Monrovia
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Monrovia clear sky chart from 2005-11-05 to 2008-11-27.

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% 67%	12289
	Night	5% 6% 66%	12139
Transparency	Day	5% 10% 18% 29% 30%	10497
	Night	5% 10% 16% 28% 30%	10352
Seeing	Day	12% 37% 44%	820
	Night	15% 38% 33% 8%	3963

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	11% 62%	838
	Night	10% 64%	1199
February	Day	9% 5% 7% 51%	809
	Night	10% 7% 55%	970
March	Day	6% 6% 5% 7% 54%	998
	Night	5% 5% 7% 60%	1041
April	Day	8% 5% 7% 55%	1077
	Night	8% 7% 5% 59%	899
May	Day	5% 5% 7% 66%	1190
	Night	14% 5% 7% 57%	855
June	Day	5% 78%	1228
	Night	7% 7% 73%	751
July	Day	7% 69%	1235
	Night	5% 5% 7% 64%	806
August	Day	82%	1108
	Night	79%	929
September	Day	82%	1022
	Night	5% 77%	953
October	Day	75%	955
	Night	75%	1077
November	Day	5% 66%	1003
	Night	5% 7% 66%	1443
December	Day	7% 5% 11% 58%	826
	Night	6% 7% 62%	1216

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	10% 18% 21% 27%	738
	Night	11% 13% 20% 36%	1051
February	Day	8% 13% 20% 34% 14%	640
	Night	7% 12% 18% 30% 20%	788
March	Day	8% 15% 25% 27% 18%	777
	Night	7% 15% 20% 32% 19%	827
April	Day	8% 17% 25% 28% 14%	826
	Night	8% 15% 26% 27% 18%	680
May	Day	14% 23% 36% 14%	1034
	Night	7% 11% 27% 26% 18%	685
June	Day	6% 16% 33% 40%	1106
	Night	9% 14% 33% 38%	640
July	Day	10% 14% 26% 39%	823
	Night	6% 11% 13% 26% 36%	523
August	Day	5% 11% 38% 36%	1060
	Night	6% 13% 36% 32%	884
September	Day	10% 34% 43%	1004
	Night	6% 9% 33% 39%	923
October	Day	5% 7% 14% 19% 46%	886
	Night	5% 12% 20% 49%	999
November	Day	8% 18% 24% 31%	894
	Night	5% 12% 16% 24% 31%	1329
December	Day	10% 13% 23% 24% 21%	709
	Night	5% 13% 18% 29% 23%	1023

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	Day	23% 44% 21%	52
	Night	24% 44% 14%	361
February	Day	14% 40% 35% 5%	77
	Night	16% 41% 27% 5%	305
March	Day	25% 42% 26%	84
	Night	27% 41% 22%	361
April	Day	24% 48% 25%	85
	Night	23% 46% 22%	343
May	Day	15% 36% 40%	92
	Night	20% 38% 31%	294
June	Day	6% 37% 50% 5%	90
	Night	8% 37% 44% 8%	199
July	Day	15% 72% 10%	79
	Night	18% 61% 15%	224
August	Day	24% 74%	89
	Night	18% 56% 19%	356
September	Day	44% 51%	88
	Night	6% 29% 46% 15%	350
October	Day	14% 44% 38%	84
	Night	17% 41% 28% 8%	366
November	Night	15% 43% 32% 6%	443
December	Night	18% 45% 22%	361

Page generated at 2008-11-27 10:47:33. Version ab11