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 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% 67%	16531
	Night	6% 66%	16423
Transparency	Day	9% 17% 29% 28%	14737
	Night	9% 16% 27% 29%	14642
Seeing	Day	13% 38% 41%	1102
	Night	16% 37% 32% 7%	5396

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	10% 65%	1110
	Night	9% 67%	1583
February	Day	12% 7% 46%	1089
	Night	11% 6% 53%	1306
March	Day	6% 7% 56%	1333
	Night	5% 5% 7% 61%	1388
April	Day	6% 5% 6% 59%	1414
	Night	6% 7% 5% 60%	1189
May	Day	5% 5% 7% 66%	1576
	Night	12% 5% 7% 59%	1122
June	Day	69%	1627
	Night	7% 5% 8% 66%	1001
July	Day	6% 72%	1633
	Night	5% 5% 6% 66%	1056
August	Day	81%	1480
	Night	79%	1239
September	Day	84%	1352
	Night	80%	1250
October	Day	77%	1265
	Night	77%	1427
November	Day	5% 67%	1300
	Night	7% 67%	1872
December	Day	9% 5% 9% 55%	1352
	Night	7% 7% 58%	1990

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	9% 15% 19% 34%	1010
	Night	9% 12% 18% 40%	1436
February	Day	6% 11% 19% 26% 14%	920
	Night	7% 11% 17% 25% 20%	1124
March	Day	6% 13% 24% 27% 17%	1103
	Night	5% 12% 24% 29% 18%	1174
April	Day	6% 14% 25% 27% 16%	1161
	Night	6% 13% 24% 27% 18%	970
May	Day	5% 12% 21% 38% 11%	1427
	Night	7% 10% 26% 29% 14%	957
June	Day	6% 13% 27% 34%	1505
	Night	6% 11% 15% 25% 31%	890
July	Day	8% 17% 29% 36%	1221
	Night	5% 9% 16% 29% 32%	773
August	Day	5% 11% 39% 35%	1432
	Night	5% 13% 40% 29%	1194
September	Day	11% 38% 37%	1334
	Night	6% 10% 36% 36%	1220
October	Day	5% 14% 25% 42%	1198
	Night	5% 12% 25% 45%	1349
November	Day	7% 17% 24% 33%	1191
	Night	10% 16% 22% 33%	1758
December	Day	6% 11% 20% 22% 19%	1235
	Night	5% 10% 17% 26% 20%	1797

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	21% 42% 21%	70
	Night	26% 42% 15%	481
February	Day	17% 38% 29%	105
	Night	17% 42% 22%	417
March	Day	26% 40% 26%	115
	Night	26% 39% 23% 5%	485
April	Day	25% 48% 23%	112
	Night	23% 45% 22%	459
May	Day	12% 40% 40%	123
	Night	18% 39% 33% 5%	387
June	Day	11% 35% 43%	120
	Night	10% 41% 39% 5%	267
July	Day	20% 70% 7%	109
	Night	18% 65% 13%	300
August	Day	27% 69%	120
	Night	21% 55% 17%	480
September	Day	45% 50%	117
	Night	5% 28% 47% 16%	462
October	Day	14% 45% 34%	111
	Night	18% 40% 28% 8%	486
November	Night	15% 41% 32% 6%	575
December	Night	20% 42% 22%	597

Page generated at 2009-12-30 02:20:42. Version ab11