NAA Ransom
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the NAA Ransom clear sky chart from 2003-08-01 to 2005-11-07.

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	16% 5% 5% 6% 5% 7% 35%	8733
	Night	20% 5% 5% 6% 35%	8441
Transparency	Day	18% 16% 42% 20%	4713
	Night	18% 15% 39% 23%	4490
Seeing	Day	7% 24% 33% 26% 8%	581
	Night	8% 30% 38% 20%	2417

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	33% 9% 9% 5% 6% 6% 5% 13%	500
	Night	32% 7% 5% 6% 5% 5% 22%	853
February	Day	23% 10% 9% 6% 8% 26%	553
	Night	30% 7% 5% 5% 31%	701
March	Day	22% 7% 6% 6% 7% 5% 6% 27%	673
	Night	24% 6% 6% 5% 5% 6% 30%	693
April	Day	14% 6% 5% 5% 5% 7% 39%	727
	Night	19% 6% 6% 6% 5% 38%	593
May	Day	14% 8% 6% 7% 8% 5% 6% 7% 29%	838
	Night	14% 5% 6% 6% 6% 9% 35%	515
June	Day	9% 6% 9% 6% 6% 10% 35%	840
	Night	7% 7% 5% 7% 11% 45%	476
July	Day	11% 5% 6% 7% 6% 9% 39%	866
	Night	9% 6% 5% 7% 13% 39%	496
August	Day	10% 5% 7% 5% 6% 8% 39%	1158
	Night	10% 5% 7% 5% 6% 44%	883
September	Day	10% 6% 5% 8% 54%	1014
	Night	11% 5% 5% 7% 54%	928
October	Day	16% 6% 6% 42%	610
	Night	17% 5% 5% 5% 5% 8% 36%	752
November	Day	32% 9% 6% 5% 5% 25%	467
	Night	37% 8% 28%	699
December	Day	22% 8% 6% 5% 36%	487
	Night	24% 11% 8% 5% 25%	852

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	37% 30% 27%	116
	Night	29% 16% 39% 14%	268
February	Day	28% 18% 40% 12%	219
	Night	27% 20% 39% 13%	299
March	Day	24% 20% 48% 6%	259
	Night	22% 24% 37% 16%	297
April	Day	17% 10% 51% 18%	385
	Night	22% 7% 42% 22% 5%	300
May	Day	23% 20% 46% 8%	386
	Night	26% 16% 38% 17%	267
June	Day	20% 13% 43% 21%	473
	Night	19% 16% 38% 22%	318
July	Day	18% 13% 40% 22%	509
	Night	20% 13% 38% 22%	311
August	Day	18% 20% 35% 21%	660
	Night	12% 15% 44% 24%	531
September	Day	9% 11% 34% 36% 7%	723
	Night	6% 9% 34% 40% 9%	666
October	Day	13% 15% 45% 24%	553
	Night	14% 14% 40% 26%	619
November	Day	12% 17% 53% 15%	204
	Night	13% 15% 50% 20%	293
December	Day	19% 26% 42% 11%	226
	Night	24% 24% 36% 13%	321

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	14% 50% 25% 9%	208
February	Night	7% 43% 33% 12%	164
March	Day	15% 36% 36% 10%	19
	Night	16% 37% 37% 9%	164
April	Day	15% 30% 35% 16%	53
	Night	11% 37% 39% 12%	153
May	Day	15% 40% 31% 9%	83
	Night	6% 42% 42% 9%	164
June	Day	6% 29% 32% 23% 8%	113
	Night	21% 52% 21%	169
July	Day	21% 35% 28% 10%	109
	Night	12% 50% 31%	170
August	Day	12% 33% 32% 17%	106
	Night	12% 40% 38% 6%	255
September	Day	13% 27% 46% 11%	80
	Night	14% 40% 38%	276
October	Day	16% 38% 44%	18
	Night	7% 27% 34% 29%	317
November	Night	12% 41% 38% 7%	156
December	Night	14% 44% 30% 9%	221

Page generated at 2008-09-02 01:07:22. Version ab11