San Diego
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the San Diego 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	8% 9% 52%	8663
	Night	13% 6% 5% 5% 8% 43%	8506
Transparency	Day	14% 9% 22% 27% 25%	6997
	Night	16% 10% 20% 23% 27%	6192
Seeing	Day	21% 45% 29%	644
	Night	11% 31% 40% 12%	2983

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	15% 6% 5% 5% 6% 41%	584
	Night	15% 5% 7% 50%	768
February	Day	24% 5% 6% 6% 36%	561
	Night	24% 5% 5% 41%	684
March	Day	6% 6% 5% 5% 7% 49%	664
	Night	9% 10% 6% 5% 6% 42%	697
April	Day	8% 62%	720
	Night	16% 5% 6% 7% 44%	600
May	Day	5% 5% 11% 53%	796
	Night	10% 7% 5% 6% 8% 9% 37%	568
June	Day	6% 6% 5% 13% 54%	780
	Night	18% 11% 8% 5% 6% 8% 26%	537
July	Day	5% 6% 6% 12% 48%	779
	Night	8% 12% 7% 7% 14% 30%	574
August	Day	5% 5% 11% 50%	1114
	Night	10% 7% 6% 6% 12% 37%	929
September	Day	5% 9% 59%	997
	Night	7% 6% 6% 5% 9% 49%	949
October	Day	11% 11% 53%	651
	Night	13% 5% 5% 5% 5% 9% 44%	712
November	Day	9% 5% 5% 56%	468
	Night	7% 5% 7% 58%	698
December	Day	16% 6% 52%	549
	Night	16% 7% 49%	790

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	20% 7% 24% 21% 25%	331
	Night	16% 8% 21% 25% 27%	496
February	Day	18% 6% 30% 20% 23%	255
	Night	16% 10% 24% 23% 25%	340
March	Day	20% 11% 26% 18% 22%	462
	Night	20% 12% 19% 22% 24%	407
April	Day	16% 8% 28% 29% 16%	594
	Night	20% 25% 25% 24%	386
May	Day	12% 11% 26% 27% 22%	662
	Night	20% 11% 16% 22% 29%	366
June	Day	19% 7% 17% 39% 16%	699
	Night	33% 11% 17% 25% 12%	352
July	Day	16% 11% 25% 22% 24%	659
	Night	18% 23% 28% 20% 9%	430
August	Day	15% 12% 20% 28% 23%	938
	Night	20% 13% 21% 23% 20%	701
September	Day	7% 7% 16% 29% 38%	913
	Night	13% 5% 18% 24% 37%	775
October	Day	13% 9% 20% 28% 27%	772
	Night	9% 14% 17% 22% 35%	790
November	Day	10% 10% 30% 23% 25%	362
	Night	12% 9% 28% 23% 25%	608
December	Day	5% 14% 32% 45%	350
	Night	14% 6% 11% 24% 42%	541

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	40% 50%	32
	Night	6% 11% 38% 37% 5%	228
February	Day	16% 40% 40%	49
	Night	7% 25% 46% 20%	188
March	Day	5% 28% 38% 28%	60
	Night	11% 37% 35% 11%	235
April	Day	6% 31% 51% 10%	60
	Night	6% 13% 38% 38%	226
May	Day	27% 48% 19%	62
	Night	13% 32% 45% 5%	191
June	Day	15% 40% 44%	59
	Night	9% 34% 46% 7%	175
July	Day	41% 53%	62
	Night	6% 15% 51% 25%	201
August	Day	5% 40% 53%	91
	Night	5% 16% 49% 27%	367
September	Day	18% 47% 32%	90
	Night	7% 23% 46% 21%	354
October	Day	24% 51% 20%	79
	Night	11% 24% 45% 15%	359
November	Night	15% 47% 30%	241
December	Night	6% 14% 41% 31% 5%	218

Page generated at 2008-09-30 02:41:07. Version ab11