Brockville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brockville clear sky chart from 2003-08-01 to 2005-11-07.

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	24% 5% 5% 5% 5% 7% 29%	8747
	Night	26% 6% 6% 5% 5% 6% 27%	8427
Transparency	Day	26% 20% 34% 17%	3799
	Night	24% 21% 36% 15%	3561
Seeing	Day	14% 31% 32% 16% 5%	495
	Night	18% 34% 31% 15%	2219

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	27% 12% 9% 6% 5% 7% 16%	500
	Night	28% 10% 7% 9% 6% 19%	853
February	Day	28% 7% 7% 5% 28%	533
	Night	24% 11% 7% 5% 6% 28%	721
March	Day	30% 6% 7% 5% 25%	676
	Night	27% 9% 9% 5% 5% 5% 5% 24%	688
April	Day	31% 5% 6% 30%	730
	Night	37% 33%	592
May	Day	21% 5% 5% 7% 5% 8% 31%	863
	Night	23% 5% 8% 6% 7% 6% 26%	490
June	Day	13% 7% 5% 6% 14% 32%	840
	Night	14% 7% 5% 10% 40%	476
July	Day	18% 5% 5% 10% 8% 31%	866
	Night	18% 6% 5% 7% 6% 7% 9% 28%	496
August	Day	20% 5% 5% 7% 6% 5% 7% 28%	1187
	Night	20% 5% 7% 6% 9% 30%	851
September	Day	18% 5% 9% 43%	1023
	Night	20% 5% 7% 40%	922
October	Day	35% 6% 6% 25%	602
	Night	29% 6% 6% 6% 27%	760
November	Day	31% 7% 5% 6% 5% 5% 21%	441
	Night	34% 6% 7% 6% 5% 21%	726
December	Day	40% 8% 6% 6% 14%	486
	Night	37% 9% 7% 5% 6% 16%	852

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	34% 21% 33% 9%	153
	Night	28% 29% 30% 12%	257
February	Day	28% 16% 34% 21%	185
	Night	19% 20% 43% 16%	267
March	Day	28% 31% 23% 11%	230
	Night	27% 27% 33% 7%	235
April	Day	22% 8% 35% 30%	288
	Night	10% 12% 38% 34%	250
May	Day	31% 18% 30% 19%	387
	Night	24% 21% 32% 21%	185
June	Day	27% 18% 34% 18%	438
	Night	24% 14% 44% 16%	283
July	Day	20% 16% 44% 18%	378
	Night	19% 14% 42% 20%	225
August	Day	23% 22% 36% 14%	515
	Night	28% 25% 32% 12%	403
September	Day	15% 23% 40% 18%	602
	Night	17% 25% 38% 18%	513
October	Day	32% 29% 27% 10%	328
	Night	28% 23% 36% 11%	441
November	Day	43% 21% 22% 12%	180
	Night	37% 20% 32% 7%	279
December	Day	33% 14% 40% 11%	115
	Night	29% 17% 38% 15%	223

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	34% 39% 19% 6%	183
February	Day	6% 60% 26% 6%	15
	Night	22% 29% 31% 16%	172
March	Day	17% 30% 36% 10%	46
	Night	19% 36% 27% 15%	188
April	Day	20% 46% 18% 9%	43
	Night	21% 40% 26% 12%	165
May	Day	17% 28% 37% 11%	45
	Night	15% 38% 34% 12%	100
June	Day	11% 37% 29% 20%	54
	Night	11% 30% 36% 20%	111
July	Day	6% 20% 44% 26%	45
	Night	8% 27% 44% 19%	107
August	Day	14% 29% 27% 20% 9%	85
	Night	5% 33% 37% 22%	250
September	Day	10% 26% 31% 21% 10%	76
	Night	12% 27% 35% 20%	309
October	Day	15% 23% 39% 20%	64
	Night	18% 31% 31% 17%	281
November	Day	36% 40% 22%	22
	Night	24% 39% 30% 6%	183
December	Night	27% 38% 26% 7%	170

Page generated at 2008-05-17 22:27:17. Version ab11