Blue Canyon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blue Canyon 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	15% 5% 58%	8706
	Night	19% 5% 52%	8464
Transparency	Day	9% 10% 28% 33% 18%	6335
	Night	10% 10% 26% 32% 20%	5722
Seeing	Day	19% 44% 32%	565
	Night	8% 20% 32% 33% 5%	2386

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% 5% 6% 5% 7% 33%	520
	Night	34% 5% 6% 30%	834
February	Day	41% 5% 28%	536
	Night	41% 5% 24%	709
March	Day	22% 5% 45%	676
	Night	22% 7% 48%	686
April	Day	21% 5% 48%	720
	Night	21% 5% 5% 44%	600
May	Day	20% 5% 6% 41%	836
	Night	21% 49%	526
June	Day	5% 7% 68%	840
	Night	7% 7% 66%	478
July	Day	89%	842
	Night	5% 80%	510
August	Day	80%	1147
	Night	75%	896
September	Day	78%	1025
	Night	79%	921
October	Day	12% 5% 61%	620
	Night	12% 7% 58%	744
November	Day	23% 5% 5% 42%	456
	Night	23% 5% 5% 41%	710
December	Day	40% 6% 5% 24%	488
	Night	40% 31%	850

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	14% 13% 42% 25%	248
	Night	24% 9% 34% 26%	367
February	Day	18% 21% 32% 20% 7%	190
	Night	16% 17% 17% 35% 13%	225
March	Day	14% 5% 34% 36% 9%	391
	Night	8% 8% 30% 39% 12%	416
April	Day	16% 20% 28% 22% 12%	443
	Night	23% 18% 19% 20% 18%	342
May	Day	19% 8% 37% 25% 9%	468
	Night	16% 7% 31% 31% 13%	306
June	Day	9% 15% 48% 25%	680
	Night	8% 15% 40% 32%	380
July	Day	13% 40% 40%	797
	Night	16% 35% 42%	456
August	Day	7% 19% 38% 30%	1017
	Night	8% 24% 33% 28%	783
September	Day	8% 19% 40% 27%	921
	Night	6% 19% 35% 36%	830
October	Day	7% 14% 31% 34% 12%	719
	Night	6% 13% 28% 28% 22%	834
November	Day	17% 18% 32% 27%	279
	Night	15% 15% 28% 30% 9%	424
December	Day	13% 6% 37% 37%	182
	Night	11% 6% 32% 39% 9%	359

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	Day	43% 17% 34%	23
	Night	12% 29% 26% 26%	167
February	Day	31% 43% 21%	32
	Night	26% 34% 24% 13%	138
March	Day	22% 40% 37%	45
	Night	9% 32% 33% 19%	183
April	Day	43% 29% 26%	41
	Night	9% 32% 33% 21%	182
May	Day	32% 36% 28%	49
	Night	16% 39% 34% 6%	125
June	Day	18% 41% 40%	55
	Night	7% 36% 52%	111
July	Day	8% 51% 40%	62
	Night	29% 59% 8%	137
August	Day	10% 64% 24%	90
	Night	6% 32% 49% 10%	325
September	Day	22% 39% 34%	86
	Night	15% 41% 35%	351
October	Day	17% 41% 39%	82
	Night	9% 20% 22% 39% 8%	331
November	Night	16% 31% 32% 18%	187
December	Night	17% 28% 34% 18%	149

Page generated at 2008-08-27 04:51:58. Version ab11