Riley Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Riley Observatory 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	17% 6% 5% 6% 5% 8% 34%	8735
	Night	20% 6% 5% 5% 6% 35%	8439
Transparency	Day	18% 19% 39% 20%	4565
	Night	18% 17% 39% 22%	4463
Seeing	Day	8% 26% 31% 23% 11%	576
	Night	12% 31% 35% 20%	2489

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	32% 9% 10% 5% 6% 5% 5% 13%	495
	Night	32% 6% 7% 6% 24%	858
February	Day	22% 12% 8% 6% 5% 5% 7% 22%	554
	Night	25% 6% 7% 5% 5% 31%	699
March	Day	21% 9% 8% 7% 6% 8% 24%	670
	Night	25% 7% 5% 5% 5% 5% 30%	695
April	Day	15% 5% 6% 7% 9% 33%	730
	Night	16% 8% 5% 5% 5% 39%	590
May	Day	17% 6% 7% 5% 7% 6% 5% 5% 7% 27%	838
	Night	14% 5% 8% 6% 7% 8% 32%	515
June	Day	11% 8% 7% 6% 9% 36%	840
	Night	7% 7% 5% 6% 11% 44%	476
July	Day	11% 5% 8% 5% 6% 10% 37%	866
	Night	12% 5% 7% 6% 11% 39%	496
August	Day	12% 5% 8% 5% 8% 38%	1167
	Night	8% 5% 5% 7% 6% 9% 42%	875
September	Day	10% 5% 8% 52%	1012
	Night	11% 5% 6% 56%	930
October	Day	18% 5% 5% 7% 39%	609
	Night	18% 5% 7% 5% 6% 9% 32%	753
November	Day	34% 7% 6% 5% 6% 23%	467
	Night	34% 9% 5% 24%	700
December	Day	23% 8% 7% 5% 35%	487
	Night	25% 11% 9% 5% 5% 6% 24%	852

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	39% 23% 26% 10%	123
	Night	26% 16% 42% 14%	269
February	Day	41% 16% 33% 8%	196
	Night	32% 21% 35% 10%	309
March	Day	26% 23% 43% 5%	238
	Night	19% 23% 41% 15%	304
April	Day	22% 14% 42% 19%	389
	Night	21% 6% 46% 23%	309
May	Day	21% 23% 48% 6%	353
	Night	19% 21% 47% 11%	268
June	Day	15% 14% 44% 23%	452
	Night	20% 13% 42% 22%	308
July	Day	16% 12% 44% 21%	507
	Night	22% 11% 38% 21% 6%	308
August	Day	13% 27% 31% 24%	624
	Night	15% 22% 34% 23%	549
September	Day	10% 17% 30% 35% 6%	707
	Night	6% 11% 35% 38% 7%	659
October	Day	15% 18% 46% 18%	553
	Night	15% 18% 38% 25%	577
November	Day	16% 20% 47% 14%	207
	Night	17% 20% 41% 20%	294
December	Day	22% 23% 41% 12%	216
	Night	26% 22% 34% 14%	309

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	18% 45% 27% 8%	209
February	Night	7% 44% 31% 15%	179
March	Day	12% 31% 43% 6% 6%	16
	Night	21% 36% 29% 11%	170
April	Day	43% 31% 17%	51
	Night	14% 35% 38% 11%	154
May	Day	17% 43% 28% 9%	88
	Night	10% 37% 43% 8%	162
June	Day	5% 31% 30% 23% 8%	107
	Night	22% 49% 24%	167
July	Day	9% 21% 32% 21% 15%	108
	Night	16% 48% 30%	166
August	Day	8% 13% 26% 29% 21%	104
	Night	12% 37% 40% 5%	259
September	Day	12% 35% 35% 12%	82
	Night	5% 17% 36% 37%	285
October	Day	25% 30% 35% 10%	20
	Night	13% 28% 32% 24%	322
November	Night	21% 47% 27%	184
December	Night	25% 39% 26% 8%	232

Page generated at 2008-09-30 04:41:18. Version ab11