Mansfield Dam
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mansfield Dam clear sky chart from 2005-11-05 to 2008-12-24.

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	14% 5% 5% 7% 42%	12507
	Night	13% 7% 48%	12525
Cloud Cover	Day	14% 5% 5% 7% 42%	12501
	Night	13% 7% 48%	12534
Transparency	Day	8% 13% 19% 22% 13%	9131
	Night	7% 15% 19% 22% 15%	9707
Seeing	Day	23% 43% 20%	640
	Night	9% 31% 35% 16%	3803

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	21% 5% 46%	849
	Night	24% 5% 5% 39%	1191
February	Day	18% 5% 5% 52%	809
	Night	15% 55%	970
March	Day	22% 5% 5% 5% 40%	1018
	Night	18% 6% 5% 5% 42%	1021
April	Day	14% 5% 5% 5% 7% 5% 6% 40%	1041
	Night	16% 5% 6% 42%	933
May	Day	17% 5% 6% 8% 8% 34%	1209
	Night	13% 7% 5% 6% 9% 43%	837
June	Day	13% 8% 6% 5% 7% 37%	1170
	Night	11% 8% 52%	810
July	Day	15% 6% 5% 6% 7% 7% 7% 7% 7% 24%	1209
	Night	10% 5% 6% 6% 13% 41%	833
August	Day	5% 5% 6% 7% 5% 9% 6% 6% 12% 31%	1127
	Night	6% 5% 8% 13% 44%	908
September	Day	10% 5% 5% 5% 5% 7% 7% 39%	985
	Night	10% 5% 5% 5% 7% 45%	990
October	Day	8% 6% 60%	956
	Night	8% 5% 63%	1072
November	Day	11% 7% 52%	1090
	Night	9% 6% 57%	1443
December	Day	13% 53%	1044
	Night	14% 5% 5% 51%	1517

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	21% 5% 46%	848
	Night	24% 5% 5% 39%	1194
February	Day	18% 5% 5% 52%	809
	Night	15% 55%	970
March	Day	22% 5% 5% 5% 5% 40%	1019
	Night	18% 5% 5% 5% 42%	1023
April	Day	14% 5% 5% 5% 7% 5% 6% 40%	1041
	Night	16% 5% 7% 42%	934
May	Day	17% 5% 6% 6% 8% 8% 34%	1208
	Night	13% 7% 6% 9% 43%	837
June	Day	13% 7% 6% 5% 7% 37%	1170
	Night	11% 8% 52%	810
July	Day	15% 6% 5% 5% 7% 7% 7% 7% 7% 24%	1209
	Night	10% 5% 5% 6% 14% 41%	834
August	Day	5% 5% 7% 6% 5% 9% 6% 6% 11% 31%	1121
	Night	6% 5% 8% 12% 44%	909
September	Day	10% 5% 5% 6% 5% 7% 8% 39%	987
	Night	10% 5% 5% 5% 7% 45%	990
October	Day	9% 5% 60%	958
	Night	8% 5% 63%	1072
November	Day	11% 6% 52%	1087
	Night	9% 7% 57%	1443
December	Day	14% 53%	1044
	Night	14% 5% 5% 50%	1518

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	5% 7% 18% 28% 20%	606
	Night	5% 9% 13% 24% 24%	829
February	Day	5% 9% 17% 30% 23%	592
	Night	5% 8% 13% 27% 32%	740
March	Day	8% 12% 18% 19% 18%	672
	Night	8% 13% 16% 22% 19%	681
April	Day	9% 10% 18% 22% 21%	690
	Night	7% 14% 19% 21% 20%	628
May	Day	12% 16% 20% 24% 5%	820
	Night	10% 18% 25% 21% 7%	621
June	Day	10% 16% 19% 29% 6%	760
	Night	11% 19% 25% 31%	590
July	Day	12% 21% 24% 12%	574
	Night	11% 39% 24% 12%	479
August	Day	12% 21% 20% 8%	971
	Night	13% 30% 23% 5%	836
September	Day	6% 11% 20% 19% 8%	823
	Night	9% 14% 18% 21% 8%	851
October	Day	5% 7% 19% 26% 23%	846
	Night	5% 10% 20% 19% 30%	932
November	Day	6% 9% 24% 20% 16%	930
	Night	6% 11% 24% 21% 18%	1277
December	Day	11% 16% 35% 12%	847
	Night	10% 16% 30% 14%	1243

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	15% 41% 24% 9%	379
February	Night	15% 49% 27%	288
March	Night	20% 42% 27%	257
April	Day	20% 38% 28% 8%	50
	Night	14% 49% 27%	247
May	Day	6% 37% 37% 10%	175
	Night	6% 39% 39% 9%	266
June	Day	22% 51% 18%	162
	Night	26% 47% 20%	241
July	Day	13% 43% 31% 6%	148
	Night	9% 47% 34%	232
August	Day	6% 47% 30% 5%	105
	Night	5% 42% 40%	266
September	Night	10% 37% 37%	256
October	Night	7% 24% 34% 26%	315
November	Night	6% 29% 39% 16%	508
December	Night	14% 35% 32% 6%	548

Page generated at 2008-12-24 21:45:21. Version ab11