Boise
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Boise 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	10% 5% 5% 7% 48%	16499
	Night	13% 6% 6% 46%	16460
Transparency	Day	5% 16% 22% 19% 11%	13640
	Night	5% 16% 23% 17% 10%	13382
Seeing	Day	12% 31% 31% 17%	935
	Night	5% 15% 37% 27% 5%	4810

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	18% 9% 9% 7% 6% 6% 6% 6% 20%	982
	Night	19% 12% 5% 8% 6% 6% 26%	1713
February	Day	10% 10% 5% 6% 6% 7% 5% 6% 9% 26%	1042
	Night	16% 9% 5% 5% 5% 5% 5% 6% 33%	1352
March	Day	14% 8% 6% 7% 5% 8% 31%	1324
	Night	14% 12% 6% 5% 5% 5% 7% 31%	1397
April	Day	11% 5% 6% 7% 42%	1463
	Night	11% 6% 5% 5% 46%	1139
May	Day	6% 6% 8% 53%	1661
	Night	6% 7% 9% 51%	1038
June	Day	7% 5% 6% 7% 52%	1669
	Night	6% 8% 54%	960
July	Day	6% 72%	1719
	Night	5% 75%	973
August	Day	73%	1581
	Night	5% 73%	1137
September	Day	7% 69%	1346
	Night	5% 71%	1256
October	Day	9% 5% 5% 5% 7% 48%	1204
	Night	8% 5% 8% 53%	1489
November	Day	15% 6% 5% 5% 6% 6% 38%	1292
	Night	20% 6% 42%	1878
December	Day	23% 10% 5% 7% 6% 5% 6% 23%	1216
	Night	24% 10% 5% 5% 6% 28%	2128

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	15% 25% 9%	712
	Night	13% 24% 14%	1238
February	Day	14% 30% 18%	753
	Night	11% 27% 27%	1010
March	Day	9% 28% 25%	973
	Night	8% 19% 33% 5%	967
April	Day	6% 23% 31% 15%	1130
	Night	17% 34% 21%	875
May	Day	16% 32% 24% 5%	1447
	Night	5% 14% 28% 31% 5%	902
June	Day	5% 12% 18% 29% 17%	1433
	Night	11% 22% 22% 21%	811
July	Day	11% 31% 45%	1280
	Night	9% 30% 50%	720
August	Day	16% 36% 28%	1518
	Night	5% 14% 32% 35%	1097
September	Day	6% 24% 35% 19%	1288
	Night	18% 35% 28%	1186
October	Day	21% 28% 15%	1149
	Night	16% 32% 21%	1398
November	Day	9% 22% 28% 8%	1035
	Night	5% 16% 30% 17%	1520
December	Day	9% 24% 15%	922
	Night	8% 24% 19%	1658

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	8% 16% 37% 21%	437
February	Day	8% 31% 23% 24%	73
	Night	5% 17% 37% 25%	398
March	Day	14% 35% 29% 8%	118
	Night	12% 20% 36% 16%	461
April	Day	16% 40% 22% 14%	110
	Night	10% 24% 34% 22%	394
May	Day	17% 28% 30% 17%	119
	Night	8% 19% 32% 28% 5%	302
June	Day	9% 34% 29% 20%	115
	Night	13% 38% 34%	223
July	Day	10% 20% 46% 17%	108
	Night	7% 39% 45%	218
August	Day	8% 34% 35% 16%	120
	Night	8% 45% 33% 6%	382
September	Day	8% 22% 38% 23%	116
	Night	10% 29% 38% 15%	457
October	Day	17% 32% 21% 8% 5%	56
	Night	15% 35% 30% 6%	480
November	Night	15% 38% 24% 7%	517
December	Night	14% 39% 19%	541

Page generated at 2009-12-30 03:20:22. Version ab11