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Toronto
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Toronto clear sky chart from 2005-11-05 to 2009-12-29.

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	16% 7% 6% 5% 5% 5% 5% 7% 31%	16434
	Night	18% 8% 6% 5% 5% 5% 6% 32%	16499
Cloud Cover	Day	16% 7% 6% 5% 5% 5% 5% 7% 31%	16448
	Night	18% 8% 5% 6% 5% 5% 6% 32%	16515
Transparency	Day	11% 18% 20% 11%	12445
	Night	10% 16% 20% 10%	12366
Seeing	Day	41% 10% 20% 13%	962
	Night	43% 14% 18% 7%	5113

By Month

Percentage Cloud Cover
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month		Occurrence of each Forecast	Data Points
January	Day	20% 15% 6% 8% 7% 6% 6% 5% 15%	1053
	Night	26% 13% 6% 8% 5% 5% 5% 18%	1646
February	Day	18% 13% 7% 7% 7% 6% 20%	995
	Night	16% 10% 7% 10% 7% 6% 5% 6% 20%	1411
March	Day	15% 7% 6% 7% 6% 5% 5% 6% 30%	1340
	Night	16% 7% 6% 6% 5% 5% 36%	1339
April	Day	22% 7% 5% 36%	1465
	Night	19% 8% 5% 5% 5% 35%	1142
May	Day	13% 5% 5% 5% 7% 41%	1683
	Night	14% 5% 6% 6% 46%	1027
June	Day	13% 7% 6% 7% 9% 36%	1663
	Night	11% 5% 5% 5% 6% 9% 40%	956
July	Day	11% 5% 5% 9% 6% 8% 9% 33%	1680
	Night	9% 5% 6% 8% 46%	1009
August	Day	8% 5% 6% 5% 6% 5% 10% 41%	1581
	Night	11% 5% 5% 5% 5% 49%	1132
September	Day	17% 5% 5% 5% 7% 40%	1352
	Night	16% 5% 6% 45%	1252
October	Day	21% 9% 5% 8% 6% 5% 5% 5% 6% 24%	1223
	Night	16% 8% 7% 6% 5% 5% 5% 31%	1471
November	Day	18% 11% 5% 8% 6% 7% 25%	1182
	Night	22% 8% 5% 5% 5% 6% 28%	1988
December	Day	24% 11% 7% 8% 5% 6% 5% 5% 5% 16%	1217
	Night	23% 11% 8% 7% 6% 6% 5% 17%	2126

Percentage Cloud Cover
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month		Occurrence of each Forecast	Data Points
January	Day	21% 15% 5% 9% 6% 6% 6% 5% 15%	1051
	Night	26% 13% 6% 9% 5% 5% 18%	1647
February	Day	18% 13% 8% 8% 7% 5% 6% 20%	993
	Night	16% 10% 8% 10% 6% 6% 7% 20%	1402
March	Day	16% 7% 6% 7% 6% 6% 6% 30%	1363
	Night	17% 7% 6% 5% 5% 5% 36%	1361
April	Day	21% 8% 5% 35%	1464
	Night	19% 8% 5% 5% 5% 5% 35%	1142
May	Day	13% 5% 5% 5% 7% 42%	1678
	Night	15% 5% 5% 6% 46%	1020
June	Day	13% 5% 7% 6% 7% 10% 36%	1672
	Night	12% 5% 5% 5% 6% 9% 40%	958
July	Day	10% 5% 5% 8% 6% 8% 10% 33%	1680
	Night	9% 6% 6% 8% 46%	1010
August	Day	8% 6% 5% 5% 5% 5% 9% 41%	1576
	Night	11% 5% 5% 5% 5% 5% 48%	1134
September	Day	17% 5% 5% 5% 6% 40%	1351
	Night	16% 6% 45%	1253
October	Day	21% 9% 8% 6% 5% 5% 5% 5% 24%	1223
	Night	17% 8% 7% 5% 5% 5% 31%	1471
November	Day	18% 12% 5% 7% 6% 5% 6% 25%	1180
	Night	22% 8% 5% 5% 5% 6% 28%	1987
December	Day	24% 11% 7% 8% 6% 6% 5% 5% 16%	1217
	Night	24% 11% 8% 7% 6% 6% 5% 17%	2130

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	15% 16% 8%	678
	Night	11% 19% 11%	1054
February	Day	13% 21% 12%	653
	Night	14% 21% 11%	963
March	Day	8% 21% 24% 9%	972
	Night	8% 15% 30% 9%	997
April	Day	6% 17% 23% 20%	1033
	Night	9% 14% 19% 20%	813
May	Day	8% 16% 26% 19%	1334
	Night	8% 12% 29% 18% 5%	842
June	Day	15% 22% 24% 11%	1351
	Night	10% 21% 24% 13%	774
July	Day	14% 21% 22% 9%	1132
	Night	11% 21% 22% 17%	679
August	Day	8% 16% 24% 19%	1415
	Night	8% 14% 27% 21%	1005
September	Day	9% 18% 26% 13%	1128
	Night	8% 16% 33% 12%	1050
October	Day	10% 15% 16% 6%	1016
	Night	10% 14% 18% 10%	1244
November	Day	15% 15% 16% 5%	888
	Night	11% 16% 16% 8%	1464
December	Day	13% 17% 6%	845
	Night	14% 17% 8%	1481

Seeing (when cloud cover <= 80%)
Color Meanings: Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month		Occurrence of each Forecast	Data Points
January	Night	54% 20% 8%	491
February	Day	40% 20% 40%	5
	Night	51% 13% 14%	430
March	Day	54% 10% 18% 5%	124
	Night	52% 14% 13%	495
April	Day	50% 10% 15% 7%	119
	Night	51% 11% 18% 6%	422
May	Day	51% 13% 16% 10%	122
	Night	52% 12% 20% 5%	286
June	Day	47% 7% 21% 14%	113
	Night	48% 7% 24% 10%	228
July	Day	45% 22% 14% 5%	110
	Night	46% 5% 25% 15%	255
August	Day	28% 8% 21% 23% 9%	121
	Night	27% 7% 32% 17%	377
September	Day	25% 9% 19% 17% 12%	116
	Night	27% 9% 20% 22% 7%	463
October	Day	27% 20% 28% 8%	121
	Night	29% 22% 23% 7%	487
November	Day	27% 27% 9% 36%	11
	Night	40% 14% 20% 5%	573
December	Night	47% 20% 12%	606

Page generated at 2009-12-30 05:20:34. Version ab11