Blackfoot
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blackfoot clear sky chart from 2005-11-05 to 2008-11-27.

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	13% 8% 6% 7% 6% 6% 5% 5% 8% 28%	12266
	Night	12% 9% 6% 7% 6% 7% 5% 6% 7% 26%	12164
Transparency	Day	12% 27% 22% 5%	8165
	Night	11% 24% 23% 6%	8064
Seeing	Day	11% 30% 34% 15%	847
	Night	9% 32% 35% 14%	3684

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	12% 8% 9% 9% 12% 6% 22%	660
	Night	7% 11% 8% 10% 7% 8% 5% 6% 7% 23%	1382
February	Day	11% 13% 12% 11% 8% 5% 20%	694
	Night	10% 10% 7% 10% 6% 7% 6% 6% 8% 22%	1083
March	Day	11% 14% 8% 8% 5% 5% 5% 8% 24%	988
	Night	14% 11% 7% 9% 9% 6% 6% 7% 7% 16%	1051
April	Day	18% 10% 5% 5% 5% 5% 5% 8% 26%	1155
	Night	17% 10% 6% 6% 5% 7% 5% 28%	818
May	Day	19% 7% 6% 6% 6% 7% 6% 6% 5% 24%	1383
	Night	21% 10% 5% 5% 7% 6% 5% 6% 22%	662
June	Day	16% 7% 5% 7% 6% 6% 5% 6% 8% 25%	1350
	Night	14% 6% 6% 5% 8% 6% 7% 7% 28%	630
July	Day	8% 7% 7% 7% 7% 9% 36%	1394
	Night	6% 5% 5% 10% 6% 6% 11% 34%	646
August	Day	15% 5% 5% 5% 6% 10% 35%	1256
	Night	12% 7% 5% 6% 6% 5% 7% 8% 35%	781
September	Day	14% 7% 6% 5% 5% 5% 11% 34%	1041
	Night	16% 5% 5% 9% 38%	936
October	Day	10% 7% 5% 5% 7% 5% 5% 5% 7% 36%	866
	Night	10% 6% 7% 7% 6% 6% 9% 32%	1164
November	Day	8% 9% 10% 12% 7% 6% 5% 7% 25%	828
	Night	10% 12% 7% 10% 7% 7% 6% 21%	1617
December	Day	8% 13% 9% 7% 6% 5% 9% 7% 5% 7% 18%	651
	Night	9% 11% 8% 8% 6% 6% 6% 8% 24%	1394

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	9% 25% 24%	365
	Night	11% 29% 23%	859
February	Day	6% 26% 24%	365
	Night	11% 29% 22% 5%	665
March	Day	12% 29% 24%	575
	Night	13% 21% 22% 7%	576
April	Day	11% 29% 16% 8%	764
	Night	11% 24% 19% 10%	541
May	Day	13% 22% 25% 8%	843
	Night	10% 23% 23% 10%	375
June	Day	16% 30% 21%	864
	Night	15% 29% 25%	411
July	Day	18% 31% 21%	794
	Night	14% 31% 27%	360
August	Day	9% 29% 22%	1111
	Night	9% 22% 26% 5%	669
September	Day	13% 27% 22% 5%	868
	Night	12% 28% 23% 6%	774
October	Day	9% 18% 29% 11%	683
	Night	10% 21% 29% 10%	904
November	Day	9% 28% 17%	561
	Night	11% 19% 19%	1057
December	Day	15% 16% 22% 6%	372
	Night	13% 22% 19% 8%	873

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	12% 33% 35% 11%	439
February	Day	33% 33% 33%	3
	Night	10% 37% 31% 13%	299
March	Day	11% 37% 34% 10%	88
	Night	9% 34% 31% 13%	343
April	Day	18% 29% 24% 17%	86
	Night	6% 31% 35% 16%	255
May	Day	12% 31% 35% 12%	167
	Night	14% 22% 40% 15%	177
June	Day	11% 25% 33% 17% 6%	160
	Night	8% 20% 44% 13%	158
July	Day	30% 35% 21%	156
	Night	25% 40% 24%	161
August	Day	7% 33% 36% 11%	100
	Night	26% 38% 19%	224
September	Day	20% 23% 42% 10%	80
	Night	6% 24% 42% 20%	294
October	Day	71% 14% 14%	7
	Night	10% 32% 36% 11%	351
November	Night	12% 42% 28% 7%	532
December	Night	10% 33% 32% 13%	451

Page generated at 2008-11-27 11:47:44. Version ab11