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 2003-08-01 to 2005-11-07.

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% 5% 66%	8694
	Night	7% 6% 59%	8473
Transparency	Day	9% 7% 20% 32% 29%	7375
	Night	13% 9% 20% 27% 28%	6887
Seeing	Day	8% 30% 46% 14%	648
	Night	16% 34% 40% 6%	2909

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	14% 5% 54%	550
	Night	14% 6% 5% 49%	804
February	Day	25% 5% 37%	561
	Night	24% 5% 42%	684
March	Day	9% 5% 60%	669
	Night	7% 7% 5% 56%	692
April	Day	5% 5% 7% 60%	720
	Night	7% 5% 6% 62%	600
May	Day	5% 6% 65%	793
	Night	6% 5% 8% 57%	571
June	Day	79%	822
	Night	10% 9% 55%	496
July	Day	79%	811
	Night	6% 5% 7% 66%	539
August	Day	5% 76%	1114
	Night	6% 8% 62%	929
September	Day	5% 77%	1007
	Night	5% 74%	939
October	Day	7% 64%	641
	Night	8% 5% 59%	721
November	Day	6% 5% 6% 61%	468
	Night	6% 65%	698
December	Day	18% 5% 54%	538
	Night	16% 5% 56%	800

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	12% 9% 26% 26% 25%	368
	Night	13% 6% 23% 34% 22%	537
February	Day	16% 5% 32% 21% 23%	277
	Night	11% 9% 29% 22% 26%	331
March	Day	13% 11% 22% 24% 27%	482
	Night	20% 9% 24% 17% 29%	500
April	Day	14% 9% 26% 28% 20%	555
	Night	12% 6% 29% 30% 20%	467
May	Day	11% 8% 27% 30% 21%	648
	Night	18% 11% 16% 28% 24%	445
June	Day	9% 6% 23% 53% 7%	781
	Night	26% 6% 25% 36%	401
July	Day	8% 6% 18% 33% 32%	751
	Night	15% 11% 24% 26% 23%	468
August	Day	7% 7% 17% 29% 37%	1020
	Night	15% 15% 17% 27% 23%	820
September	Day	10% 32% 48%	943
	Night	5% 10% 13% 30% 39%	870
October	Day	8% 7% 20% 29% 34%	794
	Night	12% 7% 19% 22% 37%	872
November	Day	10% 12% 29% 30% 16%	408
	Night	10% 10% 26% 27% 25%	620
December	Day	10% 8% 38% 40%	348
	Night	7% 5% 12% 27% 46%	556

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	5% 36% 41% 13%	36
	Night	22% 43% 28%	222
February	Day	31% 48% 20%	45
	Night	6% 40% 31% 20%	177
March	Day	16% 28% 38% 15%	59
	Night	21% 39% 33%	236
April	Day	21% 48% 25% 5%	60
	Night	19% 42% 30%	231
May	Day	14% 33% 46%	62
	Night	12% 43% 41%	196
June	Day	23% 48% 26%	60
	Night	10% 30% 53%	138
July	Day	9% 79% 11%	62
	Night	13% 66% 14%	167
August	Day	17% 64% 18%	92
	Night	8% 14% 58% 17%	371
September	Day	32% 45% 20%	90
	Night	8% 29% 49% 11%	359
October	Day	34% 40% 21%	82
	Night	12% 36% 43% 6%	356
November	Night	22% 47% 24%	242
December	Night	5% 24% 45% 21%	214

Page generated at 2008-09-30 02:41:18. Version ab11