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 2025-04-26.

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% 10% 4 9% 5% 5% 5% 4 5% 7% 32%	114431
	Night	14% 11% 4 10% 6% 5% 5% 4 5% 6% 30%	114166
Transparency	Day	50% 7% 13% 20% 10% 1	118062
	Night	53% 7% 12% 18% 10% 1	118700
Seeing	Day	18% 11% 28% 27% 13% 4	15343
	Night	20% 11% 30% 27% 11% 1	24379

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% 13% 6% 11% 7% 5% 5% 4 5% 4 26%	3597
	11th to 20th	Day	9% 16% 7% 17% 9% 9% 7% 4 4 5% 14%	3811
	21st to end	Day	13% 19% 8% 15% 7% 5% 4 4 5% 5% 15%	4466
February	1st to 10th	Day	13% 17% 7% 15% 9% 5% 4 4 5% 4 19%	1800
	11th to 20th	Day	11% 15% 7% 12% 7% 6% 3 3 5% 6% 24%	1753
	21st to end	Day	16% 15% 6% 12% 7% 6% 4 3 3 5% 22%	1517
March	1st to 10th	Day	19% 11% 4 10% 6% 5% 4 3 4 5% 30%	4932
	11th to 20th	Day	11% 12% 6% 10% 6% 6% 6% 4 6% 7% 27%	4980
	21st to end	Day	18% 12% 4 10% 5% 3 3 3 4 5% 33%	5465
April	1st to 10th	Day	18% 13% 3 9% 5% 4 5% 3 4 5% 30%	2370
	11th to 20th	Day	20% 11% 2 6% 4 3 4 3 5% 6% 36%	2467
	21st to end	Day	20% 11% 3 7% 5% 4 3 3 4 6% 34%	2535
May	1st to 10th	Day	17% 8% 3 7% 5% 4 5% 4 6% 6% 35%	4155
	11th to 20th	Day	15% 8% 3 7% 5% 4 4 3 6% 8% 37%	4398
	21st to end	Day	14% 6% 2 6% 3 4 4 4 5% 7% 45%	4837
June	1st to 10th	Day	17% 7% 2 6% 5% 5% 4 4 6% 7% 37%	2660
	11th to 20th	Day	12% 5% 2 5% 5% 5% 5% 4 7% 9% 40%	2771
	21st to end	Day	16% 7% 3 6% 5% 5% 4 4 6% 8% 38%	2850
July	1st to 10th	Day	11% 5% 2 7% 5% 6% 5% 5% 7% 10% 37%	4728
	11th to 20th	Day	10% 5% 2 6% 4 5% 4 5% 6% 8% 46%	4440
	21st to end	Day	8% 5% 3 6% 4 5% 4 4 7% 8% 46%	4596
August	1st to 10th	Day	15% 7% 3 6% 4 4 4 4 6% 9% 39%	4104
	11th to 20th	Day	13% 6% 3 6% 4 5% 5% 4 7% 10% 37%	4044
	21st to end	Day	7% 6% 2 7% 4 4 5% 5% 6% 8% 45%	4377
September	1st to 10th	Day	13% 7% 2 8% 4 5% 4 3 5% 8% 41%	2280
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 3 5% 7% 46%	2177
	21st to end	Day	16% 6% 3 7% 5% 5% 5% 5% 6% 6% 37%	2047
October	1st to 10th	Day	17% 9% 3 7% 5% 4 5% 3 6% 7% 33%	1900
	11th to 20th	Day	21% 10% 4 9% 4 6% 5% 4 6% 5% 26%	1900
	21st to end	Day	24% 11% 4 9% 6% 5% 5% 4 5% 5% 21%	2090
November	1st to 10th	Day	16% 13% 4 9% 6% 4 5% 4 6% 8% 25%	1638
	11th to 20th	Day	16% 13% 5% 9% 6% 5% 6% 6% 5% 6% 22%	1600
	21st to end	Day	18% 18% 5% 10% 6% 6% 7% 4 4 6% 16%	1600
December	1st to 10th	Day	15% 20% 7% 13% 8% 6% 5% 3 6% 5% 11%	2600
	11th to 20th	Day	16% 19% 6% 11% 6% 6% 4 3 5% 6% 18%	2986
	21st to end	Day	23% 18% 6% 14% 6% 4 4 3 4 3 15%	3960
January	1st to 10th	Night	13% 17% 8% 14% 7% 5% 5% 3 5% 5% 18%	6349
	11th to 20th	Night	11% 14% 7% 14% 9% 7% 6% 4 6% 6% 16%	6070
	21st to end	Night	13% 15% 6% 13% 6% 5% 5% 4 5% 6% 21%	6490
February	1st to 10th	Night	11% 17% 6% 14% 9% 6% 5% 4 5% 5% 18%	2600
	11th to 20th	Night	12% 14% 6% 13% 6% 4 5% 4 5% 5% 24%	2533
	21st to end	Night	14% 14% 5% 11% 7% 6% 5% 4 5% 5% 25%	2110
March	1st to 10th	Night	15% 11% 4 11% 5% 5% 5% 4 5% 6% 29%	4908
	11th to 20th	Night	9% 11% 5% 8% 6% 6% 6% 5% 7% 7% 31%	4979
	21st to end	Night	19% 9% 4 9% 5% 4 4 3 5% 5% 32%	5467
April	1st to 10th	Night	18% 12% 4 9% 5% 6% 3 3 5% 6% 29%	2030
	11th to 20th	Night	17% 9% 3 7% 4 3 5% 4 5% 5% 37%	1897
	21st to end	Night	17% 10% 3 9% 5% 5% 5% 3 6% 7% 33%	1761
May	1st to 10th	Night	17% 7% 2 6% 4 4 4 3 5% 7% 40%	2783
	11th to 20th	Night	15% 7% 3 6% 4 4 4 4 6% 8% 40%	2495
	21st to end	Night	10% 5% 2 5% 4 4 4 4 5% 8% 49%	2738
June	1st to 10th	Night	14% 7% 3 6% 4 4 4 5% 6% 7% 39%	1520
	11th to 20th	Night	9% 6% 2 7% 4 4 5% 4 7% 9% 43%	1401
	21st to end	Night	13% 7% 2 8% 5% 5% 5% 4 6% 8% 38%	1330
July	1st to 10th	Night	7% 5% 2 6% 5% 5% 5% 4 6% 6% 49%	2236
	11th to 20th	Night	12% 5% 1 5% 4 4 4 3 5% 7% 50%	2520
	21st to end	Night	8% 5% 2 5% 4 5% 5% 4 6% 9% 48%	2953
August	1st to 10th	Night	10% 6% 2 6% 4 4 5% 4 6% 8% 47%	2825
	11th to 20th	Night	12% 6% 3 6% 3 4 4 3 5% 6% 48%	2785
	21st to end	Night	12% 5% 2 6% 4 4 4 4 6% 7% 46%	3247
September	1st to 10th	Night	9% 5% 2 7% 3 4 5% 4 6% 8% 46%	1900
	11th to 20th	Night	11% 5% 2 5% 5% 4 4 4 5% 8% 50%	2000
	21st to end	Night	16% 7% 2 7% 4 4 3 4 5% 6% 41%	2133
October	1st to 10th	Night	17% 6% 2 7% 5% 5% 5% 4 5% 6% 36%	2280
	11th to 20th	Night	18% 12% 4 9% 5% 5% 5% 3 5% 7% 28%	2280
	21st to end	Night	21% 10% 3 11% 5% 5% 5% 4 5% 6% 25%	2508
November	1st to 10th	Night	17% 11% 3 7% 6% 5% 5% 3 5% 6% 32%	2654
	11th to 20th	Night	16% 15% 4 9% 6% 6% 5% 4 6% 7% 24%	2800
	21st to end	Night	18% 15% 5% 9% 6% 6% 6% 5% 6% 6% 18%	2800
December	1st to 10th	Night	15% 19% 6% 13% 7% 6% 5% 4 6% 6% 13%	4580
	11th to 20th	Night	14% 19% 6% 15% 7% 6% 5% 4 6% 6% 13%	5208
	21st to end	Night	22% 19% 7% 15% 6% 5% 4 3 3 3 13%	6996

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	59% 7% 11% 13% 9%	3598
	11th to 20th	Day	72% 7% 8% 8% 4	3844
	21st to end	Day	68% 7% 9% 9% 7%	4466
February	1st to 10th	Day	67% 7% 9% 13% 4 1	1800
	11th to 20th	Day	60% 7% 10% 14% 7% 1	1762
	21st to end	Day	66% 4 9% 14% 6%	1517
March	1st to 10th	Day	55% 7% 13% 11% 13%	4935
	11th to 20th	Day	53% 6% 16% 17% 7% 2	4980
	21st to end	Day	51% 6% 10% 19% 13% 1	5465
April	1st to 10th	Day	55% 5% 9% 19% 10% 1	2370
	11th to 20th	Day	49% 5% 10% 21% 14%	2467
	21st to end	Day	51% 6% 10% 19% 12% 3	2535
May	1st to 10th	Day	45% 8% 12% 21% 12% 1	4167
	11th to 20th	Day	42% 9% 14% 24% 10% 1	4402
	21st to end	Day	38% 8% 13% 22% 16% 3	4837
June	1st to 10th	Day	44% 7% 12% 23% 13%	2660
	11th to 20th	Day	38% 8% 13% 25% 15% 1	2771
	21st to end	Day	42% 7% 15% 22% 12% 1	2850
July	1st to 10th	Day	39% 7% 18% 22% 13% 1	4655
	11th to 20th	Day	35% 6% 16% 34% 9% 1	4365
	21st to end	Day	34% 7% 13% 29% 16% 1	4449
August	1st to 10th	Day	41% 7% 16% 24% 11% 1	4091
	11th to 20th	Day	40% 7% 18% 24% 10%	4083
	21st to end	Day	34% 7% 15% 33% 10% 1	4377
September	1st to 10th	Day	40% 6% 14% 28% 10% 1	2280
	11th to 20th	Day	36% 7% 15% 30% 12%	2177
	21st to end	Day	46% 9% 13% 24% 9%	2047
October	1st to 10th	Day	43% 7% 13% 27% 10% 1	3160
	11th to 20th	Day	48% 7% 14% 22% 8%	3140
	21st to end	Day	56% 7% 14% 17% 5%	3428
November	1st to 10th	Day	56% 8% 13% 16% 5%	1638
	11th to 20th	Day	59% 11% 11% 13% 5% 1	1600
	21st to end	Day	67% 10% 11% 10% 2	1600
December	1st to 10th	Day	74% 6% 12% 7% 1	2600
	11th to 20th	Day	67% 8% 9% 11% 5%	2986
	21st to end	Day	73% 6% 6% 9% 6%	3960
January	1st to 10th	Night	67% 7% 8% 12% 6%	6349
	11th to 20th	Night	67% 8% 10% 9% 5%	6112
	21st to end	Night	63% 7% 11% 9% 9% 1	6490
February	1st to 10th	Night	66% 7% 10% 13% 3 1	2600
	11th to 20th	Night	59% 7% 12% 15% 6%	2535
	21st to end	Night	58% 7% 12% 16% 6%	2110
March	1st to 10th	Night	54% 6% 10% 16% 11% 3	4918
	11th to 20th	Night	49% 7% 18% 17% 8% 1	4980
	21st to end	Night	51% 6% 11% 18% 12% 2	5467
April	1st to 10th	Night	56% 6% 9% 18% 10% 1	2030
	11th to 20th	Night	47% 6% 9% 21% 15% 2	1897
	21st to end	Night	50% 7% 11% 14% 15% 1	1761
May	1st to 10th	Night	42% 7% 14% 18% 17% 2	2790
	11th to 20th	Night	40% 9% 14% 24% 12% 2	2496
	21st to end	Night	33% 8% 13% 27% 18% 2	2739
June	1st to 10th	Night	42% 7% 12% 22% 15% 2	1520
	11th to 20th	Night	35% 7% 14% 25% 18% 1	1401
	21st to end	Night	43% 7% 13% 22% 13% 1	1330
July	1st to 10th	Night	35% 7% 15% 24% 18% 2	2201
	11th to 20th	Night	34% 5% 14% 32% 15%	2472
	21st to end	Night	32% 7% 13% 31% 17% 1	2859
August	1st to 10th	Night	36% 6% 16% 26% 16% 1	2814
	11th to 20th	Night	36% 7% 17% 25% 14% 1	2812
	21st to end	Night	36% 7% 12% 33% 11% 1	3247
September	1st to 10th	Night	35% 9% 16% 27% 12% 1	1900
	11th to 20th	Night	33% 7% 14% 30% 15%	2000
	21st to end	Night	43% 6% 13% 27% 10%	2133
October	1st to 10th	Night	37% 8% 12% 26% 18%	3800
	11th to 20th	Night	48% 7% 15% 21% 9%	3779
	21st to end	Night	50% 8% 15% 22% 6%	4120
November	1st to 10th	Night	52% 7% 13% 19% 8%	2654
	11th to 20th	Night	59% 9% 12% 13% 6% 1	2800
	21st to end	Night	66% 10% 13% 10% 2	2800
December	1st to 10th	Night	71% 7% 14% 6% 1	4580
	11th to 20th	Night	71% 8% 9% 8% 3	5208
	21st to end	Night	76% 5% 7% 8% 5%	6996

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	16% 20% 40% 16% 7% 2	200
	11th to 20th	Day	19% 18% 36% 20% 6% 1	251
	21st to end	Day	24% 14% 32% 24% 6% 1	330
February	1st to 10th	Day	25% 20% 37% 14% 4	300
	11th to 20th	Day	21% 20% 37% 21% 2	300
	21st to end	Day	25% 24% 29% 22%	259
March	1st to 10th	Day	21% 12% 39% 24% 4	500
	11th to 20th	Day	15% 20% 35% 25% 6%	500
	21st to end	Day	27% 11% 33% 20% 9%	550
April	1st to 10th	Day	20% 15% 36% 22% 7% 1	500
	11th to 20th	Day	25% 16% 26% 22% 9% 3	492
	21st to end	Day	24% 13% 29% 24% 8% 2	480
May	1st to 10th	Day	21% 9% 27% 28% 12% 2	463
	11th to 20th	Day	16% 6% 27% 31% 18% 3	487
	21st to end	Day	15% 6% 23% 33% 17% 5%	529
June	1st to 10th	Day	18% 6% 26% 33% 16% 1	490
	11th to 20th	Day	13% 6% 25% 35% 16% 4	601
	21st to end	Day	17% 7% 26% 34% 13% 2	680
July	1st to 10th	Day	9% 6% 21% 38% 21% 5%	653
	11th to 20th	Day	14% 3 23% 33% 19% 8%	484
	21st to end	Day	8% 4 23% 39% 18% 7%	532
August	1st to 10th	Day	13% 4 19% 33% 23% 7%	486
	11th to 20th	Day	13% 6% 15% 31% 26% 9%	479
	21st to end	Day	11% 8% 22% 29% 23% 7%	539
September	1st to 10th	Day	15% 7% 23% 29% 20% 7%	490
	11th to 20th	Day	11% 4 20% 27% 25% 13%	490
	21st to end	Day	16% 9% 27% 23% 21% 4	490
October	1st to 10th	Day	20% 11% 28% 22% 13% 6%	490
	11th to 20th	Day	20% 18% 31% 22% 7% 2	490
	21st to end	Day	27% 16% 31% 21% 5%	539
November	1st to 10th	Day	24% 21% 24% 23% 8%	249
	11th to 20th	Day	20% 23% 34% 18% 5% 1	200
	21st to end	Day	26% 17% 39% 17% 2	200
December	1st to 10th	Day	23% 24% 34% 16% 4 1	200
	11th to 20th	Day	26% 25% 30% 16% 4 1	200
	21st to end	Day	29% 20% 33% 15% 3	220
January	1st to 10th	Night	23% 18% 34% 19% 5% 1	800
	11th to 20th	Night	26% 13% 33% 23% 5% 1	800
	21st to end	Night	20% 11% 32% 30% 6% 1	880
February	1st to 10th	Night	20% 13% 40% 25% 3	800
	11th to 20th	Night	18% 14% 37% 25% 5%	783
	21st to end	Night	22% 13% 35% 25% 4	660
March	1st to 10th	Night	20% 13% 35% 28% 4	800
	11th to 20th	Night	17% 13% 39% 26% 5% 1	800
	21st to end	Night	21% 10% 31% 28% 9%	880
April	1st to 10th	Night	25% 11% 31% 27% 5%	800
	11th to 20th	Night	21% 10% 31% 27% 11% 1	713
	21st to end	Night	20% 9% 32% 28% 11%	587
May	1st to 10th	Night	19% 5% 23% 36% 15% 1	546
	11th to 20th	Night	19% 5% 25% 37% 13% 1	374
	21st to end	Night	12% 4 25% 40% 18%	411
June	1st to 10th	Night	15% 6% 28% 36% 14% 1	380
	11th to 20th	Night	11% 6% 26% 40% 17% 1	380
	21st to end	Night	14% 8% 22% 38% 16% 1	380
July	1st to 10th	Night	8% 4 19% 46% 22% 2	370
	11th to 20th	Night	11% 6% 20% 40% 21% 2	368
	21st to end	Night	10% 3 22% 40% 24% 1	542
August	1st to 10th	Night	11% 3 18% 38% 28% 2	567
	11th to 20th	Night	6% 5% 20% 36% 30% 3	564
	21st to end	Night	13% 5% 23% 32% 24% 2	698
September	1st to 10th	Night	12% 5% 24% 34% 21% 4	760
	11th to 20th	Night	13% 5% 21% 31% 23% 7%	760
	21st to end	Night	19% 8% 20% 30% 18% 5%	760
October	1st to 10th	Night	19% 7% 33% 25% 14% 2	760
	11th to 20th	Night	24% 14% 31% 22% 8% 1	760
	21st to end	Night	27% 15% 32% 22% 4	836
November	1st to 10th	Night	23% 15% 30% 23% 9% 1	780
	11th to 20th	Night	23% 18% 34% 18% 6% 1	800
	21st to end	Night	28% 17% 32% 20% 4	800
December	1st to 10th	Night	27% 21% 32% 16% 4	800
	11th to 20th	Night	24% 18% 38% 16% 4 1	800
	21st to end	Night	30% 15% 34% 19% 2	880

Page generated at 2025-04-23 09:25:05. Version ac07

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