Lafayette
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lafayette 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	12% 6% 5% 5% 6% 5% 6% 8% 34%	16550
	Night	11% 5% 5% 8% 45%	16411
Transparency	Day	9% 12% 19% 19% 7%	12993
	Night	8% 15% 20% 20% 10%	13534
Seeing	Day	11% 23% 35% 22%	877
	Night	6% 21% 32% 26% 5%	5073

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	22% 6% 5% 39%	1102
	Night	17% 5% 5% 6% 43%	1596
February	Day	14% 6% 5% 7% 44%	1098
	Night	13% 5% 5% 5% 47%	1300
March	Day	12% 6% 5% 5% 6% 8% 38%	1363
	Night	11% 5% 5% 10% 47%	1362
April	Day	9% 5% 8% 7% 10% 37%	1414
	Night	8% 5% 5% 9% 48%	1188
May	Day	9% 5% 5% 6% 6% 5% 7% 8% 33%	1485
	Night	8% 6% 5% 7% 11% 46%	1212
June	Day	6% 8% 5% 11% 9% 9% 9% 27%	1551
	Night	5% 6% 5% 6% 11% 48%	1079
July	Day	14% 7% 5% 7% 7% 9% 8% 8% 8% 18%	1594
	Night	7% 5% 8% 6% 9% 13% 34%	1097
August	Day	10% 6% 7% 6% 9% 8% 8% 10% 23%	1474
	Night	5% 5% 5% 5% 7% 9% 12% 38%	1240
September	Day	16% 7% 7% 7% 5% 6% 5% 5% 28%	1365
	Night	13% 5% 5% 5% 6% 6% 9% 36%	1233
October	Day	14% 5% 5% 6% 44%	1222
	Night	12% 5% 5% 6% 49%	1472
November	Day	9% 5% 7% 51%	1441
	Night	10% 6% 58%	1728
December	Day	17% 7% 5% 5% 6% 7% 34%	1441
	Night	17% 7% 6% 40%	1904

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	8% 16% 26% 16%	805
	Night	6% 9% 16% 26% 18%	1194
February	Day	7% 10% 21% 26% 12%	864
	Night	5% 11% 17% 24% 18%	1036
March	Day	8% 15% 26% 19% 7%	1044
	Night	6% 21% 22% 17% 12%	1139
April	Day	8% 13% 22% 21% 10%	1124
	Night	9% 16% 22% 19% 13%	996
May	Day	10% 16% 24% 18%	1151
	Night	11% 22% 25% 20%	1008
June	Day	16% 16% 24% 15%	1112
	Night	13% 15% 36% 18%	856
July	Day	18% 18% 15% 5%	885
	Night	22% 28% 22% 8%	679
August	Day	16% 19% 14% 5%	1235
	Night	15% 28% 21% 7%	1090
September	Day	9% 10% 12% 13% 5%	1195
	Night	8% 14% 14% 17% 7%	1099
October	Day	6% 6% 11% 26% 15%	1098
	Night	8% 14% 24% 20%	1293
November	Day	8% 18% 34% 10%	1294
	Night	9% 18% 31% 15%	1550
December	Day	6% 9% 23% 20%	1186
	Night	5% 8% 24% 20% 8%	1594

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	9% 41% 33% 7%	555
February	Night	14% 33% 37% 7%	397
March	Night	5% 31% 37% 14%	364
April	Day	27% 37% 19%	115
	Night	7% 32% 38% 16%	346
May	Day	11% 26% 39% 12%	124
	Night	14% 47% 28%	356
June	Day	9% 26% 40% 22%	227
	Night	33% 49% 9%	339
July	Day	7% 22% 35% 27%	205
	Night	13% 58% 20%	323
August	Day	6% 5% 33% 45%	120
	Night	13% 58% 22%	352
September	Day	9% 12% 37% 20%	86
	Night	6% 25% 45% 8%	361
October	Night	5% 17% 33% 29%	473
November	Night	19% 41% 23%	562
December	Night	11% 30% 30% 13%	645

Page generated at 2009-12-30 04:20:35. Version ab11