Roland's Astro Corral
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Roland's Astro Corral 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	11% 6% 6% 8% 45%	8711
	Night	10% 6% 5% 7% 48%	8456
Transparency	Day	13% 15% 34% 26% 10%	5831
	Night	14% 16% 35% 26% 7%	5745
Seeing	Day	12% 26% 37% 22%	553
	Night	6% 25% 45% 21%	2806

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	6% 7% 5% 8% 49%	506
	Night	10% 6% 5% 5% 51%	848
February	Day	13% 5% 6% 7% 8% 40%	540
	Night	9% 5% 7% 7% 6% 7% 39%	705
March	Day	7% 6% 6% 7% 5% 7% 44%	673
	Night	11% 5% 5% 6% 48%	689
April	Day	21% 5% 7% 5% 8% 35%	720
	Night	22% 5% 5% 5% 42%	600
May	Day	13% 8% 8% 9% 39%	846
	Night	11% 8% 6% 6% 10% 38%	517
June	Day	12% 7% 5% 7% 10% 41%	840
	Night	9% 5% 6% 5% 9% 41%	477
July	Day	7% 7% 5% 8% 8% 50%	857
	Night	7% 7% 5% 6% 10% 47%	496
August	Day	11% 6% 7% 9% 44%	1150
	Night	11% 6% 6% 7% 48%	892
September	Day	8% 5% 6% 8% 56%	1019
	Night	10% 5% 6% 57%	926
October	Day	9% 5% 5% 6% 9% 49%	612
	Night	10% 6% 5% 6% 8% 45%	750
November	Day	10% 7% 7% 5% 5% 7% 43%	460
	Night	12% 5% 5% 6% 49%	705
December	Day	5% 5% 6% 5% 5% 8% 49%	488
	Night	5% 7% 7% 55%	851

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	19% 18% 44% 17%	335
	Night	19% 19% 33% 26%	535
February	Day	20% 13% 46% 16%	320
	Night	18% 14% 33% 26% 6%	387
March	Day	18% 17% 35% 20% 7%	398
	Night	15% 17% 42% 20%	436
April	Day	16% 17% 32% 25% 8%	373
	Night	16% 17% 32% 24% 9%	324
May	Day	15% 21% 35% 20% 6%	491
	Night	23% 24% 31% 17%	288
June	Day	17% 10% 42% 22% 6%	507
	Night	22% 11% 37% 21% 7%	277
July	Day	11% 8% 27% 32% 19%	605
	Night	13% 6% 32% 34% 12%	341
August	Day	10% 15% 31% 31% 10%	736
	Night	12% 18% 35% 25% 7%	581
September	Day	6% 11% 28% 33% 18%	779
	Night	6% 13% 30% 33% 16%	665
October	Day	9% 19% 23% 34% 12%	636
	Night	12% 17% 26% 31% 11%	794
November	Day	19% 12% 41% 18% 9%	308
	Night	14% 17% 37% 23% 6%	483
December	Day	16% 20% 39% 22%	343
	Night	13% 13% 51% 21%	634

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% 45% 18%	270
February	Night	26% 52% 15%	213
March	Day	31% 25% 34% 9%	32
	Night	9% 36% 37% 14%	214
April	Day	22% 38% 34% 6%	50
	Night	12% 29% 36% 21%	149
May	Day	11% 34% 38% 15%	111
	Night	8% 26% 53% 12%	173
June	Day	9% 23% 40% 21%	105
	Night	6% 25% 50% 17%	170
July	Day	6% 18% 28% 41%	116
	Night	5% 10% 48% 35%	180
August	Day	9% 24% 47% 18%	93
	Night	5% 13% 39% 40%	257
September	Day	13% 21% 41% 23%	46
	Night	17% 48% 28%	250
October	Night	6% 22% 41% 25%	355
November	Night	10% 32% 46% 10%	280
December	Night	6% 31% 45% 15%	295

Page generated at 2008-06-05 21:07:50. Version ab11