West Columbia
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the West Columbia 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	20% 5% 5% 6% 5% 7% 32%	8702
	Night	20% 5% 6% 6% 35%	8470
Transparency	Day	18% 12% 31% 28% 8%	4127
	Night	15% 12% 32% 28% 10%	4330
Seeing	Day	7% 19% 29% 28% 14%	518
	Night	11% 24% 34% 26%	2584

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	17% 5% 5% 5% 6% 6% 40%	551
	Night	18% 6% 8% 6% 40%	802
February	Day	38% 5% 29%	557
	Night	32% 5% 5% 30%	696
March	Day	19% 5% 6% 7% 39%	682
	Night	15% 6% 5% 46%	682
April	Day	16% 5% 7% 45%	710
	Night	12% 5% 6% 5% 50%	611
May	Day	14% 5% 9% 6% 5% 8% 34%	802
	Night	19% 5% 5% 6% 7% 6% 5% 32%	551
June	Day	23% 7% 8% 6% 8% 5% 6% 8% 16%	780
	Night	23% 7% 8% 5% 9% 5% 9% 6% 5% 7% 11%	537
July	Day	22% 6% 5% 6% 10% 7% 6% 8% 18%	801
	Night	15% 5% 6% 6% 8% 11% 5% 7% 10% 18%	558
August	Day	21% 8% 7% 6% 6% 9% 6% 6% 9% 13%	1178
	Night	22% 7% 8% 8% 6% 10% 5% 5% 8% 12%	861
September	Day	18% 6% 5% 6% 38%	971
	Night	23% 6% 5% 7% 32%	975
October	Day	20% 9% 5% 5% 38%	626
	Night	24% 6% 5% 7% 34%	735
November	Day	22% 5% 6% 46%	497
	Night	18% 6% 50%	671
December	Day	14% 5% 54%	547
	Night	13% 5% 55%	791

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	11% 18% 28% 34% 6%	286
	Night	9% 14% 36% 27% 11%	422
February	Day	10% 9% 32% 39% 9%	217
	Night	14% 9% 29% 39% 7%	279
March	Day	17% 7% 41% 27% 6%	363
	Night	15% 6% 38% 31% 8%	399
April	Day	12% 5% 30% 38% 12%	413
	Night	13% 33% 39% 11%	378
May	Day	25% 12% 37% 24%	360
	Night	25% 17% 40% 15%	254
June	Day	48% 15% 20% 15%	215
	Night	48% 25% 20% 5%	135
July	Day	43% 14% 32% 9%	276
	Night	37% 13% 43% 6%	188
August	Day	38% 22% 28% 10%	340
	Night	42% 30% 20% 6%	235
September	Day	11% 13% 33% 30% 11%	506
	Night	11% 15% 31% 29% 11%	496
October	Day	14% 10% 25% 34% 14%	468
	Night	10% 12% 31% 30% 15%	530
November	Day	9% 9% 38% 30% 13%	330
	Night	10% 7% 31% 34% 15%	488
December	Day	10% 30% 39% 16%	353
	Night	5% 8% 30% 37% 17%	526

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	17% 39% 32% 9%	213
February	Day	50% 50%	2
	Night	16% 36% 43%	159
March	Day	11% 34% 40% 11%	52
	Night	16% 40% 30% 11%	213
April	Day	9% 23% 38% 23% 5%	52
	Night	13% 30% 44% 11%	209
May	Day	22% 16% 38% 20%	54
	Night	5% 24% 37% 29%	157
June	Day	11% 15% 22% 29% 20%	44
	Night	5% 16% 34% 42%	149
July	Day	6% 12% 20% 31% 29%	58
	Night	9% 11% 23% 41% 14%	173
August	Day	12% 9% 20% 28% 28%	77
	Night	10% 13% 22% 40% 12%	264
September	Day	20% 37% 29% 9%	74
	Night	7% 12% 37% 40%	300
October	Day	24% 38% 29%	75
	Night	12% 23% 36% 26%	302
November	Day	10% 20% 23% 33% 13%	30
	Night	12% 17% 31% 31% 6%	229
December	Night	9% 31% 36% 21%	216

Page generated at 2008-06-05 23:08:14. Version ab11