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 2025-02-25.

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% 28%	109436
	Night	13% 12% 5% 11% 6% 5% 5% 4 5% 6% 29%	109230
Transparency	Day	52% 7% 12% 18% 9% 1	113072
	Night	50% 8% 13% 18% 10% 1	113758
Seeing	Day	20% 19% 31% 19% 8% 3	15154
	Night	19% 18% 32% 22% 8% 1	24269

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% 14% 7% 19% 7% 5% 5% 3 4 5% 19%	3597
	11th to 20th	Day	9% 20% 9% 23% 9% 9% 6% 3 3 3 7%	3997
	21st to end	Day	14% 18% 8% 19% 9% 5% 5% 3 3 4 11%	4466
February	1st to 10th	Day	13% 17% 6% 16% 11% 6% 5% 4 3 4 16%	1800
	11th to 20th	Day	11% 13% 8% 16% 10% 5% 4 4 6% 6% 18%	1753
	21st to end	Day	16% 16% 6% 11% 8% 6% 5% 4 6% 4 20%	1520
March	1st to 10th	Day	15% 15% 5% 11% 6% 4 4 3 4 5% 26%	3419
	11th to 20th	Day	10% 16% 8% 12% 7% 4 5% 3 4 5% 26%	3480
	21st to end	Day	15% 12% 4 8% 5% 4 6% 4 5% 6% 32%	3815
April	1st to 10th	Day	16% 15% 4 9% 6% 4 4 4 5% 7% 27%	2218
	11th to 20th	Day	18% 12% 3 7% 4 5% 4 3 4 6% 34%	2371
	21st to end	Day	19% 11% 5% 7% 4 4 4 3 5% 6% 32%	2470
May	1st to 10th	Day	18% 9% 3 7% 5% 4 4 3 5% 7% 34%	4108
	11th to 20th	Day	17% 10% 3 8% 5% 5% 6% 4 6% 7% 31%	4320
	21st to end	Day	12% 6% 2 6% 5% 4 4 3 6% 7% 45%	4837
June	1st to 10th	Day	15% 7% 3 7% 5% 5% 5% 5% 6% 9% 35%	2660
	11th to 20th	Day	12% 6% 2 7% 4 4 5% 5% 7% 9% 39%	2777
	21st to end	Day	15% 7% 3 6% 5% 5% 5% 4 6% 8% 38%	2850
July	1st to 10th	Day	12% 5% 2 7% 5% 5% 6% 5% 7% 10% 34%	4738
	11th to 20th	Day	11% 6% 2 6% 5% 5% 6% 5% 7% 8% 41%	4414
	21st to end	Day	10% 6% 3 7% 5% 5% 6% 5% 6% 8% 39%	4466
August	1st to 10th	Day	16% 7% 3 7% 5% 5% 5% 4 7% 8% 34%	4104
	11th to 20th	Day	12% 8% 3 8% 6% 5% 6% 4 7% 9% 31%	4044
	21st to end	Day	9% 7% 2 7% 5% 6% 6% 5% 6% 7% 39%	4409
September	1st to 10th	Day	14% 7% 3 7% 5% 4 4 4 6% 7% 38%	2280
	11th to 20th	Day	12% 7% 3 6% 5% 5% 4 3 4 9% 42%	2127
	21st to end	Day	16% 8% 2 7% 6% 6% 6% 4 6% 8% 31%	2076
October	1st to 10th	Day	17% 10% 4 8% 6% 4 4 4 5% 6% 31%	1900
	11th to 20th	Day	20% 13% 5% 9% 5% 4 4 4 5% 5% 26%	1900
	21st to end	Day	25% 18% 3 8% 4 4 5% 3 5% 6% 19%	2090
November	1st to 10th	Day	12% 17% 4 10% 5% 5% 4 3 5% 7% 28%	1684
	11th to 20th	Day	14% 15% 6% 11% 6% 5% 5% 4 5% 7% 22%	1600
	21st to end	Day	15% 19% 7% 12% 6% 5% 4 4 4 7% 17%	1600
December	1st to 10th	Day	15% 25% 10% 14% 5% 4 4 3 5% 5% 10%	2600
	11th to 20th	Day	19% 22% 7% 11% 6% 4 4 3 3 5% 16%	2986
	21st to end	Day	21% 21% 7% 16% 7% 4 4 3 4 3 9%	3960
January	1st to 10th	Night	13% 13% 7% 19% 7% 5% 4 3 4 6% 19%	6349
	11th to 20th	Night	11% 12% 7% 21% 14% 10% 6% 4 4 4 8%	5887
	21st to end	Night	13% 14% 7% 17% 7% 6% 6% 4 6% 6% 14%	6490
February	1st to 10th	Night	12% 15% 5% 14% 8% 5% 6% 4 5% 6% 19%	2600
	11th to 20th	Night	11% 12% 6% 15% 9% 5% 5% 4 5% 6% 21%	2533
	21st to end	Night	12% 13% 4 12% 8% 5% 5% 4 6% 7% 24%	2027
March	1st to 10th	Night	14% 11% 5% 10% 5% 4 5% 5% 6% 6% 28%	3419
	11th to 20th	Night	11% 10% 5% 10% 5% 4 5% 4 5% 7% 34%	3479
	21st to end	Night	15% 8% 4 8% 5% 4 4 3 5% 5% 39%	3817
April	1st to 10th	Night	18% 13% 3 9% 5% 5% 5% 3 5% 6% 30%	1962
	11th to 20th	Night	16% 10% 3 7% 5% 4 4 4 5% 5% 37%	1775
	21st to end	Night	14% 11% 4 8% 5% 5% 4 3 6% 7% 33%	1710
May	1st to 10th	Night	15% 10% 2 6% 4 4 4 3 5% 6% 40%	2833
	11th to 20th	Night	15% 9% 3 6% 5% 4 4 4 6% 7% 37%	2572
	21st to end	Night	10% 6% 2 6% 3 3 3 3 6% 7% 51%	2738
June	1st to 10th	Night	12% 6% 2 6% 6% 6% 4 4 6% 7% 42%	1520
	11th to 20th	Night	8% 5% 2 7% 5% 5% 4 5% 7% 10% 41%	1397
	21st to end	Night	12% 6% 2 7% 3 4 2 4 6% 8% 45%	1330
July	1st to 10th	Night	7% 6% 2 7% 4 4 4 4 6% 7% 50%	2227
	11th to 20th	Night	10% 6% 2 5% 3 4 3 3 5% 7% 52%	2542
	21st to end	Night	6% 6% 2 5% 4 4 5% 4 7% 8% 49%	3087
August	1st to 10th	Night	11% 5% 2 5% 4 4 4 4 6% 6% 48%	2825
	11th to 20th	Night	12% 7% 2 5% 3 4 4 4 5% 7% 46%	2785
	21st to end	Night	12% 6% 2 6% 4 4 4 4 5% 6% 48%	3214
September	1st to 10th	Night	9% 5% 3 6% 5% 4 4 3 6% 6% 49%	1900
	11th to 20th	Night	11% 4 2 5% 3 3 3 4 6% 7% 52%	2050
	21st to end	Night	16% 9% 3 7% 5% 4 4 2 4 7% 40%	2103
October	1st to 10th	Night	16% 8% 3 7% 5% 4 4 3 5% 7% 37%	2280
	11th to 20th	Night	19% 11% 3 7% 5% 4 5% 3 5% 6% 32%	2280
	21st to end	Night	19% 13% 4 8% 6% 5% 5% 4 5% 6% 26%	2508
November	1st to 10th	Night	15% 11% 4 7% 5% 5% 5% 5% 5% 6% 32%	2607
	11th to 20th	Night	15% 14% 5% 9% 6% 5% 5% 4 7% 7% 24%	2800
	21st to end	Night	16% 15% 5% 11% 6% 5% 4 4 5% 7% 21%	2800
December	1st to 10th	Night	14% 18% 8% 16% 6% 5% 5% 4 5% 5% 13%	4580
	11th to 20th	Night	12% 22% 10% 15% 6% 4 4 3 4 5% 15%	5208
	21st to end	Night	21% 20% 8% 17% 6% 5% 4 3 3 4 9%	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	63% 8% 10% 13% 5%	3598
	11th to 20th	Day	75% 8% 8% 6% 3	4031
	21st to end	Day	71% 8% 9% 8% 4	4466
February	1st to 10th	Day	69% 7% 9% 11% 3 1	1800
	11th to 20th	Day	63% 8% 11% 12% 5% 1	1762
	21st to end	Day	62% 7% 10% 13% 6% 1	1520
March	1st to 10th	Day	57% 7% 12% 14% 8% 1	3422
	11th to 20th	Day	55% 8% 11% 19% 7% 1	3480
	21st to end	Day	48% 9% 12% 18% 11% 2	3815
April	1st to 10th	Day	56% 7% 9% 17% 9% 1	2218
	11th to 20th	Day	49% 7% 10% 20% 14% 1	2371
	21st to end	Day	52% 6% 11% 18% 11% 2	2470
May	1st to 10th	Day	45% 9% 13% 19% 12% 2	4120
	11th to 20th	Day	48% 11% 14% 19% 7% 1	4324
	21st to end	Day	36% 8% 14% 21% 17% 4	4837
June	1st to 10th	Day	43% 9% 14% 20% 14% 1	2660
	11th to 20th	Day	38% 8% 14% 23% 16% 1	2777
	21st to end	Day	42% 8% 14% 23% 13%	2850
July	1st to 10th	Day	42% 6% 17% 19% 15% 1	4664
	11th to 20th	Day	36% 7% 14% 32% 10% 1	4339
	21st to end	Day	39% 7% 15% 22% 16% 1	4324
August	1st to 10th	Day	45% 8% 14% 22% 11% 1	4091
	11th to 20th	Day	47% 6% 16% 23% 8%	4083
	21st to end	Day	40% 7% 14% 29% 9% 1	4409
September	1st to 10th	Day	42% 7% 15% 23% 10% 2	2280
	11th to 20th	Day	38% 6% 14% 27% 13%	2127
	21st to end	Day	47% 9% 13% 22% 8%	2076
October	1st to 10th	Day	45% 6% 12% 24% 11% 1	3160
	11th to 20th	Day	47% 5% 14% 20% 14% 1	3140
	21st to end	Day	60% 5% 12% 17% 6%	3428
November	1st to 10th	Day	53% 9% 14% 16% 7% 1	1684
	11th to 20th	Day	58% 9% 14% 13% 7% 1	1600
	21st to end	Day	64% 8% 14% 10% 3	1600
December	1st to 10th	Day	75% 6% 11% 6% 2	2600
	11th to 20th	Day	69% 7% 9% 9% 5%	2986
	21st to end	Day	78% 6% 5% 6% 5%	3960
January	1st to 10th	Night	62% 8% 13% 12% 5%	6349
	11th to 20th	Night	71% 9% 9% 8% 3	5928
	21st to end	Night	61% 10% 12% 8% 8% 1	6490
February	1st to 10th	Night	59% 8% 13% 15% 5%	2600
	11th to 20th	Night	60% 8% 12% 15% 6%	2535
	21st to end	Night	56% 8% 14% 15% 8%	2027
March	1st to 10th	Night	50% 10% 14% 19% 7% 1	3429
	11th to 20th	Night	43% 9% 17% 21% 9% 2	3480
	21st to end	Night	42% 7% 12% 22% 15% 1	3817
April	1st to 10th	Night	53% 6% 10% 18% 13% 1	1962
	11th to 20th	Night	46% 7% 9% 21% 15% 2	1775
	21st to end	Night	48% 7% 12% 16% 15% 2	1710
May	1st to 10th	Night	42% 9% 12% 18% 15% 4	2840
	11th to 20th	Night	41% 10% 15% 21% 10% 2	2573
	21st to end	Night	29% 9% 13% 24% 22% 2	2739
June	1st to 10th	Night	38% 8% 13% 23% 17% 1	1520
	11th to 20th	Night	35% 8% 14% 24% 19% 1	1397
	21st to end	Night	36% 8% 14% 26% 16% 1	1330
July	1st to 10th	Night	31% 6% 15% 25% 19% 4	2192
	11th to 20th	Night	31% 5% 13% 34% 17% 1	2494
	21st to end	Night	31% 8% 15% 29% 15% 2	2988
August	1st to 10th	Night	36% 5% 15% 28% 15% 2	2814
	11th to 20th	Night	35% 6% 16% 29% 14% 1	2812
	21st to end	Night	34% 7% 13% 31% 14% 1	3214
September	1st to 10th	Night	33% 9% 16% 27% 14% 1	1900
	11th to 20th	Night	29% 7% 14% 31% 19%	2050
	21st to end	Night	43% 8% 13% 25% 11% 1	2103
October	1st to 10th	Night	37% 7% 8% 26% 22% 1	3800
	11th to 20th	Night	46% 5% 12% 22% 13% 2	3779
	21st to end	Night	46% 6% 15% 24% 8%	4120
November	1st to 10th	Night	47% 8% 15% 20% 9% 1	2607
	11th to 20th	Night	54% 9% 13% 15% 7% 1	2800
	21st to end	Night	59% 9% 18% 12% 2 1	2800
December	1st to 10th	Night	69% 6% 15% 8% 2	4580
	11th to 20th	Night	67% 9% 9% 9% 6%	5208
	21st to end	Night	76% 7% 7% 7% 3	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	23% 30% 31% 14% 3 1	200
	11th to 20th	Day	23% 32% 29% 12% 3	293
	21st to end	Day	27% 29% 32% 10% 2	330
February	1st to 10th	Day	30% 33% 25% 9% 2	300
	11th to 20th	Day	29% 33% 33% 5%	300
	21st to end	Day	38% 30% 28% 4	237
March	1st to 10th	Day	22% 26% 34% 14% 3	447
	11th to 20th	Day	24% 22% 38% 12% 4	460
	21st to end	Day	29% 21% 32% 12% 5%	506
April	1st to 10th	Day	23% 25% 35% 11% 5%	460
	11th to 20th	Day	31% 23% 25% 12% 6% 3	452
	21st to end	Day	26% 22% 33% 13% 5% 2	460
May	1st to 10th	Day	22% 18% 32% 18% 8% 2	463
	11th to 20th	Day	19% 14% 33% 21% 9% 3	487
	21st to end	Day	14% 14% 32% 26% 10% 4	529
June	1st to 10th	Day	16% 18% 33% 24% 8% 1	490
	11th to 20th	Day	15% 13% 32% 28% 10% 2	607
	21st to end	Day	16% 14% 36% 25% 7% 2	680
July	1st to 10th	Day	11% 10% 33% 28% 15% 3	662
	11th to 20th	Day	13% 10% 32% 25% 14% 6%	484
	21st to end	Day	10% 9% 37% 27% 13% 5%	532
August	1st to 10th	Day	11% 8% 30% 29% 16% 6%	486
	11th to 20th	Day	11% 9% 27% 27% 18% 8%	479
	21st to end	Day	15% 10% 30% 24% 16% 5%	539
September	1st to 10th	Day	14% 12% 31% 23% 13% 7%	490
	11th to 20th	Day	10% 8% 27% 24% 20% 10%	490
	21st to end	Day	18% 16% 28% 21% 13% 4	490
October	1st to 10th	Day	23% 19% 27% 17% 11% 3	490
	11th to 20th	Day	25% 23% 33% 14% 5%	490
	21st to end	Day	31% 24% 27% 14% 3	539
November	1st to 10th	Day	27% 24% 30% 15% 3 1	262
	11th to 20th	Day	27% 27% 32% 8% 5% 2	200
	21st to end	Day	26% 26% 38% 10% 1	200
December	1st to 10th	Day	33% 30% 30% 7% 1	200
	11th to 20th	Day	34% 31% 26% 8% 1 1	200
	21st to end	Day	31% 29% 29% 8% 3	220
January	1st to 10th	Night	21% 30% 33% 12% 3	800
	11th to 20th	Night	26% 24% 32% 16% 2	800
	21st to end	Night	17% 22% 38% 19% 5%	880
February	1st to 10th	Night	22% 28% 33% 15% 1	800
	11th to 20th	Night	24% 24% 36% 13% 3	783
	21st to end	Night	21% 26% 37% 14% 2	647
March	1st to 10th	Night	20% 21% 37% 19% 3	760
	11th to 20th	Night	20% 25% 34% 16% 4	760
	21st to end	Night	21% 19% 34% 20% 6%	836
April	1st to 10th	Night	25% 19% 36% 18% 2	760
	11th to 20th	Night	20% 18% 35% 19% 7% 1	651
	21st to end	Night	21% 15% 35% 22% 7%	570
May	1st to 10th	Night	16% 12% 32% 28% 10% 2	570
	11th to 20th	Night	17% 9% 35% 28% 10% 1	425
	21st to end	Night	11% 11% 30% 33% 15%	411
June	1st to 10th	Night	12% 10% 37% 31% 10%	380
	11th to 20th	Night	8% 11% 32% 34% 13%	380
	21st to end	Night	12% 7% 36% 32% 13%	380
July	1st to 10th	Night	5% 6% 28% 42% 17% 1	370
	11th to 20th	Night	8% 7% 32% 33% 18% 1	377
	21st to end	Night	8% 5% 30% 39% 17% 1	624
August	1st to 10th	Night	10% 4 26% 35% 23% 2	567
	11th to 20th	Night	8% 5% 23% 39% 22% 2	564
	21st to end	Night	14% 6% 31% 27% 21% 2	678
September	1st to 10th	Night	10% 9% 29% 29% 18% 4	760
	11th to 20th	Night	13% 7% 27% 27% 22% 5%	760
	21st to end	Night	20% 10% 24% 28% 15% 4	760
October	1st to 10th	Night	19% 13% 32% 22% 13% 2	760
	11th to 20th	Night	25% 17% 31% 19% 7% 1	760
	21st to end	Night	24% 23% 30% 19% 3	836
November	1st to 10th	Night	23% 18% 31% 20% 7% 1	780
	11th to 20th	Night	22% 26% 29% 17% 6% 1	800
	21st to end	Night	25% 23% 32% 17% 3	800
December	1st to 10th	Night	27% 25% 32% 13% 3	800
	11th to 20th	Night	23% 25% 37% 12% 2	800
	21st to end	Night	29% 23% 30% 15% 2	880

Page generated at 2025-02-22 06:51:33. Version ac07

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