Oakville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oakville clear sky chart from 2005-11-06 to 2024-03-18.

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% 8% 4 7% 6% 4 5% 5% 6% 7% 33%	78632
	Night	15% 9% 4 7% 6% 3 5% 5% 5% 7% 34%	81144
Transparency	Day	47% 9% 14% 19% 10% 1	78349
	Night	49% 8% 13% 19% 9% 1	80961
Seeing	Day	16% 9% 27% 28% 15% 5%	13530
	Night	18% 8% 29% 29% 13% 2	23144

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% 14% 4 8% 9% 4 5% 5% 5% 6% 26%	2517
	11th to 20th	Day	11% 16% 7% 14% 10% 4 5% 4 4 6% 18%	2808
	21st to end	Day	22% 16% 6% 11% 7% 4 5% 4 4 4 17%	3124
February	1st to 10th	Day	14% 15% 4 9% 9% 4 6% 5% 5% 6% 22%	1710
	11th to 20th	Day	11% 12% 7% 10% 8% 4 6% 5% 5% 7% 25%	1663
	21st to end	Day	18% 11% 4 7% 6% 4 5% 6% 6% 6% 27%	1478
March	1st to 10th	Day	13% 9% 5% 8% 8% 4 6% 5% 5% 6% 31%	2087
	11th to 20th	Day	13% 10% 5% 9% 7% 3 5% 4 5% 7% 32%	2058
	21st to end	Day	16% 8% 4 8% 7% 4 5% 4 5% 6% 33%	2178
April	1st to 10th	Day	15% 9% 4 6% 7% 5% 5% 5% 5% 7% 31%	2114
	11th to 20th	Day	17% 8% 3 7% 5% 2 5% 5% 4 7% 37%	2208
	21st to end	Day	19% 8% 3 7% 5% 4 5% 4 5% 6% 34%	2340
May	1st to 10th	Day	13% 8% 3 8% 6% 3 4 5% 7% 8% 35%	2340
	11th to 20th	Day	14% 5% 3 6% 6% 3 5% 5% 5% 7% 39%	2433
	21st to end	Day	10% 4 3 5% 5% 3 5% 5% 6% 9% 44%	2725
June	1st to 10th	Day	12% 5% 2 5% 6% 3 5% 5% 6% 8% 42%	2520
	11th to 20th	Day	11% 5% 2 5% 6% 3 6% 6% 7% 9% 41%	2520
	21st to end	Day	12% 5% 2 4 5% 3 5% 5% 7% 9% 42%	2520
July	1st to 10th	Day	6% 4 2 4 5% 3 7% 7% 6% 10% 47%	2520
	11th to 20th	Day	11% 5% 2 4 5% 4 6% 6% 7% 9% 42%	2512
	21st to end	Day	8% 5% 2 5% 6% 5% 7% 6% 7% 11% 39%	2547
August	1st to 10th	Day	7% 5% 3 5% 6% 4 6% 5% 8% 9% 42%	2327
	11th to 20th	Day	7% 4 2 6% 7% 4 7% 6% 7% 9% 42%	2303
	21st to end	Day	9% 6% 2 5% 5% 4 5% 5% 6% 9% 44%	2484
September	1st to 10th	Day	12% 5% 2 6% 5% 3 5% 5% 6% 8% 42%	2160
	11th to 20th	Day	9% 5% 2 5% 5% 2 5% 6% 6% 8% 47%	2038
	21st to end	Day	12% 5% 3 5% 5% 4 7% 5% 6% 9% 38%	1954
October	1st to 10th	Day	17% 8% 2 6% 6% 4 4 6% 5% 7% 36%	1800
	11th to 20th	Day	19% 8% 3 8% 5% 4 5% 6% 6% 7% 30%	1800
	21st to end	Day	23% 10% 3 7% 8% 4 6% 4 6% 6% 24%	1980
November	1st to 10th	Day	12% 7% 4 8% 5% 4 5% 6% 7% 8% 33%	1626
	11th to 20th	Day	14% 9% 4 8% 8% 4 7% 5% 6% 8% 27%	1520
	21st to end	Day	18% 11% 5% 7% 7% 3 6% 5% 7% 7% 24%	1520
December	1st to 10th	Day	15% 13% 5% 10% 8% 5% 6% 6% 5% 6% 20%	1520
	11th to 20th	Day	17% 12% 4 9% 7% 5% 6% 6% 6% 7% 22%	1906
	21st to end	Day	29% 16% 6% 10% 7% 4 5% 4 4 4 11%	2772
January	1st to 10th	Night	16% 13% 4 9% 8% 4 6% 6% 5% 6% 23%	4429
	11th to 20th	Night	14% 12% 6% 10% 9% 5% 6% 5% 5% 6% 21%	4148
	21st to end	Night	22% 13% 5% 8% 7% 4 5% 4 5% 6% 21%	4532
February	1st to 10th	Night	14% 13% 5% 10% 8% 3 5% 5% 5% 7% 24%	2470
	11th to 20th	Night	12% 11% 5% 9% 7% 5% 6% 5% 5% 6% 27%	2403
	21st to end	Night	14% 10% 4 9% 7% 4 5% 5% 5% 7% 28%	1972
March	1st to 10th	Night	14% 7% 3 8% 6% 4 6% 6% 6% 7% 35%	2080
	11th to 20th	Night	15% 10% 5% 9% 6% 3 4 4 5% 6% 35%	2067
	21st to end	Night	16% 9% 4 6% 6% 3 4 4 4 5% 38%	2178
April	1st to 10th	Night	17% 8% 4 7% 6% 3 6% 5% 5% 6% 34%	1846
	11th to 20th	Night	15% 7% 3 7% 5% 3 4 4 6% 7% 37%	1715
	21st to end	Night	16% 9% 3 6% 5% 2 5% 5% 4 7% 38%	1620
May	1st to 10th	Night	16% 6% 3 6% 5% 3 5% 4 6% 7% 39%	1620
	11th to 20th	Night	16% 4 2 4 5% 3 4 5% 5% 7% 44%	1456
	21st to end	Night	9% 5% 1 4 4 3 4 5% 5% 9% 50%	1550
June	1st to 10th	Night	12% 4 2 4 6% 4 5% 5% 6% 9% 44%	1440
	11th to 20th	Night	12% 4 2 5% 4 3 6% 5% 6% 9% 44%	1440
	21st to end	Night	10% 4 2 6% 5% 3 4 5% 6% 8% 45%	1440
July	1st to 10th	Night	5% 4 1 4 5% 2 5% 4 4 8% 58%	1440
	11th to 20th	Night	9% 4 2 5% 4 3 5% 5% 6% 8% 50%	1444
	21st to end	Night	8% 4 2 4 5% 3 5% 5% 7% 9% 50%	1771
August	1st to 10th	Night	8% 4 2 5% 5% 4 4 6% 7% 7% 49%	1611
	11th to 20th	Night	7% 4 2 4 5% 3 4 5% 6% 9% 52%	1598
	21st to end	Night	9% 5% 2 6% 5% 3 4 5% 6% 8% 48%	1854
September	1st to 10th	Night	10% 6% 2 5% 5% 4 5% 5% 5% 8% 46%	1800
	11th to 20th	Night	10% 5% 3 4 4 2 4 4 4 7% 54%	1919
	21st to end	Night	13% 6% 3 6% 6% 3 5% 5% 5% 8% 41%	2006
October	1st to 10th	Night	17% 6% 2 6% 4 3 4 5% 5% 7% 41%	2160
	11th to 20th	Night	17% 8% 3 6% 5% 3 6% 5% 5% 7% 34%	2160
	21st to end	Night	22% 8% 3 6% 6% 3 5% 5% 5% 6% 29%	2376
November	1st to 10th	Night	16% 6% 2 6% 5% 3 6% 5% 5% 7% 40%	2447
	11th to 20th	Night	14% 9% 4 7% 6% 4 5% 6% 7% 8% 31%	2660
	21st to end	Night	18% 9% 5% 6% 6% 4 5% 5% 5% 8% 29%	2660
December	1st to 10th	Night	19% 12% 5% 8% 6% 4 6% 5% 5% 6% 24%	2660
	11th to 20th	Night	16% 13% 6% 9% 8% 3 6% 5% 5% 7% 23%	3288
	21st to end	Night	29% 15% 6% 9% 7% 3 5% 4 4 5% 13%	4884

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	55% 12% 16% 11% 6%	2518
	11th to 20th	Day	67% 7% 12% 12% 2	2808
	21st to end	Day	70% 8% 10% 9% 2	3124
February	1st to 10th	Day	63% 8% 13% 13% 3 1	1710
	11th to 20th	Day	58% 8% 13% 16% 5% 1	1672
	21st to end	Day	55% 10% 15% 13% 7% 1	1478
March	1st to 10th	Day	51% 9% 14% 17% 7% 1	2090
	11th to 20th	Day	50% 9% 12% 17% 10% 2	2058
	21st to end	Day	49% 7% 12% 19% 11% 2	2178
April	1st to 10th	Day	50% 7% 13% 17% 12% 1	2114
	11th to 20th	Day	45% 7% 12% 20% 15% 1	2208
	21st to end	Day	48% 7% 12% 18% 11% 3	2340
May	1st to 10th	Day	44% 8% 13% 21% 13% 1	2340
	11th to 20th	Day	42% 9% 12% 23% 13% 1	2437
	21st to end	Day	33% 9% 18% 23% 14% 2	2725
June	1st to 10th	Day	38% 9% 13% 23% 15% 2	2520
	11th to 20th	Day	36% 9% 14% 24% 16% 1	2520
	21st to end	Day	34% 9% 16% 26% 15%	2520
July	1st to 10th	Day	27% 11% 14% 26% 18% 3	2450
	11th to 20th	Day	33% 9% 19% 26% 12% 1	2437
	21st to end	Day	34% 12% 18% 22% 14% 2	2405
August	1st to 10th	Day	31% 11% 18% 25% 13% 2	2314
	11th to 20th	Day	33% 12% 17% 26% 12% 1	2303
	21st to end	Day	33% 9% 16% 28% 13% 1	2484
September	1st to 10th	Day	37% 10% 16% 26% 10% 1	2160
	11th to 20th	Day	31% 9% 17% 29% 14% 1	2038
	21st to end	Day	40% 10% 15% 26% 9%	1954
October	1st to 10th	Day	45% 8% 16% 19% 10% 1	1800
	11th to 20th	Day	51% 8% 15% 19% 6% 1	1800
	21st to end	Day	58% 8% 14% 14% 5% 1	1980
November	1st to 10th	Day	45% 9% 17% 21% 8% 1	1626
	11th to 20th	Day	52% 10% 16% 14% 7% 1	1520
	21st to end	Day	55% 11% 16% 14% 3	1520
December	1st to 10th	Day	63% 8% 15% 10% 3	1520
	11th to 20th	Day	60% 11% 14% 11% 3	1906
	21st to end	Day	72% 11% 10% 6% 1	2772
January	1st to 10th	Night	58% 12% 14% 14% 2	4429
	11th to 20th	Night	60% 11% 14% 13% 2	4148
	21st to end	Night	64% 9% 13% 11% 3	4532
February	1st to 10th	Night	59% 8% 13% 16% 3	2470
	11th to 20th	Night	56% 7% 13% 17% 7%	2405
	21st to end	Night	53% 9% 15% 17% 7%	1972
March	1st to 10th	Night	49% 7% 16% 20% 7% 1	2090
	11th to 20th	Night	50% 6% 11% 19% 11% 2	2068
	21st to end	Night	48% 5% 9% 21% 14% 2	2178
April	1st to 10th	Night	50% 7% 11% 19% 13% 1	1846
	11th to 20th	Night	45% 7% 10% 20% 15% 3	1715
	21st to end	Night	46% 8% 9% 20% 15% 3	1620
May	1st to 10th	Night	44% 6% 10% 20% 17% 3	1620
	11th to 20th	Night	39% 6% 11% 26% 14% 4	1457
	21st to end	Night	32% 8% 14% 24% 19% 4	1551
June	1st to 10th	Night	37% 8% 13% 24% 17% 2	1440
	11th to 20th	Night	35% 7% 13% 22% 20% 3	1440
	21st to end	Night	36% 8% 14% 24% 17% 2	1440
July	1st to 10th	Night	26% 8% 11% 25% 27% 4	1400
	11th to 20th	Night	32% 6% 13% 29% 18% 2	1396
	21st to end	Night	29% 8% 18% 25% 18% 3	1672
August	1st to 10th	Night	32% 10% 16% 29% 13% 2	1600
	11th to 20th	Night	28% 8% 18% 32% 14% 1	1598
	21st to end	Night	34% 8% 13% 28% 15% 2	1854
September	1st to 10th	Night	36% 8% 16% 26% 13% 2	1800
	11th to 20th	Night	30% 7% 13% 33% 16%	1919
	21st to end	Night	41% 8% 12% 27% 11% 1	2006
October	1st to 10th	Night	43% 7% 13% 22% 14% 1	2160
	11th to 20th	Night	49% 7% 13% 22% 8%	2160
	21st to end	Night	54% 8% 12% 16% 9% 1	2376
November	1st to 10th	Night	44% 7% 14% 23% 12% 1	2447
	11th to 20th	Night	48% 9% 15% 19% 8% 1	2660
	21st to end	Night	53% 10% 18% 15% 3	2660
December	1st to 10th	Night	59% 10% 14% 14% 3	2660
	11th to 20th	Night	60% 9% 14% 13% 3	3288
	21st to end	Night	73% 10% 10% 6% 2	4884

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	18% 14% 34% 22% 10% 2	180
	11th to 20th	Day	21% 20% 36% 14% 7% 2	261
	21st to end	Day	22% 14% 35% 22% 6%	297
February	1st to 10th	Day	20% 17% 41% 17% 5%	270
	11th to 20th	Day	20% 18% 37% 23% 2	270
	21st to end	Day	24% 24% 32% 17% 2	235
March	1st to 10th	Day	18% 13% 36% 25% 8%	460
	11th to 20th	Day	17% 18% 33% 25% 7% 1	449
	21st to end	Day	25% 9% 31% 25% 9% 2	462
April	1st to 10th	Day	14% 14% 33% 28% 10% 1	420
	11th to 20th	Day	21% 12% 28% 24% 10% 4	412
	21st to end	Day	20% 7% 31% 29% 10% 2	420
May	1st to 10th	Day	16% 9% 28% 26% 15% 5%	423
	11th to 20th	Day	15% 6% 23% 32% 19% 6%	447
	21st to end	Day	11% 5% 20% 35% 20% 9%	485
June	1st to 10th	Day	10% 5% 27% 37% 17% 4	450
	11th to 20th	Day	12% 5% 23% 30% 25% 4	450
	21st to end	Day	13% 5% 20% 34% 21% 6%	450
July	1st to 10th	Day	7% 2 13% 38% 27% 14%	445
	11th to 20th	Day	12% 2 16% 32% 26% 10%	444
	21st to end	Day	8% 2 18% 39% 26% 7%	488
August	1st to 10th	Day	7% 4 17% 31% 28% 13%	446
	11th to 20th	Day	7% 4 18% 31% 26% 14%	439
	21st to end	Day	10% 4 21% 31% 23% 12%	495
September	1st to 10th	Day	12% 4 20% 31% 22% 12%	450
	11th to 20th	Day	8% 3 20% 28% 26% 15%	450
	21st to end	Day	12% 7% 29% 27% 16% 8%	450
October	1st to 10th	Day	20% 9% 27% 20% 17% 8%	450
	11th to 20th	Day	20% 13% 32% 22% 11% 2	450
	21st to end	Day	27% 12% 28% 23% 9% 1	495
November	1st to 10th	Day	17% 16% 29% 26% 9% 3	269
	11th to 20th	Day	22% 18% 27% 23% 8% 1	180
	21st to end	Day	23% 12% 39% 21% 5% 1	180
December	1st to 10th	Day	20% 17% 34% 24% 4	180
	11th to 20th	Day	24% 23% 31% 20% 2	180
	21st to end	Day	24% 14% 44% 14% 4	198
January	1st to 10th	Night	23% 16% 36% 18% 7%	760
	11th to 20th	Night	27% 14% 33% 22% 4	760
	21st to end	Night	19% 11% 38% 25% 8%	836
February	1st to 10th	Night	22% 14% 39% 22% 3	760
	11th to 20th	Night	21% 13% 38% 25% 4	743
	21st to end	Night	19% 15% 38% 24% 4	628
March	1st to 10th	Night	20% 9% 36% 27% 8%	760
	11th to 20th	Night	22% 11% 34% 26% 7%	752
	21st to end	Night	20% 9% 28% 32% 10% 1	792
April	1st to 10th	Night	20% 8% 34% 31% 7% 1	720
	11th to 20th	Night	18% 8% 33% 28% 11% 2	651
	21st to end	Night	20% 6% 29% 33% 13%	540
May	1st to 10th	Night	17% 4 26% 32% 19% 3	540
	11th to 20th	Night	17% 3 22% 41% 16% 1	395
	21st to end	Night	11% 2 22% 36% 27% 2	389
June	1st to 10th	Night	12% 3 22% 43% 19% 1	360
	11th to 20th	Night	13% 2 26% 36% 22% 1	360
	21st to end	Night	10% 3 20% 43% 24% 1	360
July	1st to 10th	Night	6% 2 15% 45% 28% 3	350
	11th to 20th	Night	11% 2 18% 38% 27% 3	352
	21st to end	Night	9% 2 15% 47% 25% 3	591
August	1st to 10th	Night	9% 3 12% 41% 32% 4	537
	11th to 20th	Night	8% 1 14% 37% 34% 5%	534
	21st to end	Night	11% 2 19% 34% 30% 4	666
September	1st to 10th	Night	11% 6% 17% 33% 26% 7%	720
	11th to 20th	Night	11% 4 18% 30% 30% 7%	720
	21st to end	Night	15% 5% 22% 30% 23% 5%	720
October	1st to 10th	Night	19% 5% 27% 25% 21% 3	720
	11th to 20th	Night	21% 10% 31% 27% 9% 2	720
	21st to end	Night	26% 9% 30% 29% 5%	792
November	1st to 10th	Night	21% 8% 26% 32% 12% 1	740
	11th to 20th	Night	19% 11% 37% 22% 9% 2	760
	21st to end	Night	23% 11% 36% 24% 6%	760
December	1st to 10th	Night	27% 13% 35% 19% 6%	760
	11th to 20th	Night	22% 14% 39% 20% 5%	760
	21st to end	Night	28% 13% 35% 22% 2	836

Page generated at 2024-03-15 14:01:45. Version ac07

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