Sacramento Mountains Astronomy Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sacramento Mountains Astronomy Park 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	5% 5% 5% 5% 7% 54%	16466
	Night	8% 60%	16490
Cloud Cover	Day	5% 5% 5% 5% 7% 53%	16459
	Night	5% 5% 8% 59%	16497
Transparency	Day	7% 10% 18% 27% 20%	14389
	Night	6% 10% 18% 30% 22%	14669
Seeing	Day	17% 26% 31% 17%	864
	Night	18% 25% 29% 19%	5263

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% 7% 6% 62%	1105
	Night	5% 5% 6% 7% 59%	1592
February	Day	8% 68%	1087
	Night	5% 5% 8% 70%	1307
March	Day	5% 5% 5% 6% 5% 55%	1357
	Night	5% 5% 7% 59%	1363
April	Day	6% 70%	1415
	Night	5% 70%	1188
May	Day	5% 5% 5% 8% 53%	1507
	Night	6% 6% 8% 58%	1190
June	Day	5% 5% 7% 7% 7% 8% 46%	1663
	Night	5% 10% 6% 6% 7% 47%	965
July	Day	15% 5% 6% 9% 7% 8% 11% 24%	1588
	Night	9% 6% 7% 8% 14% 35%	1102
August	Day	12% 6% 7% 8% 7% 8% 9% 28%	1480
	Night	8% 5% 7% 12% 40%	1239
September	Day	9% 6% 5% 5% 7% 48%	1379
	Night	6% 8% 57%	1222
October	Day	5% 69%	1228
	Night	5% 72%	1464
November	Day	6% 73%	1349
	Night	7% 68%	1818
December	Day	5% 8% 65%	1308
	Night	8% 67%	2040

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% 7% 61%	1104
	Night	7% 6% 58%	1594
February	Day	8% 67%	1087
	Night	5% 7% 70%	1307
March	Day	5% 5% 7% 5% 55%	1358
	Night	5% 7% 58%	1365
April	Day	6% 69%	1415
	Night	5% 5% 70%	1188
May	Day	6% 6% 5% 6% 8% 51%	1506
	Night	5% 6% 5% 8% 57%	1190
June	Day	5% 7% 7% 6% 9% 45%	1663
	Night	5% 10% 5% 7% 7% 46%	965
July	Day	14% 5% 6% 9% 9% 8% 10% 23%	1588
	Night	9% 5% 7% 7% 8% 14% 35%	1103
August	Day	11% 6% 8% 9% 7% 8% 8% 26%	1474
	Night	7% 6% 5% 7% 13% 40%	1240
September	Day	8% 5% 5% 6% 8% 46%	1381
	Night	6% 5% 5% 9% 55%	1222
October	Day	5% 69%	1229
	Night	6% 72%	1464
November	Day	6% 72%	1346
	Night	7% 68%	1818
December	Day	5% 8% 64%	1308
	Night	9% 66%	2041

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	7% 9% 18% 29% 26%	990
	Night	7% 12% 15% 31% 26%	1399
February	Day	16% 41% 28%	990
	Night	14% 44% 28%	1215
March	Day	6% 10% 18% 30% 22%	1168
	Night	5% 8% 16% 34% 25%	1181
April	Day	6% 8% 33% 41%	1270
	Night	6% 9% 33% 40%	1068
May	Day	8% 10% 15% 25% 26%	1311
	Night	8% 9% 15% 29% 27%	1034
June	Day	8% 14% 14% 22% 23%	1393
	Night	10% 15% 13% 22% 24%	802
July	Day	14% 17% 18% 13%	1051
	Night	12% 26% 22% 19% 5%	736
August	Day	13% 19% 21% 10%	1223
	Night	10% 22% 28% 10%	1052
September	Day	8% 12% 20% 25% 10%	1284
	Night	8% 15% 24% 21% 11%	1148
October	Day	7% 15% 33% 27%	1165
	Night	5% 6% 16% 31% 29%	1386
November	Day	6% 25% 33% 21%	1315
	Night	20% 35% 24%	1742
December	Day	5% 9% 26% 37% 11%	1229
	Night	8% 22% 36% 17%	1906

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	33% 29% 24% 8%	479
February	Night	32% 31% 23% 8%	415
March	Day	42% 42% 9%	91
	Night	25% 33% 27% 9%	451
April	Day	47% 42% 7%	107
	Night	29% 36% 25% 7%	349
May	Day	20% 35% 26% 9%	141
	Night	11% 31% 33% 16%	357
June	Day	9% 20% 34% 27%	225
	Night	5% 21% 37% 29%	341
July	Day	16% 48% 24%	107
	Night	5% 32% 49% 6%	322
August	Day	8% 47% 26% 7%	119
	Night	26% 49% 11%	353
September	Day	27% 36% 20%	74
	Night	5% 8% 36% 40% 5%	338
October	Night	13% 25% 32% 18% 7%	471
November	Night	11% 26% 31% 18% 9%	653
December	Night	28% 31% 23% 8%	734

Page generated at 2009-12-30 03:20:39. Version ab11