Orangeville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Orangeville clear sky chart from 2005-11-06 to 2026-07-01.

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% 6% 5% 5% 4 5% 7% 30%	138876
	Night	13% 11% 5% 11% 6% 5% 5% 4 5% 6% 30%	133439
Transparency	Day	51% 6% 12% 19% 10% 1	142469
	Night	50% 7% 12% 18% 11% 1	137935
Seeing	Day	21% 19% 31% 18% 8% 3	16969
	Night	20% 18% 32% 22% 8% 1	25902

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	14% 15% 7% 20% 7% 5% 4 3 4 5% 17%	4661
	11th to 20th	Day	8% 21% 11% 22% 9% 10% 5% 3 2 3 6%	5203
	21st to end	Day	12% 15% 7% 19% 11% 8% 7% 3 3 5% 10%	5780
February	1st to 10th	Day	12% 17% 6% 16% 11% 5% 6% 4 3 4 16%	1890
	11th to 20th	Day	12% 13% 7% 16% 10% 5% 4 3 5% 6% 18%	1843
	21st to end	Day	15% 16% 6% 11% 8% 6% 5% 4 6% 4 20%	1636
March	1st to 10th	Day	15% 13% 5% 12% 8% 4 3 3 4 5% 27%	5028
	11th to 20th	Day	11% 13% 7% 11% 6% 5% 5% 4 5% 7% 27%	5090
	21st to end	Day	16% 15% 6% 9% 4 4 4 3 4 5% 30%	5586
April	1st to 10th	Day	17% 15% 4 10% 6% 4 4 4 4 7% 27%	2452
	11th to 20th	Day	18% 12% 4 7% 4 5% 4 3 4 6% 34%	2623
	21st to end	Day	18% 12% 4 7% 4 4 4 3 6% 6% 32%	2730
May	1st to 10th	Day	17% 10% 3 7% 5% 4 4 3 5% 7% 34%	7642
	11th to 20th	Day	15% 11% 3 8% 5% 4 5% 3 5% 7% 34%	8061
	21st to end	Day	17% 7% 2 5% 4 4 4 3 5% 6% 43%	9060
June	1st to 10th	Day	14% 7% 3 7% 5% 4 5% 5% 6% 8% 36%	2940
	11th to 20th	Day	12% 6% 2 7% 4 5% 5% 5% 7% 9% 39%	3069
	21st to end	Day	15% 6% 2 6% 5% 5% 5% 4 6% 8% 37%	3150
July	1st to 10th	Day	11% 6% 2 8% 5% 5% 6% 4 7% 10% 36%	6784
	11th to 20th	Day	9% 6% 2 6% 5% 5% 5% 4 6% 8% 44%	6320
	21st to end	Day	8% 5% 2 6% 5% 5% 5% 4 6% 8% 46%	6424
August	1st to 10th	Day	15% 7% 3 7% 5% 5% 5% 4 7% 8% 34%	4234
	11th to 20th	Day	12% 8% 3 8% 6% 5% 6% 4 7% 9% 31%	4174
	21st to end	Day	9% 7% 2 7% 5% 6% 6% 5% 6% 7% 39%	4548
September	1st to 10th	Day	14% 7% 3 7% 5% 4 4 4 6% 7% 38%	2400
	11th to 20th	Day	12% 7% 3 6% 4 5% 4 3 4 9% 43%	2239
	21st to end	Day	16% 8% 3 7% 6% 5% 6% 4 6% 7% 32%	2185
October	1st to 10th	Day	17% 10% 3 8% 5% 4 4 4 5% 6% 33%	2000
	11th to 20th	Day	20% 12% 4 9% 5% 4 4 4 5% 5% 26%	2000
	21st to end	Day	24% 17% 4 8% 4 4 5% 3 5% 6% 19%	2200
November	1st to 10th	Day	13% 17% 4 9% 4 5% 4 3 5% 7% 28%	1770
	11th to 20th	Day	13% 16% 6% 11% 6% 5% 5% 4 5% 7% 23%	1680
	21st to end	Day	15% 20% 7% 12% 6% 5% 4 4 4 7% 17%	1680
December	1st to 10th	Day	15% 25% 10% 14% 5% 4 4 3 4 5% 10%	2680
	11th to 20th	Day	18% 21% 7% 11% 6% 4 4 3 3 5% 16%	3066
	21st to end	Day	21% 21% 7% 16% 7% 4 4 3 4 3 9%	4048
January	1st to 10th	Night	13% 13% 7% 19% 8% 5% 4 3 4 6% 17%	8234
	11th to 20th	Night	9% 16% 9% 21% 14% 9% 5% 3 3 3 8%	7667
	21st to end	Night	10% 12% 6% 16% 9% 8% 7% 4 6% 6% 13%	8401
February	1st to 10th	Night	11% 15% 5% 13% 8% 5% 6% 4 5% 6% 20%	2730
	11th to 20th	Night	11% 12% 6% 15% 9% 5% 5% 4 5% 6% 21%	2663
	21st to end	Night	12% 14% 4 12% 8% 5% 5% 5% 5% 7% 24%	2168
March	1st to 10th	Night	13% 11% 5% 12% 5% 4 5% 4 6% 7% 28%	5030
	11th to 20th	Night	9% 9% 5% 10% 6% 5% 6% 4 7% 8% 33%	5089
	21st to end	Night	18% 10% 3 8% 4 3 4 3 5% 5% 36%	5588
April	1st to 10th	Night	18% 12% 3 10% 5% 4 5% 3 5% 6% 29%	2168
	11th to 20th	Night	16% 10% 3 7% 5% 4 4 4 5% 5% 37%	1964
	21st to end	Night	13% 11% 4 8% 5% 5% 4 3 6% 7% 34%	1890
May	1st to 10th	Night	17% 9% 2 6% 4 4 4 4 5% 6% 39%	5257
	11th to 20th	Night	14% 10% 2 6% 4 4 4 4 5% 6% 40%	4784
	21st to end	Night	17% 6% 2 5% 3 3 3 3 5% 6% 47%	5114
June	1st to 10th	Night	12% 6% 2 6% 5% 5% 3 4 5% 7% 44%	1680
	11th to 20th	Night	9% 5% 2 7% 5% 5% 4 5% 7% 10% 41%	1544
	21st to end	Night	12% 6% 2 7% 4 4 3 4 6% 8% 45%	1470
July	1st to 10th	Night	7% 7% 2 7% 4 4 4 4 5% 7% 48%	3177
	11th to 20th	Night	10% 7% 2 6% 3 4 3 3 5% 7% 50%	3636
	21st to end	Night	8% 6% 2 5% 4 4 4 4 6% 8% 50%	4428
August	1st to 10th	Night	11% 5% 2 5% 4 4 4 4 6% 6% 49%	2915
	11th to 20th	Night	12% 7% 2 5% 4 4 4 4 5% 7% 46%	2875
	21st to end	Night	11% 6% 2 6% 4 4 4 4 6% 6% 48%	3316
September	1st to 10th	Night	9% 5% 3 6% 5% 4 4 3 6% 7% 49%	2000
	11th to 20th	Night	10% 4 2 4 3 3 3 3 6% 7% 54%	2158
	21st to end	Night	16% 9% 3 7% 5% 4 4 2 4 7% 40%	2214
October	1st to 10th	Night	16% 8% 3 7% 5% 4 4 3 5% 7% 39%	2400
	11th to 20th	Night	19% 11% 3 7% 5% 4 5% 3 5% 6% 33%	2400
	21st to end	Night	19% 13% 4 8% 5% 5% 4 4 5% 6% 27%	2640
November	1st to 10th	Night	15% 12% 4 7% 5% 5% 5% 4 5% 6% 31%	2741
	11th to 20th	Night	14% 14% 5% 9% 6% 5% 5% 4 6% 7% 25%	2940
	21st to end	Night	16% 16% 6% 11% 6% 5% 4 4 5% 7% 21%	2940
December	1st to 10th	Night	14% 18% 8% 16% 6% 5% 5% 4 5% 5% 13%	4720
	11th to 20th	Night	12% 21% 9% 16% 6% 5% 4 3 4 5% 15%	5348
	21st to end	Night	21% 20% 8% 17% 6% 5% 4 3 3 4 9%	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	65% 7% 10% 12% 6%	4662
	11th to 20th	Day	78% 7% 6% 5% 3	5237
	21st to end	Day	72% 8% 8% 9% 4	5780
February	1st to 10th	Day	69% 6% 9% 12% 4 1	1890
	11th to 20th	Day	64% 7% 11% 12% 5% 1	1852
	21st to end	Day	62% 7% 11% 13% 6% 1	1636
March	1st to 10th	Day	57% 6% 14% 12% 11% 1	5031
	11th to 20th	Day	52% 6% 14% 19% 6% 3	5090
	21st to end	Day	53% 6% 10% 17% 11% 2	5586
April	1st to 10th	Day	57% 6% 9% 18% 10% 1	2452
	11th to 20th	Day	50% 6% 9% 21% 13% 1	2623
	21st to end	Day	52% 6% 12% 18% 10% 2	2730
May	1st to 10th	Day	48% 6% 13% 18% 10% 5%	7651
	11th to 20th	Day	48% 8% 11% 18% 15% 1	8065
	21st to end	Day	41% 5% 9% 27% 15% 2	9061
June	1st to 10th	Day	42% 8% 13% 20% 16% 1	2940
	11th to 20th	Day	39% 8% 14% 23% 15% 1	3069
	21st to end	Day	42% 7% 15% 23% 13% 1	3150
July	1st to 10th	Day	42% 5% 16% 22% 14% 1	6711
	11th to 20th	Day	34% 5% 13% 32% 15% 1	6245
	21st to end	Day	34% 6% 15% 30% 15% 1	6240
August	1st to 10th	Day	45% 7% 14% 23% 11% 1	4221
	11th to 20th	Day	46% 6% 16% 23% 8%	4213
	21st to end	Day	39% 7% 14% 30% 9% 1	4548
September	1st to 10th	Day	42% 7% 15% 24% 10% 2	2400
	11th to 20th	Day	37% 6% 15% 29% 13%	2239
	21st to end	Day	47% 8% 13% 22% 9%	2185
October	1st to 10th	Day	45% 6% 12% 25% 11% 1	3260
	11th to 20th	Day	47% 5% 14% 20% 14% 1	3240
	21st to end	Day	60% 5% 12% 17% 6%	3538
November	1st to 10th	Day	53% 8% 14% 17% 7% 1	1770
	11th to 20th	Day	58% 8% 13% 13% 7% 1	1680
	21st to end	Day	65% 8% 14% 10% 3	1680
December	1st to 10th	Day	74% 6% 11% 6% 2	2680
	11th to 20th	Day	69% 7% 9% 9% 5%	3066
	21st to end	Day	78% 6% 5% 6% 5%	4048
January	1st to 10th	Night	63% 7% 13% 12% 5%	8234
	11th to 20th	Night	73% 8% 7% 8% 3 1	7708
	21st to end	Night	61% 9% 11% 9% 10%	8401
February	1st to 10th	Night	58% 8% 12% 16% 5%	2730
	11th to 20th	Night	59% 7% 12% 15% 6%	2665
	21st to end	Night	56% 7% 14% 15% 8%	2168
March	1st to 10th	Night	50% 8% 13% 17% 10% 2	5040
	11th to 20th	Night	43% 7% 19% 20% 9% 2	5090
	21st to end	Night	47% 6% 11% 19% 15% 2	5588
April	1st to 10th	Night	54% 6% 10% 17% 13% 1	2168
	11th to 20th	Night	47% 7% 9% 21% 15% 1	1964
	21st to end	Night	47% 7% 12% 17% 15% 2	1890
May	1st to 10th	Night	45% 6% 11% 18% 15% 6%	5264
	11th to 20th	Night	43% 7% 12% 21% 14% 2	4785
	21st to end	Night	37% 6% 11% 27% 18% 2	5115
June	1st to 10th	Night	37% 7% 12% 24% 19% 2	1680
	11th to 20th	Night	35% 7% 14% 25% 18% 1	1544
	21st to end	Night	36% 7% 14% 26% 16% 1	1470
July	1st to 10th	Night	35% 5% 15% 24% 18% 3	3142
	11th to 20th	Night	32% 5% 12% 31% 19% 1	3588
	21st to end	Night	31% 6% 12% 31% 17% 2	4297
August	1st to 10th	Night	35% 5% 15% 27% 16% 2	2904
	11th to 20th	Night	35% 6% 16% 29% 14% 1	2902
	21st to end	Night	34% 7% 13% 31% 14% 1	3316
September	1st to 10th	Night	32% 8% 16% 28% 14% 1	2000
	11th to 20th	Night	28% 7% 14% 32% 19%	2158
	21st to end	Night	43% 7% 13% 25% 11% 1	2214
October	1st to 10th	Night	36% 6% 8% 27% 22% 1	3920
	11th to 20th	Night	46% 5% 12% 22% 14% 2	3899
	21st to end	Night	46% 6% 15% 24% 8%	4252
November	1st to 10th	Night	48% 8% 14% 20% 9% 1	2741
	11th to 20th	Night	54% 9% 13% 15% 7% 1	2940
	21st to end	Night	60% 8% 17% 12% 2 1	2940
December	1st to 10th	Night	68% 6% 14% 9% 2	4720
	11th to 20th	Night	67% 9% 9% 9% 6%	5348
	21st to end	Night	76% 7% 7% 7% 3	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	24% 30% 30% 13% 2	220
	11th to 20th	Day	26% 33% 27% 11% 2	322
	21st to end	Day	28% 29% 31% 10% 2	363
February	1st to 10th	Day	29% 33% 26% 10% 2	330
	11th to 20th	Day	28% 31% 35% 5%	330
	21st to end	Day	36% 30% 30% 4	273
March	1st to 10th	Day	24% 27% 34% 13% 2	526
	11th to 20th	Day	29% 21% 35% 11% 4	540
	21st to end	Day	32% 22% 31% 11% 5%	594
April	1st to 10th	Day	28% 24% 34% 10% 4	540
	11th to 20th	Day	32% 23% 25% 13% 5% 2	532
	21st to end	Day	26% 21% 34% 13% 4 1	540
May	1st to 10th	Day	23% 20% 32% 16% 7% 2	543
	11th to 20th	Day	19% 17% 34% 19% 8% 3	567
	21st to end	Day	17% 17% 31% 24% 8% 4	617
June	1st to 10th	Day	15% 18% 34% 23% 8% 1	570
	11th to 20th	Day	15% 14% 35% 25% 9% 1	699
	21st to end	Day	16% 13% 37% 24% 7% 2	780
July	1st to 10th	Day	11% 10% 33% 28% 14% 3	712
	11th to 20th	Day	12% 10% 33% 25% 14% 6%	524
	21st to end	Day	10% 9% 37% 27% 12% 5%	576
August	1st to 10th	Day	10% 8% 30% 31% 16% 5%	526
	11th to 20th	Day	11% 8% 27% 28% 17% 8%	519
	21st to end	Day	15% 10% 31% 25% 15% 5%	583
September	1st to 10th	Day	14% 13% 30% 23% 13% 7%	530
	11th to 20th	Day	10% 8% 26% 25% 21% 10%	530
	21st to end	Day	17% 15% 27% 22% 14% 4	530
October	1st to 10th	Day	22% 18% 27% 19% 12% 3	530
	11th to 20th	Day	25% 23% 33% 14% 5%	530
	21st to end	Day	30% 24% 28% 15% 3	583
November	1st to 10th	Day	31% 23% 29% 14% 2 1	288
	11th to 20th	Day	27% 28% 32% 7% 5% 1	220
	21st to end	Day	27% 25% 38% 9%	220
December	1st to 10th	Day	33% 29% 30% 8%	220
	11th to 20th	Day	35% 30% 25% 8% 1	220
	21st to end	Day	33% 29% 28% 8% 2	242
January	1st to 10th	Night	21% 30% 33% 12% 3	840
	11th to 20th	Night	27% 24% 31% 15% 2	840
	21st to end	Night	17% 23% 37% 19% 4	924
February	1st to 10th	Night	22% 28% 33% 16% 1	840
	11th to 20th	Night	24% 24% 36% 14% 3	823
	21st to end	Night	23% 26% 36% 13% 2	692
March	1st to 10th	Night	21% 22% 36% 18% 3	840
	11th to 20th	Night	22% 25% 33% 16% 4	840
	21st to end	Night	22% 20% 34% 19% 5%	924
April	1st to 10th	Night	26% 19% 36% 17% 2	840
	11th to 20th	Night	21% 18% 34% 19% 7% 1	720
	21st to end	Night	21% 15% 34% 23% 7%	630
May	1st to 10th	Night	17% 13% 32% 28% 9% 2	630
	11th to 20th	Night	18% 10% 34% 27% 9% 1	470
	21st to end	Night	13% 11% 30% 31% 13%	455
June	1st to 10th	Night	12% 10% 37% 30% 10%	420
	11th to 20th	Night	10% 12% 33% 33% 13%	420
	21st to end	Night	12% 7% 35% 32% 13%	420
July	1st to 10th	Night	5% 6% 29% 42% 17% 1	390
	11th to 20th	Night	9% 8% 32% 34% 18% 1	398
	21st to end	Night	8% 5% 31% 38% 17% 1	657
August	1st to 10th	Night	10% 4 26% 37% 23% 2	597
	11th to 20th	Night	9% 4 23% 39% 22% 2	594
	21st to end	Night	13% 6% 32% 27% 20% 2	714
September	1st to 10th	Night	10% 10% 29% 29% 18% 4	800
	11th to 20th	Night	12% 7% 26% 28% 23% 5%	800
	21st to end	Night	20% 10% 24% 28% 15% 4	800
October	1st to 10th	Night	18% 13% 31% 23% 13% 2	800
	11th to 20th	Night	25% 17% 31% 19% 7% 1	800
	21st to end	Night	24% 22% 31% 20% 3	880
November	1st to 10th	Night	24% 18% 31% 20% 7% 1	820
	11th to 20th	Night	23% 25% 29% 17% 6% 1	840
	21st to end	Night	25% 24% 32% 16% 3	840
December	1st to 10th	Night	27% 25% 31% 13% 3	840
	11th to 20th	Night	23% 27% 36% 11% 2	840
	21st to end	Night	30% 24% 30% 15% 2	924

Page generated at 2026-06-28 02:10:47. Version ac07

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