This page made possible by the sponsorship of: , .

Cherry Springs State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cherry Springs State Park 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	24% 7% 6% 5% 5% 6% 5% 6% 24%	8731
	Night	24% 6% 6% 5% 6% 7% 27%	8440
Transparency	Day	24% 17% 39% 17%	3491
	Night	25% 16% 38% 17%	3729
Seeing	Day	14% 30% 21% 20% 11%	505
	Night	20% 33% 27% 17%	2237

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	29% 9% 12% 7% 5% 18%	527
	Night	30% 8% 10% 6% 6% 5% 17%	826
February	Day	25% 8% 8% 5% 5% 5% 6% 25%	527
	Night	19% 7% 8% 8% 6% 8% 26%	727
March	Day	30% 10% 7% 5% 5% 7% 5% 13%	681
	Night	32% 10% 7% 5% 18%	682
April	Day	27% 8% 5% 5% 32%	730
	Night	31% 5% 5% 5% 5% 30%	591
May	Day	16% 6% 7% 6% 6% 6% 5% 5% 5% 29%	845
	Night	14% 5% 5% 6% 6% 5% 5% 9% 34%	508
June	Day	17% 6% 6% 5% 7% 5% 5% 7% 28%	840
	Night	9% 5% 7% 5% 9% 5% 6% 10% 32%	476
July	Day	23% 5% 6% 6% 8% 6% 6% 8% 20%	848
	Night	14% 5% 5% 7% 8% 12% 30%	514
August	Day	19% 6% 6% 5% 6% 9% 6% 6% 8% 21%	1173
	Night	17% 6% 6% 6% 5% 8% 33%	865
September	Day	22% 5% 5% 5% 5% 6% 34%	1014
	Night	21% 5% 5% 6% 38%	930
October	Day	34% 7% 5% 5% 6% 25%	618
	Night	29% 6% 5% 5% 30%	744
November	Day	30% 7% 5% 7% 7% 6% 6% 18%	442
	Night	36% 6% 5% 8% 20%	725
December	Day	37% 12% 6% 6% 5% 6% 12%	486
	Night	30% 10% 6% 7% 5% 7% 16%	852

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	28% 10% 47% 13%	143
	Night	32% 16% 44% 7%	236
February	Day	23% 10% 39% 26%	203
	Night	29% 9% 33% 23%	286
March	Day	33% 18% 34% 12%	175
	Night	29% 19% 34% 16%	203
April	Day	15% 12% 41% 26%	341
	Night	10% 14% 37% 34%	234
May	Day	22% 20% 41% 15%	360
	Night	23% 24% 42% 10%	266
June	Day	20% 11% 46% 20%	350
	Night	19% 16% 40% 22%	241
July	Day	32% 18% 32% 13%	304
	Night	31% 8% 36% 18% 5%	269
August	Day	30% 27% 35% 6%	445
	Night	27% 22% 34% 13%	414
September	Day	14% 16% 39% 27%	526
	Night	11% 10% 50% 27%	516
October	Day	26% 17% 40% 14%	354
	Night	26% 17% 43% 11%	509
November	Day	32% 17% 43% 6%	190
	Night	39% 21% 24% 12%	305
December	Day	35% 18% 26% 19%	100
	Night	36% 21% 29% 8%	250

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	45% 34% 16%	158
February	Day	8% 33% 50% 8%	12
	Night	28% 42% 22% 5%	185
March	Day	27% 45% 20%	48
	Night	32% 43% 19%	169
April	Day	19% 40% 21% 10% 8%	47
	Night	27% 40% 21% 10%	170
May	Day	18% 41% 15% 16% 7%	53
	Night	11% 49% 24% 14%	129
June	Day	9% 29% 23% 25% 11%	51
	Night	7% 34% 37% 20%	113
July	Day	25% 24% 31% 14%	54
	Night	21% 38% 34%	127
August	Day	7% 20% 25% 27% 20%	80
	Night	23% 37% 31%	270
September	Day	8% 18% 20% 27% 24%	69
	Night	11% 25% 27% 31%	297
October	Day	19% 28% 22% 23% 5%	67
	Night	16% 32% 25% 22%	271
November	Day	41% 41% 12%	24
	Night	28% 28% 34% 6%	176
December	Night	34% 37% 23%	172

Page generated at 2008-06-05 23:07:24. Version ab11