Halton Hills
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Halton Hills 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% 11% 4 9% 6% 5% 5% 4 5% 7% 30%	109235
	Night	14% 10% 4 9% 6% 5% 5% 4 5% 6% 32%	109420
Transparency	Day	50% 7% 13% 19% 10% 1	112874
	Night	49% 6% 12% 20% 11% 1	113945
Seeing	Day	19% 18% 30% 20% 9% 3	15066
	Night	19% 17% 31% 23% 9% 1	24306

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	11% 14% 7% 17% 7% 6% 4 3 4 4 24%	3597
	11th to 20th	Day	9% 19% 9% 20% 9% 7% 5% 3 5% 4 10%	4007
	21st to end	Day	16% 16% 7% 16% 8% 6% 4 3 4 4 15%	4466
February	1st to 10th	Day	13% 17% 6% 15% 9% 6% 5% 4 4 5% 18%	1800
	11th to 20th	Day	12% 14% 5% 14% 10% 5% 4 3 5% 6% 21%	1753
	21st to end	Day	17% 14% 6% 12% 7% 6% 4 3 4 4 24%	1520
March	1st to 10th	Day	18% 13% 6% 10% 6% 4 4 3 4 4 28%	3426
	11th to 20th	Day	11% 15% 5% 10% 7% 6% 4 3 6% 5% 29%	3480
	21st to end	Day	15% 12% 3 8% 4 4 5% 4 6% 6% 33%	3815
April	1st to 10th	Day	17% 13% 4 9% 6% 5% 3 3 5% 7% 28%	2218
	11th to 20th	Day	18% 10% 3 7% 5% 4 3 4 5% 6% 35%	2358
	21st to end	Day	20% 10% 3 8% 5% 4 3 4 5% 6% 32%	2470
May	1st to 10th	Day	18% 8% 3 8% 5% 4 4 4 6% 7% 34%	4108
	11th to 20th	Day	16% 10% 3 8% 5% 5% 5% 4 5% 7% 31%	4298
	21st to end	Day	12% 5% 2 6% 4 4 4 4 5% 8% 46%	4837
June	1st to 10th	Day	14% 7% 2 7% 5% 5% 5% 4 6% 9% 36%	2660
	11th to 20th	Day	11% 6% 3 7% 4 4 5% 4 7% 8% 39%	2714
	21st to end	Day	13% 6% 2 6% 6% 5% 5% 5% 6% 8% 38%	2850
July	1st to 10th	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 10% 39%	4642
	11th to 20th	Day	9% 5% 2 5% 4 5% 6% 4 8% 10% 42%	4390
	21st to end	Day	8% 6% 2 7% 5% 5% 6% 5% 8% 8% 41%	4466
August	1st to 10th	Day	17% 7% 2 6% 4 4 5% 4 6% 9% 36%	4104
	11th to 20th	Day	11% 7% 3 8% 6% 5% 6% 5% 7% 10% 33%	4044
	21st to end	Day	10% 5% 3 6% 4 6% 5% 5% 7% 8% 41%	4388
September	1st to 10th	Day	11% 7% 2 7% 5% 5% 5% 4 5% 8% 40%	2280
	11th to 20th	Day	12% 6% 2 7% 4 4 4 4 6% 9% 43%	2129
	21st to end	Day	15% 8% 3 7% 6% 6% 5% 4 6% 8% 33%	2075
October	1st to 10th	Day	18% 10% 3 8% 5% 4 4 3 5% 7% 33%	1900
	11th to 20th	Day	20% 11% 4 9% 5% 5% 4 3 5% 5% 29%	1900
	21st to end	Day	23% 13% 4 9% 6% 5% 5% 3 5% 6% 22%	2090
November	1st to 10th	Day	13% 12% 3 9% 6% 5% 5% 4 6% 6% 30%	1704
	11th to 20th	Day	13% 15% 5% 11% 5% 5% 5% 4 6% 6% 26%	1600
	21st to end	Day	16% 17% 5% 12% 6% 6% 4 4 5% 6% 19%	1600
December	1st to 10th	Day	16% 20% 7% 14% 7% 5% 5% 3 5% 5% 13%	2600
	11th to 20th	Day	22% 18% 5% 10% 6% 7% 4 3 4 5% 18%	2986
	21st to end	Day	25% 19% 7% 14% 6% 5% 4 2 3 3 11%	3960
January	1st to 10th	Night	13% 12% 6% 13% 7% 6% 6% 3 5% 6% 24%	6349
	11th to 20th	Night	11% 12% 7% 16% 12% 9% 7% 5% 6% 5% 11%	5877
	21st to end	Night	14% 12% 7% 14% 7% 5% 6% 4 6% 6% 18%	6490
February	1st to 10th	Night	13% 14% 4 11% 8% 6% 5% 5% 5% 6% 22%	2600
	11th to 20th	Night	12% 12% 5% 13% 8% 6% 6% 3 5% 5% 24%	2533
	21st to end	Night	13% 13% 4 11% 6% 6% 4 5% 6% 6% 26%	2026
March	1st to 10th	Night	17% 10% 4 9% 5% 5% 5% 4 5% 6% 30%	3413
	11th to 20th	Night	11% 9% 4 8% 5% 4 4 4 6% 7% 38%	3479
	21st to end	Night	15% 8% 3 7% 4 5% 4 3 5% 5% 41%	3817
April	1st to 10th	Night	18% 11% 3 8% 5% 4 4 3 5% 7% 31%	1961
	11th to 20th	Night	14% 9% 3 8% 6% 5% 4 4 4 5% 38%	1787
	21st to end	Night	15% 10% 3 7% 5% 4 4 4 5% 6% 36%	1710
May	1st to 10th	Night	17% 7% 2 6% 4 5% 4 4 5% 6% 40%	2833
	11th to 20th	Night	15% 9% 3 7% 5% 5% 5% 3 5% 7% 36%	2591
	21st to end	Night	9% 4 2 5% 4 3 4 5% 6% 8% 50%	2738
June	1st to 10th	Night	11% 5% 2 6% 6% 4 4 5% 6% 9% 42%	1520
	11th to 20th	Night	10% 5% 2 6% 4 4 5% 5% 7% 8% 43%	1457
	21st to end	Night	11% 6% 2 6% 5% 4 3 3 5% 6% 48%	1330
July	1st to 10th	Night	6% 5% 1 5% 4 4 4 4 6% 9% 52%	2318
	11th to 20th	Night	11% 3 2 5% 4 4 4 3 5% 8% 52%	2567
	21st to end	Night	6% 5% 2 5% 4 4 5% 3 7% 8% 50%	3087
August	1st to 10th	Night	10% 5% 2 7% 4 4 4 4 5% 7% 47%	2825
	11th to 20th	Night	11% 5% 2 5% 3 4 4 4 6% 8% 47%	2785
	21st to end	Night	10% 5% 2 6% 4 4 4 4 5% 7% 48%	3234
September	1st to 10th	Night	10% 5% 2 6% 4 4 4 4 6% 7% 48%	1900
	11th to 20th	Night	11% 5% 2 4 3 3 4 3 5% 8% 54%	2047
	21st to end	Night	16% 7% 2 7% 5% 4 3 3 5% 6% 40%	2104
October	1st to 10th	Night	16% 7% 3 7% 4 5% 4 3 5% 7% 40%	2280
	11th to 20th	Night	17% 10% 2 8% 5% 5% 4 3 5% 6% 34%	2280
	21st to end	Night	20% 9% 3 8% 5% 5% 5% 4 5% 6% 30%	2508
November	1st to 10th	Night	14% 9% 3 7% 5% 5% 5% 4 6% 7% 36%	2590
	11th to 20th	Night	14% 12% 4 9% 6% 5% 5% 4 6% 7% 27%	2800
	21st to end	Night	17% 12% 4 10% 6% 5% 4 3 6% 7% 25%	2800
December	1st to 10th	Night	13% 15% 7% 14% 7% 7% 6% 4 7% 6% 15%	4580
	11th to 20th	Night	15% 19% 6% 12% 7% 6% 6% 3 4 5% 18%	5208
	21st to end	Night	23% 19% 7% 12% 6% 5% 4 3 4 4 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	61% 6% 11% 10% 10% 1	3598
	11th to 20th	Day	74% 4 9% 9% 4	4041
	21st to end	Day	70% 5% 11% 8% 6%	4466
February	1st to 10th	Day	66% 8% 9% 13% 4 1	1800
	11th to 20th	Day	62% 6% 9% 14% 7% 2	1762
	21st to end	Day	61% 6% 10% 14% 7% 1	1520
March	1st to 10th	Day	58% 6% 11% 17% 7% 1	3429
	11th to 20th	Day	53% 7% 13% 18% 7% 2	3480
	21st to end	Day	48% 7% 12% 19% 11% 2	3815
April	1st to 10th	Day	55% 6% 11% 16% 11% 1	2218
	11th to 20th	Day	48% 6% 11% 20% 14% 1	2358
	21st to end	Day	52% 6% 11% 18% 12% 2	2470
May	1st to 10th	Day	47% 6% 13% 19% 12% 2	4120
	11th to 20th	Day	49% 9% 13% 21% 7% 1	4302
	21st to end	Day	36% 7% 13% 22% 18% 4	4837
June	1st to 10th	Day	42% 8% 11% 22% 15% 1	2660
	11th to 20th	Day	39% 7% 14% 24% 15% 1	2714
	21st to end	Day	40% 8% 14% 23% 15%	2850
July	1st to 10th	Day	37% 6% 16% 24% 15% 2	4571
	11th to 20th	Day	33% 6% 15% 34% 11% 1	4315
	21st to end	Day	37% 8% 15% 23% 17% 1	4324
August	1st to 10th	Day	43% 7% 13% 23% 13% 1	4091
	11th to 20th	Day	43% 8% 16% 24% 9%	4083
	21st to end	Day	37% 7% 15% 31% 10% 1	4388
September	1st to 10th	Day	41% 7% 14% 26% 11% 1	2280
	11th to 20th	Day	36% 7% 13% 29% 14%	2129
	21st to end	Day	47% 8% 13% 23% 8% 1	2075
October	1st to 10th	Day	43% 5% 13% 25% 13% 1	3160
	11th to 20th	Day	43% 4 14% 21% 16%	3140
	21st to end	Day	55% 5% 13% 20% 7%	3428
November	1st to 10th	Day	50% 7% 14% 20% 8% 1	1704
	11th to 20th	Day	55% 8% 15% 14% 8%	1600
	21st to end	Day	62% 8% 13% 13% 4	1600
December	1st to 10th	Day	69% 6% 13% 9% 3	2600
	11th to 20th	Day	67% 5% 11% 10% 6%	2986
	21st to end	Day	76% 6% 6% 7% 5%	3960
January	1st to 10th	Night	56% 7% 11% 17% 8% 1	6349
	11th to 20th	Night	68% 7% 10% 10% 4	5918
	21st to end	Night	62% 5% 11% 13% 8% 1	6490
February	1st to 10th	Night	59% 8% 11% 16% 5% 1	2600
	11th to 20th	Night	58% 5% 12% 16% 8%	2535
	21st to end	Night	54% 8% 12% 17% 8%	2026
March	1st to 10th	Night	51% 7% 14% 21% 7% 1	3423
	11th to 20th	Night	43% 7% 17% 20% 12% 2	3480
	21st to end	Night	42% 6% 11% 22% 17% 2	3817
April	1st to 10th	Night	52% 6% 9% 18% 14% 1	1961
	11th to 20th	Night	47% 6% 10% 20% 16% 2	1787
	21st to end	Night	46% 6% 10% 19% 16% 2	1710
May	1st to 10th	Night	43% 7% 11% 19% 16% 4	2840
	11th to 20th	Night	44% 9% 15% 20% 9% 2	2592
	21st to end	Night	30% 8% 13% 23% 23% 3	2739
June	1st to 10th	Night	37% 8% 12% 25% 18% 1	1520
	11th to 20th	Night	36% 6% 13% 25% 19% 2	1457
	21st to end	Night	36% 6% 13% 27% 17% 1	1330
July	1st to 10th	Night	28% 5% 14% 25% 22% 4	2280
	11th to 20th	Night	30% 4 13% 34% 17% 1	2519
	21st to end	Night	30% 7% 16% 29% 16% 2	2988
August	1st to 10th	Night	37% 5% 13% 28% 15% 3	2814
	11th to 20th	Night	33% 6% 16% 31% 12% 1	2812
	21st to end	Night	34% 5% 13% 32% 15% 1	3234
September	1st to 10th	Night	33% 8% 14% 29% 15% 1	1900
	11th to 20th	Night	29% 6% 11% 33% 20% 1	2047
	21st to end	Night	43% 6% 12% 27% 11% 1	2104
October	1st to 10th	Night	34% 5% 9% 27% 24% 1	3800
	11th to 20th	Night	45% 5% 11% 24% 15%	3779
	21st to end	Night	42% 5% 15% 26% 11% 1	4120
November	1st to 10th	Night	44% 7% 13% 22% 12% 1	2590
	11th to 20th	Night	52% 8% 14% 16% 8% 1	2800
	21st to end	Night	54% 9% 17% 14% 5%	2800
December	1st to 10th	Night	63% 7% 16% 11% 3	4580
	11th to 20th	Night	64% 6% 10% 13% 6%	5208
	21st to end	Night	73% 6% 9% 8% 4	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	22% 28% 32% 15% 3 1	200
	11th to 20th	Day	24% 33% 29% 12% 2	297
	21st to end	Day	25% 29% 32% 12% 2	330
February	1st to 10th	Day	26% 34% 28% 10% 2	300
	11th to 20th	Day	27% 33% 34% 7%	300
	21st to end	Day	35% 26% 34% 5%	237
March	1st to 10th	Day	23% 23% 33% 17% 4	454
	11th to 20th	Day	22% 25% 35% 13% 4	460
	21st to end	Day	28% 20% 31% 16% 5% 1	506
April	1st to 10th	Day	22% 27% 32% 13% 6%	460
	11th to 20th	Day	30% 21% 28% 13% 6% 2	452
	21st to end	Day	25% 18% 34% 15% 7% 2	460
May	1st to 10th	Day	22% 17% 31% 18% 8% 3	463
	11th to 20th	Day	16% 13% 33% 23% 11% 3	487
	21st to end	Day	12% 13% 32% 25% 13% 5%	529
June	1st to 10th	Day	14% 15% 35% 26% 7% 2	490
	11th to 20th	Day	13% 16% 27% 30% 12% 2	544
	21st to end	Day	16% 12% 34% 27% 8% 3	680
July	1st to 10th	Day	10% 7% 32% 31% 16% 5%	608
	11th to 20th	Day	12% 8% 31% 26% 17% 7%	484
	21st to end	Day	10% 7% 33% 31% 14% 5%	532
August	1st to 10th	Day	12% 6% 29% 28% 18% 7%	486
	11th to 20th	Day	10% 8% 27% 27% 19% 9%	479
	21st to end	Day	14% 8% 27% 28% 17% 6%	539
September	1st to 10th	Day	12% 14% 25% 25% 16% 8%	490
	11th to 20th	Day	10% 7% 24% 26% 21% 12%	490
	21st to end	Day	18% 14% 26% 22% 14% 5%	490
October	1st to 10th	Day	23% 18% 27% 18% 12% 3	490
	11th to 20th	Day	23% 21% 34% 13% 7% 1	490
	21st to end	Day	29% 20% 29% 16% 5%	539
November	1st to 10th	Day	25% 23% 33% 15% 4 1	280
	11th to 20th	Day	23% 30% 30% 11% 5% 1	200
	21st to end	Day	27% 25% 37% 11% 1	200
December	1st to 10th	Day	32% 31% 25% 13% 1	200
	11th to 20th	Day	31% 30% 30% 9% 1	200
	21st to end	Day	30% 30% 27% 11% 1 1	220
January	1st to 10th	Night	21% 29% 34% 13% 3	800
	11th to 20th	Night	26% 24% 32% 16% 2	800
	21st to end	Night	18% 22% 37% 18% 5%	880
February	1st to 10th	Night	20% 31% 31% 17% 2	800
	11th to 20th	Night	22% 24% 34% 16% 3	783
	21st to end	Night	20% 26% 35% 16% 3	647
March	1st to 10th	Night	19% 21% 37% 19% 4	760
	11th to 20th	Night	21% 22% 35% 17% 5%	760
	21st to end	Night	20% 18% 34% 21% 6%	836
April	1st to 10th	Night	22% 18% 35% 22% 3	760
	11th to 20th	Night	19% 17% 35% 20% 8% 1	663
	21st to end	Night	19% 14% 34% 24% 9%	570
May	1st to 10th	Night	17% 12% 31% 27% 12% 2	570
	11th to 20th	Night	16% 9% 31% 31% 13% 1	431
	21st to end	Night	12% 8% 28% 35% 16%	411
June	1st to 10th	Night	12% 8% 33% 33% 12% 1	380
	11th to 20th	Night	11% 8% 32% 36% 12% 1	380
	21st to end	Night	12% 7% 31% 37% 13%	380
July	1st to 10th	Night	6% 5% 28% 41% 19% 1	370
	11th to 20th	Night	9% 5% 31% 34% 19% 1	389
	21st to end	Night	9% 4 28% 38% 20% 2	624
August	1st to 10th	Night	10% 2 26% 37% 23% 2	567
	11th to 20th	Night	8% 5% 21% 38% 25% 3	564
	21st to end	Night	14% 5% 27% 30% 22% 2	685
September	1st to 10th	Night	12% 9% 26% 31% 18% 4	760
	11th to 20th	Night	12% 7% 24% 28% 24% 6%	760
	21st to end	Night	19% 12% 21% 26% 18% 4	760
October	1st to 10th	Night	19% 11% 31% 23% 14% 3	760
	11th to 20th	Night	21% 18% 29% 23% 8% 1	760
	21st to end	Night	24% 19% 32% 21% 4	836
November	1st to 10th	Night	21% 17% 29% 24% 8% 1	780
	11th to 20th	Night	21% 23% 30% 20% 5% 1	800
	21st to end	Night	22% 23% 33% 17% 4	800
December	1st to 10th	Night	26% 25% 31% 13% 5%	800
	11th to 20th	Night	23% 26% 35% 13% 3	800
	21st to end	Night	28% 24% 28% 17% 2	880

Page generated at 2025-02-22 06:51:34. Version ac07

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