Casper
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Casper clear sky chart from 2005-11-05 to 2009-12-29.

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	7% 5% 5% 7% 52%	16474
	Night	6% 5% 5% 7% 53%	16489
Transparency	Day	8% 19% 25% 17% 7%	13828
	Night	8% 19% 26% 17% 6%	13900
Seeing	Day	16% 26% 29% 17%	1078
	Night	16% 35% 29% 11%	5475

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	5% 6% 7% 54%	1024
	Night	5% 8% 5% 5% 7% 48%	1676
February	Day	8% 5% 6% 9% 45%	1018
	Night	6% 5% 5% 6% 8% 47%	1376
March	Day	6% 5% 6% 5% 10% 47%	1347
	Night	5% 6% 5% 7% 9% 46%	1374
April	Day	11% 7% 6% 6% 44%	1418
	Night	11% 7% 6% 48%	1184
May	Day	11% 5% 5% 6% 8% 46%	1713
	Night	10% 6% 54%	986
June	Day	7% 5% 7% 57%	1670
	Night	5% 8% 64%	960
July	Day	5% 8% 61%	1718
	Night	7% 7% 64%	972
August	Day	5% 5% 5% 6% 59%	1554
	Night	5% 7% 69%	1165
September	Day	9% 6% 59%	1371
	Night	9% 6% 65%	1230
October	Day	10% 8% 6% 52%	1204
	Night	11% 9% 5% 50%	1485
November	Day	5% 5% 5% 7% 55%	1220
	Night	5% 5% 7% 56%	1952
December	Day	5% 7% 6% 5% 6% 7% 44%	1217
	Night	5% 7% 5% 5% 5% 5% 7% 43%	2129

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	9% 34% 23% 7%	866
	Night	10% 26% 25% 9%	1345
February	Day	13% 30% 27% 5%	802
	Night	12% 27% 29% 6%	1128
March	Day	9% 30% 28% 11%	1058
	Night	13% 23% 27% 10%	1130
April	Day	8% 19% 23% 17%	1114
	Night	9% 20% 26% 20%	925
May	Day	9% 18% 30% 15%	1427
	Night	6% 17% 28% 24%	847
June	Day	6% 13% 22% 23% 14%	1483
	Night	6% 15% 25% 22% 15%	868
July	Day	6% 12% 20% 20% 23%	1238
	Night	5% 13% 21% 23% 25%	706
August	Day	6% 7% 21% 27% 17%	1442
	Night	8% 25% 27% 22%	1093
September	Day	12% 24% 30% 8%	1242
	Night	11% 27% 28% 11%	1135
October	Day	5% 15% 26% 21%	1075
	Night	5% 14% 23% 20% 5%	1310
November	Day	7% 25% 27% 17%	1078
	Night	7% 22% 29% 19%	1679
December	Day	14% 28% 24%	1003
	Night	10% 24% 27% 5%	1734

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	28% 46% 14%	562
February	Night	20% 52% 18%	425
March	Day	38% 36% 12%	86
	Night	20% 37% 30% 6%	467
April	Day	31% 36% 19%	115
	Night	12% 36% 37% 5%	341
May	Day	18% 24% 28% 18%	227
	Night	10% 25% 37% 17%	358
June	Day	13% 22% 33% 20%	227
	Night	5% 26% 41% 19%	341
July	Day	5% 20% 35% 32%	217
	Night	17% 45% 31%	327
August	Day	9% 38% 35% 11%	121
	Night	19% 46% 23%	356
September	Day	17% 23% 28% 16%	85
	Night	23% 38% 22%	359
October	Night	12% 35% 25% 11%	485
November	Night	23% 40% 25% 5%	707
December	Night	26% 44% 17%	747

Page generated at 2009-12-30 03:20:39. Version ab11