HiRes 1
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the HiRes 1 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	6% 7% 54%	12309
	Night	7% 5% 6% 52%	12122
Transparency	Day	7% 16% 18% 21% 21%	9728
	Night	6% 17% 21% 20% 17%	9503
Seeing	Day	16% 28% 35% 15%	665
	Night	7% 19% 37% 25% 5%	3788

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	10% 9% 5% 7% 7% 5% 7% 5% 5% 5% 31%	835
	Night	11% 10% 7% 5% 7% 37%	1203
February	Day	7% 8% 5% 7% 11% 41%	771
	Night	6% 7% 5% 5% 6% 5% 5% 45%	1008
March	Day	9% 7% 5% 7% 6% 5% 9% 37%	1003
	Night	9% 6% 5% 10% 43%	1037
April	Day	5% 5% 5% 5% 5% 7% 50%	1104
	Night	7% 5% 5% 5% 7% 47%	871
May	Day	6% 7% 57%	1209
	Night	6% 5% 6% 54%	837
June	Day	6% 69%	1203
	Night	5% 6% 66%	776
July	Day	7% 63%	1227
	Night	5% 7% 9% 57%	814
August	Day	7% 71%	1196
	Night	68%	840
September	Day	72%	989
	Night	74%	986
October	Day	8% 5% 59%	932
	Night	5% 5% 63%	1100
November	Day	8% 5% 8% 50%	1003
	Night	8% 6% 53%	1443
December	Day	15% 13% 8% 5% 5% 7% 29%	837
	Night	16% 9% 5% 5% 5% 7% 32%	1207

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	20% 36% 13%	539
	Night	13% 33% 27%	847
February	Day	12% 38% 25%	583
	Night	9% 26% 30% 10%	735
March	Day	9% 29% 29% 10%	685
	Night	5% 29% 33% 11%	742
April	Day	6% 17% 24% 28% 8%	847
	Night	7% 19% 26% 23% 9%	644
May	Day	6% 8% 17% 36% 17%	1006
	Night	5% 10% 16% 35% 16%	682
June	Day	6% 10% 24% 50%	1046
	Night	5% 11% 23% 45%	688
July	Day	6% 11% 13% 56%	782
	Night	5% 10% 10% 15% 48%	522
August	Day	10% 25% 46%	1141
	Night	5% 8% 21% 48%	791
September	Day	5% 14% 37% 29%	920
	Night	11% 37% 35%	901
October	Day	12% 27% 31% 5%	819
	Night	13% 24% 35% 8%	987
November	Day	9% 25% 26% 18%	827
	Night	6% 16% 31% 20% 7%	1158
December	Day	14% 34% 15%	533
	Night	11% 27% 24% 7%	806

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	11% 18% 37% 21% 6%	359
February	Day	34% 39% 16%	43
	Night	6% 20% 44% 21%	310
March	Day	26% 36% 23% 10%	86
	Night	9% 22% 42% 19%	352
April	Day	29% 35% 20% 8%	84
	Night	15% 31% 31% 17%	296
May	Day	15% 31% 38% 10%	89
	Night	8% 23% 34% 25%	274
June	Day	16% 32% 35% 13%	87
	Night	20% 38% 30%	220
July	Day	6% 6% 54% 30%	79
	Night	8% 37% 43% 5%	225
August	Day	6% 34% 43% 13%	89
	Night	23% 41% 25%	270
September	Day	17% 21% 32% 26%	87
	Night	11% 35% 35% 10%	345
October	Day	23% 23% 28% 14%	21
	Night	18% 33% 30% 8%	361
November	Night	6% 18% 36% 24% 9%	430
December	Night	9% 19% 39% 19%	346

Page generated at 2008-11-27 11:47:40. Version ab11