Tombstone Sky Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tombstone Sky Observatory clear sky chart from 2005-11-05 to 2008-11-20.

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% 6% 63%	12217
	Night	6% 65%	12070
Transparency	Day	7% 13% 31% 32%	10388
	Night	7% 14% 33% 30%	10431
Seeing	Day	12% 26% 31% 22%	665
	Night	15% 40% 34% 5%	3859

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	6% 5% 8% 58%	835
	Night	8% 5% 59%	1203
February	Day	6% 5% 68%	802
	Night	5% 67%	977
March	Day	5% 5% 5% 67%	1020
	Night	6% 67%	1020
April	Day	75%	1048
	Night	75%	928
May	Day	77%	1193
	Night	5% 78%	852
June	Day	5% 6% 68%	1170
	Night	70%	810
July	Day	12% 7% 6% 6% 6% 11% 33%	1208
	Night	5% 5% 7% 10% 6% 8% 13% 31%	833
August	Day	16% 6% 6% 6% 5% 6% 7% 33%	1156
	Night	8% 5% 6% 5% 5% 5% 6% 10% 39%	880
September	Day	6% 5% 65%	993
	Night	5% 65%	981
October	Day	5% 77%	929
	Night	79%	1104
November	Day	6% 73%	1026
	Night	7% 72%	1275
December	Day	6% 6% 68%	837
	Night	5% 73%	1207

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	10% 19% 31% 23%	712
	Night	6% 9% 18% 27% 25%	1031
February	Day	6% 15% 46% 23%	684
	Night	5% 14% 41% 28%	854
March	Day	9% 38% 39%	855
	Night	6% 12% 39% 35%	865
April	Day	5% 30% 54%	946
	Night	6% 36% 48%	809
May	Day	10% 31% 47%	1100
	Night	14% 34% 39%	795
June	Day	5% 5% 7% 24% 54%	991
	Night	6% 24% 58%	681
July	Day	10% 16% 18% 17% 5%	711
	Night	14% 26% 17% 11% 5%	488
August	Day	12% 17% 17% 14%	881
	Night	15% 20% 20% 16%	705
September	Day	9% 18% 36% 19%	911
	Night	9% 18% 37% 15%	902
October	Day	5% 10% 28% 49%	861
	Night	5% 8% 28% 51%	1016
November	Day	13% 39% 31%	984
	Night	17% 35% 31%	1214
December	Day	5% 19% 43% 20%	752
	Night	5% 19% 48% 18%	1071

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	25% 49% 17%	362
February	Day	36% 38% 14% 10%	47
	Night	23% 43% 23%	317
March	Day	31% 34% 24% 6%	90
	Night	28% 40% 24%	366
April	Day	28% 43% 17% 9%	87
	Night	26% 51% 15%	295
May	Day	9% 35% 35% 14%	92
	Night	16% 44% 34%	279
June	Day	26% 46% 20%	90
	Night	5% 45% 42%	252
July	Day	9% 45% 31%	77
	Night	25% 60% 6%	240
August	Day	6% 32% 44% 9%	86
	Night	16% 55% 17%	263
September	Day	22% 28% 34%	87
	Night	9% 35% 46% 6%	337
October	Day	33% 66%	9
	Night	12% 42% 34% 7%	365
November	Night	9% 36% 39% 8%	418
December	Night	13% 46% 27% 6%	365

Page generated at 2008-11-20 22:15:45. Version ab11