Huntington Beach
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Huntington Beach 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	7% 9% 54%	8706
	Night	11% 7% 5% 7% 45%	8459
Transparency	Day	7% 25% 34% 29%	6656
	Night	5% 7% 24% 30% 31%	5642
Seeing	Day	17% 35% 40%	653
	Night	7% 5% 28% 45% 13%	2833

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	12% 5% 5% 5% 49%	567
	Night	13% 6% 6% 50%	783
February	Day	17% 6% 5% 7% 42%	561
	Night	21% 5% 5% 5% 43%	684
March	Day	7% 6% 5% 5% 49%	669
	Night	11% 6% 6% 6% 47%	693
April	Day	5% 7% 64%	720
	Night	9% 5% 6% 7% 51%	600
May	Day	10% 59%	792
	Night	9% 9% 5% 5% 8% 44%	572
June	Day	6% 6% 9% 58%	813
	Night	17% 18% 8% 5% 5% 9% 22%	504
July	Day	6% 6% 5% 12% 48%	803
	Night	10% 15% 7% 6% 8% 5% 5% 10% 24%	548
August	Day	6% 11% 52%	1114
	Night	11% 12% 6% 6% 5% 5% 12% 31%	929
September	Day	5% 9% 58%	1005
	Night	6% 6% 5% 8% 49%	940
October	Day	8% 8% 54%	645
	Night	12% 10% 6% 46%	718
November	Day	7% 9% 62%	468
	Night	7% 64%	698
December	Day	14% 5% 5% 53%	549
	Night	13% 56%	790

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	12% 5% 27% 27% 26%	377
	Night	10% 7% 24% 29% 28%	514
February	Day	13% 8% 36% 17% 23%	312
	Night	13% 9% 29% 19% 28%	353
March	Day	6% 13% 25% 25% 28%	418
	Night	12% 11% 27% 20% 28%	429
April	Day	7% 9% 32% 30% 19%	561
	Night	37% 29% 23%	426
May	Day	13% 31% 28% 23%	628
	Night	6% 10% 18% 33% 31%	355
June	Day	31% 56% 7%	589
	Night	5% 32% 55%	209
July	Day	25% 38% 31%	589
	Night	5% 33% 34% 26%	238
August	Day	5% 23% 40% 30%	868
	Night	8% 22% 41% 25%	523
September	Day	13% 36% 49%	811
	Night	15% 37% 44%	672
October	Day	9% 22% 29% 35%	717
	Night	9% 26% 24% 38%	732
November	Day	7% 13% 34% 27% 16%	426
	Night	6% 15% 27% 28% 22%	635
December	Day	8% 10% 33% 45%	360
	Night	6% 16% 26% 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	21% 40% 29% 8%	37
	Night	9% 37% 44% 5%	220
February	Day	10% 46% 31% 10%	47
	Night	7% 19% 40% 30%	184
March	Day	8% 23% 25% 38%	59
	Night	7% 7% 33% 44% 7%	229
April	Day	8% 30% 48% 13%	60
	Night	7% 5% 36% 48%	227
May	Day	24% 45% 25%	62
	Night	5% 26% 57% 6%	187
June	Day	11% 30% 55%	60
	Night	8% 25% 60% 6%	130
July	Day	22% 69%	62
	Night	8% 6% 53% 32%	164
August	Day	29% 63%	91
	Night	13% 8% 47% 29%	339
September	Day	7% 39% 47%	89
	Night	7% 23% 43% 23%	347
October	Day	17% 45% 32%	86
	Night	5% 27% 45% 19%	347
November	Night	5% 7% 44% 37%	245
December	Night	8% 41% 39% 5%	214

Page generated at 2008-09-30 02:40:54. Version ab11