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 2008-11-27.

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% 8% 53%	12267
	Night	7% 5% 7% 53%	12164
Transparency	Day	8% 21% 26% 18% 7%	9622
	Night	9% 21% 27% 17% 7%	9570
Seeing	Day	17% 27% 29% 18%	799
	Night	16% 36% 29% 11%	3990

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% 7% 56%	773
	Night	6% 5% 5% 5% 5% 8% 47%	1267
February	Day	9% 5% 7% 10% 43%	756
	Night	5% 6% 5% 6% 6% 8% 46%	1022
March	Day	7% 6% 6% 5% 5% 10% 45%	1009
	Night	5% 7% 5% 6% 10% 45%	1030
April	Day	9% 6% 5% 5% 7% 46%	1079
	Night	9% 6% 5% 7% 47%	896
May	Day	13% 5% 6% 8% 46%	1294
	Night	13% 5% 5% 7% 52%	752
June	Day	5% 5% 7% 60%	1260
	Night	9% 67%	720
July	Day	5% 8% 63%	1301
	Night	7% 7% 63%	740
August	Day	6% 5% 7% 59%	1164
	Night	5% 6% 7% 67%	873
September	Day	12% 5% 5% 58%	1037
	Night	11% 5% 62%	937
October	Day	8% 6% 8% 56%	908
	Night	12% 5% 5% 56%	1122
November	Day	6% 5% 5% 8% 53%	942
	Night	6% 5% 5% 7% 54%	1505
December	Day	5% 6% 5% 5% 7% 9% 44%	744
	Night	5% 6% 5% 5% 6% 5% 5% 7% 42%	1300

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	11% 40% 29% 5%	615
	Night	11% 33% 30% 8%	935
February	Day	15% 36% 26%	540
	Night	14% 34% 28%	774
March	Day	10% 37% 25% 9%	729
	Night	16% 26% 28% 9%	786
April	Day	8% 21% 28% 20%	776
	Night	9% 20% 28% 23%	638
May	Day	8% 21% 30% 16%	1001
	Night	6% 19% 29% 24%	608
June	Day	6% 13% 28% 27% 12%	1073
	Night	5% 15% 30% 27% 14%	628
July	Day	6% 13% 18% 22% 29%	821
	Night	7% 12% 21% 20% 32%	474
August	Day	7% 8% 21% 26% 20%	1052
	Night	8% 22% 27% 25%	801
September	Day	12% 24% 28% 10%	908
	Night	12% 25% 26% 11%	842
October	Day	5% 16% 25% 27%	777
	Night	5% 15% 24% 25% 7%	947
November	Day	8% 29% 28% 14%	800
	Night	8% 24% 30% 17%	1232
December	Day	17% 33% 26%	530
	Night	14% 27% 29% 6%	905

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% 48% 15%	422
February	Night	20% 51% 19%	313
March	Day	42% 31% 12%	63
	Night	18% 40% 31% 6%	348
April	Day	35% 37% 17%	88
	Night	16% 39% 37%	254
May	Day	17% 24% 30% 19%	169
	Night	7% 24% 38% 18%	271
June	Day	14% 21% 35% 22%	168
	Night	6% 25% 41% 22%	253
July	Day	22% 35% 32% 5%	158
	Night	17% 44% 30%	240
August	Day	10% 38% 35% 11%	90
	Night	5% 20% 48% 20%	263
September	Day	20% 26% 23% 14%	63
	Night	25% 36% 21%	270
October	Night	12% 32% 30% 12%	362
November	Night	27% 42% 21%	543
December	Night	25% 45% 20%	451

Page generated at 2008-11-27 11:47:52. Version ab11