Mission Trails Regional Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mission Trails Regional Park 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	5% 7% 61%	12243
	Night	7% 5% 7% 55%	12188
Transparency	Day	9% 20% 30% 28%	10199
	Night	8% 18% 26% 31%	9893
Seeing	Day	7% 31% 46% 13%	815
	Night	6% 32% 40% 14%	3938

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	8% 5% 58%	886
	Night	10% 5% 59%	1152
February	Day	13% 6% 5% 5% 8% 44%	809
	Night	12% 5% 5% 6% 47%	970
March	Day	7% 7% 5% 9% 49%	992
	Night	11% 5% 5% 8% 48%	1048
April	Day	9% 5% 7% 54%	1077
	Night	12% 8% 6% 50%	899
May	Day	9% 60%	1195
	Night	9% 13% 6% 6% 40%	850
June	Day	5% 8% 68%	1170
	Night	7% 5% 9% 54%	810
July	Day	5% 5% 7% 63%	1187
	Night	5% 7% 5% 5% 9% 50%	852
August	Day	5% 73%	1108
	Night	6% 8% 56%	929
September	Day	5% 73%	1012
	Night	6% 66%	963
October	Day	5% 68%	967
	Night	6% 67%	1065
November	Day	5% 5% 5% 7% 58%	1003
	Night	5% 6% 7% 56%	1443
December	Day	5% 7% 61%	837
	Night	7% 6% 62%	1207

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	10% 14% 21% 33%	746
	Night	9% 13% 18% 39%	949
February	Day	9% 20% 31% 22%	597
	Night	7% 20% 23% 29%	722
March	Day	10% 28% 31% 18%	716
	Night	10% 19% 30% 23%	753
April	Day	12% 28% 36% 14%	790
	Night	10% 30% 27% 16%	638
May	Day	13% 29% 31% 14%	1032
	Night	17% 18% 21% 21%	612
June	Day	7% 15% 32% 40%	1031
	Night	6% 12% 28% 41%	688
July	Day	12% 20% 25% 33%	774
	Night	9% 22% 27% 27%	540
August	Day	5% 20% 37% 24%	1053
	Night	7% 21% 35% 18%	841
September	Day	13% 41% 31%	986
	Night	13% 34% 35%	913
October	Day	6% 15% 19% 45%	864
	Night	5% 14% 18% 47%	963
November	Day	9% 21% 20% 31%	905
	Night	9% 19% 20% 32%	1262
December	Day	12% 20% 27% 26%	705
	Night	10% 18% 28% 29%	1012

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	10% 50% 28% 6%	50
	Night	13% 41% 25% 8%	360
February	Day	15% 37% 35% 10%	79
	Night	9% 36% 35% 9%	290
March	Day	12% 48% 33%	89
	Night	5% 8% 43% 31% 8%	342
April	Day	11% 51% 32%	84
	Night	8% 47% 29% 6%	321
May	Day	10% 29% 45% 13%	91
	Night	9% 37% 38% 7%	272
June	Day	19% 62% 16%	89
	Night	28% 54% 12%	251
July	Day	7% 56% 35%	78
	Night	13% 58% 25%	252
August	Day	7% 65% 23%	89
	Night	6% 57% 32%	350
September	Day	28% 57% 11%	88
	Night	22% 57% 15%	349
October	Day	10% 39% 37% 11%	78
	Night	6% 39% 36% 11%	364
November	Night	35% 39% 14%	434
December	Night	7% 39% 31% 15%	353

Page generated at 2008-11-27 10:47:34. Version ab11