Wasat Star
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wasat Star 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% 6% 5% 7% 40%	8681
	Night	15% 5% 5% 6% 45%	8493
Transparency	Day	13% 12% 31% 30% 12%	5130
	Night	13% 12% 29% 27% 16%	5291
Seeing	Day	11% 16% 36% 31%	484
	Night	10% 22% 40% 24%	2569

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	20% 6% 5% 5% 6% 5% 36%	566
	Night	22% 5% 5% 5% 6% 38%	788
February	Day	31% 6% 5% 5% 31%	570
	Night	31% 5% 6% 5% 33%	684
March	Day	19% 5% 45%	674
	Night	21% 48%	690
April	Day	19% 5% 49%	703
	Night	15% 5% 50%	616
May	Day	12% 5% 8% 6% 10% 38%	803
	Night	9% 8% 6% 10% 46%	550
June	Day	12% 7% 5% 6% 7% 41%	780
	Night	15% 6% 6% 6% 8% 43%	537
July	Day	12% 5% 5% 8% 5% 5% 10% 35%	801
	Night	7% 5% 5% 5% 8% 11% 43%	558
August	Day	9% 5% 10% 8% 8% 10% 31%	1131
	Night	8% 5% 6% 6% 6% 12% 38%	911
September	Day	14% 5% 6% 5% 9% 38%	970
	Night	14% 5% 5% 5% 6% 6% 40%	975
October	Day	17% 5% 5% 6% 6% 8% 33%	648
	Night	13% 5% 5% 6% 5% 5% 6% 43%	712
November	Day	23% 50%	487
	Night	22% 49%	681
December	Day	10% 61%	548
	Night	6% 70%	791

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	16% 8% 41% 30%	281
	Night	11% 12% 34% 32% 9%	402
February	Day	12% 15% 37% 29% 6%	254
	Night	7% 9% 41% 31% 9%	276
March	Day	7% 9% 19% 41% 22%	378
	Night	7% 26% 37% 23%	386
April	Day	5% 7% 34% 33% 19%	426
	Night	8% 7% 32% 24% 26%	368
May	Day	19% 14% 43% 15% 7%	471
	Night	23% 21% 34% 17%	352
June	Day	17% 9% 36% 29% 7%	455
	Night	24% 10% 29% 27% 7%	318
July	Day	19% 10% 31% 33% 5%	419
	Night	29% 10% 31% 23%	345
August	Day	29% 26% 29% 12%	592
	Night	26% 24% 32% 13%	556
September	Day	10% 17% 27% 30% 14%	581
	Night	10% 14% 29% 24% 19%	566
October	Day	9% 12% 32% 34% 10%	542
	Night	11% 17% 26% 29% 14%	678
November	Day	7% 21% 35% 30%	329
	Night	9% 7% 15% 32% 36%	430
December	Day	8% 20% 44% 23%	402
	Night	30% 37% 27%	614

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% 36% 41% 8%	236
February	Night	14% 35% 43% 6%	166
March	Night	8% 40% 42% 8%	159
April	Day	21% 57% 18%	38
	Night	20% 39% 38%	161
May	Day	15% 20% 36% 25%	116
	Night	7% 30% 44% 17%	175
June	Day	11% 16% 44% 25%	110
	Night	6% 26% 38% 26%	160
July	Day	6% 10% 40% 39%	120
	Night	12% 40% 38%	181
August	Day	8% 6% 30% 45% 11%	100
	Night	31% 55% 5%	264
September	Night	6% 37% 43% 7%	245
October	Night	7% 13% 44% 30%	298
November	Night	20% 21% 40% 15%	238
December	Night	10% 29% 38% 20%	286

Page generated at 2008-09-30 04:41:00. Version ab11