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Boise
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Boise 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	13% 5% 5% 7% 47%	8726
	Night	14% 6% 5% 7% 43%	8439
Cloud Cover	Day	13% 5% 5% 7% 47%	8719
	Night	14% 6% 5% 7% 42%	8449
Transparency	Day	15% 16% 28% 25% 13%	5786
	Night	18% 18% 30% 21% 10%	5195
Seeing	Day	13% 30% 32% 20%	537
	Night	6% 17% 38% 33%	2571

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	22% 9% 8% 5% 5% 9% 5% 7% 7% 15%	488
	Night	22% 9% 8% 6% 6% 7% 6% 19%	866
February	Day	21% 5% 5% 7% 40%	546
	Night	18% 5% 5% 6% 9% 39%	707
March	Day	18% 6% 5% 9% 40%	666
	Night	14% 6% 7% 50%	698
April	Day	15% 6% 5% 5% 5% 7% 41%	744
	Night	16% 6% 5% 7% 8% 39%	575
May	Day	17% 5% 6% 5% 5% 6% 6% 34%	834
	Night	18% 8% 5% 6% 5% 36%	518
June	Day	5% 6% 5% 5% 10% 52%	840
	Night	5% 8% 6% 8% 9% 46%	478
July	Day	71%	865
	Night	5% 6% 68%	496
August	Day	7% 5% 66%	1187
	Night	6% 9% 61%	854
September	Day	5% 5% 8% 59%	992
	Night	5% 5% 6% 59%	943
October	Day	13% 5% 5% 6% 9% 43%	610
	Night	15% 5% 5% 5% 8% 46%	753
November	Day	29% 6% 37%	466
	Night	19% 6% 5% 7% 5% 7% 29%	701
December	Day	28% 6% 6% 5% 6% 24%	488
	Night	31% 6% 6% 5% 6% 25%	850

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% 10% 8% 5% 10% 5% 6% 8% 15%	488
	Night	23% 8% 8% 5% 6% 7% 6% 19%	866
February	Day	21% 5% 5% 6% 41%	537
	Night	17% 5% 6% 9% 39%	707
March	Day	16% 5% 6% 5% 9% 40%	665
	Night	13% 5% 7% 49%	697
April	Day	15% 6% 5% 5% 9% 40%	745
	Night	12% 5% 7% 5% 8% 8% 38%	575
May	Day	17% 6% 6% 5% 6% 5% 5% 5% 34%	836
	Night	18% 5% 9% 5% 6% 6% 35%	527
June	Day	5% 7% 5% 5% 10% 53%	840
	Night	5% 8% 6% 8% 9% 46%	478
July	Day	71%	856
	Night	6% 67%	496
August	Day	7% 6% 65%	1188
	Night	6% 9% 62%	854
September	Day	5% 5% 8% 59%	1001
	Night	5% 5% 5% 59%	945
October	Day	13% 5% 6% 10% 43%	610
	Night	15% 5% 5% 5% 8% 46%	753
November	Day	29% 6% 37%	465
	Night	19% 6% 5% 7% 5% 7% 29%	701
December	Day	28% 6% 6% 6% 6% 25%	488
	Night	31% 6% 6% 6% 5% 25%	850

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	63% 16% 19%	147
	Night	39% 42% 17%	261
February	Day	32% 32% 27% 8%	275
	Night	37% 20% 32% 9%	383
March	Day	21% 21% 40% 15%	387
	Night	23% 17% 40% 16%	421
April	Day	19% 24% 32% 21%	446
	Night	21% 29% 28% 18%	333
May	Day	21% 14% 40% 19%	445
	Night	14% 19% 46% 17%	268
June	Day	11% 12% 40% 28% 6%	607
	Night	17% 12% 40% 20% 8%	322
July	Day	18% 40% 34%	700
	Night	9% 15% 36% 36%	390
August	Day	9% 17% 37% 32%	953
	Night	5% 10% 22% 31% 30%	674
September	Day	7% 14% 26% 37% 14%	791
	Night	5% 14% 24% 38% 18%	697
October	Day	12% 23% 37% 20% 5%	594
	Night	13% 17% 40% 23% 5%	731
November	Day	36% 34% 25%	266
	Night	28% 26% 36% 8%	385
December	Day	41% 29% 26%	175
	Night	40% 36% 23%	330

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% 22% 35% 27%	207
February	Day	8% 27% 35% 24% 5%	37
	Night	7% 19% 39% 24% 8%	196
March	Day	12% 37% 31% 12% 5%	54
	Night	7% 15% 44% 29%	219
April	Day	27% 37% 22% 11%	54
	Night	8% 26% 39% 21%	193
May	Day	14% 45% 24% 14%	57
	Night	5% 19% 37% 35%	135
June	Day	20% 41% 26% 10%	60
	Night	19% 45% 29%	118
July	Day	11% 31% 37% 16%	61
	Night	13% 45% 36%	122
August	Day	18% 45% 27%	86
	Night	10% 35% 45% 6%	288
September	Day	11% 22% 32% 31%	87
	Night	13% 33% 44% 5%	345
October	Day	14% 24% 26% 31%	41
	Night	13% 38% 36% 7%	341
November	Night	7% 22% 39% 28%	220
December	Night	14% 20% 42% 20%	187

Page generated at 2008-08-29 14:02:59. Version ab11