Huntsville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Huntsville 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% 6% 5% 8% 33%	8702
	Night	18% 6% 5% 8% 38%	8468
Transparency	Day	18% 14% 37% 25%	4396
	Night	16% 14% 37% 27%	4827
Seeing	Day	5% 11% 25% 37% 20%	453
	Night	9% 23% 34% 27%	2521

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	25% 6% 5% 5% 5% 5% 6% 30%	574
	Night	23% 6% 5% 5% 5% 6% 32%	779
February	Day	39% 7% 5% 5% 23%	570
	Night	33% 5% 5% 5% 26%	684
March	Day	20% 7% 5% 7% 36%	665
	Night	21% 5% 5% 5% 5% 5% 37%	700
April	Day	20% 5% 5% 7% 38%	722
	Night	14% 5% 5% 8% 45%	598
May	Day	16% 9% 5% 6% 9% 33%	802
	Night	10% 5% 6% 11% 46%	551
June	Day	27% 5% 5% 9% 5% 5% 7% 21%	790
	Night	24% 5% 5% 7% 10% 26%	525
July	Day	18% 6% 8% 5% 7% 7% 6% 5% 10% 20%	807
	Night	13% 5% 5% 12% 7% 6% 10% 25%	550
August	Day	15% 5% 5% 9% 6% 7% 10% 28%	1120
	Night	12% 5% 6% 8% 5% 6% 8% 33%	923
September	Day	12% 5% 5% 5% 7% 46%	993
	Night	11% 6% 9% 50%	950
October	Day	16% 5% 6% 8% 40%	638
	Night	14% 6% 6% 8% 44%	723
November	Day	31% 5% 8% 33%	474
	Night	27% 7% 6% 35%	694
December	Day	19% 5% 5% 5% 45%	547
	Night	19% 6% 47%	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% 18% 43% 18%	237
	Night	12% 17% 41% 27%	349
February	Day	13% 12% 55% 16%	194
	Night	19% 7% 45% 27%	268
March	Day	19% 19% 43% 17%	351
	Night	14% 13% 43% 25%	348
April	Day	10% 8% 45% 28% 6%	359
	Night	8% 10% 34% 43%	359
May	Day	20% 26% 33% 20%	390
	Night	24% 15% 45% 14%	333
June	Day	33% 12% 38% 14%	254
	Night	33% 10% 41% 13%	218
July	Day	41% 16% 33% 8%	307
	Night	38% 13% 38% 8%	225
August	Day	29% 24% 35% 9%	529
	Night	29% 23% 38% 8%	469
September	Day	11% 33% 46%	610
	Night	7% 10% 36% 39% 6%	639
October	Day	10% 13% 38% 33%	550
	Night	13% 15% 31% 33% 6%	699
November	Day	18% 9% 27% 33% 11%	292
	Night	14% 14% 28% 27% 14%	429
December	Day	7% 11% 40% 34% 5%	323
	Night	8% 16% 33% 34% 7%	491

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% 39% 38% 5%	194
February	Night	22% 44% 31%	161
March	Day	16% 20% 44% 20%	25
	Night	17% 41% 28% 12%	199
April	Day	14% 22% 29% 31%	48
	Night	9% 25% 45% 18%	155
May	Day	9% 28% 30% 30%	53
	Night	6% 17% 36% 33% 6%	176
June	Day	11% 18% 43% 22%	53
	Night	10% 12% 34% 40%	149
July	Day	11% 10% 23% 30% 25%	60
	Night	7% 32% 45% 10%	167
August	Day	7% 7% 45% 37%	82
	Night	12% 19% 47% 15%	264
September	Day	6% 33% 41% 17%	80
	Night	14% 34% 43% 5%	307
October	Day	5% 11% 38% 40%	52
	Night	5% 19% 43% 29%	337
November	Night	11% 28% 36% 20%	205
December	Night	14% 31% 31% 19%	207

Page generated at 2008-08-20 17:20:59. Version ab11