Kitt Peak
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Kitt Peak clear sky chart from 2005-11-05 to 2009-12-29.

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% 64%	16509
	Night	6% 66%	16454
Transparency	Day	6% 11% 27% 38%	14802
	Night	6% 13% 27% 37%	14927
Seeing	Day	14% 32% 36% 12%	932
	Night	15% 35% 34% 8%	5326

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	5% 64%	1105
	Night	5% 63%	1592
February	Day	5% 8% 64%	1082
	Night	5% 5% 6% 60%	1312
March	Day	6% 63%	1361
	Night	6% 65%	1361
April	Day	75%	1374
	Night	75%	1229
May	Day	79%	1601
	Night	5% 77%	1098
June	Day	5% 71%	1550
	Night	5% 71%	1080
July	Day	7% 5% 5% 9% 5% 6% 10% 36%	1596
	Night	6% 8% 10% 14% 40%	1094
August	Day	6% 6% 6% 7% 7% 9% 42%	1540
	Night	6% 6% 10% 52%	1178
September	Day	5% 5% 5% 5% 66%	1303
	Night	5% 5% 71%	1299
October	Day	5% 81%	1251
	Night	80%	1442
November	Day	7% 69%	1377
	Night	5% 5% 68%	1793
December	Day	5% 6% 62%	1369
	Night	5% 66%	1976

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	6% 17% 23% 35%	994
	Night	8% 13% 23% 36%	1435
February	Day	13% 36% 32%	965
	Night	17% 31% 30%	1183
March	Day	7% 31% 43%	1155
	Night	5% 11% 30% 41%	1198
April	Day	6% 27% 54%	1268
	Night	6% 28% 55%	1096
May	Day	7% 24% 54%	1553
	Night	8% 27% 51%	1072
June	Day	24% 56%	1399
	Night	5% 22% 57%	968
July	Day	10% 13% 19% 14% 15%	1093
	Night	10% 20% 18% 18% 15%	787
August	Day	11% 15% 14% 18% 13%	1350
	Night	8% 16% 20% 22% 15%	1057
September	Day	6% 13% 33% 29%	1231
	Night	6% 18% 33% 28%	1231
October	Day	6% 26% 58%	1192
	Night	9% 23% 56%	1379
November	Day	10% 32% 39%	1325
	Night	12% 29% 39%	1707
December	Day	6% 16% 34% 23%	1277
	Night	6% 16% 35% 25%	1814

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	23% 40% 22%	483
February	Day	19% 38% 31% 6%	88
	Night	7% 19% 40% 25%	427
March	Day	32% 37% 21% 5%	119
	Night	7% 22% 39% 24%	483
April	Day	34% 33% 25%	111
	Night	7% 25% 43% 20%	402
May	Day	13% 42% 36%	122
	Night	18% 36% 34%	366
June	Day	9% 39% 43% 8%	120
	Night	13% 35% 40% 5%	340
July	Day	20% 51% 19%	107
	Night	26% 57% 11%	323
August	Day	22% 41% 27%	118
	Night	24% 52% 14%	384
September	Day	6% 24% 41% 22%	116
	Night	11% 31% 41% 13%	461
October	Day	32% 32% 29% 6%	31
	Night	16% 34% 31% 10%	485
November	Night	9% 32% 39% 12%	572
December	Night	6% 14% 38% 29% 7%	600

Page generated at 2009-12-30 03:20:32. Version ab11