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Alpha Ridge Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Alpha Ridge Park 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	19% 6% 5% 7% 34%	8727
	Night	20% 5% 6% 6% 37%	8445
Transparency	Day	17% 15% 40% 22%	4593
	Night	16% 14% 42% 23%	4591
Seeing	Day	12% 28% 28% 20% 9%	539
	Night	16% 31% 31% 18%	2421

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% 6% 5% 6% 5% 33%	533
	Night	22% 5% 5% 5% 40%	820
February	Day	16% 7% 7% 8% 38%	537
	Night	15% 6% 7% 5% 7% 40%	717
March	Day	19% 5% 5% 5% 8% 5% 5% 5% 31%	682
	Night	22% 7% 5% 5% 7% 5% 35%	682
April	Day	21% 5% 5% 6% 41%	720
	Night	24% 5% 6% 37%	600
May	Day	17% 6% 5% 5% 5% 7% 38%	835
	Night	17% 8% 5% 5% 6% 37%	518
June	Day	14% 5% 8% 6% 7% 10% 31%	840
	Night	13% 9% 5% 5% 10% 35%	476
July	Day	15% 5% 6% 7% 6% 8% 5% 8% 9% 23%	840
	Night	19% 6% 5% 9% 7% 8% 30%	521
August	Day	20% 5% 6% 5% 5% 8% 5% 5% 7% 27%	1158
	Night	17% 6% 5% 6% 6% 6% 9% 30%	881
September	Day	23% 5% 5% 7% 38%	1019
	Night	21% 5% 7% 39%	926
October	Day	26% 5% 6% 40%	618
	Night	28% 5% 5% 37%	744
November	Day	17% 5% 6% 5% 8% 37%	459
	Night	22% 5% 5% 5% 7% 34%	708
December	Day	18% 5% 45%	486
	Night	15% 7% 6% 5% 42%	852

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	36% 10% 34% 16%	232
	Night	26% 15% 41% 16%	401
February	Day	16% 16% 33% 28%	293
	Night	12% 9% 47% 22% 7%	372
March	Day	17% 26% 39% 15%	297
	Night	15% 14% 44% 23%	329
April	Day	10% 8% 42% 30% 7%	401
	Night	9% 6% 43% 32% 6%	292
May	Day	20% 17% 46% 15%	434
	Night	24% 15% 41% 17%	273
June	Day	21% 13% 44% 20%	433
	Night	19% 14% 51% 14%	257
July	Day	22% 13% 40% 21%	342
	Night	18% 20% 38% 18%	251
August	Day	18% 22% 43% 14%	531
	Night	26% 24% 29% 18%	441
September	Day	7% 12% 34% 35% 9%	553
	Night	7% 11% 38% 35% 6%	512
October	Day	12% 13% 44% 28%	490
	Night	14% 10% 43% 30%	570
November	Day	17% 21% 39% 19%	319
	Night	10% 15% 49% 22%	423
December	Day	20% 12% 45% 20%	268
	Night	17% 14% 44% 21%	470

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	30% 49% 16%	193
February	Day	20% 55% 20% 5%	20
	Night	20% 50% 23% 6%	196
March	Day	23% 41% 29% 5%	51
	Night	28% 42% 25%	190
April	Day	21% 36% 27% 10%	47
	Night	17% 38% 35% 8%	190
May	Day	7% 35% 33% 12% 11%	54
	Night	9% 36% 35% 18%	134
June	Day	5% 27% 36% 25% 5%	55
	Night	10% 24% 45% 19%	110
July	Day	26% 32% 28% 9%	53
	Night	5% 16% 37% 37%	124
August	Day	11% 13% 29% 28% 17%	81
	Night	8% 12% 35% 40%	292
September	Day	11% 21% 25% 25% 16%	71
	Night	13% 18% 37% 28%	305
October	Day	14% 32% 21% 20% 11%	70
	Night	13% 26% 32% 22%	286
November	Day	21% 24% 24% 29%	37
	Night	16% 29% 33% 20%	200
December	Night	25% 39% 28% 5%	201

Page generated at 2008-08-20 18:20:56. Version ab11