Mabee Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mabee Observatory 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	14% 5% 5% 7% 45%	8710
	Night	14% 5% 5% 6% 47%	8465
Transparency	Day	16% 17% 38% 23%	5366
	Night	15% 15% 34% 29% 5%	5458
Seeing	Day	6% 29% 41% 20%	566
	Night	9% 33% 40% 16%	2675

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% 8% 5% 6% 6% 32%	550
	Night	19% 5% 5% 6% 7% 5% 36%	803
February	Day	24% 5% 5% 5% 9% 35%	549
	Night	20% 5% 5% 5% 5% 7% 36%	707
March	Day	17% 6% 5% 47%	676
	Night	14% 5% 49%	688
April	Day	16% 7% 5% 7% 44%	730
	Night	15% 5% 50%	589
May	Day	8% 6% 6% 9% 45%	803
	Night	9% 5% 5% 8% 9% 45%	550
June	Day	12% 5% 5% 7% 47%	780
	Night	10% 5% 7% 5% 6% 7% 44%	537
July	Day	9% 7% 8% 53%	801
	Night	7% 5% 10% 57%	558
August	Day	11% 6% 5% 6% 9% 42%	1197
	Night	13% 6% 5% 6% 8% 44%	845
September	Day	10% 5% 8% 51%	970
	Night	7% 5% 6% 58%	975
October	Day	19% 5% 9% 44%	630
	Night	14% 7% 5% 5% 6% 43%	730
November	Day	22% 6% 44%	476
	Night	28% 5% 5% 40%	692
December	Day	10% 6% 54%	548
	Night	8% 5% 6% 5% 5% 57%	791

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	26% 19% 39% 12%	234
	Night	16% 16% 43% 22%	358
February	Day	20% 17% 49% 7%	281
	Night	22% 11% 37% 27%	370
March	Day	20% 17% 39% 22%	370
	Night	15% 14% 36% 32%	420
April	Day	14% 15% 35% 32%	411
	Night	11% 13% 31% 41%	351
May	Day	26% 15% 40% 14%	501
	Night	22% 18% 37% 17%	368
June	Day	15% 11% 31% 37%	427
	Night	18% 11% 31% 34%	303
July	Day	14% 11% 41% 25% 6%	556
	Night	12% 13% 38% 30% 5%	400
August	Day	17% 26% 34% 20%	705
	Night	15% 21% 38% 21%	524
September	Day	12% 18% 40% 27%	640
	Night	9% 19% 30% 34% 6%	710
October	Day	11% 19% 33% 27% 8%	578
	Night	16% 16% 25% 29% 11%	711
November	Day	15% 8% 41% 21% 12%	287
	Night	18% 7% 25% 35% 13%	389
December	Day	10% 19% 43% 23%	376
	Night	13% 16% 38% 25% 5%	554

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% 41% 36% 10%	257
February	Night	7% 44% 38% 10%	195
March	Night	17% 39% 37% 5%	175
April	Day	19% 45% 22% 12%	62
	Night	14% 36% 30% 18%	160
May	Day	9% 44% 39% 5%	118
	Night	5% 41% 47% 5%	174
June	Day	7% 35% 40% 15%	110
	Night	7% 34% 45% 11%	170
July	Day	16% 50% 25%	117
	Night	12% 56% 27%	173
August	Day	17% 42% 35%	159
	Night	14% 43% 34%	263
September	Night	28% 41% 23%	259
October	Night	9% 30% 36% 22%	319
November	Night	15% 34% 41% 7%	248
December	Night	10% 43% 36% 9%	282

Page generated at 2008-08-29 15:03:15. Version ab11