Mount Hopkins
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mount Hopkins 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	7% 5% 5% 6% 56%	8680
	Night	6% 5% 6% 57%	8489
Transparency	Day	8% 7% 17% 29% 37%	6681
	Night	8% 7% 19% 31% 32%	6577
Seeing	Day	13% 34% 37% 13%	516
	Night	17% 37% 36%	2887

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	9% 7% 6% 5% 5% 6% 7% 42%	549
	Night	14% 6% 5% 7% 42%	804
February	Day	15% 10% 6% 5% 6% 37%	558
	Night	13% 6% 6% 5% 5% 44%	686
March	Day	7% 61%	681
	Night	5% 7% 57%	681
April	Day	5% 62%	696
	Night	5% 5% 67%	624
May	Day	5% 10% 65%	805
	Night	12% 64%	558
June	Day	5% 76%	780
	Night	81%	537
July	Day	8% 5% 9% 7% 7% 6% 41%	795
	Night	7% 5% 9% 8% 9% 8% 39%	558
August	Day	11% 6% 8% 6% 7% 7% 35%	1164
	Night	8% 6% 7% 5% 8% 13% 39%	879
September	Day	5% 6% 66%	969
	Night	5% 6% 64%	977
October	Day	5% 5% 68%	631
	Night	71%	732
November	Day	5% 65%	503
	Night	7% 61%	663
December	Day	8% 5% 62%	549
	Night	6% 5% 5% 61%	790

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	15% 12% 28% 32% 11%	332
	Night	14% 9% 33% 28% 14%	466
February	Day	10% 10% 27% 33% 17%	301
	Night	12% 9% 29% 31% 16%	400
March	Day	8% 8% 25% 33% 23%	510
	Night	8% 10% 32% 26% 21%	493
April	Day	5% 11% 33% 47%	522
	Night	8% 14% 32% 39%	486
May	Day	11% 32% 46%	685
	Night	20% 34% 38%	466
June	Day	27% 63%	687
	Night	38% 52%	468
July	Day	15% 7% 20% 19% 38%	474
	Night	17% 10% 22% 12% 35%	330
August	Day	19% 16% 29% 23% 11%	655
	Night	17% 22% 26% 24% 9%	561
September	Day	7% 5% 13% 31% 41%	803
	Night	6% 6% 10% 36% 39%	775
October	Day	5% 17% 34% 37%	808
	Night	6% 20% 37% 31%	934
November	Day	7% 7% 19% 20% 44%	473
	Night	7% 7% 15% 31% 38%	596
December	Day	5% 17% 21% 50%	431
	Night	7% 14% 23% 50%	602

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	6% 20% 48% 22%	229
February	Day	28% 48% 11% 11%	35
	Night	9% 30% 44% 15%	203
March	Day	26% 36% 19% 17%	57
	Night	22% 38% 31%	244
April	Day	30% 49% 18%	55
	Night	5% 33% 45% 15%	197
May	Day	13% 42% 37% 6%	59
	Night	16% 44% 34%	183
June	Day	5% 35% 55% 5%	60
	Night	10% 42% 44%	179
July	Day	8% 30% 50% 10%	60
	Night	9% 32% 48% 5%	185
August	Day	6% 19% 46% 26%	88
	Night	6% 15% 67% 10%	272
September	Day	34% 42% 18%	87
	Night	7% 30% 51% 7%	355
October	Day	13% 26% 53% 6%	15
	Night	16% 38% 38%	366
November	Night	24% 41% 27%	241
December	Night	9% 24% 35% 27%	233

Page generated at 2008-05-11 01:45:38. Version ab11