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Minneapolis
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Minneapolis 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% 6% 5% 7% 33%	8741
	Night	19% 6% 5% 6% 6% 35%	8432
Transparency	Day	18% 24% 41% 14%	4446
	Night	18% 23% 39% 16%	4491
Seeing	Day	16% 36% 25% 17%	587
	Night	18% 35% 30% 14%	2465

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	28% 10% 8% 7% 5% 21%	512
	Night	23% 10% 9% 7% 7% 7% 5% 17%	841
February	Day	28% 9% 10% 5% 26%	519
	Night	25% 10% 7% 5% 5% 5% 25%	735
March	Day	23% 6% 6% 5% 9% 6% 28%	681
	Night	20% 7% 8% 5% 8% 5% 6% 25%	685
April	Day	18% 6% 7% 6% 5% 8% 33%	742
	Night	15% 7% 6% 7% 39%	578
May	Day	29% 7% 5% 5% 7% 5% 6% 21%	855
	Night	23% 5% 8% 5% 7% 5% 5% 28%	497
June	Day	18% 5% 6% 6% 10% 33%	840
	Night	13% 5% 7% 6% 9% 38%	476
July	Day	10% 7% 5% 6% 12% 40%	862
	Night	8% 6% 6% 9% 50%	499
August	Day	11% 6% 5% 7% 44%	1189
	Night	6% 5% 5% 8% 56%	853
September	Day	17% 6% 7% 45%	1012
	Night	14% 5% 5% 49%	929
October	Day	23% 6% 6% 6% 8% 33%	615
	Night	21% 5% 6% 36%	747
November	Day	27% 8% 7% 5% 6% 27%	427
	Night	25% 7% 7% 33%	740
December	Day	24% 10% 9% 5% 6% 5% 5% 21%	487
	Night	28% 8% 8% 6% 6% 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	36% 27% 35%	163
	Night	32% 24% 39%	265
February	Day	27% 28% 39% 5%	184
	Night	21% 28% 42% 8%	256
March	Day	32% 29% 35%	310
	Night	25% 24% 45%	280
April	Day	11% 23% 40% 20%	366
	Night	16% 17% 38% 22% 5%	327
May	Day	31% 22% 37% 7%	310
	Night	25% 24% 38% 9%	211
June	Day	17% 16% 49% 16%	433
	Night	18% 13% 43% 23%	271
July	Day	14% 18% 47% 18%	544
	Night	13% 20% 47% 15%	353
August	Day	10% 22% 37% 27%	685
	Night	14% 24% 33% 23%	618
September	Day	12% 27% 43% 16%	636
	Night	10% 22% 41% 22%	596
October	Day	17% 30% 38% 11%	448
	Night	19% 23% 38% 17%	606
November	Day	21% 24% 40% 11%	212
	Night	19% 29% 42% 8%	404
December	Day	30% 25% 40%	155
	Night	24% 22% 31% 22%	304

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	32% 37% 22% 7%	227
February	Night	17% 41% 33% 7%	197
March	Day	50% 50%	2
	Night	23% 35% 29% 10%	155
April	Day	17% 43% 24% 10%	73
	Night	10% 43% 35% 9%	148
May	Day	31% 47% 12% 6%	89
	Night	21% 45% 26% 6%	150
June	Day	17% 45% 20% 12%	105
	Night	15% 31% 38% 14%	163
July	Day	15% 32% 26% 17% 7%	114
	Night	25% 45% 21%	172
August	Day	11% 24% 33% 29%	158
	Night	5% 26% 38% 27%	262
September	Day	36% 30% 23%	46
	Night	15% 37% 25% 19%	248
October	Night	19% 32% 26% 20%	298
November	Night	27% 40% 24% 7%	233
December	Night	28% 33% 30% 7%	212

Page generated at 2008-06-05 22:07:22. Version ab11