Fremont Peak
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fremont Peak clear sky chart from 2005-11-05 to 2009-05-25.

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	8% 5% 8% 52%	14057
	Night	9% 6% 7% 49%	14242
Transparency	Day	6% 12% 21% 25% 19%	11533
	Night	6% 13% 18% 24% 18%	11619
Seeing	Day	12% 35% 39% 7%	996
	Night	13% 34% 31% 10%	4505

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	16% 6% 6% 48%	1087
	Night	13% 5% 50%	1608
February	Day	19% 8% 5% 5% 5% 7% 33%	1040
	Night	18% 5% 5% 5% 5% 36%	1354
March	Day	11% 6% 5% 5% 9% 41%	1356
	Night	12% 9% 7% 43%	1365
April	Day	11% 8% 6% 5% 7% 43%	1414
	Night	11% 5% 5% 5% 8% 43%	1189
May	Day	5% 6% 11% 52%	1520
	Night	5% 8% 5% 6% 53%	1044
June	Day	5% 7% 67%	1260
	Night	8% 61%	720
July	Day	10% 63%	1241
	Night	5% 6% 11% 54%	799
August	Day	5% 10% 65%	1139
	Night	5% 5% 5% 5% 5% 9% 52%	898
September	Day	8% 67%	1038
	Night	5% 7% 66%	936
October	Day	6% 5% 62%	920
	Night	7% 6% 61%	1113
November	Day	10% 6% 5% 5% 6% 48%	1050
	Night	9% 5% 8% 48%	1482
December	Day	18% 6% 5% 6% 40%	992
	Night	17% 6% 7% 42%	1734

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	7% 8% 16% 26% 14%	885
	Night	7% 13% 16% 21% 18%	1335
February	Day	10% 13% 23% 14% 6%	783
	Night	9% 15% 22% 13% 8%	1053
March	Day	9% 18% 25% 23%	1025
	Night	7% 19% 25% 21%	1018
April	Day	9% 15% 31% 20% 5%	1018
	Night	9% 16% 26% 23% 5%	893
May	Day	7% 15% 30% 25% 8%	1356
	Night	7% 14% 19% 32% 9%	917
June	Day	5% 15% 19% 26% 31%	1144
	Night	5% 10% 17% 25% 35%	621
July	Day	8% 10% 31% 41%	844
	Night	6% 10% 26% 42%	572
August	Day	8% 11% 34% 38%	1085
	Night	10% 11% 26% 37%	828
September	Day	14% 33% 32%	1002
	Night	5% 11% 33% 33%	889
October	Day	5% 8% 20% 17% 32%	831
	Night	8% 16% 20% 31%	991
November	Day	5% 15% 24% 21% 13%	821
	Night	6% 15% 19% 27% 13%	1196
December	Day	6% 20% 19% 22%	739
	Night	8% 17% 22% 21% 7%	1306

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	7% 29% 31% 16%	101
	Night	6% 12% 37% 25% 7%	485
February	Day	14% 32% 29% 10%	102
	Night	7% 11% 34% 25% 7%	406
March	Day	21% 47% 18%	117
	Night	6% 18% 38% 24% 5%	476
April	Day	27% 44% 22%	106
	Night	8% 24% 35% 22% 6%	457
May	Day	12% 42% 36%	114
	Night	14% 41% 31% 6%	340
June	Day	5% 44% 47%	88
	Night	16% 34% 39% 7%	170
July	Day	24% 64% 7%	77
	Night	6% 18% 52% 20%	216
August	Day	24% 67% 6%	89
	Night	5% 26% 53% 13%	328
September	Day	6% 25% 55% 9%	88
	Night	22% 50% 17%	350
October	Day	12% 30% 35% 12%	91
	Night	11% 33% 25% 20%	364
November	Day	17% 26% 30% 17%	23
	Night	12% 35% 33% 10%	449
December	Night	7% 14% 38% 23% 7%	464

Page generated at 2009-05-26 02:05:46. Version ab11