Oregon Star Party
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oregon Star Party 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	9% 7% 5% 5% 5% 5% 5% 6% 40%	12266
	Night	8% 7% 5% 6% 5% 6% 5% 5% 6% 39%	12163
Cloud Cover	Day	8% 7% 5% 5% 5% 6% 41%	12273
	Night	8% 7% 5% 6% 5% 6% 5% 5% 6% 40%	12158
Transparency	Day	11% 15% 22% 18% 9%	8613
	Night	11% 18% 23% 16% 6%	8561
Seeing	Day	24% 37% 24% 7%	748
	Night	12% 21% 33% 22%	3603

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	12% 13% 5% 9% 8% 5% 7% 5% 7% 21%	750
	Night	9% 10% 7% 8% 7% 7% 5% 6% 6% 25%	1289
February	Day	6% 11% 9% 9% 6% 8% 7% 7% 7% 19%	760
	Night	8% 10% 7% 7% 5% 9% 6% 7% 8% 25%	1018
March	Day	12% 12% 9% 10% 9% 7% 5% 6% 18%	1003
	Night	10% 9% 8% 8% 6% 5% 9% 8% 6% 7% 18%	1037
April	Day	13% 12% 9% 7% 7% 5% 27%	1085
	Night	9% 10% 8% 7% 5% 7% 5% 5% 6% 30%	887
May	Day	11% 8% 6% 5% 6% 6% 5% 6% 6% 34%	1300
	Night	9% 6% 6% 6% 8% 5% 5% 6% 37%	746
June	Day	10% 5% 5% 5% 5% 7% 45%	1260
	Night	7% 7% 55%	720
July	Day	5% 6% 69%	1301
	Night	5% 6% 70%	739
August	Day	74%	1181
	Night	76%	855
September	Day	5% 67%	1043
	Night	69%	933
October	Day	11% 5% 6% 5% 5% 5% 5% 42%	897
	Night	7% 6% 5% 5% 5% 5% 7% 47%	1137
November	Day	15% 9% 7% 7% 6% 5% 9% 26%	942
	Night	15% 8% 6% 7% 5% 5% 5% 32%	1501
December	Day	15% 11% 10% 10% 7% 6% 9% 6% 7% 11%	744
	Night	13% 11% 6% 10% 9% 8% 5% 7% 19%	1301

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	13% 11% 10% 7% 8% 5% 6% 23%	751
	Night	10% 10% 7% 7% 7% 8% 5% 5% 27%	1286
February	Day	5% 12% 8% 8% 7% 5% 8% 6% 7% 8% 20%	762
	Night	8% 10% 6% 7% 5% 8% 6% 6% 9% 25%	1017
March	Day	9% 13% 8% 10% 8% 5% 8% 5% 6% 19%	1005
	Night	8% 9% 8% 8% 6% 9% 8% 8% 8% 18%	1035
April	Day	13% 12% 8% 8% 6% 5% 28%	1086
	Night	9% 10% 5% 8% 7% 5% 5% 6% 6% 31%	889
May	Day	10% 8% 6% 6% 6% 6% 5% 5% 6% 35%	1300
	Night	9% 6% 5% 6% 7% 6% 6% 39%	746
June	Day	10% 6% 5% 7% 46%	1260
	Night	7% 5% 7% 55%	720
July	Day	6% 70%	1301
	Night	7% 71%	741
August	Day	74%	1182
	Night	76%	854
September	Day	5% 68%	1041
	Night	5% 70%	933
October	Day	10% 5% 5% 5% 6% 5% 5% 43%	897
	Night	7% 5% 5% 5% 5% 7% 48%	1136
November	Day	16% 9% 6% 6% 6% 5% 5% 9% 27%	944
	Night	16% 8% 5% 6% 5% 5% 5% 33%	1501
December	Day	15% 11% 7% 10% 9% 5% 9% 5% 6% 6% 12%	744
	Night	13% 10% 7% 9% 8% 9% 5% 7% 19%	1300

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	20% 27% 17%	423
	Night	13% 25% 24% 5%	745
February	Day	21% 20% 19% 7%	442
	Night	20% 19% 21% 9%	634
March	Day	15% 24% 21%	543
	Night	23% 25% 19%	562
April	Day	15% 19% 26% 7%	619
	Night	15% 26% 23% 7%	539
May	Day	11% 19% 22% 16%	889
	Night	13% 25% 21% 13%	513
June	Day	10% 15% 26% 27% 6%	912
	Night	9% 18% 36% 20% 5%	538
July	Day	6% 10% 20% 23% 33%	859
	Night	6% 17% 21% 21% 28%	497
August	Day	5% 26% 36% 17%	1114
	Night	7% 30% 34% 14%	815
September	Day	5% 8% 20% 34% 17%	970
	Night	7% 8% 24% 31% 18%	871
October	Day	10% 18% 22% 15%	781
	Night	9% 18% 19% 20%	1015
November	Day	13% 20% 22% 9%	656
	Night	9% 13% 22% 18%	1065
December	Day	19% 16% 16%	405
	Night	13% 25% 19%	767

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	Day	55% 11% 11% 11%	9
	Night	22% 26% 28% 16%	350
February	Day	26% 35% 26% 8%	73
	Night	13% 28% 31% 18%	305
March	Day	37% 34% 19%	88
	Night	18% 29% 32% 15%	354
April	Day	33% 39% 18%	83
	Night	19% 26% 30% 17%	338
May	Day	26% 41% 17%	89
	Night	6% 21% 40% 23%	182
June	Day	29% 35% 22% 7%	84
	Night	8% 19% 48% 20%	160
July	Day	13% 51% 30%	79
	Night	19% 53% 24%	162
August	Day	14% 34% 34% 11%	89
	Night	18% 40% 31% 6%	286
September	Day	9% 34% 29% 18%	86
	Night	15% 28% 40% 9%	346
October	Day	22% 29% 20% 11%	68
	Night	8% 14% 33% 29%	364
November	Night	18% 17% 27% 19% 6%	415
December	Night	15% 23% 31% 16%	341

Page generated at 2008-11-27 10:47:45. Version ab11