MAC-Hunter Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the MAC-Hunter 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	20% 5% 5% 7% 5% 7% 31%	8706
	Night	20% 5% 5% 6% 5% 6% 34%	8466
Transparency	Day	19% 13% 31% 28% 8%	4233
	Night	14% 11% 34% 29% 10%	4278
Seeing	Day	9% 24% 26% 25% 14%	514
	Night	10% 26% 34% 24%	2549

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	17% 5% 5% 6% 7% 39%	551
	Night	17% 5% 5% 6% 41%	802
February	Day	34% 5% 6% 31%	555
	Night	29% 5% 8% 5% 5% 29%	698
March	Day	18% 6% 6% 6% 41%	682
	Night	15% 5% 6% 8% 44%	682
April	Day	16% 8% 7% 41%	708
	Night	14% 5% 6% 6% 47%	613
May	Day	13% 5% 5% 9% 5% 8% 9% 31%	802
	Night	17% 5% 7% 6% 7% 7% 29%	551
June	Day	25% 8% 6% 6% 6% 8% 5% 6% 6% 15%	780
	Night	23% 9% 7% 7% 7% 9% 6% 6% 6% 11%	537
July	Day	18% 5% 7% 5% 8% 9% 7% 10% 17%	801
	Night	17% 6% 8% 5% 5% 8% 6% 10% 21%	558
August	Day	23% 6% 6% 6% 5% 10% 7% 7% 7% 15%	1174
	Night	25% 7% 8% 6% 5% 9% 6% 5% 5% 14%	866
September	Day	20% 7% 5% 8% 35%	983
	Night	23% 5% 5% 5% 8% 32%	962
October	Day	20% 5% 5% 5% 5% 5% 37%	622
	Night	22% 7% 6% 5% 35%	740
November	Day	23% 5% 45%	501
	Night	16% 8% 48%	666
December	Day	15% 56%	547
	Night	15% 5% 5% 53%	791

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	14% 16% 32% 30% 7%	281
	Night	8% 11% 39% 27% 11%	426
February	Day	9% 9% 34% 38% 7%	242
	Night	7% 11% 34% 38% 7%	269
March	Day	15% 11% 35% 33%	345
	Night	13% 8% 38% 31% 8%	399
April	Day	11% 9% 28% 40% 9%	414
	Night	10% 34% 39% 11%	366
May	Day	25% 14% 36% 21%	382
	Night	23% 14% 42% 19%	242
June	Day	43% 16% 23% 17%	217
	Night	49% 19% 27%	135
July	Day	42% 16% 26% 13%	291
	Night	38% 10% 42% 8%	216
August	Day	37% 23% 27% 10%	375
	Night	31% 26% 34% 5%	219
September	Day	16% 14% 32% 26% 10%	528
	Night	13% 16% 28% 30% 11%	485
October	Day	13% 11% 27% 32% 15%	459
	Night	9% 10% 31% 33% 15%	510
November	Day	10% 7% 40% 27% 14%	339
	Night	10% 7% 30% 38% 12%	497
December	Day	5% 8% 28% 41% 16%	360
	Night	6% 6% 32% 36% 19%	514

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	15% 41% 34% 7%	206
February	Day	25% 50% 25%	4
	Night	14% 40% 38% 6%	158
March	Day	7% 44% 30% 17%	52
	Night	15% 45% 30% 8%	210
April	Day	6% 28% 38% 20% 6%	49
	Night	15% 32% 36% 15%	205
May	Day	9% 20% 25% 27% 16%	54
	Night	8% 25% 37% 25%	166
June	Day	23% 18% 18% 34%	43
	Night	10% 20% 42% 25%	156
July	Day	10% 14% 12% 32% 29%	55
	Night	16% 22% 40% 15%	168
August	Day	11% 14% 15% 22% 35%	76
	Night	10% 11% 27% 38% 12%	254
September	Day	24% 33% 28% 9%	74
	Night	6% 19% 34% 36%	295
October	Day	8% 33% 33% 20%	74
	Night	10% 23% 38% 26%	298
November	Day	9% 21% 27% 27% 15%	33
	Night	8% 20% 31% 31% 7%	223
December	Night	12% 30% 37% 19%	210

Page generated at 2008-09-30 05:41:29. Version ab11