Chiefland Astronomy Village
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chiefland 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	15% 5% 5% 5% 8% 6% 6% 8% 31%	8677
	Night	14% 7% 5% 6% 9% 36%	8496
Transparency	Day	21% 15% 28% 23% 10%	4307
	Night	20% 17% 27% 24% 10%	4832
Seeing	Day	6% 14% 22% 29% 26%	567
	Night	9% 21% 29% 31% 8%	2725

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	16% 7% 5% 10% 37%	565
	Night	12% 6% 5% 7% 42%	787
February	Day	28% 6% 5% 5% 6% 27%	570
	Night	30% 7% 6% 29%	684
March	Day	15% 5% 5% 7% 7% 43%	682
	Night	16% 5% 5% 5% 5% 6% 41%	682
April	Day	7% 5% 5% 6% 6% 50%	692
	Night	9% 5% 6% 56%	630
May	Day	9% 8% 7% 8% 9% 38%	802
	Night	9% 7% 5% 8% 10% 44%	551
June	Day	15% 7% 8% 8% 6% 10% 7% 6% 8% 16%	780
	Night	15% 6% 8% 8% 5% 8% 6% 5% 10% 22%	537
July	Day	11% 6% 6% 7% 5% 13% 8% 8% 13% 15%	801
	Night	6% 5% 6% 5% 12% 9% 9% 15% 23%	558
August	Day	15% 7% 7% 8% 6% 11% 8% 8% 8% 13%	1123
	Night	11% 5% 5% 7% 10% 7% 9% 13% 21%	916
September	Day	22% 5% 6% 5% 5% 10% 5% 7% 24%	971
	Night	20% 5% 5% 5% 7% 5% 5% 9% 28%	975
October	Day	15% 5% 5% 9% 5% 8% 33%	643
	Night	11% 5% 5% 7% 6% 9% 39%	718
November	Day	6% 6% 10% 53%	501
	Night	8% 7% 5% 7% 49%	667
December	Day	13% 6% 5% 50%	547
	Night	10% 5% 5% 8% 48%	791

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	14% 18% 28% 28% 9%	312
	Night	12% 24% 27% 26% 9%	459
February	Day	16% 12% 37% 31%	237
	Night	12% 15% 28% 39%	264
March	Day	12% 8% 35% 31% 12%	400
	Night	15% 10% 32% 29% 11%	378
April	Day	8% 7% 18% 40% 25%	421
	Night	6% 6% 27% 41% 18%	433
May	Day	22% 14% 45% 14%	453
	Night	22% 15% 39% 18%	352
June	Day	57% 15% 26%	239
	Night	54% 17% 26%	203
July	Day	48% 21% 25% 5%	312
	Night	42% 25% 26%	259
August	Day	50% 31% 16%	299
	Night	49% 27% 19%	393
September	Day	24% 18% 26% 19% 10%	378
	Night	27% 21% 26% 18% 5%	468
October	Day	13% 21% 18% 30% 16%	498
	Night	12% 20% 23% 24% 18%	590
November	Day	7% 14% 28% 35% 13%	424
	Night	12% 12% 30% 34% 10%	526
December	Day	10% 8% 31% 26% 23%	334
	Night	10% 10% 26% 31% 20%	507

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% 30% 34% 20%	225
February	Night	27% 37% 26% 8%	173
March	Day	17% 21% 38% 23%	52
	Night	15% 36% 38% 9%	216
April	Day	5% 27% 34% 25% 7%	55
	Night	13% 29% 35% 21%	210
May	Day	7% 17% 33% 37%	56
	Night	11% 36% 46%	176
June	Day	12% 22% 31% 31%	58
	Night	10% 24% 43% 16%	166
July	Day	9% 8% 19% 62%	61
	Night	5% 15% 44% 31%	179
August	Day	12% 11% 18% 53%	86
	Night	5% 7% 12% 43% 31%	281
September	Day	9% 14% 25% 33% 16%	81
	Night	8% 20% 25% 39% 6%	304
October	Day	7% 15% 31% 37% 8%	83
	Night	6% 19% 33% 35%	332
November	Day	14% 17% 11% 45% 11%	35
	Night	8% 17% 31% 39%	241
December	Night	13% 27% 37% 20%	222

Page generated at 2008-05-11 04:45:42. Version ab11