Deerlick Astronomy Village
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Deerlick Astronomy Village 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% 6% 33%	8700
	Night	18% 6% 5% 7% 37%	8474
Transparency	Day	19% 11% 31% 28% 7%	4257
	Night	17% 11% 29% 31% 9%	4579
Seeing	Day	9% 22% 24% 28% 15%	495
	Night	11% 23% 32% 27%	2567

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	18% 7% 6% 5% 5% 39%	551
	Night	18% 8% 6% 5% 40%	802
February	Day	40% 6% 7% 25%	567
	Night	36% 5% 28%	687
March	Day	15% 7% 5% 5% 5% 44%	678
	Night	15% 6% 48%	686
April	Day	16% 5% 6% 49%	715
	Night	10% 7% 5% 6% 50%	606
May	Day	12% 5% 8% 5% 6% 7% 38%	802
	Night	14% 6% 5% 6% 9% 43%	551
June	Day	24% 7% 6% 7% 7% 10% 6% 6% 15%	780
	Night	26% 6% 6% 7% 6% 7% 5% 7% 8% 13%	537
July	Day	18% 5% 6% 9% 5% 6% 10% 22%	801
	Night	12% 5% 5% 5% 9% 6% 8% 11% 26%	558
August	Day	21% 6% 7% 8% 7% 8% 6% 6% 8% 16%	1162
	Night	17% 6% 8% 7% 6% 9% 6% 8% 9% 15%	877
September	Day	21% 5% 6% 39%	971
	Night	20% 5% 8% 40%	975
October	Day	26% 7% 6% 5% 36%	638
	Night	20% 5% 5% 5% 5% 8% 37%	724
November	Day	20% 5% 6% 5% 40%	488
	Night	14% 5% 5% 7% 47%	680
December	Day	16% 5% 58%	547
	Night	16% 5% 5% 54%	791

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	10% 20% 36% 23% 8%	262
	Night	14% 11% 27% 35% 11%	416
February	Day	13% 10% 31% 40%	204
	Night	10% 13% 28% 36% 10%	246
March	Day	19% 7% 40% 28%	375
	Night	17% 10% 31% 35% 5%	396
April	Day	11% 5% 37% 33% 12%	445
	Night	10% 5% 30% 43% 10%	392
May	Day	23% 17% 29% 25%	419
	Night	27% 18% 29% 24%	322
June	Day	46% 17% 25% 10%	213
	Night	32% 26% 26% 14%	153
July	Day	46% 10% 29% 13%	311
	Night	40% 12% 39% 7%	245
August	Day	40% 21% 31% 5%	353
	Night	50% 19% 21% 8%	271
September	Day	12% 10% 25% 39% 12%	519
	Night	11% 13% 30% 36% 8%	539
October	Day	12% 11% 28% 35% 12%	476
	Night	13% 11% 29% 32% 13%	596
November	Day	12% 36% 33% 12%	324
	Night	12% 5% 32% 30% 18%	490
December	Day	5% 7% 30% 41% 14%	356
	Night	8% 28% 40% 17%	513

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	14% 38% 35% 12%	205
February	Night	22% 36% 37%	157
March	Day	15% 33% 33% 15%	51
	Night	24% 34% 30% 10%	219
April	Day	18% 25% 30% 18% 7%	55
	Night	17% 30% 38% 13%	199
May	Day	24% 15% 37% 18%	53
	Night	5% 23% 36% 34%	170
June	Day	26% 26% 28% 14%	42
	Night	20% 35% 37%	136
July	Day	8% 23% 28% 35%	56
	Night	12% 21% 45% 17%	170
August	Day	7% 12% 12% 36% 30%	71
	Night	7% 9% 23% 40% 18%	265
September	Day	8% 22% 29% 32% 6%	79
	Night	5% 16% 35% 39%	304
October	Day	11% 28% 26% 27% 5%	69
	Night	8% 21% 37% 29%	301
November	Day	5% 26% 21% 31% 15%	19
	Night	10% 17% 33% 32%	228
December	Night	22% 25% 27% 24%	213

Page generated at 2008-09-30 05:41:02. Version ab11