4 6% 5% 3 6% 5% 27%	2000
	21st to end	Day	24% 12% 4 9% 6% 5% 5% 4 5% 5% 22%	2200
November	1st to 10th	Day	17% 13% 4 8% 6% 4 5% 4 6% 7% 26%	1721
	11th to 20th	Day	16% 13% 5% 9% 6% 6% 6% 5% 5% 6% 22%	1680
	21st to end	Day	18% 18% 5% 11% 6% 6% 6% 4 4 6% 16%	1680
December	1st to 10th	Day	15% 20% 7% 13% 8% 6% 5% 3 6% 5% 12%	2680
	11th to 20th	Day	16% 19% 6% 11% 6% 6% 5% 3 5% 6% 18%	3066
	21st to end	Day	23% 18% 6% 14% 6% 4 4 3 4 3 15%	4048
January	1st to 10th	Night	12% 16% 8% 17% 7% 6% 5% 3 5% 5% 17%	8234
	11th to 20th	Night	10% 16% 8% 15% 10% 7% 6% 4 5% 6% 15%	7920
	21st to end	Night	10% 13% 6% 13% 8% 6% 6% 5% 6% 6% 21%	8401
February	1st to 10th	Night	11% 17% 6% 14% 9% 5% 5% 4 5% 6% 19%	2730
	11th to 20th	Night	12% 14% 6% 13% 7% 5% 5% 4 5% 5% 24%	2663
	21st to end	Night	13% 14% 5% 11% 7% 6% 5% 4 6% 5% 24%	2212
March	1st to 10th	Night	14% 11% 4 11% 5% 5% 5% 4 5% 6% 30%	5018
	11th to 20th	Night	9% 11% 5% 8% 6% 6% 6% 5% 7% 7% 30%	5089
	21st to end	Night	19% 9% 4 8% 5% 4 4 3 5% 5% 32%	5588
April	1st to 10th	Night	18% 12% 4 9% 5% 6% 3 3 5% 6% 29%	2131
	11th to 20th	Night	17% 9% 3 7% 5% 4 5% 4 5% 6% 36%	1993
	21st to end	Night	16% 9% 3 9% 5% 4 5% 3 5% 7% 34%	1890
May	1st to 10th	Night	17% 7% 2 6% 4 4 5% 4 5% 8% 37%	5180
	11th to 20th	Night	14% 7% 3 7% 4 4 4 3 5% 7% 41%	4639
	21st to end	Night	17% 5% 2 5% 4 4 4 3 5% 7% 44%	5114
June	1st to 10th	Night	14% 7% 3 6% 4 4 4 4 6% 7% 40%	1680
	11th to 20th	Night	9% 6% 2 7% 5% 4 5% 4 7% 10% 43%	1549
	21st to end	Night	13% 7% 2 8% 5% 5% 5% 4 6% 8% 39%	1470
July	1st to 10th	Night	8% 6% 2 7% 5% 4 5% 4 6% 7% 46%	4162
	11th to 20th	Night	9% 5% 2 5% 4 4 4 3 5% 8% 51%	4680
	21st to end	Night	9% 5% 2 6% 4 4 4 3 6% 9% 48%	5494
August	1st to 10th	Night	10% 6% 2 6% 4 4 5% 4 6% 8% 47%	3005
	11th to 20th	Night	12% 6% 2 6% 3 4 4 3 5% 6% 48%	2965
	21st to end	Night	12% 5% 2 6% 4 4 4 4 6% 7% 46%	3434
September	1st to 10th	Night	9% 5% 2 7% 3 4 5% 4 6% 8% 46%	2000
	11th to 20th	Night	10% 5% 2 5% 5% 4 4 4 5% 8% 50%	2105
	21st to end	Night	16% 7% 3 7% 4 4 3 4 5% 6% 41%	2245
October	1st to 10th	Night	16% 6% 2 7% 5% 5% 5% 4 5% 7% 38%	2400
	11th to 20th	Night	18% 11% 4 9% 5% 5% 5% 3 5% 7% 28%	2400
	21st to end	Night	21% 9% 3 11% 5% 5% 5% 4 5% 6% 26%	2640
November	1st to 10th	Night	16% 11% 3 8% 6% 5% 5% 3 5% 6% 31%	2791
	11th to 20th	Night	15% 15% 4 9% 6% 6% 5% 4 6% 7% 23%	2940
	21st to end	Night	18% 15% 5% 10% 6% 6% 6% 4 6% 6% 18%	2940
December	1st to 10th	Night	15% 19% 6% 13% 7% 6% 5% 4 6% 6% 13%	4720
	11th to 20th	Night	14% 18% 6% 15% 7% 6% 5% 4 6% 6% 14%	5348
	21st to end	Night	22% 19% 7% 16% 6% 5% 4 3 3 3 13%	7150

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	62% 6% 11% 13% 8%	4662
	11th to 20th	Day	75% 6% 7% 7% 4	4994
	21st to end	Day	66% 7% 10% 10% 8%	5780
February	1st to 10th	Day	67% 6% 8% 14% 4 1	1890
	11th to 20th	Day	61% 7% 10% 14% 7% 1	1852
	21st to end	Day	66% 4 9% 14% 6%	1590
March	1st to 10th	Day	55% 7% 13% 11% 13%	5045
	11th to 20th	Day	53% 6% 16% 17% 7% 2	5090
	21st to end	Day	52% 6% 10% 19% 13% 1	5586
April	1st to 10th	Day	55% 6% 9% 19% 10% 1	2488
	11th to 20th	Day	49% 6% 9% 21% 14% 1	2592
	21st to end	Day	51% 6% 10% 19% 12% 3	2730
May	1st to 10th	Day	43% 7% 13% 21% 13% 4	7725
	11th to 20th	Day	44% 7% 11% 21% 16% 1	8225
	21st to end	Day	43% 5% 11% 25% 14% 2	9061
June	1st to 10th	Day	44% 7% 11% 23% 14%	2940
	11th to 20th	Day	38% 8% 14% 26% 14% 1	3063
	21st to end	Day	42% 7% 15% 23% 12% 1	3150
July	1st to 10th	Day	40% 5% 18% 24% 12%	8747
	11th to 20th	Day	30% 5% 13% 37% 13% 1	8205
	21st to end	Day	34% 6% 15% 31% 14%	8390
August	1st to 10th	Day	41% 7% 16% 25% 11% 1	4351
	11th to 20th	Day	40% 7% 19% 25% 10%	4343
	21st to end	Day	34% 7% 15% 33% 10% 1	4629
September	1st to 10th	Day	40% 6% 15% 28% 10% 1	2400
	11th to 20th	Day	35% 7% 14% 31% 13%	2291
	21st to end	Day	46% 9% 13% 24% 9%	2154
October	1st to 10th	Day	42% 7% 13% 27% 10% 1	3260
	11th to 20th	Day	48% 7% 14% 22% 9%	3240
	21st to end	Day	56% 7% 14% 17% 6%	3538
November	1st to 10th	Day	56% 8% 13% 17% 5%	1721
	11th to 20th	Day	59% 11% 12% 13% 5% 1	1680
	21st to end	Day	67% 10% 11% 10% 2	1680
December	1st to 10th	Day	73% 6% 12% 7% 1	2680
	11th to 20th	Day	67% 8% 9% 11% 5%	3066
	21st to end	Day	73% 6% 7% 9% 6%	4048
January	1st to 10th	Night	69% 6% 8% 11% 5%	8234
	11th to 20th	Night	70% 7% 8% 9% 5%	7962
	21st to end	Night	61% 7% 10% 10% 11% 1	8401
February	1st to 10th	Night	65% 7% 10% 14% 4 1	2730
	11th to 20th	Night	60% 6% 12% 15% 6%	2665
	21st to end	Night	59% 7% 12% 16% 6%	2212
March	1st to 10th	Night	53% 6% 10% 16% 11% 3	5028
	11th to 20th	Night	50% 7% 18% 17% 8% 1	5090
	21st to end	Night	51% 6% 11% 18% 13% 2	5588
April	1st to 10th	Night	56% 6% 9% 18% 10% 1	2131
	11th to 20th	Night	47% 6% 9% 21% 15% 2	1993
	21st to end	Night	49% 7% 11% 17% 15% 1	1890
May	1st to 10th	Night	45% 6% 11% 20% 15% 4	5187
	11th to 20th	Night	41% 6% 11% 24% 16% 1	4640
	21st to end	Night	40% 5% 11% 27% 15% 2	5115
June	1st to 10th	Night	41% 7% 11% 22% 17% 2	1680
	11th to 20th	Night	36% 7% 14% 25% 17% 1	1549
	21st to end	Night	43% 7% 14% 23% 13% 1	1470
July	1st to 10th	Night	37% 6% 18% 26% 13% 1	4127
	11th to 20th	Night	33% 4 14% 32% 17%	4632
	21st to end	Night	34% 5% 11% 32% 17% 1	5368
August	1st to 10th	Night	36% 6% 16% 25% 16% 1	2994
	11th to 20th	Night	36% 6% 18% 26% 13% 1	2992
	21st to end	Night	36% 7% 13% 33% 11% 1	3434
September	1st to 10th	Night	34% 9% 16% 28% 11% 1	2000
	11th to 20th	Night	32% 7% 14% 31% 15%	2105
	21st to end	Night	43% 6% 13% 26% 11%	2245
October	1st to 10th	Night	36% 8% 11% 26% 18% 1	3920
	11th to 20th	Night	48% 7% 15% 21% 9%	3899
	21st to end	Night	49% 8% 14% 22% 6%	4252
November	1st to 10th	Night	53% 7% 13% 18% 8%	2791
	11th to 20th	Night	59% 9% 12% 13% 5% 1	2940
	21st to end	Night	66% 10% 12% 10% 2	2940
December	1st to 10th	Night	71% 7% 14% 6% 1	4720
	11th to 20th	Night	70% 8% 10% 9% 3	5348
	21st to end	Night	76% 5% 7% 8% 4	7150

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	17% 20% 39% 16% 6% 1	220
	11th to 20th	Day	19% 20% 37% 18% 5% 1	276
	21st to end	Day	24% 14% 31% 25% 6% 1	363
February	1st to 10th	Day	24% 19% 37% 15% 5%	330
	11th to 20th	Day	21% 18% 38% 21% 2	330
	21st to end	Day	26% 22% 31% 21%	283
March	1st to 10th	Day	21% 12% 39% 24% 4	540
	11th to 20th	Day	18% 20% 33% 23% 5%	540
	21st to end	Day	27% 12% 33% 20% 8%	594
April	1st to 10th	Day	21% 15% 36% 21% 7% 1	540
	11th to 20th	Day	26% 17% 25% 20% 8% 3	532
	21st to end	Day	24% 12% 30% 24% 8% 2	540
May	1st to 10th	Day	21% 11% 30% 26% 10% 2	543
	11th to 20th	Day	17% 6% 29% 29% 16% 3	567
	21st to end	Day	17% 8% 26% 29% 16% 4	617
June	1st to 10th	Day	17% 7% 26% 32% 15% 2	570
	11th to 20th	Day	13% 7% 28% 33% 15% 4	693
	21st to end	Day	17% 7% 28% 33% 12% 2	780
July	1st to 10th	Day	9% 7% 21% 38% 20% 5%	751
	11th to 20th	Day	13% 4 23% 34% 19% 7%	564
	21st to end	Day	7% 4 26% 38% 18% 7%	620
August	1st to 10th	Day	12% 5% 19% 34% 23% 7%	566
	11th to 20th	Day	13% 6% 18% 31% 24% 8%	559
	21st to end	Day	11% 8% 23% 29% 22% 7%	619
September	1st to 10th	Day	15% 8% 22% 28% 20% 8%	530
	11th to 20th	Day	10% 4 20% 27% 25% 15%	530
	21st to end	Day	16% 10% 27% 23% 20% 4	530
October	1st to 10th	Day	19% 11% 28% 22% 15% 6%	530
	11th to 20th	Day	21% 18% 32% 22% 6% 2	530
	21st to end	Day	26% 16% 31% 22% 4	583
November	1st to 10th	Day	27% 19% 25% 22% 7%	272
	11th to 20th	Day	20% 23% 34% 17% 5% 1	220
	21st to end	Day	28% 17% 38% 16% 1	220
December	1st to 10th	Day	23% 24% 33% 16% 4	220
	11th to 20th	Day	27% 25% 30% 15% 3	220
	21st to end	Day	29% 21% 33% 14% 2	242
January	1st to 10th	Night	23% 19% 34% 19% 4 1	840
	11th to 20th	Night	26% 13% 33% 23% 5%	840
	21st to end	Night	19% 11% 32% 30% 6% 1	924
February	1st to 10th	Night	19% 13% 39% 25% 3	840
	11th to 20th	Night	18% 14% 36% 26% 5%	823
	21st to end	Night	23% 14% 35% 25% 4	692
March	1st to 10th	Night	19% 13% 36% 28% 4	840
	11th to 20th	Night	18% 13% 38% 25% 5% 1	840
	21st to end	Night	21% 10% 32% 28% 9%	924
April	1st to 10th	Night	25% 12% 31% 27% 5%	840
	11th to 20th	Night	21% 10% 31% 27% 11% 1	749
	21st to end	Night	19% 9% 32% 28% 12%	630
May	1st to 10th	Night	19% 6% 23% 36% 14% 1	604
	11th to 20th	Night	19% 6% 26% 36% 12% 1	414
	21st to end	Night	14% 4 27% 38% 17%	455
June	1st to 10th	Night	15% 6% 29% 35% 14% 1	420
	11th to 20th	Night	12% 6% 27% 38% 16%	420
	21st to end	Night	14% 7% 23% 40% 15% 1	420
July	1st to 10th	Night	7% 5% 19% 47% 20% 2	410
	11th to 20th	Night	11% 6% 20% 40% 21% 1	408
	21st to end	Night	10% 4 22% 40% 23% 1	600
August	1st to 10th	Night	11% 4 17% 38% 28% 2	627
	11th to 20th	Night	7% 5% 19% 37% 29% 3	624
	21st to end	Night	14% 5% 23% 32% 24% 2	765
September	1st to 10th	Night	12% 6% 24% 33% 21% 4	800
	11th to 20th	Night	12% 5% 21% 31% 24% 7%	800
	21st to end	Night	19% 8% 20% 31% 18% 4	800
October	1st to 10th	Night	19% 7% 32% 26% 15% 2	800
	11th to 20th	Night	24% 13% 31% 22% 8% 1	800
	21st to end	Night	26% 15% 32% 23% 4	880
November	1st to 10th	Night	23% 15% 30% 22% 9% 1	820
	11th to 20th	Night	24% 18% 34% 18% 6% 1	840
	21st to end	Night	28% 17% 32% 19% 3	840
December	1st to 10th	Night	27% 22% 32% 16% 4	840
	11th to 20th	Night	24% 19% 38% 15% 4 1	840
	21st to end	Night	31% 15% 34% 18% 2	924

Page generated at 2026-08-27 04:07:15. Version ac07

Copyright © 2026 Attilla Danko.