Edmonton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Edmonton 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	11% 9% 5% 7% 6% 6% 5% 6% 8% 29%	16514
	Night	11% 9% 6% 8% 6% 6% 5% 6% 8% 27%	16446
Transparency	Day	11% 22% 21% 5%	12334
	Night	11% 20% 21% 6%	12379
Seeing	Day	9% 28% 32% 18%	1212
	Night	7% 29% 35% 16%	5090

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	6% 11% 8% 9% 8% 8% 5% 8% 24%	880
	Night	8% 11% 7% 9% 7% 6% 5% 7% 26%	1820
February	Day	9% 14% 9% 11% 8% 5% 6% 6% 18%	937
	Night	10% 10% 6% 9% 6% 7% 7% 6% 8% 22%	1456
March	Day	10% 11% 7% 9% 8% 5% 9% 24%	1320
	Night	10% 10% 7% 10% 7% 6% 6% 7% 9% 19%	1401
April	Day	14% 13% 6% 7% 5% 5% 5% 5% 7% 24%	1512
	Night	15% 10% 5% 7% 5% 7% 7% 6% 25%	1088
May	Day	16% 8% 5% 7% 7% 7% 6% 27%	1832
	Night	16% 8% 6% 8% 8% 6% 5% 7% 25%	868
June	Day	15% 7% 6% 5% 6% 5% 6% 8% 28%	1845
	Night	14% 6% 7% 6% 8% 6% 7% 8% 26%	783
July	Day	9% 5% 6% 6% 7% 8% 9% 35%	1854
	Night	9% 5% 8% 7% 8% 12% 32%	835
August	Day	11% 7% 5% 5% 6% 9% 39%	1677
	Night	11% 5% 6% 5% 6% 5% 5% 8% 39%	1042
September	Day	12% 5% 5% 5% 5% 6% 9% 38%	1374
	Night	13% 5% 6% 8% 44%	1230
October	Day	12% 10% 6% 8% 5% 5% 5% 5% 6% 30%	1154
	Night	13% 9% 5% 7% 6% 5% 5% 6% 7% 29%	1536
November	Day	7% 10% 7% 9% 5% 5% 5% 6% 8% 29%	1065
	Night	9% 10% 8% 8% 7% 7% 5% 6% 6% 26%	2105
December	Day	9% 14% 8% 9% 7% 7% 6% 7% 6% 19%	1064
	Night	9% 11% 7% 10% 8% 6% 5% 6% 8% 23%	2282

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	12% 18% 19% 7%	598
	Night	11% 20% 19% 5%	1306
February	Day	9% 24% 17%	611
	Night	14% 23% 19%	1011
March	Day	10% 23% 25%	873
	Night	12% 18% 21% 7%	944
April	Day	8% 21% 16% 7%	1097
	Night	12% 16% 14% 13%	803
May	Day	10% 20% 21% 9%	1274
	Night	9% 19% 21% 9%	587
June	Day	13% 24% 21% 5%	1345
	Night	14% 21% 22% 6%	563
July	Day	15% 27% 22%	1237
	Night	16% 26% 24%	550
August	Day	10% 26% 20% 6%	1521
	Night	10% 24% 23% 6%	925
September	Day	12% 22% 23% 9%	1198
	Night	10% 22% 25% 10%	1072
October	Day	7% 16% 25% 7%	971
	Night	8% 17% 23% 7%	1290
November	Day	11% 24% 24% 5%	817
	Night	11% 18% 21% 6%	1553
December	Day	10% 14% 19%	792
	Night	10% 18% 19% 5%	1775

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	9% 33% 32% 13%	581
February	Day	30% 50% 10%	10
	Night	9% 25% 35% 18%	406
March	Day	5% 37% 33% 17%	118
	Night	6% 31% 33% 18%	469
April	Day	14% 26% 33% 17%	111
	Night	9% 27% 34% 16%	354
May	Day	12% 28% 33% 14%	221
	Night	6% 30% 36% 14%	239
June	Day	9% 25% 32% 22%	271
	Night	5% 25% 37% 19%	217
July	Day	31% 30% 23%	226
	Night	21% 41% 22%	216
August	Day	9% 26% 31% 16%	130
	Night	24% 39% 22%	297
September	Day	13% 26% 33% 14%	110
	Night	6% 21% 45% 17%	407
October	Day	20% 40% 6% 13% 6%	15
	Night	5% 32% 32% 12%	464
November	Night	8% 37% 33% 9%	698
December	Night	7% 27% 30% 19%	742

Page generated at 2009-12-30 03:20:35. Version ab11