MAC-Parnell
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the MAC-Parnell 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	19% 5% 5% 6% 5% 5% 7% 31%	8701
	Night	18% 5% 5% 6% 5% 6% 34%	8471
Transparency	Day	19% 11% 31% 28% 9%	4100
	Night	16% 12% 29% 30% 10%	4295
Seeing	Day	7% 22% 25% 27% 16%	522
	Night	10% 25% 33% 26%	2607

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	18% 5% 5% 5% 41%	551
	Night	14% 5% 5% 7% 8% 40%	802
February	Day	36% 6% 5% 27%	560
	Night	31% 6% 7% 7% 27%	693
March	Day	18% 6% 7% 5% 40%	682
	Night	14% 5% 5% 5% 6% 46%	682
April	Day	12% 5% 5% 7% 47%	708
	Night	12% 6% 5% 52%	613
May	Day	12% 5% 6% 7% 6% 6% 9% 33%	802
	Night	15% 5% 5% 6% 6% 5% 9% 34%	551
June	Day	25% 6% 8% 6% 6% 8% 6% 6% 8% 13%	780
	Night	27% 6% 6% 6% 5% 8% 8% 7% 8% 11%	537
July	Day	15% 6% 7% 6% 7% 8% 7% 11% 19%	801
	Night	10% 7% 7% 9% 5% 10% 7% 8% 8% 20%	558
August	Day	19% 6% 8% 8% 7% 10% 7% 6% 6% 14%	1174
	Night	21% 8% 9% 8% 8% 9% 5% 6% 5% 11%	865
September	Day	18% 5% 7% 5% 6% 9% 34%	971
	Night	22% 5% 7% 5% 7% 32%	975
October	Day	21% 5% 5% 7% 6% 35%	628
	Night	22% 5% 5% 5% 5% 5% 34%	734
November	Day	18% 5% 5% 5% 46%	497
	Night	15% 5% 6% 51%	670
December	Day	14% 55%	547
	Night	12% 6% 54%	791

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	9% 18% 28% 32% 10%	285
	Night	11% 13% 33% 30% 11%	429
February	Day	8% 8% 34% 39% 9%	208
	Night	13% 9% 25% 44% 8%	261
March	Day	21% 5% 33% 32% 7%	366
	Night	18% 8% 32% 33% 7%	412
April	Day	15% 32% 32% 15%	425
	Night	9% 5% 31% 41% 12%	378
May	Day	25% 11% 37% 23%	377
	Night	26% 17% 37% 19%	293
June	Day	45% 14% 24% 13%	201
	Night	44% 30% 20%	133
July	Day	39% 15% 36% 8%	280
	Night	37% 14% 34% 14%	185
August	Day	29% 25% 30% 13%	284
	Night	42% 31% 15% 10%	191
September	Day	16% 14% 32% 24% 11%	519
	Night	13% 13% 33% 29% 10%	472
October	Day	19% 10% 20% 35% 14%	471
	Night	13% 14% 22% 31% 17%	523
November	Day	10% 7% 37% 30% 14%	327
	Night	12% 6% 30% 34% 15%	483
December	Day	10% 26% 41% 17%	357
	Night	7% 7% 27% 38% 18%	535

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	16% 38% 32% 11%	218
February	Day	50% 50%	2
	Night	15% 41% 40%	158
March	Day	11% 30% 42% 15%	52
	Night	18% 41% 29% 10%	220
April	Day	11% 20% 30% 30% 7%	53
	Night	15% 30% 41% 11%	213
May	Day	8% 23% 10% 33% 23%	56
	Night	20% 39% 29% 6%	164
June	Day	8% 24% 24% 26% 15%	45
	Night	9% 15% 34% 39%	146
July	Day	7% 16% 40% 34%	55
	Night	6% 11% 20% 45% 16%	175
August	Day	9% 14% 22% 24% 29%	77
	Night	7% 15% 29% 35% 13%	260
September	Day	7% 25% 24% 29% 12%	78
	Night	5% 22% 33% 37%	303
October	Day	32% 34% 22% 6%	76
	Night	8% 26% 35% 27%	302
November	Day	7% 17% 28% 28% 17%	28
	Night	8% 18% 34% 32% 6%	228
December	Night	14% 25% 35% 24%	220

Page generated at 2008-08-29 16:03:14. Version ab11