Winer Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Winer Observatory 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	6% 60%	16518
	Night	5% 6% 64%	16445
Transparency	Day	7% 13% 30% 29%	14569
	Night	8% 15% 31% 28%	14765
Seeing	Day	16% 30% 36% 9%	895
	Night	5% 17% 34% 33% 6%	5293

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	6% 6% 60%	1105
	Night	5% 5% 5% 59%	1592
February	Day	7% 66%	1082
	Night	6% 7% 64%	1312
March	Day	5% 7% 60%	1361
	Night	7% 63%	1361
April	Day	5% 72%	1370
	Night	73%	1233
May	Day	5% 73%	1592
	Night	6% 74%	1106
June	Day	5% 5% 64%	1550
	Night	6% 67%	1080
July	Day	8% 5% 6% 6% 9% 7% 7% 10% 30%	1596
	Night	5% 5% 6% 8% 10% 14% 36%	1094
August	Day	8% 6% 6% 7% 7% 7% 6% 8% 34%	1548
	Night	7% 5% 5% 5% 9% 48%	1170
September	Day	5% 5% 5% 6% 59%	1303
	Night	5% 9% 65%	1299
October	Day	5% 77%	1239
	Night	78%	1454
November	Day	5% 71%	1403
	Night	5% 69%	1768
December	Day	5% 7% 62%	1369
	Night	7% 65%	1976

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	6% 18% 26% 30%	979
	Night	5% 7% 17% 24% 31%	1403
February	Day	5% 13% 40% 28%	957
	Night	5% 19% 34% 29%	1177
March	Day	5% 7% 38% 34%	1150
	Night	7% 11% 34% 33%	1186
April	Day	7% 31% 47%	1253
	Night	8% 36% 42%	1102
May	Day	11% 32% 40%	1502
	Night	5% 12% 34% 37%	1061
June	Day	8% 27% 43%	1367
	Night	5% 8% 27% 45%	948
July	Day	11% 15% 19% 17%	1087
	Night	12% 29% 15% 14% 7%	770
August	Day	11% 15% 16% 15% 8%	1270
	Night	11% 16% 18% 23% 8%	1012
September	Day	5% 9% 17% 32% 17%	1208
	Night	6% 10% 21% 35% 15%	1216
October	Day	10% 31% 45%	1169
	Night	5% 10% 29% 44%	1371
November	Day	12% 36% 30%	1356
	Night	16% 33% 30%	1686
December	Day	7% 19% 36% 17%	1271
	Night	7% 19% 37% 19%	1833

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	7% 25% 38% 22%	481
February	Day	34% 33% 18%	69
	Night	9% 24% 37% 23%	430
March	Day	37% 30% 17%	117
	Night	10% 27% 35% 23%	484
April	Day	33% 43% 16%	111
	Night	10% 30% 40% 14%	393
May	Day	13% 37% 42%	119
	Night	19% 37% 35%	366
June	Day	10% 40% 38% 6%	120
	Night	10% 42% 38%	338
July	Day	26% 54% 10%	107
	Night	24% 56% 11%	328
August	Day	14% 50% 24%	118
	Night	16% 55% 18%	358
September	Day	6% 21% 48% 19%	115
	Night	13% 29% 45% 9%	461
October	Day	10% 26% 52% 5%	19
	Night	17% 35% 33% 7%	483
November	Night	10% 33% 38% 9%	571
December	Night	7% 15% 40% 25% 6%	600

Page generated at 2009-12-30 03:20:33. Version ab11