Ottawa
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ottawa clear sky chart from 2005-11-05 to 2008-12-24.

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	21% 8% 6% 5% 5% 6% 28%	12461
	Night	23% 9% 5% 6% 5% 5% 5% 28%	12532
Cloud Cover	Day	22% 8% 5% 6% 5% 5% 6% 28%	12478
	Night	23% 9% 5% 6% 5% 5% 28%	12557
Transparency	Day	10% 17% 23% 10%	8166
	Night	9% 16% 22% 10%	8268
Seeing	Day	9% 30% 29% 16%	690
	Night	13% 33% 29% 8%	3415

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	26% 10% 7% 7% 5% 5% 5% 21%	749
	Night	24% 13% 8% 6% 5% 5% 5% 19%	1290
February	Day	13% 10% 7% 10% 8% 8% 5% 6% 20%	757
	Night	17% 10% 8% 9% 6% 8% 5% 5% 20%	1034
March	Day	19% 8% 6% 9% 5% 29%	989
	Night	19% 9% 6% 8% 6% 31%	1007
April	Day	29% 8% 32%	1099
	Night	25% 7% 5% 5% 7% 31%	880
May	Day	20% 6% 5% 5% 5% 5% 7% 32%	1302
	Night	19% 6% 6% 39%	744
June	Day	20% 6% 7% 7% 6% 5% 7% 24%	1251
	Night	22% 5% 5% 8% 5% 6% 8% 29%	718
July	Day	18% 5% 6% 5% 5% 8% 33%	1301
	Night	13% 5% 6% 6% 5% 5% 6% 38%	740
August	Day	11% 5% 5% 6% 6% 5% 9% 41%	1189
	Night	9% 5% 6% 5% 5% 46%	843
September	Day	19% 5% 5% 7% 40%	1038
	Night	21% 5% 7% 39%	937
October	Day	29% 8% 5% 5% 5% 27%	898
	Night	25% 9% 5% 6% 28%	1136
November	Day	30% 12% 5% 7% 5% 5% 5% 19%	960
	Night	31% 10% 6% 7% 7% 19%	1573
December	Day	26% 16% 7% 7% 7% 6% 13%	928
	Night	30% 13% 7% 6% 18%	1630

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	25% 11% 8% 6% 5% 5% 5% 20%	748
	Night	24% 14% 7% 6% 5% 5% 5% 19%	1291
February	Day	14% 10% 7% 11% 7% 7% 5% 6% 20%	755
	Night	16% 11% 7% 8% 5% 7% 5% 5% 21%	1025
March	Day	23% 8% 6% 6% 5% 5% 29%	1010
	Night	22% 8% 6% 7% 5% 30%	1031
April	Day	30% 7% 5% 32%	1098
	Night	26% 7% 5% 6% 31%	880
May	Day	25% 5% 5% 5% 7% 31%	1301
	Night	22% 6% 7% 38%	744
June	Day	20% 5% 5% 6% 6% 7% 6% 5% 7% 24%	1260
	Night	22% 6% 5% 7% 5% 6% 8% 28%	720
July	Day	18% 5% 5% 6% 5% 8% 33%	1301
	Night	12% 5% 5% 5% 5% 7% 38%	741
August	Day	11% 5% 6% 5% 8% 42%	1184
	Night	12% 5% 5% 5% 6% 46%	845
September	Day	20% 5% 7% 39%	1037
	Night	21% 5% 8% 38%	938
October	Day	30% 8% 5% 5% 5% 27%	898
	Night	26% 9% 5% 6% 28%	1136
November	Day	30% 11% 5% 7% 5% 20%	958
	Night	29% 11% 5% 7% 5% 21%	1572
December	Day	24% 18% 6% 7% 6% 6% 14%	928
	Night	30% 12% 6% 5% 5% 21%	1634

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	10% 24% 15% 6%	413
	Night	10% 19% 17% 7%	693
February	Day	11% 21% 22%	454
	Night	11% 20% 24%	580
March	Day	9% 18% 23% 12%	609
	Night	8% 16% 28% 11%	643
April	Day	7% 12% 25% 17% 11%	623
	Night	9% 14% 24% 20% 7%	526
May	Day	10% 15% 29% 15%	839
	Night	6% 16% 29% 17% 6%	518
June	Day	16% 21% 21% 8%	798
	Night	15% 19% 22% 13%	476
July	Day	13% 23% 22% 8%	710
	Night	11% 21% 28% 10%	420
August	Day	9% 17% 24% 17%	1049
	Night	8% 14% 27% 18%	720
September	Day	8% 15% 38% 7%	815
	Night	8% 12% 35% 10%	746
October	Day	9% 13% 19% 10%	679
	Night	6% 14% 18% 13%	898
November	Day	10% 16% 18%	613
	Night	6% 15% 14% 5%	1024
December	Day	12% 16% 12%	564
	Night	10% 18% 15%	1024

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	20% 39% 24%	321
February	Day	8% 40% 32% 12%	25
	Night	16% 40% 26%	287
March	Day	17% 35% 25% 8%	89
	Night	19% 41% 20% 6%	343
April	Day	19% 26% 27% 17% 5%	73
	Night	16% 30% 34% 9%	287
May	Day	15% 40% 25% 12%	83
	Night	9% 38% 32% 10%	165
June	Day	5% 29% 29% 18%	71
	Night	5% 29% 41% 13%	151
July	Day	22% 38% 20% 6%	72
	Night	26% 48% 14%	157
August	Day	32% 32% 15% 7%	88
	Night	28% 39% 18%	266
September	Day	6% 21% 23% 26% 6%	80
	Night	6% 27% 34% 15%	317
October	Day	7% 26% 32% 13%	79
	Night	10% 27% 29% 11%	335
November	Day	13% 26% 33% 10% 6%	30
	Night	17% 29% 24% 6%	383
December	Night	18% 34% 19%	403

Page generated at 2008-12-24 22:45:20. Version ab11