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 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	13% 5% 5% 7% 43%	16496
	Night	12% 7% 50%	16464
Cloud Cover	Day	13% 5% 5% 7% 43%	16490
	Night	12% 7% 50%	16472
Transparency	Day	7% 12% 19% 22% 12%	13119
	Night	6% 14% 19% 21% 15%	13650
Seeing	Day	21% 43% 21%	873
	Night	8% 30% 35% 15%	5095

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	18% 52%	1124
	Night	20% 44%	1576
February	Day	16% 5% 55%	1089
	Night	13% 59%	1306
March	Day	22% 5% 5% 5% 41%	1358
	Night	17% 6% 5% 6% 44%	1363
April	Day	14% 6% 5% 6% 5% 42%	1369
	Night	17% 5% 5% 46%	1232
May	Day	15% 5% 5% 7% 8% 9% 35%	1600
	Night	11% 6% 6% 9% 47%	1099
June	Day	10% 8% 5% 5% 8% 41%	1551
	Night	8% 5% 9% 56%	1079
July	Day	12% 5% 6% 6% 6% 6% 6% 7% 32%	1596
	Night	8% 5% 5% 13% 46%	1095
August	Day	6% 6% 5% 8% 5% 6% 13% 34%	1505
	Night	6% 5% 7% 13% 46%	1212
September	Day	11% 5% 5% 6% 5% 7% 9% 36%	1302
	Night	11% 5% 6% 5% 5% 6% 43%	1300
October	Day	12% 5% 55%	1268
	Night	11% 6% 59%	1419
November	Day	11% 6% 53%	1365
	Night	9% 6% 60%	1806
December	Day	15% 5% 49%	1369
	Night	15% 6% 5% 48%	1977

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	19% 52%	1123
	Night	20% 44%	1578
February	Day	16% 5% 55%	1089
	Night	13% 59%	1306
March	Day	22% 5% 5% 41%	1359
	Night	17% 5% 5% 6% 44%	1365
April	Day	14% 5% 5% 6% 5% 42%	1369
	Night	17% 5% 6% 46%	1233
May	Day	15% 5% 5% 6% 8% 8% 35%	1599
	Night	11% 6% 6% 9% 47%	1099
June	Day	10% 7% 6% 5% 8% 41%	1551
	Night	8% 5% 9% 56%	1079
July	Day	12% 5% 5% 6% 6% 6% 6% 7% 32%	1596
	Night	8% 5% 5% 13% 46%	1096
August	Day	6% 6% 5% 8% 6% 6% 13% 34%	1499
	Night	5% 6% 5% 7% 12% 46%	1213
September	Day	11% 5% 5% 6% 5% 7% 9% 36%	1304
	Night	11% 5% 6% 5% 6% 44%	1300
October	Day	12% 5% 55%	1270
	Night	11% 5% 59%	1419
November	Day	11% 6% 53%	1362
	Night	9% 6% 60%	1806
December	Day	15% 5% 49%	1369
	Night	15% 6% 5% 48%	1978

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	6% 15% 27% 24%	881
	Night	7% 12% 22% 27%	1214
February	Day	7% 18% 27% 24%	872
	Night	5% 6% 14% 27% 30%	1076
March	Day	5% 9% 16% 21% 15%	1003
	Night	7% 12% 15% 22% 17%	1023
April	Day	7% 8% 16% 21% 19%	1018
	Night	5% 11% 16% 20% 22%	925
May	Day	11% 16% 18% 22%	1217
	Night	9% 21% 25% 19% 6%	889
June	Day	9% 16% 23% 25% 5%	1141
	Night	9% 18% 26% 32%	859
July	Day	9% 18% 22% 19%	961
	Night	8% 31% 27% 17%	741
August	Day	11% 20% 22% 11%	1349
	Night	12% 28% 25% 7%	1140
September	Day	8% 13% 18% 16% 7%	1140
	Night	8% 15% 19% 17% 6%	1161
October	Day	7% 16% 25% 19%	1160
	Night	5% 9% 19% 20% 25%	1279
November	Day	5% 7% 22% 20% 18%	1205
	Night	5% 9% 22% 22% 20%	1640
December	Day	11% 16% 29% 10%	1172
	Night	9% 15% 29% 12%	1703

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	13% 39% 26% 9%	524
February	Night	16% 50% 25%	400
March	Night	18% 40% 28%	351
April	Day	20% 35% 25% 5%	68
	Night	13% 51% 23%	334
May	Day	5% 34% 37% 13%	235
	Night	5% 36% 38% 12%	353
June	Day	23% 49% 19%	221
	Night	29% 48% 17%	329
July	Day	12% 46% 31% 5%	207
	Night	10% 51% 30%	319
August	Day	5% 50% 32%	142
	Night	5% 49% 35%	359
September	Night	10% 39% 34%	340
October	Night	6% 27% 34% 20%	422
November	Night	5% 25% 38% 20%	639
December	Night	13% 34% 31% 7%	725

Page generated at 2009-12-30 04:20:33. Version ab11