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 2024-11-03.

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	13% 9% 3 8% 5% 5% 5% 4 6% 8% 34%	101423
	Night	15% 9% 3 8% 5% 5% 5% 4 5% 7% 35%	97565
Transparency	Day	45% 9% 14% 20% 10% 1	101191
	Night	47% 8% 14% 20% 10% 1	97416
Seeing	Day	16% 9% 26% 28% 16% 6%	14449
	Night	18% 8% 29% 29% 14% 2	23860

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 10% 7% 6% 5% 4 5% 6% 25%	2517
	11th to 20th	Day	10% 17% 7% 16% 8% 5% 5% 3 4 6% 18%	2808
	21st to end	Day	22% 17% 6% 12% 6% 5% 5% 3 4 4 17%	3124
February	1st to 10th	Day	13% 16% 3 11% 8% 6% 6% 4 5% 6% 22%	1710
	11th to 20th	Day	11% 14% 6% 11% 7% 5% 5% 4 5% 7% 25%	1663
	21st to end	Day	18% 12% 4 8% 6% 5% 5% 4 6% 6% 27%	1478
March	1st to 10th	Day	18% 10% 4 10% 7% 5% 5% 3 5% 4 29%	3432
	11th to 20th	Day	10% 12% 5% 10% 6% 5% 4 4 6% 7% 30%	3480
	21st to end	Day	15% 8% 3 8% 6% 5% 5% 3 6% 7% 35%	3815
April	1st to 10th	Day	15% 10% 3 8% 6% 6% 5% 4 5% 7% 31%	2232
	11th to 20th	Day	17% 8% 3 7% 4 4 4 4 4 7% 36%	2333
	21st to end	Day	19% 8% 3 8% 5% 5% 5% 3 5% 6% 34%	2470
May	1st to 10th	Day	16% 8% 3 8% 5% 4 5% 4 6% 8% 35%	4108
	11th to 20th	Day	14% 10% 4 9% 5% 4 5% 5% 8% 8% 28%	4325
	21st to end	Day	10% 5% 3 5% 4 4 4 4 6% 8% 47%	4837
June	1st to 10th	Day	12% 6% 2 6% 5% 5% 5% 4 6% 8% 40%	2660
	11th to 20th	Day	10% 5% 2 6% 5% 4 5% 5% 7% 9% 40%	2660
	21st to end	Day	12% 5% 2 6% 5% 4 5% 5% 7% 9% 41%	2660
July	1st to 10th	Day	8% 5% 2 5% 4 5% 5% 5% 8% 11% 43%	4440
	11th to 20th	Day	9% 5% 2 5% 4 4 5% 5% 7% 9% 46%	4418
	21st to end	Day	6% 4 2 5% 5% 6% 6% 5% 8% 10% 42%	4466
August	1st to 10th	Day	15% 7% 3 6% 4 4 4 4 6% 8% 39%	4104
	11th to 20th	Day	8% 6% 3 8% 5% 6% 6% 5% 7% 9% 37%	4044
	21st to end	Day	7% 6% 2 6% 4 5% 5% 4 6% 9% 46%	4372
September	1st to 10th	Day	11% 5% 2 6% 5% 5% 5% 4 6% 8% 43%	2280
	11th to 20th	Day	9% 6% 2 6% 4 3 4 5% 5% 8% 48%	2151
	21st to end	Day	13% 6% 3 6% 5% 5% 6% 4 6% 9% 37%	2062
October	1st to 10th	Day	16% 8% 2 7% 5% 4 5% 4 5% 7% 36%	1900
	11th to 20th	Day	18% 8% 3 9% 4 5% 5% 4 6% 6% 31%	1900
	21st to end	Day	22% 10% 3 8% 6% 5% 6% 3 6% 6% 24%	2090
November	1st to 10th	Day	12% 8% 3 10% 4 6% 5% 4 7% 8% 32%	1646
	11th to 20th	Day	13% 10% 3 9% 7% 6% 6% 4 6% 8% 27%	1520
	21st to end	Day	18% 11% 4 8% 6% 5% 5% 4 7% 7% 24%	1520
December	1st to 10th	Day	15% 15% 4 12% 7% 7% 5% 5% 6% 5% 20%	1520
	11th to 20th	Day	17% 13% 3 10% 6% 6% 6% 5% 6% 6% 21%	1906
	21st to end	Day	28% 16% 6% 11% 6% 5% 5% 3 4 4 11%	2772
January	1st to 10th	Night	16% 14% 4 11% 6% 6% 6% 4 5% 6% 23%	4429
	11th to 20th	Night	14% 12% 5% 12% 8% 6% 6% 4 5% 6% 21%	4148
	21st to end	Night	22% 13% 5% 9% 6% 5% 5% 3 5% 6% 21%	4532
February	1st to 10th	Night	14% 14% 4 10% 7% 5% 5% 5% 6% 7% 24%	2470
	11th to 20th	Night	12% 13% 4 10% 6% 7% 5% 4 5% 6% 27%	2403
	21st to end	Night	14% 11% 4 10% 6% 5% 5% 4 6% 7% 28%	1972
March	1st to 10th	Night	20% 7% 3 8% 5% 5% 5% 4 5% 6% 32%	3408
	11th to 20th	Night	13% 9% 4 8% 5% 3 4 3 5% 7% 39%	3479
	21st to end	Night	16% 9% 3 6% 4 4 3 3 5% 6% 42%	3817
April	1st to 10th	Night	17% 10% 3 8% 5% 5% 5% 4 5% 6% 33%	1948
	11th to 20th	Night	16% 7% 3 7% 5% 4 4 3 6% 7% 37%	1811
	21st to end	Night	16% 9% 2 7% 5% 3 5% 4 4 7% 38%	1710
May	1st to 10th	Night	17% 9% 2 7% 4 4 4 3 5% 7% 38%	2833
	11th to 20th	Night	16% 7% 3 9% 5% 6% 5% 5% 5% 7% 31%	2564
	21st to end	Night	9% 5% 2 4 3 4 4 4 6% 9% 50%	2738
June	1st to 10th	Night	12% 4 2 5% 5% 6% 4 4 6% 9% 43%	1520
	11th to 20th	Night	11% 4 2 6% 4 5% 5% 4 8% 8% 44%	1520
	21st to end	Night	10% 4 2 7% 5% 4 4 4 6% 8% 44%	1520
July	1st to 10th	Night	6% 4 2 6% 4 4 5% 4 5% 9% 52%	2520
	11th to 20th	Night	10% 4 2 4 3 4 4 4 6% 8% 51%	2538
	21st to end	Night	6% 4 2 5% 4 4 5% 4 7% 8% 51%	3087
August	1st to 10th	Night	10% 6% 2 7% 5% 5% 4 4 6% 7% 45%	2825
	11th to 20th	Night	10% 5% 2 6% 4 4 4 4 5% 8% 48%	2785
	21st to end	Night	9% 5% 2 7% 4 4 4 4 7% 9% 46%	3252
September	1st to 10th	Night	10% 6% 2 6% 4 5% 5% 4 5% 7% 47%	1900
	11th to 20th	Night	9% 5% 2 4 4 3 4 3 4 7% 55%	2026
	21st to end	Night	15% 7% 2 6% 5% 4 5% 4 5% 8% 40%	2118
October	1st to 10th	Night	17% 6% 2 7% 4 3 4 4 5% 7% 42%	2280
	11th to 20th	Night	17% 8% 2 8% 4 5% 6% 4 5% 6% 35%	2280
	21st to end	Night	20% 9% 3 7% 5% 5% 5% 4 5% 6% 31%	2508
November	1st to 10th	Night	16% 6% 2 7% 4 5% 5% 3 6% 6% 40%	2472
	11th to 20th	Night	14% 9% 3 8% 5% 5% 5% 5% 7% 7% 31%	2660
	21st to end	Night	18% 10% 4 6% 6% 5% 5% 4 5% 8% 29%	2660
December	1st to 10th	Night	18% 13% 5% 9% 5% 5% 6% 4 5% 6% 24%	2660
	11th to 20th	Night	15% 14% 5% 10% 7% 5% 5% 4 5% 6% 23%	3288
	21st to end	Night	29% 16% 5% 10% 6% 5% 5% 3 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	52% 10% 13% 18% 6% 1	3435
	11th to 20th	Day	49% 9% 15% 18% 8% 1	3480
	21st to end	Day	42% 9% 14% 22% 11% 1	3815
April	1st to 10th	Day	50% 8% 13% 17% 12% 1	2232
	11th to 20th	Day	45% 7% 12% 20% 14% 1	2333
	21st to end	Day	49% 7% 12% 18% 12% 3	2470
May	1st to 10th	Day	44% 8% 15% 19% 12% 2	4120
	11th to 20th	Day	47% 12% 14% 19% 8% 1	4329
	21st to end	Day	32% 9% 15% 23% 18% 3	4837
June	1st to 10th	Day	39% 9% 13% 22% 15% 2	2660
	11th to 20th	Day	36% 9% 14% 24% 16% 1	2660
	21st to end	Day	35% 9% 15% 26% 15% 1	2660
July	1st to 10th	Day	30% 9% 16% 27% 15% 2	4370
	11th to 20th	Day	29% 8% 16% 34% 12% 1	4343
	21st to end	Day	32% 10% 17% 21% 19% 1	4324
August	1st to 10th	Day	39% 8% 15% 22% 14% 1	4091
	11th to 20th	Day	37% 10% 17% 24% 11% 1	4083
	21st to end	Day	30% 8% 15% 35% 12% 1	4372
September	1st to 10th	Day	36% 9% 16% 27% 11% 1	2280
	11th to 20th	Day	30% 9% 16% 29% 15% 1	2151
	21st to end	Day	41% 10% 15% 25% 8%	2062
October	1st to 10th	Day	44% 8% 16% 20% 10% 1	1900
	11th to 20th	Day	50% 7% 16% 20% 7% 1	1900
	21st to end	Day	57% 8% 14% 15% 5%	2090
November	1st to 10th	Day	44% 9% 17% 21% 8% 1	1646
	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	50% 8% 14% 21% 5% 1	3418
	11th to 20th	Night	43% 8% 18% 20% 10% 2	3480
	21st to end	Night	40% 7% 10% 25% 16% 2	3817
April	1st to 10th	Night	50% 7% 11% 19% 12% 1	1948
	11th to 20th	Night	46% 7% 10% 20% 14% 3	1811
	21st to end	Night	45% 8% 10% 19% 16% 2	1710
May	1st to 10th	Night	45% 7% 12% 17% 15% 3	2840
	11th to 20th	Night	47% 10% 14% 18% 8% 2	2565
	21st to end	Night	29% 9% 13% 24% 23% 3	2739
June	1st to 10th	Night	37% 8% 13% 24% 17% 2	1520
	11th to 20th	Night	35% 8% 13% 23% 19% 2	1520
	21st to end	Night	37% 7% 13% 24% 17% 2	1520
July	1st to 10th	Night	30% 7% 14% 23% 23% 4	2480
	11th to 20th	Night	31% 6% 14% 32% 16% 1	2490
	21st to end	Night	29% 8% 18% 27% 18% 2	2988
August	1st to 10th	Night	36% 7% 13% 27% 15% 2	2814
	11th to 20th	Night	34% 7% 16% 31% 11% 1	2812
	21st to end	Night	33% 8% 14% 30% 14% 1	3252
September	1st to 10th	Night	35% 8% 15% 27% 14% 2	1900
	11th to 20th	Night	30% 6% 14% 33% 17%	2026
	21st to end	Night	42% 8% 12% 26% 11% 1	2118
October	1st to 10th	Night	42% 7% 13% 22% 15% 1	2280
	11th to 20th	Night	48% 7% 13% 23% 9%	2280
	21st to end	Night	52% 8% 12% 17% 9% 1	2508
November	1st to 10th	Night	44% 7% 14% 23% 12% 1	2472
	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	18% 17% 33% 24% 7% 1	460
	21st to end	Day	24% 10% 31% 25% 8% 1	506
April	1st to 10th	Day	15% 14% 33% 28% 9% 1	460
	11th to 20th	Day	22% 14% 28% 24% 9% 3	452
	21st to end	Day	20% 9% 31% 28% 9% 2	460
May	1st to 10th	Day	16% 10% 27% 27% 16% 5%	463
	11th to 20th	Day	15% 6% 21% 32% 20% 6%	487
	21st to end	Day	11% 5% 21% 35% 20% 8%	529
June	1st to 10th	Day	11% 6% 27% 36% 16% 4	490
	11th to 20th	Day	12% 5% 22% 31% 26% 4	490
	21st to end	Day	13% 5% 20% 35% 20% 6%	490
July	1st to 10th	Day	7% 2 13% 38% 27% 13%	485
	11th to 20th	Day	12% 3 16% 32% 27% 10%	484
	21st to end	Day	8% 2 17% 37% 28% 8%	532
August	1st to 10th	Day	10% 4 17% 31% 27% 12%	486
	11th to 20th	Day	8% 4 18% 31% 25% 14%	479
	21st to end	Day	9% 4 20% 30% 25% 12%	539
September	1st to 10th	Day	11% 4 20% 30% 21% 13%	490
	11th to 20th	Day	8% 3 19% 26% 26% 18%	490
	21st to end	Day	14% 8% 28% 28% 16% 8%	490
October	1st to 10th	Day	19% 8% 26% 22% 17% 8%	490
	11th to 20th	Day	19% 12% 30% 24% 12% 4	490
	21st to end	Day	26% 11% 28% 24% 10% 1	539
November	1st to 10th	Day	17% 17% 29% 26% 9% 3	277
	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	21% 12% 34% 26% 7%	760
	21st to end	Night	20% 9% 29% 31% 9% 1	836
April	1st to 10th	Night	20% 8% 34% 31% 6% 1	760
	11th to 20th	Night	19% 9% 32% 28% 10% 2	687
	21st to end	Night	20% 6% 29% 33% 12%	570
May	1st to 10th	Night	17% 4 26% 32% 18% 3	570
	11th to 20th	Night	16% 4 21% 41% 17% 1	417
	21st to end	Night	11% 2 22% 36% 26% 2	411
June	1st to 10th	Night	13% 3 22% 42% 18% 1	380
	11th to 20th	Night	12% 2 25% 37% 23% 1	380
	21st to end	Night	10% 3 20% 43% 23% 1	380
July	1st to 10th	Night	6% 2 15% 45% 29% 3	370
	11th to 20th	Night	11% 2 18% 37% 29% 3	373
	21st to end	Night	8% 2 14% 47% 26% 3	624
August	1st to 10th	Night	9% 3 12% 40% 32% 4	567
	11th to 20th	Night	8% 2 14% 36% 34% 5%	564
	21st to end	Night	11% 2 18% 33% 30% 4	703
September	1st to 10th	Night	11% 5% 18% 32% 27% 7%	760
	11th to 20th	Night	11% 4 18% 29% 32% 8%	760
	21st to end	Night	16% 5% 21% 30% 23% 5%	760
October	1st to 10th	Night	19% 4 27% 25% 21% 4	760
	11th to 20th	Night	20% 10% 31% 27% 10% 2	760
	21st to end	Night	25% 9% 30% 30% 6%	836
November	1st to 10th	Night	20% 9% 26% 32% 12% 1	749
	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 2024-10-31 03:39:26. Version ac07

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