Kitt Peak
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Kitt Peak 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	6% 5% 60%	8676
	Night	6% 5% 62%	8494
Transparency	Day	6% 16% 28% 43%	6811
	Night	5% 7% 18% 30% 37%	6806
Seeing	Day	14% 35% 35% 12%	524
	Night	5% 15% 37% 35% 5%	2898

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	13% 6% 5% 5% 6% 44%	549
	Night	11% 5% 5% 5% 5% 5% 5% 45%	804
February	Day	12% 5% 7% 5% 5% 5% 6% 41%	558
	Night	11% 5% 6% 50%	687
March	Day	8% 64%	681
	Night	62%	681
April	Day	5% 70%	699
	Night	73%	620
May	Day	5% 9% 65%	806
	Night	9% 68%	558
June	Day	83%	780
	Night	85%	537
July	Day	7% 6% 5% 6% 8% 49%	795
	Night	5% 8% 6% 7% 10% 45%	558
August	Day	13% 7% 5% 7% 8% 38%	1159
	Night	8% 6% 5% 6% 11% 48%	883
September	Day	71%	969
	Night	6% 71%	977
October	Day	75%	636
	Night	76%	728
November	Day	6% 66%	495
	Night	6% 5% 66%	671
December	Day	8% 65%	549
	Night	7% 62%	790

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	13% 14% 30% 26% 14%	321
	Night	6% 13% 29% 31% 19%	453
February	Day	10% 7% 30% 33% 18%	324
	Night	9% 13% 26% 34% 15%	431
March	Day	10% 24% 30% 30%	508
	Night	10% 29% 28% 26%	484
April	Day	10% 32% 50%	538
	Night	5% 15% 27% 50%	499
May	Day	7% 32% 53%	683
	Night	13% 30% 51%	468
June	Day	23% 71%	696
	Night	30% 63%	476
July	Day	8% 6% 16% 22% 45%	522
	Night	13% 6% 24% 15% 39%	362
August	Day	11% 11% 31% 27% 17%	687
	Night	12% 16% 28% 30% 12%	606
September	Day	7% 14% 23% 52%	837
	Night	5% 15% 29% 45%	834
October	Day	14% 35% 44%	810
	Night	6% 18% 36% 37%	951
November	Day	9% 19% 23% 44%	456
	Night	9% 15% 33% 37%	632
December	Day	5% 14% 24% 51%	429
	Night	6% 6% 10% 27% 49%	610

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	10% 14% 47% 25%	230
February	Day	25% 51% 13% 9%	43
	Night	8% 25% 46% 18%	203
March	Day	26% 26% 25% 21%	56
	Night	5% 16% 39% 31% 5%	242
April	Day	25% 42% 28%	56
	Night	8% 30% 40% 18%	206
May	Day	17% 36% 36% 8%	57
	Night	16% 43% 33%	180
June	Day	8% 43% 43% 5%	60
	Night	15% 46% 33%	180
July	Day	8% 49% 35% 6%	59
	Night	10% 36% 42% 7%	185
August	Day	7% 28% 43% 20%	85
	Night	19% 60% 12%	284
September	Day	10% 25% 43% 18%	87
	Night	7% 31% 46% 10%	352
October	Day	9% 23% 42% 23%	21
	Night	5% 15% 38% 36%	367
November	Night	6% 17% 39% 34%	241
December	Night	9% 21% 30% 33% 5%	228

Page generated at 2008-06-05 20:07:24. Version ab11