Bruneau Dunes Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bruneau Dunes Observatory clear sky chart from 2005-11-05 to 2009-10-21.

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	7% 7% 55%	15919
	Night	9% 5% 6% 52%	15542
Transparency	Day	7% 15% 21% 21% 14%	13391
	Night	7% 17% 22% 18% 12%	12840
Seeing	Day	12% 31% 30% 17%	941
	Night	5% 22% 37% 24%	4632

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	15% 10% 6% 6% 9% 30%	982
	Night	13% 9% 5% 8% 5% 5% 7% 34%	1713
February	Day	8% 7% 5% 5% 5% 7% 7% 7% 37%	1053
	Night	11% 5% 5% 6% 9% 41%	1341
March	Day	8% 7% 6% 5% 6% 6% 8% 37%	1322
	Night	10% 6% 5% 7% 5% 5% 8% 39%	1399
April	Day	7% 5% 5% 8% 50%	1466
	Night	9% 5% 8% 48%	1137
May	Day	6% 8% 58%	1645
	Night	6% 7% 60%	1054
June	Day	6% 7% 60%	1669
	Night	5% 6% 60%	960
July	Day	5% 74%	1719
	Night	5% 74%	973
August	Day	5% 75%	1571
	Night	78%	1146
September	Day	74%	1341
	Night	75%	1261
October	Day	6% 5% 7% 55%	1110
	Night	8% 5% 6% 58%	1340
November	Day	11% 6% 5% 5% 5% 5% 7% 41%	1039
	Night	15% 5% 6% 45%	1495
December	Day	19% 9% 5% 5% 7% 6% 32%	1002
	Night	21% 10% 5% 6% 32%	1723

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	21% 24% 13%	753
	Night	12% 28% 17%	1274
February	Day	12% 28% 25% 5%	781
	Night	12% 32% 27%	1033
March	Day	12% 22% 32% 6%	990
	Night	12% 19% 35% 7%	1033
April	Day	6% 23% 29% 22%	1172
	Night	6% 19% 30% 23%	897
May	Day	7% 12% 29% 27% 9%	1486
	Night	8% 11% 28% 28% 10%	964
June	Day	5% 11% 17% 30% 21%	1472
	Night	7% 11% 19% 22% 24%	847
July	Day	8% 26% 49%	1310
	Night	5% 25% 55%	731
August	Day	5% 11% 35% 34%	1526
	Night	6% 10% 29% 43%	1117
September	Day	6% 15% 38% 24%	1287
	Night	5% 14% 34% 32%	1215
October	Day	8% 14% 32% 18%	1063
	Night	5% 14% 31% 24%	1275
November	Day	13% 22% 29% 8%	813
	Night	8% 18% 29% 19%	1154
December	Day	11% 29% 18%	738
	Night	10% 26% 21%	1300

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	28% 39% 16%	456
February	Day	16% 25% 29% 20%	77
	Night	29% 40% 18%	408
March	Day	15% 42% 24% 9%	119
	Night	9% 32% 35% 15%	475
April	Day	22% 35% 23% 12%	113
	Night	10% 27% 34% 19%	395
May	Day	15% 25% 33% 20%	120
	Night	7% 21% 33% 30% 5%	316
June	Day	9% 36% 31% 14% 6%	116
	Night	6% 13% 39% 34%	226
July	Day	29% 42% 21%	107
	Night	14% 40% 39%	218
August	Day	5% 28% 42% 16% 5%	120
	Night	13% 47% 28%	390
September	Day	8% 19% 25% 31% 9%	116
	Night	5% 12% 31% 37% 11%	458
October	Day	20% 37% 16% 11%	53
	Night	19% 36% 27%	436
November	Night	22% 40% 21%	420
December	Night	23% 36% 16%	434

Page generated at 2009-10-21 17:32:01. Version ab11