Old Town Pasadena
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Old Town Pasadena 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% 6% 67%	16523
	Night	6% 66%	16428
Transparency	Day	8% 18% 30% 27%	14620
	Night	8% 17% 28% 28%	14405
Seeing	Day	12% 32% 46% 5%	1109
	Night	13% 36% 34% 8%	5386

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%	1105
	Night	9% 67%	1588
February	Day	11% 5% 7% 47%	1089
	Night	11% 5% 5% 53%	1306
March	Day	6% 5% 7% 58%	1334
	Night	5% 7% 62%	1386
April	Day	6% 5% 60%	1414
	Night	6% 5% 61%	1189
May	Day	8% 65%	1574
	Night	8% 8% 60%	1125
June	Day	6% 68%	1632
	Night	6% 7% 64%	996
July	Day	7% 72%	1634
	Night	5% 7% 66%	1054
August	Day	81%	1480
	Night	75%	1239
September	Day	82%	1354
	Night	81%	1248
October	Day	77%	1264
	Night	78%	1427
November	Day	5% 67%	1300
	Night	7% 67%	1872
December	Day	9% 10% 54%	1343
	Night	7% 6% 59%	1998

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	10% 15% 19% 35%	1000
	Night	8% 14% 17% 41%	1440
February	Day	10% 23% 26% 13%	908
	Night	5% 11% 18% 24% 21%	1111
March	Day	5% 12% 26% 27% 18%	1112
	Night	5% 12% 25% 30% 18%	1162
April	Day	14% 27% 30% 15%	1170
	Night	13% 28% 25% 18%	956
May	Day	11% 24% 38% 11%	1397
	Night	11% 26% 31% 14%	916
June	Day	6% 13% 28% 34%	1473
	Night	12% 16% 30% 27%	837
July	Day	5% 6% 17% 30% 35%	1218
	Night	5% 6% 18% 31% 29%	755
August	Day	11% 43% 32%	1421
	Night	5% 11% 42% 28%	1157
September	Day	13% 40% 35%	1320
	Night	11% 39% 33%	1187
October	Day	6% 15% 26% 41%	1196
	Night	12% 26% 45%	1345
November	Day	7% 18% 24% 33%	1199
	Night	8% 17% 23% 34%	1744
December	Day	13% 19% 22% 21%	1206
	Night	10% 17% 27% 21%	1795

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	20% 34% 28% 6%	73
	Night	22% 43% 18%	479
February	Day	19% 30% 36%	106
	Night	17% 39% 25%	419
March	Day	29% 35% 32%	117
	Night	20% 43% 24% 5%	479
April	Day	22% 49% 26%	113
	Night	5% 18% 46% 24%	459
May	Day	10% 38% 43% 5%	123
	Night	19% 36% 33% 5%	391
June	Day	10% 29% 46% 10%	120
	Night	9% 35% 45% 5%	262
July	Day	12% 68% 17%	108
	Night	13% 66% 15%	295
August	Day	20% 75%	120
	Night	16% 56% 20%	480
September	Day	35% 59%	117
	Night	27% 47% 17%	462
October	Day	13% 35% 39% 8%	112
	Night	13% 40% 31% 8%	486
November	Night	11% 42% 37% 5%	575
December	Night	16% 44% 23% 5%	599

Page generated at 2009-12-30 02:20:33. Version ab11